Analyses Of A Novel Micro-inertial Sensor With Actuators Drived By Electrostatic Force For Increasing The Initial Sensing Capacitance

Represented by accelerometer, MEMS sensor is the most widely used MEMS devices, and with the advantage of high sensitivity, small size, low power consumption and intelligent, etc., MEMS capacitive accelerometer has a very wide range of applications in automotive, consumer products, earthquake monitoring, oil exploration, navigation, biomedical and other fields. This paper focus on study the methode of improving the the precision of the capacitive sensor, designs and fabricates a novel MEMS accelerometer sensor.The basic principle, basic structure and dynamic working model of the capacitive accelerometer are introduced, and the main factors which affect the sensor performance are discussed. Then the reasons for the formation of air damping are discussed, which shows that squeeze film damping are one of the main factors affecting the device performance. Secondly, in order to depress the limitation of DRIE (Deep Reactive Ion Etching) on high aspect ratio, the paper designs a driver on the sensor structure, which improves the aspect ratio from 15:1 to 75:1, significantly increasing the initial capacitance.In order to reduce the air damping, the fixed electrodes of the sensor are etched to groove, and the air damping of which is also been analyzed, the result shows that the squeeze film damping can be reduced from 0.046 Nm/s of non-slotted electrodes to 0.0015 Nm/s. The optimization design of sensor structure makes system noise reduce from 1.395μg/(?) to 0.591μg/(?), greatly enhancing the resolution.The fringe effect of the non-overlap parts of comb capacitor, the design of distance between two slot holes in comb electrodes and the slot depth aspect ratio on sensing capacitance are simulated by 3D finite element method (FEM) of ANSOFT Maxwell software, the calculation of capacitance with considering fringe effect of groove structure is verified. The results show that the capacitance error caused by fringe effect is relatively large with small length of electrode plate; the fringe effect is very small for non-overlap length between 100μm and 180μm with 500μm≤L≤1200μm. The capacitance error caused by fringe effect is the smallest when slot gap is 35μm, slot depth is 25μm and slot width is 20μm. By utilizing equivalent circuit model, the performance theory and simulation results of open loop processing circuit are compared with those of closed loop processing circuit, and the results show that closed loop detected circuit has higher stability. Thus the dynamic circuit model of this new device is established, the results imply that the displacement error caused by the fringe effect is 0.61%. So for small sized capacitive sensor, the fringe effect can not be negligible.This paper also uses finite element software to analyze the performances of the accelerometer, and the results show that the displacement sensitivity reached 0.901μm/g; the influence of driver's structure on sensor is also analyzed. Finally, layout of the new sensor is designed based on Silicon-Glass bonding technology, and the initial production of the device is given, the pictures give initial prove that the design is reasonable.