Magnetic sensor

Abstract

This reduces the effects of non-uniformity in the direction of magnetic field application within the sensor chip. [Solution] The magnetic sensor is composed of multiple magnetoresistive elements R1, R2 and multiple fixed resistors R11, R12. The magnetoresistive elements R1 and R2 are arranged in orientations that are 90° apart from each other.

Description

[Technical Field]

[0001] This invention relates to a magnetic sensor. [Background technology]

[0002] An AMR (Anisotropic-Magneto-Resistive) sensor consists of a substrate made of Si or glass and a thin film of an alloy mainly composed of ferromagnetic metals such as Ni and Fe formed on the substrate. By patterning the thin film, the magnetic domain walls (boundaries between magnetic domains) are aligned in the longitudinal direction, exhibiting shape anisotropy. A magnetoresistive angle sensor that utilizes this shape anisotropy changes its resistance value when the direction of application of an external magnetic field is changed. Therefore, as shown in Figure 7, a bridge circuit is used in which four magnetoresistive elements (AMR elements) R1 to R4 are wired with their orientations shifted by 90° each, allowing a sine output to be obtained and used for angle detection. To expand the detection angle range, a double bridge circuit is often used in sensors, in which each resistance pattern is shifted by 45° and these bridge circuits are combined.

[0003] Figure 8 shows the output in the case of a double bridge circuit. V1 in Figure 8 is the potential difference V at the output of the first bridge circuit. + -V - This shows that V2 is the potential difference V of the second bridge circuit, which is formed by placing resistor patterns outside the first bridge circuit, shifted by 45°. + -V - This shows that α in Figure 8 indicates the direction of application of the external magnetic field calculated from the AMR sensor obtained by {Arctan2(v2, v1)} / 2, using the values ​​v1 and v2 obtained by normalizing V1 and V2, respectively. v1 and v2 are calculated from v1=(V1-(V1max+V1min) / 2) / ((V1max-V1min) / 2) and v2=(V2-(V2max+V2min) / 2) / ((V2max-V2min) / 2). V1max and V1min are the maximum and minimum values ​​of V1, and V2max and V2min are the maximum and minimum values ​​of V2.

[0004] A magnetoresistive material utilizing shape anisotropy exhibits a resistance fluctuation in the direction of the applied magnetic field, resulting in a resistance fluctuation response with a 180° period relative to the direction of the applied magnetic field. However, in reality, the magnetization direction of the resistance pattern due to shape magnetic anisotropy does not perfectly follow the direction of the external magnetic field, resulting in a deviation. Therefore, even when the saturation magnetic field strength is applied, the output of the AMR sensor differs slightly from an ideal sine wave. The deviation between the magnetization direction of the resistance pattern and the direction of the external magnetic field is reflected in the resistance pattern as a sinusoidal output containing harmonic components, as shown in Figure 9. In Figure 9, 100 is the fundamental wave component, 101 is the second harmonic component, and 102 is the third harmonic component.

[0005] The angular accuracy of angle sensors using magnetoresistive elements deteriorates due to the influence of harmonic components contained in each magnetoresistive element. However, as shown in Figure 7, a bridge circuit is created by wiring four identical magnetoresistive elements rotated 90° apart, which cancels out even-numbered harmonic components. The mechanism is explained below.

[0006] The resistance values ​​of the four resistors R1 to R4 in the bridge circuit shown in Figure 7 can be expressed using the external magnetic field θ as shown in equations (1) and (2), taking into account constant terms and harmonic components.

[0007]

number

[0008] r n This is a constant that represents the amplitude of the harmonic component obtained by multiplying the frequency of the fundamental wave by n. The output signal V obtained from the sensor can be expressed as shown in equation (3).

[0009]

number

[0010] At this point, the numerator term of equation (3) becomes as shown in equation (4).

[0011]

number

[0012] Also, since the component amount becomes smaller for higher-order harmonics and r0≫r1>r2>r3····, the term in the numerator of Equation (3) can be converted as in Equation (5).

[0013]

Number

[0014] Therefore, Equation (3) can finally be expressed as Equation (6).

[0015]

Number

[0016] As is clear from Equation (6), even-order harmonic components (n = 2, 4, 6, ···) do not affect the sensor output V. From the above, in the case of a bridge circuit, only odd-order harmonic components are a problem. Also, since the component amount becomes smaller for higher-order harmonics, it is particularly important to suppress the third-order harmonic component.

