JP5473970B2 - Glass ceramics as dielectrics in the high frequency range. - Google Patents

Description

  The present invention relates to a glass ceramic that can be used as a dielectric in a high frequency region (frequency> 200 MHz), particularly in a gigahertz region (frequency f> 1 GHz).

Many applications (uses) in the high-frequency region require special materials having a very high relative dielectric constant ε and a very low dielectric loss (tan δ). Dielectric charging of antennas, filters, and other devices is particularly important to avoid proximity region detuning (referred to as “body loading”) by the user's body. This requires a dielectric having a high dielectric constant ε ≧ 15 in the high frequency region and a low dielectric loss (tan δ) not higher than 10 ⁻² , preferably lower than this. Furthermore, the temperature dependence of the resonance frequency τ _f should be very small. Finally, such materials should be able to be processed in a very simple and inexpensive way in order to allow approximate molding (near net shape) at low cost.

A number of ceramic materials that are processed in the sintering process are well known in the prior art. Such materials include Mirsaneh et al., “Circularly Polarized Dielectric-Loaded Antennas—Circularly Loaded Dielectric Antennas, for use in the case of antennas dielectrically charged for the gigahertz range. : Current Technology and Future Challenges), Adv. Funct. Materials 18, (2008), BiNbO ₄ system disclosed in pages 1-8. This material is used to manufacture the two most widely used antennas, circularly polarized DLA helical antennas (D-LQH antennas) and rectangular patch antennas. For this purpose, a glass having a composition of 30 mol% Bi ₂ O ₃ , 30 mol% Nb ₂ O ₅ , 30 mol% B ₂ O ₃ and 10 mol% SiO ₂ is converted into a conventional glass. And melt at 1250 ° C. for 2 hours.

The glass was poured into a cylindrical mold, depressurized at 500 ° C. to 520 ° C., and slowly cooled to room temperature. Thereafter, crystallization was performed at various temperatures ranging from 600 ° C to 1000 ° C. In the case of heat treatment at 960 ° C., the optimum values for antenna use are said to be a relative dielectric constant ε of 15, a quality factor Q · f ₀ of 15000 GHz, and a temperature coefficient of resonance frequency τ _f of −80 MK ^−1. Yes. The crystal phase determined here was essentially orthorhombic BiNbO ₄ .

This system using bismuth and niobium is very expensive in terms of raw materials.
In addition, there are a variety of sintered ceramic materials (see US Pat. No. 6,184,845, US 2007/063902). In these references, as a dielectric material for a ceramic core of a dielectric-charged D-LQH antenna, a sintered ceramic material mainly composed of zirconium titanate or zirconium tin titanate having a relative dielectric constant of about 36 is disclosed. Yes. This material is said to be produced by extrusion or press molding, followed by sintering.

  Another sintered material is M.I. T.A. Sebastian et al., "Low loss dielectric materials for LTCC applications", International Materials Reviews, 53, 2008, pages 57-90. Some of these materials are said to be “glass ceramic”. These are sintered materials because they are produced by sintering a mixture of glass powder and crystalline powder.

US Pat. No. 6,184,845 US Patent Application Publication No. 2007/063902

Mirsaneh et al., “Circularly Loaded Dielectric-Loaded Antennas: Current Technology and Future Challenges”, Adv. Funct. Materials 18, (2008), p. 1-8 M.M. T.A. Sebastian et al., “Low loss selective materials for LTCC applications”, International Materials Reviews, Vol. 53, 2008, p. 57-90

Dielectrics produced by sintering have a number of disadvantages. That is, every sintering process always involves a certain shrinkage, which leads to inaccurate dimensional accuracy and corresponding final machining. Furthermore, all sintering processes result in a certain residual porosity, which is disadvantageous when metallizing the surface. Metal penetrates into the voids and increases the dielectric loss of the dielectric.
In addition, the production of sintered materials is basically relatively complex and expensive.

  In view of the above, it is an object of the present invention to provide an improved material that can be used as a dielectric for high frequency applications and has a high dielectric constant and low dielectric loss. Furthermore, the material should be able to be manufactured and processed in a very simple and inexpensive way.

