Magnetic field sensor, operation method, preparation method and electronic equipment

Abstract

A magnetic field sensor, an operation method, a preparation method, and an electronic device, the magnetic field sensor comprising: a piezoelectric layer, a pair of interdigital electrodes disposed on a first surface of the piezoelectric layer and configured to receive an external signal to measure an input return loss of the magnetic field sensor, and a ferromagnetic layer disposed on a second surface of the piezoelectric layer, the ferromagnetic layer is arranged on the first surface of the piezoelectric layer, is insulated from the interdigital electrode pair and is configured as an acoustic waveguide, and the ferromagnetic layer generates magnetostriction under the action of an external magnetic field so as to change the equivalent sound velocity of the magnetic field sensor. The magnetic field sensor can realize controllable expansion of the thickness of the magnetic acoustic wave guide layer, and the detection sensitivity of the magnetic field sensor is improved.

Description

Technical Field

[0001] Embodiments of the present disclosure relate to a magnetic field sensor and an operating method thereof, a method for preparing the magnetic field sensor, and an electronic device. Background Art

[0002] A magnetic field sensor is a device that converts the external magnetic field to be measured and its changes into a measurable electrical signal response output. This conversion allows the magnetic field information to be recognized and processed by electronic systems, making magnetic field sensors widely used in many fields, including navigation and positioning, safety monitoring, automotive driving assistance, scientific research, industrial automation, medical diagnosis and medical equipment.

[0003] Existing magnetic field sensors include many types, but there are still problems such as insufficient detection limit, high power consumption, difficulty in miniaturization, and limitations between sensitive areas and measurement limits. They cannot meet the requirements of small size, high integration, high sensitivity, and low detection limit. Summary of the invention

[0004] At least some embodiments of the present disclosure provide a magnetic field sensor, which includes a piezoelectric layer, a pair of interdigitated electrodes, and a ferromagnetic layer, wherein the pair of interdigitated electrodes is disposed on a first surface of the piezoelectric layer and is configured to receive an external signal to measure an input return loss of the magnetic field sensor, the ferromagnetic layer is disposed on the first surface and is insulated from the pair of interdigitated electrodes, and is configured as an acoustic waveguide, and the ferromagnetic layer undergoes magnetostriction under the action of an external magnetic field to change the equivalent sound velocity of the magnetic field sensor.

[0005] For example, at least some embodiments of the present disclosure provide a magnetic field sensor that further includes a reflection grating disposed on the first surface and at least outside at least one side of the interdigital electrode pair.

[0006] For example, in a magnetic field sensor provided by at least some embodiments of the present disclosure, the reflection grating includes a metal line formed on the piezoelectric layer, and a trench or a step formed on the first surface.

[0007] For example, at least some embodiments of the present disclosure provide a magnetic field sensor further comprising an insulating layer disposed between the ferromagnetic layer and the interdigital electrode pair so that the interdigital electrode pair and the ferromagnetic layer are insulated from each other by the insulating layer.

[0008] For example, in a magnetic field sensor provided by at least some embodiments of the present disclosure, the ferromagnetic layer covers the interdigital electrode pairs and the reflective grating via the insulating layer.

[0009] For example, in a magnetic field sensor provided by at least some embodiments of the present disclosure, the interdigital electrode pair includes a first interdigital electrode pair and a second interdigital electrode pair, and the second interdigital electrode pair is separated from the first interdigital electrode pair by a delay line.

[0010] For example, at least some embodiments of the present disclosure provide a magnetic field sensor further comprising an insulating layer, wherein the insulating layer is disposed on a side of the interdigitated electrode pair away from the piezoelectric layer, and the ferromagnetic layer is disposed on the first surface at least via the insulating layer.

[0011] For example, in a magnetic field sensor provided by at least some embodiments of the present disclosure, the ferromagnetic layer is further configured so that the surface acoustic waves propagating under the action of the external magnetic field include Love wave modes.

[0012] For example, in a magnetic field sensor provided by at least some embodiments of the present disclosure, the ferromagnetic layer includes n layers of magnetostrictive material stacked in sequence relative to the surface of the piezoelectric layer, where n is a positive integer greater than or equal to 2.

[0013] At least some embodiments of the present disclosure further provide an electronic device, which includes the magnetic field sensor provided by any embodiment of the present disclosure.

[0014] At least some embodiments of the present disclosure also provide an operating method for a magnetic field sensor, the operating method comprising: obtaining a first input return loss of the magnetic field sensor measured by receiving an external signal through the interdigitated electrode pair under the external magnetic field; obtaining a second input return loss of the magnetic field sensor measured by receiving an external signal through the interdigitated electrode pair in the absence of any external magnetic field; determining a frequency offset between the first input return loss and the second input return loss, and determining the magnitude of the external magnetic field based on a mapping relationship between the frequency offset and a value of a calibration magnetic field.

[0015] At least some embodiments of the present disclosure also provide a method for preparing a magnetic field sensor, the method comprising: forming a pair of interdigitated electrodes on a first surface on one side of a piezoelectric layer, and forming a ferromagnetic layer on the first surface, wherein the ferromagnetic layer and the pair of interdigitated electrodes are insulated from each other, wherein the pair of interdigitated electrodes are configured to receive an external signal to measure an input return loss of the magnetic field sensor, and the ferromagnetic layer is configured as an acoustic waveguide and undergoes magnetostriction under the action of an external magnetic field to change the equivalent sound velocity of the magnetic field sensor.

