CHARGE TRAPPING IN RESISTANCE DEGRADED FERROELECTRICS

Thermally stimulated current (TSC) and electron paramagnetic resonance (EPR) spectroscopies have been used to examine the role of defects in BaTiO3 capacitors that have been subjected to an electric field at el evated temperatures (an accelerated aging process). The aging process caused a reduction in the insulation resistance of the ferroelectric c apacitor and induced a voltage offset in its polarization-voltage hyst eresis loop. The TSC measurements following resistance degradation sho w the displacement of positively charged oxygen vacancies and the moti on of bulk trapped charge. It is found that the aging process is accom panied by a significant amount of charge trapping that appears to be l ocally charge compensated. EPR measurements show that some of the trap ped charge is associated with changes in the oxidation state of accept or impurities. Last, it is shown that some of the trapped charge in th e ferroelectric is directly associated with the net polarization.