INFLUENCE OF CATIONIC STOICHIOMETRY OF LA1-XSRXCOO3 ELECTRODES ON THEFERROELECTRIC PROPERTIES OF LEAD-BASED THIN-FILM MEMORY ELEMENTS

In earlier publications, we have demonstrated that La0.5Sr0.5CoO3 elec trodes dramatically improve the phase stability and electrical propert ies of lead based ferroelectric capacitors. This study evaluates the i nfluence of deviation from the cationic stoichiometry, La/Sr=1, on the ferroelectric properties. Polycrystalline Pb(Nb0.04Zr0.18Ti0.78)O-3 b ased capacitors were fabricated with La0.5Sr0.5CoO3 as the bottom elec trode and either La0.5Sr0.5CoO3 or La0.85Sr0.15CoO3 as the top electro de. The as-grown capacitors with La0.85Sr0.15CoO3 as the top electrode were slightly asymmetric about the voltage axis. However, the asymmet ry did not increase when the capacitors were subjected to single side pulses and temperature. Both capacitor structures showed good fatigue (no fatigue up to 10(11) cycles), retention, and imprint characteristi cs. Detailed pulse width and voltage dependent measurements were also carried out to further understand the impact of the change in electrod e composition. The polarization values at 1 mu s pulse width were as l arge as 13 mu C/cm(2), though the dependence was steeper for capacitor s with asymmetric electrodes. The resistance to switching during polar ization reversal, formally termed activation field, alpha, was measure d from the switching current dependence of the applied field. These va lues were slightly larger for the capacitors with asymmetric electrode s. The data indicate that the ferroelectric properties of the capacito r are almost not influenced by a change of the top electrode from La0. 5Sr0.5CoO3 to La0.85Sr0.15CoO3. (C) 1998 American Institute of Physics . [S0021-8979(98)06803-0].