Microwave dielectric ceramic material with adjustable dielectric constant and preparation method thereof

Abstract

This invention discloses a microwave dielectric ceramic material with tunable dielectric constant and its preparation method, belonging to the field of microwave dielectric materials technology. The composition of this microwave dielectric ceramic material is expressed as: x Mg2SiO4-(1-x)Mg2TiO4-0.09CaTiO3-0.005MO, where: 0.15≤x≤0.7, and MO is an additive. The material is designed as a three-phase composite, composed of two types of dielectric constants, Mg2SiO4 and Mg2TiO4, with similar but negative frequency temperature coefficients, and one type of material with a positive frequency temperature coefficient, CaTiO3. This invention's microwave dielectric ceramic material can achieve arbitrary tunability of the dielectric constant within the range of 10.0~19.9 by simply changing the x value, with a Q×f value of 47704~68149GHz and a frequency temperature coefficient τ. f ≤±10ppm / ℃.

Description

Technical Field

[0001] This invention relates to the field of microwave dielectric materials technology, specifically to a microwave dielectric ceramic material with adjustable dielectric constant and its preparation method. Background Technology

[0002] The dielectric constant affects the signal transmission speed. A low dielectric constant reduces electromagnetic coupling and improves signal transmission and response speed; the lower the dielectric constant, the smaller the signal transmission delay. A high quality factor (Q value) reduces energy consumption during signal transmission and increases the frequency selectivity of devices. Therefore, in high-frequency signal systems, ceramic materials with low dielectric constants are of great significance for reducing signal delay.

[0003] When establishing a reliable data connection, antenna technology influences the performance of the transmission channel, the characteristics of the transceiver, and the selection of digital signal processing models. Printed antennas are antennas where both the radiator and feed section are placed on a dielectric substrate. Microstrip patch antennas are a common type of printed antenna, offering advantages such as light weight, ease of fabrication, and flexible design; however, their biggest drawback is narrow bandwidth. Multilayer patch antennas, as an improved structure of patch antennas, inherit all the advantages of patch antennas while extending the antenna bandwidth. With the development and widespread adoption of multilayer patch antennas, the demand for microwave dielectric materials with adjustable dielectric constants is increasing. Developing low-dielectric-constant microwave dielectric materials with adjustable dielectric constants, while simultaneously coordinating the frequency temperature coefficient and maintaining a high Q value, to promptly meet the market and RF designers' needs for constantly changing dielectric constants, is essential and has significant commercial value.

[0004] Yin Wang et al. disclosed a two-phase Mg with adjustable dielectric constant. x Zn y Al2O 4-z Sr2TiO4 microwave dielectric material has an adjustable dielectric constant of 8.5 to 18.63. However, since the material is designed as a two-phase composite with one positive and one negative frequency temperature coefficient, its frequency temperature coefficient can only change within the range of -77 to +39 ppm / ℃ as the dielectric constant is adjustable. It can only be close to zero in a small range in the middle, which limits its application scenarios to a certain extent. Summary of the Invention

[0005] Existing designs for tunable dielectric constant systems often suffer from the drawback of uncontrollable frequency temperature coefficients. Although the dielectric constant is tunable, the frequency temperature coefficient can only approach zero near a certain dielectric constant. If a near-zero frequency temperature coefficient is required near other tunable dielectric constants, the formulation system needs to be redesigned. To address rapidly changing market demands and provide timely options for microwave dielectric ceramic material formulations with different dielectric constants and near-zero frequency temperature coefficients, this invention aims to provide a microwave dielectric ceramic material with tunable dielectric constant and its preparation method. The dielectric constant of the prepared microwave dielectric material is tunable in the range of 10 to 20, and its Q×f value (Q is the quality factor of the material, f is the resonant frequency) is 47704–68149 GHz, with a frequency temperature coefficient τ... f ≤±10ppm / ℃.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A microwave dielectric ceramic material with adjustable dielectric constant has the following composition expression: xMg2SiO4-(1-x)Mg2TiO4-0.09CaTiO3-0.005MO, where: 0.15≤x≤0.7, and MO is an additive.

[0008] The auxiliary agent MO is an oxide or a mixture of oxides, wherein M is one or more of Fe, Zn, Nb, Si and Mg.

[0009] The dielectric constant of this microwave dielectric ceramic material is adjustable in the range of 10.0 to 19.9, and the Q×f value ranges from 47704 to 68149 GHz; the frequency temperature coefficient τ f ≤±10ppm / ℃.

