CN115605070B

CN115605070B - Preparation method and application of piezoelectric polymer solution

Info

Publication number: CN115605070B
Application number: CN202211215511.6A
Authority: CN
Inventors: 纪登鑫; 王红超
Original assignee: Shenzhen Goodix Technology Co Ltd
Current assignee: Huike Singapore Holdings Private Ltd
Priority date: 2022-09-30
Filing date: 2022-09-30
Publication date: 2023-12-26
Anticipated expiration: 2042-09-30
Also published as: CN115605070A

Abstract

The application provides a preparation method and application of a piezoelectric polymer solution, wherein the piezoelectric polymer solution is used for preparing an ultrasonic transducer, and the preparation method of the piezoelectric polymer solution comprises the following steps: dissolving a piezoelectric polymer in a solvent at a predetermined temperature, wherein the predetermined temperature is 20-30 ℃; and stirring the solvent for a predetermined time to obtain a piezoelectric polymer solution. The piezoelectric polymer is dissolved in a solvent at 20-30 ℃ to prepare a piezoelectric polymer solution for preparing the ultrasonic transducer, so that the performances of transparency, piezoelectric constant and the like of a piezoelectric layer of the ultrasonic transducer prepared from the piezoelectric polymer solution can be improved, and the performances of the ultrasonic transducer can be further optimized.

Description

Preparation method and application of piezoelectric polymer solution

Technical Field

The invention relates to the field of ultrasonic transducers, in particular to a preparation method and application of a piezoelectric polymer solution.

Background

The ultrasonic transducer is a device for mutually converting acoustic energy and electric energy, wherein the piezoelectric layer has a piezoelectric effect and is used for transmitting or receiving ultrasonic waves, and the ultrasonic transducer has the advantages of penetrating a display screen or a shell, avoiding optical interference, identifying biological characteristics (such as fingerprints) and the like and is widely applied to intelligent terminal equipment. However, in the related art, the piezoelectric layer has defects of poor transparency, low piezoelectric constant, low loop sensitivity and the like, which affect the performance of the ultrasonic transducer and the terminal equipment.

Disclosure of Invention

The application provides a preparation method and application of a piezoelectric polymer solution, which at least solve the technical problems of poor transparency of a piezoelectric layer, low piezoelectric constant, low loop sensitivity and the like in the prior art.

In order to solve the technical problems, the application adopts the following technical scheme:

in one aspect of the present application, there is provided a method for preparing a piezoelectric polymer solution for preparing an ultrasonic transducer, including: dissolving a piezoelectric polymer in a solvent at a predetermined temperature, wherein the predetermined temperature is 20-30 ℃; and stirring the solvent for a predetermined time to obtain a piezoelectric polymer solution.

Optionally, after stirring the solvent for a predetermined time, obtaining the piezoelectric polymer solution includes: stirring the solvent at the preset temperature until the solvent is transparent, and then maintaining stirring for no more than 48 hours to obtain the piezoelectric polymer solution.

Optionally, the method further comprises: and after the piezoelectric polymer is dissolved in the solvent, filtering the obtained mixed solution by adopting a filter screen with the aperture of 0.5-5 mu m under the pressure condition of 1.5-3 bar to obtain the piezoelectric polymer solution.

Optionally, the piezoelectric polymer comprises one or more of polyvinylidene fluoride, polyvinylidene fluoride homopolymer, polyvinylidene fluoride-fluoromonomer copolymer.

Optionally, the solvent includes a polar organic solvent including at least one of an amide-based solvent, a sulfone-based solvent, and a ketone-based solvent.

Optionally, the mass concentration of the piezoelectric polymer in the piezoelectric polymer solution is 10% -20%.

In another aspect of the present application, a method for preparing an ultrasonic transducer is provided, including: preparing the piezoelectric polymer solution according to the preparation method of the piezoelectric polymer solution; coating the piezoelectric polymer solution on a first electrode, and forming a piezoelectric film; sequentially crystallizing and polarizing the piezoelectric film to form a piezoelectric layer; and forming a second electrode on the piezoelectric layer to obtain the ultrasonic transducer.

Optionally, the first electrode is formed on a complementary metal oxide semiconductor chip.

Alternatively, the coating is performed using a spin coating process.

Optionally, the process of performing the coating using a spin coating process includes: and placing the piezoelectric polymer solution on the first electrode, performing primary coating at a first rotating speed, and performing secondary coating at a second rotating speed, wherein the second rotating speed is higher than the first rotating speed.

Optionally, the first rotational speed ranges from 200rpm to 500rpm, and/or the second rotational speed ranges from 800rpm to 3000rpm.

Optionally, the piezoelectric polymer solution is coated on a first electrode, and after drying, the piezoelectric film is formed; wherein, the conditions of the drying are as follows: the temperature is 20-80 ℃ and the time is 30 s-10 min.

Alternatively, the piezoelectric film has a thickness of 5 μm to 20 μm.

Optionally, the crystallization process includes: and baking the piezoelectric film at a first temperature for 45-120 min, wherein the first temperature is higher than the Curie temperature of the piezoelectric film and lower than the melting temperature of the piezoelectric film.

Optionally, the polarizing process includes: the piezoelectric film is put into an electric field of 100V/mu m to 200V/mu m for polarization.

Optionally, the polarizing process includes: placing the piezoelectric film in an electric field of 100V/mu m-200V/mu m for 5 min-20 min to polarize the piezoelectric film.

Optionally, the method further comprises: patterning the polarized piezoelectric film to form the piezoelectric layer, wherein the patterning process comprises the following steps: forming a first adhesive layer on the polarized piezoelectric film; forming a photoresist layer on the first bonding layer, and forming an etching window on the photoresist layer; etching the first bonding layer and the part of the piezoelectric film exposed by the etching window; and removing the photoresist layer and the first bonding layer to form the piezoelectric layer.

Optionally, a second adhesive layer is formed on the first electrode, the piezoelectric polymer solution is coated on the second adhesive layer, and the piezoelectric film is formed, so that the piezoelectric polymer solution is coated on the first electrode, and the piezoelectric film is formed.

Optionally, the thickness of the second adhesive layer is 10 nm-200 nm.

Optionally, the thickness of the second electrode is 2 μm to 30 μm.

Optionally, the method further comprises: and forming a protective layer on the second electrode, wherein the thickness of the protective layer is 4-50 μm.

In yet another aspect of the present application, an ultrasonic transducer is provided, and is manufactured by using the method for manufacturing an ultrasonic transducer.

In yet another aspect of the present application, an electronic device is provided that includes a cover plate and the above-described ultrasonic transducer.

According to the preparation method of the piezoelectric polymer solution, the piezoelectric polymer is dissolved in the solvent at the preset temperature (20-30 ℃) to prepare the piezoelectric polymer solution, the piezoelectric polymer solution is used for preparing the ultrasonic transducer, the performances of transparency, piezoelectric constant and the like of a piezoelectric layer of the ultrasonic transducer prepared by the piezoelectric polymer solution can be improved, the performances of loop sensitivity and the like of the ultrasonic transducer are further optimized, and meanwhile, the preparation method has the advantages of mild condition, low energy consumption, simplicity in operation and the like.

Drawings

Fig. 1 is a flowchart of a method for manufacturing an ultrasonic transducer according to an embodiment of the present application;

fig. 2a to 2d are schematic top views of a process for manufacturing an ultrasonic transducer according to an embodiment of the present application;

fig. 3a to 3d are schematic cross-sectional views of a process for manufacturing an ultrasonic transducer according to an embodiment of the present application;

fig. 4a to 4f are schematic cross-sectional views of a process for manufacturing an ultrasonic transducer on a CMOS chip according to a first embodiment of the present application;

FIG. 5 is a schematic structural diagram of an ultrasonic transducer according to an embodiment of the present disclosure;

fig. 6 is a schematic structural diagram of an ultrasonic transducer according to another embodiment of the present application;

fig. 7 is a schematic structural diagram of an ultrasonic transducer according to another embodiment of the present disclosure;

fig. 8a to 8d are schematic flow diagrams of patterning a piezoelectric film of an ultrasonic fingerprint sensor according to an embodiment of the present application;

fig. 9a to 9e are schematic views of a preparation flow of an ultrasonic transducer according to a second embodiment of the present application;

fig. 10 is a graph showing the relationship between loop sensitivity of the ultrasonic transducers of test example 1 and comparative example 1 and the excitation frequency of the ultrasonic signal.

