The Effect of Hydrogen Dilution on Hot-Wire Thin-Film Transistors
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J.P. CONDE*, H. SILVA**, V. CHU** *Department of Materials Engineering, Instituto Superior Thcnico, Lisbon, Portugal "**Institutode Engenharia de Sistemas e Computadores (INESC), Lisbon, Portugal ABSTRACT Bottom-gate thin film transistors (TFT) were fabricated with amorphous and microcrystalline silicon active layers deposited by hot-wire (HW) chemical vapor deposition using different levels of hydrogen dilution. As the hydrogen dilution was increased above 80%, the active layer made a transition from amorphous to microcrystalline. This transition resulted in an increase of the TFT off-current and in an increase of the TFT subthreshold slope. The TFT oncurrent and the TFT mobility remained at levels comparable to those of the a-Si:H HW TFTs. A comparison is made between TFTs with amorphous and microcrystalline silicon active layers prepared both by rf glow discharge and HW. HW TFTs with an active layer consisting of a thin layer deposited with high hydrogen dilution underlying a thicker amorphous silicon layer are also compared to TFTs with an active layer of the same total active layer thickness consisting only of the high hydrogen dilution film. INTRODUCTION Thin-film transistors, TFT, made from hydrogenated amorphous silicon, a-Si:H, are used in matrix-addressed arrays such as flat-panel displays and image scanners [1]. High-performance TFTs incorporating a-Si:H as an active layer have field effect mobilities p[-1 cm V- s switching ratios ION/IOFF>5XlO6, and leakage currents IOFF5xl06 . The HW a-Si:H TFTs (TF-66-6 and TF-62-10, with, respectively, 0 and 50 %H2) have 0.2
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