U.S. patent application number 12/043057 was filed with the patent office on 2008-07-03 for magnetic sensor and manufacturing method therefor.
This patent application is currently assigned to YAMAHA CORPORATION. Invention is credited to Kokichi Aiso, Hideki Sato, Yukio Wakui.
Application Number | 20080160184 12/043057 |
Document ID | / |
Family ID | 32044699 |
Filed Date | 2008-07-03 |
United States Patent
Application |
20080160184 |
Kind Code |
A1 |
Sato; Hideki ; et
al. |
July 3, 2008 |
MAGNETIC SENSOR AND MANUFACTURING METHOD THEREFOR
Abstract
A magnetic sensor comprises magnetoresistive elements and
permanent magnet films, which are combined together to form GMR
elements formed on a quartz substrate having a square shape,
wherein the permanent magnet films are paired and connected to both
ends of the magnetoresistive elements, so that an X-axis magnetic
sensor and a Y-axis magnetic sensor are realized by adequately
arranging the GMR elements relative to the four sides of the quartz
substrate. Herein, the magnetization direction of the pinned layer
of the magnetoresistive element forms a prescribed angle of
45.degree. relative to the longitudinal direction of the
magnetoresistive element or relative to the magnetization direction
of the permanent magnet film. Thus, it is possible to reliably
suppress offset variations of bridge connections of the GMR
elements even when an intense magnetic field is applied; and it is
therefore possible to noticeably improve the resistant
characteristics to an intense magnetic field.
Inventors: |
Sato; Hideki; (Iwata-gun,
JP) ; Aiso; Kokichi; (Hamamatsu-shi, JP) ;
Wakui; Yukio; (Iwata-gun, JP) |
Correspondence
Address: |
DICKSTEIN SHAPIRO LLP
1177 AVENUE OF THE AMERICAS (6TH AVENUE)
NEW YORK
NY
10036-2714
US
|
Assignee: |
YAMAHA CORPORATION
Hamamatsu-Shi
JP
|
Family ID: |
32044699 |
Appl. No.: |
12/043057 |
Filed: |
March 5, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11497352 |
Aug 2, 2006 |
7360302 |
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12043057 |
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10686261 |
Oct 16, 2003 |
7170724 |
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11497352 |
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Current U.S.
Class: |
427/130 |
Current CPC
Class: |
Y10T 29/49034 20150115;
H01F 10/3268 20130101; H01F 10/3295 20130101; B82Y 25/00 20130101;
G01R 33/09 20130101; Y10T 29/49067 20150115; B82Y 40/00 20130101;
G01R 33/093 20130101; Y10T 29/49052 20150115; H01F 41/304 20130101;
Y10T 29/49043 20150115; G01R 33/0005 20130101; Y10T 29/49044
20150115 |
Class at
Publication: |
427/130 |
International
Class: |
B05D 5/12 20060101
B05D005/12; H01F 1/00 20060101 H01F001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 18, 2002 |
JP |
2002-304392 |
Mar 11, 2003 |
JP |
2003-065200 |
Claims
1. A manufacturing method of a magnetic sensor, comprising the
steps of: forming a plurality of permanent magnet films on a
substrate; forming a plurality of spin valve films each composed of
a pinning layer, a pinned layer, and a free layer; subjecting the
pinning layer to an ordering heat treatment; patterning the
plurality of spin valve layers to form a plurality of
magnetoresistive elements, which are arranged in such a way that
the plurality of permanent magnet films are paired and are
respectively connected to both ends of the magnetoresistive
elements; and magnetizing the plurality of permanent magnet films,
wherein the ordering heat treatment is performed by arranging the
substrate in such a way that a magnetization direction therefor
substantially matches a diagonal line of a cell of the substrate,
which is then heated, and wherein the plurality of permanent magnet
films are magnetized by arranging the substrate on a magnet array
in which a plurality of permanent magnets are arranged such that
adjoining permanent magnets differ from each other in polarity.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to magnetic sensors using
magnetoresistive elements such as giant magnetoresistive (GMR)
elements. This invention also relates to manufacturing methods for
manufacturing magnetic sensors.
[0003] This application claims priority on Japanese Patent
Application No. 2002-304392 and Japanese Patent Application No.
2003-65200, the contents of which are incorporated herein by
reference.
[0004] 2. Description of the Related Art
[0005] Conventionally, various types of magnetic sensors using
magnetoresistive elements such as giant magnetoresistive (GMR)
elements have been developed and reduced to practice.
[0006] A typical example of a GMR element comprises a pinned layer
in which magnetization is pinned in a prescribed direction, and a
free layer whose magnetization direction varies in response to an
external magnetic field. That is, when an external magnetic field
is applied, the GMR element presents resistance in response to a
relative relationship in magnetization direction between the pinned
layer and free layer; therefore, it is possible to detect the
external magnetic field by measuring the resistance of the GMR
element.
[0007] In order to detect minor external magnetic fields at a high
accuracy, it is necessary for the aforementioned magnetic sensor to
stably maintain the magnetization direction of each of the
magnetized sections of the free layer to match a prescribed
direction (hereinafter, referred to as an initialization direction)
under the condition where no external magnetic field is applied to
the magnetic sensor.
[0008] In general, a thin-film free layer is formed in a
rectangular shape in plan view, so that a long side (e.g., a long
axis or a longitudinal direction) of the rectangular shape is
directed to match the aforementioned initialization direction so as
to establish shape anisotropy in which the magnetization directions
are aligned to match the longitudinal direction. By using shape
anisotropy, the magnetization directions of the magnetized sections
of the free layer are aligned to match the initialization
direction. In order to stably restore and maintain the
magnetization directions of the magnetized sections of the free
layer in the initialization direction over a long term after an
external magnetic field disappears, bias magnet films corresponding
to permanent magnets are arranged at both ends of the free layer in
the longitudinal direction, so that a prescribed magnetic field of
the initialization direction is applied to the free layer by the
bias magnet films.
[0009] In magnetoresistance-effect elements (i.e., magnetoresistive
elements) of an AMR type, it is necessary to apply bias magnetic
fields in order to increase sensitivities. In order to uniformly
apply a bias magnetic field to four magnetoresistive elements, for
example, they are inclined relative to a substrate by a prescribed
angle of 45.degree.. An example of a magnetic sensor in which
magnetoresistive elements are inclined relative to a substrate is
disclosed in Japanese Patent Application Publication No. Hei
5-126577 (see paragraph [0016], and FIG. 5(a)).
[0010] When an external magnetic field, which is relatively large
and less than the coercive force of a bias magnet film and whose
magnetization direction is opposite to the initialization
direction, is applied to the conventionally-known magnetic sensor,
each of the magnetized sections of the free layer is changed in
magnetization direction; thereafter, when the external magnetic
field disappears, each of the magnetized sections of the free layer
cannot be restored and may not match the initialization direction.
This deteriorates the detection accuracy of the magnetic sensor for
sensing a magnetic field applied thereto.
[0011] It is very difficult to form two or more magnetoresistive
elements, in which the magnetization directions of the pinned
layers mutually cross each other, on a small substrate; therefore,
no single chip having such a configuration has been developed and
produced. That is, the conventionally-known magnetic sensor cannot
be reduced in size, and it is very difficult to broaden an
application range therefor due to a restriction regarding the
magnetization direction of the pinned layer.
[0012] To cope with the aforementioned situation, it is possible to
develop a two-axis magnetic sensor, using GMR elements, that can be
reduced in size and that can be broadened in the application range,
which is disclosed in Japanese Patent Application No.
2001-281703.
[0013] FIG. 26 is a plan view showing a two-axis magnetic sensor
using GMR elements, wherein a magnetic sensor 101 comprises a
quartz substrate 102 having a roughly square shape and a prescribed
thickness as well as X-axis GMR elements 111 to 114, and Y-axis GMR
elements 121 to 124. Herein, all of the X-axis GMR elements 111-114
are formed on the quartz substrate 102 and are combined together to
form an X-axis magnetic sensor for detecting magnetic fields in the
X-axis direction, and all the Y-axis GMR elements 121-124 are
formed on the quartz substrate 102 and are combined together to
form a Y-axis magnetic sensor for detecting magnetic fields in the
Y-axis direction perpendicular to the X-axis direction.
[0014] Two pairs of the X-axis GMR elements 111-112 and 113-114 are
respectively arranged in proximity to the midpoints on two sides of
the quartz substrate 102, which cross at a right angle to the
X-axis, in such a way that they are arranged in parallel with each
other. Similarly, two pairs of the Y-axis GMR elements 121-122 and
123-124 are respectively arranged in proximity to the midpoints on
two sides of the quartz substrate 102, which cross at a right angle
to the Y-axis, in such a way that they are arranged in parallel
with each other.
[0015] The X-axis GMR elements 111 to 114 and the Y-axis GMR
elements 121 to 124 differ from each other in their arrangements on
the quartz substrate 102 and in their magnetization directions
pinned in the pinned layers thereof. With the exception of these
points, they are formed in the same configuration.
[0016] Therefore, the X-axis GMR element 111 is taken as an example
whose configuration is to be described below.
[0017] As shown in FIGS. 27 and 28, the X-axis GMR element 111
comprises band-shaped spin valve films 131, which are arranged in
parallel with each other, and bias magnet films 132, each of which
corresponds to a thin film of a hard ferromagnetic substance,
composed of CoCrPt and the like, having a high coercive force and a
high squareness ratio.
