SI9600232A - Microwave dielectric ceramics based upon oxides of silver, nobium and tantalum - Google Patents

Abstract

A microwave dielectric ceramics based upon oxides of silver, niobium and tantalum with additives (V2O5, Li2O, WO3, Mn2O3 and Bi2O3) designated by their compositions in the following molar shares: x(Ag2O) = 45-55 mole %, x(Nb2O5) = 22-28 mole %, x(Ta2O5) = 22-28 mole %, x(V2O5) = 0-10 mole %, x(LiO2) = 0-10 mole %, x(WO3) = 0-10 mole %, x(Mn2O3) = 0-10 mole % and x(Bi2O3) = 0-10 mole % is manufactured according to the classical procedure of preparation of ceramic materials. The starting raw materials for the preparation of microwave ceramics, i.e. oxides of silver (Ag2O), niobium (Nb2O5), tantalum (Ta2O5) and eventual additives are mixed in a proper ratio and calcined for 1-10 hours at the temperature of 1000 degrees Celsius up to 1150 degrees Celsius. The calcined powder is then shaped according to the known procedures to products which are sintered for 5-10 hours at the temperature of 1150-1250 degrees Celsius in an oxygen atmosphere. Dielectricity amounts is between 250 and 380, while the coefficient of resonance frequency tauf can be adjusted within the required range to the precision of plus-minus 1 ppm/K exclusively by changing the content of oxides only. Dielectrical losses within the ceramic which is the subject of invention are low notwithstanding its very high dielectricity. The quality factor at the working frequency of 1 GHz amounts to 500-700, and at the one of 0,5 GHz to 1000-1400.

Description

Applicant:

Jozef Stefan Jamova Institute 39, Ljubljana

Inventors:

dr. Matjaž Valant dr. Danilo Suvorov

Microwave dielectric ceramics based on oxides of silver, niobe and tantalum

SUBJECT MATTER OF THE INVENTION

The object of the invention is microwave ceramics based on oxides of silver, niobe and tantalum. The invention belongs to the field of chemistry and relates to a new type of microwave dielectric ceramics.

According to the international patent classification, it is classified in class H01P-07/10 and additionally in C04B 35/40.

BACKGROUND OF THE INVENTION

Microwave ceramic materials in the electronics industry are used as dielectric resonators, microwave filters, substrates for microwave circuits, etc. These components are further integrated into wireless telecommunications equipment, satellite dishes, radar systems, microwave ovens, etc.

In addition to suitable dielectricity (k ¹ ), which depends on the mode of use and the operating frequency range, the material must also have the required temperature stability of the resonant frequency (r _f ) and the highest quality factor (Q xf). The quality factor describes the fraction of energy losses in a material at a resonant frequency. The higher it is, the smaller the loss ratio, while making the microwave component more selective.

-2The attainable microwave materials can be divided into three classes according to their dielectricity, as described in K. Vakino, T. Nishikawa, Y. Ishikawa, N. Tamura, Br. Ceram. Trans. J., 89, (2), 1990, pp. 39-43. In the dielectricity class K = 80-90, mainly materials based on BaO, TiO ₂ and oxides of rare earth elements are found, as described in K. Vakino, T. Minai, H. Tamura, J. Am Ceram. Soc., 67, pp. 278-281. The quality factors (Q xf) achieved by these materials are about 5000. The next class covers the dielectricity range from 30 to 40. The most commonly used material in this field is (Zr, Sn) TiO ₄ , as described in G. Wolfram, E. Gobel, Mater. Really. Buli., 16, (11), 1981, p. 1455-1463. In this field, the quality factors of materials with higher dielectric constants are about 40,000 and with lower ones up to 100,000. In the class covering materials with dielectrics below 30, quality factors above 200,000 are achieved, as described in H. Tamura, Y Sakabe, K. Vakino J. Am. Ceram. Soc., 67,1984, C-5961.

Among commercially available microwave materials, the highest dielectricity is made of barium, titanium and neodymium oxides. To regulate the temperature coefficient of the resonant frequency (x _f ), additives such as Pb or Bi oxide, respectively, are used. titanate, and finally r _{f is} balanced by the partial replacement of rare earths. Such commercial microwave ceramics have a dielectricity of 85-90 and a quality factor of about 5000 (patents: J62183608-A, J02239150-A, J01234358-A, J57080604-A).

