Method for preparing patterned molybdenum dioxide film through laser induction and flexible electronic device

Abstract

The invention relates to a method for preparing a patterned molybdenum dioxide thin film through laser induction and a flexible electronic device, and belongs to the technical field of functional material preparation and processing, precursor ink containing molybdenum trioxide nanoparticles, polyvinylpyrrolidone and isopropanol is prepared, a substrate is coated with the precursor ink to form a precursor thin film, and the patterned molybdenum dioxide thin film is prepared. And after drying and curing, carrying out laser direct writing reduction sintering on the precursor film, and reducing and sintering into molybdenum dioxide by utilizing a photothermal effect generated by surface plasmon resonance. The invention aims to overcome the dependence of a traditional process on a high-temperature vacuum environment, and provides a method for efficiently preparing a molybdenum dioxide film with high conductivity and biocompatibility in an environment atmosphere in a patterning manner, and a multifunctional flexible electronic device is constructed based on the film.

Description

Technical Field

[0001] This invention belongs to the field of functional material preparation and processing technology, specifically relating to a method for laser-induced preparation of patterned molybdenum dioxide thin films and flexible electronic devices. Technical Background

[0002] Molybdenum dioxide (MoO2), as a transition metal oxide, is known for its high theoretical conductivity (approximately 10⁻⁶). 5 With its high S / m ratio, good biocompatibility, and high photothermal / electrothermal conversion efficiency, it shows significant application potential in the fields of flexible electronics and biomedicine, and is suitable for devices such as high-sensitivity physiological electrical signal acquisition electrodes, temperature sensors, and thermotherapy patches.

[0003] However, the widespread application of molybdenum dioxide (MoO) is limited by its efficient, convenient, and patterned preparation technology. Currently, the synthesis of MoO mainly relies on traditional methods such as hydrogen reduction, chemical vapor deposition (CVD), physical vapor deposition (PVD), and hydrothermal methods. Among these, CVD and PVD processes typically require high temperature, vacuum, or inert atmosphere environments, resulting in complex processes, high energy consumption, and high costs. Hydrothermal methods and electrochemical deposition can synthesize MoO at lower temperatures. For example, patent application number 202011182474.4 discloses a method for preparing nano-MoO using a hydrothermal method, but the products obtained by this method are mostly in powder form (such as nanoparticles / rods / spheres / sheets), with long reaction cycles and difficulty in achieving patterned processing of materials and direct integration into devices, thus limiting its application in wearable electronic devices that require rapid prototyping and customized patterns.

[0004] Laser direct writing technology, as a digital processing method, can utilize instantaneous high temperatures to replace traditional high-temperature reaction environments, offering advantages such as scalability and multi-material compatibility. Currently, there are reports on laser reduction of graphene oxide, laser sintering of metal nanoparticles (such as Au and Ag), and metal oxides (such as CuO and NiO) (e.g., application number 202510334446.6 discloses a method and system for preparing flexible circuits using ultrafast laser sintering of metal nanoparticles, and application number 202010653137.2 discloses a method for preparing flexible copper circuits using laser-induced reduction sintering of copper oxide ink). However, the above material systems still have the following problems: precious metal materials are expensive; copper, nickel, and other metals may pose biocompatibility risks in long-term skin contact applications; and laser-induced conductive polymers (such as PEDOT:PSS) have conductivity 2-3 orders of magnitude lower than metals (e.g., application number 202011512381.3 discloses a method for reducing the resistance of PEDOT:PSS based on femtosecond laser modification).

[0005] Therefore, there is still a lack of existing technologies that can rapidly and accurately pattern precursors into molybdenum dioxide thin films with both high electrical conductivity and good biocompatibility under mild conditions (such as room temperature and air environment). Developing such a process is of great significance for promoting the practical application of molybdenum dioxide in flexible wearable electronic devices. Summary of the Invention

[0006] The purpose of this invention is to provide a method for laser-induced preparation of patterned molybdenum dioxide thin films and flexible electronic devices. The aim is to achieve rapid patterning, reduction, and sintering of molybdenum trioxide precursors in an ambient atmosphere using laser direct writing technology, thereby preparing molybdenum dioxide thin films with both high conductivity and good biocompatibility. Based on this, flexible wearable electronic devices integrating monitoring (such as electromyography, electrocardiography, and temperature sensing) and therapeutic (such as photothermal and electrothermal therapy) functions can be developed to solve the problems of complex processes, high costs, difficulty in patterning, and insufficient biocompatibility in traditional molybdenum dioxide preparation methods.

