CN117218689A

CN117218689A - Display equipment, fingerprint acquisition device and fingerprint acquisition method

Info

Publication number: CN117218689A
Application number: CN202311160831.0A
Authority: CN
Inventors: 赵宇鹏; 韩艳玲; 王玉波; 秦云科; 崔亮; 陈明洁; 佟月; 李扬冰
Original assignee: BOE Technology Group Co Ltd; Beijing BOE Technology Development Co Ltd
Current assignee: BOE Technology Group Co Ltd; Beijing BOE Technology Development Co Ltd
Priority date: 2023-09-08
Filing date: 2023-09-08
Publication date: 2023-12-12

Abstract

The disclosure provides a display device, a fingerprint acquisition device and a fingerprint acquisition method, wherein the fingerprint acquisition device comprises an excitation circuit, a reading circuit, a glass substrate, an ultrasonic transducer array and a driving circuit, wherein the ultrasonic transducer array and the driving circuit are arranged on the glass substrate; the ultrasonic transducer array comprises a plurality of capacitive micromachined ultrasonic transducers, and the capacitive micromachined ultrasonic transducers comprise a first polar plate and a second polar plate; the first pole plate is connected with an excitation circuit, and the excitation circuit is configured to apply alternating excitation voltage to the first pole plate; the number of the driving circuits is equal to that of the capacitive micromachined ultrasonic transducers, and a first end of one driving circuit is connected with a second polar plate of one capacitive micromachined ultrasonic transducer, and a second end of the driving circuit is connected with a reading circuit. The fingerprint acquisition device has a simplified structure and high fingerprint acquisition precision.

Description

Display equipment, fingerprint acquisition device and fingerprint acquisition method

Technical Field

The application relates to the technical field of display, in particular to display equipment, a fingerprint acquisition device and a fingerprint acquisition method.

Background

At present, electronic devices such as smart phones, tablet computers and notebook computers are increasingly provided with fingerprint acquisition and identification systems, and are applied to scenes such as mobile payment and device unlocking. One scheme for fingerprint acquisition and recognition is an ultrasonic sensing scheme, taking a high-pass under-screen fingerprint acquisition scheme as an example, and a fingerprint acquisition device is formed by an ultrasonic transmitting Sensor (Tx Sensor), a piezoelectric material PVDF (Polyvinylidene Difluoride, polyvinylidene fluoride) and an ultrasonic receiving Sensor (Rx Sensor). When fingerprint acquisition and recognition are started, an ultrasonic wave transmitting Sensor (Tx Sensor) transmits an ultrasonic wave signal under voltage excitation, the ultrasonic wave signal is reflected after encountering a finger, the reflected ultrasonic wave signal is converted into an electric signal through a PVDF piezoelectric material and an ultrasonic wave receiving Sensor (Rx Sensor), and the reflected ultrasonic wave can be converted into a fingerprint image for interpretation by utilizing the rule that the reflected energy of the ultrasonic wave is different when the reflected ultrasonic wave encounters the valley and the ridge of the fingerprint (valley intensity and ridge intensity), so that fingerprint acquisition is realized.

However, in the above-mentioned PVDF-based fingerprint acquisition scheme, an ultrasonic transmitting sensor (Tx sensor) and an ultrasonic receiving sensor (Rx sensor) are required to be respectively set, which results in a complicated structure of the fingerprint acquisition device, and is limited by the piezoelectric performance of the PVDF material, so that the problem of poor fingerprint acquisition precision exists.

Disclosure of Invention

In view of the above, the present disclosure provides a display device, a fingerprint acquisition device, and a fingerprint acquisition method, which can simplify the structure of the acquisition device, and have higher fingerprint acquisition accuracy.

In a first aspect, the present disclosure provides, by way of an embodiment, the following technical solutions:

a fingerprint acquisition device comprises an excitation circuit, a reading circuit, a glass substrate, an ultrasonic transducer array and a driving circuit, wherein the ultrasonic transducer array and the driving circuit are arranged on the glass substrate; the ultrasonic transducer array comprises a plurality of capacitive micromachined ultrasonic transducers, and the capacitive micromachined ultrasonic transducers comprise a first polar plate and a second polar plate; the first pole plate is connected with the excitation circuit, and the excitation circuit is configured to apply alternating excitation voltage to the first pole plate;

the number of the driving circuits is equal to that of the capacitive micromachined ultrasonic transducers, a first end of one driving circuit is connected with a second polar plate of one capacitive micromachined ultrasonic transducer, and a second end of the driving circuit is connected with the reading circuit; the driving circuit is configured to apply a bias voltage to the second pole plate when the excitation circuit applies an alternating excitation voltage to the first pole plate, so that the capacitive micromachined ultrasonic transducer emits first ultrasonic waves; and configured to receive a current signal of the second ultrasonic wave converted by the capacitive micromachined ultrasonic transducer when the excitation circuit stops applying the alternating excitation voltage to the first plate, and output the current signal to the readout circuit, so that the readout circuit obtains a target fingerprint based on the current signal; the second ultrasonic wave is a reflected ultrasonic wave of the first ultrasonic wave at the target fingerprint.

In some embodiments, the drive circuit includes a bias voltage input sub-circuit, a switch sub-circuit, a charge storage sub-circuit, and a signal amplification sub-circuit;

the input end of the bias voltage input sub-circuit is connected with a bias voltage signal end, the control end of the bias voltage input sub-circuit is connected with a reset signal end, the output end of the bias voltage input sub-circuit is connected with a second polar plate of the capacitive micromachined ultrasonic transducer and the input end of the switch sub-circuit to a first node, and the bias voltage input sub-circuit is used for inputting the bias voltage to the first node;

the control end of the switch sub-circuit is connected with a switch signal end, and the output end of the switch sub-circuit, the control end of the charge storage sub-circuit and the control end of the signal amplifying sub-circuit are connected to a second node; the switch sub-circuit is used for connecting or disconnecting the first node and the second node, and the charge storage sub-circuit is used for storing the current signal;

the input end of the signal amplifying sub-circuit is connected with the power supply voltage signal end, the control end is connected with the scanning signal end, and the output end is connected with the readout circuit and is used for amplifying the current signal and outputting the amplified current signal to the readout circuit.

In some embodiments, the bias voltage input sub-circuit includes a first transistor, the switch sub-circuit includes a second transistor, the charge storage sub-circuit includes a storage capacitor, and the signal amplification sub-circuit includes a third transistor and a fourth transistor;

A first electrode of the first transistor is connected with the bias voltage signal end, and a control electrode of the first transistor is connected with the reset signal end;

a second pole of the first transistor, a second pole plate of the capacitive micromachined ultrasonic transducer, and a first pole of the second transistor are connected to the first node;

the control electrode of the second transistor is connected with the switch signal end;

a second electrode of the second transistor, the storage capacitor, and a control electrode of the third transistor are connected to the second node;

the first pole of the third transistor is connected with the power supply voltage signal end, and the second pole of the third transistor is connected with the first pole of the fourth transistor;

and the control electrode of the fourth transistor is connected with the scanning signal end, and the second electrode of the fourth transistor is connected with the reading circuit.

In some embodiments, the bias voltage input sub-circuit includes N first transistors, N being an integer greater than or equal to 2, N first transistors being connected in parallel.

In some embodiments, the excitation circuit comprises a square wave signal source, a resonant inductor and a blocking capacitor which are sequentially connected in series, wherein the blocking capacitor is connected between the resonant inductor and the first polar plate; alternatively, the excitation circuit includes a sine wave signal source connected to the first plate.

