Ta 2 O 5 as gate dielectric material for low-voltage organic thin-ﬁlm transistors Carmen Bartic a, * , Henri Jansen a,b , Andrew Campitelli a , Staf Borghs a a IMEC, Dept. Microsystems, Components & Packaging, Kapeldreef 75, B-3001 Leuven, Belgium b MESA + Research Institute, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands Received 28 September 2001; received in revised form 6 March 2002; accepted 20 March 2002 Abstract In this paper we report the use of Ta 2 O 5 as gate dielectric material for organic thin-ﬁlm transistors. Ta 2 O 5 has al- ready attracted a lot of attention as insulating material for VLSI applications. We have deposited Ta 2 O 5 thin-ﬁlms with diﬀerent thickness by means of electron-beam evaporation. Being a relatively low-temperature process, this method is particularly suitable for organic thin-ﬁlm transistor fabrication on plastic substrates. Deposition and patterning are achieved in one step by the use of shadow masks. The dielectric can be evaporated on top of the semiconducting layer. In this way a large variety of structures can be realized. Poly(3-hexylthiophene) was used as semiconducting material in the transistor structure. Such transistors are operating at voltages smaller than 3 V. Having a high dielectric constant (e r ¼ 21), Ta 2 O 5 facilitates the charge carrier accumulation in the transistor channel at much lower electrical ﬁelds. The properties of the dielectric material as well as the operation of the organic transistors with a Ta 2 O 5 gate dielectric are discussed. Ó 2002 Elsevier Science B.V. All rights reserved. Keywords: Ta 2 O 5 ; Poly(3-hexylthiophene); Organic transistor; Low voltage 1. Introduction Organic thin-ﬁlm transistors (OTFTs) have gathered great interest in the last decade since or- ganic conjugated materials were considered as potential candidates to conventional inorganic ones in applications requiring large area, ﬂexibil- ity, low-temperature processing and especially low-cost. Such applications include ﬂat-panel dis- plays, low-end smart cards, electronic identiﬁca- tion tags as well as sensing devices [1]. In order to be implemented as viable solutions for this kind of applications, they must oﬀer a substantial performance advantage compared with the current technology. From the performance point of view, the most important parameters are charge carrier mobility, on/oﬀ current ratio and the operational voltage range. Up to now, the highest mobility values, superior to a:Si, have been obtained for pentacene-based OTFTs with suﬃciently high on/oﬀ ratios [2]. However, the operating voltages required to produce such per- formances were unpractically high, around 100 V. Organic Electronics 3 (2002) 65–72 www.elsevier.com/locate/orgel * Corresponding author. Tel.: +32-16-281-904; fax: +32-16- 281-501. E-mail address: carmen.bartic@imec.be (C. Bartic). 1566-1199/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII:S1566-1199(02)00034-4