Mirofabrication and characterization of an integrated 3-axis CMOS-MEMS accelerometer

This paper reports the fabrication and characterization of a monolithically integrated 3-axis CMOS-MEMS accelerometer with a single proof mass. An improved microfabrication process has been developed to solve the structure overheating and particle contamination problems in the plasma etching processes used in the device fabrication. The whole device is made of bulk silicon except for some short thin films for electrical isolation, allowing large sensing capacitance and flat device structure. A low-noise, low-power, dual-chopper amplifier is designed for each axis, which provides 40dB on-chip amplification and consumes only 1 mW power. Quasi-static and dynamic characterization of the fabricated devices has been performed. The measured sensitivities of the lateral-and z-axis accelerometers are 560 mV/g and 320 mV/g, respectively, which can be tuned by simply varying the amplitude of the modulation signal. The over-all noise floors of the lateral- and z-axis are 12 μg/√Hz and 110 μg/√Hz, respectively when tested at 200 Hz.