Haixia Yan

Study of a Novel MEMS Accelerometer with Low Noise Reduced by Actuators

A novel MEMS (Micro Electronic Mechanical System) capacitive accelerometer is presented, which is mainly composed of supporting beam, seismic mass, grid strip capacitances, comb capacitances and electrostatic driver. The damping of grid strip capacitances with variable overlapping area is mainly affected by the slide film air damping, which is small and neglectful, and the damping between comb capacitor is squeeze film air damping. The comb sensing gap can be reduced by electrostatic actuators by which the aspect ratio can reach to 75:1 which greatly depress the limitation of DRIE (Deep reactive ion etching) process on high aspect ratio, and the initial sensing capacitance increases from 2.97 pf to 14.87 pf. The squeeze film damping is reduced from 0.046 Nm/s to 0.0015 Nm/s by designing the comb-shaped grooves on the fixed comb electrodes. The comb initial sensing gap is optimized according to formation factors of system noise, and the noise is reduced from 1.395 μg/√HZ to 0.591 μg/√HZ. The simulation results show that the accelerometer sensitivity achieves 8.40 pf/g, which is two times of the conventional devices.

The Effects of Air Damping on MEMS Wine-Glass Resonator

In this paper, the Reynolds equation of air damping of MEMS wine-glass resonator is solved by numerical calculation method considering the air slip boundary conditions. The corresponding pressure distribution between internal gaps is obtained by MATLAB software. And then size effects of resonator on air damping and quality factor are analyzed. It is found that MEMS disk radius and thickness have slight effects on the change of the pressure distribution. But the effects of spacing between disk body and electrodes are very significant. The designed ratio value of disk amplitude and spacing should not be over 70%, otherwise the changes of air pressure between gaps will be very remarkable and increased exponentially, the air damping will begin to increase doubly, and the quality factor will be reduced greatly. The analyzed results are very meaningful for optimizing design size of MEMS disk resonator.

Analysis of Fringe Effect of MEMS Comb Capacitor with Slot Structures

For a super high precision MEMS sensor with the comb capacitor structure, the fringe effect of capacitors can not be neglected. In this paper, directing at the comb capacitor structure with slot holes, the effects of the non-overlap parts of comb capacitor, the distance between two slot holes in comb electrodes and slot depth aspect ratio on sensing capacitance are simulated by 3D finite element method of ANSOFT Maxwell software. The results show that when the width H and thickness t of sensing electrode plate are fixed, the fringe effect becomes larger for a smaller length L. The fringe effect is very small as non-overlap length is between 100 μm and 180 μm for 500 μm≤L≤1200 μm. The capacitance error caused by the fringe effect is the smallest for the slot distance 35 μm, slot depth 25 μm and slot width 20 μm. The error of sensing displacement caused by the fringe effect of the comb capacitor is 0.61% obtained by MATLAB Simulink.