Research On Output Drift Mechanism Of MEMS Comb Accelerometer Based On Sensitive Structure Circuit Model

Comb-finger accelerometer is a typical microelectromechanical systems(MEMS)capacitive sensor that shows promising application prospect in the fields of consume electronics and inertial navigation systems.However,output drift issues will degrade the device output stability and limits its application in the navigation field.Output drift issues is defined as the variation of the output signal,while the input signal is constant.Output drift issues of comb-finger accelerometer includes overtime drift and temperature drift.Up to now,for the drift issue of accelerometer,the main concern is the temperature drift.Researches have been conducted to reveal the relevance between ambient temperature and the output drift.The sensing structure of the accelerometer is consists of different materials,which has different temperature coefficient and elasticity modulus.When the temperature varies,these materials will generate different deformation and result in the stress among the sensing structure.This stress will affect the device performance and result in output drift.Overtime drift can be devided into short-term drift and long-term drift.This paper concentrates on the short-term drift of the comb-finger accelerometer.Researches of resonator and RF switch indicate that dielectric charging will result in short-term drift.Manufacture of the device does not include deposition of the dielectric on the sensing structure.Thus,effect of the dielectric is usually ignored in the device performance analysis.However,dielectric will be generated on the surface of the sensing structure via natural oxidation during the manufacture and affect the device performance.Therefore,analysis of the dielectric charging effect on the output drift and corresponding amend method are necessary for the improvement of the device performance.In this paper,the steady-state equilibrium of the sensing structure under constant input acceleration is established to analyze the effect of dielectric on the output drift.Furthermore,key parameters that determines the value of output drift and corresponding amend method are discussed.The contents of this paper include:1.The sensing structure steady-state model under constant input acceleration is established to analyze the relevance between the output voltage and the movement of the proof mass.The steady-state model is necessary for the analysis of the dielectric charging effect on the output voltage.2.Distribution of the dielectric among the sensing structure is analyzed to set up the sensing structure steady-state model with the dielectric charging effect considered.Influence of the dielectric charging effect on the output drift and key parameters relevant to the drift value are discussed with this model.3.Sensing circuit parameters and layout that can modify the key parameters are analyzed to mitigate the output drift.Improvement of the sensing circuit layout that can suppress output drift via the modification of the key parameters is discussed.Meanwhile,device performance with the modified sensing circuit layout is also discussed.4.Implementation of the new sensing circuit layout is carried out with printed circuit board(PCB).Output drifts generated in the original sensing circuit layout and modified sensing circuit layout are measured and analyzed to testify the validity of the modified sensing circuit in suppressing the output drift.