Low-dielectric-constant microwave dielectric ceramic as well as preparation method and application thereof

Abstract

The invention discloses low-dielectric-constant microwave dielectric ceramic as well as a preparation method and application thereof. The low-dielectric-constant microwave dielectric ceramic comprises the following raw materials: a ceramic main material with a structure as shown in a general formula (Mg1-xXx) (Al1-yRy) 2O4, and an auxiliary agent accounting for 15.5-17wt% of the ceramic main material, in the ceramic main material (Mg1-xXx) (Al1-yRy) 2O4, x is greater than or equal to 0 and less than or equal to 0.1, y is greater than or equal to 0.01 and less than or equal to 0.1, the X element comprises at least one of Zn, Ni and Cu, and the R element comprises at least one of La, Nd, Y and Cr. According to the low-dielectric-constant microwave dielectric ceramic, Zn, Ni or Cu and La, Nd, Y or Cr ions are doped, sintering of the material is promoted, extrinsic loss of the material is greatly reduced, the material keeps a high Q * f value, meanwhile, a CaTiO3 complex-phase design and a tau f compensation principle are adopted, accurate cooperative regulation and control of electromagnetic performance such as epsilon r, Q * f and tau f are achieved, and the low-dielectric-constant microwave dielectric ceramic is prepared. And the long-standing contradiction between the mechanical strength and the comprehensive dielectric property of the traditional microwave ceramic material is solved.

Description

Technical Field

[0001] This invention relates to the field of microwave dielectric ceramic materials, and more particularly to a low dielectric constant microwave dielectric ceramic, its preparation method, and its application. Background Technology

[0002] As fifth-generation (5G) and future sixth-generation (6G) communication technologies evolve towards integrated air-space-ground-sea networks, communication frequency bands are continuously expanding into millimeter-wave bands such as Ku / Ka. This places even more stringent requirements on the core basic component—microwave dielectric ceramics: on the one hand, the material needs to possess a low dielectric constant (ε...). To reduce signal delay and crosstalk, a high quality factor (Q×f value) is needed to reduce signal loss, and a near-zero temperature coefficient of resonant frequency (τf) is needed to ensure thermal stability. On the other hand, as the demand for devices to become miniaturized, highly integrated, and used in complex environments such as aerospace and automotive applications increases, the mechanical reliability of ceramic materials themselves, especially their bending strength, has become a key bottleneck restricting their engineering applications.

[0003] Magnesium aluminum spinel (MgAl2O4) ceramics are considered highly promising low-loss microwave dielectric materials due to their inherently low dielectric constant (dielectric constant ≈ 8), high Q×f value (approximately 68900 GHz), and good chemical stability. However, the flexural strength of conventionally stoichiometric MgAl2O4 ceramics is typically low, only about 152 MPa, posing a risk of failure when subjected to mechanical vibration, impact, or complex stress fields, thus limiting their application in high-end precision microwave devices.

[0004] Currently, the academic and industrial communities are trying to improve the mechanical properties of MgAl2O4 ceramics through two main approaches: (1) Using non-stoichiometric design: Studies have shown that by adjusting the ratio of MgO to Al2O3, preparing non-stoichiometric magnesium aluminum spinel (MgO·nAl2O3, n≠1) is an effective means to improve strength; for example, when n=1.5, that is, when the chemical formula of magnesium aluminum spinel is MgO·1.5Al2O3, the bending strength of the ceramic can be increased to 215MPa, which is about 41% higher than the bending strength of 152MPa of stoichiometric materials; (2) Using advanced sintering or joining technology: for example, by using electric field-assisted rapid joining technology, the bending strength of MgAl2O4 ceramic connectors can reach 256MPa, which even exceeds the strength of the parent material itself.

[0005] However, despite the aforementioned explorations, existing technologies still have significant shortcomings: while non-stoichiometric compositions improve strength, they have a substantial negative impact on microwave dielectric properties, such as dielectric constant and loss, and the process window is narrow; while connection technologies are mainly used for component integration and are not suitable for improving the inherent strength of the ceramic material itself. More importantly, how to achieve synergistic optimization of ultra-high flexural strength (>250MPa) and excellent microwave dielectric properties in the MgAl2O4 ceramic system through systematic material design remains a current technological gap and a core problem that urgently needs to be solved. Summary of the Invention

[0006] The purpose of this invention is to propose a low dielectric constant microwave dielectric ceramic, its preparation method, and its application, in order to solve the problem that the MgAl2O4 cannot reconcile the contradiction between flexural strength and excellent microwave dielectric properties in the ceramic system.

