An ultrasonic sensor, an ultrasonic fingerprint identification module and an electronic device
By adding a metal layer to the pad area and improving the top electrode structure, the chip fragmentation problem in the bonding process of ultrasonic sensors was solved, improving production yield and enhancing sensor performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- CHIPSEMI SEMICON (NINGBO) CO LTD
- Filing Date
- 2025-06-19
- Publication Date
- 2026-06-12
Smart Images
Figure CN224354860U_ABST
Abstract
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] However, the current structure of ultrasonic sensors has at least the following drawbacks: In order to achieve a thin and light module structure and better acoustic response, the substrate thickness of the sensor often needs to be reduced to less than 100 micrometers. This leads to the risk of chip fragmentation during the bonding of the sensor chip with the circuit board to obtain the ultrasonic fingerprint recognition module, which reduces the production yield of the module. 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 adding a first metal layer to the pad area, and by combining the pad area and the first metal layer to increase the toughness of the pad area, the risk of chip fragmentation during the bonding of the sensor chip to the circuit board to obtain the ultrasonic fingerprint recognition module is reduced, thereby improving the production yield of the module.
[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. In order to achieve a thin and light module structure and a better acoustic response, the substrate thickness often needs to be reduced to less than 100 micrometers, which leads to the risk of chip fragmentation during the bonding process of the sensor chip with the flexible circuit board.
[0006] Therefore, to solve the aforementioned technical problem of fragmentation risk and improve the production yield of modules, this utility model provides an improved ultrasonic sensor structure, 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; a first metal layer is disposed on the pad area, wherein the pad area with the added first metal layer is used for bonding connection with an external circuit board.
[0007] An embodiment of this utility model also provides an ultrasonic fingerprint recognition module, including: the ultrasonic sensor described above, and a circuit board connected to the ultrasonic sensor, the circuit board being used to receive signals from the ultrasonic sensor and convert the signals into fingerprint recognition information.
[0008] 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.
[0009] Compared with the prior art, the present invention improves the structure of the pad area by setting a first metal layer on the original pad area to increase the toughness of the pad area. The pad area with the added first metal layer is used for bonding connection with the external circuit board. The first metal layer can play a stress buffering role during the bonding process, thereby reducing the risk of fragmentation when the pad area is bonded to the external circuit board and improving the production yield of the module.
[0010] Additionally, the top electrode includes a second metal layer and a third metal layer; the second metal layer covers the area above the piezoelectric layer; the third metal layer covers the area above the second metal 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.
[0011] In addition, the thickness of the second metal layer is greater than the thickness of the third metal layer.
[0012] In addition, the first metal layer and the third metal layer are made of the same material.
[0013] In addition, the thickness of the first metal layer ranges from 3 micrometers to 5 micrometers.
[0014] In addition, the thickness of the substrate ranges from 90 micrometers to 110 micrometers.
[0015] In addition, the thickness of the second metal layer ranges from 10 micrometers to 30 micrometers; the thickness of the third metal layer ranges from 1 micrometer to 10 micrometers.
[0016] 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
[0017] 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.
[0018] Figure 1 This is a schematic diagram of the structure of an ultrasonic sensor with a top electrode fabricated using a multilayer screen printing method.
[0019] Figure 2 This is a schematic diagram of the ultrasonic sensor in this embodiment;
[0020] Figure 3 This is a comparison chart of the echo signal sensitivity detection results of the structure and the multi-layer screen-printed structure in this embodiment of the solution;
[0021] Figure 4 This is a comparison chart of the echo signal bandwidth detection results of the structure and the multi-layer silkscreen structure in this embodiment of the solution;
[0022] Figure 5 This is an exploded view of the ultrasonic sensor structure according to the embodiment of this solution;
[0023] Figure 6 This is an exploded view of the ultrasonic sensor structure according to the embodiment of this solution;
[0024] Figure 7 This is an exploded view of the ultrasonic sensor structure according to the embodiment of this solution;
[0025] Figure 8 This is an exploded view of the ultrasonic sensor structure according to the embodiment of this solution;
[0026] Figure 9 This is an exploded view of the ultrasonic sensor structure according to the embodiment of this solution;
[0027] Figure 10 This is an exploded view of the ultrasonic sensor structure according to the embodiment of this solution;
[0028] Figure 11 This is a structural schematic diagram of the ultrasonic fingerprint recognition module according to an embodiment of this solution. Detailed Implementation
[0029] 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.
[0030] 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.
