Ultrasonic fingerprint devices and electronic equipment

Abstract

This application provides an ultrasonic fingerprint device and an electronic device, which improves the packaging structure of the ultrasonic fingerprint device while ensuring its fingerprint recognition performance. The ultrasonic fingerprint device includes an ultrasonic fingerprint chip and a piezoelectric transducer above it. The piezoelectric transducer emits ultrasonic signals to a finger above the display screen and receives ultrasonic fingerprint signals carrying fingerprint information returned by the finger. The ultrasonic fingerprint chip is connected to a circuit board via leads. A spacer layer is provided between the ultrasonic fingerprint device and the display screen to form a space for accommodating the leads. The spacer layer includes a first matching layer, a second matching layer, and a third matching layer. The second matching layer is located between the first matching layer and the third matching layer. The acoustic impedance of the second matching layer is different from that of the first matching layer and also different from that of the third matching layer.

Description

[0001] This application claims priority to PCT application filed on September 13, 2022, with application number PCT / CN2022 / 118504 and entitled "Ultrasonic fingerprint device and electronic device", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of fingerprint recognition, and more specifically, to an ultrasonic fingerprint device and electronic device. Background Technology

[0003] With societal progress, mobile phones have become an indispensable electronic device in modern life. Currently, most mobile phones on the market offer one or more authentication methods, including digital passwords, gesture patterns, facial recognition, and fingerprint recognition. Among these, fingerprint recognition has become a standard feature in most mobile phones due to its convenience, fast recognition speed, and stable reliability. Fingerprint recognition has also evolved into different technological approaches, including capacitive fingerprint recognition, optical fingerprint recognition, and ultrasonic fingerprint recognition.

[0004] Because of its strong penetrating power, ultrasonic fingerprint recognition can identify not only the surface morphology of fingerprints but also signals from the dermis layer of the finger. Therefore, ultrasonic fingerprint recognition is gradually becoming a new fingerprint recognition method. However, the fingerprint recognition performance of ultrasonic fingerprint devices is significantly affected by their own structure and their integration with electronic devices. Therefore, how to improve the packaging structure of ultrasonic fingerprint devices without compromising their fingerprint recognition performance has become a problem that needs to be solved. Summary of the Invention

[0005] This application provides an ultrasonic fingerprint device and an electronic device, which improves the packaging structure of the ultrasonic fingerprint device and ensures its fingerprint recognition performance.

[0006] In a first aspect, an ultrasonic fingerprint device is provided, which is disposed below the display screen of an electronic device to realize under-display ultrasonic fingerprint recognition. The ultrasonic fingerprint device includes an ultrasonic fingerprint chip and a piezoelectric transducer disposed above the ultrasonic fingerprint chip. The piezoelectric transducer is used to emit ultrasonic signals to a finger above the display screen and receive ultrasonic fingerprint signals carrying fingerprint information returned by the finger. The ultrasonic fingerprint chip is connected to a circuit board via leads. A spacer layer is provided between the ultrasonic fingerprint device and the display screen to form a space between the display screen and the ultrasonic fingerprint chip for accommodating the leads. The spacer layer includes a first matching layer, a second matching layer, and a third matching layer. The second matching layer is located between the first matching layer and the third matching layer. The acoustic impedance of the second matching layer is different from that of the first matching layer and the third matching layer.

[0007] In one implementation, the acoustic impedance of the second matching layer is less than that of the first matching layer and less than that of the third matching layer.

[0008] In one implementation, the thickness of the second matching layer is set such that the ultrasonic signal passing through the second matching layer generates a predetermined transmission phase shift, such that the phase difference between the ultrasonic signals entering the first matching layer from the second matching layer is an integer multiple of the period of the ultrasonic signal.

[0009] In one implementation, the transmission phase shift is an odd multiple of T / 4 or an integer multiple of T / 2, where T is the period of the ultrasonic signal.

[0010] In one implementation, when the ultrasonic signal enters the first matching layer from the second matching layer, the phase difference between the reflected signal and the transmitted signal formed at the interface between the second matching layer and the first matching layer is T / 4, and the transmission phase shift is an odd multiple of T / 4; or, the phase difference between the reflected signal and the transmitted signal is T / 2, and the transmission phase shift is an integer multiple of T / 2.

[0011] In one implementation, the thickness of the second matching layer is an odd multiple of λ / 4 or an integer multiple of λ / 2, where λ is the equivalent wavelength of the ultrasonic signal in the second matching layer.

[0012] In one implementation, the second mating layer includes a material layer, a first adhesive layer for bonding the material layer to the first mating layer, and a second adhesive layer for bonding the material layer to the third mating layer. The difference between the thickness of the second mating layer and an odd multiple of λ / 4 is a preset value, or the difference between the thickness of the second mating layer and an integer multiple of λ / 2 is the preset value, and the preset value is determined based on the difference in the transmission speed of the ultrasonic signal in the first adhesive layer, the second adhesive layer, and the material layer.

[0013] In one implementation, the acoustic impedance of the material layer of the second matching layer is less than or equal to 10 MRayl, for example including at least one of the following materials: PET, PI, FR4, acrylic.

