Ultrasonic transducer, method of manufacturing the same, and electronic device

Abstract

The application provides an ultrasonic transducer, a preparation method thereof and an electronic device. The preparation method of the ultrasonic transducer comprises the following steps: coating a piezoelectric polymer solution on a first electrode, drying under the condition that the relative humidity is less than 30%, and forming a piezoelectric film; sequentially performing crystallization and polarization on the piezoelectric film, and forming a piezoelectric layer; and forming a second electrode on the piezoelectric layer, so as to obtain the ultrasonic transducer. Through the preparation process, the transparency and piezoelectric constant of the formed piezoelectric layer can be improved, and the performance of the ultrasonic transducer is optimized.

Description

Technical Field

[0001] This invention relates to the field of ultrasonic transducers, and more specifically to an ultrasonic transducer, its manufacturing method, and an electronic device thereof. Background Technology

[0002] Ultrasonic transducers are devices that convert acoustic energy and electrical energy into each other. The piezoelectric layer within them exhibits the piezoelectric effect and is used to emit or receive ultrasonic waves. Due to their advantages such as being able to penetrate displays or housings, avoiding optical interference, and recognizing biometric features (such as fingerprints), they are widely used in smart terminal devices. However, in related technologies, the piezoelectric layer generally suffers from defects such as poor transparency, low piezoelectric constant, and low loop sensitivity, affecting the performance of ultrasonic transducers and terminal devices. Summary of the Invention

[0003] This application provides a method for preparing a piezoelectric polymer solution and its application, in order to at least solve the technical problems existing in the prior art, such as poor transparency of the piezoelectric layer, low piezoelectric constant, and low loop sensitivity.

[0004] To solve the above-mentioned technical problems, this application adopts the following technical solution:

[0005] The first aspect of this application provides a method for fabricating an ultrasonic transducer, comprising: coating a piezoelectric polymer solution onto a first electrode and drying it under conditions of relative humidity less than 30% to form a piezoelectric thin film; sequentially crystallizing and polarizing the piezoelectric thin film to form a piezoelectric layer; and forming a second electrode on the piezoelectric layer to obtain the ultrasonic transducer.

[0006] Optionally, the first electrode is formed on a complementary metal-oxide-semiconductor chip.

[0007] Optionally, the piezoelectric polymer solution contains a piezoelectric polymer, which includes one or more of polyvinylidene fluoride, polyvinylidene fluoride homopolymer, and polyvinylidene fluoride-fluorinated monomer copolymer.

[0008] Optionally, the piezoelectric polymer solution contains a solvent, which includes a polar organic solvent, specifically at least one of amide solvents, sulfone solvents, and ketone solvents.

[0009] Optionally, the piezoelectric polymer solution contains a piezoelectric polymer, wherein the mass concentration of the piezoelectric polymer in the piezoelectric polymer solution is 10% to 20%.

[0010] Optionally, the coating can be performed using a spin coating process.

[0011] Optionally, the coating process using spin coating technology includes: placing the piezoelectric polymer solution on the first electrode, coating once at a first rotation speed, and then coating a second time at a second rotation speed, wherein the second rotation speed is higher than the first rotation speed.

[0012] Optionally, the first speed ranges from 200 rpm to 500 rpm, and / or the second speed ranges from 800 rpm to 3000 rpm.

[0013] Optionally, the drying is carried out under normal pressure conditions.

[0014] Optionally, the drying temperature is 20℃~80℃ and the time is 30s~10min.

[0015] Optionally, the thickness of the piezoelectric film is 5 μm to 20 μm.

[0016] Optionally, the crystallization process includes baking the piezoelectric film at a first temperature for 45 min to 120 min, wherein the first temperature is greater than the Curie temperature of the piezoelectric film and less than the melting temperature of the piezoelectric film.

[0017] Optionally, the polarization process includes: placing the piezoelectric thin film in an electric field of 100V / μm to 200V / μm for polarization.

[0018] Optionally, the polarization process includes placing the piezoelectric film in an electric field of 100V / μm to 200V / μm for 5 min to 20 min to polarize the piezoelectric film.

[0019] Optionally, the method further includes: patterning the polarized piezoelectric thin film to form the piezoelectric layer, wherein the patterning process includes: forming a first adhesive layer on the polarized piezoelectric thin film; forming a photoresist layer on the first adhesive layer and forming an etching window on the photoresist layer; etching the portions of the first adhesive layer and the piezoelectric thin film exposed by the etching window; and removing the photoresist layer and the first adhesive layer to form the piezoelectric layer.

[0020] Optionally, a second adhesive layer is formed on the first electrode, the piezoelectric polymer solution is coated onto the second adhesive layer, and the piezoelectric film is formed, so as to achieve the coating of the piezoelectric polymer solution onto the first electrode and the formation of the piezoelectric film.

[0021] Optionally, the thickness of the second adhesive layer is 10 nm to 200 nm.

[0022] Optionally, the thickness of the second electrode is 2 μm to 30 μm.

[0023] Optionally, it further includes forming a protective layer on the second electrode, the thickness of the protective layer being 4 μm to 50 μm.

[0024] The second aspect of this application provides an ultrasonic transducer manufactured using the above-described method for preparing ultrasonic transducers.

[0025] A third aspect of this application provides an electronic device including a cover plate for the aforementioned ultrasonic transducer.

[0026] The ultrasonic transducer fabrication method provided in this application involves drying a wet film under conditions where the relative humidity is less than 30% to form a piezoelectric thin film. This film is then combined with subsequent crystallization and polarization processes to form a piezoelectric layer. This method can improve the transparency and piezoelectric constant of the piezoelectric layer, thereby optimizing the loop sensitivity and other properties of the ultrasonic transducer. Attached Figure Description

[0027] Figure 1 A flowchart illustrating the fabrication method of the ultrasonic transducer provided in this application embodiment;

[0028] Figures 2a to 2d A top view schematic diagram of the fabrication process of the ultrasonic transducer provided in Embodiment 1 of this application;

[0029] Figures 3a to 3d A cross-sectional schematic diagram of the fabrication process of the ultrasonic transducer provided in Embodiment 1 of this application;

[0030] Figures 4a to 4f This is a cross-sectional schematic diagram showing the fabrication process of the ultrasonic transducer on a CMOS chip according to Embodiment 1 of this application;

[0031] Figure 5 This is a schematic diagram of the structure of an ultrasonic transducer provided in one embodiment of this application;

[0032] Figure 6 This is a schematic diagram of the structure of an ultrasonic transducer provided in another embodiment of this application;

[0033] Figure 7 This is a schematic diagram of the structure of an ultrasonic transducer provided in another embodiment of this application;

[0034] Figures 8a to 8d A schematic flowchart illustrating the piezoelectric thin film of the ultrasonic fingerprint sensor provided in Embodiment 1 of this application;

[0035] Figures 9a to 9e This is a schematic diagram of the fabrication process of the ultrasonic transducer provided in Embodiment 2 of this application.

