U.S. patent application number 09/784141 was filed with the patent office on 2001-11-01 for magnetic thin film head, the fabrication method, and magnetic disk.
Invention is credited to Ishikake, Kenji, Kagawa, Masayasu, Kojima, Shuichi, Kondo, Akira, Oikawa, Gen, Saiki, Noriyuki, Saito, Harunobu, Shiina, Hiromi.
Application Number | 20010036043 09/784141 |
Document ID | / |
Family ID | 18615292 |
Filed Date | 2001-11-01 |
United States Patent
Application |
20010036043 |
Kind Code |
A1 |
Oikawa, Gen ; et
al. |
November 1, 2001 |
Magnetic thin film head, the fabrication method, and magnetic
disk
Abstract
In formation of an upper shield of a magnetic thin film head by
electroplating, a current density of electroplating is regulated
stepwise with time. Thus, in the upper shield formation, a film
composition and magnetic characteristic with respect to the
direction of film thickness can be controlled precisely, making it
possible to provide a magnetic thin film head featuring
significantly reduced noise-after-write and output fluctuation.
Inventors: |
Oikawa, Gen; (Odawara,
JP) ; Kojima, Shuichi; (Hiratsuka, JP) ;
Saito, Harunobu; (Chigasaki, JP) ; Saiki,
Noriyuki; (Odawara, JP) ; Kagawa, Masayasu;
(Hiratsuka, JP) ; Kondo, Akira; (Naka-gun Ooiso,
JP) ; Ishikake, Kenji; (Odawara, JP) ; Shiina,
Hiromi; (Taka-gun Jyou, JP) |
Correspondence
Address: |
Mattingly, Stanger & Malur, P.C.
104 East Hume Avenue
Alexandria
VA
22301
US
|
Family ID: |
18615292 |
Appl. No.: |
09/784141 |
Filed: |
February 16, 2001 |
Current U.S.
Class: |
360/317 ;
29/603.07; 360/319; G9B/5.078; G9B/5.081 |
Current CPC
Class: |
B82Y 25/00 20130101;
G11B 5/3103 20130101; G11B 5/3113 20130101; Y10T 29/49044 20150115;
G11B 2005/3996 20130101; G11B 5/3163 20130101; B82Y 10/00 20130101;
Y10T 29/49032 20150115; G11B 5/3967 20130101 |
Class at
Publication: |
360/317 ;
360/319; 29/603.07 |
International
Class: |
G11B 005/39 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 31, 2000 |
JP |
2000-101206 |
Claims
What is claimed is:
1. A magnetic thin film head comprising: a write head element; and
a read head element; wherein a ferromagnetic film having a soft
magnetic characteristic and a magnetic shield function is formed of
NiFe permalloy material by electroplating in the vicinity of a
sensor film arranged as said read head element, wherein Ni in
composition of a formed layer is 80.8 wt % to 82.0 wt %.
2. A magnetic thin film head according to claim 1, in which said Ni
is composed of an initially formed layer having a thickness of 1.0
.mu.m is 80.8 to 82.0 wt %, and of an upper layer on said initially
formed layer 1.0 .mu.m thick is 81.0 to 81.2 wt %.
3. A magnetic thin film head comprising: a write head element; and
a read head element; wherein a ferromagnetic film having a soft
magnetic characteristic and a magnetic shield function is formed of
NiFe permalloy material by electroplating in the vicinity of a
sensor film arranged as said read head element, wherein a
magnetostriction constant .lambda. representing a magnetic
characteristic of said ferromagnetic film is -2.0 to
-7.0.times.1.sup.-7 in an initially formed layer having a thickness
of 1.0 .mu.m, and wherein said magnetostriction constant .lambda.
is -3.0 to -4.0.times.10.sup.-7 in an upper layer on said initially
formed layer 1.0 .mu.m thick.
4. A magnetic thin film head comprising: a write head element; and
a read head element; wherein a ferromagnetic film having a soft
magnetic characteristic and a magnetic shield function is formed of
NiFe permalloy material by electroplating in the vicinity of a
sensor film arranged as said read head element, wherein a film
thickness exceeding 1.0 .mu.m in said ferromagnetic film formed of
NiFe permalloy material has an Ni content accuracy of .+-.0.1 wt %,
and wherein a film thickness of 1.0 .mu.m or less in said
ferromagnetic film formed of NiFe permalloy material has an Ni
content accuracy of .+-.0.3 wt %.
