guarding and in insulating layers above bipolar device structures may be affected by ionizing dose, resulting in changes in the performance of certain bipolar devices. The discovery of enhanced low dose rate sensitivity (ELDRS) in bipolar devices exposed at very low dose rates has resulted in the requirement to consider such effects in assessing the suitability and performance of candidate technologies and devices. 4.1.2 Displacement Damage Dose [Dressendorfer98] Energetic protons, electrons, and heavy ions also create damage in semiconductor materials by displacing atoms by collision with lattice nuclei and through subsequent collision of the recoil atom with other lattice atoms. The result of this process is the creation of interstitial silicon and vacancy pairs which act as recombination and trapping centers. This displacement damage can reduce minority carrier lifetime, change majority carrier charge density, and reduce carrier mobility, all of which lead to changes in the electrical performance characteristics of devices. Silicon bipolar device gain may be affected by bulk displacement damage; however, narrow base widths used in modern high frequency devices decrease the level of susceptibility. Most affected are solar cells and opto-electronic devices. Displacement damage can reduce the light output of LEDs and semiconductor lasers; photo detectors and solar cell collection/conversion efficiency may be reduced by the presence of bulk displacement damage. Destructive Single Event Effects 4.2.1 Single Event Latchup and Snapback Single Event Latchup (SEL) is the condition which results from the activation of a parasitic bipolar device structure which is present in bulk CMOS semiconductor device structures. The four-layer device structure operates in a manner which is similar to a silicon- controlled rectifier device. Charge deposited by the passage of a single energetic particle results in the injection of sufficient current to turn on the parasitic latching mechanism; sustaining drive current must be provided