Due to the increasing tendency for miniaturization, especially in the frequency range up to 1 GHz, there is a need for a material with a higher dielectric constant. Such material will make it possible to produce smaller-sized electronic ceramic components that are more suitable for modern microwave circuits.

The object and object of the invention is to make microwave ceramics with a dielectricity above 250, a quality factor higher than 500 at an operating frequency (0.1 - 1.5GHz) and a temperature coefficient of resonant frequency r _f that will be possible in the interval between -50 and +50 ppm / K control to 1 ppm / K accurately. According to the invention, the problem is solved by microwave dielectric ceramics based on oxides of silver, niobe and tantalum, and these are represented in the following molar proportions:

x (Ag ₂ O) = 45-55 mol%, x (Nb ₂ O ₅ ) = 22-28 mol% and x (Ta ₂ O ₅ ) = 22-28 mol%.

The microwave dielectric ceramics based on the oxides of silver, niobe and tantalum of the invention may further comprise additives in the following mole ratios: x (V ₂ O ₅ ) = 0 -10 mol%, x (Li ₂ O) = 0- 10 mol%, x (W0 ₃ ) = 0 -10 mol%, x (Mn ₂ O ₃ ) = 0-10 mol% and x (Bi ₂ O ₃ ) = 0-10 mol%.

In the research of microwave materials based on silver, niobe and tannal, we found that ceramics with the composition x (Ag ₂ O) = 45 - 55 mol%, x (Nb ₂ O5) = 22-28 mol% and x (Ta ₂ O ₅ ) = 22-28 mol% dielectricity from 250-380, while η can be adjusted in the required range to ± 1 ppm / K with precision exclusively by varying the oxide content. The dielectric losses in the ceramics of the invention are, in view of the very high dielectricity, low. The quality factor at the operating frequency 1GHz is 500-700 and at the operating frequency 0.5GHz it is 1000-1400. Additives (V ₂ O ₅ , Li ₂ O, WO ₃ , Mn ₂ O ₃ , Bi ₂ O ₃ ) ceramics increase the quality factor or decrease the sintering temperature. The microwave dielectric properties for individual compositions are given in the embodiments and the end table.

The feedstocks, ie silver oxide (Ag ₂ O), niobe (Nb ₂ O ₅ ), tantalum (Ta ₂ O ₅ ) and any additives are mixed in an appropriate proportion. Ethanol was added to the mixture of basic oxides by weight of 30-40% and the mixture was homogenized. After homogenization, the suspension is dried by drying for 0.5 to 1 hour at 90 ° C to 100 ° C, and the powder is compressed into coils, which are calcined for 1-10 hours at 1000 ° C to 1150 ° C. The calcined powder is then ground in a ZrO ₂ mill with ZrO ₂ milling bodies up to a particle size of 1-2 // m, dried and molded by known methods into products, which are then sintered for 5-10 hours at 1150-1250 ° C in O ₂ atmospheres. Sintered ceramics are single-phase, the grain size is approximately 5gm and the porosity content does not exceed 3%.

IMPLEMENTING EXAMPLES:

Example 1:

A mixture of oxides of silver, niobe and tantalum with the composition x (Ag ₂ 0) = 50.0 mol%, x (Nb ₂ O ₅ ) = 26 mol% and x (Ta ₂ O ₅ ) = 24 mol% (composition E1) is calcined for 10 hours at temperature 1050 ° C. After grinding, the calcinate is compressed into coils which are sintered for 10 hours at a temperature of 1200 ° C in an oxygen atmosphere. Dielectricity

-4 such ceramics is 375, is -70 ppm / K. The quality factor, measured at 1 GHz, is 500, and measured at 0.5GHz is 1000.

Example 2:

A mixture of oxides of silver, niobe and tantalum with the composition x (Ag ₂ 0) = 50.0 mol%, x (Nb ₂ O ₅ ) = 25.4 mol% and x (Ta ₂ O ₅ ) = 24.6 mol% (composition E2) is calcined for 10 hours at 1050 ° C. After grinding, the calcinate is compressed into coils which are sintered for 10 hours at a temperature of 1200 ° C in an oxygen atmosphere. The dielectricity of such ceramics is 378, 0 ± 1 ppm / K. The quality factor, measured at 1 GHz, is 500, and measured at 0.5GHz is 1000.

