Ultrasonic sensor and preparation method thereof, ultrasonic fingerprint module and electronic equipment

Abstract

The invention relates to the field of ultrasonic sensors, provides an ultrasonic sensor and a preparation method thereof, an ultrasonic fingerprint module and electronic equipment, and at least facilitates improvement of the performance of the ultrasonic sensor. The preparation method comprises the following steps: forming a bottom electrode layer on a substrate; forming a piezoelectric layer on the bottom electrode layer; a top electrode is formed on the piezoelectric layer, and the top electrode layer is prepared through the steps that the surface of the piezoelectric layer is treated, so that the surface of the piezoelectric layer has hydrophilicity; carrying out silanization treatment on the piezoelectric layer to form a self-assembled molecular layer; soaking the substrate subjected to silanization treatment in a pre-polymerization solution, so that the self-assembled molecular layer and monomers in the pre-polymerization solution are polymerized to form an adhesion layer; forming a catalyst layer on the adhesion layer; the substrate with the catalyst layer is placed in a chemical plating tank, so that a catalyst in the catalyst layer catalyzes metal ions in the chemical plating tank to form a metal layer, and the adhesion layer and the metal layer form a top electrode layer; and forming a protection layer on the top electrode layer.

Description

Technical Field

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

[0002] Ultrasonic sensors use the mechanical-electrical conversion characteristics of piezoelectric materials. On the one hand, they emit ultrasonic signals through the voltage excitation output by the driving circuit, and on the other hand, they convert the ultrasonic signals reflected from the outside world into electrical signals, thereby obtaining information about the external sensing surface. They can be widely used in medical imaging, structural flaw detection, and biometric identification. For example, ultrasonic sensors are applied to ultrasonic fingerprint modules and set in specific areas of the screens of electronic devices including but not limited to smartphones. They can be used for fingerprint recognition, user identity authentication, and enhanced product anti-interference and security.

[0003] The traditional ultrasonic sensor structure usually 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. Common top electrode preparation processes mainly include metal sputtering and screen printing. The electrode film obtained by sputtering is usually nanometer-level thick due to the limitation of the sputtering rate, and the adhesion between the piezoelectric layer is weak, which is easy to be scraped off in other process steps, resulting in a large number of defects, resulting in poor performance of the ultrasonic sensor. Therefore, the existing technical solution mainly uses screen printing to prepare the top electrode. The screen printing ink usually contains larger metal particles, such as the particle size of silver particles in conductive silver ink is about 10~20 microns, which leads to a large number of blank areas in screen printing, which reduces the area of ​​the effective electrode on the piezoelectric film and increases the parasitic resistance of the upper electrode, which directly affects the emission efficiency of the ultrasonic wave. Therefore, the process needs to fill the blank areas of the screen printing particles through multiple screen printing to increase the thickness of the electrode. The specific steps of multi-layer screen printing are generally: first perform the first layer of screen printing, screen print the first layer of silver paste, bake and cure the silver paste, then perform the second layer of screen printing, bake and cure, then perform the third, fourth or more layers of screen printing and bake and cure the silver paste in sequence, 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, which affects 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 method for manufacturing the same, 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, the embodiments of the present application provide a method for preparing 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 at least covering the surface of the bottom electrode layer and a portion of the surface of the substrate; forming a top electrode layer, the top electrode layer at least covering the surface of the piezoelectric layer, the preparation steps of the top electrode layer including: performing surface treatment on the surface of the piezoelectric layer away from the substrate to make the surface of the piezoelectric layer hydrophilic; performing 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 silanized substrate in a prepolymerization solution to polymerize the self-assembled molecular layer with the monomers in the prepolymerization solution to form an adhesion layer; forming a catalyst layer on the adhesion layer; placing the substrate with the catalyst layer in a chemical plating tank to allow the catalyst in the catalyst layer to catalyze the metal ions in the chemical plating tank to form a metal layer, 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, a pad is also formed in the step of forming the bottom electrode layer, and the pad is spaced apart from the bottom electrode layer; in the step of forming the piezoelectric layer, a side of the piezoelectric layer close to the pad is inclined relative to the surface of the substrate.

