Low-temperature co-fired ceramic material with medium-high dielectric constant and preparation method of low-temperature co-fired ceramic material

Abstract

The invention belongs to the technical field of electronic ceramic materials and manufacturing thereof, and relates to a low-temperature co-fired ceramic material with medium and high dielectric constants and a preparation method of the low-temperature co-fired ceramic material. The low-temperature co-fired ceramic material comprises the following components: multiphase ceramic, glass and a simple compound, the multiphase ceramic is a multiphase ceramic composed of at least two titanate ceramics, or a multiphase ceramic composed of at least two niobate ceramics, or a multiphase ceramic composed of at least two zirconate ceramics, or a multiphase ceramic composed of at least two of titanate ceramics, niobate ceramics and zirconate ceramics; the glass is amorphous glass with the softening point of 400 to 700 DEG C; the simple compound is at least one of oxides or carbonates corresponding to metal elements of the multiphase ceramic. According to the invention, the oxide or carbonate corresponding to the multiphase ceramic composition elements is introduced to improve the wettability of the multiphase ceramic matrix, so that the compactness and reliability of the multiphase ceramic are improved, and the requirements of the communication technology on the medium-high dielectric constant LTCC material are met.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic ceramic materials and their manufacturing, and in particular to a low-temperature co-fired ceramic material with a medium to high dielectric constant and a preparation method thereof. Background Art

[0002] With the rapid development of communication technology, the market demand for electronic devices such as portable terminals, artificial intelligence devices, satellite communications, and phased array radars continues to grow. These devices place higher demands on the miniaturization, high frequency, and multifunctionality of materials. In this context, low-temperature co-fired ceramics (LTCC) technology has become a preferred high-density multi-layer ceramic packaging solution. LTCC technology can achieve high-density packaging at a lower sintering temperature, reducing manufacturing costs, while also having good thermal stability, corrosion resistance, and electrical properties. Therefore, its application in high-frequency and high-temperature fields is gradually increasing.

[0003] Currently, low-k dielectric constant (LTCC) substrate materials are relatively mature, with multiple commercialized material systems. However, medium- and high-k dielectric constant (LTCC) material systems remain relatively scarce. These materials face numerous challenges in practical application, the most significant of which is insufficient density. This is due to the following: firstly, the intrinsic sintering temperatures of most medium- and high-k dielectric materials exceed 1200°C (or even exceed 1400°C), making low-temperature sintering inherently difficult. Secondly, during low-temperature sintering, the sintering kinetics of the ceramic particles are significantly limited, resulting in low grain boundary migration rates and slow mass transfer, making it difficult to effectively eliminate voids. This directly impacts mechanical strength, thermal conductivity, and long-term stability. Although existing technologies often improve ceramic density by adding sintering aids and adjusting the sintering process, these methods often result in reduced electrical performance or increased material costs. With the advancement of communication technology, the demand for medium- and high-k dielectric constant (LTCC) materials is growing. They are widely used in filters, microwave dielectric resonators, and dielectric antennas, making the development of medium- and high-k dielectric constant (LTCC) materials particularly important.

[0004] Some researchers have attempted to prepare medium- and high-dielectric-constant LTCC materials based on the combination of single-phase ceramics and low-softening-point glass, such as niobate-based ceramics (CN114656261A, CN116813341A, CN105000883A, Journal of Alloys and Compounds, 2017, Vol. 726: 424-429, Journal of Materials Science: Materials in Electronics, 2016, Vol. 27(10): 10622-10626), barium titanate-based ceramics (CN113999005A, Advanced Materials Research, 2014, Vol. 906: 12-17, Ceramics International, 2017, Vol. 43(15): 12863-12869, ACS Sustainable Chemistry and Engineering, 2017, Vol. 5(11): 10606-10613) and barium zinc titanate (BZT)-based ceramics (CN102153341A, Ceramics International, 2016, Vol. 42(7): 7943-7949). However, the dielectric constant of single-phase ceramics has limited variation, and to achieve a gradient dielectric constant of low-temperature co-fired ceramics, multiphase ceramics are often required.

[0005] Compared with single-phase ceramics, composite ceramics are composed of different ceramic phases. By adjusting the volume fraction and distribution of each ceramic phase, a gradient design of the dielectric constant can be achieved. At the same time, the multiphase characteristics of composite ceramics enhance their adaptability to temperature changes, making their temperature coefficient of frequency (TCF) close to zero, thereby improving their reliability in complex working environments. When designing composite ceramics, materials with low dielectric constant and low loss (such as MgTiO3) are usually selected for compounding with materials with high dielectric constant but relatively high loss (such as SrTiO3 / CaTiO3), and the sintering temperature is reduced by adding low softening point glass or other sintering aids to achieve low-temperature sintering. For example, studies on MgTiO3-CaTiO3 (Journal of Alloys and Compounds, 2008, Vol. 462: L5-L8) and Li2Mg3TiO6-SrTiO3 (Materials Chemistry and Physics, 2017, Vol. 200: 264-269) have been reported in the literature. Although multiphase ceramics have a strong adjustability in dielectric constant, a single glass material cannot effectively wet multiple different types of ceramics. Therefore, in the field of LTCC, improving substrate wettability and ceramic density is often achieved by adding extremely high levels of glass (CN117069493A; CN117510085A) or multiple sintering aids (CN110041067A). Although this method can achieve good sintering density, due to the low dielectric constant and high loss of glass or sintering aids, it will deteriorate the dielectric properties of the LTCC material. Summary of the Invention

[0006] In view of the above, improving the density of low-temperature co-fired composite ceramics has become a difficult problem in the field of LTCC technology. To this end, the present invention provides a method for improving the sintering density of low-temperature co-fired ceramic materials. This method innovatively introduces oxides or carbonates corresponding to the constituent elements of the composite ceramic to enhance the wettability of the composite ceramic matrix, thereby improving the density and reliability of the composite ceramic, thereby meeting the demand for medium- and high-dielectric-constant LTCC materials in communications technology.

