Piezoelectric ceramic with double-layer electrode structure, preparation method and application thereof

Abstract

This application discloses a piezoelectric ceramic with a double-layer electrode structure, its preparation method, and its application. The piezoelectric ceramic includes: (a) a substrate layer; (b) a carbon-containing conductive layer disposed on the surface of the substrate layer, the carbon-containing conductive layer comprising conductive carbon material; and a metal conductive layer disposed between the substrate layer and the metal conductive layer, the metal conductive layer comprising a solderable metal material. This application, by introducing a carbon-containing conductive layer combined with the substrate layer, facilitates the formation of a continuous conductive network. The conductive carbon material has low thermal conductivity; therefore, during wave soldering or reflow soldering, when high temperature is transferred from the metal conductive layer, the carbon-containing conductive layer, due to its relatively low thermal conductivity perpendicular to the substrate layer, relatively slows down the heat conduction rate to the substrate layer, reducing the risk of depolarization. The metal conductive layer includes solderable metal materials such as silver, silver-clad copper, copper, tin, copper-nickel alloys, and copper-nickel-zinc alloys, which helps to provide a solderable surface, thereby enhancing welding performance and pull-out strength.

Description

Technical Field

[0001] This application relates to the field of piezoelectric ceramics and similar perovskite materials in electronic devices, and in particular to a piezoelectric ceramic with a double-layer electrode structure, its preparation method and application. Background Technology

[0002] Piezoelectric ceramic devices utilize the piezoelectric effect to achieve the interconversion of electrical energy and mechanical energy. Specifically, they generate electric charge when subjected to mechanical stress (positive piezoelectric effect) or undergo mechanical deformation when an electric field is applied (inverse piezoelectric effect). Therefore, they are widely used in fields such as audible alarms, sensing and detection, precision drives, ultrasonic applications, and medical equipment. Based on this effect, piezoelectric ceramic devices offer significant advantages such as fast response speed, low power consumption, small size, high precision, no electromagnetic interference, high reliability, and resistance to harsh environments. They are suitable for various products including piezoelectric buzzers, piezoelectric atomizers, ultrasonic transducers, and piezoelectric sensors.

[0003] However, existing piezoelectric ceramic electrode technology still has the following shortcomings: on the one hand, the preparation cost of metal electrodes using nanoscale slurries is high, but if micron-scale slurries are used instead, the resonant impedance of the resulting metal electrodes increases significantly, even reaching ≥800Ω, leading to severe energy loss. Therefore, it is urgent to develop a piezoelectric ceramic and its preparation method to improve the weldability and conductivity of the internal structure of piezoelectric ceramics and reduce production costs. Summary of the Invention

[0004] One objective of this application is to provide a piezoelectric ceramic with a double-layer electrode structure, its preparation method and application, which is beneficial to improving the heat resistance stability of the piezoelectric ceramic during hot processing and enhancing the conductivity of the piezoelectric ceramic.

[0005] Another objective of this application is to provide a piezoelectric ceramic with a double-layer electrode structure, its preparation method and application, which is beneficial to reducing production costs and improving economic benefits.

[0006] To achieve the above objectives, this application provides a piezoelectric ceramic with a double-layer electrode structure, comprising: (a) a substrate layer; (b) a carbon-containing conductive layer disposed on the surface of the substrate layer, the carbon-containing conductive layer comprising a conductive carbon material; and (c) a metal conductive layer disposed between the substrate layer and the metal conductive layer, the metal conductive layer comprising a solderable metal material.

[0007] In some embodiments, the carbon-containing conductive layer further includes a first cured binder phase, which connects the conductive carbon material to the substrate layer and / or fills between the conductive carbon materials to connect each of the conductive carbon materials; the metal conductive layer further includes a second cured binder phase, which connects the solderable metal material to the carbon-containing conductive layer and / or fills between the solderable metal materials to connect each of the solderable metal materials.

[0008] In some embodiments, the first cured adhesive phase is prepared by a first cured adhesive through a crosslinking curing reaction, and the second cured adhesive phase is prepared by a second cured adhesive through a crosslinking curing reaction. The crosslinking curing temperature of the first cured adhesive is n1, and the crosslinking curing temperature of the second cured adhesive is n2, |n1-n2| ≤ 20℃, and at least one of the following conditions is met: (a) the weldable metal material is at least one of silver, silver-clad copper, copper, tin, copper-nickel alloy, and copper-nickel-zinc alloy; (b) the thickness of the carbon-containing conductive layer is 1μm-5μm, and the gold... (c) The thickness of the conductive layer is 2μm-10μm; (d) The metal conductive layer is coated on the outer surface of the carbon-containing conductive layer, or the metal conductive layer is disposed on the outer surface of the carbon-containing conductive layer in at least one of the following shapes: dotted, annular, square, and arc-shaped; (e) The conductive carbon material is at least one of the following: conductive carbon black, carbon nanotubes, graphite, and graphene; (f) The mass ratio of the conductive carbon material to the first curing adhesive is (10-400):100, and the mass ratio of the weldable metal material to the second curing adhesive is (40-1800):100.

