An anti-interference magnetoresistance multilayer film calibration system and a calibration method thereof

Abstract

The application discloses an anti-interference magnetoresistance multilayer film calibration system and a calibration method thereof, and the system comprises two three-dimensional Helmholtz coils, a three-axis fluxgate magnetometer, a conversion circuit and a control device; when the control device detects that the feedback voltage output by the three-axis fluxgate magnetometer is zero, the second three-dimensional Helmholtz coil is excited to generate an excitation magnetic field, the output voltage of the magnetoresistance multilayer film to be measured under the excitation magnetic field is collected, and calibration is carried out. By nesting two three-dimensional Helmholtz coils, the geomagnetic field interference is monitored by using the high-sensitivity fluxgate magnetometer, and the first three-dimensional Helmholtz coil provides a negative feedback magnetic field to offset the interference of the geomagnetic field. The second three-dimensional Helmholtz coil provides an excitation magnetic field to test and calibrate the magnetoresistance multilayer film to be measured. The interference of the external geomagnetic field can be offset from any direction, the defect of poor axial shielding effect of the magnetic shielding cylinder is avoided, and the calibration of the high-sensitivity magnetoresistance multilayer film can be realized without the construction of a large magnetic shielding room.

Description

Technical Field

[0001] This invention relates to the field of magnetic field sensing technology, specifically to an anti-interference magnetoresistive multilayer film calibration system and its calibration method. Background Technology

[0002] Magnetoresistive sensors have seen increasing applications in new energy and power electronic equipment in recent years due to their characteristics of being able to measure both AC and DC signals, high sensitivity, low noise, and low power consumption. Magnetoresistive sensors are composed of multilayer magnetoresistive films, and high-sensitivity multilayer magnetoresistive films require testing and calibration of performance indicators such as sensitivity and temperature drift.

[0003] However, the excitation magnetic field amplitude is generally small during the calibration of high-sensitivity magnetoresistive multilayer films, making them highly susceptible to interference from the Earth's magnetic field, which affects the calibration results. Current techniques typically reduce interference by placing the magnetoresistive multilayer film under test in a high-permeability shielded cylinder, or by constructing a dedicated large-scale magnetically shielded laboratory for calibration testing. High-permeability shielded cylinders generally lack axial shielding because the magnetic field excitation coil needs to be placed inside axially and the signal and power lines led out. While constructing a dedicated large-scale magnetically shielded laboratory is effective, it requires a large site and incurs high construction costs. Summary of the Invention

[0004] In view of this, embodiments of the present invention provide an anti-interference magnetoresistive multilayer film calibration system and calibration method to solve the technical problems of poor shielding effect or high construction cost in the calibration of magnetoresistive multilayer films in the prior art.

[0005] The technical solutions provided by the embodiments of the present invention are as follows:

[0006] A first aspect of this invention provides an anti-interference magnetoresistive multilayer film calibration system, comprising: a first three-dimensional Helmholtz coil, a second three-dimensional Helmholtz coil, a triaxial fluxgate magnetometer, a conversion circuit, and a control device; the second three-dimensional Helmholtz coil is disposed inside the first three-dimensional Helmholtz coil, the magnetoresistive multilayer film to be tested is disposed inside the second three-dimensional Helmholtz coil, the triaxial fluxgate magnetometer is disposed between the first three-dimensional Helmholtz coil and the second three-dimensional Helmholtz coil, the conversion circuit is disposed outside the first three-dimensional Helmholtz coil, one end of the conversion circuit is connected to the triaxial fluxgate magnetometer, and the other end of the conversion circuit is connected to the first three-dimensional Helmholtz coil. The triaxial fluxgate magnetometer generates a feedback voltage based on the combined magnetic field of the Earth's magnetic field and the negative magnetic field generated by the first three-dimensional Helmholtz coil. The conversion circuit receives the feedback voltage and generates a feedback current, which is output to the first three-dimensional Helmholtz coil. The first three-dimensional Helmholtz coil generates a negative magnetic field based on the feedback current. The control device is connected to the triaxial fluxgate magnetometer and the magnetoresistive multilayer film under test. When the control device detects that the feedback voltage output by the triaxial fluxgate magnetometer is zero, it excites the second three-dimensional Helmholtz coil to generate an excitation magnetic field, collects the output voltage of the magnetoresistive multilayer film under test under the excitation magnetic field, and calibrates the magnetoresistive multilayer film under test based on the output voltage and the excitation magnetic field.

[0007] Optionally, the anti-interference magnetoresistive multilayer film calibration system further includes: a temperature chamber, in which the first three-dimensional Helmholtz coil, the second three-dimensional Helmholtz coil, the triaxial fluxgate magnetometer, and the magnetoresistive multilayer film to be tested are disposed; the control device is also used to change the temperature of the temperature chamber, and at different temperatures, to calibrate the sensitivity of the magnetoresistive multilayer film to be tested according to the output voltage and the excitation magnetic field.

[0008] Optionally, the control device is also used to acquire the zero-point bias voltage of the magnetoresistive multilayer film under test in a non-magnetic field environment at different temperatures, and calculate the average temperature drift of the sensitivity and the average zero drift of the zero-point bias voltage based on the zero-point bias voltage and sensitivity calibration.

