J. Sensor Sci. & Tech. Vol. 22, No. 2, 2013 -105- 1. INTRODUCTION Recently, transparent-oxide-semiconductor-based transistors have shown much attention in application such as active-matrix organic light-emitting displays (AMOLED), active-matrix liquid-crystal displays (AMLCDs), and flexible displays [1-3]. Thin film transistors (TFTs) using oxide-semiconductor channels have been intensively investigated because oxide semiconductors such as amorphous In-Ga-Zn-O (a-IGZO) can be formed at a low-temperature process and show larger motilities than those of hydrogenated amorphous silicon TFTs [4]. One of the essential issues to be considered for realizing the improved performance is the influence of source/drain (S/D) electrodes, including materials, contact quality, and parasitic resistance. In general, heavily doped regions below S/D electrodes were adopted to obtain good contact properties. Attempts to dope the selected contact regions of a-IGZO films by Ar plasma treatment have proven significant improvement in device performance [5]. However, this doping process possibly damages the film surface by sputtering ion (Ar + ) bombardment. Barquinha et al.[6] reported that various S/D electrodes affected the drain current of TFTs and that an annealing process improved the electrical properties. Park etal.[7] investi- gated the effects of S/D series resistance and transfer length on a-IGZO TFTs. So far, indium tin oxide (ITO), Au, Al, indium zinc oxide (IZO), and Pt/Ti were used as S/D electrodes for a-IGZO TFTs [5, 8, 9]. Although oxide based electrodes, such as ITO and IZO electrodes allow fully transparent TFTs, their large electron affinity of the oxide electrodes (and Au) causes non-ohmic behaviors in the linear regime of output characteristics due to the formation of the Schottky-like barrier between the electrodes and the a-IGZO films [9]. X. Zou etal. also reported that AZO/Al heterojunction S/D contacts showed the forming of a good ohmic contact and the improved mobility and the subthreshold gate voltage swing. Furthermore, the ohmic contact properties could be improved by replacing electrode materials and/or by modifying the contact area. Among many efforts to develop new TCO materials, the multilayer of dielectric material/metal/dielectric material (DMD) has been suggested as one of candidates to overcome the limit in electrical resistivity of single layer TCOs ever reported 1 Interface Research Center, Korea Insitute of Science and Technology, Sungbuk Gu, Hwarnagno 14 gil 5, Seoul 136-791, Korea 2 Advanced Semiconductor Research Center, Division of Electrical and Computer Engineering, Hanyang University, 17 Haengang-Dong, Seongdong-Gu, Seoul 133-791, Korea 3 Department of Physics, Yonsei University, Seoul 120-749, Korea 4 Electronic Materials Research Center, Korea Insitute of Science and Technology, Sungbuk Gu, Hwarnagno 14 gil 5, Seoul 136-791, Korea + Corresponding author: wkchoi@kist.re.kr (Received : Feb. 18, 2013, Revised : Mar. 13, 2013, Accepted : Mar. 14, 2013) This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License(http://creativecommons.org/licenses/by- nc/3.0)which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Journal of Sensor Science and Technology Vol. 22, No. 2 (2013) pp. 105-110 http://dx.doi.org/10.5369/JSST.2013.22.2.105 pISSN 1225-5475/eISSN 2093-7563 Improved Electrical Properties of Indium Gallium Zinc Oxide Thin- Film Transistors by AZO/Ag/AZO Multilayer Electrode Young-Soo No 1,2 Jeong-Do Yang 3 , Dong-Hee Park 1 , Tae-Whan Kim 2 , Ji-Won Choi 4 , and Won-Kook Choi 1, + Abstract We fabricated an a-IGZO thin film transistor (TFT) with AZO/Ag/AZO transparent multilayer source/drain contacts by rf magnetron sputtering. a-IGZO TFT with AZO/Ag/AZO multilayer S/D electrodes (W/L = 400/50 μm) showed a subs-threshold swing of 3.78 V/dec, a minimum off-current of 10 -12 A, a threshold voltage of 0.41 V, a field effect mobility of 10.86 cm 2 /Vs, and an on/off ratio of 9× 10 9 . From the ultraviolet photoemission spectroscopy, it was revealed that the enhanced electrical performance resulted from the lowering of the Schottky barrier between a-IGZO and Ag due to the insertion of an AZO layer and thus the AZO/Ag/AZO multilayer would be very appropriate for a promising S/D contact material for the fabrication of high performance TFTs. Keywords : a-IGZO TFT, AZO/Ag/AZO transparent electrode, Field effect mobility, Schottky barrier