Modeling the Ionization Damage on Excess Base Current in p-n-p BJTs for Circuit-Level Simulation

The increase of base current is the main damage effect of p-n-p bipolar junction transistors (BJTs) subjected to ionization radiation. The Gummel-Poon (G-P) model is widely used to describe the electrical performance of BJTs. For the purpose of simulating the ionization damages on bipolar circuit performance, this article develops a G-P SPICE model that incorporates the latest formula of excess base current. Then, this article reports the ionization damage effects on a p-n-p controlled common-emitter amplifier circuit that is a key unit in the bipolar integrated circuit. After γ-ray exposures, both the output voltage of the common-emitter circuit and its relaxation time decrease. Two novel phenomena are observed for the ionization damages on the common-emitter circuit, i.e., the degradation of output voltage exhibiting time-dependent effects and sublinear dependence on dose. Moreover, this article proposes, from perspectives of SPICE simulation and circuit theory, the mechanisms behind the characteristics of degradation from ionization damage in the common-emitter circuit. The SPICE simulations provide a good fit to the experimental data for the response of output voltage of a 2N2907 p-n-p controlled common-emitter circuit to ionization damage with a dose up to 2000 Gy(SiO
₂
). Also, this article presents two applications of the new SPICE model in quantitatively describing the ionization damages on basic circuits, including crosstalk-related degradation and process-related statistical distribution of degradation.