A-Si Amoled Display Backplanes on Flexible Substrates
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A-Si AMOLED DISPLAY BACKPLANES ON FLEXIBLE SUBSTRATES A. Nathan, D. Striakhilev, P. Servati, K. Sakariya, A. Sazonov, S. Alexander, S. Tao, C.-H. Lee, A. Kumar, S. Sambandan, S. Jafarabadiashtiani, Y. Vygranenko, I.W. Chan Electrical and Computer Engineering, University of Waterloo, Waterloo, Ontario N2L3G1, Canada [email protected] Abstract In view of its maturity and low-cost, the amorphous silicon (a-Si) technology is an attractive candidate for active matrix organic light emitting diode (AMOLED) display backplanes on flexible substrates. However, the a-Si material comes with significant intrinsic shortcomings related to speed (mobility) and stability of operation, requiring novel threshold-voltage-shift (∆VT) compensated thin-film transistor (TFT) pixel circuits and architectures to enable stable OLED operation. But given the dramatic progress in efficiency of OLED materials over recent years, the drive current requirement has been significantly lowered, thus relaxing the constraints on a-Si TFTs. For compatibility to plastic substrates, the a-Si TFT process temperature must be reduced from the conventional 300ºC to ~150ºC or below, which tends to compromise the integrity of thinfilm materials and device performance. Hence, optimizing the TFT process for high device performance with limited thermal budget is a necessary step towards flexible AMOLEDs with a-Si backplanes. This paper reviews the design and process challenges, and specifically examines the performance of TFTs and ∆VT-compensated integrated pixel driver circuits on plastic substrates with respect to current driving ability and long term stability. More importantly, lifetime tests of circuit degradation behaviour over extended time periods demonstrate highly stable drive currents and its ability to meet commercial standards. I. INTRODUCTION The market demand for portable, robust, and low-cost electronics with large-area fabrication and roll-to-roll manufacturing capability is fuelling rapid progress in the research and development of electronic devices and systems on mechanically flexible plastic substrates (“flexible electronics”). Potential applications include displays, solar cells, thin film batteries, MEMS, smart cards, and RF ID tags, many of which are already at the stage of commercial prototypes [1-7]. At the same time, new futuristic concepts are being developed, and include: electronic devices integrated with textiles (electrotextiles, see [8] and references therein); low-cost sensor arrays ( or “sensitive skin” [9]), with data processing capabilities for unsupervised or remotely operated machinery in hazardous environments; or bioMEMS to replace degenerated retina cells in the human eye [10]. The largest market potential, however, belongs to AMOLED displays [11-14], thanks to the rapid proliferation of information and wireless technologies, which are in a neverending quest for ever-thinner, portable, light-weight and robust displays with low power consumption and higher-performance. The OLED best fits these requirements and as
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