A two-stage amplified low-frequency magnetoresistive sensor and its preparation method

Abstract

The present invention provides a two-stage amplified low-frequency magnetoresistive sensor, comprising a substrate, a magnetoresistive sensing element, a MEMS resonator, and a two-stage amplification modulation structure, wherein the magnetoresistive sensing element is arranged on the upper end surface of the substrate, the MEMS resonator is mounted on the substrate, and the two-stage amplification modulation structure comprises two first magnetic line concentrators and a second magnetic line concentrator, wherein the two first magnetic line concentrators are symmetrically arranged on both sides of the magnetoresistive sensing element, and the second magnetic line concentrator is arranged on the surface of the MEMS resonator and vibrates in the up and down directions under the drive of the MEMS resonator. By adding a pair of magnetic line concentrators, the DC or low-frequency magnetic field sensed by the sensor is modulated to a high-frequency field, and the sensitivity of the sensor is also greatly improved, thereby more effectively suppressing 1 / f noise and further improving the resolution of the sensor.

Description

Technical Field

[0001] The present invention relates to the field of sensor technology, and in particular to a two-stage amplified low-frequency magnetoresistive sensor and a preparation method thereof. Background Art

[0002] Magnetoresistive sensors have been widely used in the measurement of weak magnetic fields in recent years due to their small size, high sensitivity, and low power consumption. However, magnetoresistive sensors are greatly interfered by 1 / f noise in the low-frequency band, and the sensor has a low resolution for DC or low-frequency magnetic fields, which greatly limits the application of sensors. Using micro-electromechanical systems (MEMS) to modulate the DC or low-frequency field sensed by the magnetoresistive sensor to a high frequency band (greater than 10kHz) is an effective means of suppressing 1 / f noise, and the magnetic field resolution of the sensor can be improved by nearly three orders of magnitude.

[0003] Existing MEMS magnetoresistive sensors often use a pair of soft magnetic films with high magnetic permeability (hereinafter collectively referred to as magnetic field concentrators) to amplify the magnetic field around the magnetoresistive sensor element. Since the local magnetic field is amplified, the sensitivity of the sensor is also increased. The MEMS structure drives the magnetic field concentrator to vibrate at high frequency, and the magnetic field sensed by the magnetoresistive sensor is also modulated to the high frequency band, effectively suppressing 1 / f noise. The resolution of the sensor for DC or low-frequency fields is also greatly improved.

[0004] For example, a team led by A. Guedes of INESC in Portugal has proposed a dual piezoelectric-driven magnetic field line modulation scheme, which places a spin valve (a type of magnetoresistive sensor) in the gap between a pair of cantilever beams. AlN is deposited on the cantilever beams, and magnetic field line concentrators are deposited on the AlN. When the cantilever beams are driven by the piezoelectric effect, the magnetic field line concentrators at both ends of the magnetoresistive sensor element also vibrate up and down, and the DC or low-frequency field sensed by the sensor is modulated to a high-frequency band, effectively suppressing 1 / f noise.

[0005] my country's National University of Defense Technology has also proposed a vertical motion modulation scheme, which also uses a pair of magnetic line concentrators to amplify the magnetic field sensed by the magnetoresistive sensor element. There is a cantilever beam with a soft magnetic film directly above the sensor element. When the cantilever beam vibrates up and down, the magnetic field sensed by the sensor element is also modulated to the high frequency band.

[0006] These modulation schemes all use only a pair of magnetic flux concentrators to amplify the magnetic field of the magnetoresistive sensor element, and there is still much room for improvement in the sensitivity of the sensor. Summary of the invention

[0007] The main purpose of the present invention is to provide a two-stage amplified low-frequency magnetoresistive sensor and a preparation method thereof, aiming to improve the technical problem of low sensor sensitivity in the prior art.

[0008] To achieve the above-mentioned purpose, the present invention provides a two-stage amplified low-frequency magnetoresistive sensor, comprising a substrate, a magnetoresistive sensing element, a MEMS resonator, and a two-stage amplification modulation structure, wherein the magnetoresistive sensing element is arranged on the upper end surface of the substrate, the MEMS resonator is installed on the substrate, and the two-stage amplification modulation structure comprises two first magnetic line concentrators and a second magnetic line concentrator, wherein the two first magnetic line concentrators are symmetrically arranged on both sides of the magnetoresistive sensing element, and the second magnetic line concentrator is arranged on the surface of the MEMS resonator and vibrates in the up and down directions under the drive of the MEMS resonator.

