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

Abstract

The invention discloses a magnetic field sensor, an operation method, a preparation method and an electronic device. The magnetic field sensor comprises a piezoelectric layer, a Bragg reflection layer and an interdigital electrode pair which are stacked, wherein the piezoelectric layer comprises a first surface and a second surface opposite to the first surface; the Bragg reflection layer is arranged on the first surface of the piezoelectric layer and configured to reflect acoustic waves, and the Bragg reflection layer comprises a plurality of first acoustic impedance layers and second acoustic impedance layers which are alternately stacked and arranged in pairs; the first acoustic impedance layer comprises a magnetostrictive material layer, and the acoustic impedance value of the second acoustic impedance layer is different from that of the first acoustic impedance layer; the pair of interdigital electrodes is disposed on the second surface of the piezoelectric layer, and is configured to feed in an electrical signal, generate an electric field in the piezoelectric layer to excite an acoustic wave, and measure an input return loss of the magnetic field sensor. The magnetic field sensor is low in process complexity, high in mechanical quality factor and high in detection sensitivity.

Description

Technical Field

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

[0002] Compared with traditional electrical devices, acoustic wave resonant devices have been widely used in microwave electronic devices due to their excellent resonant mechanical quality factor, such as acoustic filters, various types of sensors, etc. Especially for the application in magnetic field sensors, the higher resonant quality factor of acoustic wave resonant devices can improve the output accuracy of magnetic field sensors, reduce the sensing resolution of magnetic field sensors, and improve the detection performance of magnetic field sensors. Summary of the invention

[0003] At least some embodiments of the present disclosure provide a magnetic field sensor, which includes a stacked piezoelectric layer, a Bragg reflection layer, and an interdigital electrode pair, wherein the piezoelectric layer includes a first surface and a second surface opposite to the first surface; the Bragg reflection layer is disposed on the first surface of the piezoelectric layer and is configured to reflect acoustic waves, and the Bragg reflection layer includes a plurality of first acoustic impedance layers and second acoustic impedance layers that are alternately stacked and arranged in pairs; wherein the first acoustic impedance layer includes a magnetostrictive material layer, and the acoustic impedance value of the second acoustic impedance layer is different from the acoustic impedance value of the first acoustic impedance layer; the interdigital electrode pair is disposed on the second surface of the piezoelectric layer and is configured to feed an electrical signal, generate an electric field in the piezoelectric layer to excite acoustic waves, and measure the input return loss of the magnetic field sensor.

[0004] For example, in a magnetic field sensor provided by at least some embodiments of the present disclosure, the first acoustic impedance layer is directly disposed on the first surface and reused as an electrode; the interdigitated electrodes are configured to generate an electric field perpendicular to the direction of the first surface in the piezoelectric layer together with the first acoustic impedance layer during operation.

[0005] For example, in a magnetic field sensor provided by at least some embodiments of the present disclosure, the second acoustic impedance layer is directly disposed on the first surface; and the interdigitated electrodes are configured to generate an electric field in the piezoelectric layer parallel to the direction of the second surface during operation.

[0006] For example, at least some embodiments of the present disclosure provide a magnetic field sensor further comprising: a substrate disposed on a side of the surface of the Bragg reflection layer away from the piezoelectric layer.

[0007] For example, at least some embodiments of the present disclosure provide a magnetic field sensor further comprising: a reflection grating disposed on the second surface of the piezoelectric layer and at least outside at least one side of the interdigital electrode pair.

[0008] 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 second surface of the piezoelectric 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] At least some embodiments of the present disclosure further provide an electronic device, which includes the magnetic field sensor provided by an embodiment of the present disclosure.

[0011] 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 feeding an electrical signal through the interdigitated electrode pair under the external magnetic field; obtaining a second input return loss of the magnetic field sensor measured by feeding an electrical 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.

[0012] At least some embodiments of the present disclosure also provide a method for preparing a magnetic field sensor, the method comprising: providing a piezoelectric layer; providing a Bragg reflection layer comprising a plurality of alternately stacked pairs of first acoustic impedance layers and second acoustic impedance layers on a first surface of the piezoelectric layer, wherein the first acoustic impedance layer comprises a magnetostrictive material layer, and the acoustic impedance value of the second acoustic impedance layer is different from the acoustic impedance value of the first acoustic impedance layer; providing an interdigitated electrode pair on a second surface of the piezoelectric layer opposite to the first surface, wherein the interdigitated electrode pair is configured to feed an electrical signal to generate an electric field in the piezoelectric layer to excite an acoustic wave and measure the input return loss of the magnetic field sensor.

[0013] For example, in a method for preparing a magnetic field sensor provided by at least some embodiments of the present disclosure, a Bragg reflection layer including a plurality of alternately stacked pairs of first acoustic impedance layers and second acoustic impedance layers is provided on the first surface of the piezoelectric layer, including: forming the plurality of alternately stacked pairs of first acoustic impedance layers and second acoustic impedance layers by alternately growing them to form the Bragg reflection layer.