[0007] To achieve this objective, the present invention adopts the following technical solution: This invention provides a low dielectric constant microwave dielectric ceramic, the raw material composition of which includes, for example, the general formula (Mg 1-x X x (Al) 1-y R y The ceramic main material with the structure shown in Mg2O4, and the additives accounting for 15.5-17 wt% of the ceramic main material; the ceramic main material (Mg2O4) 1-x X x (Al) 1-y R y In 2O4, 0≤x≤0.1, 0.01≤y≤0.1, the X element includes at least one of Zn, Ni and Cu, and the R element includes at least one of La, Nd, Y and Cr.

[0008] In the method for preparing low dielectric constant microwave dielectric ceramics, the additives include CaTiO3 accounting for 14-15 wt% of the main ceramic material and MgO accounting for 1.5-2.5 wt% of the main ceramic material.

[0009] This invention provides a method for preparing low-dielectric-constant microwave dielectric ceramics, comprising the following steps: Preparation of ceramic main material: Mix MgO, Al2O3, XO and R2O3 powders according to the formula to obtain mixed powder; then heat the mixed powder to obtain ceramic main material; Ceramic powder preparation: Ceramic main material and additives are mixed to obtain ceramic powder; Press molding: Ceramic powder is pressed into shape to obtain a ceramic blank; Sintering: The ceramic blank is sintered to obtain microwave dielectric ceramic with low dielectric constant.

[0010] The method for preparing low dielectric constant microwave dielectric ceramics includes the following steps in the preparation of the main ceramic material: mixing MgO, Al2O3, XO, and R2O3 powders in a molar ratio of MgO:XO:Al2O3:R2O3=1-x:x:1-y:y, 0≤x≤0.1, 0.01≤y≤0.1, and then drying and grinding them; subsequently, heating to a holding temperature and holding at that temperature, and then cooling to obtain the main ceramic material.

[0011] In the method for preparing low dielectric constant microwave dielectric ceramics, the heat preservation temperature is 1145-1150℃, and the heat preservation time is 2.5-3.5h.

[0012] The method for preparing low dielectric constant microwave dielectric ceramics includes the following steps in the preparation of ceramic powder: adding additives to the main ceramic material according to the ratio, and then performing secondary grinding and drying to obtain ceramic powder.

[0013] The method for preparing low dielectric constant microwave dielectric ceramics includes the following steps in the pressing and molding process: adding 10-15 wt% polyvinyl alcohol to the ceramic main material, mixing evenly, drying, and pressing into a ceramic blank.

[0014] The method for preparing low dielectric constant microwave dielectric ceramics includes the following steps in the sintering step: placing the ceramic blank at a temperature of 1500-1550℃ for 3-6 hours to sinter it into ceramic, thereby obtaining low dielectric constant microwave dielectric ceramics.

[0015] The present invention also provides the application of the microwave dielectric ceramic described above or the microwave dielectric ceramic prepared by the above preparation method in the preparation of microwave communication equipment.

[0016] One technical solution of the present invention can have the following beneficial effects: The low dielectric constant microwave dielectric ceramic is doped with Zn, Ni or Cu, as well as La, Nd, Y or Cr ions to promote sintering, greatly reduce the intrinsic loss of the material, and maintain a high Q×f value. At the same time, by adopting the CaTiO3 multiphase design and τf compensation principle, precise synergistic control of electromagnetic properties such as εr, Q×f and τf is achieved, which solves the long-standing contradiction between the mechanical strength and comprehensive dielectric properties of traditional microwave ceramic materials. Detailed Implementation

[0017] The technical solution of the present invention will be further illustrated below through specific embodiments. To facilitate understanding of the present invention, a more comprehensive description is provided below. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.

