Patent Publication Number: US-2023159380-A1

Title: Glass ceramic and electronic component

Description:
TECHNICAL FIELD 
     The present invention relates to a glass ceramic and an electronic component. 
     BACKGROUND 
     Patent Document 1 discloses an invention of a method of manufacturing a glass ceramic substrate. The glass ceramic includes fillers that partly or entirely contain flat grains. 
     Patent Document 2 discloses an invention of a multilayer inductor. Inside the multilayer structure is an embedded coil conductor. The multilayer inductor is suitable at a high-frequency range.
     Patent Document 1: JP Patent Application Laid Open No. H09-71472   Patent Document 2: JP Patent Application Laid Open No. 2017-73536   

     SUMMARY 
     Ideal inductors have higher impedance at a higher frequency. Unfortunately, the impedance of actual inductors decreases in reciprocal proportion to their stray capacitance at a high frequency range. The stray capacitance of the inductors is in proportion to the permittivity of inductor materials. Thus, low permittivity is demanded of ceramics for radio frequency (RF) inductors used especially at the high frequency range. High strength is also demanded of the RF inductors. In particular, the RF inductors used for vehicles further require higher strength than the RF inductors for other usage. 
     It is an object of the present invention to provide a glass ceramic or so having low relative permittivity c and high strength. 
     A glass ceramic according to the present invention includes feldspar crystal phases, non-crystalline glass phases, Al 2 O 3  phases, and SiO 2  phases, wherein at least one pair of the Al 2 O 3  phases is bonded via at least one of the feldspar crystal phases. 
     The feldspar crystal phases may mainly include Sr. 
     Al 2 O 3  fillers of the Al 2 O 3  phases may have an average aspect ratio of 15 or more and 75 or less. 
     SiO 2  fillers of the SiO 2  phases may have an average grain size of 0.10 μm or more and 3.0 μm or less. 
     A value calculated by dividing the area ratio of the feldspar crystal phases by the area ratio of the non-crystalline glass phases may be 0.10 or more and less than 1.00. 
     The area ratio of the Al 2 O 3  phases may be 7.0% or more and 20.0% or less. 
     The area ratio of the SiO 2  phases may be 10.0% or more and 30.0% or less. 
     An electronic component according to the present invention includes the above-mentioned glass ceramic. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING(S) 
         FIG.  1    is a STEM image of a cross section of a glass ceramic. 
         FIG.  2    is a phase separation analysis image of the cross section of the glass ceramic. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, an exemplary embodiment of the present invention will be explained in detail with reference to the drawings. The present invention is not to be limited only to the embodiment explained below. Also, constituents described below include the ones that those skilled in the art can easily devise and the ones that are substantially the same. Furthermore, the constituents described below can be combined appropriately. 
     A glass ceramic  1  of the present embodiment includes feldspar crystal phases  13 , non-crystalline glass phases  12 , Al 2 O 3  phases  14 , and SiO 2  phases  11 . At least one pair of the Al 2 O 3  phases  14  is bonded via at least one of the feldspar crystal phases  13 . 
     The feldspar crystal phases  13  mainly include feldspar crystals. The feldspar crystals include at least one metal element of Group 2 (excluding Be), alumina, and silica, and are represented by a general formula M(Si,Al) 4 O 8 . “M” includes the at least one metal element of Group 2 (excluding Be). “M” may mainly include Sr. This means that, among all elements included in “M” of the feldspar crystals, Sr may account for the highest proportion in terms of mass. If the feldspar crystal phases  13  mainly include Sr, this also means that Sr accounts for the highest proportion in terms of mass among all elements included in “M” of the feldspar crystals in the feldspar crystal phases  13 . 
     The feldspar crystal phases  13  may include metal oxides in addition to the feldspar crystals. Examples of the metal oxides include Na 2 O, K 2 O, ZrO 2 , and Ag 2 O. The proportion of the feldspar crystals in the feldspar crystal phases  13  is not limited and may be, for example, 80 mass % or more. 
     The non-crystalline glass phases  12  include glass that does not contain crystals. The glass included in the non-crystalline glass phases  12  may have any composition. For example, the non-crystalline glass phases  12  may include oxides of “M”, oxides of Si, oxides of Al, and oxides of B at a total of 70 mass % or more. 
     The Al 2 O 3  phases  14  mainly include Al 2 O 3  (alumina) crystals. The proportion of Al 2 O 3  in the Al 2 O 3  phases  14  is not limited and may be, for example, 97 mass % or more. The SiO 2  phases  11  mainly include SiO 2  (silicon dioxide). The proportion of SiO 2  in the SiO 2  phases  11  is not limited and may be, for example, 97 mass % or more. 
     The Al 2 O 3  phases  14  are bonded via the feldspar crystal phases  13 . Not all the Al 2 O 3  phases  14  are required to be bonded via the feldspar crystal phases  13 . At least one pair of Al 2 O 3  phases  14  is bonded via at least one of the feldspar crystal phases  13 . In terms of the number of the Al 2 O 3  phases  14 , 25% or more of the Al 2 O 3  phases  14  may be bonded together via the feldspar crystal phases  13 . 
     Having the above-mentioned structure, the glass ceramic of the present embodiment has low relative permittivity ε and high strength. 
     A glass ceramic including many non-crystalline phases (e.g., the SiO 2  phases  11  and the non-crystalline glass phases  12 ) readily has low relative permittivity e. However, the glass ceramic including many non-crystalline phases readily has cracks and low strength. 
