AMR (XMR) sensors with increased linear range

Abstract

To provide anisotropic-magnetoresistive (AMR) sensors.SOLUTION: AMR sensors have a barber pole structure with multiple constant-width sections of different width. In some embodiments, two sections of greater constant width are positioned at ends of the AMR sensor, with a section of smaller width positioned in between. The sections of greater width may have a total length less than the section of smaller width. The structures described may provide enhanced linearity.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present application relates to magnetic field sensors. [Background technology]

[0002] Anisotropic magnetoresistive (AMR) sensors are used to sense magnetic fields by detecting changes in the resistance of the sensor as a result of the magnetic field. Some AMR sensors have a so-called "barber pole" structure, which comprises a resistive strip with conductive strips arranged thereon in a pattern similar to a barber pole. Summary of the Invention [Means for solving the problem]

[0003] An anisotropic magnetoresistive (AMR) sensor is described. The AMR sensor has a barberpole structure with multiple constant-width sections of different widths. In some embodiments, two wider constant-width sections are positioned at the ends of the AMR sensor, and a narrower-width section is positioned therebetween. The wider-width section can have an overall length less than the narrower-width section. The described structure can provide improved linearity.

[0004] According to some embodiments, an anisotropic magnetoresistive (AMR) sensor with improved linearity is provided, comprising: a strip of magnetoresistive material, the strip including a first section having a first constant width and a second section having a second constant width wider than the first constant width; a first plurality of conductive strips disposed in the first section and oriented at a first angle relative to the strip of magnetoresistive material; and a second plurality of conductive strips disposed in the second section and oriented at a second angle relative to the strip of magnetoresistive material.

[0005] According to some embodiments, an anisotropic magnetoresistive (AMR) sensor with improved linearity is provided, comprising a continuous strip of magnetoresistive material having a first barberpole portion and a second barberpole portion, the first barberpole portion having a first width and a first conductive strip angle, and the second barberpole portion having a second width different from the first width and a second conductive strip angle different from the first conductive strip angle.

[0006] According to some embodiments, an anisotropic magnetoresistive (AMR) sensor with improved linearity is provided, comprising: an input signal terminal; an output signal terminal; and means coupled between the input signal terminal and the output signal terminal for providing a linear change in resistance as a function of an applied external magnetic field by superimposing a positive change in resistance as a function of the applied external magnetic field and a negative change in resistance as a function of the applied external magnetic field.

[0007] Various aspects and embodiments of the present application will be described with reference to the following drawings. It should be understood that the drawings are not necessarily drawn to scale. Items that appear in more than one drawing are designated by the same reference numeral in all the drawings in which they appear. [Brief explanation of the drawings]

[0008] [Figure 1] 1 illustrates an anisotropic magnetoresistive (AMR) sensor having multiple sections of different constant widths according to a non-limiting embodiment of the present application. [Figure 2] 2 illustrates the resistive strip of FIG. [Figure 3A] 1 is a graph illustrating the response of two separate constant-width portions of an AMR sensor of the type described herein. [Figure 3B] 4B is a graph illustrating the overall response of the AMR sensor illustrated in FIG. 4A. [Figure 4] 1 illustrates an AMR sensor having multiple sections of different constant widths, according to a non-limiting embodiment of the present application. [Figure 5] 1 illustrates a magnetic field sensor according to a non-limiting embodiment of the present application. DETAILED DESCRIPTION OF THE INVENTION

[0009] According to one aspect of the present application, an anisotropic magnetoresistive (AMR) sensor is provided that exhibits a high degree of linearity. Linearity refers to the change in resistance as a function of magnetization. The AMR sensor may include a resistive strip with different constant-width sections. The conductive strips on the resistive strip may be positioned at different angles to each other depending on which constant-width section they overlap. In some embodiments, the conductive strips on the wider sections of the resistive strip may be at an opposite angle to the conductive strips on the narrower sections of the resistive strip.

[0010] 1 illustrates an anisotropic magnetoresistive (AMR) sensor according to a non-limiting embodiment of the present application having multiple segments or sections of different constant widths. The AMR sensor 100 comprises a resistive strip 102 and multiple conductive strips 104. The AMR sensor 100 exhibits a first section 106a, a second section 106b, and a third section 106c.

