Roll-to-Roll fabrication of ITO thin film for flexible optoelectronics applications: The role of post-annealing

We have developed and examined new and cost effective methods for fabrication indium tin oxide (ITO) film on flexible substrate. The ITO film is deposited to polyethylene terephthalate film using roll-to-roll (RTR) sputtering advanced technology. The film's properties are evaluated before and after heat treatment. Effect of post annealing time on the electrical, optical, structural and surface properties of RTR sputtered ITO films is estimated. In addition, mechanical flexibility of as-sputtered amorphous ITO and annealed crystalline ITO films are compared. It is estimated that post-annealing at 150 °C reduces sheet resistance and increase the optical transmittance of the ITO films. The best results are observed when annealing time is 60 min. In this case the sheet resistance of ITO is measured to be 125 Ω/sq. and optical transmittance is 87.3% at wavelength range from 380 nm to 780 nm. It is demonstrated successful operation of touch screen panels fabricated on annealed ITO film. It is estimated that post-annealing significantly improves ITO performance as compare of that as-deposited film. Based on Hall measurement and transmittance electron microscopy examinations, possible mechanism to explain the effect of post-annealing time on RTR sputtered ITO films is manifested.