Ultrasonic fingerprint identification device, electronic equipment and lamination thickness adjusting method thereof

Abstract

The embodiment of the invention provides an ultrasonic fingerprint recognition device, electronic equipment and a lamination thickness adjusting method thereof, and relates to the technical field of fingerprint recognition. The ultrasonic fingerprint identification device comprises an integrated chip and a piezoelectric transducer, wherein the back surface of the integrated chip is connected with an application layer through a first bonding layer; the piezoelectric transducer is positioned on the surface of the integrated chip; the first bonding layer is an acoustic impedance matching layer and is used for promoting propagation of an ultrasonic signal; under the excitation of the driving pulse, the piezoelectric transducer transmits an ultrasonic signal to the application layer through the integrated chip, and a signal receiving circuit of the integrated chip receives an ultrasonic echo signal returned from the finger through the application layer; the piezoelectric transducer comprises a lower electrode, an upper electrode and a piezoelectric layer located between the upper electrode and the lower electrode. The lower electrode is electrically connected with the signal receiving circuit, and the signal receiving circuit receives an ultrasonic echo signal through the lower electrode. According to the embodiment, interference of surface defects of the lamination on fingerprint imaging can be avoided, and the fingerprint identification precision is improved.

Description

[0001] The present disclosure is a divisional application of the invention patent with the invention name “Ultrasonic fingerprint recognition device, electronic device and laminate thickness adjustment method thereof”, the application date is October 17, 2023, and the application number is 202311350805.4. Technical Field

[0002] The present disclosure relates to the field of fingerprint recognition technology, and in particular to an ultrasonic fingerprint recognition device, an electronic device, and a method for adjusting the thickness of a laminate thereof. Background Art

[0003] Ultrasonic fingerprint recognition involves transmitting ultrasonic signals to the application layer and identifying the user's fingerprint based on the ultrasonic echo signal reflected by the user's finger touching the application layer. Ultrasonic fingerprint recognition is widely used because it can accurately identify signals reflected from the skin and is unaffected by various liquids and stains on the skin surface.

[0004] In existing ultrasonic fingerprint recognition devices, due to the different materials and molding methods of each laminate, the laminate surface is not a completely flat plane. The transmission path of the ultrasonic echo signal is subject to various path interferences. For example, surface defects such as bumps and pits cause background image defects such as spots and block coverage in the fingerprint imaging, reducing the accuracy of fingerprint recognition. Summary of the Invention

[0005] In view of this, the embodiments of the present disclosure provide an ultrasonic fingerprint recognition device, an electronic device, and a method for adjusting the laminate thickness thereof, which can solve the problem in existing ultrasonic fingerprint recognition that interference in the signal transmission path causes image defects in the fingerprint imaging and reduces the fingerprint recognition accuracy.

[0006] To achieve the above objectives, according to one aspect of the present disclosure, an ultrasonic fingerprint recognition device is provided, comprising: an integrated chip and a piezoelectric transducer, wherein the integrated chip is a CMOS chip, the back surface of the integrated chip being connected to an application layer, the back surface of the integrated chip being the substrate of the integrated chip, which is a smooth plane, and the back surface of the integrated chip being connected to the application layer via a first adhesive layer; the piezoelectric transducer is located on the surface of the integrated chip; the first adhesive layer is an acoustic impedance matching layer for promoting ultrasonic signal propagation;

[0007] Under the excitation of the driving pulse, the piezoelectric transducer transmits an ultrasonic signal to the application layer through the integrated chip, and the signal receiving circuit of the integrated chip receives the ultrasonic echo signal returned from the finger through the application layer;

[0008] The piezoelectric transducer includes a lower electrode and an upper electrode provided on the surface of the integrated chip, and a piezoelectric layer located between the lower electrode and the upper electrode; the lower electrode is electrically connected to the signal receiving circuit, and the signal receiving circuit receives the ultrasonic echo signal through the lower electrode, and the lower electrode is an electrode array composed of a plurality of pixel electrodes;

[0009] An upper electrode driving line is provided on the surface of the integrated chip. The longitudinal cross-section of the upper electrode is a step-type, including a first electrode platform and a second electrode platform parallel to the surface of the integrated chip, and a longitudinal electrode connecting portion connecting the first electrode platform and the second electrode platform. The upper electrode driving line is electrically connected to the second electrode platform.

[0010] According to another aspect of the present disclosure, there is provided an electronic device, comprising:

[0011] application layer; and an ultrasonic fingerprint recognition device for recognizing the fingerprint of a finger touching the application layer.

[0012] According to another aspect of the present disclosure, a method for adjusting the stack thickness of an ultrasonic fingerprint recognition device is provided, wherein the piezoelectric transducer includes a lower electrode, an upper electrode, a piezoelectric layer, and a protective layer provided on a surface of the integrated chip, and the stack thickness adjustment method includes:

[0013] Obtaining a target operating frequency of the driving pulse;

[0014] Calculating the return frequency of the ultrasonic echo signal according to the longitudinal wave sound velocity of the ultrasonic echo signal in the protective layer, the upper electrode, the piezoelectric layer and the integrated chip using the thickness of the protective layer, the thickness of the upper electrode layer, the thickness of the piezoelectric layer and the thickness of the integrated chip;

[0015] According to the difference between the return frequency and the target operating frequency, the protective layer thickness, the upper electrode layer thickness, the piezoelectric layer thickness, and / or the integrated chip thickness are gradually adjusted according to the preset adjustment step size to determine the target protective layer thickness, target upper electrode layer thickness, target piezoelectric layer thickness, and / or target integrated chip thickness when the return frequency is equal to the target operating frequency.

