The ultimate thin film transistor on flexible platform will need to have performance close to its counterpart on rigid substrate in order to meet future requirements for high performance, large area and flexible electronic applications such as x-ray imager. However, most flexible substrates cannot withstand processing temperatures above 300 °C. This poses great challenges on further improving TFT performance. The temperature limits can be effectively eliminated by using metal foil substrates. This talk focus on our findings on flexible polycrystalline silicon TFT on flexible metal foil. It will be shown that high temperatures allow processes such as diffusion and thermal oxidation to be conducted, and these processes can improve device performance and device reliabilities. Our metal induced laterally crystallized TFTs on flexible foil demonstrate a saturation mobility (μsat) of 135 cm2/v∙s, a threshold voltage (VTH) of 2.9 V, an ON/OFF ratio close to 105, and a subthreshold swing (S.S) of 890 mV/dec. Electrical stress test shows great stability of the aforementioned parameters up to 10000 s.