Design And Fabrication Of A Novel Silicon Micro-accelerometer

Micro-accelerometer is one of the most important components of the inertial navigation system, its accuracy level directly affects the accuracy of navigation and guidance. Among these accelerometers, capacitive accelerometers become more and more popular in both academia and industry because of their high sensitivity, good noise performance, low drift and low temperature sensitivity. In order to obtain high sensitivity, large proof mass and flexible suspension beam are needed. The large proof mass of the reported MEMS accelerometers is typically formed by wafer bonding and bulk micromachining. Multiple wafer bonding is a viable three dimensional (3-D) fabrication technology for micro-sensors and micro-actuators. However, silicon-silicon wafer bonded accelerometers require high temperature processing and could potentially drift. Post-bonding high-temperature treatment and anneal has been suggested to relieve the stresses and minimize drift in silicon-silicon bonded structures. Heavy boron doped beam can be flexible, however, this process introduces intrinsic stress to the beam, degrading the performance.This paper reports a capacitive accelerometer whose double-sided beam-mass structure is fabricated by anisotropic etching of single-crystal silicon in TMAH solution, without heavy boron doping or Si–Si bonding. Subsequent research contents are included in this dissertation.1. Because of the mismatching between detective capacitance and capacitor on the measurement circuit, we design a micro-accelerometer with matching capacitance on-chip. Theoretical modeling of its structure is given in this paper, including the analysis of mechanical properties of triangle cross-section beam and the modal frequency. The dimensions of this accelerometer are optimized according to the structure design theory and fabrication conditions. Finite element method was also used in the design and simulation of this accelerometer.2. The fabrication procedure of this micro-accelerometer with triangle cross-section beam is shown in this paper and several key problems have been solved. MATLAB was used to simulate the evolution of the beam geometry with time. It was also verified by experiments. Several samples are fabricated.3. A single-carrier modulation-type measurement circuit is designed for capacitance sensitive MEMS accelerometer. The circuit structure of each module has been analyzed. The parameter of the circuits has been decided according to theory. A performance test scheme is made with reference to test guides on micro-accelerometers. The performance of open-loop system is measured according to this scheme. The measurement shows a sensitivity of 259mV/g, nonlinearity of 2.815% within±1g, and zero-drift of 1.4mg.4. The errors of fabrication and the noise of accelerometer and measurement circuit are analyzed. Some improvement programs of fabrication have been proposed.