     When a glass ceramic simply includes crystal phases (e.g., the Al 2 O 3  phases  14 ), not only the relative permittivity E increases, but also the strength does not improve sufficiently, compared to when the glass ceramic does not include the crystal phases. However, the present inventors have found that, when the glass ceramic includes the feldspar crystal phases  13  in addition to the Al 2 O 3  phases  14  and the Al 2 O 3  phases  14  are bonded via the feldspar crystal phases  13 , the glass ceramic has low relative permittivity E and high strength. 
     The microstructure of the glass ceramic can be checked by observing its cross section with STEM-EDS or so and further performing phase separation analysis.  FIG.  1    is an image (may simply be referred to as a “STEM image”) generated in the observation of a cross section of the glass ceramic of the present embodiment with STEM.  FIG.  2    is an image (may simply be referred to as a “phase separation analysis image”) generated through RGB image phase analysis as phase separation analysis of the same field of view as  FIG.  1   . The field of view may have any size and may be observed at any magnification as long as the microstructure of the glass ceramic is observed without fail. For example, the field of view is 200 μm 2  or more, and the magnification of the image is 5000× or more. The field of view may include a plurality of fields of view. The total size of the fields of view is, for example, 200 μm 2  or more. 
     As shown in  FIGS.  1  and  2   , the glass ceramic  1  includes the feldspar crystal phases  13 , the non-crystalline glass phases  12 , the Al 2 O 3  phases  14 , and the SiO 2  phases  11 . In  FIG.  1    (STEM image), boundaries between the feldspar crystal phases  13  and the Al 2 O 3  phases  14  are not clear. Using both  FIG.  1    (STEM image) and  FIG.  2    (phase separation analysis image) clarifies the boundaries between the feldspar crystal phases  13  and the Al 2 O 3  phases  14 . Surrounding the Al 2 O 3  phases  14  are the feldspar crystal phases  13  and/or the non-crystalline glass phases  12 . At least one pair of Al 2 O 3  phases  14  is bonded via the feldspar crystal phases  13 . 
     For identifying the phases, they may be irradiated with an electron beam to measure electron diffraction patterns. When the electron diffraction pattern of the non-crystalline glass phases  12  is measured, only halo patterns attributable to amorphousness are generated, and no spots attributable to crystals are generated. In contrast, when the electron diffraction patterns of the feldspar crystal phases  13  and the Al 2 O 3  phases  14  are measured, a number of spots attributable to crystals are generated. When the electron diffraction pattern of the SiO 2  phases  11  is measured, halo patterns attributable to amorphousness and/or spots attributable to crystals are generated. 
     In the glass ceramic, phases other than the four types of phases, namely the feldspar crystal phases  13 , the non-crystalline glass phases  12 , the Al 2 O 3  phases  14 , and the SiO 2  phases  11 , may be so small that the phases other than the four can be ignored. For example, the phases other than the four may occupy an area ratio of 5% or less (including 0%). 
     The glass ceramic may have pores. However, the glass ceramic is so dense that it may have few pores. Having few pores is preferable with regard to improvement of the strength. For example, the pores may occupy an area ratio of 5% or less (including 0%). 
     Al 2 O 3  fillers of the Al 2 O 3  phases  14  may have an average aspect ratio of 15 or more and 75 or less. When the average aspect ratio of the Al 2 O 3  fillers is within the above-mentioned range, the glass ceramic readily has higher strength than when the average aspect ratio of the Al 2 O 3  fillers is smaller than the above-mentioned range. When the average aspect ratio of the Al 2 O 3  fillers exceeds 75, the glass ceramic readily has lower sinterability, more pores, and lower strength. 
     The average aspect ratio of the Al 2 O 3  fillers can be calculated by measuring the aspect ratio of each Al 2 O 3  phase  14  in the phase separation analysis image and working out the average. 
     SiO 2  fillers of the SiO 2  phases  11  may have an average grain size of 0.10 μm or more and 3.0 μm or less. The smaller the average grain size of the SiO 2  fillers, the more likely it is to reduce the sinterability, and the less likely it is for the Al 2 O 3  phases  14  to be bonded via the feldspar crystal phases  13 . The larger the average grain size of the SiO 2  fillers, the more likely it is for a sheet including the glass ceramic to have higher surface roughness. 
     The average grain size of the SiO 2  fillers can be calculated by measuring the equivalent circular diameter of each SiO 2  phase  11  in the phase separation analysis image and working out the average. The equivalent circular diameter of the SiO 2  phase  11  means the diameter of a circle having the same area as the projected area of the SiO 2  phase  11 . 
     The non-crystalline glass phases  12  mainly include a glass component, and the feldspar crystal phases  13  mainly include a glass component. In the glass ceramic of the present embodiment, the SiO 2  fillers and the Al 2 O 3  fillers are dispersed in each glass component. 
     The value calculated by dividing the area ratio of the feldspar crystal phases  13  by the area ratio of the non-crystalline glass phases  12  may be 0.10 or more and less than 1.00. The smaller the value, the less likely it is for the Al 2 O 3  phases  14  to be bonded via the feldspar crystal phases  13 . The larger the value, the more likely it is to increase the strength and unfortunately the relative permittivity e. 
     The area ratio of the Al 2 O 3  phases  14  may be 7.0% or more and 20.0% or less. The smaller the area ratio of the Al 2 O 3  phases  14 , the less likely it is for the Al 2 O 3  phases  14  to be bonded via the feldspar crystal phases  13 . 
     The area ratio of the SiO 2  phases  11  may be 10.0% or more and 30.0% or less. The smaller the area ratio of the SiO 2  phases  11 , the more likely it is to increase the relative permittivity. The larger the area ratio of the SiO 2  phases  11 , the more likely it is to reduce the sinterability, and the less likely it is for the Al 2 O 3  phases  14  to be bonded via the feldspar crystal phases  13 . 
