Large-size high-dielectric-constant gyromagnetic ferrite substrate and preparation method thereof

Abstract

The invention relates to the technical field of electronic materials, in particular to a large-size high-dielectric-constant gyromagnetic ferrite substrate and a preparation method thereof.The preparation method comprises the following steps that S1, high-dielectric-constant Bi-YIG gyromagnetic ferrite powder and an additive are subjected to ball milling and mixing to prepare tape casting slurry; s2, defoaming the tape casting slurry, and carrying out tape casting to obtain a Bi-YIG gyromagnetic ferrite raw ceramic material strip; s3, cutting and laminating the raw ceramic material belt, performing hot isostatic pressing by using a warm isostatic press to obtain a raw ceramic blank sheet, and performing cold isostatic pressing on the raw ceramic blank sheet by using a cold isostatic press to obtain a compact raw ceramic blank sheet; and S4, stacking a plurality of the compact green ceramic pieces, placing Bi-YIG gyromagnetic ferrite polishing substrates with the same size as the green ceramic pieces between every two layers of compact green ceramic pieces as clamping pieces for separation, placing Bi-YIG gyromagnetic ferrite polishing cover pieces at the top ends, and finally placing the stacked green ceramic pieces on a setter plate.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic materials, and in particular to a large-size high-dielectric-constant gyromagnetic ferrite substrate and a preparation method thereof. Background Art

[0002] Gyromagnetic ferrite substrates, also known as microwave ferrite substrates, are a key material used in the manufacture of microwave devices. They are typically made from materials with gyromagnetic properties, with garnet ferrite and spinel ferrite being the most widely used. These materials exhibit unique gyromagnetic and microwave properties at microwave frequencies, making gyromagnetic substrates widely useful in microwave devices. In the field of microwave communications, gyromagnetic substrates are crucial components of devices such as circulators and isolators, which perform signal transmission, isolation, and reflection in microwave communication systems. Furthermore, high-power circulators, ferrite switches, and phase shifters play a vital role in phased array radar systems, navigation and positioning systems, and remote control and telemetry systems, with gyromagnetic ferrite substrates providing the necessary microwave device support. In the current environment of rapid microwave technology development, the design of electronic devices must meet the requirements of increasingly smaller size, wider operating bandwidth, and higher safety and stability. High-dielectric-constant gyromagnetic ferrites can improve circuit stability, reduce signal attenuation and distortion during transmission, better filter noise and interference signals in communication systems, improve filter performance, and enhance signal clarity and stability. In addition, when electromagnetic waves propagate within ferrite components, their wavelength is inversely proportional to the square root of the ferrite material's dielectric constant, while the size of ferrite components is directly proportional to the wavelength of the electromagnetic wave. Therefore, increasing the dielectric constant of ferrite materials to reduce device size is one of the important ways to achieve device miniaturization.

[0003] In the manufacturing of microwave devices such as circulators and isolators, the designed circuits are usually printed in batches on high-dielectric-constant gyromagnetic ferrite substrates, then punched and filled, and finally divided into independent substrate units with printed circuits for subsequent welding and assembly.

[0004] In addition, certain special devices also require large-scale, high-dielectric-constant gyromagnetic ferrite substrates for assembly. Therefore, the size and specifications of these high-dielectric-constant gyromagnetic ferrite substrates can have a serious impact on the efficiency and cost of microwave device production. Currently, a high-dielectric-constant Bi-YIG gyromagnetic ferrite substrate used in microwave devices is mainly produced by traditional compression molding followed by sintering. However, due to the limitations of traditional compression molding process characteristics, it is impossible to produce larger-sized substrates, resulting in reduced microwave device production efficiency and increased production costs. However, when Bi-YIG gyromagnetic ferrite is tape-casted, the size range of the gyromagnetic ferrite green ceramic sheets can be adjusted greatly. Therefore, large-sized gyromagnetic ferrite substrates of 2 inches, 4 inches, and above can be sintered to meet the production and manufacturing needs of microwave devices. In addition, the thickness of the molded substrate is relatively large, and often cutting and polishing are required to meet the thickness requirements, which increases the production cost of the substrate. The tape-casting method not only allows the production of large-sized substrates, but also has the advantage of being able to adjust the thickness of the substrate, reducing the production cost of Bi-YIG gyromagnetic ferrite substrates.