[0009] Optionally, the conversion circuit includes an integrator, an adder, and a transconductance amplifier; one end of the integrator is connected to the triaxial fluxgate magnetometer, the other end of the integrator is connected to the first input terminal of the adder, the second input terminal of the adder is connected to the triaxial fluxgate magnetometer, the output terminal of the adder is connected to one end of the transconductance amplifier, and the other end of the transconductance amplifier is connected to the first three-dimensional Helmholtz coil; the integrator receives the feedback voltage, integrates it, and inputs it to the adder; the adder receives the integrated feedback voltage and adds it to the feedback voltage output by the triaxial fluxgate magnetometer, and inputs it to the transconductance amplifier; the transconductance amplifier converts the added voltage into a feedback current and inputs it to the first three-dimensional Helmholtz coil.

[0010] Optionally, the control device includes: a current source, a voltmeter, and a microprocessor; the microprocessor is connected to the current source and the voltmeter respectively, the current source is connected to the second three-dimensional Helmholtz coil, the voltmeter is connected to the magnetoresistive multilayer film under test, when the microprocessor detects that the feedback voltage output by the three-axis fluxgate magnetometer is zero, it controls the current source to excite the second three-dimensional Helmholtz coil to generate an excitation magnetic field, and the microprocessor controls the voltmeter to collect the output voltage of the magnetoresistive multilayer film under test under the excitation magnetic field.

[0011] Optionally, the anti-interference magnetoresistive multilayer film calibration system further includes: a power supply, which provides power to the magnetoresistive multilayer film under test and the triaxial fluxgate magnetometer; the magnetoresistive multilayer film under test includes a magnetoresistive layer composed of multiple layers of films stacked together, a substrate, and a printed circuit board, wherein the metal pads on the substrate and the metal pads on the printed circuit board are bonded together as a power port and an output voltage port.

[0012] A second aspect of this invention provides a calibration method for an anti-interference magnetoresistive multilayer film, applied to the anti-interference magnetoresistive multilayer film calibration system described in the first aspect and any one of the first aspects of this invention. The method includes: controlling the operation of the triaxial fluxgate magnetometer; monitoring whether the feedback voltage output by the triaxial fluxgate magnetometer is zero; when it is zero, stimulating the second three-dimensional Helmholtz coil to generate an excitation magnetic field; acquiring the output voltage of the magnetoresistive multilayer film under test under the excitation magnetic field; and calibrating the magnetoresistive multilayer film under test based on the output voltage and the excitation magnetic field.

[0013] Optionally, exciting the second three-dimensional Helmholtz coil to generate an excitation magnetic field includes: exciting the second three-dimensional Helmholtz coil to generate a first excitation magnetic field with a first direction greater than zero and a second direction and a third direction equal to zero; exciting the second three-dimensional Helmholtz coil to generate a second excitation magnetic field with a second direction greater than zero and a first direction and a third direction equal to zero; exciting the second three-dimensional Helmholtz coil to generate a third excitation magnetic field with a third direction greater than zero and a first direction and a second direction equal to zero; and acquiring the output voltage of the magnetoresistive multilayer film under test under the excitation magnetic field includes: acquiring the first output voltage of the magnetoresistive multilayer film under test under the first excitation magnetic field, the second output voltage of the magnetoresistive multilayer film under test under the second excitation magnetic field, and the third output voltage of the magnetoresistive multilayer film under test under the third excitation magnetic field.

[0014] Optionally, the magnetoresistive multilayer film under test is calibrated according to the output voltage and the excitation magnetic field, including: obtaining the zero-point bias voltage of the magnetoresistive multilayer film under test in a magnetic field-free environment; and calibrating the sensitivity of the magnetoresistive multilayer film under test according to the zero-point bias voltage, the first output voltage, the second output voltage, the third output voltage, the first excitation magnetic field, the second excitation magnetic field, and the third excitation magnetic field.

[0015] Optionally, the anti-interference magnetoresistive multilayer film calibration method further includes: changing the ambient temperature around the first three-dimensional Helmholtz coil, the second three-dimensional Helmholtz coil, the triaxial fluxgate magnetometer, and the magnetoresistive multilayer film under test; collecting the sensitivity calibration results at different temperatures and the zero-point bias voltage of the magnetoresistive multilayer film under test in a non-magnetic field environment at different temperatures; and calculating the average temperature drift of the sensitivity and the average zero drift of the zero-point bias voltage based on the zero-point bias voltage and the sensitivity calibration results.