[0018] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0020] This invention provides a low dielectric constant microwave dielectric ceramic, the raw material composition of which includes, for example, the general formula (Mg 1-x X x (Al) 1-y R y The ceramic main material with the structure shown in Mg2O4, and the additives accounting for 15.5-17 wt% of the ceramic main material; the ceramic main material (Mg2O4) 1-x X x (Al) 1-y R y In 2O4, 0≤x≤0.1, 0.01≤y≤0.1, the X element includes at least one of Zn, Ni and Cu, and the R element includes at least one of La, Nd, Y and Cr.

[0021] The low dielectric constant microwave dielectric ceramic incorporates specific elements such as Zn, Ni, Cu, La, Nd, Y, or Cr. Through the doping and substitution of these specific elements, a "lattice anchoring" effect is generated in the MgAl2O4 spinel lattice. 2+ Dopant ions replace the original Mg 2+ , and R 3+ Doped ions replace the original Al 3+When the radius of a dopant ion differs from that of the matrix ion, a local elastic strain field is introduced into the surrounding lattice. For example, a larger radius ion causes the surrounding lattice to expand under pressure, while a smaller radius ion causes the lattice to stretch. This lattice distortion stores additional elastic energy, or distortion energy, placing the lattice in a "metastable" or "activated" state, which is converted into an additional driving force for atomic migration during sintering heating. To release this local strain, the lattice significantly increases the diffusion mobility of atoms or vacancies, thereby accelerating mass transport and densification during sintering. Furthermore, introducing equivalent ions of different radii can indirectly affect the formation energy or concentration of cation vacancies, further modulating diffusion kinetics and enabling the material to achieve full sintering at lower temperatures. This not only optimizes sintering kinetics and process temperature but also effectively suppresses excessive migration of grain boundaries and defect aggregation at high temperatures through pinning effects, refining the microstructure and thus significantly improving the material's density and mechanical strength.

[0022] Furthermore, by precisely controlling the type and valence state of dopant ions, the electrically neutral balance of the crystal lattice is maintained, minimizing the increase in microwave dielectric loss caused by the increase of defects such as oxygen vacancies, thus ensuring excellent microwave dielectric performance. Moreover, this composition design can effectively fine-tune the temperature coefficient τf of the resonant frequency, bringing it closer to zero, significantly improving the temperature stability of the material.

[0023] The low dielectric constant microwave dielectric ceramic is doped with Zn, Ni or Cu, as well as La, Nd, Y or Cr ions to promote sintering, greatly reduce the intrinsic loss of the material, and maintain a high Q×f value. At the same time, by adopting the CaTiO3 multiphase design and τf compensation principle, precise synergistic control of electromagnetic properties such as εr, Q×f and τf is achieved, which solves the long-standing contradiction between the mechanical strength and comprehensive dielectric properties of traditional microwave ceramic materials.

[0024] Specifically, the additives include CaTiO3 accounting for 14-15 wt% of the ceramic main material and MgO accounting for 1.5-2.5 wt% of the ceramic main material.

[0025] CaTiO3 is a material with a high dielectric constant, which can adjust the dielectric constant, improve the temperature coefficient of the resonant frequency, and optimize the dielectric loss. At the same time, it can lower the sintering temperature, improve the density and uniformity of the ceramic body, and thus improve the mechanical strength of microwave dielectric ceramics.

[0026] MgO acts as a sintering aid, forming eutectic materials and promoting liquid-phase sintering, thereby achieving ceramic densification at a lower temperature and reducing the sintering temperature.

[0027] This invention also provides a method for preparing low-dielectric-constant microwave dielectric ceramics, comprising the following steps: Preparation of ceramic main material: Mix MgO, Al2O3, XO and R2O3 powders according to the formula to obtain mixed powder; then heat the mixed powder to obtain ceramic main material; Ceramic powder preparation: Ceramic main material and additives are mixed to obtain ceramic powder; Press molding: Ceramic powder is pressed into shape to obtain a ceramic blank; Sintering: The ceramic blank is sintered to obtain microwave dielectric ceramic with low dielectric constant.

