Magnetoresistive element and manufacturing process

Abstract

A giant magnetoresistive element (GMR) for a magnetic multiturn sensor, the giant magnetoresistive element comprising: a reference layer; a non-magnetic layer (318) adjacent to the reference layer; and a free layer (308) made of a ferromagnetic material, the free layer (308) comprising a first layer made of a ferromagnetic material adjacent to the non-magnetic layer and a multilayer arrangement (314) comprising at least a plurality of layers (316) made of a first material, the first material being ferromagnetic, and a plurality of layers (318) made of a second material, a thickness of the free layer being greater than 30 nm, and the plurality of layers (316) made of the first material having a first magnetostriction and the plurality of layers (318) made of the second material having a second magnetostriction that reduces the magnetostriction of the free layer (308).

Description

Area of Revelation

[0001] The present disclosure relates to magnetic sensors. More particularly, the present disclosure relates to a giant magnetoresistive element for use in a multiturn magnetic sensor. background

[0002] Magnetic multiturn sensors are commonly used in applications where there is a need to monitor the number of revolutions of a device. An example of this is a steering wheel in a vehicle. Magnetic multiturn sensors typically have giant magneto-resistance (GMR) elements that are sensitive to an applied external magnetic field. The resistance of the GMR elements can be changed by rotating a magnetic field near the sensor. Variations in the resistance of the GMR element can be tracked to determine the number of revolutions in the magnetic field, which can be translated into the number of revolutions of the device being monitored.

[0003] The GMR elements are often based on a GMR spin valve stack using an artificial antiferromagnetic (AAF) material, such as the one used in Fig. 1. The stack 1 comprises a substrate 100 at the base, followed by a seed layer 102 to promote the growth of the following layers by providing a smooth surface and a favorable crystal structure for growth thereon. The next layer is an AAF multilayer 104, which comprises a sequence of layers consisting of a natural antiferromagnetic layer (such as platinum manganese (PtMn) or iridium manganese (IrMn)), a ferromagnetic layer (typically cobalt iron (CoFe)), a non-magnetic spacer (ruthenium (Ru)), and another ferromagnetic layer (CoFe), also referred to as the "pinned" layer. The main purpose of the AAF layer 104 is to keep the magnetization of the pinned layer aligned in an orientation defined in the annealing process during manufacturing.

[0004] A non-magnetic spacer layer 106 (typically copper (Cu)) is provided directly on the pinned layer of the AAF layer 104, followed by the so-called free layer 108. The free layer 108 is a ferromagnetic layer that can freely align its magnetization with an external magnetic field. The free layer 108 is typically formed from two ferromagnetic layers, typically a CoFe layer followed by a nickel-iron (NiFe) layer. The GMR effect is observed as a change in sheet resistance associated with the relative angle between the magnetization of the free layer 108 and the magnetization of the pinned layer in the AAF layer 104. When the magnetizations are parallel, a low resistance is observed, and when they are antiparallel, a high resistance is observed.Accordingly, the purpose of the non-magnetic layer 106 is to create a distance between the free layer 108 and the pinned layer, and the thickness of this spacer layer 106 is chosen to minimize the magnetic coupling between the pinned layer and the free layer 108.

[0005] A cover layer 110, typically a non-magnetic metal layer, is then typically applied to the stack 1 to protect the stack 1 and reduce diffusions when the stack 1 is bonded to other metal layers (such as aluminum, copper, or gold) to form interconnects for connecting the stack 1 to other components of the magnetic sensor.

[0006] US 2017 / 0 018 703 A1 relates to a magnetoresistive (MR) device and a method for manufacturing the MR device. The MR device has a pinned layer, a spacer layer proximate the pinned layer, and a free layer proximate the spacer layer. The free layer comprises a first magnetic layer proximate the spacer layer, the first magnetic layer having positive magnetostriction, a laminated magnetic insert layer proximate the first magnetic layer, and a second magnetic layer proximate the magnetic insert layer, the second magnetic layer having negative magnetostriction. The laminated magnetic insert layer has a first magnetic sublayer and a first non-magnetic sublayer proximate the first magnetic sublayer.With the exposed laminated magnetic insertion layer, the free layer has low overall magnetostriction and results in an MR device with a high MR ratio.

