  Guiding and manipulating GHz frequency acoustic waves in $\mu$m-scale
waveguides and resonators opens 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
($fQ$) products approaching $4*10^{13}$ Hz at 3.4 GHz. The low dissipation
measured exceeds the $fQ$ 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 $\mu$s,
corresponding to an equivalent electromagnetic delay of $\approx$ 750 m. Given
GaN is a well-established semiconductor with high electron mobility, our work
opens up the prospect of engineering traveling wave acoustoelectric
interactions in $\mu$m-scale waveguide geometries, with associated implications
for chip-scale RF signal processing.
