Sensing electrodes with nanoporous anodic aluminum oxide for performance enhancement of CMOS-MEMS accelerometer

Performance enhancement of CMOS-MEMS accelerometer by growing nanoporous anodic aluminum oxide (np-AAO) thin layer on sensing electrodes has been developed and demonstrated for the first time. Such device has the following advantages: (1) initial capacitance and sensitivity of accelerometer are improved by np-AAO layer, (2) np-AAO could directly grow on Al layer at low temperature to ease the implementation on CMOS-MEMS sensors, and (3) the nanoporous layer is selectively anodized on MEMS structures using CMOS electrical-routings, and the depth of np-AAO layer is easily adjusted by process. In applications, this study demonstrates an accelerometer with np-AAO layers using standard TSMC 0.35μm 2P4M CMOS process. Measurements show the initial capacitance and sensitivity respectively increase for 1.43-fold and 2.34-fold after adding np-AAO layers. Moreover, the minimum detectable signal improved from 0.2G to 0.05G (Table1). Note that the np-AAO layers could be further exploited to improve other CMOS-MEMS sensors.