The Performance Analysis Of The Comb Micro-accelerometer Based On The Capacitor Edge Effect

MEMS accelerometers are widely applied in automotive airbags, smart phones and other consuming electronics in the normal life. Comb micro-accelerometer has received continuous attention in the fields of MEMS accelerometer, due to its advantages of low cost, high precision, low temperature sensitivity and good noise characteristics. In the design of the comb micro-accelerometer, the ideal capacitance calculation formula is widely used. However, the ideal capacitance calculation formula ignores the capacitance induced by edge effects of the electrodes, which will lead to difference in capacitances between theoretical calculation and practical use. This discrepancy will affect the output accuracy of the comb micro-accelerometer. Therefore, it will be of great help to study the impact of the edge effects on the comb micro-accelerometer’s output to improve the accuracy of the comb micro-accelerometer.The calculation formula of the capacitance with the edge effects has been extensively discussed in presented researches. However, the impact of the edge effects on the performances of comb micro-accelerometer is rarely mentioned. This article analyzes the impact of the edge effects on the electrostatic stiffness, sensitivity and nonlinearity of the comb micro-accelerometer. Firstly, based on the present capacitance calculation formula of parallel plate capacitor, the capacitance calculation formula of comb capacitor with the edge effects is derived and verified by simulation. Secondly, the impact of the edge effects on the capacitance of comb capacitor is analyzed to indicate the relationship between the parameters of the sensing structure and the edge effects on comb capacitor. Finally, electrostatic stiffness, sensitivity and nonlinearity of the comb micro-accelerometer are calculated through the capacitance formula with edge effects. These calculations indicate the impact of the edge effects on the performances of accelerometer.The results show that the capacitance calculation formula of comb capacitor derived in this article can accurately calculate the capacitance of comb capacitor in comb micro-accelerometer. Theoretical analysis indicates that the impact of the edge effects on the capacitance of comb capacitor is determined by the structural parameters of the comb micro-accelerometer. Increase of the width and the number of parallel electrodes or decrease of the electrode gap and thickness will reduce the impact of the edge effects on the capacitance of comb capacitor. According to the theoretical calculation, the electrostatic force and electrostatic stiffness of the proof mass will be larger due to the edge effects. Meanwhile, the edge effects will raise the system nonlinearity and reduce the system sensitivity.