WO2022021375A1

WO2022021375A1 - Ultrasonic fingerprint recognition apparatus and electronic device

Info

Publication number: WO2022021375A1
Application number: PCT/CN2020/106324
Authority: WO
Inventors: 谢浩
Original assignee: 深圳市汇顶科技股份有限公司
Priority date: 2020-07-31
Filing date: 2020-07-31
Publication date: 2022-02-03

Abstract

Embodiments of the present application provide an ultrasonic fingerprint recognition apparatus and an electronic device, which can effectively improve the accuracy of fingerprint recognition. The ultrasonic fingerprint recognition apparatus is applicable to an electronic device having a display screen, is provided below the display screen, and comprises: a pixel unit array, comprising a first type pixel unit and a second type pixel unit. The first type pixel unit has piezoelectricity, and is used for transmitting an ultrasonic signal to a finger above the display screen and receiving the returned ultrasonic signal to obtain a first pixel signal. The second type pixel unit does not have piezoelectricity, and is used for obtaining a second pixel signal when the first type pixel unit obtains the first pixel unit. A first difference signal between the first pixel signal and the second pixel signal is used for obtaining a fingerprint image.

Description

Ultrasonic fingerprint identification device and electronic equipment

technical field

The embodiments of the present application relate to the technical field of fingerprint identification, and more particularly, to an ultrasonic fingerprint identification device and an electronic device.

Background technique

With the rapid development of the terminal industry, the application of fingerprint recognition technology in mobile terminals is becoming more and more common. For example, it can be used for unlocking, payment and other functions. The mainstream fingerprint recognition generally includes capacitive fingerprint recognition, optical fingerprint recognition and ultrasonic fingerprint recognition. identify. Ultrasonic fingerprint recognition has been widely used due to its strong penetrating ability and the ability to identify dirty and wet fingers.

At present, consumers have higher requirements on the accuracy of fingerprint identification. Therefore, how to improve the accuracy of fingerprint recognition is an urgent problem to be solved.

SUMMARY OF THE INVENTION

Embodiments of the present application provide an ultrasonic fingerprint identification device and electronic equipment, which can effectively improve the accuracy of fingerprint identification.

In a first aspect, an ultrasonic fingerprint identification device is provided, which is suitable for an electronic device with a display screen, is arranged below the display screen, and includes: a pixel unit array, including a first type of pixel unit and a second type of pixel unit, the The first type of pixel unit has piezoelectric effect, and is used to transmit ultrasonic signals to the finger above the display screen and receive the returned ultrasonic signal to obtain the first pixel signal, and the second type of pixel unit does not have piezoelectric effect, It is used to acquire a second pixel signal when the first type of pixel unit acquires the first pixel signal, and a first difference signal between the first pixel signal and the second pixel signal is used to acquire a fingerprint image.

In a possible implementation manner, the first type of pixel unit is further configured to acquire a third pixel signal when the ultrasonic signal is not sent, and the second type of pixel unit is further configured to acquire a third pixel signal at the first type of pixel unit The fourth pixel signal is obtained when the third pixel signal is used; wherein the third difference signal between the first difference signal and the second difference signal is used to obtain the fingerprint image, and the second difference signal is used to obtain the fingerprint image. The signal is a difference signal of the third pixel signal and the fourth pixel signal.

In a possible implementation manner, the moment at which the first type of pixel unit acquires the third pixel signal is earlier than the moment at which the first pixel signal is acquired.

In a possible implementation manner, the ultrasonic fingerprint identification device further includes: a double correlation sampling circuit, including a first capacitor and a second capacitor, the double correlation sampling circuit is used to compare the first difference signal and the obtained sampling the second difference signal, storing the first difference signal in the first capacitor, and storing the second difference signal in the second capacitor; a buffer circuit for sampling A third difference signal of the first difference signal and the second difference signal.

In a possible implementation manner, the first type of pixel unit includes a piezoelectric layer and a cavity for the vibration of the piezoelectric layer, and the second type of pixel unit does not include the piezoelectric layer and/or the cavity.

In a possible implementation manner, the second type of pixel unit does not include the cavity, and the second type of pixel unit includes a support structure, a bottom electrode layer, the piezoelectric layer and A top electrode layer, the supporting structure is also disposed on both sides of the second type pixel unit for supporting the piezoelectric layer, and there is no cavity between the bottom electrode layer and the supporting structure.

In a possible implementation manner, the second type of pixel unit does not include the piezoelectric layer, and the second type of pixel unit includes a support structure, a cavity, a bottom electrode layer, and a supporting structure arranged in sequence from bottom to top. The dielectric constant of the piezoelectric layer is the same as the first layer and the top electrode layer without piezoelectric effect, and the support structure is also arranged on both sides of the second type of pixel unit for supporting the first layer .

In a possible implementation manner, the second type of pixel unit does not include the cavity and the piezoelectric layer, and the second type of pixel unit includes a support structure, a bottom electrode layer, The first layer and the top electrode layer have the same dielectric constant as the piezoelectric layer but do not have piezoelectric effect, and the support structure is also arranged on both sides of the second type of pixel unit for supporting the first layer. layer.

In a possible implementation manner, the second type of pixel unit is arranged in an outermost circle of the pixel unit array.

In a possible implementation manner, the size of the second type of pixel unit and the first type of pixel unit is 25-75 μm.

In a possible implementation manner, the distance between the centers of two pixel units in the pixel unit array does not exceed 70 μm.

In a possible implementation manner, the distance between the centers of two pixel units in the pixel unit array is 50 μm or 70 μm.

In a possible implementation manner, the pixel unit array includes a super pixel unit, and the super pixel unit includes a plurality of the first type of pixel units and at least one of the second type of pixel units, and the super pixel unit A pixel value used to form the fingerprint image.

In a possible implementation manner, the super pixel unit includes three pixel units of the first type and one pixel unit of the second type.

In a possible implementation manner, the distance between the centers of two adjacent super pixel units is 50 μm or 70 μm.

In a possible implementation manner, the size of the second type of pixel unit and the first type of pixel unit is 25-35 μm.

