Influence of the morphology of the copper(II) phthalocyanine thin film on the performance of organic field-effect transistors
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Saturation (graph theory)
In this paper, we proposed a novel voltage-programmed pixel circuit based on amorphous indium gallium zinc-oxide thin-film transistor (a-InGaZnO TFT) for active-matrix organic light-emitting display (AMOLED) with an enhanced electrical stability and uniformity. Through an extensive simulation work based on a-InGaZnO TFT and OLED experimental data, we confirm that the proposed pixel circuit can compensate for both mobility variation and threshold voltage shift of the driving TFT.
AMOLED
Oxide thin-film transistor
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Amorphous InGaZnO junctionless thin-film transistors (a-IGZO JL-TFTs) with different active layer thicknesses and thermal treatments were fabricated. The unique feature of a-IGZO JL-TFTs is that all of the active layer and source/drain (S/D) electrodes are realized by the deposition of the InGaZnO thin film. A quantitative analysis to completely deplete the active layer when the device is turned OFF has been performed according to the active layer thickness. The impact of active layer thickness and thermal treatment on the performance of a-IGZO JL-TFTs has been investigated. With the increase in active layer thickness and annealing temperature, the transfer curves shifted to the negative direction. From the effects of S/D series resistance on the performance of a-IGZO JL-TFTs, the series resistance cannot be a serious problem when the contact size is small enough and the active layer is thick enough. To completely deplete the active layer, the impacts of the key device design parameters such as gate oxide thickness, gate workfunction, and high-κ dielectrics on the device performance have been investigated using device simulation.
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Oxide thin-film transistor
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Field effect
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The channel length (L) and width (W) scaling behavior of amorphous In-Ga-Zn-O thin-film transistors (TFTs) have been investigated. The fabricated TFTs have a mobility of ∼12 cm2/V-s, sub-threshold slope (S) of ∼110 mV/decade, threshold voltage around 0.3 V and off-current below 10−13 A. Even though the TFTs with smaller channel length (L ≤ 5 μm) show proper switching characteristics, threshold voltage lowering and sub-threshold slope degradation are observed, while off-current and mobility are not changed. The mobility degradation with L, which was observed in amorphous silicon TFTs, is not seen for short channel a-IGZO TFTs. Lastly, the necessity of the TFT scaling for a pixel electrode in AM-LCD applications is discussed.
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Active layer
X-ray reflectivity
Oxide thin-film transistor
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A voltage-programmed a-IGZO TFT pixel circuit for AMOLED display systems is proposed in this paper. Compensation schemes together with a simple driving strategy are proposed for threshold voltage shift and mobility variations of the driving TFT, as well as the OLED degradation. Simulation results indicate that the current error rates (CERs) are reduced to lower than 11.9% when the mobility variation of the driving TFT is ±30%, and 8.1% when the threshold voltage shift of the driving TFT is ±0.5 V, for the entire data input range.
AMOLED
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In this paper, we proposed a novel voltage-programmed pixel circuit based on amorphous indium gallium zinc oxide thin-film transistor (a-InGaZnO TFT) for active-matrix organic light-emitting display (AMOLED) with an enhanced electrical stability and uniformity. Through an extensive simulation work based on a-InGaZnO TFT and OLED experimental data, we confirm that the proposed pixel circuit can compensate for both mobility variation and threshold voltage shift of the driving TFT.
AMOLED
Oxide thin-film transistor
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In this study, we explored the threshold voltage instability behavior in amorphous indium-gallium-zinc oxide (α-IGZO) thin-film transistor (TFT). A tow-step electrical degradation behavior of α-IGZO TFT was found under gate-bias stress. A usual small positive shift followed by a special negative shift of threshold voltage is characterized in the α-IGZO TFT. We suggest that the positive shift of the threshold voltage is because of charge trapping in the gate dielectric and/or at the channel/dielectric interface, while the negative shift of threshold voltage may be attributed to electric field induced extra electron carriers from H 2 O molecules in the back channel protective layer.
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Oxide thin-film transistor
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The stability of thin-film transistors (TFTs) with amorphous InAlZnO (a-IAZO) thin films as the channel layers was investigated. The devices annealed at 300 °C had a large threshold voltage (Vth) shift under gate voltage sweep, while the devices annealed at 400 °C were quite stable. The S value of the transfer characteristic curve was effectively reduced after 400 °C annealing as compared to 300 °C annealing. X-ray photo-electron spectroscopy results also showed oxygen deficiencies decreased as the annealing temperature increased. The improvement of TFTs stability might attribute to the reduction of trap states related to oxygen deficiencies. The 400 °C annealed a-IAZO TFTs exhibited small positive shift of threshold voltages under bias stress conditions, suggesting the a-IAZO might be a promising candidate for application in TFTs.
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A driving method of pixel circuit using amorphous indium gallium zinc oxide (a-IGZO) thin-film transistor (TFT) is proposed to improve the image quality of active matrix light-emitting diode displays. The proposed pixel circuit employs a diode-connected structure to compensate for variation in threshold voltage (Vth) of the a-IGZO TFT. In addition, the proposed driving method adopts negative bias annealing to suppress the Vth shift. The annealing time is optimized based on the experimental observation of the minimum Vth shift. After a stress time of 30000 s, the measurement results show that the Vth shift is reduced by 29.6%, using an optimized annealing time of 5% of one frame time. In addition, the maximum deviation in the emission current using the proposed driving method was measured to be less than 4.32% after a stress time of 30 000 s.
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