Hidetoshi Shinohara

Studies on low-temperature direct bonding of VUV/O3-, VUV- and O2 plasma-pre-treated poly-methylmethacrylate

Low-temperature direct bonding of poly-methylmethacrylate (PMMA) plates was achieved by pre-treatment with vacuum ultraviolet irradiation in the presence of oxygen gas (VUV/O3), with vacuum ultraviolet irradiation in a nitrogen atmosphere (VUV), or with oxygen plasma. Based on surface analysis by attenuated total reflection Fourier-transform infrared spectrometry (ATR-FT-IR), x-ray photoelectron spectroscopy and near edge x-ray absorption fine structure spectroscopy, chemical changes of the PMMA surface after the pre-treatment were investigated. Changes in morphology and softening point were also investigated by nano-thermal analysis and atomic force microscopy. From the results, the bonding mechanisms proposed are described as follows: during the bonding process, the increased or generated polar groups cause an increase in the dipolar interactions (such as hydrogen bonding) between two pre-treated PMMA surfaces; in the case of VUV/O3 or VUV pre-treatment, a low-Tg layer is generated on the surface and this layer acts as an adhesive for the direct bonding of layers by diffusion.

Cyclo-olefin polymer direct bonding using low temperature plasma activation bonding

Low temperature direct bonding method of Cyclo-Olefin Polymer (COP) plates (20mm /spl times/ 40mm /spl times/ 2.0mm) has been developed employing surface plasma treatment with various gases such as N/sub 2/, O/sub 2/, and 10%-H/sub 2//Ar. Surface energy of the bonded interface has been measured by razor blade method. Reasonable bonding strength for flow devices was achieved even at room temperature. The contact angle measurement on the sample surfaces after plasma exposure indicated that the plasma activated surfaces became hydrophilic and this activated state lasted for longer than 2 months. This method is useful to fabricate micro-flow devices for single-molecule level optical bio-detection systems that requires less residual stress and deformation after bonding.

Fabrication of a microchannel device by hot embossing and direct bonding of poly(methyl methacrylate)

We have fabricated a 50-µm-wide and a 30-µm-deep microchannel device by hot embossing and the direct bonding of poly(methyl methacrylate) (PMMA) plates with dimensions of 20×20×1 mm3 and evaluated the devices mechanical, optical, and fluidic characteristics. The devices bond strength was confirmed to be sufficiently high for practical use as well as for withstanding severe cleaning conditions, such as ultrasonic cleaning in deionized water. The optical loss around the bonded interface was also evaluated, and no increase in light absorption was observed. There was no leakage or obstacles to smooth fluidic flow when methylene blue test liquid flowed in the channel. The above results confirmed that the hot embossing and direct bonding technologies for microchannel manufacturing using PMMA plates can realize high-performance microchannel devices.

Polymer Microchip for Electrophoresis-Mass Spectrometry Fabricated by Hot Embossing and Low Temperature Direct Bonding

Integrated electrophoresis-mass spectrometry polymer devices were fabricated. The electrospray ionization (ESI) emitter tip structure was formed directly at the microchip electrophoresis (MCE) outlet. Since these devices enable negligible dead volume at the electrospray port, efficient spray of the sample necessary for high resolution mass spectrometry (MS) was realized. Stable spray was also achieved at the low flow rate (-0.1 muL/min) without additional pump. Low cost and high performance COP MCE-MS chip was fabricated by hot embossing and low temperature direct bonding.

Simple and Low-Cost Fabrication of Flexible Capacitive Tactile Sensors

We fabricated novel flexible capacitive tactile sensors that can detect both the direction and distribution of an applied force. The sensor consists of a conductive silicone rubber as a movable electrode and fixed electrodes formed on a poly(ethylene terephthalate) (PET) film with silver paste. The dimensions of sensor head are 10.4 ×10.4 ×0.8 mm3. We developed the tactile sensor using screen-printing techniques and atmospheric-pressure plasma pretreatments. We experimentally evaluated the tactile responses to the applied force. The sensor detected the input force-distribution with a force ranging up to 10 N. The flexible thin PET film substrate enables fitting to the tight space and curved surface, and this capacitive tactile sensor is applicable for low-cost controllers of cellular phones and personal computers.