[0005] CN106747391A discloses a method for preparing a circulator substrate based on a tape casting process, which belongs to the field of electronic materials technology. The present invention comprises the following steps: 1. Main material formula: using Y 3-x Ca x Sn x Fe 5-x O 12 , x = 0.06; 2. Primary ball milling; 3. Pre-sintering: Pre-sintering at 1000°C–1200°C for 1–3 hours; 4. Doping: Adding the following additives: 0.2 wt% Bi₂O₃, 0.10 wt% BaTiO₃; 5. Secondary ball milling: Adding 40–50 wt% organic binder and 40–50 wt% anhydrous ethanol to the powder and milling for 4–8 hours; 6. Tape casting: The slurry is tape-casted to produce a green film tape with a thickness of 100–120 μm; 7. Lamination: Depending on the required thickness, the green film tape is laminated into 8–15 layers and pressed under 6 MPa; 8. Sintering: Sintering at 1360–1440°C in air for 4 hours. This method can produce smooth and flat ferrite dielectric substrates for circulators of varying thicknesses, exhibiting X-band performance, good temperature stability, low linewidth, and low dielectric loss. However, this method only prepares ferrite dielectric substrates of different thicknesses for garnet ferrite, and does not mention the size and how to prepare large-size spinmagnetic ferrite substrates.

[0006] CN115925404A discloses a YIG ferrite substrate and its preparation method, particularly relating to a microwave gyromagnetic YIG ferrite substrate and its preparation method, and a microstrip circulator / isolator. The preparation method comprises the following steps: S1, obtaining gyromagnetic YIG ferrite powder; S2, preparing the powder into a casting slurry and then casting to obtain a cast film; S3, punching and laminating the cast film, and pre-pressing to form a green porcelain block; S4, pressing the pre-pressed green porcelain block to form a dense green porcelain block; S5, cutting, debinding, and sintering the dense green porcelain block to obtain a microwave gyromagnetic YIG ferrite substrate. The preparation method provided by the present invention can realize the recovery of waste materials generated during the punching and cutting process, thereby effectively reducing production and development costs. However, this invention only prepares large-sized raw porcelain blocks, which are then cut into small-sized raw porcelain blocks for sintering, and does not prepare large-sized ferrite substrates, which does not meet the current demand for large-sized spin-magnetic ferrite substrates at the microwave device production end. Summary of the Invention

[0007] The purpose of the present invention is to provide a large-scale high dielectric constant gyromagnetic ferrite substrate and a preparation method thereof, so as to solve the technical problem of the consistency of electromagnetic properties of different regions of large-scale high dielectric constant Bi-YIG gyromagnetic ferrite substrate in the prior art.

[0008] The present invention discloses a method for preparing a large-sized high-dielectric-constant gyromagnetic ferrite substrate, comprising the following steps: S1. The high dielectric constant Bi-YIG spin magnetic ferrite powder and additives were ball-milled to prepare a tape-casting slurry; S2 the casting slurry defoaming, after casting to obtain Bi-YIG spin magnetic ferrite green porcelain tape; S3. The green porcelain strips are cut and laminated, and then hot isostatic pressing is performed using a warm isostatic press to obtain green porcelain sheets, followed by cold isostatic pressing of green porcelain sheets to obtain dense green porcelain sheets; S4. The dense green porcelain sheets are stacked in multiple pieces, and between each layer of dense green porcelain sheets are placed Bi-YIG spin magnetic ferrite polished substrates of the same size as green porcelain sheets as clips to separate them, and Bi-YIG spin magnetic ferrite polished cover sheets are placed on top, and finally the stacked green porcelain sheets are placed on the firing plate; S6. Place the stacked green ceramic sheets into a sintering furnace for debinding and sintering to obtain a high dielectric constant Bi-YIG gyromagnetic ferrite substrate.

[0009] By placing a Bi-YIG spin-magnetic ferrite polishing substrate, adhesion during sintering can be prevented, and at the same time, the surface composition of the green ceramic sheets after sintering can be changed by using substrates or powders of other components to separate them. In addition, a Bi-YIG spin-magnetic ferrite polishing cover sheet of the same size as the green ceramic sheets is placed on the top of the stack of green ceramic sheets.