[0010] The microwave dielectric ceramic material contains Mg₂SiO₄ and Mg₂TiO₄, which have different dielectric constants but similar temperature coefficients of frequency. Both can coexist independently with MO-optimized CaTiO₃. This characteristic of Mg₂SiO₄ and Mg₂TiO₄ allows the prepared microwave dielectric ceramic material to achieve variations in dielectric constant while maintaining a near-zero temperature coefficient of frequency throughout the entire process.

[0011] The dielectric constant of this microwave dielectric ceramic material gradually increases as the value of x in its composition expression decreases.

[0012] The preparation method of the microwave dielectric ceramic material with adjustable dielectric constant is as follows: First, pre-synthesized powder I (Mg2SiO4-Mg2TiO4 phase) and pre-synthesized powder II (0.09CaTiO3-0.005MO) are prepared respectively; then, pre-synthesized powder I and pre-synthesized powder II are mixed again to complete the three-phase composite; finally, the microwave dielectric ceramic material with adjustable dielectric constant is obtained by ball milling and sintering.

[0013] The method specifically includes the following steps:

[0014] (1) Ingredients: Magnesium oxide, silicon dioxide, titanium dioxide, calcium carbonate and MO additive are used as raw materials. First, according to the molar ratio of Mg, Si and Ti in Mg2SiO4 and Mg2TiO4 in the microwave dielectric ceramic material composition expression, magnesium oxide, silicon dioxide and titanium dioxide are weighed and mixed evenly to obtain mixture I. Then, according to the molar ratio of Ca, Ti and MO in CaTiO3 and MO in the microwave dielectric ceramic material composition expression, titanium dioxide, calcium carbonate and MO additive are weighed and mixed evenly to obtain mixture II.

[0015] (2) Mixing: The mixture I and mixture II obtained in step (1) are ball-milled and dried to obtain dried powder I and dried powder II;

[0016] (3) Pre-calcination: The dried powder I and dried powder II obtained in step (2) are placed in different alumina crucibles and pre-calcined in a carbon rod furnace to obtain pre-synthesized powder I and pre-synthesized powder II;

[0017] (4) Secondary batching: Weigh and mix the pre-synthesized powder I (x Mg2SiO4-(1-x)Mg2TiO4) and pre-synthesized powder II (0.09CaTiO3-0.005MO) obtained in step (3) according to the composition of the microwave dielectric ceramic material to obtain secondary raw material powder;

[0018] (5) Pulping: The secondary raw material powder obtained in step (4) is ball-milled for 20 to 26 hours. The ball-milling media are zirconium balls and deionized water to obtain a viscous slurry.

[0019] (6) Molding: Add 5-20 wt% binder (polyvinyl alcohol solution) to the slurry obtained in step (5), then perform spray granulation and pressing molding in sequence, and finally sinter in a carbon rod furnace to obtain the microwave dielectric ceramic material with adjustable dielectric constant.

[0020] Furthermore, in step (2), during the ball milling process, the ball milling media are zirconium balls and deionized water; after ball milling, the balls are placed in an oven at 150°C for 12 hours for drying.

[0021] Furthermore, in step (3), the pre-firing temperature in the carbon rod furnace is 1000℃~1200℃, and the pre-firing time is 2~4 hours.

[0022] Furthermore, in step (6), the sintering temperature in the carbon rod furnace is 1250℃~1300℃, and the sintering time is 3 hours.

[0023] The advantages and beneficial effects of this invention are as follows:

[0024] 1. In the formulation design of the microwave dielectric ceramic material of the present invention, the CaTiO3-yMO part in the composition expression is first pre-synthesized separately, so that the single-phase CaTiO3 reduces the pre-synthesis temperature and controls the titanium reduction phenomenon with the help of MO additive. Then, it is combined with another part in the pre-synthesized expression, xMg2SiO4-(1-x)Mg2TiO4, to form a three-phase composite, so that the three phases after the composite exist independently and exert their respective properties.

[0025] 2. The Mg2SiO4 phase and Mg2TiO4 phase in the material formulation of this invention are preferred phase systems, which have the characteristics of different dielectric constants, similar frequency temperature coefficients and no reaction between them. Thus, by changing the ratio of the two phases, the dielectric constant can be linearly adjusted, while ensuring that the frequency temperature coefficient is close to zero throughout the process.

[0026] 3. The formulation of this invention introduces a specific amount of CaTiO3 (the amount introduced accounts for 9% of the total molar amount of Mg2SiO4 and Mg2TiO4). This introduction ratio is uniquely designed and repeatedly verified, which can meet the near-zero control of the frequency temperature coefficient in the overall material system when the x value varies from 0.15 to 0.7.

