CN112079631B - Low-dielectric LTCC material with near-zero temperature coefficient and preparation method thereof - Google Patents

Abstract

The invention provides a low-dielectric LTCC material with a near-zero temperature coefficient and a preparation method thereof, wherein the low-dielectric LTCC material comprises gamma-LiAlO₂And Ba₅Si₈O₂₁The ceramic material is formed by mixing two phases, and then doping 2-4 wt% of LMBBA glass which is used as a cosolvent and is mixed with the ceramic material, wherein the chemical general formula of the LMBBA glass is (1-x) LiAlO₂–xBa₅Si₈O₂₁-yLMBBA, x is 57-61 wt%, y is 2-4 wt%; the sintering temperature is 900 ℃; the LMBBA glass comprises Li₂CO₃‑MgO‑Bi₂O₃‑B₂O₃‑Al₂O₃. Having a temperature coefficient (tau) of near-zero resonance frequency_f6.6 to 4 ppm/DEG C) and high Qf value, can be sintered at low temperature of 900 ℃ to realize densification, has low dielectric constant, and has good application prospect in LTCC integrated substrates and devices.

Description

Low-dielectric LTCC material with near-zero temperature coefficient and preparation method thereof

[ technical field ] A

The invention relates to the field of microwave electronic ceramic materials and manufacturing thereof, in particular to a low-dielectric constant temperature co-fired ceramic (LTCC) material with a near-zero temperature coefficient and a preparation method thereof.

[ background of the invention ]

LTCC (low temperature Co-fired Ceramic) technology is currently the most important and mainstream passive integration technology, and is widely used in national defense and military industry, automobiles, and information products. The key point of the LTCC technology is the development of high-performance LTCC materials. With the development of microwave communication technology and radar systems, the available communication frequencies extend from microwaves to millimeter waves. The high frequency of microwave communication frequencies and the large amount of information transmission require the development of LTCC materials having a low dielectric constant (dielectric constant lower than 8 or less), a high Qf value and a vanishing τ_fThe value is obtained. The low dielectric constant can not only expand the applicable frequency of the LTCC device, but also shorten the transmission delay time of signals. The high Qf value is the zero-going tau for reducing energy dissipation and enhancing frequency selectivity_fThe values are to ensure stability of the dielectric constant and the frequency of the device.

LiAlO₂Ceramic materials are mainly used in fuel cells, and few are used in microwave ceramic materials, but through the reaction to LiAlO₂Research on materials shows that LiAlO₂Many properties of the material can be applied in the microwave ceramic field, especially LiAlO₂The material has a very low dielectric constant compared to other ceramics.

Hirano studied LiAlO₂Of (a) three allotropes of alpha-LiAlO₂、β-LiAlO₂And gamma-LiAlO₂In particular for gamma-LiAlO₂In more detailIn the text, it is indicated that beta-LiAlO₂Starting at 700-750 ℃ to gamma-LiAlO₂Transformation, gamma-LiAlO at 1000 ℃₂The fracture surface has uniform texture and better particle size consistency. Yang studied LiAlO in his Master thesis₂Ceramic tubes and LiAlO are described₂The ceramic sintered by the method has good microwave dielectric property. In the research, the obtained LiAlO2 belongs to a low-consumption material, no impurities and second phases appear in an XRD pattern, the dielectric constant is 4.4-4.8, and the sintering density can reach 2.29-2.36g/cm³And the powder has good forming performance, and the phenomena of cracking and the like can not occur in the sintering process. In the aspect of microstructure, SEM test shows that the structure of the LiAlO2 is compact after sintering into porcelain, the grain size is uniform and consistent, the air holes are few, and no obvious crack exists. However, LiAlO₂The sintering temperature of the ceramic is high, exceeding 1200 ℃, and the ceramic cannot be compatible with the LTCC technology. At present, only Su birch, Zuohuan and the like, which is the university of electronic technology, researches LiAlO₂Low temperature sintering characteristics of ceramics, it was found that LiAlO can be doped by 3 wt% of LBSCA glass₂The sintering temperature of the ceramic material is reduced to 900-950 ℃, and the material performance can reach: at 900 ℃ of epsilon_r＝4.48，Q×f＝35,540GHz，τ_f-53ppm/° c; at 950 ℃ of epsilon_r＝4.50，Q×f＝38,979GHz，τ_f-55ppm/° c. Although the Qf value is high, the temperature coefficient is too poor, and the requirement of high stability of the LTCC microwave/millimeter wave device is difficult to meet.