[0014] For example, in a method for preparing a magnetic field sensor provided by at least some embodiments of the present disclosure, providing a piezoelectric layer includes: directly growing the piezoelectric layer on the Bragg reflection layer, or transfer bonding the piezoelectric layer to the Bragg reflection layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] 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.

[0016] Figure 1 A schematic diagram of the structure of a magnetic field sensor provided in some embodiments of the present disclosure;

[0017] Figure 2 A partial structural schematic diagram of a magnetic field sensor 101 provided in some embodiments of the present disclosure;

[0018] Figure 3 A partial structural schematic diagram of a magnetic field sensor 102 provided in some embodiments of the present disclosure;

[0019] Figure 4 A partial structural schematic diagram of a magnetic field sensor 200 provided in some embodiments of the present disclosure;

[0020] Figure 5 A partial structural schematic diagram of a magnetic field sensor 300 provided in some embodiments of the present disclosure;

[0021] Figure 6 An operating method of a magnetic field sensor provided in some embodiments of the present disclosure;

[0022] Figure 7 A flow chart of a method for preparing a magnetic field sensor provided in some embodiments of the present disclosure;

[0023] Figure 8 A flow chart of a process for preparing a magnetic field sensor provided in some embodiments of the present disclosure;

[0024] Fig. 9 for Figure 1 The simulation curve of the magnetic field sensor limiting the bulk acoustic wave shown; and

[0025] Fig.10 for Figure 1 The input return loss of the magnetic field sensor (S 11 )Simulation curve. DETAILED DESCRIPTION

[0026] 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.

[0027] 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.

[0028] 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, the detailed description of known functions and known components (elements) may be omitted. When any part (element) of the embodiments of the present disclosure appears in more than one figure, the part (element) is represented by the same or similar reference numeral in each figure.

[0029] The acoustic wave resonance type magnetic field sensor can be made of a composite of piezoelectric material and magnetostrictive material, and works at the acoustic resonance frequency of the device. The acoustic wave resonance type magnetic field sensor includes a passive acoustic resonance type magnetic field sensor (hereinafter referred to as "passive magnetic field sensor") and an active acoustic wave resonance type magnetic field sensor (hereinafter referred to as "active magnetic field sensor").

[0030] The working principle of the passive magnetic field sensor is: under the action of the external AC magnetic field, the magnetostrictive material undergoes periodic deformation due to the magnetostrictive effect, causing the acoustic resonance of the piezoelectric-ferromagnetic composite structure, and then the piezoelectric effect of the piezoelectric material generates an electrical signal output, and the magnitude of the external magnetic field to be measured is sensed by detecting the magnitude of the output electrical signal. Passive acoustic resonance magnetic field sensors are mainly based on d 31 Bulk acoustic wave stretch resonance mode, the main device configurations include micro-electro-mechanical systems (MEMS) cantilever beams or nanoplate resonator structures (NPR).

[0031] The working principle of active magnetic field sensor is: by applying electrical signals, the inverse piezoelectric effect of piezoelectric materials is used to generate sound waves and stimulate acoustic resonance. Under the action of the external magnetic field to be measured, the acoustic properties of the magnetostrictive material change, thereby affecting the resonant frequency and other parameters of the device. By detecting the changes in the resonant frequency or related electrical parameters, the magnitude of the magnetic field can be sensed. At present, active acoustic wave resonant magnetic field sensors can be divided into magnetic field sensors based on surface acoustic wave (SAW) resonant structure and magnetic field sensors based on bulk acoustic wave (BAW) resonant structure according to the type of acoustic wave.

[0032] The acoustic wave resonant magnetic field sensor excites surface acoustic waves by preparing interdigitated electrodes on the substrate. Since the surface acoustic wave leaks into the substrate, the mechanical quality factor of the device is low. The emerging IHP (Incredible high performance) surface acoustic wave structure can greatly improve the quality factor of the surface acoustic wave resonator. However, due to the planar interdigitated electrode structure of the surface acoustic wave, in the preparation process of the magnetic film formed by the magnetostrictive material, it is necessary to introduce an insulating layer between the magnetic film and the substrate to prevent the magnetic film from short-circuiting with the interdigitated electrodes, thereby causing the device to fail to work. Since the structure of the interdigitated electrodes is periodic, the magnetic film will also have periodic steps, and the flatness of the magnetic film is poor, which will have a great impact on the soft magnetic properties of the magnetic film and directly affect the performance of the acoustic wave resonant magnetic field sensor. If you want to obtain a relatively flat magnetic film, you need to introduce an additional thin film mechanical chemical polishing process, which will greatly increase the process complexity of the device and reduce the consistency of the device on the one hand; on the other hand, the introduction of the insulating layer will weaken the interaction between the acoustic wave and the magnetostrictive material, reducing the detection sensitivity of the device.

[0033] Magnetic field sensors based on bulk acoustic wave resonance structure can be divided into film bulk acoustic resonator (FBAR) type magnetic field sensors (hereinafter referred to as "film bulk acoustic wave magnetic field sensors") and solid mounted resonator (SMR) type magnetic field sensors (hereinafter referred to as "solid mounted magnetic field sensors") according to the resonance structure.