     The area ratio of each phase can be calculated by performing image analysis of the phase separation analysis image. 
     Hereinafter, a method of manufacturing the glass ceramic of the present embodiment, especially a method of manufacturing a glass ceramic element body (glass ceramic sintered body), will be explained. 
     The glass ceramic element body is manufactured by mixing a glass raw material, a SiO 2  filler raw material, and an Al 2 O 3  filler raw material and heating the mixture for sintering. 
     As the glass raw material, crystallized glass and non-crystalline glass are prepared and mixed. 
     The crystallized glass includes a component that grows into the feldspar crystals during heating (described later). Examples of the component that grows into the feldspar crystals during heating (described later) include oxides of “M”, oxides of Si, and oxides of Al. The crystallized glass may include other components. The crystallized glass may appropriately include any glass components, such as various oxides (e.g., oxides of B), in addition to the component that grows into the feldspar crystals. 
     The non-crystalline glass may be of any type. For example, the non-crystalline glass may be glass that includes oxides appropriately selected from various oxides (e.g., oxides of Si, oxides of B, and oxides of K) and does not include crystals. The glass component in the crystallized glass may mostly be included in the feldspar crystal phases  13  in the end, and the non-crystalline glass may mostly be included in the non-crystalline glass phases  12  in the end. 
     The non-crystalline glass may combine with the crystallized glass during heating (described later). Oxides not included in the non-crystalline glass may be included in the non-crystalline glass phases  12 . 
     When the glass raw material includes only the non-crystalline glass, the feldspar crystal phases  13  are difficult to be generated. When the glass raw material includes only the crystallized glass, it is likely that the non-crystalline glass phases  12  account for a small proportion. Controlling the proportion of each raw material allows the area ratio of each phase to be controlled. In particular, controlling the proportion of the crystallized glass and the non-crystalline glass allows the value calculated by dividing the area ratio of the feldspar crystal phases  13  by the area ratio of the non-crystalline glass phases  12  to be controlled. 
     The glass raw material may have any particle size. For example, the glass raw material may have a D90 of 1 to 5 μm measured with a laser diffraction type particle size distribution meter. 
     The Al 2 O 3  filler raw material is preferably α-alumina having a relatively high melting point so that the glass ceramic after heating includes the Al 2 O 3  phases  14 . The Al 2 O 3  filler raw material may have a particulate shape or a plate shape. Controlling the shape of the Al 2 O 3  filler raw material allows the average aspect ratio of the Al 2 O 3  phases  14  to be controlled. For example, the Al 2 O 3  fillers have a low aspect ratio when the Al 2 O 3  filler raw material has a particulate shape, and have a high aspect ratio when the Al 2 O 3  filler raw material has a plate shape. Although part of Al 2 O 3  in the Al 2 O 3  filler raw material may react with “M” and Si and be incorporated into the feldspar crystal phases  13 , a large part of Al 2 O 3  in the Al 2 O 3  filler raw material is included in the Al 2 O 3  phases  14 . The higher the aspect ratio of the Al 2 O 3  fillers, the more likely it is to increase the surface area of the Al 2 O 3  phases  14  (their perimeters in the STEM image) and the area ratio of the feldspar crystal phases  13  in contact with the Al 2 O 3  phases  14 . 
     As the SiO 2  filler raw material, quartz glass (amorphous silica) can be used. Controlling the particle size of the SiO 2  filler raw material allows the average grain size of the SiO 2  phases  11  to be controlled. Although part of SiO 2  in the SiO 2  filler raw material may be incorporated into the non-crystalline glass phases  12  or the feldspar crystal phases  13  by heating, a large part of SiO 2  in the SiO 2  filler raw material is included in the SiO 2  phases  11 . 
     Next, the mixed raw materials are mixed in wet manner for 24 hours with a solvent or so normally used in the technical field to give a raw material slurry. The solvent may be alcohol, which is normally used in the technical field. Any device may be used for wet mixing. For example, a ball mill may be used. The raw material slurry is dried until the solvent is removed to give a glass ceramic material. Any device may be used for drying. For example, a spray dryer may be used. 
     Next, a binder or so normally used in the technical field is added to the glass ceramic material for granulation, and the granulated material is sized into granules with a sieve. The granules are pressure-molded to give a green compact. Then, the green compact is heated in the air to give a glass ceramic element body (glass ceramic sintered body). 
     By heating, part of SiO 2  in the SiO 2  filler raw material is incorporated into the non-crystalline glass. Also, by heating, the feldspar crystals are generated with Al 2 O 3  as a core. Thus, the feldspar crystal phases  13  are generated around the Al 2 O 3  phases  14 , and the Al 2 O 3  phases  14  bond via the feldspar crystal phases  13 . 
     The shorter the heating time, the more likely it is to reduce the value calculated by dividing the area ratio of the feldspar crystal phases  13  by the area ratio of the non-crystalline glass phases  12 , and the less likely it is for the Al 2 O 3  phases  14  to be bonded via the feldspar crystal phases  13 . With a long enough heating time, the Al 2 O 3  phases  14  bond via the feldspar crystal phases  13 . With a still longer heating time, the SiO 2  phases  11  and the non-crystalline glass phases  12  are reduced and the feldspar crystal phases  13  are increased. 
     The present invention is not limited to the above-described embodiment, and can variously be modified within the scope of the present invention. 
