Transparent AMOLED display driven by hafnium-indium-zinc oxide thin film transistor array Tae Sang Kim, Joon Seok Park, Kyoung Seok Son, Ji Sim Jung, Kwang-Hee Lee, Wan Joo Maeng, Hyun-Suk Kim, Jang-Yeon Kwon * , Bonwon Koo, Sangyun Lee Display Lab., Samsung Advanced Institute of Technology, Mt.14-1, Nongseo-Dong, Giheung-Gu, Yongin-Si, Gyeonggi-Do 446-712, Republic of Korea article info Article history: Received 25 March 2010 Received in revised form 7 March 2011 Accepted 8 March 2011 Available online 16 March 2011 Keywords: Oxide semiconductor Thin film transistor Transparent display AMOLED abstract The fabrication and electrical characteristics of transparent hafnium-indium-zinc oxide (HIZO) thin film transistors (TFTs) are presented in detail. The devices incorporate an etch stopper structure, which may consist of either a single SiO x layer deposited by plasma enhanced chemical vapor deposition (PECVD) at 150  C, or a dual stack of SiO x layers grown at 150  C and 350  C. The electrical properties suggest that the latter is more effective at protecting the underlying oxide semiconductor in the course of source-drain etching, hence resulting in high performance transparent TFTs. The saturation mobility and the subthreshold swing of the transparent HIZO TFTs fabricated with the dual etch stopper are 7.6 cm 2 /Vs and 0.30 V/decade, respectively. A 4-inch QVGA (320  240) transparent active matrix organic light emitting diode (AMOLED) display was realized using a backplane array of the above TFTs. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction Oxide semiconductor based thin film transistors (TFTs) are being subject of attention as the next generation switching devices for active matrix displays such as liquid crystal displays (LCDs) or organic light emitting diode (OLED) displays [1,2]. With high field effect mobility compared to conventional amorphous silicon (a-Si) TFTs and excellent scalability due to its amorphous nature, oxide semiconductor based TFTs are anticipated to drive the next generation displays with higher resolution and frame rate. They are also strong candidates for back- planes of large-sized OLED displays due to their stability under constant current stress [3]. Another apparent advantage of oxide semiconductor based TFTs compared to silicon based TFTs is that since most of oxide semiconductors are transparent in the visible light region, they can be used for realizing transparent displays. A promising application may involve a see-through mobile phone, which allows the user to access both sides of the panel as independent touch screen panels, thereby providing a resourceful user interface. Although oxide semiconductor will certainly increase the transmittance of the display in the form of TFTs for the backplane, transparent electrodes must also be employed in order to truly realize a transparent display, since the majority of the non-transparent region of a conventional pixel design consists of metal electrodes. Thus a suitable TFT structure and fabri- cation process must be designed so as to manufacture a high performance transparent display backplane. Several types of TFT structures have been considered up-to-date for transparent TFT backplanes that incorporate oxide semiconductors and transparent conducting oxide (TCO) electrodes. Park et al. have reported the characteristics of both a staggered structure (top gateebottom contact) and an inverted coplanar (bottom gateebottom contact) structure [4,5]. For a staggered structure, it is not so easy to control the electrical properties of oxide semiconductor during the deposition of gate insulator, since the gate insulator is formed directly on top of the semiconductor layer [5]. In their work, atomic layer deposition (ALD) was used to manufacture high performance TFTs by reducing the damage, but this process is not suitable for mass production of large size TFT backplanes. For an inverted coplanar structure, although this will eliminate wet etching process compatibility issues between the source/drain electrode and the oxide semiconductor layer [4], contact resistance between the source/drain electrode and the semiconductor layer could be increased. In this study, we report the characteristics of 4-inch QVGA (320  240) transparent AMOLED display employing HfInZnO (HIZO) TFTs whose structure is inverted staggered that is equivalent to conventional a-Si TFTs for large-sized glass substrates. 2. Experiments The devices were fabricated on a 150 mm by 150 mm Corning glass substrate. In the case of the conventional back-channel etch * Corresponding author. Tel.: þ82 10 6250 2492. E-mail address: jykwon@snu.ac.kr (J.-Y. Kwon). Contents lists available at ScienceDirect Current Applied Physics journal homepage: www.elsevier.com/locate/cap 1567-1739/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.cap.2011.03.031 Current Applied Physics 11 (2011) 1253e1256