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 ofW 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.