Physical/chemical characterization and device applications of transparent zinc–tin–oxide thin films deposited using RF sputtering

Amorphous Zn–Sn–O (zinc–tin–oxide, ZTO) thin films were deposited with a mixed ZnO/SnO2 target through RF sputtering. The deposited Zn–Sn–O thin films were characterized using physical/chemical probing tools, such as optical characterization based on spectroscopic ellipsometry, surface morphology via atomic force microscopy, chemical information determined through X-ray photoelectron spectroscopy, and structural monitoring of crystallinity using X-ray diffraction. The ZTO thin-film transistors were constructed with a bottom-gate structure using thermally grown SiO2 as the gate dielectric. The Zn–Sn–O TFTs were characterized in terms of the channel thickness, dielectric thickness, and annealing temperatures, and degradation tests were performed at higher temperatures than under ambient conditions. The Zn–Sn–O thin film transistors were optimized at a ZTO thickness of 40 nm, a SiO2 gate dielectric thickness of 100 nm after annealing at 500 °C, and had an on/off ratio of 8.22×10+7, a field-effect mobility of 12.90 cm2/V s, a threshold voltage of 4.32 V, and an S-slope of 0.69 V/decade.