Reference numerals illustrate: 10: a first adhesive layer; 20: a photoresist layer; 21: etching a window; 1000: a CMOS chip; 2000: a piezoelectric film; 100: an ultrasonic fingerprint chip; 101: an operable region; 110: a substrate; 120: a first electrode; 130: a passivation layer; 140: an electrode pad; 150: a pin pad; 161: a first connecting line; 162: a second connecting line; 200: a piezoelectric layer; 210: an inclined surface; 300: a second electrode; 400: a protective layer; 500: a second adhesive layer; 600: and a conductive protective layer.

Detailed Description

Ultrasonic transducers (or ultrasonic sensors) are devices that transduce acoustic and electrical energy to each other, and are increasingly used, for example, for biometric (e.g., fingerprint) identification. For example, an ultrasonic fingerprint sensor is an ultrasonic transducer for fingerprint recognition, which utilizes ultrasonic waves to have the ability to penetrate materials, and when the ultrasonic waves reach surfaces of different materials, reflected ultrasonic energy and a path traveled by the ultrasonic waves are different, so that the difference of the impedance of skin and air to sound waves is utilized to distinguish the positions of ridges and valleys of the fingerprint, the ultrasonic fingerprint sensor can penetrate below the skin surface to recognize unique three-dimensional characteristics of the fingerprint, and recognize true and false fingers, and because the ultrasonic waves have certain penetrability, the ultrasonic waves can still be recognized under the condition that the fingers have little dirt or moisture, and can penetrate through a display screen or a shell of the device, so that the ultrasonic fingerprint sensor is increasingly applied to intelligent terminal equipment.

Specifically, the piezoelectric layer of the ultrasonic transducer has a piezoelectric effect, and when the piezoelectric layer is deformed, voltage difference is generated at two ends of the piezoelectric layer; when a voltage difference exists between the two ends of the piezoelectric layer, the piezoelectric layer can generate shape vibration to generate ultrasonic waves. By utilizing such characteristics of the piezoelectric layer, the mutual conversion of the mechanical vibration and the alternating current signal is realized.

The higher the working frequency of the ultrasonic transducer is, the better the penetrability is, which is more beneficial to producing clear biological feature images and improving the accuracy of biological feature identification. The operating frequency of an ultrasonic transducer is inversely proportional to the thickness of the piezoelectric layer, meaning a thinner piezoelectric layer when higher accuracy of biometric identification is required. Meanwhile, in order to obtain sufficient imaging performance, the interval between two adjacent piezoelectric pillars (i.e., the first electrode described below) of the ultrasonic transducer should be smaller than the ultrasonic wavelength, and for a typical ultrasonic fingerprint sensor, the interval between two adjacent piezoelectric pillars is generally between 50 μm and 100 μm.

Therefore, the preparation process of the piezoelectric layer is critical to the performance of the ultrasonic transducer. The piezoelectric material forming the piezoelectric layer can be piezoelectric ceramic lead zirconate titanate (PZT) or high polymer piezoelectric material (such as polyvinylidene fluoride (PVDF)), and the like, and under the condition of the same thickness, compared with the PZT, the ultrasonic transducer adopting the high polymer piezoelectric material such as PVDF and the like has larger loop sensitivity and is widely focused and applied. In the process of preparing an ultrasonic transducer using a polymer piezoelectric material such as PVDF, the polymer piezoelectric material such as PVDF is usually dissolved in a solvent at a high temperature (generally, more than 50 ℃ and usually 60 to 80 ℃) to prepare a solution, and the solution is used to form a piezoelectric layer.

However, in the related art, the piezoelectric layer generally has defects of poor transparency, low piezoelectric constant and the like, which affect the performance of the ultrasonic transducer and the terminal device.

In view of the above problems, embodiments of the present application provide a method for preparing a piezoelectric polymer solution for preparing an ultrasonic transducer, including: dissolving a piezoelectric polymer in a solvent at a predetermined temperature, wherein the predetermined temperature is 20-30 ℃; and stirring the solvent for a predetermined time to obtain a piezoelectric polymer solution.

Illustratively, the predetermined temperature may be 20 ℃, 22 ℃, 25 ℃, 28 ℃, 30 ℃, or a range of any two or more thereof.

According to long-term researches of the inventor, from the preparation process of the piezoelectric polymer solution for preparing the ultrasonic transducer, the piezoelectric polymer is dissolved in a solvent at 20-30 ℃ to prepare the piezoelectric polymer solution for preparing the ultrasonic transducer, the piezoelectric polymer solution is specifically used for forming a piezoelectric layer of the ultrasonic transducer, compared with the conventional high-temperature (such as 60-80 ℃) dissolution process, the low-temperature dissolution process of the embodiment of the application can improve the performances such as transparency and piezoelectric constant (d 33) of the piezoelectric layer formed by adopting the piezoelectric polymer solution, and presumably, the reason is that the dissolution of the piezoelectric polymer at different temperatures can influence the conditions such as molecular structure (such as chain length) of the polymer, and further influence the performances such as transparency and piezoelectric constant of the piezoelectric layer, and the piezoelectric polymer in the piezoelectric layer is dissolved at 20-30 ℃ to ensure that the piezoelectric polymer in the piezoelectric layer has more suitable characteristics such as molecular structure, and further improve the performances such as transparency and piezoelectric constant of the piezoelectric layer.

Studies have shown that the d33 of a piezoelectric layer (or piezoelectric film) formed using the piezoelectric polymer solution prepared in the examples of the present application can be as high as 25±1pC/N or more, whereas in the related art, the d33 of a piezoelectric film formed by dissolving a piezoelectric polymer at a high temperature is generally lower than 21±2pC/N to prepare a piezoelectric polymer solution. For an ultrasonic transducer, the relation between the sensitivity and d33 satisfies S _loop ∝S _Tx *S _Rx ∝d33 ³ Loop sensitivity S of ultrasonic transducer _loop Proportional to the sensitivity S of the emitted ultrasonic wave _Tx And receiving ultrasonic sensitivity S _Rx Proportional to the third power of the piezoelectric constant d33, and when d33 increases from about 21pC/N to about 25pC/N, the sensitivity of the ultrasonic transducer increases to the original (25/21) ³ =1.69 times, i.e. the boost is close to 70%; in practical tests, the sensitivity of the ultrasonic transducer is improved by approximately 50% possibly due to the influence of parasitic capacitance and other factors, which is beneficial to improving the ultrasonic signal intensity and the ultrasonic imaging definition.

In addition, the preparation method of the piezoelectric polymer solution provided by the embodiment of the application prepares the piezoelectric polymer solution by dissolving the piezoelectric polymer at a low temperature (20-30 ℃), and has the advantages of mild condition, low energy consumption, simplicity in operation and the like.

In some embodiments, the process of obtaining the piezoelectric polymer solution after stirring the solvent for a predetermined time includes: after the solvent is stirred to be transparent at the preset temperature (20-30 ℃), stirring is maintained for no more than 48 hours to obtain the piezoelectric polymer solution, so that the piezoelectric polymer solution is fully dissolved, and meanwhile, the performances of transparency, piezoelectric constant and the like of a piezoelectric layer formed by adopting the piezoelectric polymer solution are further optimized.

In the specific implementation, the solvent can be added into the reaction kettle, stirring is started, then the piezoelectric polymer is slowly added into the reaction kettle, meanwhile, the reaction kettle is regulated to a preset temperature (namely 20-30 ℃), the reaction kettle can be regulated to the preset temperature in a water bath heating mode, and the like, after the solution is transparent, stirring is continuously maintained for a period of time (not more than 48 hours), and then the solution is taken out from the reaction kettle, so that the piezoelectric polymer solution is prepared.

In addition, after the piezoelectric polymer is dissolved in the solvent, the obtained mixed solution may be filtered, for example, by using a filter screen with a pore diameter of 0.5 μm to 5 μm, and the filtrate is collected to obtain the piezoelectric polymer solution. Wherein, the filtration process can be pressurized, for example, the filtration can be performed under the pressure condition of 1.5bar to 3bar, so as to improve the filtration efficiency.

