Etching a substrate: processes – Forming or treating an article whose final configuration has...
Reexamination Certificate
2001-08-30
2004-12-28
Olsen, Allan (Department: 1763)
Etching a substrate: processes
Forming or treating an article whose final configuration has...
C216S022000, C216S042000, C216S045000, C216S063000, C216S076000, C216S079000, C216S081000
Reexamination Certificate
active
06835317
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a slider member having micro-protrusions for reducing the sliding friction and a method of forming such micro-protrusions on the substrate surfaces, for example, between a magnetic disc and a slider of the magnetic head.
2. Description of the Related Art
Reading and writing on magnetic memories are performed by the relative sliding of a slider of a magnetic head sliding against a magnetic disc (hard disc). A dynamic pressure (wind pressure) is generated by the relative motion of the sliding surfaces, and forces the slider to separate from the disc surface; however, to obtain high strength signals, it is desired that the separation force be overcome and the distance between the slider and disc surfaces be minimized. In order to satisfy this condition even at low relative speeds without crashing the slider against the disc, the two surfaces may be made planar; however, when such two planar surfaces are brought close together, sticking (adherence) is generated because of the presence of moisture in the ambient air. Also, if a lubricant is used to reduce the friction, the phenomenon of sticking becomes even more aggravated. Sticking becomes more severe as the surface roughness (height of protrusions) diminishes, as the humidity increases and as the lubricant thickness increases. Therefore, to satisfy the above requirements in the presence of humidity and lubricant, the surfaces should be sufficiently smooth to minimize the distance between the slider and disc surfaces while sufficiently rough to prevent sticking. To meet such contradictory requirements, it has been a practice to provide micro-protrusions of the order of 10 nanometers (nm) on the sliding surfaces. This will be explained further with reference to FIG.
20
.
FIG. 20
is a cross sectional view of micro-protrusions formed on a sliding surface by a conventional technique. In
FIG. 20
, the reference numeral
1
refers to a substrate of the magnetic disc made of an aluminum alloy, which may be covered with a nickel plating, or a glass substrate. The substrate
1
is first made into a plain surface
2
a
, then the surface
2
a
is abraded lightly with abrading tape or cloth containing powder particles so as to produce a roughened surface containing micro-protrusions
2
a
1
,
2
a
2
,
2
a
3
, of the order of 10 nm height. On top of the irregular shaped surface thus formed, a magnetic film layer and & protective film layer, made of a carbon film, SiO
2
film, ceramic film or other type of protective films, are deposited in succession to ultimately produce a sliding surface so that the contour of the outermost protective surface reproduces the irregular surface structure of the substrate.
FIG. 21
is a cross sectional view of micro-protrusions on a sliding surface produced by another conventional technique. In this figure, as in
FIG. 20
, the reference numeral
1
refers to a substrate of a magnetic disc. As in the previous case, the surface of the substrate
1
is made as a plain surface
2
b
, and is then processed by such processes as sputtering and vapor deposition to form numerous protrusions
2
b
1
,
2
b
2
, and
2
b
3
, on the top surface
2
b
. This step is followed, as before, by deposition of a magnetic film layer and a protective film layer to ultimately produce a sliding surface having micro-protrusions. In this case, the top surface
2
b
may not necessary be a surface of the substrate, and may be a flat surface of a magnetic film or a protective film to which similar deposition techniques can be applied to ultimately produce a protective film layer having micro-protrusions
2
b
1
,
2
b
2
, and
2
b
3
, to be used as the sliding surface.
FIG. 22
is a cross sectional view of micro-protrusions, on a sliding surface made by yet another conventional technique. The reference numeral
1
refers again to a substrate of a magnetic disc as in the case shown in FIG.
20
. As in the previous case, the surf ace is first made as a plain surface
2
c
, then, depressions are produced by a dry etching or wet etching, thereby producing a top surface
2
c
having numerous protrusions
2
c
1
,
2
c
2
, and
2
c
3
. This step is followed, as before, by deposition of a magnetic layer and a protective layer, to ultimately produce a protective top sliding layer having an irregular surface structure. In this case also, the top surface
2
c
may not necessary be a surface of the substrate, and may be a flat surface of a magnetic film or a protective film to which similar deposition techniques can be applied to ultimately produce a protective film layer having micro-protrusions
2
c
1
,
2
c
2
, and
2
c
3
to be used as the sliding surface.
There has been a serious problem in the actual use of the magnetic discs produced by the techniques described above. It has been found that, during the use of the magnetic disc in sliding contact with the slider of a magnetic head, foreign particles such as debris due to wearing as a result of the sliding action are entrapped between the slider and the disc, and are outstretched so as to stick to the slider or the disc thereby resulting in impeded transmission of signals. Furthermore, because moisture and lubricant may not be distributed uniformly across the surface of the disc, local sticking can occur between the slider and the disc, thereby causing abnormally high friction or, in some cases, self-vibration of the head (referred to as stick-slip), caused by sudden release from sticking, can result in plastic deformation or irregular friction phenomenon.
The debris biting and sticking phenomenon related to the conventional devices were examined in detail by the present inventors that led to the following observations. The primary causes are that, in the conventional devices, the inclusive angle of contact of the upright surface (side surface) of the micro-protrusions opposing the direction of relative movement of the sliding surface is small, which promotes the formation of a large meniscus. The formation of a meniscus on each of the various shaped of micro-protrusions will be explained in more detail with reference to
FIGS. 23A
,
23
B and
23
C which correspond to meniscus formation on micro-protrusions,
2
a
1
,
2
b
1
, and
2
c
1
, having profiles show in
FIGS. 20
,
21
and
22
, respectively. In FIGS.
23
A~
23
C, the slider surface
3
(on a magnetic head for example) is in contact with a liquid substance
4
(moisture in air or lubricant) and the magnetic disc moves in the direction D relative to the slider surface
3
- The meniscus means a curved boundary surface having a radius of curvature R formed between the air phase and the liquid phase. The relationship between the radius R and the profile shape of the micro-protrusions will be discussed further with reference to FIG.
24
.
FIG. 24
is a cross sectional view of a micro-protrusion. As a representative profile of a micro-protrusion, the profile of the protrusion
2
c
, shown in
FIG. 23C
has been chosen; however, this discussion applies in general to other profiles of micro-protrusions. The reference numerals are the same as those used earlier. A foreign debris particle
5
is present in the fore direction. In this example, the distance between the slider surface
3
and the bottom surface of the protrusion
2
c
1
is shown to be about 10 nm (the height of the micro-protrusion), and the profile is assumed to be symmetrical. The angle of the meniscus is &thgr; which refers to the inclusive angle of contact between the slider surface
3
and the leading surface in the moving direction of the micro-protrusion
2
c
1
. Force F
1
is exerted to the micro-protrusion
2
c
1
, by the liquid substance
4
.
If the inclusive angle &thgr; is small, there is a larger area of contact between the slider surface
3
and the micro-protrusion
2
c
1
, and the meniscus, i.e. a radius of curvature R, becomes large. The larger the meniscus, the larger the force F
1
to cause more sticking. Furthermore, it can be seen that if the inclusive angle &thgr; is small,
Hatamura Yotaro
Nakao Masayuki
Ebara Corporation
Olsen Allan
Wenderoth , Lind & Ponack, L.L.P.
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