A comparison of the effects of cobalt-60 γ ray irradiation on DPSA bipolar transistors at high and low injection levels

We investigate the γ-ray total dose induced degradation of double polysilicon self-aligned (DPSA) bipolar NPN transistors at low dose rate. Through comparing the measured results in low- and high-level injection regions, we find that the main irradiation damages related defects in two regions are quite different. In the case of lower emitter-base (E-B) bias, the damage is mainly localized in E-B interface region. For high-level injection, excess base current mainly results from radiation induced defects in intrinsic base region. Furthermore, a phenomenological model based on qualitatively analytical calculation is adopted to explain the experimental results.