Silicon nitride sintered body

Abstract

A silicon nitride sintered body according to the present disclosure contains silicon nitride particles and yttrium silicon oxynitride particles, and has a porosity of 14% or lower.

Description

[Technical Field]

[0001] The present disclosure relates to a silicon nitride sintered body. [Background technology]

[0002] BACKGROUND ART Silicon nitride sintered bodies have been attracting attention as materials excellent in heat resistance, strength and hardness, and have been used, for example, as engine parts.

[0003] In recent years, power modules that perform highly efficient power conversion and control have been used in electric vehicles and the like. Power modules require insulating substrates that not only have insulation properties but also high thermal conductivity for efficiently transferring heat generated from semiconductor elements and high mechanical properties for withstanding stresses generated by temperature cycles. As an insulating substrate material that meets these requirements, the present applicant previously disclosed a silicon nitride sintered body, as shown in Patent Document 1 below. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2005 / 019133 Summary of the Invention

[0005] A silicon nitride sintered body according to one embodiment of the present disclosure contains silicon nitride particles and yttrium silicon oxynitride particles, and has a porosity of 14% or less. DETAILED DESCRIPTION OF THE INVENTION

[0006] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a mode for carrying out a silicon nitride sintered body according to the present disclosure (hereinafter referred to as an "embodiment") will be described in detail with reference to the drawings.

[0007] In recent years, for example, power modules used in electric vehicles have tended to operate at higher temperatures in order to achieve high efficiency and energy savings, and therefore there is a demand for silicon nitride sintered bodies that can be used stably even in higher temperature environments.

[0008] The silicon nitride sintered body according to the embodiment contains silicon nitride particles and yttrium silicon oxynitride particles and has a porosity of 14% or less. Such a silicon nitride sintered body is further suitable for use in high-temperature environments. Specifically, the silicon nitride sintered body according to the embodiment can maintain high thermal conductivity even in high-temperature environments (for example, about 100 to 200°C). That is, the silicon nitride sintered body according to the embodiment can maintain high thermal conductivity and heat dissipation properties in high-temperature environments, making it suitable for use in high-temperature environments.

[0009] The silicon nitride sintered body according to the embodiment contains yttrium silicon oxynitride particles, such as YSi 11 N 20 The crystalline silicon dioxide may contain at least one of YSi3O3N4 particles (hereinafter referred to as "phase A"), YSi3O3N4 particles (hereinafter referred to as "phase B"), Y4Si2O7N2 particles (hereinafter referred to as "phase C"), and Y2Si3O3N4 particles (hereinafter referred to as "phase D").

[0010] The silicon nitride sintered body according to the embodiment may contain, as yttrium silicon oxynitride particles, two of phases A, B, C, and D. Specifically, the silicon nitride sintered body according to the embodiment may contain two of phases A and B. The silicon nitride sintered body according to the embodiment may also contain two of phases C and D.

[0011] In the silicon nitride sintered body according to the embodiment, the volume ratio of phase A to phase B (ratio of phase A to phase B) may be 1.4 or more. By adopting this configuration, it is possible to obtain a silicon nitride sintered body having a thermal conductivity of 67 W / m K or more at 100°C and a thermal conductivity of 49 W / m K or more at 200°C.

[0012] In the silicon nitride sintered body according to the embodiment, the volume ratio of phase A to phase B (ratio of phase A to phase B) may be 2.0 or more. By adopting this configuration, it is possible to obtain a silicon nitride sintered body having a thermal conductivity of 72 W / m K or more at 100°C and a thermal conductivity of 55 W / m K or more at 200°C.

[0013] In the silicon nitride sintered body according to the embodiment, the volume ratio of phase A to phase B (ratio of phase A to phase B) may be 3.0 or more. By adopting this configuration, it is possible to obtain a silicon nitride sintered body having a thermal conductivity of 74 W / m K or more at 100°C and a thermal conductivity of 57 W / m K or more at 200°C.

