Recently, some studies have addressed the use of a folded substrate to realize stretchable electronic devices including stretchable thermoelectric generators (TEGs). However, the utilization of the folded substrate as a heat radiation fin has not been achieved. Herein, we have proposed the construction of a TEG with an origami-like folded structure substrate called an "origami-fin" that can achieve a high heat radiation performance and is also highly stretchable. The origami-fin increases the stretchability of the TEG by bending a non-stretchable material into a folded shape, and it also works as a heat radiator because of its large surface area compared to that of a flat structure. We evaluated the heat radiation performance of the origami-fin and the stability of the performance when it was stretched. The results demonstrate that the origami-fin works as a heat radiator and enhances the output of the TEG, while also exhibiting a high stretchability with only a slight output reduction.

Development of sinter-free stretchable conductive inks is critically important to expand the range of materials and applications for flexible electronics. However, conventional stretchable conductive inks require high temperature sintering, which may damage the heat-frail substrates. In this study, we developed sinter-free stretchable conductive inks composed of polystyrene-block-polybutadiene-block-polystyrene (SBS) and silver flakes in tetrahydrofuran (THF). The high volatility and polarity of THF induced the densification and alignment of silver flakes in the SBS matrix, where silver flakes with large surface area and high aspect ratio were formed into the multistacked structure, resulting in the increase of conductive pathways in the stretched wiring.

We modeled a kirigami structure by considering the influence of non-uniform deforming cuts in order to theoretically design the mechanical characteristics of the structure. It is known that the end regions of kirigami structures are non-uniformly deformed when stretched, because the deformation is inhibited at the regions close to both the ends connected to the uncut region in the longitudinal direction. The non-uniform deformation affects the overall mechanical characteristics of the structure. Our model was intended to elucidate how cuts at both ends influence these characteristics. We focused on the difference in the deformation degree caused by a cut between the regions close to the ends and the center of the stretched kirigami device. We proposed a model comprising of connected springs in series with different rigidities in the regions close to the ends and the center. The spring model showed good prediction tendency with regard to the curve of the stress-strain diagram obtained using the tensile test with a test piece. Therefore, the results show that it is possible to theoretically design the mechanical characteristics of a kirigami structure, and that such a design can well predict the influence of cuts, which induce non-uniform deformation at both ends.

For mounting electronic components through contact pressure using elastic adhesives, a high contact resistance is an inevitable issue in achieving solderless wiring in a low-temperature and low-cost process. To decrease the contact resistance, we investigated the resistance change mechanism by measuring the contact resistance with various contact pressures and copper layer thicknesses. The contact resistivity decreased to 4.2 × 10−8 Ω·m2 as the contact pressure increased to 800 kPa and the copper layer thickness decreased to 5 µm. In addition, we measured the change in the total resistance with various copper layer thicknesses, including the contact and wiring resistance, and obtained the minimum combined resistance of 123 mΩ with a copper-layer thickness of 30 µm using our mounting method. In this measurement, a low contact resistance was obtained with a 5-µm-thick copper layer and a contact pressure of 200 kPa or more; however, there is a trade-off with respect to the copper layer thickness in obtaining the minimum combined resistance because of the increasing wiring resistance. Subsequently, based on these measurements, we developed a sandwich structure to decrease the contact resistance, and a contact resistivity of 8.0 × 10−8 Ω·m2 was obtained with the proposed structure.

We measured the conformability and adhesion energy of a polymeric ultrathin film "nanosheet" with hundreds of nanometer thickness to a skin model with epidermal depressions. To compare the confirmability of the nanosheets with different thicknesses and/or under different attaching conditions, we proposed a measurement method using skin models with the same surface profile and defined the surface strain ϵS as the quantified value of the conformability. Then, we measured the adhesion energy of the nanosheet at each conformability through a vertical tensile test. Experimental results indicate that the adhesion energy does not depend on the liquid used in wetting the nanosheet before attaching to the skin model and increases monotonously as the surface strain ϵS increases.

We propose a design method of a micro self-rolling up structure using a temperature-responsive hydrogel sheet with rigid plate array. Our self-rolling up is a method for developing a micro three-dimensional (3D) structure performed by rolling up a two-dimensional (2D) flat sheet, like making a croissant, through a continuous self-folding. The local curvature of the self-rolled up structure could be controlled by the length of rigid plates. By controlling the local curvature, we designed and developed self-rolled up structures with or without gaps between the self-rolled up layers, such as cylindrical and croissant-like ellipsoidal structures. In addition, all the structures demonstrated repetitive deformation of forward and backward rolling up by changing a temperature of water.

This paper reports the analysis of the crack configuration of a stretched metal conductive track that is embedded in a stretchable elastomer. The factor determining the crack configurations is analyzed by modeling as well as experiments. The modeling analysis indicates that the crack configuration is determined by the ratio of the elongation stiffness of the track and elastomer, and is classified into two types: multiple-crack growth and single-crack growth. When the track stiffness is considerably lower than the elastomer stiffness, multiple-crack growth type occurs
in the opposite case, single-crack growth type occurs. Hence, to verify the modeling analysis, metal conductive tracks with different thicknesses are fabricated, and the cracks are studied with respect to the crack width, number of cracks, and crack propagation speed. In this study, two conventional metal-track shapes are studied: straight-shaped tracks with track thickness of 0.04-1.17 μm, and wave-shaped tracks with track thickness of 2-10 μm. For straight-shaped tracks, multiple-crack growth type occurred, when the track thickness was 0.04 μm, and the crack configuration gradually changed to a single crack, with the increase in the track thickness. For wave-shaped tracks with track thickness of 2-10 μm, only single-crack growth type occurred
however, the crack propagation speed decreased and the maximum stretchability of the track increased, with the increase in the track thickness.

Signal reception of nuclear magnetic resonance (NMR) usually relies on electrical amplification of the electromotive force caused by nuclear induction. Here, we report up-conversion of a radio-frequency NMR signal to an optical regime using a high-stress silicon nitride membrane that interfaces the electrical detection circuit and an optical cavity through the electro-mechanical and the opto-mechanical couplings. This enables optical NMR detection without sacrificing the versatility of the traditional nuclear induction approach. While the signal-to-noise ratio is currently limited by the Brownian motion of the membrane as well as additional technical noise, we find it can exceed that of the conventional electrical schemes by increasing the electro-mechanical coupling strength. The electro-mechano-optical NMR detection presented here opens the possibility of mechanical parametric amplification of NMR signals. Moreover, it can potentially be combined with the laser cooling technique applied to nuclear spins.

This paper proposes a micro self-folding using a self-rolling up deformation. In the fabrication method at micro scale, self-folding is an especially useful method of easily fabricating complex three-dimensional (3D) structures from engineered two-dimensional (2D) sheets. However, most self-folded structures are limited to 3D structures with a hollow region. Therefore, we made 3D structures with a small hollow region by self-rolling up a 2D sheet consisting of SU-8 and a temperature-responsive hybrid hydrogel of poly(N-isopropylacrylamide- co-acrylic acid) (pNIPAM-AAc). The temperature-responsive hydrogel can provide repetitive deformation, which is a good feature for micro soft robots or actuators, using hydrogel shrinking and swelling. Our micro self-rolling up method is a self-folding method for a 3D structure performed by rolling up a 2D flat sheet, like making a croissant, through continuous self-folding. We used our method to fabricate 3D structures with a small hollow region, such as cylindrical, conical, and croissant-like ellipsoidal structures, and 3D structures with a hollow region, such as spiral shapes. All the structures showed repetitive deformation, forward rolling up in 20 degrees C cold water and backward rolling up in 40 degrees C hot water. The results demonstrate that self-rolling up deformation can be useful in the field of micro soft devices.

Here, the voltage and current conditions required to form a nanoparticle chain bridging a gap between electrodes that is several tens of micrometres wide have been examined. When a voltage is applied to a gap between electrodes covered with a dispersion of nanoparticles, the nanoparticles are trapped in the gap by dielectrophoresis, forming a nanoparticle chain. It has been considered that a nanoparticle chain is formed in a gap only when a voltage higher than a certain value with a current lower than a certain value is applied to the gap. In this work, certain voltages were first applied with changing current to a 10 mu m-wide gap between electrodes covered with a dispersion of 150 nm-diameter gold nanoparticles, and they found that a nanoparticle chain was formed only when 6.1 V-rms or more with 15 mA(rms) or less was applied. Next, the process of nanoparticle chain formation in a 10 mu m-wide gap was directly observed with high-magnification and high-speed microscopy, and they clarified the behaviour of nanoparticle chain formation when a low voltage, high voltage with high current, and high voltage with low current were applied. Finally, they measured the critical value of current for nanoparticle chain formation in a gap several tens of micrometres wide.

