Ultrasonic sensor, ultrasonic fingerprint identification module and electronic equipment

Abstract

The embodiment of the utility model relates to the field of ultrasonic sensors, and discloses an ultrasonic sensor, an ultrasonic fingerprint identification module and electronic equipment. The ultrasonic sensor comprises a substrate, a bonding pad area, a bottom electrode, a piezoelectric layer and a top electrode, the bottom electrode is arranged on the upper surface of the substrate, the piezoelectric layer is arranged above the substrate and covers the bottom electrode, the bonding pad area is arranged on the upper surface of the substrate, and the bonding pad area and the bottom electrode are arranged at an interval; the top electrode comprises a first metal layer and a second metal layer, and the thickness of the first metal layer is smaller than that of the second metal layer; the first metal layer covers the piezoelectric layer, extends to the bonding pad area along the surface of the piezoelectric layer and the surface of the substrate connected with the piezoelectric layer, and is electrically connected with the bonding pad area; the second metal layer covers a partial region above the first metal layer, and a first projection region of the second metal layer in the direction of the substrate is located in a second projection region of the piezoelectric layer in the direction of the substrate. The preparation of the ultrasonic sensor is simplified, and the production cost is reduced.

Description

Technical Field

[0001] This utility model relates to the field of ultrasonic sensors, and in particular to an ultrasonic sensor, an ultrasonic fingerprint recognition module, and an electronic device. Background Technology

[0002] Ultrasonic sensors utilize the direct and inverse piezoelectric properties of piezoelectric materials. On one hand, the inverse piezoelectric effect, driven by a high voltage output from a circuit, excites the sensor to emit ultrasonic signals. On the other hand, the direct piezoelectric effect converts reflected ultrasonic signals into electrical signals, thus acquiring information about the external sensing surface. After decades of development, ultrasonic sensors are now widely used in medical imaging, structural flaw detection, and biometric identification. For example, ultrasonic sensors can be applied to ultrasonic fingerprint modules, positioned in specific areas of the screens of electronic devices, including but not limited to smartphones, for fingerprint recognition, user authentication, and enhanced product anti-interference capabilities and security.

[0003] The inventors discovered that current ultrasonic sensors have at least the following drawbacks in their structure: the top electrode in ultrasonic sensors is fabricated using a multi-layer screen printing method, which is complex, technically challenging, and time-consuming. Furthermore, the use of materials in ultrasonic sensors leads to unnecessary material waste, increasing production costs. Utility Model Content

[0004] The purpose of this utility model embodiment is to provide an ultrasonic sensor, an ultrasonic fingerprint recognition module, and an electronic device. By adjusting the internal structure of the ultrasonic sensor, the manufacturing process of the ultrasonic sensor is simplified, and the production cost of the ultrasonic sensor is reduced to a certain extent.

[0005] like Figure 1 As shown, an ultrasonic sensor typically includes a substrate 1, a bottom electrode 2, a piezoelectric layer 3, a top electrode 4, and a protective layer 5. To achieve a thin and lightweight module structure and good acoustic response, ultrasonic sensors used for fingerprint recognition usually employ flexible materials as the piezoelectric layer, commonly including polyvinylidene fluoride (PVDF) and PVDF-TrFE copolymers. However, the poor heat resistance of flexible polymers poses a challenge to the subsequent processing of the top electrode. Figure 1As shown, if conductive silver paste and screen printing are used to prepare the top electrode, the silver paste used for screen printing is generally composed of silver (Ag) particles, resin, solvent, additives, etc. After screen printing, most of the solvent can be removed by baking the sample in an oven, leaving only micron or nano-sized silver particles and some resin. To achieve a certain top electrode thickness using the above method, multiple layers of screen printing are usually required. That is, the first layer of screen printing is performed, coating the first layer of silver paste, and after the silver paste is baked and cured, the second layer of screen printing is performed, and then baked and cured again. This process is repeated for the third or more layers of screen printing and silver paste baking and curing until the target thickness of the top electrode is achieved.

[0006] Fabricating the top electrode using multi-layer screen printing involves numerous steps to achieve the desired thickness. Furthermore, each layer requires a different screen printing stencil design, necessitating stencil switching for each printing operation. This increases the complexity of the process, extends the production cycle, and raises the probability of production anomalies, leading to increased production costs. Additionally, the uniform thickness of the top electrode across all areas created by screen printing results in material waste when thickness requirements are low in certain regions. Finally, during multi-layer screen printing, the silver paste layer is prone to internal air voids or resin agglomeration. The presence of large metal particles in the silver paste, such as silver particles with a diameter of approximately micrometers, results in a high surface roughness of the top electrode layer, increasing the acoustic attenuation coefficient of ultrasonic waves and ultimately reducing the sensitivity of the ultrasonic sensor.

