s Q. For the purpose of modeling, the issue is to find out the different channels of release and interaction, and chain equations together in a coherent manner with the correct parameters. The table 9 depicts a framework in the case of processes relevant to first-order kinetics. 1) Release of a Species X in a Given Volume X = G.Y.D' G = conversion factor between the absorbed dose D and the species X 2) Transport towards an active Site Current Flux J = F.X in the coefficient F : drift-diffusion, CTRW, multiple trapping-detrapping, etc 3) Formation of an electrically-active species Reaction forward dQ/dt=(N-Q).R.X With R = trapping coefficient Reaction backward -Q.R'.Z With R'= detrapping coefficient Z=e0 .exp-Ea/kt, Z=Tunneling probability, etc Table 9. Types of quantities and equations for release and transformation of species in MOS structures. III-80 8. BIPOLAR TRANSISTORS The primary effect of radiation exposure on bipolar transistor is the reduction of gain, with larger degradation at low operating currents. Total Dose (krad(SIO,)) Figure 68 displays bipolar NPN characteristics. One sees that for a reduction of the maximum current gain of near 50% (approximately Vbe=0.7-0.8V or I.=10-5-10-3 A), the reduction being much worse at lower current levels. Globally, it is observed an inverse dependence of gain versus dose Vbe (V) (exponent m with m<1), but with a proportionality factor depending largely on the drain current (formula on fig. 69). Figure 68. Typical degradation of the gain in a bipolar transistor [Nowl-92]. Gain degradation comes from minority carrier recombination at the base interface in the separation or passivation oxide (base/emitter Electric Field Trapped Positive Charges In Passivation in Passivation Oxide spacer). If positive charge is trapped in this Oxide oxide, it induces depletion or inversion at the surface of the base (P-type for a NPN), and it Emitter Contact results in a diffusion of minority carrier current toward the depleted zone and Emitter recombination in this zone. Recent works 