JP2000322714A - Tunnel magnetoresistive magnetic field detecting element, method of manufacturing the same, and magnetic head using the same - Google Patents

Abstract

[PROBLEMS] To realize a tunnel magnetoresistive effect type magnetic field detecting element having a low electric resistance and a high signal-to-noise ratio (S / N) while maintaining a high magnetoresistance change rate. A noble metal layer (4) is provided on a first ferromagnetic layer (3), and a very thin metal film such as aluminum is formed thereon, and then oxidized to form an insulating layer (5). In the oxidation treatment of aluminum, the oxidation reaction stops at the noble metal layer 4 and does not reach the ferromagnetic layer 3 thereunder. For this reason, the thickness of the insulating layer 5 is limited to a layer obtained by oxidizing the metal film such as aluminum. Further, in this method, since the underlying ferromagnetic layer 3 is not oxidized, the metal film having a predetermined thickness can be reliably oxidized to form a high-quality insulating layer. Therefore, the potential barrier for electrons in the tunnel effect can be made high and thin, and both high magnetoresistance ratio and low electric resistance can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic field detecting element using a tunnel magnetoresistive film, a method of manufacturing the same, a magnetic head using the same, and a magnetic recording / reproducing apparatus having the magnetic head.

[0002]

2. Description of the Related Art In a magnetic disk drive currently in practical use, a reproducing magnetic head used for reproducing information recorded on a magnetic disk includes, for example, Ni-F.
A magnetic head using an anisotropic magnetoresistive (AMR) film generated in an e film or the like (hereinafter, this type of head is referred to as an AMR head) is widely used.

In this magnetic head, the rate of change in magnetoresistance is about 2%. Furthermore, recently, a magnetic head using a giant magnetoresistive (GMR) film having a structure in which a nonmagnetic metal layer is sandwiched between two ferromagnetic layers having different magnetic properties (hereinafter, this type of head is referred to as a GMR head) is also in practical use. Has begun.

The GMR head has a magnetoresistance change ratio of 4 to
At 5%, it is more sensitive than the AMR head described above. For this reason, magnetic information from smaller magnetic domains can be detected, and recording at a density of 10 gigabits per square inch is possible. However, in order to greatly improve the recording density in the future, a reproducing magnetic head having an even higher magnetoresistance ratio is required.

As a magnetoresistive film having such a high magnetoresistance change rate, a tunnel magnetoresistive film including a tunnel junction having a structure in which an insulating layer is sandwiched between two ferromagnetic layers has attracted attention. In this film, for example, as shown in Journal of Magnetics and Magnetic Materials, Vol. 139, page L231 (published in 1995), an aluminum oxide layer was sandwiched between thin films of iron. A large magnetoresistance change rate has been reported, for example, a magnetoresistance change rate of 18% was obtained in a tunnel magnetoresistance effect film having a structure.

Thus, the tunnel magnetoresistive film has
Since a large rate of change in magnetoresistance occurs, it is promising if it is applied as a high-sensitivity magnetic field detecting element, particularly as a reproducing head of a magnetic head, and is expected to be applied to high-density recording / reproducing such as 40 gigabits per square inch. You.

To apply this tunnel magnetoresistive film to a high-density recording / reproducing magnetic head (hereinafter referred to as a tunnel magnetoresistive magnetic head), the dimensions of the tunnel junction (specifically, the insulating layer is formed of a ferromagnetic layer and 1 μm
Must be about ² or smaller. Here, since the electric resistance is proportional to the area of the bonding portion, it is very high when a minute bonding portion is formed, and generally shows a resistance value which is 1000 times or more that of the aforementioned AMR head.

For this reason, a tunneling magneto-resistance effect type magnetic head cannot use a drive circuit for an AMR head which is widely used at present, and has a large signal-to-noise ratio (S / N) due to large thermal noise. The problem of becoming smaller has become apparent.

That is, although the magnetoresistance ratio is high, the electrical resistance is high and the signal-to-noise ratio (S / N) is small.
If it is left as it is, it is impossible to apply it as a high-sensitivity magnetic field detecting element, particularly a magnetic head for reproducing a high-density magnetic recording medium such as a magnetic disk.

[0010]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned conventional problems, and to provide a sufficiently low electric resistance value while maintaining a high magnetoresistance change rate of a tunnel magnetoresistive film. It is an object of the present invention to provide a high-sensitivity magnetic field detecting element using a tunnel magnetoresistive film having a magnetic field, a method of manufacturing the same, a magnetic head using the same, and a magnetic recording / reproducing apparatus including the magnetic head.

[0011]

A magnetic field detecting element and a magnetic head using a tunnel magnetoresistive film (hereinafter referred to as a tunnel magnetoresistive element) are different from the above-mentioned AMR and GMR elements. It has a laminated structure in which a thin insulating layer is sandwiched between two ferromagnetic metal layers (hereinafter simply referred to as a ferromagnetic layer), and has a configuration in which a constant voltage is applied between the two ferromagnetic layers via electrode terminals. Have That is, a voltage is applied in the direction perpendicular to the surface of the laminated film of both ferromagnetic layers, and the current flowing in the direction perpendicular to the film surface when the angle between the magnetization directions of the two ferromagnetic layers is changed by an external magnetic field.
That is, it utilizes the fact that the current (tunnel current) flowing from one electrode to the other electrode via the thin insulating layer changes.