5. A method of fabricating a magnetic thin film comprising the step
of: (a) forming a write head element; (b) forming a read head
element; wherein a ferromagnetic film having a soft magnetic
characteristic and a magnetic shield function is formed of NiFe
permalloy material by electroplating in the vicinity of a sensor
film arranged as said read head element, wherein Ni in composition
of an initially formed layer having a thickness of 1.0 .mu.m is
80.8 to 82.0 wt %, and wherein Ni in composition of an upper layer
on said initially formed layer 1.0 .mu.m thick is 81.0 to 81.2 wt
%, (c) timewise regulating a current density of permalloy
electroplating under control of a personal computer; wherein a
plurality of time periods and a plurality of current values are
preset for film formation.
6. A method of fabricating a magnetic thin film comprising the step
of: (a) forming a write head element; and (b) forming a read head
element; wherein a ferromagnetic film having a soft magnetic
characteristic and a magnetic shield function is formed of NiFe
permalloy material by electroplating in the vicinity of a sensor
film arranged as said read head element, wherein a magnetostriction
constant .lambda. representing a magnetic characteristic of said
ferromagnetic film is -2.0 to -7.0.times.10.sup.-7 in an initially
formed layer having a thickness of 1.0 .mu.m, and wherein said
magnetostriction constant .lambda. is -3.0 to -4.0.times.10.sup.-7
in an upper layer on said initially formed layer 1.0 .mu.m thick,
(c) timewise regulating a current density of permalloy
electroplating under control of a personal computer; wherein a
plurality of time periods and a plurality of current values are
preset for film formation.
7. A method of fabricating a magnetic thin film comprising the step
of: (a) forming a write head element; and (b) forming a read head
element; wherein a ferromagnetic film having a soft magnetic
characteristic and a magnetic shield function is formed of NiFe
permalloy material by electroplating in the vicinity of a sensor
film arranged as said read head element, wherein a film thickness
exceeding 1.0 .mu.m in said ferromagnetic film formed of NiFe
permalloy material has an Ni content accuracy of .+-.0.1 wt %, and
wherein a film thickness of 1.0 .mu.m or less in said ferromagnetic
film formed of NiFe permalloy material has an Ni content accuracy
of .+-.0.3 wt %, (c) timewise regulating a current density of
permalloy electroplating under control of a personal computer;
wherein a plurality of time periods and a plurality of current
values are preset for film formation.
8. A magnetic disk apparatus having a magnetic thin film head
comprising: a write head element; and a read head element; wherein
a ferromagnetic film having a soft magnetic characteristic and a
magnetic shield function is formed of NiFe permalloy material by
electroplating in the vicinity of a sensor film arranged as said
read head element, wherein Ni in composition of an initially formed
layer having a thickness of 1.0 .mu.m is 80.8 to 82.0 wt %, and
wherein Ni in composition of an upper layer on said initially
formed layer 1.0 .mu.m thick is 81.0 to 81.2 wt %.
9. A magnetic disk apparatus having a magnetic thin film head
comprising: a write head element; and a read head element; wherein
a ferromagnetic film having a soft magnetic characteristic and a
magnetic shield function is formed of NiFe permalloy material by
electroplating in the vicinity of a sensor film arranged as said
read head element, wherein a magnetostriction constant .lambda.
representing a magnetic characteristic of said ferromagnetic film
is -2.0 to -7.0.times.10.sup.-7 in an initially formed layer having
a thickness of 1.0 .mu.m, and wherein said magnetostriction
constant .lambda. is -3.0 to -4.0.times.10.sup.-7 in an upper layer
on said initially formed layer 1.0 .mu.m thick.
10. A magnetic disk apparatus having a magnetic thin film head
comprising: A magnetic thin film head comprising: a write head
element; and a read head element; wherein a ferromagnetic film
having a soft magnetic characteristic and a magnetic shield
function is formed of NiFe permalloy material by electroplating in
the vicinity of a sensor film arranged as said read head element,
wherein a film thickness exceeding 1.0 .mu.m in said ferromagnetic
film formed of NiFe permalloy material has an Ni content accuracy
of .+-.0.1 wt %, and wherein a film thickness of 1.0 .mu.m or less
in said ferromagnetic film formed of NiFe permalloy material has an
Ni content accuracy of .+-.0.3 wt %.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a plating film fabrication
method, and more particularly to a magnetic thin film head
fabrication method. Still more particularly, the invention relates
to a magnetic thin film head fabrication method using an
electroplating technique in which the composition of an initially
formed layer in an upper shield of a magnetic thin film head is
precisely controlled. Furthermore, the invention pertains to a
magnetic thin film head manufactured by the magnetic thin film head
fabrication method, and to a magnetic disk apparatus comprising the
magnetic thin film head thus manufactured.
