Analysis of the valence state of tin in ZnSnO x thin-film transistors

Zinc tin oxide (ZTO) thin-film transistors (TFTs) were fabricated using the co-sputtering method with Sn and zinc oxide (ZnO) as targets. The Sn-sputtering power was varied to optimize the device performance of the ZTO TFTs. The chemical states of Sn3d and O 1s at the surface of the ZTO films were analyzed by X-ray photoelectron spectroscopy to explain the effect of different Sn contents of the ZTO films on the device performance of the ZTO TFTs. The oxygen vacancy and the ratio of Sn 4+ and Sn 2+ were found to significantly effect on the device performance. When the ZTO film has the highest concentration of Sn 4+ and lowest content of oxygen vacancy, the device achieves the optimal mobility of 15.67 cm 2 /Vs, and the on–off current ratio reaches 1.17 × 10 8 .