[0009] In some embodiments, the first curing adhesive and the second curing adhesive have the same composition, and the first curing adhesive phase and the second curing adhesive phase are obtained by curing at least one of an epoxy resin curing system and a polyurethane curing system.

[0010] In some embodiments, the first curing adhesive and the second curing adhesive have different compositions. The first curing adhesive phase is obtained by curing at least one of an epoxy resin curing system and a polyurethane curing system, and the second curing adhesive phase is obtained by curing at least one of an epoxy resin curing system and a polyurethane curing system.

[0011] In some embodiments, the median D50 grain size of the weldable metal material is ≥0.4 μm.

[0012] To achieve the above objectives, this application provides a method for preparing a piezoelectric ceramic with a double-layer electrode structure, comprising the following steps: S100, coating a carbon paste on the surface of a substrate layer and drying it to obtain a first intermediate substrate, wherein the carbon paste comprises a first curing binder and a conductive carbon material; S200, coating a solderable metal paste on the surface of the first intermediate substrate and drying it to obtain a second intermediate substrate, wherein the solderable metal paste comprises a second curing binder and a solderable metal material; S300, subjecting the second intermediate substrate to a heating treatment to allow the first curing binder and the second curing binder to undergo a curing reaction to obtain a cured substrate; S400, subjecting the cured substrate to a polarization treatment to obtain the piezoelectric ceramic with a double-layer electrode structure.

[0013] In some embodiments, step S300 includes the steps of: heating the second intermediate substrate to allow the first curing adhesive and the second curing adhesive to cure at the same temperature to obtain a cured substrate, wherein the curing temperature is n3, the range of n3 is 120℃-160℃, and n3=0.5(n1+n2)±5℃, the curing time is 7min-60min, and the heating rate is 2℃ / min-30℃ / min; and at least one of the following conditions is met: (a) the drying temperature in step S100 is 80℃-170℃, and the drying time is 5min-30min; (b) the drying temperature in step S200 is 80℃-170℃, and the drying time is 5min-30min.

[0014] To achieve the above objectives, this application provides a piezoelectric element, including a piezoelectric ceramic with a double-layer electrode structure as described above, or a piezoelectric ceramic with a double-layer electrode structure prepared by the aforementioned preparation method, wherein the piezoelectric element is at least one of a piezoelectric buzzer, a piezoelectric atomizing sheet, an ultrasonic transducer, or a piezoelectric sensing sheet.

[0015] To achieve the above objectives, this application provides an electronic device including at least one piezoelectric element as described above.

[0016] Compared with the prior art, the beneficial effects of this application are as follows: This application introduces a carbon-containing conductive layer combined with a substrate layer. The carbon-containing conductive layer includes conductive carbon materials such as conductive carbon black, carbon nanotubes, and graphite, which facilitates the formation of a continuous conductive network. This reduces the interfacial resistance between the carbon-containing conductive layer and the substrate layer while providing a low-resistance conductive substrate for the metal conductive layer. It is understood that conductive carbon materials such as conductive carbon black, carbon nanotubes, and graphite have lower thermal conductivity compared to metal materials. Therefore, during wave soldering or reflow soldering, when high temperatures are transferred from the metal conductive layer, the relatively low thermal conductivity of the carbon-containing conductive layer slows down the heat transfer to the substrate layer, acting as a thermal buffer or delay, and reducing the risk of depolarization. Furthermore, the dense carbon-containing conductive layer also acts as a physical barrier, preventing metal ions from the upper metal conductive layer from migrating into the substrate layer, thereby reducing the risk of short-circuit failure due to electrochemical migration under humid environments and DC electric fields, and improving reliability during long-term use. Building upon this foundation, the metallic conductive layer, comprising weldable metal materials such as silver, silver-clad copper, copper, tin, copper-nickel alloys, and copper-nickel-zinc alloys, provides a weldable surface, thereby enhancing weldability and pull-out strength. On one hand, the metallic materials, bonded by the carbon-based conductive layer, improve overall conductivity and reduce the overall resistance of the piezoelectric ceramic. On the other hand, since the metallic conductive layer covers the outer surface of the carbon-containing conductive layer, it provides physical protection, preventing mechanical wear during subsequent processes or use, further extending the service life of the piezoelectric ceramic and ensuring reliability during long-term use. Detailed Implementation

[0017] The present application will be further described below with reference to specific embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0018] As used herein, the terms “prepared from” and “comprising” are synonymous. The terms “comprising,” “including,” “having,” “containing,” or any other variation thereof, as used herein, are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements and may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0019] When a quantity, concentration, or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range is disclosed as “1 to 5”, the described range should be interpreted as including ranges “1 to 4”, “1 to 3”, “1 to 2 and 4 to 5”, “1 to 3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range includes its endpoints and all integers and fractions within that range.

