High orientation degree hexagonal ferrite thick film and hot-pressing preparation method thereof

Abstract

The present application belongs to the field of ferrite thick film preparation, and particularly relates to a high orientation degree hexagonal ferrite thick film and a hot-pressing preparation method thereof. The present application aims at the problem that high orientation degree and high density of the hexagonal ferrite thick film are difficult to be realized simultaneously, and proposes a two-step hot-pressing sintering method to improve the orientation degree of the thick film. The low-temperature hot-pressing magnetic field orientation process and the high-temperature hot-pressing sintering process are organically combined to form a two-step hot-pressing sintering method for preparing the high-orientation and dense BaFe 12 O 19 thick film. The electromagnet and the heating plate in the low-temperature hot-pressing magnetic field orientation equipment are combined in a discrete manner, which effectively improves the stability of the magnetic field and is beneficial to the improvement of the orientation degree of the thick film.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of ferrite thick film preparation, and particularly relates to a high orientation degree hexaferrite thick film and a hot-pressing preparation method thereof. BACKGROUND

[0002] With the rapid development of communication and micro-radar technology, miniaturization and integration of signal transmitting and receiving systems are important development trends. M-type hexaferrite is one of the key materials for realizing communication circulators and micro-electromechanical systems, and promoting planarization and miniaturization of devices, due to its intrinsic magnetocrystalline anisotropy and moderate saturation magnetization. Hexaferrite thick film is an important method for realizing self-biased circulators and monolithic integrated microwave circuit devices.

[0003] Common processes for preparing ferrite thick films include screen printing and tape casting. In order to meet the high orientation characteristics of hexaferrite thick films, the thick film needs to be subjected to magnetic field orientation during the printing process. The magnetic field orientation process can be divided into dry magnetic field orientation and wet magnetic field orientation. The method of directly applying a magnetic field during powder pressing is dry magnetic field forming. The traditional wet magnetic field orientation steps are as follows: first, a slurry is formed by mixing the powder with additives such as binders and leveling agents, and then the slurry is placed in a magnetic field for orientation forming. The thick film prepared by the wet magnetic field forming method has a high orientation degree, but the thick film has many pores, which affects the microwave performance of the thick film.

[0004] Hot-pressing sintering is one of the common methods for preparing dense ceramics (AlN and SiC, etc.). Pressureless sintering technology can improve the density of ceramics by adding a cosolvent, but it will introduce impurities, which will damage other properties of the ceramics, such as thermal conductivity, mechanical properties and magnetic properties. Therefore, the hot-pressing sintering process is a suitable method for preparing dense and highly oriented hexaferrite thick films. The traditional hot-pressing sintering process is a sintering method in which the dried powder is placed in a mold, and then pressure and heat are applied from a single axis direction to make the forming and sintering occur simultaneously. The application of pressure at high temperature is beneficial to the rearrangement of particles, promotes the transmission of atoms between grains, and improves the diffusion coefficient, ultimately achieving the densification of the sample. Compared with conventional solid-phase sintering, the hot-pressing sintering process requires a lower sintering temperature, and the sample density after sintering is higher. SUMMARY

[0005] The existing technology has the following disadvantages:

[0006] 1. Traditional thick film processes such as screen printing and tape casting are difficult to prepare highly oriented and dense hexaferrite thick films.

[0007] 2. No external pressure in wet field orientation process. This results in difficulty to further increase the thick film density. In order to obtain high orientation thick film, wet field orientation process is usually used. Wet field orientation makes more porosity in thick film. After high temperature sintering, it is difficult to further increase the thick film density. Low density thick film is not good for further improving the device performance (insertion loss).

[0008] 3. Difficulty to stabilize the magnetic field for a long time in wet field orientation. This results in difficulty to further increase the thick film orientation. In traditional wet field orientation equipment, high temperature resistant samarium cobalt magnet is usually selected as the magnetic field source. At 200℃, the magnetism of samarium cobalt magnet reduces more, which results in difficulty to rotate the grains in thick film. This is not good for thick film orientation.