[0003] The invention is also applicable as a plating film
fabrication method other than the magnetic thin film head
fabrication method mentioned above, and it is possible to
manufacture electronic circuit substrates using the plating film
fabrication method according to the invention.
[0004] 2. Description of the Related Art
[0005] Recently, there has been an ever increasing demand for
higher density of recording and higher-rate signaling of data in
magnetic disk apparatus. As a magnetic thin film head for use in a
magnetic disk apparatus, an integrated head comprising an MR or GMR
read head element and an inductive write head element has been
developed.
[0006] In the magnetic thin film head, it is required to increase
BPI (bits per inch) and TPI (tracks per inch) for realizing higher
recording density. As the BPI and TPI increase, a read output tends
to decrease. With a decrease in the read output, noise-after-write
and output fluctuation have a significantly adverse effect thereon
to cause a read error.
[0007] For realizing higher-rate communication, a write frequency
has been shifted to a higher level, causing a tendency to increase
noise-after-write.
[0008] The term "noise-after-write" used herein signifies a
phenomenon in which noise is produced on a read output at the time
of reading data recorded on a magnetic disk.
[0009] As demonstrated in FIG. 2, evaluation of noise-after-write
can be performed in the following manner: A write current having a
predetermined frequency is applied for a period of several tens of
microseconds, and then after the write current is turned off, noise
outputs exceeding a predetermined slice level are counted through a
read head output terminal for a period of several tens of
microseconds. In the evaluation of noise-after-write exemplified in
FIG. 2, a write-read operation was repeated 10,000 times per
magnetic thin film head slider, and a magnetic thin film head was
judged to be defective if the number of noise outputs was larger
than a predetermined value.
[0010] The term "output fluctuation" used herein signifies a
phenomenon in which a read output amplitude decreases or increases
at the time of reading data recorded on a magnetic disk. Since this
phenomenon is accelerated by addition of a write operation, output
fluctuation dVpp is expressed as shown in FIG. 3:
dVpp=.vertline.Vpp(MAX)-Vpp(min).vertline./Vpp(Ave).times.100
(%)
[0011] In the evaluation of output fluctuation exemplified in FIG.
3, a write-read operation was repeated 10,000 times per magnetic
thin film head slider, and a magnetic thin film head was judged to
be defective if the output fluctuation dVpp was higher than a
predetermined percentage (%).
[0012] Conventionally, for effective reduction of noise-after-write
and output fluctuation in the magnetic thin film head, shield film
formation on the upper and lower sides of a sensor film serving as
a read element is made in such a fashion that a film thickness of
an upper shield and a magnetostriction constant .lambda.
representing a magnetic characteristic thereof are controlled. FIG.
4 shows relationships among shield film thickness,
noise-after-write, and output fluctuation. As the shield film
thickness increases, both the noise-after-write and output
fluctuation tend to decrease. The noise-after-write is minimized at
a level of 4.5 .mu.m in shield film thickness, and the output
fluctuation is minimized at a level of 3.0 .mu.m in shield film
thickness. In the range of more than 3.5 .mu.m in shield film
thickness, however, read-track and write-track positioning
accuracies are decreased on inner and outer tracks of a magnetic
disk. Therefore, in consideration of the allowable ranges of
noise-after-write and output fluctuation, it is required to provide
a shield film thickness of 2.7 to 3.5 .mu.m.
