ZnO-based transparent thin-film transistors

Highly transparent ZnO-based thin-film transistors (TFTs) are fabricated with optical transmission (including substrate) of similar to75% in the visible portion of the electromagnetic spectrum. Current-voltage measurements indicate n-channel, enhancement-mode TFT operation with excellent drain current saturation and a drain current on-to-off ratio of similar to10(7). Threshold voltages and channel mobilities of devices fabricated to date range from similar to10 to 20 V and similar to0.3 to 2.5 cm2/V s, respectively. Exposure to ambient light has little to no observable effect on the drain current. In contrast, exposure to intense ultraviolet radiation results in persistent photoconductivity, associated with the creation of electron-hole pairs by ultraviolet photons with energies greater than the ZnO band gap. Light sensitivity is reduced by decreasing the ZnO channel layer thickness. One attractive application for transparent TFTs involves their use as select-transistors in each pixel of an active-matrix liquid-crystal display. (C) 2003 American Institute of Physics.