Top-gate microcrystalline silicon TFTs processed at low temperature (<200 °C)

N-type as well P-type top-gate microcrystalline silicon thin film transistors (TFTs) are fabricated on glass substrates at a maximum temperature of 200 °C. The active layer is an undoped μc-Si film, 200 nm thick, deposited by Hot-Wire Chemical Vapor. The drain and source regions are highly phosphorus (N-type TFTs) or boron (P-type TFTs)-doped μc-films deposited by HW-CVD. The gate insulator is a silicon dioxide film deposited by RF sputtering. Al-SiO2-N type c-Si structures using this insulator present low flat-band voltage,−0.2 V, and low density of states at the interface Dit=6.4×1010 eV−1 cm−2. High field effect mobility, 25 cm2/V s for electrons and 1.1 cm2/V s for holes, is obtained. These values are very high, particularly the hole mobility that was never reached previously.