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

Abstract

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.

Effects of Post-Annealing on the Properties of ZnO:Ga Films with High Transparency (94%) and Low Sheet Resistance (29 Ω/square)

“…The samples with 450 • C post-treatment (HN450) achieved the best transmittance (over 95%) in the visible spectrum, which is good for TCO. These results are much better than the ITO thin film with the same deposition method by PVD on a glass substrate with a thickness of 200 nm, a sheet resistance of 32 Ω/square, and a transmittance of over 84% [35]. These improvements in transmittance have several causes.…”

Impact of UV-ozone (UVO) treatment on optical and electrical properties of RF sputtered Ga2O3 thin films for opto-electronic application

“…The production of the monoclinic Ga2O3 phase necessitates a high temperature (>600°C), which significantly increases the thermal budget and restrict the substrate choices [5]. Amorphous Ga2O3 thin film, on the other hand, may be produced on practically any substrate at a low growth temperature using relatively easy chemical and physical vapour deposition processes such as atomic-layer deposition (ALD) and radio frequency sputtering (RF) [6]. Sputtering is used more frequently than other methods for the deposition of oxide thin films due to its suitability for largearea deposition, reproducible stoichiometry, affordability, controllable growth, uniformity, use of non-toxic gase, low operating temperatures, improved substrate adhesion, etc.…”