Dielectric ceramic composition and ceramic electronic parts using the same

Abstract: A dielectric ceramic composition is formed of a mixture including a BaO- TiO 2 -REO 3/2 ceramic composition, wherein RE represents a rare earth element, and a glass composition containing about 13-50 wt.% SiO 2 , about 3-30 wt.% B 2 O 3 , about 40-80 wt.% alkaline earth metal oxide, and about 0.5-10 wt.% Li 2 O. The dielectric ceramic composition has a high dielectric constant and a high Q value, as well as excellent temperature stability, and is capable of being sintered at a relatively low temperature. The dielectric ceramic composition is advantageously used in ceramic electronic parts.

Description: The present invention relates generally to a dielectric ceramic composition, which is a glass-ceramic composite material for low temperature firing, more particularly, to a dielectric composition for use in a microwave resonator, a LC filter, a laminated capacitor, and a multilayered circuit board or the like. With miniaturizing of the electronic devices such as a microwave resonator and a microwave filter, efforts have been made to replace cavity resonators with ceramic dielectrics having a high relative dielectric constant. Resonators and the filters are miniaturized by use of an effect that a wavelength of electromagnetic waves in dielectrics is shortened to 1/ε 1/2 times that in free space, wherein £ represents the relative dielectric constant of dielectrics. However, the dielectric material has not met a recent demand for further miniaturization since the relative dielectric constant ε of a ceramic dielectric material having a temperature coefficient suitable for use as a dielectric resonator has so far been limited to 100 or less. A method employing an LC resonator, which has conventionally been known in microwave circuits, is effective for meeting the demand under restriction of a relative dielectric constant ε of a ceramic dielectric material. Thus, a further miniaturized electronic apparatus having high reliability may be produced by applying to fabrication of LC circuits a lamination method which is adapted in practice for a laminated capacitor and a multilayered board. However, producing by way of a lamination method an LC resonator having a high Q value in a microwave region requires high electric conductivity of an internal electrode which is built into a laminated capacitor and a multilayered circuit board. A metal having high electric conductivity such as gold, silver, or copper must be used for an internal electrode which is fired simultaneously with a dielectric or a multilayered circuit board. For this reason, a dielectric material must be able to be sintered at low temperature simultaneously with internal electrodes formed of a metal material having a low melting point, and as well must have a high dielectric constant, a high Q value, and enhanced temperature stability. However, a dielectric material which meets all of these criteria has not yet been found. EP-A-0 740 310 describes a dielectric ceramic composition having a glass subcomponent with the formula BaO-Li 2 O-B 2 O 3 -SiO 2 and consisting of 48.2 wt.% BaO, 9.4 wt.% Li 2 O, 18.5 wt.% B 2 O 3 and 23.9 wt.% SiO 2 . It is an object of the present invention to provide a dielectric ceramic composition which has a high relative dielectric constant, a high Q value and temperature stability, and which is capable of being sintered at relatively low temperature. Another object of the present invention is to provide ceramic electronic parts which. have excellent high frequency characteristics and are able to be miniaturized. These objects are achieved with a dielectric ceramic composition having the features of claim 1, a ceramic electronic part having the features of claim 8 or a method of producing a ceramic composition having the features of claim 10. The subclaims are directed to preferable embodiments. Examples of the rare earth elements RE which are a component of the first ceramic composition of the inventive dielectric ceramic composition include Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and these elements may be used singly or in combination as desired. If, according to one preferable embodiment, the inventive dielectric ceramic composition further comprises at least one species of a ceramic compound selected from the group consisting of TiO 2 , CaTiO 3 , SrTiO 3 , and Nd 2 Ti 2 O 7 , these ceramic compounds are referred to as "second ceramic compositions" for the sake of making contrast to the said first ceramic composition. According to the present invention, since a dielectric ceramic composition is formed of a mixture comprising a first BaO-TiO 2 -REO 3/2 ceramic composition (RE represents a rare earth element) and an SiO 2 -B 2 O 3 -alkaline earth metal oxide-Li 2 O glass composition, it can be sintered at a temperature lower than the melting point of an electric conductor containing, as a primary component, one of a low-specific-resistance metal selected from silver, gold, and copper. Moreover, the present invention successfully provides a dielectric ceramic composition having a high relative dielectric constant within a high-frequency region, particularly within a microwave region and a millimeter wave region, as well as excellent temperature stability. Addition of CuO, as a secondary component, to the mixture comprising a first ceramic composition and a glass composition further lowers sintering temperature of the resultant mixture and increases the Q value and the relative dielectric constant thereof. Therefore, when used as a dielectric ceramic layer, such a dielectric ceramic composition can be fired simultaneously with a low-specific-resistance