A single-electrode ac electroluminescent fingerprint visualization sensor based on human coupling

Abstract

The application discloses a single-electrode alternating current electroluminescent fingerprint visualization sensor based on human body coupling. The sensor comprises a transparent conductive substrate and a luminescent dielectric composite layer arranged on the substrate, and the luminescent dielectric composite layer comprises alternating current electroluminescent material, high dielectric constant filler and flexible elastic medium. A finger contacts the surface of the luminescent dielectric composite layer, and the difference between the ridge and valley of the fingerprint in the contact distance and the equivalent capacitance causes the spatial non-uniform change of the alternating electric field distribution in the composite layer. The nonlinear response of the alternating current electroluminescent material to the electric field intensity directly converts the difference into visible light distribution, and realizes the real-time visualization display of the fingerprint topography. The flexible dielectric composite layer is deformed by pressing, the local electric field intensity is modulated, the light brightness changes with the contact state and the pressing degree, and the fingerprint depth or pressure information acquisition is realized. The application does not need a multi-electrode array or an independent imaging system, realizes the integration of fingerprint sensing and display, and is suitable for application scenes such as identity recognition and anti-counterfeiting.

Description

Technical Field

[0001] This invention relates to the field of sensing and display technology, specifically a single-electrode AC electroluminescent fingerprint visualization sensor based on human body coupling. Background Technology

[0002] Fingerprint recognition technology, as an important biometric identification method, has been widely used in fields such as identity authentication, access control systems, mobile terminals, and financial payments due to its uniqueness and stability. Existing fingerprint recognition devices mainly collect and identify fingerprint information based on principles such as optics, capacitance, ultrasound, thermal sensing, or electrostatics, and have formed a relatively mature technical system in practical applications.

[0003] Optical fingerprint recognition devices typically identify fingerprints by acquiring a two-dimensional optical image of the fingerprint surface. For example, US Patent 5781651A discloses an optical fingerprint recognition scheme that uses an electroluminescent device to provide illumination for fingerprint imaging. This type of technology has a relatively intuitive structure, but its recognition performance is easily affected by ambient light, dirt, and surface contamination. Furthermore, it relies primarily on two-dimensional image information and struggles to reflect the force or depth characteristics of the fingerprint. Capacitive fingerprint recognition devices reconstruct fingerprint patterns by detecting changes in capacitance between the finger skin and an electrode array. For example, US Patent 5963679 proposes a fingerprint sensing structure based on changes in electric field distribution. This type of technology typically relies on high-density electrode arrays and complex signal readout circuits, and is prone to recognition instability under conditions of wet hands, dry hands, or surface contamination.

[0004] In recent years, some technical solutions have attempted to integrate fingerprint sensing functionality with display units. For example, US patents US9274553B2 and US9501631B2 disclose biometric identification schemes that integrate fingerprint sensors with display devices; international patent application WO2015051644A1 discloses a fingerprint recognition element and display device that acquires and displays fingerprint information through capacitance changes. These solutions have, to some extent, promoted the development of fingerprint recognition and display integration, but they generally rely on multi-electrode arrays, independent imaging modules, or complex signal processing systems, resulting in relatively complex device structures and high manufacturing costs and power consumption.

[0005] Furthermore, while ultrasonic fingerprint recognition devices can acquire three-dimensional fingerprint structural information and have strong anti-counterfeiting capabilities, their systems typically require transducer arrays and supporting signal acquisition and processing circuits, resulting in a complex overall structure and high cost, which limits their adoption in cost-sensitive applications. In general, existing fingerprint recognition technologies mostly achieve fingerprint information acquisition through a "sensing-imaging-display" separation approach, generally suffering from complex structures, high dependence on multi-electrode arrays or independent imaging systems, and difficulty in simultaneously achieving low cost, miniaturization, and real-time intuitive display.

