Aluminum nitride sintered body and method for producing same
11319254 · 2022-05-03
Assignee
Inventors
Cpc classification
C04B2235/3225
CHEMISTRY; METALLURGY
C04B2235/96
CHEMISTRY; METALLURGY
C04B2235/3418
CHEMISTRY; METALLURGY
C04B2235/3244
CHEMISTRY; METALLURGY
C04B2235/9607
CHEMISTRY; METALLURGY
C04B2235/3227
CHEMISTRY; METALLURGY
C04B2235/5436
CHEMISTRY; METALLURGY
C04B2235/80
CHEMISTRY; METALLURGY
International classification
Abstract
An aluminum nitride sintered body with improved mechanical strength without compromised thermal dissipating properties. The aluminum nitride sintered body contains 100 parts by weight of AlN, 3 to 20 parts by weight on an oxide basis of at least one type of nitride selected from the group consisting of Zr and Ti as an additive, and 1 to 10 parts by weight of Y.sub.2O.sub.3 as a sintering aid. The oxygen content in the sintered body is 1.8 wt % or less, and the thermal conductivity is 130 W/m.Math.K or higher.
Claims
1. An aluminum nitride sintered body comprising 100 parts by weight of AlN, 5 to 20 parts by weight on an oxide basis of ZrN, 1 to 10 parts by weight of Y.sub.2O.sub.3 as a sintering aid, and 0.025 to 0.15 parts by weight on a Si element basis of a Si component as a Si additive, wherein the sintered body has an oxygen content of 1.8 wt % or less, the sintering aid phase in the aluminum nitride sintered body contains YAM as a crystal phase and does not contain YAG as the crystal phase, a thermal conductivity of 130 W/m.Math.K or higher, and three-point flexural strength is 600 MPa or more.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
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DETAILED DESCRIPTION
(5) An aluminum nitride sintered body substrate according to an embodiment of the present invention is produced through a mixing step of mixing an aluminum nitride raw material powder, an additive consisting of at least one type of nitride selected from the group consisting of Zr and Ti, a sintering aid, a Si additive, an organic binder, and an organic solvent to create a raw material mixture, a forming step of forming the raw material mixture into a compact, a first heating step (debinding process) of heating the compact in a nitrogen atmosphere in a first temperature range to partially (incompletely) debind the organic binder from the compact and leave the carbon component in the compact, a second heating step (decarbonization process) of heating the compact in a nitrogen atmosphere in a second temperature range to remove the residual carbon from the compact, and following the second heating step, a sintering step of raising the temperature from the second temperature range to a third temperature range and heating the compact in a nitrogen atmosphere in the third temperature range to sinter the compact. (See the flowchart of
(6) The aluminum nitride sintered body according to the embodiment of the present invention is made by sintering a powder mixture containing 100 parts by weight of AlN, 3 to 20 parts by weight on an oxide basis of at least one nitride selected from the group consisting of Zr and Ti as an additive, and 1 to 10 parts by weight of Y.sub.2O.sub.3 as a sintering aid. “On an oxide basis” as used here means a value calculated by converting a compound containing a metallic element into an oxide of the metallic element. Specifically, ZrN and TiN were added upon being converted to ZrO and TiO.sub.2.
(7) First, in the mixing step, a suitable amount of aluminum nitride raw material powder, a suitable amount of additive powder, a suitable amount of sintering aid powder, and a suitable amount of Si additive powder or gel are prepared. The aluminum nitride raw material powder used as the base material and the nitride powder used as an additive are preferably fine powders of a high purity, with few metallic impurities and low oxygen content. The sintering aid is Y.sub.2O.sub.3. In addition, the Si additive may be at least one type selected from the group consisting of SiO.sub.2, amorphous SiO.sub.2, silicon alkoxide hydrolysate, etc.
