Masayuki Kataoka

Dielectric Properties of (Ba, Sr)TiO3 Thin Films Deposited by RF Sputtering

Thin films of (Ba0.65Sr0.35)TiO3 (BST) have been prepared by an rf-sputtering method at substrate temperatures of 500 to 700°C. The dielectric constant of these films ranges from 190 to 700 at room temperature. This value changes with the grain size rather than the film thickness. The dielectric constant of about 300 and leakage current density of about 1×10-8 A/cm2 are obtained in the 65-nm-thick film deposited at a substrate temperature of 600°C. This shows the BST film can be applied to dielectrics of dynamic random access memory (DRAM) capacitors.

In-plane orientation and coincidence site lattice relation of (001) Bi2Sr2CaCu2Ox formed on (001) MgO

Abstract A (001) Bi 2 Sr 2 CaCu 2 O x thin film fabricated on a (001) MgO substrate has been found to consist of two kinds of domain with in-plane orientation of Bi 2 Sr 2 CaCu 2 O x [100]∥MgO [510] and Bi 2 Sr 2 CaCu 2 O x [100] ∥MgO [5 1 0]. It is shown that near coincidence site lattice theory supports the occurence of this in-plane orientation. The dependence of the in-plane orientation on the substrate temperature was also investigated.

The effect of pulsed laser annealing on wear and corrosion properties of electroless Ni-P plating

Electroless nickel-phosphorous alloy was plated onto quenched and hardened stainless steel. Laser surface treatments by YAG laser beams were carried out with the objective of improving -both the wear and the corrosion resistance of the platings. The friction and wear properties of the laser-treated platings were compared to unplated, untreated plated, and 400°C heat-treated plated substrates in pin-on-disc tests under unlubricated conditions. It was shown that laser treatments gave about a ten percent reduction in the friction coefficient compared with unplated substrates, and that controlled laser-treated plating improved the wear resistance of untreated plating to a level equivalent to 400°C heat-treated plating. It was found that the salt-spray corrosion resistance of the laser-treated platings was much greater than the unplated material and the 400°C heat-treated plating. The laser treatment is capable of improving both wear and corrosion resistance; and the wear resistance is externally governed by t...

(01n)-Oriented BiSrCaCuO Thin Films Formed on CeO2 Buffer Layers

With the use of RF magnetron sputtering, (01n)-oriented BiSrCaCuO superconducting films were first formed using MgO(110) substrates with CeO2(110) buffer layers. The film obtained using the just MgO(110) substrate had (01n)- and (0n)-preferred orientations with the c-axis tilted 45° against the surface of the CeO2 buffer layer. Moreover, with the use of an off-oriented MgO(110) substrate, a uniquely oriented BiSrCaCuO film with the c-axis not perpendicular to the substrate surface was obtained without twin boundaries.

BiSrCaCuO Thin Film Grown on SrTiO3 Substrate with Off-Oriented (110) Surface

A Bi2(Sr, Ca)3Cu2Ox thin film with the (117) orientation was formed on a slightly off-oriented (110) SrTiO3 substrate by single-target sputtering. The (110) substrate off-oriented by 5° is considered to have limited film growth in one direction. From RHEED and cross-sectional TEM observations, it was found that the c-axis of the film tilts against the substrate surface by 46-47° and the SrTiO3(110) plane by 41-42°. Also, the surface morphology observed by SEM has been much improved.

45° grain boundary junctions in (001)-oriented BiSrCaCuO films

In this study, 45°-rotated [001] tilt boundary junctions were fabricated by controlling the in-plane epitaxy using an MgO seed layer grown on an SrTiO3(001) substrate. The in-plane preferential orientation of the BiSrCaCuO film (2223 composition) grown on the MgO seed layer on the SrTiO3(001) substrate of BiSrCaCuO [100], [010]//MgO[100]//SrTiO3[100] was found using X-ray diffraction. The 45°-rotated [001] tilt boundary junction in the BiSrCaCuO film exhibited RSJ-like behavior. With the use of these junctions, a dc SQUID was fabricated and operated at temperatures up to 65 K.

Artificial Grain Boundary Junctions in BiSrCaCuO Thin Films with (11n) and (001) Orientation

Artificial grain boundary junctions in sputtered BiSrCaCuO films on SrTiO3 (110) substrates have been fabricated by controlling the orientation of the films using a MgO buffer layer. A grain boundary with large twist misorientation is formed along the edge of the MgO buffer layer that is placed perpendicular to the [001] direction of the SrTiO3 substrate. The grain boundary junctions thus obtained exhibited clear Shapiro steps in response to microwave irradiation (15.7 GHz). This indicates that the artificial grain boundaries obtained by controlling the orientation of the BiSrCaCuO films behave as a weak link.

Microscopic Study on (11n)-Oriented BiSrCaCuO Films by Cross-Sectional Transmission Electron Microscopy

Microstructures of superconducting BiSrCaCuO films with (11n) orientation grown on SrTiO3(110) substrates by sputtering were first observed by cross-sectional transmission electron microscopy (TEM). Two kinds of films, which have 2212 and 2223 compositions, were studied here. Both films have two preferred orientations with the c-axes almost parallel to the [100] and [010] directions of the SrTiO3 substrate. High-resolution TEM observation of 2223-composition film showed that there is a transient region consisting of a few atomic layers at the interface.

Bi2(Sr, Ca)3Cu2Ox and Bi2(Sr, Ca)4Cu3Ox Thin Films with (11n) Orientation

As-grown Bi2(Sr, Ca)3Cu2Ox and Bi2(Sr, Ca)4Cu3Ox thin films with the (11n) orientation were formed on SrTiO3(110) substrates by consecutive sputtering. RHEED patterns and XRD analysis indicated that the c-axis of the Bi2(Sr, Ca)3 Cu2Ox and Bi2(Sr, Ca)4Cu3Ox films are tilted against the substrate surface by approximately 41° and 45°, respectively. The Bi2(Sr, Ca)3Cu2O3 film was found to have mainly a (117) orientation, whereas the Bi2(Sr, Ca)4Cu3Ox film is considered to have mainly a (1110) orientation.

Dependence of Crystal Orientation of BiSrCaCuO Thin Films on Off-Angles of Vicinal SrTiO3 (110) Surfaces

Crystal orientation of BiSrCaCuO(11n) films depends on off-angles of vicinal SrTiO3(110) surfaces. Surfaces of SrTiO3(110) were cut 2°, 5° and 10° toward the [100] direction, and BiSrCaCuO thin films, which had a 2212 phase, were formed on these vicinal surfaces by RF magnetron sputtering. C-axes almost parallel to the [100] and [010] directions of the substrate were observed when the 2°- and 10°-off substrates were used, but only the c-axis parallel to the [010] was observed when the 5°-off substrate was used. These results suggest that there is an appropriate off-angle to obtain BiSrCaCuO thin films with the c-axis almost parallel to [010] only.