CMOS polycrystalline silicon circuits on steel substrates

We report the fabrication and performance of complementary metal-oxide-silicon (CMOS) circuits made from polycrystalline silicon films on steel substrates. The steel substrate was coated with ∼0.5 μm SiO2 for planarization and insulation. The polysilicon film was crystallized from a-Si:H at 750 °C in 2 min. The n- and p-channel transistors and circuits were made with a self-aligned process and ion-implanted source/drain. The field-effect mobilities were ∼20 cm2/V s for electrons and ∼15 cm2/V s for holes. Inverters and ring oscillators operate in the MHz range. These results lay the groundwork for a circuit technology based on furnace processing on non-breakable and flexible substrates and with performance much better than that of amorphous silicon.