Research On The Evolution And Physical Models Of Ionization Defects In Bipolars

The rules and characteristics of ionization defects’ revolution are studied by irradiaiton experiment and model calculation.To fully obtain ionizaiton defects in bipolars,60Co-gamma ray is used as irradiation source.In order to study the evolution characteristics and laws of ionization defects,the electric field conditions at the time of irradiation and the initial defect state of the device are regulated.Based on the gate-controlled bipolar transistor,the radiation damages’ law and the defects’ evolution behavior of the bipolar transistor under different conditions are studied.In order to study the radiation damage characteristics of the transistor in different states,the main adopted treatment measures before and after irradiation include different irradiation dose rate,different electric field conditions and pre-irradiation high temperature pretreatment.The results show that the lower the irradiation dose rate,the greater the damage caused by the same absorbed dose conditions,the higher the oxide charge and the interfacial concentration.That is,the gate-controlled bipolar transistor has obvious low dose rate radiation damage enhancement effect.Under the same irradiation environment,the device performance degradation is the most serious when the device gate oxygen is in the positive bias field,and the degree of damage under the negative bias condition is the smallest.The radiation damage of the device subjected to high temperature pretreatment is exacerbated by the high temperature pretreatment device without irradiation.In order to reveal the damage mechanism of the above test results,this paper establishes a physical model of defect evolution to carry out numerical simulation analysis.In the model,the Poisson equation and the continuity equation are used to calculate the electrostatic potential and the carrier concentration.Then,based on the influence of electric field and pre-irradiation heat treatment,the interaction model of free carrier(electron,hole)and different types of defects(trapping defects and recombination centers)is established to describe the evolution of defects.Finally,the defect evolution behavior at different dose rates was analyzed by this model.It was found that the concentration of interface traps decreased with the increase of dose rate,while the oxide traps and recombination heart concentration increased with the dose rate.The oxide traps and interface state had the highest concentration in the forward electric field,,The reverse bias when the smallest.However,the state of the composite defect is the opposite of the state of the hole.The influence of the initial defect concentration on the radiation-induced oxide charge and the interface traps was studied.It was found that the trapped defect concentration had a great influence on the interface state and the oxide traps.The larger the concentration of the traps,the larger the interface state and the oxide charge concentration,and the complex defect concentration has no obvious effect on the interface state and the oxide charge.However,recombination centers can affect the recombination of free carriers in the oxide layer.The higher the recombination centers concentration,the more serious the carriers’ recombination occurs.With comprehensive analysis of the results of the irradiation test and the model calculation,it is found that the laws of the defect physical model established in this paper are consistent with the results of the irradiation test.The physical model established in this paper can reveal the influence mechanism of different dose rate,pre-irradiation high temperature pretreatment and irradiation process on the evolution of radiation induced defects.The defect evolution model can fully describe and predict the generation and evolution of ionizing radiation induced defects.