A low-k microwave dielectric ceramic with positive resonant frequency temperature coefficient and its preparation method

Abstract

The present invention discloses a low-k dielectric microwave ceramic with a positive resonant frequency temperature coefficient and a preparation method thereof. 12 O 19 The preparation method of the present invention is simple, and the dielectric constant (ε r ) is 14.0~15.5, the quality factor (Q×f) is 35000~115000 GHz, and the resonant frequency temperature coefficient (τ f ) is +60.0 ppm / ℃~+68.0 ppm / ℃.

Description

Technical Field

[0001] The present invention relates to a microwave dielectric ceramic material for manufacturing microwave components such as ceramic substrates, resonators and filters used at microwave frequencies and a preparation method thereof, belonging to the technical field of microwave dielectric ceramic materials. Background Art

[0002] Microwave dielectric ceramics (MWDC) refer to ceramics used as dielectric materials in microwave frequency band (300 MHz-300 GHz) circuits, fulfilling one or more functions such as microwave waveguiding, shielding, and resonance. They are key materials for the manufacture of microwave devices such as microwave dielectric resonators, filters, and dielectric antennas. They are currently widely used in modern communications, military radar, navigation, electronic countermeasures, automotive anti-collision radar systems, Global Positioning Systems (GPS), Bluetooth technology, and wireless local area networks (WLAN). The three main performance indicators for microwave dielectric materials are dielectric constant, quality factor, and resonant frequency temperature coefficient. With the development of 5G / 6G communication technology, the high frequency and wide bandwidth characteristics require more densely populated macro and micro base stations to ensure full signal coverage, which will inevitably create huge market demand for microwave dielectric ceramic materials and components (dielectric antennas, dielectric filters, and substrates). At the same time, as communication frequencies and device integration continue to increase, signal delays will become more pronounced, heat generation due to system losses will also increase significantly, and device thermal stability will gradually deteriorate. Therefore, materials with low dielectric constants (ε) are urgently needed. r <20) to reduce time delay and high quality factor (Q×f), that is, low loss to improve frequency selection characteristics and device loss and heat generation, and also need to have high temperature stability, that is, near-zero resonant frequency temperature coefficient (τ f ) to reduce signal drift. However, most of the single-phase low-pass (ε r <20) Ceramics usually exhibit a large negative τ f Value (-20 ~ -80 ppm / o C), there is a lack of single-phase low-dielectric material systems that can meet the performance requirements. For example, the ε r The Q×f value ranges from 22000 to 270000 GHz, but it shows a large negative τ f value (-61 ~ -67ppm / °C); ε of cubic spinel (Zn / Mg)Al2O4 ceramics r is between 8.5 and 9.0, and the Q×f value can reach 56000 ~ 100000 GHz, but its τ f A relatively negative value of -70 to 80 ppm / °C; cubic garnet Y3Al5O 12 With low εr (~10.5), high Q×f value (~440000 GHz) and large negative τ f Value (~-60 ppm / °C); ε of clinopyroxene structure CaMgSi2O6 ceramics r The lowest is 7.6, and the Q×f value can be as high as 120000 GHz, but τ f The value is -66 ppm / °C; the ε of wolframite structure (Mg / Zn) WO4 ceramics r is between 10 and 13.5, the Q×f value can reach 62800 GHz, τ f The value range is -30~-64 ppm / °C.

[0003] To adjust the resonant frequency temperature coefficient (τ f ) is close to zero to ensure the thermal stability of microwave components. The main method currently used is to add high dielectric constant materials with large positive resonant frequency temperature coefficients (such as CaTiO3 or TiO2) for material composite, but this method usually results in the dielectric constant (ε r ) significantly increases and the quality factor (Q×f) decreases. Therefore, there is an urgent need to explore and develop single-phase, low-K microwave dielectric ceramics with a positive resonant frequency temperature coefficient and low loss to mitigate existing single-phase, low-K microwave dielectric ceramic materials with a large negative resonant frequency temperature coefficient. To address these issues, the present invention provides a low-K microwave dielectric ceramic with a positive resonant frequency temperature coefficient and a method for preparing the same. Summary of the Invention

[0004] To address the above-mentioned issues, the present invention provides a compound for use in preparing a low-K dielectric microwave ceramic with a positive resonant frequency temperature coefficient. The low-K dielectric microwave ceramic with a positive resonant frequency temperature coefficient of the present invention has a low dielectric constant and a high quality factor, and the resonant frequency temperature coefficient ranges from +60ppm / °C to +68ppm / °C.