[0010] Furthermore, the particle size D50 of the high dielectric constant Bi-YIG gyromagnetic ferrite powder is 0.5-2.5 μm.

[0011] Furthermore, the additives include solvents, dispersants, binders and plasticizers.

[0012] Furthermore, the solvent is 7-18% by mass of butanone and 7-18% by mass of anhydrous ethanol; the dispersant is 0.4-1.2% by mass of castor oil; the binder is 5-15% by mass of polyvinyl butyral; and the plasticizer is 2-8% by mass of dioctyl phthalate.

[0013] Furthermore, the Bi-YIG ferrite powder is first mixed with a solvent and a dispersant for a first ball milling, and then a binder and a plasticizer are added for a second ball milling, and then a uniform Bi-YIG ferrite casting slurry is prepared. The first ball milling time is 5 to 12 hours, and the second ball milling time is 12 to 24 hours.

[0014] Furthermore, the defoaming is achieved by a vacuum mixer.

[0015] Furthermore, in step S2, the thickness of the Bi-YIG gyromagnetic ferrite green tape is 50-200 μm.

[0016] Furthermore, the hot isostatic pressing conditions are: temperature of 50-75° C., pressure of 5-60 MPa, and holding time of 5-30 minutes after reaching the predetermined pressure.

[0017] Furthermore, the cold isostatic pressing conditions are: room temperature, pressure 100-300 MPa, and holding time after reaching a predetermined pressure is 10-30 minutes.

[0018] Furthermore, the heating time of the debinding stage is 12h~36h, and the temperature is kept at 400~500℃ for 3~8h. The heating time of the sintering stage is 12h~60h, and the temperature is kept at 880~1500℃ for 4~60h.

[0019] Furthermore, the setter plate is made of alumina, and the surface roughness parameter is 0.4-0.9 μm.

[0020] Furthermore, the Bi-YIG gyromagnetic ferrite polishing substrate has a surface roughness parameter of 0.05-0.2 μm and a thickness of 0.4-1.2 mm.

[0021] Furthermore, the Bi-YIG gyromagnetic ferrite polished cover sheet has a surface roughness parameter of 0.05-0.2 μm, a thickness of 1.0-2.0 mm, and the same size as the green porcelain sheet.

[0022] Furthermore, the number of stacked layers of the green porcelain sheets is 3-8 layers.

[0023] A large-sized high-dielectric-constant gyromagnetic ferrite substrate is prepared using the method.

