Effects of Hydrogen Plasma Treatment on Hysteresis Phenomenon and Electrical Properties for Solid Phase Crystallized Sil
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1153-A21-05
Effects of Hydrogen Plasma Treatment on Hysteresis Phenomenon and Electrical Properties for Solid Phase Crystallized Silicon Thin Film Transistors Sung-Hwan Choi, Sang-Geun Park, Chang-Yeon Kim, and Min-Koo Han School of Electrical Engineering and Computer Science, Seoul National University, 599 Gwanangno, Gwanak-gu, Seoul, 151-744, Korea ABSTRACT We have investigated the effects of hydrogen plasma treatment on the hysteresis phenomenon and electrical properties of solid phase crystallized silicon thin film transistors (SPC-Si TFTs) employing alternating magnetic field crystallization (AMFC). We employed H2 plasma treatment on the SPC-Si active layer before SiO2 gate insulator deposition. By increasing the power and time duration of H2 plasma treatment, it was observed that the hysteresis phenomenon of SPC-Si TFT was effectively suppressed and electrical properties such as threshold voltage, field effect mobility was improved considerably. This is due to the role of hydrogen atoms by passivating the defects and grain boundary trap states in SPC-Si film. However, relatively high power and long hydrogen plasma treatment (100W, 5 minutes) could degrade the electrical characteristics of the device. SPC-Si TFT for 100W power of PECVD and 3 minutes with the H2 plasma treatment exhibit the significant improvement of electrical characterics (VTH = -3.85V, µ FE = 21.16cm2/Vs), and a smaller hysteresis phenomenon (∆VTH = -0.30V) which is suitable for high quality AMOLED Display. INTRODUCTION Active matrix organic light emitting diode (AMOLED) employing thin film transistor (TFT) pixel circuits have been considered as a future display technology due to its high brightness, compactness, fast response time and wide viewing angle [1]. Therefore the quality of TFTs as well as a life time of electroluminescence should be improved. Recently, solid phase crystallized silicon TFT (SPC-Si TFT) on the glass substrate has gained a considerable attention as a pixel element of the driving circuit in the AMOLED technology because it shows superior current stability than hydrogenated amorphous silicon (a-Si:H) TFTs, and it has better current uniformity than low temperature polycrystalline silicon (LTPS) TFTs. However the threshold voltage of SPC-Si TFT is relatively high and leakage current of device is also large. They also suffer from a hysteresis phenomenon similar to other devices, especially in p-type devices. Residual image sticking has still served as a critical problem in the AMOLED display. Residual image sticking might be observed for a few minutes due to the hysteresis phenomenon of the driving transistor in the AMOLED display [2]. The purpose of this work is to improve the electrical characteristics of SPC-Si TFTs and reduce the hysteresis phenomenon of p-type devices on glass substrates by employing H2 plasma treatment on the solid phase crystallized silicon before gate insulator deposition. The threshold voltage of SPC-Si TFT was decreased and leakage current level was also reduced with the H2 plasma treatment. It
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