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For high throughput size controllable micro droplet generation, a three step half and half size/volume division of source droplet device using three stage cascade channel is introduced. Passive and active size/volume ratio controllable source droplet division devises are reported next. Finally, two types of microdroplet (daughter) generation devices using hydrodynamic droplet breakup of source droplet (mother) are described.

This study uses vacuum ultraviolet (VUV) light with a wavelength of 172 nm as a surface treatment to enhance the adsorption capacity of wood-based activated carbon (AC). The AC surface treatment is performed under three O2 partial pressure conditions—5.0 × 104 Pa, where ozone (O3) effects dominate, 6.3 × 10−6 Pa, where VUV effects dominate, and 1.9 × 103 Pa for a balanced condition. For the O3-dominant condition, only graphene edge defects are etched (no aromatic carbon bonds are etched), resulting in increased surface roughness. When the VUV effects dominate, aromatic carbon bonds are cleaved, which then reacted with O2 or water adsorbed inside the pores. This increased both the number and size of the mesopores. Under the balanced conditions, the water adsorption capacity was enhanced by 45.5%, which is higher than that obtained before VUV exposure or with VUV under other conditions. This is because the surface roughness increased, as well as the pore sizes and numbers under the balanced condition. These results indicate that we can control VUV-based AC surface treatments via O2 partial pressure.

Organic light-emitting diodes (OLEDs) using a liquid organic semiconductor (LOS) are expected to provide extremely flexible displays. Recently, microfluidic OLEDs were developed to integrate and control a LOS in a device combined with microfluidic technology. However, LOS-based OLEDs show poor-colour-purity light emissions owing to their wide full width at half maximum (FWHM). Here we report liquid/solution-based microfluidic quantum dots light-emitting diodes (QLEDs) for high-colour-purity light emission. Microfluidic QLEDs contain liquid materials of LOS for a backlight and QDs solutions as luminophores. The microfluidic QLED exhibits red, green, and blue light emissions and achieves the highest light colour purity ever reported among LOS-based devices for green and red lights with narrow FWHMs of 26.2 nm and 25.0 nm, respectively. Additionally, the effect of the channel depth for the luminophore on the peak wavelength and FWHM is revealed. The developed device extends the capabilities of flexible microfluidic OLEDs-based and QDs-based displays.

We developed an RGB microfluidic quantum dots light-emitting diode (QLED). All emitter and luminophores were liquid materials, including liquid organic semiconductor (LOS) as a backlight and quantum dots (QDs) solutions for high-color-purity luminophores. A deep-blue LOS backlight was used to excite QDs solutions. RGB lights were achieved with narrow full width at half maximum (FWHM) of 26.2 nm (green) and 25.0 nm (red), and were close to the boundary of CIE color space. The color purity of the RGB microfluidic QLED was the highest in that of ever reported LOS based devices. The proposed device is expected to provide future flexible displays with high-color-purity.

We developed a novel naphthalene derivative to function as a wide-energy-gap liquid organic semiconductor (LOS) host material for the limited range of liquid deep-blue light-emitting materials that have been developed to date. The naphthalene derivative 1-naphthaleneacetic acid 2-ethylhexyl ester (NLQ), which shows a low viscosity of 20 mPa·s at 25 °C, was synthesized as a LOS by introducing an ethylhexyl group into naphthalene. We doped 9,10-diphenylanthracene (DPA) into NLQ as a guest deep-blue dye. The highest occupied molecular orbital (HOMO) energy level of NLQ was estimated to be − 6.40 eV from photoelectron spectroscopy measurements in air. The energy gap of NLQ was estimated to be 4.08 eV from its absorption spectrum, indicating that NLQ has the widest energy gap of any such host material to date. The lowest unoccupied molecular orbital energy level of NLQ was calculated to be − 2.31 eV. Deep-blue electroluminescence emission in a liquid state was obtained by doping DPA into NLQ. Light emission could be achieved by a combination of Forster resonance energy transfer and direct recombination of trapped holes and electrons because the energy gap of DPA is straddled by the wider energy gap of NLQ.

