U.S. patent application number 10/384310 was filed with the patent office on 2004-01-01 for magnetic head slider and method of manufacturing the same.
This patent application is currently assigned to Hitachi, Ltd.. Invention is credited to Furusawa, Kenji, Isono, Yukihiro, Seki, Takateru, Takakura, Akio, Tanaka, Hideaki.
Application Number | 20040001285 10/384310 |
Document ID | / |
Family ID | 29766233 |
Filed Date | 2004-01-01 |
United States Patent
Application |
20040001285 |
Kind Code |
A1 |
Tanaka, Hideaki ; et
al. |
January 1, 2004 |
Magnetic head slider and method of manufacturing the same
Abstract
In order to realize a shape of an air bearing surface of a
magnetic head slider which is capable of coping with a lowering of
flying height and which has high reliability, at the time of
polishing the air bearing surface of the magnetic head slider by
bringing the air bearing surface and the surface of a polishing
machine into contact with each other, machining is conducted in the
condition where the stiffness acting between both the members is
enhanced, and the standard deviation of the flatness of the air
bearing surface machined and the standard deviation of the recess
amount between the air bearing surface and a magnetic element are
controlled. Thus, it is possible to efficiently manufacture a
magnetic head slider which enables driving at a low flying
height.
Inventors: |
Tanaka, Hideaki; (Yokohama,
JP) ; Furusawa, Kenji; (Hiratsuka, JP) ; Seki,
Takateru; (Yokohama, JP) ; Takakura, Akio;
(Odawara, JP) ; Isono, Yukihiro; (Hadano,
JP) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW, LLP
TWO EMBARCADERO CENTER
EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Assignee: |
Hitachi, Ltd.
Tokyo
JP
|
Family ID: |
29766233 |
Appl. No.: |
10/384310 |
Filed: |
March 6, 2003 |
Current U.S.
Class: |
360/234.7 ;
360/235.1; G9B/5.231 |
Current CPC
Class: |
Y10T 29/49048 20150115;
G11B 5/6005 20130101 |
Class at
Publication: |
360/234.7 ;
360/235.1 |
International
Class: |
G11B 005/60 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 6, 2002 |
JP |
2002-059668 |
Claims
We claim:
1. A magnetic head slider including in a group of magnetic head
sliders, each having a shape of an air bearing surface formed on a
slider substrate, such that the standard deviation of said group
for a recess amount X.sub.1 between said air bearing surface and
the surface of a magnetic head element that is disposed on said
slider substrate with an insulating film and a shield portion
interposed therebetween is not more than 0.8 nm, and the standard
deviation of said group for the dispersion X.sub.2 of surface
flatness of said air bearing surface is not more than 0.6 nm.
2. A magnetic head slider as set forth in claim 1, wherein said
group of the magnetic head sliders having quantity of the magnetic
head sliders being able to statistically processed for the recess
amount X.sub.1 and the dispersion X.sub.2.
3. A magnetic head slider as set forth in claim 1, wherein said
group of the magnetic head sliders having quantity of the magnetic
head sliders judged, within the range of a level of significance of
5%, to be not significantly different from said group for the
recess amount X.sub.1 and the dispersion X.sub.2, when subjected to
F-test on a Wilks'.LAMBDA. obtained from said group.
4. A magnetic head slider as set forth in claim 1, wherein said
slider substrate is made of aluminum titanium carbide or silicon
carbide.
5. A magnetic head slider as set forth in claim 1, wherein the
hardness of said slider substrate is higher than that of said
insulating film, and the hardness of said insulating film is higher
than that of said magnetic head element.
6. A method of manufacturing a magnetic head slider comprising a
magnetic head element that is disposed on a slider substrate having
an air bearing surface with an insulating film and a shield portion
interposed therebetween, wherein said air bearing surface of said
slider held on a workpiece-holding unit is polished by a polished
surface of a polishing surface plate being rotated while
maintaining a relative angular relationship between said air
bearing surface and said polishing surface.
7. A method of manufacturing a magnetic head slider as set forth in
claim 6, wherein the relative angular relationship between said air
bearing surface and said polishing surface is a substantially
parallel relationship.
8. A method of manufacturing a magnetic head slider as set forth in
claim 6, wherein the polishing of said air bearing surface is
conducted by relatively moving said polishing surface of said
polishing surface plate and said air bearing surface.
9. A method of manufacturing a magnetic head slider as set forth in
claim 6, wherein the polishing of said air bearing surface is
finished by stopping the rotation of said polishing surface plate
after separating said air bearing surface away from said polishing
surface of said polishing surface plate.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a magnetic head slider for
recording and reading back information onto and from recording
media such as magnetic recording disks with the magnetic head being
moved relatively to the recording media.
[0002] In recent years, it has been required to reduce the flying
height of the magnetic head relative to the magnetic recording
medium to 10 nm or less as the magnetic recording disk drives have
remarkably been enhanced in recording density.
[0003] Generally, a magnetic recording disk drive is composed by
combining a magnetic head fixed to a support spring with a magnetic
recording disk which is a recording medium. The writing and reading
of magnetic records onto and from the magnetic recording disk being
rotated is carried out by the magnetic head which is moved relative
to the magnetic recording disk by a head access system. Therefore,
the unit length per bit is reduced as the plane recording density
of the magnetic recording disk is enhanced; viewing from the
magnetic head side, this means that it is required to achieve a
lower flying height and thereby to read the leakage field
efficiently.
[0004] In view of the performance of the magnetic head, it is
necessary to set the flying height at about 10 nm in the case of a
recording density of 100 Gb/in.sup.2, and, particularly, the
variation of the air bearing surface shape is an obstacle in
realizing the above-mentioned flying height. Further, for the
purpose of efficient reading of the leakage field, a lower flying
height is required at the portion corresponding to the recess
amount X.sub.1 between a slider substrate and a read element
(magnetic head element) disposed via a shield element, since the
effective head reading performance is deteriorated if the recess
amount X.sub.1 is large.
