Ultrasonic fingerprint recognition device, electronic device and stacking thickness adjustment method thereof

Abstract

The disclosed embodiments provide an ultrasonic fingerprint recognition device, an electronic device and a method for adjusting the thickness of a laminate, which relate to the field of fingerprint recognition technology. The specific implementation of the ultrasonic fingerprint recognition device includes: an integrated chip and a piezoelectric transducer, the back of the integrated chip is connected to the application layer, and the piezoelectric transducer is located on the surface of the integrated chip; under the excitation of a 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. This implementation can avoid the interference of the surface defects of the laminate on the fingerprint imaging and improve the fingerprint recognition accuracy.

Description

Technical Field

[0001] The present disclosure relates to the technical field of fingerprint recognition, and in particular, to an ultrasonic fingerprint recognition device, an electronic device, and a method for adjusting the laminated thickness thereof. Background Art

[0002] Ultrasonic fingerprint recognition refers to emitting an ultrasonic signal to the application layer and recognizing the user's fingerprint according to the ultrasonic echo signal reflected by the user's finger touching the application layer. Since ultrasonic waves can accurately recognize the skin reflection signal and are not affected by various liquids, stains, etc. on the skin surface, ultrasonic fingerprint recognition has been widely used.

[0003] In the existing ultrasonic fingerprint recognition device, due to the different materials and forming methods of each laminated layer, the surface of the laminated layer is not a completely flat plane, and there are various path interferences in the transmission path of the ultrasonic echo signal. For example, surface defects such as bumps and pits cause background image defects such as dot spots and block coverage in fingerprint imaging, reducing the fingerprint recognition accuracy. Summary of the Invention

[0004] In view of this, embodiments of the present disclosure provide an ultrasonic fingerprint recognition device, an electronic device, and a method for adjusting the laminated thickness thereof, which can solve the problem that in the existing ultrasonic fingerprint recognition, there are interferences in the signal transmission path, resulting in image defects in fingerprint imaging and reducing the fingerprint recognition accuracy.

[0005] To achieve the above object, according to one aspect of the present disclosure, there is provided an ultrasonic fingerprint recognition device, including: an integrated chip and a piezoelectric transducer, the back surface of the integrated chip is connected to the application layer, and the piezoelectric transducer is located on the surface of the integrated chip;

[0006] Under the excitation of a driving pulse, the piezoelectric transducer transmits an ultrasonic signal through the integrated chip to the application layer, and the signal receiving circuit of the integrated chip receives the ultrasonic echo signal returned from the finger through the application layer.

[0007] According to another aspect of the present disclosure, there is provided an electronic device, including:

[0008] An application layer; and an ultrasonic fingerprint recognition device for recognizing the fingerprint of a finger touching the application layer.

[0009] According to still another aspect of the present disclosure, there is provided a method for adjusting the laminated thickness of an ultrasonic fingerprint recognition device, the piezoelectric transducer includes a lower electrode, an upper electrode, a piezoelectric layer, and a protective layer disposed on the surface of the integrated chip, and the method for adjusting the laminated thickness includes:

[0010] Obtaining the target operating frequency of the driving pulse;

[0011] According to the longitudinal wave sound velocities of the ultrasonic echo signal in the protective layer, the upper electrode, the piezoelectric layer, and the integrated chip, and 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;

[0012] According to the difference between the return frequency and the target operating frequency, and in accordance with a preset adjustment step size, gradually adjust the thickness of the protective layer, the thickness of the upper electrode layer, the thickness of the piezoelectric layer, and / or the thickness of the integrated chip, to determine the target protective layer thickness, the target upper electrode layer thickness, the target piezoelectric layer thickness, and / or the target integrated chip thickness at which the return frequency is equal to the target operating frequency.

[0013] In one or more technical solutions provided in the embodiments of the present application, by directly attaching the back surface of the integrated chip to the application layer, the ultrasonic echo signal returning from the finger through the application layer can be directly received and processed by the signal receiving circuit of the integrated chip, without passing through multiple stacked layers, which can prevent image defects in fingerprint imaging caused by interference of stacked layer defects with the signal propagation path, and improve the technical effect of fingerprint recognition accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In the following description of the exemplary embodiments with reference to the drawings, more details, features, and advantages of the present disclosure are disclosed. In the drawings:

[0015] Figure 1 Shows a schematic diagram of an ultrasonic fingerprint recognition device according to an exemplary embodiment of the present disclosure;

[0016] Figure 2 Shows a schematic diagram of the attachment of an integrated chip and an application layer according to an exemplary embodiment of the present disclosure;

