A light-weight borate microwave dielectric ceramic material, a preparation method and application thereof

Abstract

The application discloses a kind of lightweight borate microwave dielectric ceramic materials and its preparation method and application, belong to ceramic material field, including the following steps: (1) according to the stoichiometric ratio of Li2BAlO4 LiBO2, Al2O3 And Li2CO3 Raw materials are weighed, mixed after ball milling, drying, pre-sintering, obtain powder.(2) The powder is dried after ball milling, then it is pressed into shape, vacuum treatment, cold isostatic pressing, sintering, obtain the lightweight borate microwave dielectric ceramic material.The lightweight borate microwave dielectric ceramic material prepared by the above preparation method and its application in dielectric substrate, resonator and filter are simultaneously disclosed.The application can reduce the sintering temperature of ceramic, improve sintering characteristics.Li2BAlO4 Ceramic prepared by the application has low dielectric constant and high quality factor, and has potential to be widely used in the manufacture of lightweight microwave dielectric substrate, filter, antenna and other microwave devices.

Description

Technical Field

[0001] The present invention relates to the field of ceramic materials, and in particular to a light borate microwave dielectric ceramic material and a preparation method and application thereof. Background Art

[0002] Microwave dielectric ceramics (MWDC) are new ceramic materials used as dielectric materials in microwave frequency circuits (mainly UHF, SHF bands, 300MHz~300GHz bands with wavelengths between 0.1mm-1m) and perform one or more functions. In modern communications, they are widely used as components such as resonators, filters, dielectric substrates and dielectric waveguide circuits. They are key basic materials for modern communication technology and can meet the requirements of miniaturization, integration, high reliability and low cost of microwave circuits.

[0003] In recent years, with the rapid development of electronic information technology, the demand for miniaturization, portability, multi-function, digitization, reliability, and high performance in electronic devices has become increasingly urgent, placing an increasingly urgent demand on the miniaturization, integration, and modularization of components. Due to the rapid development of electronic information technology and the trend toward miniaturization, lightweighting, and high performance in electronic devices, including smartphones and fifth-generation cellular wireless systems (5G) networks, microwave multi-chip module (MCM) technology has attracted widespread attention due to its technical advantages of light weight, small size, low cost, and high reliability. Microwave dielectric ceramic materials are one of the primary materials used in the application of MCM technology, and their widespread application in both civilian and military fields is an urgent and necessary issue.

[0004] Low Temperature Co-fired Ceramics (LTCC) is a new material technology developed by Hughes Corporation in 1982. It uses thick film materials and is manufactured according to the structure of co-fired ceramic design. It is a technology used to achieve high integration and high performance electronic packaging, and provides great potential in terms of design flexibility, wiring density and reliability. The materials used in low temperature co-fired ceramic technology should meet the following conditions: 1. Meet the required dielectric constant (5≤ε r ≤20); 2. High quality factor or low dielectric loss (Q×f>10,000GHz); 3. Sintering temperature below the electrode melting point (the melting point of Ag is 961°C, and the melting point of Cu is 1084°C); 4. The ceramic material must not undergo interfacial reactions with the electrode material, and the two must have a high degree of sintering shrinkage matching. However, the sintering temperatures of commercially available microwave dielectric materials are generally higher than the melting points of internal electrode materials such as Cu and Ag. Few microwave dielectric materials have inherently low sintering temperatures and meet these requirements.

[0005] The methods for obtaining microwave dielectric ceramic materials with low dielectric constant and low temperature sintering mainly include the following: 1. Adding a certain amount of low-melting-point oxides or glass phases as sintering aids to the material system. The liquid phase produced during the sintering process can accelerate material transfer, thereby reducing the sintering temperature; 2. Microwave dielectric ceramics are usually synthesized using the traditional solid-phase method. This method has a simple process and can be mass-produced, but it is difficult to ensure the uniform size of the powder prepared. Larger particles have poor reactivity, resulting in a higher sintering temperature for the ceramic; 3. Selecting a material system with a low inherent sintering temperature, but the addition of low-melting-point oxides and glass phases may react with the matrix to produce a second phase, thereby deteriorating the dielectric properties of the ceramic; and the use of chemical synthesis methods and the preparation of ultrafine powders are relatively complicated, which increases costs and is not conducive to industrial production.

