CN104446376B - Ultralow dielectric microwave dielectric ceramic Li2TiB4O9And preparation method thereof - Google Patents

Abstract

The invention discloses a temperature-stable ultra-low dielectric constant microwave dielectric ceramic Li ₂ TiB ₄ O ₉ capable of low-temperature sintering and a preparation method thereof. (1) Weigh the original powder of Li ₂ CO ₃ , TiO ₂ and H ₃ BO ₃ with a purity of 99.9% (weight percent) or more according to the composition of Li ₂ TiB ₄ O ₉ ; (2) Mix the ingredients in step (1) The raw materials were mixed by wet ball milling for 12 hours, the ball milling medium was anhydrous ethanol, and after drying, they were pre-fired for 12 hours in the atmosphere at 700°C; (3) After adding a binder to the powder prepared in step (2) and granulating, Then press molding, and finally sintering in the atmosphere at 800-840°C for 10 hours; the binder uses a polyvinyl alcohol solution with a mass concentration of 5%, and the amount of polyvinyl alcohol added accounts for 3% of the total mass of the powder. The ceramic prepared by the invention is well sintered, the dielectric constant reaches 8.3-8.7, its quality factor Qf value is as high as 85000-127000 GHz, and the temperature coefficient of resonance frequency is small, so it has great application value in industry.

Description

Ultra-low dielectric constant microwave dielectric ceramic Li2TiB4O9 and its preparation method

technical field

The invention relates to a dielectric ceramic material, in particular to a dielectric ceramic material for manufacturing microwave components such as ceramic substrates, resonators and filters used in microwave frequencies and a preparation method thereof.

Background technique

Microwave dielectric ceramics refer to ceramics that are used as dielectric materials in circuits in the microwave frequency band (mainly UHF and SHF bands) and perform one or more functions. They are widely used as resonators, filters, and dielectric substrates in modern communications. Components such as chips and dielectric waveguide circuits are the key basic materials of modern communication technology. They have been used in portable mobile phones, car phones, cordless phones, TV satellite receivers and military radars. They are used in modern communication tools. It is playing an increasingly important role in the process of miniaturization and integration.

Dielectric ceramics used in the microwave frequency band should meet the following requirements for dielectric properties: (1) Serialized dielectric constant ε _r to meet the requirements of different frequencies and different applications; (2) High quality factor Q value or low The dielectric loss tanδ to reduce noise, generally requires Qf≥3000 GHz; (3) The temperature coefficient τ _ƒ of the resonant frequency should be as small as possible to ensure good thermal stability of the device, generally requiring -10 ppm /℃≤τ _ƒ ≤ +10 ppm/°C. Internationally, since the late 1930s, some people have tried to apply dielectric materials to microwave technology, and prepared TiO ₂ microwave dielectric filters, but the temperature coefficient τ _ƒ of its resonant frequency is too large to be practical. Since the 1970s, a large-scale development of dielectric ceramic materials has begun. According to the relative permittivity ε _r and the frequency band used, the microwave dielectric ceramics that have been developed and are being developed can usually be divided into 4 categories: kind.

(1) Ultra-low dielectric constant microwave dielectric ceramics, mainly represented by Al ₂ O ₃ -TiO ₂ , Y ₂ BaCuO ₅ , MgAl ₂ O ₄ and Mg ₂ SiO ₄ , etc., whose ε _r ≤ 20, quality factor Q× f≥50000GHz, τ _ƒ ≤10 ppm/°C. Mainly used for microwave substrates and high-end microwave components.

(2) Microwave dielectric ceramics with low ε _r and high Q value, mainly BaO-MgO-Ta ₂ O ₅ , BaO-ZnO-Ta ₂ O ₅ or BaO-MgO-Nb ₂ O ₅ , BaO-ZnO-Nb ₂ O ₅ system or composite system MWDC materials between them. Its ε _r =20～35, Q=(1～2)×10 ⁴ (at f≥10 GHz), τ _ƒ ≈0. It is mainly used as a dielectric resonator device in microwave communication devices such as satellite broadcasting with f≥8 GHz.

(3) Microwave dielectric ceramics with medium ε _r and Q value, mainly MWDC materials based on BaTi ₄ O ₉ , Ba ₂ Ti ₉ O ₂₀ and (Zr, Sn) TiO ₄ , whose ε _r = 35~ 45, Q=(6~9)×10 ³ (at f=3~-4GHz), τ _ƒ ≤5 ppm/°C. It is mainly used as a dielectric resonant device in microwave military radar and communication systems in the frequency range of 4-8 GHz.

