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ABSTRACT: This paper presents the characteristics of the electrochemical etching of a TiNi shape memory alloy sheet in a non-aqueous electrolyte solution of LiCl–ethanol. It emerged that the etch rate, etch factor (etched depth/under-cut) and cross-sectional profile of the etched grooves were varied by the width of mask opening. The etch rate peaks with the opening width of 20–30 µm and the etched profile was U-shaped in the narrow opening grooves; in contrast, the etched profile became W-shaped in the wide opening grooves due to the electrolytic current becoming concentrated at the edge of the grooves. When electrochemical etching was carried out with a uniform mask pattern of 20 µm opening, the etching proceeded uniformly from the beginning of the etching in a 1 M solution. In contrast, the SMA surface was etched non-uniformly as etch-holes at low applied voltage in a 0.1 M solution. The etch rate and etch factor changed nonlinearly due to saturation during etching.
Journal of Micromechanics and Microengineering 11/2010; 20(12):125012. · 2.11 Impact Factor
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ABSTRACT: This paper describes the ductile removal behavior of a Pyrex glass substrate in a wet blasting process with an aqueous fine abrasive slurry of 4 µm Al2O3 particles in water. Glass was removed in a ductile cutting mode when the blasting was carried out with low applied pressure or with a long nozzle distance. Although the removal rate in the ductile mode was much lower than with brittle-mode blasting, a smooth surface within a roughness of 50 nm Ra was obtained. Using ductile-mode blasting, a micro groove with a smooth surface (roughness <50 nm Ra) was successfully obtained. The profile of the micro groove was U-shaped, in contrast to the V-shaped profile obtained with conventional brittle-mode blasting. Ductile-mode blasting was also used for surface finishing after a rough pre-blasting process. The roughness of the pre-blasted surface was reduced from 200 nm Ra to about 100 nm Ra by the finishing process.
Journal of Micromechanics and Microengineering 12/2008; 19(1):015031. · 2.11 Impact Factor
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ABSTRACT: In order to fabricate polymer-based microstructures with feature sizes on the order of micrometers, we have been developing
a microimprint technology with a fine nickel (Ni) mold instead of a conventional photolithography technique. The Ni mold was
successfully fabricated by electroforming using a positive thick photoresist microstructure patterned on a silicon substrate
as a replication master. The photoresist microstructure with excellent edge quality can be obtained under irradiation with
single wavelength (g line) selected from a high-pressure mercury lamp. In addition, its sidewall angle in the range of 65° to 84° can be controlled
precisely by varying the distance between a photomask and a photoresist surface. On the structured photoresist master, Ni
was electroplated up to a thickness of about 110μm, and then removed from the master. In this process, two-step electroplating
at different current densities was carried out in order to prevent deformation of the photoresist master due to stress generated
in a Ni electrodeposit. With the Ni mold, fine patterns with a width of 10 or 30μm and a depth of 24μm were almost completely
transferred to polymetric materials (PMMA). The geometrical dimensions of the fabricated PMMA microstructures were found to
be only about 10% reduction against the Ni mold.
Microsystem Technologies 09/2008; 14(9):1359-1365. · 0.93 Impact Factor
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ABSTRACT: a b s t r a c t Layer manufacturing is generally utilized for the development of micro electromechanical systems (MEMS) and micro total analysis systems (TAS). However, the preparation of multiple masks and repet-itive exposure procedure prevents the rapid fabrication of 3D microstructures. An active mask fabrication by using a liquid crystal display (LCD) as an electrically controllable photomask can simplify the layer manufacturing process. In addition, the gray-tone photolithography is available by using LCD lithography system, since the exposure distribution is easily controlled by an LCD. We have developed the LCD mask exposure system by using UV light source. Firstly, the patterning characteristics of the UV photoresist by exposing line and space patterns are evaluated, and then, a fundamental step shape is produced in order to verify the feasibility of gray-tone UV photolithography by using LCD. A shape with a different height can be fabricated without any repetitive exposure and development procedures. Finally, we confirmed the high patterning resolution such as 11 m using check patterns and fabricated 3D step shapes by using the LCD as a gray-scale photomask.
