JPH08316548A - Magnetoresistive element - Google Patents

Abstract

PURPOSE: To enhance a magnetoresistive element in rate of resistance change at a room temperature by a method wherein a first and a second ferromagnetic thin film are both free from magnetic anisotropy through their surfaces, the first ferromagnetic thin film is larger than the second ferromagnetic thin film in coercive force, and both the thin films are possessed of a stepwise magnetization curve and an angular hysteresis curve respectively. CONSTITUTION: Electrodes 14 and 15 are provided to ferromagnetic thin films 11 and 12 ferromagnetic tunnel-coupled interposing a non-magnetic film 13 between them and formed on a board 16. When a current is made to flow between the electrodes 14 and 15, the ferromagnetic thin films 11 and 12 are changed in direction of magnetization, and a magnetoresistive effect is induced. The ferromagnetic thin films 11 and 12 are so structured as to be kept free from magnetic anisotropy through their surfaces. The first ferromagnetic thin film 11 is set larger than the second ferromagnetic thin film 12 in coercive force. Both the first ferromagnetic thin film 11 and the second ferromagnetic thin film 12 are possessed of a stepwise magnetization curve and an angular hysteresis curve respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetoresistive element suitable for a magnetically sensitive portion such as a magnetic encoder, a magnetic head and a magnetic bubble detector. More specifically, the present invention relates to a magnetoresistive element that detects a magnetic signal by utilizing the magnetoresistive effect of a ferromagnetic tunnel junction.

[0002]

2. Description of the Related Art As shown in FIG. 9, a magnetically sensitive portion 1 of an element which is practically used as a magnetoresistive element is formed by processing a single-layered ferromagnetic thin film having a magnetoresistive effect into stripes having a constant width. After that, the electrodes 2 are provided on both ends in the longitudinal direction (y direction).
Made by forming 3. From the resistance value calculated based on the voltage between the electrodes 2 and 3 when a constant current is applied to these electrodes 2 and 3 and a magnetic field to be detected is applied in the width direction (x direction) of the magnetic sensing unit 1. The magnetic field is detected. As shown in FIG. 10, the conventional magnetoresistive element has a maximum resistance change rate (ΔR / R) of 2 depending on the magnitude of the magnetic field orthogonal to the direction of current flow.
It has the property of changing by ~ 6%. Utilizing this characteristic, the magnetoresistive element is used for an FG (Frequency Generator) detection sensor which is a magnetic rotation sensor such as a servomotor. When this magnetoresistive element is used as a rotation sensor to detect the rotation of the rotary drum, a rotary drum 5 made of a permanent magnet is attached to the rotary shaft 4 as shown in FIGS. The pattern 5a is provided at the magnetizing pitch M, and the sensor stripe 7 of the magnetoresistive element (magnetic rotation sensor) 6 is provided in the vicinity of the drum surface.
a, 7b, 7c, 7d (resistance values of R ₁ , R ₂ , R respectively
₃ and R ₄ ) are arranged at intervals P = M / 2. Reference numeral 8 is a substrate, and 9 is an output terminal. With this configuration, the sensor stripes 7a ...
The resistance values R _{1 to} R _{4 of} 7d change regularly, and the AC signal B is obtained at the output terminal 9 with respect to the input signal A as shown in FIG.

On the other hand, in an element in which two ferromagnetic thin films are joined with a thin insulating layer sandwiched therebetween, a constant tunnel current is caused to flow between the ferromagnetic thin films, and in this state, different magnetic fields are applied parallel to the film surface of the ferromagnetic thin films. It has been reported that this element has a new magnetoresistive effect due to the change in resistance when it is exposed (S.
Maekawa and U.Gafvert, IEEE Trans. Magn. MAG-18 (19
82) 707). The inventors have joined the two ferromagnetic thin films with a non-magnetic film including a thin insulating layer sandwiched therebetween, and utilize the resulting ferromagnetic tunnel junction to make the two ferromagnetic thin films have their respective easy magnetization axes. A magnetoresistive device, which is arranged so as to be orthogonal to each other, wherein the coercive force of one ferromagnetic thin film in the direction of easy axis of magnetization is twice or more the coercive force of the other ferromagnetic thin film in the direction of easy axis of magnetization. He invented the device and applied for a patent (JP-A-6-244477). A magnetoresistive element using this ferromagnetic tunnel junction has a resistance change rate (ΔR / R) of 2% or more at room temperature, has a good sensitivity in a weak magnetic field, and has a stable magnetic field range within an effective magnetic field range. It has the feature that it can be doubled or more.