This object is achieved by a glass ceramic having at least the following components (units are mol% on oxide basis):
SiO ₂ 5~50
Al ₂ O ₃ 0-20
B ₂ O ₃ 0~25
BaO 0-25
TiO ₂ 10~60
RE ₂ O ₃ 5~35
In the above composition, Ba can be partially substituted, preferably 10% up to Sr, Ca, Mg, RE can be lanthanum, another lanthanide, or yttrium, Ti can be partly, preferably up to 10% Further, Zr, Hf, Y, Nb, V, and Ta can be substituted.

The object of the invention is completely solved in this way.
It has been discovered that a homogeneous glass that can be subsequently converted to a homogeneous glass-ceramic with a high dielectric constant, low dielectric loss, and low temperature dependence of the resonant frequency, can be melted using such a glass composition by ceramicization treatment. ing. The material can be produced as a glass ceramic in a simple and inexpensive way, allowing approximate forming by melt technology processes, in particular casting or optionally pressing.

For the purposes of the present application, the term “glass ceramic” refers to a portion where a large amount of crystallites is essentially homogeneously distributed in the residual glass phase starting from a homogeneous glass produced by melting and with a specific heat treatment. A material converted into a crystal.
In an advantageous embodiment of the invention, the glass-ceramic has the following components (in mol% on oxide basis):
SiO ₂ 10~40
Al ₂ O ₃ 0-10
B ₂ O ₃ 5~25
BaO 0-20
TiO ₂ 15-50
RE ₂ O ₃ 10-30
In the above composition, Ba can be partially substituted with Sr, Ca, Mg, preferably up to 10%, RE is lanthanide or yttrium, Ti is partially, preferably up to 10%, Zr, Hf , Y, Nb, V, Ta can be substituted.

Furthermore, the glass ceramic can contain a refining agent in a customary amount, preferably 0.01 mol% to 3 mol%, and the refining agent is preferably selected from the group consisting of Sb ₂ O ₃ and As ₂ O _3. The
The glass ceramic of the present invention preferably has a dielectric loss (tan δ) of 10 ⁻² or less, preferably 10 ⁻³ or less, in a high frequency application (f> 200 MHz).

Furthermore, the glass ceramic preferably has a relative dielectric constant ε of at least 15, preferably> 18, preferably 20 to 80.
The glass ceramic of the present invention preferably has a temperature dependency t _f of the resonance frequency of 200 ppm / K or less, preferably 50 ppm / K or less, particularly preferably 10 ppm / K or less.

  In another advantageous embodiment of the invention, the glass-ceramic of the invention has at least one mixed crystal phase based on RE, Ti, Si, O and optionally Ba, Ba can be at least partially substituted with Sr, Ca, Mg, RE can be lanthanide or yttrium, and Ti can be substituted at least partially with Zr, Hf, Y, Nb, V, Ta.

In particular, the glass ceramic of the present invention has at least one mixed crystal phase selected from the group consisting of Ba, RE, TiO, RE ₂ Ti ₂ O ₇ , RE ₂ Ti ₂ SiO ₉ , and RE ₄ Ti ₉ O _24. In the above composition, RE is lanthanum, another lanthanide or yttrium, up to 10% of Ba can be replaced with Sr, Ca, Mg, and up to 10% of Ti can be Zr, Hf, Y, Nb, V and Ta can be substituted.

The glass ceramic of the present invention can preferably have a proportion of crystalline material of at least 30% by volume, preferably up to 95% by volume.
The average crystallite size is preferably 10 nm to 50 μm, preferably 100 nm to 1 μm.
The glass ceramic of the present invention is particularly suitable as a dielectric for a dielectric resonator, an electronic frequency filter element, or an antenna element in a high frequency region (f> 200 MHz).

It is particularly useful for use as a dielectric for cylindrical antenna elements or patch antenna elements.
The dielectric according to the present invention having a dielectric loss of 10 ⁻² or less in the high frequency region can be manufactured by the following steps.
-Melting and homogenizing the starting glass containing the following components (in mol% on oxide basis):
SiO ₂ 5~50
Al ₂ O ₃ 0-20
B ₂ O ₃ 0~25
BaO 0-25
TiO ₂ 10~60
RE ₂ O ₃ 5~35
In the above composition, Ba may be partially substituted with Sr, Ca, Mg, preferably up to 10%, RE may be lanthanide or yttrium, Ti may be partially substituted, preferably up to 10%, Zr , Hf, Y, Nb, V, Ta can be substituted.
-Pouring the starting glass into the desired mold.
-Cooling the starting glass to room temperature;
-Ceramicizing the starting glass by heat treatment.

