Hypersonic phononic crystal structures for integrated nano-electromechanical/optomechanical devices

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Dehghannasiri, Razi
Adibi, Ali
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This dissertation embraces the study, design, and fabrication of integrated phononic devices on silicon chips for enabling new integrated radio frequency (RF)-photonics devices as well as new integrated nano/micro-electromechanical systems for on-chip sensing and RF signal processing. These integrated phononic devices are realized in fully CMOS-compatible platforms in the form of phononic crystal (PnC) structures (i.e., periodic structures supporting phononic bandgaps) and double-layer crystalline silicon (Si) structures. The designed phononic structures are compatible with integrated optics/electronics, and possess a higher efficiency and lower phononic/photonic losses. In particular, I developed a hypersonic pillar-based PnC platform with a wideband phononic bandgap at GHz frequencies on a thin film of aluminum nitride deposited on a Si substrate. This platform allows for designing low-loss integrated surface acoustic waveguides and resonators with piezoelectric excitation for filtering applications in wireless communication. In addition, I extended the application of PnC structures to design efficient on-chip stimulated Brillouin scattering (SBS) nano-devices for RF-photonics. These nanostructures are realized in silicon nitride membranes and therefore are fully compatible with integrated optics platforms. My studies on SBS in silicon nitride suggest further investigation of silicon nitride for enabling promising SBS-based systems. Moreover, in this dissertation, I studied and fabricated the integrated optomechanical resonators in the double-layer crystalline Si platform. The tiny air gap between the silicon layers of the structure allows for a highly-efficient optomechanical interaction. The applications of such double-layer optomechanical structures include on-chip RF oscillators (with no external electric feedback) and wide-band high-speed integrated optical switches for optical interconnects.
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