WO2024065805A1 - Capteur d'empreintes digitales à ultrasons et son procédé de fabrication, et dispositif électronique - Google Patents

Capteur d'empreintes digitales à ultrasons et son procédé de fabrication, et dispositif électronique Download PDF

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WO2024065805A1
WO2024065805A1 PCT/CN2022/123577 CN2022123577W WO2024065805A1 WO 2024065805 A1 WO2024065805 A1 WO 2024065805A1 CN 2022123577 W CN2022123577 W CN 2022123577W WO 2024065805 A1 WO2024065805 A1 WO 2024065805A1
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piezoelectric
piezoelectric film
electrode
temperature
ultrasonic fingerprint
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PCT/CN2022/123577
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English (en)
Chinese (zh)
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纪登鑫
王红超
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深圳市汇顶科技股份有限公司
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Priority to PCT/CN2022/123577 priority Critical patent/WO2024065805A1/fr
Publication of WO2024065805A1 publication Critical patent/WO2024065805A1/fr

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  • the present application relates to the field of fingerprint recognition technology, and in particular to an ultrasonic fingerprint sensor and a preparation method thereof, and an electronic device.
  • Ultrasonic fingerprint sensors identify fingerprints by emitting and detecting reflected ultrasonic waves. They are increasingly being used in smart terminal devices because of their ability to penetrate display screens or housings, avoid optical interference, and identify real and fake fingers.
  • the piezoelectric layer of the ultrasonic fingerprint sensor has a piezoelectric effect and is used to transmit or receive ultrasonic waves.
  • the polarization of the piezoelectric layer is usually polarized at a Curie temperature higher than room temperature.
  • the present application provides an ultrasonic fingerprint sensor and a preparation method thereof, and an electronic device to solve the technical problems of the existing polarization process being time-consuming and having low production efficiency.
  • a first aspect of the present application provides a method for preparing an ultrasonic fingerprint sensor, which comprises:
  • Crystallizing the piezoelectric film at a first temperature is greater than the Curie temperature of the piezoelectric film and less than the melting temperature of the piezoelectric film;
  • the second temperature ranges from 20° C. to 30° C.
  • a second electrode is formed on the piezoelectric layer.
  • the method for preparing the ultrasonic fingerprint sensor provided in the first aspect of the present application has the following advantages:
  • the preparation method of the ultrasonic fingerprint sensor provided in the present application polarizes the piezoelectric film by applying voltage at a temperature of 20°C to 30°C, without the need for a waiting process of cooling or heating the temperature, thereby shortening the polarization process time of the ultrasonic fingerprint sensor during the production process and improving production efficiency; and after the piezoelectric film is polarized and patterned to form a piezoelectric layer, there is no need to consider the influence of the polarization method on the second electrode, and the polarization method of the second electrode is more flexible.
  • a second aspect of the present application provides an ultrasonic fingerprint sensor, which is prepared by the method for preparing the ultrasonic fingerprint sensor according to the first aspect.
  • the ultrasonic fingerprint sensor provided in the second aspect of the present application is prepared by the preparation method of the ultrasonic fingerprint sensor described in the first aspect, so the ultrasonic fingerprint sensor provided in the second aspect of the present application also has the same advantages as the preparation method described in the first aspect.
  • a third aspect of the present application provides an electronic device, which includes a cover plate and the second ultrasonic fingerprint sensor, wherein the ultrasonic fingerprint sensor is installed below the cover plate.
  • the electronic device provided in the third aspect of the present application includes the ultrasonic fingerprint sensor described in the second aspect, so the electronic device provided in the third aspect of the present application also has the same advantages as the ultrasonic fingerprint sensor described in the second aspect.
  • FIG1 is a flow chart of a method for preparing an ultrasonic fingerprint sensor provided in an embodiment of the present application
  • FIGS. 2a to 2d are schematic top views of the preparation process of the ultrasonic fingerprint sensor provided in Example 1 of the present application;
  • 3a to 3d are cross-sectional schematic diagrams of the preparation process of the ultrasonic fingerprint sensor provided in Example 1 of the present application;
  • 4a to 4f are cross-sectional schematic diagrams of the preparation process of the ultrasonic fingerprint sensor on the CMOS chip provided in the first embodiment of the present application;
  • FIG5 is a schematic diagram of the structure of an ultrasonic fingerprint sensor provided in an embodiment of the present application.
  • FIG6 is a schematic diagram of the structure of an ultrasonic fingerprint sensor provided by another embodiment of the present application.
  • FIG7 is a schematic diagram of the structure of an ultrasonic fingerprint sensor provided by another embodiment of the present application.
