Stock material or miscellaneous articles – Circular sheet or circular blank – Recording medium or carrier
Reexamination Certificate
1999-08-23
2002-06-11
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
Circular sheet or circular blank
Recording medium or carrier
C428S216000, C428S336000, C428S408000, C428S690000, C428S900000
Reexamination Certificate
active
06403194
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a magnetic recording medium which has an excellent reliability and permits magnetic recording at a high density, a process for producing said magnetic recording medium, and a magnetic disc apparatus used as an auxiliary storage for computer.
Magnetic disc apparatus used in storages such as large computers, workstations, personal computers, etc. are growing in importance year by year and have been increased in capacity and reduced in size. For the capacity increase and size reduction of the magnetic disc apparatus, increasing their density is indispensable. An example of technique for realizing the density increase is the reduction of the distance between the magnetic recording layer of a magnetic recording medium and a magnetic head.
Magnetic recording media produced by sputtering have comprised a protective film for protecting a magnetic film against sliding on a magnetic head. The reduction of thickness of the protective film and the reduction of the distance between the protective film surface and the magnetic head are the most effective means for reducing the distance between the magnetic recording layer and the magnetic head. As the protective film, carbon films formed by DC sputtering, RF sputtering (JP-A-5-174369) or CVD (JP-A-4-90125) are most generally used. For obtaining a protective film having a higher strength, a method of incorporating nitrogen atoms, hydrogen atoms, etc. into the film (JP-A-62-246129 and JP-A-5-22556) has been generally adopted.
As a conventional interface method for a magnetic recording medium and a magnetic head, there is contact-start-and-stop (CSS) method in which at the time of non-working, the magnetic head is stationary in contact with the magnetic recording medium at a predetermined position on the medium where very small concavities and convexities have been formed for preventing adhesion between the magnetic recording medium and the magnetic head, and at the time of working, i.e., the time of record writing, record reading or waiting, the magnetic head is lifted while keeping a very narrow space between the magnetic head and the magnetic recording medium.
In the case of magnetic disc apparatus to which this method is applied, the problem of wear and fracture of the protective film of a magnetic recording medium caused by contact or friction between the magnetic recording medium and a magnetic head at the beginning or end of working becomes more serious with a reduction in the thickness of the protective film. Also at the time of working, the problem of wear and fracture of the protective film caused by accidental contact between the magnetic recording medium and the magnetic head becomes more serious with a reduction in the distance between the protective film surface of the magnetic recording medium and the magnetic head.
It has been proposed that the durability of the protective film is improved by making the thickness of the protective film in an area where CSS is carried out (hereinafter referred to as CSS area), larger than that in an area where data are written (hereinafter referred to as data area) (JP-B-60-23406). However, no sufficient effect can be obtained by merely changing the film thickness because at present, the increase of the capacity and the reduction of the size are absolutely necessary. In detail, the above-mentioned data area has to be as wide as possible in order to record data as much as possible in the limited area of a disc. Therefore, the CSS area and the data area are unavoidably adjacent to each other. In such a condition, it is industrially difficult to make the film thickness in the CSS area widely different from that in the data area. Even if such a thickness change is realized, the reference position of the disc surface is abruptly changed when a head is allowed to seek between the CSS area and the data area. Thus, the thickness change causes an attitude change.
Therefore, the possible thickness difference is at most about 5 nm, and merely changing the thickness of a single film has been hardly effective. In addition, a thinned portion of about 10 nm thick of the protective film in the data area has to have a certain degree of hardness because it is easily fractured by its accidental collision with a magnetic head. However, when the protective film has such a hardness, it is too hard in the CSS area and hence has a high contact resistance with the head, resulting in a deteriorated durability.
From such a point of view, it seems effective to make physical properties of the protective film in the CSS area different from those in the data area. It has been proposed to form a protective film composed mainly of diamond in the CSS area and composed mainly of a mixture of graphite and diamond in the data area (JP-A-3-272017). However, when such a protective film is thinned to about 10 nm, it is not sufficient in strength in the CSS area and hence is easily fractured by contact or friction between a magnetic recording medium and a magnetic head at the beginning or end of working.
Further, it has been proposed to form a graphite structure in the CSS area and an amorphous structure in the data area (JP-A-4-32021). However, it is clear that a thin film with a graphite structure having a thickness of about 10 nm cannot withstand CSS. Even by combining the technique of JP-B-60-23406 with the techniques of JP-A-3-272017 and JP-A-4-32021, there could not be obtained a magnetic recording medium which had a sufficient strength to withstand its accidental collision with a magnetic head and was free from wear and fracture of its protective film in the CSS area by contact or friction between the magnetic recording medium and the magnetic head at the beginning or end of working even if the thickness of the protective film in the data area was adjusted to about 10 nm or less.
In addition, when a protective film composed of a portion having properties suitable for the CSS area and a portion having properties suitable for the data area is formed by a sputtering method, or when the thickness of a protective film is increased only in the CSS area by a sputtering method, even the formation of the protective film in the data area by the use of, for example, a masking shield out of contact with a magnetic recording medium can limit, only to a certain extent, sputtering particles which pass around behind the masking shield and intrude the data area, because of properties of sputtering. Thus, it has been difficult to make film properties in the CSS area strikingly different from those in the data area or change the film thickness markedly in a short distance.
Ion beam deposition is known as a means for forming a protective filmy layer which is tough even at a film thickness smaller than that of a protective filmy layer composed mainly of carbon by sputtering. However, it is industrially difficult to form a protective filmy layer only by ion beam deposition because the life of a hot filament used in an ion gun is short.
SUMMARY OF THE INVENTION
The present invention was made in view of such problems. A first object of the present invention is to provide a magnetic recording medium which has a sufficient impact resistance to withstand its accidental collision with a magnetic head and is free from wear and fracture of its protective film in the CSS area by contact or friction between the magnetic recording medium and the magnetic head at the beginning or end of working even if the thickness of the protective film in the data area is reduced to about 10 nm or less.
A second object of the present invention is to provide a process for producing a magnetic recording medium capable of achieving the first object. A third object of the present invention is to provide a magnetic storage suitable for attaining both a high packing density and a high reliability by using a magnetic recording medium obtained by achieving the above first object.
A fourth object of the present invention is to provide a process for producing a magnetic recording medium comprising a substrate, a magnetic film forme
Honda Yoshinori
Kokaku Yuuichi
Ono Toshinori
Suzuki Hiroyuki
Hitachi , Ltd.
Kenyon & Kenyon
Resan Stevan A.
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