     For example, the glass ceramic material may be kneaded with a binder and a solvent normally used in the technical field to give a glass ceramic paste. The glass ceramic paste and a conductor paste including Ag or so may be printed and laminated alternately and then fired to form a laminated body including the glass ceramic and conductors (printing method). Instead, the glass ceramic paste may be used to form green sheets, where an internal electrode paste is to be printed, and the green sheets with internal electrode patterns may be laminated and fired to form a laminated body including the glass ceramic and conductors (sheet method). 
     When the glass ceramic and the conductors are fired simultaneously as described above, metal (e.g., Ag) in the conductors may be dispersed into the glass ceramic. In that case, oxides of the metal in the conductors are likely to be included in the non-crystalline glass phases  12  and the feldspar crystal phases  13 , especially those in the vicinity of the conductors. 
     The glass ceramic according to the present embodiment may be used for any purpose. For example, the glass ceramic is suitable for electronic components, especially radio frequency (RF) inductors. In particular, the glass ceramic is suitable for RF inductors for vehicles requiring especially high strength. 
     Examples 
     Hereinafter, the present invention will be explained based on more detailed examples, but the present invention is not limited thereto. 
     Experiment 1 
     A glass raw material, a SiO 2  filler raw material, and an Al 2 O 3  filler raw material were prepared. As the glass raw material, crystallized glass and non-crystalline glass were prepared. These materials were mixed at a mass ratio shown in Table 1. 
     The crystallized glass had a Si—Sr—Al-based composition (the amount of SiO 2 : 37 to 45 mass %, the amount of SrO: 35 to 40 mass %, the amount of Al 2 O 3 : 5 to 15 mass %, and the amount of B 2 O 3 : 1 to 5 mass %). 
     The non-crystalline glass had a Si—B—K-based composition (the amount of SiO 2 : 75 to 84 mass %, the amount of B 2 O 3 : 15 to 20 mass %, and the amount of K 2 O: 1 to 5 mass %). 
     The SiO 2  filler raw material had an average particle size so that SiO 2  fillers observed in the end had an average grain size shown in Table 2. The Al 2 O 3  filler raw material had an average particle size of 1 to 3 μm. The Al 2 O 3  filler raw material had an aspect ratio so that Al 2 O 3  fillers observed in the end had an average aspect ratio shown in Table 2. 
     Next, the mixed raw materials were mixed in wet manner with a solvent (99% methanol-denatured ethanol) using a ball mill (media: zirconia balls) for 24 hours to give a raw material slurry. This raw material slurry was dried with a drying machine until the solvent was removed to give a glass ceramic material. 
     Next, 2.5 parts by mass of an acrylic resin-based binder (Elvacite manufactured by DuPont) was added as a binder to 100 parts by mass of the glass ceramic material for granulation, and they were sized into granules with a 20-mesh sieve. The granules were pressure-molded at 74 MPa (0.75 ton/cm 2 ) to give φ17 disc-shaped green compacts having a diameter of 17 mm and a thickness of 8.5 mm. Then, the green compacts were heated in the air at 900° C. for the time shown in Table 2 to give glass ceramic sintered bodies. 
     Next, the microstructure and various characteristics of the glass ceramic sintered bodies were evaluated under the following conditions. Table 2 shows the results. 
     Microstructure 
     STEM images of cross sections of the glass ceramic sintered bodies were taken with STEM (JEM-2200FS). Further, phase separation analysis was performed through RGB image phase analysis. Fields of view had a size of 7.5 μm×7.5 μm and were observed at a magnification of 7500×. The fields of view were determined at five different locations for each of the present examples. At each field of view, the STEM image was taken, and phase separation analysis was performed. The five STEM images and the five phase separation analysis images were used to calculate the average grain size of the SiO 2  fillers, the average aspect ratio of the Al 2 O 3  fillers, and the area ratio of each phase. Then, a value was calculated by dividing the area ratio of feldspar crystal phases by the area ratio of non-crystalline glass phases. 
     Whether there were any Al 2 O 3  phases bonded via the feldspar crystal phases was checked. Among the present examples, those having any Al 2 O 3  phases bonded via the feldspar crystal phases were treated as satisfactory, and those having no such Al 2 O 3  phases were treated as unsatisfactory. 
     In the present examples, the non-crystalline glass did not include oxides of Sr or oxides of Al. However, it was confirmed that the non-crystalline glass phases included in the glass ceramic sintered bodies manufactured in the end included SrO and Al 2 O 3 . 
     Relative Permittivity ε 
     The relative permittivity ε (no unit) was measured with a network analyzer (8510C manufactured by HEWLETT PACKARD) using a resonance method (JIS R 1627). Among the present examples, those having a relative permittivity ε of 6.20 or less were treated as good, and those having a relative permittivity ε of 6.00 or less were treated as better. 
     Sinterability 
     Fracture surfaces of the glass ceramic sintered bodies were observed with FE-SEM. Among the present examples, those that had few pores and were deemed to be sufficiently densified were treated as satisfactory, and those that had many pores and were not deemed to be sufficiently densified were treated as unsatisfactory. 
     Strength 
     The strength (bending strength) of the glass ceramic sintered bodies was measured in a three-point bending test with a universal testing machine 5543 manufactured by INSTRON. The distance between the points was 15 mm. Among the present examples, those with a bending strength of 100 MPa or more were treated as good. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 Glass raw material 
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                 Non-crystalline 
                 Al 2 O 3  filler 
                 SiO 2  filler 
               