[0005] A method of producing the air bearing surface of the
magnetic head with such a low flying height generally employs
polishing. In particular, if a magnetoresistive (MR) or giant
magnetoresistive (GMR) head is used for reading the information
from the magnetic recording disks, the element height of the MR or
GMR element must be machined with high accuracy. Specific
processing methods are described in detail in Japanese Patent
Laid-open No. Hei 2-95572 and Japanese Patent Laid-open No.
2000-158335.
SUMMARY OF THE INVENTION
[0006] The above-mentioned processing methods employ a lapping
method for polishing on a soft metal-based surface plate.
Specifically, while a lapping liquid mainly containing hard
abrasive grains of diamond or the like is dripped through a slurry
supply tube onto a soft metal-made polishing surface plate being
rotated, a head adhered to a polishing jig is slid under pressure,
whereby processing is conducted by the abrasive grains embedded in
the polishing surface plate or by rolling abrasive grains rolling
between the surface plate and the head.
[0007] However, in the above-mentioned polishing process by use of
a computer lapping, processing on the order of about several .mu.m
is conducted, and, therefore, it is indispensable to continuously
drip the slurry containing free abrasive grains from the viewpoint
of enhancement of processing efficiency with respect to throughput.
Specifically, from the start of processing to a point of about 1
.mu.m before the target size, the dripping of free abrasive grains
is continued, whereby the polishing process is performed at a
processing rate of about 1 .mu.m/min. Next, the dripping of free
abrasive grains is stopped, dripping of only a lubricating oil is
conducted instead and, further, the relative velocity between the
workpiece and the surface plate is reduced to a value of 1/n (n is
a number corresponding to the term "several") of the preceding
value, whereby finish processing is conducted at a low processing
rate of not more than 0.1 .mu.m/min. In this manner, the desired
accuracy of the element height is obtained.
[0008] In this case, a contrivance has been attempted in which, for
example, the free abrasive grains remaining on the surface plate
are wiped off immediately before the transition from the rough
machining using the free abrasive grains to the finish machining
using the dripping of only the lubricating oil. However, since the
processing or machining is conducted continuously on the same
surface plate, it is difficult to transit to the finish machining
by completely removing the free abrasive grains. Therefore, the use
of only this step has a limitation as to the reduction of the
selective polishing of soft portions due to the action of the free
abrasive grains, i.e., dents in the element, or the so-called
recess amount, and the variation of flatness of the air bearing
surface produced by the machining is large.
[0009] One of the reasons for this resides in that the members
constituting the magnetic head slider which differ in hardness and
arranged in a stack form as a whole, such as a slider substrate
(aluminum titanium carbide or the like), an insulating film
(alumina), a shield portion (permalloy) and the magnetic head
element (magnetic material) are simultaneously subjected to the
polishing. Incidentally, the hardness of the slider substrate is
higher than that of the insulating film, the hardness of the
insulating film is higher than that of the shield portion or the
magnetic head element, and thus, the successful polishing is
difficult.
[0010] In such a prior art in which the finish polishing as a
separate step is conducted, it is often the practice to slidingly
move the workpiece holding jig mounted with a row bar in random
directions relative to the surface plate so as to contrive a
reduction in the surface roughness of the work surface as a whole.
In addition, in the apparatus for such finish machining, the
workpiece holding jig is frequently so constructed that it can be
freely oscillated relative to the support mechanism.
[0011] That is to say, after the parallelism between the workpiece
surface of the workpiece and the polishing surface of the surface
plate is adjusted, the work holding jig is pressed from the upper
side, and thereafter the work holding jig is forced to swing in the
radial direction of the surface plate, whereby polishing process by
relative sliding motions in conjunction with the rotating motion of
the surface plate is carried out.
[0012] In this case, the support mechanism for exerting a pressing
load on the work holding jig is so designed as to maintain the
parallelism between the workpiece surface of the workpiece and the
polishing surface of the surface plate through spontaneous
self-adjustment by the free oscillating mechanism, even when the
orientation of the longitudinal axis of the support mechanism and
the orientation of the normal axis of the polishing surface of the
surface plate are staggered from each other at the stage before the
contact between the workpiece and the surface plate.
[0013] In this type of machining, the work holding jig and the
support mechanism are connected through the free oscillating
mechanism. Therefore, at the time of inversion of the swing of the
work, the frictional force in the shearing direction exerted on the
workpiece surface to be polished of the workpiece is also inverted.
For this reason, the distribution of the polishing load exerted on
the work during machining becomes nonuniform and instable in the
bar, with the result that the flatness and the recess amount of the
air bearing surface in the bar are also nonuniform and
instable.
[0014] In view of the performance of a magnetic head, it is an
object of the present invention to provide an air bearing surface
shape, and a method of producing the air bearing surface, which
maintains such a high reliability as to be free of the fear of head
crash even in the case of a flying height of about 10 nm for high
recording density, and in which a recess amount X1 between a slider
substrate and a read element disposed via a shield portion is
small, and a reading resolution in head leakage magnetic field is
high.
[0015] In order to attain the above object, according to the
present invention, there is provided a magnetic head slider which
includes in a group of magnetic head sliders, each having a shape
of an air bearing surface formed on a slider substrate, such that
the standard deviation of the group for recess amount between the
air bearing surface and the surface of a magnetic head element that
is disposed on the slider substrate with an insulating film and a
shield portion interposed therebetween is not more than 0.8 nm,
and, as will be described later, in the shape of the air bearing
surface of the head slider shown in FIG. 3, particularly the
standard deviation of the group for dispersion of the flatness in
the direction of section A-A' is not more than 0.6 nm.
