Sensitivity tunable capacitive type micro accelerometer

In this paper, we present a novel sensitivity tunable capacitive type micro accelerometer which could adjust its sensitivity. The previous bulk-micromachined accelerometer is hard to make a pattern which is smaller than 1 um with high aspect ratio because of ICP etching errors such as loading effect and footing. In this paper, by making movable ground electrodes which have MEMS actuators, we present a high sensitivity micro accelerometer with a narrow sensing gap under 1 um using conventional bulk micromachining. Unlike previous capacitive type MEMS accelerometers which have anchored ground electrodes, the proposed micro accelerometer has movable ground electrodes. By simply applying DC bias to MEMS actuators, the ground electrodes are moved to the sensing electrodes. The fabricated sensing gap is 1.9 um and it could be reduced to 0.8 um according to the actuation voltage, V_DD. The working sensitivity of the micro accelerometer is 0.410 pF/g at V_DD=1.0 V, which is higher than 0.125 pF/g with no actuation, V_DD=0 V.