[0013] In FIG. 5, there are shown relationships among
magnetostriction constant .lambda., noise-after-write, and output
fluctuation. The noise-after-write is minimized in the vicinity of
"magnetostriction constant .lambda.=-3.5.times.10.sup.-7 ", and
appreciably increases in the range of "magnetostriction constant
.lambda..gtoreq.0.times.10.sup.-7 ". The output fluctuation is
minimized in the vicinity of "magnetostriction constant
.lambda.=-2.0.times.10.sup.-7". NiFe permalloy used as a shield
material has a magnetostriction constant which shifts to the range
of +1.0 to +2.0.times.10.sup.-7 in heat treatment taken as a
post-process step. Therefore, in consideration of a shift of the
magnetostriction constant due to the heat treatment along with the
allowable ranges of noise-after-write and output fluctuation, it is
required to provide a magnetostriction constant .lambda. of -2.0 to
-4.0.times.10.sup.-7. Under this condition, "Ni=80.8 to 81.2 wt %"
is given in terms of relationship between magnetostriction constant
.lambda. and film composition shown in FIG. 6. However, on a
plating under-layer film, an initially formed layer of an upper
shield film is liable to be Fe-rich, i.e., it has been found that
Ni is 78.9 wt % and .lambda. is +4.8.times.10.sup.-7 in an
initially formed layer of 0.2 .mu.m in thickness in a case where Ni
is 81.1 wt % and .lambda. is -3.5.times.10.sup.-7 in an upper
shield film of 3.5 .mu.m in thickness.
[0014] In view of the above, it is apparent that the
noise-after-write and output fluctuation largely depend on the
composition and magnetostriction constant of the initially formed
layer of the upper shield film disposed in the vicinity of the
sensor film. It is therefore required to improve the upper shield
film for achieving higher recording density and higher-rate
communication in magnetic disk apparatus.
SUMMARY OF THE INVENTION
[0015] For successful realization of higher recording density and
higher-rate communication in magnetic disk apparatus, there is a
necessity to use a magnetic thin film head capable of substantially
reducing noise-after-write and output fluctuation.
[0016] As an upper shield film, a permalloy film having a
magnetostriction constant .lambda. of -2.0 to -4.0.times.10.sup.-7
and an Ni content of 80.8 to 81.2 wt % after plating could be
provided for reducing the noise-after-write and output fluctuation.
However, since the upper shield film tends to be Fe-rich in an
initially formed plating layer, this film formation is
unsatisfactory for substantially reducing the noise-after-write and
output fluctuation in a magnetic disk apparatus scheme for
higher-density higher-frequency recording.
[0017] It is therefore an object of the present invention to
provide a magnetic thin film head which can overcome the
above-mentioned disadvantage.
[0018] Another object of the present invention is to provide a
high-performance magnetic disk apparatus comprising the
above-stated magnetic thin film head.
[0019] In accomplishing these objects of the present invention,
there is provided a magnetic thin film head which is fabricated in
the following manner: In fabrication of the magnetic thin film
head, an upper shield film is formed by electroplating with NiFe
permalloy material so that the composition of an initially formed
layer thereof is equivalent to that of an upper layer or Ni-rich in
comparison therewith or so that the magnetostriction constant of
the initially formed layer is equivalent to or smaller than that of
the upper layer. In this film formation, a current value of
electroplating is regulated in the same plating bath.
[0020] In carrying out the present invention and according to a
first aspect thereof, there is provided a magnetic thin film head
comprising: a write head element; and a read head element; wherein
a ferromagnetic film having a soft magnetic characteristic and a
magnetic shield function is formed of NiFe permalloy material by
electroplating in the vicinity of a sensor film arranged as the
read head element, wherein Ni in composition of an initially formed
layer having a thickness of 1.0 .mu.m is 80.8 to 82.0 wt %, and
wherein Ni in composition of an upper layer on the initially formed
layer 1.0 .mu.m thick is 81.0 to 81.2 wt %.
[0021] Further, according to a second aspect of the present
invention, there is provided a magnetic thin film head comprising:
a write head element; and a read head element; wherein a
ferromagnetic film having a soft magnetic characteristic and a
magnetic shield function is formed of NiFe permalloy material by
electroplating in the vicinity of a sensor film arranged as the
read head element, wherein a magnetostriction constant .lambda.
representing a magnetic characteristic of the ferromagnetic film is
-2.0 to -7.0.times.10.sup.-7 in an initially formed layer having a
thickness of 1.0 .mu.m, and wherein the magnetostriction constant
.lambda. is -3.0 to -4.0.times.10.sup.-7 in an upper layer on the
initially formed layer 1.0 .mu.m thick.
