Capacitive sensing type surface micromachined silicon accelerometer with a stiffness tuning capability

A novel concept surface micromachined silicon accelerometer which has a stiffness tuning capability to improve the sensor resolution is developed. The stiffness of the sensor structure is reduced by providing an electrostatic negative stiffness. By adopting the stiffness tuning, the initially stiff structure guarantees the stability of the fabrication and the reduced stiffness only along the sensing direction produces the improved resolution. In particular, one of the improved structure of this accelerometer is a branched comb-finger that senses the relative position between the mass and the electrode itself. Maintaining the same capacitance variation, it is able to achieve a larger initial gap between the mass and the electrode which fences the clash problem. The accelerometer has an active size of 650×530 μm², a thickness of polysilicon structure of 7 μm, and a proof mass of about 1 μg. Experimental results shows that the equivalent noise level of the accelerometer is improved by 30 dB through the stiffness tuning. The accelerometer has a bandwidth of 350 Hz, a linearity of 0.3% FS, and a sensing range of 50 g