In some embodiments, the excitation circuit includes: an ac exciter sub-circuit and a dc exciter sub-circuit in parallel with the ac exciter sub-circuit; the direct current excitation subcircuit comprises a direct current signal source and a resistor connected in series, wherein the resistor is connected between the direct current signal source and the first polar plate.

In some embodiments, the readout circuitry includes a multiplexing switch and a conversion sub-circuit; one end of the multi-path gating switch is connected with the second ends of all the driving circuits, and the other end of the multi-path gating switch is connected with the conversion sub-circuit and is used for gating the current signals output by each driving circuit; the conversion sub-circuit is used for converting the current signal into a digital voltage signal.

In a second aspect, based on the same inventive concept, the present disclosure provides, through an embodiment, the following technical solutions:

a fingerprint acquisition method applied to a fingerprint acquisition device provided in an embodiment of the first aspect, the method comprising:

in the transmitting stage, controlling the exciting circuit to apply alternating current exciting voltage to the first polar plate, and controlling the driving circuit to apply first bias voltage to the second polar plate so as to enable the capacitive micromachined ultrasonic transducer to transmit first ultrasonic waves;

In the acquisition stage, controlling the excitation circuit to stop applying alternating excitation voltage to the first polar plate, and receiving a current signal of second ultrasonic waves converted by the capacitive micromachined ultrasonic transducer; the second ultrasonic wave is the reflected ultrasonic wave of the first ultrasonic wave at the target fingerprint;

in a readout phase, the driving circuit is controlled to output the current signal to the readout circuit so that the readout circuit obtains the target fingerprint based on the current signal.

In a third aspect, based on the same inventive concept, the present disclosure provides, by an embodiment, the following technical solutions:

the fingerprint acquisition method is applied to the fingerprint acquisition device provided by the embodiment of the first aspect, and the excitation circuit comprises an alternating current excitation sub-circuit and a direct current excitation sub-circuit which are connected in parallel; the method comprises the following steps:

in the transmitting stage, the exciting circuit is controlled to apply direct current exciting voltage and alternating current exciting voltage to the first polar plate, and the driving circuit is controlled to apply second bias voltage to the second polar plate so as to enable the capacitive micromachined ultrasonic transducer to transmit first ultrasonic waves; the second bias voltage is less than the first bias voltage;

In the acquisition stage, controlling the excitation circuit to apply the direct-current excitation voltage to the first polar plate and receiving a current signal of the second ultrasonic wave converted by the capacitive micromachined ultrasonic transducer; the second ultrasonic wave is the reflected ultrasonic wave of the first ultrasonic wave at the target fingerprint;

According to a fourth aspect, based on the same inventive concept, the present disclosure provides, through an embodiment, the following technical solutions:

a display device comprising a fingerprint acquisition apparatus provided by an embodiment of the first aspect.

Through one or more technical schemes of the present disclosure, the present disclosure has the following beneficial effects or advantages:

the present disclosure provides a fingerprint acquisition device employing an ultrasonic transducer array composed of Capacitive Micromachined Ultrasonic Transducers (CMUTs) to replace PVDF ultrasonic transducers for fingerprint acquisition, having: firstly, the CMUT device simultaneously plays roles of transmitting ultrasonic waves and receiving ultrasonic waves, and compared with the PVDF fingerprint acquisition device, the PVDF fingerprint acquisition device is respectively provided with the transmitting sensor and the receiving sensor, so that the structure of the fingerprint device can be simplified; and secondly, based on the characteristics of the CMUT device and the driving circuit, the signal excitation and ultrasonic signal acquisition modes are adjusted, a CMUT array and a corresponding driving circuit are manufactured on the glass substrate, one driving circuit is connected to a second polar plate of one CMUT device and is used for driving the CMUT device to emit or acquire ultrasonic waves, an excitation circuit which is arranged outside the glass substrate and is used for providing an alternating current excitation signal is connected to a first polar plate of the CMUT device, so that the alternating current excitation signal with high voltage can be isolated from the driving circuit which is not resistant to high voltage on the glass substrate, and fingerprint information is read out by combining a reading circuit, so that the high-precision spontaneous self-acquisition of the large-array CMUT ultrasonic signal integrated on the glass substrate is realized, and the fingerprint acquisition precision is improved.

The foregoing description is merely an overview of the technical solutions of the present disclosure, and may be implemented according to the content of the specification in order to make the technical means of the present disclosure more clearly understood, and in order to make the above and other objects, features and advantages of the present disclosure more clearly understood, the following specific embodiments of the present disclosure are specifically described.

Drawings

Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the disclosure. Also, like reference numerals are used to designate like parts throughout the figures.

In the drawings:

FIG. 1A shows a schematic diagram of an ultrasound fingerprinting scheme based on PVDF material;

fig. 1B shows a microstructure photograph of a silicon-based CMUT;

FIG. 1C provides a schematic diagram of the connection of an excitation circuit to a gating circuit, CMUT array;

fig. 2 shows a schematic diagram of a CMUT ultrasound transducer array based fingerprint acquisition device according to an embodiment of the disclosure;

FIG. 3 illustrates a schematic diagram of a capacitive micromachined ultrasonic transducer according to an embodiment of the present disclosure;

FIG. 4 shows a schematic circuit configuration of a fingerprint acquisition device according to an embodiment of the present disclosure;

FIG. 5 illustrates a circuit block diagram when an excitation circuit includes an AC excitation subcircuit according to an embodiment of the present disclosure;

FIG. 6 illustrates a circuit block diagram of an excitation circuit including a DC excitation sub-circuit and an AC excitation sub-circuit in parallel according to an embodiment of the present disclosure;

FIG. 7A is a schematic diagram of a circuit configuration of an AC excitation sub-circuit employing a sine wave signal source according to an embodiment of the present disclosure;

FIG. 7B is a schematic diagram of a circuit configuration of an AC excitation sub-circuit employing a square wave signal source according to an embodiment of the present disclosure;

FIG. 8 shows a block schematic diagram of a drive circuit according to an embodiment of the present disclosure;

fig. 9 illustrates a structural schematic diagram of a 4T1C driving circuit according to an embodiment of the present disclosure;

FIG. 10A is a schematic diagram showing the equivalent circuit structure of the first transistor and AC excitation subcircuit of FIG. 9;

fig. 10B illustrates a circuit configuration schematic of a plurality of first transistors connected in parallel according to an embodiment of the present disclosure;

FIG. 11 shows a schematic diagram of a configuration of a readout circuit according to an embodiment of the disclosure;

FIG. 12 shows a flow diagram of a fingerprint acquisition method according to an embodiment of the present disclosure;

Fig. 13A shows a schematic diagram of a CMUT array and corresponding driving circuitry when the excitation circuitry provides ac excitation, according to an embodiment of the disclosure;

FIG. 13B shows a schematic diagram of the connection of the drive circuit according to FIG. 13A to the read-out circuit of the back-end;

FIG. 13C shows a timing control schematic of the pixel circuit according to FIG. 13A;

FIG. 14 shows a flow diagram of another fingerprint acquisition method according to an embodiment of the present disclosure;

fig. 15A shows a schematic diagram of a CMUT array and corresponding driving circuitry when the driving circuitry provides ac and dc excitation, according to an embodiment of the disclosure;

FIG. 15B shows a timing control schematic of the pixel circuit according to FIG. 15A;

FIG. 16 shows a schematic view of a display panel according to an embodiment of the disclosure;

FIG. 17 shows a schematic diagram of a display device according to an embodiment of the disclosure;

reference numerals illustrate:

10. a glass substrate; 20. an ultrasonic transducer array; CMUT, capacitive micromachined ultrasonic transducer; 21. a first plate; 22. a second polar plate; 23. a vibrating diaphragm; 24. a cavity;

30. an excitation circuit; 31. a DC exciter sub-circuit; DC. A direct current signal source; r, resistance; 32. an ac exciter sub-circuit; AC1, square wave signal source; AC2, sine wave signal source; l, resonant inductance; cb. A blocking capacitor;

40. A driving circuit; 41. a bias voltage input sub-circuit; 42. a switch sub-circuit; 43. a charge storage sub-circuit; 44. a signal amplifying sub-circuit; t1, a first transistor; t2, a second transistor; t3, third transistor; t4, fourth transistor; c1, a storage capacitor; n1, a first node; n2, a second node; vbias, bias voltage signal terminal; VDD, supply voltage signal terminal; vrst, reset signal terminal; vclose, switch signal end; gate, scanning signal end;

50. a readout circuit; 51. a multi-way gating switch; 52. a conversion sub-circuit;

EN, encapsulation layer; an OLED, electroluminescent device layer; platen, cover plate layer; ML, matching layer.

