Cu2S (at) RuO2 (at) SiO2 thick film resistor material and preparation method and application thereof

Abstract

The invention provides a Cu2S-coated RuO2-coated SiO2 thick film resistance material and a preparation method and application thereof, the preparation method comprises the following steps: taking Cu2S nano powder as a nuclear phase, performing in-situ deposition of a RuO2 shell layer by a hydrothermal method to obtain core-shell structure powder, and coating SiO2 by a sol-gel method to form composite powder; mixing and grinding the thick-film resistor paste with glass powder and an organic carrier according to a preset proportion to prepare uniform thick-film resistor paste; and carrying out silk-screen printing, drying and curing, carrying out segmented high-temperature sintering, and naturally cooling to obtain the target material. According to the method, through a three-layer core-shell structure, Cu2S and RuO2 synergistically guarantee conductive continuity and heat resistance, a SiO2 layer obstructs oxygen, inhibits S volatilization and Cu < + > migration, and improves wettability with a glass phase, so that the conductive phase is stable in high-temperature and long-term use, the use amount and cost of ruthenium are remarkably reduced, and the resistance performance is not sacrificed.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electronic functional materials and thick film resistance materials, and particularly relates to a Cu2S@RuO2@SiO2 thick film resistance material, a preparation method and application thereof. BACKGROUND

[0002] Thick film resistance materials are widely used in the fields of precision resistors, sensors and hybrid integrated circuits due to excellent thermal stability, adhesion and large-area printing processing characteristics. The traditional thick film resistance system takes ruthenium oxide (RuO2) as the main conductive phase, and has stable electrical properties, controllable TCR (temperature coefficient) and high reliability. However, since ruthenium is a noble metal, it is expensive and limited in resources, which leads to a long-term high cost of thick film resistance materials, thereby restricting its large-scale application in consumer electronics and automotive electronics. Therefore, developing a low-ruthenium or ruthenium-free alternative system has become an important direction of current thick film resistance research.

[0003] In order to reduce the amount of ruthenium, some studies attempt to use copper or sulfide systems to form a synergistic conductive structure with RuO2. Chinese patent CN106024408B discloses a ruthenium oxide-copper sulfide composite material and its application in supercapacitor electrodes. This technology improves the electrochemical performance of the electrode by compounding Cu2S with RuO2, but its applicable temperature is low (≤300℃), and it is mainly used in the field of energy storage. Under the condition of high-temperature sintering (600-850℃) of thick film resistance paste, Cu2S is easily oxidized to Cu2O or CuO, or even phase decomposition occurs, leading to the breakage of the conductive network and the decay of the electrical properties. Chinese patent CN113782249B further proposes a low-cost chip resistor paste with copper sulfide-ruthenium oxide as the conductive phase. This scheme reduces the amount of ruthenium to some extent, but it still has the following problems under the condition of sintering at 850℃: (1) Cu2S is oxidized to non-conductive copper oxide phase in high-temperature air; (2) Cu + ions migrate in the glass phase to form local conductive channels, causing resistance drift; (3) RuO2 reacts with PbO-B2O3-SiO2 glass phase at high temperature to generate ruthenate or lead ruthenate byproducts, leading to the destruction of the conductive phase structure and the rise of TCR; (4) Cu2S has poor wettability with the glass phase, and the film layer has insufficient adhesion, which is prone to microcracks and aging failure. In addition, long-term exposure to a humid environment will also accelerate the migration and oxidation of Cu ions, causing resistance and TCR drift, thereby affecting the long-term stability of the resistor.

[0004] Therefore, there is an urgent need for a new type of thick film resistance material to solve the above technical problems. SUMMARY

[0005] The application aims to provide a Cu2S@RuO2@SiO2 thick film resistor material, which is used to solve the technical problems of existing Cu2S-RuO2 composite system thick film resistor material in the high-temperature sintering process, such as oxidation instability, ion migration and poor glass phase compatibility.

[0006] To solve the above technical problems, the application first provides a preparation method of a Cu2S@RuO2@SiO2 thick film resistor material, which comprises the following steps: S10, taking Cu2S nano-powder as a conductive inner core phase, depositing a RuO2 shell layer on the surface of the Cu2S nano-powder by a hydrothermal method to obtain Cu2S@RuO2 core-shell structure powder; S20, coating a SiO2 coating layer on the surface of the RuO2 shell layer by a sol-gel method to obtain Cu2S@RuO2@SiO2 composite powder; S30, mixing the Cu2S@RuO2@SiO2 composite powder, glass powder and organic carrier according to a preset mass ratio, and grinding by a pressure roller to obtain uniformly dispersed thick film resistor paste; S40, performing screen printing treatment on the thick film resistor paste, and forming a preliminary solidification film layer after drying and solidification; S50, performing segmented high-temperature sintering treatment on the preliminary solidification film layer, and naturally cooling to room temperature to obtain the Cu2S@RuO2@SiO2 thick film resistor material.

