High-performance polysilicon thin film transistors on steel substrates

We fabricated thin film transistors in polycrystalline silicon on steel substrates. The polycrystalline silicon films were made by thermally annealing hydrogenated amorphous silicon precursor films, which had been deposited on stainless steel coated with ∼0.5 μm thick 810°C-annealed SiO₂. We employed annealing temperatures ranging from 600°C, which is the furnace annealing temperature limit for conventional glass substrates, to 750°C. Films were crystallized at 650°C in 1 h with 1-h hydrogen plasma seeding, at 700°C in 10 min either with or without hydrogen plasma seeding, and at 750°C in 2 min. The best top-gate transistors were made from films crystallized at 650°C and had an average electron field-effect mobility of 64 cm²/V s in both the linear and saturated regimes. Thus steel substrates permit a substantial reduction in crystallization time over conventional glass substrates, and produce polycrystalline silicon with an electron mobility greater than other substrates.