[0006] Therefore, there is an urgent need for a fingerprint sensing technology that is simple in structure, does not require a multi-electrode array or independent imaging system, and can directly visualize fingerprint information during fingerprint contact, in order to meet the reliability and integration requirements of applications such as identity recognition and anti-counterfeiting.

[0007] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0008] The technical problem this invention aims to solve is to address the common issues in existing fingerprint recognition and display technologies, such as the separation of sensing and imaging processes, reliance on independent imaging systems or multi-electrode arrays, complex device structures, and difficulty in achieving real-time and intuitive display of fingerprint information. This invention provides a single-electrode AC electroluminescent fingerprint visualization sensing technology based on human body coupling. This technology enables fingerprints to directly appear in the form of light emission during contact without the need for complex readout circuits or independent imaging modules, thereby achieving instant visualization of fingerprint information and improving the simplification of device structure and system integration.

[0009] The main feature of this invention is that it achieves integrated conversion of fingerprint information perception and display in the same device through the synergistic design of human body coupling electrical mechanism and alternating current electroluminescence effect, rather than simply relying on high-density electrode array or back-end signal reconstruction process. This overcomes the shortcomings of existing optical and capacitive fingerprint display technologies in terms of complex structure, insufficient environmental adaptability, and limited information acquisition dimensions.

[0010] To address the aforementioned issues, the present invention provides a single-electrode AC electroluminescent fingerprint visualization sensor based on human body coupling. The sensor comprises a transparent conductive substrate and a light-emitting dielectric composite layer disposed thereon. The light-emitting dielectric composite layer comprises an AC electroluminescent material, a high dielectric constant filler, and a flexible elastic medium.

[0011] The method for preparing the sensor includes the following steps:

[0012] S1. Cleaning of transparent electrodes: The transparent conductive substrate is ultrasonically cleaned with deionized water, ethanol or acetone in sequence and then dried. Finally, it is dried in an oven for later use.

[0013] S2. Prepare the light-emitting layer precursor and prepare the elastomer precursor according to the set mass ratio; add electroluminescent particles and high-dielectric particles to it, mechanically stir and ultrasonically disperse; then degas under vacuum.

[0014] S3. Light-emitting layer film formation: A composite layer or a light-emitting layer and a dielectric reinforcement layer are formed sequentially on a transparent conductive substrate by spin coating, blade coating, casting or spraying.

[0015] S4. Heat and cure at 60–120 ℃ for 0.5–2 h; insulate and encapsulate the electrode leads and edges;

[0016] S5. Analysis of human body coupled fingerprint display and pressure response mechanism;

[0017] S6. Based on human body coupled fingerprint display and pressure response performance test.

[0018] Preferably, in step S1, the transparent electrode is any one of ITO glass, ITO / PET, FTO glass, graphene transparent conductive film, or metal mesh transparent electrode, and after drying, it can be subjected to plasma / UV-Ozone treatment to improve adhesion.

[0019] Preferably, in step S2, the inorganic electroluminescent particles are selected from one or more of ZnS:Cu, ZnS:Mn, ZnS:Ag, GaN, and CdS; the high dielectric constant filler is selected from one or more of BaTiO3, (Ba,Sr)TiO3, TiO2, and ZrTiO2; and the elastic medium matrix is ​​selected from one or more of Ecoflex, PDMS, silicone rubber, and PVDF-based elastomers.

[0020] Preferably, in step S3, the total thickness of the light-emitting layer film does not exceed 200 μm.

[0021] Preferably, step S5 includes the following steps:

[0022] S51. When a human finger touches the surface of the composite layer, an AC displacement current loop is formed through the capacitance coupling between the human body and the ground. The device generates a spatial light emission distribution in the contact area, presenting a fingerprint ridge or valley image. The pressure changes the local deformation and equivalent capacitance, thereby causing changes in light emission intensity to characterize pressure or depth features.

[0023] S52, Fingerprint Display: A camera or photodetector is set under a transparent conductive substrate to collect and identify luminescent images, and to observe the changes in luminescent images under voltage and frequency.

