Toshiro Hiraoka

Nanopatterning with Microdomains of Block Copolymers using Reactive-Ion Etching Selectivity

Block copolymers are known to generate nanoscale microdomains by microphase separation, if they are annealed at a temperature lower than their order-disorder transition temperatures. We attempted to transfer the microdomains onto substrates by only using the reactive-ion etching (RIE) method, which is widely used in semiconductor manufacturing processes. Block copolymers consisting of an aromatic polymer and an acrylic polymer were used since there is a large difference in the dry-etch resistance, in that only the acrylic polymer was selectively etched by RIE. Furthermore, nanometer-scale dot patterns can be easily obtained on the substrates by the continuous RIE process. Dot patterns of arbitrary diameters could be transferred to silicon wafers, glass substrates and so forth using these materials and processes.

Large Area Fabrication of Moth-Eye Antireflection Structures Using Self-Assembled Nanoparticles in Combination with Nanoimprinting

A moth-eye structure, which suppresses the reflection on a surface, was fabricated on the entire surface of a large silicon wafer by the formation of a self-assembled particle monolayer as a dry-etch mask formed by our embedded particle monolayer (EPM) method. We optimized the shape of moth-eye structures by optical calculation and improved the fabrication procedure to allow formation over a large area. As a result, we succeeded in fabricating a moth-eye structure on the entire surface of a 12-in. silicon wafer and the surface reflectance was reduced to less than 0.8% in the visible light range. A large nickel mold, which is able to transfer the pattern to an 8-in. display, could be formed using the 12-in. silicon substrate as a master. A moth-eye film was fabricated by UV nanoimprinting using the nickel mold and the high antireflection performance was confirmed. The fabrication cost of the moth-eye structure over a large area would be markedly reduced by the use of the self-assembly technique in combination with nanoimprinting.

Improvement of the light extraction efficiency of top-emitting organic light-emitting diodes by a two-dimensional diffraction layer fabricated using self-assembled nanoparticles

The light extraction efficiency of top-emitting organic light-emitting diodes (OLEDs) was improved by insertion of a two-dimensional (2D) diffraction layer. The 2D diffraction layer was fabricated by our original nanofabrication technique, the embedded particle monolayer method, which could form a self-assembled particle monolayer. As a result, the electroluminescence intensity of the device with the 2D diffraction layer was improved by 1.67 times (in total luminous flux) and 2.07 times (in peak wavelength). High luminance top-emitting OLEDs were fabricated using the potentially low-cost self-assembling technique.

Novel approach for hole-blocking in light-emitting electrochemical cells

Abstract The light emission from solid-state conjugated polymer light-emitting electrochemical cells (LECs) has been studied when a hole-blocking layer was employed. A multilayer LEC consists of an indium-tin oxide (ITO) electrode, an emissive (EM) layer of poly (1,4-phenylenevi-nylene) (PPV) containing poly(ethylene oxide) (PEO) complexed with lithium trifluoromethanesulfonate, a hole-blocking (HB) layer of PEO complexed with poly (lithium 4-styrenesulfonate) (PSS-Li), and an aluminum (Al) electrode. The light emission intensity and external quantum efficiency of ITO/EM/HB/EM/Al cells were clearly greater than those of ITO/EM/Al cells. These results indicate that holes on the PPV main chain are trapped by immovable PSS anions and that the HB layer is effective for improving light-emitting properties of LECs.

Novel method for simultaneous formation of wires and vias of a printed circuit board using nanoporous body

A new type of a flexible printed circuit board with landless vias is developed using a novel method called interconnection via nanoporous structure (INPS). This method can make wires and vias of the printed circuit board simultaneously by a single photo-exposure process. A new photo-induced selective plating method was used to impregnate a nanoporous substrate with copper, and a new photomask was designed, which constitutes of a completely vacant large hole for via and aggregation patterns of very fine holes for wire. Because of the simple process, the INPS board is characterized by landless vias and very fine circuit. Owing to the structure, it is also characterized by flexibility and detachable wires.

Anomalous transition in charge transport behavior of polysilane

Anomalous transition of the dispersion parameter α was observed for the first time in poly( n-butyl- n-pentylsilane) (PBPS). Time-of-flight photocurrent (I) of PBPS was measured. The photocurrent transient was dispersive: I∝t-(1-α). The dispersion parameter α dropped around the glass transition temperature T g with increasing temperature, and became temperature-independent above T g. The mobility was described within the framework of a formalism based on disorder due to Bassler and coworkers. Both the diagonal disorder parameter σ, the variance of the density of states, and the off-diagonal disorder parameter Σ, the degree of positional disorder, decreased around T g. Nevertheless the ratio of the off-diagonal disorder parameter Σ to the diagonal disorder parameter σ was found to increase above the transition temperature. This anomalous transition is rationalized by the assumption that the off-diagonal disorder dominates charge transport in PBPS above T g.

Oxygen-crosslinked polysilane: the new class of Si-related material for electroluminescent devices

The preparation and optical properties of the novel silicon-related material named oxygen-crosslinked polysilane were investigated. The oxygen-crosslinked polysilane was prepared by the thermal annealing of the precursor polysilane bearing alkoxyl groups. The photoluminescence consisting of a broad visible band at about 440 nm and a relatively sharp band at about 360 nm was observed at room temperature. The relative intensities of the visible emission were changed during the crosslinking. The visible emission was greatly affected by the steric hindrance of the alkoxyl groups of the precursor. The visible electroluminescene (EL) was also observed uniformly from the EL cell consisting of the oxygen-crosslinked polysilane film sandwiched between A1 electrode and indium-tin-oxide (ITO) electrode. The current densities of the EL cell increased with an increase in the oxygen-crosslinking.

A Novel Method for the Fabrication of 3D-wiring within a Nanoporous Membrane for High-density Circuit Substrates

The authors have developed a new wiring method to obtain high-density wiring and fine vias for ultra-thin package substrates. Nanoporous substrates and photoinduced selective plating consisting of photo-exposure and metal plating processes were used. However, when miniaturization of wiring pitch and via diameter advanced, deformation of patterns and irregular deposition of metal between wiring became obvious. In order to solve these problems, alkali resistance of the photosensitizers after photoirradiation was increased by crosslinking the photosensitizer molecules. Consequently, in the case of use of diazido chalcone as a crosslinking agent, the crosslinking reaction advanced effectively without changing a process and it was found to be possible to fabricate wiring or via patterns with the designed width or diameter. So far, we have fabricated penetrated copper via patterns with 30 mum diameters and surface copper wiring patterns with 10 mum widths simultaneously within substrates.

Nano-lithography using self-assembled block-copolymer for patterned media

Block-copolymers are known to generate nano-scale microdomains by microphase-separation, if they are annealed at a temperature lower than their order-disorder transition temperatures. We tried to transfer microdomains onto substrates by only using the reactive-ion etching method, which is widely used in semiconductor manufacturing processes. Regarding the application of this nano-patterning technique, we demonstrated the first circumferential magnetic patterned media for hard disk, which were prepared on a 2.5-inch diameter glass plate.