Low-Loss GHz Frequency Phononic Integrated Circuits in Gallium Nitride for Compact Radio Frequency Acoustic Wave Devices

Guiding and manipulating GHz frequency acoustic waves in
$\mu \text{m}$
-scale waveguides and resonators open up new degrees of freedom to manipulate radio frequency (RF) signals in chip-scale platforms. A critical requirement for enabling high-performance devices is the demonstration of low acoustic dissipation in these highly confined geometries. In this work, we show that gallium nitride (GaN) on silicon carbide (SiC) supports low-loss acoustics by demonstrating acoustic microring resonators with frequency-quality factor (
$\textit {fQ}$
) products approaching
${10}^{{13}}$
Hz at 3.4 GHz. The low dissipation measured exceeds the
$\textit {fQ}$
bound set by the simplified isotropic Akhiezer material damping limit of GaN. We use this low-loss acoustics platform to demonstrate spiral delay lines with on-chip RF delays exceeding
$2.5 ~\mu \text{s}$
, corresponding to an equivalent electromagnetic delay of
$\approx 750$
m. Given GaN is a well-established semiconductor with high electron mobility, this work opens up the prospect of engineering traveling wave acoustoelectric interactions in
$\mu \text{m}$
-scale waveguide geometries, with associated implications for chip-scale RF signal processing.