  • FIGS 8a to 8d are schematic diagrams of the process of patterning the piezoelectric film for ultrasonic fingerprint sensing provided in Example 1 of the present application;
  • 9a to 9e are schematic diagrams of the preparation process of the ultrasonic fingerprint sensor provided in the second embodiment of the present application.
  • Ultrasonic fingerprint sensors use the ability of ultrasound to penetrate materials, and when ultrasound reaches the surface of different materials, the reflected ultrasound energy and the distance it travels are different, so fingerprint recognition is performed. Therefore, by using the difference in acoustic impedance between skin and air, the location of the ridges and valleys of the fingerprint can be distinguished. Ultrasonic fingerprint sensors can penetrate under the surface of the skin to identify the unique three-dimensional features of fingerprints and identify real and fake fingers; and because ultrasound has a certain degree of penetration, it can still be recognized when there is a small amount of dirt or moisture on the finger, and can penetrate the display or casing of the device. Therefore, it is increasingly being used in smart terminal devices.
  • the piezoelectric layer of the ultrasonic fingerprint sensor has a piezoelectric effect. Specifically, when the piezoelectric layer is deformed, a voltage difference is generated at its two ends; when a voltage difference is generated at its two ends, the piezoelectric layer can be deformed. By using this characteristic of the piezoelectric layer, mechanical vibration and AC signals can be converted to each other, so that ultrasonic waves can be emitted or received.
  • the operating frequency of the ultrasonic fingerprint sensor is inversely proportional to the thickness of the piezoelectric layer. When the higher the fingerprint recognition accuracy is required, it means a thinner piezoelectric layer.
  • the interval between two adjacent piezoelectric columns of the ultrasonic fingerprint sensor should be less than the ultrasonic wavelength. For a typical ultrasonic fingerprint sensor, the interval between two adjacent piezoelectric columns is usually between 50 ⁇ m and 100 ⁇ m. Therefore, the formation process of the piezoelectric layer is crucial to the performance of ultrasonic fingerprints.
  • the polarization of the piezoelectric layer is usually carried out at a Curie temperature higher than room temperature.
  • the piezoelectric layer at the Curie temperature cannot be directly removed from the machine, and needs to wait for cooling and the high voltage during polarization needs to be maintained during the cooling process. Since it is necessary to consider the stress release of the material during the cooling process, the cooling process is usually slow, and the temperature needs to be raised again when the next piece of material is polarized, which results in a long polarization process in the production process of the ultrasonic fingerprint sensor and low production efficiency.
  • a voltage is applied to the piezoelectric layer at room temperature to polarize the piezoelectric layer, and an electric field polarization of 100 to 200 V/um is used.
  • an electric field polarization of 100 to 200 V/um is used.
  • FIG1 is a flow chart of a method for preparing an ultrasonic fingerprint sensor provided in an embodiment of the present application
  • FIG2a to FIG2d are schematic top views of the preparation process of an ultrasonic fingerprint sensor provided in Embodiment 1 of the present application
  • FIG3a to FIG3d are schematic cross-sectional views of the preparation process of an ultrasonic fingerprint sensor provided in Embodiment 1 of the present application
  • FIG4a to FIG4f are schematic cross-sectional views of the preparation process of an ultrasonic fingerprint sensor on a CMOS chip provided in Embodiment 1 of the present application.
  • FIG2a to FIG2d are top views of the preparation process of an ultrasonic fingerprint sensor, taking an ultrasonic fingerprint chip 100 as an example, and FIG3a to FIG3d are A-A cross-sectional views corresponding to FIG2a to FIG2d; and FIG4a to FIG4f show the process of preparing an ultrasonic fingerprint sensor on a circular CMOS chip 1000, wherein a plurality of ultrasonic fingerprint chips 100 are usually arranged on the CMOS chip 1000.
  • Step S110 With reference to FIG. 1 , FIG. 2 a , FIG. 3 a and FIG. 4 b , a piezoelectric copolymer solution is coated on the first electrode 120 to form a piezoelectric film 2000 .
  • the piezoelectric copolymer solution is prepared first.
  • the specific process includes: weighing to determine the mass of the solvent and the solute, preparing the solution and filtering to form the piezoelectric copolymer solution.
  • the reactor is heated to 20°C to 30°C in a water bath.
  • the piezoelectric film formed by the piezoelectric copolymer solution thus prepared has a large piezoelectric constant d33, and the piezoelectric constant d33 is as high as 25 ⁇ 1pC/N.