[0006] In the process of exploring and developing new lightweight microwave dielectric ceramic materials that can be sintered at low temperatures, LTCC technology can meet the requirements of miniaturization, lightweight, chip-type, and multifunctionality of electronic products, and can be made into high-density circuits that do not interfere with each other in three-dimensional space, and can also be made into passive / active integrated functional modules or circuits. Compared with single-layer processing of materials, it can effectively improve efficiency and reduce costs. In addition, B2O3 has a low melting point (only 450°C), and borates have a high melting point because of B 3+ Due to their extremely low polarizability, borates are a promising material system for LTCC applications. However, boric acid (H₃BO₃ or B₂O₃), used as a boron source, is highly hygroscopic. This water absorption during weighing can cause the precursor to deviate from the stoichiometric ratio, preventing the target compound from being obtained.

[0007] Therefore, how to provide a method for preparing microwave dielectric ceramic materials using borates is a technical problem that those skilled in the art urgently need to solve. Summary of the Invention

[0008] The purpose of the present invention is to provide a lightweight borate microwave dielectric ceramic material and a preparation method thereof for application, so as to solve the problems existing in the above-mentioned prior art.

[0009] To achieve the above object, the present invention provides the following solutions:

[0010] A method for preparing a lightweight borate microwave dielectric ceramic material comprises the following steps:

[0011] (1) LiBO2, Al2O3, and Li2CO3 were weighed according to the stoichiometric ratio of Li2BAlO4, mixed, ball-milled, dried, and pre-calcined to obtain powder.

[0012] (2) The powder is ball-milled and dried, and then subjected to pressing, vacuum treatment, cold isostatic pressing, and sintering to obtain the lightweight borate microwave dielectric ceramic material.

[0013] Preferably, the purities of LiBO2, Al2O3 and Li2CO3 in step (1) are all ≥99.9%.

[0014] Beneficial Effects: The present invention uses lithium metaborate LiBO2 as a boron source and precisely controls the stoichiometric ratio to obtain high-purity Li2BAlO4 ceramics. On the one hand, the LiBO2 in the present invention does not contain crystal water and is not easy to absorb water; on the other hand, LiBO2 has a low dielectric constant ε r =5.3 and a high quality factor Q×f=18200GHz, and its densification temperature is 640°C, which is lower than the melting point of silver (961°C) and does not react with Ag electrodes, so it can be applied to LTCC technology. The present invention uses LiBO2 to introduce the boron element, and uses original powders of LiBO2, Al2O3 and Li2CO3 with a purity of more than 99.9% (weight percentage) to synthesize and explore the compounds of the Li2O-B2O3-Al2O3 system according to the composition of Li2BAlO4. Finally, the synthesis temperature of Li2BAlO4 is lower than 800°C, and it has good comprehensive microwave dielectric properties, and can be used as a lightweight, low-temperature sintered microwave dielectric ceramic.

[0015] Preferably, the pre-calcination temperature in step (1) is 550-650° C., and the pre-calcination time is 2-8 hours;

[0016] Beneficial Effects: Thermal analysis of the ball-milled raw materials, combined with the resulting images, revealed a pre-calcination temperature of 550-600°C. Pre-calcining the raw materials in this invention is performed to initially synthesize the desired phases. During the pre-calcination process, Li₂CO₃ decomposes to produce Li₂O and CO₂. XRD analysis of the pre-calcined samples, compared to standard charts, revealed the synthesis of the primary phase, Li₂BAlO₄.

[0017] Preferably, the ball milling media in steps (1) and (2) are yttrium-stabilized zirconia balls with diameters of 1 mm, 5 mm, and 7 mm, respectively, and a mass ratio of 3:5:2;

[0018] The ball milling aid used in the ball milling is anhydrous ethanol;

[0019] The mass ratio of the raw materials, ball milling media and ball milling aid is 1:2:2;

[0020] The ball milling speed is 300 r / min and the time is 6 h;

[0021] The drying temperature is 120° C. and the drying time is 0.5 h.

[0022] Beneficial effect: The above drying process is to volatilize the anhydrous ethanol mixed during the sample ball milling to obtain a dry sample.

[0023] Preferably, the pressure during the compression molding process in step (2) is 1 MPa.