[0016] For example, in a method for preparing a magnetic field sensor provided in at least some embodiments of the present disclosure, forming a ferromagnetic layer on the first surface includes: stacking n layers of magnetostrictive material layers on the first surface to form a ferromagnetic layer, where n is a positive integer greater than or equal to 2.

[0017] For example, in a method for preparing a magnetic field sensor provided by at least some embodiments of the present disclosure, stacking n magnetostrictive material layers to form a ferromagnetic layer includes: stacking n magnetostrictive material layers to form a ferromagnetic layer using an adhesive or bonding process. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the drawings of the embodiments will be briefly introduced below. Obviously, the drawings in the following description only relate to some embodiments of the present disclosure, but are not intended to limit the present disclosure.

[0019] Figure 1 A schematic diagram of the structure of a magnetic field sensor provided in some embodiments of the present disclosure;

[0020] Figure 2 A partial structural schematic diagram of a magnetic field sensor provided in some embodiments of the present disclosure;

[0021] Figure 3 A partial structural schematic diagram of another magnetic field sensor provided in other embodiments of the present disclosure;

[0022] Figure 4 A flowchart of an operating method of a magnetic field sensor provided in some embodiments of the present disclosure;

[0023] Figure 5 A flow chart of a method for preparing a magnetic field sensor provided in some embodiments of the present disclosure;

[0024] Figure 6 A flow chart of a process for preparing a magnetic field sensor provided in some embodiments of the present disclosure;

[0025] Figure 7 A schematic diagram of the structure of a ferromagnetic layer provided for some embodiments of the present disclosure; and

[0026] Figure 8 A simulation curve showing that the frequency offset of a magnetic field sensor provided in some embodiments of the present disclosure varies with the thickness of a ferromagnetic layer. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solution and advantages of the embodiments of the present disclosure clearer, the technical solution of the embodiments of the present disclosure will be clearly and completely described below in conjunction with the drawings of the embodiments of the present disclosure. Obviously, the described embodiments are part of the embodiments of the present disclosure, not all of the embodiments. Based on the described embodiments of the present disclosure, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present disclosure.

[0028] Unless otherwise defined, the technical terms or scientific terms used in the present disclosure should be understood by people with ordinary skills in the field to which the present disclosure belongs. The "first", "second" and similar words used in the present disclosure do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0029] The present disclosure is described below through several specific embodiments. In order to keep the following description of the embodiments of the present disclosure clear and concise, detailed descriptions of known functions and known components (elements) may be omitted. When any component (component) of the embodiments of the present disclosure appears in more than one drawing, the component (component) is represented by the same or similar reference numeral in each drawing.

[0030] Magnetic field sensors can be classified according to their acoustic response characteristics, and can include non-acoustic resonant magnetic field sensors and acoustic resonant magnetic field sensors.

[0031] Among non-acoustic resonant magnetic field sensors, the superconducting quantum interference device (SQUID) is essentially a flux sensor that converts magnetic flux into voltage. Its basic principle is based on the superconducting Josephson effect and the phenomenon of magnetic flux quantization. When a superconductor closed loop containing a Josephson tunnel junction is biased by a current of appropriate size, a macroscopic quantum interference phenomenon will be presented, that is, the voltage at both ends of the tunnel junction is a periodic function of the change in the external magnetic flux in the loop hole of the closed loop. This periodic change enables the SQUID to detect tiny changes in the magnetic field extremely sensitively. The optical-pumping magnetometer (OPM) is based on the magnetic resonance absorption (optical pump absorption) phenomenon of helium, mercury, nitrogen, hydrogen, and alkali metals such as rubidium and cesium under specific conditions. The frequency of the electromagnetic field absorbed by the optical pump is proportional to the strength of the external magnetic field, and the value of the external magnetic field can be obtained based on this frequency.

[0032] Hall magnetic field sensor refers to a magnetic field sensor made by using the Hall effect of some semiconductor materials. The Hall effect refers to the phenomenon that when a current passes through a conductor in a magnetic field, an electric potential is generated in the conductor perpendicular to the direction of the current and the external magnetic field. Anisotropic magnetoresistance sensor (AMR) is a magnetic field sensor made of anisotropic materials and sensing magnetic field changes based on the magnetoresistance effect. Giant magnetoresistance (GMR) magnetic field sensor uses the giant magnetoresistance effect of certain magnetic or alloy materials to sense the external magnetic field. When the external magnetic field acts on these magnetic or alloy materials through the giant magnetoresistance effect, their resistance will change greatly. Tunnel magnetoresistance (TMR) magnetic field sensor uses the tunnel magnetoresistance effect of magnetic multilayer film materials to sense the magnetic field. The magnetic tunnel resistance effect uses the magnetic tunnel junction (MTJ) made by multilayer thin film preparation technology as a magnetic sensitive element. The general structure of MTJ is a "sandwich" structure of ferromagnetic layer / non-magnetic insulating layer / ferromagnetic layer. The inductive magnetic field sensor is based on Faraday's law of electric field induction. Its basic component is a coil. It senses the external AC magnetic field through the induced current generated by the change of magnetic flux in the coil. The fluxgate sensor measures the external magnetic field through the mechanism that the external magnetic field affects the magnetization of the magnetic core. It consists of three structures: a magnetic core, an excitation coil, and a detection coil.