[0034] The thin film bulk acoustic wave magnetic field sensor forms a three-layer structure of "suspended electrode-piezoelectric layer-electrode" by releasing the substrate or sacrificial layer under the piezoelectric material, and can use the air cavity under the device to achieve acoustic isolation. The thin film bulk acoustic wave magnetic field sensor has a high mechanical quality factor and a small device size, but the suspended structure makes the device have limited heat dissipation capacity, poor device stability, and complex and difficult preparation process. In addition, the existence of stress after the substrate is released often introduces undesirable magnetocrystalline anisotropy in the magnetic film.

[0035] Solid-state assembly magnetic field sensors first prepare a Bragg reflector made of high and low acoustic impedance materials (usually metal and oxide) of a specific thickness under the resonator structure to achieve reflection of the resonator sound waves. It has good heat dissipation capacity, low process difficulty, and high flatness of the magnetic film. However, since the multi-layer structure only serves as an acoustic reflector, a magnetic sensitive layer still needs to be prepared on the device to achieve the sensing function. In addition, if a forked electrode structure is used, the problem of flatness and insulation layer will also be encountered, which will have a great impact on the sensing performance of the device.

[0036] In order to enhance the sensing performance of acoustic resonance magnetic field sensors, the magnetic sensitive layer on the device is generally thicker, and thicker magnetic films often bring about greater eddy current losses, which reduces the quality factor of the device. By introducing an insulating material intercalation design in the magnetic film layer, the eddy current loss in the magnetic film can be effectively reduced and the performance of the magnetic film can be improved. However, the design of magnetic metal / insulating material periodic intercalation will make the acoustic impedance in the film inconsistent, thus affecting the acoustic resonance.

[0037] The present disclosure provides a magnetic field sensor, which includes a stacked piezoelectric layer, a Bragg reflection layer and an interdigital electrode pair, wherein the piezoelectric layer includes a first surface and a second surface opposite to the first surface; the Bragg reflection layer is arranged on the first surface of the piezoelectric layer and is configured to reflect acoustic waves, and the Bragg reflection layer includes a plurality of first acoustic impedance layers and second acoustic impedance layers that are alternately stacked and arranged in pairs; the first acoustic impedance layer includes a magnetostrictive material layer, and the acoustic impedance value of the second acoustic impedance layer is different from the acoustic impedance value of the first acoustic impedance layer; the interdigital electrode pair is arranged on the second surface of the piezoelectric layer and is configured to feed an electrical signal, generate an electric field in the piezoelectric layer to excite the acoustic wave, and measure the input return loss of the magnetic field sensor.

[0038] In the magnetic field sensor provided by the above embodiment of the present disclosure, the Bragg reflection layer includes a plurality of first acoustic impedance layers and second acoustic impedance layers that are alternately stacked and arranged in pairs, the first acoustic impedance layer includes a magnetostrictive material layer, and the acoustic impedance value of the second acoustic impedance layer is different from the acoustic impedance value of the first acoustic impedance layer, for example, the acoustic impedance value of the second acoustic impedance layer can be less than or greater than the acoustic impedance value of the first acoustic impedance layer. On the one hand, the Bragg reflection layer can reflect sound waves within a specific frequency, limit acoustic energy, improve the resonance characteristics of the magnetic field sensor, and increase the quality factor of the magnetic field sensor; on the other hand, since the first acoustic impedance layer includes a magnetostrictive material layer, the magnetostrictive material has magnetic field sensitivity and can be used as a magnetic field sensing layer. The elastic mechanical parameters of the magnetostrictive material will change under the influence of the external magnetic field, thereby affecting the resonant frequency of the magnetic field sensor and realizing the perception of the external magnetic field. The first acoustic impedance layer / second acoustic impedance layer in the Bragg reflection layer, that is, the periodic multilayer structure composed of the magnetostrictive material layer / acoustic impedance difference material can increase the quality factor of the magnetic field sensor, and significantly reduce the eddy current loss in the magnetostrictive material, improve the magnetic properties of the thin film, and realize the output accuracy of the magnetic field sensor and the reduction of the sensing resolution, so as to improve the detection performance of the magnetic field sensor. In addition, the unification of the Bragg reflection layer and the magnetic sensing layer in the magnetic field sensor can reduce the process complexity of preparing the magnetic field sensor.

[0039] The magnetic field sensor in the above embodiment can meet the detection requirements of weak magnetic field signals in fields such as space science research, marine environment monitoring, geomagnetic exploration, biomedicine, etc. in a small size.