[0016] In order to attain the above object, according to the
present invention, there is also provided a magnetic head slider
which includes in the group of magnetic head sliders having the air
bearing surfaces which are judged, within the range of a level of
significance of 5%, to be not significantly different from the
group of the magnetic head sliders such characteristics that the
total .SIGMA.X.sub.1 of recess amounts X.sub.1 is 30.5 nm, the
total .SIGMA.X.sub.1.sup.2 of squares of the recess amounts X.sub.1
is 51.1 nm.sup.2, the total .SIGMA.X.sub.2 of dispersion X.sub.2 of
surface flatness of the air bearing surface is -1 nm, the total
.SIGMA.X.sub.2.sup.2 of squares of the dispersion X.sub.2 of the
surface flatness is 4.8 nm.sup.2, and the total
.SIGMA.X.sub.1X.sub.2 of the products of the recess amount X.sub.1
and the surface flatness dispersion X.sub.2 of the air bearing
surface is -0.95 nm.sup.2, when subjected to F-test on a Wilks'
.LAMBDA. obtained from the group of the magnetic head sliders
having the air bearing surfaces having the characteristics.
[0017] In order to attain the above object, according to the
present invention, there is further provided a magnetic head slider
which includes in the group of the magnetic head sliders having the
air bearing surfaces which are decided, within the range of a level
of significance of 5%, to be not significantly different from a
magnetic head slider group having air bearing surfaces having such
characteristics that the total .SIGMA.X.sub.1 of recess amounts
X.sub.1 is 30.5 nm, the total .SIGMA.X.sub.1.sup.2 of squares of
the recess amounts X.sub.1 is 51.1 nm.sup.2, the total
.SIGMA..vertline.X.sub.2.vertline. of the absolute values of
dispersion X.sub.2 of surface flatness of the air bearing surface
is 4.8 nm.sup.2, and the total .SIGMA.X.sub.1.vertline.X.sub.2.ve-
rtline. of the products of the recess amount X.sub.1 and the
surface flatness dispersion X.sub.2 of the air bearing surface is
12.6 nm.sup.2, when subjected to F-test on a Wikls'.LAMBDA.
obtained from the group of the magnetic head sliders having the air
bearing surfaces having the characteristics.
[0018] In addition, the magnetic head slider is produced by
polishing the air bearing surface for a polishing surface of a
polishing surface plate being rotated while maintaining a relative
angular relationship between the air bearing surface of the slider
held on the work and the polishing surface.
[0019] The magnetic head slider is produced by a method in which
the air bearing surface is processed by bringing a slider substrate
into contact with the polishing surface of the polishing surface
plate after rotating the polishing surface, and the processing of
the air bearing surface is finished, i.e., the polishing surface
plate is stopped by separating the air bearing surface away from
the polishing surface while continuing the relative motion between
the polishing surface and the air bearing surface.
BRIEF DESCRIPTION OF THE DRAWING
[0020] These and other features, objects and advantages of the
present invention will become more apparent from the following
description taken in conjunction with the accompanying drawings
wherein:
[0021] FIG. 1 is a general view for illustrating a polishing
apparatus according to the present invention;
[0022] FIG. 2 is a schematic diagram for illustrating the magnetic
spacing and the recess amount of a magnetic head slider;
[0023] FIG. 3 is a schematic diagram for illustrating a sectional
structure of a magnetic head element;
[0024] FIG. 4 is a schematic diagram for illustrating an air
bearing surface of the magnetic head slider;
[0025] FIGS. 5A and 5B are a schematic diagram for illustrating the
crown and the camber in the air bearing surface;
[0026] FIG. 6 is a diagram showing the relationship between the
flatness (standard deviation) of the air bearing surface and the
number of measurement pieces;
[0027] FIG. 7 is a diagram showing the relationship between the
recess amount (standard deviation) of the air bearing surface and
the number of measurement pieces;
[0028] FIG. 8 is a diagram for illustrating the relationship
between the flatness dispersion and the recess amount of the
magnetic head slider;
[0029] FIG. 9 is a diagram for illustrating the flying
characteristics in Example 1;
[0030] FIG. 10 shows structural dimensions of the magnetic head
slider for illustrating Example 2;
[0031] FIG. 11 shows structural dimensions of the magnetic head
slider for comparison with Example 2;
[0032] FIG. 12 shows structural dimensions of the magnetic head
slider for illustrating Example 3; and
[0033] FIG. 13 shows structural dimensions of the magnetic head
slider for comparison with Example 3.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0034] A first embodiment of the present invention will be
described in detail below with reference to the drawings.
[0035] FIG. 1 is a general view of a polishing apparatus for
illustrating the first embodiment. The polishing apparatus mainly
includes a disk-shaped polishing surface plate (polishing surface
plate 8) placed on a rotary table supported by a frame 6, a bridge
5 disposed on the frame in the form of spanning the surface plate,
a linear actuator 7 which is a reciprocation-driving device mounted
on the bridge, a workpiece holding device comprising a workpiece
holding jig 2 mounted on a slider table of the reciprocation-
driving device, a workpiece holding jig support plate 3 and the
like, an angle adjusting mechanism 4a, 4b for adjusting the
relative orientations of a workpiece surface to be polished of a
workpiece 1 held by the work holding jig 2 located at a lower
portion of the workpiece holding device and the polishing surface
of the polishing surface plate 8, and a mechanism for adjusting the
relative distance between the workpiece surface to be polished of
the workpiece 1 and the surface plate polishing surface which is
provided in the inside of the workpiece holding device.
[0036] Here, if it is difficult to measure the actual orientation
of the work 1 during polishing, the angle adjustment of the
relative orientations can be realized by adjusting the relative
orientations and relative angle between the polishing surface of
the polishing surface plate 8 and the workpiece-holding lower
surface of the workpiece-holding jig 2. In the present embodiment,
two gonio-stages 4a and 4b are used to constitute the angle
adjusting mechanism.
