Ultrasonic sensor, electronic device and preparation method for ultrasonic sensor

Abstract

An ultrasonic sensor, an electronic device and a preparation method for an ultrasonic sensor, which relate to the technical field of electronic devices. The ultrasonic sensor comprises a substrate, a plurality of piezoelectric layers and a plurality of electrode layers. The piezoelectric layers and the electrode layers are alternately stacked, and each piezoelectric layer is arranged between two adjacent electrode layers. In the direction away from the substrate, the Curie temperature of the piezoelectric layers gradually decreases. In the provided ultrasonic sensor, the polarization of piezoelectric layers is stable, and the degree of polarization is relatively high, thereby effectively improving the performance of the ultrasonic sensor.

Description

Ultrasonic sensor, electronic device, and method for manufacturing ultrasonic sensor

[0001] This application claims priority to the Chinese patent application filed with the State Intellectual Property Office on February 21, 2024, with application number 202410198120.0 and application name “Ultrasonic sensor, electronic device and method for preparing ultrasonic sensor”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the technical field of electronic equipment, and in particular to an ultrasonic sensor, an electronic device, and a method for manufacturing an ultrasonic sensor. Background Art

[0003] In an ultrasonic sensor, an ultrasonic transceiver may be used to transmit ultrasonic waves toward an object to be detected through an ultrasonic transmission medium and receive ultrasonic waves reflected back from the object to be detected, thereby completing detection of the object to be detected.

[0004] For example, in a fingerprint ultrasonic sensor, ultrasonic waves emitted by an ultrasonic transceiver are transmitted to the finger and reflected back to the transceiver at varying intensities at the ridges and valleys of the fingerprint. The reflected signals are processed to generate an image of the fingerprint, enabling fingerprint image acquisition and recognition.

[0005] However, with the diversification of application scenarios, higher requirements are placed on the performance of ultrasonic sensors.

[0006] Summary of the Invention

[0007] The embodiments of the present application provide an ultrasonic sensor, an electronic device, and a method for manufacturing an ultrasonic sensor, the purpose of which is to ensure that the piezoelectric layer has a high degree of polarization, thereby improving the performance of the ultrasonic sensor.

[0008] To achieve the above objectives, the embodiments of the present application adopt the following technical solutions:

[0009] In a first aspect, an ultrasonic sensor is provided. The ultrasonic sensor includes a substrate, a multi-layer piezoelectric layer, and a multi-layer electrode layer.

[0010] The multi-layer piezoelectric layer and the multi-layer electrode layer are arranged on the same side of the substrate, the piezoelectric layer and the electrode layer are alternately stacked, and each piezoelectric layer is arranged between two adjacent electrode layers. The Curie temperature of the piezoelectric layer gradually decreases as it moves away from the substrate.

[0011] In the ultrasonic sensor provided in the embodiment of the present application, the Curie temperature of the multi-layer piezoelectric layer is set to gradually decrease in the direction away from the substrate, so that the Curie temperature of the multi-layer piezoelectric layer changes in a gradient, thereby facilitating setting the annealing temperature of the subsequently prepared piezoelectric layer between the Curie temperature of the previously prepared piezoelectric layer and the Curie temperature of the subsequently prepared piezoelectric layer, thereby avoiding depolarization of the previously prepared piezoelectric layer during the annealing process of the subsequently prepared piezoelectric layer, thereby ensuring that each piezoelectric layer can have a high degree of polarization. During the operation of the ultrasonic sensor, the piezoelectric layer is ensured to have a good piezoelectric effect, for example, the intensity of the ultrasonic wave generated by the piezoelectric layer can be increased, thereby improving the performance of the ultrasonic sensor.

[0012] In a possible implementation of the first aspect, the difference in Curie temperature between two adjacent piezoelectric layers is 5° C. to 20° C. This ensures that all piezoelectric layers have good piezoelectric effect.

[0013] In a possible implementation of the first aspect, the annealing temperature of the piezoelectric layer farther from the substrate is lower than the Curie temperature of the piezoelectric layer closer to the substrate. This ensures that the piezoelectric layer farther from the substrate is fully annealed, maintaining its polarization level. Furthermore, the high-temperature annealing of the piezoelectric layer farther from the substrate prevents depolarization of the piezoelectric layer closer to the substrate, thereby ensuring that all piezoelectric layers exhibit a good piezoelectric effect.

[0014] In a possible implementation of the first aspect, an electrode layer located between two adjacent piezoelectric layers is a predetermined electrode layer. The thickness of the predetermined electrode layer is less than or equal to 0.1λ1, where λ1 is the wavelength of the sound wave passing through the predetermined electrode layer. This forms an acoustically transparent layer, allowing sound waves generated by the piezoelectric layers or reflected by the object to be detected to pass through the predetermined electrode layer almost intact. This prevents the predetermined electrode layer located between the two piezoelectric layers from increasing sound wave transmission losses, further improving the performance of the ultrasonic sensor.

[0015] In a possible implementation of the first aspect, the thickness of each of the multiple electrode layers is less than or equal to 0.1λ, where λ is the wavelength of the sound wave passing through the electrode layer itself. That is, the thickness of each of the multiple electrode layers is one-tenth the wavelength of the sound wave passing through it. This allows the sound waves generated by the piezoelectric layer or reflected by the object to be detected to pass through all of the electrode layers almost intact, further reducing sound wave transmission losses in the ultrasonic sensor and thereby further improving the performance of the ultrasonic sensor.

[0016] In a possible implementation of the first aspect, the sum of the thickness-to-wavelength ratios of the multi-layer piezoelectric layers and the thickness-to-wavelength ratios of the multi-layer electrode layers is 0.15N to 0.35N, where N is an odd number.

[0017] By setting the sum of the thickness-to-wavelength ratios of the multi-layer piezoelectric layers and the thickness-to-wavelength ratios of the multi-layer electrode layers to 0.15N to 0.35N, the ultrasonic sensor can form a resonant body that fluctuates approximately at an odd multiple of a quarter wavelength, so that the ultrasonic waves emitted by different piezoelectric layers can be effectively superimposed, thereby enhancing the sound pressure emission intensity of the ultrasonic sensor. At the same time, the overall thickness of the ultrasonic sensor can also be controlled within a smaller range, thereby reducing the attenuation of ultrasonic waves in each membrane layer and further improving the performance of the ultrasonic sensor.

[0018] In a possible implementation of the first aspect, the sum of the thickness-to-wavelength ratios of the multilayer piezoelectric layers and the thickness-to-wavelength ratios of the multilayer electrode layers is 0.25N, where N is an odd number. This facilitates the ultrasonic sensor forming a resonant body having an odd multiple of a quarter wavelength, thereby improving the performance of the ultrasonic sensor.

[0019] In a possible implementation of the first aspect, the sum of the thickness-to-wavelength ratios of the substrate, the multilayer piezoelectric layers, and the multilayer electrode layers is 0.35M to 0.65M, where M is an integer. This allows the ultrasonic sensor to form a resonant body that approximates an integer multiple of one-half wavelength, further facilitating ultrasonic wave superposition and thereby enhancing the resonance effect, thus improving the electrical performance of the ultrasonic sensor.

[0020] In a possible implementation of the first aspect, the ultrasonic sensor further includes a protective layer, which is stacked on a side of the electrode layer furthest from the substrate, and is insulated from the electrode layer. The provision of the protective layer can improve the strength and signal-to-noise ratio of the ultrasonic sensor.

[0021] In a possible implementation manner of the first aspect, the material of the protective layer includes a metal material.

[0022] In a possible implementation of the first aspect, the sum of the thickness-to-wavelength ratios of the film layers from the protective layer to the electrode layer closest to the substrate is 0.15N to 0.35N, where N is an odd number.

[0023] In a possible implementation of the first aspect, the ultrasonic sensor further includes a contact layer, which is laminated on a side of the substrate away from the protective layer, or laminated on a side of the protective layer away from the substrate. That is, the contact layer can be applied top-down or bottom-down, and protects key structures of the ultrasonic sensor from damage by the object to be detected.

[0024] In a possible implementation of the first aspect, the ultrasonic sensor further includes a circuit layer disposed between the electrode layer closest to the substrate and the substrate, the circuit layer including a plurality of pixel circuits spaced apart. The electrode layer closest to the substrate includes a plurality of electrode blocks spaced apart, and the plurality of electrode blocks are electrically connected to the plurality of pixel circuits, thereby enabling image restoration of the object to be detected.

[0025] In a possible implementation of the first aspect, in the multi-layer electrode layer, two spaced-apart electrode layers are electrically connected, with an electrode layer disposed between the two electrically connected electrode layers. This results in different electric potentials on both sides of the piezoelectric layer between two adjacent electrode layers, thereby triggering the piezoelectric effect of the piezoelectric layer.