[0007] On the one hand, the present invention provides a method for laser-induced preparation of patterned molybdenum dioxide thin films, employing the following technical solution: A method for laser-induced fabrication of patterned molybdenum dioxide thin films includes the following steps: 1) Take molybdenum trioxide nanoparticles, polyvinylpyrrolidone and isopropanol, mix them, and disperse them to form a uniform precursor ink; 2) Take a substrate and pre-treat it. Coat the substrate surface with the precursor ink obtained in step 1), dry and cure it to form a precursor film. 3) Under ambient conditions, a laser beam is used to scan and irradiate the precursor film prepared in step 2) according to a preset pattern, thereby reducing and sintering the molybdenum trioxide in the precursor film into molybdenum dioxide in situ, thus obtaining a patterned molybdenum dioxide film.

[0008] Preferably, in step 1), the precursor ink contains 33-63% molybdenum trioxide, 5.6-10.1% polyvinylpyrrolidone, and 31.4-56.9% isopropanol by mass. The molybdenum trioxide nanoparticles have a particle size of 5-50 nm.

[0009] Preferably, in step 2), the pretreatment of the substrate includes at least one of ultrasonic alcohol cleaning, ultrasonic water cleaning, drying, and corona discharge treatment.

[0010] Preferably, in step 3), the wavelength of the laser is 532 nm, and the energy density of the laser scan is 216-343 J / cm². 2 .

[0011] On the one hand, the present invention also provides a method for fabricating a flexible electronic device, which adopts the following technical solution: A method for fabricating a flexible electronic device includes the following steps: 1) A patterned molybdenum dioxide thin film is prepared on a substrate by any of the preparation methods described above; 2) Remove the precursor film from the areas of the substrate that were not irradiated by the laser; 3) Coat a conductive connection layer in a designated area of ​​the molybdenum dioxide thin film and connect it to the lead-out electrode; 4) A protective layer is coated onto the molybdenum dioxide thin film and conductive connection layer for encapsulation.

[0012] Preferably, the substrate comprises a flexible polymer film or a circuit board containing a flexible polymer film; The flexible polymer film is polyimide or polyethylene terephthalate.

[0013] Preferably, in step 3), the connecting layer includes, but is not limited to, silver paste.

[0014] Preferably, in step 3), the lead-out electrodes include, but are not limited to, FPC cables.

[0015] Preferably, in step 4), the material of the protective layer is polydimethylsiloxane or polybutylene terephthalate.

[0016] Furthermore, the present invention also provides a flexible electronic device, which adopts the following technical solution: A flexible electronic device includes a flexible electronic device prepared by the above method, specifically including any one of a signal acquisition electrode, a temperature sensor, an electrothermal therapy patch, and a photothermal therapy patch.

[0017] In summary, the present invention has the following beneficial technical effects: 1. This invention does not rely on high temperature, vacuum or inert atmosphere, and the entire preparation is completed in a room temperature atmospheric environment, which greatly simplifies the process, reduces equipment investment and operating energy consumption, and shortens the preparation cycle, thus meeting the needs of rapid prototyping manufacturing.

[0018] 2. The molybdenum dioxide thin film prepared by this invention has an electrical conductivity of 8.55 × 10⁻⁶. 4 With a S / m ratio, and after undergoing cytotoxicity and acute skin irritation tests, the molybdenum dioxide thin film material is friendly to human cells and skin, meeting the core safety requirements for materials in wearable devices and biomedical applications.

[0019] 3. This invention achieves in-situ patterning of precursor films through laser direct writing, allowing for the customization of complex patterns to meet specific needs and offering high design freedom. It is also compatible with flexible substrates such as polyimide (PI) and flexible printed circuit boards (FPC), resulting in strong adhesion between the finished film and the substrate, and the film can withstand bending and deformation in wearable applications. Flexible electronic devices, after flexible packaging, exhibit excellent bending fatigue resistance, can closely conform to human skin, and are suitable for long-term wear applications such as health monitoring and localized heat therapy, combining portability and practicality. Attached Figure Description

