Flexible paper-based electronic device and preparation method

Abstract

The invention discloses a flexible paper-based electronic device and a preparation method, and belongs to the technical field of flexible electronics, and the electronic device is used for improving the performance of the flexible electronic device. The smooth layer covers and is cured on the surface of one side of the paper substrate, and the surface, away from the side of the paper substrate, of the smooth layer is a flat surface; the circuit layer comprises a conductive circuit and a functional unit connected with the conductive circuit; and the packaging layer covers the surface of one side, deviating from the smooth layer, of the circuit layer and is used for isolating environmental water vapor and mechanical damage.

Description

Technical Field

[0001] This application belongs to the field of flexible electronics technology, specifically relating to a flexible paper-based electronic device and its fabrication method. Background Technology

[0002] With the rapid development of the Internet of Things, smart packaging, and wearable devices, the demand for low-cost, flexible, and environmentally friendly electronic devices is increasing. Paper, as a widely available, flexible, and biodegradable material, is considered an ideal substrate for flexible electronic devices. Related technologies have enabled the implementation of simple conductive lines or sensors on paper substrates.

[0003] However, current paper-based electronic devices still have shortcomings in terms of stability and reliability, especially in maintaining performance under complex environments, which needs further improvement and restricts their large-scale practical application. Summary of the Invention

[0004] This application provides a flexible paper-based electronic device and its fabrication method to improve the performance of the paper-based electronic device.

[0005] The first aspect of this application provides a flexible paper-based electronic device, the electronic device comprising: sequentially stacked layers: Paper substrate; A smoothing layer, which covers and is cured on one side surface of the paper substrate, and the surface of the smoothing layer opposite to the paper substrate is a flat surface; A circuit layer, the circuit layer including conductive lines and functional units connected by the conductive lines; An encapsulation layer covers the surface of the circuit layer opposite to the smooth layer, serving to isolate it from environmental moisture and mechanical damage.

[0006] In some embodiments, the material used for the smoothing layer is at least one of the following: gelatin, chitosan, polylactic acid (PLA), polybutylene succinate (PBS), or polycaprolactone (PCL).

[0007] In some embodiments, the conductive lines are formed by a printing process using conductive ink, wherein the conductive ink is one of the following: silver nanowire ink or carbon nanotube ink.

[0008] In some embodiments, the functional unit includes at least one of the following: Temperature sensing unit, humidity sensing unit, biochemical sensing unit, heating unit, light-emitting diode, microchip.

[0009] In some embodiments, the microchip includes at least one of the following: a radio frequency identification (RFID) chip, a microcontroller (MCU), a memory chip, and a sensor signal conditioning chip.

[0010] In some embodiments, the material used for the encapsulation layer is at least one of the following: Beeswax, polylactic acid (PLA), polybutylene succinate (PBS).

[0011] The second aspect of this application also provides a method for preparing a flexible paper-based electronic device. The method is used to prepare the flexible paper-based electronic device described in the first aspect of this application. The method includes: Prepare a paper base; A smooth layer is prepared on one side surface of the paper substrate, the smooth layer covers and is cured on one side surface of the paper substrate, and the surface of the smooth layer opposite to the paper substrate is a flat surface; A circuit layer is formed on one side surface of the smooth layer, the circuit layer including conductive lines and functional units connected by the conductive lines; An encapsulation layer is prepared on the surface of the circuit layer opposite to the smooth layer, the encapsulation layer being used to isolate environmental moisture and mechanical damage.

[0012] In some embodiments, fabricating a circuit layer on one side surface of the smooth layer includes: A circuit pattern containing conductive lines and functional units is printed on one side surface of the smooth layer using inkjet printing or screen printing. The circuit pattern is cured at low temperature.

[0013] In some embodiments, the temperature of the low-temperature curing is greater than or equal to 60°C and less than or equal to 100°C.

[0014] In some embodiments, preparing a smooth layer on one side surface of the paper substrate includes: The smoothing layer material is coated onto one side surface of the paper substrate by dip coating, spin coating, spray coating, or scraping coating, and then cured.

