Deposition of aluminum doped ZnO as electrode for transparent ZnO/Glass surface acoustic wave devices

Unlike metal electrodes such as Al and Au, aluminum doped zinc oxide (AZO) with high conductivity and transparency can be used as transparent electrodes for surface acoustic wave (SAW) resonators, and thus realize fully transparent and invisible ZnO SAW devices on glass. This paper reports the fabrication of transparent SAW resonators using AZO as the transparent electrode and investigation of effects of deposition parameters on the crystal structures of the AZO thin films deposited by magnetron sputtering. Results show that a low sputtering pressure and an optimal sputtering power are beneficial for the deposition of (0002) orientation of AZO. The optimal deposition parameters are found to be: deposition pressure of 0.3 Pa, sputtering power of 300W, substrate temperature of 200°C. The fabricated transparent SAW devices have different wavelengths (from 16 to 32μm) and all the devices exhibit two types of wave modes: Rayleigh and Sezawa waves. Compared with Sezawa wave, the Rayleigh wave has a large signal amplitude up to 25 dB. In addition, as the wavelength increases, the resonant frequencies of both the Rayleigh and Sezawa waves increase whereas their phase velocities decrease. The transparent SAW devices have also demonstrated their ability to induce a strong acoustic streaming in a water droplet with a streaming velocity up to 2.27 cm/s. This research opens a door for further exploration of the SAW devices in transparent electronics.