               
                   
                 Crystallized glass 
                 glass 
                 raw material 
                 raw material 
               
               
                   
                 (Parts by mass) 
                 (Parts by mass) 
                 (Parts by mass) 
                 (Parts by mass) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Composition 1 
                 45.5 
                 30.0 
                 24.5 
                 10.0 
               
               
                 Composition 2 
                 45.5 
                 30.0 
                 24.5 
                 3.0 
               
               
                 Composition 3 
                 45.5 
                 30.0 
                 24.5 
                 15.0 
               
               
                 Composition 4 
                 45.5 
                 30.0 
                 24.5 
                 17.5 
               
               
                 Composition 5 
                 45.0 
                 30.0 
                 30.0 
                 5.0 
               
               
                 Composition 6 
                 40.0 
                 30.0 
                 35.0 
                 5.0 
               
               
                 Composition 7 
                 55.0 
                 30.0 
                 15.0 
                 10.0 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
             
            
               
                   
                   
                   
                 Average 
                   
                   
               
               
                   
                   
                   
                 grain 
                 Average 
                 Phase area ratio 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                   
                 size of 
                 aspect 
                   
                 Non- 
                 Feldspar 
                   
               
               
                   
                   
                 Heating 
                 SiO 2   
                 ratio of 
                 SiO 2   
                 crystalline 
                 crystal 
                 Al 2 O 3   
               
               
                   
                   
                 time 
                 fillers 
                 Al 2 O 3   
                 phases 
                 glass 
                 phases 
                 phases 
               
               
                   
                 Composition 
                 (min) 
                 (μm) 
                 fillers 
                 (%) 
                 phases (%) 
                 (%) 
                 (%) 
               
               
                   
               
               
                 Comparative 
                 Composition 1 
                 30 
                 0.05 
                 &lt;2 
                 23.0 
                 62.0 
                 7.0 
                 8.0 
               
               
                 Example 1 
               
               
                 Example 1 
                 Composition 1 
                 30 
                 0.30 
                 &lt;2 
                 23.0 
                 62.0 
                 7.0 
                 8.0 
               