[0022] Still further, according to a third aspect of the present
invention, there is provided a magnetic thin film head comprising:
a write head element; and a read head element; wherein a
ferromagnetic film having a soft magnetic characteristic and a
magnetic shield function is formed of NiFe permalloy material by
electroplating in the vicinity of a sensor film arranged as the
read head element, wherein a film thickness exceeding 1.0 .mu.m in
the ferromagnetic film formed of NiFe permalloy material has an Ni
content accuracy of .+-.0.1 wt %, and wherein a film thickness of
1.0 .mu.m or less in the ferromagnetic film formed of NiFe
permalloy material has an Ni content accuracy of .+-.0.3 wt %.
[0023] Furthermore, according a fourth aspect of the present
invention, there is provided a method of fabricating a magnetic
thin film head as in any of the above-mentioned first to third
aspects of the present invention, comprising the step of: timewise
regulating a current density of permalloy electroplating under
control of a personal computer; wherein a plurality of time periods
and a plurality of current values are preset for film
formation.
[0024] Still further, according to a fifth aspect of the present
invention, there is provided a magnetic disk apparatus comprising a
magnetic thin film head as in any of the above-mentioned first to
third aspects of the present invention.
[0025] The above and other objects, features and advantages of the
present invention will become more apparent from the following
detailed description with reference to the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a diagram showing a region of Ni in film
composition and a region of magnetostriction constant .lambda. with
respect to film thickness according to the present invention;
[0027] FIG. 2 shows diagrams indicating noise-after-write;
[0028] FIG. 3 is a diagram showing output fluctuation;
[0029] FIG. 4 shows diagrams indicating noise-after-write and
output fluctuation with respect to film thickness;
[0030] FIG. 5 shows diagrams indicating noise-after-write and
output fluctuation with respect to magnetostriction constant
.lambda.;
[0031] FIG. 6 is a diagram showing a relationship between Ni in
film composition and magnetostriction constant .lambda.;
[0032] FIG. 7 is a diagram showing a relationship between plating
current density and Ni in film composition;
[0033] FIG. 8 shows diagrams indicating Ni in film composition and
magnetostriction constant .lambda. with respect to film thickness
in comparison between products according to the present invention
and conventional products;
[0034] FIG. 9 is a diagram showing a cumulative frequency of
occurrences of noise-after-write in comparison between products
according to the present invention and conventional products;
[0035] FIG. 10 is a diagram showing a cumulative frequency of
output fluctuation in comparison between products according to the
present invention and conventional products;
[0036] FIG. 11 is a diagram showing a plating current sequence
according to the present invention;
[0037] FIG. 12 is a diagram illustrating an upper write pole formed
by electroplating;
[0038] FIG. 13 is a sectional view showing the tip end of a
magnetic thin film head; and
[0039] FIG. 14 is a schematic diagram showing a magnetic disk
apparatus comprising a magnetic thin film head according to the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0040] The present invention concerning a magnetic thin film head
and a method of fabricating the same will now be described in
detail by way of example with reference to the accompanying
drawings. In the following embodiments of the present invention, a
glass substrate having a diameter of five inches was used, and as a
plating conductive under-layer film, an NiFe permalloy film having
a thickness of 0.15 .mu.m and a magnetostriction constant .lambda.
of -3 to -4.times.10.sup.-7 was formed by sputtering technique.
[0041] For electroplating, a bath temperature of 30.degree. C. and
a pH value of 3.6 were provided. In bath composition, an Fe.sup.+2
metal ion concentration was 0.5 to 1.5 g/l, and an Ni.sup.+2 metal
ion concentration was 10 to 30 g/l. Sodium benzosulfimide, boric
acid, and sodium chloride had concentrations of 1.0 to 2.0 g/l, 20
to 30 g/l, and 20 to 30 g/l, respectively.
[0042] As plating power supply, a constant-current source was used,
and for setting time periods and current values of plating, a
personal computer was employed. Thus, it was allowed to set up an
arbitrary impressed current sequence in increments of one second
and one mA.
[0043] For film composition measurement, a fluorescent X-ray
analyzer was used, and for magnetostriction constant measurement, a
thin film B-H tracer was used. With respect to variation in an
anisotropic magnetic field Hk of a film at the time of stress
application, calculation was performed using the following Equation
(1):
Hk=Hk0.+-.3.lambda..sigma.(1+.nu.)/Is (A/m) (1)
[0044] where "Hk0" is an anisotropic magnetic field of each film
under no stress (A/m), ".lambda." is a magnetostriction constant,
".nu." is a Poisson ratio of each film (taken as 0.32), ".sigma."
is a stress (Pa), and "Is" is a saturation flux density (taken as
1T).