[0014] In one implementation, the first matching layer is bonded to the display screen via a third adhesive layer, and the third matching layer is bonded to the ultrasonic fingerprint device via a fourth adhesive layer.

[0015] In one implementation, the acoustic impedance of the first matching layer and the acoustic impedance of the third matching layer are greater than or equal to 30 MRayl; and / or, the thickness of the first matching layer and the thickness of the third matching layer are less than or equal to 10 μm.

[0016] In one implementation, the first matching layer and the third matching layer are made of the same or different materials, and the first matching layer and the third matching layer include at least one of the following materials: gold, silver, copper, steel, iron, nickel, palladium, copper-nickel alloy, and nickel-palladium-gold.

[0017] In one implementation, the first adhesive layer, the second adhesive layer, the third adhesive layer, and the fourth adhesive layer comprise at least one of the following materials: double-sided adhesive, acrylic adhesive, optical adhesive (OCA), and water-based adhesive.

[0018] In one implementation, the piezoelectric transducer includes a piezoelectric layer, an upper electrode located above the piezoelectric layer, and a lower electrode located below the piezoelectric layer, wherein the surface of the upper electrode is covered with a protective layer.

[0019] In one implementation, the piezoelectric layer is made of PVDF or PVDF-TrFE.

[0020] In one implementation, the circuit board is an FPC, and the FPC and the ultrasonic fingerprint chip are disposed on a substrate.

[0021] In one implementation, the ultrasonic fingerprint chip is a CMOS chip.

[0022] In a second aspect, an electronic device is provided, comprising: a display screen; an ultrasonic fingerprint device as described in the first aspect or any implementation thereof; and a spacer layer disposed between the ultrasonic fingerprint device and the display screen.

[0023] Based on the above technical solution, the ultrasonic fingerprint device includes an ultrasonic fingerprint chip and a piezoelectric transducer above it. The ultrasonic fingerprint chip and the circuit board are connected via COB (Chip-on-Board) connection. The two ends of the lead are soldered and fixed to the ultrasonic fingerprint chip and the circuit board, respectively. By setting a spacer layer between the ultrasonic fingerprint device and the display screen, the space between the display screen and the ultrasonic fingerprint chip is increased to accommodate the lead, effectively preventing the arc height of the lead from affecting the integration between the display screen and the ultrasonic fingerprint device. To reduce the attenuation of the ultrasonic signal in the spacer layer, this application uses a three-layer spacer layer structure, including a first matching layer, a third matching layer, and a second matching layer located between the first and third matching layers. By selecting appropriate materials, the acoustic impedance of the first and third matching layers is different from that of the second matching layer. This allows the ultrasonic signal to be reflected multiple times at the interfaces between the second and first matching layers and between the second and third matching layers, and finally transmitted into the first matching layer. This results in amplitude superposition of the ultrasonic signal within the first matching layer, increasing the intensity of the ultrasonic signal. Similarly, this also increases the intensity of the ultrasonic fingerprint signal carrying fingerprint information entering the third matching layer, solving the problem of significant signal attenuation caused by the spacer layer. Attached Figure Description

[0024] Figure 1 This is a schematic structural diagram of the ultrasonic fingerprint device according to an embodiment of this application.

[0025] Figure 2 This is a schematic diagram of the spacer layer in an embodiment of this application.

[0026] Figure 3 This is a schematic diagram of the signal transmission path in the spacer layer.

[0027] Figure 4 This is a schematic block diagram of an electronic device according to an embodiment of this application. Detailed Implementation

[0028] The technical solutions in this application will now be described with reference to the accompanying drawings.

[0029] Ultrasonic fingerprint detection is based on piezoelectric transducers, which typically have a sandwich structure, including an upper electrode, a lower electrode, and a piezoelectric layer between the upper and lower electrodes. Piezoelectric transducers require complex transmitting and receiving circuits to function. These circuits can be fabricated as application-specific integrated circuits (ASICs) to reduce system size and complexity. Integrating the piezoelectric transducer with the integrated circuit further reduces system size and minimizes noise from the interconnects between the transducer and the circuitry. This application's embodiment employs a "piezoelectric transducer + CMOS chip" structure, combined with specific integration processes, to form an ultrasonic fingerprint device.

[0030] Figure 1 A schematic diagram shows the ultrasonic fingerprint device mounted directly beneath the display screen. Figure 1 As shown, the ultrasonic fingerprint device 200 is disposed below the display screen 100. The ultrasonic fingerprint device 200 includes an ultrasonic fingerprint chip 210 and a piezoelectric transducer 220 located above the ultrasonic fingerprint chip 210. The ultrasonic fingerprint chip 210 is connected to the circuit board 230 via a lead 211. The lead 211 has a certain height. To avoid the lead 211, a spacer layer 300 is provided between the piezoelectric transducer 220 and the display screen 100. The thickness of the spacer layer 300 is set such that the height difference between the upper surface of the ultrasonic fingerprint chip 210 and the lower surface of the display screen 100 is greater than the height of the lead 211, so as to avoid the display screen 100 pressing on the lead 211 and causing the lead 211 to short-circuit or break.