In a possible implementation manner, the first type of pixel unit is configured to receive a positive-phase excitation signal, and the positive-phase excitation signal is used to vibrate the piezoelectric layer in the first type of pixel unit, so as to provide all The finger above the display screen emits a positive-phase ultrasonic signal, and the positive-phase ultrasonic signal includes an aftershock signal, and the aftershock signal is the vibration of the piezoelectric layer after the first type of pixel unit stops receiving the positive-phase excitation signal. The generated signal; the first type of pixel unit is further configured to receive an inversion excitation signal, and the inversion excitation signal is used to cancel at least part of the aftershock signals in the aftershock signals.

In a possible implementation manner, the positive-phase excitation signal is a positive-phase pulse signal, the negative-phase excitation signal is a reverse-phase pulse signal, and the number of the negative-phase pulse signals is less than the number of the positive-phase pulse signals quantity.

In a possible implementation manner, the ultrasonic fingerprint identification device further includes: a differential amplifying circuit, two input ends of the differential amplifying circuit respectively receive the first pixel signal and the second pixel signal; a filtering circuit , used to receive the output signal of the differential amplifier circuit and filter the output signal of the differential amplifier circuit; an analog-to-digital conversion circuit, the input end of the analog-to-digital conversion circuit is connected to the output end of the filter circuit , for converting the output signal of the filter circuit into a digital signal.

In a possible implementation manner, the ultrasonic fingerprint identification device further includes: a rectifier circuit, connected to the filter circuit, for receiving the output signal of the filter circuit and converting the output signal of the band filter circuit into a DC signal; an integrating circuit, connected to the output end of the rectifier circuit, for receiving the DC signal, and accumulating the half-wave signals with the same polarity in the DC signal; the analog-to-digital conversion circuit is used for The output signal of the integrating circuit is received, and the output signal of the integrating circuit is converted into a digital signal.

In a possible implementation manner, the rectifier circuit is a full-wave rectifier circuit.

In a second aspect, an electronic device is provided, including: a display screen and the ultrasonic fingerprint identification device in the first aspect and any possible implementations thereof.

In the above technical solution, the ultrasonic fingerprint identification device includes a second type of pixel unit without piezoelectric effect, and the pixel signals obtained by the second type of pixel unit are all noise signals. In this way, when the first type of pixel unit with piezoelectric effect acquires the pixel signal, the second type of pixel unit also acquires the pixel signal, so that the noise signal in the first type of pixel signal and the second type of pixel signal is the same, then the first type of pixel signal and the noise signal in the second type of pixel signal are the same. The first difference signal between the pixel signal of the pixel unit of the second type and the pixel signal of the pixel unit of the second type is the pixel signal that removes noise interference, so that the signal-to-noise ratio of the ultrasonic fingerprint identification device can be improved. The fingerprint recognition performed has a high accuracy rate.

Description of drawings

1A and 1B are schematic diagrams of electronic devices to which embodiments of the present application may be applied.

FIG. 2 is a schematic diagram of a laminated structure of an ultrasonic fingerprint identification device according to an embodiment of the present application.

FIG. 3 is a schematic structural diagram of a pixel unit according to an embodiment of the present application.

FIG. 4 is a schematic structural diagram of an ultrasonic fingerprint identification device according to an embodiment of the present application.

5A-5C are schematic structural diagrams of a second type of pixel unit according to an embodiment of the present application.

6 to 8 are schematic diagrams of the distribution of the second type of pixel units according to the embodiments of the present application.

FIG. 9 is a collection timing diagram of pixel signals collected by an ultrasonic fingerprint identification device according to an embodiment of the present application.

FIG. 10 is a schematic frame diagram of an analog front-end circuit according to an embodiment of the present application.

FIG. 11 is a specific embodiment of an analog front-end circuit according to an embodiment of the present application.

FIG. 12 is a schematic block diagram of an electronic device according to an embodiment of the present application.

detailed description

The technical solutions in the present application will be described below with reference to the accompanying drawings.

It should be understood that the embodiments of the present application can be applied to fingerprint systems, including but not limited to optical, ultrasonic or other fingerprint detection systems and medical diagnostic products based on optical, ultrasonic or other fingerprint imaging, and the embodiments of the present application only take the ultrasonic fingerprint system as an example For illustration, the embodiments of the present application should not constitute any limitation, and the embodiments of the present application are also applicable to other systems using optics or other imaging technologies.

As a common application scenario, the ultrasonic fingerprint system provided in the embodiments of the present application can be applied to smart phones, tablet computers, and other mobile terminals with display screens or other electronic devices; more specifically, in the above electronic devices, ultrasonic fingerprints The identification device can be arranged in a partial area or the whole area under the display screen, thereby forming an under-display or under-screen ultrasonic fingerprint system. Alternatively, the ultrasonic fingerprint identification device may also be partially or fully integrated into the display screen of the electronic device, thereby forming an in-display or in-screen ultrasonic fingerprint system.

1A and 1B show schematic diagrams of an electronic device 100 to which the embodiments of the present application may be applied, wherein an ultrasonic fingerprint identification device is provided in a partial area below the display screen 120 . Therefore, when the user needs to unlock the electronic device 100 or perform other fingerprint verification, the user only needs to press the finger 130 on the fingerprint identification area 103 located on the display screen 120 to realize fingerprint input. Since fingerprint recognition can be implemented in the screen, the electronic device 100 using the above structure does not need to reserve a space on the front of the electronic device 100 to set the fingerprint button (such as the Home button), so that a full-screen solution can be adopted, that is, the display area of the display screen 120 can be basically Extends to the entire front of the electronic device 100 .

The ultrasonic fingerprint identification device includes a fingerprint sensor, and the fingerprint sensor includes a plurality of pixel units (also called pixels, sensing units, etc.). The area where the pixel unit is located or its sensing area is the fingerprint identification area 103 of the ultrasonic fingerprint identification device. In some implementations, as shown in FIG. 1A , the ultrasonic fingerprint identification device may include only one fingerprint sensor. In this case, the fingerprint identification area 103 of the ultrasonic fingerprint identification device has a small area and a fixed position. Therefore, when the user inputs a fingerprint It is necessary to press the finger 130 to a specific position of the fingerprint identification area 103 , otherwise the ultrasonic fingerprint identification device may fail to collect the fingerprint image, resulting in poor user experience.