[0007] Therefore, to solve the above-mentioned technical problems, improve the structural design and manufacturing process of ultrasonic sensors, and enhance the performance of ultrasonic sensors, this utility model provides an ultrasonic sensor comprising: a substrate, a pad area, a bottom electrode, a piezoelectric layer, and a top electrode; the bottom electrode is disposed on the upper surface of the substrate, the piezoelectric layer is disposed above the substrate and covers the bottom electrode, the pad area is disposed on the upper surface of the substrate and spaced apart from the bottom electrode; the top electrode comprises a first metal layer and a second metal layer, the thickness of the first metal layer being less than the thickness of the second metal layer; the first metal layer covers the piezoelectric layer and extends along the surface of the piezoelectric layer and the substrate surface in contact with the piezoelectric layer to the pad area, and is electrically connected to the pad area; the second metal layer covers a portion of the area above the first metal layer, and the first projection area of ​​the second metal layer toward the substrate is within the second projection area of ​​the piezoelectric layer toward the substrate.

[0008] An embodiment of this utility model also provides an ultrasonic fingerprint recognition module, including: the ultrasonic sensor described above, and a processor connected to the ultrasonic sensor, the processor being used to receive signals from the ultrasonic sensor and convert the signals into fingerprint recognition information.

[0009] An embodiment of this utility model also provides an electronic device, including: the ultrasonic sensor described above or the ultrasonic fingerprint recognition module described above.

[0010] Compared to existing technologies, this invention adjusts the structural design and fabrication process of the top electrode of the ultrasonic sensor. The adjusted top electrode structure includes a first metal layer and a second metal layer, with the thickness of the first metal layer being less than that of the second metal layer. The first metal layer covers the piezoelectric layer and extends along the surface of the piezoelectric layer and the substrate surface adjacent to the piezoelectric layer to the pad area, where it is electrically connected. The second metal layer covers a portion of the area above the first metal layer, and the first projection area of ​​the second metal layer toward the substrate is within the second projection area of ​​the piezoelectric layer toward the substrate. The top electrode structure comprises only two metal layers, reducing the fabrication process. Furthermore, metal layers of different thicknesses can provide different thickness requirements for different areas of the top electrode, ensuring suitable materials for the product and reducing unnecessary material waste.

[0011] In addition, the first metal layer is a thin film metal formed by deposition.

[0012] In addition, the first metal layer is the thin film metal formed by vacuum sputtering, electron beam evaporation or chemical plating.

[0013] In addition, the second metal layer is a metal foil with a conductive adhesive layer on its surface, and the surface of the metal foil with the conductive adhesive layer is attached to the surface of the first metal layer.

[0014] In addition, the second metal layer is a thick film metal formed by electroplating.

[0015] In addition, the second metal layer is a thick film metal grown on an external substrate and is bonded to the corresponding position of the first metal layer by flip-chip bonding.

[0016] In addition, the thickness of the first metal layer ranges from 0.1 micrometers to 5 micrometers; the thickness of the second metal layer ranges from 5 micrometers to 30 micrometers.

[0017] In addition, the ultrasonic sensor also includes a protective layer; the protective layer covers the top electrode and extends along the surface of the top electrode to cover the sides of the top electrode and the piezoelectric layer. Attached Figure Description

[0018] One or more embodiments are illustrated by way of example with reference numerals in the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Elements with the same reference numerals in the drawings are denoted as similar elements. Unless otherwise stated, the figures in the drawings are not to be limited by scale.

[0019] Figure 1This is a schematic diagram of the structure of an ultrasonic sensor with a top electrode fabricated using a multilayer screen printing method.

[0020] Figure 2 This is a schematic diagram of the ultrasonic sensor in this embodiment;

[0021] Figure 3 This is a top view of the ultrasonic sensor in this embodiment of the solution.

