Steps and fine structure in the drain current of MISFETs after X-irradiation under bias

In addition to the commonly known effects of ionizing radiation (X-rays) on the electrical characteristics of Si-MISFETs two new effects are reported. 1) Extreme charge inhomogeneties arise in the oxide when the devices are irradiated under bias. 2) Fine structure which can be detected in the second derivative of the drain current accompanies the inhomogeneties. Possible explanations are given in terms of a clustering model at the SiO₂ interfaces and localised states in the Si inversion layer.