DESIGN OF MEMS-BASED TUNABLE ANTENNAS, ORGANIC TRANSISTORS 
AND MEMS-BASED ORGANIC CONTROL CIRCUITS 
 
 
Except where reference is made to work of others, the work described in this thesis is my 
own or was done in collaboration with my advisory committee. This thesis does not 
include proprietary or classified information. 
 
 
_______________________________ 
Madhurima Maddela 
 
 
 
Certificate of Approval: 
 
 
 
______________________________                        ______________________________ 
Lloyd S. Riggs     Ramesh Ramadoss, Chair 
Professor      Assistant Professor 
Electrical and Computer Engineering              Electrical and Computer Engineering 
 
 
 
______________________________                        ______________________________ 
Stuart M. Wentworth     Joe F. Pittman 
Associate Professor     Interim Dean 
Electrical and Computer Engineering              Graduate School 
 
 
 
 
 
 
 
DESIGN OF MEMS-BASED TUNABLE ANTENNAS, ORGANIC TRANSISTORS 
AND MEMS-BASED ORGANIC CONTROL CIRCUITS 
 
Madhurima Maddela 
 
A Dissertation  
Submitted to 
the Graduate Faculty of  
Auburn University 
in Partial Fulfillment of the 
Requirements for the  
Degree of 
Doctor of Philosophy 
 
Auburn, Alabama 
May 10, 2008 
 
DESIGN OF MEMS-BASED TUNABLE ANTENNAS, ORGANIC TRANSISTORS 
AND MEMS-BASED ORGANIC CONTROL CIRCUITS 
 
 
Madhurima Maddela 
 
Permission is granted to Auburn University to make copies of this dissertation at its 
discretion, upon request of individuals or institutions and at their expense. The author 
reserves all publication rights. 
 
 
_____________________________________ 
          Signature of Author 
 
_____________________________________ 
          Date of Graduation 
 
 
 
 
 
 
 
 
 
 
 
 
iii 
VITA 
 
 
Madhurima Maddela, daughter of (Late) Dr. M. S. Venkateswarlu and (Late) Dr. M. 
Sundaramma, was born on June 25, 1981 in Tirupathi, India. She graduated with a 
Bachelor?s of Electronics and Communications Engineering in July 2002 from Osmania 
University, Hyderabad, India. She then joined the Electrical and Computer Engineering 
department of Auburn University as a graduate student in January 2003. The focus of her 
graduate research was on designing antennas for radio frequency identification systems 
and the realization of a wireless mobile sensor platform for the detection of pathogens in 
food products. After receiving her master?s degree, she has been working on 
(Microelectromechanical systems) MEMS devices, employing them for different 
applications like developing MEMS-based tunable antennas and integration of MEMS 
devices with organic transistors.  
 
 
 
 
 
 
 
iv 
DISSERTATION ABSTRACT 
DESIGN OF MEMS-BASED TUNABLE ANTENNAS, ORGANIC TRANSISTORS 
AND MEMS-BASED ORGANIC CONTROL CIRCUITS 
 
Madhurima Maddela 
 
Doctor of Philosophy, May 10, 2008 
(Master of Science, December 17, 2004) 
 
 
118 Typed Pages 
 
Directed by Ramesh Ramadoss 
 
 
The advent of precision three-dimensional micromachining technologies in the last 
couple of decades has seen the birth of an exciting and potentially revolutionary field 
called Microelectromechanical Systems (MEMS). Predictions about the far-reaching 
implications and widespread prevalence of such miniaturized, smart, integrated systems 
and sub-systems have been made and yet as of today only modest market presence and 
commercial success has been attained. Having arisen out of the silicon IC 
microfabrication technology in academic and research environment, the initial 
developments in MEMS were driven mainly by technical curiosity and demonstrability. 
Like in any emerging field, most of the developments have therefore been an array of 
new fabrication techniques, new materials, and new device structures for a host of sensor
v 
and actuator applications. However, the commercial viability and success of MEMS 
devices in the industrial and academic communities require tackling some of the daunting 
technical and commercialization issues impeding the market presence of such systems. 
This dissertation explores two varied and vital applications of MEMS devices. One 
application involves the development of MEMS-based tunable antennas and the other 
explores the integration of MEMS sensors with organic transistors.  
Tunable antennas are drawing interest because instead of having multiple antennas 
switched into multiple transceiver chains covering different frequency ranges, a single 
multi-band tunable antenna assembly would provide size advantages and minimize 
product packaging complexity. This dissertation demonstrates a coplanar patch antenna 
made tunable by the use of a MEMS varactor.  
The second application explored was to develop a ?Polymer Microsystem? by the 
integration of a Polymer MEMS device and Organic Electronics. Traditionally, 
microsystems have been fabricated using silicon-like semiconductor substrates by 
micromachining techniques. Silicon (or thin-film in general) may be the ideal substrates 
for semiconductor devices, but they may not be suitable for all microsystem applications. 
In particular, silicon based wafer level technology may not be suitable for cost effective 
manufacturing and packaging of microsystems for large area and large volume 
applications. The proposed work was to demonstrate a plastic microsystem using low 
cost fabrication techniques. As a proof-of-concept of the proposed plastic microsystem, 
this project demonstrated the integration of a Polymer MEMS pressure sensor with an 
organic field effect transistor. 
 
vi 
ACKNOWLEDGEMENTS 
 
 
I would like to express my deepest gratitude to Dr. Ramesh Ramadoss for providing 
exemplary guidance and encouragement throughout the course of my doctoral program. 
His patience and timely help during some very trying times will always be remembered. I 
would also like to thank Dr. Stuart M. Wentworth for his kind and continued support. My 
colleague and friend, Ananth Sundaram played a big role in helping me learn the ropes. 
Brian Holland, Ron Jackson Jr. and Lia Almeida made the office a congenial work 
atmosphere. Thanks are also due to Charles Ellis, Drew Sellers, Senthil Sivaswamy and 
Abhishek Davray for helping me with the lab work. I appreciate Mr. Joe Haggerty and 
Ms. Linda Barresi for giving me a lot of guidance and material support for my research 
experiments.  
A special mention goes to my husband, Subramanian Nambi, the wind beneath my 
wings, and my in-laws and extended family, who have enthusiastically supported the 
pursuit of my doctoral program.  
I would like to dedicate this dissertation to my late parents, Dr. M. S. Venkateswarlu 
and Dr. M. Sundaramma whose lives will always inspire me to be the best that I can be. 
 
 
 
vii 
 Style manual of journal used Graduate School Guide to preparation and 
submission of    theses and dissertation 
 
Computer software used Microsoft Office XP                                                                                   
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
viii 
TABLE OF CONTENTS 
 
LIST OF FIGURES ........................................................................................................... xi  
LIST OF TABLES.............................................................................................................xv 
CHAPTER I: INTRODUCTION.........................................................................................1                        
1.1.  Tackling MEMS Issues................................................................................2 
1.2.   Biasing considerations .................................................................................3 
1.3.   Frequency agile antennas.............................................................................3 
1.4.   Organic electronics ......................................................................................4 
   
CHAPTER II: MEMS-BASED TUNABLE COPLANAR PATCH ANTENNA...............6      
2.1. Tunable Antenna Design and Simulation ....................................................7 
  2.1.1.   Antenna Configuration.....................................................................8 
2.1.2.   MEMS Varactor.............................................................................12 
 2.1.3.   Equivalent Transmission Line Model............................................16 
      2.1.4.    Frequency Tuning Characteristics .................................................18 
 2.2.  Fabrication and Assembly..........................................................................21  
2.2.1.    Substrate.........................................................................................21 
 2.2.2.    Spacer.............................................................................................21 
 2.2.3.  Polyimide film ...............................................................................21 
 2.2.4.  Thermo-Compression Bonding......................................................22 
 2.3.  Experimental Characterization...................................................................23 
2.3.1.  MEMS Profile Characterization ....................................................24 
2.3.2.  RF Measurements ..........................................................................25 
 
CHAPTER III: ORGANIC FIELD EFFECT TRANSISTORS ........................................30 
3.1.  Choosing a semi-conductor Polymer.........................................................31 
 3.2.  Different Configurations............................................................................33 
 3.3.  Fabrication .................................................................................................35 
3.4.  Testing and modifications..........................................................................36 
 
CHAPTER IV: INTEGRATION OF AN ORGANIC FIELD EFFECT TRANSISTOR 
WITH A POLYMER MEMS-BASED PRESSURE SENSOR.........................................41 
 4.1.  Principle of operation.................................................................................42 
 
ix 
 4.2.  MEMS Pressure Sensor .............................................................................49 
 4.3.  Integration of MEMS Pressure Sensor and the OFET...............................51 
 4.4.  Monolithic Integration of MEMS Pressure Sensor and the OFET............54 
 
CHAPTER V: CONCLUSIONS AND FUTURE WORK................................................61 
 5.1.  MEMS-based Frequency agile antennas....................................................61 
5.2.  Organic electronics and micro-systems .....................................................62 
 
REFERENCES ..................................................................................................................65 
           
APPENDIX A: Traveler for fabricating a tunable coplanar patch antenna.......................72 
 
APPENDIX B: Measurements with the WYKO optical profilometer ..............................83 
 
APPENDIX C: Traveler for fabricating an OFET in the coplanar configuration .............88 
 
APPENDIX D: Traveler for fabricating a bottom contact OFET......................................91 
 
APPENDIX E: MATLAB code for generating plots showing the variation of MEMS 
capacitance and drain current with applied pressure .........................................................95 
 
APPENDIX F: Traveler for fabricating a bottom contact OFET integrated with a MEMS 
pressure sensor...................................................................................................................97 
 
x 
LIST OF FIGURES 
 
 
Figure 2.1. Coplanar patch antenna with CPW feed at the bottom Radiating Edge (RE) 
and varactor diode mounted at the top RE.........................................................................11 
 
Figure 2.2. Simulated and measured return loss for the coplanar patch antenna without 
the varactor diode...............................................................................................................11 
 
Figure 2.3. Photograph of the fabricated CPA with varactor diode mounted at the center 
of the top RE. .....................................................................................................................11 
 
Figure 2.4. Measured return loss results of the CPA for various bias voltages applied to 
the varactor diode...............................................................................................................12 
 
Figure 2.5. Coplanar patch antenna with CPW feed at the bottom radiating edge and a 
MEMS varactor mounted at the top radiating edge...........................................................15 
 
Figure 2.6. MEMS Varactor configuration on the antenna (a) Schematic view, and (b) 
Top view (Figure not to scale)...........................................................................................15 
 
Figure 2.7. Transmission line model for the tunable CPA with the MEMS varactor........17 
 
Figure 2.8. Simulated gap capacitance (C
gap
) between the actuation pad (pad 1) and the 
ground plane (pad 2) for various gap widths (g
a
) .............................................................19  
 
Figure 2.9. Simulated return loss of the coplanar patch antenna without and with the 
MEMS varactor (up and down states). ..............................................................................19 
 
Figure 2.10. Measured radiation patterns of the MEMS tunable antenna for various 
applied voltages: (a) H-plane Co-polarization, (b) H-plane Cross-polarization, (c) E-plane 
Co-polarization, and (d) E-plane Cross-polarization.........................................................20 
 
Figure 2.11. Three layers of the MEMS tunable CPA (a) Substrate layer coated with 
BCB, (b) Milled polyflon bonding film, and (c) Kapton film layer after DRIE................23 
 
Figure 2.12. Photograph of the fabricated MEMS tunable coplanar patch antenna..........24 
 
xi 
Figure 2.13. Biasing arrangement used for RF testing of the tunable CPA.......................24 
 
Figure 2.14. 2D profile of the MEMS varactor in the CPA measured using WYKO NT 
2000 optical profiler (a) top view of the MEMS varactor membrane showing xx? and yy? 
reference planes, (b) xx? profile of the MEMS varactor membrane, and (c) yy? profile of 
the MEMS varactor membrane..........................................................................................27 
 
Figure 2.15.  Return loss results of the tunable MEMS antenna for various applied DC 
bias voltages.......................................................................................................................28 
 
Figure 2.16. Measured radiation patterns of the MEMS tunable antenna for various 
applied voltages: (a) H-plane Co-polarization, (b) H-plane Cross-polarization, (c) E-plane 
Co-polarization, and (d) E-plane Cross-polarization.........................................................28 
 
Figure 3.1. Energy level comparison of Gold and Pentacene............................................33 
 
Figure 3.2. Three different configurations used for the OFET..........................................34 
 
Figure 3.3. Fabrication  process of the preliminary design for the Coplanar OFET. ........35 
 
Figure 3.4. Crosssectional view of the modified design for the OFET. ............................37 
 
Figure 3.5. Output characteristics of the modified design for the OFET. .........................37 
 
Figure 3.6. Transfer characteristics of the modified design for the OFET........................38 
 
Figure 3.7. Fabrication process of the finalized design for the OFET...............................38 
 
Figure 3.8. A photograph of a 1000 ?m (W) X 50 ?m (L) OFET......................................39 
 
Figure 3.9. Output Characteristics of the OFET................................................................39 
 
Figure 3.10. Transfer Characteristics of the OFET............................................................40 
 
Figure 4.1. A capacitive type MEMS pressure sensor connected in series with the gate of 
the OFET............................................................................................................................43 
 
Figure 4.2. Equivalent electrical circuit for the Polymer MEMS pressure sensor 
integrated with an OFET....................................................................................................44 
 
Figure 4.3. (a) Cross-sectional view of the MEMS pressure sensor with a circular 
membrane, (b) Close-up view of the MEMS varactor area, (c) Close-up view of the 
circular membrane. ............................................................................................................44 
 
xii 
Figure 4.4. The electrical circuit connections of the OFET to obtain the gate-to-channel 
capacitance.........................................................................................................................47 
 
Figure 4.5. A plot of the capacitance of the MEMS pressure sensor with varying pressure. 
 47 
 
Figure 4.6. A graph of the drain current, I
DS
 to the pressure, P applied to the MEMS 
sensor. ................................................................................................................................49 
 
Figure 4.7. The three layers of the polymer MEMS pressure sensor: (a) Bottom electrode, 
(b) Spacer Film and (c) Top Electrode. .............................................................................50 
 
Figure 4.8. Photograph of the MEMS pressure sensor after thermo-compression bonding.  
50 
 
Figure 4.9. A graph showing the variation of the measured MEMS capacitance with 
applied pressure. ................................................................................................................51 
 
Figure 4.10. Schematic diagram of the wire integration of the MEMS pressure sensor and 
the OFET: (a) Cross-sectional view and (b) Top view......................................................52 
 
Figure 4.11. The experimental setup used for obtaining the pressure sensor vs. the drain 
current characteristics. .......................................................................................................53 
 
Figure 4.12. Pressure Versus Drain Current Characteristics for the Polymer MEMS 
sensor. ................................................................................................................................53 
 
Figure 4.13. Schematic configuration of the Polymer MEMS pressure sensor 
monolithically integrated with an OFET: (a) Cross-sectional view and (b) Top View.....54 
 
Figure 4.14. Fabrication process for the monolithically integrated OFET and MEMS 
pressure sensor.   ...............................................................................................................56 
 
Figure 4.15. Photograph of the fabricated MEMS pressure sensor monolithically 
integrated with an OFET....................................................................................................57 
 
Figure 4.16. Output characteristics of the OFET monolithically integrated with a MEMS 
pressure sensor.   ...............................................................................................................57 
  
Figure 4.17. Transfer characteristics of the OFET monolithically integrated with a 
MEMS pressure sensor. .....................................................................................................58 
 