[0024] S53. Pressure Response: Use a universal testing machine to test the pressure changes under different pressures.

[0025] S54. Internal morphology analysis: The distribution of luminescent material in the luminescent layer is observed using an optical microscope.

[0026] Preferably, step S6 includes the following steps:

[0027] S61. Luminescence spectroscopy test: Analyze the emission spectrum of the visualized optical image displayed by the luminescent layer using a fiber optic spectrometer;

[0028] S62. Fingerprint display image: Use a camera to capture fingerprint images of a finger pressed on the luminescent layer, and observe the changes in fingerprints under different people, different pressure levels, and different contact areas.

[0029] This invention also discloses the application of an electroluminescent sensor for the identification of fingerprints from different individuals: the invention is used to collect fingerprint image information from multiple groups of different individuals; deep learning is used to model the fingerprint information, and a classification model is used to analyze the accuracy of the computer's image processing of the fingerprints generated by the invention.

[0030] The advantages of this invention compared to existing technologies are:

[0031] 1. This invention is based on a single-electrode AC electroluminescence mechanism driven by human body coupling, enabling fingerprints to be directly emitted as light during contact, thus achieving the integration of fingerprint sensing and display. While ensuring the visualization of fingerprint information, it effectively reduces the number of component units, simplifies the system structure, and improves the integration and feasibility of the device.

[0032] 2. This invention utilizes the equivalent capacitance difference caused by the fingerprint ridge structure to directly modulate the alternating electric field distribution in the light-emitting dielectric layer, and through the nonlinear response of the alternating electroluminescent material to the electric field intensity, directly maps the microscopic morphology of the fingerprint into a light-emitting image. At the same time, the changes in light intensity reflect different contact states and pressure, thereby expanding the expression dimension of fingerprint information without adding additional sensing units.

[0033] 3. In this invention, the formation of the fingerprint luminescent image is modulated by multiple factors such as fingerprint morphology, contact area and pressure, so that the obtained fingerprint image has high distinguishability in spatial distribution and brightness characteristics, which is beneficial to improving the stability and anti-counterfeiting ability of the fingerprint display process.

[0034] 4. The human body coupling driving method adopted in this invention does not require direct electrical connection to the human body. It only relies on the inherent distributed capacitance between the human body and ground to enable the device to work, reducing the dependence on complex electrode connections and external hardware systems and enhancing the adaptability of the device in different usage environments. Based on the obtained fingerprint luminescence image, it can be further combined with image processing or pattern recognition methods to achieve individual differentiation, verifying the feasibility of this invention in identity recognition applications.

[0035] In summary, compared with existing fingerprint recognition and display technologies that rely on independent imaging systems or multi-electrode arrays, this invention utilizes a single-electrode alternating current electroluminescence mechanism driven by human body coupling. This enables real-time visualization of fingerprint information, and by rationally controlling the composition and structure of the luminescent dielectric composite layer, the device not only presents the fingerprint morphology with high contrast but also generates distinguishable optical responses to contact pressure and contact area, thereby enhancing the dimensionality and security of fingerprint information. Compared with traditional fingerprint recognition technologies that rely on multi-electrode arrays or independent imaging systems, this invention has significant advantages in terms of structural simplification, anti-counterfeiting capabilities, and information acquisition methods, making it suitable for identity authentication, anti-counterfeiting identification, and related human-computer interaction applications. Attached Figure Description

[0036] Figure 1 This is a circuit equivalent schematic diagram of a single-electrode AC electroluminescent fingerprint visualization sensor based on the human body coupling principle, and an example image of the fingerprint emission it collects.

[0037] Figure 2 This is a schematic diagram of the three-dimensional morphology of a fingerprint obtained by processing the acquired fingerprint luminescence image using a three-dimensional reconstruction algorithm (3D Plot).

[0038] Figure 3 The images show the emission spectra of Examples 1, 2, and 3 obtained under different applied AC voltages and different ratios of electroluminescent materials.

