Three-axis magnetic field sensor

Abstract

Magnetic field sensor (100), comprising: a first bridge circuit (121) comprising a first magnetoresistive sensor, a second magnetoresistive sensor, a third magnetoresistive sensor, and a fourth magnetoresistive sensor connected as a Wheatstone bridge to detect a magnetic field along a first direction orthogonal to a plane of the first, second, third, and fourth magnetoresistive sensors; wherein The first magnetoresistive sensor includes: a first detection element (122); and a first flux guide (132; 136) comprising a first high permeability magnetic material, the first flux guide (132; 136) being disposed (i) adjacent to and (ii) above or below the first sensing element (122); the second magnetoresistive sensor includes: a second detection element (123); and a second flux guide (133; 137) comprising a second high permeability magnetic material, the second flux guide (133; 137) being disposed (i) adjacent to and (ii) above or below the second sensing element (123); the third magnetoresistive sensor includes: a third sensing element (124); and a third flux guide (134; 138) comprising a third high-permeability magnetic material, the third flux guide (138; 143) being disposed (i) adjacent to and (ii) above or below the third sensing element (124); and the fourth magnetoresistive sensor includes: a fourth detection element (125); and a fourth flux guide (135; 139) comprising a fourth high permeability magnetic material, the fourth flux guide (135; 139) being disposed (i) adjacent to and (ii) above or below the fourth sensing element (125); wherein the first (132; 136), the second (133; 137), the third (134; 138) and the fourth (135; 139) flux guides are arranged asymmetrically, so that two of the first flux guide (132; 136), the second flux guide (133; 137), the third flux guide (134; 138) and the fourth flux guide (135; 139) are arranged directly above a first edge of the respective detection element (121; 122; 123; 124) and two others of the first flux guide (132; 136), the second flux guide (133; 137), the third flux guide (134; 138) and the fourth flux guide (135; 139) are arranged directly below a second edge of the respective detection element (121; 122; 123; 124), wherein the first and second edges are arranged on opposite sides of the respective detection elements (121; 122; 123; 124).

Description

Area

[0001] The present invention relates generally to the field of magnetoelectronic devices and, more particularly, to CMOS-compatible magnetoelectronic field sensors used to detect magnetic fields in three mutually perpendicular directions. background

[0002] Sensors are widely used in modern systems to measure or detect physical parameters such as position, motion, force, acceleration, temperature, pressure, etc. Although a variety of different sensor types exist for measuring these and other parameters, they all have different limitations. For example, low-cost weak-field sensors, such as those used in an electronic compass or for other similar magnetic sensing applications, generally consist of anisotropic magnetoresistance-based devices, so-called AMR devices. To achieve the required sensitivity and suitable resistances that provide good match with CMOS, the sensing units of these sensors generally have dimensions on the order of square millimeters.For mobile applications, such AMR sensor configurations are expensive in terms of complexity, circuit area, and power consumption.

[0003] Other types of sensors, such as Hall sensors, supermagnetoresistance sensors (GMR sensors), and magnetic tunnel junction sensors (MTJ sensors), have been used to create smaller sensors, but these sensors also have certain problems, such as insufficient sensitivity and influences from temperature changes. To solve these problems, MTJ sensors and GMR sensors have been used in a Wheatstone bridge structure to increase sensitivity and eliminate temperature-dependent changes in resistance. Many magnetic sensing technologies inherently often respond to the orientation of the applied field, excluding perpendicular axes. However, dual-axis magnetic field sensors have been developed for use in electronic compasses, which determine the direction of the Earth's field using a Wheatstone bridge structure for each sensing axis.

[0004] For example, Hall sensors generally respond to out-of-plane field components perpendicular to the substrate surface, whereas magnetoresistive sensors respond to in-plane magnetic fields. When these axes of response are utilized, developing a small-footprint three-axis sensing solution typically involves a multi-chip module with one or more chips positioned at right angles to each other. For magnetoresistive sensors, the normal in-plane components can be achieved by balanced sensor design, but response to out-of-plane components is generally achieved through vertical bonding or solder reflow to make contact with a secondary chip that has been mounted vertically.Since the size of the vertically bonded chip is usually determined by the distance between two pads (pad pitch), which depends on the processing constraints, such a process results in a large vertical expansion of the finished assembly, high chip and assembly costs, and makes so-called "chip scale packaging" difficult and expensive because of the need to integrate contact holes running through the chip.

[0005] US Pat. No. 7,505,233 B2 discloses a magnetic sensor having at least a first and a second structure made of a soft magnetic material, wherein the structures are spatially separated and define a gap therebetween. The first and second structures are configured to form a gap magnetic field in response to an external magnetic field, which gap magnetic field is oriented in a direction perpendicular to the extension of the first gap. Additionally, the magnetic sensor comprises at least one magnetoresistive layer structure arranged near the first gap, including within the first gap, and which responds to the gap magnetic field.