This paper describes low-temperature bonding realized by squeegee-embedded Au nanoporous bumps that were activated by vacuum ultraviolet in the presence of oxygen (VUV/O3). The VUV/O3 technology is confirmed to be a suitable surface treatment technique for Au nanoporous bump bonding because it maintains the highly reactive surface of the Au nanoporous bumps during the treatment. X-ray photoelectron spectroscopy confirmed that the VUV/O3 treatment was capable of removing organic contamination on the nanoporous surface, and scanning electron microscopy images showed that the ligament size of the nanoporous bumps stayed the same. After bonding, the ligament size of the VUV/O3-treated nanoporous structure grew to 54 nm compared with 27 nm for the untreated samples. This increase in ligament size was attributed to the improvement in nanoporous coalescence by removing organic contamination that obstructed Au atom diffusion. Furthermore, the highest strength of the VUV/O3-treated samples reached 8.9 MPa at a low temperature of 200°C, which was three times higher than that of the untreated sample. This technology is expected to assist manufacturing of future 3-D integrations.

Copper-copper (Cu-Cu) direct bonding assisted by direct immersion gold (DIG) was demonstrated. Cu-Cu direct bonding is a critical technology for inductively coupled memory interconnections. To solve the problems of conventional methods of Cu-Cu direct bonding, a plating process using DIG to form an intermediate layer was selected. The concept of the developed bonding process is to use deformation of DIG to compensate for the surface roughness of the Cu substrates during application of pressure and annealing. Using this method, precise surface flattening of Cu substrates is not necessary. Bonding can be achieved even in an air atmosphere. A sample bonded at a temperature of 350°C failed within the chip in a shear test. It was found that bonding can be achieved when the gold (Au) thickness is greater than the half of the surface roughness of Cu at the bonding temperature. Transmission electron microscopy-energy-dispersive x-ray spectroscopy revealed that Au diffused into Cu during bonding. The diffusion constant of Au into Cu was investigated through a numerical calculation. The obtained results showed good agreement with the literature values.

We fabricated a microfluidic device with a three-dimensional (3D) structure and verified its droplet-generation performance for the stable production of droplets of around 10 μm in size. We compared the performance of the 3D device with that of conventional simple T-junction and cross-junction structures. The continuous phase sheared the dispersed phase into droplets from eight directions in the 3D device, compared with only one direction in the T-junction device and two in the cross-junction device. Droplets were produced efficiently over a wide range of fluid properties and flow conditions with the 3D device, unlike with the two conventional planar devices. Fluidic experiments were conducted using mineral oil with a surfactant as the continuous phase, deionized (DI) water as the dispersed phase, and DI water with glycerin to change the viscosity of the dispersed phase. The minimum droplet length was 47.2 μm in the T-junction device, 39.0 μm in the cross-junction device, and 22.4 μm in the 3D device when using a water and glycerin mixture with a viscosity of 9.0 mPa·s. Compared with the conventional devices, smaller droplets were produced using our 3D device, indicating that it has excellent droplet-generation performance.

A novel strategy for fabricating nanostructures was demonstrated that combined nanoimprint lithography and anisotropic wet etching. The resolution of proposed method does not depend on that of an original imprint mold. Atomically sharp V-grooves were formed by anisotropic wet etching using a SiO 2 etching mask fabricated by nanoimprint lithography. Atomic scale precision was performed by anisotropic etchant of tetramethylammonium hydroxide solution with adding a small amount of surfactant at room temperature. Using the V-grooves as a template, Al 2 O 3 /Al was deposited and etched by angled Ar ion milling after planarization with thick resin. Sub-50-nm metal structures were achieved with 72% size reduction of the initial mold structure.

This paper presents the formation of complex cross-sectional microfibers using three-dimensional microfluidic devices. The compartments and shapes of core and shell layers in the microfibers were independently controlled via three-dimensional fluidic channels fabricated by the combination of sheath units. The number of layers is easily expanded by the stacking of these units. Therefore, the highly heterogeneous microfibers of alginate hydrogel are obtained in polydimethylsiloxane structures. This widely expandable method has great potential for the development of functional and complex fiber-shaped materials.

This paper presents a method for utilizing three-dimensional microfluidic channels fully to realize multiple functions in a single device. The final device structure was achieved by combining three independent modules that consisted of horizontal and vertical channels. The device allowed for the one-step generation of water-in-oil-in-water droplets without the need for partial treatment of the polydimethylsiloxane channel surface using separate modules for generating water-in-oil droplets on the horizontal plane and oil-in-water droplets on the vertical plane. The second vertically structured module provided an efficient flow for the generation of highly wettable liquid droplets, and tuning of the first horizontally structured module enabled different modes of inner-core encapsulation within the oil shell. The successful integration of the vertical and horizontal channels for core-shell droplet generation and the chemical synthesis of a metal complex within the droplets were evaluated. The proposed approach of integrating independent modules will expand and enhance the functions of microfluidic platforms.

