Study On Neutron/Gamma Irradiation Effect Of Bipolar Transistor

This article takes bipolar transistors as the research object,makes full use of the excellent irradiation facilities and precise parameter test conditions of the relying unit,constructs effective research methods,and carries out a series of neutron irradiation experiments and gamma ray irradiation experiments.The experimental data of neutron and gamma irradiation effects are obtained for the bipolar transistors of N1?N5 and P1?P2 types,which can guide the study of the damage law and mechanism of neutron and gamma irradiation effects.In this study,we obtained abundant data on the neutron/gamma synergistic radiation effect of bipolar transistors,and explored the macroscopic electrical performance change laws and microscopic physical evolution mechanisms of the bipolar transistors'ionization effect,displacement effect,and ionization/displacement combined effect.This study reveals the radiation damage mechanism of neutrons and gamma rays to bipolar transistors,which plays a very good supporting role in the in-depth study of the synergistic mechanism.This study provides a reference for the analysis of radiation hardening for the radiation damage of bipolar devices in aerospace and nuclear energy applications.Taking the relative change of current gain before and after irradiation of model A NPN bipolar transistor when the emission junction voltage VBE=0.65V as an example,the experimental results show that after 1000Gy(Si),3000Gy(Si),6000Gy(Si),9000Gy(Si),15000Gy(Si)gamma-ray irradiation,the percentages of the difference between the current gain after irradiation and the current gain before irradiation in the current gain before irradiation are:29.3%,44.7%,55.0%,58.4%,62.6%,respectively.The bipolar transistor ionization effect causes the bipolar transistor current gain to degrade.And with the increase of the total dose,the degradation degree of the current gain of the bipolar transistor gradually deepens and tends to saturation.The changes of collector current IC and base current IB under different total dose conditions are analyzed,and it is found that with the increase of total dose,collector current IC is basically unchanged,and base current IB is significantly increased.The curve of excess base current(the increment of base current before and after irradiation)with emitter voltage shows that with the increase of total dose,the density of trapped charge and interface state of oxide layer increase,and the increase rate decreases.For NPN bipolar transistors,the accumulation of charge trapped in the oxide layer induced by total dose radiation will cause the space charge region to expand toward the base region,resulting in a larger surface area of the depletion region.The positive trapped charge in the oxide layer and the interface state generated at the Si/SiO2 interface act on the space charge region on the surface of the emitter junction,resulting in an increase in the surface recombination current,an excess base current ?IB increases,and a base current IB,eventually leading to the common emitter of the bipolar transistor gain hFE decreased.For PNP bipolar transistors,the total dose effect leads to the decrease of gain hFE,which is mainly caused by the increase of the density of the interface state surface and the rise on the base current IB.Experimental results of neutron irradiation of bipolar transistors show that after irradiation with different cumulative neutrons,the reciprocal of the current gain of the bipolar transistor decreases approximately linearly with the increase of the cumulative fluence,indicating that the displacement damage and cumulative neutrons of the bipolar transistor There is a linear relationship between fluences.The degradation of the current gain of the bipolar transistor after being irradiated with neutrons is mainly caused by the increase of the base current.According to the analysis of the excess base current curve,neutron irradiation leads to an increase in the recombination rate in the space charge region of the emitter junction,not just in the oxide layer.This will introduce defects in the silicon substrate.These defects will cause the lifetime of minority carriers to decrease,causing the base current to increase and the current gain to deteriorate,thereby degrading the performance of the bipolar transistor.Through the experiments of different order neutron and gamma ray irradiation,the ionizing/displacement synergistic effects of the bipolar transistors is simulated,and the macroscopic electrical change law and microscopic physical mechanism of the integrated radiation effect of ionization and displacement of bipolar transistors are explored.For the selected bipolar transistors,the experimental results show that the damage caused by the ionization/displacement combined radiation effect is not equal to the simple sum of the two effects,but the former is smaller than the latter.Both NPN bipolar transistors and PNP bipolar transistors are irradiated by different orders of neutrons and gamma rays,and the experimental results show that the radiation damage of neutrons before gamma rays is greater than that of neutrons after gamma rays.This phenomenon is especially obvious in PNP bipolar transistors.In terms of the mechanism of ionization effect and displacement effect of bipolar transistors,the evolution mechanism of micro defects is analyzed.It is believed that 60Co gamma ray will introduce defects into the silicon base of bipolar transistors,which will lead to the "annealing" of displacement defects that have been produced by neutron irradiation,and have a certain "aggravating" effect on the displacement defects produced by subsequent neutron irradiation.