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Abstract— A novel pixel circuit for electrically stable AMOLEDs with an a‐Si:H TFT backplane and top‐anode organic light‐emitting diode is reported. The proposed pixel circuit is composed of five a‐Si:H TFTs, and it does not require any complicated drive ICs. The OLED current compensation for drive TFT threshold voltage variation has been verified using SPICE simulations.

Significant progress has been made in recent years in flexible AMOLED displays and numerous prototypes have been demonstrated. Replacing rigid glass with flexible substrates and thin-film encapsulation makes displays thinner, lighter, and non-breakable -all attractive features for portable applications. Flexible AMOLEDs equipped with phosphorescent OLEDs are considered one of the best candidates for low-power, rugged, full-color video applications. Recently, we have demonstrated a portable communication display device, built upon a full-color 4.3-inch HVGA foil display with a resolution of 134 dpi using an all-phosphorescent OLED frontplane. The prototype is shaped into a thin and rugged housing that will fit over a user's wrist, providing situational awareness and enabling the wearer to see real-time video and graphics information.

We proposed the hydrogenated amorphous silicon thin-film transistor (a-Si:H TFT) pixel electrode circuit with current-scaling function which is suitable for active-matrix organic light-emitting displays (AM-OLEDs). In contrast to the conventional current-mirror circuit, this circuit with the cascaded storage capacitors can provide a high data-to-organic light-emitting device (OLED) current ratio without increasing the a-Si:H TFT size. Moreover, since the number of signal line is reduced in the proposed pixel electrode circuit, the pixel electrode layout and the driving scheme can be simplified in comparison to previously reported cascade capacitor circuit. Finally, the proposed circuit can compensate for the threshold voltage variation of the driving TFT as well as the device geometric size mismatch and temperature effect.

We have suggested and developed a novel 6 photo‐mask process for the p‐channel poly‐Si thin film transistor TFT panel fabrication of active matrix organic light‐emitting diode AMOLED. By removing power line Vdd and bank photo process, we simplified the fabrication process from 8 to 6 mask steps. The p‐channel TFT fabricated by the 6 photo‐mask process had a field effect mobility of ∼80 cm2/Vsec, a sub‐threshold voltage swing of ∼0.3 V/dec., and a threshold voltage of ∼−2 V. Using the 6 photo‐mask process, we have successfully realized a 7‐inch WVGA 720×480 AMOLED panel, which is controlled by the voltage driving method.