Ultrasonic Sensor, Preparation Method Thereof, Ultrasonic Fingerprint Module, and Electronic Device

Abstract

The present application relates to the field of ultrasonic sensors, and provides an ultrasonic sensor, a preparation method thereof, an ultrasonic fingerprint module, and an electronic device, which are at least beneficial to improving the performance of the ultrasonic sensor. The preparation method includes: forming a bottom electrode layer on a substrate; forming a piezoelectric layer on the bottom electrode layer; forming a top electrode on the piezoelectric layer. The preparation steps of the top electrode layer include: treating the surface of the piezoelectric layer to make the surface of the piezoelectric layer hydrophilic; performing a silanization treatment on the piezoelectric layer to form a self-assembled molecular layer; immersing the substrate after the silanization treatment in a prepolymer solution so that the self-assembled molecular layer polymerizes with the monomers in the prepolymer solution to form an adhesion layer; forming a catalyst layer on the adhesion layer; placing the substrate with the catalyst layer in an electroless plating bath so that the catalyst in the catalyst layer catalyzes metal ions in the electroless plating bath to form a metal layer, and the adhesion layer and the metal layer constitute the top electrode layer; forming a protective layer on the top electrode layer.

Description

Technical Field

[0001] The present application relates to the field of ultrasonic sensors, and particularly to an ultrasonic sensor and a preparation method thereof, an ultrasonic fingerprint module, and an electronic device. Background Art

[0002] An ultrasonic sensor utilizes the mechanical-electrical conversion characteristics of a piezoelectric material. On the one hand, it emits ultrasonic signals externally by the voltage excitation output by a driving circuit. On the other hand, it converts the ultrasonic signals reflected from the outside into electrical signals, thereby obtaining information on the external sensing surface, and can be widely applied to the fields of medical imaging, structural flaw detection, and biometric identification. For example, when an ultrasonic sensor is applied to an ultrasonic fingerprint module and is arranged in a specific area of the screen of an electronic device including but not limited to a smart phone, it can be used for fingerprint recognition, realizing user identity authentication, and enhancing the anti-interference performance and security of the product.

[0003] The structure of a traditional ultrasonic sensor generally includes a substrate, a bottom electrode, a piezoelectric layer, a top electrode, and a protective layer, among which the processing of the top electrode is particularly difficult. The common preparation processes for the top electrode mainly include two methods: metal sputtering and screen printing. Among them, due to the limitation of the sputtering rate, the electrode film obtained by the sputtering method usually has a thickness in the nanometer range, and the adhesion force between the electrode film and the piezoelectric layer is weak, and it is easily scraped off in other process steps, resulting in a large number of defects, leading to poor performance of the ultrasonic sensor. Therefore, the existing technical solutions mainly select the screen printing process to prepare the top electrode. The ink in screen printing usually contains relatively large metal particles. For example, the particle size of the silver particles in conductive silver ink is about 10-20 microns, resulting in a large number of blank areas in screen printing, reducing the area of the effective electrode on the piezoelectric film and increasing the parasitic resistance of the upper electrode, directly affecting the emission efficiency of ultrasonic waves. Therefore, in the process, it is necessary to fill the blank areas of the screen printing particles through multiple screen printings to increase the thickness of the electrode. The specific steps of multi-layer screen printing are generally as follows: first, perform the first layer of screen printing to screen-print the first layer of silver paste. After baking and curing the silver paste, then perform the second layer of screen printing, and then perform baking and curing. Then, successively perform the third, fourth, or more layers of screen printing and baking and curing of the silver paste until the target thickness required for the top electrode is reached.

[0004] However, the current method of screen-printing the top electrode is prone to failure in appearance or performance, affecting the production cost of the ultrasonic sensor. Therefore, it is necessary to improve the preparation process of the ultrasonic sensor to improve the performance of the ultrasonic sensor. Summary of the Invention

[0005] The embodiments of the present application provide an ultrasonic sensor and a preparation method thereof, an ultrasonic fingerprint module, and an electronic device, which are at least beneficial to improving the performance of the ultrasonic sensor.

[0006] According to some embodiments of the present application, on the one hand, an embodiment of the present application provides a method for manufacturing an ultrasonic sensor, including: providing a substrate; forming a bottom electrode layer, the bottom electrode layer being located on the surface of the substrate; forming a piezoelectric layer, the piezoelectric layer covering at least the surface of the bottom electrode layer and a part of the surface of the substrate; forming a top electrode layer, the preparation steps of the top electrode layer including: performing a surface treatment on the surface of the piezoelectric layer away from the substrate to make the surface of the piezoelectric layer hydrophilic; performing a silanization treatment on the surface of the piezoelectric layer away from the substrate to form a self-assembled molecular layer on the surface of the piezoelectric layer; immersing the substrate after the silanization treatment in a prepolymer solution so that the self-assembled molecular layer polymerizes with the monomers in the prepolymer solution to form an adhesion layer; forming a catalyst layer on the adhesion layer; placing the substrate with the catalyst layer in an electroless plating bath so that the catalyst in the catalyst layer catalyzes metal ions in the electroless plating bath to form a metal layer, and the adhesion layer and the metal layer together constitute the top electrode layer; forming a protective layer, the protective layer covering the surface of the metal layer.

