Low-silver composite electrode for piezoelectric ceramics, and preparation method and application thereof

Abstract

The present application relates to the technical field of piezoelectric ceramic electrode, and particularly relates to a low-silver composite electrode for piezoelectric ceramic, a preparation method and application thereof. The low-silver composite electrode for piezoelectric ceramic is arranged on at least one electrode forming surface of a piezoelectric ceramic substrate, and comprises a first layer of non-precious metal electrode, an outer protective layer arranged on the surface of the first layer of non-precious metal electrode, and an optional second layer of silver-based solderable electrode arranged on the surface of the first layer of non-precious metal electrode; and the outer protective layer covers at least the exposed area and / or the edge area of the first layer of non-precious metal electrode which are not covered by the second layer of silver-based solderable electrode. In the present application, the first layer of non-precious metal electrode is used to bear the main charge transmission area, the outer protective layer is used to prevent the erosion of the first layer of non-precious metal electrode by oxygen, water vapor, cleaning liquid, seawater medium, oil medium or high-temperature humid atmosphere, and the second layer of silver-based solderable electrode is used to form a solderable, crimpable, wire-connectable or terminal-connectable electrical connection area when needed. The present application cooperatively designs the area, pattern and lap joint relationship of the first layer of non-precious metal electrode, the outer protective layer and the optional second layer of silver-based solderable electrode, thereby greatly reducing the amount of precious metal while maintaining the electrical performance, soldering performance and long-term reliability of the piezoelectric ceramic.

Description

Technical Field

[0001] This invention relates to the field of piezoelectric ceramic electrode technology, and in particular to a low-silver composite electrode for piezoelectric ceramics, its preparation method, and its application. Background Technology

[0002] Piezoelectric ceramics are functional ceramic materials that utilize the direct and inverse piezoelectric effects to achieve the interconversion of mechanical energy and electrical energy. Lead zirconate titanate-based piezoelectric ceramics and their modified systems have long been used in ultrasonic cleaning, underwater sonar, ultrasonic welding, ultrasonic atomization, piezoelectric sound generation, industrial detection, sensing, and actuation due to their high piezoelectric constant, large electromechanical coupling coefficient, mature technology, and wide applicable frequency range. Piezoelectric ceramic elements typically require the formation of conductive electrodes on the surface of the sintered ceramic substrate, through which a polarization electric field or working excitation electric field is applied. The electrodes not only provide conductivity but also affect the welding reliability, environmental stability, vibration fatigue life, and long-term impedance stability of the device.

[0003] Currently, silver electrodes are the primary surface electrodes for piezoelectric ceramics. Common preparation methods include screen printing silver paste followed by sintering, spraying silver paste followed by sintering, vacuum deposition of silver layers, or curing with silver-containing conductive pastes. Silver electrodes possess advantages such as good conductivity, good solderability, a wide process window, and good compatibility with most piezoelectric ceramics, thus maintaining a dominant position in the piezoelectric ceramics industry for a long time. However, silver is a precious metal, and its raw material price is high and easily affected by market fluctuations. For large-area piezoelectric ceramic sheets, thick sheets, ring sheets, tubular transducers, as well as underwater acoustic and industrial ultrasonic transducers, the electrode area is large, resulting in significant silver paste consumption and sintering losses. Electrode costs constitute a significant proportion of the device production cost. With silver prices remaining high for a long time and facing the risk of further increases, traditional all-silver electrodes are continuously pushing up the manufacturing cost of piezoelectric ceramic components, thereby restricting their application in large-scale ultrasonic equipment, low-cost sensor arrays, underwater acoustic arrays, and mass-produced industrial transducers.

[0004] To reduce precious metal consumption, the industry has attempted to replace silver electrodes with low-cost electrode materials such as aluminum, copper, nickel, and graphite. Aluminum electrodes, in particular, offer advantages such as low material cost, low density, high conductivity, and abundant availability, theoretically making them suitable for large-area piezoelectric ceramic electrodes. However, aluminum readily forms a dense alumina film in air, which has high resistance and hinders subsequent welding. When aluminum electrodes operate long-term in humid, high-temperature, seawater, underwater acoustic, or ultrasonic cleaning fluid environments, the surface oxide film and interface corrosion may continue to thicken or spread along the edges, leading to a reduction in the effective conductive area of ​​the electrode, increased contact impedance, and uneven distribution of polarization and driving electric field. Ultimately, this results in piezoelectric ceramic performance degradation, increased device heating, decreased output acoustic power, or solder joint failure.

[0005] Existing technologies disclose methods for preparing metallic aluminum electrodes on PZT piezoelectric ceramic sheets. These methods improve the bonding strength between the aluminum electrode and the ceramic by adjusting the low-melting-point lead-free glass powder and antioxidants in the aluminum paste formulation. They also propose single-sided aluminum electrodes, double-sided aluminum electrodes, and aluminum electrodes with a small-area silver electrode welding zone. While these technologies demonstrate that aluminum electrodes can reduce costs to some extent, their core focus remains primarily on the aluminum paste formulation and aluminum electrode sintering process. They lack a systematic design for addressing the oxidation propagation of exposed aluminum electrode areas under long-term exposure to air, humidity, cleaning solutions, seawater, or high-temperature environments, as well as the synergistic relationship between electrode area distribution, silver zone morphology, and protective layer coverage strategies.

[0006] On the other hand, while placing silver pads only locally on the aluminum electrodes can solve localized soldering problems, the large-area exposure of the aluminum layer can still become an entry point for environmental corrosion. For underwater sonar and ultrasonic cleaning transducers, components are typically subjected to the combined effects of mechanical vibration, alternating electric fields, temperature rise, liquid media, water vapor infiltration, and assembly stress. If oxidation, corrosion, or interface peeling occurs at the edges or micropores of the aluminum layer, its effects may extend from the local area to the effective electrode area, causing long-term drift in electrode sheet resistance, dielectric loss, resonant impedance, and capacitance. Therefore, simply replacing silver with aluminum cannot meet the industrial application requirements for high-reliability piezoelectric devices.

[0007] Therefore, a new piezoelectric ceramic electrode technology solution is urgently needed. Summary of the Invention

[0008] The purpose of this invention is to provide a low-silver composite electrode for piezoelectric ceramics and its preparation method, overcoming the technical defects of traditional silver electrodes, such as high cost, easy oxidation and difficult soldering of single aluminum electrodes, and insufficient protection of large-area aluminum layers by local silver pads. Through the coordinated design of the area, pattern, and overlap relationship of the first-layer non-precious metal electrode, the outer protective layer, and the optional second-layer silver-based solderable electrode, this invention significantly reduces the amount of precious metals used while maintaining the electrical performance, solderability, and long-term reliability of piezoelectric ceramics. This invention belongs to the field of piezoelectric ceramic electrodes, piezoelectric transducers, and functional ceramic metallization technology, specifically relating to a low-silver composite electrode for piezoelectric ceramics, a piezoelectric ceramic element containing this composite electrode, its preparation method, and its applications in underwater acoustics, ultrasonic cleaning, ultrasonic welding, and ultrasonic sludge purification. More specifically, this invention relates to a composite electrode structure formed on the surface of a piezoelectric ceramic substrate, in which a non-precious metal electrode forms the main conductive area, a silver or silver alloy electrode forms the local solderable area, and a carbon-based or other protective layer serves as a barrier against oxidation and water vapor erosion.

[0009] To achieve the above objectives, the present invention provides the following solution: One of the technical solutions of the present invention is to provide a low-silver composite electrode for piezoelectric ceramics, which is disposed on at least one electrode forming surface of a piezoelectric ceramic substrate, comprising: a first-layer non-precious metal electrode, an outer protective layer disposed on the surface of the first-layer non-precious metal electrode, and a second-layer silver-based solderable electrode optionally disposed on the surface of the first-layer non-precious metal electrode; the outer protective layer at least covers the exposed area and / or edge area of ​​the first-layer non-precious metal electrode that is not covered by the second-layer silver-based solderable electrode.

[0010] In this invention, the first-layer non-precious metal electrode bears the main charge transport area, while the outer protective layer protects against corrosion from oxygen, water vapor, cleaning fluid, seawater, oil, or high-temperature and humid atmospheres. The second-layer silver-based solderable electrode forms an electrical connection area that can be soldered, crimped, wire-connected, or terminal-connected when needed. This invention, through the coordinated design of the area, pattern, and overlap of the first-layer non-precious metal electrode, the outer protective layer, and the optional second-layer silver-based solderable electrode, significantly reduces the amount of precious metals used while maintaining the electrical performance, solderability, and long-term reliability of piezoelectric ceramics.

[0011] Optionally, the secondary silver-based solderable electrode is disposed in a partial or complete area of ​​the primary non-precious metal electrode. Preferably, the secondary silver-based solderable electrode is disposed in a local area of ​​the primary non-precious metal electrode, wherein the local area is an edge area, a central area, or a dispersed area; Optionally, the projected shape of the secondary silver-based solderable electrode is any combination of one or more of the following: circular, elliptical, polygonal, annular, semi-annular, fan-shaped, strip-shaped, grid-shaped, island-shaped, dot matrix-shaped, interdigitated, end pad-shaped, and edge pad-shaped. Preferably, the polygon is a square, rectangle, rhombus, and / or triangle; Preferably, the secondary silver-based solderable electrodes are distributed locally; More preferably, the distribution of the secondary silver-based solderable electrodes can be a centrally concentrated distribution, an edge-concentrated distribution, a multiple pad-dispersed distribution, a symmetrical distribution along the polarization direction, or an asymmetrical distribution along the device mounting terminals. Preferably, the outer protective layer is disposed on the area of ​​the first non-precious metal electrode not covered by the second silver-based solderable electrode, the non-soldering area of ​​the second silver-based solderable electrode, and the area adjacent to both. Preferably, the projected shape of the outer protective layer is a full-coverage film that completely covers the electrode forming surface or a partial-coverage film; More preferably, the projected shape of the outer protective layer is a continuous film covering the exposed area of ​​the first layer non-precious metal electrode, an annular film covering the exposed area of ​​the first layer non-precious metal electrode and avoiding the welding window of the second layer silver-based solderable electrode, a continuous film covering the non-welding areas of the first layer non-precious metal electrode and the second layer silver-based solderable electrode, a strip covering film, a dot matrix covering film, or an edge sealing film. Optionally, based on the geometric area of ​​the electrode forming surface, the projection coverage of the first non-precious metal electrode is 0.1% to 100%, the projection coverage of the second silver-based solderable electrode is 0% to 100%, the projection coverage of the outer protective layer is 0% to 100%, and when the projection coverage of the second silver-based solderable electrode is 0%, the projection coverage of the outer protective layer is greater than 0%.

[0012] Optionally, the first non-precious metal electrode is one or more composite layers selected from aluminum electrode, aluminum alloy electrode, copper electrode, copper alloy electrode, nickel electrode, nickel alloy electrode, tin electrode, tin alloy electrode, zinc electrode, zinc alloy electrode, indium electrode, and indium alloy electrode. Preferably, the first non-precious metal electrode is an aluminum electrode or an aluminum alloy electrode with an aluminum content of not less than 50 wt%. Optionally, the secondary silver-based solderable electrode is one of the following: silver electrode, silver-palladium alloy electrode, silver-platinum alloy electrode, silver-copper alloy electrode, silver-nickel alloy electrode, silver paste sintering electrode containing glass binder phase, low-temperature curing silver paste electrode, silver-coated metal powder electrode, or silver-based composite conductive electrode. Optionally, the silver element in the secondary silver-based solderable electrode is 5% to 100% based on the mass of the conductive solid phase of the layer, preferably 20% to 100%; in order to maintain the surface electrical connection performance required for soldering, brazing, ultrasonic welding, conductive adhesive bonding or flexible terminal crimping while reducing the amount of silver used.

[0013] Optionally, the outer protective layer includes a carbon-based conductive protective layer; preferably, the outer protective layer is one or more composite layers selected from carbon paste sintering layer, carbon paste curing layer, graphite conductive layer, carbon black conductive layer, graphene conductive layer, carbon nanotube conductive layer, conductive polymer protective layer, glass phase protective layer, ceramic phase protective layer, organosilicon moisture-proof layer and epoxy moisture-proof layer. Preferably, the sheet, particle, or network structure of the carbon-based conductive protective layer covers the exposed surface of the first non-precious metal electrode, thereby slowing down the thickening of the oxide film on the non-precious metal surface and the spread of water vapor along the interface.

[0014] Optionally, the piezoelectric ceramic matrix is ​​one or more composite ceramics selected from lead zirconate titanate-based piezoelectric ceramics, modified lead zirconate titanate-based piezoelectric ceramics, lead titanate-based piezoelectric ceramics, lead metaniobate-based piezoelectric ceramics, lead magnesium niobate titanate-based piezoelectric ceramics, barium titanate-based piezoelectric ceramics, potassium sodium niobate-based lead-free piezoelectric ceramics, sodium bismuth titanate-based lead-free piezoelectric ceramics, and silver niobate-based piezoelectric ceramics. Preferably, the piezoelectric ceramic matrix includes one of P8, P4, P5, P5A, P5H or modified materials thereof.

[0015] Preferably, a transition bonding phase is provided between the first-layer non-precious metal electrode and the piezoelectric ceramic substrate; Optionally, the transition bonding phase includes low-melting-point lead-free glass, borosilicate glass, bismuth borosilicate glass, zinc borosilicate glass, phosphate glass, titanate glass, alumina micropowder, zinc oxide micropowder, bismuth oxide micropowder, silicon oxide micropowder, titanium oxide micropowder, or an inorganic bonding phase that can improve the adhesion strength between the electrode and the ceramic interface.

