Tin monoxide-based p-channel thin-film transistors fabricated by reactive sputtering and post-annealing

Thin film transistors (TFTs) having a SnOx film as the channel layer were fabricated by reactive sputtering followed by post-annealing. In microscopic observation, the as-deposited SnOx film exhibited a brown color, and gradually turned to light blue upon post-annealing. For a 16-nm-thick SnO x film, post-annealing at 200 °C yielded a p -channel TFT with a field-effect mobility of 2.3 cm 2 V -1 s -1 and an on/off current ratio of 10 3 . Deposited SnO x films were examined by X-ray photoelectron spectroscopy (XPS). The XPS spectrum was deconvoluted into three peaks corresponding to Sn 0 , Sn 2+ , and Sn 4+ . For a SnO x film annealed at 200 °C, the relative contents of Sn 0 , Sn 2+ , and Sn 4+ were 7.6%, 83.9%, and 8.6%, respectively. The XPS analysis indicates that a SnOx film exhibiting a light blue color under microscopic observation is mainly composed of SnO. Thus, microscopic observation is useful for confirming whether a film is composed of SnO.