[0017] The inventor proposed a method of suppressing this third-order harmonic component by curving the magnetoresistive element and continuously changing the longitudinal direction of the shape magnetic anisotropy as shown in FIG. 10 (Patent Document 1, Patent Document 2). The AMR angle sensor 10 in FIG. 10 is configured to detect the relative rotation angle of the magnet M disposed opposite to the sensor 10 with respect to the sensor 10. The magnet M and the AMR angle sensor 10 are two members that rotate relative to each other. For example, one member is a base, and the other member is attached to the base and the object to be detected for the relative rotation angle, respectively. By detecting the rotation angle of the magnet M, the rotation angle of the detection object is detected.

[0018] The AMR angle sensor 10 includes a substrate 20, anisotropic magnetoresistive elements (AMR elements) 31 to 34, 41 to 44, and connection terminals 51 to 58, 61 to 64. The substrate 20 is made of, for example, a silicon substrate or a glass substrate. The magnetoresistive elements 31 to 34, 41 to 44 and the terminals 51 to 58, 61 to 64 are integrally formed in a film shape from the same material. Examples of the material include an alloy mainly composed of a ferromagnetic metal. Each of the magnetoresistive elements 31 to 34, 41 to 44 has the same shape but different orientations. The shape will be described with reference to FIG. 11 using the magnetoresistive element 31 as an example. The magnetoresistive element 31 is formed in a meander shape. The meander-shaped magnetoresistive element 31 includes a plurality of linear portions 31A parallel to each other and a plurality of folding portions 31B connecting the plurality of linear portions 31A in series. Each folding portion 31B connects one end (for example, the lower end in FIG. 11) or the other end (for example, the upper end in FIG. 11) of two adjacent linear portions among the plurality of linear portions. Each linear portion 31A is formed in an arc pattern with a central angle φ. Hereinafter, each linear portion of the magnetoresistive elements 31 to 34, 41 to 44 may be referred to as linear portions 31A to 34A, 41A to 44A, respectively, and each folding portion may be referred to as folding portions 31B to 34B, 41B to 44B, respectively.

[0019] The substrate 20 on which the magnetoresistive element 31 and the like are formed includes a substrate body and an insulating film formed on the substrate body. The magnetoresistive element 31 and the like are formed on the surface of the insulating film. As shown in FIG.  10, the orientation of the magnetoresistive element 32 is the orientation obtained by rotating the magnetoresistive element 31 by 90°, the orientation of the magnetoresistive element 33 is the orientation obtained by rotating the magnetoresistive element 31 by 180°, and the orientation of the magnetoresistive element 34 is the orientation obtained by rotating the magnetoresistive element 31 by 270°. Similarly, the magnetoresistive elements 42 to 44 are also formed in orientations obtained by sequentially rotating the magnetoresistive element 41 by 90°. The magnetoresistive elements 41 to 44 are arranged on a first circumference centered on the rotation center C, and the magnetoresistive elements 31 to 34 are arranged on a second circumference outside the first circumference centered on the rotation center C. The overall orientation of the magnetoresistive elements 41 to 44 is the orientation obtained by rotating the overall orientation of the magnetoresistive elements 31 to 34 by 45° around the rotation center C.

[0020] Each end of magnetoresistors 41-44 is connected to one of terminals 61-64, and magnetoresistors 41-44 are fully bridged via terminals 61-64. Terminal 61 is connected to the power line +V, and terminal 63 is connected to ground. Terminal 62 is connected to output terminal OUT3, and terminal 64 is connected to output terminal OUT4. An electrical signal representing the difference between the potentials of output terminal OUT3 (VOUT3) and OUT4 (VOUT4) (VOUT3-VOUT4) is output as the first bridge output.

[0021] Each end of magnetoresistors 31-34 is connected to terminals 51-58, respectively. Magnetoresistors 31-34 are fully bridged via terminals 51-58. Terminals 51 and 58 are connected to the power line Vcc, and terminals 54 and 55 are connected to ground. Terminals 52 and 53 are connected to output terminal OUT1, and terminals 56 and 57 are connected to output terminal OUT2. An electrical signal representing the difference between the potential of output terminal OUT1 (VOUT1) and the potential of OUT2 (VOUT2) (VOUT1-VOUT2) is output as the second bridge output.