[0036] Explanation of reference numerals in the attached figures: 10: First adhesive layer; 20: Photoresist layer; 21: Etching window; 1000: CMOS chip; 2000: Piezoelectric thin film; 100: Ultrasonic fingerprint chip; 101: Operable area; 110: Substrate; 120: First electrode; 130: Passivation layer; 140: Electrode pad; 150: Lead pad; 161: First connection line; 162: Second connection line; 200: Piezoelectric layer; 210: Inclined surface; 300: Second electrode; 400: Protective layer; 500: Second adhesive layer; 600: Conductive protective layer. Detailed Implementation

[0037] Ultrasonic transducers (or ultrasonic sensors) are devices that convert sound energy into electrical energy and vice versa, and are increasingly being used, for example, in biometric identification (such as fingerprints). For instance, an ultrasonic fingerprint sensor is an ultrasonic transducer used for fingerprint recognition. It utilizes the ability of ultrasound to penetrate materials, and how the reflected energy and path of ultrasound waves differ depending on the surface of the material. Therefore, by using the difference in acoustic impedance between skin and air, the location of the ridges and valleys of a fingerprint can be distinguished. Ultrasonic fingerprint sensors can penetrate beneath the skin surface to identify the unique three-dimensional features of a fingerprint, distinguishing between real and fake fingers. Furthermore, because ultrasound has a certain degree of penetrability, it can still identify fingerprints even when the fingers are slightly dirty or damp, and can penetrate the display screen or casing of devices. Therefore, it is increasingly being used in smart terminal devices.

[0038] Specifically, the piezoelectric layer of an ultrasonic transducer exhibits the piezoelectric effect. When the piezoelectric layer deforms, a voltage difference is generated across its two ends. When there is a voltage difference across its two ends, the piezoelectric layer can vibrate to generate ultrasonic waves. This property of the piezoelectric layer can be used to achieve the mutual conversion between mechanical vibration and alternating current signals.

[0039] The higher the operating frequency of an ultrasonic transducer, the better its penetration, which is more conducive to producing clear images of biological features and improving the accuracy of biological feature recognition. The operating frequency of an ultrasonic transducer is inversely proportional to the thickness of the piezoelectric layer; higher accuracy in biological feature recognition means a thinner piezoelectric layer. Simultaneously, to obtain sufficient imaging performance, the spacing between two adjacent piezoelectric pillars (i.e., the first electrode below) of the ultrasonic transducer should be smaller than the ultrasonic wavelength. For typical ultrasonic fingerprint sensors, the spacing between two adjacent piezoelectric pillars is usually between 50 μm and 100 μm.

[0040] Therefore, the fabrication process of the piezoelectric layer is crucial to the performance of ultrasonic transducers. The piezoelectric material forming the piezoelectric layer can be lead zirconate titanate (PZT) piezoelectric ceramics or polymeric piezoelectric materials (such as polyvinylidene fluoride (PVDF)). Under the same thickness conditions, ultrasonic transducers using polymeric piezoelectric materials such as PVDF have greater loop sensitivity than those using PZT, and have received widespread attention and application.

[0041] However, in related technologies, piezoelectric layers generally suffer from defects such as poor transparency and low piezoelectric constant, which affect the performance of ultrasonic transducers and terminal equipment.

[0042] In view of the above problems, this application provides a method for preparing an ultrasonic transducer, comprising: coating a piezoelectric polymer solution onto a first electrode and drying it under conditions of relative humidity less than 30% to form a piezoelectric thin film; sequentially crystallizing and polarizing the piezoelectric thin film to form a piezoelectric layer; and forming a second electrode on the piezoelectric layer to obtain an ultrasonic transducer.

[0043] Based on the inventor's long-term research, in the preparation process of the above-mentioned ultrasonic transducer, a piezoelectric polymer solution is coated on the first electrode, and the formed wet film is dried in an environment with a relative humidity of less than 30% to form a piezoelectric thin film. Then, in conjunction with subsequent crystallization and polarization processes, a piezoelectric layer is formed, which can improve the transparency and piezoelectric constant of the piezoelectric layer, thereby optimizing the loop sensitivity and other performance of the ultrasonic transducer.

[0044] Studies show that the piezoelectric layer (or piezoelectric film) formed using the above process can have a d33 as high as 25±1 pC / N or more, while in related technologies, the d33 of piezoelectric films formed under high relative humidity (e.g., around 50%) is generally lower than 21±2 pC / N. For ultrasonic transducers, the relationship between their sensitivity and d33 satisfies S... loop ∝S Tx *S Rx ∝d33 3 That is, the loop sensitivity S of the ultrasonic transducer loop Proportional to the ultrasonic wave emission sensitivity S Tx and the sensitivity of receiving ultrasonic waves S Rx The product of is proportional to the cube of the piezoelectric constant d33. When d33 increases from about 21 pC / N to about 25 pC / N, the sensitivity of the ultrasonic transducer increases to (25 / 21) of the original value. 3 =1.69 times, which is an improvement of nearly 70%; in actual tests, due to factors such as parasitic capacitance, the sensitivity of the ultrasonic transducer is improved by nearly 50%, which is beneficial to improve the intensity of ultrasonic signals and the clarity of ultrasonic imaging.

[0045] For example, the relative humidity of the environment during drying can be 0, 1%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 29%, or any combination thereof.

[0046] The embodiments of this application can control the relative humidity during drying using conventional methods in the art, and there are no particular limitations thereto.

[0047] The aforementioned piezoelectric polymer solution includes a solvent and a piezoelectric polymer. Specifically, it can be prepared by dissolving the piezoelectric polymer in a solvent. The temperature during the dissolution process can be between 20°C and 80°C, for example, 20°C, 22°C, 25°C, 28°C, 30°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, or any combination thereof.

[0048] Based on the inventors' long-term research, compared to high-temperature (e.g., 60℃~80℃) dissolution processes, dissolving piezoelectric polymers in solvents at 20℃~30℃ to prepare piezoelectric polymer solutions can further improve the transparency and piezoelectric constant (d33) of the piezoelectric layer formed using such solutions. The reason for this is speculated to be that dissolving the piezoelectric polymer at different temperatures affects the polymer's molecular structure (e.g., chain length), thus influencing the transparency and piezoelectric constant of the piezoelectric layer. In this application, the piezoelectric polymer is dissolved at 20℃~30℃, giving the piezoelectric polymer in the piezoelectric layer a more suitable molecular structure and other characteristics, thereby improving the transparency and piezoelectric constant of the piezoelectric layer.

[0049] Meanwhile, by dissolving the piezoelectric polymer at low temperatures (20℃~30℃) to prepare a piezoelectric polymer solution, it also has advantages such as mild conditions, low energy consumption, and simple operation.

[0050] In some specific embodiments, the process of dissolving the piezoelectric polymer in a solvent includes: adding the piezoelectric polymer to the solvent, stirring at 20°C to 80°C, preferably 20°C to 30°C until transparent, and then maintaining stirring for no more than 48 hours to obtain a piezoelectric polymer solution. This facilitates the full dissolution of the piezoelectric polymer and further optimizes the transparency and piezoelectric constant and other properties of the piezoelectric layer formed using the piezoelectric polymer solution.

[0051] In practice, the solvent can be added to the reaction vessel and stirred. Then, the piezoelectric polymer can be slowly added to the reaction vessel while the reaction vessel is adjusted to the preset temperature (i.e., 20℃~80℃). Specifically, the preset temperature can be adjusted by water bath heating or other methods. After the solution becomes transparent, stirring can be continued for a period of time (not exceeding 48 hours). Then, the solution can be taken out of the reaction vessel to obtain the piezoelectric polymer solution.

[0052] Furthermore, after dissolving the piezoelectric polymer in a solvent, the resulting mixture can be filtered, for example, using a filter screen with a pore size of 0.5 μm to 5 μm, and the filtrate collected to obtain the piezoelectric polymer solution. During the filtration process, pressure can be applied, for example, at a pressure of 1.5 bar to 3 bar, to improve filtration efficiency.

