Support loss suppression in micromechanical resonators by the use of phononic band gap structures

By modifying the supporting structures of a conventional piezoelectric-on-substrate micromechanical (MM) resonator using phononic crystal (PC) slab structures with complete phononic band gaps (PBGs) the support loss in micromechanical resonators is suppressed and the quality factor of the fundamental extensional resonant mode is improved from approximately 1,200 to approximately 6,000. The conventional MM resonator and the PC resonators are both fabricated on the same chip and using the same fabrication process. The PC is made by etching a hexagonal (honeycomb) array of holes in a 15μm-thick slab of silicon. The radii of the holes are approximately 6.4μm and the spacing between the centers of the nearest holes is 15 μm. The conventional MM resonator is made of a rectangular structure with dimensions of 600 μm by 60 μm and the fundamental flexural and extensional modes of the structure in the smaller dimension are excited. In the third dimension, all the structures are made of a 15 μm silicon (Si) slab, a 100 nm layer of gold, a ~1 μm layer of zinc oxide, and a patterned 100 nm layer of aluminum electrodes stacked on top of each other to serve as the resonant mass and the transduction medium. The significant improvement obtained using the PC resonator structures makes them excellent candidates for next generation of MM resonators for wireless communication and sensing applications despite some minor remaining challenges.