Highly Stable, Nanocrystalline, ZnO Thin-Film Transistor by Spray Pyrolysis Using High-K Dielectric

We report a highly stable, nanocrystalline, zinc oxide (ZnO) thin-film transistor (TFT) fabricated by spray pyrolysis using purified ZrOxas a gate insulator. The crystalline ZnO layer shows an average grain size of 30 nm and a smooth surface with an average rms roughness value of 1.21 nm. The smoothness of the ZnO film is due to the alignment of all grains with the (002) c-axis. The TFTs exhibit a saturation mobility of 12.76 cm2/V · s, a subthreshold swing of 260 mV/dec, and an ON/OFF current ratio of ~108with negligible hysteresis voltage. The ZnO TFT shows excellent stability under bias stress because of the high-quality ZnO film and its excellent interface with ZrOx. The conduction band tail width of ZnO was obtained from the TCAD fitting to the measurement data and was found to be 65 meV.