Electrical Stability of High-Mobility Microcrystalline Silicon Thin-Film Transistors

The electrical stability of high-mobility microcrystalline silicon (c-Si: H) thin-film transistors (TFTs) was investigated and compared to amorphous silicon (a-Si: H) TFTs. Under prolonged bias stress the microcrystalline silicon TFTs exhibit an improved electrical stability compared to amorphous silicon TFTs. The microcrystalline silicon TFTs were prepared by plasma-enhanced chemical vapor deposition at temperatures compatible with flexible substrates. The realized microcrystalline silicon transistors exhibit electron charge carrier mobilities exceeding 30 cm(2)/V s. Prolonged operation of the transistors leads to a shift of the threshold voltage towards positive and negative gate voltages depending on the gate biasing conditions (positive or negative gate voltage). The shift of the threshold voltage increases with increasing positive and negative gate bias stress. The behavior is fundamentally different from the behavior of the amorphous silicon TFTs, which exhibit only a shift of the threshold voltage towards positive gate voltages irrespective of the polarity of the gate bias stress. The threshold voltage shift of the microcrystalline silicon TFTs saturates after a few minutes to a few hours, depending on the gate voltage. After prolonged bias stress, a recovery of the initial threshold voltage is observed without any thermal annealing or biasing of the transistors, which is not the case for the measured amorphous silicon TFTs.