  
Figure 4.18. A graph of the capacitance of the pressure sensor to the pressure applied. ..58 
xiii 
Figure 4.19. A graph of the drain current of the OFET discussed in chapter 3 tested in 
conjunction with the new Kapton-based MEMS pressure sensor. ....................................59 
 
Figure 4.20. A graph of the drain current of the monolithically integrated OFET tested 
with the new Kapton-based MEMS pressure sensor. ........................................................60 
 
Figure 5.1. (a) and (b): Possible configurations of MEMS-based frequency agile 
antennas..............................................................................................................................62
xiv 
 
 
 
 
 
 
LIST OF TABLES 
 
 
Table 2.I: Simulated and measured resonant frequencies and return losses for the antenna 
     29 
 
Table 3.I: Organic thin film transistor parameters.............................................................35 
 
Table 4.I. Different parametric values employed to determine the variations of the MEMS 
capacitance and drain current with applied pressure.  ......................................................46 
 
 
 
 
 
 
 
 
 
 
 
 
 
xv 
CHAPTER I: INTRODUCTION 
 
 
In recent years, miniature electromechanical components suitable for Microsystem 
applications have been developed by Micro-electro-mechanical Systems (MEMS) 
technologies. A MEMS system involves the fabrication of mechanical elements, sensors, 
actuators, and electronics on a common substrate through the utilization of micro-
fabrication technology. Typical sizes for MEMS components range from nanometers to 
millimeters (100 nm to 1000 ?m). The characteristics of MEMS components are low-
cost, high functionality, and small size and light weight. MEMS devices can sense, 
control and actuate on micro-scale, and function individually (or in combination with 
other devices) to generate macro-scale effects. MEMS devices are already in mass use in 
applications ranging from inertial sensors for automobile airbags to monitoring patient 
blood pressure at the bedside [1]. Microsystems/MEMS have proved to be a 
revolutionary technology in many application arenas, including accelerometers, pressure 
sensors, displays, inkjet nozzles, optical scanners, and fluid pumps. Typical examples for 
commercial MEMS devices/Microsystems include ADXL series accelerometers from 
Analog Devices Inc., pressure sensors and accelerometers from FreeScale Semiconductor 
Inc., DLP displays from Texas Instruments Inc., SiSonic MEMS microphone from 
Knowles Electronics Inc., etc. But, issues like the reliability and lifetime of MEMS 
1 
devices, and their packaging difficulties have given cause for skepticism about the 
growth of this industry. 
1.1 Tackling MEMS Issues 
For several years, reliability and packaging issues have prevented the insertion of 
MEMS switches in military and commercial systems. Ohmic contact MEMS switch 
reliability issues, such as failure due to stiction and contact degradation, have been 
observed to be the key failure modes. Stiction is the unintentional adhesion of the 
movable and fixed parts in MEMS caused by surface adhesion forces. In capacitive 
contact type MEMS switches, reliability issues such as stiction due to charge 
accumulation in the dielectric layer and downstate capacitance degradation with actuation 
are commonly encountered failure modes.  
The typical lifetime requirement for military applications is in the range of 100-500 
billion cycles. Over the past five years, steady progress has been made in improving both 
the reliability and packaging of RF MEMS switches. Many successful MEMS switches 
have been demonstrated with lifetimes in excess of 100 million cycles. Reliable MEMS 
switches are commercially available from TeraVicta Technologies and Radant MEMS 
Inc. Radant MEMS Inc. has demonstrated 900 billion cycles of operation for their ohmic 
contact switches. MEMtronics Corporation demonstrated over 100 billion cycles of 
switch lifetime for capacitive MEMS switches. TeraVicta switches have been tested up to 
100 million cycles over the 0? to 70? C operating range of the device. Radant MEMS Inc. 
has developed a high-power MEMS switch with power handling in the range of 1 to 4 
watts and is developing MEMS switches capable of handling up to 20 watts. Advantest 
2 
produces electro-thermally activated relays for use in Automated Test Equipment (ATE). 
The expected lifetime is greater than 20 million cycles. The Packaging issue is resolved 
by hermetic sealing of MEMS switches after completion of the micromachining process. 
Recent improvements in reliability and packaging make MEMS switches attractive for 
reconfigurable antenna applications [2]. 
1.2 Biasing considerations 
MEMS devices typically require higher voltages than conventional semiconductor 
devices and thus would require high voltage DC sources in the antenna assembly. In spite 
of the high bias voltage requirements, the power consumption is low when compared to 
their semiconductor counterparts. MEMS devices integrated with RF circuits and 
antennas can be biased using resistive bias lines between the DC power supply and the 
MEMS devices. The resistive bias line allows a DC current flow from the DC power 
supply to the MEMS device. The resistance of the bias lines is designed to provide a high 
impedance path (> 10 k? for 0.1?) from the MEMS device to the DC power supply and 
thus preventing the leakage of RF signal into the supply [2]. 
1.3 Frequency agile antennas 
With the advent of RF MEMS switches, there has been a considerable interest in the 
development of multi-band reconfigurable antennas. Multi-mode, multi-band, and multi-
standard mobile devices create the need to simplify RF front ends. Instead of having 
multiple antennas switched into multiple transceiver chains covering different frequency 
ranges, a single multi-band tunable antenna assembly would provide size advantages and 
3 
minimize product packaging complexity. Multi-band antenna technology can be fully 
utilized for seamless mobility of next generation wireless devices. Multi-band antennas 
can be created to cover combinations of existing law enforcement bands, Homeland 
Security applications, cellular bands, Wireless Local Area Network (WLAN) bands, 
Bluetooth, 3G applications, Ultra Wide Band (UWB), for both voice, video, and high-
data-rate wireless communications with tunable performance, high RF power handling, 
and low power consumption. Two important characteristics parameters of an antenna are: 
1) the operating frequency, and 2) the radiation pattern. RF MEMS devices can be 
integrated with antennas for altering the operating frequency (tunable/switchable 
antennas) and/or the radiation pattern (phase shifters). Chapter 2 describes a MEMS-
based tunable antenna made tunable in the range 5.185 GHz to 5.545 GHz. 
1.4 Organic electronics 
An Organic Field Effect Transistor (OFET) belongs to a new class of electronics 
that can be fabricated directly on plastic films at ambient temparatures; therefore it is 
mechanically flexible, light-weight, very thin, shock resistant and easy to transport 
compared to their silicon-based counterparts. Weak Van der walls forces hold the organic 
semi-conductor molecules together. Low charge hopping from molecule to molecule is 
the major factor limiting the mobility of the semi-conductor. The main disadvantages of 
organic transistors are the low mobilities and slow switching times. But unlike traditional 
FETs, OFETs can handle much high voltages of the order of about 100 V. Some 
successful applications of organic electronics are Organic Light Emitting Diodes 
(OLEDs). Chapter 3 presents an all organic polymer transistor made using 
4 
BenzoCycloButene (BCB), a promising, moisture resistant dielectric and Pentacene, an 
aromatic compound from the Benzene family as the p-type semi-conductor. Integration of 
an OFET and OLED completes the need for controlling circuitry for the operation of the 
OLED, making it an independent all polymer micro-system. A similar integration of a 
MEMS-based pressure sensor and an OFET is presented in Chapter 4. This field is 
drawing a lot of interest now as some experiments have shown that bulk Silicon is 
susceptible to fatigue [3].  
Chapter 5 presents the conclusions and suggests possible avenues for future work. 
 
5 
 CHAPTER II: MEMS-BASED TUNABLE COPLANAR PATCH ANTENNA 
 
In recent years, there has been a considerable interest in the development of tunable 
antennas because of the increasing number of global wireless standards in close 
proximity to one another. A single tunable antenna would eliminate the need for multiple 
antennas operating in various frequency bands. Several tunable printed antennas using 
varactor diode(s) were reported in [4]-[10]. The operating frequency of the antenna was 
altered by varying the DC bias applied to the varactor diode(s). With the advent of 
MEMS technology, there have been considerable research efforts in the development of 
frequency tunable and reconfigurable (or switchable) antennas using RF MEMS devices 
[1]-[21]. In [13], a patch antenna operating at 25 GHz was made tunable over a range of 
1.6 %, i.e., 400 MHz. In [14], a tunable MEMS patch antenna using an electrostatic 
actuator with a wrapped metallization was reported. The area of the wrapped 
metallization was changed to obtain operating frequencies at 23.8 GHz and 12.4 GHz for 
0 V and 150 Volts, respectively. In [15],[16], dual-band frequency reconfigurable planar 
antennas integrated with RF MEMS switches were reported. In [17], a triple-band 
reconfigurable microstrip antenna that employs two RF MEMS switches was reported. 
The antenna resonates at 1.8 GHz, 2.4 GHz, and 1.9 GHz with return losses better than 
10 dB when both the switches are OFF, only one switch is ON, and both the switches are 
ON, respectively. In [18], a quadruple-band reconfigurable mini-nest patch antenna was 
6 
developed using half u-slots integrated with RF MEMS switches to achieve frequency 
bands like GSM (0.9 GHz), GPS (1.57 GHz), DCS (1.8 GHz) and WLAN (2.4 GHz and 
5.2 GHz). The return losses were reported to be in the range of 14 dB to 22 dB. RF 
MEMS switches were also used in conjunction with fractal antenna structures to obtain a 
reconfigurable array antenna structure. In [19], a multi-band frequency reconfigurable 
modified sierpinski gasket type fractal antenna was reported. Different configurations of 
the fractal antenna were achieved using RF MEMS switches to obtain operation in 
multiple frequency bands ranging from 0.6 GHz to 1.95 GHz. 
Recently, printed circuit board (PCB) process compatible MEMS-based frequency 
tunable and reconfigurable antennas have been reported in [20][21]. The advantages of 
PCB compatible MEMS technology include low cost, compatibility with organic 
laminate substrates, ease of integration with surface mount components, suitability for 
batch fabrication in large panels, and high volume manufacturing [22]. In [20], 
monolithic integration of RF MEMS switches with a diversity antenna on a PCB 
substrate was reported. In [21], a MEMS-based tunable circular microstrip patch antenna 
fabricated on a flexible Kapton polyimide film using printed circuit processing 
techniques was reported by our group. A 6 mm diameter circular patch antenna was 
reported that was tunable from 16.91 GHz at 0 V to 16.64 GHz at 165 V, for a tuning 
range of 270 MHz.  
 
2.1 Tunable Antenna Design and Simulation 
 
A Coplanar Patch Antenna (CPA) made tunable using a MEMS varactor fabricated 
using printed circuit processing techniques is investigated in this chapter. CPAs have 
7 
many advantages like low radiation loss, low dispersion, and uni-planar configuration. 
Due to their uni-planar configuration, CPAs facilitate integration with coplanar feed lines 
that enable shunt and series mounting of active and passive components. They also 
exhibit wider bandwidth and lower cross-polarization radiation as compared to microstrip 
patch antennas [4]. The concept of a coplanar antenna structure was first introduced by J. 
W. Greiser [23]. The antenna consists of a patch surrounded by a closely spaced ground 
conductor, and is suitable for being fed using Coplanar lines. Electromagnetic (EM) field 
simulations of the structure revealed that the antenna behaves more like a microstrip 
patch antenna than a loop slot antenna. Particularly, the resonant frequency of the antenna 
is primarily determined by the patch length (L) of about a half guide-wavelength instead 
of the total loop size. Electromagnetic simulations also show that the electric field 
distributions around the slots of the CPA resemble that of the microstrip patch edges. The 
variation of the input impedance of the CPA with the length of the patch exhibits a 
behavior similar to that of a microstrip patch. This characteristic allows impedance 
matching of the CPA to the feed line by only adjusting the width, W of the patch. In the 
following sections, design, simulation, fabrication, and experimental results for the PCB 
MEMS based tunable coplanar patch antenna are discussed. 
 
2.1.1 Antenna Configuration 
 
A Coplanar Patch Antenna (CPA) is based on the concept of a half-wavelength, 
open-ended coplanar waveguide (CPW) resonator. It consists of an open-ended CPW 
resonator section (along the y direction) fed by a CPW feed line as shown in Figure 2.1. 
8 
The characteristic parameters of the CPA are: length L, width W, and slot S. The field 
distributions in the slots of the half-wavelength resonator section (along y-direction) are 
out-of-phase and hence these slots behave as Non-Radiating Edges (NRE). On the other 
hand, the field distributions in the slots at the open-ends (along x-direction) are in-phase 
and therefore these slots are referred as Radiating Edges (RE). The CPA is fed by a 50 ? 
CPW line connected to one of the radiating edges of the CPA. 
An initial design for the CPA is obtained by choosing the length, L of the non-
radiating edges to be ?
g
/2 at the required operating frequency, where ?
g
 is the guide-
wavelength of the CPW line that forms the resonator section. The antenna was designed 
on a 30-mil thick RT/Duroid 6002 substrate (?
r
 = 2.94) with 1/4 ounce copper 
metallization. For a chosen operating frequency (f
r
) of 4 GHz, the approximate length, L 
of the patch is calculated using ?
eff
 ? ?
r
 [10]. 
mm
f
c
f
c
L
rreffr
g
21
22
2
=?==
??
?
                            (2.1) 
The patch width W and slot S were chosen to be 30 mm and 2.2 mm, respectively. Using 
LineCalc (a transmission line calculator available in [24]), the dimensions of a 50? CPW 
feed line were calculated to be g = 0.1 mm and s = 1.642 mm. It should be pointed out 
that the designed CPA would resonate at a frequency slightly lower than 4 GHz due to 
fringing-field effect at the radiating edges. An effective length L
eff 
can be defined to 
account for the fringing fields at the radiating edges. The expected resonant frequency 
can be estimated using an approximate value for the effective length L
eff
 ? L + S and ?
eff
 ? 
?
r
 as given below. 
9 
reffeff
r
SL
c
L
c
f
?? )(22 +
?=     (2.2) 
For a chosen slot dimension S = 2.2 mm, the expected resonant frequency of the designed 
CPA is calculated to be 3.8 GHz. For this design, the simulated return loss is 43dB at a 
resonant frequency of 3.526 GHz as shown in Figure 2.2. The simulated input 
impedance, Z
in
 is 50.73 + j0.21? which provides for good matching. A varactor diode 
MA46H200 has been mounted at top of the radiating edge of the antenna as shown in 
Figure 2.2. The photograph of the fabricated antenna along with the varactor diode is 
shown in Figure 2.3. The return loss of the antenna has been measured using an Agilent 
8510C vector network analyzer. The return loss results of the antenna for various bias 
voltages in the range of 0 to 19.5 V applied to the varactor diode are shown in Figure 2.4. 
It can be seen that the operating frequency of the antenna is tunable from 4.92 GHz at 0 
V with a return loss of 14 dB to 5.40 GHz at 19.5 V with a return loss of 56 dB. It should 
be pointed out that in the tunable frequency range of 5.16 to 5.40, the return loss is better 
than 32 dB. The radiation patterns were measured at the operating frequency of the 
antenna for various tunable states.  Whereas the nominal shape of the pattern remains the 
same, there is a very slight tilt in the beam.  This is due to the phase change across the 
structure due to the new operating frequency.  As the resonance of the antenna changes 
from the design frequency, it will match less and less due to the fixed physical length of 
the antenna. In the following sections, MEMS varactor design and frequency tuning 
characteristics of the antenna are discussed. 
10 
 
 
Figure 2.1. Coplanar patch antenna with CPW feed at the bottom Radiating 
the top RE. 
Figure 2.2. Simulated and measured return loss for the coplanar pa
 
 
Figure 2.3. Photograph of the fabricated CPA with varactor diode mounted 
11 
Edge (RE) and varactor diode mounted at 
 
tch antenna without the varactor diode. 
 
