I. Introduction
For the last decades, the demands on MEMS inertial sensors have grown rapidly for the application on consumer electronics, automotive electronics and so on [1]–[3]. Among the reported inertial sensors, differential sensing accelerometers especially with differential sensing comb attracted widely attentions with the advantages of high sensitivity and high reliability [4]–[5] while many differential sensing mechanisms of Z-axis accelerometers had been developed. References [2]–[3] reported gap closing differential sensing electrodes, and reference [6] realized the differential sensing by rotational displacement detection, while asymmetrical vertical comb sensing were reported by [5],[7].