[0007] US 2019 / 0 165 253 A1 relates to a magnetoresistive stack and methods for fabricating and using the disclosed magnetoresistive stacks. A magnetically free region of a magnetoresistive device comprises at least a first ferromagnetic region and a second ferromagnetic region separated by a non-magnetic insertion region. At least one of the two regions, the first ferromagnetic region and the second ferromagnetic region, may contain at least one boron-rich ferromagnetic layer disposed proximate a boron-free ferromagnetic layer.

[0008] US 2015 / 0 185 297 A1 relates to a device which may comprise a magnetoresistive structure having a magnetic free layer with a spontaneously generated closed-flux in-plane magnetization pattern and a magnetic reference layer with a non-closed-flux magnetization pattern. Brief description of Revelation

[0009] The present disclosure provides a giant magnetoresistance (GMR) element for use in a multiturn magnetic sensor, wherein the free layer, i.e., the layer that changes its magnetization direction in response to an external field such that a resistance change is provided, is thick enough to provide good shape anisotropy without exhibiting an AMR effect. To achieve this, at least a portion of the free layer comprises multiple layers of at least two different conductive materials, in particular, multiple layers of at least one first material that is ferromagnetic and multiple layers of at least one second material that is known not to exhibit an AMR effect and that does not interfere with the GMR effect of the layers of ferromagnetic material.

[0010] A first aspect of the present invention provides a giant magnetoresistance (GMR) element for a magnetic multiturn sensor having the features of claim 1.

[0011] Preferably, the second material is a material with a negligible or nearly negligible anisotropic magnetoresistive (AMR) effect. The multiple layers of the first material and the multiple layers of the second material can then be arranged in an alternating configuration.

[0012] Therefore, by having layers of two different materials, one of which is ferromagnetic and the other exhibiting a negligible or nearly negligible AMR effect, a free layer thick enough to provide good shape anisotropy while exhibiting no AMR effect or a very small AMR effect relative to the magnitude of the exhibited GMR effect can be achieved. In this respect, the layers of the material exhibiting a negligible AMR effect will attenuate any AMR effect that may be present in the layers of the ferromagnetic material.

[0013] In some arrangements, the first material may be one of NiFe and CoFe. The second material may be one of CoFeB, CoZrTa, CoZrTaB, CoZrNb, and CoZrO.

[0014] In some arrangements, a thickness and / or composition of the first material and the second material may be configured such that the free layer is free of magnetostriction. That is, there will be no mechanical strain or deformation in the free layer when the magnetization changes.

[0015] Each of the plurality of layers of the first material and the plurality of layers of the second material may have a thickness of about 0.5 nm to about 8 nm. It is also understood that any suitable number of layers may be used depending on the required thickness of the free layer and the thickness of the individual layers.

[0016] It is understood that the term "free layer" is used to mean that at least the first layer of ferromagnetic material has a magnetization that can freely align with an externally applied magnetic field. The first layer of ferromagnetic material can be CoFe or any other suitable ferromagnetic material with strong GMR properties.

[0017] It should also be understood that the reference layer is so referred to in that at least a portion of the reference layer has magnetization that is in a fixed direction. The portion of the reference layer with a fixed magnetization direction may also be referred to as the "pinned" layer, where the pinned layer is a layer of ferromagnetic material. The GMR effect is observed as a change in sheet resistance associated with the relative angle between the magnetization of the free layer and the magnetization of the pinned layer. The reference layer may comprise a sequence of layers defining an artificial antiferromagnetic material, where a layer of the artificial antiferromagnetic material has magnetization in a fixed direction.The artificial antiferromagnetic material may comprise a natural antiferromagnetic layer, a first ferromagnetic layer, a non-magnetic spacer, and a second ferromagnetic layer, wherein the second ferromagnetic layer is the pinned layer.

[0018] In other arrangements disclosed herein, the second material may be a non-magnetic material. As before, the ferromagnetic material may be one of NiFe and CoFe, while the non-magnetic material may be one of Ta, Ru, and Cu.

[0019] In such cases, each of the plurality of layers of the ferromagnetic material and the plurality of layers of the non-magnetic material may have a thickness of about 0.2 nm to about 0.4 nm.

