Direct Visualization of Gigahertz Acoustic Wave Propagation in Suspended Phononic Circuits

We report direct visualization of gigahertz-frequency Lamb-wave propagation in aluminum nitride phononic circuits by transmission-mode microwave impedance microscopy (TMIM). Consistent with finite-element modeling, the acoustic eigenmodes both a horn-shaped coupler and subwavelength waveguide are revealed TMIM images. Using fast Fourier-transform filtering, we quantitatively analyze loss individual Lamb modes along power-coupling coefficient between parabolic couplers. Our work provides insightful information on propagation, mode conversion, attenuation waves piezoelectric nanostructures, which is highly desirable for designing optimizing devices microwave-signal processing quantum-information transduction.