Passivation of Thin Channel Zinc Tin Oxide TFTs Using Al2O3 Deposited by O3-Based Atomic Layer Deposition

Abstract

Here, we fabricate solution processed zinc tin oxide bottom gate top contact thin film transistors (TFTs) with active layer thickness down to 6 nm by varying the solution molarity and number of layers. As-fabricated devices show hysteresis as large as 12.65 V. The hysteresis is then studied under vacuum to understand the important role of the back channel in electrical performance. After vacuum treatment, the hysteresis measured under vacuum was reduced to −0.05 V. Alumina deposited on the back channel using atomic layer deposition (ALD) is used for passivation. The TFTs passivated with an H2O-based ALD process show conductive behavior after passivation while an O3-based ALD process results in a negative threshold voltage shift dependent on the thickness of the active layer. O3-based passivated devices show good stability with a field effect mobility of 8.3 cm2V−1s−1, ${V}_{t}$ of 5.5 V, and hysteresis of 0.85 V.