[0009] Optionally, the magnetoresistive sensor element includes an AMR sensor device, a GMR sensor device, or a TMR sensor device.

[0010] Optionally, the MEMS resonator includes a silicon layer and a piezoelectric driving layer, the piezoelectric driving layer is arranged on the upper end surface of the substrate, the silicon layer is installed on the lower end surface of the substrate, and the second magnetic field line concentrator is arranged on the lower surface of the silicon layer.

[0011] Optionally, the MEMS resonator includes a silicon layer, a metal layer and an AC excitation gate, the silicon layer is installed on the upper end surface of the substrate, the metal layer is installed on the upper surface of the silicon layer, the second magnetic line concentrator is arranged on the upper surface of the metal layer, and the AC excitation gate is arranged below the silicon layer.

[0012] In addition, in order to achieve the above-mentioned purpose, the present invention also provides a method for preparing a low-frequency magnetoresistive sensor with two-stage amplification based on a piezoelectric driving principle, comprising the following method steps:

[0013] Step 1: Clean the SOI substrate with acetone, anhydrous ethanol, and deionized water in sequence;

[0014] Step 2: Thermally oxidize a 300-600 nm thick SiO 2 ;

[0015] Step 3: sputtering a magnetoresistive sensor element on the SOI substrate using a magnetron sputtering device;

[0016] Step 4: After photolithography, etch the magnetoresistive sensor element to the bottom electrode, and etch the magnetoresistive sensor element into 180um 2 -270um 2 Rectangle;

[0017] Step 5: Etch the bottom electrode after photolithography to 1600um 2 -2400um 2 square;

[0018] Step 6: After photolithography, the SiO 2 Passivation layer;

[0019] Step 7: Peel off the SiO 2 , exposing the top electrode and the bottom electrode;

[0020] Step 8: Sputtering of metal layer (Ti / Au, Ti / Al, Ti / Pt) after photolithography;

[0021] Step 9: peeling off the metal layer (Ti / Au, Ti / Al, Ti / Pt) to define the shapes of the top electrode and the bottom electrode;

[0022] Step 10: Electroplating high magnetic permeability material after photolithography;

[0023] Step 11: peeling off the high magnetic permeability material to define the shape of the magnetic field line concentrator;

[0024] Step 12: sputtering piezoelectric material after photolithography;

[0025] Step 13: peeling off the piezoelectric material to define the shape of the piezoelectric driving layer;

[0026] Step 14: Etch SiO using reactive ion etching after photolithography 2 , exposing part of the Si layer on the SOI wafer;

[0027] Step 15: sputtering the metal layer (Ti / Au, Ti / Al, Ti / Pt) after photolithography;

[0028] Step 16: peeling off the metal layer (Ti / Au, Ti / Al, Ti / Pt) to define the shape of the piezoelectric material electrode;

[0029] Step 17: After photolithography, the exposed Si layer on the SOI is etched using deep reactive ion etching to define the shape of the cantilever beam;

[0030] Step 18: After photolithography, the Si layer on the back of the SOI is etched using deep reactive ion etching;

[0031] Step 19: After photolithography, use reactive ion etching to etch the SiO on the back of SOI 2 layer, so that the cantilever beam is suspended in the air;

[0032] Step 20: Electroplating high magnetic permeability material after photolithography;

[0033] Step 21: peeling off the high magnetic permeability material to define the shape of the magnetic flux concentrator;

[0034] Step 22: Annealing the magnetoresistive sensor to rearrange the magnetic domains of the magnetoresistive sensor element.

[0035] In addition, in order to achieve the above-mentioned purpose, the present invention also provides a method for preparing a low-frequency magnetoresistive sensor with two-stage amplification based on the electrostatic drive principle, comprising the following method steps:

[0036] Step 1: Clean Si / SiO with acetone, anhydrous ethanol, and deionized water in sequence 2 substrate;

[0037] Step 2: sputtering a magnetoresistive sensor element on the substrate using a magnetron sputtering device;

[0038] Step 3: After photolithography, etch the magnetoresistive sensor element to the bottom electrode, and etch the magnetoresistive sensor element into 180um 2 -270um 2 Rectangle of size;

