Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
1999-09-20
2002-05-28
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S690000, C428S690000, C428S690000, C428S212000
Reexamination Certificate
active
06395412
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to magnetic recording medium, such as a magnetic disk, particularly of a quality wherein low noise and high recording density is obtained with flying stability at an ultra low flying height, and the manufacturing method and magnetic storage apparatus making and employing such medium.
Although
FIG. 1
relates to a general magnetic recording disk drive of the present invention, it employs features that are broadly conventional, that is a magnetic recording disk
1
, spindle
2
to hold and rotate the disk, a magnetic recording head
3
for reading and writing with respect to the disk, servomechanism
4
to position the head, and an electric circuit
5
for driving the above elements. In general, such a disk employs a magnetic recording medium that has an underlayer, a magnetic layer, and a protective layer, all laminated on a substrate. It is important that the read/write characteristics required in the magnetic recording medium provide for durability against the damage of the medium surface by contact with the magnetic head. Especially, it is important to prevent or reduce adsorption or adhesion between the magnetic disk and the magnetic head in the prior art by deposition to produce minute grooves, which are called texture, on the substrate surface, particularly in the circumferential direction or randomly by mechanical polishing using minute abrasive grains, or the like. This type of texture can also be obtained by deposition, particularly by sputtering to produce minute protrusions of the substrate or magnetic layer surface, or both. PTFE (Poly-tetrafluoroethylene) powder may be applied after a protective film is formed as a mask material, then the surface is etched by a dry etching method, and this produces an etching texture of the type mentioned above that has a ruggedness on the protective film surface. Examples of such prior art technology are the following.
Japanese patent Laid-Open No. 61-202324 discloses a mechanical polishing method, called “Texture” that forms microgrooves on a substrate, for example in the circumferential direction, to prevent the adsorption or adhesion between a magnetic disk and a magnetic head. Japanese patent Laid-Open No. 60-119635 discloses a sputtering method, called “Depot Texture” by forming minute protrusions on a substrate or a magnetic layer to obtain an effect r to that of “Texture”. Japanese patent Laid-Open No. 58-53026 discloses a dry etching method, called “Etching Texture”, that forms a ruggedness on the protective layer by dry etching using masks made of PTPE powder, etc., to obtain an effect similar to that of “Texture”.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a magnetic recording medium, an apparatus employing such medium, and a method to produce such medium, wherein roughness of the magnetic layer is smaller than the roughness of the substrate, in the field or area where writing and reading is carried out by a magnetic recording head. Therefore, a magnetic recording medium and magnetic recording apparatus is obtained with high recording density and high reliability, by the method and structure of the present invention that reduces media noise and provides flying stability of the magnetic recording head at ultra low flying height, because of the reduced ruggedness of one or more of the underlayer, magnetic layer and protective layer, with respect to the roughness of the prior art.
An object of the present invention is to reduce or prevent adhesion of the magnetic head to the magnetic disk for increased reliability for assurance-proof of the contact start-stop (referred to as CS/S), which according to the above-mentioned prior art has previously involved increasing roughness and therefore reducing flying height in the prior art and reducing recording density in the prior art. Therefore, the present invention has simultaneously two objects that have heretofore been mutually exclusive of each other.
The inventors' analysis of the prior art problems and causes are a part of the present invention.
At the present time, high recording density involves a flying height of the magnetic head that is below 20 nm. As shown by conventional evaluation methods such as CS/S, durability and adhesion (friction) became difficult to obtain with respect to proof stress of the data plane because of irregularity in contacting between the head and medium. This was especially true with the adoption of LZT (Laser Zone Texture), wherein the CS/S zone and data plane or data field are distinguished, and this becomes more important with respect to reliability of the data plane. In general, damage from impact was lessened and adhesion of the magnetic head prevented by the prior art adoption of a lubricant and by adding minute grooves, previously referred to as texture or TEX, by the conventional machining of the data plane, which has the same surface as the CS/S zone. According to such prior art method, the TEX processing itself increases surface roughness of the substrate, and as the surface roughness of the substrate increases, necessarily the flying height of the magnetic head inevitably rises. Therefore, levitation start height in the medium plane of the magnetic head, Hto (the head takeoff height), also rises. Therefore, with such prior art technology, it is not possible to make the flying height of the magnetic head less than 20 nm or less, which is necessary to obtain ultra low flying height and high density. To obtain the flying height of 20 nm or less, it is necessary that the starting height of the levitation, that is Hto, be 10 nm or less, when dispersion of the buoyancy of the head and assembly accuracy of the drive are considered.
With respect to the conventional technology, it is shown in
FIG. 2
, that the surface roughness of underlayers
8
,
9
, a magnetic film
7
and a protective film
6
, which are laminated on a substrate
10
, have a surface roughness dependent upon the surface roughness of the substrate. In general, the inventors' analysis of the prior art shows that the surface roughness of the finally completed magnetic recording medium is increased with respect to the surface roughness of the substrate.
FIG. 3
shows a substrate surface (a) obtained by texture-processing using abrasive grain and formed of 30 nm of Cr deposited on the substrate surface (b), and Table 1 shows data for the surfaces as measured by an atomic force microscope (AFM) for comparison.
TABLE 1
Sample
Ra (nm)
Rp (nm)
Rmax nm)
(a) On a substrate
1.9
6.2
7.0
(b) On a Cr underlayer
1.3
6.5
12.4
A numerical value, as an index to surface roughness, is obtained by the following formula for center line average roughness of the roughness curve: Ra,
Ra
=
1
/
L
∫
0
L
&LeftBracketingBar;
f
(
x
)
&RightBracketingBar;
ⅆ
x
(
Equation
1
)
L is the length of a roughness curve (distance of actual measurement), the roughness curve (data of actual roughness was shown as a curve, and Ra is obtained by the integral of this absolute value): y=f(x).
Ra: center line average roughness shown in the above equation.
Rp: The largest center line height (largest interval with the center line in the summit in the roughness curve). Rmax; Maximum height above rail level in the roughness curve (peak to peak). The index to this surface roughness has generally been adopted. The AFN used was a NANO-SCOPE III made by DI (Digital Instruments, Inc.). As it is clear from FIG.
3
and Table 1, the substrate surface by the mechanical TEX working method has actually considerable abnormal points (protrusions), and this is shown in maximum height above rail level, Rmax. As shown in Table 1, Rmax of the underlayer shows a larger value than the substrate, because the surface which formed the underlayer reflects the surface of the substrate, and there is the growth of the protrusion of Cr by the abnormal growth which will occur in epitaxial growth of Cr at the abnormal point of the substrate. Therefore, it is not aft possible to obtain
Honda Yoshinori
Kokaku Yuuichi
Ono Toshinori
Shoda Mitsuhiro
Hitachi , Ltd.
Mattingly Stanger & Malur, P.C.
Rickman Holly
Thibodeau Paul
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