[0031] 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, and the pad area 6 is disposed on the upper surface of the substrate 1 and spaced apart from the bottom electrode 1. A first metal layer 7 is disposed on the pad area 6, wherein the pad area 6 with the added first metal layer 7 is used for bonding connection with an external circuit board. The thickness of the first metal layer can be adjusted according to the sensor's sensitivity and toughness requirements. Specifically, the thickness of the first metal layer ranges from 3 micrometers to 5 micrometers. To avoid the first metal layer affecting the original circuit connection of the pad area, the first metal layer can be added in the area where the pad area is bonded to the circuit board. In areas of the pad area where there is no risk of bonding fragments, no additional first metal layer is needed, saving space occupied by the ultrasonic sensor.
[0032] Compared with the prior art, the present invention improves the structure of the pad area by setting a first metal layer on the original pad area to increase the toughness of the pad area. The pad area with the added first metal layer is used for bonding connection with the external circuit board. The first metal layer can play a stress buffering role during the bonding process, thereby reducing the risk of fragmentation when the pad area is bonded to the external circuit board and improving the production yield of the module.
[0033] Furthermore, ultrasonic sensors used for fingerprint recognition typically 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 challenges to the subsequent fabrication 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.
[0034] 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, screen-printed top electrodes exhibit uniform thickness across all areas, making thickness control difficult. 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 micrometer-scale diameters, results in a high surface roughness of the top electrode layer, increasing the acoustic attenuation coefficient and ultimately reducing the sensitivity of the ultrasonic sensor.
[0035] For fabrication using multi-layer screen printing, embodiments of this invention provide an ultrasonic sensor, such as... Figure 2 As shown, the top electrode 4 includes a second metal layer 41 and a third metal layer 42. The second metal layer 41 covers the piezoelectric layer 3. The third metal layer 42 covers the area above the second metal layer 41 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, where it is electrically connected. The top electrode structure contains only two metal layers, reducing the fabrication process. Furthermore, the second and third metal layers cover different areas, allowing for thickness control of different areas by adjusting the thickness of the second and third metal layers, thus avoiding material waste.
[0036] The thickness of the second metal layer is greater than that of the third metal layer. The second metal layer is a thick film metal layer ranging from 10 micrometers to 30 micrometers; the third metal layer is a thin film metal layer ranging from 1 micrometer to 10 micrometers. Both the second and third metal layers can be generated by electroplating. Specifically, the second metal layer is processed by electroplating directly above the piezoelectric layer, and then the third metal layer is deposited by electroplating a second time from the surface of the second metal layer to the surface of the substrate. When electroplating to form the third metal layer, the electroplated metal layer can cover the pad area. After removing the metal layer between the piezoelectric layer and the pad area, the metal layer covering the piezoelectric layer becomes the third metal layer, and the metal layer covering the pad area becomes the first metal layer. The first and third metal layers are made of the same material and are processed using the same process, which allows for simultaneous control of the thickness of the top electrode and the pad area, saving one processing step.
[0037] In addition, such as Figure 2 As shown, the ultrasonic sensor also includes a protective layer 5; the protective layer 5 covers the top electrode 4 and extends along the surface of the top electrode 4, covering the sides of the top electrode 4 and the piezoelectric layer 3. The protective layer can protect the internal structure of the ultrasonic sensor from damage by the external environment and extend the service life of the ultrasonic sensor.
[0038] When the ultrasonic sensor is working, the bottom electrode 2, the piezoelectric layer 3, the top electrode 4, and the protective layer 5 together constitute the 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.
[0039] 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.
[0040] like Figures 3 to 4 The diagram shows a comparison of the loop sensitivity and signal bandwidth detection results of an ultrasonic sensor structure fabricated by multilayer screen printing and an ultrasonic sensor structure fabricated by two metal layers according to this invention, in the same frequency band. Figure 3 It can be seen that the ultrasonic sensor structure of this utility model has better echo signal sensitivity, with an echo signal sensitivity improvement of 133% compared to the multi-layer screen printing fabrication method. Figure 4 It can be seen that the ultrasonic sensor structure of this invention has a better echo signal bandwidth, which is 31% higher than that of the multi-layer screen printing method. Therefore, the improved structural design of this invention can enable the ultrasonic sensor to have better performance.
[0041] The following details the specific parameter settings for each layer of the ultrasonic sensor structure through the fabrication method of the ultrasonic sensor:
[0042] like Figure 5As 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 2 and pad area 6 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.
[0043] Next, as follows Figure 6 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°.
[0044] Next, as follows Figure 7 As shown, a second metal layer 41 (thick film metal layer) of 10 micrometers to 30 micrometers is processed on top of the piezoelectric layer using electroplating. Specifically, photoresist can be used to protect the non-piezoelectric layer area on the substrate surface first, and then a thick film metal layer can be deposited on top of the piezoelectric layer using electroplating. After deposition, the photoresist on the surface is removed to release the structure.