               
                 Example 2 
                 Composition 1 
                 30 
                 0.50 
                 &lt;2 
                 23.0 
                 62.0 
                 7.0 
                 8.0 
               
               
                 Example 3 
                 Composition 1 
                 30 
                 2.5 
                 &lt;2 
                 23.0 
                 62.0 
                 7.0 
                 8.0 
               
               
                 Example 4 
                 Composition 1 
                 30 
                 4.0 
                 &lt;2 
                 23.0 
                 62.0 
                 7.0 
                 8.0 
               
               
                 Example 5 
                 Composition 2 
                 30 
                 0.50 
                 &lt;2 
                 5.0 
                 76.5 
                 8.6 
                 9.9 
               
               
                 Example 2 
                 Composition 1 
                 30 
                 0.50 
                 &lt;2 
                 23.0 
                 62.0 
                 7.0 
                 8.0 
               
               
                 Example 6 
                 Composition 3 
                 30 
                 0.50 
                 &lt;2 
                 30.0 
                 56.4 
                 6.4 
                 7.3 
               
               
                 Comparative 
                 Composition 4 
                 30 
                 0.50 
                 &lt;2 
                 35.0 
                 52.3 
                 5.9 
                 6.8 
               
               
                 Example 2 
               
               
                 Comparative 
                 Composition 1 
                 10 
                 0.50 
                 &lt;2 
                 23.0 
                 63.5 
                 5.5 
                 8.0 
               
               
                 Example 3 
               
               
                 Example 7 
                 Composition 1 
                 20 
                 0.50 
                 &lt;2 
                 23.0 
                 62.5 
                 6.5 
                 8.0 
               
               
                 Example 2 
                 Composition 1 
                 30 
                 0.50 
                 &lt;2 
                 23.0 
                 62.0 
                 7.0 
                 8.0 
               
               
                 Example 8 
                 Composition 1 
                 60 
                 0.50 
                 &lt;2 
                 18.0 
                 62.0 
                 12.0 
                 8.0 
               
               
                 Comparative 
                 Composition 7 
                 30 
                 0.50 
                 &lt;2 
                 24.0 
                 66.0 
                 6.0 
                 4.0 
               
               
                 Example 4 
               
               
                 Example 2 
                 Composition 1 
                 30 
                 0.50 
                 &lt;2 
                 23.0 
                 62.0 
                 7.0 
                 8.0 
               
               
                 Example 9 
                 Composition 5 
                 30 
                 0.50 
                 &lt;2 
                 12.0 
                 55.0 
                 20.0 
                 13.0 
               
               
                 Example 10 
                 Composition 6 
                 30 
                 0.50 
                 &lt;2 
                 10.0 
                 40.0 
                 30.0 
                 20.0 
               
               
                 Example 11 
                 Composition 6 
                 60 
                 0.50 
                 &lt;2 
                 10.0 
                 35.0 
                 35.0 
                 20.0 
               
               
                 Example 2 
                 Composition 1 
                 30 
                 0.50 
                 &lt;2 
                 23.0 
                 62.0 
                 7.0 
                 8.0 
               
               
                 Example 12 
                 Composition 1 
                 30 
                 0.50 
                 20 
                 10.0 
                 55.0 
                 25.0 
                 10.0 
               
               
                 Example 13 
                 Composition 1 
                 30 
                 0.50 
                 70 
                 10.0 
                 53.0 
                 27.0 
                 10.0 
               
               
                 Example 14 
                 Composition 1 
                 30 
                 0.50 
                 100 
                 10.0 
                 50.0 
                 30.0 
                 10.0 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                   
                 Feldspar 
                   
                   
                   
                   
               
               
                   
                   
                 crystal 
               
               
                   
                   
                 phases/Non- 
                   
                 Al 2 O 3   
                 Relative 
               
               
                   
                   
                 crystalline 
                   
                 phase 
                 permittivity 
                 Strength 
               
               
                   
                   
                 glass phases 
                 Sinterability 
                 bonding 
                 ε 
                 (MPa) 
               
               
                   
                   
               
               
                   
                 Comparative 
                 0.11 
                 Unsatisfactory 
                 Unavailable 
                 5.30 
                 85 
               
               
                   
                 Example 1 
               
               
                   
                 Example 1 
                 0.11 
                 Satisfactory 
                 Available 
                 5.50 
                 135 
               
               
                   
                 Example 2 
                 0.11 
                 Satisfactory 
                 Available 
                 5.50 
                 135 
               
               
                   
                 Example 3 
                 0.11 
                 Satisfactory 
                 Available 
                 5.50 
                 130 
               
               
                   
                 Example 4 
                 0.11 
                 Satisfactory 
                 Available 
                 5.50 
                 130 
               
               
                   
                 Example 5 
                 0.11 
                 Satisfactory 
                 Available 
                 5.70 
                 103 
               