[0045] The direction of an applied magnetic field was matched with
that of a stress, and a three-point bending method was used for
stress application. While varying the stress .sigma., the
anisotropic magnetic field Hk was measured. Based on a rate of
change in the anisotropic magnetic field Hk, the magnetostriction
constant .lambda. was determined.
[0046] A plating current value per unit area represents a plating
current density (or referred to simply as a current density), and
according to the current density, a plating film having such a film
composition (Ni content) as shown in FIG. 7 is formed in a plating
bath under the above-mentioned conditions.
[0047] Based on the film composition indicated in FIG. 7, the
magnetostriction constant .lambda. representing a magnetic
characteristic of the plating film can be attained as shown in FIG.
6. Note that since each film indicated in FIGS. 6 and 7 was formed
to have a thickness of 3.5 .mu.m by applying a constant current for
initial and upper layers, the values in these figures include
variations in the film composition and magnetostriction constant
.lambda. of the initial layer.
[0048] Since the thickness of a plating film depends on the amount
of electrolysis, it is proportional to a plating time with respect
to a constant current. In a situation where a plating film having a
magnetostriction constant .lambda. of -3.5.times.10.sup.-7 and a
thickness of 3.5 .mu.m is formed as an upper shield film, an Ni
content of 81.1 wt % and a current density i of 4 mA/cm.sup.2 are
provided as shown in FIGS. 6 and 7. Further, since the area to be
plated is 112.5 cm.sup.2 according to the configuration of the
substrate, a current value I of 450 mA is provided.
[0049] In a conventional technique, a constant current I of 450 mA
is applied from the start of plating to the end thereof. Therefore,
as shown in FIG. 8, the Ni content decreases significantly in the
film thickness range below 1.0 .mu.m. Where Ni is 81.1 wt % and
.lambda. is -3.5.times.10.sup.-7 in a film of 3.5 .mu.m in
thickness, Ni is 78.9 wt % and .lambda. is +4.8.times.10.sup.-7 in
an initial layer of 0.2 .mu.m in thickness, resulting in a film
composition difference .DELTA. Ni of 2.2 wt % and a
magnetostriction constant shift .DELTA..lambda. of
8.3.times.10.sup.-7. Besides, magnetostriction becomes positive.
FIG. 8 presents the results of measurements of film compositions
and magnetostriction constants .lambda. using substrates plated in
respective film thicknesses.
[0050] In the exemplary embodiments of the present invention, a
current value I and a current applying time t at the start of
plating were set on the low current side as follows; I.sub.1=160 mA
(i=1.42 mA/cm.sup.2) and t.sub.1=120 sec. Then, the current value
was increased stepwise to the high current side as follows;
I.sub.2=240 mA (i=2.13 mA/cm.sup.2) and t.sub.2=30 sec, I.sub.3=360
mA (i=3.20 mA/cm.sup.2) and t.sub.3=30 sec, I.sub.4=420 mA (i=3.73
mA/cm.sup.2) and t.sub.4=150 sec, I.sub.5=440 mA (i=3.91
mA/cm.sup.2) and t.sub.5=180 sec, I.sub.6=445 mA (i=3.96
mA/cm.sup.2) and t.sub.6=1125 sec, and I.sub.7=450 mA (i=4.00
mA/cm.sup.2) and t.sub.7=1125 sec. FIG. 11 shows this current
sequence for plating. Using such a stepwise current sequence, it
was allowed to provide a film composition shown in FIG. 8. More
specifically, in an example where Ni was 81.1 wt % and .lambda. was
-3.5.times.10.sup.-7 in a film of 3.5 .mu.m in thickness, Ni was
80.9 wt % and .lambda. was -3.3.times.10.sup.-7 in an initial layer
of 0.2 .mu.m in thickness, i.e., it was enabled to form a film
having a film composition difference .DELTA. Ni of 0.2 wt % and a
magnetostriction constant shift .DELTA..lambda. of
1.2.times.10.sup.-7. Unlike the aforementioned conventional
technique in which a film is formed by applying the constant
current I of 450 mA, the film composition and magnetostriction
constant of the initial layer could be equivalent to those of the
upper layer in the embodiment of the present invention.