[0017] Figure 3 Shows a detailed diagram of an ultrasonic fingerprint recognition device according to an exemplary embodiment of the present disclosure;

[0018] Figure 4 Shows a schematic diagram of the array pattern of the lower electrode according to an exemplary embodiment of the present disclosure;

[0019] Figure 5 Shows a schematic diagram of a signal receiving circuit according to a first exemplary embodiment of the present disclosure;

[0020] Figure 6 Shows a schematic diagram of a signal receiving circuit according to a second exemplary embodiment of the present disclosure;

[0021] Figure 7 Shows a top view of the upper electrode according to an exemplary embodiment of the present disclosure;

[0022] Figure 8Shows a cross-sectional view of the upper electrode according to an exemplary embodiment of the present disclosure;

[0023] Figure 9 Shows a top view of the protective layer according to an exemplary embodiment of the present disclosure;

[0024] Figure 10 Shows a cross-sectional view of the protective layer according to an exemplary embodiment of the present disclosure;

[0025] Figure 11 Shows a schematic diagram of the drive circuit according to an exemplary embodiment of the present disclosure;

[0026] Figure 12 Shows a schematic diagram of an ultrasonic fingerprint recognition device according to another exemplary embodiment of the present disclosure;

[0027] Figure 13 Shows a schematic diagram of the return path of the ultrasonic echo signal according to an exemplary embodiment of the present disclosure;

[0028] Figure 14 Shows a flowchart of a method for adjusting the stack thickness of an ultrasonic fingerprint recognition device according to an exemplary embodiment of the present disclosure;

[0029] Figure 15 Shows a trend graph of the return frequency varying with the thickness of the upper electrode layer according to an exemplary embodiment of the present disclosure. Detailed implementation manners

[0030] Embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although some embodiments of the present disclosure are shown in the 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 set forth herein. On the contrary, these embodiments are provided to more thoroughly and completely understand the present disclosure. It should be understood that the drawings and embodiments of the present disclosure are only for exemplary purposes and are not used to limit the protection scope of the present disclosure.

[0031] As used herein, the term "including" and its variations are open-ended, that is, "including but not limited to". The term "based on" is "at least partially based on". The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment". The relevant definitions of other terms will be given in the following description. It should be noted that the concepts such as "first" and "second" mentioned in the present disclosure are only used to distinguish different components and are not used to limit the order or interdependence relationship of the functions performed by these components.

[0032] It should be noted that the modifications of "one" and "multiple" mentioned in the present disclosure are illustrative rather than restrictive. Those skilled in the art should understand that unless clearly stated otherwise in the context, it should be understood as "one or more".

[0033] 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 used to limit the scope of these messages or information.

[0034] bongding: Bonding, which is a wire bonding method in the chip production process and is used to connect the circuit with gold wires to the package pins.

[0035] The solution of the present disclosure will be described below with reference to the accompanying drawings.

[0036] Figure 1 A schematic diagram of an ultrasonic fingerprint recognition device according to an exemplary embodiment of the present disclosure is shown. As Figure 1 shown, the ultrasonic fingerprint recognition device 100 of the present disclosure includes: an integrated chip 10 and a piezoelectric transducer 20, where:

[0037] The back surface 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. Under the excitation of a driving pulse, the piezoelectric transducer 20 transmits an ultrasonic signal through the integrated chip 10 to the application layer 200, and 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:

[0038] Further, as Figure 2 shown, the material of the integrated chip 10 can be silicon, and the back surface of the integrated chip 10 is adhesively connected to the application layer 200 through a first adhesive layer 300. The back surface 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, and its flatness is close to the mirror effect, when the substrate is connected to the application layer, the smooth plane of the substrate can be closely attached to the application layer. Correspondingly, when the ultrasonic echo signal returns to the signal receiving circuit, it does not need to pass through traditional multiple laminations and can be directly received by the signal receiving circuit. That is, 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 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.

[0039] Furthermore, the integrated chip 10 is a CMOS (Complementary Metal Oxide Semiconductor) chip, which realizes the simplification and miniaturization of the ultrasonic fingerprint recognition device while ensuring the signal processing sensitivity.

[0040] In the embodiment of the present disclosure, as Figure 3As shown, the piezoelectric transducer 20 includes a lower electrode 21, an upper electrode 22 disposed on the surface of the integrated chip 10, and a piezoelectric layer 23 located between the lower electrode 21 and the upper electrode 22.

