New Bidirectional T-Shaped Triple-Gate n-Type Polycrystalline Silicon Thin-Film Transistors Formed by Low-Temperature Sequential Lateral Solidification Process to Reduce of Kink Effects

Abstract

A new bidirectional T-shaped triple-gate device structure, which suppresses the kink effect of sequential lateral solidification (SLS)-processed polycrystalline silicon thin film transistors (poly-Si TFTs), is proposed and fabricated without any additional process. The proposed poly-Si TFTs have a lateral grain growth in channels, similar to TFTs fabricated by SLS or continuous wave (CW) laser crystallization. The whole current flow of the proposed device is mainly affected by the grain boundaries of lateral grain growth. The bidirectional T-shaped triple-gate structure has incorporated a channel located parallel to the lateral grain growth direction, and the another channel located vertically to the lateral grain growth direction. It is verified from experimental and simulation results that the proposed bidirectional T-shaped triple-gate TFT effectively suppresses the kink current of poly-Si TFT with anisotropic mobility in the triple-gate structure. Our experimental results show that the proposed bidirectional T-shaped triple-gate TFT can suppress the kink effect more effectively than the conventional dual-gate TFT, and L-shaped dual-gate TFT and can improve reliability under the high drain bias condition. The proposed device demonstrates that bidirectional operation is possible for integrated circuits compared with the L-shaped dual-gate structure that shows only fixed one-directional behavior. The proposed device exhibits a very low output conductance in the saturation regime, and this result indicates that higher output resistance is obtained in the proposed bidirectional T-shaped triple-gate TFT.