[0024] Beneficial effect: The pressing molding at this time uses low pressure to initially make the powder sample into a round green body.

[0025] Preferably, the vacuum treatment in step (2) is performed by placing the green body in a rubber sleeve, specifically comprising the following steps: arranging the pressed green body neatly into the rubber sleeve, exhausting the air in the rubber sleeve by using a vacuum pump, and finally sealing the rubber sleeve with a plastic rope.

[0026] Beneficial effect: Vacuum treatment can isolate the green body from the oil medium in the next step, preventing contamination of the sample.

[0027] Preferably, the cold isostatic pressing in step (2) utilizes vacuum pump oil as the pressure medium, and the pressure is 250-300 MPa.

[0028] Beneficial effects: The present invention utilizes cold isostatic pressing to densify the circular green body, which can better promote sintering densification.

[0029] Preferably, the sintering temperature in step (2) is 760-800° C., and the sintering time is 4 hours.

[0030] The sintering temperature in the present invention is obtained by heat treatment analysis of the sample after the first ball milling.

[0031] A light borate microwave dielectric ceramic material is prepared by a method for preparing a light borate microwave dielectric ceramic material.

[0032] Beneficial effects: The lightweight microwave dielectric ceramics provided by the present invention can better achieve lightweight and miniaturization of materials. The lithium metaborate LiBO2 in the present invention is used as a boron source, and the stoichiometric ratio is precisely controlled to obtain high-purity Li2BAlO4 ceramics. LiBO2 not only does not contain crystal water and is not easy to absorb water, but also has a low dielectric constant ε r =5.3 and a high quality factor Q×f=18200 GHz, and its densification temperature is 640°C, which is lower than the melting point of silver (961°C) and does not react with the Ag electrode.

[0033] The invention discloses an application of a lightweight borate microwave dielectric ceramic material in dielectric substrates, resonators and filters.

[0034] Beneficial Effects: The LiBO2 raw material in this invention has a low dielectric constant and a high quality factor. The synthesized Li2BAlO4 ceramic has low density, a low dielectric constant, and a high quality factor. It can be applied to advanced wireless communication technologies such as 5G, where miniaturization and lightweighting are the foundations of antenna design.

[0035] More preferably, the components prepared using the microwave dielectric ceramic material provided by the present invention can be applied to mobile communication base stations. Dielectric resonators, dielectric filters, duplexers and multiplexers are all key components of the radio frequency unit of the communication base station.

[0036] Resonators can generate resonant frequencies and control them, and can be used in radar detection, satellite reception, communication base stations, etc.; filters can filter signals and allow specific signals to pass through, and are used in consumer electronics such as routers, car navigation, satellite TV, drones, and other industry user fields such as mobile communications, radar, and 5G wifi; duplexers (multiplexers) have the bidirectional function of receiving and transmitting microwave signals, and can be used in microwave communications, optical indoor distribution systems, GMS, WCD and other mobile communications fields; antennas can be used to receive and send microwave signals, and are mainly used in GPS and Beidou satellite navigation.

[0037] The present invention discloses a lightweight borate microwave dielectric ceramic material, its preparation method and application. The present invention uses LiBO2 as a raw material to introduce boron into Li2BAlO4 ceramics, which can not only accurately control the stoichiometric ratio, but also reduce the sintering temperature of the ceramics and improve the sintering characteristics. The density of the Li2BAlO4 ceramics prepared by the present invention is 2.1-2.3g / cm 3 , with a low dielectric constant ε r =3.9-5.2 and a high quality factor Q×f=14440-26886GHz, and has the potential to be widely used in the manufacture of lightweight microwave dielectric substrates, filters, antennas and other microwave devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0039] Figure 1 XRD pattern and SEM image of Li2BAlO4 ceramic prepared in Example 1;

[0040] Figure 2 XRD pattern and SEM image of Li2BAlO4 ceramic prepared in Example 2;

[0041] Figure 3 XRD pattern and SEM image of Li2BAlO4 ceramic prepared in Example 3;

[0042] Figure 4 XRD pattern of Li2BAlO4 ceramic prepared in Comparative Example 1;

[0043] Figure 5 XRD pattern of Li2BAlO4ceramic prepared for Comparative Example 2. DETAILED DESCRIPTION

[0044] The technical solutions in the embodiments of the present application will be apparently and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0045] In order to make the above objectives, characteristics and advantages of the present application more apparent and comprehensible, the present application will be further described in detail below with reference to the drawings and specific embodiments.