[0006] There is a need for an improved design and manufacturing process for forming a single-chip magnetic sensor that responds to an applied magnetic field in three dimensions. Furthermore, there is a need for a three-axis sensor that can be constructed more efficiently and cost-effectively than an integrated circuit structure for use in mobile applications. Furthermore, there is a need for an improved magnetic field sensor and improved manufacturing to solve the above-identified problems in the art. Furthermore, other advantageous features and characteristics of the present invention will become apparent from the following detailed description and the appended claims, taken in conjunction with the accompanying drawings and the present background. Short description of the drawings

[0007] Embodiments of the invention are described below in conjunction with the following figures, in which the same reference numerals designate the same elements, wherein Fig. 1 illustrates an electronic compass structure using differential sensors consisting of three bridge structures with MTJ sensors according to an exemplary embodiment; Fig. 2 a partial sectional view of the Z-axis bridge structure in Fig. 1 according to the exemplary embodiment; Fig. 3 is a view of flow lines as obtained by finite element simulation of two of the four MTJ sensors in Fig. 2 be calculated; Fig. 4 a partial sectional view of the Z-axis bridge structure in Fig. 1 according to another exemplary embodiment; Fig. 5 a partial sectional view of the Z-axis bridge structure in Fig. 1 according to another exemplary embodiment; Fig. 6 is another form of flux conductor, as in Fig. 5 is shown; Fig. 7 is another form of flux conductor, as it is in Fig. 5 is shown; Fig. 8 is another form of flux conductor, as it is in Fig. 6 is shown; and Fig. Figure 9 is a graph illustrating the Z sensitivity, expressed as a percentage of the X sensitivity, for a single (non-differentially wired) MTJ sensing element as a function of the enclosure-to-sensor distance.

[0008] It should be understood that, for simplicity and clarity of illustration, elements depicted in the drawings are not necessarily drawn to scale. For example, the dimensions of some elements are exaggerated relative to others to promote and enhance clarity and understanding. Furthermore, where considered appropriate, reference numerals have been repeated in the drawings to designate corresponding or analogous elements. Summary

[0009] A ferromagnetic thin-film magnetic field sensor includes a first magnetoresistive sensor comprising a substrate having a planar surface and a first sensing element having a first side parallel to the planar surface of the substrate, the first sensing element having a second side opposite the first side and having first and second edges opposite each other, and a first flux guide arranged non-parallel to the first side of the substrate and having an end proximate to the first edge and the first side of the first sensing element. An optional second flux guide may be arranged non-parallel to the first side of the substrate and have an end proximate to the second edge and the second side of the first sensing element.

[0010] In another exemplary embodiment, a ferromagnetic thin film based magnetic field sensor includes a first, a second and a third magnetoresistive sensor.The first MTJ sensor includes a first pinned layer and a first sensing element formed on the first pinned layer, the second MTJ sensor includes a second pinned layer and a second sensing element formed on the second pinned layer and perpendicular to the first sensing element, and the third MTJ sensor includes a third pinned layer and a third sensing element formed on the third pinned layer, the third pinned layer being arranged at approximately 45° to the first and second pinned layers, and the third sensing element having first and second edges and first and second sides.A flux guide is arranged non-parallel to a planar surface of the substrate and has one end located close to the first edge and the first side of the third sensing element. Detailed description

[0011] The following detailed description is provided by way of example only and is not intended to limit the invention or its intended use or uses. Furthermore, no obligation is intended to be bound by any theory presented in the foregoing background or the following detailed description.

[0012] By integrating high-aspect-ratio vertical rods (flux guides) made of a high-permeability material, such as nickel-iron (NiFe), whose ends terminate close to opposite edges and opposite sides of a magnetic sensing element, a portion of the Z-axis field can be brought into the XY plane. These flux guides serve to capture magnetic flux from an applied field oriented in the Z direction, thereby bending the field lines near the ends of the flux guides essentially horizontally.By asymmetrically positioning the flux guides, for example, the flux guide segment above the left edge of the sensing elements in two of the four legs of a Wheatstone bridge and the flux guide above the right edge of the sensing elements in the other two legs, the horizontal components can act in opposite directions for the two paired legs, resulting in a strong differential signal. A field acting in the X or Y direction is projected evenly onto all four legs of the bridge and therefore subtracted and does not contribute to the final sensor signal.Separate bridges are included elsewhere in the magnetic sensor chip to determine the X and Y components of the magnetic signal. In this way, a field with components in all three spatial orientations can be accurately determined using a single-chip magnetoresistive sensing module based, for example, on MTJ sensing elements. FEM simulations have shown that a pair of high-aspect-ratio flux guides, for example, 25 nm wide and 500 nm high, spanning several µm in the third direction, when optimally positioned, generate a signal at a single element that is 80% of the signal measured in a plane (X-axis) field of the same strength. Additional signal can be achieved by bringing the flux guide closer to the sensor, increasing the height of the flux guide, and further shaping the guide geometry.One example is adding horizontal segments parallel to the sensing element that extend beyond the edges of the sensing element. Other examples include forming a U-shape located within the inner horizontal segment and aligned with the outer edge of the sensing element, angular termination of the vertical segments through which the flux guide extends partially in the plane of the sensing element, and a similarly arranged box structure. These shapes serve to further amplify the horizontal component of the guided flux and shift it to a more central region of the sensor.A structure with individual 25 nm wide vertical rods used as flux guides is tolerant to overlay errors and produces an apparent XZ field conversion (for a differentially wired Wheatstone bridge) at the rate of 2.5% at a misalignment of 85 nm (3 sigma) between a single flux guide layer and the sensing layer.

