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Flexible or stretchable devices have been attracting attention because of the increase in popularity of internet-of-things devices and wearables. Because lithium-ion secondary batteries have rigid bulk shapes and therefore affect bodily motion, their use in such devices is problematic. Demand for plantar pressure-measuring devices has increased because impairment of ambulation leads not only to accidental falls by elderly people but also to arthritic disorders such as backaches induced by hallux valgus, calluses, and ingrown nails. Because the design of such a small, lightweight device with a medium-capacity lithium-ion battery is impossible, the collection of sufficient data has been impossible. We designed a novel all-solid-state battery produced with a solid-state electrolyte. The battery discharged even when folded, cut, or pushed. This 440 mAh battery could be used to improve overall usability of a prototype of an insole device that would consist of pressure sensors, a wireless communication device, and the battery.

This paper reports on an efficient fabrication process for a polymeric cantilever covered with conductive nano silver. The entire structure can be constructed additively using a printing process, without the use of an etching process or a sacrificial layer. The fabricated cantilever exhibits good linearity and forms a submillimeter-ordered air gap between itself and the substrate surface. Fine operation of a capacitive force gauge was obtained using the capacitance between the conductive cantilever and an electrode on the substrate. This process is expected to make possible the efficient manufacturing of various types of sensors that measure mechanical strain in a cantilever structure.

Screen printing is widely used to form conductive patterns due to its simple process, inexpensive equipment and masks, and fewer printing errors. In the field of electronics, there has recently been a growing demand to print both low-width and high-thickness electrodes, not only on flat surfaces but also on cylindrically curved ones. However, screen printing cannot form fine patterns due to ink bleeding, and in principle, printing on concave surfaces is impossible with conventional screen printing. Further, overprinting forms a thick pattern that requires subjecting the conductive ink to a drying process before printing the next layer of ink, leading to longer processing times. To address these issues, we developed an advanced screen printing technique called screen-offset curved-surface printing to form fine patterns on a curved substrate. In this method, ink is screen-printed onto a roll-type silicone blanket, and the ink is then transferred from the blanket onto a final substrate. During the transfer process, the roll-type blanket is moved in the vertical direction with a rotational motion along the surface of the curved substrate. It is this compound motion of the blanket that enables printing on a curved surface. Moreover, a simple overprinting technique for thick patterns was successfully performed on the curved substrate. This technique leverages the fact that the silicone blanket absorbs the organic solvents in the ink; the increase in the viscosity of the first layer of ink, owing to the solvent absorption, enables the next layer of ink to be easily overprinted on the blanket. In this paper, the developed printing method is presented in detail.

Adhesion contrast planography (ACP) is a printing method wherein a difference in adhesion forces between a semi-dried ink layer and a polydimethylsiloxane (PDMS) surface is used to form fine patterns. In the present study, direct laser surface modification of PDMS surfaces by a 193-nm excimer laser aiming at the use as an ACP printing plate was investigated in order to realize on-demand printed electronics. Various processing parameters were investigated systematically, including laser energy, laser pulse repetition frequency, scanning rate, and a thin primer film composed of a silane coupling agent. The results showed that appropriate laser conditions for a subsequent ACP process were found such that a cumulative energy density given at silane coupling agent-mediated PDMS surfaces by laser irradiation was in the range of 8–11 mJ/mm2. Under such conditions, the adhesion force on the treated PDMS surface was changed from 2.3 to 3.8 μN against a silica probing sphere. Complementary atomic force microscopy measurements on the laser-treated and pristine PDMS surfaces showed a gradual increase of the surface stiffness of PDMS, validating the idea that laser irradiation induced a conversion of PDMS into a mineralized SiO2 network. To further test the applicability of the present process, several complicated shapes were also examined.

We have fabricated hybrids of two-dimensional silica colloidal crystals and gold nanospheres for the development of platforms showing effective SERS phenomenon with a high spatial reproducibility. The SERS signal of 4-mercaptobenzoic acid immobilized on the hybrids was enhanced up to 10.4 times by optimizing the silica diameter, as compared with that on the gold nanospheres immobilized on a planar glass plate. We propose that the effective enhancement is induced by hot spots generated at the junction regions between the silica nanospheres.

