Polar phonons in some compressively stressed epitaxial and polycrystalline SrTiO3 thin films

Several SrTiO3 (STO) thin films without electrodes processed by pulsed laser deposition, of thicknesses down to 40 nm, were studied using infrared transmission and reflection spectroscopy. The complex dielectric responses of polar phonon modes, particularly ferroelectric soft mode, in the films were determined quantitatively. The compressed epitaxial STO films on (100) La0.18Sr0.82Al0.59-Ta0.41O3 substrates (strain 0.9%) show strongly stiffened phonon responses, whereas the soft mode in polycrystalline film on (0001) sapphire substrate shows a strong broadening due to grain boundaries and/or other inhomogeneities and defects. The stiffened soft mode is responsible for a much lower static permittivity in the plane of the compressed film than in the bulk samples.Comment: 11 page

Ferroelektrische Eigenschaften von Kondensatoren mit epitaktischen BaTiO3-Dünnschichten

Abstract Epitaxial BaTiO3 films are interesting for the integration into microelectronics due to the ferroelectric properties and high permittivity. In this work epitaxial BaTiO3 thin-films were grown on conductive layers, SrRuO3 und La2/3Ca1/3MnO3, by pulsed laser deposition. The growth on different single crystalline substrates resulted in BaTiO3 films with high structural perfection and c-axis orientation. An effect of the substrate due to different misfit strain was not observed. For the electrical characterization of the BaTiO3 films in a thin film capacitor structure, Pt top electrodes were deposited by e-beam evaporation. The influence of the BaTiO3 film thickness (100 - 400nm) on the polarization (size effect) was studied. Surprisingly the thinner films show a higher spontaneous polarization. Moreover, the coercive voltage of the films is independent of the film thickness. A correlation between the spontaneous polarization and the misfit strain was not observed. The ferroelectric behavior of the BaTiO3 capacitors was explained qualitatively by a model using an interfacial layer between the bottom electrode and the BaTiO3

Ferroelectric properties of epitaxial BaTiO3 thin films and heterostructures on different substrates

Ferroelectric thin films of BaTiO3 and BaTiO3/SrRuO3 epitaxial heterostructures on different single-crystalline substrates were fabricated by pulsed laser deposition. The BaTiO3 films of 100-400 nm thickness show high structural perfection and c-axis-oriented growth. For the electrical characterization of the BaTiO3 in a thin-film capacitor structure, Pt top electrodes were deposited by e-beam evaporation. The results are compared to the current experimental and theoretical models. Special consideration is given to the model of charge injection from the electrodes

Ferroelektrische Eigenschaften von Kondensatoren mit epitaktischen BaTiO3-Dünnschichten

Abstract Epitaxial BaTiO3 films are interesting for the integration into microelectronics due to the ferroelectric properties and high permittivity. In this work epitaxial BaTiO3 thin-films were grown on conductive layers, SrRuO3 und La2/3Ca1/3MnO3, by pulsed laser deposition. The growth on different single crystalline substrates resulted in BaTiO3 films with high structural perfection and c-axis orientation. An effect of the substrate due to different misfit strain was not observed. For the electrical characterization of the BaTiO3 films in a thin film capacitor structure, Pt top electrodes were deposited by e-beam evaporation. The influence of the BaTiO3 film thickness (100 - 400nm) on the polarization (size effect) was studied. Surprisingly the thinner films show a higher spontaneous polarization. Moreover, the coercive voltage of the films is independent of the film thickness. A correlation between the spontaneous polarization and the misfit strain was not observed. The ferroelectric behavior of the BaTiO3 capacitors was explained qualitatively by a model using an interfacial layer between the bottom electrode and the BaTiO3

Structural and optical properties of epitaxial BaTiO3 thin films grown on GdScO3(110).

We have prepared 1-mum-thick epitaxial BaTiO3 thin films on GdScO3(110) using pulsed laser deposition. The structural perfection of the films was revealed by a rocking curve width of Deltaomega=0.13degrees for the 002 BaTiO3 reflection and a Rutherford backscattering spectrometry/channeling minimum yield, chi(min), of 0.5% measured for the Ba signal behind the surface peak. High-resolution transmission electron microscopy revealed an epitaxial relationship between BaTiO3 and GdScO3 and a sharp interface between the substrate and the film. The refractive index of the BaTiO3 film was n(o)=2.329+/-0.002 and n(e)=2.307+/-0.002 at a wavelength of 632.8 nm and n(o)=2.248+/-0.002 and n(e)=2.228+/-0.002 at a wavelength of 1523 nm. The optical losses were less than 2 dB/cm at a wavelength of 632.8 nm. (C) 2003 American Institute of Physics

Integrated optical Mach-Zehnder modulator based on polycrystalline BaTiO3

Good-quality polycrystalline BaTiO3 thin films are deposited on MgO substrates by pulsed laser deposition. The deposition parameters are optimized to achieve optical-quality films with an attenuation coefficient of 4 dB/cm at the 633-nm wavelength. Thin-film electro-optic Mach-Zehnder modulators are fabricated with standard lithography and ion-beam etching. The waveguides patterned by lithography are the ridge type, and they ensure single-mode propagation in the wavelength range of 633 - 1550 nm. An electro-optic coefficient of 22 pm/V is estimated for the polycrystalline BaTiO3 films. (C) 2003 Optical Society of America