JP2623337B2 - Low dielectric loss A (1) (2) O (3) ceramics and their manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention particularly relates to an Al ₂ O ₃ based porcelain suitably used as a microwave dielectric material, and a method for producing the same.

[Conventional technology and problems]

Al ₂ O ₃ ceramics are used for electronic components such as IC substrates due to their low dielectric constant.

However, microwave dielectric materials, which are attracting attention in recent years, such as microwave integrated circuit (MIC) substrate materials, are required to have stricter dielectric properties. As a result, conventional Al ₂ O ₃ porcelains were inadequate, especially in terms of dielectric loss.

[Means for solving the problems, actions, and effects]

The present invention solves such a problem by the following means. (1) The alumina content is 99.7% or more, and the spectral intensity ratio (Auger analysis) of SiO ₂ and Al ₂ O _{3 on} the surface is
And 0.33 or more, a low dielectric loss Al ₂ O ₃ based ceramic surface roughness (Ra) is equal to or is 0.15μm or less.

(2) After polishing an Al ₂ O ₃ based sintered body having an alumina content of 99.7% or more, a low dielectric loss Al ₂ O ₃ is characterized in that Si is oxidized by sputtering or SiO ₂ is sputtered.
Method of manufacturing porcelain.

Normally, sintered porcelain is ground and polished to predetermined dimensions as a final step, but the present inventors have confirmed that this step increases high-frequency loss. That is, when the component concentration on the Al ₂ O ₃ porcelain surface was analyzed by Auger analysis, it was confirmed that the porcelain as fired had a high SiO ₂ concentration but a low concentration after processing. Therefore, increasing the SiO ₂ concentration in the surface by sputtering the Al ₂ O ₃ sintered ceramic surface after machining or SiO ₂ sputtering was oxidized with Si, the dielectric properties, in particular the dielectric loss tangent characteristic recover Is found. Accordingly, dielectric loss can be significantly reduced without impairing other characteristics such as surface smoothness, strength, and thermal expansion property.

In the present invention, the Al ₂ O ₃ based porcelain refers to a porcelain (ceramic) containing Al ₂ O ₃ and SiO ₂ as essential components. Even with microwaves of high frequency, for example, 7 to 45 GHz, the dielectric constant [ε] can be kept low, for example, 10 or less, preferably 9.9 or less. The amount of Al ₂ O _{3 in} the whole porcelain is 99.7 wt% or more. If it is less than 99.7 wt%, dielectric loss and the like will be impaired. If necessary, a small amount of a sintering aid such as MgO or CaO may be contained. For example, it is preferable to set SiO _{2 /} MgO = _{1 to} 0.2.

Auger analysis of SiO ₂ and Al ₂ O ₃
Have a spectral intensity ratio (SiO ₂ / Al ₂ O ₃ ) of 0.33 or more.
This is to keep the high-frequency loss low even after the grinding and polishing. Preferably, it is good to be 0.5 or more. “Surface” refers to a depth of about 0-100 °, preferably about 0-20 °. Of course, the spectral intensity ratio may not be uniform at each depth. For example, the intensity ratio at the outermost surface may be maximized, and may be gradually reduced as the depth increases. Auger analysis refers to a chemical analysis method using Auger electrons emitted from a solid when a solid substance is irradiated with an electron beam. Since Auger electrons are in the range of several tens to 2,000 eV, analysis can be performed from the surface to a depth of several to several tens of millimeters.

The surface roughness [Ra] of the porcelain is 0.15 μm or less. 0.15μ
If it exceeds m, it cannot be preferably applied to a MIC substrate or the like. Preferably, the thickness is 0.10 μm or less. The lower limit should be about 0.09 from the viewpoint of mass productivity.

Average crystal grain size of porcelain is 1-20μm, relative theoretical density is 98%
It is good to do above.

The Al ₂ O ₃ based porcelain of the present invention is manufactured as follows. A predetermined amount of each raw material powder is mixed with a binder and the like, dried, molded and fired. It is preferable to use a powder having a particle diameter of 1 μm or less for each raw material. As the binder, for example, polyvinyl alcohol, cellulose and the like are used. The mixing is performed by dry mixing using a raikai machine or the like or wet mixing using a ball mill or the like. The mixed powder is dried by spray drying or the like to obtain a granulated powder having a particle size of about 10 to 200 μm. The granulated powder is pressed into a predetermined shape. In this case, it is performed by two-stage pressing: die pressing (forming pressure 500 to 1000 kg / cm ² ) and then hydrostatic pressing (forming pressure 1500 to 2000 kg / cm ² ). Good. The surface becomes smooth due to the reduction in pinholes. Next, the obtained molded body is fired under a pressure or non-pressure in an oxidizing or non-oxidizing atmosphere at a temperature of 1500 to 1700 ° C. for a predetermined time. Next, the obtained sintered body is finished to predetermined dimensions by grinding or polishing.

In the present invention, Al ₂ O ₃ thus ground and polished
A sputtering process is performed on the porcelain. As described above, in the conventional manufacturing method, high-frequency loss increases due to grinding and polishing as the final step, but this is because the SiO ₂ concentration on the sintered porcelain surface is greatly reduced by grinding and polishing. It was because. However, by subjecting the porcelain that has been ground and polished as in the present invention to a sputtering treatment as a post-treatment, the SiO ₂ concentration on the surface can be restored to the initial state immediately after firing. Therefore, Al ₂
The dielectric loss of O ₃ porcelain can be reduced by about 90%.