[0051] Moreover, by setting the plating current values I.sub.1 to
I.sub.4 further stepwise on the low current side, it was allowed to
provide an initial layer having an Ni-rich film composition as
shown in FIG. 8. In an example where Ni was 81.1 wt % and .lambda.
was -3.5.times.10.sup.-7 in a film of 3.5 .mu.m in thickness, Ni
was 82.0 wt % and .lambda. was -7.0.times.10.sup.-7 in an initial
layer of 0.2 .mu.m in thickness, i.e., it was enabled to form a
film having a film composition difference .DELTA. Ni of -0.9 wt %
and a magnetostriction constant shift .DELTA..lambda. of
-3.5.times.10.sup.-7. Using the above-demonstrated method, the
inventors formed a film A comprising an initial layer and an upper
layer in which a film composition difference and a magnetostriction
constant shift were reduced to provide equivalent film composition,
an Ni-rich film B, and an Fe-rich film C as an upper shield in
fabrication of a magnetic thin film head. Then, each of these films
A, B and C was subjected to evaluation in terms of
noise-after-write and output fluctuation. FIGS. 9 and 10 show the
results of this evaluation. In the evaluation, for each of 350
magnetic thin film head sliders, a write-read operation was
repeated 10,000 times at a write frequency of 60 to 180 MHz, and
the number of occurrences of noise-after-write and the percentage
of output fluctuation dVpp were measured to attain cumulative
frequencies. In comparison with the conventional technique, under
target requirements that the number of occurrences of
noise-after-write (=WN) should be 10 or less per slider and the
output fluctuation dVpp should be 10% or less, the WN was reduced
by approximately 20% and the dVpp was reduced by approximately 40%
in the film A, the WN was reduced by approximately 21% and the dVpp
was reduced by approximately 39% in the film B, and the WN was
reduced by approximately 18% and the dVpp was reduced by
approximately 38% in the film C. The films A, B and C, having an
equivalent level of magnetic head electrical characteristic, could
provide advantageous effects that noise-after-write was reduced by
approximately 20% and output fluctuation was reduced by
approximately 40% in comparison with conventional products.
[0052] TABLE 1 shows the judgment results of magnetic thin film
head evaluation on the conventional products and the films A, B and
C according to the present invention.
1 TABLE 1 Total Film Initial Layer Shield .lambda. .times. Ni
.lambda. .times. Ni Judgment Result No Species thickness 10 - 7 wt
% 10 - 7 wt % NAW*** OF**** Conv.*1 2.7 .mu.m thick 2.7 .mu.m -4
81.2 4.3 78.8 X X Conc.2 3.5 .mu.m thick 3.5 .mu.m -3.5 81.1 4.8
78.9 .DELTA. .DELTA. Inv.**A Same Comp. 3.0 .mu.m -3.5 81.1 -3.5
81.8 .largecircle. .largecircle. Inv.B Ni-rich 3.0 .mu.m -3.5 81.1
-7 82 .largecircle. .largecircle. Inv.C Fe-rich 3.0 .mu.m -3.5 81.1
-2 80.8 .largecircle. .largecircle. *Conventional Product **Present
Invention Product ***Noise-After-Write *****Output Fluctuation
[0053] Further, the inventors conducted prototype examinations
using the method of varying current values stepwise. Thus, it was
allowed to form a film having a film composition and
magnetostriction constant such as shown in FIGS. 1 and 2 with
respect to the direction of film thickness. Using the film thus
formed as an upper shield, a magnetic thin film head was fabricated
so as to significantly reduce noise-after-write and output
fluctuation.
[0054] Still further, using the current sequence for the film A
shown in FIG. 11, the inventors examined dependencies of
noise-after-write and output fluctuation on film composition and
magnetostriction constant characteristics. FIGS. 4 and 5 show the
results of the examinations made by the inventors. As contrasted
with the conventional products, in a shield film thickness of 2.5
.mu.m or more, noise-after-write and output fluctuation were
minimized and a degree of film thickness dependency was reduced. In
terms of magnetostriction constant, in the range of
-3.5.times.10.sup.-7 or less, noise-after-write and output
fluctuation were minimized and a degree of magnetostriction
constant dependency was reduced.
