JP2000180524A - Magnetic field sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly sensitive and compact magnetic field sensor in which mass-productivity is satisfactory and offset is small. SOLUTION: This magnetic sensor 1 is provided with plural magnetic resistance effect elements 11-14 arrayed with prescribed intervals and plural bias magnets 21 and 25 arranged with prescribed intervals corresponding to those magnetic resistance effect elements 11-14. The plural bias magnets 21 and 25 are constituted two kinds of magnet bodies whose coercive forces are substantially different, and those two kinds of magnet bodies are arranged with the prescribed intervals along the arraying direction of those magnetic resistance effect elements 11-14 so that the absolute values of bias magnetic fields to be impressed to the plural magnetic resistance effect elements 11-14 can be made substantially equal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a magnitude of a current flowing in a circuit for monitoring a remaining amount of a battery of an electric vehicle and detecting a signal magnetic field from a magnetized body used in a rotary encoder, a linear scale and the like. On the other hand, the present invention relates to a magnetic field sensor having linearity capable of detecting a magnetic field regardless of a phase difference.

[0002]

2. Description of the Related Art In recent years, the magnitude of current flowing in a circuit for monitoring the remaining battery level of an electric vehicle has been detected,
A small and inexpensive magnetic field sensor having linearity capable of detecting a magnetic field regardless of a phase difference with respect to a signal magnetic field from a magnetized body used for a rotary encoder, a linear scale, and the like is required.

In general, when a DC magnetic field is detected with good linearity, a magnetic field sensor using the Hall effect is used. However, the sensitivity of the Hall element is as low as 5 mV / 100 Oe. It is suitable for detecting a magnetic field, but it is difficult to detect a magnetic field smaller than that.

On the other hand, a ferromagnetic magnetoresistive element measures a magnetic field strength by using a phenomenon (magnetic resistance effect, MR effect) in which the electric resistance of a ferromagnetic metal changes due to an external magnetic field. For the single-layer film, the magnetic anisotropic magnetoresistance effect (hereinafter simply referred to as the AMR effect) of a ferromagnetic metal film which has been known for a long time has been used, but recently, for example, Japanese Patent Application Laid-Open No. 5-259530
As disclosed in Japanese Patent Application Laid-Open Publication No. H11-207, a sensor using a coupled giant magnetoresistance effect (GMR effect) using a film having a multilayer structure has been developed.

In a magnetic field sensor using a magnetic film exhibiting the GMR effect, the resistance change of the GMR element does not depend on the direction of the magnetic field in the film plane, but is determined only by the absolute value. Further, the resistance change with respect to the magnetic field change is not linear in the element itself. Therefore, IEEE Trans. Mag. (30) 4608-4610 (1994)
Ya, Sensors and Actuators A (59) 30-37 (1997)
In general, a GMR element is bridged, and a magnetic field sensor that responds linearly to a change in the magnetic field is formed by applying a bias magnetic field in the opposite direction to the paired GMR element, as shown in FIG. ing. These techniques are already well known, and for reference, FIG. 6 shows an equivalent circuit when four GMR elements are bridge-connected, and a magnetoresistance curve of each GMR element with a bias applied. . FIG. 7 shows an output waveform in the case of bridge connection. The hatched portion in FIG. 7 shows an actual operating area used when detecting a DC magnetic field.

[0006]

The prior art described above,
IEEE Trans. Mag. (30) 4608-4610 (1994) states:
Means for using one permanent magnet (bias magnet) and applying bias magnetic fields in opposite directions outwardly directed from the center of two pairs of four bridge-connected GMR elements are disclosed. .

However, in the above-mentioned means, one bias magnet is provided at the most appropriate position with respect to the bridge-connected GMR element so that the offset value (ideally, preferably zero) and the resistance become desired values. There is a problem that it is necessary to arrange the magnets and it takes time to adjust the position of the magnet. Further, in this method, it is considered that four magnetic resistance elements cannot be arranged in the region inside the bias magnet, and it can be said that it is difficult to reduce the size of the magnetic field sensor itself.

[0008] Sensors and
In Actuators A (59) 30-37 (1997), as shown in FIG. 11 and the like in the literature, a magnet of a hard magnetic film made of cobalt platinum was stuck on a GMR element with an ultraviolet curing resin, Has been proposed. In this document, a hard magnetic film of cobalt platinum and GM
The R element is not formed on the same substrate. If, for example,
Even if the hard magnetic film made of cobalt platinum is formed on the back surface of the substrate on which the GMR element is formed, and the time of the attaching process and the position adjustment can be saved, the cobalt platinum magnetic film thus formed is formed. Is not uniform as shown in FIGS. 7 and 12 of the document. That is, a bias magnetic field is applied to the magnetoresistive element immediately below the magnetized hard magnetic film, and a bias magnetic field is applied to the magnetoresistive element placed between the magnetized hard magnetic film and the hard magnetic film. The bias magnetic fields are very different. As a result, since a uniform bias magnetic field is not applied to the four magnetoresistive elements, there is a problem that the offset value deviates from zero. In general, it is difficult to correct the offset even by using an electronic circuit having functions such as amplification and temperature compensation. Therefore, it is desirable to make the offset as small as possible at the stage of manufacturing the element. Also, since the magnetic field distribution directly below the hard magnetic film and the magnetic field distribution between the hard magnetic films introduced in the above-mentioned literature have a very strong correlation, if the magnetic field distribution immediately below the hard magnetic film changes, the magnetic field distribution between the hard magnetic films becomes complicated. Change. Therefore, there is also a problem that complicated simulations and the like must be performed to calculate the optimum magnet width and magnet thickness.