[0045] Next, as follows Figure 8As shown, a thin metal layer with a thickness of 1 to 10 micrometers is deposited on the substrate surface using a second electroplating method. Then, photolithography, development, and etching are used to remove the thin metal layer between the piezoelectric layer and the pad area, simultaneously forming a third metal layer 42 above the piezoelectric layer and a first metal layer 7 above the pad area. In this step, the thickness of the sensor's top electrode and the pad area is simultaneously increased. The second electroplating of the thin metal layer also facilitates the removal of the metal layer between the piezoelectric layer and the pad area; that is, the thickness of the top electrode is increased as much as possible through the second metal layer, and then the thickness of the top electrode and the first metal layer are supplemented in one process using the third metal layer.
[0046] Next, as follows Figure 9 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.
[0047] Finally, as Figure 10 As shown, the sensor substrate is thinned using mechanical grinding or chemical mechanical polishing methods, with the final substrate thickness controlled between 90 micrometers and 110 micrometers.
[0048] The ultrasonic sensor manufactured using the above method has a top electrode thickness equal to the sum of the thicknesses of the second metal layer formed by the first electroplating and the third metal layer formed by the second electroplating. The thickness of the processed pad area is equal to the sum of the bottom electrode thickness and the thickness of the first metal layer formed by the second electroplating. The bottom electrode layer thickness ranges from 0.1 micrometers to 1 micrometer, the piezoelectric layer thickness ranges from 5 micrometers to 30 micrometers, and the protective layer thickness ranges from 5 micrometers to 30 micrometers. The materials of the electroplated first, second, and third metal layers 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).
[0049] Another feasible embodiment of this utility model relates to an ultrasonic fingerprint recognition module, including: the ultrasonic sensor described above, and a circuit board connected to the ultrasonic sensor, the circuit board being used to receive signals from the ultrasonic sensor and convert the signals into fingerprint recognition information.
[0050] Specifically, such as Figure 11 As shown, the ultrasonic fingerprint recognition module includes: an ultrasonic sensor 10, a flexible printed circuit board 20, a reinforcing member 30, electronic components 40, and a connector 50. The flexible printed circuit board and the pad area 6 of the ultrasonic sensor are electrically connected through bonding with anisotropic conductive film (ACF). The first metal layer 7 added between the pad area 6 and the anisotropic conductive film 8 ensures good conductivity between the ultrasonic sensor 10 and the circuit board 20, while also acting as a stress buffer during bonding, reducing the risk of sensor cracking and improving the production yield of the ultrasonic fingerprint recognition module. 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. They mainly provide excitation signals to the ultrasonic sensor and preprocess the echo signals. The connector at the end of the flexible printed circuit board 20 away from the ultrasonic sensor is used to connect to the main control chip of the backend system, providing communication and interaction.
[0051] 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.
[0052] 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.
[0053] 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.
[0054] 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 in that, include: Substrate, pad area, bottom electrode, piezoelectric layer, and 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 spaced apart from the bottom electrode; A first metal layer is provided on the pad area, wherein the pad area with the added first metal layer is used for bonding connection with an external circuit board.
2. The ultrasonic sensor according to claim 1, characterized in that, The top electrode includes: a second metal layer and a third metal layer; The second metal layer covers the piezoelectric layer; The third metal layer covers the area above the second metal 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.
3. The ultrasonic sensor according to claim 2, characterized in that, The thickness of the second metal layer is greater than the thickness of the third metal layer.
4. The ultrasonic sensor according to claim 2, characterized in that, The first metal layer and the third metal layer are made of the same material.
5. The ultrasonic sensor according to any one of claims 1 to 4, characterized in that, The thickness of the first metal layer ranges from 3 micrometers to 5 micrometers.
6. The ultrasonic sensor according to claim 1, characterized in that, The thickness of the substrate ranges from 90 micrometers to 110 micrometers.
7. The ultrasonic sensor according to claim 2, characterized in that, The thickness of the second metal layer ranges from 10 micrometers to 30 micrometers; the thickness of the third metal layer ranges from 1 micrometer to 10 micrometers.
8. The ultrasonic sensor according to claim 1, characterized in that, Also includes: 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.
9. An ultrasonic fingerprint recognition module, characterized in that, include: The ultrasonic sensor as described in any one of claims 1 to 8, and the circuit board connected to the ultrasonic sensor, the circuit board being configured to receive signals from the ultrasonic sensor and convert the signals into fingerprint recognition information.
10. An electronic device, characterized in that, include: The ultrasonic sensor as described in any one of claims 1 to 8, or the ultrasonic fingerprint recognition module as described in claim 9.