[0041] 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 via the lower electrode 21. The form of the lower electrode 21 can be, for example, Figure 4 the electrode array composed of multiple pixel electrodes 211 as shown, or the form of the lower electrode 21 can also be a whole electrode plate, which can be selectively set according to the actual recognition environment. When the form of the lower electrode 21 is an electrode array, one pixel electrode 211 corresponds to one pixel point of fingerprint imaging, and each pixel electrode 211 receives the ultrasonic echo signals returned from different pixel points respectively. As Figure 5 shown, the signal receiving circuit 11 includes multiple receiving amplifiers 111 and multiple receiving switches 112, and the receiving amplifiers 111, the receiving switches 112 and the pixel electrodes 211 are in one-to-one correspondence. 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 turned off, the corresponding receiving amplifier 111 acquires the ultrasonic echo signal of the pixel electrode 211; when the receiving switch 112 is turned on, the corresponding receiving amplifier 111 does not acquire 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.

[0042] Or, as Figure 6As shown, the signal receiving circuit 11 includes a plurality of switch groups 113 and a plurality of receiving amplifiers 112. One switch group 113 corresponds to one receiving amplifier 112. Each switch group 113 includes a plurality of first switches 1131 and a plurality of second switches 1132. The first switches 1131 correspond one-to-one to the pixel electrodes 211, and the second switches 1132 correspond one-to-one to 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 plurality of first switches 1131 and the plurality of second switches 1132 are used to control the signal acquisition of the corresponding pixel electrode 211. When the first switch 1131 is turned off and the second switch 1132 is turned on, the corresponding receiving amplifier 112 acquires the ultrasonic echo signal of the pixel electrode 211. When the first switch 1131 is turned on and the second switch 1132 is turned off, the corresponding receiving amplifier 112 does not acquire 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 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 the first switch and the second switch in each switch group can be selectively set as needed. For example, as Figure 6 shown, every 4 first switches and second switches are divided into one switch group, corresponding to the same receiving amplifier.

[0043] Further, the lower electrode 21 can be in the form of a whole electrode plate, and each receiving amplifier 111 and receiving switch 112 are directly connected to the electrode plate, or each first switch 1131 and second switch 1132 are directly connected to the electrode plate.

[0044] Furthermore, a shielding electrode 13 is also provided on the surface of the integrated chip 10. As Figure 3 and Figure 4 shown, the shielding electrode 13 is arranged around the lower electrode 21, and is used to improve the non-uniform electric field in the edge region of the lower electrode 21 and improve the sensitivity of signal emission and reception in the edge region of the lower electrode 21.

[0045] In the embodiment of the present disclosure, as Figure 3 shown, an upper electrode driving trace 14 is also 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 it to the upper electrode 22.

[0046] Further, as Figure 7 and Figure 8As shown, the longitudinal section of the upper electrode 22 is stepped, 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 connection part 223 connecting the first electrode platform 221 and the second electrode platform 222. The longitudinal electrode connection part 223 is perpendicular to the surface of the integrated chip 10. The upper electrode driving trace 14 is electrically connected to the second electrode platform 222.

[0047] Furthermore, the surface of the upper electrode driving trace 14 is covered with a passivation layer 15. A first opening 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 opening 151.

[0048] Further, the piezoelectric layer 23 is embedded in the accommodation cavity surrounded by the first electrode platform 221 and the longitudinal electrode connection part 223. During emission, after the upper electrode 22 receives a driving pulse, the piezoelectric layer 23 is excited. The piezoelectric layer 23 converts the driving electrical signal of the driving pulse into a mechanical ultrasonic signal, and emits the ultrasonic signal through the integrated chip 10 to the application layer 200. During reception, when the user's finger touches the application layer 200, an ultrasonic echo signal is returned through the application layer 200. The mechanical ultrasonic echo signal propagates to the piezoelectric layer 23. The piezoelectric layer 23 converts the ultrasonic echo signal into an ultrasonic echo electrical signal. The upper electrode 22 and the lower electrode 21 receive it and then 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.

[0049] Furthermore, the material of the piezoelectric layer 23 can be a piezoelectric polymer material with piezoelectric effect such as polyvinylidene difluoride (PVDF), polyvinylidene difluoride-trifluoroethylene (PVDF TrFE), etc. The material of the upper electrode 22 can be silver paste. When processing the upper electrode 22, a silver paste coating mixed with silver powder and glue can be directly applied on the surface of the piezoelectric layer 23.

[0050] In the embodiment of the present disclosure, as Figure 3 shown, the piezoelectric transducer 20 further includes a protective layer 24. The protective layer 24 covers the surface of the upper electrode 22. The material can be a semiconductor material such as aluminum gallium arsenide, etc., which is used to provide protection for the upper electrode 22 to avoid damage such as friction and pressure on the surface of the upper electrode 22, and ensure the stable reception and processing of the signal of the upper electrode 22.