[0055] As another preferred embodiment for reducing variation in
film composition with respect to the direction of film thickness,
there is provided a plating method in which film plating is
performed while varying a stirring speed, bath temperature, bath
composition, pH or any other parameter with time. As a stirring
condition, a stirrer bar was reciprocated in a plating solution in
the vicinity of each substrate surface to be plated. More
specifically, while an stirring speed of 70 reciprocations/minute
was taken for an upper layer, a higher stirring speed of 100
reciprocations/minute was taken for an initial layer, resulting in
suppression of Fe richness in the initial layer. As a bath
temperature condition, a bath temperature of 38.degree. C. was set
at the start of plating, and then the bath temperature was
regulatingly decreased to 30.degree. C. in formation of initial and
upper layers using a heat cooling mechanism, resulting in the same
advantageous effect as mentioned above. As a pH condition, film
plating was started at a pH value of 2.5, and then in formation of
an upper layer, the pH value was increased to 3.0 by alkalimetry,
resulting in the same advantageous effect as mentioned above. As a
bath composition condition, from the start of plating, a
concentrated iron sulphate solution was titrated to vary a metal
ion concentration ratio (Ni.sup.2+/Fe.sup.2+), resulting in the
same advantageous effect as mentioned above.
[0056] Besides, an NiFe alloy having an Ni content of 44 to 48 wt
%, which provides a high saturation flux density, may be used as an
upper shield material. In electroplating with this material, a film
composition difference .DELTA. Ni between the initial and upper
layers can be reduced by properly varying current values
stepwise.
[0057] With reference to FIGS. 12 and 13, another embodiment of the
present invention will then be described below. FIG. 12 is a
sectional view showing an upper write pole 4 formed by
electroplating, which corresponds to the end part of a magnetic
core 10 indicated in FIG. 13. The upper write pole 4 is made of
permalloy or NiFe alloy material having an Ni content of 44 to 48
wt %, which provides a high saturation flux density. In this
example, a film composition difference .DELTA. Ni of 3.0 wt %
between the initial and upper layers was reduced to 0.5 wt %. For
composition measurement, a cross section of the upper write pole 4
was examined by EDX (Energy Dispersive X-ray analysis)method. The
upper write pole 4 can be formed in the following manner: First, on
a substrate 1, a plating conductive under-layer film 2 is formed by
sputtering technique, and then a resist frame 3 is formed into the
shape of the magnetic core 10 including the upper write pole 4.
Thereafter, film plating is performed so that the upper write pole
4 is formed in a space having an inter-frame distance of 0.5 to 1.0
.mu.m and a frame height of 5 to 10 .mu.m. Thus, the upper write
pole 4 is formed as an extremely narrow part having an aspect ratio
of 10 to 20. Since there is a significant difference in area
between the upper write pole 4 and the adjacent plating pattern
part, a difference in current density tends to occur. Further,
depending on bath stirring conditions, a difference in bath
composition tends to occur. These are the causes of composition
variation in the direction of film thickness.
[0058] Using the magnetic thin film head of the present invention,
the inventors manufactured a magnetic disk apparatus. FIG. 14 shows
a structural scheme of the magnetic disk apparatus thus
manufactured.
[0059] While the present invention has been described in detail
with respect to the preferred embodiments concerning fabrication of
a magnetic thin film head, it is to be understood that the plating
film fabrication method described herein is also applicable to
fabrication of electronic circuit substrates.
[0060] As set forth hereinabove and according to the present
invention, in fabrication of a magnetic thin film head comprising a
write head element and a read head element for use in a magnetic
recording apparatus, an upper shield film is formed in such a
fashion that the composition of an initial layer in plating is
precisely controlled by varying plating current density stepwise.
Thus, it is possible to fabricate a magnetic thin film head
featuring significantly reduced noise-after-write and output
fluctuation. Further, using the magnetic thin film head thus
fabricated, it is also possible to provide a magnetic disk
apparatus featuring higher recording density and higher-rate
communication.
[0061] The invention may be embodied in other specific forms
without departing from the spirit or essential characteristics
thereof. The present embodiments are therefore to be considered in
all respects as illustrative and not restrictive, the scope of the
invention being indicated by the appended claims rather than by the
foregoing description and all changes which come within the meaning
and range of equivalency of the claims are therefore intended to be
embraced therein.
* * * * *