Aluminum nitride ceramic and method of making and use thereof

Abstract

The application relates to the technical field of ceramic materials, in particular to an aluminum nitride ceramic and a preparation method and application thereof. The aluminum nitride ceramic comprises aluminum nitride mixture and diamond, the aluminum nitride mixture comprises aluminum nitride and yttrium oxide, the mass ratio of the aluminum nitride mixture and the diamond is (12-18):(1.6-4), and the mass content of the yttrium oxide is 1%-5% of the total mass of the aluminum nitride mixture. The aluminum nitride ceramic provided by the application uses yttrium oxide and diamond as sintering additives at a specific content ratio, on one hand, yttrium oxide reacts with aluminum oxide to generate yttrium aluminate liquid phase, so as to promote the densification of the sample, purify the aluminum nitride lattice and improve the thermal conductivity; on the other hand, the diamond improves the secondary phase problem generated by the reaction of the yttrium oxide and the aluminum oxide, and the diamond itself has extremely high thermal conductivity, good insulation and mechanical properties, so that the overall performance of the ceramic product can be further improved.

Description

Technical Field

[0001] The present invention relates to the technical field of ceramic materials, and in particular to an aluminum nitride ceramic and a preparation method and application thereof. Background Art

[0002] As electronic products become more multifunctional, intelligent, and miniaturized, the integration of electronic substrates is becoming increasingly complex. The large amount of heat generated within devices during operation is difficult to dissipate quickly. Operating electronic devices at high temperatures for extended periods not only affects their normal operation but can even shorten their service life. Therefore, high-heat dissipation substrates are urgently needed to address this problem. Aluminum nitride ceramics have attracted significant attention due to their high thermal conductivity, low dielectric constant, low dielectric loss, a linear expansion coefficient that matches that of semiconductor materials like silicon, high insulation properties, and high mechanical strength, making them the preferred insulating and heat-dissipating packaging material and semiconductor substrate material.

[0003] However, the preparation of aluminum nitride ceramics presents several challenges: 1) Due to its strong covalent nature, low self-diffusion coefficient, and high melting point, aluminum nitride is difficult to sinter to a high density. 2) Due to the presence of a surface oxide film, oxygen atoms readily dissolve into the aluminum nitride lattice, creating aluminum vacancies. This exacerbates phonon scattering and reduces the thermal conductivity of aluminum nitride. Consequently, the addition of sintering aids or component doping is widely used to achieve high thermal conductivity ceramics. Commonly used sintering aids are rare earth or alkaline earth oxides and fluorides (such as Y2O3, YF3, CaO, and CaF2). These low-melting-point sintering aids either melt to form a liquid phase or react with aluminum oxide on the aluminum nitride surface to form a liquid phase, accelerating mass transfer, thereby lowering the densification temperature and purifying the aluminum nitride lattice. However, the addition of sintering aids can create residual secondary phases that are difficult to remove, and large amounts of these residual secondary phases can directly affect the thermal conductivity of the ceramic material.

[0004] In view of this, it is indeed necessary to provide a technical solution to the above problems. Summary of the Invention

[0005] One of the purposes of the present invention is to provide an aluminum nitride ceramic to address the deficiencies of the prior art, thereby improving the secondary phase problem generated by the addition of sintering aids in the current aluminum nitride ceramic and ensuring the thermal conductivity of the aluminum nitride ceramic.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] An aluminum nitride ceramic comprises an aluminum nitride mixture and diamond, wherein the aluminum nitride mixture comprises aluminum nitride and yttrium oxide, wherein the mass ratio of the aluminum nitride mixture to the diamond is (12-18):(1.6-4), and the mass content of the yttrium oxide is 1%-5% of the total mass of the aluminum nitride mixture.

[0008] Preferably, the mass ratio of the aluminum nitride mixture to diamond is (12-18):(2.4-3.2); the particle size D50 of the aluminum nitride powder is 1 μm-3 μm, and the particle size D50 of the yttrium oxide powder is 1 μm-3 μm.

[0009] A second object of the present invention is to provide a method for preparing aluminum nitride ceramics, comprising the following steps:

[0010] S1. Mixing aluminum nitride and yttrium oxide and pressing to form a first mixed layer;

[0011] S2, laying diamond powder on the upper surface of the first mixed layer and pressing to form a first diamond layer;

[0012] S3, continuing to lay a mixture of aluminum nitride and yttrium oxide on the upper surface of the first diamond layer, and pressing to form a second mixed layer;

[0013] S4, repeating steps S2 and S3 in sequence, the number of repetitions being 0 to 2 times, to obtain a green billet;

[0014] S5. Sinter the green blank obtained in step S4 at a pressure of 30-50 MPa and a temperature of 1600-1850° C. in an inert gas atmosphere for 4-8 hours, and then cool the green blank to obtain aluminum nitride ceramics.

[0015] Preferably, the pressing pressure in steps S1 to S4 is 30-40 MPa, and the pressing time is 5-10 min; in steps S1 to S4, the total thickness of the diamond layer is 0.4 mm to 1 mm, and the total thickness of the mixed layer is 1.6 mm to 2.4 mm.

[0016] Preferably, step S4 further includes laying boron nitride powder on both sides of the green blank.

[0017] Preferably, in step S5, the sintering is performed by heating to 1600° C. to 1850° C. at a heating rate of 10 to 20° C. / min.