[0026] In a possible implementation of the first aspect, the ultrasonic sensor further includes a first side trace and a second side trace, the first side trace and the second side trace being arranged on opposite sides of the multilayer electrode layer along a first direction parallel to the substrate. The multilayer electrode layer includes multiple first sublayers and multiple second sublayers, the first sublayers and the second sublayers being alternately stacked; two adjacent first sublayers are electrically connected via the first side trace, and two adjacent second sublayers are electrically connected via the second side trace; the first side trace is insulated from the second sublayer, and the second side trace is insulated from the first sublayer.

[0027] In a second aspect, a method for preparing an ultrasonic sensor is provided, the method comprising:

[0028] Multiple electrode layers and multiple piezoelectric layers are formed on the same side of a substrate. The electrode layers and piezoelectric layers are alternately stacked, with each piezoelectric layer positioned between two adjacent electrode layers. The Curie temperature of the piezoelectric layer decreases as it moves away from the substrate.

[0029] The forming of the piezoelectric layer includes forming a piezoelectric thin film, annealing the piezoelectric thin film, wherein the annealing temperature of the piezoelectric thin film farther from the substrate is lower than the Curie temperature of the piezoelectric thin film closer to the substrate, and polarizing the piezoelectric thin film to form the piezoelectric layer.

[0030] In a third aspect, an electronic device is provided, comprising a circuit board and the ultrasonic sensor provided by any one embodiment of the first aspect, wherein the circuit board and the ultrasonic sensor are coupled to each other.

[0031] The technical effects brought about by the preparation method in the second aspect and the electronic device in the third aspect can be referred to the technical effects brought about by the design method of the ultrasonic sensor in the first aspect, and will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] FIG1 is a schematic structural diagram of an electronic device provided in an embodiment of the present application;

[0033] FIG2 is a cross-sectional view of an electronic device provided in an embodiment of the present application;

[0034] FIG3 is a cross-sectional view of an ultrasonic sensor provided in an embodiment of the present application;

[0035] FIG4 is another cross-sectional view of the ultrasonic sensor provided in an embodiment of the present application;

[0036] FIG5 is another cross-sectional view of the ultrasonic sensor provided in an embodiment of the present application;

[0037] FIG6 is another cross-sectional view of the ultrasonic sensor provided in an embodiment of the present application;

[0038] FIG7 is another cross-sectional view of the ultrasonic sensor provided in an embodiment of the present application;

[0039] FIG8 is another cross-sectional view of the ultrasonic sensor provided in an embodiment of the present application;

[0040] FIG9 is a graph showing the thickness of the electrode layer versus acoustic transmittance;

[0041] FIG10 is another cross-sectional view of the ultrasonic sensor provided in an embodiment of the present application;

[0042] FIG11 is another cross-sectional view of the ultrasonic sensor provided in an embodiment of the present application;

[0043] FIG12 is another cross-sectional view of the ultrasonic sensor provided in an embodiment of the present application;

[0044] FIG13 is a frequency-sound pressure curve diagram of the protective layer;

[0045] FIG14 is a flow chart of a preparation process of an ultrasonic sensor provided in an embodiment of the present application;

[0046] FIG15 is a flow chart of a preparation process of a piezoelectric layer provided in an embodiment of the present application. DETAILED DESCRIPTION

[0047] The following will be combined with the accompanying drawings to clearly and completely describe the technical solutions in some embodiments of the present application. Obviously, the embodiments described are only some embodiments of the present application, not all embodiments. Based on the embodiments provided in this application, all other embodiments obtained by ordinary technicians in this field are within the scope of protection of this application.

[0048] In the description of this application, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on this application.

[0049] Unless the context requires otherwise, throughout the specification and claims, the term "including" is to be interpreted as having an open, inclusive meaning, that is, "including, but not limited to." In the description of the specification, the terms "one embodiment," "some embodiments," "exemplary embodiments," "exemplarily," or "some examples" are intended to indicate that specific features, structures, materials, or characteristics associated with the embodiment or example are included in at least one embodiment or example of the present application. The schematic representations of the above terms do not necessarily refer to the same embodiment or example. In addition, the specific features, structures, materials, or characteristics may be included in any one or more embodiments or examples in any appropriate manner.

[0050] In the following, the terms "first," "second," etc. are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly specifying the number of the technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the embodiments of this application, unless otherwise specified, "plurality" means two or more.

[0051] Connection / connected: can refer to a mechanical connection relationship or a physical connection relationship, that is, A and B are connected or A and B are connected, which can mean that there is a fastening component (such as a screw, bolt, rivet, etc.) between A and B, or A and B are in contact with each other and A and B are difficult to separate, wherein A and B can be fixedly connected, detachably connected, or integrated; can be directly connected, or indirectly connected through an intermediate medium.

[0052] Coupling: can be understood as direct coupling and / or indirect coupling, and "coupling connection" can be understood as direct coupling connection and / or indirect coupling connection. Direct coupling can also be called "electrical connection", which is understood as the direct or indirect physical contact and electrical conduction between components, such as the connection between different components in the circuit structure through physical lines such as printed circuit board (PCB) copper foil or wires that can transmit electrical signals; "indirect coupling" can be understood as two conductors being electrically conductive in an airless / non-contact manner. In one embodiment, indirect coupling can also be called capacitive coupling, for example, signal transmission is achieved by forming an equivalent capacitance through coupling between the gap between two conductive parts.

[0053] “At least one of A, B and C” has the same meaning as “at least one of A, B or C” and both include the following combinations of A, B and C: A only, B only, C only, the combination of A and B, the combination of A and C, the combination of B and C, and the combination of A, B and C.

[0054] “A and / or B” includes the following three combinations: A only, B only, and a combination of A and B.

[0055] As used herein, "parallel", "perpendicular", and "equal" include the situations described and situations similar to the situations described, and the range of the similar situations is within an acceptable deviation range, wherein the acceptable deviation range is as determined by a person of ordinary skill in the art taking into account the measurement in question and the errors associated with the measurement of the specific quantity (i.e., the limitations of the measurement system). For example, "parallel" includes absolute parallelism and approximate parallelism, wherein the acceptable deviation range of approximate parallelism can be, for example, a deviation within 5°; "perpendicular" includes absolute perpendicularity and approximate perpendicularity, wherein the acceptable deviation range of approximate perpendicularity can also be, for example, a deviation within 5°. "Equal" includes absolute equality and approximate equality, wherein the acceptable deviation range of approximate equality can be, for example, that the difference between the two equals is less than or equal to 5% of either one.

[0056] Exemplary embodiments are described herein with reference to cross-sectional and / or plan views that are idealized exemplary drawings. In the drawings, the thicknesses of layers and regions are exaggerated for clarity. Therefore, variations in shape relative to the drawings due to, for example, manufacturing techniques and / or tolerances are contemplated. Therefore, the exemplary embodiments should not be construed as limited to the shapes of the regions shown herein, but rather include deviations in shape due to, for example, manufacturing. Therefore, the regions shown in the drawings are schematic in nature, and their shapes are not intended to illustrate the actual shape of regions of the device and are not intended to limit the scope of the exemplary embodiments.

[0057] In addition, the scenarios described in the embodiments of the present application are intended to more clearly illustrate the technical solutions of the embodiments of the present application, and do not constitute a limitation on the technical solutions provided in the embodiments of the present application. A person of ordinary skill in the art will know that with the emergence of new scenarios, the technical solutions provided in the embodiments of the present application are also applicable to similar technical problems.

[0058] As a mainstream interaction method, biometric recognition (such as fingerprint recognition) is widely used for user identification, unlocking, and secure payments on mobile phones, becoming an indispensable feature of today's mobile phones. Furthermore, fingerprint recognition is used to confirm user identity in everyday household applications, including tablets, laptops, and door locks. Another potential application area for fingerprint recognition is smart cars. For example, on car door handles, drivers can use fingerprint recognition to authenticate their identity and open the door, completely eliminating the cumbersome task of fumbling with car keys. Furthermore, fingerprint unlocking inside the car can also include engine ignition. When the driver presses the button to start the car, the car automatically authenticates the user using their fingerprint. Even more conveniently, fingerprint unlocking can record the driver's settings during driving by recording their information. After the vehicle starts, the user's settings and cockpit configuration (such as seats and rearview mirrors) are loaded by authenticating the driver, providing a user-friendly experience for family members. Therefore, biometric recognition technology holds great research value.

[0059] An embodiment of the present application provides an electronic device that has a biometric detection function for a pressed object. For example, the electronic device can detect fingerprints, palm prints, or handprints. The electronic device is, for example, a consumer electronic product, a home electronic product, or an in-vehicle electronic product with a biometric detection function. Among them, consumer electronic products include mobile phones, tablet computers, laptop computers, e-readers, personal computers (PCs), personal digital assistants (PDAs), desktop monitors, gaming devices, smart wearable products (e.g., smart watches, smart bracelets, smart jewelry), virtual reality (VR) terminal devices, augmented reality (AR) terminal devices, drones, electronic databases, bank ATMs, etc. Home electronic products include smart door locks, televisions, remote controls, refrigerators, and rechargeable small household appliances (e.g., soymilk makers, robot vacuums). In-vehicle electronic products include in-vehicle navigation systems, in-vehicle high-density digital video discs (DVDs), car door handles, and engine ignition. The electronic device may be an electronic device with a display function, or an electronic device without a display function, which is not limited in the embodiments of the present application.