[0007] In a first aspect, the present invention provides a low-temperature co-fired ceramic material with a medium to high dielectric constant. The low-temperature co-fired ceramic material comprises: a composite ceramic + glass + a simple compound; the composite ceramic is a composite ceramic composed of at least two titanate ceramics, or a composite ceramic composed of at least two niobate ceramics, or a composite ceramic composed of at least two zirconate ceramics, or a composite ceramic composed of at least two of titanate ceramics, niobate ceramics, and zirconate ceramics; the glass is an amorphous glass with a softening point of 400-700°C; the simple compound is at least one oxide or carbonate corresponding to the metal element of the composite ceramic; wherein, based on the total mass of the composite ceramic and the glass being 100%, the composite ceramic accounts for 60%-95% of the total mass of the composite ceramic and the glass, the glass accounts for 5%-40% of the total mass of the composite ceramic and the glass, and the simple compound accounts for 0.5%-10% of the total mass of the composite ceramic and the glass.

[0008] Preferably, based on the total mass of the composite ceramic and the glass being 100%, the composite ceramic accounts for 60% to 90% of the total mass of the composite ceramic and the glass; more preferably, the composite ceramic accounts for 70% to 80% of the total mass of the composite ceramic and the glass.

[0009] Preferably, the titanate ceramic includes at least one of MgTiO3, CaTiO3, SrTiO3, and BaTiO3; the niobate ceramic includes at least one of ZnNb2O6 and BaNb2O6; and the zirconate ceramic includes at least one of CaZrO3 and MgZrO3.

[0010] Preferably, the simple compound accounts for 0.8% to 5% of the total mass of the composite ceramic and glass.

[0011] Preferably, the glass is at least one of borosilicate glass, aluminosilicate glass, and phosphate glass.

[0012] Preferably, the sintering temperature of the low-temperature co-fired ceramic material is ≤950°C, preferably 850-950°C, more preferably 875-900°C.

[0013] Preferably, the dielectric constant of the low-temperature co-fired ceramic material is 19-60 (5-7 GHz), and the dielectric loss is less than 0.002 (5-7 GHz).

[0014] Preferably, the (volume) porosity of the sintered body of the low-temperature co-fired ceramic material is less than 2.5%.

[0015] In a second aspect, the present invention provides a method for preparing the medium-to-high dielectric constant low-temperature co-fired ceramic material. The method comprises: uniformly mixing amorphous glass powder and a multiphase ceramic in a predetermined ratio, then adding a simple compound and performing secondary mixing to obtain the medium-to-high dielectric constant low-temperature co-fired ceramic material; preferably, sintering the medium-to-high dielectric constant low-temperature co-fired ceramic material to obtain a dense low-temperature co-fired ceramic sintered body.

[0016] In a third aspect, the present invention provides a method for improving the sintering density of a low-temperature co-fired ceramic material with a medium to high dielectric constant. The low-temperature co-fired ceramic material comprises: a composite ceramic + glass + a simple compound; the composite ceramic is a composite ceramic composed of at least two titanate ceramics, or a composite ceramic composed of at least two niobate ceramics, or a composite ceramic composed of at least two zirconate ceramics, or a composite ceramic composed of at least two of titanate ceramics, niobate ceramics, and zirconate ceramics; the glass is an amorphous glass with a softening point of 400-700°C; the simple compound is at least one oxide or carbonate corresponding to the metal element of the composite ceramic; wherein, based on the total mass of the composite ceramic and the glass being 100%, the composite ceramic accounts for 60-95% of the total mass of the composite ceramic and the glass, the glass accounts for 5-40% of the total mass of the composite ceramic and the glass, and the simple compound accounts for 0.5-10% of the total mass of the composite ceramic and the glass.

[0017] The present invention has the following beneficial effects

[0018] The present invention provides a method for improving the sintering density of low-temperature co-fired ceramic materials. The low-temperature co-fired ceramics comprise a composite ceramic, glass, and a simple compound. The sintering temperature is lowered by using low-softening-point glass, while the dielectric constant is adjusted by precisely controlling the composition and ratio of the composite ceramic. Furthermore, by introducing simple compounds corresponding to the constituent elements of the composite ceramic, the wettability and flowability of the composite ceramic are improved, ultimately achieving improved ceramic density. Compared to currently available LTCC dielectric materials, the low-temperature co-fired ceramics of the present invention can flexibly adjust dielectric properties while maintaining density, meeting the diverse dielectric performance requirements of different applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The cross-sectional micromorphology and porosity of Examples 1 and 2; (a) is the cross-sectional micromorphology of Example 1 magnified 1000 times; (b) is the cross-sectional micromorphology of Example 1 when magnified 5000 times; (c) is the micromorphology of Example 1 magnified 1000 times and processed using ImageJ software; (d) is the cross-sectional micromorphology of Example 2 magnified 1000 times; (e) is the cross-sectional micromorphology of Example 2 when magnified 5000 times; (f) is the micromorphology of Example 2 magnified 1000 times and processed using ImageJ software.

[0020] Figure 2 The cross-section micro-morphology and porosity of Comparative Example 1; wherein (a) is the cross-section micro-morphology at 1000 times magnification; (b) is the cross-section micro-morphology at 5000 times magnification; (c) is the micro-morphology of Comparative Example 1 at 1000 times magnification after processing by ImageJ software.