[0039] Step 4: Etch the bottom electrode after photolithography to 1600um 2 -2400um 2 Square size;

[0040] Step 5: After photolithography, SiO is deposited using plasma enhanced chemical vapor deposition equipment. 2 Passivation layer;

[0041] Step 6: Stripping SiO 2 , exposing the top electrode and the bottom electrode;

[0042] Step 7: Sputtering of metal layer (Ti / Au, Ti / Al, Ti / Pt) after photolithography;

[0043] Step 8: Peeling off the metal layer (Ti / Au, Ti / Al, Ti / Pt) to define the top electrode and the bottom electrode shapes;

[0044] Step 9: Electroplating high magnetic permeability material after photolithography;

[0045] Step 10: peeling off the high magnetic permeability material to define the shape of the magnetic flux concentrator;

[0046] Step 11: sputtering high conductivity metal after photolithography;

[0047] Step 12: peeling off the high conductivity metal to define the shape of the AC excitation gate;

[0048] Step 13: After photolithography, PECVD equipment is used to deposit Si cantilever beams, sputter high conductivity metals, and electroplate high magnetic permeability materials in sequence;

[0049] Step 14: Remove the photoresist and clean the silicon wafer;

[0050] Step 15: Annealing the magnetoresistive sensor to rearrange the magnetic domains of the magnetoresistive sensor element.

[0051] The working principle of the two-stage amplified low-frequency magnetoresistive sensor provided by the present invention is that when a DC or low-frequency magnetic field is applied to the magnetoresistive sensor element, the detected magnetic field signal will be amplified successively by the second magnetic field line concentrator located on the surface of the MEMS resonator and the first magnetic field line concentrator located on both sides of the magnetoresistive sensor element, and at the same time, the MEMS resonator drives the second magnetic field line concentrator adhered to its surface to vibrate up and down. The magnetic field felt by the magnetoresistive sensor element also alternates between a maximum value and a minimum value over time, thereby, the magnetic field felt by the magnetoresistive sensor element is modulated from a DC or low frequency to an AC field with a higher frequency, thereby suppressing 1 / f noise. Since there are two-stage magnetic field line concentrators on both sides of the magnetoresistive sensor element to amplify the magnetic field, the AC sensitivity of the sensor can be greatly improved compared with the modulation scheme of single-stage amplification. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0053] Figure 1 A schematic structural diagram of an embodiment of a two-stage amplified low-frequency magnetoresistive sensor provided by the present invention.

[0054] Figure 2 This is a schematic structural diagram of another embodiment of the two-stage amplified low-frequency magnetoresistive sensor provided by the present invention.

[0055] Description of Figure Numbers:

[0056] Label name Label name 1 The first magnetic field concentrator 5 Metal layer 2 Piezoelectric drive layer 6 Second magnetic field concentrator 3 Magnetoresistive sensor element 7 AC Excitation Gate 4 Silicon layer

[0057] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0058] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0059] It should be noted that if a directional indication is involved in the embodiment of the present invention, the directional indication is only used to explain the relative position relationship, movement status, etc. between the components in a certain specific posture. If the specific posture changes, the directional indication will also change accordingly.

[0060] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the meaning of "and / or" appearing in the full text includes three parallel schemes. Taking "A and / or B" as an example, it includes scheme A, or scheme B, or a scheme that satisfies both A and B. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in this field to implement. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0061] Embodiment 1

[0062] See also Figure 1 The present invention discloses a two-stage amplified low-frequency magnetoresistive sensor 100 based on a piezoelectric driving principle, the specific contents of which are as follows:

[0063] The two-stage amplified low-frequency magnetoresistive sensor comprises a substrate, a magnetoresistive sensing element 3 , a silicon layer 4 , a piezoelectric driving layer 2 , and two first magnetic line concentrators 1 and a second magnetic line concentrator 6 .

[0064] The magnetoresistance sensing element 3 is arranged on the upper end surface of the substrate, the two first magnetic line concentrators 1 are symmetrically arranged on both sides of the magnetoresistance sensing element 3, the piezoelectric driving layer 2 is arranged on the upper end surface of the substrate, the silicon layer 4 is installed on the lower end surface of the substrate, and the second magnetic line concentrator 6 is arranged on the lower surface of the silicon layer 4.

