Ceramic varistor and preparation method and application thereof

Abstract

The invention belongs to the technical field of electronic components, and particularly relates to a ceramic piezoresistor and a preparation method and application thereof. The ceramic varistor comprises a ceramic substrate and a copper-based electrode formed on the surface of the ceramic substrate, the copper-based electrode comprises a metal transition layer, a copper layer, an aluminum layer, a DLC layer and a resin layer which are sequentially arranged on the ceramic substrate, and the ceramic varistor is specifically prepared by the following steps: firstly, preparing the metal transition layer on the substrate through a direct current magnetron sputtering coating process; preparing a copper layer and an aluminum layer in sequence through a high-power pulse magnetron sputtering process, preparing a DLC surface layer on the surface of the aluminum layer by adopting a plasma enhanced chemical vapor deposition technology, and finally coating the DLC layer with a resin layer. All the layers are matched with one another, so that the obtained ceramic varistor finally realizes collaborative optimization of various performances.

Description

Technical Field

[0001] This invention belongs to the field of electronic components technology, specifically relating to a ceramic varistor, its preparation method, and its application. Background Technology

[0002] In numerous fields such as electronics, power, communication equipment, and automotive electronics, the safe and stable operation of circuit systems relies heavily on effective overvoltage protection devices. Ceramic varistors, with their excellent nonlinear current-voltage characteristics, fast response speed, and high surge absorption capacity, have become one of the core components in the current overvoltage protection field, widely used in scenarios such as lightning protection and suppression of transient overvoltages. As these fields rapidly develop towards higher integration, higher reliability, and longer lifespan, more stringent requirements are being placed on the performance of ceramic varistors. The shortcomings of traditional ceramic varistors in areas such as electrode stability, oxidation resistance, corrosion resistance, and overall lifespan are becoming increasingly apparent, making it difficult to fully meet the application needs of next-generation electronic devices.

[0003] From the perspective of electrode structure and performance, traditional ceramic varistors often use silver electrodes or single metal electrodes. While silver electrodes possess good conductivity, silver is expensive, and during long-term use, silver ions easily diffuse into the ceramic substrate, triggering interfacial reactions. This leads to decreased adhesion between the electrode and the ceramic substrate, and even electrode detachment, severely affecting the electrical performance stability and lifespan of the varistor. While single copper electrodes are relatively inexpensive, their thermal expansion coefficients differ significantly from those of the ceramic substrate. Under cyclic temperature changes, this difference easily generates thermal stress, causing electrode cracking or detachment. Furthermore, copper is prone to oxidation in humid and corrosive environments; the resulting copper oxide significantly increases electrode resistance, weakening the varistor's conductivity and ultimately leading to device failure. In addition, some varistors using single metal electrodes lack effective protective structures, leaving the electrodes directly exposed to air, making them susceptible to corrosion from oxygen, moisture, and external corrosive media, further shortening the device's lifespan.

[0004] In terms of encapsulation and protection, traditional ceramic varistors are mostly encapsulated using simple resin coating or metal casing. The former offers poor protection, prone to defects such as bubbles and cracks, and fails to form an effective physical barrier, making it difficult to reliably protect the electrodes and ceramic substrate. While the latter offers superior protection, it significantly increases the size and weight of the device, contradicting the current trend of miniaturization and lightweighting in electronic devices. Furthermore, its high encapsulation cost limits its large-scale application. In addition, existing Chinese patent applications disclose a technique for preparing an antioxidant layer using a mixture of resin and alumina particles, but its protective effect remains insufficient and requires further improvement.

[0005] In summary, to address the issues of traditional ceramic varistors in terms of electrode performance and packaging protection, improve device stability, reliability and lifespan, reduce production costs, and meet the urgent demand in the current electronic field for high-performance overvoltage protection devices, it is imperative to develop a ceramic varistor with a novel electrode structure and superior performance. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the defects and shortcomings of ceramic varistors in terms of poor electrode stability and overall service life. The primary objective is to provide a ceramic varistor.

[0007] A second objective of this invention is to provide a method for preparing the ceramic varistor.

[0008] A third objective of this invention is to provide the application of the ceramic varistor in the fabrication of varistors.

[0009] The above-mentioned objective of this invention is achieved through the following technical solution: This invention protects a ceramic varistor, comprising a ceramic substrate and a copper-based electrode formed on the surface of the ceramic substrate, wherein the copper-based electrode comprises a metal transition layer, a copper layer, an aluminum layer, a DLC layer (diamond-like carbon coating), and a resin layer sequentially disposed on the ceramic substrate. The metal in the metal transition layer is selected from one or more of molybdenum, titanium, and chromium.

