Method for preparing high-frequency low-loss LTCC (Low Temperature Co-Fired Ceramic) material by utilizing external doping means

Abstract

The invention belongs to the technical field of preparation of special ceramic materials, particularly relates to a method for preparing a high-frequency low-loss LTCC (Low Temperature Co-Fired Ceramic) material by utilizing an external doping means, and aims to solve the problem of non-uniform distribution of a doping agent caused by a traditional physical mixing method. The core of the method is that an atomic layer deposition technology is adopted to carry out surface modification on ceramic main powder, dopant compound coating layers with atomic-scale thickness and accurate and controllable stoichiometry grow on the surfaces of main powder particles layer by layer, and core-shell structure composite powder is formed; the composite powder is subjected to subsequent slurry preparation, molding and sintering, and finally the high-frequency low-loss LTCC material is obtained. According to the invention, agglomeration and non-uniform distribution of the dopant are avoided from the source, so that the LTCC material has high density, a uniform microstructure and extremely low dielectric loss at a high frequency band, and customized design of performance is realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of special ceramic material preparation, and particularly relates to a method for preparing high-frequency low-loss LTCC material by means of external doping, and particularly relates to a method for performing external atomic-level precision doping on ceramic powder based on gas phase deposition. BACKGROUND

[0002] As a core technology of electronic packaging and integrated substrate, low-temperature flexible co-fired ceramic (LTCC) technology is widely used in the fields of radio frequency modules, multi-layer wiring substrates, integrated passive devices and high-density packaging in high-frequency and high-integration scenarios such as 5G / 6G communication, radar, satellite communication and Internet of Things, due to its excellent dielectric properties, high thermal conductivity, good mechanical strength and compatibility with noble metals.

[0003] The core of LTCC material preparation is to introduce specific dopants into high-melting-point ceramic main powder to reduce the co-firing temperature, realize compatible co-firing with high-conductivity metals such as silver and copper, and avoid the problems of conductor melting or oxidation caused by high-temperature sintering. The uniformity of the distribution of the dopants between the main powder particles directly determines the microstructure, dielectric properties, mechanical strength and long-term reliability of the sintered product.

[0004] Traditional LTCC composite powder preparation mainly adopts mechanical ball milling blending (dry method) and solvent evaporation precipitation (wet method) technology. The former realizes macroscopic mixing through high-energy physical action, and the latter attaches the dopant precursor to the surface of the main powder after dissolving. These technologies once met the early preparation needs, supported the development of the electronic industry, and have the characteristics of simple principle and low cost.

[0005] However, with the continuous development of related technologies and the more stringent requirements of microwave and millimeter wave communication systems on material performance indicators, the inherent limitations of traditional technologies gradually appear. Both methods rely on macroscopic or mesoscopic physical mixing and particle assembly mechanisms, and are affected by van der Waals force, electrostatic force and surface energy difference, which inevitably leads to the agglomeration of dopants, resulting in the inability to achieve atomic-level or even molecular-level uniform dispersion at the microscale, and thus forming local enrichment and barren areas.

[0006] This micro-inhomogeneity triggers a chain of problems during sintering: the enrichment area forms a liquid phase too early due to excessive flux, leading to abnormal grain growth and high dielectric loss glass phase, increasing high-frequency signal loss; the barren area hinders densification due to insufficient flux, resulting in residual pores or under-sintered areas. These defects significantly increase dielectric loss, reduce Q value, affect dielectric constant consistency and temperature stability, and become stress concentration points, reducing mechanical strength and long-term reliability, which restricts the application of LTCC in high-frequency bands.

[0007] In summary, the existing external doping technology cannot fundamentally solve the problem of uniformity of dopant distribution due to the limitation of physical mixing nature, resulting in micro defects of the material after sintering and restricting the high-frequency application performance. How to break through the traditional limitations and realize the uniform coverage of the doping elements on the main powder particles at the atomic / molecular scale to prepare high-performance and high-consistency LTCC materials has become a key technical problem to be solved. SUMMARY

[0008] To achieve the above-mentioned purposes, the present application provides a method for preparing high-frequency low-loss LTCC materials by using external doping means, the core of which is to use atomic layer deposition technology to modify the surface of ceramic main powder, so as to fundamentally solve the problem of uneven distribution of dopants caused by traditional physical mixing method, and thus obtain LTCC materials which are highly uniform in microstructure and excellent in macroscopic performance.

[0009] To achieve the above-mentioned purposes, the present application adopts the following technical scheme: A method for preparing core-shell structure composite powder for high-frequency low-loss LTCC materials, characterized in that it comprises the following steps: S1, loading of ceramic main powder: providing ceramic main powder for the preparation of the LTCC material, and loading it in a reaction chamber of an atomic layer deposition reactor under a nitrogen protective atmosphere; the powder loading amount accounts for 10% to 30% of the effective volume of the chamber; S2, powder dynamic dispersion and reaction environment construction: close the chamber, vacuumize to a background vacuum degree of less than or equal to 1.0 Pa, heat the chamber to 100-300℃, start the powder dispersion system, and simultaneously introduce inert gas with a purity of not less than 99.999% nitrogen or argon as carrier and fluidizing gas, so that the powder forms a stable fluidized bed state; wherein the flow rate of the inert gas is 50-500 standard cubic centimeters per minute; S3, atomic layer deposition cycle: repeating the atomic layer deposition cycle N times for the powder treated in S2 to form a layer of dopant compound coating on the surface of the ceramic main powder particles; wherein the cycle number N is an integer of 10-1000; S4, in-situ heat treatment and composite powder discharge: after completing S3, stop the dispersion system and the introduction of inert gas, and under a specific atmosphere of nitrogen or weak oxidizing atmosphere with an oxygen content of less than 10 ppm, anneal at 400-600℃ for 1-2 hours; after cooling to room temperature, take out the core-shell structure composite powder under the protection of the specific atmosphere.

[0010] This in-situ heat treatment step aims to promote the densification of the coating layer structure, eliminate the micro-stress inside the film, remove possible residual organic functional groups or halogen impurities, and form an interface transition zone between the coating layer and the ceramic main powder core, thereby enhancing the bonding force between the two.