[0005] In order to achieve the above-mentioned purpose, the present invention provides a low-dielectric microwave dielectric ceramic with a positive resonant frequency temperature coefficient, wherein the low-dielectric microwave dielectric ceramic is composed of a chemical formula of SrGa 12 O 19 The compound was prepared.

[0006] Preferably, the dielectric constant (ε r ) is 14.0 ~ 15.5, the quality factor (Q×f) is 35000 ~ 115000 GHz, the resonant frequency temperature coefficient (τ f) is +60.0ppm / ℃ ~ +68.0ppm / ℃.

[0007] Furthermore, the present invention also provides a method for preparing the low-K microwave dielectric ceramic having a positive resonant frequency temperature coefficient, comprising the following steps:

[0008] (1) Weigh the raw material powders of SrCO3 and Ga2O3 and mix them according to the chemical formula of SrGa 12 O 19 The ingredients are prepared in a stoichiometric ratio, mixed evenly with a dispersion medium, and then subjected to a first wet ball milling process, followed by drying and pre-firing to obtain pre-fired ceramic powder;

[0009] (2) The pre-fired ceramic powder obtained in step (1) is mixed evenly with a dispersion medium and then subjected to a second wet ball milling process. After drying, a binder is added to granulate the powder, and the powder is pressed and sintered to obtain the low-k microwave dielectric ceramic.

[0010] Preferably, the dispersion medium for the first wet ball milling treatment and the second wet ball milling treatment is 200 wt% deionized water, the ball milling medium is zirconium balls, the ball milling speed is 360 r / min, and the ball milling time is 4 to 12 h.

[0011] Preferably, in step (1), the pre-firing temperature is 1200-1300°C, and the pre-firing time is 4-12 hours.

[0012] Preferably, in step (2), the adhesive is PVA (polyvinyl alcohol), and the mass fraction of the adhesive is 4 to 10%.

[0013] Preferably, in step (2), the sintering temperature is 1350-1500°C, and the sintering time is 4-12 hours.

[0014] The beneficial effects of the present invention are:

[0015] The present invention uses the chemical formula SrGa 12 O 19 The compound is used to prepare a low dielectric constant microwave dielectric ceramic with a positive resonant frequency temperature coefficient, wherein the dielectric constant (ε r ) is between 14.0 and 15.5, the quality factor (Q×f) is between 35000 and 115000 GHz, and the resonant frequency temperature coefficient (τ f ) is between +60.0 ppm / ℃ and +68.0ppm / ℃.

[0016] Positive resonant frequency temperature coefficient can be used to adjust the currently common microwave dielectric ceramic materials with negative resonant frequency temperature coefficient to ensure the thermal stability of microwave components. The low dielectric constant characteristic increases the transmission rate of electrical signals in microwave dielectric ceramic materials. High Q×f value is conducive to improving frequency selection characteristics and reducing loss and heat generation. Especially in the field of low dielectric constant materials, there is no resonant frequency temperature coefficient (τ f ) is a positive number of the existing technology, the related products designed by the present invention fill the technical gap in the relevant field, and are used to adjust the resonant frequency temperature coefficient (τ) of other low-k microwave dielectric ceramics through a composite method. f ) close to zero, thus providing a new technical solution to ensure the thermal stability of microwave components. Furthermore, the microwave dielectric ceramics produced by the method proposed in this invention are single-phase microwave dielectric ceramics that do not contain easily variable valence elements, are not easily deliquescent, have a stable crystal structure, and are suitable for mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The low-k microwave dielectric ceramic SrGa with positive resonant frequency temperature coefficient prepared in Examples 1-9 of the present invention 12 O 19 Preparation flow chart of