Detailed Description

Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. It should be understood that the description is only exemplary and is not intended to limit the scope of the present disclosure. In addition, in the following description, descriptions of well-known structures and techniques are omitted so as not to unnecessarily obscure the concepts of the present disclosure.

Various structural schematic diagrams according to embodiments of the present disclosure are shown in the drawings. The figures are not drawn to scale, wherein certain details are exaggerated for clarity of presentation and may have been omitted. The shapes of the various regions, layers and relative sizes, positional relationships between them shown in the drawings are merely exemplary, may in practice deviate due to manufacturing tolerances or technical limitations, and one skilled in the art may additionally design regions/layers having different shapes, sizes, relative positions as actually required.

In the context of the present disclosure, when a layer/element is referred to as being "on" another layer/element, it can be directly on the other layer/element or intervening layers/elements may be present therebetween. In addition, if one layer/element is located "on" another layer/element in one orientation, that layer/element may be located "under" the other layer/element when the orientation is turned.

In the context of the present disclosure, the light-emitting side of the display panel is referred to as "top side" or "upper side", and the opposite side is referred to as "bottom side" or "lower side", unless otherwise specified, in order to describe the relative direction. Accordingly, the direction from the bottom side to the top side is the thickness direction of the display panel, and the direction perpendicular to the thickness direction is the "plane direction" or the "extending direction" of the display panel. It should be understood that these directions are relative directions rather than absolute directions.

Unless defined otherwise, technical or scientific terms used in this disclosure should be given the ordinary meaning as understood by one of ordinary skill in the art to which this disclosure belongs. The terms "first," "second," and the like, as used in this disclosure, do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. Likewise, the terms "a," "an," or "the" and similar terms do not denote a limitation of quantity, but rather denote the presence of at least one. The word "comprising" or "comprises", and the like, means that elements or items preceding the word are included in the element or item listed after the word and equivalents thereof, but does not exclude other elements or items. The terms "connected" or "connected," and the like, are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "upper", "lower", "left", "right", etc. are used merely to indicate relative positional relationships, which may also be changed when the absolute position of the object to be described is changed.

The under-screen fingerprint acquisition scheme based on PVDF ultrasonic transducer can refer to the display panel shown in FIG. 1A, and comprises a transmitting electrode layer Tx Sensor, a Glass substrate TFT Glass, a receiving electrode layer Rx Sensor, a piezoelectric material layer PVDF, a piezoelectric electrode layer PE and a cover plate layer Platen which are sequentially laminated from bottom to top, wherein the transmitting electrode layer Tx Sensor is a transducer for transmitting ultrasonic signals and can convert electric signals into ultrasonic signals for transmission; the receiving electrode layer Rx Sensor is used as a Sensor for receiving ultrasonic signals, and the piezoelectric material PVDF is combined to convert the reflected ultrasonic signals into voltage signals on the Rx Sensor. Therefore, the fingerprint collection and identification process of the display panel is as follows: under voltage excitation, an ultrasonic signal emitted by the emitting electrode layer Tx Sensor respectively passes through the Glass substrate TFT Glass, the receiving electrode layer Rx Sensor, the piezoelectric material layer PVDF and the display layer and then reaches the finger, the microscopic morphology of the fingerprint on the finger comprises valleys and ridges, the reflection energy of ultrasonic waves on the valleys and the ridges of the fingerprint is different, the valley reflection is strong, the ridge reflection is weak, and thus the fingerprint morphology (namely the distribution of the valley and the ridge) can be reflected through the energy intensity of the ultrasonic wave reflection signal; the reflected ultrasonic signals are received again by the piezoelectric material layer PVDF and the receiving electrode layer Rx Sensor, so that fingerprint collection or identification is realized.

Along with the development of ultrasonic fingerprint acquisition technology and the limitation of acquisition precision of PVDF ultrasonic transducers, an ultrasonic fingerprint acquisition scheme based on a capacitive micromachined ultrasonic transducer (Capacitive Micro Machined Ultrasonic Transducer, hereinafter referred to as a CMUT device) is beginning to be applied. In some fingerprint recognition schemes, the CMUT devices employed are ultrasonic transducers fabricated by silicon-based microelectromechanical system MEMS technology. For example, butterfly Network provides a CMUT product, which is a phased array ultrasonic transducer, with 8960 CMUT transducers arranged according to 140×64 to form a large array. These transducers are capable of emitting ultrasonic signals and receiving reflected echoes in the form of ultrasonic waves. An array of 8960 transducers is integrated with an Application Specific Integrated Circuit (ASIC) chip to achieve a highly efficient 2D phased array sensor. Thanks to the miniaturization of CMUT devices, the Butterfly iQ ultrasound probe can perform curve, linear and phase analysis. In the case of other conventional devices, however, three different ultrasound probes must be used to achieve the same analysis process. Fig. 1B provides a photograph of the microstructure of the silicon-based CMUT device, which was fabricated using silicon-based MEMS technology. Wherein the bulk silicon process and the thin film micromachining process are applied to the formation of electrodes and cavities in CMUT devices. The technical secret of the CMUT device is not only the MEMS chip but also the integration technology with the ASIC chip. The ASIC chip has the function of driving ultrasonic pulse generation and measuring echo, and in addition, it can run the algorithm developed by Butterfly Network, and has the function of communicating with a processor on a Printed Circuit Board (PCB). Each CMUT transducer is driven by a module integrating CMOS logic, analog readout circuitry, and LDMOS transistors to emit ultrasound. The ASIC chip and the MEMS chip employ wafer level bonding techniques and are electrically connected Through Silicon Vias (TSVs).

Referring to fig. 1c, the fingerprint acquisition circuit structure based on a silicon-based CMUT device uses a silicon wafer as a substrate, i.e. a CMUT array is disposed on a silicon substrate; the receiving and transmitting of the ultrasonic signals are realized by respectively placing the direct-current bias voltage Vdc and the high-voltage alternating-current pulse excitation Vac on the upper electrode and the lower electrode of the CMUT device. The high-voltage alternating current pulse excitation can be controlled by a field programmable gate array FPGA chip, a high-voltage alternating current pulse circuit is connected to one side of a T/R receiving and transmitting assembly, a receiving circuit Rx is connected to the other side of the T/R assembly, and the ultrasonic wave transmitting and receiving are isolated through the T/R assembly. The difference from the PVDF scheme is that the alternating current pulse excitation voltage required for exciting the CMUT device to emit ultrasonic waves is higher, and the voltage resistance of the T/R component is required to be good, so that the T/R component serving as an isolation module can adopt a gate circuit formed by silicon-based field effect transistors (MOS), and the silicon-based MOS tube can have high voltage resistance and can realize the isolation between the high-voltage alternating current pulse excitation Vac and a receiving circuit (Rx).

