A recoverable residual image is observed and analyzed in voltage driven active matrix organic light emitting diode (AMOLED) displays of which pixel circuits consist of two thin film transistors (TFTs) and one capacitor. The cause of the residual image is proven to be the hysteresis of the driving TFT in the pixel. The hysteresis of the p-channel TFT can be explained by hole trapping and de-trapping at the interface region of the channel. The recovery time of the residual image also strongly depends on the hysteresis level. We have found that the residual image can be eliminated by reducing the hysteresis level of TFTs.

A new poly-Si thin-film-transistor (TFT) currentmirror-active-matrix-organic-light-emitting-diode (AMOLED) pixel, which successfully compensates for the variation of the threshold voltage as well as mobility in the excimer laser annealed poly-Si TFT pixel, is designed and fabricated. The OLED current (I OLED ) of the proposed pixel does not depend on the operating temperature. When the temperature of pixel is increased from 27 • C to 60 • C, the I OLED of the new pixel circuit composed of four TFTs and one capacitor increases only about 1.5%, while that of a conventional pixel composed of two TFTs and one capacitor increases about 37%. At room temperature, nonuniformity of the I OLED in the proposed circuit was also considerably suppressed at around 9%. We have successfully fabricated a 1.2-in AMOLED panel (96 × 96 × red green blue)to evaluate the performance of the proposed pixel. A troublesome residual image caused by the hysteresis phenomenon of the poly-Si TFT was almost eliminated in the proposed AMOLED panel as a result of current programming.

We have evaluated various compensation techniques to improve the brightness uniformity of AMOLEDs fabricated by excimer laser crystallization. Every method has some limitations in terms of performance and cost in case that compensation functions are implemented in pixel arrays. Recently, we have developed a new compensation technique of which function is implemented in the driving IC chip instead of pixel arrays. In addition, we have also developed a novel solid phase crystallization (a-SPC) process so that both the uniformity of display and the fabrication cost performance can be enhanced. A 20.1-in. sized AMOLED has been successfully demonstrated by this novel crystallization technology.

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We measured the current–voltage (I–V) characteristics of amorphous Indium‐Gallium‐Zinc‐Oxide (a‐IGZO) thin film transistors (TFTs) to investigate the mechanism that causes the hump in their I–V characteristics under positive bias illumination temperature stress (PBITS) and under positive bias temperature stress (PBTS). Hump phenomenon in subthreshold region in I–V characteristics occurred under PBITS and PBTS. The hump threshold voltage (VH) shifted more negatively under PBITS than under PBTS; amount of shift of VH was 6.06 V under PBITS and 3.28 V under PBTS during same stress time, from 2000 to 10,000 s. It is because additional ionized oxygen vacancies ( or ) provided by illumination contributed to induce hump phenomenon than in darkness.