[0010] The ceramic varistor of the present invention includes a ceramic substrate and a copper-based electrode formed on the surface of the ceramic substrate. The copper-based electrode includes a specific metal transition layer, a copper layer, an aluminum layer, a DLC layer and a resin layer sequentially disposed on the ceramic substrate. The specific metal transition layer exhibits excellent compatibility and strong adhesion with the ceramic substrate, serving as a transition layer to mitigate the difference in thermal expansion coefficients between copper and the ceramic substrate. This fundamentally prevents electrode cracking and detachment due to thermal stress under temperature cycling conditions, providing stable support for subsequent electrode layers. The aluminum layer, significantly cheaper than silver, substantially reduces electrode material costs. Furthermore, aluminum readily forms a dense alumina layer in air, effectively isolating oxygen from the copper layer and preventing oxidation that increases resistance, thus addressing the poor oxidation resistance of traditional copper electrodes and extending electrode lifespan. The dense DLC layer completely isolates the copper and aluminum layers from air, moisture, and external corrosive media, preventing corrosion caused by direct electrode exposure and further enhancing electrode weather resistance. The dual isolation protection of the resin encapsulation and DLC layer ensures the varistor maintains excellent nonlinear current-voltage characteristics and conductivity stability even under temperature cycling, humid, and corrosive environments, meeting the requirements of high-reliability electronic devices. The synergistic interaction of these layers ultimately leads to the synergistic optimization of various performance characteristics in the resulting ceramic varistor.

[0011] Furthermore, the ceramic varistor satisfies one or more of the following (1) to (5): (1) The thickness of the metal transition layer is 0.05~0.3μm; (2) The thickness of the copper layer is 0.3~3μm; (3) The thickness of the aluminum layer is 0.2~3μm; (4) The thickness of the DLC layer is 0.2~0.5μm; (5) The thickness of the resin layer is 2~3μm.

[0012] Preferably, the resin layer is made from at least one of the following raw materials: (1) pure epoxy resin or its encapsulating material; (2) pure silicone resin or its encapsulating material; (3) pure phenolic resin or its encapsulating material.

[0013] Taking epoxy powder encapsulants as an example, epoxy encapsulants are thermosetting chemical materials made from epoxy resin as the matrix, with added curing agents, fillers, pigments, and various additives. The composition of other types of resin encapsulants follows the same principle.

[0014] The above-mentioned resin encapsulating material is commercially available. The purpose of this invention can be achieved by using the above-mentioned resin or its encapsulating material.

[0015] Preferably, the resin layer is made from at least one of the following raw materials: (1) epoxy resin encapsulant; (2) silicone resin encapsulant; (3) phenolic resin encapsulant.

[0016] Preferably, the thickness of the metal transition layer is 0.05~0.1μm, more preferably 0.08~0.1μm.

[0017] Preferably, the thickness of the copper layer is 2~3μm.

[0018] Preferably, the thickness of the aluminum layer is 0.2~2μm, more preferably 0.2~0.5μm.

[0019] Preferably, the thickness of the DLC layer is 0.4~0.5μm.

[0020] Preferably, the thickness of the resin layer is 2.5~3μm.

[0021] The present invention protects a method for preparing the ceramic varistor, comprising the following steps: S1. Preparation of metal transition layer: On the pretreated ceramic substrate, a metal transition layer is deposited by DC magnetron sputtering to form a metal transition layer; S2. Copper layer preparation: After the metal transition layer is deposited, a copper layer is deposited on the metal transition layer obtained in step S1 using a high-power pulsed magnetron sputtering process to form a copper layer; S3. Preparation of aluminum layer: After the copper layer deposition is completed, an aluminum layer is deposited on the surface of the copper layer obtained in step S2 using a high-power pulsed magnetron sputtering process to form an aluminum layer; S4. Preparation of DLC layer: After the aluminum layer deposition is completed, a DLC layer is deposited on the surface of the aluminum layer obtained in step S3 using plasma-enhanced chemical vapor deposition technology to form a DLC layer; S5. Preparation of resin layer: After nitrogen purging of the device with DLC coating formed in step S4, preheating is performed, resin is coated on the DLC layer obtained in step S4, and curing is performed to form resin layer; In steps S2 and S3, the average power of the high-power pulsed magnetron sputtering process is ≥2kW.

[0022] Compared to traditional evaporation-deposited copper electrodes, copper layers prepared by high-power pulsed magnetron sputtering have higher density, fewer pores, and a tighter bond with the metal transition layer. This process retains the excellent conductivity of copper while avoiding the defects of traditional copper electrodes that are prone to detachment, ensuring the long-term conductivity stability of the electrode.

