Enhanced Performance of Atomic Layer Deposited Thin-Film Transistors With High-Quality ZnO/Al₂O₃ Interface

We fabricated ZnO channel/Al2O3 gate dielectric thin-film transistors (TFTs) by atomic layer deposition (ALD) continuous growth process. The effects of the channel and the dielectric continuous growth on the performance of TFTs were investigated. Compared with noncontinuous growth ZnO/Al2O3 films, continuous growth ZnO/Al2O3 films with no obvious buffer layer and less residual O–H bonds possess superior ZnO/Al2O3 interface quality. The continuous growth TFTs exhibit a field-effect mobility of 19.6 cm $^{{{2}}}\,\,\text {V}^{{-{1}}} \text {s}^{{-{1}}}$ , a subthreshold swing of 0.13 V dec $^{{-{1}}}$ , a high $\text{I}_{ \mathrm{\scriptscriptstyle ON}}/\text{I}_{ \mathrm{\scriptscriptstyle OFF}}$ of ${4.1} \times {10}^{{{9}}}$ , a hysteresis window of 0.09 V, and an excellent uniformity of electrical characteristics. Continuous growth TFTs also demonstrate better stability with minor shifts of $\Delta \text {V}_{{\text {th}}}~0.6$ V [positive bias stress (PBS)] and $\Delta \text {V}_{{\text {th}}} -{0.3}$ V [negative bias stress (NBS)]. The faster falling rates of activation energy for continuous growth TFTs indicate that the total trap density is reduced through the continuous growth of active layer and dielectric layer. Our results suggest that the ALD-based continuous growth process could enhance the performance of TFTs.