Electrical reference resistors for GMR or TMR revolution counters formed from helically arranged magnetic domain wall conductor tracks having opposing straight conductor track sections

Abstract

The invention relates to electrical reference resistors for GMR or TMR revolution counters which are formed from helically arranged magnetic domain wall conductor tracks which have opposing straight conductor track sections. The problem addressed by the invention is that of providing reference resistors which are to be produced in as simple a manner as possible and using standard technology, such as is used for the production of the domain-transporting helixes, with the aim whereby the resistance value of the reference resistors is independent of the magnetic state in the reference resistors. The problem is solved by the reference resistors consisting of the same material layer combination as the magnetic domain wall conductor tracks of the revolution counter and by the electrical resistance thereof being determined by long straight regions having a longitudinal extension direction (La), which regions are arranged at an angle of 90° to the reference direction (201).

Description

[0001] 01092979-0016 03 / 03 / 2026 PCT / DE2026 / 000017

[0002] P2419pct 1

[0003] Electrical reference resistors for GMR or TMR revolution counters, formed from spirally arranged magnetic domain wall conductors which have opposing straight conductor sections

[0004] Magnetic sensors can detect properties of a magnetic field, such as its direction. An example of this is an angle sensor. Other types of magnetic sensors can determine how many times a magnetic field has rotated. Such rotation counters can be formed, for example, by a GMR rotation counter or a TMR rotation counter, as are well known in the prior art (see, e.g., DE 102008 063 226 A1, US 11,460,521 B2, DE102010022611B4, US10228267B2, DE102020006987B3). These rotation sensors have one or more magnetic channels that are so narrow that the magnetization is always aligned either parallel or antiparallel to the domain transport direction in the straight channel sections. Typical dimensions for the magnetic channels are lengths in the range of several millimeters to several tens of millimeters, widths between 150 nm and 400 nm, and thicknesses of approximately 40 nm.These magnetic pathways change their magnetic state when a magnetic domain wall passes through them. These magnetic pathways are typically made of soft magnetic materials such as NiFe, CoFe, or CoFeB alloys.

[0005] A cross-section through a layer stack used for a revolution counter according to the prior art is shown in Fig. 1. The approximately 40 nm thick magnetic conductors are, as schematically shown in Fig. 1, separated by a typically approximately 2 nm thick copper layer from a layer stack consisting of two CoFe layers a few nm thick, separated by an approximately 0.8 nm thick ruthenium layer. This Ru layer ensures that the magnetization of the two CoFe layers is always antiparallel to each other. 01092979-0017 03.03.2026 PCT / DE2026 / 000017

[0006] P2419pct 2

[0007] They therefore form a so-called artificial antiferromagnet, whose net moment is ideally zero. A layer of an antiferromagnet, such as platinum manganese, approximately 20 nm thick, borders the CoFe layer facing away from the copper. This antiferromagnet ensures that the magnetization of the adjacent CoFe layer points precisely in a direction homogeneously imprinted during the manufacturing process via a tempering procedure. This direction is also known as the exchange bias direction. Due to the aforementioned Ru layer, the second CoFe layer is oriented antiparallel to the exchange bias direction. Its direction defines the so-called reference direction 201 of the layer stack (see Fig. 2).

[0008] The overall structure, consisting of a magnetic domain, the intermediate layer Cu (or, in the case of TMR systems, an insulator such as Al₂O₃ or MgO), and the layer stack CoFe / Ru / CoFe / PtMn, exhibits a resistance effect such that the resistance of the entire stack depends on the angle of magnetization in the magnetic domain relative to the reference direction. At zero angles, the resistance is minimal. At an angle of 180° between the reference direction and the magnetization direction of the magnetic domain, the resistance is maximal. Since each passage through a magnetic domain wall changes the magnetization direction in the domain, the number of domain walls traversed can be determined, for example, by counting the resistance changes.

[0009] The reading of the rotation sensor, that is, the determination of the number of revolutions of an external permanent magnet (not shown here), is performed electrically. This electrical reading exploits the fact that the electrical resistance in the narrow, straight sections, which are assembled, for example, as shown in Fig. 2 to form a spiral-like structure 10 of the rotation sensor, depends on the magnetic state of these straight sections. Due to the geometry, the length of the straight, strip-shaped sections of the spiral is significantly greater than their width.