[0022] Figure 12 shows the circuit diagram of the configuration shown in Figure 10. The potential difference, or voltage value, indicated by the first and second bridge outputs changes according to the relative rotation angle of the magnet M with respect to the AMR angle sensor 10. For example, if the magnet M is rotated counterclockwise from the state shown in Figure 10, the second bridge output becomes a sinusoidal electrical signal, and the first bridge output becomes a cosine electrical signal. The angular period T of these sine and cosine waves (the period of the sine and cosine waves expressed as an angle when the horizontal axis is taken as the angle) is 180°. Based on the voltage values ​​Vcos and Vsin indicated by the first and second bridge outputs, respectively, the relative rotation angle α of the magnet M with respect to the AMR angle sensor 10, i.e., the relative rotation angle α of the object to be detected, is calculated using equation (7) below, which uses arctan².

[0023]

number

[0024] To reduce harmonic components, the inventors discovered that the central angle φ of the arc pattern of each linear section, such as the linear section 31A, should be set to an angle calculated by 180° / n. n is an odd number greater than or equal to 3, and is the order of the harmonic to be reduced, i.e., a multiple of the fundamental frequency. For example, if the third harmonic is to be reduced, n=3 and a central angle φ of 60° is adopted. The theory of harmonic component reduction is explained below. Here, we consider the second bridge output, but the same applies to the first bridge output and the relative rotation angle α calculated (detected) by the AMR angle sensor 10.

[0025] The second bridge output (voltage value) V when the linear sections 31A to 34A are straight is as shown in equation (5). Next, consider the case when the linear sections 31A to 34A are curved in an arc. Let the central angle of the arc be φ. In this case, the resistance values ​​R31 to R34 of the magnetic resistors 31 to 34 are expressed by the following equations (8) and (9).

[0026]

number

[0027] Based on equations (8) and (9), the second bridge output V is expressed by the following equation (10).

[0028]

number

[0029] The terms r1, r3, r5, ... in equation (10) correspond to the fundamental wave, the third harmonic, the fifth harmonic, ..., respectively. Generalizing the coefficients of each term gives [sin(2nθ+2nφ)-sin(2nθ)] (where n is an odd number), which is a composite function of sine waves of the same frequency and amplitude. Therefore, the coefficients of each term r1, r3, r5, ... can be expressed as a single sine wave. To reduce measurement errors, the harmonic components of the second bridge output V must be reduced. By setting φ=180° / n from equation (10), 2nφ can be set to 360° in the above coefficient [sin(2nθ+2nφ)-sin(2nθ)]. As a result, the above coefficient can be set to sin(2nθ)-sin(2nθ)=0. For example, if the third harmonic component is reduced, setting n=3 (i.e., setting the central angle φ of the linear section 31A etc. to 60°) allows the above coefficient to be set to 0, thereby eliminating the r3 term corresponding to the third harmonic in equation (9). As a result, the third harmonic component is reduced. In this way, by selecting the nth harmonic component to be reduced (for example, a harmonic component that is a large component), determining the central angle φ from φ=180° / n, and forming a magnetoresistive element in a linear section having an arc pattern with the determined central angle φ, the targeted nth harmonic component is reduced.

[0030] The mechanism for reducing the nth harmonic component will be explained using the magnetoresistive element 31 and the reduction of the third harmonic component as examples, with reference to Figure 13. The third harmonic is a sinusoidal signal with an angular period of 60°. When the linear portion 31A of the magnetoresistive element 31 is divided into six regions A to F with a central angle of 10°, the resistance changes that occur in regions A and D, B and E, and C and F, which have an angular difference of 30° (half a period), when the magnet M is rotated once, are out of phase with the same amplitude and frequency (the graph of resistance changes for regions A and D is shown on the right side of Figure 13). Therefore, if the central angle φ = 60°, the third harmonic cancels out in all regions, and the third harmonic component is reduced. The same can be considered for the fifth harmonic, the seventh harmonic, etc. (of course, the central angle φ will be 36°, 25.7°, etc.).

[0031] A second method for reducing errors is to lower the anisotropic magnetic field strength Hk of the AMR angle sensor 10. The anisotropic magnetic field strength Hk is the magnetic field strength at which magnetization in the hard axis direction reaches saturation. A smaller anisotropic magnetic field strength Hk means that the unsaturated region with respect to the external magnetic field becomes narrower, and the magnetic moments of the magnetoresistors 31-34 and 41-44 can more easily follow the magnetization direction of the magnet M. Therefore, by reducing the anisotropic magnetic field strength Hk, waveform distortion of the first and second bridge outputs can be suppressed.

