Gigahertz Focusing Acoustic Delay Lines for Phononic Integrated Circuits

This work introduces a novel design of gaussian focusing acoustic delay lines (ADLs) based on suspended aluminum nitride thin film. By focusing acoustic waves into wavelength-scale structures and precisely controlling the beam width through Gaussian acoustic field parameters, the device enhances coupling between narrow waveguides and transducers, enabling efficient electrome-chanical conversion. The wavelength-scale structures exhibit reduced dispersion, helping maintain signal integrity over long distances. Additionally, a tapered interface between the waveguide and interdigitated transducers (IDTs) minimizes reflections and unnecessary propagation loss, contributing to low-loss phonon routing. The device also demonstrates compactness and low insertion loss of 20.57 dB with the fundamental symmetric (S0) lamb mode at 1.29 GHz, further underscoring its potential for miniaturized PnICs. Overall, the combination of focusing IDTs, miniaturized waveguides, and tapered interfaces provides an integrated solution for low dispersion, low energy loss phonon routing in phononic integrated circuits (PnICs).