RF MEMS device based on micromachining

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Three-dimensional microstructures, sensors and actuators can be fabricated on a silicon chip using micromachining which is an extended technology based microfabrication for integrated circuits. RF MEMS (Radio Frequency Micro Electro Mechanical Systems) has been developed to produce RF components for wireless systems. Switches (relays), variable capacitors, micromechanical resonators for time (frequency) references or RF filters, RF interconnection and coils which are fabricated on thin self supported membranes and hence have small stray capacitances can be made by this technology. Following achievements are obtained in this research program.Packaging technologies for the RF MEMS as wafer level packaging processes and electrical feedthrough structures for an electrical interconnection for high speed signal from the top side to the backside of silicon chips were developed. MEMS switches as contact type and capacitive type which are actuated electrostatically were developed.MEMS switches … More were applied for a flexible flat panel display and commercialized as components for high speed LSI testers.Micromechanical resonators can have high resonant frequencies. The extension mode enables higher resonant frequency than the bending mode because of the high spring constant of the extension mode. By making the resonant frequency determined by the lateral dimension multiple resonators with different resonant frequencies can be integrated on a chip. An electrostatically driven wine glass mode silicon disk resonator of witch diameter is 20 μm demonstrated a resonant frequencies of approximately 100 MHz. Since the resonant frequency of such small resonators can be fluctuated by absorbing gas MEMS resonator was fabricated in a vacuum cavity in a silicon chip to stabilize the resonant frequency. Micromechanical resonators have an inherent problem of phase noise caused by thermomechanical noise.The thermomechanical noise also limit the resolution of resonating sensors. Extreme sensitivity is required for MRFM (Magnetic Resonance Force Microscopy) for the MRI (Magnetic Resonance Microscopy) of small samples as biological cell. The noise problems were studied and the phase noise could be reduced by a parametric squeeze damping. Cantilever resonant sensors which have high quality factor in atmosphere were.developed by using quartz material with thickness share mode.High aspect ratio planer coils.were fabricated to reduce the resistance.and high quality factor as high as 85 at 1.6 GHz was achieved for the purpose of the MRI for the small samples. Less