[0060] The following description will be given by taking a mobile phone as an example of an electronic device.

[0061] FIG1 is a schematic structural diagram of an electronic device provided in an embodiment of the present application, and FIG2 is a cross-sectional view of the electronic device provided in an embodiment of the present application.

[0062] As shown in FIG. 1 , the electronic device 1000 may include a cover plate 1 , a display screen 2 , a middle frame 3 and a rear shell 4 .

[0063] 1 , the rear housing 4 and the display screen 2 are located on either side of the middle frame 3 , and the middle frame 3 and the display screen 2 are disposed inside the rear housing 4 . The cover plate 1 is disposed on the side of the display screen 2 away from the middle frame 3 , with the display surface of the display screen 2 facing the cover plate 1 .

[0064] For example, the display screen 2 can be a low-temperature polysilicon (LTPS) display screen, an active-matrix organic light emitting diode (AMOLED) display screen, a low-temperature polycrystalline oxide (LTPO) display screen, a liquid crystal display (LCD), or a micro organic light emitting diode (micro LED) display screen. Of course, the embodiment of the present application does not limit the type of the display screen 2. All display screens with display functions are applicable to the embodiment of the present application. The above list is only for reference.

[0065] On this basis, as shown in FIG. 1 and FIG. 2 , the electronic device 1000 further includes an ultrasonic sensor 100 .

[0066] For example, the ultrasonic sensor 100 may be an ultrasonic fingerprint recognition sensor. Referring to FIG2 , the ultrasonic sensor 100 is disposed on one side of the display screen 2. The ultrasonic sensor 100 is used to provide a biometric feature recognition function for the electronic device 1000.

[0067] In addition, those skilled in the art will understand that the structure of the electronic device 1000 shown in the above figures does not constitute a limitation on the electronic device 1000. The electronic device 1000 may include more or fewer components than shown in the figure, or combine certain components, or arrange the components differently.

[0068] For example, referring to FIG1 and FIG2 , the electronic device 1000 may further include a circuit board 200 . Referring to FIG2 , the circuit board 200 is coupled to the ultrasonic sensor 100 . For example, the two are directly electrically connected, or the two may be indirectly coupled to each other.

[0069] The circuit board 200 may be a printed circuit board (PCB). Alternatively, the circuit board 200 may be a flexible circuit board, a rigid-flexible circuit board, or the like. Optionally, the circuit board 200 may be fixed between the middle frame 3 and the rear housing 4 by threaded connection, snap connection, or gluing.

[0070] Or for example, the electronic device 1000 may also include multiple peripheral devices, referring to Figure 2, the peripheral device may be a control chip 300. Exemplarily, the control chip 300 and the ultrasonic sensor 100 may be electrically connected through a circuit board 200, and the control chip 300 may control the ultrasonic sensor 100 to perform analysis and identification of the object to be detected (such as a fingerprint).

[0071] Or for example, the electronic device 1000 may also include components such as a battery, a camera, a microphone, a speaker, a radio frequency circuit, an input unit, a sensor, an audio circuit, a wireless fidelity (WiFi) module, a power supply, and a Bluetooth module, which are not described in detail here.

[0072] Biometric technology has been widely used in our daily lives. Fingerprints and palm prints, due to their uniqueness, difficulty in obtaining, and ease of use, have become a mainstream recognition technology in consumer electronics, smart homes, and industrial sectors. Currently, the main fingerprint recognition technologies on the market include capacitive, optical, and ultrasonic.

[0073] Ultrasonic fingerprint recognition technology, among other things, is a security authentication technology that transmits ultrasonic waves from under a screen (e.g., display screen 2), penetrating the screen's laminated layers to detect fingerprint information on the screen's surface. The ultrasonic wave then transmits it back to its original location for fingerprint information reproduction. Due to its fast unlocking speed, wide applicability, and 3D anti-counterfeiting capabilities, ultrasonic fingerprint recognition is gradually becoming a mainstream technology in biometrics.

[0074] However, with the development of screens, the acoustic performance of screens produced by different manufacturers varies. Some screens have high penetration rates, while some screens have low penetration rates. It is necessary to maximize the performance of ultrasonic fingerprint recognition sensors to cover more screen needs. In addition, many users have the habit of applying tempered films, anti-peep films, etc. These added film materials will attenuate ultrasonic signals, resulting in a decrease in the fingerprint contrast in ultrasonic fingerprint recognition sensors, affecting recognition capabilities. Moreover, with the rise of folding screens, the metal support layer in the folding screen will also severely attenuate the ultrasonic signal, or the development of COE screens may also affect the recognition performance of ultrasonic fingerprint recognition sensors. Therefore, how to further improve the recognition capability of ultrasonic fingerprint recognition sensors has become a problem to be solved in current biometric recognition technology.

[0075] To solve the above technical problems, an embodiment of the present application provides an ultrasonic sensor 100.

[0076] Exemplarily, the ultrasonic sensor 100 may employ ultrasonic under-screen fingerprint recognition technology.

[0077] For example, the ultrasonic sensor 100 may be used as a separate device, or may be applied in the aforementioned electronic device 1000 .

[0078] FIG3 and FIG4 are schematic structural diagrams of an ultrasonic sensor 100 provided in an embodiment of the present application.

[0079] As shown in FIG. 3 and FIG. 4 , the ultrasonic sensor 100 includes a substrate 10 , a multi-layer electrode layer 20 , and a multi-layer piezoelectric layer 30 .

[0080] The substrate 10 is used as a carrier plate to provide support and bearing during the manufacturing process of the electrode layer 20 and the piezoelectric layer 30 , thereby preventing the electrode layer 20 or the piezoelectric layer 30 from having defects such as breakage, cracking, or depression.

[0081] For example, the substrate 10 may be made of a polymer material such as glass, silicon wafer, polyimide (PI), or polyethylene terephthalate (PET). For example, the substrate 10 may be a glass substrate.

[0082] The electrode layer 20 is used to apply an electrical signal (e.g., a high-voltage pulse signal, a fixed voltage level, etc.), thereby creating a potential difference between the two surfaces of the piezoelectric layer 30 in contact with the electrode layer 20. This facilitates the piezoelectric layer 30 to convert into high-frequency mechanical vibrations under the inverse piezoelectric effect, i.e., to emit ultrasonic waves. Furthermore, the electrode layer 20 is used to transmit the electrical signal generated by the piezoelectric layer 30 in response to ultrasonic waves.

[0083] Exemplarily, the material of the electrode layer 20 may be a transparent conductive material or a non-transparent conductive material. For example, the material of the electrode layer 20 may include at least one of metal materials such as aluminum (Al), copper (Cu), gold (Au), and platinum (Pt), or may include an inorganic conductive material such as indium tin oxide (ITO), or may include an organic conductive material such as PEDOT:PSS and graphite, or may be a composite conductive material of metal and inorganic or organic matter, such as a composite material of silver paste and anisotropic conductive film (ACF).

[0084] The piezoelectric layer 30 is used to generate an ultrasonic signal (ie, ultrasonic wave) under the stimulation of an AC signal, and is used to receive the ultrasonic signal and convert the ultrasonic signal into an electrical signal.

[0085] Exemplarily, the material of the piezoelectric layer 30 has piezoelectricity. For example, the material of the piezoelectric layer 30 may include an organic piezoelectric material, such as at least one of polyvinylidene fluoride (PVDF), a copolymer of polyvinylidene fluoride and trifluoroethylene (PVDF-TrFE), a terpolymer of polyvinylidene fluoride, trifluoroethylene and chlorofluoroethylene (PVDF-TrFE-CFE), and composites thereof.

[0086] The ultrasonic sensor 100 operates in two phases: a transmitter (TX) and a receiver (RX). During the transmitter phase, an external circuit can output a high-voltage pulse signal, such as one with a voltage greater than 100V and a frequency in the 5-20 MHz range, to the ultrasonic sensor 100. This signal is then transmitted to an electrode layer 20 located on one side of the piezoelectric layer 30. Simultaneously, a fixed voltage is applied to the electrode layer 20 located on the other side of the piezoelectric layer 30, thereby generating an electrostatic high voltage on both sides of the piezoelectric layer 30. This voltage, through the inverse piezoelectric effect, causes the piezoelectric layer 30 to vibrate at a high frequency, generating an ultrasonic wave. This wave then passes through the various dielectric layers and reaches the object to be detected (e.g., a finger). Part of the ultrasonic wave is then reflected by the object. During the receiver phase, the reflected ultrasonic wave passes through the various dielectric layers again and reaches the piezoelectric layer 30. The piezoelectric layer 30, which is already nearly stationary, is excited by the reflected ultrasonic wave and deforms, which in turn converts the deformation into a high-frequency pulse electrical signal. This electrical signal is received by the electrode layer 20 , and relevant information of the object to be detected (such as fingerprint comparison information, etc.) can be obtained by analyzing the electrical signal.