We describe efficient visible- and near-infrared (vis/NIR) light-driven photocatalytic properties of hybrids of Cu2O and plasmonic Cu arrays. The Cu2O/Cu arrays were prepared simply by allowing a Cu half-shell array to stand in an oxygen atmosphere for 3 h, which was prepared by depositing Cu on two-dimensional colloidal crystals with a diameter of 543 or 224 nm. The localized surface plasmon resonances (LSPRs) of the arrays were strongly excited at 866 and 626 nm, respectively, at which the imaginary part of the dielectric function of Cu is small. The rate of photodegradation of methyl orange was 27 and 84 times faster, respectively, than that with a Cu2O/nonplasmonic Cu plate. The photocatalytic activity was demonstrated to be dominated by Cu LSPR excitation. These results showed that the inexpensive Cu2O/Cu arrays can be excellent vis/NIR-light-driven photocatalysts based on the efficient excitation of Cu LSPR.

We demonstrate the detection of an increase in refractive index and/or thickness by specific adsorption of proteins on a plasmonic surface on a paper substrate in the Otto configuration. Propagating surface plasmon resonance is observed on a gold surface deposited onto polymer-coated papers through angular scans of reflectivity in the Otto configuration under attenuated total reflection conditions. According to a surface analysis with atomic force microscope, the gold surface roughness on a polyvinyl chloride (PVC)-coated paper is comparable to that of a Si wafer, leading to the achievement of protein detection. On the other hand, the propagating length of the surface plasmons is shorter than that on the Si wafer. According to an observation of the gold surface with scanning electron microscope, the gold grain size on the PVC-coated paper is smaller than that on the Si wafer. Thus, many boundaries cause a reduction in the propagating length on the PVC-coated paper.

We realized the implementation of an ultrathin piezoresistive Si chip and stretchable printed wires on a flexible film substrate using simple screen-offset printing technology. This process does not require a special MEMS fabrication equipment and is applicable to face-up chips where electrodes are formed on the top surface of the chip, as well as to face-down chips where electrodes are formed on the bottom surface of the chip. This fabrication process is quite useful in the field of flexible hybrid electronics (FHE) as a method for mounting and wiring electronic components on a flexible substrate. In this study, we confirmed that face-up and face-down chips could be mounted on polyimide film tape. Furthermore, it was confirmed that the two types of chips could be simultaneously mounted even if they exist on the same substrate. Five-&mu, m-thick piezoresistive Si chips were transferred and wired on a polyimide film tape using screen-offset printing, and a band-plaster type blood pulse sensor was fabricated. Moreover, we successfully demonstrated that the blood pulse could be measured with neck, inner elbow, wrist, and ankle.

This paper addresses the characteristics of capacitive-type epidermal moisture measurements using disposable electrode films fabricated by a screen-printing method. The disposable electrode films were composed of substrates, comb-shaped electrode layers, and insulating layers. The epidermal moisture measurement obtained higher gain by optimization of the finger width of the comb-shaped electrode layer. The gain and accuracy of measurements were also improved by changing the insulating layer that covered the comb-shaped electrode layer to the striped-pattern type instead of the conventional solid-filling type. This epidermal moisture measuring instrument reduces the cleaning process of the electrode film that directly contacts the skin, simplifies the handling of the devices, and ensures hygienic operation.

We demonstrated the usefulness of Cu light-harvesting plasmonic nanoantennae for the development of inexpensive and efficient artificial organic photoelectric conversion systems. The systems consisted of the stacked structures of layers of porphyrin as a dye molecule, oxidation-suppressing layers, and plasmonic Cu arrayed electrodes. To accurately evaluate the effect of Cu nanoantenna on the porphyrin photocurrent, the production of Cu2O by the spontaneous oxidation of the electrode surfaces, which can act as a photoexcited species under visible light irradiation, was effectively suppressed by inserting the ultrathin linking layers consisting of 16-mercaptohexadecanoic acid, titanium oxide, and poly(vinyl alcohol) between the electrode surface and porphyrin molecules. The reflection spectra in an aqueous environment of the arrayed electrodes, which were prepared by thermally depositing Cu on two-dimensional colloidal crystals of silica with diameters of 160, 260, and 330 nm, showed clear reflection dips a...

