U.S. patent application number 11/678846 was filed with the patent office on 2008-03-13 for magnetic detection device including resistance adjusting unit.
This patent application is currently assigned to ALPS ELECTRIC CO., LTD.. Invention is credited to Hideto Ando, Hiroyuki Nakada, Kiyoshi Sato.
Application Number | 20080061777 11/678846 |
Document ID | / |
Family ID | 39168904 |
Filed Date | 2008-03-13 |
United States Patent
Application |
20080061777 |
Kind Code |
A1 |
Ando; Hideto ; et
al. |
March 13, 2008 |
MAGNETIC DETECTION DEVICE INCLUDING RESISTANCE ADJUSTING UNIT
Abstract
In a magnetic detection device for obtaining an output from
between a variable resistance element using the magnetoresistance
effect and a reference resistance element, a balance between
resistance values in the device can be easily adjusted in a wide
range. A voltage is applied to a resistance adjusting unit, a
reference resistance element, and a variable resistance element,
which are serially connected, and is also applied to another
variable resistance element, another reference resistance element,
and another resistance adjusting unit, which are serially
connected. When subjected to a magnetic field of a predetermined
size, resistance values of the variable resistance elements change,
and as a result, the potentials of output terminals change. Each of
the resistance adjusting units includes serially connected parallel
portions each including a plurality of parallel connected
resistance elements. The resistance value of the resistance
adjusting unit can be changed by bringing one of the parallel
connected resistance elements into a non-conduction state.
Inventors: |
Ando; Hideto; (Niigata-ken,
JP) ; Sato; Kiyoshi; (Niigata-ken, JP) ;
Nakada; Hiroyuki; (Niigata-ken, JP) |
Correspondence
Address: |
BRINKS HOFER GILSON & LIONE
P.O. BOX 10395
CHICAGO
IL
60610
US
|
Assignee: |
ALPS ELECTRIC CO., LTD.
Tokyo
JP
|
Family ID: |
39168904 |
Appl. No.: |
11/678846 |
Filed: |
February 26, 2007 |
Current U.S.
Class: |
324/252 ;
338/32R |
Current CPC
Class: |
H01L 43/08 20130101;
G01R 33/093 20130101; B82Y 25/00 20130101 |
Class at
Publication: |
324/252 ;
338/32.R |
International
Class: |
G01R 33/02 20060101
G01R033/02; H01L 43/08 20060101 H01L043/08 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 11, 2006 |
JP |
2006-245420 |
Claims
1. A magnetic detection device comprising: a variable resistance
element having an electrical resistance changed by an external
magnetic field, and a reference resistance element having an
electrical resistance unchanged by the external magnetic field, and
serially connected to the variable resistance element, and applied
with a direct current voltage to detect a midpoint potential
between the variable resistance element and the reference
resistance element, wherein at least one of the variable resistance
element and the reference resistance element is serially connected
to a resistance adjusting unit, including a plurality of serially
connected parallel portions having a plurality of parallel
connected resistance elements that are different from each other in
combined resistance value, and wherein the sum of the combined
resistance values of the resistance adjusting unit is adjusted by
bringing any one of the resistance elements into a non-conduction
state.
2. The magnetic detection device according to claim 1, wherein the
resistance adjusting unit includes a plurality of resistive layers
extending parallel to each other and connected to each other by
conductive layers at a plurality of positions, and portions of the
resistive layers sandwiched between an adjacent pair of the
conductive layers form the resistance elements forming one of the
parallel portions, wherein the parallel portions differ from each
other in combined resistance value by differently setting intervals
between the conductive layers, and wherein the sum of the combined
resistance values of the resistance adjusting unit is adjusted by
disconnecting the resistance element at a position between the
adjacent pair of the conductive layers.
3. The magnetic detection device according to claim 2, wherein the
variable resistance element is a magnetoresistance effect element,
and each of the resistive layers forming the resistance adjusting
unit is formed of the same film materials as film materials forming
the magnetoresistance effect element, and a lamination order of the
film materials is configured to prevent the resistance value
thereof from being changed by the external magnetic field.
4. The magnetic detection device according to claim 1, wherein each
of the parallel portions is configured such that the plurality of
the resistance elements are the same in resistance value, and the
combined resistance value thereof is increased in a phased manner
in the serial direction of the resistance adjusting unit.