[0087] As shown in FIG3 and FIG4 , in the embodiment of the present application, the ultrasonic sensor 100 includes a multi-layer electrode layer 20 and a multi-layer piezoelectric layer 30 arranged on the same side of the substrate 10 , and the electrode layer 20 and the piezoelectric layer 30 are alternately stacked.

[0088] For example, referring to FIG3 , the ultrasonic sensor 100 may include three electrode layers 20, which are respectively a first electrode layer 21, a second electrode layer 22, and a third electrode layer 23 in a direction away from the substrate 10. The ultrasonic sensor 100 may also include two piezoelectric layers 30, which are respectively a first piezoelectric layer 31 and a second piezoelectric layer 32 in a direction away from the substrate 10. The first piezoelectric layer 31 is disposed between the first electrode layer 21 and the second electrode layer 22, and the second piezoelectric layer 32 is disposed between the second electrode layer 22 and the third electrode layer 23.

[0089] 4 , the ultrasonic sensor 100 may include three or more piezoelectric layers 30. For example, FIG4 illustrates the structure of the ultrasonic sensor 100 by taking the ultrasonic sensor 100 including three piezoelectric layers 30 and four electrode layers 20 as an example.

[0090] Exemplarily, the signal loaded on the electrode layer 20 may be an AC signal, for example, a sinusoidal wave signal, a square wave signal, or a pulse signal.

[0091] It is understandable that there is a potential difference between the electrical signals transmitted by two adjacent electrode layers 20 , so that the piezoelectric layer 30 sandwiched between the two adjacent electrode layers 20 is in an AC electric field, so that the piezoelectric layer 30 generates ultrasonic waves.

[0092] For example, the first electrode layer 21 and the third electrode layer 23 may be loaded with a high-voltage pulse signal, while the second electrode layer 22 may be loaded with a low-voltage signal, so that both the first piezoelectric layer 31 and the second piezoelectric layer 32 are in an AC electric field.

[0093] Exemplarily, at the same moment, the directions of the electric fields of two adjacent piezoelectric layers 30 can be opposite. For example, referring to the structure of Figure 3, the first electrode layer 21 and the third electrode layer 23 can transmit exactly the same electrical signals, while the second electrode layer 22 can transmit electrical signals different from the first electrode layer 21 and the third electrode layer 23. In this case, at the same moment, the direction of the electric field formed by the first electrode layer 21 and the second electrode layer 22 is opposite to the direction of the electric field formed by the third electrode layer 23 and the second electrode layer 22.

[0094] In this embodiment, at the same time, the design of different directions of the electric fields of two adjacent piezoelectric layers 30 can simplify the connection method of the electrode layer 20. For example, two electrode layers 20 (for example, the first electrode layer 21 and the third electrode layer 23) arranged at intervals can transmit the same electrical signal. For example, the two can be electrically connected without the need to additionally design multiple different connection methods (for example, designing the first electrode layer 21 and the third electrode layer 23 to be separately connected to different electrical signals).

[0095] For example, the polarization directions of the two adjacent piezoelectric layers 30 are opposite. When the electric field directions of the two adjacent piezoelectric layers 30 are opposite at the same time, the polarization directions of the two adjacent piezoelectric layers 30 are opposite. At the same time, the ultrasonic waves generated by the two piezoelectric layers 30 are transmitted roughly in the same direction, which is conducive to the effective superposition of the ultrasonic waves generated by the two piezoelectric layers 30.

[0096] For example, referring to Figure 4, among the two adjacent piezoelectric layers 30, the polarization direction of one of the piezoelectric layers 30 (indicated by an arrow in Figure 4) can be the direction in which the piezoelectric layer 30 points to the substrate 10 (for example, from top to bottom in Figure 4), and the polarization direction of the other piezoelectric layer 30 can be the direction in which the piezoelectric layer 30 points away from the substrate 10 (for example, from bottom to top in Figure 4).

[0097] Polarization refers to placing the piezoelectric layer 30 under a polarization voltage, which causes the grain domains in the piezoelectric layer 30 to be arranged in an orderly manner, exhibiting polarity to the outside, and thus enabling the piezoelectric layer 30 to have a piezoelectric effect. The polarization direction is the direction of the grain domain arrangement.

[0098] 5 and 6 illustrate the signal connection method of the ultrasonic sensor 100 during the transmission process according to an embodiment of the present application, and FIG. 7 and 8 illustrate the signal connection method of the ultrasonic sensor 100 during the receiving stage according to an embodiment of the present application.

[0099] The working process of the ultrasonic sensor 100 provided in the embodiment of the present application may be:

[0100] Launch phase:

[0101] 5 and 6 , a first excitation voltage is loaded on the first electrode layer 21 and the third electrode layer 23, and a second excitation voltage is loaded on the second electrode layer 22. The first excitation voltage and the second excitation voltage are higher and lower voltages relative to each other, so that the first piezoelectric layer 31 emits a first ultrasonic wave under the excitation of a first electric field formed by the first excitation voltage and the second excitation voltage on both sides thereof, and the second piezoelectric layer 32 emits a second ultrasonic wave under the excitation of a second electric field formed by the second excitation voltage and the first excitation voltage on both sides thereof.

[0102] The direction of the first electric field applied to the first piezoelectric layer 31 is opposite to the direction of the second electric field applied to the second piezoelectric layer 32, and the polarization directions of the first piezoelectric layer 31 and the second piezoelectric layer 32 are opposite. Therefore, the first ultrasonic wave emitted by the first piezoelectric layer 31 and the second ultrasonic wave emitted by the second piezoelectric layer 32 can be effectively superimposed, thereby effectively enhancing the intensity of the emitted ultrasonic wave. The stronger the intensity of the emitted ultrasonic wave, the stronger the intensity of the subsequent reflected ultrasonic wave (echo), thereby optimizing the echo signal.

[0103] Receiving stage:

[0104] After being emitted, the transmitted ultrasonic wave is reflected by the object to be detected (e.g., a finger), and at least a portion of the transmitted ultrasonic wave is reflected back into the ultrasonic sensor 100. The first piezoelectric layer 31 is excited by the reflected ultrasonic wave to produce deformation, and the deformation is converted into an electrical signal to detect the object to be detected. In this process, referring to Figures 7 and 8, the first electrode layer 21 is used to transmit the electrical signal converted by the first piezoelectric layer 31 so that the electrical signal can be read and processed. The second electrode layer 22 can maintain a fixed voltage level or be grounded, and the third electrode layer 23 can maintain a fixed voltage level, be grounded, or be in a suspended state.

[0105] It can be seen from this that the embodiment of the present application can effectively achieve the enhancement of transmitted ultrasonic waves and the enhancement of echo signals by providing a multi-layer electrode layer 20 and a multi-layer piezoelectric layer 30, thereby improving the performance of the ultrasonic sensor 100.

[0106] This embodiment takes an ultrasonic sensor 100 including three electrode layers 20 and two piezoelectric layers 30 as an example to schematically illustrate the working process of the ultrasonic sensor 100 .

[0107] It can be understood that, similar to the ultrasonic sensor 100 including two piezoelectric layers 30, in the embodiment of the present application, including three or more piezoelectric layers 30 can also further realize the superposition of ultrasonic waves generated by multiple piezoelectric layers 30 in the ultrasonic sensor 100, thereby further improving the performance of the ultrasonic sensor 100.

[0108] It should be noted that the aforementioned embodiments of the present application illustrate the structure of the ultrasonic sensor 100 by taking the ultrasonic sensor 100 as an example, including three electrode layers 20 and two piezoelectric layers 30. This does not limit the number of electrode layers 20 or the number of piezoelectric layers 30. For example, referring to FIG4 , the ultrasonic sensor 100 may also include three piezoelectric layers 30 and four electrode layers 20. It is understood that any number of electrode layers 20 and piezoelectric layers 30 that can achieve superposition of ultrasonic waves is within the scope of the present embodiments and is not limited in the present embodiments.

[0109] In the ultrasonic sensor 100 provided in the embodiment of the present application, the Curie temperature of the piezoelectric layer 30 gradually decreases in a direction away from the substrate 10 .

[0110] For example, in a case where the ultrasonic sensor 100 includes the first piezoelectric layer 31 and the second piezoelectric layer 32 , the Curie temperature of the second piezoelectric layer 32 is lower than the Curie temperature of the first piezoelectric layer 31 .

[0111] The Curie temperature of the piezoelectric layer 30 refers to the temperature at which the piezoelectric effect of the piezoelectric material disappears (depolarization) when the temperature of the piezoelectric material reaches a certain value. This temperature is the Curie temperature of the piezoelectric layer 30 .