[0037] The polishing surface plate 8 can be rotated horizontally
relative to the surface of the rotary table by utilizing a motor
(not shown) provided inside the rotary table and the like. The
upper surface of the surface plate constituting the polishing
surface is machined flat on a macroscopic basis, and is provided
with a groove like a record disk groove having a width of several
tens of .mu.m and a depth of several .mu.m on a microscopic basis.
The groove promotes discharge of a lubricating liquid, whereby the
sliding condition between the workpiece 1 and the polishing surface
plate 8 is stabilized. At a projected portion of the groove,
diamond abrasive grains with a diameter of about 100 nm are densely
arranged in the state of being half-embedded by the procedure which
will be described later, and, with this constitution, the surface
plate functions as a polishing grindstone.
[0038] In addition, a lubricating liquid container and a
lubricating liquid supply mechanism which are not shown are
provided on the frame on a lateral side of the surface plate, and a
lubricating liquid is dripped onto the polishing surface of the
surface plate via a supply tube. Further, a ceramic-made correction
ring 9 is disposed on the surface plate, and is supported by a
freely rotatable pulley, whereby the correction ring 9 is rotated
about its axis on the surface plate as the polishing surface plate
8 is rotated. With these arrangements, the flatness of the
polishing surface of the surface plate is maintained, while the
lubricating liquid dripped on the surface plate is spread
uniformly.
[0039] On the other hand, on the frame, the bridge 5 with high
stiffness is disposed in the form of spanning the polishing surface
plate 8, and the actuator 7 of a ball screw type is fixed on the
bridge 5. The ball screw is connected directly to a rotary motor,
and a slider table 15 is attached to the ball screw. As the motor
repeats forward rotation and reverse rotation, the slider table 15
can be linearly reciprocated on the bridge.
[0040] On the slider table 15, the two gonio-stages (cylindrical
seats) 4a and 4b are disposed in two upper and lower stages so that
the rotational axes of the gonio-stages are parallel to the
polishing surface of the surface plate and the angle formed between
the rotational axes is 90 degrees. The gonio-stages each have the
function of varying the rotational orientation in the range of
about .+-.15 degrees, so that the normal orientation of the
workpiece surface to be polished of the workpiece 1 can be adjusted
to all directions on a three-dimensional basis, and the normal axis
matching (an operation for achieving parallelism) between the
workpiece surface to be polished of the workpiece 1 and the
polishing surface of the surface plate. After the adjustment, a
relative orientation of the workpiece set arbitrarily relative to
the polishing surface of the surface plate can be fixed by a lock
device for the rotating mechanism of the gonio-stages 4a and 4b. In
the case where the orientation is set to be substantially parallel,
the substantially parallel condition can be fixed.
[0041] By arranging a direct-movement slide guide 10 vertically
relative to the surface plate, only an additional polishing load on
the workpiece 1 in a direction vertical to the polishing surface
can be transmitted, and variation of the position of the contact
surface between the workpiece 1 and the polishing surface plate 8
in a direction perpendicular to the surface of the surface plate
due to the rotation of the surface plate and the reciprocating
motion of the workpiece can be accommodated without any chattering
in other directions. Therefore, the workpiece surface to be
polished of the workpiece 1 and the surface of the polishing
surface plate can be maintained substantially parallel even during
swinging of the workpiece 1, and the substantially parallel
condition can be maintained even at the time of inversion of the
swing at which it is most difficult to maintain the parallel
relationship.
[0042] The lower surface (the surface facing the surface plate) of
the work holding jig 2 is brought into a mirror finished surface by
lapping, and the flatness is precisely machined to 1 .mu.m or less.
A pressure adhesive elastic body 13 which is a pressure adhesive
rubber-like elastic body having a thickness of about 2 mm is
adhered to this surface, and, further, a magnetic head slider bar
as the workpiece is adhered thereto. With such a rubber-like
elastic body interposed, even where there is an abnormality in
shape comprising a long-period undulation component in the
longitudinal direction of the bar, the deformation is accommodated
by an elastic deformation of the bar itself and a deformation of
the rubber. As a result, there is obtained the effect that the work
surface to be polished of the bar is brought into close and uniform
contact with the polishing surface of the surface plate.
[0043] The rubber-like elastic body may not necessarily be pressure
adhesive, and the workpiece 1 can be adhered or attached by other
methods; these embodiments are all within the scope of the present
invention. In addition, where the bar as the workpiece is free of
longitudinal undulation or the like, the rubber-like elastic body
may not necessarily be interposed.
[0044] In order to machine the slider bar as the workpiece by use
of the polishing apparatus constituted as described above, it is
important that the parallelism between the workpiece surface to be
polished of the workpiece and the polishing surface of the
polishing surface plate is precisely adjusted, that there is not
chattering, that the stiffness is infinitively high, and that the
parallelism between the workpiece surface and the polishing surface
plate 8 adjusted before machining is not deteriorated due to
polishing resistance generated during machining or the like.
[0045] As regards the precise adjustment of the parallelism,
particularly for the adjustment of parallelism in the longitudinal
direction of the work, a sheet-like pressure sensor (not shown) is
interposed before the finish polishing step, and, while measuring
the pressure distribution in the longitudinal direction on a
real-time basis, the angle adjustment controls of the gonio-stages
are turned to thereby contrive parallel contact between the
workpiece surface to be polished of the workpiece 1 and the
polishing surface of the surface plate. As regards the adjustment
in the crosswise direction of the workpiece, also, the adjustment
can be similarly conducted by use of the pressure sensor, and the
parallelism between the workpiece surface to be polished of the
workpiece 1 and the polishing surface of the polishing surface
plate 8 can be adjusted with high precision and on a real-time
basis by use of the two gonio-meters 4a and 4b. In addition, in
place of the adjustment of the relative angle between the workpiece
surface to be polished of the workpiece 1 and the polishing surface
of the surface plate, the relative angle between the lower surface
of the workpiece-holding jig and the polishing surface of the
polishing surface plate 8 may be adjusted by the method using the
pressure sensor.
