Performance improvement of a sol–gel ZTO-based TFT due to an interfacial SnOx dopant layer

Abstract

Oxide semiconductors are promising active layer materials for thin-film transistors (TFTs). In this paper, ZnSnO (ZTO)-based TFTs are demonstrated. The active layers are prepared using a stacked structure of ZTO and SnO_x oxide semiconductors, which are synthesized using a sol–gel process. Three types of stacked semiconductor layers of SnO_x/SnO_x/SnO_x (S/S/S), ZTO/ZTO/ZTO (Z/Z/Z) and ZTO/SnO_x/ZTO (Z/S/Z) are fabricated. Among them, the Z/S/Z TFT shows the best performance. The SnO_x film between the two ZTO films acts as an interfacial dopant layer to increase the electron density and the crystallinity of the Z/S/Z layer. The S/S/S TFT shows a highly conductive and non-switching behavior. In contrast, when using Z/Z/Z as the active layer, the TFT reveals normal n-type enhancement transfer characteristics with a threshold voltage (V_th) of 5 V. The mobility (μ) is 3.15 cm² V⁻¹ s⁻¹, the sub-threshold swing (SS) is 0.17 V dec⁻¹ and the I_on/I_off ratio is 3.6 × 10⁷. A superior TFT performance can be obtained when the Z/Z/Z layer is changed to the Z/S/Z layer. μ significantly increases to 14.33 cm² V⁻¹ s⁻¹ and the I_on/I_off increases to 2.35 × 10⁸. Moreover, the Z/S/Z TFT shows a lower V_th of 0.8 V and a lower SS of 0.13 V dec⁻¹. Twelve devices in total are produced and measured to verify the repeatability. Consistent and reproducible electrical characteristics of the TFTs are observed.