[0024] Compared with the prior art, the present invention has the following beneficial effects: 1. The traditional molding method for preparing high-dielectric-constant Bi-YIG spin-magnetic ferrite blocks has significant limitations, preventing the production of larger or thinner blocks. However, the present invention utilizes a tape-casting process to laminate green ceramic sheets, resulting in a wide and controllable thickness range. This reduces the cost of cutting and polishing high-dielectric-constant Bi-YIG spin-magnetic ferrite blocks produced by traditional molding methods. 2. The present invention designs a corresponding tape casting slurry formula for high dielectric constant Bi-YIG gyromagnetic ferrite powder, which can produce Bi-YIG gyromagnetic ferrite green tape with a thickness of 50-200 μm; 3. The present invention uses a green ceramic sheet forming method that combines warm isostatic pressing and cold isostatic pressing to improve the density of the green ceramic sheet and the density of the sintered substrate. The prepared high dielectric constant Bi-YIG spin-magnetic ferrite substrate has uniform grain distribution and significantly reduced porosity defects compared to high dielectric constant Bi-YIG spin-magnetic ferrite substrates prepared by traditional molding methods. 4. The present invention stacks multiple layers of high-dielectric-constant Bi-YIG gyromagnetic ferrite green sheets and places polished Bi-YIG gyromagnetic ferrite substrates of the same size as the green sheets between the green sheets. This effectively prevents the high-dielectric-constant Bi-YIG gyromagnetic ferrite from sticking together during sintering. It also avoids changes in the surface composition of the green sheets after sintering caused by using substrates or powders made of other materials, thereby reducing substrate warpage and improving production efficiency. 5. For mass production of miniaturized microwave devices, circuit printing is required on substrates. Large-scale, high-dielectric-constant Bi-YIG gyromagnetic ferrite substrates allow for the printing of more circuit units at once, which can then be cut and divided into components, reducing production costs. Large-scale, high-dielectric-constant Bi-YIG gyromagnetic ferrite substrates are also required for direct assembly in some microwave devices. Furthermore, due to the physical properties of high-dielectric-constant Bi-YIG gyromagnetic ferrite, large-scale sintered blocks prepared by the molding method exhibit significant differences in electromagnetic properties in different regions after sintering. However, in this embodiment, different regions of the large-scale, high-dielectric-constant Bi-YIG gyromagnetic ferrite substrate exhibit uniform electromagnetic properties, which is beneficial for device applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only represent some embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0026] Figure 1 Schematic diagram of multi-layer stacking and sintering of high dielectric constant Bi-YIG gyromagnetic ferrite substrates in Example 1 of the present invention. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0028] Example 1 This embodiment discloses a large-sized high dielectric constant gyromagnetic ferrite substrate and a preparation method thereof, comprising the following steps: S1. High-dielectric-constant Bi-YIG ferrite powder was mixed with 15% by mass of butanone, 15% by mass of anhydrous ethanol, and 1% by mass of castor oil. The mixture was ball-milled for 5-12 hours on a planetary ball mill. 10% polyvinyl butyral and 5% dioctyl phthalate were then added, and the mixture was ball-milled again for 12-24 hours to produce a uniform high-dielectric-constant Bi-YIG ferrite tape-casting slurry. S2. The casting slurry was defoamed by a vacuum mixer and then cast on a casting machine with a thickness of 100 μm Bi-YIG spin magnetic ferrite green porcelain tape; S3. Cut the green porcelain strip, select 12 layers of green porcelain membranes, and stack them. Then, hot isostatic pressing (HIP) is performed on a warm isostatic press to produce green porcelain sheets. The HIP conditions are: temperature 60°C, pressure 20 MPa, and holding time at the desired pressure for 20 minutes. S4. The green porcelain sheet after hot pressing was cold pressed using a cold isostatic press to obtain a denser green porcelain sheet. The cold isostatic pressing conditions were: pressure 200MPa, holding time 10min; S5 the dense green porcelain sheet is cut, the size of the cut green porcelain sheet is 125 mm; S6. The above-mentioned cut green porcelain sheets are stacked in multiple layers, with the number of stacking layers being 4. A Bi-YIG spin-magnetic ferrite polished substrate with the same size as the green porcelain sheet, a thickness of 0.5 mm and a surface roughness of 0.1 μm is placed between each layer of green porcelain sheets as a sandwich plate for separation, and a Bi-YIG spin-magnetic ferrite polished cover sheet with the same size as the green porcelain sheet, a thickness of 1.5 mm and a surface roughness of 0.1 μm is placed on the top of the stacked green porcelain sheets. Finally, the stacked green porcelain sheets are placed on an alumina support plate, and the surface roughness parameter of the support plate is 0.9 μm.

[0029] S7. Place the stacked green ceramic sheets and the support plate into a sintering furnace for debinding and sintering. During the debinding stage, the green ceramic sheets are heated for 12 hours and held at 550°C for 6 hours. During the sintering stage, the green ceramic sheets are heated for 24 hours and held at 1100°C for 20 hours, thereby obtaining a 2-inch high-dielectric-constant Bi-YIG gyromagnetic ferrite substrate.

[0030] Comparative Example 1: The difference between this comparative example and Example 1 is only the additive content of the casting slurry, including the solvent content, binder content and plasticizer content. The results of the green porcelain tape cast by the prepared slurry are shown in Table 1 below.

[0031] Table 1

[0032] It can be seen from Table 1 that changes in the proportion of additive content will directly affect the quality of the cast green porcelain tape. In Comparative Example 1, when the content of the solvent, binder, and plasticizer changed to a level outside the formulation of the present invention, the green porcelain tape cracked and its quality deteriorated significantly, making it unusable for the next process.

[0033] Comparative Example 2: The difference between this comparative example and Example 1 is that the S3 isostatic pressing method is different, namely, only hot isostatic pressing, only cold isostatic pressing, and only changing the cold isostatic pressing pressure in the two isostatic pressings from 200 MPa to 50 MPa. The results of the substrates prepared after molding are shown in Table 2 below.