[0016] One or more technical solutions provided in the embodiments of the present application directly adhere the back side of the integrated chip to the application layer so that the ultrasonic echo signal returned from the finger through the application layer is directly received and processed by the signal receiving circuit of the integrated chip without passing through multiple layers. This can prevent image defects in fingerprint imaging caused by interfering with the signal propagation path due to layer defects, thereby improving the technical effect of fingerprint recognition accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Further details, features and advantages of the present disclosure are disclosed in the following description of exemplary embodiments in conjunction with the accompanying drawings, in which:

[0018] Figure 1 A schematic diagram of an ultrasonic fingerprint recognition device according to an exemplary embodiment of the present disclosure is shown;

[0019] Figure 2 A schematic diagram illustrating the bonding of an integrated chip and an application layer according to an exemplary embodiment of the present disclosure is shown;

[0020] Figure 3 A detailed diagram of an ultrasonic fingerprint recognition device according to an exemplary embodiment of the present disclosure is shown;

[0021] Figure 4 A schematic diagram showing an array pattern of lower electrodes according to an exemplary embodiment of the present disclosure;

[0022] Figure 5 A schematic diagram showing a signal receiving circuit according to a first exemplary embodiment of the present disclosure is shown;

[0023] Figure 6 A schematic diagram showing a signal receiving circuit according to a second exemplary embodiment of the present disclosure is shown;

[0024] Figure 7 shows a top view of an upper electrode according to an exemplary embodiment of the present disclosure;

[0025] Figure 8 shows a cross-sectional view of an upper electrode according to an exemplary embodiment of the present disclosure;

[0026] Figure 9 shows a top view of a protective layer according to an exemplary embodiment of the present disclosure;

[0027] Figure 10 shows a cross-sectional view of a protective layer according to an exemplary embodiment of the present disclosure;

[0028] Figure 11 shows a schematic diagram of a driving circuit according to an exemplary embodiment of the present disclosure;

[0029] Figure 12 A schematic diagram of an ultrasonic fingerprint recognition device according to another exemplary embodiment of the present disclosure is shown;

[0030] Figure 13 A schematic diagram showing a return path of an ultrasonic echo signal according to an exemplary embodiment of the present disclosure;

[0031] Figure 14 A flow chart showing a method for adjusting the stack thickness of an ultrasonic fingerprint recognition device according to an exemplary embodiment of the present disclosure is shown;

[0032] Figure 15 A trend diagram showing how the foldback frequency varies with the thickness of the upper electrode layer according to an exemplary embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0033] The following describes embodiments of the present disclosure in more detail with reference to the accompanying drawings. Although certain embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be construed as limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the present disclosure. It should be understood that the drawings and embodiments of the present disclosure are for illustrative purposes only and are not intended to limit the scope of protection of the present disclosure.

[0034] The term "including" and its variations used in this document are open inclusions, that is, "including but not limited to". The term "based on" means "based at least in part on". The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one other embodiment". The relevant definitions of other terms will be given in the following description. It should be noted that the concepts of "first", "second", etc. mentioned in this disclosure are only used to distinguish different components, and are not used to limit the order or interdependence of the functions performed by these components.

[0035] It should be noted that the modifications of "one" and "multiple" mentioned in the present disclosure are illustrative rather than restrictive, and those skilled in the art should understand that unless otherwise clearly indicated in the context, they should be understood as "one or more".

[0036] The names of the messages or information exchanged between multiple components in the embodiments of the present disclosure are for illustrative purposes only and are not intended to limit the scope of these messages or information.

[0037] Bongding: Bonding is a wire bonding method in the chip production process, which is used to connect the circuit to the package pins with gold wire.

[0038] Aspects of the present disclosure are described below with reference to the accompanying drawings.

[0039] Figure 1 A schematic diagram of an ultrasonic fingerprint recognition device according to an exemplary embodiment of the present disclosure is shown. Figure 1 As shown, the ultrasonic fingerprint recognition device 100 of the present disclosure includes: an integrated chip 10 and a piezoelectric transducer 20, wherein:

[0040] The back of the integrated chip 10 is connected to the application layer 200. The piezoelectric transducer 20 is located on the surface of the integrated chip 10. Under the excitation of the driving pulse, the piezoelectric transducer 20 transmits an ultrasonic signal through the integrated chip 10 to the application layer 200. The signal receiving circuit 11 of the integrated chip 10 receives the ultrasonic echo signal returned from the finger through the application layer 200. Specifically:

[0041] Further, if Figure 2 As shown, the material of the integrated chip 10 can be silicon, and the back side of the integrated chip 10 is bonded to the application layer 200 via a first adhesive layer 300. The back side of the integrated chip 10 is the substrate 12 of the integrated chip 10. On the one hand, since the substrate can be ground and polished to a flatness close to that of a mirror, when the substrate is connected to the application layer, the smooth surface of the substrate can be tightly adhered to the application layer. Accordingly, when the ultrasonic echo signal returns to the signal receiving circuit, it does not need to pass through the traditional multiple stacking layers and can be directly received by the signal receiving circuit. In other words, the transmission path of the ultrasonic echo signal returning to the signal receiving circuit is not interfered by defects such as pits, so that the fingerprint imaging background of the ultrasonic echo signal is not interfered, effectively improving the clarity of the fingerprint imaging and enhancing the fingerprint recognition accuracy. On the other hand, the first adhesive layer can also serve as an acoustic impedance matching layer to promote signal propagation.

[0042] Furthermore, the integrated chip 10 is a CMOS (Complementary Metal Oxide Semiconductor) chip, which can achieve simplification and miniaturization of the ultrasonic fingerprint recognition device while ensuring signal processing sensitivity.

[0043] In the embodiment of the present disclosure, Figure 3 As shown, the piezoelectric transducer 20 includes a lower electrode 21 , an upper electrode 22 , and a piezoelectric layer 23 located between the lower electrode 21 and the upper electrode 22 , which are disposed on the surface of the integrated chip 10 .