Sensors and Actuators A. 01/2008; 144:381-388.
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ABSTRACT: In order to realize flexible micro actuators with a high operational force, TiNiCu shape memory alloy (SMA) films with thickness exceeding 10 μm were fabricated by flash-evaporation. The addition of a small amount of copper to the films with TiNi main composition provided fine and compact crystallographic structures followed by high flexibility, while actuation force increased with increasing thickness. These thick films will be applied to medical MEMS devices, such as active catheters and meandering spring actuators.
Microelectronic Engineering 86:1274-1277. · 1.56 Impact Factor
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ABSTRACT: In order to realize cell patterning for the investigation of single-cell properties and cellular network analysis, we have been developing a micromanipulator array capable of massively parallel trapping and manipulation of single living cells. An array of hollow silicon dioxide (SiO2) microneedles with a hemispherical tip shape was successfully fabricated by an anisotropic deep reactive ion etching (DRIE) process followed by wet oxidation. The hemispherical tip integrated to each microneedle was successfully structured by the positive use of notching effect in the DRIE process. Moreover, preliminary experiments revealed that fabricated microneedles have the ability to trap polymer particles with a diameter of approximately 10 μm, giving around 90% probability. It was also found that computational fluidic dynamics (CFD) analysis is potentially useful in estimating particle trapping.
Microelectronic Engineering 86:1439-1442. · 1.56 Impact Factor
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ABSTRACT: In order to realize cellular network analysis on a chip-based system, our group has been developing a patterned cell culture microdevice with pillars in an array for tapping cells into space surrounded by the pillars. The pillar structures has advantages to trap both adhesive and non-adhesive cells and to precisely control positions of cells and distances between cells for understanding effects of various cell patterns on functions of a cellular network such as cell proliferation, differentiation, and network formation. In this paper, HeLa cell cultivation with the patterned cell culture microdevice having a pillar array fabricated by dry film of thick negative photoresist SU-8 on a glass substrate was executed as a feasibility study on a cellular network analysis. The results revealed that the device performance was found to be enough to culture HeLa cells for more than 48 h. In addition, relative extensibility of blocks of multiple cells compared with single cells tapped on the device was observed. Thus, the patterned cell culture microdevice proposed here could be applicable to analysis of cellular functions.
Microelectronic Engineering 87:704-707. · 1.56 Impact Factor
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ABSTRACT: In this paper, we describe a shape memory alloy (SMA) thin film actuator which can hold a fine blood vessel for a pulsation monitor. The device has a function of two-step actuation with integrated micro-heaters which can heat up the SMA locally. The TiNiCu ternary SMA thin film was deposited onto a sacrificial copper substrate by flash evaporation method. Phase transformation temperatures can be controlled to be higher than human body temperature for secure actuation by timed operation of a shutter during flash evaporation of a series of pellets. The actuator holds the vessel securely by the first actuation, and allows continuous monitoring after microsurgery. After using, it can release the blood vessel easily by the second actuation and is removed completely without any additional surgical invasions. The micro-heaters can heat up the SMA actuator over 65 °C locally within 10 s when it was heated by an electric current of 10 mA.
Sensors and Actuators A: Physical.
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ABSTRACT: This paper describes development of a sphincter actuator with bimorph cantilever structures fabricated with PDMS silicone rubber and shape memory alloy (SMA) thick film (>10 μm). The PDMS layer gives a bias force to bend the cantilever, whereas the SMA layer gives a recover force to go back to an original straight shape. First, effects of thickness and elongation ratio of the PDMS layers, as well as thickness and width of the SMA layers, were studied for simple rectangular shape cantilevers. The cantilever fabricated with the SMA film of 30 μm thick, 5 mm wide and 15 mm long, and together with the PDMS layer of 90 μm thick at stretching state (elongation ratio of 120%) gave deflection of about 5 mm at 30 °C and almost 100% shape recovery at 75 °C. Based on these data, we developed the sphincter actuator with a mouth opening of several millimetres in diameter by using eight triangular shape bimorph cantilevers.
Microelectronic Engineering 88(8):2662-2665. · 1.56 Impact Factor