[0053] For example, the pore size of the filter screen can 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 any combination thereof. The pressure conditions during the filtration process are, for example, 1.5 bar, 2 bar, 2.5 bar, 3 bar, or any combination thereof.

[0054] In some embodiments, the piezoelectric polymer may include one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride homopolymer, and polyvinylidene fluoride-fluorinated monomer copolymer.

[0055] It is understood that polyvinylidene fluoride-fluorinated monomer copolymers are polymers copolymerized from PVDF and fluorinated monomers. Fluorinated monomers include one or more of trifluoroethylene (TrFE), chlorotrifluoroethylene (CTFE), and tetrafluoroethylene (TFE). That is, polyvinylidene fluoride-fluorinated monomer copolymers can include one or more of the following: binary copolymers copolymerized from PVDF and one of these monomers; ternary copolymers copolymerized from PVDF and two of these monomers; and quaternary copolymers copolymerized from PVDF and three of these monomers.

[0056] In some specific embodiments, the polyvinylidene fluoride-fluorinated monomer copolymer includes one or more of the following: polyvinylidene fluoride-trifluoroethylene copolymer (PVDF-TrFE), polyvinylidene fluoride-trifluorochloroethylene copolymer (PVDF-CTFE), polyvinylidene fluoride-tetrafluoroethylene copolymer (PVDF-TFE), polyvinylidene fluoride-trifluoroethylene-trifluorochloroethylene copolymer (PVDF-TrFE-CTFE-TFE), polyvinylidene fluoride-trifluorochloroethylene-tetrafluoroethylene copolymer (PVDF-TFE), and polyvinylidene fluoride-trifluoroethylene-trifluorochloroethylene-tetrafluoroethylene copolymer (PVDF-TrFE-CTFE-TFE).

[0057] Furthermore, in the above-mentioned polyvinylidene fluoride-fluorinated monomer copolymer, the mass content of the fluorinated monomer can be 10% to 50%, for example, 10%, 15%, 18%, 20%, 22%, 25%, 30%, 35%, 40%, 45%, 50%, or any combination thereof.

[0058] The content of fluorinated monomers typically affects the melting point, Curie temperature, dielectric constant, and piezoelectric constant of the piezoelectric film formed from the copolymer. Taking PVDF-TrFE as an example, when the mass content of TrFE is approximately 20%, the resulting piezoelectric film has a melting point of approximately 150°C, a Curie temperature of approximately 136°C, a dielectric constant between 9 and 12, and a piezoelectric constant between 24 and 30. When the mass content of TrFE is approximately 25%, the resulting piezoelectric film has a melting point of approximately 150°C, a Curie temperature of approximately... The melting point of the piezoelectric film is approximately 151℃, the Curie temperature is approximately 100℃, the dielectric constant is between 10-14, and the piezoelectric constant is between 18-22. When the mass content of TrFE is approximately 30%, the melting point of the piezoelectric film is approximately 151℃, the Curie temperature is approximately 100℃, the dielectric constant is between 10-14, and the piezoelectric constant is between 18-22. When the mass content of TrFE is approximately 45%, the melting point of the piezoelectric film is approximately 158℃, the Curie temperature is approximately 60℃, the dielectric constant is between 10-14, and the piezoelectric constant is between 18-22.

[0059] Generally, as the content of fluorine-containing monomers increases, the melting point increases, the Curie temperature decreases, the dielectric constant increases, and the piezoelectric constant decreases. The greater the difference between the melting point and the temperature, the larger the process window for preparing the piezoelectric layer. For example, the preparation of a piezoelectric layer generally involves the crystallization of the piezoelectric film. The crystallization temperature is higher than the Curie temperature of the piezoelectric film but lower than its melting point. Thus, the greater the difference between the Curie temperature and the melting point, the larger the crystallization process window, allowing crystallization to be carried out over a wider temperature range. A larger dielectric constant results in a larger capacitance and less signal attenuation caused by parasitic capacitance. A larger piezoelectric constant also results in a stronger ultrasonic signal and a stronger electrical signal converted from the received ultrasonic signal.

[0060] In some specific embodiments, taking into account the above factors and the process requirements in the preparation of ultrasonic transducers (such as when the ultrasonic transducer is an ultrasonic fingerprint sensor, reliability tests are usually required at around 120°C), PVDF-TrFE with a TrFE mass content of about 20% can be selected.

[0061] In addition, the solvents mentioned above may include polar organic solvents, such as one or more of amide solvents, sulfone solvents, and ketone solvents. For example, amide solvents may include dimethylformamide and / or dimethylacetamide, sulfone solvents may include dimethyl sulfoxide, and ketone solvents may include methyl ethyl ketone (MEK).

[0062] To further optimize the performance of the piezoelectric layer, the piezoelectric polymer solution prepared through the above process has a piezoelectric polymer mass concentration of 10% to 20%, that is, the ratio of the mass of the piezoelectric polymer to the sum of the masses of the piezoelectric polymer and the solvent is 10% to 20%, for example, 10%, 12%, 15%, 18%, 20%, or any combination within this range.

[0063] The ultrasonic transducer and its manufacturing method according to embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0064] Example 1

[0065] Figure 1 A flowchart illustrating the fabrication method of the ultrasonic transducer provided in this application embodiment; Figures 2a to 2d A top view schematic diagram of the fabrication process of the ultrasonic transducer provided in Embodiment 1 of this application; Figures 3a to 3d A cross-sectional schematic diagram of the fabrication process of the ultrasonic transducer provided in Embodiment 1 of this application; Figures 4a to 4f This is a cross-sectional schematic diagram showing the fabrication process of the ultrasonic transducer on a CMOS chip according to Embodiment 1 of this application. Figures 2a to 2d Taking an ultrasonic fingerprint chip 100 as an example, this is a top view of the ultrasonic transducer manufacturing process. Figures 3a to 3d for Figures 2a to 2d The corresponding AA-direction sectional view; and Figures 4a to 4f The illustration shows the process of fabricating an ultrasonic transducer on a circular CMOS chip 1000, wherein multiple chip units 100 are typically disposed on the CMOS chip 1000. The method for fabricating the ultrasonic transducer according to this application includes the following steps S100, S110, S130, S140, and S150.

[0066] Step S100: Prepare the piezoelectric polymer solution. The specific preparation process of the piezoelectric polymer solution described above will not be repeated.

[0067] Step S110: Combining Figure 1 , Figure 2a , Figure 3a as well as Figure 4b A piezoelectric polymer solution is coated on the first electrode 120 and dried under conditions of relative humidity less than 30% to form a piezoelectric thin film 2000.

[0068] In this embodiment of the application, the first electrode 120 is located on the chip unit 100. For example, 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 (ASIC) for ultrasonic fingerprint recognition.

[0069] Specifically, the embodiments of this application may employ a complementary metal-oxide-semiconductor (CMOS) chip, hereinafter referred to as CMOS chip 1000, with the first electrode formed on the CMOS chip 1000.

[0070] Combination Figure 4a The CMOS chip 1000 has multiple chip units 100. Each chip unit 100 includes a substrate 110 and a first electrode 120 disposed on the substrate 110. The first electrode 120 may be a metal electrode array formed on the surface of the substrate 110 by sputtering or vapor deposition. The material of the metal electrode may be aluminum or gold, etc.

[0071] Combination Figure 4b In this embodiment of the application, the substrate 110 of the CMOS chip 1000 is a wafer, which is circular in shape.

