Cordierite sintered body, method for producing the same, composite substrate, and electronic device

Abstract

The present invention provides a cordierite sintered body, a method for producing the same, a composite substrate, and an electronic device, the cordierite sintered body having a ratio of a sum of intensities of the largest peaks of each component other than the cordierite component to the peak top intensity of the (110) plane of the cordierite in an X-ray diffraction pattern in a range of 0.0009 to 0.0020, and a bulk density in a range of 2.497 to 2.507 g / cm 3 In the cordierite sintered body, heterophases other than the cordierite component are extremely small, and thus the surface flatness when the surface is polished to a mirror surface is high.

Description

[0001] This application is a divisional application of Chinese invention application No. 201580002729.5, filed on May 26, 2015, entitled "Cordierite Sintered Body, Method Thereof, Composite Substrate and Electronic Device". Technical Field

[0002] This invention relates to cordierite sintered bodies, their preparation methods, composite substrates, and electronic devices. Background Technology

[0003] Cordierite sintered body is a material with high heat resistance and low coefficient of thermal expansion, and is therefore well known as a material with high thermal shock resistance. In particular, it is widely used as a catalyst carrier and filter for exhaust gas purification in automobiles and other applications when sintered into a porous structure.

[0004] For dense cordierite sintered bodies, taking advantage of their low thermal expansion and lightweight characteristics, their use as stage components in exposure devices (Patent Document 1) and as substrates for ultra-precision mirrors (Patent Document 2) is being promoted in recent years. In Patent Document 1, improvements were made, particularly to obtain high rigidity, by setting the CaO content in the cordierite sintered body to 0.2 to 0.8% by mass and containing a predetermined amount of Al2O3 as a subgrain. CaO has the effect of increasing Young's modulus by promoting cordierite grain growth and sinterability, while Al2O3 has the effect of inhibiting abnormal grain growth in cordierite and densifying it. In Patent Document 2, the goal is to reduce surface roughness while maintaining high rigidity. A dense cordierite sintered body is produced by adding a predetermined amount of a specific rare earth metal component as a sintering aid. The obtained sintered body does not contain any crystalline phases other than cordierite. The rare earth metal components exist as amorphous phases along the grain boundaries of cordierite particles in a film-like form. It can be considered that the absence of crystalline components other than cordierite avoids the generation of unevenness caused by differences in the grinding characteristics between different particles.

[0005] Patent Document 3 provides an example of producing a dense cordierite sintered body without adding sintering aids. In this example, a shaped body was obtained by uniaxial die stamping cordierite powder with an average particle size of less than 0.7 μm. The shaped body was then sintered at 1400°C for 12 hours under a nitrogen atmosphere to produce a cordierite sintered body with the following characteristics: cordierite content of 97.6% by mass and bulk density of 2.54 g / cm³. 3 The open porosity is 0%, the total porosity is 0.1%, and it contains mullite, spinel, pseudosapphire, etc. in the heterogeneous phase (Example 1). In this sintered body, based on the total porosity and open porosity, the closed porosity is 0.1%, and based on... Figure 2 The photograph of the polished surface after thermal etching shows that at approximately 20 μm...2 There are about 20 closed pores with a major diameter of about 0.2 to 0.5 μm in the surface.

[0006] On the other hand, in recent years, as a surface acoustic wave (SAW) element, a structure consisting of a main substrate and an auxiliary substrate has been developed. For example, Patent Document 4 shows an SAW element obtained by directly bonding a main substrate containing lithium tantalate, lithium niobate, etc., to an auxiliary substrate containing glass or silicon. In this SAW element, the coefficient of thermal expansion of the auxiliary substrate is smaller than that of the main substrate, and the thickness of the auxiliary substrate is greater than that of the main substrate. By combining such a main substrate and an auxiliary substrate, compressive stress is applied near the surface of the main substrate when the substrate temperature rises, resulting in a smaller thermal expansion than the original thermal expansion of the main substrate. This demonstrates that the frequency-temperature dependence of the SAW element on the main substrate is improved. It is also stated that the coefficient of thermal expansion is 4.5 ppm / ℃ when the auxiliary substrate is glass, and the amorphous nature of the glass facilitates bonding with the main substrate, which is a single crystal. However, the surface states of the main substrate and the auxiliary substrate supplied for bonding are not described in detail.

[0007] Patent Document 5, similar to Patent Document 4, describes a technology for improving the temperature dependence of an elastic surface wave element. The piezoelectric substrate (main substrate) is either lithium tantalate or lithium niobate, and the support substrate (auxiliary substrate) is either sapphire, alumina, aluminum nitride, or silicon nitride (coefficient of thermal expansion 2.6 ppm / °C). The bonding substrate is fabricated by direct bonding. However, the required surface conditions for the support substrate, etc., are not described.

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent Application Publication No. 2010-173878

[0011] Patent Document 2: Japanese Patent Application Publication No. 2012-87026

[0012] Patent Document 3: Japanese Patent Application Publication No. 2005-314215

[0013] Patent Document 4: Japanese Patent Application Publication No. 11-55070

[0014] Patent Document 5: Japanese Patent No. 3774782 Summary of the Invention

[0015] The problem that the invention aims to solve

[0016] In the cordierite sintered bodies described in Patent Documents 1 and 2, since a predetermined amount of sintering aid is also contained in addition to cordierite, the phases other than cordierite exist either as crystalline phases or as amorphous phases, resulting in a sintered body structure that is a mixture of cordierite and other phases. Because these phases have different chemical and physical properties, differences arise in the ease of grinding during surface finishing processes such as polishing. In particular, these differences become significant when using acidic or alkaline slurries for chemical mechanical polishing (CMP), contributing to surface unevenness. Therefore, improving surface smoothness in cordierite sintered bodies like those in Patent Documents 1 and 2 is extremely difficult. On the other hand, in the cordierite sintered body of Patent Document 3, no sintering aid is added, but heterogeneous phases such as mullite and spinel, which are not cordierized, are present. Furthermore, although densification continues, a large number of closed pores remain. These heterogeneous phases and closed pores prevent the achievement of sufficient surface smoothness.

