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 elevated temperatures (an accelerated aging process). The aging process caused a reduction in the insulation resistance of the ferroelectric capacitor and induced a voltage offset in its polarizationvoltage hysteresis loop. The TSC measurements following resistance degradation show the displacement of positively charged oxygen vacancies and the motion of bulk trapped charge. It is found that the aging process is accompanied by a significant amount of charge trapping that appears to be locally charge compensated. EPR measurements show that some of the trapped charge is associated with changes in the oxidation state of acceptor impurities. Last, it is shown that some of the trapped charge in the ferroelectric is directly associated with the net polarization.