[0011] 2, resistive strip 102 is a continuous strip having different widths, shown herein as W1, W2, and W3. Specifically, section 106a has width W1, section 106b has width W2, and section 106c has width W3. The widths are oriented along the y-axis in this example. Returning to FIG. 1, the resistive section of section 106a has a length L1, which is the portion of resistive strip 102 between conductive strips 104 of section 106a. a , L1 b , L1 c , and L1 dThe resistive section of section 106b has a combined length L1, which represents the sum of the length L2, which is the portion of the resistive strip 102 between the conductive strips 104 of section 106b. a …L2 n The resistive section of section 106c has a combined length L2 representing the sum of the length L3, which is the portion of the resistive strip 102 between the conductive strips 104 of section 106c. a , L3 b , L3 c , and L3 d and has a combined length L3, which represents the sum of

[0012] Widths W1, W2, and W3 are constant widths across their respective lengths. That is, W1 is constant across length L1, W2 is constant across length L2, and W3 is constant across length L3. Widths W1 and W3 are wider than W2. In some embodiments, W1 and W3 are equal. W1 and W3 may be wider than W2 by a factor between 1.1 and 2.5. That is, the ratio of width W1 (and similarly W3) to width W2 may be between 1.1 and 2.5, including any value within that range. In other words, W1 (and similarly W3) may be 10% to 150% wider than W1. In some embodiments, both W1 and W2 may be in the range of 1 μm to 20 μm. Making W1 and W3 wider than W2 can facilitate magnetization of the AMR sensor 100. Typically, a magnetizing field is applied to one or more ends of the AMR sensor. The wider the section, the easier it is to magnetize. Magnetization can travel along the length of the sensor, so making them wider than the ends can aid the magnetization process by making them more easily magnetized.

[0013] The fact that widths W1, W2, and W3 are constant means that the current through the resistive strip portions of sections 106a, 106b, and 106c is in the same direction. In the example of FIG. 2, the current through those sections would flow in the x-direction. Passing current through sections 106a, 106b, and 106c in the same direction may help achieve the improved linear magnetic field response provided by AMR sensor 100.

[0014] Lengths L1, L2, and L3 may have any suitable values to provide the desired magnetization, as described further below. In some embodiments, L1 and L3 may be equal, although not all embodiments are limited in this respect. In some embodiments, the total length of L1 + L3 may be less than L2. For example, the ratio of L2 / (L1 + L3) may be between 1.2 and 40, including any value within that range. The total length of a resistive strip, such as resistive strip 102, may be within a length range of 50 μm to 1000 μm in some non-limiting embodiments.

[0015] 2 also illustrates how resistive strip 102 has tapered ends 120. Indeed, in the illustrated example, resistive strip 102 has a tapered end adjacent section 106a and a tapered end adjacent section 106c. The tapered ends may promote magnetization stability of the resistive strip.

[0016] Returning to FIG. 1 , it can be seen that the conductive strips 104 are oriented at different angles depending on which section they are part of. That is, the conductive strips in section 106a are oriented at one angle, and the conductive strips in section 106b are oriented at another angle. In an illustrative, non-limiting example, the conductive strips in section 106a are oriented at an opposite angle relative to a line in the plane of, and perpendicular to, the resistive strip 102 than those in section 106b. Thus, for illustrative purposes, the conductive strips in section 106b may be said to be oriented at an angle θ, while the conductive strips in section 106a may be said to be oriented at −θ. The value of θ may be any suitable value that provides the desired level of linearization of the magnetic response of the AMR sensor. As a non-limiting example, θ may take any value within the range of 30 degrees to 60 degrees.

[0017] 1 that AMR sensor 100 comprises multiple barberpole sections. Section 106a may represent a first barberpole section, section 106b may represent a second barberpole section, and section 106c may represent a third barberpole section. The barberpole sections may represent portions of a continuous AMR sensor that differ in some way from adjacent sections in their width and / or conductive strip configuration.