(8) The prepared raw materials (aluminum nitride, additives, sintering aid, and Si additive) are introduced into a crushing/mixing machine such as a ball mill, an organic solvent, a dispersing agent, an organic binder, and/or a plasticizer are added, and the mixture is thoroughly crushed and mixed for a predetermined amount of time. The organic solvent is prepared by mixing for example toluene and ethanol in a predetermined ratio. The amount of the organic solvent is about 30 to 50 parts by weight with the aluminum nitride raw material powder as 100 parts by weight. The dispersing agent is for example a trace amount of a phosphorus-based surfactant. However, the organic solvent and the dispersing agent may be selected freely. Further, the organic binder may be for example a polyvinyl butyral resin, and is added in an amount of about 5 to 10 parts by weight with the raw material powder as 100 parts by weight. The plasticizer may be for example dibutyl phthalate (DBP), and is added in an amount of about 1 to 5 parts by weight with the raw material powder as 100 parts by weight. The ingredients are mixed until a slurry-like raw material mixture is obtained, in which all ingredients are sufficiently dispersed and mixed.
(9) In the forming step, the obtained raw material mixture is formed into a compact having a predetermined shape, by means of extrusion, cast molding, a doctor blade method or the like.
(10) Next, in the first heating step (debinding process) the compact is introduced into a first heating apparatus (oven) and is heated for an hour or longer in a first temperature range in a nitrogen atmosphere at atmospheric pressure (although the step is not so limited), so that the added organic binder is partially or incompletely debinded and removed. The first temperature range is at this time about 400° C. to 600° C. (so as not to sinter the compact). In other words, by heating the compact under conditions such that the debinding process is incomplete, the carbon component of the organic binder is intentionally left in the compact. The residual carbon content in the compact after the first heating step can be quantifiably detected using oxygen airflow combustion-infrared absorptiometry. Debinding processing conditions are defined such that the carbon content in the compact after the first heating step is preferably 0.3 wt % to 1 wt %, and more preferably 0.4 wt % to 0.8 wt %. In other words, the method for producing the aluminum nitride sintered body according to the embodiment of the present invention further includes a step of measuring the carbon content in a sample of the compact after the first heating step, and then, based on the measured results of the carbon content in the sample, determining the heating conditions for the debinding process of the compact. It is thought that by heating the organic binder in a nitrogen atmosphere, oxidation of the additives at the time of debinding can be suppressed, and compared to a standard atmosphere (an oxygen atmosphere into which air is introduced) carbon can be effectively made to remain without excessive combustion. Following the first heating step (debinding process), the second heating step (decarbonization step) and the sintering step are performed in sequence. In the present embodiment, the first heating step and the second heating step and sintering step are carried out using different heating apparatuses, but they may also be carried out in sequence using the same heating apparatus.
(11) In the second heating step (decarbonization process), the incompletely debinded compact is introduced into a second heating apparatus and is heated for one hour or longer in a second temperature range in a nitrogen atmosphere at atmospheric pressure (although the step is not so limited), so that the residual carbon in the compact is removed. The second temperature range is at this time about 1400° C. to 1700° C. (so as not to sinter the compact). In this decarbonization step preceding the sintering step, the trace amounts of oxygen dissolved in the compact (e.g. within the AlN particles) and the residual carbon can be subjected to a high-temperature thermal reaction and be completely debinded, allowing for a further reduction of oxygen content.
(12) In the sintering step, the decarbonized compact is sintered through heating for one hour or longer in the second heating apparatus in a third temperature range in a nitrogen atmosphere at atmospheric pressure (although the step is not so limited). The third temperature range is about 1700° C. to 1800° C. At this time, due to the addition of a minute amount of the Si component, the compact can be sintered at a relatively low temperature of less than 1800° C. In this way, a substrate of an aluminum nitride sintered body is obtained.
(13) The crystal phase of the aluminum nitride sintered body was identified by X-ray diffraction.
(14) As shown in the flowchart of
(15) From the X-ray diffraction pattern of the aluminum nitride sintered body according to the embodiment of the present invention shown in
(16) It is thus understood that the aluminum nitride sintered body according to the present embodiment has an effectively reduced oxygen content due to the formation of YAM instead of YAG in the sintering aid phase. As a result, it can enjoy the benefit of improved mechanical strength by the addition of Zr or Ti, while suppressing a decrease in thermal conductivity.
(17) The properties of the aluminum nitride sintered body according to the present embodiment were assessed by performing thermal conductometry, flexural strength measurement, and crystal phase identification by X-ray diffraction on the aluminum nitride sintered body.
