MEMS谐振式压力传感器谐振器设计与分析

发布时间：2019-05-19 07:15

【摘要】：谐振式压力传感器是一种典型的利用外界压力作用时结构频率的改变来实现压力测量的MEMS器件。该类传感器一般使用单晶硅制作感受外界压力的压力膜以及间接敏感元件谐振梁,实现了二次敏感模式,它可以直接输出频率信号,其传输与测量都可直接应用数字技术,具有广阔的应用前景。本文谐振器采用静电驱动/电容检测原理,当封装层施加电压U后,封装层与谐振梁之间产生电容,进而产生作用于谐振梁的静电力。在谐振器的设计过程,电容一般采用理想电容公式,而忽略了边缘效应产生的影响,从而使得设计结果与实际应用存在误差。本文除了考虑边缘效应对谐振器电容的影响外,还考虑了边缘效应对机电耦合时谐振梁变形、临界电压、静电刚度的影响;同时对谐振器进行建模,分析系统参数以及电压、边缘效应对系统频率、灵敏度等系统性能的影响,具体内容如下:(1)对现有的电容边缘效应理论计算公式进行分析,在考虑长度与厚度对边缘效应影响下,选取误差较小的计算公式;同时对本文中封装层远大于谐振梁的极板之间的电容公式进行了推导,应用现有平板电容公式计算本文模型有较大的误差,而本文推导的电容计算公式误差较小;同时对封装层尺寸对电容的影响进行了仿真分析,当封装层尺寸远远大于谐振梁尺寸时,在一定范围内,封装层的尺寸变化基本不会改变电容值。(2)当静电力作用于谐振梁时,谐振梁会产生变形,当静电力大于谐振梁回复力时,谐振梁会吸附到封装层;利用数值与有限元分析的方式,对谐振梁的翘曲变形与临界电压进行求解;当谐振梁存在静电力时会引入静电刚度,当电压较小时,忽略谐振梁变形的影响,求解谐振梁的静电刚度;同时考虑了边缘效应对谐振梁变形、临界电压、静电刚度的影响。(3)建立谐振梁自由振动模型,求解谐振梁振型与频率以及谐振梁的等效质量;当谐振梁引入静电刚度,谐振梁等效刚度软化,谐振频率相对减小,通过求解静电刚度以及机械刚度的比值,从而进一步求解机电耦合下谐振频率,分析电压以及边缘效应对谐振频率的影响;建立谐振器模型,分析谐振梁、压力膜、锚点、电压等系统参数以及边缘效应对谐振频率以及灵敏度的影响。
[Abstract]:Resonant pressure sensor is a typical MEMS device which makes use of the change of structure frequency under the action of external pressure to realize pressure measurement. This kind of sensor usually makes pressure film and indirect sensitive element resonance beam to feel external pressure, and realizes the secondary sensitive mode. It can output frequency signal directly, and its transmission and measurement can be directly applied to digital technology. It has a broad application prospect. In this paper, the principle of electrostatic drive / capacitance detection is adopted in the resonator. When the voltage U is applied to the package layer, the capacitance between the package layer and the resonance beam is produced, and then the electrostatic force acting on the resonance beam is generated. In the design process of resonator, the ideal capacitance formula is generally adopted, and the influence of edge effect is ignored, which makes the design results error with the practical application. In this paper, not only the influence of edge effect on the capacitance of resonator is considered, but also the influence of edge effect on the deformation, critical voltage and electrostatic stiffness of resonant beam in electromechanical coupling is also considered. At the same time, the resonator is modeled, and the effects of system parameters, voltage and edge effect on the frequency and sensitivity of the system are analyzed. The specific contents are as follows: (1) the existing theoretical formula of capacitance edge effect is analyzed. Considering the influence of length and thickness on the edge effect, the formula with small error is selected. At the same time, the capacitance formula between the plates whose packaging layer is much larger than that of the resonant beam is deduced. The calculation error of the model is large by using the existing plate capacitance formula, but the error of the capacitance calculation formula derived in this paper is small. At the same time, the influence of the size of the packaging layer on the capacitance is simulated and analyzed. When the size of the packaging layer is much larger than the size of the resonant beam, in a certain range, The size change of the package layer basically does not change the capacitance value. (2) when the electrostatic force acts on the resonant beam, the resonant beam will deform, and when the electrostatic force is greater than the recovery force of the resonant beam, the resonant beam will be adsorbed to the package layer; The warping deformation and critical voltage of resonant beam are solved by numerical and finite element analysis. When there is electrostatic force in the resonant beam, the electrostatic stiffness will be introduced. when the voltage is small, the influence of the deformation of the resonant beam will be ignored, and the electrostatic stiffness of the resonant beam will be solved. At the same time, the influence of edge effect on the deformation, critical voltage and electrostatic stiffness of resonant beam is considered. (3) the free vibration model of resonant beam is established, and the vibration mode and frequency of resonant beam and the equivalent mass of resonant beam are solved. When the electrostatic stiffness is introduced into the resonant beam, the equivalent stiffness of the resonant beam is softened and the resonant frequency is relatively reduced. by solving the ratio of electrostatic stiffness and mechanical stiffness, the resonant frequency under electromechanical coupling is further solved. The influence of voltage and edge effect on resonance frequency is analyzed. The resonator model is established, and the effects of system parameters such as resonance beam, pressure film, anchor point, voltage and edge effect on resonance frequency and sensitivity are analyzed.
【学位授予单位】：电子科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TP212

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