[0018] Preferably, the number of repetitions in step S4 is 1;

[0019] The preparation steps of the green billet are:

[0020] Aluminum nitride and yttrium oxide are mixed and pressed to form a first mixed layer;

[0021] Diamond powder is laid on the upper surface of the first mixed layer and pressed to form a first diamond layer;

[0022] A mixture of aluminum nitride and yttrium oxide is continuously laid on the upper surface of the first diamond layer and pressed to form a second mixed layer;

[0023] laying diamond powder on the upper surface of the second mixed layer and pressing to form a second diamond layer;

[0024] A mixture of aluminum nitride and yttrium oxide is continuously laid on the upper surface of the second diamond layer, and pressed to form a third mixed layer to obtain a green blank.

[0025] Preferably, the thickness of the first mixed layer after pressing is a, the thickness of the second mixed layer after pressing is b, the thickness of the third mixed layer after pressing is c, the thickness of the first diamond layer after pressing is m, and the thickness of the second diamond layer after pressing is n, satisfying the following relationship: 0<a≤b, 0<c≤b, 0<m≤b, 0<n≤b.

[0026] Preferably, the value of m or n is independently selected from 0.2 mm to 0.5 mm, the value of b is independently selected from 0.8 mm to 1.2 mm, and the value of a or c is independently selected from 0.4 mm to 0.6 mm.

[0027] A third object of the present invention is to provide an application of the aluminum nitride ceramic described above or the aluminum nitride ceramic prepared by the method for preparing the aluminum nitride ceramic described above in electronic devices.

[0028] The beneficial effects of the present invention are as follows: the aluminum nitride ceramic provided by the present invention uses yttrium oxide as a sintering aid at a specific content ratio, and utilizes the extremely strong affinity of yttrium oxide for oxygen and the low Gibbs free energy of the reaction between yttrium oxide and aluminum oxide on the surface of aluminum nitride, so that the reaction of aluminum oxide and yttrium oxide can be carried out at a lower temperature, and the generated yttrium aluminate liquid phase accelerates mass transfer and promotes the densification of aluminum nitride; in addition, the generation of the liquid phase causes the surface layer of the aluminum nitride grains to dissolve in the liquid phase. During the dissolution-precipitation process, it promotes a full reaction between oxygen impurities and the sintering aid, thereby purifying the crystal lattice, thereby improving the thermal conductivity of the aluminum nitride ceramic. At the same time, diamond is added, not only to improve the thermal conductivity of the product by utilizing the extremely high thermal conductivity of diamond itself, but more importantly, diamond can promote the carbon thermal reduction-nitridation reaction of yttrium aluminate, so that the second phase generated by yttrium oxide and aluminum oxide can continue to react in a reducing atmosphere. In this way, the driving force for the migration of the second phase to the surface includes not only physical factors (capillary force) but also chemical factors (transfer of chemical equilibrium). The second phase is more easily eliminated from the grain boundary, and the contact between aluminum nitride grains is closer, thereby further improving the thermal conductivity. DETAILED DESCRIPTION

[0029] To make the technical solutions and advantages of the present invention more clear, the present invention and its beneficial effects are described in further detail below, but the embodiments of the present invention are not limited thereto.

[0030] The aluminum nitride ceramics of the present invention can be used as insulating and heat-dissipating materials in electronic devices, such as insulating and heat-dissipating packaging materials or semiconductor substrate materials. Of course, they can also be used in other fields requiring insulation and heat dissipation, which is not limited here.

[0031] The aluminum nitride ceramic comprises an aluminum nitride mixture and diamond, wherein the aluminum nitride mixture comprises aluminum nitride and yttrium oxide, wherein the mass ratio of the aluminum nitride mixture to the diamond is (12-18):(1.6-4), and the mass content of the yttrium oxide is 1%-5% of the total mass of the aluminum nitride mixture.

[0032] The aluminum nitride ceramic provided by the present invention utilizes yttrium oxide and diamond as sintering additives at the same time. On the one hand, yttrium oxide can react with aluminum oxide to generate an yttrium aluminate liquid phase, thereby promoting sample densification, purifying the aluminum nitride lattice, and improving thermal conductivity. On the other hand, diamond is utilized to improve the secondary phase problem generated by the reaction of yttrium oxide and aluminum oxide. At the same time, diamond itself has extremely high thermal conductivity, good insulation and mechanical properties, which can further improve the overall performance of the product.

[0033] Compared to other high-thermal-conductivity additives (such as graphene), while they can also improve the thermal conductivity of the system, they often have other side effects. For example, graphene increases electrical conductivity while affecting insulation performance. Furthermore, other high-thermal-conductivity additives cannot resolve the secondary phase issues introduced by sintering aids. The use of diamond additives not only ensures the insulation performance of the system, but the synergistic effect of yttrium oxide and diamond results in a low secondary phase content in the resulting aluminum nitride ceramics, resulting in extremely high thermal conductivity and excellent practical application results.

[0034] In addition, compared with other sintering aids (such as samarium oxide), yttrium oxide and diamond have a synergistic effect. Diamond not only serves as an additive to improve thermal conductivity, but also can improve the secondary phase problem caused by yttrium oxide.

[0035] In order to ensure the various properties of aluminum nitride ceramics, it is equally important to control the content of each raw material.