[0016] Preferably, the secondary silver-based solderable electrode at least covers the area on the primary non-precious metal electrode where solder leads, solder terminals, solder metal housings, connecting conductive springs, connecting conductive adhesives, connecting spring pins, and / or connecting external circuits are required. Preferably, the overlap width between the secondary silver-based solderable electrode and the primary non-precious metal electrode is not less than 0.05 mm, and more preferably 0.2 mm to 10 mm, in order to reduce the contact resistance of the overlap area and suppress local current concentration. Preferably, the outer protective layer forms a sealing structure at the edge of the first non-precious metal electrode; Preferably, the sealing structure covers the outer periphery, hole edges, notch edges, cut edges, chamfered edges, and / or interface edges adjacent to the piezoelectric ceramic substrate of the first-layer non-precious metal electrode. The sealing structure serves to prevent oxygen and water vapor from entering the interface between the first-layer non-precious metal electrode and the piezoelectric ceramic substrate from the edges.

[0017] Preferably, the low-silver composite electrode is disposed on one main surface, two opposite main surfaces, side surface, end face, inner hole surface, outer cylindrical surface, arc surface and / or irregular surface of the piezoelectric ceramic substrate; when the low-silver composite electrode is disposed on both opposite main surfaces of the piezoelectric ceramic substrate, the coverage, shape and distribution of the first non-precious metal electrode, the second silver solderable electrode and the outer protective layer on the two surfaces can be the same or different.

[0018] Preferably, the thickness of the first non-precious metal electrode is 0.05 micrometers to 80 micrometers, and more preferably 1 micrometer to 35 micrometers; Preferably, the thickness of the secondary silver-based solderable electrode is 0.05 micrometers to 50 micrometers, and more preferably 1 micrometer to 20 micrometers; Preferably, the thickness of the outer protective layer is from 0.05 micrometers to 100 micrometers, and more preferably from 1 micrometer to 40 micrometers.

[0019] In this invention, stable interfaces are formed between the layers through sintering, molten glass bonding, mechanical interlocking, intermetallic diffusion, conductive adhesive bonding, surface activation bonding, or a combination of the above.

[0020] Preferably, the coverage ratio of the first non-precious metal electrode, the second silver-based solderable electrode, and the outer protective layer is any one of Schemes 1 to 5: Option 1: The first-layer non-precious metal electrode is an all-aluminum electrode with a coverage of 100%, the second-layer silver-based solderable electrode has a coverage of 0.1% to 100%, and the outer protective layer is a carbon-based conductive protective layer with a coverage of 0.1% to 100%. Preferably, the second-layer silver-based solderable electrode has a coverage of 1% to 20%, the outer protective layer is a carbon-based conductive protective layer with a coverage of 80% to 99%, and the carbon-based conductive protective layer covers the area of ​​the all-aluminum electrode surface not covered by the second-layer silver-based solderable electrode, and overlaps with the edge of the silver electrode by 0.2 mm to 2 mm.

[0021] Option 2: The first layer of non-precious metal electrode is an all-aluminum electrode with a coverage of 100%, the second layer of silver-based solderable electrode has a coverage of 0.1% to 100%, and the outer protective layer is an edge-sealing protective layer or a partial protective layer with a coverage of 0.1% to 20%; thereby forming a low-silver electrode structure with a local solderable silver area and edge-sealing protection.

[0022] Option 3: The first-layer non-precious metal electrode is an all-aluminum electrode with 100% coverage; the second-layer silver-based solderable electrode has 0% coverage; and the outer protective layer is a carbon-based conductive protective layer with 0.1% to 100% coverage; thus forming a silver-free, anti-oxidation electrode structure. Preferably, the carbon-based conductive protective layer has a coverage of 80% to 100%, more preferably 90% to 100%.

[0023] Option 4: The first-layer non-precious metal electrode is an aluminum electrode with a coverage of 0.1% to 100%, but not 100%; the second-layer silver-based solderable electrode has a coverage of 0.1% to 100%; and the outer protective layer is a carbon-based conductive protective layer with a coverage of 100%. This forms a low-silver composite electrode structure with full surface protection. Preferably, the first-layer non-precious metal electrode has a coverage of not less than 80%, the second-layer silver-based solderable electrode has a coverage of 5% to 10%, and is completely located within and overlaps with the coverage area of ​​the first-layer non-precious metal electrode; the carbon-based conductive protective layer has a coverage of 100%.

[0024] Option 5: The first-layer non-precious metal electrode is an aluminum electrode with a coverage of 0.1% to 100%, the second-layer silver-based solderable electrode has a coverage of 0.1% to 100%, and the outer protective layer is a carbon-based conductive protective layer with a coverage of 0.1% to 100%, but not 100%. This forms a low-silver composite electrode structure with localized protection, localized solderability, or localized drag reduction. Preferably, the first-layer non-precious metal electrode has a coverage of 100%, the second-layer silver-based solderable electrode has a coverage of 5%, and the carbon-based conductive protective layer has a coverage of 30% to 70%.

[0025] More preferably, in Scheme 1 to Scheme 5, the outer protective layer preferably avoids the welding window of the secondary silver-based solderable electrode.

[0026] The second technical solution of the present invention provides a method for preparing the above-mentioned low-silver composite electrode for piezoelectric ceramics, comprising the following steps: Using the first-layer non-precious metal electrode precursor as raw material, a first-layer non-precious metal electrode precursor layer is prepared on the surface of the piezoelectric ceramic substrate to be polarized. After drying, sintering, curing, heat treatment and / or deposition post-treatment, a piezoelectric ceramic containing the first-layer non-precious metal electrode is obtained. And / or, using a secondary silver-based solderable electrode precursor as raw material, a secondary silver-based solderable electrode precursor layer is prepared on the surface of the piezoelectric ceramic containing the primary non-precious metal electrode, and the piezoelectric ceramic containing the secondary silver-based solderable electrode is obtained by drying, sintering, curing and / or heat treatment. And / or, using an outer protective layer precursor as raw material, an outer protective layer precursor layer is prepared on the surface of the piezoelectric ceramic containing a secondary silver-based solderable electrode, and the piezoelectric ceramic containing the outer protective layer is obtained by drying, sintering, curing and / or heat treatment, which is the low silver composite electrode for piezoelectric ceramics.

[0027] Optionally, the preparation methods of the first non-precious metal electrode precursor layer, the second silver-based solderable electrode precursor layer, and the outer protective layer precursor layer are independently selected from any one or a combination of multiple methods from screen printing, pad printing, spraying, brushing, scraping, dispensing, dip coating, spin coating, roll coating, laser transfer, thermal spraying, vacuum evaporation, magnetron sputtering, electroplating, chemical plating, and aerosol spraying. Preferably, before preparing the first non-precious metal electrode precursor layer, the surface of the piezoelectric ceramic substrate to be electrodeified is subjected to grinding, polishing, cleaning, drying and surface activation treatment. Preferably, the method further includes the step of electrically polarizing the piezoelectric ceramic containing the outer protective layer; Preferably, the parameters of the electric field polarization are: polarization electric field strength of 0.5 kV / mm to 6 kV / mm, polarization temperature of 20°C to 200°C, and polarization medium of air, silicone oil, transformer oil, water-based medium or inert atmosphere; Preferably, after polarization, soldering, brazing, conductive adhesive bonding, metal spring pressing, riveting, or terminal welding are performed on the secondary silver-based solderable electrode.

[0028] Preferably, the first non-precious metal electrode is formed by screen printing aluminum paste and then sintering it at 500°C to 750°C. Preferably, the secondary silver-based solderable electrode is formed by screen printing silver paste or silver alloy paste and then sintering it at 450°C to 800°C. Preferably, the outer protective layer is formed by carbon paste screen printing followed by curing or sintering at 120°C to 650°C.

[0029] Optionally, the sintering process is independently selected from one co-firing, two firings, three firings, firing before curing, curing before polarization, or polarization followed by local application of a protective layer; when multiple firings are used, the sintering temperature of the subsequent layers is not higher than the temperature that could cause severe oxidation, melt flow, interface peeling, or depolarization of the previous electrode layer.

[0030] Preferably, the first non-precious metal electrode is an aluminum electrode, which is formed by sintering an electrode slurry containing aluminum powder. The raw materials of the electrode slurry containing aluminum powder include metallic aluminum powder, inorganic binder, organic carrier, dispersant, leveling agent, defoamer, and antioxidant. The antioxidant includes one or more of the following: boron powder, red phosphorus, phosphate, boron-containing compound, silicon-containing compound, antioxidant glass phase, or additives that can reduce the oxidation degree of aluminum powder during sintering.

[0031] The third technical solution of the present invention provides the application of the above-mentioned low-silver composite electrode for piezoelectric ceramics in the preparation of devices, wherein the devices are ultrasonic transducers, underwater acoustic transducers, ultrasonic cleaning transducers, ultrasonic welding transducers, ultrasonic sludge purification transducers, atomizing plates, buzzer plates, buzzers, piezoelectric sensors, piezoelectric actuators, piezoelectric transformers, piezoelectric motors, medical ultrasonic devices, non-destructive testing probes, flow meter transducers, or marine acoustic devices.

[0032] The fourth technical solution of the present invention provides a piezoelectric ceramic element, comprising a piezoelectric ceramic substrate and a low-silver composite electrode for piezoelectric ceramics disposed on at least one surface of the piezoelectric ceramic substrate. After polarization, the piezoelectric ceramic element can be excited by applying an electric field or outputting piezoelectric charge through the low-silver composite electrode; the secondary silver-based solderable electrode serves as a lead wire soldering area, a terminal connection area, or an elastic contact area; and the outer protective layer serves as a protection zone against oxidation, water vapor, media erosion, or pollution.

[0033] Optionally, the piezoelectric ceramic element is a circular plate, square plate, ring plate, tubular body, columnar body, spherical cap, arc surface body, thick plate, thin plate, stacked plate or irregularly shaped plate; Preferably, the first non-precious metal electrode of the low-silver composite electrode forms a continuous conductive area within the effective vibration region, the second silver-based solderable electrode is positioned at a location that does not significantly reduce the effective vibration area, and the outer protective layer is positioned at a location that does not significantly increase mechanical damping or significantly change the resonant frequency.

[0034] The fifth technical solution of the present invention provides the application of the above-mentioned piezoelectric ceramic element in the preparation of devices, wherein the devices are ultrasonic transducers, underwater acoustic transducers, ultrasonic cleaning transducers, ultrasonic welding transducers, ultrasonic sludge purification transducers, atomizing plates, buzzer plates, buzzers, piezoelectric sensors, piezoelectric actuators, piezoelectric transformers, piezoelectric motors, medical ultrasonic devices, non-destructive testing probes, flow meter transducers, or marine acoustic devices.

[0035] The present invention discloses the following technical effects: The present invention focuses on improvements such as the non-precious metal main conductive layer, the outer protective layer covering the exposed and edge areas, and the localization and overlapping synergy of the optional silver-based connection area, in order to simultaneously solve the problems of low silver content, connectivity, and long-term anti-oxidation reliability.

[0036] This invention forms a first-layer non-precious metal electrode on at least one surface of a piezoelectric ceramic substrate. The first-layer non-precious metal electrode is preferably an aluminum electrode or an aluminum alloy electrode, which is adjacent to the surface of the piezoelectric ceramic substrate and bears the main charge transport area. A second-layer silver-based solderable electrode is formed in a localized, edged, central, or all-area region of the first-layer non-precious metal electrode. The second-layer silver-based solderable electrode is preferably a silver electrode or a silver-palladium alloy electrode, which is used to form connectable areas for soldering, brazing, conductive adhesive bonding, spring pressing, or terminal connection. An outer protective layer is formed in the exposed area of ​​the first-layer non-precious metal electrode and / or the non-soldering area of ​​the second-layer silver-based solderable electrode. The outer protective layer is preferably a carbon-based conductive protective layer, used to block oxygen, water vapor, cleaning fluid, seawater, and high-temperature, humid atmospheres.

[0037] The three-layer structure in this invention is not a simple superposition. The first layer, a non-precious metal electrode, provides a large-area, low-cost conductive channel, significantly reducing the amount of silver paste used. The second layer, a silver-based solderable electrode, is only placed where soldering or connection is required, ensuring the reliability of device assembly and external circuit connections. The outer protective layer covers the exposed surface and interface edges of the first layer of non-precious metal electrodes, inhibiting the continuous thickening of the oxide film on the surface of the non-precious metal layer and blocking the spread of oxidation and moisture corrosion along the electrode edges or interface to the effective area. Through this functional partitioning, low-cost conductivity, reliable connection, and environmental protection are achieved simultaneously.

[0038] In this invention, the large-area conductivity is handled by a low-cost non-precious metal layer, while the welding and external connection functions are handled by a small-area silver or silver alloy layer. Simultaneously, an outer protective layer blocks oxygen and moisture from corroding the non-precious metal layer. A balance is achieved between weldability, cost, conductivity, moisture resistance, high-temperature resistance, and piezoelectric stability through different coverage areas and patterns. This solution should be applicable to various hard and soft piezoelectric ceramic systems such as P8, P4, P5, P5A, and P5H, and should also be suitable for different geometric shapes such as discs, squares, rings, tubes, and irregular shapes, as well as various application environments such as ultrasonic cleaning, underwater sonar, ultrasonic welding, and ultrasonic sludge purification.

[0039] Compared with the prior art, the present invention has at least the following beneficial effects: First, the present invention replaces large-area silver electrodes with non-precious metal electrodes, significantly reducing the amount of silver used and lowering electrode costs, making it particularly suitable for large-size and high-volume piezoelectric ceramic components.

[0040] Secondly, this invention solves the problem of soldering non-precious metal electrodes such as aluminum by using local silver-based solderable electrodes, so that the traditional wire welding, terminal welding and transducer assembly processes do not need to be changed.

[0041] Third, the present invention blocks oxygen and moisture through carbon-based or other protective layers, inhibits the oxidation and expansion of the aluminum layer, and improves durability in humid, underwater, ultrasonic cleaning fluid, and high-temperature environments.

[0042] Fourth, through the categorized design of electrode area and pattern, this invention can adapt to different piezoelectric ceramic materials, different device sizes, different welding methods, and different service environments.

