The Effect of Electrical Stress on the New Top Gate N-type Depletion Mode Polycrystalline Thin Film Transistors Fabricat
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1066-A16-02
The Effect of Electrical Stress on the New Top Gate N-type Depletion Mode Polycrystalline Thin Film Transistors Fabricated by Alternating Magnetic Field Enhanced Rapid Thermal Annealing Won-Kyu Lee1,2, Sang-Myeon Han1, Sang-Geun Park1, Sung-Hwan Choi1, Joonhoo Choi2, and Min-Koo Han1 1 School of Electrical Engineering, Seoul National University, Gwanak-ro 599, Sillim9-dong, Gwanak-gu, Seoul, 151-742, Korea, Republic of 2 LCD Business, Samsung Electronics Co. Ltd., Yongin, 449-711, Korea, Republic of ABSTRACT We have fabricated the new top gate depletion mode n-type alternating magnetic field enhanced rapid thermal annealing (AMFERTA) polycrystalline silicon (poly-Si) thin film transistors (TFTs), which show the excellent electrical characteristics and superior stability compared with hydrogenated amorphous silicon (a-Si:H) TFTs and excimer laser crystallized (ELC) low temperature polycrystalline silicon (LTPS) TFTs. The fabricated AMFERTA poly-Si TFTs were not degraded under hot-carrier stress, and highly biased vertical field stress. The considerably large threshold voltage shift (ΔVTH) and trap state density reducing were occurred when the gate bias and drain bias were both large enough. The dominant mechanism of instability in the fabricated depletion mode AMFERTA poly-Si TFTs may be due to carrier induced donor-like defects reduction within the channel layer, especially near the drain junction. INTRODUCTION LTPS TFTs based on an ELC method have high field-effect carrier mobility for pixel elements of active matrix organic light-emitting diode (AMOLED) displays. But the nonuniformity of the TFT characteristics caused by the laser shot characteristics needs to be improved. And the degradation of the ELC TFTs under the strong lateral field was severe. In order to obtain uniform TFT characteristics and reliable devices without using a laser, several crystallization methods have been proposed [1,2]. The solid phase crystallization (SPC) of amorphous silicon (a-Si) is a useful method of obtaining poly-Si film and it has many advantages over ELC such as simplicity, low cost, higher uniformity, good reliability, and large-area applicability. However, the heat treatment of the SPC requires a high temperature above 600 °C and a long annealing time (typically longer than 10 hours), which prevent its use on a thermally susceptible glass substrate [3,4]. Recently, the results of AMFERTA on a glass substrate have been reported [5-7]. AMFERTA employs field enhanced rapid thermal annealing in which the rapid thermal annealing induced by halogen lamps is combined with alternating magnetic fields. Induction of alternating magnetic field inside the silicon film leads to generation of electromagnetic force, which is the driving force for the kinetic enhancement. The electromagnetic force generates a selective joule heating of the silicon films and the movement of the silicon atoms through the effect of the applied field on the charged defects (such as vacancies, interstitial atoms and
impurities) [8-10]. This methodo
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