[0028] Specifically, the preparation of the main ceramic material includes the following steps: mixing MgO, Al2O3, XO, and R2O3 powders in a molar ratio of MgO:XO:Al2O3:R2O3=1-x:x:1-y:y, 0≤x≤0.1, 0.01≤y≤0.1, and then drying and grinding them; subsequently, heating to a holding temperature and holding at that temperature, and then cooling to obtain the main ceramic material.

[0029] The molar ratio between MgO, XO, Al2O3, and R2O3 is determined by the stoichiometry of the material itself, with 0 ≤ x ≤ 0.1 and 0.01 ≤ y ≤ 0.1. If the ion doping amount is too low, it will not promote sintering, and if it is too high, too many impurity phases will appear, which will lead to a significant deterioration in the microwave dielectric properties of the material.

[0030] Specifically, the heat preservation temperature is 1145-1150℃, and the heat preservation time is 2.5-3.5h.

[0031] In the method for preparing low dielectric constant microwave dielectric ceramics, (Mg) is first synthesized. 1-x X x (Al) 1-y R y Powdered 2O4 is mixed with CaTiO3 and MgO powders to obtain ceramic powder. The ceramic powder is then added to polyvinyl alcohol, mixed evenly, and pressed into cylindrical blanks. Finally, it is sintered at 1500–1550℃ for 3–6 hours to obtain microwave dielectric ceramics with high mechanical strength, low dielectric constant, high quality factor, and adjustable temperature coefficient of resonant frequency. Performance tests show that the low dielectric constant microwave dielectric ceramics can achieve good microwave dielectric properties: dielectric constant εr is between 12 and 13, temperature coefficient of resonant frequency τf is between -10 and 0 ppm / ℃, and the product of quality factor and resonant frequency Q×f is between 50000 and 80000 GHz.

[0032] Specifically, the ceramic powder preparation process includes the following steps: adding additives to the main ceramic material according to the specified ratio, followed by secondary grinding and drying to obtain the ceramic powder.

[0033] The material components are uniformly mixed and the particles are refined through secondary grinding, and the physicochemical stability of the powder is ensured by drying. This significantly improves the uniformity, density and electrical properties of the final ceramic material, while also enhancing the controllability of the process.

[0034] Specifically, the pressing and molding step includes the following steps: adding 10-15 wt% of polyvinyl alcohol as the main ceramic material, mixing evenly, drying, and pressing into a ceramic blank.

[0035] Polyvinyl alcohol (PVA) transforms dry, loose ceramic powder into a green body with sufficient plasticity and mechanical strength. Furthermore, PVA decomposes upon heating, slowly and steadily burning and releasing gases during sintering. Pressing then shapes the ceramic powder into a specific form.

[0036] Specifically, the sintering process includes the following steps: sintering the ceramic blank at 1500–1550°C for 3–6 hours to obtain a low dielectric constant microwave dielectric ceramic.

[0037] The high temperature of 1500~1550℃ promotes the formation, stabilization and optimized growth of the target crystal phase, while the long temperature holding time of 3~6h ensures that the reaction has enough time to proceed fully.

[0038] The present invention also provides the application of the microwave dielectric ceramic described above or the microwave dielectric ceramic prepared by the above preparation method in the preparation of microwave communication equipment.

[0039] The (Mg1) prepared by this invention -x X x (Al) 1-y R y The MgAl2O4 + 14.5wt%CaTiO3 + 2wt%MgO microwave ceramic has lower preparation requirements than traditional MgAl2O4 ceramics and significantly improved mechanical strength. Performance tests show that, compared with traditional MgAl2O4 microwave ceramics, it can achieve comparable microwave dielectric properties: dielectric constant εr is between 12 and 13, resonant frequency temperature coefficient τf is between -10 and +0 ppm / ℃, Q×f value is between 50000 and 80000 GHz, and bending strength is greater than 250 MPa. It can meet the requirements of microwave ceramic materials in harsh service environments, such as aerospace, automotive, and base station scenarios involving vibration, shock, and temperature cycling.