In a microfluidic device developed using a Si micro-pillar array directly coated with an iron catalyst, 4,8-dibromo-1-hydroxy-2-naphthaldehyde was catalytically synthesized with high efficiency. This represents the first dibromination of the organic compound in a microfluidic device. Typical beaker synthesis of the compound takes one day at 50 °C, but the method proposed here was performed at uncontrolled room temperature (23 °C), while reducing the reaction time to about 1 sec.

Recently, we developed Cu-Cu quasi-direct bonding with Pt intermediate layer deposited by atomic layer deposition (ALD). In this report, we study about a role of inserted Pt layer deposited by ALD. The improvement of bonding strength by quasi direct bonding was explained by two kinds of mechanisms.

LiTaO 3 (LT) or LiNbO 3 (LN)/Quartz bonded substrates with an amorphous intermediate layer were proposed to achieve both a large surface acoustic wave (SAW) velocity and a smaller temperature coefficient of frequency. Residual stress reduction of the amorphous film is expected to improve the bonding strength of a SAW substrate. In this report, we studied a method of low-residual stress amorphous film deposition for LT or LN/Quartz bonding. The residual stress of the LT substrate with an amorphous SiO 2 or Al 2 O 3 film deposited by ion beam sputtering, electron cyclotron resonance sputtering, and atomic layer deposition was evaluated. The LT substrate with the amorphous Al 2 O 3 film deposited by ALD had the minimum warpage (-0.152 μm) and residual stress (127.3 MPa). The residual stress of the Al 2 O 3 film deposited by ALD might be reduced because almost the same thickness of the Al 2 O 3 film was deposited on both sides of the LT substrate at the same time. The maximum bonding strength of 3.7 MPa was achieved in the substrate with the Al 2 O 3 film deposited by ALD. From these results, LT or LN/Quartz substrates with the Al 2 O 3 film deposited by ALD are promising materials to reduce residual stress toward SAW devices for 5G mobile communication.

A low temperature Cu-Cu bonding technique using an atomically thin-Pt intermediate layer deposited by atomic layer deposition (ALD) was recently reported. In this study, we investigated the characteristic of the Cu-Cu quasi-direct bonding using different metal intermediate layers. A thin-Pt or Au intermediate layer were deposited on the Cu surface by ALD in angstrom level. Both the thin-Pt and the Au intermediate layer successfully improved the Cu-Cu bonding strength compared with that without thin-metal intermediate layer. Although Au is widely used as a thick-intermediate layer in conventional Cu-Cu bonding methods, the Cu-Cu quasi-direct bonding with thin-Pt layer obtained three times lager bonding strength (9.52 MPa) than that with thin-Au layer (3.20 MPa). These results are essential for developing low temperature Cu-Cu bonding for highly integrated 3D IC chips.

We developed a water-electrokinetic energy harvester using a flexible woody carbon film (FWCF). The proposed device induced streaming current/voltage by water-vapor flow and thermal-evaporation flow in natural microchannels of wood, which called tracheid. In addition, high specific area of the FWCF can improve the output. The fabricated device showed a streaming voltage of about $9.7\ \mu \mathrm{V}$ with the water-vapor flow. Moreover, the output of the device were enhanced by thermal-evaporation flow. The maximum output voltage was $421.3\ \mu \mathrm{V}$ . After stabilization, $217.8\ \mu \mathrm{V}$ was continuously observed over 30 minutes at 80 °C. These results indicate that the proposed FWCF based water-electrokinetic power generation device has a high potential in power sources for Internet of things society.

A simple printing process to design a novel piezoelectric energy-harvesting device made from vinylidene fluoride/trifluoroethylene copolymers is presented. Fabrication using a metal nanoink and a household printer dramatically reduced the fabrication complexity. In addition, this process employed low-temperature steps, and thus the structural damage to the polymers resulting from high-temperature annealing was avoided. By stacking the devices and connecting them in parallel, the generated energy was increased and electric power of ∼1.12 μJ was obtained.

