Nanocrystalline Silicon Thin Film Transistors on Optically Clear Polymer Foil Substrates

Abstract

AbstractWe have fabricated TFTs of nanocrystalline silicon (nc-Si) at 150°C on clear polymer substrates (coefficients of thermal expansion, α∼45 to 55ppm/K), on Kapton® 200E (α=17ppm/K), and on Corning 1737 glass (α=3ppm//K) for comparison. Because thermally stable polymers, such as Kapton® 200E polyimide, have glass transition temperatures as high as 325°C, they are candidates for direct substitution of display glass. The stresses developed in the substrate and device layers, due to à, are reduced by decreasing the thickness of the active layers, by cutting the layers into islands separated by exposed substrate, and by designing stresses, via plasma conditions, into the SiNx passivating layers. By using these three techniques we have made nc-Si TFTs on high Tg, and high α, clear polymer foils with electron mobilities of up to 18cm2/Vs. When integrated with bottom-emitting organic light emitting diodes, such devices will allow for a 10x reduction in pixel TFT areas, compared to TFTs of amorphous silicon.