Synthetic Metals 155 (2005) 485–489 Influence of organic gate dielectrics on the performance of pentacene thin film transistors D. Knipp a,∗ , P. Kumar a , A.R. V ¨ olkel b , R.A. Street b a School of Engineering and Science, International University Bremen, Bremen, Germany b Palo Alto Research Center, 3333 Coyote Hill Road, Palo Alto, CA 94304, USA Received 10 January 2005; received in revised form 13 June 2005; accepted 15 June 2005 Available online 10 November 2005 Abstract The electronic transport of polycrystalline pentacene thin film transistors is investigated. The thermally evaporated pentacene films prepared on organic dielectrics like benzocyclobutane exhibit mobilities comparable with inorganic dielectrics like thermal oxide and plasma enhanced chemical vapor deposited silicon nitride. To gain insights in the electronic transport behavior of the organic thin film transistors (TFTs) the I/V characteristics were simulated by a one-dimensional density-of-states transistor model. The experimental data can be described by using a broad distribution of acceptor-like states deep in the bandgap and a narrow distribution of donor-like states close to the valance band. The influence of the different dielectrics on the defect distribution and the electronic transport will be discussed. © 2005 Elsevier B.V. All rights reserved. Keywords: Pentacene; Thin film transistors; Organic dielectrics; Electronic transport 1. Introduction Research in material science has lead to the development of a wide range of novel organic and polymeric semiconducting materials. So far, pentacene is amongst the most widely stud- ied organic semiconductors [1]. Polycrystalline pentacene has demonstrated the highest carrier mobility of organic based thin film transistors (TFTs) [2]. Pentacene thin film transistors are of potential interest for large area and/or flexible electronics like smart cards, radio frequency information tags (RFID tags) and display media. Pentacene transistors are usually fabricated by using bottom gate TFT structures. Consequently, the pentacene film is pre- pared on top of a dielectric, which can be an organic or inorganic dielectric. The performance of the pentacene TFTs strongly depends on the properties of the dielectric, the growth condi- tions of the pentacene molecules and the structural properties of the film. Throughout this study we will concentrate on organic dielectrics, which can be easily processed via spin casting, dip coating or inkjet printed on large area substrates. Several organic ∗ Corresponding author. Tel.: +49 421 200 3570. E-mail address: d.knipp@iu-bremen.de (D. Knipp). dielectrics have been studied so far including polyvinyl phenol (PVP), polyimide, benzocyclobutane (BCB) or parylene [2–6]. We will focus here on benzocyclobutane, because the material is well known in semiconductor industry and photo-definable derivatives are available. Thermally evaporated pentacene molecules form polycrys- talline films. The crystal size of the pentacene crystals depends on the underlying substrate and the deposition conditions [7]. The dielectric has to be smooth to form large pentacene crys- tals on the substrate. For rougher dielectrics the film exhibits a distinctly reduced crystal size, which again leads to reduced electronic transport properties [8]. The transport properties of the films are limited by grain boundaries and defects located in the film and at the semiconductor–substrate interface. In order to gain insights in the electronic transport properties of polycrystalline pentacene TFTs different electronic transport models have been proposed like a grain boundary model [9],a potential well model [10] and trapping by localized gap states [11,12]. In our study of pentacene thin film transistors, we used a one-dimensional density-of-states model, which accounts for localized states [13]. The model is used to study pentacene thin film transistors fabricated on organic gate dielectrics (benzocy- clobutane (BCB)). The results will be compared with pentacene TFTs on thermal oxide and PECVD silicon nitride [7]. The influ- 0379-6779/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.synthmet.2005.06.018