Analysis of Membrane Phononic Crystals with Wide Band Gaps and Low-Mass Defects
We present techniques to model and design membrane phononic crystals with low-mass defects, optimized for force sensing. Further, we identify the importance of the phononic crystal mass contrast as it pertains to the size of acoustic band gaps and to the dissipation properties of defect modes. In particular, we quantify the tradeoff between high-mass-contrast phononic crystals, with their associated robust acoustic isolation, and a reduction of soft clamping of the defect mode. We fabricate a set of phononic crystals with a variety of defect geometries out of high-stress stoichimetric silicon-nitride membranes and measure at both room temperature and 4 K in order to characterize the dissipative pathways across a variety of geometries. Analysis of these devices highlights a number of design principles integral to the implementation of low-mass low-dissipation mechanical modes into optomechanical systems.
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Physical Review Applied