[0051] Further, as Figure 9 and Figure 10As shown, the longitudinal section of the protective layer 24 is also stepped, including a first protection platform 241 and a second protection platform 242 parallel to the surface of the integrated chip 10, and a longitudinal protection connection part 243 connecting the first protection platform 241 and the second protection platform 242. The longitudinal protection connection part 243 is perpendicular to the surface of the integrated chip 10.

[0052] In the embodiment of the present disclosure, as Figure 3 shown, the ultrasonic fingerprint recognition device 100 further includes a driving circuit 30. The driving circuit 30 is electrically connected to the upper electrode 22 of the piezoelectric transducer 20 through an upper electrode driving trace 14 arranged on the surface of the integrated chip 10 to send a driving pulse to the piezoelectric transducer 20.

[0053] Furthermore, as Figure 11 shown, the driving circuit 30 includes a driver 31, a resonant circuit 32 and a braking circuit 33. The driver 31 includes a driving switch 311, a grounding switch 312 and a driving resistor 313. One end of the driving switch 311 is connected to a driving power supply (the driving voltage is represented as VH), and the other end is connected to the driving resistor 313. One end of the grounding switch 312 is grounded, and the other end is connected to the side of the driving resistor 313 where the driving switch 311 is connected. The resonant circuit 32 includes an inductor 321, an equivalent resistor 322 and a capacitor 323, and is used for resonating the pulse sent by the driver 31 so that the driving circuit 30 outputs a driving pulse. One end of the inductor 321 is connected to the side of the driving resistor 313 away from the driving 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. One end of the capacitor 323 away from the equivalent resistor 322 is grounded, and the driving pulse is output between the equivalent resistor 322 and the capacitor 323. The braking circuit 33 includes a damping resistor 331, and is used for absorbing the residual vibration energy of the resonant circuit 32 so that the resonant circuit 32 quickly returns to zero. One end of the damping resistor 331 is connected between the driving resistor 313 and the inductor 321, and the other end is grounded.

[0054] Even further, the driving circuit 30 further includes a control circuit 34. The control circuit 34 can be arranged on the integrated chip 10 or in other environmental structures in the specific application scenario of the ultrasonic fingerprint recognition device 100, and is used for sending 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. Among them, when the first control signal and the second control signal respectively control the driving switch 311 and the grounding switch 312 to open and close alternately, a square wave pulse can be generated. The resonant circuit 32 resonates the square wave pulse generated by the driver 31 so that the driving circuit 30 outputs a sine wave pulse with a resonant frequency of the target operating frequency f s of.

[0055] In another embodiment of the present disclosure, as Figure 12 shown, a support layer 400 is further provided between the back surface of the integrated chip 10 and the application layer 200, which is used to support the integrated chip 10 and enhance the stability of the ultrasonic fingerprint recognition device.

[0056] Furthermore, the support layer 400 can also be used as a waveguide layer to perform impedance matching on the signal and enhance signal conduction.

[0057] Even further, the support layer 400 is adhered to the back surface of the integrated chip 10 through the first adhesive layer 300 and adhered to the application layer 200 through the second adhesive layer 500.

[0058] In an embodiment of the present disclosure, as Figure 3 shown, the ultrasonic fingerprint recognition device 100 includes an integrated chip 10, a piezoelectric transducer 20, and a driving circuit 30. The back surface 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. 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 through the integrated chip 10 to the application layer 200, and then the integrated chip 10 receives the ultrasonic echo signal returned from the finger through the application layer 200. Specifically:

[0059] The integrated chip 10 includes a signal receiving circuit 11, a substrate 12, a shielding electrode 13, an upper electrode driving trace 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 braking circuit 33, and a control circuit 34.

[0060] The substrate 12 of the integrated chip 10 is attached to the application layer 200 through the 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. The shielding electrode 13 and the upper electrode driving 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 driving trace 14 can be referred to as the Top Metal. The upper electrode driving trace 14 is used to be electrically connected to the upper electrode 22 and is fixed to the integrated chip 20 through a bongding process at one end to connect to the driving circuit 30 and receive the driving pulse sent by the driving circuit 30.

