Experimental studies of collector-emitter voltage bias influence on the total ionization dose effects in NPN Si BJTs

The voltage VCE, bias influence studies on total ionizing dose (TID) in bipolar junction transistors (BJTs) were investigated. The BJTs were set at forward active mode of base-emitter voltage (VBE) swept from 0 to 1.0 V at different biased conditions of VCE, ranging from 1 V to 2 V at an interval of 0.25 V during 60Co γ irradiation. The damage mechanism of TID in BJTs at different VCE bias conditions were analysed by forward Gummel characteristics, forward current gain (βf), normalized excess base current (ΔIB/IBpre), normalized excess collector current (ΔIC/ICpre), normalized current gain (βfpost/βfpre), ideality factor (n) and power dissipation (Pd). The results show that the increments of base current (IB) and collector current (IC) are slightly different in various VCE bias conditions which also effects slight changes in their current gain (Δβf) degradation. The current gain degradation (βf) at high bias VCE degraded more slightly than low bias VCE. The ΔIB/IBpre, ΔIC/ICpre and βfpost/βfpre estimated shows similar trend of different VCE bias conditions resulting into varying distribution of performance degradation of the BJT. The ideality factors (n) for excess base current (ΔIB) were ∼2 for VBE from 0.35 V to 0.6 V at different VCE bias conditions. Thus, ideality factor (n) slightly increases as the VCE bias rises and decreases with the increased accumulated total dose level after the n peak value was obtained at TID equals to 130 krad (Si) for irradiated BJTs. Finally, the power dissipated (Pd) by BJTs were compared as VCE = 2 V  >  1.75>1.5 V  >  1.25>1 V and were noted to be more effective at VBE>0.6 V which also concur with temperature rise TR. The TR in BJTs resulted into self-heating effects.