[0034] Table 2

[0035] Table 2 shows that when hot isostatic pressing alone is used to form the green ceramic sheets, the density of the sintered substrate is lower than that of Example 1, and its flexural strength is significantly lower than that of Example 1. When cold isostatic pressing alone is used, the forming temperature does not reach the glass transition temperature of the binder, preventing a dense connection between the green ceramic sheets. This results in a loose bond between the green ceramic sheets and delamination of the sintered substrate, making it unusable. In Comparative Example 2, when cold isostatic pressing is performed at a pressure of 50 MPa, the density and flexural strength of the sintered substrate are almost the same as those of the sintered substrate formed using hot isostatic pressing alone, due to the lower pressure. The sintered substrate of Example 1 has significantly higher density and flexural strength.

[0036] Comparative Example 3: The difference between this comparative example and Example 1 is that there is only one S5 green ceramic sheet, which is not stacked or covered, but is directly placed on a setter for sintering.

[0037] Table 3

[0038] The warpage performance of Example 1 and Comparative Example 3 is compared. In Example 1, 1#, 2#, 3# and 4# respectively represent Figure 1 As shown in Table 3 above, the four green ceramic sheets from top to bottom show that by stacking multiple layers of high-dielectric-constant Bi-YIG gyromagnetic ferrite green sheets and covering them with a Bi-YIG gyromagnetic ferrite substrate, the warpage of the stacked green sheets after sintering is around one thousandth, which is significantly smaller than that of a substrate sintered with only a single layer. This significantly improves the efficiency and yield of producing large-scale high-dielectric-constant Bi-YIG gyromagnetic ferrite substrates.

[0039] Comparative Example 4 The difference between this comparative example and Example 1 is that S6 uses alumina powder to spread between each layer of green porcelain sheets for separation, and the Bi-YIG spin-magnetic ferrite polishing cover sheet at the top of the stacked green porcelain sheets is changed to an alumina cover sheet, and then sintered according to the sintering method of Example 1 to obtain a Bi-YIG spin-magnetic ferrite substrate.

[0040] Comparative Example 5 The difference between this comparative example and Example 1 is that the Bi-YIG gyromagnetic ferrite cover sheet placed between each layer of green porcelain sheets of S6 and the topmost sheet is not polished and has a roughness of 1.2 μm. The Bi-YIG gyromagnetic ferrite substrate is then sintered according to the sintering method of Example 1.

[0041] Table 4

[0042] From Comparative Example 4 in Table 4, it can be found that the conventional use of alumina powder as a substrate interlayer results in residual alumina particles on the substrate after sintering, resulting in a rough substrate surface and compositional segregation in the sintered substrate, which affects the surface performance of the substrate and requires the surface layer to be removed before use. Comparative Example 5, due to the use of an unpolished, rough Bi-YIG gyromagnetic ferrite substrate as an interlayer, results in a rough sintered substrate surface and adhesion. The sintered substrate surface obtained using the method of the present invention is smoother, has no adhesion, and is of good substrate quality, saving costs for subsequent processing.

[0043] Comparative Example 6 A method for preparing a high-dielectric-constant Bi-YIG gyromagnetic ferrite substrate differs from Example 1 in that: a 12 wt% PVA solution is added to high-dielectric-constant Bi-YIG gyromagnetic ferrite powder, the mixture is uniformly mixed, and the mixture is granulated through a 40-mesh sieve to obtain a granulated powder. The granulated powder is then placed in a 125 mm x 125 mm square mold and pressed into a green ceramic block using a hydraulic press. The green ceramic block is then debinded and sintered according to step S6 of Example 1 to obtain a dense high-dielectric-constant Bi-YIG gyromagnetic ferrite block. The gyromagnetic ferrite block is then wire-cut to obtain a 2-inch substrate.

[0044] Table 5

[0045] Comparing the electromagnetic properties of Example 1 and Comparative Example 6, as shown in Table 5 above, it can be found that the saturation magnetization intensity and ferromagnetic resonance linewidth of the high dielectric constant Bi-YIG gyromagnetic ferrite substrate prepared by the traditional molding method are greatly different in the central area and the edge area of ​​the substrate, and the electromagnetic performance of the central area is deteriorated. However, the electromagnetic performance of different areas of the high dielectric constant Bi-YIG gyromagnetic ferrite substrate obtained by the method of the present invention is uniform, thereby improving the yield rate.

