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Magnetic Printing Technology
Kaoru Matsuoka, Matsushita Electric Industrial Co. Ltd., Kiyokazu
Tohma, Matsushita Electric Industrial Co. Ltd., Hideyuki Hashi, Matsushita
Electric Industrial Co. Ltd., Taizou Hamada, Matsushita Electric
Industrial Co. Ltd., and Tatsuaki Ishida, Matsushita Electric Industrial
Co. Ltd.
1. Outline
As the recording density of hard disk drives (HDDs) is
being rapidly increased, current servo signal writing method using a
conventional servo track writer has become more costly and technically
difficult. In order to realize a very accurate and cost effective servo
signal writing of HDDs, we developed and industrialized a new magnetic
printing technology using a lithographically patterned master disk.
2. Contents of Technology
Fig. 1
shows a schematic illustration on basic principle of the magnetic printing
technology. On the master disk, a magnetic film patterned according to the
information signal to be recorded on magnetic disks is processed by a
lithography technique. After the master disk is placed facing a DC erased
magnetic disk, an external field is applied to the master disk. Then,
owing to the shielding effect of the individual patterned magnetic film on
the master disk, flux leaks and reverses the initial magnetization on the
magnetic disk only at the portion between the neighboring patterned films,
and magnetic signal information according to the magnetic film pattern on
the master is printed on the magnetic disk.
This technology can provide
a very productive and inexpensive way for servo signal writing process of
HDDs, because it is essentially the areal lump-sum recording covering a
full surface area of the magnetic disk. Also, since the signal information
stored in the master is not a magnetization pattern, but provided as a
physical shape pattern of the magnetic films, the master information never
disappears when a large external field is applied to the master disk
during the printing process. Another important feature of this technology
is that various magnetization pattern which can never be written by using
a magnetic head is easily recorded, since the physical shape pattern on
the master disk can be freely designed and lithographically processed into
a variety of geometry.
For securing adequate printed signal quality, it
is required to ensure close and full surface area contact between the two
hard material surfaces, i.e. the master disk surface and the magnetic disk
surface. Fig. 2 shows schematic
illustrations of a master disk surface and method for achieving close and
full surface area contact between the master disk and the slave disk.
Since the servo signals are discrete signals to be reproduced at
intervals, magnetic film patterns according to the servo signals are
provided on the master disk at certain angular spaces with groove
structure formed in-between. In the magnetic printing stage, this groove
structure functions as an air channel for evacuating the air between the
master disk and the slave disk, resulting in close and full surface area
contact between them and uniform signal quality over the magnetic disk
surface.
In a product HDD, since the magnetic head is flying over the
magnetic disk surface with the flying height of as small as 10 nm or so,
super cleanliness, physically and chemically, is required on the magnetic
disk surface. In order not to damage or contaminate the magnetic disk
surface though the magnetic contact printing process, we proprietarily
established and introduced a cleanliness management method and a disk
inspection method, thus realized sufficient practicability and reliability
of the magnetic printing technology for practical implementation to the
product HDDs.
3. Conclusion
Mass production of the first product drives in the
world by using the magnetic printing technology began in July, 2001 at
Matsushita Kotobuki Electronics Industries, Ltd., a subsidiary of
Matsushita Electric Industrial Co. Ltd. The magnetic printing technology
is now being developed to the HDD industry as a new technology proven in
commercial mass production. It is expected to contribute to the industry
through the realization of higher recording density growth and price
reduction demanded in HDDs for PCs and consumer electronic devices
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