Illustratively, the pore size of the filter mesh may be 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, or a range of any two of them. The pressure conditions during filtration are for example in the range of 1.5bar, 2bar, 2.5bar, 3bar or any two in between.

In some embodiments, the piezoelectric polymer may include one or more of polyvinylidene fluoride (Polyvinylidene Fluoride, PVDF), polyvinylidene fluoride homopolymer, polyvinylidene fluoride-fluoromonomer Copolymer (Copolymer).

It is understood that the polyvinylidene fluoride-fluoromonomer copolymer is a polymer obtained by copolymerizing PVDF and fluoromonomer, and the fluoromonomer includes, for example, one or more of Trifluoroethylene (TrFE), chlorotrifluoroethylene (CTFE), and Tetrafluoroethylene (TFE), that is, the polyvinylidene fluoride-fluoromonomer copolymer may include one or more of a binary copolymer obtained by copolymerizing PVDF and one of these monomers, a ternary copolymer obtained by copolymerizing PVDF and two of these monomers, and a quaternary copolymer obtained by copolymerizing PVDF and three of these monomers.

In some embodiments, the polyvinylidene fluoride-fluoromonomer copolymer comprises one or more of polyvinylidene fluoride-trifluoroethylene copolymer (PVDF-TrFE), polyvinylidene fluoride-chlorotrifluoroethylene copolymer (PVDF-CTFE), polyvinylidene fluoride-tetrafluoroethylene copolymer (PVDF-TFE), polyvinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene copolymer (PVDF-TrFE-CTFE), polyvinylidene fluoride-trifluoroethylene-tetrafluoroethylene copolymer (PVDF-TrFE-TFE), polyvinylidene fluoride-chlorotrifluoroethylene-tetrafluoroethylene copolymer (PVDF-TFE), polyvinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene-tetrafluoroethylene copolymer (PVDF-TrFE-CTFE-TFE).

In the polyvinylidene fluoride-fluoromonomer copolymer, the mass content of the fluoromonomer may be 10% to 50%, for example, 10%, 15%, 18%, 20%, 22%, 25%, 30%, 35%, 40%, 45%, 50% or a range of any two of them.

The content of the fluorine-containing monomer generally affects the properties such as the melting point, curie temperature, dielectric constant, and piezoelectric constant of the piezoelectric film formed from the copolymer, and for example, PVDF-TrFE, when the mass content of TrFE is about 20%, the melting point of the formed piezoelectric film is about 150 ℃, the curie temperature is about 136 ℃, the dielectric constant is between 9 and 12, and the piezoelectric constant is between 24 and 30; when the mass content of TrFE is about 25%, the melting point of the formed piezoelectric film is about 150 ℃, the Curie temperature is about 115 ℃, the dielectric constant is between 9 and 12, and the piezoelectric constant is between 24 and 30; when the mass content of TrFE is about 30%, the melting point of the formed piezoelectric film is about 151 ℃, the Curie temperature is about 100 ℃, the dielectric constant is between 10 and 14, and the piezoelectric constant is between 18 and 22; when the TrFE content is about 45%, the melting point of the formed piezoelectric film is about 158 ℃, the Curie temperature is about 60 ℃, the dielectric constant is between 10 and 14, and the piezoelectric constant is between 18 and 22.

In general, as the fluorine-containing monomer content increases, the melting point increases, the curie temperature decreases, the dielectric constant increases, and the piezoelectric constant decreases. The larger the difference between the melting point and the distance temperature, the larger the process window for preparing the piezoelectric layer, for example, in the preparation process of the piezoelectric layer, the crystallization generally involves crystallization of the piezoelectric film, and the temperature at the time of crystallization is larger than the curie temperature of the piezoelectric film and smaller than the melting point of the piezoelectric film, so that when the difference between the curie temperature and the melting point is larger, the larger the process window for crystallization is, and crystallization can be performed in a larger temperature range; the larger the dielectric constant is, the larger the capacitance is, and the signal attenuation caused by parasitic capacitance is smaller; the larger the piezoelectric constant, the stronger the ultrasonic signal that occurs, while the stronger the intensity of the received ultrasonic signal converted into an electrical signal.

In some embodiments, PVDF-TrFE with a TrFE mass content of about 20% may be selected by considering the above factors, and factors such as process requirements during the preparation of the ultrasound transducer (e.g., reliability testing is typically required at about 120 ℃ when the ultrasound transducer is an ultrasound fingerprint sensor).

Further, the above-mentioned solvents may include polar organic solvents, for example, include one or more of amide-based solvents, sulfone-based solvents, ketone-based solvents, and the like, and the amide-based solvents may include dimethylformamide and/or dimethylacetamide, and the like, and the sulfone-based solvents include dimethylsulfoxide, and the like, and the ketone-based solvents include butanone (Methyl ethyl ketone, MEK), and the like, as examples.

To further optimize the piezoelectric layer properties, the mass concentration of the piezoelectric polymer in the piezoelectric polymer solution formulated by the above procedure is 10% to 20%, i.e. the ratio of the mass of the piezoelectric polymer to the sum of the mass of the piezoelectric polymer and the mass of the solvent is 10% to 20%, e.g. 10%, 12%, 15%, 18%, 20% or any two composition ranges therebetween.

The piezoelectric polymer solution prepared by the preparation process can form a piezoelectric layer in the ultrasonic transducer, and the piezoelectric layer has good transparency, piezoelectric constant and other performances, so that the performance of the ultrasonic transducer can be optimized. Hereinafter, an ultrasonic transducer and a method for manufacturing the same according to an embodiment of the present application will be described in detail with reference to the accompanying drawings.

Example 1

Fig. 1 is a flowchart of a method for manufacturing an ultrasonic transducer according to an embodiment of the present application; fig. 2a to 2d are schematic top views of a process for manufacturing an ultrasonic transducer according to an embodiment of the present application; fig. 3a to 3d are schematic cross-sectional views of a process for manufacturing an ultrasonic transducer according to an embodiment of the present application; fig. 4a to 4f are schematic cross-sectional views of a process for manufacturing an ultrasonic transducer on a CMOS chip according to an embodiment of the present application. Fig. 2a to 2d are plan views illustrating an ultrasonic fingerprint chip 100, and fig. 3a to 3d are A-A cross-sectional views corresponding to fig. 2a to 2d, during the process of manufacturing an ultrasonic transducer; while fig. 4a to 4f show a process of fabricating an ultrasonic transducer on a circular CMOS chip 1000, a plurality of chip units 100 are generally disposed on the CMOS chip 1000. The preparation method of the ultrasonic transducer comprises the following steps S100, S110, S130, S140 and S150.

Step S100: according to the preparation method of the piezoelectric polymer solution, the piezoelectric polymer solution is prepared, and the details are not repeated.

Step S110: referring to fig. 1, 2a, 3a, and 4b, a piezoelectric polymer solution is coated on the first electrode 120 (i.e., the piezoelectric polymer solution is coated on the first electrode 120), and a piezoelectric film 2000 is formed.

In the present embodiment, the first electrode 120 is located on the chip unit 100, and the ultrasonic transducer is an ultrasonic fingerprint sensor for fingerprint recognition, and the chip unit 100 is an ultrasonic fingerprint chip, specifically an application specific integrated circuit (application specific integrated circuit, ASIC) for ultrasonic fingerprint recognition.

In particular, the embodiments of the present application may use a complementary metal oxide semiconductor (complementary metal-oxide-semiconductor transistor, CMOS) chip, hereinafter referred to as CMOS chip 1000, and the first electrode is formed on the CMOS chip 1000.

Referring to fig. 4a, a cmos chip 1000 has a plurality of chip units 100 thereon. Each of the chip units 100 includes a substrate 110 and a first electrode 120 disposed on the substrate 110, and the first electrode 120 may be an array of metal electrodes formed on a surface of the substrate 110 by sputtering or evaporation, and a material of the metal electrodes may be aluminum or gold, etc.

Referring to fig. 4b, the substrate 110 of the CMOS chip 1000 in the embodiment of the present application is a wafer (wafer), which is circular in shape.

