CN104591701A - Temperature-stabilized type ultralow-dielectric-constant microwave dielectric ceramic Li2Mg5O6 and preparation method thereof - Google Patents

Abstract

The invention discloses a temperature-stabilized type ultralow-dielectric-constant microwave dielectric ceramic Li2Mg5O6 capable of being sintered at a low temperature and a preparation method thereof. The preparation method comprises the following steps: (1) weighing and mixing Li2CO3 and MgO original powder with the purity of more than 99.9% (weight percentage) according to the composition of Li2Mg5O6; (2) performing wet ball milling mixing on the raw materials of the step (1) for 12 hours by using a ball milling medium of anhydrous ethanol, drying, and then pre-burning in an air atmosphere of 800 DEG C for 6 hours; (3) adding a bonding agent into the powder prepared in the step (2), pelleting, then pressing for molding, and finally sintering in an air atmosphere of 850-900 DEG C for 4 hours, wherein the bonding agent is a polyvinyl alcohol solution with the mass concentration of 5%, and the added amount of polyvinyl alcohol accounts for 3% of the total mass of the powder. The ceramic prepared by the method disclosed by the invention is good in sintering, the dielectric constant of the ceramic reaches 7.5-7.9, the quality factor (Qf) value of the ceramic reaches 131000-167000GHz, and the temperature coefficient of resonance frequency is small, so that the ceramic has a great application value in industry.

Description

Temperature-stable ultralow dielectric microwave dielectric ceramic Li 2mg 5o 6and preparation method thereof

Technical field

The present invention relates to dielectric ceramic material, particularly relate to dielectric ceramic material of the microwave devices such as ceramic substrate, resonator and the wave filter used for the manufacture of microwave frequency and preparation method thereof.

Background technology

Microwave dielectric ceramic refers to and to be applied in microwave frequency band (mainly UHF and SHF frequency range) circuit as dielectric material and to complete the pottery of one or more functions, the components and parts such as resonator, wave filter, dielectric substrate and medium wave circuit are widely used as in modern communication, it is the key foundation material of modern communication technology, in portable mobile phone, automobile telephone, cordless telephone, telestar susceptor and military radar etc., there is very important application, in the miniaturization, integrated process of modern communication instrument, just playing increasing effect.

Be applied to the dielectric ceramic of microwave frequency band, the requirement of following dielectric characteristics should be met: (1) seriation DIELECTRIC CONSTANT ε _rto adapt to the requirement of different frequency and different application occasion; (2) high quality factor q value or low dielectric loss tan δ to reduce noise, general requirement Qf>=3000 GHz; (3) the temperature factor τ of resonant frequency _?little of as far as possible to ensure the thermostability that device has had, general requirement-10 ppm/DEG C≤τ _?≤+10 ppm/ DEG C.From late 1930s, just someone attempts dielectric substance to be applied to microwave technology in the world, and prepares TiO ₂microwave dielectric filter, but its temperature coefficient of resonance frequency τ _?too greatly cannot be practical.Since the seventies in last century, start the large-scale development to medium ceramic material, according to relative permittivity ε _rsize from use frequency range different, usually the microwave-medium ceramics be developed and developing can be divided into 4 classes.

(1) ultralow dielectric microwave dielectric ceramic, main representative is Al ₂o ₃-TiO ₂, Y ₂baCuO ₅, MgAl ₂o ₄and Mg ₂siO ₄deng, its ε _r≤ 20, quality factor q × f>=50000GHz, τ _?≤ 10 ppm/ ° C.Be mainly used in microwave base plate and high-end microwave device.

(2) low ε _rwith the microwave dielectric ceramic of high q-factor, mainly BaO-MgO-Ta ₂o ₅, BaO-ZnO-Ta ₂o ₅or BaO-MgO-Nb ₂o ₅, BaO-ZnO-Nb ₂o ₅system or the composite system MWDC material between them.Its ε _r=20 ~ 35, Q=(1 ~ 2) × 10 ⁴(under the GHz of f>=10), τ _?≈ 0.Be mainly used in the microwave communication equipments such as the direct broadcasting satellite of f >=8 GHz as dielectric resonance device.

(3) medium ε _rwith the microwave dielectric ceramic of Q value, mainly with BaTi ₄o ₉, Ba ₂ti ₉o ₂₀(Zr, Sn) TiO ₄deng the MWDC material for base, its ε _r=35 ~ 45, Q=(6 ~ 9) × 10 ³(under f=3 ~-4GHz), τ _?≤ 5 ppm/ ° C.Be mainly used in microwave military radar in 4 ~ 8 GHz range of frequency and communication system as dielectric resonance device.

(4) high ε _rand the microwave dielectric ceramic that Q value is lower, be mainly used in civilian mobile communcations system in 0.8 ~ 4GHz range of frequency, this is also the emphasis of microwave dielectric ceramic research.Since the eighties, the people such as Kolar, Kato in succession find and have studied perovskite-like tungsten bronze type BaO-Ln ₂o ₃-TiO ₂series (Ln=La, Sm, Nd or Pr etc. are called for short BLT system), complex perovskite structure CaO-Li ₂o-Ln ₂o ₃-TiO ₂series, lead base series material, Ca _1-xln _2x/3tiO ₃be contour ε _rmicrowave dielectric ceramic, the wherein BaO-Nd of BLT system ₂o ₃-TiO ₂material dielectric constant reaches 90, lead base series (Pb, Ca) ZrO ₃specific inductivity reaches 105.