[0043] Fifth, this invention has been verified through long-term testing in the fields of underwater acoustic and ultrasonic cleaning. In terms of piezoelectric ceramic characteristics, piezoelectric device characteristics, and durability under 150°C conditions, it can reach a level comparable to traditional silver electrode piezoelectric ceramics and silver electrode devices. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0045] Figure 1 This is a schematic diagram of the low-silver composite electrode structure according to Embodiment 1 of the present invention, wherein the first layer is an aluminum electrode with 100% coverage, the second layer is a partially silver electrode, and the outer layer is an optional carbon-based protective layer.

[0046] Figure 2This is a schematic diagram of the low-silver composite electrode structure according to Embodiment 2 of the present invention, wherein the first layer is an aluminum electrode with 100% coverage, the second layer is a partial silver electrode, and no outer carbon-based protective layer is provided.

[0047] Figure 3 This is a schematic diagram of the low-silver composite electrode structure of Embodiment 3 of the present invention, wherein the first layer is an aluminum electrode with 100% coverage, the second layer is a silver electrode with 0% coverage, and the outer layer is an optional carbon-based protective layer.

[0048] Figure 4 This is a schematic diagram of the low-silver composite electrode structure of Embodiment 4 of the present invention, wherein the first layer aluminum electrode has a coverage of 0.1% to 100%, the second layer silver electrode has a coverage of 0.1% to 100%, and the outer carbon-based protective layer has a coverage of 100%.

[0049] Figure 5 This is a schematic diagram of the low-silver composite electrode structure of Embodiment 5 of the present invention, wherein the first layer aluminum electrode and the second layer silver electrode are distributed in a concentrated or irregular pattern, and the outer carbon-based protective layer has a coverage of 100%.

[0050] Figure 6 This is a schematic diagram of the low-silver composite electrode structure of Embodiment Six of the present invention, wherein the first layer aluminum electrode has a coverage of 0.1% to 100%, the second layer silver electrode has a coverage of 0.1% to 100%, and the outer carbon-based protective layer has a coverage of 0.1% to 100%.

[0051] Explanation of reference numerals in the attached figures: 1 is the piezoelectric ceramic substrate; 2 is the first-layer non-precious metal electrode, preferably an aluminum electrode; 3 is the second-layer silver-based solderable electrode, preferably a silver electrode or a silver-palladium electrode; 4 is the outer protective layer, preferably a carbon-based conductive protective layer; 5 is the solderable area. Detailed Implementation

[0052] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0053] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0054] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0055] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0056] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0057] This invention provides a low-silver composite electrode for piezoelectric ceramics, which is disposed on at least one electrode forming surface of a piezoelectric ceramic substrate. The low-silver composite electrode includes a first-layer non-precious metal electrode adjacent to the surface of the piezoelectric ceramic substrate, and a second-layer silver-based solderable electrode disposed on a partial, edge, central, dispersed, or all regions of the first-layer non-precious metal electrode, and / or includes an outer protective layer disposed on a region of the first-layer non-precious metal electrode not covered by the second-layer silver-based solderable electrode, a non-solderable region of the second-layer silver-based solderable electrode, and a region adjacent to both. The electrode... Based on the geometric area of ​​the electrode forming surface, the projected coverage of the first-layer non-precious metal electrode is from 0.1% to 100% (e.g., it can be 0.1%, 1%, 5%, 10%, 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 99%, 100%, or any value between these values), and the projected coverage of the second-layer silver-based solderable electrode is from 0% to 100% (e.g., it can be 0, 0.1%, 1%, 5%, 10%, 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 99%, 100%, or any value between these values). The projection coverage of the outer protective layer is 0% to 100% (e.g., 0%, 95%, 99%, 100%, or any value between these values), and when the projection coverage of the secondary silver-based solderable electrode is 0%, the projection coverage of the outer protective layer is greater than 0% (e.g., 0.1%, 1%, 5%, 10%, 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 99%, 100%, or any value between these values), and when the projection coverage of the secondary silver-based solderable electrode is 0%, the projection coverage of the outer protective layer is greater than 0% (e.g., 0.1%, 1%, 5%, 10%, 15%). (20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 99%, 100%, or any value between these values); the first-layer non-precious metal electrode is used to bear the main charge transmission area, the second-layer silver-based solderable electrode is used to form an electrical connection area that can be soldered, crimped, wire-connected, or terminal-connected, and the outer protective layer is used to block the corrosion of the first-layer non-precious metal electrode by oxygen, water vapor, cleaning fluid, seawater, oil, or high-temperature and humid atmosphere. Therefore, preferably, the outer protective layer completely covers the first-layer non-precious metal electrode.

[0058] In this invention, the first non-precious metal electrode is one or a composite layer of two or more of the following: aluminum electrode, aluminum alloy electrode, copper electrode, copper alloy electrode, nickel electrode, nickel alloy electrode, tin electrode, tin alloy electrode, zinc electrode, zinc alloy electrode, indium electrode, and indium alloy electrode; preferably, the first non-precious metal electrode is an aluminum electrode or an aluminum alloy electrode with an aluminum content of not less than 50 wt% (for example, the aluminum content can be 50 wt%, 60 wt%, 70 wt%, 80 wt%, 90 wt%, 100 wt%, or between these values). (Any numerical value); more preferably, the first-layer non-precious metal electrode is composed of sinterable aluminum paste (e.g., comprising, by weight, 60 to 80 parts of spherical aluminum powder, 3 to 12 parts of bismuth boron zinc glass powder, 1 to 5 parts of ethyl cellulose, 10 to 25 parts of terpineol or butyl carbitol acetate, 0.2 to 2 parts of dispersant, and 0.1 to 3 parts of boron powder or aluminum phosphate) and curable aluminum paste (e.g., comprising, by weight, 50 to 75 parts of flake aluminum powder, 10 to 30 parts of epoxy resin or silicone resin, 2 to 8 parts of latent curing agent, and 0.2 parts of coupling agent). The following are examples of aluminum powders: 1 to 2 parts aluminum powder and 5 to 20 parts solvent; sprayable aluminum paste (e.g., comprising 30 to 60 parts aluminum powder with a particle size of 1 to 10 micrometers, 5 to 20 parts acrylic resin or silicone resin, 20 to 55 parts butyl acetate or isopropanol, and 0.1 to 1 part leveling agent); aluminum powder glass phase conductive paste (e.g., comprising 65 to 78 parts aluminum powder, 5 to 15 parts low-melting-point lead-free glass powder, 0.5 to 5 parts zinc oxide or bismuth oxide, and 15 to 25 parts organic carrier); and vacuum-deposited aluminum films (e.g., with a purity of not less than 99.5%). The aluminum target or aluminum evaporation material is used as raw material, and it is vapor-deposited or sputtered under a vacuum degree not higher than 5×10-3Pa, with a film thickness of 0.1 micrometer to 5 micrometers. After deposition, it is kept at 120°C to 250°C for 10 to 60 minutes. Alternatively, a thermally sprayed aluminum layer is formed (for example, using aluminum powder or aluminum alloy powder with a particle size of 10 micrometers to 45 micrometers as raw material, a 10-micrometer to 80-micrometer aluminum layer is formed by plasma spraying, flame spraying or cold spraying, and then heat-treated at 150°C to 350°C for 10 to 120 minutes). (All of the above parts are by mass).

[0059] In this invention, the secondary silver-based solderable electrode is a silver electrode, a silver-palladium alloy electrode, a silver-platinum alloy electrode, a silver-copper alloy electrode, a silver-nickel alloy electrode, or a silver paste sintered electrode containing a glass binder phase (for example, prepared by screen printing, drying at 80°C to 150°C, and sintering at 500°C to 750°C using 70 to 90 parts of silver powder, 2 to 8 parts of low-melting-point glass powder, 1 to 4 parts of ethyl cellulose, and 8 to 22 parts of terpineol or butyl carbitol acetate as raw materials). Low-temperature curing silver paste electrodes (e.g., prepared by applying or printing 60 to 85 parts of flake or spherical silver powder, 8 to 25 parts of epoxy resin or acrylic resin, 1 to 8 parts of amine or anhydride curing agent, 0.1 to 2 parts of coupling agent, and 3 to 15 parts of solvent, and then curing at 120°C to 200°C for 20 to 120 minutes), and silver-coated metal powder electrodes (e.g., using 50 parts of silver-coated copper powder, silver-coated nickel powder, or silver-coated aluminum powder). The electrode is prepared by printing, curing, or sintering using 85 parts of silver powder, 5 to 25 parts of organic resin, 0 to 8 parts of glass powder, and 5 to 25 parts of solvent as raw materials, or by silver-based composite conductive electrode (e.g., prepared by printing and sintering at 450°C to 750°C using 20 to 70 parts of silver powder, 10 to 60 parts of copper or nickel powder, 2 to 10 parts of glass powder, and 10 to 25 parts of organic carrier as raw materials); the silver element in the secondary silver-based solderable electrode is 5% to 100% (e.g., it can be 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, or any value between these values) based on the mass of the conductive solid phase of the layer, preferably 20% to 100%, so as to maintain the surface electrical connection performance required for soldering, brazing, ultrasonic welding, conductive adhesive bonding, or elastic terminal crimping while reducing the amount of silver used (wherein, the above parts are all parts by mass).

[0060] In this invention, the outer protective layer is a carbon-based conductive protective layer (e.g., prepared by screen printing and curing at 150°C to 220°C or sintering at 350°C to 600°C using 25 to 55 parts graphite powder, 3 to 15 parts conductive carbon black, 10 to 30 parts phenolic resin, epoxy resin or organosilicon resin, 0 to 10 parts glass powder, 0.2 to 2 parts dispersant and 20 to 45 parts solvent as raw materials), a carbon paste sintering layer (e.g., prepared by printing, drying and sintering at 450°C to 650°C using graphite powder, carbon black, glass powder and organic carrier as raw materials), and a carbon paste curing layer (e.g., prepared by screen printing and curing and sintering at 450°C to 650°C using graphite powder, carbon black, glass powder and organic carrier as raw materials), and a carbon paste curing layer (e.g., prepared by screen printing and curing and sintering at 450°C to 650°C using graphite powder, carbon black, glass powder and organic carrier). The following are examples of conductive layers prepared by curing carbon black, epoxy resin or silicone resin and curing agent at 120°C to 220°C: graphite conductive layer (e.g., prepared by spraying or printing using flake graphite, binder resin and solvent as raw materials), carbon black conductive layer (e.g., prepared by coating and curing using high-structure carbon black, resin binder and solvent as raw materials), graphene conductive layer (e.g., prepared by coating and heat treatment using graphene slurry or graphene oxide reduced slurry, resin and dispersant as raw materials), and carbon nanotube conductive layer (e.g., prepared using 0.5 to 5 parts of multi-walled carbon nanotubes, 20 to 50 parts of graphite powder, and 10 to 3 parts of resin). The following are examples of protective layers prepared from raw materials: a conductive polymer protective layer (e.g., prepared from PEDOT:PSS, polyaniline or polypyrrole dispersion and crosslinking agent, through dispersion, coating and low-temperature drying); a glassy phase protective layer (e.g., prepared from low-melting-point glass powder, organic carrier and a small amount of conductive filler, through printing and sintering); a ceramic phase protective layer (e.g., prepared from alumina, silica, titanium dioxide or zirconium oxide micropowder, organic carrier and binder, through coating and heat treatment); and an organosilicon moisture-proof layer (e.g., prepared from organosilicon resin, silane coupling agent and solvent cured at room temperature or by heating). The outer protective layer is prepared by brushing or spraying with an agent as raw material, an epoxy moisture-proof layer (e.g., prepared by coating and curing with low-viscosity epoxy resin, curing agent, silane coupling agent and diluent as raw materials), or a composite protective layer of the above materials (e.g., first forming a conductive carbon layer, and then forming an organosilicon or epoxy moisture-proof sealing layer in the non-connected area); preferably, the outer protective layer is a carbon-based conductive protective layer, and the sheet, particle or network structure of the carbon-based conductive protective layer can cover the exposed surface of the first non-precious metal electrode, thereby slowing down the thickening of the oxide film on the non-precious metal surface and the spread of water vapor along the interface (wherein, the above parts are all parts by mass).

[0061] In this invention, the projected shape of the secondary silver-based solderable electrode is circular, elliptical, square, rectangular, rhomboid, triangular, polygonal, annular, semi-annular, fan-shaped, strip-shaped, grid-shaped, island-shaped, dot-matrix-shaped, interdigitated, end pad-shaped, edge pad-shaped, or any combination of the above shapes; the distribution of the secondary silver-based solderable electrode is localized, centrally concentrated, edge-concentrated, dispersed among multiple pads, symmetrically distributed along the polarization direction, or asymmetrically distributed along the device mounting terminals.

[0062] In this invention, the projected shape of the outer protective layer can be a continuous film covering the exposed area of ​​the first-layer non-precious metal electrode, an annular film covering the exposed area of ​​the first-layer non-precious metal electrode and avoiding the welding window of the second-layer silver-based solderable electrode, a continuous film covering the non-welding areas of the first-layer non-precious metal electrode and the second-layer silver-based solderable electrode, a full-coverage film completely covering the electrode forming surface, a partial-coverage film, a strip-coverage film, a dot matrix-coverage film, or an edge-sealing film.

[0063] In this invention, the thickness of the first-layer non-precious metal electrode is from 0.05 micrometers to 80 micrometers (e.g., 0.05 micrometers, 0.1 micrometers, 0.5 micrometers, 1 micrometer, 5 micrometers, 10 micrometers, 20 micrometers, 30 micrometers, 40 micrometers, 50 micrometers, 60 micrometers, 70 micrometers, 80 micrometers, or any value between these values), preferably from 1 micrometer to 35 micrometers; the thickness of the second-layer silver-based solderable electrode is from 0.05 micrometers to 50 micrometers (e.g., 0.05 micrometers, 0.1 micrometers, 0.5 micrometers, 1 micrometer, 5 micrometers, 10 micrometers, 20 micrometers, 30 micrometers, 40 micrometers, 50 micrometers, or these values). The thickness of the outer protective layer is 0.05 micrometers to 100 micrometers (e.g., 0.05 micrometers, 0.1 micrometers, 0.5 micrometers, 1 micrometer, 5 micrometers, 10 micrometers, 20 micrometers, 30 micrometers, 40 micrometers, 50 micrometers, 60 micrometers, 70 micrometers, 80 micrometers, 90 micrometers, 100 micrometers or any value between these values), preferably 1 micrometer to 40 micrometers; the layers are bonded together by sintering, molten glass bonding, mechanical interlocking, intermetallic diffusion, conductive adhesive bonding, surface activation bonding or a combination of the above to form a stable interface.