[0020] Approximate terms used in the specification and claims to modify quantities indicate that the invention is not limited to that specific quantity, but also includes acceptable modifications close to that quantity that do not alter the relevant essential function. Correspondingly, the use of "about," "approximately," etc., to modify a numerical value means that the invention is not limited to that precise value. In some instances, approximate terms may correspond to the precision of the instrument used to measure the value. In this application's specification and claims, scope definitions can be combined and / or interchanged, unless otherwise stated, these scopes include all subscopes contained therein.

[0021] This application provides a piezoelectric ceramic with a double-layer electrode structure, comprising: (a) a substrate layer; (b) a carbon-containing conductive layer disposed on the surface of the substrate layer, the carbon-containing conductive layer comprising a conductive carbon material; and (c) a metal conductive layer disposed between the substrate layer and the metal conductive layer, the metal conductive layer comprising a solderable metal material.

[0022] This application introduces a carbon-containing conductive layer combined with a substrate layer. The carbon-containing conductive layer includes conductive carbon materials such as conductive carbon black, carbon nanotubes, graphite, and graphene, which facilitates the formation of a continuous conductive network. This reduces the interfacial resistance between the carbon-containing conductive layer and the substrate layer while providing a low-resistance conductive substrate for the metal conductive layer. It is understood that conductive carbon materials such as conductive carbon black, carbon nanotubes, and graphite have lower thermal conductivity compared to metal materials. Therefore, during wave soldering or reflow soldering, when high temperatures are transferred from the metal conductive layer, the relatively low thermal conductivity of the carbon-containing conductive layer slows down the heat transfer to the substrate layer, acting as a thermal buffer or delay, and reducing the risk of depolarization. Furthermore, the dense carbon-containing conductive layer also acts as a physical barrier, preventing metal ions from the upper metal conductive layer from migrating into the substrate layer, thereby reducing the risk of short-circuit failure due to electrochemical migration under humid environments and DC electric fields, and improving reliability during long-term use. Building upon this foundation, the metallic conductive layer, comprising weldable metal materials such as silver, silver-clad copper, copper, tin, copper-nickel alloys, and copper-nickel-zinc alloys, provides a weldable surface, thereby enhancing weldability and pull-out strength. On one hand, the bonding between the metallic conductive layer and the carbon-based conductive layer reduces the overall resistance of the piezoelectric ceramic. On the other hand, since the metallic conductive layer covers the outer surface of the carbon-containing conductive layer, it provides physical protection, preventing mechanical wear during subsequent processes or use, further extending the lifespan of the piezoelectric ceramic and ensuring reliability during long-term use.

[0023] In some embodiments, the carbon-containing conductive layer further includes a first cured binder phase, which connects the conductive carbon material to the substrate layer and / or fills between the conductive carbon materials to connect each conductive carbon material; the metal conductive layer further includes a second cured binder phase, which connects the solderable metal material to the carbon-containing conductive layer and / or fills between the solderable metal materials to connect each solderable metal material.

[0024] Understandably, the first cured binder phase fills the spaces between the conductive carbon materials, connecting the dispersed conductive carbon particles into a continuous three-dimensional conductive network. Without the first cured binder phase, the conductive carbon particles would only rely on physical contact, which could easily lead to poor contact during use, resulting in resistance fluctuations or failure. Therefore, the first cured binder phase helps to lock the conductive carbon particles within the conductive pathway, improving the conductivity stability during long-term use.

[0025] Simultaneously, the second cured binder phase fills the spaces between the weldable metal particles, connecting them into a continuous conductive path with low resistance. In other words, the second cured binder phase creates a tight contact between the weldable metal particles, reducing the gaps between them and thus decreasing the resulting resistance. This ensures that the metal conductive layer and the carbon-based conductive layer can effectively combine to achieve their high conductivity.

[0026] In some embodiments, the substrate layer can be at least one of lead zirconate titanate, potassium sodium niobate, barium titanate, sodium bismuth titanate, lithium niobate, and lithium tantalate to meet the needs of various applications. By selecting a suitable substrate layer material, piezoelectric ceramics with high curing degree and high interfacial bonding strength can be obtained.

