An Organic FET structure for unconventional substrates
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An Organic FET structure for unconventional substrates Annalisa Bonfiglio1,2, Fulvia Mameli1, Ornella Sanna1, Laurence Lutsen3 1 INFM - Dept. of Electrical and Electronic Engineering, University of Cagliari, Piazza d'Armi, 09123 Cagliari, Italy 2 INFM S3 - nanoStructures and bioSystems at Surfaces, Via Campi 213/A, 41100 Modena, Italy 3 IMEC-IMOMEC Division, L.U.C. Campus, SBG Department, Building D, B-3590 Diepenbeek, Belgium
ABSTRACT A structure for organic TFTs suitable for being transferred on unusual substrates is described in each technological step. The proposed device consists in a "bottom-structure" assembled on a flexible and transparent insulating layer, without any substrate, with source and drain contacts on one side and the gate on the opposite side. The main advantage is to avoid the substrate because the insulator itself is able to support the whole structure. For this reason, application to any kind of substrates after the built-in process is possible. INTRODUCTION Organic Thin Film Transistors (OTFTs) have been so far object of a great research interest due to the fact that they represent the building block of electronic systems based on flexible, large-area substrates [1]. The potential market of such application is great and this has stimulated big efforts both in the academic and industrial field, which have resulted in the last decade in an impressive improvement in performance and efficiency [2, 3, 4, 5, 6]. Basically, all organic and hybrid structures presented so far are assembled starting from a substrate. In hybrid devices it is heavily doped silicon; in all-organic devices generally plastic or glass. Then it is necessary to perform the technological steps necessary for obtaining the various functional layers of the structure, according to two different models known as "bottom-contact" and "top-contact". A variety of techniques and materials have been proposed so far for obtaining such kinds of structures [1]. In this paper, we describe how a wholly flexible OTFT has been fabricated. An unusual layer, less than one micrometer thick, operates as an insulator and, at the same time, as a free standing surface for device assemblying, therefore avoiding the inclusion of a substrate in the overall structure. Particular emphasis is to be given to the fact that this TFT structure has a vertical design in which there is no supporting layer. This can be applied after the complete fabrication of the device, therefore allowing to employ such structures for adhesion on unusual substrates such as textiles, paper or 3-D surfaces. EXPERIMENTAL DETAILS The basic structure of the device is described in fig. 1. It consists of a thin insulating film with metal contacts (source-drain and gate) deposited on opposite sides of the insulating film. Finally, by depositing a suitable organic semiconductor on the upper side of the film, the complete OTFT structure is obtained. Fabrication steps have been assessed and applied to different device geometries.
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Previous to the device assembly, the quali
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