[0009] In order to solve the above technical problems, the present application provides the following technical solutions:

[0010] The present application provides a hot-pressing preparation method of high orientation degree hexaferrite thick film, comprising the following steps:

[0011] S1: ball milling the hexaferrite particles after solid phase sintering to obtain hexaferrite powder;

[0012] S2: mixing the hexaferrite particles and additives to obtain thick film slurry after smearing on the substrate; the additives comprise curing agent, epoxy resin, tributyl citrate, terpineol and castor oil;

[0013] S3: under the orientation magnetic field, the thick film slurry is subjected to pressure and heating, and then cooled to obtain hexaferrite thick film; the strength of the orientation magnetic field is 5000-15000 Oe, the temperature of pressure and heating is 200-500℃, and the pressure is 2-15 MPa;

[0014] S4: after high temperature hot-pressing sintering of the hexaferrite thick film, cooling to room temperature (25±5℃) to obtain the high orientation degree hexaferrite thick film; the temperature of high temperature hot-pressing sintering is 1000-1200℃, and the pressure is 100-500 MPa.

[0015] Preferably, in the step S1, the particle size of the hexaferrite powder is 100-1000 nm.

[0016] Preferably, the hexaferrite particles are selected from M-type hexaferrite material and W-type hexaferrite material.

[0017] Preferably, the mass ratio of the curing agent, epoxy resin, tributyl citrate, terpineol and castor oil is 45-55:12-18:3-9:19-27:3-8.

[0018] Further, the mass ratio of the curing agent is 45%-55%, the mass ratio of the epoxy resin is 12%-18%, the mass ratio of the tributyl citrate is 3%-9%, the mass ratio of the terpineol is 19%-27%, and the mass ratio of the castor oil is 3%-8%.

[0019] Preferably, in the step S2, the substrate is placed in a low-temperature heating mold after being coated.

[0020] Preferably, in the step S3, the time of pressure heating is 0.5-15 min.

[0021] Preferably, in the step S3, the orientation magnetic field is applied by an electromagnet connected to a direct current power supply.

[0022] Further, in the step S3, the pressure is reduced by rotating the knobs on both sides of the electromagnet to reduce the distance between the magnetic poles of the electromagnet.

[0023] Preferably, in the step S4, the time of high-temperature hot-pressing sintering is 15-120 min.

[0024] Preferably, in the step S4, the high-temperature hot-pressing sintering is performed by applying high-temperature pressure by an alumina column and a press.

[0025] Specifically, the hot-pressing preparation method of the high-orientation degree hexaferrite thick film comprises the following steps:

[0026] 1. Mechanical ball milling of the solid-phase sintered hexaferrite particles to obtain powder particles of different particle sizes. The hexaferrite composition is M-type and W-type hexaferrite material.

[0027] 2. Mixing the hexaferrite powder with additives to form a slurry with certain fluidity and adhesion. The binder and organic solvent play important roles in the slurry, and the appropriate proportion makes the slurry have certain fluidity and viscosity. The slurry with appropriate viscosity and fluidity is helpful for the orientation of the hexaferrite thick film. The types and proportions of the curing agent and the organic solvent in the additive are determined as follows: curing agent: epoxy resin: tributyl citrate: terpineol: castor oil = 50wt%: 16wt%: 7wt%: 23wt%: 4wt%.

[0028] 3. Spinning the hexaferrite slurry on the substrate to form a thick film slurry, and placing it in a low-temperature heating mold. Then, the low-temperature heating mold plate with the thick film slurry is placed in the magnetic field area of the electromagnet.

[0029] 4. Turning on the direct current power supply of the electromagnet to apply different sizes of orientation magnetic field. The magnetic field size is: 5000 Oe to 15000 Oe.

[0030] 5. Set the heating program of the low-temperature heating mold, and heat the thick film paste in the mold. The heating temperature is 200-500 DEG C.

[0031] 6. The knobs on both sides of the rotating electromagnet reduce the magnetic pole spacing of the electromagnet, and pressurize the thick film in the low-temperature heating mold. The pressure is 2-15 MPa.