The authors examined a shape of sample on micro-volume, which is a several L, nuclear magnetic resonance (NMR) spectroscopy in order to obtain uniformed magnetic flux density in the sample and a sharp NMR spectrum by using a conventional NMR apparatus. Firstly, they simulated the magnetic flux density distribution in spherical and cubic shaped samples and calculated NMR spectra from each shape. The simulated NMR spectra from spherical samples were sharp enough, being <0.1 ppb in a full width at half maximum (FWHM). On the other hand, the simulated NMR spectra from cubic samples were much broader than those from spherical samples. Then, they made polydimethylsiloxane sample chambers with spherical or cubic sample of several mu L in volume and they evaluated NMR spectra from those micro-volume sample chambers. As a result, they obtained a sharp NMR spectrum with FWHM of 2 ppb from the sample chamber with the spherical sample, and a broad spectrum with FWHM of 220 ppb from the sample chamber with the cubic sample. These results indicate that the spherical shape is essential to obtain a shape spectrum in micro-volume NMR spectroscopy by using a conventional NMR apparatus.

We have realized a three-dimensional (3D) operation of a microelectromechanical systems (MEMS) mirror with three resonant modes and a single driving apparatus by a single superposed signal with three frequencies. We fabricated a 3D MEMS mirror with a single pair of beams having three resonant modes (x-and y-axis rotational modes and a z-axis vertical mode). We demonstrated the 3D operation by a single driving apparatus using the Lorentz force. In addition, we have shown that the x-and y-axis rotational angles and z-axis vertical displacement are proportional to the voltage amplitudes of each resonant frequency in the superposed signal, and the proportionality constants for each angle and deformation are approximately determined as 0.10 degrees/V, 0.10 degrees/V, and 70nm/V, respectively. This result indicates that the mechanical amplitude of each mode is easy to control by the signal amplitude of each resonant frequency in the superposed signal. (C) 2017 The Japan Society of Applied Physics

We herein report the micropatterning of flexible multiple photonic colloidal crystal gels (PCCGs) using single-layered microchannels. These patterned PCCGs exhibit structural colors that can be tuned by adjustment of the diameter and concentration of the colloidal particles in precursor solutions of N-isopropylacrylamide (NIPAM) or polyethylene glycol diacrylate (PEGDA). The precursor solutions containing dispersed colloidal particles were selectively injected into single-layered microchannels where they polymerized rapidly. The shape, density, and height of the patterned PCCG pixels were determined by the microchannels, which in turn determined the optical properties of the PCCG arrays. Furthermore, the preparation of three different types of PCCGs exhibiting three different structural colors at a high pixel density was demonstrated successfully using the single-layered polydimethylsiloxane (PDMS) microchannels. Finally, the optical reflective properties and the mechanical flexibility of the patterned multiple PCCG arrays were evaluated. We expect that our method for the preparation of such patterned PCCG arrays will contribute to the development of flexible optical devices.

In this paper, we present a simple method for manufacturing electronic devices using ultrathin polymer films, and develop a high-frequency RF identification. To expand the market for flexible devices, it is important to enhance their adhesiveness and conformability to surfaces, to simplify their fabrication, and to reduce their cost. We developed a method to design an antenna for use on an operable RF identification whose wiring was subjected to commercially available inkjet or simple screen printing, and successfully fabricated the RF identification. By using ultrathin films made of polystyrene-block-polybutadiene-block-polystyrene (SBS) as substrates-less than 750nm-the films could be attached to various surfaces, including soft surfaces, by van der Waals force and without using glue. We succeeded in the simple fabrication of an ultrathin RF identification including a commercial or simple printing process. (C) 2017 The Japan Society of Applied Physics

© 2017 IEEE. Effective design and fabrication of 3-D electronic circuits are among the most pressing issues for future engineering. Although a variety of flexible devices have been developed, most of them are still designed two-dimensionally. In this letter, we introduce a novel idea to fabricate a 3-D wiring board. We produced the 3-D wiring board from one desktop inkjet printer by printing conductive pattern and a 2-D pattern to induce self-folding. We printed silver ink onto a paper to realize the conductive trace. Meanwhile, a 3-D structure was constructed with self-folding induced by water-based ink printed from the same printer. The paper with the silver ink self-folds along the printed line. The printed silver ink is sufficiently thin to be flexible. Even if the silver ink is already printed, the paper can self-fold or self-bend to consist the 3-D wiring board. A paper scratch driven robot was developed using this method. The robot traveled 56 mm in 15 s according to the vibration induced by the electrostatic force of the printed electrode. The size of the robot is 30 × 15 × 10 mm. This work proposes a new method to design 3-D wiring board, and shows extended possibilities for printed paper mechatronics.

We fabricated free-standing, flexible and physically adhesive ultrathin elastomeric films (nanosheets) for application as electronic substrates and packaging films. In this work, electronic elements such as a chip resistor and a chip LED were sandwiched between elastomeric nanosheets of less than 1 mu m thickness to obtain electrical conduction in silver lines that were inkjet-printed on the nanosheet. This sandwich-fixation process contributed to the development of an electronic device showing conformable adhesion and operation on the skin surface.

We demonstrated coloring elements with high ratio change of the coloring area by using bending deformation of electroactive hydrogel. By using the nondimensional deflection of a gel, we showed that the response time for the color change and the thickness of the coloring element can be designed. We fabricated a 3 x 3 dot-matrix display with of 0.56 and evaluated the performance of the coloring element. As a result, the coloring area ratios in black state and colored state were 7.64 +/- 4.6% and 92.1 +/- 4.6%, respectively. The response times were 12 s from blank state to colored state, and 13 s from colored state to blank state.

<p>We proposed divided-type dihedral corner reflector array (DCRA) in order to display floating image with wide viewing angle. DCRA is a kind of optical device which can display floating image of real object by retrotransmission. The viewing angle of the floating image is, however, narrow, because the angle of incident ray which can be retrotransmission is limited. Therefore, we expand a range of viewing angle by dividing and combining DCRA to use the region in which the ray can be retrotransmission. In this paper, we evaluated the viewing angle of our divided DCRA by analyzing angular distribution of retrotransmissive ratio. As a result, we showed that the divided DCRA can be expanded the viewing angle of floating image to 180 deg.</p>

<p>We investigated an effect of an elongation stiffness of a substrate and a metal wire to stretchability of a wavy metal wire. We focused on a ratio of the elongation stiffness of the substrate to that of the metal wire. In tensile test using two kinds of wavy specimens, most of the results showed increase of the maximum elongation at increase of the elongation stiffness ratio. When the elongation stiffness ratio is changed from 0 to 0.910, the stretchability is increased from 0.322 to 0.594 and from 0.337 to 0.425. This result suggests that stretchability can be improved by designing the elongation stiffness ratio.</p>

<p>Our goal is to realize a mechanical resonator with large freestanding nanomembrane. First of all, we measured residual stress caused by deposition of gold layer and designed the thickness of the gold layer on the nanomenbrane as 500 nm. Then, we practically fabricated and measured a structure of a nanomechanical resonator with a 500-nm-thick gold layer on a 50-nm-thick silicon nitride nanomembrane. In the part of freestanding nanomembrane, there was no breaks nor bucking, and roughness of the surface was less than 100 nm. The average height of pillars was 578 nm. Finally, we measured that the resonant frequency of the fabricated structure was 188.83 kHz and the Quality factor was 797 in the atmosphere.</p>

<p>We proposed a skin moisture sensor with multiple temperature measuring parts for self-calibration. A resistance temperature detector (RTD) can be used for both heat source and temperature measurement. We fabricated a device with four RTDs to measure the skin moisture content. The temperature coefficients of resistance of the fabricated RTDs are almost the same. On the other hand, a fluctuation of temperature rise was, however, observed. Therefore, we proposed a method of self-calibration of the difference in the calorific value of the heat source by the temperature rise measured by the heat source. By using the proposed method, we showed that the temperature rise fluctuation measured by the resistance can be reduced.</p>

This paper reports a stretchable electronic device with repeat self-healing ability of a wire crack caused by stretching deformation. The crack of metal wire is healed with assembled metal nanoparticles by dielectrophoresis, when a voltage is applied to the cracked wire covered with the nanoparticle solution. By designing a circuit, we controlled the applied voltage and current for the self-healing to be avoid excessive Joule heating in the assembled nanoparticles. This consideration enables us to heal a crack of tens of micrometers in width and to practically achieve a stretchable electronic device.

We developed a two-dimensionally (2-D) stretchable electronic device with stress-free region by applying origami folding. The key idea is to achieve "a stretching deformation of whole device" by "a local bending deformation". Because our device has stress-free region, we can use a rigid chip (such as LED chips and MEMS sensors) and a metal wire without mechanical fracture or metal fatigue. In this paper, first, we proposed a 2-D stretchable structure by developing "miura-ori" folding. Next, we fabricated a 2-D stretchable electronic device, and confirmed that wire fatigue or cracks are not generated by repeated deformation. Finally, we demonstrated 2-D stretchability and bendability using the device with inorganic LED chips.