The resistance value of the tunnel magnetoresistive element depends not only on the junction size (the area of the insulating layer, that is, the area where the insulating layer is in contact with the ferromagnetic layer) but also on the characteristics inherent in the insulating layer. The insulating layer functions as a potential barrier when electrons travel in the direction perpendicular to the film surface, and the resistance value is determined by the height and thickness of the potential barrier.

[0013] From the viewpoint of electric resistance, it is generally required to reduce the height of the potential barrier and the thickness thereof to reduce the resistance. However, the higher the potential barrier, the larger the value of the magnetoresistance change. For this reason, even if the height of the potential barrier is adjusted, it is difficult to achieve both a high magnetoresistance change rate and a low resistance value. Therefore, in the present invention, a method is used in which the resistance value is reduced while maintaining a large rate of change in magnetoresistance by substantially reducing the thickness of the barrier without reducing the height of the potential barrier.

[0014] Reducing the thickness of the potential barrier corresponds to reducing the thickness of the insulating layer, and the insulating layer itself is deposited on the ferromagnetic layer by a film forming technique such as sputtering. Is required to reduce the thickness of the deposited layer.

However, if the thickness of the insulating layer is made smaller than about 1.5 nm by directly depositing the insulator itself on the ferromagnetic layer, pinholes are formed in the insulating layer, and a tunnel effect is not generated. Since there are moving electrons, the rate of change in magnetoresistance becomes extremely small.

For this reason, the method of directly depositing the insulator itself on the ferromagnetic layer is not appropriate, and a reaction such as forming a metal film such as aluminum or magnesium on the ferromagnetic layer in advance and oxidizing the metal film is performed. It is common to form an insulating layer by the following method.

When an insulating layer is formed by this method of oxidizing a metal film, if the metal film such as aluminum or magnesium is thick, the entire film reacts and becomes an insulator, which is not suitable because the insulating layer becomes thick. In order to reduce the thickness of the insulating layer, it is necessary to cause a partial reaction only in the vicinity of the surface of the metal layer. For this purpose, conditions such as lowering the oxygen gas pressure are required.

However, under such conditions, even if the insulating layer becomes thin, the reaction in the insulating layer is not sufficient, so that the ratio of the unreacted metal element is high, the potential barrier is low, and the magnetoresistance change is low. There was a problem that the rate was low.

As described above, when a metal film such as aluminum or magnesium is thick when the insulating layer is formed, the height of the potential barrier can be increased and the thickness can be reduced at the same time even when the reaction conditions are selected. Have difficulty.

On the other hand, when a metal film such as aluminum or magnesium which is to be an insulating layer is simply thinned by a reaction such as oxidation, the reaction proceeds through the metal film and a part of the ferromagnetic layer adjacent to the metal film is formed. The reaction reaches up. As the ferromagnetic substance, a ferromagnetic metal such as iron, nickel, cobalt or the like or an alloy thereof is usually used, and these ferromagnetic substances also become an insulating layer when reacted. For this reason, even if a metal film such as aluminum or magnesium which becomes an insulating layer by a reaction such as oxidation is simply thinned, the insulating layer actually includes the ferromagnetic metal reaction layer. Thickness will be large.

As described above, when a metal film such as aluminum or magnesium is formed on a ferromagnetic layer and an insulating layer is formed by a reaction such as oxidizing the metal film, regardless of the thickness of the metal film, It is difficult to increase the height and the thickness of the potential barrier. That is, with this method, it is difficult to achieve both a high rate of change in magnetoresistance and a low electrical resistance.

The present inventors have studied various experiments to overcome such difficulties. As a result, on the ferromagnetic layer,
First, a sufficiently thin noble metal layer is formed, and then a metal film such as aluminum or magnesium used as an insulating layer is formed thereon by a reaction such as oxidation. Thermal oxidation at the heating temperature,
Further, it was confirmed that it was possible to react with oxygen or the like under sufficiently strong reaction conditions to form an insulating layer having a residual ratio of an unreacted metal element of several percent or less. Under preferable conditions, the metal film could be completely oxidized to form an insulating layer composed of 100% oxide.

When this method is used, a metal film such as aluminum or magnesium reacts sufficiently to form an insulating layer having a high potential barrier. However, since the reaction with oxygen or the like stops at the noble metal layer serving as the base, the region where the oxidation reaction occurs is limited to only the metal film such as aluminum or magnesium, and the reaction of the ferromagnetic layer thereunder is prevented. . That is, the noble metal layer functions as a protective layer for preventing oxidation of the underlying ferromagnetic layer when the metal film formed thereon is oxidized into an insulating layer.