[0027] 4. The microwave dielectric material of the present invention has an adjustable dielectric constant, which is adjustable in the range of 10.0 to 19.9, and a Q×f value of 47704 to 68149 GHz; the frequency temperature coefficient τ f With a temperature of ≤±10ppm / ℃, it can be widely used in fields such as multilayer patch antennas, baseband antennas, navigation antennas, and dielectric waveguide filters. Attached image description:

[0028] Figure 1 The X-ray diffraction patterns are those of the microwave dielectric ceramic materials prepared in Examples 1-6. Detailed Implementation

[0029] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0030] Examples 1-6:

[0031] The microwave dielectric ceramic material composition formula in this invention is: xMg2SiO4-(1-x)Mg2TiO4-0.09CaTiO3-0.005MO, where: 0.15≤x≤0.7, and MO is an additive. The additive MO is an oxide mixture composed of Fe, Zn, Nb, Si, and Mg (M is one or more of Fe, Zn, Nb, Si, and Mg).

[0032] The values ​​of x in the composition expressions of microwave dielectric ceramic materials in Examples 1-6 are shown in Table 1.

[0033] The specific preparation methods of microwave dielectric ceramic materials in Examples 1-6 are as follows:

[0034] (1) Ingredients: Magnesium oxide, silicon dioxide, titanium dioxide, calcium carbonate and MO additive are used as raw materials. First, according to the molar ratio of Mg, Si and Ti in Mg2SiO4 and Mg2TiO4 in the microwave dielectric ceramic material expression (i.e., the molar ratio of Mg, Si and Ti is 2:x:(1-x)), magnesium oxide, silicon dioxide and titanium dioxide are weighed and mixed evenly to obtain mixture I. Then, according to the molar ratio of Ca, Ti and MO in CaTiO3 and MO in the microwave dielectric ceramic material expression (i.e., the molar ratio of Ca, Ti and MO is 0.09:0.09:0.005), titanium dioxide, calcium carbonate and MO additive are weighed and mixed evenly to obtain mixture II.

[0035] (2) Mixing: Mixture I and mixture II after batching are ball-milled and dried to obtain dry powder I (xMg2SiO4-(1-x)Mg2TiO4) and dry powder II (0.09CaTiO3-0.005MO);

[0036] (3) Pre-calcination: The obtained dry powder I and dry powder II were placed in different alumina crucibles and pre-calcined in a carbon rod furnace at 1100℃ to obtain pre-synthesized powder I (xMg2SiO4-(1-x)Mg2TiO4) and pre-synthesized powder II (0.09CaTiO3-0.005MO);

[0037] (4) Secondary batching: Weigh and mix pre-synthesized powder I and pre-synthesized powder II according to the molar ratio in the composition expression of the microwave dielectric ceramic material to obtain secondary raw material powder;

[0038] (5) Pulping: The secondary raw material powder is ball-milled for 24 hours. The ball-milling media are zirconium balls and deionized water to obtain a viscous slurry.

[0039] (6) Molding: Add 12wt% of binder (10wt.% polyvinyl alcohol solution) to the slurry obtained in step (5), then perform spray granulation and pressing molding in sequence, and finally sinter in a carbon rod furnace at 1280℃ to obtain the microwave dielectric ceramic material with adjustable dielectric constant.

[0040] The microwave dielectric properties of the materials obtained in Examples 1-6 are shown in Table 1, and the X-ray diffraction patterns of the obtained materials are shown in Table 1. Figure 1 .

[0041] Table 1 Microwave dielectric properties of microwave dielectric ceramic materials in Examples 1-6

[0042] serial number x <![CDATA[ε r ]]> Q×f / GHz <![CDATA[τ f / (ppm / ℃) ]]> Example 1 0.7 10.0 68149 -7.5 Example 2 0.6 12.1 57641 -2.6 Example 3 0.5 14.4 57010 1.1 Example 4 0.4 15.8 54924 4.2 Example 5 0.3 17.3 48326 5.8 Example 6 0.15 19.9 47704 10.0

[0043] As shown in Table 1, as the value of x decreases, the dielectric constant gradually increases; the Q×f value gradually decreases, but remains at a relatively high level; and the frequency temperature coefficient changes little, all meeting the practical application requirements of ≤±10ppm / ℃.