[0010] P2419pct 3

[0011] Since these regions are significantly larger than their thickness, the magnetization is always aligned parallel to the longitudinal orientation of the strip-shaped regions and can therefore only be parallel or antiparallel to the strip. Typical geometries of these straight regions 100 shown in Fig. 2 are, for example, 200 pm long, 300 nm wide, and 40 nm thick. The magnetic state changes when a magnetic domain wall passes through a straight strip due to the rotation of an external magnetic field. This passage leads to a remagnetization of the strip and thus to a reversal of the direction of magnetization within it. That is, a magnetization direction parallel to the longitudinal orientation of the strip-shaped regions becomes antiparallel, and vice versa. The geometry of the spiral structure shown in Fig. 2 indicates that the straight regions preferably assume an angle of ±45° to the reference direction 201.Depending on the magnetization state of the straight sections, the magnetization in these sections has an angle of + / -45° or + / -135° to the reference direction 201. Therefore, in the first case, they are in a lower-resistance state (low state) than in the second case (high state), where the angle is 135°.

[0012] As a magnetic domain wall is traversed and the direction of magnetization changes, its resistance also changes. Therefore, the resistance values ​​of the straight sections forming the spiral sensor uniquely represent the domain state and thus the number of revolutions. The usable resistance changes are in the range of a few percent. They are thus comparable to, or significantly smaller than, the resistance changes that occur when the rotation counter's temperature changes, and must therefore be carefully separated from them.

[0013] The state of the art for suppressing the temperature dependence of electrical resistances is the use of half-bridges or full bridges, also known as Wheatstone half-bridges or bridges. 01092979-0019 03.03.2026 PCT / DE2026 / 000017

[0014] P2419pct 4

[0015] As described in patent DE102010010893B4, various half-bridges are formed in the sensor, namely the center taps L1 - L4 and R1 to R3 between the supply voltage Vcc and the ground Gnd in Fig. 3. These half-bridges are now compared with a reference half-bridge.

[0016] One possibility for constructing a reference half-bridge is an external half-bridge built with external resistors, as described in DE102010010893B4.

[0017] This variant has the advantage that the external half-bridge is independent of the magnetic field acting on the sensor and, when suitable resistors are used, is not dependent on the operating temperature. It therefore allows for a simple readout method and is used, for example, in a manufactured revolution counter (type RSM-2800: see https: / / www.novotechnik.de / uploads / tx_extprodfind / RSM-2800.pdf). With this type of readout, the same power supply is used for both half-bridges, the internal and the external half-bridge. Readout errors can occur if, due to lead resistance, particularly in the case of the revolution counter, the externally applied bridge voltage at the sensor location is reduced. This reduction leads to a decrease in the voltage across the half-bridge and can therefore result in incorrect determinations of the domain state in one or more segments if the voltage drop exceeds a critical value.

[0018] The problem that can arise from the use of an external half-bridge, as described above, is solved according to the invention of US patent 11,460,521 B2 by arranging the reference resistors on the chip itself. This eliminates voltage drops occurring on the lead path to the chip. Furthermore, all relative resistance changes resulting from changes in sensor temperature are identical in the reference resistor and in the spiral. This allows the resistances of the straight sections of the spiral to be directly compared with the 01092979-0020 03.03.2026 PCT / DE2026 / 000017

[0019] P2419pct 5

[0020] to compare the reference resistor or the reference resistors. The reference resistors themselves are, as shown in Fig. 2 in patent US

[0021] 111,460, 521 B2 described, arranged parallel to the long, straight sections forming the spiral.

[0022] Straight strips are used as reference resistors, which are not part of the spiral and in which the resistance should not change when an external magnetic field moves, since, due to their geometric shape, they do not pass through any magnetic domain walls.

