High temperature polycrystalline silicon thin film transistor on steel substrates

Polycrystalline silicon thin film transistors were fabricated using both self-aligned and non-self-aligned structures on 0.2 mm steel foil substrates coated with 0.5 μm SiO₂. The polycrystalline silicon was formed by furnace crystallization of PECVD hydrogenated amorphous silicon films at temperatures from 600 to 950°C. The corresponding annealing times at high temperature can be as short as 20 seconds. No evidence is found for transistor contamination by the steel with drain current on/off ratio of ≥10⁵ in all cases. The short crystallization times achievable on steel substrates provide a considerable advantage over glass substrates, which require crystallization times of ≥6 hours because of their strain temperatures of approx.600°C. Our results lay the groundwork for polycrystalline silicon transistor roll-to-roll technology on continuous web.