5. The magnetic detection device according to claim 4, wherein the
combined resistance value of one of a pair of the parallel portions
adjacent to each other in the serial direction is twice as great as
the combined resistance value of the other one of the pair.
Description
[0001] This patent document claims the benefit of Japanese Patent
Application No. 2006-245420 filed on Sep. 11, 2006, which is hereby
incorporated by reference.
BACKGROUND
[0002] 1. Field
[0003] The present embodiments relate to a magnetic detection
device for detecting an external magnetic field by detecting a
change of the resistance value of the device, and in particular, an
object of the present invention is to provide a magnetic detection
device having highly accurate magnetic detection by adjusting the
resistance value.
[0004] 2. Description of the Related Art
[0005] Usually, to detect a change of an external environment by
using a variable resistance element whose resistance value is
changed by the external environment, the variable resistance
element is connected in series to a reference resistance element
whose resistance value does not change, and the thus serially
connected variable resistance element and reference resistance
element are subjected to a direct current voltage. Then, a midpoint
potential between the variable resistance element and the reference
resistance element is detected. Thereby, the change of the
resistance value of the variable resistance element can be
accurately detected without being affected by the environmental
temperature.
[0006] In this type of magnetic detection device, it is necessary
to adjust the midpoint potential between the variable resistance
element and the reference resistance element by adjusting the
resistance value of the reference resistance element. The midpoint
potential is preferably set to be one half the value of a power
supply voltage.
[0007] As described in Japanese Unexamined Patent Application
Publication Nos. 2001-35702 and 2001-44001, a conventional method
of adjusting the resistance value is performed by forming a
resistance element on a substrate and thereafter removing a part of
the resistance element through trimming.
[0008] In the resistance value adjusting method described in the
above publications, resistive films formed into square frames are
partially removed. However, the resistive films positioned on the
respective sides of each of the squares all have the same
resistance value. Thus, when any one of the resistive films is
trimmed, the amount of change of the overall resistance value is
small. It is therefore difficult to obtain a wide adjustment range
of the resistance value.
[0009] Further, to obtain the wide adjustment range of the
resistance value, it is necessary to provide a large number of the
square frames formed by the resistive films, as described in
Japanese Unexamined Patent Application Publication No. 2001-44001.
Furthermore, to trim the resistive films, it is necessary to
calculate the positions of the resistive films to be removed by
using a complicated formula. As a result, the structure of the
resistive films for adjusting the resistance value becomes
complicated, and the adjustment operation of the resistance value
also becomes complicated.
SUMMARY
[0010] In light of the above-described problems associated with
conventional techniques, it is an object of the present invention
to provide a magnetic detection device capable of obtaining a wide
adjustment range of the resistance value and permitting easy
adjustment of the resistance value.
[0011] The present invention provides a magnetic detection device
in which a variable resistance element having an electrical
resistance changed by an external magnetic field and a reference
resistance element having an electrical resistance not changed by
the external magnetic field, are serially connected to each other
and applied with a direct current voltage to detect a midpoint
potential between the variable resistance element and the reference
resistance element. In the magnetic detection device, at least one
of the variable resistance element and the reference resistance
element are serially connected to a resistance adjusting unit
including a plurality of serially connected parallel portions, each
of which includes a plurality of parallel connected resistance
elements, and which are different from one another in combined
resistance value. The sum of the combined resistance values of the
resistance adjusting unit is adjusted by bringing any one of the
resistance elements into a non-conduction state.
[0012] In the magnetic detection device according to the present
invention, the plurality of the parallel portions are connected in
series and are different from one another in combined resistance
value. Therefore, the sum of the combined resistance values of the
resistance adjusting unit can be changed in a wide adjustment range
by selecting a resistance element of any one of the parallel
portions and bringing the resistance element into a non-conduction
state.
[0013] In a later-described embodiment of the present invention,
two resistance elements are connected in parallel in each of the
parallel portions. Alternatively, three or more resistance elements
may be connected in parallel in each of the parallel portions. In
this case, it is possible to perform such an adjustment that the
resistance elements included in one parallel portion excluding one
of the resistance elements are all brought into the non-conduction
state.
