Ceramic substrate

Abstract

Provided is a ceramic substrate including alumina particles and zirconia particles and comprising: a non-dense layer which has pores scattered in plane directions; and a dense layer which has a lower pore content than the non-dense layer. The ceramic substrate has a structure in which the non-dense layer and the dense layer are arranged in layers along the thickness direction.

Description

Ceramic substrate

[0001] The disclosed embodiments relate to ceramic substrates.

[0002] Alumina-zirconia ceramics containing alumina particles and zirconia particles have been attracting attention because of their high strength.

[0003] Japanese Patent Application Laid-Open No. 2005-211252

[0004] The ceramic substrate of the present disclosure has a structure in which a non-dense layer contains alumina particles and zirconia particles and in which pores are scattered in a planar direction, and a dense layer in which the proportion of pores is smaller than that of the non-dense layer, and the non-dense layer and the dense layer are arranged in layers in the thickness direction.

[0005] FIG. 1 is an enlarged cross-sectional view showing an example of the configuration of a ceramic substrate according to an embodiment. FIG. 2 is an enlarged cross-sectional view showing an example of the configuration of a ceramic substrate according to Alternative Embodiment 1. FIG. 3 is an enlarged cross-sectional view showing an example of the configuration of a ceramic substrate according to Alternative Embodiment 2. FIG. 4 is an enlarged cross-sectional view showing an example of the configuration of a ceramic substrate according to Alternative Embodiment 3. FIG. 5 is an enlarged cross-sectional view showing an example of the configuration of a ceramic substrate according to Alternative Embodiment 4. FIG. 6 is an enlarged cross-sectional view showing an example of the configuration of a ceramic substrate according to Alternative Embodiment 5. FIG. 7 is a view showing a cross-sectional SEM image of the ceramic substrate of Sample 1.

[0006] Hereinafter, a mode for carrying out a ceramic substrate according to the present disclosure (hereinafter referred to as an "embodiment") will be described in detail with reference to the drawings. Note that the present disclosure is not limited to the embodiment. Furthermore, each embodiment can be appropriately combined within a range that does not cause contradiction in processing content. Furthermore, the same components in each of the following embodiments will be given the same reference numerals, and duplicated explanations will be omitted.

[0007] Alumina-zirconia ceramics containing alumina particles and zirconia particles have been attracting attention because of their high strength.

[0008] However, when the above-mentioned conventional ceramics are used as a ceramic substrate for mounting electric elements, the dielectric constant of the substrate tends to be high because it contains particles of zirconia, which has a higher dielectric constant than alumina as a single component, and therefore, when electric elements operating in the high frequency band are mounted on such a substrate, there is a risk of increased dielectric loss.

[0009] Therefore, it is desired to realize a ceramic substrate that can solve the above problems and has a low relative dielectric constant while maintaining high strength.

[0010] First, the configuration of a ceramic substrate 1 according to an embodiment will be described with reference to Fig. 1. Fig. 1 is an enlarged cross-sectional view showing an example of the configuration of a ceramic substrate 1 according to an embodiment.

[0011] 1, the ceramic substrate 1 according to the embodiment includes a non-dense layer 2 and a dense layer 3. The ceramic substrate 1 according to the embodiment may also include an electrode 4.

[0012] Both the non-dense layer 2 and the dense layer 3 are made of ceramic containing alumina particles (not shown) and zirconia particles (not shown). Pores V (see FIG. 7) are scattered in the planar direction of the non-dense layer 2. The porosity of the non-dense layer 2 may be, for example, 2% or more.

[0013] The dense layer 3 has a smaller proportion of pores V than the non-dense layer 2. The porosity of the dense layer 3 may be, for example, 0.2% or less.

[0014] In the present disclosure, the pores V have a maximum diameter of 0.1 μm or more. In the present disclosure, the porosity of the non-dense layer 2 or the dense layer 3 is determined by dividing the total area of ​​the pores by the area of ​​the observation region (e.g., an area of ​​300 μm × 50 μm) in an image observed with a scanning electron microscope (SEM).

[0015] As shown in FIG. 1, the ceramic substrate 1 according to the embodiment may have a structure in which a non-dense layer 2 and a dense layer 3 are layered in the thickness direction.