[0027] In some embodiments, the first cured adhesive phase is obtained by a first cured adhesive through a crosslinking curing reaction, and the second cured adhesive phase is obtained by a second cured adhesive through a crosslinking curing reaction. The crosslinking curing temperature of the first cured adhesive is n1, and the crosslinking curing temperature of the second cured adhesive is n2, where |n1-n2| ≤ 20℃. It is worth noting that since the values ​​of n1 and n2 are not significantly different, meaning there is an overlap in the curing temperature windows of the first and second cured adhesives, the two cured adhesives can simultaneously complete the crosslinking curing reaction in the same heating process. Compared to existing technologies that require step-by-step curing, this application can shorten the production cycle, reduce energy consumption, and improve production efficiency. On the other hand, since the first and second cured adhesives can be cured at the same temperature, if the two layers use the same or compatible resin system and have similar curing temperatures, during the co-curing process, the molecular chains of the cured adhesives at the interface of the two layers are not yet fully crosslinked, and the active groups can react with each other, thereby forming chemical covalent bonds or interpenetrating polymer networks at the interface. In other words, when the cross-linking and curing reaction is completed simultaneously in the same heating process, a network structure is formed at the interface, making the interfacial bonding strength much higher than that of the product obtained by stepwise curing.

[0028] Where the value of |n1-n2| can be 0℃, 1℃, 2℃, 3℃, 4℃, 5℃, 6℃, 7℃, 8℃, 9℃, 10℃, 12℃, 14℃, 16℃, 18℃, or 20℃. It can be understood that when the curing temperature of the first curing adhesive is within a certain range, the value of n1 can be the midpoint of that range; similarly, when the curing temperature of the second curing adhesive is within a certain range, the value of n2 can be the midpoint of that range.

[0029] In some embodiments, the median D50 particle size of the weldable metal material is ≥0.4 μm, specifically, the median D50 particle size of the weldable metal material is ≥1 μm, and more preferably, the median D50 particle size is 1 μm-3 μm. The weldable metal material is at least one of silver, silver-clad copper, copper, tin, copper-nickel alloy, and copper-nickel-zinc alloy; the conductive carbon material is at least one of conductive carbon black, carbon nanotubes, graphite, and graphene. Since the piezoelectric ceramic provided in this application uses a carbon-containing conductive layer as the conductive substrate, micron-sized weldable metal materials with a median D50 particle size ≥0.4 μm can be used in the metal conductive layer, reducing or even eliminating the need for expensive nanoscale metal pastes, further reducing production costs. On the other hand, since the metal conductive layer provides a weldable surface, the carbon-containing conductive layer can slow down the heat conduction rate to the substrate layer, acting as a thermal buffer or thermal delay.

[0030] It is understandable that graphite-based materials exhibit significant differences in thermal conductivity between the transverse and longitudinal directions, and have relatively low thermal conductivity in the direction perpendicular to the substrate layer. Therefore, when the conductive carbon material used in this application is a graphite-based material, heat is difficult to transfer between the carbon-containing conductive layer and the substrate layer in the direction perpendicular to the substrate layer, thereby enhancing thermal shock resistance.

[0031] In existing technologies, to achieve good conductivity and adhesion, the solderable metal material typically requires a particle size in the nanometer range, or even less than 100 nm, for direct printing of metal paste onto the substrate surface. However, the preparation process for nanoscale metal materials is complex and costly. In contrast, this application uses a carbon-containing conductive layer as the conductive substrate, thus allowing the use of solderable metal materials with a larger D50 median particle size in the metal conductive layer. This reduces or even eliminates the need for expensive nanoscale metal paste, further lowering production costs.

[0032] Furthermore, if micron-sized metal paste is directly printed onto the surface of the substrate layer, numerous point contacts rather than surface contacts are formed between the solderable metal particles and the substrate surface. Therefore, electrons must overcome potential barriers at the interface, resulting in significant contact resistance, with resonant impedance even exceeding 800Ω, thereby reducing the electrochemical performance of the piezoelectric ceramic. In contrast, this application forms a conductive network within a carbon-containing conductive layer. Therefore, even when using micron-sized solderable metal materials, the carbon-containing conductive layer still provides a continuous conductive path. In other words, by introducing a carbon-containing conductive layer, micron-sized solderable metal materials can achieve low impedance while reducing production costs.

[0033] The median D50 particle size of the weldable metal material can be 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, 1.5μm, 2μm, 2.5μm, or 3μm. More preferably, the median D50 particle size of the weldable metal material is 2μm.

[0034] In some embodiments, the thickness of the carbon-containing conductive layer is 1μm-5μm, and the thickness of the metal conductive layer is 2μm-10μm. It is understood that the carbon-containing conductive layer can form a strong bond with the substrate layer. When the thickness of the carbon-containing conductive layer is too small, an effective continuous conductive layer cannot be formed; when the thickness of the carbon-containing conductive layer is too large, it reduces physical anchoring and easily leads to localized delamination. On the other hand, the metal conductive layer needs a certain thickness to ensure welding reliability. When the thickness of the metal conductive layer is too small, it is easily damaged during welding, thereby reducing welding strength. When the thickness of the metal conductive layer is too large, the shrinkage stress generated during curing is large, which may lead to warping or interlayer delamination.

[0035] The thickness of the carbon-containing conductive layer can be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, or 5 μm. The thickness of the metal conductive layer can be 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, or 10 μm.

