Investigation on Characteristic Variation of Polycrystalline Silicon Thin-Film Transistor Using Laterally Grown Film

The characteristic variation of thin-film transistors (TFTs) fabricated on laterally grown polycrystalline silicon (poly-Si) prepared by pulsed laser scanning was investigated. TFTs with various channel designs were fabricated and investigated: TFTs with n- and p-channels, TFTs whose channel was set either parallel or perpendicular to the grain growth direction, and TFTs whose channel is composed of a single channel or multiple stripes. It was found that the variation in current drive is not due to the variation in threshold voltage but primarily due to the variation in carrier mobility. The variation in carrier mobility was found to be larger in perpendicular-aligned TFTs than in parallel-aligned TFTs and also larger in n-channel TFTs than in p-channel TFTs. From the investigation of TFTs with multiple stripes, it was found that the characteristic variation depended on the total channel width. We also evaluated the potential barrier height at the grain boundaries from the temperature-dependent carrier mobility, which gave us a potential barrier height of 13.2 meV for the n-channel TFT and 7.18 meV for the p-channel TFT. The potential barrier height was found to decrease with increasing gate voltage. The experimental results indicate that the characteristic variation of poly-Si TFTs decreases with decreasing potential barrier at the grain boundaries. In fact, it is shown that TFTs whose potential barrier was reduced by hydrogen plasma treatment show a reduced characteristic variation.