Akihiro Sumi

Metalorganic chemical vapor deposition of epitaxial perovskite SrIrO3 films on (100)SrTiO3 substrates

(001)c-oriented 60–70-nm-thick SrIrO3 films with a high-pressure-stable perovskite phase were epitaxially grown on (100)SrTiO3 substrates by metalorganic chemical vapor deposition, and the crystal structure and the resistivity of the films were investigated. X-ray diffraction techniques including general θ–2θ scan, the rocking curve and high-resolution reciprocal space mapping, were used to determine crystal quality, lattice constant, and crystal structure of the SrIrO3 films. It was demonstrated that the film crystal structure was tetragonal distorted by strong mechanical constraints due to the in-plane matching with the lattice parameters of SrTiO3 substrates, and maintained almost the same unit cell volume as the reported one for the perovskite cubic SrIrO3 phase. The resistivity of the film at room temperature was 740 µΩ cm, and it decreased with decreasing temperature down to 100 K. Finally, an atomically flat surface was obtained on atomically stepped (100)SrTiO3 substrates.

Metalorganic chemical vapor deposition of atomically flat SrRuO3 films on stepped SrTiO3 substrates

Epitaxial SrRuO3 films with thicknesses of 50–80nm were systematically grown at 750°C on (100)SrTiO3 substrates by metalorganic chemical vapor deposition with different supply rates of the Sr and Ru source gases. Stoichiometric films with a low resistivity of 240–260μΩcm can be grown on polished (100)SrTiO3 substrates over a wide range of source gas supply rates. However, the surface flatness of the deposited film was very sensitive to changes the input source gas supply rate. SrRuO3 films having step and trace structured surfaces were grown on polished and atomically flat SrTiO3 substrates under an optimized input gas supply rate. A height of 7–8nm with a terrace width of 500–1000nm were obtained on polished SrTiO3 substrates, but a single unit cell height of about 0.4nm was obtained with a 200–300nm terrace width on atomically flat SrTiO3 substrates. This opens the possibility of the mass production of atomically flat conductive perovskite layers.

Comparison of electrical properties of (100)∕(001)-oriented epitaxial Pb(Zr0.35,Ti0.65)O3 thin films with the same (001) domain fraction grown on (100)Si and (100)SrTiO3 substrates

Epitaxial tetragonal Pb(Zr0.35Ti0.65)O3 (PZT) films with a (100)∕(001) orientation and one and three in-plane variants were grown, respectively, on (100)cSrRuO3∕∕(100)SrTiO3 and (100)cSrRuO3∕∕(111)Pt∕∕(100)yttria stabilized zirconia (YSZ)∕∕(100)Si substrates by pulsed-metalorganic chemical vapor deposition, and their domain structure and electrical properties were investigated systematically. PZT films with the same volume fraction of c domains were grown on SrTiO3 and Si substrates by controlling the deposition temperature and film thickness. The relative dielectric constants at 1kHz were 370 and 450, respectively, for the films on the SrTiO3 and on the Si, even though both films had the same volume fractions, whereas the dielectric losses were almost the same. The remanent polarization and coercive field at the maximum applied electric field of 350kV∕cm were almost the same for both films, 30μC∕cm2 and 135kV∕cm, respectively. These results suggest that the key factor determining the ferroelectric proper...

“LOCAL EPITAXIAL GROWTH” OF TETRAGONAL (111)-ORIENTED Pb(Zr,Ti)O3 THIN FILM

ABSTRACT Tetragonal Pb(Zr0.35Ti0.65)O3 [PZT] thin films were deposited on (111) c SrRuO3//(111) SrTiO3 nd (111) c SrRuO3//(111)Pt/TiO2/SiO2/(100)Si substrates at 540°C by metalorganic chemical vapor deposition. Surface-normal-(111)-oriented PZT films with in-plane aligned (epitaxial) and in-plane-random oriented (fiber-textured) films were found to be grown on (111) c SrRuO3//(111)SrTiO3 and (111) c SrRuO3/(111) Pt/TiO2/SiO2/(100)Si substrates, respectively, by x-ray diffraction analysis. It was also confirmed by transmission electron microscope that the interface between PZT and SrRuO3 had coherently lattice matched on (111) c SrRuO3/(111)Pt/TiO2/SiO2/(100)Si substrates, and this structure was locally the same with epitaxially grown PZT//SrTiO3 interface. This suggests that the local epitaxial PZT thin films were successfully grown on SrRuO3 covered (111)Pt/TiO2/SiO2/(100)Si substrates. The remanent polarization (P r ) and the squareness of polarization-electric field (P−E) hysteresis loops defined as P r < eqid1 > P sat (P sat is a saturation polarization) were 45 μ C/cm2 and 0.92, respectively at a maximum applied electrical field of 190 kV/cm. These values were almost the same with those of epitaxially grown thin films on (111) c SrRuO3//(111)SrTiO3 substrates, P r and the squareness of P−E loops were respective 44 μ C/cm2 and 0.93 at a maximum applied electrical field of 270 kV/cm. As a result, (111)-oriented fiber-textured PZT thin films having epitaxial grade ferroelectricity were realized on polycrystalline (111)Pt/TiO2/SiO2/(100)Si substrates with conductive SrRuO3 buffer layer.

Low-Temperature Preparation of (111)-oriented Pb(Zr,Ti)O3 Films Using Lattice-Matched (111)SrRuO3/Pt Bottom Electrode by Metal–Organic Chemical Vapor Deposition

Pb(Zr0.35Ti0.65)O3 (PZT) films 170 nm thick were prepared at 415 °C by pulsed metal-organic chemical vapor deposition. The (111)-oriented PZT films with local epitaxial growth were obtained on (111)SrRuO3/(111)Pt/TiO2/SiO2/Si substrates and their ferroelectricities were ascertained. Ferroelectricity was improved by postannealing under O2 gas flow up to 550 °C. Larger remanent polarization and better fatigue endurance were obtained using a SrRuO3 top electrode compared to a Pt top electrode for PZT films after annealing at 500 °C.