Example 3:

A mixture of oxides of silver, niobe and tantalum with the composition x (Ag ₂ 0) = 50.0 mol%, x (Nb ₂ O ₅ ) = 24 mol% and x (Ta ₂ O ₅ ) = 26 mol% (composition E3) calcined for 10 hours at temperature 1050 ° C. After grinding, the calcinate is compressed into coils which are sintered for 10 hours at a temperature of 1200 ° C in an oxygen atmosphere. The dielectricity of such ceramics is 377, r _f is 80 ppm / K. The quality factor, measured at 1 GHz, is 500, and measured at 0.5GHz is 1000.

Example 4:

A mixture of oxides of silver, niobe and tantalum with the composition x (Ag ₂ 0) = 50.0 mol%, x (Nb ₂ O ₅ ) = 23.0 mol% x (Ta ₂ O5) = 24.0 mol% and x (V ₂ O ₅ ) = 6.0 mol% (composition E4) was calcined for 10 hours at 1000 ° C. After grinding, the calcinate is compressed into coils which are sintered for 10 hours at a temperature of 1200 ° C in an oxygen atmosphere. The dielectricity of such ceramics is 250, r _f is 0 ± 1 ppm / K. The quality factor, measured at 1 GHz, is 700, and measured at 0.5GHz is 1400.

The microwave ceramic elements of the invention are distinguished by their extremely high dielectric constant according to the Comparison Elements (EO), which enables the miniaturization of microwave assemblies. Ceramics are further distinguished by a fully adjustable resonance frequency coefficient and a suitable quality factor. An additional advantage of the described composition is that it does not contain toxic additives such as PbO, which means that production is environmentally friendly.

-5Table 1: Microwave properties of ceramics from embodiments

composition k ' QlGHz / Qo.5GHz Tf (ppm / K) El 375 > 500/1000 -70 E2 378 > 500/1000 0 E3 377 > 500/1000 80 E4 250 > 700/1400 0 BaO-PbO-Nd ₂ O ₃ -TiO ₂ * -E0 88 5000 / - 0

* ... lit. citation: K. Wakino, T. Minai, H. Tamura, J. Am. Ceram. Soc., 67, p. 278-281

G \

Mr

Claims (1)

PATENT APPLICATION: Microwave dielectric ceramics based on oxides of silver, niobe and tantalum, with additions (V ₂ O ₅ , Li ₂ O, WO ₃ , Mn ₂ O ₃ and Bi ₂ O ₃ ), manufactured by standard methods for the production of microwave ceramic dielectrics, characterized in that the compositions are in the following mole ratios: x (Ag ₂ O) = 45-55 mol%, x (Nb ₂ O ₅ ) = 22-28 mol%, x (Ta ₂ O ₅ ) = 22-28 mol%, x (V ₂ O ₅ ) = 0 -10 mol%, x (Li ₂ O) = 0-10 mol%, x (WO ₃ ) = 0 -10 mol%, x (Mn ₂ O ₃ ) = 0-10 mol% and x (Bi ₂ 0 ₃ ) = 0-10 mol%. j 'jjc · J ^V U -7 SUMMARY: Microwave dielectric ceramics based on oxides of silver, niobe and tantalum, with additions (V ₂ O ₅ , Li ₂ O, WO ₃ , Mn ₂ O ₃ and Bi ₂ O ₃ ), characterized in that the compositions are in the following mole ratios: x (Ag ₂ O) = 45-55 mol%, x (Nb ₂ O ₅ ) = 22-28 mol%, x (Ta ₂ O ₅ ) = 22-28 mol%, x (V ₂ O ₅ ) = 0 -10 mol%, x (Li ₂ O) = 0-10 mol%, x (W0 ₃ ) = 0-10 mol%, x (Mn ₂ O ₃ ) = 0-10 mol%, and x (Bi ₂ O ₃ ) = 0 10 mol% is produced according to the classical method of preparing ceramic materials. The starting materials for the preparation of microwave ceramics, ie silver oxide (Ag ₂ O), niobe (Nb ₂ O ₅ ), tantalum (Ta ₂ O ₅ ) and any additives, are mixed in an appropriate ratio and calcined for 1-10 hours at 1000 ° G. to 1150 ° C. The calcined powder is then formed by known methods into products, which are then sintered for 5-10 hours at a temperature of 1150-1250 ° C in an O ₂ atmosphere, and the dielectricity of 250-380 can be adjusted in the required range to ± 1 ppm / K precisely exclusively by varying the oxide content. The dielectric losses in the ceramics of the invention are, in view of the very high dielectricity, low. The quality factor at the operating frequency 1GHz is 500-700 and at the operating frequency 0.5GHz it is 1000-1400.