Performance Evaluation of Indium Zinc Oxide Thin Films for Flexible Organic Light-emitting Device Applications

In this report, high-quality indium zinc oxide (IZO) films (60-220 nm) were first grown on hardness poly-carbonate (HPC) substrate by ion-assisted deposition (IAD) dc magnetron sputtering without a post deposition annealing treatment. The electrical, optical, and structural properties of these films were investigated as a function of substrate temperature, oxygen pressure, and film thickness. IAD dc magnetron sputtering provides very uniform IZO films with high transparency (ges 80% in 550 nm spectrum) and low electrical resistivity (3times10^-4 Omega-cm). The Hall mobility and carrier density for a 120-nm-thick film at 100 W are 12 cm²/V-s and 2.5times10²¹ cm^-3, respectively. Atomic force microscopy measurements of the IZO films indicated that their root mean-square values (R_MS ~ 0.44-0.69 nm) are superior to that (~ 4 nm) of commercially available indium tin oxide (ITO) films deposited by sputtering. Next, IZO films grown at low temperature by IAD dc magnetron sputtering were used to study the electroluminescence (EL) performance of organic light-emitting devices (OLEDs). Under a current density of 100 (mA/cm²), the developed OLEDs show an excellent efficiency (12 V turn-on voltage) and a luminance of 1200 (cd/m²) in average, which is better than that measured with commercial ITO anodes and well above the electro-optical application standard.