[0017] Furthermore, in the elastic surface wave elements of Patent Documents 4 and 5, polycrystalline materials (sintered bodies) such as alumina, aluminum nitride, and silicon nitride are used as support substrates, but there is no mention of the heterogeneous phases and pores mentioned above, and the degree of surface flatness is unclear. In this elastic surface wave element, the smaller the frequency temperature dependence, the higher the characteristic stability to changes in ambient temperature, making it a high-performance element. In order to achieve a higher performance element than previous elements, it is necessary to further reduce the thermal expansion of the element.

[0018] This invention was made to solve such problems, and its main objective is to provide a cordierite sintered body with high surface flatness when ground to a mirror finish. Another objective is to provide a composite substrate using such a cordierite sintered body as a support substrate.

[0019] Methods for solving problems

[0020] In the X-ray diffraction pattern of the cordierite sintered body of the present invention, the sum of the intensities of the maximum peaks of all components other than cordierite is less than 0.0025 relative to the peak intensity of the (110) plane of cordierite. This cordierite sintered body contains very few heterogeneous phases other than cordierite, resulting in high surface smoothness when the surface is polished to a mirror finish.

[0021] The method for preparing cordierite sintered bodies of the present invention involves sintering cordierite raw material powder containing MgO, Al2O3, and SiO2 under an inactive atmosphere using a hot-pressing method. In the cordierite raw material powder, the molar ratio of MgO / Al2O3 is 0.96–1.04, the molar ratio of SiO2 / Al2O3 is 2.46–2.54, and the proportions of MgO, SiO2, and Al2O3 in the total composition are 99.9% by mass or more. The average particle size D50 of the cordierite raw material powder is less than 1 μm. The hot-pressing sintering conditions are a pressing pressure of 20–300 kgf / cm². 2 The firing temperature is 1410–1450°C. This method is suitable for manufacturing the cordierite sintered body of the present invention as described above.

[0022] The composite substrate of the present invention is a composite substrate obtained by bonding a functional substrate with a cordierite sintered support substrate, wherein the proportion of the area actually bonded at the bonding interface (bonding area ratio) is 80% or more. In this composite substrate, when the cordierite sintered body is the cordierite sintered body of the present invention as described above, the bonding area ratio increases as above, exhibiting good bonding properties.

[0023] The electronic device of the present invention utilizes the aforementioned composite substrate. In this electronic device, the coefficient of thermal expansion of the cordierite sintered body serving as the support substrate is approximately 1.1 ppm / K (40–400°C), which is very small, thus significantly improving the frequency-temperature dependence when fabricating elastic surface wave devices. Furthermore, in optical waveguide devices, LED devices, and switching devices, the coefficient of thermal expansion of the support substrate is also very small, thereby improving performance. Attached Figure Description

[0024] Figure 1 The manufacturing process of cordierite sintered body.

[0025] Figure 2 This is a three-dimensional view of the composite substrate 10.

[0026] Figure 3 A perspective view of an electronic device 30 fabricated using a composite substrate 10.

[0027] Figure 4 The image shows the XRD diffraction pattern of the cordierite sintered pulverized material from Experiment Example 1.

[0028] Figure 5 The image shows the SEM image of the ground surface of the cordierite sintered body in Experiment Example 1.

[0029] Figure 6 The transmittance curve of the cordierite sintered body in Experiment Example 1 is shown.

[0030] Figure 7 This is a photograph of the appearance of the cordierite sintered body from Experiment Example 1.

[0031] Figure 8 The image shows the XRD diffraction pattern of the cordierite sintered pulverized material from Experiment Example 10. Detailed Implementation

[0032] The following describes specific embodiments of the present invention. However, it should be understood that the present invention is not limited to the following embodiments. Changes, modifications, etc., can be appropriately made based on the common knowledge of those skilled in the art without departing from the spirit of the present invention.

[0033] In the cordierite sintered body of the present invention, the sum of the intensities of the maximum peaks of all components other than cordierite in the X-ray diffraction pattern is 0.0025 or less relative to the peak intensity of the (110) plane of cordierite. It should be noted that the X-ray diffraction pattern was measured under the following conditions: CuKα, 50 kV, 300 mA, 2θ = 5-70°. This cordierite sintered body contains very few heterogeneous phases other than cordierite, resulting in high surface smoothness when the surface is polished to a mirror finish. Regarding surface smoothness, for example, when performing AFM observation on a polished mirror-finished surface, it is preferable to satisfy at least one of the following conditions: the average surface roughness Ra along the centerline in a 10 μm square measurement range is 1 nm or less; the maximum peak height Rp in a 70 μm square measurement range is 30 nm or less; and the number of pores with a maximum length of 0.1 μm or more in any 4 μm × 4 μm range is 10 or less. Furthermore, if there is a large amount of heterogeneous components, the ease of grinding between cordierite and heterogeneous components will differ. In particular, heterogeneous components are not easy to grind and are prone to leaving convex residues, thus the surface smoothness cannot be sufficiently high.

[0034] In the cordierite sintered body of the present invention, the molar ratio of MgO / Al2O3 is preferably 0.96 to 1.04, and the molar ratio of SiO2 / Al2O3 is preferably 2.46 to 2.54. Furthermore, the proportion of MgO, Al2O3, and SiO2 in the total composition is 99.9% by mass or more; in other words, the proportion of components other than these three is preferably less than 0.1% by mass. Further, the average particle size of the cordierite sintered particles is preferably 1 μm or less. Moreover, the bulk density is preferably 2.495 to 2.515 g / cm³. 3 (True density is 2.505 g / cm³) 3 This operation can further reduce heterogeneous components in cordierite sintered bodies.