[0007] In some embodiments, during the step of forming the bottom electrode layer, a pad is also formed, and the pad is spaced apart from the bottom electrode layer; during the step of forming the piezoelectric layer, the side surface of the piezoelectric layer close to the pad is inclined with respect to the surface of the substrate.

[0008] In some embodiments, after forming the piezoelectric layer and before forming the top electrode layer, it includes: forming a mask layer, the mask layer exposing the surface of the piezoelectric layer and a part of the surface of the substrate on the side of the piezoelectric layer close to the pad.

[0009] In some embodiments, the polarity of the monomers in the prepolymer solution is opposite to the polarity of the catalyst in the catalyst layer.

[0010] In some embodiments, the monomers in the prepolymer solution are [2-(methacryloyloxy)ethyltrimethylammonium chloride]; the material of the catalyst layer includes polyethylene glycol and ammonium chloropalladate, and the mass ratio of polyethylene glycol to ammonium chloropalladate is (8~12):(5~10).

[0011] In some embodiments, after forming the adhesion layer and before forming the catalyst layer, it further includes: a cleaning treatment, using deionized water to clean the substrate to remove the residual prepolymer solution in the adhesion layer.

[0012] According to some embodiments of the present application, on the other hand, an embodiment of the present application further provides an ultrasonic sensor, including: a substrate; a bottom electrode layer, the bottom electrode layer being located on the surface of the substrate; a piezoelectric layer, the piezoelectric layer covering at least the surface of the bottom electrode layer away from the substrate and a part of the surface of the substrate; a top electrode layer, the top electrode layer including an adhesion layer and a metal layer, the adhesion layer covering at least the surface of the piezoelectric layer away from the substrate, and the metal layer covering at least the surface of the adhesion layer away from the substrate; a protective layer, the protective layer covering at least the surface of the metal layer away from the substrate.

[0013] In some embodiments, in a direction perpendicular to the substrate surface, the thickness of the bottom electrode layer is 0.1 μm to 1 μm; the thickness of the piezoelectric layer is 10 μm to 30 μm; the thickness of the top electrode layer is 0.1 μm to 20 μm; and the thickness of the protective layer is 10 μm to 40 μm.

[0014] According to some embodiments of the present application, on the other hand, the present application embodiments further provide an ultrasonic fingerprint module, including: an ultrasonic sensor, which is formed by using the preparation method of the ultrasonic sensor in the above embodiments, or the ultrasonic sensor in the above embodiments; a flexible circuit board, which is electrically connected to the ultrasonic sensor, and at least one electronic component is provided on the flexible circuit board; a reinforcing member, which is located on the surface of the flexible circuit board away from the electronic component; and a connector, which is electrically connected to one end of the flexible circuit board away from the ultrasonic sensor, and the connector is used for electrically connecting to a main control chip.

[0015] According to some embodiments of the present application, on yet another aspect, the present application embodiments further provide an electronic device, including: the ultrasonic fingerprint module in the above embodiments; and / or, an ultrasonic sensor, which is formed by using the preparation method of the ultrasonic sensor in the above embodiments, or the ultrasonic sensor in the above embodiments.

[0016] The technical solutions provided by the embodiments of the present application have at least the following advantages:

[0017] In the preparation method of the ultrasonic sensor provided by the embodiments of the present application, after the bottom electrode layer and the piezoelectric layer are sequentially formed on the substrate, the surface of the piezoelectric layer is first surface-treated to make the surface of the piezoelectric layer hydrophilic, and then the hydrophilic piezoelectric layer is silanized to form a self-assembled molecular layer on the surface of the piezoelectric layer. In this way, the subsequent formed polymer adhesion layer can have good adhesion to the self-assembled molecular layer. After the catalyst layer is formed on the adhesion layer, electroless plating is carried out. The catalyst in the catalyst layer promotes metal ions in the electroless plating bath to form a metal layer on the adhesion layer. The adhesion layer and the metal layer together constitute the top electrode layer, and there is a good interfacial bonding effect between the metal layer and the piezoelectric layer. The top electrode prepared by the polymer-assisted metal deposition method has uniform thickness, good electrical conductivity, relatively smooth surface, no abnormal phenomena such as delamination, pores, and resin agglomeration inside the metal layer, and strong adhesion to the piezoelectric layer, which is very beneficial to improving the performance of the prepared ultrasonic sensor. Description of the Drawings

[0018] One or more embodiments are exemplarily illustrated by pictures in the corresponding drawings. These exemplary illustrations do not constitute a limitation on the embodiments. Unless otherwise stated, the figures in the drawings do not constitute a scale limitation. To more clearly illustrate the technical solutions in the embodiments of the present application or in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0019] Figure 1 Schematic structural diagram of an ultrasonic sensor corresponding to the step of providing a substrate;