[0014] The silicon nitride sintered body according to the embodiment has a fracture toughness of 6.5 MPa m 1 / 2 The dielectric strength may be 10 kV or more, and the three-point bending strength may be 521 MPa or more. According to this configuration, a silicon nitride sintered body having excellent magnetic properties can be obtained.

[0015] (Example) A raw powder was obtained by mixing Si3N4 powder, Si powder, Y2O3, and MgO in proportions of 23.4 wt%, 70.2 wt%, 4.9 wt%, and 1.5 wt%. Y2O3 and MgO are sintering aids. The raw powder, ethanol, and silicon nitride grinding media were then placed in a barrel mill and mixed. Polyvinyl alcohol (PVA) was then added to the resulting slurry as an organic binder and mixed, followed by granulation using a spray dryer. The resulting granulated powder was compacted using a powder press molding method using a mold at a molding pressure of 80 MPa and degreased at 600°C in N2 to obtain multiple compacts.

[0016] Next, the obtained compact was subjected to a nitriding step in which Si in the compact was nitrided to Si3N4 by heat treatment at a nitrogen partial pressure (0.3 MPa or 0.6 MPa), temperature (1350°C), and time (15 hours) shown in Table 1. Thereafter, the temperature was further increased and the compact was fired under the same nitrogen partial pressure as in the nitriding step at a temperature (1900°C, 1925°C, or 1945°C) and time (6 hours or 12 hours) shown in Table 1 to obtain samples (No. 1 to No. 5) of the present disclosure.

[0017] In addition, Si3N4 powder, Si powder, Y2O3, and MgO were mixed in proportions of 65.5 wt%, 21.9 wt%, 11.9 wt%, and 0.7 wt% to obtain a raw powder. Y2O3 and MgO are sintering aids. Next, the raw powder, ethanol, and silicon nitride grinding media were placed in a barrel mill and mixed. Next, polyvinyl alcohol (PVA) was added as an organic binder to the resulting slurry, which was then mixed and granulated using a spray dryer. The resulting granulated powder was compacted using a powder press molding method using a mold at a molding pressure of 80 MPa and degreased at 600°C in N2 to obtain multiple compacts.

[0018] The resulting compact was then subjected to nitriding treatment under normal pressure under the conditions shown in Table 1. Note that sample No. 8 was subjected to a nitriding step in which Si in the compact was nitrided to Si3N4 by heat treatment at 1100°C to 1400°C for 40 hours. Thereafter, the compact was fired under conditions of 0.7 MPa, 1900°C, and 12 hours to obtain sample No. 8 of the present disclosure. Note that "1100°C to 1400°C" means that the heat treatment was performed while increasing the temperature from 1100°C to 1400°C over 40 hours.

[0019] Table 1 shows samples No. 6 and No. 7 as comparative examples. Sample No. 6 is a silicon nitride sintered body described in Japanese Patent No. 6822362. Sample No. 6 was manufactured as follows: Si powder, Y2O3, and MgO were mixed in proportions of 89.0 wt%, 1.2 wt%, and 9.8 wt% to obtain a raw powder. A dispersant (sorbitan trioleate) was added to this raw powder at a concentration of 0.5 wt% relative to the total of the dispersion medium (toluene) and raw powder to obtain a slurry with a concentration of 42 wt%, and the slurry was milled for 24 hours using a ball mill with 5φ silicon nitride balls as the media.

[0020] The resulting slurry was adjusted in concentration by adding a dispersion medium and an organic binder (acrylic resin), and then degassed to form a coating solution. This coating slurry was formed into a sheet using the doctor blade method to obtain a sheet-like molded body. After degreasing, the resulting sheet-like molded body was nitrided in a BN (boron nitride) crucible under a nitrogen atmosphere (nitrogen partial pressure 0.1 MPa) at 1450°C for 10 hours, and then sintered in a BN crucible under a nitrogen atmosphere (nitrogen partial pressure 0.9 MPa) at 1900°C for 12 hours to obtain Sample No. 6.

