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 ZrO
_x
as 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 cm
²
/V · s, a subthreshold swing of 260 mV/dec, and an ON/OFF current ratio of ~10
⁸
with negligible hysteresis voltage. The ZnO TFT shows excellent stability under bias stress because of the high-quality ZnO film and its excellent interface with ZrO
_x
. The conduction band tail width of ZnO was obtained from the TCAD fitting to the measurement data and was found to be 65 meV.