Takuya Shimada

Fabrication of 5 Tdot/in.2 bit patterned media with servo pattern using directed self-assembly

The fabrication of an etching template for 5 Td/in.2 bit patterned media using a self-organization material, namely, poly(styrene)-poly(dimethylsiloxane) (PS-PDMS), was investigated. The molecular weight of the PS-PDMS for forming the areal density of 5 Td/in.2 dot pattern was estimated from the polymerization index related to the Flory–Huggins interaction parameter. Annealing was carried out to obtain a fine-order dot pattern. PS-PDMS films were subjected to thermal treatment or solvent annealing. The ordering of the dot array in these films was evaluated by using Voronoi diagrams. The results indicate that the film annealed in N-methylpyrrolidone (NMP) vapor showed finer ordering than did the thermally treated film. This seemed to be attributable to the high solubility parameter of NMP. The soaking of NMP into the PS phase slightly shifted the phase separation energy of the polymer matrix. The lattice spacing of the obtained hexagonal pattern was 11 nm. By using low-molecular-weight PS-PDMS with solvent...

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.

Nanoimprint Mold for 2.5 Tbit/in.2 Directed Self-Assembly Bit Patterned Media with Phase Servo Pattern

We demonstrate the mold fabrication and replication process for the production of 0.8 and 2.5 Tbit/in.2 directed self-assembly bit patterned media (DSA-BPM). These devices are fabricated with 33 and 17 nm dot pitch patterns using the microphase segregation structure of polystyrene–poly(dimethylsiloxane) as an etching mask template. The self-assembled dot arrays are simultaneously ordered on both the circular tracks for the data area and the arbitrary marks for the servo area by DSA using groove guides. We fabricated the Si mold with dot pillars of 19.3 nm height for the 2.5 Tbit/in.2 DSA-BPM from the poly(dimethylsiloxane) dot mask. We also demonstrated the nickel mold replication of the 0.8 Tbit/in.2 DSA-BPM by electroforming from the Si mold.

Dzyaloshinskii-Moriya interaction in Pt/Co/Pt films prepared by chemical vapor deposition with various substrate temperatures

We deposited perpendicularly magnetized Co(∼1nm)/Pt(6nm) bilayers by thermal chemical vapor deposition (CVD) on top of 3nm thick Pt layer using various deposition temperature. Observed Ms increased with the increase of deposition temperature Ts, and reached the value of pure-Co at Ts = 500°C. We measured a (left-handed) negative Dzyaloshinskii-Moriya interaction in CVD films indicating a dominant role of the bottom Pt/Co interface.

Evaluation of ordering of directed self-assembly of block copolymers with pre-patterned guides for bit patterned media

Bit patterned media (BPM) is a promising candidate for next-generation magnetic recording media beyond 2.5 Tb/in2. To realize such high-density patterned media, directed self-assembling (DSA) technology is a possible solution to form fine dots. In order to read and write magnetic signals on a magnetic dot of magnetic media, the position of magnetic dots must be controlled. We examined ordering of directed self-assembly of diblock copolymer dots with a variety of prepatterned guides in some conditions and evaluated the ordering of the dots by using Delaunay triangulation and Voronoi diagram. Applying the optimized conditions, we obtained highly controlled dot pattern suitable for magnetic recording media.

Nanoimprint process for 2.5Tb/in2 bit patterned media fabricated by self-assembling method

Bit patterned media (BPM) is a promising candidate for high-density magnetic recording media beyond 2.5 Tb/in2. To realize such a high-density BPM, directed self-assembling (DSA) technology is a possible solution. On the other hand, from the viewpoint of low-cost production, nanoimprint lithography is a promising process for the mass-production of such a high-density BPM. We examine the replication of the BPM etching mask by UV nanoimprint process. At first, the BPM silicon master mold consisting of servo pattern with dot array is made by the DSA method using PS-PDMS. For the 30-nm pitch corresponding to the density of 2.5 Tb/in2, the nickel stamper is replicated from the silicon master mold by electroplating. The etching mask is transcribed by the UV nanoimprint process with the transparent mold replicated from the nickel mother stamper. On the other hand, as for the DSA-BPM pattern of 17-nm pitch corresponding to the density of 2.5 Tb/in2, we adopt an alternative process and confirm the replication possibility.

High-purity cobalt thin films with perpendicular magnetic anisotropy prepared by chemical vapor deposition

A study of the chemical vapor deposition (CVD) of high-purity cobalt thin films is described. The Co layer prepared by a thermal CVD technique with a Pt/Ta underlayer and a Pt cap layer shows a saturation magnetization (Ms) of ~1.8 T and perpendicular magnetic anisotropy (PMA) with an anisotropy energy (Ku) of ~105 J/m3. The cobalt thickness dependence of Ku reveals that the interfacial anisotropy at the Pt/Co interface is most likely the origin of the obtained PMA.

A magnetic shift register with periodic potential energy modulation

For the first time, we demonstrated the intentional DW-position control and the shift operation of the 500-nm-long 7-bits in the magnetic shift register with the periodically potential energy modulated NW.