In this paper, we describe hybrid bonding technology of single-micron pitch with planar structure for three-dimensional (3D) interconnection. Conventionally, underfill method utilizing capillary force was used after the bonding of microbump. However, the filling becomes insufficient in a gap less than 10 μm between chips or bumps. One promising technology is the hybrid bonding technology that microbumps and an adhesive can be simultaneously bonded. To realize a single-micron pitch hybrid bonding, we fabricated a planar structure that consists of 8 μm-pitch Cu/Sn microbumps and a non-conductive film (NCF) by a chemical mechanical polishing (CMP) of resin. After planarization, the Cu/Sn bumps and the NCF were simultaneously bonded at 250 °C for 60 s. Cross-sectional scanning electron microscope (SEM) images and energy dispersive X-ray spectroscopy (EDX) images show that the adhesive resin on the bump surface was successfully removed by the CMP. In addition, SEM images of the bonded sample show that the adhesive filled the 2.5-μm gap between the chip and substrate. The Cu/Sn bumps were properly bonded in a corner on the chip. The proposed bonding method is expected to enable single-micron pitch interconnection for ultra-high density 3D LSI of next generation.

Recently, chemical operations with microfluidic devices, especially droplet-based operations, have attracted considerable attention because they can provide an isolated small-volume reaction field. However, analysis of these operations has been limited mostly to aqueous-phase reactions in water droplets due to device material restrictions. In this study, we have successfully demonstrated droplet formation of five common organic solvents frequently used in chemical synthesis by using a simple silicon/glass-based microfluidic device. When an immiscible liquid with surfactant was used as the continuous phase, the organic solvent formed droplets similar to water-in-oil droplets in the device. In contrast to conventional microfluidic devices composed of resins, which are susceptible to swelling in organic solvents, the developed microfluidic device did not undergo swelling owing to the high chemical resistance of the constituent materials. Therefore, the device has potential applications for various chemical reactions involving organic solvents. Furthermore, this droplet generation device enabled control of droplet size by adjusting the liquid flow rate. The droplet generation method proposed in this work will contribute to the study of organic reactions in microdroplets and will be useful for evaluating scaling effects in various chemical reactions.

We propose a low temperature bonding technique using an ultrathin intermediate layer deposited by atomic layer deposition. The ultrathin Pt film is selectively deposited on Cu surfaces without any masks. In order to reduce a deterioration of a reliability caused by impurities in the bonding interface, quasi-direct bonding was realized by thinning Pt intermediate layer. The shear strength of Cu-Cu bonding with the Pt intermediate layer achieved 9.5 MPa, which was five times higher than that without the Pt intermediate layer. We expect that the proposed bonding technique has a high potential to low temperature packaging technologies.

We developed a fabrication method of high-aspect-ratio fine vias with a build-up resin. The build-up resin composed of a thermosetting resin and silica fillers has low coefficient of thermal expansion and low dielectric constant. Thermal imprint was performed to form the high-aspect-ratio fine via holes on the build-up resin. The imprint mold with high-aspect-ratio fine pillar patterns was fabricated by photolithography and deep reactive ion etching. The residual layer consisted of the thermosetting resin and the silica filler was removed by O 2 /CHF 3 plasma etching. The via of 1.2 µm in diameter with aspect ratio of 5.5, and 5.0 µm in pitch was successfully fabricated followed by Au electroplating. The proposed fabrication method is applicable for high-density 3-dimensional and 2.5-dimensional integration technologies.

This paper presents a simple method of droplet formation using liquids that easily wet polydimethylsiloxane (PDMS) surfaces without any surface treatment. Using only structural features and uniform flow focusing, Oil-in-Water (O/W) and Water-in-Oil-in-Water (W/O/W) droplets were formed in the full PDMS structure. Extrusion channel and three-dimensional flow focusing resulted in effective fluidic conditions for droplet formation and the droplet size could be precisely controlled by controlling the flow rate of each phase. The proposed structure can be utilized as an important element for droplet based research, as well as a droplet generator.

We developed a novel microchannel-TEM grid that enables observation of interfacial biochemical reactions. A Y-shaped microchannel, which was sandwiched between two alumina membranes, realizes observation of interfacial reactions by lamellar flow. Reliable sealing of the microchannel was achieved by highly stable Al 2 O 3 /SU-8 bonding of 2.90 MPa at 180 °C. TEM images indicate the TEM grid has sufficient electron transparency and it was successfully fabricated without microchannel distortion. These results suggest that proposed TEM grid will become a powerful tool for revealing mechanisms of chemical reactions.