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

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

[0010] In some embodiments, the monomer in the prepolymer solution is [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, the method further includes: 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, the embodiments of the present application further provide an ultrasonic sensor, including: a substrate; a bottom electrode layer, the bottom electrode layer is located on the surface of the substrate; a piezoelectric layer, the piezoelectric layer at least covers the surface of the bottom electrode layer away from the substrate and a portion of the surface of the substrate; a top electrode layer, the top electrode layer includes an adhesion layer and a metal layer, the adhesion layer at least covers the surface of the piezoelectric layer away from the substrate, and the metal layer at least covers the surface of the adhesion layer away from the substrate; a protective layer, the protective layer at least covers 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 embodiments of the present application further provide an ultrasonic fingerprint module, including: an ultrasonic sensor, which is formed by the preparation method of the ultrasonic sensor in the above embodiment, or adopts the ultrasonic sensor in the above embodiment; a flexible circuit board, which is electrically connected to the ultrasonic sensor, and has at least one electronic component on the flexible circuit board; a reinforcement, which is located on the surface of the flexible circuit board away from the electronic component; a connector, which is electrically connected to one end of the flexible circuit board away from the ultrasonic sensor, and the connector is used to be electrically connected to the main control chip.

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

[0016] The technical solution provided by the embodiments of the present application has at least the following advantages: The method for preparing an ultrasonic sensor provided in an embodiment of the present application is to first perform surface treatment on the surface of the piezoelectric layer to make the surface of the piezoelectric layer hydrophilic after forming a bottom electrode layer and a piezoelectric layer on the substrate in sequence, and then perform silanization treatment on the hydrophilic piezoelectric layer to form a self-assembled molecular layer on the surface of the piezoelectric layer, so that the polymer adhesion layer formed subsequently can have good adhesion with the self-assembled molecular layer, and then perform chemical plating after forming a catalyst layer on the adhesion layer, and the catalyst in the catalyst layer promotes the metal ions in the chemical plating tank to form a metal layer on the adhesion layer, and the adhesion layer and the metal layer together constitute the top electrode layer, and there is a good interface 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, high surface smoothness, and is dense inside the metal layer without stratification, holes, resin agglomeration and other abnormalities. It has strong adhesion with the piezoelectric layer, which is very beneficial to improving the performance of the prepared ultrasonic sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] One or more embodiments are exemplarily illustrated by the pictures in the corresponding drawings. These exemplified descriptions do not constitute a limitation on the embodiments. Unless otherwise specified, the pictures in the drawings do not constitute a scale limitation. In order to more clearly illustrate the embodiments of the present application or the technical solutions in the traditional technology, the drawings required for use in the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 A schematic diagram of the structure of an ultrasonic sensor corresponding to the step of providing a substrate; Figure 2 A schematic diagram of the structure of the ultrasonic sensor corresponding to the step of forming the bottom electrode layer; Figure 3 A schematic diagram of the structure of an ultrasonic sensor corresponding to the step of forming a mask layer; Figure 4 A schematic diagram of the structure of an ultrasonic sensor corresponding to the step of forming a mask layer; Figure 5 A schematic diagram of the structure of the ultrasonic sensor corresponding to the step of forming the top electrode layer; Figure 6 A schematic diagram of the structure of the ultrasonic sensor corresponding to the step of forming a protective layer; Figure 7 Loop sensitivity test results of an ultrasonic sensor formed in a conventional manner and a sensor prepared by the method for preparing an ultrasonic sensor provided in the present application; Figure 8 A schematic diagram of the structure of an ultrasonic fingerprint module provided in an embodiment of the present application; Fig. 9 A schematic diagram of the structure of an ultrasonic fingerprint module provided in an embodiment of the present application applied to an electronic device. DETAILED DESCRIPTION

[0019] As can be seen from the background art, the current method of screen printing the top electrode is prone to failure in appearance or performance, which affects the production cost of the ultrasonic sensor.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] In the accompanying drawings corresponding to the embodiments of the present application, the thickness and area of ​​the layers are magnified for better understanding and ease of description. When describing a component on another component or on the surface of another component, the component may be "directly" located on the surface of the other component, or a third component may be present between the two components. On the contrary, when describing a component on the surface of another component or when another component is formed or provided on the surface of a component, it means that there is no third component between the two components. In addition, when describing a component as being "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 is it formed on a partial edge of the entire surface.

[0027] In the description of the embodiments of the present application, when a certain component “includes” another component, unless otherwise stated, other components are not excluded and other components may be further included.

