Seishiro Ohya

Water glass bonding for micro-total analysis system

We used water glass solution for bonding two glass wafers on which electrodes and a micro-channel were fabricated. This bonding technique makes possible to bond two glass wafers without concerning the problem of surface roughness. We evaluated many properties of the water glass bonding for using micro-chemical analysis, such as, effect of bond temperature on bond strength, thickness of bonding layer dependence on applied pressure during bonding, and so on. Because of high content rate of sodium in water glass, we evaluated cleaning effect to decrease sodium dissolution from bonding layer. Additionally, we studied the effect of the pH of solutions on bond strength. By using this technology, we made a micro-electrochemical chip as one of applications and identified an oxygen evolution current without break down of the chip. We show this bonding technique is very useful to make a micro-chip.

Growth of β-FeSi2 Thin Film on Si (111) by Metal-Organic Chemical Vapor Deposition

We succeeded for the first time in preparing a high-quality (101)-oriented epitaxial β-FeSi2 film on Si(111) wafer by metal-organic chemical vapor deposition (MOCVD) using Fe(CO)5 and SiH4 as source materials. The full width at half maximum (FWHM) of the rocking curve of the β-FeSi2 (202) peak was 0.46 degree for the film deposited at 750°C at a rate of 4 nm/min. Moreover, a smooth-surface film of up to 650 nm thickness could be deposited by this method. Carbon content in the film was less than 0.1 at%.

Preparation of BiSrCaCuO Multilayers by Use of Slower Q-switched 266 nm YAG Laser

Multilayers of Bi2Sr2Ca1Cu2Ox/Bi2Sr2Cu1Ox were prepared by pulsed laser deposition (PLD) using the fourth harmonic 266 nm YAG. Compared to an excimer laser, YAG PLD required the higher oxygen atmosphere. The higher oxygen pressure together with the lower energy generated by YAG laser collapsed the region of plume emission. In order to produce the same energy density as an excimer, only Q-switch was modulated by 2 Hz while the flash lamp kept the original repetition rate of 10 Hz. With the rate of 2 Hz, we obtained the higher energy density per pulse, and more stable laser output of the fourth harmonics, 266 nm. To characterize the multilayers, reflection high-energy electron diffraction (RHEED) and X-ray diffraction (XRD) were employed, and indicative of epitaxial layers with limited in-plane order. The resistivities of multilayers were measured by the Van der Pauw method, and showed the temperatures of superconducting transition, Tc0 (R=0), around 65 K on the multilayers.

Characterization of a microfluidic device fabricated using a photosensitive sheet

We investigated the characteristics of microfluidic devices fabricated using photosensitive sheets adhered to substrates. We evaluated them in regard to practical criteria, namely chemical resistance, pressure sealing, electrical resistance and elution of ions. No samples exhibited peeling after postbaking when we investigated the adhesion characteristics by dicing. The sheet swelled dramatically on exposure to an alkaline solution. The microfluidic devices consisting of photosensitive sheet sandwiched by two Pyrex substrates and a photosensitive sheet sandwiched by two PMMA substrates had a pressure sealing of 0.6 MPa, were capable of withstanding a pressure of 0.2 MPa for 1 h when ultrapure water was injected. The sheets had a high volume resistivity (9.7 ? 1012 ? cm) and a high surface resistivity (2.3 ? 1011 ?) after postbaking. Sodium ions were adsorbed onto the photosensitive sheet and then gradually desorbed. The total amount of sodium ion elution per unit area over 24 h was 8.3 ? 10?9 mol mm?2 as measured by ion exchange chromatography. These results confirm that microfluidic devices fabricated using photosensitive sheets are suitable for use as disposable devices for certain applications.

Structural modulation on multilayered bismuth cuprate observed by x-ray reciprocal space mapping

Epitaxial Bi2Sr2Ca1Cu2Ox(Bi-2212)∕Bi2Sr2Cu1Ox(Bi-2201) multilayer was investigated by x-ray diffraction methods in order to investigate the effect of internal strain on structural modulation. In multilayered structure, the effect of internal strain is more prominent than in an aliovalent substitution, such as a substitution of La3+ for Sr2+. X-ray reciprocal space mapping (XRSM) was taken on the ω-2θ plane (cross-section XRSM) in order to estimate the lattice constants along the in-plane and out-of-plane directions, and θ-2θ scan was used to verify the multilayered structure. Another XRSM method, plan-view XRSM, was employed to verify the in-plane symmetry of structural modulation on the ω-ψ plane. The structural modulation was observed on both the cross-section and plan-view XRSM. The lattice constants together with the modulation vector in multilayer were varied by the multilayer periods without any substitution in the original structure.