[0032] The anisotropic magnetic field strength Hk is expressed by the following equation (11), where t is the film thickness of the magnetoresistive elements 31-34 and 41-44, w is the line width (see Figure 11; in particular, the line width of each linear part such as linear part 31A), Ms is the saturation magnetization (A / m), and Hk0 is the material anisotropy. Hk = (t / w)·Ms + Hk0 ···(11)

[0033] From equation (11), in order to reduce the anisotropic magnetic field strength Hk, it is necessary to reduce the film thickness t of the magnetoresistive element 31 and widen the line width w. However, as the film thickness t decreases, defects are more likely to occur in the magnetoresistive element 31, and variations in resistance values ​​between magnetoresistive elements become more likely. Also, increasing the line width w increases the sensor size. The AMR angle sensor 10 may have a structure in which the anisotropic magnetic field strength Hk is calculated by an equation other than equation (11). However, the anisotropic magnetic field strength Hk is proportional to the film thickness of the magnetoresistive element and inversely proportional to the line width of the magnetoresistive element. The inventors have found that in order to obtain an overall angle detection error of 0.1° or less, which is said to be good angle detection accuracy, it is good to set Hk to 30Oe or less.

[0034] In the design method for the AMR angle sensor 10, first, the material of the substrate 20 is determined, as well as the materials of the magnetoresistive elements 31-34, 41-44, and terminals 51-58, 61-64. By determining the materials of the magnetoresistive elements 31, etc., and terminals 51, etc., the saturation magnetization Ms and material anisotropy Hk0 in equation (11) are determined. Therefore, the anisotropic magnetic field strength Hk can be adjusted by the film thickness t and line width w.

[0035] Next, the nth harmonic to be removed, i.e., the order n of the harmonic to be removed (where n is an odd number greater than or equal to 3), is determined from the output signal of the AMR angle sensor 10 (a signal indicating the relative rotation angle α). For example, if the influence of the third harmonic is large, n=3 is set. Then, the central angle φ of the shape of the linear sections 31A~34A and 41A~44A (i.e., the arc pattern of 1) is determined by T / n (where T=180°). When n=3, the central angle φ is 60°.

[0036] Next, the other patterns of the magnetoresistive elements 31-34 and 41-44 (number of linear sections 31A-34A and 41A-44A, and pattern shapes of folded sections 31B-34B and 41B-44B) and the patterns of the terminals 51-58 and 61-64 are determined. Then, the anisotropic magnetic field strength Hk is adjusted by adjusting the film thickness t and line width w of the magnetoresistive elements 31-34 and 41-44. Specifically, the film thickness t and line width w are determined within a range where the anisotropic magnetic field strength Hk has an upper limit of 30Oe. With the above steps, the AMR angle sensor 10 is designed.

[0037] As described above, the AMR angle sensor 10 requires four magnetoresistive elements, each oriented 90° differently, for each bridge circuit in order to filter harmonics. Therefore, it is necessary to form four (eight in the case of a double bridge) magnetoresistive elements on the sensor chip.

[0038] Ideally, the external magnetic field applied to the sensor should be uniform in its direction of application. However, in real-world environments, this is rarely the case, and as shown in Figure 14, the direction of magnetic field application becomes non-uniform within the chip. When the direction of the magnetic field applied to each magnetoresistive element differs, a problem arises in that the angular accuracy that the magnetic sensor can detect deteriorates. Furthermore, because magnetoresistive elements are components that rely on their precise structure, they also increase the probability of defects occurring. Therefore, if there are many magnetoresistive elements on a single chip, a problem arises in that the chip's defect rate increases relatively (or probabilistically).

[0039] The configurations disclosed in Patent Documents 1 and 2 can realize sensors with high angular accuracy by suppressing harmonics using four or eight magnetoresistive elements, but they cannot solve the above-mentioned problems because many magnetoresistive elements must be placed on a single chip. As described above, while the magnetoresistive element itself is an indispensable component, it is also a component that has a high probability of negatively impacting detection accuracy and failure rates, and therefore improvement is needed. [Prior art documents] [Patent Documents]

[0040] [Patent Document 1] Japanese Patent Publication No. 2024-136963 [Patent Document 2] International Publication No. WO2024 / 203588 [Overview of the Initiative] [Problems that the invention aims to solve]

[0041] The present invention was made to solve the above problems and aims to provide a magnetic sensor that can reduce the effects of non-uniformity in the direction of magnetic field application within the sensor chip. [Means for solving the problem]

