Amorphous Silicon Thin Film Transistors on Kapton Fibers

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Amorphous Silicon Thin Film Transistors on Kapton Fibers Eitan Bonderover1 , Sigurd Wagner1 and Zhigang Suo2 1 Department of Electrical Engineering, Princeton University, Princeton, NJ 08544, U.S.A. 2 Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ 08544, U.S.A. ABSTRACT The textile industry uses weaving to create very large quantities of fabric very quickly. The goal of our research is to use this well established technology to create complex large-area circuits quickly and efficiently. In our laboratory we have previously shown that amorphous silicon (a-Si) can be used to make thin-Film transistors (TFTs) on Kapton (a highly temperature-resistant polyimide from DuPont). We also previously showed that these TFTs can survive mechanical loads. A process has been designed to make “TFT fibers” by fabricating a-Si TFTs on Kapton. A special TFT geometry has also been developed. The structure consists of 3 large gold contact pads – one for each terminal of the TFT – running along the fiber. These contact pads allow connections to be made between TFT fibers using conductor fibers – Kapton fibers coated only with gold. The TFT fabrication process is based on a low temperature (150◦ C) Plasma Enhanced Chemical Vapor Deposition (PECVD) process. The TFTs are fabricated on a Kapton sheet from which flat fibers are made by the slit film technique. So far the best method for cutting a Kapton sheet into fibers has been plasma etching. We will describe the electronic characteristics of these TFTs as well as the electrical characteristics of the contacts between TFT fibers. INTRODUCTION The integration of electronics into clothing is a growing field in both academia [1] and industry [2],[3],[4]. Our approach is to weave circuits from component fibers. We call such fabrics, e-Textiles. Weaving has many advantages. It is a well established technology and has a large industrial base. It can potentially create flexible large area circuits very quickly. It can also create very complex patterns[6]. Thus, by weaving circuits, it should be possible to create a large variety of very complex, flexible, large area electronic circuits. Another advantage is that only a handful of component fibers are needed. Since the circuit function will be determined by the weaving pattern, the same component fibers can be used to create any number of circuits. This simplifies the device fabrication, as only a small number of different devices need be made. DESIGN The design of our fabric is a basic one. It is meant as a proof of concept and also to test various features. The basic design is shown in Figure 1. As shown the “circuit” has no

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Figure 1. The basic design of the e-Textile. Two of the vertical (warp) fibers are transistor fibers. The large squares are the gold contact pads. The horizontal (weft) fibers going over the contact pads are the conductor fibers. This design can be easily modified to create actual circuits. function, but it can be easily modified to form an actual circuit. The fibers

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