[0035] The cordierite sintered body of the present invention preferably has a total light transmittance of 60% or more and a linear transmittance of 550 nm or more, more preferably 70% or more and 60% or more, respectively. With these settings, the light transmittance is high, and furthermore, the linear transmittance is high and transparent, thus enabling it to function as a light-transmitting support substrate when fabricated into a composite substrate. Furthermore, regarding the cordierite sintered body of the present invention, due to the high thermal stability and thermal shock resistance of cordierite, it can be used as a material for heat-resistant and light-transmitting devices such as high-temperature furnace window materials and concentrating furnace reaction tubes. Conventionally, quartz glass and transparent alumina have been used as such materials. However, quartz glass needs to be used below 1000°C. While transparent alumina can be used above 1000°C, it requires thermal shock protection. In contrast, the cordierite sintered body of the present invention exhibits higher heat resistance than quartz glass, thus allowing it to be used at temperatures above 1000°C. It also demonstrates higher thermal shock resistance compared to transparent alumina, eliminating the need for thermal shock protection and making it suitable as a material for heat-resistant and transparent appliances. Furthermore, annealing the cordierite sintered body at 1200–1400°C further enhances its light transmittance and transparency.

[0036] Next, embodiments of the method for manufacturing the cordierite sintered body of the present invention will be described. For example... Figure 1 As shown, the manufacturing process of cordierite sintered body includes the process of making cordierite raw material powder and the process of making cordierite sintered body.

[0037] (Preparation of cordierite raw material powder)

[0038] A mixed powder containing MgO, Al2O3, and SiO2 in a predetermined ratio is sintered to produce coarse cordierite granules. Figure 1 (S1). Here, the mixed powder refers to a powder obtained by mixing the three components that become cordierite through sintering, preferably a mixed powder obtained by, for example, blending MgO at 13.8% by mass, Al2O3 at 34.9% by mass, and SiO2 at 51.3% by mass. Alternatively, if the amount of components to be mixed in the pulverizing process can be estimated in advance, for example, if the amount of alumina component from the alumina medium (alumina balls, alumina cans, etc.) used in the pulverizing process can be estimated in advance, the amount of Al2O3 component blended in the mixed powder can be reduced in advance. Furthermore, in the cordierite sintered body of the present invention, it is important to avoid the formation of heterogeneous phases by impurity components, therefore it is preferable to use raw materials with the highest possible purity, and the purity of each component blended in the mixed powder is preferably 99.9% or higher. However, components that dissipate through heating, such as CO2 and H2O, are not included in the impurities.

[0039] Next, the coarse cordierite particles obtained by calcining the mixed powder are pulverized to produce cordierite powder. Figure 1 (S2). The mixed powder can be sintered, for example, by heating at 1300–1450°C in an atmospheric atmosphere. When pulverizing the coarse cordierite particles, pulverization is carried out in such a way that the average particle size (D50) of the cordierite pulverized material is 2 μm or less, preferably 1 μm or less, and more preferably 0.8 μm or less. In this way, by reducing the average particle size of the cordierite pulverized material, a high-density cordierite sintered body can be produced even without adding sintering aids. There is no particular limitation on the lower limit of the average particle size of the cordierite pulverized material, but since the smaller the particle size, the longer the pulverization time becomes, and the more components are mixed in from the pulverizing medium (balls, cans, etc.) during the pulverization process, the average particle size is preferably 0.1 μm or more, and more preferably 0.3 μm or more. It should be noted that this average particle size can be determined by laser diffraction.

[0040] There are no particular restrictions on the pulverization method; for example, ball mills, atritors, bead mills, and jet mills can be used. However, careful attention must be paid to the composition and quantity of components mixed into the pulverizing media. Specifically, alumina beads or cans, which do not become impurities even if mixed in, are preferred as the media. Resin cans or beads can also be used, as they can be removed during the firing process, but pulverization requires a longer time when using beads. On the other hand, when using zirconium oxide media, the pulverization time needs to be shortened, and in particular, large-scale mixing in should be avoided. Metal media are not preferred due to the increased amount of impurities.

[0041] The cordierite powder was dried, and the MgO, Al2O3, and SiO2 content in the dried cordierite powder was analyzed. The required components were added only in the required amounts to the dried cordierite powder in a manner that ensured the proportions of each component conformed to the composition of cordierite, and this powder was used as the cordierite raw material powder. Figure 1(S3). For example, when using an alumina medium to pulverize coarse cordierite particles, the Al2O3 content becomes excessive relative to the cordierite composition. Therefore, a predetermined amount of MgO powder and SiO2 powder are added to the dried cordierite pulverized material to readjust it to a cordierite composition, and the readjusted powder is used as cordierite raw material powder. It should be noted that the readjusted powder is also subjected to a mixing process similar to the pulverization process, but importantly, the mixing time is set to a short time to suppress the mixing from the medium. Alternatively, the amounts of each component in the mixed powder can be adjusted in advance so that the components contained in the dried cordierite pulverized material become cordierite composition, and the dried cordierite pulverized material can be used directly as cordierite raw material powder. For example, when using an alumina medium to pulverize coarse cordierite particles, the amount of Al2O3 in the mixed powder can be reduced in advance by estimating the amount of Al2O3 content mixed from the pulverization medium. If this is done, the dried cordierite pulverized material can be directly used as cordierite raw material powder. Through this operation, high-purity cordierite raw material powder with adjusted composition and particle size can be prepared. In the cordierite raw material powder obtained through this operation, for example, the molar ratio of MgO / Al2O3 is 0.96–1.04, the molar ratio of SiO2 / Al2O3 is 2.46–2.54, the proportion of MgO, SiO2, and Al2O3 in the total composition is 99.9% by mass or more, and the average particle size D50 of the cordierite raw material powder is less than 1 μm.

[0042] (Production of Cordierite Sintered Body)

[0043] The obtained cordierite raw material powder is shaped into a predetermined shape. Figure 1 (S4). There are no particular restrictions on the forming method; general forming methods can be used. For example, the cordierite raw material powder described above can also be directly stamped using a metal mold. In the case of stamping, if the cordierite raw material powder is pre-formed into granules using spray drying, the formability becomes better. In addition, organic binders can be added to make blanks for extrusion molding, or slurries can be made for sheet forming. In these processes, the organic binder components need to be removed before or during the firing process. Alternatively, high-pressure forming can be performed using a CIP (cold isostatic press).

