MXPA96006701A - Sensible device for the magnet field - Google Patents

Abstract

The present invention relates to a device sensitive to the magnetic field formed by at least one series of layers, which have opposite directions of magnetization, said series of layers characterized in that it comprises: an electrically insulating substrate, a layer of an electrically magnetic material conductor sauve, a layer of giant magnetoresistive material (GMR) arranged in electrical contact with the layer of soft electrically conductive magnetic material, the thickness of the material layer GMR is not greater than twice the mean free path of an electron in said material GMR, the layers are arranged so that the electric current through the layers alternately passes through a layer of soft magnetic material and deoxidized material GMR and have opposite magnetic field magnetization directions applied

Description

SENSITIVE DEVICE QL MAGNETIC CTIFlPO This invention relates to devices sensitive to the magnetic field and relates more particularly to a magnetic field responsive device having improved sensitivity and performance and includes one or more giant agneoresistant materials (Gr? R). Up to now, a variety of magnetic field detectors have been proposed. The simplest of these are the Hall effect magnetometers in which the size of the magnetic field is derived from the measurement of? N transverse voltage in a semiconductor carrying current placed in the magnetic field. These devices are extremely sensitive to temperature, and in fact the measured values depend exponentially on the temperature. Classical magnetoresistive materials, such as fierronickel, have also been used for scattering field capture, but these devices are too insensitive for many applications. Saturation magnetsometers are also used to measure magnetic fields. In these devices a soft magnetic material is excited with a PC excitation field, the response modified by the ambient field being observed. Stratified sandwich magnetoresistive devices have been proposed which comprise at least two deposited layers of magnetic thin films separated by a layer of non-magnetic thin film, to be used as magnetic memory cells and transducer assemblies for reading agnetoresis iva. Examples of these devices are illustrated in the specifications of European Patent Nos. 0276784 and 0314343, US Patent No. 4897288, and International Patent Application No. W091 / 18424, the full disclosures of which are incorporated herein by reference. Giant magnetoresistive materials (GMR) of the chromofierro or coppercobalt type have been proposed for use in magnetic field detectors. The sensitivity of these devices incorporating GMR materials can be improved by the use of stratified sandwich structures, but again the change in electrical resistance to low magnetic fields is not sufficient for many applications. However, in higher fields an 8R / R of BOX is reached at room temperature. Other magnetoresistive materials that have been suggested include platacobalt, but this is a very fine grain material and inherently hard magnetically. It is only useful in devices for measuring high magnetic field resistance. In Phys Rev Lett 71 (1993) 2331, the full disclosure of which is incorporated herein by reference, a GMR material comprising a mixed oxide of lanthanum, barium and manganese is described with which a 6R / R of 97 * at room temperature in upper fields. None of the magnetic field detectors that have been proposed so far have achieved the combination of sensitivity, size and ease of manufacture necessary for many applications and any improvement in this regard would be highly desirable. According to the present invention there is provided a magnetic field sensitive device comprising a soft electrically conductive magnetic material and a giant magnetoresistive material proximate thereto in electrical contact with each other. In one aspect of the invention there is provided a magnetic field sensitive device comprising: an electrically insulating substrate; a layer of a soft electrically conductive magnetic material; a layer of a giant magneto-realistic material (GMR) disposed in electrical contact with the electrically conductive soft magnetic material layer, the thickness of the GMR material layer is not greater than twice the mean free path of an electron in said GMR material; the layers are arranged in any order or position on the substrate and have opposite magnetization directions in zero applied magnetic field. In another aspect, the invention provides a method of manufacturing a magnetic field sensitive device comprising: depositing on an electrically insulating substrate, in any order, i) - an electrically conductive layer of a soft magnetic material. ii) a layer of a giant magnetoresistive material (GMR), of a thickness not greater than twice the mean free path of an electron in the GMR material; the layers are deposited to be in electrical contact, and if necessary, treat the layers so that they have opposite directions of magnetization in zero applied magnetic field. The magnetic field sensitive device may be, for example, a magnetic field detector, a proximity detector, a security device, a magnetoresistive reading translator, a saturation magnetometer or a direction search device. The electrically insulating substrate preferably has a smooth surface and most preferably a flat surface and may comprise, for example, a glass layer, a silicon wafer, a plastics material or other suitable electrically insulating film or surface. In this specification, a soft magnetic material is in which it has its magnetization direction changed into low magnetic fields of the order of, for example, less than about 1000 Ornps per meter. The electrically conductive soft magnetic material can be any suitable ferromagnetic material or alloy, and for example, very good results are obtained with iron alloys with nickel and / or cobalt, for example. The preferred soft magnetic material is In principle, any suitable GMR material, preferably with low electrical conductivity, can be used in the devices of the invention. Preferably, the GMR material is a semiconductor or an electrical insulator, for example a magnetic oxide, such as, for example, iron oxide; or a mixed oxide of lanthanum, a metal of group Ia and manganese, such as, for example, lanthanum oxide, barium, manganese; lanthanum oxide, calcium, manganese; or lanthanum oxide, strontium, manganese. Particularly good results have been obtained using a mixed oxide of lanthanum, barium, manganese of the type mentioned above. If desired, a plurality of layers of soft magnetic material and GMR material can be used. The layers of soft magnetic material and GMR material are arranged on the substrate so