[ summary of the invention ]

In view of the above, the technical problem to be solved by the present invention is to provide a low-k LTCC material with a near-zero temperature coefficient and a low dielectric constant, and a preparation method thereof, wherein the LTCC material has a near-zero resonant frequency temperature coefficient tau_fAnd the high Qf value characteristic, can realize densification at low temperature of 900 ℃, has low dielectric constant, and has good application prospect in LTCC integrated substrates and devices.

In a first aspect, the present invention provides a near-zero temperature coefficient low dielectric constant low temperature co-fired ceramic (LTCC) material, which is characterized in that: comprising gamma-LiAlO₂And Ba₅Si₈O₂₁Two-phase mixed ceramic material, and then mixed inThe mixed ceramic material is prepared by sintering LMBBA glass with the weight percent of 2-4% as a cosolvent, and the chemical general formula is (1-x) LiAlO₂–xBa₅Si₈O₂₁-yLMBBA, x is 57-61 wt%, y is 2-4 wt%; the sintering temperature is 900 ℃; the LMBBA glass comprises Li₂CO₃-MgO-Bi₂O₃-B₂O₃-Al₂O₃。

In a second aspect, the invention provides a method for preparing a low-dielectric LTCC material with a near-zero temperature coefficient, which comprises the following steps:

s1 preparation of LiAlO₂Pre-sinter and Ba₅Si₈O₂₁Pre-firing the batch, preparing LMBBA glass powder, namely:

will analyze pure Li₂CO₃And Al₂O₃In molar ratio of Li₂CO₃：Al₂O₃1: 1; then, carrying out primary ball milling to uniformly mix the ingredients, drying to obtain dried powder, putting the dried powder into a crucible after passing through a screen with 40-80 meshes for compaction, raising the temperature to 920-980 ℃ at the heating rate of 2-5 ℃/min for presintering, keeping the temperature for 2-4 h, and cooling along with the furnace to obtain LiAlO₂Pre-firing the material;

will analyze pure BaCO₃And SiO₂According to molar ratio BaCO₃：SiO₂Preparing materials in a ratio of 5: 8; then, carrying out primary ball milling to uniformly mix the ingredients, drying to obtain dried powder, putting the dried powder into a crucible after passing through a screen with 40-80 meshes for compaction, raising the temperature to 1050-1120 ℃ at a heating rate of 2-5 ℃/min for presintering, keeping the temperature for 2-4 h, and cooling along with the furnace to obtain Ba₅Si₈O₂₁Pre-firing the material;

in molar ratio of Li₂CO₃:MgO:Bi₂O₃:B₂O₃:Al₂O₃Weighing materials at a ratio of 45:5:20:26:4, performing primary ball milling, drying and crushing, then preserving heat at 1100 ℃ for 2 hours, then quickly pouring deionized water to obtain LMBBA glass crystals, and finally grinding the LMBBA glass crystals into LMBBA glass powder;

s2, mixing LiAlO₂Pre-sinter, Ba₅Si₈O₂₁Pre-sinter and LMBBA glass powder according to (1-x) LiAlO₂–xBa₅Si₈O₂₁Weighing and proportioning yLMBBA in percentage by mass, and then carrying out secondary ball milling in a ball mill; wherein x is 57-61 wt%, y is 2-4 wt%, and x and y are both LiAlO₂Pre-sinter, Ba₅Si₈O₂₁Mass ratio of the pre-sintering material two-phase mixture;

s3, drying the secondary ball grinding material, adding LiAlO₂Pre-sinter, Ba₅Si₈O₂₁Granulating and dry-pressing a PVA solution which is 10-20 wt% of the total mass of the pre-sintered material and the LMBBA glass powder to obtain a sample;

s4, placing the obtained sample into a sintering furnace, slowly heating to 300 ℃ at the heating rate of 2 ℃/minute, preserving heat for 2 hours, continuously heating to 500 ℃ and preserving heat for 2 hours to remove water and glue in the green body; and then heating to 900 ℃ according to the heating rate of 4 ℃/min for sintering, preserving the heat for 3-4 hours, then cooling to 500 ℃ according to the cooling rate of 4 ℃/min, and finally cooling along with the furnace to obtain the LTCC microwave dielectric ceramic material.

