CN104446377A - Temperature stable microwave dielectric ceramic LiZn2B3O7 and its preparation method - Google Patents

Abstract

The invention discloses a temperature stable ultra-low dielectric constant microwave dielectric ceramic LiZn ₂ B ₃ O ₇ and a preparation method thereof. (1) Weigh the original powder of Li ₂ CO ₃ , ZnO and H ₃ BO ₃ with a purity of 99.9% (weight percent) or more according to the composition of LiZn ₂ B ₃ O ₇ ; (2) Mix the raw materials in step (1) Wet ball milling and mixing for 12 hours, the ball milling medium is anhydrous ethanol, and after drying, it is pre-fired in the atmosphere at 800°C for 6 hours; (3) After adding a binder to the powder prepared in step (2) and granulating, then Compression molding, and finally sintering in the atmosphere at 850-890°C for 4 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 5.5-5.9, its quality factor Qf value is as high as 121000-147000 GHz, and the temperature coefficient of resonance frequency is small, so it has great application value in industry.

Description

Temperature stable microwave dielectric ceramics LiZn2B3O7 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 its resonant frequency temperature coefficient and quality factor and other microwave dielectric properties, explore and develop a series of different dielectrics with near-zero resonant frequency temperature coefficient (-10 ppm/℃≤τ _ƒ ≤+10 ppm/℃) and higher quality factor Constant microwave dielectric ceramics is a difficult problem that those skilled in the art have been eager to solve, but it has always been difficult to achieve success, which limits the development of microwave dielectric ceramics and devices to a large extent. We have studied the microwave dielectric properties of a series of compounds composed of LiZn ₂ B ₃ O ₇ , LiMg ₂ B ₃ O ₇ , LiCu ₂ B ₃ O ₇ , and LiNi ₂ B ₃ O ₇ , and found that their sintering temperature is lower than 900 ℃, of which only LiZn ₂ B ₃ O ₇ has near-zero resonant frequency temperature coefficient and high quality factor. The resonant frequency temperature coefficient τ _ƒ of LiMg ₂ B ₃ O ₇ ceramics is too large (respectively +17 ppm/℃) and cannot be used as a practical microwave dielectric ceramic; while LiCu ₂ B ₃ O ₇ and LiNi ₂ B ₃ O ₇ are Semiconductors whose dielectric loss is too large to be used as microwave dielectric ceramics.

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 LiZn ₂ B ₃ O ₇ .

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

(1) The raw powders of Li ₂ CO ₃ , ZnO and H ₃ BO ₃ with a purity of more than 99.9% (weight percent) were weighed and prepared according to the composition of LiZn ₂ B ₃ O ₇ .

(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 an atmosphere at 800°C for 6 hours.

(3) Add a binder to the powder prepared in step (2) and granulate it, then press it into shape, and finally sinter it in the air atmosphere at 850-890°C for 4 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.

Advantages of the present invention: the dielectric constant of LiZn ₂ B ₃ O ₇ ceramics reaches 5.5-5.9, the temperature coefficient τ _ƒ of its resonant frequency is small, and the temperature stability is good; the quality factor Qf value is as high as 121000-147000 GHz, and can be widely used in various The manufacture of microwave devices such as dielectric resonators and filters can meet the technical needs of low-temperature co-firing technology and microwave multilayer devices, and has great application value in industry.

Detailed ways

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 temperature-stable ultra-low dielectric constant microwave dielectric ceramic, characterized in that the chemical composition of the microwave dielectric ceramic is: LiZn ₂ B ₃ O ₇ ; The specific steps of the preparation method of the microwave dielectric ceramic are: (1) The raw powders of Li ₂ CO ₃ , ZnO and H ₃ BO ₃ with a purity of more than 99.9% (weight percent) are weighed according to the composition of LiZn ₂ B ₃ O ₇ ; (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-fire in the atmosphere at 800°C for 6 hours; (3) Add a binder to the powder prepared in step (2) and granulate it, then press it into shape, and finally sinter it in the air atmosphere at 850-890°C for 4 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.