[0039] Figure 4 The graph shows the response relationship between the device's luminous intensity and pressure under different pressure levels.

[0040] Figure 5 This is a graph showing the relationship between the brightness of the fingerprint luminescent image and the effective contact area between the human finger and the luminescent dielectric layer.

[0041] Figure 6 Examples of actual fingerprint emission images of different individuals collected using the device prepared in Example 1.

[0042] Figure 7 The image shows the result obtained using a convolutional neural network (CNN) deep learning classification algorithm based on the collected fingerprint luminescence images. Detailed Implementation

[0043] To make the content of this invention easier to understand, the technical solutions in the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings.

[0044] A single-electrode AC electroluminescent fingerprint visualization sensor based on human body coupling, the fabrication method of which includes the following steps:

[0045] 1. Cleaning of transparent electrodes: Use any one of ITO glass, ITO / PET, FTO glass, graphene transparent conductive film, or metal mesh transparent electrodes. Clean the transparent conductive substrate sequentially with deionized water, then ultrasonically clean it with ethanol / acetone, and finally dry it in an oven before use. Plasma / UV-Ozone treatment can be performed to improve adhesion.

[0046] 2. Prepare the light-emitting layer precursor by selecting one or more inorganic electroluminescent particles such as ZnS:Cu, ZnS:Mn, ZnS:Ag, GaN, and CdS; select one or more high-dielectric-constant fillers such as BaTiO3, (Ba,Sr)TiO3, TiO2, and ZrTiO4; and select one or more elastic medium matrices such as Ecoflex, PDMS, silicone rubber, and PVDF-based elastomers. Prepare the elastomer precursor according to the set mass ratio; add the electroluminescent particles and high-dielectric-constant particles, mechanically stir and ultrasonically disperse; then vacuum degas.

[0047] 3. Forming of the light-emitting layer: A composite layer or a light-emitting layer and a dielectric reinforcement layer are formed sequentially on a transparent conductive substrate by spin coating, blade coating, casting or spraying; the total thickness is controlled to not exceed 200 μm.

[0048] 4. Heat and cure at 60–120 ℃ for 0.5–2 h (or cure at room temperature for a longer time); insulate and seal the electrode leads and edges (to prevent arcing and leakage).

[0049] Electroluminescent fingerprint visualization sensor based on human body coupled fingerprint display and pressure response mechanism analysis:

[0050] 1. When a human finger touches the surface of the composite layer, an AC displacement current loop is formed through the capacitance coupling between the human body and the ground. The device generates a spatial light emission distribution in the contact area, presenting a fingerprint ridge / valley image. The pressure changes the local deformation and equivalent capacitance, thereby causing changes in light emission intensity to characterize the pressure / depth features.

[0051] 2. Fingerprint display: A camera / photodetector is set under a transparent conductive substrate to capture and identify the emitted light images, and the changes in the emitted light images under voltage and frequency are observed.

[0052] 3. Pressure response: Use a universal testing machine to test the pressure changes under different pressures.

[0053] 4. Internal morphology analysis: The distribution of luminescent material in the luminescent layer was observed using an optical microscope.

[0054] Electroluminescent fingerprint visualization sensor based on human fingerprint coupling display and pressure response performance testing:

[0055] 1. Luminescence spectroscopy test: Analyze the luminescence spectrum of the visualized optical image displayed by the luminescent layer using a fiber optic spectrometer.

[0056] 2. Fingerprint display image: Use a camera to capture fingerprint images of a finger pressing on the luminescent layer, and observe the changes in fingerprints under different people, different pressure levels, and different contact areas.

[0057] Electroluminescent fingerprint visualization sensors are used for the identification of fingerprints from different individuals:

[0058] 1. This invention is used to collect fingerprint image information from multiple groups of different people.

[0059] 2. Fingerprint information is obtained by using deep learning modeling, and the accuracy of image processing generated by the computer based on the fingerprint of this invention is analyzed by obtaining a classification model.