[0046] Embodiment 1

[0047] A preparation method of a lightweight borate microwave dielectric ceramic, comprising the following steps:

[0048] (1) LiBO2, Al2O3 and Li2CO3 with a purity of 99.9% or above are weighed according to the stoichiometric ratio of Li2BAlO4 (accurate to 0.0001 g) and mixed, and the obtained mixture is loaded into a nylon tank with zirconium balls and anhydrous ethanol at a mass ratio of 1:2:2, and then ball-milled at a rotation speed of 300 r / min for 6 hours, and then dried at 120°C for 2 hours;

[0049] (2) The dried mixture in step (1) is placed in an alumina crucible and pre-fired at 600°C for 4 hours to obtain a pre-fired powder;

[0050] (3) The pre-fired powder, zirconium balls and anhydrous ethanol are added into a nylon tank at a mass ratio of 1:2:2, and then ball-milled at a rotation speed of 300 r / min for 6 hours, and then dried at 120°C for 2 hours to obtain a dried pre-fired powder;

[0051] (4) The dried pre-fired powder in step (3) is pressed into a cylindrical green body using a powder tablet press, and then the green body is placed in a rubber sleeve for vacuum treatment, and then cold isostatic pressing is performed at a pressure of 250-300 MPa using vacuum pump oil as a pressure medium, and then the cylindrical green body is sintered at 760°C for 4 hours to obtain a lightweight borate microwave dielectric ceramic. The XRD pattern and SEM pattern thereof are as shown in Figure 1As shown in the figure, the X-ray diffraction peak of the material at 760°C can be identified as Li₂BAlO₄ (PDF: 01-089-4364), with no secondary phase present, indicating that a single Li₂BAlO₄ phase can be formed at this temperature. Combined with the SEM images, it can be seen that when sintered at 760°C, the Li₂BAlO₄ ceramic has smaller grain size, more distinct grain boundaries, more pores, and a relatively small Q×f value.

[0052] Example 2

[0053] A method for preparing a light borate microwave dielectric ceramic is different from that in Example 1. In step (4), the cylindrical green body is sintered at 780°C for 4 hours. The remaining steps and parameters are the same as those in Example 1. A light borate microwave dielectric ceramic is prepared. Its XRD pattern and SEM pattern are as follows: Figure 2 As shown in the figure, it can be seen that the X-ray diffraction peak of the material at 780℃ completely corresponds to that of Li2BAlO4 (PDF: 01-089-4364). Combined with the SEM image, it can be found that when sintered at 780℃, the grain size of Li2BAlO4 ceramics becomes larger than that at 760℃, the porosity decreases, and the Q×f value increases compared with that at 760℃.

[0054] Example 3

[0055] A method for preparing a light borate microwave dielectric ceramic is different from that of Example 1 in that, in step (4), the cylindrical green body is sintered at 800°C for 4 hours. The remaining steps and parameters are the same as those of Example 1 to prepare a light borate microwave dielectric ceramic. Its XRD pattern and SEM pattern are shown in FIG. Figure 3 As shown in the figure, the X-ray diffraction peak of the material at 800°C corresponds exactly to that of Li2BAlO4 (PDF: 01-089-4364), with no secondary phase present. Combined with the SEM images, it is clear that sintering at 800°C causes excessive grain growth in the Li2BAlO4 ceramic, reducing the opportunity for oxygen to enter the ceramic and undergo reoxidation. This results in an increase in the relative content of oxygen vacancies, and consequently, a decrease in the ceramic's quality factor, Q×f.

[0056] Comparative Example 1

[0057] A method for preparing a light borate microwave dielectric ceramic is different from that of Example 1 in that, in step (4), the cylindrical green body is sintered at 700°C for 4 hours. The remaining steps and parameters are the same as those of Example 1 to prepare a light borate microwave dielectric ceramic. The XRD pattern of the obtained light borate microwave dielectric ceramic is as follows: Figure 4 As shown, it can be seen that when the material is sintered at 700℃, the material phase is mainly Li2BAlO4, accompanied by a small amount of LiAlO2 impurity phase and unknown phase peaks, indicating that changing the conditions cannot synthesize a single phase.

