GB2351604A

GB2351604A - Giant magnetoresistance cell

Info

Publication number: GB2351604A
Application number: GB0011595A
Authority: GB
Inventors: Bosch Gmbh Robert; Peter Schmollngruber; Martin Freitag; Hubert Brueckl; Sonja Heitmann; Andras Huetten; Guenter Reiss
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1999-05-29
Filing date: 2000-05-12
Publication date: 2001-01-03
Anticipated expiration: 2020-05-12
Also published as: DE19924756A1; ITMI20001075A0; ITMI20001075A1; FR2794288A1; IT1317590B1; GB0011595D0; GB2351604B

Abstract

A magnetoresistive element, in particular a giant magnetoresistance (GMR) cell has first layers (10) separated by non-magnetic second layers (20). The first layers (10) are composed of at least three strata (10a, 10b, 10c), where at least two of the three have magnetic properties. In the presence of a magnetic field, the magnetic strata in the first layers (10) may have parallel or antiparallel orientation with respect to one another.

Description

2351604 MAGNETORESISTIVE ELEMENT The present invention relates to a

magnetoresistive element, for example a giant magnetoresistance (GMR) cell.

Lamination bodies of ultra-thin magnetic and non-magnetic individual layers can, subject to certain conditions, exhibit the known per se magnetoresistive or GMR effect. Elements, which in the simplest case consist of two thin magnetic layers separated by a nonmagnetic intermediate layer, are termed coupled layer systems. The magnetic layers interact, in which case the magnetic moments in the layers orient themselves parallelly or antiparallelly in dependence on the thickness of the intermediate layer. For example, in the case of elements in which the magnetic layers consist of cobalt and the non-magnetic layer is made of copper, an antiparallel orientation of the magnetisations of neighbouring layers (first and second antiferromagnetic maximum) results with usual thicknesses of the magnetic layer of 10 to 40 angstroms and a thickness of the non-magnetic layer of about 10 or about 20 angstroms, and a parallel orientation of the magnetisation of the magnetic layers (first ferromagnetic maximum) results with an intermediate layer thickness of about 15 angstrbms. It is usual to arrange a large number of such threestrata elements one above the other.

Elements or materials constructed in such a manner are of significance as functional layer materials for magnetic sensors of different kinds. However, the resistance characteristic, which is dependent on the magnetic field, of the elements (MR characteristic) must have characteristic magnitudes specific to the application. It is known, for example, to influence the MR characteristic by material selection of the individual layers, the layer sequence, the thickness of the individual layers and process parameters during the production. Relevant characteristic magnitudes are, for example, the absolute change in the electrical resistance of the magnetoresistive element in an applied magnetic field, the so-called effect magnitude, the magnetic field for which no change in resistance occurs any longer, the so-called saturation field, and the hysteresis of the characteristic of the magnetoresistive element. These characteristic magnitudes cannot, however, be set as desired and independently of each other by means of variation of the mentioned parameters (material selection, layer sequence, individual layer thicknesses, process parameters) in the case of conventional magnetoresistive elements, in particular conventional GIVIR cells.

2 There is accordingly a need for a magnetoresistive element, especially a GIVIR cell, in which the characteristic magnitudes of the element, i.e. the magnitudes of the MR characteristic of the element, may be able to be set to a greater degree and with greater independence from each other by comparison with conventional elements.

According to the present invention there is provided a magnetoresistive element, in particular GIVIR cell, with first layers, which are arranged in alternation one above the other, with magnetic properties and second layers with non-magnetic properties, characterised in that the first layers have an at least three-strata build-up, wherein at least two of the at least three strata have magnetic properties.

With a magnetoresistive element embodying the invention, the magnitudes of the MR characteristic can be set to substantially greater degree and more independently of each other than possible for conventional magnetoresistive elements. Consequently, substantially more flexible functional layer materials for different cases of application can be realised. In the simplest case, in particular of a multi-layer magnetoresistive element in which magnetic and non-magnetic layers are arranged in alternation one above the other, the respective magnetic layer is formed as a so-called trilayer or in three strata, wherein a nonmagnetic stratum is formed between two magnetic strata. The term "stratum" is used in the sense of an individual stratum-like component of a "layer", wherein the magnetoresistive elements consist of a number of "layers" which are, in turn, composed of a number of strata.

Preferably, all strata of the layers having the respective magnetic property have magnetic properties in their turn. Due to the co-operation of the layers having magnetic properties with the intermediate layers having non-magnetic properties, the setting of characteristics, which are improved by comparison with conventional elements, can be undertaken by variation of the parameters of the individual strata of the magnetic layer.

Preferably, also, a middle one of three strata of a magnetic layer has a thickness which causes a parallel or antiparallel orientation of the magnetisation of the two adjacent outer strata. By contrast to conventional magnetoresistive elements, it is possible to allocate "internally" different magnetisation states to the magnetic layers. Whilst only two "internal" states could be realised for a conventional magnetic layer, four states of magnetisation 3 can be realised within a magnetic layer of an element embodying the invention. Advantageous applications are thus possible in the case of the use of the magnetoresistive element as, for example, a storage element or sensor element.

For preference, the magnetic strata of the respective magnetic layers are made of different materials. If, for example, cobalt (Co) is used for the first magnetic stratum and nickel-iron (NiFe) is used for the second magnetic stratum, MR characteristics with a substantial degree of variation can be produced by choice of the thickness of the individual strata.

