Anti-reduction high-performance X7R type ceramic material and preparation method thereof

Abstract

The invention discloses an anti-reduction high-performance X7R type ceramic material and a preparation method thereof, and belongs to the technical field of electronic materials. The ceramic material is prepared by mixing two superfine BaTiO3 ceramic materials, BaTiO3 powder with the average particle size of about 250 nm is defined as A-type BaTiO3, and BaTiO3 powder with the average particle size of about 120 nm is defined as B-type BaTiO3. The mass ratio of the A-type BaTiO3 to the B-type BaTiO3 ranges from 8: 1 to 4: 1, and the A-type BaTiO3 and the B-type BaTiO3 account for 97.70-98.60% of the total weight of the dielectric material. Various secondary additives, including oxides of one or more of MgCO3, ZrO2, SiO2, Mn3O4, ZnO and rare earth elements Y, Dy and Ho, account for 1.40%-2.30% of the total amount of the dielectric material, and are used for preparing the anti-reduction high-performance X7R type ceramic material. The ceramic material prepared by the invention has good temperature stability, continuously adjustable dielectric constant (2500-3350), relatively high insulation resistivity (rho is greater than or equal to 1.5 * 10 < 12 > omega.cm), dielectric loss of less than 2%, dielectric strength of more than 9kV / mm, simple preparation process and good repeatability, and is suitable for preparing miniaturized, high-voltage-resistant and high-layer BME-MLCC.

Description

Technical Field

[0001] The present invention belongs to the field of electronic materials technology, particularly capacitor material technology. It is suitable for preparing multilayer ceramic capacitors with high reliability, high capacity, and high voltage ratings, and does not pollute the environment during preparation and use. Background Art

[0002] With the continuous development of electronic information technology, related devices are gradually developing towards miniaturization, lightweight, high integration and high reliability, which has prompted electronic components to put forward higher requirements in terms of performance, volume and adaptability to the working environment. Among them, multilayer ceramic capacitors (Multilayer Ceramic Capacitors, referred to as MLCC) have been widely used in mobile communications, automotive electronics, industrial control and consumer electronics. MLCC is usually composed of alternating stacked ceramic dielectric layers and metal inner electrodes, which are co-sintered to form an integrated capacitor structure and form end electrode connection circuits at both ends of the device. X7R type ceramic material is characterized by its capacitance change rate (ΔC / C (25℃) ) is controlled within ±15%, taking into account both dielectric constant and temperature stability, making it one of the preferred dielectric materials for the current mainstream medium and high capacitance MLCCs. In recent years, in order to reduce costs and increase production capacity, the MLCC industry has gradually transformed from precious metal internal electrodes (PME) to base metal internal electrodes (BME). Base metal internal electrodes (BME) are easily oxidized at high temperatures and lose their conductivity, so they need to be sintered in a reducing atmosphere. This requires the ceramic dielectric to have excellent reduction resistance to ensure the stability of its structure and electrical properties during the co-sintering process, thereby meeting the reliability requirements of BME-MLCC. However, traditional BaTiO3-based X7R-type ceramic materials are prone to generate oxygen vacancies in a reducing atmosphere, resulting in problems such as degradation of dielectric properties, decreased resistance, and reduced breakdown strength of the dielectric layer, which seriously affects the safety and service life of the device in high-voltage, high-reliability application scenarios.