The present invention has been made in view of such circumstances, and its object is to arrange two types of magnet bodies having substantially different coercive forces in a predetermined manner so as to function as a bias magnet. , Good mass productivity, small offset,
An object of the present invention is to realize a highly sensitive and small magnetic field sensor.

[0010]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention has a plurality of magnetoresistive elements arranged at predetermined intervals, and corresponds to these magnetoresistive elements. A magnetic field sensor having a plurality of bias magnets arranged at predetermined intervals in the magnetic field sensor, wherein the plurality of bias magnets are composed of two types of magnets having substantially different coercive forces. Are arranged at predetermined intervals along the arrangement direction of the magnetoresistive elements, and are arranged such that the absolute values of the bias magnetic fields applied to the plurality of magnetoresistive elements are substantially equal. It is composed of

In the present invention, two kinds of magnet bodies are alternately arranged along the arrangement direction of the magnetoresistive elements so that the bias magnetic fields exerted on adjacent magnetoresistive elements are in opposite directions. It is configured to be.

Further, in the present invention, the plurality of bias magnets are arranged such that the first magnets are oriented in an arbitrary direction in the arrangement direction of the two magnet bodies so that the magnetizing directions of the two magnet bodies are the same. A magnetizing operation is performed, and then a second magnetizing operation is performed in a direction opposite to the arbitrary direction so that only the magnet body having a small coercive force reverses magnetization.

In a preferred aspect of the present invention, the arrangement pitch D of the plurality of magnetoresistance effect elements and the arrangement pitch P of the plurality of bias magnets are the same, and the magnetoresistance effect element and the bias magnet are substantially Are arranged in the same positional relationship.

In a preferred aspect of the present invention, the difference between the coercive forces of the two types of magnets is 200 Oe or more.

In a preferred embodiment of the present invention, 4n
(N: positive integer) number of magnetoresistive elements are provided, and these magnetoresistive elements are bridge-connected.

In a preferred aspect of the present invention, the magnetoresistance effect element is formed from a magnetic film exhibiting a giant magnetoresistance effect.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a plan view of a magnetic field sensor 1 of the present invention, and FIG. 2 is a sectional view taken along the line AA of FIG. In FIG. 1, the substrate 5 and the insulating film 8 are omitted in the drawing for easy understanding of the invention. As shown in these drawings (particularly, FIG. 2), the magnetic field sensor 1 of the present invention includes a plurality of bias magnets (21, 25) arranged and formed at predetermined intervals on a substrate 5, An insulating film 8 formed to fill these bias magnets (21, 25), and four magnetoresistive elements 11, 12, 13, 14 (effective lengths of the elements) formed on the insulating film 8. Has L; FIG. 1). The four magnetoresistive elements 11, 12, 13, 14 are arranged in a positional relationship corresponding to the plurality of bias magnets (21, 25) as shown in FIG.

In the embodiment of the present invention, the four magnetoresistive elements 11, 12, 13, and 14 are arranged at a predetermined distance D (the distance D between the centers of the elements is a distance between the centers of the elements, as shown). In the example of FIG. 1, they are arranged at regular intervals because they are equally spaced.) The positions of these magnetoresistive elements 11, 12, 13, and 14 are considered as a reference. Then, it can be said that a plurality of bias magnets (21, 25) are arranged and formed in the states of FIGS. 1 and 2 so as to correspond to these magnetoresistive elements 11, 12, 13, and 14.

Although the plurality of bias magnets (21, 25) used in the present invention are collectively referred to as bias magnets, in reality, in a more preferable embodiment, the residual magnetic flux densities are substantially equal, and the coercive force is substantially equal. Are substantially different 2
Kind of magnet body 21 and magnet body 25 are used. Then, these two types of magnet bodies 21 and 25 are separated by a predetermined distance K (FIG. 1).
Are arranged alternately along the arrangement direction (FIG. 2: arrow (α) direction) of the magnetoresistance effect elements. In addition, the width W (FIG. 1) of the magnet body 21 and the magnet body 25 is usually the same constant width, and in the embodiment shown in FIG. 1 and FIG. The arrangement pitch P and the arrangement pitch D of the magnetoresistive elements are the same, and the magnetoresistive elements and the bias magnets are arranged in substantially the same positional relationship.

As shown in FIGS. 1 and 2, the magnet bodies 21 and the magnet bodies 25 arranged alternately are provided for applying a bias magnetic field to the magnetoresistive elements 11, 12, 13, and 14. . In the example of FIG. 1, the magnet bodies 21 and the magnet bodies 25 are arranged alternately so that the bias magnetic fields exerted on the adjacent magnetoresistive elements are opposite to each other with respect to the four magnetoresistive elements. Are set so that the magnetization directions thereof are opposite to each other. In the present invention, after the magnet body 21 and the magnet body 25 are formed in a predetermined pattern using a thin film process, a predetermined magnetization operation is performed so that the magnetization directions are opposite to each other. That is, after film formation, the magnet body 21 and the magnet body 25 that are not magnetized
The first magnetizing operation is performed so that the magnetizing directions of the two types of magnets are the same in any direction of the arrangement direction of the types of magnets, and thereafter, only the magnets having a small coercive force are applied. The second magnetization operation is performed in a direction opposite to the arbitrary direction so that the magnetization is reversed. As a result, the magnets 21 and 25 are finally magnetized as shown in FIGS. The first and second magnetization operations may be performed by using an electromagnet or the like and changing the generated magnetic field.