[0060] Working mechanism:

[0061] The principle of human body coupling refers to the fact that under high-frequency alternating current driving conditions, the human body does not act as a direct conducting electrode, but participates in the circuit operation through the inherent distributed capacitance between itself and ground, thereby forming an energy coupling channel based on displacement current between the device and the human body. In this invention, when only one electrode is connected and alternating current is applied, when the human finger touches the surface of the light-emitting dielectric layer, the human body acts as a floating electrode through its capacitance to ground, causing a closed alternating current displacement loop to be formed inside the device, thereby establishing an alternating electric field in the light-emitting dielectric composite layer. Figure 1 a). The surface of human fingers naturally contains fingerprint ridges and valleys. Differences in contact distance and effective contact area in different regions lead to uneven distribution of equivalent capacitance, which in turn modulates the spatial distribution of the alternating electric field within the luminescent dielectric layer, making it correspond to the fingerprint morphology. Because alternating current electroluminescent materials have a significant nonlinear response to electric field intensity, this electric field difference is effectively amplified and directly converted into a visible luminescent distribution, thus achieving the visualization of the fingerprint morphology. Figure 2 In the luminescent dielectric composite layer, the content of luminescent material has a significant impact on electric field enhancement and luminous efficiency: when the content of luminescent material is too low, the number of luminescent centers is insufficient, leading to a decrease in luminous intensity and image contrast; while when the content of luminescent material is too high, particle agglomeration and electric field shielding effects are enhanced, weakening the local electric field and suppressing luminous efficiency. Figure 3 Therefore, a proper match needs to be achieved between the luminescent material, the high-dielectric filler, and the elastic matrix. Furthermore, under pressure, the flexible elastic medium undergoes reversible deformation, changing the effective distance between the human body coupling electrode and the transparent conductive substrate, thereby altering the local equivalent capacitance and alternating electric field intensity distribution. Since the alternating current electroluminescence intensity has a nonlinear dependence on the electric field, different pressure intensities are directly mapped to differences in luminous brightness, enabling the device to possess optical response capabilities to pressure or depth information. Figure 4Furthermore, since this device is a single-electrode AC electroluminescent system driven by human body coupling, the luminescence brightness is also closely related to the fingerprint contact area. When the contact area increases, the equivalent capacitance increases, leading to a decrease in the electric field strength per unit area, thus weakening the luminescence. In small contact area regions such as fingerprint ridges, the electric field is relatively concentrated, and the luminescence is more significant. Figure 5 This characteristic helps distinguish fingerprint ridge structures and improves fingerprint display contrast and anti-counterfeiting capabilities. (Mechanism)

[0062] To verify the effectiveness of the fingerprint luminescence images obtained by this invention in individual differentiation, multiple different volunteers were selected, and their index fingers were used to collect fingerprint luminescence images on the device of this invention, and a fingerprint image sample set was constructed. Figure 6 The fingerprint luminescence image was further trained and classified using a convolutional neural network, and the classification results are as follows: Figure 7 As shown, the fingerprint luminescence images of different volunteers exhibit significant discriminative power in the feature space, and the classification results are highly consistent with the actual individual identities. This indicates that the fingerprint luminescence images obtained by this invention can stably reflect individual fingerprint characteristics and possess the feasibility and reliability for identity recognition.

[0063] The local coupling capacitance between the finger and the device can be approximated by a parallel plate:

[0064]

[0065] in Represents the capacitance distribution on a plane. Represents the vacuum permittivity. This represents the equivalent dielectric constant after the interaction of multiple dielectrics between the finger and the bottom electrode of the device. For local effective contact area, Local effective electrode spacing.

[0066] Fingerprint ridges and fingerprint valleys Transformed into a spatial template. Fingerprint ridge. Small, then Large; conversely, fingerprint valleys contain air gaps, therefore fingerprint valleys Small, Small. This results in a spatial distribution of capacitance. Because electroluminescence is sensitive to electric fields and can be radiated in the form of visible light, this spatial distribution of capacitance can form an optical image of a fingerprint.