[0064] In this invention, a transition bonding phase is provided between the first-layer non-precious metal electrode and the piezoelectric ceramic substrate. The transition bonding phase includes low-melting-point lead-free glass (e.g., bismuth borosilicate glass, zinc borosilicate glass, phosphate glass, or lead-free glass with a softening point of 350°C to 550°C), borosilicate glass, bismuth borosilicate glass, zinc borosilicate glass, phosphate glass, titanate glass, alumina micropowder, zinc oxide micropowder, bismuth oxide micropowder, silicon oxide micropowder, titanium oxide micropowder, or an inorganic bonding phase that can improve the adhesion strength between the electrode and the ceramic interface (e.g., silane coupling agent hydrolysis layer, aluminophosphate bonding phase, zinc aluminum borosilicate glass phase, or titanium-containing coupling interface phase). Preferably, the transition bonding phase can be formed by the in-situ softening, wetting and penetrating into the micropores of the ceramic surface by glass powder and oxide additives in the aluminum paste during sintering, or it can be formed by additionally coating a glass-oxide undercoat of 0.05 micrometers to 5 micrometers before printing the aluminum paste and then pre-firing at 350°C to 600°C; preferably, the thickness is 0.1 micrometers to 3 micrometers.

[0065] In this invention, when the first non-precious metal electrode is an aluminum electrode, the aluminum electrode is formed by sintering an electrode slurry containing aluminum powder. The electrode slurry containing aluminum powder includes metallic aluminum powder, inorganic binders (e.g., bismuth boron zinc glass powder, zinc borosilicate glass powder, phosphate glass powder, aluminophosphate, or silica sol), organic carriers (e.g., ethyl cellulose, terpineol, butyl carbitol, butyl carbitol acetate, or acrylic resin solution), and dispersants (e.g., polycarboxylates, phosphate dispersants, BYK-type dispersants, or stearates). The electrode slurry contains, by weight, one or more of the following: leveling agents (e.g., polyether-modified siloxanes or acrylate leveling agents), defoamers (e.g., silicone defoamers or mineral oil defoamers), and antioxidants (e.g., boron powder, red phosphorus, aluminum phosphate, zinc borate, silica powder, or boron-containing low-melting-point glass); the antioxidants include boron powder, red phosphorus, phosphates, boron-containing compounds, silicon-containing compounds, antioxidant glass phases, or additives that can reduce the oxidation degree of aluminum powder sintering (e.g., zinc borate, aluminum phosphate, silica powder, fluoroborate, or borosilicate glass powder). Preferably, the aluminum powder-containing electrode slurry comprises, by weight, 70 parts aluminum powder with an average particle size of 2 to 8 micrometers, 8 parts bismuth boron zinc glass powder, 1 part zinc oxide, 2 parts ethyl cellulose, 16 parts terpineol, 0.8 parts phosphate dispersant, 0.2 parts silicone leveling agent, 0.2 parts silicone defoamer, and 1.8 parts boron powder.

[0066] In this invention, the secondary silver-based solderable electrode at least covers the area on the primary non-precious metal electrode where solder leads, solder terminals, solder metal housings, connecting conductive springs, connecting conductive adhesives, connecting spring pins, and / or connecting external circuits are required. The overlap width between the secondary silver-based solderable electrode and the primary non-precious metal electrode is not less than 0.05 mm (e.g., 0.05 mm, 0.1 mm, 0.2 mm, 0.5 mm, 1 mm, 2 mm, 5 mm, 8 mm, 10 mm, 15 mm, 20 mm, or any value between these values), preferably 0.2 mm to 10 mm, to reduce the contact resistance of the overlap area and suppress local current concentration.

[0067] In this invention, the outer protective layer forms a sealing structure at the edge of the first non-precious metal electrode. The sealing structure covers the outer periphery, hole edge, notch edge, cut edge, chamfer edge, or interface edge adjacent to the piezoelectric ceramic substrate of the first non-precious metal electrode. The sealing structure is used to block oxygen and water vapor from entering the interface between the first non-precious metal electrode and the piezoelectric ceramic substrate from the edge.

[0068] In this invention, the piezoelectric ceramic matrix is ​​a lead zirconate titanate-based piezoelectric ceramic, a modified lead zirconate titanate-based piezoelectric ceramic, a lead titanate-based piezoelectric ceramic, a lead metaniobate-based piezoelectric ceramic, a lead magnesium niobate titanate-based piezoelectric ceramic, a barium titanate-based piezoelectric ceramic, a potassium sodium niobate-based lead-free piezoelectric ceramic, a sodium bismuth titanate-based lead-free piezoelectric ceramic, a silver niobate-based piezoelectric ceramic, or a composite ceramic of the above systems (from commercially available sources); preferably, the piezoelectric ceramic matrix includes one of P8, P4, P5, P5A, P5H, and their modified materials (from commercially available sources).

[0069] In this invention, the low-silver composite electrode is disposed on one main surface, two opposite main surfaces, side surface, end face, inner hole surface, outer cylindrical surface, arc surface, or irregular surface of the piezoelectric ceramic substrate; when the low-silver composite electrode is disposed on both opposite main surfaces of the piezoelectric ceramic substrate, the coverage, shape, and distribution of the first non-precious metal electrode, the second silver solderable electrode, and the outer protective layer on the two surfaces can be the same or different.

[0070] In this invention, the low-silver composite electrode for piezoelectric ceramics is suitable for ultrasonic transducers, underwater acoustic transducers, ultrasonic cleaning transducers, ultrasonic welding transducers, ultrasonic sludge purification transducers, atomizing plates, buzzer plates, buzzers, piezoelectric sensors, piezoelectric actuators, piezoelectric transformers, piezoelectric motors, medical ultrasonic devices, non-destructive testing probes, flow meter transducers, or marine acoustic devices.

[0071] This invention also provides a piezoelectric ceramic element, comprising a piezoelectric ceramic substrate and a low-silver composite electrode for piezoelectric ceramics disposed on at least one surface of the piezoelectric ceramic substrate; the piezoelectric ceramic element, after polarization, can apply an excitation electric field or output piezoelectric charge through the low-silver composite electrode; the secondary silver-based solderable electrode serves as a lead wire soldering area, a terminal connection area, or an elastic contact area, and the outer protective layer serves as a protection zone against oxidation, water vapor, media erosion, or pollution.

[0072] In this invention, the piezoelectric ceramic element is a circular plate, square plate, ring plate, tubular body, columnar body, spherical cap, arc surface, thick plate, thin plate, stacked plate, or irregularly shaped plate; the first layer of the low-silver composite electrode, a non-precious metal electrode, forms a continuous conductive area within the effective vibration region; the second layer of the silver-based solderable electrode is positioned at a location that does not significantly reduce the effective vibration area; and the outer protective layer is positioned at a location that does not significantly increase mechanical damping or significantly change the resonant frequency.

[0073] The method for preparing the low-silver composite electrode for piezoelectric ceramics in this invention includes the following steps: grinding, polishing, cleaning, drying, and surface activation treatment of the surface to be polarized of the piezoelectric ceramic substrate. The surface activation treatment may be oxygen plasma treatment for 30 to 300 seconds, ultraviolet ozone treatment for 5 to 20 minutes, micro-etching with 0.5 wt% to 5 wt% dilute nitric acid or citric acid for 10 to 120 seconds followed by water washing and drying, or 0.2 wt% to 2 wt% silane coupling agent solution. After liquid immersion coating for 1 to 10 minutes, it is dried at 80°C to 120°C. A first non-precious metal electrode precursor layer is formed on the surface to be electrodelated according to a predetermined pattern. This first non-precious metal electrode precursor layer is then subjected to drying at 80°C to 180°C for 5 to 30 minutes, sintering at 500°C to 750°C for 5 to 60 minutes, curing at 120°C to 250°C for 20 to 120 minutes, heat treatment at 150°C to 350°C for 10 to 120 minutes, or post-deposition treatment. A first-layer non-precious metal electrode is formed adjacent to the piezoelectric ceramic substrate; a second-layer silver-based solderable electrode precursor layer is formed in a local area, edge area, central area, dispersed area, or all area of ​​the first-layer non-precious metal electrode, and then subjected to drying at 80°C to 150°C for 5 to 30 minutes, sintering at 450°C to 800°C for 5 to 60 minutes, curing at 120°C to 220°C for 20 to 120 minutes, or heat treatment at 150°C to 300°C for 10 to 60 minutes to form the second-layer silver electrode. The electrode is a solderable electrode; an outer protective layer precursor layer is formed in at least one of the exposed areas of the first non-precious metal electrode, the non-soldering areas of the second silver solderable electrode, and the adjacent areas of the two, and is subjected to drying at 80°C to 150°C for 5 to 30 minutes, sintering at 300°C to 650°C for 5 to 60 minutes, curing at 120°C to 250°C for 20 to 120 minutes, or heat treatment at 150°C to 300°C for 10 to 120 minutes to form an outer protective layer.

[0074] In this invention, the methods for forming the first non-precious metal electrode, the second silver-based solderable electrode, and the outer protective layer are each independently selected from screen printing (e.g., using 200-400 mesh stainless steel or polyester screens, squeegee hardness 60A-80A, and squeegee speed 30 mm / s-150 mm / s), pad printing (e.g., using a silicone pad printing head and etching a steel plate to a depth of 10-40 micrometers), spraying (e.g., nozzle diameter 0.2-1.0 mm, atomization pressure 0.1 MPa-0.4 MPa), brushing, squeegeeing, dispensing (e.g., needle inner diameter 0.1-1.0 mm), dip coating, spin coating (e.g., 500 rpm-3000 rpm), roll coating, laser transfer, thermal spraying (e.g., powder particle size 10-45 micrometers), and vacuum evaporation (e.g., vacuum degree not exceeding 5 × 10⁻⁶). -3(Pa), magnetron sputtering (e.g., argon pressure 0.2 Pa to 1.0 Pa, power 50 W to 500 W), electroplating, electroless plating, aerosol printing, or a combination of the above methods; preferably, the first-layer non-precious metal electrode is formed by screen printing aluminum paste and sintering at 500°C to 750°C, wherein the aluminum paste comprises, by weight, 70 parts aluminum powder, 8 parts bismuth boron zinc glass powder, 1 part zinc oxide, 2 parts ethyl cellulose, 16 parts terpineol, 0.8 parts dispersant, 0.2 parts leveling agent, 0.2 parts defoamer, and 1.8 parts boron powder. The screen printing parameters are as follows: 325 mesh screen, emulsion thickness 10 to 20 micrometers, squeegee hardness 70A, and squeegee speed 50 mm / s to 100 mm / s; the sintering temperature can be 550℃, 600℃, 650℃, 700℃, 750℃ or any value between these values, preferably 620℃ to 660℃, the holding time is 10 minutes to 30 minutes, the heating rate is 2℃ / min to 5℃ / min, and the sintering atmosphere is air, nitrogen or a weak oxidizing atmosphere with an oxygen content of less than 1% in nitrogen. The secondary silver-based solderable electrode is formed by screen printing silver paste or silver alloy paste and then sintering it at 450°C to 800°C. The silver paste, by weight, includes 82 parts silver powder, 4 parts low-melting-point glass powder, 2 parts ethyl cellulose, and 12 parts terpineol. The silver alloy paste, by weight, includes 50 parts silver powder, 25 parts copper or nickel powder, 5 parts glass powder, and 20 parts organic carrier. The screen printing parameters are 250-350 mesh screen, squeegee hardness of 65A to 75A, and squeegee speed of 40 mm / s to 120 mm / s. The preferred sintering temperature is 520°C to 680°C, the holding time is 10 minutes to 30 minutes, and the heating rate is 2°C / min to 5°C / min. The outer protective layer is formed by screen printing carbon paste and then curing or sintering it at 120°C to 650°C. The carbon paste, by weight, includes 40 parts of flake graphite, 8 parts of conductive carbon black, 18 parts of phenolic resin or epoxy resin, 4 parts of low-melting-point glass powder, 28 parts of solvent, 1 part of dispersant, and 1 part of leveling agent. The preferred curing conditions are 180°C for 60 minutes and sintering conditions are 450°C to 550°C for 10 to 30 minutes.

[0075] In this invention, the first non-precious metal electrode, the second silver-based solderable electrode, and the outer protective layer can be manufactured using the following methods: single co-firing (e.g., printing and drying three pastes sequentially, then holding at 580°C to 650°C for 10 to 30 minutes), double firing (e.g., sintering aluminum paste at 620°C to 660°C first, then sintering silver paste at 520°C to 650°C), triple firing (e.g., sintering or curing aluminum, silver, and carbon layers separately), or firing followed by curing (e.g., sintering aluminum and silver layers separately). The process involves the following steps: after bonding, the carbon or silicone layer is cured at 150°C to 220°C; curing is performed before polarization (e.g., low-temperature curing of silver paste and carbon paste followed by polarization); or local application of a protective layer after polarization (e.g., applying a silicone or epoxy moisture-proof layer to the non-welding area after wire bonding and curing it at 80°C to 150°C). When multiple firings are used, the sintering temperature of subsequent layers should not be higher than the temperature that could cause severe oxidation, melt flow, interface peeling, or depolarization of the previous electrode layer.

[0076] In this invention, the piezoelectric ceramic substrate is electrically polarized after the low-silver composite electrode is formed. The polarization electric field strength is from 0.5 kV / mm to 6 kV / mm (e.g., it can be 0.5 kV / mm, 1 kV / mm, 2 kV / mm, 3 kV / mm, 4 kV / mm, 5 kV / mm, 6 kV / mm or any value between these values), and the polarization temperature is from 20°C to 200°C (e.g., it can be 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 120°C, 140°C). The polarization temperature is 160℃, 180℃, 200℃ or any value between these values. The polarization medium is air, silicone oil, transformer oil, water-based medium or inert atmosphere. The polarization time is 1min-60min (for example, it can be 1min, 2min, 5min, 10min, 20min, 30min, 40min, 50min, 60min or any value between these values). After polarization, tin soldering, brazing, conductive adhesive bonding, metal spring pressing, riveting or terminal welding are performed on the secondary silver-based solderable electrode.