In addition, the chip unit 100 includes, in addition to the first electrodes 120, other devices for electrical connection, such as a pad, an amplifier, and a switch, which may be specifically disposed in a circuit layer of the substrate 110, where each first electrode 120 in the metal electrode array is a Pixel electrode, and each Pixel electrode is electrically coupled to one or more devices in the circuit layer, and is capable of collecting charges generated by the piezoelectric layer when receiving an ultrasonic signal, or is grounded or provides a bias signal when transmitting an ultrasonic signal.

In addition, the chip unit 100 further includes a passivation layer 130 disposed on the upper surface of the substrate 110, where the first electrode 120 is formed on the upper surface of the substrate 110 (i.e., the passivation layer 130 and the first electrode 120 are located on the same surface of the substrate 110).

In practice, the passivation layer 130 covers the first electrode 120 and the upper surface of the substrate 110 from which the remaining portion of the first electrode 120 is removed, and the passivation layer 130 corresponding to the area of the first electrode 120 is removed, for example, by removing the passivation layer 130 in the area of the first electrode 120 by using an etching process, so that the first electrode 120 is exposed. By the arrangement, the first electrode 120 can be in contact with the piezoelectric layer 200, parasitic capacitance is reduced, and the voltage of an excitation signal of the first electrode 120 is ensured to be acted on the piezoelectric layer 200 completely, so that the ultrasonic fingerprint identification effect is improved.

The parasitic capacitance is referred to as parasitic capacitance, which is also called stray capacitance, because the mutual capacitance is always present between the wirings as if it were parasitic between the wirings, although the parasitic capacitance is not designed in "that place". In the ultrasonic transducer, if the passivation layer corresponding to the first electrode 120 is not removed, a capacitance formed between the piezoelectric layer 200 and the passivation layer 130, and a capacitance formed between the passivation layer 130 and the first electrode 120 are parasitic capacitances; and the capacitance between the first electrode 120 and the piezoelectric layer 200, and between the piezoelectric layer 200 and the second electrode 300 is an effective capacitance.

Of course, the passivation layer 130 corresponding to the pad region is also removed to expose the pad, so that the pad can be electrically connected with other components. Referring to fig. 2a, the pads of the chip unit 100 may include electrode pads 140 and lead pads 150. The electrode pad 140 is electrically connected to the second electrode 300, and the lead pad 150 is connected to an external circuit board, and illustratively, two ends of a wire such as a gold wire or an aluminum wire are welded to the lead pad 150 and a pad of the circuit board, respectively, so as to electrically connect the ultrasonic transducer and the circuit board. The lead pad 150 is electrically connected with the electrode pad 140 so that an electrical signal of the first electrode 120 can be transmitted to an external circuit board. There are various ways of electrically connecting the lead pad 150 and the electrode pad 140.

FIG. 5 is a schematic structural diagram of an ultrasonic transducer according to an embodiment of the present disclosure; fig. 6 is a schematic structural diagram of an ultrasonic transducer according to another embodiment of the present application.

In some embodiments, referring to fig. 5, the lead pad 150 and the electrode pad 140 are electrically connected through a first connection line 161, the first connection line 161 is located at the same layer as the first electrode 120, and the first connection line 161 is formed when the first electrode 120 is formed, with simple process.

In other embodiments, referring to fig. 6, the lead pad 150 and the electrode pad 140 are electrically connected through the second connection wire 162, and the second connection wire 162 is located inside the substrate 110, so as to protect the second connection wire 162 and ensure the electrical connection between the lead pad 150 and the electrode pad 14.

In general, there are various ways of applying the piezoelectric polymer solution on the first electrode 120, for example, slit coating, dip coating, spray coating, and the like. The slit coating can only make simple patterns, namely strip-shaped images, and if the slit coating is used for coating on the CMOS chip 1000, part of the coating can be sprayed onto a machine, and the machine needs to be cleaned after each coating, so that the production efficiency is affected; the dip-coating mode is utilized to coat both sides of the CMOS chip 1000, so that not only is the paint wasted, but also the ultrasonic fingerprint identification effect is affected; the thickness of the piezoelectric film formed on the CMOS chip 1000 by the spray coating method is not uniform, and the thickness control accuracy is poor.

According to the research of the inventor, the embodiment of the application can specifically adopt a spin coating process to coat the piezoelectric polymer solution on the first electrode 120 and form the piezoelectric film, and compared with the conventional coating modes such as slit coating and the like, the embodiment of the application adopts the spin coating mode to form the piezoelectric film 2000, can be directly matched with the circular CMOS chip 1000, does not need an additional custom machine, and can obtain an ultrasonic transducer with higher precision and more complex graph by matching with the photoetching process in the follow-up process; and the paint is not sprayed to the machine, and the thickness of the formed piezoelectric film 2000 is uniform.

In specific implementation, the process of performing the coating using the spin coating process may include: placing the piezoelectric polymer solution on the first electrode 120, specifically, dropping the piezoelectric polymer solution onto the first electrode 120, and then performing one-time coating at a first rotation speed, that is, laying the piezoelectric polymer solution onto the first electrode 120 at the first rotation speed, and combining fig. 4b, coating the piezoelectric polymer solution to cover the whole CMOS chip 1000; the second coating is then performed at a second rotational speed to uniformly spread the piezoelectric polymer solution over the entire CMOS chip 1000.

The second rotation speed is higher than the first rotation speed, so that the piezoelectric polymer solution is uniformly rotated at a low speed and then is further uniformly rotated at a high speed, the uniformity of the piezoelectric film 2000 is better, defects such as bubbles can be reduced, and the product yield is improved.

Illustratively, the first rotational speed ranges from 200rpm to 500rpm, such as a range of 200rpm, 250rpm, 300rpm, 350rpm, 400rpm, 450rpm, 500rpm, or any two of these. The second rotational speed is in the range of 800rpm to 3000rpm, such as 800rpm, 1000rpm, 1100rpm, 1500rpm, 2000rpm, 2500rpm, 3000rpm, or any two of these. Therefore, the coating efficiency is prevented from being influenced by the too small first rotating speed and the coating effect is prevented from being influenced by the too large second rotating speed while the second rotating speed is ensured to be higher than the first rotating speed.

Optionally, the coating is performed at the first rotational speed for 3s to 30s, i.e., the time for the coating at the first rotational speed is 3s to 30s, for example, 3s, 5s, 10s, 15s, 20s, 25s, 30s or any two of them, so that the uniformity of the piezoelectric film 2000 is prevented from being affected by the too short low-speed coating time, and the production efficiency is prevented from being affected by the too long coating time.

Alternatively, the coating is performed at the second rotational speed for a period of 20s to 180s, i.e., at the second rotational speed for a period of 20s to 180s, such as 20s, 60s, 90s, 120s, 150s, 180s, or any two of these.

After the piezoelectric polymer solution is coated (i.e., spin-coated), the piezoelectric polymer solution coated uniformly needs to be dried to form the piezoelectric film 2000 of a predetermined thickness, and the drying method may be natural drying (i.e., drying in an environment of normal temperature (room temperature) and normal pressure), heating drying in an oven, heating drying on a hot plate, or the like, or a combination of at least two of these drying methods, and the like, which is not particularly limited.

Specifically, the conditions of drying may be: the drying temperature is 20 to 80 ℃, such as 20 ℃, 25 ℃, 30 ℃, 35 ℃, 40 ℃, 45 ℃, 50 ℃, 55 ℃, 60 ℃, 65 ℃, 70 ℃, 75 ℃, 80 ℃ or any two of them, the drying time can be 30s to 10min, such as 30s, 1min, 2min, 3min, 4min, 5min, 6min, 7min, 8min, 9min, 10min or any two of them, such as 30s to 5min.

Illustratively, the drying temperature may be room temperature, e.g., 20-30 ℃, and the drying time is within 30 minutes; naturally, in order to shorten the drying time and improve the production efficiency, the drying temperature may be increased to be higher than the room temperature, for example, 40 to 80 ℃. In some embodiments, the drying temperature is 60℃and the drying time may be 3min to 5min.

Controlling the drying temperature and drying time within the above ranges not only improves the drying efficiency, but also makes the formed piezoelectric film 2000 appear as a transparent film having high transparency, low haze, and high film formation quality. It can be understood that the higher the crystallinity of the piezoelectric film with higher transparency is, the larger the corresponding value of the piezoelectric constant d33 is, so that the performance such as the sensitivity of the ultrasonic transducer is improved.