[0018] The spin valve films 131 are respectively paired and
connected together via the bias magnet films 132 at both ends
thereof in such a way that one bias magnet film is arranged at one
end of the `paired` spin valve films, and the other bias magnetic
film is arranged at the other end of the `adjacent paired` spin
valve films. In short, the spin valve films 131 are connected
together via the bias magnet films 132 in a zigzag manner.
[0019] As shown in FIG. 29, the spin valve film 131 is formed in a
sequential lamination of various layers on the quartz substrate
102, namely: a free layer F; a conductive spacer layer S, composed
of Cu, having a film thickness of 2.4 nm (or 24 .ANG.); a pinned
layer PD composed of CoFe; a pinning layer PN composed of PtMn; and
a capping layer C made of a thin metal film composed of titanium
(Ti), tantalum (Ta), and the like.
[0020] The free layer F is changed in magnetization direction in
response to the direction of an external magnetic field applied
thereto, and it is formed by a CoZrNb amorphous magnetic layer 131a
having a film thickness of 8 nm (or 80 .ANG.), a NiFe magnetic
layer 131b having a film thickness of 3.3 nm (or 33 .ANG.) that is
laminated on the CoZrNb amorphous magnetic layer 131a, and a CoFe
layer 131c whose film thickness approximately ranges from 1 nm to 3
nm (or 10 .ANG. to 30 .ANG.) that is laminated on the NiFe magnetic
layer 131b.
[0021] In order to maintain single-axis anisotropy of the free
layer F, a bias magnetic field is applied to the free layer F by
the bias magnet film 132 in the Y-axis direction shown in FIG.
27.
[0022] The spacer layer S is a thin metal film composed of Cu or a
Cu alloy.
[0023] Both of the CoZrNb amorphous magnetic layer 131a and the
NiFe magnetic layer 131b are formed from soft ferromagnetic
substances. In addition, the CoFe layer 131c blocks Ni diffusion of
the NiFe magnetic layer 131b and Cu diffusion of the spacer layer
S.
[0024] The pinned layer PD is formed by a CoFe magnetic layer 131d
having a film thickness of 2.2 nm (or 22 .ANG.). The CoFe magnetic
layer 131d is backed by an antiferromagnetic film 131e, which will
be described later, in a switched connection manner so that the
magnetization direction thereof is subjected to pinning (or
anchoring) in the negative direction of the X-axis.
[0025] The pinning layer PN is formed by the antiferromagnetic film
131e having a film thickness of 24 nm (or 240 .ANG.) laminated on
the CoFe magnetic layer 131d, wherein the antiferromagnetic film
131e is composed of a PtNm alloy including Pt at 45-55 mol %. When
a magnetic field is applied in the negative direction of the
X-axis, the antiferromagnetic film 131e is changed to an ordered
lattice.
[0026] Hereinafter, the combination of the pinned layer PD and the
pinning layer PN will be generally called a pin layer.
[0027] All of the other X-axis GMR elements 112-114 and the Y-axis
GMR elements 121-124 have the same configuration as the X-axis GMR
element 111 described above; hence, the detailed descriptions
thereof will be omitted.
[0028] Next, a description will be given with respect to the
magnetic properties (or magnetic characteristics) of the X-axis GMR
elements 111-114 and the Y-axis GMR elements 121-124.
[0029] FIG. 30 shows a graph regarding variations of resistance
relative to the magnitude of an external magnetic field applied to
the X-axis GMR element 111. Herein, `solid` curves represent
hysteresis characteristics relative to variations of the external
magnetic field in the X-axis, in which the resistance varies
approximately proportional to the external magnetic field in a
prescribed range between -Hk and +Hk, but the resistance is
maintained substantially constant in both of the other ranges
outside of the prescribed range. In addition, `dotted` curves
represent characteristics relative to variations of the external
magnetic field in the Y-axis, in which the resistance is maintained
substantially constant.
[0030] In FIG. 26, magnetization directions of pinned layers
adapted to the X-axis GMR elements 111-114 and the Y-axis GMR
elements 121-124 are shown by arrows, which are directed opposite
to each other.
[0031] That is, both of the X-axis GMR elements 111 and 112 have
the same magnetization direction of the pinned layer that is pinned
by the pinning layer along the negative direction of the
X-axis.
[0032] Both of the X-axis GMR elements 113 and 114 have the same
magnetization direction of the pinned layer that is pinned by the
pinning layer along the positive direction of the X-axis.
[0033] In addition, both of the Y-axis GMR elements 121 and 122
have the same magnetization direction of the pinned layer that is
pinned by the pinning layer along the positive direction of the
Y-axis.
[0034] Both of the Y-axis GMR elements 123 and 124 have the same
magnetization direction of the pinned layer that is pinned by the
pinning layer along the negative direction of the Y-axis.
[0035] The aforementioned X-axis magnetic sensor is constituted by
arranging the X-axis GMR elements 111-114 in a full bridge
connection as shown in FIG. 31, wherein arrows accompanied with
blocks show magnetization directions of pinned layers pinned by
pinning layers. In the aforementioned constitution, a dc power
source is used to apply voltage Vxin+ (e.g., 5 V) at one terminal
and to apply voltage Vxin- (e.g., 0 V) at the other terminal,
whereby Vxout+ appears at a terminal H that is derived from the
connection between the X-axis GMR elements 111 and 113, and Vxout-
appears at a terminal L that is derived from the connection between
the X-axis GMR elements 112 and 114. Herein, it is possible to
extract a potential difference (or a voltage difference)
(Vxout+-Vxout-) as an output voltage Vxout.
[0036] In short, the X-axis magnetic sensor presents
characteristics relative to variations of an external magnetic
field in the X-axis, in which, as shown by the solid curves in FIG.
32, the output voltage Vxout thereof is changed substantially
proportional to the external magnetic field in a prescribed range
between -Hk and +Hk, and it is maintained substantially constant in
other ranges outside of the prescribed range.
[0037] In addition, the output voltage Vout is substantially
maintained at 0 V relative to variations of the external magnetic
field in the Y-axis, which is shown by the dotted curves in FIG.
32.
[0038] Similar to the aforementioned X-axis magnetic sensor, the
Y-axis magnetic sensor is constituted by arranging the Y-axis GMR
elements 121-124 in a full bridge connection as shown in FIG. 33.
In this constitution, a dc power source is used to apply voltage
Vyin+ (e.g., 5 V) at one terminal and to apply voltage Vyin- (e.g.,
0 V) at the other terminal, whereby Vyout+ appears at a terminal H
that is derived from the connection between the Y-axis GMR elements
122 and 124, and Vyout- appears at a terminal L that is derived
from the connection between the Y-axis GMR elements 121 and 123.
Herein, it is possible to extract a potential difference
(Vyout+-Vyout-) as an output voltage Vyout.
[0039] In short, the Y-axis magnetic sensor presents hysteresis
characteristics relative to variations of an external magnetic
field in the Y-axis, in which, as shown by dotted curves in FIG.
34, the output voltage Vyout thereof is changed substantially
proportional to the external magnetic field in a prescribed range
-Hk and +Hk, and it is maintained substantially constant in other
ranges outside of the prescribed range.
[0040] In addition, the output voltage Vyout is substantially
maintained at 0 V relative to variations of the external magnetic
field in the Y-axis, which is shown by the solid curves in FIG.
34.
[0041] Next, a description will be given regarding a manufacturing
method of the magnetic sensor 101.
[0042] As shown in FIG. 35, a plurality of island-like regions,
corresponding to films M which contribute to formation of
individual GMR elements, are formed on the surface of a quartz
glass 141 having a rectangular shape. When the quartz glass 141 is
subjected to a cutting process along break lines B and is thus
divided into individual quartz substrates 102, the films M are
arranged at prescribed positions to match the X-axis GMR elements
111-114 and the Y-axis GMR elements 121-124. In addition, alignment
marks (i.e., positioning marks) 142 are formed on four corners of
the quartz glass 141, wherein each of them is formed in a roughly
rectangular shape from which a cross-shaped region is removed.
[0043] Next, there are provided a plurality of rectangular metal
plates 144, each of which, as shown in FIGS. 36 and 37, has a
plurality of through holes 143 having square openings, which are
formed and regularly arranged in a lattice-like manner. In
addition, permanent magnets 145, each having a rectangular
parallelopiped shape whose cross-sectional shape substantially
matches the opening shape of each of the through holes 143, are
respectively inserted into the through holes 143 in such a way that
the upper end surfaces of the permanent magnets 145 respectively
inserted into the through holes 143 are all arranged in the same
plane substantially in parallel with the surface of the metal plate
144, wherein the `adjacent` permanent magnets 145 differ from each
other in polarity.
[0044] Next, there is provided a plate 151, which is shown in FIG.
38, made of a transparent quartz glass having substantially the
same shape as the metal plate 144. In addition, cross-shaped
alignment marks (or positioning marks) 152 are formed on the four
corners of the plate 151 to cooperate with the aforementioned
alignment marks 142 of the quartz glass 141, thus establishing
positioning between the quartz glass 141 and the plate 151. In
addition, a plurality of alignment marks 153, each of which matches
the contour shape of each of the permanent magnets 145, are formed
in conformity with the positions of the through holes 143 of the
metal plate 144.