The reciprocating needle dispensing technique is capable of patterning functional inks with a wide range of viscosities. As injections are performed by extruding an ink driven by the reciprocating needle motion, the mechanical specifications and the ink properties are expected to influence the amount of ink conveyed by the needle, thereby affecting the size of drops formed on a substrate. Needle dispensing tests were performed by using Newtonian silicone oils of different viscosities and a pseudoplastic conductive ink with various needle speeds and positions of the needle and the ink reservoir. Time-resolved analysis of the dispensing motions indicated that the formation of the dynamic meniscus around the needle was primarily described by the Landau–Levich–Derjaguin ink-coating theory. However, a slight modification that accounted for the initial gap between the needle and the glass capillary was needed to precisely describe the ink extrusion behaviors. The scaling analysis presented herein provides a perspective for the precise control of drop formation via optimal tuning of the ink injection. Regarding ink filament pinch-off, we discovered that the pseudoplastic liquid exhibited a faster pinch-off at higher needle retraction speed, which is attributed to a reduction of the apparent viscosity due to shear thinning. This behavior is preferable for needle dispensing with better stability.

Stencil contact printing is widely used to fabricate conductive patterns, and it is particularly used with solder paste to create interconnections. However, stencil contact printing is becoming inefficient for electronic components owing to the ever decreasing size of the components. An alternative method for fine pattern formation is screen printing, i.e. gap printing with a screen mask, which exploits the thixotropic characteristics of solder paste. Nevertheless, the mesh of the screen mask prevents the paste from permeating, resulting in irregular patterns. To address this issue, we propose gap printing with a mesh-cut screen mask. In this paper, we describe the fabrication procedure of the mask, and demonstrate the effectiveness of the proposed printing in the formation of fine and thick circular patterns; the patterns are shown to have low variations in size compared with conventional printing methods. The proposed method is expected to contribute to the further miniaturisation of electronic devices.

The submicrometer resolution printing of various metal acetylacetonate complex inks including Fe, V, Mn, Co, Ni, Zn, Zr, Mo, and In was enabled by a robust ink formulation scheme which adopted a ternary solvent system where solubility, surface wettability, and drying as well as absorption behavior on a polydimethylsiloxane sheet were optimized. Hydrogen plasma in heated conditions resulted in bombarded, resistive, or conductive state depending on the temperature and the metal species. With a conductivity-bestowed layer of MoOx and a plasma-protecting layer of ZrOx situated on the top of an IGZO layer, a solution-processed TFT exhibiting an average mobility of 0.17 cm2/(V s) is demonstrated.

In this paper, we present fully-printed vertical interconnections by reverse offset printing. In contact hole patterning, a vapor annealing of dielectric ink layers was used to add a taper structure on the edge of the dielectric layers. The technique involved rewetting of the layer by solvent adsorption from the vapor and subsequent morphological change according to Laplace pressure. It was also confirmed that the transfer of subsequent conductive layers was much reliable when the taper structure was added. With the optimization of silicone blanket specifications, a fully printed contact chain with the hole size of 25 μm was successfully demonstrated.

A vacuum chuck is often used to fix substrates in the field of electronic device fabrication including printing of the device electrodes. A conventional vacuum chuck plate locally sucks only where suction holes exist. However, when we employ a film as the substrate to be printed, suction from the holes causes the film distortion, which results in misprinting. Thus, we have newly developed a chucking assist sheet to fix a film substrate on a vacuum chuck stage for high-quality electrode printing. When printing is performed, the sheet is located between the film substrate and the vacuum chuck stage. The developed sheet is composed of lower and upper layers of woven stainless steel mesh and non-woven fabric, respectively, and such a structure can significantly decrease misprinting resulting from the film distortion caused by suction. In the present paper, we present the design concept of this chucking assist sheet and details of its features.

