Top-interface-controlled switching and fatigue endurance of (Pb, La)(Zr,Ti)O3 ferroelectric capacitors

Mechanisms of polarization switching and fatigue in (Pb, La)(Zr, Ti)O-3 (PLZT) films are studied by comparative analysis of degradation and leakage conduction of PLZT capacitors with Pt, SrRuO3 (SRO), and layered Pt/SRO (80/5 nm) electrodes. It is found that the asymmetrical Pt/SRO/PLZT/Pt structure exhibits a good fatigue performance in combination with low leakage like that on identically processed Pt/PLZT/Pt capacitor. This asymmetrical structure exhibits very unusual dependence of the endurance of switching polarization on the driving alternating-current (ac) electric field amplitude. Specifically, for high ac electric field amplitude it shows good switching endurance similar to SRO/PLZT/SRO capacitors, whereas for amplitude lower than 80 kV/cm a pronounced polarization fatigue similar to that of the conventional Pt/PLZT/Pt capacitors is observed. Based on the analysis of our results on fatigue and leakage conduction we conclude that: (i) In asymmetrical Pt/SRO/PLZT/Pt system the physical mechanisms of polarization switching vary depending on the driving voltage amplitude. The polarization switching endurance under high-amplitude cycling is governed only by the top SRO interface, whereas the degradation properties of the bottom Pt interface do not play any role. On the contrary, for driving voltage amplitudes lower than 80 kV/cm the bottom Pt-interface degradation is a limiting factor for the fatigue performance. (ii) The fatigue in PZT films is controlled by a mechanism related to the inhibition of near-by-electrode nucleation of opposite domains, as suggested earlier. (C) 1999 American Institute of Physics. [S0003-6951(99)04623-9].