[0040] Example Group A A method for preparing low dielectric constant microwave dielectric ceramics includes the following steps: Preparation of ceramic main material: Select MgO, Al2O3, XO, and R2O3 powders with a purity of ≥99.5% as raw materials, mix them according to the molar ratio of MgO:XO:Al2O3:R2O3=1-x:x:1-y:y, then mix them thoroughly in a high-energy ball mill, take them out, dry them, grind them, and keep them at 1150℃ for 3 hours to obtain the ceramic main material; Ceramic powder preparation: CaTiO3 accounting for 14.5 wt% of the ceramic main material and MgO accounting for 2 wt% of the ceramic main material and other additives are added to the ceramic main material, and the mixture is ground twice in a high-energy ball mill and dried to obtain ceramic powder. Compression molding: Polyvinyl alcohol accounting for 12.5 wt% of the main ceramic material is added to the ceramic powder, dried, and pressed into a cylindrical blank on a press; Sintering: The cylindrical blank is sintered at 1525℃ for 4 hours to obtain low-loss microwave ceramic.

[0041] The sintering temperature and main components of the microwave ceramic are shown in Table 1.

[0042] Table 1 - Specific Parameters

[0043] The low-loss microwave ceramics obtained in Examples 1-8 were tested using microwave dielectric properties and three-point flexural strength methods. The microwave dielectric properties test method followed IEC 60089-2-721 standard; the three-point flexural strength test method followed GB / T 6569-2006: "Test Method for Bending Strength of Fine Ceramics". The test results are shown in Table 2.

[0044] Table 2 - Test Results

[0045] As shown in Table 2, the microwave dielectric ceramics prepared using the methods described in the embodiments of this invention exhibit excellent comprehensive dielectric properties, including dielectric constant εr, quality factor Q×f, and temperature coefficient of resonant frequency τf. Their mechanical strength is also significantly superior to that of previously reported MgAl2O4-based microwave dielectric ceramic materials. This fully demonstrates the scientific rigor and synergy of the material composition design in this invention, achieved through a combination of "specific element lattice anchoring doping" and CaTiO3 composite compensation, which systematically improves the comprehensive performance of microwave dielectric ceramics.

[0046] Examples 1-8 involve precisely controlling the X content in low-loss microwave ceramics. 2+ R 3+The doping amount of ions and the recombination amount of CaTiO3 achieved linear tunability of the dielectric constant within the range of 12 to 13. The mechanism lies in the fact that CaTiO3 itself possesses a high dielectric constant εr≈170, and its content as a second phase directly affects the overall dielectric constant according to the mixing rules of composite materials, causing a rapid increase in the material's dielectric constant. Furthermore, the larger radius X... 2+ R 3+ Ions dissolved into the spinel lattice increase the cell volume, thereby enhancing the overall polarizability of the material and causing a slight increase in the dielectric constant εr. Ultimately, the dielectric constant εr of the material can be finely tuned. This dual-track strategy of coarse adjustment through main phase recombination and fine adjustment through doping content provides flexible and reliable design freedom for achieving the target εr value in the material of this invention.

[0047] Furthermore, Examples 1-8 achieve this by precisely controlling X in the low-loss microwave ceramic. 2+ R 3+ The doping amount of ions and the composite amount of CaTiO3 enabled precise adjustment of the material's resonant frequency temperature coefficient within the range of -10 ppm / ℃ to 0. Since many metal cavities have positive temperature coefficients, the ceramic was designed with a slightly negative temperature coefficient to counteract the positive temperature coefficient effect of the metal cavities. The mechanism is that CaTiO3 itself has a positive resonant frequency temperature coefficient (+800 ppm / ℃), and its content change as a second phase directly affects the overall temperature coefficient according to the principles of composite materials, causing the material's temperature coefficient to shift rapidly in the positive direction. Simultaneously, a larger radius X... 2+ R 3+ Ions dissolved into the spinel lattice increase the material’s coefficient of thermal expansion and temperature coefficient of dielectric constant, causing the temperature coefficient of the material to shift in the negative direction. This allows the material to maintain its temperature coefficient in the range of -10ppm / ℃ to 0ppm / ℃ under suitable dielectric constant (12-13).

