Complementary metal-oxide-semiconductor thin-film transistor circuits from a high-temperature polycrystalline silicon process on steel foil substrates

We fabricated CMOS circuits from polycrystalline silicon films on steel foil substrates at process temperatures up to 950/spl deg/C. The substrates were 0.2-mm thick steel foil coated with 0.5-/spl mu/m thick SiO/sub 2/. We employed silicon crystallization times ranging from 6 h (600/spl deg/C) to 20 s (950/spl deg/C). Thin-film transistors (TFTs) were made in either self-aligned or nonself-aligned geometries. The gate dielectric was SiO/sub 2/ made by thermal oxidation or from deposited SiO/sub 2/. The field-effect mobilities reach 64 cm/sup 2//Vs for electrons and 22 cm/sup 2//Vs for holes. Complementary metal-oxide-silicon (CMOS) circuits were fabricated with self-aligned TFT geometries, and exhibit ring oscillator frequencies of 1 MHz. These results lay the groundwork for polycrystalline silicon circuitry on flexible substrates for large-area electronic backplanes.