internal electrode made of gold, silver, copper, etc., to thereby yield ceramic electronic parts such as dielectrics and multilayer circuit boards containing such an internal electrode therein and having excellent high-frequency characteristics. Ceramic electronic parts such as LC resonators and LC filters having a high Q value can be further miniaturized by use of a lamination method and the dielectric ceramic composition as a dielectric ceramic layer. In the present invention, the above-described dielectric ceramic composition encompasses a powder comprising a mixture of the first ceramic composition and the glass composition (optionally the second ceramic composition); a paste composition in which the powder composition is dispersed in a medium such as an organic vehicle; a ceramic green sheet obtained by forming the paste composition; and a ceramic composition obtained by firing the green sheet. Fig. 1 is a ternary diagram of a BaO-TiO 2 -REO 3/2 ceramic composition; Fig. 2 is a fragmentary perspective view of an LC filter employing the ceramic electronic parts of the present invention; Fig. 3 is a schematic perspective view of the LC filter; and Fig. 4 is a circuit diagram of the LC filter. Fig. 1 shows a ternary diagram referring to the compositional ranges of a first BaO-TiO 2 -REO 3/2 ceramic composition which is a primary component of the first ceramic composition used in the dielectric ceramic composition according to the present invention. The compositional proportions of the BaO-TiO 2 -REO 3/2 ceramic composition, when represented by xBaO-yTiO 2 -zREO 3/2 , are such that x, y, and z fall within the ranges satisfying 5 ≤ x ≤ 15, 52.5 ≤ y ≤ 70, 15 ≤ z ≤ 42.5; and x + y + z = 100 on a mole % basis, and the composition preferably falls within the domain indicated by oblique lines in Fig. 1. In contrast, a composition falling within the domain A is difficult to sinter and in some cases does not provide a porous ceramic even at 1400°C, which is the conventional sintering temperature. When a composition falls within the domain B, a temperature-dependent characteristic, i.e., a temperature coefficient of dielectric constant of a capacitor formed inside a multilayered circuit board, tends to decrease drastically onto the negative side. When a composition falls within the domain C, the relative dielectric constant is extremely small and in some cases the sintered property is not good. Furthermore, when a composition falls within the domain D, the temperature coefficient of dielectric constant increases drastically onto the positive side and the relative dielectric constant tends to decrease. The first ceramic composition used in the dielectric ceramic composition according to the present invention preferably contains about 20 parts by weight or less of PbO in addition to a BaO-TiO 2 -NdO 3/2 ceramic composition which falls within the compositional domain indicated by oblique lines in Fig. 1. In practice, addition of PbO provides a dielectric ceramic composition having more stabilized characteristics; however, addition of PbO in excess of 20 parts by weight makes the temperature coefficient of change in dielectric constant negative and high, and the Q value decreases. The glass composition will next be described. The glass composition comprises about 13-50 wt.% SiO 2 , about 3-30 wt.% B 2 O 3 , about 40-80 wt.% alkaline earth metal oxide (BaO, SrO, CaO, MgO), and about 0.5-10 wt.% Li 2 O. B 2 O 3 contained in the glass composition lowers the glass viscosity and accelerates sintering of a dielectric ceramic composition. However, when the content of B 2 O 3 is in excess of about 30 wt.%, moisture resistance is adversely affected; whereas when it is less than about 3 wt.%, the composition is not sintered at about 1000°C or less. When the content of SiO 2 is in excess of about 50 wt.%, the glass softening temperature increases drastically and ceramic compositions containing SiO 2 in such a high amount cannot be sintered; whereas when it is less than about 13 wt.%, moisture resistance is adversely affected. The alkaline earth metal oxide promotes reaction between the ceramic composition and the glass composition and lowers the softening point of the glass composition. When the content of the alkaline earth metal oxide is less than about 40 wt.%, the sintered property decreases to induce difficulty in sintering at about 1000°C or less; whereas when it is in excess of about 80 wt.%, moisture resistance is adversely affected. When the content of BaO in the alkaline earth metal oxide is in excess of about 95 wt.%, moisture resistance is adversely affected; whereas when it is less than about 40 wt.%, the sinterability might decrease. In view of moisture resistance, the composition preferably contains at least one species among SrO, CaO, and MgO in an amount of about 5 wt.% or more. Li 2 O lowers the glass softening point. However, when the Li 2 O content is in excess of about 10 wt.%, moisture resistance is unsatisfactory; whereas when it is less than about 0.5 wt.%, the softening point increases drastically to prevent sintering. When the amount of the glass composition contained in the dielectric ceramic composition is less than about 5 wt.%, sintering might be difficult; whereas when it is in excess of about 20 wt.%, moisture resistance might deteriorate to lower the relative dielectric constant. CuO also functions as a sintering aid. When the content is in excess of about 3 wt.