Transparent thin-film transistors with zinc oxide semiconductor fabricated by reactive sputtering using metallic zinc target

We have investigated transparent thin-film transistors (TTFTs) with active channel of zinc oxide (ZnO) films, reactively grown by RF magnetron sputtering using metallic zinc target. According to the ratio of oxygen to the total gas (O2/(O2 + Ar)), microstructures of the films changed drastically, and especially, ZnO films formed at 20% of O2 had good crystallinity with larger grains. ZnO films showed above 84% transparency in the wavelength range from 400 nm to 750 nm. Our bottom-gate ZnO-TTFTs showed n-type character with field-effect mobility of about 1.5 cm2/Vs, an on/off ratio> 106, subthreshold swing of 1.1 V/decade, and threshold voltage of 15.9 V, after annealing at 250 °C for 30 min in O2 ambient.