Advanced amorphous silicon thin film transistor active-matrix organic light-emitting displays design for medical imaging

Constant-current, active-matrix organic light-emitting displays (AM-OLEDs) with the advanced hydrogenated amorphous silicon thin film transistor (a-Si:H TFT) pixel electrode circuits have been designed in our laboratory for medical applications. An extensive pixel electrode circuit simulation and analysis indicate that a continuous pixel electrode excitation can be achieved with these circuits, and a pixel electrode driving output current level up to 1.4 muA can be reached with an a-Si:H TFT technology. Small feed-through voltage (few tenth of mV) that can be achieved with this circuit will enhance the display gray level controllability needed for medical imaging. Each pixel electrode has a threshold voltage compensation circuit to adjust the pixel electrode driving current level for threshold voltage shifts of both the organic light-emitting diodes (OLEDs) and the current driving a-Si:H TFT. For a 16-inch VGA full-color AM-OLED with a pixel electrode size of similar to 60x115 mum(2), the output current level is equivalent to a pixel current density of 20 mA/cm(2). Assuming the OLEDs with an external quantum efficiency of 1%, the AM-OLED brightness of similar to 88, similar to 960, and similar to 160 cd/m(2) for red (650 nm), green (540 nm), and blue (480 nm) light emission, respectively, can be achieved with this type of pixel electrode circuits.