[0004]

However, the resistance change rate (ΔR / R) of the conventional magnetoresistive element shown in FIG. 9 is usually 2 to 3% at room temperature, and at most 6%. . Since the output signal of the magnetic resistance element (magnetic rotation sensor) 6 described above is an AC signal as described above, it is necessary to shape the waveform into a square wave signal as shown in FIG. 15 in order to improve the detection accuracy. Moreover, as shown in FIG. 14, the amplitude of the output signal B is small when inputting with the zero magnetic field at the center, so an amplifier circuit is used, or a bias magnet is provided near the magnetoresistive element as shown in FIG. It is necessary to amplify the output signal B by providing a bias magnetic field H _B. Further, as apparent from FIG. 11, it is necessary to match the pitch P of the sensor stripes with the pitch M of the magnetic poles. For these reasons, in order to obtain high output characteristics from the conventional magnetoresistive element, there is a problem that the element structure and the circuit configuration become complicated. The ferromagnetic tunnel junction disclosed in JP-A-6-244477 has a low rate of change in resistance due to magnetism at room temperature of 5% or less, and its application has not been considered yet.

An object of the present invention is to obtain a ferromagnetic material which has a rate of change in resistance (ΔR / R) at room temperature of 10% or more, has good sensitivity in a weak magnetic field, and which does not need to shape the output waveform into a square wave. An object is to provide a magnetoresistive element using a tunnel junction. Another object of the present invention is to provide a magnetoresistive element that does not need to have its operating point biased by a bias magnet, has a simple structure and circuit configuration, and can be miniaturized.

[0006]

The inventors of the present invention have found that the conduction electrons are spin-polarized in the ferromagnetic metal, and therefore the electronic states of the upward spin and the downward spin on the Fermi surface are different. When a ferromagnetic tunnel junction consisting of a ferromagnet, an insulator, and a ferromagnet is made by using a nonferromagnetic metal, conduction electrons tunnel while maintaining their spins. It was thought that the probability would change and that it would appear as a change in tunnel resistance, and the present invention was reached with this point in mind.

That is, as shown in FIG. 1, the first magnetoresistive element 10 of the present invention includes a first ferromagnetic thin film 11 and a second ferromagnetic thin film 12 sandwiching a nonmagnetic film 13 including a thin insulating layer. This is an improvement of the one using the ferromagnetic tunnel junction generated by the above, and the characteristic constitution is that both the first and second ferromagnetic thin films 11 and 12 have magnetic anisotropy in the film plane. However, the coercive force of the first ferromagnetic thin film 11 is larger than the coercive force of the second ferromagnetic thin film 12, and the magnetization curves of the first ferromagnetic thin film 11 and the second ferromagnetic thin film 12 are square as shown in FIG. It has a shape hysteresis curve, and the whole magnetization curve is a stepwise and angular hysteresis curve.

As shown in FIG. 2, the second magnetoresistive element 30 of the present invention has a third ferromagnetic thin film 31 and a fourth ferromagnetic thin film 32 with a non-magnetic film 33 including a thin insulating layer interposed therebetween. The third ferromagnetic thin film 31 has a magnetic anisotropy in the film plane, which is an improvement of a structure utilizing a ferromagnetic tunnel junction generated by the junction.
2 has no magnetic anisotropy in the film plane, and the third ferromagnetic thin film 31
When a magnetic field is applied in the easy magnetization axis direction of the third ferromagnetic thin film 31, the coercive force of the third ferromagnetic thin film 31 in the easy magnetization axis direction is
5, the magnetization curves of the third ferromagnetic thin film 31 and the fourth ferromagnetic thin film 32 each have a square hysteresis curve, and the entire magnetization curve is stepwise and square. Is a hysteresis curve.

The present invention will be described in detail below. (a) Magnetoresistance Effect by Ferromagnetic Tunnel Junction As shown in FIGS. 1 to 3, a ferromagnetic tunnel junction is formed on a substrate 16 (or 36) with a non-magnetic film 13 (or 33) including a thin insulating layer interposed therebetween. Ferromagnetic thin films 11 and 12 (or 31)
And 32) are provided with electrodes 14 and 15 (or 34 and 35), respectively, and when a current is passed between the electrodes 14 and 15 (or 34 and 35), both electrodes 14 and 15 (or 34 and 35)
The tunnel current flowing between the two ferromagnetic thin films 11, 12
Depending on the mutual relationship of the magnetization directions of (or 31, 32), a magnetoresistive effect appears in which the resistance value changes when the magnetization direction changes. That is, the resistance value when the magnetization directions M ₁ and M ₂ (or M ₃ and M ₄ ) of the ferromagnetic thin films 11 and 12 (or 31 and 32) are orthogonal to each other as indicated by solid arrows in FIG.
_{When set to 0} , the ferromagnetic thin films 11, 12 (or 31, 32)
When the magnetization directions of are the same (M ₂ is indicated by a dashed arrow), the resistance value is [R ₀ −ΔR / 2], and the magnetization directions of the ferromagnetic thin films 11 and 12 are opposite to each other. At some time (M ₂ is indicated by an alternate long and short dash line arrow), the resistance value is [R ₀ + ΔR / 2].