This paper reports design optimization of vibration based energy harvest device fabricated by simple printing and laminating process using polymeric piezoelectric material (VDF/TrFE). Modified trapezoidal design increased the output voltage and energy dramatically by adhesion strength as well as improvement of internal stress distribution of the device. The process guaranteed simple (fast and low cost) fabrication of energy harvest device and the new design achieved 277 V and 1014 nJ outputs which is about 3 times higher than that of our previous device. Furthermore, by stacking the devices and connecting them in parallel, we increased the output energy into about $\mathbf{2.58}\ \mu \mathbf{J}$.

The future development of low-temperature and low-pressure bonding technology is necessary for fine-pitch bump application. We propose a bump structure using Ag nanoparticles as an intermediate layer coated on a fine-pitch Cu pillar bump. The intermediate layer is prepared using an efficient and cost-saving squeegee-coating method followed by a 100°C baking process. This bump structure can be easily flattened before the bonding process, and the low-temperature sinterability of the nanoparticles is retained. The bonding experiment was successfully performed at 250°C and 39.8 MPa and the bonding strength was comparable to that achieved via other bonding technology utilizing metal particles or porous material as bump materials.

This paper presents methods for the formation of hollow microcapsules and microlenses using multiphase microdroplets. Microdroplets, which consist of a gas core and an organic phase shell, were generated at a single junction on a silicon device without surface treatment of the fluidic channels. Droplet, core and shell dimensions were controlled by varying the flow rates of each phase. When the organic solvent was released from the organic phase shell, the environmental conditions changed the shape of the solidified polymer shell to either a hollow capsule or a microlens. A uniform solvent release process produced polymeric capsules with nanoliter gas core volumes and a membrane thickness of approximately 3 μm. Alternatively physical rearrangement of the core and shell allowed for the formation of polymeric microlenses. On-demand formation of the polymer lenses in wells and through-holes polydimethylsiloxane (PDMS) structures was achieved. Optical properties of the lenses were controlled by changing the dimension of these structures.

In this study, we propose on-demand multi-color microfluidic organic light-emitting diodes (microfluidic OLEDs) using fluorescent guest emitter-doped liquid organic semiconductors. We use 1-pyrenebutyric acid 2-ethylhexyl ester (PLQ) not only for a greenish-blue liquid emitter, but also for a liquid host. 5,12-Diphenyltetracene (DPT), 5,6,11,12-tetraphenyltetracene (rubrene), and tetraphenyldibenzoperiflanthene (DBP) are doped into PLQ to obtain green, yellow, and red liquid emitters, respectively. Single-micrometer-thick SU-8-based microchannels sandwiched between an indium tin oxide (ITO) anode and a 3-aminopropyltriethoxysilane (APTES)-modified ITO cathode are fabricated on a glass substrate using photolithography and heterogeneous bonding techniques, and emitting layers are formed on-demand by simply injecting liquid emitters into the target microchannels. The microfluidic OLEDs with liquid emitters successfully exhibited multi-color electroluminescence (EL) emissions. Furthermore, the maximum luminance reached 26.0 cd/m2 at 61 V for 2.5-μm-thick microfluidic OLED with PLQ, and the decreased EL luminance was recovered by replacing the degraded emitting layer with a fresh liquid emitter. We expect that on-demand multi-color EL emissions and refreshable luminance features of the proposed microfluidic OLEDs will be highly promising technologies for future long-life light-emitting device applications.

This paper presents a droplet sampling device driven by horizontal pneumatic actuators. A high aspect ratio and highly flexible PDMS (polydimethylsiloxane) structure was proposed for carrying out larger number of sampling than the number of actuators. Large deformation of the actuators caused domino-deformation of parallel walls, and the deformations allowed for selective collection of target droplets. The dimensions of the PDMS structure and the ratio of resin to curing agent were optimized for efficient sampling under the low pressure applied to the actuators. Five sampling modes were achieved in the simple one-layer structure consisting of one inlet, four walls, one drain channel, and two pneumatic actuators, formed by single-step soft lithography process.

