Site: TDK Corporation
Chikumagawa #2 Technical Center
Data Storage Components Business Group
543 Otai, Saku, Nagano, Japan
Date Visited: 13 March 1998
TDK is a $6 billion per year company, of which about one-fourth is in data storage components. Product development is performed at the Nagano facilities, but advanced projects aimed at technologies more than three years in the future are also conducted at the corporate R&D center in Chiba.
TDK's reputation and income in the storage business are based on its optical storage media and its thin film recording heads. This visit dealt only with heads. TDK has been shipping MR heads since 1994 and was planning spin valve head production for 1998. At the time of this WTEC visit, the company was capable of producing about 50 million heads per year.
Dr. Ezaki presented TDK's long-term technical strategy. In terms of basic head technology, spin valves are expected to continue beyond 20 Gb/in2, followed by some sort of tunneling GMR devices. Since TDK does not make media, it is spared the need to deal immediately with the superparamagnetic effect, but it is prepared to design heads for either perpendicular or longitudinal media, patterned or not. In the very long term, beyond 200 Gb/in2, TDK managers anticipate replacing magnetic recording with something else, such as holographic storage or probe storage.
Dr. Ezaki observed that the current rapid pace of advances in HDD areal density is having a chilling effect on alternative technologies. For example, ferroelectric RAM, which was being pursued at TDK as an alternative to disk storage, has been de-emphasized at TDK in recent years for this reason. Probe storage was also discussed, but the data rate problems of this technology remain a key inhibitor. No specific programs in these areas were presented.
TDK's primary advanced technology thrust at this time is aimed at improving read head sensitivity and write head bandwidth, and at addressing the problems of the ultra-high track densities that will soon be needed. The first topic does not fit this WTEC study's charter of pre-competitive technologies, and was not pursued, but dual-stage actuators were discussed. TDK's strength in ceramics and integrated suspension design leads naturally to a piezoelectric actuator approach. Its first attempt uses a small laminated PZT bender bonded between the slider and the suspension. TDK researchers can achieve a one micron displacement for a 10 volt swing, with a first resonance at 20 kHz. This is a very impressive result, and could be extremely important to the industry. The principal negative is the additional disk-to-disk spacing required. Other details not addressed include the necessary scheme for carrying conductive leads from the suspension to the head.
Another important project involves placing a silicon chip near the head end of the suspension, to eliminate transmission line effects in writing. TDK researchers were able to minimize non-linear transition shift to beyond 400 Mtps in this manner.
The discussion then turned to modeling of the magnetic recording process. The WTEC panel saw presentations of a number of papers that have been or will be published in this area. Of particular interest to this study were discussions of the comparative results on longitudinal and perpendicular recording, and on GMR head sensitivity during scaling to very narrow tracks.
It appears that TDK managers agree with the U.S. panelists on the important strategic issues, and have a good program for addressing the head/suspension problems of the next ten years, provided that magnetic recording continues to prevail. The WTEC team did not review GMR heads in detail but did see impressive work on a PZT dual-stage actuator and high bandwidth chip-on-suspension technology.
Piezoelectric piggy-back microactuator for hard disk drive. Submitted to APMRC '98