Ultrasonic fingerprint recognition device and ultrasonic fingerprint recognition chip

Abstract

This specification discloses an ultrasonic fingerprint recognition device and an ultrasonic fingerprint recognition chip. The device includes: an ultrasonic sensor for transmitting and receiving ultrasonic signals. The ultrasonic sensor has two opposite sides. A first dielectric layer is provided on one side, and a second dielectric layer is provided on the other side. A third dielectric layer is provided above the second dielectric layer facing away from the ultrasonic sensor. The ultrasonic sensor forms a structure for ultrasonic resonance between the first dielectric layer and the second dielectric layer. The ultrasonic signal emitted by the ultrasonic sensor can be transmitted out from the second dielectric layer, enter the third dielectric layer after resonance, and be reflected by an object above the third dielectric layer and then enter the ultrasonic sensor. This application can enhance the acoustic intensity of the ultrasonic signal and improve the signal-to-noise ratio of the fingerprint image.

Description

Technical Field

[0001] This application relates to the field of fingerprint recognition technology, and particularly to an ultrasonic fingerprint recognition device and an ultrasonic fingerprint recognition chip. Background Art

[0002] The description in this part only provides background information related to the disclosure of this specification, and does not constitute prior art.

[0003] The information carrier of ultrasonic fingerprint recognition technology is ultrasonic waves. Ultrasonic waves can penetrate multiple media, so they can penetrate the epidermal layer and detect the three-dimensional details of fingerprints. Such live fingerprint recognition enhances security. At the same time, since ultrasonic recognition is not affected by the dirt that may exist on the finger, the usability of fingerprint recognition is greatly improved.

[0004] When the ultrasonic fingerprint recognition module is in use, it needs to be placed under the detection area (usually a specific area on the display screen). The acoustic impedance of the finger ridge is quite different from that of the air in the finger valley. Therefore, the reflectivity of ultrasonic waves at the finger ridge and the finger valley is different, and thus the reflected sound waves will be different. Therefore, after circuit signal processing, a fingerprint image containing the information of the finger ridge and the finger valley can be obtained.

[0005] For the ultrasonic fingerprint recognition module, it currently includes a detection part and a signal processing part, and the detection part and the signal processing part are two separate chips. With users pursuing a better experience, the detection part currently uses a fingerprint recognition chip with a large TFT array. The fingerprint recognition chip with a large TFT array generally uses a glass substrate as the underlying layer, and TFT pixel circuits are fabricated on the glass substrate. After fabrication, they are respectively connected to the circuit board with the chips in the signal processing part. This leads to the following problems:

[0006] 1) Using the TFT circuit process, the active layer is polysilicon, and the grain size is smaller than the CD size of the TFT pixel circuit. Therefore, grain boundaries may exist at the channel of each thin film transistor. The grain boundaries are material defects and will randomly capture electrons, thus generating electrical noise, resulting in a low signal-to-noise ratio of the ultrasonic fingerprint recognition module;

[0007] 2) The TFT circuit is limited by the CD size (the CD size is relatively large), and the required pixel unit size is relatively large. Therefore, the resolution of the module imaging is relatively low; at the same time, the relatively large pixel unit size results in a relatively large circuit parasitic capacitance, reducing the amount of charge signal obtained;

[0008] 3) Since it involves the separate packaging of the detection part and the signal processing part, multiple I / O interfaces need to be reserved on the chips in both the detection part and the signal processing part, increasing the difficulty of packaging.

[0009] It should be noted that the above introduction to the technical background is only for the convenience of clearly and completely explaining the technical solutions in this specification and facilitating the understanding of those skilled in the art. It cannot be considered that the above technical solutions are well-known to those skilled in the art merely because these solutions are described in the background art section of this specification. Summary of the Invention

[0010] To solve at least one technical problem existing in the prior art, an object of the present application is to provide an ultrasonic fingerprint recognition device and an ultrasonic fingerprint recognition chip, which can enhance the acoustic intensity of ultrasonic signals and improve the signal-to-noise ratio of fingerprint images.

[0011] To achieve the above at least one object, the present application adopts the following technical solutions:

[0012] An ultrasonic fingerprint recognition device includes:

[0013] An ultrasonic sensor for transmitting and receiving ultrasonic signals. The ultrasonic sensor has two opposite sides. A first dielectric layer is provided on one side, and a second dielectric layer is provided on the other side. A third dielectric layer is provided above the second dielectric layer facing away from the ultrasonic sensor.

[0014] The ultrasonic sensor forms a structure for ultrasonic resonance between the first dielectric layer and the second dielectric layer. The ultrasonic signal emitted by the ultrasonic sensor can pass out of the second dielectric layer, enter the third dielectric layer after resonance, and enter the ultrasonic sensor after being reflected by an object above the third dielectric layer.

[0015] As a preferred embodiment, the first dielectric layer is air.

[0016] As a preferred embodiment, the ultrasonic sensor has a first surface and a second surface facing each other. The first surface is in contact with the first dielectric layer. The ultrasonic sensor includes: a protective layer, an electrode layer, and a piezoelectric layer stacked in sequence from the first surface to the second surface. The acoustic impedances of the protective layer, the electrode layer, and the piezoelectric layer are close to or equal to each other. The thickness of the ultrasonic sensor in the stacking direction is an odd multiple of one-fourth of its wavelength.

[0017] As a preferred embodiment, the protective layer, the electrode layer, and the piezoelectric layer are formed of a polymer, and the acoustic impedance of the ultrasonic sensor is 1 to 10 MRayls.

[0018] As a preferred embodiment, the electrode layer is made of a metal material, and the thickness of the electrode layer is less than 1 μm.

[0019] As a preferred embodiment, the second dielectric layer is a silicon-based substrate.

[0020] As a preferred embodiment, the substrate is rectangular with side lengths of 3 to 40 mm.

[0021] As a preferred embodiment, the silicon-based substrate has opposite third and fourth surfaces. The third surface faces the ultrasonic sensor. The third surface includes an identification area and a non-identification area. The identification area is used to arrange a CMOS pixel unit array and a bottom electrode for the electrical coupling of the CMOS pixel unit array with the ultrasonic sensor. The non-identification area is used to form a signal processing circuit electrically connected to the CMOS pixel unit array and the ultrasonic sensor. The signal processing circuit is used to provide a driving voltage for the ultrasonic sensor and process the electrical signals sent out by the CMOS pixel unit array.

[0022] As a preferred embodiment, a circuit film layer for forming a CMOS pixel unit array and the signal processing circuit is arranged on the third surface. The acoustic impedance of the circuit film layer is close to or equal to the acoustic impedance of the silicon-based substrate. The acoustic impedance of the silicon-based substrate is 21 - 23 MRayls.

[0023] As a preferred embodiment, the non-identification area includes: an I / O interface area, and the I / O interface area is used to connect an FPC circuit board.

[0024] As a preferred embodiment, the third dielectric layer is a display screen.

[0025] As a preferred embodiment, the thickness of the third dielectric layer is greater than 300 μm.

[0026] As a preferred embodiment, a glue is arranged between the third dielectric layer and the second dielectric layer. The acoustic impedance of the glue is between that of the third dielectric layer and the second dielectric layer.

[0027] As a preferred embodiment, the glue is a thermosetting epoxy resin or a UV-curable epoxy resin, and the thickness of the glue is one-fourth of its wavelength.