[0020] Figure 1 This is a flowchart illustrating the laser-induced fabrication process for patterned molybdenum dioxide thin films according to Example 1 of the present invention. Figure 2 This is a schematic diagram showing the processing result of laser-patterned molybdenum dioxide thin film in Embodiment 1 of the present invention; Figure 3 This is a schematic flowchart of a method for fabricating a flexible electronic device according to Embodiment 8 of the present invention; Figure 4 Here are schematic diagrams and physical images of the flexible electronic device prepared by the method in Example 8 of this invention; Figure 5 Image I is a SEM micrograph of the precursor ink in Example 1 of this invention; Figure 5 Image II is a SEM image of the patterned molybdenum dioxide film prepared in Comparative Example 1. Figure 5 Image III is a SEM image of the patterned molybdenum dioxide thin film prepared in Example 1 of this invention; Figure 5 Image IV is a SEM image of the patterned molybdenum dioxide film prepared in Comparative Example 2. Figure 6 This is a Raman characterization image of the patterned molybdenum dioxide thin film in Embodiment 1 of the present invention; Figure 7 These are XRD characterization images of the precursor ink in Example 1 of the present invention and the molybdenum dioxide films in Comparative Examples 1 and 5. Figure 8 XPS characterization images of the precursor ink, molybdenum dioxide film, and molybdenum dioxide films in Comparative Examples 1 and 5 of the present invention are shown. Figure 9 This is a comparison chart of the conductivity of molybdenum dioxide thin films prepared by Example 1 of the present invention and existing methods such as CVD, PVD, hydrothermal method, electrochemical deposition, and spray pyrolysis deposition. Figure 10 This is a comparison chart of the sheet resistance changes of the molybdenum dioxide thin films prepared in Examples 1, 5-7, and Comparative Examples 3-4 of the present invention; Figure 11 This is a comparison graph showing the sheet resistance changes of the molybdenum dioxide thin films prepared in Examples 1-4 and Comparative Examples 6-7 of the present invention; Figure 12 Image a shows fluorescence images of L929 cells stained after 1, 3, and 5 days of culture with the material extract; Figure 12 In the middle b, the relative cell viability of L929 cells after culturing with its extract for 5 days compared to the control group; Figure 13 Images of molybdenum dioxide film and Ag / AgCl electrode adhered to skin for 2, 4, 6 and 24 hours, respectively; Figure 14 Electromyography waveforms recorded by the molybdenum dioxide surface electromyography signal acquisition electrode and the Ag / AgCl electrode; Figure 15 Continuous electrocardiogram (ECG) signals recorded by molybdenum dioxide ECG signal acquisition electrodes; Figure 16 In the figure, 'a' represents the resistance curve of the molybdenum dioxide thin film temperature sensor as a function of temperature. Figure 16 Figure b shows the cycling performance of the molybdenum dioxide thin film temperature sensor in the temperature range of 20-55℃. Figure 16 Figure c shows the response time diagram of the molybdenum dioxide thin film temperature sensor; Figure 17 In the image, 'a' represents an infrared thermal image of a molybdenum dioxide electrothermal therapy patch at a voltage of 1V-6V. Figure 17 Figure b shows the temperature change curve of the molybdenum dioxide electrothermal therapy patch as the voltage increases. Figure 17 In the middle, c represents the stability test of the molybdenum dioxide electrothermal therapy patch during the constant voltage process; Figure 18 Image a shows the thermal imaging of a molybdenum dioxide photothermal therapy patch applied to the wrist and elbow. Figure 18 In Figure b, the temperature of the molybdenum dioxide photothermal therapy patch varies with the near-infrared laser power density, and the corresponding thermal image is shown. Figure 18 Figure c shows the temperature cycle response curve of the molybdenum dioxide photothermal therapy patch. Detailed Implementation

[0021] The following examples, comparative examples, and appendices are used in conjunction with the embodiments. Figure 1-18 The present invention will be described in further detail below.

[0022] Example Example 1 Reference Figure 1 and Figure 2A method for laser-induced fabrication of patterned molybdenum dioxide thin films includes the following steps: S1. Weigh 0.49g of polyvinylpyrrolidone and place it in a reagent bottle. Use a pipette to measure 3.5ml of isopropanol and inject it into the reagent bottle. Stir the mixture on a magnetic stirrer at 1000rpm and 45℃ for 6h to obtain the functional solvent. Weigh 1.22g of molybdenum trioxide nanoparticles with a particle size of 5-50nm and add them to the functional solvent. Disperse the mixture in an ultrasonic cell disruptor for at least 2min. Then weigh another 1.22g of molybdenum trioxide nanoparticles with a particle size of 5-50nm and add them to the functional solvent. Disperse the mixture in an ultrasonic cell disruptor for at least 2min to obtain a uniform precursor ink. The mass fraction of molybdenum trioxide nanoparticles was 43.0%. The mass fraction of polyvinylpyrrolidone is 8.6%; The mass fraction of isopropanol is 48.4%; S2. Select a flexible printed circuit board based on polyimide as the substrate, place the flexible printed circuit board in alcohol and deionized water and sonicate for 2 minutes respectively, take it out and dry it in a vacuum drying oven at 60°C, and finally treat the surface with 24kV corona discharge for 4 minutes. S3. Place the substrate processed in step S2 into a spin coater, turn on the air pump to draw a vacuum, adsorb and fix the substrate, drop an appropriate amount of precursor ink prepared in step S1 onto the center of the substrate, spin coat at 1000 rpm for 15 seconds to ensure that the precursor ink is evenly coated on the substrate. The spin-coated substrate was placed on a heating table and dried at 45°C for 2 hours to form a precursor film. S4. Draw the pattern to be processed using CAD software, import it into the laser control software, and use an energy density of 255J / cm². 2 The 532nm continuous green light reduces and sintersulates the precursor film in step S3 into a molybdenum dioxide film.

