WO1998014793A1

WO1998014793A1 - Magnetic-field sensitive thin film sensor with a tunnel effect barrier layer

Info

Publication number: WO1998014793A1
Application number: PCT/DE1997/002236
Authority: WO
Inventors: Hugo Van Den Berg
Original assignee: Siemens Aktiengesellschaft
Priority date: 1996-10-02
Filing date: 1997-09-29
Publication date: 1998-04-09
Also published as: JP2001501309A; GB2333900B; GB9907727D0; GB2333900A; DE19781061D2

Abstract

The invention concerns a magnet-field sensitive thin film sensor (8) having a multiple layer system with at least one soft magnetic measuring layer (Ms). Said layer (Ms) should be separated from a series of layers (Sf) by a tunnel effect barrier layer (Tb) having a higher magnetic stiffness than the measuring layer (Ms). Advantageously, the sensor comprises a semiconductor area (H1), which forms, with an adjacent magnetic layer (Ms), a Schottky barrier (Sb).

Description

description

Magnetic field sensitive thin film sensor with a tunnel barrier layer

The invention relates to a magnetic field-sensitive thin film sensor with a multilayer system, which has at least one magnetic layer on both sides of a tunnel barrier layer. A corresponding thin-film sensor can be found in the publication “Phys. Rev. Let t. ", Vol. 74, No. 26, June 26, 1995, pages 5260 to 5263 and WO96 / 07208.

The well-known thin film sensor represents a magnetic field sensor with an electron spin valve effect, which acts as a

"Spin valve transistor" is referred to. This transistor has a semiconductor / metal / semiconductor structure, in which the metallic base is constructed in particular from a Co-Cu multilayer system with four periods. Such multilayer systems can have a high magnetoresistive effect show that can be over 2% at room temperature and is then generally referred to as "giant magnetoresistive effects" (GMR). The number of periods of 4 provided in the known thin-film device leads to a total thickness of the base of the order of magnitude of 140 Å. The so-called collector efficiency F _c = I _c / Ie _/ ie the ratio of the collector current I _c to the emitter current I _{e is given} by the following relationship:

F _c = C • exp (-W _b / Λ). (1)

C = a constant here, and W _b and λ are the base width and the free path length of the electrons, respectively. The free path length is at room temperature in magnetic multilayer systems around 80 Å and 5 Ä for majority electrons and minority electrons, respectively (see e.g. W094 / 15223). The typical thickness of a sensor with a GMR multilayer system is approximately 150 Å, so that a value of the collector efficiency F _c of 0.15 results for the majority electrons. If the basic width W _{b is} only 30 Å, the value for F _{c is} 0.7 or three times the collector current.

In the known spin valve transistor, a semiconductor is used on the injector side, which forms a Schottky barrier with the GMR multilayer system. However, this barrier is difficult to implement due to the structural sensitivity of the semiconductor material. A first possibility is the deposition of the semiconductor material on the GMR multilayer system by vapor deposition or sputtering. However, semiconductor materials deposited on metals are mostly amorphous or polycrystalline, so that Schottky barriers that are hardly reproducible can be realized. A second possibility is a so-called "vacuum bonding", in which a monocrystalline Si wafer is pressed onto the GMR multilayer system. However, the corresponding method must be carried out in an ultra-high vacuum. The emitter wafer is etched from the back to a membrane however, such technology is difficult to implement on an industrial scale and cannot be combined, in particular, with standard planar techniques.

In a further embodiment of a spin valve transistor, which can be gathered from the WO document mentioned at the outset, a non-magnetic layer made of insulating or semiconducting material between adjacent magnetic layers forms a tunnel barrier layer within its multilayer system. The layer or layers arranged on both sides of the tunnel barrier layer have an at least largely identical, different relatively low magnetic rigidity. It turns out, however, that with this known transistor the tunnel current through this tunnel barrier layer is dependent to a relatively lesser extent on external field changes. The measurement signal to be taken from the known transistor is accordingly inaccurate and difficult to reproduce.

The object of the present invention is to provide a magnetic-field-sensitive thin-film sensor with the features mentioned at the beginning, in which the aforementioned manufacturing difficulties are reduced. In addition, this sensor is said to have an improved tunnel current dependency with regard to external field changes.