[0020] Figure 2 Schematic structural diagram of an ultrasonic sensor corresponding to the step of forming a bottom electrode layer;

[0021] Figure 3 Schematic structural diagram of an ultrasonic sensor corresponding to the step of forming a mask layer;

[0022] Figure 4 Schematic structural diagram of an ultrasonic sensor corresponding to the step of forming a mask layer;

[0023] Figure 5 Schematic structural diagram of an ultrasonic sensor corresponding to the step of forming a top electrode layer;

[0024] Figure 6 Schematic structural diagram of an ultrasonic sensor corresponding to the step of forming a protective layer;

[0025] Figure 7 Test results of the loop sensitivity of an ultrasonic sensor formed by a conventional method and a sensor prepared by the preparation method of the ultrasonic sensor provided in the present application;

[0026] Figure 8 Schematic structural diagram of an ultrasonic fingerprint module provided by an embodiment of the present application;

[0027] Figure 9 Schematic structural diagram of an ultrasonic fingerprint module applied to an electronic device provided by an embodiment of the present application. Detailed implementation manners

[0028] As can be seen from the background art, currently, the method of screen-printing the top electrode is prone to appearance or performance failures, affecting the production cost of ultrasonic sensors.

[0029] The method of preparing the top electrode by multi-layer screen printing has too many operating steps to achieve the required target thickness, and the screen printing screens used for each layer of screen printing are mostly of different screen designs, resulting in the need to switch screen production for each screen printing. Therefore, the process is more difficult, the time cycle is longer, and the probability of production abnormalities is higher.

[0030] Cleanliness needs to be controlled during multiple screen printing processes. Foreign matter introduced between layers will reduce the effectiveness of the ultrasonic sensor, for example, leading to poor fingerprint recognition in ultrasonic fingerprint modules. At the same time, there are also misalignments at the boundaries of different layers due to alignment deviations. The fluctuations in the viscosity of the superimposed material itself and the process flow make the top electrode boundary position unstable and irregular, directly leading to poor appearance and failure of the ultrasonic transducer.

[0031] The above-mentioned failures in appearance and performance will have a significant impact on the processing yield of the ultrasonic sensor and affect the production cost of the ultrasonic sensor. Therefore, it is necessary to improve the preparation process of the ultrasonic sensor to improve the performance of the ultrasonic sensor.

[0032] The present application provides an ultrasonic sensor and a method for preparing the same, an ultrasonic fingerprint module and an electronic device, which are at least beneficial to improving the performance of the ultrasonic sensor.

[0033] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0034] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists, A and B exist at the same time, and B exists. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0035] In the accompanying drawings corresponding to the embodiments of the present application, for better understanding and description, the thickness and area of the layers are enlarged. When describing that a component is on another component or on the surface of another component, the component can be "directly" on the surface of the other component, or there can be a third component between the two components. On the contrary, when describing that a component is on the surface of another component or when a surface of a component forms or is provided with another component, it means that there is no third component between the two components. In addition, when describing that a component is "substantially" formed on another component, it means that the component is not formed on the entire surface (or front surface) of the other component, nor on a partial edge of the entire surface.

[0036] In the description of the embodiments of the present application, when a certain component "includes" another component, unless otherwise specified, other components are not excluded, and other components may further be included.

[0037] The terms used in the description of the various embodiments herein are only for describing specific embodiments and are not intended to be limiting. As used in the description of the various embodiments and the appended claims, "component" is also intended to include the plural form unless the context clearly indicates otherwise.

[0038] The embodiments of the present application will be described in detail below with reference to the accompanying drawings. However, those of ordinary skill in the art can understand that in the embodiments of the present application, many technical details are provided to enable readers to better understand the present application. However, even without these technical details and various changes and modifications based on the following embodiments, the technical solutions claimed in the present application can still be implemented.

[0039] According to some embodiments of the present application, on the one hand, a method for preparing an ultrasonic sensor is provided.

[0040] Figures 1 to 6 FIG. is a schematic structural diagram of an ultrasonic sensor corresponding to each step in the method for preparing an ultrasonic sensor provided by the embodiments of the present application.

[0041] Reference Figures 1 to 6 , the method for preparing an ultrasonic sensor includes:

[0042] Reference Figure 1 , provide a substrate 101.

[0043] The material of the substrate 101 can be a semiconductor material, glass, polyimide or other materials, and the semiconductor material includes silicon, silicon germanium or germanium.

[0044] Reference Figure 2 , form a bottom electrode layer 102, and the bottom electrode layer 102 is located on the surface of the substrate 101.

[0045] The specific steps of forming the bottom electrode layer 102 may include: coating a photoresist on the substrate 101, patterning the photoresist by developing to form the pattern required for the bottom electrode layer 102; then forming the bottom electrode layer 102 on the exposed substrate 101 by electron beam evaporation or sputtering; and then removing the photoresist.