In some embodiments, the uniformly applied piezoelectric polymer solution may be dried at a relative humidity (ambient humidity) of less than 30% to form the piezoelectric film 2000, i.e., a relative humidity at drying of less than 30%, such as 0, 5%, 8%, 10%, 11%, 13%, 15%, 17%, 20%, 22%, 25%, 28%, or a range of any two of the compositions therein. By controlling the relative humidity at the time of drying to be less than 30%, the properties such as transparency and piezoelectric constant of the formed piezoelectric layer 200 can be further improved.

The thickness of the piezoelectric film 2000 affects the operating frequency and performance of the ultrasonic transducer. Alternatively, the thickness of the piezoelectric film is 5 μm to 20 μm, for example, 5 μm, 7 μm, 9 μm, 11 μm, 13 μm, 15 μm, 17 μm, 20 μm or a range of any two thereof, so that it is possible to avoid the thickness of the piezoelectric film being too thin to cause the operating frequency of the ultrasonic transducer to be too high, resulting in complicated circuit design, and to avoid the thickness of the piezoelectric film being too thin to cause the sensitivity of receiving ultrasonic waves to be lowered; meanwhile, the influence of the overlarge thickness of the piezoelectric film on the intensity of the emitted ultrasonic wave can be avoided.

Wherein the thickness of the piezoelectric film 200 is substantially equal to the thickness of the piezoelectric layer 200 formed by the subsequent crystallization, polarization, patterning, etc.

In general, the thickness of the piezoelectric film 2000 formed by single spin coating is in the range of 5 μm to 12 μm, and when the thickness of the piezoelectric film 2000 required is large, it can be realized by multiple spin coating.

Fig. 7 is a schematic structural diagram of an ultrasonic transducer according to another embodiment of the present application. Referring to fig. 7, in some embodiments, before the piezoelectric polymer solution is coated on the first electrode 120 and the piezoelectric film is formed, further comprising: forming a second adhesive layer 500 on the first electrode 120, for example, forming the second adhesive layer 500 by spin coating or vapor deposition; then, the piezoelectric polymer solution is coated on the second adhesive layer 500 as described above, and the piezoelectric film 2000 is formed, so that the piezoelectric polymer solution is coated on the first electrode 120, and the piezoelectric film 2000 is formed. Among them, the second adhesive layer 500 functions to increase the adhesion of the first electrode 120 and the piezoelectric film 200. Alternatively, the second adhesive layer 500 may include a silane-based coupling agent.

The thickness of the second adhesive layer 500 affects the contact of the piezoelectric layer 200 with the first electrode 120 and forms parasitic capacitance, thereby affecting the performance of the ultrasonic transducer. In general, the thickness of the second adhesive layer 500 is less than 1.5 μm to achieve the effect of increasing the adhesion between the first electrode 120 and the piezoelectric film 2000; alternatively, the thickness of the second adhesive layer 500 is 10nm to 200nm, for example, 10 μm, 30 μm, 50 μm, 80 μm, 100 μm, 120 μm, 150 μm, 180 μm, 200 μm or a range of any two of them, so that not only the adhesion of the piezoelectric layer 200 and the chip unit 100 can be improved, but also the performance of the ultrasonic transducer can be prevented from being affected by an excessive thickness. In the quality control stage, the adhesion force between the piezoelectric layer 200 and the chip unit 100 is subjected to a film drawing test, and the second adhesive layer 500 is beneficial to ensuring that the adhesion force between the piezoelectric layer 200 and the chip unit 100 reaches more than 4B, so that the product yield is improved. Wherein, the 4B rating is an ISO rating of 1=astm rating, indicating an actual failure of less than or equal to 5% in the cross-hatch area in the adhesion test.

It should be noted that, if the second adhesive layer 500 affects the conductivity of the lead pad 150 or affects the lead electrically connected to the lead pad 150 and the circuit board, the second adhesive layer may be removed by using a photolithography method, and the photolithography method may refer to the photolithography method of the subsequent piezoelectric film 2000, so as to ensure the conductivity of the lead pad 150 and the lead.

Step S120: crystallizing the piezoelectric film 2000 so that the molecular orientation of the piezoelectric film 2000 is uniform; illustratively, for PVDF-TrFE piezoelectric films, crystallization causes the orientation of the molecules to largely change to the β phase.

The piezoelectric film 2000 may be crystallized at a first temperature, which is greater than the curie temperature of the piezoelectric film 2000 and less than the melting temperature of the piezoelectric film 2000.

In some embodiments, the crystallization process may include: the piezoelectric film 2000 is baked at the first temperature for 45 to 120 minutes, for example, 45 minutes, 50 minutes, 60 minutes, 70 minutes, 80 minutes, 90 minutes, 100 minutes, 110 minutes, 120 minutes, or any two of them. The crystallinity of the piezoelectric film 2000 is increased along with time and finally saturated, and the piezoelectric film is baked for 45-120 min, so that the influence of too short baking time on the crystallinity and the influence of too long baking time after the saturation of the crystals on the production efficiency can be avoided.

In other words, the crystallization of the piezoelectric film 2000 is baking the CMOS chip 1000 formed with the piezoelectric film 2000 at the first temperature. Specifically, the oven is preheated to a first temperature, and the CMOS chip 1000 with the piezoelectric film 2000 formed thereon is put into the oven and is left waiting for 45 to 120 minutes. It will be appreciated that after the oven is baked for a predetermined period of time, the CMOS chip 1000 with the piezoelectric film 2000 formed thereon is taken out and cooled to room temperature in an air environment.

Step S130: the crystallized piezoelectric film 2000 is polarized, so that molecules in the piezoelectric film 2000 are regularly arranged, and dipoles of the molecules face the same direction, thereby representing the piezoelectric characteristics of the piezoelectric film 2000.

Alternatively, the piezoelectric film may be polarized at a second temperature, i.e., the temperature of the piezoelectric film 2000 is regulated to the second temperature, and a voltage is applied to perform the polarization, and the second temperature may range from 20 to 30 ℃, for example, 20 ℃, 22 ℃, 25 ℃, 28 ℃, 30 ℃, or any two ranges therebetween. For example, in the actual manufacturing process, the temperature of the piezoelectric film 2000 may be adjusted to room temperature for polarization.

In general, piezoelectric materials at curie temperature polarize faster than normal temperature polarize at the same voltage. However, the piezoelectric material at curie temperature cannot be directly moved out of the machine after polarization is completed, and needs to wait for cooling; and the polarization applied during this process cannot be turned off with high voltage, otherwise depolarization of the already polarized piezoelectric material occurs, i.e. the polarization is lost. Because the problems of material stress release and the like in the cooling process are required to be considered, the cooling process is generally slow and takes longer time; and, time is also required to raise the temperature to curie temperature before the next piece of material enters the machine for polarization. This makes the whole polarization process time-consuming and inefficient. The embodiment of the application polarizes at the temperature of 20-30 ℃ without waiting processes of cooling and heating, so that the polarization process time of the ultrasonic transducer in the production process is shortened, and the production efficiency is improved.

In general, the polarization mode of the applied voltage may be a contact type polarization mode, such as an oil-immersed type polarization mode; non-contact polarizations, such as corona polarizations, are also possible. The embodiment of the application can specifically adopt a corona polarization mode, the polarization device is provided with an upper electrode and a lower electrode, the upper electrode is arranged above the lower electrode, and the upper electrode and the lower electrode are both in grid structures. The CMOS chip to be polarized is placed under the lower electrode and is not in direct contact with the lower electrode. A polarizing voltage is applied to the piezoelectric film by applying voltages to the upper electrode and the lower electrode, wherein the upper electrode has a voltage greater than the lower electrode.

In an embodiment of the present application, the polarization process may include: the piezoelectric film 2000 is polarized by being placed in an electric field of 100V/. Mu.m to 200V/. Mu.m. The polarization electric field is usually required to be higher than the coercive electric field (45V/μm to 55V/μm) of the piezoelectric film 2000, avoiding the polarization time from being excessively long. As the voltage of the polarized electric field increases, the polarization time is shortened, but the power supply requirement for the polarization equipment is increased, and the chip is possibly damaged. According to the preparation method of the embodiment of the application, the piezoelectric film 2000 is placed in an electric field of 100V/mu m-200V/mu m for polarization, so that the polarization time is shortened, the production efficiency is improved, and meanwhile, the chip is prevented from being damaged due to overlarge polarization electric field.