[0018] Figure 2 The low-k microwave dielectric ceramic SrGa prepared in Example 5 of the present invention 12 O 19 X-ray diffraction (XRD) patterns;

[0019] Figure 3 The low-K microwave dielectric ceramic SrGa prepared in Example 5 of the present invention 12 O 19 Scanning electron microscope (SEM) surface morphology;

[0020] Figure 4 The low-K microwave dielectric ceramic SrGa prepared in Example 5 of the present invention 12 O 19 XRD refinement diagram and crystal structure diagram;

[0021] Figure 5 The low-K microwave dielectric ceramic SrGa prepared in Example 5 of the present invention 12 O 19 High-resolution transmission electron microscopy image. DETAILED DESCRIPTION

[0022] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] Example 1

[0024] This embodiment provides a method for preparing a low-K microwave dielectric ceramic having a positive resonant frequency temperature coefficient, comprising the following steps:

[0025] (1) SrCO3 and Ga2O3 with a purity of 99.99% were respectively 12 O 19 After uniformly mixing the stoichiometric ratio of the raw materials and the raw materials, the powders were mixed and stirred in a ball mill at a speed of 360 r / min for 6 h using zirconium balls as the ball milling medium and deionized water (200 wt%) as the dispersion medium. The obtained slurry was dried and pre-calcined at 1200 °C for 4 h to obtain pre-calcined ceramic powder.

[0026] (2) Deionized water dispersion medium (200 wt%) was added to the pre-fired ceramic powder obtained in step (1) and wet ball milled. After drying, 4 wt% PVA binder was added to the dried powder for granulation. The pellets were pressed under a pressure of 200 MPa into cylindrical green specimens with a thickness to diameter ratio of 0.4 to 0.6. After tableting, the pellets were sintered in air at 1350°C for 4 h. The properties of the microwave dielectric ceramics obtained are shown in Table 1.

[0027] Examples 2 to 9

[0028] The only difference between Examples 2 to 9 and Example 1 is that the pre-firing temperature and time when preparing the pre-firing ceramic powder in step (1) are different, the mass fraction of the binder in step (2) is different, and the sintering temperature and time of the sintering process are different. The other steps are basically the same as those in Example 1 and will not be repeated here. The properties of the obtained microwave dielectric ceramics are shown in Table 1:

[0029] Table 1 Properties of low-k microwave dielectric ceramics obtained in Examples 1 to 9

[0030]

[0031] From the data in Table 1, it can be seen that the SrGa prepared by the present invention 12 O 19 Microwave dielectric ceramics have positive resonant frequency temperature coefficient, low dielectric constant and excellent quality factor. r ) is 14.0 ~ 15.5, excellent quality factor (Q×f) is 35000 ~ 115000 GHz, positive resonant frequency temperature coefficient (τ f ) is +60ppm / ℃ ~ +68ppm / ℃. In addition, the SrGa prepared by the present invention 12 O 19The physical phase of microwave dielectric ceramics is single phase, the relative density reaches more than 90%, does not contain easily variable valence elements, is not easy to deliquesce, has a stable crystal structure and is suitable for mass production.

[0032] Figure 1 The low-k microwave dielectric ceramic SrGa with positive resonant frequency temperature coefficient prepared in Examples 1-9 of the present invention 12 O 19 Preparation flow chart of .

[0033] Figure 2 The low-k microwave dielectric ceramic SrGa with positive resonant frequency temperature coefficient prepared in Example 5 of the present invention 12 O 19 X-ray diffraction (XRD) spectrum of SrGa 12 O 19 The physical phase of microwave dielectric ceramics is pure hexagonal phase of magnetoplumbite structure, which is similar to SrGa 12 O 19 The PDF card PDF # 01-082-0712 matches.

