Polarization-induced trapped charge in ferroelectrics

We have examined the nature of the defects in BaTiO3 capacitors that have been subjected to an electric field at elevated temperatures (an accelerated aging process) using thermally stimulated current (TSC) and electron paramagnetic resonance measurements. The accelerated aging stress causes the ferroelectric capacitor to exhibit a reduction in its insulating resistance and a voltage offset in its polarization-voltage hysteresis loop. Following the accelerated aging treatment, the trapped charge estimates obtained from the TSC and the hysteresis measurements (as ascertained from the voltage offset) differ significantly and are attributed to either local charge compensation or uniform charge trapping within the dielectric. We also show that some of the trapped charge in ferroelectric materials is directly associated with the net polarization.