[0036] Specifically, the mass ratio of the aluminum nitride mixture to the diamond may be (12-18):(1.6-2.0), (12-18):(2.0-2.4), (12-18):(2.4-2.8), (12-18):(2.8-3.2), (12-18):(3.2-3.6), or (12-18):(3.6-4.0), for example, including but not limited to 12:1.6, 12:2.4, 12:3.2, 15:1.6, 15:2.4, 15:2.8, 15:3.2, 15:3.6, 15:4, 18:2.4, 18:4, etc. Preferably, the mass ratio of the aluminum nitride mixture to the diamond is (12-18):(2.4-3.2).

[0037] The mass content of yttrium oxide can be 1%, 2%, 3%, 4% or 5% of the total mass of the aluminum nitride mixture. Preferably, the mass content of yttrium oxide can be 2% to 4% of the total mass of the aluminum nitride mixture.

[0038] In some embodiments, the particle size D50 of the aluminum nitride powder is 1 μm to 3 μm, specifically 1 μm to 1.5 μm, 1.5 μm to 2 μm, 2 μm to 2.5 μm, or 2.5 μm to 3 μm.

[0039] In some embodiments, the particle size D50 of the yttrium oxide powder is 1 μm to 3 μm, specifically 1 μm to 1.5 μm, 1.5 μm to 2 μm, 2 μm to 2.5 μm, or 2.5 μm to 3 μm.

[0040] Relatively fine particles are used for mixing to increase the contact area and allow for a more complete reaction between yttrium oxide and oxygen impurities to ensure the purification effect of the aluminum nitride lattice.

[0041] In addition, the present invention also provides a method for preparing aluminum nitride ceramics, comprising the following steps:

[0042] S1. Mixing aluminum nitride and yttrium oxide and pressing to form a first mixed layer;

[0043] S2, laying diamond powder on the upper surface of the first mixed layer and pressing to form a first diamond layer;

[0044] S3, continuing to lay a mixture of aluminum nitride and yttrium oxide on the upper surface of the first diamond layer, and pressing to form a second mixed layer;

[0045] S4, repeating steps S2 and S3 in sequence, the number of repetitions being 0 to 2 times, to obtain a green billet;

[0046] S5. Sinter the green blank obtained in step S4 at a pressure of 30-50 MPa and a temperature of 1600-1850° C. in an inert gas atmosphere for 4-8 hours, and then cool the green blank to obtain aluminum nitride ceramics.

[0047] The preparation method provided by the present invention, in combination with the added auxiliary agents yttrium oxide and diamond, can effectively eliminate the problem of secondary phases. Specifically, the use of diamond can promote the carbon thermal reduction-nitridation reaction of yttrium aluminate, so that the second phase generated by yttrium oxide and aluminum oxide can continue to react in a reducing atmosphere. The design of the diamond layered arrangement pre-sets the migration direction of the second phase, allowing it to migrate toward the diamond. In this way, the driving force for the migration of the second phase to the surface is not only the original physical factor (capillary force), but also incorporates chemical factors (transfer of chemical equilibrium), thereby making it easier to eliminate the generated second phase from the grain boundary, thereby effectively solving the problem of the current aluminum nitride ceramic that the secondary phase generated after the addition of sintering aids is difficult to eliminate. After the second phase is eliminated, the contact between the aluminum nitride grains is closer, and the direct contact between the aluminum nitride grains also provides a more direct channel for heat flow diffusion, and the thermal conductivity is further improved.

[0048] After many experimental studies, the inventors found that compared to the preparation method of directly uniformly mixing aluminum nitride powder, yttrium oxide and diamond, although it can also improve the thermal conductivity of the fired aluminum nitride ceramic, it still does not solve the problem of the secondary phase very well, and the improvement effect needs to be improved. To this end, the inventors continued to explore and found that the use of the layered preparation method of the present invention is equivalent to setting the migration direction of the second phase in the system in advance, increasing the driving force for the second phase to migrate to the surface, thereby greatly reducing the second phase remaining at the grain boundary, so that the thermal conductivity of the aluminum nitride ceramic is further improved, and the performance of the aluminum nitride ceramic is even better.

[0049] In addition, to ensure the sintering effect, the inventors found through experimental research that sintering the green billet at a temperature of 1600-1850°C for 4h-8h can ensure the sufficiency of the system reaction, the secondary phase can migrate more fully, and the thermal conductivity of the sample is guaranteed.

[0050] Specifically, the sintering temperature can be 1600-1650°C, 1650-1700°C, 1700-1750°C, 1750-1800°C, or 1800-1850°C. Generally speaking, as the sintering temperature increases, the performance of aluminum nitride improves. When the temperature is low, the additive and aluminum oxide do not react sufficiently, resulting in low thermal conductivity and density of the final product. Preferably, the sintering temperature is 1800-1850°C.

[0051] The holding time can be 4h-5h, 5h-6h, 6h-7h or 7h-8h. As the holding time increases, the density and thermal conductivity of the product will also increase. However, based on energy consumption considerations, the holding time is preferably 6h-8h.

[0052] In some embodiments, the pressing pressure in steps S1 to S4 is 30-40 MPa, and the pressing time is 5-10 minutes. Pressing at a higher pressure can better ensure the compactness of the green blank at the beginning of sintering, and the migration of the secondary phase to the diamond layer is smoother, thereby achieving a better elimination effect on the secondary phase.