  • the relationship between its sensitivity and d33 satisfies S loop ⁇ S Tx *S Rx ⁇ d33 3 , that is, the loop sensitivity S loop of the ultrasonic fingerprint sensor is proportional to the product of the transmitting ultrasonic sensitivity S Tx and the receiving ultrasonic sensitivity S Rx , and is proportional to the cube of the piezoelectric constant d33.
  • the solute of the piezoelectric copolymer solution is a piezoelectric copolymer, which can be polyvinylidene fluoride (PVDF) or polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) and the like.
  • PVDF polyvinylidene fluoride
  • PVDF-TrFE polyvinylidene fluoride-trifluoroethylene
  • the piezoelectric copolymer solution on the first electrode 120 there are many ways to apply the piezoelectric copolymer solution on the first electrode 120, such as slit coating, dip coating, spray coating, etc.
  • the first electrode 120 is located on the ultrasonic fingerprint chip 100, and the ultrasonic fingerprint chip 100 is an application specific integrated circuit (ASIC) for ultrasonic fingerprint recognition.
  • ASIC application specific integrated circuit
  • the embodiment of the present application adopts a complementary metal oxide semiconductor (complementary metal-oxide-semiconductor transistor, CMOS) chip, hereinafter referred to as CMOS chip 1000. For this reason, the embodiment of the present application adopts spin coating to apply the piezoelectric copolymer solution.
  • CMOS complementary metal oxide semiconductor
  • each ultrasonic fingerprint chip 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 positive electrode deposition.
  • the material of the metal electrode may be aluminum or gold.
  • the ultrasonic fingerprint chip 100 also includes pads for electrical connection and other devices such as amplifiers and switches.
  • the ultrasonic fingerprint chip 100 of the embodiment of the present application further includes a passivation layer 130 disposed on the upper surface of the substrate 110, and the first electrode 120 is formed on the upper surface of the substrate 110; the passivation layer 130 covers the first electrode 120 and the upper surface of the substrate 110 where the remaining portion of the first electrode 120 is removed.
  • the passivation layer 130 corresponding to the first electrode 120 region is removed, for example, by using an etching process to remove the passivation layer 130 in the first electrode 120 region, so that the first electrode 120 is exposed.
  • Such a configuration enables the first electrode 120 to contact the piezoelectric layer 200, reduces parasitic capacitance, and ensures that the voltage of the excitation signal of the first electrode 120 acts entirely on the piezoelectric layer 200, which is beneficial to improving the ultrasonic fingerprint recognition effect.
  • parasitic capacitance refers to the capacitance that was not originally designed in "that place", but because there is always mutual capacitance between the wirings, the mutual capacitance is like parasitic between the wirings, so it is called parasitic capacitance, also known as stray capacitance.
  • parasitic capacitance also known as stray capacitance.
  • the capacitance formed between the piezoelectric layer 200 and the passivation layer 130, and the capacitance formed between the passivation layer 130 and the first electrode 120 are parasitic capacitance; and the capacitance between the first electrode 120 and the piezoelectric layer 200, and the capacitance between the piezoelectric layer 200 and the second electrode 300 are effective capacitance.
  • the pad of the ultrasonic fingerprint chip 100 may include an electrode pad 140 and a pin pad 150.
  • the electrode pad 140 is used to electrically connect to the second electrode 300
  • the pin pad 150 is used to connect to an external circuit board.
  • the two ends of the lead wire such as a gold wire or an aluminum wire are respectively welded to the pin pad 150 and the pad on the circuit board to achieve the electrical connection between the ultrasonic fingerprint sensor and the circuit board.
  • the pin pad 150 is electrically connected to the electrode pad 140, so that the electrical signal of the first electrode 120 can be transmitted to the external circuit board. There can be many ways to electrically connect the pin pad 150 and the electrode pad 140.
  • FIG5 is a schematic diagram of the structure of an ultrasonic fingerprint sensor provided in one embodiment of the present application
  • FIG6 is a schematic diagram of the structure of an ultrasonic fingerprint sensor provided in another embodiment of the present application.
  • the pin pad 150 and the electrode pad 140 are electrically connected via a first connection line 161 .
  • the first connection line 161 and the first electrode 120 are located in the same layer.
  • the first connection line 161 is formed when the first electrode 120 is formed, and the process is simple.
  • the pin pad 150 and the electrode pad 140 are electrically connected via a second connection line 162 , and the second connection line 162 is located inside the substrate 110 , which is beneficial to protecting the second connection line 162 and ensuring electrical connection between the pin pad 150 and the electrode pad 14 .
  • the substrate 110 of the CMOS chip 1000 in the embodiment of the present application is a wafer, and its shape is circular.
  • the preparation method in the embodiment of the present application forms the piezoelectric film 2000 by coating the piezoelectric copolymer solution on the first electrode 120 using a spin coating process.