[0061] The upper electrode 22 includes a first electrode platform 221, a second electrode platform 222, and a longitudinal electrode connection portion 223. The piezoelectric layer 23 is embedded in the accommodation cavity surrounded by the first electrode platform 221 and the longitudinal electrode connection portion 223. The surface of the metal top layer is covered with a passivation layer 15, which is used to reduce wear or corrosion phenomena such as friction and pressure on the metal top layer, such as Figure 3 As shown, a first opening window 151 is provided in the area of the passivation layer 15 corresponding to the upper electrode driving trace 14, so that the upper electrode driving trace 14 is electrically connected to the second electrode platform 222 where the upper electrode 22 extends out of the piezoelectric layer 23 through the first opening window 151; a second opening window 152 is provided in the area of the passivation layer 15 corresponding to 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.

[0062] The lower electrode 21 is an electrode array composed of a plurality of pixel electrodes 211. One pixel electrode 211 corresponds to one pixel point of 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 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 are in one-to-one correspondence. 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.

[0063] The driving circuit 30 includes a driver 31, a resonant circuit 32, a braking circuit 33, and a control circuit 34. The driver 31 includes a driving switch 311, a grounding switch 312, and a driving resistor 313. One end of the driving switch 311 is connected to the driving power supply, and the other end is connected to the driving resistor 313; one end of the grounding switch 312 is grounded, and the other end is connected to the side of the driving resistor 313 where the driving switch 311 is connected. 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 driving resistor 313 away from the driving 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; one end of the capacitor 323 away from the equivalent resistor 322 is grounded. The braking circuit 33 includes a damping resistor 331. One end of the damping resistor 331 is connected between the driving resistor 313 and the inductor 321, and the other end is grounded. The control circuit 34 is used to send a first control signal and a second control signal to the driving switch 311 and the grounding switch 312 respectively to control the opening and closing of the driving switch 311 and the grounding switch 312.

[0064] In an embodiment of the present disclosure, when in the transmission mode, the receiving switch 112 of the signal receiving circuit 11 is closed. When the control circuit 34 controls the driving switch 311 and the grounding switch 312 to alternately open and close by using the first control signal and the second control signal respectively, the driver 31 generates a square wave pulse; the resonant circuit 32 performs resonance processing on the square wave pulse, and the driving circuit 30 outputs a sine wave pulse with a resonant frequency of the target operating frequency f s from between the equivalent resistor 322 and the capacitor 323. The sine wave pulse is loaded onto the upper electrode 22 through the upper electrode driving trace 14, exciting the piezoelectric layer 23 to generate mechanical movement to produce an ultrasonic signal, and transmitting it through the integrated chip 10 to the application layer 200.

[0065] 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 impedance state. 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 a fingerprint image is generated after being processed by the integrated chip 200.

[0066] Furthermore, when in the transmission mode, multiple receiving switches 112 do not need to be closed simultaneously. According to the actual recognition scenario, the closing sequence of each receiving switch 112 can be selected according to the pixel point position corresponding to the pixel electrode 211; when in the receiving mode, multiple receiving switches 112 do not need to be disconnected simultaneously. According to the actual recognition scenario, the disconnection sequence of each receiving switch 112 can be selected according to the pixel point position corresponding to the pixel electrode 211.

[0067] Compared with the existing ultrasonic echo signal that needs to pass through multiple layers such as the protective layer and the upper electrode before reaching the piezoelectric layer, the surfaces of each layer are not completely smooth planes, and it is easy to cause interference to the fingerprint imaging background due to the existence of raised pinholes, sunken pits, etc. 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 through the back substrate of the integrated chip to the application layer, and the ultrasonic echo signal returned from the finger through the application layer directly reaches the piezoelectric layer, only passing through the integrated chip and not passing through other layers, and the integrated chip is a smooth plane. Therefore, the ultrasonic echo signal does not have imaging interference caused by surface defects, improving the clarity of fingerprint imaging and the recognition accuracy of fingerprint imaging.

[0068] 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 transmission mode, it is transmitted along the surface of the integrated chip 10 towards the back surface, and is transmitted through the integrated chip 10 to the application layer 200; when in the reception 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 path as shown in Figure 13 After passing through the integrated chip 10, the piezoelectric layer 23, the upper electrode 22, and the protective layer 24, it reversely folds back along the protective layer 24, the upper electrode 22, the piezoelectric layer 23, and the integrated chip 100. In order to ensure that the folding-back frequency of the ultrasonic echo signal reaches the target operating frequency f of the usage scenario s , as shown in Figure 14 , the present disclosure adjusts the stacked thicknesses of the integrated chip 10, the piezoelectric layer 23, the upper electrode 22, and the protective layer 24 to make the folding-back frequency reach the target operating frequency f s to ensure the strongest superposition effect and maximize the energy of the transmitted ultrasonic wave.