[0072] In addition to the first electrode 120, the chip unit 100 also includes other devices such as pads for electrical connection, amplifiers, and switches. These devices can be specifically disposed in the circuit layer of the substrate 110. Each first electrode 120 in the metal electrode array is a pixel electrode. Each pixel electrode is electrically coupled to one or more devices in the circuit layer and can collect the charge generated by the piezoelectric layer when receiving ultrasonic signals, or ground or provide a bias signal when emitting ultrasonic signals.

[0073] In addition, the chip unit 100 also includes a passivation layer 130 disposed on the upper surface of the substrate 110, and a first electrode 120 is formed on the upper surface of the substrate 110 (that is, the passivation layer 130 and the first electrode 120 are located on the same surface of the substrate 110).

[0074] In a specific implementation, the passivation layer 130 covers the first electrode 120 and the upper surface of the substrate 110 after removing the remaining portion of the first electrode 120. The passivation layer 130 corresponding to the region of the first electrode 120 is removed, for example, by using an etching process to remove the passivation layer 130 in the region of the first electrode 120, thereby exposing the first electrode 120. This arrangement allows the first electrode 120 to contact the piezoelectric layer 200, reducing parasitic capacitance and ensuring that the voltage of the excitation signal of the first electrode 120 is entirely applied to the piezoelectric layer 200, which is beneficial for improving the ultrasonic fingerprint recognition effect.

[0075] Parasitic capacitance refers to capacitance that is not actually designed into "that place," but exists as a parasitic presence between wirings due to mutual capacitance. It is also called stray capacitance. In an ultrasonic transducer, if the passivation layer corresponding to the first electrode 120 is not removed, the capacitance formed between the piezoelectric layer 200 and the passivation layer 130, and between the passivation layer 130 and the first electrode 120, are parasitic capacitances; while the capacitances between the first electrode 120 and the piezoelectric layer 200, and between the piezoelectric layer 200 and the second electrode 300, are effective capacitances.

[0076] Of course, the passivation layer 130 corresponding to the pad area is also removed, exposing the pads so that they can be electrically connected to other components. Figure 2a The pads of the chip unit 100 may include electrode pads 140 and pin pads 150. Electrode pads 140 are used for electrical connection to the second electrode 300, and pin pads 150 are used for connection to an external circuit board. For example, the two ends of a gold or aluminum wire are soldered to the pin pads 150 and the circuit board pads, respectively, to achieve an electrical connection between the ultrasonic transducer and the circuit board. The electrical connection between pin pads 150 and electrode pads 140 allows the electrical signal from the first electrode 120 to be transmitted to the external circuit board. There are various ways to electrically connect the pin pads 150 and electrode pads 140.

[0077] Figure 5 This is a schematic diagram of the structure of an ultrasonic transducer provided in one embodiment of this application; Figure 6 This is a schematic diagram of the structure of an ultrasonic transducer provided in another embodiment of this application.

[0078] In some embodiments, refer to Figure 5 The pin pad 150 and the electrode pad 140 are electrically connected by the first connection line 161. The first connection line 161 is located on the same layer as the first electrode 120. The first connection line 161 is formed when the first electrode 120 is formed, which is a simple process.

[0079] In other embodiments, reference is made to Figure 6The pin pad 150 and the electrode pad 140 are electrically connected through a second connection line 162. The second connection line 162 is located inside the substrate 110, which helps to protect the second connection line 162 and ensures the electrical connection between the pin pad 150 and the electrode pad 14.

[0080] There are several common methods for coating the piezoelectric polymer solution onto the first electrode 120, such as slot coating, dip coating, and spray coating. Slot coating can only create simple patterns, i.e., strip-shaped images. Furthermore, if slot coating is used on the CMOS chip 1000, some coating material will be sprayed onto the machine, requiring cleaning after each coating, thus affecting production efficiency. Dip coating coats both sides of the CMOS chip 1000, wasting coating material and affecting the ultrasonic fingerprint recognition effect. Spray coating results in uneven piezoelectric film thickness on the CMOS chip 1000, with poor thickness control precision.

[0081] According to the inventors' research, the embodiments of this application can specifically employ a spin coating process for coating, that is, a spin coating process is used to coat the piezoelectric polymer solution onto the first electrode 120 to form a piezoelectric thin film. Compared with conventional coating methods such as slot coating, the embodiments of this application utilize spin coating to form a piezoelectric thin film 2000, which can be directly matched with the circular CMOS chip 1000 without the need for additional customized equipment. Furthermore, subsequent photolithography processes can yield ultrasonic transducers with higher precision and more complex patterns. Moreover, the coating material will not be sprayed onto the equipment, and the formed piezoelectric thin film 2000 has a uniform thickness.

[0082] In specific implementation, the coating process using spin coating technology may include: placing the piezoelectric polymer solution on the first electrode 120, specifically dripping it onto the first electrode 120, and then performing a single coating at a first rotation speed, that is, spreading the piezoelectric polymer solution onto the first electrode 120 at the first rotation speed, combined with... Figure 4b The piezoelectric polymer solution is coated to cover the entire CMOS chip 1000; then a second coating is performed at a second rotation speed to evenly spread the piezoelectric polymer solution on the entire CMOS chip 1000.

[0083] The second rotation speed is higher than the first rotation speed. In this way, by first rotating the piezoelectric polymer solution at a low speed to homogenize it, and then rotating it at a high speed to further homogenize the piezoelectric polymer solution, not only can the uniformity of the piezoelectric film 2000 be improved, but defects such as bubbles can also be reduced, thereby improving the product yield.

[0084] For example, the first rotational speed ranges from 200 rpm to 500 rpm, such as 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm, or any combination thereof; the second rotational speed ranges from 800 rpm to 3000 rpm, such as 800 rpm, 1000 rpm, 1100 rpm, 1500 rpm, 2000 rpm, 2500 rpm, 3000 rpm, or any combination thereof. This ensures that the second rotational speed is higher than the first rotational speed while avoiding the first rotational speed being too low and affecting coating efficiency, and avoiding the second rotational speed being too high and affecting coating effect.

[0085] Optionally, the coating is performed at a first rotation speed for 3s to 30s, that is, the coating time at the first rotation speed is 3s to 30s, such as 3s, 5s, 10s, 15s, 20s, 25s, 30s or any combination of two of these ranges, to avoid the uniformity of the piezoelectric film 2000 being affected by too short a low-speed coating time, and to avoid the production efficiency being affected by too long a coating time.

[0086] Optionally, the coating is performed at a second rotation speed for 20s to 180s, that is, the coating time at the second rotation speed is 20s to 180s, for example, 20s, 60s, 90s, 120s, 150s, 180s or any combination thereof.

[0087] After the piezoelectric polymer solution is coated (i.e., after spin coating), the uniformly coated piezoelectric polymer solution (wet film) needs to be dried to form a piezoelectric film 2000 of a predetermined thickness. As mentioned above, the drying is carried out under conditions of relative humidity less than 30%, that is, the wet film is placed in an environment with relative humidity less than 30% for drying. The drying method can be natural drying (i.e., drying in an environment of normal temperature (room temperature) and normal pressure), heating drying in an oven, or heating drying on a hot plate, or a combination of at least two of these drying methods, etc. There are no particular restrictions on this.

[0088] In some embodiments, drying can be carried out under normal pressure conditions. Even if the wet film is dried under normal pressure conditions with a relative humidity of less than 30%, this not only facilitates operation but also helps to further optimize the performance of the piezoelectric film.