For this reason, if the thickness of the metal film on which the insulating layer is formed by reacting with oxygen such as aluminum or magnesium is made sufficiently thin, the thickness of the insulating layer can be made sufficiently thin, and the potential Barriers can be made thinner.

Judging from the experimental results so far, the thickness of the potential barrier is 3.0 nm or less, preferably 0.1 nm.
It is desired to have a height of about 6 to 0.9 nm and a height of at least 1 eV, preferably about 2 to 3 eV. It is difficult to obtain 3 eV, but 2.2
If it is about electron volts, it can be easily obtained with an oxide of aluminum.

Here, the height of the potential barrier is related to the amount of the metal element which has not reacted with oxygen or the like in the insulating layer, and the potential barrier height of 2 eV or more is determined by the ratio of the unreacted metal element. This corresponds to less than 6%.
By using the above-described film configuration and using conditions for sufficiently reacting the metal film, such as increasing the oxygen gas pressure and lengthening the oxidation time, it is possible to satisfy the condition relating to such a potential barrier, and to achieve a high magnetoresistance change. It is possible to achieve both a low rate and a low electrical resistance.

The influence of the presence of the noble metal layer is as follows.
If this is made sufficiently thin, the decrease in the magnetoresistance ratio can be ignored. The preferable thickness of the noble metal layer is such that when oxidizing a metal film such as aluminum or magnesium to form an insulating layer, on the one hand, the anti-oxidation function of the ferromagnetic layer is taken into consideration, and on the other hand, the metal film is sufficiently oxidized. It must satisfy the conditions for obtaining a good quality insulating layer.

According to the experimental studies by the present inventors, the upper limit of the preferable thickness of the noble metal layer is about 1.5 nm, and the lower limit is about 0.1 nm.
At least one atomic layer is required at about 24 nm,
A practically particularly preferable film thickness is 0.4 to 1.0 nm.

The noble metal layer is made of Au, Pt, P
At least one kind of noble metal element selected from the group consisting of d, Rh, Ir, and Ru, or a layer of an alloy thereof is applied.

The present invention has been made based on the results of the study on the tunnel magnetoresistive element described above, and the features of the present invention that can achieve the above-mentioned objects of the present invention will be specifically described below. .

(1) First, in the tunneling magneto-resistance effect type magnetic field detecting element of the present invention, an insulating layer is present between two ferromagnetic metal layers having different magnetic reversing magnetic fields to form a tunnel junction. In a magnetic field detecting element including a tunnel magnetoresistive effect element and an electrode terminal for applying a voltage between the two ferromagnetic metal layers, Au, Pt, Pd, and Pd are disposed between one ferromagnetic metal layer and an insulating layer. A feature is that a noble metal layer made of at least one element selected from the noble metal element group of Rh, Ir and Ru or an alloy of these elements is provided.

The thickness of the noble metal layer is preferably 1.5 nm or less, more preferably 0.4 to 1.0 nm.
It is.

The thickness of the insulating layer is preferably 3.0 nm or less, more preferably 0.6 to 0.9.
nm. That is, when the thickness of the insulating layer is represented by the height of the potential barrier of the insulating layer with respect to the ferromagnetic film, it is desired that the thickness be at least 1 eV or more, preferably about 2 to 3 eV. It is very difficult to obtain 3 eV, but if it is about 2.2 eV, it can be easily obtained from an oxide of aluminum. Representative examples of such an insulating layer include at least one metal oxide of aluminum and magnesium.

(2) According to the manufacturing method of the invention for manufacturing such a tunneling magneto-resistance effect type magnetic field detecting element, an insulating layer exists between two ferromagnetic metal layers having different magnetic fields for reversing magnetization. In a method for manufacturing a magnetic field detecting element comprising a tunnel magnetoresistive element forming a tunnel junction and an electrode terminal for applying a voltage between the two ferromagnetic metal layers, an insulating layer is provided on one of the ferromagnetic metal layers. The step of forming a layer is performed by forming Au, Pt, Pd, Rh, Ir, and R having a thickness of 1.5 nm or less as an underlayer on the ferromagnetic metal layer.
forming a noble metal layer made of at least one element selected from the noble metal element group of u or an alloy of these elements; and oxidizing the noble metal layer to easily form an insulating layer, and Forming a metal film having a thickness of 3 nm or less having a potential barrier height of at least 1 eV with respect to the ferromagnetic metal layer, and protecting the noble metal layer as an antioxidant film of the ferromagnetic metal layer. And a step of forming an insulating layer for selectively oxidizing and converting it to an oxide layer.

The noble metal layer and the metal film can be easily formed by a vacuum evaporation method or a sputtering method. In addition, the step of forming an insulating layer that oxidizes the metal film to convert it into an oxide layer can be any one of a natural oxidation treatment, a thermal oxidation treatment, and a plasma oxidation treatment in an oxygen atmosphere.

