Stable organic thin-film transistor in a pixel for plastic electronics Seung Hoon Han a , Yong Hee Kim a , Sun Hee Lee a , Min Hee Choi a , Jin Jang a, * , Dong Joon Choo b a Department of Information Display and Advanced Display Research Center, Kyung Hee University, Dongdaemoon-ku, Seoul 130-701, Republic of Korea b Department of Chemistry and Advanced Display Research Center, Kyung Hee University, Seoul 130-701, Republic of Korea article info Article history: Received 19 June 2008 Received in revised form 24 July 2008 Accepted 8 August 2008 Available online 15 August 2008 PACS: 72.80.Le 81.65.Rv 81.05.Lg Keywords: Organic TFT Stability Backplane abstract We have studied the fabrication of stable organic thin-film transistor (OTFT) for plastic electronics using hybrid multi-layer (HML) of parylene/Au/photoacryl/IZO (indium zinc oxide) on organic semiconductor. The HML-passivated OTFTs exhibited the field-effect mobility (l fe ) of 0.2–0.3 cm 2 /V s with an on/off current ratio of 10 7 after annealing at 180 °C. The changes in on-, off- and subthreshold-currents of the HML-passivated OTFT were negligibly small during the storage of 781 h. Moreover, the hysteresis in transfer characteristics was negligible even after exposure of the OTFT to air for 781 h. These results indicate that HML-passivation is suitable for stable OTFT array for plastic electronics. Ó 2008 Elsevier B.V. All rights reserved. The performance of organic thin-film transistor (OTFT) has been improved remarkably for the last two decades. As a result, its performance using oligothiophene, penta- cene or tetracene as a p-type organic semiconductor, is suitable for display applications. Recently, prototypes of li- quid crystal display (LCD) [1,2], organic light emitting diode (OLED) [3–5] and electrophoretic display (EPD) [6] based on OTFTs were successfully demonstrated on glass and plastic substrates. However, there are still issues on stability for commercial applications because the perfor- mance of the OTFT changes with time in ambient air although they are passivated to block water and oxygen permeations. The passivation of OTFT is widely studied using single or multi-layer of poly(vinyl alcohol) (PVA) [2–4,7], photo- acryl (PA) [2,7], parylene [3,5,8], SiO 2 [4], Cu [8], SnO 2 [9] and tetratetracontane [10]. The initial on-currents (I on ) of the OTFTs do not change with time in air. However, the subthreshold swing (S) and turn-on voltage (V on ) and off- state currents (I off ) change with time in ambient air. The changes in these parameters shift the range of driving volt- age, resulting in the fail of their display application. The currents in subthreshold and off-state regions are more sensitive to impurities, gap states and interface states. Therefore, better barrier performance is needed to obtain stable current in subthreshold and off-state regions. As a promising barrier, organic/inorganic multi-layer stacks named Barix TM encapsulation was developed by Vitex Sys- tems Inc. for OLED [11]. The key of this encapsulation is to use an organic layer on inorganic barrier to avoid defect creation, which can be a path of water permeation. In the present work, we passivated pentacene OTFTs using hybrid multi-layer (HML) of parylene/Au/ photo–acryl(PA)/indium zinc oxide(IZO). This structure can be used in LCD and EPD using organic planarization layer and indium tin oxide (ITO) or IZO for a pixel. The water vapor transmission rate (WVTR) of the HML was found to be less than 10 3 g/m 2 /day which is the limit of MOCON measurement and this value is required for stable 1566-1199/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.orgel.2008.08.002 * Corresponding author. Tel.: +82 2 961 9153; fax: +82 2 961 9154. E-mail address: jjang@khu.ac.kr (J. Jang). Organic Electronics 9 (2008) 1040–1043 Contents lists available at ScienceDirect Organic Electronics journal homepage: www.elsevier.com/locate/orgel