[0045] The upper end surfaces of the permanent magnets 145 are
adhered to the lower surface of the plate 151 by use of a
prescribed adhesive. At this time, a prescribed positioning is
established between the metal plate 144 (holding the permanent
magnets 145) and the plate 151 by use of the alignment marks
153.
[0046] Thereafter, the metal plate 144 is removed from the lower
side of the plate 151. Thus, it is possible to produce a magnet
array in which the permanent magnet 145 are arranged on the plate
151 in a lattice-like manner and in which the `adjacent` permanent
magnets differ from each other in polarity.
[0047] As shown in FIG. 40, the quartz glass 141 is brought into
contact with the plate 151 in such a way that the aforementioned
films M come into contact with the upper surface of the plate 151.
Herein, the prescribed positioning is established between the
quartz glass 141 and the plate 151 by mutually matching the
alignment marks 142 with the alignment marks 152. Then, fixing
members 155 such as clips are used to fix the quartz glass 141 and
the plate 151 together.
[0048] In the aforementioned state, as shown in FIG. 41, magnetic
forces are formed in directions from the N pole of one permanent
magnet 145 towards the S poles of adjacent permanent magnets 145.
Therefore, as shown in FIG. 42, magnetic forces are applied to the
films M, which are arranged to encompass one permanent magnet 145,
in four directions, that is, the positive direction of the Y-axis,
the positive direction of the X-axis, the negative direction of the
Y-axis, and the negative direction of the X-axis.
[0049] The quartz glass 141 and the plate 151 fixed together by the
fixing members 155 are subjected to a heat treatment for four hours
at a prescribed temperature ranging from 250.degree. C. to
280.degree. C., for example. Thus, it is possible to order the
pinning layers and to pin the pinned layers of the GMR elements.
The quartz glass 141 and the plate 151 are separated from each
other, and passivation films and polyimide films are formed for the
purpose of protection; then, the quartz glass 141 is subjected to
cutting on break lines B. Thus, the magnetic sensor 101 is
produced.
[0050] Compared with the conventionally-known magnetic sensor in
which magnetoresistive elements of the AMR type are inclined at
45.degree. relative to the substrate, the aforementioned two-axis
magnetic sensor has an advantage which allows magnetic measurement
on geomagnetic levels without using bias magnetic fields; however,
when applied with an intense magnetic field, the magnetized states
thereof are unexpectedly changed so as to cause unwanted offsets in
the bridge configurations of the GMR elements.
[0051] To cope with the aforementioned drawback, it is possible to
suppress offset variations against the influence of an intense
magnetic field by attaching permanent magnets to both ends of the
GMR elements. Specifically, a relatively great magnetic field that
is greater than the coercive force Hc of the permanent magnet is
applied to the GMR element in the longitudinal direction, i.e.,
longitudinal direction of the free layer, so that the free layer is
being initialized at the same time that the permanent magnet is
attached so as to cause magnetization. Herein, it is possible to
use the aforementioned magnet array, which is used in an ordering
heat treatment of pin layers, in this method.
[0052] In the aforementioned method, however, it is necessary to
apply a magnetic field in a direction perpendicular to the
longitudinal direction of the GMR element in the ordering heat
treatment, and it is also necessary to apply a magnetic field whose
magnetism is identical to that of the permanent magnet in the
longitudinal direction of the GMR element. Herein, magnetic fields
of different directions are required in the aforementioned
steps.
[0053] In the magnet array, under the ordering heat treatment, each
of the permanent magnets should be arranged such that the center of
gravity thereof is coincident with the center of each cell on the
quartz glass, and when each of them is arranged to cause
magnetization, it should be shifted in position so that the center
of gravity thereof is coincident with each of the four corners of
the quartz glass. This may cause positional deviations, which in
turn cause the initialization direction to be shifted and thus
deteriorates the measurement accuracy. When the aforementioned
magnetic sensor is used under the influence of an intense magnetic
field, offsets become easy to vary.
[0054] As described above, the aforementioned two-axis magnetic
field may have an advantage in the reduction of the hysteresis
characteristics of the GMR elements under the influence of a weak
magnetic field; however, this would not sufficiently contribute to
the stability of the offsets.
[0055] Magnetized states that are unexpectedly moved under the
influence of an intense magnetic field may be restored to the
original ones by applying an initialization magnetic field to form
thin film coils, which are embedded beneath the GMR elements.
However, this method does not sufficiently contribute to the
stability of the offsets.
SUMMARY OF THE INVENTION
[0056] It is an object of the invention to provide a magnetic
sensor that can be controlled in offset variations, regardless of
the influence of an intense magnetic field applied thereto, so as
to improve the magnetic characteristics with respect to the intense
magnetic field.
[0057] It is another object of the invention to provide a
manufacturing method for manufacturing the aforementioned magnetic
sensor.
[0058] A magnetic sensor of this invention comprises
magnetoresistive elements and permanent magnet films, which are
combined together to form GMR elements formed on a quartz substrate
having a square shape, wherein the permanent magnet films are
paired and connected to both ends of the magnetoresistive elements.
That is, the magnetic sensor detects the magnitude of an external
magnetic field applied thereto in two axial directions, so that an
X-axis magnetic sensor and a Y-axis magnetic sensor are realized by
adequately arranging the GMR elements relative to the four sides of
the quartz substrate. In particular, this invention is
characterized in that the magnetization direction of the pinned
layer of the magnetoresistive element forms a prescribed angle of
45.degree. relative to the longitudinal direction of the
magnetoresistive element. Alternatively, the magnetization
direction of the pinned layer of the magnetoresistive element forms
a prescribed angle of 45.degree. relative to the magnetization
direction of the permanent magnet film. Thus, it is possible to
reliably suppress offset variations of bridge connections of the
GMR elements even when an intense magnetic field is applied; and it
is therefore possible to noticeably improve the resistant
characteristics to an intense magnetic field.
[0059] A manufacturing method of the magnetic sensor of this
invention is characterized in that an ordering heat treatment is
performed by arranging a substrate on a magnet array in which a
plurality of permanent magnets are arranged such that adjoining
permanent magnets differ from each other in polarity, wherein the
permanent magnets are positioned respectively or selectively on the
four corners of a cell (corresponding to the quartz substrate)
within the substrate, which is then heated. Alternatively, the
ordering heat treatment is performed by arranging the substrate
such that the magnetization direction of the pinned layer of the
magnetoresistive element matches the diagonal line of the
substrate, which is then heated, wherein the permanent magnet films
are adequately magnetized using a magnet array in which adjoining
permanent magnets differ from each other in polarity.
[0060] Thus, it is possible to produce the magnetic sensor, in
which the magnetization direction of the pinned layer of the
magnetoresistive element forms a prescribed angle of 45.degree.
relative to the magnetization direction of the permanent magnet
film, by simple processes with ease.