To manufacture printed devices, the wetting and dewetting of inks on a plate is an important factor to achieve precise printing. The Wilelmy plate method is more precise than sessile drop method, but has never been applied to polymer films with different film sides as used in printable electronics. In this study, we applied the Wilhelmy plate method to unilaterally affixed polymer film and found a good agreement between the dynamic contact angles of affixed films and the corresponding original films. This provided the usability of Wilhelmy plate method for affixed film.

We succeeded in controlling the wavelength range in which the photocurrent of porphyrin is enhanced by tuning as well as expanding the wavelength ranges in which the localized surface plasmon resonance (LSPR) occurs. We fabricated photoelectric conversion systems consisting of 5,10,15,20-tetrakis(p-carboxyphenyl)porphyrin (TCPP) and silver nanoprisms with small (SAgPRs) and large (LAgPRs) aspect ratios as plasmonic nano-antennae. Their photocurrents were much larger than those from TCPP-modified Ag planar electrodes at the specific wavelengths corresponding to their LSPR bands (SAgPRs: 460–610 nm; LAgPRs: 610–690 nm). The maximum enhancement factors (EFs) for the SAgPRs and the LAgPRs were 37 and 35, respectively. In order to enhance the photocurrents, we expanded the LSPR bands by the combined use of SAgPRs and LAgPRs. The system consisting of the mixture (MAgPRs) showed enhancement of the photocurrent over the entire Q-band region (480–690 nm). Finally, the total EFs of the photocurrents were evaluated by irradiation with AM1.5G sunlight through a long-pass filter of 480 nm and the results revealed that the EFs were in the order of MAgPRs > SAgPRs > LAgPRs. Furthermore, the system showed stability without loss of the enhancement property for at least 10 min under the solar irradiation.

We fabricate a wearable blood leakage sensor on a cotton textile by combining two newly developed techniques. First, we employ a screen-offset printing technique that avoids blurring, short circuiting between adjacent conductive patterns, and electrode fracturing to form an interdigitated electrode structure for the sensor on a textile. Furthermore, we develop a scheme to distinguish blood from other substances by utilizing the specific dielectric dispersion of blood observed in the sub-megahertz frequency range. The sensor can detect blood volumes as low as 15 μL, which is significantly lower than those of commercially available products (which can detect approximately 1 mL of blood) and comparable to a recently reported value of approximately 10 μL. In this study, we merge two technologies to develop a more practical skin-friendly sensor that can be applied for safe, stress-free blood leakage monitoring during hemodialysis.

We describe efficient visible- and near-infrared (vis/NIR) light-driven photocatalytic properties of hybrids of Cu

Nowadays, sensor devices have been increasingly attracted because of that they have been expected to play an important role to achieve the internet of things. Highly improved sensors have been proposed which can detect the condition of human [1-2], object [3] and environment [4]. These progresses indicate that a huge number of sensors will be produced in the near future to help us every scene in our life. In fact, it has been forecasted that the production amount of sensor will reach to one million per year [5]. For the forecasted future, it is all important that highly efficient manufacturing of them to keep the social sustainability.

For the fabrication of an organic thin film transistor (OTFT) array on a plastic film using printing techniques, fine patterns with widths less than 10 μm were required. We have already succeeded to fabricate the OTFT arrays on a film substrate using microcontact printing and reverse-offset printing of silver nanoparticle ink; a width of the source and drain electrodes of the OTFT fabricated reached 5 μm, and its channel distance was also 5 μm. In this report, we introduce and explain our newly developed printing techniques based on microcontact printing, to obtain fine, high precision, and thick patterns for the manufacturing of the practical printed and flexible electronic devices.

Microcontact printing is a technique that is widely used in the patterning of various materials ranging from small molecules to polymers and nanoparticles. In industrial applications, the roof-collapse of the stamp due to printing pressure is known to cause defective printing. To address this problem, a direct observation system for the patterning step of R2S microcontact printing was devised and used in conducting investigations. Results showed that several modes of roof-collapse were a function of the stamp thickness and area of the raised surface during the patterning step. In developing a model for this relationship, contact mechanics was investigated taking into account the effect of the finite thickness of the deformable poly(dimethylsiloxane).