[0044] Depend on Figure 1 It can be seen that diffraction peaks of the three phases Mg2SiO4, Mg2TiO4, and CaTiO3 were found in all six embodiments, but no diffraction peaks of the MO additive were found. This indicates that the three phases of the present invention exist independently and perform as expected according to the design scheme. Meanwhile, as the x value changes from 0.7 to 0.15, the intensity of the diffraction peak corresponding to Mg2SiO4 with a lower dielectric constant gradually weakens, while the intensity of the diffraction peak corresponding to Mg2TiO4 with a higher dielectric constant gradually strengthens. This explains why the dielectric constant of the material of the present invention gradually increases and is adjustable as the x value decreases. Furthermore, because the frequency temperature coefficients of the two phases Mg2SiO4 and Mg2TiO4 are similar, the frequency temperature coefficient of the material of the present invention is not affected by changes in the dielectric constant.

[0045] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0046] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A microwave dielectric ceramic material with adjustable dielectric constant, characterized in that: The compositional formula of the microwave dielectric ceramic material is: xMg2SiO4-(1-x)Mg2TiO4-0.09CaTiO3-0.005MO, where: 0.15≤x≤0.4, and MO is an additive; in the additive MO, M is one or more of Fe, Zn, Nb, Si and Mg; The dielectric constant of this microwave dielectric ceramic material is adjustable in the range of 15.8 to 19.9, and the Q×f value ranges from 47704 to 68149 GHz; the frequency temperature coefficient τ f ≤±10ppm / ℃; The preparation method of the microwave dielectric ceramic material with tunable dielectric constant is as follows: First, pre-synthesized powder I (Mg2SiO4-Mg2TiO4 phase) and pre-synthesized powder II (0.09CaTiO3-0.005MO) are prepared separately; then, pre-synthesized powder I and pre-synthesized powder II are subjected to secondary batching to complete the three-phase composite; finally, the microwave dielectric ceramic material with tunable dielectric constant is obtained by ball milling and sintering. The preparation method includes the following steps: (1) Ingredients: Magnesium oxide, silicon dioxide, titanium dioxide, calcium carbonate and MO additive are used as raw materials. First, according to the molar ratio of Mg, Si and Ti in Mg2SiO4 and Mg2TiO4 in the microwave dielectric ceramic material composition expression, magnesium oxide, silicon dioxide and titanium dioxide are weighed and mixed evenly to obtain mixture I. Then, according to the molar ratio of Ca, Ti and MO in CaTiO3 and MO in the microwave dielectric ceramic material composition expression, titanium dioxide, calcium carbonate and MO additive are weighed and mixed evenly to obtain mixture II. (2) Mixing: The mixture I and mixture II obtained in step (1) are ball-milled and dried to obtain dried powder I and dried powder II; (3) Pre-calcination: The dried powder I and dried powder II obtained in step (2) are placed in different alumina crucibles and pre-calcined in a carbon rod furnace to obtain pre-synthesized powder I and pre-synthesized powder II; (4) Secondary batching: Weigh and mix the pre-synthesized powder I (x Mg2SiO4-(1-x)Mg2TiO4) and pre-synthesized powder II (0.09CaTiO3-0.005MO) obtained in step (3) according to the composition of the microwave dielectric ceramic material to obtain secondary raw material powder; (5) Pulping: The secondary raw material powder obtained in step (4) is ball-milled for 20-26 hours. The ball milling media are zirconium balls and deionized water to obtain a viscous slurry. (6) Molding: Add 5-20 wt% binder to the slurry obtained in step (5), then perform spray granulation and pressing molding in sequence, and finally sinter in a carbon rod furnace to obtain the microwave dielectric ceramic material with adjustable dielectric constant.

2. The microwave dielectric ceramic material with adjustable dielectric constant according to claim 1, characterized in that: The dielectric constant of this microwave dielectric ceramic material gradually increases as the value of x decreases.

3. The microwave dielectric ceramic material with adjustable dielectric constant according to claim 1, characterized in that: In step (2), the ball milling medium is zirconium balls and deionized water; after ball milling, the balls are placed in a 150°C oven for 12 hours to dry.

4. The microwave dielectric ceramic material with adjustable dielectric constant according to claim 1, characterized in that: In step (3), the pre-firing temperature in the carbon rod furnace is 1000℃~1200℃ and the pre-firing time is 2~4 hours.

5. The microwave dielectric ceramic material with adjustable dielectric constant according to claim 1, characterized in that: In step (6), the sintering temperature in the carbon rod furnace is 1250℃~1300℃ and the sintering time is 3 hours.

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