In other alternative embodiments, as shown in FIG. 1B , the ultrasonic fingerprint identification device may include multiple fingerprint sensors. The plurality of fingerprint sensors can be arranged side by side under the display screen 120 by splicing, and the sensing areas of the plurality of optical fingerprint sensors together constitute the fingerprint recognition area 103 of the ultrasonic fingerprint recognition device, so that the fingerprint recognition area 103 of the ultrasonic fingerprint recognition device It can be extended to the main area of the lower half of the display screen 120 , that is, to the area where the finger 130 is habitually pressed, so as to realize the blind-pressing fingerprint input operation. Further, when the number of fingerprint sensors is sufficient, the fingerprint recognition area 103 can also be extended to half of the display area or even the entire display area, so as to realize half-screen or full-screen fingerprint recognition.

FIG. 2 is a schematic diagram of a laminated structure of an ultrasonic fingerprint identification device. The fingerprint sensor 111 can be attached to the display screen 120 by the ultrasonic coupling glue 112 , and the edge of the display screen 120 can be fixed by the ultraviolet curing glue (UV glue) 116 . The fingerprint sensor 111 is placed on the substrate 113 and can be electrically connected to the substrate 113 through a wire bonding process, that is, the fingerprint sensor 111 can be electrically connected to the substrate 113 through a gold wire 115 . Of course, the fingerprint sensor 111 may also be electrically connected to the substrate 113 through a through silicon via (TSV) packaging process. The substrate 113 may connect the signal of the fingerprint sensor 111 to the outside world or may transmit the signal of the outside world to the fingerprint sensor 111 . For example, after the substrate 113 is laminated by an anisotropic conductive film (ACF), the fingerprint sensor 111 can be electrically interconnected with other peripheral circuits or other components in the electronic device 100 through the substrate 113 and the circuit board 114 . connection and signal transmission. For example, the fingerprint sensor 111 can receive the control signal of the processing unit of the electronic device 100 through the circuit board 114, and can also output the fingerprint identification signal (such as a fingerprint image) to the processing unit or the control unit of the electronic device 100 through the circuit board 114. Optionally, the circuit board 114 may be a flexible printed circuit (Flexible Printed Circuit, FPC), and the FPC may be connected to a corresponding PFC connector port (Host BTB) on the electronic device 100 .

FIG. 3 is a schematic structural diagram of a pixel unit 200 according to an embodiment of the present application. As shown in FIG. 3 , the pixel unit 200 may include a support structure 210 , a cavity (cavity) 220 , a bottom electrode layer 230 , a piezoelectric layer 240 and a top electrode layer 250 arranged in order from bottom to top. Of course, the support structures 210 may also be disposed on both sides of the pixel unit 200 for supporting the piezoelectric layer 240 . The cavity 220 may be used for the piezoelectric layer 240 to vibrate.

Wherein, the piezoelectric layer 240 is composed of piezoelectric material, and the piezoelectric material can perform conversion between electrical signals and ultrasonic waves. The piezoelectric material may be, but is not limited to, lead zirconate titanate (PZT), aluminum nitride (Aluminum Nitride, AIN) or polyvinylidene fluoride (PVDF) and other materials.

The working principle of the ultrasonic fingerprint identification device can be as follows:

Transmitting state: By providing excitation signals, such as high-frequency oscillation signals, through electrodes at both ends of the piezoelectric material (bottom electrode layer 230 and top electrode layer 250 ), the piezoelectric material can generate vibrations in response to the frequency and emit ultrasonic signals. After passing through the display screen, the ultrasonic signal transmitted upward reaches the fingerprint ridge and fingerprint valley of the finger in contact with the surface of the screen. The ultrasonic signal encounters the surface of the fingerprint ridge, partly reflected and partly transmitted, due to the acoustic resistance characteristics of the air in the fingerprint valley. It is much higher than the fingerprint ridge, so the ultrasonic signal is almost totally reflected when it encounters the fingerprint valley, so the reflected signal strength of the ultrasonic signal from the fingerprint ridge and the fingerprint valley is different.

Receiving state: When the reflected ultrasonic signal passes through the display screen again and reaches the top electrode layer, it causes the piezoelectric material to vibrate to generate an electrical signal. The vibration intensity of the piezoelectric material in the area where the top electrode layer corresponding to the fingerprint valleys and fingerprint ridges at different positions is located. Therefore, the potential difference received by the top electrode layer at different positions is also different. After that, the pixel unit can convert the potential difference into an image signal, thereby obtaining a fingerprint image.

The existing under-screen ultrasonic fingerprint identification device is relatively sensitive to noise signals. In addition, the reflected ultrasonic signal (ie echo signal) received by the ultrasonic fingerprint identification device is relatively weak, such as AIN piezoelectric micro-electromechanical system (Piezoelectric Micro-Electro-Electro- Mechanical System, MEMS) piezoelectric ultrasonic sensor (PMUT) echo signal on the organic light-emitting diode (Organic Light-Emitting Diode, OLED) display screen is about 4mVpp, in this case, the noise signal to the ultrasonic fingerprint recognition device. The influence of the echo signal is greater, which greatly reduces the accuracy of fingerprint recognition.

In view of this, an embodiment of the present application proposes an ultrasonic fingerprint identification device, which can remove the interference of noise signals and improve the signal-to-noise ratio of the ultrasonic fingerprint identification device, thereby effectively improving the accuracy of fingerprint identification.

It should be noted that the ultrasonic fingerprint identification device in the embodiments of the present application may also be referred to as an ultrasonic fingerprint identification module, a fingerprint identification module, a fingerprint module, a fingerprint collection device, an ultrasonic fingerprint device, etc., and the above terms can be interchanged with each other.

Hereinafter, with reference to FIGS. 4 to 11 , the ultrasonic fingerprint identification device according to the embodiment of the present application will be described in detail.

