Yuji Nagai

Self-Propagating Explosive Reactions in Nanostructured AL/NI Multilayer Films Asalocalized Heat Process Technique Formems

This paper describes a novel local heating technique for MEMS soldering and bonding technologies. Nanostructured aluminum/nickel (Al/Ni) multilayer films show self-propagating exothermic reactions, driven by a reduction in atomic bond energy. In this work, we demonstrate the validity of the Al/Ni reactive films as a heat source in manufacturing MEMS solder packages. Dual-source DC magnetron sputtering was employed to deposit the alternative layers of Al and Ni under controlling their thicknesses. By inducing spark, the Al/Ni multilayer film that generates heat enough to melt Au-Sn solder films is ignited, thereby having succeeded in fabrication of Au-Sn film-bonded MEMS elements. The local heating technique using Al/Ni multilayer film’s exothermic reactions is expected to have the great potential as soldering technologies in MEMS.

Raman Spectrum Curve Fitting for Estimating Surface Stress Distribution in Single-Crystal Silicon Microstructure

This paper describes evaluation of surface stress distribution in single-crystal silicon (SCS) microstructure using laser Raman spectroscope. An in-house uniaxial tensile tester was employed to apply the uniaxial tensile stresses to SCS (001)[100] and (001)[110] film specimens with a number of microscale convex structures. A linear relationship between the applied tensile stress and Raman peak shift increment was obtained from Raman spectroscopy at a flat section of the specimen. Raman spectroscopy was also conducted to observe nonuniform stress distribution around the convex structures under uniaxial tensile loading. In observations around a convex structure, two-curve fitting was adopted for the asymmetric spectrum, which had been observed clearly under the tensile stresses of over 1000 MPa. The two-curve fitting was able to separate information of the top corner from that of the bottom one at the edge. The stress distribution estimated by the two peak positions was much closer to finite element analysis (FEA) results than that obtained by the one peak position.

New write shift compensation method modified for optical disk systems to which partial response maximum likelihood (PRML) detection is applied

A new write shift compensation method is proposed in this paper. The method is suitable for an optical disk system which adopts partial response maximum likelihood (PRML) detection, and it can optimize adaptive controlled writing pulses even under severe inter-symbol interference (ISI) conditions to reduce detection errors. This advantage is attributable to the use of the Euclidean distance as the estimation index of the mark edge shift error. The effect is confirmed by the experimental results for blue laser systems.

Development of bi-axial tensile tester to investigate yield locus for aluminum film under multi-axial stresses

This paper describes novel biaxial tensile test technique for a film specimen to investigate material responses to uniaxial and biaxial tensile forces. We have developed biaxial tensile tester that consists of four sets of actuator, load cell, and displacement meter in order to apply an arbitrary amount of tensile force to a film specimen in each axis. With the uniaxial test specimen of sputtered Al film, average Youngs modulus of 35 GPa and yield strength of 115 MPa have been obtained. With the biaxial test specimen, evaluation of the yield locus for Al film has carried out by applying biaxial stresses with various strain rate ratios. The obtained yield stresses could be fitted by the yield criterion based on Logan-Hosford equation. This indicates that the flow stress under biaxial stress condition differ from that under uniaxial condition. Information about the yield locus would be useful for the structural design of MEMS including Al film structures subjected to biaxial stresses.

A new method of evaluating signal quality for systems to which partial response and maximum likelihood is applied

The partial response and maximum likelihood (PRML) detection method is promising as a detection scheme for next-generation optical disk systems. For application of the PRML detection, a new value is required in order to evaluate signal quality instead of jitter, which is used in current optical disk systems. For this requirement, we developed a new evaluation method that is based on the principle of the PRML detection. This evaluation value is defined as the occurrence probability of miss-detection in the PRML detection. We evaluated the proposed method using a simulated waveform and an experimental waveform for two systems. Each system consists of a phase change disk with cover layer thickness of 0.6 mm and 0.1 mm, a blue laser with wavelength of 409 nm and 407 nm and an objective lens with numerical aperture of 0.65 and 0.85, respectively. As a result, we confirmed the validity of the proposed method for each system.

Micro-Raman spectroscopic analysis of single crystal silicon microstructures for surface stress mapping

In this paper, an experimental analysis using a micro-Raman spectroscope for surface stress distribution in single crystal silicon (SCS) microstructures is described. Specially developed tensile test equipment applies a uniaxial tensile stress on SCS specimens with a 270 nm-high, 4 µm2 convex structures in the gauge section. Raman spectra around the convex region are measured using an ultraviolet laser with an excitation line of 363.8 nm. The shape of the Raman spectrum on the flat surface is symmetrical, whereas that around the edge of the convex is asymmetrical due to the multi-stress condition. Two-curve fitting is adopted for the asymmetric spectrum obtained at the edge, and the stress distribution estimated by the two peak positions is much closer to finite element analysis (FEA) results than that obtained by the one peak position. In partial least squares (PLS) analysis that is performed at the edge of the convex section only, explanatory variables are Raman spectral parameters, such as peak position, peak intensity, and full width at half maximum, and the response variable is the FEA stress distribution. The plane stress distributions derived from PLS analyses on each component are in good agreement with that from FEA. The combination of micro-Raman spectroscopy and tensile testing enables us to directly determine the stress components as well as stress magnitudes on SCS microstructures.

In-Situ Raman Spectroscopic Surface Stress Measurement of Single Crystal Silicon Microstructures Subjected to Uniaxial Tensile Loading

This paper describes Raman spectroscopic stress analysis of single crystal silicon (SCS) microstructures for development of reliability evaluation technique utilized for silicon-based microelectromechanical systems (MEMS). An in-house tensile tester was employed to apply a uniaxial tensile stress to the SCS specimen with a 270 nm-height, 4 mum-square SCS boss in the gauge section. Raman spectra on the boss were obtained under a constant tensile stress applied. The stress distribution obtained from two-curve fitting of Raman spectrum was in good agreement with that estimated by finite element analysis (FEA). The Raman spectroscopic stress evaluation method would be effective for nondestructive reliability testing for silicon-MEMS.

Combined Adaptive Controlled Partial Response and Maximum Likelihood Signal Processing for High-Density Optical Disks

The partial response and maximum likelihood (PRML) signal processing method is effective for fabricating high-density optical disks because it allows inter-symbol interference in decoding. However, some deterioration factors, namely impulse response fluctuations and signal level fluctuations, still exist even though PRML signal processing is adopted. A combined adaptive controlled PRML signal processing method is proposed to surmount the problem of these two deterioration factors simultaneously. The key points of the combined adaptive controlled PRML signal processing are that the gain of the Viterbi decoder is unity and the expected signal takes into account the reference levels controlled in the adaptive controlled Viterbi decoder. The effectiveness of such processing is confirmed using simulated reproduced signals and actual reproduced signals. The characteristics in terms of the tangential tilt of the disk and the signal asymmetry are ameliorated by adopting the combined adaptive controlled PRML signal processing method.