In some embodiments, the polarization may specifically include: the CMOS chip 1000 crystallized by the piezoelectric film 2000 is placed in an electric field of 100V/μm to 200V/μm for 5min to 20min to polarize the piezoelectric film 2000, so that the influence of the too short polarization time on the piezoelectric performance and the production efficiency can be avoided.

Step S140: referring to fig. 2b, 3b and 4c, the polarized piezoelectric film 2000 is patterned to form a piezoelectric layer 200.

In the embodiment of the present application, the polarized piezoelectric film 2000 may be patterned by using a photolithography process, and fig. 8a to 8d are schematic flow diagrams of patterning the piezoelectric film for ultrasonic fingerprint sensing according to the first embodiment of the present application.

According to the study of the inventor, if the photoresist is directly coated on the piezoelectric film 2000, the adhesion between the photoresist and the piezoelectric film 2000 is weak, which affects the patterning, and therefore, in combination with fig. 8a to 8d, the process of patterning the polarized piezoelectric film 2000 according to the embodiment of the present application includes:

step 1: referring to fig. 8a, a first adhesive layer 10 is formed on the polarized piezoelectric film 2000, thereby increasing the adhesion between the piezoelectric film 2000 and the photoresist layer 20; the first adhesive layer 10 may contain a silane coupling agent or the like.

Step 2: referring to fig. 8b, a photoresist layer 20 is formed on the first adhesive layer 10, for example, the photoresist layer 20 is formed on the first adhesive layer 10 by spin coating; referring to fig. 8c, an etching window 21 is formed on the photoresist layer 20, specifically, the photoresist layer 20 is exposed by a photolithography machine, and then developed by a developing solution, so that the etching window 21 is formed on the photoresist layer 20.

Step 3: referring to fig. 8d, the first adhesive layer 10 and the portion of the piezoelectric film 2000 exposed from the etching window 21 may be etched using an etching process, for example, a plasma etching process. In the above etching process, the etching gas used may include oxygen and an assist gas, and the assist gas may include fluorine-based gas and/or argon, and the fluorine-based gas may include tetrafluoromethane and/or trifluoromethane, for example. According to the studies of the present inventors, oxygen is generally used as an etching gas during etching, and when the first adhesive layer 10 is provided, the etching rate of oxygen is slow and the problem of non-uniformity of etching easily occurs, and for this reason, the etching rate and uniformity of etching can be improved by adding the above auxiliary gas to oxygen.

It should be noted that, when the piezoelectric film 2000 is etched, the edge of the piezoelectric layer 200 may be formed into the inclined surface 210 by adjusting the curing temperature of the photoresist, the flow rate of the etching gas, the configuration of the etching gas, etc., so that the coating of the second electrode 300 can better electrically connect to the electrode pad 140 at the connection position when the second electrode 300 is formed by coating.

Step 4: referring to fig. 3b, the photoresist layer 20 and the first adhesive layer 10 are removed to form a piezoelectric layer 200. For example, the photoresist layer 20 and the first adhesive layer 10 may be removed by wet cleaning; of course, the photoresist layer 20 and the first adhesive layer 10 may be removed by dry plasma etching.

Referring again to fig. 2b, the chip unit 100 has an Active Area (AA Area) 101 thereon, and the first electrode 120 is located in the Active Area 101. The area of the piezoelectric layer 200 formed in a patterning manner is larger than that of the operable region 101, so that the projection of the piezoelectric layer 200 on the operable region 101 covers the operable region 101 and a partial region outside the operable region 101, and thus the piezoelectric layer 200 with a larger area is arranged, which is beneficial to improving the antistatic breakdown performance of the chip unit 100. This is because the piezoelectric layer 200 formed on the chip unit 100 requires static electricity of a greater strength with respect to one "insulating layer" and with respect to a passivation layer having a breakdown thickness of less than 2 μm, and thus, providing the piezoelectric layer 200 of a larger area is advantageous in improving the anti-static breakdown capability of the chip unit 100.

Step 150: referring to fig. 2c, 3c and 4d, a second electrode 300 is formed on the piezoelectric layer 200. The material of the second electrode 300 may be one or more of conductive silver paste, conductive ink, conductive carbon paste, and the like. The second electrode 300 may be formed by screen printing, spray coating, or the like. The second electrode 300 may be formed by a silk-screen printing method, and specifically, the hollowed-out area of the silk-screen printing plate may allow the electrode coating to permeate therethrough and be coated, and other portions may not permeate therethrough. After the screen printing plate and the CMOS chip are aligned, the electrode coating is scraped from one side of the CMOS chip to the other side by a scraper, and the screen printing plate pattern can be transferred onto the piezoelectric layer 200. When the second electrode 300 is formed by coating, an electrical connection region where the second electrode 300 is electrically connected to the electrode pad 140 is coated at the same time.

Alternatively, the thickness of the second electrode 300 is in the range of 2 μm to 30 μm, for example 25 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm or any two of them, so that the thinner second electrode 300 is advantageous for improving the performance of the ultrasonic transducer while ensuring the conductive performance. In addition, the second electrode 300 needs to be controlled by a circuit board, the second electrode 300 is electrically connected with the electrode pad 140 on the chip unit 100, and in combination with fig. 3d, a height difference exists between the second electrode 300 and the electrode pad 140, and the thickness of the second electrode 300 is too small, which may cause breakage at a step opposite to the inclined plane 210 of the piezoelectric layer 200, and affect the product yield, so that controlling the thickness of the second electrode 300 in the above range can also avoid breakage phenomenon caused by too small thickness of the second electrode 300, and improve the product yield and performance.

In some embodiments, referring to fig. 2c, the projection of the second electrode 300 on the piezoelectric layer 200 is located inside the piezoelectric layer 200, so that the area of the piezoelectric layer 200 is larger than that of the second electrode 300, which can reduce the influence of the fringe electric field on the performance of the chip unit 100 when the voltage is applied between the second electrode 300 and the first electrode 120, and can also improve the anti-electrostatic breakdown performance of the chip unit 100.

In some embodiments, the projection of the operable area 101 of the chip unit 100 on the second electrode 300 is located inside the second electrode 300, so that the area of the second electrode 300 is larger than the area of the operable area 101, and it is ensured that all the first electrodes 120 can be covered with the second electrode 300, and the area of ultrasonic fingerprint recognition is ensured.

Referring to fig. 2d, 3d and 4e, since the piezoelectric layer 200 is relatively sensitive to humidity and the second electrode 300 of silver paste material is easily oxidized, the preparation method according to the embodiment of the present application further includes: a protective layer 400 is formed on the second electrode 300 to protect the piezoelectric layer 200, the second electrode 300, and the chip unit 100. The protective layer 400 may be applied by silk screen printing, spray coating, dip coating, slit coating, or the like, for example. The protective layer 400 is a nonconductive insulating material, including, for example, an epoxy material, or the like.

Optionally, the protective layer 400 covers not only the second electrode 300, but also the protective layer 400 covers the outer sides of the piezoelectric layer 200 and the electrode pad 140, so as to prevent the piezoelectric layer 200 and the electrode pad 140 from being corroded by water vapor to affect performance.

Alternatively, the thickness of the protective layer 400 is 4 μm to 50 μm, for example, 4 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm or any two of them, so that it is possible to avoid not only an excessive thickness of the protective layer 400 affecting the protective effect but also an excessive thickness of the protective layer 400 leading to attenuation of ultrasonic waves.

It is understood that the resonant frequency of the ultrasonic transducer can be adjusted by adjusting the thickness of the protective layer 400 within the range of the thickness of the protective layer 400.

Referring to fig. 4e and 4f, the CMOS chip 1000 is ground until the CMOS chip 1000 is separated to form a plurality of chip units 100, and the piezoelectric layer 200, the second electrode 300, and the protective layer 400 are stacked on the chip units 100 at this time. The manner of grinding the CMOS chip 1000 may refer to the manner of thinning the existing wafer to form the DIE, such as grinding wheel grinding.

Example two

Fig. 9a to 9e are schematic views of a preparation flow of an ultrasonic transducer according to a second embodiment of the present application. Referring to fig. 9a to 9e, the present embodiment is an improvement based on the first embodiment, and other specific process flows can refer to the first embodiment and will not be repeated. The difference between the present embodiment and the first embodiment is that a step of forming the conductive protection layer 600 is added between the step S130 and the step S140.

