Dynamic magnetic information storage or retrieval – Fluid bearing head support – Disk record
Reexamination Certificate
1999-03-16
2001-03-06
Evans, Jefferson (Department: 2754)
Dynamic magnetic information storage or retrieval
Fluid bearing head support
Disk record
C360S236700, C360S237000
Reexamination Certificate
active
06198601
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thin film magnetic head which has a small flying height above a disc, as well as to a process for production thereof. More particularly, the present invention relates to a thin film magnetic head in which the width, groove depth and tapered angle of each rail at the surface side of said magnetic head to face a magnetic disc are formed to provide a high accuracy and at a high efficiency and which can give a small flying height stably and also can prevent head crush, as well as to a process for production thereof.
The present invention relates also to a plasma etching process using an etching gas. More particularly, the present invention relates to a process for etching using an etching gas that can process a material having a small etching rate (e.g., a ceramic or a high dielectric) in a short time, at a high accuracy, safely and easily.
2. Prior Art
In order to increase the recording density of a thin film magnetic head (hereinafter referred to simply as a magnetic head), it is essential to reduce and stabilize the flying height of the magnetic head. For achievement thereof to develop a magnetic head allowing for high-density recording, a particularly important task is to form, on a magnetic head, rail(s) which can minimize the variation in flying height of the magnetic head, caused by the difference in circumferential speed of a disc between the inner and outer circumferences of the disc.
Description is made on the formation of rail(s) by referring to FIG.
29
and FIG.
30
.
FIGS. 29A and 29B
are drawings showing the shapes of magnetic heads and processes for production thereof;
FIGS. 30A
to
30
C are schematic drawings for explaining the flying state of a magnetic head;
FIG. 31
is a graph showing the relation between rail width and flying height; and
FIG. 32
is a graph showing the relation between rail groove depth and flying height.
In order to allow a magnetic head
1
to fly, there is utilized an air bearing slider preloaded by a suspension spring, such as shown in FIG.
30
. The air bearing slider is a bearing mechanism consisting of an air layer between a magnetic disc
9
and the top surface of a magnetic head
1
facing the magnetic disc
9
, i.e. the top surface of each rail
2
formed on a rail substrate
8
and, as shown in
FIG. 30B
, is formed by air which enters said layer from an air inlet
21
. When the air, which has entered the layer, leaves the layer from an air outlet
22
at the end of the element portion
20
of the magnetic head
1
, the resulting air current caused by viscosity resistance of air between the magnetic head
1
and the magnetic disc
9
imparts a flying force to each rail
2
. In this case, the flying height
4
of the magnetic head
1
as shown in
FIG. 30C
is controlled by said flying force and the pressure of a spring
3
added to the magnetic head
1
from outside. The magnetic head
1
is in physical contact with the magnetic disc
9
when the magnetic disc
9
is in a stopped condition; when the magnetic disc
9
reaches a certain number of rotations per minute, an air bearing as mentioned above is formed, a flying force is generated, and the magnetic head
1
is separated from the magnetic disc
9
and keeps flying at a given flying height
4
. With respect to the flying state of the magnetic head
1
, its flying height
4
is smaller at the air outlet
22
than at the air inlet
21
, as shown in
FIG. 30B
, and consequently the magnetic head
1
contacts with the magnetic disc
9
more easily at the air outlet
22
when the magnetic disc
9
is in rotation and also when stationary.
The shape of the portion of the magnetic head
1
at the air inlet
22
is desirably as smooth as possible to prevent, for example, the damage of the magnetic disc
9
or the element portion
20
of the magnetic head
1
. To achieve such a shape efficiently for a large number of magnetic heads
1
is difficult using known techniques. As an approach, there is known a technique of chaffering the portion of a magnetic head
1
at the air outlet
22
by mechanical processing, specifically polishing.
Chaffering of each edge of rail top surface
2
a
(rail top surface
2
a
is hereinafter referred to simply as top surface
2
a
) has been conducted for the purposes of, for example, prevention of rail
2
sticking to magnetic disc
9
, acceleration of flow of air onto top surface
2
a
(top surface
2
a
is a point of generation of the air dynamic pressure) at the start of flying of magnetic head
1
, and prevention of magnetic disc
9
damage caused by the edge of top surface
2
a
and consequent destruction of recorded information. For this edge chaffering, there are proposed mechanical processing methods, for example, a method of polishing each rail
2
on a lapping sheet-attached rotating disc by allowing the rail
2
to repeat flying and contact with the disc in a stare similar to that experienced on a magnetic disc >e.g. Japanese Patent Application Laid-Open No. 60-9656.
The flying height
4
depends upon the number of rotations per minute of magnetic disc
9
, the dimension and shape of each rail
2
of magnetic head
1
, the pressure of spring
3
, etc. This flying height
4
must be minimized and moreover maintained stably in order for a magnetic disc device to allow for high-density recording. It is desirably 100 nm or less. Hence, a strict accuracy is required for the dimension of each rail
2
formed at the air bearing surface, the top surface of a magnetic head
1
which is to contact with a magnetic disc.
The relation between the flying height
4
and the width or groove depth of rail
2
is generally such as shown in
FIG. 31
or
32
, although it varies slightly depending upon the shape of rail
2
.
FIG. 31
shows a relation between rail width (&mgr;m) and flying height
4
(&mgr;m) when the rail groove depth (&mgr;m) is constant. It is shown that the flying height
4
is larger when the rail width is larger.
FIG. 32
shows a relation between rail groove depth and flying height
4
when the rail width is constant. It is shown that the flying height
4
is minimum when the rail groove depth is at a particular value and that the flying height
4
is larger when the rail groove depth is smaller or larger than the particular value. For example, in a case where the rail has a shape such as the non-linear rail
5
shown in
FIG. 29B
, the flying height
4
is minimum when the rail groove depth is 5-6 &mgr;m (particular value). In this case, the design value of rail groove depth is set generally at 5-6&mgr;m. With respect to the geometrical shape of rail
2
top surface, curved line shapes (e.g. a non-linear rail
5
) are used practically to obtain a desired flying height
4
in an air bearing mechanism, or to minimize the adverse effects caused by the error in rail
2
formation or the error in formation of rail groove depth, or to minimize the change in flying height
4
by the difference in circumferential speed between the inner and outer circumferences of magnetic disc
9
. Examples of other shapes are proposed in Japanese Patent Publication No. 5-8488 and Japanese Patent Application Laid-Open No. 4-276367.
For formation of a rail
2
which has a complicated shape as mentioned above and yet must have a dimension of high accuracy, a dry processing technique, particularly an ion milling technique is in use in place of the conventional mechanical processing using a whetstone as shown in FIG.
29
A. The dry processing technique comprises forming a resist pattern matching the shape of a rail
2
to be formed, by photolithography, applying an ion beam
6
using the resist pattern as a mask, as shown in
FIG. 29B
, to etch a rail substrate
8
, and finally removing the mask to form a rail
2
.
In the dry processing technique, there is used, as the etching apparatus, an ion milling apparatus. The ion milling apparatus includes the following, for example:
(1) an ion milling apparatus wherein thermoelectrons are generated from a filament, a troidal moveme
Fujisawa Masayasu
Hagiwara Yoshiki
Hira Yasuo
Imayama Hirotaka
Ishizaki Hiroshi
Evans Jefferson
Hitachi , Ltd.
Kenyon & Kenyon
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