Ultra-flexible Amorphous Indium-Gallium-Zinc Oxide (a-IGZO) Thin Film Transistor Hsin-Cheng Lai 1 , Bo-Jie Tzeng 1 , Zingway Pei 1,* Chun-Ming Chen 2 , and Chein-Jung Huang 2 1 Graduate Institute of Optoelectronic Engineering, Department of Electrical Engineering, National Chung Hsing University, Taichung, 40227, Taiwan, R.O.C. 2 ITRI South, ITRI, Liujia Dist., Tainan, 734, Taiwan, R.O.C. * E-mail: zingway@dragon.nchu.edu.tw Phone No.+886-4-22851549 Ext.801; Fax. +886-4-2285141 Abstract: In this work, we demonstrate an ultra-flexible a-IGZO TFT on PEN plastic substrate. The a-IGZO TFT could be operated well with almost unchanged performance after banding at radius of 4 mm (strain~1.5%) for more than 100 times. This was implemented the utilization of polymer gate dielectric, poly(4-vinylpheonol) (PVP). The PVP was then demonstrated with no damage after plasma process equivalent the the a-IGZO deposition process. Due to the large Young’s modulus difference, the stress was believed mainly within polymer gate dielectric. Therefore, after bending, the a-IGZO was not damaged. In addition to the ultra- flexibility, the a-IGZO TFT exhibit mobility around 1.3 cm 2 /Vs with nearly 6 orders of magnitude current on/off ratio at operation of 10V. The mobility could be further increase by fine- tuning the a-IGZO deposition condition. Combing the ultra- flexibility and the acceptable performance, this technology is suitable to integrate into LCD or OLED implementing ultra- flexible display. Keywords Ultra-flexible, a-IGZO, Thin film Transistor, Polymer Dielectric 1. Introduction Flexible flat panel display (FPD) has been recently attracting extensively attention due to its light-weight, cheaper, rugged in shape and potentially rollable based on the plastic substrate [1]. However, the current material used as the active material for thin film transistor (TFT) in FPD is hydrogenated amorphous Si (a- Si:H). The low mobility and high processing temperature of a- Si:H limit the flexible can only rugged and fabricate on expensive plastic substrate. Since the invention of the amorphous Indium- Gallium-Zinc Oxide (a-IGZO) as the channel material in a TFT [2], large amount of research works and applications has been developed and demonstrated [3][4]. The a-IGZO has high mobility in amorphous phase at low process temperature that potentially replaces the hydrogenated amorphous Si as TFT for flat-panel display with high resolution. The mobility as high as 79 cm 2 /V.s has been demonstrated [5]. Several reports demonstrate the a-IGZO TFT could be operated in a flexible form with minor modification of the performance. Nomura et al., [1] demonstrate the a-IGZO TFT could operate well with a bending radius of 25 mm. Park, et al., [6] demonstrated full-color AMOLED driven by a-IGZO TFT. The a-IGZO TFT has not failed at bending radius of 5 mm with strain of 0.9 %. Cherenack et al., [7] further utilize mechanical bending demonstrate the performance of a-IGZO almost unaltered at radius of 10 mm. Those studies indicate the a- IGZO is bendable. However, the rollable is not yet been demonstrated. This probability due to the gate dielectric is inorganic material; the interface of semiconductor/dielectric was damaged during bending due to the high stress. In this study, we adopt polymer material as gate dielectric. The stress was assume relief to the depth of the polymer, remaining the interface unaltered based on the large difference of Young’s modulus and thickness between polymer and a-IGZO. The process temperature was well below 150 o C to keep the integrity of the plastic substrate. (a) PVP 400nm Al Al PEN (125 μm) Ag a‐IGZO (60nm) (b) Fig. 1. (a) The schematic diagram of the flexible a-IGZO TFT on PEN substrate. (b) The photograph of a-IGZO TFT on the PEN substrate. 2. Experiment An 125μm thick polyethylene naphthalate (PEN) film was used as the substrate. The PEN was first attach on glass by a Gel-pak film and was clean by IPA. After clean, an 30 nm thick Ag was deposited by a thermal evaporator through a shadow mask as the gate electrode. The polymer solution for gate dielectric material 56.3 / H.-C. Lai 764 • SID 2012 DIGEST ISSN 0097-966X/12/4302-0764-$1.00 © 2012 SID