Transparent Surface Acoustic Wave Devices on ZnO/Glass Using Al-Doped ZnO as the Electrode

This letter reports the design of transparent surface acoustic wave (SAW) resonators using aluminum-doped ZnO (AZO) as the transparent electrode on ZnO/glass substrates. SAW devices with a resonant frequency up to 204.4 MHz and signal amplitude up to 25 dB were obtained with transparency above 80%. An AZO layer of more than 250 nm is needed to minimize the series resistance of the electrode to achieve reasonable performance. Temperature sensing showed that they have a temperature coefficient of frequency of
${\sim}{\rm 50}~{\rm ppm/K}$
. This demonstrates the great potential of transparent SAW devices for widespread applications, as such devices are one the of building blocks of electronics, sensors, and microsystems.