[0020] Other arrangements described herein provide a magnetoresistive element for a magnetic multiturn sensor, the magnetoresistive element comprising a reference layer of an antiferromagnetic material, a non-magnetic layer adjacent to the reference layer, and a free layer of a ferromagnetic material, the free layer comprising a first layer of a ferromagnetic material adjacent to the non-magnetic layer and a second layer of an amorphous ferromagnetic material.

[0021] The amorphous ferromagnetic material can be one of the following: CoFeB, CoZrTa, CoZrTaB, CoZrNb, and CoZrO, while the first layer can comprise a crystalline ferromagnetic material. For example, the first layer of ferromagnetic material can be CoFe.

[0022] Another aspect of the present disclosure provides a magnetic multiturn sensor having the features of claim 12.

[0023] As described above, the second material is preferably a material with a negligible or nearly negligible anisotropic magnetoresistive (AMR) effect. In some arrangements, the first material may be one of NiFe and CoFe. The second material may be one of CoFeB, CoZrTa, CoZrTaB, CoZrNb, and CoZrO.

[0024] Yet another aspect provides a method of manufacturing a giant magnetoresistive element having the features of claim 16.

[0025] The method comprises forming a plurality of layers of the first material and a plurality of layers of the second material in an alternating sequence to provide the multilayer arrangement of the free layer.

[0026] For example, the method may include forming a first layer of the first material, forming a first layer of the second material on the first layer of the first material, forming a second layer of the first material on the first layer of the second material, and forming a second layer of the second material on the second layer of the first material. Of course, it is understood that this process may be continued for as many layers as necessary.

[0027] Again, the second material is preferably a material having a negligible or nearly negligible anisotropic magnetoresistive (AMR) effect such that when alternated with the layers of ferromagnetic material, any AMR effect present in the layers of ferromagnetic material is attenuated.

[0028] Forming the reference layer may include forming multiple layers to form an artificial antiferromagnetic material. The artificial antiferromagnetic material may include a natural antiferromagnetic layer, a first ferromagnetic layer, a non-magnetic spacer, and a second ferromagnetic layer, wherein the second ferromagnetic layer is the layer having magnetization in a fixed direction.

[0029] The method may further comprise providing a substrate and forming the antiferromagnetic material or the free layer on the substrate. This forms a GMR stack, with the reference layer disposed on the bottom or top side of the stack.

[0030] It is also understood that the stack may include other layers, such as a seed layer formed on the substrate to promote growth of subsequent layers and a cap layer to protect the stack and provide interconnections to other components of the magnetic multiturn sensor.

[0031] Any of the layers described above may be formed using any suitable manufacturing process, such as sputtering or ion beam deposition. Short description of the drawings

[0032] The present disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a schematic side view of a prior art GMR stack; Fig. 2 is a schematic side view of a GMR stack according to an embodiment of the disclosure; Fig. 3 is a schematic side view of a GMR stack according to another embodiment of the disclosure; Fig. 4 is an example of a magnetic multiturn system including GMR elements, according to embodiments of the disclosure; Fig. 5A-5I are schematic side views illustrating the method of manufacturing a GMR stack according to embodiments of the present disclosure. Detailed description

[0033] Magnetic multiturn sensors can be used to count the number of revolutions of a rotating shaft. Typically, a magnet is mounted on the end of the rotating shaft, and the multiturn sensor is sensitive to the rotation of the magnetic field as the magnet rotates with the shaft. Such magnetic sensing can be applied to a wide variety of applications, including automotive, medical, industrial control, consumer, and many other applications that require information regarding the position of a rotating component.

[0034] Magnetic multiturn sensors typically feature giant magnetoresistance (GMR) elements, which are sensitive to an applied external magnetic field. The GMR elements are often based on a GMR spin-valve stack, which features a free layer made of a ferromagnetic material that can freely align its magnetization with the external magnetic field. In a typical GMR stack, the thickness of the free layer is usually less than 5 nm. However, to generate strong shape anisotropy in long and narrow film tracks, the free layer must be very thick (>30 nm). As a result of this thickness, a strong anisotropic magnetoresistance (AMR) effect is exhibited in the free layer, making the electrical resistance further dependent on the angle between the direction of the electric current and the direction of the magnetization.Generally, when the current is parallel to the magnetization, a higher resistance is observed, and when the current is perpendicular to the magnetization, a lower resistance is observed. Consequently, this creates an undesirable resistance change that is superimposed on the desired resistance change due to the GMR effect and interferes with the sensor output.

