Radiation resistant MOS devices

A detailed study indicates that the radiation resistance of MOS transistors is controlled by the details of technology. It has been found that an MOS structure can be created that remains operational for gamma doses above 10⁷rad. It will be shown how the radiation resistance varies with gate oxidation and the metals employed. Two metals were used in the experiments: aluminum and chromium. The interrelationship between radiation and thermal stability will also be discussed. It will be shown that there is some connection between the two as long as the same basic technology is used. It is possible however, that combinations that result in thermal stability can still show a low radiation resistance. The radiation generates positive-charge centers in the oxide and these centers are related to "minor" bonds in the oxide. In this respect, the oxide-metal interactions have been considered. It follows from our studies that the greatest radiation resistance will be found for -enhancement devices and for certain -depletion structures. The measurements will show results for -enhancement units with radiation resistance one-hundred times greater than previously reported figures, both for MOS and bipolar transistros.