(B) Characteristics peculiar to the first magnetoresistive element 10 of the present invention As shown in FIG. 1, the first characteristic constitution of the magnetoresistive element 10 is that two ferromagnetic thin films 11 and 12 are both films. The point is that there is no magnetic anisotropy in the plane. With such a configuration, when the external magnetic field H is first applied in a specific direction and is larger than the coercive force of the two ferromagnetic thin films 11 and 12 and then the external magnetic field is set to zero, the two ferromagnetic thin films as shown in FIG. 1
Orientation M _1, M ₂ of the magnetization of the 1 and 12 becomes parallel as shown in M ₁ and dashed M ₂ in solid lines in FIG. 3, the resistance value between both film becomes [R ₀ -ΔR / 2]. Next, when the direction of the external magnetic field is set to the opposite direction (that is, the direction of magnetization M ₁ ) and the magnetic field is increased, the direction of magnetization M ₂ of the ferromagnetic thin film 12 having a small coercive force is When the coercive force is exceeded, it is inverted in the direction of the external magnetic field as shown by the one-dot chain line arrow in FIG. 3, and the resistance value becomes [R ₀ + ΔR / 2]. Further, the external magnetic field becomes large, and the ferromagnetic thin film 11 having a large coercive force is obtained.
As you greater than the coercive force, inverted orientation M ₁ of the magnetization of the ferromagnetic film 11, the resistance value becomes [R ₀ -ΔR / 2] from _{[R 0 + ΔR / 2]} , this condition following The magnetic field is reversed and the magnetic field is maintained until the coercive force of the ferromagnetic thin film 12 is exceeded.

A method for preventing both the first and second ferromagnetic thin films 11 and 12 from having magnetic anisotropy in the film plane is as follows.
Instead of forming the ferromagnetic thin films 11 and 12 into stripes by an ion beam evaporation method, a vacuum evaporation method, a sputtering method, or the like, the ferromagnetic thin films 11 and 12 are formed into a shape having no magnetic anisotropy, such as a circle or a square, and a magnetic field is not applied during film formation. There is a method. FIG. 1 shows a case where the thin films 11 and 12 are square. The order of forming the thin films 11 and 12 shown in FIG. 1 is that the first ferromagnetic thin film 12 is formed on the substrate 16 in a shape such as a square having no magnetization anisotropy, and no magnetic field is applied during the deposition. Next, a non-magnetic film 13 is deposited on the central portion of the ferromagnetic thin film 12,
The first ferromagnetic thin film 11 is also formed into a square shape having no magnetic anisotropy at the center of the non-magnetic film so that no magnetic field is applied during deposition. That is, the easy axes of magnetization of the two thin films 11 and 12 are not arranged in a specific direction. In particular, after forming an Al film on the second ferromagnetic thin film 12 by the sputtering method, the Al film is oxidized to form an Al film on its surface.
_{When the} non-magnetic film 13 is formed by forming the ₂ O ₃ layer, the non-magnetic film 13 can be made uniform and dense.

As shown in FIG. 1, one end of the first ferromagnetic thin film 11 and the second ferromagnetic thin film 12 are used to effectively detect only the magnetoresistive effect generated between the two ferromagnetic thin films 11 and 12. First electrodes 14 and 15 for supplying a constant current to both thin films are respectively provided at one end of the first thin film, and a voltage applied between the second thin films at the other end of the first ferromagnetic thin film 11 and the other end of the second ferromagnetic thin film 12. It is preferable to provide the second electrodes 17 and 18 for measuring respectively.