[0035] The present disclosure therefore provides a giant magnetoresistance (GMR) element for use in a multiturn magnetic sensor, wherein the free layer, i.e., the layer that changes its magnetization direction in response to an external field such that a resistance change is provided, is thick enough to provide good shape anisotropy while exhibiting no AMR effect or a very small AMR effect relative to the extent of the GMR effect exhibited (less than 10%). To achieve this, at least a portion of the free layer comprises multiple layers of at least two different materials, in particular multiple layers of at least one first material that is ferromagnetic and multiple layers of at least one second material that is known not to exhibit an AMR effect and that does not interfere with the GMR effect of the layers of ferromagnetic material.

[0036] An embodiment according to the present disclosure is described in Fig. 2. As shown with reference to Fig. 1, the GMR element is formed as a spin valve stack 2 comprising a substrate 200, a seed layer 202, an AAF layer 204, and a non-magnetic spacer layer 206. The free layer, shown at 208, comprises a first ferromagnetic layer 212, preferably a crystalline ferromagnetic material with a low AMR effect, such as CoFe, followed by a multilayer assembly 214. As discussed above, the GMR effect is observed at the interfaces of the pinned layer of the AAF layer 204, the non-magnetic spacer layer 206, and the first ferromagnetic layer 212. The multilayer assembly 214 comprises multiple layers of both crystalline ferromagnetic material 216 and amorphous ferromagnetic material 218 arranged in alternating layers.The crystalline ferromagnetic layers 216 are formed from a crystalline ferromagnetic material, such as NiFe, while the amorphous ferromagnetic layers 218 may be formed from any suitable amorphous ferromagnetic materials, such as cobalt iron boron (CoFeB), cobalt zirconium tantalum (CoZrTa), cobalt zirconium tantalum boron (CoZrTaB), cobalt zirconium niobium (CoZrNb), or cobalt zirconium oxide (CoZrO). The magnetization of the layers of amorphous ferromagnetic material 218 will also be aligned with an externally applied magnetic field, and accordingly, the multilayer assembly 214 will behave as a ferromagnetic layer that aligns with the external magnetic field and accordingly provides good shape anisotropy.However, no or very little AMR effect is observed in amorphous ferromagnetic materials because there is very little effect on current flow as a result of changing the magnetization direction, and the layers of crystalline ferromagnetic material 216 will individually be too thin to exhibit any AMR effect, or will at least exhibit a negligible or very small amount. Therefore, by interspersing the layers of crystalline ferromagnetic material 216 with layers of amorphous ferromagnetic material 218, a ferromagnetic multilayer assembly 214 is provided that is thick enough to provide the desired shape anisotropy without introducing any undesirable AMR effect.Indeed, it will be understood by one skilled in the art that the ferromagnetic multilayer assembly 214 may comprise layers of any two ferromagnetic materials, at least one of which ferromagnetic materials exhibits a negligible or nearly negligible amount of AMR effect, thereby mitigating any AMR effect exhibited by the other ferromagnetic material.

[0037] The individual layers 216, 218 of the multilayer arrangement 214 may be between about 0.5 nm to about 8 nm, with the total thickness of the free layer 208 being approximately 10 nm to 50 nm.

[0038] When choosing the thickness of layers 216, 218, as well as the composition, the resulting magnetostriction experienced by the multilayer assembly 214 may also need to be considered. Magnetostriction is the relationship between mechanical stress on a material and its magnetization. This relationship works in both directions, in that a change in magnetization results in mechanical stretching or deformation, and a mechanical deformation results in a change in magnetization. A measure of magnetostriction can have a positive or negative sign depending on whether a material lengthens or shortens when magnetized in a particular direction.

[0039] For sensor applications, very low or ideally no magnetostriction is necessary. Some crystalline ferromagnetic materials, such as NiFe, exhibit very low magnetostriction. For example, NiFe with a Ni:Fe ratio of 81:19 is free of magnetostriction. Therefore, such materials are typically preferred for providing the free layer in GRM sensors. On the other hand, other crystalline ferromagnetic materials, such as CoFe, and amorphous ferromagnetic materials, such as CoFeB, exhibit significant magnetostriction.Therefore, for a multilayer assembly 214 comprising the amorphous ferromagnetic material 218 having positive magnetostriction, the thickness and composition of the layer of crystalline ferromagnetic material 216 may need to be adjusted to have negative magnetostriction to compensate for the positive magnetostriction of the other layers, resulting in a free layer 208 that is totally free of magnetostriction.