[0015] The beneficial effects of this application's embodiments are as follows: By introducing a specially designed smoothing layer between the paper substrate and the circuit layer, this application's embodiments effectively overcome the adverse effects of the rough and porous surface of paper. This smoothing layer not only fills the fiber pores, providing a flat and continuous adhesion interface for subsequent circuit printing, but also significantly improves the forming quality, conductivity, and mechanical reliability of the conductive lines, fundamentally enhancing the electrical performance and structural stability of the device. Furthermore, this application's embodiments employ a layered encapsulation structure, particularly the encapsulation layer covering the circuit layer, which, together with the smoothing layer, constitutes a dual protection system against environmental humidity and mechanical stress. This design significantly enhances the long-term stability and durability of the device under complex operating environments (especially humidity changes), extending its service life. In summary, this solution effectively solves the core problem of insufficient performance and stability when paper substrates are used as electronic device substrates, while maintaining the advantages of low cost, flexibility, and environmental friendliness, providing a practical and feasible path for the development of high-performance, high-reliability, green, flexible electronic devices.

[0016] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments or related technologies of this application, the accompanying drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. It should be noted that the scale in the drawings is for illustration only and does not represent the actual scale.

[0018] Figure 1 This is a schematic diagram of the structure of a flexible paper-based electronic device proposed in the embodiments of this application; Figure 2 This is a flowchart illustrating the steps of a method for fabricating a flexible paper-based electronic device as proposed in the embodiments of this application; Figure reference numerals: 1. Paper substrate; 2. Smoothing layer; 3. Circuit layer; 4. Encapsulation layer. Detailed Implementation

[0019] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] The terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and not to describe a specific order or sequence. It should be understood that such terms can be used interchangeably where appropriate so that embodiments of this application can be implemented in orders other than those illustrated or described herein, and the objects distinguished by "first" and "second" are generally of the same class, not limited in number; for example, the first object can be one or at least two. Furthermore, in the specification and claims, "and / or" indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0021] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0022] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0023] With the rapid development of the Internet of Things (IoT), smart packaging, and wearable devices, the demand for low-cost, flexible, and environmentally friendly electronic devices is increasing. Paper, as a widely available, flexible, and biodegradable material, is considered an ideal substrate for flexible electronic devices. Related technologies have enabled the implementation of simple conductive circuits or sensors on paper (such as common blood glucose test strips). However, current paper-based electronic devices still have shortcomings in terms of stability and reliability, especially in maintaining performance under complex environments, which requires further improvement and restricts their large-scale practical application.

[0024] Despite its promising prospects, using paper directly as a substrate for high-performance electronic devices still faces fundamental challenges, primarily including: 1. Rough and porous surface: Paper, composed of interwoven fibers, has a high surface roughness, resulting in poor continuity, high resistance, and easy breakage of conductive lines printed on it, severely limiting device performance and reliability. 2. Poor environmental stability: Paper is hydrophilic and hygroscopic, easily deforming and warping when environmental humidity changes, leading to circuit performance drift or failure and short device lifespan. 3. Lack of effective packaging: Existing plastic packaging solutions are incompatible with the flexibility and biodegradability of paper, making it difficult to maintain its environmental advantages while ensuring device stability. 4. Low system integration: Related technologies are mostly limited to single functions (such as only conductivity or only sensing), making it difficult to achieve complete microsystem integration including power supply, sensing, logic, and communication on a paper substrate.

[0025] To address the aforementioned issues, this application proposes a flexible paper-based electronic device. By introducing a specially designed smoothing layer between the paper substrate and the circuit layer, the adverse effects of the rough and porous paper surface are effectively overcome. This smoothing layer not only fills the fiber pores, providing a flat and continuous adhesion interface for subsequent circuit printing, but also significantly improves the forming quality, conductivity, and mechanical reliability of the conductive lines, fundamentally enhancing the device's electrical performance and structural stability. Furthermore, the layered encapsulation structure, particularly the encapsulation layer covering the circuit layer, together with the smoothing layer, constitutes a dual protection system against environmental humidity and mechanical stress. This design significantly enhances the long-term stability and durability of the device under complex operating environments (especially humidity variations), extending its service life.

[0026] The first aspect of this application provides a flexible paper-based electronic device, with reference to... Figure 1 , Figure 1 A schematic diagram of the structure of a flexible paper-based electronic device is shown, such as... Figure 1 As shown, the electronic device comprises the following components stacked sequentially: Paper substrate; A smoothing layer, which covers and is cured on one side surface of the paper substrate, and the surface of the smoothing layer opposite to the paper substrate is a flat surface; A circuit layer, the circuit layer including conductive lines and functional units connected by the conductive lines; An encapsulation layer covers the surface of the circuit layer opposite to the smooth layer, serving to isolate it from environmental moisture and mechanical damage.

