Enhanced Mobility Top-Gate Amorphous Silicon Thin-Film Transistor with Selectively Deposited Source/Drain Contacts

Abstract

Amorphous silicon thin-film transistors (TFT's), in a top-gate staggered electrode structure, have been prepared using selectively deposited doped silicon contact layers, formed in-situ by plasma-enhanced chemical vapor deposition (PECVD). Selective deposition reduces the number of processing steps and assures the formation of low-resistance contacts. Devices fabricated with two photomasks and one plasma deposition step show saturation and linear mobilities as high as 1.1 and 0.9 cm2/V s, respectively, with threshold voltages between 3 and 6 V. On/off ratios are ≥ 106, with a subthreshold slope of 0.8 V/decade. The mobilities are at least a factor of 2 higher than previously reported for top-gate structures, and are similar to values reported for bottom-gate (inverted staggered) TFT's. © 1992 IEEE