Radiation Effects And Damage Mechanisms Caused By Charged Particles On Bipolar Devices Used For Spacecraft

The degradation caused by protons, electrons, Br ions with various energies and Co-60 ??ray radiation are examined for the domestic NPN transistors (3DG112D, 3DG130D), PNP transistors (3CG130D) and TTL ICs (54LS86), based on the analyse of space environment factors and ground-based simulation experiments. The mechanisms of ionization damage, displacement damage and their synersistic function are investigated. The model of ionization damage for the bipolar transistors is given, and the NIEL (Non-Ionizing Energy Loss) method for displacement damage is improved.Experimental results show that with increasing irradiation fluence, the degradation trends of different bipolar transistor and bipolar ICs are similar, under a given condition for different particles, fluxes and energies. The susceptibility of various bipolar transistors to radiation damage can be assessed by using a given parameter of electric properties (e.g., the current gain). The effect of irradiation flux on the degradation in electric properties of bipolar devices is limited, in the chosen flux range. However, the 1MeV electron exposure with high fluxes aggravates the degradation of some electric property parameters (e.g., the VOH for the 54LS86 device).Based on the analyses of degradation in electric properties due to radiation damage for bipolar transistors and the calculation of ionization and displacement doses per unit fluence of incident particles (designated as Di and Dd, respectively), a parameter of Dd/(Dd+Di) is proposed to evaluate the displacement damage ability of an incident particles. The bigger the ratio of Dd/(Dd+Di), in the sensitive region caused by incident particles, the severer the displacement damage, and thus showing an obvious feature of displacement damage for bipolar devices. The displacement damage caused by various particles can be normalized by using a displacement dose equivalent method based on the NIEL in the sensitive region.It is shown that under the exposure of 70keV and 110keV electrons and 70keV protons, the change in the reciprocal of the current gain of bipolar transistors increases and is gradually saturated with increasing the fluence, the saturation is induced by ionization damage. Under a given fluence, due to their different abilities for ionization damage, the different type particles with various energies would lead to different ionization damage magnitudes. Based on the theoretical calculation and analyses on the electric property degradation, it is indicated that the larger the ionization dose per unit fluence of incident particle, the smaller the ionization damage magnitude for the bipolar transistors.During the exposure of charged particles, it is observed that the influence of bias condition on the ionization and displacement damage is different. If voltage on the base-emitter junction is forward, the exhausted region becomes narrow, resulting in weaker effect of ionization damage on the bipolar transistors. On the contrary, the ionization damage gives stronger effect on the transistors. The diffence in the bias condition gives little contribution to the bulk defects caused by displacement damage. However, when the the base-emitter voltage is forward, the electric charges will be injected into the base region, inducing an annealing effect on the displacement damage.Through the combined irradiation experiments of protons and electrons, it is revealed that the bipolar transistors show a synergistic effect of displacement damage with ionization damage. Under the combined exposure of 170keV protons and 110keV (or 70keV) electrons, the displacement damage dominates the current gain degradation for the transistors, and the ionization gives both annealing and aggravation effect on the displacement damage. The photocurrent induced by ionization damage in Si bulk will passivate a portion of the bulk defects, inducing the annealing effects. Meanwhile, the interface state and oxide charge caused by ionization damage in the Si/SiO2 interface and oxide layer will move the peak of the surface recombination current into Si bulk, leading to more server displacement damage. The trend of degradation of current gain, caused by the synergistic effect of displacement damage with ionization damage, for NPN and PNP transistors is the same.Based on the calculation of space environment parameters, the ground-based simulation experiments and the analyses of radiation effects and mechanisms, a prediction method is given for the electric degradation of bipolar devices in orbit, in which all the contributions can be considered for the ionization and displacement effects induced by different types of charged particles with various energies. This method could be used in practice.