  • the embodiment of the present application forms the piezoelectric film 2000 by spin coating, which can be directly matched with the circular CMOS chip 1000 without the need for additional customized machines, and the subsequent cooperation with the photolithography process can obtain an ultrasonic fingerprint sensor with higher precision and more complex graphics; and the coating will not be sprayed onto the machine, and the thickness of the formed piezoelectric film 2000 is uniform.
  • slit coating can only be used for simple graphics, that is, the production of strip images, and if slit coating is used to coat the CMOS chip 1000, part of the coating will be sprayed onto the machine, and the machine needs to be cleaned after each coating, affecting production efficiency; using the dip coating method, both sides of the CMOS chip 1000 will be coated, which not only wastes the coating, but also affects the ultrasonic fingerprint recognition effect; the piezoelectric film formed on the CMOS chip 1000 by spraying is uneven in thickness, and the thickness control accuracy is poor.
  • the piezoelectric copolymer solution is dripped onto the first electrode 120, and the piezoelectric copolymer solution is applied onto the first electrode 120 at a first rotation speed.
  • the piezoelectric copolymer solution is applied to cover the entire CMOS chip 1000.
  • the solution is applied again at a second rotation speed and dried to form a piezoelectric film 2000 of a preset thickness.
  • the first speed ranges from 300rpm to 500rpm; the second speed ranges from 800rpm to 3000rpm, while ensuring that the second speed is higher than the first speed, avoiding the first speed being too low to affect the coating efficiency, and avoiding the second speed being too high to affect the coating effect.
  • the embodiment of the present application first rotates the piezoelectric copolymer solution at a low speed to make it uniform, and then rotates the piezoelectric copolymer solution at a high speed to further make it uniform, which can not only make the piezoelectric film 2000 more uniform, but also reduce defects such as bubbles and improve product yield.
  • the piezoelectric copolymer solution is coated onto the first electrode 120 at a first rotation speed for 3s to 30s to avoid low-speed coating time that is too short and affects the uniformity of the piezoelectric film 2000 and avoids too long coating time that affects production efficiency.
  • the uniformly coated piezoelectric copolymer solution needs to be dried to form a piezoelectric film 2000 with a preset thickness.
  • it includes: coating again at a second rotation speed, drying at a preset drying temperature for a preset time to form a piezoelectric film 2000 of a preset thickness, the preset drying temperature ranges from 40°C to 80°C, and the preset time ranges from 30s to 5min.
  • the preset drying temperature can be room temperature, such as 20-30°C, and the preset time is within 30 minutes; of course, in order to shorten the drying time, the preset drying temperature can be increased so that the preset drying temperature can be higher than room temperature.
  • the preset drying temperature range can be 40-80°C.
  • the preset drying temperature is 60°C, and the preset time can be 3min-5min.
  • the piezoelectric film 2000 is formed during drying to ensure production efficiency.
  • the thickness of the piezoelectric film 2000 affects the operating frequency and performance of the ultrasonic fingerprint sensor.
  • the thickness of the piezoelectric film is 5 ⁇ m to 20 ⁇ m, and further, the thickness of the piezoelectric film is 9 ⁇ m to 11 ⁇ m.
  • This arrangement can avoid the piezoelectric film being too thin, which may cause the operating frequency of the ultrasonic fingerprint sensor to be too high, resulting in a complex circuit design, and avoid the piezoelectric film being too thin, which may reduce the sensitivity of receiving ultrasonic waves; it can also avoid the piezoelectric film being too thick, which may affect the intensity of transmitting ultrasonic waves.
  • the thickness of the piezoelectric film 2000 formed by a single spin coating process ranges from 5 ⁇ m to 12 ⁇ m.
  • the thickness of the piezoelectric film 2000 required is greater, it can be achieved by multiple spin coating processes.
  • FIG7 is a schematic diagram of the structure of an ultrasonic fingerprint sensor provided by another embodiment of the present application.
  • the preparation method of the present application further includes: forming a second adhesive layer 500 on the first electrode 120, for example, by spin coating or vapor deposition to form the second adhesive layer 500; then applying the piezoelectric copolymer solution on the second adhesive layer 500, and forming a piezoelectric film.
  • the second adhesive layer 500 serves to increase the adhesion between the first electrode 120 and the piezoelectric film.
  • the second adhesive layer 500 may be a silane coupling agent.
  • the thickness of the second adhesive layer 500 affects the contact between the piezoelectric layer 200 and the first electrode 120, and forms a parasitic capacitor, which reduces the performance of the ultrasonic fingerprint sensor.
