Dynamic magnetic information storage or retrieval – Record copying – Contact transfer
Reexamination Certificate
2001-06-22
2004-06-08
Hudspeth, David (Department: 2697)
Dynamic magnetic information storage or retrieval
Record copying
Contact transfer
C360S016000
Reexamination Certificate
active
06747822
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for writing servo signals for positioning a read-write head into a magnetic disk surface by means of magnetic transfer technique in a hard disk drive (HDD) which uses magnetic film as recording material, is now a main stream of external memory. In particular, the present invention relates to magnetic transfer technique in a perpendicular magnetic recording medium, in which the direction of recorded magnetization is perpendicular to the medium surface.
BACKGROUND OF THE INVENTION
The recording density of a magnetic recording medium for HDD is as high as 20 Gbit/in
2
in the development stage at present and the memory capacity is increasing in the rate of 60% a year. With the enhancement of recording density, the size per bit of the magnetic material is diminishing. It is becoming difficult to read-write data by so-called longitudinal magnetic recording system, in which the direction of recorded magnetization is a longitudinal direction, that is, a direction in the surface of the magnetic recording medium. Accordingly, a so-called perpendicular magnetic recording system has been proposed, in which the direction of recorded magnetization is perpendicular to the surface of the magnetic recording medium. A perpendicular magnetic recording medium includes a magnetic recording layer of hard magnetic substance and a backing layer of soft magnetic material
16
that serves to concentrate the magnetic flux generated by the magnetic head and used for recording to the magnetic recording layer.
In a common HDD, recording and reproduction of data are performed with a magnetic head floating over the surface of the rotating magnetic recording medium of a hollow disk shape. The floating is effected by a floating mechanism called a slider and the flying height is several tens of nm. Bit information on the magnetic recording medium is stored in the data tracks concentrically positioned on the medium. In the recording and reproduction of data, a read-write head moves to the target data track with high speed. The recording surface of the magnetic recording medium contains preformat information that includes tracking servo signals for detecting relative position between the head and the data track, and address signals or regenerative clock signals. The preformat information corresponding to a data track is recorded on a circle concentric with the data track at certain angular intervals. The preformat information of the whole magnetic recording medium is recorded on linear preformat regions
35
with a sector form, which is substantially a linear form, arranged at certain angular intervals as shown in FIG.
11
. For preventing the center of the row of preformat signals from diverting from the center of the magnetic recording medium or from the center of the orbit of the read-write head, the preformat information has been conventionally recorded using a special writing apparatus called a track writer after mounting the magnetic recording medium on the HDD.
Accompanying the above-described enhancement of recording density, the recording density of the preformat information is also increasing, to prolong the time for writing the preformat information. This is becoming a serious factor to lower efficiency in HDD production and to raise HDD cost.
Recently, a method for writing the preformat information to a magnetic recording medium has been proposed, in which the information is written to the recording medium in an a real manner by means of magnetic transfer technique using a master disk carrying the preformat information, in place of writing to each of the tracks with linear manner using the signal-writing head of a servo slider. For example, Japanese Unexamined Patent Application Publication (KOKAI) No. H10-40544 discloses a method for transferring preformat information to a longitudinal magnetic recording medium using a master disk that has protrusions and recesses, the protrusions being composed of ferromagnetic material. Japanese Unexamined Patent Application Publication (KOKAI) No. H11-25455 discloses a method for close contact between a master disk and a magnetic recording medium in the magnetic transfer process by means of supplying and exhausting air in the groove of the master disk. However, these references don't disclose a magnetic transfer method for a perpendicular magnetic recording medium.
A technology for magnetic transfer to a perpendicular magnetic recording medium that is a recording medium where the direction of magnetization for recording is perpendicular to the medium surface has never been devised. FIG.
3
(A) and FIG.
3
(B) show an initialization step and a transfer step, respectively, in a devised magnetic transfer method to a perpendicular recording medium
1
. The structure of a master disk
2
used in the method is the same as that in the case of a longitudinal magnetic recording medium. In the step for initializing the perpendicular magnetic recording medium
1
, a magnetic field perpendicular to the magnetic recording medium
1
surface is applied using single magnetic pole heads
16
as illustrated in the FIG.
3
(A). Two single magnetic pole heads
16
and
16
are symmetrically arranged such that the two magnetic poles of different polarity are opposing with the medium put between the poles. This arrangement is taken because (1) spread of magnetic field in the longitudinal direction is smaller than in the case using one single magnetic pole head
16
, and (2) only perpendicular component of magnetic field is applied to the medium. In the step for transferring, the master disk
2
is closely contacted to the medium, and two single magnetic pole heads
16
and
16
are likewise symmetrically arranged such that the two magnetic poles of different polarity are opposing with the master disk
2
and the medium put between the poles, as shown in FIG.
3
(B). Here, the direction of the magnetic field is reversed in the transfer step from in the initialization step.
FIG. 4
also shows a prior art, in which one single magnetic pole head
16
having a yoke
7
is used. In the opposite side of the medium to the head, a thick plate made of soft magnetic substance called a back pole
8
is provided in place of a single magnetic pole head. This arrangement leads the magnetic flux
9
generated by the permanent magnet
4
through the yoke
7
and the back pole
8
so that the magnetic field is perpendicular to the medium surface
1
.
FIG.
5
(A), FIG.
5
(B) and FIG.
5
(C) show a principle of magnetic transfer in a perpendicular magnetic recording medium
1
. FIG.
5
(B) and FIG.
5
(C) show magnetic field distribution when a magnetic field is applied to the master disk
2
and the recording medium
1
closely contacted each other, with the field direction perpendicular to their surfaces, using lines of magnetic force
13
and a graph showing the distribution of perpendicular component of the magnetic field. When a uniform and perpendicular magnetic field is applied to the master disk
2
, the uniform flux is concentrated to the embedded soft-magnetic material
6
having high permeability. Hence, magnetic flux density or magnetic field intensity in the recording medium is large in the position the soft-magnetic material
6
is arranged and small in the position in the space between the soft-magnetic material
6
, as shown in FIG.
5
(B). If a perpendicular magnetic recording medium
1
having coercive force Hc of proper value is used, the direction of magnetization in the region of the medium beneath the soft-magnetic material
6
can be reversed in the transfer step from the direction in the initialization step; in FIG.
5
(A), the direction is reversed from upward to downward. In the region of the medium beneath the space area where the soft-magnetic material
6
does not exist, the magnetization is not reversed and the direction of magnetization holds. FIG.
5
(A) illustrates above-described situation and the distribution of intensity of signals when the magnetization transferred to the perpendicular magnetic r
Fuji Electric & Co., Ltd.
Rodriguez Glenda P
Rossi & Associates
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