[0027] Specifically, this application proposes an innovative multi-layer stacked electronic device packaging structure. The device, from bottom to top, consists of: a paper substrate 1, serving as the mechanical support and flexible carrier of the entire system; the surface of the paper substrate may be rough and uneven; a smoothing layer 2, which is tightly attached to the paper substrate and forms a flat intermediate layer through curing; its core function is to physically fill the rough surface and pores of the paper, providing a high-quality adhesion interface for the upper circuitry; a circuit layer 3, formed on the smoothing layer through a printing process, containing conductive lines for electrical connections and functional units for specific functions (such as sensing, driving, etc.); and an outermost encapsulation layer 4, which completely covers the circuit layer; its main function is to isolate external moisture intrusion and mechanical damage, protecting the internal circuitry.

[0028] The paper substrate serves as the mechanical support for the entire system, providing a physical foundation for the attachment of the functional layers above (smoothing layers, circuit layers, encapsulation layers, etc.), and imparting good flexibility and resilience to the entire device, maintaining its basic shape and dimensional stability (under controlled humidity). The material used for the paper substrate can be low-cost, biodegradable paper. Specifically, the paper substrate is typically made from natural cellulose fibers (such as wood pulp, cotton pulp) or regenerated cellulose, such as filter paper, printing paper, and cellulose membranes. Its core characteristics include inherent flexibility, lightweight, low cost, wide availability, and the environmental advantage of being biodegradable, making it an ideal substrate for constructing green electronic devices. In some embodiments, the material used for the paper substrate may be filter paper, cellulose paper, etc.

[0029] However, the surface of untreated raw paper substrates is rough, porous, and highly hydrophilic, which directly leads to poor performance and instability of circuits printed on them. Therefore, this embodiment does not directly construct circuits on the raw paper surface, but rather modifies the substrate surface by preparing a smoothing layer through interface engineering to overcome its inherent defects. In other words, the paper substrate in this embodiment is a modified object treated with interface engineering, which, together with the smoothing layer, constitutes a composite substrate system suitable for the fabrication of high-performance electronic devices.

[0030] The smoothing layer primarily fills the pores and depressions between paper fibers, forming a significantly smoother and flatter surface compared to the original paper surface, greatly reducing surface roughness. Furthermore, it provides a continuous and uniform physical interface for the printing and adhesion of the upper conductive ink layer, reducing ink loss due to penetration into the fiber pores, thereby improving the continuity, conductivity, and adhesion of the conductive circuitry. In addition, the smoothing layer has a certain encapsulation effect, isolating water and oxygen. The dense film structure can, to a certain extent, prevent environmental moisture from directly penetrating to the paper substrate, reducing the impact of paper swelling and deformation due to moisture absorption on the upper circuitry, and improving the environmental stability of the device.

[0031] In some embodiments, the material used for the smoothing layer is at least one of the following: gelatin, chitosan, polylactic acid (PLA), polybutylene succinate (PBS), or polycaprolactone (PCL).

[0032] The smoothing layer is mainly composed of liquid or solution-based film-forming materials applied to the surface of a paper substrate through coating processes (such as spin coating, blade coating, and dip coating), followed by curing (such as drying and thermal crosslinking) to form a solid film. The materials selected for the smoothing layer must have good adhesion to the paper substrate and be able to form a dense, smooth surface. Typical materials include: natural biodegradable polymers, such as gelatin and chitosan, which have good biocompatibility; and synthetic biodegradable polyesters, such as polylactic acid (PLA), polybutylene succinate (PBS), and polycaprolactone (PCL), which combine biodegradability and film-forming properties.

[0033] The circuit layer is directly constructed on the flat surface provided by the smoothing layer. It is a planar functional thin film layer used to fill fiber pores, provide a smooth surface, and initially block moisture. The core of the circuit layer is fabricated using printed electronics techniques, such as inkjet printing and screen printing. These processes are characterized by flexible patterning, high material utilization, and low processing temperatures (compatible with paper substrates), enabling low-cost, large-scale manufacturing.