[0077] In this invention, optionally, the first non-precious metal electrode is an all-aluminum electrode with a coverage of 100%, the second silver-based solderable electrode has a coverage of 0.1% to 100% (for example, it can be 0.1%, 1%, 5%, 10%, 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 99%, 100%, or any value between these values), the outer protective layer is a carbon-based conductive protective layer with a coverage of 0.1% to 100% (for example, it can be 0.1%, 1%, 5%, 10%, 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 99%, 100%, or any value between these values), and the outer protective layer preferably avoids the welding window of the second silver-based solderable electrode.

[0078] In this invention, optionally, the first non-precious metal electrode is an all-aluminum electrode with a coverage of 100%, the second silver-based solderable electrode has a coverage of 0.1% to 100% (for example, it can be 0.1%, 1%, 5%, 10%, 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 99%, 100%, or any value between these values), and the outer protective layer is an edge-sealing protective layer or a partial protective layer with a coverage of 0.1% to 20%, thereby forming a low-silver electrode structure with a local solderable silver area and edge-sealing protection.

[0079] In this invention, optionally, the first non-precious metal electrode is an all-aluminum electrode with a coverage of 100%, the second silver-based solderable electrode has a coverage of 0%, and the outer protective layer is a carbon-based conductive protective layer with a coverage of 0.1% to 100% (for example, it can be 0.1%, 1%, 5%, 10%, 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 99%, 100%, or any value between these values), thereby forming a silver-free or extremely low-silver anti-oxidation electrode structure.

[0080] In this invention, optionally, the first non-precious metal electrode is an aluminum electrode with a coverage of 0.1% to 100% (e.g., 0.1%, 1%, 5%, 10%, 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 99%, 99.9%, or any value between these values), the second silver-based solderable electrode has a coverage of 0.1% to 100% (e.g., 0.1%, 1%, 5%, 10%, 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 99%, 99.9%, or any value between these values), and the outer protective layer is a carbon-based conductive protective layer with a coverage of 100%, thereby forming a low-silver composite electrode structure with full surface protection.

[0081] In this invention, optionally, the first-layer non-precious metal electrode is an aluminum electrode with a coverage of 0.1% to 100% (e.g., 0.1%, 1%, 5%, 10%, 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 99%, 99.9%, or any value between these values), and the second-layer silver-based solderable electrode has a coverage of 0.1% to 100% (e.g., 0.1%, 1%, 5%, 10%, 15%, 20%, 30%, 40%, 50%). The outer protective layer is a carbon-based conductive protective layer with a coverage of 0.1% to 100% (e.g., 0.1%, 1%, 5%, 10%, 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 99%, 99.9%, or any value between these values), thereby forming a low-silver composite electrode structure with local protection, local solderability, or local drag reduction.

[0082] In this invention, the piezoelectric ceramic element is used in ultrasonic cleaning, underwater sonar, ultrasonic welding, ultrasonic sludge purification, ultrasonic emulsification, ultrasonic dispersion, marine acoustic transmission and reception, industrial non-destructive testing, medical ultrasound, piezoelectric sound generation, piezoelectric drive, piezoelectric sensing, or high-temperature piezoelectric devices.

[0083] In this invention, the projected coverage of the first non-precious metal electrode, the second silver-based solderable electrode, and the outer protective layer is an important technical feature. Based on the area of ​​the target electrode formation surface, the coverage of the first non-precious metal electrode is 0.1% to 100%, preferably 80% to 100%, and most preferably 100%; the coverage of the second silver-based solderable electrode is 0% to 100%, preferably 0.1% to 30%, more preferably 0.5% to 15%; the coverage of the outer protective layer is 0% to 100%, preferably 0.1% to 100%, and may be absent, partially covered, or fully covered depending on the usage environment. When the silver-based solderable electrode is absent, the outer protective layer is preferably present to maintain the protective advantage over a single aluminum electrode.

[0084] The present invention also provides a piezoelectric ceramic element, comprising a piezoelectric ceramic substrate and the aforementioned low-silver composite electrode disposed on at least one surface of the substrate. The piezoelectric ceramic element can be a disc, square disc, ring disc, thick disc, thin disc, tubular body, columnar body, or irregular shape. The piezoelectric ceramic substrate can be a commercial piezoelectric ceramic system such as P8, P4, P5, P5A, P5H, or other PZT-based, lead titanate-based, lead metaniobate-based, barium titanate-based, potassium sodium niobate-based, sodium bismuth titanate-based, or composite piezoelectric ceramic system.

[0085] This invention further provides a method for preparing the low-silver composite electrode. The method includes: cleaning and activating the surface of a piezoelectric ceramic substrate; forming a first-layer non-precious metal electrode according to a preset pattern and sintering or curing it; forming a second-layer silver-based solderable electrode on the first-layer non-precious metal electrode and sintering or curing it; forming an outer protective layer in the exposed area of ​​the first-layer non-precious metal electrode and / or the non-soldering area of ​​the second-layer silver-based solderable electrode and sintering or curing it. Each of the above layers can be prepared using screen printing, spraying, brushing, pad printing, dispensing, vacuum deposition, thermal spraying, or a combination thereof.

[0086] The present invention will be further described below with reference to the accompanying drawings and embodiments. It should be understood that the following embodiments are used to illustrate the technical concept of the present invention, and not to limit the scope of protection of the present invention. Any equivalent substitutions or conventional adjustments made to the electrode material, slurry composition, sintering process, pattern shape, area ratio, connection method, or usage environment under the technical concept of the present invention shall fall within the scope of protection of the present invention.

[0087] The target electrode forming surface, as referred to in this invention, is the piezoelectric ceramic surface on which the electrode is to be formed. Its geometric area can be the single-sided area of ​​a circular piece, the single-sided area of ​​a square piece, the annular surface area of ​​a ring piece, the end or side surface area of ​​a tubular body, or the area of ​​the effective electrode region defined according to the device structure. The coverage rate refers to the percentage of the vertical projection area of ​​the corresponding electrode layer on the target electrode forming surface to the area of ​​that target electrode forming surface. For ring pieces, irregularly shaped pieces, or perforated pieces, the coverage rate can be calculated based on the area of ​​the electrode forming region.

[0088] In this invention, the term "first layer" refers to the conductive layer closest to the surface of the piezoelectric ceramic substrate in the thickness direction. The term "second layer" refers to a silver-based conductive layer located above the first layer, at least partially overlapping it, and used to enhance welding or connection performance. The term "outer layer" refers to a protective layer located above the exposed areas of the first layer and / or the non-welded areas of the second layer, used for protection against oxidation, water vapor, corrosion, or contamination. The outer layer can be a conductive protective layer, or an insulating or semi-insulating protective layer disposed in areas that do not impede electrode connection; in ultrasonic, underwater acoustic, and high-power driving scenarios, a conductive carbon-based protective layer is preferred to avoid the accumulation of localized charges.

[0089] This invention provides a general preparation process for the product of this invention as follows: First, the sintered piezoelectric ceramic substrate is processed into sheet, ring, tubular, or irregularly shaped structures according to the device dimensions. The polarized surface is then ground or polished, and dust, oil, and adsorbed impurities are removed using deionized water, ethanol, acetone, or other cleaning agents. It is then dried at 80°C to 150°C to ensure thorough removal of surface moisture. If necessary, plasma cleaning (e.g., oxygen plasma power 50W to 200W, treatment for 30 to 300 seconds), ultraviolet ozone treatment (e.g., treatment for 5 to 20 minutes), micro-etching (e.g., treatment with 0.5wt% to 5wt% dilute nitric acid, citric acid, or acetic acid for 10 to 120 seconds followed by thorough rinsing with water), or silane coupling agent treatment (e.g., treatment with 0.2wt% to 2wt% aminopropyltriethoxysilane, glycidyl etheroxypropyltrimethoxysilane, or titanate coupling agent solution for 1 to 10 minutes) can be used to improve surface adhesion.

[0090] Secondly, a first-layer non-precious metal electrode is formed on the surface of the piezoelectric ceramic substrate according to a preset pattern. When aluminum electrodes are a preferred embodiment, an aluminum paste containing aluminum powder, inorganic binder, organic carrier, and antioxidant can be used. This paste is formed on the ceramic surface by screen printing or spraying. After drying at 80°C to 180°C, it is sintered at 500°C to 750°C, preferably at 560°C to 680°C, so that the aluminum powder is sintered into a continuous conductive network and bonded to the piezoelectric ceramic through a glass phase or interfacial reaction. Alternatively, an aluminum layer can be formed by vacuum evaporation, magnetron sputtering, thermal spraying, or cold spraying, followed by a low-temperature heat treatment at 120°C to 300°C for 10 to 120 minutes to enhance adhesion.

[0091] Optionally, a second-layer silver-based solderable electrode is formed on the first-layer non-precious metal electrode. The silver-based solderable electrode can be silver paste, silver-palladium paste, low-silver silver alloy paste, silver-coated copper powder paste, or silver-based conductive adhesive. The silver layer pattern is determined based on the solder wire location, terminal location, device vibration mode, and assembly method; it can be located at the center, edge, end, outer circumference, around inner holes, or at multiple discrete pads. After drying, the silver-based solderable electrode is sintered at 450°C to 800°C or cured at 80°C to 250°C. The overlap area between the silver layer and the aluminum layer preferably has a width of 0.2 mm to 10 mm, more preferably 0.5 mm to 3 mm, to reduce contact resistance and prevent localized delamination caused by soldering thermal shock.

[0092] Finally (optionally), an outer protective layer is formed over the exposed areas of the first-layer non-precious metal electrodes and / or the non-soldering areas of the silver-based solderable electrodes. Preferably, a carbon-based protective layer is formed using carbon paste through screen printing, brushing, or spraying. The carbon paste may contain graphite, carbon black, graphene, carbon nanotubes, organic resin, glass powder, ceramic powder, dispersant, and solvent. After curing at 120°C to 250°C or sintering at 300°C to 650°C, the carbon-based protective layer forms a continuous or semi-continuous conductive barrier, covering the exposed areas of the aluminum layer and sealing the edges. For silver areas requiring soldering, the carbon layer can avoid the soldering window; for devices requiring full coverage protection, local openings, grinding, or through-hole soldering terminals can be used before soldering.

[0093] The fabricated piezoelectric ceramic element can be polarized. During polarization, a DC electric field is applied between the opposing electrodes, with a field strength ranging from 0.5 kV / mm to 6 kV / mm, a polarization temperature ranging from 20°C to 200°C, and a polarization time ranging from 1 minute to 60 minutes. After polarization, leads are soldered or external terminals are connected using silver-based solderable electrodes. The element is then assembled into a metal housing, transducer front cover, rear cover, prestressed bolt structure, cleaning tank, sonar array element, or ultrasonic welding system according to application requirements.

[0094] The specific experimental methods for verifying the product in the following embodiments (1 to 6) of this invention are as follows: An impedance analyzer is used to scan the sample impedance curve, read the resonant frequency Fs and resonant resistance R1, and calculate the mechanical quality factor Qm and electromechanical coupling coefficient Kp based on the resonance and anti-resonance characteristics; an LCR meter is used to test the electrostatic capacitance CT under 1kHz and 1Vrms conditions; and a quasi-static d33 meter is used to test the piezoelectric constant D33. The tests can be conducted according to the standard testing methods of GB / T 3389 series piezoelectric ceramic materials performance testing methods, GB / T 2413 piezoelectric ceramic materials volume density measurement methods, IEC 60483 dynamic measurement methods, and IEEE 176 piezoelectric standards. Unless otherwise specified, the test temperature is 23℃±2℃, the relative humidity is 45% to 65%, and the sample is placed at room temperature for 24 hours before testing.

[0095] The comparative sample was a P5H disc with silver electrodes on both sides of the same specification. Both the example sample and the comparative sample were polarized in silicone oil at 120°C with a DC electric field of 2.5 kV / mm for 20 minutes, and then left to stand for 24 hours after polarization. Solderability was evaluated using Sn-3.0Ag-0.5Cu lead-free solder and a 350°C soldering iron for 2 to 3 seconds of contact for wetting and conductivity. Adhesion was tested using 3M tape peeling and 0.5N to 2N lead pull force. Resistance and appearance were retested after being placed at 85°C and 85%RH for 96 hours. The following data are exemplary test results for representative samples.

[0096] In the following embodiments of the present invention, all raw materials are commercially available, and their source does not affect the technical effect of the present invention.

[0097] Example 1 like Figure 1 As shown, on at least one of the two main surfaces of a circular P5H piezoelectric ceramic, aluminum paste is first screen-printed and sintered to form a first-layer aluminum electrode, covering 100% of the target electrode formation surface. Subsequently, silver paste is printed and sintered at locations where solder leads are required to form a second-layer silver electrode. The silver electrode coverage can be selected from 0.1% to 100%, preferably 1% to 20%. Then, carbon paste is printed and cured or sintered in areas where the aluminum electrode is not covered by the silver electrode to form an outer carbon-based protective layer. The carbon-based protective layer coverage can be selected from 0.1% to 100%, preferably covering the exposed aluminum electrode area and avoiding the silver pads. This structure is suitable for underwater acoustic transducers, ultrasonic cleaning transducers, and piezoelectric sheets requiring solder leads. Because the large-area electrode is supported by aluminum, the amount of silver used is significantly lower than in a full-silver electrode; and because the exposed aluminum surface is covered by a carbon layer, oxygen and moisture are less likely to continuously corrode the aluminum layer.

