Research On Electromagnetic Excitation Resonant Sensor Based On MEMS

Based on the piezoresistive effect and electromagnetic induction, this paper studies an electromagnetic excitation resonant sensor, including excitation structure and vibration picking structure. By analyzing the sensor structure theoretically, it shows that the interactional magnetic force exists between the magnetic field generated by excitation coil of the structure and applied magnetic field, making the output voltage signal of vibration picking structure changes. Theoretical analysis shows that the structure can complete electromagnetic excitation resonant sensor function. On this basis, Ansys software will be applied to build and analyze the simulation model of excitation structure and vibration picking structure, optimizing the design of the electromagnetic excitation resonant sensor. By using Matlab software calculation and analysis of silicon membrane stress distribution, it optimizes the design position of nc-Si thin film transistors of vibration picking structure on silicon membrane. According to the simulation results and theoretical analysis, the size of electromagnetic excitation resonant sensor chip is 5000μm×5000μm, the silicon membrane thickness is 45μm, and its size is 3000μm×3000μm. The inductance coil of excitation structure is 35 turns, and its material is Al, the coil width is 7μm, spacing is 11μm, thickness is 1μm. The channel length and the width nc-Si thin film transistors of vibration picking is 320μm and 80μm respectively.CMOS technology and MEMS technology are used to produce electromagnetic excitation resonant sensor on n-type <100> orientation high resistance silicon wafer. The production of excitation structure, which is the metal inductance coil generating alternating magnetic field, adopts the method of an internal down-lead produced by ohm contact electrode which is formed by heavily boron- diffused and the Al evaporated on the middle of silicon cup surface. CMOS technology is adopted to produce four nc-Si thin film transistor channel resistances as varistors on the square silicon membrane, constituting a wheatstone bridge as vibration picking structure. It is given by experimental results that the excitation structure of electromagnetic excitation resonant sensor can induce the magnetic field changes and generate induced voltage, when an alternating excitation voltage is applied in excitation structure, which can produce alternating magnetic field. When a constant voltage is applied in excitation structure, interacting with the external alternating magnetic field, it can make the silicon membrane produces vibration, which frequency is the same as the frequency of alternating magnetic field. The inductance values of square and circular inductance coils are 27.43 n H and 31.07 n H at the working frequency of 200 k Hz. When silicon membrane is vibrating, vibration picking structure of electromagnetic excitation resonant sensor can respond on the vibration, and when working voltage of vibration picking structure is 5.0V, the response sensitivity is 0.146 m V/k Pa.Experimental results show that the design of the electromagnetic excitation resonant sensor can realize electromagnetic excitation to produce silicon membrane vibration, which can be detected by vibration picking structure of the sensor.