In Jet and Flash Imprint Lithography (JFIL), ambient gas is trapped between the resist, the substrate and the mold. The volume of the trapped ambient gas is estimated about 9.7 ~ 21.5% of the resist volume. It takes time for the bubbles to disappear in the closed space. By using carbon dioxide as the atmospheric gas and applying an organic layer such as Spin on Carbon (SOC) to the top surface layer of the substrate, it is proposed by theoretical calculation that the gas disappearance time is shortened and the throughput is improved. When the thickness of the SOC layer on the substrate was 5 nm or more, it was indicated that the gas disappearance time was shorter in carbon dioxide ambient than in helium ambient.

In this work, total internal reflection fluorescence microscopy (TIRFM) was combined with the refractive index matching method to measure the three-dimensional motion of a nanoparticle on a nanosized step structure in water. A step (height = 64 nm) based on an ultraviolet (UV)-curable resin was fabricated using UV nanoimprint lithography. The step has a refractive index similar to that of water to eliminate the optical distortion due to light refraction and reflection at the interface between the nano structure and water. TIRFM could clearly capture the motion of a fluorescent nanoparticle in the vicinity of the nanostep in water. Diffusion coefficients of the particle in the vicinity of the nanostep edge were obtained from its time-lapse images, indicating that the diffusion coefficient measured along the edge of the step was 1.2 times larger than that measured across the step. Molecular dynamics simulations were also conducted to calculate the diffusion coefficients of a rigid particle close to the top of the step. The simulation results were qualitatively consistent with the experimental observations. The experimental and simulation methods presented here would help understand the nanoparticle motions and solvent flow dynamics around more complicated nanostructures.

Rose petals exhibit functionalities, such as high contact angles (CAs) and high adhesion with water. Their surfaces comprise hierarchical micro/nanostructures. Nanopatterns can be fabricated on a microstructure via several conventional processes. However, the shortcoming of this approach is the challenge of fabricating a large hydrophobic surface. To address this issue, we employ a technology, which we had introduced to fabricate a large moth-eye film. First, we fabricate a nanostructure (moth-eye) as the hydrophobic surface, after which we fabricate the microstructure via a roll-press process on it to obtain the adhesion area. The fabricated surface exhibits high hydrophobicity and adhesion.

Performing the minimum number of ultraviolet nanoimprint lithography imprints is important for ensuring high throughput and low costs. The stamp lifetime can be estimated quickly from little information during imprint processing. We proposed two methods to predict the stamp lifetime from durability test data with a line-patterned mold. We characterized the contact angle, concentration of release resin, and the number of imprints from the data. Both of the proposed methods used machine learning. One method was binary classification, and the other was regression analysis. Under the binary classification method, the recall was 50% and the prediction showed that the recall becomes 0% when Gaussian random noise is added. Under the regression analysis, the prediction did not drastically change, with an approximately 100-fold increase in the mean absolute error. The results show that regression analysis is useful for predicting the lifetime of a line-patterned mold.

Recently, flexible electronic devices such as printed electronics have attracted attention. Interposers are required to flexibly connect circuit devices. However, most conventional interposers are not flexible because they are composed of silicon or glass substrates. To solve this problem, we developed a manufacturing process for flexible interposers. We used photolithography to fabricate columnar master molds with diameters of 10 μm and 20 μm. After applying a release agent to the master molds, hole patterns were produced using UV nanoimprint lithography. The holes were filled with silver ink. The flexible interposer was then completed.

Droplet-dispensed ultraviolet nanoimprint lithography (UV-NIL) in helium enables adaptive material deposition to match pattern variations in a mold. It is a potential lithographic technology for semiconductor devices, but process throughput is an issue. UV-NIL in trans-1,3,3,3-tetrafluoro-propene (TFP) and 1-chloro-3,3,3-trifluoropropene (CTFP) gases has enabled bubble-free and high-throughput processes for spin-coated films. This study investigated the applicability of a mixed condensable TFP/CTFP gas to droplet-dispensed UV-NIL. The filling time in a local area of the mold in a mixed condensable gas atmosphere was as low as 1/30^th that in helium. Similarly, the filling in the entire mold was faster in a mixed condensable gas atmosphere than in helium, and micropatterns could be filled within 1.6 s. When the droplets were exposed to the mixed TFP/CTFP gas, the droplet diameter of 108 µm increased to 127 µm owing to gas absorption. The quality obtained for an L/S 90-nm pattern was the same as for the pattern of a spin-coated film, but the line width of patterns fabricated by UV-NIL in ambient TFP/CTFP was 6 nm narrower than that for UV-NIL in He.

An in-plane micro-supercapacitor (MSC) which has a unique interdigitated electrode structure with through-holes was developed by laser annealing and ablation of a carbon/polyamide acid composite coating on a polyimide film. The laser annealing of a composite film consisting of multi-layer graphene or activated carbon remarkably lowered the resistivity by laser carbonization of polyamide acid. The laser ablation was conducted to make an interdigitated electrode with a through-hole structure. The through-holes were effective to improve the capacitance of an in-plane MSC by enhancing the ion diffusion in carbon layer because the surface area of carbon layer can be increased using front and back sides of a polyimide film. An in-plane MSC consisting of an asymmetric interdigitated electrode which had an activated carbon composite layer on the front side and a multi-layer graphene composite on back side of a polyimide film showed the improvement of capacitance.