[0022] Figure 4 It is based on the loop sensitivity detection curve of structure one in this embodiment;

[0023] Figure 5 This is a signal bandwidth detection curve based on structure one in this embodiment of the solution;

[0024] Figure 6 This is based on the loop sensitivity detection curve of structure two in this embodiment;

[0025] Figure 7 This is a signal bandwidth detection curve based on structure two in this embodiment of the solution;

[0026] Figure 8 This is an exploded view of the ultrasonic sensor structure according to the embodiment of this solution;

[0027] Figure 9 This is an exploded view of the ultrasonic sensor structure according to the embodiment of this solution;

[0028] Figure 10 This is an exploded view of the ultrasonic sensor structure according to the embodiment of this solution;

[0029] Figure 11 This is an exploded view of the ultrasonic sensor structure according to the embodiment of this solution;

[0030] Figure 12 This is an exploded view of the ultrasonic sensor structure according to the embodiment of this solution;

[0031] Figure 13 This is a structural schematic diagram of the ultrasonic fingerprint recognition module according to an embodiment of this solution. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the various embodiments of this utility model will be described in detail below with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details have been presented in the various embodiments of this utility model to enable readers to better understand this application. However, the technical solutions claimed in this application can be implemented even without these technical details and various changes and modifications based on the following embodiments.

[0033] The division of the following embodiments is for ease of description and should not constitute any limitation on the specific implementation of this utility model. The various embodiments can be combined with or referenced by each other without contradiction.

[0034] Embodiments of this utility model relate to an ultrasonic sensor, such as... Figure 2 As shown, the ultrasonic sensor includes: a substrate 1, a pad area 6, a bottom electrode 2, a piezoelectric layer 3, and a top electrode 4; the bottom electrode 2 is disposed on the upper surface of the substrate 1, the piezoelectric layer 3 is disposed above the substrate 1 and covers the bottom electrode 2, the pad area 6 is disposed on the upper surface of the substrate 1 and is spaced apart from the bottom electrode 1; the top electrode 4 includes a first metal layer 41 and a second metal layer 42, the thickness of the first metal layer 41 is less than the thickness of the second metal layer 42; the first metal layer 41 covers the piezoelectric layer 3 and extends along the surface of the piezoelectric layer 3 and the surface of the substrate 1 connected to the piezoelectric layer 3 to the pad area 6, and is electrically connected to the pad area 6; the second metal layer 42 covers a portion of the area above the first metal layer 41, and the first projection area of ​​the second metal layer 42 toward the substrate 1 is within the second projection area of ​​the piezoelectric layer 3 toward the substrate 1.

[0035] Compared to existing technologies, this invention adjusts the structural design and fabrication process of the top electrode of the ultrasonic sensor. The adjusted top electrode structure includes a first metal layer and a second metal layer, with the thickness of the first metal layer being less than that of the second metal layer. The first metal layer covers the piezoelectric layer and extends along the surface of the piezoelectric layer and the substrate surface adjacent to the piezoelectric layer to the pad area, where it is electrically connected. The second metal layer covers a portion of the area above the first metal layer, and the first projection area of ​​the second metal layer toward the substrate is within the second projection area of ​​the piezoelectric layer toward the substrate. The top electrode structure comprises only two metal layers, reducing the fabrication process. Furthermore, metal layers of different thicknesses can provide different thickness requirements for different areas of the top electrode, ensuring suitable materials for the product and reducing unnecessary material waste.

[0036] In this embodiment of the invention, the bottom electrode 2, the piezoelectric layer 3, the top electrode 4, and the protective layer 5 together constitute an acoustic-electric conversion structure. When the ultrasonic sensor is in acoustic emission mode, the bottom electrode 2 is grounded, and the top electrode 4 is used to be excited by an excitation signal to excite the piezoelectric layer 3 to emit ultrasonic signals. When the ultrasonic sensor is in acoustic reception mode, the top electrode 4 is grounded, and the bottom electrode 2 is used to receive the voltage echo signal generated between the top electrode 4 and the bottom electrode 2 when the returned ultrasonic signal acts on the piezoelectric layer 3.