The invention relates to a microwave dielectric ceramic material of LTCC and a preparation method thereof, which is based on LiAlO₂And Ba₅Si₈O₂₁A composite system obtained by a solid phase method; when the sintering temperature is about 900 ℃, the dielectric constant is low, and epsilon_rThe dielectric ceramic material is-6.02-6.30, and has a high Qf value of 38000-45000 GHz and a near-zero resonant frequency temperature coefficient tau_fThe carbon nano tube is-6.6-4 ppm/DEG C, and has very high application prospect and value in the technical field of LTCC. The microwave dielectric ceramic can be widely applied to LTCC substrates, laminated microwave devices and modules.

[ description of the drawings ]

FIG. 1 is a flow chart of the preparation method of the microwave dielectric ceramic material of the present invention.

[ detailed description ] A

The low-dielectric-coefficient LTCC material with the near-zero temperature coefficient and the preparation method thereof provided by the embodiment of the invention have the advantages of higher dielectric constant, very low microwave dielectric loss and near-zero temperature coefficient, and have very high application value in an LTCC radio frequency microwave device.

In order to solve the above problems, the technical solution in the embodiments of the present invention has the following general idea: the latest research found Ba₅Si₈O₂₁Not only the dielectric constant ε_rLow (about 7.2) and a positive temperature coefficient of resonance frequency tau_f(about +25 to 30 ppm/DEG C), the sintering temperature is about 1200 ℃. Therefore, the invention uses low negative temperature coefficient LiAlO₂With positive temperature coefficient of Ba₅Si₈O₂₁Compounding in proper proportion to compensate temperature coefficient, and using Ba with low dielectric constant₅Si₈O₂₁Replaces the CaTiO with overhigh dielectric constant adopted in the prior art₃、TiO₂The temperature compensator material is equal to the temperature of the ceramic, and the LMBBA glass is used for fluxing, so that the sintering temperature of the ceramic is reduced from about 1200 ℃ to 900 ℃, the resonant frequency temperature is close to zero, and the overall dielectric constant epsilon_rAlso lower LTCC materials.

Examples 1 to 6

The LTCC materials with near-zero temperature coefficient and low dielectric constant provided in the embodiments 1 to 6 comprise gamma-LiAlO₂And Ba₅Si₈O₂₁The ceramic material is formed by mixing two phases, and then doping 2-4 wt% of LMBBA glass which is used as a cosolvent and is mixed with the ceramic material, wherein the chemical general formula of the LMBBA glass is (1-x) LiAlO₂–xBa₅Si₈O₂₁-yLMBBA, x is 57-61 wt%, y is 2-4 wt%; the sintering temperature is 900 ℃; the LMBBA glass comprises Li₂CO₃-MgO-Bi₂O₃-B₂O₃-Al₂O₃。

Wherein the content of the first and second substances,

the LiAlO₂The raw materials comprise the following raw materials in molar ratio:

Li2CO3：Al2O3＝1:1。

said Ba₅Si₈O₂₁The raw materials comprise the following raw materials in molar ratio:

BaCO₃：SiO₂＝5:8。

the LMBBA glass comprises the following components in molar ratio:

Li₂CO₃:MgO:Bi₂O₃:B₂O₃:Al₂O₃＝45:5:20:26:4。

for convenience of description, LiAlO is used₂Named material A, Ba₅Si₈O₂₁The material B is named, the proportion of the material A to the material B of each example and the mass ratio of the LMBBA glass to the total of the material A and the material B are shown in the table 1.

