Constant-current study of dielectric breakdown of Pb(Zr,Ti)O-3 ferroelectric film capacitors

This paper addresses the problem of time-dependent dielectric breakdown of Pb(Zr,Ti)O-3 (PZT) thin films. It is shown by using constant-current breakdown measurements, that for PZT film capacitors with Pt and SrRuO3 (SRO) electrodes the breakdown onset is controlled by charge to breakdown (Q(BR)) rather than the voltage applied to the capacitor. The QBR value for the asymmetrical Pt/SrRuO3/PZT/Pt capacitors is found to be much higher that for the Pt/PZT/Pt system. Polarization fatigue caused by bipolar voltage stress provokes a substantial decrease in charge to breakdown. These results can be interpreted in terms of percolation model used for breakdown in SiO2, where the QBR is associated with injected-carrier-assisted creation of the critical concentration of defects required for formation of the breakdown paths. The observed variation of the QBR values depending on the electrode material (i) and polarization fatigue (ii) are interpreted in terms of current redistribution across the area of the capacitor, specifically current redistribution between grains and grain boundaries (case (i)) or current redistribution between fatigued and nonfatigued areas (case(ii)).