EP1373161A1 - Composition ceramique dielectrique hyperfrequence et procede de preparation de ladite composition - Google Patents

Composition ceramique dielectrique hyperfrequence et procede de preparation de ladite composition

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Publication number
EP1373161A1
EP1373161A1 EP01934303A EP01934303A EP1373161A1 EP 1373161 A1 EP1373161 A1 EP 1373161A1 EP 01934303 A EP01934303 A EP 01934303A EP 01934303 A EP01934303 A EP 01934303A EP 1373161 A1 EP1373161 A1 EP 1373161A1
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EP
European Patent Office
Prior art keywords
range
composition
formula
microwave dielectric
dielectric constant
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP01934303A
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German (de)
English (en)
Inventor
Naseemabeevi Jawahar Isuhak
Thomas Sebastian Mailadil
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Council of Scientific and Industrial Research CSIR
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Council of Scientific and Industrial Research CSIR
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Application filed by Council of Scientific and Industrial Research CSIR filed Critical Council of Scientific and Industrial Research CSIR
Priority claimed from PCT/IN2001/000077 external-priority patent/WO2002079115A1/fr
Publication of EP1373161A1 publication Critical patent/EP1373161A1/fr
Withdrawn legal-status Critical Current

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Definitions

  • Conventional ceramics for use in such applications include BaO-TiO 2 system, Ba(Mg!
  • Ba 5 Nb Oi5 type hexagonal perovskites have high dielectric constant and high Q factor.
  • the ceramics have hexagonal crystal structure.
  • C. Veneis, P. K. Davies, T. Negas and S. Bell (Mater. Res. Bull.
  • Yet another object of the present invention is to provide to tune the microwave dielectric properties of the above ceramics and hence to achieve temperature compensation by stacking dielectric resonators with positive and negative its.
  • Figure 1 shows the variation of ⁇ r and Tf with x.
  • Figure 2 shows the effective ⁇ r versus volume fraction of 5ZnO-2Nb 2 O5.
  • Figure 3 shows the effective Tf versus volume fraction of 5ZnO-2Nb 2 O5.
  • the dielectric constant is in the range
  • the ceramic composition is of the formula Ba 5 Ta 4 Oi5 and wherein the dielectric constant is 28 ⁇ 1, quality factor freq ency product greater than 32000 and temperature variation of resonant frequency 8 ⁇ 4 ppm °C.
  • the ceramic composition is of the, formula 5ZnO-2Nb 2 O 5 , and wherein the dielectric constant is 22 ⁇ 1, quality factor- frequency product greater than 88,000 and temperature variation of resonant frequency -73 ⁇ 5ppm/°C.
  • the ceramic composition is of the formula xZnO- (5-x)MgO- 2Nb 2 O 5 wherein 0 ⁇ x ⁇ 5.
  • the ceramic composition is of the formula xCaO - (5-x)ZnO - 2Nb 2 O 5 wherein 0 ⁇ x ⁇ l and wherein the dielectric constant is in the range 20+ 1 and 21 + 1, quality factor-frequency product is in the range 44,000 to 79,000 and temperature variation of resonant frequency is in the range -55 ⁇ 3 and -69 ⁇ 5 ppm °C.
  • the ceramic composition is of the formula 0.5CaO-4.5ZnO-2Nb 2 O5 wherein the dielectric constant is 21 ⁇ 1, quality factor-frequency product > 79,000 and temperature variation of resonant frequency is in the range -55 ⁇ 3 ppm °C.
  • the ceramic composition is of the formula A5B' x B" 4 .
  • the invention also relates to stacked resonators consisting of the above ceramics with opposite T f values to tune the T f to near to zero values.
  • the stacked resonators are between Ba5Nb O 15 and 5ZnO-2Nb 2 O5 ceramics wherein the volume fraction of 5ZnO-2Nb 2 O 5 is in the range 0.6 and 0J where the dielectric constant varies from 26 to 30 and Tf varies between 20 and -20 ppm/°C.
  • 0 ⁇ x ⁇ l when A' Ca and A' - Zn.
  • the microwave dielectric ceramic comprises MgsT ⁇ O ⁇ Mg 5 Ta O ⁇ 5 ; Sr J Ta O ⁇ 5 ; BajT ⁇ uOis; Mg 5 Nb 4 O ⁇ 5 ; Mg 5 Nb 4 O ⁇ 5 ; 5ZnO-2Nb 2 O 5 ; 5CaO-2Ta 2 O 5 and 5CaO-2Nb 2 O 5 .
