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Thin SiO 2 films were used to modify the Ta 2 O 5 insulator (STS) in the ZnO-TFTs fabricated at room temperature by RF magnetron sputtering. The performance of the device was obviously improved after adding thin SiO 2 layers, such as: enhancement of on/off ratio by one order of magnitude, reduction of the subthreshold swing from 0.32 to 0.28 V/dec, increase of the field effect mobility (from 46.2 to 52.4 cm 2 /V s), as well as reduction of the hysteresis in I DS versus V GS curves and capacitance-voltage characteristics. The capacitancevoltage and C À2 versus voltage characteristics were investigated, from which the trapped charge density at or near the interface between insulator and ZnO layer as well as the carriers concentration of the ZnO film are calculated. The performance enhancements are attributed to the reduce of leakage current, smoother surface morphology, and suppress of charge trapping by using SiO 2 films to modify the high-k Ta 2 O 5 dielectric.

Transparent conducting oxide films of boron and gallium co-doped ZnO (BGZO) were prepared on glass substrates by radio frequency magnetron sputtering at room temperature and 200°C, respectively. The dependence of structural, electrical and optical properties on the thickness and substrate temperature were investigated. All films demonstrated c-axis preferred orientation and showed highly transparent in the visible wavelength region. With the increase thickness and substrate temperature, the grain size of BGZO films increased and the full width at half maximum decreased, the carrier mobility increased and resistivity decreased, which indicated that the crystallinity and conductivity of films were improved. The research also found that the optical band gap (E g ) of BGZO thin films decreased with increased substrate temperature and thickness.