[0011] Further, the step S1 also needs to be pre-processed, the specific steps are as follows: (1) Select the ceramic main powder that meets the application requirements of low temperature co-fired ceramic (LTCC), the chemical composition of the ceramic main powder is one or more selected from the combination of alumina, silica, calcium borosilicate glass, magnesium alumino-silicate glass, the particle morphology of the ceramic main powder is spherical or near-spherical, and the particle size D50 distribution range is between 0.5 and 3.0 microns; (2) Put the ceramic main powder in a vacuum oven, and perform vacuum drying treatment at a temperature of 120 to 150°C for 4 to 8 hours to completely remove the water molecules and other volatile impurities physically adsorbed on the surface of the particles.

[0012] Further, in step S2, the powder dispersion system works cooperatively through a mechanical vibration device connected to the bottom of the reaction chamber and an inert gas fluidization device penetrating through the powder layer, the mechanical vibration device applies micro-vibration to the chamber at a frequency of 20 to 60 Hz and an amplitude of 0.5 to 2.0 mm.

[0013] Further, in step S3, the determination of the number of cycles N is based on the desired weight percentage of the target dopant in the final LTCC material, the unit cycle growth rate of the selected atomic layer deposition process, the specific surface area and average particle size of the ceramic main powder; the cycle specifically includes; (1) Pulse of the first precursor vapor and chemical adsorption: Through precise control by a mass flow controller, the first precursor vapor containing one or more target doping elements selected from silicon, boron, aluminum, zinc, bismuth, and copper is introduced into the reaction chamber in a dynamic dispersion state in a pulsed manner, the duration of the pulse is set to 0.2 to 2.0 seconds, so that the molecules of the first precursor vapor chemically react with the surface of the ceramic main powder particles to form a self-limiting, saturated monomolecular chemical adsorption layer; During this period, the molecules of the first precursor vapor are carried by the transport carrier gas to contact the exposed surface of the ceramic main powder particles, and form a self-limiting, saturated monomolecular chemical adsorption layer by chemical reaction with the active functional groups (such as hydroxyl groups) on the particle surface; Due to the self-limiting effect, once all available reaction sites on the particle surface are occupied, the surface reaction will automatically terminate, and any excess precursor molecules introduced subsequently will not continue to react or physically adsorb on the formed adsorption layer; (2) First purging: Immediately after the completion of the pulse introduction of the first precursor vapor, the supply thereof is interrupted, while the flow of high-purity inert gas into the reaction chamber is continued or increased, the flow rate being raised to 200 to 1000 standard cubic centimeters per minute, the purging process lasting 5 to 30 seconds, in order to remove all residual first precursor vapor molecules not involved in the reaction and any precursor molecules physically adsorbed on the particle surfaces from the reaction chamber space; (3) Pulse of the second reactant gas and surface chemical reaction: After the completion of the first purging, a second reactant gas is introduced into the reaction chamber in pulses, the second reactant gas being selected in accordance with the chemical nature of the first precursor vapor, and it reacts with the monolayer of the first precursor vapor previously chemisorbed on the surface of the ceramic primary powder particles in a ligand exchange reaction or a redox reaction, thereby generating a monolayer of the target dopant compound, the duration of the pulse process being set to 0.1 to 5.0 seconds; This surface chemical reaction is also self-limiting, the reaction occurring only between the adsorbed layer and the second reactant gas until the adsorbed layer is completely converted; (4) Second purging: The supply of the second reactant gas is interrupted, and high-purity inert gas is again introduced into the reaction chamber at a flow rate of 200 to 1000 standard cubic centimeters per minute, a second purging being carried out for 10 to 60 seconds in order to completely remove all unreacted second reactant gas molecules and all gaseous reaction byproducts generated in the previous step from the reaction chamber.

[0014] By precisely controlling the number of cycles N, a dopant compound coating layer of uniform thickness and complete conformity can be grown on each ceramic primary powder particle surface, the thickness control accuracy being in the order of angstroms. When N cycles have been completed, the product obtained is a composite powder having a core-shell structure, the core being the original ceramic primary powder particle and the shell being the dopant compound layer generated in situ by the atomic layer deposition method.

[0015] The first precursor vapor is a compound containing the target dopant element, the selection rules being as follows: for silicon, bisdiethylaminosilane is selected, for boron, trisdimethylaminoborane is selected, for aluminum, trimethylaluminum is selected, for zinc, diethylzinc is selected, for bismuth, tris(diethylamino)bismuth is selected, and for copper, bis(hexafluoroacetylacetonato)copper is selected; the corresponding second reactant gas is: for silicon, boron and aluminum, an oxygen plasma is selected, for zinc and bismuth, water vapor is selected, and for copper, hydrogen is selected. The skilled person selects the appropriate combination accordingly.

[0016] Further, in step S3, the second reactant gas is introduced into the reaction chamber in a plasma enhanced manner, and a radio frequency plasma generator coupled to the reaction chamber is activated; the radio frequency plasma generator has a working frequency of 13.56 MHz, and the output power is set between 50-300 W.

[0017] Further, by alternately using different first precursor vapors and corresponding second reactant gases in different atomic layer deposition cycles, a multi-component dopant coating layer or a gradient dopant coating layer with a gradient change in composition along the thickness direction can be prepared.

[0018] For example, by performing a super cycle sequence of "(first precursor vapor A + second reactant gas A') x M times" + "(first precursor vapor B + second reactant gas B') x P times", layers A and B of dopant compounds with two different chemical compositions can be sequentially deposited on the surface of the ceramic primary powder particles, forming a composite coating structure with a specific functional layering.

[0019] For example, a component with a liquid phase formation temperature lower than 800℃ (such as B2O3) is first deposited, and then a component with a liquid phase formation temperature higher than 850℃ and capable of inhibiting grain growth (such as SiO2) is deposited, and the gradient is controlled by adjusting the cycle ratio (such as B2O3: SiO2 transitioning from 3:1 to 1:3); for example, high B2O3 (melting point 450℃) in the inner layer promotes early liquid phase, and high SiO2 (melting point 1700℃) in the outer layer inhibits abnormal grain growth.