[0042] The magnetic sensor of the present invention comprises a bridge circuit composed of a plurality of magnetoresistive elements and a plurality of fixed resistors, characterized in that the plurality of magnetoresistive elements are arranged in orientations that are 90° apart from each other. Furthermore, in one example configuration of the magnetic sensor of the present invention, the plurality of magnetoresistive elements are formed on the substrate of the sensor chip, and the plurality of fixed resistors are arranged outside the sensor chip. Furthermore, in one example configuration of the magnetic sensor of the present invention, the plurality of magnetoresistive elements are formed on a substrate of the sensor chip, and the plurality of fixed resistors are formed on the substrate in a different layer from the magnetoresistive elements. Furthermore, in one example of the configuration of the magnetic sensor of the present invention, the bridge circuit is formed by connecting in parallel a circuit in which two magnetoresistive elements are connected in series and a circuit in which two fixed resistors are connected in series.

[0043] Furthermore, in one example configuration of the magnetic sensor of the present invention, each of the plurality of magnetoresistive elements has a planar shape including one or more arc patterns, and the central angle φ of the arc pattern is within the range of (180° / n) × m - 3° ≤ φ ≤ (180° / n) × m + 3° (where m is a natural number and n is an odd number of 3 or more). Furthermore, in one example of the configuration of the magnetic sensor of the present invention, each of the plurality of magnetoresistive elements has a planar shape comprising a plurality of linear portions of the arc pattern parallel to each other, and a plurality of folded portions connecting two adjacent linear portions so that the plurality of linear portions are connected in series. [Effects of the Invention]

[0044] According to the present invention, by configuring a bridge circuit with multiple magnetoresistive elements and multiple fixed resistors, the number of magnetoresistive elements arranged on the sensor chip can be reduced compared to conventional methods, and the magnetoresistive elements can be concentrated in the center of the sensor chip. This reduces the effect of non-uniformity in the direction of magnetic field application within the sensor chip. As a result, the present invention can improve robustness against external magnetic fields. If the present invention is used in an angle sensor, high-precision angle detection can be achieved. [Brief explanation of the drawing]

[0045] [Figure 1] Figure 1 is a circuit diagram showing the configuration of a magnetic sensor according to the first embodiment of the present invention. [Figure 2] Figure 2 is a plan view of the sensor chip of a magnetic sensor according to the first embodiment of the present invention. [Figure 3] Figure 3 shows the magnetic distribution of the sensor chip of a magnetic sensor according to the first embodiment of the present invention. [Figure 4] Figure 4 is a circuit diagram showing the configuration of a magnetic sensor according to a second embodiment of the present invention. [Figure 5] Figure 5 is a cross-sectional view of the sensor chip of a magnetic sensor according to a second embodiment of the present invention. [Figure 6] Figure 6 is a cross-sectional view showing another configuration of the sensor chip of a magnetic sensor according to a second embodiment of the present invention. [Figure 7] Figure 7 is a plan view showing the configuration of a conventional AMR sensor. [Figure 8] Figure 8 shows an example of the output of a conventional AMR sensor. [Figure 9] Figure 9 shows the fundamental and harmonic components that appear in the output of a conventional AMR sensor. [Figure 10] Figure 10 is a plan view showing another configuration of a conventional AMR sensor. [Figure 11] Figure 11 is an enlarged plan view of the magnetoresistive element shown in Figure 10. [Figure 12] Figure 12 is the circuit diagram of the AMR sensor shown in Figure 10. [Figure 13] Figure 13 is a graph showing the change in resistance values ​​in the arc pattern of the linear portion and in regions A and B of the arc pattern, depending on the rotation angle of the magnet. [Figure 14] Figure 14 shows the magnetic distribution of the sensor chip. [Modes for carrying out the invention]

[0046] [First Embodiment] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Figure 1 is a circuit diagram showing the configuration of a magnetic sensor according to the first embodiment of the present invention. The magnetic sensor consists of a first bridge circuit 1 and a second bridge circuit 2. The first bridge circuit 1 is formed by connecting in parallel a series circuit in which a first magnetoresistive element (AMR element) R1 and a second magnetoresistive element (AMR element) R2 are connected in series, and a series circuit in which a first fixed resistor R11 and a second fixed resistor R12 are connected in series. The second bridge circuit 2 is formed by connecting in parallel a series circuit in which a third magnetoresistive element (AMR element) R1' and a fourth magnetoresistive element (AMR element) R2' are connected in series, and a series circuit in which a third fixed resistor R11' and a fourth fixed resistor R12' are connected in series.

