$1/f$ Noise Model for NPN Bipolar Junction Transistors Based on Radiation Effect

Radiation-induced current gain and 1/f noise degradations in NPN bipolar junction transistors are due to accumulation of oxide-trapped charges and interface states at the surface of the device. Based on an available model of base surface current of NPN bipolar junction transistors, a simplified model is presented with some approximations at low total dose level, which can explain the degradation mechanisms of the current gain. Based on the theory of carrier number fluctuation and the simplified model of base surface current, a 1/f noise model is developed, which can be used to explain the 1/f noise degradation induced by the radiation at low total dose level. The model suggests that the gain and 1/f noise degradations can be attributed to the same physical origin, and these two kinds of degradations are the result of accumulation of oxide-trapped charges and interface states. The radiations were performed in a Co⁶⁰ source at a dose rate of 10 rad(Si)/s up to a total dose of 70 krad(Si). The degradations of the current gain and 1/f noise are compared, and the relationship between 1/f noise and the current gain is given, which accords well with the experimental results. Compared to the current gain, the 1/f noise parameter is more sensitive, so it may be used to evaluate the radiation resistance capability of bipolar junction transistors.