[0089] In addition, the drying temperature can be 20℃ to 80℃, for example, 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃ or any combination thereof, and the drying time can be 30s to 10min, for example, 30s, 1min, 2min, 3min, 4min, 5min, 6min, 7min, 8min, 9min, 10min or any combination thereof, such as 30s to 5min.

[0090] For example, the drying temperature can be room temperature, such as 20–30°C, and the drying time can be within 30 minutes. Of course, in order to shorten the drying time and improve production efficiency, the drying temperature can be increased to a temperature higher than room temperature, such as 40–80°C. In some specific embodiments, the drying temperature is 60°C, and the drying time can be 3–5 minutes.

[0091] Controlling the drying temperature and time within the aforementioned range not only improves drying efficiency but also further optimizes the transparency and other properties of the piezoelectric film 2000, resulting in a transparent film with high transparency, low haze, and high film quality. It can be understood that a piezoelectric film with higher transparency has higher crystallinity, corresponding to a larger piezoelectric constant d33 value, which in turn benefits the improvement of the sensitivity and other performance characteristics of the ultrasonic transducer.

[0092] The thickness of the piezoelectric film 2000 affects the operating frequency and performance of the ultrasonic transducer. Optionally, the thickness of the piezoelectric film is 5μm to 20μm, for example, 5μm, 7μm, 9μm, 11μm, 13μm, 15μm, 17μm, 20μm, or any combination thereof. This avoids the situation where the piezoelectric film is too thin, causing the ultrasonic transducer to operate at an excessively high frequency, which would lead to complex circuit design, and also avoids the situation where the sensitivity of receiving ultrasonic waves decreases due to the piezoelectric film being too thin. At the same time, it avoids the situation where the piezoelectric film is too thick, which would affect the intensity of the emitted ultrasonic waves.

[0093] The thickness of the piezoelectric thin film 200 is basically equal to the thickness of the piezoelectric layer 200 formed after subsequent crystallization, polarization and patterning processes.

[0094] Generally, the thickness of the piezoelectric film 2000 formed by a single spin coating ranges from 5μm to 12μm. When a larger thickness of the piezoelectric film 2000 is required, it can be achieved by multiple spin coatings.

[0095] Figure 7 This is a schematic diagram of an ultrasonic transducer provided in yet another embodiment of this application. (Combined with...) Figure 7In some embodiments, before coating the piezoelectric polymer solution onto the first electrode 120 and forming a piezoelectric film, the method further includes: forming a second adhesive layer 500 on the first electrode 120, for example, by spin coating or vapor deposition; then coating the piezoelectric polymer solution onto the second adhesive layer 500 to form a piezoelectric film 2000, thereby achieving the coating of the piezoelectric polymer solution onto the first electrode 120 and the formation of the piezoelectric film 2000. The second adhesive layer 500 serves to increase the adhesion between the first electrode 120 and the piezoelectric film 2000. Optionally, the second adhesive layer 500 may contain a silane coupling agent.

[0096] The thickness of the second adhesive layer 500 affects the contact between the piezoelectric layer 200 and the first electrode 120, and forms parasitic capacitance, thereby affecting the performance of the ultrasonic transducer. Typically, a thickness of less than 1.5 micrometers for the second adhesive layer 500 is sufficient to increase the adhesion between the first electrode 120 and the piezoelectric film 2000. Optionally, the thickness of the second adhesive layer 500 is 10 nm to 200 nm, such as 10 μm, 30 μm, 50 μm, 80 μm, 100 μm, 120 μm, 150 μm, 180 μm, 200 μm, or any combination thereof. This improves the adhesion between the piezoelectric layer 200 and the chip unit 100 while avoiding excessive thickness that could negatively impact the performance of the ultrasonic transducer. During the quality control phase, a film-stretching test is conducted to assess the adhesion between the piezoelectric layer 200 and the chip unit 100. The second adhesive layer 500 helps ensure that the adhesion between the piezoelectric layer 200 and the chip unit 100 reaches 4B or higher, thereby improving product yield. Here, 4B is equivalent to ISO grade 1 = ASTM grade, indicating that the actual breakage within the crossed-out area in the adhesion test is less than or equal to 5%.

[0097] It should be noted that if the second adhesive layer 500 affects the conductivity of the pin pad 150 or the lead wires that electrically connect the pin pad 150 to the circuit board, it can be removed by photolithography. The photolithography method can refer to the photolithography method of the subsequent piezoelectric film 2000 to ensure the conductivity of the pin pad 150 and the lead wires.

[0098] Step S120: Crystallize the piezoelectric film 2000 so that the molecular orientation of the piezoelectric film 2000 is consistent; for example, for a PVDF-TrFE piezoelectric film, crystallization causes the orientation of most molecules to become the β phase.

[0099] Specifically, the piezoelectric film 2000 can 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.

[0100] In some specific embodiments, the crystallization process may include baking the piezoelectric film 2000 at a first temperature for 45 min to 120 min, for example, 45 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, 120 min, or any combination thereof. The crystallinity of the piezoelectric film 2000 increases over time and eventually saturates. Baking the piezoelectric film for 45 min to 120 min avoids the effect of excessively short baking time on crystallinity, and avoids the effect of excessively long baking time after crystallization saturation on production efficiency.

[0101] In other words, the crystallization of the piezoelectric thin film 2000 involves baking the CMOS chip 1000 with the piezoelectric thin film 2000 formed at a first temperature. Specifically, the oven is preheated to the first temperature, and the CMOS chip 1000 with the piezoelectric thin film 2000 formed is placed in the oven and left for 45 to 120 minutes. Understandably, after baking in the oven for the preset time, the CMOS chip 1000 with the piezoelectric thin film 2000 formed is removed and cooled to room temperature in air.

[0102] Step S130: Polarize the crystallized piezoelectric film 2000 so that the molecules in the piezoelectric film 2000 are arranged regularly and the dipoles of the molecules face the same direction, thus exhibiting the piezoelectric properties of the piezoelectric film 2000.

[0103] Optionally, the piezoelectric film can be polarized at a second temperature, that is, the temperature of the piezoelectric film 2000 is adjusted to the second temperature and a voltage is applied to polarize it. The range of the second temperature can be 20°C to 30°C, for example, 20°C, 22°C, 25°C, 28°C, 30°C, or any combination thereof. Exemplarily, in the actual preparation process, the temperature of the piezoelectric film 2000 can be adjusted to room temperature for polarization.

[0104] Typically, under the same voltage, piezoelectric materials polarize faster at the Curie temperature than at room temperature. However, piezoelectric materials at the Curie temperature cannot be directly removed from the machine after polarization; they need to wait for cooling. Furthermore, the applied high voltage for polarization cannot be turned off during this process, otherwise the already polarized piezoelectric material will depolarize, i.e., the polarization will disappear. Because stress release during cooling needs to be considered, the cooling process is usually slow and time-consuming. Additionally, before the next piece of material enters the machine for polarization, time is required to raise the temperature to the Curie temperature. This makes the entire polarization process time-consuming and inefficient. In contrast, the embodiments of this application polarize at a temperature of 20°C to 30°C, eliminating the need for cooling and heating, thus shortening the polarization process time in the production of ultrasonic transducers and improving production efficiency.

