Pentacene organic field-effect transistors with polymeric dielectric interfaces: Performance and stability Xiao-Hong Zhang, Shree Prakash Tiwari, Bernard Kippelen * Center for Organic Photonics and Electronics (COPE), School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, United States article info Article history: Received 1 April 2009 Accepted 1 June 2009 Available online 6 June 2009 PACS: 85.30.Tv 72.80.Le 77.55.+f 81.15.z Keywords: Pentacene Organic field-effect transistors Operational stability Bias stress effect abstract Low-voltage pentacene organic field-effect transistors (OFETs) with different gate dielectric interfaces are studied and their performance in terms of electrical properties and opera- tional stability is compared. Overall high electrical performance is demonstrated at low voltage by using a 100 nm-thick high-j gate dielectric layer of aluminum oxide (Al 2 O 3 ) fab- ricated by atomic layer deposition (ALD) and modified with hydroxyl-free low-j polymers like polystyrene (PS), divinyltetramethyldisiloxane-bis(benzocyclobutene) (BCB) (Cyclo- tene TM , Dow Chemicals), and as well as with the widely used octadecyl-trichlorosilane (OTS). Devices with PS and BCB dielectric surfaces exhibit almost similar electrical perfor- mance with high field-effect mobilities, low subthreshold voltages, and high on/off current ratios. The higher mobility in pentacene transistors with PS can be correlated to the better structural ordering of pentacene films, as demonstrated by atomic force microscopy (AFM) images and X-ray diffraction (XRD). The devices with PS show good electrical stability under bias stress conditions (V GS = V DS = 10 V for 1 h), resulting in a negligible drop (2%) in saturation current (I DS ) in comparison to that in devices with OTS (12%), and to a very high decay (30%) for the devices with BCB. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction The operational stability of OFETs, including hysteresis, reproducibility, reliability, and bias stress (BS) effect, are important issues that need to be addressed for practical applications such as flexible displays and low cost RFIDs. The electrical instability induced by BS effects leads simul- taneously to a drain-source current decay and a threshold voltage shift under prolonged operation time with a fixed gate voltage. There exist several potential mechanisms for the electrical instability, which include trapping of charges, defect generation [1], charge tunneling within the gate dielectrics, at the semiconductor/dielectric inter- face [2,3], in the semiconductor itself, or at the interface near the source/drain contacts [4,5]. The current instability has been investigated with different gate dielectric sur- faces and the results indicate that SiOH groups and water molecules absorbed on the surface are the main origins of the trap sites [6]. Low-j polymeric dielectrics have been demonstrated as good dielectric insulators for organic transistors. The device performance of organic transistors was correlated with the dielectric surface energy and the glass transition temperature of the polymers [7–9]. How- ever, no polymeric interface providing both high electrical performance and good operational stability for low voltage pentacene p-channel OFETs has yet been identified. In this work, we studied the electrical performance and the operational stability of pentacene organic field-effect transistors (OFETs) in which the gate dielectric is coated with hydroxyl-free low-j polymers. The polymers chosen for this work were divinyltetramethyldisiloxane-bis(ben- zocyclobutene) (BCB) (Cyclotene TM 3022, Dow Chemicals), and polystyrene (PS) (see chemical structures in Fig. 1). 1566-1199/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.orgel.2009.06.001 * Corresponding author. Tel.: +1 404 385 5163; fax: +1 404 385 5170. E-mail address: kippelen@ece.gatech.edu (B. Kippelen). Organic Electronics 10 (2009) 1133–1140 Contents lists available at ScienceDirect Organic Electronics journal homepage: www.elsevier.com/locate/orgel