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 use. 


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