[0016] The technical solution of this invention has the following advantages:

[0017] The anti-interference magnetoresistive multilayer film calibration system and method provided in this invention utilizes two nested three-dimensional Helmholtz coils and a highly sensitive fluxgate magnetometer to monitor geomagnetic field interference. An external first three-dimensional Helmholtz coil provides a negative feedback magnetic field to counteract the geomagnetic field interference. Furthermore, an internal second three-dimensional Helmholtz coil provides an excitation magnetic field to test and calibrate the magnetoresistive multilayer film under test. Additionally, this system can counteract external geomagnetic field interference from any direction, avoiding the poor axial shielding effect of magnetic shielding cylinders, and achieving high-sensitivity magnetoresistive multilayer film calibration without the need for a large magnetic shielding chamber. Attached Figure Description

[0018] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0019] Figure 1 This is a structural block diagram of the anti-interference magnetoresistive multilayer film calibration system in an embodiment of the present invention;

[0020] Figures 2(a) to 2(c) This is a schematic diagram of the anti-interference magnetoresistive multilayer film calibration system in different directions according to an embodiment of the present invention;

[0021] Figure 3 This is a structural block diagram of an anti-interference magnetoresistive multilayer film calibration system according to another embodiment of the present invention.

[0022] Figure 4 This is a calibration schematic diagram of the anti-interference magnetoresistive multilayer film calibration system in an embodiment of the present invention.

[0023] Figure 5 This is a schematic diagram of the structure of the magnetoresistive multilayer film under test in an embodiment of the present invention;

[0024] Figure 6 This is a flowchart of the anti-interference magnetoresistive multilayer film calibration method in an embodiment of the present invention. Detailed Implementation

[0025] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0027] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can also refer to the internal connection of two components; and they can refer to a wireless connection or a wired connection. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0028] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0029] This invention provides an anti-interference magnetoresistive multilayer film calibration system, such as... Figure 1 As shown, the system includes: a first three-dimensional Helmholtz coil 1, a second three-dimensional Helmholtz coil 2, a triaxial fluxgate magnetometer 3, a conversion circuit 4, and a control device 6. The second three-dimensional Helmholtz coil 2 is disposed inside the first three-dimensional Helmholtz coil, and the magnetoresistive multilayer film 5 to be measured is disposed inside the second three-dimensional Helmholtz coil 2. The triaxial fluxgate magnetometer 3 is disposed between the first three-dimensional Helmholtz coil and the second three-dimensional Helmholtz coil 2. The conversion circuit 4 is disposed outside the first three-dimensional Helmholtz coil, with one end connected to the triaxial fluxgate magnetometer 3 and the other end connected to the first three-dimensional Helmholtz coil. The system 3 generates a feedback voltage based on the combined magnetic field of the Earth's magnetic field and the negative magnetic field generated by the first three-dimensional Helmholtz coil. The conversion circuit 4 receives the feedback voltage and generates a feedback current, which is output to the first three-dimensional Helmholtz coil. The first three-dimensional Helmholtz coil generates a negative magnetic field based on the feedback current. The control device 6 connects the triaxial fluxgate magnetometer 3 and the magnetoresistive multilayer film 5 to be tested. When the control device 6 detects that the feedback voltage output by the triaxial fluxgate magnetometer 3 is zero, it excites the second three-dimensional Helmholtz coil 2 to generate an excitation magnetic field, collects the output voltage of the magnetoresistive multilayer film 5 under the excitation magnetic field, and calibrates the magnetoresistive multilayer film 5 based on the output voltage and the excitation magnetic field.

[0030] Specifically, the structure and positional relationship of the first three-dimensional Helmholtz coil 1, the second three-dimensional Helmholtz coil 2, the triaxial fluxgate magnetometer 3, and the magnetoresistive multilayer film to be measured 5 are as follows: Figures 2(a) to 2(c) As shown, a triaxial fluxgate magnetometer is used to monitor the composite magnetic field, thereby detecting the X, Y, and Z components of the composite magnetic field and generating proportional feedback voltages X in three directions based on these three components. fluxgate Y fluxgate and Zfluxgate Taking the X direction as an example, assuming the X-direction sensitivity of the triaxial fluxgate magnetometer is 50mV / μT, then its output feedback voltage in the X direction is:

[0031] Xfluxgate=(Xgeo-Xfeedback)·Fx

[0032] X in the formula fluxagete The feedback voltage in the X direction output by the triaxial fluxgate magnetometer, X geo Let X be the magnitude of the Earth's magnetic field component in the X direction. feedback F is the negative feedback magnetic field in the X direction of the first three-dimensional Helmholtz coil. x The sensitivity of the triaxial fluxgate magnetometer in the X direction is 50 mV / μT.

[0033] The anti-interference magnetoresistive multilayer film calibration system provided in this invention utilizes two nested three-dimensional Helmholtz coils and a highly sensitive fluxgate magnetometer to monitor geomagnetic field interference. An external first three-dimensional Helmholtz coil provides a negative feedback magnetic field to counteract the geomagnetic field interference. Furthermore, an internal second three-dimensional Helmholtz coil provides an excitation magnetic field to test and calibrate the magnetoresistive multilayer film under test. Additionally, this system can counteract external geomagnetic field interference from any direction, avoiding the poor axial shielding effect of magnetic shielding cylinders, and achieving high-sensitivity magnetoresistive multilayer film calibration without the need for a large magnetic shielding chamber.