[0013] The flux guide layer may consist of layers commonly used in the MRAM process flow, which employs bit and digit lines encapsulated with a high-permeability magnetic material (such as in typical magnetic memory devices), referred to below as a flux guide, to enhance the existing field factors and reduce the current required to switch the memory element. In the sensor application, the same process flow may be employed with the optional additional step of sputtering the underside of the digit line to remove any cladding present at the bottom of the trench. Modifications may be made to the process so that the height and width of the cladding used for flux guidance purposes are reduced instead of the 500 nm and 1000 nm, respectively.25 nm, which are used in the exemplary process described above, have optimal values.

[0014] The following describes in more detail a method and apparatus for effecting multi-axis pinning on a bulk wafer. This method can be used to form an IC sensor with different reference layers having three different pinning directions, two of which are substantially perpendicular to each other, and which are defined by a single process for depositing material to pin the magnetization direction and for adjusting a bulk wafer. In a preparatory step, an array of one or more layers of ferromagnetic and antiferromagnetic materials are etched into shaped reference layers having a two-dimensional shape with a high aspect ratio, the shape allowing differentiation of the desired magnetization direction for each reference layer.Depending on the materials and processes used, the final magnetization direction can be along the short axis or the long axis of the formed layer. For example, if the fixed-direction layer is provided with a slightly asymmetric synthetic antiferromagnet (SAF) patterned in micrometer-scale dimensions, the magnetization will be along the short axis. The SAF embodiment, as is known to those skilled in the art, has a number of advantages associated with the use of fixed-direction SAF reference layers in magnetoelectronic devices. In other embodiments, if the thickness of the fixed-direction and stationary layers, as well as the spatial extent of the in-plane structural arrangement, are controlled, the final magnetization can be along the long axis.When shape anisotropy is utilized, different magnetization directions are induced in the reference layers by heating in the presence of an aligning field aligned between the desired magnetization directions for the reference layers. In selected embodiments, the reference layers are heated sufficiently to reduce the material component of the anisotropy and allow the shape and external field to determine the magnetization direction. Thus, when the aligning field is removed, the shape anisotropy aligns the magnetization in the desired direction. Upon removal of the aligning field, the reference layers relax and follow the shape of the reference layers, inducing magnetization aligned along the desired axis of the shaped reference layer.An optional compensating field can be applied to induce perpendicularity, and the reference layers are then heated above the phase transition temperature of the antiferromagnetic pinning layers. For example, if two reference layers are shaped to have longer dimensions that are perpendicular to each other, the magnetizations induced for the two reference layers are nearly perpendicular to each other.

[0015] Various illustrative embodiments of the present invention are described in detail below with reference to the accompanying figures. While various details are set forth in the following description, it is understood that the present invention may be practiced without these specific details, and that numerous choices for implementing the invention described herein may be made to achieve specific design goals, such as compliance with process technology or design constraints that vary from one implementation to another. While this development effort may be complex and time-consuming, it is nevertheless routine work for those skilled in the art who can utilize the present disclosure.Furthermore, selected aspects are illustrated with reference to simplified cross-sectional drawings, without including each individual structure or shape of the device, in order to avoid limiting or obscuring the present invention. It should also be noted that throughout the detailed description, conventional techniques and features related to the construction and function of magnetic sensors, the construction of MRAM (Magnetoresistive Random Access Memory), the function of MRAM, the fabrication of semiconductor devices, and other aspects of integrated circuit devices may not be described in detail.Although certain materials are formed and removed to fabricate the IC sensors as part of an existing process for manufacturing MRAM, the specific operations for forming or removing these materials are not described in detail below, as these details are well known and are not considered necessary to teach one skilled in the art how to make or use the present invention. Furthermore, circuit / component designs and configurations illustrated in the various figures included herein are intended to represent exemplary embodiments of the invention. It should be noted that many alternative or additional circuit / component designs may be present in a practical embodiment.