[0016] The ceramic substrate 1 having such a configuration has the non-dense layer 2 with high porosity, and therefore can reduce the relative dielectric constant by the amount of the pores V with low relative dielectric constant compared to an alumina-zirconia substrate not having the non-dense layer 2. Therefore, according to the embodiment, the ceramic substrate 1 can have high strength and a reduced relative dielectric constant.

[0017] For example, in an embodiment, the dielectric constant of ceramic substrate 1 may be equal to or greater than 9 and equal to or less than 15. This allows, when an electric element (not shown) is mounted on ceramic substrate 1, to maintain good electrical characteristics of the electric element.

[0018] Furthermore, in the embodiment, the dense layer 3 is disposed so as to overlap the non-dense layer 2, which can reduce a decrease in mechanical strength across the entire plane of the ceramic substrate 1. In this case, since there are fewer pores V on the dense layer 3 side, it is possible to suppress the occurrence of cracks that originate from the pores V.

[0019] In addition, in the embodiment, since the non-dense layer 2 is arranged in layers, the fracture toughness of the ceramic substrate 1 can be maintained at a good level, and the ceramic substrate 1 is easily bent and deformed, making it less likely to crack.

[0020] 1 , the thickness t1 of the non-dense layer 2 may be larger than the thickness t2 of the dense layer 3. Increasing the proportion of the non-dense layer 2 in the entire ceramic substrate 1 in this manner increases the porosity of the entire ceramic substrate 1, thereby further reducing the relative dielectric constant of the ceramic substrate 1.

[0021] In the embodiment, the thickness ratio t1 / t2 of the non-dense layer 2 to the dense layer 3 may be 2 or more and 20 or less, and more preferably 5 or more and 15 or less. This makes it possible to achieve a good balance between good mechanical strength and a low relative dielectric constant of the ceramic substrate 1, and the ceramic substrate 1 can be used for many applications.

[0022] The thickness t1 of the non-dense layer 2 and the thickness t2 of the dense layer 3 are measured by cutting and polishing the cross section of the ceramic substrate 1 using, for example, a digital microscope. The measurement range is preferably 500 μm or longer in the planar direction of the ceramic substrate 1. Measurements are taken at approximately 10 equally spaced locations within this measurement range, and the average values ​​are determined as the thickness t1 and the thickness t2, respectively.

[0023] In the case where the ceramic substrate 1 has a structure in which a dense layer 3 is provided on both sides of a non-dense layer 2, the thicknesses of the dense layer 3 on both sides are measured, and the average value is taken as the thickness t2 of the dense layer 3. The method for separating the non-dense layer 2 region from the dense layer 3 region in the cross section of the ceramic substrate 1 is as shown in Figure 7, by identifying the pores V closest to the front and back surfaces of the ceramic substrate 1 among the multiple pores V present in the cross section of the ceramic substrate 1 being observed, and drawing a line through these pores V. The line is arranged so as to be approximately parallel to the front or back surface of the ceramic substrate 1. For example, pores V having a maximum diameter of 2 µm or more are selected.

[0024] In the embodiment, the pores V may be positioned so as to be in contact with the zirconia particles, thereby enabling the pores V to stop the propagation of cracks at the grain boundaries between the zirconia particles, thereby providing the ceramic substrate 1 with high strength, high toughness, and a large bending deformation rate.

[0025] Furthermore, in the embodiment, the pores V are positioned so as to be in contact with the zirconia particles, thereby weakening the restraining force exerted by the alumina particles, facilitating the phase transformation of the zirconia particles and enhancing the resistance to crack propagation due to the phase transformation of the zirconia particles.

[0026] In the embodiment, when the average particle size of the alumina particles contained in the non-dense layer 2 and the dense layer 3 is D1 and the average particle size of the zirconia particles is D2, D1 may be greater than D2.

[0027] In this manner, in the embodiment, since the size of the alumina particles is larger than the size of the zirconia particles, the alumina particles can contribute to the rigidity and hardness of the entire ceramic substrate 1 .

[0028] Furthermore, in the embodiment, since the size of the zirconia particles is small, the three-point bending strength and fracture toughness of the ceramic substrate 1 are improved, and the amount of deflection of the ceramic substrate 1 can be increased.

