Compensation For Threshold Instability Of Thin-Film Transistors



Flores, Roberto W

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Organic Light Emitting Diode (OLED) has attracted an incredible interest for display applications due to benefits such as a wide viewing angle, high contrast ratio, vivid color, low power consumption, high response speed in comparison to Liquid Crystal Display (LCD). OLED displays do not require backlight and it can display deeper black color than LCDs. The fast response and self-emissive nature of OLEDs have made this technology a good candidate for three-dimensional displays. The thin and light structure of OLED displays have create a strong interest for researcher to advance the OLED’s technology into flexible and transparent displays. However, the uniformity of the image of OLED displays have been affected by the degradation of OLEDs and by the instability of the threshold of thin-film transistors (TFTs) utilized in the pixel area in displays known as Active-Matrix Light-Emitting Diodes (AMOLED) displays. TFTs backplane are required for switching and driving current to OLEDs in AMOLED displays. Driver-TFTs are responsible to provide current to each pixel of the AMOLED displays. Subsequently, if the driver-TFTs provide a small variation in the current, then the variation can be distinguished as non-uniformity by the user or MURA effect. The human eyes are very sensitive to changes in luminance and can perceive MURA effects produced by the display. Therefore, there is a recognized need for urgent progress in the display technology to achieve better display quality at a low cost, fast response and accurate compensation. Currently, several approaches are under investigation and/or evaluation in order to compensate the deterioration of the TFT and/or OLED. However, the speed of the compensation, accuracy of the compensation and the impact of the display resolution are still a concern. Therefore, this thesis describes new driving methodologies and circuit schematics for compensating the instability of threshold of thin-film transistor (TFT) and degradation of organic-light emitting diode (OLED) achieving improvements in the accuracy of the compensation and speed of the circuits.



Threshold, Compensation, Degradation, OLED, TFT, AMOLED