[0053] In some embodiments, in steps S1 to S4, the total thickness of the diamond layer is 0.4 mm to 1 mm, and the total thickness of the mixed layer is 1.6 mm to 2.4 mm. Controlling the thickness of the diamond layer and the mixed layer within the aforementioned ranges ensures both the thermal conductivity and mechanical stability of the aluminum nitride ceramic, ensuring its stability in applications in electronic devices.

[0054] In some embodiments, step S4 further includes laying boron nitride powder on both sides of the green body. To prevent graphite in the sintering tool from affecting the product, boron nitride powder is laid on both sides of the green body during the preparation process, thereby preventing the sintering tool from affecting the experiment.

[0055] In some embodiments, in step S5, sintering is performed by heating to 1600°C to 1850°C at a heating rate of 10 to 20°C / min. The inventors have found that as the heating rate increases during the sintering process, the performance of aluminum nitride ceramics tends to decrease. This is because when the heating rate is too fast (such as a heating rate of 20°C / min), the reaction between aluminum nitride and the additive is not sufficient, so the thermal conductivity is low. However, for production cost considerations, it is preferred to heat at a heating rate of 10°C / min, which can save costs, avoid energy waste, and also make the sintered product have excellent performance.

[0056] Specifically, the number of repetitions in step S4 may be 0 to 2 times:

[0057] 1) When the number of repetitions in step S4 is 0, the green blank includes the first mixed layer, the first diamond layer, and the second mixed layer arranged in sequence.

[0058] 2) When the number of repetitions in step S4 is 1, the green blank includes the first mixed layer, the first diamond layer, the second mixed layer, the second diamond layer, and the third mixed layer arranged in sequence;

[0059] The preparation steps of the green billet are:

[0060] Aluminum nitride and yttrium oxide are mixed and pressed to form a first mixed layer;

[0061] Diamond powder is laid on the upper surface of the first mixed layer and pressed to form a first diamond layer;

[0062] A mixture of aluminum nitride and yttrium oxide is continuously laid on the upper surface of the first diamond layer and pressed to form a second mixed layer;

[0063] laying diamond powder on the upper surface of the second mixed layer and pressing to form a second diamond layer;

[0064] A mixture of aluminum nitride and yttrium oxide is continuously laid on the upper surface of the second diamond layer, and pressed to form a third mixed layer to obtain a green blank.

[0065] 3) When the number of repetitions in step S4 is 2, that is, the green blank includes the first mixed layer, the first diamond layer, the second mixed layer, the second diamond layer, the third mixed layer, the third diamond layer, and the fourth mixed layer arranged in sequence, the preparation method can refer to the above description.

[0066] Preferably, the number of repetitions in step S4 is 1. The inventors found that when a five-layer blank design is adopted, on the one hand, diamond layers are set at both ends of the blank, the traction direction of the second phase is more, both ends can move, and the effect of directional traction of the second phase is better, thereby achieving the purpose of eliminating the residual secondary phase and further improving the density and thermal conductivity of aluminum nitride; on the other hand, the resistance to the migration of the secondary phase will not increase due to the excessive number of diamond layers, but will be detrimental to the elimination of the secondary phase, and too much diamond will also increase the difficulty of processing due to its high hardness.

[0067] In addition, the outermost layer is still stacked with an aluminum nitride mixture. On the one hand, the thermal conductivity of the system is better. On the other hand, when aluminum nitride ceramics are used as electronic substrates, they can be better processed on the ceramic surface, making their application more convenient and more practical.

[0068] For a five-layer blank, the thickness of the first mixed layer after pressing is a, the thickness of the second mixed layer after pressing is b, the thickness of the third mixed layer after pressing is c, the thickness of the first diamond layer after pressing is m, and the thickness of the second diamond layer after pressing is n, then the thickness satisfies the following relationship: 0<a≤b, 0<c≤b, 0<m≤b, 0<n≤b.

[0069] Preferably, the thickness satisfies the following relationship: 0 < a < b, 0 < c < b, 0 < m < b, 0 < n < b. While the secondary phase in the second mixed layer can migrate toward both ends, the first and third mixed layers can only migrate toward the diamond layer at one end. Therefore, setting the outer first and third mixed layers to relatively thinner thicknesses can better ensure the overall density of the aluminum nitride and improve the thermal conductivity of the product.

[0070] In addition, the thickness of the first diamond layer and the second diamond layer is set to be lower than the thickness of the second mixed layer, so as to avoid the diamond layer being too thick and affecting the migration of the secondary phase.

[0071] In some embodiments, the value of m or n is independently selected from 0.2 mm to 0.5 mm, the value of b is 0.8 mm to 1.2 mm, and the value of a or c is independently selected from 0.4 mm to 0.6 mm.

[0072] Specifically, the thickness m of the first diamond layer can be 0.2mm, 0.3mm, 0.4mm or 0.5mm; the thickness n of the second diamond layer can be 0.2mm, 0.3mm, 0.4mm or 0.5mm; the thickness b of the second mixed layer can be 0.8mm, 0.9mm, 1.0mm, 1.1mm or 1.2mm; the thickness a of the first mixed layer can be 0.4mm, 0.5mm or 0.6mm; the thickness c of the third mixed layer can be 0.4mm, 0.5mm or 0.6mm.