[0016] Fig. Figure 1 shows a magnetic field sensor 100 provided with a first, a second and a third differential sensor 101, 111, 121, with which the directions of the components of an acting field along a first axis 120 (e.g., the Y-axis direction), a second axis 110 (e.g., the X-axis direction) and a third axis 130 (e.g., the Z-axis direction) are detected. The Z-axis direction is shown as a point and a crosshair, which extends either in the side on which Fig. 1. Exemplary embodiments of the first and second sensors 101, 111 are described in detail in U.S. patent application Ser. No. 12 / 433,679. Each sensor 101, 111, 121, as shown therein, is provided with unshielded sensing elements connected in a bridge arrangement. Thus, the first sensor 101 consists of connecting a plurality of sensing elements 102-105 in a bridge arrangement over a corresponding plurality of fixed-magnetization layers 106-109, each of the fixed-magnetization layers 106-109 being magnetized in the X-axis direction.Similarly, the second sensor 111 consists of connecting a plurality of sensing elements 112-115 in a bridge arrangement over a corresponding plurality of fixed-magnetization-direction layers 116-119, each magnetized in the Y-axis direction perpendicular to the magnetization direction of the fixed-magnetization-direction layers 106-109. Furthermore, the third sensor 121, in the same plane as the first and second sensors 101-111, consists of connecting a plurality of sensing elements 122-125 in a bridge arrangement over a plurality of fixed-magnetization-direction layers 126-129, each magnetized in the XY-axis direction at a 45° angle to the magnetization direction of the magnetically aligned layers 106-109 and 116-119.In the illustrated bridge arrangement 101, the sensing elements 102-104 are configured to have a first easy magnetization direction, and the sensing elements 103, 105 are configured to have a second easy magnetization direction, wherein the first and second easy magnetization directions are perpendicular to each other and are oriented to differ equally from the magnetization direction of the fixed-magnetization layers 106-109. Regarding the second bridge arrangement 111, the sensing elements 112, 114 have a first easy magnetization direction perpendicular to the second easy magnetization direction for the sensing elements 113, 115, such that the first and second easy magnetization directions are oriented to differ equally from the magnetization direction of the fixed-magnetization layers 116-119.In the third bridge arrangement, the sensing elements 122, 123, 124, and 125 all have an easy magnetization direction perpendicular to the aligned magnetization direction of the fixed-magnetization-direction layers 126, 127, 128, and 129. The third bridge arrangement 121 further includes flux guides 132-135 positioned adjacent to the right edge of the sensing elements 122-125, and flux guides 136-139 positioned adjacent to the left edge of the sensing elements 122, 125. Flux guides 132, 137, 134, and 139 are positioned above the sensing elements 122-125, and flux guides 136, 133, 138, and 135 are positioned below the sensing elements 122-125. The positioning of these flux conductors 132-139 is described in more detail below. Fig. 2. In the illustrated sensors 101, 111, 121, no shielding is required for the sensing elements, nor are any special reference elements required. In an exemplary embodiment, this is achieved by relating each active sensing element (e.g., 102, 104) to another active sensing element (e.g., 103, 105) using shape anisotropy techniques to set the easy magnetic axes of the related sensing elements to be offset by 90° for the X and Y sensors, and by establishing a reference to a sensing element that responds in an opposite manner to a field acting in the Z direction for the Z sensor. The establishment of the reference for the Z sensor is described in more detail below. The Fig. The arrangement shown in Figure 1 may not have the advantages of the arrangement shown in Fig. 2 described in more detail and serves only as an example.

[0017] By positioning the first and second sensors 101, 111 so that they are aligned perpendicular to each other, while equally offsetting the orientations of the sensing elements relative to the sensor's fixation direction and perpendicular to each other for each sensor, the sensors can detect the directions of the components of an acting field along the first and second axes. Flux guides 132-139 are positioned asymmetrically in sensor 121 above and below the opposing edges of elements 122-125 between legs 141, 143 and legs 142, 144. Since flux guides 132, 134 are arranged above the sensing elements 122, 124, the magnetic flux from the Z field can be guided through the flux guides 132 and 134 along the right side into the XY plane and cause the magnetization of the sensing elements 122 and 124 to rotate in a first direction toward a higher resistance.Likewise, the magnetic flux from the Z field can be guided through flux paths 133 and 135 along the right side of the sensing element into the XY plane, causing the magnetization of sensing elements 123 and 125 to rotate in a second direction opposite to the first direction toward low resistance because these flux guides are located below sensing elements 123, 125. Thus, sensor 121 can sense the directions of the components of an acting field along the third axis. Although in the preferred embodiment, the flux guides lie in a plane perpendicular to the plane of the field sensor, the flux guides are also effective if the angle they form with the sensor is not exactly 90°.In other embodiments, the angle between the flux guide and the field sensor could be in a range of 45° to 135°, with the exact angle being determined depending on other factors, such as ease of manufacture.

[0018] As can be seen from the above, a magnetic field sensor can consist of differential sensors 101, 111, 121, employing unshielded sensing elements 102-105, 112-115 and guided flux sensing elements 122-125, connected in a bridge arrangement over respective fixed magnetization direction or reference layers 106-109, 116-119, and 126-129 to detect the presence and direction of an applied magnetic field. This configuration enables the magnetic field sensor to achieve good sensitivity and also offers the temperature compensation characteristics of a bridge arrangement.

[0019] The bridge circuits 101, 111, 121 can be fabricated as part of an existing process for manufacturing MRAM or thin-film sensors, with only minor modifications to control the magnetic alignment of the various sensor layers and the cross-section of the flux guide structures. Each of the fixed magnetization layers 106-109, 116-119, and 126-129 can be formed with one or more lower ferromagnetic layers, and each of the sensing elements 102-105, 112-125, 122-125 can be formed with one or more upper ferromagnetic layers. An insulating dielectric tunneling layer (not shown) may be disposed between the sensing elements 102-105, 112-125, 122, 125 and the fixed magnetization direction layers 106-109, 116-119 and 126-129.The electrodes and the sense electrodes are advantageously made of magnetic materials whose magnetization layer can be aligned. Suitable electrode materials and arrangements of materials into structures commonly used for electrodes of MRAM devices and other MTJ devices are known in the art. For example, pinned magnetization direction layers 106-109, 116-119, and 126-129 can be formed with one or more layers of ferromagnetic or antiferromagnetic materials with a total thickness in the range of 10 to 1000 Å, and in selected embodiments in the range of 250 to 350 Å. In an exemplary implementation, each of pinned magnetization direction layers 106-109, 116-119, and 126-129 is formed with a single ferromagnetic layer and an underlying antiferromagnetic layer for pinning the magnetization direction.In another exemplary embodiment, each pinned magnetization layer 106-109, 116-119, and 126-129 includes a synthetic antiferromagnetic layer component (e.g., a stack of CF (cobalt-iron), ruthenium (Ru), and CFB) that is 20 to 80 Å thick and an underlying pinned magnetization layer that is approximately 200 Å thick. The bottom antiferromagnetic materials can be resettable materials, such as IrMn, although other materials, such as PtMn, that cannot be readily reset at normal temperatures may also be used. The pinned magnetization layers 106-109, 116-119, and 126-129 act as a pinned magnetic layer, respectively.A magnetic layer with a fixed direction of magnetization is formed when the direction of its magnetization is fixed in a direction that does not change under normal operating conditions. The heating properties of the materials used to fix the magnetization direction of the fixed direction layers 106-109, 116-119, and 126-129 can, as disclosed herein, alter the manufacturing process used to form these layers.