[0112] The Curie temperature is a key parameter in piezoelectric materials, determining their piezoelectric performance at different temperatures. Different piezoelectric materials can have different Curie temperatures. For example, the Curie temperature of each piezoelectric layer 30 can be adjusted by adjusting the material formulation of each piezoelectric layer 30.

[0113] During the preparation of the ultrasonic sensor 100 , the piezoelectric layer 30 needs to be subjected to high-temperature annealing and crystallization, so that the piezoelectric layer 30 forms a complete molecular chain, and then a polarization operation is performed to enable the piezoelectric layer 30 to have a piezoelectric effect.

[0114] Polarization refers to placing the piezoelectric layer 30 under a polarization voltage so that the electric domains of the grains in the piezoelectric layer 30 are arranged in an orderly manner and show polarity to the outside, so that the piezoelectric layer 30 has a piezoelectric effect.

[0115] The annealing temperature of the piezoelectric layer 30 is higher than its Curie temperature. For example, when the material of the piezoelectric layer 30 includes an organic piezoelectric material, the annealing temperature of the organic piezoelectric material is higher than its Curie temperature.

[0116] When preparing a multilayer piezoelectric layer 30, if the Curie temperatures of the multilayer piezoelectric layers 30 are the same, the annealing temperature of the piezoelectric layer 30 prepared later (for example, the second piezoelectric layer 32 in Figure 3) must be greater than the Curie temperature of the piezoelectric layer 30 prepared earlier (for example, the first piezoelectric layer 31 in Figure 3), which can easily cause the piezoelectric layer 30 prepared earlier and already polarized to depolarize, seriously affecting the piezoelectric performance of the piezoelectric layer 30 prepared earlier.

[0117] In the ultrasonic sensor 100 provided in the embodiment of the present application, the Curie temperature of the multi-layer piezoelectric layer 30 is set to gradually decrease in the direction away from the substrate 10, so that the Curie temperature of the multi-layer piezoelectric layer 30 changes in a gradient, thereby facilitating setting the annealing temperature of the subsequently prepared piezoelectric layer 30 between the Curie temperature of the previously prepared piezoelectric layer 30 and the Curie temperature of the subsequently prepared piezoelectric layer 30, thereby avoiding depolarization of the previously prepared piezoelectric layer 30 during the annealing process of the subsequently prepared piezoelectric layer 30, thereby ensuring that each piezoelectric layer 30 can have a high degree of polarization. During the operation of the ultrasonic sensor 100, the piezoelectric layer 30 is ensured to have a good piezoelectric effect, for example, the intensity of the ultrasonic wave generated by the piezoelectric layer 30 can be increased, thereby improving the performance of the ultrasonic sensor 100.

[0118] Exemplarily, the difference in Curie temperature between two adjacent piezoelectric layers 30 is 5° C. to 20° C. For example, the Curie temperature of the second piezoelectric layer 32 is 5° C. to 20° C. lower than the Curie temperature of the first piezoelectric layer 31. For example, the difference is 5° C., 9.8° C., 13.87° C., 18.358° C., or 20° C. lower.

[0119] That is, the annealing temperature of the piezoelectric layer 30 prepared later can be 5°C to 20°C higher than its own Curie temperature. On the one hand, it can ensure that it is fully annealed and its own polarization degree is guaranteed. On the other hand, it ensures that the piezoelectric layer 30 prepared later will not cause the piezoelectric layer 30 prepared earlier to be depolarized during the high-temperature annealing process, thereby ensuring that all piezoelectric layers 30 have good piezoelectric effects.

[0120] Exemplarily, the annealing temperature of the piezoelectric layer 30 farther from the substrate 10 is lower than the Curie temperature of the piezoelectric layer 30 closer to the substrate 10 .

[0121] For example, referring to FIG3 , when the ultrasonic sensor 100 includes a first piezoelectric layer 31 and a second piezoelectric layer 32, the annealing temperature of the second piezoelectric layer 32 is lower than the Curie temperature of the first piezoelectric layer 31. This avoids the problem of the first piezoelectric layer 31 losing its piezoelectric effect during the annealing of the second piezoelectric layer 32.

[0122] In addition to improving the performance of the ultrasonic sensor 100 by controlling the Curie temperature of the piezoelectric layer 30 in the above embodiment, the performance of the ultrasonic sensor 100 may also be improved by the following embodiments.

[0123] In some embodiments, the electrode layer 20 located between two adjacent piezoelectric layers 30 is a predetermined electrode layer (e.g., the second electrode layer 22 in FIG. 3 ), and the thickness d1 of the predetermined electrode layer is less than or equal to 0.1λ1. For example, the thickness d1 of the predetermined electrode layer can be 0.1λ1, 0.05λ1, 0.0135λ1, etc.

[0124] Wherein, λ1 is the wavelength of the sound wave passing through the preset electrode layer. Wherein, C1 is the wave velocity of the sound wave passing through the preset electrode layer, and the wave velocity is related to the material of the preset electrode layer. f1 is the operating frequency of the ultrasonic sensor 100 .

[0125] That is, in the multi-layer electrode layer 20, the thickness d1 of the electrode layer 20 located in the middle membrane layer is approximately one tenth of the wavelength of the sound wave passing through it itself, thereby tending to form an acoustically transparent layer, so that the sound waves generated by the piezoelectric layer 30 or the sound waves reflected by the object to be detected can pass through the preset electrode layer almost without loss, avoiding the preset electrode layer located between the two piezoelectric layers 30 increasing the loss during sound wave transmission, and further improving the performance of the ultrasonic sensor 100.

[0126] FIG. 9 is a graph showing the relationship between the thickness and acoustic transmittance of the second electrode layer 22 (ie, the preset electrode layer) in FIG. 3 .

[0127] As shown in FIG9 , when the thickness of the second electrode layer 22 is large, its acoustic transmittance will be significantly reduced. However, when the thickness of the second electrode layer 22 is less than or equal to one tenth of the wavelength (the wavelength of the acoustic wave passing through it), for example, in FIG9 , when the thickness is 5 μm, its acoustic transmittance can reach approximately 90%, that is, the acoustic wave can pass through the second electrode layer 22 almost without loss, thereby effectively improving the performance of the ultrasonic sensor 100.

[0128] In some embodiments, the thickness d (see FIG. 3 ) of each electrode layer 20 in the multi-layer electrode layer 20 is less than or equal to 0.1λ. For example, the thickness d of the electrode layer 20 may be 0.1λ, 0.0789λ, 0.05λ, or 0.012λ.

[0129] Wherein, λ is the wavelength of the sound wave passing through the electrode layer 20 itself. The wavelength of the sound wave passing through the electrode layer Wherein, C is the wave velocity of the sound wave passing through the electrode layer 20 , and the wave velocity is related to the material of the electrode layer 20 , and f is the operating frequency of the ultrasonic sensor 100 .

[0130] That is, in the multi-layer electrode layer 20, the thickness d of each electrode layer 20 (see Figure 3) is one tenth of the wavelength of the sound wave passing through it, so that the sound waves generated by the piezoelectric layer 30 or the sound waves reflected by the object to be detected can pass through all the electrode layers 20 almost without loss, further reducing the loss of the sound waves when transmitting in the ultrasonic sensor 100, thereby further improving the performance of the ultrasonic sensor 100.

[0131] In some embodiments, the sum of the thickness-to-wavelength ratio of the multilayer piezoelectric layer 30 and the thickness-to-wavelength ratio of the multilayer electrode layer 20 is 0.15N to 0.35N.

[0132] Wherein, N is an odd number. For example, N can be 1, 3, 5, or 7.

[0133] That is, the sum of the thickness-to-wavelength ratios of all the film layers from the electrode layer 20 closest to the substrate 10 to the electrode layer 20 farthest from the substrate 10 is 0.15N-0.35N.

[0134] For example, referring to FIG. 3 , the sum of the thickness-to-wavelength ratios of the first electrode layer 21 , the first piezoelectric layer 31 , the second electrode layer 22 , the second piezoelectric layer 32 , and the third electrode layer 23 is 0.15N˜0.35N.

[0135] Exemplarily, the sum of the thickness-to-wavelength ratio of the multilayer piezoelectric layer 30 and the thickness-to-wavelength ratio of the multilayer electrode layer 20 may be 0.15 N, 0.2 N, 0.275 N, or 0.35 N. For example, the sum of the thickness-to-wavelength ratio of the multilayer piezoelectric layer 30 and the thickness-to-wavelength ratio of the multilayer electrode layer 20 may be 0.25 N.

[0136] The thickness-to-wavelength ratio refers to the ratio of the thickness of the membrane layer itself to the wavelength of the sound wave passing through the membrane layer. For example, the wavelength of each electrode layer 20 is The thickness-to-wavelength ratio of the single-layer electrode layer 20 is Wherein, C is the wave velocity of the sound wave passing through the electrode layer 20, which is related to the material of the electrode layer 20, f is the operating frequency of the ultrasonic sensor 100, and d is the thickness of the electrode layer 20. The same applies to the piezoelectric layer 30.

