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0989-A11-03

Contact Effects in High Mobility Microcrystalline Silicon Thin-Film Transistors Kah Yoong Chan1,2, Eerke Bunte2, Helmut Stiebig2, and Dietmar Knipp1 1 School of Engineering and Science, Jacobs University Bremen, Campus Ring 1, Bremen, 28759, Germany 2 Institute of Photovoltaics, Research Center J¸lich, J¸lich, 52425, Germany ABSTRACT Microcrystalline silicon (µc-Si:H) has recently been proven to be a promising material for thin-film transistors (TFTs). We present µc-Si:H TFTs fabricated by plasma-enhanced chemical vapor deposition at temperatures below 200 °C in a condition similar to the fabrication of amorphous silicon TFTs. The µc-Si:H TFTs exhibit device mobilities exceeding 30 cm2/Vs and threshold voltages in the range of 2.5V. Such high mobilities are observed for long channel devices (50-200 µm). For short channel device (2 µm), the mobility reduces to 7 cm2/Vs. Furthermore the threshold voltage of the TFTs decreases with decreasing channel length. A simple model is developed, which explains the observed reduction of the device mobility and threshold voltage with decreasing channel length by the influence of drain and source contacts.

INTRODUCTION With the advance of flat panel display technologies, an increasing demand occurred for thin-film transistors (TFTs). To date, amorphous silicon (a-Si:H) has established itself as an inexpensive and reliable technology for display backplanes. A-Si:H TFTs are mainly applied as pixel switches in active-matrix liquid crystal displays (LCDs) even though they exhibit relatively low (electron) mobility of 0.5 to 1 cm2/Vs. However, their performance is not good enough to operate electronic circuits at frequencies well above video rate, for examples column and row drivers for LCDs or radio frequency identification tags (RFID tags). Furthermore, the hole mobility of a-Si:H TFTs is much lower than the electron mobility. Therefore, complimentary metal oxide semiconductor circuits cannot be realized. Finally, biasing of a-Si:H TFTs over a longer period of time leads to a shift of the threshold voltage. This effect complicates the realization of circuits like pixel drivers for organic light-emitting diode (oLED) displays or column multiplexer and row shift register circuits [2]. Polycrystalline silicon (poly-Si) TFTs exhibit high electron and hole mobilities above 20 cm2/Vs and stable device performance, which recommend the technology for advanced applications like electronic circuits on glass, column and row drivers for displays, pixel switches for projector displays and pixel engines for oLED technology. However, poly-Si technology is expensive due to the need of high deposition temperature and/or crystallization steps. In recent years a lot of alternative TFT technologies including organic and polymeric TFTs have been developed and are of interest for large area electronic applications. The performance of small molecule based TFTs is comparable to the a-Si:H TFTs. In particular pentacene has proven to be a very promising material [3,4]. However, the materials are