A major purpose of this study was to discover how the strategic outlook for HDD technology differs in Japan from that elsewhere. The short answer is: it doesn't. This is due to several factors: the technology lead is still with the United States, and the physics challenges ahead are recognized to be the same by leaders in both countries. For example, the areal density targets from ASET/SRC are very similar to those of NSIC (Figs. 3.2 and 3.3).
These challenges include the superparamagnetic effect, the need for increasing read head sensitivity, the need to scale head-to-disk spacing with the linear density, the need to follow extremely narrow data tracks, and the need to switch magnetic materials at increasing speeds. They are the same challenges faced around the world, but the Japanese bring certain special skills to the search for solutions. These include special understanding of magnetic materials and national strengths in micromechatronics. The latter was seen in the number of different proposals that we saw for two-stage actuators that will be necessary for the rapidly increasing track densities that will be seen in the next few years. For example, Fig. 3.4 and Fig. 3.5 show some of the widely differing approaches being pursued.
Fig. 3.2. Roadmap (IBM).
Fig. 3.3. ASET/SRC areal density projection (Miura, March 1998).
Fig. 3.4. Possible microactuator designs (Miura, March 1998).
Fig. 3.5. TDK microactuator (described at TMRC, August 1998).
The ASET presentation at the March 1998 WTEC workshop in Tokyo contains a succinct summary of some of the materials work that the panel saw. Japan's leadership in magnetic materials predates the disk drive business and reflects its prowess in solid state physics, in high tech fabrication methods, and the benefits of being the leader in magnetic recording for audio and video applications. Figs. 3.6 through 3.8 show a portion of that summary.
An alternative form of magnetic recording called "perpendicular recording" has been an almost exclusively Japanese domain for 20 years (Fig. 3.9). Until recently it had no particular advantages over conventional recording, but as one begins to see superparamagnetic effects limiting areal density, perpendicular media hold the promise of being more stable than longitudinal media for the same number of grains per bit. This is primarily because perpendicular media are thicker for the same areal density than longitudinal media (which allows more stored energy per grain); because the demagnetizing fields in perpendicular recording favor high bit densities (the opposite of the longitudinal case); and because the strength of the field from the write head can be stronger for perpendicular recording. If this turns out to be true, then Japan has a substantial lead in gaining experience with this technology.
Fig. 3.6. Storage materials (Y. Miura, WTEC workshop, March 1998).
Fig. 3.7. ASET/SCR storage issues (Y. Miura, WTEC workshop, March 1998).
Fig. 3.8. Storage media materials and efficiencies.
Auxiliary facing-pole driven type (1) 1975 Flexible media (Tohoku Univ.)
Auxiliary back-pole driven type (2) 1984 Flexible media (Sony)
Auxiliary back-pole driven type 1991 Hard media (Tohoku Univ.)
Micro Flexhead (3) 1991 Hard media (Censtor)
Ring/MR merged thin film head (4) 1997 Hard media (IBM Japan)
Film conductor driven type head (4) 1997 Hard media (Tohoku Univ.)
Figure 3.9. Perpendicular magnetic recording with a single-pole head
(Nakamura, Tohoku Univ., 1998).