[0032] 7. Keep the above magnetic field, temperature and pressure for a certain time. The time is 0.5-15 minutes. Turn off the DC power supply and the temperature control power supply in turn, and release the pressure. After cooling, take out the hexaferrite thick film sample. End the low-temperature magnetic field hot pressing step.

[0033] 8. High-temperature magnetic field hot pressing step: put the hexaferrite thick film into the muffle furnace, set the temperature control program, and apply high-temperature pressure with the alumina column and the press. Perform high-temperature hot pressing sintering. The sintering temperature range is 1000-1200 DEG C. The holding time is 15-120 minutes. The pressure range is 100-500 MPa.

[0034] 9. End the high-temperature hot step, cool the heating furnace to room temperature, and take out the hexaferrite thick film.

[0035] The application also provides a high-orientation hexaferrite thick film prepared by the above-mentioned hot pressing preparation method of high-orientation hexaferrite thick film.

[0036] The technical scheme of the application has the following advantages compared with the prior art:

[0037] The application proposes a two-step hot pressing sintering method to improve the orientation degree of the thick film in view of the difficulty in simultaneously achieving high orientation degree and high density of the hexaferrite thick film.

[0038] 1. The low-temperature hot pressing magnetic field orientation process and the high-temperature hot pressing sintering process are organically combined to form a two-step hot pressing sintering method for preparing high-orientation and dense BaFe 12 O 19 thick film.

[0039] 2. The low-temperature hot pressing magnetic field orientation equipment independently built by the application introduces mechanical pressure parallel to the magnetic field direction, which effectively reduces the porosity of the thick film before high-temperature sintering. This is beneficial to the improvement of the density of the thick film.

[0040] 3. The electromagnet and the heating plate in the low-temperature hot pressing magnetic field orientation equipment adopt a discrete combination mode. This mode effectively improves the stability of the magnetic field, which is beneficial to the improvement of the orientation degree of the thick film. DETAILED DESCRIPTION

[0041] Figure 1 It is a flow chart of the two-step hot pressing sintering method for preparing the hexaferrite thick film.

[0042] Figure 2 BaFe 12 O 19 XRD of thick film.

[0043] Figure 3 BaFe 12 O 19 Cross-sectional view of thick film.

[0044] Figure 4 BaFe 12 O 19 Magnetization curve of thick film out-of-plane and in-plane.

[0045] Figure 5 BaFe 12 O 19 Magnetic hysteresis loop of thick film out-of-plane. DETAILED DESCRIPTION

[0046] The present application will be further described with reference to the drawings and specific examples, so that those skilled in the art can better understand the present application and implement it.

[0047] Example 1

[0048] (1) The solid-phase sintered M-type hexaferrite material particles were mechanically ball-milled to obtain powder particles of different sizes.

[0049] (2) The hexaferrite powder was mixed with additives to form a slurry having a certain fluidity and cohesiveness. In the additives, the solidifying agent: epoxy resin: tributyl citrate: terpineol: castor oil = 50wt%: 16wt%: 7wt%: 23wt%: 4wt%.

[0050] (3) The hexaferrite slurry was spin-coated on a substrate to form a thick film slurry, and was placed in a low-temperature heating mold. Subsequently, the low-temperature heating mold plate with the thick film slurry was placed in the magnetic field region of an electromagnet.

[0051] (4) The direct current power supply of the electromagnet was turned on to apply an orientation magnetic field with a magnetic field strength of 10,000 Oe.

[0052] (5) The heating program of the low-temperature heating mold was set to heat the thick film slurry in the mold to 350°C.

[0053] (6) The knobs on both sides of the electromagnet were rotated to reduce the distance between the magnetic poles of the electromagnet, and pressure was applied to the thick film in the low-temperature heating mold. The pressure was 8 MPa.

[0054] (7) The above magnetic field, temperature and pressure are maintained for 8 minutes. The direct current power and the temperature control power are turned off in sequence, and the pressure is released. After cooling, the hexaferrite thick film sample is removed, and the low temperature magnetic field hot pressing step is completed.

