Ionization damage in NPN transistors caused by lower energy electrons

Electrical degradation of two type NPN bipolar junction transistors (BJTs) with different emitter sizes was examined under exposures of 70 and 110 keV electrons. Base and collector currents as a function of base–emitter voltage were in-situ measured during exposure. Experimental results show that both the 70 and 110 keV electrons produce an evident ionization damage to the NPN BJTs. With increasing fluence, collector currents of the NPN BJTs hardly change in the whole range of base–emitter voltage from 0 to 1.2 V, while base currents increase in a gradually mitigative trend. Base currents vary more at lower base–emitter voltages than at higher ones for a given fluence. The change in the reciprocal of current gain at a fixed base–emitter voltage of 0.65 V increases non-linearly at lower fluences and tends to be gradually saturated at higher fluences. Sensitivity to ionization damage increases for BJTs with an emitter having a larger perimeter-to-area ratio.