In order to solve the problem of complex structure and insufficient fingerprint acquisition precision in the PVDF fingerprint acquisition scheme, in a first aspect, in an alternative embodiment, referring to fig. 2 to 4, a CMUT array-based fingerprint acquisition device applicable to a glass substrate is provided, which specifically includes:

The fingerprint acquisition device comprises an excitation circuit 30, a readout circuit 50, a glass substrate 10, and an ultrasonic transducer array 20 and a drive circuit 40 which are arranged on the glass substrate 10; the ultrasonic transducer array 20 comprises a plurality of capacitive micromachined ultrasonic transducers CMUTs comprising a first plate 21 and a second plate 22; the first plate 21 is connected to the excitation circuit 30. The number of driving circuits 40 is equal to the number of capacitive micro-machined ultrasonic transducers CMUTs, and a first terminal of one driving circuit 40 is connected to the second plate 22 of one capacitive micro-machined ultrasonic transducer CMUT, and a second terminal is connected to the readout circuit 50.

The glass substrate 10 may be used as a glass base for manufacturing an array substrate or a driving back plate of a display panel, and a thin film transistor (Thin Film Transistor, abbreviated as TFT) for driving a pixel may be formed on the glass substrate 10. The ultrasonic transducer array 20 includes array elements of a plurality of capacitive micromachined ultrasonic transducer CMUTs formed on a glass substrate 10, one CMUT array element representing one CMUT device, and "a plurality of" means that the ultrasonic transducer array 20 includes at least two CMUT devices. The CMUT device may be structured as shown in fig. 3, and includes a second electrode plate 22, a diaphragm 23, and a first electrode plate 21 sequentially stacked on a glass substrate 10 from bottom to top. Depending on the stacking position, the second plate 22 may be used as a lower plate of the CMUT, and the first plate 21 may be used as an upper plate of the CMUT; a cavity 24 is formed between the second plate 22 and the diaphragm 23. The first electrode plate 21 and the second electrode plate 22 may be disposed on the same layer as the metal wiring layer on the glass substrate 10, for example, the first electrode layer is disposed on the same layer as the source/drain metal layer, the second electrode layer is disposed on the same layer as the gate metal layer, and the diaphragm 23 may be disposed on the same layer as the insulating layer, for example, the gate insulating layer.

The process flow for manufacturing the CMUT device or array element on the glass substrate 10 is as follows:

1) A pixel circuit is fabricated on a Glass substrate 10 (TFT Glass) as a driving circuit 40, and the upper layer of the driving circuit 40 is the lower electrode of the CMUT device: a second pole plate 22;

2) Depositing a silicon nitride SiNx film as an insulating layer by Plasma Enhanced Chemical Vapor Deposition (PECVD) to prevent shorting of the second plate 22;

3) Sputtering (Sputter) metal as a sacrificial layer, wherein only metal at the cavity of the CMUT device is left after patterning (pattern), and the sputtered metal can be Mo, cu, al and the like;

4) Depositing SiNx as a wall of a cavity solid support and a vibrating diaphragm 23, etching according to the thickness of the vibrating diaphragm 23, punching SiNx at a reserved etching hole, and exposing the metal of the sacrificial layer;

5) The upper electrode was formed by sputtering Sputer: a first plate 21, and is patterned;

6) Etching the sacrificial layer at the cavity through the reserved etching holes by the sacrificial layer etching liquid to form a cavity 24;

7) And depositing a layer of SiNx for packaging to finish the manufacturing of the CMUT device.

By the method, the CMUT devices with the radius of 10 mu m can be densely arranged, and 107×107 CMUT array elements can be manufactured on the glass substrate 10 with the radius of 8mm×8 mm.

The CMUT device is a capacitive device, and its working principle when transmitting ultrasonic waves is: when a DC bias voltage is applied, the polar plates generate and accumulate opposite charges, and generate an electrostatic force which attracts each other, and the electrostatic force bends the diaphragm 23 downwards and tightens the diaphragm 23; when alternating voltage is applied to the first polar plate 21 or the second polar plate 22, the number of charges accumulated on the first polar plate 21 and the second polar plate 22 is changed, and the change of the number of charges causes the change of electrostatic force, so that the vibrating diaphragm 23 is driven to vibrate up and down, and the vibrating diaphragm 23 resonates to push surrounding media to do work to generate ultrasonic waves. The working principle of the ultrasonic wave receiving device when receiving ultrasonic waves is as follows: in a state that the diaphragm 23 is tensioned by the direct-current bias voltage, the diaphragm 23 is vibrated by the incident ultrasonic wave, so that the capacitance of the CMUT device is changed, and the charge change between the first polar plate 21 and the second polar plate 22 is converted into a current signal output under the direct-current bias voltage driving.

Therefore, in order to implement ultrasonic fingerprint acquisition, the configuration of the fingerprint acquisition device provided in the embodiment of the present disclosure may be:

the excitation circuit 30 is configured to apply an alternating excitation voltage to the first plate 21; the driving circuit 40 is configured to apply a bias voltage to the second plate 22 to cause the capacitive micromachined ultrasonic transducer CMUT to emit a first ultrasonic wave when the excitation circuit 30 applies an alternating excitation voltage to the first plate 21; and receiving a current signal of the second ultrasonic wave converted by the capacitive micromachined ultrasonic transducer CMUT and outputting the current signal to the readout circuit 50 when the excitation circuit 30 stops applying the alternating excitation voltage to the first plate 21, so that the readout circuit 50 obtains a target fingerprint based on the current signal; the second ultrasonic wave is a reflected ultrasonic wave of the first ultrasonic wave at the target fingerprint.

Specifically, the excitation circuit 30 is a circuit for providing ac excitation, in cooperation with the driving circuit 40, to control the CMUT device to transmit or receive ultrasonic waves. When the excitation circuit 30 applies ac excitation to the first electrode plate 21 and the driving circuit 40 applies dc excitation to the second electrode plate 22, the CMUT device satisfies the ultrasonic emission condition, and the emitted first ultrasonic wave generates a reflected signal after encountering the fingerprint of the user: and second ultrasonic waves. When the second ultrasonic wave returns to the diaphragm 23 of the CMUT device, the diaphragm 23 is driven to vibrate, thereby generating a corresponding current signal. It will be appreciated that to ensure accuracy of fingerprint acquisition and identification, the excitation circuit 30 should be disabled from continuing to output ac excitation after the completion of the ultrasonic transmission. The second ultrasonic wave carries the appearance signal of the target fingerprint because the amplitude or intensity distribution of the second ultrasonic wave is different between the valley and the ridge of the target fingerprint, the second ultrasonic wave signal is received by the CMUT device and converted into a current signal to be output and analyzed, and the acquisition and the identification of the user fingerprint can be realized.

In the embodiment of the present disclosure, the excitation circuit 30 that controls the CMUT device to emit the first ultrasonic wave is provided outside the glass substrate 10. For example, the excitation circuit 30 may be disposed on the timing controller TCON circuit board in the form of an integrated circuit chip IC, the output terminal is connected to the CMUT device on the glass substrate 10 through a wire, the control terminal is connected to the timing controller, and the timing controller controls the timing of the ac excitation output by the excitation circuit 30. The reason for this design is that when the glass substrate 10 is used as a display substrate of a display panel or a driving back plate, thin film transistors are often formed by an Array process as switching devices of pixel circuits, and the ac excitation voltage required for driving CMUT devices to emit ultrasonic waves is high beyond the withstand voltage range of the thin film transistors TFT on the glass substrate 10, so that if the excitation circuit 30 is provided on the glass substrate 10, quality problems of thin film transistor damage are easily caused. While silicon-based field effect transistors (MOS) fabricated on a silicon substrate may have a high withstand voltage capability, there is no problem in integrating the excitation circuit 30 on the silicon substrate for a silicon-based CMUT array.