[0007] Preferably, in the step S10, the particle size of the Cu2S nano-powder is 50-100 nm, and the mass percentage content of the Cu2S nano-powder in the Cu2S@RuO2 core-shell structure powder is 60-80 wt%.

[0008] Preferably, the step S20 specifically comprises the following steps: S201, mixing the Cu2S@RuO2 core-shell structure powder, an organic solvent and an alkali solution, uniformly dispersing for 10-30 min, slowly adding tetraethyl orthosilicate under stirring, stirring and hydrolyzing at room temperature for 2-6 h to obtain a hydrolysis product; S202, sequentially performing washing and drying treatment on the hydrolysis product, heating to 300-400℃ at a rate of 3-5℃ / min in an inert atmosphere and keeping the temperature for 0.5-1.5 h, and cooling to obtain the Cu2S@RuO2@SiO2 composite powder.

[0009] Preferably, in the step S202, the mass percentage content of the SiO2 coating layer in the Cu2S@RuO2@SiO2 composite powder is 1-5 wt%, and the thickness is 5-20 nm.

[0010] Preferably, in the step S30, the mass ratio of the Cu2S@RuO2@SiO2 composite powder, the glass powder and the organic carrier is (5-7):(2-4):1.

[0011] Preferably, step S40 specifically includes: printing thick film resistor paste onto the surface of an Al2O3 substrate through a 325-mesh stainless steel mesh, and then drying it in a hot air oven at 110~120℃ for 10~20 minutes to obtain a pre-cured film layer.

[0012] Preferably, step S50 specifically includes: heating the pre-cured film layer to 380-420℃ at 1-3℃ / min and holding it for 8-12 minutes, then heating it to 600-800℃ at 3-5℃ / min and holding it for 8-12 minutes, and finally naturally cooling it to room temperature under an air-nitrogen mixed atmosphere to obtain Cu2S@RuO2@SiO2 thick film resistor material.

[0013] Accordingly, the present invention also provides a Cu2S@RuO2@SiO2 thick film resistive material, which is prepared by the preparation method of Cu2S@RuO2@SiO2 thick film resistive material as described in any of the above claims.

[0014] Preferably, the temperature coefficient of the Cu2S@RuO2@SiO2 thick film resistive material is controlled within ±150ppm / ℃.

[0015] Accordingly, the present invention also provides an application of the above-mentioned Cu2S@RuO2@SiO2 thick film resistive material in thick film resistors and chip resistor elements.

[0016] The beneficial effects of this invention are as follows: Unlike existing technologies, this invention provides a Cu2S@RuO2@SiO2 thick-film resistor material, its preparation method, and its applications. The preparation method includes: First, using Cu2S nanoparticles as the conductive core phase, a RuO2 shell layer is deposited in situ on its surface using a hydrothermal method to obtain Cu2S@RuO2 core-shell structured powder; second, a SiO2 coating layer is formed on the RuO2 shell surface using a sol-gel method to obtain Cu2S@RuO2@SiO2 composite powder; third, the Cu2S@RuO2@SiO2 composite powder, glass powder, and organic carrier are mixed according to a preset mass ratio, and then ground by roller mill to obtain a uniformly dispersed thick-film resistor slurry; fourth, the thick-film resistor slurry is screen-printed, and after drying and curing, a preliminary cured film layer is formed; finally, the preliminary cured film layer is subjected to segmented high-temperature sintering, and after natural cooling to room temperature, the Cu2S@RuO2@SiO2 thick-film resistor material is obtained. The above-mentioned preparation method of the present invention constructs a Cu2S@RuO2@SiO2 three-layer core-shell composite conductive phase. The Cu2S core and the RuO2 intermediate shell synergistically ensure conductivity continuity and heat resistance, while the outer SiO2 layer effectively blocks oxygen diffusion, inhibits S volatilization, and reduces Cu content. +Ion migration and improved wettability with the glass phase enable chemical and structural stability of the conductive phase during high-temperature sintering and long-term use. This significantly reduces ruthenium usage to lower costs without sacrificing resistivity, achieving the dual benefits of stable performance and reduced costs. Attached Figure Description

[0017] Figure 1 This is a flowchart illustrating the preparation method of Cu2S@RuO2@SiO2 thick film resistive material provided in an embodiment of the present invention. Figure 2 This is a schematic diagram of the three-layer core-shell structure of the Cu2S@RuO2@SiO2 thick film resistor material provided in the embodiments of the present invention; Figure 3 The image shows a SEM image of the Cu2S@RuO2@SiO2 composite powder prepared in Example 1. Figure 4 The image shows the XRD pattern of the Cu2S@RuO2@SiO2 composite powder prepared in Example 1. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] To address the shortcomings of existing Cu2S-RuO2 composite thick-film resistive materials, the inventors discovered a mechanism-related issue: the Cu2S conductive phase is easily oxidized and exhibits ion migration during high-temperature sintering, while RuO2 may be partially reduced to Ru metal in a locally reducing atmosphere, leading to discontinuous conductive pathways. Furthermore, the system suffers from poor compatibility with the glass phase. Introducing an inert insulating layer onto the surface of the composite particles can block oxygen diffusion, inhibit ion migration, and improve interfacial compatibility, thereby enhancing thermal stability and electrical performance consistency.