[0034] The circuit layer mainly consists of two parts: conductive lines (wires and electrodes), which are the interconnecting networks that form the circuit and are used to transmit electrical signals and energy. The conductive lines are conductive traces composed of conductive inks (such as high aspect ratio silver nanowires and carbon nanotubes). The conductive materials mainly use functional conductive inks suitable for printing, such as silver nanowire inks and carbon nanotube inks, which combine high conductivity with flexibility. Since the smoothing layer is in contact with the circuit layer, a smoothing layer material stable to the conductive ink solvent needs to be selected during its preparation. For example, for water-based silver nanowire inks, cross-linked chitosan or polyester layers are used, as they have better solvent resistance. The functional units are electrically connected to the conductive lines to achieve specific functions. Functional units can be divided into active units (such as microchips, RFID chips, and microcontrollers (MCUs)) and passive units (such as printed resistive temperature sensors, humidity sensors, microheaters, and light-emitting diodes). The materials used for the functional units depend on the specific functional unit; for example, they may be temperature-sensitive materials, humidity-sensitive materials, semiconductor materials, or light-emitting materials.

[0035] In some embodiments, the conductive lines are formed by a printing process using conductive ink, wherein the conductive ink is one of the following: silver nanowire ink or carbon nanotube ink.

[0036] In some embodiments, the functional unit includes at least one of the following: Temperature sensing unit, humidity sensing unit, biochemical sensing unit, heating unit, light-emitting diode, microchip.

[0037] Functional units include: sensing units (such as temperature, humidity, and biochemical sensors) and actuation units (such as miniature heating units, light-emitting diodes (LEDs), and miniature power supplies (such as printed batteries)). Biochemical sensors specifically refer to miniaturized electronic devices that utilize functional sensitive materials to convert the concentration, presence, or reaction of a target biological or chemical substance into an electrical signal that can be detected and processed by the circuit layer. For example, a biochemical sensor can be a disposable electrochemical biosensor for detecting disease biomarkers (such as uric acid, cholesterol, and specific antigens).

[0038] In some embodiments, the microchip includes at least one of the following: a radio frequency identification (RFID) chip, a microcontroller (MCU), a memory chip, and a sensor signal conditioning chip.

[0039] Radio Frequency Identification (RFID) chips endow paper-based devices with passive wireless communication and identification capabilities. They can extract energy from the reader's RF signal and transmit data (such as sensor readings or unique IDs), enabling item tracking, smart packaging, and disposable wireless sensor tags (such as temperature sensor tags). Microcontrollers (MCUs) provide basic logic control, data acquisition, processing, and simple algorithm execution functions, allowing the device to operate according to preset programs and achieve intelligent responses. Memory chips are used for temporary or long-term data storage, such as sensor history records, calibration parameters, or identification information, enabling data recording and retrieval. Sensor signal conditioning chips are specifically designed to process the raw, weak signals from sensors (especially analog sensors, such as biochemical sensors), performing amplification, filtering, analog-to-digital conversion (ADC), etc., converting the signals into a format that the MCU or RFID chip can reliably identify and process, improving measurement accuracy and reliability. For example, an RF antenna, a resistive temperature sensor, and an integrated miniature RFID chip can all be integrated on the same paper substrate within the same circuit layer.

[0040] The encapsulation layer is the outermost protective structure covering the circuit layer, and it is a key barrier to ensure the long-term stable operation of flexible paper-based electronic devices in complex environments. The encapsulation layer is a continuous, dense film formed from protective materials through processes such as coating, printing, or lamination. As the primary barrier layer against moisture and oxygen, the encapsulation layer effectively prevents environmental moisture from corroding the internal circuit layers and paper substrate, avoiding circuit performance drift, short circuits, or device failure due to moisture absorption and deformation of the paper substrate. Furthermore, it provides physical isolation for the delicate circuit layers below, preventing mechanical damage such as scratches, wear, and impacts, thus improving the device's durability. It also isolates external contaminants, acids, alkalis, or salts, protecting the sensitive surfaces of functional units (especially sensors). By tightly integrating the internal layers into a whole, it enhances the structural stability of the device and maintains its flexibility to a certain extent. In some embodiments, to achieve optimal technical results, the encapsulation layer completely covers the circuit layer and also covers the underlying smooth layer and paper substrate.