[0073] The present invention and its beneficial effects will be further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0074] Example 1

[0075] An aluminum nitride ceramic comprises an aluminum nitride mixture and diamond, wherein the aluminum nitride mixture comprises aluminum nitride and yttrium oxide, wherein the mass ratio of the aluminum nitride mixture to the diamond is 15:2.4, and the mass content of the yttrium oxide is 3% of the total mass of the aluminum nitride mixture; the particle size D50 of the aluminum nitride powder is 2 μm, and the particle size D50 of the yttrium oxide powder is 2 μm.

[0076] The preparation method of the aluminum nitride ceramic is as follows:

[0077] Aluminum nitride and yttrium oxide were mixed according to the above mass ratio. Specifically, 0.9 g of yttrium oxide and 29.1 g of aluminum nitride powder were weighed and placed in a polytetrafluoroethylene can. The polytetrafluoroethylene can was then placed on a mixer at 300 rpm and rotated for 12 hours to achieve uniform mixing of the powders.

[0078] 3.75 g of a mixture of aluminum nitride and yttrium oxide was placed in a graphite mold and pressed at 30 MPa for 10 minutes to form a first mixed layer with a thickness of 0.5 mm.

[0079] 1.2 g of diamond powder was laid on the upper surface of the first mixed layer and pressed at 30 MPa for 10 minutes to form a first diamond layer with a thickness of 0.3 mm.

[0080] 7.5 g of a mixture of aluminum nitride and yttrium oxide was laid on the upper surface of the first diamond layer and pressed at 30 MPa for 10 minutes to form a second mixed layer with a thickness of 1 mm.

[0081] 1.2 g of diamond powder was laid on the upper surface of the second mixed layer and pressed at 30 MPa for 10 min to form a second diamond layer with a thickness of 0.3 mm.

[0082] 3.75 g of a mixture of aluminum nitride and yttrium oxide was further laid on the upper surface of the second diamond layer and pressed at 30 MPa for 10 minutes to form a third mixed layer with a thickness of 0.5 mm. A green blank was obtained, and boron nitride powder was evenly laid on both sides of the green blank to prevent the graphite mold from affecting the experiment.

[0083] The graphite mold was placed in a hot pressing furnace in a nitrogen atmosphere, heated to 1850°C at a temperature rise rate of 10°C / min at room temperature under a pressure of 40 MPa to sinter the green blank, and sintered at 1850°C for 8 hours, and then cooled to room temperature to obtain aluminum nitride ceramics.

[0084] Example 2

[0085] The difference from Example 1 is the thickness of the diamond layer. The thickness of the first diamond layer and the second diamond layer is 0.2 mm. The corresponding amount of the first diamond layer and the second diamond layer added is 0.8 g, the total amount of diamond added is 1.6 g, and the mass ratio of the aluminum nitride mixture to diamond is 15:1.6. The rest can be referred to in Example 1 and will not be repeated here.

[0086] Example 3

[0087] The difference from Example 1 is the thickness of the diamond layer. The thickness of the first diamond layer and the second diamond layer is 0.4 mm. The corresponding amount of the first diamond layer and the second diamond layer added is 1.6 g, the total amount of diamond added is 3.2 g, and the mass ratio of the aluminum nitride mixture to diamond is 15:3.2. The rest can be referred to in Example 1 and will not be repeated here.

[0088] Example 4

[0089] The difference from Example 1 is the thickness of the diamond layer. The thickness of the first diamond layer and the second diamond layer is 0.5 mm. The corresponding amount of the first diamond layer and the second diamond layer added is 2 g, the total amount of diamond added is 4 g, and the mass ratio of the aluminum nitride mixture to diamond is 15:4. The rest can be referred to in Example 1 and will not be repeated here.

[0090] Example 5

[0091] Different from Example 1, the diamond powder addition method of this embodiment does not adopt a layered stacking structure. Aluminum nitride, yttrium oxide and diamond powder are evenly mixed. The sintering method and sintering conditions can be found in Example 1 and will not be repeated here.

[0092] Example 6

[0093] Unlike Example 1, the green blank of this example has a three-layer structure, including a first mixed layer, a first diamond layer, and a second mixed layer. The thickness of the first mixed layer is 1 mm, the thickness of the first diamond layer is 0.6 mm, and the thickness of the second mixed layer is 1 mm. The remaining details can be found in Example 1 and will not be repeated here.

[0094] Example 7

[0095] Unlike Example 1, the green blank of this example has a seven-layer structure, including a first mixed layer, a first diamond layer, a second mixed layer, a second diamond layer, a third mixed layer, a third diamond layer, and a fourth mixed layer. The thickness of the first, second, third, and fourth mixed layers is 0.5 mm, and the thickness of the first, second, and third diamond layers is 0.2 mm. The remaining details can be found in Example 1 and will not be repeated here.

[0096] Example 8

[0097] The difference from Example 1 is that the mass content of yttrium oxide in this embodiment is 1% of the total mass of the aluminum nitride mixture. The rest can be referred to Example 1 and will not be repeated here.

[0098] Example 9

[0099] The difference from Example 1 is that the mass content of yttrium oxide in this embodiment is 5% of the total mass of the aluminum nitride mixture. The rest can be referred to Example 1 and will not be repeated here.