[0020] Based on this, the present invention proposes a Cu2S@RuO2@SiO2 composite conductive phase thick film resistive material with low ruthenium content. A three-layer core-shell structure achieves chemical and structural stability of the conductive phase at high temperatures: Cu2S serves as the conductive core, RuO2 as the intermediate shell, synergistically ensuring conductive continuity and heat resistance; an inert SiO2 coating layer is introduced on the outer layer to block oxygen diffusion, inhibit S volatilization, and reduce Cu content. + Ion migration is achieved, while simultaneously improving wettability with the glass phase. Ultimately, without sacrificing electrical resistance, the amount of ruthenium used is significantly reduced, achieving the dual goals of stable performance and reduced cost.

[0021] Please seeFigure 1 , Figure 1 A flowchart illustrating the preparation method of Cu2S@RuO2@SiO2 thick film resistive material provided in this embodiment of the invention; wherein, the connection between each step of the above preparation method needs to maintain the cleanliness and dispersibility of the system, specifically including: S10 uses Cu2S nanoparticles as the conductive core phase and a RuO2 shell layer is deposited in situ on its surface using a hydrothermal method to obtain Cu2S@RuO2 core-shell structured powder.

[0022] In step S10, Cu2S nanoparticles of 50-100 nm are selected as the conductive core phase. This ensures a suitable specific surface area to provide sufficient reaction sites and promotes the uniform in-situ deposition of the RuO2 shell on its surface. This, in turn, ensures the regularity of the morphology and the uniformity of the composition of the Cu2S@RuO2 core-shell structure powder, laying the foundation for the stability of the subsequent composite powder and thick film resistor materials.

[0023] In step S10, the mass percentage of Cu2S nanoparticles in the Cu2S@RuO2 core-shell structured powder is 60-80 wt%. When the Cu2S content is below 60 wt%, the conductive network is discontinuous, and the resistance increases. When Cu2S is excessive (>80 wt%), the oxidation sensitivity of the system increases, easily leading to high-temperature oxidation and drift. By adjusting the ratio within this range, a complete conductive path can be formed in the RuO2 shell, while reducing ruthenium consumption. Those skilled in the art can fine-tune the ratio within this range according to different resistance design requirements to obtain the desired electrical performance.

[0024] S20, using the sol-gel method to coat the RuO2 shell surface to form a SiO2 coating layer, thus obtaining Cu2S@RuO2@SiO2 composite powder.

[0025] Specifically, step S20 also includes: S201: Cu2S@RuO2 core-shell structured powder, organic solvent and alkaline solution are mixed and ultrasonically dispersed for 10-30 min until uniform. Then, tetraethyl orthosilicate (TEOS) is slowly added dropwise under stirring. Hydrolysis is carried out at room temperature for 2-6 h to obtain the hydrolysis product. S202, the hydrolysis products are washed and dried sequentially, then heated to 300-400℃ in an inert atmosphere at 3-5℃ / min and held for 0.5-1.5h, and then cooled to obtain Cu2S@RuO2@SiO2 composite powder.

[0026] Specifically, in step S20, Cu2S@RuO2 core-shell powder is first uniformly dispersed by ultrasonic dispersion for 10-30 minutes, followed by a controlled hydrolysis reaction at room temperature for 2-6 hours to ensure uniform and dense deposition of the SiO2 coating layer. Then, impurities are removed by washing and drying, and the SiO2 layer is further improved by a gentle heating at 3-5℃ / min and a heat preservation and curing at 300-400℃ under an inert atmosphere. This further enhances the structural stability and bonding strength of the SiO2 layer, ultimately obtaining a composite powder with regular morphology and uniform composition. This not only effectively isolates and protects the conductive phase in the core but also improves its compatibility with the glass phase, providing a key guarantee for the high-temperature stability and electrical performance consistency of thick film resistor materials.

[0027] In step S202, the SiO2 coating layer in the Cu2S@RuO2@SiO2 composite powder has a mass percentage of 1-5 wt% and a thickness of 5-20 nm. The SiO2 coating layer primarily functions to block oxygen and ion migration, while also improving the wettability between the conductive and glassy phases. If the SiO2 coating layer thickness is less than 5 nm, the blocking effect is insufficient; if the thickness exceeds 20 nm, it may lead to a decrease in overall conductivity. The SiO2 coating layer thickness can be precisely adjusted by controlling the TEOS feed amount and ammonia concentration. pH control during the sol-gel reaction is crucial for coating uniformity, with an optimal range of 8-10. Low-temperature heat treatment (300-400℃) of the coated composite powder enhances the shell density without damaging the conductive network.

[0028] S30: Cu2S@RuO2@SiO2 composite powder, glass powder and organic carrier are mixed in a preset mass ratio and then ground by a pressure roller to obtain a uniformly dispersed thick film resistive slurry.

