WO1998003446A1

WO1998003446A1 - Microwave dielectric ceramics based on silver, niobium and tantalum oxides

Info

Publication number: WO1998003446A1
Application number: PCT/SI1997/000022
Authority: WO
Inventors: Matjaz^¿ VALANT; Danilo Suvorov
Original assignee: Ins^?titut Joz^?ef Stefan; Institut Jozef Stefan
Current assignee: Ins^?titut Joz^?ef Stefan; Institut Jozef Stefan
Priority date: 1996-07-19
Filing date: 1997-07-11
Publication date: 1998-01-29
Anticipated expiration: 1999-01-19
Also published as: SI9600232A

Abstract

Microwave dielectric ceramic based on silver, niobium and tantalum oxides with additives (V2O5, Li2O, WO3, Mn2O3 and Bi2O3), characterized in that the contents in mole fractions are as follows: x(Ag2O) = 45-55 mol %, x(Nb2O5) = 22-28 mol %, x(Ta2O5) = 22-28 mol %, x(V2O5) = 0-10 mol %, x(Li2O) = 0-10 mol %, x(WO3) = 0-10 mol %, x(Mn2O3) = 0-10 mol% , and x(Bi2O3) = 0-10 mol %, is manufactured according to the classic method for the manufacturing of ceramic material. The starting materials, i.e. silver oxide (Ag2O), niobium oxide (Nb2O5), tantalum oxide (Ta2O5) and eventual additives are mixed in the proper ratio and calcined for 1-10 hours at a temperature of 1000 °C to 1150 °C. Thereafter, the calcined powder is formed by using known methods, into products, which are then sintered for 5-10 hours at a temperature of 1150 °C - 1250 °C in O2 atmosphere. The permittivity ranges between 250 and 380, and at the same time it is possible to adjust τf in the required range with a precision of +/- 1 ppm/K exclusively by changing the oxide contents. The dielectric losses in the ceramics, being the object of this invention, are low regarding the extraordinarily high permittivity. The quality factor at a working frequency of 1 GHz is 500-700, and at a working frequency of 0.5 GHz 1000-1400.

Description

MICROWAVE DIELECTRIC CERAMICS BASED ON SILVER, NIOBIUM AND TANTALUM OXIDES

OBJECT OF THE INVENTION

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

According to the international patent classification, the invention is ranged into the class H01 P-07/10 and additionally in C04B 35/40.

BACKGROUND OF THE INVENTION

Microwave ceramic materials in the electronic industry are used as dielectric resonators, microwave filters, substrates for microelectronic circuits, etc. Further, this components are built into wireless telecommunication equipment, satellite antennas, radar systems, microwave ovens, etc.

In addition to the appropriate permittivity (k'), depending on the application manner and on the working frequency range, the material must also have the required temperature stability of the resonant frequency (τ,) and a quality factor (Q x f) as high as possible. The quality factor represents the fraction of energy losses in the material at the resonant frequency. The higher it is, the lower is the loss fraction, and at the same time the microwave component is more selective.

According to their permittivity the available microwave materials can be classified into three classes, as described by K. Wakino, T. Nishikawa Y. Ishikava, N. Tamura, Br. Ceram. Trans. J., 89 (2), 1990, pp.39-43. In the permittivity class K=80-90 mostly materials based on BaO, TiO₂ and on rare earth element are to be found, as described by K.Wakino, T. Minai, H. Tamura, J. Am. Ceram. Soc., 67, pp. 278-281. Quality factors (Q x f) achieved by this materials are about 5000. The next class comprises the dielectric range from 30 to 40. The most frequently used material in this range is (Zr,Sn)TiO₄, as described by G. , Y. Ishikawa, N. Tamura, Br. Ceram. Trans. J., 89 (2), 1990, Wolfram, E. Gobel, Mater. Res. Bull., 16, (11 ), 1981 , pp. 1455-1463. In this range the quality factors of the materials with higher dielectric constants are about 40000 and with lower one up to 100000. In the class comprising materials with permittivity below 30, quality factors over 200000 can be achieved as described by H. Tamura, Y. Sakabe, K. Wakino, J.Am.Ceram.Soc, 67, 1984, C-59-61.