[0055] (8) High temperature magnetic field hot pressing step: The hexaferrite thick film is placed in a muffle furnace, and a temperature control program is set. High temperature pressure is applied using an alumina column and a press, and high temperature hot pressing sintering is performed. During high temperature hot pressing sintering, the sintering temperature range is 1100°C, the holding time is 60 minutes, and the pressure is 300 MPa.

[0056] (9) The high temperature hot step is completed, the heating furnace is cooled to room temperature, and the hexaferrite thick film is removed.

[0057] Example 2

[0058] (1) The solid phase sintered M-type hexaferrite material particles are mechanically ball milled to obtain powder particles of different particle sizes.

[0059] (2) The hexaferrite powder is mixed with additives to form a slurry with certain fluidity and cohesiveness. In the additives, the solidifying agent: epoxy resin: tributyl citrate: terpineol: castor oil = 50wt%: 16wt%: 7wt%: 23wt%: 4wt%.

[0060] (3) The hexaferrite slurry is spin-coated on the substrate to form a thick film slurry, and is placed in a low temperature heating mold. Subsequently, the low temperature heating mold plate with the thick film slurry is placed in the magnetic field area of the electromagnet.

[0061] (4) The direct current power of the electromagnet is turned on, and an orientation magnetic field with a magnetic field strength of 15000 Oe is applied.

[0062] (5) The heating program of the low temperature heating mold is set, and the thick film slurry in the mold is heated to 500°C.

[0063] (6) The knobs on both sides of the electromagnet are rotated to reduce the distance between the magnetic poles of the electromagnet, and pressure is applied to the thick film in the low temperature heating mold. The pressure is 15 MPa.

[0064] (7) The above magnetic field, temperature and pressure are maintained for 15 minutes. The direct current power and the temperature control power are turned off in sequence, and the pressure is released. After cooling, the hexaferrite thick film sample is removed, and the low temperature magnetic field hot pressing step is completed.

[0065] (8) High temperature magnetic field hot pressing step: The hexaferrite thick film is placed in a muffle furnace, and a temperature control program is set. High temperature pressure is applied using an alumina column and a press, and high temperature hot pressing sintering is performed. During high temperature hot pressing sintering, the sintering temperature range is 1200°C, the holding time is 120 minutes, and the pressure is 500 MPa.

[0066] (9) End the high temperature heat step, cool the furnace to room temperature, and take out the hexaferrite thick film.

[0067] Example 3

[0068] (1) Mechanically ball mill the solid phase sintered M-type hexaferrite material particles to obtain powder particles of different sizes.

[0069] (2) Mix the hexaferrite powder with additives to form a slurry with certain fluidity and cohesiveness. In the additives, the solidifying agent: epoxy resin: tributyl citrate: terpineol: castor oil = 50wt%: 16wt%: 7wt%: 23wt%: 4wt%.

[0070] (3) Spin the hexaferrite slurry on the substrate to form a thick film slurry, and place it in a low temperature heating mold. Then, place the low temperature heating mold plate with the thick film slurry in the magnetic field area of the electromagnet.

[0071] (4) Turn on the direct current power supply of the electromagnet to apply an orientation magnetic field with a magnetic field strength of 5000 Oe.

[0072] (5) Set the heating program of the low temperature heating mold to heat the thick film slurry in the mold to 200°C.

[0073] (6) Rotate the knobs on both sides of the electromagnet to reduce the distance between the magnetic poles of the electromagnet, and apply pressure to the thick film in the low temperature heating mold. The pressure is 2 MPa.

[0074] (7) Maintain the above magnetic field, temperature and pressure for 0.5 minutes. Turn off the direct current power supply and the temperature control power supply in turn, and release the pressure. After cooling, take out the hexaferrite thick film sample, and end the low temperature magnetic field hot pressing step.

[0075] (8) High temperature magnetic field hot pressing step: place the hexaferrite thick film in a muffle furnace, set the temperature control program, and apply high temperature pressure with an alumina column and a press. During high temperature hot pressing sintering, the sintering temperature range is 1000°C, the holding time is 15 minutes, and the pressure is 100 MPa.