[0046] The bottom electrode layer 102 can be a transparent conductive layer or a non-transparent conductive layer. The material of the bottom electrode layer 102 can be a metal material, an inorganic conductive material, an organic conductive material, or a composite conductive material of a metal and an inorganic or organic substance. The metal materials include at least one of aluminum, copper, gold, or platinum, etc.; the inorganic conductive materials include indium tin oxide (ITO); the organic conductive materials include PEDOT (3,4-ethylenedioxythiophene polymer): PSS (polystyrene sulfonate) copolymer or graphite, etc.

[0047] In some embodiments, referring to Figure 2 , in the step of forming the bottom electrode layer 102, a pad 112 can also be formed on the substrate 101, and the pad 112 is spaced from the bottom electrode layer 102. The pad 112 is used to electrically connect the ultrasonic sensor to other devices.

[0048] When the materials of the bottom electrode layer 102 and the pad 112 are the same, the specific steps of forming the bottom electrode layer 102 and the pad 112 may include: coating a photoresist on the substrate 101, patterning the photoresist by developing to form the patterns required for the bottom electrode layer 102 and the pad 112; then forming the bottom electrode layer 102 and the pad 112 on the exposed substrate 101 by electron beam evaporation or sputtering; and then removing the photoresist.

[0049] When the materials of the bottom electrode layer 102 and the pad 112 are different, the photoresist coating and photolithography steps can be carried out twice to form the bottom electrode layer 102 and the pad 112 respectively.

[0050] Referring to Figure 3 , a piezoelectric layer 103 is formed, and the piezoelectric layer 103 covers at least the surface of the bottom electrode layer 102 and part of the surface of the substrate 101.

[0051] The formation method of the piezoelectric layer 103 can be spin coating, spraying, or screen printing, etc.

[0052] The material of the piezoelectric layer 103 can be an organic polymer or a mixture of a piezoelectric ceramic material and glue. The organic polymers include polyvinylidene fluoride (PVDF), copolymer of polyvinylidene fluoride and trifluoroethylene (P(VDF-TrFE)), or PVDF-graphene composite material; the piezoelectric ceramic materials include lead zirconate titanate piezoelectric ceramic (PZT) and its alloy materials (such as lanthanum lead zirconate titanate ceramic (PLZT)), lead magnesium niobate (PNZT), potassium sodium niobate (K x Na 1-x NbO 3 , KNN), perovskite phase structured lead magnesium titanate niobate (PMN-PT), etc.

[0053] In the step of forming the piezoelectric layer 103, the side surface of the piezoelectric layer 103 close to the pad 112 is inclined with respect to the surface of the substrate 101. The space between the bottom electrode layer 102 and the pad 112 is used for subsequent wiring. The gentle slope formed by the side surface of the piezoelectric layer 103 close to the pad 112 being inclined with respect to the surface of the substrate 101 can facilitate the connection of the wiring after the top electrode layer is formed subsequently.

[0054] Reference Figure 4 , in some embodiments, after forming the piezoelectric layer 103 and before forming the top electrode layer, it includes: forming a mask layer 122, and the mask layer 122 exposes the surface of the piezoelectric layer 103 and a part of the surface of the substrate 101 on the side of the piezoelectric layer 103 close to the pad 112. This can facilitate the subsequent formation of the top electrode layer extending onto the substrate 101, and further facilitate the connection of the wiring.

[0055] The material of the mask layer 122 can be photoresist.

[0056] In other embodiments, the mask layer can also cover the entire substrate surface between the piezoelectric layer and the pad.

[0057] Reference Figure 5 , form the top electrode layer 104, and the top electrode layer 104 covers at least the surface of the piezoelectric layer 103.

[0058] The preparation steps of the top electrode layer 104 include: performing surface treatment on the surface of the piezoelectric layer 103 away from the substrate 101 to make the surface of the piezoelectric layer 103 hydrophilic; performing silanization treatment on the surface of the piezoelectric layer 103 away from the substrate 101 to form a vinyl-terminated self-assembled monolayer (SAM) on the surface of the piezoelectric layer 103. The main function of this self-assembled monolayer is to adapt to the piezoelectric layer 103 and increase the adhesion between polymer molecules and the piezoelectric layer 103 in subsequent processes; immersing the substrate 101 after silanization treatment in a prepolymer solution to form an adhesion layer 114 after the self-assembled monolayer polymerizes with the monomers in the prepolymer solution; forming a catalyst layer on the adhesion layer 114; placing the substrate 101 with the catalyst layer in an electroless plating bath to make the catalyst in the catalyst layer catalyze metal ions in the electroless plating bath to form a metal layer 124. The adhesion layer 114 and the metal layer 124 together constitute the top electrode layer 104.

[0059] The surface treatment can be carried out by using oxygen plasma to treat the surface of the piezoelectric layer 103, and the treatment time can be 3 min to 5 min. During the surface treatment of the piezoelectric layer 103, the surface of the substrate 101 exposed by the mask layer 122 may also be hydrophilic.