[0036] In some embodiments, the mass ratio of conductive carbon material to the first curing adhesive is (10-400):100, and the mass ratio of weldable metal material to the second curing adhesive is (40-1800):100, such that the solid content in the weldable metal slurry formed by the weldable metal material and the second curing adhesive is 25%-95%. The mass ratio of conductive carbon material to the first curing adhesive can be 10:100, 15:100, 20:100, 25:100, 30:100, 35:100, 40:100, 100:100, 200:100, 300:100, or 400:100. The mass ratio of the weldable metal material to the second curing adhesive can be 40:100, 100:100, 200:100, 300:100, 400:100, 500:100, 600:100, 700:100, 800:100, 900:100, 1000:100, 1100:100, 1200:100, 1300:100, 1500:100, or 1800:100. It should be understood that by selecting appropriate contents of conductive carbon material and weldable metal material, piezoelectric ceramics with good thermal shock resistance and electrical conductivity can be produced.

[0037] In some embodiments, a metallic conductive layer covers the outer surface of the carbon-containing conductive layer, or the metallic conductive layer is disposed on the outer surface of the carbon-containing conductive layer in at least one of the following shapes: dotted, annular, square, or arc-shaped. It should be understood that by adjusting the shape of the metallic conductive layer to suit the shape of the corresponding solder joint, the range of applications is increased.

[0038] In some embodiments, the first and second cured adhesive phases are obtained by curing at least one of an epoxy resin curing system and a polyurethane curing system. Since the first and second cured adhesives have the same composition, their curing temperatures are the same, meaning they can complete the cross-linking curing reaction simultaneously at the same temperature. On the other hand, during co-curing, because the first and second cured adhesives use the same resin system, the molecular chains of the cured adhesives at the interface are not yet fully cross-linked, and the active groups can react with each other, thereby forming chemical covalent bonds or interpenetrating polymer networks at the interface. In other words, when the cross-linking curing reaction is completed simultaneously in the same heating step, a network structure is formed at the interface, resulting in an interfacial bonding strength much higher than that of products obtained through stepwise curing.

[0039] Furthermore, epoxy resin curing systems exhibit strong adhesion, good heat resistance, high mechanical strength, and moderate curing temperature. Moreover, the epoxy resin molecular chain contains polar hydroxyl groups (-OH) and ether bonds (-O-), which can form hydrogen bonds and chemical adsorption with the hydroxyl groups on the surface of the substrate layer. At the same time, epoxy resin has a low curing shrinkage rate, which is beneficial to enhancing the stability of use.

[0040] Polyurethane curing systems have the advantages of good flexibility, good impact resistance, and low temperature resistance, making them suitable for applications that need to withstand large mechanical impacts or low-temperature environments.

[0041] In some embodiments, the first curing adhesive and the second curing adhesive have different compositions. The first curing adhesive phase is prepared by curing at least one of an epoxy resin curing system and a polyurethane curing system, and the second curing adhesive phase is prepared by curing at least one of an epoxy resin curing system and a polyurethane curing system. It should be understood that although the epoxy resin curing system and the polyurethane curing system are not entirely identical in composition, they have partial compatibility due to their similar polarity and hydrogen bonding, as well as similar curing temperature windows. During curing, molecular chains at the interface penetrate into each other's regions, thereby enhancing the interfacial bonding strength.

[0042] In some embodiments, when either the first cured adhesive phase or the second cured adhesive phase is cured by an epoxy resin curing system, the corresponding cured adhesive includes an epoxy resin and a crosslinking agent. The epoxy resin is at least one of bisphenol A type epoxy resin, bisphenol F type epoxy resin, and phenolic epoxy resin. The crosslinking agent is at least one of isocyanate, dicyandiamide, 2-methylimidazole, and 2-ethyl-4-methylimidazole. The mass ratio of epoxy resin to crosslinking agent is 100:(1-150). When either the first cured adhesive phase or the second cured adhesive phase is cured by a polyurethane curing system, the corresponding cured adhesive includes a polyol and an isocyanate component. The polyol is at least one of polypropylene glycol, polytetrahydrofuran ether, polyethylene adipate, polycaprolactone polyol, and polycarbonate diol. The isocyanate component is a blocked isocyanate. The mass ratio of polyol to isocyanate component is 100:(1-150). It is understandable that by selecting appropriate reaction raw materials and their contents, piezoelectric ceramics with high curing degree and high interfacial bonding strength can be obtained.

[0043] The blocked isocyanate is preferably at least one of blocked hexamethylene diisocyanate, blocked isophorone diisocyanate, blocked toluene diisocyanate, and blocked diphenylmethane diisocyanate.

