Innovative and cost-effective synthesis of indium tin oxide films

Abstract

This paper presents significant progress in the synthesis of transparent and conducting indium tin oxide (ITO) films using a novel and cost-effective electrostatic spray assisted vapour deposition (ESAVD) method. ESAVD is a variant of the chemical vapour deposition (CVD) process, which involves spraying atomised precursor droplets across an electric field where the precursor droplets undergo decomposition and chemical reaction near the vicinity of the heated substrate and produce a stable solid film. The process can be performed in an open atmosphere without the use of a sophisticated reactor and vacuum system. Tin tetrachloride and indium chloride were used as the starting precursors. The ITO films were deposited onto soda lime glass substrates. The effects of deposition temperature and input Sn/In ratio on the microstructure, optical transmission and electrical resistivity of the deposited ITO films was investigated. A combination of XRD, SEM, AFM, Raman spectroscopy, optical and resistivity measurement techniques was used to characterise the deposited films. An optimum input Sn/In ratio of 1:40 was found to produce the desired film properties. The deposited ITO films were polycrystalline consisting of grains ranging from 250 to 600 nm in size. The electrical resistivity of ITO films deposited at temperatures ranging from 200 to 550°C was found to vary from 8×10 −4 to 2×10 −5 Ω cm −1. The optical transmittance (in the visible range, at 400 nm) of the films deposited at these temperatures was in excess of 76%, which is comparable to those films produced using more expensive and sophisticated vapour deposition techniques such as CVD and sputtering. This simple and cost-effective technique can potentially be incorporated for on-line large scale processing application.