[0034] In one implementation, such as Figure 3 As shown, the conversion circuit includes an integrator 42, an adder 41, and a transconductance amplifier 43. One end of the integrator 42 is connected to the triaxial fluxgate magnetometer, the other end of the integrator 42 is connected to the first input terminal of the adder 41, the second input terminal of the adder 41 is connected to the triaxial fluxgate magnetometer, the output terminal of the adder 41 is connected to one end of the transconductance amplifier 43, and the other end of the transconductance amplifier 43 is connected to the first three-dimensional Helmholtz coil. The integrator 42 receives and integrates the feedback voltage and inputs it to the adder 41. The adder 41 receives and adds the integrated feedback voltage and the feedback voltage output by the triaxial fluxgate magnetometer and inputs it to the transconductance amplifier 43. The transconductance amplifier 43 converts the added voltage into a feedback current and inputs it to the first three-dimensional Helmholtz coil.

[0035] Specifically, since the feedback voltage output by the triaxial fluxgate magnetometer includes voltages in the X, Y, and Z directions, the first input terminal of the integrator includes the X, Y, and Z input terminals, and the second input terminal of the adder includes the X, Y, and Z input terminals. The voltages in the X, Y, and Z directions are respectively input to the corresponding input terminals of the integrator and adder for processing. Taking the X direction as an example, the feedback voltage in the X direction of the triaxial fluxgate magnetometer is input to the X input terminals of both the integrator and the adder. The output of the integrator is connected to the first input terminal of the adder, so the output terminal of the adder is:

[0036] Xo = X1 + X2

[0037] In the formula, X1 represents the feedback voltage in the X direction of the three-axis fluxgate magnetometer received at the X input terminal of the adder, and X2 represents the voltage output by the integrator received at the first input terminal of the adder.

[0038] The voltage Xo output from the adder is input to the transconductance amplifier, which converts the voltage Xo into a current. Figure 4 The transconductance amplifier has a gain of 1, meaning a 1mV voltage is converted into a 1mA current. The output current of the transconductance amplifier is input to the X-direction coil of the first three-dimensional Helmholtz coil, generating a negative feedback magnetic field. Figure 4 The X-axis conversion factor of the intermediate coil is 1, which means that a current of 1mA generates a magnetic field of 1μT.

[0039] Combination Figure 4 , Figure 4 The triaxial fluxgate magnetometer measures the current error, which is input to the integrator as the historical cumulative error for the next moment. The adder adds the current error to the historical cumulative error. Without the integrator, there would be no historical cumulative error in the negative feedback, making it impossible to enter the locked state. Therefore, by setting up an integrator and an adder in the conversion circuit, the integrator can record the historical cumulative error, and the adder adds the current error to the historical cumulative error and inputs it into the negative feedback. Only when the negative feedback completely cancels out the current error and the historical cumulative error does the system enter the locked state, that is, it enters the subsequent excitation magnetic field generation and calibration process of the magnetoresistive multilayer film under test.

[0040] In one implementation, such as Figure 3As shown, the anti-interference magnetoresistive multilayer film calibration system further includes: a temperature chamber 7, in which the first three-dimensional Helmholtz coil 1, the second three-dimensional Helmholtz coil 2, the triaxial fluxgate magnetometer 3, and the magnetoresistive multilayer film to be tested are disposed; the control device is also used to change the temperature of the temperature chamber 7, and at different temperatures, to calibrate the sensitivity of the magnetoresistive multilayer film to be tested based on the output voltage and the excitation magnetic field. The control device is also used to acquire the zero-point bias voltage of the magnetoresistive multilayer film to be tested in a magnetic field-free environment at different temperatures, and to calculate the average temperature drift of the sensitivity and the average zero drift of the zero-point bias voltage based on the zero-point bias voltage and the sensitivity calibration.

[0041] Specifically, by setting up a temperature chamber, the first three-dimensional Helmholtz coil, the second three-dimensional Helmholtz coil, the three-axis fluxgate magnetometer, and the multilayer magnetoresistive film to be measured are placed in the temperature chamber. By changing the temperature of the temperature chamber, the corresponding output voltage and excitation magnetic field at different temperatures are obtained. The sensitivity is calibrated based on the output voltage and excitation magnetic field at different temperatures, and a curve of sensitivity change with temperature in the temperature chamber can be plotted. In addition, the zero-point bias voltage at different temperatures can be measured, and a curve of zero-point bias voltage change with temperature can be plotted. From this, the average temperature drift of the sensitivity and the average zero drift of the zero-point bias voltage can be calculated.

[0042] Since the second three-dimensional Helmholtz coil can generate excitation magnetic fields in three directions, the sensitivity in each of these three directions can be calculated. Specifically, when exciting the second three-dimensional Helmholtz coil, it first generates a first excitation magnetic field H with the first direction being greater than zero and the second and third directions being equal to zero. x The first output voltage V of the magnetoresistive multilayer film under test is collected under the first excitation magnetic field. x Then, the second three-dimensional Helmholtz coil is excited to generate a second excitation magnetic field H with the second direction being greater than zero and the first and third directions being equal to zero. Y The second output voltage V of the magnetoresistive multilayer film under test is collected under the second excitation magnetic field. Y Finally, the second three-dimensional Helmholtz coil is excited to generate a third excitation magnetic field H with the third direction being greater than zero and the first and second directions being equal to zero. Z The third output voltage V of the magnetoresistive multilayer film under test is collected under the third excitation magnetic field. Z .