[0041] To maintain environmentally friendly characteristics with paper-based devices, the preferred materials for the encapsulation layer include: natural biodegradable materials, such as beeswax, which have good hydrophobicity and flexibility; synthetic biodegradable polymers, such as polylactic acid (PLA) and polybutylene succinate (PBS), which have excellent film-forming properties, mechanical strength and controllable degradation performance; and other compatible materials, such as ultrathin oxides (such as insulating, dense inorganic oxide films that can be prepared at low temperatures, such as alumina and silicon oxide), which can form a high-barrier layer through low-temperature deposition, or pure oxide ceramic films that can be grown directly on the device surface through advanced processes such as atomic layer deposition (ALD).

[0042] In some embodiments, the material used for the encapsulation layer is at least one of the following: Beeswax, polylactic acid (PLA), polybutylene succinate (PBS).

[0043] This application embodiment effectively overcomes the adverse effects of the rough and porous surface of paper by introducing a specially designed smoothing layer between the paper substrate and the circuit layer. This smoothing layer not only fills the fiber pores, providing a flat and continuous adhesion interface for subsequent circuit printing, but also significantly improves the forming quality, conductivity, and mechanical reliability of the conductive lines, fundamentally enhancing the electrical performance and structural stability of the device. Furthermore, this application embodiment employs a layered encapsulation structure, particularly the encapsulation layer covering the circuit layer, which, together with the smoothing layer, constitutes a dual protection system against environmental humidity and mechanical stress. This design significantly enhances the long-term stability and durability of the device under complex operating environments (especially humidity variations), extending its service life. In summary, this solution effectively solves the core problem of insufficient performance and stability when paper substrates are used as electronic device substrates, while maintaining the advantages of low cost, flexibility, and environmental friendliness, providing a practical path for achieving high-performance, high-reliability, green, and flexible electronic devices. The synergistic effect of each layer systematically improves the electrical performance, environmental stability, and reliability of electronic devices while retaining the environmental and flexibility advantages of paper substrates.

[0044] The paper-based electronic device proposed in this application can be widely used in various technical fields, such as smart logistics and packaging, where it can serve as an intelligent tracking and status monitoring tag. Specifically, in high-value logistics such as fresh food or pharmaceuticals, the paper-based electronic device can be integrated into the inside of the packaging box. The functional units in the electronic device mainly include: a temperature / humidity sensor (for real-time monitoring of the cold chain environment), a micro RFID chip and printed antenna (for passive wireless identification, positioning, and data transmission), and an optional pressure sensor. It can record and wirelessly report the location of the goods and whether the ambient temperature and humidity exceed the standards throughout the entire process. In case of abnormalities, it can issue an immediate warning, greatly ensuring the safety and quality of the logistics goods. Moreover, the tag itself can be recycled and degraded along with the packaging.

[0045] The second aspect of this application also provides a method for preparing a flexible paper-based electronic device. This method is used to prepare the flexible paper-based electronic device described in the first aspect of this application. (Refer to...) Figure 2 , Figure 2 A flowchart illustrating the steps of a method for fabricating a flexible paper-based electronic device is shown, as follows: Figure 2 As shown, the method includes: Step S101: Prepare a paper base; Step S102: A smooth layer is prepared on one side surface of the paper substrate. The smooth layer covers and is cured on one side surface of the paper substrate, and the surface of the smooth layer opposite to the paper substrate is a flat surface. Step S103: A circuit layer is prepared on one side surface of the smooth layer, the circuit layer including conductive lines and functional units connected by the conductive lines. Step S104: An encapsulation layer is prepared on the surface of the circuit layer opposite to the smooth layer. The encapsulation layer is used to isolate environmental moisture and mechanical damage.

[0046] In some embodiments, step S102, preparing a smooth layer on one side surface of the paper substrate, includes: The smoothing layer material is coated onto one side surface of the paper substrate by dip coating, spin coating, spray coating, or scraping coating, and then cured.

[0047] Specifically, the coating process allows the liquid smoothing layer material to fully saturate the paper surface, penetrating and filling the microscopic pores and depressions between the fibers. Subsequently, through a curing process (such as solvent evaporation, thermal crosslinking, or UV curing), the liquid transforms into a solid film, forming a continuous film layer that adheres tightly to the paper substrate surface. The solid smoothing layer formed after curing has a smooth and flat upper surface (the side facing away from the paper substrate), thus transforming the originally rough paper substrate, which was unsuitable for direct printing, into a film-like substrate with a high-quality surface.

