Kei Masunishi

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.

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.

Highly sensitive spintronic strain-gauge sensor based on a MgO magnetic tunnel junction with an amorphous CoFeB sensing layer

We investigated spintronic strain-gauge sensors (Spin-SGSs) based on magnetic tunnel junctions (MTJs). To enhance the strain sensitivity of Spin-SGSs, which is defined as the gauge factor = (ΔR/R)/Δe, we investigated MgO-MTJs with an amorphous CoFeB sensing layer that exhibits high magnetostriction and soft magnetic properties. To maintain the amorphous structure of the CoFeB sensing layer even after post annealing, we applied a MgO capping layer (MgO-cap) to the CoFeB sensing layer and compared it with a Ta capping layer (Ta-cap). After post annealing at 320 °C, the CoFeB sensing layer with a MgO-cap maintained a low coercivity of 3 Oe, whereas that with a Ta-cap exhibited a high coercivity of 25 Oe. Microstructure analysis revealed that the CoFeB sensing layer with the MgO-cap has an amorphous structure because boron remains in the CoFeB sensing layer even after post annealing. The gauge factor for the Spin-SGS with the MgO-cap was 4016, which was four times larger than 942 for the Spin-SGS with the Ta-cap.

Spin-MEMS microphone based on highly sensitive spintronic strain-gauge sensors

We report a novel spintronic MEMS (Spin-MEMS) microphone, which is a new type of resistive microphone. For this microphone, spintronic strain-gauge sensors (Spin-SGSs) are integrated on a bulk micromachined diaphragm. The Spin-SGSs are based on magnetic tunnel junctions (MTJs) similar to those used as magnetic sensors in hard disk drives. In work to date, we have experimentally confirmed that the Spin-SGS exhibits a high gauge factor in excess of 5000, which is 100-fold that for a conventional poly-Si piezoresistor, by adopting a novel amorphous Fe-B-based sensing layer with high magnetostriction and low coercivity. Thanks to the high strain sensitivity of the Spin-SGSs, the Spin-MEMS microphone exhibits a signal-to-noise ratio (SNR) of 57 dB(A). A Spin-MEMS microphone with a first resonance frequency of over 70 kHz was also fabricated that exhibits an SNR of 49 dB(A), which is promising for acoustic health monitoring. In this study, we compared the operation sounds of defective and normal bearings using the Spin-MEMS microphone. The Spin-MEMS microphone detected differences in the operation sounds between the defective and normal bearings in the high-frequency range of 10 kHz to 50 kHz.We report a novel spintronic MEMS (Spin-MEMS) microphone, which is a new type of resistive microphone. For this microphone, spintronic strain-gauge sensors (Spin-SGSs) are integrated on a bulk micromachined diaphragm. The Spin-SGSs are based on magnetic tunnel junctions (MTJs) similar to those used as magnetic sensors in hard disk drives. In work to date, we have experimentally confirmed that the Spin-SGS exhibits a high gauge factor in excess of 5000, which is 100-fold that for a conventional poly-Si piezoresistor, by adopting a novel amorphous Fe-B-based sensing layer with high magnetostriction and low coercivity. Thanks to the high strain sensitivity of the Spin-SGSs, the Spin-MEMS microphone exhibits a signal-to-noise ratio (SNR) of 57 dB(A). A Spin-MEMS microphone with a first resonance frequency of over 70 kHz was also fabricated that exhibits an SNR of 49 dB(A), which is promising for acoustic health monitoring. In this study, we compared the operation sounds of defective and normal bearings using ...

Spin-MEMS microphone integrating a series of magnetic tunnel junctions on a rectangular diaphragm

We investigate the enhancement of the signal-to-noise ratio (SNR) of spintronic micro-electro mechanical-system (Spin-MEMS) microphones in which spintronic strain-gauge sensors (Spin-SGSs) are integrated on a micro-electro mechanical-system (MEMS) diaphragm by using a large array of N Spin-SGSs connected in series similar to that in a previous report on magnetic tunnel junction magnetic sensors. Since the strain-gauge properties of Spin-SGSs strongly depend on the angle between the applied uniaxial strain and the magnetization direction of the reference layer, in order to obtain the same signals from each Spin-SGS in an array, it is necessary to locate the Spin-SGS array in a region where the uniaxial strain occurs uniformly on the MEMS diaphragm. We theoretically and experimentally investigate the effect of the diaphragm shape on uniaxial strain on the diaphragm surface. As a result, it is found that a rectangular-shaped diaphragm provides a larger region in which a uniform uniaxial strain is applied to the Spin-SGS array compared with the generic circular diaphragm. Finally, an SNR enhancement of 18 dB by connecting N = 62 Spin-SGSs in series is successfully confirmed in a Spin-MEMS microphone with a rectangular diaphragm.We investigate the enhancement of the signal-to-noise ratio (SNR) of spintronic micro-electro mechanical-system (Spin-MEMS) microphones in which spintronic strain-gauge sensors (Spin-SGSs) are integrated on a micro-electro mechanical-system (MEMS) diaphragm by using a large array of N Spin-SGSs connected in series similar to that in a previous report on magnetic tunnel junction magnetic sensors. Since the strain-gauge properties of Spin-SGSs strongly depend on the angle between the applied uniaxial strain and the magnetization direction of the reference layer, in order to obtain the same signals from each Spin-SGS in an array, it is necessary to locate the Spin-SGS array in a region where the uniaxial strain occurs uniformly on the MEMS diaphragm. We theoretically and experimentally investigate the effect of the diaphragm shape on uniaxial strain on the diaphragm surface. As a result, it is found that a rectangular-shaped diaphragm provides a larger region in which a uniform uniaxial strain is applied to ...

Investigation of PD-CU-SI metallic glass film for hysterisis-free and fast response capacitive mems hydrogen sensors

We show that PdCuSi metallic glass (MG) is a promising material for Pd-based capacitive MEMS hydrogen sensors, reducing both hysteresis and response time of the sensing operation. Firstly, we demonstrate that the fabricated PdCuSi MG film exhibits no hysteresis during hydrogen absorption and desorption. Drastic reduction of the response time is also shown. We also show that, to eliminate the hysteresis and to reduce the response time, PuCuSi needs to be MG, not microcrystal. Secondly, based on the measured strain property, we show that the capacitive sensing scheme has advantage in sensing low concentration hydrogens.

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.

Evaluation of gas permeability for micro-scale thin polymer film with encapsulated MEMS damped oscillator

We present a practical method to evaluate gas permeability for thin polymer films using an encapsulated micro-electro-mechanical-system (MEMS) oscillator. Previously, we have developed a hermetic thin-film dome structure for RF-MEMS tunable capacitor, using conventional back-end-of-the-line (BEOL) processes. The dome is made of multiple layers including a polymer film, whose gas permeability is an important factor with respect to productivity and reliability. So far, it had been difficult to evaluate the gas permeability for such small and thin polymer films with sub-millimeter diameter and micron-scale thickness. In this evaluation method, the pressure dependence of air-damping oscillation is used to measure the permeability. As a demonstration, we carried out a permeability measurement of a 0.5-mm-diameter dome sealed with a thin (1 μm) polymer film. The resulting permeability coefficient is found to be 1×10-16 mol/m/Pa/s, at room temperature.

Novel Adaptive Optics System with an Electrostatically-driven Deformable Mirror and Wavefront Compensation Algorithm

We have fabricated a membrane deformable mirror (DM) for ophthalmologic adaptive optics. An algorithm is demonstrated to compensate wavefront aberration of eyes, effectively. We have developed analysis systems that can predict the DM characteristics.