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

[0041] like Figure 1 As shown, the magnetic field sensor 100 includes a Bragg reflection layer 120, a piezoelectric layer 130 and an interdigital electrode pair 140. The piezoelectric layer 130 includes a first surface 10 and a second surface 20 opposite to the first surface 10. The Bragg reflection layer 120 is disposed on the first surface 10 of the piezoelectric layer 130 and is configured to reflect acoustic waves. The Bragg reflection layer 120 includes a plurality of first acoustic impedance layers and second acoustic impedance layers that are alternately stacked and arranged in pairs (the first acoustic impedance layers and the second acoustic impedance layers are not shown in the figure). The first acoustic impedance layer includes a magnetostrictive material layer, and the acoustic impedance value of the second acoustic impedance layer is different from the acoustic impedance value of the first acoustic impedance layer. The interdigital electrode pair 140 is disposed on the second surface 20 of the piezoelectric layer 130 and is configured to feed an electrical signal, generate an electric field in the piezoelectric layer 130 to excite acoustic waves, and measure the input return loss of the magnetic field sensor. As shown Figure 1 The magnetic field sensor 100 shown may further include a substrate 110 disposed on a side of the surface of the Bragg reflection layer 120 away from the piezoelectric layer 130 .

[0042] In the above embodiment, the sensing mechanism of the magnetic field sensor is to apply electrical excitation through the interdigital electrode pair, and use the inverse piezoelectric effect of the piezoelectric layer to excite the acoustic wave, based on the magnetostrictive effect of the magnetostrictive material layer in the Bragg reflection layer, that is, under the action of the external magnetic field, the magnetostrictive material will produce deformation, thereby causing the elastic modulus of the magnetostrictive material to change, which is also called the ΔE effect. The change in elastic modulus will affect the resonant frequency of the magnetic field sensor, and the electrical parameters of the magnetic field sensor can be tested by the interdigital electrode pair on the surface of the piezoelectric layer to detect the size of the external magnetic field.

[0043] In the magnetic field sensor provided by the above embodiment, for a certain acoustic wave mode, the frequency of the acoustic wave reflected by the Bragg reflector is related to the acoustic velocity and thickness of the first acoustic impedance layer and the second acoustic impedance layer, and the reflection ability of the Bragg reflector is related to the acoustic impedance ratio of the two. For example, when the first acoustic impedance layer is a FeGaB layer (FeGaB material has excellent magnetostrictive properties) and the second acoustic impedance layer is a SiO2 layer, the frequency of the acoustic wave reflected by it is related to the thickness and acoustic velocity of the FeGaB layer and the SiO2 layer, and its reflection ability is related to the acoustic impedance ratio of the FeGaB layer and the SiO2 layer.

[0044] It should be noted that the Bragg reflector is generally composed of two materials with very different acoustic impedances, commonly used metal (large acoustic impedance) and oxide (small acoustic impedance) materials. Although the acoustic impedance value of FeGaB material is smaller than that of the commonly used tungsten material, the difference between its acoustic impedance and that of SiO2 is still large, so FeGaB and SiO2 can be used to form the Bragg reflector.

[0045] When the external magnetic field changes, the elastic modulus of the FeGaB material will change due to the magnetostrictive effect, causing changes in the acoustic velocity and acoustic impedance of the FeGaB layer. Taking Young's modulus E as an example, the acoustic velocity c of FeGaB FeGaB Acoustic impedance Z FeGaB They are determined by the following formulas:

[0046]

[0047] Where ρ is the density of FeGaB material.

[0048] The frequency of the sound wave reflected by the Bragg reflector is f res for:

[0049]

[0050] Among them, c eqis the equivalent acoustic velocity of the reflective layer, and λ is the total thickness of a single period of the Bragg reflective layer. A single period of the Bragg reflective layer refers to a first acoustic impedance layer and a second acoustic impedance layer, for example, in the above embodiment, it can be understood as a FeGaB layer and a SiO2 layer, and the total thickness of a single period is the sum of the thickness of a FeGaB layer and the thickness of a SiO2 layer. The number of periods included in the Bragg reflective layer can be designed according to the actual application scenario.

[0051] It can be seen from the above formula that when the Young's modulus of FeGaB increases under an external magnetic field, its acoustic velocity and acoustic impedance both increase. The equivalent acoustic velocity of the Bragg reflector increases, which increases the frequency (resonance frequency) of the acoustic wave reflected by the Bragg reflector. At the same time, the acoustic impedance of the FeGaB layer increases, which increases the ratio of the acoustic impedance of the FeGaB layer to the SiO2 layer, enhancing the acoustic wave reflection capability. Therefore, the quality factor of the magnetic field sensor resonance increases.

[0052] In the magnetic field sensor provided by the above embodiments of the present disclosure, the piezoelectric material used to form the piezoelectric layer may include piezoelectric films grown by bonding or direct growth, such as AlN (aluminum nitride), AlScN (scandium aluminum nitride), ZnO (zinc oxide), GaN (gallium nitride), PZT (lead zirconate titanate), PMN-PT (lead magnesium niobate titanate), LiNbO3 (lithium niobate) and LiTaO3 (lithium tantalate) of different tangents, etc.

[0053] In the magnetic field sensor provided in the above embodiments of the present disclosure, the material used to form the substrate may include Si (silicon), SiO (silicon oxide), SiC (silicon carbide), SiN (silicon nitride), diamond or sapphire, etc.