[0029] In step S30, the mass ratio of Cu2S@RuO2@SiO2 composite powder, glass powder, and organic carrier is (5~7):(2~4):1. Mixing the Cu2S@RuO2@SiO2 composite powder, glass powder, and organic carrier according to this specific mass ratio, combined with a roller milling process, can precisely balance the synergistic effects of the conductive phase, binder phase, and dispersion medium, while also achieving uniform dispersion of each component and avoiding agglomeration. This ultimately yields a thick-film resistive paste with excellent dispersibility and suitable rheological properties, providing crucial assurance for the uniformity of film thickness in subsequent screen printing, the density of the structure after sintering, and the stability of electrical properties.

[0030] S40 involves screen printing the thick film resistor paste, followed by drying and curing to form a preliminary cured film layer.

[0031] Specifically, step S40 also includes: Thick-film resistor paste is printed onto the surface of an Al2O3 substrate through a 325-mesh stainless steel mesh. After printing, it is dried in a hot air oven at 110~120℃ for 10~20 minutes to obtain a pre-cured film layer. The above steps ensure that the film layer is uniform in thickness and regular in shape, and also effectively remove volatiles from the paste, avoid film layer cracking or pore defects, and form a dense pre-cured film layer. This lays a solid foundation for the synergistic reaction of various components during subsequent high-temperature sintering, the firm bonding between the film layer and the substrate, and the stable electrical properties of the final thick-film resistor material.

[0032] S50, the initially cured film layer is subjected to segmented high-temperature sintering treatment, and after natural cooling to room temperature, Cu2S@RuO2@SiO2 thick film resistor material is obtained.

[0033] Specifically, step S50 also includes: The pre-cured film was first heated to 380-420℃ in air at a rate of 1-3℃ / min and held for 8-12 minutes. Then, it was heated to 600-800℃ in nitrogen at a rate of 3-5℃ / min and held for 8-12 minutes. Finally, it was naturally cooled to room temperature in an air-nitrogen mixed atmosphere to obtain Cu2S@RuO2@SiO2 thick film resistive material. Figure 2 As shown.

[0034] Specifically, the low-temperature stage (≤400℃) is mainly used to remove organic components and prevent gas accumulation that could cause film blistering; the medium-temperature stage (600~800℃) is the key stage for the bonding of the conductive phase and the glass. An air atmosphere promotes the flow of the glass phase and interface wetting, while a nitrogen atmosphere helps to suppress Cu2S oxidation and sulfur volatilization. This segmented atmosphere sintering process ensures the density of the film and the stability of the conductive phase. The preferred heating rate is 3~5℃ / min to prevent film cracking caused by thermal stress.

[0035] The preparation method provided by this invention requires maintaining system cleanliness and dispersibility between each step: the particle size of each Cu2S nanoparticle is controlled at 50~100nm to ensure the uniformity of specific surface area and subsequent coating reaction; the hydrothermal reaction conditions should be controlled at 150~180℃ for 8~10h to obtain a continuous RuO2 shell; the SiO2 outer layer is formed using a sol-gel process, with TEOS hydrolysis and condensation reaction carried out in an ethanol-ammonia system, and the uniform and dense outer layer structure can be achieved by controlling the dropping rate and reaction time; the mixed thick film resistor paste needs to be dispersed by three-roll milling to obtain rheological properties suitable for screen printing; finally, segmented atmosphere sintering is carried out at 600~800℃, with the air stage used to remove organic matter and the nitrogen stage used to suppress Cu2S oxidation, thereby obtaining a dense and flat thick film resistor layer.

[0036] Accordingly, the present invention also provides a Cu2S@RuO2@SiO2 thick film resistive material, which is prepared by the preparation method of Cu2S@RuO2@SiO2 thick film resistive material as described in any of the above claims.

[0037] Preferably, the temperature coefficient of the Cu2S@RuO2@SiO2 thick-film resistive material is controlled within ±150 ppm / ℃. The stability of the Cu2S@RuO2@SiO2 thick-film resistive material originates from the synergistic compensation mechanism of the conductive pathways of Cu2S and RuO2. RuO2 has a positive temperature coefficient, while Cu2S exhibits a negative temperature coefficient; their combination cancels out the temperature dependence of conductivity. Simultaneously, the presence of the SiO2 layer stabilizes the interfacial chemical structure, preventing fluctuations in the current-carrying channels caused by high-temperature reactions. Therefore, this system can maintain resistance stability over a relatively wide temperature range.

[0038] Specifically, the ruthenium usage in Cu2S@RuO2@SiO2 thick-film resistor materials is reduced by more than 40% compared to traditional Cu2S-RuO2 composite thick-film resistor materials. The Cu2S core provides the main conductive channels, while the RuO2 shell only serves as an interfacial conductivity and stability compensation layer, significantly improving ruthenium utilization efficiency. Simultaneously, the SiO2 outer layer prevents ruthenium diffusion and loss during sintering, further reducing the overall usage. This approach effectively reduces raw material costs while ensuring stable thick-film resistor performance.