[0023] Example 2 The method for laser-induced preparation of patterned molybdenum dioxide thin films differs from that in Example 1 in that the mass fraction of molybdenum trioxide nanoparticles is 53.0%; the mass fraction of polyvinylpyrrolidone is 7.1%; the mass fraction of isopropanol is 39.9%; and the remaining steps are the same as in Example 1.

[0024] Example 3 The method for laser-induced preparation of patterned molybdenum dioxide thin films differs from that in Example 1 in that, in step S1, the mass fraction of molybdenum trioxide nanoparticles is 33.0%; the mass fraction of polyvinylpyrrolidone is 10.1%; and the mass fraction of isopropanol is 56.9%; the remaining steps are the same as in Example 1.

[0025] Example 4 The method for laser-induced preparation of patterned molybdenum dioxide thin films differs from that in Example 2 in that, in step S1, the mass fraction of molybdenum trioxide nanoparticles is 63.0%; the mass fraction of polyvinylpyrrolidone is 5.6%; and the mass fraction of isopropanol is 31.4%; the remaining steps are the same as in Example 2.

[0026] Example 5 The method for laser-induced fabrication of patterned molybdenum dioxide thin films differs from Example 1 in that the energy of the continuous green light in step S4 is 294 J / cm². 2 The remaining steps are the same as in Example 1.

[0027] Example 6 The laser-induced fabrication method for patterned molybdenum dioxide thin films differs from Example 1 in that the energy of the continuous green light in step S4 is 216 J / cm². 2 The remaining steps are the same as in Example 1.

[0028] Example 7 The laser-induced fabrication method for patterned molybdenum dioxide thin films differs from Example 1 in that the energy of the continuous green light in step S4 is 343 J / cm². 2 The remaining steps are the same as in Example 1.

[0029] Example 8 Reference Figure 3 and Figure 4 A method for fabricating a flexible electronic device includes the following steps: S1. Take the molybdenum dioxide film prepared in Example 1 and remove the molybdenum dioxide film in the area of ​​the substrate that was not irradiated by the laser. S2. Apply conductive silver paste by hand between the molybdenum dioxide film and the FPC cable as a conductive connection layer, and dry at 65°C for 1.5 hours to cure the conductive connection layer, forming a conductive path and connecting it to the lead-out electrode. S3. Fix the product obtained in step S2 onto the processing platform; set the ultraviolet nanosecond laser pulse width to 10ns, the pulse frequency to 30kHz, and the cutting speed to 16mm / s to remove the excess part of the substrate. S4. Based on the application of the flexible electronic device, determine the parts of the flexible electronic device that need to be exposed and cover them with transparent tape. Using Dow Corning Sylgard 184 as the protective layer material, the basic components and curing agent were mixed at a weight ratio of 10:1 and placed in a vacuum degassing machine at 1500 rpm for 2 minutes to degas. The flexible electronic device was then adsorbed onto a spin coater, and the air pump was turned on to create a vacuum, thus adsorbing and fixing the flexible electronic device. An appropriate amount of the degassed and mixed Sylgard 184 was dripped onto the bonding layer and spin-coated at 1500 rpm for 15 seconds. The flexible electronic device was then heated and cured at 60°C for 2 hours on a heating stage to obtain the flexible electronic device.

[0030] Comparative Example Comparative Example 1 The method for laser-induced fabrication of patterned molybdenum dioxide thin films differs from Example 1 in that the energy of the continuous green light in step S4 is 78 J / cm². 2 The remaining steps are the same as in Example 1.

[0031] Comparative Example 2 The method for laser-induced fabrication of patterned molybdenum dioxide thin films differs from Example 1 in that the energy of the continuous green light in step S4 is 392 J / cm². 2 The remaining steps are the same as in Example 1.

[0032] Comparative Example 3 The method for laser-induced fabrication of patterned molybdenum dioxide thin films differs from Example 1 in that the energy of the continuous green light in step S4 is 147 J / cm². 2 The remaining steps are the same as in Example 1.

[0033] Comparative Example 4 The method for laser-induced fabrication of patterned molybdenum dioxide thin films differs from Example 1 in that the energy of the continuous green light in step S4 is 180 J / cm². 2 The remaining steps are the same as in Example 1.

[0034] Comparative Example 5 The method for laser-induced fabrication of patterned molybdenum dioxide thin films differs from Example 1 in that the energy of the continuous green light in step S4 is 10⁸ J / cm². 2 The remaining steps are the same as in Example 1.