[0023] Furthermore, in step S1, the DC magnetron sputtering coating process satisfies one or more of the following (1) to (4): (1) Power 3~10kW; (2) The pressure of the inert gas is 0.2~0.8 Pa; (3) Base bias voltage: -400~-600V; (4) Duty cycle: 5%~20%.

[0024] Preferably, in step S1, the power is 5~8kW.

[0025] Preferably, in step S1, the pressure of the inert gas is 0.5~0.8 Pa.

[0026] Preferably, in step S1, the substrate bias voltage is -500 to -600V.

[0027] Preferably, in step S1, the duty cycle is 10%~20%.

[0028] Preferably, the inert gas includes at least one of argon, neon, and krypton.

[0029] Furthermore, in steps S2 and S3, each of the high-power pulsed magnetron sputtering processes independently satisfies one or more of the following (1) to (5): (1) Average power 2~8kW; (2) Frequency: 50~500Hz; (3) Pulse width: 30~300μs; (4) Inert gas pressure: 0.2~0.8 Pa; (5) Base bias: -30~-200V.

[0030] Preferably, in step S2 or step S3, the average power is 5~8kW.

[0031] Preferably, in step S2 or step S3, the frequency is 300~500Hz.

[0032] Preferably, in step S2 or step S3, the pulse width is 150~300μs.

[0033] Preferably, in step S2 or step S3, the pressure of the inert gas is 0.5~0.6 Pa.

[0034] Preferably, in step S2 or step S3, the substrate bias voltage is -50 to -80V.

[0035] Preferably, the inert gas includes at least one of argon, neon, and krypton.

[0036] Further, in step S4, the plasma-enhanced chemical vapor deposition technique satisfies one or more of the following (1) to (5): (1) Voltage: -300~-600V; (2) Frequency: 80~240kHz; (3) Duty cycle: 2%~10%; (4) The gas is a combination of carbon-containing gas and hydrogen, wherein the carbon-containing gas is selected from methane or acetylene, and the flow ratio of the carbon-containing gas to H2 is (5~1):1; (5) Air pressure: 0.5~5Pa.

[0037] Preferably, in step S4, the voltage is -400 to -600V, more preferably 450 to 600V.

[0038] Preferably, in step S4, the frequency is 80~100kHz.

[0039] Preferably, in step S4, the duty cycle is 2% to 3%.

[0040] Preferably, in step S4, the gas is a combination of carbon-containing gas and hydrogen, wherein the carbon-containing gas is selected from methane or acetylene, and the flow ratio of the carbon-containing gas to H2 is (5~3):1.

[0041] Preferably, in step S4, the air pressure is 0.5~3.5 Pa, more preferably 0.5~1 Pa.

[0042] Preferably, in step S5, the preheating temperature is 130~150 ℃.

[0043] More preferably, the ceramic substrate is a metal oxide ceramic substrate. The core component of the metal oxide ceramic substrate is a ceramic substrate mainly composed of metal oxides.

[0044] More preferably, the metal oxide is at least one of zinc oxide, titanium oxide, and tin oxide.

[0045] Furthermore, the pretreatment includes washing and drying.

[0046] Furthermore, the cleaning process involves ultrasonically cleaning the substrate in water.

[0047] Furthermore, the cleaning time is 10-30 minutes, preferably 12-18 minutes.

[0048] Furthermore, the drying process involves first air drying and then heating to dry.

[0049] Preferably, the drying temperature is 90~110℃.

[0050] Specifically, the pretreatment includes the following steps: ultrasonically cleaning the ceramic substrate in deionized water, air-drying it with nitrogen after cleaning, and further drying it in an oven at 100~110℃.

[0051] Furthermore, the curing process includes natural leveling and drying.

[0052] Preferably, the temperature of the natural leveling is 130~150℃.

[0053] Preferably, the drying temperature is 150~180℃.

[0054] Specifically, the curing conditions are as follows: natural leveling at 130~150℃ for 30~60s, and drying and curing at 150~180℃ for 10~30min (preferably 10~15min).

[0055] This invention protects the application of the ceramic varistor in the manufacture of varistors.

[0056] Compared with the prior art, the present invention has the following beneficial effects: The ceramic varistor of this invention comprises a ceramic substrate and a copper-based electrode formed on the surface of the ceramic substrate. The copper-based electrode includes a metal transition layer, a copper layer, an aluminum layer, a DLC layer, and a resin layer sequentially disposed on the ceramic substrate. Specifically, it is fabricated by the following method: first, a metal transition layer is prepared on the substrate using a magnetron sputtering process; then, a copper layer and an aluminum layer are sequentially prepared using a high-power pulsed magnetron sputtering process; next, a DLC surface layer is prepared on the aluminum layer using plasma-enhanced chemical vapor deposition; finally, a resin layer is coated on the DLC layer. The various layers work together to achieve synergistic optimization of performance, lifespan, and cost in the resulting ceramic varistor. Detailed Implementation

[0057] The present invention will be further illustrated below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in this technical field.