[0060] The method of performing silanization treatment can be to coat a silicon source on the surface of the piezoelectric layer 103. The silicon source includes organic silicon sources and inorganic silicon sources. The main organic silicon sources are: octenyltrichlorosilane (OTS), methyltrimethoxysilane (TMOS), tetraethyl orthosilicate (TEOS), polyethoxydisiloxane (PEDS), methyltrimethoxysilane (MTMS), methyltriethoxysilane (MTES), etc.; the main inorganic silanes are: industrial sodium silicate (Na 2 SiO 3 ), rice husk ash, diatomite, fly ash, etc.

[0061] The monomers in the prepolymer solution can be [2-(methacryloyloxy)ethyltrimethylammonium chloride] or acrylic acid.

[0062] The monomers in the prepolymer solution form a polymer through a polymerization reaction, and the polymer forms an adhesion layer 114 on the surface of the piezoelectric layer 103 by means of covalent bonds. For example, when the monomer in the prepolymer solution is [2-(methacryloyloxy)ethyltrimethylammonium chloride], the material of the adhesion layer 114 is poly[2-(methacryloyloxy)ethyltrimethylammonium chloride] (PMETAC); when the monomer in the prepolymer solution is acrylic acid, the material of the adhesion layer 114 is polyacrylic acid (PAA).

[0063] In some embodiments, the polarity of the monomers in the prepolymer solution is opposite to that of the catalyst in the catalyst layer. Monomers and catalysts with opposite polarities have better adsorption effects, which is conducive to improving the interfacial stability between the subsequently formed metal layer and the polymer adhesion layer 114.

[0064] For example, when the monomer in the prepolymer solution is [2-(methacryloyloxy)ethyltrimethylammonium chloride], the materials of the catalyst layer include polyethylene glycol and ammonium chloropalladate, and the mass ratio of polyethylene glycol to ammonium chloropalladate is (8 - 12):(5 - 10); when the monomer in the prepolymer solution is acrylic acid, the materials of the catalyst layer include copper salt aqueous solution, nickel salt aqueous solution or tetraamine palladium nitrate solution.

[0065] In some embodiments, after forming the adhesion layer 114 and before forming the catalyst layer, it further includes: a cleaning treatment, using deionized water to clean the substrate 101 to remove the residual prepolymer solution in the adhesion layer 114. The unreacted monomers on the substrate 101 and the monomers remaining by physical adsorption are washed away by rinsing with deionized water, thereby avoiding the problem that such monomers cause a decrease in the interfacial bonding effect between the subsequently formed metal layer and the adhesion layer 114.

[0066] The method for forming the catalyst layer can be dip-pen nanolithography (DPN), inkjet printing, screen printing, etc.

[0067] In the electroless plating process, metal ions are first in-situ reduced to nanoparticles by a reducing agent (such as sodium borohydride, formaldehyde or dimethylamine borane), and the obtained nanoparticles act as seeds in the electrochemical process to catalyze the formation of the metal layer 124 on the surface of the adhesion layer 114.

[0068] The material of the metal layer 124 can be gold, silver, copper or nickel.

[0069] Reference Figure 6 , remove the mask layer 122 to form a protective layer 105, and the protective layer 105 covers the surface of the metal layer 124.

[0070] The method for forming the protective layer 105 can be by coating, deposition or attachment.

[0071] The material of the protective layer 105 can be a polymer material. For example, the polymer material includes a glue material, plastic, or a mixture of resin and metal particles. The glue material includes optically clear adhesive (OCA) or pressure sensitive adhesive (PSA); the plastic includes polyimide (PI) or polyethylene terephthalate (PET); the mixture of resin and metal particles includes epoxy resin or a mixture of epoxy resin and metal particles. The material of the protective layer 105 can also be a metal material, including but not limited to gold, silver, copper, or nickel.

[0072] The protective layer 105 can be a single-layer material or a combination of multi-layer materials.

[0073] In the preparation method of the ultrasonic sensor provided by the embodiment of the present application, after the bottom electrode layer 102 and the piezoelectric layer 103 are sequentially formed on the substrate 101, the surface of the piezoelectric layer 103 is first surface-treated to make the surface of the piezoelectric layer 103 hydrophilic, and then the hydrophilic piezoelectric layer 103 is silanized to form a self-assembled molecular layer on the surface of the piezoelectric layer 103. In this way, the subsequent formed polymer adhesion layer 114 can have good adhesion with the self-assembled molecular layer. After a catalyst layer is formed on the adhesion layer 114, electroless plating is performed. The catalyst in the catalyst layer promotes metal ions in the electroless plating bath to form a metal layer 124 on the adhesion layer 114. The adhesion layer 114 and the metal layer together constitute the top electrode layer 104, and there is a good interfacial bonding effect between the metal layer 124 and the piezoelectric layer 103.