(C) Features peculiar to the second magnetoresistive element 30 of the present invention As shown in FIG. 2, the first characteristic constitution of the magnetoresistive element 30 is that the third ferromagnetic thin film 31 is in the film plane. It has magnetic anisotropy, and the fourth ferromagnetic thin film 32 does not have magnetic anisotropy in the film plane. With this configuration, the first 2
When the external magnetic field H, which is larger than the coercive force of the two ferromagnetic thin films 31 and 32, is applied in the direction of the easy axis M ₃ of the ferromagnetic thin film 31 and then the external magnetic field is set to zero, the two ferromagnetic thin films 31 and 32 are formed as shown in FIG. orientation M _3, M ₄ of the magnetization of become parallel as shown in the solid line of M ₃ and the broken line of M ₄ in FIG. 3, the resistance value between both film becomes [R ₀ -ΔR / 2]. Next, when the direction of the external magnetic field is set opposite to the direction (that is, the direction of magnetization M ₃ ) up to now and the magnetic field is increased, the direction of magnetization M ₄ of the ferromagnetic thin film 32 having a small coercive force is When the coercive force is exceeded, it is inverted in the direction of the external magnetic field as shown by the one-dot chain line arrow in FIG. 3, and the resistance value becomes [R ₀ + ΔR / 2]. When the external magnetic field further increases and becomes larger than the coercive force of the ferromagnetic thin film 31 having a large coercive force, the ferromagnetic thin film 3
The magnetization direction M _{3 of 1} is reversed, and the resistance value is [R ₀ + ΔR /
2] to [R ₀ −ΔR / 2], and this state is maintained until the magnetic field is reversed and the coercive force of the ferromagnetic thin film 32 is exceeded.

As a method for maintaining the magnetic anisotropy in the film surface of the third ferromagnetic thin film 31, as shown in FIG. 2, the ferromagnetic thin film 31 is ion beam deposited, vacuum deposited, or sputtered. To form a stripe shape by the easy axis M
_Although not shown, a method of obtaining ₃ or a method of forming a shape having no magnetic anisotropy such as a circle or a square and applying a magnetic field at the time of film formation, or a method of combining these can be mentioned. The method for preventing the fourth ferromagnetic thin film 32 from having magnetic anisotropy in the film plane is the same as the method for forming the first and second ferromagnetic thin films described above. As the order of forming the thin films 31 and 32 shown in FIG. 2, first, the fourth ferromagnetic thin film 32 is formed into a square shape having no magnetic anisotropy on a substrate 36 such as glass, and a magnetic field is not applied at the time of film formation. Next, a non-magnetic film 33 is deposited on the central part of the ferromagnetic thin film 32, and the third ferromagnetic thin film 31 is formed in stripes on the central part of the non-magnetic film so that the longitudinal direction thereof is the easy axis of magnetization M _3. When formed, a magnetic field is applied in the longitudinal direction of the stripe as required during film formation. Alternatively, the third ferromagnetic thin film 31 is formed first, and then the nonmagnetic film 33 is formed,
Finally, the fourth ferromagnetic thin film 32 may be formed.

In particular, after forming an Al film on the fourth ferromagnetic thin film 32 by the sputtering method, the Al film is oxidized to form an Al ₂ O ₃ layer on the surface of the non-magnetic film 33. When made, the nonmagnetic film 33 can be made uniform and dense. Further, as shown in FIG. 2, in order to effectively detect only the magnetoresistive effect generated between the two ferromagnetic thin films 31 and 32, one end of the third ferromagnetic thin film 31 and one end of the fourth ferromagnetic thin film 32 are provided. Third for passing a constant current through both thin films
Electrodes 34 and 35 are provided respectively, and fourth electrodes 37 and 38 for measuring a voltage applied between both ends of the third ferromagnetic thin film 31 and the fourth ferromagnetic thin film 32 are provided respectively. It is preferable.

(D) Features common to the first and second magnetoresistive elements 10 and 30 of the present invention The second characteristic configuration of each of the magnetoresistive elements 10 and 30 is the coercive force of the ferromagnetic thin film 11 and A difference is provided between the coercive force of the ferromagnetic thin film 12 or the coercive force of the ferromagnetic thin film 31 when the magnetic field is applied in the easy axis direction and the coercive force of the ferromagnetic thin film 32. It is a point. Thus, when an external magnetic field exceeding the magnetic field range D is applied to the magnetoresistive element as shown in FIG. 4, its characteristics reversibly change and a square wave output is obtained as shown in FIG. The coercive force difference between the two ferromagnetic thin films determines the width W of the square wave output shown in FIG.

