Neutron Hardness Assurance Considerations for Temperature Compensated Reference Diodes

Extremely large variations have been observed in the susceptibility of modern MIL-SPEC temperature compensated reference diodes to permanent damage caused by fast neutron irradiation. Changes in reference voltage (¿VZ) ranging from <0.1 to >60 mV have been measured following a neutron fluence of approximately 1012 n/cm2. Using the maximum allowable voltage change over the military temperature range as a failure criterion, these devices have been shown to fail at fluences as low as 5 × 1010 n/cm2. The source of this variation is shown to be a function of the lifetime and the number of forward biased compensating diodes used in the composite reference device. Due to these potentially large variations, some means of hardness assurance for these devices is mandatory for practically all tactical and strategic military systems having a requirement to survive a nuclear weapon environment.