Aqueous solution-based synthesis and deposition of crystalline In-Ga-Zn-Oxide films via spray-coating

Abstract

The last decade has seen an increased attention towards the implementation of InGaZnO (IGZO) as a metal oxide channel material in TFT-devices. Crystalline IGZO shows a high electron mobility and low off-state leakage current, which results in an improved device performance compared to amorphous IGZO [Yamazaki et al., Jpn. J. Appl. Phys. 53 (2014)]. Thin film deposition of the IGZO superlattice structure requires a good layer homogeneity in addition to control of the stoichiometry, which can be achieved by using a solution-based process. In practice, this is usually achieved using 2-methoxyethanol (2-ME) based precursors. However, due to its harmful and teratogenic properties, alternative solvents are being explored. In this work, an aqueous precursor system is developed, in which the metal ions are stabilized by α-hydroxy carboxylic acids as ligands. By spray-coating this precursor, dense and uniform layers are deposited. Through an optimized multi-step thermal treatment, crystalline thin films of IGZO are obtained that show a preferential c-axis orientation after rapid thermal annealing at 1000°C in inert conditions. Preliminary electrical characterization of the deposited thin films already shows promising resistivities of around 8 mΩ*cm, which can apply to several areas of interest.