[0137] By setting the sum of the thickness-to-wavelength ratios of the multi-layer piezoelectric layer 30 and the thickness-to-wavelength ratios of the multi-layer electrode layer 20 to 0.15N to 0.35N, the thickness of the structure of the ultrasonic sensor 100 located on one side of the substrate 10 constitutes a resonant body that is an odd multiple of a quarter wavelength, so that the ultrasonic waves emitted by different piezoelectric layers 30 can be effectively superimposed, thereby enhancing the sound pressure emission intensity of the ultrasonic sensor 100. At the same time, the overall thickness of the ultrasonic sensor 100 can also be controlled to be within a smaller range, thereby reducing the attenuation of ultrasonic waves in each membrane layer and further improving the performance of the ultrasonic sensor 100.

[0138] In some embodiments, the sum of the thickness-to-wavelength ratios of the substrate 10 , the multilayer piezoelectric layer 30 , and the multilayer electrode layer 20 is approximately 0.35M to 0.65, for example, 0.35M, 0.5M, 0.623M, or 0.65M.

[0139] Here, M is an integer, for example, M can be an integer such as 1, 2, 3 or 4.

[0140] That is, the thickness of the overall structure of the ultrasonic sensor 100 forms a resonant body that is close to an integer multiple of half the wavelength, which further facilitates the superposition of ultrasonic waves, thereby enhancing the resonance effect and the electrical performance of the ultrasonic sensor 100.

[0141] Taking the structure in FIG3 as an example, the thickness and wavelength of the substrate 10 are d a and λ a , then the thickness-to-wavelength ratio of the substrate 10 is Similarly, the thickness and wavelength of the first electrode layer 21 are d1 and λ1 respectively, then the thickness-to-wavelength ratio of the first electrode layer 21 is The thickness and wavelength of the first piezoelectric layer 31 are d2 and λ2 respectively, then the thickness-to-wavelength ratio of the first piezoelectric layer 31 is The thickness and wavelength of the second electrode layer 22 are d3 and λ3 respectively, then the thickness-to-wavelength ratio of the second electrode layer 22 is The thickness and wavelength of the second piezoelectric layer 32 are d4 and λ4 respectively, so the thickness-to-wavelength ratio of the second piezoelectric layer 32 is The thickness and wavelength of the third electrode layer 23 are d5 and λ5 respectively, and the thickness-to-wavelength ratio of the third electrode layer 23 is The sum of the thickness-to-wavelength ratio of the substrate 10, the thickness-to-wavelength ratio of the multilayer piezoelectric layer 30, and the thickness-to-wavelength ratio of the multilayer electrode layer 20 is The value of R is approximately 0.5M.

[0142] FIG10 is another schematic structural diagram of the ultrasonic sensor 100 provided in an embodiment of the present application.

[0143] In some embodiments, referring to FIG. 10 , among the multiple electrode layers 20 , two electrode layers 20 spaced apart are electrically connected, and one electrode layer 20 is disposed between the two electrically connected electrode layers 20 .

[0144] That is, the two adjacent electrode layers 20 are insulated from each other, so that the two adjacent electrode layers 20 can transmit different electrical signals respectively, so that an electric potential can be formed on both sides of the piezoelectric layer 30 sandwiched between the two adjacent electrode layers 20 (for example, the top and bottom in Figure 10), so that the piezoelectric layer 30 can generate ultrasonic waves.

[0145] For example, referring to FIG. 10 , the ultrasonic sensor 100 includes four electrode layers 20, comprising two first sublayers 2A and two second sublayers 2B, with the first sublayers 2A and the second sublayers 2B alternately stacked. The two first sublayers 2A are electrically connected, and the two second sublayers 2B are electrically connected to each other. This facilitates transmission of a first signal (e.g., a first excitation voltage) through all first sublayers 2A, and transmission of a second signal (e.g., a second excitation voltage) through all second sublayers 2B, thereby creating a potential difference between the upper and lower sides of all piezoelectric layers 30.

[0146] 10 , the ultrasonic sensor 100 further includes a first side trace 41 and a second side trace 42 , which are disposed on both sides of the multilayer electrode layer 20 along a first direction X. The first direction X is parallel to the substrate 10 .

[0147] For example, referring to FIG. 10 , the first side trace 41 and the second side trace 42 are respectively disposed on the left and right sides of the multi-layer electrode layer 20 along the first direction X.

[0148] Two adjacent first sub-layers 2A are electrically connected via a first side wiring 41 , and two adjacent second sub-layers 2B are electrically connected via a second side wiring 42 .

[0149] 10 , the first side trace 41 is insulated from the second sub-layer 2B, and the second side trace is insulated from the first sub-layer 2A.

[0150] Exemplarily, referring to FIG. 10 , the first side trace 41 is insulated from the second sub-layer 2B by a portion of the piezoelectric layer 30 , and the second side trace is insulated from the first sub-layer 2A by a portion of the piezoelectric layer 30 .

[0151] For example, referring to Figure 10, the first side trace 41 also includes a portion located on the substrate 10, which can serve as a first signal input port. The first signal input port is used to electrically connect to an external circuit (such as the control chip 300 in Figure 2), thereby transmitting a first signal to the first sublayer 2A to which the first side trace 41 is connected.

[0152] For example, referring to Figure 10, the second side trace 42 also includes a portion located on the substrate 10, which can serve as a second signal input port. The second signal input port is used to electrically connect to an external circuit (such as the control chip 300 in Figure 2), thereby transmitting a second signal to the second sublayer 2B to which the second side trace 42 is connected.

[0153] In addition to the structures of the substrate 10, the electrode layer 20, and the piezoelectric layer 30 in the aforementioned embodiments, the ultrasonic sensor 100 provided in the embodiment of the present application may further include the following structures.

[0154] 11 and 12 are another structural schematic diagram of the ultrasonic sensor 100 provided in an embodiment of the present application.

[0155] In some embodiments, referring to FIG. 5 to FIG. 8 , and FIG. 11 and FIG. 12 , the ultrasonic sensor 100 further includes a circuit layer 50 .

[0156] 11 , the circuit layer 50 is disposed between the electrode layer 20 closest to the substrate 10 and the substrate 10 . For example, as shown in FIG. 11 , the circuit layer 50 may be embedded in the surface of the substrate 10 close to the electrode layer 20 .

[0157] 11 and 12 , the circuit layer 50 includes a plurality of pixel circuits 51 arranged at intervals. For example, the pixel circuit 51 may be a circuit unit including analog and digital modules, and the plurality of pixel circuits 51 may be arranged in an array.

[0158] 11 and 12 , among the multi-layer electrode layers 20, the electrode layer 20 closest to the substrate 10 may include a plurality of electrode blocks 2C spaced apart from each other. The plurality of electrode blocks 2C are electrically connected to the plurality of pixel circuits 51. For example, the plurality of electrode blocks 2C and the plurality of pixel circuits 51 are coupled in a one-to-one correspondence, and a group of coupled electrode blocks 2C and pixel circuits 51 constitutes a pixel unit for fingerprint detection.

[0159] The multiple electrode blocks 2C can transmit the electrical signals (including fingerprint information) generated by the piezoelectric layer 30 in response to the ultrasonic waves reflected by the object to be detected. The multiple electrode blocks 2C discretize the electrical signals and realize point-by-point image restoration of the object to be detected through multiple pixel circuits 51, for example, fingerprint imaging can be realized.

[0160] For example, referring to FIG. 3 , FIG. 4 and FIG. 10 , in other embodiments, when the ultrasonic sensor 100 does not need to restore the image of the object to be detected, the electrode layer 20 closest to the substrate 10 may also be provided as a whole layer.

[0161] In some embodiments, as shown in FIG. 4 to FIG. 8 , FIG. 10 to FIG. 12 and other figures, the ultrasonic sensor 100 further includes a protective layer 60 .

[0162] 11 and 12 , the protection layer 60 is stacked on a side of the electrode layer 20 that is farthest from the substrate 10 , and the protection layer 60 is insulated from the electrode layer 20 .

[0163] Exemplarily, the material of the protection layer 60 includes a metal material, for example, the material of the protection layer 60 includes aluminum (Al), copper (Cu), and the like.

[0164] FIG13 is a frequency-sound pressure comparison diagram when the electrode layer 20 is made of a metal material or a polymer material. As shown in FIG13 , when the protective layer 60 is made of a polymer material, there is a large attenuation when the sound wave is transmitted in the ultrasonic sensor 100, which will reduce the performance of the ultrasonic sensor 100. By setting the material of the protective layer 60 to be a metal material, the same frequency resonance can be achieved with a thinner thickness than that of the polymer material, which is beneficial to reducing the overall thickness of the ultrasonic sensor 100 and facilitating miniaturization.