[0105] Generally, voltage-applied polarization can be achieved through contact polarization, such as oil immersion polarization, or through non-contact polarization, such as corona polarization. This application embodiment specifically employs corona polarization. The polarization device has an upper electrode and a lower electrode, with the upper electrode positioned above the lower electrode. Both the upper and lower electrodes are grid structures. The CMOS chip to be polarized is placed below the lower electrode and does not directly contact it. A polarization voltage is applied to the piezoelectric thin film by applying voltage to the upper and lower electrodes, wherein the voltage at the upper electrode is greater than the voltage at the lower electrode.

[0106] In this embodiment, the polarization process may include placing the piezoelectric thin film 2000 in an electric field of 100V / μm to 200V / μm for polarization. Typically, the polarization electric field needs to be higher than the coercive electric field of the piezoelectric thin film 2000 (45V / μm to 55V / μm) to avoid excessively long polarization times. As the polarization electric field voltage increases, the polarization time shortens, but the power requirements for the polarization equipment also increase, potentially damaging the chip. The fabrication method in this embodiment places the piezoelectric thin film 2000 in an electric field of 100V / μm to 200V / μm for polarization, which shortens the polarization time, improves production efficiency, and avoids damage to the chip caused by an excessively large polarization electric field.

[0107] In some specific embodiments, the polarization process may include placing the crystallized CMOS chip 1000 of the piezoelectric thin film 2000 in an electric field of 100V / μm to 200V / μm for 5 min to 20 min to polarize the piezoelectric thin film 2000, which can avoid the piezoelectric performance and production efficiency being affected by too short a polarization time.

[0108] Step S140: Refer to Figure 2b , Figure 3b as well as Figure 4c The polarized piezoelectric thin film 2000 is patterned to form a piezoelectric layer 200.

[0109] In this embodiment, the polarized piezoelectric thin film 2000 can be patterned using photolithography. Figures 8a to 8d This is a schematic flowchart illustrating the piezoelectric thin film pattern of the ultrasonic fingerprint sensor provided in Embodiment 1 of this application.

[0110] According to the inventors' research, if photoresist is directly coated onto the piezoelectric thin film 2000, the adhesion between the photoresist and the piezoelectric thin film 2000 is weak, affecting patterning. Therefore, combining... Figures 8a to 8d The process of patterning the polarized piezoelectric thin film 2000 in this embodiment includes:

[0111] Step 1: Combining Figure 8aA first adhesive layer 10 is formed on the polarized piezoelectric film 2000 to increase the adhesion between the piezoelectric film 2000 and the photoresist layer 20; the first adhesive layer 10 may contain silane coupling agents, etc.

[0112] Step 2: Combining Figure 8b A photoresist layer 20 is formed on the first adhesive layer 10, for example, by spin-coating the photoresist layer 20 onto the first adhesive layer 10; Figure 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 developer to form the etching window 21 on the photoresist layer 20.

[0113] Step 3: Refer to Figure 8d The portion of the first adhesive layer 10 and the piezoelectric film 2000 exposed by the etching window 21 is etched. Specifically, an etching process, such as plasma etching, can be used. During the etching process, the etching gas used may include oxygen and an auxiliary gas. The auxiliary gas may include fluorine-based gases and / or argon, and fluorine-based gases may include, for example, tetrafluoromethane and / or trifluoromethane. According to the inventors' research, oxygen is typically used as the etching gas during the etching process. However, when the first adhesive layer 10 is present, the etching rate with oxygen is slow and uneven etching is prone to occur. Therefore, by adding the aforementioned auxiliary gas to the oxygen, the etching rate and etching uniformity can be improved.

[0114] It should be noted that when etching the piezoelectric thin film 2000, the edge of the piezoelectric layer 200 can be made to form an inclined surface 210 by adjusting the photoresist curing temperature, the flow rate of the etching gas, and the configuration of the etching gas. This is beneficial for the coating of the second electrode 300 to better "climb" and electrically connect at the connection point with the electrode pad 140 when the second electrode 300 is coated.

[0115] Step 4: Refer to Figure 3b The photoresist layer 20 and the first adhesive layer 10 are removed to form the piezoelectric layer 200. For example, the photoresist layer 20 and the first adhesive layer 10 can be removed by wet cleaning; of course, the photoresist layer 20 and the first adhesive layer 10 can also be removed by dry plasma etching.

[0116] Combined again Figure 2bThe chip unit 100 has an active area (AA area) 101, and the first electrode 120 is located within the active area 101. The area of ​​the patterned piezoelectric layer 200 is larger than the area of ​​the active area 101, so that the projection of the piezoelectric layer 200 onto the active area 101 covers the active area 101 and a portion of the area outside the active area 101. This larger area of ​​the piezoelectric layer 200 improves the electrostatic discharge (ESD) resistance of the chip unit 100. This is because, compared to a passivation layer with a breakdown thickness of less than 2 micrometers, the piezoelectric layer 200 on the chip unit 100 is an "insulating layer." Breaking down a thicker "insulating layer" requires a greater electrostatic discharge than a passivation layer with a breakdown thickness of less than 2 micrometers. Therefore, a larger area of ​​the piezoelectric layer 200 improves the ESD resistance of the chip unit 100.

[0117] Step 150: Refer to Figure 2c , Figure 3c as well as Figure 4d A second electrode 300 is formed on the piezoelectric layer 200. The material of the second electrode 300 can be one or more of conductive silver paste, conductive ink, conductive carbon paste, etc. The coating method for forming the second electrode 300 can be screen printing, spraying, etc. In this embodiment, the second electrode 300 can be formed by screen printing. Specifically, the cutout areas of the screen printing stencil allow electrode coating to pass through, while other areas do not allow electrode coating to pass through. After the screen printing stencil and the CMOS chip are aligned, the electrode coating is scraped from one side of the CMOS chip to the other by a squeegee, thus transferring the screen printing pattern onto the piezoelectric layer 200. During the coating process to form the second electrode 300, the electrical connection area where the second electrode 300 is electrically connected to the electrode pad 140 is also coated simultaneously.

[0118] Optionally, the thickness of the second electrode 300 is 2μm to 30μm, for example, 25μm, 10μm, 15μm, 20μm, 25μm, 30μm, or any combination thereof. This thinner second electrode 300, while ensuring conductivity, is beneficial for improving the performance of the ultrasonic transducer. Furthermore, the second electrode 300 needs to be controlled via a circuit board, and is electrically connected to the electrode pads 140 on the chip unit 100. Figure 3d There is a height difference between the second electrode 300 and the electrode pad 140. If the thickness of the second electrode 300 is too small, it may cause breakage at the step opposite to the inclined surface 210 of the piezoelectric layer 200, affecting the product yield. Therefore, controlling the thickness of the second electrode 300 within the above range can also avoid the breakage caused by the thickness of the second electrode 300 being too small, thereby improving the product yield and performance.

[0119] In some embodiments, combined with Figure 2cThe projection of the second electrode 300 onto the piezoelectric layer 200 is located inside the piezoelectric layer 200, making the area of ​​the piezoelectric layer 200 larger than the area of ​​the second electrode 300. This can reduce the impact of the edge electric field on the performance of the chip unit 100 when a voltage is applied between the second electrode 300 and the first electrode 120, and can also improve the anti-static breakdown performance of the chip unit 100.

[0120] In some embodiments, the projection of the operable area 101 of the chip unit 100 onto the second electrode 300 is located inside the second electrode 300, such that the area of ​​the second electrode 300 is larger than the area of ​​the operable area 101, ensuring that the second electrode 300 can cover all the first electrodes 120, thus ensuring the area of ​​ultrasonic fingerprint recognition.