[0074] The top electrode layer 104 of the ultrasonic sensor is prepared by a polymer-assisted metal deposition preparation method, which is different from the traditional metal sputtering and screen printing methods of the top electrode. The remarkable feature of this method is that the surface-bound polymer adhesion layer 114 is used to connect the piezoelectric layer 103 and the metal layer 124. The polymer adhesion layer 114 provides rich binding sites for the activator in the electroless plating process, thereby promoting the efficient deposition of the metal layer 124 and overcoming the limitation of metal selection because the metal grows in a reducing environment where oxidation does not occur. Therefore, many metals that are difficult to achieve with the "metal ink" screen printing strategy, such as copper and nickel, can be manufactured by the preparation method provided in this embodiment, and the thickness of the metal layer 124 can be adjusted, ranging from a few hundred nanometers to dozens of micrometers.

[0075] The metal layer 124 made by the polymer-assisted metal deposition method is dense and uniform. On the one hand, the conductivity of the metal layer 124 can be of the same order of magnitude as that of bulk metal. On the other hand, the surface of the metal layer 124 can be relatively smooth (with a roughness of several nanometers). High conductivity and high surface smoothness are crucial for the performance of ultrasonic sensors because the contact resistance affects electrical losses, resulting in a reduction in energy conversion efficiency, and the roughness of the interface has a greater impact on reflection and refraction during ultrasonic wave propagation.

[0076] Since the metal layer 124 grows chemically from the polymer adhesion layer 114, an interpenetrating polymer / metal network is formed at the interface, which significantly improves the adhesion between the metal layer 124 and the piezoelectric layer 103 and gives the metal electrode significant flexibility. This is very important for the electrode stability during the operation of the ultrasonic sensor, and the long-term reliability of the ultrasonic sensor is enhanced.

[0077] In addition to depositing the continuous metal layer 124, the preparation method provided by the embodiments of the present application is also compatible with different printing techniques, including but not limited to screen printing, inkjet printing, and dip-pen nanolithography. These techniques can achieve different patterns on the substrate 101 and can deposit metal traces with line widths ranging from nanometers to micrometers.

[0078] In summary, the top electrode layer 104 prepared by the polymer-assisted metal deposition method has a uniform thickness, good conductivity, relatively high surface smoothness, is dense inside the metal layer 124 without abnormalities such as delamination, holes, and resin agglomeration, and has a strong adhesion to the piezoelectric layer 103, which is very beneficial to improving the performance of the prepared ultrasonic sensor.

[0079] Correspondingly, on the other hand, the embodiments of the present application also provide an ultrasonic sensor, which can be fabricated by using the preparation method of the ultrasonic sensor in the above embodiments to improve the performance of the ultrasonic sensor. The ultrasonic sensor provided by another embodiment of the present application will be described in detail below with reference to the accompanying drawings. For the same or corresponding parts as those in the previous embodiment, reference may be made to the corresponding description of the previous embodiment, and details will not be repeated below.

[0080] Reference Figure 6 , the ultrasonic sensor includes: a substrate 101, a bottom electrode layer 102, a piezoelectric layer 103, a top electrode layer 104, and a protective layer 105. The bottom electrode layer 102 is located on the surface of the substrate 101; the piezoelectric layer 103 covers at least the surface of the bottom electrode layer 102 away from the substrate 101 and a part of the surface of the substrate 101; the top electrode layer 104 includes an adhesion layer 114 and a metal layer 124, the adhesion layer 114 covers at least the surface of the piezoelectric layer 103 away from the substrate 101, and the metal layer 124 covers at least the surface of the adhesion layer 114 away from the substrate 101; the protective layer 105 covers at least the surface of the metal layer 124 away from the substrate 101.

[0081] In the direction perpendicular to the surface of the substrate 101, the thickness of the bottom electrode layer 102 is 0.1 μm to 1 μm, for example, specifically it can be 0.1 μm, 0.3 μm, 0.5 μm, 0.8 μm or 1 μm; the thickness of the piezoelectric layer 103 is 10 μm to 30 μm, for example, specifically it can be 10 μm, 13 μm, 16 μm, 19 μm, 20 μm, 22 μm, 25 μm, 28 μm or 30 μm; the thickness of the top electrode layer 104 is 0.1 μm to 20 μm, for example, specifically it can be 0.1 μm, 0.5 μm, 0.8 μm, 1 μm, 3 μm, 5 μm, 8 μm, 10 μm, 15 μm, 18 μm or 20 μm; the thickness of the protective layer 105 is 10 μm to 40 μm, for example, specifically it can be 10 μm, 13 μm, 16 μm, 19 μm, 20 μm, 25 μm, 28 μm, 30 μm, 33 μm, 36 μm, 39 μm or 40 μm.

[0082] It should be noted that the thickness of the top electrode layer 104 is the sum of the thicknesses of the adhesion layer 114 and the metal layer 124. Since the thickness of the adhesion layer 114 is relatively small and can be ignored, the thickness of the top electrode layer 104 is equivalent to the thickness of the metal layer 124.