The third characteristic structure of the magnetoresistive elements 10 and 30 is the respective magnetization curves of the first ferromagnetic thin film 11 and the second ferromagnetic thin film 12, or the third ferromagnetic thin film 31 and the fourth ferromagnetic thin film.
Each magnetization curve of the ferromagnetic thin film 32 is represented by the symbol a in FIG.
As shown by b and b, it has an angular hysteresis curve of a broken line and a dash-dotted line, and the entire magnetization curve is a stepwise and angular hysteresis curve of a solid line as indicated by reference sign c. As a concrete means for obtaining this angular hysteresis curve, it is desirable that the magnetization direction does not fluctuate in the ferromagnetic thin film, and a magnetic field is applied in that direction at the time of film formation, or As shown in FIG. 5, the stripe shape is formed, and the longitudinal direction of the stripe shape is aligned with the easy magnetization axis. Particularly, if the coercive force is small, the squareness is difficult to appear. Therefore, it is desirable that the ferromagnetic thin film 12 or the ferromagnetic thin film 32 having a small coercive force be close to the large coercive force of the ferromagnetic thin film 11 or the ferromagnetic thin film 31. Further, in order for the magnetoresistive element of the present invention as a novel magnetic sensor to obtain a square wave output, it is necessary to apply a magnetic field exceeding the magnetic field range D when used with the sensor. Therefore, in order to obtain a square wave output in a weak magnetic field, it is necessary to make the coercive force of the ferromagnetic thin film 11 or the ferromagnetic thin film 31 relatively small. Therefore, the coercive force of the ferromagnetic thin film 11 or the ferromagnetic thin film 31 is equal to the ferromagnetic thin film 12 or the ferromagnetic thin film 32.
It is preferable to increase the coercive force so as not to exceed twice.

In order to enhance the magnetoresistive effect by the ferromagnetic tunnel junction by the magnetoresistive element of the present invention, the first ferromagnetic thin film 11 or the third ferromagnetic thin film 31 having a large coercive force contains Fe or Fe and Co as main components. Then, the second ferromagnetic thin film 12 or the fourth ferromagnetic thin film 32 having a small coercive force is made of Fe as a main component, or the insulating layer included in the nonmagnetic film 13 or 33 is oxidized by the nonmagnetic metal film. It is conceivable to adopt a means constituted by an oxide layer. You may combine both said means and. When the main component of both ferromagnetic thin films is Fe, the second ferromagnetic thin film 12 may be formed from the substrate temperature at the time of forming the first ferromagnetic thin film 11 or the third ferromagnetic thin film 31.
Alternatively, it is preferable to increase the substrate temperature at the time of forming the fourth ferromagnetic thin film 32 to form both ferromagnetic thin films 11, 12 or 31, 32, respectively. As a result, a coercive force difference can be provided even if the two ferromagnetic thin films are the same Fe single layer film. In order to prevent the coercive force difference from exceeding twice, the substrate temperature difference is preferably 100 ° C. or less. As another means for increasing the coercive force of the first ferromagnetic thin film,
Fe as the main component of the second ferromagnetic thin film 12 or the fourth ferromagnetic thin film
However, there is a method in which Fe and Co are the main components of the first ferromagnetic thin film or the third ferromagnetic thin film. This is a property that the anisotropy is likely to occur and the coercive force is increased when the Co component is increased. This method may be combined with the above-described method in which the substrate temperature at the time of forming the ferromagnetic thin film is set higher in the second ferromagnetic film or the fourth ferromagnetic thin film than in the first ferromagnetic film or the third ferromagnetic thin film. Here, the ratio of the main components is such that, in the case of the first ferromagnetic thin film or the third ferromagnetic thin film, the total of Fe and Co is 80 at.
%, And in the case of the second ferromagnetic thin film or the fourth ferromagnetic thin film, Fe is preferably 80 at% or more.

When the nonmagnetic film 13 or 33 including an insulating layer sandwiched between the ferromagnetic thin films 11, 12 or 31, 32 includes an oxide layer obtained by oxidizing a nonmagnetic metal film, the nonmagnetic film 1
3 or 33 is a uniform layer of about several tens of angstroms. Examples of the insulating layer include an Al ₂ O ₃ layer and a NiO layer. The Al ₂ O ₃ layer is preferable because it has high insulation and is dense. The film sandwiched between the ferromagnetic thin films 11, 12 or 31, 32 must be non-magnetic in order for electrons to hold spins and tunnel. The entire nonmagnetic film may be an insulating layer, or a part thereof may be an insulating layer. The magnetoresistive effect can be further enhanced by forming a part of the insulating layer and minimizing its thickness. An example of forming the oxidized layer of the non-magnetic metal film is an example in which a part of the Al film is oxidized in air to form an Al ₂ O ₃ layer.