BRIEF DESCRIPTION OF THE DRAWINGS
[0061] These and other objects, aspects, and embodiments of the
present invention will be described in more detail with reference
to the following drawings, in which:
[0062] FIG. 1 is a plan view showing a magnetic sensor using GMR
elements in accordance with a first embodiment of the
invention;
[0063] FIG. 2 is a plan view showing a quartz substrate arranging
GMR elements for use in the manufacture of the magnetic sensor of
the first embodiment;
[0064] FIG. 3 is a partial plan view showing a metal plate for use
in the manufacture of the magnetic sensor of the first
embodiment;
[0065] FIG. 4 is a partial plan view showing a metal plate for use
in the manufacture of a conventional magnetic sensor;
[0066] FIG. 5 is a plan view showing sensing directions F1 and F2
with regard to X-axis and Y-axis GMR elements incorporated in the
magnetic sensor of the first embodiment;
[0067] FIG. 6 is a plan view showing the arrangements of GMR
elements and permanent magnets on the quartz substrate for use in
the manufacture of the magnetic sensor of the first embodiment;
[0068] FIG. 7 is a block diagram simply showing a bridge connection
established among the X-axis GMR elements;
[0069] FIG. 8 is a block diagram simply showing a bridge connection
established among the Y-axis GMR elements;
[0070] FIG. 9 is a graph showing the magnetic characteristics of
the X-axis and Y-axis GMR elements incorporated in the magnetic
sensor of the first embodiment;
[0071] FIG. 10 is a graph showing the magnetic characteristics of
the X-axis and Y-axis GMR elements incorporated in the conventional
magnetic sensor;
[0072] FIG. 11A is a cross sectional view showing a combination of
a substrate and a metal plate for holding permanent magnets in the
manufacture of the magnetic sensor;
[0073] FIG. 11B is a cross sectional view in which the substrate
and the metal plate are fixed together using fixing members;
[0074] FIG. 12 is a plan view showing a magnetic sensor in
accordance with a second embodiment of the invention;
[0075] FIG. 13 is a plan view showing a magnet array for use in the
magnetic sensor of the second embodiment, in which a plurality of
bar magnets are arranged in parallel;
[0076] FIG. 14A is a cross sectional view showing a silicon
substrate in which slots are formed in parallel with each other in
the manufacture of a modified example of a magnet array for use in
the magnetic sensor of the second embodiment;
[0077] FIG. 14B is a cross sectional view showing the magnet array
in which bar magnets are respectively inserted into the slots of
the silicon substrate;
[0078] FIG. 15 is a partial perspective view in cross section
showing an arrangement of the bar magnets of different polarities
inserted into the slots of the silicon substrate;
[0079] FIG. 16 is a plan view showing the positional relationships
between the bar magnets of different polarities and a quartz
substrate derived from a quartz glass;
[0080] FIG. 17A is a cross sectional view showing a substrate in
which slots are formed in parallel with each other in the
manufacture of a modified example of a magnet array for use in the
magnetic sensor of the second embodiment;
[0081] FIG. 17B is a cross sectional view showing the magnet array
in which bar magnets are respectively inserted into the slots of
the substrate;
[0082] FIG. 18 is a partial perspective view in cross section
showing an arrangement of the bar magnets of the same polarity
inserted into the slots of the substrate;
[0083] FIG. 19 is a plan view showing the positional relationships
of the bar magnets of the same polarity and a quartz substrate;
[0084] FIG. 20 is a plan view showing a quartz glass on which GMR
elements and bar magnets are arranged in the manufacture of a
magnetic sensor in accordance with a second embodiment of the
invention;
[0085] FIG. 21 is a plan view showing an arrangement of the GMR
elements of the magnetic sensor of the second embodiment in
connection with X-axis and Y-axis sensing directions;
[0086] FIG. 22 is a plan view showing an arrangement of permanent
magnets relative to the GMR elements formed on the quartz substrate
for use in the manufacture of the magnetic sensor of the second
embodiment;
[0087] FIG. 23 is a plan view showing a magnetic sensor in
accordance with a fourth embodiment of the invention;
[0088] FIG. 24 is a plan view showing an arrangement of GMR
elements on a quartz glass in the manufacture of the magnetic
sensor of the fourth embodiment;
[0089] FIG. 25 is a plan view showing sensing directions actualized
by the magnetic sensor of the fourth embodiment;
[0090] FIG. 26 is a plan view showing a two-axis magnetic sensor
using GMR elements;
[0091] FIG. 27 is a plan view showing the configuration of a GM
element for use in the two-axis magnetic sensor;
[0092] FIG. 28 is a cross sectional view taken along line A-A in
FIG. 27;
[0093] FIG. 29 is a cross sectional view diagrammatically showing
the constitution of a spin valve film used in the GMR element shown
in FIG. 27;
[0094] FIG. 30 is a graph showing the magnetic characteristics of
the GMR element;
[0095] FIG. 31 is a block diagram simply showing a full bridge
connection of GMR elements adapted to an X-axis magnetic
sensor;
[0096] FIG. 32 is a graph showing the magnetic characteristics of
the X-axis magnetic sensor;
[0097] FIG. 33 is a block diagram simply showing a full bridge
connection of GMR elements adapted to a Y-axis magnetic sensor;
[0098] FIG. 34 is a graph showing the magnetic characteristics of
the Y-axis magnetic sensor;
[0099] FIG. 35 is a plan view showing the formation of GMR element
films on a quartz glass, which is used in the manufacture of the
two-axis magnetic sensor;
[0100] FIG. 36 is a plan view showing a metal plate arranging
permanent magnets, which is used to manufacture the two-axis
magnetic sensor;
[0101] FIG. 37 is a cross sectional view taken along line B-B in
FIG. 36;
[0102] FIG. 38 is a plan view showing a transparent quartz glass
plate for use in the manufacture of the two-axis magnetic
sensor;
[0103] FIG. 39 is a cross sectional view showing that permanent
magnets of a magnet array are adhered to the transparent quartz
glass plate;
[0104] FIG. 40 is a cross sectional view showing that a quartz
glass and the transparent quartz glass plate holding the permanent
magnets are fixed together via fixing members;
[0105] FIG. 41 is a perspective view diagrammatically showing the
directions of magnetic forces applied among permanent magnets,
which are arranged adjacent to each other in the magnet array;
[0106] FIG. 42 is a plan view showing the method in which thin
magnetic films are magnetized under influences of permanent magnets
in the manufacture of the two-axis magnetic sensor; and
[0107] FIG. 43 is a table showing the experimental results upon
comparison between the embodiments and a comparative example
corresponding to a two-axis magnetic sensor.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0108] This invention will be described in further detail by way of
examples with reference to the accompanying drawings.
[0109] 1. First Embodiment
[0110] FIG. 1 is a plan view showing a two-axis magnetic sensor
using GMR elements in accordance with a first embodiment of the
invention.
[0111] That is, a magnetic sensor 1 comprises a quartz substrate 2
having a prescribed thickness and a roughly square shape, X-axis
GMR elements 11 to 14 that are formed on the quartz substrate 2 so
as to form an X-axis magnetic sensor for detecting magnetic fields
in an X1-axis direction, and Y-axis GMR elements 21 to 24 that are
formed on the quartz substrate 2 so as to form a Y-axis magnetic
sensor for detecting magnetic fields in a Y1-axis direction, which
is perpendicular to the X1-axis direction. Specifically, the
sensing direction of the X-axis magnetic sensor lies in the X1-axis
direction that is formed 45.degree. relative to the X-axis
direction, and the sensing direction of the Y-axis magnetic sensor
lies in the Y1-axis direction that is formed 45.degree. relative to
the Y-axis direction.
[0112] In the above, it is possible to substitute silicone for the
material of the quartz substrate 2.
[0113] In FIG. 1, the X-axis GMR elements 11 to 14 are paired and
respectively arranged in proximity to the midpoints on two sides of
the quartz substrate 2, which are perpendicular to the X-axis, in
such a way that they are arranged in parallel with each other.
Similarly, the Y-axis GMR elements 21 to 24 are paired and
respectively arranged in proximity to the midpoints on the other
two sides of the quartz substrate 2, which are perpendicular to the
Y-axis, in such a way that they are arranged in parallel with each
other.
[0114] Each of the X-axis GMR elements 11-14 and the Y-axis GMR
elements 21-24 is constituted by a plurality of band-shaped
magnetoresistive elements 31, which are composed of spin valve
films arranged in parallel with each other, and a plurality of
permanent magnet films 32, which are connected with both ends of
the magnetoresistive elements 31 in longitudinal directions and
which are composed of thin films of a hard ferromagnetic substance
such as CoCrPt having a high coercive force and a high squareness
ratio, wherein a prescribed angle of 45.degree. is formed between
the longitudinal direction of the magnetoresistive element 31 and
the longitudinal direction of the adjoining permanent magnet film
32.
[0115] In addition, each of the magnetoresistive elements 31 is
arranged in such a way that the longitudinal direction thereof
forms a prescribed angle of 45.degree. relative to the proximate
side of the quartz substrate 2. In addition, each of the permanent
magnet films 32 is arranged in such a way that the longitudinal
direction thereof is in parallel with the proximate side of the
quartz substrate 2, wherein the permanent magnet film 32 arranged
at one end of the magnetoresistive element 31 differs from the
other permanent magnet film 32 arranged at the other end of the
magnetoresistive element 31 in the distance measured from the
proximate side of the quartz substrate 2.
[0116] The magnetization direction of the free layer of the
magnetoresistive element 31 lies in the longitudinal direction
thereof, and the magnetization direction of the permanent magnet
film 32 also lies in the longitudinal direction thereof Hence, a
prescribed angle of 45.degree. is formed between the magnetization
direction of the free layer of the magnetoresistive element 31 and
the magnetization direction of the permanent magnet film 32.
[0117] In addition, the magnetization direction pinned in the
pinned layer of the magnetoresistive element 31 is formed
45.degree. relative to the longitudinal direction of the
magnetoresistive element 31. That is, the direction of a magnetic
field applied in the ordering heat treatment is formed 45.degree.
relative to the longitudinal direction of the magnetoresistive
element 31.
[0118] Furthermore, the magnetization direction pinned in the
pinned layer of the magnetoresistive element 31 is identical to the
magnetization direction of the permanent magnet film 32. That is,
the direction of a magnetic field applied in the ordering heat
treatment is identical to the direction of a magnetic field applied
to magnetize the magnetoresistive element 31.
[0119] The structure of the spin valve film of the magnetoresistive
element 31 is identical to the foregoing structure of the spin
valve film 131 used for the X-axis GMR elements 111-114 and the
Y-axis GMR elements 121-124; hence, the detailed description
thereof will be omitted.
[0120] The present embodiment is characterized in that each of the
X-axis GMR elements 11-14 and the Y-axis GMR elements 21-24 defines
the magnetization direction of the pinned layer PD of the
magnetoresistive element 31 so as to be identical to the
magnetization direction of the permanent magnet film 32.
[0121] In addition, the magnetoresistive element 31 and the
permanent magnet film 32 are connected together in such a way that
the longitudinal direction of the free layer F is inclined against
the longitudinal direction of the permanent magnet film 32 by
45.degree..
[0122] Next, a manufacturing method of the magnetic sensor I will
be described in detail.
[0123] Similar to the foregoing magnetic sensor 101, a plurality of
island regions corresponding to the permanent magnet films 32,
which are connected with GMR elements respectively, are arranged
and formed on the surface of a rectangular-shaped quartz glass 41.
As shown in FIG. 2, films N corresponding to the permanent magnet
films 32 define regions M for arranging the GMR elements, so that
when the quartz glass 41 is subjected to a cutting process along
break lines B and is thus divided into individual quartz substrates
2, the regions M are aligned to match prescribed positions of the
X-axis GMR elements 11-14 and the Y-axis GMR elements 21-24.
[0124] In addition, alignment marks (not shown) are formed on the
four comers of the quartz glass 41. After formation of the
permanent magnet films 32, a film (or films) for forming the GMR
elements is formed on the overall surface of the quartz glass
41.