[0031] When excited, the piezoelectric transducer 220 emits an ultrasonic signal with a specific frequency and length, typically a sine wave, a cosine wave, or a combination of both. The following description uses a sine wave as an example to illustrate the technical solution of this application. The ultrasonic signal passes through the spacer layer 300 and the display screen 100 before reaching the finger. After being reflected or scattered by the fingerprint ridges and valleys, it forms an echo signal carrying fingerprint information. This echo signal then passes through the display screen 100, the spacer layer 300, and the piezoelectric transducer 220, and is received by the ultrasonic fingerprint chip 210. After appropriate processing, a fingerprint image of the finger is obtained.

[0032] When the spacer layer 300 uses a single adhesive, such as double-sided tape, acrylic adhesive, optically clear adhesive (OCA), or water-based adhesive, or a combination of adhesive and fillers such as polyethylene terephthalate (PET), polyimide (PI), or epoxy glass cloth laminate (FR4), the adhesive and fillers such as PET, PI, and FR4 significantly attenuate the ultrasonic signal. This attenuation is even greater when the adhesive layer is thick. Before the ultrasonic signal emitted by the piezoelectric transducer 220 reaches the lower surface of the display screen 100 through the spacer layer 300, the ultrasonic signal is attenuated. The echo signal carrying fingerprint information exits from the lower surface of the display screen 100, passes through the spacer layer 300, and undergoes another attenuation before reaching the ultrasonic transducer 220. This results in a very weak effective signal received by the ultrasonic fingerprint chip 210, ultimately leading to poor fingerprint image quality.

[0033] This application aims to provide an ultrasonic fingerprint device, wherein the spacer layer 300 between the device and the display screen has a three-layer structure. By reasonably matching the acoustic impedance and / or thickness of each layer material, the ultrasonic signal is enhanced to a certain extent when passing through the spacer layer 300, thus solving the problem of large attenuation of the ultrasonic signal by the spacer layer 300.

[0034] Figure 2 A schematic structural diagram of an ultrasonic fingerprint device according to an embodiment of this application is shown. Figure 2 As shown, the ultrasonic fingerprint device 200 is attached directly below the display screen 100 of the electronic device to achieve under-display ultrasonic fingerprint recognition. The ultrasonic fingerprint device 200 includes an ultrasonic fingerprint chip 210 and a piezoelectric transducer 220 disposed above the ultrasonic fingerprint chip 210. The piezoelectric transducer 220 is used to emit ultrasonic signals to the finger above the display screen 100 and receive the ultrasonic fingerprint signal carrying fingerprint information returned by the finger.

[0035] The piezoelectric transducer 220 typically includes a piezoelectric layer, an upper electrode located above the piezoelectric layer, and a lower electrode located below the piezoelectric layer. The upper electrode is a metal or metal paste coating, such as silver paste, formed on the upper surface of the piezoelectric layer by sputtering, and it is a full-surface electrode; the lower electrode can be, for example, a metal electrode array formed on the upper surface of the ultrasonic fingerprint chip 210 by sputtering or vapor deposition, and the material of the metal electrode can be aluminum or gold, etc.

[0036] Furthermore, a protective layer can be applied to the surface of the upper electrode to protect the upper electrode and the piezoelectric layer, preventing penetration and failure of the piezoelectric layer and the upper electrode under conditions such as high temperature and high humidity, thereby improving the security of the ultrasonic fingerprint device 200. The protective layer can be formed of, for example, a polymeric organic material or an inorganic material, and is also called a passivation layer.

[0037] The piezoelectric layer is formed of piezoelectric materials, such as polyvinylidene fluoride (PVDF) or polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE).

[0038] The ultrasonic fingerprint chip 210 is an application-specific integrated circuit (ASIC) for ultrasonic fingerprint recognition, such as a complementary metal-oxide-semiconductor (CMOS) chip. When a CMOS chip is used as the ultrasonic fingerprint chip 210, since it uses a silicon substrate, wire bonding can be achieved on the silicon substrate. The ultrasonic fingerprint chip 210 and the circuit board 600 can be connected in a chip-on-board (COB) manner, so that the ultrasonic fingerprint chip 210 and the circuit board 230 are connected by leads 211, thereby realizing the interconnection between the piezoelectric transducer 220 and the circuit board 230.

[0039] COB (Chip-on-Board) refers to a method of electronically connecting chips to a circuit board using wires. Also known as bonding or wire bonding, it offers advantages such as simplicity and low cost. For example... Figure 1 As shown, the two ends of the lead 211 are soldered and fixed to the ultrasonic fingerprint chip 210 and the circuit board 230, respectively. The upper and lower electrodes of the piezoelectric transducer 220 can be interconnected with the circuit board 230 through the lead 211 on the ultrasonic fingerprint chip 210. The lead 211 is also called a bonding wire, and can be, for example, a gold wire or an aluminum wire.

