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    by: ali

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    1 : TUNABLE CAPACITOR MEMS Presented by Ali Hemati Science and Research Branch (Hormozgan), Islamic Azad University 1
    2 : Outline 1)CONCEPT 2) Introduction 3) MEMS Capacitor 4) The three-plate micromachined 5) Electric Double Layer Capacitor 6) Electrical Properties of a Capacitor 7) fabrication process 8) MEMS capacitors tuning 9) Clasfication 10) MEMS gap-tuning capacitors 11) electrostatic force 12) Electro-thermal tuning 13) Piezoelectric-actuator tuning 14) MEMS area-tuning capacitors 15) Important point for disigning 16) Application 17) Advantage 18) Limitation 19)Referance 2
    3 : Concept The quality factorQ is a measure of loss in a linear-circuit element and is defined as the maximum energy stored during a cycle divided by the energy lost per cycle. Q= 1/(2pfCR) Pull-in effect is an intrinsic phenomenon to electrostatically actuated devices, which greatly limits the tuning range of the tunable capacitor. 3
    4 : Introduction MEMS technology has the potential of realizing variable capacitors with a performance that is superior to varactor diodes in areas such as non-linearity and losses. Over the past, variable capacitors was theoretical tuning range of 50% - 100%, in practice, the capacitor operate over a smaller tuning range away from the collapse voltage. Proposed MEMS capacitor Fig. 1 illustrates a schematic diagram. 4
    5 : Introduction Fig. 1 A schematic diagram of the proposed capacitor 5
    6 : Introduction It consists of two movable plates with an insulation dielectric layer on top of the bottom plate. With the two plates being flexible, makes it possible for the two plates to attract each other and decrease the maximum distance before the pull-in voltage occurs. Construction of proposed capacitor ? Two structural layers, three sacrificial layers, and two insulating layers of Nitride. 6
    7 : Introduction The top plate is fabricated from nickel with a thickness of 24? covered by a gold layer of thickness 2?. The bottom plate is made of polysilicon covered by a Nitride layer of a thickness of 0.35?. ============================================ Making process ? Metal MUMPs (Multi-User MEMS Process) Simulation ? Coventor Ware 7
    8 : Introduction They include low-noise amplifiers, harmonic frequency generators and frequency controllers. Many of the modern wireless systems place stringent requirements on high-quality, stable, low-phase noise with wide tuning- range voltage-controlled oscillators (VCOs). 8
    9 : Introduction The electronically tunable capacitors are the key elements in such VCOs. Components such as band select channel select and tuning elements of VCOs are still external to the chip because inductors and tunable capacitors (varactors) with a high quality factor are not available in standard silicon processes. MEMS allow precise positioning and repositioning of suspended membranes and cantilevers. 9
    10 : Pull-in Effect in Electrostatically Actuated Parallel-Plate Tunable Capacitors x0 Fixed plate C Suspended plate Spacing VDC 0 x0 Capacitance VDC 0 10
    11 : Pull-in Effect in Electrostatically Actuated Parallel-Plate Tunable Capacitors Spacing VDC 0 x0 Capacitance VDC 0 Fixed plate C VDC Suspended plate 11
    12 : Pull-in Effect in Electrostatically Actuated Parallel-Plate Tunable Capacitors Spacing VDC 0 x0 Capacitance VDC 0 Fixed plate VPI Suspended plate VPI VPI Max. controllable tuning range = 50% Controllable displacement Unstable Snap-in 12
    13 : To Extend Tuning Range … Require full-gap positioning Spacing VDC 0 x0 Capacitance 0 VPI VPI 13

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