Design, Fabrication, and Dynamic Modeling of a Printed Circuit Based MEMS Accelerometer

Abstract

A MEMS capacitive-type accelerometer fabricated using printed circuit processing techniques is presented. A Kapton polymide film is used as the structural layer for fabricating the MEMS accelerometer. The accelerometer proof mass along with four suspension beams are defined in the Kapton polyimide film. The proof mass is suspended above a RT/Duroid (Teflon) substrate using a spacer. The deflection of the proof mass is detected using a pair of capacitive sensing electrodes. The top electrode of the accelerometer is defined on the top surface of the Kapton film. The bottom electrode is defined in the metallization on the RT/Duroid substrate. The initial gap height between the bottom electrode and the Kapton film is approximately 41.8 µm. For an applied external acceleration/deceleration (normal to the proof mass), the proof mass deflects towards or away from the fixed bottom electrode due to inertial force. This deflection causes either a decrease or increase in the air gap height thereby either increasing or decreasing the capacitance between the top and the bottom electrodes.

An example PCB MEMS accelerometer with a square proof mass of membrane area 6.4 mm×6.4 mm is reported. The measured resonant frequency of 375 Hz and the Q-factor in air is 1.5.

The ability to build MEMS accelerometers using low-cost printed circuit processing techniques allows for integration of electronics, suitability for high-volume manufacturing, and large surface area applications for low-g accelerometers. These are all key advantages for using PCB MEMS accelerometers.