[0040] Since the upper electrode 3202 is typically made of materials such as silver paste, its density is very low and it does not support wire bonding. Therefore, it needs to be led out to the surface of the ultrasonic fingerprint chip 210 and then connected to the lead 211. In one implementation, the surface of the ultrasonic fingerprint chip 210 is provided with a driving trace. The upper electrode is led out from the upper surface of the piezoelectric layer to the surface of the ultrasonic fingerprint chip 210 and connected to the lead 211 through the driving trace. One end of the lead 211 is connected to the driving trace at a pad on the surface of the ultrasonic fingerprint chip 210, and the other end of the lead 211 is connected to the circuit board 230. This achieves the interconnection between the piezoelectric transducer 220 and the circuit board 230.

[0041] Typically, the lead 211 has a certain arc height. When the arc height exceeds the upper surface of the ultrasonic fingerprint device 200, the ultrasonic fingerprint device 200 cannot be properly attached to the lower surface of the display screen 100. Therefore, in this embodiment, a spacer layer 300 is provided between the upper surface of the ultrasonic fingerprint device 200 and the lower surface of the display screen 100. The spacer layer 300 increases the space between the display screen 100 and the ultrasonic fingerprint chip 210, accommodating the lead 211, thereby effectively preventing the arc height of the lead 211 from affecting the integration between the display screen 100 and the ultrasonic fingerprint device 200. For example, as... Figure 2As shown, a spacer layer 300 is provided between the ultrasonic fingerprint device 200 and the display screen 100 so that a space H for accommodating the lead wire 211 is formed between the display screen 100 and the ultrasonic fingerprint chip 210.

[0042] During fingerprint recognition, the driving signal generated by circuit board 230 is applied to the upper and lower electrodes of piezoelectric transducer 220 via lead 211. Under the action of this driving signal, the piezoelectric layer of piezoelectric transducer 220 vibrates based on the piezoelectric effect, thereby emitting an ultrasonic signal to the finger above display screen 100. This ultrasonic signal is transmitted to the surface of the finger and is reflected or scattered at the fingerprint valleys and ridges, returning an ultrasonic fingerprint signal carrying fingerprint information. When the ultrasonic fingerprint signal is transmitted to the piezoelectric layer, a potential difference is generated between the upper and lower electrodes based on the inverse piezoelectric effect, resulting in a corresponding electrical signal. Circuit board 230 receives this electrical signal via lead 211. After processing this electrical signal, a fingerprint image can be obtained. Circuit board 30 can be, for example, a flexible printed circuit (FPC).

[0043] The display screen 100 may include an emissive layer and a cover plate. The emissive layer may be formed of, for example, an organic light-emitting diode (OLED) or an active matrix organic light-emitting diode (AMOLED). The cover plate covers the emissive layer. The ultrasonic fingerprint device 200 may be disposed below the emissive layer, or it may be disposed alongside the emissive layer under different areas of the cover plate, thus enabling under-display ultrasonic fingerprint recognition.

[0044] like Figure 2 As shown, the ultrasonic fingerprint device 200 may further include a substrate 240, which may be, for example, a steel plate. The ultrasonic fingerprint chip 210 and the circuit board 230 are disposed on the substrate 240. The ultrasonic fingerprint chip 210 and the substrate 240 can be connected by an adhesive layer such as glue, die attach film (DAF), or epoxy resin. The substrate 240 provides support for the ultrasonic fingerprint device 200 and the circuit board 230 and improves the structural stability of the ultrasonic fingerprint device 200; therefore, it can also be referred to as a reinforcing plate.

[0045] Based on the above description, by setting a spacer layer 300 between the ultrasonic fingerprint device 200 and the display screen 100, the space between the display screen 100 and the ultrasonic fingerprint chip 210 is increased to accommodate the lead wire 211, which can effectively prevent the arc height of the lead wire 211 from affecting the integration between the display screen 100 and the ultrasonic fingerprint device 200.

[0046] Ultrasonic signals attenuate when passing through the spacer layer 300. To reduce this attenuation, this embodiment further designs and improves the spacer layer 300. Specifically, a three-layer structure is adopted for the spacer layer 300, including a first matching layer 310, a third matching layer 330, and a second matching layer 320 located between the first and third matching layers 310 and 330. By selecting appropriate materials, the acoustic impedance of the first and third matching layers 310 and 330 is different from that of the second matching layer 320. This allows the ultrasonic signal to be reflected multiple times at the interfaces between the second and third matching layers 320 and 310, and between the second and third matching layers 320 and 330, and finally transmitted into the first matching layer 310. This results in amplitude superposition of the ultrasonic signal within the first matching layer 310, increasing the intensity of the ultrasonic signal. Similarly, this also increases the intensity of the ultrasonic fingerprint signal carrying fingerprint information entering the third matching layer 330, solving the problem of significant signal attenuation caused by the spacer layer 300.

[0047] The spacer layer 300 of the present application embodiment will be described in detail below.

[0048] The spacer layer 300 includes a first matching layer 310, a second matching layer 320, and a third matching layer 330, with the second matching layer 320 located between the first matching layer 310 and the third matching layer 330. The acoustic impedance of the second matching layer 320 is different from that of the first matching layer 310 and also different from that of the third matching layer 330.

[0049] In one implementation, the materials of the first matching layer 310 and the third matching layer 330 are both high acoustic impedance materials, for example, acoustic impedance greater than or equal to 30 MRayl; the material of the second matching layer 320 is a low acoustic impedance material, for example, acoustic impedance less than or equal to 10 MRayl.