This object is achieved with the measures of

Main claim solved. The term “magnetic rigidity in the sense of the magnetic hardness of the entire (sub) system of the layer sequence is to be understood (cf. for example“ IEEE Transactions on Magnet i es ”, vol. 32, pages 4624 to 4626 or“ Journal of Magnetism and Magnetic Materials ", vol. 165, 1996, pages 524 to 526).

The starting point here is the knowledge that the tunnel current change can be improved in the desired manner by increasing the magnetic rigidity of the layer sequence forming, for example, a magnetic injector. The reason for this can be seen in the following: The magnetization on one side of the tunnel barrier layer is practically fixed in the area of the layer sequence. This then results in two spin channels, namely a channel for majority electrons in a parallel magnetization alignment and a channel for minority electrons in an opposite alignment. The electron transport current therefore depends on the direction of magnetization of the measuring layer located on the opposite side of the tunnel barrier layer from. Depending on this direction, the energy level densities on the measuring layer side change for the two spin channels and thus the tunnel probability accordingly. A high signal swing and a high reversibility of the response function of the sensor therefore result in the highest possible magnetic rigidity of the layer sequence and a magnetically soft measuring layer. In contrast, differences in the scattering of the electrons are primarily exploited in the known spin valve transistor.

In the case of an embodiment of the sensor according to the invention as a spin valve transistor, it is to be regarded as particularly advantageous with regard to simple manufacture if the magnetically softer, relatively thin measuring layer is arranged on a semiconductor region of the transistor and serves as the base.

Advantageous refinements of the magnetic field-sensitive thin film sensor according to the invention emerge from the dependent claims.

To further explain the invention, reference is made below to the drawing. 1 shows a schematic arrangement of several sensors according to the invention, FIGS. 2 to 5 show different sensors according to the invention with different magnetic injectors, FIGS. 6 and 7 show the differences between a tunnel sensor with and without a semiconducting area, and FIG. 8 shows the differences Energy level density distribution in different bands for the two spin polarization directions of the majority and minority electrons, 9 shows a circuit diagram for reducing the temperature dependence of the tunnel current, FIGS. 10 and 11 show the differences between a spin valve transistor with a GMR multilayer system and a thin film sensor, and FIGS. 12 and 13 show two further basic training options for thin film sensors according to the invention.

In the figures, corresponding parts are provided with the same reference symbols. In this case, H1 is a layer made of a semiconductor material such as Si or a corresponding substrate, Ms is a soft magnetic measuring layer, Tb is a tunnel barrier layer, Ij is a magnetic injector, Bs is a bias layer and Sf is a layer sequence that is magnetically stiffer (harder) than the measuring layer. Known thin-film systems with a semiconductor / metal / transistor function, which have a tunnel and a Schottky barrier (see the literature references mentioned at the beginning), and thin-film systems with an increased, in particular GMR effect (see, for example, EP 0 483 373 A or DE-A-writings 42 32 244, 42 43 357 and the aforementioned W094 / 15223). So-called hard-soft systems and their modifications such as e.g. B. the so-called "Exchange-biased systems" or systems acting as "artificial anti-ferromagnets" are suitable. In contrast to the known GMR thin-film systems, in the multilayer system of the thin-layer sensors according to the invention, a hard magnetic part (= layer sequence Sf) and a soft magnetic measuring layer Ms are not covered by a non-magnetic metal Layer (as with the GMR systems), but separated by a tunnel barrier layer Tb. A corresponding basic structure is shown in Figure 1. A matrix of islands made of semiconducting material Hl is defined on a Si wafer 2 and is electrically isolated from one another, for example, by being impressed by a voltage. These islands H1 form, for example, the collectors K1 from a magnetic transistor structure Ts of a thin-film sensor 3 according to the invention. A metallic, soft-magnetic measuring layer Ms is applied to each island, which is indicated by a reinforced line

Schottky barrier Sb forms at the interface with the semiconductor Hl. This measuring layer is separated by means of a tunnel barrier layer Tb from a layer sequence Sf of at least two layers of a hard magnetic injector Ij.

Figures 2 to 5 show transistor structures with different training options for the layer sequence Sf serving as injector Ij. A semiconducting layer H1 can have a collector Kl with a Schottky barrier on it

Form an interface with a metallic layer applied to it.