[0018] The AMR sensor 100 may exhibit improved linearity compared to conventional AMR sensors. The magnetic response of a barber-pole AMR sensor depends on both the width of the sensor and the angle of the conductive strips. For AMR sensors with a fixed width and a single conductive strip angle, the response is typically nonlinear. Reversing the angle of the conductive strips from a positive angle to a negative angle (or vice versa) changes the slope of the response curve from positive to negative (or vice versa). The inventors have recognized that having a multi-section AMR sensor, where one section has a positive slope response and another section has a negative slope response, can facilitate achieving a more linear response curve. Figures 3A and 3B illustrate a non-limiting example.

[0019] FIG. 3A is a graph illustrating simulated response curves for two sections of an AMR sensor. The x-axis represents the magnetic field in amperes per meter (A / m), and the y-axis represents the sensor's output voltage (V output ) and the supply voltage (V supply ) Curve 302 represents the response curve of a narrower, constant-width section of the AMR sensor having a positive relative angle of the conductive strips. Curve 304 represents the response curve of a wider, constant-width section of the AMR sensor having a negative relative angle of the conductive strips. For example, curve 302 may represent the response of section 106b of AMR sensor 100, while curve 304 may represent the response of section 106a of AMR sensor 100. As can be seen in FIG. 3A , curve 302 may exhibit a negative slope, while curve 304 may exhibit a positive slope. However, the magnitude of the slopes is different, with curve 304 exhibiting a slope of a smaller absolute value.

[0020] 3B illustrates the result of superimposing curves 302 and 304 of FIG. 3A. As in FIG. 3A, the x-axis represents magnetic field in A / m, and the y-axis represents V. output / V supply As shown, curve 306, which represents the combination of curves 302 and 304, exhibits an excellent linear response. The positive going curve 304 serves to remove some of the nonlinear behavior of the AMR sensor, contributing to an overall linear response.

[0021] 3A and 3B that a multi-section AMR sensor of the type described herein can exhibit an excellent linear response in the presence of a magnetic field, for example, as illustrated in Figure 1. The relative widths of the constant-width sections can be selected to provide a desired degree of linear response.

[0022] Moreover, it should be appreciated that, in accordance with one aspect of the present application, the inventors have recognized that it may be desirable to use an AMR sensor to create two distinct magnetic response regions and overlap the magnetic responses of those regions to provide a more linear overall response. To do this, it is desirable for the magnetic response of a first region of the AMR sensor to exhibit its peak resistance change (ΔR / R) over a smaller range of external magnetic fields than a second region of the AMR sensor, as shown in FIG. 3A.

[0023] Returning to Figure 1, the conductive strip 104 completely covers the transition regions 108a and 108b, where sections 106a and 106b transition to 106c, respectively. The transition regions represent the transition between the wider and narrower constant-width sections. Complete coverage of these transition regions with the conductive strip ensures proper behavior of the AMR sensor.

[0024] The resistive strip 102 and the conductive strip 104 may be made of any suitable material. The resistive strip 102 may be a magnetoresistive material formed from permalloy, for example, NiFe. Other alloys may alternatively be used, such as alloys containing Ni, Fe, or Co (e.g., CoFe alloys). The conductive strip 104 may be formed from a metal alloy, such as Al, Au, Cu, or AlCu.

[0025] While FIG. 1 illustrates an AMR sensor having two ends that are wider than the center section, alternatives are possible. For example, according to one alternative, the AMR sensor has a single end that is wider than the remainder of the AMR sensor. For example, referring to FIG. 1, an alternative embodiment may omit section 106c entirely. FIG. 4 illustrates this example. AMR sensor 400 is the same as AMR sensor 100 of FIG. 1, except that section 106c is omitted.

[0026] One aspect of the present application provides a means for sensing a magnetic field. One aspect of the present application provides a means for providing a linear response to magnetic field variations. The linear response can be a linear change in resistance or a linear change in voltage. The linear response can be exhibited over the operating range of the means. Some embodiments include a means for providing a combined magnetic field response that is a superposition of a positive gradient magnetic response and a negative gradient magnetic response. In some embodiments, a magnetic field sensor is provided that includes electrical contacts and a means for providing a linear response to the magnetic field. The linear response can be a linear change in resistance or a linear change in voltage. The electrical contacts can be positioned to allow electrical connection to an end of the magnetic field sensor.