  • the thickness of the second adhesive layer 500 is less than 1.5 microns to increase the adhesion between the first electrode 120 and the piezoelectric film; optionally, the thickness of the second adhesive layer 500 is 10nm to 200nm, which can not only improve the adhesion between the piezoelectric layer 200 and the ultrasonic fingerprint chip 100, but also avoid the excessive thickness affecting the performance of the ultrasonic fingerprint sensor.
  • the adhesion between the piezoelectric layer 200 and the ultrasonic fingerprint chip 100 is tested by pulling the film.
  • the second adhesive layer 500 is conducive to ensuring that the adhesion between the piezoelectric layer 200 and the ultrasonic fingerprint chip 100 reaches 4B or more, thereby improving the product yield.
  • the second adhesive layer 500 affects the conductive properties of the pin pad 150, or affects the lead that electrically connects the pin pad 150 to the circuit board, it can be removed by photolithography.
  • the photolithography method can refer to the subsequent photolithography method of the piezoelectric film 2000 to ensure the conductive properties of the pin pad 150 and the lead.
  • Step S120 crystallize the piezoelectric film 2000 at a first temperature so that the molecular orientation of the piezoelectric film 2000 is consistent; illustratively, for the PVDF-TrFE piezoelectric film, crystallization causes most of the molecular orientation to become a ⁇ phase.
  • the first temperature is greater than the Curie temperature of the piezoelectric film 2000 and less than the melting temperature of the piezoelectric film 2000.
  • the piezoelectric film is baked continuously at the first temperature for 45 minutes to 120 minutes.
  • the crystallinity of the piezoelectric film 2000 increases with time and eventually saturates. Baking the piezoelectric film for 45 minutes to 120 minutes can avoid the influence of too short baking time on the crystallinity, and avoid the influence of too long baking time on the production efficiency after the crystallization is saturated.
  • the crystallization of the piezoelectric film 2000 is to bake the CMOS chip 1000 formed with the piezoelectric film 2000 at the first temperature. Specifically, the oven is preheated to the first temperature, and the CMOS chip 1000 formed with the piezoelectric film 2000 is placed in the oven and waited for 45 minutes to 120 minutes. It can be understood that after the oven is baked for a preset time, the CMOS chip 1000 formed with the piezoelectric film 2000 is taken out and cooled to room temperature in an air environment.
  • Step S130 lowering the temperature of the piezoelectric film 2000 to a second temperature, and applying a voltage for polarization, so that the molecules in the piezoelectric film 2000 are regularly arranged, so that the dipoles of the molecules face the same direction, reflecting the piezoelectric characteristics of the piezoelectric film 2000.
  • the second temperature ranges from 20°C to 30°C. In the actual preparation process, the temperature of the piezoelectric film 2000 can be lowered to room temperature.
  • the polarization of piezoelectric materials at the Curie temperature is indeed faster than that at room temperature.
  • the piezoelectric material at the Curie temperature cannot be directly removed from the machine after polarization is completed, and needs to wait for cooling; and the high voltage applied for polarization in this process cannot be turned off, otherwise the polarized piezoelectric material will depolarize, that is, the polarization disappears.
  • the cooling process is usually slow and time-consuming; and before the next piece of material enters the machine for polarization, it takes time to heat up to the Curie temperature. This makes the entire polarization process time-consuming and low in production efficiency.
  • the embodiment of the present application is polarized at a room temperature of 20°C to 30°C, without the need for a waiting process of cooling or heating, thereby shortening the polarization process time of the ultrasonic fingerprint sensor during the production process and improving production efficiency.
  • the polarization electric field needs to be higher than the coercive electric field (45-55V/ ⁇ m) of the piezoelectric film 2000 to avoid the polarization time being too long.
  • the polarization electric field voltage increases, the polarization time is shortened, but the power supply requirements for the polarization equipment also increase, and the chip may be damaged.
  • the preparation method of an embodiment of the present application places the piezoelectric film 2000 in an electric field of 100V/ ⁇ m to 200V/ ⁇ m at the second temperature for polarization, which shortens the polarization time and improves production efficiency while avoiding excessive polarization electric field and damage to the chip.
  • the polarization mode of applying voltage can be a contact polarization mode, such as an oil-immersion polarization mode; or it can be a non-contact protection mode, such as a corona polarization mode.
  • the embodiment of the present application adopts a corona polarization mode, and the polarization device has an upper electrode and a lower electrode, the upper electrode is above the lower electrode, and the upper electrode and the lower electrode are both 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 polarization voltage is applied to the piezoelectric film, wherein the voltage of the upper electrode is greater than the voltage of the lower electrode.