[0125] Next, as shown in FIG. 3, there is provided a metal plate 44
in which a plurality of through holes 43 each having a
square-shaped opening are formed in a lattice-like manner. A
plurality of permanent magnets 45 each having a rectangular
parallelopiped shape whose cross-sectional shape substantially
matches the opening of the through hole 43 are respectively
inserted into the through holes 43 in such a way that the upper end
surfaces thereof are aligned substantially in the same plane in
parallel with the surface of the metal plate 44, and the
`adjoining` permanent magnets 45 differ from each other in
polarity.
[0126] Next, there is provided a plate made of a transparent quartz
glass, which has substantially the same shape as the metal plate
44. Similar to the foregoing plate 151 shown in FIG. 38, alignment
marks 153 are formed at prescribed positions in correspondence with
the through holes 43.
[0127] In the above, the foregoing alignment marks 152 are formed
at the four corners of the plate in order to establish prescribed
positioning between the quartz glass 41 and the plate, wherein in
the present embodiment compared with the foregoing example shown in
FIG. 38, each of them is shifted in position in both the negative
direction of the X-axis and the negative direction of the Y-axis by
half of the length of the side of the quartz substrate 2, in other
words, it is shifted by a half pitch. Of course, it is possible to
form both of the foregoing alignment marks 152 and the half-pitch
shifted alignment marks on the plate.
[0128] A magnet array is constituted by arranging the permanent
magnets 45 in a lattice-like manner, wherein the upper end surfaces
of the permanent magnets 45 are adhered to the lower surface of the
plate by use of a prescribed adhesive. At this time, the prescribed
positioning is established between the permanent magnets 45 and the
plate by use of the aforementioned alignment marks 153.
[0129] Next, the metal plate 44 is removed, so that the magnet
array is produced in which the permanent magnets 45 are arranged in
a lattice-like manner in such a way that the adjoining permanent
magnets 45 differ from each other in polarity.
[0130] The quartz glass 41 and the plate are combined in such a way
that the films M are brought into contact with the upper surface of
the plate. Herein, the prescribed positioning is established
between the quartz glass 41 and the plate by mutually matching
half-pitch shifted alignment marks of the plate with the foregoing
alignment marks of the quartz glass 41. Thus, it is possible for
the four corners of the quartz substrate 2, which forms an
individual cell derived from the quartz glass 41, to coincide with
the centers of gravity of the permanent magnets 45 respectively.
Thereafter, the quartz glass 41 and the plate are fixed together by
using a plurality of fixing members such as clips.
[0131] Next, the pinning layer PN of the magnetoresistive element
31 is subjected to an ordering heat treatment, wherein the pinned
layer PD is subjected to pinning as well.
[0132] Under the condition where the quartz glass 41 and the plate
are fixed together, as shown in FIG. 2, permanent magnets 45 are
arranged at the four corners of the quartz substrate 2, which is
divided by the subsequent cutting process, in such a way that
adjacent permanent magnets differ from each other in polarity.
Therefore, a magnetic field is caused to occur in a direction from
the N pole of the permanent magnet 45 to the S pole of the other
`adjacent` permanent magnet 45, wherein it is directed in parallel
to each side of the quartz substrate 2. That is, a magnetic field
is applied to each film M in a direction that is inclined by
45.degree. with respect to the longitudinal direction of the pin
layer of the magnetoresistive element 31.
[0133] Next, the quartz glass 41 and the plate, which are fixed
together using the fixing members, are subjected to a heat
treatment for four hours under vacuum at a prescribed temperature
ranging from 250.degree. C. to 280.degree. C.
[0134] Thus, it is possible to complete an ordering heat treatment
on the pinning layer PN within the pin layer of the
magnetoresistive element 31 belonging to each of the X-axis GMR
elements 11-14 and the Y-axis GMR elements 21-24. Herein, the
pinned layer PD is subjected to pinning in a switched connection
manner.
[0135] Thereafter, the X-axis GMR elements 11-14 and the Y-axis GMR
elements 21-24 are subjected to patterning and are thus arranged in
prescribed patterns, wherein the permanent magnets 32 are
adequately connected together in a zigzag manner.
[0136] The aforementioned magnetic sensor 1 has an X-axis sensing
direction F1 and a Y-axis sensing direction F2 with respect to the
pin layers of the magnetoresistive elements 31 as shown in FIG. 5,
wherein the X-axis sensing direction F1 is inclined by 45.degree.
relative to one side of the quartz substrate 2, and the Y-axis
sensing direction F2 is inclined by 45.degree. relative to the
other side of the quartz substrate 2.
[0137] Next, the same magnet array is used without changing the
position thereof, so that, as shown in FIG. 6, the permanent magnet
films 32 are arranged to start magnetization thereby under the
condition where the permanent magnets 45 are arranged such that the
centers of gravity thereof coincide with the four corners of the
quartz substrate 2 respectively. Herein, magnetization directions
of the permanent magnets 32 are set to be identical to the
magnetization directions of the pinned layers PD of the
magnetoresistive elements 31. Therefore, the pinned layers PD of
the magnetoresistive elements 31 are reliably subjected to pinning;
hence, it is possible to produce the magnetic sensor I that is
influenced by magnetization of the permanent magnets 32.
[0138] FIG. 7 shows a bridge connection established among the
X-axis GMR elements 11-14 forming the X-axis magnetic sensor
incorporated in the magnetic sensor 1, wherein reference symbol
X.sub.1 designates the X-axis GMR elements 11 and 12, and X.sub.2
designates the X-axis GMR elements 13 ad 14. All the sensing
directions of the X-axis GMR elements 11-14 match the
aforementioned X-axis sensing direction F1 shown in FIG. 5; hence,
when an external magnetic field is applied in a direction opposite
to the X-axis sensing direction F1, a terminal `L` becomes higher
in potential compared with another terminal `H`.
[0139] FIG. 8 shows a bridge connection established among the
Y-axis GMR elements 21-24 forming the Y-axis magnetic sensor
incorporated in the magnetic sensor 1, wherein reference symbol
Y.sub.1 designates the Y-axis GMR elements 21 and 22, and Y.sub.2
designates the Y-axis GMR elements 23 and 24. All the sensing
directions of the Y-axis GMR elements 21-24 match the
aforementioned Y-axis sensing direction F2 shown in FIG. 5; hence,
when an external magnetic field is applied in a direction opposite
to the Y-axis sensing direction F2, a terminal `L` becomes higher
in potential compared with another terminal `H`.
[0140] FIG. 9 shows the magnetic characteristics of the X-axis GMR
elements 11-14 and the Y-axis GMR elements 21-24 incorporated in
the magnetic sensor 1, and FIG. 10 shows the magnetic
characteristics of the X-axis GMR elements 111-114 and the Y-axis
GMR elements 121-124 incorporated in the foregoing magnetic sensor
101. Herein, solid curves represent the magnetic characteristics of
the sensing directions of the GMR elements, and dotted curves
represent the magnetic characteristics of the non-sensing
directions of the GMR elements.
[0141] As shown in FIG. 9, a hysteresis loop cannot be recognized
with regard to the sensing directions of the GMR elements 11-14 and
21-24. In addition, a hysteresis loop may also be recognized with
regard to the non-sensing directions of the GMR elements 11-14 and
21-24, whereas it disappears at or in proximity to a `zero` value
of the magnetic field; thus, it is possible to improve the
resistant characteristics to an intense magnetic field.
[0142] FIG. 10 shows that a hysteresis loop may be recognized with
regard to the non-sensing directions of the foregoing GMR elements
111-114 and 121-124, wherein it lies in proximity to a `zero` value
of the magnetic field; hence, the resistant characteristics to an
intense magnetic field must be reduced.
[0143] In summary, it is possible to noticeably improve the
resistant characteristics to an intense magnetic field in the GMR
elements incorporated in the magnetic sensor 1 of the present
embodiment, in which each of the permanent magnet films 32 is
arranged to form a prescribed angle of 45.degree. relative to the
longitudinal direction of each of the magnetoresistive elements 31,
compared with the GMR elements incorporated in the foregoing
magnetic sensor 101.
[0144] As described above, the magnetic sensor 1 of the present
embodiment is produced in such a way that the X-axis GMR elements
11-14 and the Y-axis GMR elements 21-24 are formed on the quartz
substrate 2, wherein the magnetoresistive elements 31 thereof are
arranged such that each of the magnetization directions of the
pinned layers PD forms a prescribed angle of 45.degree. relative to
each of the magnetization directions of the free layers F.
Therefore, even when an intense magnetic field is applied, it is
possible to reliably suppress offset variations of the bridges,
which in turn contributes to a noticeable improvement in the
resistant characteristics to an intense magnetic field.
[0145] According to the manufacturing method of the magnetic sensor
1 of the present embodiment, the permanent magnets 45 are arranged
at the four corners of the quartz substrate 2, which is divided in
the subsequent cutting process, in such a way that the adjoining
permanent magnets 45 differ from each other in polarity, in which a
magnetic field is applied to each permanent magnet film M in the
longitudinal direction; therefore, even when an intense magnetic
field is applied, it is possible to reliably suppress offset
variations of the bridge circuits. In summary, it is possible to
produce the magnetic sensor 1, which can noticeably improve the
resistant characteristics to an intense magnetic field, with ease
by simple processes.