[0027] One aspect of the present application provides a means for providing a linear change in resistance as a function of an applied external magnetic field by superimposing a positive change in resistance as a function of the applied external magnetic field and a negative change in resistance as a function of the applied external magnetic field. The AMR sensor may include an input signal terminal, an output signal terminal, and means coupled between the input signal terminal and the output signal terminal. The means may comprise means for providing a linear change in resistance as a function of the applied external magnetic field by superimposing a positive change in resistance as a function of the applied external magnetic field and a negative change in resistance as a function of the applied external magnetic field, wherein a slope of the positive change in resistance as a function of the applied external magnetic field has a different absolute value than a slope of the negative change in resistance as a function of the applied external magnetic field.

[0028] 5 illustrates a magnetic field sensor according to a non-limiting embodiment of the present application. The magnetic field sensor 500 comprises a coil 502 and a group of eight AMR sensors 504a, 504b, 506a, 506b, 508a, 508b, 510a, and 510b of the type previously described herein. A supply voltage Vdd is applied to the group of AMR sensors at the input signal terminals, and a differential output signal is taken from the output signal terminals as differential output signals Vout+ and Vout−. One end of the group of AMR sensors is grounded (GND) as shown. Vdd and GND in combination may represent the input signal terminals.

[0029] The coil 502 may be used to magnetize the AMR sensor. The coil 502 overlies the AMR sensor in this non-limiting example and may have any suitable configuration. The illustrated shape is a non-limiting example. The coil 502 may be formed from any suitable conductive material. For example, metal wiring on a printed circuit board (PCB) may be used, although alternatives are possible. In some embodiments, the coil 502 may be micro-fabricated.

[0030] The magnetization field generated by coil 502 can point in either the positive y-direction or the negative y-direction, depending on where a particular AMR sensor is positioned relative to the coil. Again assuming coil 502 overlaps the AMR sensors, when current flows clockwise through coil 502, the magnetic field experienced by AMR sensors 504a, 506a, 508a, and 510a can point in the positive y-direction, while the magnetic field experienced by AMR sensors 504b, 506b, 508b, and 510b can point in the negative y-direction. This can be said to represent a situation where the magnetization field points outward toward the ends or edges of the group of AMR sensors. When current flows counterclockwise through coil 502, the magnetic field experienced by AMR sensors 504a, 506a, 508a, and 510a can point in the negative y-direction, while the magnetic field experienced by AMR sensors 504b, 506b, 508b, and 510b can point in the positive y-direction. This can be said to represent a situation where the magnetization field points inward toward the center of the group of AMR sensors. As previously explained, wider sections of an AMR sensor can be magnetized more easily than narrower sections. Thus, in magnetic field sensor 500, individual AMR sensors 504a, 504b, 506a, 506b, 508a, 508b, 510a, and 510b can be magnetized from the wider areas of the AMR sensors toward the center of the AMR sensors. The group of AMR sensors can be magnetized at various points during operation using coil 502.

[0031] AMR sensors 504a, 504b, 506a, 506b, 508a, 508b, 510a, and 510b may be of a type previously described herein. For example, each may be an example of AMR sensor 100. As shown, pairs of AMR sensors may exhibit opposing barberpole configurations based on the angles of the conductive strips. For example, it can be seen that the angle of conductive strips 512a of AMR sensor 504a is opposite the angle of conductive strips 512b of AMR sensor 504b in the x-direction. More specifically, the angle of conductive strips 512a at the ends of AMR sensor 504a is opposite the angle of conductive strips 512b at the ends of AMR sensor 504b, and the angle of conductive strips 512a along a central segment of AMR sensor 504a is opposite the angle of conductive strips 512b along a central segment of AMR sensor 504b in the x-direction. Similarly, AMR sensors 506a and 506b exhibit a barberpole configuration facing each other, AMR sensors 508a and 508b exhibit a barberpole configuration facing each other, and AMR sensors 510a and 510b exhibit a barberpole configuration facing each other.

