Effect of bias on thermally stimulated current (TSC) in irradiated MOS devices

The electric-field dependence of thermally stimulated current (TSC) in irradiated MOS capacitors for TSC fields ranging from -3 MV/cm to +2 MV/cm was studied. TSC measurements at negative bias following positive-bias irradiation provide useful estimates of the net oxide-trap charge, ΔG_ot, if the TSC bias is large enough to overcome trapped-hole space-charge effects. Very little TSC is observed for positive-bias irradiation. Under proper TSC bias conditions, TSC and C-V estimates of ΔG_ot agree well for thick, soft oxides, but differ significantly for thin, hard oxides. Differences between TSC and C-V estimates of ΔG _ot for thin, hard oxides are attributed to electron injection into the oxide and capture at trap sites associated with the radiation-induced trapped holes. It is shown that TSC measurements can provide insight into the location of hole traps in MOS oxides that cannot be obtained from standard C-V tests