[0046] The above are the implementation methods listed in this embodiment, but this embodiment is not limited to the above optional implementation methods. Those skilled in the art can arbitrarily combine the above methods to obtain other various implementation methods. Anyone can derive other various forms of implementation methods based on the inspiration of this embodiment. The above specific implementation methods should not be understood as limiting the scope of protection of this embodiment. The scope of protection of this embodiment shall be based on the definition in the claims, and the description can be used to interpret the claims.

Claims

1. A method for preparing a large-scale high-dielectric-constant gyromagnetic ferrite substrate, characterized in that: The following steps are involved: S1. The high dielectric constant Bi-YIG spin magnetic ferrite powder and additives were ball-milled to prepare a tape-casting slurry; S2 the casting slurry defoaming, after casting to obtain Bi-YIG spin magnetic ferrite green porcelain tape; S3. The green porcelain strips are cut and laminated, and then hot isostatic pressing is performed using a warm isostatic press to obtain green porcelain sheets, followed by cold isostatic pressing of green porcelain sheets to obtain dense green porcelain sheets; S4. The dense green porcelain sheets are stacked in multiple pieces, and between each layer of dense green porcelain sheets are placed Bi-YIG spin magnetic ferrite polished substrates of the same size as green porcelain sheets as clips to separate them, and Bi-YIG spin magnetic ferrite polished cover sheets are placed on top, and finally the stacked green porcelain sheets are placed on the firing plate; S6. Place the stacked green ceramic sheets into a sintering furnace for debinding and sintering to obtain a high dielectric constant Bi-YIG gyromagnetic ferrite substrate.

2. The method for preparing a large-scale high dielectric constant gyromagnetic ferrite substrate according to claim 1, characterized in that: The particle size D50 of the high dielectric constant Bi-YIG gyromagnetic ferrite powder is 0.5-2.5 μm.

3. The method for preparing a large-scale high dielectric constant gyromagnetic ferrite substrate according to claim 1, characterized in that: The additives include solvents, dispersants, binders and plasticizers.

4. The method for preparing a large-scale high dielectric constant gyromagnetic ferrite substrate according to claim 3, characterized in that: The solvent is 7-18% by mass of butanone and 7-18% by mass of anhydrous ethanol; the dispersant is 0.4-1.2% by mass of castor oil; the binder is 5-15% by mass of polyvinyl butyral; and the plasticizer is 2-8% by mass of dioctyl phthalate.

5. The method for preparing a large-scale high dielectric constant gyromagnetic ferrite substrate according to claim 1, characterized in that: In step S2, the thickness of the Bi-YIG gyromagnetic ferrite green ceramic tape is 50-200 μm.

6. The method for preparing a large-scale high-dielectric-constant gyromagnetic ferrite substrate according to claim 1, characterized in that: The hot isostatic pressing conditions are: temperature at 50-75°C, pressure at 5-60 MPa, and holding time at the predetermined pressure of 5-30 minutes; the cold isostatic pressing conditions are: temperature at room temperature, pressure at 100-300 MPa, and holding time at the predetermined pressure of 10-30 minutes.

7. The method for preparing a large-scale high dielectric constant gyromagnetic ferrite substrate according to claim 1, characterized in that: The heating time of the debinding stage is 12h~36h, and the temperature is kept at 400~500℃ for 3~8h. The heating time of the sintering stage is 12h~60h, and the temperature is kept at 880~1500℃ for 4~60h.

8. The method for preparing a large-scale high dielectric constant gyromagnetic ferrite substrate according to claim 1, characterized in that: The Bi-YIG ferrite polishing substrate has a surface roughness parameter of 0.05-0.2 μm and a thickness of 0.4-1.2 mm. The Bi-YIG ferrite polishing cover has a surface roughness parameter of 0.05-0.2 μm and a thickness of 1.0-2.0 mm. The size is the same as that of the green porcelain sheet.

9. The method for preparing a large-scale high dielectric constant gyromagnetic ferrite substrate according to claim 1, characterized in that: The setter plate is made of alumina, and the surface roughness parameter is 0.4-0.9 μm.

10. A large-sized high dielectric constant gyromagnetic ferrite substrate, characterized in that: The invention is prepared by using the method for preparing a large-sized high dielectric constant gyromagnetic ferrite substrate according to any one of claims 1 to 9.

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