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Thin-film transistors have been fabricated in polycrystalline silicon films on steel foil. The polycrystalline silicon films were formed by the crystallization of hydrogenated amorphous silicon, which had been deposited on 200-m-thick foils of stainless steel coated with ϳ0.5-m-thick layers of SiO 2 . We employed crystallization temperatures ͑and duration͒ of 600°C ͑6 h͒, 650°C ͑1 h͒, and 700°C ͑10 min͒. Top-gate transistors made from films crystallized at 650°C have an average electron field-effect mobility of 64 cm 2 /V s, with equal values in the linear and saturated regimes. Thus steel substrates permit a substantial reduction in crystallization time over glass substrates, and afford polysilicon with high electron mobility.Considerable effort is expended at present to develop processes for making thin-film transistors ͑TFTs͒ of polycrystalline silicon ͑polysilicon͒ on glass substrates. 1 Owing to their high carrier mobilities compared to those in amorphous silicon, n and p type channel polysilicon TFTs conduct large currents when on, which qualifies them for use in driver circuits. 2 The capability of polysilicon to form n and p channel devices enables complementary metal-oxidesemiconductor ͑CMOS͒ circuits, which are the technology of choice when low power consumption is desired. Polysilicon films for TFTs are made by crystallizing amorphous silicon at elevated temperature. Because the strain points of affordable glass substrates lie just above 600°C, 3 crystallization techniques are restricted to either furnace annealing up to 600°C, 4 or rapid thermal processing by lamp heating, 5 or laser annealing. 6 Furnace annealing is preferred, as it is isothermal and thus produces uniform transport properties over the entire glass plate, which now may be as large as 0.5 m 2 . However, conventional furnace crystallization at 600°C takes close to one day. Catalyzed 7 and preanneal nucleation 8,9 approaches can cut this time to ϳ5 h, which still is long when compared to the throughput of one plate per minute desired of the single-substrate cluster tools employed in the manufacture of active-matrix liquid-crystal displays. 1 These results point to the need for isothermal annealing that can be conducted quickly on low-cost substrates. This can be done with silicon films on substrates of quartz glass, 4 but quartz glass substrates are expensive. Reducing the annealing time was our principal motive for experimenting with steel substrates, which can be heated to well above 600°C. Previous work with steel foil substrate was limited to amorphous silicon TFTs ͑electron mobility ϳ1 cm 2 /V s͒ at temperature р350°C, 10,11 and very recently, to laser crystallized films. 12 In the present study, we found that the crystallization of films of hydrogenated amorphous silicon (a-Si:H) by furnace annealing at temperatures up to 700°C can be conducted in short times, and does produce polysilicon TFTs with high field-effect electron mobility.200-m-thick foils of American Iron and Steel Institute ͑AISI͒ grade 304 stainless steel ͑Fe/Ni/Cr...

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