This paper proposes, for the first time, a MEMS-based digitally tunable micromechanical resonator (DTMR). A general
methodology of tuning the resonant frequency of a MEMS comb-driven resonator using digital voltages is presented. In
this mechanism, a microelectromechanical digital-to-analog converter (MEMDAC) is employed as the tuning unit. The
resonant frequency of the DTMR shifts in response to the input digital voltage. Several structures have been proposed,
while the one using the number of the vertical beams as the scale factor features the optimum linearity. In a modified
design, the resonate frequency can be tuned from approximately 65 to 94 kHz. The maximum deviation from ideal
linearity can be reduced to 0.31 kHz, which is remarkably less than those of the preliminary designs.
As an alternative to the visual observation method used conventionally, a new approach of sensing the displacement of suface-micromachined polysilicon actuators or microactuator arrays by the measurement of capacitance variation of the electrodes is proposed in this paper. Finite element analysis (FEA) is used to provide the relation between the lateral displacement and the capacitance. In the preliminary design, the capacitance variation is on the order of fF. In order to measure the displacement precisely, the electrode arrays are proposed. This method could be useful for testing a variety of laterally driven microactuators and arrays, including MEMDACs.
A micromachined variable capacitor consisting of a suspended plate and a bottom plate fixed on the substrate is proposed as an alternative to vertically movable micromachined capacitors used for wireless communication systems. The suspended plate is driven laterally by thermal actuator arrays. The overlapped area of the two plates is changed so that the capacitance is tuned by an input voltage less than 4 V. Finite element method is used here to analyze the device. The capacitor exhibits a variation from 5.6 fF to 10.3 fF. For getting a capacitance large enough for radio frequency (RF) applications, the plates are periodically arranged to build an array. The capacitance of the array is tuned from 0.58 pF to 0.78 pF. In order to improve the linearity and increase the variation range, design modifications are made.
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