[0020] Further, the steps of slurry preparation, molding and sintering are also included, which are as follows: (1) The core-shell structure composite powder of step S4 is mixed with an organic carrier system, the organic carrier system is composed of a solvent, a binder, a plasticizer and a dispersant, the solvent is a mixture of α-terpineol and anhydrous ethanol with a purity of ≥99.5%, the mass ratio is 7:3, the binder is polyvinyl butyral PVB, the plasticizer is dibutyl phthalate DBP, and the composite powder and the organic carrier system are ball-mixed in a planetary ball mill at a low speed of 120 revolutions per minute for 36 hours, until a uniform and stable slurry with a viscosity of 20±2 Pa·s is formed at a temperature of 25℃; wherein a typical slurry formula is: the core-shell structure composite powder accounts for 60% by mass percentage, and the organic carrier system accounts for 40%; in the organic carrier system, the solvent accounts for 75%, the binder accounts for 20%, the plasticizer accounts for 4%, and the dispersant accounts for 1%; (2) The slurry is cast on the polyester film base tape by a doctor blade with a gap set to 250 microns at a speed of 0.4 meters per minute to form a flexible green ceramic tape with a thickness of 120±5 microns. (3) The green ceramic tape is stacked and hot-pressed according to the circuit design to form a multilayer ceramic body; (4) The body is placed in a sintering furnace, and a degassing treatment is performed at a temperature in the range of 300 to 500 DEG C at a temperature rising rate of 0.5-3 DEG C / min to completely remove the organic carrier component, and then the temperature is raised to a final sintering temperature of 850 to 950 DEG C at a temperature rising rate of 2-5 DEG C / min, and the temperature is kept for 1 to 3 hours to complete the densification sintering process, and finally the high-frequency low-loss LTCC material is obtained.

[0021] Further, the ceramic main powder is composed of 55% of alpha phase aluminum oxide and 45% of calcium borosilicate glass by mass fraction after high-energy ball milling and grinding.

[0022] Further, when the dopant compound is zinc oxide ZnO, the first precursor vapor is diethyl zinc vapor, and the second reactant gas is water vapor.

[0023] Further, the multi-component dopant coating layer is a silicon oxide / boron oxide composite doping layer, the first precursor vapor for depositing silicon oxide SiO2 is bis-diethylaminosilane vapor, the first precursor vapor for depositing boron oxide B2O3 is tris-dimethylaminoborane vapor, and the second reactant gas of the two dopants is oxygen plasma, and a basic unit of "1 SiO2 atomic layer deposition cycle + 2 B2O3 atomic layer deposition cycles" is repeatedly executed to form a borosilicate glass coating layer on the surface of the ceramic main powder particles.

[0024] The present application has the following advantages: (1) The present application introduces atomic layer deposition technology to pretreat the LTCC ceramic main powder, and the dopant is coated on the surface of each main powder particle in the form of a chemical bonding, atomically uniform coating layer to construct a core-shell structure composite powder, which completely solves the inherent problems of dopant agglomeration and uneven distribution in the traditional physical mixing process at the atomic scale.

[0025] (2) Efficient sintering and microstructure optimization: In the subsequent sintering process, the uniform coating layer melts to form a transient liquid phase with uniform thickness, which can perfectly wet each main powder particle; the capillary force efficiently promotes the particle rearrangement and densification process, and finally the LTCC material obtained has a density close to the theoretical density and a low microstructure defect rate.

[0026] (3) Macroscopic electrical performance leap: The optimization of the microstructure of the present application directly leads to a revolutionary improvement in the macroscopic electrical performance, which is specifically manifested in that the dielectric constant has high stability and batch consistency; in the high frequency band, especially in the millimeter wave band, the dielectric loss factor (tan delta) of the material is extremely low.

[0027] (4) Performance customization technology path: the application has the ability to accurately control the thickness and composition of the coating layer, opening up a new technical path for the performance customization design of LTCC materials; the dielectric constant, temperature coefficient and sintering behavior of the material can be accurately controlled according to specific application requirements, meeting the extreme performance requirements of the next generation of high-frequency communication systems for substrate materials. DETAILED DESCRIPTION

[0028] The core of the disclosed technical solution is to systematically introduce atomic layer deposition technology to perform precise surface chemical modification on the ceramic main powder used in low-temperature co-fired ceramic (LTCC), thereby constructing a core-shell structure composite powder with uniform and controllable chemical composition and thickness on a single particle scale. This composite powder fundamentally solves the series of problems such as uneven distribution of dopants, agglomeration, and microstructure defects caused during sintering that are difficult to avoid in traditional mechanical mixing processes. The LTCC material prepared by this method exhibits high uniformity and density in the microstructure, and thus exhibits excellent low dielectric loss characteristics and performance consistency in the macroscopic electrical properties, especially in high-frequency application fields such as millimeter waves.

[0029] In order to enable those skilled in the art to better understand the technical solutions in the present application, the following will further describe the present application in conjunction with embodiments.

[0030] A method for preparing high-frequency low-loss LTCC material using external doping means, comprising the following steps: S1, pretreatment and loading of ceramic main powder: (1) Selecting a ceramic main powder that meets the application requirements of low-temperature co-fired ceramic (LTCC), the chemical composition of the ceramic main powder being one or more combinations selected from alumina, silica, calcium borosilicate glass, and magnesium alumino-silicate glass, the particle morphology of the ceramic main powder being spherical or near-spherical, and the particle size D50 distribution range being between 0.5 and 3.0 microns; (2) Placing the ceramic main powder in a vacuum oven and performing vacuum drying treatment at a temperature of 120 to 150°C for 4 to 8 hours to completely remove physically adsorbed water molecules and other volatile impurities on the particle surface; (3) After completing the drying treatment, the ceramic main powder is transferred and loaded into the reaction chamber of a powder atomic layer deposition reactor under a nitrogen protective atmosphere, and the powder loading amount occupies 10%-30% of the effective volume of the chamber.