[0067] Example 1:

[0068] Prepare a precursor solution of 5 grams of PDMS curing agent at a mass ratio of 10:1, and then prepare a precursor solution at a mass ratio of M. ZnS:Cu M PDMS=0.75:1, that is, 3.75 grams of ZnS:Cu electroluminescent powder, and then at a mass ratio M BaTiO3 M PDMS The ratio is 0.5:1, which is 2.5 grams of BaTiO3 nanoparticles. After stirring evenly, the mixture is placed in a vacuum chamber and evacuated for 10 minutes to remove air bubbles from the precursor, thus obtaining the luminescent dielectric layer precursor solution.

[0069] After ultrasonically cleaning the ITO glass with deionized water, it is then ultrasonically cleaned with acetone for a certain period of time until it is completely clean. On the cleaned ITO glass, the prepared emissive layer precursor solution is spin-coated at 2000 rpm for 60 seconds to form an emissive layer with a film thickness controlled at 100 μm. The spin-coated device is then placed in a 100°C oven and heated for 1 hour. The formed device is connected to a 14kHz, 150V AC power supply (only a single electrode needs to be connected to the ITO glass). When a bare finger is directly touched to the dielectric layer surface, the fingerprint pattern is displayed on the emissive layer and transmitted through the transparent ITO electrode, captured by a camera mounted at the bottom for fingerprint recognition.

[0070] Comparative Example 1:

[0071] Prepare a precursor solution of 5 grams of PDMS curing agent at a mass ratio of 10:1, and then prepare a precursor solution at a mass ratio of M. ZnS:Cu M PDMS =0.5:1, that is, 2.5 grams of ZnS:Cu electroluminescent powder, and then at a mass ratio M BaTiO3 M PDMS The ratio is 0.5:1, which is 2.5 grams of BaTiO3 nanoparticles. After stirring evenly, the mixture is placed in a vacuum chamber and evacuated for 10 minutes to remove air bubbles from the precursor, thus obtaining the luminescent dielectric layer precursor solution.

[0072] After ultrasonically cleaning the ITO glass with deionized water, it is then ultrasonically cleaned with acetone for a certain period of time until it is clean. On the cleaned ITO glass, a prepared ZnS:Cu dispersion is spin-coated at 2000 rpm to form a 60-fold luminescent layer. The spin-coated device is then placed in a 100°C oven and heated for 1 hour. The formed device is connected to a 14kHz, 150V AC power supply (only a single electrode needs to be connected to the ITO glass). When a bare finger is directly touched to the dielectric layer surface, the fingerprint pattern is displayed on the luminescent layer and passes through the transparent ITO electrode, captured by a camera mounted at the bottom for fingerprint recognition.

[0073] This comparative example compares the impact of insufficient electroluminescent powder content on the light-emitting layer of the device, illustrating the effect of the overall mass ratio of electroluminescent powder on the forming performance and luminescence performance of the light-emitting dielectric layer compared to Example 1. Insufficient content leads to a decrease in powder density in the light-emitting layer, resulting in a reduction in the number of light-emitting points per unit area, which in turn leads to insufficient luminescence resolution and insufficient luminescence brightness.

[0074] Comparative Example 2:

[0075] Prepare a precursor solution of 5 grams of PDMS curing agent at a mass ratio of 10:1, and then prepare a precursor solution at a mass ratio of M. ZnS:Cu M PDMS =1:1, that is, 5 grams of ZnS:Cu electroluminescent powder, and then with a mass ratio M BaTiO3 M PDMS The ratio is 0.5:1, which is 2.5 grams of BaTiO3 nanoparticles. After stirring evenly, the mixture is placed in a vacuum chamber and evacuated for 10 minutes to remove air bubbles from the precursor, thus obtaining the luminescent dielectric layer precursor solution.