[0098] The specific preparation steps are as follows: Step 1. Screen print aluminum paste onto one or both main surfaces of the circular P5H piezoelectric ceramic and sinter to form the first layer of aluminum electrode. The aluminum electrode covers 100% of the target electrode formation surface, denoted as M1 (aluminum electrode prepared on one surface) and M2 (aluminum electrode prepared on two surfaces; in subsequent fabrication processes, the coverage, shape, and distribution of the first layer non-precious metal electrode, the second layer silver-based solderable electrode, and the outer protective layer are the same on both surfaces). Wherein: Before use, the circular P5H piezoelectric ceramic should undergo the following pretreatment: the surface to be polarized should be ground with 800 to 2000 grit sandpaper and polished with alumina, and then ultrasonically cleaned with deionized water, ethanol and acetone for 5 to 10 minutes each to remove dust, oil and adsorbed impurities; then dried at 100°C for 30 minutes to fully remove surface moisture; then treated with oxygen plasma at 100W power for 120 seconds, or immersed in a 1wt% silane coupling agent ethanol aqueous solution for 3 minutes and then dried at 100°C for 10 minutes for surface activation.

[0099] The aluminum paste consists of the following components by weight: 70 parts of spherical aluminum powder with an average particle size of 2 to 8 micrometers, 8 parts of bismuth-boron-zinc low-melting-point glass powder, 1 part of zinc oxide, 2 parts of ethyl cellulose, 16 parts of terpineol, 0.8 parts of phosphate dispersant, 0.2 parts of silicone leveling agent, 0.2 parts of silicone defoamer, and 1.8 parts of boron powder. All components are ground by three roller mills to a fineness of no more than 15 micrometers.

[0100] Screen printing parameters: 325 mesh stainless steel screen, emulsion thickness of about 15 microns, squeegee hardness of 70A, squeegee angle of about 60°, printing speed of 50 mm / s to 100 mm / s, and static leveling for 3 to 10 minutes after printing.

[0101] Drying parameters: Dry in a 120℃ hot air oven for 15 to 20 minutes.

[0102] Sintering parameters: Heat to 640℃ at 3℃ / min, hold for 20 minutes, and then cool with the furnace; sintering atmosphere is a weak oxidizing atmosphere with nitrogen oxygen content of less than 1% (air or nitrogen protective atmosphere is also acceptable).

[0103] The thickness of the first aluminum electrode is approximately 12 micrometers (8 to 18 micrometers are acceptable).

[0104] Step 2. Take M1 and M2, print silver paste at the locations where lead wires need to be soldered, and sinter to form secondary silver electrodes. The silver electrode coverage rates are 0.1% (covering the central area, circular shape), 1% (covering the central area, circular shape), 10% (covering the central area, circular shape), 20% (covering the central area, circular shape), 30% (covering the central area, circular shape), 40% (covering the central area, circular shape), 50% (covering the central area, circular shape), 60% (covering the central area, circular shape), 70% (covering the central area, circular shape), and 80% (covering the central area, circular shape). The coverage areas are 90% (circular), 100% (circular), and 100% (complete coverage), denoted as M1-Ag0.1, M1-Ag1, M1-Ag10, M1-Ag20, M1-Ag30, M1-Ag40, M1-Ag50, M1-Ag60, M1-Ag70, M1-Ag80, M1-Ag90, M1-Ag100, M2-Ag0.1, M2-Ag1, M2-Ag10, M2-Ag20, M2-Ag30, M2-Ag40, M2-Ag50, M2-Ag60, M2-Ag70, M2-Ag80, M2-Ag90, and M2-Ag100. Where: Silver paste composition: by weight, 82 parts flake silver powder, 4 parts low melting point glass powder, 2 parts ethyl cellulose, 12 parts terpineol; 0.2 to 1 part phosphate ester dispersant is added to improve printing uniformity.

[0105] Screen printing parameters: 300 mesh stainless steel screen, emulsion thickness 10 to 15 microns, squeegee hardness 70A, squeegee angle about 60°, printing speed 40 mm / s to 100 mm / s, and allow to stand for 3 to 5 minutes after printing to level.

[0106] Drying parameters: Dry in a hot air oven at 110℃ to 130℃ for 10 to 20 minutes.

[0107] Sintering parameters: temperature 500℃, holding time 15 minutes, heating rate 3℃ / minute, sintering atmosphere is air or nitrogen; when using organic resin type carbon paste, it is preferable to only cure without high-temperature sintering.

[0108] The thickness of the secondary silver electrode is 5 micrometers to 15 micrometers, preferably about 8 micrometers; the overlap width between the silver electrode and the aluminum electrode is not less than 0.5 millimeters, and the diameter of the center pad is calculated from the surface area of ​​the target electrode formation according to the target coverage.

[0109] Step 3. Print carbon paste onto the entire area of ​​the aluminum electrode surface not covered by the silver electrode obtained in Step 2, and then cure or sinter it to form an outer carbon-based protective layer, denoted as M1-Ag0.1-C99.9, M1-Ag1-C99, M1-Ag10-C90, M1-Ag20-C80, M1-Ag30-C70, M1-Ag40-C60, M1-Ag50-C50, M1-Ag60-C40, M1-Ag70-C30. , M1-Ag80-C20, M1-Ag90-C10, M2-Ag0.1-C99.9, M2-Ag1-C99, M2-Ag10-C90, M2-Ag20-C80, M2-A g30-C70, M2-Ag40-C60, M2-Ag50-C50, M2-Ag60-C40, M2-Ag70-C30, M2-Ag80-C20, M2-Ag90-C10. in: Carbon paste composition: by weight, 40 parts flake graphite, 8 parts conductive carbon black, 18 parts phenolic resin, 4 parts low melting point glass powder, 28 parts butyl carbitol or terpineol, 1 part dispersant and 1 part leveling agent, ground to a fineness of no more than 20 microns using three roller mills.

[0110] Screen printing parameters: Use 250-325 mesh screen, emulsion thickness 10-20 micrometers, squeegee hardness 65A-75A, squeegee speed 40-100 mm / s; reserve silver pad windows through mask or screen pattern.

[0111] Curing parameters: Temperature 180℃, hold for 60 minutes, heating rate 2℃ / min to 5℃ / min; for assemblies that are not resistant to high temperatures, hold at 150℃ for 120 minutes.

[0112] Sintering parameters: temperature 500℃, holding time 15 minutes, heating rate 3℃ / minute, sintering atmosphere is air or nitrogen; when using resin-cured carbon paste, it is preferred to use only the curing process.

[0113] The outer carbon-based protective layer has a thickness of 3 to 20 micrometers, preferably about 8 micrometers.

[0114] The overlap parameters of the aluminum electrode surface, silver electrode and protective layer are as follows: the carbon-based protective layer covers the area of ​​the aluminum electrode not covered by the silver electrode and overlaps with the edge of the silver electrode by 0.2 mm to 2 mm, preferably 0.5 mm; the center of the silver electrode retains an exposed welding window with a diameter of 1 mm to 4 mm. If the protective layer fully covers the silver electrode, the welding window is formed before welding by laser, mechanical scraping or mask pre-reservation.

[0115] The performance verification results of the product prepared in this embodiment are as follows: Table 1 Analysis of the data in Table 1 shows that, under the condition of 100% aluminum electrode coverage and partial silver electrode coverage, the Fs, CT, Kp, and D33 values ​​of samples with silver coverage of 1% to 20% are relatively similar to those of the full-silver comparison sample. When the silver coverage is less than 1%, the weldable area is smaller, and the welding window and assembly tolerance are reduced. When the silver coverage is greater than 30%, the performance improvement is limited while the silver consumption increases. Therefore, Example 1 preferably uses a structure with a silver coverage of 1% to 20% and a carbon layer covering the exposed aluminum area.

[0116] Example 2 like Figure 2 As shown, a first-layer aluminum electrode with 100% coverage is formed on the surface of a piezoelectric ceramic substrate, and a second-layer silver electrode with coverage ranging from 0.1% to 100% is formed locally on the aluminum electrode, without an outer carbon-based protective layer. This structure is suitable for applications with relatively dry environments, low operating temperatures, weak liquid media corrosion, or where the device requires minimal external mass. Compared to a single aluminum electrode, this structure retains the advantages of solderability and terminal connection in the silver area; compared to an all-silver electrode, this structure reduces silver loss by having the aluminum layer cover the majority of the area.

[0117] The parameters for each step are the same as in Example 1. The performance verification results of the product prepared in this example are as follows: Table 2 Analysis of the data in Table 2 shows that without a carbon-based protective layer, the initial electrical properties of the sample can still be maintained at a level similar to that of an all-silver electrode. However, after damp heat treatment, the aluminum exposed area is more prone to increased contact resistance (see subsequent experimental results). Therefore, this method is suitable for dry packaging or low-humidity environments.

[0118] Example 3 like Figure 3 As shown, a first-layer aluminum electrode with 100% coverage is formed on the surface of a piezoelectric ceramic substrate, a second-layer silver electrode with 0% coverage, and an outer carbon-based protective layer with a coverage of 0.1% to 100%. This structure is suitable for device structures that can be connected via elastic metal crimping, conductive adhesive bonding, mechanical clamping, or without soldering. The carbon-based protective layer covers all or part of the exposed area of ​​the aluminum layer, reducing surface oxidation and moisture erosion. For piezoelectric ceramic elements requiring further cost reduction and connections that do not rely on soldering, this implementation can achieve silver-free or extremely low-silver content.

[0119] The parameters for each step are the same as in Example 1, and the resulting products are denoted as M1-Ag0-C100, M1-Ag0-C99, M1-Ag0-C90, M1-Ag0-C80, M1-Ag0-C70, M1-Ag0-C60, M1-Ag0-C50, M1-Ag0-40, M1-Ag0-30, M1-Ag0-C20, M1-Ag0-C10, M1- Ag0-C0.1, M2-Ag0-C100, M2-Ag0-C99, M2-Ag0-C90, M2-Ag0-C80, M2-Ag0-C70, M2-Ag 0-C60, M2-Ag0-C50, M2-Ag0-40, M2-Ag0-30, M2-Ag0-C20, M2-Ag0-C10, M2-Ag0-C0.1.

[0120] The performance verification results of the product prepared in this embodiment are as follows: Table 3 Analysis of the data in Table 3 shows that in the silver-free structure, the carbon-based protective layer can improve the environmental stability of the aluminum electrode, but due to the lack of silver-based solderable areas, it is more suitable for spring pressing, conductive adhesive bonding or clamping connection; when the carbon layer coverage is 80% to 100%, the resistance change after damp heat is small (see subsequent experimental results).

[0121] Example 4 like Figure 4 As shown, a first-layer aluminum electrode with a coverage of 0.1% to 100% is formed on the surface of a piezoelectric ceramic substrate, followed by a second-layer silver electrode with a coverage of 0.1% to 100%, and an outer carbon-based protective layer with a 100% coverage. In this embodiment, the outer carbon-based protective layer can cover the entire target electrode formation surface, achieving full-surface protection against oxidation and water vapor. The silver electrode can be multiple discrete pads, dispersed island-like regions, or localized conductive enhancement areas. For high-humidity, high-temperature, underwater acoustic, seawater, or cleaning fluid environments, the 100% coverage carbon-based protective layer can provide an overall barrier for the aluminum layer edges, the silver-aluminum interface, and the ceramic electrode boundary.

[0122] The parameters for each step are the same as in Example 1, and the resulting product is denoted as: M1-Al80-Ag5-C100: The first layer of aluminum electrode is a continuous area with a central circular or near-circular shape, covering 80% of the target electrode formation surface; the second layer of silver electrode is a central circular pad with a coverage of 5%, fully overlapping with the aluminum electrode; the outer carbon-based protective layer covers 100% of the target electrode formation surface, with a 2 mm diameter welding window reserved at the central silver pad.

[0123] Similarly, M1-Al90-Ag5-C100, M1-Al100-Ag5-C100, and M1-Al80-Ag10-C100 were prepared; M2-Al80-Ag5-C100: Both main surfaces adopt the Al80-Ag5-C100 structure. The aluminum electrodes, silver electrodes and carbon-based protective layers on both surfaces have the same shape and are symmetrically distributed along the thickness direction. Alternatively, one silver pad can be located in the center and the other silver pad can be located at the edge to accommodate the assembly terminals.

[0124] Similarly, M2-Al100-Ag5-C100 was prepared.

[0125] The performance verification results of the product prepared in this embodiment are as follows: Table 4 Analysis of the data in Table 4 shows that partial coverage can be used for both the first aluminum electrode and the second silver electrode. When the carbon layer fully covers the electrode and a welding window is reserved or opened later, both protection and electrical connection can be achieved. The aluminum layer coverage should not be too low, preferably not less than 80%, in order to maintain the effective electrode area and capacitance.

[0126] Example 5 like Figure 5 As shown, the first layer of aluminum electrode has a coverage of 0.1% to 100%, the second layer of silver electrode has a coverage of 0.1% to 100%, and the outer carbon-based protective layer has a coverage of 100%. However, the silver electrodes use concentrated or irregular patterns, such as rhomboid, polygonal, elliptical, or large-area pad patterns. This embodiment is used to illustrate that, within the same area range, the pattern of the silver electrode is not limited to a circle or a regular rectangle, but can be optimized according to the lead direction, terminal shape, sound field distribution, vibration node position, and assembly space. After the carbon layer has full coverage, connection can be achieved through reserved windows, later window opening, or conductive piercing terminals.

[0127] The parameters for each step are the same as in Example 1, and the resulting product is denoted as: M1-Al100-Ag5-C100-Rhombus (hereinafter referred to as Rhombus Ag5): The first layer of aluminum electrode has a coverage of 100%; the second layer of silver electrode is a central rhombus pad with a coverage of 5%, and the long diagonal of the rhombus is arranged along the lead direction; the outer carbon-based protective layer has a coverage of 100%, and a welding window is reserved in the center of the rhombus silver pad.

[0128] M1-Al100-Ag5-C100-Pentagon (hereinafter referred to as Pentagon Ag5): The first layer of aluminum electrode has a coverage of 100%; the second layer of silver electrode is a pentagonal pad with a coverage of 5%, one side of which faces the lead exit; the outer carbon-based protective layer has a coverage of 100% and overlaps with the edge of the silver pad by about 0.5 mm.