Among commercially available microwave materials, the materials made from barium, titanium and neodymium oxides have the highest permittivity. Addition of e.g. Pb or Bi oxides or titanates respectively is used to regulate the temperature coefficient of the resonant frequency (τ_f), while ultimately the τ_r is adjusted by partially replacing the rare earths. The permittivity of such a commercial microwave ceramics is 85-90 and the quality factor about 5000 (patents: J62183608-A, J02239150-A, J01234358-A. J57080604-A).

Due to the growing tendency towards miniaturization, particularly in the frequency range up to 1 GHz, the need for a material having higher dielectric constant became evident. Such a material will enable the manufacturing of ceramic electronic components of smaller dimensions, beeing more suitable for modern microwave circuits. The task and the aim of the invention is to produce a microwave ceramics having permittivity above 250, a quality factor higher than 500 at a working frequency (0.1 - 1.5

GHz) and a temperature coefficient of the resonant frequency τ_f which can be controlled in the interval between -50 and +50 ppnrvK with a precision of 1 ppm/K. In accordance with the invention the task is solved by a microwave dielectric ceramics based on silver, niobium and tantalum oxides, wherein said oxides are present in mole fractions as follows: x(Ag₂0) = 45 - 55 mol% x(Nb₂O₅) = 22 - 28 mol% x(Ta₂O₅) = 22 - 28 mol%

Microwave dielectric ceramics based on silver, niobium and tantalum oxides, as the object of the invention, can contain additives in mole fractions as follows: x(V₂O₅ ) = 0 - 10 mol%, x(Li₂O) = 0 - 10 mol%, x(WO₃) = 0 - 10 mol%, x(Mn₂O₃) = 0 - 10 mol% and x(Bi₂O₃) = 0 - 10 mol%.

By investigation of microwave materials based on silver, niobium and tantalum we established that ceramics composed of x(Ag₂O) = 45-55mol%, x(Nb₂O₅) = 22-28mol% and x(Ta₂O₅)=22-28mol% has a permittivity from 250 to 380, having the possibility to adjust τ, in the required range with the precision of +/-1 ppm K exclusively by changing the oxide contents. Dielectric losses in the ceramics of the invention are low regarding to the very high permittivity. The quality factor at a working frequency of 1 GHz is 500-700, and 1000 - 1400 at a working frequency of 0.5 GHz. Additions ( V₂O₅, Li₂O, WO₃, Mn₂O₃, Bi₂O₃) to the ceramics increase the quality factor and decrease the sintering temperature respectively. The starting materials, i.e. silver oxide (Ag₂O), niobium oxide (Nb₂O_s), tantalum oxide (Ta- s) and eventual additives were mixed in the proper ratio. 30-40wt.% of ethanol were added to the base oxide mixture and the mixture was homogenized. After homogenization the suspension was dried for 0.5 to 1 hour at 90°C - 100°C, thereafter the powder was pressed into discs, which underwent calcination for 1 - 10 hours at a temperature of 1000°C to 1150°C. Thereafter the calcined powder was milled in a ZrO₂ mill with ZrO₂ milling bodies to a particle size of 1 - 2 μm, then it was dried and formed by using known procedures into products, which were sintered for 5-10 hours at a temperature of 1150°C to 1250°C in oxygen atmosphere. The sintered ceramics was mono-phase, the grain size was about 5μm and the porosity fraction did not exceed 3%.

