JP2000206220A - Magnetic field detecting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase a tunnel resistance change ratio by setting an insulator of a thickness with which a tunnel current can be detected and exchange interelectrode magnetic coupling can be shielded between an electrode of a perovskite type conductive oxide magnetic body and a metallic electrode of a ferromagnetic body. SOLUTION: For example, a platinum film is formed as a lower lead wiring 2 by sputtering onto a silicon wafer substrate 1. The substrate is heated to 700 deg.C. An La0.67Sr0.33MnO3 film of a thickness of 80 nm is formed as an electrode 3 of a perovskite type conductive oxide magnetic body by laser ablation, on which an aluminum film of a thickness of 1.5 nm is formed by sputtering. An insulating film 5 is formed by sputter etching and modifying the aluminum film to Al2O3 in Ar+O2 gas. An Ni80Fe20 film of a thickness of 50 nm is formed as a metallic electrode 4 of a ferromagnetic body by sputtering on the insulating film. A layered structure of films 3, 4 and 5 is patterned to a size of 10 μm×30 μm. An insulating layer 7 is formed of an SiO2 film by a lift-off method and an upper lead wiring 6 is formed of a gold sputter film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetic field detecting element for detecting a magnetic field electrically.

[0002]

2. Description of the Related Art Hitherto, a magnetic field detecting element called an MR element utilizing a change in electric resistance (magnetoresistive effect) due to a magnetic field of a magnetic material has been used as a position sensor or a magnetic head for a magnetic disk drive. In recent years, practical use of a GMR element having a magnetoresistance effect with higher magnetic field detection sensitivity has started. This element structure is a magnetic thin film having a multilayer structure. In the future, CMR elements are expected as higher sensitivity magnetic field detection elements, and use the magnetoresistance effect of perovskite-type manganese oxide. On the other hand, another future magnetic field detecting element is called a TMR element, which utilizes the magnetic field dependence of a tunnel current between magnetic materials.

A perovskite-type manganese oxide studied for a CMR element is described in, for example, "Phy
local Review B "53 (1996) R1
689-R1692. Tomioka,
A. Asamitsu, H .; Kuwahara, Y .; M
oritomo and Y .; Pr in Tokura's paper
_1-x Ca _x MnO ₃ single crystal is introduced, and 0.3 <x
When a magnetic field of 12 T is applied at a temperature of 77 K to a single crystal having a composition range of <0.4, the electric resistance decreases by 6 to 8 digits.
Also, “Appl. Phys. Lett.” 66 (199)
5) G. G. published in 1689 to 1691; C. Xion
g, Q. Li, L .; Ju, R .; l. Greene and T.W. Venkatesan's paper states that N
It has been shown that when a magnetic field of 8 T is applied to a d _0.7 Sr _0.3 MnO ₃ thin film at a temperature of 60 K, its electric resistance decreases by almost two orders of magnitude.

[0004] The cause of such a huge magnetoresistance effect in perovskite-type manganese oxide is generally considered as follows. Certain perovskite-type manganese oxides represented by the general formula R _1-x A _x MnO ₃ (R is a trivalent rare earth metal and A is a divalent alkaline earth metal) are ferromagnetic and good conductive at low temperatures. Body, and its conduction mechanism is so-called hopping conduction. That is, since a part of the R element is replaced by the A element, a part of the trivalent manganese becomes tetravalent manganese, so that an empty level is generated in the conduction electron level, through which electrons are converted to manganese atoms. Jumping between creates electrical conduction. At this time, the spins of the electrons are preserved in the same direction before and after the jump, but in the ferromagnetic state, the spins of the outer electrons of the manganese atom are aligned in the same direction. Therefore, the jump of the electrons is easy and a good conductor is obtained. On the other hand, when the perovskite-type manganese oxide changes from a ferromagnetic material to a paramagnetic material at a high temperature, or changes its composition to an antiferromagnetic material, the spins of adjacent manganese atoms are not aligned in the same direction, so the electron It becomes difficult to jump
The electrical resistance becomes very large. In order to use this phenomenon as a CMR element, the composition of the perovskite-type manganese oxide is such that it is in a paramagnetic or antiferromagnetic state at the operating temperature and can be changed to a ferromagnetic state by applying an external magnetic field. Keep it. In that case, the application of an external magnetic field causes a large change in electric resistance, and can be used as a magnetic field sensor.