[0048] In addition, X 2+ R 3+ The common and core role of the doping ions is to significantly promote the sintering densification process of the material, increase the sintering driving force, activate grain boundary diffusion, and obtain a higher density and more uniform fine-grained microstructure, thereby increasing the bending strength by >70% and greatly improving the flexural strength of the material. Furthermore, the high density of the microwave dielectric ceramic material reduces extrinsic losses, allowing the material to still maintain a high Q×f value. Meanwhile, data from Examples 4, 5, and 6 show that Y... 3+ The sintering-promoting effect of Cr is better than that of Cr. 3+ 、Nd 3+ Because its flexural strength is significantly superior among the three. Data from Examples 4 and 7 show that Y... 3+ When the doping amount is large, other impurity phases will appear in the material, resulting in a decrease in the material's Qf.

[0049] The technical principles of the present invention have been described above with reference to specific embodiments. These descriptions are merely for explaining the principles of the invention and should not be construed as limiting the scope of protection of the invention in any way. Based on this explanation, those skilled in the art can readily conceive of other specific embodiments of the invention without inventive effort, and these equivalent variations or substitutions are all included within the scope defined by the claims of this application.

Claims

1. A low dielectric constant microwave dielectric ceramic, characterized in that, Its raw material composition includes, for example, general formula (Mg 1-x X x (Al) 1- y R y The ceramic main material with the structure shown in Mg2O4, and the additives accounting for 15.5-17 wt% of the ceramic main material; the ceramic main material (Mg2O4) 1-x X x (Al) 1-y R y In 2O4, 0.01≤x≤0.1, 0.01≤y≤0.1, the X element includes at least one of Zn, Ni and Cu, and the R element includes at least one of La, Nd, Y and Cr.

2. The low dielectric constant microwave dielectric ceramic according to claim 1, characterized in that, The additives include CaTiO3 accounting for 14-15 wt% of the main ceramic material and MgO accounting for 1.5-2.5 wt% of the main ceramic material.

3. A method for preparing low dielectric constant microwave dielectric ceramics, characterized in that, The method for preparing the low dielectric constant microwave dielectric ceramic according to claim 1 or 2 includes the following steps: Preparation of ceramic main material: Mix MgO, Al2O3, XO and R2O3 powders according to the formula to obtain mixed powder; then heat the mixed powder to obtain ceramic main material; Ceramic powder preparation: Ceramic main material and additives are mixed to obtain ceramic powder; Press molding: Ceramic powder is pressed into shape to obtain a ceramic blank; Sintering: The ceramic blank is sintered to obtain microwave dielectric ceramic with low dielectric constant.

4. The method for preparing a low-dielectric-constant microwave dielectric ceramic according to claim 3, characterized in that, The steps in preparing the main ceramic material include: mixing MgO, Al2O3, XO, and R2O3 powders in a molar ratio of MgO:XO:Al2O3:R2O3=1-x:x:1-y:y, 0≤x≤0.1, 0.01≤y≤0.1, and then drying and grinding them; subsequently, heating to a holding temperature and holding at that temperature, and then cooling to obtain the main ceramic material.

5. The method for preparing a low-dielectric-constant microwave dielectric ceramic according to claim 4, characterized in that, The heat preservation temperature is 1145-1150℃, and the heat preservation time is 2.5-3.5h.

6. The method for preparing a low-dielectric-constant microwave dielectric ceramic according to claim 3, characterized in that, The steps in preparing ceramic powder include: adding additives to the main ceramic material according to the formula, and then performing secondary grinding and drying to obtain ceramic powder.

7. The method for preparing a low-dielectric-constant microwave dielectric ceramic according to claim 3, characterized in that, The pressing and molding process includes the following steps: adding 10-15 wt% polyvinyl alcohol to the ceramic main material, mixing evenly, drying, and pressing into a ceramic blank.

8. The method for preparing a low-dielectric-constant microwave dielectric ceramic according to claim 3, characterized in that, The sintering process includes the following steps: placing the ceramic blank at a temperature of 1500-1550℃ for 3-6 hours to sinter it into ceramic, thereby obtaining a low dielectric constant microwave dielectric ceramic.

9. The use of the microwave dielectric ceramic of claim 1 or the microwave dielectric ceramic prepared by any one of claims 2 to 8 in the preparation of microwave communication equipment.

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