Polycrystalline Silicon Thin-Film Transistors on Flexible Steel Foil Substrates for Complementary-Metal-Oxide-Silicon Technology

摘要

We made complementary metal-oxide-silicon circuits from polycrystalline silicon thin film transistors on steel foil substrates. As-rolled steel foils can be planarized and electrically insulated with a combination of spin-on and plasma-deposited SiO_2, which also functions as the barrier against contaminant diffusion. The processes at temperatures of up to 950°C include the furnace crystallization of amorphous silicon precursor films, thermal annealing of ion implants in self-aligned geometries, and thermal oxidation of the polycrystalline silicon film. Individual thin film transistors have reached electron and hole mobilities of 60 cm~2V~(-1)s~(-1) and 15 cm~2V~(-1)s~(-1), respectively. The propagation delay in ring oscillators is 1 μs per gate, and is determined by the channel resistance and the coupling capacitance between thin film transistor and substrate. Our work introduces polycrystalline silicon circuits on steel foil as a robust technology for flexible backplanes.