It should be understood that, in the embodiments shown below, for the structures shown in different embodiments, the same reference numerals are used for the same structure, and the detailed description of the same structure is omitted for brevity.

It should also be understood that the heights or thicknesses of various structural components in the embodiments of the present application shown below are only exemplary, and should not constitute any limitation to the present application.

FIG. 4 is a schematic structural diagram of an ultrasonic fingerprint identification device 300 according to an embodiment of the present application. The ultrasonic fingerprint identification device 300 is arranged below the display screen for fingerprint identification. As shown in FIG. 4 , the ultrasonic fingerprint identification device may include a pixel unit array 310 , and the pixel unit array 310 includes a first type of pixel unit 3101 and a second type of pixel unit 3102 .

The display screen may be the display screen 120 shown in FIG. 1A and FIG. 1B . The first type of pixel unit 3101 has a piezoelectric effect, and is used to transmit ultrasonic signals to the finger above the display screen (such as the finger 130 in FIG. 1A and FIG. 1B ) and receive the returned ultrasonic signal to obtain the first pixel signal. The pixel unit 3102 has no piezoelectric effect, and is used to obtain the second pixel signal when the first type pixel unit 3101 obtains the first pixel signal, and the first difference signal between the first pixel signal and the second pixel signal is used to obtain the fingerprint image. .

In the embodiment of the present application, the ultrasonic fingerprint identification device includes a second type of pixel unit without piezoelectric effect, and the pixel signals obtained by the second type of pixel unit are all noise signals. In this way, when the first type of pixel unit with piezoelectric effect acquires the pixel signal, the second type of pixel unit also acquires the pixel signal, so that the noise signal in the first type of pixel signal and the second type of pixel signal is the same, then the first type of pixel signal and the noise signal in the second type of pixel signal are the same. The first difference signal of the pixel signal of the pixel-like unit and the pixel signal of the second-type pixel unit is the pixel signal of the noise-removed interference, so that the signal-to-noise ratio of the ultrasonic fingerprint identification device can be improved. Based on the pixel signal of the noise-removed signal The fingerprint recognition performed has a high accuracy rate.

It should be understood that, in the embodiments of the present application, "first" and "second" are only used to distinguish different objects, but do not limit the scope of the embodiments of the present application.

It should also be understood that the embodiments of the present application do not limit the names of the first type of pixel unit and the second type of pixel unit, that is, they may also be expressed as other names. For example, the first type of pixel unit may also be expressed as an active pixel unit (Active Pixel) or other names, and the second type of pixel unit may also be expressed as a dead pixel unit (Dead Pixel unit) or other names.

The piezoelectric effect may include a positive piezoelectric effect and an inverse piezoelectric effect. The positive piezoelectric effect means that when the piezoelectric material is deformed under the action of force, the center of positive and negative charges inside the piezoelectric material is displaced relative to each other, so that bound charges with opposite signs are generated at both ends of the piezoelectric material, and the amount of charge is proportional to the pressure. This is the process of converting mechanical energy into electrical energy. When the ultrasonic fingerprint identification device 300 is in the receiving state, using the positive piezoelectric effect of the piezoelectric material, after the returned ultrasonic signal reaches the top electrode layer, the piezoelectric material can vibrate, thereby generating an electrical signal.

The inverse piezoelectric effect means that when a voltage is applied across the piezoelectric material, deformation occurs inside the piezoelectric material, and the amount of deformation is proportional to the voltage, which is the process of converting electrical energy into mechanical energy. When the ultrasonic fingerprint identification device 300 is in the transmitting state, using the inverse piezoelectric effect of the piezoelectric material, the electrodes at both ends of the piezoelectric material provide excitation signals, such as oscillation signals, and the piezoelectric material can vibrate, thereby generating ultrasonic signals.

The structure of the first type of pixel unit 3101 is the same as that of the pixel unit 200 shown in FIG. 3 , and the specific content may refer to the description of FIG. 3 , which is not repeated here for brevity.

It can be known from the above description that in order for the pixel unit to have the piezoelectric effect, two conditions need to be met: the first condition is to have a piezoelectric material (such as the piezoelectric layer 240 in FIG. 3 ) to generate an electrical signal or an ultrasonic signal ; The second condition is to have a cavity for the piezoelectric material to vibrate (such as cavity 220 in Figure 3). Therefore, the second type of pixel unit 3102 in the embodiment of the present application does not include a piezoelectric layer and/or a cavity, and other structures are similar to those of the first type of pixel unit, which can ensure the self-noise and coupling of the second type of pixel unit 3102 The resulting noise is approximately equal to the noise of the first type of pixel unit 3101, so that a better denoising effect can be achieved.

Optionally, the noise coupled to the pixel unit may include two types: (1) the noise coupled to the pixel unit from the outside world, such as the noise coupled from the display screen of the electronic device or the noise coupled from the antenna of the electronic device, etc.; (2) The noise coupled to the pixel unit from the ultrasonic fingerprint identification device.

It should be understood that the term "and/or" in this document is only an association relationship to describe associated objects, indicating that there can be three kinds of relationships, for example, A and/or B, which can mean that A exists alone, and A and B exist at the same time , there are three cases of B alone.

5A-5C show schematic structural diagrams of the second type of pixel unit 3102 . The implementation of the second type of pixel unit 3102 in FIG. 5A is to remove the cavity based on the structure of the first type of pixel unit 3101, that is, not to include the cavity, then the second type of pixel unit 3102 includes supports arranged in sequence from bottom to top Structure 321 , bottom electrode layer 322 , piezoelectric layer 323 and top electrode layer 324 . It can be seen that there is no cavity between the bottom electrode layer 322 and the support structure 321 . The implementation of the second type of pixel unit 3102 in FIG. 5B is to remove the piezoelectric layer on the basis of the structure of the first type of pixel unit 3101, and use the first layer to replace the piezoelectric layer, wherein the material of the first layer is the same as the piezoelectric layer. If the dielectric constant of the material is close to but does not have piezoelectric properties, the second type of pixel unit 3102 may include a support structure 321 , a cavity 325 , a bottom electrode 322 , a first layer 326 and a top electrode layer 324 arranged in order from bottom to top. It can be seen that a cavity 325 exists between the bottom electrode layer 322 and the support structure 321 . The implementation of the second type of pixel unit 3102 in FIG. 5C is to remove the piezoelectric layer and the cavity on the basis of the structure of the first type of pixel unit 3101, then the second type of pixel unit 3102 includes support structures 321 arranged in sequence from bottom to top , a bottom electrode layer 322 , a first layer 326 and a top electrode layer 324 .