[0023] The magnetization direction in these strips remains unchanged during normal operation. However, the resistance value depends on the direction of magnetization within the strips. This is determined by the so-called magnetic reference direction 201, which is uniformly imprinted on the sensor and always points along the diagonal of the nearly square, spirally shaped rotation sensor. Consequently, the magnetization in the strips can be at an angle of either -45° or +45°, in which case the resistance is in the so-called low state, or at an angle of -135° or +135°, in which case the resistance is in a high state. Errors can occur with this method of using reference resistors if unfavorable external conditions cause a change in the magnetization state of at least one of the reference resistors.This condition cannot be monitored using measurement technology and therefore cannot be reliably ruled out.

[0024] Figure 2 shows the typical structure of a spirally arranged GMR loop 10 usable for revolution counting, which essentially consists of straight sections 100 connected by quarter circles to form a spiral. An enlarged section of the structure is usually located either at the inner or outer end of the spiral. This section, designated as the domain wall generator 301, is responsible for recording a change in the number of revolutions of a rotating object located, for example, above or below the plane of the spiral, every half revolution.

[0025] P2419pct 6

[0026] Magnets are used to generate a 180° domain wall. The functionality of domain wall generation and its transport within the spiral are explained in detail in patent DE 102008 063 226A1. The reference direction, marked 201 in the figures, is crucial for the functionality of the spiral utilizing the GMR or TMR effect. It is generated by a component of the GMR layer system and indicates the direction in which the electrical resistance reaches a minimum in certain areas of the spiral when the magnetization points precisely in that direction.

[0027] Figure 3 shows a possible electrical contacting of a spirally constructed revolution counter according to the known state of the art.

[0028] Electrical readout is typically performed by measuring a Wheatstone half-bridge voltage. For this purpose, quarter-circle-shaped areas, as used in patent DE102010010893B4 and shown in Fig. 3, are provided with contact pads. The contacts not pointing in the direction of the reference direction 201 are each connected to Vcc and Gnd. The half-bridge electrodes L1 to L4 lie between the voltage potentials Vcc and Gnd, covering the corners to the left of the reference direction 201. The same applies to the half-bridge electrodes R1 to R3, which form further half-bridges.

[0029] The geometric distance between the different contacts is usually chosen to be the same length, which is not mandatory with the half-bridge arrangement used. The only important thing is that the length Lb of the spiral 101 not covered by the contacts between the strips forming the respective half-bridge, here e.g., the distance Gnd to L1 and L1 to Vcc, is the same.

[0030] Depending on the magnetization state of the coil, half-bridge voltages are obtained that either correspond exactly to half the voltage difference between the Vcc and Gnd contacts, or to a voltage that is a few percent below or above this voltage. 01092979-0022 03.03.2026 PCT / DE2026 / 000017

[0031] P2419pct 7

[0032] An electronically advantageous readout of this state, which allows direct inferences about the magnetization state and thus the number of domain walls stored in the spiral, utilizes a second half-bridge that ideally generates exactly half the voltage difference between Vcc and Gnd. This voltage can be subtracted from the half-bridge voltages L1 to L4 and R1 to R3, amplified electrically, and is then either close to zero volts or significantly positive or negative. By defining voltage thresholds, it can then be easily determined whether the half-bridge voltage is a few percent below or above the half-bridge voltage, or identical within permissible deviations.

[0033] Furthermore, DE 102020 132914 A1 describes a device for initializing a magnetic multiturn sensor, which, however, does not disclose any information relating to the present invention.

[0034] The object of the present invention is to provide a reference resistor that is as simple as possible and can be manufactured using a uniform technology such as that used for the production of the domain-transporting spiral, with the aim that the resistance value of the reference resistors is independent of the magnetic state in the reference resistors.

[0035] This is solved according to the invention by arranging the reference resistors near the revolution counters forming the spiral such that the straight strips or parallel strip sections forming the reference resistors are not aligned parallel to the strips of the spiral structure, but rotated by 45°. They are arranged precisely so that their longitudinal direction (see La in Fig. 7), or the sum of parallel longitudinal directions, is perpendicular to the direction of the so-called reference direction 201 of the GMR sensor. Furthermore, the strips forming the reference resistors are made of the same material as those of the domain conductor spiral, thus giving them the same temperature coefficient. That is to say, a 01092979-0023 03.03.2026 PCT / DE2026 / 000017

[0036] P2419pct 8

[0037] The relative resistance change caused by a temperature change is identical for the reference resistor(s) to the relative resistance change caused by this temperature change in the domain conductor spiral.