[0029] In addition, in an embodiment, when the average particle size of the alumina particles contained in the non-dense layer 2 and the dense layer 3 is D1 and the average particle size of the zirconia particles is D2, the particle size ratio D1 / D2 may be 3 or more and 10 or less.

[0030] This allows the alumina particles to further contribute to the rigidity and hardness of the entire ceramic substrate 1. In addition, the three-point bending strength and fracture toughness of the ceramic substrate 1 are further improved, and the amount of deflection of the ceramic substrate 1 can be further increased.

[0031] 1 , the exposed surface of the dense layer 3 may be a mounting surface 1a for an electric element (not shown). That is, in the embodiment, an electrode 4 on which an electric element is mounted may be located on the mounting surface 1a, which is the exposed surface of the dense layer 3.

[0032] As a result, the ceramic layer located near the electric element becomes the dense layer 3 which has higher rigidity than the non-dense layer 2, thereby improving the reliability of the electric device comprising the ceramic substrate 1 and the electric element.

[0033] In the embodiment, the non-dense layer 2 and the dense layer 3 may contain a glass phase in addition to the alumina particles and the zirconia particles. The glass phase is present around the alumina particles and the zirconia particles, for example.

[0034] In an embodiment, the presence of a glass phase adjacent to the alumina particles and zirconia particles weakens the restraining forces between the alumina particles, between the zirconia particles, and between the alumina particles and the zirconia particles.

[0035] The glass phase contained in the non-dense layer 2 and the dense layer 3 is a grain boundary phase surrounding the alumina particles and zirconia particles. The glass phase may contain a small amount of crystalline phase. The glass phase is preferably contained in a proportion sufficient to be evenly distributed around the alumina particles and zirconia particles, as long as it can achieve predetermined values ​​or higher in the properties of the ceramic substrate 1, such as deflection, fracture toughness, and three-point bending strength. In this case, the proportion of the glass phase is preferably 1% or more and 7% or less by area.

[0036] The alumina particles, zirconia particles, and glass phase have different Young's moduli. Specifically, the Young's moduli increase in the order of glass phase < zirconia particles < alumina particles. In the ceramic substrate 1 according to the embodiment, the zirconia particles have a small contact area with the alumina particles, which have a high Young's modulus, and the glass phase, which has a lower Young's modulus than the alumina particles, is present around the alumina particles and zirconia particles. This results in a ceramic substrate 1 with a large deflection amount and high deformation.

[0037] In an embodiment, for example, the area ratio per unit area of ​​the alumina particles and zirconia particles contained in the ceramic substrate 1 is preferably 40% to 60% for the alumina particles and 30% to 40% for the zirconia particles, with the remaining glass phase being 5% to 20%.

[0038] Alternative Embodiment 1 Next, various alternative embodiments of the present disclosure will be described with reference to Fig. 2 to Fig. 6. Fig. 2 is an enlarged cross-sectional view showing an example of the configuration of a ceramic substrate 1 according to alternative embodiment 1.

[0039] 2 , in a ceramic substrate 1 according to another embodiment 1, thicknesses t1 and t2 of the non-dense layer 2 and the dense layer 3 are different from those in the above-described embodiment (see FIG. 1 ). Specifically, in another embodiment 1, thickness t2 of the dense layer 3 may be greater than thickness t1 of the non-dense layer 2.

[0040] In this way, by increasing the proportion of the dense layer 3 in the entire ceramic substrate 1, the three-point bending strength of the ceramic substrate 1 can be maintained at a good level.

[0041] <Another Embodiment 2> Fig. 3 is an enlarged cross-sectional view showing an example of the configuration of a ceramic substrate 1 according to another embodiment 2. As shown in Fig. 3, in the ceramic substrate 1 according to another embodiment 2, a non-dense layer 2 may be sandwiched between two dense layers 3.

[0042] As described above, in another embodiment 2, the non-dense layer 2 is sandwiched between two dense layers 3, which reduces deformation of one surface of the ceramic substrate 1 so that the other surface is convex and the other surface is concave. Therefore, according to another embodiment 2, a ceramic substrate 1 with high flatness can be obtained.

[0043] In another embodiment 2, the thickness t1 of the non-dense layer 2 may be larger than the thickness t2 of each of the two dense layers 3. Increasing the proportion of the non-dense layer 2 in the entire ceramic substrate 1 in this way increases the porosity of the entire ceramic substrate 1, thereby further reducing the relative dielectric constant of the ceramic substrate 1.