We have been employing novel printing technologies in three-dimensional printed electronics applications, to form electronic devices on curved or three-dimensional object surfaces. In this paper, we report on a newly developed printing technology named ‘soft blanket reverse-offset’ (SBR) printing, which was developed to create wide and flat patterned layers with uniform thicknesses on curved surfaces. SBR printing is an extension of conventional reverse-offset printing and uses an extremely thick and soft blanket (referred to as a “soft blanket”) as an offset roller. We also created a new thick stencil printing plate and a two-layered soft blanket construction that avoids the formation of contact-defects. In addition, we have also succeeded in printing wide and flat patterned layers onto curved surfaces using commercially available silver nanoparticle inks. The printed layers are also characterized by uniform thicknesses and low resistivities, equivalent to those of layers printed on planar substrates.

Pad printing is a simple but effective method for fabricating electrodes onto complex curved surfaces. In this method, ink is picked up from the gravure plate by the soft pad, after which the ink pattern is transcriptionally formed from the pad to the final substrate. However, this printing method has some problems; primarily, it is difficult to form thick and large patterns. To address these limitations, we developed a new printing technique called "screen-pad printing." In this technique, ink is first screen-printed onto a blanket made of silicone resin, after which the ink pattern is picked up by the soft pad, and the pattern on the pad is transferred to the substrate. In this paper, we describe the features of the developed screen-pad printing technique when forming patterns on objects that have complex surfaces. Further, the impact of our new method is analyzed by comparing the experimental results of screen-pad printing with results obtained from conventional pad printing.

We have characterized a non-contact measurement system to concentrations of electrolytic solutions using a sensor film that is pasted on the outer surface of the solution vessel. This sensor film has asymmetrically sized circular electrodes printed facing each other on the both faces of substrate, and operates as a mutual-capacitive sensor. This measurement system shows the response depend on the strength of the electrolyte dissociation. In addition, it is found that the resolution and the sensing range could be controlled by adjusting the frequency of the applied voltage in the range from 10 kHz to 1 MHz.

We synthesized viscous precursors to indium gallium zinc oxide (IGZO) using three kinds of alcoholamines, ethanolamine (EA), diethanolamine (DEA), and triethanolamine (TEA), by a simple process. The viscous precursors are obtained just by vigorous stirring of alcoholamine and urea in an aqueous solution containing the metal nitrates during heating at 150-160 °C. The precursor containing EA (EA-precursor) is a pale-orange suspension containing aggregates of the metal hydroxides and shows pseudoplastic flow. The precursors containing DEA (DEA-precursor) and TEA (TEA-precursor) are transparent pale-yellow and dark-orange sols, respectively. They give Newtonian flow in the lower shear rate and pseudoplastic flow in the higher shear rate. Higher concentration of metal salts leads to higher viscosity of the precursors. According to thermogravimetry-differential thermal analysis (TG-DTA) for the EA- and DEA-precursors, evaporation of alcoholamine occurs at around each boiling point and subsequently formation of metal oxides occur at around 300 °C. In the case of the TEA-precursor, formation of metal oxides occurs before pyrolysis of TEA attributed to the higher boiling point of TEA. The thin IGZO film, which is prepared by spin-coating of the diluted DEA-precursor and subsequent sintering at 450 °C for 30 min, shows 0.02 cm2 ·V-1s-1 of the mobility and 10-5 of the on/off ratio. The highly viscous DEA-precursor containing high concentration of metal ions allows patterning in an area of 100 cm2 onto a surface of a silicon wafer with screen printing.