Mixing is difficult in microfluidic devices due to the low Reynolds' number. We proposed and demonstrated a surface-acoustic-wave (SAW)-based microfluidic system which can control the temperature by mounting a heater. This device has a hollow cylindrical reservoir made of resin on a piezoelectric substrate (LiNbO₃), and the solution can be rotated by injecting SAWs from both sides, which are shifted parallel to the central axis of the reservoir. 0.75 W of power was supplied to the IDT to generate SAWs, and the temperature rise of the liquid was measured with a thermographic camera when 0 to 0.55 W of power was supplied to the heater. As a result, by mounting the heater on the SAW actuator, it was possible to uniformly raise the temperature of a 40 µL micro-liquid by 8 to 40 ℃ in about 80 seconds, demonstrating the usefulness of this heater-mounted SAW agitation device.

Novel temporary bonding/debonding system including high heat resistant temporary bonding adhesive and debonding methods with conventional laser ablation or newly developed photonic release by Xe flash light irradiation will be introduced. Our new temporary bonding adhesive shows no delamination and no voiding after thermal treatment over 300 ℃ and can be easily removed by peeling off after debonding from the support carrier. In addition, by adopting the dual layer structure with adhesive layer and laser release layer, we can form the suitable structure for debonding with laser ablation. Furthermore, in the case that metal layer is applied instead of laser release layer, debonding by one-shot Xe flash light irradiation within 5 ms can be achieved, indicating the increased throughput at debonding process as compared to the other dobonding methods. Process demonstration results of wafer thinning down to 50 μm, fan-out wafer level packaging (FOWLP) will also be shown in this paper.

We newly developed a negative photo-definable polyimide dry films with higher photoreactivity than conventional ones. We succeeded in fine and high aspect ratio patterning with 90 μm thickness and 8 μm width by using new polyimide dry films. When compared after curing, the tensile breaking strength and share strength of new and conventional polyimide dry films were almost the same. However, when compared after PEB and exposure, the new ones showed clearly higher properties than conventional one. Using this polyimide dry film as an inter-layer dielectrics or a permanent resist was effective in improving the wiring density of electric devices.

A reworkable resin, which is degradable after use, was developed for application as a dental resin with an enhanced stability. A dimethacrylate monomer containing a ketal linkage in the molecule was used as a reworkable monomer. The reworkable monomer was successfully cured by blue light irradiation (470-nm light) using the camphorquinone/amine photoinitiating system. The cured reworkable resins were degraded in the presence of a UV- and violet-light sensitive photoacid generator by subsequent irradiation of UV light (365-nm light) at room temperature. The degradation was due to the acid-catalyzed decomposition of the ketal linkages in the cured reworkable monomers. Selection of the evaluated photoacid generators is very important in order to improve the stability of the cured resin. The result suggested the possibility of application of the reworkable monomer as a dental resin.

Polyphthalaldehyde (PPA) is a representative degradable polymer that can be end-to-end depolymerized. Herein polymers bearing two and three PPA chains have been prepared, and their photochemical behaviors were investigated. The PPA chains were linked to fluorene and truxene cores via oxime ether units that are photoreactive moiety. Di- and trifunctional PPAs were obtained by anionic polymerization of phthalaldehyde monomer (o-PA) initiated by corresponding oximes and 1,8-diazabicyclo[5.4.0]undec-7-ene, even though the conversion of was low after purification. From the ¹H NMR spectral changes of CDCl₃ solutions of both PPA on irradiation with Hg-Xe lamp, it was found that PPAs decreased along with the formation of o-PA, and then the o-PA reduced along with the formation of phthalide. PPAs were also coated on CaF₂ substrates and irradiated with the lamp. UV spectral changes of the films showed the photochemical reaction of oxime ether moieties, and IR spectral changes indicated the formation of phthalide. These results clearly show that depolymerization and following photo-isomerization into phthalide proceeded both in solution and solid state. 2,7-Diacetylfluorene O,O'-dibenzyldioxime was newly prepared to discuss the photochemical reaction of oxime ether with fluorene chromophore.

Compared to amines as coinitiators applied in photopolymerization, benzodioxole derivatives exhibit similar reactivity but less yellowing and lower toxicity. In this paper, a series of unimolecular type II photoinitiators, containing coumarins as chromophores and benzodioxoles as coinitiators, were synthesized. The substituents with different electron donating/withdrawing abilities were designed for systematical investigation of structure-property relationship. Under LED irradiation, the novel photoinitiators can induce not only free radical polymerization of acrylate monomers, but also cationic polymerization of epoxy monomers via radical promoted cationic polymerization mechanism.

The progress of organic solar cells (OSCs) largely depends on the development of nonfullerene acceptors (NFAs) based on electron-accepting π-conjugated compounds. Therefore, the creation of its building unit is important to tune the properties and increase the OSC performance. In this contribution, a new electron-accepting building unit, fluoranthenedione (FDO), was designed by extending the π-conjugation of representative indene-1,3-dione (IDO) framework. The electron-accepting π-conjugated compound (FL-FDO) composed of thiophene-linked fluorene (FL) as a central unit and FDO as terminal units was designed and synthesized. Compared to the corresponding IDO-containing NFAs, the introduction of FDO led to the red-shifted absorption and increased frontier orbital energy levels. The OSCs based on FL-FDO and poly(3-hexylthiophene) (P3HT) as a donor showed improved power conversion efficiency, compared to the P3HT/FL-IDO-based devices. These results indicate that the FDO unit has the potential to act as a promising terminal unit of NFAs.