               
                   
                 Example 2 
                 0.11 
                 Satisfactory 
                 Available 
                 5.50 
                 135 
               
               
                   
                 Example 6 
                 0.11 
                 Satisfactory 
                 Available 
                 5.40 
                 110 
               
               
                   
                 Comparative 
                 0.11 
                 Unsatisfactory 
                 Unavailable 
                 5.35 
                 90 
               
               
                   
                 Example 2 
               
               
                   
                 Comparative 
                 0.09 
                 Satisfactory 
                 Unavailable 
                 5.41 
                 80 
               
               
                   
                 Example 3 
               
               
                   
                 Example 7 
                 0.10 
                 Satisfactory 
                 Available 
                 5.45 
                 105 
               
               
                   
                 Example 2 
                 0.11 
                 Satisfactory 
                 Available 
                 5.50 
                 135 
               
               
                   
                 Example 8 
                 0.19 
                 Satisfactory 
                 Available 
                 5.65 
                 145 
               
               
                   
                 Comparative 
                 0.09 
                 Satisfactory 
                 Unavailable 
                 5.30 
                 80 
               
               
                   
                 Example 4 
               
               
                   
                 Example 2 
                 0.11 
                 Satisfactory 
                 Available 
                 5.50 
                 135 
               
               
                   
                 Example 9 
                 0.36 
                 Satisfactory 
                 Available 
                 5.73 
                 160 
               
               
                   
                 Example 10 
                 0.75 
                 Satisfactory 
                 Available 
                 5.90 
                 185 
               
               
                   
                 Example 11 
                 1.00 
                 Satisfactory 
                 Available 
                 6.10 
                 190 
               
               
                   
                 Example 2 
                 0.11 
                 Satisfactory 
                 Available 
                 5.50 
                 135 
               
               
                   
                 Example 12 
                 0.45 
                 Satisfactory 
                 Available 
                 5.65 
                 225 
               
               
                   
                 Example 13 
                 0.51 
                 Satisfactory 
                 Available 
                 5.68 
                 220 
               
               
                   
                 Example 14 
                 0.60 
                 Unsatisfactory 
                 Available 
                 5.40 
                 190 
               
               
                   
                   
               
            
           
         
       
     
     In Examples 1 to 4 and Comparative Example 1, the average grain size of the SiO 2  fillers was changed. In Comparative Example 1, in which the SiO 2  fillers had a small average grain size, the sinterability was unsatisfactory, and there were no Al 2 O 3  phases bonded via the feldspar crystal phases. This resulted in reduction of the strength. In Example 4, in which the SiO 2  fillers had a large average grain size, it was confirmed that the surface roughness was reduced more than in Examples 1 to 3 and Comparative Example 1, when the glass ceramic was processed into a sheet. 
     In Examples 5 and 6 and Comparative Example 2, the proportion of the SiO 2  filler raw material was changed from that of Example 2 to change the area ratio of each phase without changing the value calculated by dividing the area ratio of the feldspar crystal phases by the area ratio of the non-crystalline glass phases. In Comparative Example 2, in which the proportion of the SiO 2  filler raw material was too large, the sinterability was unsatisfactory, and there were no Al 2 O 3  phases bonded via the feldspar crystal phases. This resulted in reduction of the strength. 
     In Examples 7 and 8 and Comparative Example 3, heating time was changed from that of Example 2 to change the value calculated by dividing the area ratio of the feldspar crystal phases by the area ratio of the non-crystalline glass phases without significantly changing the area ratio of the SiO 2  phases and the area ratio of the Al 2 O 3  phases. In Comparative Example 3, in which the heating time was too short, the value calculated by dividing the area ratio of the feldspar crystal phases by the area ratio of the non-crystalline glass phases decreased. This resulted in nonexistence of the Al 2 O 3  phases bonded via the feldspar crystal phases and reduction of the strength. 
     In Comparative Example 4, the crystallized glass was increased and the Al 2 O 3  filler raw material was decreased from those of Example 2. In Examples 9 and 10, the crystallized glass and the SiO 2  filler raw material were decreased from those of Example 2, and the Al 2 O 3  filler raw material was increased from that of Example 2. That is, in Comparative Example 4 and Examples 9 and 10, the composition was changed from that of Example 2 to change the value calculated by dividing the area ratio of the feldspar crystal phases by the area ratio of the non-crystalline glass phases. Further, in Example 11, the heating time was increased from that of Example 10 to increase the value calculated by dividing the area ratio of the feldspar crystal phases by the area ratio of the non-crystalline glass phases. 
     According to Examples 2 and 9 to 11 and Comparative Example 4, as the value calculated by dividing the area ratio of the feldspar crystal phases by the area ratio of the non-crystalline glass phases increased, the relative permittivity ε and the strength increased. In Comparative Example 4, the value calculated by dividing the area ratio of the feldspar crystal phases by the area ratio of the non-crystalline glass phases decreased. This resulted in nonexistence of the Al 2 O 3  phases bonded via the feldspar crystal phases and reduction of the strength. 
     In Examples 12 to 14, the average aspect ratio of the Al 2 O 3  filler raw material was changed from that of Example 2 to change the average aspect ratio of the Al 2 O 3  fillers. In Examples 12 and 13, in which the Al 2 O 3  fillers had an average aspect ratio of 15 or more and 75 or less, the strength was particularly increased from that of Example 2, in which the Al 2 O 3  fillers had an average aspect ratio of less than 15. In Example 14, in which the Al 2 O 3  fillers had an average aspect ratio of over 75, the sinterability was unsatisfactory, and the strength decreased from that of Examples 12 and 13. However, Example 14 had good relative permittivity ε and good strength. 
     Experiment 2 
     Experiment 2 was conducted under the same conditions as in Example 2 of Experiment 1 except that the metal element mainly included in the crystallized glass in the glass raw material was changed from Sr to Mg, Ca, or Ba. Table 3 shows the results. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
             