[0028] The terms used in the description of the various described embodiments herein are used only to describe specific embodiments and are not intended to be limiting. As used in the description of the various described embodiments and the appended claims, "components" are also intended to include plural forms unless the context clearly indicates otherwise.

[0029] The following will describe the various embodiments of the present application in detail with reference to the accompanying drawings. However, it will be appreciated by those skilled in the art that in the various embodiments of the present application, many technical details are provided in order to enable the reader to better understand the present application. However, even without these technical details and various changes and modifications based on the following embodiments, the technical solution claimed in the present application can be implemented.

[0030] According to some embodiments of the present application, on one hand, an embodiment of the present application provides a method for preparing an ultrasonic sensor.

[0031] Figures 1 to 6 This is a schematic diagram of the structure of the ultrasonic sensor corresponding to each step in the method for preparing the ultrasonic sensor provided in an embodiment of the present application.

[0032] refer to Figures 1 to 6 , the preparation method of the ultrasonic sensor comprises: refer to Figure 1 , providing a substrate 101.

[0033] The material of the substrate 101 may be a semiconductor material, glass, polyimide or other materials. The semiconductor material includes silicon, silicon germanium or germanium.

[0034] refer to Figure 2 , forming a bottom electrode layer 102 , and the bottom electrode layer 102 is located on the surface of the substrate 101 .

[0035] 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 a desired pattern 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.

[0036] The bottom electrode layer 102 may be a transparent conductive layer or a non-transparent conductive layer, and the material of the bottom electrode layer 102 may be a metal material, an inorganic conductive material, an organic conductive material, or a composite conductive material of metal and inorganic or organic matter. The metal material includes at least one of aluminum, copper, gold, or platinum; the inorganic conductive material includes indium tin oxide (ITO); the organic conductive material includes PEDOT (3,4-ethylenedioxythiophene polymer): PSS (polystyrene sulfonate) copolymer or graphite.

[0037] In some embodiments, reference Figure 2In the step of forming the bottom electrode layer 102, a pad 112 may be formed on the substrate 101, and the pad 112 is spaced apart from the bottom electrode layer 102. The pad 112 is used to electrically connect the ultrasonic sensor to other devices.

[0038] When the material of the bottom electrode layer 102 and the pad 112 is 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, and patterning the photoresist by developing to form the desired pattern of 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.

[0039] When the bottom electrode layer 102 and the pad 112 are made of different materials, the bottom electrode layer 102 and the pad 112 can be formed separately by coating photoresist and performing photodevelopment twice.

[0040] refer to Figure 3 , forming a piezoelectric layer 103 , the piezoelectric layer 103 at least covers the surface of the bottom electrode layer 102 and a portion of the surface of the substrate 101 .

[0041] The piezoelectric layer 103 may be formed by spin coating, spray coating, or screen printing.

[0042] The material of the piezoelectric layer 103 can be a mixture of organic polymer or piezoelectric ceramic material and glue. Organic polymers include polyvinylidene fluoride (PVDF), copolymers of polyvinylidene fluoride and trifluoroethylene (P(VDF-TrFE)) or PVDF-graphene composite materials; piezoelectric ceramic materials include lead zirconate titanate piezoelectric ceramics (PZT) and its alloy materials (such as lead zirconate titanate lanthanum ceramics (PLZT)), lead magnesium niobate (PNZT), potassium sodium niobate (K x Na 1-x NbO3, KNN), perovskite phase structure lead magnesium niobate titanate (PMN-PT), etc.

[0043] In the step of forming the piezoelectric layer 103, the side of the piezoelectric layer 103 close to the pad 112 is inclined relative to the surface of the substrate 101. The area between the bottom electrode layer 102 and the pad 112 is used for subsequent wiring, and the gentle slope formed by the side of the piezoelectric layer 103 close to the pad 112 relative to the surface of the substrate 101 can facilitate the connection of the wiring after the top electrode layer is subsequently formed.

[0044] refer to Figure 4In some embodiments, after forming the piezoelectric layer 103 and before forming the top electrode layer, the process includes: forming a mask layer 122, wherein the mask layer 122 exposes the surface of the piezoelectric layer 103 and the surface of a portion of the substrate 101 on the side of the piezoelectric layer 103 close to the pad 112. This can facilitate the subsequent top electrode layer to extend onto the substrate 101, thereby facilitating the connection of the wiring.