[0031] S2, powder dynamic dispersion and reaction environment construction: (1) Close the reaction chamber and start the vacuum system to pump the background vacuum in the chamber to below 1.0 Pa; (2) Start the heating system of the reaction chamber, heat the inner wall of the chamber and the ceramic master powder loaded therein as a whole to a preset atomic layer deposition process temperature, the process temperature is set in the range of 100-300°C, the core principle is to ensure that the temperature is higher than the condensation point of the used precursor but lower than the thermal decomposition temperature thereof; (3) After reaching and stabilizing at the process temperature, start the powder dispersion system, which works cooperatively through a mechanical vibration device connected to the bottom of the reaction chamber and an inert gas fluidization device penetrating through the powder layer. The mechanical vibration device applies slight vibration to the chamber at a frequency of 20 to 60 Hz and an amplitude of 0.5 to 2.0 mm, while high-purity inert gas is introduced from the bottom of the chamber as a carrier gas and fluidization gas. The inert gas is nitrogen or argon with a purity of not less than 99.999%, and its flow rate is controlled between 50 and 500 standard cubic centimeters per minute. Under the combined action of mechanical vibration and gas flow, the ceramic master powder forms a uniform, continuous and dynamic fluidized bed state in the reaction chamber.

[0032] S3, atomic layer deposition cycle: Repeat a cycle containing four basic sub-steps N times, N is a pre-calculated and set integer, N is in the range of 10 to 1000, the cycle specifically includes: S3-1, pulse of first precursor vapor and chemical adsorption: Through precise control by a mass flow controller, introduce the first precursor vapor, which is a metal organic compound or metal halide containing one or more target doping elements selected from silicon, boron, aluminum, zinc, bismuth, copper, into the reaction chamber in a dynamic dispersion state in a pulse manner, the pulse duration is set between 0.2 and 2.0 seconds, so that the molecules of the first precursor vapor chemically react with the surface of the ceramic master powder particles to form a self-limiting, saturated monomolecular chemical adsorption layer; S3-2, first purge: After completing the pulse introduction of the first precursor vapor, immediately interrupt its supply, while continuously or increasing the flow rate of high-purity inert gas introduced into the reaction chamber, the flow rate is increased to 200 to 1000 standard cubic centimeters per minute, the purging process lasts for 5 to 30 seconds to remove all unreacted, residual first precursor vapor molecules in the reaction chamber space and any physically adsorbed precursor molecules on the particle surface; S3-3, pulse of second reactant gas and surface chemical reaction: After the first purge is completed, a second reactant gas is introduced into the reaction chamber in a plasma-enhanced form while a radio frequency plasma generator coupled to the sidewalls of the reaction chamber is activated, with an electrode in a ring array design to ensure uniform gas distribution; the second reactant gas is selected according to the chemical properties of the first precursor vapor, and a ligand exchange reaction or a redox reaction occurs between the monolayer of the first precursor vapor previously chemisorbed on the surface of the ceramic primary powder particles, thereby generating a monatomic layer of the target dopant compound, with the duration of the pulse process being set to 0.1-5.0 seconds; the working frequency of the radio frequency plasma generator is 13.56 MHz, and the output power is set to 50-300 W; the power density is controlled to be 0.1-0.5 W / cm³, and the plasma stability is maintained by adjusting the carrier gas flow rate in the range of 300-800 standard cubic centimeters per minute; the specific adjustment method is: the plasma glow intensity is monitored in real time, and if the intensity fluctuation exceeds ±5%, the carrier gas flow rate is increased or decreased by 50-100 standard cubic centimeters per minute to restore stability; S3-4, second purge: The supply of the second reactant gas is interrupted, and high-purity inert gas is again introduced into the reaction chamber at a flow rate of 200-1000 standard cubic centimeters per minute for a second purge lasting 10-60 seconds to completely remove all unreacted second reactant gas molecules and all gaseous reaction byproducts generated in the previous step in the reaction chamber; N is calculated by the following formula: N = ceil(W_t x SSA / (G x p)), where W_t is the desired weight percentage of the target dopant in the final LTCC material; SSA is the specific surface area (m 2 / g) of the ceramic primary powder, measured by a Micromeritics ASAP 2460 BET analyzer after 2 hours of pretreatment at 150°C, with an error range of ±0.2m 2 / g; G is the unit cycle growth rate (g / m 2 / cycle) of the selected atomic layer deposition process, obtained by in-situ calibration of a quartz crystal microbalance, with the calibration method being: placing a reference substrate in the reaction chamber and measuring the growth thickness after performing a single atomic layer deposition cycle to calculate the G value; for different dopants, the G calibration reference is provided: SiO2 is 0.03 ng / cm 2 / cycle (calibration conditions: 200°C, BDEAS precursor), B2O3 is 0.04 ng / cm 2 / cycle (calibration conditions: 200°C, TDMAB precursor), and ZnO is 0.05 ng / cm 2 / cycle (calibration conditions: 200°C, DEZ precursor); p is the density (g / cm 3), taken from the standard values of the CRC Handbook of Chemistry and Physics; for example, for a zinc oxide coating layer, G = 0.05 ng / cm 2 / cycle (calibration conditions: 200 °C, DEZ precursor), p = 5.6 g / cm 3 ; the skilled person can calculate the value of N depending on the specific parameters, ensuring that it is in the range of 10-1000.

[0033] S4, in-situ heat treatment and composite powder discharge: (1) after completing N atomic layer deposition cycles, stop the work of the powder dispersion system, and stop the inert gas input; (2) under the condition of maintaining the vacuum or a specific atmosphere of the reaction chamber, the specific atmosphere being nitrogen or a weak oxidizing atmosphere with an oxygen content of less than 10 ppm, the chamber temperature is raised from the atomic layer deposition process temperature to a higher annealing temperature, the annealing temperature being set between 400 and 600 °C, and maintained at this temperature for 1 to 2 hours; (3) after the heat treatment is completed, the reaction chamber is naturally cooled to room temperature; (4) under the protection of inert gas, the prepared core-shell structure composite powder is taken out of the reaction chamber.