[0050] The materials of the first matching layer 310 and the third matching layer 330 may include at least one of the following materials: gold, silver, copper, steel, iron, nickel, palladium, copper-nickel alloy, and nickel-palladium-gold. The material of the third matching layer 330 may be the same as or different from the material of the first matching layer 310.

[0051] like Figure 2 As shown, the first matching layer 310 and the display screen 100 can be bonded together by the third adhesive layer 343, and the third matching layer 330 and the ultrasonic fingerprint device 200 can be bonded together by the fourth adhesive layer 344.

[0052] The second mating layer 320 comprises a material layer 321 and a first adhesive layer 341 and a second adhesive layer 342 located on both sides of the material layer 321. The first adhesive layer 341 is used for bonding the material layer 321 to the first mating layer 310, and the second adhesive layer 342 is used for bonding the material layer 321 to the third mating layer 330. The material layer 321 may include at least one of the following materials: polyethylene terephthalate (PET), polyimide (PI), epoxy glass cloth laminate (FR4), or acrylic adhesive.

[0053] The first adhesive layer 341, the second adhesive layer 342, the third adhesive layer 343 and the fourth adhesive layer 344 mentioned above can be used to fix and connect the stacked layers on both sides, and can also prevent air gaps from forming between the stacked layers on both sides, so as to ensure the signal transmission performance in the stacked layers.

[0054] The materials of the first adhesive layer 341, the second adhesive layer 342, the third adhesive layer 343, and the fourth adhesive layer 344 may be the same or at least partially different. For example, the first adhesive layer 341, the second adhesive layer 342, the third adhesive layer 343, and the fourth adhesive layer 344 may include at least one of double-sided adhesive, acrylic adhesive, optical adhesive (OCA), and water-based adhesive.

[0055] To reduce signal attenuation when passing through the first adhesive layer 341, the second adhesive layer 342, the third adhesive layer 343, and the fourth adhesive layer 344, the thicknesses of the first adhesive layer 341, the second adhesive layer 342, the third adhesive layer 343, and the fourth adhesive layer 344 can be set to be relatively small, for example, less than or equal to 10 μm.

[0056] Because the acoustic impedance of the second matching layer 320 differs from that of the first matching layer 310 and also differs from that of the third matching layer 330, reflective interfaces can be formed between the second matching layer 320 and the third matching layer 330, as well as between the second matching layer 320 and the first matching layer 310. The ultrasonic signal is reflected multiple times at these interfaces and oscillates within the second matching layer 320, forming multiple transmitted signals. These transmitted signals enter the first matching layer 310 and are superimposed in amplitude within it, thereby increasing the intensity of the ultrasonic signal entering the first matching layer 310. Similarly, the intensity of the ultrasonic fingerprint signal entering the third matching layer 330 can also be increased.

[0057] In one implementation, the thickness of the first matching layer 310 and the thickness of the third matching layer 330 can be set to be relatively small, for example, less than or equal to 10 μm, in order to reduce the attenuation of the signal when passing through the first matching layer 310 and the third matching layer 330.

[0058] In one implementation, the thickness of the second matching layer 320 is set such that the ultrasonic signal passing through the second matching layer 320 generates a predetermined transmission phase shift, so that the phase difference between the ultrasonic signals entering the first matching layer 310 from the second matching layer 320 is an integer multiple of the period T of the ultrasonic signal. When a series of sinusoidal signals of the same frequency with a phase difference of an integer multiple of period T enter the first matching layer 310 from the second matching layer 320, positive linear superposition in amplitude can be achieved, thereby resulting in enhancement.

[0059] Typically, when an ultrasonic signal travels from a material with low acoustic impedance to a material with high acoustic impedance, the reflected signal at the interface between the two materials will exhibit a phase difference, known as a reflection phase shift, while the phase difference of the transmitted signal remains unchanged. This reflection phase shift is usually related to the material with low acoustic impedance and the material with high acoustic impedance.

[0060] When the first matching layer 310 and the third matching layer 330 are made of the high acoustic impedance material described above, and the second matching layer 320 is made of the low acoustic impedance material described above, the reflection phase shift may be T / 2, T / 4, or other values.

[0061] The ultrasonic signal passing through the second matching layer 320 generates a predetermined transmission phase shift. This transmission phase shift is related to the reflection phase shift generated at the interface between the second matching layer 320 and the first matching layer 310 or at the interface between the second matching layer 320 and the third matching layer 330. The transmission phase shift can be determined based on the reflection phase shift, so that the phase difference between the ultrasonic signals entering from the second matching layer 320 to the first matching layer 310 is an integer multiple of the period T.

[0062] Both the reflection phase shift and the transmission phase shift are related to the period T of the ultrasonic signal. For example, the transmission phase shift can be an odd multiple of T / 4 or an integer multiple of T / 2.

[0063] If the reflected phase shift generated at the interface between the second matching layer 320 and the first matching layer 310 when the ultrasonic signal enters the first matching layer 310 from the second matching layer 320 is T / 4, then the transmission phase shift is an odd multiple of T / 4, i.e. (2n+1)T / 4, where n is 0 or a positive integer.

