High-Performance Solution-Processed Amorphous Zinc−Indium−Tin Oxide Thin-Film Transistors

摘要

Films of the high-performance solution-processed amorphous oxide semiconductor a-ZnIn₄Sn₄O₁₅, grown from 2-methoxyethanol/ethanolamine solutions, were used to fabricate thin-film transistors (TFTs) in combination with an organic self-assembled nanodielectric as the gate insulator. This structurally dense-packed semiconductor composition with minimal Zn2+ incorporation strongly suppresses transistor off-currents without significant mobility degradation, and affords field-effect electron mobilities of 90 cm2 V−1 s−1 (104 cm2 V−1 s−1 maximum obtained for patterned ZITO films), with I_on/I_off ratio 105, a subthreshhold swing of 0.2 V/dec, and operating voltage <2 V for patterned devices with W/L = 50. The microstructural and electronic properties of ZITO semiconductor film compositions in the range Zn_9−2xIn_xSn_xO_9+1.5x (x = 1−4) and ZnIn_8−xSn_xO_13+0.5x (x = 1−7) were systematically investigated to elucidate those factors which yield optimum mobility, I_on/I_off, and threshold voltage parameters. It is shown that structural relaxation and densification by In3+ and Sn4+ mixing is effective in reducing carrier trap sites and in creating carrier-generating oxygen vacancies. In contrast to the above results for TFTs fabricated with the organic self-assembled nanodielectric, ZnIn₄Sn₄O₁₅ TFTs fabricated with SiO₂ gate insulators exhibit electron mobilities of only 11 cm2 V−1 s−1 with I_on/I_off ratios 105, and a subthreshhold swing of 9.5 V/dec.