Site: Toshiba Corporation
(optical storage presentations)
Research and Development Center
1 Komukai Toshiba-cho, Saiwai-ku
Kawasaki 210-8582, Japan
Date Visited: 12 March 1998
Toshiba is a large producer of computing and communications systems, electronic devices, consumer electronics, household appliances, and power generation and distribution equipment. With 186,000 employees, Toshiba had net sales for FY 97 (ending 3/31/97) of nearly $44 billion, and about $2.7 billion was allocated for research and development (6.1% of net sales).
Toshiba's R&D is organized into Corporate Laboratories for long range research (5 + years), Development Laboratories for medium term research (3-5 years), and Business Group Engineering Departments for short range (< 3 years) work. The Research and Development Center, one of two corporate laboratory centers, employs about 1,300 scientists and engineers (~13% PhD, ~61% MS) divided among 9 laboratories.
Toshiba has been very active in optical data storage, and was a founding member of the DVD alliance (and developer of the Super Density format before the DVD consolidation).
The 31/2 hour meeting included summaries of Monday's workshop presentations from the WTEC panelists and five presentations from Toshiba scientists, two of which discussed optical storage. Before the presentations, the panel was treated to a demonstration of high-definition video recorded on HD-DVD (a 15 GB 120 mm disc).
Dr. Naito's talk on "novel optical memory functions using organic dot structures" described work to find a high density recording material applicable to near-field scanning microscopy. Dr. Naito described a method based on photoluminescence, motivated in part by his comment that conventional materials have low contrast (1% for magneto-optic and 10% for phase change). He has prepared 10 ~ 100 nm diameter organic dots by vacuum evaporation and read the photoluminescence from each island with an NSOM probe. To record, a gold-coated AFM tip held at a voltage injects charge into the organic islands. If charge isn't injected, the maximum luminescence is observed. Injecting holes into the island, however, quenches the luminescence, and minimal light is detected by the NSOM probe. The quenched state is stable for at least 9 hours. In addition, the amount of injected charge can be varied by the tip voltage and the quenching of photoluminescence controlled, raising the possibility of multilevel recording.
The diameter and thickness of the islands can be somewhat controlled. The spatial distribution of dots is not well controlled, however, and work is underway to improve dot placement.
Mr. Kobori presented a talk on the "future prospects of DVD technology." For replicated DVD, he predicts that a 30 GB disc will be available by 2001 and will double in capacity to 60 GB by 2006. Toshiba demonstrated 15 GB using a green SHG source last year, and is working on 30 GB using a blue laser. For DVD-RAM, based on phase change media, 9.4 GB will be available next year, and 30 GB should arrive by 2005. The intent is to increase density through media and system changes rather than increasing NA. Systems using blue lasers and PRML will be introduced in 2001, and media superresolution will be used in 2005.
Key technologies for the 30 GB HD-DVD include blue (410 nm) laser and PRML. The smallest mark length is 0.2 Ám, and the track pitch is 0.4 Ám. Track pitch deviation must be (5 nm, requiring mastering improvements such as short-wavelength lasers (260 to 350 nm), improved resists, better servo control, and possibly superresolution technology. A future format, UD-DVD, would hold 50 to 60 GB, use a 0.2 Ám track pitch (with 2.5 nm maximum deviation) and 0.1 Ám minimum mark length. Mastering will require electron beam sources or possibly SIL methods.
Toshiba is doing little or no magneto-optic work and is not involved in the ASMO format. MO is considered to be too wavelength sensitive and not a good material for blue laser recording.
Toshiba has a well developed roadmap for increasing DVD capacity and performance. The plan includes holding the numerical aperture to 0.6 for cross-compatibility, while pushing other aspects of the system and media to gain improvements. Phase change material is considered to be the best choice for RAM discs.