title: Low-voltage operation of ZrO2-gated n-type thin-film transistors based on a channel formed by hybrid phases of SnO and SnO2.
abstract: With SnO typically regarded as a p-type oxide semiconductor, an oxide semiconductor formed by hybrid phases of mainly SnO and a small amount of SnO2 with an average [O]/[Sn] ratio of 1.1 was investigated as a channel material for n-type thin-film transistors (TFTs). Furthermore, an appropriate number of oxygen vacancies were introduced into the oxide during annealing at 400 °C in ambient N2, making both SnO and SnO2 favorable for current conduction. By using high-κ ZrO2 with a capacitance equivalent thickness of 13.5 nm as the gate dielectric, the TFTs processed at 400 °C demonstrated a steep subthreshold swing (SS) of 0.21 V/dec, and this can be ascribed to the large gate capacitance along with a low interface trap density (Dit) value of 5.16 × 10(11) cm(-2) eV(-1). In addition, the TFTs exhibit a relatively high electron mobility of 7.84 cm(2)/V·s, high ON/OFF current ratios of up to 2.5 × 10(5), and a low gate leakage current at a low operation voltage of 3 V. The TFTs also prove its high reliability performance by showing negligible degradation of SS and threshold voltage (VT) against high field stress (-10 MV/cm). When 3% oxygen annealing is combined with a thinner channel thickness, TFTs with even higher ION/IOFF ratios exceeding 10(7) can also be obtained. With these promising characteristics, the overall performance of the TFTs displays competitive advantages compared with other n-type TFTs formed on binary or even some multicomponent oxide semiconductors and paves a promising and economic avenue to implement an n-type oxide semiconductor without doping for production-worthy TFT technology. Most importantly, when combined with the typical SnO-based p-type oxide semiconductor, it would usher in a new era in achieving high-performance complementary metal oxide semiconductor circuits by using the same SnO-based oxide semiconductor.
authors.affiliation: Department of Engineering and System Science, National Tsing Hua University, Hsinchu, Taiwan.
authors.forename: Hsin-Chueh
authors.initials: HC
authors.lastname: Chu
authors.affiliation: Department of Engineering and System Science, National Tsing Hua University, Hsinchu, Taiwan.
authors.forename: Yung-Shao
authors.initials: YS
authors.lastname: Shen
authors.affiliation: Department of Engineering and System Science, National Tsing Hua University, Hsinchu, Taiwan.
authors.forename: Ching-Heng
authors.initials: CH
authors.lastname: Hsieh
authors.affiliation: Department of Engineering and System Science, National Tsing Hua University, Hsinchu, Taiwan.
authors.forename: Jia-Hong
authors.initials: JH
authors.lastname: Huang
authors.affiliation: Department of Engineering and System Science, National Tsing Hua University, Hsinchu, Taiwan.
authors.forename: Yung-Hsien
authors.initials: YH
authors.lastname: Wu
keywords: CET; SnO2/SnO hybrid channel; ZrO2; interface trap density; mobility; n-type TFTs; reliability; subthreshold swing