[0003] In response to the "semiconductorization" problem that occurs in BaTiO3 ceramics during low oxygen partial pressure sintering, early studies proposed the use of acceptor elements (such as Fe, Co, and Mn) for doping to compensate for electrons and form an association state with oxygen vacancies, inhibiting their migration and thus improving insulation resistance. However, experiments have shown that this type of doping method is difficult to effectively control the generation of oxygen vacancies, and may introduce additional defects. Later reoxidation treatment is usually still required to restore the insulating properties and thermal stability of the material. In recent years, studies have found that rare earth elements, whose ionic radius is between Ba and 2+ With Ti 4+It has the characteristics of "amphoteric doping" and can occupy the A site or the B site at the same time, with both donor and acceptor functions. On the one hand, it can compensate for the charge of free electrons and oxygen vacancies, and on the other hand, by forming a defect association structure, it effectively limits the migration of oxygen vacancies, thereby improving the stability of electrical performance on the basis of improving the reduction resistance. For example, patent No. 200810155056.9 discloses a low-temperature sintered high-dielectric ceramic system. Although it can effectively improve the reliability of the material, under the premise of meeting the X7R temperature stability requirements, its dielectric constant is only 2436, and it is difficult to further improve the capacity density. Patent 201710919573.8 significantly improves the dielectric properties and reduction resistance through composite doping such as Y-Zn, but the particle size of the ceramic material produced is relatively large, which is not conducive to the miniaturization of high-layer count and small-chip MLCC devices. Patent 201810110293.7 discloses a ceramic material with high breakdown strength and meets the X7R standard, but its dielectric constant is only 800-1200, which is difficult to meet the design requirements of large-capacity, small-size capacitors. In addition, the formula involves multiple modified dopants, and the system is complex, which increases the difficulty of subsequent process optimization and batch consistency control.

[0004] There is still room for improvement in the existing X7R ceramic materials in achieving high dielectric constant, anti-reduction properties and high breakdown strength at the same time. Therefore, in the ultrafine material system, there is an urgent need to develop an X7R ultrafine ceramic material system with high dielectric properties, excellent temperature stability and high breakdown strength to meet the application requirements of the next generation of high-capacity, high-voltage and high-reliability BME-MLCC devices. Summary of the Invention

[0005] The purpose of the present invention is to provide an ultra-fine, high-performance, anti-reduction X7R ceramic material that is anti-reduction, highly reliable, low-loss, has a high dielectric constant, complies with the X7R capacitance temperature coefficient variation standard, and is suitable for multilayer ceramic capacitors, and a preparation method thereof.

[0006] The technical solution of the present invention is:

[0007] A high-performance, reduction-resistant X7R ceramic material is provided. The main component of this dielectric material is prepared by mixing two ultrafine BaTiO3 ceramic materials. BaTiO3 powder with an average particle size of approximately 250 nm is defined as type A BaTiO3, and BaTiO3 powder with an average particle size of approximately 120 nm is defined as type B BaTiO3. The mass ratio of type A BaTiO3 to type B BaTiO3 ranges from 8:1 to 4:1, accounting for 97.70% to 98.60% of the total weight of the dielectric material. The high-performance, reduction-resistant X7R ceramic material is prepared by adding various secondary additives, including oxides of one or more of the rare earth elements Y, Dy, and Ho, which account for 1.40% to 2.30% of the total weight of the dielectric material. The mass ratio of the materials is: [100-(a+b+c+d+e+f)]BaTiO3+aMgCO3+b ZrO2+c SiO2+d Mn3O4+e ZnO+fRe2O3, where a, b, c, d, e, and f are coefficients, calculated as weight percentages: 0.30wt%≤a≤0.60wt%, 0.10wt%≤b≤0.60wt%, 0.10wt%≤c≤0.20wt%, 0.20wt%≤d≤0.40wt%, 0.10wt%≤e≤0.20wt%, and 0.20wt%≤f≤0.60wt%. The ceramic material has a dielectric constant between 2500 and 3350, a dielectric strength greater than 9kV / mm, a dielectric loss less than 2%, and a capacitance temperature variation rate less than ±15%, and is a dielectric ceramic material that meets the X7R standard.

