Engineering of Flexo- and Gravure-Printed Indium-Zinc-Oxide Semiconductor Layers for High-Performance Thin-Film Transistors

Flexo-and gravure-printed indium-zincoxide (IZO) semiconductor thin-film transistors (TFTs) with bottom-gate bottom-contact device architecture are investigated systematically. A strong dependence of the TFT characteristics is observed on the number of printed IZO layers and on the cell volume of the printing cylinder. White-light interferometry and scanning electron microscopy data show that homogeneous and only few nanometer thin films are printed and that the variation of the TFT characteristics is correlated with significant differences in the IZO film morphology on the nanometer scale. For optimized printing conditions, flexo- and gravure-printed IZO TFTs with the average field-effect mobility mu sat of 8.1 +/- 1.7 and 9.1 +/- 1.4 cm(2)V(-1)s(-1) are fabricated, respectively, with the dense IZO semiconductor films of similar to 10 nm thickness. The TFTs show a positive threshold voltage, a very small hysteresis, and a high ON/OFF-current ratio. Therefore, this paper demonstrates the great potential of cost-efficient high-throughput roll-to-roll printing techniques for the fabrication of IZO semiconductor thin films and TFTs of high quality.