Improvement of the long-term stability of ZnSnO thin film transistors by tungsten incorporation using a solution-process method

In this paper, W-doped ZnSnO (WZTO) thin films and TFT devices are successfully fabricated by a wet-solution technique. The impact of W doping on the film structure, surface morphology, optical properties and chemical compositions of ZTO thin films is analyzed by atomic force microscopy, X-ray diffraction, UV-visible spectroscopy and X-ray photoelectron spectroscopy. The results show that the WZTO thin films have a smooth surface, amorphous structure and fewer oxygen vacancies with increasing W levels. The oxygen vacancy concentration of WZTO thin films is reduced from 40% to 27% with W incorporation. Compared with films free of W doping, for example ZnSnO TFTs, the positive bias stress stability of WZTO TFTs and long-term stability in air are improved obviously and the shift of the threshold voltage (V(T)) is restrained about six times. The critical reason for the improvement of the ZTO TFT properties is attributed to W-doping, wherein the suppression of oxygen vacancies by W ions plays a dominant role in changing the performance of ZTO thin films and the stability of TFTs.