%, the Q value tends to decrease to shift the temperature coefficient of dielectric constant to a high positive value. Each of TiO 2 , CaTiO 3 , and SrTiO 3 which serve as the second ceramic composition has a negative temperature coefficient of dielectric constant, whereas Nd 2 Ti 2 O 7 is a composition having a positive temperature coefficient of dielectric constant. Briefly, in the present invention, there is incorporated, as an additive for modifying temperature characteristic, at least one species of a second ceramic composition selected from the group consisting of TiO 2 , CaTiO 3 , SrTiO 3 , and Nd 2 Ti 2 O 7 , in an appropriate amount into a mixture comprising the first ceramic composition and the glass composition, to thereby preset the temperature characteristic of the dielectric ceramic composition of the present invention to a desired value. When the second ceramic composition is incorporated into the dielectric composition of the present invention, preferably, the first ceramic composition accounts for about 50-95 wt.%, the glass composition accounts for about 5-20 wt.%, CuO accounts for about 3 wt.% or less, and the second ceramic composition accounts for about 30 wt.% or less. When the content of the second ceramic composition is in excess of about 30 wt.%, the sinterability of the dielectric ceramic composition of the present invention tends to deteriorate. The first ceramic composition is preferably contained in an amount of about 50-95 wt.%. When the content is less than about 50 wt.% (or when the glass composition is incorporated in an amount of more than about 20 wt.%), the sintered property of the ceramic composition (or the dielectric constant) tends to deteriorate; whereas when the content of the first ceramic composition is in excess of about 95 wt.%, the sintered property of the ceramic composition may also deteriorate. As one embodiment of the ceramic electronic parts of the present invention, an LC filter will next be described with reference to Figs. 2 through 4. A paste composition is prepared by adding an organic vehicle to the powder composition corresponding to the dielectric ceramic composition of the present invention, and the paste composition is formed into a ceramic green sheet having a thickness of, e.g., 40 µm through a casting method by use of a doctor blade. The sheet is dried and punched to provide a piece having a predetermined size. As shown in Fig. 2, via-holes 14 are formed by use of, e.g., a silver paste in the obtained ceramic green sheets 13, if required, and capacitor patterns 15 and coil patterns 16 are subsequently formed by use of, e.g., a silver paste through screen printing. Then, the green sheets are laminated and pressed, to form a laminated sheet. The laminated sheet is fired at, e.g., 900°C, then outer contacts 17, 18, 19, and 20 are formed, to thereby obtain an LC filter 10 having a capacitor C1 and coils L1 and L2 therein. Fig. 4 shows an equivalent circuit of the LC filter 10. Since the LC filter 10 employs the dielectric ceramic composition of the present invention as a dielectric ceramic layer, it can be produced by simultaneous sintering with an electrically conductive material as an internal conductor layer containing, as a primary component, one of a low-specific-resistance metal selected from gold, silver, and copper. Moreover, the filter has high-frequency characteristics within a microwave region and a millimeter wave region and excellent temperature stability, and can be sufficiently miniaturized. In addition to an LC filter shown in Figs. 2 through 4, examples of the ceramic electronic parts of the present invention include chip parts such as LC resonators, laminated chip capacitors, and chip antennas; and ceramic substrates (or ceramic multilayered substrates) such as ceramic substrates for hybrid ICs, VOCs, multichip modules, ceramic packages, etc. In addition to a method for producing the ceramic electronic parts of the present invention by shaping the dielectric ceramic composition of the present invention into a green sheet, laminating, and firing; the ceramic electronic parts may be produced by forming a paste composition of the dielectric ceramic composition of the present invention and printing the paste composition to a thick film. EXAMPLES The dielectric ceramic composition of the present invention will next be described by way of examples. Production of First Ceramic Compositions BaCO 3 , TiO 2 , Nd 2 O 3 , La 2 O 3 , Pr 2 O 3 , and Sm 2 O 3 were weighed and mixed together, to obtain mixtures having compositional ratios with regard to BaO, TiO 2 , and REO 3/2 indicated in the columns showing primary components in Table 1. Then, PbO powder was added to each of the above mixtures so as to realize a compositional ratio (parts by weight based on 100 parts of a primary component) indicated in the column showing a secondary component in Table 1, and the resultant mixture was mixed thoroughly. The mixture was calcined at 1150°C for one hour to form a calcined compact, which was then crushed and mixed. The mixture was then fired at 1300-1400°C, to thereby obtain a ceramic. Ceramic compositions S1 through S25 shown in Table 1 were produced by crushing the corresponding ceramics again. The obtained ceramics were subjected to measurement of relative dielectric constant, Q value, and temperature coefficient of change in capacitance. Results of the measurement are shown in Table 1. These first ceramic compositions were used to prepare dielectric ceramic compositions shown below. First ceramic composition No. Primary component (mole%) Secondary component (parts by weight) Relative dielectric constant (ε) Q value at 1 GHz Temperature coefficient of dielectric constant (ppm/°C) BaO TiO 2 ReO 3/2 PbO S1 10 63 Nd:27 13 95 5000 -5 S2 15 70 Nd:15 13 85 2500 -80 S3 15 55 Nd:30 13 80 3000 -100 S4 5 70 Nd:25 13 65 4000 -70 S5 5 55 Nd:40 13 54 2200 +20 S6 20 60 Nd:20 13 105 3500 -100 S7 10 75 Nd:15 