[0065] By applying high-frequency alternating current to the piezoelectric material, the silicon layer 4 drives the second magnetic flux concentrator 6 adhered to its lower surface to vibrate up and down, and the magnetic field felt by the magnetoresistive sensor element also alternates between a maximum value and a minimum value over time. As a result, the magnetic field felt by the magnetoresistive sensor element is modulated from a DC or low frequency to an AC field with a higher frequency, thereby suppressing 1 / f noise. Since there are two-stage magnetic flux concentrators on both sides of the magnetoresistive sensor element to amplify the magnetic field, the AC sensitivity of the sensor can be greatly improved compared with the modulation scheme of single-stage amplification.

[0066] Figure 1 The preparation scheme of the two-stage amplified low-frequency magnetoresistive sensor 100 is as follows:

[0067] 1. Use acetone, anhydrous ethanol and deionized water to clean the SOI (Silicon-On-Insulator) substrate in sequence.

[0068] 2. Thermal oxidation of 300-600nm thick SiO on SOI substrate 2 .

[0069] 3. Sputter magnetoresistive sensor elements (AMR sensor device, GMR sensor device, TMR sensor device) on the substrate using a magnetron sputtering device.

[0070] 4. Etch the magnetoresistive sensor element after photolithography until the bottom electrode is etched into 180um 2 -270um 2 rectangle.

[0071] 5. Etch the bottom electrode after photolithography to 1600um 2 -2400um 2 square.

[0072] 6. After photolithography, SiO is deposited using plasma enhanced chemical vapor deposition (PECVD) equipment. 2 The passivation layer is used to prevent the magnetic layer of the magnetoresistive sensor element from being oxidized, and also to prevent the short circuit between the top electrode and the bottom electrode when the electrode is led out.

[0073] 7. Stripping SiO 2 , exposing the top electrode and the bottom electrode.

[0074] 8. Sputtering of metal layer (Ti / Au, Ti / Al, Ti / Pt) after photolithography.

[0075] 9. Peel off the metal layer to form the top electrode and bottom electrode shapes.

[0076] 10. Electroplating of high magnetic permeability materials (such as NiFe alloy, CoZrNb alloy) after photolithography.

[0077] 11. Peel off the high magnetic permeability material to form the shape of the magnetic field concentrator.

[0078] 12. Sputtering of piezoelectric materials (such as ZnO, AlN, PZT composite materials) after photolithography.

[0079] 13. Peel off the piezoelectric material to form the shape of the piezoelectric driving layer.

[0080] 14. After photolithography, use reactive ion etching (RIE) to etch SiO 2 , exposing part of the Si layer on the SOI wafer.

[0081] 15. Sputtering of metal layer (Ti / Au, Ti / Al, Ti / Pt) after photolithography.

[0082] 16. Peel off the metal layer to form the piezoelectric material electrode shape.

[0083] 17. After photolithography, deep reactive ion etching (DRIE) is used to etch the exposed Si layer on the SOI to form the shape of a cantilever beam.

[0084] 18. After photolithography, deep reactive ion etching (DRIE) is used to etch the Si layer on the back of SOI.

[0085] 19. After photolithography, reactive ion etching (RIE) is used to etch the SiO on the back of SOI. 2 layer, leaving the cantilever beam suspended in the air.

[0086] 20. Electroplating of high magnetic permeability material after photolithography.

[0087] 21. Peel off the high magnetic permeability material to form the shape of the magnetic field line concentrator.

[0088] 22. Annealing the magnetoresistive sensor to rearrange the magnetic domains of the magnetoresistive sensor element.

[0089] Among them, steps 1-9 are used to make a magnetoresistive sensor element; steps 10-11 are used to make a first magnetic field line concentrator; steps 12-19 are used to make a piezoelectrically driven vibration device; and steps 20-21 are used to make a second magnetic field line concentrator 6.

[0090] Example 2

[0091] See also Figure 2 The present invention discloses a two-stage amplified low-frequency magnetoresistive sensor 200 based on the electrostatic driving principle, the specific contents are as follows:

[0092] The two-stage amplified low-frequency magnetoresistive sensor comprises a substrate, a magnetoresistive sensing element 3, a silicon layer 4, a metal layer 5, two first magnetic flux concentrators 1 and a second magnetic flux concentrator 6, and an AC excitation gate 7.