[0121] The following reference Figure 2d , Figure 3d as well as Figure 4e Since the piezoelectric layer 200 is sensitive to humidity and the second electrode 300 of the silver paste material is easily oxidized, the preparation method of this embodiment further includes forming a protective layer 400 on the second electrode 300 to protect the piezoelectric layer 200, the second electrode 300, and the chip unit 100. Exemplarily, the protective layer 400 can be applied by screen printing, spraying, dip coating, slot coating, etc. The protective layer 400 is a non-conductive insulating material, such as epoxy resin.

[0122] Optionally, the protective layer 400 not only covers the second electrode 300, but also covers the outside of the piezoelectric layer 200 and the electrode pad 140 to prevent the piezoelectric layer 200 and the electrode pad 140 from being corroded by moisture and affecting their performance.

[0123] Optionally, the thickness of the protective layer 400 is 4μm to 50μm, such as 4μm, 10μm, 20μm, 30μm, 40μm, 50μm or any combination of two of these. This avoids the protective layer 400 being too thin, which would affect the protective effect, and also avoids the protective layer 400 being too thick, which would cause ultrasonic wave attenuation.

[0124] Understandably, within the thickness range of the protective layer 400, the resonant frequency of the ultrasonic transducer can be adjusted by adjusting the thickness of the protective layer 400.

[0125] Combination Figure 4e and Figure 4f The CMOS chip 1000 is ground until it is separated into multiple chip units 100. At this time, a piezoelectric layer 200, a second electrode 300, and a protective layer 400 are stacked on the chip unit 100. The grinding method of the CMOS chip 1000 can refer to the existing wafer thinning method to form a bare die (DIE), such as grinding with a grinding wheel.

[0126] Example 2

[0127] Figures 9a to 9e This is a schematic diagram illustrating the fabrication process of the ultrasonic transducer provided in Embodiment 2 of this application. Please refer to... Figures 9a to 9e This embodiment is an improvement on Embodiment 1. Other specific process flows can be referred to Embodiment 1 and will not be repeated here. The difference between this embodiment and Embodiment 1 is that a step of forming a conductive protective layer 600 is added between steps S130 and S140.

[0128] Figure 9a and Figure 3a same, Figure 9c and Figure 3b same, Figure 9d and Figure 3c same, Figure 9e and Figure 3d The same applies, so I won't repeat it here.

[0129] Figure 9b Before patterning the polarized piezoelectric thin film 2000, a conductive protective film is formed on the piezoelectric thin film 200, and then patterned to form a conductive protective layer 600. Specifically, an indium tin oxide (ITO) thin film is deposited on the piezoelectric thin film 2000 using physical vapor deposition (PVD). After patterning the ITO thin film, the conductive protective layer 600 is formed. The patterning method can be photolithography, lift-off processes, etc. The conductive protective layer 600 can also be other metal materials, as long as they are dense enough to protect the covered piezoelectric layer 200 from the influence of the solution during the patterning process.

[0130] This application provides a method for fabricating an ultrasonic transducer, which involves forming a conductive protective layer 600 on a piezoelectric thin film 2000 to protect the piezoelectric thin film 2000 from being immersed in a solution during the patterning process, thus preventing performance degradation.

[0131] Optionally, the thickness of the conductive protective layer 600 is 50nm to 500nm, such as 50nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, or any combination thereof. This avoids the protective effect being affected by an excessively thin conductive protective layer 600, and avoids the performance of the piezoelectric layer 200 being affected by an excessively thick conductive protective layer 600.

[0132] Optional, continue to refer to Figure 9dThe projection of the conductive protective layer 600 onto the piezoelectric layer 200 is located inside the piezoelectric layer 200, making the area of ​​the conductive protective layer 600 smaller than the area of ​​the piezoelectric layer 200. This arrangement can reduce parasitic capacitance outside the operable area and avoid setting an excessively large conductive protective layer 600, which would cause the conductive protective layer 600 to form capacitance with circuits outside the operable area, affecting the performance of the ultrasonic transducer.

[0133] Example 3

[0134] This application provides an ultrasonic transducer, which is prepared using the ultrasonic transducer preparation method of Embodiment 1 or Embodiment 2. Therefore, the ultrasonic transducer provided in Embodiment 3 of this application also has the same advantages as the preparation method of Embodiment 1 or Embodiment 2, and will not be described again here.

[0135] Specifically, the ultrasonic transducer in this embodiment can be an ultrasonic sensor for identifying biological characteristics, such as an ultrasonic fingerprint sensor for fingerprint recognition. Taking an ultrasonic transducer for fingerprint recognition as an example, the specific working process of the ultrasonic transducer in this embodiment is described as follows: An excitation signal is applied between the first electrode 120 and the second electrode 300, and the piezoelectric layer 200 vibrates based on the piezoelectric effect, thereby emitting an ultrasonic signal; the ultrasonic signal passes through the electronic device and reaches the surface of the finger to generate an echo signal; the echo returns and is transmitted to the piezoelectric layer 200, and based on the inverse piezoelectric effect, a potential difference is generated between the first electrode 120 and the second electrode 300 to obtain a corresponding electrical signal. The relevant processing circuit, such as the circuit board of the electronic device, acquires and forms fingerprint information based on the electrical signal. Finally, by comparing the fingerprint information with pre-stored fingerprint information, the purpose of fingerprint recognition is achieved.

[0136] Example 4

[0137] This application provides an electronic device including a cover plate and an ultrasonic transducer as described in Embodiment 3, the ultrasonic transducer being mounted below the cover plate. The electronic device provided in Embodiment 4 of this application, since it includes the ultrasonic transducer described in Embodiment 3, also has the same advantages as the ultrasonic transducer described in Embodiment 3, and will not be repeated here.

[0138] Specifically, the cover plate serves a protective function, thereby improving the reliability of the ultrasonic transducer. The top surface of the cover plate faces the object being contacted (e.g., a user's finger). The cover plate can be made of a material that can be penetrated by ultrasonic waves, such as glass, metal, or composite materials. Alternatively, the cover plate can be directly integrated into the housing or display screen of the electronic device, or it can be embedded within the housing of the electronic device.

[0139] By way of example and not limitation, the electronic devices in the embodiments of this application can be portable or mobile computing devices such as terminal devices, mobile phones, tablets, laptops, desktop computers, gaming devices, in-vehicle electronic devices, or wearable smart devices, as well as other electronic devices such as electronic databases, automobiles, and automated teller machines (ATMs). Wearable smart devices include devices that are fully functional, large in size, and capable of performing complete or partial functions without relying on a smartphone, such as smartwatches or smart glasses, as well as devices that focus on only one type of application function and require cooperation with other devices such as smartphones, such as various smart bracelets and smart jewelry for vital sign monitoring.

[0140] The following, in conjunction with experimental examples and comparative examples, further illustrates the solutions and effects of the embodiments of this application.

[0141] Experimental Example 1

[0142] 1. Preparation of piezoelectric polymer solution

[0143] (1-1) Weigh the solvent and piezoelectric polymer according to the preset concentration of the piezoelectric polymer solution;

[0144] (1-2) Add the solvent to the reaction vessel and start stirring; add the piezoelectric polymer to it, adjust the temperature of the reaction vessel to 25℃ (i.e., the dissolution temperature), stir at 25℃ until the system becomes transparent, continue stirring for 12 hours, and then take the solution out of the reaction vessel.