We report a hybrid film that is composed of "polymer nanosheet" with a hundreds-of-nanometer-thick film and "punched film" with hundreds-of-micrometer-thick film. Because of the thickness, the nanosheet is able to adhere to biological tissues without a glue, but is sometimes difficult to handling. Our hybrid film is established both adhesiveness of the nanosheet and shape-controlling ability of the punched film. In this paper, first, we fabricated the cylindrical-shaped hybrid film. Next, we achieved the hybrid film unfold into flat shape. Finally, we evaluated the adhesion force of the hybrid film and confirmed that the hybrid film can adhere to biological tissues.

This paper describes a system through which the self-assembly of anisotropic hydrogel microparticles is achieved, which also enables dynamic transformation of the assembled structures. Using a centrifuge-based microfluidic device, anisotropic hydrogel microparticles encapsulating superparamagnetic materials on one side are fabricated, which respond to a magnetic field. We successfully achieve dynamic assembly using these hydrogel microparticles and realize three different self-assembled structures (single and double pearl chain structures, and close-packed structures), which can be transformed to other structures dynamically via tuning of the precessional magnetic field. We believe that the developed system has potential application as an effective platform for a dynamic cell manipulation and cultivation system, in biomimetic autonomous microrobot organization, and that it can facilitate further understanding of the self-organization and complex systems observed in nature. Published by AIP Publishing.

We proposed a sheet shape-controlling method for a hundreds-of-nanometers-thick polymeric ultrathin film (referred to as a "nanosheet") for folding the film into a cylindrical shape and unfolding the film into a flat shape. To control the shape of the nanosheet, we used a triple-layered structure, which included a nanosheet and additional two layers of a water-soluble polymer. The additional two layers are thicker than the nanosheet, and one of the two layers was loaded to prestretch that layer. Therefore, the triple-layered structure was folded into a cylindrical shape owing to strain mismatch between the two layers and unfolded into a flat shape after the dissolution of the two layers. In this study, we could successfully estimate the radius of curvature of the triple-layered structure by considering the strain mismatch between the two layers. In addition, we confirmed that the triple-layered structure unfolded into a flat shape by the dissolution of the two layers. (C) 2016 The Japan Society of Applied Physics

On a metal wire with a self-healing function of a crack using electric field trapping of metal nanoparticles, we examined a healable crack width by using the different particle size. The electric field trapping is a phenomenon where the nanoparticles are trapped in the crack by the electric field in the region of the crack only, when a voltage is applied to the cracked wire covered with the nanoparticle solution. In this paper, first, we theoretically analyzed and calculated the particle size dependence of forces acting on the nanoparticles. Next, we fabricated gold wires with patterned cracks on a glass substrate, and measured the healable crack width by comparing 20 nm, 100 nm and 200 nm in particle radius. In the experiments, gold nanoparticles aqueous solution was used as nanoparticles solution. As a result, in the each case of 20 nm, 100 nm and 200 nm in particle radius, cracks up to 1.5 μm, 2.5 μm and 4.0 μm were successfully healed by applying less than 4.2 V in amplitude and 100 kHz in frequency of AC voltage, respectively. These results indicate that the larger nanoparticle can heal the wider crack with the same cross-sectional shape of the wire and the approximately same applied voltage. After the experiments, we confirmed that assembled nanoparticles were bridging the crack at the inside of the crack through scanning electron microscope (SEM) observations.

This paper describes a micropatterning method of hemispherical dome shape photonic colloidal crystals (PCCs) in microchannels for a wide-viewing-angle optical color filter of a reflective display. We fabricated hemispherical dome-top PDMS microchannels and crystalized colloidal particles inside the microchannel. These dome-shape micorchannels enable us to observe reflected light (structural color) from the PCCs in wide viewing-angle (Fig. I). We succeeded in patterning of two types of hemispherical PCCs in the dome-top micorchannels, and confirmed that those patterned PCCs reflected their structural color in wide-viewing-angle. Our patterning method could be effective to realize an optical filter for full-color, wide-viewing-angle and low-energy consumption reflective displays

We propose the design for three-dimensional (3-D) scanning micromirror with single pair of beams. A 3-D scanning micromirror is powerful solution for projection/detection of a 3-D image in tiny devices. We succeed in designing and fabricating the micromirror having three separated resonance modes (two torsion modes and one parallel mode) with high fill-factor. Our design of single pair of beams can contribute to simpleness and compactness of a 3-D scanner because of easy fabrication and high fill-factor.

We demonstrated coloring elements with high ratio change of the coloring area by using bending deformation of electroactive hydrogel. By using the nondimensional deflection α of a gel, we showed that the response time for the color change and the thickness of the coloring element can be designed. We fabricated a 3 × 3 dot-matrix display with α of 0.56 and evaluated the performance of the coloring element. As a result, the coloring area ratios in blank state and colored state were 7.6±4.6% and 92.1±4.6%, respectively. The response times were 12 seconds from blank state to colored state, and 13 seconds from colored state to blank state.

This paper presents a thermal-based skin moisture sensor that is insusceptible to thin coating materials on skin. To realize this sensor, numerical simulations are performed to evaluate the influence of surface-coating materials, such as Vaseline moisturizer, on the heat transfer from a heat source in the sensor to the skin. The simulation results show that the influence of the thin Vaseline layer on the temperature change of the heat source is negligible, but the existence of air gaps between the sensor and the skin drastically interrupts the heat transfer. Considering the simulation results, the thermal-based skin moisture sensor is designed and fabricated with a microelectromechanical systems (MEMS) pressure sensor to avoid heat transfer interruption due to air gaps. The measurement results of water content in a water-absorbing polymer, covered with a 10-mu m-thick polyethylene film, show that the moisture sensor can assess the water content of materials that are covered with a thin layer. Finally, we demonstrate the hydration measurement of skin with Vaseline coating. The measurement results confirm the potential of the moisture sensor to measure the water content of skin covered with moisturizing substances. (C) 2015 Elsevier B.V. All rights reserved.

By using an electroactive hydrogel, we proposed and fabricated a deformable coloring element. The proposed element is composed of a dyed electroactive hydrogel piece and bottom-arranged electrodes. By using the bottom arrangement of electrodes, we can use a simple fabrication and achieve a high fill factor (FF). To design the element, we analyzed the electric field in various dimensions of the electrodes by using a charge simulation method. The bending factor (BF) was defined as an index of bending direction and speed of the gel. From the difference between the BFs for each dimension, we found the optimal parameters required to maximize BF on the chosen boundary condition of FF &gt;= 0.9. We then determined the dimensions of a coloring element on the basis of the results of the analysis. Finally, a 3 x 3 dot-matrix display was fabricated to demonstrate a color change in all nine cells. (C) 2015 The Japan Society of Applied Physics

We propose a self-healing metal wire using electric field trapping of gold nanoparticles by a dielectrophoresis force. A cracked gold wire can retrieve its conductivity through the self-healing function. In this paper, we examine the healing voltage causing the electric field trapping and determine the healing time, which is relevant to future device applications. First, the forces acting on a nanoparticle are analyzed and a theoretical healing voltage curve is calculated. Then, gold wires with 200- to 1,600-nm-wide cracks are fabricated on glass substrate and the self-healing function is verified through healing experiments. As a result, gold wires with cracks of up to 1,200 nm in width are successfully healed by applying less than similar to 2.5 V (on average), and the experimental results correspond almost exactly with the calculated healing voltage curve. The average healing times are 10 to 285 s for 200- to 1,200-nm-wide cracks. Through scanning electron microscope analysis after the healing experiments, we confirm that the cracks are healed by assembled nanoparticles. (C) 2015 The Japan Society of Applied Physics

We developed a self-healing metal wire using an electric field trapping of gold nanoparticles. A cracked metal wire on a stretchable substrate can get its conductivity again by the self-healing function. In this paper, first, we theoretically analyzed force acting on a nanoparticle and calculated a critical voltage which cause the electric field trapping. Next, we fabricated gold wires with artificially patterned cracks on a glass substrate and verified the self-healing function by experiments of a crack healing. Finally, we demonstrated the self-healing of a cracked metal wire on a stretchable substrate to show a usefulness of the self-healing for flexible devices.

We demonstrated the nonlinear mechanics of an optomechnaically driven silicon membrane suspended 100nm over a nearby substrate. The estimated optical force-induced Duffing nonlinearity is 10(28)Hz(2)/m(2), significantly larger than that afforded by the nonlinear Casimir potential.

We describe a simple and rapid micropatterning method of multiple types of photonic colloidal crystals (PCCs) on a single substrate for an optical color filter of a reflective display. We developed a "Channel-Cut Method" to introduce multiple colloidal suspensions selectively and sequentially into a microchannel network. By combining this method with centrifugal crystallization, we succeeded in patterning of two different PCCs made of silica or polystylene in a single-layered microchannel. We believe that our method could contribute to develop a colorized reflective display that achieves low energy consumption and high color expression.

