High-performance polysilicon thin ®lm transistors on steel substrates

We fabricated thin ®lm transistors in polycrystalline silicon on steel substrates. The polycrystalline silicon ®lms were made by thermally annealing hydrogenated amorphous silicon precursor ®lms, which had been deposited on stainless steel coated with 0.5 lm 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 ®lms crystallized at 650°C and had an average electron ®eld-e€ect mobility of 64 cm/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. Ó 2000 Elsevier Science B.V. All rights reserved.