[0035] Comparative Example 6 The method for laser-induced preparation of patterned molybdenum dioxide thin films differs from that in Example 1 in that, in step S1, the mass fraction of molybdenum trioxide nanoparticles is 13.0%; the mass fraction of polyvinylpyrrolidone is 13.0%; and the mass fraction of isopropanol is 74%. The remaining steps are the same as in Example 1.

[0036] Comparative Example 7 The method for laser-induced preparation of patterned molybdenum dioxide thin films differs from that in Example 1 in that, in step S1, the mass fraction of molybdenum trioxide nanoparticles is 23.0%; the mass fraction of polyvinylpyrrolidone is 11.7%; and the mass fraction of isopropanol is 65.3%. The remaining steps are the same as in Example 1.

[0037] Test case Test Example 1 Reference Figure 5 , Figure 5 Image I is a SEM micrograph of the precursor ink in Example 1 of this invention; Figure 5 Image II is a SEM image of the patterned molybdenum dioxide film prepared in Comparative Example 1. Figure 5 Image III is a SEM image of the patterned molybdenum dioxide thin film prepared in Example 1 of this invention; Figure 5 Figure IV shows a SEM image of the patterned molybdenum dioxide film prepared in Comparative Example 2. As can be seen from the figure, the precursor ink exhibits a loose, irregularly aggregated structure of molybdenum trioxide nanoparticles / platelets, with no obvious bonding between particles. This represents the original precursor state before laser treatment; at this stage, the material is insulating molybdenum trioxide and does not possess electrical conductivity. (78 J / cm) 2 The morphology after laser energy density treatment remains relatively loose, with some adhesion between particles but no continuous structure. Local pores and fragmented particles are present. This is because the laser energy density is too low; the photothermal effect is insufficient to completely reduce molybdenum trioxide to conductive molybdenum dioxide, and uniform sintering of the particles cannot be achieved. Therefore, the product has poor electrical conductivity. (255 J / cm²) 2 The morphology after laser energy density treatment exhibits a dense, continuous honeycomb-like thin film structure. The particles are fully sintered and connected into a complete conductive network. At this energy density, the surface plasmon resonance photothermal effect of the laser and the molybdenum trioxide nanoparticles achieves the effect of completely reducing molybdenum trioxide to molybdenum dioxide and uniformly sintering the film. The continuous microstructure provides a smooth path for electron transport; 392 J / cm 2 The morphology after laser energy density treatment is porous and fragmented, with obvious ablation holes in some areas. If the laser energy density is too high, the excessive photothermal effect will cause local overheating of the material, and the particles will evaporate / break down after melting, which will destroy the continuity of the conductive network. Therefore, the conductivity of the product will decrease as the structure is damaged.

[0038] Reference Figure 6 , Figure 6 This is a Raman characterization image of the patterned molybdenum dioxide thin film in Example 1 of the present invention. The Raman peaks appearing in this image perfectly match the characteristic Raman peak positions of molybdenum dioxide, indicating that at 255 J / cm²... 2 The nearby laser energy density (254.65 J / cm²) 2), molybdenum trioxide has been fully reduced to the target product molybdenum dioxide, and the product has a high phase purity.

[0039] Refer to Figure 7 , Figure 7 is the XRD characterization diagram of the precursor ink in Example 1 of the present invention and the molybdenum dioxide thin films in Comparative Example 1 and Comparative Example 5; when the laser energy density is around 78 J / cm in Comparative Example 1 2 (78.5 J / cm 2 ), the characteristic peak of molybdenum dioxide appears at 2θ≈26°, and at the same time, weak peaks appear at 50° and 61°. This phenomenon may be due to insufficient laser energy, only partially reducing molybdenum trioxide; when the laser energy density reaches about 108 J / cm 2 , the results show that the obtained molybdenum dioxide can be confirmed as monoclinic molybdenum dioxide, and characteristic peaks corresponding to weak elemental molybdenum appear near 41°, 59° and 74°.

[0040] The main reaction process can be summarized as the following equations: MoO3 + xHCOOH → MoO3 x + xCO2↑ + xH2O↑ MoO3 x +(1 x)HCOOH → MoO2 + (1 x)CO2↑ + (1 x)H2O↑ MoO2 + 2HCOOH → Mo + 2CO2↑ + 2H2O↑ (a small amount).

[0041] Formic acid is generated by the decomposition of polyvinylpyrrolidone under laser irradiation. Under the action of carboxyl groups, fully stoichiometric Mo with a wide bandgap (>2.7 eV) 6+ (MoO3) is reduced to MoO 3-x (2 < x < 3), resulting in an average oxidation state of Mo 5+ , and finally further reduced to Mo 4+ (MoO2) and metallic Mo.

