A first-principles study of oxygen vacancy pinning of domain walls in PbTiO3

We have investigated the interaction of oxygen vacancies and 180-degree domain walls in tetragonal PbTiO3 using density-functional theory. Our calculations indicate that the vacancies do have a lower formation energy in the domain wall than in the bulk, thereby confirming the tendency of these defects to migrate to, and pin, the domain walls. The pinning energies are reported for each of the three possible orientations of the original Ti-O-Ti bonds, and attempts to model the results with simple continuum models are discussed.Comment: 8 pages, with 3 postscript figures embedded. Uses REVTEX and epsf macros. Also available at http://www.physics.rutgers.edu/~dhv/preprints/lh_dw/index.htm

Contribution of electrodes and microstructures to the electrical properties of Pb(Zr0.53Ti0.47)O3 thin film capacitors

Pb(Zr0.53Ti0.47)O3 (PZT) thin film capacitors have been fabricated with four electrode combinations: Pt/PZT/Pt/SiO2Si, RuO2/PZT/Pt/SiO2/Si, RuO2/PZT/RuO2/SiO2/Si, and Pt/PZT/RuO2/SiO2/Si. It is shown that polarization fatigue is determined largely by the electrode type (Pt vs RuO2), and microstructure has only a second-order effect on fatigue. If either the top or bottom electrode is platinum, significant polarization fatigue occurs. Fatigue-free capacitors are obtained only when both electrodes are RuO2. In contrast, the bottom electrode is found to have a major effect on the leakage characteristics of the PZT capacitors, presumably via microstructural modifications. Capacitors with bottom RuO2 electrodes show high leakage currents (J = 10−3-10−5 A/cm2 at 1 V) irrespective of the top electrode material. Capacitors with Pt bottom electrodes have much lower leakage currents (J = 10−8 A/cm2 at 1 V) irrespective of the top electrode material. At low voltage, the I-V curves show ohmic behavior and negligible polarity dependence for all capacitor types. At higher voltages, the leakage current is probably Schottky emission controlled for the capacitors with Pt bottom electrodes

RF magnetron sputter-deposition of La{sub 0.5}CoO{sub 3}//Pt composite electrodes for Pb(Zr,Ti)O{sub 3} thin film capacitors

La{sub 0.5}Sr{sub 0.5}CoO{sub 3} (LSCO) thin films have been deposited using RF magnetron sputter-deposition for use as an electrode material for PZT (PbZrTiO{sub 3}) thin film capacitors. Effect of O{sub 2}:Ar sputter gas ratio during deposition, on LSCO film properties was studied. It was found that the resistivity of the LSCO films deposited at ambient temperature decreases as the O{sub 2}: Ar ratio was increased for both as-deposited and annealed films. It was also found that thin overlayers of LSCO tend to stabilize the underlying Pt//Ti electrode structure during subsequent thermal processing. The LSCO//Pt//Ti composite electrode stack has a low resistivity and provides excellent fatigue performance for PZT capacitors. Furthermore, the LSCO//Pt//Ti electrode sheet resistance does not degrade with annealing temperature and the electrode does not display hillock formation. Possible mechanisms for the stabilization of the Pt//Ti electrode with LSCO overlayers are discussed

La{sub 0.5}Sr{sub 0.5}CoO{sub 3} electrode technology for Pb(Zr, Ti)O{sub 3} thin film nonvolatile memories

Oxide electrode technology is investigated for optimization of Pb(Zr,Ti)O{sub 3} (PZT) thin film capacitor properties for high density nonvolatile memory applications. PZT thin film capacitors with RF sputter deposited La{sub 0.5}Sr{sub 0.5}CoO{sub 3} (LSCO) electrodes have been characterized with respect to the following parameters: initial dielectric hysteresis loop characteristics, fatigue performance, microstructure and imprint behavior. Our studies have determined that the fatigue of PZT capacitors with LSCO electrodes is less sensitive to B site cation ratio and underlying electrode stack technology than with RuO{sub 2} electrodes. Doping PZT thin films with Nb (PNZT) improves imprint behavior of LSCO//PZT//LSCO capacitors considerably. We have demonstrated that PNZT 4/30/70 // LSCO capacitors thermally processed at either 550{degrees}C or 675{degrees}C have almost identical initial hysteresis properties and exhibit essentially no fatigue out to approximately 10{sup 10} cycles

Structure and properties of heteroepitaxial Pb(Zr{sub 0.35}Ti{sub 0.65})O{sub 3}/SrRuO{sub 3} multilayer thin films on SrTiO{sub 3}(100) prepared by MOCVD and RF sputtering

Epitaxial SrRuO{sub 3} thin films were deposited on SrTiO{sub 3}(100) substrates by RF sputtering for use as bottom electrodes and epitaxial buffer layers. On these conductive substrates, epitaxial Pb(Zr{sub 0.35}Ti{sub 0.65})O{sub 3} (PZT) thin films were deposited by metalorganic chemical vapor deposition (MOCVD). X-ray diffraction (XRD), transmission electron microscopy (TEM) and optical waveguiding were used to characterize the phase, refractive index, and film thickness of the deposited films. The epitaxial PZT films were c-axis oriented and contained {approximately}19.7% volume fraction of 90{degrees} domains. Ferroelectric hysteresis and dielectric measurements of epitaxial PZT ferroelectric capacitor structures formed using sputtered ITO top electrodes showed: a remanent polarization of 51.8{mu}C/cm{sup 2}, a coercive field of 54.9 kV/cm, a dielectric constant of 410, a bipolar resistivity of {approximately}5.8x10{sup 9}{Omega}-cm at a field of 275 kV/cm, and a breakdown strength of >400 kV/cm. The cyclic fatigue behavior of the films showed a strong dependence on the choice of electrode materials and the fatiguing wave form. These data support the model that the fatigue mechanism in these films arises from the trapping of injected charge carriers and is predominately an electronic phenomenon