[0021] Figure 3 The cross-section micro-morphology of Comparative Examples 2 and 3; wherein (a) is the cross-section micro-morphology of Comparative Example 2 at 1000 times magnification; (b) is the cross-section micro-morphology of Comparative Example 3 at 1000 times magnification; (c) is the micro-morphology of Comparative Example 2 at 1000 times magnification after processing by ImageJ software; (d) is the micro-morphology of Comparative Example 3 at 1000 times magnification after processing by ImageJ software.

[0022] Figure 4 The cross-section micro-morphology of Examples 7 and 8; wherein (a) is the cross-section micro-morphology of Example 7 at 1000 times magnification; (b) is the cross-section micro-morphology of Example 7 at 5000 times magnification; (c) is the cross-section micro-morphology of Example 8 at 1000 times magnification; (d) is the cross-section micro-morphology of Example 8 at 5000 times magnification. DETAILED DESCRIPTION

[0023] The application is further illustrated by the following embodiments. It should be understood that the following embodiments are only used to illustrate but not limit the application. Embodiments of the application will be apparent to those of ordinary skill in the art in view of the detailed description of the application and its embodiments, and based on the appended claims. It is to be understood that while a certain number of embodiments have been used for the purposes of examples, any and all modifications, variations or equivalent arrangements that fall within the scope of the present application should be considered as within the scope of the application.

[0024] The application provides a method for improving the sintering density of low-temperature co-fired ceramic materials. The low-temperature co-fired ceramic system comprises: a complex ceramic + glass + a simple compound (a variable-valence oxide).

[0025] The complex ceramic comprises, but is not limited to, at least two of titanate, niobate and zirconate. The complex ceramic can be a complex ceramic composed of at least two of titanate, niobate and zirconate. The complex ceramic can also be a complex ceramic composed of at least two independent titanates, a complex ceramic composed of at least two independent niobates, or a complex ceramic composed of at least two independent zirconates. The titanate comprises, but is not limited to, MgTiO3, CaTiO3, SrTiO3, BaTiO3, etc. The niobate comprises, but is not limited to, ZnNb2O6, BaNb2O6, etc. The zirconate comprises, but is not limited to, CaZrO3, MgZrO3, etc.

[0026] Glass is a non-crystalline glass with a softening point of 400-700°C. The glass phase softens and flows at low temperature, providing necessary liquid sintering environment for low temperature co-fired ceramic system. The glass can be borosilicate glass, aluminosilicate glass, phosphate glass, etc. The borosilicate glass includes but is not limited to Li2O-B2O3-SiO2or ZnO-B2O3-SiO2, etc. The aluminosilicate glass includes but is not limited to MgO-Al2O3-B2O3-SiO2, etc.

[0027] The total mass of the composite ceramic and the glass is 100%, and the composite ceramic accounts for 60%-95% of the total mass of the composite ceramic and the glass. The intrinsic sintering temperature of the composite ceramic is relatively high. If the content of the composite ceramic is too high, low-temperature sintering may not be achieved; and if the content of the composite ceramic is too low, the dielectric constant of the composite ceramic cannot meet the medium-high dielectric requirement. In some embodiments, the composite ceramic accounts for 60%-90% of the total mass of the composite ceramic and the glass, preferably 70%-80%.

[0028] The total mass of the composite ceramic and the glass is 100%, and the glass accounts for 5%-40% of the total mass of the composite ceramic and the glass. If the amount of the glass is insufficient, the sintering driving force will be insufficient, and the densification process will be hindered. The glass phase itself has relatively high dielectric loss and relatively low dielectric constant, and excessive addition will significantly deteriorate the dielectric performance of the material. In some embodiments, the glass accounts for 5%-30% of the total mass of the composite ceramic and the glass, preferably 10%-30%, and further preferably 10%-20%.

[0029] The simple compound is a simple compound corresponding to the (metal) elements of the composite ceramic composition. The simple compound includes at least one selected from simple oxides or simple carbonates corresponding to the elements of the composite ceramic composition. For example, the simple compound includes but is not limited to one of simple oxides AO x (A=Mg, Ti, Zn, etc.) and simple carbonates BCO x (B=Ca, Ba, Sr, etc.). If the simple compound is replaced by a sintering aid (B2O3, Li2CO3, BaCuB2O5, etc.), the wettability between the glass and the composite ceramic is not significantly improved, and the densification of the composite ceramic is also not significantly improved.

[0030] The simple compound accounts for 0.5% to 10% of the total mass of the composite ceramic and the glass, preferably 0.8% to 5%. If the simple compound is added in too small an amount, the simple compound cannot fully play its wetting role, and the densification of the composite ceramic cannot be improved; and if the simple compound is added in too large an amount, too many impurity phases may be introduced, and the dielectric properties of the ceramic material are deteriorated. For example, when MgTiO3 ceramic is used as part of the composition of the composite ceramic, and TiO2 is additionally added in excess, the MgTi2O5 phase is easily produced.

[0031] If the amorphous ceramic in the system of the present application is replaced by a crystalline ceramic, the densification of the medium-high dielectric constant LTCC material cannot be improved. This is because: due to the high intrinsic sintering temperature of the medium-high dielectric constant material, a glass sintering aid is usually introduced to reduce the sintering temperature. However, the crystallization of the crystalline glass occurs during the sintering process, and the crystallization and densification are competitive mechanisms. Once the crystallization starts, the viscosity of the glass phase rises sharply, and the densification process stops, resulting in the failure of the sintering aid, and finally it is difficult to achieve the full densification of the material. In addition, the composite ceramic + amorphous glass + simple compound system of the present application is also not suitable for the densification regulation of low dielectric constant LTCC materials. At present, the low dielectric constant LTCC material system based on ceramic is relatively limited, and the system based on composite ceramic for low dielectric constant regulation is even rarer. In the low dielectric constant LTCC system, the material is usually composed of a crystalline glass or a crystalline glass-filler composite system, and the content of the crystalline glass is usually high (usually more than 50wt%, even up to 70wt%), and the densification of such materials is mainly regulated by the high content of the crystalline glass phase or the content of the regulated sintering system.