[0028] As a preferred embodiment, the glue is a composite film layer of a conductive material and an organic substance. The total thickness of the glue is 5 - 50 μm, wherein the thickness of the conductive material is 1 - 15 μm.

[0029] As a preferred embodiment, a glue is arranged between the third dielectric layer and the second dielectric layer. The acoustic impedance of the glue is close to or equal to the acoustic impedance of the third dielectric layer.

[0030] An ultrasonic fingerprint recognition chip, comprising:

[0031] An ultrasonic sensor, configured to transmit and receive ultrasonic signals. The ultrasonic sensor has two opposite sides, with a first dielectric layer provided on one side and a silicon-based substrate provided on the other side. The silicon-based substrate is used to provide a display screen above the side facing away from the ultrasonic sensor.

[0032] An identification area and a non-identification area are formed on the silicon-based substrate. The identification area is used to form a CMOS pixel unit array, and the non-identification area is used to form a signal processing circuit.

[0033] The ultrasonic sensor forms a structure for ultrasonic resonance between the first dielectric layer and the silicon-based substrate. The ultrasonic signal emitted by the ultrasonic sensor can be transmitted out of the silicon-based substrate after resonance, enter the display screen, and be reflected by an object above the display screen and then enter the ultrasonic sensor.

[0034] Advantageous effects:

[0035] In the ultrasonic fingerprint recognition device according to the embodiment of the present application, a first dielectric layer and a second dielectric layer are formed on two sides of the ultrasonic sensor to form a structure for ultrasonic resonance. The ultrasonic signal emitted by the ultrasonic sensor can be transmitted out of the second dielectric layer after resonance and then enter a third dielectric layer. Among them, the amplitude of the ultrasonic wave will increase during each resonance, which is manifested as the phase of the transmitted wave being the same as or similar to that of the reflected wave reflected back from the two interfaces on both sides of the ultrasonic sensor, so they can be superimposed and enhanced. Therefore, each time the wave is reflected, the sound wave will be enhanced once, and thus the amplitude will continue to increase, making the sound wave intensity increase. When the transmitted wave is transmitted out of the second dielectric layer, the sound waves with mismatched frequencies can be filtered out through the filtering effect of the second dielectric layer, thereby reducing noise. And the propagation of the sound wave in the third dielectric layer can increase the time for the reflected wave to return, so that the echo signal and the transmitted signal can be distinguished in time, and the received echo signal is purer. Thus, the ultrasonic signal emitted by the ultrasonic sensor reaches the object only after passing through the resonance structure, the second dielectric layer, and the third dielectric layer in sequence. During this process, the sound wave is enhanced, filtered, and delayed, which can improve the signal-to-noise ratio.

[0036] In addition, the ultrasonic fingerprint recognition chip provided by the embodiment of the present application uses a silicon substrate, and an identification area and a non-identification area are formed on the silicon substrate. The identification area is used to manufacture a CMOS pixel unit array, and the non-identification area is used to manufacture a signal processing circuit, thereby integrating the existing detection part and signal processing part on the same chip, with a higher degree of integration.

[0037] Compared with the common method of fabricating TFT pixel circuits on a glass substrate, the active layer of the silicon substrate is made of single crystal silicon with fewer grain boundary defects, so the noise is smaller. At the same time, the size (CD) of the silicon-based CMOS process is smaller. Currently, the minimum size of the mass production process can reach 5nm. The size of the pixel unit fabricated by the CMOS process is much smaller than that of the pixel unit fabricated by the TFT process. Therefore, the size of the CMOS pixel unit is smaller, enabling the chip to have a higher imaging resolution.

[0038] Specific embodiments of the present invention are disclosed in detail with reference to the following description and the accompanying drawings, indicating the ways in which the principles of the present invention can be employed. It should be understood that the embodiments of the present invention are not limited in scope thereby.

[0039] Features described and / or illustrated for one embodiment can be used in the same or similar way in one or more other embodiments, combined with the features in other embodiments, or replace the features in other embodiments.

[0040] It should be emphasized that the term "comprising / including" when used herein refers to the presence of features, wholes, steps, or components, but does not exclude the presence or addition of one or more other features, wholes, steps, or components. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or in the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those skilled in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0042] Figure 1 is a schematic diagram of an ultrasonic fingerprint recognition device provided by an embodiment of the present application;

[0043] Figure 2 is a top view schematic diagram of the circuit layout of an ultrasonic fingerprint recognition device (ultrasonic sensors not shown) provided by an embodiment of the present application;

[0044] Figure 3 is Figure 2 a cross-sectional schematic diagram taken along the A-A direction;

[0045] Figure 4 is Figure 2 a cross-sectional schematic diagram taken along the B-B direction;

[0046] Figure 5 is a transmission wave curve diagram of the ultrasonic signal provided by an embodiment of the present application;

[0047] Figure 6 isFigure 1 Displacement variation curve of the midpoint 1 and point 2 over time;

[0048] Figure 7 is Figure 1 Displacement variation curve of the midpoint 3 and point 4 over time;

[0049] Figure 8 is Figure 1 Voltage signal variation curve of the sensing unit 1 and sensing unit 2 in the middle;

[0050] Figure 9 is Figure 1 Corresponding diagram of the relationship between the thickness of the first stack and the acoustic wave energy in the first stack;

[0051] Figure 10 Schematic diagram of a CMOS pixel array circuit provided by an embodiment of the present application;

[0052] Figure 11 Schematic diagram of a module of an ultrasonic fingerprint recognition chip provided by an embodiment of the present application;

[0053] Figure 12 Schematic diagram of a packaging structure of an ultrasonic fingerprint recognition chip provided by an embodiment of the present application.

[0054] Explanation of reference numerals:

[0055] 100, ultrasonic fingerprint recognition chip;

[0056] 1, second dielectric layer / silicon-based substrate; 10, recognition area; 101, CMOS pixel unit array; 11, non-recognition area; 111, control module; 112, RX module; 113, data processing module; 114, analog-to-digital conversion module; 115, row selection driving module; 14, I / O interface area; 15, third surface; 16, fourth surface; 17, bottom electrode;

[0057] 2, ultrasonic sensor; 21, first surface; 22, second surface; 23, protective layer; 24, electrode layer; 25, piezoelectric layer;

[0058] 3, third dielectric layer;

[0059] 4, glue;

[0060] 5, FPC circuit board; 6, anisotropic conductive glue; 7, reinforcing steel plate

[0061] A, first stack; B, second stack; C, third stack. Detailed implementation manners

[0062] To enable those skilled in the art to better understand the technical solutions in the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0063] It should be noted that when an element is referred to as being "disposed on" another element, it can be directly on the other element or there can also be another intermediate element. When an element is considered to be "connected" to another element, it can be directly connected to the other element or there may be another intermediate element at the same time. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only and do not represent the only implementation.

[0064] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0065] Please refer to Figures 1 to 12 , this application specification provides an ultrasonic fingerprint recognition device and an ultrasonic fingerprint recognition chip. The ultrasonic fingerprint recognition device and the ultrasonic fingerprint recognition chip provided in this application specification can be used in electronic devices such as mobile phones, smart watches, smart wearable devices, smart earphones, laptop computers, tablets and cameras. At the same time, it can also be applied to other devices such as automobiles, electronic switch devices, access control systems, etc.