[0058] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0059] Example 1: A ceramic varistor S1. Cleaning the zinc oxide ceramic substrate: Ultrasonically clean the ceramic substrate in deionized water for 15 minutes, then air dry it with nitrogen and further dry it in an oven at 105℃. S2. Preparation of molybdenum layer: The dried zinc oxide ceramic substrate obtained in step S1 is placed in a vacuum coating chamber and a vacuum is drawn. When the coating conditions are met, a molybdenum layer is deposited using a magnetron sputtering molybdenum target. The magnetron sputtering conditions are as follows: power 6kW, argon gas pressure 0.5Pa, substrate negative bias voltage 500V (i.e., the substrate bias voltage is -500V), duty cycle 10%, and molybdenum layer thickness 0.1μm. S3. Copper layer preparation: After the molybdenum layer deposition is completed, a copper layer is deposited on the molybdenum layer obtained in step S2 using a high-power pulsed magnetron sputtering copper target. The average power is 5kW, the frequency is 300Hz, the pulse width is 150μs, the Ar gas pressure is 0.5Pa, the substrate negative bias voltage is 80V, and the copper layer thickness is 3μm. S4. Preparation of aluminum layer: After the copper layer deposition is completed, turn off the copper target, turn on the aluminum target, and adjust the average power: 5kW, frequency: 300Hz, pulse width: 150μs, argon gas pressure: 0.6Pa, substrate negative bias voltage: 50V, and deposit an aluminum layer on the surface of the copper layer obtained in step S3. The aluminum layer thickness is 0.2μm. S5. Preparation of DLC layer: After the aluminum layer deposition is completed, turn off the aluminum target and introduce a C2H2 / H2 mixed gas. Deposit a DLC layer on the surface of the aluminum layer obtained in step S4 using plasma-enhanced chemical vapor deposition technology. Voltage: -450V, frequency: 100kHz, duty cycle: 3%, C2H2 / H2 flow ratio: 5:1, gas pressure: 0.5Pa, DLC layer thickness: 0.5μm; S6. Resin Coating: After the DLC layer deposition is completed, the device with the DLC coating formed in step S5 is purged with nitrogen. The ceramic resistor is preheated to 130°C to keep it dry. Then, it is impregnated with epoxy resin powder encapsulant (commercially available epoxy powder encapsulant: Tianjin Kaihua Insulation Materials Co., Ltd. EF-150 type). After impregnation (which will melt instantly at high temperature), it is allowed to level naturally at 130°C for 60 seconds and dried at 180°C for 10 minutes. Finally, a 3μm thick resin layer is formed on the DLC layer obtained in step S5. The resulting varistor includes a ceramic substrate and a copper-based electrode formed on the surface of the ceramic substrate (the copper-based electrode includes a molybdenum layer, a copper layer, an aluminum layer, a DLC layer, and a resin layer sequentially disposed on the ceramic substrate).

[0060] Example 2: A ceramic varistor S1. Cleaning the zinc oxide ceramic substrate: Ultrasonically clean the ceramic substrate in deionized water for 15 minutes, then air dry it with nitrogen and further dry it in an oven at 110℃. S2. Preparation of molybdenum layer: The dried zinc oxide ceramic substrate obtained in step S1 is placed in a vacuum coating chamber and a vacuum is drawn. When the coating conditions are met, a molybdenum layer is deposited using a magnetron sputtering molybdenum target. The magnetron sputtering conditions are as follows: power 10kW, argon gas pressure 0.8Pa, substrate negative bias voltage 600V, duty cycle 20%, and molybdenum layer thickness 0.05μm. S3. Copper layer preparation: After the molybdenum layer deposition is completed, a copper layer is deposited on the molybdenum layer obtained in step S2 using a high-power pulsed magnetron sputtering copper target. The average power is 8kW, the frequency is 50Hz, the pulse width is 100μs, the Ar gas pressure is 0.8Pa, the substrate negative bias voltage is 200V, and the copper layer thickness is 0.3μm. S4. Preparation of aluminum layer: After the copper layer deposition is completed, turn off the copper target, turn on the aluminum target, and adjust the average power: 8kW, frequency: 50Hz, pulse width: 100μs, argon gas pressure: 0.8Pa, substrate negative bias voltage: 200V, and deposit an aluminum layer on the surface of the copper layer obtained in step S3. The aluminum layer thickness is 2μm. S5. Preparation of DLC layer: After the aluminum layer deposition is completed, turn off the aluminum target and introduce a C2H2 / H2 mixed gas. Deposit a DLC layer on the surface of the aluminum layer obtained in step S4 using plasma-enhanced chemical vapor deposition technology. Voltage: -600V, frequency: 80kHz, duty cycle: 10%, C2H2 / H2 flow ratio: 1:1, gas pressure: 0.5Pa, DLC layer thickness: 0.2μm; S6. Resin Coating: After the DLC layer deposition is completed, the device with the DLC coating formed in step S5 is purged with nitrogen, and the ceramic resistor is preheated to 150°C to keep the varistor dry. Then, it is impregnated with epoxy resin powder encapsulant (commercially available phenolic resin encapsulant: PF-3112, Suzhou Xingye Materials Technology Co., Ltd.). After impregnation, it is allowed to level naturally at 150°C for 30 seconds and dried at 150°C for 10 minutes. Finally, a 2μm thick resin layer is formed on the DLC layer obtained in step S5. The resulting varistor includes a ceramic substrate and a copper-based electrode formed on the surface of the ceramic substrate (the copper-based electrode includes a molybdenum layer, a copper layer, an aluminum layer, a DLC layer, and a resin layer sequentially disposed on the ceramic substrate).