[0047] The connection points between magnetoresistor R1 and magnetoresistor R2, and between magnetoresistor R1' and fixed resistor R11', are connected to ground (GND). The connection points between fixed resistor R11 and fixed resistor R12, and between magnetoresistor R2' and fixed resistor R12', are connected to the power supply voltage Vcc. The connection point between magnetoresistor R1 and fixed resistor R11 is connected to output terminal OUT3. The connection point between magnetoresistor R2 and fixed resistor R12 is connected to output terminal OUT4. The connection point between fixed resistor R11' and fixed resistor R12' is connected to output terminal OUT1. The connection point between magnetoresistor R1' and magnetoresistor R2' is connected to output terminal OUT2.

[0048] Figure 2 is a plan view of the sensor chip 10a of the magnetic sensor in this embodiment. The sensor chip 10a comprises a substrate 20, magnetoresistive elements R1, R1', R2, and R2' formed on the substrate 20, electrodes formed on the substrate 20 for connection to the outside, and wiring connecting the electrodes to the magnetoresistive elements R1, R1', R2, and R2'. In Figure 2, the electrodes and wiring are omitted from the diagram.

[0049] As in the conventional method, the substrate 20 is made of, for example, a silicon substrate or a glass substrate. The magnetoresistive elements R1, R1', R2, and R2' are formed in film form from the same material. An example of the material for the magnetoresistive elements R1, R1', R2, and R2' is an alloy mainly composed of a ferromagnetic metal, such as a NiFe alloy. An example of a NiFe alloy is a permalloy with Ni:83% and Fe:17%, which has both low hysteresis and low magnetostrictive properties. As an example, permalloy with other ratios may be used.

[0050] The orientation of magnetoresistor R2 is the same as that of magnetoresistor R1 rotated by 90°. The orientation of magnetoresistor R2' is the same as that of magnetoresistor R1' rotated by 90°. In other words, the two magnetoresistors in the same bridge circuit are arranged with orientations that are 90° different from each other. The magnetoresistors R1, R1', R2, and R2' are arranged, for example, on the same circumference with a rotation center C. The overall orientation of magnetoresistors R1' and R2' in the second bridge circuit 2 is the same as the overall orientation of magnetoresistors R1 and R2 in the first bridge circuit 1, rotated by 45° around the rotation center C.

[0051] As shown in Figures 1 and 2, in this embodiment, only the magnetoresistive resistors R1 and R2 of half of the first bridge circuit 1 (half-bridge) and the magnetoresistive resistors R1' and R2' of half of the second bridge circuit 2 are placed on the sensor chip 10a, while the fixed resistors R11 and R12 of the remaining half of the first bridge circuit 1 and the fixed resistors R11' and R12' of the remaining half of the second bridge circuit 2 are placed outside the sensor chip 10a.

[0052] In this embodiment, the number of magnetoresistive elements arranged on the sensor chip 10a can be reduced from the conventional four or eight to two or four, making it possible to reduce the chip size. As a result, as shown in Figure 3, the magnetoresistive elements R1, R1', R2, and R2' can be concentrated in the center of the chip, which reduces the influence of the direction of non-uniform external magnetic fields and improves angular accuracy. Consequently, robustness against external magnetic fields is ultimately improved.

[0053] Furthermore, in this embodiment, the number of magnetoresistive elements on the sensor chip 10a is reduced, which can relatively (or probabilistically) improve the yield of the sensor chip 10a. The fixed resistors R11, R11', R12, and R12' installed outside the sensor chip 10a can be freely customized. For example, if one of the fixed resistors R11, R11', R12, or R12' is defective, only that one needs to be replaced, making maintenance easier.

[0054] The magnetic sensor in this embodiment, like conventional sensors, can suppress even-numbered harmonic components included in the output of the magnetic sensor. The mechanism is explained below using mathematical formulas. Here, we describe the first bridge circuit 1, but the same applies to the second bridge circuit 2. The resistance values ​​of the two magnetoresistors R1 and R2 of the first bridge circuit 1 can be expressed using the external magnetic field θ as shown in equations (12) and (13), taking into account constant terms and harmonic components.

[0055]

number

[0056] Therefore, the output signal V obtained from the first bridge circuit 1 is given by equation (14).

[0057]

number

[0058] In equation (14), R0 is the resistance value of fixed resistors R11 and R12, r n is a constant that represents the amplitude of the harmonic component obtained by multiplying the frequency of the fundamental wave by n. In this case, the numerator term of equation (14) becomes equation (15).