[0100] Example 10

[0101] Different from Example 9, the diamond powder addition method of this embodiment does not adopt a layered stacking structure. Aluminum nitride, yttrium oxide and diamond powder are evenly mixed. The sintering method and sintering conditions can be found in Example 9 and will not be repeated here.

[0102] Example 11

[0103] An aluminum nitride ceramic comprises an aluminum nitride mixture and diamond, wherein the aluminum nitride mixture comprises aluminum nitride and yttrium oxide, wherein the mass ratio of the aluminum nitride mixture to the diamond is 12:2.4, the particle size D50 of the aluminum nitride powder is 1 μm, and the particle size D50 of the yttrium oxide powder is 1 μm.

[0104] The preparation method of the aluminum nitride ceramic is as follows:

[0105] Aluminum nitride and yttrium oxide were mixed according to the above mass ratio. Specifically, 0.9 g of yttrium oxide and 29.1 g of aluminum nitride powder were weighed and placed in a polytetrafluoroethylene can. The polytetrafluoroethylene can was then placed on a mixer at 300 rpm and rotated for 12 hours to achieve uniform mixing of the powders.

[0106] 3 g of a mixture of aluminum nitride and yttrium oxide was placed in a graphite mold and pressed at 40 MPa for 8 minutes to form a first mixed layer with a thickness of 0.4 mm.

[0107] 1.2 g of diamond powder was laid on the upper surface of the first mixed layer and pressed at 40 MPa for 8 minutes to form a first diamond layer with a thickness of 0.3 mm.

[0108] 6 g of a mixture of aluminum nitride and yttrium oxide was laid on the upper surface of the first diamond layer and pressed at 40 MPa for 8 minutes to form a second mixed layer with a thickness of 0.8 mm.

[0109] 1.2 g of diamond powder was laid on the upper surface of the second mixed layer and pressed at 40 MPa for 8 minutes to form a second diamond layer with a thickness of 0.3 mm.

[0110] 3 g of a mixture of aluminum nitride and yttrium oxide was further laid on the upper surface of the second diamond layer and pressed at 40 MPa for 8 minutes to form a third mixed layer with a thickness of 0.4 mm. A green blank was obtained, and boron nitride powder was evenly laid around the side of the green blank to prevent the graphite mold from affecting the experiment.

[0111] The graphite mold was placed in a hot pressing furnace in a nitrogen atmosphere, heated to 1850°C at a temperature rise rate of 10°C / min at room temperature under a pressure of 40 MPa to sinter the green blank, and sintered at 1850°C for 6 hours, and then cooled to room temperature to obtain aluminum nitride ceramics.

[0112] Example 12

[0113] An aluminum nitride ceramic comprises an aluminum nitride mixture and diamond, wherein the aluminum nitride mixture comprises aluminum nitride and yttrium oxide, wherein the mass ratio of the aluminum nitride mixture to the diamond is 18:2.4, the particle size D50 of the aluminum nitride powder is 3 μm, and the particle size D50 of the yttrium oxide powder is 3 μm.

[0114] The preparation method of the aluminum nitride ceramic is as follows:

[0115] Aluminum nitride and yttrium oxide were mixed according to the above mass ratio. Specifically, 0.9 g of yttrium oxide and 29.1 g of aluminum nitride powder were weighed and placed in a polytetrafluoroethylene can. The polytetrafluoroethylene can was then placed on a mixer at 300 rpm and rotated for 12 hours to achieve uniform mixing of the powders.

[0116] 4.5 g of a mixture of aluminum nitride and yttrium oxide was placed in a graphite mold and pressed at 50 MPa for 5 minutes to form a first mixed layer with a thickness of 0.6 mm.

[0117] 1.2 g of diamond powder was laid on the upper surface of the first mixed layer and pressed at 50 MPa for 5 minutes to form a first diamond layer with a thickness of 0.3 mm.

[0118] 9 g of a mixture of aluminum nitride and yttrium oxide was laid on the upper surface of the first diamond layer and pressed at 50 MPa for 5 minutes to form a second mixed layer with a thickness of 1.2 mm.

[0119] 1.2 g of diamond powder was laid on the upper surface of the second mixed layer and pressed at 50 MPa for 5 minutes to form a second diamond layer with a thickness of 0.3 mm.

[0120] 4.5 g of a mixture of aluminum nitride and yttrium oxide was further laid on the upper surface of the second diamond layer and pressed at 50 MPa for 5 minutes to form a third mixed layer with a thickness of 0.6 mm. A green blank was obtained, and boron nitride powder was evenly laid around the side of the green blank to prevent the graphite mold from affecting the experiment.

[0121] The graphite mold was placed in a hot pressing furnace in a nitrogen atmosphere, heated to 1850°C at a temperature rise rate of 10°C / min at room temperature under a pressure of 50 MPa to sinter the green blank, and sintered at 1850°C for 8 hours, and then cooled to room temperature to obtain aluminum nitride ceramics.

[0122] Example 13

[0123] The difference from Example 1 is that the sintering conditions in the preparation process of the aluminum nitride ceramic are: heating to 1850° C. at a heating rate of 15° C. / min. The rest can be referred to Example 1 and will not be repeated here.

