The effects of nuclear radiation on integrated circuits

Memory and logic circuits employed in military, space, and civilian nuclear plant applications are exposed to neutron and ionizing radiation. The effects produced vary with the overall dose and the intensity of the dose. C-MOS semiconductors are more resistant to neutron radiation than transistor-transistor logic (TTL) circuits, while TTL circuits tolerate gamma and X ray inputs better than C-MOS devices. The intensity of the dose has a critical level at which the logic state of a circuit is modified and gamma rays, if sufficiently intense, can disturb the electrical functioning of a circuit. Ionized MOS transistors are biased toward negative charges by the creation of a positive space charge in the oxide layer, accompanied by electron enrichment in the layer beneath the interface grid. Parasitic electrical currents arise under ionization pulses, as do intrinsic photocurrents at the junctions. Experimental determinations of the radiation damage thresholds of various devices are reported. SiO2 layers and CMOS/SOS structures offer nuclear radiation resistance.