[0054] In the magnetic field sensor provided in the above embodiment of the present disclosure, the material used to form the magnetostrictive material layer in the first acoustic impedance layer in the Bragg reflection layer may include Metglas (metallic glass), FeGaB (iron gallium boron), FeGaC (iron gallium carbon), Terfenol-D (Tb-Dy-Fe), Ni (nickel), Fe (iron), FeGa (iron gallium alloy), CoFe (cobalt iron alloy), CoFeO (cobalt iron oxide), NiFe (nickel iron alloy), FeAl (iron aluminum alloy) or YIG (yttrium iron garnet), etc. It should be noted that the components of the above magnetostrictive material may include different element ratios, for example, FeGaB is only an example of iron gallium boron material, and the embodiment of the present disclosure does not limit the element ratio in the magnetostrictive material.

[0055] In the magnetic field sensor provided in some embodiments of the present disclosure, the material used to form the second acoustic impedance layer in the Bragg reflection layer may include AlN (aluminum nitride), GaN (gallium nitride), ZnO (zinc oxide), AlO (aluminum oxide), SiO (silicon oxide), or metal W (tungsten), Au (gold), etc. It should be noted that the components of the above-mentioned nitrides and oxides may include different element ratios, for example, SiO2 is only an example of silicon oxide, and the embodiments of the present disclosure do not limit the element ratios in the nitrides and oxides.

[0056] In the magnetic field sensors provided in some embodiments of the present disclosure, the materials used to form the interdigitated electrode pairs may include, for example, Ti (titanium), Al (aluminum), Cu (copper), Pt (platinum), Au (gold), Ag (silver), Mo (molybdenum), etc. and any alloys thereof.

[0057] It should be noted that the above description of the materials used for the piezoelectric layer, the Bragg reflection layer, and the interdigital electrode pair of the magnetic field sensor provided by the present disclosure should not be regarded as a limitation to the present disclosure.

[0058] The structure of the magnetic field sensor provided in the embodiment of the present disclosure can support multiple acoustic resonance modes and multiple electrical excitation methods, has a large degree of design freedom, and can achieve extremely high device performance through design, which will be described in detail below.

[0059] Figure 2 A partial structural diagram of a magnetic field sensor 101 provided in some embodiments of the present disclosure.

[0060] like Figure 2 As shown, the magnetic field sensor 101 includes a Bragg reflection layer 121, a piezoelectric layer 131 and an interdigital electrode pair 141. The Bragg reflection layer 121 is arranged on the first surface 11 of the piezoelectric layer 131, and the Bragg reflection layer 121 includes a plurality of first acoustic impedance layers 1211 and second acoustic impedance layers 1212 that are alternately stacked and arranged in pairs, and the first acoustic impedance layer 1211 is directly arranged on the first surface 11 of the piezoelectric layer 131 and reused as an electrode; the interdigital electrode pair 141 is configured to generate an electric field perpendicular to the direction of the first surface 11 of the piezoelectric layer 131 in the piezoelectric layer 131 together with the first acoustic impedance layer 1211 during operation.

[0061] In the above embodiment, the first acoustic impedance layer 1211 is not in direct contact with the interdigital electrode pair 141, but because the magnetostrictive material included in the first acoustic impedance layer 1211 is conductive, the first acoustic impedance layer 1211 can be used as an electrically suspended electrode, and work together with the interdigital electrode pair 141 to introduce a vertical electric field in the piezoelectric layer 131. Thus, electrical excitation is applied without the need to additionally connect the electrode below the piezoelectric layer 131, which greatly reduces the complexity of the preparation process.

[0062] The magnetic field sensor provided in the above embodiment can excite different acoustic wave modes according to the piezoelectric material and size parameters selected for the piezoelectric layer. For example, the thickness expansion bulk acoustic wave mode or the thickness shear bulk acoustic wave mode can be excited by the upper and lower surface electrodes of the piezoelectric layer in the above embodiment; for example, when the spacing between the interdigital electrode pairs is reduced to the same order of magnitude as the thickness of the piezoelectric layer, the excited acoustic wave mode will gradually change to the Lamb wave mode.

[0063] Compared with the surface acoustic wave mode, the bulk acoustic wave mode supported by the above embodiment can make the interaction between the magnetostrictive material and the acoustic wave stronger, thereby improving the sensitivity of the sensor. In addition, the magnetic field sensor supporting the bulk acoustic wave mode also has a larger quality factor and a smaller size, thereby improving the overall sensitivity of the sensor. Moreover, the resonant frequency and electromechanical coupling coefficient of the magnetic field sensor mode provided by the above embodiment of the present disclosure will not be significantly reduced due to the introduction of the magnetostrictive material layer, thereby reducing the impact on the detection resolution.

[0064] Figure 3 A partial structural diagram of the magnetic field sensor 102 provided in some embodiments of the present disclosure.

[0065] like Figure 3 As shown, the magnetic field sensor 102 includes a Bragg reflection layer 122, a piezoelectric layer 132, and an interdigital electrode pair 142. The Bragg reflection layer 122 is disposed on the first surface 12 of the piezoelectric layer 132, and the Bragg reflection layer 122 includes a plurality of first acoustic impedance layers 1221 and second acoustic impedance layers 1222 that are alternately stacked and arranged in pairs, and the second acoustic impedance layer 1222 is directly disposed on the first surface 12 of the piezoelectric layer 132. The electrical signal can generate a transverse electric field between the interdigital electrode pairs 142, and excite acoustic waves through the inverse piezoelectric effect.