The sputtering may be performed by high-frequency sputtering using SiO ₂ as a sample (cathode) or reactive sputtering using Si. In this case, the former
It is preferable to carry out the treatment at a pressure of 10 ^-3 to 10 ^-4 Torr, and the latter at a pressure of 10 ^-2 to 10 ^-3 Torr. Similar effects can be obtained by ion plating, CVD, vapor deposition, and the like. However, sputtering is advantageous in terms of ease of handling and stability (reproducibility) of the apparatus.

Al ₂ O ₃ based ceramic according to the present invention, microwave dielectric materials, e.g. MIC substrate, package, dielectric resonators, microwave line, is suitably used in such as a microwave transmission window material. Particularly, it is preferable at a used frequency of 12 to 20 GHz. still,
Of course, it can be applied to ordinary electronic components such as an IC substrate. It is also effective for fired bodies of any shape, such as a plate or a column.

〔Example〕

 Hereinafter, embodiments of the present invention will be described.

Alumina (commercial product, purity 99.995%, average particle size 0.5 μm) 300 g Silicic anhydride (special grade reagent, average particle size 0.5 μm) 0.45 g Magnesium carbonate (special grade reagent, average particle size 0.3 μm) 0.95 g deionized water 250 ml 3 g or more of polyvinyl alcohol was put into a polyethylene ball mill together with 99.99% pure alumina cobblestone (10φ, 600 g) and mixed at 120 rpm for 72 hours. The thus obtained plasma is spray-dried and the average particle size is 60μ.
m of granulated powder. This granulated powder is pressed by a die pressing method to a disc-shaped substrate having a size of 65 × 65 × 2 mm t at a pressure of 800 kg / cm ^2.
In molding, after isostatic pressing further pressure 1500 kg / cm ^2, 165
It was fired in an electric furnace at a temperature of 0 ° C. for 1 hour in an air atmosphere. Thereafter, the fired substrate was polished to a size of 50.8 × 50.8 × 0.75 mm.

Next, silicon (purity 99.99%) was applied to the fired and polished substrate.
%), And sputtering was performed for 20 minutes in an argon gas atmosphere at a pressure of 10 ^-2 Torr while maintaining the substrate at a temperature of 500 ° C.

Next, the electrical characteristics and surface SiO ₂ , Mg _{2 of} the porcelain substrate thus obtained and the polished one (comparative example) were measured.
The concentrations of O and Al ₂ O ₃ were measured.

(A) Measurement of electrical characteristics: Measurement was performed by the cavity resonator method. That is, diameter D, length H
A dielectric disk sample (diameter D, thickness L) is inserted into the center of a (2M + L) conductor cylindrical cavity. Various characteristic values are measured from the measured value of the resonance frequency (fo) in the TE ₀₁₁ mode.

Relative permittivity: ε _r = {(πLfo) / C} ² [x ² −Y ² ｛L / (2M)｝ ² ] +
1 Dielectric loss tangent: tan δ = A / (Qu ) -R S B (A = 1 + (W 1 / W 2), B = P C / (ωR S W 1), R S = (Wμo) / 2δ W 1 , W ₂ is the area [I] [II] the temperature coefficient of stored energy) the relative dielectric constant of the electric field (tau): calculated from the dielectric constant in the temperature range of 25 ° C. to 80 ° C.. In these measurements, the resonance frequency (fo) was set to 15 GHz.

(B) Measurement of spectral intensity of Al ₂ O ₃ , SiO ₂ and MgO: Based on Auger analysis. The SiO ₂ / Al ₂ O ₃ intensity ratio was calculated from the Al peak at an energy of about 50 eV and the Si peak at an energy of about 70 eV.

The results are shown in Table 1 below. The spectrum intensity of MgO was hardly detected, and the intensity of the porcelain substrate was 3100 kg / cm ²
Degree and thermal expansion coefficient were about 8.1 × 10 ^-6 .

As is evident from Table 1 above, the Al ₂ O ₃ porcelain that has been polished and sputtered has a SiO ₂ / Al ₂ O
_{3 It} can be seen that the intensity ratio is large, the dielectric loss tangent is small in the microwave region, and the dielectric loss is significantly improved. Further, there is a correlation between the SiO ₂ / Al ₂ O ₃ intensity ratio and the dielectric loss tangent (tan δ), and the level of the dielectric loss tangent can be determined and adjusted by defining the SiO ₂ concentration on the porcelain surface.

Claims (2)

(57) [Claims] (1) The alumina content is 99.7% or more, the spectral intensity ratio of SiO ₂ and Al ₂ O _{3 on} the surface (Auger analysis) is 0.33 or more, and the surface roughness (Ra) is 0.15 μm or less. A low dielectric loss Al ₂ O ₃ porcelain. 2. After polishing an Al ₂ O ₃ based sintered body having an alumina content of 99.7% or more, Si is sputtered and oxidized or
Low dielectric loss A characterized by sputtering iO ₂
l ₂ O ₃ porcelain manufacturing method.