13 72 3000 -120 S8 2 65 Nd:33 13 50 2500 +10 S9 10 50 Nd:40 13 47 2400 +50 S10 10 63 Nd:27 0 65 3500 +30 S11 10 63 Nd:27 3 80 4000 +30 S12 10 63 Nd:27 20 100 5000 -30 S13 10 63 Nd:27 25 90 900 -100 S14 13 65 Nd:22 0 69 3400 -20 S15 13 60 Nd:27 0 60 3600 +20 S16 20 60 Nd:20 0 75 2000 -100 S17 2 65 Nd:33 0 35 2500 +40 S18 10 63 La:27 13 100 4000 -20 S19 10 63 Pr:27 13 97 4500 -15 S20 10 63 Sm:27 13 92 5000 0 S21 10 63 27 (La/Nd=0.5/0.5) 13 97 5000 -10 S22 10 63 27 (Pr/Nd=0.25/0.75) 13 96 5000 -10 S23 13 65 22 (Pr/Nd=0.25/0.75) 13 101 4000 -10 S24 13 65 22 (Pr/Nd=0.5/0.5) 13 100 4500 -5 S25 10 63 27 (Sm/Nd=0.5/0.5) 13 94 5000 -5 S26 10 45 Nd:45 13 43 2000 +60 S27 10 63 27 (Pr/Nd=0.5/0.5) 13 100 4500 -5 Production of Glass Compositions B 2 O 3 , SiO 2 , BaO, SrO, CaO, MgO, and Li 2 O were weighed and thoroughly mixed together, to obtain mixtures having compositional ratios indicated in Table 2. Each of the mixtures was melted at 1100-1400°C and quenched by pouring into water, then wet-milled to thereby obtain glass compositions G1 through G31. Glass composition No. Alkaline earth metal oxide RO B 2 O 3 (wt%) SiO 2 (wt%) Li 2 O (wt%) Total amount of RO Proportions of respective components in RO (wt%) BaO SrO CaO MgO G1 61 82 11 5 2 14 23 2 G2 30 82 11 5 2 29 39 2 G3 40 82 11 5 2 25 33 2 G4 80 82 11 5 2 5 13 2 G5 90 82 11 5 2 3 5 2 G6 67 82 11 5 2 1 30 2 G7 66 82 11 5 2 3 29 2 G8 50 82 11 5 2 30 18 2 G9 44 82 11 5 2 40 14 2 G10 70 82 11 5 2 20 8 2 G11 68 82 11 5 2 17 13 2 G12 40 82 11 5 2 8 50 2 G13 30 82 11 5 2 8 60 2 G14 63 82 11 5 2 14 23 0 G15 62.5 82 11 5 2 14 23 0.5 G16 62 82 11 5 2 14 23 1 G17 57 82 11 5 2 12 21 10 G18 55 82 11 5 2 11 19 15 G19 61 30 35 25 10 14 23 2 G20 61 40 33 24 3 14 23 2 G21 61 95 2 2 1 14 23 2 G22 61 100 0 0 0 14 23 2 G23 61 85 0 13 2 14 23 2 G24 61 45 35 18 2 14 23 2 G25 61 40 45 13 2 14 23 2 G26 61 85 13 0 2 14 23 2 G27 61 50 12 35 2 14 23 2 G28 61 40 13 45 2 14 23 2 G29 61 83 12 5 0 14 23 2 G30 61 60 15 5 20 14 23 2 G31 61 55 15 5 25 14 23 2 Production of Dielectric Ceramic Compositions Dielectric ceramic compositions comprising a mixture of a first ceramic composition and a glass composition (and CuO) were prepared, then evaluated. To each of the thus-obtained first ceramic compositions S1 through S25, a glass composition selected from G1 through G31 was added so as to produce mixtures having compositional ratios indicated in Tables 3 to 5. To each of the mixtures, CuO powder serving as a secondary component was added so as to produce mixtures having compositional proportions indicated in Tables 3 to 5, which were then mixed thoroughly. To the raw mixtures, appropriate amounts of a binder, a plasticizer, and a solvent were added, and the mixtures were kneaded to provide slurries. Each of the thus-obtained slurries was molded, through a doctor blade coating method, into a sheet having a thickness of 50 µm, and the produced ceramic green sheet was cut into pieces having a size of 30 mm X 10 mm. The pieces were laminated and pressed to form a sheet having a thickness of 0.5 mm. Plate-like dielectric ceramics of sample Nos. 1 to 67 listed in Tables 3 to 5 were obtained by firing the corresponding pressed sheets in N 2 at 1000°C for one hour. The dielectric ceramics obtained as above were subjected to measurement of relative dielectric constant (ε), Q value, and temperature coefficient of change in dielectric constant (ppm/°C). The relative dielectric constant was measured at a frequency of 1 MHz. The results of measurement are shown in Tables 3 to 5. Sample No. First ceramic composition Glass composition CuO content (wt%) Firing temperature (°C) Relative dielectric constant (ε) Q value Temperature coefficient of dielectric constant (ppm/°C) Remarks No. Amount (wt%) No. Amount (wt%) 1 S1 90 G1 10 0 1000 60 2500 0 2 S1 90 G4 10 0 1000 62 2000 -20 3 S1 88 G4 12 0 1000 63 2000 -30 4 S1 88.5 G2 10 1.5 1000 - - - Not sintered 5 S1 88.5 G3 10 1.5 1000 65 4000 -20 6 S1 88.5 G4 10 1.5 1000 77 3500 -30 7 S1 88.5 G5 10 1.5 1000 78 3000 -40 Poor moisture resistance 8 S1 88.5 G6 10 1.5 1000 - - - Not sintered 9 S1 88.5 G7 10 1.5 1000 70 4500 -10 10 S1 88.5 G8 10 1.5 1000 75 3000 -15 11 S1 88.5 G9 10 1.5 1000 75 3000 -30 Poor moisture resistance 12 S1 88.5 G10 10 1.5 1000 80 2500 -20 Poor moisture resistance 13 S1 88.5 G11 10 1.5 1000 77 3000 -15 14 S1 88.5 G12 10 1.5 1000 73 3500 -5 15 S1 88.5 G13 10 1.5 1000 - - - Not sintered 16 S1 88.5 G14 10 1.5 1000 - - - Not sintered 17 S1 88.5 G15 10 1.5 1000 70 2500 +10 18 S1 88.5 G16 10 1.5 1000 72 4500 0 19 S1 88.5 G17 10 1.5 1000 77 3000 -30 20 S1 88.5 G18 10 1.5 1000 78 2500 -30 Poor moisture resistance 21 S14 88.5 G1 10 1.5 1000 53 3000 -25 22 S15 88.5 G1 10 1.5 1000 48 3100 +15 23 S16 88.5 G1 10 1.5 1000 60 1700 -120 24 S17 88.5 G1 10 1.5 1000 27 1500 +35 Sample No. First ceramic composition Glass composition CuO content (wt%) Firing temperature (°C) Relative dielectric constant (ε) Q value Temperature coefficient of dielectric constant (ppm/°C) Remarks No. Amount (wt%) No. Amount (wt%) 25 S1 88.5 G1 10 1.5 1000 75 4000 -10 26 S2 88.5 G1 10 1.5 1000 65 2000 -50 27 S3 88.5 G1 10 1.5 1000 60 2300 -70 28 S4 88.5 G1 10 1.5 1000 55 3000 -70 29 S5 88.5 G1 10 1.5 1000 50 2000 0 30 S6 88.5 G1 10 1.5 1000 80 2500 -120 31 S7 88.5 G1 10 1.5 1000 55 2000 -150 32 S8 88.5 G1 10 1.5 1000 35 1500 -10 33 S9 88.5 G1 10 1.5 1000 30 1500 +20 34 S10 88.5 G1 10 1.5 1000 50 3000 0 35 S11 88.5 G1 10 1.5 1000 65 4000 +10 36 S12 88.5 G1 10 1.5 1000 80 2000 -20 37 S13 88.5 G1 10 1.5 1000 70 1000 -150 38 S1 88.5 G19 10 1.5 1000 - - - Insufficiently sintered 39 S1 88.5 G20 10 1.5 1000 67 4000 +10 40 S1 88.5 G21 10 1.5 1000 77 4000 -20 41 S1 88.5 G22 10 1.5 1000 78 3700 -25 Poor moisture