Aqueous solution-based synthesis and deposition of crystalline In-Ga-Zn-Oxide films via spin-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. 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 general, 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, starting from the individual metal (hydr)oxides. A stable multimetal precursor is acquired, in which the metal ions are stabilized by α-hydroxy carboxylic acids which fulfill the role of ligands. 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 well below 5 mΩ*cm, which can apply to several areas of interest.