A driving circuit 40 connected to the CMUT device, on the one hand, for applying a dc bias voltage Vbias to the second plate 22, and in combination with the ac excitation voltage provided by the excitation circuit 30, causing the CMUT device to emit ultrasonic waves, and also tensioning the first plate 21 and the second plate 22 of the CMUT before receiving the reflected second ultrasonic waves, so as to accurately convert the second ultrasonic waves into current signals; on the other hand, the current signal converted by the CMUT device is output to the readout circuit 50 through the current output terminal. The driving circuit 40 is formed on the glass substrate 10, and a pixel circuit of a thin film transistor T-capacitor C formed based on an Array process can be used, and a control end of the driving circuit 40 is connected with a timing controller through a wire to realize the transceiving control of ultrasonic waves.

The readout circuit 50 may be disposed on the glass substrate 10, or may be disposed outside the glass substrate 10, and may be connected to a current output terminal of the driving circuit 40 through a circuit board or a wire to achieve conversion and readout of a current signal.

The fingerprint acquisition device provided by the embodiment of the disclosure adopts an ultrasonic transducer array 20 consisting of Capacitive Micromachined Ultrasonic Transducers (CMUTs) to replace PVDF ultrasonic transducers for fingerprint acquisition; firstly, the CMUT device simultaneously plays roles of transmitting ultrasonic waves and receiving ultrasonic waves, and compared with the PVDF fingerprint acquisition device, the PVDF fingerprint acquisition device is respectively provided with the transmitting sensor and the receiving sensor, so that the structure of the fingerprint device can be simplified; secondly, based on the characteristics of the CMUT devices and the driving circuits 40, the signal excitation and the collection mode of the ultrasonic signals are adjusted, by manufacturing the CMUT array and the corresponding driving circuits 40 on the glass substrate 10, one driving circuit 40 is connected to the second pole plate 22 of one CMUT device for driving the CMUT device to emit or collect the ultrasonic waves, and the excitation circuit 30 which is arranged outside the glass substrate 10 and is used for providing the alternating current excitation signals is connected to the first pole plate 21 of the CMUT device, so that the alternating current excitation signals with large voltage can be isolated from the driving circuits 40 which are not resistant to high voltage on the glass substrate 10, and the fingerprint information is read by combining the reading circuit 50, so that the high-precision spontaneous self-collection of the CMUT ultrasonic signals with large array integrated on the glass substrate 10 is realized, and the fingerprint collection precision is further improved.

Therefore, the present disclosure provides a novel fingerprint acquisition scheme based on the CMUT array, which can be applied to various display panels and display devices using glass substrates as substrates.

In some embodiments, referring to fig. 5, the excitation circuit 30 includes an ac excitation subcircuit 32, the ac excitation subcircuit 32 being configured to apply an ac excitation voltage to the first plate 21. At this time, the driving circuit 40 may continuously apply a dc bias voltage to the second electrode plate 22 to satisfy the transmission and reception conditions of the ultrasonic wave.

In other embodiments, referring to fig. 6, the excitation circuit 30 includes an ac excitation sub-circuit 32 and a dc excitation sub-circuit 31 arranged in parallel; wherein the ac excitation subcircuit 32 is for applying an ac excitation voltage to the first plate 21 and the dc excitation subcircuit 31 is for applying a dc excitation voltage to the first plate 21. When the exciting circuit 30 inputs a dc exciting voltage and an ac exciting voltage to the first electrode plate 21 and the driving circuit 40 inputs a dc bias voltage to the second electrode plate 22 at the same time, the CMUT device can emit ultrasonic waves; when the excitation circuit 30 inputs a dc excitation voltage to the first electrode plate 21 and the drive circuit 40 inputs a dc bias voltage to the second electrode plate 22, the CMUT device can receive ultrasonic waves.

The configuration of the excitation circuit 30 is related to the voltage resistance of the circuit elements in the driving circuit 40, and if the voltage resistance of the driving circuit 40 is good, the excitation circuit 30 may supply only an ac excitation voltage so that the CMUT device satisfies the conditions for transmitting and receiving ultrasonic waves. If the voltage resistance of the circuit elements in the driving circuit 40 is poor, the driving circuit 30 needs to simultaneously supply a dc driving voltage and an ac driving voltage, wherein the dc driving voltage may continuously act on the first electrode plate 21, and the ac driving voltage acts on the first electrode plate 21 together with the dc driving voltage when the CMUT device is required to emit ultrasonic waves.

In some embodiments, AC excitation subcircuit 32 may output AC excitation using sine wave signal source AC2, or alternatively, square wave signal source AC 1. When the sine wave signal source AC2 is used, referring to fig. 7A, the AC excitation sub-circuit 32 includes the sine wave signal source AC2, and the sine wave signal source AC2 is connected to the first plate 21. When the square wave signal source AC1 is used, referring to fig. 7B, the AC exciter sub-circuit 32 includes the square wave signal source AC1, the resonant inductor L and the dc blocking capacitor Cb connected in series in this order, and the dc blocking capacitor Cb is connected between the resonant inductor L and the first electrode plate 21. For DC excitation, the DC excitation subcircuit 31 comprises a DC signal source DC and a resistor R connected in series, the resistor R being connected between the DC signal source DC and the first plate 21.

The input end of the square wave signal source AC1 may be a chip capable of providing a square wave signal, such as TC6320, and then is changed into a sinusoidal excitation signal through LC resonance, so as to provide a suitable AC excitation voltage for the first polar plate 21. Therefore, a resonant inductor L and a blocking capacitor Cb are connected in series on the branch where the square wave signal source AC1 is located, where the resonant inductor L is used to form LC resonance with the CMUT device, and convert the square wave signal into a sine wave signal; the dc blocking capacitor Cb can be used to isolate the dc signal, thereby further improving the signal quality of the ac excitation voltage. The capacitance of the blocking capacitor Cb needs to be much larger than that of the CMUT device.

The DC signal source DC can select a DCDC power chip, such as chips of LT1085, LT8365 and the like, to generate DC excitation voltage; the resistor R connected in series with the direct current signal source DC can be used for controlling the output direct current excitation voltage, and plays a role in protecting the CMUT device.

In some embodiments, referring to fig. 8, the driving circuit 40 includes a bias voltage input sub-circuit 41, a switch sub-circuit 42, a charge storage sub-circuit 43, and a signal amplification sub-circuit 44; the input end of the bias voltage input sub-circuit 41 is connected with a bias voltage signal end Vbias, the control end is connected with a reset signal end Vrst, and the output end of the bias voltage input sub-circuit 41, the second pole plate 22 of the capacitive micromachined ultrasonic transducer CMUT and the input end of the switch sub-circuit 42 are connected to a first node N1 for inputting bias voltage to the first node N1; the control end of the switch sub-circuit 42 is connected with the switch signal end Vclose, and the output end of the switch signal end Vclose is connected with the control ends of the charge storage sub-circuit 43 and the signal amplifying sub-circuit 44 to the second node N2; the switch sub-circuit 42 is used for switching on or off the first node N1 and the second node N2, and the charge storage sub-circuit 43 is used for storing a current signal; the input terminal of the signal amplifying sub-circuit 44 is connected to the power voltage signal terminal VDD, the control terminal is connected to the scan signal terminal Gate, and the output terminal is connected to the readout circuit 50, for amplifying the current signal and outputting to the readout circuit 50.