The sintering temperature of these material systems is generally higher than 1300 ° of C above, directly can not burn formation laminated ceramic capacitor altogether with the low melting point metal electrode such as low-cost Ag and Cu.In recent years, along with LTCC Technology (Low Temperature Co-fired Ceramics, the requirement of development LTCC) and the development of microwave multilayer device, researchist both domestic and external has carried out exploring widely and studying to some low fever's system materials, mainly adopt devitrified glass or glassceramic composites system, because low melting glass has relatively high dielectric loss mutually, the existence of glassy phase substantially increases the dielectric loss of material.Therefore development is the emphasis of current research without the low fired microwave dielectric ceramic material of glassy phase.

Can in the process of low fired microwave dielectric ceramic materials in exploration and development of new, the material systems such as the Li based compound that intrinsic sintering temperature is low, Bi based compound, tungstate architecture compound and tellurate architecture compound get the attention and research, but due to three performance index (ε of microwave dielectric ceramic _rwith Qf and τ _f) between be that the relation of mutually restriction is (see document: the restricting relation between microwave dielectric ceramic materials dielectric properties, Zhu Jianhua, Liang Fei, Wang little Hong, Lv Wenzhong, electronic component and material, phase March the 3rd in 2005), meet three performance requriementss and the single-phase microwave-medium ceramics of low temperature sintering is considerably less, their temperature coefficient of resonance frequency is usually excessive or quality factor are on the low side and cannot production application.Current is the summary of experience drawn by great many of experiments to the research major part of microwave-medium ceramics, but complete theory is not had to set forth the relation of microtexture and dielectric properties, in theory also cannot predict its microwave dielectric property such as temperature coefficient of resonance frequency and quality factor from the composition of compound and structure, explore with exploitation can low-temperature sintering have again near-zero resonance frequency temperature coefficient (-10 ppm/DEG C≤τ _?≤+10 ppm/ DEG C) be that those skilled in the art thirst for solving always but are difficult to the difficult problem that succeeds all the time with the microwave dielectric ceramic of higher figure of merit.

We are to composition Li ₂mg ₅o ₆, Li ₂zn ₅o ₆, Li ₂cu ₅o ₆, Li ₂fe ₅o ₆series compound carried out the research of microwave dielectric property, find that their sintering temperature is lower than 950 DEG C, wherein only has Li ₂mg ₅o ₆there are near-zero resonance frequency temperature coefficient and high quality factor.Li ₂zn ₅o ₆the temperature coefficient of resonance frequency τ of pottery _?(being respectively+33 ppm/ DEG C) bigger than normal and cannot as practical microwave-medium ceramics; And Li ₂cu ₅o ₆, Li ₂fe ₅o ₆for semi-conductor, its dielectric loss too greatly cannot as microwave-medium ceramics.

Summary of the invention

The object of this invention is to provide one and there is good thermal stability and low-loss low temperature sintering ultralow dielectric microwave dielectric ceramic material and preparation method thereof simultaneously.

The chemical constitution of microwave dielectric ceramic material of the present invention is Li ₂mg ₅o ₆.

Preparation method's step of this microwave dielectric ceramic material is:

(1) be 99.9%(weight percent by purity) more than Li ₂cO ₃li is pressed with the starting powder of MgO ₂mg ₅o ₆composition weigh batching.

(2) step (1) raw material wet ball-milling is mixed 12 hours, ball-milling medium is dehydrated alcohol, pre-burning 6 hours in 800 DEG C of air atmosphere after oven dry.

(3) in the powder that step (2) is obtained, binding agent is added and after granulation, then compression moulding, finally in 850 ~ 900 DEG C of air atmosphere, sinter 4 hours; Described binding agent adopts mass concentration to be the polyvinyl alcohol solution of 5%, and polyvinyl alcohol addition accounts for 3% of powder total mass.

Advantage of the present invention: Li ₂mg ₅o ₆ceramic dielectric constant reaches 7.5 ~ 7.9, the temperature factor τ of its resonant frequency _?little, temperature stability is good; Quality factor q f value, up to 131000-167000GHz, can be widely used in the manufacture of the microwave devices such as various dielectric resonator and wave filter, can meet the technology needs of low temperature co-fired technology and microwave multilayer device, industrially have great using value.

Embodiment

Embodiment:

Table 1 shows 3 specific embodiments and microwave dielectric property thereof that form different sintering temperature of the present invention.Its preparation method is described above, carries out the evaluation of microwave dielectric property by cylindrical dielectric resonator method.

This pottery can be widely used in the manufacture of the microwave devices such as various medium substrate, resonator and wave filter, can meet the technology needs of the system such as mobile communication and satellite communications.

Table 1:

Claims (1)

1. a temperature-stable ultralow dielectric microwave dielectric ceramic, is characterized in that the chemical constitution of described microwave dielectric ceramic is: Li ₂mg ₅o ₆;

Preparation method's concrete steps of described microwave dielectric ceramic are:

(1) be 99.9%(weight percent by purity) more than Li ₂cO ₃li is pressed with the starting powder of MgO ₂mg ₅o ₆composition weigh batching;

(2) step (1) raw material wet ball-milling is mixed 12 hours, ball-milling medium is dehydrated alcohol, pre-burning 6 hours in 800 DEG C of air atmosphere after oven dry;

(3) in the powder that step (2) is obtained, binding agent is added and after granulation, then compression moulding, finally in 850 ~ 900 DEG C of air atmosphere, sinter 4 hours; Described binding agent adopts mass concentration to be the polyvinyl alcohol solution of 5%, and polyvinyl alcohol addition accounts for 3% of powder total mass.