[0042] Refer to Figure 8 , Figure 8 is the XPS characterization diagram of the precursor ink in Example 1 of the present invention, the molybdenum dioxide thin film, and the molybdenum dioxide thin films in Comparative Example 1 and Comparative Example 5; the heat generated by the low energy density is not enough to penetrate the entire layer of the thin film, and only the shallow layer of molybdenum trioxide can be reduced; while the high energy density re-oxidizes the shallow layer of molybdenum dioxide, but at the same time, the heat diffusion is enhanced, effectively reducing the molybdenum trioxide in the deep layer of the thin film.

[0043] Test Example 2 The process of preparing molybdenum dioxide thin film in Example 1 of the present invention is compared with the existing processes of preparing molybdenum dioxide thin film using CVD, PVD, hydrothermal method, electrochemical deposition, and spray pyrolysis deposition techniques. The comparison is shown in Table 1.

[0044] Table 1 Comparison of molybdenum dioxide film preparation processes

[0045] Table 1 compares the key process parameters of existing technologies with this example (i.e., the laser-induced reduction method of the present invention) as a reference, to verify the quantitative comparison basis of the technical advantages of the present invention, such as process simplification, efficiency improvement, and mild conditions. As shown in Table 1, firstly, this embodiment uses laser reduction, with the main materials being a system of molybdenum trioxide nanoparticles, polyvinylpyrrolidone, and isopropanol; while existing technologies (such as CVD, PVD, hydrothermal methods, etc.) either require a single molybdenum-based powder / nanofiber or a complex mixed solution of multiple components, making the material system far less simple than that of Example 1 of the present invention; secondly, the preparation time of Example 1 is only 10 minutes; while in existing technologies, CVD requires 30-40 minutes, electrochemical deposition exceeds 2 hours, and hydrothermal methods take up to 10 hours. Example 1 offers significant time cost advantages, meeting the needs of rapid prototyping. Furthermore, Example 1 of this invention only requires "room temperature / atmospheric environment / laser" to complete the preparation, without the need for additional high temperature, high pressure or special atmosphere. Existing technologies generally rely on harsh conditions, such as CVD requiring 800℃ / 80Torr, 550℃ / H2 atmosphere, PVD requiring 730-810℃ / Ar atmosphere, hydrothermal method requiring 180℃ / autoclave, and electrochemical deposition requiring an additional constant voltage power supply. These conditions will significantly increase equipment investment, energy consumption and process complexity.

[0046] Therefore, compared with the prior art, the present invention achieves synergistic optimization of simpler material system, shorter preparation time and milder reaction conditions (no need for high temperature / high pressure / special atmosphere), solves the pain points of high energy consumption, complex process and strict equipment requirements in the preparation of existing molybdenum-based materials, and provides a feasible solution for low-cost and high-efficiency preparation of molybdenum dioxide thin films.

[0047] Reference Figure 9 The conductivity of the molybdenum dioxide film prepared in Example 1 of this invention was compared with that of molybdenum dioxide films prepared by existing methods such as CVD, PVD, hydrothermal deposition, electrochemical deposition, and spray pyrolysis deposition. The conductivity of the molybdenum dioxide film prepared in Example 1 of this invention is higher than that of other methods, approximately 8.55 × 10⁻⁶. 4 S / m.

[0048] Test Example 3 Reference Figure 10 When the laser energy density is 147 J / cm²2 Increased to 255J / cm 2 At that time, the sheet resistance continuously decreased from 29.3Ω / Sq to 255J / cm. 2 The laser energy reaches a minimum of 0.9 Ω / Sq. Within this energy range, the laser energy gradually becomes sufficient with increasing density, enabling complete reduction of molybdenum trioxide to molybdenum dioxide. Simultaneously, it allows for the complete sintering of nanoparticles to form a continuous and dense conductive network, ensuring unobstructed electron transport paths and thus optimal conductivity. When the laser energy density exceeds 255 J / cm², the conductivity is optimal. 2 At that time, the sheet resistance slightly increased from 0.9Ω / Sq to 1Ω and then 5.4Ω. The excessively high laser energy density and excessive photothermal effect led to localized overheating of the material, causing particle melting and subsequent breakage / vaporization, disrupting the continuity of the conductive network, hindering electron transport, and thus slightly reducing conductivity. Furthermore, at 255J / cm²... 2 Up to 294 J / cm 2 The molybdenum dioxide thin film obtained at the laser energy density has superior electrical properties.