[0044] In another embodiment 2, the thickness ratio t1 / t2 of the non-dense layer 2 to the dense layer 3 may be 3 or more and 20 or less, and more preferably 5 or more and 15 or less. This makes it possible to achieve a balance between good mechanical strength and a low relative dielectric constant of the ceramic substrate 1, enabling the ceramic substrate 1 to be used in many applications.

[0045] <Another Embodiment 3> Fig. 4 is an enlarged cross-sectional view showing an example of the configuration of a ceramic substrate 1 according to another embodiment 3. As shown in Fig. 4, in the ceramic substrate 1 according to another embodiment 3, the thickness of the dense layer 3 is different from that of the above-described another embodiment 2 (see Fig. 3).

[0046] Specifically, in another embodiment 3, the thickness t2a of the dense layer 3A having the mounting surface 1a may be smaller than the thickness t2b of the dense layer 3B on the opposite side of the dense layer 3A. The dense layer 3A is an example of one dense layer 3, and the dense layer 3B is an example of the other dense layer 3. The exposed surface of the dense layer 3B is the back surface 1b of the ceramic substrate 1.

[0047] By making the thickness t2a of the dense layer 3A smaller than the thickness t2b of the dense layer 3B, the distance between the non-dense layer 2 having a low dielectric constant and an electric element (not shown) can be shortened. Therefore, according to another embodiment 3, when an electric element is mounted on the ceramic substrate 1, the electric characteristics of the electric element can be maintained at a good level.

[0048] In another embodiment 3, the thickness t1 of the non-dense layer 2 may be larger than the thicknesses t2a and t2b of the two dense layers 3. Increasing the proportion of the non-dense layer 2 in the entire ceramic substrate 1 in this manner increases the porosity of the entire ceramic substrate 1, thereby further reducing the relative dielectric constant of the ceramic substrate 1.

[0049] In another embodiment 3, the thickness ratios t1 / t2a and t1 / t2b of the non-dense layer 2 to the dense layers 3A and 3B may be 3 or more and 20 or less, and more preferably 5 or more and 15 or less. This makes it possible to achieve a balance between good mechanical strength and a low relative dielectric constant of the ceramic substrate 1, enabling the ceramic substrate 1 to be used in many applications.

[0050] Alternative Embodiment 4 Fig. 5 is an enlarged cross-sectional view showing an example of the configuration of a ceramic substrate 1 according to Alternative Embodiment 4. As shown in Fig. 5, in the ceramic substrate 1 according to Alternative Embodiment 4, the thickness of the dense layer 3 differs from that of the aforementioned Alternative Embodiment 2 (see Fig. 3) and Alternative Embodiment 3 (see Fig. 4).

[0051] Specifically, in another embodiment 4, the thickness t2a of the dense layer 3A having the mounting surface 1a may be greater than the thickness t2b of the dense layer 3B on the opposite side to the dense layer 3A.

[0052] In this way, by making the thickness t2a of the dense layer 3A greater than the thickness t2b of the dense layer 3B, the thickness t2a of the dense layer 3A, which is located near the electrical element and has high rigidity, can be made thicker, thereby improving the reliability of the electrical device comprising the ceramic substrate 1 and the electrical element.

[0053] In another embodiment 4, the thickness t1 of the non-dense layer 2 may be larger than the thicknesses t2a and t2b of the two dense layers 3. Increasing the proportion of the non-dense layer 2 in the entire ceramic substrate 1 in this manner increases the porosity of the entire ceramic substrate 1, thereby further reducing the relative dielectric constant of the ceramic substrate 1.

[0054] In another embodiment 4, the thickness ratios t1 / t2a and t1 / t2b of the non-dense layer 2 to the dense layers 3A and 3B may be 3 or more and 20 or less, and more preferably 5 or more and 15 or less. This makes it possible to achieve a balance between good mechanical strength and a low relative dielectric constant of the ceramic substrate 1, enabling the ceramic substrate 1 to be used in many applications.

[0055] <Another Embodiment 5> Fig. 6 is an enlarged cross-sectional view showing an example of the configuration of a ceramic substrate 1 according to another embodiment 5. As shown in Fig. 6, in the ceramic substrate 1 according to another embodiment 5, the thickness t2 of the dense layer 3 is different from that of the above-described other embodiments 2 to 4 (see Figs. 3 to 5).