[0039] Specifically, Cu2S@RuO2@SiO2 thick-film resistive materials can be widely used in the manufacture of thick-film resistors and chip resistor elements. Their rheological properties are compatible with printing processes, allowing them to be used on conventional screen printing production lines. The resistive film layer formed after printing, drying, and sintering is smooth and has strong adhesion, making it suitable for automated printing and mass production packaging. This system is also compatible with different glass powder systems, including PbO—B2O3—SiO2 and ZnO—B2O3—SiO2.

[0040] The technical solution of the present invention will now be further described with reference to specific embodiments.

[0041] Example 1: This embodiment 1 provides a Cu2S@RuO2@SiO2 thick film resistive material and its preparation method. The specific steps of the preparation method are as follows: Step (1), Preparation of Cu2S nanopowder: Weigh 20 mmol CuCl2·2H2O and 40 mmol thiourea and dissolve them in 200 mL ethylene glycol. Stir magnetically for 30 min to form precursor solution A. Transfer it to a 250 mL polytetrafluoroethylene-lined reactor and react hydrothermally at 160 °C for 10 h. After cooling, centrifuge, wash three times with ethanol, and vacuum dry at 60 °C to obtain Cu2S nanopowder with a particle size of 50~100 nm and a pure crystalline phase. Its formation mechanism is: Cu 2+ Cu2S nanocrystals are generated with thiourea in a reducing environment, accompanied by the slow release of sulfur source by ethylene glycol to control the grain size.

[0042] Step (2), formation of the RuO2 shell: 1g of the above Cu2S powder was dispersed in 100mL of deionized water, and 20mL of 15mg / mL RuCl3 solution was added. The pH was adjusted to 8-9, and the mixture was subjected to hydrothermal reaction at 160℃ for 8h. After centrifugation, washing, and drying, it was calcined at 350℃ in air atmosphere for 1h to form a Cu2S@RuO2 core-shell structure. At this stage, Ru... 3+ RuO2 nanocrystals are generated through hydrothermal oxidation and deposited in situ on the Cu2S surface to form a continuous and dense shell.

[0043] Step (3), formation of the SiO2 coating layer: 1g of Cu2S@RuO2 powder was added to a mixture of 150mL anhydrous ethanol and 10mL ammonia. After ultrasonic dispersion for 20min, 2mL of TEOS was slowly added dropwise, and the mixture was stirred for 2h. The hydrolysis reaction was: Si(OC2H5)4+2H2O→SiO2+4C2H5OH. After washing and drying, the mixture was kept at 350℃ under N2 atmosphere for 1h to obtain Cu2S@RuO2@SiO2 composite powder with a coating layer thickness of approximately 10±5nm.

[0044] Step (4), slurry preparation: Mix Cu2S@RuO2@SiO2 composite powder, PbO—B2O3—SiO2 glass powder and organic carrier at a mass ratio of 60:30:10; wherein, the softening point of the glass powder is 550℃, and the particle size D 50 =1.5μm; the carrier is prepared by dissolving ethyl cellulose (10wt%) in α-terpineol. After mixing, it is milled three times with a three-roll mill and a roller gap of 5μm to ensure uniform dispersion of the paste. The viscosity of the thick film resistive paste is controlled at 100~150Pa·s, which is suitable for screen printing.

[0045] Step (5), printing and drying: The paste is printed onto the surface of an Al2O3 substrate (0.6 mm thick) through a 325-mesh stainless steel mesh, with a dry film thickness of approximately 15-20 μm. After printing, the substrate is placed in a 120°C hot air oven for 15 min to remove solvent and form a preliminary cured film layer.

[0046] Step (6), sintering process: A segmented heating control is adopted. First, the temperature is increased to 400℃ at 2℃ / min in an air atmosphere and held for 10min to remove organic matter; then, the temperature is increased to 700℃ at 5℃ / min in a nitrogen atmosphere and held for 10min; finally, it is cooled in an air-nitrogen mixed atmosphere. Figure 3 The scanning electron microscope (SEM) shown shows that the obtained thick film has a smooth, dense, and crack-free surface, with the glass phase uniformly encapsulating the conductive phase particles and good interfacial bonding.

[0047] Please see Figure 4 , Figure 4 The image shows the XRD pattern of the Cu2S@RuO2@SiO2 composite powder prepared in Example 1. Figure 4 As can be seen, the XRD pattern shows characteristic diffraction peaks of RuO2 (marked in blue) and Cu2S (marked in green), with no other impurity phase peaks. Meanwhile, SiO2, due to its amorphous structure, did not exhibit sharp diffraction peaks. This indicates that the present invention successfully prepared a Cu2S@RuO2 core-shell structure and effectively coated its surface with a SiO2 layer using the sol-gel method. The phase composition is consistent with the designed three-layer core-shell structure, with no secondary phase formation, demonstrating that the composite powder has a stable phase structure and a controllable preparation process.