[0044] In the embodiment of the present disclosure, the lower electrode 21 is electrically connected to the signal receiving circuit 11, and the signal receiving circuit 11 receives the ultrasonic echo signal returned from the finger through the application layer 200 through the lower electrode 21. The form of the lower electrode 21 can be as follows Figure 4 The electrode array shown is composed of multiple pixel electrodes 211, or the lower electrode 21 can also be in the form of a whole electrode plate, which can be selectively set according to the actual recognition environment. In the case where the lower electrode 21 is in the form of an electrode array, one pixel electrode 211 corresponds to one pixel point of fingerprint imaging, and each pixel electrode 211 receives the ultrasonic echo signal returned by different pixel points, such as Figure 5As shown, the signal receiving circuit 11 includes a plurality of receiving amplifiers 111 and a plurality of receiving switches 112, and the receiving amplifiers 111, the receiving switches 112 and the pixel electrodes 211 correspond one to one. Each receiving amplifier 111 is connected to the corresponding pixel electrode 211; one end of each receiving switch 112 is connected to the corresponding pixel electrode 211, and the other end is grounded. The receiving switch 112 is used to control the signal acquisition of the corresponding pixel electrode 211. When the receiving switch 112 is disconnected, the corresponding receiving amplifier 111 collects the ultrasonic echo signal of the pixel electrode 211; when the receiving switch 112 is closed, the corresponding receiving amplifier 111 does not collect the ultrasonic echo signal of the pixel electrode 211. Therefore, by controlling the opening and closing sequence or the opening and closing time of the receiving switch 112, the signal acquisition sequence of the corresponding pixel electrode 211 can be controlled, for example, synchronous reception or sequential reception.

[0045] Or, as Figure 6 As shown, the signal receiving circuit 11 includes multiple switch groups 113 and multiple receiving amplifiers 112, with each switch group 113 corresponding to one receiving amplifier 112. Each switch group 113 includes multiple first switches 1131 and multiple second switches 1132. The first switches 1131 correspond one-to-one with the pixel electrodes 211, and the second switches 1132 correspond one-to-one with the pixel electrodes 211. One end of the first switch 1131 is connected to the corresponding pixel electrode 211, and the other end is grounded. One end of the second switch 1132 is connected to the corresponding pixel electrode 211, and the other end is connected to the receiving amplifier 112 corresponding to the switch group 113. The multiple first switches 1131 and the multiple second switches 1132 are used to control the signal acquisition of the corresponding pixel electrodes 211. When the first switches 1131 are open and the second switches 1132 are closed, the corresponding receiving amplifier 112 acquires the ultrasonic echo signal from the pixel electrodes 211. When the first switches 1131 are closed and the second switches 1132 are open, the corresponding receiving amplifier 112 does not acquire the ultrasonic echo signal from the pixel electrodes 211. Therefore, by controlling the on / off sequence or on / off time of the first switch 1131 and the second switch 1132, the signal acquisition sequence of the corresponding pixel electrode 211 can be controlled. It should be noted that the number of first switches and second switches in each switch group can be selectively set as needed, for example, Figure 6 As shown, every four first switches and second switches are divided into a switch group, corresponding to the same receiving amplifier.

[0046] Furthermore, the lower electrode 21 may be in the form of a whole electrode plate, and each receiving amplifier 111 and receiving switch 112 may be directly connected to the electrode plate, or each first switch 1131 and second switch 1132 may be directly connected to the electrode plate.

[0047] Furthermore, a shielding electrode 13 is provided on the surface of the integrated chip 10. Figure 3 and Figure 4 As shown, the shielding electrode 13 is arranged around the lower electrode 21 to improve the uneven electric field in the edge area of the lower electrode 21 and improve the sensitivity of signal transmission and reception in the edge area of the lower electrode 21.

[0048] In the embodiment of the present disclosure, Figure 3 As shown, an upper electrode driving trace 14 is further provided on the surface of the integrated chip 10 . The upper electrode driving trace 14 is electrically connected to the upper electrode 22 and is used to receive a driving pulse and guide the driving pulse to the upper electrode 22 .

[0049] Further, if Figure 7 and Figure 8 As shown, the longitudinal cross-section of the upper electrode 22 is a step-type, including a first electrode platform 221 and a second electrode platform 222 parallel to the surface of the integrated chip 10, and a longitudinal electrode connecting portion 223 connecting the first electrode platform 221 and the second electrode platform 222. The longitudinal electrode connecting portion 223 is perpendicular to the surface of the integrated chip 10, and the upper electrode driving trace 14 is electrically connected to the second electrode platform 222.

[0050] Furthermore, the surface of the upper electrode driving trace 14 is covered with a passivation layer 15 , and a first window 151 is provided on the passivation layer 15 . The upper electrode driving trace 14 is electrically connected to the second electrode platform 222 through the first window 151 .

[0051] Furthermore, the piezoelectric layer 23 is embedded in the accommodating cavity surrounded by the first electrode platform 221 and the longitudinal electrode connecting portion 223. During transmission, after the upper electrode 22 receives the driving pulse, it excites the piezoelectric layer 23. The piezoelectric layer 23 converts the driving electrical signal of the driving pulse into a mechanical ultrasonic signal, and transmits the ultrasonic signal to the application layer 200 through the integrated chip 10; during reception, the user's finger touches the application layer 200, and the ultrasonic echo signal is returned through the application layer 200. The mechanical ultrasonic echo signal propagates to the piezoelectric layer 23, and the piezoelectric layer 23 converts the ultrasonic echo signal into an ultrasonic echo electrical signal. After receiving, the upper electrode 22 and the lower electrode 21 transmit it to the signal receiving circuit 11, so that the integrated chip 10 processes the ultrasonic echo electrical signal to identify the user's fingerprint.

[0052] Furthermore, the material of the piezoelectric layer 23 can be a piezoelectric polymer material having a piezoelectric effect, such as polyvinylidene difluoride (PVDF) or polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE). The material of the upper electrode 22 can be silver paste. When processing the upper electrode 22, a silver paste coating composed of a mixture of silver powder and glue can be directly applied to the surface of the piezoelectric layer 23.

[0053] In the embodiment of the present disclosure, Figure 3As shown, the piezoelectric transducer 20 also includes a protective layer 24, which covers the surface of the upper electrode 22. The material of the protective layer 24 can be a semiconductor material such as gallium aluminum arsenide, which is used to provide protection for the upper electrode 22, avoid damage such as friction and pressure on the surface of the upper electrode 22, and ensure smooth reception and processing of the upper electrode 22 signal.

[0054] Further, if Figure 9 and Figure 10 As shown, the longitudinal cross-section of the protective layer 24 is also step-shaped, including a first protective platform 241 and a second protective platform 242 parallel to the surface of the integrated chip 10, and a longitudinal protective connection portion 243 connecting the first protective platform 241 and the second protective platform 242, and the longitudinal protective connection portion 243 is perpendicular to the surface of the integrated chip 10.