[0064] The thickness of the second matching layer 320 is set such that the transmission phase shift is (2n+1)T / 4. It can be understood that the thicknesses of the first adhesive layer 341 and the second adhesive layer 342 in the second matching layer 320 are very small compared to the material layer 321. Therefore, the acoustic difference between them and the material layer 321 can be ignored. Assuming that the transmission speed of the ultrasonic signal in the second matching layer 320 is constant and always ν, where ν is the transmission speed of the ultrasonic signal in the material layer 321, then the thickness of the second matching layer 320 is D = [(2n+1)T / 4] × ν = [(2n+1)(λ / ν) / 4] × ν = (2n+1)λ / 4, where λ is the wavelength of the ultrasonic signal in the material layer 321.

[0065] If the reflection phase shift generated at the interface between the second matching layer 320 and the first matching layer 310 when the ultrasonic signal enters the first matching layer 310 from the second matching layer 320 is T / 2, then the transmission phase shift is an integer multiple of T / 2, i.e., nT / 2, where n is a positive integer. Similarly, the thickness D of the second matching layer 320 is set to nλ / 2.

[0066] See Figure 3 The acoustic impedance of the third matching layer 330 is greater than that of the second matching layer 320, and interface A is formed between the third matching layer 330 and the second matching layer 320; the acoustic impedance of the first matching layer 310 is greater than that of the second matching layer 320, and interface B is formed between the first matching layer 310 and the second matching layer 320. Assuming the ultrasonic signal emitted by the piezoelectric transducer 302 is a sinusoidal signal, the signal I0 incident on the third matching layer 330 of the spacer layer 300 is generated when signal I0 is incident on interface A, producing a reflected signal R0 and a transmitted signal T0, where signal T0 enters the second matching layer 320. When signal T0 at interface A is transmitted to interface B between the second matching layer 320 and the first matching layer 310, it becomes signal T0'. Signal T0' generates a transmitted signal Tt1 and a first reflected signal Tr1 at interface B. Signal Tt1 enters the first matching layer 310. When the reflected signal Tr1 returns from interface B to interface A, it becomes signal Tr1'. Signal Tr1' generates a second reflected signal Tr2 at interface A. When signal Tr2 returns from interface A to interface B, it becomes Tr2'. Tr2' generates a transmitted signal Tt2 and a third reflected signal Tr3 at interface B. Signal Tt2 enters the first matching layer 310. The reflected signal Tr3 continues to be reflected within the second matching layer 320 until the reflected signal within the second matching layer 320 attenuates to 0. Finally, signal Tt entering the first matching layer 310 from the second matching layer 320 is the superposition of signals Tt1, Tt2, ..., Ttk that have passed through interface B multiple times, i.e., Tt = Tt1 + Tt2 + ... + Ttk, where k is a positive integer.

[0067] During the above process, the ultrasonic signal attenuates as it propagates within the second matching layer 320. Reflection and transmission at interfaces A and B result in reflection attenuation and transmission attenuation, respectively. When the ultrasonic signal is incident from interface B to the first matching layer 310 and from interface A to the third matching layer 330, the reflected signals at interfaces A and B will have a phase difference relative to the incident signals, while the transmitted signals will not have a phase difference.

[0068] Assuming the reflected signals at interfaces A and B have a phase difference of T / 4 relative to the incident signals, and the thickness of the second matching layer 320 is set such that the transmission phase shift of the ultrasonic signal passing through the second matching layer 320 is (2n+1)T / 4, then assuming the phase of the signal I0 entering the third matching layer 330 is... Then we can get:

[0069]

[0070]

[0071]

[0072]

[0073]

[0074]

[0075]

[0076] ...;

[0077]

[0078]

[0079] Where k is a positive integer and n is 0 or a positive integer.

[0080] It can be seen that the signals Tt1, Tt2, ..., Ttk entering the first matching layer 310 from the second matching layer 320 are a series of sinusoidal signals of the same frequency with gradually decreasing amplitude and phase differences of (n+1) periods T, i.e. These series of sinusoidal signals of the same frequency, which are phased by (n+1) periods T, can be linearly superimposed in the positive direction in terms of amplitude, thus obtaining an enhanced transmission signal Tt.

[0081] The above example uses a reflection phase shift of T / 4 at interfaces A and B. More generally, it is as follows:

[0082]

[0083]

[0084]

[0085] in, The phase shift caused by the transmission of the ultrasonic signal in the second matching layer 320, or the phase shift caused by the transmission of the ultrasonic signal between the first matching layer 310 and the third matching layer 330, is related to the thickness of the second matching layer.

[0086] and These are the reflection phase shifts at interfaces A and B, respectively, and these reflection phase shifts are related to the materials of the first matching layer 310, the second matching layer 320, and the third matching layer 330.

[0087] For example, hour, That is, when the reflection phase shift is one-quarter of a period, the thickness of the second matching layer 320 is an odd multiple of one-quarter of the wavelength; for example, hour, That is, when the reflection phase shift is half a period, the thickness of the second matching layer 320 is an integer multiple of half the wavelength.

