Piezoresistor design for deflection angles decoupling measurement of two-dimensional MOEMS scanning mirror

A novel micro-optical-electro mechanical systems (MOEMS) sensor technique is developed for optical scanning and space detection. As the core technology of the system, a two-dimensional scanning mirror with small volume, large deflection angles and high frequency is presented. A reflected optical beam on the mirror can be scanned more than 20 deg two-dimensionally. For the deflection angles decoupling measurement, piezoresistors are fabricated on the flexible beam linked with mirror. The coupling motions of the flexible beam are analyzed and the stress states of the piezoresistors are presented when the mirror is scanning two-dimensionally. For the measurement of one direction, four piezoresistors form a full Wheatstone bridge to counteract the influence of another direction. The motion of the flexible beam is decoupled and the deflection angles of each direction are obtained independently and precisely. The appropriate crystal directions and doping types of the piezoresistors are designed to obtain the larger piezoresistive coefficients for the high sensitivities. The method is proved correct and effective by the theoretic calculation and simulation analysis. The deflection angles measurement sensitivities for two directions are 396 mV/deg and 348 mV/deg respectively.