The temperature dependence of threshold voltage and mobility of polysilicon thin film transistors on flexible stainless steel foil and quartz substrates

We have fabricated polycrystalline silicon thin film transistors and circuits on flexible stainless steel foil substrates. The threshold voltage and the effective mobility of n-channel devices have been measured over the high temperature range from 25/spl deg/C to 145/spl deg/C. In this paper we present the experimental data taken from these devices, having furnace crystallized polysilicon, and the temperature dependence of the free running frequency of a ring oscillator circuit over the same temperature range. We have found that both the film effective mobility and the threshold voltage vary according to the theory, but the sensitivity on temperature is somewhat greater, and associated with the polysilicon film quality. We compare this data with that obtained from similarly fabricated devices on quartz substrates.