[0014] In the present invention, it is preferable, for example,
that the resistance adjusting unit includes a plurality of
resistive layers extending parallel to one another and connected to
one another by conductive layers at a plurality of positions, and
that parts of the resistive layers sandwiched by an adjacent pair
of the conductive layers form the resistance elements forming one
of the parallel portions. It is preferable that the parallel
portions are made different from one another in combined resistance
value by differently setting intervals between the conductive
layers, and that the sum of the combined resistance values of the
resistance adjusting unit is adjusted by disconnecting the
resistance element at a position between the adjacent pair of the
conductive layers.
[0015] In the above-described configuration, the resistance
adjusting unit can be easily formed by forming the resistive layers
extending parallel to one another and by establishing conduction
between the resistive layers at the plurality of positions by using
the plurality of the conductive layers. Further, the combined
resistance values of the respective parallel portions can be
individually set by varying the intervals between the conductive
layers.
[0016] In the present invention, it is preferable, for example,
that the variable resistance element is a magnetoresistance effect
element, and that each of the resistive layers forming the
resistance adjusting unit is formed by the same film materials as
film materials forming the magnetoresistance effect element, and is
determined in lamination order of the film materials to prevent the
resistance value thereof from being changed by the external
magnetic field.
[0017] If the resistance adjusting unit is formed by the same
materials as the materials forming the variable resistance element,
it is possible to equalize a characteristic change caused by a
temperature change between the resistance elements of the
resistance adjusting unit and the variable resistance element.
[0018] In the present invention, it is preferable, for example,
that each of the parallel portions is configured such that the
plurality of the resistance elements included therein are the same
in resistance value, and that the combined resistance value thereof
is increased in a phased manner in the serial direction of the
resistance adjusting unit. Thus configured, the degree of
adjustment can be accurately recognized in the adjustment of the
resistance value of the resistance adjusting unit.
[0019] In the above case, it is preferable in the present invention
that the combined resistance value of one of a pair of the parallel
portions adjacent to each other in the serial direction is twice as
great as the combined resistance value of the other one of the
pair. With the combined resistance value thus set to be doubled
from one of the adjacent pair of the parallel portions to the other
one of the pair, the adjustment range of the resistance value
adjusted by the resistance adjusting unit can be increased by
bringing any one of the resistance elements into the non-conduction
state. Further, the resistance value changed by the adjustment can
be accurately recognized.
[0020] According to the present invention, the resistance value can
be easily adjusted, and a wide adjustment range of the resistance
value can be obtained. Accordingly, a good balance can be set
between the resistance value of the variable resistance element and
the resistance value of the reference resistance element connected
in series to the variable resistance element.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a plan view illustrating a magnetic detection
device according to an embodiment of the present invention;
[0022] FIG. 2A is a cross-sectional view of a variable resistance
element;
[0023] FIG. 2B is a cross-sectional view of a reference resistance
element;
[0024] FIG. 3 is a circuit diagram of the magnetic detection
device;
[0025] FIG. 4 is a circuit diagram illustrating a resistance
adjusting unit; and
[0026] FIG. 5 is an explanatory diagram illustrating adjustment
phases and adjustment ranges of the resistance adjusting unit.
DETAILED DESCRIPTION
[0027] FIG. 1 is a plan view of a magnetic detection device
according to an embodiment of the present invention. FIG. 2A is a
cross-sectional view of a variable resistance element, and FIG. 2B
is a cross-sectional view of a reference resistance element. FIG. 3
is a circuit diagram of the magnetic detection device shown in FIG.
1. FIG. 4 is a circuit diagram illustrating details of a resistance
adjusting unit.
[0028] A magnetic detection device 1 is formed on a surface of a
substrate 2 by a thin film process. As illustrated in the circuit
diagram of FIG. 3, the magnetic detection device 1 includes a first
resistance adjusting unit 3, a first reference resistance element
4, a first variable resistance element 5, a second variable
resistance element 6, a second reference resistance element 7, and
a second resistance adjusting unit 8.
[0029] As illustrated in FIG. 1, the surface of the substrate 2 is
provided with a power supply terminal 11. The power supply terminal
11 is connected to one end of the first resistance adjusting unit 3
via a lead layer 12a and to one end of the second variable
resistance element 6 via a lead layer 12b.