[0032] The present application also provides a preparation process of the low-temperature co-fired ceramic material and an addition sequence of the simple compound. In an optional embodiment, the amorphous glass powder and the composite ceramic powder are first mixed uniformly according to a predetermined ratio, and then the simple compound is added for secondary mixing to obtain the low-temperature co-fired ceramic material. The mixing method includes but is not limited to ball milling. The low-temperature co-fired ceramic material is sintered to obtain a dense low-temperature co-fired ceramic sintered body.

[0033] The following describes an exemplary method for preparing low-temperature co-fired ceramic materials. Accurately weigh the corresponding raw materials required for glass (including but not limited to oxides, carbonates, etc.) in molar ratio, mix them evenly, and then heat and keep them warm in an air atmosphere until they melt to obtain glass liquid. Pour the molten glass liquid into deionized water and quench it with water to obtain glass slag. Ball mill the glass slag to obtain amorphous glass powder. Accurately weigh the raw materials required for preparing composite ceramics (including but not limited to oxides) in molar ratio, mix them evenly, and then heat and keep them warm in an air atmosphere to obtain pre-fired composite ceramics. Ball mill the composite pre-fired ceramics to obtain composite ceramic powder. Weigh the amorphous glass powder and the composite ceramic powder according to mass ratio, and add a certain mass of simple compounds corresponding to the constituent elements of the composite ceramics to mix, and obtain low-temperature co-fired ceramic material raw material powder after ball milling. The raw material powder is mixed with a binder, granulated, and pressed to obtain a green body. In an air atmosphere, the green body is heated from room temperature to the required sintering temperature, cooled to room temperature with the furnace, and a sintered body of low-temperature co-fired ceramic material is obtained.

[0034] In an optional embodiment, the sintering temperature is ≤ 950°C. Sintering temperatures that are too high may result in abnormal ceramic grain growth and poor co-firing with silver; while sintering temperatures that are too low may result in incomplete densification of the ceramic and insufficient interfacial bonding strength. In some embodiments, the sintering temperature is 850-950°C, preferably 875-900°C. The method of the present invention can control the sintering temperature of low-temperature co-fired ceramic materials to below 900°C.

[0035] The particle size of amorphous glass powder is 1 to 3 μm. A glass particle size that is too large may reduce sintering activity, resulting in insufficient densification and poor interface bonding; while a glass particle size that is too small may easily cause premature softening and deformation and residual pores, deteriorating the dielectric properties of the ceramic.

[0036] The particle size of composite ceramic powder is 0.5 to 3 μm. A particle size that is too large may reduce sintering activity and make densification difficult, while a particle size that is too small may cause powder agglomeration and excessive sintering shrinkage.

[0037] The particle size of the simple compound is 1 to 3 μm. If the particle size of the simple compound is too large, it will not be able to effectively wet the composite ceramic due to insufficient sintering activity; while if the particle size of the simple compound is too small, it may react with the composite ceramic and affect the interface bonding.

[0038] The binder includes but is not limited to polyvinyl alcohol (water) solution. The amount of the binder can be adjusted as needed. For example, the amount of the binder can be 1% to 10% of the raw material powder.

[0039] The low-temperature co-fired ceramic material sintered body has a relative dielectric constant of 19 to 60 (5 to 7 GHz), a loss tangent of less than 0.002 (5 to 7 GHz), and a 1000-fold cross-sectional microscopic porosity of less than 2.5%.

[0040] In an optional embodiment, the low-temperature co-fired ceramic material includes: lithium borosilicate glass + MgTiO3-SrTiO3 composite ceramic + simple compound. For example, in MgTiO3-SrTiO3 composite ceramic, the mass percentages of SrTiO3 and MgTiO3 are 20% to 90% and 10% to 80%, respectively. A MgTiO3-SrTiO3 composite ceramic system with an intrinsic sintering temperature of 1300 to 1400°C is selected, and the sintering density of the material is significantly improved by introducing functional simple compounds. The present invention addresses the densification problem of high sintering temperature composite ceramics (1300 to 1400°C), and utilizes simple compounds to mainly improve the interfacial wettability of glass relative to composite ceramics to increase the density. Through the material system of composite ceramics + amorphous glass + simple compounds, the densification problem caused by the difficulty of a single glass phase in simultaneously wetting multiple ceramic phases is mainly solved.

[0041] In an optional embodiment, the composition of the lithium borosilicate glass is Li2O-B2O3-SiO2-K2O-Na2O. In some embodiments, the composition of Li2O-B2O3-SiO2-K2O-Na2O includes, by mole percentage, 5% to 15% Li2O, 20% to 40% B2O3, 20% to 40% SiO2, 5% to 15% K2O, and 5% to 15% Na2O. As an example, the composition of Li2O-B2O3-SiO2-K2O-Na2O includes, by mole percentage, 10% Li2O, 35% B2O3, 35% SiO2, 10% K2O, and 10% Na2O. Lithium borosilicate glass can be prepared using a molten water quenching method. For example, Li2CO3, B2O3, SiO2, K2CO3, and Na2CO3 are weighed in a stoichiometric ratio and mixed thoroughly. The mixture is then heated to 1150°C in an uncovered platinum crucible at a rate of 10°C / min and held for 2 hours. The molten glass is then quickly poured into deionized water to produce lithium borosilicate glass slag. The lithium borosilicate glass slag is crushed and ball-milled to produce lithium borosilicate glass powder. The particle size of the lithium borosilicate glass powder ranges from 1 to 3 μm. Excessively large glass particle sizes can reduce sintering activity, leading to insufficient densification and poor interfacial bonding. Excessively small glass particle sizes can lead to premature softening and deformation, residual pores, and deterioration of the ceramic's dielectric properties.