Varactor
at the center of the top RE. 
 
Figure 2.4. Measured return loss results of the CPA for various bias voltages applied to the varactor diode. 
 
 
2.1.2 MEMS Varactor 
 
A Tunable Coplanar Patch Antenna (TCPA) has been demonstrated in [10] by 
using a pin diode at one of the radiating edges. In this chapter, a MEMS based TCPA has 
been designed by integrating a MEMS varactor at one of the radiating edges as shown in 
Figure 2.5. Figure 2.6(a) illustrates the detailed cross sectional view of the MEMS 
varactor and Figure 2.6(b) shows the top view of the MEMS varactor on the antenna. An 
actuation pad is included in the antenna metallization layer to facilitate electrostatic 
actuation of the MEMS varactor. An air gap is present between the MEMS varactor 
membrane and the actuation pad on the antenna. The MEMS varactor is controlled by a 
DC bias voltage. As the DC bias is increased, the movable MEMS varactor membrane is 
pulled towards the actuation pad due to electrostatic force of attraction caused by the 
applied DC bias voltage. The deflection of the varactor membrane decreases the air gap 
12 
thereby increasing the capacitive load at the radiating edge of the CPA. The increase in 
the loading capacitance increases the effective length of the CPA and hence results in a 
downward shift in the resonant frequency of the CPA. 
The close-up view of the MEMS varactor configuration on the antenna is shown in 
Figure 2.6(b). The dimensions of the suspension beams are L
A 
= 1.4 mm, L
B 
= 0.75 mm, 
L
C
 = 1.4 mm, L
D
 = 1 mm and the flexure width is 0.2 mm. From Figure 2.7, the 
capacitance of the MEMS varactor is given by 
,,
, 12
,
12
ud ud
ud
MEMS
ud ud
CC
C
CC
=
+
,
                                                    (2.3) 
where C
1
 is the capacitance between pad 1 and the MEMS electrode and C
2
 is the 
capacitance between pad 2 and the MEMS electrode. Superscripts u and d represent the 
up and down states, respectively. 
By ignoring the fringe effects, the MEMS varactor capacitance in the up and down 
states are given by  
0,,
12
,12
udud
MEMS
ud
AA
C
hAA
?? ??
=
?
+
??
?                                                  (2.4) 
where A
1 
= w
e
l
1
 is the area of overlap between the MEMS electrode and pad 1, A
2
 = w
e
l
2
 
is area of overlap between the MEMS electrode and pad 2, ?
u
 (=1) is the relative 
dielectric constant of air, ?
d
 (=2.65) is the relative dielectric constant of the BCB 
dielectric layer, h
u
 is the air gap measured from the top surface of the dielectric to the 
MEMS electrode, and h
d
 is the dielectric thickness of the BCB layer.  
 
 
13 
The capacitance ratio between the down state capacitance, C
d
, and the up state 
capacitance, C
u
, can be written as 
  
u
MEMS
d
MEMS
C
C
=?                                                             (2.5) 
Using Eqn. (2.4) and Eqn. (2.5), the capacitance ratio can be expressed as 
i.e. 
du
d
h
h
?
? =
                                                        (2.6) 
From Figure 2.6(a), the thickness of the spacer film is 2 mils (~ 50 ?m). It can be noted 
that the sum of h
u
 + h
d
 + copper thickness (3 ?m) should be equal to the spacer thickness. 
If the dielectric thickness h
d
 is chosen to be 7 ?m, the air gap h
u
 can be calculated to be 
40 ?m. In this case, using Eqn. (2.6), the capacitance ratio can be calculated to be 15.  
Using Eqn. (2.3), the MEMS varactor capacitance in the down state is given by  
12
12
dd
d
MEMS
dd
CC
C
CC
=
+
                                                      (2.7) 
For design purposes, is assumed to be smaller than . In this case, from Eqn. (2.4), 
the capacitance in the down state is given by  
2
d
C
1
d
C
02d d
MEMS
d
A
C
h
??
?
                                                       (2.8) 
For a chosen MEMS electrode width w
e
 = 1 mm and overlap length l
2
 = 0.45 mm, the 
capacitance 
d
MEMS
C  can be calculated to be 1.5 pF. Using Eqn. (2.5), C
u
 can be estimated 
to be 100 fF.  
14 
 
Figure 2.5. Coplanar patch antenna with CPW feed at the bottom radiating edge and a MEMS varactor mounted at the 
top radiating edge. 
 
 
 
Figure 2.6. MEMS Varactor configuration on the antenna (a) Schematic view, and (b) Top view (Figure not to scale). 
15 
2.1.3 Equivalent Transmission Line Model 
The equivalent transmission line model for the tunable CPA capacitively loaded 
by the MEMS varactor (along with the parasitic gap and open capacitances) is shown in 
Figure 2.7. It should be noted that this model ignores discontinuity reactances at the feed 
junction. From the model, the total capacitance can be expressed as 
,,ud ud
T gap openMEMS
CC CC=++
                                        (2.9) 
where C
gap
 is the capacitance between the actuation pad and pad 2, and C
open
 is the 
capacitance between pad 1 and pad 2. Superscripts u and d represent the up and down 
states, respectively. 
The total capacitance loading the transmission line can be modeled as an equivalent 
open-circuited line section of length ?l. By equating the impedance of the capacitive load 
to an open circuited line section of length ?l, we obtain  
)cot(
0
ljZ
C
j
Z
T
OC
??=
?
= ?
?
                                   (2.10) 
The equivalent line length extension ?l can be expressed as 
11
00
11 1
cot cot
2
2
TT
eff
c
l
CZ Z fC
f
?? ?
??
??
?? ?
?= =
?? ?
?? ?
?
?
?
                       (2.11) 
For a chosen slot width of S = 2.2 mm, the capacitance C
gap
, was obtained using 
CoventorWare [25] for various gap widths (g
a
) in the range of 0.1 mm to 2.1 mm. In 
order to generously account for any misalignment between the MEMS electrode and the 
actuation pad, the width of the actuation pad, w
a
 was chosen to be 2 mm. Figure 2.8 
shows a plot of the variation of the gap capacitance, C
gap
 as a function of the gap width, 
16 
g
a
. The gap value was chosen to be g
a
 = 0.1 mm so as to obtain a long actuation pad that 
would provide high actuation force and hence a reasonably low actuation voltage for 
PCB MEMS varactors. The corresponding C
gap
 is 2.04 fF. Using CoventorWare [25], 
C
open 
was estimated to be around 9 fF.  Substituting these values into Eqn. (2.7), the total 
capacitances in the up and down states of the MEMS varactor are calculated to be 111 fF 
and 1.5 pF, respectively. Using the afore mentioned design parameters, an antenna model 
including an actuation pad but without a MEMS varactor was built in Agilent ADS [24] 
and Electromagnetic (EM) simulation was carried out. The simulated return loss of the 
antenna is shown in Figure 2.9. From Figure 2.9, it can be seen that the antenna resonates 
at 5.583 GHz with a return loss better than 45 dB. Also, using the LineCalc tool (a 
transmission line calculator) in Agilent ADS [24] for the antenna parameters yielded Z
0 
= 
66.26 ? and ?
eff
 = 1.198. After substituting all these values in (2.11), the equivalent line 
length extension (?l), in the up and down states are calculated to be 2.1 mm and 10 mm, 
respectively. 
 
Figure 2.7. Transmission line model for the tunable CPA with the MEMS varactor. 
17 
2.1.4 Frequency Tuning Characteristics 
The effective length of the transmission line, L
eff
 can be expressed 
as where ?l is the equivalent line length extension that accounts for the 
capacitive loading. The resonant frequency of the antenna can be expressed as a function 
of the effective length, L
eff
 as  
lSLL
eff
?++=
effeff
L
c
f
?2
=                                                 (2.12) 
Assuming ?
eff
 remains constant; the ratio of the antenna resonant frequencies in the down 
and up states of the MEMS varactor can be obtained from Eqn. (2.12) as 
d
u
u
d
lSL
lSL
f
f
?++
?++
=                                              (2.13) 
The frequency ratio (FR) is defined as the ratio of the change in the antenna resonant 
frequency to the up state resonant frequency.  
u
du
f
ff
FR
?
=                                                  (2.14) 
Using these design parameters, a MEMS varactor model was created and included on top 
of the rectangular patch antenna for EM simulation in Agilent ADS [24]. The return 
losses of the antenna for the up and down states are shown in Figure 2.9. We can observe 
that as the air gap between the MEMS varactor membrane and the substrate decreases, 
the capacitance increases and hence the resonant frequency decreases. This antenna 
design is expected to be tunable in the frequency range from 4.94 GHz (down state) to 
5.44 GHz (up state). The return loss values are 28.85 dB and 44.67 dB at 4.94 GHz and 
5.44 GHz, respectively.  From the simulated results, the frequency ratio was calculated to 
18 
be 0.09. The radiation patterns shown in Figure 2.10 were simulated in Ansoft HFSS 
[26]. In the following sections, fabrication and experimental characterization of this 
antenna design are discussed. 
 
Figure 2.8. Simulated gap capacitance (C
gap
) between the actuation pad (pad 1) and the ground plane (pad 2) for 
various gap widths (g
a
). 
 
Figure 2.9. Simulated return loss of the coplanar patch antenna without and with the MEMS varactor (up and down 
states). 
 
19 
 
 
Figure 2.10. Measured radiation patterns of the MEMS tunable antenna for various applied voltages: (a) H-plane Co-
polarization, (b) H-plane Cross-polarization, (c) E-plane Co-polarization, and (d) E-plane Cross-polarization. 
 
 
 
 
 
 
 
20 
2.2 Fabrication and Assembly 
The three layers that make up the configuration of the tunable coplanar patch 
antenna are: substrate, spacer, and a polyimide film. 
 
2.2.1 Substrate 
A 2? x 2? RT/Duroid 6002 (30 mils thick with 9 ?m copper cladding, ?
r
 = 2.94) 
substrate was used. Coplanar Waveguide (CPW) lines are defined on the metallization 
layer on the substrate by photolithography and etching processes. Photosensitive 
BenzoCycloButene (BCB) is spin-coated on the substrate and patterned to form the 
dielectric layer on the bottom electrode metallization. Figure 2.11(a) shows a photograph 
of the substrate with the patterned antenna, CPW line, and BCB dielectric layer. 
 
2.2.2 Spacer 
The spacer layer provides the required spacing between the substrate and the 
polyimide layer. Hence, the thickness of the spacer film determines the up-position gap 
height. A 2 mil thick polyflon bonding film is used as the spacer film. This film is 
machined using a milling machine to create openings for the contact pads and the MEMS 
varactor in the polyimide film. A milling machine processed spacer film is shown in 
Figure 2.11(b). 
 
2.2.3 Polyimide film 
A 2 mil thick flexible Kapton E polyimide film (?
r
 = 3.1) with 100 ? -150 ? 
nichrome seed layer and 3 micron thick copper cladding is used. The Kapton film is used 
as the MEMS structural layer because of its ability to withstand millions of mechanical 
21 
flexing cycles. First, the electrode is defined on the 3 micron thick copper cladding on the 
Kapton film by photolithography and etching processes. Then, the film is machined using 
Deep Reactive Ion Etching (DRIE) to create slot openings required for the formation of a 
movable membrane. These flexures separate the membrane from its adjacent area and 
thus reduce the stiffness of the movable membrane. The equipment used for the DRIE 
process is an STS AOE (Advanced oxide etcher). The configuration of the gases used for 
this etch in our facility is 8 sccm CF4 and 35 sccm oxygen with 500 Watts of RF power. 
These processing parameters take about 70 minutes to etch a 2 mil thick Kapton film. 
Finally, resistive bias lines are defined in the nichrome seed layer for DC biasing of the 
MEMS varactor. These bias lines prevent leakage of the RF signal from the MEMS 
varactor to the DC supply. Figure 2.11(c) shows the photograph of a processed Kapton 
film. 
 
2.2.4 Thermo-Compression Bonding 
Thermo-compression bonding is performed using a Carver Press consisting of two 
platens. The platens are heated using heaters, which are controlled by a thermocouple. 
The fixture consists of two steel plates with alignment holes at four corners. The substrate 
forms the bottom most layer, the spacer is the middle layer and the Kapton film forms the 
top most layer in this structure. The different layers are aligned by aligning the marks 
created on the three layers during the fabrication process described earlier. This unit is 
now placed between the press platens. The bonding is performed at a pressure of 65 psi (a 
load of 165 lbs.) and a temperature of 130?C. Both pressure and temperature are 
maintained for 5 min during bonding. Before pressure is released, the assembly is cooled 
22 
down to the room temperature. A detailed traveler of the fabrication process is provided 
in Appendix A. 
   
Figure 2.11. Three layers of the MEMS tunable CPA (a) Substrate layer coated with BCB, (b) Milled polyflon bonding 
film, and (c) Kapton film layer after DRIE. 
Circular Patch 
Flexure 
Bias pad 
 
 
2.3 Experimental Characterization 
A photograph of the fabricated tunable coplanar patch antenna is shown in Figure 
2.12. Figure 2.13 shows the biasing arrangement for the MEMS based tunable coplanar 
patch antenna. A bias-T (Picosecond Model No. 5542-203) with a maximum DC bias 
voltage rating of 100 V was used. The bias-T ensures that the applied DC voltage does 
not leak into the RF input thereby providing proper isolation between the RF test 
equipment and the DC power supply. An SMA launcher was soldered to the CPW feed 
line for RF testing. To ensure rigidity of the MEMS devices during testing, the substrate 
was mounted on a Lucite frame. Two types of measurements were taken to characterize 
the antenna: MEMS varactor profile and RF measurements.  
23 
 
Figure 2.12. Photograph of the fabricated MEMS tunable coplanar patch antenna. 
 
Figure 2.13. Biasing arrangement used for RF testing of the tunable CPA. 
 
 
2.3.1 MEMS Profile Characterization 
The WYKO optical profilometer was used to measure the profile of the MEMS 
varactor in the CPA and the measured profile is shown in Figure 2.14. The procedure to 
24 
use this equipment is provided in Appendix B. Profile measurements of the initial design 
yielded the height of the MEMS varactor above the ground plane when measured at the 
center of the MEMS varactor to be about 100 microns and the variation of the height 
from the edge to the center to be around 50 microns. In order to reduce this warpage, 
during lamination of the final design, spare Kapton pieces were placed in the air gap 
between the BCB on the bottom electrode (plate 1 and plate 2) and the Kapton 
membrane. This helped in bringing down the warpage to about 5 to 10 microns across the 
MEMS varactor plate. The slight warpage could be attributed to the thermal coefficient of 
expansion mismatch between the copper patch (17 ppm) and Kapton (16 ppm) polyimide 
film. 
                            