[0066] It should be noted that the ultrasonic fingerprint recognition device and the ultrasonic fingerprint recognition chip provided in this application are not limited to detecting biological fingerprints. In expandable application scenarios, they can also be used for palmprint recognition, heart rate detection, blood pressure detection and 3D imaging of human superficial tissues (such as eyes, ears, nose, etc.). Among them, this application specification mainly describes fingerprint recognition as the main scenario, but it should be understood that the scope of protection of this application is not limited thereby.

[0067] As Figure 1 shown, the ultrasonic fingerprint recognition device provided in this application mainly includes an ultrasonic sensor 2. The ultrasonic sensor 2 is used to transmit and receive ultrasonic signals. The ultrasonic sensor 2 has two opposite sides, with a first dielectric layer disposed on one side and a second dielectric layer 1 disposed on the other side.

[0068] The first dielectric layer and the second dielectric layer 1 are media through which sound waves can penetrate, and can have a solid structure or not. For example, sound waves can penetrate air and water and propagate in air and water. Although air and water do not have a solid structure, air and water should also be regarded as dielectric layers of sound waves.

[0069] The ultrasonic sensor 2 has a first surface 21 and a second surface 22 facing each other. The first dielectric layer is in contact with the first surface 21, and the second dielectric layer 1 is in contact with the second surface 22. Therefore, by selecting the first dielectric layer and the second dielectric layer 1 whose acoustic impedances meet predetermined requirements, a structure for ultrasonic resonance can be formed for the ultrasonic sensor 2.

[0070] Specifically, according to the calculation formula of the sound wave reflectivity: r = (z1 - z2) 2 / (z1 + z2) 2 , where z1 represents the acoustic impedance of one of the two contacting dielectric layers, z2 represents the acoustic impedance of the other of the two contacting dielectric layers, and r represents the reflectivity at the interface of the two dielectric layers. It can be seen from the above formula that the greater the difference in the acoustic impedances (z1 and z2) of the dielectric layers at the interface, the greater the sound wave reflectivity at the interface; the smaller the difference in the acoustic impedances (z1 and z2) of the dielectric layers at the interface, the smaller the sound wave reflectivity at the interface. In order to form a resonant structure for the ultrasonic sensor 2, it is necessary to ensure that the difference in acoustic impedance between the ultrasonic sensor 2 and the first dielectric layer is as large as possible, so that when the ultrasonic wave propagates to the interface between the first dielectric layer and the ultrasonic sensor 2, it can be close to total reflection. Similarly, the difference in acoustic impedance between the ultrasonic sensor 2 and the second dielectric layer 1 should also be as large as possible. For example, the interface sound wave reflectivity is greater than 0.4. In this way, when the ultrasonic wave propagates in the ultrasonic sensor 2, it can be reflected back and forth at the interface between the first dielectric layer and the ultrasonic sensor 2 and at the interface between the second dielectric layer 1 and the ultrasonic sensor 2 to form resonance, so as to increase the amplitude of the ultrasonic wave and improve the signal-to-noise ratio. In addition, the difference in acoustic impedance between the ultrasonic sensor 2 and the second dielectric layer 1 cannot be set too large. For example, the interface sound wave reflectivity should be less than 0.9, so that the resonant sound wave can propagate from the interface between the ultrasonic sensor 2 and the second dielectric layer 1 to the second dielectric layer 1.

[0071] The principle that resonance in the ultrasonic sensor 2 can improve the signal-to-noise ratio is as follows: After the sound wave resonates within the ultrasonic sensor 2, when the phase of the transmitted wave is the same as or close to that of the reflected wave reflected back at the interface of the adjacent dielectric layer, they can be superimposed and enhanced. Therefore, each time the sound wave is reflected, it will be enhanced once, and thus the amplitude continuously increases. At the same time, only the sound wave components with the same thickness frequency as the ultrasonic sensor 2 will be left. Therefore, N in the signal-to-noise ratio SNR decreases. When the sound wave is transmitted to the target object, the intensity of the received echo information also increases. Therefore, S in the signal-to-noise ratio SNR increases, N decreases, and the signal-to-noise ratio SNR increases.

[0072] Furthermore, the first dielectric layer is air, and the acoustic impedance of air is the smallest, usually 411 Rayls. The acoustic impedance of solid dielectrics is often larger and can reach the unit of MRayls relative to air. Therefore, the difference between z1 and z2 and the sum of z1 and z2 are approximately equal to the acoustic impedance of the ultrasonic sensor 2 itself, so that the acoustic wave reflectivity at the interface between the first dielectric layer and the ultrasonic sensor 2 is close to 1. In some feasible embodiments, the first dielectric layer can be other materials with an acoustic impedance lower than the unit of MRayls and can be other low-impedance materials other than air.

[0073] As Figure 2 shown, the second dielectric layer 1 is a substrate layer for fabricating the circuit of the ultrasonic detection part and can be a glass substrate or a silicon substrate, preferably a silicon substrate. The second dielectric layer 1 has opposite third and fourth surfaces 15 and 16. The third surface 15 faces the second surface 22, and a recognition area 10 is provided on the third surface 15. The recognition area 10 is used to set the pixel circuit for detecting ultrasonic signals. The pixel circuit is an array of pixel units and a bottom electrode 17 for electrically coupling the pixel unit array to the ultrasonic sensor 2.

[0074] The ultrasonic signal emitted by the ultrasonic sensor 2 can be transmitted out of the second dielectric layer 1 after resonance. The second dielectric layer 1 is used to filter the resonated sound wave, thereby filtering out the sound waves with unmatched frequencies and further reducing noise.

[0075] The acoustic impedance of the second dielectric layer 1 is 21 - 23 MRayls, which is set to be much greater than the acoustic impedance of the ultrasonic sensor 2. Since there is a half - wave loss when sound waves are reflected at the interface between the silicon - based substrate and the ultrasonic sensor 2, when the transmitted wave (for example, with a waveform of sin(ωt)) returns to the position of the transmitted wave after passing through a path that is twice the 1 / 4 wavelength and experiencing a half - wave loss, it exactly undergoes a phase change of one - wavelength path. That is, the reflected wave (with a waveform of A*sin(ωt + 2π), A < 1) and the transmitted wave (with a waveform of sin(ωt)) can be superimposed and enhanced, and the waveform of the superimposed resonant wave is (1 + A)sin(ωt). That is, reflecting once at the interface between the second dielectric layer 1 and the ultrasonic sensor 2 can nearly double the amplitude.

[0076] In a preferred embodiment, the second dielectric layer 1 is a silicon - based substrate. The silicon - based substrate is single - crystal silicon, and the substrate material is more uniform compared to traditional glass substrates. The roughness of the interface between the second dielectric layer 1 and the ultrasonic sensor 2 and the interface between the second dielectric layer 1 and the glue 4 is small, and the thickness uniformity is good. When sound waves penetrate the second dielectric layer 1, they can be further filtered, and sound waves with mismatched frequencies will be filtered out. Therefore, N in the signal - to - noise ratio SNR is further reduced, further improving the signal - to - noise ratio.

[0077] In some possible embodiments, a glass substrate can also be used to play a filtering role, which can reduce the device cost. When using a glass substrate, the thickness uniformity of the glass substrate is not as good as that of the silicon - based substrate. At the same time, since glass is an amorphous material, the material uniformity is worse than that of single - crystal silicon. Therefore, the grinding process is more complex and difficult, resulting in a worse surface roughness of the thinned wafer than that of single - crystal silicon. Thus, the filtering effect will be a bit worse.