that an electric current passing through the layers must alternately pass through a layer of magnetic material and a layer of GMR material. In a first preferred embodiment, the substrate, and one or more layers of the soft magnetic material layer and the GMR material may, for example, be arranged in a sandwich-like laminated construction on the substrate. Preferred GMR oxide materials are semiconductors or insulators and it is thus important that the thickness of the layer, or each of the layers, of the GMR material be sufficiently small to allow the electrons to pass transversely through the GMR material. Preferably, the thickness of the layer or each of them is not more than one and a half times the mean free path of an electron in the GMR material and very preferably the thickness is equal to or less than the mean free path of an electron in the GMR material. In general, this requires that the thickness of the layer or layers be around 10 to 100 grid spaces (0.2μ), and preferably 500-1500 angstroms, at one point, at least. The thickness of the layer, or each of the layers, of soft magnetic material is also preferably small, but in this case the thickness is not critical, and for example suitable thicknesses from 1 to 100 u. In a second preferred embodiment, the magnetic field sensitive device comprises: an electrically insulating subtracter, an electrically conductive layer on the substrate, the layer comprising a plurality of elongated strips of a soft electrically conductive magnetic material and a magnetoresistive material (GMR) arranged alternately and side by side with their adjacent surfaces in electrical contact. the amplitude of each of the strips of GMR material in the plane dβ the electrically conductive layer is not greater than twice the average free path of an electron in said GMR material; and the adjacent strips of soft magnetic material and GMR material have opposite magnetization directions in zero applied magnetic field. In this aspect of the invention, such a device can be manufactured by a method comprising: depositing an electrically conductive layer of a soft magnetic material on a substrate. removing the thin elongated strips of the soft magnetic material at intervals so as to form pathways in the layer whereby elongated strips or plateaus of soft magnetic material electrically insulated from one another by the tracks are produced in the layer. deposit a giant magnetoresistive electrically insulating material (GMR) on the layer, so as to fill, or at least put the tracks in the layer. the amplitude of each of the paths in at least one point along this length is not more than twice the average free path of an electron in the GMR material, and if necessary, treat the layer so that the Adjacent strips or plateaus of soft magnetic material and strips of GMR material that fill or bridge the tracks have opposite magnetization directions in zero applied magnetic field. The strips or plateaus of soft magnetic material and strips of GMR material or filled channels are alternately arranged on the substrate in such a way that an electric current passing through the layer must pass through alternating plateaus of soft magnetic material and tracks of GMR material. The amplitude of each of the pathways is small enough to allow the electrons to pass through the deposited layer of GMR material that fills or lays the pathway. Preferably, the amplitude of each path is not greater than one and a half times the average free path of an electron in the GMR material, and most preferably the amplitude is equal to or less than the mean free path of an electron in the GMR material. In general, this requires that the amplitude of the tracks be around ten to one hundred grid spaces (0.2 u) at least one point. The thickness of the soft magnetic layer deposited is preferably small, consistent with the layer having adequate electrical resistance. Thicknesses of about 0.1 to 5 microns can be used, but preferably the thickness is about 1 micron. The amplitude of each of the plateau strips of soft magnetic material is also preferably small, and for example amplitudes of 1 to 100 microns are suitable. In some preferred devices according to the invention, the soft magnetic material can be in close physical contact with the GMR material although this is not essential. The adjacent surfaces of soft magnetic material and GMR material can for example be separated by a thin layer of an electrically conductive metallic material for example, a noble metal such as copper, silver or gold. Where this separation layer is used, an "instantaneous" layer of eg gold, a few nanometers thick, is preferable. Electrodes can be attached to the device by any suitable means. For example, an electrode may be welded onto the layer of soft magnetic material, or joined by means of a conductive adhesive. An electrode can be attached to the layer of GMR material by, for example, applying an instantaneous layer of a conductive material, for example, gold, and then welding or applying a conductive adhesive to make the electrical connection. Although the invention is not intended to be linked to any particular theory, it is believed that by arranging the magnetic material s? Ave and the GMR material to have opposite directions of magnetization in zero applied magnetic field, the conduction of electrons through the GMR material is aided when the magnetism of the soft magnetic material is inverted, which increases the efficiency of the device. If necessary, the layers can be treated to ensure that the magnetization directions are opposite, by, for example, the application of a magnetic field of sufficient intensity to change the magnetization direction of soft magnetic material in a zero applied magnetic field. In the method of the invention the soft magnetic material layer is preferably deposited on the substrate, or the GMR material, by any of the known deposition techniques, for example sputtering, molecular beam epitaxy, electrodeposition, or laser ablation, up to that a layer of approximately 100 microns thick has been obtained. The plateaus and tracks are preferably obtained by an etching method, and lithographic techniques such as electron beam lithography or X-ray lithography can possibly be used. In electron beam lithography a mask is first used to make a pattern on the surface and plateaus and tracks are formed by plasma engraving. The tracks do not need to be of parallel sides, and for example, it may be advantageous for the tracks to become progressively narrower in amplitude towards their bottom, that is, when approaching the substrate. However, it is important to provide that none of the soft magnetic materials bridge the tracks to avoid non-optimal interchange of magnetic materials.