[0040] A cover layer 210 is then typically applied to the stack 2, typically a non-magnetic metal layer such as tantalum (Ta) or titanium tungsten (TiW), which protects the stack 2 and reduces diffusions when the stack 2 is bonded to other metal layers (such as aluminum, copper, or gold) to form interconnects for connecting the stack 2 to other components of the magnetic sensor.

[0041] A further embodiment according to the present disclosure is also described in Fig. 3. As before, the GMR element is formed as a spin valve stack 3 comprising a substrate 300, a seed layer 302, an AAF layer 304, and a non-magnetic spacer layer 306. The free layer, generally shown at 308, comprises a first ferromagnetic layer 312, preferably a crystalline ferromagnetic material with a low AMR effect, such as CoFe, followed by another multilayer arrangement 314. In this embodiment, the multilayer arrangement 314 is formed from a plurality of ferromagnetic layers 316 formed from a soft magnetic material, such as NiFe, and a plurality of non-magnetic layers 318, again arranged as alternating layers. The non-magnetic material layers 318 may be any suitable material, for example, Ta, Ru, or Cu.The non-magnetic layers 318 do not add any magnetic moments to the free layer 308 and therefore exhibit no AMR effect, while the layers of ferromagnetic material 316 will individually be too thin to exhibit any AMR effect, or at least will exhibit a negligible or very small amount. Therefore, by interspersing the layers of ferromagnetic material 316 with layers of non-magnetic material 318, a ferromagnetic multilayer assembly 314 is provided that is thick enough to provide the desired shape anisotropy without introducing any undesirable AMR effect.

[0042] In such an arrangement, it is important that the ferromagnetic layers 316 are thin enough so that they do not produce an AMR effect, and that the non-magnetic layers 318 are thin enough to ensure strong ferromagnetic coupling between the ferromagnetic layers, that is, so that the shape anisotropy exhibited by the multilayer arrangement 314 corresponds to the sum of the ferromagnetic layers 316 as opposed to each individual ferromagnetic layer 316. For example, the thickness of both sets of layers 316, 318 may be about 0.2 nm to about 0.4 nm.

[0043] Furthermore, as discussed above, the ferromagnetic layers 316 may be formed from a soft magnetic material that has very low or no magnetostriction, such as NiFe. Because these ferromagnetic layers 316 are interspersed with the non-magnetic layers 318, the free layer 308 is, overall, a soft magnet that is not magnetostrictive.

[0044] A cover layer 210, typically a non-magnetic metal layer, is then typically applied to the stack 3 to protect the stack 3 and reduce diffusions when the stack 3 is bonded to other metal layers (such as aluminum, copper, or gold) to form interconnects for connecting the stack 3 to other components of the magnetic sensor.

[0045] It should be understood that in each of the above embodiments, any number of layers (and thickness of layers) may be used in the multilayer assemblies 214, 314, depending on the thickness and shape anisotropy required. For example, there may be four layers in total, or up to twenty layers in total.

[0046] Furthermore, it is understood that in any of the above embodiments, a natural antiferromagnetic layer, such as platinum manganese (PtMn), may be used instead of the AAF layer 204, 304, with which a measurable GMR effect is also observed.

[0047] Fig. 4 shows an example of a magnetic stripe layout representation of a magnetic multiturn sensor 4 having multiple GMR elements 400 according to embodiments of the present disclosure. In the example of Fig. 4, the magnetic stripe 400 is a giant magnetoresistive track physically laid out in a spiral configuration. As such, the magnetic stripe 400 includes multiple segments formed from the magnetoresistive elements 402 arranged in series with one another. The magnetoresistive elements 402 act as variable resistors that change a resistance value in response to a magnetic alignment state. One end of the magnetic stripe 400 is coupled to a domain wall generator (DWG) 404. In this regard, it should be understood that the DWG 404 can be coupled to either end of the magnetic stripe 400. The DWG 404 generates domain walls in response to rotations in an external magnetic field or the application of any other strong magnetic field beyond the operating magnetic window of the sensor 4. These domain walls can be injected into the magnetic stripe 400.As the magnetic domain position changes, the resistance of the GMR elements 402 will also change due to the resulting change in magnetic orientation.