[0048] Electrical performance tests on the Cu2S@RuO2@SiO2 thick film resistive material provided in Example 1 showed that: at 25℃, the sheet resistance was adjustable from 100Ω to 10kΩ, and the TCR was ±150ppm / ℃; after 100h of humid heat aging at 85℃ / 85%RH, the resistance drift was <0.2%; after 100 temperature cycles (–40~125℃), the sheet resistance change rate was <0.5%, and there was no film cracking or peeling.

[0049] Example 2 (Low coating ratio system): This embodiment 2 provides a Cu2S@RuO2@SiO2 thick film resistive material and its preparation method. The preparation method is roughly the same as that provided in embodiment 1, except that the SiO2 coating ratio is reduced to 1wt% in step (3) to form a thinner coating layer (about 5nm). Step (3), formation of the SiO2 coating layer: 1g of Cu2S@RuO2 powder was added to a mixture of 150mL anhydrous ethanol and 10mL ammonia. After ultrasonic dispersion for 20min, 1mL of TEOS was slowly added dropwise, and the mixture was stirred for 2h. After washing and drying, the mixture was kept at 350℃ under N2 atmosphere for 1h to obtain Cu2S@RuO2@SiO2 composite powder with a relatively thin coating layer of about 5nm.

[0050] Electrical performance tests on the Cu2S@RuO2@SiO2 thick film resistive material provided in Example 2 showed that the sheet resistance was adjustable from 120Ω to 9kΩ at 25℃, and the TCR was ±180ppm / ℃. After 100h of humid heat aging at 85℃ / 85%RH, the resistance drift was <0.4%.

[0051] Example 3 (Thick Coating System): This embodiment 3 provides a Cu2S@RuO2@SiO2 thick film resistive material and its preparation method. The preparation method is largely the same as that provided in embodiment 1, except that the SiO2 coating ratio is increased to 5wt% in step (3), and the coating layer thickness is about 20nm. Step (3), formation of the SiO2 coating layer: 1g of Cu2S@RuO2 powder was added to a mixture of 150mL anhydrous ethanol and 10mL ammonia. After ultrasonic dispersion for 20min, 4mL of TEOS was slowly added dropwise, and the mixture was stirred for 3h. After washing and drying, the mixture was kept at 350℃ under N2 atmosphere for 1h to obtain Cu2S@RuO2@SiO2 composite powder with a relatively thin coating layer of about 20nm.

[0052] Electrical performance tests on the Cu2S@RuO2@SiO2 thick film resistive material provided in Example 3 showed that the sheet resistance was adjustable from 150Ω to 12kΩ at 25℃, and the TCR was ±130ppm / ℃. After 100h of humid heat aging at 85℃ / 85%RH, the resistance drift was <0.15%.

[0053] Example 4 (Different sintering atmospheres): This embodiment 4 provides a Cu2S@RuO2@SiO2 thick film resistor material and its preparation method. The preparation method is roughly the same as that provided in embodiment 1, except that the sintering atmosphere in step (6) is different. Step (6), sintering process: segmented temperature control was adopted, and the temperature was increased to 700℃ at 5℃ / min under nitrogen atmosphere, held for 20min, and then cooled. The surface color of the resulting thick film changed from light gray to dark gray, and no copper oxide signal was detected by EDS spectrum (energy dispersive X-ray spectroscopy).

[0054] Electrical performance tests on the Cu2S@RuO2@SiO2 thick film resistive material provided in Example 4 showed that the sheet resistance was adjustable from 110Ω to 8kΩ at 25℃, and the TCR was ±160ppm / ℃. After 100h of humid heat aging at 85℃ / 85%RH, the resistance drift was <0.25%.

[0055] Comparative Example 1: Comparative Example 1 provides a Cu2S@RuO2 thick film resistive material and its preparation method. The specific steps of the preparation method are as follows: Step (1), Preparation of Cu2S nanopowder: Weigh 20 mmol CuCl2·2H2O and 40 mmol thiourea and dissolve them in 200 mL ethylene glycol. Stir magnetically for 30 min to form precursor solution A. Transfer it to a 250 mL polytetrafluoroethylene-lined reactor and react hydrothermally at 160 °C for 10 h. After cooling, centrifuge, wash three times with ethanol, and vacuum dry at 60 °C to obtain Cu2S nanopowder with a particle size of 50~100 nm and a pure crystalline phase. Its formation mechanism is: Cu 2+ Cu2S nanocrystals are generated with thiourea in a reducing environment, accompanied by the slow release of sulfur source by ethylene glycol to control the grain size.

[0056] Step (2), formation of the RuO2 shell: 1g of the above Cu2S powder was dispersed in 100mL of deionized water, and 20mL of 15mg / mL RuCl3 solution was added. The pH was adjusted to 8-9, and the mixture was subjected to hydrothermal reaction at 160℃ for 8h. After centrifugation, washing, and drying, it was calcined at 350℃ in air atmosphere for 1h to form a Cu2S@RuO2 core-shell structure. At this stage, Ru... 3+ RuO2 nanocrystals are generated through hydrothermal oxidation and deposited in situ on the Cu2S surface to form a continuous and dense shell.