The bias voltage input sub-circuit 41 is used for applying a direct-current bias voltage signal to the second diode 22, the switch sub-circuit 42 is used for controlling the on-off state of the circuit, and when the switch sub-circuit 42 is turned off, the bias voltage input sub-circuit 41 can charge the first node N1, raise the node voltage to the bias voltage, and simultaneously apply the bias voltage signal to the second diode 22 of the CMUT device; when the switch sub-circuit 42 is turned on, the bias voltage input sub-circuit 41 may charge the second node N2, and a current signal obtained by converting the second ultrasonic wave by the CMUT device may be stored in the charge storage sub-circuit 43. The other end of the charge storage sub-circuit 43 may be connected to a fixed potential or ground. The signal amplifying sub-circuit 44 may further amplify the current signal of the second ultrasonic wave and output the current signal to the readout circuit 50 through the current output terminal.

When the fingerprint acquisition device is applied to a display module or a display device, the driving circuit 40 can drive by adopting a pixel circuit on the glass substrate 10, and the pixel circuit is controlled by a time sequence controller.

In some embodiments, referring to fig. 9, a 4T1C pixel circuit is provided as the driving circuit 40 of each CMUT device, where T represents a transistor and C represents a capacitance. The bias voltage input sub-circuit 41 includes a first transistor T1, the switch sub-circuit 42 includes a second transistor T2, the charge storage sub-circuit 43 includes a storage capacitor C1, and the signal amplification sub-circuit 44 includes a third transistor T3 and a fourth transistor T4; specifically, a first pole of the first transistor T1 is connected to the bias voltage signal terminal Vbias, and a control pole is connected to the reset signal terminal Vrst; the second pole of the first transistor T1, the second pole plate 22 of the capacitive micromachined ultrasonic transducer CMUT and the first pole of the second transistor T2 are connected to a first node N1; the control electrode of the second transistor T2 is connected with the switch signal end Vclose; the second pole of the second transistor T2, the storage capacitor C1 and the control pole of the third transistor T3 are connected to the second node N2; the first pole of the third transistor T3 is connected with the power voltage signal end VDD, and the second pole is connected with the first pole of the fourth transistor T4; the control electrode of the fourth transistor T4 is connected to the scan signal terminal Gate, and the second electrode is connected to the readout circuit 50.

The bias voltage signal terminal Vbias is used for providing direct-current bias voltage, and the power supply voltage signal terminal VDD is used for providing VDD power supply voltage; the scan signal terminal Gate may be connected to a Gate line, and the reset signal terminal Vrst and the switching signal terminal Vclose may be connected to a timing controller through corresponding wirings, and on-off control of the transistor is performed through the timing controller.

The transistor used in the driving circuit 40 may be a thin film transistor (Thin Film Transistor, TFT). Since the source and the drain of the transistor can be interchanged under certain conditions, there is no essential difference in description of the connection relationship between the source and the drain. Thus, to distinguish between the source and drain of a transistor, one of the poles is referred to as the first pole, the other pole is referred to as the second pole, and the gate is referred to as the control pole. Transistors can be classified into N-type and P-type according to characteristics, and the above scheme is described with reference to the transistors being N-type transistors. When an N-type transistor is used, the first electrode is the source of the transistor, the second electrode is the drain of the transistor, and when the gate inputs a high level, the N-type transistor is turned on. The opposite is the case for P-type transistors. One skilled in the art may employ P-type transistors to replace one or more of the N-type transistors in the drawings without departing from the spirit and scope of the present disclosure.

On the other hand, considering that the fingerprint acquisition accuracy is positively correlated with the ultrasonic signal intensity, which is positively correlated with the ac excitation voltage of the CMUT device, the further improved ac excitation voltage Vac may affect the TFT by the CMUT device by combining the characteristics of the ac and capacitive devices, and exceed the withstand voltage value of the current thin film transistor TFT to cause damage thereof. Referring to the equivalent circuit of fig. 10A, the AC excitation voltage Vac output by the sine wave signal source AC2 acts on the internal resistance R0 of the sine wave signal source AC2, the CMUT device and the first transistor T1, and since the internal resistance of the first transistor T1 is large, more voltage in Vac acts on the first transistor T1, on one hand, the voltage division on the CMUT device is reduced, resulting in reduced capability of the CMUT device to emit ultrasonic waves, and reduced fingerprint acquisition accuracy; on the other hand, the first transistor T1 is also easily damaged due to the voltage division exceeding the withstand voltage range.

In order to improve the above problem, referring to fig. 10B, the bias voltage input sub-circuit 41 may be connected in parallel by N first transistors T1, where N is equal to or greater than 2 and is an integer. The parallel first transistor T1 can effectively reduce the resistance, thereby reducing the voltage division acting on the first transistor T1, and improving the voltages of the first polar plate 21 and the second polar plate 22 of the CMUT device, so that high-voltage ac excitation can be realized, fingerprint acquisition and recognition accuracy can be improved by emitting ultrasonic waves with higher sound pressure, the first transistor T1 can be effectively protected, and the service life can be prolonged. The number N of the first transistors T1 is determined comprehensively according to the required voltage of the CMUT device and the resistance value of the first transistors T1 after parallel connection, and the higher the ac excitation voltage Vac required by the CMUT device is, the worse the withstand voltage capability of the first transistors T1 is, and the larger the value of N is. The parallel connection of 3 first transistors T1 in fig. 10B is for exemplary illustration, and is not intended to limit the value of N.

In some embodiments, referring to fig. 11, the readout circuit 50 includes a multiplexing switch 51 and a conversion sub-circuit 52; the multiplexing gate switch 51 is connected between the second terminal of the driving circuit 40 and the conversion sub-circuit 52 for gating the current signal of the second ultrasonic wave transmitted by the CMUT device or devices. The conversion sub-circuit 52 may include a current-to-voltage conversion sub-circuit IV and an analog-to-digital conversion sub-circuit 52 (ADC) for converting the current signal into a digital voltage signal, and a fingerprint image may be drawn through analysis and conversion of the digital voltage signal.

In summary, compared with the silicon-based CMUT ultrasonic fingerprint acquisition scheme, the fingerprint acquisition device provided in the embodiments of the present disclosure changes the excitation and signal acquisition modes, and the single CMUT array element signals can realize signal acquisition through the driving circuit 40 (pixel circuit) on the glass substrate 10, and provides the system excitation and driving scheme based on the characteristics of the CMUT device and the driving circuit 40 on the glass substrate 10, so as to realize: (1) integration of the fingerprint acquisition device on the glass substrate 10; (2) the system excitation required by fingerprint acquisition, the CMUT array device and the driving circuit 40 are combined, the whole-surface emission and whole-surface receiving integration of ultrasonic waves are realized through the cooperation of time sequence control, and the spontaneous self-receiving of the ultrasonic signals of the large-array CMUT is realized; (3) the problem that a glass-based thin film transistor TFT is not resistant to high-voltage alternating current excitation is solved, and a brand-new fingerprint acquisition scheme of the array CMUT is provided.

In a second aspect, referring to fig. 12, a fingerprint acquisition device provided according to an embodiment of the first aspect provides a corresponding fingerprint acquisition method, including steps S1201 to S1203, specifically including the following steps:

s1201: in the transmitting phase, the control exciting circuit 30 applies an alternating exciting voltage to the first polar plate 21, and the control driving circuit 40 applies a first bias voltage to the second polar plate 22 so that the capacitive micromachined ultrasonic transducer CMUT transmits a first ultrasonic wave;

s1202: in the acquisition phase, the control excitation circuit 30 stops applying alternating excitation voltage to the first polar plate 21 and receives a current signal of the second ultrasonic wave converted by the capacitive micromachined ultrasonic transducer CMUT; the second ultrasonic wave is the reflected ultrasonic wave of the first ultrasonic wave at the target fingerprint;

s1203: in the readout phase, the control driving circuit 40 outputs a current signal to the readout circuit 50 so that the readout circuit 50 obtains a target fingerprint based on the current signal.