[0146] The present embodiment uses the plate that has the through
holes 43 without changing the shapes and distances compared with
the foregoing through holes 143, in which each of the alignment
marks is shifted in position by a half pitch. Of course, it is
possible to use another plate in which each of the through holes is
shifted in position by a half pitch. In addition, it is possible to
use a plate in which both of the foregoing alignment marks and the
new alignment marks each shifted in position by a half pitch are
formed.
[0147] The magnet array adapted to the present embodiment is not
necessarily limited to one in which the permanent magnets 45 are
adhered to the plate 44 made by the aforementioned quartz glass.
That is, it is possible to use a substrate 46 composed of a
Ni.sub.42Fe.sub.58 alloy, and a metal plate 47 composed of tungsten
(W) in which a plurality of through holes 43 conforming with the
exterior shapes of the permanent magnets 45 are formed, so that the
substrate 46 and the metal plate 47 are adhered together as shown
in FIG. 11A, whereby the permanent magnets 45 are respectively
inserted into the through holes 43.
[0148] Similar to the foregoing magnetic sensor 101 in which the
quartz glass 141 and the plate 151 are fixed together using the
fixing members 155 such as clips (see FIG. 40), the quartz glass 41
is fixed using the fixing members 155 as shown in FIG. 11B.
[0149] In the aforementioned magnet array, both of the
Ni.sub.42Fe.sub.58 alloy and tungsten (W) are close to silicon (Si)
in terms of thermal expansion coefficient; therefore, even when a
thermal expansion is caused to occur due to heating, there is no
possibility of causing positional deviations between the substrate
46 and the metal plate 47; hence, it is possible to improve the
positional accuracy of the magnet array. Herein, the metal plate 47
is used as a part of the magnet array and does not need to be
removed; hence, it is possible to improve the holding accuracy of
the permanent magnets 45, and it is therefore possible to
manufacture the magnetic sensor 1 with ease.
[0150] 2. Second Embodiment
[0151] FIG. 12 is a plan view showing a magnetic sensor 50 in
accordance with a second embodiment of the invention, wherein GMR
elements are arranged along the four sides of a quartz substrate 2,
and each of them is constituted by magnetoresistive elements 31 and
permanent magnet films 32. The magnetic sensor 50 of the second
embodiment differs from the magnetic sensor 1 of the first
embodiment in that the longitudinal direction of each
magnetoresistive element 31 lies parallel to the proximate side of
the quartz substrate 2.
[0152] Specifically, the magnetic sensor 2 comprises the `roughly
square-shaped` quartz substrate 2 having a prescribed thickness as
well as X-axis GMR elements 51-54 and Y-axis GMR elements 61-64
that are formed on the quartz substrate 2, wherein the X-axis GMR
elements 51-54 form an X-axis magnetic sensor for detecting a
magnetic field in the X-axis direction, and the Y-axis GMR elements
61-64 form a Y-axis magnetic sensor for detecting a magnetic field
in the Y-axis direction.
[0153] In the above, the X-axis GMR elements 51-54 are paired and
respectively arranged in proximity to the midpoints of two sides of
the quartz substrate 2 perpendicular to the X-axis in such a way
that the two pairs of them are arranged in parallel with each
other. Similarly, the Y-axis GMR elements 61-64 are paired and
respectively arranged in proximity to the midpoints of the other
two sides of the quartz substrate 2 perpendicular to the Y-axis in
such a way that the two pairs of them are arranged in parallel with
each other.
[0154] Each of the X-axis GMR elements 51-54 and the Y-axis GMR
elements 61-64 is constituted by magnetoresistive elements 31, each
of which is roughly shaped as a parallelogram and comprises
band-shaped spin valve films arranged in parallel with each other,
and permanent magnet films 32 that are connected with both ends of
the magnetoresistive element 31 in the longitudinal direction, and
each of which is made by a roughly square-shaped thin film composed
of a hard ferromagnetic substance such as CoCrPt having a high
coercive force and a high squareness ratio, wherein the
magnetoresistive elements 31 and the permanent magnet films 32 are
arranged such that the longitudinal directions thereof conform with
each other.
[0155] Each of the magnetoresistive elements 31 is formed such that
the longitudinal direction thereof lies in parallel with the
proximate side of the quartz substrate 2. In addition, each of the
permanent magnet films 32 is formed such that the longitudinal
direction thereof lies in parallel with the proximate side of the
quartz substrate 2, wherein the `paired` permanent magnet films 32,
which are connected with both ends of the same magnetoresistive
element 31, are arranged with the same distance from the proximate
side of the quartz substrate 2.
[0156] In the above, the magnetization direction of the pinned
layer is inclined by 45.degree. relative to the longitudinal
direction of the magnetoresistive element 31, whereas the
magnetization direction of the permanent magnet film 32 lies along
the longitudinal direction of the permanent magnet film 32. That
is, the magnetization direction of the pinned layer of the
magnetoresistive element 31 forms a prescribed angle of 45.degree.
relative to the magnetization direction of the permanent magnet
film 32.
[0157] Similar to the magnetic sensor 1 of the first embodiment,
the structure of the spin valve film adapted to each of the X-axis
GMR elements 51-54 and the Y-axis GMR elements 61-64 is identical
to the structure of the foregoing spin valve film 131 adapted to
each of the X-axis GMR elements 111-114 and the Y-axis GMR elements
121-124; hence, the detailed description regarding the structure of
the spin valve film will be omitted.
[0158] In each of the X-axis GMR elements 51-54 and the Y-axis GMR
elements 61-64, the longitudinal direction of the pinned layer PD
of the magnetoresistive element 31 matches the longitudinal
direction of the permanent magnet film 32. Herein, the
magnetization direction of the pinned layer PD is inclined by
45.degree. relative to the longitudinal direction of the
magnetoresistive element 31. That is, the magnetization direction
of the pinned layer PD of the magnetoresistive element 31 forms a
prescribed angle of 45.degree. relative to the magnetization
direction of the permanent magnet film 32.
[0159] Next, a manufacturing method of the magnetic sensor 50 will
be described in detail.
[0160] The second embodiment is characterized by using two types of
magnet arrays. That is, similar to the magnetic sensor 1 of the
first embodiment, spin valve films are formed on a
rectangular-shaped quartz glass in order to form permanent magnet
films 32 and individual GMR elements.
[0161] Next, as shown in FIG. 13, there is prepared a first metal
plate 67 having a rectangular shape in which a plurality of through
holes 43 each having a rectangular-shaped opening are slanted by
45.degree. and are arranged in parallel with each other, wherein a
plurality of bar magnets 68 made of rectangular-parallelopiped
permanent magnets whose cross-sectional shapes substantially match
the opening shapes of the through holes 43 are respectively
inserted into the through holes 43 in such a way that the upper end
surfaces thereof are arranged substantially in the same plane in
parallel with the surface of the first metal plate 67, and the
adjoining bar magnets 68 differ from each other in polarity.
[0162] Thereafter, similar to the first embodiment, there is
provided a first plate made of a transparent quartz glass whose
shape substantially matches the shape of the first metal plate 67,
wherein the upper end surfaces of the bar magnets 68 that are
arranged in parallel with each other in the magnet array are
adhered to the lower surface of the first plate by using a
prescribed adhesive. At this time, alignment marks are used to
establish prescribed positioning between the first plate and the
bar magnets 68.
[0163] Next, the first metal plate 67 is removed so as to produce a
magnet array in which the bar magnets 68 are arranged in parallel
with each other, and the adjoining bar magnets 68 differ from each
other in polarity.
[0164] There is arranged a quartz substrate that is brought into
contact with the upper surface of the first plate. That is, a
prescribed positioning between the aforementioned quartz glass 41
and the first plate is established by mutually matching their
alignment marks together. Next, a plurality of fixing members such
as clips are used to fix the quartz glass 41 and the first plate
together.
[0165] The aforementioned magnet array in which the bar magnets 68
are arranged in parallel with each other results in good accuracy
because even when they are unexpectedly shifted in position and in
distance therebetween, the magnetization directions thereof would
not be deviated so that no dispersion occurs in an ordering heat
treatment.
[0166] Similar to the first embodiment, the second embodiment can
be designed so as to provide a substrate composed of a
Ne.sub.42Fe.sub.58 alloy, and a metal plate composed of tungsten
(W) in which a plurality of through holes conform with the exterior
shapes of the bar magnets 68, wherein the substrate and the metal
plate are adhered together so that the bar magnets 68 are
respectively inserted into the through holes.
[0167] As the magnet array, it is possible to use various types of
magnet arrays, other than the aforementioned magnet array, as
follows: [0168] (1) A magnet array in which bar magnets each having
a different polarity are alternately arranged.
[0169] As shown in FIG. 14A, a dicing saw 72 is used to form a
plurality of slots 73, which are arranged in parallel with each
other with a prescribed distance therebetween, on a surface (or a
main surface) 71a of a silicon (Si) substrate 71. Each of the slots
73 has a prescribed width that is substantially identical to the
width of the bar magnet 68 inserted therein and is substantially
identical to the width of the dicing saw 72. Similar to the
aforementioned magnet array, the distance between the adjacent
slots 73 is set to half of the length of the diagonal line of the
quartz substrate 2.
[0170] Then, as shown in FIG. 14B, the bar magnets 68 are
respectively inserted into the slots 73 in such a way that the
adjoining bar magnets 68 differ from each other in polarity. In
this case, the bar magnets 68 are arranged and exposed on the
surface 71a of the silicon substrate 71 in such a way that as shown
in FIG. 15, the adjoining bar magnets 68 differ from each other in
polarity, whereby poles N, S, N, . . . are sequentially arranged.