[0045] The material of the mask layer 122 may be photoresist.

[0046] In other embodiments, the mask layer may also cover the entire substrate surface between the piezoelectric layer and the pad.

[0047] refer to Figure 5 , forming a top electrode layer 104 , wherein the top electrode layer 104 at least covers the surface of the piezoelectric layer 103 .

[0048] 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 molecular layer (self-assembled Monolayer, SAM) on the surface of the piezoelectric layer 103, the function of the self-assembled molecular layer is mainly to adapt the piezoelectric layer 103 and increase the adhesion between the polymer molecules and the piezoelectric layer 103 in the subsequent process; immersing the substrate 101 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 114; forming a catalyst layer on the adhesion layer 114; placing the substrate 101 with the catalyst layer in 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 124, and the adhesion layer 114 and the metal layer 124 together constitute the top electrode layer 104.

[0049] The surface treatment may be performed by treating the surface of the piezoelectric layer 103 with oxygen plasma, and the treatment time may be 3 minutes to 5 minutes. 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.

[0050] The method for silanization treatment can be to coat the surface of the piezoelectric layer 103 with a silicon source, wherein the silicon source includes an organic silicon source and an inorganic silicon source. The organic silicon source mainly includes: octenyltrichlorosilane (OTS), methyl orthosilicate (TMOS), ethyl orthosilicate (TEOS), polyethoxydisiloxane (PEDS), methyltrimethoxysilane (MTMS), methyltriethoxysilane (MTES), etc.; the inorganic silane mainly includes: industrial sodium silicate (Na2SiO3), rice husk ash, diatomaceous earth, fly ash, etc.

[0051] The monomer in the prepolymerization solution may be [2-(methacryloyloxy)ethyltrimethylammonium chloride] or acrylic acid.

[0052] The monomers in the prepolymer solution form polymers through polymerization reaction, and the polymers form an adhesion layer 114 on the surface of the piezoelectric layer 103 through 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).

[0053] In some embodiments, the polarity of the monomer in the prepolymer solution is opposite to the polarity of the catalyst in the catalyst layer. Monomers and catalysts with opposite polarities have better adsorption effects, which is beneficial to improve the interface stability between the subsequently formed metal layer and the polymer adhesion layer 114.

[0054] For example, when 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 polyethylene glycol to ammonium chloropalladate is (8~12):(5~10); when the monomer in the prepolymerization solution is acrylic acid, the material of the catalyst layer includes a copper salt aqueous solution, a nickel salt aqueous solution or a tetraaminopalladium nitrate solution.

[0055] In some embodiments, after forming the adhesion layer 114 and before forming the catalyst layer, the process further includes: a cleaning process, in which the substrate 101 is cleaned with deionized water 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 cleaned by the deionized water, thereby preventing such monomers from causing a decrease in the interface bonding effect between the subsequently formed metal layer and the adhesion layer 114.

[0056] The catalyst layer can be formed by dip pen nanolithography (DPN), inkjet printing or screen printing.

[0057] In the chemical plating process, metal ions are first reduced in situ into nanoparticles by a reducing agent (such as sodium borohydride, formaldehyde or dimethylamine borane), and the resulting nanoparticles act as seeds in an electrochemical process to catalyze the formation of the metal layer 124 on the surface of the adhesion layer 114.

[0058] The material of the metal layer 124 may be gold, silver, copper or nickel.

[0059] refer to Figure 6 , remove the mask layer 122 to form a protection layer 105 , which covers the surface of the metal layer 124 .

[0060] The protective layer 105 can be formed by coating, deposition or attachment.

[0061] The material of the protective layer 105 may be a polymer material, for example, the polymer material includes a glue material, a plastic, or a mixture of a resin and metal particles, the glue material includes an optically clear adhesive (OCA) or a 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 may also be a metal material, including but not limited to gold, silver, copper or nickel.

[0062] The protective layer 105 may be a single layer of material or a combination of multiple layers of material.