The injector Ij can, for example, in accordance with FIG. 2 in the sensor 4 shown there, by a so-called “exchange-biased” layer sequence with a bias layer Bs and an antiferromagnetic layer 5, or in accordance with FIG. 3 in the sensor 8 shown there by an artificial one Antiferromagnetic layer sequence with a magnetic layer 6, which is antiferromagnetic via a coupling layer 7 to a

Bias layer Bs is coupled (cf. the W094 / 15223 mentioned).

In general, in the thin-film sensor according to the invention, its injector Ij is constructed from several layers in order to to combine temporal electron polarization and hard magnetic properties. In the embodiment according to FIG. 2, the magnetization of the magnetic layer Bs, which is preferably a ferromagnetic layer, is caused by the antiferromagnetic layer 5, which can also be a ferrimagnetic layer with a compensation temperature in the vicinity of the operating temperature of the sensor uniform condition recorded. The magnetic layer Bs, which must take care of the polarization of the electrons and which can optionally also be composed of several layers, lies directly on the tunnel barrier layer Tb. In the embodiment according to FIG. 3, too, with the injector Ij resting on the tunnel barrier layer Tb as an artificial antiferromagnet, its individual layers can also consist of several layers. Here, as in the other embodiments, the desired magnetic rigidity can advantageously be provided by the choice of material of an alloy of a rare earth and a transition metal and by the arrangement of the ferromagnetic layer directly on the tunnel barrier layer Tb for a desired spin polarization. Compared to an "Exchange-biased system", higher temperature stability can be expected here.

If necessary, it is also possible to reverse the stacking of measuring layer Ms, tunnel barrier layer Tb and injector Ij of the embodiments of thin-film devices 4 and 8 according to FIGS. 2 and 3. Accordingly, in the embodiment of a thin-film sensor 9 shown in FIG. 4, the positions of the measuring layer Ms and the injector Ij with respect to the tunnel barrier layer Tb are reversed compared to the embodiment 8 according to FIG.

In the embodiment of a thin-film sensor 10 shown in FIG. 5, its injector Ij provides a special artificial borrowed antiferromagnets with two outer bias layers Bs and Bs '. These layers are each coupled in an antiferromagnetic manner to a common flux-conducting magnetic layer Fs via two coupling layers 7 and 7'. In both embodiments 9 (according to FIG. 4) and 10 (according to FIG. 5), the distribution of the injected electrons is controlled via channels. A corresponding exchange for the thin-film device 4 according to FIG. 2 is only possible if necessary because the antiferromagnetic layer 5 is relatively thick here and the two spin channels are characterized by a very high resistance p. That is, their collector efficiency F _c is small. In contrast, a system acting as an artificial antiferromagnet is much thinner and advantageously has a lower p. The difference in resistance of the artificial antiferromagnet between the two spin channels can be made as large as possible by choosing the size α of the layers of the artificial antiferromagnet so that between the flux-guiding layer Fs and the bias layers

Bs or Bs' an inverse GMR effect occurs. The quantity α is a characteristic quantity for the spin dependence of the GMR effect and is expressed by the ratio pj, / pτ (cf., for example, the book “Ferro agnetic materials”, vol. 3, ed.: EP Wohlfarth, North Holland Publ. Co., Amsterdam et al., 1982, pages 747 to 804, especially pages 758 to 762), where pj and pt are the resistivities of the minority and majority electrons, respectively.

The same inverse GMR effect can also be used advantageously for the flux-guiding layer Fs of the embodiment according to FIG. 5 with two bias layers Bs and Bs'. This embodiment has the advantage over that according to FIG. 4 that a difference in the bias resistivity of the two spin channels is achieved even without an inverse GMR effect. Both versions Forms according to Figures 4 and 5 also have the advantage of high strength of the magnetization and long-term temperature stability with a suitable choice of the individual materials.

The thin film sensors according to the invention operate according to two different sensor principles, namely

1) after that of a spin valve transistor according to the embodiments of Figures 1 to 5 (with Schottky barrier) and

2) after that of a magnetic tunnel sensor without a semiconducting area or without a Schottky barrier.

The corresponding sensor types are referred to below as type I tunnel sensors with or type II tunnel sensors without semiconductor areas.

Advantages of the embodiments according to the invention result from a comparison with known sensor types and are explained below.