A stretchable cell culture platform in which elastic micropneumatic actuators are embedded has been developed. By using the softlithography of polydimethylsiloxane (PDMS), the platform can be fabricated to any size and shape. It also permits cell culture by using the same standard methods that one would use with a Petri dish and it is transparent, permitting optical inspection of the cells. Thus, the platform is promising for studying cell responses because of mechanical stimulus. In this reported work, cells were cultured on a PDMS diaphragm of the micropneumatic actuators. Owing to input pressure, the micropneumatic actuators swell like a balloon, thereby stretching the cell membranes on the PDMS. The design flexibility of the presented approach is demonstrated by developing two kinds of stretchable platforms with diaphragm diameters of 558 and 24.8 m to stretch whole and local cell membranes, respectively. Then, the cell membranes attached on the PDMS diaphragms are stretched by applying pressure on the pneumatic actuators. The applied stress causes an increase in the intracellular calcium ion concentration that is a fast cellular mechanotransduction. Therefore, it is concluded that the method for stretching cell membranes can stimulate either whole or local cell membranes, thus showing the potential to be used in in vitro studies of cellular mechanotransduction.

We demonstrate actuation of a silicon photonic crystal membrane with a repulsive optical gradient force. The extent of the static actuation is extracted by examining the optical bistability as a combination of the optomechanical, thermo-optic, and photo-thermo-mechanical effects using coupled-mode theory. Device behavior is dominated by a repulsive optical force which results in displacements of approximate to 1 nm/mW. By employing an extended guided resonance which effectively eliminates multi-photon thermal and electronic nonlinearities, our silicon-based device provides a simple, non-intrusive solution to extending the actuation range of micro-electromechanical devices. (C) 2013 AIP Publishing LLC.

This paper describes a parallel piezoresistive cantilever that is composed of a force-sensing cantilever in addition to a reference cantilever for photoresponse compensation. Piezoresistive cantilevers have been applied in many cellular mechanical measurement studies because of their high sensitivity, high time resolution and ease of handling. However, the electrical resistance changes in response to the excitation light of the fluorescence microscope, which affects the cell measurements. We measured the I-V characteristics of a piezoresistive layer. These photoresponses occurred due to the internal photoelectric effect. We canceled the photoresponses using the reference cantilever. This paper demonstrates compensation of the cantilever photoresponse under irradiation at different angles, wavelengths and light intensities. As a result, the photoresponse could be decreased by 87%. © 2013 IOP Publishing Ltd.

We present here an optomechanical system fabricated with novel stress management techniques that allow us to suspend an ultrathin defect-free silicon photonic-crystal membrane above a Silicon-on-Insulator (SOI) substrate with a gap that is tunable to below 200 nm. Our devices are able to generate strong attractive and repulsive optical forces over a large surface area with simple in-and out-coupling and feature the strongest repulsive optomechanical coupling in any geometry to date (g(OM)/2 pi approximate to -65 GHz/nm). The interplay between the optomechanical and photo-thermal-mechanical dynamics is explored, and the latter is used to achieve cooling and amplification of the mechanical mode, demonstrating that our platform is well-suited for potential applications in low-power mass, force, and refractive-index sensing as well as optomechanical accelerometry. (C) 2013 Optical Society of America

We propose a flexible tactile sensor using sub-mu m-thick Si piezoresistive cantilevers for shear stress detection. The thin Si piezoresistive cantilevers were fabricated on the device layer of a silicon on insulator (SOI) wafer. By using an adhesion-based transfer method, only these thin and fragile cantilevers were transferred from the rigid handling layer of the SOI wafer to the polydimethylsiloxane layer without damage. Because the thin Si cantilevers have high durability of bending, the proposed sensor can be attached to a thin rod-type structure serving as the finger of a robotic hand. The cantilevers were arrayed in orthogonal directions to measure the X and Y directional components of applied shear stresses independently. We evaluated the bending durability of our flexible tactile sensor and confirmed that the sensor can be attached to a rod with a radius of 10 mm. The sensitivity of the flexible tactile sensor attached to a curved surface was 1.7 x 10(-6) Pa-1 on average for a range of shear stresses from -1.8 x 10(3) to 1.8 x 10(3) Pa applied along its surface. It independently detected the X and Y directional components of the applied shear stresses.

This paper reports on the development of a micro electro mechanical system microphone consisting of a piezoresistive cantilever and a micro HR (Helmholtz resonator) for use as an ultrasonic proximity sensor. The resonance frequency of the HR was designed to be equal to that of the cantilever. Therefore, the HR increases the sensitivity of the microphone to ultrasonic waves. The dimensions of the fabricated HR and the cantilever are 1.2 mm x 1.2 mm x 0.6 mm and 130 mu m x 40 mu m x 0.3 mu m, respectively. At a resonance frequency of 22.6 kHz, the cantilever with the HR detected ultrasonic waves with 14 times greater sensitivity than that of the cantilever without the HR. We demonstrated that the fabricated sensor is capable of measuring distances between 0.5 and 6.0 m.

In this paper we describe a general method to avoid stress-induced buckling of thin and large freestanding membranes. We show that using properly designed supports, in the form of microbeams, we can reduce the out-of-plane deflection of the membrane while maintaining its stiffness. As a proof of principle, we used a silicon-on-insulator (SOI) platform to fabricate 30 mu m wide, 220 nm thick, free-standing Si membranes, supported by four 15 mu m long and 3 mu m wide microbeams. Using our approach, we are able to achieve an out-of-plane deformation of the membrane smaller than 50 nm in spite of 39 MPa of compressive internal stress. Our method is general, and can be applied to different material systems with compressive or tensile internal stress.

By engineering supporting beams of a thin opto-mechanical membrane, we are able to reduce the stress-induced deflection, and realize devices that feature strong optical force for probing the Casimir force.

We experimentally studied the effects of optical gradient and photothermal forces on the optomechanics of tethered silicon membranes. Novel engineering of support arms facilitates tunable optomechanical coupling and probing of Casimir interactions.

We propose an optomechanical structure consisting of a photonic-crystal (holey) membrane suspended above a layered silicon-on-insulator substrate in which resonant bonding/antibonding optical forces created by externally incident light from above enable all-optical control and actuation of stiction effects induced by the Casimir force. In this way, one can control how the Casimir force is expressed in the mechanical dynamics of the membrane, not by changing the Casimir force directly but by optically modifying the geometry and counteracting the mechanical spring constant to bring the system in or out of regimes where Casimir physics dominate. The same optical response (reflection spectrum) of the membrane to the incident light can be exploited to accurately measure the effects of the Casimir force on the equilibrium separation of the membrane. (C) 2011 American Institute of Physics. [doi:10.1063/1.3589119]

The optical bonding (attractive) and antibonding (repulsive) forces between a suspended, holey Silicon membrane and a Silicon-on-Insulator (SOI) substrate are shown to offer a sensitive new method for plane-plane geometry Casimir force detection. (C) 2010 Optical Society of America

We demonstrate that tunable attractive (bonding) and repulsive (anti-bonding) forces can arise in highly asymmetric structures coupled to external radiation, a consequence of the bonding/anti-bonding level repulsion of guided-wave resonances that was first predicted in symmetric systems. Our focus is a geometry consisting of a photonic-crystal (holey) membrane suspended above an unpatterned layered substrate, supporting planar waveguide modes that can couple via the periodic modulation of the holey membrane. Asymmetric geometries have a clear advantage in ease of fabrication and experimental characterization compared to symmetric double-membrane structures. We show that the asymmetry can also lead to unusual behavior in the force magnitudes of a bonding/antibonding pair as the membrane separation changes, including nonmonotonic dependences on the separation. We propose a computational method that obtains the entire force spectrum via a single time-domain simulation, by Fourier-transforming the response to a short pulse and thereby obtaining the frequency-dependent stress tensor. We point out that by operating with two, instead of a single frequency, these evanescent forces can be exploited to tune the spring constant of the membrane without changing its equilibrium separation. (C) 2011 Optical Society of America

We propose a method to maintain the symmetry of the refractive index with respect to an Au film, in which the refractive indices are the same near both surfaces of the Au film, for LRSPR (long-range surface plasmon resonance) sensors. Maintenance of the symmetry is necessary for exciting the LRSPR mode. However, because the buffer layer under the Au film is usually made of a solid dielectric material with a constant refractive index, the quality of the measurement is reduced when the refractive index of the analyte used is dramatically different from that of the buffer layer. To solve this problem, the proposed sensor is equipped with liquid channels under the Au film. The Au film used in this study was supported by a thin (100 nm) polymer film forming parallel, one-dimensional liquid channels with a 29 mu m pitch. Because the analyte solution flows in the channels, both surfaces of the Au film face the same analyte. Thus, this configuration automatically satisfies the symmetry condition for analytes with a wide range of refractive indices. We examined the validity of the sensor and compared it to that of a conventional sensor by measuring the LRSPR for five analyte solutions with different refractive indices. LRSPR dips were clearly observed for all of the analytes tested. The dip of the conventional LRSPR sensor became shallow when the refractive index increased, with the final dip depth being 65% of the initial dip depth for a refractive index of 1.358. In contrast, the dip depth of the proposed LRSPR sensor remained constant over the entire measured refractive index range of 1.331 to 1.358. These results indicate that the proposed sensor maintains the symmetry condition and confirm that the proposed method is effective for highly sensitive LRSPR measurements for a wide variety of analyte species.

