Accelerated Lifetime Characterization and Development of Test Protocols for Class I/Class II Micro-Machined Sensors and Flexible Li-ion Power Sources
Type of DegreePhD Dissertation
Restriction TypeAuburn University Users
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Modern day applications have led to extensive miniaturization of consumer electronics along with incorporation of state-of-the-art sensor devices and acceptance of flexible materials within an electronic assembly. With the introduction of portable electronics, given the harsh environments they can be exposed to, reliable and efficient operation is of utmost importance. For harsh environment reliability data, consumer electronic assemblies need to be monitored under conditions mimicking their areas of applications but not much attention has been paid to the incremental shift and degradation in output parameters of the assemblies while under operation. Present day consumer electronics is an amalgamation of Micro-Electro-Mechanical Systems (MEMS) and flexible electronics which allow for the development of thin form-factors with the ability to bend, stretch and fold in electronics applications. The existing electronics ecosystem and supply-chain is geared towards the manufacture of rigid electronics. The manufacturing of thin electronic architecture requires the development of solutions for unique challenges including the integration of thin-chips, flexible encapsulation and compliant interconnects. Harsh environmental operating conditions have been known to have an impact on the life-time of a MEMS device. Therefore, reliable operation is a quintessential requirement for such devices especially in the areas of military, automotive and space navigation applications. Primarily, the major focus of the current MEMS studies encompasses novel fabrication techniques, effective internal design in order to achieve high quality factors, improved packaging techniques and harsh environmental survivability but in very few works. This section encompasses development of test protocols for MEMS sensors as per their areas of applications, harsh environment life characterization and conducting failure analysis. Harsh environment operating conditions which the MEMS sensors have been exposed to are drop and shock (1500G), high vibration amplitudes (14G), high relative humidity and temperature (85C/85%RH), low temperature storage (-35C), thermal cyclic stresses and long term aging. The survivability of class I and class II MEMS devices such as gyroscopes, oscillators, microphones, pressure sensors and accelerometers need to be demonstrated as a function of change in their output parameters. On a very similar note harsh environmental operating conditions present in our daily routines such as varying temperatures and bending loads can affect flexible/wearable electronics such as Li-Ion power sources. The development of electric vehicles (EVs) in the past few years has given rise to the lithium-ion battery technology from a standalone and flexible electronics standpoint. This particular battery chemistry has been the go-to product of the battery community due to its high energy density, long lifetime and high power density but just as in other electronics reliability and safety is still a concern. Combined effects of distinct bending load(s) and operating temperatures (25°C and 50°C) can significantly attenuate the life of flexible Li-Ion batteries in foldable wearable electronics. Present day technologies call for battery applications, which require exposure to bending stresses, human body and varying ambient temperatures. Current health monitoring techniques and test standards for flexible power sources are still in the nascent stages. Flexible power sources such as Li-Ion batteries may undergo multiple charge-discharge cycles during operation, therefore development of a hardware test-bed, which mimics the operating conditions in their areas of applications, is needed. This work comprises of two reliability sections where the first focuses on damage progression in MEMS whereas the other section provides insight into the overall behavior of flexible Li-Ion power sources under harsh operating environments. Section I Focuses on obtaining lifetime trend of class I and class II MEMS characteristics when operating within the specified environmental conditions and reporting the evolution of damage progression as a function of MEMS functionalities. This study also analyzes the behavioral trends over multiple cyclic and long term stresses using statistical methods and identifies potential failure sites, if any. Section II Shows the combined effects of deep-charge, shallow-charge, distinct bending load(s) and operating temperatures have been characterized for Li-Ion batteries. Thin flexible battery cells were cycled through multiple charge-discharge cycles under simultaneous bending loads plus thermal stresses. Output parameters such as efficiency, power, capacity and charge-discharge time have been analyzed for battery state assessment. The sensitivity of capacity degradation to a number of charge-discharge parameters has been quantified with regression models.