As described above, in the present invention, two types of magnet bodies 21 and magnet bodies 25 having substantially different coercive forces are used, and these are alternately arranged at a predetermined interval K. Therefore, the magnet bodies 21 and 25 as shown in FIGS. 1 and 2 are magnetized by sequentially performing the first and second magnetizing operations using predetermined two large and small magnetic fields. Moreover, the absolute values of the bias magnetic fields exerted on the respective elements by the magnet body 21 and the magnet body 25 after such a magnetization operation are performed are set to be equal. When the absolute value of the bias magnetic field applied to the element is substantially equal, the difference between the maximum value and the minimum value of the bias magnetic field applied to a plurality of elements in the magnetic field sensor is 30 Oe or less, more preferably 150 Oe or less.
e.

In the case of this embodiment, the bias magnetic field desired in the present invention can be obtained by using the magnet body 21 and the magnet body 25 having substantially the same residual magnetic flux density as one suitable means.

The relationship between the residual magnetic flux density and the coercive force of the two types of magnets 21 and 25 will be described in more detail.
The residual magnetic flux density of the magnet body 21 is Br ₁ , the coercive force is H _c1 , the residual magnetic flux density of the magnet body 25 is Br ₂ , and the coercive force is H _c2.
When (H _c2 <H _c1 ), the coercive forces of the two types of magnets are substantially different, and the difference (H _c1 −H _c2 ) between them is 200 Oe.
Or more, more preferably 400 Oe
Above, more preferably 500 Oe. If the difference (H _c1 −H _c2 ) is less than 200 Oe, the magnet body 25 having the smaller coercive force is magnetized in the opposite direction (the second direction).
The magnetization state of the magnet body 21 having a large coercive force is affected, and the residual magnetic flux density of the magnet body 21 having a large coercive force tends to be slightly smaller than the intended Br ₁ value. In the present invention, as a preferable means for equalizing the absolute value of the bias magnetic field applied to each element, the residual magnetic flux density Br ₁ of the magnet body 21 and the residual magnetic flux density Br ₂ of the magnet body 25 are set to be substantially equal. Have been. The term “substantially equal” means a range where the absolute value of the value of (Br ₁ −Br ₂ ) / (Br ₁ + Br ₂ ) is within 10%, more preferably within 5%. Beyond this range (Br ₁ -Br ₂ )
When the absolute value of the value of / (Br ₁ + Br ₂ ) increases, the offset of the magnetic field sensor increases, which tends to be impractical.

The magnet body 21 and the magnet body 25 are preferably formed in a predetermined pattern by using a thin film process as described above. Moreover, these magnet bodies 21 and 25 need to satisfy the above-mentioned predetermined relationship in relation to the residual magnetic flux density and the coercive force. Co-Pt, Co-Ir, Co-N
i, Co-Rh, Co-Pd, Co-Cr, Co-S
m, a Co alloy such as Co-R (R is a rare earth), Nd-
Fe-B, Fe-R (R is a rare earth), MnAlC and the like. For example, in Co-Pt, Pt is 20
In the composition range of 密度 30 at%, the residual magnetic flux density has an almost constant value of 0.9 T (tesla), and the coercive force is 930 to 1430.
Oe greatly changes. Therefore, for example, if Pt is 20a
Co-Pt of t% and Co-Pt of 30 at% Pt can be used as the thin film magnet material of the magnet body 21 and the magnet body 25, respectively. In the case of Co-Ir, when the composition of Ir becomes 10 at%, the residual magnetic flux density becomes approximately 0.9 T (tesla) and the coercive force becomes 400 Oe. Therefore, as another combination example, Co-Ir with 10 at% Ir and Pt
Can be used as the thin film magnet material of the magnet body 21 and the magnet body 25, respectively. When the residual magnetic flux density is constant, the magnitude of the bias magnetic field applied to the magnetoresistive element is proportional to the thickness of the thin film magnet to some extent. The strength of the bias magnetic field can be adjusted only by the thickness of the magnet.

After forming a film such as cobalt-platinum as a material of the bi-ice magnet, the film itself is coated with 600 μm.
When using a material that requires heat treatment at about ° C, it is important to prevent the characteristics of the magnetoresistive element from deteriorating. Therefore, as shown in FIGS. 1 and 2, after a thin film magnet pattern is formed on a substrate, a predetermined heat treatment is performed, an insulating film is formed thereon, and a magnetoresistive element is formed on the insulating film. It is desirable to form. However, when the thin film magnets (bias magnets (21, 25)) do not require heat treatment at a high temperature, the bias magnets (21, 25) and the magnetoresistive elements 11, 12, 13, in FIG. 14 may be reversed.

FIG. 6 shows an equivalent circuit of four bridge-connected magnetoresistive elements 11, 12, 13, and 14 in the arrangement of the magnetoresistive elements and the bias magnets as shown in FIG. As a result, the opposite bias magnetic fields having the same absolute value and opposite directions are applied to two adjacent elements, so that the resistance change rate is the same as that of one magnetoresistive element. Not only is obtained, but also the output waveform with respect to the external magnetic field becomes linear.

Even when the performance of the two magnets of the magnet body 21 and the magnet body 25, that is, the external magnetic field strengths are different from each other, it is possible to apply a bias magnetic field of the same strength to the element (magnetic sensing part). For example, it can be easily dealt with by changing the distance between the magnet and the element (magnetically sensitive portion), that is, the thickness of the interposed insulating layer.