[0008] The method for preparing the ceramic material is characterized by comprising the following steps:

[0009] Step 1: ball-milling and uniformly mixing A-type BaTiO3, B-type BaTiO3, and a modifying additive consisting of MgCO3, ZrO2, SiO2, Mn3O4, ZnO, and rare earth oxides Y2O3, Dy2O3, and Ho2O3, followed by granulation and molding to obtain a green material; wherein the amount of the modifying additive added accounts for 1.40% to 2.30% of the total mass of the barium titanate powder and the additive;

[0010] Step 2: sintering: the green body obtained in step 1 is sintered in a 1-2% H2 / N2 / H2O reducing atmosphere at a heating rate of 3°C / min and a cooling rate of 4°C / min.

[0011] Sintering at 1280℃~1310℃ for 2~4 hours;

[0012] Step 3: Reoxidation; the sample obtained in step 2 is reoxidized under the protection of an N2 atmosphere containing O2 at a temperature of 900°C to 1100°C for 2 hours to obtain a high-performance X7R-type ceramic material that is resistant to reduction.

[0013] Furthermore, the ball milling process in step 1 is as follows: deionized water, zirconium balls, and powder are mixed in a mass ratio of 2:1:1, and ball milled at a speed of 360 rpm for 3 to 16 hours;

[0014] Furthermore, the granulation process in step 1 is as follows: the ball-milled mixture is dried and mixed with a polyvinyl alcohol aqueous solution before granulation, and the granulation size is controlled at 80 to 220 meshes;

[0015] Furthermore, the molding process in step 1 is as follows: placing the granulated material into a molding die and dry pressing the granulated material under a pressure of 10 MPa to obtain a green material;

[0016] Furthermore, the reoxidation process in step 3 is as follows: the oxygen content in the N2 atmosphere containing O2 is 10-200 ppm and the gas flow rate is 50-70 sccm.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. The present invention uses two ultrafine BaTiO3 ceramics as the main materials. By mixing the ceramics, it is conducive to forming a microstructure with uniform particle size and fine distribution, which is suitable for high-layer count and miniaturized MLCC. At the same time, it helps to reduce the sintering temperature and improve density and reliability. Mixing ultrafine ceramics of different particle sizes not only effectively controls grain growth, but also optimizes the interaction between particles during the sintering process. By accurately adjusting the ratio of ceramics, the present invention achieves precise control of key dielectric properties, promotes uniform grain growth, and optimizes the microstructure, thereby meeting the design requirements of high-frequency and miniaturized electronic devices.

[0019] 2. The secondary additives in this invention contain alkaline earth metal Mg, variable valence element Mn, and amphoteric rare earth elements Y, Dy, and Ho, whose ionic radii are between those of Ba and Ti. The combined action of Mg and the rare earth elements facilitates the formation of a shell-core structure, thereby improving dielectric temperature stability. Zr can also be enriched at grain boundaries or within the crystal, limiting the migration of oxygen vacancies and improving dielectric strength to a certain extent. Trivalent Mn is reduced in a reducing atmosphere and acts as an acceptor to occupy the B site, compensating for electrons to a certain extent while protecting Ti from reduction. The resulting [Mn" Ti ·V″ OThe defect dipole pairs inhibit the migration of oxygen vacancies. The ZnO in the secondary additive effectively inhibits the formation of abnormal grains and improves the anti-reduction performance and reliability of the BaTiO3 ceramic dielectric layer. The prepared anti-reduction high-performance X7R ceramic material has been tested to have low dielectric loss (tgδ≤2%) and high insulation resistivity (ρ≥1.5*10 12 Ω·cm), good dielectric strength (Eb≥9.0kV / mm), capacitance temperature coefficient that meets X7R standard, continuously adjustable dielectric constant (2500~3350) and good processability, with broad market application prospects.

[0020] Compared with the prior art, the present invention has the following characteristics:

[0021] 1. In the formula of the present invention, no secondary synthetic additives are required, and the overall doping amount of additives is relatively low, which is conducive to industrial large-scale production and effectively reduces the complexity of the preparation process.

[0022] 2. In the formula of the present invention, the mixing ratio of the two ultrafine BaTiO3 ceramic materials is comprehensively controlled, which is conducive to forming a microstructure with uniform particle size and fine distribution, helping to reduce the sintering temperature, improve density and reliability, and achieve precise control of key dielectric properties, thereby meeting the design requirements of high-frequency and miniaturized electronic devices.