[0048] To measure the varying resistance of the GMR elements 402 as domain walls are created, the magnetic strip 400 is connected to a supply voltage VDD 406 and to ground GND 408 to apply a voltage between a pair of opposite corners. The corners halfway between the power supplies are provided with electrical connections 410 so that they provide half-bridge outputs. As such, the multiturn sensor 4 comprises multiple Wheatstone bridge circuits, with each half-bridge 410 corresponding to a half turn or 180° rotation of an external magnetic field. Measurements of the voltage at the electrical connections 410 can accordingly be used to measure changes in the resistance of the GMR elements 402, which indicates changes in the magnetic orientation of the free layer.

[0049] The Fig. The example shown in Figure 4 has four spiral windings and eight half-bridges 410 and is accordingly configured to count four revolutions of an external magnetic field. However, it should be understood that a multi-turn sensor may have any number of spiral windings, depending on the number of GMR elements. In general, multi-turn sensors can count as many revolutions as they have spiral windings. It should also be understood that the GMR elements 402 may be electrically connected in any suitable manner to provide sensor outputs representing changes in the magnetic alignment state. For example, the GMR elements 402 may be connected in a matrix arrangement, such as that described in US 2017 / 0261345, which is hereby incorporated by reference in its entirety. As a further alternative, each magnetoresistive segment may be connected individually rather than in a bridge arrangement.

[0050] In this example, the magnetic multi-turn sensor 4 also includes an integrated circuit 412 on which the magnetic stripe 400 is disposed and which may also include processing circuitry (not shown) for processing the sensor outputs.

[0051] A method for manufacturing the GMR stack 2 will now be described with reference to Fig. 5A to 5I. However, it is obvious that the GMR stack 3 can be fabricated in a similar manner.

[0052] Fig. Figure 5A shows the first step in the manufacturing process. A silicon wafer is used as the substrate 200. The process for forming one device is described below, but several hundred devices can be formed in parallel on the wafer. The substrate 200 is used for mechanical support and could be replaced with another type of material, such as glass or sapphire.

[0053] Typically, the silicon wafer is oxidized to isolate the subsequent layers from the bare silicon, or an insulator such as aluminum oxide may be used. In some arrangements, the substrate 200 may also include electronic circuitry.

[0054] A seed layer 202 is then deposited on the substrate 200, as shown in Fig. 5B. Seed layer 202 provides a smooth surface and a favorable crystal structure to promote the growth of subsequent layers. Seed layer 202 may be a layer of tantalum, ruthenium, or tantalum nitride (TaN), and may also include another layer of other compounds.

[0055] Fig. Figure 5C shows the formation of the AAF layer 204 deposited on the seed layer 202. The AAF layer 204 can be formed by first depositing a natural antiferromagnetic layer on the seed layer 202. A ferromagnetic layer is then deposited on the antiferromagnetic layer, followed by a non-magnetic spacer layer. Finally, a second ferromagnetic layer is deposited on the non-magnetic layer. This second ferromagnetic layer is the so-called "pinned" or "reference" layer. The antiferromagnetic material used in the AAF layer 204 can be PtMn, IrMn, NiMn, or any other suitable antiferromagnetic material. The ferromagnetic material can be CoFe or any other suitable ferromagnetic material, while the non-magnetic material is typically ruthenium.

[0056] As in Fig. As shown in Figure 5D, the non-magnetic spacer layer 206 is formed on the pinned layer of the AAF layer 204. This acts as a spacer between the pinned layer and the following free layer to reduce any magnetic coupling.

[0057] Fig. Figure 5E shows the beginning of the free layer formed by first depositing the first ferromagnetic layer 212.

[0058] The multilayer assembly is then deposited onto the first ferromagnetic layer, first by depositing a layer of the crystalline ferromagnetic material 216, as in Fig. 5F, and then depositing a layer of the ferromagnetic material 218 as shown in Fig. 5G. This process is repeated as often as necessary until the entire multilayer assembly 214 is formed, as shown in Fig. 5H shown.