[0069] Furthermore, as shown in Figure 14 , the method for adjusting the stacked thickness of the ultrasonic fingerprint recognition device of the present disclosure includes the following steps:

[0070] Step S1401: Obtain the target operating frequency of the driving pulse.

[0071] Step S1402: According to the longitudinal wave sound velocities of the ultrasonic echo signal in the protective layer, the upper electrode, the piezoelectric layer, and the integrated chip, and using the protective layer thickness, the upper electrode layer thickness, the piezoelectric layer thickness, and the integrated chip thickness, calculate the folding-back frequency of the ultrasonic echo signal.

[0072] In the embodiment of the present disclosure, after the ultrasonic echo signal returned 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, it reversely folds back along the protective layer 23, the upper electrode 22, the piezoelectric layer 23, and the integrated chip 100. The folding-back frequency is determined by the folding-back time of the ultrasonic echo signal passing through each stacked layer. Specifically:

[0073] Determine the folding-back time of the ultrasonic echo signal according to the transmission path of the ultrasonic echo signal to obtain the folding-back frequency.

[0074] In the embodiments of the present disclosure, when the refolded 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 sine wave pulse output by the drive circuit 30 passing through the piezoelectric layer 23. Therefore, in order to ensure that the energy of the transmitted ultrasonic signal after superposition is the largest, that is, to make the phase difference between the ultrasonic signal excited by the drive pulse and the ultrasonic signal re-excited by the ultrasonic echo signal zero, and to ensure the best energy intensity to improve the signal transmission intensity, the refolding time t of the ultrasonic echo signal d is shown in the following formula (1):

[0075]

[0076] In the above formula:

[0077] D Si is the integrated chip thickness of the integrated chip 10, and u Si is the longitudinal wave sound velocity when the ultrasonic signal is transmitted in the integrated chip 10; D p is the piezoelectric layer thickness of the piezoelectric layer 23, and u p is the longitudinal wave sound velocity when the ultrasonic signal is transmitted in the piezoelectric layer 23; D Ag is the upper electrode layer thickness of the upper electrode 22, and u Ag is the longitudinal wave sound velocity when the ultrasonic signal is transmitted in the upper electrode 22; D OC is the protective layer thickness of the protective layer 24, and u OC is the longitudinal wave sound velocity when the ultrasonic signal is transmitted in the protective layer 24.

[0078] Further, the refolding frequency f of the ultrasonic echo signal d is the reciprocal f d of the refolding time t d = 1 / t d .

[0079] Step S1403, according to the difference between the refolding frequency and the target operating frequency, and in accordance with a preset adjustment step size, gradually adjust the protective layer thickness, the upper electrode layer thickness, the piezoelectric layer thickness, and / or the integrated chip thickness, and determine the target protective layer thickness, the target upper electrode layer thickness, the target piezoelectric layer thickness, and / or the target integrated chip thickness when the refolding frequency is equal to the target operating frequency.

[0080] Step S14031, according to the fact that the phase difference between the ultrasonic signal excited by the drive pulse and the ultrasonic signal re-excited by the ultrasonic echo signal is zero, determine the relationship between the refolding frequency of the ultrasonic echo signal and the target operating frequency of the drive pulse.

[0081] In the embodiments of the present disclosure, the phase difference between the ultrasonic signal excited by the driving pulse and the ultrasonic signal re-excited by the ultrasonic echo signal is zero, which means the round-trip time t of the ultrasonic echo signal d is an integer multiple of the pulse period T of the driving pulse s , as shown in the following formula (2):

[0082] t d = nT s , n = 1, 2, …, N (2)

[0083] And the pulse period T of the driving pulse s is the reciprocal T of the target operating frequency f of the driving pulse s , substituting the sum of formula (2) into formula (1) together, as shown in the following formula (3): s = 1 / f s , substituting into formula (3) can obtain the relationship between the round-trip frequency f of the ultrasonic echo signal

[0084]

[0085] and the target operating frequency f of the driving pulse d , as shown in the following formula (4): s In the above formula, for example, the longitudinal wave sound velocities of ultrasonic signals in various materials include:

[0086]

[0087] For PMMA is 2.73 um / ns, for copper is 4.7 um / ns, for steel is 5.9 um / ns, for aluminum is 6.3 um / ns, for beryllium is 12.9 um / ns, for gold is 3.2 um / ns, for iron is 5.9 um / ns, for Inconel is 5.7 um / ns, for lead is 2.2 um / ns, for nickel is 5.6 um / ns, for polystyrene is 2.4 um / ns, for polyethylene is 1.9 um / ns, for rubber is 1.8 um / ns, for tin is 3.3 um / ns, for titanium is 6.1 um / ns, for PVDF is 2.2 um / ns, for silicon (Si) is 2.33 um / ns, for silver paste is 1.5 - 2.5 um / ns, for polyvinyl chloride (PVC) is 2.39 um / ns, for polypropylene (PP) is 2.1 um / ns, for perfluoroalkoxy alkane (PFA) is 1.23 um / ns, for acrylonitrile-butadiene-styrene (ABS) is 2.25 um / ns.

