Transparent dielectric films for organic thin-film transistors: A perspective for low cost, low size technologies E. Orgiu a,b, ⁎ , I. Manunza a,b , M. Sanna a , P. Cosseddu a,b , A. Bonfiglio a,b a Department of Electrical and Electronic Engineering, University of Cagliari and INFM, Italy b INFM Centre S3 “nanoStructures and bioSystems at Surfaces”, Modena, Italy Available online 5 April 2007 Abstract In this paper we will show the advantages of employing transparent free-standing dielectric films to realize OFETs devices with optimized performances. These advantages concern several aspects, ranging from optimized device performances, to extended versatility in applications. Organic field effect transistors made from a Polyethilene Terephtalate film (Mylar) as a dielectric are presented: these devices are particularly interesting especially in sight of possible applications as chemical and mechanical sensors. In addition, we will show preliminary results obtained from films of Poly Dimethyl Siloxane (PDMS), a polymer whose surface is hydroxyl-free. This feature should allow to obtain ambipolar transport properties in OFETs. Preliminary results on MIS structures are presented. © 2007 Elsevier B.V. All rights reserved. Keywords: Transparent dielectrics; Free-standing film; Polydimethylsiloxane; Organic thin-film transistor 1. Introduction Organic thin-film transistors (TFTs) have made an impres- sive progress over the past ten years , and the first electronic applications are now beginning to appear. Different research groups have demonstrated integrated circuits [1–4], active-matrix displays [5–8] and chemical sensors [9–11] using organic TFTs, while the Plastic Logic group has reported organic integrated circuits fabricated in part with the use of inkjet printing. [12,13]. Since organic TFTs are targeting low-cost, large-area elec- tronic applications, alternative materials and fabrication methods are of interest, including spin-coated dielectrics [1,2,7,8,12,13] and conducting-polymer source and drain contacts [1,2,12,13]. Organic TFT materials are considered appealing because of their unique property of being flexible and processable at lower tem- peratures than those required in amorphous silicon technology. With this aim, we investigated the possibility to employ different transparent, free-standing, and flexible films as TFT dielectrics for innovative, low cost and scientifically challeng- ing applications. The transparency of the film is a very interesting feature that paves the way for many other interesting applications. In the following we will show several techniques for fabricating OFET devices that exploit the transparency of the film to optimize device fabrication and performances. Source and drain contacts can be obtained both with tradi- tional photolithography and by a soft lithography technique. Transparent, free-standing, insulating layers are commercially available (e.g. Mylar by Dupont), or can be assembled starting from suitable precursor materials. In our case we have inves- tigated the possibility of fabricating such a film starting from PDMS. PDMS has been selected for two main reasons: 1) it allows to obtain extremely thin and flat films, provided the prepolymer is cast and spun over a very flat substrate; 2) after the preparation the surface is hydroxyl groups free, and a recent paper by Friend et al, has suggested the idea of exploiting this characteristic to obtain n-type conduction in OFET. MIS (Metal– Insulator–Semiconductor) structures further have been realized and characterized. This has been done to better understand the transport properties of pentacene grown on PDMS. At the same time, some atomic force microscopy (AFM) images in order to Available online at www.sciencedirect.com Thin Solid Films 516 (2008) 1533 – 1537 www.elsevier.com/locate/tsf ⁎ Corresponding author. Department of Electrical and Electronic Engineering, University of Cagliari Piazza d’Armi, 09123 Cagliari, Italy and INFM-S3 NanoStructures and BioSystems at Surfaces, Modena, Italy. E-mail address: emanuele.orgiu@diee.unica.it (E. Orgiu). 0040-6090/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2007.03.157