[0055] In the embodiment of the present disclosure, Figure 3 As shown, the ultrasonic fingerprint recognition device 100 further includes a driving circuit 30 , which is electrically connected to the upper electrode 22 of the piezoelectric transducer 20 via an upper electrode driving trace 14 provided on the surface of the integrated chip 10 to send a driving pulse to the piezoelectric transducer 20 .

[0056] Further, if Figure 11 As shown, the drive circuit 30 includes a driver 31, a resonant circuit 32, and a brake circuit 33. The driver 31 includes a drive switch 311, a grounding switch 312, and a drive resistor 313. One end of the drive switch 311 is connected to a drive power supply (the drive voltage is represented as VH), and the other end is connected to the drive resistor 313. One end of the grounding switch 312 is grounded, and the other end is connected to the side of the drive resistor 313 connected to the drive switch 311. The resonant circuit 32 includes an inductor 321, an equivalent resistor 322, and a capacitor 323, which is used to resonate the pulses emitted by the driver 31 so that the drive circuit 30 outputs a drive pulse. One end of the inductor 321 is connected to the side of the drive resistor 313 away from the drive switch 311, and the other end is connected to the equivalent resistor 322. The side of the equivalent resistor 322 away from the inductor 321 is connected to the capacitor 323. The end of the capacitor 323 away from the equivalent resistor 322 is grounded, and the drive pulse is output between the equivalent resistor 322 and the capacitor 323. The brake circuit 33 includes a damping resistor 331 for absorbing residual vibration energy of the resonant circuit 32 so that the resonant circuit 32 returns to zero quickly. One end of the damping resistor 331 is connected between the driving resistor 313 and the inductor 321 , and the other end is grounded.

[0057] Furthermore, the driving circuit 30 also includes a control circuit 34. The control circuit 34 can be set on the integrated chip 10 or in other environmental structures of the specific application scenario of the ultrasonic fingerprint recognition device 100, and is used to send a first control signal and a second control signal to the driving switch 311 and the grounding switch 312 respectively. The first control signal controls the opening and closing of the driving switch 311, and the second control signal controls the opening and closing of the grounding switch 312. When the first control signal and the second control signal respectively control the alternate opening and closing of the driving switch 311 and the grounding switch 312, a square wave pulse can be generated; the resonant circuit 32 resonates the square wave pulse generated by the driver 31, so that the resonant frequency output by the driving circuit 30 is the target operating frequency f s sine wave pulses.

[0058] In another embodiment of the present disclosure, Figure 12 As shown, a support layer 400 is further provided between the back surface of the integrated chip 10 and the application layer 200 for supporting the integrated chip 10 and enhancing the stability of the ultrasonic fingerprint recognition device.

[0059] Furthermore, the support layer 400 may also serve as a waveguide layer for impedance matching of signals and enhancing signal conduction.

[0060] Furthermore, the support layer 400 is bonded to the back surface of the integrated chip 10 through the first adhesive layer 300 , and is bonded to the application layer 200 through the second adhesive layer 500 .

[0061] In the embodiment of the present disclosure, Figure 3 As shown, the ultrasonic fingerprint recognition device 100 includes an integrated chip 10, a piezoelectric transducer 20, and a driving circuit 30. The back of the integrated chip 10 is connected to the application layer 200, and the piezoelectric transducer 20 is located on the surface of the integrated chip 10. The driving circuit 30 is electrically connected to the piezoelectric transducer 20 to send a driving pulse to the piezoelectric transducer 20. Under the excitation of the driving pulse, the piezoelectric transducer 20 transmits an ultrasonic signal to the application layer 200 through the integrated chip 10, and then the integrated chip 10 receives the ultrasonic echo signal returned from the finger through the application layer 200. Specifically:

[0062] The integrated chip 10 includes a signal receiving circuit 11, a substrate 12, a shielding electrode 13, an upper electrode driving line 14 and a passivation layer 15. The piezoelectric transducer 20 includes a lower electrode 21, an upper electrode 22, a piezoelectric layer 23 located between the lower electrode 21 and the upper electrode 22, and a protective layer 24 covering the surface of the upper electrode 22. The driving circuit 30 includes a driver 31, a resonant circuit 32, a brake circuit 33 and a control circuit 34.

[0063] The substrate 12 of the integrated chip 10 is bonded to the application layer 200 via a first adhesive layer 300. The lower electrode 21 is disposed on the surface of the integrated chip 10 and is electrically connected to the signal receiving circuit 11 of the integrated chip 10. A shielding electrode 13 and an upper electrode drive trace 14 are also disposed on the surface of the integrated chip 10. The shielding electrode 13 is arranged around the lower electrode 21. The combination of the lower electrode 21, the shielding electrode 13, and the upper electrode drive trace 14 can be referred to as the top metal. The upper electrode drive trace 14 is used to electrically connect to the upper electrode 22. One end of the upper electrode drive trace 14 is fixed to the integrated chip 20 via a bonding process to connect to the drive circuit 30 and receive the drive pulses emitted by the drive circuit 30.

[0064] The upper electrode 22 includes a first electrode platform 221, a second electrode platform 222 and a longitudinal electrode connecting portion 223. The piezoelectric layer 23 is embedded in the accommodation cavity surrounded by the first electrode platform 221 and the longitudinal electrode connecting portion 223. The surface of the metal top layer is covered with a passivation layer 15 to reduce the occurrence of wear or corrosion of the metal top layer due to friction, pressure, etc. Figure 3 As shown, a first window 151 is provided in the area corresponding to the passivation layer 15 and the upper electrode driving line 14, so that the upper electrode driving line 14 is electrically connected to the second electrode platform 222 extending from the piezoelectric layer 23 of the upper electrode 22 through the first window 151; a second window 152 is provided in the area corresponding to the passivation layer 15 and the lower electrode 21 and the shielding electrode 13, which is used to ensure the electrical connection between the piezoelectric layer 23 and the lower electrode 21 and the shielding electrode 13.

