The mobile ion area density of MOS capacitors

before and after irradiation with different doses and bias

has been examined using the triangular voltage sweep technique. It is found that after irradiation the mobile ion area density is reduced for MOS capacitors oxidized both with dry oxygen and TCE and with dry oxygen only. The reductions of the density are compared among the samples under irradiation but with positive

negative and zero bias respectively. At zero bias the density steadily decreases with the increasing irradiation dose

but at positive bias it is nearly invariable when dose is increased to over 1 × 103Gy（Si）. Small increment of the density is found when increasing the times of TVS measurement at high temperature. The experimental results are qualitatively explained.