[0124] Example 14

[0125] The difference from Example 1 is that the sintering conditions in the preparation process of the aluminum nitride ceramic are: heating to 1850° C. at a heating rate of 20° C. / min. The rest can be referred to Example 1 and will not be repeated here.

[0126] Example 15

[0127] The difference from Example 1 is that the sintering conditions in the preparation process of the aluminum nitride ceramic are: heating to 1600° C. at a heating rate of 10° C. / min. The rest can be referred to Example 1 and will not be repeated here.

[0128] Example 16

[0129] The difference from Example 1 is that the sintering conditions in the preparation process of the aluminum nitride ceramic are: heating to 1750° C. at a heating rate of 10° C. / min. The rest can be referred to Example 1 and will not be repeated here.

[0130] Example 17

[0131] Different from Example 1, the sintering conditions in the preparation process of the aluminum nitride ceramic are: heating to 1850° C. at a heating rate of 10° C. / min and sintering for 4 hours. The rest can be found in Example 1 and will not be repeated here.

[0132] Example 18

[0133] Different from Example 1, the sintering conditions in the preparation process of the aluminum nitride ceramic are: heating to 1850° C. at a heating rate of 10° C. / min and sintering for 6 hours. The rest can be found in Example 1 and will not be repeated here.

[0134] Comparative Example 1

[0135] The difference from Example 1 is that the sintering aid in this comparative example is that yttrium oxide is replaced by samarium oxide. The rest can be referred to Example 1 and will not be repeated here.

[0136] Comparative Example 2

[0137] The difference from Example 1 is that the mass ratio of the aluminum nitride mixture to diamond in this comparative example is 15:1.0. The rest can be referred to Example 1 and will not be repeated here.

[0138] Comparative Example 3

[0139] The difference from Example 1 is that the mass ratio of the aluminum nitride mixture to diamond in this comparative example is 15:7.5. The rest can be referred to Example 1 and will not be repeated here.

[0140] Comparative Example 4

[0141] The difference from Example 1 is that the sintering conditions in the preparation process of the aluminum nitride ceramic are: heating to 2000° C. at a heating rate of 10° C. / min. The rest can be referred to Example 1 and will not be repeated here.

[0142] The aluminum nitride ceramics obtained in Examples 1 to 18 and Comparative Examples 1 to 4 were subjected to performance tests, including density testing using the Archimedean drainage method, and the theoretical density of aluminum nitride was 3.26 g / cm 3 Calculate the relative density. Since components with different densities may be generated during the sintering process, the relative density may differ slightly from the actual density. Use a laser thermal constant analyzer to measure the thermal diffusivity of the product and calculate its thermal conductivity.

[0143] The test results are shown in Table 1 below.

[0144] Table 1 Aluminum nitride ceramic performance test results

[0145]

[0146]

[0147] From the comparison in Table 1 above, it can be seen that the aluminum nitride ceramics provided by the present invention use yttrium oxide and diamond as additives. At a certain content, yttrium oxide can better purify the lattice structure, while diamond can improve the secondary phase problem caused by yttrium oxide. In particular, the layered preparation method can effectively improve the density and thermal conductivity of the aluminum nitride ceramics.

[0148] Among them, in Comparative Example 1, yttrium oxide is replaced with samarium oxide. Although the density of the ceramic does not change significantly, the thermal conductivity is reduced, which shows that the matching of yttrium oxide-diamond is better than that of samarium oxide-diamond. In Comparative Example 2, the diamond content is reduced, resulting in a significant decrease in thermal conductivity. This is attributed to the fact that the low diamond content cannot effectively promote the carbon thermal reduction-nitridation reaction, and the secondary phase cannot migrate in time at the aluminum nitride grain boundary. In Comparative Example 3, the diamond content is increased. Due to the high thermal conductivity of diamond itself, the thermal conductivity of the ceramic also reaches a higher level. However, due to the mismatch between the thermal expansion coefficients of diamond and semiconductors such as silicon, in practical applications, excessive diamond content will accelerate the mechanical failure of the chip and the ceramic substrate. In Comparative Example 4, the sintering temperature is increased compared to Example 1, but the improvement in thermal conductivity is very small. In addition, the high sintering temperature causes huge energy loss. Therefore, the aluminum nitride ceramics prepared by the preparation method of aluminum nitride ceramics adopted in the present invention have excellent performance and do not cause energy waste, and have broad prospects in applications such as electronic devices.

[0149] From the comparison of Examples 1 to 4, it can be seen that as the thickness of the diamond layer increases, the thermal conductivity shows an increasing trend. When the diamond layer is 0.5 mm, the thermal conductivity of the aluminum nitride ceramic reaches a maximum value of 210.8 (W·m -1 ·K -1 This is due to the extremely high thermal conductivity of diamond itself; the higher the diamond content, the greater the thermal conductivity. However, in practical applications such as electronics, diamond's coefficient of linear expansion is smaller than that of semiconductors like silicon, making it prone to mechanical failure. Therefore, it is best to control the mass ratio of the diamond to aluminum nitride mixture within the above range.