[0083] In the ultrasonic sensor provided by the embodiment of the present application, the top electrode layer 104 prepared by the polymer-assisted metal deposition method has a uniform thickness, good conductivity, a relatively smooth surface, no abnormal phenomena such as delamination, holes, and resin agglomeration inside the metal layer 124, and a strong adhesion force with the piezoelectric layer 103, which is beneficial to improving the performance of the ultrasonic sensor.

[0084] Figure 7 The test results of the loop sensitivity of the ultrasonic sensor formed by the conventional method and the sensor prepared by the preparation method of the ultrasonic sensor provided by the present application are shown. Among them, Figure 7 in (a) is the ultrasonic sensor formed by the conventional method, Figure 7 in (b) is the ultrasonic sensor prepared by the preparation method of the ultrasonic sensor provided by the present application. Among the two ultrasonic sensors, the thickness of the protective layer is 20 μm, the thickness of the top electrode layer is 20 μm, the thickness of the piezoelectric layer is 15 μm, the thickness of the bottom electrode layer is 0.1 μm, and the thickness of the substrate is 70 μm. The difference is that the top electrode layer of the ultrasonic sensor formed by the conventional method is screen-printed.

[0085] The loop sensitivity (S Loop , loop sensitivity) is often used to characterize the performance of the ultrasonic sensor, and its definition is: the voltage value (V out , Volts out) of the echo signal received by the ultrasonic sensor and the voltage value (Vin , the ratio of (Volts in), is commonly expressed in decibels (dB):

[0086]

[0087] Reference Figure 7 It can be seen that within the same frequency band, compared with the ultrasonic sensor prepared by the screen printing method, the ultrasonic sensor fabricated by the preparation method of the ultrasonic sensor provided in the embodiments of the present application has better loop sensitivity, with an improvement of 4.64 dB (about 70.6%), and has better performance.

[0088] Figure 8 This is a schematic structural diagram of an ultrasonic fingerprint module provided by an embodiment of the present application.

[0089] Correspondingly, on the other hand, an embodiment of the present application further provides an ultrasonic fingerprint module. Refer to Figure 8 , including: an ultrasonic sensor, a flexible circuit board 106, a reinforcing member 107, and a connector 108. Among them, the ultrasonic sensor is formed by using the preparation method of the ultrasonic sensor in the above embodiment, or the ultrasonic sensor in the above embodiment. The following will describe in detail the ultrasonic fingerprint module provided by another embodiment of the present application with reference to the accompanying drawings. For the same or corresponding parts as those in the previous embodiment, reference may be made to the corresponding description in the previous embodiment, and details will not be repeated hereinafter.

[0090] The flexible circuit board 106 is electrically connected to the top electrode layer 104 and the pad 112 of the ultrasonic sensor. The flexible circuit board 106 and the ultrasonic sensor can be connected by means of low-temperature bonding, and the bonding medium includes but is not limited to anisotropic conductive adhesive (ACF). There is at least one electronic component 116 on the flexible circuit board 106. The electronic component 116 includes but is not limited to passive devices such as inductors, capacitors, and resistors, and active devices such as boost chips and signal preprocessing chips, which mainly provide an excitation signal for the ultrasonic sensor and preprocess the echo signal.

[0091] The reinforcing member 107 is located on the surface of the flexible circuit board 106 away from the electronic component 116, and is used to improve the mechanical strength of the flexible circuit board 106.

[0092] The connector 108 is electrically connected to one end of the flexible circuit board 106 away from the ultrasonic sensor, and the connector 108 is used to be electrically connected to the main control chip to provide communication and interaction functions.

[0093] The ultrasonic fingerprint module provided by the embodiment of the present application includes an ultrasonic sensor. The ultrasonic sensor is formed by using the preparation method of the ultrasonic sensor in the above embodiment, or the ultrasonic sensor in the above embodiment. Therefore, it has good performance and can better realize the ultrasonic fingerprint recognition function.

[0094] Correspondingly, on the other hand, an embodiment of the present application further provides an electronic device, including: the ultrasonic fingerprint module in the above embodiment; and / or, an ultrasonic sensor, which is formed by using the preparation method of the ultrasonic sensor in the above embodiment, or uses the ultrasonic sensor in the above embodiment. The following will describe in detail the electronic device provided by another embodiment of the present application. For the same or corresponding parts as the previous embodiment, reference may be made to the corresponding description of the previous embodiment, and details will not be repeated below.

[0095] The electronic device includes, but is not limited to, a mobile phone or a computer, etc.

[0096] Figure 9 It is a schematic structural diagram of an ultrasonic fingerprint module provided by an embodiment of the present application applied to an electronic device.

[0097] Refer to Figure 9 , the ultrasonic fingerprint module is bonded below the screen 200 of the electronic device through the adhesive layer 109 for under-screen ultrasonic biometric detection.

[0098] In the electronic device provided by the embodiment of the present application, the ultrasonic fingerprint module includes an ultrasonic sensor, which is formed by using the preparation method of the ultrasonic sensor in the above embodiment, or uses the ultrasonic sensor in the above embodiment, so it has a good ultrasonic fingerprint function.