Above all, the plasma oxidation treatment is preferable because the metal film can be reliably oxidized even if the treatment time is shorter than other treatment methods, and a good insulating layer can be obtained. As preferable conditions in this case, for example, an oxygen gas pressure of 0.8 to 2.5 Torr
r, power 200 to 500 W, processing time 10 seconds to 3 minutes.

(3) In the magnetic head of the present invention to which the above-mentioned tunneling magneto-resistance effect type magnetic field detecting element is applied, an insulating layer exists between two ferromagnetic layers having different magnetic fields for reversing magnetization, and a tunnel junction is formed. , A magnetic field detecting element having an electrode terminal for applying a voltage between the two ferromagnetic layers, and a constant voltage power supply for applying a predetermined voltage between the two ferromagnetic layers through the electrode terminals And at least one element selected from the group of noble metal elements of Au, Pt, Pd, Rh, Ir, and Ru, or these elements, between the one ferromagnetic layer and the insulating layer. With a noble metal layer made of an alloy of the, as the insulating layer formed on the noble metal layer,
An insulating layer having a potential barrier height of at least 1 eV with respect to the ferromagnetic metal layer is provided.

Although this magnetic head is a reproducing magnetic head, a recording / reproducing magnetic head can be easily realized by combining this magnetic head with a well-known magnetic induction type magnetic head.

(4) Since this recording / reproducing magnetic head enables high-density recording / reproducing, a magnetic recording / reproducing apparatus having excellent magnetic recording / reproducing characteristics can be provided in combination with a high-density magnetic recording medium. Can be realized.

[0040]

FIG. 1 is a sectional view schematically showing a basic structure of a tunnel magnetoresistive element according to the present invention. Here, 1 is a silicon substrate (100), 2 is a thermal oxide film (SiO ₂ ) provided thereon, 3 is a first ferromagnetic film, 4 is a noble metal layer, 5 is an insulating layer, and 6 is a second Ferromagnetic layer,
2 'is an insulator serving as a protective film, and 7 is an Au electrode for applying a voltage between the first ferromagnetic film 3 and the second magnetic layer 6.

In the above structure, a feature of the present invention resides in that an insulating layer 5 is provided on the first ferromagnetic film 3 with a noble metal layer 4 interposed therebetween. First, as the noble metal layer 4, Au, Pt, P
A noble metal layer made of at least one element selected from the noble metal element group of d, Rh, Ir and Ru or an alloy of these elements is formed.

The thickness of the noble metal layer 4 is such that the first ferromagnetic film 3 (magnetic metal) serving as a base has an antioxidant effect during the step of forming the insulating layer 5 through oxidation treatment as described later. , It is desirable to be as thin as possible, and the upper limit is 1.5n
m, the lower limit is about 0.24 nm of one atomic layer or more at the minimum thickness having an antioxidant effect, and practically 0.4 to 1.
A thickness of 0 nm is preferred.

In addition, the noble metal layer 4 has a small specific resistance as well as an antioxidant effect, so that a tunnel current can flow while maintaining the information of electron spin. As a result, a high rate of change in magnetoresistance is maintained. This contributes to a reduction in electric resistance of the tunneling magneto-resistance effect type magnetic sensing element.

The insulating layer 5 is formed on the noble metal layer 4 by, for example, A
This is formed by forming a metal film such as 1 or Mg and selectively oxidizing the metal film from the surface. That is, when a metal film, such as Al or Mg, formed in advance on the noble metal layer 4 is oxidized from the surface, the metal film is selectively oxidized to form an insulating layer. 1 is not oxidized, the thickness of the insulating layer is set to Al or M
The region where the metal film such as g is oxidized is limited, and the sufficiently thin insulating layer 5 is surely formed with the designed thickness.

In this oxidation of the metal film, a sufficient potential barrier can be formed because sufficient oxidation can be achieved by the effect of preventing the noble metal layer 4 from being oxidized.

The thickness of the insulating layer 4 is 3 nm or less, preferably 0.6 to 0.9 nm, in which the height of the potential barrier to the ferromagnetic layer is at least 1 eV.

The first and second ferromagnetic layers 3 and 6 are each composed of a magnetic layer having a difference in the magnetic field where magnetization reversal occurs. The first ferromagnetic layer 3 is made of, for example, Co-17 at% Pt.
The Co-based (hard magnetic layer) such as an alloy and the second ferromagnetic layer 6 are formed by vacuum deposition or sputtering of a Ni-Fe (soft magnetic layer) such as a Ni-20 at% Fe alloy. As the magnetic properties of these two ferromagnetic layers 3 and 6, the relationship of first magnetic layer 3> second magnetic layer 6 is required for coercive force and magnetic anisotropy.

The electrode 7 does not necessarily need to be Au, but may be another metal as long as it has corrosion resistance and good conductivity.

The underlayer of the first magnetic film 3 is made of Ni—O
The antiferromagnetic layer may be formed to give the ferromagnetic layer 3 magnetic anisotropy in one direction.