[0044] Next, the obtained shaped body is heated to produce a cordierite sintered body. Figure 1(S5). At this point, to improve the surface smoothness of the cordierite sintered body, it is important to maintain the sintered particles to be fine and to expel pores during sintering. Hot pressing is a very effective technique for this. By using hot pressing, densification occurs at a low temperature in a fine-grained state compared to atmospheric pressure sintering, suppressing the residue of large pores commonly found in atmospheric pressure sintering. The firing temperature during hot pressing is preferably 1410–1450°C, and more preferably 1420–1440°C to minimize heterogeneous phases. Furthermore, the pressing pressure during hot pressing is preferably set to 20–300 kgf / cm². 2 Especially under low stamping pressure, the hot pressing fixture can be miniaturized and have a longer lifespan, making it even more preferable. Regarding the holding time at the firing temperature (maximum temperature), an appropriate time can be selected considering the shape and size of the formed body, the characteristics of the heating furnace, etc. Specifically, a preferred holding time is, for example, 1 to 12 hours, and more preferably 2 to 8 hours. There are no particular restrictions on the firing atmosphere; the atmosphere during hot pressing is generally an inactive atmosphere such as nitrogen or argon.

[0045] The composite substrate of the present invention is a composite substrate obtained by bonding a functional substrate to a cordierite sintered support substrate, wherein the proportion of the area actually bonded at the bonding interface (bonding area ratio) is 80% or more. Regarding this composite substrate, when the cordierite sintered body is the cordierite sintered body of the present invention described above, the bonding area ratio increases as described above, exhibiting good bonding properties. There are no particular limitations on the functional substrate; examples include lithium tantalate, lithium niobate, gallium nitride, and silicon. The bonding method can be direct bonding or bonding through an adhesive layer, but direct bonding is preferred. In the case of direct bonding, after activating the bonding surfaces of the functional substrate and the support substrate, the two substrates are pressed together with the two bonding surfaces facing each other. Activation of the bonding surfaces can be performed, for example, by irradiating the bonding surfaces with an ion beam of an inactive gas (such as argon), or by irradiation with plasma, neutral atom beams, etc. On the other hand, when bonding through an adhesive layer, the adhesive layer can be, for example, epoxy resin, acrylic resin, etc. The ratio of the thickness of the functional substrate to the thickness of the support substrate (thickness of the functional substrate / thickness of the support substrate) is preferably 0.1 or less. Figure 2 An example of a composite substrate is shown. The composite substrate 10 is obtained by bonding the piezoelectric substrate 12, which serves as a functional substrate, to the support substrate 14 by direct bonding.

[0046] The electronic device of the present invention utilizes the aforementioned composite substrate. Examples of such electronic devices include elastic wave elements (elastomers, Lamb wave elements, thin-film resonators (FBARs), etc.), as well as LED devices, optical waveguide devices, and switching devices. When the aforementioned composite substrate is used in the elastic wave element, the coefficient of thermal expansion of the cordierite sintered body serving as the supporting substrate is approximately 1.1 ppm / K (40–400°C), which is very small, thus significantly improving the frequency-temperature dependence. Figure 3 An example of an electronic device 30 fabricated using a composite substrate 10 is shown. The electronic device 30 is a single-port SAW resonator, i.e., a surface wave device. First, a pattern of multiple electronic devices 30 is formed on the piezoelectric substrate 12 of the composite substrate 10 using conventional photolithography. Then, individual electronic devices 30 are cut out by dicing. The electronic device 30 is obtained by forming IDT (Interdigital Transducer) electrodes 32 and 34 and a reflective electrode 36 on the surface of the piezoelectric substrate 12 using photolithography.

[0047] It should be noted that mullite sintered bodies also show promise. Mullite sintered bodies have the following advantages: compared to cordierite sintered bodies and silicon, they have high strength and high Young's modulus, making them less prone to warping and cracking. Furthermore, the coefficient of thermal expansion of mullite sintered bodies is close to that of silicon and GaN, thus allowing them to be used in existing silicon and GaN processes. Additionally, they possess insulating properties, making them suitable as support substrates for existing devices utilizing high-resistivity silicon. Mullite sintered bodies can have a mirror-finished surface, wherein the average surface roughness Ra along the centerline in a 10 μm square measurement range is preferably 1 nm or less; or, the maximum peak height Rp in a 70 μm square measurement range is preferably 30 nm or less; or, the number of pores with a maximum length of 0.1 μm or more in any 4 μm × 4 μm range is preferably 10 or less. Furthermore, the mullite sintered body is preferably sintered by hot pressing. Furthermore, the mullite sintered body may also contain at least one of cordierite, alumina, silica, spinel, and pseudosapphire as a subphase. A composite substrate can also be fabricated by bonding such a mullite sintered body to a support substrate and a functional substrate, wherein the thickness ratio of the two substrates (thickness of the functional substrate / thickness of the support substrate) is preferably 0.1 or less. Additionally, such a composite substrate can be used in the aforementioned electronic devices.

[0048] Example

[0049] The present invention will be further described in detail below based on examples of the present invention, but the present invention is not limited to these examples.

[0050] 1. Preparation of Cordierite Raw Material Powder

[0051] (Raw material powder A~I)

[0052] In the production of cordierite raw material powders A to H, commercially available high-purity magnesium oxide, aluminum oxide, and silica powders with an average particle size of less than 1 μm and a purity of 99.9% or higher were used. In comparison, in raw material powder I, kaolin and talc, which are natural raw materials, were used as a portion of the aluminum oxide, magnesium oxide, and silica source.