resistance 42 S1 88.5 G23 10 1.5 1000 76 4000 -15 43 S1 88.5 G24 10 1.5 1000 67 3500 +5 44 S1 88.5 G25 10 1.5 1000 - - - Insufficiently sintered 45 S1 88.5 G26 10 1.5 1000 75 4200 -10 46 S1 88.5 G27 10 1.5 1000 65 4000 +10 47 S1 88.5 G28 10 1.5 1000 - - - Insufficiently sintered 48 S1 88.5 G29 10 1.5 1000 77 4000 -5 49 S1 88.5 G30 10 1.5 1000 60 4000 -10 50 S1 88.5 G31 10 1.5 1000 - - - Insufficiently sintered Sample No. First ceramic composition Glass composition CuO content (wt%) Firing temperature (°C) Relative dielectric constant (ε) Q value Temperature coefficient of dielectric constant (ppm/°C) Remarks No. Amount (wt%) No. Amount (wt%) 51 S1 89.8 G1 10 0.2 1000 70 4000 -5 52 S1 87 G1 10 3.0 1000 78 3000 -20 53 S1 87 G1 10 5.0 1000 85 100 +200 54 S1 95.5 G1 3 1.5 1000 - - - Insufficiently sintered 55 S1 93.5 G1 5 1.5 1000 70 5000 -10 56 S1 78.5 G1 20 1.5 1000 50 1500 +20 57 S1 68.5 G1 30 1.5 1000 40 800 +40 Poor moisture resistance 58 S1 87.5 G12 12 0.5 1000 64 4000 -10 59 S1 87.0 G16 12 1.0 1000 70 3000 -20 60 S18 88.5 G1 10 1.5 1000 78 3500 -30 61 S19 88.5 G1 10 1.5 1000 76 4000 -20 62 S20 88.5 G1 10 1.5 1000 73 4500 -5 63 S21 88.5 G1 10 1.5 1000 76 4500 -20 64 S22 88.5 G1 10 1.5 1000 75 4500 -25 65 S23 88.5 G1 10 1.5 1000 80 3500 -20 66 S24 88.5 G1 10 1.5 1000 79 4000 -15 67 S25 88.5 G1 10 1.5 1000 74 4000 -10 As is apparent from Tables 3, 4, and 5, dielectric ceramic compositions formed of a mixture comprising a first BaO-TiO 2 -REO 3/2 ceramic composition - wherein RE represents a rare earth element - and a glass composition - which comprises about 13-50 wt.% SiO 2 , about 3-30 wt.% B 2 O 3 , about 40-80 wt.% alkaline earth metal oxide, and about 0.5-10 wt.% Li 2 O - have excellent characteristics; i.e., a high relative dielectric constant, a high Q value, and a low temperature coefficient of change in dielectric constant, as shown for sample Nos. 1 to 3 among sample Nos. 1 to 24. Furthermore, the dielectric compositions are obtained by firing at about 1000°C or less. Compositions further containing CuO serving as a secondary component have excellent characteristics; i.e., a high relative dielectric constant, a high Q value, and a low temperature coefficient of change in dielectric constant, as shown for sample Nos. 5, 6, 9, 10, 13, 14, 17 to 19, and 21 to 24 among sample Nos. 1 to 24. Furthermore, more stable dielectric ceramic compositions are obtained by firing at about 1000°C or less. Briefly, incorporation of CuO enhances Q value and relative dielectric constant as shown in comparison between sample No. 1 and sample Nos. 51 to 53, and, although data are not shown, can lower the sintering temperature. In contrast, as shown in sample Nos. 4, 7, 8, 11, 12, 15, 16, and 20 among sample Nos. 1 to 24, the dielectric ceramic compositions having a composition falling outside the above-described compositional ranges are not sintered at 1000°C or are sintered insufficiently, to yield poor moisture resistance. As shown in sample Nos. 25 to 29, 35, and 36 among sample Nos. 25 to 37, dielectric ceramic compositions having a lower temperature coefficient of change in dielectric constant are obtained by designating the compositional ranges of the first BaO-TiO 2 -REO 3/2 ceramic compositions as xBaO-yTiO 2 -zREO 3/2 , wherein x, y, and z are each based on mole% and are represented by 5 ≤ x < 15, 52.5 ≤ y ≤ 70, and 15 ≤ z ≤ 42.5; and x + y + z = 100, and incorporating about 20 parts by weight or less of PbO to 100 parts by weight of the corresponding first ceramic compositions. Preferably, the alkaline earth metal oxide contained in the glass compositions comprises BaO and at least one species selected from the group consisting of SrO, CaO, and MgO, and the compositional ratio thereof lies within the following ranges: about 35 wt.% or less for SrO; about 35 wt.% or less for CaO; about 20 wt.% or less for MgO; and about 40-95 wt.% for BaO, as shown in sample Nos. 39, 40, 42, 43, 45, 46, 48, and 49 among sample Nos. 38 to 50. Preferably, the proportions of the first ceramic composition, glass composition, and CuO are respectively about 80-95 wt.%, about 5-20 wt.%, and about 3 wt.% or less, as shown in sample Nos. 51, 52, 55, 58, and 59 among sample Nos. 51 to 59. CuO serving as a secondary component may be incorporated by adding CuO powder into a mixture of the first ceramic composition and the glass composition as shown in the above examples, as well as by mixing a glass composition containing CuO prepared in advance and the ceramic composition. In either case, the same effect can be obtained. Moreover, as shown in sample Nos. 60 to 67, dielectric ceramic compositions having excellent characteristics; i.e., a high relative dielectric constant, a high Q value, and a low temperature coefficient of change in dielectric constant, are produced by firing at about 1000°C or less, when La, Pr, or Sm rather than Nd is used as RE, i.e., a rare earth element, of a BaO-TiO 2 -REO 3/2 ceramic composition. Therefore, examples of rare earth elements RE, which may be used singly or in combination, include Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Dielectric ceramic compositions comprising a mixture of a first ceramic composition, a glass composition, and a second dielectric ceramic composition (and CuO) were prepared, then evaluated. An appropriate amount of CuO powder was added to the first ceramic compositions shown in Table 1 and the glass compositions shown in Table 2. To each of the thus-obtained mixtures, TiO 2 , CaTiO 3 , SrTiO 3 , and Nd 2 Ti 2 O 7 serving as second ceramic compositions were then added so as to produce mixtures having compositional proportions indicated in Tables 6 to 11, which were then mixed