Z-axis capacitive MEMS accelerometer with moving ground masses

We design, fabricate and characterize a noble high sensitivity z-axis capacitive type MEMS accelerometer which has moving ground masses. The previous MEMS capacitive accelerometers detect the acceleration by measuring the capacitance change between fixed reference electrode and movable sensing electrode. However, capacitive MEMS accelerometer for sensing out-of-plane acceleration shows relatively low sensitivity due to its small displacement. In this paper, we increase the relative displacement between reference electrode and sensing electrode by using movable ground masses. In this way, the reference and sensing electrodes move to an opposite direction for the applied out-of-plane acceleration. The capacitance of the fabricated accelerometer is changed from -135.1 to 140.7fF with average standard deviation of 0.77fF at OV bias and from -190 to 211.6fF with average standard deviation of 0.74fF at IV bias for the applied gravitational force (from -1g to 1g). Nonlinearity is 0.1% at 0V bias and 0.23% at IV bias, respectively.