[0053] Cordierite raw material powder A

[0054] Magnesium oxide, aluminum oxide, and silicon dioxide powders were weighed in order to form a cordierite composition. The mixture was heated at 1400°C for 5 hours under atmospheric conditions to obtain coarse cordierite particles. Aluminum oxide was then used as spheroids in the obtained cordierite particles. Cordierite powder with an average particle size of approximately 0.5–0.6 μm was prepared by grinding in a mill using ion-exchanged water as a solvent for 70 hours. The composition of this powder was analyzed using methods described later. Magnesium oxide and silica powder were appropriately added relative to the amount of alumina incorporated during grinding, thereby readjusting the composition to achieve a cordierite composition. The mixture was then stirred again for 4 hours. The resulting slurry was dried under a nitrogen atmosphere at 110°C. The dried material was sieved to obtain cordierite raw material powder A.

[0055] Cordierite raw material powder B, C

[0056] Magnesium oxide, aluminum oxide, and silicon dioxide powders were weighed in such a way that the composition was obtained by subtracting the amount of alumina mixed in from the alumina medium during the pulverization process from the composition of cordierite. The powders were prepared using the same method as cordierite raw material powder A, except that no magnesium oxide or silicon dioxide powders were added after pulverization.

[0057] Cordierite raw material powder D

[0058] Except that no magnesium oxide or silicon dioxide was added after crushing, it was made using the same method as cordierite raw material powder A.

[0059] Cordierite raw material powder E~H

[0060] Except for adjusting the magnesium oxide and silicon dioxide to be excessive or insufficient after pulverization, it is produced using the same method as cordierite raw material powder A.

[0061] Cordierite raw material powder I

[0062] Except for the use of kaolin and talc as natural raw materials in a portion of the alumina, magnesium oxide, and silica sources, it is produced using the same method as cordierite raw material powder A.

[0063] Table 1 shows the final composition, impurity content, and average particle size of the prepared cordierite raw material powders A to I.

[0064] Table 1

[0065]

[0066] 2. Preparation and Evaluation of Cordierite Sintered Body

[0067] The cordierite raw material powders A to I prepared as described above were respectively subjected to a concentration of 50 kgf / cm³. 2 Single-axis die stamping is performed to obtain The resulting molded body is approximately 25 mm thick. The molded body is then placed in a graphite mold and pressed in a hot press at a pressure of 20–200 kgf / cm². 2 Cordierite sintered bodies were prepared by firing at a maximum temperature of 1400–1425℃ for 5 hours. The firing atmosphere was set to argon, with a heating rate of 200℃ / hr and a cooling rate of 200℃ / hr. During cooling, furnace cooling was used below 1200℃. Flexural bars and other structural members were cut from each obtained cordierite sintered body. Disc-shaped samples, etc., are supplied for evaluation tests. The evaluation tests are as follows.

[0068] Composition analysis

[0069] The amounts of MgO, Al2O3, SiO2, and impurities in cordierite raw material powder and cordierite sintered powder were determined using high-frequency inductively coupled plasma optical emission spectrometry.

[0070] • Bulk density of sintered body

[0071] The bulk density was determined using Archimedes' method with pure water, employing a flexural bar.

[0072] ·Crystal phase

[0073] The cordierite sintered body was crushed, and the cordierite and heterogeneous phases were identified using an X-ray diffraction apparatus, and the peak intensities of each phase were calculated. The measurement conditions were set as CuKα, 50kV, 300mA, 2θ=5-70°, and a rotating cathode-type X-ray diffractometer (Rigaku Denki's "RINT") was used. Based on the X-ray diffraction pattern, the ratio (Ix) of the sum of the intensities (Ip, Iq, Ir, ...) of the maximum peaks of each detected heterogeneous phase (P, Q, R, ...) to the peak intensity (Ic) of the (110) plane of cordierite was calculated. It should be noted that the second peak was used when the first peak (the strongest line) overlapped.

[0074] Ix = (Ip + Iq + Ir...) / Ic

[0075] Surface flatness

[0076] For test pieces of cordierite sintered bodies measuring 4×3×10mm, one side was polished to a mirror finish through grinding. The centerline average surface roughness Ra and maximum peak height Rp of the mirror-finished surface were measured using AFM. The measurement ranges were set to 10μm×10μm and 70μm×70μm. It should be noted that the grinding was performed in the order of 3μm diamond abrasive particles followed by 0.5μm diamond abrasive particles. The final finishing process involved polishing with a silica gel slurry (pH=11, particle size 80nm) and a non-woven fabric pad.

[0077] • Average particle size of sintered particles

[0078] The polished surface of the sintered body, as described above, was subjected to thermal etching at 1400°C for 2 hours. The size of the cordierite sintered particles was calculated using SEM as the average particle size. Linear analysis was used in the calculation, and 1.5 times the measured value was set as the average particle size.

[0079] Number of pores

[0080] For the polished surface of the sintered body that has been finely processed as described above, AFM observation was performed on any 4μm×4μm range to determine the number of pores with a maximum length of 0.1μm or more.

[0081] Optical properties

[0082] For test pieces of cordierite sintered body with a thickness of 0.5 mm, the total transmittance and linear transmittance for light with wavelengths of 200–3000 nm were measured. A spectrophotometer was used in the measurements, with a nearly parallel beam of light incident from the normal direction of the sample surface, and the transmitted light was measured. For the standard sample, an air layer was considered in the optical path without the sample inserted, and its spectroscopic transmittance was set to 1. The total transmittance was calculated by receiving the transmitted light from the sample using an integrating sphere, and the linear transmittance was calculated based on the transmitted light from the normal direction of the sample surface. The total transmittance and linear transmittance for a wavelength of 550 nm were used as representative values.

[0083] Detailed descriptions of the preparation and evaluation of cordierite sintered bodies are provided in Experimental Examples 1-17 below. Table 2 shows the sintering conditions and composition of the obtained cordierite sintered bodies for each experimental example, and Table 3 shows the results of the evaluation tests for each experimental example, i.e., the characteristics of the cordierite sintered bodies. It should be noted that Experimental Examples 1-3 and 12-17 correspond to embodiments of the present invention, while Experimental Examples 4-11 correspond to comparative examples of the present invention. The present invention is not limited to these experimental examples.