[0034] Figure 3 The low-K microwave dielectric ceramic SrGa prepared in Example 5 of the present invention 12 O 19 The SEM scanning electron microscope image shows that the prepared ceramic has uniform grain size, dense structure and no obvious pores and second phases.

[0035] Figure 4 The low-K microwave dielectric ceramic SrGa prepared in Example 5 of the present invention 12 O 19 The Rietveld XRD refinement diagram and crystal structure diagram. SrGa low dielectric microwave ceramic with positive resonant frequency temperature coefficient 12 O 19 The crystal structure is composed of salt rock layers and spinel layers stacked along the c-axis.

[0036] Figure 5 The low-K microwave dielectric ceramic SrGa prepared in Example 5 of the present invention 12 O 19 High-resolution transmission electron microscopy image.

[0037] In summary, the present invention provides a low-dielectric microwave dielectric ceramic with a positive resonant frequency temperature coefficient, wherein the dielectric constant (ε r ) is 14.0 ~ 15.5, the quality factor (Q×f ) is 35000 ~ 115000GHz, the resonant frequency temperature coefficient (τ f) is +60.0 ppm / °C to +68.0 ppm / °C. A positive resonant frequency temperature coefficient can be used to adjust the currently common microwave dielectric ceramic materials with negative resonant frequency temperature coefficients to ensure the thermal stability of microwave components. The low dielectric constant improves the transmission rate of electrical signals in microwave dielectric ceramic materials, and a high Q×f value helps reduce losses. The microwave dielectric ceramic produced by the method proposed in this invention has a single-phase phase composition, is free of easily variable valence elements, is non-deliquescent, has a stable crystal structure, and is suitable for mass production.

[0038] The above content is a further detailed description of the present invention in combination with specific preferred embodiments. It cannot be determined that the specific embodiments of the present invention are limited to these. For ordinary technicians in the technical field to which the present invention belongs, they can make several simple deductions or substitutions without departing from the concept of the present invention, which should be regarded as falling within the scope of patent protection determined by the claims submitted by the present invention.

Claims

1. A low-k microwave dielectric ceramic with a positive resonant frequency temperature coefficient, characterized in that: The low dielectric microwave ceramic is composed of a chemical formula of SrGa 12 O 19 The dielectric constant (ε r ) ranges from 14.0 to 15.5, the quality factor (Q×f) ranges from 35000 to 115000 GHz, and the resonant frequency temperature coefficient (τ f ) is +60ppm / °C to +68ppm / °C, and the preparation method of the low-K microwave dielectric ceramic comprises the following steps: (1) Weigh the raw material powders of SrCO3 and Ga2O3 and mix them according to the chemical formula of SrGa 12 O 19 The ingredients are prepared in a stoichiometric ratio, mixed evenly with a dispersion medium, and then subjected to a first wet ball milling process, followed by drying and pre-firing to obtain pre-fired ceramic powder; (2) The pre-fired ceramic powder obtained in step (1) is mixed evenly with a dispersion medium and then subjected to a second wet ball milling process. After drying, a binder is added to granulate the powder, and the powder is pressed and sintered to obtain the low-k microwave dielectric ceramic.

2. The method for preparing low-k microwave dielectric ceramics according to claim 1, characterized in that: The dispersion medium for the first wet ball milling treatment and the second wet ball milling treatment is 200% by mass of deionized water, the ball milling medium is zirconium balls, the ball milling speed is 360 r / min, and the ball milling time is 4 to 12 hours.

3. The method for preparing low-k microwave dielectric ceramics according to claim 1, wherein: In step (1), the pre-firing temperature is 1200-1300°C, and the pre-firing time is 4-12 hours.

4. The method for preparing low-k microwave dielectric ceramics according to claim 1, characterized in that: In step (2), the adhesive is PVA, and the mass fraction of the adhesive is 4 to 10%.

5. The method for preparing low-K microwave dielectric ceramics according to claim 1, wherein: In step (2), the sintering temperature is 1350 to 1500°C, and the sintering time is 4 to 12 hours.

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