Research On RF MEMS Free Free Beam Resonator

With high performance, miniaturization demand of electronic systems gradually increasing, MEMS resonators with its high Q value, easy to integrate, impact resistance and other advantages have been on the stage. Due to compatibility with IC manufacture technology, plus its excellent electrical Performance, thus it gradually become a hot research topic in recent years.This paper analyzes the operating mechanism and the factors which may influence the performance of MEMS free beam resonator, and discusses the relationship between the Q value and structure with air damping,and the relationship between the dynamic impedance and the electrode gap with dielectric materials. According to the process of the surface micro machining technology, a resonator is designed, manufactured and tested including the main contents as follows.1. The MEMS free beam resonator is equivalent to a spring damping vibration system, and then equivalent elasticity coefficient and mass are extracted with its structure and material, and the mechanical three-dimensional structure of the resonator is equivalent to RLC equivalent circuit model to analyze theperformance of the resonator by adopting the electromechanical analogy method;2. Energy loss mechanism of free beam resonator is studied. From the perspective of vibration mechanics, the power which is done by the end of the support beam to anchor is calculated, the mechanical wave energy passing to the base is obtained, Based on the above work, anchor loss of free beam resonator is obtained; In accordance with Reynolds equation, air damping of the MEMS resonator is analyzed in the rarefied air and equivalent damping coefficients is deduced, in combination with d’Alembert equation of the resonator vibration, the damping loss of resonator is acquired; Finally through elastic thermodynamics, loss model of thermo elastic damping of MEMS resonators is established, and then the results of the analysis is verified by finite element software;3. The movement electrode method is studied to low the dynamic impedance of resonator. It is analyzed that the influence of different parameters on the dynamic impedance, then several methods are designed including increasing the stop block, plus drive electrode, to decrease dynamic impedance by reducing the gap capacitance of resonator, meanwhile the influence of the electrode of resonator is analyzed, at last the feasibility of the scheme is verified by the simulation analysis;4. The resonator is processed and tested. MEMS micro machining process of free beam resonator is designed, the resonator mask is made and the processing of resonator is completed. According to the characteristics of the resonator, the test circuit is designed, the equivalent electrical parameters of the bonding line are extracted and their equivalent circuit model is established, the influence of the bonding line and test board on performance of the resonator is analyzed by the simulation, finally the performance of the resonator is tested by vacuum probing station.