Transparent thin film transistors using ZnO as an active channel layer and their electrical properties

TLDR

ZnO layers were deposited by pulsed laser deposition at 450 °C in 3 m Torr O₂, yielding a background carrier density <5×10¹⁶ cm⁻³, and a SiO₂/SiNx double‑layer gate insulator suppressed leakage and enabled successful operation. The fabricated ZnO–TFTs achieved an Ion/Ioff ratio exceeding 10⁵ on Si wafers and optical transmittance above 80 % on glass, demonstrating that a transparent transistor can function even under visible illumination.

Abstract

Bottom-gate-type thin film transistors using ZnO as an active channel layer (ZnO–TFT) have been constructed. The ZnO layers were deposited using pulsed laser deposition at 450 °C at an oxygen pressure of 3 m Torr, and the material that was formed had a background carrier concentration of less than 5×1016 cm−3. A double layer gate insulator consisting of SiO2 and SiNx was effective in suppressing leakage current and enabling the ZnO–TFT to operate successfully. The Ion/Ioff ratio of ZnO–TFTs fabricated on Si wafers was more than 105 and the optical transmittance of ZnO–TFTs fabricated on glass was more than 80%. These results show that it is possible to fabricate a transparent TFT that can even be operated in the presence of visible light.