[0033] Among the aforementioned non-acoustic resonant magnetic field sensors, SQUID and OPM have extremely high measurement accuracy and extremely high magnetic field detection limits, which are about the order of fT, but they are large in size, work in a low-temperature environment, and are difficult to miniaturize and integrate. Hall magnetic field sensors have the advantages of simple principle, small size, low power consumption, high reliability, and low cost, but their magnetic field detection limits are limited by physical properties and are only in the order of uT, which cannot meet the requirements of high-precision magnetic field measurement. AMR, GMR, and TMR magnetic field sensors are micromagnetic sensors based on the magnetoresistance effect, which have the advantages of small size and easy integration, but poor magnetic field detection limits. Fluxgate sensors and inductive magnetic field sensors have simple working principles and are easy to make, but the device sensitivity and size are seriously contradictory, and the magnetic field resolution is relatively poor.

[0034] Acoustic resonant magnetic field sensors are mainly composed of piezoelectric materials and magnetostrictive materials, and they work at the acoustic resonance frequency of the device. Acoustic resonant magnetic field sensors are divided into two categories: active acoustic resonant magnetic field sensors and passive acoustic resonant magnetic field sensors (hereinafter referred to as active magnetic field sensors and passive magnetic field sensors).

[0035] The working principle of the active magnetic field sensor is to sense the size of the magnetic field by detecting the changes in the device's resonant frequency or related electrical parameters under the action of the external magnetic field to be measured; the working principle of the passive magnetic field sensor is that under the action of the external AC magnetic field, the magnetic material produces periodic deformation due to the magnetostrictive effect, causing the acoustic resonance of the piezoelectric-ferromagnetic composite structure, so that the piezoelectric layer produces an electrical signal output due to the piezoelectric effect, and the size of the external magnetic field to be measured is sensed by detecting the output electrical signal.

[0036] Passive magnetic field sensors have high detection sensitivity for external AC magnetic fields at resonant frequencies, but have weaker detection capabilities for external magnetic fields at non-resonant frequencies. In addition, lowering its operating frequency means an increase in device size, which is not conducive to the miniaturization of sensor devices. Existing passive magnetic field sensors include delay line-based surface acoustic wave magnetic field sensors and resonance-based surface acoustic wave magnetic field sensors. In a delay line-based surface acoustic wave magnetic field sensor, the magnetic material interacts with the acoustic wave through the interface. The sensitivity of the sensor can be improved by increasing the length of the delay line, but this will reduce the signal-to-noise ratio of the receiver and increase the size of the device. The resonant surface acoustic wave magnetic field sensor uses thick silicon oxide as the waveguide layer and thin magnetic material as the sensitive layer, which will cause acoustic energy leakage.

[0037] At present, active magnetic field sensors are manufactured using the Micro-Electro-Mechanical Systems (MEMS) process. Since the magnetic sensitive layer used to sense the size of the external magnetic field is grown by magnetron sputtering, it is impossible to prepare a thick film of the magnetic sensitive layer. The thickness of the magnetic sensitive layer limits the further improvement of the performance of the active magnetic field sensor.

[0038] The present disclosure provides a magnetic field sensor, comprising a piezoelectric layer, a pair of interdigital electrodes and a ferromagnetic layer. The interdigital electrode pair is arranged on a first surface of the piezoelectric layer and is configured to receive an external signal to measure the input return loss of the magnetic field sensor. The ferromagnetic layer is arranged on the first surface of the piezoelectric layer and is insulated from the interdigital electrode pair. The ferromagnetic layer is configured as an acoustic waveguide. Under the action of an external magnetic field, the ferromagnetic layer undergoes magnetostriction to change the equivalent sound velocity of the magnetic field sensor.

[0039] The magnetic field sensor provided by the above-mentioned embodiments of the present disclosure utilizes a ferromagnetic layer as an acoustic waveguide to gather acoustic energy in the ferromagnetic layer, thereby enhancing the interaction between the surface acoustic wave and the magnetic sensitive layer, and thus improving the sensor's detection sensitivity to the external magnetic field; and, in at least one example, the magnetic field sensor can increase the sensitive area of ​​the magnetic field sensor device by increasing the thickness of the ferromagnetic layer, thereby improving the magnetic field detection sensitivity of the magnetic field sensor, reducing the magnetic field detection limit of the magnetic field sensor, and achieving a substantial improvement in the sensing performance of the acoustic resonance type magnetic field sensor.

[0040] Figure 1 It is a schematic diagram of the structure of the magnetic field sensor provided in some embodiments of the present disclosure.