[0059] Finally, the cover layer 210 is placed over the stack 2, as shown in Fig. 5I. As discussed above, the cap layer 210 is typically made of a non-magnetic metal layer that protects the stack 2 and reduces diffusions when the stack 2 is connected to other metal layers to provide interconnections.

[0060] Once deposition is complete, the GMR film can then be annealed in a magnetic field and patterned using standard photolithography techniques followed by ion etching to remove excess material and form the desired resistor shape.

[0061] In the embodiment from Fig. 3, it will be understood that the stack 3 can be formed in substantially the same manner, with the ferromagnetic layers 316 and the non-magnetic layers 318 of the multilayer arrangement 314 being formed in substantially the same manner as those in Fig. 5F-5H shown.

[0062] It is understood that each of the layers within the stacks 2, 3 described above may be formed using a suitable physical vapor deposition method, such as sputtering. Likewise, the deposition of each stack 2, 3 may be performed in a single vacuum step, so that there is no exposure to an ambient atmosphere between the individual steps, thereby avoiding contamination or oxidation of the various layers. For example, the entire stack 2, 3, starting from the seed layer 202, 302 up to the cap layer 210, 310, is deposited by either sputtering or ion beam deposition with a single tool, without breaking the vacuum between the different layers, to prevent surface contamination and changes due to exposure to atmospheric gases.

[0063] In another embodiment of the disclosure, a GMR stack may be provided wherein the free layer comprises a first layer of a crystalline ferromagnetic material with low AMR effect, such as CoFe, and a second layer of an amorphous ferromagnetic material, such as CoFeB. Such an arrangement eliminates the use of any ferromagnetic material exhibiting a strong AMR effect, but is in turn subject to greater magnetostriction.

[0064] Although arrangements described above show the AAF layer 204, 304 on the bottom side of the stack 2, 3 (referred to as "bottom-pinned"), it is understood that the stack 2, 3 may alternatively be arranged with the AAF layer 204, 304 on top of the stack 2, 3 (referred to as "top-pinned") with the non-magnetic spacer 206, 306 and the free layer 208, 308 underneath.

[0065] Likewise, it should be understood that although the above arrangements describe the use of an AAF layer 204, a simple antiferromagnetic layer may be used instead, comprising, for example, a layer of an antiferromagnetic material such as PtMn, IrMn, NiMn, and a layer of a ferromagnetic material such as CoFe acting as the "pinned" layer. Applications

[0066] Any of the principles and advantages discussed herein may be applied to other systems, not just those described above. Some embodiments may include a subset of features and / or advantages set forth herein. The elements and acts of the various embodiments described above may be combined to provide additional embodiments. The acts of the methods discussed herein may be performed in any order, as appropriate. Furthermore, the acts of the methods discussed herein may be performed in series or in parallel, as appropriate. Although circuits are illustrated in specific arrangements, other equivalent arrangements are possible.

[0067] Any of the principles and advantages discussed herein may be implemented in conjunction with any other systems, devices, or methods that may benefit from any of the teachings herein. For example, any of the principles and advantages discussed herein may be implemented in conjunction with any devices requiring correction of rotational angular position data derived from rotating magnetic fields. Furthermore, the devices may include any magnetoresistive or Hall-effect devices capable of sensing magnetic fields.

[0068] Aspects of this disclosure may be implemented in various electronic devices or systems. For example, phase correction methods and sensors implemented according to any of the principles and advantages discussed herein may be included in various electronic devices and / or in various applications. Examples of electronic devices and applications may include, but are not limited to, servo systems, robotics, aircraft, submarines, toothbrushes, biomedical sensing devices, and portions of consumer electronic products such as a semiconductor die and / or packaged modules, electronic test equipment, etc. Furthermore, the electronic devices may include unfinished products, including those for industrial, automotive, and / or medical applications.