[0084] Table 2

[0085]

[0086] Table 3

[0087]

[0088] (Experimental Example 1)

[0089] The cordierite sintered body in Experimental Example 1 was formed under a pressing pressure of 200 kgf / cm². 2 The cordierite sintered body was obtained by sintering cordierite raw material powder A at 1425℃ for 5 hours. The molar ratios of MgO / Al2O3 and SiO2 / Al2O3 in the obtained cordierite sintered body were 1.00 and 2.50, respectively, which were very close to the stoichiometric ratio of cordierite, and the amount of impurities was also low. The bulk density of the sintered body was found to be 2.507 g / cm³. 3 It is extremely close to the true density of cordierite, which is 2.505 g / cm³. 3 It contains almost no closed stomata. Figure 4 The XRD diffraction pattern of the cordierite sintered pulverized body from Experimental Example 1 is shown. As a phase other than cordierite, only corundum (● in the figure) was detected, but the peak intensity ratio Ix relative to the peak intensity of cordierite (110) (○ in the figure) was extremely small, at 0.0020. Figure 5 The image shows the results of thermal etching and SEM observation of the polished surface of the cordierite sintered body. It can be seen that the average particle size of the cordierite sintered particles is 0.6 μm, indicating that the very fine cordierite particles are densely sintered. Furthermore, within a 4 μm × 4 μm area of ​​the polished surface, there are 3 pores with a maximum length of 0.1 μm or more. Regarding the surface smoothness of the polished surface, the average surface roughness Ra along the centerline is low at 0.8 nm, and the maximum peak height is also low at 20 nm. Figure 6 The transmittance curves are shown as optical properties. It can be seen that the linear transmittance is over 60% in the 500–3000 nm range, which is extremely high, indicating a very transparent material. Photographs of the obtained cordierite sintered body sample are shown below. Figure 7 .exist Figure 7 The mark depicted in the image bearing the NGK logo is a registered trademark of Nippon Yuko Co., Ltd.

[0090] (Experimental Examples 2 and 3)

[0091] The cordierite sintered bodies of Experiments 2 and 3 were obtained by sintering cordierite raw material powders B and C under the same conditions as in Experiment 1. The composition and molar ratios of the obtained cordierite sintered bodies are shown in Table 2, and the deviations from the stoichiometric ratio of cordierite are very small. In other properties, similar characteristics to those of Experiment 1 were also obtained, indicating that sintering can be carried out with high density and few pores in a state with few heterogeneous phases, and materials with high surface smoothness can be produced. The transparency is also as high as in Experiment 1.

[0092] (Experimental Example 4)

[0093] In Experiment 4, cordierite sintered bodies were prepared under the same conditions as in Experiment 1, except that the firing temperature was set to 1400℃. It was found that due to the low firing temperature, the cordierization reaction of raw materials such as alumina and silica was not fully carried out, resulting in a large amount of residual corundum and cristobalite heterogeneous phases. Regarding the surface smoothness of the ground surface, the average surface roughness Ra along the centerline was 1.8 nm, and the maximum peak height Rp was 28 nm, which is high. Based on these, it can be inferred that the ease of grinding differs between cordierite and heterogeneous components; in particular, because heterogeneous components are difficult to grind, they tend to remain as convex structures.

[0094] (Experimental Example 5)

[0095] In Experiment 5, cordierite sintered bodies were prepared under the same conditions as in Experiment 2, except that the firing temperature was set to 1400℃. Similar to Experiment 4, due to the low firing temperature, corundum and cristobalite remained as heterogeneous phases, resulting in poor surface smoothness of the polished surface, with Ra of 1.3 nm and Rp of 31 nm.

[0096] (Experimental Example 6)

[0097] In Experiment 6, cordierite sintered bodies were prepared under the same conditions as in Experiment 1, except that cordierite raw material powder D was used. Due to the excess alumina in the raw material, the sintered body also had an excess of alumina, with a MgO / Al2O3 molar ratio of 0.94 and a SiO2 / Al2O3 molar ratio of 2.36, which were smaller than those of cordierite. The presence of high amounts of corundum and cristobalite as heterogeneous phases resulted in large surface roughness (Ra = 3.5 nm, Rp = 88 nm), making high-level finishing impossible.

[0098] (Experiment Example 7)

[0099] In Experiment 7, cordierite sintered bodies were prepared under the same conditions as in Experiment 1, except that cordierite raw material powder E was used. The molar ratio of MgO / Al2O3 in the cordierite sintered body was 0.93. MgO was insufficient, and corundum and cristobalite were detected as heterogeneous phases, and their amounts were also excessive, as indicated by the peak intensity ratio Ix. Therefore, in terms of the surface smoothness of the polished surface, Ra was 3.3 nm and Rp was 67 nm, which were large, making it impossible to achieve high smoothness through fine processing.

[0100] (Experimental Example 8)

[0101] In Experiment 8, cordierite sintered bodies were prepared under the same conditions as in Experiment 1, except that cordierite raw material powder F was used. The molar ratio of SiO2 / Al2O3 in the cordierite sintered body was 2.42. SiO2 was insufficient, and corundum was detected as a heterogeneous phase, with a high amount also indicated by the peak intensity ratio Ix. Therefore, in terms of surface smoothness of the polished surface, Ra was 2.1 nm and Rp was 40 nm, which were large, making it impossible to achieve high smoothness through fine finishing.

[0102] (Experimental Example 9)

[0103] In Experiment 9, cordierite sintered bodies were prepared under the same conditions as in Experiment 1, except that cordierite raw material powder G was used. The molar ratio of MgO / Al2O3 in the cordierite sintered body was 1.09, with an excess of MgO. Based on XRD, enstatite was detected as a heterogeneous phase, and small amounts of corundum and cristobalite were also identified. The peak intensity in the XRD was higher than Ix, indicating a large amount of heterogeneous phase. Therefore, in terms of surface flatness of the polished surface, Ra was 1.5 nm and Rp was 29 nm, which were large, making it impossible to achieve high flatness through fine processing.