[0030] The first resistance adjusting unit 3, the first reference
resistance element 4, and the first variable resistance element 5
are connected in series, and the other end of the first variable
resistance element 5 is connected to an earth terminal 13.
Meanwhile, the second variable resistance element 6, the second
reference resistance element 7, and the second resistance adjusting
unit 8 are connected in series, and the other end of the second
resistance adjusting unit 8 is connected to the earth terminal 13.
Further, a connection midpoint between the first reference
resistance element 4 and the first variable resistance element 5 is
connected to a first output terminal 14. Meanwhile, a connection
midpoint between the second variable resistance element 6 and the
second reference resistance element 7 is connected to a second
output terminal 15.
[0031] FIG. 2A is the cross-sectional view illustrating the first
variable resistance element 5 and the second variable resistance
element 6 cut along a plane extending in the directions of X1 and
X2. The first variable resistance element 5 and the second variable
resistance element 6 are the same in lamination structure.
[0032] Each of the first variable resistance element 5 and the
second variable resistance element 6 is a magnetoresistance effect
element using the giant magnetoresistance effect. The
magnetoresistance effect element is formed into a film, with an
antiferromagnetic layer 21, a fixed magnetic layer 22, a
nonmagnetic conductive layer 23, and a free magnetic layer 24
laminated on the substrate 2, in this order. A surface of the free
magnetic layer 24 is covered by a protective layer 25.
[0033] The antiferromagnetic layer 21 is formed of an
antiferromagnetic material such as an Ir--Mn alloy (an
iridium-manganese alloy). The fixed magnetic layer 22 is formed of
a soft magnetic material such as a Co--Fe alloy (a cobalt-iron
alloy). The nonmagnetic conductive layer 23 is formed of Cu
(copper), for example. The free magnetic layer 24 is formed of a
soft magnetic material such as a Ni--Fe alloy (a nickel-iron
alloy). The protective layer 25 is a layer formed of Ta
(tantalum).
[0034] In each of the first variable resistance element 5 and the
second variable resistance element 6, the magnetization direction
of the fixed magnetic layer 22 is fixed due to the
antiferromagnetic coupling between the antiferromagnetic layer 21
and the fixed magnetic layer 22. In the present embodiment, the
magnetization direction of the fixed magnetic layer 22 is directed
and fixed in the direction of X2. Further, the fixed magnetic layer
22 and the free magnetic layer 24 are magnetically coupled to each
other with the interposition of the nonmagnetic conductive layer
23. Thus, when there is no action by an external magnetic field,
the magnetization direction of the free magnetic layer 24 is
directed and stabilized in the direction of X2.
[0035] As illustrated in FIG. 1, each of the first variable
resistance element 5 and the second variable resistance element 6
has an elongated shape, and the width-to-length aspect ratio of the
element is 1 to approximately 50 to 120. Further, the planar
pattern of each of the first variable resistance element 5 and the
second variable resistance element 6 is in a meandering or
serpentine shape, and the most part of the planar pattern extends
in the directions of Y1 and Y2, i.e., the directions perpendicular
to the fixing direction of the magnetization of the fixed magnetic
layer 22. Since each of the first variable resistance element 5 and
the second variable resistance element 6 has the elongated shape
extending mainly in the directions of Y1 and Y2, the base
resistance value of the element is set to be high.
[0036] In each of the first variable resistance element 5 and the
second variable resistance element 6, when there is no action by
the external magnetic field, the fixing direction of the
magnetization of the fixed magnetic layer 22 and the magnetization
direction of the free magnetic layer 24 both correspond to the
direction of X2. Therefore, the electrical resistance value of the
element is minimized. If a magnet or the like approaches in the
direction of X1 to provide the magnetic detection device 1 with a
magnetic field directed in the direction of X1, and if the strength
of the magnetic field is increased to a predetermined amount, the
magnetization direction of the free magnetic layer 24 is directed
to the direction of X1. In this case, the fixing direction of the
magnetization of the fixed magnetic layer 22 corresponds to the
direction of X2, and thus the electrical resistance value of each
of the first variable resistance element 5 and the second variable
resistance element 6 is maximized.
