A Study on the Estimation of RIC (Radiation-Induced Conductivity) of Proton Irradiated Polyimide

The recent expansion of the application environment of power electronics to high-radiation environments will cause the deterioration of insulation materials used in power electronics due to charging caused by cosmic ray irradiation. The charging phenomena should induce malfunctions in power electronics. Therefore, it is important to understand the insulation characteristics of insulation materials irradiated with protons, electrons, etc., to improve the reliability of power electronics. With respect to the above, there are few reports on the RIC (radiation-induced conductivity) of insulation materials irradiated with proton beams. In this paper, we experimentally evaluated the RIC of PI (polyimide) films irradiated with proton beams under various irradiation conditions. We also studied a calculation method to estimate the measured RIC of the PI. As a result, we clarified that the total conductivity of the PI increased under non-penetrating irradiation conditions and saturated under penetrating irradiation conditions. The reason for this is that the higher the irradiation energy, the deeper the maximum proton penetration depth under non-penetrating irradiation conditions. On the other hand, the conductivity characteristics did not change under penetrating conditions because the penetration depth was the same as the sample thickness. We also developed a calculation method to estimate the conductivity of the entire PI irradiated with proton beams. The estimated data calculated by the above method were analytically fitted with the measured data for most irradiation energy conditions. It is suggested that the above calculation method can estimate the conductivity of the entire PI irradiated with proton beams, regardless of penetrating or non-penetrating irradiation, based on the relationship between the RIC and dose rate of the PI irradiated under penetrating conditions. In the future, we will incorporate the results of this study into a computational model of space charge accumulation inside insulation materials to verify the influence of the RIC caused by proton irradiation on space charge accumulation.