[0041] like Figure 1 As shown, the magnetic field sensor 100 includes a piezoelectric layer 110, a pair of interdigitated electrodes 120, and a ferromagnetic layer 140. For example, the pair of interdigitated electrodes 120 is disposed on the first surface (the upper surface in the figure) of the piezoelectric layer 110; the ferromagnetic layer 140 is also disposed on the first surface of the piezoelectric layer 110 and is insulated from the pair of interdigitated electrodes 120. For example, the pair of interdigitated electrodes 120 is disposed on a side away from the piezoelectric layer 110. The ferromagnetic layer 140 is configured as an acoustic waveguide, and magnetostriction occurs under the action of an external magnetic field to change the equivalent sound velocity of the magnetic field sensor 100. Figure 1 The illustrated magnetic field sensor may further include an insulating layer 130 disposed between the ferromagnetic layer 140 and the interdigital electrode pair 120 to insulate the interdigital electrode pair 120 and the ferromagnetic layer 140 from each other.

[0042] The sensing mechanism of the magnetic field sensor provided by the above-mentioned embodiment of the present disclosure is based on the magnetostrictive effect of the magnetic material in the ferromagnetic layer. The magnetostrictive effect refers to the deformation of the magnetic material under the action of an external magnetic field, which causes the Young's modulus of the magnetic material to change, also known as the ΔE effect. The change in Young's modulus will affect the resonant frequency of the acoustic resonator, and the change in the resonant frequency will be reflected in the electrical parameters of the magnetic field sensor, such as the input return loss. The detection of the external magnetic field size can be achieved by completing the input return loss test of the magnetic field sensor through the interdigitated electrodes on the surface of the piezoelectric layer.

[0043] The magnetic field sensor in the above embodiment is a surface acoustic wave device, and its operating frequency is affected by the period length of the interdigital electrode pair and the structural sound velocity, which is specifically expressed as follows:

[0044] fres=v / λ

[0045] Wherein, fres represents the operating frequency of the magnetic field sensor, v represents the equivalent sound velocity of the magnetic field sensor, and λ represents the period length of the interdigital electrode pair.

[0046] The equivalent sound velocity of the magnetic field sensor is jointly affected by the piezoelectric layer, the interdigital electrode pair and the ferromagnetic layer. When the relative frequency offset of the magnetic field sensor is constant, the higher the operating frequency, the greater the absolute frequency offset of the input return loss of the magnetic field sensor, and the higher the sensitivity. However, the operating frequency will affect the back-end readout circuit of the magnetic field sensor. The reduction of the operating frequency of the magnetic field sensor can reduce the design difficulty of the back-end circuit to reduce the complexity of the entire system. The equivalent sound velocity of the magnetic field sensor can be reduced by increasing the thickness of the ferromagnetic layer to reduce the operating frequency of the magnetic field sensor and the complexity of the entire sensor system. Therefore, the magnetic field sensor provided in the embodiment of the present disclosure can be designed according to the requirements of the sensitivity and linear range of the magnetic field sensor in practical applications.

[0047] In the magnetic field sensors provided in some embodiments of the present disclosure, the surface acoustic waves propagated by the ferromagnetic layer under the action of the external magnetic field include Love wave modes. Love waves are a type of horizontal shear wave that tends to propagate in a waveguide layer with a lower sound velocity. In the magnetic field sensors of the above embodiments, the sound velocity of the ferromagnetic layer is lower than that of the piezoelectric layer, so the ferromagnetic layer has a better capture effect on the Love waves, which can better concentrate the sound waves to improve the sensitivity of the magnetic field sensor. It should be noted that the magnetic field sensor provided in the embodiments of the present disclosure can be excited by non-single acoustic surface waves such as high-order Love waves, Sisava waves, etc., so that the sensor performance can be better stimulated.

[0048] In the magnetic field sensor provided by some embodiments of the present disclosure, the piezoelectric material forming the piezoelectric layer includes, for example, bulk piezoelectric materials, such as PZT (lead zirconate titanate), PMN-PT (lead magnesium niobate-lead titanate), LiNbO3 (lithium niobate) of different tangents, LiTaO3 (lithium tantalate) of different tangents, and Quartz (quartz). The piezoelectric material may also include, for example, a composite structure substrate bonded or grown with a piezoelectric film, so as to adjust the working performance of the magnetic field sensor by changing the substrate configuration. In the magnetic field sensor provided by some embodiments of the present disclosure, for example, the piezoelectric material forming the piezoelectric layer may adopt a composite structure bonded or grown with a piezoelectric film. Piezoelectric film materials include, for example, AlN (aluminum nitride), ZnO (zinc oxide), GaN (gallium nitride), PZT (lead zirconate titanate), LiNbO3 (lithium niobate) of different tangents, LiTaO3 (lithium tantalate), etc.; the substrate is used to support the piezoelectric film, including, for example, Si (silicon), SiO (silicon oxide), SiC (silicon carbide), SiN (silicon nitride), diamond, sapphire, etc.

[0049] In the magnetic field sensor provided in some embodiments of the present disclosure, the material used to form the interdigital electrode pair includes Ti (titanium), Al (aluminum), Cu (copper), Pt (platinum), Mo (molybdenum), Au (gold), Ag (silver), etc. and any alloy thereof.

