Bias Conditions in Gamma Radiation Assurance Tests of Bipolar Technologies for HEP Applications

In common irradiation tests performed with electronics to be used in space applications, devices are kept with their terminals shorted together during the irradiation time. However, in HEP experiments, devices are generally biased during the irradiation periods. Therefore, unbiased irradiation tests are not realistic anymore. We have performed systematic experiments irradiating different bipolar transistors in the same conditions but with different bias configurations. We have found that bipolar transistors suffer much more damage when irradiated under unbiased conditions (floating terminals) than when biased during the irradiation. For this reason, unbiased irradiations would largely overestimate the irradiation damage in these devices. Grounding or shorting the devices during irradiation lead to slight more damages, and can be considered worst-case configurations. No irradiation bias effects have been observed for neutron irradiations.