Yasushi Tomizawa

Adhesion of micrometer-sized polymer particles under a scanning electron microscope

Techniques for manipulating micrometer-sized objects and assembling them into a microstructure in a scanning electron microscope (SEM) are important for research related to microscale physics. It has been demonstrated that micro-objects ranging from sub-μm to several 10 μm can be freely manipulated by adhering them to the tip of a probe. However, the present micromanipulation technique in a SEM is still inefficient, because little is known about the adhesion mechanisms of micro-objects in a SEM environment. In this study, the adhesion forces of micrometer-sized polymer particles deposited on a substrate during SEM observation have been directly measured. The adhesion forces between a polyvinyltoluene sphere of 1 μm radius deposited on a Au substrate, and a glass probe with a hemispherical tip with a typical radius of 0.75 μm coated with Au, were found to show various complicated behaviors. An irreversible increase in the adhesion forces initiated by the electron-beam (EB) irradiation, and the dependence o...

Adhesion force measurement system for micro-objects in a scanning electron microscope

An in situ measurement system for the adhesion forces acting on micrometer-sized objects in a scanning electron microscope has been developed. This system is used to measure the adhesion forces at the object–probe (needle) or the object–substrate interface, while a micro-object which is deposited on the substrate is manipulated with a single probe. The measurement of forces ranging from 50 to 3000 nN with a resolution of about 1 nN has become possible by the combination of a V-shaped double cantilever system with a stiffness of 0.1–0.3 N/m and a heterodyne laser interferometer with a resolution of 10 nm. A numerical analysis showed that the V-shaped double cantilever system is compliant only for normal displacements and is rigid toward other movements. Therefore, the reliable measurement of separation forces without applying unwanted stresses to the contact interfaces has become possible. The value of the stiffness was experimentally determined from the change in the resonant frequency when known masses w...

Adhesive forces acting on micro-objects in manipulation under SEM

In this paper, a system for measuring adhesive forces acting on micro objects under SEM and the obtained experimental results are discussed. In order to manipulate micro objects as small as 0.1 to 100 micrometers under scanning electron microscope (SEM) reliably, it is necessary to examine microadhesive forces acting on the objects by direct measurement. This is because adhesive forces acting on micro objects such as electrostatic force, surface tension force and van der Waals force are affected by various factors not considered in idealized theories. We have constructed an in situ micro force measurement system under SEM with a resolution of 1nN. The system is attached to the micro object handling system under SEM developed by the authors. The forces are obtained by measuring the displacement of a V-shaped parallel leaf cantilever with the laser interferometer. A worktable is attached to the cantilever is calculated from the change of its natural frequency, which is caused when a known mass is added at the tip. Utilizing this system, we have measured adhesive forces acting on micro solder spheres of 25 micrometers in diameter in situ while manipulating them and found the magnitude of the force is several 100nN. Besides, we proved the effectiveness of the micro object handling skills modifying facing area proposed by the authors.

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.

Quasistatic and dynamic mechanical properties of Al–Si–Cu structural films in uniaxial tension

In this article, the quasistatic and dynamic tensile properties of aluminum–silicon–copper (Al–Si–Cu) alloy films are described. The films were deposited by sputtering onto thermally oxidized Si wafers, and then half of the wafers were heat treated at 623 K in nitrogen gas for 1 h. Specially developed environment-controlled uniaxial tensile test equipment was used to carry out the quasistatic tensile test, stress relaxation test, and cyclic loading test at temperatures ranging from room temperature (RT) to 573 K in high vacuum, and the influence of annealing on the mechanical characteristics was investigated. The Young’s modulus did not show annealing dependency. The mean value was 65 GPa at RT, and gradually decreased with increasing test temperature. The yield stresses of nonannealed and annealed films were 168.5 and 129.6 MPa, respectively, which also decreased with temperature rise. In stress relaxation test results, creep exponents in respective films were obtained from curve fitting using the Norton...