[0046] On the other hand, as regards the stiffness, the dispersion
of machining depth volume or the recess is increased if the
stiffness is low in the direction of reciprocating motion and the
rotating direction of the surface plate. This is probably due to
that when the stiffness is low, the parallelism between the work
surface and the polishing surface plate is deteriorated due to the
polishing resistance generated during machining, so that the work
surface cannot be machined uniformly. The stiffness in X direction
and Y direction shown in the workpiece-holding jig 2 located at a
position nearest to the machining point is not less than 0.2
N/.mu.m.
[0047] The concrete contents about the polishing apparatus and the
polishing method explained above are indicated by the U.S.
application Ser. No. 10/024,962.
[0048] Now, specific examples will be described in detail
below.
EXAMPLE 1
[0049] Specific conditions and the like under which a
magnetoresistive effect head was produced as a trial by use of the
polishing apparatus shown in FIG. 1 will be shown below.
[0050] A disk-shaped plate formed of a comparatively soft metal
such as a tin alloy was used as the polishing surface plate 8. The
plate was formed with a high-precision plain surface by machining
on a machining apparatus for polishing or on a special different
machining device. In this instance, to promote the discharge of a
lubricating liquid during polishing or a sludge generated due to
removal of material, a fine groove having a width of 30 .mu.m and a
depth of 10 .mu.m were formed in the surface.
[0051] Next, while dripping a slurry liquid containing diamond
abrasive grains with a grain size of about 100 nm onto the
high-precision plain surface of the polishing surface plate 8 via a
slurry supply tube, a weight of about 10 kgf was placed on a
ceramic ring. Consequently, the flatness of the surface of the
surface plate was further enhanced, and fixed abrasive grains such
as the diamond abrasive grains were pressed into the surface of the
surface plate through plastic deformation of the metallic material
of the surface plate and were thereby held there.
[0052] Now, an air bearing surface of the magnetic head slider is
polished by use of the polishing apparatus as described above.
Before the specific description, the structure of the magnetic head
slider which plays an important role in achieving a lower flying
height will be briefly described.
[0053] FIG. 2 is a general diagram illustrating the relationship
between the magnetic head slider 20 and a magnetic recording disk
22 and a sectional structure in the vicinity of the magnetic head
element portion. The magnetic head element portion 21 is disposed
in the range of an effective leakage field from the magnetic
recording disk 22, whereby writing of information onto the magnetic
recording disk 22 and reading of information from the magnetic
recording disk 22 can be performed. The distance between the
magnetic head element portion 21 and the surface of the magnetic
recording disk 22 which enables the writing and reading of
information is referred to as the so-called magnetic spacing 24,
and it is possible to cope with a higher density magnetic recording
as the magnetic spacing 24 is smaller.
[0054] On the other hand, considering the magnetic head slider 20,
it is indispensable to precisely machine the air bearing surface 23
of the magnetic head slider 20. In this case, since the materials
constituting the slider 20 and the magnetic head element portion 21
are different from each other, a step is necessarily generated
between the polished surfaces of the two members. In FIG. 2, when
the magnetic recording disk 22 and the magnetic head element
portion 21 come close to each other, the physical spacing between
their surfaces is called the flying height 37; for higher density
recording, it is necessary to reduce the flying height 37 as much
as possible and thereby to reduce the magnetic spacing 24.
[0055] An enlarged view of the magnetic head element portion 21 is
shown in FIG. 3. In order to reduce the magnetic spacing 24, it is
important to reduce the interval 36 between an end portion 38 of a
magnetoresistive element (a magnetic head element) (magnetic
material) 32 constituting the magnetic head element portion (device
portion) 21 and a slider substrate (aluminum titanium carbide,
silicon carbide or the like) 34, i.e., the recess amount 36. In
addition, it is important to reduce the dispersion of the recess
amount 36 as much as possible when the high-density magnetic
recording disk drives are put into practical use.
[0056] At the same time, in order to operate the magnetic recording
disk drive stably, it is necessary for the magnetic head slider to
fly up from the surface of the magnetic recording disk while
constantly maintaining a stable posture. For the purpose of
achieving this, it is important to reduce as much as possible the
dispersion of flatness of the air bearing surface 23 of the
magnetic head slider 20.
[0057] Incidentally, in the case where a protective layer (for
example, a carbon layer) having a thickness of about several nm is
formed on the air bearing surface or the surface of the magnetic
head element, the recess amount between both of the members or the
flatness of the air bearing surface may be similarly considered on
the basis of the surface of the protective layer.
[0058] Moreover, 33 is an aluminium oxide insulating film and 35 is
a coil for writing.
[0059] Next, the air bearing surface which greatly influences the
magnetic characteristics will be described. FIG. 4 is a perspective
view of the magnetic head slider 20 as viewed from the side facing
the magnetic recording disk 22. As shown in FIG. 4, the air bearing
surface 23 is projected in shape with respect to the moving
direction (direction A; the direction in which an airflow is
generated) of the magnetic head slider 20 (clearly shown in the
figure), and the amount of bend is called "crown". The air bearing
surface 23 is projected in shape also in a direction orthogonal to
the moving direction, and the amount of bend is called
"camber".
[0060] FIG. 5 is a diagram for illustrating FIG. 4, in which FIG.
