Design & Fabrication of a MEMS Piezoresistive Accelerometer with Beam-film Combined Structure

In this paper, a MEMS (micro-electro-mechanical system) accelerometer has been developed utilizing piezoresistive sensing elements for vibration measurements in large-scale rotating machineries. The accelerometer consists of highly symmetric beam-film combined structure with 4 p-type piezoresistors diffused on beam surface. The beam and two same films, acting as a whole, give the structure a higher mechanical stiffness making the accelerometer's nature frequency enhanced. During the chip design, classical vibration and elasticity theories are taken advantaged of to determine the dimensions of the sensor chip based on the requirements of industrial practical application. FEM (finite element method) is also used to investigate the performances of the sensor under acceleration load. The device is fabricated by using bulk micromachining technology, and an n-type, (100) oriented silicon wafer is used as the blank of the chip. The packaged sensor is tested and the experimental results show that the sensor has a sufficient linear response (non-linearity <= 0.26%FS) up to 50g with a sensitivity of 1.5mV/g/8V. The resonance frequency of the sensor is about2860Hz, and this allows the usage of the sensor in state monitoring with the necessary bandwidth.