Monolithic integration of capacitive sensors using a double-side CMOS MEMS post process

Abstract

This study presents a novel double-side CMOS (complementary metal-oxide-semiconductor) post-process to monolithically integrate various capacitance-type CMOS MEMS sensors on a single chip. The CMOS post-process consists of three steps: (1) front-side bulk silicon etching, (2) backside bulk silicon etching and (3) sacrificial surface metal layers etching. Using a TSMC 2P4M CMOS process and the present double-side post-process this study has successfully integrated several types of capacitive transducers and their sensing circuits on a single chip. Monolithic integration of pressure sensors of different sensing ranges and sensitivities, three-axes accelerometers, and a pressure sensor and accelerometer are demonstrated. The measurement results of the pressure sensors show sensitivities ranging from 0.14 mV kPa−1 to 7.87 mV kPa−1. The three-axes accelerometers have a sensitivity of 3.9 mV G−1 in the in-plane direction and 0.9 mV G−1 in the out-of-plane direction; and the accelerated measurement ranges from 0.3 G to 6 G.