In this study, we propose a mixing method using alternate pulsed flows from three inlets with flow direction control. In conventional pulsed mixing, a residual flow near the sidewalls inhibits the ...rapid mixing of two solutions at high switching frequency. In this study, we addressed this issue in order to perform rapid mixing in a short distance with a low Reynolds number. We fabricated a microfluidic mixing device consisting of a cross-shaped mixing channel with three inlet microchannels and three valveless micropumps. In conventional T-shaped or Y-shaped mixing channels, a residual flow is observed because of the incomplete switching of solutions. The three inlet configuration enabled us to split the residual flow at a switching frequency of pumping of up to 200 Hz, thus resulting in rapid mixing. Furthermore, by controlling the flow direction at the confluent area using the reverse flow of the micropump, the mixing speed was dramatically increased because of the complete switching of the two solutions. As a result, we achieved the mixing time of 3.6 ms and the mixing length of 20.7 µm, which were necessary to achieve a 90% mixing ratio at a high micropump switching frequency of 400 Hz and reverse flow ratio of 1/4.
A new tensile tester using an electrostatic-force grip was developed to evaluate the tensile strength and the reliability of thin-film materials. The tester was constructed in a scanning electron ...microscope (SEM) chamber for in situ observation and was applied for tensile testing of polycrystalline silicon (poly-Si) thin films with dimensions of 30-300 /spl mu/m long, 2-5 /spl mu/m wide, and 2 /spl mu/m thick. It was found that the mean tensile strengths of nondoped and P-doped poly-Si are 2.0-2.8 and 2.0-2.7 GPa, respectively, depending on the length of the specimens, irrespective of the specimen width. Statistical analysis of these size effects on the tensile strength predicted that the location of the fracture origin was on the edge of the specimen, which was Identified by the SEM observation of the fracture surface of the thin films.
We describe a novel on-chip microfabrication technique for the alkali-metal vapor cell of an optically pumped atomic magnetometer (OPAM), utilizing an alkali-metal source tablet (AMST). The newly ...proposed AMST is a millimeter-sized piece of porous alumina whose considerable surface area holds deposited alkali-metal chloride (KCl) and barium azide (BaN6), source materials that effectively produce alkali-metal vapor at less than 400 °C. Our experiments indicated that the most effective pore size of the AMST is between 60 and 170 µm. The thickness of an insulating glass spacer holding the AMST was designed to confine generated alkali metal to the interior of the vapor cell during its production, and an integrated silicon heater was designed to seal the device using a glass frit, melted at an optimum temperature range of 460-490 °C that was determined by finite element method thermal simulation. The proposed design and AMST were used to successfully fabricate a K cell that was then operated as an OPAM with a measured sensitivity of 50 pT. These results demonstrate that the proposed concept for on-chip microfabrication of alkali-metal vapor cells may lead to effective replacement of conventional glassworking approaches.
Replica microchips for capillary array electrophoresis containing 10 separation channels (50 microm width, 50 microm depth and 100 microm pitch) and a network of sacrificial channels (100 microm ...width and 50 microm depth) were successfully fabricated on a poly(methyl methacrylate) (PMMA) substrate by injection molding. The strategy involved development of moving mask deep X-ray lithography to fabricate an array of channels with inclined channel sidewalls. A slight inclination of channel sidewalls, which can not be fabricated by conventional deep X-ray lithography, is highly required to ensure the release of replicated polymer chips from a mold. Moreover, the sealing of molded PMMA multichannel chips with a PMMA cover film was achieved by a novel bonding technique involving adhesive printing and a network of sacrificial channels. An adhesive printing process enables us to precisely control the thickness of an adhesive layer, and a network of sacrificial channels makes it possible to remove air bubbles and an excess adhesive, which are crucial to achieving perfect sealing of replica PMMA chips with well-defined channel and injection structures. A CCD camera equipped with an image intensifier was used to simultaneously monitor electrophoretic separations in ten micro-channels with laser-induced fluorescence detection. High-speed and high-throughput separations of a 100 bp DNA ladder and phi X174 Hae III DNA restriction fragments have been demonstrated using a 10-channel PMMA chip. The current work establishes the feasibility of mass production of PMMA multichannel chips at a cost-effective basis.
