UV-Cured Reactive Mesogen-YInZnO Hybrid Materials as Semiconducting Channels in Thin-Film Transistors Using a Solution-Process

Abstract

Electrical performance of thin-film transistors (TFTs) is important for their applications. Solution-processed TFTs have low mobility and high sub-threshold swings (S.Ss) because there are many pores and pin-holes in the films. These characteristics are attributed to electron trapping in the YInZnO (YIZO) channel, the SiO 2 gate insulator, or their interface. We fabricated hybrid YIZO TFTs with and without UV radiation, and observed that UV-curing of the film affected TFT performance through promoting a response to reactive mesogen (RM). The UV irradiated TFT showed better performance because of the alignment of the channel materials in the source-drain direction. The Recently, amorphous oxide semiconductors (AOSs) have been researched extensively for a use as the channel layer in thin-film transistors (TFTs), 1-3 which exhibit superior electrical and optical characteristics to amorphous Si (a-Si) TFTs. a-Si TFTs have a relatively low mobility of approximately 0.5 cm 2 /Vs because of the angular distortion of the strongly directive sp 3 orbital. 1 In contrast, AOSs have a different carrier-path mechanism that permits them to achieve high mobility, as demonstrated by Nomura et al.1 They proposed a unique mechanism: direct overlapping between neighboring s orbitals that have insensitive angular distortion because of the chemical bonding between heavy-metal ions, such as the In in the InGaZnO (IGZO) system. Thus, despite the amorphous phase, AOSs have mobility that is almost comparable to that of the crystalline phase. 4 Previously, Shin et al. studied using YInZnO (YIZO) for the TFT channels by replacing the Ga in the IGZO system with Y.5 Y has a lower standard electrode potential (SEP) (−2.372 eV) and a lower electronegativity (1.22) than those of Ga; therefore, Y can easily form chemical bonds with oxygen, thereby decreasing the oxygen vacancies.Solution-processed TFTs have low electrical performance in terms of characteristics such as low mobility and high sub-threshold swing (S.S) because they contain many pores and pin-holes, which lead to electron trapping.6-8 Therefore, reactive mesogen (RM) was added to the YIZO system to obtain high electrical performance by inducing the channel material to become positioned along the source-drain direction. When a hybrid YIZO film is irradiated with UV radiation, a uniaxial directivity of the channel material is formed because RM is sensitive to UV light. [9][10][11] In this study, we produced hybrid YIZO TFTs using a solutionprocess with and without UV irradiation and investigated the role of UV-irradiated RM in the hybrid YIZO system in attaining high electrical performance.A 0. in 2-methoxyethanol (2ME). The molar ratio of Y:In:Zn was fixed at 2:11:7. To ensure a stable and homogeneous solution, we added mono-ethanolamine (MEA) and acetic acid as stabilizers. The solution was stirred at 75• C for 2 h and then aged for 1 day. Prior to the deposition, parallel-aligned RM(RMS03-015, Merck) was added to the YIZO system making a weight ratio of RM and YIZO to be 1:9. z E-m...