[0005] Using perovskite type manganese oxide
A magnetic field sensor based on another principle has been proposed.
"Physical Review B" 54 (199
6) Y. published in R8357 to R8360. Lu,
X. W. Li, G .; Q. Gong, G .; Xiao, A .;
Gupta, P .; Lecoeur, J .; Z. Sun,
Y. Y. Wang and V.W. P. In Dravid's paper
Is a tunnel using perovskite-type manganese oxide as an electrode.
Has been reported. This is a two-layer La_0.67Sr
_0.33MnO_ThreeSrTiO_ThreeLaminated via insulating film
It was done. La_{0. 67}Sr_0.33MnO_ThreeThe membrane is 4.2
K is a ferromagnetic conductor, and its coercive force is
e, the upper layer is 160 Oe. The thickness of the insulating layer is 3
Voltage is applied between upper and lower electrodes because it is as thin as ~ 6 nm
Tunnel current flows through the insulating layer. This tunnel
Electrons moving between the layers due to current maintain their spin directions
There must be. Therefore, the upper and lower La_0.67Sr_0.33
MnO_ThreeWhen the magnetization directions of the films are the same, tunnel current flows.
It is easy to flow, and it is hard to flow when it is in the opposite direction. Therefore external
Changes the magnetic field, which exceeds the coercive force of the upper and lower layers
The magnetization direction of the layer changes, and the magnetization directions of the upper and lower layers
Become parallel or anti-parallel and simultaneously tunnel
The current also increases and decreases. The change amount of the tunnel current at 4.2K is
When converted to tunnel resistance, a magnetic field of 110 Oe or less
About 80%.

A magnetic field sensor using a tunnel junction of a magnetic material has been reported in which a ferromagnetic metal is used for the upper and lower layer electrodes instead of a perovskite-type manganese oxide as the magnetic material. "Appl. Phys. Lett." 73 (1
998) J98-670. Nassa
r, M. Hehn, A .; Vaures, F.C. Petro
ff and A.I. Fert's paper states that Co / Al ₂ O ₃ / N
Tunnel junction layer structure has been reported that i ₈₀ Fe _20. The tunnel resistance change rate of this tunnel junction at 4.2 K is about 17% in a magnetic field of 5 Oe or less, and about 6% at room temperature.
%.

[0007]

The various magnetic field sensors described above have advantages and disadvantages in their characteristics. A perovskite-type manganese oxide magnetoresistive element exhibits a large change in resistance, but requires a large magnetic field for transition from a paramagnetic or antiferromagnetic state to a ferromagnetic substance. In order to operate this element even in a weak magnetic field, a method of sandwiching it between ferromagnetic cores having a large magnetic permeability such as MnZn ferrite or permalloy can be considered. Difficulty limits applications.

In the case of a perovskite-type manganese oxide tunnel junction device, the operating magnetic field is significantly reduced as described above because the magnetization direction is reversed in the ferromagnetic state instead of the magnetic state transition. Nevertheless, in order to detect a smaller magnetic field or a magnetic field generated in a minute area, it is necessary to further reduce the operating magnetic field. For example, a magnetoresistive head used in a hard disk drive having a high recording density uses a magnetic film that operates with a magnetic field of about 5 Oe, and such an operating magnetic field is desired.

On the other hand, in a tunnel junction between ferromagnetic metals, it is relatively easy to reduce the magnitude of the magnetization reversal magnetic field of the ferromagnetic metal, so that the operating magnetic field can be extremely reduced as in the above example. However, the maximum change rate of the tunnel resistance is considerably smaller than that of a perovskite-type manganese oxide tunnel junction device.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has a magnetic field detecting element having an operating magnetic field as small as a ferromagnetic metal tunnel junction element and a tunnel resistance change rate larger than that. The purpose is to get.

[0011]

The magnetic field detecting element according to claim 1 of the present invention is provided between a perovskite-type conductive oxide magnetic electrode, a ferromagnetic metal electrode, and the two electrodes, An insulating film having a thickness capable of detecting a tunnel current and interrupting exchange magnetic coupling between the two electrodes is provided.

In the magnetic field detecting element according to a second aspect of the present invention, the magnetization direction of the perovskite-type conductive oxide magnetic material electrode does not substantially change with respect to an external magnetic field within a magnetic field strength range to be detected. The magnitude of the coercive force of the two electrodes is controlled so that the magnetization direction of the ferromagnetic metal electrode changes substantially.

According to a third aspect of the present invention, there is provided a magnetic field detecting element, wherein the perovskite-type conductive oxide magnetic material electrode is formed on a substrate, and the insulating film and the ferromagnetic material electrode are disposed thereon. It is.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The basic structure of a magnetic field detecting element according to the present invention is such that an electrode of a perovskite-type conductive oxide magnetic material such as a perovskite-type manganese oxide is provided on one side with an insulating film interposed therebetween, and the other is strong. It is provided with a magnetic metal electrode. The insulating film is thin enough to allow a tunnel current to flow, has a thickness that has an insulating property to block exchange magnetic coupling between two electrodes on both sides and withstand an applied voltage for measuring the tunnel current. Such an insulating film can be formed using a metal oxide or a stacked body of a metal and a metal oxide.