[0061] Example 3: A ceramic varistor The only difference from Example 1 is: S2. Preparation of molybdenum layer: The dried zinc oxide ceramic substrate obtained in step S1 is placed in a vacuum coating chamber and a vacuum is drawn. When the coating conditions are met, a molybdenum layer is deposited using a magnetron sputtering molybdenum target. The magnetron sputtering conditions are as follows: power 3kW, argon gas pressure 0.2Pa, substrate negative bias voltage 400V, duty cycle: 5%, molybdenum layer thickness: 0.3μm; The other steps and conditions are the same as in Example 1.

[0062] Example 4: A ceramic varistor The only difference from Example 1 is that, in S3, copper layer preparation: after the molybdenum layer deposition is completed, a copper layer is deposited on the molybdenum layer obtained in step S2 using a high-power pulsed magnetron sputtering copper target. The average power is 2kW, the frequency is 500Hz, the pulse width is 30μs, the Ar gas pressure is 0.2Pa, the substrate negative bias is 30V, and the copper layer thickness is 2μm. The other steps and conditions are the same as in Example 1.

[0063] Example 5: A ceramic varistor The only difference from Example 1 is that, in step S4, aluminum layer preparation: after the copper layer deposition is completed, the copper target is turned off, the aluminum target is turned on, and the average power is adjusted to 2kW, frequency to 500Hz, pulse width to 30μs, argon gas pressure to 0.2Pa, and substrate negative bias to 30V. An aluminum layer is deposited on the surface of the copper layer obtained in step S3, with an aluminum layer thickness of 1μm. The other steps and conditions are the same as in Example 1.

[0064] Example 6: A ceramic varistor The only difference from Example 1 is that, in step S5, the DLC layer is prepared: after the aluminum layer deposition is completed, the aluminum target is turned off, and a C2H2 / H2 mixed gas is introduced. A DLC layer is deposited on the surface of the aluminum layer obtained in step S4 using plasma-enhanced chemical vapor deposition technology. The voltage is -400V, the frequency is 240kHz, the duty cycle is 5%, the C2H2 / H2 flow ratio is 3:1, the gas pressure is 3.5Pa, and the DLC layer thickness is 0.35μm. The other steps and conditions are the same as in Example 1.

[0065] Example 7 A ceramic varistor Compared with Example 1, the metal transition layer is a titanium layer, and titanium layer deposition is performed using a titanium target. Other steps and parameters are the same as in Example 1.

[0066] Example 8: A ceramic varistor Compared with Example 1, the metal transition layer is a chromium layer, and a chromium target is used for chromium layer deposition. Other steps and parameters are the same as in Example 1.

[0067] Comparative Example 1: A ceramic varistor The only difference from Example 1 is that in step S1, the molybdenum layer is replaced with a nickel layer, and a nickel target is used for nickel layer deposition. The other steps and conditions are the same as in Example 1.

[0068] Comparative Example 2: A ceramic varistor The only difference from Example 1 is that in step S1, the molybdenum layer is replaced with an aluminum layer, and an aluminum target is used to deposit the aluminum layer. The other steps and conditions are the same as in Example 1.