[0042] The preparation of MgTiO3 and SrTiO3 is a common method in this field. For example, MgO and TiO2 are weighed in a molar ratio of approximately 1:1, mixed uniformly, and then heated from room temperature to 1300°C in an air atmosphere and maintained at this temperature for 2 hours to obtain pre-calcined MgTiO3 powder. SrCO3 and TiO2 are weighed in a molar ratio of approximately 1:1, mixed uniformly, and then heated from room temperature to 1300°C in an air atmosphere and maintained at this temperature for 2 hours to obtain pre-calcined SrTiO3. The pre-calcined MgTiO3 and pre-calcined SrTiO3 are ball-milled separately to obtain MgTiO3 and SrTiO3 powders. The particle size of the MgTiO3 and SrTiO3 powders is independently selected from 0.5 to 3.0 μm. A ceramic particle size that is too large may reduce sintering activity, making densification difficult; while a ceramic particle size that is too small may cause powder agglomeration and excessive sintering shrinkage.

[0043] In an optional embodiment, the simple compound is a simple oxide AO x (A=Mg, Ti) or simple carbonate BCO x (B=Sr).

[0044] In an optional embodiment, the mass ratio of lithium borosilicate glass, MgTiO3 and SrTiO3 in the low-temperature co-fired ceramic is 20:16~72:8~64.

[0045] In an optional embodiment, the additional amount of the simple compound is 1% to 5%. If the addition amount is too low, the simple compound will not fully exert its wetting effect and will not improve the densification of the composite ceramic; while excessive addition may introduce too many impurity phases, thereby degrading the dielectric properties of the ceramic material.

[0046] In an optional embodiment, lithium borosilicate glass powder, MgTiO3, and SrTiO3 powders are weighed in a mass ratio, mixed uniformly, and then ball-milled with a simple compound to obtain a raw material powder. The raw material powder is mixed with a 5wt% polyvinyl alcohol (water) solution, granulated, and pressed to obtain a green body. In an air atmosphere, the green body is heated to 450°C at a heating rate of 5°C / min and held at this temperature for 2 hours to fully debind; then, the temperature is increased to 875°C at a heating rate of 5°C / min, held at this temperature for 2 hours, and then cooled in the furnace.

[0047] In summary, the density-enhancing method proposed in the present invention is primarily achieved by adding a small amount of a simple compound (typically less than 5 wt%). The present method for improving the sintering density of low-temperature co-fired ceramic materials improves the density of the low-temperature co-fired ceramic system by introducing a simple compound into the amorphous glass + composite ceramic low-temperature co-fired ceramic system.

[0048] The following examples are further listed to describe the present invention in detail. It should be understood that the following examples are only used to further illustrate the present invention and cannot be interpreted as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention all fall within the scope of protection of the present invention. The specific process parameters of the following examples are only examples within a suitable range, and those skilled in the art can make selections within a suitable range through the description herein, and are not limited to the specific numerical values ​​exemplified below. Unless otherwise specified, the drugs / reagents used are all commercially available.

[0049] Examples 1 to 8

[0050] Examples 1 to 8 provide methods for improving the density of low-temperature co-fired ceramics by introducing simple compounds (oxides) corresponding to the constituent elements of the composite ceramic. Low-temperature co-fired ceramics with medium to high dielectric constants are prepared primarily from lithium borosilicate glass, SrTiO3, and MgTiO3 composite ceramics. The low-temperature co-fired ceramics are composed of lithium borosilicate glass, MgTiO3, SrTiO3 composite ceramics, and simple compounds, as shown in Table 2. The mass ratio of lithium borosilicate glass, SrTiO3, and MgTiO3 is 20:16 to 72:8 to 64. The raw materials for the lithium borosilicate glass are composed of Li2CO3, B2O3, SiO2, K2CO3, and Na2CO3 in a molar ratio of 10:35:35:10:10. The simple compound is 1 wt% to 5 wt% of MgO or TiO2.

[0051] Example 1: The mass ratio of lithium borosilicate glass, SrTiO3, and MgTiO3 is 20:48:32. The molar ratio of Li2CO3, B2O3, SiO2, K2CO3, and Na2CO3 in the raw materials for the lithium borosilicate glass is 10:35:35:10:10. MgO is added at an additional mass fraction of 3%, based on the total mass of the lithium borosilicate glass, SrTiO3, and MgTiO3 being 100%.

[0052] Example 2: The mass ratio of lithium borosilicate glass, SrTiO3, and MgTiO3 is 20:48:32. The molar ratio of Li2CO3, B2O3, SiO2, K2CO3, and Na2CO3 in the raw materials for the lithium borosilicate glass is 10:35:35:10:10. TiO2 is added at a mass fraction of 3%, based on the total mass of the lithium borosilicate glass, SrTiO3, and MgTiO3 being 100%.

[0053] Example 3: The mass ratio of lithium borosilicate glass, SrTiO3, and MgTiO3 is 20:16:64. The molar ratio of Li2CO3, B2O3, SiO2, K2CO3, and Na2CO3 in the raw materials for the lithium borosilicate glass is 10:35:35:10:10. MgO is added at an additional mass fraction of 3%, based on the total mass of the lithium borosilicate glass, SrTiO3, and MgTiO3 being 100%.

[0054] Example 4: The mass ratio of lithium borosilicate glass, SrTiO3, and MgTiO3 is 20:32:48. The molar ratio of Li2CO3, B2O3, SiO2, K2CO3, and Na2CO3 in the raw materials for the lithium borosilicate glass is 10:35:35:10:10. MgO is added at an additional mass fraction of 3%, based on the total mass of the lithium borosilicate glass, SrTiO3, and MgTiO3 being 100%.