This paper presents direct measurements of the aerodynamic forces on the wing of a free-flying, insect-like ornithopter that was modeled on a hawk moth (Manduca sexta). A micro differential pressure sensor was fabricated with micro electro mechanical systems (MEMS) technology and attached to the wing of the ornithopter. The sensor chip was less than 0.1% of the wing area. The mass of the sensor chip was 2.0 mg, which was less than 1% of the wing mass. Thus, the sensor was both small and light in comparison with the wing, resulting in a measurement system that had a minimal impact on the aerodynamics of the wing. With this sensor, the 'pressure coefficient' of the ornithopter wing was measured during both steady airflow and actual free flight. The maximum pressure coefficient observed for steady airflow conditions was 1.4 at an angle of attack of 30 degrees. In flapping flight, the coefficient was around 2.0 for angles of attack that ranged from 25 degrees to 40 degrees. Therefore, a larger aerodynamic force was generated during the downstroke in free flight compared to steady airflow conditions.

A transparent conductive polymer-based strain-sensor array, designed especially for touch input sheets of flexible displays, was developed. A transparent conductive polymer, namely poly(3, 4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS), was utilized owing to its strength under repeated mechanical bending. PEDOT: PSS strain sensors with a thickness of 130 nm exhibited light transmittance of 92%, which is the same as the transmittance of ITO electrodes widely used in flat panel displays. We demonstrated that the sensor array on a flexible sheet was able to sustain mechanical bending 300 times at a bending radius of 5 mm. The strain sensor shows a gauge factor of 5.2. The touch point on a flexible sheet could be detected from histograms of the outputs of the strain sensors when the sheet was pushed with an input force of 5 N. The touch input could be detected on the flexible sheet with a curved surface (radius of curvature of 20 mm). These results show that the developed transparent conductive polymer-based strain-sensor array is applicable to touch input sheets of mechanically bendable displays.

Three-dimensional silicon fabrication is demanded in optical lenses for collecting far infrared radiation. We propose a method for the fabrication of shapes, which have depths varying in the x and y directions, vertical walls and smooth surfaces. A mask design with rectangular apertures was used in a two-stage etching process consisting of anisotropic etching to rough out the three-dimensional shape followed by isotropic etching to smooth the surface. The relationship between the etching depth and area and the aspect ratio (length-to-height ratio) of the rectangular apertures was determined experimentally. Based on this relationship, we describe a procedure for designing rectangular apertures. We fabricated a convex microlens with a diameter of 150 mu m and a height of 4.3 mu m surrounded by a vertical wall. The arithmetic mean surface roughness of the microlens was 100 nm.

We fabricated and demonstrated electrochromic voxel arrays for a three-dimensional (3D) display prototype. A voxel is a cubic display element of a 3D image. The voxels were constructed with ultraviolet-curable polymer on a substrate with a MEMS process and coated with poly-(3,4-ethylenedioxythiophene): poly-styrenesulfonate (PEDOT:PSS). The resultant substrates were stacked in three-dimensional space. The PEDOT: PSS color changes from transparent to blue when -1V is applied. The coloration of one voxel was observed from the top and side views, and the coloration of a 3 x 3 x 3 voxel array was also observed.

We have developed a package for disposable glucose sensor chips using Parylene encapsulation of a glucose oxidase solution in the liquid phase and a cover structure made of an ultraviolet (UV) curable adhesive. Parylene was directly deposited onto a small volume (1 mu L) of glucose oxidase solution through chemical vapor deposition. The cover and reaction chamber were constructed on Parylene film using a UV-curable adhesive and photolithography. The package was processed at room temperature to avoid denaturation of the glucose oxidase. The glucose oxidase solution was encapsulated and unsealed. Glucose sensing was demonstrated using standard amperometric detection at glucose concentrations between 0.1 and 100 mM, which covers the glucose concentration range of diabetic patients. Our proposed Parylene encapsulation and UV-adhesive cover form a liquid phase glucose-oxidase package that has the advantages of room temperature processing and direct liquid encapsulation of a small volume solution without use of conventional solidifying chemicals.

In this paper, we propose a method to maintain the symmetry of the refractive index about the Au film for the LongRange Surface Plasmon Resonance (LRSPR) sensor. The proposed sensor is equipped with liquid channels under the Au film. Because both sides of the Au film face the analyte, the symmetrical condition of the refractive index, which is necessary for LRSPR excitation, is automatically satisfied. We fabricated the device using microfabrication technology, and verified maintaining of the symmetrical condition by applying five analytes with different refractive indices. The result indicated that the symmetrical condition was kept for the refractive index ranging from 1.331 to 1.358.

We propose a force sensor based on gold nanoparticles, which enable optical detection of force by measurement of the scattering light spectrum. Gold nanoparticles were dispersed on an elastomer sheet. The scattering spectrum changes due to strain were observed to investigate applicability of the sensor to force measurement. The force deforms the elastomer sensor body, and increases the interparticle distance of gold nanoparticles on the sheet. The increase of the interparticle distance gives rise to the scattering characteristic changes. We fabricated a prototype sensor using PDMS sheet and 40 nm of diameter gold nanoparticles. It was demonstrated that 21% strain induced 60% increase of scattering intensity of gold nanoparticles.

We propose a triaxial force measurement cantilever with piezoresistors fabricated by rapid thermal diffusion sidewall-doping. The device is developed as a tool for applying quantitative mechanical stimuli to cells and measuring their mechanical properties at the same time. The device consists of a sensing tip, two sensing beams, and four wiring beams. We form piezoresistors on the surface of the sensing tip and the sidewalls of the two sensing beams. We confirmed that our device was able to measure triaxial forces. The displacement sensitivities of the device were 1.59x10(-3) mu m(-1), 1.18x10(-3) mu m(-1) and 3.26x10(-4) mu m(-1) for x, y, and z-direction, respectively.

This paper reports on a method for estimating direction of a sound with one directional acoustic sensor. Inspired by the two input structure of bushcricket ear, our sensor was designed to have an acoustic channel and a micro piezo-resistive cantilever. The radiated sound acts simultaneously on the external and on the inner surface of the cantilever. As the result, the directionality of our sensor varies with the frequency of incident sound. The sound direction was estimated by using directional responses of the sensor at multiple frequencies so that it does not require either angle scanning or microphone arrays. We demonstrated that this method enables the sound direction to be estimated with the average error of 4 degrees in laboratory experiments.

This paper presents the design, fabrication, and the characterization of a photo-response compensated piezoresistive cantilever. The application field of the cantilever is to measure cellular mechanical properties under fluorescence microscopy. Photo-response which is caused by an excitation light of a fluorescence microscope interferes with measurement. We proposed piezoresistive cantilevers consist of a force-sensing cantilever with a reference cantilever to cancel out the photo-response. We measured the photo-response of the fabricated device, by varying wavelength, light intensity and light incidence angle. The experimental results show that the photo-response was decreased by 87%. This verified that present device has effective photo-response compensation by using the reference cantilever.

We directly measured the stresses induced on impact between a golf ball and a golf club head. The strain sensors were embedded into grooves on the face of the club head. 3-axis strain sensors were able to measure one normal stress and two shear stresses at each location. The shear stress directions indicated by the outputs of the sensors were in good agreement with the direction of the ball spin obtained from high speed camera images. The peak of the normal stress and shear stress on the contact face were measured to be 4x10(8) Pa and 1x10(8) Pa, respectively.

This paper reports on a thermal-based device for measuring water content in human skin. The device consists of resistive temperature detectors (RTD) and a pressure sensor. The RTD was also used as a heat source, and the pressure sensor was used to obtain constant thermal contact. Water content was measured by heat extraction rate across device interface under constant contact pressure. The device detected difference in water content of a contact object from 0.02 to 0.56g/cm(3) by measuring step response of the RTD in 3 seconds. Difference in water content of the human skin was actually detectable with the device in 3 seconds.

In this paper, we propose a stretchable tactile sensor composed of a pair of silicone rubber channels filled with electro conductive liquid. When a force was applied to this channel, its length and cross-sectional area deforms. By measuring the resistance change of the electro conductive liquid in the channel, its deformation can be measured. The proposed tactile sensor is composed of two parallel channel filled with electro conductive liquid, therefore, by comparing the resistance changes of each channel to the deformation, only the contacting force can be measured independently. Since a liquid is used for the sensing material, the proposed liquid tactile sensor can be easily attached to movable portions as the joints of robots.
In the paper, we measured the sensing characteristics of the liquid tactile sensor to the stretch, bend, and contact force. Finally, the efficiency of the sensor was demonstrated by measuring the contact force from 0 to 3.0N by attaching the 20% stretched liquid tactile sensor to curved surfaces with 0.05mm(-1) in curvature.