[0037] FIG. 2B is the cross-sectional view illustrating the first
reference resistance element 4 and the second reference resistance
element 7 cut along a plane extending in the directions of X1 and
X2. The first reference resistance element 4 and the second
reference resistance element 7 are the same in lamination
structure. Similar to the first variable resistance element 5 and
the second variable resistance element 6, the first reference
resistance element 4 and the second reference resistance element 7
have a multilayer structure. The first reference resistance element
4 and the second reference resistance element 7 are the same as the
first variable resistance element 5 and the second variable
resistance element 6 in terms of materials and thicknesses of the
respective layers forming the elements. However, the lamination
order of the nonmagnetic conductive layer 23 and the free magnetic
layer 24 is opposite between the first and second reference
resistance elements 4 and 7 and the first and second variable
resistance elements 5 and 6. In the layer structure of each of the
reference resistance elements 4 and 7, the antiferromagnetic layer
21, the fixed magnetic layer 22, the free magnetic layer 24, the
nonmagnetic conductive layer 23, and the protective layer 25 are
laminated in this order from the side of the substrate 2.
[0038] The films of the reference resistance elements 4 and 7 and
the variable resistance elements 5 and 6 are formed on the same
substrate 2. Thus, the magnetization direction of the fixed
magnetic layer 22 included in each of the reference resistance
elements 4 and 7 illustrated in FIG. 2B is fixed in the direction
of X2, in a similar manner as in the variable resistance elements 5
and 6 illustrated in FIG. 2A. In each of the reference resistance
elements 4 and 7, however, the free magnetic layer 24 is directly
superimposed on the fixed magnetic layer 22. Thus, even if the
element is acted upon by the external magnetic field, the overall
resistance value of the element does not change.
[0039] Further, the reference resistance elements 4 and 7 are the
same as the variable resistance elements 5 and 6 in layer structure
and film thickness. Therefore, a characteristic change caused by an
ambient temperature change or the like can be made equal between
the reference resistance elements 4 and 7 and the variable
resistance elements 5 and 6.
[0040] The first resistance adjusting unit 3 and the second
resistance adjusting unit 8 are the same in structure and planer
pattern shape. The first resistance adjusting unit 3 is provided
between a leading end 4a of the first reference resistance element
4 and a basal end 12a1 of the lead layer 12a, while the second
resistance adjusting unit 8 is provided between a leading end 7a of
the second reference resistance element 7 and a basal end 13a of
the earth terminal 13.
[0041] The first resistance adjusting unit 3 and the second
resistance adjusting unit 8 are the same in structure. Thus, only
of the first resistance adjusting unit 3 is described below, and
description of the second resistance adjusting unit 8 will be
omitted. The components of the second resistance adjusting unit 8
will be denoted with the same reference numerals as the reference
numerals used to denote the components of the first resistance
adjusting unit 3.
[0042] The first resistance adjusting unit 3 includes a first
resistive layer 31 and a second resistive layer 32, which extend
parallel to each other. The first resistive layer 31 and the second
resistive layer 32 are the same in width, thickness, and overall
length. The first resistance adjusting unit 3 is the same in
lamination structure as the first reference resistance element 4
and the second reference resistance element 7 illustrated in FIG.
2B. Further, the respective layers forming the first resistance
adjusting unit 3 are the same in thickness as the respective layers
forming each of the first reference resistance element 4 and the
second reference resistance element 7.
[0043] As illustrated in FIG. 1, the first resistance adjusting
unit 3 includes conductive layers 33a, 33b, 33c, 33d, 33e, 33f, and
33g to establish conduction between the first resistive layer 31
and the second resistive layer 32. The conductive layers 33a, 33b,
33c, 33d, 33e, 33f, and 33g are formed of conductive ink or the
like containing copper, silver, gold, or conductive filler
including silver or gold. The specific resistance of the conductive
layers 33a, 33b, 33c, 33d, 33e, 33f, and 33g is substantially lower
than the average specific resistance of the first resistive layer
31 and the second resistive layer 32. Further, the power supply
terminal 11, the lead layers 12a and 12b, the earth terminal 13,
the first output terminal 14, and the second output terminal 15 are
also formed of a conductive material having a substantially low
specific resistance. The conductive layers 33a, 33b, 33c, 33d, 33e,
33f, and 33g may be formed of the same conductive material as the
conductive material forming the respective terminals 11, 13, 14,
and 15 and the lead layers 12a and 12b.