[0021] Sample No. 7 is a silicon nitride sintered body described in Japanese Patent Publication No. 6297188. The manufacturing method for Sample No. 7 is as follows: Si3N4 powder, Y2O3, and MgO are mixed in proportions of 95.0 wt%, 3 wt%, and 2 wt% to obtain raw powder. A dispersant and an organic solvent are added to the raw powder and ball milled. Next, 100 parts by mass of the raw powder are mixed with 10 parts by mass of butyl methacrylate as an organic binder and 4 parts by mass of dibutyl phthalate as a plasticizer, and an organic solvent is added. Further ball mill mixing is performed to prepare a slurry-like raw material mixture. The viscosity of the slurry is adjusted to 5,000 to 15,000 cps, and the slurry is then formed into a sheet using a doctor blade method and dried to prepare a green sheet. The green sheet is then degreased by heating the compact in a nitrogen gas atmosphere at 500 to 800°C for 1 to 4 hours. Next, the degreased compact is sintered in a nitrogen atmosphere at 1900°C for 9 hours to obtain sample No. 7.

[0022] [Table 1]

[0023] The Si3N4 powder, Si powder, YO3, and MgO used as raw materials for Samples No. 1 to No. 5 and No. 8 were analyzed for their components. The results are shown in Tables 2 to 4. The Si3N4 powder was analyzed by X-ray fluorescence (XRF) analysis and ICP optical emission spectroscopy (Table 2). The Si powder, YO3, and MgO were analyzed by X-ray fluorescence (XRF) analysis (Tables 3 and 4).

[0024] [Table 2]

[0025] [Table 3]

[0026] [Table 4]

[0027] It was found that the Si3N4 powder, Si powder, Y2O3, and MgO used as raw materials each contained the impurities shown in Tables 2 to 4. Specifically, the Si3N4 powder contained Al2O3, CaO, and Fe2O3 in addition to Si3N4, the Si powder contained O, Fe, Ni, and K in addition to Si, the Y2O3 contained SiO2, Fe2O3, Cr2O3, and CaF2, and the MgO contained SiO2, Al2O3, CaO, Fe2O3, and B2O3.

[0028] For the samples No. 1 to No. 5 of the examples, the obtained samples were pulverized, and the crystalline phases were identified using X-ray diffraction. Then, the ratio of each crystalline phase was determined using the Rietveld method. The results are shown in Table 5.

[0029] [Table 5]

[0030] As shown in Table 5, Samples No. 1 to No. 5 and No. 8 all contained silicon nitride particles and yttrium silicon oxynitride particles. Specifically, Samples No. 1 to No. 5 contained β-phase SiN as the silicon nitride particles. Furthermore, Samples No. 1 to No. 5 contained YSi as the yttrium silicon oxynitride particles. 11 N 20 The samples contained yttrium silicon oxynitride particles, namely, Y4Si2O7N2 particles (phase C) and Y2Si3O3N4 particles (phase D). Sample No. 8 contained β-phase SiN as silicon nitride particles. Sample No. 8 also contained yttrium silicon oxynitride particles, namely, Y4Si2O7N2 particles (phase C) and Y2Si3O3N4 particles (phase D).

[0031] The volume ratio of phase A to phase B (phase A / phase B) was 2.0 for sample No. 1, 3.1 for sample No. 2, 1.4 for sample No. 3, 0.1 for sample No. 4, and 0.2 for sample No. 5.

[0032] (Porosity) For samples No. 1 to No. 5 and No. 8, each sample was polished, and the polished surface was photographed using an electron microscope. The pores present in a unit area (20 μm × 20 μm) of the photograph were extracted. The area of ​​the extracted pores was then calculated by image analysis, and the area ratio based on the unit area was calculated.

[0033] As shown in Table 5, the porosity of samples Nos. 1 to 5 and 8 was 0.5% for sample No. 1, 0.9% for sample No. 2, 0.4% for sample No. 3, 13.6% for sample No. 4, 11.3% for sample No. 5, and 0.3% for sample No. 8. The porosity of sample No. 6, which is a comparative example, was 1.5%.