[0078] As Figure 1 shown in the sound wave propagation path, the ultrasonic fingerprint recognition device further includes: a third dielectric layer 3 disposed above the second dielectric layer 1 away from the ultrasonic sensor 2. The ultrasonic signal emitted by the ultrasonic sensor 2 can pass through the second dielectric layer 1 and enter the third dielectric layer 3 after resonance, and then be reflected by the target above the third dielectric layer 3 and enter the ultrasonic sensor 2. It can be seen that the ultrasonic signal emitted by the ultrasonic sensor 2 reaches the target after passing through the resonance structure, the second dielectric layer 1, and the third dielectric layer 3 in sequence. During this process, the ultrasonic signal is enhanced, filtered, and delayed, improving the signal - to - noise ratio.

[0079] The third dielectric layer 3 can be a display screen for users to press or touch with their fingers. For different application scenarios, the third dielectric layer 3 can be a material such as plastic, glass, metal, etc., or a multi - layer stack composed of several dielectrics. In particular, for a common mobile phone OLED screen, this dielectric is a composite film layer composed of organic substances (such as PI, OCA, etc.) and a glass cover plate.

[0080] Further, the third dielectric layer 3 faces the fourth surface 16 of the second dielectric layer 1, and the two are usually connected by glue 4. Thus, in the ultrasonic fingerprint recognition device provided by the embodiment of the present application, the substrate layer is disposed between the display screen and the ultrasonic sensor 2. During application, the fingerprint recognition chip composed of the substrate layer and the ultrasonic sensor 2 can be reversely attached below the display screen, so as to form the sound wave propagation path of the present application.

[0081] Commonly, in the solution where the ultrasonic sensor 2 is disposed between the display screen and the substrate layer, that is, the fingerprint recognition module is directly attached below the display screen. Then the interfaces between the ultrasonic sensor 2 and the adjacent two sides are respectively the interface between the ultrasonic sensor 2 and the glue 4 and the interface between the ultrasonic sensor 2 and the substrate layer. The acoustic impedances (z1 and z2) of the media on both sides of these two interfaces are relatively close, and the acoustic wave reflectivity of the two interfaces is relatively low, which is not conducive to forming a resonant structure. In addition, if the fingerprint recognition module is directly attached below the display screen, the substrate layer will be located below the ultrasonic sensor 2, and the transmitted wave generated by the ultrasonic sensor 2 cannot penetrate through the substrate layer, so the filtering effect cannot be achieved.

[0082] As Figure 3 and Figure 4 shown, the ultrasonic sensor includes a protective layer 23, an electrode layer 24, and a piezoelectric layer 25 which are stacked. The protective layer 23 is in contact with the first dielectric layer. The acoustic impedances of the protective layer 23, the electrode layer 24, and the piezoelectric layer 25 are close or equal. The thickness of the ultrasonic sensor 2 in the stacking direction is an odd multiple of one-fourth of its wavelength.

[0083] Among them, the piezoelectric layer 25 is used for both ultrasonic transmission and ultrasonic reception, and its working state is controlled by the timing signal sent by the signal processing circuit. The piezoelectric layer 25 is specifically a piezoelectric film, and the material can be one or a combination of polyvinylidene fluoride (PVDF), polyvinyl chloride, poly-γ-methyl-L-glutamate, polycarbonate, polyvinylidene fluoride copolymer, etc. It covers at least the recognition area 10. Considering the edge effect, the edge distance from the edge of the recognition area 10 should be greater than 0.2 mm, and it covers part of the non-recognition area 11. The part of the piezoelectric film in the recognition area 10 is divided into a plurality of piezoelectric units, and each piezoelectric unit corresponds to a bottom electrode 17 and a pixel unit.

[0084] In addition, taking Figure 1Taking the direction shown as an example, the piezoelectric layer 25 is disposed close to the substrate layer. The ultrasonic signal emitted by the piezoelectric layer 25 first propagates in the direction of the protective layer 23, forms resonance within the ultrasonic sensor 2, and after the acoustic wave amplitude is enhanced, it passes through the second medium layer 1 and the third medium layer 3 along the shown acoustic path and reaches the target body above the third medium layer 3. After being reflected by the target body to form an echo signal, when the echo signal returns to the ultrasonic sensor 2 along the shown acoustic path, it can directly reach the piezoelectric layer 25.

[0085] The electrode layer 24 is used to provide a given level for the piezoelectric thin film, which is usually a pulsed AC signal during the emission stage, with a peak-to-peak voltage of 30 - 300V, and is a low-level bias (<10V) or grounded during the reception stage. The electrode layer 24 is usually a metallized electrode, and the materials are metals such as Ag, Cu, Ni, Al, mixtures of metals and polymers, conductive rubber, etc., covering above the piezoelectric thin film.

[0086] During actual operation, the electrode layer 24 is connected to an AC voltage. After receiving the TX drive signal of pulsed AC, the piezoelectric layer 25 is triggered to vibrate, generating ultrasonic signals of corresponding frequencies, thereby establishing an ultrasonic field of a corresponding pulse. When the echo is formed after the transmitted wave is reflected by the target body, each piezoelectric unit on the piezoelectric layer 25 can receive the echo, convert the echo acoustic signal into an electrical signal through the piezoelectric effect, and then couple the corresponding electrical signal to the pixel circuit unit through the bottom electrode 17, and finally convert the echo signal into an electrical signal carrying fingerprint information.

[0087] The protective layer 23 is used to protect the device. The materials are usually organic substances such as ink and dry film, covering above the electrode layer 24. Since the protective layer 23 is in contact with the first medium layer, in order to better reflect the ultrasonic signal at this interface, the surface needs to be flat, with a surface roughness <20nm, thereby reducing noise.

[0088] In this application, the ultrasonic sensor 2 with the protective layer 23, the electrode layer 24, and the piezoelectric layer 25 stacked is set as a resonant structure. When designing the device, try to make the acoustic impedances of these three layers of materials close. In a specific embodiment, the protective layer 23, the electrode layer 24, and the piezoelectric layer 25 are formed of polymers, with an acoustic impedance of 1 - 10 MRayls and a thickness of 10 - 30μm. Preferably, they are PVDF, silver paste, and thermoplastic ink, with an acoustic impedance of about 5 MRayls. Or, in some feasible embodiments, the electrode layer 24 can also be set as a metal. Generally speaking, the acoustic impedance of a metal is relatively large (>10 MRayls), so its thickness is set to be much smaller than its wavelength (the wavelength is usually greater than 400μm, and much smaller means at least less than one-tenth of its value), such as less than 1μm, then the blocking effect of this high-acoustic-impedance layer on the acoustic wave can be ignored.

[0089] In this specification, the "wavelength" refers to the wavelength when the acoustic wave propagates in the corresponding medium. Different medium materials have different "wavelengths", and for different thicknesses under the same medium, the acoustic wave energy behaves differently. For example, Figure 9 As shown, when the thickness of the ultrasonic sensor 2 is approximately one - quarter or three - quarters of its wavelength, the acoustic wave energy penetrating into the medium reaches a maximum value. When the thickness of the ultrasonic sensor 2 is approximately two - quarters or one wavelength of its wavelength, the acoustic wave energy penetrating into the medium reaches a minimum value.