We report a real time method to monitor the chemical reaction in microdroplets, which contain an organic dye, 5(6)carboxynaphthofluorescein and a CdSe/ZnS quantum dot using fluorescence spectra. Especially, the relationship between the droplet diameter and the reaction rate of the two reagents was investigated by changing an inlet flow rate. key words: Microfluidic Device, Fluorescence Spectroscopy, Real-Time Monitoring, Semiconductor Quantum Dot, Fluorescence Energy Transfer

Here, we propose simple diamond functionalization by carboxyl termination for adenosine triphosphate (ATP) detection by an aptamer. The high-sensitivity label-free aptamer sensor for ATP detection was fabricated on nanocrystalline diamond (NCD). Carboxyl termination of the NCD surface by vacuum ultraviolet excimer laser and fluorine termination of the background region as a passivated layer were investigated by X-ray photoelectron spectroscopy. Single strand DNA (amide modification) was used as the supporting biomolecule to immobilize into the diamond surface via carboxyl termination and become a double strand with aptamer. ATP detection by aptamer was observed as a 66% fluorescence signal intensity decrease of the hybridization intensity signal. The sensor operation was also investigated by the field-effect characteristics. The shift of the drain current-drain voltage characteristics was used as the indicator for detection of ATP. From the field-effect characteristics, the shift of the drain current-drain voltage was observed in the negative direction. The negative charge direction shows that the aptamer is capable of detecting ATP. The ability of the sensor to detect ATP was investigated by fabricating a field-effect transistor on the modified NCD surface.

A direct bonding of polyoxymethelene (POM) was feasible at 100 °C by using self-assembled monolayers (SAM) as surface modification method. (3-Aminopropyl)triethoxysilane (APTES) and (3-Glycidyloxypropyl)trimethoxysilane (GOPTS) were applied in our work. Surface modification carried out with different VUV/O3 irradiation conditions showed different bonding strength. In addition, the bonding condition with highest strength had an average strength of 0.37 MPa. This technology was expected to be used in packaging for micro/nano electromechanical systems (MEMS/NMES), such as bio-/medical devices.

Cu-Cu direct bonding under help of direct immersion gold (DIG) for multi-die fan-out wafer level package was demonstrated. Cu-Cu direct bonding is a critical technology for high-frequency applications. To solve challenges of conventional methods, the DIG was used. As a result, a cohesion failure was obtained in shear test.

Direct bonding of polyoxymethylene (POM) at 100 °C was feasible using self-assembly monolayers (SAM). The POM substrates were first activated by vacuum ultraviolet irradiation in presence of oxygen gas (VUV/O 3 ) and then modified with SAM: (3-Aminopropyl)triethoxysilane (APTES) and (3-Glycidyloxypropyl)trimethoxysilane (GOPTS), respectively. Fourier transform infrared spectroscopy showed that both APTES and GOPTS modifications were successful. The bonding reached an average bonding strength of 0.37 MPa, and bulk fracture was observed after the debonding test. Surface observation results showed VUV activation process time played an important role in bonding. This technology is expected to be applied in future bio-inert electron devices.

We developed a highly bendable transparent indium tin oxide (ITO) electrode with mesh pattern for flexible electronic devices. Mesh pattern reduces an effect of tensile stress and propagation of cracks when the electrode is bent. The proposed ITO electrode was fabricated on a polyethylene terephthalate by means of photolithography and wet etching. The bendability was investigated through cyclic bending test. Resistance increase rate of the mesh patterned ITO electrode after 1000 times bending was approximately 9.18 × 102 times as low as that on a plane ITO electrode. In addition, the distinct cracks were not observed on the mesh patterned ITO electrode after cyclic bending. Mesh patterned ITO electrode was applied to a liquid-based organic light-emitting diode (OLED). Even the use of the mesh patterned ITO after 100 times bending, electroluminescence emission was confirmed without obvious damages. These results indicate that the mesh patterned ITO electrode gives an impact in flexible electronic devices.

We proposed a novel fabrication method of a pillar patterned self-standing curved film by spherical soft-UV imprint lithography. Soft-UV imprint lithography was performed using a patterned polydimethylsiloxane (PDMS) mold and a convex mold in order to pattern pillar onto large curved film. A mother patterned mold of spherical soft UV imprint lithography was prepared by unique 3D printer method. The curved film with the pillar pattern was successfully fabricated with a curvature radius of 40 mm. The proposed method is useful for 3D-structured fabrication of the optical devices.