When this tunneling magneto-resistance effect element is used as a tunneling magneto-resistance effect type magnetic field detecting element or a magnetic head, the Au electrode 7 connected to the first and second ferromagnetic layers 3 and 6 is connected to a constant voltage source. A predetermined voltage may be applied by connecting to E. The constant voltage source E is generally a DC power supply, but may be an AC or pulse power supply.

This tunnel magnetoresistance effect element can be easily obtained by a manufacturing method using a well-known film forming technique and a well-known pattern forming technique using a lithography technique, except for a method of forming an insulating layer by oxidizing a metal film.

[0052]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below with reference to the drawings. Embodiment 1 FIG. 1 is a sectional view showing the structure of a magnetoresistive effect type magnetic field detecting element and a magnetic head element according to the present invention. As shown in this figure, the thickness of 400nm of SiO ₂
Silicon single crystal substrate [Si (10
0)] First, as the first magnetic layer 3, a film thickness of 30 n
m Co-17 at% Pt layer (hard magnetic layer), noble metal layer 4
An Au layer having a thickness of 1.0 nm and an Al film having a thickness of 0.6 nm as a metal layer 5 'were sequentially formed by sputtering.

In this state, the uppermost Al film was oxidized by a plasma oxidation method to form an insulating layer 5. Here, the oxygen gas pressure was set to 1 mTorr, and oxidation was performed for 1 minute under an input power of 300 W.

Next, a 15 nm-thick Ni-20 at% Fe layer (soft magnetic layer) was formed on the insulating layer 5 as a second ferromagnetic layer 6 by sputtering.

A photomask is formed on the laminate thus obtained, and the first magnetic layer 3 is exposed by a well-known lithography process and is processed to a depth at which the first magnetic layer 3 is slightly etched to form a predetermined convex pattern. .

Next, an insulator _{2 ′ made} of SiO ₂ is formed by sputtering, a photomask is formed on the insulator 2 ′, and a hole is formed by a well-known lithography process to form an electrode. The layer 3 and the second magnetic layer 6 are exposed.

Finally, an Au layer as an electrode material was formed by vapor deposition or sputtering, and a predetermined electrode pattern 7 was formed by selective etching, whereby the magnetoresistive effect type magnetic head element shown in FIG. 1 was formed.

A voltage is applied between the first and second magnetic layers 3 and 6 on both sides of the insulating layer 5 via an electrode 7.
Since the electric resistance of the magnetic head element is almost the resistance when a current tunnels through the insulating layer 5, a voltage drop due to electric resistance other than the tunnel resistance of the insulating layer 5 can be ignored. Therefore, the voltage applied between the electrodes is the first and second voltages.
May be considered to be equal to the voltage E applied between the magnetic layers 3 and 6.

In the above-described multilayer film, the Co-17 at% Pt alloy layer constituting the first magnetic layer 3 has a higher coercive force than the second magnetic layer, so that even if a magnetic field from the magnetic recording medium is applied, The direction of magnetization of the Co-17 at% Pt alloy layer (first magnetic layer 3) does not change.

On the other hand, N constituting the second magnetic layer 6
Since the coercive force of the i-20 at% Fe alloy layer is lower than that of the first magnetic layer 3, when a magnetic field from a magnetic recording medium is applied,
The direction of magnetization of the Ni-20 at% Fe alloy layer (second magnetic layer 6) rotates.

Ni-20 at% F as the second magnetic layer 6
The change in the magnetization of the e-alloy layer changes the current tunneling through the insulating layer 5, and the change in the tunnel current makes it possible to detect the change in the external magnetic field.

The rate of change in magnetoresistance is determined by comparing the first magnetic layer 3 with the second magnetic layer 3.
Is expressed by a difference in electric resistance between the case where the magnetization of the magnetic layer 6 is parallel and the case where the magnetization is antiparallel. In the example of this element, the magnetoresistance ratio was 22%.

The electric resistance between the first magnetic layer 3 and the second magnetic layer 6 is 10 in the comparative example in which the Au layer 4 is not provided.
In contrast to 0 kΩμm ⁻² , this embodiment uses 2.5 kΩμm ^−2.
Ωμm ^-2, which was drastically reduced to 1/40. Signal to noise ratio (S /
N) was slightly more than twice that of the comparative example.

When the magnetoresistive effect type magnetic field detecting element shown in this embodiment is used as a magnetic head, it is used exclusively for a reproducing head and has no recording capability. Therefore, in order to perform recording and reproduction, it is necessary to use in combination with a well-known recording induction type magnetic head.

Embodiment 2 FIG. 2 schematically shows a sectional view of a tunnel magnetoresistive effect type magnetic field detecting element. A tunnel magnetoresistive effect type magnetic field detecting element having a basic structure having a cross section shown in FIG. 2 was produced by ion beam sputtering on a silicon substrate 1 having an oxide layer (not shown) having a thickness of 100 nm.

On the substrate 1, NiO was formed with a thickness of 30 nm as the antiferromagnetic layer 8, and a 15-nm-thick Co layer was formed thereon as the first ferromagnetic layer 3. On this, a noble metal layer 4 for preventing oxidation from reaching the first ferromagnetic layer 3 in an oxidation process for forming an insulating layer 5 described later.
An Au layer having a thickness of 1.5 nm was formed.

