Appendix C: Hitachi Central Research Laboratory

Site: Hitachi Central Research Laboratory (HCRL)
(magnetic storage presentations)
1-280 Higashi-koigakubo
Kokubunji, Tokyo 185, Japan
http://koigakubo.hitachi.co.jp/

BACKGROUND

Hitachi, Ltd. has seven corporate laboratories, whose responsibilities and research fields change in response to market and social needs. Dr. Ryo Imura presented an overview of these laboratories. These research laboratories and the approximate number of personnel at each are as follows:

Hitachi Central Research Laboratory concentrates its R&D efforts in the fields of information and media, electronic devices and medical electronics. Michiharu Nakamura, General Manager of the Central Research Laboratory states that the lab's aim is to develop a new industrial frontier through endeavors in research that extend from the development of new scientific technologies to their practical application. He states that the researchers put a special emphasis on the creation of new technological trends and the speedy transfer of new technology to commercial products.

Within the Central Research Laboratory, the Information Storage Research Department has approximately 30 people working on optical recording and about 70 people working on magnetic recording. Within the magnetic recording area, there are groups working on magnetic recording heads, magnetic simulation, magnetic recording media and read/write electronics (where work on channels is done). Work on servos and actuators is done in the Mechanical Engineering Research Laboratory. Within the optical recording area, there are groups working on magnetic super-resolution magneto-optic recording, DVD-RAM, optical heads and optical media.

DISCUSSION

Dr. T. Yamaguchi made a presentation on future track-following and servo technology for magnetic disk drives. He presented a track misregistration (TMR) budget for a 10 Gb/in² disk drive (Table C.5):

Dr. Yamaguchi also described work in which researchers were putting an accelerometer on the head suspension and using the signal from it as a feedback to actively suppress resonances in the suspension. He indicated the lab was doing work on dual stage actuators, and that there was work on voice coil microactuators, piezoelectric actuators and MEMS-type actuators. He indicated that the piezoelectric approach was currently favored and that he considered the MEMS-based actuator to be further away from practical implementation.

Table C.5
TMR Budget for 10 Gb/in² Disk
Track density	31,600 tracks per inch
Track pitch (Tp)	0.8 micron
Non-repeatable runout (NRRO)	0.096 micron
Synchronization	0.084 micron
Settling	0.08 micron
TMR	15% of T_p
Position error at write	12% of T_p
Position error at read	14% of T_p

Mr. Takano presented a roadmap for hard disk drives and projected the following for hard disk drives at 40 and 100 Gbit/in² (Table C.6):

Table C.6
Disk Drive Roadmap
	40 Gb/in²	100 Gb/in²
Track density (ktpi)	75	140
Linear density (kbpi)	530	707
Erase band width (microns)	0.06	0.03
TMR (microns)	0.03	0.02
Tolerance (D Tw) (microns)	0.04	0.02
Write track width (Tw) (microns)	0.27	0.14
Read track width (TR) (microns)	0.24	0.12

He also presented simulations of recording at 100 Gb/in² using both perpendicular and longitudinal recording. The perpendicular recording system used a ring head and a single layer medium without a soft underlayer. The work indicates that one can use a thicker medium in perpendicular recording than in longitudinal; the researchers assumed a 7 nm medium thickness in longitudinal recording and a 30 nm medium thickness in perpendicular recording. Other parameters of the systems were as shown in Table C.7.

The simulations indicated that the transitions were considerably better defined in the case of perpendicular recording; although, in the case of perpendicular recording, regions where there were no transitions became noisy because they tended to self-demagnetize. The researchers also showed simulations that indicated that exchange coupling between grains tended to improve the definition of the transitions in the perpendicular recording case.

Table C.7
Simulations of 100 Gb/in² Disk: Longitudinal vs. Perpendicular Recording
	Longit.	Perp.
Grain size (nm)	7	6
Thickness of magnetic layer (nm)	7	30
Anisotropy constant, Ku (J/m³)	3 x 10⁵	0.75 x 10⁵
Exchange coupling between grains, A (J/m)	0	1 x 10^-13
Saturation flux density (Tesla)	0.816	0.478
Gap length (microns)	0.1	0.1
Write track width (TW) (microns)	0.14	0.14
Coercive force of media (Oe)	4,500	3,400
Saturation flux density x media thickness, Brt (Gm m)	45	104
Fly height (nm)	10	10

Hitachi is one of several companies working on 40 Gb/in² recording density under the MITI-sponsored ASET program, and is responsible for work on media and on advanced heads. Hitachi is working on a spin-valve head design that is to have a sensitivity of 1,560 (V/(m. Hitachi engineers have demonstrated CoFe spin-valve sensors with a magnetoresistance ((R/R) of 7% using a 10 nm thick IrMn exchange bias layer. Simulations indicate that one can obtain more output using designs in which the track width is defined by the lead structure, rather than the self-aligned abutted permanent magnet structure.

Dr. M. Futamoto presented work on the effects of superparamagnetism on both longitudinal and perpendicular media. He indicated that thermal stability was considerably better in perpendicular media, because of the larger media thickness. He also indicated that if the perpendicular remanent squareness could be increased to 1, the tendency for perpendicular media to demagnetize was greatly reduced. He projected his personal description of a roadmap for future magnetic recording technology. He indicated that he expected longitudinal recording to use Co-alloy media like those in current products up to 20-40 Gb/in² and that to extend the density to 100 Gb/in², new media such as SmCo, CoPt or FePt would be required. He suggested that, alternatively, perpendicular recording could begin using a thin film ring head, and a single- layer Co-alloy medium. Later generations could use, first, advanced thin film ring heads with continuously exchange-coupled amorphous media like those used for magneto-optic media, single pole heads with double-layer polycrystalline media and, ultimately, single pole heads with continuously exchange-coupled amorphous media on a soft underlayer. He indicated that such perpendicular recording approaches would lead to 3-4 times higher linear density and 3-5 times higher track density than possible with longitudinal recording, resulting in densities in the 200-400 Gb/in² range.

SUMMARY

The presentations in the magnetic recording area at Hitachi Central Research Laboratory indicated that the researchers are working very hard on advanced magnetic recording technologies. Company researchers are working on advanced actuator and track following technologies for very high track densities, and have, to our knowledge, the most active industrial research effort in the world on perpendicular magnetic recording. Their simulations and experimental data indicate that perpendicular recording can use media that are 3-4 times thicker than longitudinal media at an equivalent density and that such media, consequently have superior thermal stability at high recording densities where superparamagnetic effects are a problem in longitudinal recording. The hosts also indicated that continuously exchange coupled perpendicular media may offer superior signal to noise ratio and thermal stability.

Published: June 1999; WTEC Hyper-Librarian

Hitachi Central Research Laboratory	1000 (approximately 820 of these are technical research staff)
Hitachi Research Laboratory	1050
Mechanical Engineering Research Laboratory	550
Production Engineering Research Laboratory	480
Systems Development Laboratory	490
Design Center	170
Advanced Research Laboratory	140