Top-Gated Indium–Zinc–Oxide Thin-Film Transistors With In Situ Al2O3/HfO2 Gate Oxide

We report on top-gated indium-zinc-oxide (IZO) thin-film transistors (TFTs) with a 3-nm layer of aluminum between the IZO active layer and high-k HfO
₂
gate insulator. A series of anneals at 300°C was used to convert the Al metal into Al
₂
O
₃
, resulting in high-performance top-gated TFTs. The 8-h-annealed TFT with Al layer has a threshold voltage |V
_T
| <; 0.5 V, an ON/OFF ratio of 1 × 10
⁷
, a subthreshold slope (SS) of 0.14 V/decade, and a saturation mobility μs ~115 cm
^2/
V · s in devices with L
_G
= 50μm gate length. For smaller devices with L
_G
= 5 μm, the threshold voltage and SS are similar, but the ON/OFF ratio and mobility are lower. Cross-sectional TEM images and C-V
_G
characteristics with little hysteresis confirm that the thin Al layer, converted in situ into Al
₂
O
₃
, can protect the IZO channel during processing and produce a good high-k gate-stack.