[0034] (thermal conductivity) For samples No. 1 to No. 5 and No. 8, 10 mm square, 0.32 mm thick test pieces were cut out from each sample, and the thermal conductivity of the cut test pieces in the thickness direction was measured using the laser flash method. The measurement temperatures were room temperature, 100°C, and 200°C. The results are shown in Table 6.

[0035] [Table 6]

[0036] As shown in Table 6, the thermal conductivity at room temperature was 94 W / m·K for sample No. 1, 96 W / m·K for sample No. 2, 86 W / m·K for sample No. 3, 76 W / m·K for sample No. 4, 81 W / m·K for sample No. 5, and 88 W / m·K for sample No. 8. The thermal conductivities of comparative samples No. 6 and No. 7 were 123 W / m·K and 90 W / m·K, respectively.

[0037] The thermal conductivities at 100°C were 72 W / m·K for sample No. 1, 74 W / m·K for sample No. 2, 67 W / m·K for sample No. 3, 57 W / m·K for sample No. 4, 61 W / m·K for sample No. 5, and 62 W / m·K for sample No. 8. The thermal conductivities at 100°C for comparative samples No. 6 and No. 7 were 86 W / m·K and 63 W / m·K, respectively. The thermal conductivities at 200°C were 55 W / m·K for sample No. 1, 57 W / m·K for sample No. 2, 49 W / m·K for sample No. 3, 42 W / m·K for sample No. 4, 47 W / m·K for sample No. 5, and 44 W / m·K for sample No. 8. The thermal conductivities at 100°C of comparative samples No. 6 and No. 7 were 62 W / m·K and 45 W / m·K, respectively.

[0038] As described above, it can be seen that Samples No. 1 to No. 5 and No. 8, which are examples of the present disclosure, maintain high thermal conductivity even in high-temperature environments. In other words, Samples No. 1 to No. 5 and No. 8, which are examples, can maintain high heat dissipation properties in high-temperature environments, making them suitable for use in high-temperature environments.

[0039] The comparative sample No. 6 has a higher thermal conductivity at 100°C than the example samples Nos. 1 to 5 and No. 8. The comparative sample No. 7 has a higher thermal conductivity at 100°C than the example sample No. 5.

[0040] However, for both Samples No. 6 and No. 7, the reduction rate ((RT-100) / RT) was 30%, meaning that the rate of change in the thermal conductivity of the material was large when the temperature was changed from room temperature (RT, 25°C) to 100°C. Therefore, for example, if a power element is installed on a board made using Samples No. 6 and No. 7, there is a risk that the temperature change rate of the power element itself will be large when the power element is operating. This will impair stable operation of the power element, making the output value of the power module more likely to vary and making stable operation difficult.

[0041] On the other hand, although samples No. 1 to No. 5 have lower thermal conductivity at temperatures such as room temperature, 100°C, and 200°C than sample No. 6, the rate of change in thermal conductivity from room temperature to 100°C and from room temperature to 200°C is small, so stable operation of the power element as well as stable operation of the power module can be expected.

[0042] Furthermore, since Samples No. 1 to No. 5 have higher fracture toughness than Samples No. 6 and No. 7, the probability of the power element itself being damaged due to temperature changes is low.

[0043] (fracture toughness) Fracture toughness measurements were performed on samples No. 1 to No. 5 and No. 8 using the IF method. The fracture toughness measurements conformed to JIS R1607-1995, and involved pressing a Vickers indenter into a mirror-polished test piece, and measuring the fracture toughness based on the length of the indentation and crack that occurred. The indentation load was 98 N (= 10 kgf), and the indentation time was 15 seconds.

[0044] As shown in Table 6, the fracture toughness of samples No. 1 to No. 5 and No. 8 was 7.1 MPa m 1 / 2 ", and sample No. 2 is "7.5 MPa m 1 / 2 ", and sample No. 3 is "7.3 MPa m 1 / 2 ", and sample No. 4 is "6.7 MPa m 1 / 2 ", and sample No. 5 is "6.5 MPa m 1 / 2 ", and sample No. 8 is "6.2 MPa m 1 / 2 Sample No. 6 was 6.3 MPa m 1 / 2 , and sample No. 7 is 6.4 MPa m 1 / 2 It was.