[0076] After ultrasonically cleaning the ITO glass with deionized water, it is then ultrasonically cleaned with acetone for a certain period of time until it is clean. On the cleaned ITO glass, the prepared emissive layer precursor solution is spin-coated at 2000 rpm for 60 seconds to form an emissive layer. The spin-coated device is then placed in a 100°C oven and heated for 1 hour. The formed device is connected to a 14kHz, 150V AC power supply (only a single electrode needs to be connected to the ITO glass). A bare finger is then directly touched to the dielectric layer surface; the fingerprint pattern is displayed on the emissive layer and passes through the transparent ITO electrode, captured by a camera mounted at the bottom for fingerprint recognition.

[0077] This comparative example compares the impact of excessive electroluminescent powder content on the light-emitting layer of the device, illustrating the effect of the overall mass ratio of electroluminescent powder on the forming performance and light-emitting performance of the light-emitting dielectric layer compared to Example 1. Excessive content may lead to higher viscosity of the precursor liquid, making it difficult to form the light-emitting layer, and causing the light-emitting layer to thicken and the brightness to begin to decrease.

[0078] Comparative Example 3:

[0079] Prepare a precursor solution of 5 grams of PDMS curing agent at a mass ratio of 10:1, and then prepare a precursor solution at a mass ratio of M. ZnS:Cu M PDMS =0.75:1, that is, 3.75 grams of ZnS:Cu electroluminescent powder, and then at a mass ratio M BaTiO3 M PDMS The ratio is 1:1, which is 5 grams of BaTiO3 nanoparticles. After stirring evenly, the mixture is placed in a vacuum chamber and evacuated for 10 minutes to remove air bubbles from the precursor, thus obtaining the luminescent dielectric layer precursor solution.

[0080] After ultrasonically cleaning the ITO glass with deionized water, it is then ultrasonically cleaned with acetone for a certain period of time until it is clean. On the cleaned ITO glass, the prepared emissive layer precursor solution is spin-coated at 2000 rpm for 60 seconds to form the emissive layer. The spin-coated device is then placed in a 100°C oven and heated for 1 hour. The formed device is connected to a 14kHz, 150V AC power supply (only a single electrode needs to be connected to the ITO glass). A bare finger is then directly touched to the dielectric layer surface, and the fingerprint pattern is displayed on the emissive layer and transmitted through the transparent ITO electrode. This fingerprint is then captured by a camera mounted at the bottom for fingerprint recognition.

[0081] This comparative example demonstrates the impact of excessive dielectric powder content on the light-emitting layer of the device, compared to Example 1. Excessive dielectric powder content may lead to increased viscosity of the precursor solution, making it difficult to form the light-emitting layer. Furthermore, the nanoscale particle size of the dielectric powder results in higher surface energy, which can cause agglomeration and defects.

[0082] Comparative Example 4:

[0083] Prepare a precursor solution of 5 grams of PDMS curing agent at a mass ratio of 10:1, and then prepare a precursor solution at a mass ratio of M. ZnS:Cu M PDMS =0.75:1, that is, 3.75 grams of ZnS:Cu electroluminescent powder, after being stirred evenly, is placed in a vacuum chamber and vacuumed for 10 minutes to remove air bubbles in the precursor, thus obtaining the luminescent dielectric layer precursor solution.

[0084] After ultrasonically cleaning the ITO glass with deionized water, it is then ultrasonically cleaned with acetone for a certain period of time until it is clean. On the cleaned ITO glass, a prepared ZnS:Cu precursor solution is spin-coated at 2000 rpm for 60 seconds to form a light-emitting layer. The spin-coated device is then placed in a 100℃ oven and heated for 1 hour. The formed device is connected to a 14kHz, 150V AC power supply (only a single electrode needs to be connected to the ITO glass). When a bare finger is directly touched to the dielectric layer surface, the fingerprint pattern is displayed on the light-emitting layer and passes through the transparent ITO electrode, captured by a camera mounted at the bottom for fingerprint recognition.