[0059]

number

[0060] Also, the higher the harmonic, the smaller the component amount, and r0≫r1>r2>r3,····, so the term in the numerator of Equation (14) can be converted as in Equation (16).

[0061] [Number] ···(16)

[0062] Therefore, Equation (14) can ultimately be expressed as Equation (17).

[0063] [Number]

[0064] In this embodiment as well, it can be seen that the even - multiple harmonic components (n = 2, 4, 6…) do not affect the sensor output V, and it becomes a magnetic sensor that maintains high accuracy similar to the conventional sensor.

[0065] The output of the first bridge circuit 1 (Vcos + -Vcos - ) and the output of the second bridge circuit 2 (Vsin + -Vsin - ) change according to the relative rotation angle of the magnet M with respect to the sensor chip 10a shown in FIG. 2. For example, when the magnet M is rotated counter - clockwise once in a plane parallel to the paper surface of FIG. 2 with the rotation center C as the rotation axis, the output of the first bridge circuit 1 becomes a cosine - wave electrical signal, and the output of the second bridge circuit 2 becomes a sine - wave electrical signal. The magnet M may be above or below the sensor chip 10a.

[0066] Similar to the conventional case, the angular periods T of the cosine wave and the sine wave (the periods of the sine wave and the cosine wave represented by angles when the angle is taken on the horizontal axis) are 180°. Let the output of the first bridge circuit 1 be Vcos = Vcos + -Vcos - , and the output of the second bridge circuit 2 be Vsin = Vsin + -Vsin -Therefore, equation (7) allows us to calculate the relative rotation angle α of the magnet M with respect to the sensor chip 10a, that is, the relative rotation angle α of the object being detected.

[0067] In this embodiment, a double-bridge circuit was used as an example of the magnetic sensor configuration, but a single-bridge circuit configuration with only one of the first bridge circuit 1 or the second bridge circuit 2 may also be used.

[0068] [Second Example] Next, a second embodiment of the present invention will be described. Figure 4 is a circuit diagram showing the configuration of a magnetic sensor according to the second embodiment of the present invention. The circuit configuration of the magnetic sensor is the same as that of the first embodiment, but the magnetoresistive elements R1 and R2 of the first bridge circuit 1 (half bridge) and the magnetoresistive elements R1' and R2' of the second bridge circuit 2 are arranged on one layer 10b-1 of the sensor chip, and the fixed resistors R11 and R12 of the remaining half of the first bridge circuit 1 and the fixed resistors R11' and R12' of the remaining half of the second bridge circuit 2 are arranged on another layer 10b-2 of the sensor chip.

[0069] The top view of layer 10b-1, on which the magnetoresistive elements R1, R1', R2, and R2' of the sensor chip are formed, is the same as in Figure 2, so it is omitted from the description. Figure 5 is a cross-sectional view of the sensor chip 10b of this embodiment. In the example in Figure 5, layer 10b-1 on which the magnetoresistive elements R1, R1', R2, and R2' are formed, layer 10b-2 on which the fixed resistors R11, R11', R12, and R12' are formed, and layer 10b-3 on which the electrodes and wiring are formed are arranged in the insulating film 21 on the substrate 20. Electrical connections between layer 10b-1 and layer 10b-2, and between layer 10b-2 and layer 10b-3 are made via vias 22.

[0070] As shown in Figure 6, the top-bottom relationship of layers 10b-1 and 10b-2 may be reversed. Similar to the first embodiment, the magnet M may be above or below the sensor chip 10b. The mechanism for suppressing even-numbered harmonic components included in the output of the magnetic sensor, and the method for calculating the relative rotation angle α of the magnet M with respect to the sensor chip 10b, are the same as in the first embodiment.

[0071] In Figure 4, an example of a double-bridge circuit was shown as the configuration of the magnetic sensor. However, as in the first embodiment, a single-bridge circuit configuration with only one of the first bridge circuit 1 or the second bridge circuit 2 may also be used.

[0072] Similar to the first embodiment, in this embodiment, the number of magnetoresistive elements arranged on the sensor chip 10b is reduced from the conventional four or eight to two or four, making it possible to reduce the chip size. As a result, as shown in Figure 3, the magnetoresistive elements R1, R1', R2, and R2' can be concentrated in the center of the chip, which reduces the influence of the direction of non-uniform external magnetic fields and improves angular accuracy. Consequently, robustness against external magnetic fields is ultimately improved.