Also in this case, when the magnetization direction of the perovskite-type manganese oxide is parallel to the magnetization direction of the ferromagnetic metal, the tunnel resistance is small, and when the magnetization direction is antiparallel, the tunnel resistance is large. However, the magnitude of each coercive force is controlled so that the magnetization direction of the perovskite-type manganese oxide does not change with respect to the magnetic field within the detection range, and only the magnetization direction of the ferromagnetic metal changes. . This control can be performed by adjusting the material composition, forming method, shape, and the like of the electrode. The operating magnetic field of the magnetic field detecting element having such a configuration is determined only by the magnitude of the coercive force of the ferromagnetic metal, and it is possible to reduce the magnitude by the conventional technology. Can be.

The rate of change in electric resistance of this magnetic field detecting element is greater than that of the conventional ferromagnetic metal tunnel junction element. The reason is that the following relationship exists between the tunnel current characteristics between the ferromagnetic electrodes and the ferromagnetic material. That is, it is known that the maximum rate of change of the tunnel resistance between the ferromagnetic electrodes is theoretically expressed by the following equation.

(Rap−Rp) / Rp = 2P _A P _B (1−P _A P _B ) ‥‥‥ (1) where Rp is the tunnel resistance when the magnetization directions of both electrodes are parallel, and Rap is Parallel tunnel resistance. P _A ,
P _B is the spin polarizability of each electrode, and is given by the following equation, where the numbers of upward spins and downward spins are n ↑ and n ↓, respectively.

P = (n ↑ −n ↓) / (n ↑ + n ↓) ‥‥‥ (2) Therefore, as the spin polarizability increases, the maximum rate of change of the tunnel resistance increases. Although this theoretical formula does not always exactly match the measured value at various tunnel junctions,
The tendency that the higher the spin polarization of the ferromagnetic electrode is, the larger the rate of change in the tunnel resistance is, which is consistent with the measured results. According to the literature, the spin polarizabilities of Ni ₈₀ Fe ₂₀ and Co at room temperature are 0.30 and 0.34, respectively, and slightly increase at low temperatures. On the other hand, "Solid State Physics" 32 (1997) 29
The papers by Kimura and Tokura published in Nos. 8 to 308 state that the spin polarizability of perovskite-type manganese oxides at low temperatures is theoretically close to 1.0, and La _0.67 Sr _0.33 MnO ₃ is measured by actual measurement. 0.54 at the membrane (temperature 4.2
K) has been reported.

Using the spin polarizabilities of the various materials and calculating the tunnel resistance change rate based on equation (1), the following is obtained. That is, when the electrode is made of a combination of Ni ₈₀ Fe ₂₀ and Co, 23% and La _0.67 Sr _0.33 MnO are used.
₃ comrades when was the electrode 82%, Ni ₈₀ Fe ₂₀ and La
_When a combination of _0.67 Sr _0.33 MnO ₃ is used as an electrode, the ratio is 39%. Therefore, the tunnel junction type magnetic field detecting element having the configuration according to the present invention operates with a weaker magnetic field than that using the perovskite type manganese oxide as an electrode, and has a larger tunnel resistance change than that using the ferromagnetic metal as an electrode. Rate will be obtained.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of a magnetic field detecting element according to the present embodiment. In FIG. 1, 1 is a substrate, 2 is a lower lead wiring, 3 is a perovskite-type conductive oxide magnetic material electrode,
Is a ferromagnetic metal electrode, 5 is an insulating film provided at a tunnel junction, 6 is an upper lead wiring, and 7 is an insulating layer between the lead wirings.

As the substrate 1, a silicon wafer is used, and
Forming a platinum film as the lower lead wiring 2 by sputtering
To achieve. While heating this substrate to 700 ° C.,
The electrode type conductive oxide magnetic material electrode 3 has a thickness of 80 nm.
La_0.67Sr_0.33MnO_ThreeLaser ablation of film
And then 1.5 nm thick aluminum
A film was formed by sputtering. The insulating film 5
Ar + O minium film _TwoSputter etch in gas
l_TwoO_ThreeIt was formed by changing to Therefore insulating film
The exact thickness of 5 is unknown, but the sputter etch conditions
Sample under conditions that change the conditions to obtain the optimal tunnel current
It was created. According to other reports, estimates from properties and
There is a report that the range may be 1.5 to 6 nm. Sa
Furthermore, a 50 nm thick Ni₈₀Fe₂₀Sputter film
The ferromagnetic metal electrode 4 was formed by a ring. Next photo
Form resist pattern by plate making, ion milling
By etching at 3, the laminated structure of 3, 4, 5
Patterning was performed to a size of 10 μm × 30 μm. Continued
And the insulating layer 7 is made of SiO_TwoFormed with film
Then, the upper lead wiring 6 is formed with a gold sputtered film.
Was. Coercivity of perovskite-type conductive oxide magnetic electrode 3
The force was about 80 Oe. Magnetic characteristics of ferromagnetic metal electrode 4
Is optimized by heat treatment in a magnetic field before patterning.
The coercive force after turning should be less than 5 Oe
I made it.