[0085] This comparative example compares the impact of the light-emitting layer of the device without dielectric powder, illustrating the difference compared to Example 1. The dielectric constant of the light-emitting layer without dielectric powder is lower, resulting in insufficient control over the electric field. The electric field cannot be concentrated in the electroluminescent powder, leading to insufficient luminescence performance.

[0086] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A single-electrode AC electroluminescent fingerprint visualization sensor based on human body coupling, characterized in that, The sensor includes a transparent conductive substrate and a light-emitting dielectric composite layer disposed thereon, wherein the light-emitting dielectric composite layer includes an AC electroluminescent material, a high dielectric constant filler, and a flexible elastic medium; The method for preparing the sensor includes the following steps: S1. Cleaning of transparent electrodes: The transparent conductive substrate is ultrasonically cleaned with deionized water, ethanol or acetone in sequence and then dried. Finally, it is dried in an oven for later use. S2. Prepare the light-emitting layer precursor and prepare the elastomer precursor according to the set mass ratio; add electroluminescent particles and high-dielectric particles to it, mechanically stir and ultrasonically disperse; then degas under vacuum. S3. Light-emitting layer film formation: A composite layer or a light-emitting layer and a dielectric reinforcement layer are formed sequentially on a transparent conductive substrate by spin coating, blade coating, casting or spraying. S4. Heat and cure at 60–120 ℃ for 0.5–2 h; insulate and encapsulate the electrode leads and edges; S5. Analysis of human body coupled fingerprint display and pressure response mechanism; S6. Based on human body coupled fingerprint display and pressure response performance test.

2. The single-electrode AC electroluminescent fingerprint visualization sensor based on human body coupling according to claim 1, characterized in that: In step S1, the transparent electrode is any one of ITO glass, ITO / PET, FTO glass, graphene transparent conductive film, or metal mesh transparent electrode. After drying, it can be subjected to plasma / UV-Ozone treatment to improve adhesion.

3. The single-electrode AC electroluminescent fingerprint visualization sensor based on human body coupling according to claim 1, characterized in that: In step S2, the inorganic electroluminescent particles are selected from one or more of ZnS:Cu, ZnS:Mn, ZnS:Ag, GaN, and CdS; the high dielectric constant filler is selected from one or more of BaTiO3, (Ba,Sr)TiO3, TiO2, and ZrTiO2; and the elastic medium matrix is ​​selected from one or more of Ecoflex, PDMS, silicone rubber, and PVDF-based elastomer.

4. The single-electrode AC electroluminescent fingerprint visualization sensor based on human body coupling according to claim 1, characterized in that: In step S3, the total thickness of the light-emitting layer film does not exceed 200 μm.

5. A single-electrode AC electroluminescent fingerprint visualization sensor based on human body coupling according to claim 1, characterized in that: Step S5 includes the following steps: S51. When a human finger touches the surface of the composite layer, an AC displacement current loop is formed through the capacitance coupling between the human body and the ground. The device generates a spatial light emission distribution in the contact area, presenting a fingerprint ridge or valley image. The pressure changes the local deformation and equivalent capacitance, thereby causing changes in light emission intensity to characterize pressure or depth features. S52, Fingerprint Display: A camera or photodetector is set under a transparent conductive substrate to collect and identify luminescent images, and to observe the changes in luminescent images under voltage and frequency. S53. Pressure Response: Use a universal testing machine to test the pressure changes under different pressures. S54. Internal morphology analysis: The distribution of luminescent material in the luminescent layer is observed using an optical microscope.

6. The single-electrode AC electroluminescent fingerprint visualization sensor based on human body coupling according to claim 1, characterized in that: Step S6 includes the following steps: S61. Luminescence spectroscopy test: Analyze the emission spectrum of the visualized optical image displayed by the luminescent layer using a fiber optic spectrometer; S62. Fingerprint display image: Use a camera to capture fingerprint images of a finger pressed on the luminescent layer, and observe the changes in fingerprints under different people, different pressure levels, and different contact areas.

Images