[0090] Considering that the thicker the piezoelectric layer 25, the greater the emission voltage required, and also considering the coating process of the piezoelectric material, it is usually set not to be greater than 30 um, specifically 7 um, 9 um, 11 um, 13 um, and 15 um, etc. On the other hand, the thicker the piezoelectric layer 25, the larger the proportion it occupies in the ultrasonic sensor 2, and the greater the finally output voltage. Considering both aspects, the total thickness of the ultrasonic sensor 2 is usually set to be one - quarter of its wavelength, approximately 10 - 100 um. Among them, the thicker the electrode layer 24, the better the conductivity, but its acoustic impedance is relatively large, and the thickness cannot be set too large. The protective layer 23 is used to supplement the thickness so that the total thickness of the ultrasonic sensor 2 reaches one - quarter wavelength.

[0091] During operation, an emission signal as shown in Figure 5 is generated through the circuit. Generally, it is 1 - 8 cycles, and the peak - to - peak voltage is generally 50 - 300 V, which is specifically related to the withstand voltage ability of the piezoelectric layer 25 material and the voltage - boosting ability of the circuit. Here, an example is given that the emission signal frequency is 12 MHz, with a total of 5 cycles and Vpp = 180 V. The electrode layer 24 receives the AC signal, and the bottom electrode 17 is grounded or connected to a fixed low level (<10 V). After the piezoelectric unit receives the AC voltage, due to the inverse piezoelectric effect, corresponding deformation occurs. Since the electric field direction is longitudinal and the polarization direction of the piezoelectric layer 25 material is also longitudinal (achieved through the polarization process), this piezoelectric effect is the d33 mode, and the piezoelectric layer 25 will undergo stretching and compression in the thickness direction, thereby generating a plane wave propagating outward.

[0092] From Figure 1 the shown propagation path, according to the similarity degree of the acoustic impedance of the materials, the fingerprint recognition device provided by the embodiment of the present application is divided into a first stack A, a second stack B, and a third stack C. The first stack A is the overall structure of the ultrasonic sensor 2, the second stack B is mainly composed of a substrate layer, and the third stack C is composed of glue and a third dielectric layer 3.

[0093] According to different surface textures of the finger, points 1 representing finger ridges and points 2 representing finger valleys are defined on the finger. According to the different textures of the finger corresponding to directly above the ultrasonic sensor 2, two acoustic paths can be divided, namely acoustic path 1 corresponding to the finger ridge and acoustic path 2 corresponding to the finger valley. During the ultrasonic emission stage, the ultrasonic waves resonate continuously in the first stack A to form standing waves, then pass through the second stack B, and reach the finger above the third dielectric layer 3 after passing through the third stack C. The acoustic impedance of the skin at the finger ridge (1.5 - 2 MRayls) is quite different from the acoustic impedance of the air at the finger valley (411 Rayls), so the acoustic wave reflectivities at the finger ridge and finger valley are different. Therefore, the reflected acoustic waves will be different, specifically corresponding to different acoustic waves at points 1 and 2. As Figure 6 shown, the amplitude of the acoustic wave at point 2 is larger.

[0094] On the ultrasonic sensor 2, there are points 3 corresponding to point 1 and points 4 corresponding to point 2. The pixel unit array on the substrate layer has a sensing unit 1 coupled to point 3 and a sensing unit 2 coupled to point 4. When the acoustic waves with amplitude differences are reflected along acoustic path 1 and acoustic path 2 respectively, they reach points 3 and 4. Points 3 and 4 produce different changes due to different acoustic waves, and different electrical signals are obtained through the processing of sensing unit 1 and sensing unit 2.

[0095] Among them, as Figure 7 shown, when the time is less than 1.7 us, the acoustic waves at the finger interface have not returned yet, and the displacement magnitudes of points 3 and 4 are the same; when the time is greater than 1.7 us, the acoustic waves at the finger interface return to the first stack A, and points 3 and 4 show different displacement magnitudes. Due to the piezoelectric effect, the voltages generated by sensing unit 1 and sensing unit 2 are different. As Figure 8 shown by the voltage signals generated by sensing unit 1 and sensing unit 2, it can be seen that at about 1.9 us, the valley-ridge voltage difference reaches the maximum value, about 70 mV. The voltage value is read through the pixel circuit and finally imaged after signal processing.

[0096] In the embodiment of the present application, through the third dielectric layer 3, the echo time of the ultrasonic waves reflected back to the ultrasonic sensor 2 after being reflected by the target object can be increased, so as to be distinguished from the emission time, making the received echo signal purer. In the present application, the ultrasonic sensor 2 is set as a structure for ultrasonic resonance, so there is a trailing time. At this time, during the acoustic wave resonance process, the ultrasonic sensor 2 continuously receives the resonant echo signals reflected after resonance (the resonant echo signals do not reach the target object, and are actually still the transmitted wave signals). If no delay layer is provided above the substrate layer, the echo signal formed by being reflected by the target object cannot be distinguished from the resonant echo signal (transmitted wave signal). Therefore, by setting the delay layer, the received echo signal is made purer.

[0097] In a specific embodiment, the thickness of the third dielectric layer 3 is greater than 300 μm to ensure that the echo signal can be distinguished from the transmitted wave signal. Of course, the third dielectric layer 3 is not limited to this thickness and can be adjusted based on this thickness.

[0098] In one embodiment, the acoustic impedance of the glue 4 is between that of the third dielectric layer 3 and the second dielectric layer 1. Specifically, the glue 4 is a thermosetting epoxy resin or a UV-curable epoxy resin, and the thickness of the glue 4 is one-quarter of its wavelength to ensure that the sound wave maintains a large amount of energy when passing through the glue 4. Alternatively, the glue 4 is a composite film layer of a conductive material and an organic substance, and the total thickness of the glue 4 is 5 - 50 μm, where the thickness of the conductive material is 1 - 15 μm. The conductive thin film plays a role in conduction and support, such as copper foil glue, conductive carbon tape, etc., and the acoustic impedance of the conductive material is preferably greater than 20 MRayls.

[0099] In one embodiment, the acoustic impedance of the glue 4 is close to or equal to that of the third dielectric layer 3. The thickness of the glue 4 can be considered together with the thickness of the third dielectric layer 3, and the total thickness is set to an odd multiple (when the acoustic impedance is between the second dielectric layer 1 and the skin) or an even multiple (when the acoustic impedance is not between the second dielectric layer 1 and the skin) of one-quarter wavelength of the third stack C. Particularly, when the medium to be penetrated is composed of several different material film layers, the glue needs to be set according to the film layer material in contact with the glue at this time.

[0100] In a specific application scenario, the acoustic impedance of the ultrasonic sensor 2 is 5 MRayls, the first dielectric layer is air, the acoustic impedance of the second dielectric layer 1 is 22 MRayls, and the acoustic impedance of the glue 4 is 10 MRayls. Then, using the formula r = (z1 - z2) 2 / (z1 + z2) 2 It can be calculated that the reflectivity between the first stack A and air is close to 1, and the reflectivity between the first stack A and the second stack B is about 0.4. Therefore, there is a half-wave loss when the sound wave is reflected between the first stack A and the second stack B. When the transmitted wave (for example, the waveform is sin(ωt)) returns to the transmitted wave position after passing through a path twice the length of 1 / 4 wavelength and a half-wave loss, it exactly experiences a phase change of one wavelength path, that is, the reflected wave (the waveform is 0.4*sin(ωt + 2π)) can be superimposed and enhanced with the transmitted wave (the waveform is sin(ωt)), and the resulting resonant wave waveform is 1.4*sin(ωt), that is, the amplitude can be doubled by reflecting once at the interface between the second dielectric layer 1 and the ultrasonic sensor 2. The reflectivity between the second stack B and the third stack C is about 0.14. It can be seen that most of the sound waves transmitted from the second dielectric layer 1 enter the third dielectric layer 3 to be received by the target above the third dielectric layer 3.