[0165] The protective layer 60 provides support for the ultrasonic sensor 100, enhancing the module strength of the ultrasonic sensor 100. This is particularly true when the substrate 10 is a flexible substrate. Furthermore, simulations have shown that the protective layer 60 can enhance the ultrasonic sensor 100's signal-to-noise ratio and improve the consistency of the ultrasonic signal.

[0166] For example, referring to Figures 5 to 8 , the protective layer 60 can be grounded or suspended. For example, when grounded, the protective layer 60 can provide effective electromagnetic shielding, protecting the ultrasonic sensor 100 from external electromagnetic interference in a loaded environment and preventing electromagnetic interference generated by the ultrasonic sensor 100 from external devices.

[0167] Exemplarily, referring to FIG. 4 to FIG. 8 , FIG. 10 to FIG. 12 and other figures, the ultrasonic sensor 100 further includes a first adhesive layer 70 .

[0168] Referring to Figures 11 and 12 , a first adhesive layer 70 is disposed between the electrode layer 20 and the protective layer 60. The first adhesive layer 70 protects the electrode layer 20 from damage and prevents unintended electrical connections within the electrode layer 20. Furthermore, the frequency of the ultrasonic sensor 100 can be adjusted by adjusting the thickness of the first adhesive layer 70.

[0169] Exemplarily, the material of the first adhesive layer 70 is an insulating material, for example, it can be a polymer and its polymers, for example, it can include optical clarity adhesive (OCA), PI, PET, polystyrene-acrylonitrile (PSA) and other polymers, and can also include composites of these polymers doped with fillers.

[0170] Exemplarily, the material of the first adhesive layer 70 is a material having an acoustic impedance between that of the electrode layer 20 and the protective layer 60 , forming an acoustic impedance matching layer, which is beneficial to efficient acoustic transmission.

[0171] Exemplarily, the sum of the thickness-to-wavelength ratios of the various film layers from the protective layer 60 to the electrode layer 20 closest to the substrate 10 is 0.15N to 0.35N, where N is an odd number.

[0172] For example, when the ultrasonic sensor 100 includes a protective layer 60 and a first adhesive layer 70, the sum of the thickness-wavelength ratio of the protective layer 60, the thickness-wavelength ratio of the first adhesive layer 70, the thickness-wavelength ratio of the multilayer piezoelectric layer 30, and the thickness-wavelength ratio of the multilayer electrode layer 20 is 0.15N to 0.35N, for example, 0.25N.

[0173] That is, when the ultrasonic sensor 100 includes the protective layer 60 and the first adhesive layer 70, the thickness of all structures of the ultrasonic sensor 100 located on one side of the substrate 10 also constitutes a resonant body that is an odd multiple of a quarter wavelength, so that the ultrasonic waves emitted by different piezoelectric layers 30 can be effectively superimposed, thereby enhancing the sound pressure emission intensity of the ultrasonic sensor 100.

[0174] Exemplarily, in the case where the ultrasonic sensor 100 includes a protective layer 60 and a first adhesive layer 70, the sum of the thickness-wavelength ratio of the substrate 10, the thickness-wavelength ratio of the protective layer 60, the thickness-wavelength ratio of the first adhesive layer 70, the thickness-wavelength ratio of the multilayer piezoelectric layer 30, and the thickness-wavelength ratio of the multilayer electrode layer 20 is approximately 0.35M to 0.65, for example, 0.35M, 0.5M, 0.623M or 0.65M.

[0175] Here, M is an integer, for example, M can be an integer such as 1, 2, 3, 4 or 5.

[0176] That is, when the ultrasonic sensor 100 includes the protective layer 60 and the first adhesive layer 70, the thickness of the overall structure of the ultrasonic sensor 100 also constitutes a resonant body that is close to an integer multiple of one-half wavelength, which further facilitates the superposition of ultrasonic waves, enhances the resonance effect, and enhances the electrical performance of the ultrasonic sensor 100.

[0177] Taking the structure in FIG5 as an example, the thickness and wavelength of the substrate 10 are d a and λ a , then the thickness-to-wavelength ratio of the substrate 10 is The thickness and wavelength of the first electrode layer 21 are d1 and λ1 respectively, then the thickness-to-wavelength ratio of the first electrode layer 21 is The thickness and wavelength of the first piezoelectric layer 31 are d2 and λ2 respectively, then the thickness-to-wavelength ratio of the first piezoelectric layer 31 is The thickness and wavelength of the second electrode layer 22 are d3 and λ3 respectively, then the thickness-to-wavelength ratio of the second electrode layer 22 is The thickness and wavelength of the second piezoelectric layer 32 are d4 and λ4 respectively, so the thickness-to-wavelength ratio of the second piezoelectric layer 32 is The thickness and wavelength of the third electrode layer 23 are d5 and λ5 respectively, and the thickness-to-wavelength ratio of the third electrode layer 23 is The thickness and wavelength of the first adhesive layer 70 are d6 and λ6 respectively, so the thickness-to-wavelength ratio of the first adhesive layer 70 is The thickness and wavelength of the protective layer 60 are d7 and λ7 respectively, so the thickness-to-wavelength ratio of the protective layer 60 is The sum of the thickness-to-wavelength ratio of the substrate 10, the thickness-to-wavelength ratio of the multilayer piezoelectric layer 30, the thickness-to-wavelength ratio of the multilayer electrode layer 20, the thickness-to-wavelength ratio of the first adhesive layer 70, and the thickness-to-wavelength ratio of the protective layer 60 is: The value of R is approximately 0.5M.

[0178] It should be noted that when the thickness of the electrode layer 20 is very thin relative to the thickness of other layers (such as the piezoelectric layer 30), for example, the first electrode layer 21 in Figure 3 is a thin film prepared by metal deposition or the like, and its thickness is at the nanometer level, the thickness-to-wavelength ratio of the very thin electrode layer 20 can be ignored, and only the sum of the thickness-to-wavelength ratios of other film layers needs to be calculated.

[0179] In some embodiments, as shown in FIG. 11 and FIG. 12 , the ultrasonic sensor 100 further includes a contact layer 80 .

[0180] That is, the contact layer 80 is arranged between the core structure such as the electrode layer 20 and the object to be detected (such as a finger), thereby protecting the core structure such as the electrode layer 20. For example, the contact layer 80 can be used for pressing or contacting by a finger, so that the ultrasonic sensor 100 can detect the fingerprint of the finger.

[0181] Exemplarily, referring to FIG. 11 , the contact layer 80 is stacked on a side of the substrate 10 away from the protective layer 60 , which can be understood as what is commonly referred to in the art as a back sticker or reverse sticker.

[0182] For example, referring to FIG. 12 , the contact layer 80 is stacked on the side of the protective layer 60 away from the substrate 10 , which can be understood as what is commonly known in the art as facing forward.

[0183] 2 , when the ultrasonic sensor 100 is applied to an electronic device 1000 , the contact layer 80 can be reused as the display screen 2 . In this case, the ultrasonic sensor 100 can also realize imaging display of the object to be detected through the contact layer 80 .

[0184] Exemplarily, the contact layer 80 may be a multi-layer composite material such as a rigid display screen, a flexible display screen, a curved display screen, a 2.5D display screen, or a 3D display screen.

[0185] In other embodiments, the contact layer 80 is a cover plate.

[0186] Exemplarily, the contact layer 80 may be a curved cover glass, a flat cover glass, a metal cover, a glass cover, a polymeric area cover, or the like.

[0187] 11 and 12 , the ultrasonic sensor 100 further includes a second adhesive layer 90. The second adhesive layer 90 is disposed on a side of the contact layer 80 that is closer to the substrate 10. This allows the contact layer 80 to be bonded and fixed to the substrate 10 or the protective layer 60 via the second adhesive layer 90.

[0188] For example, the material of the second adhesive layer 90 may be the same as the material of the first adhesive layer 70 .

[0189] The embodiment of the present application also provides a method for preparing the ultrasonic sensor 100 .

[0190] The preparation method may include forming a multi-layer electrode layer 20 and a multi-layer piezoelectric layer 30 on the same side of a substrate 10 .

[0191] The electrode layers 20 and the piezoelectric layers 30 are alternately stacked, and each piezoelectric layer 30 is disposed between two adjacent electrode layers 20 .

[0192] That is, the electrode layer 20 and the piezoelectric layer 30 may be alternately stacked on the substrate 10 in sequence, and the last film layer is the electrode layer 20 .

[0193] FIG14 is a flowchart of the preparation of the ultrasonic sensor 100 provided in an embodiment of the present application.

[0194] As shown in FIG14 , in some embodiments, when the ultrasonic sensor 100 includes three electrode layers 20 (a first electrode layer 21 , a second electrode layer 22 , and a third electrode layer 23 ) and two piezoelectric layers 30 (a first piezoelectric layer 31 and a second piezoelectric layer 32 ), the preparation method may include:

[0195] S1: providing a substrate 10.