Claims

[1] A giant magnetoresistive (GMR) element for a magnetic multiturn sensor, the giant magnetoresistive element comprising: a reference layer; a non-magnetic layer (318) adjacent to the reference layer; and a free layer (308) made of a ferromagnetic material, the free layer (308) comprising a first layer made of a ferromagnetic material adjacent to the non-magnetic layer and a multilayer arrangement (314) comprising at least a plurality of layers (316) made of a first material, the first material being ferromagnetic, and a plurality of layers (318) made of a second material, a thickness of the free layer being greater than 30 nm, and the plurality of layers (316) made of the first material having a first magnetostriction and the plurality of layers (318) made of the second material having a second magnetostriction that reduces the magnetostriction of the free layer (308). [2] The giant magnetoresistive element according to claim 1, wherein the second material is a material having a negligible or nearly negligible anisotropic magnetoresistive (AMR) effect. [3] The giant magnetoresistive element of claim 1, wherein the plurality of layers (316) of the first material and the plurality of layers (318) of the second material are arranged in an alternating configuration. [4] The giant magnetoresistive element according to claim 1, wherein the first material is one of NiFe and CoFe. [5] The giant magnetoresistive element according to claim 1, wherein the second material is one of the following: CoFeB, CoZrTa, CoZrTaB, CoZrNb and CoZrO. [6] The giant magnetoresistive element according to claim 1, wherein a thickness and / or composition of the first material and the second material are configured such that the free layer is free of magnetostriction. [7] The giant magnetoresistive element of claim 1, wherein each of the plurality of layers (316) of the first material and the plurality of layers (318) of the second material has a thickness of about 0.5 nm to about 8 nm. [8] A giant magnetoresistive element according to claim 1, wherein the first layer of ferromagnetic material has a magnetization that can freely align with an externally applied magnetic field. [9] A giant magnetoresistive element according to claim 1, wherein the first layer of ferromagnetic material is CoFe. [10] The giant magnetoresistive element according to claim 1, wherein at least a part of the reference layer has a magnetization that is in a fixed direction. [11] The giant magnetoresistive element of claim 1, wherein the reference layer comprises a sequence of layers defining an artificial antiferromagnetic material, wherein a layer of the artificial antiferromagnetic material has a magnetization that is in a fixed direction. [12] A magnetic multiturn sensor comprising one or more giant magnetoresistive elements, each giant magnetoresistive element comprising: a reference layer; a non-magnetic layer (318) adjacent to the reference layer; and a free layer (308) made of a ferromagnetic material, the free layer (308) comprising a first layer made of a ferromagnetic material adjacent to the non-magnetic layer and a multilayer arrangement (314) comprising at least a plurality of layers (316) made of a first material, the first material being ferromagnetic, and a plurality of layers (318) made of a second material, a thickness of the free layer being greater than 30 nm, and the plurality of layers (316) made of the first material having a first magnetostriction and the plurality of layers (318) made of the second material having a second magnetostriction that reduces the magnetostriction of the free layer (308). [13] A magnetic multiturn sensor according to claim 12, wherein the second material is a material with a negligible or nearly negligible anisotropic magnetoresistive (AMR) effect. [14] A magnetic multiturn sensor according to claim 12, wherein the first material is one of the following: NiFe and CoFe. [15] A multi-turn magnetic sensor according to claim 12, wherein the second material is one of the following: CoFeB, CoZrTa, CoZrTaB, CoZrNb and CoZrO. [16] A method of manufacturing a giant magnetoresistive element, the method comprising: Forming a reference layer; Forming a non-magnetic layer adjacent to the reference layer; and Forming a free layer (308) of a ferromagnetic material, wherein the free layer (308) comprises a first layer of a ferromagnetic material adjacent to the non-magnetic layer and a multilayer arrangement (314) comprising at least a plurality of layers (316) of a first ferromagnetic material, wherein the first material is ferromagnetic, and a plurality of layers (318) of a second material, wherein a thickness of the free layer (308) is greater than 30 nm, and wherein the plurality of layers (316) of the first material have a first magnetostriction and the plurality of layers (318) of the second material have a second magnetostriction that reduces the magnetostriction of the free layer (308). [17] The method of claim 16, wherein the method comprises forming a plurality of layers (316) of the first material and a plurality of layers (318) of the second material in an alternating sequence to provide the multi-layer arrangement (314) of the free layer (308). [18] The method of claim 17, wherein the second material is a material having a negligible or nearly negligible anisotropic magnetoresistive (AMR) effect. [19] The method of claim 16, wherein forming the reference layer comprises forming multiple layers to provide an artificial antiferromagnetic material. [20] The method of claim 19, further comprising: Providing a substrate (300); and Forming the artificial antiferromagnetic material or free layer (308) on the substrate (300).

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