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 C. The substrates were 0.2-mm thick steel foil coated with 0.5m thick SiO2. We employed silicon crystallization times ranging from 6 h (600 C) to 20 s (950 C). Thin-film transistors (TFTs) were made in either self-aligned or nonself-aligned geometries. The gate dielectric was SiO2 made by thermal oxidation or from deposited SiO2. The field-effect mobilities reach 64 cm Vs for electrons and 22 cm 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.