[0050] In the magnetic field sensors provided in some embodiments of the present disclosure, the materials used to form the ferromagnetic layer include, for example, Metglas (metallic glass), FeGaB (iron gallium boron), FeGaC (iron gallium carbon), Terfenol-D (Tb-Dy-Fe), Ni (nickel), Fe (iron), FeGa (iron gallium), CoFe (cobalt iron), CoFeO (cobalt iron oxide), NiFe (nickel iron), FeAl (iron aluminum), YIG (yttrium iron garnet) and other magnetostrictive metals and alloy strips.

[0051] It should be noted that the above description of the materials used for the piezoelectric layer, the interdigital electrode pair, and the ferromagnetic layer of the magnetic field sensor provided by the present disclosure should not be regarded as a limitation to the present disclosure.

[0052] Figure 2 A partial structural schematic diagram of a magnetic field sensor provided in some embodiments of the present disclosure.

[0053] Figure 2 The magnetic field sensor 200 shown includes a piezoelectric layer 210 , an interdigital electrode pair 220 , and a reflection grating 250 . The interdigital electrode pair 220 and the reflection grating 250 are disposed on the surface of the piezoelectric layer 210 , and the reflection grating 250 is disposed outside the interdigital electrode pair 220 .

[0054] For example, in the magnetic field sensor 200 , the interdigital electrode pairs 220 are arranged periodically, and their width may be λ / 4, where λ is the acoustic wavelength at the corresponding frequency.

[0055] For example, Figure 2 The magnetic field sensor 200 shown can be called a resonant magnetic field sensor. Under the action of the external magnetic field, due to the magnetostrictive effect, the magnetic material undergoes periodic deformation, causing the acoustic resonance frequency of the piezoelectric-ferromagnetic composite structure to change. By testing the input return loss of the magnetic field sensor through the interdigital electrodes under different external magnetic fields to obtain the relationship between the operating frequency and the external magnetic field, the frequency offset can be obtained, thereby realizing the perception of the external magnetic field to be measured.

[0056] For example, the magnetic field sensor provided by the above-mentioned embodiment of the present disclosure can design the interdigital electrode pair into a single-port or dual-port structure according to the application scenario or test requirements.

[0057] like Figure 2 The reflection grating 250 shown may be formed by metal lines on the piezoelectric layer 210 , or may be formed by, for example, etching to form a trench on the surface of the piezoelectric layer 210 or, for example, forming a step at the edge of the piezoelectric layer 210 as the reflection grating.

[0058] In the magnetic field sensor provided by the above embodiments of the present disclosure, the function of the reflective grating is to reasonably limit the acoustic energy so that the magnetic field sensor can achieve better working characteristics. It should be noted that: Figure 2 Some of the interdigital electrode pairs 220 are led out through the outside of the reflective grid 250 for the convenience of testing, and the present disclosure does not impose any limitation on this.

[0059] A magnetic field sensor provided in the above-mentioned embodiments of the present disclosure may also include an insulating layer, for example, the insulating layer is disposed between the ferromagnetic layer and the interdigital electrode pair, so that the interdigital electrode pair and the ferromagnetic layer are insulated from each other by the insulating layer. It should be noted that in the magnetic field sensor provided in some embodiments of the present disclosure, the insulating layer is disposed to avoid the interference of the conductivity of the ferromagnetic layer caused by material properties on the interdigital electrode pair. For example, in Figure 2 The magnetic field sensor 200 shown also includes an insulating layer and a ferromagnetic layer ( Figure 2 (not shown in the figure), the ferromagnetic layer may cover the interdigital electrode pair 220 and the reflective grating 250 through an insulating layer.

[0060] Figure 3 A partial structural schematic diagram of another magnetic field sensor provided in some embodiments of the present disclosure.

[0061] Figure 3 The magnetic field sensor 300 shown includes a piezoelectric layer 310, a first interdigital electrode pair 321, a second interdigital electrode pair 322, and a delay line 360. The first interdigital electrode pair 321 and the second interdigital electrode pair 322 are arranged on a surface of one side of the piezoelectric layer 310, and the first interdigital electrode pair 321 and the second interdigital electrode pair 322 are separated by the delay line 360.

[0062] For example, the first interdigital electrode pair 321 and the second interdigital electrode pair 322 can be used as a transmitting electrode and a receiving electrode, respectively. For example, in the magnetic field sensor provided in the above embodiment, the transmitting electrode and the receiving electrode are configured to receive / output an alternating voltage. For example, the first interdigital electrode pair 321 and the second interdigital electrode pair 322 are separated by a delay line 360.

[0063] In a surface acoustic wave device such as the magnetic field sensor provided in the above embodiment, for example, the propagation region formed by using the piezoelectric material of the piezoelectric layer as the propagation medium of the surface acoustic wave (for example, the ferromagnetic layer can also be used as the propagation medium) can be called a delay line (or delay region). For example, reference can be made to Figure 3 Delay line 360 ​​is shown.

[0064] like Figure 3 The magnetic field sensor 300 shown may be referred to as a delay line type magnetic field sensor. The delay line type magnetic field sensor also tests its input return loss through the interdigital electrode pair and detects the external magnetic field through the operating frequency offset.

