Surface acoustic wave devices on bulk ZnO at low temperature

TL;DR

This study demonstrates the viability of surface acoustic wave devices on bulk ZnO crystals at low temperatures, achieving high quality factors and revealing temperature-dependent SAW velocity, thus opening new avenues for low-temperature applications.

Contribution

The paper presents the first effective operation of SAW devices on bulk ZnO crystals at low temperatures, with detailed characterization of their performance and temperature dependence.

Findings

SAW devices on bulk ZnO operate effectively at cryogenic temperatures.

Maximum quality factor achieved is approximately 1.5×10^5.

SAW velocity reaches about 2.68 km/s at 10 mK.

Abstract

Surface acoustic wave (SAW) devices based on thin films of ZnO are a well established technology. However, SAW devices on bulk ZnO crystals are not practical at room temperature due to the significant damping caused by finite electrical conductivity of the crystal. Here, by operating at low temperatures, we demonstrate effective SAW devices on the (0001) surface of bulk ZnO crystals, including a delay line operating at SAW wavelengths of {\lambda} = 4 and 6 {\mu}m and a one-port resonator at a wavelength of {\lambda} = 1.6 {\mu}m. We find that the SAW velocity is temperature dependent, reaching $v \simeq 2.68$ km/s at 10mK. Our resonator reaches a maximum quality factor of $Q_i \simeq 1.5\times 10^5$, demonstrating that bulk ZnO is highly viable for low temperature SAW applications. The performance of the devices is strongly correlated with the bulk conductivity, which quenches SAW transmission above about 200 K.