Moreover, In and Sn have similar electronic structures and electrical properties. Therefore, substituting Sn for In is a reasonable countermeasure for avoiding the use of rare earth metals. The abundance of Ga and Sn in the Earth’s upper continental crust is 18 ppm and 2.2 ppm, respectively, much higher than that of In (0.25 ppm) 13, as shown in Fig. The stability of the GTO TFT was evaluated under various stress conditions and compared to that of IGZO TFTs.Ībundance in the Earth’s upper continental crust This material is a dual metallic oxide without rare metals such as In. In this paper, we first report a stable TFT with a high μ FE that incorporate Ga-Sn-O (GTO) as the amorphous and transparent oxide semiconductor. Therefore, new semiconductor materials that do not use rare metals and consist of fewer elements are being explored. Furthermore, there are many defects in the semiconductor films 4, 24, 25, 26, 27, 28, 29, 30, 31, and it is difficult to control the density of oxygen vacancies induced during the deposition 32, 33, 34. Sputtering targets can be of poor quality due to low crystallinity or incomplete oxidation of compounds 23, which may reduce device performance. In addition, multi-metallic materials (especially IGZO) are difficult to mass produce because the stoichiometry of the deposited films can be different to that of the sputtering target due to preferential sputtering of some elements 2. ![]() The electrical characteristics and those stability of In-free TFTs were not enough for application to the novel devices. On the other hand, the In-free oxide semiconductor materials such as ZnO 14, 15, 16, 17, 18, Al-Zn-Sn-O (AZTO) 19, Zn-Sn-O (ZTO) 20, ZnON 21 include Zn, which is thought to be the reason of the instability of devices with forming the weak Zn-O bond 22. However, IGZO, ITZO, IGO, and ITO include In in the matrix which is associated with high fabrication costs as In is a rare metal with few mining sites 13 and is hence expensive. Hence, not only information displays but also novel devices have been proposed such as memories 11, processors, and other electronic elements 12. The fabrication processes for oxide semiconductors can be easily integrated into or replace conventional TFT processes, such as photolithography and etching. ![]() These techniques are used in the TFT fabrication processes to deposit IGZO as semiconductor, ITO as the transparent electrodes for displays, and metallic materials (Cr, Mo, and Al) for electrodes. In addition, oxide TFTs have high field effect mobility ( μ FE) and can be easily fabricated on large-area substrates by deposition processes with low cost, low toxicity, and low risk of explosion, such as radiofrequency (RF) or direct current (DC) magnetron sputtering. Oxide semiconductor materials such as In-Ga-Zn-O (IGZO) 1, 2, 3, 4, In-Sn-Zn-O (ITZO) 5, 6, In-Ga-O (IGO) 7, and In-Sn-O (ITO) 8 have several advantages as active layer of thin film transistors (TFTs) such as steep subthreshold swing ( S factor), transparency, and extremely low leak current in off state when compared to conventional semiconductors such as hydrogenated amorphous silicon (a-Si:H) 9 and polycrystalline silicon 10.
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