As shown in fig. 1 again, the preparation method of examples 1 to 6 includes the steps of compounding, primary ball milling, drying, pre-sintering, secondary ball milling, material shaping, and low-temperature sintering, and specifically includes the following steps:

s1 preparation of LiAlO₂Pre-sinter and Ba₅Si₈O₂₁Pre-firing the batch, preparing LMBBA glass powder, namely:

will analyze pure Li₂CO₃And Al₂O₃In molar ratio of Li₂CO₃：Al₂O₃1: 1; then, carrying out primary ball milling to uniformly mix the ingredients, drying to obtain dried powder, putting the dried powder into a crucible after passing through a screen with 40-80 meshes for compaction, raising the temperature to 920-980 ℃ at the heating rate of 2-5 ℃/min for presintering, keeping the temperature for 2-4 h, and cooling along with the furnace to obtain LiAlO₂Pre-firing the material;

will analyze pure BaCO₃And SiO₂According to molar ratio BaCO₃：SiO₂Preparing materials in a ratio of 5: 8; then, carrying out primary ball milling to uniformly mix the ingredients, drying to obtain dried powder, putting the dried powder into a crucible after passing through a screen with 40-80 meshes for compaction, raising the temperature to 1050-1120 ℃ at a heating rate of 2-5 ℃/min for presintering, keeping the temperature for 2-4 h, and cooling along with the furnace to obtain Ba₅Si₈O₂₁Pre-firing the material;

in molar ratio of Li₂CO₃:MgO:Bi₂O₃:B₂O₃:Al₂O₃Weighing 45:5:20:26:4, ball-milling, drying and crushing, and keeping the temperature at 1100 ℃ for 2 hoursThen, quickly pouring deionized water to obtain LMBBA glass crystals, and finally grinding the LMBBA glass crystals into LMBBA glass powder;

s2, mixing LiAlO₂Pre-sinter, Ba₅Si₈O₂₁Pre-sinter and LMBBA glass powder according to (1-x) LiAlO₂–xBa₅Si₈O₂₁Weighing and proportioning yLMBBA in percentage by mass, and then carrying out secondary ball milling in a ball mill; wherein x is 57-61 wt%, y is 2-4 wt%, and x and y are both LiAlO₂Pre-sinter, Ba₅Si₈O₂₁Mass ratio of the pre-sintering material two-phase mixture;

and S3, drying the secondary ball grinding material, adding 10-20 wt% of PVA solution for granulation and dry pressing for forming to obtain a sample, wherein the 10-20 wt% is the percentage of the total mass of three mixed ball grinding drying materials of (1-x) LiAlO 2-xBa 5Si8O 21-yLMBBA. For example, 100 g of the mixed and dried material is added with 10-20 g of PVA solution to assist granulation. The PVA addition only affects the molding quality and does not affect the performance of the sample, and the PVA solution is removed during rubber removal, so that the concentration and the addition of the PVA solution only need to ensure the molding of the sample.

S4, placing the obtained sample into a sintering furnace, slowly heating to 300 ℃ at the heating rate of 2 ℃/minute, preserving heat for 2 hours, continuously heating to 500 ℃ and preserving heat for 2 hours to remove water and glue in the green body; and then heating to 900 ℃ according to the heating rate of 4 ℃/min for sintering, preserving the heat for 3-4 hours, then cooling to 500 ℃ according to the cooling rate of 4 ℃/min, and finally cooling along with the furnace to obtain the LTCC microwave dielectric ceramic material.

TABLE 1

From the above table, it can be seen that the LTCC material according to the above embodiments of the present invention is obtained by performing the test by using the international standard resonant cavity method (i.e. Hakki-Coleman method, which is currently the most widely used method for measuring the performance of the microwave medium): its dielectric constant ε_rBetween-6.02 and 6.30, Qf valueAt 38000-45000 GHz and temperature coefficient tau_fIs between-6.6 and 4 ppm/DEG C. Therefore, the microwave ceramics of the embodiments have high dielectric constant, low loss and small temperature coefficient, and have good application prospect in LTCC radio frequency microwave integrated devices and assemblies.

Although specific embodiments of the invention have been described above, it will be understood by those skilled in the art that the specific embodiments described are illustrative only and are not limiting upon the scope of the invention, and that equivalent modifications and variations can be made by those skilled in the art without departing from the spirit of the invention, which is to be limited only by the appended claims.