[0034] S5, slurry preparation, molding and sintering: (1) the core-shell structure composite powder of step S4 is mixed with an organic carrier system, the organic carrier system being composed of a solvent, a binder, a plasticizer and a dispersant, the solvent being a mixture of a-terpineol and anhydrous ethanol with a purity of ≥99.5%, the mass ratio being 7:3, the binder being polyvinyl butyral PVB, the plasticizer being dibutyl phthalate DBP, the composite powder and the organic carrier system are uniformly mixed at low speed in a planetary ball mill to form a uniform slurry with a specific viscosity; wherein a typical slurry formula is: the core-shell structure composite powder accounts for 60%, the organic carrier system accounts for 40% by mass percentage; in the organic carrier system, the solvent accounts for 75%, the binder accounts for 20%, the plasticizer accounts for 4%, and the dispersant accounts for 1%; (2) using a tape casting process, the slurry is cast through a doctor blade with a gap setting of 250 microns at a speed of 0.4 meters per minute on a polyester film base to form a flexible green ceramic tape with a thickness of 120 ± 5 microns; (3) the green ceramic tape is stacked and hot pressed according to the circuit design to form a multilayer ceramic body; (4) Put the green body into a sintering furnace, perform a degumming treatment at a temperature range of 300 to 500°C with a temperature rising rate of 0.5-3°C / min, to completely remove the organic carrier component, then raise the temperature from the degumming end point to a final sintering temperature of 850 to 950°C with a temperature rising rate of 2-5°C / min, and keep the temperature for 1 to 3 hours, to complete the densification sintering process, and finally obtain a high-frequency low-loss LTCC material.

[0035] Example 1: Preparation of SiO2 and B2O3 dual-component doped LTCC material A high-frequency low-loss LTCC material is prepared by the method of the present application.

[0036] 1. Pretreatment and loading of ceramic main powder (1) Mix and grind 55% by mass of α-Al2O3 powder and 45% by mass of calcium borosilicate glass powder by high-energy ball milling for 4 hours, then perform 4 hours of homogenization mixing with anhydrous ethanol as the medium, and then dry and sieve the mixed slurry to obtain spherical ceramic main powder with a D50 of 2.0 microns; (2) Load 2000 grams of ceramic main powder into a powder atomic layer deposition reactor under nitrogen protection, and the loading amount accounts for 20% of the effective volume of the chamber.

[0037] 2. Dynamic dispersion of powder and construction of reaction environment (1) Close the chamber and vacuumize to a background vacuum degree of ≤1.0 Pa; (2) Heat the chamber and the powder to 200°C; (3) Start the powder dispersion system: bottom mechanical vibration (40 Hz, amplitude 1.3 mm) cooperates with inert gas fluidization (99.999% nitrogen, flow rate 200 standard cubic centimeters / minute) to form a dynamic fluidized bed.

[0038] 3. Atomic layer deposition cycle A PE-ALD process is adopted, and "1 SiO2 cycle + 1 B2O3 cycle" is taken as one super cycle, and a total of 120 cycles are performed, each cycle specifically including: (1) SiO2 cycle: S3-1, first precursor vapor pulse adsorption: accurately control through a mass flow controller, pulse introduce BDEAS vapor into the reaction chamber in a dynamic dispersion state, pulse duration 1 second, make BDEAS molecules react with the surface of ceramic main powder particles to form a self-limiting saturated monomolecular chemical adsorption layer.

[0039] S3-2, first purge: interrupt BDEAS supply, pass high-purity inert gas at a flow rate of 600 standard cubic centimeters / minute, and continue to purge for 17 seconds to remove residual BDEAS and physically adsorbed molecules.

[0040] S3-3, second reactant gas pulse reaction: pulse introduction of O2 plasma for 2.5 seconds, while starting a radio frequency plasma generator with a working frequency of 13.56 MHz and an output power of 200 W to react with the surface-adsorbed BDEAS monolayer to generate a SiO2 monatomic layer.

[0041] S3-4, second purge: interrupting the supply of O2 plasma, and passing in inert gas at the same flow rate for 35 seconds of continuous purging to remove unreacted O2 plasma and gaseous by-products.

[0042] (2) B2O3 cycle: The first precursor vapor is replaced by TDMAB vapor, and the remaining steps are consistent with the steps of the SiO2 cycle.

[0043] After calculation, a BSG coating layer with an average thickness of about 30 nanometers and a total weight percentage of about 3.5wt% is finally formed on the surface of the main powder particles.

[0044] S4, in-situ heat treatment and composite powder discharge (1) After the deposition is completed, stop the dispersion system and the inert gas input; (2) Anneal at 500℃ for 1.5 hours under nitrogen atmosphere; (3) After cooling to room temperature, take out the core-shell structure composite powder under nitrogen atmosphere protection.

[0045] S5, slurry preparation, molding and sintering (1) The composite powder and the organic carrier (terebene alcohol-ethanol solvent, PVB binder, DBP plasticizer, dispersant) are mixed into slurry by a planetary ball mill at low speed; (2) Cast into a green ceramic tape and stack and hot-press into a multilayer body; (3) Perform a degassing treatment by increasing the temperature to 450℃ at a rate of 2℃ / min, and then sinter at 900℃ for 2 hours at a rate of 3℃ / min to obtain a high-frequency low-loss LTCC material.

[0046] Example 2: Preparation of a ZnO single-component doped LTCC material A high-frequency low-loss LTCC material is prepared by the method of the application.

[0047] 1, ceramic main powder pretreatment and loading (1) Selecting ceramic main powder as 60% by mass of silicon dioxide (SiO2) and 40% of magnesium-aluminum silicate glass, after mixing, a near-spherical composite main powder is obtained, D50=0.5μm; (2) Take 1500 grams of the above main powder and place it in a vacuum oven, dry at 120°C for 4 hours to remove surface moisture and impurities; (3) Under nitrogen protection, load 1000 grams of ceramic main powder into the powder atomic layer deposition reactor, with a loading capacity of 10% of the effective volume of the chamber.

[0048] 2. Dynamic dispersion of powder and construction of reaction environment (1) Close the chamber and vacuum to a base vacuum of ≤1.0 Pa; (2) Heat the chamber and the powder to 100°C; (3) Start the powder dispersion system: mechanical vibration frequency 20 Hz, amplitude 0.5 mm, simultaneously introduce 99.999% argon as fluidizing gas, flow rate 50 standard cubic centimeters / minute, form a stable fluidized bed.

[0049] 3. Atomic layer deposition cycle Using PE-ALD process, diethyl zinc (DEZ) as the first precursor vapor, deionized water vapor as the second reactant gas, perform 300 cycles, specific steps: (1) First precursor vapor pulse adsorption: pulse introduction of DEZ vapor, duration 0.2 seconds, DEZ molecules react with surface hydroxyl groups to form a saturated chemisorbed layer; (2) First purge: introduce argon at a flow rate of 200 standard cubic centimeters / minute, continuous purging for 5 seconds, remove residual DEZ; (3) Second reactant gas pulse reaction: pulse introduction of deionized water vapor, duration 0.1 seconds, simultaneously start a radio frequency plasma generator with a working frequency of 13.56 MHz and an output power of 50 watts, react with the surface adsorbed DEZ to form a monolayer of ZnO; (4) Second purge: introduce argon at the same flow rate, continuous purging for 10 seconds, remove unreacted water vapor and byproducts.