[0037] Furthermore, in this embodiment of the invention, the top electrode 4 does not employ a uniform thickness structure; that is, the coverage areas of the first metal layer 41 and the second metal layer 42 are different, and the thicknesses of the first metal layer 41 and the second metal layer 42 are different. The top electrode 4 is thicker directly above the piezoelectric layer 3 region, with the first metal layer 41 and the second metal layer 42 stacked sequentially above the piezoelectric layer 3 region. However, the thickness of the top electrode 4 is less in the areas of the piezoelectric layer 3 near the sidewall of the pad area 6 and the surface of the substrate 1, or in the area above the substrate 1 that contacts the bottom electrode 2, than the thickness of the top electrode 4 directly above the piezoelectric layer 3 region. In these thinner top electrode regions, only the first metal layer 41 needs to be disposed, without the need to stack the second metal layer 42, thus reducing material waste. The first metal layer 41 is made of thin film metal material, and the second metal layer 42 is made of thick film metal material. The metal types of the first metal layer 41 and the second metal layer 42 include, but are not limited to, alloys of one or more of the following metals: aluminum (Al), copper (Cu), gold (Au), platinum (Pt), tin (Sn), nickel (Ni), and silver (Ag). The first metal layer 41 and the second metal layer 42 can be made of the same type of metal or different types of metal, as long as the electrical connection between the first metal layer 41 and the second metal layer 42 is ensured.

[0038] Furthermore, the first metal layer is a thin-film metal formed by deposition, including methods such as vacuum sputtering, electron beam evaporation, or chemical plating. After the first metal layer is deposited, photolithography, development, and etching are used to remove portions of the first metal layer, forming the desired conductive pathways, such as... Figure 3 As shown, to achieve partial electrical connection between the top electrode 4 and the pad area 6 or the metal traces on the surface of the substrate 1, the top electrode 4 at locations where electrical connection is not required needs to be removed, thereby forming the desired conductive path. After forming the first metal layer, a second metal layer is processed in the region directly above the piezoelectric layer in the first metal layer. Before processing the second metal layer, photoresist can be used to protect the non-processed areas; that is, photoresist is applied to the non-piezoelectric layer areas on the substrate surface, and the photoresist is removed after processing the second metal layer. The second metal layer can be a thick film metal formed by electroplating, or a thick film metal grown externally and bonded to the corresponding position of the first metal layer by flip-chip bonding. Alternatively, the second metal layer can also be a metal foil with a conductive adhesive layer on its surface, with the surface of the metal foil with the conductive adhesive layer attached to the surface of the first metal layer.

[0039] In addition, the thickness control parameters for the ultrasonic sensor material stack are as follows: substrate layer (50–150 micrometers (µm)), bottom electrode layer (0.1–1 µm), piezoelectric layer (5–30 µm), top electrode layer directly above the piezoelectric layer (5–30 µm), top electrode layer in other areas (0.1–5 µm), and protective layer (10–40 µm). In this embodiment, the thickness of the top electrode directly above the piezoelectric layer differs from that of the top electrodes in other areas, and the material used for the top electrode is not conductive silver paste; a metal material more suitable for deposition and electroplating processes has been chosen. Furthermore, the lower limit of the protective layer thickness in this embodiment is reduced, which also reduces processing costs.

[0040] Regarding the structure of the ultrasonic sensor in this embodiment, to verify its performance, the detection results of two indicators—loop sensitivity and signal bandwidth—of the ultrasonic sensor are described below. Loop sensitivity is defined as the ratio of the voltage value of the received echo signal (Volts out) to the voltage value of the transmitted excitation signal (Volts in), commonly expressed as V / V. Signal bandwidth refers to the frequency range corresponding to the signal amplitude dropping to 50% of its peak amplitude (i.e., -6dB). In practical applications, it is usually expressed as a percentage (%) of the difference between the upper and lower limits of the -6dB range and the peak frequency. In applications such as ultrasonic imaging, loop sensitivity is closely related to the system's signal-to-noise ratio (SNR), and bandwidth is closely related to the system's resolution. Generally speaking, the higher the loop sensitivity, the wider the signal bandwidth, the smaller the smallest detail of the imaged object that the system can resolve, and the higher the contrast between the imaged object and the background environment; that is, the higher the imaging resolution of the ultrasonic system and the better the imaging effect.

[0041] like Figures 4 to 7 The following table shows schematic diagrams illustrating the detection results of loop sensitivity and signal bandwidth for two ultrasonic sensor structures. Figure 4 and Figure 5 The graphs show the loop sensitivity and signal bandwidth for Structure 1 (top electrode structure fabricated by multilayer screen printing). Figure 6 and Figure 7 The curves represent the loop sensitivity and signal bandwidth of structure two (a structure with two metal films forming the top electrode).