The GMR material can be deposited on the surface of the substrate, or the layer of soft magnetic material, by any suitable technique, but preferably the deposit is by laser ablation. Sizzle may be used in some cases, but usually it is not preferred. The GMR material can also be deposited on the surface of the recorded layer of soft magnetic material by any suitable technique, but preferably the reservoir is by laser ablation. This procedure is highly directional and can therefore more easily fill the tracks with the GMR material. In practice, it has been found that it is highly desirable to deposit the GMR material on an appropriate reticular equaled oxide layer. Suitable oxides include, for example, yttrium / barium / copper oxide (preferable in its metallic rather than superconductive phase). The method of the invention therefore preferably includes the step of depositing a layer of a lattice-matched oxide before depositing the GMR material. After the . deposit of the layers, the entire device can be fixed, if desired, for example at a temperature of 100 to 600 ° C. Preferred embodiments of magnetic field sensitive devices according to the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows a diagrammatic representation of a first device in sectional lateral elevation; Figure 2 shows the device of figure 1 in plan view; Figure 3 shows a diagrammatic representation of a second device in sectional lateral elevation; and Figure 4 shows the device of Figure 3 in plan view. With reference to the drawings, the first device, illustrated generally in 1, comprises a substrate dß silicon electrically insulating slice 2, which has deposited on it, by a crackling technique, a layer 3 of fierronickel NÍ3Fe dß lμ thickness . An instant coating 4 of a noble metal such as gold, titanium or tantalum of 1 to 100 nanometers in thickness can then be applied to the deposited layer of NF3Fe by vapor deposition. The layer dÍ NÍ3Fe covered instantaneously soon is covered with a thin layer of o * i or of yttrium, barium, copper 4a, followed by deposit of a layer of material GMR 5 by laser ablation. GMR laser-laced material is a mixed oxide of lanthanum, barium and manganese, as described in Phys Rev. Lett. 71 (1993) 2331, previously referenced. A second layer of NF3Fe (not shown) can be deposited on the layer of GMR material if desired.