  • the CMOS chip 1000 after the crystallization of the piezoelectric film 2000 is placed in an electric field of 100V/ ⁇ m to 200V/ ⁇ m for 5min to 20min to polarize the piezoelectric film, thereby avoiding the influence of too short polarization time on piezoelectric performance and the influence of too short polarization time on production efficiency.
  • Step S140 referring to FIG. 2 b , FIG. 3 b and FIG. 4 c , the polarized piezoelectric film 2000 is patterned to form a piezoelectric layer 200 .
  • the embodiment of the present application uses a photolithography process to pattern the polarized piezoelectric film 2000.
  • photoresist is directly applied on the piezoelectric film 2000, the adhesion between the photoresist and the piezoelectric film 2000 is weak, which affects the imaging.
  • Figures 8a to 8d are schematic diagrams of the process of patterning the piezoelectric film for ultrasonic fingerprint sensing provided in the first embodiment of the present application.
  • the embodiment of the present application patterns the polarized piezoelectric film 2000 to form a piezoelectric layer 200, specifically including:
  • Step 1 Referring to FIG. 8 a , a first adhesive layer 10 is formed on the polarized piezoelectric film 2000 to increase adhesion between the piezoelectric film 2000 and the photoresist layer 20 ; the first adhesive layer 10 may be made of a silane coupling agent or the like.
  • Step 2 In conjunction with Figure 8b, a photoresist layer 20 is formed on the first bonding layer 10, for example, the photoresist layer 20 is formed by spin coating on the first bonding layer 10; in conjunction with 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 with a developer to form an etching window 21 on the photoresist layer 20.
  • Step 3 Referring to FIG. 8d, the first adhesive layer 10 and the piezoelectric film 2000 exposed by the etching window 21 are etched using an etching process.
  • etching is performed using a plasma etching process, and oxygen is usually used as an etching gas during the etching process; when a second adhesive layer is provided, the etching rate of oxygen is slow and uneven etching is prone to occur.
  • a fluorine-based gas such as tetrafluoromethane, trifluoromethane, etc., can be added to oxygen, or argon gas can be added to oxygen to increase the etching rate and etching uniformity.
  • the edge of the piezoelectric layer 200 can form an inclined surface 210 by adjusting the temperature of photoresist curing, the flow rate of etching gas, the configuration of etching gas, etc. This is beneficial when coating to form the second electrode 300.
  • the coating of the second electrode 300 can better "climb" and electrically connect with the electrode pad 140.
  • Step 4 Referring to FIG. 3b, the photoresist layer 20 and the first adhesive layer 10 are removed to form the piezoelectric layer 200.
  • 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 also be removed by dry plasma etching.
  • the ultrasonic fingerprint chip 100 has an operable area (Active Area, AA area) 101, and the first electrode 120 is located in the operable area 101.
  • the area of the patterned piezoelectric layer 200 is larger than the area of the operable area 101, so that the projection of the piezoelectric layer 200 on the operable area 101 covers the operable area 101 and part of the area outside the operable area 101.
  • a larger area of the piezoelectric layer 200 is provided, which is beneficial to improving the anti-static breakdown performance of the ultrasonic fingerprint chip 100.
  • the piezoelectric layer 200 formed on the ultrasonic fingerprint chip 100 requires a greater strength of static electricity to break through the thicker "insulating layer” relative to the passivation layer with a thickness of less than 2 microns. Therefore, a larger area of the piezoelectric layer 200 is provided to improve the anti-static breakdown capability of the ultrasonic fingerprint chip 100.
  • Step 150 Referring to FIG. 2c, FIG. 3c and FIG. 4d, a second electrode 300 is formed on the piezoelectric layer 200.
  • the material of the second electrode 300 may be conductive silver paste, conductive ink, conductive carbon paste, etc.
  • the coating method for forming the second electrode 300 may be screen printing, spraying, etc.
  • the embodiment of the present application forms the second electrode 300 by screen printing. Specifically, the hollow area of the screen printing plate allows the electrode coating to pass through and be coated, and the other parts will not have the electrode coating pass through.
  • 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 to the piezoelectric layer 200.
  • the second electrode 300 is formed by coating, the electrical connection area where the second electrode 300 is electrically connected to the electrode pad 140 is also coated.
  • the thickness of the second electrode 300 is 2 ⁇ m to 30 ⁇ m. While ensuring the conductivity, the thinner second electrode 300 is conducive to improving the performance of the ultrasonic fingerprint sensor.
  • the second electrode 300 needs to be controlled by the circuit board.