EXAMPLES
(18) The present invention is described below in further detail based on examples and comparative examples, but it should be noted that the invention is not limited to these examples.
(19) The aluminum nitride sintered bodies according to Examples 1 to 11 were created by performing some or all of the steps described below.
(20) (1) A predetermined amount of aluminum nitride powder was prepared. The aluminum nitride powder used had an average grain size of 1.1 μm and a specific surface area of 2.6 m.sup.2/g.
(21) (2) As the sintering aid, a high-purity yttrium oxide (Y.sub.2O.sub.3) powder was prepared. It is already known in this technical field that an amount of sintering aid of 1 to 10 parts by weight is preferable. In all of these Examples, the amount was set to 5 parts by weight for the purpose of relative assessment between samples.
(22) (3) As the optional additive, ZrN powder (for Examples 1 to 7) and TiN powder (for Examples 8 to 11) were prepared.
(23) (4) A predetermined amount of silica sol was prepared as a colloidal silicon compound (for Examples 1 to 4 and 6 to 11). A suitable amount of silica sol was prepared based on an additive amount on a Si element basis, with the aluminum nitride raw material powder as 100 parts by weight.
(24) (5) Suitable amounts of each raw material was added to the aluminum nitride raw material powder to prepare a raw material composition. At the time of preparation, Y, and ZrN or TiN were calculated on an oxide basis, and the Si component was calculated on a Si element basis, and mixed.
(25) (6) The raw materials were introduced into a ball mill in steps, where they were crushed and mixed.
(26) (7) The raw material mixture was formed into a sheet using the doctor blade method, and punched into a desired shape.
(27) (8) The sheet-shaped compact of the raw material mixture in packed powder form was introduced into an oven, where it was heated and debinded for about two hours at a temperature of about 500° C. in a nitrogen atmosphere at a pressure of 1 atm, to control the amount of residual carbon. The debinded sheet compact was then removed from the oven and introduced into a different oven, where it was heated and decarbonized for about 10 hours at a temperature of about 1,500° C. in a nitrogen gas atmosphere at a pressure of 1 atm. At this temperature, the sheet compact is not sintered. Then, in the same oven, the sheet compact was heated for about 5 hours at a temperature of about 1,800° C. in a nitrogen gas atmosphere at a pressure of 1 atm to sinter the sheet compact and obtain an aluminum nitride sintered body substrate according to Examples 1 to 11.
(28) The aluminum nitride sintered body according to Comparative Examples 1 to 4 and 6 to 14 was obtained through the steps (1) to (7) described above, but under different heating conditions than those of step (8). Specifically, the sheet-shaped compact of the raw material mixture in packed powder form was introduced into an oven, where it was heated and debinded for about two hours at a temperature of about 500° C. in a standard atmosphere (an oxygen atmosphere into which air is introduced) at a pressure of 1 atm, so that no carbon component remained. The debinded sheet compact was then removed from the oven and introduced into a different oven, where it was heated for about five hours at a temperature of about 1,800° C. in a nitrogen gas atmosphere at a pressure of 1 atm to sinter the sheet compact and obtain an aluminum nitride sintered body substrate according to Comparative Examples 1 to 4 and 6 to 14. Meanwhile, the aluminum nitride sintered body according to Comparative Example 5 was obtained under the same heating conditions as those of step (8).