We propose a method of submicroparticle pattern formation with high productivity, flexibility, and accuracy. The proposed process is composed of template-assisted self-assembly for particle ...self-assembly and a subsequent two-step transfer of the assembled particles. Optimization of the process parameters was performed by carrying out experiments to evaluate the effects of the parameters on the yields of each process. Polystyrene particles that are 500 nm in diameter were used, and a silicon wafer was used as a target substrate in the experiments that are described in this paper. In the self-assembly process, 70% of the pattern was successfully self-assembled on a silicon template substrate. In the first transfer step, a transfer yield of 79% was obtained with a self-assembled-monolayer-coated polydimethylsiloxane carrier substrate. In the second transfer step, a transfer temperature of 115 provided the maximum transfer yield of 85%. The overall process yield of 48% was achieved by the optimized process parameters, and it was successfully demonstrated that the proposed method can fabricate any submicroparticle pattern.
Simple graphical designs for bridge- and diaphragm-type actuators using shape-memory alloy (SMA) thin films are proposed. The performance (force and displacement) of these actuators is predicted on ...the basis of the stress-strain curves of an SMA film by introducing the material parameter K that represents the mechanical properties of both the austenite and martensite films. The methods of designing actuators are presented along with numerical examples and their validity is discussed, referring to some actual devices such as a microvalve and a micropump. A comparison of theory and actual device performance shows that the proposed design gives a useful approximation for practical applications. The advantage of the proposed design method is that, once the value of K is obtained for a given SMA film, one can design various actuators with various dimensions without detailed information about its mechanical properties.
This paper presents a newly developed 3-Dimensional (3-D) simulation system for Moving Mask Deep X-ray Lithography (M/sup 2/DXL) technique, and its validation. The simulation system named X-ray ...Lithography Simulation System for 3-Dimensional Fabrication (X3D) is tailored to simulate a fabrication process of 3-D microstructures by M/sup 2/DXL. X3D consists of three modules: mask generation, exposure and resist development (hereafter development). The exposure module calculates a dose distribution in resist using an X-ray mask pattern and its movement trajectory. The dose is then converted to a resist dissolution rate. The development module adopted the "Fast Marching Method" technique to calculate the 3-D dissolution process and resultant 3-D microstructures. This technique takes into account resist dissolution direction that is required by 3-D X-ray lithography simulation. The comparison between simulation results and measurements of "stairs-like" dose deposition pattern by M/sup 2/DXL showed that X3D correctly predicts the 3-D dissolution process of exposed PMMA.
Improvements in micropowder blasting have been realized for rapid prototyping of channels in glass substrates. The technique presented in this study consists of laser patterning of Au nanoparticles ...dispersed polymer and micropowder blasting. The patterned polymer was utilized as a mask material for the subsequent mechanical removal of the glass by the micropowder blasting. Five different polymers were tested for the matrix material. Using a line and space mask pattern of 110 /spl mu/m in width, fabricated channels were created in the glass with a maximum aspect ratio of 2.1. The validity of the micropowder blasting using Au nanoparticles dispersed polymer mask was confirmed; additionally, we demonstrated that the micropowder blasting technique with elevated polymer mask temperature was able to reduce erosion of the polymer mask.
Microscale silicon structures oriented along and orientations were laser treated with different conditions with the cross section shape and tensile strength investigated after the treatment. ...Finite element simulation was performed to examine the temperature distribution at different conditions during laser treatment. Using a low energy (1.2 J/cm
2
) and high tilt angle (65°) led to a more preserved cross section with a slight strength improvement. The strength improvement was limited due to other surfaces that were not affected by laser treatment. An improvement of 30 % in tensile strength was achieved with a higher energy (4 J/cm
2
) lower tilt angle (45°) treatment that was consistent for different sample orientations. The cross section of the samples treated at such condition was significantly changed however. The effect of sample orientation on fracture behaviour was studied and unstable crack propagation was observed for oriented samples that was more significant after laser treatment.
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