A new a-Si:H TFT pixel circuit compensating the threshold voltage shift of a-Si:H TFT and OLED for active matrix OLED
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We propose a new hydrogenated amorphous silicon thin-film transistor (a-Si:H TFT) pixel circuit for an active matrix organic light-emitting diode (AMOLED) employing a voltage programming. The proposed a-Si:H TFT pixel circuit, which consists of five switching TFTs, one driving TFT, and one capacitor, successfully minimizes a decrease of OLED current caused by threshold voltage degradation of a-Si:H TFT and OLED. Our experimental results, based on the bias-temperature stress, exhibit that the output current for OLED is decreased by 7% in the proposed pixel, while it is decreased by 28% in the conventional 2-TFT pixel.Keywords:
AMOLED
Oxide thin-film transistor
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.
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Oxide thin-film transistor
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We propose a new hydrogenated amorphous silicon thin-film transistor (a-Si:H TFT) pixel circuit for an active matrix organic light-emitting diode (AMOLED) employing a voltage programming. The proposed a-Si:H TFT pixel circuit, which consists of five switching TFTs, one driving TFT, and one capacitor, successfully minimizes a decrease of OLED current caused by threshold voltage degradation of a-Si:H TFT and OLED. Our experimental results, based on the bias-temperature stress, exhibit that the output current for OLED is decreased by 7% in the proposed pixel, while it is decreased by 28% in the conventional 2-TFT pixel.
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Oxide thin-film transistor
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In this paper, we propose a driving method for compensating the electrical instability of hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFTs) and the luminance degradation of organic light-emitting diode (OLED) devices for large active matrix OLED (AMOLED) displays. The proposed driving method senses the electrical characteristics of a-Si:H TFTs and OLEDs using current integrators and compensates them by an external compensation method. Threshold voltage shift is controlled a using negative bias voltage. After applying the proposed driving method, the measured error of the maximum emission current ranges from -1.23 to +1.59 least significant bit (LSB) of a 10-bit gray scale under the threshold voltage shift ranging from -0.16 to 0.17 V.
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This paper proposes a new amorphous indium gallium zinc oxide (a‐IGZO) pixel circuit for the simultaneous emission active‐matrix organic light‐emitting diode (AMOLED) displays, which can compensate for the non‐uniform threshold voltage (V TH ) and mobility (μ) of the thin‐film transistor (TFT). The Negative V TH are successfully compensated by adopting the source follower method, and then mobility compensation is carried out by additional voltage adjustment. The OLED current error rate is within 9 % against the V TH and mobility variations in the simulation.
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Oxide thin-film transistor
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We report the fabrication of a video-brightness, active-matrix organic LED (AMOLED), two-transistor-pixel based on amorphous silicon (a-Si) TFT technology, with a maximum process temperature of 350 C. The process should be compatible with existing a-Si TFT manufacturing technology for AMLCDs.
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By combining three key components in an AMOLED display pixel: the drive transistor, the storage capacitor, and the OLED stack into a single, gate voltage controlled, light-emitting element, the vertical organic light emitting transistor (VOLET) works together with low-cost, mature TFT technology to enable high performance AMOLED display panels that can be mass produced on fully depreciated LCD lines.
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Active matrix organic light emitting diode (AMOLED) displays based on amorphous indium-gallium-zinc oxide thin-film transistor (a-IGZO TFT) pixel circuit encounter problems as instability of threshold voltage (V T ) under gate voltage bias-stress, the non-uniformity of mobility (μ) resulting from the large area TFT scale fabrication, and OLED degradation, etc. In this paper, we proposed a current compensation method. An improved current mirror is designed to overcome the channel length modulation effect of TFTs. The SPICE simulation results show that the proposed scheme not only effectively compensates for non-uniformity related with deviations of V T and μ in a-IGZO TFTs, the OLED degradation, but also guarantees a good linearity between I DATA and I OLED .
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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.
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Oxide thin-film transistor
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This letter proposes a new voltage-programmed amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistor (TFT) pixel circuit for active-matrix organic light-emitting diode (AMOLED) displays. The proposed circuit detects the VTH of the driving TFT only in a periodically executed compensation frame, allowing the other frames to perform only data input and emission for high-speed applications. An HSPICE model is also established based on the measured electrical characteristics of a fabricated a-IGZO TFT. The simulation results reveal that the proposed circuit can compensate for the degradation of the driving TFT and the OLED without external circuits. Moreover, the current error rates are <;6.32%, so the proposed circuit is effective for use in AMOLED displays.
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Abstract An 8‐in. flexible active‐matrix organic light‐emitting diode (AMOLED) display driven by oxide thin‐film transistors (TFTs) has been developed. In‐Ga‐Zn‐O (IGZO)‐TFTs used as driving devices were fabricated directly on a plastic film at a low temperature below 200 °C. To form a SiO x layer for use as the gate insulator of the TFTs, direct current pulse sputtering was used for the deposition at a low temperature. The fabricated TFT shows a good transfer characteristic and enough carrier mobility to drive OLED displays with Video Graphic Array pixels. A solution‐processable photo‐sensitive polymer was also used as a passivation layer of the TFTs. Furthermore, a high‐performance phosphorescent OLED was developed as a red‐light‐emitting device. Both lower power consumption and longer lifetime were achieved in the OLED, which used an efficient energy transfer from the host material to the guest material in the emission layer. By assembling these technologies, a flexible AMOLED display was fabricated on the plastic film. We obtained a clear and uniform moving color image on the display.
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