Systematic Analysis On Variable-Capacitance Micromechanical Accelerometer

Variable-capacitance micromechanical accelerometer developed by MEMS technology is widely used for having simple process,small temperature coefficient, good stability and easily controllable damping coefficient. Therefore, it is worthy to study the kind of micromechanical accelerometer.According to the operation principle of variable-capacitance micromechanical accelerometer, this paper establishes its mechanics model by analysis, and gives relevant movement equations, then gives dynamic controllable model. I summarize and compare the features of three kinds of variable-capacitance micromechanical accelerometer, and on the basis of mechanics characteristic of several kinds of beams structure, it is shown that the best structure of variable-capacitance micromechanical accelerometer is the bias stationary finger-shaped structure with folded beams fabricated by bulk silicon micromechining process by analysis and comparison. I take the closed-loop bias stationary finger-shaped variable-capacitance accelerometer as an example, and design its capacitance measurement circuits, then research and analyze its properties such as electronical negative rigidity, full scale, stability, resolution, noise, air damp and so on. The results prove that it is usally necessary for electrostatic force to produce good negative feedback effect when bias voltage polarity is positive-negative configuration in order to increase accuracy and extend measurement range; at the same time bias voltage should be established appropriately to meet full scale and stability; some methods should be adopted to decrease mechanical noise and increase resolution; damp of accelerometer can be optimized by adjusting parameters of structure of the closed-loop accelerometer measurement circuit. This work will provide a theoretic foundation for the further optimum design of variable-capacitance micromechanical accelerometer.