[0023] 3. Zr and Mg doping are introduced into the formula of the present invention to stabilize the dielectric properties by constructing a shell-core structure. At the same time, the synergistic doping of amphoteric rare earth elements and variable valence acceptor ions is combined to inhibit the formation and migration of oxygen vacancies, further improving the insulation performance and reliability of barium titanate-based ceramics in a reducing atmosphere.

[0024] 4. The present invention optimizes the production process and adopts a two-stage sintering method. After sintering in a reducing atmosphere, reoxidation is performed, which reduces the oxygen vacancy concentration and improves the interface barrier, suppressing the degradation of insulation performance caused by oxygen vacancy migration, thereby improving the reliability of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic flow chart of the preparation method of the anti-reduction high-performance X7R ceramic material of the present invention.

[0026] Figure 2 3 is a characteristic curve diagram of the dielectric constant of the samples of Examples 1-5 of the present invention changing with temperature.

[0027] Figure 3 3 is a characteristic curve diagram showing the change of dielectric constant with temperature for samples of Examples 6 to 10 of the present invention.

[0028] Figure 4Graph showing the capacitance temperature change rate of samples of Examples 1-5 of the present invention as a function of temperature.

[0029] Figure 5 Graph showing the capacitance temperature change rate of samples of Examples 6-10 of the present invention as a function of temperature.

[0030] Figure 6 This is a scanning electron microscope (SEM) image of the sample of Example 2 of the present invention. DETAILED DESCRIPTION

[0031] Examples 1-10

[0032] Step 1: Ingredients: Accurately weigh the ingredients according to the mass ratio of each raw material in Table 1;

[0033] Step 2: ball milling: put the prepared powder into a ball mill, mix deionized water, zirconium balls, and powder in a mass ratio of 2:1:1, and ball mill at a speed of 360 rpm for 6 hours;

[0034] Step 3: Granulation and molding; the ball-milled powder is placed in an oven at 100°C and dried, and 15% by weight of polyvinyl alcohol is added to granulate the powder. The granulation size is controlled at 80 to 220 mesh and pressed at 10 MPa into a green body with a diameter of 1 cm and a thickness of 0.1 cm.

[0035] Step 4: sintering; the green body obtained in step 3 is sintered in a 1-2% H2 / N2 / H2O reducing atmosphere at a heating rate of 3°C / min and a cooling rate of 4°C / min at a temperature of 1280°C to 1310°C for 2 to 4 hours;

[0036] Step 5: Reoxidation; The sample obtained in step 4 is sintered at a temperature of 900-1060°C for 2 hours under the protection of an O2-containing N2 atmosphere (oxygen content of 10-200 ppm) to obtain the final anti-reduction ceramic material. The specific ingredients are shown in Table 1, the specific processes of different embodiments are shown in Table 2, and the performance test results of the obtained material (dielectric loss, dielectric constant, insulation resistivity, dielectric strength and capacitance temperature change rate) are shown in Table 3.

[0037] Table 1 Ingredients of Examples 1-10 of Anti-reduction High-performance X7R Ceramic Materials

[0038]

[0039] Table 2 Processing of Examples 1-10 of Anti-reduction High-performance X7R Ceramic Materials

[0040]

[0041]

[0042] Table 3 Performance of Anti-reduction High-performance X7R Ceramic Material Examples 1-10

[0043]

Claims

1. A high-performance X7R type ceramic material with an anti-reduction property and a preparation method thereof, belonging to the field of electronic materials technology, particularly capacitor material technology. The main material of the high-performance X7R type ceramic material with an anti-reduction property is prepared by mixing two ultrafine BaTiO3 powders, wherein: BaTiO3 powder with an average particle size of approximately 250 nm is defined as type A BaTiO3, while BaTiO3 powder with an average particle size of approximately 120 nm is defined as type B BaTiO3. The material composition ratio of type A BaTiO3 to type B BaTiO3 ranges from 8:1 to 4:1, accounting for 97.70% to 98.60% of the total weight of the dielectric material. Various secondary additives, including MgCO3, ZrO2, SiO2, Mn3O4, ZnO, and oxides of one or more of the rare earth elements Y, Dy, and Ho, are added, constituting 1.40% to 2.30% of the total weight of the dielectric material, to produce a high-performance, reduction-resistant X7R ceramic material.