GaN Lateral Overgrowth by Hydride Vapor Phase Epitaxy through Nanometer-Size Channels Fabricated with Nanoimprint Lithography

Epitaxial lateral overgrowth (ELO) has been used for reducing the dislocation density to grow high-quality GaN crystals. In conventional ELO, micrometer-size channels formed on a mask material such as SiO2, where GaN growth starts, are generally used. In the present study, ELO through nanometer-size (50–80 nm) channels is investigated to improve the dislocation reduction ability. Channels are fabricated using nanoimprint lithography and dry etching. We demonstrate for the first time successful hydride vapor phase epitaxy (HVPE)-based GaN ELO growth through nanochannels. In the growth interface, distinct facet structures appear and coalescence between neighboring facets proceeds. The surface of a 20-µm-thick GaN layer becomes flat by the valleys between facet structures being buried. The dislocation density is shown to decrease to approximately 5×107 cm-2 for a 20-µm-thick GaN layer on sapphire. Photoluminescence measurements show a decay time of over 3 times longer than that of a conventional metalorganic chemical vapor deposition (MOCVD) template.

Fabrication of a Polymer High-Aspect-Ratio Pillar Array Using UV Imprinting

This paper presents UV imprinting methods for fabricating a high-aspect-ratio pillar array. A polydimethylsiloxane (PDMS) mold was selected as the UV imprinting mold. The pillar pattern was formed on a 50 × 50 mm2 area on a polyethylene terephthalate (PET) film without remarkable deformation. The aspect ratios of the pillar and space were about four and ten, respectively. The mold was placed into contact with a UV-curable resin under a reduced pressure, and the resin was cured by UV light irradiation after exposure to atmospheric pressure. The PDMS mold showed good mold releasability and high flexibility. By moderately pressing the mold before UV-curing, the thickness of the residual layer of the imprinted resin was reduced and the pattern was precisely imprinted. Both batch pressing and roll pressing are available.

XPS and NEXAFS studies of VUV/O3-treated aromatic polyurea and its application to microchip electrophoresis

In this study, the authors performed X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) studies of vacuum ultraviolet (VUV)/O₃-treated aromatic polyurea films to investigate their treatment effects. XPS and NEXAFS spectra indicate that the benzene ring was cleaved after treatment and that carboxyl, hydroxyl, ketone and aldehyde groups were formed at the cleaved sites. The VUV/O₃-treated polyurea film was applied to a polymethylmethacrylate (PMMA) microchip for microchip electrophoresis (MCE) of bovine serum albumin (BSA). Fast electro-osmotic mobility of 4.6×10(-4) cm²/V/s as well as reduction of the BSA adhesion was achieved. This functional surface is useful for high-speed MCE analysis.

Cyclo-Olefin polymer direct bonding using low temperature plasma activation bonding

Low temperature direct bonding method of Cyclo-Olefin Polymer (COP) plates (20mm /spl times/ 40mm /spl times/ 2.0mm) has been developed employing surface plasma treatment with various gases such as N/sub 2/, O/sub 2/, and 10%-H/sub 2//Ar. Surface energy of the bonded interface has been measured by razor blade method. Reasonable bonding strength for flow devices was achieved even at room temperature. The contact angle measurement on the sample surfaces after plasma exposure indicated that the plasma activated surfaces became hydrophilic and this activated state lasted for longer than 2 months. This method is useful to fabricate micro-flow devices for single-molecule level optical bio-detection systems that requires less residual stress and deformation after bonding.

Evaluation of UV roller imprinting using replicated fluorinated film molds

In this study, a fluorinated UV-curable resin was replicated by UV imprinting and used as a film mold. The film mold was fabricated by anti-sticking process (ACP). A remarkable advantage of the application for easy mold fabrication is expected, because it uses only UV imprinting. We evaluated two types of the pattern replications, directions between the stage movement and line and space (L&S) patterns in perpendicular as well as in parallel. The results of replication tests show obvious difference between UV roller imprinting and UV roller press imprinting. In addition, Vickers hardness is measured to evaluate the thermal property of UV roller imprinting. The results indicate that temperature is effective not only to improve pattern replication, but also to accelerate UV curing.