[0045] (Dielectric strength) The dielectric strength voltage was measured for Samples No. 1 to No. 5 and Sample No. 8. The dielectric strength voltage was measured by forming brass electrodes on the top and bottom surfaces of a 0.32 mm thick substrate and applying a voltage between the electrodes.

[0046] As shown in Table 6, the dielectric strength voltages of samples Nos. 1 to 5 and No. 8 were 12 kV for sample No. 1, 12 kV for sample No. 2, 11 kV for sample No. 3, 10 kV for sample No. 4, 11 kV for sample No. 5, and 11 kV for sample No. 8. The dielectric strength voltages of samples Nos. 6 and 7, which are comparative examples, were 11 kV and 11 kV, respectively.

[0047] (3-point bending strength) The three-point bending strength of Samples No. 1 to No. 5 and No. 8 was measured at room temperature based on JIS R1601.

[0048] As shown in Table 6, the three-point bending strengths of samples Nos. 1 to 5 and No. 8 were 613 MPa for sample No. 1, 602 MPa for sample No. 2, 604 MPa for sample No. 3, 534 MPa for sample No. 4, 521 MPa for sample No. 5, and 748 MPa for sample No. 8. The three-point bending strengths of samples Nos. 6 and 7, which are comparative examples, were 716 MPa and 600 MPa, respectively.

[0049] Thus, it was found that Samples No. 1 to No. 5 and No. 8, which are examples of the present disclosure, have excellent magnetic properties.

[0050] As described above, the silicon nitride sintered body according to the embodiment is made of silicon nitride particles (for example, SiN) and yttrium silicon oxynitride particles (YSi 11 N 20 O particles and YSi3O3N4 particles). The silicon nitride sintered body has a porosity of 14% or less. Therefore, the silicon nitride sintered body according to the embodiment provides a silicon nitride sintered body that is more suitable for use in high-temperature environments.

[0051] The disclosed embodiments should be considered in all respects as illustrative and not restrictive. Indeed, the above-described embodiments may be embodied in various forms. Furthermore, the above-described embodiments may be omitted, substituted, or modified in various ways without departing from the scope and spirit of the appended claims.

Claims

1. silicon nitride particles and yttrium silicon oxynitride particles, The porosity is 14% or less, A silicon nitride sintered body, wherein the yttrium silicon oxynitride particles include at least two of Y 6 Si 11 N 20 O particles, YSi 3 O 3 N 4 particles, Y 4 Si 2 O 7 N 2 particles, and Y 2 Si 3 O 3 N 4 particles.

2. The Y ６ Si １１ N ２０ O particles / YSi ３ O ３ N ４ 2. The silicon nitride sintered body according to claim 1, wherein the particles have a volume ratio of 1.4 or more.

3. The Y ６ Si １１ N ２０ O particles / YSi ３ O ３ N ４ 3. The silicon nitride sintered body according to claim 2, wherein the particles have a volume ratio of 2.0 or more.

4. The Y ６ Si １１ N ２０ O particles / YSi ３ O ３ N ４ 4. The silicon nitride sintered body according to claim 3, wherein the particles have a volume ratio of 3.0 or more.

5. Fracture toughness is 6.5 MPa m １／２ That's all, The dielectric strength is 10 kV or more, 5. The silicon nitride sintered body according to claim 1, having a three-point bending strength of 521 MPa or more.

6. A composition comprising silicon nitride particles and yttrium silicon oxynitride particles, The porosity is 14% or less, The fracture toughness is 6.5 MPa·m 1 / 2 or more; The dielectric strength is 10 kV or more, A silicon nitride sintered body having a three-point bending strength of 521 MPa or more.

7. The silicon nitride sintered body of claim 6, wherein the yttrium silicon oxynitride particles include at least one of Y 6 Si 11 N 20 O particles, YSi 3 O 3 N 4 particles, Y 4 Si 2 O 7 N 2 particles and Y 2 Si 3 O 3 N 4 particles.

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