[0065] In the magnetic field sensor provided in the above embodiment, an insulating layer ( Figure 3 (not shown in the figure), the insulating layer is arranged on the side of the interdigital electrode pair away from the piezoelectric layer, and the ferromagnetic layer is arranged on the first surface of the piezoelectric layer at least through the insulating layer.

[0066] For example, the ferromagnetic layer can be directly arranged on the delay line, and the ferromagnetic layer can be prevented from directly contacting the interdigital electrodes without the need for an insulating layer. For example, when the surface acoustic wave mode is a Love wave mode, an insulating layer covering the interdigital electrode pair can be arranged. For a delay line type magnetic field sensor, the ferromagnetic layer can be arranged on the delay line.

[0067] At least one embodiment of the present disclosure further provides an electronic device, which includes the magnetic field sensor of any of the above embodiments.

[0068] Figure 4 A flowchart of an operating method of a magnetic field sensor provided in some embodiments of the present disclosure is shown, and the operating method includes steps S10-S30.

[0069] Step S10, obtaining the first input return loss of the magnetic field sensor measured by receiving an external signal through the interdigital electrodes under an external magnetic field, and obtaining the first input return loss. The input return loss is an indicator to measure the size of the reflected signal at the input port of the device, which can indicate the size of the reflected signal relative to the incident signal, and is usually expressed in decibels (dB). The larger the value, the smaller the reflected signal and the better the matching.

[0070] Step S20 , obtaining a second input return loss of the magnetic field sensor measured by receiving an external signal through the interdigital electrode pair in the absence of any external magnetic field.

[0071] In step S20, in the absence of any external magnetic field, an external signal is received through the interdigitated electrode pair in the same manner as in step S10 to obtain the measured second input return loss of the magnetic field sensor. It should be noted that there is no sequential relationship between the execution of step S10 and the execution of step S20. For example, step S20 can be executed in advance before using the magnetic field sensor to measure the external magnetic field, and the second input return loss is obtained and stored, and then step S10 is executed. It is also possible to execute step S10 first and then step S20 when using the magnetic field sensor in real time.

[0072] Step S30, determining the frequency offset between the first input return loss and the second input return loss, and determining the magnitude of the external magnetic field according to a mapping relationship between the frequency offset and the value of the calibration magnetic field.

[0073] According to the working principle of the magnetic field sensor provided by the above embodiment of the present disclosure, there is a frequency offset between the first input return loss and the second input return loss. For example, the frequency point at which the first input return loss has a minimum value can be compared with the frequency point at which the second input return loss has a minimum value to obtain the frequency offset.

[0074] The magnetic field sensor provided in the embodiment of the present disclosure can be calibrated in advance to determine the external magnetic field value according to the frequency offset in actual measurement. For example, the magnetic field sensor can be calibrated before being used to measure the external magnetic field. In the calibration stage, a standard magnetic field source is used to generate magnetic fields of different strengths, and the frequency offset under different magnetic field strengths is obtained by using the above-mentioned test input return loss method, and a mapping relationship between the frequency offset and the value of the calibration magnetic field is established to determine the size of the external magnetic field according to the mapping relationship.

[0075] It should be noted that for the magnetic field sensor provided in the embodiment of the present disclosure, a network analyzer or a signal source can be used as an external signal to test the input return loss, or an auxiliary circuit with the same function can be built to test the magnetic field sensor. The use of the auxiliary circuit is conducive to the system integration of the magnetic field sensor.

[0076] Figure 5 A flow chart of a method for preparing a magnetic field sensor provided in some embodiments of the present disclosure is shown, and the method comprises steps S100-S200.

[0077] Step S100: forming an interdigital electrode pair on a first surface of one side of the piezoelectric layer.

[0078] The interdigitated electrode pairs are configured to receive an applied signal to measure an input return loss of the magnetic field sensor.

[0079] Step S200: forming a ferromagnetic layer on a first surface of the piezoelectric layer, wherein the ferromagnetic layer and the interdigital electrode pairs are insulated from each other.

[0080] The ferromagnetic layer is configured as an acoustic waveguide and undergoes magnetostriction under the action of an external magnetic field to change the equivalent acoustic velocity of the magnetic field sensor.

[0081] Figure 6 The following is a flow chart of the preparation process of the magnetic field sensor provided in some embodiments of the present disclosure. Figure 6 right Figure 5 The preparation method is described in detail.

[0082] In step S100, the interdigital electrode pairs may be formed by using a metal lift-off patterning process or a metal etching patterning process. Figure 6 The steps of photolithography of the interdigital electrode layer - metal growth of the interdigital electrode pair - lift-off and patterning of the interdigital electrode pair are used to form the interdigital electrode pair.

[0083] After step S100, an insulating layer may be formed on the surface of the piezoelectric layer on the interdigital electrode pair. For example, a magnetron sputtering process (physical vapor deposition) or a chemical vapor deposition process may be used. Figure 6 The spin coating / growth method shown is used to form an adhesive layer as an insulating layer on the interdigital electrode pairs of the piezoelectric layer.

