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

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 SnOx oxide semiconductors, which are synthesized using a sol-gel process. Three types of stacked semiconductor layers of SnOx/SnOx/SnOx (S/S/S), ZTO/ZTO/ZTO (Z/Z/Z) and ZTO/SnOx/ZTO (Z/S/Z) are fabricated. Among them, the Z/S/Z TFT shows the best performance. The SnOx 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 (mu) is 3.15 cm(2) 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 x 10(7). A superior TFT performance can be obtained when the Z/Z/Z layer is changed to the Z/S/Z layer. mu significantly increases to 14.33 cm(2) V-1 s(-1) and the I-on/I-off increases to 2.35 x 10(8). 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.