We have developed a silicon-microfabrication-based surface plasmon resonance (SPR) sensor with Si prisms and an optical grating. Since this sensor is compatible with microelectromechanical systems technology. it can be further miniaturized and integrated with optical parts or fluidic components for the realization of a one-chip SPR sensor. The Si prism structure, transparent in the near-infrared range, was used to lead the 1550-nm measuring light to the sensing Surface where the evanescent light was generated. Smooth prism slopes were obtained by using anisotropic etching to Utilize the (1 1 1) planes on the (1 0 0) Surface plane of single-crystalline Si wafer. The result Was a 200-mu m-pitch array of prisms with 54.74 slope angles. In this configuration the range of incident angles at which near-infrared light produces an SPR dip is from 38.26 degrees to 71.24 degrees. Because the SPR angles for major specimens (16.60 degrees for air. 22.06 degrees for water, and 22.79 degrees for ethanol) are Out of range, we used an optical grating with a roughly 400-nm-pitch to make an SPR clip position move to fit within the available angle range by the diffraction effect. SPR measurements with several specimens confirmed that the combination of Si prisms and the optical grating excited Surface plasmons. The measured SPR dip positions and their sensitivity to refractive index were compared with the theoretical values, and their consistency confirmed the utility of this device as an SPR sensor. (C) 2009 Elsevier B.V. All rights reserved.

We propose a fabrication method of three-dimensional silicon slopes using RIE-lag. RIE-lag is a lag of an etching rate depending on square openings area of a mask. We measured relationship between area of square openings and etched depths. We confirmed that etched depths were defined as a function of the square openings. With this relationship, we designed a mask with various sizes of the squares for slope structures. Square openings of various sizes were patterned using EB lithography. Silicon was etched vertically with ICP-RIE (Inductive Coupled Plasma - Reactive Ion Etching). By RIE-lag, trenches with multiple depths depending on the area of the square openings were formed. Silicon surface was smoothed by SF6 isotropic dry etching. As a result, by the combination of ICP-RIE anisotropic etching RIE-lag and SF6 isotropic etching, we fabricated 57° silicon slopes of surface roughness 10 nm in plane and 35 nm in slope surface. © 2010 The Institute of Electrical Engineers of Japan.

We propose a method to fix the positioning error of transferred bare chips on a substrate after the Temperature-Controlled Transfer (TCT) that we have previously developed. This TCT method is important for large area integration of heterogeneous materials. In the TCT process, the bare chips on an adhesive sheet are transferred and electrically connected to the substrate via Low-Melting Point Solder (LMPS). We reflowed the LMPS and used the surface tension of the LMPS to self-align the bare chips in position on the substrate. We experimentally confirmed that the self-alignment works when contact pads on the bare chip and the substrate were overlapped. The positioning error after the self-alignment process was within 0-15 % of the contact pad size. © 2010 The Institute of Electrical Engineers of Japan.

To achieve flight, an insect generates aerodynamic force by flapping its wings. However, this aerodynamic force acting on the wings has not been directly measured during free-flight. In this study, we fabricated an ornithopter modeled on a hawk moth, and attached a MEMS differential pressure sensor on its wing. Then, we measured differential pressure between upper and lower surfaces of the wing during free-flight. Reynolds number of the wing and wing load of the ornithopter were designed to be 4.2 × 10³[–], and 7.5[N/m²], which were close to those of a hawk moth. The mass, wing length and flapping frequency were 6.8[g], 110[mm] and 13[Hz], respectively. The maximum differential pressures at the center of the wing were 39[Pa] and 18[Pa] during downstroke and upstroke, which were 5 and 2 times larger than the wing load. The differential pressure contributed vertical pressure of 38[Pa] during downstroke and horizontal pressure of 15[Pa] during upstroke. The time average of vertical differential pressure was 7.0[Pa], which was as large as the wing load of the ornithopter.

We developed new encapsulation method of glucose oxidase solution with ionic liquid solvent and direct Parylene deposition for the application to MEMS glucose sensors. Glucose oxidase has been immobilized in gel or polymer on MEMS sensors, but its weak mechanical property has been remained to be solved. Then, its encapsulation has been demanded, but high-temperature MEMS bonding process (&gt
150*deg
C) for packaging the solution is destructive to glucose oxidase which is denatured over 50 °C. To solve these problems, we encapsulated the glucose oxidase-ionic liquid solution with room-temperature packaging (25 °C) of direct Parylene deposition process. The glucose oxidase solution array with the area of 1 ×3) mm2 (approximately 1 μl) was patterned on the hydrophilic-hydrophobic surface modification on the MEMS electrochemical electrodes in the use of the wetting phenomenon of the solution and, then, packaged by the chemical vapor deposition of 1.5 μm Parylene. Parylene packages could be opened by pushing when used. The opened glucose oxidase solution reacted to 150 mM glucose solution, revealing the electrochemical potential of 150 mV. The sensitivity of our sensor ranged from 1 to 100 mM, which is the glucose concentration in the blood of the diabetic patients. Therefore, proposed encapsulation method exhibits the potential application to glucose sensor packages for diabetic patients. © 2010 The Institute of Electrical Engineers of Japan.

We report on an ellipsoidal liquid lens fabricated by PoLD (Parylene on liquid deposition). We fabricated ellipsoidal liquid lenses of 0.50, 1.00, 1.50, and 2.00 μl in volume on hydrophilic elliptical domains with 5.00mm major diameter and 2.50mm minor diameter. We measured the two focal lengths corresponding to major and minor diameters by observing the image formed by a laser beam. We verified that measured focal lengths agreed with theoretical calculated results. In addition, we showed that our method enables us to fabricate ellipsoidal lenses which have the focal lengths as designed. ©2009 IEEE.

We propose a heat flow sensing device with a heat source to discriminate a contact object. The device was a three-layered structure separated by 600μm-thick PDMS (Polydimethylsiloxane) spacer, and consisted of a micro heater and three resistance-temperature detectors (RTD). We detected transient heat flow with pulse-heating method when 10mm-cubic blocks of cork, acrylic and aluminum were on contact with the device. Temperature gradient induced by heat flow differed by materials of contact objects. We also evaluated the surface temperature from two RTDs. Our device identified relative difference in thermal effusivity of materials. ©2009 IEEE.

We propose an optical device which appends pan/tilt functions to cameras by moving mirrors with electrowetting force. The device is composed of two plates and a liquid pillar holding two mirrors. On the lower plate, electrodes are patterned and a hydrophobic layer is coated. When a voltage is applied to the electrode on the lower plate, the liquid is moved toward the electrode by electrowetting force. Consequently, the mirror is tilted and the light path that comes into the device is controlled. When a camera was put below our device, the field of view of the camera was shifted by 25 degrees with 50 V applied. ©2009 IEEE.

We fabricated a peristaltic micropump by depositing Parylene on liquid directly (PoLD method), and tested its pumping characteristics. The Parylene thin film deposited on liquid not only forms the membrane of the micropump, but also composes the whole structure of the microfluidic system. The pumping membrane can be deformed by electrostatic force. This deformation can create liquid flow. Our micropump can transfer liquid at the flow rate of 2.7μl/min and generate a differential pressure of 41Pa. On the other hand, this pump made a wrinkle when the voltage applied and it leaked liquid. We devised the shape of the channel and electrodes and enabled it to close tightly. ©2009 IEEE.

This paper reports on an evaluation of the adhesion force between silicon and carbon nanotubes (CNTs), which were directly synthesized on a silicon substrate by chemical vapor deposition (CVD). CNTs bridging between silicon tips were pushed with a force-sensing cantilever to break the adhesion between silicon and CNTs. We measured the force acting on the cantilever at the moment of breaking the adhesion between silicon and CNTs. This force was measured to be 28 nN. ©2009 IEEE.

This paper reports on a micro Helmholtz resonator (HR) enhancing the sensitivity of an ultrasonic distance sensor. Attaching an HR to the sensor that consists of a piezoresistive cantilever microphone makes its sensitivity against ultrasonic wave higher. A HR of 600 μm height demonstrated a 17.5 times larger maximum amplitude of the cantilever vibration against single frequency wave. We also evaluated the dependence of the sensitivity on frequency and acoustic pressure. Our sensor was able to detect the distance of 0.5-6.0 m with the maximum error of 2.0%. ©2009 IEEE.

This paper presents a micro liquid prism. Two flat transparent plates float on a liquid droplet and these plates serve as prism faces. The two plates are positioned automatically by surface tension, just by putting the plates on the ellipsoidal droplet. Therefore the proposed prism can be fabricated accurately in micro scale without difficulty. As the liquid and the plates are encapsulated by Parylene, the prism can retain its shape. The prism which faces were 400ptm in diameter and whole size was smaller than 1mm3 was fabricated. The adequate function of the fabricated prism for Surface Plasmon Resonance (SPR) measurement was verified. ©2009 IEEE.