[0048] To uniformly and continuously apply liquid or solution-based smoothing layer materials to the surface of a paper substrate, different coating methods can be selected. Dip coating / spin coating: Simple process, suitable for large-area, continuous (e.g., roll-to-roll) production, and easy to control film thickness. Spin coating: Can obtain films with extremely high uniformity and smoothness, suitable for small-size, high-precision sample preparation. Spray coating: Non-contact operation, suitable for irregular surfaces or localized coating, with high material utilization. The coating method can be flexibly selected according to production scale, material viscosity, paper size, and required film thickness; in this embodiment, it is not limited.

[0049] In some embodiments, step S103, which involves fabricating a circuit layer on one side surface of the smooth layer, includes: A circuit pattern containing conductive lines and functional units is printed on one side surface of the smooth layer using inkjet printing or screen printing. The circuit pattern is cured at low temperature.

[0050] Specifically, printing is performed on the flat, dense surface provided by the smooth layer. This ensures that the conductive ink adheres precisely to the predetermined positions, forming clear, continuous lines and effectively preventing ink penetration and diffusion into the rough paper substrate, a prerequisite for obtaining high-performance circuits. The printed wet or semi-solid circuit pattern undergoes a curing process to remove solvents or initiate cross-linking, creating tight electrical contacts between conductive material particles, thereby achieving stable conductivity and mechanical adhesion. During this process, printing process parameters that match the paper characteristics must be selected. Specifically, low-temperature treatment (usually below the temperature below the paper's thermal decomposition or significant deformation) ensures that the substrate and functional layers do not suffer thermal damage, deformation, or performance degradation during processing, maintaining the integrity and flexibility of the device.

[0051] In some embodiments, the temperature of the low-temperature curing is greater than or equal to 60°C and less than or equal to 100°C.

[0052] In this embodiment, the curing temperature is ≥60℃. Temperatures above this level are sufficient to allow the solvent in the conductive ink (such as silver nanowire ink containing polymer binders) to fully evaporate, or to trigger necessary physicochemical changes within the functional material (such as particle sintering, polymer chain relaxation and compact stacking), thereby forming a circuit pattern with stable conductivity and sufficient adhesion. Temperatures that are too low may result in incomplete curing, unstable circuit performance (such as resistance), or easy detachment. A curing temperature ≤100℃ can protect the paper substrate. The main component of paper (cellulose) undergoes thermal degradation, yellowing, embrittlement, and even charring under long-term or high-temperature conditions (usually significantly above 100℃). Strictly controlling the temperature at or below 100℃ can minimize irreversible thermal damage to the paper fibers, maintaining its mechanical strength and flexibility.

[0053] Furthermore, most smoothing layer materials (such as gelatin, chitosan, PLA, and other biodegradable polymers) have low glass transition temperatures or heat distortion temperatures. Excessively high curing temperatures (such as well as well above 100°C) may cause these polymer films to soften, flow, recrystallize, or thermally decompose, thereby destroying their already formed smooth and dense structure, losing their smoothing and barrier functions on the paper substrate, and may even lead to delamination or cracking due to a mismatch in the coefficient of thermal expansion with the circuit layer.

[0054] This application embodiment effectively overcomes the adverse effects of the rough and porous surface of paper by introducing a specially designed smoothing layer between the paper substrate and the circuit layer. This smoothing layer not only fills the fiber pores, providing a flat and continuous adhesion interface for subsequent circuit printing, but also significantly improves the forming quality, conductivity, and mechanical reliability of the conductive lines, fundamentally enhancing the electrical performance and structural stability of the device. Furthermore, this application embodiment employs a layered encapsulation structure, particularly the encapsulation layer covering the circuit layer, which, together with the smoothing layer, constitutes a dual protection system against environmental humidity and mechanical stress. This design significantly enhances the long-term stability and durability of the device under complex operating environments (especially humidity variations), extending its service life. In summary, this solution effectively solves the core problem of insufficient performance and stability when paper substrates are used as electronic device substrates, while maintaining the advantages of low cost, flexibility, and environmental friendliness, providing a practical and feasible path for the development of high-performance, high-reliability, green, flexible electronic devices.

