Study of Gallium-Doped Zinc Oxide Thin Films Processed by Atomic Layer Deposition and RF Magnetron Sputtering for Transparent Antenna Applications

Gallium-doped zinc oxide (GZO) films were fabricated using RF magnetron sputtering and atomic layer deposition (ALD). The latter ones demonstrate higher electrical conductivities (up to 2700 S cm^-1) and enhanced charge mobilities (18 cm² V^-1 s^-1). The morphological analysis reveals differences mostly due to the very different nature of the deposition processes. The film deposited via ALD shows an increased transmittance in the visible range and a very small one in the infrared range that leads to a figure of merit of 0.009 Ω^-1 (10 times higher than for the films deposited via sputtering). A benchmarking is made with an RF sputtered indium-doped tin oxide (ITO) film used conventionally in the industry. Another comparison between ZnO, Al:ZnO (AZO), and Ga:ZnO (GZO) films fabricated by ALD is presented, and the evolution of physical properties with doping is evidenced. Finally, we processed GZO thin films on a glass substrate into patterned transparent patch antennas to demonstrate an application case of short-range communication by means of the Bluetooth Low Energy (BLE) protocol. The GZO transparent antennas' performances are compared to a reference ITO antenna on a glass substrate and a conventional copper antenna on FR4 PCB. The results highlight the possibility to use the transparent GZO antenna for reliable short-range communication and the achievability of an antenna entirely processed by ALD.