[0058] Comparative Example 2

[0059] A method for preparing a light borate microwave dielectric ceramic is different from Example 1 in that the raw material LiBO2 is replaced by H3BO3. The XRD pattern of the obtained light borate microwave dielectric ceramic is as follows: Figure 5 As shown, it can be seen that in addition to the main phase Li2BAlO4, the material is also accompanied by LiAlO2 impurity phase and unknown phase, which also shows that a single phase cannot be synthesized by replacing the raw materials.

[0060] Table 1 shows Examples 1-3 of the present invention with different sintering temperatures and their microwave dielectric properties. The preparation methods are as described above, and the microwave dielectric properties are evaluated using the cylindrical dielectric resonator method.

[0061] Table 1

[0062] Composition Sintering temperature (°C) <![CDATA[ρ(g / cm 3 )]]> e r ]] Q x f (GHz) Example 1 <![CDATA[Li2BAlO4]]> 760 2.1184 5.2 14440 Example 2 <![CDATA[Li2BAlO4]]> 780 2.1908 4.0 26880 Example 3 <![CDATA[Li2BAlO4]]> 800 2.2290 3.9 24210

[0063] As can be seen from Table 1, the density of the lightweight borate microwave dielectric ceramic provided by the present invention is 2.1184-2.2290 g / cm 3 , dielectric constant ε r The frequency range is 3.9-5.2, and the quality factor is 14440-26886GHz. It can be widely used in the manufacture of various microwave devices such as dielectric substrates, resonators and filters, and can meet the technical needs of systems such as mobile communications and satellite communications.

[0064] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing a lightweight borate microwave dielectric ceramic material, characterized in that: The steps include: (1) Raw materials LiBO2, Al2O3, and Li2CO3 were weighed according to the stoichiometric ratio of Li2BAlO4, mixed, ball-milled, dried, and pre-calcined to obtain powder; The pre-firing temperature in step (1) is 550-650°C and the pre-firing time is 2-8h; (2) ball-milling the powder, drying it, and then pressing, vacuum-treating, cold isostatically pressing, and sintering it to obtain the lightweight borate microwave dielectric ceramic material; The sintering temperature is 760-800°C.

2. The method for preparing a lightweight borate microwave dielectric ceramic material according to claim 1, characterized in that: The purities of LiBO2, Al2O3 and Li2CO3 in step (1) are all ≥99.9%.

3. The method for preparing a lightweight borate microwave dielectric ceramic material according to claim 1, characterized in that: The ball milling media in steps (1) and (2) are yttrium-stabilized zirconia balls with diameters of 1 mm, 5 mm, and 7 mm, respectively, and a mass ratio of 3:5:2; The ball milling aid used in the ball milling is anhydrous ethanol; The mass ratio of the raw materials, ball milling media and ball milling aid is 1:2:2; The ball milling speed is 300 r / min and the time is 6 h; The drying temperature is 120° C. and the drying time is 0.5 h.

4. The method for preparing a lightweight borate microwave dielectric ceramic material according to claim 1, characterized in that: The pressure during the pressing process in step (2) is 1 MPa.

5. The method for preparing a lightweight borate microwave dielectric ceramic material according to claim 1, characterized in that: The vacuum treatment in step (2) is carried out by placing the green body in a rubber sleeve, and specifically includes the following steps: arranging the pressed green body neatly into the rubber sleeve, using a vacuum pump to expel the air in the rubber sleeve, and finally sealing it with a plastic rope.

6. The method for preparing a lightweight borate microwave dielectric ceramic material according to claim 1, characterized in that: The cold isostatic pressing in step (2) uses vacuum pump oil as the pressure medium, and the pressure is 250 ~ 300MPa.

7. The method for preparing a lightweight borate microwave dielectric ceramic material according to claim 1, characterized in that: The sintering time in step (2) is 4 hours.

8. A light borate microwave dielectric ceramic material prepared by the method for preparing a light borate microwave dielectric ceramic material according to any one of claims 1 to 7.

9. Use of the lightweight borate microwave dielectric ceramic material according to claim 8 in dielectric substrates, resonators and filters.

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