thoroughly. To the raw mixtures, an appropriate amount of an organic vehicle such as a binder, a plasticizer, and a solvent were added, and the mixtures were kneaded to provide slurries. Each of the thus-obtained slurries was molded, through a doctor blade coating method, into a sheet having a thickness of 50 µm, and the produced ceramic green sheet was cut into pieces having a size of 30 mm X 10 mm. The pieces were laminated and pressed to form a sheet having a thickness of 0.5 mm. Dielectric ceramics of samples Nos. 68 to 132 listed in Tables 6 to 11 were obtained by firing the corresponding pressed sheets in air at 1000°C or less for one hour. The dielectric ceramics obtained as above were subjected to measurement of relative dielectric constant (ε), Q value, and temperature coefficient of change in dielectric constant (ppm/°C). The relative dielectric constant was measured at a frequency of 1 MHz. The results of measurement are shown in Tables 6 to 11. Sample No. First ceramic composition Glass composition Second ceramic composition CuO (wt%) No. Amount (wt%) No. Amount (wt%) Species Amount (wt%) 68 S1 95.5 G1 3.5 TiO 2 0.5 0.5 69 S1 94.0 G1 5 TiO 2 0.5 0.5 70 S1 68.5 G1 20 TiO 2 10 1.5 71 S1 58.5 G1 30 TiO 2 10 1.5 72 S1 80 G1 10 TiO 2 10 0 73 S1 77.0 G1 10 TiO 2 10 3.0 74 S1 75.0 G1 10 TiO 2 10 5.0 75 S1 86.5 G1 10 TiO 2 2 1.5 76 S1 78.5 G1 10 TiO 2 10 1.5 77 S1 58.5 G1 10 TiO 2 30 1.5 78 S1 48.5 G1 10 TiO 2 40 1.5 79 S1 86.5 G1 10 CaTiO 3 2 1.5 80 S1 58.5 G1 10 CaTiO 3 30 1.5 81 S1 48.5 G1 10 CaTiO 3 40 1.5 82 S1 86.5 G1 10 SrTiO 3 2 1.5 83 S1 58.5 G1 10 SrTiO 3 30 1.5 84 S1 48.5 G1 10 SrTiO 3 40 1.5 85 S1 78.5 G1 10 SrTiO 3 /TiO 2 5/5 1.5 86 S1 48.5 G1 10 SrTiO 3 /TiO 2 20/20 1.5 87 S1 83.5 G1 10 Nd 2 Ti 2 O 7 5 1.5 Sample No. First ceramic composition Glass composition Second ceramic composition CuO (wt%) No. Amount (wt%) No. Amount (wt%) Species Amount (wt%) 88 S1 78.5 G1 10 Nd 2 Ti 2 O 7 10 1.5 89 S1 58.5 G1 10 Nd 2 Ti 2 O 7 30 1.5 90 S1 48.5 G1 10 Nd 2 Ti 2 O 7 40 1.5 91 S1 58.5 G1 10 TiO 2 30 1.5 92 S1 48.5 G1 10 TiO 2 40 1.5 93 S1 86.5 G1 10 CaTiO 3 2 1.5 94 S1 58.5 G1 10 CaTiO 3 30 1.5 95 S1 48.5 G1 10 CaTiO 3 40 1.5 96 S1 86.5 G1 10 SrTiO 3 2 1.5 97 S1 58.5 G1 10 SrTiO 3 30 1.5 98 S1 48.5 G1 10 SrTiO 3 40 1.5 99 S1 78.5 G1 10 SrTiO 3 /TiO 2 5/5 1.5 100 S1 48.5 G1 10 SrTiO 3 /TiO 2 20/20 1.5 101 S1 83.5 G1 10 Nd 2 Ti 2 O 7 5 1.5 102 S1 78.5 G1 10 Nd 2 Ti 2 O 7 10 1.5 103 S1 58.5 G1 10 Nd 2 Ti 2 O 7 30 1.5 104 S1 48.5 G1 10 Nd 2 Ti 2 O 7 40 1.5 Sample No. Firing temperature (°C) Relative dielectric constant (ε) Q value Temperature coefficient of dielectric constant (ppm/°C) Remarks 68 1000 - - - Insufficiently sintered 69 1000 83 5000 -60 70 1000 53 1600 -80 71 1000 45 1000 -60 Low ε 72 1000 75 2800 -50 73 1000 80 3500 -60 74 1000 110 200 +150 Low Q value 75 1000 76 4000 -20 76 1000 78 4100 -50 77 1000 86 2700 -120 78 1000 - - - Insufficiently sintered 79 1000 78 3800 -30 80 1000 90 2500 -180 81 1000 - - - Insufficiently sintered 82 1000 79 3500 -40 83 1000 120 2000 -250 84 1000 - - - Insufficiently sintered 85 1000 95 2500 -100 86 1000 - - - Insufficiently sintered 87 1000 73 3500 0 Sample No. Firing temperature (°C) Relative dielectric constant (ε) Q value Temperature coefficient of dielectric constant (ppm/°C) Remarks 88 1000 71 3000 +10 89 1000 62 2000 +30 90 1000 - - - Insufficiently sintered 91 1000 86 2700 -120 92 1000 - - - Insufficiently sintered 93 1000 78 3800 -30 94 1000 90 2500 -180 95 1000 - - - Insufficiently sintered 96 1000 79 3500 -40 97 1000 120 2000 -250 98 1000 - - - Insufficiently sintered 99 1000 95 2500 -100 100 1000 - - - Insufficiently sintered 101 1000 73 3500 0 102 1000 71 3000 +10 103 1000 62 2000 +30 104 1000 - - - Insufficiently sintered Sample No. First ceramic composition Glass composition Second ceramic composition CuO (wt%) No. Amount (wt%) No. Amount (wt%) Species Amount (wt%) 105 S2 78.5 G1 10 TiO 2 10 1.5 106 S3 78.5 G1 10 TiO 2 10 1.5 107 S4 78.5 G1 10 TiO 2 10 1.5 108 S5 78.5 G1 10 TiO 2 10 1.5 109 S6 78.5 G1 10 TiO 2 10 1.5 110 S7 78.5 G1 10 TiO 2 10 1.5 111 S8 78.5 G1 10 TiO 2 10 1.5 112 S26 78.5 G1 10 TiO 2 10 1.5 113 S10 78.5 G1 10 TiO 2 10 1.5 114 S11 78.5 G1 10 TiO 2 10 1.5 115 S12 78.5 G1 10 TiO 2 10 1.5 116 S13 78.5 G1 10 TiO 2 10 1.5 117 S19 78.5 G1 10 TiO 2 10 1.5 118 S20 78.5 G1 10 TiO 2 10 1.5 119 S27 78.5 G1 10 TiO 2 10 1.5 Sample No. Firing temperature (°C) Relative dielectric constant (εr) Q value Temperature coefficient of dielectric constant (ppm/°C) Remarks 105 1000 68 1500 -120 106 1000 64 2000 -150 107 1000 53 2800 -120 108 1000 45 1200 -30 109 1000 90 2500 -160 110 1000 58 2000 -180 111 1000 37 900 -40 Low Q value 112 1000 30 900 0 Low Q value 113 1000 50 2500 -10 114 1000 65 2800 0 115 1000 85 3000 -75 116 1000 75 500 -150 Low Q value 117 1000 80 3500 -60 118 1000 75 3800 -40 119 1000 82 3500 -45 Sample No. First ceramic composition Glass composition Second ceramic composition CuO (wt%) No. Amount (wt%) No. Amount (wt%) Species Amount (wt%) 120 S1 78.5 G2 10 TiO 2 10 1.5 121 S1 78.5 G3 10 TiO 2 10 1.5 122 S1 78.5 G4 10 TiO 2 10 1.5 123 S1 78.5 G5 10 TiO 2 10 1.5 124 S1 78.5 G6 10 TiO 2 10 1.5 125 S1 78.5 G8 10 TiO 2 10 1.5 126 S1 78.5 G9 10 TiO 2 10 1.5 127 S1 78.5 G12 10 TiO 2 10 1.5 128 S1 78.5 G13 10 TiO 2 10 1.5 129 S1 78.5 G14 10 TiO 2 10 1.5 130 S1 78.5 G15 10 TiO 2 10 1.5 131 S1 78.5 G17 10 TiO 2 10 1.5 132 S1 78.5 G18 10 TiO 2 10 1.5 Sample No. Firing temperature (°C) Relative dielectric constant (ε) Q value Temperature coefficient of dielectric constant (ppm/°C) Remarks 120 1000 - - - Not sintered 121 1000 75 3500 -50 122 1000 80 3700 -53 123 1000 81 3800 -54 Moisture resistance: Not good 124 1000 - - - Not sintered 125 1000 80 3700 -50 126 1000 81 3800 -52 Moisture resistance: Not good 127 1000 73 3300 -45 128 1000 - - - Not sintered 129 1000 - - - Not sintered 130 1000 70 2500 -40 131 1000 81 2000 -50 132 1000 82 1700 -54 Moisture resistance: Not good As is apparent from Tables 6 to 11, the temperature characteristics of the dielectric ceramic compositions can be preset to desired values more effectively by incorporating at least one species of a second ceramic composition selected from the group consisting of TiO 2 , CaTiO 3 , SrTiO 3 , and Nd 2 Ti 2 O 7 into a dielectric ceramic composition comprising a mixture of a first BaO-TiO 2 -REO 3/2 ceramic composition (wherein RE represents a rare earth element) and a glass composition, wherein the glass composition comprises about 13-50 wt.