FIG. 3 shows an example of the use of the magnetic field sensor 1 of the present invention. The magnetic field sensor 1 shown in FIG.
Are installed at a distance of the gap G in order to detect the rotation speed of the rotating magnetized body 300 in a non-contact manner. In this example, the rotating magnetized body 300 has a disk shape, and N-S poles are alternately magnetized on the peripheral side surface as shown in the figure,
The magnetization pitch in this case is indicated by Q. As shown in FIG. 3, when a leakage magnetic field from a detection target having a magnetization pitch Q is detected, in the related art, an interval of Q / 2 (a phase difference of 1) is used.
(80 degrees), the magnetic field sensor must be used for detection, and the magnetic field sensor cannot be made smaller than the order of the magnetization pitch Q. However, by using the magnetic field sensor of the present invention, the magnetoresistive elements can be arranged at intervals smaller than the magnetization pitch of the detection target, that is, the phase difference of Q / 2 of the detection target is built in by the bias magnetic field. Therefore, it is possible to manufacture the magnetic field sensor smaller than the order of the magnetization pitch Q of the object to be detected. As a result, a large number of small magnetic field sensors can be obtained from one wafer without wasting area. be able to.

Furthermore, since thin film magnets having the same residual magnetic flux density are used, the magnetic fields applied to the four elements are equal, and if the four elements have the same shape, the offset voltage is always zero. In a bridge structure as shown in FIG. 6, it is common to read a change in an external magnetic field as a change in a potential difference at a middle point (points B and D) of the bridge circuit. In the case of bridge connection, the number of magnetoresistive elements is 4n (n: a positive integer, usually n = 1).

FIGS. 4 and 5 show an application of the sensor according to the invention. FIG. 4 is a plan view showing this application mode. FIG. 4 shows a magnetic field generating electrode 50 and magnetoresistive elements 11, 12 and
Only 13 and 14 are shown. Also, FIG.
It is -B sectional drawing. The magnetic field sensor 2 shown in FIG. 5 is obtained by further forming an insulating film 9 on the uppermost part of the magnetic field sensor 1 shown in FIG. 2, and on this protective film 9, a magnetic field generating electrode 50 is formed. I have. The magnetic field generating electrode 50 includes a plurality of plate-shaped magnetic field generating portions 55 as shown in FIGS. 4 and 5, and a current I flows through the magnetic field generating portions 55, as shown in FIG. 5. Such magnetic fields 55a are generated and act to cancel the external magnetic field H (the magnetic field directions of the external magnetic field H and the magnetic field 55a are reversed). Then, as shown in FIGS. 4 and 5, the magnetic field generating electrode 50 (magnetic field generating portion 55) acting to cancel the external magnetic field H is connected to the magnetoresistive element 1.
It is also possible to detect the external magnetic field H by providing the magnetic field so that the potential difference at the midpoint of the bridge circuit is always zero, provided on the 1, 12, 13, and 14. That is, the strength of the external magnetic field can be measured from the value of the current flowing through the magnetic field generating electrode 50. Here, the magnetic field generating electrode 50 can be formed from a material such as Cu, Au, Al, or Ag by a vacuum film forming method, an electroplating method, or the like.
When the magnetic field generating electrode 50 is formed, the insulating film 9 made of SiO ₂ or the like is previously formed on the surfaces of the magnetoresistive elements 11, 12, 13, 14 as described above. The magnetic field generating electrodes 50 are formed in a predetermined pattern.

The bias magnetic field will be described in more detail. In the magnetic field sensor according to the present invention, the bi-ice magnets 21 and 25 are arranged along the direction in which the magnetoresistive elements are arranged so that the magnetic poles change. That is, a plane including the direction in which the four magnetoresistive elements 11, 12, 13, and 14 are arranged (FIG. 2; the direction of the arrow (α)) and the direction in which the magnetic poles of the bi-ice magnets 21 and 25 change (FIG. ; Arrow (β)
Directions) are parallel to each other, and the magnetoresistive elements 11, 12, 13, 14 and the bi-ice magnet 2
The distance between 1, 2 and 25 is constant (vertical distance in FIG. 2)
It is arranged so that it becomes.

More specifically, the direction in which the magnetoresistive elements are arranged refers to a direction parallel to a straight line connecting adjacent magnetoresistive elements as shown in FIG. On the other hand, the direction in which the magnetic poles of the bi-ice magnets 21 and 25 change indicates the direction in which the magnetic poles change in the order of S → N → S → N. Bi-ice magnets 21 and
The preferred film forming and magnetizing method of 5 is as described above, but by appropriately selecting a resin and a solvent, a magnetic fluid having high fluidity is applied, which is applied by a spin coater to form a magnetic layer of the base material. It can also be formed directly on top.

The magnetoresistive elements (magnetic films) 11, 12, 13, and 14 for detecting a magnetic field used in the present invention are films having a magnetoresistive effect and have either a single-layer film structure or a multilayer film structure. You may. The magnetoresistance effect refers to a phenomenon in which electric resistance changes due to a change in a magnetic field. The magnetic film constituting the element is a giant magnetoresistive film (GM) which has particularly high detection sensitivity and can greatly change the magnetic field strength to be detected.
R film).

The giant magnetoresistive film is a metal artificial lattice (Hiroshi Fujimori, Agne Technical Center, issued in 1995) 347
As described on the page, it is a multilayer film of a ferromagnetic film and a non-magnetic film, and it is known that the resistance changes due to a change in interface scattering of the multilayer film.

As the giant magnetoresistive film, an antiferro (coupling) type having a (ferromagnetic / non-magnetic conductor) structure,
(High coercivity ferromagnetic / non-magnetic conductor / low coercivity ferromagnetic) Inductive ferri (non-coupling) type, (semi-ferromagnetic /
It is roughly classified into a spin valve type having a (ferromagnetic material / non-magnetic conductor / ferromagnetic material) structure and a non-solid solution type granular type of Co / Ag system.