5A is a sectional view taken along line A-A' of FIG. 4, showing the
crown of the air bearing surface, and FIG. 5B is a sectional view
taken along line B-B' of FIG. 4, showing the camber of the air
bearing surface. Both the crown and the camber are parameters
necessary for stable flying-up of the magnetic head slider. As the
dispersion of surface flatness of the air bearing surface is
smaller, it is possible to provide a magnetic head slider having
higher reliability, i.e., higher quality capable of obtaining equal
characteristics.
[0061] Taking into account the various problems required for
formation of the air bearing surface of the magnetic head slider,
the air bearing surface of the magnetic head slider was machined by
use of the above-mentioned polishing apparatus, and the condition
of the thus machined air bearing surface was evaluated. One of the
characteristics evaluated was the flatness of the air bearing
surface, which was measured by HD3300, an optical shape measuring
apparatus produced by WYKO Inc. In this instance, the differential
between the measured value and the designed value was deemed as the
dispersion of flatness.
[0062] Height distribution in the range of about 50 .mu.m.sup.2
including an upper shield portion 30, a lower shield portion 31 and
a read head (a MR or GMR head) 32, and a slider substrate 34 of the
magnetic head was measured by use of Manoscope III, an atomic force
microscope (AFM) produced by Digital Instruments, and the recess
amount 36 was defined as the differential between the mean height
inclusive of the upper and lower shield portions 30, 31 and the
mean height of the slider substrate portion 34.
[0063] The product is machined with a certain dispersion, with
respect to a specification value of flatness and a specification
value of recess. Therefore, the width of dispersion differs
depending on the machining method, and a machining method leading
to a smaller dispersion width can be judged as a preferable
machining method from the viewpoint of a higher production
yield.
[0064] In FIG. 6, the relationship between the dispersion (standard
deviation) of the flatness of the air bearing surface of the
magnetic head element portion produced by the polishing apparatus
shown in FIG. 1 from the designed value and the number of the
magnetic head sliders that are measured is shown as Group (A). In
the figure, as a comparative example, the case of polishing the air
bearing surface by a computer lapping machine (for example, Robo 4,
a product by Advanced Imaging Inc.), which is a polishing method
conventionally used, is shown as Group (B).
[0065] Magnetic head sliders differing in production lot and having
a quality enough to be a product were extracted at random as
specimens to be used. Here, the magnetic head slider capable of
becoming a product means a magnetic head slider such that when the
magnetic head slider is combined with a magnetic recording disk to
constitute a magnetic recording disk drive, the magnetic recording
disk drive can normally operates at a level required for the social
needs at present and can sufficiently display the characteristics
thereof.
[0066] Therefore, the magnetic head sliders capable of becoming a
product include not only the magnetic head sliders manufactured by
the above-mentioned manufacturing method but also those magnetic
head sliders which have been shipped as products after being
selected from the magnetic head sliders manufactured. As is clear
from the results, by individually polishing the air bearing
surfaces of the magnetic head sliders by use of the polishing
apparatus shown in FIG. 1 (Group (A)), the standard deviation of
the flatness is substantially constant, independent of the
machining volume (the number of measurement sliders). In other
words, the results show that it is possible to provide magnetic
head sliders uniform in quality, extremely stably.
[0067] Incidentally, in the case of a computer lapping method (a
bar-like magnetic head slider in which 20 to 40 magnetic head
sliders are arranged in a row is used) according to the prior art,
the flatness of each of the elements (devices) is largely different
from the designed specification even when the magnetic head sliders
are polished under the same conditions, and the dispersion of
flatness of the air bearing surface increases as the number of
elements (devices) polished increases. This means that some
selection is necessarily required for supplying magnetic head
sliders uniform in quality.
[0068] Similarly, in FIG. 7, the relationship between the
dispersion (standard deviation) of the recess amount 36 in the air
bearing surface of the magnetic head element (device portion) from
the designed value and the number of measurement sliders is shown
as Group (A). In addition, Group (B) in the figure is a comparative
example, showing the case where the bar-like magnetic head slider
was machined by a computer lapping machine according to the prior
art. The specimens evaluated and the evaluation method are the same
as in the case of FIG. 6.
[0069] As is clear from the results shown in FIG. 7, in the range
where the number of pieces polished (the number of measurement
sliders) is small, the dispersion of recess amount of the air
bearing surface is substantially the same, irrespective of whether
the magnetic head sliders are machined individually or they are
machined simultaneously by arranging them in a bar form. However,
as the number of pieces polished increases, the dispersion of the
recess amount in the prior-art polishing method (Group (B))
increases conspicuously. It is clear that, according to the
polishing method shown in FIG. 1 (Group (A)), the increase in the
recess amount dispersion can be suppressed to a comparatively small
level.
[0070] FIG. 8 shows the relationship between the flatness
dispersion (standard deviation) and the recess dispersion (standard
deviation), evaluated by varying the number of measurement pieces.
It is clear from the diagram that, by individually polishing the
air bearing surfaces of the magnetic head sliders (see FIG. 1), the
conditions of the air bearing surfaces of the magnetic head sliders
obtained, i.e., the dispersions (standard deviations) of the
flatness and the recess amount of the air bearing surface required
for realization of high density recording can be controlled to
within the ranges of not more than 0.6 nm and not more than 0.8 nm,
respectively.
[0071] Meanwhile, it is seen that in the case of Group (B) shown in
FIG. 8, the dispersions (standard deviations) of both the flatness
and the recess amount of the air bearing surface are distributed
over wide ranges. In the case of using the magnetic head sliders
having these specifications as the magnetic head slider for
high-density recording, uniformization of the specifications by
some selection means is required.
