Observation of bound states in the continuum in a micromechanical resonator

Abstract: Bound states in the continuum (BICs) refer to physical states that possess intrinsic zero dissipation loss even though they are located in the continuous energy spectrum. BICs have been widely explored in optical and acoustic structures, leading to applications in sensing and lasing. Realizing BICs in micromechanical structures is of significant importance for both fundamental research and engineering applications. Here, we fabricated, with CMOS-compatible processes on a silicon chip, a wheel-shaped micromechanical resonator, in which we experimentally observed the BIC in the micromechanical domain. Such BICs result from destructive interference between two dissipative modes of the mechanical structure under broken azimuthal symmetry. These BICs are found to be robust against size variations of the dissipation channels. The demonstrated mechanical BIC can be obtained with a large and robust supporting structure, which substantially reduces device fabrication difficulty and allows for its operation in versatile environments for broader application areas. Our results open a new way of phonon trapping in micromechanical structures with dissipation channels, and produce long phonon lifetimes that are desired in many mechanical applications such as mechanical oscillators, sensors, and quantum information processors.