Hajime Utsunomiya

Inorganic Write-Once Disc for High Speed Recording

We have developed an inorganic write-once disc based of the Blu-ray disc format. Our write-once disc has a double layer recording stack of a Cu alloy layer and a Si layer. These materials are environmentally friendly and low in cost. We designed a new write pulse strategy for high-speed recording while maintaining low recording peak power. As a result of using our write strategy, we obtained a jitter value of less than 8% with optimum recording power of 5 mW in the range of 36 Mbps to 144 Mbps.

The Phase Change Optical Disc with the Data Recording Rate of 140 Mbps

We have been developing a new phase change optical disc on the base of the recording system (DVR) with a blue laser (405 nm) and dual objective lens with a numerical aperture (NA) of 0.85. We have achieved the data recording rate of 140 Mbps. The significant techniques to achieve the recording rate as follows: rearrangement of the AgInSbTeGe composition for the rate of 140 Mbps and controlling the re-crystallization by SRC structure (the super-rapid cooling structure) and development of Write Strategy for the high data recording. As a result of the techniques, less than 10% jitter value and more than 1,000 times overwriting possibility at 140 Mbps have been achieved.

Inorganic write-once disc with quadruple recording layers for Blu-ray Disc system

The optical disc with larger capacity and higher speed data recording rate will be required in coming broadband network society. We have developed the inorganic write-once disc with quadruple recording layers for the blu-ray system. We obtained the reflectivity of more than 5% and a jitter value of less than 10% for each recording layer. As a result, we proved the possibility of 100 GB user capacity of 120 mm diameter size.

High-Performance Hard Coat for Cartridge-Free Blu-ray Disc

A practical way of realizing cartridge-free Blu-ray disc using nanocomposite UV-curable resin as a hard coat on a laser incident surface of the disc is described. The hard coat is a composite material of UV-curable acrylic resin and nanoparticles of silica. A lubricant that exhibits oil repellency as well as low friction coefficient was added to the hard coat in order to facilitate the removal of fingerprints. It effectively prevents abrasions, scratches and problems of fingerprints on the disc surface. Abrasion and scratch resistances, and ease of fingerprint removal were evaluated and compared with those of a polycarbonate surface and a conventional UV-curable hard coat.

Phase Change Disc for High Data Rate Recording

We have developed a phase change disc having a thin transparent cover layer corresponding to the new optical recording system (DVR) using a blue laser (405 nm) and a numerical aperture (NA) of 0.85. We have achieved a user capacity of 22 GB per side of the 120 mm diameter disc, and a user data recording rate of 70 Mbps by designing a highly flat transparent cover layer, a recording layer having high crystallization speed and a film structure for rapid cooling.

Scanning Probe Microscope Observation of Recorded Marks in Phase Change Disks.

This is the first report on observation of phase change recorded marks by use of the scanning probe microscope (SPM). The amorphous mark and crystalline blank were clearly observed by surface potential mode (SPoM) that visualized the surface potential difference among phases or materials. SPoM observation has an advantage over conventional transmission electron microscope (TEM) observation in that the sample preparation is much easier, and that amorphous mark and crystalline blank are clearly distinguished. The possibility of a novel readout method of phase change disks, and the possibility of the novel medium with a surface potential detection method are also proposed.

The phase-change optical disc with the data-recording rate of 216 Mbps

New recording material with higher crystallization speed and higher thermal stability is required to realize a phase-change disc for higher data recording rate. We have developed a new phase-change material that consists of TbSbTeGe material based on eutectic composition. This new phase-change material improves the crystallization speed and the crystallization temperature simultaneously. We have achieved the practical use characteristic of data recording rate of 216 Mbps (6X-speed of Blu-ray Disc) by using TbSbTeGe new phase-change material.

Antifingerprint property of the hard coat for cartridge-free Blu-ray Disc

We made improvements on the previously reported hard-coat for cartridge-free Blu-ray disc from a viewpoint of an anti-fingerprint property. As a result of this study, two types of the hard-coat have been obtained. One is for Blu-ray discs of ROM and write-once types, and the other is for that of rewritable type. The former well inhibited a deterioration of bit error rate (bER) of the signal written prior to the fingerprint adhesion. The later exhibited low bER for the data signals written both before and after the fingerprint adhesion. These results are attributable to the area ratio of drops of fingerprint-ingredient on the disc surface, and the low area ratio resulted in a low bER. Moreover, it was confirmed that the disc with higher contact angle of oily compound exhibited the lower area ratio of the fingerprint.

Functional hard-coat for cartridge-free DVR-blue

Optical discs with larger storage capacity and higher data recording rates are required for the coming digital network society, for example, to realize non-linear editing and long term data archiving on broadcasting tasks. We have been developing a new phase change optical disc, which has much higher data recording rate of up to 140 Mbps (T. Kato et al, Tech. Dig. ISOM2001, pp. 200-201, 2001), based on the DVR system (/spl lambda/=405 nm, NA=0.85, cover layer thickness=100 /spl mu/m) (Y. Kuroda et al, 1999; M.J. Dekker et al, 2000; Y. Kasami et al, 2000). As a general rule, the smaller the laser spot size on the disc surface, the more sensitive the disc becomes to scratches or fingerprints on it. In such a system, the distance between the disc surface and objective lens (i.e. working distance) is very narrow due to a high NA. Therefore it is also feared that the objective lens hits the disc surface due to an external impact. To avoid these problems when the disc is taken out of a cartridge, we have developed a new hard-coat. The cartridge-free DVR-blue disc was expected to be accomplished by the following properties: (1) abrasion resistance; (2) scratch resistance; (3) water and oil repellency (low surface free energy). Among these properties, the abrasion resistance is considered to be the most important.

Spin-Coating Technology of the Cover Layer for Digital Video Recording-Blue Disc

We have achieved the cover layer thickness distribution of 100±1.5 µm on a disc by improving the spin-coating method and developing an original spin-coating machine. The small skew of the disc is achieved by using a newly developed UV-curable resin.