The above-described scheme is suitable for the case where the voltage resistance of the circuit elements in the driving circuit 40 is sufficient to support the driving circuit 40 to output a high first bias voltage signal, and at this time, the excitation circuit 30 only needs to provide the ac excitation sub-circuit 32, and the ac excitation voltage is output in the transmission stage of the ultrasonic wave so that the CMUT device transmits the ultrasonic wave.

The fingerprint acquisition circuit scheme applied to a display device is illustrated by way of example in fig. 13A and 13B. The ultrasonic transducer array 20 comprises 100×100 CMUT devices, and the excitation circuit 30 comprises an ac excitation sub-circuit 32 connected to the first plate 21 of all CMUT devices in the ultrasonic transducer array 20 for applying an ac excitation voltage to the first plate 21; the ac excitation subcircuit 32 may be implemented as a chip (e.g., TC 6320) capable of generating a square wave signal, which is then LC-resonated to become a sinusoidal excitation signal. The number of driving circuits 40 is equal to the number of CMUT devices and is arranged in a one-to-one correspondence, i.e. each CMUT device is connected to one driving circuit 40. The driving circuit 40 may adopt a 4T1C structure as shown in fig. 9 for applying a first bias voltage to the second electrode plate 22 of the CMUT and transmitting a current signal of the second ultrasonic wave converted by the CMUT to the readout circuit 50 through the current output terminal Iout. Unless otherwise specified, the first plate 21 corresponds to an upper plate or an upper electrode of the CMUT device, and the second plate 22 corresponds to a lower plate or a lower electrode of the CMUT device. The readout circuit 50 includes a multiplexing gate switch 51 and a conversion sub-circuit 52; the input end of the multi-path gating sub-circuit is connected with the current output ends Iout of all the driving circuits 40, the output end is connected with the conversion sub-circuit 52, and the current-voltage conversion sub-circuit 52IV in the conversion sub-circuit 52 is used for converting the current signal of the second ultrasonic wave into a voltage signal and then converting the voltage signal into a digital voltage signal through the analog-to-digital conversion circuit ADC.

The fingerprint acquisition control sequence can refer to fig. 13C, and can be controlled by the sequence controller, specifically as follows:

emission phase (t 1-t 2): the control excitation circuit 30 applies an ac excitation voltage Vac to the first plate 21, controls the reset signal terminal Vrst to input a high level signal, and the switch signal terminal Vclose to input a low level signal, so that the first transistor T1 is turned on, the second transistor T2 is turned off, and the bias voltage signal terminal Vbias applies a first bias voltage to the second plate 22 of the CMUT device through the first transistor T1; at the moment, the CMUT device starts to emit ultrasonic waves outwards according to the ultrasonic wave emission condition, and the ultrasonic waves are reflected back after touching the valley and the ridge of the fingerprint, so that second ultrasonic waves are formed.

Writing phase (t 2 to t 3): the control switch signal terminal Vclose inputs a high level signal to turn on the second transistor T2, and increases the voltage of the second node N2 to the first bias voltage.

Acquisition stage (t 3-t 4): the reset signal terminal Vrst is controlled to input a low level signal, the switch signal terminal Vclose is controlled to input a high level signal, so that the first transistor T1 is turned off, at this time, the voltage of the first node N1 is maintained at a first bias voltage, which meets the ultrasonic receiving condition of the CMUT device, and when the second ultrasonic wave returns to the diaphragm 23 of the CMUT device, the diaphragm 23 vibrates, the second ultrasonic wave is converted into a corresponding current signal, and the second transistor T2 is turned on, and the fourth transistor T4 is turned off, so that the current signal is stored in the storage capacitor C1. Alternatively, during the acquisition phase, the reset signal terminal Vrst may be continuously input with a high level signal, so that the first transistor T1 is kept in the on state, and the first bias voltage is continuously applied to the first plate 21.

Readout phase (t 4 and beyond): the control switch signal terminal Vclose inputs a low level signal, the scan signal terminal Gate outputs a high level signal to turn off the second transistor T2, the fourth transistor T4 is turned on, and the current signal in the storage capacitor C1 is transconductance-amplified by the third transistor T3 and then output to the readout circuit 50 through the current output terminal Iout. At this stage, the timing controller turns on the fourth transistor T4 row by row through the scan signal terminal Gate, and reads the current signal of the second ultrasonic wave row by row in cooperation with the readout circuit 50. The Gate of each row of scan signal terminal controls the turn-on time of the fourth transistor T4 to be T _gate The delay time of turning on the fourth transistor T4 at the Gate of two adjacent rows of scanning signal terminals is T _n 。

In the above control process, the first bias voltage acts as a direct current excitation signal continuously acting on the second plate 22 of the CMUT device, so the reset signal terminal Vrst outputs a normally high signal, and the power supply voltage signal terminal VDD and the bias voltage signal terminal Vbias likewise output a normally high signal.

As mentioned above, the application condition of the above scheme is that the thin film transistor in the driving circuit 40 has enough voltage resistance, if the voltage resistance is insufficient, the bias voltage signal terminal Vbias cannot output the first bias voltage capable of serving as the dc excitation signal, and then the excitation circuit 30 needs to output the ac excitation voltage and the dc excitation voltage at the same time, that is, the excitation circuit 30 includes the ac excitation sub-circuit 32 and the dc excitation sub-circuit 31 connected in parallel, and the corresponding fingerprint acquisition method can refer to fig. 14, which includes steps S1401-S1403 specifically as follows:

S1401: in the transmitting phase, the control exciting circuit 30 applies a direct current exciting voltage Vac and an alternating current exciting voltage Vdc to the first electrode plate 21, and the control driving circuit 40 applies a second bias voltage to the second electrode plate 22 to cause the capacitive micromachined ultrasonic transducer CMUT to transmit the first ultrasonic wave; the second bias voltage is less than the first bias voltage;

s1402: in the acquisition stage, the control excitation circuit 30 applies a direct-current excitation voltage Vdc to the first polar plate 21 and receives a current signal of the second ultrasonic wave converted by the capacitive micromachined ultrasonic transducer CMUT; the second ultrasonic wave is the reflected ultrasonic wave of the first ultrasonic wave at the target fingerprint;

s1403: in the readout phase, the control driving circuit 40 outputs a current signal to the readout circuit 50 so that the readout circuit 50 obtains a target fingerprint based on the current signal.

Taking the fingerprint acquisition circuit scheme applied in a display device provided in fig. 15A as an example, the ultrasonic transducer array 20 includes 100×100 CMUT devices, and the excitation circuit 30 includes an ac excitation sub-circuit 32 and a dc excitation sub-circuit 31 connected in parallel, both being connected to the first plates 21 of all CMUT devices at the same time, for applying an ac excitation voltage Vac and a dc excitation voltage Vdc to the first plates 21; the dc excitation subcircuit 31 may select DCDC power chips such as LT1085, LT8365, etc.; the ac excitation may be selected from a chip that provides a square wave signal, such as TC6320, and then becomes a sinusoidal excitation signal through LC resonance. The number of driving circuits 40 is equal to the number of CMUT devices and is arranged in a one-to-one correspondence, i.e. each CMUT device is connected to one driving circuit 40. The driving circuit 40 may adopt a 4T1C structure as shown in fig. 9 for applying a second bias voltage to the second plate 22 of the CMUT and transmitting a current signal of the second ultrasonic wave converted by the CMUT to the readout circuit 50 through the current output terminal Iout, and the configuration of the driving circuit 40 and the readout circuit 50 is the same as that of fig. 11. The readout circuit 50 includes a multiplexing gate switch 51 and a conversion sub-circuit 52; the input end of the multi-path gating sub-circuit is connected with the current output ends Iout of all the driving circuits 40, the output end is connected with the conversion sub-circuit 52, and the current-voltage conversion sub-circuit 52IV in the conversion sub-circuit 52 is used for converting the current signal of the second ultrasonic wave into a voltage signal and then converting the voltage signal into a digital voltage signal through the analog-to-digital conversion circuit ADC.

