Yoshio Aoki

A magneto-optic recording system using TbFeCo

A large capacity magneto-optic recording system has been developed for mass data storage. The recording material is an amorphous magnetic film of TbFeCo, which is magnetizes vertically. The TbFeCo film is deposited onto a plastic substrate by sputtering. It has a Kerr rotation angle of 0.35°, a Curie temperature of 190°C, and an amorphous-crystal transition temperature of 240°C. The 30cm-diameter disk has a double-sided structure and each side consists of a magnetic layer and protective layers. Using mastering and replication techniques, grooves with address headings are produced in the polycarbonate plastic substrate at a track-pitch of 1.6μm. A lightweight, high performance optical pickup is operated at an average seek time of less than 100msec. The raw bit error rate (BER) of the disk is currently of the order of 10-5and the system is designed to provide the corrected BER of 10-12using a Cross Interleave Reed-Solomon Code. The system consists of a 1-Gbyte magneto-optical memory disk drive to be used as a code memory for computers, a controller unit capable of being expanded to 4-Gbytes, and an interface module called the Small Computer System Interface (SCSI).

Magneto-optical recording on Tb-Fe based thin films

Amorphous Tb-Fe based thin films of Tb-Fe, TbGd-Fe and Tb-FeCo have been investigated for magneto-optical recording media. The films were deposited by using a two-source DC-sputtering method. The magnetic and magneto-optical properties of the films were investigated as a function of composition and it was found that the films with low rare-earth composition had perpendicular magnetization and showed a high squareness of hysteresis loop. In magneto-optical recording on the Tb-Fe based thin films deposited on plastic disks, a high carrier-to-noise ratio was obtained over a wide frequency range. The recording of FM video signal has been made possible on these high C/N disks.

Development of a high-density magnetic recording system for a consumer VCR using an MR head

We present a new consumer VCR format, MICROMV, and a higher density recording technique. Applying the MR head to a helical-scan tape recorder, we have successfully recorded at an areal density of 0.8 Gb/in/sup 2/ making it possible to store 6.5 GB of data on a small cassette of 12 cc volume. We also report a technique of electric-power transmission through a rotary drum and a method to compensate for the amplitude asymmetry of the MR head output signal.

High-density magneto-optical recording with magnetic field modulation and pulsed laser irradiation

We have developed high density overwriting of a magneto-optical disk. A sharp pit-edge recording is achieved by a newly developed magnetic head and pulsed laser irradiation.

Holographic Versatile Disc (HVD) System

Holographic versatile disc (HVDtrade) system using Collineartrade holographic technologies is one of the best candidates for the ultra-high density and ultra-high speed removable storage media. The HVDtrade structure and its unique selectable capacity recording format are proposed to assure data interchangeability as well as upward and downward compatibility

New Optical Recording Material for Data Storage

A high-performance optial recording disc has been developed. The recording material is so sensitive that the disc can be recorded and played back by a single optical head using a commercially available laser diode. The recording sensitivity of the disc is enhanced by the unique double-layer structure consisting of a recording layre (Sb-Se compound metal) and a heat absorbing layre (Bi-Te compound metal). In the signal recording process, the recording material changes its physical phase from amorphous to crystalline, when it is heated by laser at 170°C . This phase transition triples the reflectivity of the recording layer. Because the phase transition occurs over a narrow temperature range of about 20 degrees, the pit edge of the recording layer becomes sharp and its pit length is rigidly determined. This ensures a high carrier-to-noise ratio over a wide frequency range. The newly developed disc is, therefore, not only capable of digital recording but also adapt to any pit-length change necessitated by analog video recording. Since the disc recording is facilitated by the changing of the optical characteristics of the recording material, the physical disc form is never affected by laser heat, i.e., neither melted nor evaporated. Therefore, the signal surface can be directly sealed by a protective layer and the disc offers higher storage reliability and greater ease of operation. Direct sealing of the signal surface by protective film also makes a double-sided disc structure possible, enabling the disc to record on both sides. This structure increases the flatness of the disc and enhances its recordability and playability significantly. The new disc will be applied to mass storage as high-performance and massive-information recording medium.

New Optical Recording Material For Direct-Read-After-Write (DRAW) Disks

The optical characteristics of Sb2Se3 and Sb2 Te 3 films changed as a result of an amorphous crystalline phase transition below 200 °C. The respective reflectivity of 400 A Sb2Se3 and 300 A Sb2Te3 films, each on a Te reflective layer, increased from 10% to 30% and from 45% to 65% by laser radiation. The recording sensitivity of a disc is enhanced by using this unique double-layer structure which consists of a recording layer and a heat (laser) absorbing layer. A high-performance optical laser disc on which both digital and analog signals can be recorded by a diode laser has been developed using these newly developed, highly sensitive recording materials.