  • temperature compensation is achieved by stacking the resonators with positive and negative temperature coefficients of resonant frequency by preparing the perovskites of the invention in the powder form, moulding of the powder in the suitable shape, drying, sintering and final treatment.
  • a 5 B Oi 5 ceramic in A 5 B Oi 5 ceramic the valency of A is two and that of B is five.
  • the solid solutions or mixture phases with the general formula xA ⁇ - (5-x)A" - 2Nb 2 O5 are prepared by mixing calcium carbonate or magnesium oxide and zinc oxide with niobium pentoxide in the x: 5-x: 2 ratio.
  • the mixture phases are prepared for using the solid state ceramic route.
  • a 5 B4O1 5 ceramic the valency of A is two and that of B is five.
  • the calcium, Magnesium and zinc are attempted to substitute at A site keeping niobium at B site to get the respective niobates.
  • barium, strontium, calcium and magnesium are attempted to substitute at A site in order to obtain the respective tantalates.
  • the atoms of a particular site may be replaced by another atom of the same valency and nearly the same ionic radius to form solid solution phases with intermediate dielectric constant and temperature coefficient of resonant frequencies.
  • the A 5 B 4 O 15 system provides ceramic materials with large range of dielectric constant, Q factor and positive and negative temperature coefficient of resonant frequencies and hence provides good scope for tuning the dielectric properties of ceramics with similar structure.
  • the present system of ceramics is useful for applications as dielectric resonators in communication systems and as substrates in microwave integrated circuits. Compared to the use of alumina substrates they decrease the size not only for strip line resonators and filters but also for all microwave circuits. It is also possible to use these dielectric materials in the fabrication of devices such as circulators, phase shifters etc. for impedance matching.
  • the dielectric resonators based on the above compounds are also useful for the fabrication of dielectric resonator antennas. Solid solution formation in the above system enables to tune the dielectric constant and temperature variation of resonant frequency in the Ba 5 Nb 4 Oi5 type hexagonal perovskites.
  • the oxides or carbonates of A are wet mixed with niobium pentoxide/tantalum pentoxide in the molar ratio.
  • the mixed powder is calcined in the range 1100°C - 1400°C and cooled to the room temperature. The calcine is ground well, PVA is added as the binder, dried and again ground.
  • the resultant fine powder is pellettized in the appropriate size for the measurement (5- 9 mm in height and 11 mm in diameter).
  • the careful design of the dimensions of the samples is a prerequisite for the accuracy of the microwave dielectric measurements.
  • the height of the sintered samples should be less than their diameter for the accuracy of the results.
  • the sintering temperatures of the samples were optimized at different temperatures in the range 1220-1625°C.
  • the sintered samples are polished well to avoid any irregularities on the flat surface and are used for measurements
  • the microwave dielectric constant is measured using Hakki- Coleman dielectric post resonator method.
  • the resonator is placed between two gold-coated copper metallic plates and microwave energy is coupled through an E- field probe to excite various resonant modes. Among the various resonant modes the TEon mode is selected for the measurement.
  • the above ceramics resonate at frequencies between 4 and 10 GHz
  • the quality factors of the samples are measured at the TE 01 ⁇ mode resonant frequency using a cavity method [Jerzy Krupka, Krzytof Derzakowsky, Bill Riddle and James Baker Jarviz, Meas. Sci. Technol. 9(1998), 1751- 1756].
  • the inner wall of the copper metallic cavity is silver coated.
  • the sample is mounted on a cylindrical quartz crystal. The measurement is done in the transmission mode
  • the temperature variation of resonant frequency (T f ) can be measured by noting the variation of TEoi ⁇ mode resonant frequency with temperature.