Each of these giant magnetoresistive films has a detectable magnetic field strength, that is, a saturation magnetic field strength of the magnetoresistive effect, which differs greatly depending on the structure and composition. For example, (F
e / Cr) type antiferro type, 10KOe or more, (C
oNiFe / Cu) antiferro type is 0.1 Oe
To 1 KOe, (NiFe / Cu / Co / Cu) -based ferrielectric ferritypes have about 5 to 20 Oe, (FeMn /
NiFe / Cu / NiFe) spin valve type, several Oe, and granular type from 100 Oe to 5K
Magnetic field detection up to about Oe is possible. The magnetic field sensitivity is obtained by dividing the maximum magnetoresistance change rate by the saturation magnetic field strength. Even if the maximum magnetoresistance change rate is large, the magnetic field sensitivity is poor when the saturation magnetic field is large. Conversely, even if the maximum magnetoresistance ratio is small, the magnetic field sensitivity is good when the saturation magnetic field is very small. For this reason, a basic system is selected from the above-mentioned various giant magnetoresistive films, and further, a composition system is changed and a detailed structure is optimized so that the highest magnetic field sensitivity is obtained depending on the magnetic field intensity to be detected. .

Preferred structures of the giant magnetoresistive film are (Co / Cu), (NiFe / Cu), (NiFeCo / Cu), (CoFe / Cu), (NiF
eCo / Cu / Co / Cu), (NiFe / Cu / Co / Cu), (CoFe / Cu / NiFe / Cu)
And the like are repeated five or more times to form a multilayer structure. In the giant magnetoresistive film having such a multilayer structure, the thickness of the thinnest layer is preferably 10 nm or less, particularly preferably 3 nm or less. If the thickness of the thinnest layer exceeds 10 nm, it tends to be difficult to obtain a high MR ratio.

Since the magnetoresistance effect element is made of a ferromagnetic metal, its temperature coefficient of resistance (TCR: Temper
ature coefficient of resistivity) is a positive value. For example, a coupled giant magnetoresistance effect element having a multilayer structure in which a (NiFeCo / Cu) structure is repeatedly formed five or more times has a NiFeCo thickness of 1.5 nm and a Cu layer thickness of 2. In the case of 0 nm, the TCR value is 1000 × 10 ⁻⁶ /
It becomes K. However, if the layer thickness of Cu is reduced,
When the thickness of the NiFeCo layer is increased, the value of TCR is increased. Conversely, when the thickness of the Cu layer is increased,
When the layer thickness of is reduced, the value of TCR decreases. For example, if the layer thickness of NiFeCo is 5.0 nm and the layer thickness of Cu is 2.0 nm, the value of TCR is 2500 × 10 ⁻⁶ /
It becomes K. Further, for example, the layer thickness of NiFeCo is set to 1.
If the thickness of the Cu layer is 5 nm and the thickness of the Cu layer is 1.0 nm, the TCR value is 1800 × 10 ⁻⁶ / K. By thus increasing the value of TCR and driving the magnetic field sensor at a constant current, the effect of the MR change rate having a negative temperature coefficient (MR change rate that decreases as the temperature rises) is reduced, and the output of the sensor is reduced. It is possible to improve the temperature characteristics.

The tendency (characteristic) of the TCR as described above is as follows.
The same applies to other materials. Even in the case of a giant magnetoresistive element having a multilayer structure formed by repeating the (Co / Cu) structure five times or more, for example, the Co layer thickness is 1.5 nm and the Cu layer thickness is 2.0 nm. Then, the value of TCR is 1200 × 1
0 ⁻⁶ / K. The Co layer thickness is 1.5 nm,
When the layer thickness of u is 1.0 nm, the value of TCR is 1800.
× 10 ^-6 / K.

In the magnetic field sensor of the present invention, when increasing the width of the operating region, that is, the operating magnetic field region as shown in FIG. 7, the stripe width of the element is reduced, and the effect of shape anisotropy is utilized. By doing so, it can be realized. For example, when the layer thickness of NiFeCo is 1.5 nm, Cu
Is a multilayer film obtained by repeating the structure of (NiFeCo / Cu) 20 times with a layer thickness of 2.0 nm. When the stripe width is 15 μm, the saturation magnetic field is 140 Oe, but when the stripe width becomes 1.5 μm. , The saturation magnetic field is 320 Oe.

When a (giant) magnetoresistive film is formed, the surface roughness of the substrate on which the film is formed affects the properties of the (giant) magnetoresistive film. For example, NiFe
Co layer thickness 1.5 nm, Cu layer thickness 2.0 nm
When a multilayer film obtained by repeating the structure of (NiFeCo / Cu) 20 times is formed on a hard glass substrate or a silicon substrate, when the center line average roughness (Ra) of the substrate exceeds 30 nm, the MR change rate is reduced. It starts to deteriorate, especially when it becomes larger than 90 nm.
The rate of change drops below 80%. Conversely, the resistivity of the formed film tends to increase as Ra increases, and when Ra exceeds 30 nm, the resistivity starts to increase, and Ra increases.
Is 300 nm, the resistivity becomes 30 μΩcm, and thereafter, the resistivity increases as Ra increases.

