The Impact Of Equilibrium Material On The Total Ionization Dose Effect Of Bipolar Devices

With the rapid development of modern space technology and the continuous progress of microelectronics technology and small satellite technology,the size of electronic components used in spacecraft is getting smaller and thinner,and the application of surface-mounted package devices is becoming more and more extensive.It is possible to accurately measure the dose rate of the irradiation position of the devices in the dose field,but the irradiation sensitive region of the devices cannot reach the secondary electron equilibrium when such electronic components were tested in the total dose ionizing irradiation.As a result,the actual absorbed dose in the irradiation-sensitive area of the device is less than the equilibrium dose,the radiation hardness level of the total dose of the device is likely to be overvalued and causes hidden trouble to the normal operation of the spacecraft.Therefore,it is necessary to study the influence of secondary electron non-equilibrium in irradiated sensitive areas of electronic components on the total ionization dose effect of electronic components,and it is of great reference significance for people to evaluate the radiation hardness level of electronic components for aerospace use and the development of radiation resistance reinforcement technology.The main work of this paper and conclusions are as follows:Choose three different models of a bipolar transistor as the research object.Polyethylene was used as the equilibrium material to make the sensitive area of the device meet the secondary electron equilibrium condition.By measuring and comparing the changes of the radiation sensitive electrical parameters of the test device with or without equilibrium materials,the phenomenon that the sensitive area of the device does not reach the secondary electronic equilibrium is judged,and further analysis device sensitive area did not meet secondary electron equilibrium on the degree of impact ionization total dose effect.In addition,Monte Carlo method is used to simulate the actual absorbed dose and the deviation between the absorbed dose and the equilibrium dose of each structure layer of the device,which provides reference for analyzing the impact of secondary electronic non-equilibrium in sensitive region of the device on the total ionization dose effect of the device,and provides suggestions for the use of the equilibrium material in the irradiation test.The degradation law of current gain with total radiation dose of three different bipolar transistors was obtained by ground simulated total dose radiation test of Co source.The results show that the degradation law of current gain of plastic package NPN bipolar transistor MPS2222A and PNP bipolar transistor MPS2907A is the same,and there is no significant difference,while the experimental results of plastic package surface mount package NPN bipolar transistor bc817-16 are quite different.The current gain degradation of devices with equilibrium materials is more obvious than that of devices without equilibrium materials.The relative variation of transistor current gain degradation was 36.69%at 100 krad（Si）and 17.41%at 300 krad（Si）under the two experimental conditions,and the overestimated radiation hardness level of the device gradually decreased with the total dose of cumulative devices.In addition,irradiation experiments were carried out with only the pre-equilibrium material and only the back-equilibrium material.The influence of equilibrium materials on the total ionizing dose effect of devices under these two experimental conditions is discussed.The results shown that the influence of the pre-equilibrium material on the current gain degradation of the device is greater than that of the back-equilibrium material,and the sum of the current gain degradation values of the device under these two test conditions is approximately equal to the current gain degradation values of the devices set the pre-equilibrium material and back-equilibrium material.Finally,Monte Carlo method was used to calculate the actual absorbed dose of each structure layer of the device under four experimental conditions:no equilibrium material was set,the pre-equilibrium material and back-equilibrium material were set at one time,only the pre-equilibrium material was set as the accumulation layer,only the back-equilibrium material was set as the backscattering layer.and the peak of depth dose distribution of⁶⁰Co-γray in silicon was used as the equilibrium dose to calculate the deviation between the actual absorbed dose and the equilibrium dose.The results show that the equilibrium material can effectively achieve secondary electron equilibrium in the sensitive area of the device,and the actual absorbed dose of the device irradiation sensitive area reached 99.34%and 92.60%and 32.49%of the equilibrium dose respectively when the pre-equilibrium material and back-equilibrium material were set at one time,only the pre-equilibrium material was set and only the back-equilibrium material was set.