Transparent thin film transistors of polycrystalline SnO2−x and epitaxial SnO2−x

We report on transparent thin film field effect transistors (TFTs) based on polycrystalline SnO2−x and epitaxial SnO2−x. Polycrystalline SnO2−x TFTs of the top and the bottom gate geometries exhibited high mobility values of 145.7 cm2/V s and 160.0 cm2/V s, respectively. However, our polycrystalline SnO2−x devices showed non-ideal behaviors in their output and transfer characteristics; a large hysteresis was observed along with large voltage dependence. The probable origin of these non-ideal behaviors is the barrier formation across grain boundaries of polycrystalline SnO2. To confirm this, we used SnO2−x epitaxially grown on r-plane sapphire substrates as a channel layer and compared their performance with those of polycrystalline SnO2−x based TFTs. Although the mobility of epitaxial SnO2−x TFTs was not as high as that of the polycrystalline SnO2−x TFTs, the non-ideal voltage dependence in output and transfer characteristics disappeared. We believe our direct experimental comparison clearly demonstrates the grain boundary issue in polycrystalline SnO2−x.