[0084] Spin coating is a process that can be used to deposit dielectric insulators and organic material layers. Spin coating equipment is simple, requiring only a variable speed rotating stage with appropriate safety barriers, and then using a nozzle to drop the material in the form of a liquid solution onto the surface of the interdigitated electrode pair. The rotating stage can rotate the piezoelectric layer and interdigitated electrode pair at a speed of 500 to 5,000 rpm for 30 to 60 seconds to spread the material to a uniform thickness.

[0085] In the method for preparing a magnetic field sensor provided by some embodiments of the present disclosure, step S200 may include step S210.

[0086] S210, stacking n layers of magnetostrictive material layers on a first surface of the piezoelectric layer to form a ferromagnetic layer, where n is a positive integer greater than or equal to 2.

[0087] In step S210, stacking n magnetostrictive material layers to form a ferromagnetic layer may include stacking n magnetostrictive material layers to form a ferromagnetic layer using an adhesive or bonding process. Figure 6 As shown, a bonding or adhesive process is used to connect every two magnetostrictive material layers, and the connection process is repeated n-1 times to form n stacked magnetostrictive material layers.

[0088] On the surface of the n-layer stacked magnetostrictive material layer, that is, on the surface of the ferromagnetic layer, you can use Figure 6 The bonding layer is made by the spin coating / growth method shown in the figure. The bonding layer of the piezoelectric layer and the ferromagnetic layer can be fused and cured by thermocompression bonding (TCB), thereby completing the bonding of the piezoelectric layer and the magnetostrictive material layer.

[0089] Thermocompression bonding is a process in which the end of a welding wire (such as a gold wire) is melted into a ball shape by the pressure of a hot press head under high temperature and high pressure conditions, and the ball end is pressed and welded to the port or surface to be connected by a wire feeding press head to form a reliable electrical connection.

[0090] Figure 7 A schematic structural diagram of a ferromagnetic layer provided in some embodiments of the present disclosure is shown.

[0091] Figure 7 The ferromagnetic layer 141 shown includes n magnetostrictive material layers 142 stacked in sequence relative to the surface of the piezoelectric layer, where n is a positive integer greater than or equal to 2. Figure 7 The thicknesses of the medium magnetostrictive material layer 142 and the adhesive layer 143 are for illustration only and should not be considered as limitations of the present disclosure.

[0092] For example, the ferromagnetic layer provided in the above embodiment of the present disclosure may further include an adhesive layer 143 formed by an adhesive or bonding process, and the magnetostrictive material layer 142 and the adhesive layer 143 are alternately arranged to form the ferromagnetic layer 141 .

[0093] In the above embodiments, the bonding or bonding process includes a hot pressing fusion scheme between glue, metal, and non-metal oxides; the materials used for the bonding layer of the bonding or bonding process may include organic glue materials, such as epoxy resin glue, photoresist, polyimide glue, etc.; low melting point metal materials, such as Sn (tin), Cu (copper), CuSn (copper tin), AuSn (gold tin), etc.; non-metal oxide materials, such as SiO (silicon oxide), etc.

[0094] It should be noted that the above description of the bonding or adhesive process of the magnetic field sensor provided by the present disclosure and the materials used for the adhesive layer of the bonding or adhesive process should not be regarded as a limitation to the present disclosure.

[0095] As mentioned above, the ferromagnetic layer in the existing magnetic field sensor is generally deposited by MEMS magnetron sputtering. The deposition rate is generally a few nm / min. It takes several hours to grow a magnetic material with a thickness of μm, which is inefficient. Therefore, it is impossible to complete the preparation of ferromagnetic thick films.

[0096] The method for preparing the magnetic field sensor provided in the above embodiment of the present disclosure can connect multiple layers of magnetostrictive materials to achieve controllable expansion of the thickness of the ferromagnetic layer, thereby effectively enhancing the detection sensitivity of the magnetic field sensor and improving the working performance of the magnetic field sensor. In addition, the preparation method is simple and fast, has low cost and strong practicality.

[0097] Figure 8 A simulation curve showing that the frequency offset of a magnetic field sensor provided in some embodiments of the present disclosure varies with the thickness of a ferromagnetic layer.

[0098] Based on the finite element method (FEM), a simulation model of the magnetic field sensor provided in the embodiment of the present disclosure is established, and the following is obtained: Figure 8 The curve shown. Figure 8 The horizontal axis is the thickness of the ferromagnetic layer, in nm. The vertical axis is the frequency offset of the magnetic field sensor, in MHZ. Figure 8As shown in the figure, when the thickness of the ferromagnetic layer is 500nm, the frequency offset is about 2MHZ. As the thickness of the ferromagnetic layer increases, the frequency offset increases accordingly. When the thickness of the ferromagnetic layer is 2500nm, the frequency offset can reach 9MHZ. After the thickness of the ferromagnetic layer reaches 3000nm, the increase in the frequency offset slows down with the increase in the thickness of the ferromagnetic layer. Therefore, within the thickness range of at least 3000nm, the increase in the thickness of the ferromagnetic layer will increase the frequency offset of the magnetic field sensor.

