Design And Analysis Of The Resonator Inside The MEMS Resonant Pressure Sensor

The resonant pressure sensor is a typical MEMS device which can realize the pressure measurement by the resonant frequency variance of the structure.This kind of sensor generally uses monocrystalline silicon to manufacture the pressure-sensitive film and resonant beam.The resonant pressure sensor applies two sensitive modes and generates the output frequency signal,signal transmission and measurement can be directly applied to digital technology.Thus,the resonant pressure sensor has broad application prospects.In this paper,the principle of electrostatic drive and capacitance detection is applied in the resonator.Driven voltage is applied to the packaging layer to gerenate the electrostatic force between the packaging layer and the resonant beam.In the design process of the resonator,the capacitance is generally calculated by the ideal capacitance formula,in which the influence of the edge effect is neglected.Thus,a discrepancy will be induced between the actual capacitance and the original design.In this paper,the influence of edge effect on resonator capacitor is discussed.In addition,the edge effect on electromechanical coupling resonant beam deformation,threshold voltage,effect of electrostatic stiffness is also discussed.Meanwhile,the resonantor model is set up to analyze the effects of system parameters,voltage and edge effect on the performance of the system frequency and sensitivity of the system.The specific contents are as follows:(1)Analyze the existing capacitance calculation formula,which takes the edge effect into consideration.With the effect of length and thickness considered,calculation formula with error smaller is chosen.The capacitance calculation formula between the encapsulation layer and the resonant beam is derived in this paper.Compared with the existing plate capacitor model,the capacitance calculation formula in this paper has smaller error.The effect of encapsulation layer size on the capacitor is discussed through simulation.Simulation result shows that when the encapsulation layer size is far greater than resonant beam size,the encapsulation layer size variance of a certain range will not change the capacitance value.(2)Electrostatic force will change the form of the resonant beam.If the electrostatic force is greater than the resonant beam force,resonant beam will be adsorbed to the package layer.The resonant beam deformation and the critical voltage are discussed with numerical and finite element analysis method.Electrostatic force will affect the beam stiffness.When the voltage is low,beam stiffness is analyzed by ignoring the effect of resonant beam deformation.The edge effect on the resonant beam deformation,critical voltage and stiffness is also discussed.(3)Resonant beam free vibration model is established to derive the resonant beam vibration type,resonant frequency and equivalent mass.When the effect of electrostatic force on the stiffness is induced,the beam equivalent stiffness is soften and the resonant frequency is reduced.The ratio between the electrostatic stiffness and mechanical stiffness is considered to calculate the resonant frequency in the electromechanical coupling model.Influence of voltage and edge effect on the resonant frequency of the resonator is also discussed.The resonantor model is established to analyze the influence of resonant beam,pressure film,anchor,voltage,edge effect and other system parameters on the resonant frequency and sensitivity.