As described above, it is possible to produce a magnet array in
which the bar magnets 68 each having a different polarity are
alternately arranged in the silicon substrate 71.
[0171] In the aforementioned magnet array, the distance between the
adjacent bar magnets 68 is set to half of the length of the
diagonal line of the quartz substrate 2. Therefore, when the magnet
array is mounted on the quartz glass 41 in such a way that, as
shown in FIG. 16, a single bar magnet 68 is arranged to match the
diagonal line of each single cell 75 (i.e., a region corresponding
to the quartz substrate 2 divided in the subsequent cutting
process), its `adjoining` bar magnets 68 are positioned at opposite
corners of the cell 75 to be symmetrical with the diagonal line.
[0172] (2) A magnet array in which bar magnets of the same polarity
are arranged in parallel with each other.
[0173] As shown in FIG. 17A, a dicing saw 72 is used to form a
plurality of slots 73, which are arranged in parallel with each
other with a prescribed distance therebetween, on a surface (or a
main surface) 77a of a Ni.sub.42Fe.sub.58 alloy substrate 77,
wherein the slot 73 has a prescribed width that is roughly set
identical to the width of the bar magnet 68 inserted therein. The
distance between the `adjacent` slots 73 are substantially set
identical to the length of the diagonal line of the quartz
substrate 2.
[0174] Next, as shown in FIG. 17B, the bar magnets 68 are
respectively inserted into the slots 73 of the substrate 77 in such
a way that all the adjoining bar magnets 68 have the same polarity.
In this case, all the bar magnets 68 are arranged with the same
polarity on the surface 77a of the Ni.sub.42Fe.sub.58 alloy
substrate 77, whereby the same polarity `N` appears in turn on the
surface 77a as shown in FIG. 18.
[0175] In the above, an intermediate portion of the
Ni.sub.42Fe.sub.58 alloy substrate 77 between the adjacent bar
magnets 68 having the same polarity `N` on the surface 77a has an
inverse polarity, that is, polarity `S`. That is, it apparently
seems as if different polarities N, S, N, . . . are sequentially
arranged in a prescribed direction (i.e., a direction from the left
to the right in FIG. 18) in parallel upon a parallel arrangement of
the bar magnets 68 with a prescribed distance therebetween, which
is substantially identical to half of the length of the diagonal
line of the quartz substrate 2.
[0176] As described above, it is possible to produce a magnet array
in which the bar magnets 68 having the same polarity are arranged
in parallel with each other in the Ni.sub.42Fe.sub.58 alloy
substrate 77.
[0177] In the aforementioned magnet array, the distance between the
adjacent bar magnets 68 is set to be identical to the length of the
diagonal line of the quartz substrate 2. That is, when the magnet
array is mounted on the quartz glass 41 in such a way that a single
bar magnet 68 is arranged on the diagonal line of a single cell 75
as shown in FIG. 19, each of the comers of the cell 75 that lie
symmetrically with respect to the diagonal line matches a line
segment 76 that is drawn at a position equally dividing the
distance between the adjacent bar magnets 68. Herein, each of the
positions of the line segments 76 that respectively cross the
opposite corners of the cell 75 and are drawn to be symmetric with
respect to the diagonal line of the cell 75 corresponds to a
different polarity (i.e., `S`) that differs from the polarity `N`
of the bar magnet 68. That is, it apparently seems as if magnets
having the polarity `S` are arranged on the corners of the cell
75.
[0178] In the aforementioned magnet array, it is possible to
reliably prevent the bar magnets 68 from attracting each other and
falling over or from unexpectedly rotating by themselves.
Therefore, it is possible to fix the bar magnets 68, which cannot
be fixed using a thin metal plate, at prescribed positions with
ease and with good accuracy.
[0179] Thereafter, the pinning layer PN within the pin layer of the
magnetoresistive element 31 is subjected to an ordering heat
treatment.
[0180] First, as shown in FIG. 20, three bar magnets 68 are
arranged with a prescribed distance therebetween to be inclined by
45.degree. relative to a prescribed side of the quartz glass 41 in
such a way that the adjoining bar magnets 68 differ from each other
in polarity.
[0181] In this case, a prescribed magnetic field is established in
a direction from one adjacent bar magnet 68 to the other, wherein
the magnetic field is inclined by 45.degree. relative to the
prescribed side of the quartz substrate 2, so that a magnetic field
is applied in a direction inclined by 45.degree. with respect to
the longitudinal direction of each spin valve film M.
[0182] Next, the quartz glass 41 and the aforementioned plate are
fixed together using the fixing members, and are subjected to a
heat treatment under a vacuum state for four hours at a prescribed
temperature ranging from 250.degree. C. to 280.degree. C., for
example.
[0183] Thus, it is possible to perform an ordering heat treatment
on the pinning layers of the magnetoresistive elements 31
incorporated in each of the X-axis GMR elements 51-54 and the
Y-axis GMR elements 61-64. Then, similar to the first embodiment,
the spin valve layers are subjected to patterning. As a result, it
is possible to produce the magnetic sensor 50 in which the X-axis
sensing direction Fl and the Y-axis sensing direction F2 lie in the
pinned layers P of the magnetoresistive elements 31 as shown in
FIG. 21.
[0184] Thereafter, as shown in FIG. 22, a magnet array whose
constitution is similar to the constitution of the magnet array
used in the first embodiment is used to magnetize the permanent
magnet films 32.
[0185] In the above, similar to the first embodiment, the permanent
magnets 45 are arranged on the four corners of the quartz substrate
2, which is divided by the subsequent cutting process, in such a
way that the adjoining permanent magnets 45 differ from each other
in polarity, whereby a magnetic field is established from one
permanent magnet 45 of the N pole to the other permanent magnet 45
of the S pole. This magnetic field is effected in parallel with
each single side of the quartz substrate 2; hence, it is possible
to establish a magnetic field in a direction substantially matching
the longitudinal direction of each permanent magnet film 32.
[0186] As described above, it is possible to produce the magnetic
sensor 50 in which the free layers F of the pin layers of the
magnetoresistive elements 31 are initialized in magnetization, and
the permanent magnets films 32 are adequately magnetized.
[0187] The magnetic sensor 50 of the second embodiment employs the
same bridge connection adapted to the magnetic sensor 1 of the
first embodiment. In short, the second embodiment can offer the
same effects realized in the aforementioned first embodiment.
[0188] 3. Third Embodiment
[0189] The second embodiment uses the magnet array whose
constitution is identical to the constitution of the magnet array
used in the first embodiment so as to adequately attach the
permanent magnets 45 and to magnetize the permanent magnet films
32. Herein, the magnetization of the permanent magnet films 32 can
be realized directly using the aforementioned magnet array that is
used in the ordering heat treatment in the second embodiment
without changing the arranging positions of the magnets.
[0190] In this magnetization, a magnetic field is established along
the diagonal line of the quartz substrate 2, which is divided in
the subsequent cutting process, and in a direction inclined by
45.degree. relative to one side of the quartz substrate 2.
Therefore, a magnetic field is applied to the permanent magnet film
32 whose longitudinal direction is set in parallel with one side of
the quartz substrate 2 in a direction 45.degree. inclined relative
to the longitudinal direction of the permanent magnet 32.
[0191] In this case, the terminal end of the free layer F is
initialized in a direction identical to the magnetization direction
of the permanent magnet film 32. In general, the initialization
direction of the free layer F is aligned in the longitudinal
direction due to shape anisotropy. For this reason, each of the GMR
elements is initialized in magnetization along the longitudinal
direction thereof, which is set in parallel with a prescribed side
of the quartz substrate 2.
[0192] As described above, it is possible to produce a magnetic
sensor of the third embodiment in which the free layer F of the
magnetoresistive element 31 is initialized in magnetization, and
the permanent magnet film 32 is adequately magnetized.
[0193] The third embodiment allows a small loss at the terminal end
of the free layer F, which may slightly deteriorate the sensitivity
compared with the second embodiment; however, the third embodiment
is designed in such a way that the magnetization direction is set
similar to the first embodiment; hence, it is possible to
noticeably reduce offset variations even when an intense external
magnetic field is applied to the magnetic sensor.
[0194] 4. Fourth Embodiment
[0195] FIG. 23 is a plan view showing a magnetic sensor in
accordance with a fourth embodiment of the invention, wherein,
similar to the aforementioned embodiments, a magnetic sensor 81 of
the fourth embodiment is constituted using GMR elements and
permanent magnet films formed on a quartz substrate 2. Herein, the
magnetic sensor 81 differs from the magnetic sensor 50 of the
second embodiment, in which the X-axis GMR elements 51-52 are
arranged in parallel with each other in proximity to the midpoint
of one side of the quartz substrate 2 lying in the negative
direction of the X-axis, and the Y-axis GMR elements 63-64 are
arranged in parallel with each other in proximity to the midpoint
of the other side of the quartz substrate 2 lying in the negative
direction of the Y-axis, such that in order to cancel the
sensitivities realized by the X-axis GMR elements 51-52 and the
Y-axis GMR elements 63-64, they are arranged substantially in the
center of the quartz substrate 2 and are inclined by 45.degree.
relative to a prescribed side of the quartz substrate 2.
