Improvement in bias-stress and long-term stabilities for in-Ga-Zn-O thin-film transistors using solution-process-compatible polymeric gate insulator

Abstract

Abstract We fabricated the indium-gallium-zinc-oxide (IGZO) thin-film transistors (TFTs) employing a new coatable polymeric insulator, Zeocoat™ (produced by ZEON Corp., Japan) as gate insulators. Zeocoat film thickness was modulated by controlling the dilution ratio and spin-speed. The film showed low leakage current density (10−7 A/cm2 at 1 MV/cm for 215-nm-thick film) and no significant differences in dielectric constants depending on the film thicknesses or the measurement frequencies. Typical device parameters of the IGZO TFTs fabricated with optimum conditions exhibited the carrier mobility at saturation region of 2.4 cm2/V·s and subthreshold swing of 0.25 V/dec. While there were no marked instabilities in the negative-bias stress tests, the threshold voltage shift under the positive-bias stress was reduced as small as 1.5 V by increasing the deposition temperature of the Al2O3 protection layer from 150 °C to 200 °C. The device stability for long shelf-time was also improved through 100-nm-thick Al2O3 passivation layer deposited on top of the TFT.