[0050] After calculation, an average thickness of about 50 nanometers, a weight percentage of 4.2% of the ZnO coating layer is formed on the surface of the main powder.

[0051] 4. In-situ heat treatment and composite powder discharge (1) After deposition, stop the dispersion system and inert gas introduction; (2) In a weak oxidizing atmosphere with oxygen content ≤10 ppm, anneal at 400°C for 1 hour to promote the densification of the ZnO coating layer; (3) After cooling to room temperature, take out the core-shell structure composite powder under nitrogen protection.

[0052] 5. Slurry preparation, shaping and sintering (1) The composite powder and the organic carrier (same as the single formula in Example 1) are mixed into a slurry by a planetary ball mill at a low speed; (2) The green ceramic tape is prepared by tape casting and is laminated and hot-pressed into a multilayer body; (3) The glue removal treatment is performed at a temperature rising rate of 0.5 ℃ / min to 300 ℃, and then the sintering is performed at a temperature rising rate of 2 ℃ / min to 850 ℃ for 1 hour, to obtain the high-frequency low-loss LTCC material.

[0053] Example 3: Preparation of a SiO2 and B2O3 dual-component gradient-doped LTCC material The method can be used to prepare a high-frequency low-loss LTCC material.

[0054] 1. Pretreatment and loading of ceramic main powder The same α-Al2O3 / calcium borosilicate glass composite main powder (55% / 45%) as in Example 1 is selected, but the D50 is 3.0 μm, 3000 grams are taken, vacuum dried at 150 ℃ for 5 hours, and then loaded into the reactor under nitrogen protection, with a loading amount of 30%.

[0055] 2. Dynamic dispersion of powder and construction of reaction environment The chamber is vacuumed to ≤1.0 Pa, heated to 300 ℃, and a fluidized bed is formed by mechanical vibration (60 Hz, amplitude 2.0 mm) and nitrogen flow (flow rate 500 standard cubic centimeters / minute).

[0056] 3. Atomic layer deposition gradient cycle The PE-ALD process is used to perform the cycle in two stages: (1) The first stage (inner high boron): a super cycle of "1 SiO2 cycle + 3 B2O3 cycles" is performed for 60 times, the precursors are BDEAS (SiO2) and TDMAB (B2O3), and the second reactant gas is O2 plasma (13.56 MHz, power 300 W); (2) The second stage (outer high silicon): a super cycle of "3 SiO2 cycles + 1 B2O3 cycle" is performed for 60 times, and the process parameters are the same as in the first stage; The total cycle number is 240 times, and a gradient coating layer with a thickness of about 60 nanometers is finally formed, with an inner layer B2O3 proportion of 65% and an outer layer SiO2 proportion of 60%, and a total doping amount of 4.0 wt%.

[0057] 4. In-situ heat treatment and subsequent process The powder was taken out after annealing at 600 ℃ for 2 hours under nitrogen atmosphere. The composite powder was mixed with the organic vehicle (same as in Example 1) in a planetary ball mill at low speed to form a slurry, which was cast and subjected to a degassing treatment by heating at a rate of 3 ℃ / min to 500 ℃, followed by sintering at a rate of 5 ℃ / min to 950 ℃ for 2 hours to obtain a high-frequency low-loss LTCC material.

[0058] Comparative Example 1 An LTCC material was prepared using a conventional physical mixing method.

[0059] 1. Main powder and dopant The same 2000 grams of ceramic main powder as in Example 1 was selected.

[0060] A commercially available borosilicate glass powder was selected, which had the same composition as the target cladding layer in Example 1, and 70 grams of the glass powder were weighed (so that the total weight percentage in the mixture was 3.5 wt%).

[0061] 2. Mixing The ceramic main powder and the borosilicate glass powder were placed in the same planetary ball mill and subjected to high-energy ball milling for 48 hours using anhydrous ethanol as the medium to achieve as uniform a mixture as possible.

[0062] 3. Slurry preparation, molding, and sintering The mixed and dried powder was processed using the same slurry formulation, molding process, and sintering regime as in Example 1. The sintering temperature was set to 900 ℃ for 2 hours.

[0063] Comparative Example 2 An LTCC material was prepared using a conventional wet precipitation process.

[0064] 1. Preparation of main powder and dopant precursor (1) The same 1000 grams of ceramic main powder as in Example 2 was selected.

[0065] (2) Preparation of ZnO precursor solution: zinc nitrate (Zn(NO3)2·6H2O) was dissolved in deionized water to prepare a solution with a concentration of 0.5 mol / L, and the required solution volume was calculated based on the target 4.2 wt% ZnO doping amount.

[0066] 2. Wet precipitation coating (1) The ceramic main powder was dispersed in anhydrous ethanol to form a suspension with a solid content of 30%, and ultrasonic dispersion was performed for 30 minutes.

[0067] (2) The zinc nitrate solution was slowly added to the suspension under stirring, and ammonia water was added to adjust the pH to 8.0, so that Zn²⁺ was hydrolyzed on the surface of the main powder to form zinc hydroxide precipitate.

[0068] (3) After stirring for 2 hours, the precipitate was filtered, washed to neutral, dried at 120°C for 12 hours, and then calcined at 500°C for 2 hours to convert the zinc hydroxide to ZnO.

[0069] 3. Preparation of slurry, molding and sintering The same slurry formulation, mixing parameters, tape casting process and sintering regime (850°C x 1 hour) as in Example 2 were used.

[0070] Effect comparison

[0071] The final sintered ceramic samples prepared in Examples 1-3 and Comparative Examples 1-2 were tested for performance and microstructure characterization, and the results are shown in Table 1.