% SiO 2 , about 3-30 wt.% B 2 O 3 , about 40-80 wt.% alkaline earth metal oxide, and about 0.5-10 wt.% Li 2 O. Briefly, target temperature characteristics of the dielectric compositions can be realized through incorporation of TiO 2 , CaTiO 3 , and SrTiO 3 having a negative temperature coefficient of dielectric constant or Nd 2 Ti 2 O 7 having a positive temperature coefficient thereof as secondary components. In contrast, as in the case of sample No. 120, a dielectric composition containing a lower amount of an alkaline earth metal oxide in the glass composition cannot be sintered at 1000°C; whereas, as in the case of sample No. 123, a dielectric composition containing a higher amount of an alkaline earth metal oxide and a lower amount of SiO 2 has unsatisfactory moisture resistance. As in the case of sample No. 124, a dielectric composition containing a lower amount of B 2 O 3 in the glass composition cannot be sintered at 1000°C, whereas, as in the case of sample No. 126, a dielectric composition containing a higher amount of B 2 O 3 has unsatisfactory moisture resistance. Moreover, as in the case of sample No. 128, a dielectric composition having a lower content ratio of an alkaline earth metal oxide and a higher content ratio of SiO 2 in the glass composition cannot be sintered at 1000°C; whereas, as in the case of sample No. 129, a dielectric composition not containing a predetermined amount of Li 2 O in the glass composition cannot be sintered and a dielectric ceramic composition containing an excessive amount of Li 2 O has unsatisfactory moisture resistance as in the case of sample No. 132. As in the case of sample No. 68, the sintered property of a dielectric ceramic composition having a higher content ratio of the first ceramic composition and having a lower content ratio of the glass composition tends to deteriorate; whereas as in the case of sample No. 71, the dielectric constant of a dielectric ceramic composition having a higher content ratio of glass composition tends to decrease. As in the case of sample No. 74, the Q value of a dielectric ceramic composition having a higher content ratio of CuO in the glass composition tends to decrease. As in the case of sample Nos. 81, 84, 86, 90, 92, 95, 98, 100, and 104, the sintered property of a dielectric ceramic composition having a lower content ratio of the first ceramic composition and a higher content ratio of the second ceramic composition tends to deteriorate. Furthermore, as indicated in the case of sample Nos. 109 and 110, a dielectric ceramic composition having a compositional range of the first ceramic composition falling within the domain A or the domain B indicated in Fig. 1 tends to have a greater temperature coefficient. Although examples are not shown here, when the range falls within the domain A, sintering of a ceramic composition tends be difficult and a porous ceramic might be produced. As in the case of sample Nos. 111 and 112, when a compositional range of the first ceramic composition falls in the domain C and the domain D indicated in Fig. 1, the relative dielectric constant tends to decrease. When the PbO content in the first ceramic composition is excessively high, as indicated in sample No. 116, the relative dielectric constant tends to decrease. In the above Tables, the term "not sintered" denotes that firing at a predetermined temperature can never be performed, and the term "insufficiently sintered" denotes that firing is completed insufficiently under the above conditions and may be possible by modifying the conditions. The term "poor moisture resistance" refers to moisture resistance of a dielectric ceramic composition causing fatal problems and the term "insufficient moisture resistance" refers to moisture resistance that may be insufficient depending on conditions. As described herein above, the present invention provides a dielectric ceramic composition which is sintered at a temperature lower than the melting point of an electric conductor containing, as a primary component, one of a low-specific-resistance metal selected from gold, silver, and copper. Moreover, there can be obtained a dielectric ceramic composition having a high relative dielectric constant within a high-frequency region, particularly within a microwave region and a millimeter wave region, as well as excellent temperature stability. Therefore, such a dielectric ceramic composition can be fired simultaneously with a low-specific-resistance internal electrode made of gold, silver, copper, etc., and there can be obtained ceramic electronic parts such as dielectrics and multilayer circuit boards containing such an internal electrode therein and having excellent high-frequency characteristics. Ceramic electronic apparatus such as an LC resonator and an LC filter having a high dielectric constant and a high Q value can be further miniaturized in a lamination method making use of the dielectric ceramic composition.