To form the insulating layer 5 thereon, an Al film 5 ′ (not shown) having a thickness of 0.6 nm is first formed, and in this state, the surface of the sample is oxidized by a plasma oxidation method to form the insulating layer 5. Formed. Here, the oxygen gas pressure is 1 Torr and 300
Oxidation was performed for 1 minute under a power of W.

A 15-nm thick Ni—Fe layer was further formed thereon as the second ferromagnetic layer 6. Thereafter, an electrode terminal 7 is attached to each of the two ferromagnetic layers 3 and 6 of the tunnel magnetoresistive effect laminated film, and a voltage is applied between both ferromagnetic layers. The properties were measured.

FIG. 3 shows that a DC power supply E is connected to the electrode terminal 7 of the tunnel magnetoresistive effect type magnetic field detecting element shown in FIG.
This is a result of measuring a current flowing when a voltage (v) is applied between the two ferromagnetic layers 3 and 6.

Here, the vertical axis represents the current value obtained by dividing the current value by the area of the junction (the contact area of the insulating layer 5 with the ferromagnetic layers 3 and 6). As a result of analyzing this curve, it was found that the height of the potential barrier for electrons in the insulating layer 5 formed here was 2.1 eV and the thickness was 0.8 nm.

When a magnetic field is applied to the sample and the magnetic field is changed, the magnetization direction of the Co layer (first ferromagnetic layer 3) which is coupled to the antiferromagnetic layer 8 and whose magnetization direction is difficult to change does not change. The magnetization direction of the Ni—Fe layer (second ferromagnetic layer 6) having small coercive force and magnetic anisotropy easily changes, and the angle between the magnetization directions of both ferromagnetic layers changes. This allows
A magnetoresistance change occurs. As a result, a change in the magnetic field is detected and output as a change in the voltage.

In this sample, both ferromagnetic layers 3, 6
The difference in electrical resistance between when the magnetization of the
That is, the magnetoresistance ratio was 22%. The unreacted metal element in the insulating layer 5 (here, A
l) The ratio was less than 1% in this sample.

The electric resistance between the first magnetic layer 3 and the second magnetic layer 6 is 10 in the comparative example in which the Au layer 4 is not provided.
In contrast to 0 kΩμm ⁻² , this embodiment uses 2.5 kΩμm ^−2.
Ωμm ^-2, which was drastically reduced to 1/40. Signal to noise ratio (S /
N) was 2.2 times that of the comparative example.

In the above embodiment, the Au layer was used as the noble metal layer 4, but Pt, Pd,
Similar effects were obtained with Rh, Ir, and Ru.

When the thickness of the noble metal layer 4 was increased, the rate of change in magnetoresistance generally tended to decrease. This is considered to be because when the polarized electrons proceed from one ferromagnetic layer to the other ferromagnetic layer, electron spins are scattered by the noble metal layer and the spin-polarized state is disturbed. The thickness dependence of the noble metal layer differs depending on the type of the noble metal. However, when the noble metal layer thickness is 1.5 nm or less, the influence of the spin scattering can be ignored for any noble metal.

In the case of the present embodiment, the first ferromagnetic layer 3
In order to fix the direction of the magnetic field in a certain direction, an antiferromagnetic layer 8 made of NiO having a thickness of 30 nm was provided as an underlayer.
An Ir-based alloy and an alloy of Mn such as Mn-Pt and a noble metal are used. Generally, the film thickness is preferably 5 to 30 nm. The antiferromagnetic layer 8 can be omitted as shown in FIG. 1 of the first embodiment.

<Embodiment 3> FIG. 4 is a schematic cross-sectional view of a tunneling magneto-resistance effect type magnetic field detecting element in which a magnetic layer 61 having a high polarizability is formed under a second ferromagnetic layer 6 in Embodiment 2. This is shown in FIG.

The magnetoresistance change rate is related to not only the shape of the potential barrier of the insulating layer 5 but also the polarizabilities of the first and second ferromagnetic layers 3 and 6. Is high. In the second embodiment, one of the ferromagnetic layers (the second ferromagnetic layer 6) is made of Ni—Fe. A Co layer 61 having a high polarizability was provided under the Ni—Fe layer as the magnetic layer 6.

That is, as shown in FIG. 4, an antiferromagnetic layer 8 of NiO having a thickness of 30 nm and a ferromagnetic layer 3 of Co having a thickness of 15 nm, which is a first ferromagnetic layer, were sequentially stacked on the substrate 1. A Ru noble metal layer 4 having a thickness of 1 nm and a thickness of 0.7 n
An Al film 5 '(not shown) for forming an insulating layer was formed, and plasma oxidation was performed under the above-described conditions.

A 2 nm-thick Co layer 61 and a 15 nm-thick Ni—Fe layer 6 as a second ferromagnetic layer were sequentially formed on the insulating layer 5 formed in the oxidation process.