Thermal Annealing Effect on Elastic-Plastic Behavior of Al-Si-Cu Structural Films Under Uniaxial and Biaxial Tension

In this paper, the influence of thermal annealing on the elastic-plastic behavior of Al-Si-Cu films under uniaxial and biaxial tensile stress states is described. For the mechanical evaluation of the films, we used an in-plane biaxial tensile test equipment that was specially designed and developed. In the uniaxial tensile test in which the strain rate was varied from 4.0×10-4 to 5.0×10-3 s-1, annealing at 623 K (350 °C) in N2 gas for 1 h did not affect the Youngs modulus. The mean value was found to be 64.5±5.6 GPa. The yield strength showed annealing dependency. The mean yield strength was 168.5±2.2 GPa and 128.1 ± 9.7 GPa for as-deposited and annealed films, respectively. In the biaxial tensile test in which the strain rate ratio was changed between 1:1 and 1:5 in Cartesian coordinates, tensile force and displacement were well controlled. The stresses at the time of yielding were fitted well using the yield equation of Hill with different Lankford coefficient values. X-ray diffraction and electron backscatter diffraction (EBSD) analyses demonstrated that the films had a <;111> fiber texture. The grain growth and sharpening of the texture with annealing were observed in the EBSD analysis. Auger electron spectroscopy analysis suggested that a reduction in yield strength after annealing was related to Cu segregation at the grain boundaries, in addition to grain growth during annealing.

A trench-type anti-wear microprobe with nano-scale electric contacts for AFM LAO lithography

A novel trench-type anti-wear microprobe with nano-scale electric contacts was proposed as an AFM probe to overcome the problem of probe tip wear and improve patterning stability in Atomic force microscope (AFM) local anodic oxidation (LAO) lithography. The proposed microprobe was fabricated using MEMS technique. The patterning and wear properties of the fabricated microprobe in AFM LAO lithography were investigated in terms of the change in the drawn line width and probe tip shape before and after a 20 mm scan. SEM images of the probe tips before and after the scan indicated that there was no obvious damage in the fabricated probe tip while apparent damage could be found on the conventional type probe tip. AFM LAO lithography results showed that the fabricated microprobe maintained a stable pattering performance before and after the 20 mm scan while the conventional type probe was unable to draw due to tip wear after the scan.

Mechanical degrandation mechanism of aluminum-alloy structural films evaluated by environment-controlled tensile testing

This paper describes the mechanical degradation mechanism of sputtered aluminum-alloy (Al-alloy) film used as a structural material in microelectromechanical systems (MEMS). The environment-controlled uniaxial tensile test system with elongation measurement image analysis function was developed to investigate the material characteristics at temperatures ranging from room temperature (RT) to 358 K. From the quasi-static tensile test results, no specimen size effect on Youngs modulus and yield stress was found, whereas the annealing and temperature influences were clearly observed. To investigate mechanical degradation to cycling loading, the cyclic loading tests were conducted under constant stress-and strain-amplitude modes. In constant stress-amplitude mode, stain amplitude increased with an increase of loading cycles due to creep-like deformation. Almost of the specimens fractured during the tests. Meanwhile, in constant strain-amplitude mode, stress amplitude gradually decreased with increasing cycles due to stress relaxation, but no fatigue failure was found. The cyclic loading and stress relaxation tests revealed that creep deformation was dominant in the degradation of Al-alloy film subjected to cyclic motion.

Electric contact stability of anti-wear probes

For the practical realization of precise processes or devices utilizing scanning nanoprobes, not only improvement in the wear resistance of the probe tip but also a stable electric contact at the sliding probe electrode is required. To meet both these requirements, the authors developed an anti-wear probe having a supporting Si tip and a metal electrode, both of which slide on the substrate simultaneously. Probes with various electrode materials were evaluated to investigate the key factors of the material choice for maintaining good electric contact over a long sliding distance. The results show that the optimal management of material hardness, surface roughness, and probe contact force was important to realize an optimum performance from the probe.

A Catch-and-Release drive MEMS gyroscope with enhanced sensitivity by mode-matching

This paper presents a novel MEMS gyroscope that employs intermittent free vibration and mode matching. An intermittent operation is realized by a “Catch-and-Release (CR)” technique, which enables significant reduction of the drive power. Sensitivities of the mode-matching and mode-split conditions are investigated by electrostatically tuning the sense-mode frequency. A sensitivity as high as 2.14 mV/dps, 52 times higher than the mode-split case, is obtained when the drive and sense frequency difference Δƒ is reduced to 50 Hz. Optimization for mode matching and quadrature nulling is also demonstrated.