[0065] The lower electrode 21 is an electrode array consisting of multiple pixel electrodes 211, each pixel electrode 211 corresponding to a pixel point of the fingerprint imaging. The signal receiving circuit 11 is electrically connected to the lower electrode 21, and receives ultrasonic echo signals returned from different pixel points through each pixel electrode 211 of the lower electrode 21. The signal receiving circuit 11 includes multiple receiving amplifiers 111 and multiple receiving switches 112, with each receiving amplifier 111, receiving switch 112 and pixel electrode 211 corresponding to each other. Each receiving amplifier 111 is connected to a corresponding pixel electrode 211; one end of each receiving switch 112 is connected to the corresponding pixel electrode 211, and the other end is grounded.

[0066] The drive circuit 30 includes a driver 31, a resonant circuit 32, a brake circuit 33, and a control circuit 34. The driver 31 includes a drive switch 311, a grounding switch 312, and a drive resistor 313. One end of the drive switch 311 is connected to the drive power supply and the other end is connected to the drive resistor 313. One end of the grounding switch 312 is grounded, and the other end is connected to the side of the drive resistor 313 connected to the drive switch 311. The resonant circuit 32 includes an inductor 321, an equivalent resistor 322, and a capacitor 323. One end of the inductor 321 is connected to the side of the drive resistor 313 away from the drive switch 311, and the other end is connected to the equivalent resistor 322. The side of the equivalent resistor 322 away from the inductor 321 is connected to the capacitor 323. The end of the capacitor 323 away from the equivalent resistor 322 is grounded. The brake circuit 33 includes a damping resistor 331. One end of the damping resistor 331 is connected between the drive resistor 313 and the inductor 321, and the other end is grounded. The control circuit 34 is configured to send a first control signal and a second control signal to the driving switch 311 and the grounding switch 312 respectively, so as to control the opening and closing of the driving switch 311 and the grounding switch 312 .

[0067] In the embodiment of the present disclosure, when in the transmitting mode, the receiving switch 112 of the signal receiving circuit 11 is closed, and the control circuit 34 uses the first control signal and the second control signal to control the driving switch 311 and the grounding switch 312 to be alternately opened and closed, respectively, and the driver 31 generates a square wave pulse; the resonant circuit 32 resonates the square wave pulse, and the driving circuit 30 outputs a resonant frequency between the equivalent resistor 322 and the capacitor 323, which is the target operating frequency f s The sine wave pulse is applied to the upper electrode 22 via the upper electrode drive trace 14, stimulating the mechanical movement of the piezoelectric layer 23 to generate an ultrasonic signal, which is then transmitted to the application layer 200 via the integrated chip 10.

[0068] When the user's finger touches the application layer, it switches to the receiving mode. At this time, the receiving switch 112 of the signal receiving circuit 11 is disconnected, the control circuit 34 stops sending the first control signal and the second control signal, the driving switch 311 and the grounding switch 312 are disconnected, so that the driving resistor 313 is in a high-resistance state, and the mechanical ultrasonic echo signal returned from the application layer 200 propagates to the piezoelectric layer 23 and is converted into an ultrasonic echo electrical signal. After being received by the upper electrode 22 and the lower electrode 21, the ultrasonic echo electrical signal is collected by the receiving amplifier 111, and processed by the integrated chip 200 to generate a fingerprint image.

[0069] Furthermore, when in the transmitting mode, multiple receiving switches 112 do not need to be closed at the same time, and the closing order of each receiving switch 112 can be selected according to the actual recognition scenario and the pixel position corresponding to the pixel electrode 211; when in the receiving mode, multiple receiving switches 112 do not need to be opened at the same time, and the opening order of each receiving switch 112 can be selected according to the actual recognition scenario and the pixel position corresponding to the pixel electrode 211.

[0070] Compared with the existing ultrasonic echo signal, which needs to pass through the protective layer, upper electrode and other layers before reaching the piezoelectric layer, the surface of each layer is not a completely smooth plane, and it is easy to cause interference to the background of fingerprint imaging due to the presence of protrusions, pinholes, depressions and pits on the surface. In the embodiment of the present disclosure, through the ultrasonic fingerprint recognition device of the present disclosure, the ultrasonic signal is transmitted to the application layer through the back substrate of the integrated chip, and the ultrasonic echo signal returned from the finger through the application layer directly reaches the piezoelectric layer, only passing through the integrated chip without passing through other layers, and the integrated chip is a smooth plane, so the ultrasonic echo signal does not have imaging interference from surface defects, thereby improving the clarity of fingerprint imaging and the recognition accuracy of fingerprint imaging.

[0071] In the embodiment of the present disclosure, during the actual use of the ultrasonic fingerprint recognition device, the ultrasonic signal excited by the piezoelectric layer 23 is a longitudinal wave signal. When in the transmitting mode, it is transmitted along the surface of the integrated chip 10 to the back direction, and is transmitted to the application layer 200 through the integrated chip 10; when in the receiving mode, in response to the touch of the user's finger, the ultrasonic echo signal returned through the application layer 200 is transmitted along the same direction as the ultrasonic echo signal. Figure 13 The ultrasonic echo signal is transmitted along the path shown, after passing through the integrated chip 10, the piezoelectric layer 23, the upper electrode 22, and the protective layer 24, it is returned along the protective layer 24, the upper electrode 22, the piezoelectric layer 23, and the integrated chip 100. In order to ensure that the return frequency of the ultrasonic echo signal reaches the target operating frequency f in the use scenario, s ,like Figure 14 As shown, the present disclosure adjusts the stacking thickness of the integrated chip 10, the piezoelectric layer 23, the upper electrode 22, and the protective layer 24 so that the return frequency reaches the target operating frequency f s , to ensure the strongest superposition effect and maximize the energy of the transmitted ultrasound.

[0072] Further, if Figure 14 As shown, the method for adjusting the thickness of the laminate of the ultrasonic fingerprint recognition device disclosed herein includes the following steps:

[0073] Step S1401: Acquire the target operating frequency of the driving pulse.

[0074] Step S1402, according to the longitudinal wave sound velocity of the ultrasonic echo signal in the protective layer, upper electrode, piezoelectric layer and integrated chip, using the thickness of the protective layer, the thickness of the upper electrode layer, the thickness of the piezoelectric layer and the thickness of the integrated chip, calculate the return frequency of the ultrasonic echo signal.

