Leakage Current Reduction Techniques in Poly-Si TFTs for Active Matrix Liquid Crystal Displays: A Comprehensive Study

Abstract

This paper critically examines the leakage current reduction techniques for improving the performance of polycrystalline silicon (poly-Si) thin-film transistors (TFTs) used in active matrix liquid crystal displays. This is a first comprehensive study in literature on this topic. The review assesses important proposals to circumvent the leakage current problem in poly-Si TFTs and a short evaluation of strengths and weaknesses specific to each method is presented. Also, a new device structure called the triple-gate poly-Si TFT (TG-TFT) is discussed. The key idea in the operation of this device is to make the dominant conduction mechanism in the channel to be controlled by the accumulation charge density modulation by the gate and not by the gate-induced grain barrier lowering. Using two-dimensional and two-carrier device simulation, it is demonstrated that the TG-TFT exhibits a significantly diminished pseudosubthreshold conduction leading to several orders of magnitude reduction in the OFF-state leakage current when compared with a conventional poly-Si TFT. The reasons for the improved performance are explained.Index Terms-Active liquid crystal displays, leakage current, polycrystalline silicon (poly-Si), thin-film transistor (TFT), traps.

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