Takeshi Tai

Preparation and Characterization of Ba(ZrxTi1-x)O3 Thin Films Using Reactive Sputtering Method

Ba(ZrxTi1-x)O3 (BZT) thin films with different Zr contents were deposited on (100) MgO and (100) Pt/(100) MgO substrates by RF-magnetron reactive sputtering using metal targets. The BZT (0 < x < 0.89) thin films had a single perovskite phase with only (001)/(100) orientation. In all cases, the ratio of Ba/Ti was stoichiometric according to X-ray fluorescence spectrometry (WDX) measurement. Atomic force microscopy (AFM) study proved that BZT films possess a dense microstructure without cracks or voids. The grain size was found to decrease with increasing of Zr content. The effect of Zr content on the dielectric constant and leakage current was studied. BZT thin films showed ferroelectric-to-paraelectric properties with increasing Zr content and excellent leakage properties according to measurements of electrical properties. These results indicated that we succeeded in depositing high-quality and low-sputter-damage BZT thin films by reactive sputtering using metal targets.

EVALUATION OF RELATIVE VOLUME FRACTION OF TETRAGONAL PHASE AND RHOMBOHEDRAL PHASE IN Pb(Zr,Ti)O3 FILM BY RAMAN SPECTROSCOPY

ABSTRACT Volume fractions of tetragonal phase (V T) in the epitaxial Pb(Zr,Ti)O3 (PZT) thick films were evaluated using micro-Raman spectroscopy. The crystal structure was the single phase of tetragonal and rhombohedral when Zr/(Zr+Ti) ratio was under 0.43 and over 0.6, respectively. There was the two phases coexistence between 0.43 and 0.6 of Zr/(Zr+Ti) ratio. It was found that the dominant crystal phase change from tetragonal to rhombohedral one with increasing the Zr/(Zr+Ti) ratio. However, crystal symmetry was not uniform; V T was found to gradually change along film thickness direction from near the substrate to the film surface.

Growth and evaluation of epitaxial BaTiO3 thin films of less than 100 nm thickness by metal–organic chemical vapor deposition

Epitaxial BaTiO3 (BTO) thin films of less than 100 nm thickness were grown on Pt(001)/MgO(001) substrates at growth temperatures of 500?700 ?C with a low deposition rate of about 25 nm/h by metal?organic chemical vapor deposition (MOCVD). The BaTiO3 thin films were epitaxialy grown with (001) orientation. These films show quadrangular grains and a dense cross-sectional structure. The relative permittivities of these films grown at 500, 600, and 700 ?C with thicknesses of 62, 65, and 82 nm were 338, 455, and 566 at 1 kHz, respectively. These relative permittivities were higher than those of BTO films prepared by other methods and BTO ceramics with thicknesses less than 100 nm.

In-situ Raman Spectroscopic Investigation of the Effect of Cooling Speed on Domain Formation in PbTiO3 Films

The influence of the post-deposition cooling speed on the domain formation process of PbTiO3 films was investigated using MOCVD equipment combined with in-situ Raman spectroscopy. The accumulation and relaxation of strain during the post-deposition cooling process is responsible for the domain structure. The Curie temperature for fast cooling is lower than that for slow cooling. Additionally, the residual strain with fast cooling is smaller than that with slow cooling. These observations suggest that the volume fraction of the c-domain is larger for fast cooling and that the atmospheric conditions during the first post-deposition cooling process may control the domain structure.

Identification of the occupation site of Dy- or Y-substituted PZT films and the correlation between occupation site and ferroelectric property

The occupation sites of Dy- or Y-substituted PZT films were identified using Raman spectroscopy, and the correlation between the occupation site and ferroelectric property was investigated. When Dy or Y was less than 2%, the ferroelectric properties improved because substitution occurred at the B-sites of the PZT films. However, the ferroelectric properties decreased when the substituted ions exceeded 4% because substitution occurred at both B- and A-sites. Consequently, it is important to accurately introduce substituted ions into the B-sites in a PZT film to improve the ferroelectric properties.

Structural Investigation of Highly Polarized Single-c-Domain thin Films Grown by Magnetron Sputtering with Raman Spectroscopy

Single-c-domain/single-crystal PZT thin films grown by rf magnetron sputtering on SrRuO3/Pt/MgO substrates was investigated by Raman spectroscopy. The Raman spectroscopy measurement revealed that the sputter deposited thin film has high quality and highly c domain oriented. In addition, Raman spectroscopy revealed the local strain configuration in the sputtered thin films from the surface to the substrates. These local stresses were discussed with dielectric property.

Investigation of Sputtering Damage in SrRuO3 Films Prepared by Sputtering with Raman and X-ray Photoemission Spectroscopies

Sputtering damage of SrRuO3 (SRO) films prepared by RF magnetron sputtering under various growth pressures was investigated by Raman spectroscopy and X-ray photoemission spectroscopy (XPS). Phonon modes that were related to Ru and Sr ions changed and XPS spectra shifted with decreasing growth pressure. These results indicate that Sr ions switched place with Ru ions in SRO films when the SRO films had sputtering damage under low-growth-pressure sputtering condition as determined from Raman spectroscopy and XPS measurement. The antisite ion content increased with decreasing growth pressure. The resistivity of the SRO films also increased with increasing antisite ion content. The dynamics of sputtering damage revealed that the antisite Sr and Ru ions were formed in SRO films.

Rapid and high sensitive structure evaluation of ferroelectric films using micro-Raman spectroscopy: In-situ observation of stress accumulation and release in PbTiO3 films during first cooling process

Stress changes of the (100)/(001)-oriented PbTiO3 (PT) films deposited on MgO(100), Pt(100)/MgO(100) and Pt(111)/Ti/SiO2/Si(100) substrates under the cooling process after film deposition was investigated by in-situ observation using metal organic chemical vapor deposition (MOCVD)-Raman spectroscopy combined system. The stress changed from compressive to tensile near Tc and large compressive stress made high c-domain volume fraction. It was made clear that the stress condition at Tc affects the c-domain volume fraction at room temperature (R.T.). These results indicate that in-situ Raman spectroscopy measurement is useful tool for monitoring the stress state under the cooling process.