[0101] In this specification, the second dielectric layer 1 serves as a substrate layer for fabricating the circuit of the ultrasonic detection part, and is usually in a rectangular structure or other shapes. In an embodiment using a silicon-based substrate, an identification area 10 and a non-identification area 11 can be formed on the third surface 15 of the silicon-based substrate, as Figure 2 and Figure 11 shown. The identification area 10 is used to set the CMOS pixel unit array 101 and the bottom electrode 17 for electrically coupling the CMOS pixel unit array 101 to the ultrasonic sensor 2. The non-identification area 11 is used to form a signal processing circuit electrically connected to the CMOS pixel unit array 101 and the ultrasonic sensor 2. The signal processing circuit is used to provide a driving voltage for the ultrasonic sensor 2 and process the electrical signals sent out by the CMOS pixel unit array 101.

[0102] Thus, the signal processing circuit part and the CMOS detection circuit part can be directly fabricated on silicon. The signal processing circuit part and the CMOS detection circuit part can be integrated on the same chip, with a high degree of integration. Compared with the common method of fabricating a TFT pixel circuit on a glass substrate, the active layer of the silicon-based substrate is single-crystalline silicon, with fewer grain boundary defects, so the noise is smaller. At the same time, the CMOS process size (CD) of the silicon-based substrate is smaller. Currently, the minimum mass production process can reach 5 nm (the minimum size of the TFT process is generally greater than 1 μm). The pixel unit size fabricated by the CMOS process is much smaller than that fabricated by the TFT process. Therefore, the size of the CMOS pixel unit is smaller, making the imaging resolution of the chip higher.

[0103] In addition, according to the parasitic capacitance calculation formula C = εS / d, the CMOS process size is small, and the area S of the silicon-based transistor is smaller. The active region materials of the silicon-based and glass-based transistors are both silicon, so the dielectric constant ε is close. And the thickness d is related to the junction depth, and d of the two process circuits is close. Therefore, compared with the glass substrate, the parasitic capacitance of the CMOS pixel unit array fabricated with silicon is smaller, and the circuit noise is smaller. Thus, the signal-to-noise ratio of the chip can be effectively improved.

[0104] On the third surface 15 of the second dielectric layer 1, the ultrasonic sensor 2 is disposed on the identification area 10, and the identification area 10 is also used to set the CMOS detection circuit for detecting ultrasonic signals. The CMOS detection circuit and the signal processing circuit can be electrically coupled through the metal interconnect layer in the integrated circuit process. The CMOS detection circuit is specifically the CMOS pixel unit array 101, which is used to detect ultrasonic signals. The signal processing circuit is fabricated in the non-identification area 11 and is configured to control all aspects of fingerprint recognition. Thus, the signal processing part and the CMOS detection circuit can be integrated on the same substrate to form a single chip, with a simple packaging structure and a higher degree of integration.

[0105] Further, an I / O interface area 14 is provided on the non-identification area 11. The I / O interface area 14 is used to connect to external devices and a signal processing circuit. The external device can input signals to the chip or receive signals fed back by the chip through the I / O interface area 14. Preferably, as Figure 12 shown, the I / O interface area 14 is used to connect to an FPC circuit board 5.

[0106] In a preferred embodiment, the FPC circuit board 5 is located above the non-identification area 11. When projected along the thickness direction of the silicon-based substrate, the projection of the FPC circuit board 5 on the silicon-based substrate does not overlap with the projection of the ultrasonic sensor 2 on the silicon-based substrate. Thus, there is no interference between the FPC circuit board 5 and the ultrasonic sensor 2. On the one hand, it saves the material of the FPC circuit board 5. On the other hand, it is convenient for the FPC circuit board 5 to be electrically connected to the I / O interface area 14, reducing the process difficulty. In addition, since the FPC circuit board 5 is made of a flexible material, a reinforcing steel plate 7 can be provided below the FPC circuit board 5 to play a supporting role. In addition, with this packaging structure, the flexible circuit board can be bent arbitrarily, thus saving the internal space of the electronic device. Preferably, the FPC circuit board 5 is connected to the I / O interface area 14 through an anisotropic conductive adhesive 6.

[0107] In a preferred embodiment, the identification area 10 is located in the central area of the third surface 15, and the non-identification area 11 is located in the peripheral area of the identification area 10. Generally speaking, when ultrasonic waves used for fingerprint identification penetrate a medium, they have a certain degree of divergence and are difficult to be equivalent to a plane wave emission. Therefore, the acoustic information obtained in the edge area and the central area of the substrate layer is not equivalent, that is, an edge effect is generated. If the entire surface of the substrate is used to form the identification area 10 and fabricate the detection circuit, when actually identifying an image, some fingerprint images obtained in the edge area are usually discarded, resulting in the edge area not being reasonably utilized.

[0108] In this embodiment, the central area of the third surface 15 of the silicon-based substrate forms the identification area 10, and the edge area of the third surface 15 forms the non-identification area 11, effectively utilizing the edge area of the chip and making the effective usage area of the chip higher.

[0109] In a specific embodiment, the silicon-based substrate is rectangular with an outer contour dimension of 3 to 40 mm. The identification region 10 is rectangular and is 0.2 to 10 mm away from the chip edge on each side. The side length of each pixel unit on the identification region 10 is generally 20 to 100 μm. The specific value is related to the resolution required by the device and the circuit process, and is generally 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm. The top of the CMOS detection circuit is an array of bottom electrodes 17 made of metals such as Al, Au, Cu, Pt, Mo, etc. The thickness can be 0.01 to 20 μm, the spacing between electrode units is 1 to 20 μm, and it is connected to the ultrasonic sensor 2 above it.

[0110] In this embodiment, the pixel unit size fabricated on the silicon-based substrate based on the CMOS process is much smaller than that fabricated by the TFT process. Therefore, the size of the CMOS pixel unit is smaller, resulting in a higher imaging resolution of the chip. Thus, the overall size of the silicon-based substrate can be made smaller. Since both the CMOS detection circuit and the signal processing circuit are fabricated on the silicon-based substrate, the size of the silicon-based substrate can be equivalent to the size of the ultrasonic fingerprint recognition chip 100. The chip size is 3 to 40 mm, which is much smaller than the size of the fingerprint recognition chip using a large TFT array, facilitating cost reduction in production.

[0111] To fabricate a circuit on the silicon-based substrate, a circuit film layer for forming the CMOS pixel unit array 101 and the signal processing circuit is provided on the third surface 15 of the substrate. The acoustic impedance of the circuit film layer is close to or equal to the acoustic impedance of the silicon-based substrate. Thus, the laminate formed by the entire silicon-based substrate and the circuit film layer serves as a filtering layer for filtering. The circuit film layer is usually thin, preferably <10 μm, and is composed of inorganic substances such as silicon, silicon oxide, and silicon nitride. Its acoustic impedance is close to that of single-crystalline silicon, so it is equivalent to the same laminate as the silicon-based substrate.

[0112] Generally speaking, the acoustic impedance of the silicon-based substrate is about 22 MRayls and is set to be much greater than the acoustic impedance of the ultrasonic sensor 2. The silicon-based substrate should be as thin as possible, such as 50 μm, 100 μm, 150 μm, or 200 μm, etc.