            
               
                   
                 Average 
                   
                 Phase area ratio 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                 grain 
                 Average 
                   
                   
                 Non- 
                   
                   
               
               
                   
                   
                 size of 
                 aspect 
                   
                   
                 crystalline 
                 Feldspar 
               
               
                   
                   
                 SiO 2   
                 ratio of 
                 Heating 
                 SiO 2   
                 glass 
                 crystal 
                 Al 2 O 3   
               
               
                   
                   
                 fillers 
                 Al 2 O 3   
                 time 
                 phases 
                 phases 
                 phases 
                 phases 
               
               
                   
                 Composition 
                 (μm) 
                 fillers 
                 (min) 
                 (%) 
                 (%) 
                 (%) 
                 (%) 
               
               
                   
               
               
                 Example 2 
                 Composition 1 
                 0.50 
                 &lt;2 
                 30 
                 23.0 
                 62.0 
                 7.0 
                 8.0 
               
               
                 Example 21 
                 Composition 1 
                 0.50 
                 &lt;2 
                 30 
                 23.0 
                 62.0 
                 6.7 
                 8.0 
               
               
                 Example 22 
                 Composition 1 
                 0.50 
                 &lt;2 
                 30 
                 23.0 
                 62.0 
                 7.0 
                 8.0 
               
               
                 Example 23 
                 Composition 1 
                 0.50 
                 &lt;2 
                 30 
                 23.0 
                 61.0 
                 8.0 
                 8.0 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                   
                 Feldspar 
                   
                   
                   
                   
                   
               
               
                   
                   
                 crystal 
                 Metal 
               
               
                   
                   
                 phases/Non- 
                 element 
               
               
                   
                   
                 crystalline 
                 in glass 
                   
                 Al 2 O 3   
                 Relative 
               
               
                   
                   
                 glass 
                 raw 
                   
                 phase 
                 permittivity 
                 Strength 
               
               
                   
                   
                 phases 
                 material 
                 Sinterability 
                 bonding 
                 ε 
                 (MPa) 
               
               
                   
                   
               
               
                   
                 Example 2 
                 0.11 
                 Sr 
                 Satisfactory 
                 Available 
                 5.50 
                 135 
               
               
                   
                 Example 21 
                 0.11 
                 Mg 
                 Satisfactory 
                 Available 
                 5.30 
                 110 
               
               
                   
                 Example 22 
                 0.11 
                 Ca 
                 Satisfactory 
                 Available 
                 5.45 
                 120 
               
               
                   
                 Example 23 
                 0.13 
                 Ba 
                 Satisfactory 
                 Available 
                 6.00 
                 145 
               
               
                   
                   
               
            
           
         
       
     
     Changing the metal element mainly included in the crystallized glass from Sr to Mg, Ca, or Ba resulted in the change of the metal element mainly included in the feldspar crystal phases from Sr to Mg, Ca, or Ba. 
     Examples 21 to 23, in which the metal element mainly included in the feldspar crystal phases was changed from Sr to Mg, Ca, or Ba, had good characteristics. In Examples 21 and 22, in which the metal element was changed to Mg and Ca respectively, the strength decreased from that of Example 2. In Example 23, in which the metal element was changed to Ba, the relative permittivity e increased from that of Example 2. 
     In all Examples of Experiments 1 and 2, it was confirmed that 25% or more of the Al 2 O 3  phases  14  were bonded together via the feldspar crystal phases  13  in terms of the number of the Al 2 O 3  phases  14 . 
     NUMERICAL REFERENCES 
     
         
           1  . . . glass ceramic 
           11  . . . SiO 2  phase 
           12  . . . non-crystalline glass phase 
           13  . . . feldspar crystal phase 
           14  . . . Al 2 O 3  phase