MEMS Accelerometer Research And Readout Circuit

As a key device in micro inertial measurement equipment, MEMS accelerometer, which has advantages of small size, light weight, low cost, low power consumption, compatible with integrated circuit technology, is widely used in automotive, medical, aerospace, military and other fields. Therefore, research of MEMS accelerometer has a very important significance and value.According to the basic principle of accelerometer, this article proposed a kind structure of MEMS capacitive accelerometer based on the SOI technology, and done a lot of research work on it, such as theoretical analysis, modeling and simulating of the mechanical-electrical integration, experimental testing and verification.Firstly, a detail description is given of the structure and readout circuit of MEMS capacitive accelerometer. With analyzing the damping coefficient, stiffness coefficient, a structure of readout circuit based on switch capacitor amplifier is proposed, and the mechanical noise and circuit noise is analyzed.Secondly, according to the structure of MEMS accelerometer, the model of comb capacitor and electrostatic force and the modified method of stiffness coefficient based on the stress gradient of SOI technology are analyzed. Because the electrostatic force is about10"7N and the damping coefficient is about10-10Ns/μm, if the displacement of sensing mass is far less than the distance of combs, the electrostatic force and damping coefficient can be ignored. According to the structure of the readout circuit and the kinetic theory, a Simulink system simulation model of MEMS accelerometer based on SOI technology is proposed, in which the noise mechanism and fringe capacitance model are considered. The model shows the respond time of system is about5ms, the sensitivity of output voltage is about2.01mV/g, and the sensitivity of capacitive is about397.4aF/g. And modeling a mechanical-electrical integration model based on the MEMS software CoventorWare, the results of simulation shows the sensitivity of output voltage is about2.21mV/g, and the sensitivity of capacitive is about438.787aF/g.Finally, the layout of MEMS accelerometer is finished based on the specific process step of SOI technology and the samples are manufactured. The MEMS accelerometer is tested by using special detection chip of micro capacitor. And the result of testing is compared with the simulation results of system model. The results shows that the accelerometer works properly, the test results and the model simulation results are very close, the error of output voltage sensitivity is less than2%, the error of capacitor sensitivity is less than8%, and the error of test acceleration and actual acceleration is less than10%. Therefore, the test results verify the correctness and reliability of the mechanical-electrical integration model. The model can be helpful in fast optimization of the parameter of structure and circuits, and has better reference function to the research of MEMS inertial device.