Claims: A dielectric ceramic composition comprising a mixture of a first ceramic composition represented by xBaO-yTiO 2 -zREO 3/2 , wherein x, y and z are based on mole% and satisfy the following relations: 5 ≤ x ≤ 15, 52.5 ≤ y ≤ 70, 15 ≤ z ≤ 42.5, and x + y + z = 100; and a glass composition comprising 13-50 wt.% SiO 2 , 3-30 wt.% B 2 O 3 , 40-80 wt.% alkaline earth metal oxide, and 0.5-10 wt.% Li 2 O. The dielectric ceramic composition according to claim 1, further comprising CuO as a secondary component. The dielectric ceramic composition according to anyone of the claims 1 or 2, wherein the first ceramic composition contains PbO in an amount of 20 parts per weight or less with respect to 100 parts per weight of the first ceramic composition. The dielectric ceramic composition according to anyone of the claims 1 or 2, wherein the alkaline earth metal oxide contained in the glass composition comprises BaO and at least one species selected from the group consisting of SrO, CaO, and MgO, and the compositional proportions of SrO, CaO, MgO, and BaO fall within the ranges of 35 wt.% or less, 35 wt.% or less, 20 wt.% or less, and 40-95 wt.%, respectively. The dielectric ceramic composition according to claim 2, wherein the first ceramic composition accounts for 80-95 wt.%, the glass composition accounts for 5-20 wt.%, and CuO accounts for 3 wt.% or less. The dielectric ceramic composition according to anyone of the claims 1 or 2, which comprises at least one species of a second ceramic composition selected from the group consisting of TiO 2 , CaTiO 3 , SrTiO 3 , and Nd 2 Ti 2 O 7 . The dielectric ceramic composition according to Claim 6, wherein the first ceramic composition accounts for 50-95 wt.%, the glass composition accounts for 5-20 wt.%, CuO accounts for 3 wt.% or less, and the second ceramic composition accounts for 30 wt.% or less. A ceramic electronic part which comprises as a dielectric ceramic layer the dielectric ceramic composition as recited in one of the claims 1 to 7. A ceramic electronic part according to claim 8, further comprising an internal electrode disposed in said dielectric ceramic layer and including at least one of Au, Ag and Cu, said ceramic layer and said internal electrode being formed by firing a ceramic green sheet and metal paste associated with said green sheet at a temperature of 1000°C or less. A method of producing a ceramic composition comprising the steps of: firing raw materials of BaO-TiO 2 -REO 3/2 system ceramic composition represented by xBaO-yTiO 2 -zREO 3/2, with x, y and z being based on mole% and satisfy the following relations 5 ≤ x ≤ 15, 52.5 ≤ y ≤ 70, 15 ≤ z ≤ 42.5, and x + y + z = 100; heating raw materials of a glass composition including SiO 2 , B 2 O 3 , alkaline earth metal oxide, and Li 2 O; abruptly cooling said heated materials; mixing powder of said ceramic composition and said glass composition with organic binder; forming ceramic green sheet of said mixture; firing said green sheet; wherein said glass composition comprises 13-50 wt.% SiO 2 , 3-30 wt.% B 2 O 3 , 40-80 wt.% alkaline earth metal oxide, and 0.5-10 wt.% Li 2 O in said green sheet. The method of producing a ceramic composition according to claim 10, wherein said step of firing said green sheet is carried out at a temperature of 1000°C or below. The method of producing a ceramic composition according to claim 11, wherein said step of firing said green sheet is carried out for about 1 hour. The method of producing a ceramic composition according to claim 11, wherein said step of firing said green sheet is carried out in nitrogen gas.

Inventors: SUGIMOTO YASUTAKA, SUGOU KIMIHIDE, SUNAHARA HIROFUMI, TAKAGI HIROSHI, SUGIMOTO, YASUTAKA, SUGOU, KIMIHIDE, SUNAHARA, HIROFUMI, TAKAGI, HIROSHI, Sugimoto, Yasutaka c/o Murata Manufacturing Co.Ltd, Sugou, Kimihide c/o Murata Manufacturing Co.,Ltd., Sunahara, Hirofumi c/o Murata Manufacturing Co.Ltd, Takagi, Hiroshi c/o Murata Manufacturing Co.,Ltd.
Applicants: MURATA MANUFACTURING CO, MURATA MANUFACTURING CO., LTD.
Application year: 1998
Main classification: C04B35
IPC codes: H01G4, H05K1, C03C14, H01B3, C04B35