[0066] The magnetic field sensor provided in the above embodiment can apply a transverse electric field through the interdigital electrode pair to excite surface acoustic waves, Lamb waves or shear bulk acoustic wave modes, etc. The vibration direction of the shear bulk acoustic wave mode can be designed by, for example, the interdigital electrode pair structure and material tangent.

[0067] Different embodiments of the present disclosure may excite different acoustic wave resonance modes depending on the selected piezoelectric materials and size parameters, and the embodiments of the present disclosure are not limited to this.

[0068] It should be noted that the embodiment of the present disclosure can design the thickness and period number of the first acoustic impedance layer and the second acoustic impedance layer in the Bragg reflection layer differently according to actual needs, and the embodiment of the present disclosure is not limited to this. For example, the thickness of the first acoustic impedance layer and the second acoustic impedance layer can be set to one quarter of the main resonant wavelength of the magnetic field sensor.

[0069] Figure 4A partial structural diagram of a magnetic field sensor 200 provided in some embodiments of the present disclosure.

[0070] Figure 4 The magnetic field sensor 200 shown includes a piezoelectric layer 210, an interdigital electrode pair 240 and a reflection grating 250. The interdigital electrode pair 240 and the reflection grating 250 are arranged on the second surface (upper surface in the figure) of the piezoelectric layer 210, and the reflection grating 250 is arranged outside the interdigital electrode pair 220.

[0071] For example, in the magnetic field sensor 200, the interdigital electrode pairs 240 are arranged periodically, and their width may be λ1 / 4, where λ1 is the acoustic wavelength at the corresponding frequency.

[0072] For example, Figure 4 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 magnetostrictive material undergoes periodic deformation, causing the acoustic resonance frequency to change. By testing the input return loss of the magnetic field sensor through 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.

[0073] 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.

[0074] like Figure 4 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.

[0075] 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 4 Some of the interdigital electrode pairs 240 are led out through the outside of the reflective grid 250 for the convenience of testing, but the present disclosure does not limit this.

[0076] Figure 5 A partial structural diagram of another magnetic field sensor 300 provided in some embodiments of the present disclosure.

[0077] Figure 5 The magnetic field sensor 300 shown includes a piezoelectric layer 330, a first interdigital electrode pair 341, a second interdigital electrode pair 342, and a delay line 360. The first interdigital electrode pair 341 and the second interdigital electrode pair 342 are disposed on the second surface of the piezoelectric layer 330, and the first interdigital electrode pair 341 and the second interdigital electrode pair 342 are separated by the delay line 360.

[0078] For example, the first interdigital electrode pair 341 and the second interdigital electrode pair 342 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 341 and the second interdigital electrode pair 342 are separated by a delay line 360.

[0079] like Figure 5 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 may be configured to measure the transmission coefficient (S) of its signal through the interdigital electrode pair. 21 ) is used for testing, and the external magnetic field is detected by the offset of the operating frequency or phase.

[0080] 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.

[0081] The electronic device of the embodiment of the present disclosure may include any of the magnetic field sensors as described above, and the electronic device may include at least one memory and at least one processor, wherein the memory stores computer executable instructions non-transiently, and the processor is configured to run the computer executable instructions, for example, the processor or the memory includes the above magnetic field sensor. For example, the electronic device of the embodiment of the present disclosure may be implemented as but not limited to mobile terminals such as mobile phones, laptop computers, digital broadcast receivers, PDAs (personal digital assistants), PADs (tablet computers), PMPs (portable multimedia players), vehicle-mounted terminals (such as vehicle-mounted navigation terminals), etc., and fixed terminals such as digital TVs, desktop computers, etc. The above electronic device is only an example and should not bring any limitation to the functions and scope of use of the embodiment of the present disclosure.

[0082] Figure 6 The operating method of the magnetic field sensor provided in some embodiments of the present disclosure includes S110-S130.

[0083] Step S110 , obtaining a first input return loss of the magnetic field sensor measured by feeding an electrical signal through the interdigital electrode pair under an external magnetic field.

[0084] Input return loss is an indicator that measures the size of the reflected signal at the input port of a device. It can indicate the size of the reflected signal relative to the incident signal. It is usually expressed in decibels (dB). The smaller the value (the larger the absolute value), the smaller the reflected signal and the better the match.

[0085] Step S120 , obtaining a second input return loss of the magnetic field sensor measured by feeding an electrical signal through the interdigital electrode pair in the absence of any external magnetic field.

[0086] In the absence of an external magnetic field, the electrical signal is also fed through the interdigitated electrodes to measure the second input return loss of the magnetic field sensor. According to the working principle of the magnetic field sensor provided by the aforementioned 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.

[0087] Step S130, 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 according to a mapping relationship between the frequency offset and a value of a calibration magnetic field.