[0042]

[0043] from Figure 4 and Figure 5The test results show that the resonant center frequency of structure one is 13.8MHz, the echo voltage is 1.97mV / V, and the signal bandwidth is 36%. From... Figure 6 and Figure 7 The test results show that the resonant center frequency of structure two is 13.9MHz, the echo voltage is 4.6mV / V, and the signal bandwidth is 47.2%. This indicates that the ultrasonic sensor of structure two has better loop sensitivity and signal bandwidth in the same frequency band, with signal sensitivity improved by 133% and bandwidth improved by 31% compared to structure one. Therefore, the improved structural design of this invention enables the ultrasonic sensor to have better performance.

[0044] The following details the specific parameter settings for each layer of the ultrasonic sensor structure through the fabrication method of the ultrasonic sensor:

[0045] like Figure 8 As shown, the required patterns for the bottom electrode 2 and pad area 6 are first formed on the upper surface of the substrate 1 by coating, photolithography, and development. Then, the bottom electrode and pad area are fabricated on the substrate by sputtering or electron beam evaporation. The material of the bottom electrode layer can be a transparent conductive material or a non-transparent conductive material. For example, at least one of the metals such as aluminum (Al), copper (Cu), gold (Au), and platinum (Pt), or inorganic conductive materials such as indium tin oxide (ITO), or organic conductive materials such as PEDOT:PSS and graphite, or composite conductive materials of metals and inorganic or organic materials. The material of the bottom electrode layer is at least one of the metals such as aluminum (Al), copper (Cu), gold (Au), and platinum (Pt). The substrate material includes silicon, glass, or polyimide.

[0046] Next, as follows Figure 9 As shown, the piezoelectric layer 3 is processed above the bottom electrode using spin coating, spray coating, slot coating, or screen printing. The piezoelectric layer 3 is preferably made of an organic polymer, such as PVDF and its copolymers PVDF-TRFE or blends PVDF-graphene; alternatively, the piezoelectric layer can also be a mixture of piezoelectric ceramic material and adhesive, such as lead zirconate titanate piezoelectric ceramics (PZT) and its alloys (e.g., lead zirconate titanate lanthanum ceramics (PLZT), lead magnesium niobate (PNZT), potassium sodium niobate (KxNa1-xNbO3, KNN), perovskite phase structure lead magnesium titanate niobate (PMN-PT)), etc., mixed with adhesive; the edge of the piezoelectric layer forms a certain angle with its projection on the substrate, with the angle ranging from 0 to 90°.

[0047] Next, as follows Figure 10As shown, a first metal layer 41 (thin film metal) with a thickness between 0.5-5 μm is deposited on the substrate surface (including the piezoelectric layer and the area outside the piezoelectric layer). Then, a portion of the thin film metal layer is removed using photolithography, development, and etching to form the required conductive path. In order to realize the connection between the top electrode and the external driving circuit, in a certain area, the top electrode is in contact with the metal traces or pads on the substrate surface. The methods for depositing the metal thin film include vacuum sputtering, electron beam evaporation, or chemical plating.

[0048] Next, as follows Figure 11 As shown, a second metal layer 42 (thick film metal) of 5-30 μm is further processed directly above the piezoelectric layer. This can be achieved by first protecting the non-piezoelectric layer areas on the substrate surface with photoresist, then depositing a thick film metal layer directly above the piezoelectric layer using electroplating. After deposition, the photoresist is removed to release the structure. Alternatively, a metal foil with a conductive adhesive layer (not shown) is directly attached and pressed onto the piezoelectric layer. This conductive adhesive layer, after degassing, has a thickness of less than 5 μm and serves to fix the second metal layer while providing electrical connection between the first and second metal layers. Another option is to grow a thick film metal on a temporary substrate and then bond it to the thin film metal above the piezoelectric layer using a flip-chip bonding method. After bonding, the temporary substrate is removed.

[0049] Next, as follows Figure 12 As shown, a protective layer 5 covering the top electrode and piezoelectric layer is prepared on the substrate surface by screen printing, slot coating, or attachment, protecting the top electrode and piezoelectric layer to obtain an ultrasonic sensor. The protective layer can be made of various polymer materials, such as optically clear adhesive (OCA), pressure-sensitive adhesive (PSA), plastics such as polyimide and polyethylene terephthalate (PET), epoxy resin, or a mixture of epoxy resin and metal particles. The protective layer can also be made of metallic materials, including but not limited to Au, Ag, Cu, or Ni; the protective layer can be a single layer or a combination of multiple layers.