We developed liquid luminescent flexible displays using electrochemiluminescent solution as deformable luminescent material. The solution consisted of ruthenium complexes as light emitting material and ionic liquid as nonvolatile solvent. We injected the solution, to pattern and seal it, into microfluidic cells between two flexible films of polyethylene terephthalate substrates with indium tin oxide electrodes. The light emitting area of one cell was 2×2 mm2 The gap between the electrodes was 100 μm. We measured the luminance of the cell during application of 5OHz/4.OVpp (peak-to-peak value) rectangular waves of voltage in bent condition. The device was bent along the convex curvature with radii of 60, 30 and 20 mm. The luminance was reduced by only 30 00 when the radius of curvature reached 20 mm. We conclude the electrochemiluminescent cells are suitable for flexible displays because they can tolerate large deformation of bending. ©2009 IEEE.

This paper presents the design, fabrication, and the characterization of a stretchable substrate, achieving the change of intracellular calcium ion concentration by mechanical stress. We propose the stretchable substrate integrated with the air chambers of the pneumatic actuator. We have measured the areal strain depending on input pressure and the intracellular calcium ion concentration increase in response to the mechanical stress. The present stretchable substrate is able to provide the areal strain of 5.21%~12.3% for the input pressure of 34.5kPa~103kPa. We also verified that the present stretchable substrate is able to stimulate cells by the mechanical stress applied through integrins, showing potential feasible application for monitoring the calcium ion influx caused by the mechanical stress. ©2000 IEEE.

This paper describes an integration method of bridging-structural single-walled carbon nanotubes (SWNTs) onto the flexible PDMS sheet by stamping transfer. Silicon microstructures and the SWNTs which directly synthesized between the gaps of the microstructures were lifted off by PDMS stamp sheets with high yield (97.8 %) and accuracy (position error &lt; 100 nm). From the SEM observation of our transferred structures, we confirmed that our method could transfer the bridging-structural SWNTs on to the flexible materials without any damage to the SWNTs' bridging.
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We propose an integration method for arranging LED bare chips on a flexible substrate to fabricate a multi-color LED display. LED chips (240 mu m x 240 mu m x 75 mu m) which were arrayed on an adhesive sheet were transferred to a flexible circuit substrate using our temperature-controlled transfer (TCT) and self-wiring (SW) method. Using these methods, we demonstrated a 5-by-5 LED flexible device and a two-color (blue and green) LED device, and observed light emission from the LED chips.

We present a stretchable substrate integrated with pneumatic actuators, designed to be able to supply mechanical stress to live cells on a microchip. The fabricated substrate shows areal strain of 2.49∼5.88% for input pressure of 5∼30psi. The fibroblasts plated on the present devices are stretched for the input pressure. Therefore, we experimentally verified that the fabricated stretchable substrates are able to culture and stretch the fibroblasts, showing potential applications for monitoring the mechanical-stress-dependent cell response. © 2008 CBMS.

This paper reports on a thin piezoresistive cantilever for measuring air flow velocity around flapping wings. To measure the air flow velocity at a point of the wing directly, our sensor was attached to the leading edge of the wing. The sensor was designed to be 1 ?m thick. Because of the scale effect, the influence of the inertial force was small during flow measurement. The sensor had the sensitivity of 0.56 - 0.96 × 10-3 (m/s)-2 as well as the directivity. By using the micro flow sensor, we measured the perpendicular air flow velocity at the point of the leading edge of the wing. ©2008 IEEE.

We propose a liquid motor using surface tension. Our liquid motor is composed of a liquid droplet floating plate and a lower plate. The plate floating on thee droplet is rotated continuously by electrowetting actuation. The floating plate is asymmetrically and has four cogs. By electrowetting actuation, the shape of the droplet is deformed. Then, the floating plate rotates to the position where the surface energy of the sandwiched liquid takes a minimum value. On the lower plate, electrodes are patterned in an annular shape. By choosing the voltage-applied electrodes, the position of the floating plate is controlled. In this research, a 2 mm floating plate with a 500 mu m silicon cube was rotated at 180 rpm. This motor is useful for optical devices because the components of the liquid motor can be made of transparent materials.

This paper presents a scanning micromirror using deformation of a Parylene-Encapsulated Liquid Structure (PELS). Silicone fluid is put between a silicon plate and an electrode-patterned plate. Both of the plates and liquid are encapsulated by a Parylene membrane. Gold is deposited on the surface of the Parylene membrane to fabricate an upper electrode. By applying voltage between the upper and lower electrodes, the encapsulated liquid is deformed and the silicon plate is tilted. The silicon plate is supported by the PELS, instead of usual torsion beams. When a set of four appropriately synchronized voltages is applied between the four lower electrodes and the upper electrode, two dimensional scanning motion is achieved.

This paper reports complex three-dimensional (3-D) MEMS devices (polydimethylsiloxane) fabricated on PDMS by a parts-transfer method. Our target size of parts is 100-mu m-order in our parts-transfer method. First, we evaluate the transfer yield and the positioning accuracy. Secondly, we assemble a hidden vertical comb-drive actuator, including comb-electrodes and a support beam underneath its upper plate. Finally, we measure the drive characteristics of the actuator. Our actuators are the first demonstration of fabricating movable MEMS devices by parts-transfer technique. The demonstration indicates that complex 3-D MEMS devices with movable mechanical functions can be fabricated simply using our method.

We synthesized carbon nanotubes (CNTs) at the tips of commercial atomic force microscope (AFM) probes by chemical vapor deposition (CVD) process with applying an electric field. Applying the electric field during the CVD process increased the yield of AFM probes with CNTs at the tips (CNT-AFM probes). We formed a catalyst layer on the surface of AFM probes, and carried out the CVD process to synthesize CNTs. After the CVD process, we observed the tips of the AFM probes with a scanning electron microscope (SEM). The yield of CNT-AFM probes was about 52 %. The CNTs were determined by resonance Raman spectroscopy using a 488 nm argon ion laser. Observed Raman peaks were peculiar to single-walled carbon nanotubes (SWNTs). Then we obtained AFM images of a sample grating with the CNT-AFM probes. The CNT-AFM probes had higher horizontal resolution than standard commercial AFM probes.

We report a tapered liquid waveguide for an optical fiber-to-chip coupler. The tapered liquid waveguide has a smooth surface and has both a large structure and a micro structure on one chip. The waveguide is able to couple optical fibers of large-diameter to small MEMS devices. A Parylene film on the liquid prevented the liquid from deformation and evaporation. We fabricated the silicone oil waveguide by hydrophobicity of CYTOP. We measured a propagation loss of the tapered waveguide by entering the laser beam from the incident face. From a measurement result, this tapered waveguide can be a coupler which connects optical fibers to MEMS devices.

We developed a tunable wedge prism by electrowetting actuation. Our prism can shift the field of view to the left or to the right and is useful for small cameras and endoscopes because its field of view can be changed without the need for large instruments. It consists of two plates that face each other, and a liquid is sandwiched between them. The liquid and plates form a wedge when the angle between the plates is changed. We used electrowetting to change the angle between the plates. The wedge prism is small because the liquid driven by electrowetting works as a prism. In addition, the prism produces a clear field of view because its optical flatness is determined by the flatness of the plates.

We propose a method of integrating heterogeneous silicon microstructures ( typical scale of 10-100 mu m) into a single silicon substrate to fabricate MEMS structures. It includes adhesion-based liftoff and stamping transfer ( LIST) processes using poly-(dimethylsiloxane) ( PDMS) sheets. Silicon microstructures fabricated on different wafers are lifted onto the PDMS sheets by breaking the narrow columns supporting the microstructures by applying a vertical load to the PDMS sheet, and then transferred onto the silicon substrate with high yield ( more than 90%) and superior positioning accuracy ( within 0.3 mu m on average in a 2 x 3 mm area). Multiple heterogeneous silicon structures are integrated into a single silicon substrate by repeating this LIST process. We fabricated two-dimensional arrays, three-dimensional pyramidal structures and overhanging bridge microstructures with our method, which proved that the LIST process could be used to integrate heterogeneous MEMS structures into a single wafer.

We demonstrated the control system for local reaction in a micro channel with liposome as solution carrier. The dynamics of two-phase flow of liposome and water in our micro channel systems was observed. In this report, some results of the liposome motion in the diffuser, the inducer and the phase control channel in the systems are shown and discussed.

We developed an electrochromic voxel array for realizing a three-dimensional (3D) display. A voxel is a unit of 3D graphic data just as a pixel of 2D data. The color of voxels is tuned not by their light emission but by their light absorption in the same way as the coloration of things in the real world. Our voxels consist of ITO electrodes on glass substrates and 1 mm cubes of an UV-curing polymer coated with electrochromic material which can change its color electrically. We utilized poly-(3,4-ethylenedioxy-thiophene): polystyrenesulfonate (PEDOT:PSS) as the electrochromic material. Our voxel array and its Al counter electrode were soaked in CaCl2 solution. Voxels were operated with a very low voltage of about 1.0 V. We demonstrated a 4×4 voxel array, and the color change of the voxels was observed not only in the top view but also in the side view. ©2007 IEEE.