[0044] As illustrated in FIG. 3, between the conductive layers 33a
and 33b, a resistance element R1 is formed by a part of the first
resistive layer 31, and another resistance element R1 is formed by
a part of the second resistive layer 32. That is, a parallel
portion including the parallel connected resistance elements R1 and
R1 is formed between the conductive layers 33a and 33b. Further,
between the conductive layers 33b and 33c, resistance elements R2
and R2 are formed by the first resistive layer 31 and the second
resistive layer 32, respectively, and the mutually parallel
resistance elements R2 and R2 form another parallel portion.
[0045] In a similar manner, a parallel portion including parallel
connected resistance elements R3 and R3 is formed between the
conductive layers 33c and 33d, and a parallel portion including
parallel connected resistance elements R4 and R4 is formed between
the conductive layers 33d and 33e. Further, a parallel portion
including parallel connected resistance elements R5 and R5 is
formed between the conductive layers 33e and 33f, and a parallel
portion including parallel connected resistance elements R6 and R6
is formed between the conductive layers 33f and 33g. In the first
resistance adjusting unit 3, the respective parallel portions from
the parallel portion including the resistance elements R1 and R1 to
the parallel portion including the resistance elements R6 and R6
are connected in series.
[0046] Each pair of the resistance elements R1 and R1 to R6 and R6
is formed by a part of the first resistive layer 31 and a part of
the second resistive layer 32, which have the same width and film
thickness. Thus, the resistance elements R1 and R1 forming the same
parallel portion have the same resistance value. Similarly, the
resistance value is the same between the two resistance elements
forming each of the parallel portions, i.e., between the resistance
elements R2 and R2, between the resistance elements R3 and R3,
between the resistance elements R4 and R4, between the resistance
elements R5 and R5, and between the resistance elements R6 and
R6.
[0047] Further, the above-described conductive layers for
establishing conduction between the first resistive layer 31 and
the second resistive layer 32 are disposed at different intervals.
The interval between the conductive layers 33b and 33c is twice as
long as the interval between the conductive layers 33a and 33b.
Further, the interval between the conductive layers 33c and 33d is
twice as long as the interval between the conductive layers 33b and
33c. Similarly, the interval between the conductive layers 33e and
33f is twice as long as the interval between the conductive layers
33d and 33e.
[0048] As a result, the resistance value of the resistance element
R2 is twice as great as the resistance value of the resistance
element R1. Further, the resistance value of the resistance element
R3 is twice as great as the resistance value of the resistance
element R2, and the resistance value of the resistance element R4
is twice as great as the resistance value of the resistance element
R3. Furthermore, the resistance value of the resistance element R5
is twice as great as the resistance value of the resistance element
R4, and the resistance value of the resistance element R6 is twice
as great as the resistance value of the resistance element R5.
[0049] FIG. 4 illustrates a circuit configuration of the first
resistance adjusting unit 3. In the present embodiment, the
resistance values of the resistance elements R1, R2, R3, R4, R5,
and R6 are 10.OMEGA., 20.OMEGA., 40.OMEGA., 80.OMEGA., 160.OMEGA.,
and 320.OMEGA., respectively. Therefore, the combined resistance of
the parallel portion including the resistance elements R1 and R1 is
5.OMEGA., and the combined resistance of the parallel portion
including the resistance elements R2 and R1 is 10.OMEGA.. Further,
the combined resistance of the parallel portion including the
resistance elements R3 and R3 is 20.OMEGA., and the combined
resistance of the parallel portion including the resistance
elements R4 and R4 is 40.OMEGA.. Furthermore, the combined
resistance of the parallel portion including the resistance
elements R5 and R5 is 80.OMEGA., and the combined resistance of the
parallel portion including the resistance elements R6 and R6 is
160.OMEGA.. That is, the combined resistance is sequentially
doubled from one to the next of the parallel portions in the serial
direction.