[0055] Example 5: The mass ratio of lithium borosilicate glass, SrTiO3, and MgTiO3 is 20:64:16. The molar ratio of Li2CO3, B2O3, SiO2, K2CO3, and Na2CO3 in the raw materials for the lithium borosilicate glass is 10:35:35:10:10. MgO is added at an additional mass fraction of 3%, based on the total mass of the lithium borosilicate glass, SrTiO3, and MgTiO3 being 100%.

[0056] Example 6: The mass ratio of lithium borosilicate glass, SrTiO3, and MgTiO3 is 20:72:8. The molar ratio of Li2CO3, B2O3, SiO2, K2CO3, and Na2CO3 in the raw materials for the lithium borosilicate glass is 10:35:35:10:10. MgO is added at an additional mass fraction of 3%, based on the total mass of the lithium borosilicate glass, SrTiO3, and MgTiO3 being 100%.

[0057] Example 7: The mass ratio of lithium borosilicate glass, SrTiO3, and MgTiO3 is 20:48:32. The raw material composition of the lithium borosilicate glass includes the molar ratios of Li2CO3, B2O3, SiO2, K2CO3, and Na2CO3 of 10:35:35:10:10. MgO is added at an additional mass fraction of 1%, based on the total mass of the lithium borosilicate glass, SrTiO3, and MgTiO3 being 100%.

[0058] Example 8: The mass ratio of lithium borosilicate glass, SrTiO3 and MgTiO3 is 20:48:32. In the raw material composition of the lithium borosilicate glass, the molar ratio of Li2CO3, B2O3, SiO2, K2CO3 and Na2CO3 is 10:35:35:10:10. 5% of MgO is additionally added in terms of the total mass of the lithium borosilicate glass, SrTiO3 and MgTiO3.

[0059] Comparative Examples 1-3

[0060] Comparative Examples 1-3 mainly focus on the type of simple compound, and study the influence of different types of simple compound on the densification of ceramic material with medium-high dielectric constant.

[0061] Comparative Example 1: The mass ratio of lithium borosilicate glass, SrTiO3 and MgTiO3 is 20:48:32. In the raw material composition of the lithium borosilicate glass, the molar ratio of Li2CO3, B2O3, SiO2, K2CO3 and Na2CO3 is 10:35:35:10:10. No simple compound is additionally added.

[0062] Comparative Example 2: The mass ratio of lithium borosilicate glass, SrTiO3 and MgTiO3 is 20:48:32. In the raw material composition of the lithium borosilicate glass, the molar ratio of Li2CO3, B2O3, SiO2, K2CO3 and Na2CO3 is 10:35:35:10:10. 3% of ZnO is additionally added in terms of the total mass of the lithium borosilicate glass, SrTiO3 and MgTiO3.

[0063] Comparative Example 3: The mass ratio of lithium borosilicate glass, SrTiO3 and MgTiO3 is 20:48:32. In the raw material composition of the lithium borosilicate glass, the molar ratio of Li2CO3, B2O3, SiO2, K2CO3 and Na2CO3 is 10:35:35:10:10. 3% of BaCuB2O5 is additionally added in terms of the total mass of the lithium borosilicate glass, SrTiO3 and MgTiO3.

[0064] The particle size characteristic parameters of MgTiO3 and SrTiO3 powders in the present application are shown in Table 1.

[0065] Table 1 <![CDATA[D 10 (μm)]]> <![CDATA[D 30 (μm)]]> <![CDATA[D 50 (μm)]]> D 90 (μm) D 100 (μm) MgTiO3 0.193 0.348 0.619 1.11 1.87 <![CDATA[SrTiO3]]> 0.402 0.638 0.828 1.50 3.10

[0066] Lithium borosilicate glass powder, MgTiO3, and SrTiO3 powders were weighed in a certain mass ratio, mixed evenly, and then ball-milled with a simple compound to obtain LTCC raw material powder. The LTCC raw material powder was mixed with a 5% by mass polyvinyl alcohol (water) solution, granulated, and pressed to obtain a green body. The amount of polyvinyl alcohol solution used was 5% of the raw material powder. In an air atmosphere, the green body was heated to 450°C at a heating rate of 5°C / min and held at this temperature for 2 hours to fully debind; then, the temperature was increased to 875°C at a heating rate of 5°C / min, held at this temperature for 2 hours, and then cooled in the furnace to obtain a sintered body of LTCC material. The dielectric morphology, micromorphology, and density of the sintered body were tested.

[0067] The Archimedean drainage method is used to determine the density of sintered ceramics. When a ceramic sample is not dense, it will absorb water and produce a large number of bubbles when immersed in water. When a ceramic sample is completely dense, there are no open pores within it, and no liquid will penetrate when immersed in water. At this point, the dry weight of the sample in air should be equal to the wet weight measured after wiping off the surface moisture after immersion in water. Use a high-density balance with an accuracy range of 0.001g to weigh. When no bubbles are generated when the ceramic is immersed in water, and the dry weight and wet weight of the ceramic are equal or the difference is less than 0.001g, it indicates that there are no open pores inside the sample, which indirectly reflects that the density of the ceramic is acceptable. Combined with SEM observation of the sample micromorphology and Imagej software calculation of the porosity, when there are no obvious closed pores in SEM observation and the porosity calculated by Imagej software is less than 3%, the sample density can be judged as OK; conversely, when there are obvious bubbles when the ceramic is immersed in water, and the dry weight and wet weight of the ceramic are equal or the difference is greater than 0.001g, it indicates that there are open pores that can be penetrated inside the material or the density is insufficient, and the sample density can be judged as NG.