When a large current flows through a (giant) magnetoresistive element, the temperature of the element rises and the element itself may be broken. Therefore, when increasing the current value flowing through the element, the element itself can be prevented from being broken by increasing the line width of the element or increasing the film thickness. For example,
When a multilayer film in which a NiFeCo layer thickness of 1.5 nm and a Cu layer thickness of 2.0 nm is repeated 20 times (NiFeCo / Cu) on a polyimide substrate, the stripe width is 15 μm. In this case, a current of 7 mA can flow, and when the stripe width is 50 μm, a current of 13 mA can flow. The value of the current that can flow can be further improved by applying a heat-radiating resin to the surface of the element. When a silicone resin is applied, a current of 10 mA can flow when the stripe width is 15 μm, and a current of 20 mA can flow when the stripe width is 50 μm.

Such a magnetoresistive film (magnetic film)
The film is formed by a vacuum film forming method, for example, a vapor deposition method, a sputtering method, or the like. More specifically, for example, after forming a magnetoresistive film on the entire surface of the base material, patterning into a desired pattern shape is used as a magnetoresistive effect element for magnetic field detection, Conductor electrode film 3 for flowing
1 (FIG. 1) is formed in a predetermined pattern. It is important that the conductor electrode film 31 has a smaller resistance than the magnetic film portion which is a magnetoresistive element. For this reason, the conductor electrode film is made of a metal having high conductivity, for example, copper, gold, aluminum, or the like, and has a relatively thick specification, for example, 0.3 to 5.0.
The film is formed to a thickness of 0 μm. For the formation of the conductor electrode film,
In addition to the vacuum film forming method, a wet film forming method can also be used. Further, the magnetoresistive element may be formed after the conductive layer of the conductor electrode film is formed first.

Further, instead of separately forming the magnetoresistive element and the conductor electrode film from different materials, the magnetoresistive element and the conductor electrode film are all integrally formed from the same material ( Film formation). However, in this case, it is necessary to use the same material as long as the respective functions of the magnetoresistive element and the conductor electrode film can be exhibited. The portion of the magnetic film is the magneto-sensitive pattern portion, and the portion of the conductor electrode film does not need to be the magneto-sensitive pattern portion. Therefore, in order to change the current density between the magneto-sensitive pattern portion and the electrode portion, the width of the electrode portion is designed to be wider than the width of the magneto-sensitive pattern portion. That is, by increasing the width of both ends of the pattern made of the same material, a function as a conductor electrode film can be provided. By using the same material, the magnetoresistive element as the magneto-sensitive portion and the conductor electrode film as the electrode portion can be simultaneously formed in one patterning step, and extremely high productivity can be realized.

The magnetoresistance effect element is generally 200 nm
Since it is formed as the following thin film, corrosion resistance in a use environment often becomes a problem. For this reason, it is preferable to provide a protective film at least on the upper layer of the magnetoresistive element to protect the magnetoresistive element from the surrounding atmosphere. As the material of the protective film, it is preferable to use an inorganic material such as SiO ₂ or Al ₂ O ₃ or an organic material such as a polyimide resin or a novolak resin. The material of the substrate 5 used in the present invention is not particularly limited, and glass, silicon,
Any of inorganic materials such as ceramics and organic materials such as resins may be used. Among them, it is particularly preferable to use a thin and light one having excellent so-called flexibility. For example, a substrate similar to a plastic film widely used as a printed wiring board or the like can be suitably used.
More specifically, various materials known as plastic film materials such as polyimide, polyethylene terephthalate (PET), polypropylene (PP), and Teflon can be used.

The thickness of the substrate 5 used in the magnetic field sensor of the present invention is usually preferably 500 μm, particularly preferably 100 μm or less (1 to 100 μm).

In the present invention, by bridging the elements as shown in FIG. 1, a gradient for detecting an external magnetic field having a so-called strength gradient (an external magnetic field that gradually increases and / or decreases gradually) is detected. As a measuring device, this magnetic field sensor can be applied to a gear tooth sensor or the like.

As described above, in the magnetic field sensor of the present invention, magnets having different coercive forces are arranged at predetermined intervals,
Since these are functioned as bias magnets and arranged so that the absolute values of the bias magnetic fields applied to the plurality of magnetoresistive elements are substantially equal, the offset is small and the sensitivity is high. In addition, the magnetic field sensor including the bias magnet can be formed simply and compactly by a series of thin film processes, and furthermore, the positional relationship between the bias magnet and the element can be formed in an extremely accurate state.

[0050]

EXAMPLES Hereinafter, the present invention will be described in more detail by showing specific examples of the present invention. (Example 1)

A 300 μm-thick silicon substrate whose surface was oxidized was heated to 250 ° C., and a cobalt platinum film (Pt: 2) was deposited on the substrate by a dual ion beam sputtering apparatus.
0 at% Co-Pt, residual magnetic flux density Br ₁ = 0.9T
(Tesla), coercive force H _C1 = 1430 Oe) to 1500 °
The film was formed to a thickness, and then exposed and developed through a mask using a photoresist by a photolithography technique to form a predetermined pattern, and then etched by ion milling to form a pattern of the magnet body 21.

Next, a cobalt platinum film (Co-Pt with Pt of 30 at%, residual magnetic flux density Br ₂ = 0.9 T (tesla), coercive force H _C2 = 930) is formed by the same thin film process.
Oe) is formed into a film having a thickness of 1500 °, and then exposed and developed through a mask using a photoresist by a photolithography method to form a predetermined pattern, and then etching by ion milling to form a pattern of the magnet body 25. did. The patterns of the two types of magnet bodies 21 and 25 are as follows.
As shown in FIGS. 1 and 2, each pattern was formed so as to be alternated. After forming the patterns of the two types of magnet bodies 21 and 25, these thin film magnets are heated at 600 ° C. for 2 hours.
Heat treated for hours. Each width of the patterns of the magnet bodies 21 and 25 was 50 μm.