[0069] Comparative Example 3: A ceramic varistor S1. Cleaning the zinc oxide ceramic substrate: Ultrasonically clean the ceramic substrate in deionized water for 15 minutes, then air dry it with nitrogen and further dry it in an oven at 105℃. S2. Preparation of molybdenum layer: The dried zinc oxide ceramic substrate obtained in step S1 is placed in a vacuum coating chamber and a vacuum is drawn. When the coating conditions are met, a molybdenum layer is deposited using a magnetron sputtering molybdenum target. The magnetron sputtering conditions are as follows: power 6kW, argon gas pressure 0.5Pa, substrate negative bias voltage 500V, and molybdenum layer thickness 0.1μm. S3. Copper layer preparation: After the molybdenum layer deposition is completed, a copper layer is deposited on the molybdenum layer obtained in step S2 using a high-power pulsed magnetron sputtering copper target. The average power is 5kW, the frequency is 300Hz, the pulse width is 150μs, the Ar gas pressure is 0.5Pa, the substrate negative bias is 80V, and the copper layer thickness is 3μm. S4. Preparation of the antioxidant layer: A suspension was prepared from polyimide resin (CAS: 62929-02-6), polyaniline, N-methylpyrrolidone, and alumina nanoparticles (ALuna-100, Huifu Nano), as well as polyvinylpyrrolidone and graphene (Merck Life Sciences) in the following mass percentages: polyaniline 10%, alumina nanoparticles 8%, graphene 2%, polyimide resin 35%, polyvinylpyrrolidone 0.8%, and the balance being N-methylpyrrolidone; then, the formed suspension was coated onto a copper layer and cured to form an antioxidant layer with a thickness of 4μm. The specific curing procedure was as follows: First, the temperature was raised to 85℃ and held for 2 hours. Then, the temperature is raised to 125°C, held for 50 minutes, then raised to 175°C, held for 25 minutes, and cooled. The resulting varistor consists of a ceramic substrate and a copper-based electrode formed on the surface of the ceramic substrate (the copper-based electrode consists of a molybdenum layer, a copper layer, and an anti-oxidation layer sequentially disposed on the ceramic substrate).

[0070] Comparative Example 4: A ceramic varistor The only difference from Example 1 is that the DLC layer in step S5 is missing, that is, the final resin layer is prepared on the aluminum layer obtained in step S4; The other steps and conditions are the same as in Example 1.

[0071] Comparative Example 5: A ceramic varistor The only difference from Example 1 is that the aluminum layer in step S4 is missing, i.e., the DLC layer is prepared on the copper layer obtained in step S3; The other steps and conditions are the same as in Example 1.

[0072] Comparative Example 6: A ceramic varistor The only difference from Example 1 is that the order of steps S4 and S5 is reversed, that is, the DLC layer is prepared on the copper layer obtained in step S3; then the aluminum layer and the resin layer are prepared sequentially on the DLC layer. The other steps and conditions are the same as in Example 1.

[0073] Performance testing (1) Aging test Before aging tests on varistors, lead wires must be soldered onto the copper layer. When preparing other protective layers after the copper layer (such as the Al layer, DLC layer, and resin coating layer), care must be taken to avoid the solder joints to ensure good conductivity of the lead wires. The sample is then placed in the aging equipment, and the test temperature is raised to 125°C, with a continuous application of 0.85U. 1mA After 12 hours, the sample was taken out and the varistor DC parameter instrument was used to test the varistor performance parameters of the sample before and after aging and to calculate the parameter change rate.

[0074] Varistor voltage U 1mAThis refers to the voltage across the varistor when a 1 mA DC current flows through it during normal operation.

[0075] Nonlinear coefficient: determined by the formula Calculate the "nonlinear coefficient α". U1 and U2 are the terminal voltages corresponding to the DC currents flowing through the varistor I1=0.1mA and I2=1mA when the varistor is working normally.

[0076] Nonlinear coefficient: A parameter describing the degree of nonlinearity of the current-voltage (IV) characteristics of ceramic resistors. It reflects the sensitivity of the material to the transition from a high-resistivity state to a low-resistivity state. The larger the α value, the more significant the nonlinearity, the faster the overvoltage response, and the better the surge suppression effect.

[0077] Leakage current: 0.75U applied across the varistor 1mA The smaller the leakage current value, the better the stability and safety of the varistor during operation, and the longer its service life.

[0078] Varistor voltage change rate: The varistor voltage change rate is calculated using the formula "varistor voltage change rate = (voltage after aging - voltage before aging) / voltage before aging × 100%" to assess its long-term stability.

[0079] Accelerated aging test equipment for varistors (Xi'an Haiwo High Voltage Electrical Equipment Research Institute Co., Ltd., AGTS-IV), DC parameter meter for varistors (Changzhou Chuangjie Lightning Protection Electronics Co., Ltd., CJ 1001). (2) Adhesion (cross-cut test) Use a crisscross tool to draw a grid with a 1mm spacing on the coating surface, penetrating the copper-based film to the ceramic substrate. Then, apply pressure-sensitive adhesive tape to the grid area, quickly peel off the tape, and assess the adhesion level based on the number and area of ​​the detached grid.

