Visualization of Gaussian Acoustic Fields in Surface-Acoustic-Wave Resonators

Surface-acoustic-wave (SAW) resonators operating at gigahertz (GHz) frequencies are widely used in wireless telecommunication and quantum information processing. Successful implementation of such resonators calls for detailed microscopic understanding of mode profiles, energy dissipation channels, and imperfections from microfabrication. In this work, we report on the visualization of acoustic waves in 128^◦ Y-cut LiNbO₃ SAW resonators by transmission-mode microwave impedance microscopy (T-MIM). The Gaussian-like mode profile tightly confined by reflection mirrors is vividly seen in the T-MIM images. The frequency-dependent data inside the cavity and the negligible leakage outside the reflectors are consistent with the high-Q nature of the resonators and demonstrate the ability to confine the modes using curved mirrors. The spatially resolved acoustic profile also allows us to perform failure analysis on malfunctioned devices. Our work paves the road to optimize the design of SAW resonators for classical and quantum acoustic applications.