Direct Visualization of Gigahertz Acoustic Wave Propagation in Suspended Phononic Circuits

TL;DR

This paper demonstrates the direct visualization of gigahertz Lamb wave propagation in aluminum nitride phononic circuits using microwave impedance microscopy, providing detailed insights into acoustic modes, loss, and coupling for device optimization.

Contribution

It introduces a novel application of TMIM for visualizing high-frequency acoustic waves in phononic circuits, advancing understanding of mode behavior and attenuation.

Findings

Visualization of Lamb wave propagation in phononic circuits

Quantitative analysis of acoustic loss and mode coupling

Insights into wave propagation and attenuation mechanisms

Abstract

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