The fingerprint acquisition control sequence can be realized by a sequence controller referring to fig. 15B, and is specifically as follows:

the transmitting stage: the control dc excitation subcircuit 31 applies a dc excitation voltage Vdc to the first electrode plate 21, the ac excitation subcircuit 32 applies an ac excitation voltage Vac to the first electrode plate 21, the control reset signal terminal Vrst inputs a high level signal, the switch signal terminal Vclose inputs a low level signal to turn on the first transistor T1, the second transistor T2 turns off, and the bias voltage signal terminal Vbias applies a second bias voltage to the second electrode plate 22 through the first transistor T1; at the moment, the CMUT device starts to emit ultrasonic waves outwards according to the ultrasonic wave emission condition, and the ultrasonic waves are reflected back after touching the valley and the ridge of the fingerprint, so that second ultrasonic waves are formed.

Writing phase: the control switch signal end Vclose inputs a high-level signal to enable the second transistor T2 to be started, and the voltage of the second node N2 is increased to a second bias voltage;

and (3) an acquisition stage: the reset signal terminal Vrst is controlled to input a low level signal, the switch signal terminal Vclose is controlled to input a high level signal, so that the first transistor T1 is turned off, at this time, the ultrasonic wave receiving condition of the CMUT device is met, when the second ultrasonic wave returns to the diaphragm 23 of the CMUT device, the diaphragm 23 vibrates, the second ultrasonic wave is converted into a corresponding current signal, and the second transistor T2 is turned on, the fourth transistor T4 is turned off, so that the current signal is stored in the storage capacitor C1. Similarly, the reset signal Vrst may also input a high signal to keep the first transistor T1 in the on state.

A reading stage: the control switch signal end Vclose inputs low level signal, and scans signalThe Gate terminal Gate outputs a high level signal to turn off the second transistor T2, turn on the fourth transistor T4, and the current signal in the storage capacitor C1 is transconductance-amplified by the third transistor T3 and then output to the readout circuit 50 through the current output terminal Iout. In this process, the timing controller turns on the fourth transistor T4 row by row through the scan signal terminal Gate, and reads the current signal of the second ultrasonic wave row by row in cooperation with the readout circuit 50. The Gate of each row of scan signal terminal controls the turn-on time of the fourth transistor T4 to be T _gate The delay time of turning on the fourth transistor T4 at the Gate of two adjacent rows of scanning signal terminals is T _n 。

In the above process, the direct current excitation signal always acts on the first plate 21 of the CMUT device, while the power supply voltage signal terminal VDD and the bias voltage signal terminal Vbias output a normally high signal.

In a third aspect, based on the same inventive concept, in another alternative embodiment, a display device is provided, comprising the fingerprint acquisition device provided by the embodiment of the first aspect. The display device may be a display panel on which the fingerprint acquisition device provided in the embodiment of the present disclosure is mounted, or a display device using the display panel.

As for the display panel, the type thereof may be liquid crystal type (LCD) or Light Emitting Diode (LED) type, taking an organic light emitting diode OLED type display panel as an example, referring to fig. 16, the display panel includes, in addition to the glass substrate 10, the CMUT array formed on the glass substrate 10:

a packaging layer EN disposed overlying the ultrasound transducer array 20; the encapsulation layer EN may be formed of silicon nitride or an organic functional material for fabricating a planarization layer;

an electroluminescent device layer OLED disposed on the encapsulation layer EN;

a cover layer Platen is provided covering the electroluminescent device layer OLED arrangement.

The electroluminescent device layer OLED and the corresponding pixel driving circuit 40 may be integrated with the cover layer Platen to form a display layer. A matching layer ML can be further arranged between the packaging layer EN and the electroluminescent device layer OLED, and the matching layer ML is used for attaching the packaging layer EN and the electroluminescent device layer OLED, so that ultrasonic waves can be transmitted more easily, and if the ultrasonic wave transmittance is higher, the matching layer ML can be omitted.

As for the display device, electronic apparatuses such as a display for a desktop computer, an integrated computer, a notebook computer, a tablet computer, a flat panel television, a conference integrated machine, a smart phone, and a vehicle-mounted display may be used, and a display panel used for the display device includes the fingerprint acquisition device of the embodiment of the first aspect, as shown in fig. 17.

While preferred embodiments of the present application have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. It is therefore intended that the following claims be interpreted as including the preferred embodiments and all such alterations and modifications as fall within the scope of the application.

It will be apparent to those skilled in the art that various modifications and variations can be made to the present application without departing from the spirit or scope of the application. Thus, it is intended that the present application also include such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Claims

1. The fingerprint acquisition device is characterized by comprising an excitation circuit, a reading circuit, a glass substrate, an ultrasonic transducer array and a driving circuit, wherein the ultrasonic transducer array and the driving circuit are arranged on the glass substrate; the ultrasonic transducer array comprises a plurality of capacitive micromachined ultrasonic transducers, and the capacitive micromachined ultrasonic transducers comprise a first polar plate and a second polar plate; the first pole plate is connected with the excitation circuit, and the excitation circuit is configured to apply alternating excitation voltage to the first pole plate;

2. The fingerprint acquisition device of claim 1, wherein the drive circuit includes a bias voltage input sub-circuit, a switch sub-circuit, a charge storage sub-circuit, and a signal amplification sub-circuit;

3. The fingerprint acquisition device of claim 2, wherein the bias voltage input subcircuit includes a first transistor, the switch subcircuit includes a second transistor, the charge storage subcircuit includes a storage capacitor, and the signal amplification subcircuit includes a third transistor and a fourth transistor;

4. The fingerprint acquisition device of claim 3, wherein the bias voltage input sub-circuit comprises N first transistors, N being greater than or equal to 2 and being an integer, N first transistors being connected in parallel.

5. The fingerprint acquisition device of claim 1, wherein the excitation circuit comprises a square wave signal source, a resonant inductor and a blocking capacitor connected in series in sequence, the blocking capacitor being connected between the resonant inductor and the first plate; alternatively, the excitation circuit includes a sine wave signal source connected to the first plate.

6. The fingerprint acquisition device of claim 1, wherein the excitation circuit comprises: an ac exciter sub-circuit and a dc exciter sub-circuit in parallel with the ac exciter sub-circuit; the direct current excitation subcircuit comprises a direct current signal source and a resistor connected in series, wherein the resistor is connected between the direct current signal source and the first polar plate.

7. The fingerprint acquisition device of claim 1, wherein the readout circuit comprises a multiplexing switch and a switching sub-circuit; one end of the multi-path gating switch is connected with the second ends of all the driving circuits, and the other end of the multi-path gating switch is connected with the conversion sub-circuit and is used for gating the current signals output by each driving circuit; the conversion sub-circuit is used for converting the current signal into a digital voltage signal.

8. A fingerprint acquisition method, applied to a fingerprint acquisition device according to any one of claims 1 to 7, the method comprising:

9. A fingerprint acquisition method, characterized in that it is applied to a fingerprint acquisition device according to any one of claims 1 to 7, the excitation circuit comprising an ac excitation sub-circuit and a dc excitation sub-circuit connected in parallel; the method comprises the following steps:

10. A display device comprising a fingerprint acquisition apparatus as claimed in any one of claims 1 to 7.