[0020]

In the first and second magnetoresistive elements of the present invention, first, Fe having a large amount of vertical spin polarization on the Fermi surface is selected as the magnetic material that is the main component of the two ferromagnetic thin films. Co is selected as the second component, and secondly, for example, Al
A dense and uniform thin insulating layer such as a ₂ O ₃ layer is formed by oxidizing a non-magnetic metal film such as an Al film to increase the difference in resistance value due to the tunnel current that changes depending on the magnetization state, and By decreasing the resistance value due to the current flowing through the insulating layer regardless of the magnetization state, the ferromagnetic tunnel effect caused by holding the spin of conduction electrons and tunneling through the insulating layer remarkably appears, and the magnetoresistance curve of FIG. As shown in, the rate of change in resistance (ΔR / R) exceeds 10%.

In the first and second magnetoresistive elements of the present invention, by providing a difference in coercive force between the two ferromagnetic thin films, preferably by providing a difference not exceeding twice, As shown in FIG. 4, the reluctance curve is a curve having two substantially symmetrical square waveforms centered on the zero magnetic field. For example, if the coercive force and the difference between them are set arbitrarily, the threshold value Hc seen in this curve is obtained. ₁ and Hc ₂ and the rectangular width (Hc ₁ −Hc ₂ ) can be set arbitrarily. If the magnetic force of the input magnetic field of each magnetoresistive element is Hc ₁ or more, the output waveform itself becomes an output close to a square wave as shown in FIG. Further, if the output value is differentiated, high detection sensitivity can be obtained.

When the first magnetoresistive element 10 according to the present invention is applied to a rotation sensor, the conventional element shown in FIG. 11 is replaced with a main element as shown in FIGS. 7 (a) and 7 (b). The magnetoresistive element 10 of the invention may be combined with the resistor R ₁₁ . FIG. 7A corresponds to FIG. In order to remove the influence of the temperature change for higher accuracy, the operation output may be taken as shown in FIGS. 8 (a) and 8 (b). To this end, FIG.
As shown in (a), two magnetoresistive elements 1 are formed on the substrate 16.
0 and 20 are provided. After the square second ferromagnetic thin film 12 and the ferromagnetic thin film 22 having the same shape and size as the thin film 12 are provided on the substrate 16 at intervals, the thin films 12 and 22 are connected. Next, square first ferromagnetic thin films 11 and 21 are provided on the thin films 12 and 22 via the non-magnetic films 13 and 23, respectively. The magnetoresistive element 20 also has a ferromagnetic tunnel effect like the magnetoresistive element 10. Here, in the magnetoresistive element 20 not on the detection side, the entire element is covered with a metal thin film 24 such as permalloy (FeNi alloy) with an insulating film sandwiched between the element and the first element of the element 20.
The ferromagnetic thin film 21 may be magnetically shielded by forming it with a non-magnetic film such as Al. In FIGS. 7 and 8, reference characters R _M and R _M ′ are resistance values of the magnetoresistive element elements 10 and 20, respectively. Although not shown, the second magnetoresistive element 30 of the present invention can also be configured in the same manner as in FIGS. 7 and 8.

[0023]

As described above, the rate of change in resistance (ΔR /
R) was about 3% at room temperature and about 6% for a practically used ferromagnetic magnetoresistive element, but according to the magnetoresistive element of the present invention, it was 10% or more at room temperature. A magnetic wave having a square wave output can be obtained by obtaining a rate of change in resistance and by making the magnetization curve obtained by the two ferromagnetic thin films into a square hysteresis curve so as to provide a difference in coercive force between the two ferromagnetic thin films. A resistance curve is obtained.

Further, since the magnetoresistive element of the present invention has a large change in resistance change rate in a weak magnetic field, the change in magnetic field can be detected with high sensitivity, which is different from the conventional magnetoresistive element.
(a) No need for a highly sensitive amplifier circuit, (b) No need to change the output waveform to a square waveform, (c) No need to apply a bias magnetic field using a magnet to bias the operating point,
(d) It is not necessary to match the element pitch with the pitch of the magnetic poles, which is advantageous in that the structure and circuit configuration can be simplified and downsized.
Accordingly, it can be suitably used as an element for detecting magnetism such as a magnetic encoder of a rotation sensor or a magnetic sensor. In particular, when both the two ferromagnetic thin films have no magnetic anisotropy like the first magnetoresistive element, a large resistance change rate can be obtained in any direction of the external magnetic field in the plane. When this magnetoresistive element is used in a rotation sensor, it is not necessary to match the direction of the axis of easy magnetization of the magnetic anisotropy with the direction of the external magnetic field, and therefore, adjustment when mounting the sensor is easy. When only one ferromagnetic thin film has magnetic anisotropy like the second magnetoresistive element, it is necessary to match the direction of the easy axis of this film with the direction of the external magnetic field, but the magnetic anisotropy of both is different. Since it is not necessary to accurately align the axes of easy magnetization of both as compared with the case of being anisotropic, the manufacture of the magnetoresistive element is easy.