Finally, an additional instant coating 6 of gold, titanium or tantalum is applied to the surface of the deposited GMR material, and the device is connected by making electrical connections 7, 8 to the fierronickel layer 3 and the gold coating 6, respectively. If necessary, the device is "polarized" by applying a magnetic field of sufficient intensity to change the magnetization direction of the NF3Fe layer in a zero applied magnetic field, to ensure that the magnetic layers have opposite directions of magnetization. To operate the device is connected to an EMF source 9 and a voltmeter 10. During the operation, the device is placed in the magnetic field whose intensity is to be measured and the EMF source is turned on. Generally, an applied current of approximately 1 to 10 milliamperes will be adequate. The effect of the magnetic field intensity alters the number of electrons that can pass through the GMR material and thus alters the apparent resistivity. The change in potential is measured with the voltmeter and is directly related to the intensity of the field. Referring to Figures 3 and 4, the second device, illustrated generally at 11, comprises a plastic film substrate 12 that has deposited thereon, by means of a crackling technique., a layer 13 of lμ thickness of fierronickel NÍ3Fe. The layer NÍ3Fe has recorded * -. on its surface, by electron beam lithography, a plurality of parallel tracks 14 extending to the surface of the substrate 12 and to adjacent isolated plateaus of fierro-nickel 15 from one another. In the illustrated device the tracks are parallel side, but other configurations are possible, for example, the tracks can be made narrower in the direction of the substrate 12. In the upper part of the layer of fierronickel 13 "There is deposited by laser ablation a layer of GMR material 16 comprising a mixed oxide of lanthanum and manganese. As shown in Figure 3, the tracks can be completely filled with GMR material as in 17, but this is not essential, and the GMR material could only partially fill the track or simply form a bridge between adjacent plateaus as illustrated in 18 The electrical connections 19, 20 are made to the fierronickel layer, which extends to a current source 21 and a voltmeter 22. During the operation, the device is placed in the magnetic field whose intensity is to be measured and subjected to an applied current of 1 to 10 milliamperes. The change in potential is measured with the voltmeter and is directly related to the magnetic field strength. As illustrated, the sensitivity of the device is greater in one direction along the plateaus. However, the dimensions of the device may be chosen to give extreme directionality, or relative non-directionality if desired. The reader's attention is directed to all documents that are presented concurrently with this specification and which are open to public inspection with this specification, and the content in all these papers and documents are incorporated herein by reference. All the features described in this specification (including any claims, attached drawings and summary) and / or all the steps or any method or procedure so described, can be combined in any combination, except combinations where at least part of these characteristics and / or steps are mutually exclusive. Each characteristic described in this specification (including any claim, summary, attached drawings) may be replaced by alternative features that serve equal, equivalent, or similar purposes, unless expressly stated otherwise. Therefore, unless otherwise expressly specified, each characteristic described is an example only of a generic series of equivalent or similar characteristics.

Claims (31)

NOVELTY OF THE INVENTION CLAIMS

1. - A device sensitive to the magnetic field comprising, an electrically insulating substrate, a layer of electrically conductive soft magnetic material; a layer of giant magnetoresistive material (GMR) disposed in electrical contact with the electrically conductive soft magnetic material layer; the thickness of the GMR material layer is not more than twice the mean free path of an electron in said GMR material; the layers are arranged in any order or position on the substratum and have opposite magnetization directions in zero applied magnetic field.

2. A device sensitive to the magnetic field according to claim 1, further characterized in that it is a magnetic field detector, a proximity detector, a safety device, a magnetoresistive reading transducer, a saturation magnetometer, or a device of address search.

3. A device sensitive to the magnetic field according to claim 1 or 2, further characterized in that the substrate comprises a flat surface of a glass, a slice of silicon or a plastic material.

4. A device sensitive to the magnetic field according to any of the preceding claims further characterized in that the soft magnetic material comprises a ferromagnetic material or alloy.

5. A device sensitive to the magnetic field according to claim 4 further characterized in that the soft magnetic material is fierronickel.

6. A device sensitive to the magnetic field according to any of the preceding claims further characterized in that the material GMR is a magnetic oxide.

7. A device sensitive to the magnetic field according to claim 6, further characterized in that the magnetic oxide is iron oxide or a lanthanium-barium-manganese oxide.

8. A device sensitive to the magnetic field according to any of the preceding claims further characterized in that the substrate and the layers of electrically conductive soft magnetic material and the GMR material are arranged in a sandwich construction.

9. A device sensitive to the magnetic field according to claim 8 further characterized in that the thickness of the layer of material GMR is equal to or less than the mean free path of an electron in the GMR material.

10. A device sensitive to the magnetic field according to claim 8 or 9, further characterized in that the thickness of the layer of material GMR is from 10 to 100 reticular spaces approximately in at least one point.