[0056] Specifically, in another embodiment 5, the thickness t1 of the non-dense layer 2 may be smaller than the thickness t2 of each of the two dense layers 3. In this way, by increasing the proportion of the dense layer 3 in the entire ceramic substrate 1, the three-point bending strength of the ceramic substrate 1 can be maintained favorably.

[0057] Examples of the present disclosure will be specifically described below, but the present disclosure is not limited to the following examples.

[0058] <Sample 1> First, a mixed powder of 70 mass% alumina particles (average particle size 1.3 μm) and 30 mass% zirconia powder (average particle size 0.2 μm) was prepared as a primary mixed powder. Next, 3.6 mass parts of glass powder (borosilicate glass) was added to 100 mass parts of this primary mixed powder to prepare a secondary mixed powder.

[0059] Next, 15 parts by mass of a binder (butyral resin) and 5 parts by mass of a plasticizer (dioctyl phthalate (DOP)) were added to 100 parts by mass of the secondary mixed powder, and a slurry was prepared using toluene as a solvent.

[0060] Next, an alumina-zirconia green sheet having a thickness of 70 μm was produced from the prepared slurry by a doctor blade method.

[0061] In parallel with the production of the alumina-zirconia green sheets, alumina green sheets were produced by adding a binder (butyral resin) and a plasticizer (dioctyl phthalate (DOP)) to a powder of alumina particles (average particle size 3 μm) and using toluene as a solvent to prepare a slurry.

[0062] Next, two alumina green sheets each having a thickness of 150 μm were prepared from the prepared slurry by a doctor blade method.

[0063] Next, one alumina-zirconia green sheet was sandwiched between two alumina green sheets to form a laminate, which was then fired at a maximum temperature of 1550° C. for a holding time of 5 hours.

[0064] Finally, the alumina sintered bodies resulting from the alumina green sheets were peeled off from both sides of the sintered laminate, thereby obtaining the ceramic substrate 1 of sample 1.

[0065] <Sample 2> Ceramic substrate 1 of sample 2 was obtained by the same method and conditions as those for sample 1, except that the holding time in the firing step of the laminate was set to 10 hours.

[0066] <Sample 3> Two alumina-zirconia green sheets and two alumina green sheets were prepared using the same method as in Sample 1. Two laminates each consisting of one alumina-zirconia green sheet and one alumina green sheet were then prepared.

[0067] Next, the alumina-zirconia green sheets were placed facing each other, and a release powder (alumina powder) was spread between them, and the two laminates were stacked to form one laminate, which was then fired at a maximum temperature of 1550°C for a holding time of 5 hours.

[0068] Next, the fired body was divided into two at the interface where the release powder was spread, and the alumina fired body resulting from the alumina green sheet was peeled off from one side of the divided fired body, thereby obtaining ceramic substrate 1 of sample 3.

[0069] <Sample 4> One alumina-zirconia green sheet was prepared using the same method as for Sample 1. Next, the alumina-zirconia green sheet was placed on a base plate of an alumina sintered body. Finally, the alumina-zirconia green sheet placed on the base plate was fired at a maximum temperature of 1550°C for a holding time of 5 hours to obtain ceramic substrate 1 of Sample 4. The thickness of Samples 1 to 4 prepared after firing was approximately 50 μm.

[0070] <Various Evaluations> Next, the ceramic substrate 1 of each sample obtained above was cut, the cut surface was mirror-polished, and the cross section was observed with a scanning electron microscope (SEM). Fig. 7 is a diagram showing a cross-sectional SEM image of the ceramic substrate 1 of Sample 1. Note that the example shown in Fig. 7 shows a sample in which electrodes 4 are formed on both the mounting surface 1a and the back surface 1b of the ceramic substrate 1.

[0071] 7, sample 1 has a structure in which a non-dense layer 2 having many pores V and a dense layer 3 having few pores V are arranged in layers in the thickness direction. In sample 1, the non-dense layer 2 is sandwiched between two dense layers 3.

