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Characteristic Change Due to Polarization Fatigue of Sol-Gel Ferroelectric Pb(Zr0.4Ti0.6)O3 Thin-Film Capacitors

We studied the fatigue characteristics of sol-gel ferroelectric Pb(Zr0.4Ti0.6)O3 (PZT) thin-film capacitors measuring hysteresis loops, time-zero current voltage characteristics and the dielectric constant after polarization switching. All evaluations were carried out on samples with certain switching cycles at the slow fatigue stage, logarithmic fatigue stage and saturated stage. Oxygen-deficient regions at the interfaces at both the top and bottom electrodes were formed after fatigue, as found by observing Auger electron spectroscopy (AES) depth profiles. Time-zero current-voltage (I-V) characteristics show that ohmic leakage current increased as the switching cycles increased during fatigue. This indicates that oxygen vacancies as donors arising during fatigue may compensate the lead vacancies as acceptors. The electric field dependence of Pr+-Pr- and that of the dielectric constant show that the motion of domains, which can move in the electric field near a coercive field, is suppressed after fatigue. We conclude that the oxygen vacancies suppress the domain motion and cause remanent polarization degradation. Since the biased-dielectric constant beyond 150 kV/cm showed no significant change after fatigue, it seems that no low-dielectric-constant regions adjacent to the electrode were generated during fatigue.