[0032] During operation, magnetic field sensor 500 can be magnetized using coil 502. A supply voltage Vdd can then be applied as shown, and the differential output signals Vout+, Vout− can be monitored. The supply voltage Vdd can have any suitable value. When magnetic field sensor 500 is exposed to an externally applied magnetic field, the group of AMR sensors of magnetic field sensor 500 can experience a change in resistance. The change in resistance can generate a change in the differential output signals Vout+, Vout−. The strength of the externally applied magnetic field can be determined from the change in the differential output signals Vout+, Vout−. As a non-limiting example, magnetizing the AMR sensors by passing a current through coil 502 in a clockwise direction and then exposing magnetic field sensor 500 to an external field in the x-direction increases the resistance of AMR sensors 504a, 504b, 508a, and 508b, and decreases the resistance of AMR sensors 506a, 506b, 510a, and 510b. The resistances of AMR sensors 504a, 504b, 508a, and 508b increase due to the angle between the current flow in those resistors and the external magnetic field in the x-direction in this example, while the resistances of AMR sensors 506a, 506b, 510a, and 510b decrease because the current flow direction differs due to the opposite angles of the conductive strips of those AMR sensors.

[0033] As previously discussed, aspects of the present application provide a means for providing a linear change in resistance as a function of an applied external magnetic field by superimposing a positive change in resistance as a function of the applied external magnetic field with a negative change in resistance as a function of the applied external magnetic field. In some embodiments according to such aspects, it can be seen from FIG. 5 that an AMR sensor including the above means comprises a plurality of barber-pole AMR sensors. In some embodiments, the means comprises a plurality of pairs of barber-pole AMR sensors having opposing barber-pole configurations.

[0034] Magnetic field sensors according to aspects of the present application, such as magnetic field sensor 500, may be used in a variety of settings to sense external magnetic fields. For example, magnetic field sensors may be used in industrial equipment to sense magnetic fields experienced by the equipment. Magnetic field sensors may be used in medical equipment or structural monitoring (such as building monitoring or sensors on buildings). Magnetic field sensors may be used as compasses. Magnetic field sensors may be used as current sensors. Other applications are possible.

[0035] One aspect of the present application provides a magnetic field sensor including two or more pairs of AMR sensors, where the AMR sensors in a pair are arranged in a barberpole configuration facing each other, as can be seen from FIG. 5. Each of the AMR sensors can have a wider constant-width section and a narrower constant-width section. In some embodiments, the ends of each AMR sensor have a wider constant width than the center section of the AMR sensor.

[0036] Magnetic field sensors with different configurations than that of FIG. 5 are also possible. For example, a magnetic field sensor may differ from magnetic field sensor 500 by omitting AMR sensors 504b, 506b, 508b, and 510b. A magnetic field sensor may differ from magnetic field sensor 500 in including only AMR sensors 504a, 504b, 506a, and 506b. Such a configuration may be considered a half-bridge magnetic field sensor. Moreover, such a half-bridge magnetic field sensor may be magnetized in only a single direction by a magnetizing coil. Furthermore, it should be understood that one or more AMR sensors of FIG. 5 may actually be implemented as multiple barber-pole AMR sensors connected in series.

[0037] Aspects of the present application may provide various advantages, some of which are described. It should be understood that not every embodiment necessarily provides all advantages, and advantages other than those listed may be provided. According to one aspect of the present application, an AMR sensor is provided that exhibits improved linearity. The AMR sensor may exhibit substantial linearity in its magnetic field response over an operating range of magnetic fields. In some embodiments, the operating range may include a range of magnetic fields up to 10,000 A / m, up to 5,000 A / m, or up to 2,000 A / m, although other ranges are possible. According to aspects of the present application, an AMR sensor is provided that exhibits improved ease of magnetization. The AMR sensor may have opposing ends of a constant width that is wider than a center section of the AMR sensor.