The embodiments of the present application do not specifically limit the arrangement of the second type of pixel units 3102 in the pixel unit array 310 .

In a possible embodiment, the second type of pixel units may be arranged in the edge area of the pixel unit array 310 . As an example, as shown in FIG. 6 , the second type of pixel units 3102 may be arranged around the outermost periphery of the pixel unit array 310 . In this way, when performing row or column scanning, the first type of pixel unit 3101 can acquire pixel signals simultaneously with the second type of pixel unit 3102 located in the same row or the same column. For example, the first type of pixel unit 3101 includes the pixel unit 3111, the second type of pixel unit 3102 includes the pixel unit 3112, and the pixel unit 3111 and the pixel unit 3112 are located in the same column. When the finger transmits the ultrasonic signal and receives the returned ultrasonic signal to obtain the first pixel signal, the pixel unit 3112 also obtains the second pixel signal, and the first difference signal between the first pixel signal and the second pixel signal is used to obtain the fingerprint image.

It can be seen from FIG. 6 that the pixel unit 3112 includes two pixel units, and the second pixel signal may be the average value of the pixel signals of the two pixel units, or may be the higher of the pixel signals of the two pixel units. A large value, or, can be any value in the pixel signals of the two pixel units.

Optionally, the size of each pixel unit in the pixel unit array 310 (that is, the values of a and b) may be 25-75 [mu]m.

The period of the fingerprint valley and the fingerprint ridge is generally greater than 400 μm. According to Shannon’s sampling theorem, the pitch between the centers of two adjacent pixel units in the pixel unit array 310 needs to be at least less than 200 μm. In practical applications, the pitch can generally be less than 100 μm.

Optionally, the pitch may not exceed 70 μm. Illustratively, the pitch may be 50 μm or 70 μm. If the pitch exceeds 70 μm, the fingerprint resolution of the ultrasonic fingerprint identification device 300 may be reduced, thereby resulting in a decrease in the performance of the ultrasonic fingerprint device.

As another example, as shown in FIG. 7 , the second type of pixel units 3102 may be arranged in the outermost half-circle area of the pixel unit array 310 . That is to say, there is only one pixel unit of the second type located in the same row or column as the pixel unit of the first type.

In another possible embodiment, the pixel unit 3101 of the first type may surround the pixel unit 3102 of the second type.

In another possible embodiment, multiple rows or columns of first-type pixel units 3101 may share a second-type pixel unit 3102, and each first-type pixel unit 3101 in the multiple rows or columns of first-type pixel units 3101 The pixel signal of the pixel-like unit is the first pixel signal.

In another possible embodiment, a plurality of pixel units in the pixel unit array 310 may be used to form a pixel value of a fingerprint image, and the plurality of pixel units (for the convenience of description, referred to as super pixel units in this application) include A plurality of first type pixel units 3101 and at least one second type pixel unit 3102. Referring to FIG. 8 , the super pixel unit includes three first-type pixel units 3101 and one second-type pixel unit 3102 .

Optionally, the first pixel signal may be the average value of the pixel signals of the three first-type pixel units 3101 , or the first pixel signal may be the sum of the pixel signals of the three first-type pixel units 3101 . In this way, the noise elimination effect can be further improved, thereby further improving the accuracy of fingerprint identification.

Alternatively, the values of a and b may be 25 μm to 35 μm.

Optionally, the area of the pixel unit array 310 may be greater than or equal to 36mm ² , and the size may be 4mm*9mm or 6mm*6mm.

Optionally, the pitch (Pitch) between the centers of two adjacent superpixel units may not exceed 70 μm.

It should be understood that the arrangement of the second type of pixel units 3102 shown in FIGS. 6-8 is only an example, but the embodiment of the present application is not limited thereto. For example, the second type of pixel unit 3102 in the superpixel unit can be arranged anywhere in the superpixel unit. For another example, the super pixel unit may include 2 first type pixel units 3101 and 2 second type pixel units 3102.

Optionally, in this embodiment of the present application, the ultrasonic fingerprint identification device may further include an analog front-end circuit and an analog-to-digital converter (Analog-to-Digital Converter, ADC). The analog front-end circuit may include a differential amplifying circuit and a filtering circuit, and two input ends of the differential amplifying circuit may receive the first pixel signal and the second pixel signal, respectively, and perform a differential signal between the first pixel signal and the second pixel signal ( That is, the first difference signal) is amplified, and the filter circuit can be used to receive the output signal of the differential amplifier circuit, and filter the output signal of the differential amplifier circuit. The input end of the ADC is connected to the output end of the filter circuit for two The output signal of the filter circuit is converted into a digital signal.

Optionally, the differential amplifier circuit may be a programmable gain amplifier (Pmgrammable Gain Amplifier, PGA) circuit.

Optionally, the filter circuit may be a band-pass filter (Band-Pass Filter, BPF). For example, the first type of pixel unit 3101 adopts a PMUT, the resonant frequency Fs of the PMUT is 10MHz-50MHz, the center frequency of the band-pass filter is the resonant frequency Fs, and the bandwidth is 10%-20% Fs. Assuming that the resonant frequency Fs of the PMUT is 20MHz, and the bandwidth of the band-pass filter is 10% Fs, that is, 2MHz, the band-pass filter can allow signals with a frequency of 19MHz to 21MHz to pass.