[0088]

[0089] ​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 stacked layers as the solution target. The objective function is that the sum of the propagation times of the different stacked layers is equal to half of the reciprocal of the target operating frequency.

[0090] In the embodiments of the present disclosure, the return frequency f of the ultrasonic signal re-excited by the ultrasonic echo signal d is closer to the target operating frequency f of the driving pulse s , the stronger the superposition effect. As can be seen from the above formula (4), when n = 1, the superposition effect is the strongest. Therefore, in order to achieve the strongest superposition effect, with the return frequency f when n = 1 d equal to the target operating frequency f s as the target, the obtained objective function is shown in the following formula (5):

[0091]

[0092] The above formula (5) indicates that the sum of the propagation times of the different stacked layers is equal to half of the reciprocal of the target operating frequency.

[0093] Step S14033: Construct constraint conditions for the objective function according to the thickness ranges of the integrated chip thickness, the piezoelectric layer thickness, the upper electrode layer thickness, the protective layer thickness, and the total thickness.

[0094] In the embodiments of the present disclosure, as can be seen from the above formula (5), since the longitudinal wave sound velocity of the ultrasonic signal in the stacked layer is constant, the present disclosure adjusts the stacked layer thickness of each stacked layer to achieve the requirement of reaching the target operating frequency f s . However, due to differences in materials and processing technologies, there are limitations on the thickness ranges of the stacked layer thicknesses of each stacked layer. The constraint conditions are shown in the following formula (6):

[0095]

[0096] The application scenario of the ultrasonic fingerprint recognition device also has limitations on the device thickness of the entire device. Therefore, the constraint condition for the total thickness of each stacked layer is shown in the following formula (7):

[0097] D Si +D p +D Ag +D OC =D sum ≤D sum,max (7)

[0098] Step S14034: According to the objective function and the constraint conditions, gradually adjust the integrated chip thickness, the piezoelectric layer thickness, the upper electrode layer thickness, and / or the protective layer thickness according to a preset adjustment step size, 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.

[0099] In an embodiment of the present disclosure, under the constraint conditions of formulas (6)-(7), at least one of the integrated chip thickness, the piezoelectric layer thickness, the upper electrode layer thickness, and / or the protective layer thickness in the objective function of formula (5) is adjusted to solve for the target protective layer thickness, the target upper electrode layer thickness, the target piezoelectric layer thickness, and / or the target integrated chip thickness.

[0100] Further, taking D Si = 110um, D p = 9um, D OC = 9um as fixed and adjusting the upper electrode layer thickness D Ag as an example for illustration, as Figure 15 shown, the abscissa is the upper electrode layer thickness D Ag (um), and the ordinate is the fold-back frequency f d (MHz). It can be seen from Figure 15 that as the upper electrode layer thickness D Ag increases, the fold-back frequency f d gradually decreases. When the target operating frequency f s is 13MHz, the target upper electrode layer thickness is 22um.

[0101] Furthermore, similarly, by adjusting ① the integrated chip thickness, ② or the piezoelectric layer thickness, ③ or the protective layer thickness, ④ or the integrated chip thickness and the piezoelectric layer thickness, ⑤ or the integrated chip thickness and the upper electrode layer thickness, ⑥ or the integrated chip thickness and the protective layer thickness, ⑦ or the piezoelectric layer thickness and the upper electrode layer thickness, ⑧ or the piezoelectric layer thickness and the protective layer thickness, ⑨ or the upper electrode layer thickness and the protective layer thickness, ⑩ or the integrated chip thickness, the piezoelectric layer thickness and the upper electrode layer thickness, or the integrated chip thickness, the piezoelectric layer thickness and the protective layer thickness, or the integrated chip thickness, the upper electrode layer thickness and the protective layer thickness, or the piezoelectric layer thickness, the upper electrode layer thickness and the protective layer thickness, or the integrated chip thickness, the piezoelectric layer thickness, the upper electrode layer thickness and the protective layer thickness, the fold-back frequency f d can be made equal to the target operating frequency f s .