Claims (3)

1. A low-dielectric LTCC material with a near-zero temperature coefficient is characterized in that: comprising gamma-LiAlO₂And Ba₅Si₈O₂₁The ceramic material is formed by mixing two phases, and then doping LMBBA glass which accounts for 2-4 wt% of the ceramic material mixed with two phases as a cosolvent for sintering, wherein the chemical general formula is (1-x) LiAlO₂–xBa₅Si₈O₂₁–yLMBBA，x=57~61 wt%，y=2-4 wt%; the sintering temperature is 900 ℃; the LMBBA glass comprises Li₂CO₃-MgO-Bi₂O₃-B₂O₃-Al₂O₃；

The LiAlO₂The raw materials comprise the following raw materials in molar ratio:

Li₂CO₃：Al₂O₃=1: 1；

said Ba₅Si₈O₂₁The raw materials comprise the following raw materials in molar ratio:

BaCO₃：SiO₂=5: 8；

the LMBBA glass comprises the following components in molar ratio:

Li₂CO₃:MgO: Bi₂O₃:B₂O₃:Al₂O₃=45: 5: 20: 26:4。

2. a preparation method of a low-dielectric LTCC material with a near-zero temperature coefficient is characterized by comprising the following steps of: the method comprises the following steps:

s1 preparation of LiAlO₂Pre-sinter and Ba₅Si₈O₂₁Pre-firing the batch, preparing LMBBA glass powder, namely:

will analyze pure Li₂CO₃And Al₂O₃In molar ratio of Li₂CO₃：Al₂O₃1:1 ingredient; then, carrying out primary ball milling to uniformly mix the ingredients, drying to obtain dried powder, putting the dried powder into a crucible after passing through a screen with 40-80 meshes for compaction, raising the temperature to 920-980 ℃ according to the temperature rise rate of 2-5 ℃ per min for presintering, carrying out heat preservation for 2-4 h, and cooling along with the furnace to obtain LiAlO₂Pre-firing the material;

will analyze pure BaCO₃And SiO₂According to molar ratio BaCO₃：SiO₂(ii) =5: 8 ingredients; then, carrying out primary ball milling to uniformly mix the ingredients, drying to obtain dried powder, putting the dried powder into a crucible after passing through a screen with 40-80 meshes for compaction, raising the temperature to 1050-1120 ℃ according to the temperature rise rate of 2-5 ℃ per min for presintering, carrying out heat preservation for 2-4 h, and cooling along with a furnace to obtain Ba₅Si₈O₂₁Pre-firing the material;

in molar ratio of Li₂CO₃:MgO: Bi₂O₃:B₂O₃:Al₂O₃Weighing materials according to a ratio of 45:5:20:26:4, performing primary ball milling, drying and crushing, performing heat preservation at 1100 ℃ for 2 hours, then quickly pouring deionized water to obtain LMBBA glass crystals, and finally grinding the LMBBA glass crystals into LMBBA glass powder;

s2, mixing LiAlO₂Pre-sinter, Ba₅Si₈O₂₁Pre-sintered material and LMBBA glass powder according to (1-x) LiAlO₂–xBa₅Si₈O₂₁-yWeighing and proportioning LMBBA in percentage by mass, and then carrying out secondary ball milling in a ball mill; wherein the content of the first and second substances,x=57~61 wt%，y=2~4 wt%，xand y is LiAlO₂Pre-sinter, Ba₅Si₈O₂₁Mass ratio of the pre-sintering material two-phase mixture;

s3, drying the secondary ball grinding material, adding LiAlO₂Pre-sinter, Ba₅Si₈O₂₁Granulating and dry-pressing a PVA solution which is 10-20 wt% of the total mass of the pre-sintered material and the LMBBA glass powder to obtain a sample;

s4, placing the obtained sample into a sintering furnace, slowly heating to 300 ℃ at the heating rate of 2 ℃/minute, preserving heat for 2 hours, continuously heating to 500 ℃ and preserving heat for 2 hours to remove water and glue in the green body; and then heating to 900 ℃ according to the heating rate of 4 ℃/min for sintering, preserving the heat for 3-4 hours, then cooling to 500 ℃ according to the cooling rate of 4 ℃/min, and finally cooling along with the furnace to obtain the LTCC microwave dielectric ceramic material.

3. The method for preparing a low dielectric constant LTCC material with a near zero temperature coefficient as claimed in claim 2, wherein: the PVA solution has a mass concentration of 8-12%.

Images