[0113] As Figure 10 and Figure 11 shown, the CMOS detection circuit is the CMOS pixel unit array 101, which includes a number of CMOS pixel units. The number of CMOS pixel units can be arranged in a regular form of multiple rows and multiple columns. This circuit further includes row selection lines and column selection lines. When the row selection lines are turned on row by row or every other row, the corresponding row of CMOS pixel units is turned on, and the electrical signals stored in the CMOS pixel units are read out through the corresponding column selection lines.

[0114] In a specific embodiment, as Figure 10 shown, each pixel unit includes: a piezoelectric unit, a peak detection transistor M1, a locking transistor M2, a source follower transistor M3, a capacitor C1, and a readout transistor M4. The control module 111 provides independent control signals: TX, Bias, OD_1, and OD_2, etc. In the pixel readout stage, the readout transistor M4 is turned on by the row selection switch, and the charge signal of the sensing unit is output from the out terminal, and after being amplified, filtered, analog-to-digital converted, and digitally processed by the charge amplifier, an image is output.

[0115] Correspondingly, the signal processing circuit on the non-identification area 11 may include a control module 111 (bias driver, TX transmitter driver, driver 1, and driver 2), an RX module 112 (charge amplifier, filter), an analog-to-digital conversion module 114, and a data processing module 113. The control module 111 is configured to control the timing of the ultrasonic TX driver and the generation of the TX waveform, the bias of the sensing unit and the peak detection transistor, row selection, the timing control of the drivers required by the detection circuit, the readout frame rate, signal filtering, and analog-to-digital conversion, etc. The drivers required by the detection circuit include the driving of the OD_1 and OD_2 signals. The data processing module 113 receives data from the RX module 112, converts the digitized data into fingerprint image data, and then provides an I / O interface area 14 for further processing.

[0116] Specifically, the control module 111 generates TX signals at regular time intervals, which are transmitted to the ultrasonic sensor 2 through the TX driver, thereby driving the ultrasonic sensor 2 to generate ultrasonic waves. When the ultrasonic waves carrying fingerprint information return to the ultrasonic sensor 2, the control module 111 controls the bias driver, driver 1, and driver 2 to lock the charge information of each pixel unit after the above-mentioned receiving process of the ultrasonic receiver. The control module 111 further controls the row selection switch of the RX module 112 and the readout transistor M4 of the pixel module to perform row-by-row signal reading. When reading each row of pixel signals, the control module 111 can control the multiplexer of the RX module 112 to achieve signal reading. Further, the signal is amplified, filtered, analog-to-digital converted, and digitally processed, and finally sent out through the I / O interface area 14.

[0117] Of course, the specific structure of the pixel unit may not be limited to the above examples. Correspondingly, the signal processing circuit on the non-identification area 11 is not limited to the above list either. Those skilled in the art can make other changes under the inspiration of the technical essence of this application, but as long as the functions and effects achieved are the same or similar to those of this application, they should all be covered by the protection scope of this application. However, this signal processing circuit should at least include the timing control of the ultrasonic TX driver, the timing control of the drivers required by the detection circuit, and the processing of the readout signal.

[0118] In this specification, when forming the ultrasonic sensor 2 on a silicon-based substrate, first, a circuit including a CMOS detection circuit and a signal processing circuit is formed on a silicon wafer through conventional integrated circuit processes. The main film layers include a doped layer, an insulating layer, a metal interconnection layer, a passivation layer, etc. At the same time, a bottom electrode 17 and an I / O interface region 14 are respectively formed above the circuit. A metal conductive layer can be provided on the I / O interface region 14 to facilitate connection with an external circuit board or other electronic devices.

[0119] Furthermore, a solution with a piezoelectric copolymer can be coated above the CMOS detection circuit, or it can be achieved through spin coating, slot coating, screen printing, spraying, printing, lamination, or other coating methods. In particular, before coating the piezoelectric copolymer, a seed layer solution can be pre-coated to change the surface properties of the wafer, thereby obtaining a piezoelectric layer 25 with better piezoelectric properties. Then, the silicon wafer is baked at a high temperature to volatilize the adhesive in the film layer and crystallize the piezoelectric copolymer. The temperature needs to be higher than the Curie temperature of the copolymer and lower than the melting point. The piezoelectric copolymer is crystallized to form the piezoelectric layer 25. After crystallization, the piezoelectric layer 25 is polarized in a strong electric field, and the polarization direction is along the thickness direction of the piezoelectric layer 25. Specifically, it can be achieved through in-situ polarization. The polarization electrode (not shown in the figure) of the piezoelectric film layer is grounded. Then, the I / O interface region of the wafer is protected by an insulating fixture and placed under the polarization device. Under the action of the electric field, the ambient gas between the piezoelectric film layer and the polarization device is ionized to form a plasma. These gases accumulate on the surface of the piezoelectric layer 25, forming an in-film electric field in the thickness direction within the piezoelectric layer 25, thereby realizing the polarization of the piezoelectric layer 25. In addition, after polarization is completed, patterning of the piezoelectric film layer can also be achieved through wet etching or dry etching methods.

[0120] Then, the electrode layer 24 is prepared, which can be achieved through spin coating, screen printing, chemical vapor deposition, physical vapor deposition, plasma sputtering, etc. In addition, patterning can be achieved through wet etching or dry etching methods. Finally, the protective layer 23 can be prepared in the same way, thus completing the fabrication of the ultrasonic sensor on the recognition region 10 to form a complete wafer, which can be used for subsequent packaging with a circuit board.

[0121] Before packaging, the wafer needs to be thinned, diced, packaged, and tested to form a module. Specifically, first, the silicon substrate is thinned to 50 - 200 μm through mechanical grinding or chemical etching, the thickness uniformity is controlled to be less than ±5 μm, and the surface roughness < 100 nm; then, single chips are formed through laser or mechanical scribing; finally, as Figure 12 shown, it is bonded to the FPC circuit board 5 through an anisotropic conductive adhesive 6 to form a packaged module.

[0122] This specification also provides an ultrasonic fingerprint recognition chip 100, as Figures 1 to 4 shown, including: an ultrasonic sensor 2 for transmitting and receiving ultrasonic signals. The ultrasonic sensor 2 has two opposite sides. A first dielectric layer is provided on one side, and a silicon-based substrate 1 is provided on the other side. The silicon-based substrate 1 is used to provide a display screen above the side facing away from the ultrasonic sensor; an identification area 10 and a non-identification area 11 are formed on the silicon-based substrate 1. The identification area 10 is used to form a CMOS pixel unit array 101, and the non-identification area 11 is used to form a signal processing circuit; the ultrasonic sensor 2 forms a structure for ultrasonic resonance between the first dielectric layer and the silicon-based substrate 1. The ultrasonic signal emitted by the ultrasonic sensor 2 can be transmitted out of the silicon-based substrate 1 after resonance, enter the display screen, and enter the ultrasonic sensor 2 after being reflected by an object above the display screen.

[0123] The ultrasonic fingerprint recognition chip 100 can solve the technical problems solved by the embodiments in the above ultrasonic fingerprint recognition device and achieve the technical effects of the above embodiments accordingly. Specifically, this application will not be elaborated herein.