(29) The structure and production conditions of the aluminum nitride sintered bodies of Examples 1 to 11 and Comparative Examples 1 to 14 are shown in Table 1 below. In Table 1, the “Debinding/Decarbonization in N Atmosphere” column is marked “Y” for the samples made according to the flowchart shown in
(30) TABLE-US-00001 TABLE 1 Added Amount (Parts by Weight) Carbon Carbon Additive Debinding/ Content Content Main Sintering ZrN ZrO.sub.2 TiN Si Decarbonization (wt %) (wt %) agent aid (Oxide (Oxide (Oxide Additive in N After After AlN Y.sub.2O.sub.3 Basis) Basis) Basis) Si Atmosphere Debinding Sintering Example 1 100 5 3 0.05 Y 0.50 0.15 Example 2 100 5 5 0.05 Y 0.55 Example 3 100 5 10 0.05 Y 0.66 Example 4 100 5 20 0.05 Y 0.75 Example 5 100 5 3 0.00 Y 0.49 Example 6 100 5 3 0.10 Y 0.51 Example 7 100 5 3 0.20 Y 0.51 Example 8 100 5 3 0.05 Y 0.48 0.09 Example 9 100 5 5 0.05 Y Example 10 100 5 10 0.05 Y Example 11 100 5 20 0.05 Y Comparative 100 5 3 0.05 N 0.09 0.09 Example 1 Comparative 100 5 5 0.05 N 0.12 Example 2 Comparative 100 5 10 0.05 N 0.19 Example 3 Comparative 100 5 20 0.05 N 0.25 Example 4 Comparative 100 5 10 0.05 Y Example 5 Comparative 100 5 10 0.05 N Example 6 Comparative 100 5 3 0.00 N 0.08 Example 7 Comparative 100 5 3 0.10 N 0.09 Example 8 Comparative 100 5 3 0.20 N 0.11 Example 9 Comparative 100 5 3 0.05 N 0.08 0.08 Example 10 Comparative 100 5 5 0.05 N Example 11 Comparative 100 5 10 0.05 N Example 12 Comparative 100 5 20 0.05 N Example 13 Comparative 100 5 0.05 N Example 14
(31) Properties A to D of the aluminum nitride sintered bodies according to Examples 1 to 11 and Comparative Examples 1 to 14 shown in Table 1 were assessed using the following methods.
(32) A. Three-Point Flexural Strength
(33) For the three-point flexural strength measurement, a three-point flexural test based on the JIS-R1601 standard was used. The measuring device was a model AG-IS made by Shimadzu Corporation, and the measuring conditions were a crosshead speed of 0.5 mm/min, a distance between the supports of 30 mm, a specimen width of 20 mm, and a specimen thickness of 0.3 to 0.4 mm.
(34) B. Thermal Conductivity
(35) For the conductivity measurement, a laser flash technique based on the JIS-R1611 standard was used. A TC-9000 system made by ULVAC, Inc. was used for the measuring.
(36) C. Oxygen Content
(37) Using an EMGA-920 made by HORIBA, Ltd., measuring was performed by means of inert gas fusion-nondispersive infrared absorptiometry.
(38) D. Crystal Phase Identification
(39) X-ray diffraction using Cu-Kα rays was used for the crystal phase identification. An UltimaIV apparatus made by Rigaku Corporation was used for the measuring.
(40) Part or all of the properties of the aluminum sintered bodies according to the Examples are shown in Tables 2 to 5 below. As for the composition ratio, the Tables show, relative to a 100 parts by weight of AlN, the parts by weight of Y.sub.2O.sub.3, the parts by weight of ZrN, ZrO.sub.2, and TiN on an oxide basis, as well as the parts by weight of the silicon compound on a Si element basis.
(41) Table 2 shows the measurements of the flexural strength, thermal conductivity, and oxygen content of Examples 1 to 4 and Comparative Examples 1 to 6, where the additive was Zr. As such, Table 2 shows the type (additive form) of the additives (ZrN, ZrO.sub.2), and the tendency of each property depending on the amount added.