Optionally, in this embodiment of the present application, the analog front-end circuit may further include a rectifying circuit and an integrating circuit. The rectifier circuit is connected with the filter circuit, and can be used for receiving the output signal of the filter circuit and converting the output signal of the filter circuit into a DC signal. One input end of the integrating circuit is connected to the output end of the rectifying circuit, which is used to receive the DC signal output by the rectifying circuit, and accumulate the half-wave signals with the same polarity in the DC signal to obtain the energy sum of the half-wave signals in the integration time. . Since the half-wave signal in the DC signal contains a DC bias signal, the other input terminal of the integrating circuit can receive the same DC bias signal as the DC bias signal contained in the half-wave signal, so as to be consistent with the DC bias signal in the half-wave signal. Set the signal to make a difference, so that the integrating circuit can only accumulate the energy of the half-wave signal.

Optionally, the rectifier circuit may be a full-wave rectifier circuit.

In this way, the ultrasonic fingerprint identification device adopts the method of rectification + integration, and the signal-to-noise ratio of the ultrasonic fingerprint identification device can be further improved by repeatedly coding and accumulating signals.

In order to further reduce the background noise of the pixel signal itself, optionally, the first type of pixel unit 3101 can also be used to acquire a third pixel signal when the ultrasonic signal is not sent, and the second type of pixel unit 3102 can also be used to The pixel unit 3101 acquires the fourth pixel signal when acquiring the third pixel signal. The difference between the third pixel signal and the fourth pixel signal is the second difference signal, and the third difference signal between the first difference signal and the second difference signal can be used to acquire a fingerprint image.

The above technical solution can further reduce the noise signal, improve the signal-to-noise ratio of the ultrasonic fingerprint identification device, and improve the accuracy of fingerprint identification.

In this technical solution, the analog front-end circuit may further include a Correlated Double Sampling (CDS) circuit and a buffer (Buffer) circuit, and the CDS circuit is used to sample and hold the first difference signal and the second difference signal , the CDS circuit may include a first capacitor and a second capacitor, the CDS circuit may store the first difference signal in the first capacitor after sampling the first difference signal, and store the second difference signal after sampling the second difference signal The signal is held in the second capacitor. The Buffer circuit may be used for sampling the first difference signal and the third difference signal of the second difference signal.

As an example, the first type of pixel unit 3101 and the second type of pixel unit 3102 may first acquire the first pixel signal and the second pixel signal respectively, and then the first type of pixel unit 3101 and the second type of pixel unit 3102 respectively acquire The third pixel signal and the fourth pixel signal.

As another example, the first type of pixel unit 3101 and the second type of pixel unit 3102 may first obtain the third pixel signal and the fourth pixel signal respectively, and then the first type of pixel unit 3101 and the second type of pixel unit 3102 respectively A first pixel signal and a second pixel signal are acquired.

FIG. 9 is a collection timing diagram of a pixel signal collected by the ultrasonic fingerprint identification device 300, assuming that the first type of pixel unit is a PMUT. First, the ultrasonic fingerprint identification device 300 is reset to initialize the first capacitor and the second capacitor in the CDS circuit. Then the PMUT obtains the third pixel signal, and the second type pixel unit corresponding to the PMUT obtains the fourth pixel signal, and the CDS circuit is in

The phase collects the second difference signal between the third pixel signal and the fourth pixel signal, and after collecting the second difference signal, saves the second difference signal to

Among the capacitors corresponding to the phases, that is, the second capacitor. Next, the PMUT obtains the coding (or excitation) signal, and the PMUT begins to vibrate. The piezoelectric material in the PMUT uses the inverse piezoelectric effect to generate an ultrasonic signal. The ultrasonic signal is transmitted to the surface of the display screen and then reflected by the finger after encountering the finger, resulting in a return signal. wave signal, the PMUT obtains the first pixel signal, and the second type pixel unit corresponding to the PMUT obtains the second pixel unit, and the CDS circuit is in

The phase samples the difference signal (the first difference signal) between the first pixel signal and the second pixel signal and stores it in

The capacitor corresponding to the phase is in the first capacitor. After that, the Buffer circuit collects the difference between the first capacitor and the second capacitor, the difference collected by the Buffer circuit is the output signal of the PMUT, and the difference is the third difference signal.

FIG. 10 shows a schematic frame diagram of an analog front-end circuit 320 , and FIG. 11 shows a specific embodiment of the analog front-end circuit 320 corresponding to FIG. 10 .

Assuming that the first type pixel unit 3101 and the second type pixel unit 3102 first obtain the third pixel signal and the fourth pixel signal respectively, first initialize the capacitors in the integrating circuit 3204 and the CDS circuit 3205, the PGA circuit 3201 receives the third pixel signal and After the fourth pixel signal, differential amplification is performed on the second difference signal of the third pixel signal and the fourth pixel signal. Then, the differentially amplified second difference signal is filtered by the BPF 3202. Since the filtered second difference signal is an AC signal, the filtered second difference signal is input to the full-wave rectifier circuit 3203. to convert the second difference signal into a DC signal. After that, the second difference signal converted into a DC signal is input to the integrating circuit 3204, and the integrating circuit 3204 accumulates the energy of the second difference signal by coding multiple times, and inputs the output signal to the CDS circuit 3205, and the CDS circuit 3205 is in the

The output signal of the phase acquisition and integration circuit 3204 is the second difference signal after a series of processing, and the second difference signal is stored in the

in the corresponding capacitor.

Next, the first type pixel unit 3101 obtains the excitation signal, the piezoelectric material in the first type pixel unit 3101 starts to vibrate and generates ultrasonic signals, when the first type pixel unit 3101 receives the echo signal, the first type pixel unit 3101 starts to vibrate and generates ultrasonic signals. The unit 3101 obtains the first pixel signal, and the second type pixel unit 3102 obtains the second pixel signal. After receiving the first pixel signal and the second pixel signal, the PGA circuit 3201 differentially amplifies the first difference signal of the first pixel signal and the second pixel signal. After the differentially amplified second difference signal passes through the BPF 3202, the full-wave rectifier circuit 3203 and the integrating circuit 3204, the CDS circuit 3205 is

The output signal of the phase acquisition and integration circuit 3204 is the first difference signal after a series of processing, and the first difference signal is stored in the

in the corresponding capacitor.