I. Consideration of tunnel sensors without and with semiconductor area

FIGS. 6 and 7 show simple versions of a tunnel sensor 12 of type II and a tunnel sensor 3 of type

I (according to Figure 1) compared. The magnetization in the hard magnetic injector Ij is indicated by an arrowed line M. Instead, the tunnel sensor 12 without a semiconductor region has a substrate 13 made of a common material without forming a Schottky barrier.

In addition to the potential across the tunnel barrier Tb, the tunnel probability depends above all on the energy level densities on both sides of the barrier at approximately the Fermi level. In the case of magnetic layers, a given this density from the spin direction, the

Density n for the minority electrons is significantly greater than nt for the majority electrons. For this purpose, reference is made to FIG. 8, in which d-band structures are shown in the form of a diagram based on known parameters in a conventional manner (see, for example, the book “Handbook of the band structure of elemental solids” by DA. Papconstantopoulus, Plenum Press, New York et al., 1986, especially pages 73 to 126. The diagram shows the energy level E of the electrons in the ordinate direction and the state densities Z _mi for the minority electrons and Z _ma for the majority electrons in the abscissa direction The Fermi level is labeled E _F. The state densities for the s and p bands are also shown in the diagram, and the corresponding, much smaller area for these bands is highlighted in the diagram by a different hatching and with s + marked p.

The spin direction remains in the tunnel process, so that the majority electron current I | and the minority electron current lτ through the tunnel barrier layer Tb given parallel magnetization of the two magnetic layers are given by the relationship

Itt = IT + Ii - = "C (nr + nj) (2)

If, on the other hand, the magnetizations of the measuring layer and the harder layer sequence are opposite, then the following applies to the entire tunnel current In at the same voltage across the barrier:

In = IT + Ii ~ 2 C ntnj ,. (3) It must be taken into account here that the tunneling current is always larger when the magnetizations are aligned parallel to both sides of the tunnel barrier than when the alignment is opposite.

In the above rough estimation it was assumed that the two magnetic layers or layer sequences on both sides of the tunnel barrier have the same energy level densities. In this case, the change in the tunnel current I is:

Δl = In - In = C (n _τ ² + nj. ² ) - 2 C n-rnj. (4)

The following then applies to the relative change Δl / IfJ:

The ratio n ^ / nt is known to be about 2 for both Co and Fe at room temperature, so that Δl / Itj. 25% would result. Concrete measured values of 11% are known. According to equation (5), the result for nj./nτ is approximately 1.6.

The thin-film sensor 3 according to FIG. 1 is considered below. Two extreme cases have to be distinguished here: Case I: The majority electrons are completely scattered in the measuring layer Ms and do not reach the semiconductor region H1 functioning as collector Kl, while the minority electrons can reach the base without being scattered. Case II: The minority electrons are completely scattered in the measuring layer and do not reach the collector, while the majority electrons can reach the base without being scattered.

: In general, the scattering interaction in ferromagnetic elements and alloys is for

Majority electrons relatively small; i.e., α = pj, / pτ> 1 • By alloying components for a magnetic element, scattering centers can be formed so that α <1. These elements are generally found in the columns of the periodic system of the elements, which are to the left of the respective magnetic element. For Fe and Co, for example, these are V and Cr. It is not absolutely necessary that this scattering takes place in the volume (also referred to as “bulk”) of the measuring layer Ms. By lamination of the magnetic layer with thin metallic intermediate layers with boundary layer scattering with an effective α <1, such as for the elements V and Cr The exchange coupling across the interlayers should be ferromagnetic, which can be achieved simply by choosing the interlayer thicknesses to be sufficiently small.

It is assumed that the spreading conditions are met. Deviations from this will be discussed later.

Then the collector current is in the parallel direction

in Ii ~ C nj. (6a) and for anti-parallel alignment

This results in the relative change Δl ^c / Δlti ^c

«I ^{~ n} ϊ ⁿ l

Δl ^c / Iti ^c = (6c) nn _l

For nj, / nτ = 2 or 1.6, Δl ^c / Iu ^c results in about 100% and 60%, respectively. A gain of a factor of 4 or 6 is therefore achieved for nj, / nτ is equal to 2 or 1, 6.