[0129] M1-Al100-Ag5-C100-Elliptical (hereinafter referred to as Elliptical Ag5): The first layer of aluminum electrode has a coverage of 100%; the second layer of silver electrode is an elliptical pad with a coverage of 5%, and the major axis is set along the lead direction; the outer carbon-based protective layer has a coverage of 100%, and the center of the silver pad is exposed.

[0130] M1-Al100-Ag20-C100-Large Area Pad Pattern (hereinafter referred to as Large Area Pad Ag20): The first layer of aluminum electrode has a coverage of 100%; the second layer of silver electrode is a rectangular, rounded rectangle or end pad with a coverage of 20%, used for larger pads or metal terminals; the outer carbon-based protective layer has a coverage of 100%, and the welding area is reserved through a mask.

[0131] M2-Al100-Ag5-C100-Rhombus: Both main surfaces use central rhombus-shaped silver pads with identical shapes and symmetrical positions; the carbon layer fully covers the surface and provides a soldering window.

[0132] M2-Al100-Ag5-C100-Pentagon: Both main surfaces use pentagonal silver pads; the pentagonal pads on both surfaces can be arranged in the same direction or mirrored depending on the lead exit direction.

[0133] M2-Al100-Ag5-C100-Elliptical (hereinafter referred to as M2 Elliptical Ag5): Both main surfaces use elliptical silver pads with the major axis set along the assembly lead direction; the carbon layer covers the non-soldering edge of the silver pads and retains the center window.

[0134] M2-Al100-Ag20-C100-Large Area Pad Pattern (hereinafter referred to as M2 Large Area Ag20): Both main surfaces use large area end pads, which are suitable for metal springs, pads or housings. The overlap area between the silver pad and the aluminum electrode is not less than 90% of the area of ​​the silver pad.

[0135] The performance verification results of the product prepared in this embodiment are as follows: Table 5 Analysis of the data in Table 5 shows that when the silver coverage area is the same or similar, rhombus, pentagon, ellipse and large area pad patterns can all achieve effective connection; ellipse and large area pads are easy to arrange along the lead direction, while rhombus and polygon are suitable for avoiding vibration nodes or assembly interference areas.

[0136] Example 6 like Figure 6As shown, the first aluminum electrode layer has a coverage of 0.1% to 100%, the second silver electrode layer has a coverage of 0.1% to 100%, and the outer carbon-based protective layer has a coverage of 0.1% to 100%. This embodiment is suitable for devices requiring a trade-off between cost, solderability, protective strength, and mechanical added mass. For example, the carbon layer can be placed only at the edges of the aluminum layer and at the silver-aluminum overlap, or only in areas easily exposed to moisture, leaving the silver pads exposed for direct soldering. This structure is particularly suitable for small-sized piezoelectric components or piezoelectric elements whose resonant frequency is sensitive to added mass.

[0137] The parameters for each step are the same as in Example 1, and the resulting product is denoted as: M1-Al100-Ag5-C50: The first layer of aluminum electrode has a 100% coverage; the second layer of silver electrode is a central circular pad with a 5% coverage; the outer carbon-based protective layer has a 50% coverage, prioritizing the coverage of the outer periphery of the aluminum electrode, the silver-aluminum overlap boundary, and the area expected to be exposed to moisture, while the center of the silver pad remains exposed.

[0138] Similarly, M1-Al100-Ag5-C10, M1-Al100-Ag5-C30, M1-Al100-Ag5-C70, and M1-Al100-Ag5-C90 were prepared. M2-Al100-Ag5-C50: Both main surfaces adopt the Al100-Ag5-C50 structure; when one surface is on the liquid side and the other surface is on the inner side of the package, the carbon layer coverage on the liquid side can be increased to 70% to 100%, and the carbon layer coverage on the package side can be reduced to 10% to 50%.

[0139] The performance verification results of the product prepared in this embodiment are as follows: Table 6 Analysis of the data in Table 6 shows that a local carbon protective layer can protect the edges of the aluminum layer and the silver-aluminum interface while reducing the added mass. When the carbon layer coverage is 30% to 70% and focuses on covering the edges, the overlap area and the exposed aluminum area, the performance, cost and protective effect are relatively balanced.

[0140] Comparative Experiment Example 1: The representative low-silver composite electrode samples selected in Examples 1 to 6 of this invention (denoted as E1 to E6, where E1 is M1-Ag10-C90, E2 is M1-Ag10, E3 is M1-Ag0-C100, E4 is M1-Al100-Ag5-C100, E5 is M1-Al100-Ag5-C100-elliptical, and E6 is M1-Al100-Ag5-C50) and the traditional all-silver electrode sample (denoted as S0, using commercially available P5H piezoelectric ceramic discs of the same specifications, with silver paste screen-printed on both sides and sintered at 650°C to form an all-silver electrode with a thickness of about 10 micrometers) were respectively assembled into a hydroacoustic transducer and an ultrasonic cleaning transducer. Under the same polarization conditions (2.5kV / mm DC electric field applied in silicone oil at 120℃ for 20 minutes), the same assembly structure (same size metal shell, same specification epoxy potting and same specification lead welding), and the same small signal test voltage (1Vrms), the resonant frequency Fs, mechanical quality factor Qm, electrostatic capacitance CT, resonant resistance R1, electromechanical coupling coefficient Kp and piezoelectric constant D33 of the sample were tested. The connection reliability was evaluated in combination with the results of solder joint continuity, lead pull force and damp heat resistance retest.

[0141] The experimental method is as follows: The testing method is as follows: An impedance analyzer is used to scan within the range of 1kHz to 1MHz to read the resonant frequency Fs and resonant resistance R1, and Qm and Kp are calculated; an LCR meter is used to test the electrostatic capacitance CT at 1kHz and 1Vrms; a quasi-static d33 tester is used to test D33; the transducer output sound effect is compared using relative values ​​from hydrophones or sound pressure probes under the same water tank, installation depth, and drive power. The above tests can refer to the dynamic testing and piezoelectric parameter testing methods in GB / T 3389 series, IEC 60483, and IEEE 176.

[0142] Experimental results show that under the same test conditions, the deviation of Fs from S0 for samples E1 to E6 is no more than about 1.5%, the deviation of CT is no more than about 3%, and Qm, Kp and D33 are at the same level. E1, E4, E5 and E6 have solder joint conductivity and solder pull force close to S0 because they retain the silver-based soldering area. E3 does not have a silver layer and is more suitable for crimping or conductive adhesive connection.

[0143] The results show that the main piezoelectric parameters of the sample of the present invention are at the same level as those of the traditional silver electrode sample, and no significant performance damage is caused by using aluminum as the first main electrode.

[0144] Comparative Experiment Example 2: Experimental methods: Samples E1 to E6 and S0 were subjected to comparative tests of 96 hours of damp heat aging at 85℃ and 85%RH and 8 hours of continuous energization in water at room temperature. Electrode sheet resistance, lead contact resistance, appearance peeling and impedance parameter changes were measured before and after the test. The water energization test used the same fixture, the same immersion depth and the same driving power.

[0145] Experimental data: After 96 hours of humid heat, the contact resistance change rate of sample S0 was approximately 2% to 5%, the contact resistance change rate of samples E1, E4, E5 and E6 was approximately 3% to 8%, the change rate of sample E2 (without carbon protective layer) was approximately 10% to 18%, and the change rate of sample E3 (under crimp connection conditions) was approximately 5% to 10%. After 8 hours of continuous energization in water, no large-area peeling or powdering was observed in samples E1, E3, E4, E5 and E6 with carbon-based protective layers, while slight oxidation and darkening were visible on the edge aluminum layer of sample E2.

[0146] The results showed that during long-term operational testing, the samples of this invention, subjected to continuous or intermittent operation in underwater acoustic and ultrasonic cleaning environments, did not exhibit large-area pulverization, peeling, solder joint failure, or significant resistance increase due to aluminum layer oxidation. For samples with a carbon-based protective layer, the exposed aluminum layer was significantly reduced, and edge oxidation and moisture intrusion were suppressed. For samples with locally silver-based solderable electrodes, the wire bonding process was similar to that of traditional silver electrode samples, and the weld strength and conductivity stability met the device assembly requirements.

[0147] Comparative Experiment Example 3: The heat resistance or thermal aging comparison was carried out at 150℃. The specific method is as follows: E1 to E6 and S0 samples were placed in a 150℃ hot air oven and kept at that temperature for 168 hours. Every 24 hours, a group of samples was taken out and cooled to room temperature before testing the electrode conductivity, solder joint appearance, Fs, CT and R1 changes. For samples with leads, 20 thermal cycles from room temperature to 150℃ were performed, with each temperature point held for 20 minutes.

[0148] The experimental results are as follows: After holding at 150℃ for 168 hours, the solder joints of samples E1, E4, E5, and E6 did not fall off, the change rate of Fs was less than 1%, the change rate of CT was less than 3%, and the change rate of R1 was less than 10%; sample E2 showed slight oxidation in the exposed aluminum area, and the change rate of R1 was approximately 12% to 18%; sample E3 had no solder joint failure issues, but the pressure of the crimping or conductive adhesive connection needed to be maintained. After thermal cycling, no continuous cracks or large-area peeling were observed in the samples with the carbon-based protective layer.

[0149] The results show that the piezoelectric ceramic samples using the low-silver composite electrode of this invention exhibit comparable durability to those using conventional silver electrodes. The carbon-based protective layer maintains its coverage and barrier function over the aluminum layer within this temperature range, and the silver-based solderable electrode maintains its electrical connection to leads or terminals. Therefore, this invention is suitable not only for room-temperature ultrasonic and underwater acoustic devices, but also for piezoelectric ceramic components operating under medium-to-high temperature conditions, thermal cycling conditions, or high-humidity and heat storage conditions.

[0150] The low-silver composite electrode of the present invention can employ the same or different layer structures on one or both surfaces according to actual needs. For example, one side of the piezoelectric ceramic can employ the all-aluminum, partially silver, and partially carbon structure of Example 1, while the other side can employ the all-aluminum, partially silver, and carbon-free structure of Example 2; alternatively, a fully covered carbon protective layer can be used on the side of the underwater acoustic device that is in contact with the liquid, while a partially carbon protective layer or a carbon-free protective layer can be used on the side that is dry and encapsulated. Such combinations do not depart from the technical concept of the present invention, which uses a first non-precious metal layer, a second silver-based solderable layer, and an outer protective layer for functional partitioning.

[0151] This invention is not limited to aluminum as the first non-precious metal electrode. When the device's operating environment, sintering process, or material costs need to be changed, aluminum alloys, copper, nickel, tin, zinc, indium, and their alloys or composite metal layers can be used as the first electrode. Regardless of the non-precious metal material used, as long as it is adjacent to the piezoelectric ceramic substrate and bears the main conductive area, and welding and environmental stability issues are resolved through a local silver-based solderable layer and an optional protective layer, it falls within the technical concept of this invention.

[0152] The temperatures, times, thicknesses, area ratios, and material compositions listed in the above embodiments are preferred or optional ranges for ease of explanation. Those skilled in the art can make conventional adjustments to these parameters based on the piezoelectric ceramic system, device dimensions, resonant frequency, polarization conditions, sintering atmosphere, packaging method, and service medium without departing from the spirit of the invention.

[0153] In summary, this invention relates to a low-silver composite electrode for piezoelectric ceramics, its preparation method, and its applications. The composite electrode is disposed on the surface of a piezoelectric ceramic substrate and includes a first-layer non-precious metal electrode adjacent to the substrate, a second-layer silver-based solderable electrode disposed in a partial or complete area of ​​the substrate, and an optional outer protective layer. The first layer is preferably an aluminum electrode and bears the main conductive area; the second layer is preferably a silver or silver alloy electrode and provides a welding or terminal connection area; and the outer layer is preferably a carbon-based protective layer that blocks oxygen and moisture. The projected coverage of the three layers is 0.1% to 100%, 0% to 100%, and 0% to 100%, respectively. The electrode pattern can be circular, elliptical, square, rhomboid, polygonal, dotted, or a combination thereof. This invention reduces the amount of silver used, improves the solderability and oxidation and moisture resistance of the aluminum electrode, and is suitable for piezoelectric ceramics such as P8, P4, P5, P5A, and P5H, as well as ultrasonic cleaning, underwater sonar, ultrasonic welding, and ultrasonic sludge purification.

[0154] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A low-silver composite electrode for piezoelectric ceramics, disposed on at least one electrode forming surface of a piezoelectric ceramic substrate, characterized in that, include: The first layer is a non-precious metal electrode, an outer protective layer disposed on the surface of the first layer is a non-precious metal electrode, and a second layer is a silver-based solderable electrode optionally disposed on the surface of the first layer is a non-precious metal electrode; the outer protective layer at least covers the exposed area and / or edge area of ​​the first layer is not covered by the second layer is a silver-based solderable electrode.

2. The low-silver composite electrode for piezoelectric ceramics according to claim 1, characterized in that, The secondary silver-based solderable electrode is disposed in a local area or the entire area of ​​the primary non-precious metal electrode; preferably, the secondary silver-based solderable electrode is disposed in a local area of ​​the primary non-precious metal electrode, wherein the local area is an edge area, a central area or a dispersed area. And / or, the projected shape of the secondary silver-based solderable electrode is any combination of one or more of the following: circular, elliptical, polygonal, annular, semi-annular, fan-shaped, strip-shaped, grid-shaped, island-shaped, dot-matrix-shaped, interdigitated, end pad-shaped, and edge pad-shaped; preferably, the polygon is square, rectangular, rhomboid, and / or triangular. And / or, the distribution of the secondary silver-based solderable electrodes is a local distribution; preferably, the distribution of the secondary silver-based solderable electrodes is a central concentrated distribution, an edge concentrated distribution, a multiple pad dispersed distribution, a symmetrical distribution along the polarization direction, or an asymmetrical distribution along the device mounting terminals; And / or, the outer protective layer is disposed on the area of ​​the first non-precious metal electrode not covered by the second silver-based solderable electrode, the non-soldering area of ​​the second silver-based solderable electrode, and the area adjacent to both. And / or, the projected shape of the outer protective layer is a full-coverage film or a partial-coverage film that completely covers the electrode forming surface; preferably, the projected shape of the outer protective layer is a continuous film covering the exposed area of ​​the first layer non-precious metal electrode, an annular film covering the exposed area of ​​the first layer non-precious metal electrode and avoiding the welding window of the second layer silver-based solderable electrode, a continuous film covering the non-welding areas of the first layer non-precious metal electrode and the second layer silver-based solderable electrode, a strip covering film, a dot matrix covering film, or an edge sealing film; And / or, based on the geometric area of ​​the electrode forming surface, the projected coverage of the first non-precious metal electrode is 0.1% to 100%, the projected coverage of the second silver-based solderable electrode is 0% to 100%, the projected coverage of the outer protective layer is 0% to 100%, and when the projected coverage of the second silver-based solderable electrode is 0%, the projected coverage of the outer protective layer is greater than 0%.