2.3.2 RF Measurements 
The return loss of the MEMS patch antenna was measured using an HP 8510C 
Vector Network Analyzer (VNA). A DC bias voltage was applied to the patch and return 
loss measurements were taken for a various bias voltages in the range of 0 to 116 V, at 5 
or 10 V increments. Figure 2.15 shows the plot of the return loss measurements for 
various applied voltages. It can be observed that the resonant frequency of the antenna 
shifts downward with increasing bias voltage. At 0 V, the MEMS varactor is in the ?up? 
state and the antenna resonates at 5.545 GHz with a return loss of 40 dB. When the 
applied voltage is below 80 V, no significant frequency shift was observed. The antenna 
provides a downward shift in the resonant frequency as the applied DC bias is increased 
to 110 V. When the DC bias voltage is increased to 116 V, the MEMS varactor reaches 
the ?down? state and the antenna resonates at 5.185 GHz with a return loss of 41.12 dB. 
25 
The tunable frequency range of the antenna between the up and down states of the 
MEMS varactor is 360 MHz. The measured frequency ratio is 0.065.  
The radiation patterns of the antenna have been measured using a Diamond 
Engineering 6000 Series Desktop Antenna Measurement system (DAMS) (available from 
Diamond Engineering [27]). Measured radiation patterns for various bias voltages of 0, 
110, 113, 115 and 116 V are shown in Figure 2.16. The null along the broad-side 
direction in the E-field co-polarization patterns can be attributed to the asymmetry caused 
by the presence of the MEMS varactor and the feed line at the center of the radiating 
edges. It can be noted that there is no significant change in the overall patterns throughout 
the tuning range for various applied voltages. 
Table 2.I shows the comparison of the simulated and measured resonant frequencies 
in the up and down states. The simulated results were obtained by EM simulation of the 
CPA (including the MEMS varactor) in the HP-Momentum available in the Agilent?s 
Advanced Design System (ADS) [24]. In the up state, the real part of the input 
impedance obtained from the simulated and measured return losses are 47.51 ? and 
49.53 ?, respectively. Hence the antenna exhibits a better impedance match to the 50 ? 
feed line in the measured case when compared to the simulated case. From Table 2.I, it 
can be noted that the simulated tuning range is about 9 % whereas the measured tuning 
range is about 6.5 % [28]. The lower measured tuning range can be attributed to a slight 
decrease in the down state capacitance caused by factors like the surface roughness of the 
RT/Duroid substrate and fabrication tolerances. Typical surface roughness for RT/Duroid 
26 
substrate is in the range of 1-2 ?m. A similar trend was observed in [29] for RF MEMS 
switches fabricated on RT/Duroid substrates. 
                     
                                                                             
(a) 
 
Figure 2.14. 2D profile of the MEMS varactor in the CPA measured using WYKO NT 2000 optical profiler (a) top 
view of the MEMS varactor membrane showing xx? and yy? reference planes, (b) xx? profile of the MEMS varactor 
membrane, and (c) yy? profile of the MEMS varactor membrane. 
27 
 
Figure 2.15.  Return loss results of the tunable MEMS antenna for various applied DC bias voltages. 
 
Figure 2.16. Measured radiation patterns of the MEMS tunable antenna for various applied voltages: (a) H-plane Co-
polarization, (b) H-plane Cross-polarization, (c) E-plane Co-polarization, and (d) E-plane Cross-polarization. 
28 
Table 2.I: Simulated and measured resonant frequencies and return losses for the antenna 
in the up and down states of the MEMS varactor 
 
Simulated Measured 
Frequency 
(GHz) 
S
11
 
(dB) 
Z
in
 
(?) 
Frequency 
(GHz) 
S
11
 
(dB) 
Z
in
 
(?) 
Up State 5.44 -28.85 47.51-2.486i 5.545 -40 49.53-1.045i 
Down State 4.94 -45 49.97-0.583i 5.185 -41 50.43-0.88i 
 
This project is sponsored by the Motorola's University Partnership in Research (UPR) 
program, Motorola, Schaumburg, IL. 
 
 
 
 
 
 
 
29 
 CHAPTER III: ORGANIC FIELD EFFECT TRANSISTORS 
 
The last three decades have seen an explosive growth in silicon-based 
microelectronics. The rapid growth in mass-scale manufacturing has been possible due to 
reduction of dimensions of the transistors, reduction of the power consumption, and yet 
maintaining a high degree of reliability. Though the cost of setting up new manufacturing 
plants has steadily increased over the years, the cost per transistor for logic, memory, 
application specific circuits, and other related applications has been decreasing for every 
generation of semiconductor products [30]. Thus, the continuous progress in the design, 
process and testing has made it possible to achieve higher performance, yields, and 
reliability; making the semiconductor industry one of the important drivers of economical 
growth. In search of flexible and low-cost substrates, organic semi-conductor-based 
integrated circuits (ICs) have been suggested as an alternate to silicon ICs [31]. The 
discovery that the electrical conductivity of some polymers can be increased from 
insulator to semiconductor range or metallic range by doping has been a driving force for 
research in this area [32],[33]. Over the last two decades, there has been a tremendous 
interest in the electrically conducting polymers [34],[35],[36]. The main processing 
techniques employed in the deposition of polymer films on glass or silicon substrates are 
electro-polymerization, solution-processed deposition by casting, and vacuum 
evaporation [37],[38]. These techniques are relatively less complicated and cheaper 
30 
compared to the techniques used in the traditional semiconductor industry [39],[40],[41]. 
Ebisawa et al. fabricated the first polymer-based transistor in 1983 [42]. Since then, a 
great deal of research work has been done in the area of organic material-based 
transistors. The driving force for developing organic field effect transistor (OFET) or 
organic thin-film transistor (OTFT)-based electronics is the fact that they are flexible, 
light weight and have the prospect of low-cost manufacturing. Major barriers in the 
practical realization of OTFT-based electronic systems are the need for larger power 
supplies, lower gain, lower switching speeds and reliability problems. New directions 
leading to changes in the design of transistors, materials used in the fabrication, and 
processing techniques are warranted for developing processes and equipment that can 
lead to the manufacturing of OTFT-based electronics. OTFTs are being investigated in 
this chapter to lay the ground work for future utilization of OTFTs to control Polymer 
MEMS actuators like the ones discussed in the earlier chapters. They are currently 
controlled manually. Silicon based transistors do not have the capability to withstand the 
high actuation voltages. 
 
 
3.1 Choosing a semi-conductor Polymer 
 
Large varieties of organic compounds have been tested for making OFETs and 
there are many new materials being synthesized for this purpose. Currently, most organic 
materials used in OFETs are ?-conjugated organic oligomers and polymer-based organic 
semiconductors. Conjugated polymers present the advantage of being amenable to 
specific deposition techniques that have been developed for conventional polymers. Their 
31 
main drawback is that their performance is still lower than that of small-moleculed 
organic oligomers. 
Depending on the type of charge carriers, the organic semiconductors can be 
classified as p-type and n-type. In p-type semiconductors, the majority carriers are holes, 
while in n-type semiconductors, the majority carriers are electrons. Both type materials 
have been used in OFETs. N-type materials are mainly characterized by their high 
electron affinity and p-type materials, by their low ionization potential. In most 
applications, the investigated organic semiconductor materials are p-type. Because of 
their sensitivity to air and moisture, most n-type semiconductors are not suitable for 
OFETs. Also, n-type materials have relatively low field effect mobilities. Recently, Chua 
has discussed n-type materials in Nature [45]. Commonly used organic semiconductors 
include Phthalocyanine (PC) [46],[47], Pentacene [48], ?-Sexithiophene [49], poly(3-
hexylthiophene), 3,4,9,10-Perylenetetracarboxylic dianhydride (PTCDA) [50], 
Hexadecahalo-genated metallophthalocyanines (F
16
CuPc) [51], etc. 
At present, almost all devices are made of small molecule semiconductors, especially 
Pentacene, Oligothiophenes, and their derivatives. These two materials possess the best 
electronic characteristics by offering high charge carrier mobilities, the mobilities can 
reach 6 cm
2
/V-s for Pentacene [48] and 1 cm
2
/V-s for ?-Sexithiophene [49]. 
Pentacene is an aromatic compound with five condensed benzene rings and has been 
widely studied for its application in OFETs. Due to the poor solubility of Pentacene, it is 
mainly used in its polycrystalline thin film form and deposited by vacuum evaporation. 
The characteristics of Pentacene have been described in many reviews [52],[53],[54]. 
32 
Molecules have similar energy band levels as atoms. The valance band energy level of an 
atom is analogous to the energy level of Highest Occupied Molecular Orbital (HOMO). 
Similarly, the conduction band energy level of an atom is analogous to the energy level of 
Lowest Unoccupied Molecular Orbital (LUMO). The LUMO and HOMO energy levels 
are in the vicinity of 3.21 eV and 4.99 eV respectively as shown in Figure 3.1 [55]. The 
Fermi level of gold is 5.2 eV. Hence, it can be seen that the HOMO energy level of 
Pentacene and the Fermi level of Pentacene are in good agreement. So, it can be inferred 
that when sufficient reverse bias is provided at the Gold-Pentacene interface, there will be 
a current flow due to the holes in the valence band. 
5.2 eV
3.21 eV
4.99 eV
HOMO
LUMO
Au                      Pentacene
HOMO: Highest Occupied Molecular orbital ~ E
V
LUMO: Lowest Unoccupied Molecular orbital ~ E
C
E
F
 
 
Figure 3.1. Energy level comparison of Gold and Pentacene. 
 
3.2 Different Configurations 
 
Three different configurations (shown in Figure 3.2) used for designing an OFET 
are discussed below.  
33 
 (i) Top contact configuration: Here, the gate electrode is defined first and then 
surrounded by the gate dielectric. The semiconductor polymer is then deposited/coated 
followed by the source and drain contacts as the top-most layer. 
(ii) Bottom contact configuration: This formation varies from the above one in that the 
upper two layers are interchanged. 
(iii) Co-planar configuration: In this configuration, the gate, source and drain are 
defined in the same layer. The gate dielectric isolates the gate while the semiconductor 
polymer forms the top-most layer. 
 
Figure 3.2. Three different configurations used for the OFET. 
 
 
In this experiment, the organic gate dielectric used is BenzoCycloButene (BCB).   Table 
3.I shows the various parameters chosen for this design. Masks were made with the 
channel widths ranging from 25-100 ?m and channel lengths from 100-200 um for a 
coplanar configuration.  
34 
Table 3.I: Organic thin film transistor parameters 
 
Layers Material Thickness 
Source, Drain and Gate Electrodes Gold 
(? = 4.1 x 10
7
 S/m) 
~100 nm 
Gate Dielectric BCB 
(?
i 
= 2.65) 
~500 nm 
Semiconductor Polymer Pentacene 
(?
s
 = 0.8e-4 cm
2
.V/S) 
~700 nm 
 
3.3 Fabrication 
Gold electrodes are deposited on a plain oxidized silicon wafer through Chemical 
Vapor Deposition (CVD) and photolithography techniques. BCB is then spin-coated and 
patterned on top of the gate. In order to obtain a thin BCB coating of 500 nm, 1 part of 
BCB was diluted using 1 part of T1100 solvent and the mixture was spin-coated at 2700 
rpm. The final step is to deposit Pentacene through thermal evaporation. The electrode 
pads are covered before Pentacene can be deposited so that they are available for probe 
testing. Figure 3.3 shows the different steps involved in the fabrication process.  
 
Figure 3.3. Fabrication  process of the preliminary design for the Coplanar OFET. 
35 
3.4 Testing and modifications 
 
When this device was tested by varying the output and input voltages while 
measuring the output current, it was observed that the gate voltage did not have any 
significant impact on the device performance. It was suspected that the field effect 
generated by this device might not be sufficient to function as an FET. In order to 
confirm this suspicion, the device was modified so that the silicon on the wafer now acted 
as the gate while the silicon oxide layer acted as the gate dielectric. This configuration is 
shown in Figure 3.4. Figure 3.5 and Figure 3.6 show the electrical characteristics of the 
above modified OFET. It can be observed that the device performance resembled that of 
a FET. From these experiments, it was gathered that the masks needed to be modified to 
allow for a wider gate and that the bottom contact configuration would be better suited in 
order for the field effect to take place. Hence a new configuration was developed while 
maintaining Pentacene as the top layer in order to prevent any interaction with other 
chemicals. Figure 3.7 shows the different fabrication steps involved. Detailed travelers 
for the fabrication of the transistor in the coplanar and bottom contact configurations are 
provided in Appendix C and Appendix D respectively.  
The devices were fabricated through photolithography, CVD and thermal evaporation 
techniques and the experiment was repeated. Figure 3.8 shows the photograph of a device 
with width, W = 1000 ?m and length, L = 50 ?m. The fabricated OFET was characterized 
using an HP 4156A semiconductor parametric analyzer. Figure 3.9 shows a plot of the 
output characteristics of the aforementioned device while Figure 3.10 shows the transfer 
characteristics [56]. It can be seen from these characteristics that this device behaves like 
36 
a p-type FET albeit with a lower drain current which causes a drop in the mobility. It is 
also shown that the device can handle high voltages of ~70 V.  
 
Figure 3.4. Crosssectional view of the modified design for the OFET. 
 
 
 
 
Figure 3.5. Output characteristics of the modified design for the OFET. 
 
37 
 
Figure 3.6. Transfer characteristics of the modified design for the OFET. 
 
 
 
Figure 3.7. Fabrication process of the finalized design for the OFET. 
38 
               
 
Figure 3.8. A photograph of a 1000 ?m (W) X 50 ?m (L) OFET. 
 
 
 
Figure 3.9. Output Characteristics of the OFET. 
39 
 
 
Figure 3.10. Transfer Characteristics of the OFET. 
 
 
In conclusion, this chapter presents the design, fabrication and measured 
characteristics of an organic transistor. The highlight of this work is the use of a thin 
BCB layer (500 nm) as the gate dielectric for Pentacene based organic transistors. The 
mobility of the transistor is not as high, but it can handle higher voltages than a silicon 
transistor. 
 
 
 
 
 
 
 
40 
 CHAPTER IV: INTEGRATION OF AN ORGANIC FIELD EFFECT TRANSISTOR WITH A 
POLYMER MEMS-BASED PRESSURE SENSOR 
 
By the end of 20th century, semiconductor based micro-systems were omnipresent in 
everyday life. Microsystems are very ?small systems? or ?systems made of very small 
components? [57]. Microsystems perform special functions by manipulation of electrons, 
photons, phonons, atoms, molecules etc. Microsystems are realized by integration of 
mixed-domain components such as electrical, electronic, optical, mechanical, thermal, 
chemical and fluidics. We are now facing a new electronics revolution that has become 
possible due to the development and understanding of a new class of materials, 
commonly known as Organic (or Polymer) conductors, semiconductors, and insulators 
[58]-[64]. Interest in plastic electronics stems from the ability to deposit organic films on 
a wide variety of very low-cost substrates such as glass, plastic or metal foils. The most 
advanced organic electronic systems already in commercial production are high-
efficiency, very bright and colorful thin displays based on organic light-emitting devices 
(OLEDs). Significant progress is also being made in the realization of organic thin-film 
transistors (OTFTs) and organic photovoltaic devices (OPVs) for low-cost solar energy 
generation. The enormous progress in this field has been driven by the expectation to 
realize new applications, such as large area, flexible displays, sensors arrays, disposable 
41 
low-cost integrated circuits or plastic solar cells. Also, almost all Microsystems and 
MEMS devices manufactured today are fabricated on silicon substrates using 
traditionally expensive semiconductor equipment and facilities. Silicon-based MEMS 
technology may not be the ideal technology for large area sensor array applications. Also, 
recent experiments showing that bulk silicon is susceptible to fatigue [3]. So, integration 
of polymer MEMS with organic electronics has been drawing considerable interest in the 
recent years [65]-[68]. Integration of an OFET and an OLED or another organic device 
completes the need for controlling circuitry for the operation of the OLED making it an 
independent all polymer micro-system. For demonstration of one such integration with 
the OFET, a polymer MEMS pressure sensor is chosen. The pressure sensor changes the 
input voltage applied to the gate of the OFET and thereby controls the output drain 
current corresponding to the sensing movement for various pressures.  
 