[0020] Each of the sensing elements 102-105, 112-125, 122-125 and each of the fixed magnetization direction layers 106-109, 116-119, 126-129 form an MTJ sensor. For example, in bridge circuit 121, sensing element 122 and the fixed magnetization direction layer 126 form an MTJ sensor 141. Likewise, sensing element 123 and the fixed magnetization direction layer 127 form an MTJ sensor 142, sensing element 124 and the fixed magnetization direction layer 128 form an MTJ sensor, and sensing element 125 and the fixed magnetization direction layer 129 form an MTJ sensor 144.

[0021] The fixed magnetization direction layers 106-109, 116-119, and 126-129 can be formed with a single patterned ferromagnetic layer having a magnetization direction (indicated by the arrow) aligned along the longitudinal direction of the patterned reference layer(s). However, in other embodiments, the fixed magnetization direction reference layer can be implemented with a synthetic antiferromagnetic (SAF) layer that serves to align the magnetization of the fixed magnetization direction reference layer along the short axis of the patterned reference layer(s).As is clear, the SAF layer can be implemented in combination with an underlying antiferromagnetic layer to fix the magnetization direction. However, for SAF structures with suitable geometry and suitable materials that ensure sufficiently strong magnetization, the underlying antiferromagnetic layer to fix the magnetization direction may not be required, thus allowing a simple manufacturing process with cost savings.

[0022] The sensing elements 102-105, 112-125, 122-125 can be formed with one or more layers of ferromagnetic materials in a thickness range from 10 to 5000 Å, and in selected embodiments, in the range from 10 to 60 Å. The upper ferromagnetic materials can be magnetically soft materials, such as NiFe, CoFe, Fe, CFB, and the like. In each MTJ sensor, the sensing elements 102-105, 112-125, 122-125 serve as a sensing layer or free magnetic layer, respectively, since the direction of their magnetization can be deflected by the presence of an external acting field, such as the Earth's magnetic field. In final form, the sensing elements 102-105, 112-125, 122-125 may be formed with a single ferromagnetic layer having a magnetization layer (indicated by the arrows) aligned along the longitudinal axis of the structured shapes.

[0023] The fixed magnetization direction layers 106-109, 116-119, 126-129 and the sensing elements 102-105, 112-125, 122-125 can be formed to have different magnetic properties. For example, the fixed magnetization direction layers 106-109, 116-119, 126-129 can be formed with an antiferromagnetic film exchange layer coupled to a ferromagnetic film, resulting in layers with high coercivity and offset hysteresis curves, and their magnetization layers aligned in one direction, making them essentially unaffected by an external magnetic field.In contrast, the sensing elements 102-105, 112-125, 122-125 can be formed with a soft magnetic material, creating different magnetization directions with comparatively low anisotropy and coercive force, and the magnetization direction of the sensing electrode can be changed by an externally applied magnetic field. In selected embodiments, the strength of the field for fixing the magnetization direction is approximately twice the anisotropy field of the sensing electrodes, although different ratios can be used by adjusting the respective magnetic properties of the electrodes using known methods to vary their composition.

[0024] The layers with fixed magnetization direction 106-109, 116-119, 126-129 in the MTJ sensors are designed in such a way that they have a magnetization direction determined by the shape in the plane of the layers with fixed magnetization direction 106-109, 116-119, 126-119 (by the vector arrows for each sensor bridge labeled “Direction for fixing the magnetization direction” in Fig. 1). The magnetization direction of the pinned-direction layers 106-109, 116-119, 126-129 can be achieved, as described, using shape anisotropy of the pinned-direction electrodes, in which case the shapes of the pinned-direction layers 106-109, 110-119, 126-129 can each be longer in the alignment direction for a single aligned layer. Alternatively, in a pinned-direction SAF structure, the reference layer and the pinned-direction layers can be shorter in the direction of pinning the magnetization direction.In particular, the magnetization direction of the fixed-magnetization-direction layers 106-109, 116-119, 126-129 can be achieved by first heating the formed fixed-magnetization-direction layers 106-109, 116-119, 126-129 in the presence of an orienting magnetic field that is not perpendicular to the axis of longest alignment for the formed fixed-magnetization-direction layers 106-109, 116-119, 126-129, such that the acting orienting field includes a field component in the direction of the desired direction for fixing the magnetization direction for the fixed-magnetization-direction layers 106-109, 116-119, 126-129. The magnetization directions of the fixed-magnetization-direction layers are at least temporarily aligned in a predetermined direction.However, by appropriately heating the fixed magnetization direction layers during this treatment and removing the aligning field without reducing the heat, the magnetization of the fixed magnetization direction layers relaxes along the desired axis of alignment for the formed fixed magnetization direction layers 106-109, 116-119, 126-129. Once the magnetization relaxes, the fixed magnetization direction layers can be annealed and / or cooled, so that the magnetic field direction of the fixed magnetization direction electrode layers is set in the desired direction for the formed fixed magnetization direction layers 106-109, 116-119, 126-119, 126-129.

