The Characteristics Analyses Of A Comb Vibratory Mems Resonator

With the development of science and technology, MEMS is gradually becoming a widely used technology in military and civil applications, and among which micro resonator is a very important kind of MEMS devices. According to its advantages of realizing transformation between mechanical and other types of energies and producing large vibration amplitude as well as flexible structural design etc., micro resonators become very important in the areas of RF communication, national defense, military industry, and consumer electronics etc.Comb micro resonator is the main study object in this dissertation. At first, its driving method, structural components, dynamic characteristics, as well as air damping and other basic theory are analyzed. Then electrostatic force is adopted as its driving force; dynamics theory of comb resonator is analyzed; damping of the comb resonator components is also analyzed according to the theory of slide-film and squeeze-film damping and the influence on the resonator of each component damping is discussed.Influence of comb effect on the capacitance, electrostatic force and overall performance of small-scale micro resonator were analyzed based on typical comb structure. Fringe effect of the micro resonator is divided into entirely-overlapped comb fringe effect, partly-overlapped comb fringe effect and comb lateral fringe effect and then a comparably-precise formula of entirely-overlapped 3D comb fringe effect is deduced. The correctness of the formula is verified through analyses by using electro-magnetic FEM analyze software Ansoft-Maxwell. The analyzing results show that fringe effect becomes more significant with the decrease of non-overlap comb length and the increase of controlling voltage; and that the fringe effect also becomes significant with the decrease of comb lateral distance and the increase of controlling voltage.FEM software Ansys was used to model the comb resonator and to do modal analyses and electrostatic force analyses. The analyze results show that the effective working modal is the third modal, which is translational move in x-axis direction, with resonant frequency of 40255Hz, and the resonant frequency is comparatively in accordance with the theory result; and that the maxim displacement in static force analyses is 0.019um. Electromechanical coupling equivalent circuit and F-V voltage equivalent circuit of the device are derived based on the theory of electromechanical analogy, and then S(2,1) parameter and resonant frequency of 41KHz are derived through analyses by using RF circuit simulation software ADS, which proves the correctness of F-V voltage equivalent circuit. Meanwhile, the corresponding resistance and capacitance of damping coefficient and system coefficient in equivalent circuit are modified to fulfill further analyses. The results show that output amplitude of the circuit decrease with the increase of damping coefficient while the frequency is unchanged; otherwise, frequency increases with the increase of elastic coefficient of the device while the circuit output amplitude is unchanged.With respect to the problem of frequency adjustment of comb micro resonator, a curve adjustable comb structure was introduced, which consists of stable rectangular comb and movable curve comb. The electrostatic elastic coefficient and effective elastic coefficient of the device can be changed through adjustment of controlling voltage on comb so that the resonant frequency of the resonator can be changed. Capacitance, electrostatic force, electrostatic elastic coefficient and frequency were analyzed by using the software of Ansoft. The analyze results show that the effective elastic coefficient of the entire resonator is decreased by 27% and the resonant frequency is decreased by 15% through the controlling voltage increase of the curve comb so that the frequency adjustment is achieved.In the end, the main MEMS manufacturing processes are introduced and the two manufacturing flows by using surface micromachining and bulk-silicon micromachining respectively are designed. Conglutination, which may appear in the manufacturing process, is explained and analyzed, and a method of anti-conglutination by improvement of manufacturing process to build a structural layer support point is proposed to avoid the conglutination.