4.1    Principle of operation 
In this section, the principle of operation of the polymer MEMS pressure sensor 
integrated with the OFET is discussed. Figure 4.1 shows a capacitive type MEMS 
pressure sensor connected in series with the gate terminal of an OFET.  
The equivalent electrical circuit of this series combination is shown in Figure 4.2. 
For a series combination of capacitors, the charge on both the capacitors becomes the 
same. 
MEMS
gsg
MEMSgsgMEMSMEMS
C
VC
VVCVCQ =?==                               (4.1) 
 
42 
Also, using Kirchoff?s Voltage Law, we can see that, 
gsMEMSGS
VVV +=                                               (4.2) 
Substituting Eqn. (4.1) in Eqn. (4.2), we have, 
gs
MEMS
g
gs
MEMS
gsg
GS
V
C
C
V
C
VC
V
?
?
?
?
?
?
?
?
+=+= 1       
?
?
?
?
?
?
?
?
+
=?
MEMS
g
GS
gs
C
C
V
V
1
                  (4.3) 
In the linear region, drain to source current, I
DS
 can be expressed as  
()
?
?
?
?
?
?
??
?
?
?
?
?
?
?
?
?
?
?
?
?
?
=
2
2
0 DS
DStgs
i
i
sDS
V
VVV
L
W
t
I
??
?                                (4.4) 
Substituting Eqn. (4.3) in Eqn. (4.4), we have, 
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
+
?
?
?
?
?
?
?
?
?
?
?
?
?
?
=
2
2
0 DS
DSt
gMEMS
MEMS
GS
i
i
sDS
V
VV
CC
C
V
L
W
t
I
??
?                       (4.5) 
 
Figure 4.1. A capacitive type MEMS pressure sensor connected in series with the gate of the OFET.  
 
43 
 
 
Figure 4.2. Equivalent electrical circuit for the Polymer MEMS pressure sensor integrated with an OFET.  
 
 
Figure 4.3. (a) Cross-sectional view of the MEMS pressure sensor with a circular membrane, (b) Close-up 
view of the MEMS varactor area, (c) Close-up view of the circular membrane.  
 
Using the equations of the pressure sensor, the MEMS pressure sensor capacitance can be 
expressed as [69] 
?
?
?
?
?
?
?
?
+?
?
?
?
?
?
+?
?
?
?
?
?
+= ...
5
1
3
1
1
2
00
0
d
w
d
w
CC
MEMS
                                         (4.6) 
where w
0
 is the deflection from the center of the membrane,  
44 
d is the gap between the top and bottom electrodes as shown in Figure 4.3(a), and  
C
0
 is the capacitance of the sensor when no pressure is applied. 
From Figure 4.3(b), it can be seen that, 
( )
()
?
?
?
?
?
?
?
?
+?
=
k
k
k
t
td
a
C
?
??
2
0
0
                                                               (4.7) 
where a is the radius of the circular membrane as shown in Figure 4.3(c). 
The deflection profile of the circular membrane for an applied pressure is given by,  
( )
D
ra
Pw
r
64
2
22
?
=                                                              (4.8) 
where r is the radial distance from the center of the membrane, ar ??0  ; 
          P is the applied pressure, and 
          D is the flexural rigidity/spring constant given by 
 
()
2
3
112 v
Et
D
?
=                                                               (4.9) 
where E is the Elastic modulus of the membrane,  
           t is the thickness of the membrane, and  
          ? is the Poisson?s ratio of the membrane. 
So from Eqn. (4.8), for radial distance, r = 0, 
D
Pa
w
64
4
0
=                                             (4.10) 
Substituting Eqn. (4.10) in Eqn. (4.6), we have, 
?
?
?
?
?
?
?
?
+
?
?
?
?
?
?
?
?
+
?
?
?
?
?
?
?
?
+= ...
645
1
643
1
1
2
4
2
4
0
D
Pa
dD
Pa
d
CC
MEMS
                            (4.11) 
45 
Neglecting the higher order terms, (11) can be reduced to 
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
+
?
?
?
?
?
?
?
?
+=
2
4
2
4
0
645
1
643
1
1
D
Pa
dD
Pa
d
CC
MEMS
                                (4.12) 
Using these expressions, the capacitance-to-pressure variation and drain current-to-
pressure variation can be estimated. Table 4.I shows the different parameters employed 
and their values.  
 
Table 4.I. Different parametric values employed to determine the variations of the MEMS capacitance and 
drain current with applied pressure. 
 
Parameter Value 
Permittivity of free space, ?
0
 8.854e-12 F/m
Young?s modulus of elasticity of Kapton, E 5.38 MPa
Poisson?s ratio of Kapton, ? 0.32
Relative permittivity of Kapton, ?
k
 3.1 
Thickness of Kapton, t
k
50e-06 m
Relative permittivity of the dielectric, BCB, ?
i
 2.65 
Thickness of BCB, t
i
 0.4e-06 m
Gap between the top and bottom electrodes, d 100e-06 m
Radius of the circular membrane, a 1e-03 m
Width of the OFET, W 1000e-06 m
Length of the OFET, L 50e-06 m
Gate-to-source voltage, V
GS
 -70 V
Drain-to-source voltage, V
DS
  -70 to 0 V 
Estimated threshold voltage, V
t
-20 V
Estimated mobility of the OFET, ?
s
 0.8e-08 m
2
/V-s 
 
46 
The gate-to-channel capacitance, C
g
 was calculated to be about 36 pF by connecting 
the OFET as shown in Figure 4.4. Figure 4.5 shows the plot of the MEMS capacitance as 
the pressure is varied from 0 to 160 kPa. The code for this plot, which was generated 
using MATLAB, is provided in Appendix E. From the plot, it can be gathered that the 
capacitance of the MEMS pressure membrane varies from 0.42 pF to about 0.49 pF 
causing a 70 fF variation overall. 
 
Figure 4.4. The electrical circuit connections of the OFET to obtain the gate-to-channel capacitance. 
 
Figure 4.5. A plot of the capacitance of the MEMS pressure sensor with varying pressure. 
47 
 
In order to obtain a relation between the drain current, I
DS
 and applied pressure, P, we can 
substitute Eqn. (4.12) in Eqn. (4.5) which yields 
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
+
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
+
?
?
?
?
?
?
?
?
+
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
+
?
?
?
?
?
?
?
?
+
?
?
?
?
?
?
?
?
?
?
?
?
?
?
=
2
645
1
643
1
1
645
1
643
1
1
2
2
4
2
4
0
2
4
2
4
0
0 DS
DSt
g
GS
i
i
sDS
V
VV
C
D
Pa
dD
Pa
d
C
D
Pa
dD
Pa
d
C
V
L
W
t
I
??
?
       (4.13) 
Eqn. (4.13) draws a complex relation between the variation of the drain current, I
DS
 with 
applied pressure, P. When the pressure outside the sensor cavity is increased above the 
atmospheric level, the pressure sensor membrane deflects downward toward the bottom 
electrode and increases the sensor capacitance, C
MEMS
 between the top and bottom 
electrodes. When C
MEMS
 is small compared to C
g
, an increase in the sensor capacitance 
decreases the voltage drop across the sensor and increases the gate voltage, V
gs
 applied to 
the OFET. In the OFET, the increase in the gate voltage, V
gs
 increases the drain current, 
I
DS
. Thus, the mechanical movement of the pressure sensor in response to an applied 
external pressure is used to modulate the OFET drain current. Figure 4.6 is a plot of I
DS
 
generated using MATLAB with the parameters mentioned in Table 4.I as the pressure is 
varied from 0 to 200 kPa. This plot shows that there is a steady increase in current as the 
pressure applied on the membrane is increased. A detailed MATLAB code is provided in 
Appendix E. 
48 
 
Figure 4.6. A graph of the drain current, I
DS
 to the pressure, P applied on the MEMS sensor. 
 
4.2 MEMS Pressure Sensor 
 The MEMS pressure sensor described in this section has been developed by our 
research group [70]. It was fabricated using printed circuit processing techniques. The 
MEMS pressure sensor consists of a cylindrical cavity formed by a sandwich of a 30 mil 
thick Liquid Crystal Polymer (LCP) substrate, a 2 mil thick LCP spacer film (with 
circular holes) and a 2 mil thick LCP MEMS layer. The photographs of the three layers 
are shown in Figure 4.7. The bottom electrode of the sensor is defined on the substrate by 
photolithography and wet etching processes. The top electrode of the sensor is defined on 
the bottom side of the LCP MEMS layer by photolithography and wet etching processes. 
In the spacer layer, circular holes are defined by mechanical machining. These three 
layers are laminated by thermo-compression bonding at normal atmospheric pressure 
49 
using a press. After bonding, the sealed cavity of the pressure sensor is at atmospheric 
level. A photograph of the fabricated MEMS pressure sensor is shown in Figure 4.8. 
     
                          (a)                                                    (b)                                                    (c) 
 
Figure 4.7. The three layers of the polymer MEMS pressure sensor: (a) Bottom electrode, (b) Spacer Film 
and (c) Top Electrode. 
 
 
 
Figure 4.8. Photograph of the MEMS pressure sensor after thermo-compression bonding. 
 
The MEMS pressure sensor was placed in a sealed pressure chamber and the 
capacitance variation with a change in the pressure applied was recorded. Figure 4.9 
shows the plot of the measured capacitance of the MEMS pressure sensor as the pressure 
50 
was varied from 0 to 160 kPa [56]. The capacitance with no pressure applied was 
measured to be 3.52 pF. It was observed that as the pressure increased, the capacitance 
increased steadily and settled at 3.59 pF. Hence the variation is about 70 fF. 
 
Figure 4.9. A graph showing the variation of the measured MEMS capacitance with applied pressure. 
 
 
4.3 Integration of MEMS Pressure Sensor and the OFET 
Experiments were conducted by simply connecting the MEMS pressure sensor and 
the OFET demonstrated in the previous chapter through wires. Figure 4.10(a) shows the 
cross-sectional view and Figure 4.10(b) shows the top view of the connections. The 
experimental setup employed for the testing of these devices is shown in Figure 4.11. It 
consists of a probe station, a semi-conductor parametric analyzer, and a pressure 
chamber. The MEMS pressure sensor is placed inside the chamber and the OFET drain 
current is measured at various pressures. Figure 4.12 shows the generated pressure vs. the 
51 
drain current characteristics. This plot was generated for a gate source voltage, V
GS
 = -65 
V. From the plot, it can be observed that for a drain voltage, V
DS
 = -50 V, the drain 
current increases from -103 nA to -282 nA when the pressure is increased from 0 to 50 
kPa. Hence, we can see that there is a considerable increase in the drain current of the 
OFET when pressure is applied to the MEMS pressure sensor. 
 
 
(a) 
(b) 
Figure 4.10. Schematic diagram of the wire integration of the MEMS pressure sensor and the OFET: (a) 
Cross-sectional view and (b) Top view. 
52 
      
Figure 4.11. The experimental setup used for obtaining the pressure sensor vs. the drain current 
characteristics. 
 
 
Figure 4.12. Pressure Versus Drain Current Characteristics for the Polymer MEMS sensor. 
53 
4.4 Monolithic Integration of MEMS Pressure Sensor and the OFET 
The ultimate goal of this project is to develop a monolithic all polymer integration 
of the MEMS pressure sensor and the OFET. Figure 4.13 shows the schematic diagram of 
one such integration.  
 
(a) 
 
(b) 
 
Figure 4.13. Schematic configuration of the Polymer MEMS pressure sensor monolithically integrated with 
an OFET: (a) Cross-sectional view and (b) Top View. 
 
Based on the capacitance measurements and the range of the pressure sensor, a new 
design was developed where in both the pressure sensor and OFET would be fabricated 
54 
on the same substrate. This design was then fabricated using printed circuit processing 
techniques. Kapton film was employed as the top MEMS layer and polyflon film was cut 
through mechanical machining to form the spacer film. A step-by-step account of the 
fabrication process is provided in Figure 4.14. A traveler detailing the fabrication process 
is provided in Appendix F. A photograph of the fabricated device is shown in Figure 
4.15.  
Before tests can be run on the integrated device, the organic field effect transistor and 
the MEMS pressure sensor were tested separately. The OFET was tested using a HP 
4145A parametric analyzer. The output and transfer characteristics of the transistor are 
shown in Figure 4.16 and Figure 4.17, respectively. It can be observed that the OFET 
exhibits characteristics similar to a traditional FET. Also, the pressure sensor variation 
was tested in a sealed pressure chamber. The capacitance variation to the change in 
pressure is plotted in Figure 4.18. It can be seen that the capacitance varies about 250 fF 
from 7.7 to 7.95 pF. This test was repeated about 4-5 times with less than 1% tolerance 
error. The 250 fF capacitance variation is almost thrice as much as the previous MEMS 
pressure sensor employed for the wire integration. In addition to this, the OFET 
employed in the previous section is connected in series with the new sensor and the 
sensing mechanism is tested. A plot of the measured drain current of the OFET with 
changes in the applied pressure is shown in Figure 4.19. It can be noted that as the 
pressure increases, the drain current also increases. It can also be seen that the drain 
current is lower as is the change in the drain current when compared to the results of the 
wire integration.  
55 
 
Figure 4.14. Fabrication process for the monolithically integrated OFET and MEMS pressure sensor. 
56 
 
 
Figure 4.15. Photograph of the fabricated MEMS pressure sensor monolithically integrated with an OFET. 
 
 
 
Figure 4.16. Output characteristics of the OFET monolithically integrated with a MEMS pressure sensor. 
57 
 
Figure 4.17. Transfer characteristics of the OFET monolithically integrated with a MEMS pressure sensor. 
 
 
Figure 4.18. A graph of the capacitance of the pressure sensor to the pressure applied. 
 
58 
 
Figure 4.19. A graph of the drain current of the OFET discussed in chapter 3 tested in conjunction with the 
new Kapton-based MEMS pressure sensor. 
 
 
Since both the devices were shown to be working well, the monolithically integrated 
OFET and MEMS pressure sensor were analyzed as a series combination. Figure 4.20 
shows the graph of the drain current of the OFET plotted against the applied pressure. 
From the plots, it can be gathered that the drain current does not change significantly with 
the change in applied pressure. Some of the factors contributing to this phenomenon 
could be that the gate capacitance, C
g 
of the MEMS pressure sensor and OFET series 
combination is about 7.6 pF, which is quite higher than the design value of about 0.8 pF. 
This change could have been brought about by the parasitics in the connecting wires. 
Also, the p-type material, Pentacene is known to degrade in performance under prolonged 
exposure to light and moisture.  
59 
This chapter has presented the design, fabrication and testing of a series integration of 
a MEMS pressure sensor and an OFET. The wire integration results have successfully 
demonstrated that an increase in pressure on the MEMS pressure sensor manifests itself 
as an increase in the drain current. However, the monolithic integration did not replicate 
these results although the OFET and the MEMS pressure sensor were tested individually 
and were found to be functioning adequately.  
 
Figure 4.20. A graph of the drain current of the monolithically integrated OFET tested with the new 
Kapton-based MEMS pressure sensor. 
 