The device fabricated in this manner was operated at a temperature of 4.2.
FIG. 2 shows the result of measuring the external magnetic field dependence of the tunnel current flowing between both electrodes by applying a DC voltage between the upper and lower lead wires after cooling to K. In terms of tunnel resistance, a maximum resistance change rate of 30% was obtained at an external magnetic field of 5 Oe or less.

The perovskite-type conductive oxide used in the magnetic field detecting element of the present invention is required to have a high spin polarizability, but does not need to have a low coercive force.
Great freedom of choice. Also, there is no restriction on the forming conditions for reducing the coercive force.

In this embodiment, a La _0.67 Sr _0.33 MnO ₃ film was used as the perovskite-type conductive oxide magnetic material electrode 3 because the Curie temperature of this film was 300K.
This is because the spin polarization at a low temperature is considered to be large. La _1-x Pb _x MnO ₃ (x = 0.3-0.
4) The film and the La _1-x Sr _x NiO ₃ (x = 0.3) film also have a Curie temperature of 300 K or more and can be used similarly. Even if another perovskite-type conductive oxide magnetic material having a lower Curie temperature is used as an electrode, the operating temperature range is narrowed, but the operation is basically the same. Further, if a perovskite-type conductive oxide magnetic material having a higher Curie temperature is discovered in the future, it is possible to increase the operating temperature range with a similar element configuration. In this embodiment, the Ni ₈₀ Fe ₂₀ film is used as the ferromagnetic metal electrode 4. However, other ferromagnetic metal films containing any of Fe, Ni, and Co may be used as long as the coercive force is small. In this embodiment, the Al ₂ O ₃ film is used as the insulating film 5. However, SrZrO ₃ , SrZr (T
i) An insulating film such as O ₃ , PbTiO ₃ , MgO, or ZrO ₂ may be used.

[0025]

As described above, according to the present invention, in a tunnel junction type magnetic sensing element, a ferromagnetic metal and a perovskite type conductive oxide magnetic material are used as upper and lower electrodes, and a ferromagnetic metal electrode is used in a detection magnetic field range. Since only the magnetization direction is substantially changed, the following effects can be obtained.

1) A magnetic field detecting element which operates with a weak magnetic field similar to a tunnel junction type magnetic field detecting element having electrodes of ferromagnetic metals as electrodes and has a larger tunnel resistance change rate can be obtained.

2) In a conventional tunnel junction type magnetic field detecting element having upper and lower electrodes made of perovskite-type conductive oxide magnetic materials, the coercive force of the lower electrode must be reduced in order to reduce the detected magnetic field as much as possible. However, there are various restrictions on the conditions for forming the lower electrode, but according to the present invention, the perovskite-type conductive oxide magnetic electrode can have any coercive force, which facilitates fabrication.

[Brief description of the drawings]

FIG. 1 is a sectional view of a magnetic field detecting element according to an embodiment of the present invention.

FIG. 2 is a diagram showing the external magnetic field dependence of the tunnel current of the magnetic field detecting element of the present invention.

[Explanation of symbols]

1 substrate, 2 lower lead wiring, 3 perovskite-type conductive oxide magnetic material electrode, 4 ferromagnetic metal electrode, 5
Insulating film, 6 Upper lead wiring, 7 Insulating layer between lead wiring.

Claims (3)

[Claims] 1. A perovskite-type conductive oxide magnetic electrode, a ferromagnetic metal electrode, and a ferromagnetic metal electrode disposed between the two electrodes for detecting a tunnel current and interrupting exchange magnetic coupling between the two electrodes. A magnetic field detecting element comprising: 2. A magnetization direction of the perovskite-type conductive oxide magnetic material electrode does not substantially change with respect to an external magnetic field within a magnetic field strength range to be detected, and a magnetization direction of the ferromagnetic metal electrode changes. 2. The magnetic field detecting element according to claim 1, wherein the magnitude of the coercive force of the two electrodes is controlled so as to substantially change. 3. The magnetic field detecting element according to claim 1, wherein said perovskite-type conductive oxide magnetic material electrode is formed on a substrate, and said insulating film and said ferromagnetic material electrode are disposed thereon.