We developed a novel naphthalene-derivative to function as a wide-bandgap liquid organic semiconductor (LOS) host material for the limited range of liquid deep-blue light-emitting materials that have been developed to date. The naphthalene-derivative, 1-naphthaleneacetic acid 2-ethylhexyl ester (NLQ) was synthesized as a LOS, by introducing an ethylhexyl group into naphthalene. 9,10-Diphenyl anthracene (DPA) was doped into NLQ as a guest deep-blue dye. From the absorption spectrum, the bandgap energy of NLQ was estimated to be 4.13 eV, indicating that NLQ has the widest bandgap energy of any such host material so far as we know. Deep-blue electroluminescence (EL) emission in a liquid state was obtained by doping DPA into NLQ. Light emission could be achieved by a combination of Forster resonance energy transfer and direct recombination of trapped holes and electrons because the bandgap energy of DPA is straddle by that of the wide-bandgap NLQ. Thus, NLQ is shown to be a promising wide-bandgap LOS host material, which allows deep-blue light emission and may have applications in liquid organic light-emitting diodes.

We propose simple and high-throughput fabrication of large-area flexible microfluidic organic light-emitting diodes (microfluidic OLEDs). Flexible electro-SU-8-microchannels with a liquid emission layer were fabricated by the following four steps: (a) screen printing for transparent electrodes, (b) novel belttransfer exposure for SU-8, (c) heterogeneous low-temperature bonding using self-assembled monolayers (SAMs), and (d) injecting a liquid emitter into the microchannels. 1-Pyrenebutyric acid 2-ethylhexyl ester (PLQ), which is on of liquid organic semiconductors, was used as a liquid emitter. The liquid emitter successfully filled the flexible microchannels, and electroluminescence was obtained both in flat and curved states. The proposed microfluidic OLED is applicable for future flexible posters or displays, and can be adopted around curved surfaces.

We demonstrated multi-color microfluidic electrochemiluminescence (ECL) cells. 5,6,11,12-Tetraphenylnaphthacene (rubrene), 9,10-diphenylanthracene (DPA), tetraphenyldibenzoperiflanthene (DBP)-doped rubrene, and 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) dissolved in a mixed organic solvent of 1,2-dichlorobenzene and acetonitrile in the ratio of 2:1 (v/v) were used as yellow, blue, red, and green ECL solutions, respectively. Light emissions were confirmed using simple-structured ECL cells consisting of two indium tin oxide (ITO) coated glass substrates with an SU-8 spacer of thickness varying from 0.9 to 6 μm. The SU-8-based microfluidic ECL cells were fabricated using photolithography and heterogeneous bonding techniques through the use of epoxy- and amine-terminated self-assembled monolayers. The emitting layers were formed on-demand by injecting the chosen ECL solutions into the microchannels sandwiched between ITO anode and cathode pairs. Multi-color ECL was successfully obtained at the light-emitting pixels. The microfluidic ECL cells with DBP-doped rubrene solution showed a maximum luminance of 11.6 cd/m2 and the current efficiency of ca. 0.32 cd/A at 8 V. We expect that the proposed microfluidic device will be a highly promising technology for liquid-based light-emitting applications.

A process for the simultaneous fabrication of through-glass interconnect vias (TGVs) and gold (Au) bumps using dry film resist and submicron Au particles is proposed. A Ti/Pt/Au layer was sputtered on the top and bottom surfaces of glass vias to improve the adhesion between the glass substrate and submicron Au particles. The submicron Au particles filled the resist holes and glass vias fabricated by photolithography and by the two-electrode method, respectively, and were then sintered. The height and diameter of the fabricated Au bumps were about 20–25 and 200 µm, respectively. The Ti/Pt/Au layer on the surface of the glass substrate was removed by Ar ion milling to isolate each bump electrically. The resistance of a single Au bump and TGV was evaluated using the four-wire ohm method to be about 0.05 Ω. Furthermore, Au bump bonding was demonstrated. Fractured Au bumps and TGVs were observed by scanning electron microscopy after the bonded sample was peeled. It is expected that this fabrication process using a dry film resist and submicron Au particles will be useful in simple packaging processes to form glass interposer substrates or glass integrated circuit chips.