Analysis On Error Mechanism Of Micro Piezoresistive Accelerometers

The silicon based micro piezoresistive accelerometer has the advantages of being small, light, highly coherent, and with simple structure, simple working principle and simple testing circuit. It is one of the key parts of the MIMU (Micro Inertial Measurement Unit). In order to improve the measurement precision of MIMU, it is necessary to analyze the error mechanism of micro piezoresistive accelerometer.In this paper, the generating mechanism of 16 error sources of micro piezoresistive accelerometer are analyzed, and 12 single error models, including the microfabrication, environmental temperature and environmental vibration, are established. To testify the single error models, several three-axis micro piezoresistive accelerometers of different testing ranges are designed and fabricated. Finally, several single error source based experiments are set up to estimate the single-item based error, moreover, the total error of the accelerometer is obtained by carrying out several shock experiments.Firstly, mathematical model of a second-order single DOF (Degree of Freedom) system of the piezoresistive accelerometer is set up, the natural frequency of bridge-like-eight-beam-mass structure and the damping parameter that can be commonly used in the piezoresistive accelerometers are deduced, what's more, two typical structures are calculated using the established mathematical model.On the base of the mathematical model, the mechanism of 11 error items relating to microfabrication are analyzed, and 9 single error models, including the thickness of material, the stability of material, the position of piezoresistor, the piezoresistance shift, the first step of back-etching, salient compensation and the glass etching depth, are established.As environmental temperature and temperature vibration may have large influence on the performance of piezoresistive accelerometers, other 3 error generating mechanisms are discussed in this paper. Subsequently, 3 single error models are also built up, including the temperature coefficient, the piezoresistance coefficient as well as the vibration. What's more, the temperature compensation methods are discussed in this paper.To testify the established error models, several piezoresistive accelerometers with different testing ranges are designed and fabricated. Five single error based experiments are set up to testify the shift ranges of 5 error sources resulted mainly from microfabrication, they are the dimensions of structures, the residual stresses on the surface and the shift of piezoresistance. According to the experimental results together with the error models, the single item based errors are obtained. Finally, the total error of accelerometer with a testing range of 1000~50 000g is measured by several shock experiments.The mathematical model and the single error models established in this paper can be used in any other beam-mass based piezoresistive accelerometer, which is one of the most successful achievements of this paper.