Inductive CMOS MEMS accelerometer with integrated variable inductors

This paper reports an inductive CMOS MEMS accelerometer with integrated variable inductors as the position-sensing elements. Without conventional sensing comb fingers, the dependence of device characteristics on stress-induced structural deformation can be significantly reduced. The variable inductors are used in on-chip LC-tank oscillators. When the external acceleration deforms the inductors, the oscillation frequency variation is proportional to the inductance change and thus the acceleration. The frequency output can be easily converted to digital codes by using a counter. The integrated accelerometer was implemented by a commercial 0.18 μm 1P5M CMOS process and post-CMOS dry-etching processes. Experimental results showed the proposed accelerometer had a sensitivity of 150 kHz/g.