Polarization switching processes in epitaxial Pb (Zr, Ti) O3 (PZT) thin films grown on SrRuO3/SrTiO3 (100) were observed using piezoresponse scanning force microscopy (PFM). PFM observations were carried out directly on the PZT surface and with and on Pt top electrodes. XRD patterns exhibited that PZT thin film had only 180° domains because of a tetragonal structure and completely (001)-orientation. From PFM observations directly on PZT film, it was found that domain wall velocity in the vertical direction was estimated 89m/s. PFM observations with and on the top electrode revealed that the polarization switching processes were dependent on the switching pulse voltage. At lower switching pulse voltage regions (-1.5Vc), the polarization switching occurred from only the latent nuclei. On the other hand, at higher switching pulse voltage (>2Vc), the new nucleations during switching period were observed.
Silica-based planar lightwave circuits have been fabricated practically for optical communication networks. An optical switching device using the thermo-optic effect is fabricated, and its phase-trimming technique after their fabrication processes is developed. An approach to active waveguiding devices using silica-based material is showed by utilizing hybrid technology with semiconductor devices. A practical ONU (Optical Network Unit) device is fabricated using the hybrid PLC technology.
In the last decade, we have seen a very rapid and significant development in Raman scattering characterization of GaN and related nitrides: The Γ-point phonon frequencies are lined up for a binary compound family, GaN, AlN, and InN, of both cubic and hexagonal phases. Variation of phonon spectra with atomic composition has also been intensively studied on ternary compounds. Precise evaluation of strain, compositional fluctuation, defects, impurities and so on has now become possible based on these results. Besides lattice properties, analysis of coupled modes between LO phonon and plasmon has enabled characterization of electronic properties such as carrier density and mobility. This article briefly reviews present status of Raman scattering studies on GaN and related compounds and discuss future directions.
A new photoluminescence (PL) microscope has been developed with a conventional optical system to obtain a monochromated PL image at a low temperature with a spatial resolution in sub-micron range. The objective and sample were put in the identical vacuum chamber to ensure thermal insulation between them. The spatial resolution at 15K was confirmed to be almost equal to the diffraction limit, i.e., 0.3μm, at a wavelength of 488nm. The microscope clearly visualized defective region, and polytype domain with a spatial resolution of 0.3μm in GaN. PL emissions ascribed to free excitons (EXA) and excitons bound to donors (D0X) were discriminated in μ-PL measurements at 15K on epitaxially laterally overgrown (ELO) GaN. The emission at 3.487eV ascribed to D0X became strong above the SiO2 mask within a distance of 8μm from the mask. In a μ-PL image related to excitons bound to N atoms in a 4H-SiC homoepitaxial layer, a dark line was observed at a line-shaped surface defect. Since the PL emission from donor (N)-acceptor (B) pairs was spatially uniform, N atoms were incorporated uniformly in the 4H-SiC epilayer. The dark line is probably caused by an enhancement of nonradiative recombination at the surface defect.
A scanning capacitance microscope (SCM) has been implemented by fabricating a contact-mode atomic force microscope (AFM) with a high-sensitive capacitance sensor. The SCM has promise as next-generation characterization technique of electrical properties such as interface traps in metal-oxide-semiconductor (MOS) devices and carrier density because the measurement is inherently two dimensional with high spatial resolution at a nanometer scale. We demonstrate differential capacitance and capacitance images of the p-n junction on a Si wafer induced by different dopant density. Also we show SCM images due to negatively trapped charges in a SiO2 film, which are injected from the conductive probe tip. The resulting shift in differential capacitance (dC/dV) versus voltage (V) curves due to the locally trapped charge was measured by the high-frequency dC/dV-V measurement. Finally, we applied the SCM to characterization of a cross-sectional surface of a silicon-on-insulator (SOI) wafer. The SCM images identified the depletion layer at the SOI/buried oxide (BOX) interface, and the thickness of the depletion layer was found to vary according to the bias voltage applied to the Si substrate. These results represent that the SCM is a promising tool for sub-micron-scale electrical characterization of not only a bulk Si wafer but also a SOI wafer.
A three-aspherical-mirror system for Extreme Ultraviolet Lithography has been developed. The aspherical mirrors were fabricated using the computer controlled optical surfacing (CCOS) process and a phase shift interferometer. The mirrors have figure errors of 0.58nm and surface roughness of 0.3nm. In order to obtain a high efficiency mirror, M1 and M2 were coated with a graded d-spacing Mo/Si multilayer and M3 was coated with a uniform d-spacing Mo/Si multilayer. The peak reflectivity was 65% at the wavelength of 13.5nm. The wavelength matching of each mirror spans 0.45nm. The mirrors were aligned with a Fizeau-type phase shift interferometer, and a final wavefront error of less than 2nm was achieved. Using this system, exposure experiments were performed. 60nm L & S patterns on the exposure area of 10mm×10mm were achieved.
We have demonstrated an image sensor using SiGe BiCMOS fabrication process for detecting object illuminated by light in “eye-safe” band. The fabrication process is general 0.8μm 2-poly 2-metal SiGe BiCMOS process for RF application. SiGe-Si photodiodes and Si-SiGe-Si hetero-phototransistors as well as Si homojunction photodiodes and phototransistors have been fabricated and measured. The gain of the hetero-phototransistor was around 100. There was little difference between the sensitivity characteristics of SiGe and Si photodetectors. An image sensor with 32×32 pixels has been fabricated using a phototransistor as a detector, which of the base is made of SiGe layer. The dynamic range was 23dB and the minimum detectable light intensity was 10lux. We have successfully acquired images by using this image sensor. The future issues to use SiGe BiCMOS process for image sensors are discussed.