[0088] The signal Tt travels from the first matching layer 310 through the display screen 100 to the contact surface between the display screen 100 and the finger. After being reflected by the fingerprint ridges and valleys, it forms an ultrasonic fingerprint signal carrying fingerprint pattern information. The ultrasonic fingerprint signal travels through the display screen 100, the spacer layer 300, and the piezoelectric transducer 220 to the ultrasonic fingerprint chip 210, where it is received. During the process of the ultrasonic fingerprint signal passing through the spacer layer 300, the signal transmitted from the first matching layer 310 to the second matching layer 320 is also reflected multiple times in the second matching layer 320, and finally achieves positive linear superposition in amplitude within the third matching layer 330, thereby obtaining an enhanced transmission signal.

[0089] In this embodiment, the thickness D of the second matching layer 320 refers to the sum of the thickness D1 of the material layer 321, the thickness D2 of the first adhesive layer 341, and the thickness D3 of the second adhesive layer 342. However, since the transmission speed of the ultrasonic signal in the material layer 321 is different from that in the first adhesive layer 341 and the second adhesive layer 342 when the ultrasonic signal passes through the second matching layer 320, the thickness D of the second matching layer 320 can be further adjusted in order to make the phase shift caused by the signal passing through the second matching layer 320 meet the above conditions.

[0090] by For example, without considering the acoustic differences between the first adhesive layer 341 and the second adhesive layer 342 and the material layer 321, the theoretical thickness D of the second matching layer 320 should be D=(2n+1)λ / 4, and can be set to D1+D2+D3=(2n+1)λ / 4.

[0091] When considering the acoustic differences between the first adhesive layer 341 and the second adhesive layer 342 and the material layer 321, if the transmission speed of the ultrasonic signal in the first adhesive layer 341 and the second adhesive layer 342 is less than its transmission speed in the material layer 321, the thickness D1 of the material layer 321 can be appropriately reduced. The actual thickness D' of the second matching layer 320 will be slightly less than D = (2n+1)λ / 4, so that the total phase shift caused by the signal passing through the material layer 321, the first adhesive layer 341 and the second adhesive layer 342 is (2n+1)T / 4. If the transmission speed of the ultrasonic signal in the first adhesive layer 341 and the second adhesive layer 342 is greater than its transmission speed in the material layer 321, the thickness D1 of the material layer 321 can be appropriately increased. Then the actual thickness D' of the second matching layer 320 will be slightly greater than D = (2n+1)λ / 4, so that the total phase shift caused by the signal passing through the material layer 321, the first adhesive layer 341 and the second adhesive layer 342 is (2n+1)T / 4.

[0092] In this embodiment, the thicknesses of the first adhesive layer 341, the second adhesive layer 342, the third adhesive layer 343, the fourth adhesive layer 344, the first matching layer 310, and the third matching layer 330 can be set to be small so that the signal attenuation in these stacked layers is smaller.

[0093] like Figure 4 As shown, this application also provides an electronic device 400, which includes: a display screen 100; an ultrasonic fingerprint device 200 in any of the above implementations; and a spacer layer 300 disposed between the ultrasonic fingerprint device 200 and the display screen 100.

[0094] By way of example and not limitation, the electronic devices in 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). The wearable smart devices include fully functional, large-sized devices that can achieve complete or partial functionality without relying on a smartphone, such as smartwatches or smart glasses, as well as devices that focus on only a specific 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.

[0095] It should be noted that, without conflict, the various embodiments and / or technical features described in this application can be arbitrarily combined with each other, and the resulting technical solutions should also fall within the protection scope of this application.

[0096] The systems, apparatuses, and methods disclosed in the embodiments of this application can be implemented in other ways. For example, some features of the method embodiments described above can be ignored or not performed. The apparatus embodiments described above are merely illustrative, and the division of units is only a logical functional division. In actual implementation, there may be other division methods, and multiple units or components may be combined or integrated into another system. In addition, the coupling between units or between components can be direct coupling or indirect coupling, including electrical, mechanical, or other forms of connection.

[0097] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working process and technical effects of the above-described apparatus and equipment can be referred to the corresponding processes and technical effects in the foregoing method embodiments, and will not be repeated here.

[0098] It should be understood that the specific examples in the embodiments of this application are only for the purpose of helping those skilled in the art to better understand the embodiments of this application, and are not intended to limit the scope of the embodiments of this application. Those skilled in the art can make various improvements and modifications based on the above embodiments, and all such improvements or modifications fall within the protection scope of this application.