The magnet bodies 21 and 2 thus formed are
On the pattern No. 5, an insulating film made of SiO ₂ was formed to a thickness of 2000 ° using a dual ion beam sputtering apparatus.

After the formation of the insulating film, 100 ° -Ti (15 ° -NiFe
(Co / 20Å-Cu) × 20 multilayer GMR film (magnetoresistive element) was formed. Here the film structure is initially 100 °
Ti, then 15% NiFeCo alloy and 20% Cu
Is a multi-layer film having a total thickness of 800 Å in which 20 layers are sequentially laminated.

Each of the targets used in the dual ion beam sputtering apparatus had a target composition of 99.9% or more in purity, and the ultimate pressure was 4 × 10 ⁻⁷ Torr.
After vacuum evacuation, an argon gas was introduced, and the degree of vacuum during the film formation was 1.4 × 10 ⁻⁴ Torr. The accelerating voltage of argon ions during film formation is 300 V, the beam current (proportional to the amount of argon ions) is 30 mA, CoPt (magnet),
The average deposition rate of NiFeCo and Cu is 0.03 nm
/ Sec.

After the GMR film was formed, it was exposed and developed through a mask by a photolithography technique to form a pattern of the magnetoresistive element as shown in FIGS. 1 and 2 in accordance with the arrangement pitch of the magnet bodies. The stripe width of the device was 10 μm, and the resistivity of the device was 27 μΩcm.

After the element was manufactured in this manner, a magnetic field of 1500 Oe was applied from the outside in one direction of the magnet arrangement direction to magnetize the magnets 21 and 25 in one direction. Next, 11
The magnetization direction of the magnet body 25 was reversed by applying a magnetic field of 00 Oe.

Thus, a sample of the magnetic field sensor of Example 1 was completed.

(Embodiment 2) Thickness 300 with oxidized surface
A silicon substrate of μm is heated to 250 ° C., and a cobalt platinum film 1 (Co-Pt with 12 at% Pt, residual magnetic flux density B) is deposited on the substrate by a dual ion beam sputtering apparatus.
r ₁ = 1.15T (tesla), coercive force H _C1 = 1000O
e) is formed into a film having a thickness of 1500 mm, and thereafter, is exposed and developed through a mask using a photoresist by a photolithography method to form a predetermined pattern, and then is etched by ion milling to form a pattern of the magnet body 21. did.

Then, a cobalt platinum film (Co-Pt with Pt of 35 at%, residual magnetic flux density Br ₂ = 0.9 T (tesla), coercive force H _C2 = 500) is formed by the same thin film process.
Oe) is formed into a film having a thickness of 1500 °, and then exposed and developed through a mask using a photoresist by a photolithography method to form a predetermined pattern, and then etching by ion milling to form a pattern of the magnet body 25. did. The patterns of the two types of magnet bodies 21 and 25 are as follows.
As shown in FIGS. 1 and 2, each pattern was formed so as to be alternated. After forming the patterns of the two types of magnet bodies 21 and 25, these thin film magnets are heated at 600 ° C. for 2 hours.
Heat treated for hours. Each width of the patterns of the magnet bodies 21 and 25 was 50 μm.

The magnet bodies 21 and 2 formed as described above
On the pattern No. 5, an insulating film made of SiO ₂ was formed to a thickness of 2000 ° using a dual ion beam sputtering apparatus. Further, a photoresist is applied to the entire surface of the insulating film, and a resist pattern for lift-off is formed so that SiO ₂ is deposited on the cobalt platinum 1 (magnet body 21), and the SiO ₂ film is formed to a thickness of 1250 °. Filmed. As described above, the thickness of the insulating layer on the surface of the cobalt platinum 1 having a large external magnetic field strength is changed to the thickness of the cobalt platinum 2 having a small external magnetic field strength.
By making the insulating layer of the (magnet body 25) thicker, a bias magnetic field having the same absolute value in the opposite direction is applied to the magnetoresistive element.

After the formation of the insulating film, 100 ° -Ti (15 ° -NiFe)
(Co / 20Å-Cu) × 20 multilayer GMR film (magnetoresistive element) was formed. Here the film structure is initially 100 °
Ti, then 15% NiFeCo alloy and 20% Cu
Is a multi-layer film having a total thickness of 800 Å in which 20 layers are sequentially laminated.

Each of the targets used in the dual ion beam sputtering apparatus had a target composition of 99.9% or more in purity, and the ultimate pressure was 4 × 10 ⁻⁷ Torr.
After vacuum evacuation, an argon gas was introduced, and the degree of vacuum during the film formation was 1.4 × 10 ⁻⁴ Torr. The accelerating voltage of argon ions during film formation is 300 V, the beam current (proportional to the amount of argon ions) is 30 mA, CoPt (magnet),
The average deposition rate of NiFeCo and Cu is 0.03 nm
/ Sec.

After the GMR film was formed, it was exposed and developed through a mask by a photolithography technique, and the pattern of the magnetoresistive element as shown in FIGS. 1 and 2 was formed in accordance with the arrangement pitch of the magnets. The stripe width of the device was 10 μm, and the resistivity of the device was 27 μΩcm.

After the device was manufactured as described above, a magnetic field of 1200 Oe was applied from the outside in one direction of the magnet arrangement direction to magnetize the magnets 21 and 25 in one direction. Next, 70 mm from outside in the direction opposite to the application direction.
By applying a magnetic field of 0 Oe, the magnetization direction of the magnet body 25 was reversed.

Thus, a sample of the magnetic field sensor of Example 2 was completed.

