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 0.5-μm 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 non-self-aligned geometries. The gate dielectric was SiO2 made by thermal oxidation or from deposited SiO2. The field-effect mobilities reach 64 cm2/Vs for electrons and 22 cm2/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.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Electrical and Electronic Engineering
- Complementary metal-oxide-semiconductor devices (CMOS)
- Thin-film circuits
- Thin-film transistors (TFTs)