 
 
60 
 CHAPTER V: CONCLUSIONS AND FUTURE WORK 
 
5.1 MEMS-based Frequency agile antennas 
 
Chapter 2 described a MEMS-based tunable coplanar patch antenna. The patch 
antenna was made tunable in the range of 5.185 GHz to 5.545 GHz, achieving a 330 
MHz bandwidth. The return loss was better than -20 dB. Although the patch antenna was 
originally designed to operate at 3.5 GHz, adding an actuation pad caused a frequency 
shift to 5.5 GHz. There was a MEMS varactor warpage problem. It was overcome by 
readjusting the bonding fixture and placing Kapton pieces in the air gap between the 
MEMS electrode and the antenna. The next step would be to explore the idea of 
increasing the number of MEMS varactors on the antenna in order to elicit a larger 
bandwidth. Also, reconfigurable antennas can be modeled to be integrated with RF 
MEMS switches to achieve frequency bands like GSM (0.9 GHz), GPS (1.57 GHz), DCS 
(1.8 GHz) and WLAN (2.4 GHz and 5.2 GHz). Figure 5.1 shows two configurations 
where multiple MEMS varactors are placed along the non-radiating edges to help the 
antenna tune in a wider frequency range. These models need to be explored further. 
61 
    
                                 (a)                                                                                  (b) 
Figure 5.1. (a) and (b): Possible configurations of MEMS-based frequency agile antennas. 
 
5.2 Organic electronics and micro-systems 
 
Chapter 3 presented an Organic Field Effect Transistor (OFET) with Pentacene, a p-
type semi-conductor polymer, BenzoCycloButene (BCB) as the gate dielectric and gold 
was used for the metal pads. Although, the design was unresponsive initially, widening 
the gate electrode supplied the required field effect. The electrical characteristics of this 
transistor were observed to be similar to that of silicon-based transistors. Some key 
advantages of the OFET include no gate leakage current and the ability to handle high 
voltages. Low mobility and slow switching times are some of the drawbacks.  
Chapter 4 illustrated a wire integration of a MEMS-based pressure sensor with the 
OFET discussed in Chapter 3. It was observed that the pressure variation in the pressure 
sensor brought about a change in the output drain current of the transistor. So, the sensing 
movement was able to control the output of the transistor. However, the monolithic 
integration of the MEMS pressure sensor and the OFET could not replicate the same 
results. The reasons behind that are currently being probed. First, the measured 
62 
capacitance of the pressure sensor was 10 times the design value. So, it can be seen that a 
lot of parasitics are involved that are degrading the performance of the integrated FET. 
When the OFET discussed in Chapter 4 was tested separately, the device was found to be 
in working condition and exhibiting FET characteristics. The measured drain current of 
the OFET was a big improvement compared to the OFET presented in Chapter 3. The 
current increased from hundreds of nA to tens of ?A which also boosted the mobility of 
the new OFET. The performance of the MEMS pressure sensor was also evaluated 
separately and found to be satisfactory. When the MEMS pressure sensor and the OFET 
were tested together, a big drop was noticed in the output current of the transistor. A 
better design that will reduce the affect of parasitics needs to be developed. Also, the 
performance of Pentacene is affected by exposure to light and moisture [71]. In the future 
processes, one way to overcome this is to coat a passivation layer like poly-chloro-para-
xylylene (parylene) on top of Pentacane to protect it from atmospheric affects [72]. Also, 
other conjugated polymers that have better alignment of organic molecules leading to 
lower band gaps and higher mobilities need to be explored. Also, dipping the drain and 
source metal layers in alkane thiols can improve carrier injection between the p-type 
semiconductor polymer and the metal [73].  
The project was able to develop a ?Polymer Microsystem? by integration of a Polymer 
MEMS device and Organic Electronics. Traditionally, microsystems have been fabricated 
using silicon-like semiconductor substrates by micromachining techniques. Silicon (or 
thin-film in general) may be the ideal substrates for semiconductor devices, but they may 
not be suitable for all microsystem applications. In particular, silicon based wafer level 
63 
technology may not be suitable for cost effective manufacturing and packaging of 
microsystems for large area and large volume applications. The proposed work was to 
demonstrate a plastic microsystem using low cost fabrication techniques. As a proof-of-
concept of the proposed plastic microsystem, this project demonstrated the integration of 
a Polymer MEMS pressure sensor with an organic field effect transistor. 
 
 
 
 
 
 
 
64 
65 
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72 
APPENDIX A 
 
TRAVELER FOR FABRICATING A TUNABLE COPLANAR PATCH 
ANTENNA 
 
 
I. Substrate: 
 
The substrate to be used should have been cut to the right dimensions and should have 4 
holes drilled that are spaced 42 mm from every adjacent hole and have a diameter of 
1/16th inch + 1mil (for clearance). 
The substrate must first be cleaned with acetone, methanol and water; then dried off with 
a nitrogen gun. The substrate must subsequently be dipped in a weak sulphuric acid 
solution (a couple of drops of sulphuric acid in a regular bowl filled with water) for a 
couple of minutes to remove any oxidation. 
 
 
1. Etching copper off of the backside: This process can either be done prior to any 
processing or after defining the antenna. 
 
Step 1  Photoresist application on the side to be used to define the antenna. Stick blue 
tack film on the other (back) side so that no photo resist sticks to that side. 
Photoresist         S1813 
Spin Speed         2500 rpm 
            Spin Ramp         500 rpm 
            Spin Time          30 secs 
 
Step 2  Soft bake (Remove the tack film as it will wrinkle under high temperatures) 
Temperature        110 0C 
Time                    60 secs 
 
Step 3  Etching  
Etchant         CE-200 
Time                    4 mins 
 
Step 4  Acetone/Methanol Cleaning 
Cleaner                        First Acetone then Methanol  
DI Rinse       30 secs in a bowl of slightly agitated DI water 
N2 dry            until the substrate is completely dry 
73 
2. Defining the antenna: Take the side that has copper on it. 
 
Step 1  Acetone/Methanol Cleaning 
Cleaner                        First Acetone then Methanol  
DI Rinse       30 secs in a bowl of slightly agitated DI water 
N2 dry            until the substrate is completely dry 
 
Step 2  Photoresist application 
Photoresist         S1813 
Spin Speed         2500 rpm 
            Spin Ramp         500 rpm 
            Spin Time          30 secs 
 
Step 3  Soft bake 
Temperature        110 0C 
Time                    60 secs 
 
Step 4  Photoresist Exposure 
            Mask used    ANTENNA_TCPA 
            Exposure Time    45 secs 
 
Step 5  Post-exposure bake 
Temperature        110 0C 
Time                    60 secs 
 
Step 6  Photoresist Develop 
Developer           CD-30 
Time              45 secs 
DI Rinse        30 secs in a bowl of slightly agitated DI water 
N2 dry            until the substrate is completely dry 
 
Step 7  Acetone/Methanol Cleaning 
Cleaner                        First Acetone then Methanol  
DI Rinse       30 secs in a bowl of slightly agitated DI water 
N2 dry            until the substrate is completely dry 
 
 
3. Spincoating BCB: A mask having the pattern of the BCB should be available as a 
glass mask for this process. Note: Do not use film mask for this process. 
 
Step 1  Adhesion promoter application (AP3000) 
Spin Speed         3000 rpm 
            Spin Ramp         1000 
            Spin Time          30 secs 
 
Step 2  Soft Bake 
Temperature        120 
0
C 
Time                    30 secs 
 
Step 3  BCB (Cyclotene 4024-40) application for a thickness of ~ 7 ?m). Let BCB 
spread on the substrate for a minute. 
Spread Speed  500 rpm 
Ramp   500 
Time   5 secs 
Speed   1500 rpm 
Ramp   1000 
Time   30 secs 
 
Step 4  Soft Bake 
Temperature        95 
0
C 
Time                    90 secs 
 
Step 5  Photoresist Exposure 
            Mask used    BCB_MASK 
            Exposure Time    15 secs 
 
Step 6  Pre Develop Bake 
Temperature        80 
0
C 
Time                    30 secs 
 
Step 7  Puddle Develop Process: The spinner is used for this process.  
Developer         DS2100 (Pour it on the wafer and let it sit for 75 secs.) 
Rinse Speed  500 rpm 
Ramp   500 
Rinse Time  5 secs 
Speed   2500 rpm 
Ramp   1000 
Time   30 secs 
 
Step 8  Post Develop Bake 
Temperature        70 
0
C 
Time                    60 secs 
 
 Step 9 Curing BCB: The BCB coated substrate is cured in a nitrogen oven for 2-3 hours 
by letting the temperature ramp up to 200 
o
C.  
 
 
 
74 
II. Kapton film: 
 
1. Kapton film cleaning 
 
Step 1  Acetone/Methanol Cleaning 
Cleaner                        First Acetone then Methanol  
DI Rinse       30 secs in a bowl of slightly agitated DI water 
N
2 
dry            until film is completely dry 
 
Step 2  Oxidation Removal 
Remover                      250 ml DI water + 2 drops of H
2
SO
4
 using a pipette  
DI Rinse       30 secs in a bowl of slightly agitated DI water 
N
2 
dry            until film is completely dry 
 
Step 3  Acetone/Methanol Cleaning 
Cleaner                        First Acetone then Methanol  
DI Rinse       30 secs in a bowl of slightly agitated DI water 
N
2 
dry            until film is completely dry 
 
 
2. Etching the backside of the Kapton film 
 
Step 1  Copper Etching (Cover the front side using blue tack squares) 
Etchant     CE-200 
Time      8 secs 
DI Rinse       30 secs in a bowl of slightly agitated DI water 
N
2 
dry            until film is completely dry 
 
Step 2  Nichrome Etching 
Etchant     250 ml DI water + 10 gm KMnO
4
 + 5 gm NaOH 
            Time              60 secs 
DI Rinse       30 secs in a bowl of slightly agitated DI water 
            N
2 
dry            until film is completely dry 
 
Step 3  Acetone/Methanol Cleaning 
Cleaner                        First Acetone then Methanol  
DI Rinse       30 secs in a bowl of slightly agitated DI water 
            N
2 
dry            until film is completely dry 
 
3. Gluing the film on a wafer 
 
Step 1  4? Wafergrip application 
 Peel wafergrip and put it on a clean and smooth wafer  
 
75 
Step 2  Heat wafer on hot plate 
Temperature        110 
0
C 
Time                    till wafergrip melts and sticks to the wafer 
 
Step 3  Stick film on wafer 
While the wafer gel is still in molten state, stick the Kapton film starting with one 
e and smoothing the entire film on the gel without any unevenness edg
                   
 
4. Defining the electrode 
 
Step 1  Photoresist application 
Photoresist         S1813 
Spin Speed         2500 rpm 
            Spin Ramp         500 rpm 
            Spin Time          30 secs 
 
Step 2  Soft bake 
Temperature        110 
0
C 
Time                    60 secs 
 
Step 3  Photoresist Exposure 
            Mask used    ELECTRODE_TCPA 
            Exposure Time    15 secs 
 
Step 4  Photoresist Develop 
Developer           CD-30 
Time              45 secs 
DI Rinse        30 secs in a bowl of slightly agitated DI water 
N
2 
dry            until film is completely dry 
 
Step 5  Post Develop Bake 
Temperature        110 
0
C 
Time                    60 secs 
 
Step 6  Copper Etching 
Etchant     CE-200 
Time      8 secs 
DI Rinse       30 secs in a bowl of slightly agitated DI water 
N
2 
dry            until film is completely dry 
 
Step 7  Photoresist Removal 
Photoresist Remover   First Acetone then Methanol  
DI Rinse       30 secs in a bowl of slightly agitated DI water 
N
2 
dry            until film is completely dry 
76 
Step 8  Nichrome Etching 
Etchant     250 ml DI water + 10 gm KMnO
4
 + 5 gm NaOH 
            Time              60 secs 
DI Rinse       30 secs in a bowl of slightly agitated DI water 
            N
2 
dry            until film is completely dry 
  
Step 9  Acetone/Methanol Cleaning 
Cleaner                        First Acetone then Methanol  
DI Rinse       30 secs in a bowl of slightly agitated DI water 
N
2 
dry            until film is completely dry 
 
 
5. Aluminum deposition  
 
Step 1  Oxidation Removal 
Remover                      250 ml DI water + 2 drops of H
2
SO
4
 using a pipette  
DI Rinse       30 secs in a bowl of slightly agitated DI water 
N
2 
dry            until film is completely dry 
 
Step 2  Acetone/Methanol Cleaning 
Cleaner                        First Acetone then Methanol  
DI Rinse       30 secs in a bowl of slightly agitated DI water 
N
2 
dry            until film is completely dry 
 
Step 3  Aluminum deposition 
   Process                       E-beam 
   Thickness    5000 
0
A 
 
Step 4  Acetone/Methanol Cleaning 
Cleaner                        First Acetone then Methanol  
DI Rinse       30 secs in a bowl of slightly agitated DI water 
N
2 
dry            until film is completely dry 
 
 
6. Patterning Aluminum for Deep Reactive Ion Etching  
 
Step 1  Photoresist application 
Photoresist         S1813 
Spin Speed         2500 rpm 
            Spin Ramp         500 rpm 
            Spin Time          30 secs 
 
Step 2  Soft bake 
Temperature        110 
0
C 
Time                    60 secs 
77 
Step 3  Photoresist Exposure 
            Mask used    DRIE_TCPA 
            Exposure Time    15 secs 
 
Step 4  Photoresist Develop 
Developer           CD-30 
Time              45 secs 
DI Rinse        30 secs in a bowl of slightly agitated DI water 
N
2 
dry            until film is completely dry 
 
Step 5  Post Develop Bake 
Temperature        110 
0
C 
Time                    60 secs 
 
Step 6  Aluminum Etching 
Etchant     PAE 
Time     15 mins 
 
 
7. Deep Reactive Ion Etching (DRIE)  
 
The machine used for performing the DRIE etching of the Kapton film is an STS AOE 
(Advanced oxide etch) .The configuration of the gases used for this etch in our facility is 
8 sccm CF4 and 35 sccm Oxygen with 500 Watts of RF power. The ratio of the gases is 
the most important part and not the exact quantity of the gases. These processing 
parameters take about 75-85 minutes to etch a 2 mil thick Kapton layer. Before starting 
this process, it is extremely important to check if the Kapton film is stuck properly to a 
silicon substrate with the thermally conductive gel without any air bubbles. If air bubbles 
are present between the substrate and the film, it results in inconsistent etching of the 
Kapton film. A simple procedure to check for any trapped air bubbles in the Kapton film 
after it is glued to the silicon wafer is to put the wafer in the wafer holder of the STS 
system and hit ?Pump + Map? on the software screen. This feature will cause the Kapton 
film to be put under some pressure thereby revealing the hidden air bubbles. Once the 
bubbles are located, the wafer should be put on a hot plate. After giving the gel adequate 
time to melt again, all the bubbles should be nudged out through the corners of the 
Kapton film with the help of a small clean tissue (the clean room certified ones) which is 
rolled up to form a hard edge. After the film has been flattened out, it should be checked 
again for bubbles in the STS system. This process may be repeated until the film is 
satisfactorily flat. 
Now, 
? Place the wafer on a wafer holder in the STS system. 
? Hit ?Pump+Map? on the software screen. (Assuming that there are no bubbles, 
proceed to next step.) 
? Hit ?Load? on the software screen.  
78 
? To create a Kapton recipe program for the STS system: 
Click on ?Recipe?. Then click on ?New?. 
Any new recipe opens with two default steps- Gas Line Purge and Standby step. 
1. Gas Line Purge  
No of cycles: 1 
 
2. Standby Step 
Standby Gas:  Argon 
Flow Rate:  0 sccm 
Base Pressure:  1 mTorr 
Pressure Tip:  94 mTorr 
 
Pump Down Time: 00:00:20 hh:mm:ss 
Purge Time:  00:00:10 hh:mm:ss 
Pump Out Time: 00:00:30 hh:mm:ss 
 
1. Add New Step. This step can be renamed as desired. It comes with 6 
tabs.  
General 
Pressure 
Gases 
R.F. 
HBC and  
HeLUR 
 
General: 
Recipe Process Mode: ? Discrete O Continuous 
Pump Down Time: 00:00:20 hh:mm:ss 
Gas Stabilization: 00:00:20 hh:mm:ss 
Process Time:  00:05:00 hh:mm:ss 
Pump Out Time: 00:00:30 hh:mm:ss 
The total process time required for a 2 mil Kapton film is around 75-85 
minutes.  
  