[0150] In addition, it can be seen from the comparison of Examples 1, 8 to 9 that the content of yttrium oxide additives also affects the density and thermal conductivity of aluminum nitride ceramics. As the content of the additive increases, the density and thermal conductivity of the aluminum nitride ceramics first show an upward trend. When the additive is added in excess (the required total mass is 5wt%), the density and thermal conductivity actually decrease. This may be due to the following reasons: when the additive content is relatively low, that is, 1wt% of the total mass, the aluminum oxide film on the surface of the aluminum nitride cannot fully react with the yttrium oxide, and oxygen atoms enter the aluminum nitride lattice to affect phonon scattering, resulting in a lower thermal conductivity of the aluminum nitride. At the same time, less liquid phase is produced, which affects the density of the aluminum nitride. When the additive content is too much, there is too much liquid phase, and the second phase cannot migrate from the grain boundary in time, resulting in a decrease in thermal conductivity.

[0151] Furthermore, a comparison of Examples 1, 5-7, and 9-10 shows that compared to preparing aluminum nitride ceramics by directly mixing raw materials, the present invention's method of layering diamond powder exhibits superior performance. In particular, the five-layer green body exhibits superior thermal conductivity. This is primarily because stacking too many layers hinders the migration of the secondary phase, which in turn affects thermal conductivity.

[0152] After layering diamond powder, variations in sintering also affect the ultimate thermal conductivity of aluminum nitride ceramics. A comparison of Examples 1 and 13-18 reveals that excessively fast heating rates, low reaction temperatures, and short holding times during sintering all contribute to declining performance. This is primarily due to inappropriate reaction conditions that prevent the additive from fully reacting with the aluminum oxide.

[0153] Based on the disclosure and teachings of the above description, those skilled in the art will be able to make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the above specific embodiments. Any obvious improvements, substitutions, or modifications made by those skilled in the art based on the present invention fall within the scope of protection of the present invention. In addition, although certain specific terms are used in this description, these terms are only for convenience of description and do not constitute any limitation to the present invention.

Claims

1. A method for preparing aluminum nitride ceramics, characterized in that: The following steps are involved: Aluminum nitride and yttrium oxide are mixed and pressed to form a first mixed layer; Diamond powder is laid on the upper surface of the first mixed layer and pressed to form a first diamond layer; A mixture of aluminum nitride and yttrium oxide is continuously laid on the upper surface of the first diamond layer and pressed to form a second mixed layer; laying diamond powder on the upper surface of the second mixed layer and pressing to form a second diamond layer; A mixture of aluminum nitride and yttrium oxide is continuously laid on the upper surface of the second diamond layer and pressed to form a third mixed layer to obtain a green blank; The green body is sintered in an inert gas atmosphere at a pressure of 30-50 MPa and a temperature of 1600-1850°C for 4-8 hours, and then cooled to obtain aluminum nitride ceramics. The thickness of the first diamond layer after pressing is m, the thickness of the second diamond layer after pressing is n, and the thickness of the second mixed layer after pressing is b, satisfying the following relationship: 0<m≤b, 0<n≤b; The aluminum nitride ceramic includes an aluminum nitride mixture and diamond, and the aluminum nitride mixture includes aluminum nitride and yttrium oxide. The mass ratio of the aluminum nitride mixture to the diamond is (12-18):(1.6-4), and the mass content of yttrium oxide is 1%-5% of the total mass of the aluminum nitride mixture.

2. The method for preparing aluminum nitride ceramics according to claim 1, wherein: The pressing pressure is 30~40Mpa, and the pressing time is 5~10min; the total thickness of the diamond layer is 0.4mm~1mm, and the total thickness of the mixed layer is 1.6mm~2.4mm.

3. The method for preparing aluminum nitride ceramics according to claim 1, wherein: The method also includes laying boron nitride powder on both sides of the green blank.

4. The method for preparing aluminum nitride ceramics according to claim 1, wherein: The sintering is carried out by heating to 1600°C~1850°C at a heating rate of 10~20°C / min.

5. The method for preparing aluminum nitride ceramics according to claim 4, wherein: The thickness of the first mixed layer after pressing is a, the thickness of the second mixed layer after pressing is b, and the thickness of the third mixed layer after pressing is c, satisfying the following relationship: 0<a≤b, 0<c≤b.

6. The method for preparing aluminum nitride ceramics according to claim 5, characterized in that: The value of m or n is independently selected from 0.2 mm to 0.5 mm, the value of b is 0.8 mm to 1.2 mm, and the value of a or c is independently selected from 0.4 mm to 0.6 mm.

7. An aluminum nitride ceramic prepared by the method for preparing an aluminum nitride ceramic according to any one of claims 1 to 6, characterized in that: The invention comprises an aluminum nitride mixture and diamond, wherein the aluminum nitride mixture comprises aluminum nitride and yttrium oxide, wherein the mass ratio of the aluminum nitride mixture to the diamond is (12-18):(1.6-4), and the mass content of yttrium oxide is 1%-5% of the total mass of the aluminum nitride mixture.

8. The aluminum nitride ceramic according to claim 7, characterized in that The mass ratio of the aluminum nitride mixture to diamond is (12~18):(2.4~3.2); the particle size D50 of the aluminum nitride powder is 1μm~3μm, and the particle size D50 of the yttrium oxide powder is 1μm~3μm.

9. Use of the aluminum nitride ceramic prepared by the preparation method of the aluminum nitride ceramic according to any one of claims 1 to 6 or the aluminum nitride ceramic according to any one of claims 7 to 8 in an electronic device.

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