Effects of x-ray irradiation on polycrystalline silicon, thin-film transistors

The effects of x-ray irradiation on the transfer and noise characteristics of excimer-laser-annealed polycrystalline silicon (poly-Si) thin-film transistors (TFTs) have been examined at dose levels up to 1000 Gy. Parameters including mobility, threshold voltage, subthreshold swing, and leakage current, as well as flicker and thermal noise coefficients, were determined as a function of dose. In addition, the physical mechanisms of the observed changes in these parameters are analyzed in terms of radiation-generated charge in the gate oxide, at the Si-Si O2 interface, and at the grain boundaries. The results of the studies indicate that poly-Si TFTs exhibit sufficient radiation tolerance for the use in active-matrix flat-panel imagers for most medical x-ray applications.