In a preferred embodiment of the present invention, the starting glass comprises at least the following components (in mole percent based on oxide):
SiO ₂ 10~40
Al ₂ O ₃ 0-10
B ₂ O ₃ 5~25
BaO 0-20
TiO ₂ 15-50
RE ₂ O ₃ 10-30
In the above composition, Ba may be partially substituted with Sr, Ca, Mg, preferably up to 10%, RE may be lanthanide or yttrium, Ti may be partially substituted, preferably up to 10%, Zr , Hf, Y, Nb, V, Ta can be substituted.

The starting glass is preferably approximate shaped by a hot forming process, in particular by casting, tube drawing, rod drawing or extrusion.
Other features and advantages of the present invention will become apparent from the following description of preferred embodiments with reference to the drawings.

The result of an X-ray diffraction analysis is shown.

Table 1 shows the various glass compositions of the starting glass of the Ba-La-Ti-Si-O system.
The various glass samples of Examples 1 to 9 are first melted and homogenized in the usual manner using conventional starting materials. Here, platinum crucibles, Pt / Ir crucibles, Pt / Rh crucibles, fused quartz crucibles or aluminum oxide crucibles can be used. The sample is first melted at 1350 ° C. for 2 hours, then purified (purified) at 1400 ° C. for 30 minutes, stirred with a platinum stirrer for 20 minutes, homogenized and allowed to stand for 10 minutes, for example, steel, graphite, Pour into a suitable mold made of aluminum oxide or fused quartz and approximate mold.

After the glass is cooled to room temperature, it is subjected to a ceramization step, which can be done, for example, by an infrared heating process or a conventional process.
A typical ceramization cycle with an infrared heating furnace is as follows.
Heat to 1050 ° C. at 300 K / min.
-Hold at 1050 ° C for 7 seconds.
-Heat to 1200 ° C at a heating rate of 50K / min.
-Hold at 1200 ° C for 15 minutes.
-Turn off the furnace and cool to about 500 ° C at a cooling rate of about 50 K / min.
When the temperature reaches about 500 ° C., remove the sample from the furnace.

Ceramming in a conventional heating furnace is performed by heat treatment at 925 ° C. for 15 hours.
If necessary, after casting, the molding can be precision ground or polished, or in the case of the production of a cylindrical molding, it can be machined by coreless grinding of the cylindrical surface.
FIG. 1 shows an X-ray diffraction analysis of Sample 9 after ceramization. A prominent crystal phase is La ₂ Ti ₂ SiO ₉ . In addition, a small proportion of rutile TiO ₂ was found.

The volume fraction of the crystalline phase of this sample is about 50% to 70% by volume.
The relative dielectric constant ε of Sample 1 to Sample 9 was measured. These were all greater than 15 and in the range of 20-50.
These samples also show low dielectric loss and high quality.
The quality Q value is the reciprocal of dielectric loss (tan δ).
Q = 1 / tan (δ)
Quality is measured by the Hack-Coleman resonance method. Here, the quality factor is determined as the product of the quality Q value and the measured frequency f _0.

The quality factors Q · f ₀ of all samples 1 to 9 were in the range of 2000 GHz to 3000 GHz. In the case of Sample 1, the relative dielectric constant ε22.4 and the quality Q value 205, that is, the quality factor 2068 were measured at 10.09 GHz.
The temperature coefficient t _f of the resonant frequency is very low for all measured samples and is in the range of −40 ppm / K <t _f <40 ppm / K.

  When used as a dielectric for antennas, particularly those suitable for mobile GPS antennas in mobile phones, the frequency range is over 200 MHz, especially in the range of about 800 MHz to 70 GHz. The dielectric charging of the antenna reduces the antenna's sensitivity to user detuning.