[0093] The magnetoresistance sensor element 3 is arranged on the upper end surface of the substrate, the two first magnetic line concentrators 1 are symmetrically arranged on both sides of the magnetoresistance sensor element 3, the silicon layer 4 is installed on the upper end surface of the substrate, the metal layer 5 is installed on the upper surface of the silicon layer 4, the second magnetic line concentrator 6 is arranged on the upper surface of the metal layer 5, and the AC excitation gate 7 is arranged below the silicon layer 4.

[0094] Figure 2 The preparation scheme of the low-frequency magnetoresistive sensor 200 with two-stage amplification based on the electrostatic driving principle is as follows:

[0095] 1. Use acetone, anhydrous ethanol and deionized water to clean Si / SiO 2 Base.

[0096] 2. Sputter magnetoresistive sensor elements (AMR sensor device, GMR sensor device, TMR sensor device) on the substrate using a magnetron sputtering device.

[0097] 3. Etch the magnetoresistive sensor element after photolithography until the bottom electrode is etched into 180um 2 -270um 2 rectangle.

[0098] 4. Etch the bottom electrode after photolithography to 1600um 2 -2400um 2 square.

[0099] 5. After photolithography, SiO is deposited using plasma enhanced chemical vapor deposition (PECVD) equipment. 2 The passivation layer prevents the magnetic layer of the magnetoresistive sensor element from being oxidized, and also prevents short circuit between the top electrode and the bottom electrode when the electrode is led out.

[0100] 6. Stripping SiO 2 , exposing the top electrode and the bottom electrode.

[0101] 7. Sputter Ti / Au metal layer after photolithography.

[0102] 8. Peel off the metal layer to form the top electrode and bottom electrode shapes.

[0103] 9. Electroplating of high magnetic permeability materials (such as NiFe alloy, CoZrNb alloy) after photolithography.

[0104] 10. Stripping high magnetic permeability material alloy forms the shape of magnetic flux concentrator.

[0105] 11. Sputtering of high conductivity metals (such as Al, Ag, Au) after photolithography.

[0106] 12. Strip the metal to form the shape of the AC excitation gate.

[0107] 13. After photolithography, PECVD equipment is used to deposit Si cantilever beams, sputter high conductivity metals, and electroplate high magnetic permeability materials (such as NiFe alloys and CoZrNb alloys).

[0108] 14. Remove the photoresist and clean the silicon wafer.

[0109] 15. Annealing the magnetoresistive sensor to rearrange the magnetic domains of the magnetoresistive sensor element.

[0110] Among them, steps 1-8 are used to make a magnetoresistive sensor element; steps 9-10 are used to make a first magnetic field line concentrator; and steps 11-14 are used to make an electrostatic vibration device and a second magnetic field line concentrator.

[0111] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A two-stage amplified low-frequency magnetoresistive sensor, characterized in that: It includes a substrate, a magnetoresistive sensor element, a MEMS resonator, and a two-stage amplification modulation structure, wherein the magnetoresistive sensor element is arranged on the upper end surface of the substrate, the MEMS resonator is installed on the substrate, and the two-stage amplification modulation structure includes two first magnetic line concentrators and a second magnetic line concentrator, wherein the two first magnetic line concentrators are symmetrically arranged on both sides of the magnetoresistive sensor element, and the second magnetic line concentrator is arranged on the surface of the MEMS resonator and vibrates in the up and down directions under the drive of the MEMS resonator; The MEMS resonator comprises a silicon layer and a piezoelectric driving layer, the piezoelectric driving layer is arranged on the upper end surface of the substrate, the silicon layer is installed on the lower end surface of the substrate, and the second magnetic field line concentrator is arranged on the lower surface of the silicon layer; Alternatively, the MEMS resonator includes a silicon layer, a metal layer and an AC excitation gate, the silicon layer is installed on the upper end surface of the substrate, the metal layer is installed on the upper surface of the silicon layer, the second magnetic line concentrator is arranged on the upper surface of the metal layer, and the AC excitation gate is arranged below the silicon layer.

2. The two-stage amplified low-frequency magnetoresistive sensor according to claim 1, characterized in that: The magnetoresistive sensor element includes an AMR sensor device, a GMR sensor device, and a TMR sensor device.

3. The two-stage amplified low-frequency magnetoresistive sensor according to claim 1, characterized in that: The MEMS resonator includes a silicon layer and a piezoelectric driving layer, wherein the piezoelectric driving layer is arranged on the upper end surface of the substrate, the silicon layer is mounted on the lower end surface of the substrate, and the second magnetic flux concentrator is arranged on the lower surface of the silicon layer.