Poly(2–aminobenzylamine)/single wall carbon nanotube (P2ABA/SWNTS) thin films were fabricated for the detection of UA by using electrochemical surface plasmon resonance spectroscopy (EC–SPR) technique. The suspension of 0.01% wt of carboxylated SWNTSs was assembled on the polymer film because of the electrostatic and van der Waals interactions between the ‒COOH and ‒NH2. The P2ABA/SWNTS thin film formation on gold electrode was studied by EC–SPR technique. In this work, uric acid was detected by EC–SPR in PBS buffer comparing with the interference response with ascorbic acid. EC–SPR uric acid sensor using P2ABA/SWNTS thin film can be applied for the detection of uric acid in urine.

Reverse offset printing and microcontact printing are fascinating methods for fabricating fine patterns because both of them can attain a 1-µm/1-µm line-and-space resolution, and the resulting patterns manifest uniform layer-thicknesses irrespective of the pattern sizes. However, the printed pattern has very sharp edges; therefore, the step-coverage of subsequent overlying layers has often been a severe problem. Further, as reverse offset printing and microcontact printing use an engraved glass and a stamp, respectively, the pattern design is restricted because of bottom-contact-type defects. Thermal sintering of the printed patterns also leads to a longer processing time. To address these problems, we have developed several complementary processes. In this presentation, wet-on-wet, electrode-embedding, and push-pull processes and a newly developed high-resolution planographic method called adhesion contrast planography are discussed.

π-Conjugated polymers consisting of 9,10-disubstituted 9,10-dihydrophenenthrene, with the substituents octyl, 2-ethylhexyl, -OSiBu3, etc., units are prepared by organometallic polycondensation. Homopolymers (PH2Ph(9,10-R)) have a π-conjugation system similar to that of polymers of 9,9-dialkylfluorene and show UV-Vis peaks at ≈380 nm. In addition to the peak at ≈380 nm, some homopolymers give rise to a peak at a longer wavelength, suggesting molecular assembly of the polymers. X-ray diffraction data support the molecular assembly. The homopolymers show photoluminescence (PL) with PL peaks at ≈430 nm, and PL spectrum of the polymer film is essentially unchanged after heating the polymer film at 150 °C in air. The homopolymers undergo electrochemical p-doping at about 1.5 V versus Ag+/Ag.

In this study, we analyzed adsorption and binding behaviors of citrate-capped silver nanoparticles (AgNPs) on a pyridyl-terminated surface using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Adsorption of the AgNPs onto the pyridyl-terminated silicon wafer surface was completed through pH-controlled sol immersion. The adsorption occurred predominantly at a pH less than the pK(b) value of the pyridyl group and more than the pK(a1) of citric acid, indicating that the driving force behind adsorption was electrostatic interaction. Adsorption of citrate onto the pyridyl group also occurred at pK(a1) < pH < pK(b) without AgNPs. According to XPS in the N1s region, larger deprotonation from the pyridinium-formed pyridyl groups was demonstrated subsequent to adsorption of the AgNPs. The deprotonation from the pyridinium indicates the formation of the neutral pyridyl group as the counterpart of hydrogen bonding with the carboxyl group of citrate. The binding state between the pyridyl group and citrate surrounding AgNPs is expected to be kept stable through hydrogen bonding and van der Waals force derived from the AgNPs approach to the pyridyl surface.

Printing speed limitation is a critical issue for the high-throughput production in printed electronics. In this study, the formation mechanism of severe rash-type defects in a reverse-offset printing system operating at a high speed is discussed. A systematic investigation showed that the size and density of the defects were significantly influenced by the printing speed, indentation and by the material properties, such as thickness and elasticity of the polydimethylsiloxane (PDMS) sheets. The observation via a high-speed camera of the nip formations between a curved PDMS sheet and a flat glass revealed that, at the very initial stage of contact formation, parts of contacts were concurrently and unstably formed then widened; however, during the later stage, the coalescence of these spots led to the generation of air bubbles trapped in the contact regions, which lasted for several seconds. Based on complementary experiments on the extinction behaviours of the trapped air, we propose a new defect formation model for the rash-like transfer defects observed in the printing tests due to the trapped air regions resulting from the contact instability of PDMS.

We report a simple method that allows facile evaluation of the driving force required to move a droplet settled on a boundary of two surfaces with different surface energies. In the method, a verti...