Research On Design And Read-out Technology Of Comb Silicon Micro-mechanical Accelerometer

The micro-accelerometers which are manufactured with the MEMS technology are widely applied in automotive products, inertial guidance and vibration control because of their small size, low power consumption and high reliability. At present, there have been a increasing number of applications for high-precision and high-reliability micro-accelerometers due to controlling and guiding conventional weapons. Capacitive micro-accelerometers have a great advantage in temperature characteristics, measurement noises and long-term stability. The device employing comb structures have excellent sensitivity, but with increased cross-coupling error which can be decreased by optimized configuration. The value of the capacitance change is very tiny, usually below 10-15 F, so the low capacitance measuring circuit should have high precision to improve the measuring precision of the device.The configuration design theory, simulation method and read out technology of the comb microaccelero-meters are studied in this thesis. The main results are as follows:1. The configuration design theory of the device is studied, including the theory of the elastic supporting beam, the kinematic behavior, electrostatically actuating characteristics and the squeeze film damping. In addition, four structures of elastic supporting beams are presented and the relations between their elasticity coefficient and the structures are deduced.2. A kind of comb silicon micro-accelerometer is designed, and its modal analysis is carried out with a finite element method. The simulating result of the elasticity coefficient of the beam is matched well with their theoretical result. And the measuring modal frequency of the beam is far below other modes', which can decrease the cross-coupling error. The equivalent circuit model of the device is established, and its step response is analyzed with PSpice.3. The basic principle and implementing method of low capacitance measuring is studied. The"buffer"measuring circuit and the"integrating"are compared, and the open-loop measuring circuit with an integrator and the close-loop circuit with electrostatic feedback are both planned. Furthermore, the realizing technology of the signal measuring circuit is illustrated in detail.4. The open-loop and closed-loop micro-accelerometers are tested, and the test results shows that the scale factor and linearity of the open-loop device are 3 V/g and 1.3% separately, and those of the closed-open device are 0.185 V/g and 2.5% separately.