Next, the Buffer circuit 3206 receives the first difference signal and the second difference signal and collects the difference signal of the first difference signal and the second difference signal. After that, the Buffer circuit 3206 inputs the output signal to the ADC circuit 330, and the ADC circuit 330 performs analog-to-digital conversion on the first difference signal and the third difference signal of the second difference signal to obtain the final first type of pixel unit 3101. output signal.

In addition to being sensitive to noise signals, the ultrasonic fingerprint identification device is also sensitive to the aftershock signal of the transmitted ultrasonic signal, wherein the aftershock signal may be the first type of aftershock signal after the first type of pixel unit stops receiving the excitation signal for generating the ultrasonic signal. A type of signal generated by the continued vibration of the piezoelectric layer of the pixel unit. If there is an aftershock signal, when the ultrasonic fingerprint identification device receives the echo signal, the aftershock signal may interfere with the echo signal. For example, the superimposed signal of the echo signal and the aftershock signal may be used for fingerprint identification. less effective.

Therefore, optionally, in this embodiment of the present application, after receiving the normal-phase excitation signal for generating the ultrasonic signal, the first-type pixel unit 3101 may also receive an inverse-phase excitation signal, and the inverse-phase excitation signal can be used to cancel at least a portion of the aftershock signals. The anti-phase excitation signal can cancel the aftershock signal, so that the interference of the aftershock signal to the echo signal can be eliminated.

Optionally, the positive-phase excitation signal may be a positive-phase pulse signal, and the reverse-phase excitation signal may be an inverse-phase pulse signal. Exemplarily, the number of positive-phase pulse signals may be four, and the number of reverse-phase pulse signals may be one.

The embodiment of the present application further provides an electronic device. As shown in FIG. 12 , the electronic device 400 may include a display screen 410 and an ultrasonic fingerprint identification device 420 . The ultrasonic fingerprint identification device 420 may be the ultrasonic fingerprint identification device 300 in the foregoing embodiment, and is disposed below the display screen 410 .

It should be understood that the display screen 410 may be a non-folding display screen or a foldable display screen, that is, a flexible display screen.

As an example and not a limitation, the electronic device in the embodiment of the present application may be a portable or mobile computing device such as a terminal device, a mobile phone, a tablet computer, a notebook computer, a desktop computer, a game device, a vehicle-mounted electronic device, or a wearable smart device, and Electronic databases, automobiles, bank ATMs (Automated Teller Machine, ATM) and other electronic devices. The wearable smart device includes full functions, large size, and can realize complete or partial functions without relying on smart phones, such as smart watches or smart glasses, etc., and only focus on a certain type of application function, which needs to cooperate with other devices such as smart phones. Use, such as various types of smart bracelets, smart jewelry and other equipment for physical monitoring.

It should be noted that, on the premise of no conflict, each embodiment described in this application and/or the technical features in each embodiment can be arbitrarily combined with each other, and the technical solution obtained after the combination should also fall within the protection scope of this application .

It should be understood that the terms used in the embodiments of the present application and the appended claims are only for the purpose of describing specific embodiments, and are not intended to limit the embodiments of the present application. For example, as used in the embodiments of this application and the appended claims, the singular forms "a," "above," and "the" are intended to include the plural forms as well, unless the context clearly dictates otherwise.

Those of ordinary skill in the art can realize that the units of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of the two, in order to clearly illustrate the interchangeability of hardware and software In the above description, the components and steps of each example have been generally described in terms of function. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Skilled artisans may implement the described functionality using different methods for each particular application, but such implementations should not be considered beyond the scope of this application.

In the several embodiments provided in this application, it should be understood that the disclosed systems and apparatuses may be implemented in other manners. For example, the apparatus embodiments described above are only illustrative. For example, the division of the units is only a logical function division. In actual implementation, there may be other division methods. For example, multiple units or components may be combined or Can be integrated into another system, or some features can be ignored, or not implemented. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be indirect coupling or communication connection through some interfaces, devices or units, and may also be electrical, mechanical or other forms of connection.

The units described as separate components may or may not be physically separated, and components displayed as units may or may not be physical units, that is, may be located in one place, or may be distributed to multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solutions of the embodiments of the present application.

In addition, each functional unit in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically alone, or two or more units may be integrated into one unit. The above-mentioned integrated units may be implemented in the form of hardware, or may be implemented in the form of software functional units.

The integrated unit, if implemented in the form of a software functional unit and sold or used as an independent product, may be stored in a computer-readable storage medium. Based on this understanding, the technical solutions of the present application are essentially or part of contributions to the prior art, or all or part of the technical solutions can be embodied in the form of software products, and the computer software products are stored in a storage medium , including several instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present application. The aforementioned storage medium includes: U disk, mobile hard disk, Read-Only Memory (ROM, Read-Only Memory), Random Access Memory (RAM, Random Access Memory), magnetic disk or optical disk and other media that can store program codes .

The above are only specific embodiments of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art can easily think of various equivalents within the technical scope disclosed in the present application. Modifications or substitutions shall be covered by the protection scope of this application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

An ultrasonic fingerprint identification device, suitable for electronic equipment with a display screen, is characterized in that, the ultrasonic fingerprint identification device is arranged below the display screen, comprising:

A pixel unit array, including a first type of pixel unit and a second type of pixel unit, the first type of pixel unit has a piezoelectric effect, and is used to transmit ultrasonic signals to the finger above the display screen and receive the returned ultrasonic signals to obtain The first pixel signal, the second type of pixel unit does not have piezoelectric effect, is used for acquiring the second pixel signal when the first type of pixel unit acquires the first pixel signal, the first pixel signal and the The first difference signal of the second pixel signal is used to acquire a fingerprint image.
The ultrasonic fingerprint identification device according to claim 1, wherein the first type of pixel unit is further configured to acquire a third pixel signal when the ultrasonic signal is not sent, and the second type of pixel unit is further configured to obtaining the fourth pixel signal when the first type of pixel unit obtains the third pixel signal;

