ZnO-based transparent thin-film transistors

TLDR

Highly transparent ZnO‑based TFTs achieve ~75 % visible transmission and are suitable as pixel‑select transistors in active‑matrix LCDs. Exposure to intense UV radiation induces persistent photoconductivity via electron‑hole pair generation above the ZnO band gap. The devices exhibit n‑channel, enhancement‑mode operation with on/off ratios ~10⁷, threshold voltages 10–20 V, mobilities 0.3–2.5 cm²/Vs, negligible ambient‑light impact, and UV‑induced photoconductivity that can be mitigated by reducing channel thickness.

Abstract

Highly transparent ZnO-based thin-film transistors (TFTs) are fabricated with optical transmission (including substrate) of ∼75% 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 ∼107. Threshold voltages and channel mobilities of devices fabricated to date range from ∼10 to 20 V and ∼0.3 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.