[0068] The dielectric resonant cavity method is used to test the dielectric properties of ceramics. The basic principle is to make the material to be tested into a cylinder and place it in a resonant cavity. A 5-7 GHz TE011 microwave signal is applied to stimulate resonance in the cavity. The electromagnetic properties of the material will cause changes in the resonant frequency. By accurately measuring these frequency changes, the dielectric constant (ε r ) and dielectric loss tangent (tanδ).

[0069] The raw material ratios and properties of the low-temperature co-fired ceramics of Examples 1 to 8 and Comparative Examples 1 to 3 of the present invention are shown in Table 2.

[0070] Table 2

[0071] Figure 2The cross-sectional micromorphology of Comparative Example 1 at 1000x and 5000x magnification and the porosity at 1000x magnification are shown. As can be seen from the figure, the density of the MgTiO3 and SrTiO3 composite ceramics fired only with lithium borosilicate glass is poor. At 1000x magnification, a large number of irregular pores can be observed, and the pore volume porosity is calculated to be 5.27% using ImageJ software; and when further magnified to 5000x, it can be seen that the local gray-black MgTiO3 area and the white SrTiO3 area both show good density, indicating that lithium borosilicate glass can effectively assist in the firing of both MgTiO3 and SrTiO3 materials at this temperature; however, a large number of pores are concentrated at the junction of MgTiO3 and SrTiO3, indicating that there is a significant difference in the wettability of lithium borosilicate glass to the two materials MgTiO3 and SrTiO3, resulting in insufficient wettability between the two phases, thereby forming pores. Similarly, the cross sections of Comparative Examples 2 to 3 also have obvious large-sized hole defects.

[0072] Figure 1 and Figure 3 The cross-sectional micromorphology and porosity after adding different types of simple compounds are shown respectively. Imagej software was used for calculation. Compared with the porosity of 5.27% of comparative example 1 without adding simple compounds, Example 1, Example 2, Comparative example 2, and Comparative example 3 added 3wt% of MgO, TiO2, ZnO, and BCB, and the pore volume porosity at 1000 times was 0.93%, 1.92%, 4.03%, and 3.57%, respectively. Combined with the cross-sectional morphology, it can be seen that the density of the composite ceramics is significantly improved after adding MgO and TiO2, while larger pores will appear in the cross-sectional micromorphology after adding ZnO and BCB. This is because MgO and TiO2 are oxides corresponding to the metal elements contained in the composite ceramics MgTiO3 and SrTiO3. Adding an appropriate amount can improve the wettability between the glass and the composite ceramics, thereby improving the density of the composite ceramics. On the contrary, ZnO and BCB are not oxides or carbonates corresponding to the metal elements of the composite ceramics MgTiO3 and SrTiO3, and cannot effectively improve the wettability of glass and composite ceramics, so their density is not significantly improved.

[0073] In Comparative Example 3, BCB is used as a sintering aid to form a liquid phase during the sintering process. This liquid phase flows at high temperature and fills the gaps between the particles. Compared with Comparative Example 1, the local density is improved to a certain extent. Large holes still exist at the junction of the two phases of the composite ceramic. This may be related to the inability of BCB to wet the two ceramics at the same time. In addition, for the intermediate material system, since the dielectric constant of the additive itself is relatively low and the loss is high, the introduction of additional sintering aids will reduce its dielectric constant and quality factor, and it is impossible to take into account both dielectric properties and density at the same time. In Examples 1 and 2, although MgO and TiO2 are not sintering aids, the addition of these two materials significantly improves the density of the composite ceramic. This may be because MgO and TiO2, as oxides corresponding to the constituent elements of the composite ceramic, can form good compatibility with MgTiO3 and SrTiO3, which helps to stabilize the formation of the interface, thereby promoting the wetting and diffusion of the liquid to improve the density of the composite ceramic. In contrast, the introduction of ZnO in Comparative Example 2, which is neither a sintering aid nor an oxide corresponding to the constituent elements of the composite ceramic, leads to the formation of larger pores. This may be due to the poor compatibility of ZnO with MgTiO3 and SrTiO3, thereby worsening the density.

[0074] Based on Example 1, Examples 3 to 6 achieve flexible control of the dielectric constant of the composite ceramic by introducing MgO, an oxide corresponding to the constituent elements of the composite ceramic, and adjusting the relative content of the two phases MgTiO3 and SrTiO3. When the SrTiO3 content in the two phases is high, the dielectric constant of the composite ceramic is significantly improved, but the dielectric loss also increases sharply. For example, in Example 6, the dielectric constant of the composite ceramic is as high as 58.6, but its dielectric loss also reaches 1.87×10 -3 (f = 4.45GHz). On the contrary, when the MgTiO3 content in the two phases is high, the dielectric loss of the composite ceramic is significantly reduced, but the dielectric constant is also reduced accordingly. For example, in Example 3, the dielectric constant of the composite ceramic is only 19.7, but the dielectric loss is reduced to 1.18×10 -3 By systematically adjusting the relative contents of the two phases in the composite ceramic, the dielectric constant is gradually adjusted within the range of 19 to 60, while ensuring that the loss tangent, tanδ, remains below 0.002.

[0075] Figure 4 The cross-sectional micromorphology of the samples with 1wt% and 5wt% MgO added was observed at 1000x and 5000x magnification, respectively. Figure 1 (a), (b) and Figure 4It can be seen that the addition of a small amount of MgO can improve the wettability between the two phases of MgTiO3 and SrTiO3, thereby improving the density of the composite ceramic. When the MgO content is increased to 5%, the overall density is significantly improved compared to the comparative example 1 when no simple compound is added, but the dielectric constant is slightly lower than that of Example 1 with the addition of 3wt% MgO, and a small number of holes begin to appear in the micromorphology. Continuing to increase the MgO content will further deteriorate the density of the composite ceramic. This may be because MgO itself is not a sintering aid, and excessive addition of MgO will have a negative impact on the density of the ceramic. Therefore, when 1wt% to 5wt% MgO is added, the density of the ceramic is relatively good.