[0104] (Experimental Example 10)

[0105] In Experiment 10, cordierite sintered bodies were prepared under the same conditions as in Experiment 1, except that cordierite raw material powder H was used. The molar ratio of SiO2 / Al2O3 in the cordierite sintered body was 2.65, with SiO2 present in excess. Figure 8 The image shows the XRD diffraction pattern of the pulverized cordierite sintered body from Experimental Example 10. According to... Figure 8 Based on XRD, cristobalite and a small amount of corundum were detected as heterogeneous phases, and the peak intensity ratio Ix indicates a large amount of heterogeneous phases. Therefore, in terms of surface flatness of the polished surface, Ra is 3.1 nm and Rp is 47 nm, which are large, making it impossible to perform high-flatness finishing.

[0106] (Experimental Example 11)

[0107] In Experiment 11, cordierite sintered bodies were prepared under the same conditions as in Experiment 1, except that cordierite raw material powder I was used and the firing temperature was set to 1400°C. The sintered body contained a large amount of Fe₂O₃ and TiO₂, which are impurities derived from natural raw materials. Based on XRD, iron oxide, corundum, and pseudosapphire were detected as heterogeneous phases, with higher peak intensities than Ix and a greater quantity of these heterogeneous phases. Therefore, in terms of surface flatness, Ra was 3.5 nm and Rp was 84 nm, making high-flatness finishing impossible.

[0108] (Experimental Examples 12-14)

[0109] In Experiments 12, 13, and 14, the stamping pressure was set to 20, 50, and 100 kgf / cm², respectively. 2 In addition, cordierite sintered bodies were prepared under the same conditions as in Experimental Example 1. The composition and molar ratio of the obtained cordierite sintered bodies are shown in Table 2, and the deviations from the stoichiometric ratio of cordierite are very small. Furthermore, other properties are shown in Table 3, indicating that similar properties as in Experimental Example 1 were obtained. The materials exhibit high density and low porosity in a state with few heterogeneous phases, resulting in a material with high surface smoothness. The transparency is also as high as in Experimental Example 1. Because cordierite sintered bodies can be produced with low stamping pressure, the hot pressing fixture can be miniaturized and have a longer lifespan.

[0110] (Experimental Examples 15-17)

[0111] In Experiments 15, 16, and 17, the cordierite sintered body from Experiment 1 was annealed at 1200℃, 1300℃, and 1400℃ for 2 hours, respectively, to evaluate its optical properties. The total light transmittance was 80%, 83%, and 84%, respectively, and the linear transmittance was 70%, 70%, and 71%, respectively. Improvements in light transmittance and transparency were observed through high-temperature annealing.

[0112] 3. Fabrication and Evaluation of Composite Substrates

[0113] A composite substrate was fabricated using cordierite sintered body as a support substrate. Specific fabrication examples are shown in Experimental Examples 18-23. It should be noted that Experimental Examples 18-21 correspond to embodiments of the present invention, and Experimental Examples 22 and 23 correspond to comparative examples of the present invention.

[0114] (Experimental Examples 18-21)

[0115] In Examples 18-21, the cordierite sintered body from Example 1 was used as a support substrate to fabricate composite substrates. The following support substrate was used: [The text abruptly ends here, so the translation stops.] For a support substrate with a shape of 500 μm, the surface is finished to Ra = 0.4–0.9 nm and Rp = 6–20 nm using diamond polishing slurry and CMP polishing. After CMP polishing, the support substrate is washed with commonly used amine solution, SPM (sulfuric acid and hydrogen peroxide mixture), and RCA cleaning solution to remove organic matter, particles, etc., from the substrate surface before bonding. On the other hand, for functional substrates, any single-crystal substrate selected from lithium tantalate (LT), lithium niobate (LN), gallium nitride (GaN), and silicon (Si) is used, employing a substrate with the same shape and surface finish as the support substrate.

[0116] In Experiment 18, an attempt was made to bond a 250 μm thick LT substrate to a 230 μm thick support substrate. During the surface activation treatment prior to bonding, both substrates were irradiated with an argon ion beam using an ion gun. Subsequently, after bonding the two substrates, the support substrate and LT substrate were directly bonded at room temperature by pressing with a bonding load of 10 tons for 1 minute. In the resulting composite substrate, almost no bubbles were observed at the bonding interface, and the proportion of the area actually bonded at the bonding interface (bonding area ratio) was over 95%, indicating good bonding. It should be noted that the bonding area is the area of ​​the bubble-free portion of the bonding interface when viewed from the transparent support substrate side, and the bonding area ratio is the ratio of the bonding area to the total area of ​​the bonding interface.

[0117] In Experiment 19, an LN substrate was used instead of an LT substrate, and the same procedure as in Experiment 18 was followed to attempt direct bonding with a 500 μm thick support substrate. The bonding area ratio was over 90%, and bonding was successful, similar to Experiment 18.

[0118] In Experiment 20, a silicon substrate was used instead of the LT substrate, and the same procedure was followed as in Experiment 18 to attempt direct bonding with a 230 μm thick support substrate. The bonding area ratio was almost 100%, and the bonding was very successful.

[0119] In Experiment 21, a gallium nitride substrate was used instead of the LT substrate, and the same procedure was followed as in Experiment 18 to attempt direct bonding with a 230 μm thick support substrate. The bonding area ratio was over 80%, and the bonding was successful.

[0120] (Experimental Examples 22-23)

[0121] In Experiment 22, the cordierite sintered body from Experiment 5 was used as a support substrate to fabricate a composite substrate. The thickness of the support substrate was 230 μm, and the surface was finished to Ra = 1.4 nm and Rp = 35 nm. This support substrate was operated on in the same manner as in Experiment 18, attempting to directly bond it to the LT substrate. However, the bonding area ratio did not reach 60%, and voids were found at the interface, indicating insufficient bonding.