[0088] 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, calibration can be performed before using the magnetic field sensor 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 value of the external magnetic field according to the mapping relationship.

[0089] 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 electrical signal source. The electrical signal provided by the network analyzer or the signal source is fed into the magnetic field sensor by the interdigitated electrode pair to test the input return loss. An auxiliary circuit with the same function can also 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.

[0090] Figure 7 A flow chart of a method for preparing a magnetic field sensor provided in some embodiments of the present disclosure, including S210-S230.

[0091] Step S210, providing a piezoelectric layer.

[0092] For example, in some embodiments of the present disclosure, providing the piezoelectric layer may include: directly growing the piezoelectric layer on the Bragg reflective layer, or transfer bonding the piezoelectric layer to the Bragg reflective layer.

[0093] Step S220: providing a Bragg reflection layer including a plurality of alternately stacked pairs of first acoustic impedance layers and second acoustic impedance layers on the first surface of the piezoelectric layer.

[0094] In step S220, the first acoustic impedance layer includes a magnetostrictive material layer, and the acoustic impedance value of the second acoustic impedance layer is different from the acoustic impedance value of the first acoustic impedance layer.

[0095] For example, in the above embodiment, providing the Bragg reflection layer may include: forming a plurality of alternately stacked pairs of first acoustic impedance layers and second acoustic impedance layers by alternate growth to form the Bragg reflection layer.

[0096] Step S230 , providing an interdigital electrode pair on a second surface of the piezoelectric layer opposite to the first surface.

[0097] The interdigital electrode pairs in step S230 are configured to feed an electrical signal, generate an electric field in the piezoelectric layer to excite an acoustic wave and measure the input return loss of the magnetic field sensor.

[0098] Figure 8 The following is a flow chart of the preparation process of the magnetic field sensor provided in some embodiments of the present disclosure. Figure 8 right Figure 7 The preparation method is described in detail.

[0099] like Figure 8 As shown, providing a Bragg reflection layer on the first surface of the piezoelectric layer in step S220 can be understood as alternately growing magnetostrictive materials and acoustic impedance layers on the substrate to form a first acoustic impedance layer and a second acoustic impedance layer to form a Bragg reflection layer. It should be noted that Figure 8 The order of growing the magnetostrictive material and the acoustic impedance layer is only for illustration, and the present disclosure does not limit the order of growing the magnetostrictive material and the acoustic impedance layer.

[0100] A piezoelectric layer may be formed on a surface of the Bragg reflector layer away from the substrate, for example, by Figure 8 The piezoelectric material is directly grown or the piezoelectric material is transfer-bonded to the surface of the Bragg reflective layer. The first surface of the piezoelectric layer is in direct contact with the Bragg reflective layer.

[0101] In step S230, a pair of interdigitated electrodes is provided on a second surface of the piezoelectric layer opposite to the first surface. For example, the interdigitated electrodes are prepared on the second surface of the piezoelectric layer by a photolithography lift-off process or a film growth and then etching process.

[0102] Based on the above preparation method, the sensitivity of the device can be improved by appropriately designing the number of Bragg reflection layers. For example, in the process, two materials can be alternately deposited by magnetron sputtering, which can quickly complete the preparation of the Bragg reflection layer and realize the controllable expansion of the thickness of the magnetostrictive material. The process cost is low and the steps are simple and fast.

[0103] Fig. 9 for Figure 1 The simulation curve of the magnetic field sensor's limiting effect on bulk acoustic waves is shown.

[0104] Fig. 9 The horizontal axis in is Figure 1The cross-sectional position (m) of the magnetic field sensor shown, that is, the cross-sectional position of different structures of the magnetic field sensor, for example, the cross-sectional position of the cross-digital electrode pair with the origin of the coordinate, combined with Figure 1 It can be seen that the cross-section position of the piezoelectric layer is closer to the coordinate origin, and the cross-section of the substrate is farther from the coordinate origin. Fig. 9 The ordinate in is displacement (m), and the ordinate can represent the displacement generated by each structure in the magnetic field sensor under the acoustic wave mode. Fig. 9 The curves in represent the displacements of different cross-sectional locations in the magnetic field sensor. For example, Fig. 9 The acoustic impedance of the magnetostrictive material layer in the Bragg reflection layer used in the simulation is 2.58×10 7 kg / m 2 / s, the acoustic impedance value of the second acoustic impedance layer is 1.24×10 7 kg / m 2 / s, the acoustic impedance values ​​of the two materials constituting the Bragg reflection layer are quite different. Fig. 9 This shows that in a certain mode of bulk acoustic wave, when the acoustic impedance difference between the two materials forming the Bragg reflector is large, the structure closer to the interdigital electrode pair, for example, the displacement in the piezoelectric layer is large, the displacement in the Bragg reflector is smaller than that in the piezoelectric layer, and the displacement value in the substrate is already very small. Figure 1 The embodiment uses a composite multilayer structure of magnetostrictive material and acoustic impedance difference material as a Bragg reflection layer to complete the solid-state installation of the upper bulk acoustic wave resonator. For this bulk acoustic wave mode, the Bragg reflection layer can prevent the propagation of the bulk acoustic wave in a narrow frequency band around a frequency, forming a reflection, thereby achieving resonance at a specific frequency and improving the quality factor of the magnetic field sensor.