[0038] Due to this special orientation according to the invention, exactly perpendicular to the so-called reference direction 201 of the GMR layer stack, its resistance is independent of whether the magnetization in the strip is parallel or antiparallel. In both cases, the angle between the longitudinal direction, and thus the direction of the magnetization, and the reference direction is 90°. This means that passing through a domain wall, which changes the state of the magnetization, leaves the resistance unaffected. This fact allows for a large variability in the design of the geometry of the reference resistor or reference resistors, as illustrated in the following figures. The invention will be explained in more detail below with reference to exemplary embodiments. The figures show:

[0039] Fig. 1 A typical exemplary layer structure of a GMR revolution counter;

[0040] Fig. 2 shows an exemplary geometry of a GMR revolution counter according to the known state of the art;

[0041] Fig. 3 shows an electrical contacting of a spirally constructed GMR revolution counter according to the known state of the art;

[0042] Fig. 4 shows a possible arrangement of a reference resistor according to the invention;

[0043] Fig. 5 shows one possible arrangement of reference resistors according to the invention;

[0044] Fig. 6 shows a further possible embodiment of the reference resistors according to the invention and 01092979-0024 03.03.2026 PCT / DE2026 / 000017

[0045] P2419pct 9

[0046] Fig. 7 shows another possible design of an external reference resistor, the arrangement of which is shown in Fig. 4.

[0047] The explanations relating to Figures 1 to 3, in accordance with the prior art, have already been described at the beginning.

[0048] With reference to Fig. 4, one possible variant for forming a reference Wheatstone half-bridge using these novel reference resistors will first be described. The resistors of this reference half-bridge, as designed according to the invention, could even be located inside the spiral, as shown in Fig. 4, thus allowing optimal use of the chip area.

[0049] For this example, as shown in Fig. 4, straight sections Rw1 and Rw2, consisting of the same material and layer structure as the spiral, are arranged in the center of the spiral such that their longitudinal direction La is perpendicular to the reference direction 201. The reference resistors Rw1 and Rw2 can be configured as parallel and interconnected sections. They connect Gnd to the center tap 401 of the reference half-bridge (for resistor Rw1) and Vcc to the center tap 401 (for resistor Rw2). If the same geometry (width and uncovered distance between Gnd and 401) is used for these strips (width and uncovered distance between Gnd and 401), the reference resistors can be configured as follows: cc ), so the resistance values ​​are the same as in the even ranges 101. Thus, the heating caused by the measuring current is the same for all resistors.

[0050] Further possible configurations of the reference resistors for a reference Wheatstone half-bridge are shown by way of example in Figs. 5 and 6.

[0051] In Fig. 5, the two reference resistors Rw1 and Rw2 are arranged parallel and side by side for space reasons and their longitudinal extent is perpendicular to the reference 201. In the version shown in Fig. 6, the geometry of the straight sections, here the 01092979-0025 03.03.2026 PCT / DE2026 / 000017

[0052] P2419pct 10

[0053] The width is doubled. To achieve the same resistance again, the length is also doubled, represented as two reference resistors Rw1. If this extension is implemented as in Fig. 6, the two individual sections of the reference resistors Rw1 and Rw2 must be short-circuited with contact pads Kp1 and Kp2. This can be done either with the same material used for the bridges or with the conductor material used for contacts Gnd, Vcc, and 401. The design of the sections forming the resistors Rw1 and Rw2, which are connected to form the reference half-bridge, is highly variable. The only requirement is that they must have a longitudinal extension that is oriented perpendicular to the reference direction 201 and that the absolute resistances Rw1 and Rw2 are identical so that the voltage tapped at contact 401 corresponds exactly to half the voltage Vcc.The use of other materials for the training would be possible in principle. However, all other materials used in the manufacturing process of the revolution counter, such as gold as a contact material, exhibit a significantly lower value of the so-called sheet resistance, measured in ohms per square, since they are usually considerably thicker and also have a lower resistance than the GMR stack shown in Fig. 1.