[0043] Based on the three excitation magnetic fields and three output voltages obtained from the above three directions, the sensitivity in the three directions is calculated using the following formula:

[0044]

[0045] In the formula, S x Sy S z Let S be the sensitivity of the magnetoresistive multilayer film under test in the X, Y, and Z directions. The sensitivity S of the magnetoresistive multilayer film under test can be calculated using the following formula:

[0046]

[0047] In one implementation, such as Figure 3 As shown, the control device includes: a current source 61, a voltmeter 62, and a microprocessor; the microprocessor is connected to the current source 61 and the voltmeter 62 respectively. The current source 61 is connected to the second three-dimensional Helmholtz coil 2, and the voltmeter 62 is connected to the magnetoresistive multilayer film 5 under test. When the microprocessor detects that the feedback voltage output by the triaxial fluxgate magnetometer 3 is zero, it controls the current source 61 to excite the second three-dimensional Helmholtz coil 2 to generate an excitation magnetic field. The microprocessor controls the voltmeter 62 to collect the output voltage of the magnetoresistive multilayer film 5 under test under the excitation magnetic field. In addition, this anti-interference magnetoresistive multilayer film calibration system also includes: a power supply 8, which provides power to the magnetoresistive multilayer film 5 under test and the triaxial fluxgate magnetometer 3. Figure 5 As shown, the magnetoresistive multilayer film under test includes a magnetoresistive film composed of multiple layers of films stacked together, a substrate, and a printed circuit board. The metal pads on the substrate and the metal pads on the printed circuit board are bonded together as a power supply port and an output voltage port.

[0048] Specifically, a high-stability current source and a high-precision voltmeter can be used to improve control accuracy. Furthermore, for the magnetoresistive multilayer film under test, the magnetoresistive structure formed by the multilayer film can be fabricated on a substrate using processes such as magnetron sputtering and photolithography. The substrate is then attached to the circuit board via adhesive bonding. The output port of the power supply is connected to the power ports of the magnetoresistive multilayer film under test and the triaxial fluxgate magnetometer, providing operating power to both.

[0049] This invention also provides a calibration method for anti-interference magnetoresistive multilayer films, applied to the anti-interference magnetoresistive multilayer film calibration system described in the above embodiments, such as... Figure 6 As shown, the method includes the following steps:

[0050] Step S101: Control the operation of the triaxial fluxgate magnetometer; specifically, during calibration, first place the first three-dimensional Helmholtz coil, the second three-dimensional Helmholtz coil, the triaxial fluxgate magnetometer, and the magnetoresistive multilayer film to be tested according to the system settings, and then use the power supply to power the magnetoresistive multilayer film to be tested and the triaxial fluxgate magnetometer, then the triaxial fluxgate magnetometer starts to work, that is, it begins to collect the combined magnetic field of the geomagnetic field and the negative feedback magnetic field generated by the first three-dimensional Helmholtz coil, and outputs the feedback voltage.

[0051] Step S102: Monitor whether the feedback voltage output by the triaxial fluxgate magnetometer is zero; specifically, since the conversion circuit is connected to the triaxial fluxgate magnetometer and the first three-dimensional Helmholtz coil, a closed loop is formed between the three. By adjusting this closed loop, i.e., adjusting the input current of the first three-dimensional Helmholtz coil, the synthesized magnetic field can be gradually stabilized to 0μT, and the feedback voltage output by the triaxial fluxgate magnetometer is zero. At this time, the negative feedback magnetic field generated by the first three-dimensional Helmholtz coil cancels the interference of the Earth's magnetic field, making the magnetic field inside the first three-dimensional Helmholtz coil zero, i.e., the multilayer magnetoresistive film to be measured set inside the first three-dimensional Helmholtz coil is not affected by the Earth's magnetic field.

[0052] Step S103: When the value is zero, the second three-dimensional Helmholtz coil is excited to generate an excitation magnetic field; thereby, the second three-dimensional Helmholtz coil can generate excitation magnetic fields in three directions, exciting the second three-dimensional Helmholtz coil to generate a first excitation magnetic field in the first direction which is greater than zero, and the second and third directions which are equal to zero; exciting the second three-dimensional Helmholtz coil to generate a second excitation magnetic field in the second direction which is greater than zero, and the first and third directions which are equal to zero; exciting the second three-dimensional Helmholtz coil to generate a third excitation magnetic field in the third direction which is greater than zero, and the first and second directions which are equal to zero.

[0053] Step S104: Acquire the output voltage of the magnetoresistive multilayer film under test under the excitation magnetic field; specifically, the acquired output voltage includes the first output voltage of the magnetoresistive multilayer film under test under the first excitation magnetic field, the second output voltage of the magnetoresistive multilayer film under test under the second excitation magnetic field, and the third output voltage of the magnetoresistive multilayer film under test under the third excitation magnetic field.