[0076] The low-temperature co-fired ceramics prepared in each embodiment were tested, and the dielectric properties of the ceramic samples were tested using the dielectric resonant cavity method. The results are shown in Table 2. Lithium borosilicate glass has a low softening point and exhibits good fluidity at high temperatures, which helps to accelerate the mass transfer and rearrangement of ceramics, thereby reducing the sintering temperature. At the same time, the particle size of MgTiO3 and SrTiO3 ceramic powders is reduced from micron to submicron through the ball milling process, which can further reduce the sintering temperature of the composite ceramics. In addition, the introduction of the new phase MgO can improve the wettability between the two phases of MgTiO3 and SrTiO3, promote the wetting and diffusion of the liquid, and thus improve the density of the composite ceramics. Finally, the dielectric constant gradient is achieved by adjusting the relative content between the two phases of MgTiO3 and SrTiO3, and the density of the low-temperature co-fired ceramics is improved by introducing oxides corresponding to the constituent elements of the composite ceramics. They are successfully sintered at 850-900°C to obtain a series of composite ceramics with excellent dielectric properties, and their dielectric properties are ε r =19.7~58.6, tanδ=1.18╳10 -3 ~1.87╳10 -3 .

[0077] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. All equivalent structural transformations made by using the contents of the present invention description and drawings under the inventive concept of the present invention, or direct / indirect application in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A low-temperature co-fired ceramic material with a medium to high dielectric constant, characterized in that: The composition of the low-temperature co-fired ceramic material includes: composite ceramic + glass + simple compound; the composite ceramic is a composite ceramic composed of at least two titanate ceramics, or a composite ceramic composed of at least two niobate ceramics, or a composite ceramic composed of at least two zirconate ceramics, or a composite ceramic composed of at least two of titanate ceramics, niobate ceramics, and zirconate ceramics; the glass is an amorphous glass with a softening point of 400-700°C; the simple compound is at least one of the oxides or carbonates corresponding to the metal elements of the composite ceramic; wherein, based on the total mass of the composite ceramic and the glass as 100%, the composite ceramic accounts for 60%-95% of the total mass of the composite ceramic and the glass, the glass accounts for 5%-40% of the total mass of the composite ceramic and the glass; the simple compound accounts for 0.5%-10% of the total mass of the composite ceramic and the glass.

2. The low-temperature co-fired ceramic material according to claim 1, characterized in that: Taking the total mass of the composite ceramic and the glass as 100%, the composite ceramic accounts for 60% to 90% of the total mass of the composite ceramic and the glass; preferably, the composite ceramic accounts for 70% to 80% of the total mass of the composite ceramic and the glass.

3. The low-temperature co-fired ceramic material according to claim 1 or 2, characterized in that: The titanate ceramic includes at least one of MgTiO3, CaTiO3, SrTiO3, and BaTiO3; the niobate ceramic includes at least one of ZnNb2O6 and BaNb2O6; and the zirconate ceramic includes at least one of CaZrO3 and MgZrO3.

4. The low-temperature co-fired ceramic material according to any one of claims 1 to 3, characterized in that The simple compound accounts for 0.8% to 5% of the total mass of the composite ceramic and glass.

5. The low-temperature co-fired ceramic material according to any one of claims 1 to 4, characterized in that The glass is at least one of borosilicate glass, aluminosilicate glass, and phosphate glass.

6. The low-temperature co-fired ceramic material according to any one of claims 1 to 5, characterized in that: The sintering temperature of the low-temperature co-fired ceramic material is ≤950°C, preferably 850-950°C, and more preferably 875-900°C.

7. The low-temperature co-fired ceramic material according to any one of claims 1 to 6, characterized in that: The dielectric constant of the low-temperature co-fired ceramic material is 19-60 (5-7 GHz), and the dielectric loss is less than 0.002 (5-7 GHz).

8. The low-temperature co-fired ceramic material according to any one of claims 1 to 7, characterized in that The porosity of the sintered body of the low-temperature co-fired ceramic material is less than 2.5%.

9. A method for preparing a low-temperature co-fired ceramic material with a medium to high dielectric constant according to any one of claims 1 to 8, characterized in that: The method comprises: uniformly mixing amorphous glass powder and multiphase ceramics in a preset ratio, then adding a simple compound for secondary mixing to obtain a low-temperature co-fired ceramic material with a medium-high dielectric constant; preferably, sintering the low-temperature co-fired ceramic material with a medium-high dielectric constant to obtain a dense low-temperature co-fired ceramic sintered body.

10. A method for improving the sintering density of low-temperature co-fired ceramic materials with medium and high dielectric constants, characterized in that: The composition of the low-temperature co-fired ceramic material includes: composite ceramic + glass + simple compound; the composite ceramic is a composite ceramic composed of at least two titanate ceramics, or a composite ceramic composed of at least two niobate ceramics, or a composite ceramic composed of at least two zirconate ceramics, or a composite ceramic composed of at least two of titanate ceramics, niobate ceramics, and zirconate ceramics; the glass is an amorphous glass with a softening point of 400-700°C; the simple compound is at least one of the oxides or carbonates corresponding to the metal elements of the composite ceramic; wherein, based on the total mass of the composite ceramic and the glass as 100%, the composite ceramic accounts for 60%-95% of the total mass of the composite ceramic and the glass, the glass accounts for 5%-40% of the total mass of the composite ceramic and the glass; the simple compound accounts for 0.5%-10% of the total mass of the composite ceramic and the glass.

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