For each sample of the magnetic field sensors of Examples 1 and 2 thus prepared, the variation of the bias magnetic field was evaluated in the following manner.

(1) Variation of Bias Magnetic Field Variation of the bias magnetic field applied to each of the four bridge-connected GMR elements was evaluated. That is, after measuring the resistance of each element, the bias magnetic field applied to each element was converted using a magnetoresistance effect curve and found.

More specifically, in order to measure the magnetoresistance curve, an element having the same material and shape as the four bridge-connected GMR elements is prepared in advance, and a bias is applied to the magnetoresistance curve of the element. It was measured without. Using such a magnetoresistive effect curve, the measured resistance value of the element was converted into a value (magnetic field) on the horizontal axis, and a bias magnetic field applied to the element was obtained. With 10 samples, the difference between the maximum value and the minimum value of the bias magnetic field in each sample was determined, and the average value of the difference between the maximum value and the minimum value in 10 samples was determined.

As a result, the average value of the difference between the bias magnetic fields was 13 Oe for the sample of the present invention in Example 1 and the average value of the difference in the bias magnetic field was 13 Oe for the sample of the present invention in Example 2. Was 14 Oe, and it was confirmed that both exhibited extremely excellent effects. The offset can be reduced by reducing the average value of the difference between the bias magnetic fields.

Incidentally, as a comparative example, a magnetic field sensor was prepared by using a pasting-type bias magnet separately prepared in advance and pasting it to a substrate at a predetermined interval to use the bias magnet as a bias magnet (of the GMR film). When the average value of the difference between the bias magnetic fields was determined in the same manner as above, the result was 65 Oe, which was not good.

[0072]

The effects of the present invention are clear from the above results. That is, the magnetic field sensor of the present invention has a plurality of magnetoresistive elements arranged at predetermined intervals and a plurality of magnetoresistive elements arranged at predetermined intervals to correspond to these magnetoresistive elements. A magnetic field sensor having a bias magnet, wherein the plurality of bias magnets are composed of two types of magnets having substantially different coercive forces, and these two types of magnets are spaced apart from each other by a predetermined distance. They are arranged along the arrangement direction and are arranged such that the absolute values of the bias magnetic fields applied to the plurality of magnetoresistive elements are substantially equal.

Therefore, it is possible to provide a small-sized magnetic field sensor having high mass productivity, small offset, high sensitivity, and high sensitivity.

[Brief description of the drawings]

FIG. 1 is a plan view of a magnetic field sensor of the present invention.

FIG. 2 is a sectional view taken along the line AA of FIG. 1;

FIG. 3 is a perspective view showing an example of a usage example of the magnetic field sensor of the present invention.

FIG. 4 is a plan view showing an example of a usage example of the magnetic field sensor of the present invention.

5 is a cross-sectional view showing an example of a usage example of the magnetic field sensor of the present invention, and is a cross-sectional view taken along the line BB of FIG.

FIG. 6 is a diagram for explaining an equivalent circuit of a bridge-connected magnetoresistive element.

FIG. 7 is a diagram for explaining an output waveform when a bridge connection is made.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Magnetic field sensor 5 ... Substrate 11, 12, 13, 14 ... Magnetoresistance effect element 21, 25 ... Bias magnet (magnet body)

Continuation of the front page (72) Inventor Yukio Asakawa 1-13-1 Nihonbashi, Chuo-ku, Tokyo Inside TDK Corporation (72) Inventor Daisuke Miyauchi 1-13-1 Nihonbashi, Chuo-ku, Tokyo Inside TDK Corporation F term (reference) 2F077 AA45 CC02 NN03 NN19 NN26 PP07 PP14 RR09 VV01 VV33 2G017 AA02 AB07 AB09 AC09 AD55 AD56 AD65 BA09

Claims (7)

[Claims] 1. A semiconductor device comprising: a plurality of magnetoresistive elements arranged at predetermined intervals; and a plurality of bias magnets arranged at predetermined intervals so as to correspond to the magnetoresistive elements. A magnetic field sensor, wherein the plurality of bias magnets have substantially different coercive forces.
And two kinds of magnets are arranged along a direction in which the magnetoresistive elements are arranged at a predetermined interval, and the absolute value of a bias magnetic field applied to each of the plurality of magnetoresistive elements. Are arranged so that are substantially equal to each other. 2. The magnet device according to claim 1, wherein two kinds of magnet bodies are alternately arranged along the arrangement direction of the magnetoresistive elements so that the bias magnetic fields exerted on adjacent magnetoresistive elements are opposite to each other. A magnetic field sensor as described. 3. A first magnetizing operation is performed on the plurality of bias magnets in any direction in the arrangement direction of the two magnet bodies so that the magnetizing directions of the two magnet bodies are the same. 3. The magnetic field according to claim 1, wherein the second magnetizing operation is performed in a direction opposite to the arbitrary direction such that only the magnet body having a small coercive force reverses the magnetization. Sensor. 4. The arrangement pitch D of the plurality of magnetoresistive elements and the arrangement pitch P of the plurality of bias magnets are the same, and the magnetoresistive elements and the bias magnets are arranged in substantially the same positional relationship. The magnetic field sensor according to claim 1, wherein 5. The difference in coercive force between the two types of magnet bodies is 20
The magnetic field sensor according to claim 1, wherein the magnetic field sensor is 0 Oe or more. 6. The magnetic field sensor according to claim 1, further comprising 4n (n: positive integer) magnetoresistive elements, wherein the magnetoresistive elements are bridge-connected. 7. The magneto-resistance effect element is formed of a magnetic film exhibiting a giant magneto-resistance effect.
The magnetic field sensor according to any one of the above.