[0075] In the disclosed embodiment, the ultrasonic echo signal returning from the finger through the application layer 200 passes through the integrated chip 10, the piezoelectric layer 23, the upper electrode 22, and the protective layer 24, and then returns along the protective layer 23, the upper electrode 22, the piezoelectric layer 23, and the integrated chip 100. The return frequency is determined by the return time of the ultrasonic echo signal through each stacked layer. Specifically:

[0076] According to the transmission path of the ultrasonic echo signal, the return time of the ultrasonic echo signal is determined to obtain the return frequency.

[0077] In the embodiment of the present disclosure, when the reflected ultrasonic echo signal passes through the piezoelectric layer 23 and is transmitted to the application layer 200 as a re-excited ultrasonic signal, it will be superimposed on the initial ultrasonic signal excited by the sinusoidal wave pulse output by the driving circuit 30 through the piezoelectric layer 23. Therefore, in order to ensure that the energy of the ultrasonic signal transmitted after the superposition is maximized, that is, to make the phase difference between the ultrasonic signal excited by the driving pulse and the ultrasonic signal excited again by the ultrasonic echo signal zero, to ensure the optimal energy intensity, so as to improve the signal transmission intensity, the return time t of the ultrasonic echo signal is set to t. d As shown in the following formula (1):

[0078]

[0079] In the above formula:

[0080] D Si is the thickness of the integrated chip 10, u Si D is the longitudinal wave speed of the ultrasonic signal when it is transmitted in the integrated chip 10; p is the thickness of the piezoelectric layer 23, u p D is the longitudinal wave speed of the ultrasonic signal when it is transmitted in the piezoelectric layer 23; Ag is the thickness of the upper electrode layer of the upper electrode 22, u Ag D is the longitudinal wave speed of the ultrasonic signal when it is transmitted in the upper electrode 22; OC is the thickness of the protective layer 24, u OC It is the longitudinal wave speed of the ultrasonic signal when it is transmitted in the protective layer 24.

[0081] Furthermore, the return frequency f of the ultrasonic echo signal d The return time t d The reciprocal f d =1 / t d .

[0082] Step S1403, based on the difference between the return frequency and the target operating frequency, the protective layer thickness, the upper electrode layer thickness, the piezoelectric layer thickness, and / or the integrated chip thickness are gradually adjusted according to a preset adjustment step size to determine the target protective layer thickness, target upper electrode layer thickness, target piezoelectric layer thickness, and / or target integrated chip thickness when the return frequency is equal to the target operating frequency.

[0083] Step S14031 , based on the phase difference between the ultrasonic signal excited by the driving pulse and the ultrasonic signal excited again by the ultrasonic echo signal being zero, determine the relationship between the return frequency of the ultrasonic echo signal and the target operating frequency of the driving pulse.

[0084] In the embodiment of the present disclosure, the phase difference between the ultrasonic signal excited by the driving pulse and the ultrasonic signal excited again by the ultrasonic echo signal is zero, which means that the return time t d is an integer multiple of the pulse period T of the driving pulse s , as shown in the following formula (2):

[0085] t d =nT s ,n=1,2,…,N (2)

[0086] The pulse period of the driving pulse is T s is the target operating frequency f of the driving pulse s The reciprocal T s =1 / f s , and formula (2) are substituted into formula (1), as shown in formula (3):

[0087]

[0088] Substituting into formula (3) we can get the return frequency f of the ultrasonic echo signal: d and the target operating frequency f of the drive pulse s The relationship between them is shown in the following formula (4):

[0089]

[0090] In the above formula, for example, the longitudinal wave speed of ultrasonic signals in various materials includes:

[0091] Organic glass is 2.73um / ns, copper is 4.7um / ns, steel is 5.9um / ns, aluminum is 6.3um / ns, beryllium is 12.9um / ns, gold is 3.2um / ns, iron is 5.9um / ns, chromium-nickel alloy is 5.7um / ns, lead is 2.2um / ns, nickel is 5.6um / ns, polystyrene is 2.4um / ns, polyethylene is 1.9um / ns, rubber is 1.8um / ns, tin is 3.3um / ns, titanium is 6.1um / ns, PVDF is 2.2um / ns, silicon (Si) is 2.33um / ns, silver paste is 1.5-2.5um / ns, polyvinyl chloride (PVC) is 2.39um / ns, polypropylene (PP) is 2.1um / ns, perfluoroalkoxy The thickness of alkane (PFA) is 1.23um / ns, and that of ABS resin (Acrylonitrilebutadiene styrene) is 2.25um / ns.

[0092] Step S14032, when the return frequency is equal to the target operating frequency, obtain an objective function with the target thickness of each of the stacks as the solution target, and the objective function is that the sum of the propagation times of each different stack is equal to half of the reciprocal of the target operating frequency.

[0093] In the embodiment of the present disclosure, the return frequency f of the ultrasonic signal excited again by the ultrasonic echo signal is d The closer to the target operating frequency f of the driving pulse s , the stronger the superposition effect, from the above formula (4), when n = 1, the superposition effect is the strongest, therefore, in order to achieve the strongest superposition effect, the foldback frequency f when n = 1 is used. d Equal to the target operating frequency f s As the target, the objective function is shown in the following formula (5):

[0094]

[0095] The above formula (5) indicates that the sum of the propagation times of the different stacked layers is equal to half the inverse of the target operating frequency.

[0096] Step S14033, constructing the constraint conditions of the objective function according to the thickness of the integrated chip, the thickness of the piezoelectric layer, the thickness of the upper electrode layer, the thickness of the protective layer and the thickness range of the total thickness.