Modulation derived satellite peaks in x-ray reciprocal mapping on bismuth cuprate superconductor film

X-ray reciprocal space mapping (XRSM) was employed to investigate epitaxial Bi2Sr2Ca1Cu2Ox(Bi-2212) film. Ordinal cross section XRSM (ω-2θ) and plan view XRSM (ω-ψ) clearly indicated asymmetric intensity distribution of four satellite peaks caused by supercell structure of Bi-2212 film. Modulation vector estimated by XRSM was q=0.2b*+0.9c*. The XRSM image simulated by sawtooth wave vector showed good agreement with asymmetric satellite peaks observed on epitaxial film.

Application of Microchip Fabricated of Photosensitive Glass for Thermal Lens Microscopy

Conventional wet chemical processes have not been successful in achieving a high aspect ratio channel on glass wafers because of isotropic etching of glass by hydrogen fluoride (HF). We fabricated a microchip of photosensitive glass in order to obtain a high aspect ratio channel (width:depth:aspect ratio = 150 µm:250 µm:1.67). The water glass bonding technique was applied to bond glass wafers at low temperature (40–80°C). The results of studying the characteristics of the water glass bonding technique for the micro total analysis system (µ-TAS) use show that dissolution of the material (sodium) from water glass layer was avoided by placing it in deionized water at 60°C for 4 h, and the bond strength was weakened by keeping it at high pH for a day. The microchip was available to analyze the amount of nitrite acid present by thermal lens microscopy as one method of optical chemical analysis. Although the etched glass surface had a roughness of about 1 µm, the calibration curve of thermal lens microscopy was similar to that of spectrophotometry.

Effect of Buffer Layer on Epitaxial Growth of YSZ Deposited on Si Substrate by Slower Q-switched 266 nm YAG Laser

Yttria-stabilized zirconia (YSZ) was grown on Si(100) substrate by pulsed laser deposition (PLD). The laser used in this study was a 266 nm YAG laser with a second function generator modulating only the Q-switch while the primary generator modulated the flash lamp (slower Q-switch). Epitaxial growth was verified on YSZ film deposited without oxygen gas followed by primary deposition in oxygen atmosphere on Si substrate with a ~0.4-nm-thin oxide layer. The crystallinity was strongly dependent on the thickness of the buffer layer deposited prior to the primary deposition of YSZ. The epitaxial growth was confirmed by scan, and ω scan (rocking curve) showed the full width at half maximum (FWHM) of 1.1 deg. The required oxygen pressure for epitaxial growth was quite high compared to that of excimer deposition.

C-Axis lattice spacing control of As-grown Bi-Sr-Ca-Cu-O thin films by single-target excimer laser ablation

As-grown c-axis-oriented thin films of Bi-Sr-Ca-Cu-O on MgO(100) substrates were prepared by simultaneous deposition using the pulsed excimer laser ablation technique. The c-axis spacing of lattice planes could be controlled by the variation of Ca and Cu contents using simultaneous deposition with single targets. As Ca and Cu contents increased, the peaks of the X-ray diffraction pattern approached that of (Ca0.86Sr0.14)CuO2; the n=∞ parent of the Bi2Sr2Can-1CunOy superconductors with a lattice constant, 3.1995 A, of the c-axis. After postannealing, films with Tc,end over 100 K were obtained.

Twin-Free Epitaxial Films Lateral Relation between YSZ(111) and Si(111)

Yttria-stabilized zirconia (YSZ) films were prepared on Si(111) substrates with a slow deposition rate. X-ray diffraction clearly showed epitaxial growth of YSZ(111) film on Si(111), the X-ray scan of 3-fold symmetry confirmed single domain YSZ(111) to be rotated 180° about the surface normal from cubic on cubic relation. In contrast, single domain Si(111) films showed cubic on cubic relation with the YSZ(111) substrate.