[0080] Based on the degree of coating peeling, it is divided into levels 0 to 5. Level 0: The edges of the grid are completely smooth, with no coating peeling. Level 1: Only a very small amount of coating has peeled off at the intersections of the grid lines, and the grid edges are basically intact. Level 2: A small amount of coating has peeled off at the edges of the grid lines, and small areas of peeling off have appeared at the corners of some grids. Level 3: Obvious peeling has appeared on both sides of the grid lines and at the intersections, and the coating of some adjacent grids has peeled off in patches. Level 4: The coating in most grids has peeled off in flakes, with only a small amount of intact coating remaining. Level 5: Almost all the coating in the grid area has peeled off, or the coating has already peeled off before cutting, as detailed in ISO 2409:2020.

[0081] Table 1. Comparison of test results of ceramic varistors obtained in Examples 1-8

[0082] Table 2. Comparison of test results of ceramic varistors obtained in Example 1 and Comparative Examples 1-2

[0083] Table 3. Comparison of test results of ceramic varistors obtained in Example 1 and Comparative Examples 3-5

[0084] Table 4 shows the test results of the ceramic varistors obtained in Example 1 and Comparative Example 6.

[0085] The measurement results of the ceramic varistors obtained in Examples 1-8 are shown in Table 1. The Mo / Cu / Al / DLC / resin-encapsulated ceramic varistors, Ti / Cu / Al / DLC / resin-encapsulated ceramic varistors, and Cr / Cu / Al / DLC / resin-encapsulated ceramic varistors all achieved a coating adhesion grade of 0 in the cross-cut adhesion test. After an aging test at 125℃ for 12 hours, electrical performance tests showed a voltage change rate of less than 2%, a leakage current of less than 2μA, and a minimum nonlinear coefficient greater than 50. Among these, the molybdenum, titanium, and chromium metals showed good compatibility with the zinc oxide ceramic substrate, forming a strong metallurgical bonding interface. Furthermore, these metals acted as a transition layer to mitigate the difference in thermal expansion coefficients between the copper and ceramic substrates. The subsequent sequential fabrication of aluminum, DLC, and resin layers on the copper layer resulted in varistors that maintained good stability during testing, thus preserving their excellent performance.

[0086] The ceramic varistors obtained in Examples 1 and 2 were subjected to aging experiments and tests on their electrical properties and electrode adhesion. The test results are shown in Table 2. The nickel transition layer varistor had a surface adhesion rating of 3, a voltage change rate of 6.5%, a leakage current of 19 μA, and a nonlinear coefficient of 38. The aluminum transition layer varistor had a coating adhesion rating of 3, a voltage change rate of 7.8%, a leakage current of 23 μA, and a nonlinear coefficient of 35. Compared with the molybdenum transition layer, the nickel and aluminum transition layers had poorer compatibility and chemical stability with the ceramic substrate of the varistor, resulting in poorer adhesion. In the aging test of the varistor, changes in the interface structure were caused, thereby increasing the voltage change rate and leakage current.

[0087] The ceramic varistors obtained in Comparative Examples 3-5 were subjected to aging tests and adhesion tests. The test results are shown in Table 3. The varistor with the mixed coating obtained in Comparative Example 3 showed an adhesion level of 1, a voltage change rate of 5.5%, a leakage current of 20 μA, and a nonlinear coefficient of 31 after 12 hours of aging. The varistor without the DLC layer obtained in Comparative Example 4 showed an adhesion level of 0, a voltage change rate of 2.5%, a leakage current of 13 μA, and a nonlinear coefficient of 38 after 12 hours of aging. The varistor without the aluminum layer obtained in Comparative Example 5 showed an adhesion level of 4, a voltage change rate of 15%, a leakage current of 30 μA, and a nonlinear coefficient of 27 after 12 hours of aging. Among them, the mixed coating in Comparative Example 3, lacking the protective effects of the Al and DLC layers, led to excessive oxidation of copper, resulting in a significant increase in leakage current and voltage change rate, and a slight decrease in adhesion. The absence of the DLC layer in Comparative Example 4 reduced the protection of copper, increased the probability of copper oxidation, and significantly reduced electrical performance. The absence of the aluminum transition layer and the direct coating of the DLC layer onto the copper layer in Comparative Example 5 reduced interlayer adhesion, deteriorated coating adhesion, caused premature film failure or performance degradation, and consequently significantly increased the voltage change rate and leakage current, and reduced the linearity coefficient.

