INFLUENCE OF DEPOSITION PRESSURE ON THE OUTPUT CHARACTERISTICS OF LOW-PRESSURE CHEMICAL-VAPOR-DEPOSITED POLYCRYSTALLINE SILICON THIN-FILM TRANSISTORS

The influence of the deposition pressure on the output characteristics of low pressure chemical vapor deposited polycrystalline silicon thin -film transistors is investigated. The polysilicon films are deposited at pressures 40, 10, and 0.5 mTorr. For channel lengths L greater tha n 10 mum, the device has the conventional output characteristics domin ated by the grain boundaries. In short-channel devices (L < 10 mum), t he experimental results show the presence of the ''kink'' effect and a reduction of the threshold voltage at high drain biases. When the dep osition pressure of the polysilicon layer decreases, despite the incre ase of the grain size, the kink effect becomes more pronounced due to the enhanced diffusion of dopants from the source and drain contacts a long the grain boundaries. The enhanced dopant diffusion reduces the e ffective channel length resulting in higher channel electric fields an d increased kink effect.