[0054] Step S105: Calibrate the magnetoresistive multilayer film under test according to the output voltage and the excitation magnetic field. Specifically, during calibration, obtain the zero-point bias voltage of the magnetoresistive multilayer film under test in a magnetic field-free environment; calibrate the sensitivity of the magnetoresistive multilayer film under test according to the zero-point bias voltage, the first output voltage, the second output voltage, the third output voltage, the first excitation magnetic field, the second excitation magnetic field, and the third excitation magnetic field.

[0055] The sensitivity in the three directions is calculated using the following formula:

[0056]

[0057] In the formula, S x S y S z Let S be the sensitivity of the magnetoresistive multilayer film under test in the X, Y, and Z directions. The sensitivity S of the magnetoresistive multilayer film under test can be calculated using the following formula:

[0058]

[0059] The anti-interference magnetoresistive multilayer film calibration method provided in this invention involves nesting two three-dimensional Helmholtz coils and using a high-sensitivity fluxgate magnetometer to monitor geomagnetic field interference. The external first three-dimensional Helmholtz coil provides a negative feedback magnetic field to counteract the geomagnetic field interference. Furthermore, the internal second three-dimensional Helmholtz coil provides an excitation magnetic field to test and calibrate the magnetoresistive multilayer film under test. In addition, this method can counteract external geomagnetic field interference from any direction, avoiding the poor axial shielding effect of magnetic shielding cylinders, and achieving high-sensitivity magnetoresistive multilayer film calibration without the need for a large magnetic shielding chamber.

[0060] In one embodiment, the anti-interference magnetoresistive multilayer film calibration method further includes: changing the ambient temperature around the first three-dimensional Helmholtz coil, the second three-dimensional Helmholtz coil, the triaxial fluxgate magnetometer, and the magnetoresistive multilayer film under test; collecting sensitivity calibration results at different temperatures and the zero-point bias voltage of the magnetoresistive multilayer film under test in a non-magnetic field environment at different temperatures; and calculating the average temperature drift of the sensitivity and the average zero drift of the zero-point bias voltage based on the zero-point bias voltage and the sensitivity calibration results.

[0061] Specifically, by acquiring the corresponding output voltage and excitation magnetic field at different temperatures, and calibrating the sensitivity based on the output voltage and excitation magnetic field at different temperatures, a curve of sensitivity changing with temperature in the temperature chamber can be plotted. In addition, the zero-point bias voltage at different temperatures can be measured, and a curve of zero-point bias voltage changing with temperature can be plotted. From this, the average temperature drift of the sensitivity and the average zero drift of the zero-point bias voltage can be calculated.

[0062] In one embodiment, the anti-interference magnetoresistive multilayer film calibration method is implemented using the following process:

[0063] (1) Turn on the temperature chamber, triaxial fluxgate magnetometer, integrator, adder, transconductance amplifier, high-stability current source, high-precision voltmeter, and power supply. At this time, the power supply powers the triaxial fluxgate magnetometer and the multilayer magnetoresistive film under test.

[0064] (2) After completing step (1), the triaxial fluxgate magnetometer placed inside the first three-dimensional Helmholtz coil and outside the second three-dimensional Helmholtz coil detects the X, Y, and Z components of the composite magnetic field formed by the superposition of the Earth's magnetic field and the negative feedback magnetic field generated by the first three-dimensional Helmholtz coil, and outputs a proportional voltage signal X. fluxgate Y fluxgate and Z fluxgate To explain the negative feedback process more clearly, let's take the X direction as an example, such as... Figure 4 As shown, assuming the X-direction sensitivity of the triaxial fluxgate magnetometer is 50 mV / μT, its output voltage is...

[0065] X fluxgate =(X geo -X feedback )·F x

[0066] X in the formula fluxagete X is the output voltage in the X direction of the triaxial fluxgate magnetometer. geo Let X be the magnitude of the Earth's magnetic field component in the X direction. feedback F is the negative feedback magnetic field in the X direction of the first three-dimensional Helmholtz coil. x The sensitivity of the triaxial fluxgate magnetometer in the X direction is 50 mV / μT.

[0067] (3) The output voltage in the X direction of the triaxial fluxgate magnetometer is input to the X input terminal of the integrator and the X input terminal of the adder, respectively. The output of the integrator is connected to the first input terminal of the adder. Then the output Xo of the adder is:

[0068] Xo = X1 + X2

[0069] Xo is input to a transconductance amplifier, which converts the voltage Xo into a current. Figure 4 The transconductance amplifier has a gain of 1, meaning a 1mV voltage is converted into a 1mA current. The output current of the transconductance amplifier is input to the X-direction coil of the three-dimensional Helmholtz coil 1, generating a negative feedback magnetic field. Figure 4 The X-axis conversion factor of the intermediate coil is 1, which means that a current of 1mA generates a magnetic field of 1μT.

[0070] (4) As can be seen from steps (1)-(3), through the above closed-loop adjustment, a deep negative feedback state will be entered in the X direction. The X component of the negative feedback magnetic field will gradually lock the X component of the geomagnetic field, and the composite magnetic field will gradually stabilize to 0 μT. That is, the interference of the geomagnetic field is canceled through negative feedback. By analogy, the negative feedback process in the Y and Z directions is similar to that in the X direction.