[0050] As illustrated in FIG. 3, the second resistance adjusting
unit 8 is the same as the first resistance adjusting unit 3 in the
configuration of the resistance elements R1 to R6.
[0051] In the present magnetic detection device 1, a positive
potential is supplied from a power supply to the power supply
terminal 11, and the earth terminal 13 is grounded. When the
magnetic detection device 1 is not approached by a magnetic field,
the resistance value of the first variable resistance element 5 and
the resistance value of the second variable resistance element 6
are both at the lowest value. In this case, a midpoint potential
obtained from the output terminal 14 is minimized, while a midpoint
potential obtained from the output terminal 15 is maximized.
[0052] If the magnetic detection device 1 is approached by a
magnet, and thus if the magnetic field directed in the direction of
X1 is increased, the direction of the magnetic field of the free
magnetic layer 24 included in each of the first variable resistance
element 5 and the second variable resistance element 6 is directed
in the direction of X1. Thus, the resistance value of the first
variable resistance element 5 and the resistance value of the
second variable resistance element 6 are maximized. As a result,
the midpoint potential of the output terminal 14 and the midpoint
potential of the output terminal 15 are both maximized. If the
difference between the potential of the output terminal 15 and the
potential of the output terminal 14 is taken by using a
differential amplifier, for example, a detection output of a wide
variation range can be obtained. When the output from the
differential amplifier exceeds a predetermined threshold value, the
approach of the magnet can be detected.
[0053] To keep the change of the potential output from the output
terminal 14 and the change of the potential output from the output
terminal 15 within a predetermined standard range in consideration
of the relationship of the changes with the threshold value, it is
necessary to appropriately adjust the balance between the
resistance value of the first variable resistance element 5 and the
resistance value of the fixed resistor connected in series to the
first variable resistance element 5. When there is no action by the
external magnetic field, for example, if the potential of each of
the output terminals 14 and 15 is set to be one half a power supply
voltage, the output from the differential amplifier can be made
zero when there is no action by the external magnetic field.
[0054] In the present magnetic detection device 1, the potential
output from the output terminal 14 can be adjusted by adjusting the
resistance value of the first resistance adjusting unit 3. Further,
the potential output from the output terminal 15 can be adjusted by
adjusting the resistance value of the second resistance adjusting
unit 8.
[0055] The resistance value of each of the first variable
resistance element 5 and the second variable resistance element 6
is approximately 1 k.OMEGA. to 3 k.OMEGA. when no magnetic field is
provided. The variation of the resistance value is approximately
.+-.10%. In the present embodiment, the design value of the
resistance value of each of the first variable resistance element 5
and the second variable resistance element 6 is 2 k.OMEGA. when no
magnetic field is provided, and the variation of the resistance
value is approximately .+-.200.OMEGA.. Further, the resistance
value of each of the first reference resistance element 4 and the
second reference resistance element 7 is set to be approximately
1.5 k.OMEGA..
[0056] In the state as illustrated in FIG. 1 in which the films of
the first resistance adjusting unit 3 and the second resistance
adjusting unit 8 are not trimmed, the sum of the combined
resistance values of each of the resistance adjusting units is
315.OMEGA.. Further, the maximum adjustment range of each of the
first resistance adjusting unit 3 and the second resistance
adjusting unit 8 is 315.OMEGA.. Therefore, the design value of the
combined resistance value of the first reference resistance element
4 and the first resistance adjusting unit 3 is 1815 to 2130.OMEGA..
Similarly, the design value of the combined resistance value of the
second reference resistance element 7 and the second resistance
adjusting unit 8 is 1815 to 2130.OMEGA.. In addition, each of the
first resistance adjusting unit 3 and the second resistance
adjusting unit 8 can change the resistance value thereof by the
unit of 5.OMEGA..
[0057] In this manner, it is possible to obtain a wide adjustment
range of the resistance values in each of the first reference
resistance element 4 and the second reference resistance element 7.
Further, when there is no action by the magnetic filed, the voltage
output from each of the output terminals 14 and 15 can be easily
adjusted to one half the power supply voltage, for example, by
adjusting the resistance value by the unit of 5.OMEGA..
[0058] FIG. 5 shows, in a table, adjustment amounts of the
resistance value in each of the first resistance adjusting unit 3
and the second resistance adjusting unit 8.