  • the second electrode 300 is electrically connected to the electrode pad 140 on the ultrasonic fingerprint chip 100. In conjunction with 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 a break at the step relative to the inclined surface 210 of the piezoelectric layer 200, affecting the product yield.
  • 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 the area of the second electrode 300. This can reduce the impact of the fringe electric field on the performance of the ultrasonic fingerprint chip 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 ultrasonic fingerprint chip 100.
  • the projection of the operable area 101 of the ultrasonic fingerprint chip 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, ensuring that all the first electrodes 120 can be covered by the second electrode 300, thereby ensuring the area for ultrasonic fingerprint recognition.
  • the method for preparing the ultrasonic sensor provided in the embodiment of the present application is polarized at a room temperature of 20 to 30°C, without the need for a waiting process for cooling or heating, so that the polarization process time of the ultrasonic fingerprint sensor in the production process is shortened and the production efficiency is improved; moreover, the second electrode 300 is formed on the polarized and patterned piezoelectric layer 200, and the polarization method is more flexible, and there is no need to consider the influence of the polarization method on the second electrode 300.
  • the preparation method of the embodiment of the present application further includes: forming a protective layer 400 on the second electrode 300 to protect the piezoelectric layer 200, the second electrode 300 and the ultrasonic fingerprint chip 100.
  • the coating method of the protective layer 400 can be screen printing, spraying, dipping, slit coating, etc.
  • the protective layer 400 is a non-conductive insulating material, such as an epoxy resin material.
  • the protective layer 400 not only covers the second electrode 300 , but also 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 and thus affecting the performance.
  • the thickness of the protective layer 400 is 4 ⁇ m to 50 ⁇ m, which can prevent the protective layer 400 from being too thin, which affects the protection effect, and can also prevent the protective layer 400 from being too thick, which causes ultrasonic attenuation.
  • the resonance frequency of the ultrasonic fingerprint sensor can be adjusted by adjusting the thickness of the protection layer 400 .
  • the CMOS chip 1000 is ground until the CMOS chip 1000 is separated to form a plurality of ultrasonic fingerprint chips 100, and at this time, the ultrasonic fingerprint chip 100 is stacked with a piezoelectric layer 200, a second electrode 300 and a protective layer 400.
  • the method of grinding the CMOS chip 1000 can refer to the existing method of thinning a wafer to form a bare die DIE, such as grinding wheel grinding.
  • Figures 9a to 9e are schematic diagrams of the preparation process of the ultrasonic fingerprint sensor provided in the second embodiment of the present application. Please refer to Figures 9a to 9e.
  • This embodiment is an improvement on the basis of the first embodiment. Other specific process flows can refer to the first embodiment and will not be repeated. The difference between this embodiment and the first embodiment is that the step of forming a conductive protective layer 600 is added between step S130 and 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
  • FIG. 9e is the same as FIG. 3d , and their details will not be repeated here.
  • a conductive protective film is formed on the piezoelectric film 2000, and the conductive protective film is patterned to form a conductive protective layer 600.
  • ITO indium tin oxide
  • PVD physical vapor deposition
  • the patterning method can be photolithography, lift-off (uncover-strip) process, etc.
  • the conductive protective layer 600 can also be other metal materials, as long as it is dense enough to protect the covered piezoelectric layer 200 from being affected by the solution during the patterning process.
  • the present application provides a second method for preparing an ultrasonic fingerprint sensor, in which a conductive protective layer 600 is formed on the piezoelectric film 2000 to protect the piezoelectric film 2000 from being soaked in a solution during the patterning process, thereby preventing the performance from being degraded.
  • the thickness of the conductive protective layer 600 is 50 nm to 500 nm, so as to avoid setting a too thin conductive protective layer 600 to affect the protection effect, and to avoid setting a too thick conductive protective layer 600 to affect the performance of the piezoelectric layer 200.
  • the projection of the conductive protective layer 600 on the piezoelectric layer 200 is located inside the piezoelectric layer 200, so that the area of the conductive protective layer 600 is smaller than the area of the piezoelectric layer 200.
  • This setting can reduce the parasitic capacitance outside the operable area and avoid setting an excessively large conductive protective layer 600, which causes the conductive protective layer 600 to form capacitance with the circuit in the operable area unexpectedly, affecting the performance of the ultrasonic fingerprint sensor.
  • the embodiment of the present application provides an ultrasonic fingerprint sensor, which is prepared by the preparation method of the ultrasonic fingerprint sensor of embodiment one or embodiment two. Therefore, the ultrasonic fingerprint sensor provided by embodiment three of the present application also has the same advantages as the preparation method of embodiment one or embodiment two, which will not be repeated here.