[0097] In the embodiment of the present disclosure, it can be seen from the above formula (5) that since the longitudinal wave speed of the ultrasonic signal in the laminate is constant, the present disclosure adjusts the laminate thickness of each laminate to achieve the target operating frequency f s However, due to the differences in materials and processing technology, the thickness range of each laminate is limited, and the constraint conditions are shown in the following formula (6):

[0098]

[0099] The application scenario of the ultrasonic fingerprint recognition device also places restrictions on the thickness of the entire device. Therefore, the constraints on the total thickness of each stacked layer are as shown in the following formula (7):

[0100] D Si +D p +D Ag +D OC =D sum ≤D sum,max (7)

[0101] Step S14034, according to the objective function and the constraints, and in accordance with the preset adjustment step, gradually adjust the thickness of the integrated chip, the piezoelectric layer thickness, the upper electrode layer thickness, and / or the protective layer thickness to obtain the target protective layer thickness, the target upper electrode layer thickness, the target piezoelectric layer thickness, and / or the target integrated chip thickness.

[0102] In an embodiment of the present disclosure, under the constraints of equations (6)-(7), at least one of the integrated chip thickness, piezoelectric layer thickness, upper electrode layer thickness, and / or protective layer thickness in the objective function of equation (5) is adjusted to solve the target protective layer thickness, target upper electrode layer thickness, target piezoelectric layer thickness, and / or target integrated chip thickness.

[0103] Furthermore, D Si =110um, D p =9um, D OC =9um fixed, adjust the thickness of the upper electrode layer D Ag Take this as an example to illustrate, Figure 15 As shown, the horizontal axis is the thickness of the upper electrode layer D Ag (um), the vertical axis is the return frequency f d (MHz), by Figure 15 It can be seen that as the thickness of the upper electrode layer D Ag As the foldback frequency f d Gradually decreases, when the target operating frequency f s When the frequency is 13 MHz, the target upper electrode layer thickness is 22 μm.

[0104] Furthermore, similarly, by adjusting ① the thickness of the integrated chip, ② or the thickness of the piezoelectric layer, ③ or the thickness of the protective layer, ④ or the thickness of the integrated chip and the thickness of the piezoelectric layer, ⑤ or the thickness of the integrated chip and the thickness of the upper electrode layer, ⑥ or the thickness of the integrated chip and the thickness of the protective layer, ⑦ or the thickness of the piezoelectric layer and the thickness of the upper electrode layer, ⑧ or the thickness of the piezoelectric layer and the thickness of the protective layer, ⑨ or the thickness of the upper electrode layer and the thickness of the protective layer, ⑩ or the thickness of the integrated chip, the thickness of the piezoelectric layer and the thickness of the upper electrode layer, Or the thickness of the integrated chip, the thickness of the piezoelectric layer and the thickness of the protective layer, Or the thickness of the integrated chip, the thickness of the upper electrode layer and the thickness of the protective layer, Or the thickness of the piezoelectric layer, the thickness of the upper electrode layer and the thickness of the protective layer, Or the thickness of the integrated chip, the thickness of the piezoelectric layer, the thickness of the upper electrode layer and the thickness of the protective layer are used to make the foldback frequency f d Equal to the target operating frequency f s .

[0105] In the embodiment of the present disclosure, or according to the different stacking layers of the ultrasonic fingerprint recognition device, the objective function of formula (5) can be adaptively changed, for example, Figure 12 The ultrasonic fingerprint recognition device shown further includes a support layer 400 for impedance matching of the ultrasonic echo signal, while increasing the transmission path of the ultrasonic echo signal, increasing the return time of the ultrasonic echo signal, reducing the interference between the ultrasonic signal excited by the driving pulse and the ultrasonic signal excited again by the ultrasonic echo signal, improving the signal propagation strength, and improving the stability of fingerprint imaging, thereby ensuring the fingerprint recognition accuracy. Accordingly, the return path of the ultrasonic echo signal further includes the support layer 400. The objective function is shown in the following formula (8):

[0106]

[0107] In the above formula: D wg is the thickness of the support layer 400, u wg is the longitudinal wave speed of the ultrasonic signal when it is transmitted in the supporting layer 400.

[0108] In the embodiment of the present disclosure, or depending on whether the stack thickness of the ultrasonic fingerprint recognition device is fixed, the objective function of formula (5) can be adaptively changed, for example, the thickness D of the integrated chip 10 is Si Fixed to a known constant, the objective function is as follows (9):

[0109]

[0110] For example, the thickness D of the integrated chip 10 is Si and the piezoelectric layer thickness D of the piezoelectric layer 23p Fixed to a known constant, the objective function is as follows (10):

[0111]

[0112] For example, the thickness D of the integrated chip 10 is Si , the piezoelectric layer thickness D of the piezoelectric layer 23 p and the protective layer thickness D of the protective layer 24 OC Fixed to a known constant, the objective function is as follows (11):

[0113]

[0114] And so on.

[0115] In the embodiment of the present disclosure, through the stacking thickness adjustment method of the ultrasonic fingerprint recognition device disclosed in the present disclosure, the thickness of each stacking layer can be adjusted to determine the optimal target stacking thickness that meets the target operating frequency, thereby optimizing the signal superposition effect, maximizing the signal superposition energy, improving the fingerprint imaging clarity, and enhancing the fingerprint recognition accuracy.

[0116] The exemplary embodiments of the present disclosure further provide an electronic device, comprising: an application layer; and an ultrasonic fingerprint recognition device for recognizing the fingerprint of a finger touching the application layer. By way of example and not limitation, the electronic device in the embodiments of the present disclosure may be a portable or mobile computing device such as a terminal device, a mobile phone, a tablet computer, a laptop computer, a desktop computer, a gaming device, an in-vehicle electronic device, or a wearable smart device, as well as other electronic devices such as an electronic database, an automobile, and an ATM.

[0117] Furthermore, the application layer is a display screen.

[0118] The components shown herein, their connections and relationships, and their functions, are examples only, and are not meant to limit implementations of the disclosure described and / or claimed herein.