[0044] Understandably, since epoxy resin curing systems require multiple components to work together to promote complete curing, the corresponding curing adhesives can also include curing agents, accelerators, and viscosity-adjusting solvents. Curing agents can be amine curing agents (dicyandiamide (DICY), imidazole curing agents (2-methylimidazolium, 2-ethyl-4-methylimidazolium)), acid anhydride curing agents (methyltetrahydrophthalic anhydride, hexahydrophthalic anhydride), and isocyanate curing agents (blocked hexamethylene diisocyanate, blocked isophorone diisocyanate). Accelerators can be imidazole accelerators (2-methylimidazolium, 2-ethyl-4-methylimidazolium), tertiary amine accelerators (triethylamine, DMP-30), organotin accelerators (dibutyltin dilaurate), and organometallic salt accelerators (zinc acetylacetonate, stannous octoate). It is worth noting that the selection of components in the corresponding curing adhesives is adapted to the curing conditions and the selection of raw materials.

[0045] Since polyurethane curing systems require the combined action of multiple components to promote complete curing, the corresponding curing adhesives may also include catalysts, viscosity-adjusting solvents, coupling agents, and toughening / modifying agents. Catalysts can be components that accelerate the reaction between -NCO and -OH, lowering the curing temperature and shortening the curing time. Coupling agents can be silane coupling agents (KH-550, KH-560). Toughening / modifying agents can be liquid polybutadiene, acrylate oligomers, or epoxy resins. It is worth noting that the selection of components in the corresponding curing adhesives is adapted to the curing conditions and the choice of raw materials.

[0046] It is understandable that when the cured system is a mixture of epoxy resin and polyurethane, the content of the components in the system can be adjusted to suit the curing conditions and raw materials.

[0047] In some embodiments, the median D50 particle size of the weldable metal material is ≥0.4μm, the initial static capacitance of the piezoelectric ceramic is ≥12.5nF, the initial resonant impedance is ≤800Ω, and the static capacitance of the piezoelectric ceramic after welding at 270℃ for 5 seconds is ≥12nF, with a resonant impedance ≤800Ω. The piezoelectric ceramic prepared in this application also exhibits good heat resistance, stability, and conductivity during hot working.

[0048] This application provides a method for preparing a piezoelectric ceramic with a double-layer electrode structure, comprising the following steps: S100, coating a carbon slurry onto the surface of a substrate layer and drying it to obtain a first intermediate substrate, wherein the carbon slurry includes a first curing binder and a conductive carbon material; S200, coating a solderable metal slurry onto the surface of the first intermediate substrate and drying it to obtain a second intermediate substrate, wherein the solderable metal slurry includes a second curing binder and a solderable metal material; S300, subjecting the second intermediate substrate to a heating treatment to allow the first curing binder and the second curing binder to undergo a curing reaction, thereby obtaining a cured substrate; S400, subjecting the cured substrate to a polarization treatment to obtain a piezoelectric ceramic with a double-layer electrode structure. It should be understood that by selecting appropriate preparation steps and parameters, piezoelectric ceramics with high curing degree and high interfacial bonding strength can be obtained.

[0049] In some embodiments, step S300 includes the following steps: heating the second intermediate substrate to allow the first curing adhesive and the second curing adhesive to cure at the same temperature, thereby obtaining a cured substrate. The curing temperature is n3, where n3 ranges from 120℃ to 160℃, and n3 = 0.5(n1 + n2) ± 5℃. The curing time is 7 min to 60 min, and the heating rate is 2℃ / min to 30℃ / min. At least one of the following conditions must be met: (a) the drying temperature in step S100 is 80℃ to 170℃, and the drying time is 5 min to 30 min; (b) the drying temperature in step S200 is 80℃ to 170℃, and the drying time is 5 min to 30 min. It should be understood that by selecting appropriate preparation steps and parameters, piezoelectric ceramics with high curing degree and high interfacial bonding strength can be obtained.

[0050] Wherein, n3 can be 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, 150℃, 155℃, or 160℃, the curing time can be 7min, 10min, 20min, 25min, 30min, 35min, 40min, 45min, 50min, 55min, or 60min, and the heating rate can be 2℃ / min, 2.5℃ / min, 3℃ / min, 3.5℃ / min, 4℃ / min, 4.5℃ / min, 5℃ / min, 10℃ / min, 20℃ / min, or 30℃ / min.

[0051] In some embodiments, in step S400, the polarization conditions can be adjusted to suit the thickness of the cured substrate. For example, for a 0.1 mm thick cured substrate in air, the polarization voltage is 300 V and the polarization time is 2 seconds. It should be understood that by selecting appropriate preparation steps and parameters, piezoelectric ceramics with high curing degree and high interfacial bonding strength can be obtained.

[0052] This application provides a piezoelectric element, including a piezoelectric ceramic with a double-layer electrode structure as described above, or a piezoelectric ceramic with a double-layer electrode structure prepared by the aforementioned method. The piezoelectric element is at least one of a piezoelectric buzzer, a piezoelectric atomizing plate, an ultrasonic transducer, or a piezoelectric sensing plate. By using the piezoelectric ceramic provided in this application in the piezoelectric element, it is beneficial to improve the thermal shock resistance of the piezoelectric element, reduce the risk of depolarization, reduce production costs, and further enhance the reliability during long-term use.