[0025]

EXAMPLES Examples of the present invention will be described below. Example 1 As shown in FIG. 1, a Fe thin film 12 having a square shape of 10 mm × 10 mm and a thickness of 100 nm was formed on a glass substrate 16 by vacuum evaporation using a mask. At this time, the substrate temperature was set to 100 ° C. in order to reduce the coercive force of the film without applying a magnetic field. At this time, the vapor deposition rate was 0.3 to 0.6 nm / sec, and the degree of vacuum was about 10 ^-6 Torr. Next, using a mask in the center of the Fe thin film 12, a square Al film 1 having a thickness of 5 nm and a size of 9 mm × 9 mm is formed.
3 was deposited by high frequency sputtering. At that time, the argon pressure was 1.5 mTorr and the input power was 4.4 W /
cm ² , and the sputtering rate was 0.56 nm / sec. The Al film 13 was left in the air for 24 hours to oxidize the surface, thereby forming an insulating layer made of thin Al ₂ O ₃ . Further, using a mask at the center of the Al film 13, a square Fe film 1 of 8 mm × 8 mm smaller than the Fe thin film 12 is used.
1 was produced. This film forming method was prepared under the same conditions as the Fe thin film 12 except that the substrate temperature was set to room temperature in order to increase the coercive force of the Fe thin film 11. That is, Fe thin films 12 and 1
No. 1 has no magnetic anisotropy in the film plane.

An electrode 14 is provided at each end of the Fe thin films 11 and 12.
And 15 are provided, and electrodes 17 and 18 are provided at the other end of each to obtain the magnetoresistive element 10. At a temperature of 25 ° C,
A magnetic field H is applied to the magnetoresistive element 10 parallel to the surface of the substrate 16 and in the direction of the arrow in the figure, a constant current is applied to the electrodes 14 and 15, and the voltage between the Fe thin films 11 and 12 is measured by the electrodes 17 and 18. did. From the current value and the voltage value, the element 10
Was calculated.

As shown in the magnetic resistance curve of FIG. 4, the magnetic field H
The rate of change in resistance (ΔR / R) when the strength of was changed was an extremely high value of 18% at maximum. This magnetoresistive curve is a curve having two substantially square wave-like waveforms symmetrical about the zero magnetic field. This is because, as shown in FIG. 5, each of the two ferromagnetic thin films has a magnetization curve having a square hysteresis curve. The threshold of the square wave of the magnetoresistance curve and its width can be arbitrarily set by changing the substrate temperature to produce a ferromagnetic thin film. When a rotation sensor having the structure shown in FIG. 7A was prototyped using the magnetoresistive element 10 of this example, a square wave output characteristic as shown in FIG. 6 was obtained without special waveform shaping.

[Brief description of drawings]

FIG. 1 is a perspective view of a magnetoresistive element in which a ferromagnetic tunnel junction is composed of two ferromagnetic thin films having no magnetic anisotropy according to the present invention.

FIG. 2 is a perspective view of a magnetoresistive element in which one ferromagnetic thin film of the present invention constitutes a ferromagnetic tunnel junction by two ferromagnetic thin films having no magnetic anisotropy.

FIG. 3 is a perspective view showing the principle of a magnetoresistive element using the ferromagnetic tunnel junction of the present invention.

FIG. 4 is a magnetoresistive curve diagram of the magnetoresistive element shown in FIGS. 1 and 2.

FIG. 5 is a magnetization curve diagram thereof.

FIG. 6 is a diagram showing output characteristics with respect to the input magnetic field.

FIG. 7A is a configuration diagram of a rotation sensor using the magnetoresistive element shown in FIG. (B) The equivalent circuit diagram.

FIG. 8A is a configuration diagram when the rotation sensor of FIG. 7A is further highly sensitive. (B) The equivalent circuit diagram.

FIG. 9 is a perspective view of a magnetoresistive element utilizing a ferromagnetic magnetoresistive effect of a conventional example.

FIG. 10 shows its magnetoresistance curve.

FIG. 11 is a diagram showing the principle of a rotation sensor using a conventional magnetoresistive element.

FIG. 12 is a perspective view showing the configuration of the rotation sensor.

FIG. 13 is an equivalent circuit diagram of FIG. 11.