[0122] In Experiment 23, the cordierite sintered body from Experiment 11 was used as a support substrate to fabricate a composite substrate. This support substrate contained numerous heterogeneous phases such as impurities, corundum, and pseudosapphire. The surface after CMP polishing had Ra = 3.6 nm and Rp = 90 nm, both inferior to the materials in Experiments 18-21. This support substrate (230 μm thick) was subjected to the same procedure as in Experiment 18, attempting direct bonding with an LT substrate. However, the bonding area ratio was less than 20%, indicating insufficient bonding.

[0123] Table 4 summarizes the materials used, the ratio of the bonding area, and the quality of the bonding in Experiments 18–23.

[0124] Table 4

[0125]

[0126] It should be noted that, needless to say, the above embodiments do not limit the present invention in any way.

[0127] This application is based on Japanese Patent Application No. 2014-117926, filed on June 6, 2014, and Japanese Patent Application No. 2015-059873, filed on March 23, 2015, the entire contents of which are incorporated herein by reference.

[0128] Industrial availability

[0129] The cordierite sintered body of the present invention, for example, sintered into a porous structure, can be used as a catalyst carrier and filter for purifying exhaust gases from automobiles, etc.

[0130] Symbol Explanation

[0131] 10 Composite substrate, 12 Piezoelectric substrate, 14 Support substrate, 30 Electronic device, 32, 34 IDT electrode, 36 Reflective electrode.

Claims

1. A method for preparing a cordierite sintered body, comprising sintering cordierite raw material powder containing MgO, Al2O3, and SiO2 under an inactive atmosphere using a hot pressing method to produce a body with a bulk density of 2.497~2.507 g / cm³. 3 A method for preparing cordierite sintered bodies with an average particle size of less than 1 μm and a total light transmittance of more than 60% to a wavelength of 550 nm. In preparing the cordierite raw material powder, powders of MgO, Al2O3, and SiO2 are weighed and mixed to form the cordierite composition. The mixture is heated at 1300-1450°C under atmospheric conditions to obtain coarse cordierite particles. For these coarse particles, alumina is used as beads and the mixture is pulverized in a mill using ion-exchanged water as a solvent until the average particle size D50 is 0.5-0.6 μm. The amounts of MgO and SiO2 are readjusted relative to the Al2O3 component introduced during pulverization to form the cordierite composition, thereby producing the cordierite raw material powder. In the cordierite raw material powder, the molar ratio of MgO / Al2O3 is 0.96~1.04, the molar ratio of SiO2 / Al2O3 is 2.46~2.54, and the proportion of MgO, SiO2, and Al2O3 in the whole is more than 99.9% by mass. The conditions for sintering using the hot pressing method are a pressing pressure of 20~300 kgf / cm². 2 The firing temperature is 1410~1450℃.

2. A method for preparing a cordierite sintered body, comprising sintering cordierite raw material powder containing MgO, Al2O3, and SiO2 under an inactive atmosphere using a hot pressing method to produce a body with a bulk density of 2.497~2.507 g / cm³. 3 A method for preparing cordierite sintered bodies with an average particle size of less than 1 μm and a total light transmittance of more than 60% to a wavelength of 550 nm. In preparing the cordierite raw material powder, the powders of MgO, Al2O3, and SiO2 are weighed and mixed in a manner that constitutes the cordierite composition. Compared to the Al2O3 component mixed in during the pulverization process, the amount of Al2O3 component incorporated in the mixing is reduced beforehand. The resulting mixture is heated at 1300~1450℃ under atmospheric atmosphere to obtain cordierite coarse particles. For the cordierite coarse particles, alumina is used as beads and pulverized in a jar mill using ion-exchanged water as a solvent until the average particle size D50 is 0.5~0.6μm, thereby producing the cordierite raw material powder. In the cordierite raw material powder, the molar ratio of MgO / Al2O3 is 0.96~1.04, the molar ratio of SiO2 / Al2O3 is 2.46~2.54, and the proportion of MgO, SiO2, and Al2O3 in the whole is more than 99.9% by mass. The conditions for sintering using the hot pressing method are a pressing pressure of 20~300 kgf / cm². 2 The firing temperature is 1410~1450℃.

3. A cordierite sintered body, which is a cordierite sintered body manufactured by the method for preparing cordierite sintered bodies as described in claim 1 or 2. In the X-ray diffraction pattern, the sum of the intensities of the maximum peaks of all components except cordierite is 0.0009~0.0020 relative to the peak intensity of the (110) plane of cordierite, and the bulk density is 2.497~2.507 g / cm³. 3 .

4. In the cordierite sintered body according to claim 3, the molar ratio of MgO / Al2O3 is 0.96~1.04, and the molar ratio of SiO2 / Al2O3 is 2.46~2.

54.

5. In the cordierite sintered body according to claim 3, the proportion of the three components MgO, Al2O3 and SiO2 in the whole is more than 99.9% by mass.

6. The cordierite sintered body according to claim 3, wherein the average particle size of the cordierite sintered particles is less than 1 μm.

7. The cordierite sintered body according to claim 3 has a total light transmittance of over 60% for light with a wavelength of 550 nm.

8. The cordierite sintered body according to claim 3 has a linear transmittance of more than 50% for light with a wavelength of 550 nm.

9. The cordierite sintered body according to claim 3 has a surface that has been ground and polished to a mirror finish.

10. The cordierite sintered body according to claim 9, wherein the average surface roughness Ra of the centerline in a 10 μm square measurement range is less than 1 nm.

11. The cordierite sintered body according to claim 9, wherein the maximum peak height Rp in the 70 μm square measurement range on the surface is below 30 nm.

12. The cordierite sintered body according to claim 10, wherein the maximum peak height Rp in the 70 μm square measurement range on the surface is below 30 nm.

13. A composite substrate is obtained by bonding a functional substrate with a cordierite sintered support substrate, wherein the proportion of the area actually bonded at the bonding interface, i.e., the bonding area proportion, is 80% or more, and the cordierite sintered body is the cordierite sintered body according to any one of claims 3 to 12.

14. The composite substrate according to claim 13, wherein the bonding is a direct bonding.

15. An electronic device utilizing the composite substrate of claim 13 or 14.

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