Process: 
  APC Mode:   O Manual  ? Automatic  
  Process Pressure 
  Pressure:   60 mTorr 
  Tolerance:   25 % 
  Base Pressure:  0 mTorr 
  Pressure Tip:      94 mTorr 
 
  Gases: 
  Gas Flow (sccm) Tolerance 
79 
O
2
    35 sccm 10 % 
CF
4
 8 sccm  5 %     
Active Gases:  O
2
 and CF
4
 
Illegal Combination: H
2 
 
R.F.: 
O 13.56 MHz on Platen Only 
O 13.56 MHz on Coil Only 
? Simultaneous 
 
13.56 MHz Generator connected to Coil 
Power:   500 W 
Tolerance:  25 % 
 
Matching Auto 
Match Load:  50 % 
Match Tune:  50 % 
 
13.56 MHz Generator connected to Platen 
Power:   100 W 
Tolerance:  25 % 
 
Matching Auto 
Match Load:  50 % 
Match Tune:  50 % 
 
All the other options are left unaltered. 
   
? Save and close this recipe. 
? In order to ensure that this recipe is selected, click on ?Select? and select this 
recipe from the list. 
Hit ?Process?. Each cycle will have a process time of 5 minutes. Repeat the process until 
the process time reaches a total of about 75-85 minutes. The process time can be started 
at 5 minutes at first and increased to a suitable no. depending on the machine. 
 
 
8. Post-DRIE Aluminum Etching 
 
Step 1  Aluminum Etching 
Etchant     6 gm NaOH + 200 ml DI water 
Time      3 mins 
 
Step 2  Acetone/Methanol Cleaning 
Cleaner                       First Acetone then Methanol  
80 
DI Rinse       30 secs in a bowl of slightly agitated DI water 
            N
2 
dry            until film is completely dry 
 
 
9. Defining the bias lines  
 
Step 1  Photoresist application 
Photoresist         S1813 
Spin Speed         2500 rpm 
            Spin Ramp         500 rpm 
            Spin Time          30 secs 
 
Step 2  Soft bake 
Temperature        110 
0
C 
Time                    60 secs 
 
Step 3  Photoresist Exposure 
            Mask used    BIAS_LINES_TCPA 
            Exposure Time    60 secs 
 
Step 4  Photoresist Develop 
Developer           CD-30 
Time              45 secs 
DI Rinse        30 secs in a bowl of slightly agitated DI water 
N
2 
dry            until film is completely dry 
 
Step 5  Post Develop Bake 
Temperature        110 
0
C 
Time                    60 secs 
 
Step 6  Copper Etching 
Etchant     CE-200 
Time      8 secs 
DI Rinse       30 secs in a bowl of slightly agitated DI water 
N
2 
dry            until film is completely dry 
 
Step 7  Photoresist Removal 
Photoresist Remover   First Acetone then Methanol  
DI Rinse       30 secs in a bowl of slightly agitated DI water 
N
2 
dry            until film is completely dry 
 
 
 
 
81 
10. Final film cleaning 
 
Step 1  Wafer gel Cleaning 
Cleaner                        Amyl Acetate  
Temperature       150 
0
C 
Time   until film lifts off the wafer with no residual wafer gel on it 
             
Step 2  Acetone/Methanol Cleaning 
Cleaner                        First Acetone then Methanol  
DI Rinse       30 secs in a bowl of slightly agitated DI water 
            N
2 
dry            until film is completely dry 
 
Chemical Incompatibilities: 
 
1. Copper etchant, CE-200 removes Aluminum faster than it removes copper. 
2. Photoresist Developer, CD-30 attacks Nichrome while H
2
SO
4
 does not. 
3. Nichrome etchant reacts with photoresist, S1813. 
4. Aluminum etchant, NaOH reacts with photoresist, S1813. 
5. Aluminum etchant, PAE etches copper too. 
6. BCB process: 
a. Do not rinse the substrate in acetone/methanol after the deposition of 
BCB. 
b. BCB is very viscous. Any bubbles that may arise are hard to put out. So, 
proper care should be taken when handling BCB. 
c. A dab of T1100 on a swab can be used to remove residual BCB, if any. 
 
 
 
 
 
 
 
 
82 
APPENDIX B 
MEASUREMENTS WITH THE WYKO OPTICAL PROFILOMETER 
 
A picture of the WYKO measurement system is shown in Figure 1. As can be seen 
from Figure 1, the WYKO measurement system consists of an objective microscope, a 
field of vision microscope (controlled through software), a stage, and microscope 
movement controlling joystick all interfaced to the software Vision 32. The procedure to 
make measurements using this system will be explained in the following sections. 
1. To start measurements, open the software Vision 32 (Shortcut to V32 on desktop) 
on the interfaced computer. Once the software is opened, Hardware ? Intensity. 
The Intensity and Focus window should open up and the software screen it should 
look like in Figure 2.  
 
2. Place the device or sample to be measured under the microscope in the light beam 
and reduce the intensity to about 50% (use the sliding bar under the intensity and 
focus window to do this). The screen should look something like what is shown in 
Figure 3 (predominantly grey). 
 
3. To adjust the focus of the microscope on the device, we need to select a suitable 
objective lens. To do this, go to Hardware? Measurement options.  
a. In the options tab, change the resolution to half (this is sufficient for our 
measurement purposes).  
b. In the measurement mode, select VSI. 
c. In the objective drop down menu, select 5X or whatever is suitable and 
select 1X from the FOV dropdown menu. 
d. Now, in the VSI options tab, check 3X speed in the scan options, uncheck 
the high speed/large memory checkbox, set backscan and length to 10 um 
and 30 um respectively. (Backscan is the scan distance in the negative z 
axis from the focused surface and length is the scan distance in the 
positive z axis.)  
 
4. Focusing: We are ready to focus the interferometer on the desired surface. The 
coarse and fine movement of the microscope is controlled by two knobs shown in 
Figure 4.  
 
 
83 
 
Figure 1. The WYKO Measurement system. 
 
 
Figure 2.  Initial Intensity and Focus window. 
 
 
Use the coarse knob until you see fringe lines on the target surface. The fringe lines 
on a certain region on the surface signify that the microscope is focused on that region of 
the surface. We?d like the focus to be on the whole surface to make a consistent 
measurement throughout the field of view. To make the fringe lines focus on the whole 
surface in the field of view (spreading the fringes), we?ll need to tilt the microscope using 
the microscope lateral movement control knob and use the fine adjustment knob shown in 
Figure 4. A close up of the lateral movement control is shown in Figure 5. 
 
84 
 
Figure 3. Adjusting Image intensity. 
 
 
Figure 4. Microscope coarse and fine movement control. 
 
As was explained earlier, once the fringes are seen on the intensity and focus window, 
we need to tilt the microscope and use the fine focus adjustment to spread the fringes. 
The joystick shown in Figure 5 is used for the movement along with the tip/tilt button. 
Moving the joystick without pressing the Tip/Tilt button moves the stage in the x and y 
directions and movement of the joystick when the Tip/Tilt button is pressed tilts the 
microscope. The movement speed control button on top of the joystick is an extremely 
important part of this system since it reduces the speed with which the microscope tilts. 
There is a very high probability of the microscope hitting the substrate if the tilting of the 
microscope is not handled extremely carefully. 
85 
 
Figure 5. Lateral movement control of microscope. 
 
5. Measurement: When the fringes are spread over the target surface in the field of 
view, File? New to perform measurement. Do not touch anything on the system 
during the measurement process. 
 
6. Analysis: After the measurement is done, Analysis? 2D. The 2D analysis 
window is shown in Figure 6.  
 
7. Interpretation of results: Let us assume for example that going from left to right 
in the field of view, there is a cantilever and hence is at an elevation. The height 
from the substrate (assuming the fringes were focused on the substrate) is 
depicted by the y-axis difference between a point on the substrate and a point on 
the cantilever shown in the X profile. In other words, a step is shown in the X-
profile measurement and the height of the step is the height of the cantilever. To 
position the profile lines as required in the field of view, click on the required 
point on the field of view. Intersection of the X-profile line (red) and the Y-profile 
line (blue) is depicted. Position the markers to obtain a measurement of the height 
difference. Markers simultaneously move in the profile plot and the field of view. 
The profile lines in the field of view can be moved by dragging them on the field 
of view or clicking at a different point. 
 
86 
8. Saving the results: File?Save to save the data. If another measurement is to be 
performed, close the 2-D analysis window and reopen the Illumination window 
and follow the procedure outlined in these instructions.  
 
 
Figure 6. The x- and y- profiles of the test device. 
 
 
Important note: Before shutting the system down, make sure the illumination is 
set to zero or else when the system is restarted, the illumination bulb will be 
damaged. 
 
 
 
 
 
 
 
 
 
 
87 
APPENDIX C 
 
TRAVELER FOR FABRICATING AN OFET IN THE COPLANAR 
CONFIGURATION 
 
 
1. Defining the gate, drain and source electrodes: Choose a smooth oxidized silicon 
wafer. 
 
Step 1  Acetone/Methanol Cleaning 
Cleaner                        First Acetone then Methanol  
DI Rinse       30 secs in a bowl of slightly agitated DI water 
N
2 
dry            until wafer is completely dry 
 
Step 2  Photoresist application (~ 2 microns thick) 
Photoresist         nLOF 2035 negative photoresist 
Spin Speed         3500 rpm 
            Spin Ramp         500 rpm 
            Spin Time          30 secs 
 
Step 3  Soft bake 
Temperature        110 
0
C 
Time                    60 secs 
 
Step 4  Photoresist Exposure 
            Mask used    ELECTRODES_MASK 
            Exposure Time    15 secs 
 
Step 5  Post-exposure bake 
Temperature        110 
0
C 
Time                    60 secs 
 
Step 6  Photoresist Develop 
Developer           AZ-300 MIF 
Time              90 secs 
DI Rinse        30 secs in a bowl of slightly agitated DI water 
N
2 
dry            until wafer is completely dry 
 
 
88 
Step 7  Post Develop Bake 
Temperature        110 
0
C 
Time                    60 secs 
 
Step 8  Gold deposition 
   Process                       E-beam 
   Thickness    1000 
0
A 
 
Step 9  Defining the gold electrodes through photoresist removal 
Process                      Lift-off 
Developer    Acetone 
Time   ~ 30 mins 
 
Step 10  Acetone/Methanol Cleaning 
Cleaner                        First Acetone then Methanol  
DI Rinse       30 secs in a bowl of slightly agitated DI water 
N
2 
dry            until wafer is completely dry 
 
 
2. Spincoating BCB: A mask having the pattern of the BCB should be available as a 
glass mask for this process. Note: Do not use film mask for this process. 
 
Step 1  Adhesion promoter application (AP3000) 
Spin Speed         3000 rpm 
            Spin Ramp         1000 
            Spin Time          30 secs 
 
Step 2  Soft Bake 
Temperature        120 
0
C 
Time                    30 secs 
 
Step 3  BCB (Cyclotene 4024-40) application for a thickness of ~ 0.5 ?m). Prepare a 
mixture of 1:1 solution of BCB and T1100. Let this spread on the wafer for a minute. 
Spread Speed  500 rpm 
Ramp   500 
Time   5 secs 
Speed   2700 rpm 
Ramp   1000 
Time   30 secs 
 
Step 4  Soft Bake 
Temperature        95 
0
C 
Time                    90 secs 
 
89 
Step 5  Photoresist Exposure 
            Mask used    BCB_MASK 
            Exposure Time    15 secs 
 
Step 6  Pre Develop Bake 
Temperature        80 
0
C 
Time                    30 secs 
 
Step 7  Puddle Develop Process: The spinner is used for this process.  
Developer         DS2100 (Pour it on the wafer and let it sit for 75 secs.) 
Rinse Speed  500 rpm 
Ramp   500 
Rinse Time  5 secs 
Speed   2500 rpm 
Ramp   1000 
Time   30 secs 
 
Step 8  Post Develop Bake 
Temperature        70 
0
C 
Time                    60 secs 
 
 Step 9 Curing BCB: The BCB coated substrate is cured in a nitrogen oven for 2-3 hours 
by letting the temperature ramp up to 200 
o
C.  
 
Note:  
2. Do not rinse the substrate in acetone/methanol after this process. 
3. BCB is very viscous. Any bubbles that may arise are hard to put out. So, proper 
care should be taken when handling BCB. 
4. A dab of T1100 on a swab can be used to remove residual BCB, if any. 
 
 
3. Deposition of Pentacene: Before this step, all the contact pads to be utilized for 
probe testing should be covered with a blue tack film in order to prevent deposition of 
Pentacene on the pads. 
Process                      Thermal evaporation 
Deposition time    ~ 30 mins 
Note: Remove the tack film carefully before testing.  
 
 
 
 
 
 
 
 
90 
APPENDIX D 
 
TRAVELER FOR FABRICATING A BOTTOM CONTACT OFET 
 
 
1. Defining a gate electrode: Choose a smooth oxidized silicon wafer. 
 
Step 1  Acetone/Methanol Cleaning 
Cleaner                        First Acetone then Methanol  
DI Rinse       30 secs in a bowl of slightly agitated DI water 
N
2 
dry            until wafer is completely dry 
 
Step 2  Photoresist application (~ 2 microns thick) 
Photoresist         nLOF 2035 negative photoresist 
Spin Speed         3500 rpm 
            Spin Ramp         500 rpm 
            Spin Time          30 secs 
 
Step 3  Soft bake 
Temperature        110 
0
C 
Time                    60 secs 
 
Step 4  Photoresist Exposure 
            Mask used    GATE_ELECTRODE 
            Exposure Time    15 secs 
 
Step 5  Post-exposure bake 
Temperature        110 
0
C 
Time                    60 secs 
 
Step 6  Photoresist Develop 
Developer           AZ-300 MIF 
Time              90 secs 
DI Rinse        30 secs in a bowl of slightly agitated DI water 
N
2 
dry            until wafer is completely dry 
 
Step 7  Post Develop Bake 
Temperature        110 
0
C 
Time                    60 secs 
91 
Step 8  Gold deposition 
   Process                       E-beam 
   Thickness    1000 
0
A 
 
Step 9  Defining the gold electrode through photoresist removal 
Process                      Lift-off 
Developer    Acetone 
Time   ~ 30 mins 
 
Step 10  Acetone/Methanol Cleaning 
Cleaner                        First Acetone then Methanol  
DI Rinse       30 secs in a bowl of slightly agitated DI water 
N
2 
dry            until wafer is completely dry 
 
 
2. Spincoating BCB: A mask having the pattern of the BCB should be available as a 
glass mask for this process. Note: Do not use film mask for this process. 
 