Here, the magnetization direction of the Co layer 61, which is a magnetic layer having a high polarizability, and the direction of magnetization of the Ni—Fe layer 6, which is the second ferromagnetic layer 6, match. In addition, this combined ferromagnetic layer is a first ferromagnetic layer, C
The magnetization direction is easier to change than the o-layer 3.

For this reason, by changing the applied magnetic field, an angle difference occurs between the magnetization directions of the two ferromagnetic layers 3 and 6, causing a change in magnetoresistance. As a magnetic field detecting element, the output based on the change in the applied magnetic field changes the voltage. Obtained as a change. here,
The thickness of the insulating layer 5 was 0.89 nm, and the magnetoresistance ratio was 28%. Also in this sample, the unreacted metal element ratio in the insulating layer (here, A
l) was 1% or less.

The electric resistance between the first magnetic layer 3 and the second magnetic layer 6 is 10 in the comparative example in which the Ru layer 4 is not provided.
In contrast to 0 kΩμm ⁻² , in this embodiment, 8 kΩμm
It decreased sharply to m ^-2 and 1/13. The signal-to-noise ratio (S / N) was 2.1 times that of the comparative example.

Although the Ru layer was used as the noble metal layer 4, Au, Pt, Pd, Rh, and I were used as other noble metals.
Similar effects were obtained when r was used.

In this case, an aluminum oxide (Al ₂ O ₃ ) layer obtained by oxidizing an Al film is used as the insulating layer 5.
A magnesium oxide (MgO) layer obtained by oxidizing the g film, and an insulating layer obtained by oxidizing an alloy film of Al and Mg also gave substantially the same results as those of the aluminum oxide layer.

<Embodiment 4> FIG. 5 basically shows Embodiment 1.
Co layer 61 (film thickness) having the same structure as that of the tunnel magnetoresistive effect type magnetic field detecting element of the third embodiment, but having a high polarizability between the second magnetic layer 6 and the insulating layer 5 as in the third embodiment. 2n
m) was inserted. The contact area of the insulating layer 5 with the ferromagnetic layer is 1.5 μm × 1.5 μm. The resistance value of this reproducing magnetic head was 1.4 kΩ, and it was confirmed that thermal noise based on this value did not pose any problem from the relationship with the magnetoresistance change rate.

Embodiment 5 A magnetic disk drive was manufactured using the magnetoresistive head of the present invention described in Embodiments 1-4. The main part of the structure of the device is shown at 65. FIG.
(A) is a plan view, and (b) of FIG.
It is A 'sectional drawing.

For the magnetic recording medium 51 rotated by the magnetic recording medium driving section 52, a magnetic material made of a Co—Cr alloy was used. The track width of the magnetic head 53 held by the magnetic head drive unit 54 was 1 μm. The reproducing section of the magnetic head 53 is mounted with the magnetoresistive head of the present invention shown in the first to fourth embodiments.

In the magnetic recording / reproducing apparatus using the magnetoresistive head of the present invention, a high-output reproduced signal was observed. This is because the magnetoresistance change of the multilayer film used in the present invention is large. Also, the noise was relatively small. This is because the S / N of the magnetoresistive head of the present invention is 20 or more.

[0090]

As described above, the intended object can be achieved by the present invention. That is, the tunneling magneto-resistance effect type magnetic field detecting element of the present invention has a low electric resistance and a high S / N while maintaining a high magnetoresistance change rate.
Since the characteristics can be obtained, it is possible to realize a highly sensitive magnetic field detecting element. In particular, since the electric resistance is low, if this is applied to a magnetic head, a conventional magnetic head drive circuit can be used, so that a magnetic head compatible with high recording density can be easily realized. Therefore, a magnetic recording / reproducing apparatus having a high recording density can be obtained, and it can greatly contribute to industrial development.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing a basic structure of a tunneling magneto-resistance effect type magnetic field detecting element of the present invention.

FIG. 2 is a sectional view schematically showing a tunnel magnetoresistive effect type magnetic field detecting element according to one embodiment of the present invention.

FIG. 3 is a graph showing a relationship between current density and voltage in a magnetic field detection element according to one embodiment of the present invention.

FIG. 4 is a cross-sectional view schematically showing a tunnel magnetoresistive effect type magnetic field detecting element according to another embodiment of the present invention.

FIG. 5 is a sectional view of a reproducing magnetic head according to an embodiment of the present invention.

FIG. 6 is an explanatory view schematically showing a main structure of the magnetic disk drive of the present invention.