[0053] This application provides an electronic device including at least one piezoelectric element as described above. By using the piezoelectric element provided in this application in the electronic device, it is beneficial to improve the thermal shock resistance of the electronic device, reduce the risk of depolarization, reduce production costs, and further enhance the reliability during long-term use.

[0054] Example A piezoelectric ceramic and its preparation method, the preparation method comprising: Step (1) Provide a lead zirconate titanate with a diameter of 9.5 mm and a thickness of 0.1 mm as a substrate layer. Coat both surfaces of the substrate layer with carbon paste and dry to obtain a first intermediate substrate. The carbon paste is a first curing binder and conductive carbon black. The mass ratio of conductive carbon black to the first curing binder is 300:100. After curing, the first curing binder is an epoxy curing system. Step (2) Coat the surface of the first intermediate substrate with a weldable metal paste and dry it to obtain the second intermediate substrate. The weldable metal paste is a second curing adhesive and silver-coated copper with a D50 median particle size of 2 micrometers. The mass ratio of silver-coated copper to the second curing adhesive is 600:100. The second curing adhesive is an epoxy curing system after curing. Step (3) The second intermediate substrate is heated to allow the first curing adhesive and the second curing adhesive to cure at the same temperature. The first curing adhesive phase is obtained by curing and crosslinking the first curing adhesive, and the second curing adhesive phase is obtained by curing and crosslinking the second curing adhesive. The curing time is 40 min, the heating rate is 5℃ / min, and the curing temperature is 150℃ to obtain the cured substrate. Step (4) In an air atmosphere, the cured substrate is polarized with a polarization voltage of 300V and a polarization time of 2 seconds to obtain a piezoelectric ceramic with a double-layer electrode structure.

[0055] In the prepared piezoelectric ceramic, a 3-micrometer-thick carbon-containing conductive layer is coated on the substrate layer, which includes conductive carbon black and a first cured binder phase. A 7-micrometer-thick metal conductive layer is provided on the carbon-containing conductive layer, which consists of silver-coated copper and a second cured binder phase.

[0056] Comparative Example 1 The difference between Comparative Example 1 and the Example is that the preparation method lacks step (2).

[0057] Comparative Example 2 The difference between Comparative Example 2 and the Example is that the preparation method lacks step (1).

[0058] Comparative Example 3 A lead zirconate titanate layer with a diameter of 9.5 mm and a thickness of 0.1 mm was provided as the substrate layer. A high-temperature paste containing 50% nano-sized silver was printed on the substrate layer, and the temperature was raised to 800°C and maintained for 30 minutes, followed by natural cooling to obtain a cured substrate. The cured substrate was then polarized in an air atmosphere with a polarization voltage of 300V and a polarization time of 2 seconds to obtain a piezoelectric ceramic.

[0059] Fifteen examples were prepared and labeled as Examples 1-15. All piezoelectric ceramic sheets prepared in Comparative Examples 1-3 were compared with those prepared in Comparative Examples 1-3. All the prepared piezoelectric ceramic sheets were then bonded with a round copper sheet with a diameter of 12.5 mm and a thickness of 0.9 mm using epoxy resin.

[0060] The thermal shock test procedure is as follows: The initial electrostatic capacitance and resonant frequency of each piezoelectric ceramic sample are measured using an LCR bridge. A soldering iron is heated to 300℃ and stabilized for 2 minutes. The soldering iron tip is designed to be circular with a diameter of 4mm. The tip is applied to the piezoelectric ceramic sample with a pressure of 0.5-1N and held for 10 seconds before being removed. The sample is allowed to cool naturally to room temperature. After the sample has completely cooled, the electrostatic capacitance and resonant frequency of each piezoelectric ceramic sample are measured again using an LCR bridge. Finally, the number of depolarized piezoelectric ceramic samples is counted, and the proportion of samples failing the depolarization test is calculated.

[0061] Table 1: Electrochemical Performance Test Table for Piezoelectric Ceramics

[0062] By comparing Examples 1-15 and Comparative Examples 1-3, it can be seen that the single-layer electrode structure in Comparative Examples 1-3 has poor initial performance and cannot withstand thermal shock at all due to high interface resistance or inability to be welded.

[0063] The basic principles, main features, and advantages of this application have been described above. Those skilled in the art should understand that this application is not limited to the above embodiments. The embodiments and descriptions in the specification are merely the principles of this application. Various changes and modifications can be made to this application without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claims. The scope of protection claimed by this application is defined by the appended claims and their equivalents.