[0063] The method for preparing an ultrasonic sensor provided in an embodiment of the present application is as follows: after a bottom electrode layer 102 and a piezoelectric layer 103 are sequentially formed on a substrate 101, a surface treatment is first performed on the surface of the piezoelectric layer 103 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, so that a polymer adhesion layer 114 formed subsequently can have good adhesion to the self-assembled molecular layer, and chemical plating is performed after a catalyst layer is formed on the adhesion layer 114. The catalyst in the catalyst layer promotes metal ions in the chemical plating tank to form a metal layer 124 on the adhesion layer 114, and the adhesion layer 114 and the metal layer together constitute a top electrode layer 104, and there is a good interface bonding effect between the metal layer 124 and the piezoelectric layer 103.

[0064] The top electrode layer 104 of the ultrasonic sensor is prepared by a preparation method of polymer-assisted metal deposition. Different from the metal sputtering and screen printing methods of the traditional top electrode, the significant feature of this method is that the piezoelectric layer 103 and the metal layer 124 are connected by a surface-bound polymer adhesion layer 114. The polymer adhesion layer 114 provides abundant binding sites for the activator in the chemical 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 using the preparation method provided in this embodiment, and the thickness of the metal layer 124 can be adjusted, ranging from hundreds of nanometers to tens of microns.

[0065] The metal layer 124 formed by the metal deposition method assisted by the polymer adhesion layer 114 is dense and uniform. On the one hand, the conductivity of the metal layer 124 can be at the same order of magnitude as that of bulk metal, and on the other hand, the surface of the metal layer 124 can be relatively smooth (roughness of several nanometers). High conductivity and high surface smoothness are crucial to the performance of ultrasonic sensors, because contact resistance affects electrical losses and reduces energy conversion efficiency, and the roughness of the interface has a significant impact on reflection and refraction during ultrasonic propagation.

[0066] Since the metal layer 124 is chemically grown from the polymer adhesion layer 114, an interpenetrating network of polymer / metal is formed at the interface, which significantly improves the adhesion between the metal layer 124 and the piezoelectric layer 103 and makes the metal electrode have 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.

[0067] In addition to depositing the continuous metal layer 124, the preparation method provided in the embodiment of the present application is also compatible with different printing technologies, including but not limited to screen printing, inkjet printing and dip pen nanolithography. These technologies can achieve different patterns on the substrate 101 and can deposit metal traces with resolutions ranging from nanometers to micrometers in line width.

[0068] In summary, the top electrode layer 104 prepared by the polymer-assisted metal deposition method has uniform thickness, good conductivity, and a smooth surface. The metal layer 124 is dense and has no abnormalities such as stratification, holes, and resin agglomeration. It has strong adhesion to the piezoelectric layer 103, which is very beneficial to improving the performance of the prepared ultrasonic sensor.

[0069] Accordingly, another aspect of the embodiment of the present application further provides an ultrasonic sensor, which can be manufactured using the method for manufacturing the ultrasonic sensor in the above embodiment to improve the performance of the ultrasonic sensor. The ultrasonic sensor provided in another embodiment of the present application will be described in detail below in conjunction with the accompanying drawings. For the parts that are the same or corresponding to the previous embodiment, refer to the corresponding description of the previous embodiment, and will not be described in detail below.

[0070] refer to 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 at least covers the surface of the bottom electrode layer 102 away from the substrate 101 and 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 at least covers the surface of the piezoelectric layer 103 away from the substrate 101, and the metal layer 124 at least covers the surface of the adhesion layer 114 away from the substrate 101; the protective layer 105 at least covers the surface of the metal layer 124 away from the substrate 101.

[0071] In a 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, 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, 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 .1μm~20μm, for example, it can be 0.1μm, 0.5μm, 0.8μm, 1μm, 3μm, 5μm, 8μm, 10μm, 15μm, 18μm or 20μm; the thickness of the protective layer 105 is 10μm~40μm, for example, it can be 10μm, 13μm, 16μm, 19μm, 20μm, 25μm, 28μm, 30μm, 33μm, 36μm, 39μm or 40μm.

[0072] 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 .

[0073] In the ultrasonic sensor provided in the embodiment of the present application, the top electrode layer 104 prepared by the polymer-assisted metal deposition method has uniform thickness, good conductivity, and a smooth surface. The metal layer 124 is dense and has no abnormalities such as stratification, holes, and resin agglomeration. The adhesion between the metal layer 124 and the piezoelectric layer 103 is strong, which is beneficial to improving the performance of the ultrasonic sensor.