2. The ceramic material according to claim 1, characterized in that The mass ratio of the materials is: The mass ratio of the materials is: [100-(a+b+c+d+e+f)]BaTiO3+a MgCO3+b ZrO2+c SiO2+d Mn3O4+e ZnO+fRe2O3, wherein a, b, c, d, e, and f are coefficients, calculated as weight percentage, 0.30wt%≤a≤0.60wt%, 0.10%≤b≤0.60wt%, 0.10wt%≤c≤0.20wt%, 0.20wt%≤d≤0.40wt%, 0.10wt%≤e≤0.20wt%, and 0.20wt%≤f≤0.60wt%.

3. A method for preparing a high-performance X7R ceramic material with high reduction resistance, characterized in that: The following steps are involved: Step 1: A-type BaTiO3 and B-type BaTiO3 powders are mixed in a ratio of 1:0 (pure A-type) to 4:1, and are evenly mixed with a modifying additive consisting of MgCO3, ZrO2, SiO2, Mn3O4, ZnO, and one or more rare earth elements Y, Dy, and Ho by ball milling, and then granulated and formed to obtain a green material; wherein the amount of the modifying additive added accounts for 1.40% to 2.30% of the total mass of the barium titanate original powder and the additive; Step 2: Sintering: The green body obtained in step 1 is sintered at 1280°C to 1310°C for 2 to 4 hours in a reducing atmosphere of 1 to 2% H2 / N2 / H2O at a heating rate of 3°C / min and a cooling rate of 4°C / min; Step 3: Reoxidation; the sample obtained in step 2 is reoxidized under the protection of an N2 atmosphere containing O2 at a temperature of 900°C to 1060°C for 2 hours to obtain a high-performance X7R-type ceramic material that is resistant to reduction.

4. The method for preparing the anti-reduction high-performance X7R ceramic material according to claim 3, characterized in that: The percentage contents of the secondary additives described in step 1 to the total mass of the ceramic material are MgCO3: 0.30~0.60wt%, ZrO2: 0.10~0.60wt%, SiO2: 0.10~0.20wt%, Mn3O4: 0.20~0.40wt%, ZnO: 0.10~0.20wt%, and Re2O3: 0.20~0.60wt%.

5. The method for preparing the anti-reduction high-performance X7R ceramic material according to claim 3 or 4, characterized in that: The ball milling process in step 1 is as follows: deionized water, zirconium balls, and powder are mixed in a mass ratio of 2:1:1, the rotation speed is 360 rpm, and the ball milling is performed for 3 to 16 hours.

6. The method for preparing the anti-reduction high-performance X7R ceramic material according to claim 3 or 4, characterized in that: The granulation process in step 1 is as follows: the ball-milled mixture is dried and mixed with a polyvinyl alcohol aqueous solution before granulation, and the granulation size is controlled at 80 to 220 meshes.

7. The method for preparing the anti-reduction high-performance X7R ceramic material according to claim 3 or 4, characterized in that: The molding process in step 1 is as follows: placing the granulated material into a molding die and dry pressing it under a pressure of 10 MPa to obtain a green material.

8. The method for preparing the anti-reduction high-performance X7R ceramic material according to claim 3 or 4, characterized in that: The reoxidation process in step 3 is as follows: the oxygen content in the N2 atmosphere containing O2 is 10-200 ppm, and the gas flow rate is 50-70 sccm.

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