[0124] Any numerical value cited herein includes all values from the lower value to the upper value increasing in increments of one unit between the lower limit value and the upper limit value, provided that there is at least a two-unit interval between any lower value and any higher value. For example, if the value of the number of components or process variables (such as temperature, pressure, time, etc.) is stated as being from 1 to 90, preferably from 20 to 80, more preferably from 30 to 70, then the intention is to illustrate that values such as 15 to 85, 22 to 68, 43 to 51, 30 to 32, etc. are also explicitly listed in this specification. For values less than 1, a unit is appropriately considered to be 0.0001, 0.001, 0.01, 0.1. These are merely examples of what is intended to be clearly expressed, and it can be considered that all possible combinations of the numerical values listed between the lowest value and the highest value are explicitly stated in this specification in a similar manner.

[0125] Unless otherwise specified, all ranges include the endpoints and all numbers between the endpoints. "About" or "approximate" used with a range applies to both endpoints of the range. Thus, "about 20 to 30" is intended to cover "about 20 to about 30", including at least the specified endpoints.

[0126] All articles and references disclosed, including patent applications and publications, are incorporated herein by reference for various purposes. The term "consisting essentially of" in describing a combination shall include the recited elements, ingredients, components, or steps as well as other elements, ingredients, components, or steps that do not materially affect the basic novel characteristics of the combination. The use of the terms "comprising" or "including" to describe the combinations of elements, ingredients, components, or steps herein also contemplates embodiments consisting essentially of these elements, ingredients, components, or steps. By using the term "may" herein, it is intended that any of the attributes described as "may" include be optional.

[0127] It should be understood that the above description is for purposes of illustration and not of limitation. Many embodiments and many applications other than the examples provided will be apparent to those skilled in the art upon reading the above description. Therefore, the scope of the present teachings should not be determined with reference to the above description, but should be determined with reference to the appended claims and the full scope of equivalents to which such claims are entitled. For the sake of completeness, all articles and references, including patent applications and published disclosures, are incorporated herein by reference. The omission of any aspect of the subject matter disclosed herein from the foregoing claims is not intended to abandon such subject matter nor should it be considered that the inventors did not regard such subject matter as part of the disclosed inventive subject matter.

Claims

1. An ultrasonic fingerprint recognition device, characterized in that, Comprising: An ultrasonic sensor for transmitting and receiving ultrasonic signals. The ultrasonic sensor has two opposite sides. A first dielectric layer is provided on one side, and a second dielectric layer is provided on the other side. A third dielectric layer is provided above the second dielectric layer facing away from the ultrasonic sensor. The ultrasonic sensor forms a structure for ultrasonic resonance between the first dielectric layer and the second dielectric layer. The ultrasonic signal emitted by the ultrasonic sensor can be transmitted out of the second dielectric layer, enter the third dielectric layer after resonance, and be reflected by a target above the third dielectric layer and then enter the ultrasonic sensor. The acoustic impedance of the second dielectric layer 1 is 21 - 23 MRayls, the acoustic impedance of the ultrasonic sensor is 1 - 10 MRayls, and the interfacial acoustic wave reflectivity between the ultrasonic sensor and the second dielectric layer is greater than 0.4 and less than 0.

9. The second dielectric layer has a third surface and a fourth surface facing each other. The third surface faces the ultrasonic sensor. The third surface includes an identification area and a non-identification area. The identification area is used to set a CMOS pixel unit array and a bottom electrode for electrical coupling between the CMOS pixel unit array and the ultrasonic sensor. The non-identification area is used to form a signal processing circuit electrically connected to the CMOS pixel unit array and the ultrasonic sensor. The signal processing circuit is used to provide a driving voltage for the ultrasonic sensor and process the electrical signals emitted by the CMOS pixel unit array.

2. The ultrasonic fingerprint recognition device according to claim 1, wherein The first dielectric layer is air.

3. The ultrasonic fingerprint recognition device according to claim 1, wherein The ultrasonic sensor has a first surface and a second surface facing each other. The first surface is in contact with the first dielectric layer. The ultrasonic sensor includes: a protective layer, an electrode layer, and a piezoelectric layer stacked in sequence between the first surface and the second surface. The acoustic impedances of the protective layer, the electrode layer, and the piezoelectric layer are close to or equal. The thickness of the ultrasonic sensor in the stacking direction is an odd multiple of one-fourth of its wavelength.

4. The ultrasonic fingerprint recognition device according to claim 3, wherein, The protective layer, the electrode layer, and the piezoelectric layer are formed of a polymer.

5. The ultrasonic fingerprint recognition device according to claim 3, characterized in that, The electrode layer is made of a metal material, and the thickness of the electrode layer is less than 1 μm.

6. The ultrasonic fingerprint recognition device according to claim 1, characterized in that, The second dielectric layer is a silicon-based substrate.

7. The ultrasonic fingerprint recognition device according to claim 6, characterized in that, The outer contour size of the substrate is 3 - 40 mm.

8. The ultrasonic fingerprint recognition device according to claim 6, wherein, A circuit film layer for forming the CMOS pixel unit array and the signal processing circuit is provided on the third surface. The acoustic impedance of the circuit film layer is close to or equal to the acoustic impedance of the silicon-based substrate.

9. The ultrasonic fingerprint recognition device according to claim 1, wherein, The non-identification area includes: an I / O interface area for connecting an FPC circuit board.

10. The ultrasonic fingerprint recognition device according to claim 1, characterized in that, The third dielectric layer is a display screen.

11. The ultrasonic fingerprint recognition device according to claim 10, wherein, The thickness of the third dielectric layer is greater than 300 μm.

12. The ultrasonic fingerprint recognition device according to claim 1, wherein, An adhesive is provided between the third dielectric layer and the second dielectric layer. The acoustic impedance of the adhesive is between that of the third dielectric layer and the second dielectric layer.

13. The ultrasonic fingerprint recognition device according to claim 12, wherein The adhesive is a thermosetting epoxy resin or a UV curable epoxy resin, and the thickness of the adhesive is one-fourth of its wavelength.

14. The ultrasonic fingerprint recognition device according to claim 12, characterized in that, The glue is a composite film layer of conductive material and organic matter, and the total thickness of the glue is 5-50 μm, wherein the thickness of the conductive material is 1-15 μm.

15. The ultrasonic fingerprint recognition device according to claim 1, wherein Glue is provided between the third dielectric layer and the second dielectric layer, and the acoustic impedance of the glue is close to or equal to the acoustic impedance of the third dielectric layer.

16. An ultrasonic fingerprint recognition chip, characterized in that, include: An ultrasonic sensor, used for transmitting and receiving ultrasonic signals, the ultrasonic sensor having two opposite sides, one side being provided with a first dielectric layer, and the other side being provided with a silicon-based substrate, the silicon-based substrate being used for providing a display screen on an upper side away from the ultrasonic sensor; An identification area and a non-identification area are formed on the silicon-based substrate, wherein the identification area is used to form a CMOS pixel unit array, and the non-identification area is used to form a signal processing circuit; The ultrasonic sensor forms a structure for ultrasonic resonance between the first dielectric layer and the silicon-based substrate. The ultrasonic signal emitted by the ultrasonic sensor can be transmitted from the silicon-based substrate and enter the display screen after resonance, and then enter the ultrasonic sensor after being reflected by the target above the display screen; The acoustic impedance of the silicon-based substrate is 21-23 MRayls, the acoustic impedance of the ultrasonic sensor is 1-10 MRayls, and the acoustic wave reflectivity of the interface between the ultrasonic sensor and the silicon-based substrate is greater than 0.4 and less than 0.9.

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