[0025] The exemplary embodiments described herein may be fabricated using known lithographic processes as set forth below. The fabrication of integrated circuits, microelectronic devices, microelectromechanical devices, microfluidic devices, and photonic devices involves the creation of multiple layers of materials that interact in specific ways. One or more of these layers may be patterned so that different regions of the layer have different electrical or other properties, which may be interconnected within the layer or connected to other layers to create electrical components and circuits. These regions may be created by selectively introducing or removing different materials. The structures forming these regions are often created using lithographic processes.For example, a layer of photoresist material is applied to a layer overlying a wafer substrate. A photomask (containing transparent and opaque zones) is used to selectively expose this photoresist material to a form of radiation, such as ultraviolet light, photons, or x-rays. Either the photoresist material exposed to the radiation or the photoresist material not exposed to the radiation is removed by applying a developer. An etch can then be performed on the layer not protected by the remaining resist, and once the resist is removed, the layer overlying the substrate is patterned. Alternatively, an additive process could be used, for example, by building a structure using the photoresist as a stencil.

[0026] As mentioned with reference to Fig. As can be seen in Figure 2, according to an exemplary embodiment of the present invention, the structure of the MTJ devices 141-144 of the third bridge circuit 121 includes the fixed magnetization direction layers 126-129, the sensing elements 122-125, and the flux guides 132-139, all formed in the dielectric material 140. The flux guide 136 is positioned adjacent to a line 145, and one end thereof is positioned below an edge of the sensing element 122. The flux guides 133 and 138 are positioned on opposite sides of a line 146, and their ends are positioned below edges of the sensing elements 123 and 124, respectively. The flux guide 135 is positioned adjacent to a line 147, and one end thereof is positioned below an edge of the sensing element 125.The flux guides 132 and 137 are spaced apart by a top lead 148, and ends of which are positioned above edges of the sensor elements 122 and 123, respectively, and the flux guides 134 and 139 are spaced apart by a top lead 149, and ends of which are positioned above edges of the sensor elements 134 and 139, respectively. The leads 145-149 are preferably made of copper, but in some embodiments may be made of a dielectric. A metal stabilizing lead 150 is positioned above the MTJ devices 141-144 to create a stabilizing field for the sensing elements. The ends of the flux guides can be arranged as close to the sensing elements as possible, with a preferred spacing of 250 nm or less between the two. The sensing elements are arranged as close as possible for the highest density array, i.e., preferably spaced less than 2.5 µm apart.

[0027] Fig. Figure 3 is a view of flow lines as obtained by finite element simulation of MTJ devices 141, 142 of Fig. 2, where a magnetic field in the Z direction acts on the sensing elements 122-123. FEM modeling shows the resulting magnetic flux lines 160, which have an in-plane component of the sensor. The MTJ device 141 is represented by flux guides 132 and 136 at opposite ends of the sensing element 122. The MTJ device 142 is represented by flux guides 133 and 137 at opposite ends of the sensing element 123. That is, the sensing element 122 extends from the flux guides 132 and 136, and the sensing element 123 extends from the flux guides 133 and 137. The magnetic field 160 along the Z-axis 130 causes an asymmetric response of the detection elements 122, 123 along the X-axis 120, as indicated by the arrows 170.In this way, for a field 160 in the Z direction 130 directed toward the underside of the sheet, the magnetization of sensing element 122 rotates away from the direction of pinning the magnetization direction (toward the higher resistance) of the pinned magnetization direction layer 126, while the magnetization of sensing element 123 rotates toward the direction of pinning the magnetization direction (and toward the lower resistance) of the pinned magnetization direction layer 127. For a field in the X direction 120, both elements 122, 123 exhibit induced magnetization in the same direction (toward the higher or lower resistance). Therefore, by wiring MTJ elements 141, 142 in a Wheatstone bridge for differential measurement and subtracting the resistances of the MTJ devices 141, 142, the X-field response is eliminated and the Z-field response is measured twice.

[0028] When a strong magnetic field acts, which can cause magnetization disturbances and domain structure in the flux guides 132-139, as again referring to Fig. 2, a strong current pulse is generated along the metal lines 145-149 and resets the flux guide region structure.