Preferably, the non-magnetic layers between magnetic layers and the nonmagnetic strata within the magnetic layers are made of different materials. By this measure, too, the MR characteristics can be varied to a much greater degree than was hitherto possible.

It is furthermore possible according to an advantageous embodiment of the magnetoresistive element that the magnetic strata of at least one magnetic layer have different thicknesses.

An embodiment of the present invention will now be more particularly described by way of example with reference to the accompanying drawings, in which:

Fig. 1 is a schematic sectional view of a prior art GMR cell; Fig. 2 is a schematic section of a magnetic layer which is formed as trilayer and which represents a component of a magnetoresistive element embodying the present invention; and Fig. 3 is a schematic sectional view of a GMR cell embodying the present invention.

Referring now to the drawings there is shown in Fig. 1 a prior art GMR cell comprising a coupled layer system in which individual magnetic layers 1 are each separated by nonmagnetic intermediate layers 2. The thickness of the layers 2 is selected so that an antiparallel orientation of the magnetic moments of the layers 1 results, as indicated by means of arrows (first or second antiferromagnetic maximum). If it is endeavoured in the case of such a GIVIR cell to, for example, achieve an increase in the effect magnitude by

4 variation of the material selection or the individual layer thicknesses, the saturation field also increases. For example, if alloys containing Co are used for the magnetic layers 1, in the case of arrangement according to Fig. 1 a hysteresis always arises, which is disadvantageous for most applications.

For the avoidance of disadvantages of that kind, in a preferred embodiment of the present invention the homogeneous magnetic layers 1, as illustrated in Fig. 1 are replaced, by magnetic trilayers, as illustrated in Fig. 2. It can be seen in Fig. 2 that such a trilayer, which is denoted by 10, comprises two outer magnetic strata 10a and 1015 and an intermediate stratum 10c. Although the intermediate stratum 10c can also be formed to be magnetic, it is presupposed for the purpose of the following explanation that the stratum 10c consists of a non-magnetic material, for example copper or ruthenium (Ru). A parallel or antiparallel orientation of the magnetisations of the strata 1 Oa and 1 Ob can be effected in the case of suitable magnetic fields by choice of the thickness of the intermediate stratum 10c.

A preferred embodiment of a GMR cell, in which the magnetic strata 10 are formed as trilayers, is illustrated in Fig. 3. Non-magnetic layers 20 are formed between the individual trilayers 10. The materials used for the non-magnetic layers 20 of the GIVIR cell can differ from the material for the non-magnetic intermediate stratum 1 Oc of the magnetic layer 10.

A comparison of the state of magnetisation (antiparallel orientation of the individual strata), as illustrated in Fig. 3, of the respective magnetic layers with the state of magnetisation as illustrated in Fig. 1 indicates that four different states of magnetisation can be realised within a magnetic layer in a GIVIR cell as illustrated in Fig. 3, whilst merely two states are possible in the case of a conventional magnetic layer as illustrated in Fig. 1.

The magnetoresistive element shown in Fig. 3 is further distinguished by the fact that a variation of the individual stratum thicknesses is possible within the magnetic layers 10.

For example, the effect magnitude as well as also the saturation field and thereby the sensitivity of the strata or layers can be optimised at the same time by the mentioned possibilities of variation. If the nonmagnetic intermediate layers 20 are, for example, optimised in the direction of smaller saturation fields by way of a small exchange interaction, the magnetic layers 10 formed as trilayers can at the same time be optimised to obtain greater magnitudes of effect, whereby a MR characteristic with small saturation fields and great effect magnitudes can be achieved. Both magnitudes can thus be set and optimised substantially independently of each other.

The individual stratum thicknesses of the respective magnetic layers 10 can have different thicknesses, as already mentioned. For example, a stratum 10a can have a thickness different from that of a stratum 10b. It is to be noted that the illustrated formation of the magnetic layers 10 as trilayer is merely one preferred example. Any desired multilayer structures of the individual layers 10 are feasible.

The MR characteristic of the magnetoresistive element can be detected in conventional manner, for example by measurement as well as by analysis of the strata or layer construction of the element.

6

Claims

1 A magnetoresistive element comprising a plurality of first layers with magnetic properties and arranged in succession and a respective second layer with non-magnetic properties and arranged between the or each two first layers in the succession, wherein each of the first layers comprises at least three strata and tat least two of those strata have magnetic properties.

2. An element as claimed in claim 1, wherein all of the strata of at least one of the first layers have magnetic properties.

3. An element as claimed in claim 1 or claim 2, wherein at least one of the strata of at least one of the first layers has a thickness which in the presence of a given magnetic field causes a parallel or antiparallel orientation of the magnetisation of the other strata of that layer.

4. An element as claimed in any one of the preceding claims, wherein the strata having magnetic properties in at least one of the first layers are made of different materials.

5. An element as claimed in any one of the preceding claims, wherein one of the strata of at least one of the first layers has non-magnetic properties, and that stratum and the second layer or at least one of the second layers are made of different materials.

6. An element as claimed in any one of the preceding claims, wherein the strata having magnetic properties in at least one of the first layers are of different thickness.

7. A magnetoresistive element substantially as hereinbefore described with reference to Figs. 2 and 3 of the accompanying drawings.