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1196-C02-02

Effects of Mechanical Strain on the Electrical Performance of Amorphous Silicon ThinFilm Transistors with a New Gate Dielectric Katherine W. Song1, Lin Han1, Sigurd Wagner1, and Prashant Mandlik1,2 1 Department of Electrical Engineering, Princeton University, Princeton, NJ 08544, U.S.A. 2 Present address: Universal Display Corporation, Ewing, NJ 08618, U.S.A. ABSTRACT The stiff SiNx gate dielectric in conventional amorphous silicon thin film transistors (TFTs) limits their flexibility by brittle fracture when in tension. We report the effect on the overall flexibility of TFTs of replacing the brittle SiNx gate dielectric with a new, resilient SiO2-silicone hybrid material, which is deposited by plasma enhanced chemical vapor deposition. Individual TFTs on a 50µm-thick polyimide foil were bent to known radii, and measurement of transfer characteristics were made both during strain and after re-flattening. Compared with conventional TFTs made with SiNx, TFTs made with the new hybrid material demonstrated similar flexibility when strained in compression and significantly increased flexibility when strained in tension. Under bending to compressive strain, all TFTs tested delaminated from the substrate for compressive strains greater than 2%. Conventional a-Si:H/SiNx TFTs have been previously found to delaminate at a similar compressive strain. Under bending to tensile strain, the most flexible TFTs made with the new hybrid material that were tested after re-flattening did not exhibit significant changes in transfer characteristics up to strains of ~2.5%. Conventional aSi:H/SiNx TFTs have been found to remain functional for strains of up to 0.5%, a value only one-fifth of that for TFTs made with the new hybrid material. INTRODUCTION Hydrogenated amorphous silicon thin-film transistors (a-Si:H TFTs) are vital components of many large-area electronics such as displays and sensors. The earliest TFTs were fabricated on glass substrates, which are brittle and thus impractical for applications in flexible electronics [1]. In 1999, attempting to address this issue, Suo, Ma, Gleskova, and Wagner studied the mechanics of straining a-Si:H/SiNx TFTs that were deposited on compliant polyimide foils instead of traditional glass substrates and suggested that such film-on-foil devices could be made to be very flexible [2]. Since then, various approaches have been taken to further enhance the mechanical properties of TFTs [3]. For instance, in 1999, Gleskova, Wagner, and Suo reported that removing the SiNx encapsulation layer backing the polyimide substrate in the traditional substrate “sandwich” structure resulted in more flexible TFTs [4]. While these efforts have indeed been productive, the stiffness of the SiNx used as the gate dielectric and substrate encapsulation material in conventional TFTs ultimately limits the greatest degree of flexibility that may be achieved with such structural alterations alone. In order to produce TFTs that function over an even wider range of mechanical strains, the SiNx itself must be rep