[0072] Although not shown in the figure, a cross-sectional SEM image of Sample 2 showed a cross-sectional structure in which the dense layers 3 on both sides were thicker than those of Sample 1. Furthermore, a cross-sectional SEM image of Sample 3 showed a cross-sectional structure in which one thick non-dense layer 2 and one thin dense layer 3 were provided, as schematically shown in FIG.

[0073] In addition, in the cross-sectional SEM image of Sample 4, a cross-sectional structure was observed in which pores V were distributed throughout the entire surface from the mounting surface 1a to the back surface 1b.

[0074] Furthermore, a deflection test was conducted on each sample of the obtained ceramic substrate 1, and the amount of deflection of each sample was measured. Specifically, for the deflection test, a measurement sample was cut out from the prepared sample, and a three-point bending strength test was conducted. The amount of deflection was measured as the amount of change from the flat state at the time of fracture. The size of the sample was approximately 40 mm in length, 4 mm in width, and 50 μm in thickness.

[0075] The fracture toughness of each sample of the obtained ceramic substrate 1 was measured in accordance with the indentation method (IF method) specified in JIS R1607-1995. In this case, a sample having a thickness of 2 mm was separately prepared.

[0076] Furthermore, using each sample of the obtained ceramic substrate 1, the relative permittivity at a frequency of 1 MHz was measured using a Q meter (manufactured by Yokogawa Hewlett-Packard Co., Ltd.) and a PNA network analyzer (N5227A, N5261A, manufactured by Keyence Corporation) in accordance with JIS C2138:2007 under the following measurement conditions. The samples were prepared by cutting the prepared ceramic substrate into individual pieces measuring 10 mm x 10 mm (t 50 μm), and coating both surfaces of each piece with In—Ga as an electrode material. The measurement was carried out in an environment of a temperature of 23 to 25°C and a humidity of 30 to 50% RH.

[0077] Table 1 shows the evaluation results of Samples 1 to 4 regarding deflection, fracture toughness, three-point bending strength and relative dielectric constant.

[0078]

[0079] As shown in Table 1, a comparison of the evaluation results of sample 4 with those of samples 1 to 3 reveals that the ceramic substrate 1 can have high strength and a reduced dielectric constant by having a structure in which a non-dense layer 2 with many pores V and a dense layer 3 with few pores V are layered in the thickness direction.

[0080] Furthermore, in the embodiment, the evaluation results of samples 1 to 3 show that by arranging the non-dense layer 2 in a layered manner on the ceramic substrate 1, the deflection amount, fracture toughness, and three-point bending strength of the ceramic substrate 1 can be maintained well.

[0081] Furthermore, in the cross-sectional SEM images of Samples 1 to 3, it was observed that the pores V formed in the non-dense layer 2 were closer to the zirconia particles than to the alumina particles.

[0082] Furthermore, in the cross-sectional SEM images of Samples 1 to 3, it was observed that the average particle size D1 of the alumina particles was larger than the average particle size D2 of the zirconia particles (i.e., D1 > D2). Furthermore, in the cross-sectional SEM images of Samples 1 to 3, it was observed that the particle size ratio D1 / D2 was about 7 and the average diameter of the pores V was about 3 μm.

[0083] It was also observed that the total thickness ratio t1 / 2 (t2) of the non-dense layer 2 and the dense layer 3 in Sample 1 was approximately 4, and the thickness ratio t1 / t2 in Sample 3 was approximately 9. The total thickness ratio t1 / 2 (t2) in Sample 2 was approximately 2. The thicknesses t1 and t2 were measured using the method described above.

[0084] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present disclosure.

[0085] For example, in the above embodiment, the case where the thickness t1 of the non-dense layer 2 is larger and smaller than the thickness t2 of the dense layer 3 is described, but the present disclosure is not limited to such an example, and for example, the thickness t1 of the non-dense layer 2 may be approximately equal to the thickness t2 of the dense layer 3. This also makes it possible to provide the ceramic substrate 1 with high strength and a reduced dielectric constant.