[0076] (9) End the high temperature heat step, cool the furnace to room temperature, and take out the hexaferrite thick film.

[0077] Effect evaluation 1

[0078] Figure 1 Among them, (a) is ball milling, (b) is slurry mixing, (c) is low temperature hot pressing orientation, and (d) is high temperature hot pressing sintering.

[0079] The present application uses BaFe 12 O 19hexaferrite BaFe 12 O 19 hexaferrite thick film, the results are shown as follows. Figures 2 to 5

[0080] The above results show that:

[0081] hexaferrite BaFe 12 O 19 The c-axis out-of-plane peaks (006), (008) and (0012) are dominant in the XRD pattern of the hexaferrite thick film, which indicates a good crystal orientation.

[0082] The SEM image shows that the grains have a good c-axis uniform orientation, which is consistent with the XRD Figure 1 results.

[0083] hexaferrite BaFe 12 O 19 The hexaferrite thick film has a very high remanence ratio (M R / M s = 0.92).

[0084] The above results show that the hexaferrite thick film BaFe 12 O 19 prepared by the two-step hot-pressing sintering method has a good potential for self-bias high-frequency electronic device applications.

[0085] Obviously, the above examples are merely illustrative for the sake of clarity and are not intended to limit the embodiments. Based on the above description, other different forms of changes or variations can be made by those of ordinary skill in the art. It is not necessary or possible to exhaust all embodiments. The obvious changes or variations derived therefrom are still within the protection scope of the present invention.​

Claims

1. A hot-pressing method for preparing a high orientation degree hexaferrite thick film, characterized in that, The method comprises the following steps: S1: ball-milling the sintered hexaferrite particles to obtain hexaferrite powder; S2: mixing the hexaferrite powder and additives to obtain thick film paste, wherein the additives comprise curing agent, epoxy resin, tributyl citrate, terpineol and castor oil; S3: applying pressure and heating the thick film paste in an orientation magnetic field to obtain hexaferrite thick film, wherein the strength of the orientation magnetic field is 5000-15000 Oe, the temperature of the pressure and heating is 200-500℃, and the pressure is 2-15 MPa; S4: high-temperature hot-pressing sintering the hexaferrite thick film and cooling to room temperature to obtain the high orientation degree hexaferrite thick film, wherein the temperature of the high-temperature hot-pressing sintering is 1000-1200℃, and the pressure is 100-500 MPa; The hexaferrite particles are selected from M-type hexaferrite material and W-type hexaferrite material; the mass ratio of the curing agent, epoxy resin, tributyl citrate, terpineol and castor oil is 45-55:12-18:3-9:19-27:3-8; in the step S3, the orientation magnetic field is applied by electromagnet connected with direct current power supply, and the pressure is applied by rotating the knobs on both sides of the electromagnet to reduce the distance between the magnetic poles of the electromagnet.

2. The hot-pressing method for preparing a high degree of orientation hexaferrite thick film according to claim 1, wherein In the step S2, the paste is placed in a low-temperature heating mold after being applied on the substrate.

3. The hot-pressing method for preparing a high-oriented hexaferrite thick film according to claim 1, wherein the step of hot-pressing is performed at a temperature of 800 to 950°C. In the step S3, the time of the pressure and heating is 0.5-15 min.

4. The hot-pressing method for preparing a high-oriented hexaferrite thick film according to claim 1, wherein the step of hot-pressing is performed at a temperature of 800 to 950°C. In the step S4, the time of the high-temperature hot-pressing sintering is 15-120 min.

5. The hot-pressing method for preparing a high-oriented hexaferrite thick film according to claim 1, wherein the step of hot-pressing is performed at a temperature of 800- 1,000°C and a pressure of 5-20 MPa for 1-10 minutes. In the step S4, the high-temperature hot-pressing sintering is applied by alumina column and pressure machine.

6. The high orientation degree hexaferrite thick film prepared by the hot-pressing method of the high orientation degree hexaferrite thick film according to any one of claims 1-5.

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