(4) Microwave dielectric ceramics with high ε _r and low Q value are mainly used in civil mobile communication systems in the frequency range of 0.8-4GHz, which is also the focus of research on microwave dielectric ceramics. Since the 1980s, Kolar, Kato and others have successively discovered and studied perovskite-like tungsten bronze BaO—Ln ₂ O ₃ —TiO ₂ series (Ln=La, Sm, Nd or Pr, etc., referred to as BLT series), composite calcium Titanite structure CaO—Li ₂ O—Ln ₂ O ₃ —TiO ₂ series, lead-based series materials, Ca _1-x Ln _2x/3 TiO ₃ series and other high ε _r microwave dielectric ceramics, among which BaO—Nd of BLT system The dielectric constant of ₂ O ₃ —TiO ₂ materials reaches 90, and the dielectric constant of lead-based series (Pb, Ca)ZrO ₃ reaches 105.

Since the three performance indicators of microwave dielectric ceramics (ε _r and Q f and τ _ƒ ) are mutually restrictive (see literature: The restrictive relationship between the dielectric properties of microwave dielectric ceramic materials, Zhu Jianhua, Liang Fei, Wang Xiaohong , Lu Wenzhong, Electronic Components and Materials, Issue 3, March 2005), there are very few single-phase microwave dielectric ceramics that meet the three performance requirements, mainly because their resonant frequency temperature coefficient is usually too large or the quality factor is too low to be able to Practical application requirements. At present, most of the research on microwave dielectric ceramics is a summary of experience obtained through a large number of experiments, but there is no complete theory to explain the relationship between microstructure and dielectric properties. Predict the microwave dielectric properties such as the resonant frequency temperature coefficient and quality factor, explore and develop a series of microwaves with different dielectric constants with near-zero resonant frequency temperature coefficient (-10 ppm/℃≤τ _ƒ ≤+10ppm/℃) and high quality factor Dielectric ceramics is a difficult problem that those skilled in the art have been eager to solve but have been seldom successful, which largely limits the development of microwave dielectric ceramics and devices.

Contents of the invention

The object of the present invention is to provide an ultra-low dielectric constant microwave dielectric ceramic material with good thermal stability and low loss and a preparation method thereof.

The chemical composition of the microwave dielectric ceramic material of the present invention is Li ₂ TiB ₄ O ₉ .

The preparation method steps of this microwave dielectric ceramic material are:

(1) The raw powders of Li ₂ CO ₃ , TiO ₂ and H ₃ BO ₃ with a purity of more than 99.9% (weight percent) were weighed and dosed according to the composition of Li ₂ TiB ₄ O ₉ .

(2) Mix the raw materials in step (1) by wet ball milling for 12 hours. The ball milling medium is anhydrous ethanol. After drying, pre-calcine in the atmosphere at 700°C for 12 hours.

(3) Add a binder to the powder prepared in step (2) and granulate it, then press and shape it, and finally sinter it in the atmosphere at 800-840°C for 10 hours; the binder is used at a mass concentration of 5 % polyvinyl alcohol solution, the amount of polyvinyl alcohol added accounts for 3% of the total mass of the powder.

The advantages of the present invention: Li ₂ TiB ₄ O ₉ ceramics have a low sintering temperature, a dielectric constant of 8.3 to 8.7, a small temperature coefficient τ _ƒ of its resonance frequency, and good temperature stability; the quality factor Qf value is as high as 85000-127000 GHz, and can be widely used It is used in the manufacture of microwave devices such as various dielectric substrates, resonators and filters, and can meet the technical needs of low-temperature co-firing technology and microwave multilayer devices, and has great application value in industry.

detailed description

Example:

Table 1 shows three specific examples of different sintering temperatures constituting the present invention and their microwave dielectric properties. The preparation method is as above, and the microwave dielectric performance is evaluated by the cylindrical dielectric resonator method.

The ceramics can be widely used in the manufacture of microwave devices such as various dielectric substrates, resonators and filters, and can meet the technical needs of mobile communication and satellite communication systems.

Table 1:

Claims (1)

1. a low temperature sintering temperature-stable ultralow dielectric microwave dielectric ceramic, is characterized in that described microwave is situated betweenThe chemical composition of electroceramics is: Li₂TiB₄O₉；

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

(1) be 99.9%(percentage by weight by purity) above Li₂CO₃、TiO₂And H₃BO₃Starting powder press Li₂TiB₄O₉'sComposition weigh batching;

(2) by step (1) raw material wet ball-milling mix 12 hours, ball-milling medium is absolute ethyl alcohol, after oven dry 700 DEG C of pre-burnings 12Hour;

(3) in the powder making in step (2), add after binding agent granulation, more compressing, finally at 800 ~ 840 DEG C of atmosphereSintering 10 hours in atmosphere; Described binding agent adopts the poly-vinyl alcohol solution that mass concentration is 5%, and polyvinyl alcohol addition accounts for3% of powder gross mass.