A method for improving out-of-plane robustness of an area-changed capacitive displacement transducer used in a micro-accelerometer

Abstract

Area-changed capacitive displacement transducers have been widely applied in micro-electro-mechanical-system (MEMS) sensors such as sandwich-type MEMS accelerometers to detect in-plane displacement with a high sensitivity. The cross-axis disturbance could result in out-of-plane displacement of the proof mass, which brings a gap variation of sensing capacitor electrodes and lead to an undesirable variation of the accelerometer’s scale factor. In order to solve this problem, this paper presents a novel method to improve out-of-plane robustness of an Area-changed capacitive displacement transducer in a MEMS accelerometer. An on-chip capacitor, sensitive to the out-of-plane displacement of proof mass, was integrated as the feedback capacitor of the charge amplifier. Thus, the influence of the out-of-plane displacement on the scale factor caused by cross-axis disturbance is compensated. The method was verified by theoretical calculation, simulation and experiments. The results indicated that the cross-sensitivity of the MEMS accelerometer with an on-chip feedback capacitor was less than 1/3 of that with off-chip feedback capacitor when acceleration was applied on the out-of-plane direction. Besides, the noise floor of the accelerometer maintained at 60 ng/√Hz regardless of the on-chip or off-chip feedback capacitors.