[0086] Further advantages and other aspects may readily occur to those skilled in the art. Therefore, the disclosure in its broader aspects is not limited to the specific details and representative embodiments shown and described above. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

[0087] The present technology can also be configured as follows. (1) A ceramic substrate including alumina particles and zirconia particles, having a non-dense layer with pores scattered in a planar direction, and a dense layer having a smaller proportion of pores than the non-dense layer, wherein the non-dense layer and the dense layer are layered in the thickness direction. (2) The ceramic substrate according to (1), wherein the non-dense layer is sandwiched between two dense layers. (3) The ceramic substrate according to (1) or (2), wherein, when the thickness of the non-dense layer is t1 and the thickness of the dense layer is t2, the thickness ratio t1 / t2 is 2 or more and 20 or less. (4) The ceramic substrate according to any one of (1) to (3), wherein, when the thickness of the non-dense layer is t1 and the thickness of the dense layer is t2, the thickness ratio t1 / t2 is 5 or more and 15 or less. (5) The ceramic substrate according to any one of (1) to (4), wherein the non-dense layer is thicker than the dense layer. (6) The ceramic substrate according to (1) or (2), wherein the dense layer is thicker than the non-dense layer. (7) The ceramic substrate according to any one of (1) to (6), wherein the pores are located so as to be in contact with the zirconia particles. (8) The ceramic substrate according to any one of (1) to (7), wherein D1 is the average particle size of the alumina particles and D2 is the average particle size of the zirconia particles, D1 > D2. (9) The ceramic substrate according to (8), wherein D1 / D2 is 3 or more and 10 or less. (10) The ceramic substrate according to any one of (1) to (9), wherein the exposed surface of the dense layer is a mounting surface for an electric element. (11) The ceramic substrate according to any one of (1) to (10), wherein the non-dense layer is sandwiched between two dense layers, an exposed surface of one of the dense layers is a mounting surface for an electric element, and a thickness of one of the dense layers is smaller than a thickness of the other of the dense layers. (12) The ceramic substrate according to any one of (1) to (10), wherein the non-dense layer is sandwiched between two dense layers, an exposed surface of one of the dense layers is a mounting surface for an electric element, and a thickness of one of the dense layers is larger than a thickness of the other of the dense layers.

[0088] REFERENCE SIGNS LIST 1 ceramic substrate 1a mounting surface 1b back surface 2 non-dense layer 3 dense layer 3A dense layer (an example of one dense layer) 3B dense layer (an example of the other dense layer) 4 electrode t1, t2, t2a, t2b thickness V pore

Claims

1. A ceramic substrate having a structure in which a non-dense layer contains alumina particles and zirconia particles and has pores scattered in a planar direction, and a dense layer in which the proportion of pores is smaller than that of the non-dense layer, the non-dense layer and the dense layer being arranged in a layered manner in the thickness direction.

2. The ceramic substrate according to claim 1, wherein the non-dense layer is sandwiched between two of the dense layers.

3. The ceramic substrate according to claim 1 or 2, wherein the thickness ratio t1 / t2 is 2 or more and 20 or less, where t1 is the thickness of the non-dense layer and t2 is the thickness of the dense layer.

4. A ceramic substrate according to any one of claims 1 to 3, wherein the thickness ratio t1 / t2 is 5 or more and 15 or less, where t1 is the thickness of the non-dense layer and t2 is the thickness of the dense layer.

5. The ceramic substrate according to any one of claims 1 to 4, wherein the non-dense layer is thicker than the dense layer.

6. The ceramic substrate according to claim 1 or 2, wherein the dense layer has a thickness greater than a thickness of the non-dense layer.

7. The ceramic substrate according to any one of claims 1 to 6, wherein the pores are positioned so as to be in contact with the zirconia particles.

8. The ceramic substrate according to any one of claims 1 to 7, wherein, when the average particle size of the alumina particles is D1 and the average particle size of the zirconia particles is D2, D1>D2.

9. The ceramic substrate according to claim 8, wherein D1 / D2 is 3 or more and 10 or less.

10. The ceramic substrate according to any one of claims 1 to 9, wherein an electric element mounting surface is provided on the exposed surface of the dense layer.

11. The ceramic substrate according to any one of claims 1 to 10, wherein the non-dense layer is sandwiched between two of the dense layers, an exposed surface of one of the dense layers is a mounting surface for an electric element, and the thickness of one of the dense layers is smaller than the thickness of the other of the dense layers.

12. A ceramic substrate according to any one of claims 1 to 10, wherein the non-dense layer is sandwiched between two of the dense layers, an exposed surface of one of the dense layers is a mounting surface for an electric element, and the thickness of one of the dense layers is greater than the thickness of the other of the dense layers.

Images