[0072] Table 1: Test results table Performance parameters Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Sintered density (g / cm 3 ) 3.91（99.5%） 3.78（98.9%） 3.89（99.2%） 3.80（96.9%） 3.65（95.5%） Dielectric constant (εr) at 10 GHz 9.75 8.92 9.68 9.81 9.05 Dielectric loss (tan δ) at 10 GHz 6.2 x 10 -4 ]]> 8.5 x 10 -4 ]]> 7.8 x 10 -4 ]]> 2.5 x 10 -3 ]]> 3.2 x 10 -3 ]]> Quality factor (Q value) at 10 GHz 1282 1176 1613 400 313 Standard deviation of εr between batches 0.01 0.03 0.02 0.15 0.21 Microstructure defect rate (%) <0.3 <0.8 <0.5 >4 >5 Bending strength (MPa) 310 285 290 235 220 By comparing the performance data of Examples 1-3 and Comparative Examples 1-2, the core advantages of the present application in the preparation of high-frequency low-loss LTCC materials can be clearly highlighted, as follows: (1) Significantly improve sintering density, close to theoretical density The sintering density of Examples 1-3 all reached more than 98.9%, among which the density of Example 1 was as high as 99.5%, close to the theoretical density (100%); while the densities of Comparative Example 1 (traditional physical mixing) and Comparative Example 2 (traditional wet precipitation) were only 96.9% and 95.5%.

[0073] The present application forms a uniform dopant coating layer on the surface of the main powder particles by atomic layer deposition, and the coating layer uniformly melts to form a transient liquid phase during sintering, which efficiently promotes particle rearrangement and densification with the help of capillary force, fundamentally solving the problem of local under-sintering caused by dopant agglomeration in traditional methods.

[0074] (2) High-frequency dielectric loss is greatly reduced, and the quality factor (Q value) is significantly improved At 10 GHz high frequency, the dielectric loss (tan δ) of Examples 1-3 was only 6.2 x 10 -4 -8.5 x 10 -4 , while the dielectric loss of Comparative Examples 1 and 2 was as high as 2.5 x 10 -3 -3.2 x 10 -3 , with a loss reduction of more than 70% for Examples.

[0075] In terms of the corresponding quality factor (Q value), the Q value of Examples 1-3 was 1176-1613, which was more than 3 times that of Comparative Examples (313-400).

[0076] The present application avoids the problem of forming high-loss glass phase in the rich region of dopants and residual pores in the barren region in the traditional method by the atomically uniform distribution of dopants, eliminates the micro root cause of high-frequency signal loss, and makes the material exhibit excellent low-loss characteristics in high-frequency scenarios such as millimeter waves.

[0077] (3) The performance consistency is extremely strong, and the batch difference is negligible The standard deviation of the dielectric constant between batches of examples 1-3 is only 0.01-0.03, while the standard deviation of comparative examples 1 and 2 is as high as 0.15-0.21, with a difference of 5-7 times.

[0078] The present application realizes the angstrom-level regulation of the thickness of the dopant coating layer by precisely controlling the number of atomic layer deposition cycles (N), ensures the uniformity of doping of each batch and each particle, and guarantees the stability of material performance from the source, providing a reliable foundation for large-scale industrial production.

[0079] (4) The microstructure defect rate is extremely low, and the mechanical strength is significantly improved The microstructure defect rate of examples 1-3 is less than 0.8% (even <0.3% for example 1), while the defect rate of the comparative examples is more than 4%-5%, with a defect reduction of more than 80%.

[0080] In terms of bending strength, examples 1-3 reach 285-310 MPa, an increase of about 25%-38% compared to the comparative examples (220-235 MPa).

[0081] The present application eliminates the stress concentration points and micro pores caused by the agglomeration of dopants in traditional physical mixing through the core-shell structure composite powder of atomic layer deposition, making the material microstructure more uniform and dense, and directly improving the mechanical reliability.

[0082] In summary, the present application realizes the atomic-level uniform coating of dopants through atomic layer deposition technology, fundamentally solves the inherent defects of traditional physical mixing methods, and ultimately achieves a qualitative leap in key indicators such as density, high-frequency dielectric loss, performance consistency and mechanical strength of the obtained LTCC material, perfectly meeting the stringent requirements of 5G / 6G communication, radar and other high-frequency high-integration scenarios for substrate materials.

Claims

1. A method for preparing high-frequency low-loss LTCC material by external doping means, characterized in that, The method comprises the following steps: S1, loading of ceramic main powder: providing ceramic main powder for preparation of the LTCC material, and loading the ceramic main powder into a reaction chamber of an atomic layer deposition reactor under a nitrogen protective atmosphere; the powder loading amount accounts for 10% to 30% of the effective volume of the chamber; S2, dynamic dispersion of powder and construction of reaction environment: closing the chamber, vacuumizing to a background vacuum degree of less than or equal to 1.0 Pa, heating the chamber to 100-300 ℃, starting the powder dispersion system, and synchronously introducing inert gas with a purity of not less than 99.999% nitrogen or argon as carrier and fluidizing gas to make the powder form a stable fluidized bed state; wherein the flow rate of the inert gas is 50-500 standard cubic centimeters per minute; S3, atomic layer deposition cycle: repeating the atomic layer deposition cycle N times on the powder treated in S2 to form a layer of dopant compound coating on the surface of the ceramic main powder particles; wherein the cycle number N is an integer of 10-1000; S4, in-situ heat treatment and discharge of composite powder: after S3 is completed, the dispersion system and the inert gas introduction are stopped, and the temperature is raised to 400-600 ℃ for annealing for 1-2 hours under a specific atmosphere of nitrogen or a weak oxidizing atmosphere with an oxygen content of less than 10 ppm; after cooling to room temperature, the core-shell structure composite powder is taken out under the protection of the specific atmosphere.

2. The method for preparing high-frequency low-loss LTCC material by external doping means according to claim 1, characterized in that, Before the step S1, pretreatment needs to be performed, and the specific steps are as follows: (1) selecting ceramic main powder meeting the application requirements of low-temperature co-fired ceramic LTCC, the chemical composition of the ceramic main powder being a combination of one or more selected from alumina, silicon dioxide, calcium borosilicate glass, and magnesium alumino-silicate glass, the particle morphology of the ceramic main powder being spherical or near-spherical, and the particle size D50 distribution range being between 0.5 and 3.0 microns; (2) placing the ceramic main powder in a vacuum oven, and performing vacuum drying treatment at a temperature of 120 to 150 ℃ for 4 to 8 hours to completely remove water molecules and other volatile impurities physically adsorbed on the surface of the particles.