[Explanation of symbols]

1 ... substrate, 2 ... thermal oxide layer, 2'... insulator (SiO _2), 3 ... first ferromagnetic layer, 4 ... noble metal layer, 5 ... insulating layer, 6 ... second ferromagnetic layer, 61 ... Magnetic layer having high polarizability, 7: electrode, 8: antiferromagnetic layer, E: constant voltage power supply.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Noboru Shimizu 1-280 Higashi Koigakubo, Kokubunji-shi, Tokyo F-term in Central Research Laboratory, Hitachi, Ltd. 5D034 BA03 BA15 BA17 BA18 BA21 CA04 DA07

Claims (16)

[Claims] A tunnel magnetoresistive element in which an insulating layer is present between two ferromagnetic metal layers having a difference in a magnetic field for reversing magnetization to form a tunnel junction; and a voltage between the two ferromagnetic metal layers. In the magnetic field detecting element provided with an electrode terminal for applying a voltage, between one ferromagnetic metal layer and the insulating layer,
A tunnel magnetoresistance effect type magnetic field detecting element, comprising a noble metal layer made of at least one element selected from a noble metal element group of Au, Pt, Pd, Rh, Ir and Ru or an alloy of these elements. . 2. The tunnel magneto-resistance effect type magnetic field detecting element according to claim 1, wherein said noble metal layer has a thickness of 1.5 nm or less. 3. The tunneling magneto-resistance effect type magnetic field detecting element according to claim 1, wherein the thickness of the insulating layer is 3.0 nm or less. 4. A tunnel magnetoresistive effect type magnetic field detecting element according to claim 1, wherein said insulating layer has a thickness of 0.6 to 0.9 nm. 5. The tunnel magnetoresistive effect type according to claim 1, wherein said insulating layer comprises a metal oxide layer having a potential barrier height to said ferromagnetic metal layer of at least 1 eV. Magnetic field detection element. 6. The tunneling magneto-resistance effect type magnetic field detecting element according to claim 1, wherein said insulating layer is made of at least one metal oxide of aluminum and magnesium. 7. A tunnel magnetoresistive element in which an insulating layer is present between two ferromagnetic metal layers having a difference in a magnetic field for reversing magnetization to form a tunnel junction, and a voltage between the two ferromagnetic metal layers. And a step of forming an insulating layer on one of the ferromagnetic metal layers, wherein the step of forming an insulating layer on the one of the ferromagnetic metal layers comprises: Forming a noble metal layer made of at least one element selected from a noble metal element group of Au, Pt, Pd, Rh, Ir and Ru or an alloy of these elements of 5 nm or less; By doing so, a metal film having a thickness of 3 nm or less in which the height of a potential barrier of the insulating layer with respect to the ferromagnetic metal layer is at least 1 eV is formed. Forming an insulating layer for selectively oxidizing the metal film and converting it to an oxide layer while protecting the noble metal layer as an antioxidant film for the ferromagnetic metal layer. Of manufacturing a magnetic field detecting element. 8. A metal film having a thickness of 0.6 to 0.9 nm.
8. The method for manufacturing a tunnel magnetoresistive effect type magnetic field detecting element according to claim 7, wherein: 9. The method according to claim 7, further comprising a step of forming an insulating layer for forming the metal film with at least one metal layer of aluminum and magnesium and oxidizing the metal layer to an oxide layer. Or a method for manufacturing a tunnel magnetoresistive effect type magnetic field detecting element according to item 8. 10. The formation of the noble metal layer and the metal film,
The step of forming an insulating layer formed by a vacuum evaporation method or a sputtering method and oxidizing the metal film to convert it to an oxide layer is performed by any of natural oxidation treatment, thermal oxidation treatment, or plasma oxidation treatment in an oxygen atmosphere. The method for manufacturing a tunnel magnetoresistive effect type magnetic field detecting element according to claim 7, wherein the method is a processing step. 11. A tunnel magnetoresistive element in which an insulating layer is present between two ferromagnetic layers having a difference in a magnetic field for reversing magnetization to form a tunnel junction, and a voltage is applied between the two ferromagnetic layers. A magnetic field detection element having an electrode terminal
In a magnetic head having a constant voltage power supply for applying a predetermined voltage between the two ferromagnetic layers through the electrode terminals, Au, P is provided between the one ferromagnetic layer and the insulating layer.
A noble metal layer made of at least one element selected from the noble metal element group of t, Pd, Rh, Ir and Ru or an alloy of these elements is provided, and the insulating layer formed on the noble metal layer is A tunnel magnetoresistive magnetic head comprising an insulating layer having a potential barrier height of at least 1 eV with respect to a ferromagnetic metal layer. 12. The tunnel magnetoresistive head according to claim 11, wherein the thickness of the noble metal layer is 1.5 nm or less, and the thickness of the insulating layer is 3 nm or less. 13. The tunnel magnetoresistive effect type according to claim 11, wherein said noble metal layer has a thickness of 1.5 nm or less, and said insulating layer has a thickness of 0.4 to 1.0 nm. Magnetic head. 14. A tunnel magnetoresistive head according to claim 11, wherein said insulating layer is made of at least one metal oxide of aluminum and magnesium. 15. A recording / reproducing magnetic head comprising a combination of the tunneling magneto-resistance effect type magnetic head according to claim 11 and an inductive type magnetic head. 16. A magnetic recording / reproducing apparatus comprising the magnetic head according to claim 11.