[0196] S2: preparing a first electrode layer 21 on the substrate 10 .

[0197] S3: preparing a first piezoelectric layer 31 on a side of the first electrode layer 21 away from the substrate 10 .

[0198] S4: preparing a second electrode layer 22 on a side of the first piezoelectric layer 31 away from the substrate 10 .

[0199] S5: preparing a second piezoelectric layer 32 on a side of the second electrode layer 22 away from the substrate 10 .

[0200] S6: preparing a third electrode layer 23 on a side of the second piezoelectric layer 32 away from the substrate 10 .

[0201] The Curie temperature of the piezoelectric layer 30 gradually decreases as it moves away from the substrate 10. For example, the first piezoelectric layer 31 has a first Curie temperature, and the second piezoelectric layer 32 has a second Curie temperature, which is lower than the first Curie temperature. This facilitates controlling the annealing temperature of the second piezoelectric layer 32 between the first Curie temperature and the second Curie temperature. That is, the annealing temperature of the second piezoelectric layer 32 is controlled to be higher than its own Curie temperature (the second Curie temperature) so as to form a molecular chain, thereby facilitating the polarization of the second piezoelectric layer 32. At the same time, the annealing temperature of the second piezoelectric layer 32 is controlled to be lower than the Curie temperature (the first Curie temperature) of the first piezoelectric layer 31, thereby avoiding the defect of depolarization of the first piezoelectric layer 31 caused by high temperature during the annealing process of the second piezoelectric layer 32.

[0202] Exemplarily, the thickness of at least one of the first electrode layer 21, the second electrode layer 22 and the third electrode layer 23 can be less than or equal to one tenth of the wavelength (the wavelength of the sound wave passing through it itself), thereby effectively reducing the degree of attenuation of the sound wave when passing through the electrode layer 20 and improving the performance of the ultrasonic sensor 100.

[0203] For example, referring to FIG14 , the preparation method may further include:

[0204] S7 : forming a protective layer 60 on a side of the third electrode layer 23 away from the substrate 10 .

[0205] It is understandable that this step may further include forming a first adhesive layer 70 between the protective layer 60 and the third electrode layer 23 .

[0206] It is understandable that the method for preparing the ultrasonic sensor 100 provided in the embodiment of the present application may further include steps of forming other structures of the ultrasonic sensor 100 provided in the aforementioned embodiment, such as the step of forming the contact layer 80 , etc., which will not be repeated here.

[0207] For example, the electrode layer 20 may be prepared by sputtering, physical or chemical deposition, distillation, or screen printing.

[0208] Illustratively, the piezoelectric layer 30 may be prepared by the following embodiments.

[0209] FIG15 is a flow chart of the preparation of the piezoelectric layer 30 .

[0210] As shown in FIG15 , the steps of forming the piezoelectric layer 30 may include:

[0211] K1: Forming a piezoelectric film. For example, the piezoelectric film can be prepared by scraping or spin coating the piezoelectric material.

[0212] K2: Annealing the piezoelectric film to achieve crystallization of the piezoelectric film and form complete molecular chains inside it, facilitating subsequent polarization.

[0213] During the annealing process, the annealing temperature of the piezoelectric film farther away from the substrate 10 is lower than the Curie temperature of the piezoelectric film closer to the substrate 10, thereby avoiding the annealing process of the piezoelectric layer 30 farther away from the substrate 10 from causing depolarization defects in the piezoelectric layer 30 closer to the substrate 10.

[0214] K3: Polarize the piezoelectric film to form a piezoelectric layer 30. For example, the polarization can be achieved by corona poling or contact poling.

[0215] The preparation method provided in the aforementioned embodiment of the present application solves the problem of mutual restriction between the annealing temperature and the Curie temperature during the preparation of the multilayer piezoelectric layer 30. The preparation method is simple and can realize the mass production of the ultrasonic sensor 100. The obtained ultrasonic sensor 100 has good performance and low cost, and has a relatively good application prospect.

[0216] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that a person skilled in the art can conceive within the technical scope disclosed in this disclosure should be included within the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. An ultrasonic sensor, characterized in that: include: substrate; Multiple electrode layers and multiple piezoelectric layers are provided on the same side of the substrate; the electrode layers and the piezoelectric layers are alternately stacked, and each piezoelectric layer is provided between two adjacent electrode layers; Wherein, the Curie temperature of the piezoelectric layer gradually decreases in a direction away from the substrate.

2. The ultrasonic sensor according to claim 1, wherein The difference in Curie temperature between two adjacent piezoelectric layers is 5°C to 20°C.

3. The ultrasonic sensor according to claim 1 or 2, characterized in that: The annealing temperature of the piezoelectric layer farther from the substrate is lower than the Curie temperature of the piezoelectric layer closer to the substrate.

4. The ultrasonic sensor according to any one of claims 1 to 3, characterized in that: The electrode layer located between two adjacent piezoelectric layers is a preset electrode layer, and the thickness of the preset electrode layer is less than or equal to 0.1λ1, wherein λ1 is the wavelength of the sound wave passing through the preset electrode layer.

5. The ultrasonic sensor according to any one of claims 1 to 4, characterized in that: In the multi-layer electrode layer, the thickness of each electrode layer is less than or equal to 0.1λ, where λ is the wavelength of the sound wave passing through the electrode layer itself.

6. The ultrasonic sensor according to any one of claims 1 to 5, characterized in that: The sum of the thickness-to-wavelength ratios of the multi-layer piezoelectric layer and the thickness-to-wavelength ratios of the multi-layer electrode layer is 0.15N to 0.35N, wherein N is an odd number.

7. The ultrasonic sensor according to claim 6, characterized in that The sum of the thickness-to-wavelength ratios of the multilayer piezoelectric layers and the thickness-to-wavelength ratios of the multilayer electrode layers is 0.25N, where N is an odd number.

8. The ultrasonic sensor according to any one of claims 1 to 7, characterized in that: The sum of the thickness-to-wavelength ratio of the substrate, the thickness-to-wavelength ratio of the multilayer piezoelectric layer, and the thickness-to-wavelength ratio of the multilayer electrode layer is 0.35M to 0.65M, wherein M is an integer.

9. The ultrasonic sensor according to any one of claims 1 to 8, characterized in that: Also includes: The protective layer is stacked on a side of the electrode layer farthest from the substrate and away from the substrate, and the protective layer is insulated from the electrode layer.

10. The ultrasonic sensor according to claim 9, characterized in that The material of the protection layer includes metal material.

11. The ultrasonic sensor according to claim 9 or 10, characterized in that: The sum of the thickness-to-wavelength ratios of the various film layers from the protective layer to the electrode layer closest to the substrate is 0.15N to 0.35N, wherein N is an odd number.

12. The ultrasonic sensor according to any one of claims 9 to 11, characterized in that: Also includes: The contact layer is stacked on a side of the substrate away from the protective layer, or is stacked on a side of the protective layer away from the substrate.

13. The ultrasonic sensor according to any one of claims 1 to 12, characterized in that: Also includes: a circuit layer, disposed between the electrode layer closest to the substrate and the substrate, the circuit layer comprising a plurality of pixel circuits spaced apart; Among the multi-layer electrode layers, the electrode layer closest to the substrate includes a plurality of electrode blocks arranged at intervals; and the plurality of electrode blocks are electrically connected to the plurality of pixel circuits accordingly.

14. The ultrasonic sensor according to any one of claims 1 to 13, characterized in that: In the multi-layer electrode layer, two electrode layers arranged at intervals are electrically connected, and an electrode layer is provided between the two electrically connected electrode layers.

15. The ultrasonic sensor according to claim 14, characterized in that Also includes: A first side wiring and a second side wiring are arranged on both sides of the multi-layer electrode layer along a first direction; the first direction is parallel to the substrate; In which, the multilayer electrode layer includes multiple layers of first sublayers and multiple layers of second sublayers, and the first sublayers and the second sublayers are alternately stacked; the two adjacent first sublayers are electrically connected through the first side routing, and the two adjacent second sublayers are electrically connected through the second side routing; the first side routing is insulated from the second sublayer, and the second side routing is insulated from the first sublayer.

16. A method for preparing an ultrasonic sensor, characterized in that: include: A plurality of electrode layers and a plurality of piezoelectric layers are formed on the same side of the substrate; the electrode layers and the piezoelectric layers are alternately stacked, and each piezoelectric layer is arranged between two adjacent electrode layers; The Curie temperature of the piezoelectric layer gradually decreases in a direction away from the substrate; Wherein, forming the piezoelectric layer comprises: forming a piezoelectric film; Annealing the piezoelectric film; the annealing temperature of the piezoelectric film further away from the substrate is lower than the annealing temperature of the piezoelectric film closer to the substrate Curie temperature; The piezoelectric film is polarized to form a piezoelectric layer.

17. An electronic device, characterized in that: include: The ultrasonic sensor according to any one of claims 1 to 15; A circuit board is coupled to the ultrasonic sensor.

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