[0088] Compared to Example 1, the ceramic varistor obtained in Comparative Example 6 was obtained by swapping the aluminum layer and the DLC layer. After a 12-hour aging test, the electrical performance test results are shown in Table 4. The copper-DLC-aluminum-resin varistor showed an adhesion rating of 4, a voltage change rate of 16%, a leakage current of 32 μA, and a nonlinearity coefficient of 24. Due to the sequential swapping of the DLC layer and Al, the DLC adhered poorly to the Cu layer, while the Al adhered to the poorly adhered DLC layer, resulting in a decrease in the overall adhesion of the coating, accelerating the oxidation of the copper layer and the deterioration of the surface resin layer, and significantly increasing the resistance change rate and leakage current.

[0089] The above results demonstrate that the varistor obtained by constructing multilayer copper-based electrodes of a specific type and sequence in this invention exhibits excellent environmental stability, structural integrity, and reliability, meeting the requirements for use in extreme environments.

[0090] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A ceramic pressure sensitive resistor, characterized by, The invention includes a ceramic substrate and a copper-based electrode formed on the substrate surface. The copper-based electrode includes a metal transition layer, a copper layer, an aluminum layer, a DLC layer and a resin layer sequentially disposed on the ceramic substrate. The metal in the metal transition layer is selected from one or more of molybdenum, titanium, and chromium.

2. The ceramic varistor according to claim 1, characterized in that, The ceramic varistor satisfies one or more of the following (1) to (5): (1) The thickness of the metal transition layer is 0.05~0.3μm; (2) The thickness of the copper layer is 0.3~3μm; (3) The thickness of the aluminum layer is 0.2~3μm; (4) The thickness of the DLC layer is 0.2~0.5μm; (5) The thickness of the resin layer is 2~3μm.

3. The ceramic varistor according to claim 1, characterized in that, The resin layer is made from at least one of the following raw materials: (1) pure epoxy resin or its encapsulating material; (2) pure silicone resin or its encapsulating material; (3) pure phenolic resin or its encapsulating material.

4. The ceramic varistor according to claim 1, characterized in that, The ceramic substrate is a metal oxide ceramic substrate.

5. The method for preparing the ceramic varistor according to any one of claims 1 to 4, characterized in that, Includes the following steps: S1. Preparation of metal transition layer: On the pretreated ceramic substrate, a metal transition layer is deposited by DC magnetron sputtering to form a metal transition layer; S2. Copper layer preparation: After the metal transition layer is deposited, a copper layer is deposited on the metal transition layer obtained in step S1 using a high-power pulsed magnetron sputtering process to form a copper layer; S3. Preparation of aluminum layer: After the copper layer deposition is completed, an aluminum layer is deposited on the surface of the copper layer obtained in step S2 using a high-power pulsed magnetron sputtering process to form an aluminum layer; S4. Preparation of DLC layer: After the aluminum layer deposition is completed, a DLC layer is deposited on the surface of the aluminum layer obtained in step S3 using plasma-enhanced chemical vapor deposition technology to form a DLC layer; S5. Preparation of resin layer: After nitrogen purging of the device with DLC coating formed in step S4, preheating is performed, resin is coated on the DLC layer obtained in step S4, and curing is performed to form resin layer; In steps S2 and S3, the average power of the high-power pulsed magnetron sputtering process is ≥2kW.

6. The preparation method according to claim 5, characterized in that, In step S1, the DC magnetron sputtering coating process satisfies one or more of the following (1) to (4): (1) Power 3~10kW; (2) The pressure of the inert gas is 0.2~0.8 Pa; (3) Base bias voltage: -400~-600V; (4) Duty cycle: 5%-20%.

7. The preparation method according to claim 5, characterized in that, In steps S2 and S3, each of the high-power pulsed magnetron sputtering processes independently satisfies one or more of the following (1) to (5): (1) Average power 2~8kW; (2) Frequency: 50~500Hz; (3) Pulse width: 30~300μs; (4) The pressure of the inert gas is 0.2~0.8 Pa; (5) Base bias: -30~-200V.

8. The preparation method according to claim 5, characterized in that, In step S4, the plasma-enhanced chemical vapor deposition technique satisfies one or more of the following (1) to (5): (1) Voltage: -300~-600V; (2) Frequency: 80~240kHz; (3) Duty cycle: 2~10%; (4) The gas is a combination of carbon-containing gas and hydrogen, wherein the carbon-containing gas is selected from methane or acetylene, and the flow ratio of the carbon-containing gas to H2 is (5~1):1; (5) Air pressure: 0.5~5Pa.

9. The preparation method according to claim 5, characterized in that, In step S5, the preheating temperature is 130~180℃.

10. The application of the ceramic varistor according to any one of claims 1 to 4 in the preparation of varistors.

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