In general, the size (= pi / pt) of ferromagnetic elements and alloys corresponds to the above conditions. Alloying elements that form scattering centers for the magnetic element with α> 1 can further increase the effective α of a magnetic layer. These elements are generally found in the columns of the periodic system of the elements, which are to the right of the respective magnetic element. For Fe and Co, for example

Cu, Pd, Pt, Ag and Ni. It is not absolutely necessary that this scattering takes place in the bulk of the measuring layer. By laminating the magnetic layer with thin metallic interlayers, the desired reinforcement can also be achieved due to boundary surface scattering with effective α> 1. The exchange coupling should be ferromagnetic across the interlayers. This can be achieved simply by choosing the intermediate layer thicknesses to be sufficiently small.

Here, too, it is assumed that the scattering conditions are met, deviations will be discussed later.

The collector current In ^c is when the magnetizations are aligned in parallel

In ^c = lτ »C nt ² , (7a)

while Iu ° for the anti-parallel alignment

The relative change Δl ^c / In ^c is then

For ni / nt = 2 or 1.6, Δl ^c / In ^{c have} the same values as in case I of 100% and 60%. A profit of a factor of 4 or 6 for nj, / nτ of 2 or 1.6 is also achieved here.

From the above case studies it can be concluded that compared to an ideal tunnel barrier and ideal polarization of the usual ferromagnetic materials results in an increase in the relative current change by a factor of 4. With non-ideal polarization, the gain is higher. There are semimetals like Perovskite and Heusler see alloys with a polarization of almost 100%. In this case, only a minimal gain can be achieved if such a material is used both for the measuring layer and for the magnetically harder layer sequence. Problems with material deposition occur with these materials.

Temperature dependence of the tunnel current

The tunnel current shows a relatively strong temperature dependence. It is therefore possible to use a constant current source to reduce this influence. It can be seen from the circuit diagram indicated in FIG. 9 how this can be achieved with a relatively high resistance Rj in series with the injector Ij. For this purpose, the resistance Rj should be chosen so high that the voltage across the tunnel barrier | Ub-Uj | is negligible, where Uj is the injector voltage. The base voltage U i is practically independent of the base current due to the relatively low values of the voltage divider resistors Ri and R ₂ . In the figure, a collector resistor is also designated R ₃ . A corresponding constant current principle is not appropriate in the case of a simple tunnel barrier. Therefore, the following only checks to what extent a relative current swing changes. A limitation is made to the above approaches for cases I and II:

Case I: Scattering of majority electrons only.

The collector current is with parallel alignment of the magnetizations In ^c = IA * nj, ² / (nt ² + nχ ² ) I (8a)

and for anti-parallel alignment

IU ^C = V- I. (8b)

The relative change Δl ^c / Iu ^c is then

where Δl ^c applies to the signal swing

n, —n.

Δl ^c = (8d)

2 (n, ² + n, ² )

For ni / nt = 2 or 1.6, 60% or 44% results for Δl ^c / Iu ^c . This means that a gain of a factor of 2.5 or 4 is achieved for the case nj, / nτ = 2 or 1.6.

Case II: Scattering of minority electrons only

The collector current In ^c is when the magnetizations are aligned in parallel

ItT ^c = Iτ ^* = I ² / (nτ ² + nj. ² ) (9a)

and for anti-parallel alignment

IT4 ^C = 1/2. (9b)

The relative change Δl ^c / Iττ ^c is then 2 2

Δl ^c / In ^c = ₂ ^T • (9c)

For nj, / nτ = 2 or 1.6, the results for Δl / Iττ ^{c are} 150% and 80%. In this case, a gain of a factor of 6 or 7 is achieved for nj, / nτ = 2 or 1.6.

Here is the signal swing

2 2 ΔI ^C = ^τ I. (9d)

2 (n _τ -ln ^)

The constant current control not only has advantages in terms of temperature sensitivity, but also entails an increased relative current change. The signal swing is the same in both cases.

Current change for realistic scatter values in the base

The free path lengths for the majority electrons ΔT and minority electrons Δ ₄ are different and finite. Therefore, the above consideration requires a corresponding correction. This is based on a constant current control with standardized injection current. The collector flow with parallel alignment of the injection and scattering layers can then be represented as follows

ITT ^C = exp (-W _b / Λτ), (10a)

while an opposite orientation leads to the relationship:

Iτi ^c = exp (-W _b / Λi) / 2 + exp (-W _b / Λτ) / 2 (10b)

Some realistic values are assumed for the following table, namely

ΛT = 80 Ä, Λ. = 6 Ä, W _b = 30 Ä and nj, / nτ = 2 or 1.6.

table

The deviations from the values according to relationships (9a) to (9d) are irrelevant.