[0196] In the manufacture of the magnetic sensor 81, the pinning
layers of the magnetoresistive elements 31 are subjected to an
ordering heat treatment in which the quartz glass 41 is heated for
four hours in a vacuum state at a prescribed temperature ranging
from 250.degree. C. to 280.degree. C., for example, wherein a
magnetic field is applied in a direction parallel to the X-axis GMR
elements 51-52 and the Y-axis GMR elements 63-64. That is, as shown
in FIG. 24, it is preferable that a magnetic field having uniform
intensity be applied along the longitudinal directions of the
X-axis GMR elements 51-52 and the Y-axis GMR elements 63-64 and in
a direction from the lower left to the upper right.
[0197] Similar to the aforementioned embodiments, the magnetic
sensor 81 is subjected to magnetization by fixing the quartz glass
and plate together.
[0198] As described above, it is possible to initialize the free
layers F of the magnetoresistive elements 31 incorporated in the
X-axis GMR elements 51-54 and the Y-axis GMR elements 61-64 and to
adequately magnetize the permanent magnet films 32. Thus, it is
possible to produce the magnetic sensor 81 in which the pinned
layers PD of the magnetoresistive elements 31 and the permanent
magnet films 32 are adequately magnetized.
[0199] As shown in FIG. 25, the aforementioned magnetic sensor 81
presents an X-axis sensing direction F1 and a Y-axis sensing
direction F2 with respect to the pinned layers PD of the
magnetoresistive elements 31, except for the magnetoresistive
elements 31 incorporated in the GMR elements 51-52 and 63-64
arranged substantially in the center of the quartz substrate 2.
[0200] The bridge connections of the GMR elements incorporated in
the magnetic sensor 81 are identical to those of the magnetic
sensor 1 of the first embodiment. Therefore, the fourth embodiment
can offer effects similar to those of the first embodiment.
[0201] 5. Fifth Embodiment
[0202] The fifth embodiment is basically identical to the fourth
embodiment but is characterized in that the aforementioned magnet
array is not used but a uniform magnetic field is applied in order
to magnetize the permanent magnet films 32 similar to the
aforementioned ordering heat treatment.
[0203] Herein, the magnetization of the permanent magnet films 32
will be described in detail.
[0204] That is, a uniform magnetic field whose intensity is uniform
is applied in a direction from the lower left to the upper right in
FIG. 24 similar to the aforementioned ordering heat treatment.
[0205] With respect to the X-axis GMR elements 53-54, which are
arranged in parallel with one side of the quartz glass 41, and the
Y-axis GMR elements 61-62, which are arranged in parallel with the
other side of the quartz substrate 41, a magnetic field is applied
along the diagonal line of the quartz substrate 2, which is divided
by the subsequent cutting process, and in a direction inclined by
45.degree. relative to each side of the quartz substrate 2. That
is, a magnetic field is applied to each of the permanent magnet
films 32 whose longitudinal directions are parallel to prescribed
sides of the quartz substrate 2 in a direction inclined by
45.degree. relative to each of the longitudinal directions of the
permanent magnet films 32.
[0206] The terminal end of the free layer F is initialized in a
direction identical to the magnetization direction of the permanent
magnet 32, wherein the free layer F is magnetized in the
longitudinal direction thereof due to shape anisotropy thereof, so
that the free layer F is initialized in magnetization in the
longitudinal direction of the corresponding GMR element, that is,
along the prescribed side of the quartz glass 41.
[0207] The fifth embodiment allows a small loss at the terminal end
of the free layer F, which may slightly reduce the sensitivity
compared with the sensitivity of the magnetic sensor of the second
embodiment; however, the fifth embodiment is designed to realize
the same magnetization direction(s) actualized in the first
embodiment; hence, it is possible to noticeably reduce offset
variations even when an intense external magnetic field is applied
to the magnetic sensor.
[0208] FIG. 43 shows the results of a comparison between the
magnetic sensor of this invention (i.e., Embodiments 1-5) and the
foregoing magnetic sensor (i.e., Comparative Example), wherein
Embodiment 1 corresponds to the magnetic sensor 1 of the first
embodiment; Embodiment 2 corresponds to the magnetic sensor 50 of
the second embodiment; Embodiment 3 corresponds to the magnetic
sensor of the third embodiment; Embodiment 4 corresponds to the
magnetic sensor 81 of the fourth embodiment; and Embodiment 5
corresponds to the magnetic sensor of the fifth embodiment.
[0209] FIG. 43 shows that compared with the Comparative Example,
all the magnetic sensors of Embodiments 1-5 are superior in the
resistant characteristics to an intense magnetic field. In each of
Embodiments 1-5 compared with the Comparative Example, it is
possible to reduce offset variations after exposure of a magnetic
field of 100 Oe, which shows the resistant characteristics to an
intense magnetic field.
[0210] Each of Embodiments 1-5 may be reduced in sensitivity
compared with the Comparative Example in which the longitudinal
direction of the GMR element crosses at a right angle to the
magnetization direction of the pinned layer realized in the
ordering heat treatment; however, it can be said that each of them
presents the good resistant characteristics to an intense magnetic
field.
[0211] In addition, it can be said that, compared with Embodiments
2 and 4 in which the magnetization direction of the permanent
magnet film differs from the magnetization direction of the pinned
layer realized in the ordering heat treatment, Embodiments 1, 3,
and 5, in which the magnetization direction of the permanent magnet
film is identical to the magnetization direction realized in the
ordering heat treatment, can offer the good resistant
characteristics to an intense magnetic field.
[0212] In each of Embodiments 1, 3 and 5 in which the magnetization
direction of the permanent magnet film does not match the
longitudinal direction of the GMR element (i.e., the longitudinal
direction of the free layer), the terminal end of the free layer is
magnetized in the magnetization direction of the permanent magnet
film; hence, a small loss may occur so as to slightly reduce the
sensitivity. However, variation ratios with respect to the
sensitivity are small because of the `good` resistant
characteristics to an intense magnetic field.
[0213] As described heretofore, this invention has a variety of
effects and technical features, which will be described below.
[0214] (1) A magnetic sensor of this invention is characterized in
that the magnetization direction of a pinned layer of a
magnetoresistive element forms a prescribed angle of 45.degree.
relative to the longitudinal direction of the magnetoresistive
element; therefore, even when an intense magnetic field is applied,
it is possible to reliably suppress offset variations of the bridge
connections of the GMR elements; hence, it is possible to
noticeably improve the resistant characteristics to an intense
magnetic field. [0215] (2) In addition, it is possible to modify
the magnetic sensor in such a way that the magnetization direction
of a pinned layer of a magnetoresistive element forms a prescribed
angle of 45.degree. relative to the magnetization direction of a
permanent magnet film, whereby even when an intense magnetic field
is applied, it is possible to reliably suppress offset variations
of the bridge connections of the GMR elements; hence, it is
possible to noticeably improve the resistant characteristics to an
intense magnetic field. [0216] (3) According to a manufacturing
method of the magnetic sensor of this invention, an ordering heat
treatment is performed using a magnet array in which a plurality of
permanent magnets are arranged in such a way that adjoining
permanent magnets differ from each other in polarity, wherein a
substrate is arranged on the magnet array such that the permanent
magnets are positioned to respectively or selectively match the
four corners of a cell within the substrate, which is then heated.
Herein, the permanent magnet films are magnetized by arranging the
substrate on the magnet array without changing the relative
positional relationship therebetween; therefore, it is possible to
initialize the free layer of the magnetoresistive element and to
magnetize the permanent magnet film with ease. As a result, it is
possible to produce the magnetic sensor, in which the magnetization
direction of the magnetoresistive element forms a prescribed angle
of 45.degree. relative to the magnetization direction of the
permanent magnet film, by simple processes with ease. [0217] (4) It
is possible to modify the manufacturing method in such a way that
the ordering heat treatment is performed by heating the substrate
in which the magnetization direction of the pinned layer
substantially matches the diagonal line of the cell within the
substrate, wherein the permanent magnet films are magnetized by
arranging the substrate on the magnet array in which adjoining
permanent magnets are arranged to differ from each other in
polarity, whereby it is possible to initialize the free layer of
the magnetoresistive element and to magnetize the permanent magnet
film with ease. Thus, it is possible to produce the magnetic
sensor, in which the magnetization direction of the pinned layer of
the magnetoresistive element forms a prescribed angle of 45.degree.
relative to the magnetization direction of the permanent magnet
film, by simple processes with ease. [0218] (5) It is possible to
further modify the manufacturing method in such a way that the
ordering heat treatment is performed by heating the substrate in
which the magnetization direction of the pinned layer matches the
diagonal line of the cell within the substrate, wherein the
permanent magnet films are magnetized by arranging the substrate
such that the magnetization direction of the pinned layer
substantially matches the diagonal line of the cell, whereby it is
possible to initialize the free layer of the magnetoresistive
element and to magnetize the permanent magnet film with ease. Thus,
it is possible to produce the magnetic sensor, in which the
magnetization direction of the pinned layer of the magnetoresistive
element forms a prescribed angle of 45.degree. relative to the
magnetization direction of the permanent magnet film, by simple
processes with ease.
[0219] As this invention may be embodied in several forms without
departing from the spirit or essential characteristics thereof, the
present embodiments are therefore illustrative and not restrictive,
since the scope of the invention is defined by the appended claims
rather than by the description preceding them, and all changes that
fall within metes and bounds of the claims, or equivalents of such
metes and bounds are therefore intended to be embraced by the
claims.
* * * * *