[0057] Step (3), slurry preparation: Mix Cu2S@RuO2 composite powder, PbO-B2O3-SiO2 glass powder and organic carrier at a mass ratio of 60:30:10; wherein, the softening point of the glass powder is 550℃, and the particle size D 50 =1.5μm; the carrier is prepared by dissolving ethyl cellulose (10wt%) in α-terpineol. After mixing, it is milled three times with a three-roll mill and a roller gap of 5μm to ensure uniform dispersion of the paste. The viscosity of the thick film resistive paste is controlled at 100~150Pa·s, which is suitable for screen printing.

[0058] Step (4), printing and drying: The paste is printed onto the surface of an Al2O3 substrate (0.6 mm thick) through a 325-mesh stainless steel mesh, with a dry film thickness of approximately 15-20 μm. After printing, the substrate is placed in a 120°C hot air oven for 15 min to remove solvent and form a preliminary cured film layer.

[0059] Step (5), sintering process: adopt segmented heating control, first heat to 400℃ at 2℃ / min in air atmosphere and hold for 10min to remove organic matter; then heat to 700℃ at 5℃ / min in nitrogen atmosphere and hold for 10min, and finally cool in air-nitrogen mixed atmosphere.

[0060] Electrical performance tests on the Cu2S@RuO2 thick film resistor material provided in Comparative Example 1 showed that the resistance fluctuated significantly (±10%) at 25℃, with a TCR of ±260ppm / ℃. After 100h of humid heat aging at 85℃ / 85%RH, the resistance drift was >0.6%.

[0061] Specifically, Table 1 shows a comparison of the comprehensive performance of the Cu2S@RuO2@SiO2 thick film resistive materials prepared in Examples 1-4 and the Cu2S@RuO2 thick film resistive material prepared in Comparative Example 1: Table 1. Overall Performance Comparison Table

[0062] As shown in Table 1, the introduction of the SiO2 coating layer plays a key regulatory role in the performance of Cu2S@RuO2@SiO2 thick film resistor materials: with the increase of SiO2 content (coating thickness), the temperature coefficient of resistance (TCR) of the material decreases significantly (e.g., TCR ±130ppm / ℃ in Example 3), the wet heat aging drift rate decreases (e.g., only 0.15% in Example 3), and the structural stability is improved; however, too low SiO2 coating (e.g., SiO2 content 1wt%, coating thickness 5nm in Example 2) will lead to an increase in TCR and a decrease in wet heat stability, with only a slight advantage in conductivity. At the same time, the sintering atmosphere affects the oxidation resistance of the material. A pure nitrogen atmosphere (Example 4) can further optimize the oxidation resistance and reduce performance fluctuations; while using an air-nitrogen mixed sintering (e.g., Example 1) can achieve a balance between performance and process cost.

[0063] Compared with Comparative Example 1 (TCR±260ppm / ℃, damp heat drift>0.6%) without SiO2 coating, this invention, through the Cu2S@RuO2@SiO2 three-layer core-shell structure, significantly reduces the amount of ruthenium used while greatly improving the sheet resistance stability, temperature coefficient and long-term damp heat reliability of thick film resistors, achieving the dual goals of "low cost and high performance".

[0064] This invention discloses a Cu2S@RuO2@SiO2 thick-film resistor material with low ruthenium content and its preparation method. This invention belongs to the field of electronic functional materials and thick-film resistor technology. The method includes: firstly, preparing Cu2S nanopowder using an ethylene glycol-thiourea system; then generating a Cu2S@RuO2 core-shell structure through a secondary hydrothermal reaction in a RuCl3 solution; next, forming a SiO2 coating layer on the outer layer using a sol-gel method to obtain a Cu2S@RuO2@SiO2 three-layer composite conductive phase powder; finally, mixing the composite powder with glass powder and an organic carrier, and then obtaining a thick-film resistor film through screen printing and sintering at 700℃. This structure effectively inhibits Cu2S oxidation and S volatilization, improves wettability and adhesion with the glass phase, controls the temperature coefficient (TCR) of the thick-film resistor to ±150ppm / ℃, and reduces long-term drift to less than 0.2%, while reducing ruthenium usage by 40%, achieving a balance between high stability and low cost.

[0065] Compared with the prior art, the advantages of the present invention are as follows: (1) The introduction of the SiO2 outer layer plays a dual role of physical isolation and chemical passivation at high temperatures. Firstly, it can prevent Cu2S from being oxidized to form Cu2O / CuO, thereby maintaining the continuity of conductivity; secondly, it can inhibit Cu + Ions migrate into the glassy phase, avoiding the formation of parasitic conductive channels. Simultaneously, the SiO2 shell has a similar chemical composition to PbO–B2O3–SiO2 glass, improving interfacial wetting and matching, and preventing film cracking caused by thermal stress. Therefore, the Cu2S@RuO2@SiO2 three-layer core-shell structure provided by this invention can achieve high-temperature stabilization of the conductive phase, significantly reducing oxidation and migration risks. It is significantly superior to existing Cu2S–RuO2 systems in terms of chemical stability, electrical stability, and structural compatibility.

