Charge injection and polarization fatigue in ferroelectric thin films

Abstract

Typical experimental data of polarization fatigue in Pb(Zr,Ti)O3 thin films have been presented: (1) The coercive voltage Vc and the shape of the polarization-electric (P-E) hysteresis loop unnecessarily change with the number N of fatigue cycles except the remanent polarization; (2) the capacitance at voltages close to Vc decreases monotonically with increased N, in comparison with its enhancement at voltages far away from Vc; (3) electrode damage occurs after the appearance of the amount of pinned domain walls; and (4) domain-wall pinning and depinning coexist during fatigue cycling. All phenomena mentioned above are interpreted in terms of charge injection into regions with the inhomogeneities of dielectric constant, conductivity, and polarization, especially near film-electrode interfaces. Pinning and depinning coefficients of domain walls are extracted from fatigue profiles and found to be useful in the prediction of charge injection depending on the fatigue voltage and frequency. Domain-wall motion impeded by screening carriers within film thickness is suggested during fatigue through the mimic of two in-series ferroelectric capacitors with different polarizations.