The third difference signal between the first difference signal and the second difference signal is used to acquire the fingerprint image, and the second difference signal is the third pixel signal and the fourth difference signal. The difference signal of the pixel signal.
The ultrasonic fingerprint identification device according to claim 2, wherein the time when the first type of pixel unit obtains the third pixel signal is earlier than the time when the first pixel signal is obtained.
The ultrasonic fingerprint identification device according to claim 2 or 3, wherein the ultrasonic fingerprint identification device further comprises:

A double-correlated sampling circuit includes a first capacitor and a second capacitor, and the double-correlated sampling circuit is configured to sample the first difference signal and the second difference signal, and to sample the first difference signal storing in the first capacitor, storing the second difference signal in the second capacitor;

The buffer circuit is used for collecting the third difference signal between the first difference signal and the second difference signal.
The ultrasonic fingerprint identification device according to any one of claims 1 to 4, wherein the first type of pixel unit comprises a piezoelectric layer and a cavity for vibration of the piezoelectric layer, and the second type of pixel unit includes a piezoelectric layer and a cavity for vibration of the piezoelectric layer. The pixel-like unit does not include the piezoelectric layer and/or the cavity.
The ultrasonic fingerprint identification device according to claim 5, wherein the second type of pixel unit comprises a support structure, a bottom electrode layer, the piezoelectric layer and a top electrode layer arranged in sequence from bottom to top, and the support Structures are also arranged on both sides of the second type of pixel unit for supporting the piezoelectric layer, and there is no cavity between the bottom electrode layer and the supporting structure.
The ultrasonic fingerprint identification device according to claim 5, wherein the second type of pixel unit does not include the piezoelectric layer, and the second type of pixel unit includes a support structure and a cavity that are sequentially arranged from bottom to top , a bottom electrode layer, a first layer and a top electrode layer that have the same dielectric constant as the piezoelectric layer but do not have piezoelectric effect, and the support structure is also arranged on both sides of the second type of pixel unit, using for supporting the first layer.
The ultrasonic fingerprint identification device according to claim 5, wherein the second type of pixel unit does not include the cavity and the piezoelectric layer, and the second type of pixel unit includes a series of pixels arranged in sequence from bottom to top. A support structure, a bottom electrode layer, a first layer and a top electrode layer with the same dielectric constant as the piezoelectric layer but without piezoelectric effect, the support structure is also arranged on both sides of the second type of pixel unit , for supporting the first layer.
The ultrasonic fingerprint identification device according to any one of claims 1 to 8, wherein the second type of pixel unit is arranged in an outermost circle of the pixel unit array.
The ultrasonic fingerprint identification device according to claim 9, wherein the size of the second type pixel unit and the first type pixel unit is 25-75 μm.
The ultrasonic fingerprint identification device according to claim 9 or 10, wherein the distance between the centers of two adjacent pixel units in the pixel unit array is not more than 70 μm.
The ultrasonic fingerprint identification device according to claim 11, wherein the distance between the centers of two adjacent pixel units in the pixel unit array is 50 μm or 70 μm.
The ultrasonic fingerprint identification device according to any one of claims 1 to 8, wherein the pixel unit array includes a super pixel unit, and the super pixel unit includes a plurality of the first type pixel units and at least one pixel unit. In the second type of pixel unit, the super pixel unit is used to form one pixel value of the fingerprint image.
The ultrasonic fingerprint identification device according to claim 13, wherein the super pixel unit comprises three pixel units of the first type and one pixel unit of the second type.
The ultrasonic fingerprint identification device according to claim 13 or 14, wherein the distance between the centers of two adjacent super pixel units is 50 μm or 70 μm.
The ultrasonic fingerprint identification device according to any one of claims 13 to 15, wherein the size of the second type pixel unit and the first type pixel unit is 25-35 μm.
The ultrasonic fingerprint identification device according to any one of claims 1 to 16, wherein the first type of pixel unit is used to receive a positive-phase excitation signal, and the positive-phase excitation signal is used to make the first type of pixel unit The piezoelectric layer in the pixel-like unit vibrates to transmit a positive-phase ultrasonic signal to the finger above the display screen. After the positive-phase excitation signal, the signal generated by the piezoelectric layer vibration;

The first type of pixel unit is further configured to receive an inversion excitation signal, and the inversion excitation signal is used to cancel at least part of the aftershock signals in the aftershock signals.
The ultrasonic fingerprint identification device according to claim 17, wherein the positive-phase excitation signal is a positive-phase pulse signal, the reverse-phase excitation signal is a reverse-phase pulse signal, and the number of the reverse-phase pulse signals is less than The number of the positive-phase pulse signal.
The ultrasonic fingerprint identification device according to any one of claims 1 to 18, wherein the ultrasonic fingerprint identification device further comprises:

a differential amplifying circuit, two input ends of the differential amplifying circuit respectively receive the first pixel signal and the second pixel signal;

a filtering circuit, configured to receive the output signal of the differential amplifying circuit, and perform filtering processing on the output signal of the differential amplifying circuit;

An analog-to-digital conversion circuit, the input end of the analog-to-digital conversion circuit is connected to the output end of the filter circuit, and is used for converting the output signal of the filter circuit into a digital signal.
The ultrasonic fingerprint identification device according to claim 19, wherein the ultrasonic fingerprint identification device further comprises:

a rectifier circuit, connected to the filter circuit, for receiving the output signal of the filter circuit and converting the output signal of the filter circuit into a DC signal;

an integrating circuit, the input end of the integrating circuit is connected to the output end of the rectifying circuit, and is used for receiving the DC signal and accumulating the half-wave signals with the same polarity in the DC signal;

Wherein, the analog-to-digital conversion circuit is used for receiving the output signal of the integrating circuit, and converting the output signal of the integrating circuit into a digital signal.
The ultrasonic fingerprint identification device according to claim 20, wherein the rectifier circuit is a full-wave rectifier circuit.
An electronic device, comprising:

display screen;

And the ultrasonic fingerprint identification device according to any one of claims 1 to 21, the ultrasonic fingerprint identification device is arranged below the display screen.