Fig. 9a is the same as fig. 3a, fig. 9c is the same as fig. 3b, fig. 9d is the same as fig. 3c, and fig. 9e is the same as fig. 3d, and will not be described again.

Fig. 9b, before patterning the polarized piezoelectric film 2000, a conductive protective film is formed on the piezoelectric film 200 and patterned to form a conductive protective layer 600. Specifically, an indium tin oxide (Indium Tin Oxides, ITO) film is formed on the piezoelectric film 2000 by vapor deposition using physical vapor deposition ((Physical Vapor Deposition, PVD), and the conductive protective layer 600 is formed by patterning the indium tin oxide film by photolithography, lift-off process, or the like.

In the method for manufacturing the ultrasonic transducer provided in the second embodiment, the conductive protection layer 600 is formed on the piezoelectric film 2000, so that the piezoelectric film 2000 is protected from being soaked in the solution in the patterning process to reduce the performance.

Alternatively, the thickness of the conductive protection layer 600 is in a range of 50nm to 500nm, for example, 50nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm or any two of them, so that the provision of an excessively thin conductive protection layer 600 can be avoided from affecting the protection effect, and the provision of an excessively thick conductive protection layer 600 can be avoided from affecting the performance of the piezoelectric layer 200.

Optionally, with continued reference to fig. 9d, the projection of the conductive protection layer 600 on the piezoelectric layer 200 is located inside the piezoelectric layer 200, so that the area of the conductive protection layer 600 is smaller than that of the piezoelectric layer 200, and this arrangement can reduce parasitic capacitance outside the operable area, and avoid setting an excessively large conductive protection layer 600, so that the conductive protection layer 600 forms capacitance with an unexpected circuit in the operable area, and affects the performance of the ultrasonic transducer.

The first and second embodiments adopt the piezoelectric polymer solution prepared by the preparation process to form the piezoelectric layer in the ultrasonic transducer, and the piezoelectric layer has good transparency, piezoelectric constant and other performances, so that the loop sensitivity performance of the ultrasonic transducer can be improved.

Example III

The present embodiment provides an ultrasonic transducer, which is formed by adopting the method for preparing the ultrasonic transducer of the first embodiment or the second embodiment, so that the ultrasonic transducer provided in the third embodiment of the present application also has the same advantages as the method for preparing the ultrasonic transducer of the first embodiment or the second embodiment, and is not described herein again.

Specifically, the ultrasonic transducer of the present embodiment may be an ultrasonic sensor for identifying a biological feature, for example, an ultrasonic fingerprint sensor for identifying a fingerprint, or the like. Taking an ultrasonic transducer as an ultrasonic fingerprint sensor for fingerprint identification as an example, the specific working process of the ultrasonic transducer in the embodiment of the application is described specifically as follows: applying an excitation signal between the first electrode 120 and the second electrode 300, the piezoelectric layer 200 generating vibration based on the piezoelectric effect, thereby emitting an ultrasonic signal; the ultrasonic signals pass through the electronic equipment to reach the surface of the finger to generate echo signals; the echo is transmitted back to the piezoelectric layer 200, a potential difference is generated between the first electrode 120 and the second electrode 300 based on the inverse piezoelectric effect, a corresponding electrical signal is obtained, a relevant processing circuit, such as a circuit board of an electronic device, acquires and forms fingerprint information according to the electrical signal, and finally fingerprint identification is achieved by comparing the fingerprint information with pre-stored fingerprint information.

Example IV

The embodiment of the application provides electronic equipment, which comprises a cover plate and the ultrasonic transducer of the third embodiment, wherein the ultrasonic transducer is arranged below the cover plate. The electronic device provided in the fourth embodiment of the present application, because it includes the ultrasonic transducer described in the third embodiment, has the same advantages as those of the ultrasonic transducer described in the third embodiment, and will not be described again here.

Specifically, the cover plate plays a protective role, so that the reliability of the ultrasonic transducer can be improved. The top surface of the cover plate is oriented to contact an object (e.g., a user's finger). The cover plate may be a material that is penetrable by ultrasonic waves, such as glass, metal, or composite materials. In addition, the cover plate can be directly a shell or a display screen of the electronic device, or the cover plate can be inlaid in the shell of the electronic device.

By way of example, and not limitation, the electronic device in the embodiments of the present application may be a portable or mobile computing device such as a terminal device, a mobile phone, a tablet computer, a notebook computer, a desktop computer, a game device, an in-vehicle electronic device, or a wearable smart device, and other electronic devices such as an electronic database, an automobile, and a bank automated teller machine (Automated Teller Machine, ATM). The wearable intelligent device comprises a device which has full functions and large size and can realize complete or partial functions independent of a smart phone, such as a smart watch, a smart glasses and the like, and comprises a device which is only focused on certain application functions and needs to be matched with other devices such as the smart phone, such as various devices for monitoring physical signs, such as a smart bracelet, a smart jewelry and the like.

The following further describes the embodiments and effects of the present application in detail by combining test examples and comparative examples.

Test example 1

1. Preparation of piezoelectric Polymer solutions

(1-1) weighing a solvent and a piezoelectric polymer according to a preset concentration of the piezoelectric polymer solution;

(1-2) adding a solvent into the reaction kettle, and starting stirring; adding a piezoelectric polymer into the reaction kettle, regulating the temperature of the reaction kettle to 30 ℃ (namely, the dissolution temperature), stirring at 30 ℃ until the system is transparent, continuously maintaining stirring for 12 hours, and then taking out the solution from the reaction kettle;

(1-3) filtering the solution taken out of the reaction vessel with a filter screen having a pore size of 2. Mu.m, and collecting the filtrate to obtain a piezoelectric polymer solution.

2. Preparation of ultrasonic transducer

Referring to the method for manufacturing an ultrasonic transducer of the first embodiment, a piezoelectric layer 200 is formed on a first electrode of a wafer, and an ultrasonic transducer is manufactured; wherein, the relevant parameters are as follows:

in step S110, the piezoelectric polymer solution is coated on the first electrode 120 by using a spin coating process, wherein in the spin coating process, the first rotation speed is 300rpm, the time of coating at the first rotation speed is 10S, the second rotation speed is 1150rpm, and the time of coating at the second rotation speed is 60S;

after spin coating, the piezoelectric polymer solution applied on the first electrode 120 is dried to form the piezoelectric film 2000, wherein the drying conditions are: the drying mode is natural drying (room temperature), the drying time is about 10min, and the relative humidity during drying is about 11%;

The thickness of the piezoelectric film 200 is 9 μm;

the thickness of the second adhesive layer 500 formed on the first electrode 120 is 100nm;

in step S120, the piezoelectric film 2000 is baked at 140 ℃ for 120min to crystallize the piezoelectric film 2000, the crystallization temperature being greater than the curie temperature of the piezoelectric film and less than the melting temperature of the piezoelectric film;

in step S130, the crystallized piezoelectric film 2000 is placed in an electric field of 100V/μm for 10min at room temperature to polarize the piezoelectric film 2000;

in step 150, the material of the second electrode 300 is silver paste, and the thickness of the second electrode is 4 μm;

in addition, the thickness of the protective layer 400 is 8 μm;

the rest of the procedures and conditions are described in the first embodiment, and will not be described again.

Test examples 2 to 13: the difference from test example 1 is that the dissolution temperature in step S (1-2), or the spin-coating conditions in step S110, and the drying conditions after spin-coating are different, specifically, see tables 1 and 2, and the other conditions are the same except for the differences shown in tables 1 and 2.

Comparative examples 1 to 13: the difference from test example 1 is that the dissolution temperature in step (1-2), or the spin-coating conditions in step S110, and the drying conditions after spin-coating are different, specifically, see tables 1 and 2, and the other conditions are the same except for the differences shown in tables 1 and 2.

The dissolution temperature of step (1-2) in test examples 1 to 10 and comparative examples 1 to 9, spin-coating conditions (second rotation speed and time of coating at second rotation speed) in step S110, drying conditions (drying system and temperature, drying time) after spin-coating, and observed apparent phenomena of the piezoelectric layer are summarized in table 1, and the dissolution temperature of step (1-2) in test examples 8, 11 to 13 and comparative examples 10 to 13, drying conditions (relative humidity) after spin-coating at step S110, and observed apparent phenomena of the piezoelectric layer are summarized in table 2.