[0066] (2) The present invention can improve the wetting and bonding properties of the glass phase and enhance the adhesion of the film by using an inert SiO2 coating layer; (3) The present invention can suppress high-temperature side reactions and ensure the continuity of the conductive network by using a segmented atmosphere sintering process; (4) The TCR of the Cu2S@RuO2@SiO2 thick film resistor material provided by the present invention is controlled at ±150ppm / ℃, and the sheet resistance stability and consistency are improved by 30%; (5) The amount of ruthenium used in the Cu2S@RuO2@SiO2 thick film resistor material provided by the present invention is reduced by about 40% compared with the traditional Cu2S-RuO system thick film resistor material, and the material cost is reduced by more than 35%; (6) The Cu2S@RuO2@SiO2 thick film resistor material provided by the present invention has good compatibility with the paste process and can be directly used in existing screen printing thick film production lines to realize industrial application.

[0067] It should be noted that all the above embodiments belong to the same inventive concept, and the descriptions of each embodiment have different focuses. Where the description in a particular embodiment is not detailed, please refer to the description in other embodiments.

[0068] The above embodiments merely illustrate implementation methods of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing a Cu2S@RuO2@SiO2 thick film resistive material, characterized in that, include: S10, using Cu2S nanoparticles as the conductive core phase, and depositing a RuO2 shell layer on its surface in situ using a hydrothermal method to obtain Cu2S@RuO2 core-shell structured powder; S20, using the sol-gel method to coat the RuO2 shell surface to form a SiO2 coating layer, thus obtaining Cu2S@RuO2@SiO2 composite powder; S30, the Cu2S@RuO2@SiO2 composite powder, glass powder and organic carrier are mixed according to a preset mass ratio, and then ground by a pressure roller to obtain a uniformly dispersed thick film resistive slurry; S40, the thick film resistor paste is screen printed and then dried and cured to form a preliminary cured film layer; S50, the pre-cured film layer is subjected to segmented high-temperature sintering treatment, and after natural cooling to room temperature, Cu2S@RuO2@SiO2 thick film resistor material is obtained.

2. The method for preparing Cu2S@RuO2@SiO2 thick film resistive material according to claim 1, characterized in that, In step S10, the particle size of the Cu2S nanoparticles is 50~100nm, and the mass percentage of the Cu2S nanoparticles in the Cu2S@RuO2 core-shell structure powder is 60~80wt%.

3. The method for preparing Cu2S@RuO2@SiO2 thick film resistive material according to claim 2, characterized in that, The S20 step specifically includes: S201, the Cu2S@RuO2 core-shell structured powder, organic solvent and alkaline solution are mixed, ultrasonically dispersed for 10-30 min until uniform, and then tetraethyl orthosilicate is slowly added dropwise under stirring. Hydrolysis is carried out at room temperature for 2-6 h to obtain the hydrolysis product. S202, the hydrolysis product is washed and dried sequentially, then heated to 300-400℃ in an inert atmosphere at 3-5℃ / min and held for 0.5-1.5h, and then cooled to obtain the Cu2S@RuO2@SiO2 composite powder.

4. The method for preparing Cu2S@RuO2@SiO2 thick film resistive material according to claim 3, characterized in that, In step S202, the SiO2 coating layer in the Cu2S@RuO2@SiO2 composite powder has a mass percentage content of 1~5wt% and a thickness of 5~20nm.

5. The method for preparing Cu2S@RuO2@SiO2 thick film resistive material according to claim 1, characterized in that, In step S30, the mass ratio of the Cu2S@RuO2@SiO2 composite powder, glass powder, and organic carrier is (5~7):(2~4):

1.

6. The method for preparing Cu2S@RuO2@SiO2 thick film resistive material according to claim 1, characterized in that, The S40 step specifically includes: printing the thick film resistor paste onto the surface of an Al2O3 substrate through a 325-mesh stainless steel mesh, and then drying it in a hot air oven at 110~120℃ for 10~20 minutes to obtain the preliminary cured film layer.

7. The method for preparing Cu2S@RuO2@SiO2 thick film resistive material according to claim 1, characterized in that, The S50 step specifically includes: first heating the pre-cured film layer to 380-420℃ at 1-3℃ / min and holding it for 8-12 minutes, then heating it to 600-800℃ at 3-5℃ / min and holding it for 8-12 minutes, and finally naturally cooling it to room temperature under an air-nitrogen mixed atmosphere to obtain the Cu2S@RuO2@SiO2 thick film resistor material.

8. A Cu2S@RuO2@SiO2 thick film resistive material, characterized in that, It is prepared by the method for preparing Cu2S@RuO2@SiO2 thick film resistive material as described in any one of claims 1 to 7.

9. The Cu2S@RuO2@SiO2 thick film resistive material according to claim 8, characterized in that, The temperature coefficient of the Cu2S@RuO2@SiO2 thick film resistor material is controlled within ±150ppm / ℃.

10. The application of the Cu2S@RuO2@SiO2 thick film resistive material as described in claim 9 in thick film resistors and chip resistor elements.

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