EXAMPLES OF EMBODIMENTS

Example of embodiment 1 :

A mixture of silver, niobium and tantalum oxides having a composition of x(Ag₂O) = 50.0 mol%, x(Nb₂O₅) = 26 mol% and x(Ta₂O₅) = 24 mol% (hereinafter composition E1 ) was calcined for 10 hours at a temperature of 1050°C. After milling the calcinate was pressed into discs, which were sintered for 10 hours at a temperature of 1200°C in oxygen atmosphere. The permittivity of such ceramics was 375, τ_f was -70 ppm/K. The quality factor measured at 1 GHz was 500, and 1000 when measured at 0.5 GHz.

Example of embodiment 2:

A mixture of silver, niobium and tantalum oxides having a composition of x/Ag₂O) = 50.0 mol%, x(Nb₂O₅) = 25.4 mol% and (Ta₂O₅) = 24.6 mol% (hereinafter composition E2) was calcined for 10 hours at a temperature of 1050°C. After milling the calcinate was pressed into discs, which were sintered for 10 hours at a temperature of 1200°C in oxygen atmosphere. The permittivity of such a ceramics was 378, τ_f was 0 +/-1 ppm/K. The quality factor measured at 1 GHz was 500, and 1000 when measured at 0.5 GHz. Example of embodiment 3:

A mixture of silver, niobium and tantalum oxides having a composition of x(Ag₂O) = 50.0 mol%, x(Nb₂O₅) = 24 mol% and x(Ta₂O₅) = 26 mol% (hereinafter composition E3) was calcined 10 hours at a temperature of 1050^OoC. After milling the calcinate was pressed into discs, which were sintered for 10 hours at a temperature of 1200°C in oxygen atmosphere.

The permittivity of such a ceramics was 377, and X. was 80 ppm K. The quality factor measured at 1 GHz was 500, and 1000 when measured at 0.5 GHz.

Example of embodiment 4:

A mixture of silver, niobium and tantalum oxides having a composition of x(Ag₂O) = 50.0 mol%, x(Nb₂O₅) = 23.0 mol%, x(Ta₂O₅) = 24.0 mol% and x(V₂O₅) = 6.0 mol% (hereinafter composition E4) was calcined for 10 hours at a temperature of 1000°C. After milling the calcinate was pressed into discs, which were sintered for 10 hours at a temperature of

1200°C in oxygen atmosphere. The permittivity of such a ceramics was 250, τ, is 0+/-1 ppm K. The quality factor measured at 1 GHz was 700, and 1400 when measured at 0.5 GHz.

The microwave ceramic elements, as the object of this invention, are set apart from comparative elements (EO) particularly by their extraordinarily high dielectric constant, that makes possible the miniaturization of the microwave joints. Further, the ceramics are set apart by an entirely adaptable temperature coefficient of the resonant frequency and by an adequate quality factor. An additional advantage of the said composition is that it does not contain toxic additives like e.g. PbO, making its production ecologically acceptable. Table 1 : Microwave properties of the ceramics from examples of embodiment

composition k' QlGH^** Qθ.5GHz τ, (ppm/K) E1 375 >500/1000 -70 E2 378 >500/1000 0 E3 377 >500/1000 80 E4 250 >700/1400 0

BaO-PbO-Nd₂O₃-TiO₂*-EO 88 5000/— 0

♦...literature citation: K. Vakino, T. Minai, H. Tamura, J. Am. Ceram. Soc, 67, pp. 278-281

Claims

CLAIM

Microwave dielectric ceramics based on silver, niobium, and tantalum oxides with additives

(V₂O_5? Li₂O, WO₃, Mn₂O₃ and Bi₂O₃), produced according to standard methods for manufacturing of microwave ceramic dielectrics, characterized by compositions in mole fractions as follows: x(Ag₂O)= 45-55 mol% x(Nb₂O₅)= 22-28 mol% x(Ta₂O_s)= 22-28 mol% x(V₂O₅)= 0-10 mol% x(Li₂O)= 0-10 mol% x(WO₃)= 0-10 mol% x(Mn₂O₃)= 0-10 mol% and x(Bi₂O₃)= 0-10 mol%.