[0049] Reference Figure 11 When the molybdenum trioxide (Mo) trioxide mass percentage increased from 13% to 43%, the sheet resistance dropped sharply from 68.4 Ω / sq to 0.9 Ω / sq. When the Molybdenum trioxide percentage was too low, there were insufficient reducible Molybdenum trioxide nanoparticles in the precursor, making it difficult to form a continuous Molybdenum dioxide conductive network after laser reduction, thus hindering electron transport and resulting in higher resistance. A Molybdenum trioxide mass percentage of 43% ensured uniform dispersion of Molybdenum trioxide nanoparticles in the ink, allowing for the formation of a dense and continuous Molybdenum dioxide film after laser reduction, with unobstructed electron transport paths, thus achieving optimal conductivity. When the Molybdenum trioxide mass percentage continued to increase from 43% to 63%, the sheet resistance rebounded to 8.9 Ω / sq. An excessively high Molybdenum trioxide mass percentage led to decreased ink dispersibility, making it difficult to uniformly sinter localized particle accumulation areas during laser reduction, resulting in defects in the film structure and disrupting the continuity of the conductive network, hence the slight increase in resistance. As shown in the figure, the molybdenum dioxide thin film exhibits superior electrical properties when the mass fraction ratios of molybdenum trioxide nanoparticles, polyvinylpyrrolidone, and isopropanol are in the ranges of 43%-53%, 7.1%-8.6%, and 39.9%-48.4%, respectively.

[0050] Test Example 4 Reference Figure 12The cytotoxicity of molybdenum dioxide (MoD) films was evaluated. L929 cells were cultured using the film leachate. Cell viability and mortality staining was performed on days 1, 3, and 5 of the experiment in both the MoD film leachate experimental group and the PI film control group. Both groups showed dense green fluorescence (indicating a high number of viable cells) and no significant red fluorescence (indicating a very low number of dead cells). Furthermore, the differences between the experimental and control groups were minimal, indicating that the MoD film did not inhibit cell viability and had minimal impact on cytotoxicity, exhibiting the same low toxicity level as the PI substrate.

[0051] Reference Figure 13 From 2 hours to 24 hours, no irritation reactions such as redness, rashes, or itching were observed on the skin areas where the molybdenum dioxide film and Ag / AgCl electrodes were attached. The skin condition was not significantly different from the surrounding normal skin, indicating that the skin irritation of the molybdenum dioxide film and commercial Ag / AgCl electrodes are at the same low-risk level. Molybdenum dioxide films have the potential to replace traditional commercial electrodes in terms of skin compatibility. Combined with high conductivity and excellent biocompatibility, molybdenum dioxide films can be safely and stably applied in wearable health monitoring (such as electromyography / electrocardiogram acquisition) and local hyperthermia applications requiring long-term skin contact.

[0052] Test Example 5 Reference Figure 14 Comparison of electromyographic signals of the biceps brachii muscle during relaxation (I) and contraction (II) acquired by the molybdenum dioxide electrode and the commercial Ag / AgCl electrode clearly shows the changes in signal intensity during relaxation (I) and contraction (II). The signal acquired by the molybdenum dioxide electrode shows a higher signal-to-noise ratio (30.71 dB) compared with that of the commercial Ag / AgCl electrode (21.44 dB).

[0053] Reference Figure 15 The ECG signal acquired by the molybdenum dioxide electrode remained stable within a 70-second monitoring period, with no obvious signal interruption or distortion. The amplitude fluctuations were consistent with the physiological characteristics of human electrocardiogram signals. Furthermore, the core characteristic waves of the electrocardiogram signal (P wave, QRS complex, and T wave) could be clearly distinguished, indicating that the signal quality acquired by the molybdenum dioxide electrode was high.

[0054] Reference Figure 16During heating and cooling processes, the molybdenum dioxide temperature sensor exhibits a positive temperature coefficient (PTC) of 0.253% / K, and its resistance change rate changes stably and linearly with temperature. Under multiple temperature cycles from 20 to 55°C, it demonstrates good stability, consistency, and cyclic correlation within the temperature range, making it suitable for wearable devices that require "multiple start-stop and continuous monitoring." When the heater is activated, the sensor only needs about 0.15 seconds to complete the temperature response, proving its low-latency response characteristic for real-time temperature capture, which meets the practical needs of "dynamic real-time monitoring" of human skin temperature, local hyperthermia temperature, etc.

[0055] Reference Figure 17 As the voltage increased from 1V to 6V, the temperature of the molybdenum dioxide electrothermal therapy patch rose from room temperature to 60℃. Temperature and voltage showed a clear positive correlation, and the temperature distribution in the heating area was relatively uniform at all voltages, without localized overheating or uneven heating, demonstrating the uniformity of the heating area of ​​the molybdenum dioxide electrothermal therapy patch. The device exhibited a rapid response to voltage jumps from 0.5V to 6V, without significant lag or fluctuation, proving that the molybdenum dioxide electrothermal therapy patch can achieve continuous and precise temperature control through voltage, adapting to the temperature requirements of different thermotherapy scenarios. Under various constant voltages, the molybdenum dioxide electrothermal therapy patch could stably maintain the target temperature after heating and rapidly cool down after being turned off, with consistent curve shapes, proving that the heating performance of the molybdenum dioxide electrothermal therapy patch was stable at different voltage levels, possessing the characteristics of "multi-level adjustable and stable repeated use."

