Tomokazu Umezawa

High-Density Optical Disk Mastering Using Multilayer Coating Method

For the next-generation optical disk system using blue laser diodes, a capacity of more than 20 GB with a compact disk size is required. To realize such high-density optical disk systems, it is very important to develop a high-density mastering technique. In this report, we propose a multilayer coating (MLC) method as a new method to improve the resolution of conventional UV laser mastering. We confirm experimentally that this method is effective for resolution improvement and roughness reduction. We also show that grooves and preformat pits of the 22.5 GB digital-video-recording disk can be fabricated using a UV laser recorder with the MLC method.

Improvements of Resolution and Surface Roughness using Alkaline Treatment of Photoresist Surface in High-Density Optical Disk Mastering

In the next-generation optical disk using blue laser diodes, the track pitch will be reduced to 0.3 µm, that is about half of the track pitch of digital versatile disks. To realize such high-density optical disks, it is important to develop a high-density optical disk mastering technique. In particular, in this mastering technique, two major improvements, resolution improvement and surface roughness reduction, are required. In this work, we fabricate grooves with track pitches of 0.28–0.40 µm land/groove using an ultraviolet laser beam recorder, and investigate the influences of an alkaline treatment of positive photoresist surface on the resolution and the surface roughness of the grooves. We confirm experimentally that the alkaline treatment is effective for the resolution improvement and the roughness reductions of the surface and sidewall. We also show that these effects are attributed to the contrast enhancement and the decrease of photoresist film thickness loss.

UV Laser Mastering with a Multilayer Coating Method Producing Land/Groove Type of Optical Disk with Track Pitch of 0.3 µm or Less

The possibility of realizing grooves with the track pitch of 0.3 µm land/groove or less by using UV laser mastering with a multilayer coating (MLC) method was investigated. By using the MLC method, the profile and the wall roughness of grooves were improved. Furthermore, both the profile and the wall roughness of grooves with the track pitch of 0.28 µm land/groove were the same as those with the track pitch of 0.40 µm land/groove, and this track pitch dependence suggests that UV laser mastering with the MLC method is applicable to the fabrication of the land/groove type of high-density optical disk. Moreover, the roles of two additional layers in the MLC method, a dissolution control layer and a super resolution layer, for the improvements of profile and roughness were clarified experimentally.

Imaging of Digital Versatile Rewritable Disc using the Reflection-Mode Scattering-Type Scanning Near-Field Optical Microscope

Recording marks written on the digital versatile rewritable disc (so called DVD-RAM) by a blue violet laser diode were observed using a reflection-mode scattering-type scanning near-field optical microscope (RS-SNOM) for the first time. The RS-SNOM is based on the atomic force microscope (AFM) and thus both the AFM and SNOM observations are simultaneously performed. In the AFM image, the land/groove structure was clearly observed and no other contrast appeared, while in the SNOM image, the 180-nm-long recording marks were clearly observed at the position of the groove. The contrast originated from the difference in the refractive index, faithfully traced in the SNOM image with a resolution of 50 nm. This result indicates that the RS-SNOM can be used as an observation tool for the next-generation high-density optical media.

Magnetic and magneto-optical properties of CoPtM (M=Re, Ru) alloy films for a new magneto-optical recording material

Abstract CoPtM (M = Re, Ru) ternary alloy films have been investigated as new magneto-optical materials for blue laser recording. The CoPtRe and CoPtRu alloy films were prepared by sputtering without a heating process, and exhibited good perpendicular magnetic anisotropy and magnetic hysteresis loop squareness. For the magneto-optical properties, the figure of merit for the CoPtRe alloy film with less than 15 at% Re at λ

Magneto-optical recording on CoPtRe alloy films as a novel material

Magneto-optical (MO) disks using CoPtRe ternary alloy films have been investigated as a novel recording material for a blue laser recording. For various types of disk structure, the Kerr rotation, the Kerr ellipticity, and the figure of merit were calculated and an optimum structure was estimated. Magneto-optical recordings were made on a CoPtRe MO disk at wavelengths of 830 and 530 nm. The recording properties were almost equivalent to those for Co/Pt multilayers.

Feasibility of high-speed recording on oxonol dye double-layer recordable digital versatile discs produced by inverted stack method

The feasibility of high-speed recording on oxonol dye double-layer recordable digital versatile discs (DVD+R DL and DVD-R DL) produced using the inverted stack method was investigated. Jitter of less than 9% was achieved at 2.4–16× recording speeds on DVD+R DL discs, and a high aperture ratio (AR) and jitter of less than 8% were achieved at 2–12× recording speeds on DVD-R DL discs. From these results it was concluded that oxonol dye is suitable for high-speed recording on DVD+R DL and DVD-R DL discs. Recording principles of the L1 layer were also investigated.

Influence of Injection Molding Process on the Local Fluctuations of Magneto-Optical Signals.

The local fluctuations of magneto-optical (MO) signals were investigated in the vicinity of the preformat pits of polycarbonate (PC) substrates fabricated under different injection molding conditions and also using stampers which had different shapes of grooves and preformat pits. A strong correlation was observed between the substrate birefringence and the fluctuation of the MO signal. The rate-of-change of the fluctuations, as the phase shift of the optical head was varied, was attributed to the shapes of preformat pits and grooves. The fluctuation of the MO signal could be controlled by varying the injection molding conditions and the shapes of preformat pits and grooves.

The Influence of Adjacent Preformat Pits on Magneto-Optical Signals

Fluctuations in magneto-optical (MO) signals have been observed in 3.5-in. 640 MB MO disks which have the zone constant angular velocity (ZCAV) format. They were found to occur at the border of each band (zone) when there were preformat pits in the adjacent band. The fluctuations were observed in those MO disks whose substrates were injection molded polycarbonate (PC). The degree of these MO signal fluctuations depended on the injection molding conditions of the substrates and the phase shift of the optical head. It is thought that such phenomena can be attributed to tilted ellipsoids of substrate birefringence that occur around preformat pits, and which are caused by stresses induced around the preformat pits during the injection molding process.

Jitter Analysis for Preformat Pits in Header Field of 4.7 GB Digital Versatile Rewritable Disc

A novel simulation method of jitter was proposed for designing preformat pits. By using this method, the relationships between pit shapes and jitter values resulting from intersymbol interference, crosstalk and noise were clarified in the header field of a 4.7 GB digital versatile rewritable disc (DVD-RAM). Comparisons were made between simulation results and experimental ones. The simulation results were in good agreement with the experimental ones. This indicates that the presented simulation method is effective.