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Recent advances in organic light emitting diode (OLED) device efficiencies are making the amorphous silicon (a-Si) backplane a viable solution for a large range of display sizes. This paper presents the possibilities and design challenges of a-Si active-matrix organic light-emitting-diode (AMOLED) backplanes for applications ranging from small full color cell phone displays to HDTV screens. An analytical model for the minimum pixel-area, and hence the maximum resolution for both bottom and top emitting AMOLED architectures is presented in terms of the a-Si thin-film transistor (TFT) device parameters, the process design-rules, and the pixel circuit parameters. It is established that the lower device mobility of a-Si TFTs is no longer the limiting factor. For instance, in a 20'' W/SXGA panel with full color red-green-blue subpixels, the state-of-the-art TFT processes yield a square pixel size of ∼266 μm. Further, quantitative analysis of charge-injection/charge-feedthrough error in the pixel, and the maximum allowable leakage current for the TFT is also presented.
Date of Publication: Nov. 2005