[0102] In the embodiments of the present disclosure, or, according to the different laminations of the ultrasonic fingerprint recognition device, the objective function of Equation (5) can change adaptively. For example, as Figure 12 shown, the ultrasonic fingerprint recognition device further includes a support layer 400, which is used to perform impedance matching on the ultrasonic echo signal, while increasing the transmission path of the ultrasonic echo signal, increasing the reflection time of the ultrasonic echo signal, reducing the interference between the ultrasonic signal excited by the driving pulse and the ultrasonic signal re-excited by the ultrasonic echo signal, enhancing the signal propagation intensity, improving the stability of fingerprint imaging, and thus ensuring the fingerprint recognition accuracy. Correspondingly, the reflection path of the ultrasonic echo signal further includes the support layer 400, and the objective function is as shown in the following Equation (8):

[0103]

[0104] In the above formula: D wg is the thickness of the support layer 400, and u wg is the longitudinal wave sound velocity when the ultrasonic signal is transmitted in the support layer 400.

[0105] In the embodiments of the present disclosure, or, according to whether the lamination thickness of the ultrasonic fingerprint recognition device is fixed, the objective function of Equation (5) can change adaptively. For example, the thickness D Si of the integrated chip 10 is fixed as a known constant, and the objective function is as shown in the following Equation (9):

[0106]

[0107] For another example, the thickness D Si of the integrated chip 10 and the thickness D p of the piezoelectric layer 23 are fixed as known constants, and the objective function is as shown in the following Equation (10):

[0108]

[0109] For still another example, the thickness D Si of the integrated chip 10, the thickness D p of the piezoelectric layer 23, and the thickness D OC of the protective layer 24 are fixed as known constants, and the objective function is as shown in the following Equation (11):

[0110]

[0111] And so on.

[0112] In the embodiments of the present disclosure, through the method for adjusting the stacked thickness of the ultrasonic fingerprint recognition device of the present disclosure, the stacked thickness of each layer can be adjusted to determine the optimal target stacked 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.

[0113] The exemplary embodiments of the present disclosure further provide an electronic device, including: 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, a vehicle-mounted electronic device, or a wearable intelligent device, as well as other electronic devices such as an electronic database, an automobile, and an automated teller machine.

[0114] Further, the application layer is a display screen.

[0115] The components shown herein, their connections and relationships, and their functions are merely exemplary and are not intended to limit the implementation of the present 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 is connected to the application layer, the back side of the integrated chip is the substrate of the integrated chip, the substrate is a smooth plane, and the back side of the integrated chip is connected to the application layer through 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, which is used to promote 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 comprises a lower electrode, an upper electrode and a piezoelectric layer between the lower electrode and the upper electrode, which are arranged on the surface of the integrated chip; 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; 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 bonding layer and to the application layer through a second bonding layer. The supporting layer is a waveguide layer for strengthening the conduction of the ultrasonic signal and the ultrasonic echo signal.

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 to each other one by 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, characterized in that: 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, characterized in that: An upper electrode driving wiring is arranged on the surface of the integrated chip, and the upper electrode driving wiring is electrically connected to the upper electrode.

7. The ultrasonic fingerprint recognition device according to claim 6, characterized in that: The longitudinal cross-section of the upper electrode is step-shaped, 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 and perpendicular to the surface of the integrated chip, and the upper electrode drive wiring is electrically connected to the second electrode platform.

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

9. The ultrasonic fingerprint recognition device according to claim 7, characterized in that: The piezoelectric layer is embedded in a receiving cavity surrounded by the first electrode platform and the longitudinal electrode connecting portion.

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

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

12. The ultrasonic fingerprint recognition device according to claim 1, characterized in that: It also includes a driving circuit, which is electrically connected to the upper electrode of the piezoelectric transducer through an upper electrode driving trace arranged on the surface of the integrated chip to send a driving pulse to the piezoelectric transducer; the driving circuit includes a driver and a resonant circuit; The driver comprises a driving switch, a grounding switch and a driving resistor, wherein one end of the driving switch is connected to a driving power source 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 a 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.

13. The ultrasonic fingerprint recognition device according to claim 12, characterized in that: The driving circuit further includes a brake circuit, and 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.

14. The ultrasonic fingerprint recognition device according to claim 12, characterized in that: The driver further includes a control circuit disposed on the integrated chip, and the control circuit controls the opening and closing of the drive switch and the ground switch, so that the drive pulse generated by the drive circuit is a sine wave pulse.

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

16. The electronic device according to claim 15, characterized in that: 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: Acquiring a target operating frequency of the driving pulse; 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, the return frequency of the ultrasonic echo signal is calculated by 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 a preset adjustment step 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.

Images