  • Table-I The microwave dielectric data for the system of materials is presented in Table- 1.
  • the magnesium oxide powder is heated at 1000°C for 3 hours to convert the small percentage of carbonate into oxide.
  • the preparation and characterization of the compounds follow the same procedure described in Example 1.
  • the calcination and sintering are done at temperatures in the range 1100 - 1250°C and 1250°C - 1400°C respectively.
  • the results are shown in Table-2.
  • a plot of the variation of ⁇ r and T f with x is also shown in Fig- 1.
  • Table-2 The microwave dielectric properties of xZnO-(5-x)MgO-2Nb 2 O 5
  • the preparation and characterization of the compounds follow the same procedure described in EXAMPLE- 1.
  • the calcinations and sintering are done at temperatures in the range 1050- 1075°C and 1 190-1200°C respectively. Results are shown in Table-3.
  • the magnesium oxide powder is usually heated at 1000°C for 3 hours to convert the small percentage of carbonate into oxide weighed before cooling.
  • the preparation and characterization of the compounds follow the same procedure described in Example 1.
  • the calcination are done in the temperature range 1250- 1400°C for 4 to 8 hours and sintering in the range 1435-1600°C for 2 to 4 hours.
  • Table-4 Table-4
  • the formation of solid solution between the above two ceramics for the tuning of microwave dielectric properties is not possible due to large difference in the ionic radii of Ba and Zn and also due to the difference in crystal structure. Hence a stacked resonator between, the. above ceramics is tried.
  • the Ba 5 Nb 4 Oi 5 is formed from a stoichiometric mixture of high purity BaCO 3 and Nb2 ⁇ 5 by calcining at 1200-1225°C for 5 hour and sintered at 1200°C for 2 hour where as 5ZnO-2Nb 2 O 5 is formed from a stoichiometric mixture of high purity ZnO and Nb 2 O 5 at 1050°C for 4 hour and sintered at 1380°C for 2 hour through the solid state route.
  • the preparation conditions are well controlled such that diameters of the final sintered pellets are nearly the same (The mean deviation is ⁇ 0.5 %).
  • the sintered pellets were polished well.
  • the microwave dielectric constants and Q factors of the pellets were characterized accurately using the cavity method.
  • the dimensions and the microwave parameters measured for the samples were shown in Table-5.
  • the average dielectric constant measured for Ba5Nb O 15 pellets is 39.5 and that of 5ZnO-2Nb 2 O 5 pellets is 22 with less than 0.3% deviation.
  • the average value of Qxf 'for BajNb 4 Oi5 samples is 21845 with a maximum deviation of 16% and those for 5ZnO-2Nb2 ⁇ 5 are 77,560 and 4% respectively.
  • the pellets of one type say 5ZnO-2Nb2 ⁇ 5 are placed over the other in between two gold-coated copper metallic plate (the Hakki-Coleman setup) and microwave is applied.
  • the pellets can be glued together using low-loss ceramic glues like cyanoacrylic.
  • the resonant structure act like a single dielectric resonator mounted in the set up.
  • the equivalent dielectric resonator can be assumed to have a dielectric constant ⁇ cf rwith length and diameter is respectively obtained from the sum of lengths and average of the diameters of the individual pellets.
  • the TEo ⁇ mode resonant frequency of the resonant system is noted.
  • the pellets are reversed and the resonant frequency is noted.
  • the effective dielectric constant ( ⁇ C fr) is calculated using the formulae suggested by Hakki and Coleman.
  • the experiment is repeated for different possible combinations of the pellets.
  • the results are tabulated in Table-6.
  • the variation of the dielectric constant with volume fraction is also given in Fig-2.
  • the quality factors were measured using a cavity method described in Example- 1.
  • the Q factor and resonant frequency vary with the reversal of the pellets.
  • the experiment is repeated with different possible combination of pellets.
  • the results were tabulated in Table-7
  • the inventive system of microwave ceramics has high dielectric constant, high quality factor and small temperature variation of resonant frequencies.
