Investigation of irradiation effect on npn BJT electrical properties

• Results of irradiation effect on npn BJT transistor are reported.
• The radiations were a mixed neutrons-fission gamma rays and Co-60 gamma source.
• Main effect was the decreasing of the transistor current gain hFE.
• The influence of hFE decreasing on other transistor parameters was also analyzed.

The irradiation effects of neutrons and gamma rays on a commercial type of npn Bipolar Junction Transistors (BJTs) are reported. The decrease of the current gain factor hFE for increasing dose was analyzed. Reduction ratio for hFE between 84% and 98% at the saturated reduction level have been obtained. This is due to a small decreasing in the collector current IC and a large increasing in the base current IB, where hFE=IC/IB. Reduction ratio per dose indicates the higher influence of the neutrons than that of gamma for the same equivalent dose. Moreover, the voltage gain as a function of the frequency decremented after irradiation, and the collector saturated voltage (VCEsat) was increased. These effects illustrate the damage in the function of BJTs.