(42) TABLE-US-00002 TABLE 2 Added Amount (Parts by Weight) Additive Debinding/ Three-point Main Sintering ZrN ZrO.sub.2 Si Decarbonization Flexural Thermal Oxygen agent aid (Oxide (Oxide Additive in N Strength Conductivity Content AlN Y.sub.2O.sub.3 Basis) Basis) Si Atmosphere (MPa) (W/mK) (wt %) Example 1 100 5 3 0.05 Y 686 147 1.29 Example 2 100 5 5 0.05 Y 691 147 1.32 Example 3 100 5 10 0.05 Y 698 144 1.39 Example 4 100 5 20 0.05 Y 791 146 1.50 Comparative 100 5 3 0.05 N 677 144 2.06 Example 1 Comparative 100 5 5 0.05 N 701 107 2.29 Example 2 Comparative 100 5 10 0.05 N 721 84 2.78 Example 3 Comparative 100 5 20 0.05 N 735 81 3.18 Example 4 Comparative 100 5 10 0.05 Y 743 85 3.25 Example 5 Comparative 100 5 10 0.05 N 723 75 3.77 Example 6
(43) From the results shown in Table 2, it can be seen in Examples 1 to 4 and Comparative Examples 1 to 4 that, although there is a degree of variation in the measurements, increasing the added amount of ZrN leads to an overall improvement of the three-point flexural strength. In the Comparative Examples, it can be seen that thermal conductivity greatly decreases as the added amount of ZrN is increased, and that the oxygen content increases greatly in reverse proportion to the thermal conductivity. On the other hand, in the present Examples the thermal conductivity remains almost constant even as the added amount of ZrN is increased, and the increase in oxygen content is slight. In Example 4 in particular (where the added amount of ZrN was 20 parts by weight) a very high standard of strength and thermal conductivity was achieved, with a three-point flexural strength of 791 MPa and a thermal conductivity of 146 W/mK. In other words, in Examples 1 to 4 mechanical strength was improved while the increase in oxygen content and decrease in thermal conductivity was suppressed. Meanwhile, in Comparative Examples 5 and 6 where the additive was Zr oxide (ZrO.sub.2), compared to Example 3, the decrease in thermal conductivity was significant, and introducing the debinding and decarbonization process in a nitrogen atmosphere made almost no improvement to the thermal conductivity. In other words, using an oxide as the additive greatly increases the oxygen content compared to when using a nitride as the additive, and although the introduction of the debinding and decarbonization process in a nitrogen atmosphere results in a slight reduction of the oxygen content, the effect is insufficient, and the decrease in thermal conductivity is barely suppressed at all. It can thus be understood from these results that the combination of the nitride additive and the debinding and decarbonization process in a nitrogen atmosphere makes a significant contribution to achieving both high strength and high thermal conductivity.
(44) Table 3 shows the measurements of the oxygen content in Examples 1 and 5 to 7 and Comparative Examples 1 and 7 to 9. As such, Table 3 shows the tendency of the oxygen content depending on the added amount of Si additive.
(45) TABLE-US-00003 TABLE 3 Added Amount (Parts by Weight) Additive Debinding/ Main Sintering ZrN Si Decarbonization Oxygen agent aid (Oxide Additive in N Content AlN Y.sub.2O.sub.3 Basis) Si Atmosphere (wt %) Example 1 100 5 3 0.05 Y 1.29 Example 5 100 5 3 0.00 Y 1.14 Example 6 100 5 3 0.10 Y 0.99 Example 7 100 5 3 0.20 Y 1.37 Comparative 100 5 3 0.05 N 2.06 Example 1 Comparative 100 5 3 0.00 N 1.99 Example 7 Comparative 100 5 3 0.10 N 2.07 Example 8 Comparative 100 5 3 0.20 N 2.15 Example 9
(46) As seen in Table 3, changing the added amount of the Si additive does not exhibit much influence on the oxygen content. Comparing Examples 1 and 5 to 7 with Comparative Examples 7 to 9, it can be seen that the introduction of the debinding and decarbonization process in a nitrogen atmosphere causes a relative reduction of the oxygen content. It is thus understood that even if the added amount of the Si additive is changed, the decrease in thermal conductivity (increase in oxygen content) is suppressed according to the same tendency shown in Table 2.
(47) Table 4 shows the measurements of the flexural strength, thermal conductivity, and oxygen content of Examples 8 to 11 and Comparative Examples 10 to 13, where the additive was Ti. As such, Table 4 shows the tendency of each property depending on the amount of additive (TiN).