  • Ba 5 Ta 4 Oi5 with dielectric constant of 28-29, quality factor greater than 5500 and low T between 4 and 13 pprn °C is a potential material for practical applications.
  • the 5ZnO-2Nb 2 Os samples show very high Q factor which is greater than 1200Q, high dielectric constant of 22 and intermediate ⁇ f of -65 to -75 ppm/°C.
  • the 5AO-2B 2 O 5 ceramic compositions give the A 5 B O ⁇ 5 type ceramics only when Ba, Sr and Mg are used at the A site.
  • the mixture phases formed from 5ZnO-2Nb 2 O 5 and 5CaO-2Nb 2 ⁇ 5 have negative Tf whereas 5CaO-2Ta2 ⁇ 5 has positive ⁇ r.
  • the phases were identified to be AB 2 O6, A 2 B 2 O or A3B 2 O 8 type ceramics.
  • the ceramic system are useful for tuning the dielectric properties of the hexagonal perovskites to the extent, which is permissible by substitution, doping, solid solution or by forming mixtures without much degradation of the required properties.
  • the magnesium site is attempted to replace with zinc, which resulted in the multiphase ceramics with the compositional formula xZnO- (5-x) MgO-Nb ⁇ Os.
  • the above said ceramics show ⁇ r in the range 1 1 to 22, Qxf between 18000 and 89000 and Tf between -54 ⁇ 3 and -73 ⁇ 3 ppm °C.
  • the system gives ceramics with very high Qxf in the range 36,000 to 89,000 with ⁇ r in the range 18 ⁇ 1 to 22+ 1 for 1.5 ⁇ x ⁇ 5.
  • the zinc site in the 5ZnO-2Nb 2 O 5 mixture system is tried to replace with calcium and the resulted mixture phased ceramics may be represented by the compositional formula xCaO - (5-x)ZnO - 2Nb 2 O 5 .
  • the results are summarized in Table-3.
  • the substitution of Ca up to x 0.5 decreases the Tf from -73 ⁇ 3 to -55 ⁇ 3 ppm °C.
  • the microwave dielectric properties were given in Table-4.
  • the MgsNb . x Ta x Oi5 ceramics have ⁇ r of 11 with high quality factor.
  • the set of materials in the 5AO-2B 2 O 5 provide microwave dielectrics with a wide range of ⁇ r (1 1-42), Q factor up to 88,000 and positive and negative ⁇ »- (between -73 and 140 ppm °C) useful for applications.
  • the microwave dielectric properties can be suitably tuned by stacking cylindrical resonators with negative Tf over those with positive Xr and vice versa.
  • the microwave dielectric response of the Ba 5 Nb 4 Oi5-5ZnO-2Nb 2 O5 stacked resonator system is given in Table-6 and Table-7.
  • the Q factor of the system increases with the volume fraction of 5ZnO-2Nb 2 O 5 whereas effective dielectric constant shows a reverse trend and it decreases from 39 to 22.
  • the T f gradually decreases from high positive value to high negative value with 5ZnO-2Nb 2 O5.
  • the effective dielectric constant is between 26 and 30, Qxf between 26000 and 34000 and T f between 20 and - 20 ppm/°C.
  • Stacking provides a method suitable for tuning the dielectric properties of ceramics having high dielectric constant and Q factor even if their Tf values are very high.
  • the inventive system of materials provides a large range of dielectric constant, quality factor with small temperature variation of resonant frequencies. 2. It provides dielectric resonator materials, which are useful for tuning the hexagonal perovskite with high dielectric constant and Q factor.
  • Some of the ceramics in the system have high dielectric constant and Q factor and low Tf suitable for practical applications.

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Abstract

La présente invention concerne une nouvelle composition diélectrique hyperfréquence de formule générale 5AO-2B2O5, dans laquelle A = Ba, Sr, Ca, Mg ou Zn et B = Nb ou Ta, et un procédé de préparation de ladite composition. Dans un mode de réalisation de cette invention, la constante diélectrique est située dans la plage allant de 11±1 à 42±1, le produit facteur qualité-fréquence dans la plage de 2 000 à 88 000 et le coefficient thermique de fréquence de résonance dans la plage de +140±7 à -73±5 ppm/ C.
EP01934303A 2001-03-30 2001-03-30 Composition ceramique dielectrique hyperfrequence et procede de preparation de ladite composition Withdrawn EP1373161A1 (fr)

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