[0056] Reference Figure 18 In practical applications of molybdenum dioxide photothermal therapy patches on the wrist and elbow, thermal imaging showed significant heating in the corresponding areas after near-infrared laser irradiation. The temperature gradient in the thermal imaging was clear, proving that the molybdenum dioxide photothermal therapy patch can effectively achieve photothermal conversion locally on the human body, demonstrating its potential application prospects in accelerating microcirculation, relieving joint stiffness, and alleviating pain. The maximum equilibrium temperature of the device is linearly related to the near-infrared light irradiation power density. Thermal imaging corresponds to the heating state under different power densities. By adjusting the near-infrared laser power, the heating temperature of the molybdenum dioxide photothermal therapy patch can be precisely controlled to adapt to the diverse thermal sensitivity needs of the skin. The fixed power density is 0.21W. cm -2 After the laser is turned on, the temperature can quickly rise to 75.2℃ and quickly drop back to 29.0℃ after the laser is turned off. After multiple cycles, the heating / cooling rate and the stable temperature remain consistent, proving that the molybdenum dioxide photothermal patch has excellent cycle stability and rapid response, making it suitable for photothermal therapy scenarios with repeated start-stop cycles.

[0057] The embodiments shown in this specification are only used to illustrate the technical solutions of the present invention and are intended to help those skilled in the art understand the principles and advantages of the present invention. They do not constitute a limitation on the scope of protection of the present invention. Although the present invention has been specifically described, those skilled in the art can still make any modifications, equivalent substitutions or other reasonable variations to the implementation methods without departing from the spirit and scope of the present invention. All equivalent technical solutions resulting therefrom should be considered within the scope of protection of this patent.

Claims

1. A method for laser-induced preparation of patterned molybdenum dioxide thin films, characterized in that, Includes the following steps: 1) Take molybdenum trioxide nanoparticles, polyvinylpyrrolidone and isopropanol, mix them, and disperse them to form a uniform precursor ink; 2) Take a substrate and pre-treat it. Coat the substrate surface with the precursor ink obtained in step 1), dry and cure it to form a precursor film. 3) Under ambient conditions, a laser beam is used to scan and irradiate the precursor film prepared in step 2) according to a preset pattern, thereby reducing and sintering the molybdenum trioxide in the precursor film into molybdenum dioxide in situ, thus obtaining a patterned molybdenum dioxide film.

2. The method for laser-induced fabrication of patterned molybdenum dioxide thin films according to claim 1, characterized in that, In step 1), the precursor ink contains 33-63% molybdenum trioxide, 5.6-10.1% polyvinylpyrrolidone, and 31.4-56.9% isopropanol by mass. The molybdenum trioxide nanoparticles have a particle size of 5-50 nm.

3. The method for laser-induced fabrication of patterned molybdenum dioxide thin films according to claim 1, characterized in that, In step 2), the pretreatment of the substrate includes at least one of ultrasonic alcohol cleaning, ultrasonic water cleaning, drying, and corona discharge treatment.

4. The method for laser-induced fabrication of patterned molybdenum dioxide thin films according to claim 1, characterized in that, In step 3), the wavelength of the laser is 532 nm, and the energy density of the laser scan is 216-343 J / cm². 2 .

5. A method for fabricating a flexible electronic device, characterized in that, Includes the following steps: 1) A patterned molybdenum dioxide thin film is prepared on a substrate by any of the preparation methods described in claims 1-4; 2) Remove the precursor film from the areas of the substrate that were not irradiated by the laser; 3) Coat a conductive connection layer in a designated area of ​​the molybdenum dioxide thin film and connect it to the lead-out electrode; 4) A protective layer is coated onto the molybdenum dioxide thin film and conductive connection layer for encapsulation.

6. The method for fabricating a flexible electronic device according to claim 5, characterized in that, The substrate includes a flexible polymer film or a circuit board containing a flexible polymer film. The flexible polymer film is polyimide or polyethylene terephthalate.

7. The method for fabricating a flexible electronic device according to claim 5, characterized in that, In step 3), the connecting layer includes, but is not limited to, silver paste.

8. The method for fabricating a flexible electronic device according to claim 5, characterized in that, In step 3), the lead-out electrodes include, but are not limited to, FPC cables.

9. The method for fabricating a flexible electronic device according to claim 5, characterized in that, In step 4), the material of the protective layer is polydimethylsiloxane or polybutylene terephthalate.

10. A flexible electronic device, characterized in that, The invention includes flexible electronic devices manufactured using the method described in any one of claims 5-9, specifically including any one of signal acquisition electrodes, temperature sensors, electrothermal therapy patches, and photothermal therapy patches.

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