[0073] Furthermore, in this embodiment, the number of magnetoresistive elements on the sensor chip 10b is reduced, which can relatively (or probabilistically) improve the yield of the sensor chip 10b. Since the layer 10b-2 on which the fixed resistors R11, R11', R12, R12' are formed can be made of a different material than the layer 10b-1 on which the magnetoresistive elements R1, R1', R2, R2' are formed, a high yield of the sensor chip 10b can be maintained by selecting a material that is easy to manufacture in the process. In this embodiment, unlike the first embodiment, there is no need to provide fixed resistors R11, R11', R12, R12' outside the sensor chip 10b, thus saving space.

[0074] In the first and second embodiments, by configuring magnetoresistive element R1 as magnetoresistive element 42 in Figure 10, magnetoresistive element R2 as magnetoresistive element 43, magnetoresistive element R1' as magnetoresistive element 33, and magnetoresistive element R2' as magnetoresistive element 34, it is possible to suppress odd-order harmonic components included in the output of the magnetic sensor. In this case, each of the magnetoresistive elements R1, R1', R2, and R2' has a planar shape (meander shape) as shown in Figure 11, comprising a plurality of linear sections in the shape of parallel arc patterns (31A in Figure 11) and a plurality of folded sections (31B in Figure 11) that connect two adjacent linear sections so that the plurality of linear sections are connected in series.

[0075] To suppress odd-order harmonic components in the output of a magnetic sensor, the central angle φ of the arc pattern of each linear portion (31A in Figure 11) constituting the magnetoresistive elements R1, R1', R2, and R2' should be set to an angle calculated as 180° / n (where n is an odd number greater than or equal to 3, and represents the order of the harmonic to be reduced). For example, if the third harmonic is to be reduced, n=3 and a central angle φ of 60° is adopted.

[0076] Furthermore, as disclosed in Patent Document 2, the nth harmonic decreases as the central angle φ approaches 180° / n, so the central angle φ does not have to be exactly 180° / n. Specifically, the central angle φ may be substantially 180° / n, or it may be an angle within the range of 180° / n ± 3°, more preferably an angle within the range of 180° / n ± 1°. Therefore, the central angle φ can be an angle such that (180° / n) × m - 3° ≤ φ ≤ (180° / n) × m + 3° (where m is a natural number and n is an odd number greater than or equal to 3), more preferably (180° / n) × m - 1° ≤ φ ≤ (180° / n) × m + 1°.

[0077] Furthermore, as disclosed in Patent Document 2, by determining the film thickness and line width (W in Figure 11) of the magnetoresistive elements R1, R1', R2, and R2' within a range where the upper limit is the anisotropic magnetic field strength Hk = 30Oe at which the overall maximum angle detection error is 0.1°, the angle detection error can be kept below 0.1°. [Explanation of Symbols]

[0078] 1,2...Bridge circuit, R1,R1',R2,R2'...Magnetoresistive resistors, R11,R11',R12,R12'...Fixed resistors, 10a,10b...Sensor chips.

Claims

1. It has a bridge circuit composed of multiple magnetoresistive elements and multiple fixed resistors. The magnetic sensor is characterized in that the plurality of magnetoresistive elements are arranged in orientations that are 90° different from each other.

2. In the magnetic sensor according to claim 1, The plurality of magnetoresistive elements are formed on the substrate of the sensor chip, A magnetic sensor characterized in that the plurality of fixed resistors are arranged outside the sensor chip.

3. In the magnetic sensor according to claim 1, The plurality of magnetoresistive elements are formed on the substrate of the sensor chip, The magnetic sensor is characterized in that the plurality of fixed resistors are formed on the substrate in a layer different from the magnetoresistive element.

4. In the magnetic sensor according to any one of claims 1 to 3, The aforementioned bridge circuit is characterized by having a circuit in which two magnetoresistive elements are connected in series and a circuit in which two fixed resistors are connected in series, connected in parallel, forming a magnetic sensor.

5. In the magnetic sensor according to claim 1, Each of the plurality of magnetoresistors has a planar shape including one or more arc patterns. A magnetic sensor characterized in that the central angle φ of the circular arc pattern is within the range of (180° / n) × m - 3° ≤ φ ≤ (180° / n) × m + 3° (where m is a natural number and n is an odd number greater than or equal to 3).

6. In the magnetic sensor according to claim 5, A magnetic sensor characterized in that each of the plurality of magnetoresistive elements has a planar shape comprising a plurality of linear portions of the arc pattern parallel to each other, and a plurality of folded portions connecting two adjacent linear portions so that the plurality of linear portions are connected in series.

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