[0071] (5) After entering the deep negative feedback state, record the zero-point bias voltage b0 of the magnetoresistive multilayer film under test in a magnetic field-free environment, and adjust the X output of the high-stability current source to excite the second three-dimensional Helmholtz coil to generate the first excitation magnetic field H in the X direction. x Record the first output voltage V of the magnetoresistive multilayer film under test as monitored by the high-precision voltmeter at this time. x Adjust H x The time should be adjusted gradually from small to large to avoid H x If the magnetoresistive multilayer film under test is too large, it will enter the saturation region.

[0072] (6) Adjust the Y output of the high-stability current source to excite the second three-dimensional Helmholtz coil to generate a second excitation magnetic field H in the Y direction. YRecord the second output voltage V of the magnetoresistive multilayer film under test as monitored by the high-precision voltmeter at this time. Y Adjust H Y The time should be adjusted gradually from small to large to avoid H Y If the magnetoresistive multilayer film under test is too large, it will enter the saturation region.

[0073] (7) Adjust the Z output of the high-stability current source to excite the second three-dimensional Helmholtz coil to generate a third excitation magnetic field H in the Z direction. Z Record the third output voltage V of the magnetoresistive multilayer film under test as monitored by the high-precision voltmeter at this time. Z Adjust H Z The time should be adjusted gradually from small to large to avoid H Z If the magnetoresistive multilayer film under test is too large, it will enter the saturation region.

[0074] (8) Let the sensitivities of the magnetoresistive multilayer film under test in the X, Y, and Z directions be S, respectively. x S y S z Then the magnetic field H in steps (5), (6), and (7) x H y H z The output V of the magnetoresistive multilayer film under test x V Y and V Z The following relationships exist:

[0075]

[0076] Therefore, the sensitivity S in the X, Y, and Z directions of the magnetoresistive multilayer film under test can be calculated using the above formula. x S y S z The sensitivity S of the magnetoresistive multilayer film under test can be calculated using the following formula:

[0077]

[0078] (9) Change the temperature of the temperature chamber and repeat steps (1)-(8) to measure the sensitivity S and zero-point bias voltage b0 of the magnetoresistive multilayer film under test at different temperatures. Plot the relationship between the sensitivity S and the zero-point bias voltage b0 and the temperature of the temperature chamber, and calculate the average temperature drift of the sensitivity S and the average zero drift of the zero-point bias voltage b0.

[0079] While exemplary embodiments and their advantages have been described in detail, those skilled in the art can make various changes, substitutions, and modifications to these embodiments without departing from the spirit of the invention and the scope of protection defined by the appended claims. Such modifications and variations all fall within the scope defined by the appended claims. For other examples, those skilled in the art should readily understand that the order of process steps can be changed while remaining within the scope of the invention.

[0080] Furthermore, the scope of this invention is not limited to the processes, mechanisms, manufacturing methods, material compositions, means, methods, and steps of the specific embodiments described in the specification. From the disclosure of this invention, those skilled in the art will readily understand that any existing or future processes, mechanisms, manufacturing methods, material compositions, means, methods, or steps that perform substantially the same function or obtain substantially the same results as the corresponding embodiments described in this invention can be applied according to this invention. Therefore, the appended claims are intended to include these processes, mechanisms, manufacturing methods, material compositions, means, methods, or steps within their scope of protection.

Claims

1. An interference-resistant magnetoresistive multilayer film calibration system, characterized by, The application relates to a three-dimensional magnetic field measurement device. The second three-dimensional Helmholtz coil is arranged inside the first three-dimensional Helmholtz coil, the magnetic resistance multilayer film to be measured is arranged inside the second three-dimensional Helmholtz coil, the three-axis fluxgate magnetometer is arranged between the first three-dimensional Helmholtz coil and the second three-dimensional Helmholtz coil, the conversion circuit is arranged outside the first three-dimensional Helmholtz coil, one end of the conversion circuit is connected with the three-axis fluxgate magnetometer, and the other end of the conversion circuit is connected with the first three-dimensional Helmholtz coil. The three-axis fluxgate magnetometer generates a feedback voltage according to a resultant magnetic field of a geomagnetic field and a negative magnetic field generated by the first three-dimensional Helmholtz coil, the conversion circuit receives the feedback voltage to generate a feedback current and outputs the feedback current to the first three-dimensional Helmholtz coil, and the first three-dimensional Helmholtz coil generates a negative magnetic field according to the feedback current. The control device is connected with the three-axis fluxgate magnetometer and the magnetic resistance multilayer film to be measured; when the control device detects that the feedback voltage output by the three-axis fluxgate magnetometer is zero, the control device excites the second three-dimensional Helmholtz coil to generate an excitation magnetic field, collects an output voltage of the magnetic resistance multilayer film to be measured under the excitation magnetic field, and calibrates the magnetic resistance multilayer film to be measured according to the output voltage and the excitation magnetic field. The application further relates to a three-dimensional magnetic field measurement device.