II. Consideration of spin valve transistor and tunnel sensor with semiconductor area

FIG. 10 shows a simple embodiment of a spin valve transistor 14 with a GMR multilayer system GMR known per se as the base. This multilayer system has a soft magnetic measuring layer Ms, a hard magnetic layer Hs and an intermediate decoupling layer Es. This layer system lies between two semiconductor layers serving as collector K1 and emitter Em. For comparison purposes, this transistor 14 is compared with FIG. 11 to a tunnel sensor 3 according to the invention (of type I), according to FIG. 1). A normalized constant injection current is assumed for both this transistor 14 and the sensor 3 according to the invention. Here is the

For the sake of simplicity, assume that the decoupling layer Es has a free path length Λ, all layers are of the same thickness and the magnetic layers have the same scattering properties. The collector current for transistor 14 can be derived from the following relationships. A collector current then results for a parallel alignment of the magnetization of the measuring layer Ms and the hard magnetic layer Hs

ln ^c = exp (-W _b / (3Λτ) Hexp (-2W _b / (3Λj,)) + exp {-2W _b / (3Λ _T )) (72, (11a)

while the current Iu ^{c is given} by the opposite orientation

IU ^C = exp (-2W _b / (3Λj) exp (-W _b / (3Λτ)). (11b)

It should be noted here that the current Iττ ^{c is} always greater than Iu ^c . The relative current swing is then given by

{exp (-W "/ (3Λ _i)) - exp (-y / (3Λ _T))} ^2/2

Δl ^c / lu ^c = (11c) exp (-W „/ (3A _i )) exp (-W _b / (3Λ _T ))

For a comparison with the sensor according to the invention, the concrete data taken into account above are again taken as a basis: ΛT = 80 Ä, ΛJ, = 6 Ä, W _b = 30 Ä and nj, / nτ = 2.

It is believed that it is possible to limit the thickness of the entire GMR multilayer system in the spin valve transistor 14 to 30 Å. ΔI ^C / ITJ, then is 140% and Δl ^c = 0.36. The relative ratios are comparable, while the signal swing is 1.7 times larger than that of the transistor

14. Assuming that the measuring layer Ms and the hard- magnetic layer Hs are each 30 Å thick, then Δl ^c / Δu ^c 49 with Δl = 0.16. From the examples chosen it can be seen that the relative ratio in transistor 14 can be increased as desired by increasing the base thickness, while Δl ^c / Iu ^{c is} only limited by leakage currents and noise. However, the signal drop decreases significantly. With the sensor according to the invention, there is in principle no possibility of making Δl ^c / Iu ^c arbitrarily large if the magnetic layers on the tunnel barrier layer are not completely polarized (as is the case, for example, with Heusler alloys or perovskites). The signal advantage in the sensor according to the invention becomes clear when one takes into account the magnetic rigidity of the layer sequence according to the invention and the requirement regarding the decoupling of the measuring layer from the harder layer sequence. Due to the required rigidity, measures such as alloying of hard magnetic layers, exchange biasing with an antiferromagnet or an implementation of a layer sequence forming an artificial antiferromagnet in the base are required. The decoupling leads to relatively large decoupling layer thicknesses or buffer layers in the base and to relatively high specific resistances. For many applications, however, the size is not Δl ^c / Iτ. ^c , but Δl ^c / I ^ιnj decisive, the embodiments ^{according to} the invention being regarded as particularly advantageous.

According to the above, it was assumed that a multilayer system of a thin-film sensor according to the invention has, in addition to at least one tunnel barrier layer, a soft magnetic measuring layer and a comparatively magnetically harder layer sequence composed of at least two different layers (= layer sequence with the minimum number of layers 2). Of course, it is also possible to use a single one in a manner known per se Layer of the multi-layer system or several layers forming a subsystem to be replaced by a layer package with a comparatively larger number of layers in each case. This layer package fulfills the same function within the sensor as the replaced individual layer or the replaced layer subsystem. For example, corresponding layer packages can have periodically repeating layer subsystems.