  • 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 is transmitted back to the piezoelectric layer 200, and based on the inverse piezoelectric effect, an electric potential difference is generated between the first electrode 120 and the second electrode 300, and a corresponding electric signal is obtained.
  • the relevant processing circuit such as the circuit board of the electronic device, obtains and forms fingerprint information based on the electric signal, and finally the fingerprint information is compared with the pre-stored fingerprint information to achieve the purpose of fingerprint recognition.
  • An embodiment of the present application further provides an electronic device, which includes a cover plate and the ultrasonic fingerprint sensor described in the third embodiment, wherein the ultrasonic fingerprint sensor is installed under the cover plate.
  • the cover plate plays a protective role, thereby improving the reliability of the ultrasonic fingerprint sensor.
  • the top surface of the cover plate faces the contact object (e.g., the user's finger).
  • the cover plate can be made of a material that can be penetrated by ultrasound, such as glass, metal, or a composite material.
  • the cover plate can be directly the housing or display screen of the electronic device, or the cover plate can be embedded in the housing of the electronic device.
  • the electronic device provided in the fourth embodiment of the present application includes the ultrasonic fingerprint sensor described in the third embodiment. Therefore, the electronic device provided in the fourth embodiment of the present application also has the same advantages as the ultrasonic fingerprint sensor described in the third embodiment, which will not be repeated here.
  • the electronic device in the embodiment of the present application can be a portable or mobile computing device such as a terminal device, a mobile phone, a tablet computer, a laptop computer, a desktop computer, a gaming device, an in-vehicle electronic device or a wearable smart device, as well as other electronic devices such as an electronic database, a car, and an automated teller machine (ATM).
  • the wearable smart device includes a device with full functions and large size that can realize full or partial functions without relying on a smart phone, such as a smart watch or smart glasses, and a device that only focuses on a certain type of application function and needs to be used in conjunction with other devices such as a smart phone, such as various types of smart bracelets and smart jewelry for vital sign monitoring.

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Abstract

La présente invention concerne un capteur d'empreintes digitales à ultrasons et son procédé de fabrication, ainsi qu'un dispositif électronique. Selon le procédé de fabrication du capteur d'empreintes digitales à ultrasons selon la présente demande, une tension est appliquée à un film piézoélectrique à la température de 20 °C à 30 °C pour une polarisation. Des processus d'attente pour le refroidissement et le chauffage ne sont pas nécessaires, de telle sorte que le temps de traitement de polarisation du capteur d'empreintes digitales à ultrasons pendant la production est raccourci, et l'efficacité de production est améliorée ; de plus, après que le film piézoélectrique est polarisé et structuré pour former une couche piézoélectrique, l'influence du mode de polarisation sur une seconde électrode n'a pas besoin d'être prise en considération, de telle sorte que le mode de polarisation de formation de la seconde électrode est plus flexible.
PCT/CN2022/123577 2022-09-30 2022-09-30 Capteur d'empreintes digitales à ultrasons et son procédé de fabrication, et dispositif électronique WO2024065805A1 (fr)

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PCT/CN2022/123577 WO2024065805A1 (fr) 2022-09-30 2022-09-30 Capteur d'empreintes digitales à ultrasons et son procédé de fabrication, et dispositif électronique

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PCT/CN2022/123577 WO2024065805A1 (fr) 2022-09-30 2022-09-30 Capteur d'empreintes digitales à ultrasons et son procédé de fabrication, et dispositif électronique

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Publication number Priority date Publication date Assignee Title
CN107203739A (zh) * 2017-04-14 2017-09-26 杭州士兰微电子股份有限公司 超声波传感器及其制造方法
CN109494298A (zh) * 2017-09-12 2019-03-19 南昌欧菲生物识别技术有限公司 压电层的极化方法和超声波生物识别装置的制备方法
US20200287126A1 (en) * 2019-03-07 2020-09-10 Invensense, Inc. Piezoelectric poling with temporary electrodes
CN112895433A (zh) * 2021-01-14 2021-06-04 河北工业大学 基于3d打印的柔性传感器装置及其制备方法

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN107203739A (zh) * 2017-04-14 2017-09-26 杭州士兰微电子股份有限公司 超声波传感器及其制造方法
CN109494298A (zh) * 2017-09-12 2019-03-19 南昌欧菲生物识别技术有限公司 压电层的极化方法和超声波生物识别装置的制备方法
US20200287126A1 (en) * 2019-03-07 2020-09-10 Invensense, Inc. Piezoelectric poling with temporary electrodes
CN112895433A (zh) * 2021-01-14 2021-06-04 河北工业大学 基于3d打印的柔性传感器装置及其制备方法

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