[0050] Another feasible embodiment of this utility model relates to an ultrasonic fingerprint recognition module, including: the ultrasonic sensor described above, and a processor connected to the ultrasonic sensor, the processor being used to receive signals from the ultrasonic sensor and convert the signals into fingerprint recognition information.

[0051] Specifically, such as Figure 13As shown, the ultrasonic fingerprint recognition module includes: an ultrasonic sensor 10, a flexible printed circuit board (FPC) 20, a reinforcing member 30, electronic components 40, and a connector 50. The FPC is connected to the pad area 6 of the ultrasonic sensor via low-temperature bonding, with the bonding medium including but not limited to anisotropic conductive adhesive (ACF). The electronic components include, but are not limited to, passive devices such as inductors, capacitors, and resistors, and active devices such as boost chips and signal preprocessing chips, primarily providing excitation signals to the ultrasonic sensor and preprocessing the echo signals. The connector at the end of the FPC furthest from the ultrasonic sensor is used to connect to the main control chip of the backend system, providing communication and interaction.

[0052] Compared with related technologies, the ultrasonic fingerprint recognition module provided in this embodiment of the present invention is equipped with the ultrasonic sensor provided in the aforementioned embodiments. Therefore, it also has the technical effects provided in the aforementioned embodiments, has better performance, and can better realize the ultrasonic fingerprint function.

[0053] Another feasible embodiment of this utility model relates to an electronic device, including: the ultrasonic sensor described above or the ultrasonic fingerprint recognition module described above.

[0054] Compared with related technologies, the electronic device provided in this embodiment of the present invention is equipped with the ultrasonic sensor or ultrasonic fingerprint recognition module provided in the aforementioned embodiments. Therefore, it also has the technical effects provided in the aforementioned embodiments, which will not be elaborated here.

[0055] Those skilled in the art will understand that the above embodiments are specific embodiments for implementing the present invention, and in practical applications, various changes can be made to them in form and detail without departing from the spirit and scope of the present invention.

Claims

1. An ultrasonic sensor, characterized by, Comprising: a substrate, a pad area, a bottom electrode, a piezoelectric layer and a top electrode; the bottom electrode is disposed on the upper surface of the substrate, the piezoelectric layer is disposed above the substrate and covers the bottom electrode, and the pad area is disposed on the upper surface of the substrate and is spaced apart from the bottom electrode; the top electrode comprises a first metal layer and a second metal layer, the thickness of the first metal layer is less than the thickness of the second metal layer; the first metal layer covers the piezoelectric layer and extends along the surface of the piezoelectric layer and the surface of the substrate connected with the piezoelectric layer to the pad area and is electrically connected with the pad area; the second metal layer covers part of the area above the first metal layer, and the first projection area of the second metal layer in the direction of the substrate is within the second projection area of the piezoelectric layer in the direction of the substrate.

2. The ultrasonic sensor of claim 1, wherein, The first metal layer is a thin film metal formed by deposition.

3. The ultrasonic sensor of claim 2, wherein, The first metal layer is a thin film metal formed by vacuum sputtering, electron beam evaporation or chemical plating.

4. The ultrasonic sensor of claim 1, wherein, The second metal layer is a metal foil with a thin layer of conductive adhesive on its surface, and the surface of the metal foil with the thin layer of conductive adhesive is in contact with the surface of the first metal layer.

5. The ultrasonic sensor of claim 1, wherein, The second metal layer is a thick film metal formed by electroplating.

6. The ultrasonic sensor of claim 5, wherein, The second metal layer is a thick film metal grown on an external substrate and bonded to the corresponding position of the first metal layer by flip-chip method.

7. The ultrasonic sensor of claim 1, wherein, The thickness of the first metal layer ranges from 0.1 microns to 5 microns, and the thickness of the second metal layer ranges from 5 microns to 30 microns.

8. Ultrasonic sensor according to any one of claims 1 to 7, characterized in that Further comprising: a protective layer; the protective layer covers the top electrode and extends along the surface of the top electrode to cover the side surface of the top electrode and the piezoelectric layer.

9. An ultrasonic fingerprint identification module, characterized in that, Comprising: the ultrasonic sensor according to any one of claims 1 to 8, and a processor connected with the ultrasonic sensor, the processor being configured to receive the signal of the ultrasonic sensor and convert the signal into fingerprint identification information.

10. An electronic device, comprising: Comprising: the ultrasonic sensor according to any one of claims 1 to 8, or the ultrasonic fingerprint identification module according to claim 9.

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