[0054] If one wishes to use the method for reading the resistance values ​​described in patent US 11,460,521 B2, an additional mandatory requirement is that the resistance value Rw1, which is formed between contacts Ref1 and Ref2 as shown in Fig. 7, must be identical to the resistance value of the spiral in the straight sections 101 (see Fig. 3). There is considerable freedom in designing its geometry, unlike the solution in patent US 11,460,521 B2, where its geometry must be identical to that of the spiral. Since the longitudinal orientation is also perpendicular to the reference direction 201 according to the invention, its resistance value is independent of the direction of magnetization in the strip. Thus, the geometry of the 01092979-0026 03.03.2026 PCT / DE2026 / 000017

[0055] P2419pct 11

[0056] The ends can be arbitrarily shaped, as the formation of a domain wall there and subsequent passage through it does not affect the resistance value. The same applies if the width of the bridge is increased and its length is increased to the same extent. The former would result in the magnetic window being shifted to lower fields, meaning that even at fields permissible for counting the revolutions with the spiral, nucleation that is not allowed in the spiral itself could occur in the reference strip, but as mentioned above, it would have no influence on the resistance value Rw1. The latter ensures that the resistance forming between contacts Ref1 and Ref2 remains unchanged. This represents a technological simplification that can increase the yield, as the geometry of the reference resistor would lead to significantly fewer failures.

[0057] The invention is not limited to spiral domain wall guideways open at both ends and equipped with a domain wall generator, as described in Fig. 4. It can be used identically when variants are employed that bridge the open ends, as shown, for example, in US10228267B2.01092979-0027 03.03.2026 PCT / DE2026 / 000017

[0058] P2419pct 12

[0059] Reference symbol list

[0060] 10 - spiral-shaped structure of a rotation sensor

[0061] 100 - even areas of the rotation sensor

[0062] 101 - straight areas of the rotation sensor not covered by contacts

[0063] 201 - Reference direction

[0064] 301 - Domain Wall Generator

[0065] 401 - Center tap of the reference half-bridge

[0066] Rw1 - Reference resistor

[0067] Rw2 - Reference resistor

[0068] L1 to L4 - (left) center taps

[0069] R1 to R3 - (right) center taps

[0070] La - Longitudinal direction of the straight reference resistance ranges

[0071] Lb - the length of the spiral not covered by the contacts 101 Gnd - Ground contact

[0072] Vcc - Contact for supply voltage

[0073] Ref1 - (first) contact for reference resistor

[0074] Ref2 - (second) contact for reference resistor

[0075] Kp1 + Kp2 - Contact pads for reference resistor

Claims

01092979-0029 03 / 03 / 2026 PCT / DE2026 / 000017 P2419pct 13 Patent claims 1. Electrical reference resistors for GMR or TMR revolution counters, formed from spirally arranged magnetic domain wall conductors (10) which have opposing straight conductor sections (100) which are electrically read and which have a magnetic reference or preferred direction (201) imposed which is set at 45° to the straight conductor sections (100), characterized in that the reference resistors (Rw1 and Rw2) consist of the same material layer combination as the magnetic domain wall conductors of the revolution counter and their electrical resistance is determined by long straight areas with a longitudinal extension direction (La) which are arranged at an angle of 90° to the reference direction (201).

2. Electrical reference resistors according to claim 1, characterized in that the reference resistors (Rw1 and Rw2) are positioned centrally in the spirally arranged magnetic domain wall conductor track.

3. Electrical reference resistors according to claim 1, characterized in that the reference resistors (Rw1 and Rw2) are designed in the form of straight parallel resistor sections.

4. Electrical reference resistors according to claims 1 and 3, characterized in that, when the reference resistors (Rw1 and Rw2) are designed with the same width and thickness as the domain wall conductors, their entire effective length is equal to the length (Lb) of the straight conductor sections (101) not covered by contacts.

5. Electrical reference resistors according to claim 1, characterized in that the reference resistors (Rw1 and Rw2) are positioned next to the spirally arranged magnetic domain wall conductor (100). 01092979-0030 03.03.2026 PCT / DE2026 / 000017 P2419pct 14 6. Electrical reference resistors according to one of the preceding claims, characterized in that they are designed in their length and width such that their resistance value corresponds to the resistance value of a single straight section (101) of the domain wall conductor track (100) without an external magnetic field.

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