[0059] The leftmost column of FIG. 5 indicates the adjustment
amounts of the resistance value in each of the first resistance
adjusting unit 3 and the second resistance adjusting unit 8. For
example, the adjustment amount is 5.OMEGA. in the uppermost row of
the table. This means that the resistance value is increased by
5.OMEGA.. Meanwhile, the adjustment amount is 315.OMEGA. in the
lowermost row of the table. This means that the resistance value is
increased by 315.OMEGA.. Further, the mark ".largecircle."
appearing in the table indicates that a resistance element forming
a parallel portion is brought into the non-conduction state. That
is, the uppermost row of the table indicates that only one of the
resistance elements R1 and R1 forming a parallel portion is brought
into the non-conduction state. Meanwhile, the lowermost row of the
table indicates that one of the resistance elements R1 and R1, one
of the resistance elements R2 and R2, one of the resistance
elements R3 and R3, one of the resistance elements R4 and R4, one
of the resistance elements R5 and R5, and one of the resistance
elements R6 and R6, which form the respective parallel portions,
are brought in the non-conduction state.
[0060] As illustrated in FIG. 5, if only one of the resistance
elements R1 and R1 forming a parallel portion is brought into the
non-conduction state, for example, the resistance value of the
first resistance adjusting unit 3 or the second resistance
adjusting unit 8 can be increased by 5.OMEGA.. Further, if one of
the resistance elements R1 and R1, one of the resistance elements
R2 and R2, and one of the resistance elements R3 and R3 are
respectively brought into the non-conduction state, the resistance
value can be increased by 35.OMEGA.. Furthermore, as in the
lowermost row, if one of the resistance elements R1 and R1, one of
the resistance elements R2 and R2, one of the resistance elements
R3 and R3, one of the resistance elements R4 and R4, one of the
resistance elements R5 and R5, and one of the resistance elements
R6 and R6 are brought in the non-conduction state, the resistance
value can be increased by 315.OMEGA..
[0061] In this manner, the resistance value can be changed by the
unit of 5.OMEGA. by bringing only one of the resistance elements
included in each of the parallel portions into the non-conduction
state and by combining the resistance elements to be brought into
the non-conduction state.
[0062] One of the resistance elements R1 and R1 can be brought into
the non-conduction state by cutting off either one of the first
resistive layer 31 and the second resistive layer 32 between the
conductive layers 33a and 33b, for example. The same applies to the
cases of the other resistance elements R2 and R2 to R6 and R6.
[0063] The method of cutting off either one of the first resistive
layer 31 and the second resistive layer 32 includes cutoff using
laser light, cutoff by milling, and cutoff by a photolithographic
method, for example. Generally, the magnetic detection device 1
illustrated in FIG. 1 is obtained by forming a plurality of the
magnetic detection devices 1 of thin films on a common substrate
and thereafter cutting the thus formed devices into individual
pieces. Thus, the magnetic detection devices 1 formed in the same
area on the same substrate have very similar characteristics.
Therefore, after monitoring one of the magnetic detection devices 1
formed on the same substrate and then determining which one of the
resistance elements should be cut off, the adjustment operation of
adjusting the resistance value can be performed in a single process
on the plurality of the magnetic detection devices 1 according to
any one of the above-described methods.
[0064] Alternatively, as the method of bringing one of the
resistance elements R1 and R1 into the non-conduction state, the
conductive layers 33a and 33b may be formed to be connected to each
other on a surface of either one of the first resistive layer 31
and the second resistive layer 32, for example.
[0065] Further, the first resistance adjusting unit 3 may be
disposed between the earth terminal 13 and the output terminal 14,
instead of being disposed at the position shown in FIG. 3.
Alternatively, the first resistance adjusting unit 3 may be
provided both at the position shown in FIG. 3 and between the earth
terminal 13 and the output terminal 14. Similarly, the second
resistance adjusting unit 8 may be disposed between the power
supply terminal 11 and the output terminal 15, instead of being
disposed at the position shown in FIG. 3. Alternatively, the second
resistance adjusting unit 8 may be provided both at the position
shown in FIG. 3 and between the power supply terminal 11 and the
output terminal 15.
* * * * *