Thin Film Transistors of Microcrystalline Silicon Deposited by Plasma Enhanced-CVD

Abstract

We fabricated top gate TFTs of microcrystalline silicon (µc-Si) deposited at 360 °C. The TFTs have field-effect electron mobilities of up to 7.9 cm²/Vs in the saturation regime and 5.8 cm²/Vs in the linear regime. The highest I_ON/I_OFF ratio is 10⁵. Typical values for V_th is 6.5 V and for the subthreshold slope is 1.7 V/decade. The µc-Si is grown by PE-CVD from a source gas mixture of SiH₄, SiF₄ and H₂, with a typical flow ratio of 1:20:200, at a pressure of 120 Pa and a power density of 160 mW/cm². The TFT structure is built on un-passivated Coming 7059 glass, with 300 n⁺ µc-Si, 60 nm n⁺ µc-Si source and drain contact layers, 200 nm SiO₂ or 300 nm SiN_x gate insulator, and 100 nm Al gate, source and drain electrodes.