[0055] The preparation method proposed in this application has the following beneficial effects: 1. Significantly improved performance and stability: Through interface engineering smoothing treatment, a high-quality adhesion surface is provided for the circuit, reducing line resistance and improving the mechanical and electrical stability of the device. 2. Truly green and environmentally friendly: Biodegradable materials can be selected from the paper substrate, smoothing layer to encapsulation layer, greatly reducing electronic waste and meeting the requirements of sustainable development. 3. Extremely low cost, suitable for large-scale application: Raw materials are abundant and inexpensive, and the manufacturing process is based on printing technology, suitable for roll-to-roll production, laying the foundation for the large-scale deployment of disposable electronic devices. 4. High functional integration and flexible application: This solution provides a platform for system-level integration, allowing for flexible design and integration of sensing, power supply, communication and other functions onto a single paper substrate, meeting the needs of complex scenarios such as smart packaging and medical monitoring.

[0056] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0057] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0058] The above provides a detailed description of the probe card, circuit detection method, and preparation method provided in this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

[0059] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of this application are indicated by the following claims.

[0060] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this application is limited only by the appended claims.

[0061] The terms "an embodiment," "embodiment," or "one or more embodiments" as used herein mean that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of this application. Furthermore, please note that the examples of the phrase "in one embodiment" do not necessarily all refer to the same embodiment.

[0062] Numerous specific details are set forth in the specification provided herein. However, it will be understood that embodiments of this application may be practiced without these specific details. In some instances, well-known methods, structures, and techniques have not been shown in detail so as not to obscure the understanding of this specification.

[0063] In the claims, any reference signs placed between parentheses should not be construed as limiting the claims. The word "comprising" does not exclude the presence of elements or steps not listed in the claims. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. This application can be implemented by means of hardware comprising several different elements and by means of a suitably programmed computer. In a unit claim enumerating several means, several of these means may be embodied by the same item of hardware. The use of the words first, second, and third, etc., does not indicate any order. These words can be interpreted as names.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A flexible paper-based electronic device, characterized in that, The electronic device comprises: stacked sequentially: Paper substrate; A smoothing layer, which covers and is cured on one side surface of the paper substrate, and the surface of the smoothing layer opposite to the paper substrate is a flat surface; A circuit layer, the circuit layer including conductive lines and functional units connected by the conductive lines; An encapsulation layer covers the surface of the circuit layer opposite to the smooth layer, serving to isolate it from environmental moisture and mechanical damage.

2. The electronic device according to claim 1, characterized in that, The material used in the smoothing layer is at least one of the following: gelatin, chitosan, polylactic acid (PLA), polybutylene succinate (PBS), or polycaprolactone (PCL).

3. The electronic device according to claim 1, characterized in that, The conductive circuit is formed by a printing process using conductive ink, which is one of the following: silver nanowire ink or carbon nanotube ink.

4. The electronic device according to claim 1, characterized in that, The functional unit includes at least one of the following: Temperature sensing unit, humidity sensing unit, biochemical sensing unit, heating unit, light-emitting diode, microchip.

5. The electronic device according to claim 4, characterized in that, The microchip includes at least one of the following: radio frequency identification (RFID) chip, microcontroller (MCU), memory chip, and sensor signal conditioning chip.

6. The electronic device according to claim 1, characterized in that, The material used for the encapsulation layer is at least one of the following: Beeswax, polylactic acid (PLA), polybutylene succinate (PBS).

7. A method for fabricating a flexible paper-based electronic device, characterized in that, The preparation method is used to prepare the flexible paper-based electronic device according to any one of claims 1-6, and the method includes: Prepare a paper base; A smooth layer is prepared on one side surface of the paper substrate, the smooth layer covers and is cured on one side surface of the paper substrate, and the surface of the smooth layer opposite to the paper substrate is a flat surface; A circuit layer is formed on one side surface of the smooth layer, the circuit layer including conductive lines and functional units connected by the conductive lines; An encapsulation layer is prepared on the surface of the circuit layer opposite to the smooth layer, the encapsulation layer being used to isolate environmental moisture and mechanical damage.

8. The preparation method according to claim 7, characterized in that, The process of fabricating a circuit layer on one side surface of the smooth layer includes: A circuit pattern containing conductive lines and functional units is printed on one side surface of the smooth layer using inkjet printing or screen printing. The circuit pattern is cured at low temperature.

9. The preparation method according to claim 7, characterized in that, The low-temperature curing temperature is greater than or equal to 60°C and less than or equal to 100°C.

10. The preparation method according to claim 7, characterized in that, The preparation of a smooth layer on one side surface of the paper substrate includes: The smoothing layer material is coated onto one side surface of the paper substrate by dip coating, spin coating, spray coating, or scraping coating, and then cured.

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