[0099] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. An ultrasonic fingerprint device, characterized in that, The ultrasonic fingerprint device is located below the display screen of the electronic device to achieve under-display ultrasonic fingerprint recognition. The ultrasonic fingerprint device includes an ultrasonic fingerprint chip and a piezoelectric transducer disposed above the ultrasonic fingerprint chip. The piezoelectric transducer is used to emit ultrasonic signals to the finger above the display screen and receive ultrasonic fingerprint signals carrying fingerprint information returned by the finger. The ultrasonic fingerprint chip is connected to the circuit board via leads. A spacer layer is provided between the upper surface of the ultrasonic fingerprint device and the lower surface of the display screen to form a space between the display screen and the ultrasonic fingerprint chip for accommodating the lead wire. The spacer layer includes a first matching layer, a second matching layer, and a third matching layer. The second matching layer is located between the first matching layer and the third matching layer. The acoustic impedance of the second matching layer is less than that of the first matching layer and less than that of the third matching layer. The thickness of the second matching layer is set such that the ultrasonic signal passing through the second matching layer generates a predetermined transmission phase shift, so that the phase difference between the ultrasonic signals entering the first matching layer from the second matching layer is an integer multiple of the period of the ultrasonic signal. The first matching layer is disposed above the second matching layer, and the third matching layer is disposed below the second matching layer.

2. The ultrasonic fingerprint device according to claim 1, characterized in that, The transmission phase shift is an odd multiple of T / 4 or an integer multiple of T / 2, where T is the period of the ultrasonic signal.

3. The ultrasonic fingerprint device according to claim 2, characterized in that, When the ultrasonic signal enters the first matching layer from the second matching layer, the phase difference between the reflected and transmitted signals formed at the interface between the second and first matching layers is T / 4, and the transmission phase shift is an odd multiple of T / 4; or... The phase difference between the reflected signal and the transmitted signal is T / 2, and the transmission phase shift is an integer multiple of T / 2.

4. The ultrasonic fingerprint device according to claim 2, characterized in that, The second mating layer includes a material layer, a first adhesive layer for bonding the material layer to the first mating layer, and a second adhesive layer for bonding the material layer to the third mating layer. The thickness of the second matching layer is an odd multiple of λ / 4 or an integer multiple of λ / 2, where λ is the wavelength of the ultrasonic signal in the material layer.

5. The ultrasonic fingerprint device according to claim 2, characterized in that, The second mating layer includes a material layer, a first adhesive layer for bonding the material layer to the first mating layer, and a second adhesive layer for bonding the material layer to the third mating layer. The difference between the thickness of the second matching layer and an odd multiple of λ / 4 is a preset value, or the difference between the thickness of the second matching layer and an integer multiple of λ / 2 is the preset value. The preset value is determined based on the difference in the transmission speed of the ultrasonic signal in the first adhesive layer, the second adhesive layer and the material layer, where λ is the wavelength of the ultrasonic signal in the material layer.

6. The ultrasonic fingerprint device according to claim 5, characterized in that, The acoustic impedance of the material layer is less than or equal to 10 MRayl.

7. The ultrasonic fingerprint device according to claim 6, characterized in that, The material layer includes at least one of the following materials: Polyethylene terephthalate (PET), polyimide (PI), epoxy glass cloth laminate (FR4), acrylic.

8. The ultrasonic fingerprint device according to claim 1, characterized in that, The first matching layer is bonded to the display screen via a third adhesive layer, and the third matching layer is bonded to the ultrasonic fingerprint device via a fourth adhesive layer.

9. The ultrasonic fingerprint device according to claim 8, characterized in that, The acoustic impedance of the first matching layer and the acoustic impedance of the third matching layer are greater than or equal to 30 MRayl; and / or the thickness of the first matching layer and the thickness of the third matching layer are less than or equal to 10 μm.

10. The ultrasonic fingerprint device according to claim 9, characterized in that, The first matching layer and the third matching layer may be made of the same or different materials, and the first matching layer and the third matching layer include at least one of the following materials: Gold, silver, copper, steel, iron, nickel, palladium, copper-nickel alloys, nickel-palladium-gold.

11. The ultrasonic fingerprint device according to claim 5, characterized in that, The first adhesive layer and the second adhesive layer comprise at least one of the following materials: Double-sided tape, acrylic adhesive, optical adhesive (OCA), and water-based adhesive.

12. The ultrasonic fingerprint device according to claim 8, characterized in that, The third adhesive layer and the fourth adhesive layer comprise at least one of the following materials: Double-sided tape, acrylic adhesive, optical adhesive (OCA), and water-based adhesive.

13. The ultrasonic fingerprint device according to any one of claims 1 to 10, characterized in that, The piezoelectric transducer includes a piezoelectric layer, an upper electrode located above the piezoelectric layer, and a lower electrode located below the piezoelectric layer, with the surface of the upper electrode covered by a protective layer.

14. The ultrasonic fingerprint device according to claim 13, characterized in that, The piezoelectric layer is made of polyvinylidene fluoride (PVDF); or, the piezoelectric layer is made of polyvinylidene fluoride-trifluoroethylene copolymer (PVDF-TrFE).

15. The ultrasonic fingerprint device according to any one of claims 1 to 10, characterized in that, The circuit board is a flexible printed circuit board (FPC), and the FPC and the ultrasonic fingerprint chip are disposed on the substrate.

16. The ultrasonic fingerprint device according to any one of claims 1 to 10, characterized in that, The ultrasonic fingerprint chip is a complementary metal-oxide-semiconductor (CMOS) chip.

17. An electronic device, characterized in that, include: Display screen; as well as, The ultrasonic fingerprint device according to any one of claims 1 to 16; as well as, A spacer layer is disposed between the ultrasonic fingerprint device and the display screen.

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