Claims (22)

Containing at least the following components in mole percent on an oxide basis;
SiO ₂ 10~40
Al ₂ O ₃ 0-10
B ₂ O ₃ 5~25
BaO 0-20
TiO ₂ 15-50
RE ₂ O ₃ 10-30
Here, Ba can be partially substituted with Sr, Ca, Mg, RE is lanthanum, another lanthanide or yttrium, and Ti can be partially substituted with Zr, Hf , Nb , V, Ta , Glass ceramic. The glass ceramic according to claim 1, wherein Ba can be substituted with Sr up to 10% and Ti can be substituted with Zr, Hf , Nb , V, Ta up to 10%. Glass ceramic according to claim 1 or 2, comprising 0.01 mol% to 3 mol% of at least one fining agent. The glass ceramic according to claim 3 , wherein the fining agent is selected from the group consisting of Sb ₂ O ₃ and As ₂ O ₃ . In the high frequency region of the frequency f> 200MHz, ^{10 -2} and having less dielectric loss of the (tan [delta), glass-ceramic according to any one of claims 1 to 4. In the high frequency region of the frequency f> 200MHz, ^{10 -3} and having less dielectric loss of the (tan [delta), glass-ceramic according to any one of claims 1 to 5. Characterized in that it has at least 15 dielectric constant of epsilon, glass-ceramic according to any one of claims 1 to 6. The glass ceramic according to any one of claims 1 to 7 , characterized by having a relative dielectric constant ε in the range of 20 to 80. The glass ceramic according to any one of claims 1 to 8 , wherein the absolute value | τ _f | of the temperature dependence of the resonance frequency is 200 ppm / K or less. Absolute value of the temperature dependence of the resonant frequency | tau _{f |,} characterized in that it is 50 ppm / K or less, the glass ceramic according to any one of claims 1 to 9. Absolute value of the temperature dependence of the resonant frequency | tau _{f |,} characterized in that it is 10 ppm / K or less, the glass ceramic according to any one of claims 1 to 10. Contains at least one mixed crystal phase based on RE, Ti, Si, O, and optionally Ba, wherein Ba can be at least partially substituted with Sr, Ca, Mg, and RE can be lanthanide or yttrium, Ti is at least partially Zr, Hf, Nb, V, and wherein can be substituted with Ta, glass-ceramic according to any one of claims 1 to 11. Including at least one mixed crystal phase selected from the group consisting of BaRETiO, RE ₂ Ti ₂ O ₇ , RE ₂ Ti ₂ SiO ₉ , and RE ₄ Ti ₉ O ₂₄ , wherein RE is lanthanum, another lanthanide or yttrium, can replace up to 10% of Ba Sr, Ca, with Mg, any of up to 10% of Ti Zr, Hf, Nb, V, and wherein can be substituted with Ta, of claims 1 to 12 The glass ceramic according to claim 1. Wherein the volume ratio of the crystal material with respect to the entire glass ceramic is at least 30% by volume, the glass ceramic according to any one of claims 1 to 13. The volume ratio of crystalline material to the entire glass ceramic is characterized in that up to 95% by volume, the glass ceramic according to any one of claims 1 to 14.   The glass ceramic according to claim 14 or 15, wherein the volume ratio of the crystal material is obtained by X-ray diffraction analysis.   The glass ceramic according to any one of claims 1 to 16, wherein the glass ceramic has an average crystallite size of 10 nm to 50 µm.   Glass ceramic according to any one of the preceding claims, characterized in that it has an average crystallite size of 100 nm to 1 µm.   Use of the glass ceramic according to any one of claims 1 to 18, wherein the glass ceramic is used as a dielectric resonator for a high frequency region, an electronic frequency filter element, or a dielectric for an antenna element.   20. Use according to claim 19, as a dielectric for cylindrical or patch antenna elements. A method of manufacturing a dielectric having a dielectric loss of 10 ⁻² or less in a high-frequency region,
Melting and homogenizing a starting glass containing the following constituents in mole percent on an oxide basis:
SiO ₂ 10~40
Al ₂ O ₃ 0-10
B ₂ O ₃ 5~25
BaO 0-20
TiO ₂ 15-50
RE ₂ O ₃ 10-30
Here, Ba can be partially substituted with Sr, Ca, Mg, RE can be lanthanum, another lanthanide, or yttrium, Ti can be partially substituted with Zr, Hf , Nb , V, Ta,
Injecting the starting glass into a desired mold;
Cooling the starting glass to room temperature;
Cerazing the starting glass by heat treatment. The method according to claim 21 , characterized in that the starting glass is approximately shaped by a melting technique process.

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