[0038] The terms "approximately," "substantially," and "about" may be used in some embodiments to mean within ±20% of a target value, in some embodiments within ±10% of a target value, in some embodiments within ±5% of a target value, and even in some embodiments within ±2% of a target value. The terms "approximately" and "about" may include the target value. [Explanation of symbols]

[0039] 100 Anisotropic Magnetoresistive (AMR) Sensor 102 Resistive Strip 104 Conductive Strip 106a First Section 106b Second Section 106c Third Section 108a,108b transition region 120 Tapered End 400 AMR sensor 500 Magnetic Field Sensor 502 Coil 504a, 504b, 506a, 506b, 508a, 508b, 510a, 510b AMR sensors 512a, 512b Conductive strips L1, L2, L3 length W1, W2, W3 width

Claims

1. 1. An anisotropic magnetoresistive (AMR) sensor with improved linearity, comprising: a continuous strip of magnetoresistive material having a first section having a first constant width and a second section having a second constant width greater than the first constant width; a first plurality of conductive strips disposed in the first section and oriented at a first angle relative to the strip of magnetoresistive material; a second plurality of conductive strips disposed in the second section and oriented at a second angle relative to the strips of magnetoresistive material; An AMR sensor wherein a linear change in resistance as a function of the applied external magnetic field is provided by superimposing a positive change in resistance of the first section as a function of the applied external magnetic field and a negative change in resistance of the second section as a function of the applied external magnetic field.

2. 2. The AMR sensor of claim 1, wherein the first angle is opposite the second angle relative to a line in the plane of the strip of magnetoresistive material and perpendicular to the strip of magnetoresistive material.

3. 10. The AMR sensor of claim 1, wherein the strip of magnetoresistive material further comprises a third section having a third constant width greater than the first constant width, and a third plurality of conductive strips oriented at a third angle relative to the strip of magnetoresistive material.

4. 4. The AMR sensor of claim 3, wherein the second constant width and the third constant width are substantially the same, and the second angle and the third angle are substantially the same.

5. The AMR sensor of claim 3 , wherein the first section is between the second section and the third section.

6. 4. The AMR sensor of claim 3, wherein the combined length of the resistive portions of the first section is 1.2 to 40 times longer than the combined length of the resistive portions of the second section and the third section.

7. 2. The AMR sensor of claim 1, wherein the strip of magnetoresistive material further comprises a third section connecting the first section and the second section, the width of the third section transitioning from the first constant width on a side connecting with the first section to the second constant width on a side connecting with the second section, and the AMR sensor further comprises a conductive material covering the third section.

8. The AMR sensor of claim 1 further comprising a tapered end adjacent the second section.

9. 1. An anisotropic magnetoresistive (AMR) sensor with improved linearity, comprising: a continuous strip of magnetoresistive material having a first barberpole portion and a second barberpole portion, the first barberpole portion having a first constant width and a first conductive strip angle, and the second barberpole portion having a second constant width different from the first constant width and a second conductive strip angle different from the first constant width; An AMR sensor wherein a linear change in resistance as a function of the applied external magnetic field is provided by superimposing a positive change in resistance of the first barberpole portion as a function of the applied external magnetic field and a negative change in resistance of the second barberpole portion as a function of the applied external magnetic field.

10. 10. The AMR sensor of claim 9, wherein the angle of the first conductive strip angle is opposite to the angle of the second conductive strip angle relative to a line in-plane with the strip of magnetoresistive material and perpendicular to the strip of magnetoresistive material.

11. 10. The AMR sensor of claim 9, wherein the AMR sensor further comprises a third barberpole portion having a third constant width that is wider than the first constant width and a third conductive strip angle that is different from the first conductive strip angle.

12. 12. The AMR sensor of claim 11, wherein the second constant width and the third constant width are substantially the same, and the second conductive strip angle and the third conductive strip angle are substantially the same.

13. 12. The AMR sensor of claim 11, wherein the first barberpole portion is between the second barberpole portion and the third barberpole portion.

14. 12. The AMR sensor of claim 11, wherein the combined length of the resistive portions of the first barberpole portion is 1.2 to 40 times longer than the combined length of the resistive portions of the second barberpole portion and the third barberpole portion.

15. 10. The AMR sensor of claim 9, wherein the strip of magnetoresistive material further comprises a section connecting the first barberpole portion and the second barberpole portion, the width of the section transitioning from the first constant width on a side connecting with the first barberpole portion to the second constant width on a side connecting with the second barberpole portion, and the AMR sensor further comprises a conductive material covering the section.

16. The AMR sensor of claim 9 further comprising a tapered end adjacent the second barberpole portion.

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