[0145] (1-3) The solution taken from the reaction vessel was filtered using a filter screen with a pore size of 2 μm, and the filtrate was collected to obtain a piezoelectric polymer solution.

[0146] 2. Fabrication of ultrasonic transducers

[0147] Following the fabrication method of the ultrasonic transducer in Embodiment 1, a piezoelectric layer 200 is formed on the first electrode of the wafer to obtain the ultrasonic transducer; wherein, the relevant parameters are as follows:

[0148] In step S110, the piezoelectric polymer solution is coated onto the first electrode 120 using a spin coating process. During the spin coating process, the first rotation speed is 300 rpm and the coating time is 10 s. The second rotation speed is 1150 rpm and the coating time is 60 s.

[0149] After spin coating, the piezoelectric polymer solution coated on the first electrode 120 is dried to form a piezoelectric thin film 2000. The drying conditions are as follows: the drying method is natural drying (room temperature and normal pressure), the drying time is about 10 minutes, and the relative humidity during drying is about 11%.

[0150] The thickness of the piezoelectric thin film 200 is 9 μm;

[0151] The thickness of the second adhesive layer 500 formed on the first electrode 120 is 100 nm;

[0152] In step S120, the piezoelectric film 2000 is baked at 140°C for 120 minutes to crystallize the piezoelectric film 2000.

[0153] In step S130, the crystallized piezoelectric film 2000 is placed in an electric field of 100V / μm for 10 minutes at room temperature to polarize the piezoelectric film 2000.

[0154] In step 150, the material of the second electrode 300 is silver paste, and the thickness of the second electrode is 4 μm;

[0155] In addition, the thickness of the protective layer 400 is 8 μm;

[0156] The remaining processes and conditions are the same as described in Example 1 above, and will not be repeated here.

[0157] Experimental Examples 2-7 and Comparative Examples 1-2: The difference from Experimental Example 1 is that the dissolution temperature in step S(1-2) and the drying conditions (relative humidity and drying temperature during drying) after spin coating in step S110 are different, as shown in Table 1. Except for the differences shown in Table 1, the other conditions are the same.

[0158] Table 1 summarizes the dissolution temperature of steps (1-2) in Experimental Examples 1-7 and Comparative Examples 1-2, the drying conditions (relative humidity and drying temperature) after spin coating in step S110, and the observed piezoelectric layer appearance.

[0159] Table 1

[0160]

[0161] As can be seen from Table 1, under the same conditions of melting temperature and drying temperature, controlling the relative humidity during drying to be less than 30% can improve the transparency and piezoelectric constant d33 of the formed piezoelectric layer. The piezoelectric layer exhibits an overall uniform appearance and higher transparency.

[0162] In addition, the d33 test results of the piezoelectric layer showed that the d33 of the piezoelectric layer formed in Test Example 1 was higher than that of the piezoelectric layer formed in Test Example 3, the d33 of the piezoelectric layer formed in Test Example 2 was higher than that of the piezoelectric layer formed in Test Example 4, the d33 of the piezoelectric layer formed in Test Example 3 was higher than that of the piezoelectric layer formed in Comparative Example 1, and the d33 of the piezoelectric layer formed in Test Example 4 was higher than that of the piezoelectric layer formed in Comparative Example 2. Among them, the d33 of the piezoelectric layers formed in Comparative Example 1 and Comparative Example 2 was about 21±1 pC / N, and the d33 of the piezoelectric layers formed in Test Example 1 and Test Example 2 was higher than 26 pC / N.

[0163] In the above description, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0164] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for manufacturing an ultrasonic transducer, characterized in that, include: A piezoelectric polymer solution is coated onto a first electrode and dried under conditions of relative humidity less than 30% to form a piezoelectric film. The piezoelectric polymer solution is prepared by dissolving a piezoelectric polymer in a solvent at 20°C to 30°C. The drying is carried out under normal pressure conditions at a temperature of 20°C to 80°C for 30 seconds to 10 minutes. The thickness of the piezoelectric film is 5 μm to 20 μm. Before coating the piezoelectric polymer solution onto the first electrode and forming the piezoelectric film, the process further includes: forming a second adhesive layer on the first electrode; coating the piezoelectric polymer solution onto the second adhesive layer; and forming the piezoelectric film. This achieves the coating of the piezoelectric polymer solution onto the first electrode and the formation of the piezoelectric film. The thickness of the second adhesive layer is 10 nm to 200 nm. The second adhesive layer serves to increase the adhesion between the first electrode and the piezoelectric film. The piezoelectric thin film is sequentially crystallized and polarized to form a piezoelectric layer; the polarization process includes placing the piezoelectric thin film in an electric field of 100V / μm to 200V / μm for 5min to 20min to polarize the piezoelectric thin film; A second electrode is formed on the piezoelectric layer to obtain the ultrasonic transducer; wherein the thickness of the second electrode is 2μm to 30μm.

2. The method for preparing an ultrasonic transducer according to claim 1, characterized in that, The first electrode is formed on a complementary metal-oxide-semiconductor chip.

3. The ultrasonic transducer according to claim 1, characterized in that, The piezoelectric polymer solution contains a piezoelectric polymer, which includes one or more of polyvinylidene fluoride, polyvinylidene fluoride homopolymer, and polyvinylidene fluoride-fluorinated monomer copolymer.

4. The ultrasonic transducer according to claim 1 or 3, characterized in that, The piezoelectric polymer solution contains a solvent, which includes a polar organic solvent, specifically at least one of amide solvents, sulfone solvents, and ketone solvents.

5. The ultrasonic transducer according to claim 1 or 3, characterized in that, The piezoelectric polymer solution contains a piezoelectric polymer, and the mass concentration of the piezoelectric polymer in the piezoelectric polymer solution is 10% to 20%.

6. The method for preparing an ultrasonic transducer according to claim 1, characterized in that, The coating is performed using a spin coating process.

7. The method for preparing an ultrasonic transducer according to claim 6, characterized in that, The coating process using spin coating technology includes: placing the piezoelectric polymer solution on the first electrode, coating once at a first rotation speed, and then coating a second time at a second rotation speed, wherein the second rotation speed is higher than the first rotation speed.

8. The method for preparing an ultrasonic transducer according to claim 7, characterized in that, The first speed ranges from 200 rpm to 500 rpm, and / or the second speed ranges from 800 rpm to 3000 rpm.

9. The method for preparing an ultrasonic transducer according to claim 1, characterized in that, The crystallization process includes baking the piezoelectric film at a first temperature for 45 min to 120 min, wherein the first temperature is greater than the Curie temperature of the piezoelectric film and less than the melting temperature of the piezoelectric film.

10. The method for preparing an ultrasonic transducer according to claim 1, characterized in that, Also includes: The polarized piezoelectric thin film is patterned to form the piezoelectric layer. The patterning process includes: A first adhesive layer is formed on the polarized piezoelectric film; A photoresist layer is formed on the first adhesive layer, and an etching window is formed on the photoresist layer; The portions of the first adhesive layer and the piezoelectric film exposed by the etching window are etched. Remove the photoresist layer and the first adhesive layer to form the piezoelectric layer.

11. The method for preparing an ultrasonic transducer according to claim 1, characterized in that, Also includes: A protective layer is formed on the second electrode, the thickness of which is 4μm to 50μm.

12. An ultrasonic transducer, characterized in that, It is manufactured using the method for preparing the ultrasonic transducer according to any one of claims 1-11.

13. An electronic device, characterized in that, Includes a cover plate and the ultrasonic transducer as described in claim 12.

Images