3. The method for preparing high-frequency low-loss LTCC material by external doping means according to claim 1, characterized in that, In the step S2, the powder dispersion system cooperates with a mechanical vibration device connected to the bottom of the reaction chamber and an inert gas fluidization device penetrating through the powder layer, the mechanical vibration device applies micro-vibration to the chamber at a frequency of 20 to 60 Hz and an amplitude of 0.5 to 2.0 mm.

4. The method for preparing high-frequency low-loss LTCC material by external doping means according to claim 1, characterized in that, In the step S3, the cycle number N is determined based on the expected weight percentage of the target dopant in the final LTCC material, the unit cycle growth rate of the selected atomic layer deposition process, the specific surface area and average particle size of the ceramic main powder; The cycle specifically includes; (1) pulse of the first precursor vapor and chemical adsorption: The first precursor vapor, which is a metal organic compound or a metal halide containing one or more target dopant elements selected from silicon, boron, aluminum, zinc, bismuth, copper, is introduced into the reaction chamber in a pulsed manner with a duration of 0.2 to 2.0 seconds via a mass flow controller, so that the molecules of the first precursor vapor chemically react with the surface of the ceramic master powder particles to form a self-limiting, saturated monolayer of chemical adsorption; (2) First Purge: Immediately after the pulsed introduction of the first precursor vapor is completed, the supply of the first precursor vapor is interrupted, while the flow of high-purity inert gas into the reaction chamber is continued or increased to a flow rate of 200 to 1000 standard cubic centimeters per minute. The purge process lasts for 5 to 30 seconds to remove all unreacted residual first precursor vapor molecules in the reaction chamber space and any precursor molecules physically adsorbed on the particle surface; (3) Pulsed Surface Chemical Reaction of Second Reactant Gas: After the first purge is completed, a second reactant gas is introduced into the reaction chamber in a pulsed manner. The second reactant gas is selected according to the chemical properties of the first precursor vapor and undergoes ligand exchange or redox reactions with the monolayer of the first precursor vapor previously chemically adsorbed on the surface of the ceramic master powder particles, thereby generating a monolayer of target dopant compounds. The duration of the pulsed process is set to 0.1 to 5.0 seconds; (4) Second Purge: The supply of the second reactant gas is interrupted, and high-purity inert gas is again introduced into the reaction chamber at a flow rate of 200 to 1000 standard cubic centimeters per minute for a second purge lasting 10 to 60 seconds to completely remove all unreacted second reactant gas molecules and all gaseous reaction byproducts generated in the previous step in the reaction chamber.

5. The method for preparing high-frequency low-loss LTCC material by external doping means according to claim 1 or 4, characterized in that, In step S3, the second reactant gas is introduced into the reaction chamber in a plasma-enhanced manner, and a radio frequency plasma generator coupled to the reaction chamber is started. The operating frequency of the radio frequency plasma generator is 13.56 megahertz, and the output power is set to 50-300 watts.

6. The method for preparing high-frequency low-loss LTCC material by external doping means according to claim 1 or 4, characterized in that, By alternating the use of different first precursor vapors and corresponding second reactant gases in different atomic layer deposition cycles, multi-component dopant coating layers or gradient-doped coating layers with composition gradients along the thickness direction can be prepared.

7. The method for preparing high-frequency low-loss LTCC material by external doping means according to claim 1, characterized in that, The slurry preparation, molding, and sintering steps are also included and are as follows: (1) The core-shell structure composite powder of step S4 is mixed with an organic carrier system, which is composed of a solvent, a binder, a plasticizer and a dispersant, the solvent is a mixture of alpha-terpineol and anhydrous ethanol with a purity of 99.5%, the mass ratio is 7:3, the binder is polyvinyl butyral PVB, the plasticizer is dibutyl phthalate DBP, the composite powder and the organic carrier system are ball-mixed in a planetary ball mill at a low speed of 120 revolutions per minute for 36 hours, until a uniform and stable slurry with a viscosity of 20±2 Pa·s at a temperature of 25°C is formed; wherein a typical slurry formula is: the core-shell structure composite powder accounts for 60% by mass percentage, and the organic carrier system accounts for 40%; in the organic carrier system, the solvent accounts for 75%, the binder accounts for 20%, the plasticizer accounts for 4%, and the dispersant accounts for 1%; (2) The slurry is formed into a flexible green ceramic tape with a thickness of 120±5 microns by using a doctor blade with a gap setting of 250 microns to flow on the polyester film base at a speed of 0.4 meters per minute by using a flow casting process; (3) The green ceramic tape is stacked and hot-pressed according to the circuit design to form a multilayer ceramic body; (4) The body is placed in a sintering furnace for degassing treatment at a temperature range of 300 to 500°C with a heating rate of 0.5-3°C / min to completely remove the organic carrier components, and then the temperature is raised to the final sintering temperature of 850 to 950°C at a heating rate of 2-5°C / min and kept for 1 to 3 hours to complete the densification sintering process, and finally the high-frequency low-loss LTCC material is obtained.

8. The method for preparing high-frequency low-loss LTCC material by external doping means according to claim 1, characterized in that, The ceramic main powder is composed of 55% by mass fraction of alpha phase alumina and 45% by mass fraction of calcium borosilicate glass after high-energy ball milling and grinding.

9. The method for preparing high-frequency low-loss LTCC material by external doping means according to claim 1, characterized in that, When the dopant compound is zinc oxide ZnO, the first precursor vapor is diethyl zinc vapor, and the second reactant gas is water vapor.

10. The method for preparing high-frequency low-loss LTCC material by external doping means according to claim 6, characterized in that, The multi-component dopant coating layer is a silicon oxide / boron oxide composite doping layer, the first precursor vapor for depositing silicon oxide SiO2 is bis-diethylaminosilane vapor, the first precursor vapor for depositing boron oxide B2O3 is tri-dimethylaminoborane, and the second reactant gas of the two dopants is oxygen plasma, and by repeating the basic unit of "1 SiO2 atomic layer deposition cycle + 2 B2O3 atomic layer deposition cycles", a borosilicate glass coating layer formed by mixing SiO2 and B2O3 is formed on the surface of the ceramic main powder particles.