Study of space radiation effects on semiconductor devices

Abstract

The first Korean satellite, KITSAT-1 launched in 1992 carried out a total dose experiment using RADFETs at 1330 km altitude. Two RADFETs, specially designed p-channel MOSFETs(TOT500) with thick gate oxides, are employed in the experiment and located at different positions inside the spacecraft. The results of the experiment show peculiar oscillating behaviors in the threshold voltage, in addition to the difference in their slopes, which is suspected to be due to the different shielding thickness at the two RADFET positions. The oscillatory behaviors in the threshold voltage of RADFETs are caused by temperature changes and are verified in laboratory experiments using a Co-60 γ-ray source. A model was also developed in which both the radiation and thermal effects are incorporated. The model reproduced remarkably well the results of laboratory experiments as a function of the dose rate and the instantaneous temperature. Nevertheless, the laboratory experiments are generally carried out at high dose rates, while the dose rates for low Earth orbit satellites are usually several orders of magnitude smaller. Hence, the model should be verified against the satellite data for useful space applications, as they are obtained at low dose rates and can suffer many cycles of temperature variations. The shielding thickness is calculated from each of the RADFETs to the outside wall of the spacecraft over the entire 4pi solid angle using the Monte Carlo method. The internal KITSAT-1 structures are taken into consideration in this calculation as well as the epoxy resin of the printed circuit boards by converting the resin layer to the equivalent aluminum thickness. The linear energy transfers of MeV particles in the epoxy resin to that in aluminum are compared using the SRIM code by IBM Research for protons and the Bethe formula for electrons. And then it is found that the ratio is about 0.55 for both protons and electrons, nearly regardless of their energies. NASA``s trapped pa...