We propose an integration method of heterogeneous micro-electro-mechanical-system (MEMS) structures by liftoff and stamping transfer using a poly-(dimethylsiloxane) (PDMS) sheet. Silicon structures fabricated on multiple wafers were lifted off by PDMS sheets, and integrated onto a single wafer by the stamping transfer with high yield (&gt; 90%) and high accuracy (position error &lt; 500 nm). A two-dimensional (2D) integration and three-dimensional (3D) assembly of pyramid-like/inverted pyramid-like structures were demonstrated by our method. These demonstrations prove that our method enables us to integrate process-incompatible heterogeneous MEMS structures onto a single wafer.

The design and fabrication process of an electrically-driven varifocal liquid microlens are reported with experimental measurement results and a theoretical calculation model. Droplets of oil are sandwitched between a glass wafer and a thin-film of parylene chemical vapor deposited (CVD) directly onto the droplets' liquid surface. A method for creating fluid-filled micro chambers was realized with two core steps: 1) placing-shaping of oil droplets with hydrophobic/hydrophilic patterns and 2) coating them with a thin CVD parylene film in high vacuum condition. Liquid lenses and lens arrays of diameter from 20 mu m to 10mm were fabricated. In the tuning experiment, focal length was shortened to 20% of its initial value, from 3.8mm to 0.8mm. The values calculated from model match the data collected from experiments within the range of applied voltage from 0V to 150V.

In this paper, we proposed a thin optical system which has pan/tilt and variable focus functions for a small camera. Our optical system is composed of a tunable water prism and a tunable oil lens driven by electrowetting. The optical system can keep its thickness thin, because the oil lens is inside the prism and both of them are controlled on the same plate. In this research, we achieved the optical system capable of shifting the view direction 1.5 degrees and changing the focal plane from 25 mm to 12.5 mm. The thickness of the optical system is 2.5 mm.

We provide the design method of multi-step magnetic self-assembly using ferromagnetic-hinged structures. The process uses the magnetostatic torque generated by an external magnetic field perpendicular to the substrate to lift hinged structures. Hinged structure is composed of a rigid plate connected by elastic hinges to one side of a substrate. If hinged structures are raised in sequential order, it is possible to assemble like Japanese "origami" complex three-dimensional structures. In our previous study, we found that a dimensionless factor that depends on its shape determines the sensitivity of the hinged microstructures to a magnetic field. This factor can be used as a criterion in designing a process for sequential batch self-assembly, because the factor indicates the differences in the sensitivity. In this study, we designed multi-step sequential assembly by using the dimensionless factor. Four-step sequential batch assembly was demonstrated using this method. This method will be useful for optical systems, which consist of many complex three-dimensional structures. (c) 2006 Elsevier B.V. All rights reserved.

We propose an angle tunable liquid prism actuated by electrowetting. Our prism makes an optical scanner smaller, because the laser source of the scanner can be put just below the prism. The prism consists of two transparent plates and sandwiched liquid. The diameter and the height of the prism are 2 mm and 1.5 mm, respectively. In this research, we achieved the prism capable of shifting the light path to the right and the left by 7 degrees.

We proposed a wedge prism which is tunable by electrowetting actuation. The wedge prism is useful for a small camera or an endoscope, because the wedge prism is capable of changing the view without a large instrument. Our prism consists of two plates facing each other and liquid sandwiched between the plates. By changing the angle between the two plates, the liquid and the two plates form into the wedge shape. We used electrowetting to change the angle of the prism. The wedge prism keeps the size small, since the liquid driven by electrowetting works as a prism. In addition, the prism keeps the view clear because the optical flatness of the wedge prism is determined by the flatness of the two plates. In this research, we achieved the wedge prism with which we can shift the field of view to the right and the left.

A surface plasmon resonance (SPR) sensor with a prism array made by silicon microfabrication techniques is proposed. We fabricated silicon prisms arrayed in 200 gm in pitch by anisotropic wet etching for deflecting light. We measured SPR curves in specimen of air, water and ethanol using near-infrared laser light (1550 nm) and obtained the SPR dip in each measurement. We fabricated a flexible flap, which was actuated by Lorentz force, to change the incident angle. The silicon prism chip was attached on the flap, the SPR curve was measured by scanning the incident angle of laser light with the flap.

In this paper, we have developed a process for multistep sequential batch assembly of complex three-dimensional (3-D) ferromagnetic microstructures. The process uses the magnetic torque generated by an external magnetic field perpendicular to the substrate to lift hinged structures. We found that a dimensionless factor that depends on the volume of the magnetic material and the stiffness of the hinges determines the sensitivity of the hinged microstructures to a magnetic field. This factor was used as a criterion in designing a process for sequential batch assembly, i.e., for setting appropriate differences in sensitivity. Using a dimensionless factor in the design of the sequential assembly simplified the assembly process, which requires only placing the structures on a permanent magnet, and which can be used to carry out multistep sequential batch assembly. We fabricated hinged microstructures, which consist of 4.5-mu m-thick electroplated Permalloy plates and 200-nm-thick nickel elastic hinges of various sizes. In an experiment, four plates (600 mu m x 800 mu m) were lifted sequentially and out-of-plane microstructures were assembled in a four-step process. Assembly of more complex out-of-plane microstructures (e.g., regular tetrahedrons; 800 mu m long on one side) was also shown to be feasible using this method of sequential batch assembly.

In this paper, we demonstrate a "Pop-up" display. This display provides a pop-up image in the air with double-layered plane-convex microlenses and a hole array. This microlens array is fabricated by melting photoresists and form transfer [1] [2]. The height and diameter of the microlens was 34.6 mu m and 198 mu m, therefore the focal length was calculated as 318 mu m. To inspect the pop-up length, we estimated the position of the focal plane by measuring the light intensity of the image. The "Pop-up" image was formed at 2750 mu m higher from the original image on the display. In addition, we proved that the lens part needs no alignment with the original image.

We have developed a process for multi-step sequential batch self-assembly of complex three-dimensional ferromagnetic micro-structures. The process uses the magnetic torque generated by an external magnetic field perpendicular to the substrate to lift hinged-structures. In our previous study, we found that a non-dimensional factor that depends on its shape determines the sensitivity of the micro hinged-structures to a magnetic field. This factor can be used as a criterion in designing a process for sequential batch self-assembly, because the factor indicates the differences in the sensitivity. In this study, we designed multi-step sequential assembly by using the non-dimensional factor. Four-step sequential batch assembly was demonstrated using this method.

Male Morpho didius displays brilliant blue color with less viewing angle dependence. It is known that this coloring does not come from pigments but from the surface micro/nano-structure [1]. A less viewing angle dependent display is proposed by analyzing the coloring mechanisms. We've fabricated the structures displaying still images as well as different bright structural-colors. In addition, we placed them on an electrostatic comb-drive actuator to change the color.

This paper describes a gait generating network for a hexapod robot under various curvature turnings. Formica japonica Motschulsky, that is one of major ant with about 6 [mm] body length in Japan, was used for a gait analysis. Movements of the leg joints during free walking was recoded at 60 to 250 [frame/s] by a high-speed video camera. From the data, we found that the turning gaits were classified into two distinct patterns: a sharp turning gait in which case the radius of curvature is under 5 [mm], a gradual turning gait in which case that is 5 to 40 [mm] . A turning gait generating network, which was possible to generate each gait and to vary a radius of curvature, was devised. That is a neural network which is described by neurons and connections between them using excitation and inhibition. We made a hexapod robot with 3 DOF each leg and verified the accountability of the gait generating network using the robot. As a result, smooth and stable turning in different curvatures was achieved.

This paper describes three-dimensional (3-D) microstructure assembly using an external magnetic field. An external magnetic field perpendicular to a substrate lifts a hinged structure by the torque due to the shape magnetic anisotropy. We made micro flap structures (4.5 μm-thick electroplated Permalloy) which have 0.2 μ,m-thick nickel elastic hinges in various size, and made lift the structures in a magnetic field up to 50 kA/m. We demonstrated that the non-dimensional factor depending on the volume of magnetic material and the stiffness of the hinges determine the sensitivity to the magnetic field. As a result, we realized sequential batch assembly using the difference of the sensitivity. The each two plates 600 μm x 600 μm in size were lifted sequentially, and out-of-plane microstructures were assembled. And the complex out-of-plan microstructures, the regular tetrahedrons 800 μm on a side with a closed linkage were able to assemble by our method. © 2003, The Institute of Electrical Engineers of Japan. All rights reserved.

This paper describes three-dimensional (3-D) microstructure assembly using an external magnetic field. An external magnetic field perpendicular to a substrate lifts up a hinged structure due to the shape magnetic anisotropy. Micro, flap structures (4.5 mum-thick electroplated Permalloy) having 0.2 mum-thick nickel elastic hinges with various lengths and widths are bent in out-of-plane direction in a magnetic field up to 50 kA/m. The volume of magnetic material and the stiffness of the hinges determine the sensitivity to a magnetic field. As a result, we realized sequential batch assembly using the difference of the sensitivity. By way of the example, we have erected plates 600 mum x 600 mum in size. Also, structures bent at 90 and 45 degrees out of the plane have been obtained at the same time.