The purpose of this paper is to examine the accuracy of the analysis of the strong discontinuity with a kinking discontinuous surface. We first examine the path independent J-integral and the E-integral formula for a damage model with a kinking cohesive region. As a result, we find that the strong discontinuity analysis based on the E-integral has a high accuracy in view of the energy release rate even when the discontinuous surface kinks.
It was reported previously by the author that the effect of various factors influencing the fretting fatigue limit could be evaluated based on the local stress at the contact edge. In this report, the meaning of the local stress in fretting fatigue was studied. The two-step fatigue test showed that the value of the local stress fatigue limit was nearly the same as the fatigue limit of an edge cracked specimen containing a non-propagating crack formed by the pre-fretting fatigue. The change of stress intensity factor due to the crack growth under fretting fatigue condition was calculated by FEM. The fretting fatigue limit was the condition at which a micro-crack generated by fretting remains as a non-propagating crack. The condition to form a non-propagating crack in fretting fatigue was evaluated on the basis of the threshold condition of short fatigue crack growth.
Fatigue tests of smooth specimens cut from squeeze cast Al alloy car wheels were carried out in controlled laboratory air (t=30°C, h=60%). To clarify the statistical aspects for fatigue behavior, 3 pieces of a region whose area is 4mm2 (2×2mm) were set on the surface of a specimen. In addition to a major crack, the behavior of all cracks initiated within these regions was monitored by a plastic replica technique. Statistical characteristics of fatigue cracks were analyzed by assuming a Weibull distribution. In this material, fatigue cracks were initiated principally from the eutectic Si particles and sometimes from a slip band in the matrix. But, no initiation from microscopic defects such as pinholes and shrinkage porosities was observed. The crack density increased due to the stress cycling, but it saturated at a later stage of the cycling (N/Nf=0.6-0.7), then it decreased with an increasing the cycling. Distribution characteristics of the crack initiation life, crack propagation life, crack growth rate and crack length were represented by a Weibull distribution. Through the values of Weibull parameters and coefficient of variance, some statistical characteristics were studied quantitatively.
Hydrogen embrittlement (HE) of aged Inconel 718 was decreased by the laser surface annealing (LSA) process. By varying LSA process parameters, the applicable parameter scope of the LSA process was established concerning a plate with 3mm thickness. Dissolution kinetics of the γ" phase in this alloy was deduced via thermal cycling experiments. Via finite element method (FEM) simulations, laser absorption coefficients of the sample surface were deduced and the thermal process of each LSA process was calculated. With these thermal simulation results, the annealed surface layer thickness and the hardness distribution profile were calculated based on the established kinetic prediction equations of γ" dissolution process. Good agreements between the calculated and the measured results showed feasibilities of applying this modeling and prediction approach to practical applications.
An investigation was performed on interfacial control between adhesive and surface of GF/PP composites in the case of oxygen plasma treatment. In particular, the relationship between the adhesive strength and the surface energy of GF/PP composites in the case of oxygen plasma treatment was reported. The surface energy was determined by a contact angle measurement test and shear tensile tests were carried out using single lap joint specimens in order to estimate the adhesive strength properties of GF/PP composites. Furthermore, an XPS analysis and a SEM observation were carried out to investigate the surface characteristics of GF/PP composites. The results showed that their surface energy largely increased, and functional groups, namely, carboxyl group, hydroxyl group and carbonyl group, were formed on their surface after the oxygen plasma treatment. It was also found that their adhesive strengths using the oxygen plasma were higher than those for the non-plasma-treated specimens. In addition, from SEM observations of the surface of oxygen-plasma-treated specimens, many cracks formed due to plasma etching were observed in the interface. These results showed that the adhesive strength could be further improved by the anchor effect.
Directed Plasma Fabrication (DPF) is a rapid tooling process that is based on controlled deposition of molten powder particles according to computer-controlled patterns. It makes fully dense, near net shape metal components without molds or dies, and without forming, pressing or forging systems. Experimental works were carried out using conventional low current Plasma Transferred Arc Welding system, and metallic powder was stellite #21. Cylindrical shapes are successfully deposited as dimensions with 2.5-4.2mm wall thickness. The relation between the condition of depositing and the size of molten pool was investigated to make the models accurately as arranged. As compared to thermal conductivity theory, there is considerable effect of some physical factors like arc force on the penetration depth of the molten pool. And as the arc length becomes longer, the molten pool size becomes smaller, as if the heat input were decreased. To make this phenomenon clear, the reference value of the net heat input, n2, was defined and calculated by using the relation between the heat input and the molten pool length. As a result of examining the relations between the yield rate of supplied powder and the reference value n2, it was found that by increasing the arc length, the amount of the splashed powder that is not laminated was increased, and that the net heat input by which molten pool was formed was decreased.
A new freeform fabrication method for intermetallics named Reactive Rapid Prototyping (RRP) has been developed. A 2D structure of nickel aluminde is fabricated by micro joining of the small elemental beads which is formed due to the exothermic synthesis reaction of the molten aluminum droplets injected onto the nickel powder bed eventually forming a 3D object through the layer by layer formation process. The RRP is systematically controlled by a computer. The effect of contact area between the aluminum droplet and the nickel powder bed with different nickel bed thicknesses was investigated. The reaction heat was controlled by replacing the pure aluminum to the aluminum alloy. The addition of fine alumina particles to the nickel powder bed effectively controlled the spreading of the bead formation. A thin line of the nickel aluminide synthesized, about 0.7mm, was drawn successfully. Joinings between adjacent beads and between layers were successfully performed without cracks and pores as well. The boundary region between layers was composed of NiAl phase, but the interior did not reach the stoichiometric composition.