2. The noise immune magnetoresistive multilayer film calibration system of claim 1, wherein, The control device is further used for changing the temperature of the temperature box, and calibrating the sensitivity of the magnetic resistance multilayer film to be measured according to the output voltage and the excitation magnetic field under different temperatures. The control device is further used for acquiring a zero-point bias voltage of the magnetic resistance multilayer film to be measured in a non-magnetic field environment under different temperatures, and calculating average temperature drift of the sensitivity and average zero drift of the zero-point bias voltage according to the zero-point bias voltage and the sensitivity calibration. The conversion circuit comprises an integrator, an adder and a transconductance amplifier.

3. The noise immune magnetoresistive multilayer film calibration system of claim 2, wherein, One end of the integrator is connected with the three-axis fluxgate magnetometer, the other end of the integrator is connected with a first input end of the adder, a second input end of the adder is connected with the three-axis fluxgate magnetometer, an output end of the adder is connected with one end of the transconductance amplifier, and the other end of the transconductance amplifier is connected with the first three-dimensional Helmholtz coil.

4. The noise immune magnetoresistive multilayer film calibration system of claim 1, wherein, The integrator receives the feedback voltage and inputs the feedback voltage after integration to the adder, the adder receives the feedback voltage after integration and the feedback voltage output by the three-axis fluxgate magnetometer, adds the two feedback voltages and inputs the added voltage to the transconductance amplifier, and the transconductance amplifier converts the added voltage into a feedback current and inputs the feedback current to the first three-dimensional Helmholtz coil. The control device comprises a current source, a voltmeter and a microprocessor. ​ 5. The tamper-resistant magnetoresistive multilayer film calibration system of claim 1, wherein, ​ The microprocessor is connected with the current source and the voltmeter respectively, the current source is connected with the second three-dimensional Helmholtz coil, the voltmeter is connected with the magnetoresistance multilayer film to be measured, the microprocessor controls the current source to excite the second three-dimensional Helmholtz coil to generate an excitation magnetic field when detecting that the feedback voltage output by the three-axis fluxgate magnetometer is zero, and the microprocessor controls the voltmeter to collect the output voltage of the magnetoresistance multilayer film to be measured under the excitation magnetic field.

6. The tamper-resistant magnetoresistive multilayer film calibration system of claim 1, wherein, Further comprising: a power supply, which provides power supply for the magnetoresistance multilayer film to be measured and the three-axis fluxgate magnetometer; the magnetoresistance multilayer film to be measured comprises a magnetoresistance composed of a plurality of layers of multilayer films arranged in a stack, a substrate and a printed circuit board, and the metal pads on the substrate and the metal pads on the printed circuit board are bonded together as a power port and an output voltage port.

7. A method of calibrating an interference resistant magnetoresistive multilayer film, comprising: The method is applied to the anti-interference magnetoresistance multilayer film calibration system of any one of claims 1-6, and the method comprises: controlling the three-axis fluxgate magnetometer to work; monitoring whether the feedback voltage output by the three-axis fluxgate magnetometer is zero; when the feedback voltage is zero, exciting the second three-dimensional Helmholtz coil to generate an excitation magnetic field; collecting the output voltage of the magnetoresistance multilayer film to be measured under the excitation magnetic field; calibrating the magnetoresistance multilayer film to be measured according to the output voltage and the excitation magnetic field.

8. The method of claim 7, wherein the method further comprises: The excitation magnetic field generated by the second three-dimensional Helmholtz coil comprises: a first excitation magnetic field generated by the second three-dimensional Helmholtz coil, wherein the first direction is greater than zero, and the second direction and the third direction are equal to zero; a second excitation magnetic field generated by the second three-dimensional Helmholtz coil, wherein the second direction is greater than zero, and the first direction and the third direction are equal to zero; a third excitation magnetic field generated by the second three-dimensional Helmholtz coil, wherein the third direction is greater than zero, and the first direction and the second direction are equal to zero. The output voltage of the magnetoresistance multilayer film to be measured under the excitation magnetic field comprises: a first output voltage of the magnetoresistance multilayer film to be measured under the first excitation magnetic field, a second output voltage of the magnetoresistance multilayer film to be measured under the second excitation magnetic field, and a third output voltage of the magnetoresistance multilayer film to be measured under the third excitation magnetic field.

9. The method of claim 8, wherein the method further comprises: The calibration of the magnetoresistance multilayer film to be measured according to the output voltage and the excitation magnetic field comprises: obtaining a zero-point bias voltage of the magnetoresistance multilayer film to be measured in a magnetic field-free environment; calibrating the sensitivity of the magnetoresistance multilayer film to be measured according to the zero-point bias voltage, the first output voltage, the second output voltage, the third output voltage, the first excitation magnetic field, the second excitation magnetic field and the third excitation magnetic field.

10. The method of claim 9, wherein the method further comprises: Further comprising: changing the ambient temperature of the first three-dimensional Helmholtz coil, the second three-dimensional Helmholtz coil, the three-axis fluxgate magnetometer and the magnetoresistance multilayer film to be measured; collecting the sensitivity calibration results at different temperatures and the zero-point bias voltage of the magnetoresistance multilayer film to be measured in a magnetic field-free environment at different temperatures; calculating the average temperature drift of the sensitivity and the average zero drift of the zero-point bias voltage according to the zero-point bias voltage and the sensitivity calibration results.

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