Towards flexible full-color active matrix organic light-emitting displays: Dry dye printing for OLED integration and 280°C amorphous-silicon thin-film transistors on clear plastic substrates

The goal of this thesis is to achieve flexible full color AMOLED displays on clear plastic substrates using high temperature amorphous-silicon TFT's. Dry dye-printing and solvent-enhanced dye diffusion were used to fabricate side-by-side red, green and blue organic light emitting device (OLED) pixels. The technique was then used to make combined polymer/small molecule devices, in which the printability of polymer for color integration was combined with the superior transport properties and thin layer capabilities of small molecules for high efficiency and low leakage current. A three-color passive-matrix test array with 300mum x 1mm RGB subpixels was demonstrated with this structure.; The mechanical interaction of the TFT stack and the plastic substrate is modeled to develop design guidelines to avoid cracking due to the thermal expansion mismatch between the plastic substrate and the TFT films. The guidelines are then used to successfully fabricate a-Si TFT's on novel clear plastic substrates at a maximum process temperature of up to 280°C. The TFT's made at high temperatures have higher mobility and lower leakage current, and higher stability compared to TFT's made on conventional low-Tg clear plastic substrates. Active matrix pixel circuits for organic LEDs on both glass and clear plastic substrates were fabricated with these TFT's. The leakage current in the switching TFT is low enough to allow data storage for video graphics array (VGA) timings. The pixels provide suitable drive current for bright displays at a modest drive voltage. A small AMOLED array was successfully demonstrated with very high brightness (1500 nits) at a relatively low data voltage of 15V with only ∼9V of this across the TFT itself. These results show that amorphous silicon TFT's on clear plastic are an attractive route to AMOLED displays on clear flexible plastic substrates.