FIG. 14 is a diagram showing output characteristics with respect to an input magnetic field in the case where there is no bias magnetic field using the magnetoresistive element of the conventional example.

FIG. 15 is a diagram showing the output waveform and the waveform after shaping.

FIG. 16 is a diagram showing output characteristics with respect to an input magnetic field when a bias magnetic field is used using the magnetoresistive element of the conventional example.

[Explanation of symbols]

 10 and 20 1st magnetoresistive element 30 2nd magnetoresistive element 11 and 21 1st ferromagnetic thin film 12 and 22 2nd ferromagnetic thin film 13 and 23 non-magnetic film 14 and 15 1st electrode 16 substrate 17 and 18th 2 electrodes 31 third ferromagnetic thin film 32 fourth ferromagnetic thin film 33 non-magnetic film 34,35 third electrode 36 substrate 37,38 fourth electrode

Claims (11)

[Claims] 1. A first ferromagnetic thin film (11) and a second ferromagnetic thin film (1)
2) and are joined by sandwiching a non-magnetic film (13) including a thin insulating layer,
In the magnetoresistive element (10) using the ferromagnetic tunnel junction generated by this, both the first and second ferromagnetic thin films (11, 12) have no magnetic anisotropy in the film plane, and The coercive force of the ferromagnetic thin film (11) is the second ferromagnetic thin film.
The magnetization curves of the first ferromagnetic thin film (11) and the second ferromagnetic thin film (12) each have a square hysteresis curve, and the entire magnetization curve is stepwise. A magnetoresistive element having a square hysteresis curve. 2. The coercive force of the first ferromagnetic thin film (11) is the second coercive force.
2. The magnetoresistive element according to claim 1, which is larger than the coercive force of the ferromagnetic thin film (12) by no more than twice. 3. A first and a second ferromagnetic thin film (1) on a substrate (16).
When forming the first and the second ferromagnetic thin films 12, the substrate temperature at the time of forming the first ferromagnetic thin film 11 is made different from that at the time of forming the first and second strong thin films 12. The magnetoresistive element according to claim 1, wherein magnetic thin films (11, 12) are respectively formed. 4. A third ferromagnetic thin film (31) and a fourth ferromagnetic thin film (3
2) and are joined by sandwiching a non-magnetic film (33) including a thin insulating layer,
In the magnetoresistive element (30) using the ferromagnetic tunnel junction generated by this, the third ferromagnetic thin film (31) has magnetic anisotropy in the film plane,
When the fourth ferromagnetic thin film (32) does not have magnetic anisotropy in the film plane and a magnetic field is applied in the easy axis direction of the third ferromagnetic thin film (31), the third ferromagnetic thin film The coercive force of the easy magnetization axis direction of (31) is larger than the coercive force of the fourth ferromagnetic thin film (32), and the respective magnetizations of the third ferromagnetic thin film (31) and the fourth ferromagnetic thin film (32) A magnetoresistive element, wherein the curve has a square hysteresis curve, and the entire magnetization curve is a stepwise square hysteresis curve. 5. The magnetic resistance according to claim 4, wherein the coercive force of the third ferromagnetic thin film (31) in the direction of the easy axis of magnetization is not larger than twice the coercive force of the fourth ferromagnetic thin film (32). element. 6. The third and fourth ferromagnetic thin films (3) on the substrate (36).
1, 32) is formed, the substrate temperature at the time of forming the third ferromagnetic thin film (31) and the substrate temperature at the time of forming the fourth ferromagnetic thin film (32) are made different so that the third and fourth strong films are formed. The magnetoresistive element according to claim 4, wherein each of the magnetic thin films (31, 32) is formed. 7. A first ferromagnetic thin film (11) or a third ferromagnetic thin film
The magnetoresistive element according to claim 1 or 4, wherein (31) has Fe or Fe and Co as main components, and the second ferromagnetic thin film (12) or fourth ferromagnetic thin film (32) has Fe as main components. 8. A first ferromagnetic thin film (11) or a third ferromagnetic thin film
8. The magnetoresistive element according to claim 7, wherein each of the (31) and the second ferromagnetic thin film (12) or the fourth ferromagnetic thin film (32) is a Fe single layer film. 9. The magnetoresistive element according to claim 1, wherein the nonmagnetic film (13, 33) including an insulating layer includes an oxide layer obtained by oxidizing a nonmagnetic metal film. 10. The magnetoresistive element according to claim 9, wherein the non-magnetic metal film is Al and the oxide layer thereof is Al ₂ O ₃ . 11. The magnetoresistive element according to claim 9, wherein the nonmagnetic metal film is formed by a sputtering method.