[0099] Those of ordinary skill in the art can understand that the above embodiments are specific embodiments for implementing the present application. In actual applications, various changes can be made in form and details without departing from the spirit and scope of the present application. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present application. Therefore, the protection scope of the present application should be subject to the scope defined by the claims.

Claims

1. A method for preparing an ultrasonic sensor, characterized in that: include: providing a substrate; forming a bottom electrode layer, wherein the bottom electrode layer is located on the surface of the substrate; forming a piezoelectric layer, wherein the piezoelectric layer at least covers the surface of the bottom electrode layer and a portion of the substrate surface; A top electrode layer is formed, wherein the top electrode layer at least covers the surface of the piezoelectric layer, and the steps of preparing the top electrode layer include: Performing surface treatment on the surface of the piezoelectric layer away from the substrate so as to make the surface of the piezoelectric layer hydrophilic; Performing a silanization treatment on the surface of the piezoelectric layer away from the substrate to form a self-assembled molecular layer on the surface of the piezoelectric layer; Immersing the substrate after the silanization treatment in a prepolymerization solution, so that the self-assembled molecular layer and the monomers in the prepolymerization solution are polymerized to form an adhesion layer; forming a catalyst layer on the adhesion layer; placing the substrate with the catalyst layer into a chemical plating tank, so that the catalyst in the catalyst layer catalyzes the metal ions in the chemical plating tank to form a metal layer, and the adhesion layer and the metal layer together constitute the top electrode layer; A protection layer is formed, wherein the protection layer covers the surface of the metal layer.

2. The method for preparing an ultrasonic sensor according to claim 1, characterized in that: In the step of forming the bottom electrode layer, a pad is also formed, and the pad is spaced apart from the bottom electrode layer; In the step of forming the piezoelectric layer, a side surface of the piezoelectric layer close to the pad is inclined relative to a surface of the substrate.

3. The method for preparing an ultrasonic sensor according to claim 2, characterized in that: After forming the piezoelectric layer and before forming the top electrode layer, the method comprises: A mask layer is formed, wherein the mask layer exposes a surface of the piezoelectric layer and a portion of a surface of the substrate on a side of the piezoelectric layer close to the pad.

4. The method for preparing an ultrasonic sensor according to claim 1, characterized in that: The polarity of the monomer in the prepolymerization solution is opposite to the polarity of the catalyst in the catalyst layer.

5. The method for preparing an ultrasonic sensor according to claim 4, characterized in that: The monomer in the prepolymerization solution is [2-(methacryloyloxy)ethyltrimethylammonium chloride]; the material of the catalyst layer includes polyethylene glycol and ammonium chloropalladate, and the mass ratio of the polyethylene glycol to the ammonium chloropalladate is (8-12): (5-10).

6. The method for preparing an ultrasonic sensor according to claim 1, characterized in that: After forming the adhesion layer and before forming the catalyst layer, the method further includes: a cleaning process in which the substrate is cleaned with deionized water to remove the prepolymerization solution remaining in the adhesion layer.

7. An ultrasonic sensor, manufactured by the method for manufacturing an ultrasonic sensor according to any one of claims 1 to 6, characterized in that: include: substrate; A bottom electrode layer, wherein the bottom electrode layer is located on the surface of the substrate; a piezoelectric layer, wherein the piezoelectric layer at least covers a surface of the bottom electrode layer away from the substrate and a portion of the substrate surface; A top electrode layer, the top electrode layer comprising an adhesion layer and a metal layer, the adhesion layer at least covers a surface of the piezoelectric layer away from the substrate, and the metal layer at least covers a surface of the adhesion layer away from the substrate; A protection layer at least covers a surface of the metal layer away from the substrate.

8. The ultrasonic sensor according to claim 7, characterized in that: In the direction perpendicular to the substrate surface, the thickness of the bottom electrode layer is 0.1 μm to 1 μm; the thickness of the piezoelectric layer is 10 μm to 30 μm; the thickness of the top electrode layer is 0.1 μm to 20 μm; and the thickness of the protective layer is 10 μm to 40 μm.

9. An ultrasonic fingerprint module, characterized in that: include: An ultrasonic sensor, wherein the ultrasonic sensor is formed by the method for preparing an ultrasonic sensor according to any one of claims 1 to 6, or the ultrasonic sensor according to claim 7 or 8; A flexible circuit board, the flexible circuit board is electrically connected to the ultrasonic sensor, and the flexible circuit board has at least one electronic component; A reinforcing member, the reinforcing member being located on a surface of the flexible circuit board away from the electronic component; A connector is electrically connected to an end of the flexible circuit board away from the ultrasonic sensor, and the connector is used to be electrically connected to a main control chip.

10. An electronic device, characterized in that: include: The ultrasonic fingerprint module as described in claim 9; and / or, an ultrasonic sensor, wherein the ultrasonic sensor is formed by the preparation method of the ultrasonic sensor as described in any one of claims 1 to 6, or the ultrasonic sensor as described in claim 7 or 8.

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