[0072] FIG. 9 shows the measurements of flying-up characteristics
of the head, for the two groups mentioned above. The test method
used is such that in the condition where the magnetic head
belonging to each of the groups is incorporated in a hard disk
drive, the flying height 37 between the head and the disk is
reduced by a method of decompressing the inside of the hard disk
drive, and, while monitoring the output of the head during the
test, the lower flying height limit in each group, i.e., the
minimum flying height for obtaining normal magnetic characteristics
without contact between the air bearing surface of the magnetic
head slider and the magnetic recording disk is quantified.
[0073] Incidentally, the yield on the axis of ordinates is shown
through comparison with the case of a standard flying height of 13
nm for the magnetic recording disk drives at present, and a low
yield means that normal characteristics cannot be displayed due to
the contact between the head and the disk.
[0074] Consequently, as is clear from FIG. 9, it is seen that Group
(A) retains good characteristics as a magnetic head even at a
flying height of not more than 10 nm. It is also seen that Group
(B) cannot secure reliability as a magnetic head since the head
deteriorated in characteristics is exposed at a flying height of
not more than 10 nm. Therefore, the shape of the air bearing
surface obtained by the above-mentioned polishing method is
important in the same manner as the polishing method, and the
magnetic head group (Group (A)) constituted of the flatness
dispersion and the recess dispersion illustrated in FIGS. 6 to 8
can realize not only the flying height of 13 nm at present but also
a further lower flying height of the magnetic head.
[0075] Besides, in the case where the machined step of the air
bearing surface is small, the adhesion property of the protective
layer formed thereafter on the air bearing surface is enhanced, so
that the thickness of the protective layer can be further reduced,
and the magnetic spacing 24 affecting the important characteristics
of the magnetic recording disk drive can be reduced, in other
words, higher-density recording and reproduction can be achieved.
Incidentally, the magnetic head slider group belonging to Group (A)
showed an enhancement of 2 to 5% in resolution of the reading
element for the same flying height, as compared with Group (B).
EXAMPLE 2
[0076] From the results shown in FIGS. 6 and 7, the magnetic head
group determined by the flatness dispersion and the recess amount
dispersion in the shape of the air bearing surface of the magnetic
head can be judged whether they have been manufactured by the same
machining method or machining standard (machining specifications),
without acquiring several thousands of pieces of data. The judging
method will be described below.
[0077] Five magnetic head sliders per lot and a total of 20
magnetic head sliders were selected at random from the magnetic
head sliders which had been produced by the above-mentioned
polishing apparatus and method shown in FIG. 1, in different
production lots, and which had a quality good enough to be a
product, and the 20 magnetic head sliders are measured for the
shape of the air bearing surface. The results are shown in FIG.
10.
[0078] Here, the magnetic head slider good enough to be a product
means a magnetic head slider such that when it is combined with a
magnetic recording disk to constitute a magnetic recording disk
drive, the magnetic recording disk drive can normally operate at a
level required by the social needs at present and can sufficiently
display the characteristics thereof. Therefore, the magnetic head
sliders good enough to be a product include not only the magnetic
head sliders manufactured by the above-mentioned manufacturing
method but also the magnetic head sliders shipped as products after
being selected from the manufactured magnetic head sliders. In
addition, the definitions of the flatness and the recess amount of
the air bearing surface and the measuring method are the same as in
Example 1.
[0079] As is clear from FIG. 10, the magnetic head sliders polished
by the above-mentioned polishing apparatus constitute a magnetic
head slider group such that the standard deviation of the recess
X.sub.1 between the slider substrate and the magnetic head element
(device portion) disposed via the shield portion is 0.5 nm, and the
standard deviation of the dispersion X.sub.2 of the surface
flatness of the air bearing surface is 0.5 nm (hereinafter this
population will be referred to simply as Group (A.sub.1)).
[0080] As a polishing method generally used in the prior art as a
comparative example, air bearing surfaces were polished by use of
the above-mentioned computer lapping machine (for example, Robo 4,
a product by Advanced Imaging Inc.), and extraction of specimens
and measurement were conducted in the same manner as above. The
results are shown in FIG. 11. According to the results, the
magnetic head sliders thus obtained constitute a magnetic head
slider group such that the standard deviation of the recess amount
X.sub.3 between the slider substrate and the magnetic head element
(device portion) disposed via the shield portion is 0.64 nm, and
the standard deviation of the dispersion X.sub.4 of the surface
flatness of the air bearing surface is 1.42 nm (hereinafter, this
population will be referred to simply as Group (B.sub.1)).
[0081] In the case where the number of pieces constituting the
population is as small as 20 and Groups (A.sub.1) and (B.sub.1)
differ from each other in standard deviations of both the flatness
and the recess amount, it is statistically examined whether these
groups constitute the same population when the number of pieces is
increased. Specifically, by use of Wilks'.LAMBDA. with the two
populations as objects, a test of the hypothesis H that "there is
no statistical significance between the populations of Group
(A.sub.1) and Group (B.sub.1)" is conducted.
[0082] Based on the measurement results shown in FIGS. 10 and 11,
the following test is conducted. That is to say, for the population
(Group (A.sub.1)) with a number of samples of 20 such that the
total .SIGMA.X.sub.1 of the recess amounts X.sub.1 is 30.5 nm, the
total .SIGMA.X.sub.1.sup.2 of squares of the recess amounts X.sub.1
is 51 nm.sup.2, the total .SIGMA.X.sub.2 of the dispersions X.sub.2
of surface flatness of the air bearing surface is -1 nm, the total
.SIGMA.X.sub.2.sup.2 of squares of the dispersions X.sub.2 is 4.8
nm.sup.2, and the total .SIGMA.X.sub.1X.sub.2 of the products of
the recess amount X.sub.1 and the dispersion X.sub.2 of the surface
flatness of the air bearing surface is -0.95 nM.sup.2 and the
population (Group (B.sub.1)) with a number of samples of 20 such
that the total .SIGMA.X.sub.3 of the recess amounts X.sub.3 is 55.1
nm, the total .SIGMA.X.sub.3.sup.2 of squares of the recess amounts
X.sub.3 is 159.4 nm.sup.2, the total .SIGMA.X.sub.4 of the
dispersions X.sub.4 of the surface flatness of the air bearing
surface is 2.1 nm, the total .SIGMA.X.sub.4.sup.2 of squares of the
dispersions X.sub.4 is 38.6 nm.sup.2, and the total
.SIGMA.X.sub.3X.sub.4 of the products of the recess X.sub.3 and the
dispersion X.sub.4 of the surface flatness is 5.15 nm.sup.2, the
Wilks'.LAMBDA. is determined, and F-test is conducted with a level
of significance of 5%.
