Micromechanical Capacitive Accelerometer And Its Characteristic Research

The micromechanical comb-capacitive accelerometers fabricated by bulk silicon micromachining process are widely used for having simple process, small temperature coefficient ,good stability and easily controllable damping coefficient.A driving signal with a dc bias voltage and ac voltage is usually necessary for sensing very small capacitance. The reliable operation conditions of the capacitive sensor for foreign acceleration had been researched with the assumption of the parallel comb plates. But the comb plates are actually not parallel for the reason of the DRIE process. In the dissertation, the response characteristics of capacitive accelerometer whose sensing and driving combs have small angles of decline for step and shock signals are deeply researched for different driving voltage configurations. The dependences of the critical time of the pulse signal and the critical step signal for the different configurations and different angles of decline are developed. The effects of non-parallel comb plates on capacitance, sensitivity, electrostatic force and electrostatic spring constant are also discussed. The critical pulse acceleration or the critical step acceleration for different angles of decline can be got from the research results. The edge effects of the comb-capacitors having small angle of decline are researched by using the electronics module of the finite element tool ANSYS. The error of the capacitance, electrostatic force and sensitivity between the computed values got from these models and the simulated values got from ANSYS for different angle of decline are researched. The results are very useful for the design of the comb-capacitive accelerometer. The methods to decrease the angle of decline of the comb-plates are experimentally researched by changing the parameter of DRIE process and splashing aluminum protection layer.The effect of electrostatic force of the drive voltage on the accelerometer had been researched when the bias voltage polarity is positive-negative configuration. In the dissertation, the effects of bias voltage polarity on the measurement and the normaloperation are deeply researched when the voltage polarity is positive-positive, negative-positive and negative-negative respectively. The results are compared with the ones studied by others when the voltage polarity is positive-negative.The air damping of the laterally driven microstructures is slide-film air damping. In the dissertation, the effects of the air slide-film damping on the capacitive accelerometers having different slot structures which are completely or partly etched, and fabricated by the anodic bonding between silicon and glass and bulk silicon micromachining process are researched by changing the distance between the moving structure and substrate, the thickness of the structure, the width of the completely etched slot structure, the depth of the partly etched slot structure according to the two well known air slide-film damping models. The errors between the computed values by using the models and experimental values are discussed.The capacitive accelerometers fabricated by bulk micromachining process have large sensitive mass, small noise and high resolution compared to the ones fabricated by surface micromachining process. In the dissertation, a micromechanical comb capacitive accelerometer having U-shaped supporting beams is designed, simulated and fabricated on the base of the anodic bonding between the silicon and glass, and bulk silicon micromachining process. The accelerometer which has simple fabricated process and high sensitivity and small parasitic capacitance and residual stress is hybrid integrated with the interface circuit using IC nude chip. So the density of the package is increased, and the noise of the sensing system is decreased. These found the base of capacitive accelerometer module using the MCM method.