11. A device sensitive to the magnetic field according to any of the preceding claims further characterized in that the thickness of the layer of soft magnetic material is from 1 to 100 μ approximately.

12. A device sensitive to the magnetic field according to any of the preceding claims, further characterized in that it comprises a electrically insulating substrate, an electrically conductive layer on the substrate; the layer comprises a plurality of elongated strips of a soft electrically conductive magnetic material and a magnetoresistive material (GMR) disposed alternately and side by side with their adjacent surfaces in electrical contact; the amplitude of each of the strips of GMR material in the plane of the electrically conductive layer is not more than twice the mean free path of an electron in said GMR material; and the adjacent strips of soft magnetic material and GMR material have opposite magnetization directions in zero applied magnetic field.

13. A device sensitive to the magnetic field according to claim 12, further characterized in that the strips d, soft electrically conductive magnetic material and GMR material are disposed respectively in a series of alternating plateaus and paths.

14. A device sensitive to the magnetic field according to claim 13 further characterized in that the amplitude of each path is equal to or less than the mean free path of an electron in the GMR material.

15. A device sensitive to the magnetic field according to claims 13 or 14 further characterized in that the amplitude of each of the tracks is 10 to 100 grid spaces approximately at least at one point.

16. A device sensitive to the magnetic field according to any of claims 12 to 15, further characterized in that the thickness of the strips of the electrically conductive soft magnetic material is approximately 0.1 to 5 μ.

17. A device sensitive to the magnetic field according to any of claims 14 to 16, further characterized in that the amplitude of each of the strips of soft magnetic material is from 1 to 100 μ.

18. A device sensitive to the magnetic field according to any of the preceding claims, further characterized in that the soft magnetic material is in intimate physical contact with the GMR material.

19. A device sensitive to the magnetic field according to any of claims 1 to 17, further characterized in that the adjacent surfaces of the soft magnetic material and the GMR material are separated by a thin layer of an electrically conductive metallic material.

20. A device sensitive to the magnetic field according to claim 19, further characterized in that the separation layer comprises a noble metal.

21. A device sensitive to the magnetic field substantially as described above with reference thereto and as illustrated in the accompanying drawings.

22. A device sensitive to the magnetic field substantially as described above.

23. A method of manufacturing a device sensitive to the magnetic field comprising: depositing on an electrically insulating substrate, in any order, (i) an electrically conductive layer of a soft magnetic material; (ii) a layer of giant magnetoresistive material (GMR) of a thickness, at least one point, no greater than twice the mean free path of an electron in the GMR material, the layers are deposited so as to be in contact electrical, and, if necessary, treat the layers in such a way that they have opposite directions of magnetization in the zero applied magnetic field.

24. - A method according to claim 23 further characterized in that it comprises: depositing an electrically conductive layer of? N soft magnetic material on a substrate, remove the thin elongated strips of soft magnetic material at intervals so as to form pathways in the layer whereupon elongated strips or plateaus of soft magnetic material are produced in the layer electrically isolated from each other by the tracks, depositing a giant electrically insulating magnetoresistive material (GMR) on the layer in order to fill, or at least to put the tracks in place. the layer; the amplitude of each of the paths, at least one point, along its length, is not more than twice the average free path of an electron in the GMR material; and if necessary, treat the layer in such a way that adjacent strips or plateaus of soft magnetic material and GMR material that fill or bridge the tracks have opposite directions of magnetization in the zero applied magnetic field.

25. - A method according to claim 23 or 24, further characterized in that the layer of soft magnetic material is deposited on the substrate by sparking, molecular beam epitaxy, electrodeposition, or laser ablation.

26. A method according to claim 24 or 25, in which plateaus and tracks are obtained by a lithographic engraving process.

27. A method according to any of claims 23 or 26, wherein the GMR material is deposited by laser ablation.

28. A method according to any of claims 23 to 27, further characterized in that before depositing the GMR material a matched oxide layer is deposited.

29. - A method according to any of claims 23 to 28, further characterized in that after the deposition of the layers, the device is fixed by heating to a temperature of 100 to 600 >; C.

30. - A method according to any of claims 23 to 29, further characterized in that a magnetic field is applied to the device, of sufficient intensity to change the magnetization direction of the soft magnetic material of a zero applied magnetic field so that the magnetization directions of the soft agglomerative material and the GMR material are opposite.

31. A method according to any of claims 23 to 30, substantially as described above.