[0099] As discussed in the previous section on the operation method of the magnetic field sensor or provided in the embodiments of the present disclosure, the value of the external magnetic field to be measured is determined based on the mapping relationship between the frequency offset and the calibration magnetic field. The larger the frequency offset, the higher the test sensitivity of the magnetic field sensor. Therefore, by using the preparation method provided in the above embodiment, by connecting multiple layers of magnetostrictive material layers to increase the thickness of the ferromagnetic layer, the sensitive area of ​​the magnetic field sensor device can be increased, thereby improving the magnetic field detection sensitivity of the sensor.

[0100] Although the disclosure has been described in detail above with general descriptions and specific implementation methods, it is obvious to those skilled in the art that some modifications or improvements may be made to the embodiments of the disclosure. Therefore, these modifications or improvements made without departing from the spirit of the disclosure are within the scope of protection claimed by the disclosure.

[0101] There are a few points to note about this disclosure:

[0102] (1) The drawings of the embodiments of the present disclosure only relate to the structures related to the embodiments of the present disclosure. Other structures may refer to the general design.

[0103] (2) For the sake of clarity, in the drawings used to describe the embodiments of the present disclosure, the thickness of layers or regions is enlarged or reduced, that is, these drawings are not drawn according to the actual scale.

[0104] (3) In the absence of conflict, the embodiments of the present disclosure and the features therein may be combined with each other to obtain new embodiments.

[0105] The above description is only a specific implementation of the present disclosure, but the protection scope of the present disclosure is not limited thereto. The protection scope of the present disclosure shall be based on the protection scope of the claims.

Claims

1. A magnetic field sensor, comprising a piezoelectric layer, a pair of interdigital electrodes and a ferromagnetic layer, wherein: The interdigital electrode pair is disposed on the first surface of the piezoelectric layer and is configured to receive an external signal to measure an input return loss of the magnetic field sensor. The ferromagnetic layer is disposed on the first surface and is insulated from the interdigital electrode pair and configured as an acoustic waveguide. The ferromagnetic layer undergoes magnetostriction under the action of an external magnetic field to change the equivalent sound velocity of the magnetic field sensor.

2. The magnetic field sensor according to claim 1, further comprising: A reflection grid is disposed on the first surface and at least outside at least one side of the interdigital electrode pair.

3. The magnetic field sensor according to claim 2, wherein: The reflection grating includes a metal line formed on the piezoelectric layer, and a trench or a step formed on the first surface.

4. The magnetic field sensor according to claim 2, further comprising: The insulating layer is disposed between the ferromagnetic layer and the interdigital electrode pair, so that the interdigital electrode pair and the ferromagnetic layer are insulated from each other by the insulating layer.

5. The magnetic field sensor according to claim 4, wherein: The ferromagnetic layer covers the interdigital electrode pairs and the reflective grating via the insulating layer.

6. The magnetic field sensor according to claim 1, wherein: The interdigital electrode pairs include a first interdigital electrode pair and a second interdigital electrode pair, the second interdigital electrode pair being spaced apart from the first interdigital electrode pair by a delay line.

7. The magnetic field sensor according to claim 6, further comprising: The insulating layer is arranged on a side of the interdigital electrode pair away from the piezoelectric layer, and the ferromagnetic layer is arranged on the first surface at least through the insulating layer.

8. The magnetic field sensor according to any one of claims 1 to 7, wherein: The ferromagnetic layer is further configured such that the surface acoustic waves propagating under the external magnetic field include Love wave modes.

9. The magnetic field sensor according to any one of claims 1 to 7, wherein: The ferromagnetic layer includes n layers of magnetostrictive material stacked in sequence relative to the surface of the piezoelectric layer, where n is a positive integer greater than or equal to 2.

10. An electronic device comprising the magnetic field sensor according to any one of claims 1 to 9.

11. A method for operating a magnetic field sensor according to claim 1, comprising: Acquire a first input return loss of the magnetic field sensor measured by receiving an external signal through the interdigital electrode pair under the external magnetic field; Obtaining a second input return loss of the magnetic field sensor measured by receiving an external signal through the interdigital electrode pair in the absence of any external magnetic field; A frequency offset between the first input return loss and the second input return loss is determined, and a magnitude of the external magnetic field is determined according to a mapping relationship between the frequency offset and a value of a calibration magnetic field.

12. A method for preparing a magnetic field sensor, comprising: forming an interdigital electrode pair on a first surface on one side of the piezoelectric layer, forming a ferromagnetic layer on the first surface, wherein the ferromagnetic layer and the interdigital electrode pairs are insulated from each other, The interdigital electrode pair is configured to receive an external signal to measure the input return loss of the magnetic field sensor, the ferromagnetic layer is configured as an acoustic waveguide, and magnetostriction occurs under the action of an external magnetic field to change the equivalent sound velocity of the magnetic field sensor.

13. The preparation method according to claim 12, wherein: The forming of a ferromagnetic layer on the first surface comprises: On the first surface, n magnetostrictive material layers are stacked to form a ferromagnetic layer, where n is a positive integer greater than or equal to 2.

14. The preparation method according to claim 13, wherein: The stacking of n layers of magnetostrictive material layers to form a ferromagnetic layer comprises: The ferromagnetic layer is formed by stacking n magnetostrictive material layers using an adhesive or bonding process.

Images