TABLE 1

As can be seen from Table 1, the piezoelectric layers of test examples 1 to 10 exhibited appearance phenomena such as uniform overall, no moire, higher transparency, etc., whereas the piezoelectric layers of comparative examples 1 to 9 exhibited appearance phenomena such as water moire, etc., with large haze and low transparency.

In addition, it can be seen that the dissolution temperature during the preparation of the piezoelectric polymer solution has an important influence on the properties such as transparency of the piezoelectric layer, and it can be seen from test examples 1 to 9 that the properties such as transparency of the piezoelectric layer cannot be improved under any spin coating condition or drying condition when the dissolution temperature is more than 30 ℃, and that the piezoelectric layer can be made uniform as a whole, free of moire, high in transparency, and the like under different spin coating conditions and drying conditions when the dissolution temperature is controlled within a range of 20 ℃ to 30 ℃ from test examples 1 to 10.

TABLE 2

In addition, the piezoelectric constants (d 33) of the piezoelectric layers in test examples 1 to 10 and comparative examples 1 to 9 were each tested, five different positions of the piezoelectric layers were each tested, five test values were obtained accordingly, and the average value (Avg) of the five test values was taken as a test result. The results showed that d33 of the piezoelectric layers in test examples 1 to 10 was significantly higher than d33 of the piezoelectric layers in comparative examples 1 to 9, that d33 of the piezoelectric layers in test examples 1 to 10 was as high as 25pC/N or more, that d33 of the piezoelectric layers in comparative examples 1 to 9 was about 21±2pc/N, and that the three test values at the time of the d33 test of test example 2 and comparative example 1, and the average values of the three test values were shown in table 3.

TABLE 3 Table 3

Further, the d33 test result of the piezoelectric layer showed that the d33 of the piezoelectric layer formed in test example 8 was higher than that of the piezoelectric layer formed in test example 11, and the d33 of the piezoelectric layer formed in test example 12 was higher than that of the piezoelectric layer formed in test example 13, wherein the d33 of the piezoelectric layers formed in test example 11 and test example 13 was about 25.+ -. 1pC/N, respectively, and the d33 of the piezoelectric layers formed in comparative example 11 and comparative example 13 was about 21.+ -. 1pC/N, respectively.

In addition, the relationship between the loop sensitivities of the ultrasonic transducers of test examples 1 to 13 and comparative examples 1 to 13 and the excitation frequency of the ultrasonic signal was examined, and the results showed that the ultrasonic transducers of test examples 1 to 13 each exhibited a higher loop sensitivity at a different excitation frequency than the ultrasonic transducers of comparative examples 1 to 13, and the relationship between the loop sensitivities of the ultrasonic transducers of test example 1 and comparative example 1 and the excitation frequency of the ultrasonic signal was specifically shown in fig. 10.

In the above description, descriptions of the terms "one embodiment," "some embodiments," "examples," "specific examples," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present application. In this specification, schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, the different embodiments or examples described in this specification and the features of the different embodiments or examples may be combined and combined by those skilled in the art without contradiction.

Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention.

Claims

1. A method of preparing a piezoelectric polymer solution for use in preparing an ultrasonic transducer, comprising:

dissolving a piezoelectric polymer in a solvent at a predetermined temperature, wherein the predetermined temperature is 20-30 ℃; and

stirring the solvent at the preset temperature until the solvent is transparent, and then maintaining stirring for no more than 48 hours to obtain the piezoelectric polymer solution.

2. The method for preparing a piezoelectric polymer solution according to claim 1, further comprising: and after the piezoelectric polymer is dissolved in the solvent, filtering the obtained mixed solution by adopting a filter screen with the aperture of 0.5-5 mu m under the pressure condition of 1.5-3 bar to obtain the piezoelectric polymer solution.

3. The method of preparing a piezoelectric polymer solution according to claim 1, wherein the piezoelectric polymer comprises one or more of polyvinylidene fluoride, polyvinylidene fluoride homopolymer, and polyvinylidene fluoride-fluoromonomer copolymer.

4. The method for producing a piezoelectric polymer solution according to claim 1, wherein the solvent comprises a polar organic solvent including at least one of an amide-based solvent, a sulfone-based solvent, and a ketone-based solvent.

5. The method for preparing a piezoelectric polymer solution according to claim 1, wherein the mass concentration of the piezoelectric polymer in the piezoelectric polymer solution is 10% to 20%.

6. A method of manufacturing an ultrasonic transducer comprising:

the method for producing a piezoelectric polymer solution according to any one of claims 1 to 5, wherein the piezoelectric polymer solution is produced;

coating the piezoelectric polymer solution on a first electrode, and forming a piezoelectric film;

sequentially crystallizing and polarizing the piezoelectric film to form a piezoelectric layer;

and forming a second electrode on the piezoelectric layer to obtain the ultrasonic transducer.

7. The method of manufacturing an ultrasonic transducer of claim 6, wherein the first electrode is formed on a complementary metal oxide semiconductor chip.

8. The method of manufacturing an ultrasonic transducer according to claim 6, wherein the coating is performed using a spin coating process.

9. The method of manufacturing an ultrasonic transducer according to claim 8, wherein the process of performing the coating using a spin coating process includes: and placing the piezoelectric polymer solution on the first electrode, performing primary coating at a first rotating speed, and performing secondary coating at a second rotating speed, wherein the second rotating speed is higher than the first rotating speed.

10. The method of manufacturing an ultrasonic transducer according to claim 9, wherein the first rotational speed ranges from 200rpm to 500rpm, and/or the second rotational speed ranges from 800rpm to 3000rpm.

11. The method of manufacturing an ultrasonic transducer according to claim 6, wherein the piezoelectric polymer solution is coated on a first electrode, and the piezoelectric film is formed after drying; wherein, the conditions of the drying are as follows: the temperature is 20-80 ℃ and the time is 30 s-10 min.

12. The method of manufacturing an ultrasonic transducer according to claim 6, wherein the thickness of the piezoelectric film is 5 μm to 20 μm.

13. The method of manufacturing an ultrasonic transducer according to claim 6, wherein the crystallization process includes: and baking the piezoelectric film at a first temperature for 45-120 min, wherein the first temperature is higher than the Curie temperature of the piezoelectric film and lower than the melting temperature of the piezoelectric film.

14. The method of manufacturing an ultrasonic transducer of claim 6, wherein the polarizing comprises: the piezoelectric film is put into an electric field of 100V/mu m to 200V/mu m for polarization.

15. The method of claim 14, wherein the polarizing comprises: placing the piezoelectric film in an electric field of 100V/mu m-200V/mu m for 5 min-20 min to polarize the piezoelectric film.

16. The method of manufacturing an ultrasonic transducer of claim 6, further comprising: patterning the polarized piezoelectric film to form the piezoelectric layer, wherein the patterning process comprises the following steps:

forming a first adhesive layer on the polarized piezoelectric film;

forming a photoresist layer on the first bonding layer, and forming an etching window on the photoresist layer;

etching the first bonding layer and the part of the piezoelectric film exposed by the etching window;

and removing the photoresist layer and the first bonding layer to form the piezoelectric layer.

17. The method of manufacturing an ultrasonic transducer according to claim 6, wherein a second adhesive layer is formed on the first electrode, the piezoelectric polymer solution is coated on the second adhesive layer, and the piezoelectric film is formed, so that the coating of the piezoelectric polymer solution on the first electrode is achieved, and the piezoelectric film is formed.

18. The method of manufacturing an ultrasonic transducer of claim 17, wherein the second adhesive layer has a thickness of 10nm to 200nm.

19. The method of manufacturing an ultrasonic transducer according to claim 6, wherein the thickness of the second electrode is 2 μm to 30 μm.

20. The method of manufacturing an ultrasonic transducer of claim 6, further comprising: and forming a protective layer on the second electrode, wherein the thickness of the protective layer is 4-50 μm.

21. An ultrasonic transducer produced by the method of any one of claims 7 to 20.

22. An electronic device comprising a cover plate and the ultrasonic transducer of claim 21.