[0105] Fig.10 for Figure 1 The input return loss (S11) simulation curve of the magnetic field sensor is shown.

[0106] Fig.10 The horizontal axis is frequency (MHZ) and the vertical axis is S11 input return loss (dB). Fig.10 The different curves represent different Young's moduli of the first acoustic impedance layer, such as magnetostrictive material FeGaB, and the sharpness of the valley value of the curve reflects the quality factor. When the Young's modulus of FeGaB increases under an external magnetic field, its sound velocity and acoustic impedance both increase. At this time, the equivalent sound velocity of the Bragg reflection layer increases, so that the frequency (resonance frequency) of the sound wave reflected by the Bragg reflection layer increases. At the same time, the acoustic impedance value of FeGaB increases, so that the acoustic impedance ratio between it and the second acoustic impedance layer, such as the SiO2 layer, increases, and the acoustic wave reflection ability is enhanced, so the quality factor of the magnetic field sensor resonance increases.

[0107] 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.

[0108] There are a few points to note about this disclosure:

[0109] (1) The drawings of the embodiments of the present disclosure only relate to the structures related to the embodiments of the present disclosure, and other structures may refer to the general design.

[0110] (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.

[0111] (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.

[0112] 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 stacked piezoelectric layer, a Bragg reflection layer and an interdigital electrode pair, wherein: The piezoelectric layer includes a first surface and a second surface opposite to the first surface; The Bragg reflection layer is disposed on the first surface of the piezoelectric layer and is configured to reflect acoustic waves, and the Bragg reflection layer includes a plurality of first acoustic impedance layers and second acoustic impedance layers that are alternately stacked and arranged in pairs; Wherein, the first acoustic impedance layer comprises a magnetostrictive material layer, and the acoustic impedance value of the second acoustic impedance layer is different from the acoustic impedance value of the first acoustic impedance layer; The interdigital electrode pair is disposed on the second surface of the piezoelectric layer and is configured to feed an electrical signal, generate an electric field in the piezoelectric layer to excite an acoustic wave, and measure an input return loss of the magnetic field sensor.

2. The magnetic field sensor according to claim 1, wherein: The first acoustic impedance layer is directly disposed on the first surface and multiplexed as an electrode; The interdigitated electrode pair is configured to generate an electric field perpendicular to the first surface direction in the piezoelectric layer together with the first acoustic impedance layer during operation.

3. The magnetic field sensor according to claim 1, wherein: The second acoustic impedance layer is directly disposed on the first surface; The interdigitated electrode pair is configured to generate an electric field in the piezoelectric layer parallel to the second surface direction when in operation.

4. The magnetic field sensor according to claim 1, further comprising: The substrate is arranged on a side of the surface of the Bragg reflection layer away from the piezoelectric layer.

5. The magnetic field sensor according to claim 1, further comprising: A reflection grating is arranged on the second surface of the piezoelectric layer and at least outside at least one side of the interdigital electrode pair.

6. The magnetic field sensor according to claim 5, wherein: The reflection grating includes a metal line formed on the piezoelectric layer, and a trench or a step formed on the second surface of the piezoelectric layer.

7. The magnetic field sensor according to any one of claims 1 to 6, 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.

8. An electronic device comprising the magnetic field sensor according to any one of claims 1 to 7.

9. A method for operating a magnetic field sensor according to claim 1, comprising: Acquiring a first input return loss of the magnetic field sensor measured by feeding an electrical signal through the interdigital electrode pair under the external magnetic field; Obtaining a second input return loss of the magnetic field sensor measured by feeding an electrical 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.

10. A method for preparing a magnetic field sensor, comprising: providing a piezoelectric layer; Providing a Bragg reflection layer including a plurality of alternately stacked pairs of first acoustic impedance layers and second acoustic impedance layers on the first surface of the piezoelectric layer, wherein the first acoustic impedance layer includes a magnetostrictive material layer, and the acoustic impedance value of the second acoustic impedance layer is different from that of the first acoustic impedance layer; An interdigital electrode pair is provided on a second surface of the piezoelectric layer opposite to the first surface, wherein the interdigital electrode pair is configured to feed an electrical signal to generate an electric field in the piezoelectric layer to excite acoustic waves and measure an input return loss of the magnetic field sensor.

11. The preparation method according to claim 10, wherein: A Bragg reflection layer including a plurality of alternately stacked pairs of first acoustic impedance layers and second acoustic impedance layers is provided on the first surface of the piezoelectric layer, comprising: The plurality of alternately stacked pairs of the first acoustic impedance layer and the second acoustic impedance layer are formed by alternate growth to form the Bragg reflection layer.

12. The preparation method according to claim 10, wherein: The providing of a piezoelectric layer comprises: The piezoelectric layer is directly grown on the Bragg reflective layer, or the piezoelectric layer is transfer-bonded to the Bragg reflective layer.

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