Claims

1. An ultrasonic fingerprint recognition device, characterized in that: include: An integrated chip and a piezoelectric transducer, wherein the integrated chip is a CMOS chip, the back side of the integrated chip being connected to the application layer. The back side of the integrated chip is the substrate of the integrated chip, which is a smooth plane. The back side of the integrated chip is connected to the application layer via a first adhesive layer. The piezoelectric transducer is located on the surface of the integrated chip. The first adhesive layer is an acoustic impedance matching layer for promoting the propagation of ultrasonic signals. Under the excitation of the driving pulse, the piezoelectric transducer transmits an ultrasonic signal to the application layer through the integrated chip, and the signal receiving circuit of the integrated chip receives the ultrasonic echo signal returned from the finger through the application layer; The piezoelectric transducer includes a lower electrode and an upper electrode provided on the surface of the integrated chip, and a piezoelectric layer located between the lower electrode and the upper electrode; the lower electrode is electrically connected to the signal receiving circuit, and the signal receiving circuit receives the ultrasonic echo signal through the lower electrode, and the lower electrode is an electrode array composed of a plurality of pixel electrodes; An upper electrode driving line is provided on the surface of the integrated chip. The longitudinal cross-section of the upper electrode is a step-type, including a first electrode platform and a second electrode platform parallel to the surface of the integrated chip, and a longitudinal electrode connecting portion connecting the first electrode platform and the second electrode platform. The upper electrode driving line is electrically connected to the second electrode platform.

2. The ultrasonic fingerprint recognition device according to claim 1, wherein the signal receiving circuit comprises a plurality of receiving amplifiers and a plurality of receiving switches, and the receiving amplifiers, the receiving switches, and the pixel electrodes correspond one to one; The receiving amplifier is connected to the corresponding pixel electrode; One end of the receiving switch is connected to the corresponding pixel electrode, and the other end is grounded.

3. The ultrasonic fingerprint recognition device according to claim 1, wherein: The signal receiving circuit includes a plurality of switch groups and a plurality of receiving amplifiers, and one switch group corresponds to one receiving amplifier; Each of the switch groups includes a plurality of first switches and a plurality of second switches, wherein the first switches and the second switches correspond to the pixel electrodes one by one respectively; One end of the first switch is connected to the pixel electrode, and the other end is grounded; One end of the second switch is connected to the pixel electrode, and the other end is connected to the corresponding receiving amplifier.

4. The ultrasonic fingerprint recognition device as claimed in claim 1, wherein the electrode array is replaced by an electrode plate.

5. The ultrasonic fingerprint recognition device according to any one of claims 1 to 4, characterized in that: A shielding electrode is also provided on the surface of the integrated chip, and the shielding electrode is arranged around the lower electrode.

6. The ultrasonic fingerprint recognition device according to claim 1, wherein: The longitudinal electrode connecting portion is perpendicular to the surface of the integrated chip.

7. The ultrasonic fingerprint recognition device according to claim 1, wherein: The surface of the upper electrode driving wire is covered with a passivation layer, and a window is provided on the passivation layer. The upper electrode driving wire is electrically connected to the second electrode platform through the window.

8. The ultrasonic fingerprint recognition device according to claim 1, wherein: The piezoelectric layer is embedded in a receiving cavity surrounded by the first electrode platform and the longitudinal electrode connecting portion.

9. The ultrasonic fingerprint recognition device according to claim 8, wherein: The piezoelectric transducer further includes a protective layer, which covers a surface of the first electrode platform away from the accommodating cavity.

10. The ultrasonic fingerprint recognition device according to any one of claims 1, 6 to 9, characterized in that: The upper electrode is a silver paste coating.

11. The ultrasonic fingerprint recognition device according to claim 1, wherein: Also included is a driving circuit, the driving circuit being electrically connected to the upper electrode through the upper electrode driving trace to send a driving pulse to the piezoelectric transducer; the driving circuit including a driver and a resonant circuit; The driver includes a driving switch, a grounding switch and a driving resistor, wherein one end of the driving switch is connected to a driving power supply and the other end is connected to the driving resistor; one end of the grounding switch is grounded and the other end is connected to a side of the driving resistor connected to the driving switch; The resonant circuit includes an inductor, an equivalent resistor and a capacitor, one end of the inductor is connected to the side of the driving resistor away from the driving switch, and the other end is connected to the equivalent resistor; the side of the equivalent resistor away from the inductor is connected to the capacitor; and one end of the capacitor away from the equivalent resistor is grounded.

12. The ultrasonic fingerprint recognition device according to claim 11, wherein: The driving circuit further includes a brake circuit. The brake circuit includes a damping resistor. One end of the damping resistor is connected between the driving resistor and the inductor, and the other end is grounded.

13. The ultrasonic fingerprint recognition device according to claim 11, wherein: The driver further includes a control circuit disposed on the integrated chip, and the control circuit controls the opening and closing of the driving switch and the grounding switch, so that the driving pulse generated by the driving circuit is a sine wave pulse.

14. The ultrasonic fingerprint recognition device according to claim 1, wherein: A supporting layer is also provided between the back side of the integrated chip and the application layer. The supporting layer is bonded to the back side of the integrated chip through a first adhesive layer and to the application layer through a second adhesive layer. The supporting layer is a waveguide layer for strengthening the conduction of the ultrasonic signal and the ultrasonic echo signal.

15. An electronic device, characterized in that: include: Application layer; And, the ultrasonic fingerprint recognition device according to any one of claims 1 to 14 is used to recognize the fingerprint of a finger touching the application layer.

16. The electronic device according to claim 15, wherein: The application layer is a display screen.

17. A method for adjusting the thickness of a laminate of an ultrasonic fingerprint recognition device according to any one of claims 1 to 14, characterized in that: The piezoelectric transducer includes a lower electrode, an upper electrode, a piezoelectric layer and a protective layer arranged on the surface of the integrated chip, and the stack thickness adjustment method includes: Obtaining a target operating frequency of the driving pulse; Calculating the return frequency of the ultrasonic echo signal according to the longitudinal wave sound velocity of the ultrasonic echo signal in the protective layer, the upper electrode, the piezoelectric layer and the integrated chip using the thickness of the protective layer, the thickness of the upper electrode layer, the thickness of the piezoelectric layer and the thickness of the integrated chip; According to the difference between the return frequency and the target operating frequency, the protective layer thickness, the upper electrode layer thickness, the piezoelectric layer thickness, and / or the integrated chip thickness are gradually adjusted according to the preset adjustment step size to determine the target protective layer thickness, target upper electrode layer thickness, target piezoelectric layer thickness, and / or target integrated chip thickness when the return frequency is equal to the target operating frequency.

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