[0083] The Wilks'.LAMBDA. can be determined as follows. That is,
the Wilks'.LAMBDA. can be determined as:
.LAMBDA.=.vertline.W.vertline./.vertline.T.vertline.
[0084] constituted of the determinant .vertline.W.vertline. of a
within groups matrix of sums of squares and cross-products, W,
obtained by the total, the sum of squares sum and the sum of
products of each term:
.vertline.W.vertline.=(W.sub.11.times.W.sub.22-W.sub.12 .sup.2)
[0085] and the determinant .vertline.T.vertline. of a total matrix
of sums of squares and cross-products, T:
.vertline.T.vertline.=(T.sub.11.times.T.sub.22-T.sub.12.sup.2).
[0086] Thus, in the case of the above-mentioned magnetic head
sliders,
.LAMBDA.=.vertline.W.vertline./.vertline.T.vertline.=0.453.
[0087] In addition, the test statistic F.sub..LAMBDA. corresponding
to the .LAMBDA. statistic is represented by the following
formula:
F.sub..LAMBDA.=((N1+N2-3)/2).times.((1-.LAMBDA.)/.LAMBDA.)=22.2.
[0088] When the level of significance 0.05 is determined, and this
is compared with the statistic
F.sub.0=F.sub.(2,N1+N2-3)(0.05),
[0089] F.sub..LAMBDA.=22.3.gtoreq.F.sub.(2,N1+N2-3)(0.05)=3.23,
and, therefore, the hypothesis H is rejected, and it can be judged
that there is a statistical significance between the two Groups
(A.sub.1) and (B.sub.1).
[0090] As has been described above, the group of the magnetic head
sliders, each having air bearing surface, such that the standard
deviation of the group for the recess amount is not more than 0.8
nm and the standard deviation of the group for the flatness
dispersion of the air bearing surfaces is not more than 0.6 nm, as
shown in FIG. 8, upon measurement of the recess amount and the
surface flatness of the air bearing surface of the magnetic head
sliders extracted arbitrarily, which are quantities capable of
being statistically processed, belong statistically to Group (A)
and can be judged as magnetic head sliders having substantially the
same air bearing surface shape as the magnetic head sliders
constituting Group (A), as verified above.
EXAMPLE 3
[0091] Next, another method of discriminating Group (A.sub.1) from
Group (B.sub.1) described in Example 2 will be described.
[0092] As regards the shapes of the air bearing surfaces of five
per lot and a total of 20 magnetic head sliders extracted at random
from the magnetic head sliders differing in production lots and
capable of becoming a product of each of Group (A.sub.1) and Group
(B.sub.1) obtained in Example 2, the flatness dispersion of the air
bearing surfaces is treated as the absolute value
.vertline.X.sub.2.vertline. thereof.
[0093] FIG. 12 shows the case of evaluation of the flatness
dispersion of the air bearing surfaces as the absolute value
.vertline.X.sub.2.vertline- . thereof for the data on Group
(A.sub.1), which is defined as Group (C). FIG. 13 shows the case of
evaluation of the flatness dispersion of the air bearing surfaces
as the absolute value .vertline.X.sub.4.vertline. thereof for the
data on Group (B.sub.1), which is defined as Group (D). In the same
manner as in Example 2, for Group (C) and (D), statistical
processing was conducted by use of numerical values shown in FIGS.
12 and 13.
[0094] As a result,
.LAMBDA.=.vertline.W.vertline./.vertline.T.vertline.=0- .382, and,
as compared with a statistic F.sub.0=F.sub.(2,N1+N2-3)(0.05) with a
level of significance of 0.05,
[0095] F.sub..LAMBDA.=29.9.gtoreq.F.sub.(2,N1+N2-3)(0.05)=3.23,
which leads to the resultant conclusion that there is a significant
difference between Group (C) and Group (D).
[0096] As has been described above, the group of the magnetic head
sliders, each having the air bearing surface, such that the
standard deviation of the recess amount is not more than 0.8 nm and
a standard deviation of the flatness dispersion of the air bearing
surface is not more than 0.6 nm, upon measurement of the recess
amount and the surface flatness of the air bearing surface of
magnetic head sliders selected arbitrarily, which are quantities
capable of being statistically processed, belong statistically to
Group (C) and can be judged as magnetic head sliders having
substantially the same air bearing surface shape as the magnetic
head sliders constituting Group (C).
[0097] As has been described above, by measuring the recess amount
and the surface flatness of the air bearing surface of magnetic
head sliders extracted arbitrarily, which are quantities capable of
being statistically processed, and controlling the dispersion of
the recess amount and the dispersion of the surface flatness of the
air bearing surface, it is possible to efficiently manufacture
magnetic head sliders capable of coping with a lowering of the
flying height.
[0098] While we have shown and described several embodiments in
accordance with our invention, it should be understood that
disclosed embodiments are susceptible to changes and modifications
without departing from the scope of the invention. Therefore, we do
not intend to be bound by the details shown and described herein
but intend to cover all such changes and modifications as fall
within the ambit of the appended claims.
* * * * *