[0074] Figure 7 The loop sensitivity test results of the ultrasonic sensor formed in a conventional manner and the sensor prepared by the ultrasonic sensor preparation method provided in this application are shown in FIG. Figure 7 (a) is an ultrasonic sensor formed in a conventional manner. Figure 7 (b) is an ultrasonic sensor prepared by the preparation method of the ultrasonic sensor provided in the present application. In the two ultrasonic sensors, the thickness of the protective layer is 20μm, the thickness of the top electrode layer is 20μm, the thickness of the piezoelectric layer is 15μm, the thickness of the bottom electrode layer is 0.1μm, and the thickness of the substrate is 70μm. The difference is that the top electrode layer of the ultrasonic sensor formed by the conventional method is screen-printed.

[0075] Loop sensitivity (S Loop , loop sensitivity) is often used to characterize the performance of ultrasonic sensors. It is defined as: the voltage value (V out , Volts out) and the voltage value of the transmitting excitation signal (Vin , Volts in), usually expressed in decibels (dB):

[0076] refer to Figure 7 It can be seen that within the same frequency band, compared with the ultrasonic sensor prepared by screen printing, the ultrasonic sensor manufactured by the preparation method of the ultrasonic sensor provided in the embodiment of the present application has better loop sensitivity, which is improved by 4.64dB (about 70.6%), and has better performance.

[0077] Figure 8 A schematic diagram of the structure of an ultrasonic fingerprint module provided in an embodiment of the present application.

[0078] Accordingly, another aspect of the present application embodiment further provides an ultrasonic fingerprint module, referring to Figure 8 , including: an ultrasonic sensor, a flexible circuit board 106, a reinforcement member 107 and a connector 108, wherein the ultrasonic sensor is formed by the preparation method of the ultrasonic sensor in the above embodiment, or the ultrasonic sensor in the above embodiment is used. The ultrasonic fingerprint module provided by another embodiment of the present application will be described in detail below in conjunction with the accompanying drawings. For the parts that are the same or corresponding to the previous embodiment, please refer to the corresponding description of the above embodiment, and will not be described in detail below.

[0079] 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 low-temperature bonding. 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 components such as inductors, capacitors, resistors, and active components such as boost chips and signal preprocessing chips, which mainly increase the excitation signal for the ultrasonic sensor and preprocess the echo signal.

[0080] The reinforcing member 107 is located on a 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 .

[0081] The connector 108 is electrically connected to an end of the flexible circuit board 106 away from the ultrasonic sensor. The connector 108 is used to be electrically connected to the main control chip to provide communication and interaction functions.

[0082] The ultrasonic fingerprint module provided in the embodiment of the present application includes an ultrasonic sensor. The ultrasonic sensor is formed by the preparation method of the ultrasonic sensor in the above embodiment, or adopts the ultrasonic sensor in the above embodiment, so it has better performance and can better realize the ultrasonic fingerprint recognition function.

[0083] Accordingly, another aspect of the 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 the preparation method of the ultrasonic sensor in the above embodiment, or uses the ultrasonic sensor in the above embodiment. The electronic device provided by another embodiment of the present application will be described in detail below in conjunction with the accompanying drawings. For the parts that are the same or corresponding to the previous embodiment, refer to the corresponding description of the previous embodiment, and will not be described in detail below.

[0084] Electronic devices include but are not limited to mobile phones or computers.

[0085] Fig. 9 A schematic diagram of the structure of an ultrasonic fingerprint module provided in an embodiment of the present application applied to an electronic device.

[0086] refer to Fig. 9 The ultrasonic fingerprint module is bonded to the bottom of the screen 200 of the electronic device through the adhesive layer 109 for under-screen ultrasonic biometric detection.

[0087] In the electronic device provided in the embodiment of the present application, the ultrasonic fingerprint module includes an ultrasonic sensor. The ultrasonic sensor is formed by the preparation method of the ultrasonic sensor in the above embodiment, or the ultrasonic sensor in the above embodiment is used, so it has a better ultrasonic fingerprint function.

[0088] Those skilled in the art will appreciate that the above-mentioned embodiments are specific examples for implementing the present application, and in practical applications, various changes may be made to the embodiments in form and detail without departing from the spirit and scope of the present application. Any person skilled in the art may make various changes and modifications without departing from the spirit and scope of the present application, and therefore the scope of protection of the present application shall be subject to the scope defined in 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, 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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