[0029] In a further exemplary embodiment (in Fig. 4), each of the jacketed lines 145-149 is divided into two independent metal lines, and additional non-flux-conducting jacketing (161-168 and 191-198) is disposed between these two metal lines at the inner edges. For sensor 141, the flux conductor 161 at the left edge of the left metal line 148 conducts Z-field flux into the sensing element 122 on its left side, and the flux conductor 192 at the rightmost edge of the right metal line 145 conducts Z-field flux into the sensing element 122 on its right side. Sensors 142-144 operate in a similar manner, with the jacketed edge of the metal line adjacent to each sensing element performing the active flux-conducting function.Because these lines are separated, a current can be directed into the blade through the jacketed lines 145, 146, 182, and 183 and out of the blade through 181, 147, 148, and 149, creating a magnetic field along the jacketed edge of the lines with a Z component pointing in a consistent direction (downward in this example). These current orientations can be used to create a magnetic field with a strong component in the Z direction, which, via geometry calibration, can serve as a self-test for the functionality and sensitivity of the Z-axis response.

[0030] Another exemplary embodiment (see Fig. 5) includes extensions 152-159 formed integrally with the flux guides 132-139. The extensions 152-159 extend along the same axis as the sensor elements 122-125 and amplify the horizontal component of the flux guide and shift the horizontal component more toward the center of the corresponding sensing element 122-125.

[0031] Although various exemplary embodiments for the flux guides including the vertical elements 132-139 in Fig. 2 and the L-shaped flux guide including extensions 152-159 in Fig. 5, other exemplary embodiments can be used for both upper and lower flux guides, such as box-shaped or U-shaped flux guides. In the U-shaped structure ( Fig. 6) a horizontal NiFe segment 171 connects the two vertical segments 161, 162 along the lower metal line, while in the box-shaped structure ( Fig. 7) a horizontal segment 172 also connects the two vertical segments, both located above the metal line. A horizontal segment contributes to coupling the magnetic structure of the two vertical segments, so that the field conversion factor is increased by 10-20% compared to that of two isolated vertical flux guides. Two horizontal segments of the box-like structure provide better coupling and increase the field conversion factor by 20-40% compared to a simple vertical flux guide. Furthermore, the vertical segments of the U-shaped structure can be Fig. 6 be widened outwards (see 173, 174 in Fig. 8) so that the area near the edge of the sensing element has a horizontal component. Similar to the L-shaped flux guides, the flared segments direct the magnetic flux so that a component is present directly in the plane of the magnetic sensor, thus further enhancing the field conversion factor. However, care must be taken to ensure that the overlap is not too strong, otherwise the magnetic flux will be shielded from the sensor.

[0032] Fig.Figure 9 is a graph illustrating the Z / X sensitivity ratio versus cladding-to-sensor spacing for a 25 nm wide, 500 nm high vertical segment positioned above and below the sensing element. The Z / X sensitivity increases by approximately 75% when the cladding has a 25 nm spacing. Additional factors can be achieved via cross-sectional changes, such as those highlighted above, or via improvements in the flux guide aspect ratio. For example, making the flux guide taller and increasing the aspect ratio results in a linear increase in the Z / X sensitivity ratio. Therefore, it is important to position the flux guide as close to the sensing element as possible and to increase its aspect ratio as much as possible without adversely affecting the magnetic microstructure.

[0033] Although the described exemplary embodiments disclosed herein relate to various sensor structures and methods of fabricating the same, the present invention is not necessarily limited to the exemplary embodiments, which represent inventive aspects of the present invention that can be employed in a wide range of semiconductor processes and / or devices. Thus, the specific embodiments disclosed above are merely illustrative and should not be construed as limitations of the present invention, as the invention may be modified and practiced in various equivalent ways, as will be apparent to those skilled in the art who may benefit from the present teachings.For example, the relative positions of the sensing layers and the magnetization direction fixing layers in a sensor structure can be reversed so that the magnetization direction fixing layer is on top and the sensing layer is below. Furthermore, the sensing layers and alignment layers can be formed with materials other than those disclosed. Furthermore, the thickness of the described layers can deviate from the disclosed thickness values.Accordingly, this description is not intended to limit the invention to the specific form disclosed, but on the contrary is intended to cover alternatives, modifications, and equivalents that may be included within the spirit and scope of the invention as defined by the appended claims, so that it will be understood by those skilled in the art that various changes, substitutions, and modifications are possible without departing from the spirit and scope of the invention in its broadest form.

[0034] Benefits, further advantages, and solutions to problems have been described above with reference to specific embodiments. The advantages, benefits, solutions to problems, and any elements that provide or enhance an advantage, benefit, or solution are not to be considered a critical, required, or essential feature or element of any or all of the claims. As used herein, the terms "comprises," "comprising," or any variations thereof are intended to cover non-exclusive inclusion, such that, for example, a process, method, article, or apparatus that includes a number of elements not only includes that element, but may also include other elements not expressly recited or inherent in such process, method, article, or apparatus.

