Development of UHF Micromechanical Resonators and Arrays Based on Silicon-OnInsulator (SOI) Technology

A novel micromachining technology on SOI substrates is presented that is capable of producing on-chip high-Q resonators and resonator arrays equipped with high aspect-ratio (30:1) microstructures and nano-gap capacitive transducers filled with high-k dielectrics. The newly developed IC-compatible MEMS microfabrication process consists of merely three standard photolithography steps, which is much simpler than the other SOI-based resonator device technologies. In order to achieve the optimum performance and yield of the resonators and resonator arrays, this SOI-based fabrication process has been carefully designed and investigated step by step. For capacitively-transduced extensional mode (e.g., radial-contour and wine-glass mode) resonators, formation of nano-scale capacitive gaps and large resonator-to-electrode overlap area is essential for reducing the motional resistance Rx and DC bias voltage by strengthening the capacitive transduction. Atomic Layer Deposition (ALD) technology with superb conformability and uniformity as well as outstanding thickness controllability is used to deposit the ultra-thin layer (~10 nm) of high-k dielectric material that acts as the solid capacitive gaps, which allows the mass production of on-chip capacitively-transduced resonators and resonator arrays with greatly enhanced electromechancial coupling coefficient, and thus lower motional resistance and DC bias voltage. Using this technique, high-Q micromechanical resonators and resonator arrays on SOI substrates operating at ultra-high frequencies (UHF) have been developed. The ultimate goal of this project is to implement on-chip narrow-band micromechanical filters with unprecedented frequency selectivity and ultra-low insertion loss. By fine-tuning the nonlinear characteristics of the capacitive transducers enabled by the new SOI technology, novel on-chip mechanical signal processors for frequency manipulation, such as mixer and multiplier, will be investigated