Claims

1. A piezoelectric ceramic having a double-layer electrode structure, characterized by, include: (a) Substrate layer; (b) A carbon-containing conductive layer, wherein the carbon-containing conductive layer is disposed on the surface of the substrate layer, and the carbon-containing conductive layer comprises a conductive carbon material; (c) A metal conductive layer, wherein the carbon-containing conductive layer is disposed between the substrate layer and the metal conductive layer, and the metal conductive layer comprises a solderable metal material.

2. The piezoelectric ceramic with a double-layer electrode structure according to claim 1, characterized in that, The carbon-containing conductive layer further includes a first cured binder phase, which connects the conductive carbon material to the substrate layer and / or fills between the conductive carbon materials to connect each of the conductive carbon materials; the metal conductive layer further includes a second cured binder phase, which connects the weldable metal material to the carbon-containing conductive layer and / or fills between the weldable metal materials to connect each of the weldable metal materials.

3. The piezoelectric ceramic with a double-layer electrode structure according to claim 2, characterized in that, The first cured adhesive phase is obtained by cross-linking and curing a first cured adhesive, and the second cured adhesive phase is obtained by cross-linking and curing a second cured adhesive. The cross-linking and curing temperature of the first cured adhesive is n1, and the cross-linking and curing temperature of the second cured adhesive is n2. |n1-n2| ≤ 20℃, and satisfies at least one of the following conditions: (a) The weldable metal material is at least one of silver, silver-plated copper, copper, tin, copper-nickel alloy, and copper-nickel-zinc alloy; (b) The thickness of the carbon-containing conductive layer is 1 μm-5 μm, and the thickness of the metal conductive layer is 2 μm-10 μm; (c) The metal conductive layer covers the outer surface of the carbon-containing conductive layer, or the metal conductive layer is disposed on the outer surface of the carbon-containing conductive layer in at least one of the following shapes: dotted, annular, square, or arc-shaped. (d) The conductive carbon material is at least one of conductive carbon black, carbon nanotubes, graphite, and graphene; (e) The mass ratio of the conductive carbon material to the first curing adhesive is (10-400):100, and the mass ratio of the weldable metal material to the second curing adhesive is (40-1800):

100.

4. The piezoelectric ceramic with a double-layer electrode structure according to claim 3, characterized in that, The first curing adhesive and the second curing adhesive have the same composition, and the first curing adhesive phase and the second curing adhesive phase are obtained by curing at least one of an epoxy resin curing system and a polyurethane curing system.

5. The piezoelectric ceramic with a double-layer electrode structure according to claim 3, characterized in that, The first cured adhesive and the second cured adhesive have different compositions. The first cured adhesive phase is prepared by curing at least one of an epoxy resin curing system and a polyurethane curing system, and the second cured adhesive phase is prepared by curing at least one of an epoxy resin curing system and a polyurethane curing system.

6. The piezoelectric ceramic with a double-layer electrode structure according to any one of claims 1-5, characterized in that, The median D50 particle size of the weldable metal material is ≥0.4μm.

7. A method for preparing a piezoelectric ceramic with a double-layer electrode structure, characterized in that, Including the following steps: S100. Coating a carbon paste onto the surface of a substrate layer and drying it to obtain a first intermediate substrate, wherein the carbon paste comprises a first curing binder and a conductive carbon material; S200: Coat the surface of the first intermediate substrate with a weldable metal paste and dry it to obtain a second intermediate substrate. The weldable metal paste includes a second curing adhesive and a weldable metal material. S300: The second intermediate substrate is heated to allow the first curing adhesive and the second curing adhesive to undergo a curing reaction, thereby obtaining a cured substrate. S400. The cured substrate is subjected to polarization treatment to obtain the piezoelectric ceramic with a double-layer electrode structure.

8. The preparation method according to claim 7, characterized in that, Step S300 includes the following steps: heating the second intermediate substrate to allow the first and second curing adhesives to cure at the same temperature, thereby obtaining a cured substrate. The curing temperature is n3, which ranges from 120℃ to 160℃, and n3 = 0.5(n1 + n2) ± 5℃. The curing time is 7 min to 60 min, and the heating rate is 2℃ / min to 30℃ / min. The process also satisfies at least one of the following conditions: (a) The drying temperature in step S100 is 80℃-170℃, and the drying time is 5min-30min; (b) The drying temperature in step S200 is 80℃-170℃ and the drying time is 5min-30min.

9. A piezoelectric element, characterized in that, Includes the piezoelectric ceramic with a double-layer electrode structure as described in any one of claims 1 to 6, or the piezoelectric ceramic with a double-layer electrode structure prepared by the preparation method described in any one of claims 7 to 8, wherein the piezoelectric element is at least one of a piezoelectric buzzer, a piezoelectric atomizing sheet, an ultrasonic transducer, or a piezoelectric sensing sheet.

10. An electronic device, characterized in that, It includes at least one piezoelectric element as described in claim 9.

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