Claims

[1] Magnetic field sensor (100), comprising: a first bridge circuit (121) comprising a first magnetoresistive sensor, a second magnetoresistive sensor, a third magnetoresistive sensor, and a fourth magnetoresistive sensor connected as a Wheatstone bridge to detect a magnetic field along a first direction orthogonal to a plane of the first, second, third, and fourth magnetoresistive sensors; wherein The first magnetoresistive sensor includes: a first detection element (122); and a first flux guide (132; 136) comprising a first high permeability magnetic material, the first flux guide (132; 136) being disposed (i) adjacent to and (ii) above or below the first sensing element (122); the second magnetoresistive sensor includes: a second detection element (123); and a second flux guide (133; 137) comprising a second high permeability magnetic material, the second flux guide (133; 137) being disposed (i) adjacent to and (ii) above or below the second sensing element (123); the third magnetoresistive sensor includes: a third sensing element (124); and a third flux guide (134; 138) comprising a third high-permeability magnetic material, the third flux guide (138; 143) being disposed (i) adjacent to and (ii) above or below the third sensing element (124); and the fourth magnetoresistive sensor includes: a fourth detection element (125); and a fourth flux guide (135; 139) comprising a fourth high permeability magnetic material, the fourth flux guide (135; 139) being disposed (i) adjacent to and (ii) above or below the fourth sensing element (125); wherein the first (132; 136), the second (133; 137), the third (134; 138) and the fourth (135; 139) flux guides are arranged asymmetrically, so that two of the first flux guide (132; 136), the second flux guide (133; 137), the third flux guide (134; 138) and the fourth flux guide (135; 139) are arranged directly above a first edge of the respective detection element (121; 122; 123; 124) and two others of the first flux guide (132; 136), the second flux guide (133; 137), the third flux guide (134; 138) and the fourth flux guide (135; 139) are arranged directly below a second edge of the respective detection element (121; 122; 123; 124), wherein the first and second edges are arranged on opposite sides of the respective detection elements (121; 122; 123; 124). [2] The magnetic field sensor (100) of claim 1, wherein at least one of the first, second, third, or fourth high permeability magnetic material includes a soft ferromagnetic material. [3] The magnetic field sensor (100) of claim 1, wherein the first, second, third, and fourth high permeability magnetic materials comprise one or more of nickel, iron, cobalt, and / or an alloy comprising one or more of nickel, iron, or cobalt. [4] The magnetic field sensor (100) of claim 1, wherein each of the first, second, third and fourth magnetoresistive sensors is a magnetic tunnel junction sensor. [5] The magnetic field sensor (100) of claim 1, further comprising: a second bridge circuit (101; 111) having a plurality of magnetoresistive sensors electrically coupled to each other to detect a magnetic field along a second direction orthogonal to the first direction. [6] The magnetic field sensor (100) of claim 1, further comprising: a second bridge circuit (101; 111) having a plurality of magnetoresistive sensors electrically coupled to each other to detect a magnetic field along a second direction orthogonal to the first direction, the second direction being parallel to the plane of the first, second, third and fourth magnetoresistive sensors. [7] The magnetic field sensor (100) of claim 1, further comprising: a second bridge circuit (101) having a first plurality of magnetoresistive sensors electrically coupled to each other to detect a magnetic field along a second direction orthogonal to the first direction; and a third bridge circuit (111) having a second plurality of magnetoresistive sensors electrically coupled to each other to detect a magnetic field along a third direction orthogonal to the first and second directions. [8] The magnetic field sensor (100) of claim 1, wherein the first bridge circuit (121) includes input terminals configured for connection to an electrical source. [9] The magnetic field sensor (100) of claim 1, wherein the first bridge circuit (121) has output terminals configured for connection to a voltage measuring device. [10] Magnetic field sensor (100) according to claim 1, wherein at least one of the first (132; 136), second (133; 137), third (134; 138) and fourth (135; 139) flux guides is formed as a rod. [11] The magnetic field sensor (100) of claim 1, wherein the first magnetoresistive sensor, the second magnetoresistive sensor, the third magnetoresistive sensor, and the fourth magnetoresistive sensor each comprise a reference layer (106-109; 116-119; 126-129) and an intermediate layer. [12] The magnetic field sensor (100) of claim 11, wherein each reference layer (106-109; 116-119; 126-129) of the first magnetoresistive sensor, the second magnetoresistive sensor, the third magnetoresistive sensor, and the fourth magnetoresistive sensor has a pinning direction, and wherein each intermediate layer of the first magnetoresistive sensor, the second magnetoresistive sensor, the third magnetoresistive sensor, and the fourth magnetoresistive sensor is an insulating dielectric layer. [13] The magnetic field sensor (100) of claim 1, wherein the sensing element (122; 123; 124; 125) of each of the first magnetoresistive sensor, the second magnetoresistive sensor, the third magnetoresistive sensor, and the fourth magnetoresistive sensor is disposed adjacent to a reference layer (106-109; 116-119; 126-129), and wherein an insulating dielectric layer is disposed between the sensing element and the reference layer. [14] The magnetic field sensor (100) of claim 1, wherein the first magnetoresistive sensor, the second magnetoresistive sensor, the third magnetoresistive sensor, and the fourth magnetoresistive sensor are disposed on or in a single substrate. [15] The magnetic field sensor (100) of claim 1, wherein each flux guide of the first flux guide (132; 136), the second flux guide (133; 137), the third flux guide (134; 138) and the fourth flux guide (135; 139) comprises (i) a first vertical segment, (ii) a second vertical segment and (iii) a horizontal segment connecting the first and second vertical segments, wherein a free end of the first vertical segment is flared outwardly relative to a free end of the second vertical segment.

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