Radiation Damage Effects And Deep Level Defects In Bipolar Junction Transistor

The degradation caused by electrons, protons, heavy ions with various energiesand Co-60source radiation is examined for the bipolar junction transistors, basedon analysis of the space radiation environment and ground-based simulationexperiments. Based on the research of radiation effects and electrical degradation,deep level transient spectra (DLTS) and annealing effects on BJTs, the mechanismsof synergistic effects between ionization and displacement damage are revealed.The model of ionization and displacement damage for the bipolar transistors isgiven.Experimental results show that with increasing irradiation fluence, thedegradation trends of NPN and PNP bipolar transistors are similar, under a givencondition for different particles, fluxes and energies. For ionizing radiation damage,the degradation of bipolar transistor shows a saturated trend with increasing fluence.Based on the DLTS results, there are the DLTS signals in the base collector junctionof a transistor induced by ionizing radiation. The majority carrier trap defect isfound in the base collector junction of the NPN transistor, while the minority carriertrap defects are measured in the base collector junction of PNP transistor inducedby gamma rays and110keV electrons. However, for displacement and synergisticradiation damage, the degradation of bipolar transistor has no saturated trend. Thedeep level defect in transistor induced by displacement radiation mainly is majoritycarrier trap defect. Based on the mechanism of ionizing damage, the function of theexcess base current and the simple model of current gain degradation in bipolartransistor are built, while the model and the experimental data match well.The results of various heavy ions radiation experiments show that the electricaldegradation and concentration of defects induced by various heavy ions aredifferent. The particle with small range can produce more clusters and more deeplevel defects, induce more degradation of electrical parameters. The particles withlong range can produce fewer vacancies and interstice atom, and less deep leveldefects, induce less degradation of electrical parameters. Considering theinhomogeneity of the displacement dose in the base region of a bipolar transistorand the impact of ionizing radiation, the equivalence of damage induced by variousdisplacement sources is built, while the model and the experimental data match well.Based on the experimental results of20MeV Br ions and110keV electronssequence irradiations, the current gain of the transistor irradiated by low energy electrons after heavy ions irradiation, recovers slowly at lower fluence andcontinues degrading at higher fluence. Based on the DLTS results, the ionizingdamage can recover a part of displacement defects, which make the current gainrecovery at lower electron fluence. However, the defects induced by radiationdamage increase with the increasing electron fluence, the current gain of transistorcontinue degrading.During the sequence exposure of electrons and protons under various biascases, it is observed that the radiation damage in transistor with emitter-basejunction zero bias case is biggest, and the radiation damage under reverse bias caseis smaller, the radiation damage under forward bias case is smallest. The impact ofbias case on synergistic radiation damage is similar as the impact of bias case ondisplacement damage. Based on the combined radiation of heavy ions or lowerenergy protons and electrons, it is clear that the ionization damage could giveannealing and enhancement effect to displacement damage in bipolar junctiontransistors.In isochronal annealing experiment, the electrical parameters of bipolartransistors recovered with increasing annealing temperature. For various radiationdamages, the electrical parameters of bipolar transistors totally recovered, when theannealing temperature is up to700K. The concentration of the defects induced byionizing radiation damage goes down with the increasing temperature. Fordisplacement damage, the deeper energy level defects decrease and the shallowerenergy level defects with the increasing annealing temperature, when thetemperature is below550K. Meanwhile, all of the defects decrease with theincreasing annealing temperature, when the temperature is above550K.