Influence of cationic stoichiometry of La1-xSrxCoO3 electrodes on the ferroelectric properties of lead based thin film memory elements

In earlier publications, we have demonstrated that La0.5Sr0.5CoO3 electrodes dramatically improve the phase stability and electrical properties of lead based ferroelectric capacitors. This study evaluates the influence of deviation from the cationic stoichiometry, La/Sr=1, on the ferroelectric properties. Polycrystalline Pb(Nb0.04Zr0.18Ti0.78)O-3 based capacitors were fabricated with La0.5Sr0.5CoO3 as the bottom electrode and either La0.5Sr0.5CoO3 or La0.85Sr0.15CoO3 as the top electrode. The as-grown capacitors with La0.85Sr0.15CoO3 as the top electrode were slightly asymmetric about the voltage axis. However, the asymmetry 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 characteristics. Detailed pulse width and voltage dependent measurements were also carried out to further understand the impact of the change in electrode composition. The polarization values at 1 mu s pulse width were as large as 13 mu C/cm(2), though the dependence was steeper for capacitors with asymmetric electrodes. The resistance to switching during polarization reversal, formally termed activation field, alpha, was measured from the switching current dependence of the applied field. These values were slightly larger for the capacitors with asymmetric electrodes. The data indicate that the ferroelectric properties of the capacitor 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].