Step 1  Adhesion promoter application (AP3000) 
Spin Speed         3000 rpm 
            Spin Ramp         1000 
            Spin Time          30 secs 
 
Step 2  Soft Bake 
Temperature        120 
0
C 
Time                    30 secs 
 
Step 3  BCB (Cyclotene 4024-40) application for a thickness of ~ 0.5 ?m). Prepare a 
mixture of 1:1 solution of BCB and T1100. Let this spread on the wafer for a minute. 
Spread Speed  500 rpm 
Ramp   500 
Time   5 secs 
Speed   2700 rpm 
Ramp   1000 
Time   30 secs 
 
Step 4  Soft Bake 
Temperature        95 
0
C 
Time                    90 secs 
 
 
Step 5  Photoresist Exposure 
            Mask used    BCB_MASK 
            Exposure Time    15 secs 
92 
Step 6  Pre Develop Bake 
Temperature        80 
0
C 
Time                    30 secs 
 
Step 7  Puddle Develop Process: The spinner is used for this process.  
Developer         DS2100 (Pour it on the wafer and let it sit for 75 secs.) 
Rinse Speed  500 rpm 
Ramp   500 
Rinse Time  5 secs 
Speed   2500 rpm 
Ramp   1000 
Time   30 secs 
 
Step 8  Post Develop Bake 
Temperature        70 
0
C 
Time                    60 secs 
 
 Step 9 Curing BCB: The BCB coated substrate is cured in a nitrogen oven for 2-3 hours 
by letting the temperature ramp up to 200 
o
C.  
 
Note:  
5. Do not rinse the substrate in acetone/methanol after this process. 
6. BCB is very viscous. Any bubbles that may arise are hard to put out. So, proper 
care should be taken when handling BCB. 
7. A dab of T1100 on a swab can be used to remove residual BCB, if any. 
 
 
3. Defining the drain and source electrodes:  
 
Step 1  Cleaning 
DI Rinse       30 secs in a bowl of slightly agitated DI water 
N
2 
dry            until wafer is completely dry 
 
Step 2  Photoresist application (~ 2 microns thick) 
Photoresist         nLOF 2035 negative photoresist 
Spin Speed         3500 rpm 
            Spin Ramp         500 rpm 
            Spin Time          30 secs 
 
Step 3  Soft bake 
Temperature        110 
0
C 
Time                    60 secs 
 
 
93 
Step 4  Photoresist Exposure 
            Mask used    D_S_ELECTRODES 
            Exposure Time    15 secs 
 
 
Step 5  Post-exposure bake 
Temperature        110 
0
C 
Time                    60 secs 
 
Step 6  Photoresist Develop 
Developer           AZ-300 MIF 
Time              90 secs 
DI Rinse        30 secs in a bowl of slightly agitated DI water 
N
2 
dry            until wafer is completely dry 
 
Step 7  Post Develop Bake 
Temperature        110 
0
C 
Time                    60 secs 
 
Step 8  Gold deposition 
   Process                       E-beam 
   Thickness    1000 
0
A 
 
Step 9  Defining the gold electrodes through photoresist removal 
Process                      Lift-off 
Developer    AZ 300 MIF 
Time     ~ 30 mins 
 
Step 10  Cleaning 
DI Rinse       30 secs in a bowl of slightly agitated DI water 
N
2 
dry            until wafer is completely dry 
 
 
4. Deposition of Pentacene: Before this step, all the contact pads to be utilized for 
probe testing should be covered with a blue tack film in order to prevent deposition of 
Pentacene on the pads. 
Process                      Thermal evaporation 
Deposition time    ~ 30 mins 
Note: Remove the tack film carefully before testing.  
 
 
 
 
 
 
94 
APPENDIX E 
 
MATLAB CODE FOR GENERATING PLOTS SHOWING THE VARIATION OF 
MEMS CAPACITANCE AND DRAIN CURRENT WITH APPLIED PRESSURE 
 
%Parameter assignment 
mu=5e-7;%Estimated mobility of the OFET in m^2/V.s 
ebcb=2.65; %Permittivity of BCB 
tbcb=0.5e-6; %Thickness of BCB in Meters 
Vgs=-60; %Gate-to-Source voltage in Volts 
Vt=-20; %Estimated threshold voltage in Volts 
Cg=36e-12; %Measured Gate-to-Channel capacitance in Farads 
W=1000e-6; %Width of the OFET in Meters 
L=50e-6; %Length of the OFET in Meters 
e0=8.854e-12; %Permittivity of free space 
d=100e-6;%Spacing between the top and bottom electrodes in Meters 
a=1e-3; %Radius of the circular membrane in Meters 
tkap=50e-6;%Thickness of the Kapton membrane in Meters 
ekap=3.1; %Permittivity of Kapton 
E=780e3*6.898; %Young's modulus of Kapton in kPa 
v=0.32;%Poisson's ratio of Kapton 
  
Co=e0*(pi*(a^2))/((d-tkap)+(tkap/ekap)); %Capacitance of the circular membrane 
 D=E*(tkap^3)/(12*(1-(v^2))); %Flexural Rigidity 
 
%Variation of the MEMS capacitance with Pressure 
 m=0; 
for P=0:20:160 %Pressure range is in kPa 
m=m+1; 
Pr(m)=P; 
C(m)=Co+(Co*P*(a^4)/(192*D*d))+(((P*(a^4)/(D*d))^2)*Co/20480); %Expression for the MEMS 
capacitance, Equation 12 from Chapter 4 
Pr(m)=P; 
Cmems(m)=1e12*C(m); 
end 
plot(Pr,Cmems) 
figure 
  
%Variation of the drain current, I_DS with Pressure 
 for Vds=-60:10:0 %Voltage range is in Volts 
m=0; 
for P=0:20:160 %Pressure range is in kPa 
m=m+1; 
Pr(m)=P; 
95 
C(m)=Co+(Co*P*(a^4)/(192*D*d))+(((P*(a^4)/(D*d))^2)*Co/20480); %Expression for the MEMS 
capacitance, Equation 12 from Chapter 4 
C1=Vgs*C(m)/(C(m)+Cg); 
Ids(m)=mu*e0*(ebcb/tbcb)*(W/L).*(((C1-Vt).*Vds)-0.5*(Vds^2)); %Expression for the drain 
current, I_DS, Equation 5 from Chapter 4 
end 
plot(Pr,Ids) 
hold on; 
end 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
96 
APPENDIX F 
 
TRAVELER FOR FABRICATING A BOTTOM CONTACT OFET 
INTEGRATED WITH A PRESSURE SENSOR 
 
I. Organic Transistor 
 
1. Defining a gate electrode: Choose a smooth oxidized silicon wafer. 
 
Step 1  Acetone/Methanol Cleaning 
Cleaner                        First Acetone then Methanol  
DI Rinse       30 secs in a bowl of slightly agitated DI water 
N
2 
dry            until wafer is completely dry 
 
Step 2  Photoresist application (~ 2 microns thick) 
Photoresist         nLOF 2035 negative photoresist 
Spin Speed         3500 rpm 
            Spin Ramp         500 rpm 
            Spin Time          30 secs 
 
Step 3  Soft bake 
Temperature        110 
0
C 
Time                    60 secs 
 
Step 4  Photoresist Exposure 
            Mask used    MODIFIED_GATE_ELECTRODE 
            Exposure Time    15 secs 
 
Step 5  Post-exposure bake 
Temperature        110 
0
C 
Time                    60 secs 
 
Step 6  Photoresist Develop 
Developer           AZ-300 MIF 
Time              90 secs 
DI Rinse        30 secs in a bowl of slightly agitated DI water 
N
2 
dry            until wafer is completely dry 
 
 
97 
Step 7  Post Develop Bake 
Temperature        110 
0
C 
Time                    60 secs 
 
Step 8  Gold deposition 
   Process                       E-beam 
   Thickness    1000 
0
A 
 
Step 9  Defining the gold electrode through photoresist removal 
Process                      Lift-off 
Developer    Acetone 
Time   ~ 30 mins 
 
Step 10  Acetone/Methanol Cleaning 
Cleaner                        First Acetone then Methanol  
DI Rinse       30 secs in a bowl of slightly agitated DI water 
N
2 
dry            until wafer is completely dry 
 
 
2. Spincoating BCB: A mask having the pattern of the BCB should be available as a 
glass mask for this process. Note: Do not use film mask for this process. 
 
Step 1  Adhesion promoter application (AP3000) 
Spin Speed         3000 rpm 
            Spin Ramp         1000 
            Spin Time          30 secs 
 
Step 2  Soft Bake 
Temperature        120 
0
C 
Time                    30 secs 
 
Step 3  BCB (Cyclotene 4024-40) application for a thickness of ~ 0.5 ?m). Prepare a 
mixture of 1:1 solution of BCB and T1100. Let this spread on the wafer for a minute. 
Spread Speed  500 rpm 
Ramp   500 
Time   5 secs 
Speed   2700 rpm 
Ramp   1000 
Time   30 secs 
 
Step 4  Soft Bake 
Temperature        95 
0
C 
Time                    90 secs 
 
98 
Step 5  Photoresist Exposure 
            Mask used    BCB_MASK 
            Exposure Time    15 secs 
 
Step 6  Pre Develop Bake 
Temperature        80 
0
C 
Time                    30 secs 
 
Step 7  Puddle Develop Process: The spinner is used for this process.  
Developer         DS2100 (Pour it on the wafer and let it sit for 75 secs.) 
Rinse Speed  500 rpm 
Ramp   500 
Rinse Time  5 secs 
Speed   2500 rpm 
Ramp   1000 
Time   30 secs 
 
Step 8  Post Develop Bake 
Temperature        70 
0
C 
Time                    60 secs 
 
 Step 9 Curing BCB: The BCB coated substrate is cured in a nitrogen oven for 2-3 hours 
by letting the temperature ramp up to 200 
o
C.  
 
 
 
3. Defining the drain and source electrodes 
 
Step 1  Cleaning 
DI Rinse       30 secs in a bowl of slightly agitated DI water 
N
2 
dry            until wafer is completely dry 
 
Step 2  Photoresist application (~ 2 microns thick) 
Photoresist         nLOF 2035 negative photoresist 
Spin Speed         3500 rpm 
            Spin Ramp         500 rpm 
            Spin Time          30 secs 
 
Step 3  Soft bake 
Temperature        110 
0
C 
Time                    60 secs 
 
Step 4  Photoresist Exposure 
            Mask used    D_S_ELECTRODES 
            Exposure Time    15 secs 
99 
Step 5  Post-exposure bake 
Temperature        110 
0
C 
Time                    60 secs 
 
Step 6  Photoresist Develop 
Developer           AZ-300 MIF 
Time              90 secs 
DI Rinse        30 secs in a bowl of slightly agitated DI water 
N
2 
dry            until wafer is completely dry 
 
Step 7  Post Develop Bake 
Temperature        110 
0
C 
Time                    60 secs 
 
Step 8  Gold deposition 
   Process                       E-beam 
   Thickness    1000 
0
A 
 
Step 9  Defining the gold electrodes through photoresist removal 
Process                      Lift-off 
Developer    AZ 300 MIF 
Time     ~ 30 mins 
 
Step 10  Cleaning 
DI Rinse       30 secs in a bowl of slightly agitated DI water 
N
2 
dry            until wafer is completely dry 
 
 
II. Kapton film processing for MEMS top layer 
 
1. Kapton film cleaning 
 
Step 1  Acetone/Methanol Cleaning 
Cleaner                        First Acetone then Methanol  
DI Rinse       30 secs in a bowl of slightly agitated DI water 
N
2 
dry            until film is completely dry 
Step 2  Oxidation Removal 
Remover                      250 ml DI water + 2 drops of H
2
SO
4
 using a pipette  
DI Rinse       30 secs in a bowl of slightly agitated DI water 
N
2 
dry            until film is completely dry 
 
Step 3  Acetone/Methanol Cleaning 
Cleaner                        First Acetone then Methanol  
DI Rinse       30 secs in a bowl of slightly agitated DI water 
N
2 
dry            until film is completely dry 
100 
2. Etching the backside of the Kapton film 
 
Step 1  Copper Etching (Cover the front side using blue tack squares) 
Etchant     CE-200 
Time      8 secs 
DI Rinse       30 secs in a bowl of slightly agitated DI water 
N
2 
dry            until film is completely dry 
 
Step 2  Nichrome Etching 
Etchant     250 ml DI water + 10 gm KMnO
4
 + 5 gm NaOH 
            Time              60 secs 
DI Rinse       30 secs in a bowl of slightly agitated DI water 
            N
2 
dry            until film is completely dry 
 
Step 3  Acetone/Methanol Cleaning 
Cleaner                        First Acetone then Methanol  
DI Rinse       30 secs in a bowl of slightly agitated DI water 
            N
2 
dry            until film is completely dry 
 
 
3. Gluing the film on a wafer 
 
Step 1  4? Wafergrip application 
 Peel wafergrip and put it on a clean and smooth wafer  
 
Step 2  Heat wafer on hot plate 
Temperature        110 
0
C 
Time                    till wafergrip melts and sticks to the wafer 
 
Step 3  Stick film on wafer 
While the wafer gel is still in molten state, stick the Kapton film starting with one 
edge and smoothing the entire film on the gel without any unevenness 
 
                   
4. Defining the electrode 
 
Step 1  Photoresist application 
Photoresist         S1813 
Spin Speed         2500 rpm 
            Spin Ramp         500 rpm 
            Spin Time          30 secs 
 
Step 2  Soft bake 
Temperature        110 
0
C 
Time                    60 secs 
101 
Step 3  Photoresist Exposure 
            Mask used    ELECTRODE_MEMS 
            Exposure Time    15 secs 
 
Step 4  Photoresist Develop 
Developer           CD-30 
Time              45 secs 
DI Rinse        30 secs in a bowl of slightly agitated DI water 
N
2 
dry            until film is completely dry 
 
Step 5  Post Develop Bake 
Temperature        110 
0
C 
Time                    60 secs 
 
Step 6  Copper Etching 
Etchant     CE-200 
Time      8 secs 
DI Rinse       30 secs in a bowl of slightly agitated DI water 
N
2 
dry            until film is completely dry 
 
Step 7  Photoresist Removal 
Photoresist Remover   First Acetone then Methanol  
DI Rinse       30 secs in a bowl of slightly agitated DI water 
N
2 
dry            until film is completely dry 
 
Step 8  Nichrome Etching 
Etchant     250 ml DI water + 10 gm KMnO
4
 + 5 gm NaOH 
            Time              60 secs 
DI Rinse       30 secs in a bowl of slightly agitated DI water 
            N
2 
dry            until film is completely dry 
  
Step 9  Acetone/Methanol Cleaning 
Cleaner                        First Acetone then Methanol  
DI Rinse       30 secs in a bowl of slightly agitated DI water 
N
2 
dry            until film is completely dry 
 
 
5. Final film cleaning 
 
Step 1  Wafer gel Cleaning 
Cleaner                        Amyl Acetate  
Temperature       150 
0
C 
Time   until film lifts off the wafer with no residual wafer gel on it 
 
             
102 
Step 2  Acetone/Methanol Cleaning 
Cleaner                        First Acetone then Methanol  
DI Rinse       30 secs in a bowl of slightly agitated DI water 
            N
2 
dry            until film is completely dry 
 
 
III. Integration of the MEMS pressure sensor and the organic transistor 
 
1. Lamination: The Silicon wafer needs to be cut using a diamond scribing tool to fit 
the bonding jig shown in Figure 1. A spacer film was hand-cut and lamination of the 
MEMS Kapton layer and the organic transistor was performed by thermo-
compression bonding at a pressure of 150 psi and a temperature of 130? C. 
 
2. Deposition of Pentacene: Before this step, all the contact pads to be utilized for 
probe testing should be covered with a blue tack film in order to prevent deposition of 
Pentacene on the pads. Also, all the pressure sensors are covered with the tack film as 
thermal evaporation takes place in a vacuum chamber which might burst the pressure 
sensor. 
Process                      Thermal evaporation 
Deposition time    ~ 30 mins 
Note: Remove the tack film carefully before testing.  
 
 
(a) 
 
(b) 
Figure 1. (a) Top view of the fixture, (b) Side view of the bonding setup. 
103