4. A method for preparing a two-stage amplified low-frequency magnetoresistive sensor, applied to the two-stage amplified low-frequency magnetoresistive sensor as claimed in claim 1, characterized in that: The method comprises the following steps: Step 1: Clean the SOI substrate with acetone, anhydrous ethanol, and deionized water in sequence; Step 2: thermally oxidizing 300-600 nm thick SiO2 on the SOI substrate; Step 3: sputtering a magnetoresistive sensor element on the SOI substrate using a magnetron sputtering device; Step 4: After photolithography, the magnetoresistive sensor element is etched to the bottom electrode, and the magnetoresistive sensor element is etched into 180 -270 Rectangle of size; Step 5: Etch the bottom electrode after photolithography to 1600 -2400 Square size; Step 6: After photolithography, a SiO2 passivation layer is deposited using a plasma enhanced chemical vapor deposition device; Step 7: peeling off the SiO2 passivation layer in step 6 to expose the top electrode and the bottom electrode; Step 8: sputtering a metal layer after photolithography, wherein the metal layer includes Ti / Au, Ti / Al or Ti / Pt; Step 9: peeling off the metal layer in step 8 to define the shapes of the top electrode and the bottom electrode; Step 10: Electroplating high magnetic permeability material after photolithography; Step 11: peeling off the high magnetic permeability material to define the shape of the first magnetic flux concentrator; Step 12: sputtering piezoelectric material after photolithography; Step 13: peeling off the piezoelectric material to define the shape of the piezoelectric driving layer; Step 14: After photolithography, SiO2 is etched using reactive ion etching to expose a portion of the Si layer on the SOI wafer; Step 15: sputtering the metal layer after photolithography, wherein the metal layer includes Ti / Au, Ti / Al or Ti / Pt; Step 16: peeling off the metal layer in step 15 to define the shape of the piezoelectric material electrode; Step 17: After photolithography, the exposed Si layer on the SOI is etched using deep reactive ion etching to define the shape of the cantilever beam; Step 18: After photolithography, the Si layer on the back of the SOI is etched using deep reactive ion etching; Step 19: After photolithography, the SiO2 layer on the back of the SOI is etched using reactive ion etching to leave the cantilever beam suspended in the air; Step 20: Electroplating high magnetic permeability material after photolithography; Step 21: peeling off the high magnetic permeability material to define the shape of the second magnetic flux concentrator; Step 22: Annealing the magnetoresistive sensor to rearrange the magnetic domains of the magnetoresistive sensor element.

5. A method for preparing a two-stage amplified low-frequency magnetoresistive sensor, applied to the two-stage amplified low-frequency magnetoresistive sensor as claimed in claim 1, characterized in that: The method comprises the following steps: Step 1: Clean the Si / SiO2 substrate with acetone, anhydrous ethanol, and deionized water in sequence; Step 2: sputtering a magnetoresistive sensor element on the substrate using a magnetron sputtering device; Step 3: After photolithography, the magnetoresistive sensor element is etched to the bottom electrode, and the magnetoresistive sensor element is etched into 180 -270 Rectangle; Step 4: Etch the bottom electrode after photolithography to 1600 -2400 square; Step 5: After photolithography, a SiO2 passivation layer is deposited using a plasma enhanced chemical vapor deposition device; Step 6: Peel off the SiO2 passivation layer in step 5 to expose the top electrode and the bottom electrode; Step 7: sputtering a metal layer after photolithography, wherein the metal layer includes Ti / Au, Ti / Al or Ti / Pt; Step 8: peeling off the metal layer in step 7 to define the shapes of the top electrode and the bottom electrode; Step 9: Electroplating high magnetic permeability material after photolithography; Step 10: peeling off the high magnetic permeability material to define the shape of the first magnetic flux concentrator; Step 11: sputtering high conductivity metal after photolithography; Step 12: peeling off the high conductivity metal to define the shape of the AC excitation gate; Step 13: After photolithography, PECVD equipment is used to deposit Si cantilever beams, sputter high conductivity metals, and electroplate high magnetic permeability materials in sequence; Step 14: Remove the photoresist and clean the silicon wafer; Step 15: Annealing the magnetoresistive sensor to rearrange the magnetic domains of the magnetoresistive sensor element.

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