Of course, it is also possible to provide at least two tunnel barrier layers for a thin film sensor according to the invention. FIGS. 12 and 13 show two corresponding exemplary embodiments of thin-film sensors 15 and 16, each with two tunnel barrier layers Tb and Tb '. The embodiments shown differ in the fact that in the sensor 15, between the two tunnel barrier layers, the soft magnetic region with at least one measuring layer Ms is arranged, which consists of outer, magnetically more rigid layer sequences Sf and Sf through the tunnel barrier layers Tb and Tb 'is separated (see FIG. 12). The two layer sequences Sf and Sf do not necessarily have to have the same structure. If necessary, it is also possible to provide only a single layer instead of one of the layer sequences. In contrast, the sensor 16 has a magnetically stiffer layer sequence Sf arranged between the tunnel barrier layers Tb and Tb 'and outer, soft magnetic measuring layers Ms and Ms'. Here, too, the two measuring layers Ms and Ms' do not necessarily have to be identical. The substrate present in these sensors, which carries their multilayer systems, can in turn consist of a semiconducting material with the formation of a Schottky barrier or of one of the usual non-magnetic substrate materials without Schottky barrier formation.

Claims

claims

1. Magnetic field-sensitive thin film sensor (4, 5, 8, 9, 10, 12, 15, 16) with a multilayer system which has at least one soft magnetic measuring layer (Ms, Ms ') which is connected by means of a tunnel barrier layer (Tb, Tb') is separated from a layer sequence (Sf, Sf) which as a whole system has a higher magnetic stiffness than the at least one measuring layer (Ms, Ms') and contains at least one non-magnetic metal layer and at least two magnetic layers.

2. Sensor according to claim 1, g e k e n n z e i c h n e t through several tunnel barrier layers (Tb, Tb '), at least one of which adjoins a layer sequence (Sf, Sf) with the higher magnetic stiffness.

3. Sensor according to claim 2, so that a tunnel barrier layer (Tb, Tb ') is provided on both sides of a measuring layer (Ms), at least one of which is adjacent to a magnetically more rigid layer sequence (Sf, Sf).

4. Sensor according to claim 2, so that a tunnel barrier layer (Tb, Tb ') is provided on each side of a magnetically stiffer layer sequence (Sf), which is adjacent to a measuring layer (Ms, Ms').

5. Sensor according to one of claims 1 to 4, d a d u r c h g e k e n n e e c h n e t that further a semiconducting region (Hl) is provided which forms a Schottky barrier (Sb) with a magnetic layer attached to it.

6. Sensor according to claim 5, characterized in that the adjacent magnetic layer is a measuring layer (Ms).

7. Sensor according to claim 6, so that an injector (Ij) of a transistor (Ts) of the spin valve type is formed with the at least one magnetically more rigid layer sequence (Sf).

8. Sensor according to claim 5, so that the applied magnetic layer is a layer of the magnetically more rigid layer sequence (Sf).

9. Sensor according to claim 8, so that an injector (Ij) of a transistor (Ts) of the spin valve type is formed with the at least one measuring layer (Ms).

10. Sensor according to one of claims 1 to 9, characterized in that at least one of the magnetic layers of the at least one magnetically stiffer layer sequence (Sf, Sf) forms a bias layer (Bs, Bs') with an antiferromagnetic or ferrimagneti - The magnetic layer (5) is interchanged.

11. Sensor according to one of claims 1 to 9, characterized by at least one layer sequence (Sf, Sf) forming an artificial anti-magnet with at least one magnetic layer (6) and at least one bias layer (Bs), which magnetic layer and bias layer over at least a common coupling layer (7) is coupled antiferromagnetically.

12. Sensor according to claim 11, characterized in that the at least one magnetically stiffer layer sequence forming the artificial antiferromagnet has two outer bias layers (Bs, Bs '), which have coupling layers (7, 7') with a common flux-conducting magnetic layer ( Fs) are each coupled antiferromagnetically.

13. Sensor according to one of claims 1 to 12, so that at least one layer of the magnetically more rigid layer sequence (Sf, Sf) is formed from an alloy of a rare earth and a transition metal.

14. Sensor according to one of claims 1 to 13, characterized in that at least one of the layers of the multi-layer system or more, a subsystem of the multi-layer system layers is replaced by a layer package with a comparatively larger number of layers, which within the multi-layer system for the same function how the individual layer or how the layer subsystem is provided.