(48) TABLE-US-00004 TABLE 4 Added Amount (Parts by Weight) Additive Debinding/ Three-point Main Sintering TiN Si Decarbonization Flexural Thermal Oxygen agent aid (Oxide Additive in N Strength Conductivity Content AlN Y.sub.2O.sub.3 Basis) Si Atmosphere (MPa) (W/mK) (wt %) Example 8 100 5 3 0.05 Y 652 145 0.99 Example 9 100 5 5 0.05 Y 653 140 1.15 Example 10 100 5 10 0.05 Y 663 138 1.20 Example 11 100 5 20 0.05 Y 691 139 1.32 Comparative 100 5 3 0.05 N 663 143 2.11 Example 10 Comparative 100 5 5 0.05 N 675 100 2.44 Example 11 Comparative 100 5 10 0.05 N 678 88 3.26 Example 12 Comparative 100 5 20 0.05 N 711 80 4.91 Example 13
(49) From the results shown in Table 4, it can be seen in Examples 8 to 11 and Comparative Examples 10 to 13 that, although there is a degree of variation in the measurements, increasing the added amount of TiN leads to an overall improvement of the three-point flexural strength. In the Comparative Examples, it can be seen that thermal conductivity greatly decreases as the added amount of TiN is increased, and that the oxygen content increases greatly in reverse proportion to the thermal conductivity. On the other hand, in the present Examples the thermal conductivity decreases only slightly as the added amount of TiN is increased, and the increase in oxygen content is also slight. In Example 11 in particular (where the added amount of TiN was 20 parts by weight) a very high standard of strength and thermal conductivity was achieved, with a three-point flexural strength of 691 MPa and a thermal conductivity of 139 W/mK. In other words, in Examples 8 to 11 mechanical strength was improved while the decrease in thermal conductivity (increase in oxygen content) was suppressed.
(50) Table 5 shows the crystal phases of the sintering aid phases detected by X-ray diffraction patterns in the samples where the added amount of ZrN additive was changed (Examples 1, 3, and 4, and Comparative Examples 1, 3, 4, and 14).
(51) TABLE-US-00005 TABLE 5 Added Amount (Parts by Weight) Additive Debinding/ Main Sintering ZrN Si Decarbonization Crystal Phase of the Sintering agent aid (Oxide Additive in N Aid Phase AlN Y.sub.2O.sub.3 Basis) Si Atmosphere YAM YAL YAG Example 1 100 5 3 0.05 Y Y N N Example 3 100 5 10 0.05 Y Y N N Example 4 100 5 20 0.05 Y Y Y N Comparative 100 5 3 0.05 N N Y Y Example 1 Comparative 100 5 10 0.05 N N N Y Example 3 Comparative 100 5 20 0.05 N N N Y Example 4 Comparative 100 5 0 0.05 N Y Y N Example 14
(52) As seen in Table 5, if no additive is added, like in Comparative Example 14, then even with debinding in standard atmosphere and sintering in a nitrogen atmosphere, YAM and YAL are deposited as the crystal phase of the sintering aid phase, and YAG is not deposited. By contrast, when ZrN is added under the conditions of debinding in standard atmosphere and sintering in a nitrogen atmosphere (as in Comparative Examples 1, 3, and 4), deposition of YAM disappears, and YAG and partially YAL are deposited. In particular, when the added amount of ZrN increases to 10 to 20 parts by weight, deposition of YAL as the crystal phase of the sintering aid phase disappears, and of the three crystal phases only YAG is deposited. On the other hand, in the samples of Examples 1, 3, and 4, where the debinding and decarbonization process in a nitrogen atmosphere is introduced, YAG is not deposited as the crystal phase of the sintering aid phase, whereas YAM and partially YAL are deposited. When the added amount of ZrN becomes particularly small, deposition of YAL as the crystal phase of the sintering aid phase disappears, and of the three crystal phases only YAM is deposited. In other words, these results corroborate the influence of the debinding and decarbonization process in a nitrogen atmosphere according to the present invention on the oxygen content and thermal conductivity.
(53) Therefore, by adding Zr or Ti in the form of nitrides and introducing the debinding and decarbonization process in a nitrogen atmosphere, the aluminum nitride sintered body and the method for producing the same according to the present embodiment (Examples 1 to 11) realizes a relative improvement of the thermal conductivity compared to an aluminum nitride sintered body of the same composition that does not introduce the aforementioned process.
(54) (Variant)
(55) Even if the step of decarbonization in a nitrogen atmosphere of the raw material mixture to which nitride is added is omitted as shown in the flowchart of
(56) The present invention is not limited to the embodiments and variants described above, but may be practiced in a variety of aspects so long as they fall within the technical scope of the invention. In other words, the present invention may be modified or altered by those skilled in the art without departing from the technical scope of the invention. For example, other elements and components may be added to the structure of the invention.