Dynamic magnetic information storage or retrieval – General recording or reproducing – Thermomagnetic recording or transducers
Reexamination Certificate
2001-12-20
2004-11-09
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
General recording or reproducing
Thermomagnetic recording or transducers
C360S055000, C360S057000, C369S013010, C369S013020
Reexamination Certificate
active
06816330
ABSTRACT:
The entire disclosure of Japanese Patent Application No. 2000-390936 filed on Dec. 22, 2000 including specification, claims, drawings and summary are incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for forming a magnetic pattern in a magnetic recording medium such as a magnetic disk used for a magnetic recording device, or a photomask used for such method. Also, the present invention relates to a magnetic recording medium produced by using the photomask or a magnetic recording device.
2. Discussion of Background
Magnetic recording devices represented by a magnetic disk device (a hard disk drive) have widely been used as external memory devices for information processing devices such as computers, and have recently been used as recording devices such as devices for recording dynamic images or for set-top boxes.
A typical magnetic disk device comprises a shaft for holding a single or plurality of magnetic disks by penetrating the center of the magnetic disk or disks, a motor for rotating the magnetic disk or disks which is or are connected to the shaft by interposing a bearing or bearings, a magnetic head for recording/reproducing information, an arm for supporting the magnetic head and an actuator for moving the magnetic head via the arm to a desired position on the magnetic recording medium.
As the magnetic head for recording/reproducing signals, a flying head capable of moving above the magnetic disk at a constant flying height is generally used. Other than the flying head, a contact head is proposed in order to make the distance to the medium closer.
A magnetic recording medium (a magnetic disk) to be placed on the magnetic disk device is prepared generally by forming a NiP layer on the surface of a substrate comprising an aluminum alloy, applying a predetermined smoothing treatment, a texturing treatment or the like thereon, and then, forming successively a metallic underlayer, a magnetic layer (an information recording layer), a protective layer, a lubricant layer and the like in this order thereon. Or, it may be prepared by forming successively a metallic underlayer, a magnetic layer (an information recording layer), a protective layer, a lubricant layer and the like on the surface of a substrate made of glass or the like.
The magnetic recording medium includes a longitudinal magnetic recording medium and a perpendicular magnetic recording medium. In the longitudinal magnetic recording medium, longitudinally recording is generally conducted.
The speed of increasing the magnetic density of magnetic recording media is more year by year, and various techniques for increasing the density have been proposed. For example, there are attempts to make the flying height of the magnetic head smaller, to employ a GMR head as the magnetic head, to improve a magnetic material used for the recording layer of the magnetic disk so as to have a strong coercive force, and to reduce the space between tracks for recording information of the magnetic disk. For example, a density of track of 100 Ktpi or more is needed in order to realize 100 Gbit/inch
2
.
In each track, a magnetic pattern for controlling the magnetic head is formed. For example, it produces signals used for controlling the position of the magnetic head or signals used for synchronous control. When the space between adjacent information recording tracks is narrowed to increase the number of tracks to thereby obtain a high recording density, it is necessary to make signals for controlling the position of a data-recording/reproducing head (hereinbelow, referred to as “a servo signal”) dense in a radial direction of the disk in response to the increased number of tracks, i.e., to generate the signals much more so that a precise control can be performed.
On the other hand, it is necessary for the high recording density to increase the data recording capacity by reducing the surface area other than the area used for recording data, namely, an area used for the servo signals and gap portions between the servo areas and the data recording areas whereby the data recording area can be broadened. For this purpose, it is necessary to increase the output of the servo signals or to increase the accuracy of synchronizing signals.
As a conventional method used widely for manufacturing magnetic recording media, an opening was formed in the vicinity of the head actuator of the drive (magnetic recording device), a pin with an encoder was inserted into the opening to engage the actuator with the pin whereby servo signals were recorded by moving the head to a correct position. However, such method encountered difficulty in recording correctly the servo signals because the position of the gravity center of the actuator was different from the position of the gravity center of a positioning mechanism, so that highly accurate track position control could not be obtained.
On the other hand, there is a proposed technique that laser beams are irradiated to a magnetic disk to deform locally the surface of the disk whereby minute projections and recesses are physically formed so that servo signals are produced by the minute projections and recesses. In this technique, however, there were such problems that the formed projections and recesses made the flying magnetic head unstable to affect adversely recording or reproducing of information; laser beams having a large power was needed for forming the projections and recesses, thus being costly, and it took much time to form the projections and recesses one by one.
In view of the above, some servo signal forming methods have recently been proposed.
As an example, there is a method that a servo pattern is formed in a master disk having a magnetic layer of high coercive force, and the master disk is brought to close contact with a magnetic recording medium and then, an auxiliary magnetic field is applied to the medium from the outside whereby a magnetic pattern is printed (U.S. Pat. No. 5,991,104).
As another example, there is a method that a medium is previously magnetized along a certain direction, a soft magnetic layer of high permeability and low coercive force is formed by patterning on a master disk, and the master disk is brought to close contact with the medium and then, an external magnetic field is applied to the opposite direction of the previous magnetized direction. In this method, the soft magnetic layer functions as a shield, and a magnetic pattern is printed in an unshielded area (see, JP-A-50-60212 (U.S. Pat. No. 3,869,711), JP-A-10-40544 (EP915456), and Digest of InterMag 2000, GP-06). In the above-mentioned techniques, a master disk is used and a magnetic pattern is formed in the medium by applying a strong magnetic field.
The intensity of a magnetic field generally depends on distances. Accordingly, when a magnetic pattern is recorded by applying a magnetic field, the boundary of a formed magnetic pattern is apt to be unclear due to a leaking magnetic field. Accordingly, it is essential to bring the master disk into close contact with the medium in order to minimize the influence of the leaking magnetic field. As the magnetic pattern is finer, it is necessary to bring them to close contact without any gap. Usually, the both members are press-contacted by using vacuum suction. Further, the higher the coercive force of the medium is, the larger the magnetic field used for the printing is, and accordingly, the leaking magnetic field becomes large. Therefore, perfect close contact is desirable.
The above-mentioned techniques are easily applicable to a magnetic disk having a low coercive force or a flexible floppy disk being easy for press contact. However, it is very difficult for these techniques to apply a magnetic disk for high density recording comprising a hard substrate which has a coercive force of 3,000 Oe or more. Namely, in the magnetic disk comprising a hard substrate, there was possibility that fine dust deposits thereon at the time of bringing the disk into close contact with the master
Arita Youji
Ikeda Hiroyuki
Figueroa Natalia
Hudspeth David
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