3. The low-silver composite electrode for piezoelectric ceramics according to claim 1 or 2, characterized in that, The first non-precious metal electrode is one or more composite layers selected from aluminum electrode, aluminum alloy electrode, copper electrode, copper alloy electrode, nickel electrode, nickel alloy electrode, tin electrode, tin alloy electrode, zinc electrode, zinc alloy electrode, indium electrode, and indium alloy electrode; preferably, the first non-precious metal electrode is an aluminum electrode or an aluminum alloy electrode with an aluminum content of not less than 50 wt%. And / or, the secondary silver-based solderable electrode is one of the following: a silver electrode, a silver-palladium alloy electrode, a silver-platinum alloy electrode, a silver-copper alloy electrode, a silver-nickel alloy electrode, a silver paste sintered electrode containing a glass binder phase, a low-temperature curing silver paste electrode, a silver-coated metal powder electrode, or a silver-based composite conductive electrode; the silver element in the secondary silver-based solderable electrode is 5% to 100% based on the mass of the conductive solid phase, preferably 20% to 100%. And / or, the outer protective layer includes a carbon-based conductive protective layer; preferably, the outer protective layer is one or a composite layer of two or more of the following: a carbon paste sintering layer, a carbon paste curing layer, a graphite conductive layer, a carbon black conductive layer, a graphene conductive layer, a carbon nanotube conductive layer, a conductive polymer protective layer, a glass phase protective layer, a ceramic phase protective layer, an organosilicon moisture-proof layer, and an epoxy moisture-proof layer; preferably, the sheet, particle, or network structure of the carbon-based conductive protective layer covers the exposed surface of the first non-precious metal electrode; And / or, the piezoelectric ceramic matrix is ​​one or more composite ceramics selected from lead zirconate titanate-based piezoelectric ceramics, modified lead zirconate titanate-based piezoelectric ceramics, lead titanate-based piezoelectric ceramics, lead metaniobate-based piezoelectric ceramics, lead magnesium niobate titanate-based piezoelectric ceramics, barium titanate-based piezoelectric ceramics, potassium sodium niobate-based lead-free piezoelectric ceramics, sodium bismuth titanate-based lead-free piezoelectric ceramics, and silver niobate-based piezoelectric ceramics; preferably, the piezoelectric ceramic matrix includes one of P8, P4, P5, P5A, P5H, or their modified materials.

4. The low-silver composite electrode for piezoelectric ceramics according to any one of claims 1-3, characterized in that, A transition bonding phase is provided between the first-layer non-precious metal electrode and the piezoelectric ceramic substrate; the transition bonding phase includes low-melting-point lead-free glass, borosilicate glass, bismuth boron zinc glass, zinc boron glass, phosphate glass, titanate glass, alumina micro powder, zinc oxide micro powder, bismuth oxide micro powder, silicon oxide micro powder, titanium oxide micro powder, or an inorganic bonding phase that can improve the adhesion strength between the electrode and the ceramic interface.

5. The low-silver composite electrode for piezoelectric ceramics according to any one of claims 1-4, characterized in that, The secondary silver-based solderable electrode at least covers the area on the primary non-precious metal electrode where solder leads, solder terminals, solder metal housings, connecting conductive springs, connecting conductive adhesives, connecting spring pins, and / or connecting external circuits are required; the overlap width between the secondary silver-based solderable electrode and the primary non-precious metal electrode is not less than 0.05 mm, preferably 0.2 mm to 10 mm. And / or, the outer protective layer forms a sealing structure at the edge of the first non-precious metal electrode, the sealing structure covering the outer periphery, hole edge, notch edge, cut edge, chamfer edge and / or interface edge adjacent to the piezoelectric ceramic substrate of the first non-precious metal electrode.

6. The low-silver composite electrode for piezoelectric ceramics according to any one of claims 1-5, characterized in that, The low-silver composite electrode is disposed on one main surface, two opposite main surfaces, side surface, end face, inner hole surface, outer cylindrical surface, arc surface and / or irregular surface of the piezoelectric ceramic substrate; when the low-silver composite electrode is disposed on both opposite main surfaces of the piezoelectric ceramic substrate, the coverage, shape and distribution of the first non-precious metal electrode, the second silver solderable electrode and the outer protective layer on the two surfaces can be the same or different.

7. The low-silver composite electrode for piezoelectric ceramics according to any one of claims 1-6, characterized in that, The thickness of the first non-precious metal electrode is 0.05 micrometers to 80 micrometers, preferably 1 micrometer to 35 micrometers; And / or, the thickness of the secondary silver-based solderable electrode is from 0.05 micrometers to 50 micrometers, preferably from 1 micrometer to 20 micrometers; And / or, the thickness of the outer protective layer is from 0.05 micrometers to 100 micrometers, preferably from 1 micrometer to 40 micrometers.

8. The low-silver composite electrode for piezoelectric ceramics according to any one of claims 1-7, characterized in that, The coverage ratio of the first-layer non-precious metal electrode, the second-layer silver-based solderable electrode, and the outer protective layer is any one of Schemes 1 to 5: Option 1: The first-layer non-precious metal electrode is an all-aluminum electrode with 100% coverage; the second-layer silver-based solderable electrode has a coverage of 0.1% to 100%; and the outer protective layer is a carbon-based conductive protective layer with a coverage of 0.1% to 100%. Preferably, the second-layer silver-based solderable electrode has a coverage of 1% to 20%; the outer protective layer is a carbon-based conductive protective layer with a coverage of 80% to 99%; the carbon-based conductive protective layer covers the area of ​​the all-aluminum electrode surface not covered by the second-layer silver-based solderable electrode and overlaps with the edge of the silver electrode by 0.2 mm to 2 mm. Option 2: The first layer of non-precious metal electrode is an all-aluminum electrode with a coverage of 100%; the second layer of silver-based solderable electrode has a coverage of 0.1% to 100%; and the outer protective layer is an edge-sealing protective layer or a partial protective layer with a coverage of 0.1% to 20%. Option 3: The first non-precious metal electrode is an all-aluminum electrode with 100% coverage; the second silver-based solderable electrode has 0% coverage; and the outer protective layer is a carbon-based conductive protective layer with 0.1% to 100% coverage. Preferably, the carbon-based conductive protective layer has 80% to 100% coverage, more preferably 90% to 100%. Option 4: The first-layer non-precious metal electrode is an aluminum electrode with a coverage of 0.1% to 100%, but not 100%; the second-layer silver-based solderable electrode has a coverage of 0.1% to 100%; and the outer protective layer is a carbon-based conductive protective layer with a coverage of 100%. Preferably, the first-layer non-precious metal electrode has a coverage of not less than 80%, the second-layer silver-based solderable electrode has a coverage of 5% to 10%, and is completely located within and overlaps with the coverage area of ​​the first-layer non-precious metal electrode; the carbon-based conductive protective layer has a coverage of 100%. Option 5: The first-layer non-precious metal electrode is an aluminum electrode with a coverage of 0.1% to 100%, the second-layer silver-based solderable electrode has a coverage of 0.1% to 100%, and the outer protective layer is a carbon-based conductive protective layer with a coverage of 0.1% to 100%, but not 100%; preferably, the first-layer non-precious metal electrode has a coverage of 100%, the second-layer silver-based solderable electrode has a coverage of 5%, and the carbon-based conductive protective layer has a coverage of 30% to 70%. Preferably, in Schemes 1 to 5, the outer protective layer preferably avoids the welding window of the secondary silver-based solderable electrode.

9. A method for preparing a low-silver composite electrode for piezoelectric ceramics as described in any one of claims 1-8, characterized in that, Includes the following steps: Using the first-layer non-precious metal electrode precursor as raw material, a first-layer non-precious metal electrode precursor layer is prepared on the surface of the piezoelectric ceramic substrate to be polarized. After drying, sintering, curing, heat treatment and / or deposition post-treatment, a piezoelectric ceramic containing the first-layer non-precious metal electrode is obtained. And / or, using a secondary silver-based solderable electrode precursor as raw material, a secondary silver-based solderable electrode precursor layer is prepared on the surface of the piezoelectric ceramic containing the primary non-precious metal electrode, and the piezoelectric ceramic containing the secondary silver-based solderable electrode is obtained by drying, sintering, curing and / or heat treatment. And / or, using an outer protective layer precursor as raw material, an outer protective layer precursor layer is prepared on the surface of the piezoelectric ceramic containing a secondary silver-based solderable electrode, and the piezoelectric ceramic containing the outer protective layer is obtained by drying, sintering, curing and / or heat treatment, which is the low silver composite electrode for piezoelectric ceramics.

10. The method for preparing a low-silver composite electrode for piezoelectric ceramics according to claim 9, characterized in that, The preparation methods of the first non-precious metal electrode precursor layer, the second silver-based solderable electrode precursor layer, and the outer protective layer precursor layer are independently selected from any one or a combination of multiple methods from screen printing, pad printing, spraying, brushing, scraping, dispensing, dip coating, spin coating, roller coating, laser transfer printing, thermal spraying, vacuum evaporation, magnetron sputtering, electroplating, chemical plating, and aerosol spraying. And / or, before preparing the first non-precious metal electrode precursor layer, the surface of the piezoelectric ceramic substrate to be polarized is subjected to grinding, polishing, cleaning, drying and surface activation treatment. And / or, it further includes the step of electric field polarization of the piezoelectric ceramic containing the outer protective layer; preferably, the parameters of the electric field polarization are: polarization electric field strength of 0.5 kV / mm to 6 kV / mm, polarization temperature of 20°C to 200°C, and polarization medium of air, silicone oil, transformer oil, water-based medium or inert atmosphere; preferably, after polarization, tin soldering, brazing, conductive adhesive bonding, metal spring pressing, riveting or terminal welding are performed on the secondary silver-based solderable electrode.

11. The method for preparing a low-silver composite electrode for piezoelectric ceramics according to any one of claims 9-10, characterized in that, The first layer of non-precious metal electrode is formed by screen printing aluminum paste and sintering it at 500°C to 750°C. And / or, the secondary silver-based solderable electrode is formed by screen printing silver paste or silver alloy paste and then sintering it at 450°C to 800°C; And / or, the outer protective layer is formed by screen printing carbon paste and then curing or sintering at 120°C to 650°C.

12. The method for preparing a low-silver composite electrode for piezoelectric ceramics according to any one of claims 9-11, characterized in that, Sintering can be selected from processes such as single co-firing, double firing, triple firing, firing before curing, curing before polarization, or partial coating of protective layer after polarization. When multiple firings are used, the sintering temperature of the subsequent layer should not be higher than the temperature that could cause severe oxidation, melt flow, interface peeling, or depolarization of the previous electrode layer.

13. The method for preparing a low-silver composite electrode for piezoelectric ceramics according to any one of claims 9-12, characterized in that, The first-layer non-precious metal electrode is an aluminum electrode, which is formed by sintering an electrode slurry containing aluminum powder. The raw materials of the electrode slurry containing aluminum powder include metallic aluminum powder, inorganic binder, organic carrier, dispersant, leveling agent, defoamer, and antioxidant. The antioxidant includes one or more of the following: boron powder, red phosphorus, phosphate, boron-containing compound, silicon-containing compound, antioxidant glass phase, or additives that can reduce the oxidation degree of aluminum powder during sintering.

14. The application of a low-silver composite electrode for piezoelectric ceramics according to any one of claims 1-8 in the fabrication of devices, characterized in that, The device is an ultrasonic transducer, a hydroacoustic transducer, an ultrasonic cleaning transducer, an ultrasonic welding transducer, an ultrasonic sludge purification transducer, an atomizing plate, a buzzer plate, a buzzer, a piezoelectric sensor, a piezoelectric actuator, a piezoelectric transformer, a piezoelectric motor, a medical ultrasonic device, a non-destructive testing probe, a flow meter transducer, or a marine acoustic device.

15. A piezoelectric ceramic element, characterized in that, It includes a piezoelectric ceramic substrate and a low-silver composite electrode for piezoelectric ceramics as described in any one of claims 1 to 8 disposed on at least one surface of the piezoelectric ceramic substrate.

16. The piezoelectric ceramic element according to claim 15, characterized in that, The piezoelectric ceramic element is a circular plate, square plate, ring plate, tubular body, columnar body, spherical cap, arc surface body, thick plate, thin plate, stacked plate or irregularly shaped plate; And / or, the first non-precious metal electrode of the low-silver composite electrode forms a continuous conductive area within the effective vibration area, the second silver-based solderable electrode is positioned at a location that does not significantly reduce the effective vibration area, and the outer protective layer is positioned at a location that does not significantly increase mechanical damping or significantly change the resonant frequency.

17. The application of a piezoelectric ceramic element as described in claim 15 or 16 in the fabrication of a device, characterized in that, The device is an ultrasonic transducer, a hydroacoustic transducer, an ultrasonic cleaning transducer, an ultrasonic welding transducer, an ultrasonic sludge purification transducer, an atomizing plate, a buzzer plate, a buzzer, a piezoelectric sensor, a piezoelectric actuator, a piezoelectric transformer, a piezoelectric motor, a medical ultrasonic device, a non-destructive testing probe, a flow meter transducer, or a marine acoustic device.

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