Dielectric ceramic composition and ceramic electronic element using the same

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dielectric ceramic composition and to a ceramic electronic element using the same, particularly to a dielectric ceramic composition which is used as a material for a dielectric used in microwave resonators, filters, laminated capacitors, and other applications, or to a ceramic material for multilayer circuit boards and to a ceramic electronic element using the same.
2. Description of the Related Art
Conventionally, efforts have been made to replace cavity resonators with ceramic dielectrics having a high dielectric constant in order to miniaturize electronic apparatus such as microwave resonators and microwave filters. Briefly, the resonators and the filters are miniaturized by use of an effect that the wavelength of an electromagnetic wave in a dielectric is shortened to 1/.epsilon..sup.1/2 times that in free space, wherein .epsilon. represents the dielectric constant of the dielectric.
However, since the relative dielectric constant .epsilon. 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, the dielectric material has not met the recent demand for further miniaturization.
A method employing an LC resonator which has conventionally been known in connection with microwave circuits is effective for meeting the demand under restriction of relative dielectric constant .epsilon. of a ceramic dielectric material. Thus, a further miniaturized electronic apparatus having high reliability may be produced by application to fabrication of LC circuits of a lamination method which is adapted in practice for laminated capacitors and multilayer boards.
However, use of a lamination method to produce an LC resonator having a high Q value in a microwave region requires high electric conductivity of the internal electrode which is built into a laminated capacitor and a multilayer circuit board. Briefly, a metal material 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 multilayer circuit board. For this reason, the dielectric material must be a low-temperature-sinterable material which is able to be sintered 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 a high degree of temperature stability. However, a dielectric material which meets all of these criteria has not yet been found.
SUMMARY OF THE INVENTION
In view of the foregoing, the present invention is directed to the provision of a dielectric ceramic composition which has a high relative dielectric constant, a high Q value and desirable temperature stability, and which is sinterable at relatively low temperature, as well as to the provision of a ceramic electronic element using the same.
In one aspect of the present invention, there is provided a dielectric ceramic composition comprising a mixture of a BaO--TiO.sub.2 --REO.sub.3/2 --Bi.sub.2 O.sub.3 -based ceramic composition (wherein RE represents a rare earth element) and a glass composition, the glass composition comprising about 13-50 wt. % SiO.sub.2, about 3-30 wt. % B.sub.2 O.sub.3, about 40-80 wt. % alkaline earth metal oxide and about 0.1-10 wt. % Li.sub.2 O. Examples of rare earth elements RE 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.
The dielectric ceramic composition may also contain CuO as an auxiliary component.
Preferably, the BaO--TiO.sub.2 --REO.sub.3/2 --Bi.sub.2 O.sub.3 -based ceramic composition in the dielectric ceramic composition according to the present invention comprises xBaO--yTiO.sub.2 --zREO.sub.3/2 (wherein x, y, and z are based on mole % and satisfy the following expressions: 5.ltoreq.x.ltoreq.15, 52.5.ltoreq.y.ltoreq.70, 15.ltoreq.z.ltoreq.42.5, and x+y+z=100) as a primary component, and Bi.sub.2 O.sub.3 in an amount of about 3-30 wt. % with respect to 100 parts by weight of the primary component.
In the dielectric ceramic composition of the present invention, the alkaline earth metal oxide contained in the above-described glass composition may comprise BaO and at least one species selected from the group consisting of SrO, CaO and MgO, with the compositional proportions thereof preferably fall within the following ranges: about 35 wt. % or less SrO; about 35 wt. % or less CaO; about 20 wt. % or less MgO; and about 40-95 wt. % BaO.
Preferably, the BaO--TiO.sub.2 --REO.sub.3/2 --Bi.sub.2 O.sub.3 -based ceramic composition in the dielectric ceramic composition of the present invention accounts for about 75-95 wt. %, the glass composition accounts for about 2-20 wt. % and CuO accounts for about 5 wt. % or less.
In the dielectric ceramic composition of the present invention, the glass composition contains about 0.5-10 wt. % Li.sub.2 O and may further contain at least one additive selected from among TiO.sub.2, CaTiO.sub.3, SrTiO.sub.3, and Nd.sub.2 Ti.sub.2 O.sub.7. In this case, preferably, the BaO--TiO.sub.2 --REO.sub.3/2 --Bi.sub.2 O.sub.3 -based ceramic composition accounts for about 50-98 wt. %, the glass composition accounts for about 2-20 wt. %, the additive accounts for about 30 wt. % or less, and the CuO accounts for about 3 wt. % or less.
In another aspect of the present invention, there is provided a ceramic electronic element which employs the dielectric ceramic composition of the present invention.
In yet another aspect of the present invention, there is provided an LC composite element which employs the dielectric ceramic composition of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a ternary diagram of a BaO--TiO.sub.2 --REO.sub.3/2 ceramic composition.
FIG. 2 is an exploded perspective view of an LC filter serving as an example of the ceramic electronic element according to the present invention.
FIG. 3 is a perspective view of the LC filter illustrated in FIG. 2.
FIG. 4 is an equivalent circuit diagram of the LC filter illustrated in FIG. 3.

DESCRIPTION OF PREFERRED EMBODIMENTS
When a dielectric ceramic composition is formed of a mixture of a BaO--TiO.sub.2 --REO.sub.3/2 -based ceramic composition (wherein RE represents a rare earth element) and an SiO.sub.2 --B.sub.2 O.sub.3 -alkaline earth metal oxide-Li.sub.2 O glass composition, the dielectric ceramic composition can be sintered at a temperature lower than the melting point of an electric conductor containing, as a primary component, a low-specific-resistance metal selected from silver, gold and copper. Moreover, there can be obtained a dielectric ceramic composition having a high relative dielectric constant within the high-frequency region, particularly within the microwave region and the millimeter wave region, and excellent temperature stability.
Addition of CuO, as an auxiliary component, to the mixture comprising the ceramic composition and glass composition further lowers sintering temperature of the resultant mixture and increases the Q value and the relative dielectric constant thereof.
Moreover, TiO.sub.2, CaTiO.sub.3 and SrTiO.sub.3 have a negative temperature-dependent characteristic of dielectric constant and Nd.sub.2 Ti.sub.2 O.sub.7 has a positive temperature-dependent characteristic of dielectric constant. Therefore, addition thereof in an appropriate amount enables control of the temperature coefficient of dielectric constant of the produced dielectric ceramic composition and ceramic electronic element.
Therefore, 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 dielectrics or multilayer circuit boards containing such an internal electrode and having excellent high-frequency characteristics and a desirable temperature coefficient of dielectric constant. An electronic apparatus such as an LC resonator, an LC filter or a laminated capacitors having a high Q value can be further miniaturized by use of the lamination method and the dielectric ceramic composition.
Reasons why the above compositional proportions are preferred will next be described.
The glass composition comprises about 13-50 wt. % SiO.sub.2, about 3-30 wt. % B.sub.2 O.sub.3, about 40-80 wt. % alkaline earth metal oxide (BaO, SrO, CaO, MgO) and about 0.1-10 wt. % Li.sub.2 O.
When the SiO.sub.2 content is in excess of about 50 wt. %, the glass softening temperature increases drastically and ceramic compositions containing SiO.sub.2 in such a large amount cannot be sintered, whereas when the SiO.sub.2 content is less than about 13 wt. %, moisture resistance is adversely affected.
In addition, B.sub.2 O.sub.3 contained in the glass composition lowers the glass viscosity and accelerates sintering of a dielectric ceramic composition. However, when the B.sub.2 O.sub.3 content 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 1000.degree. C. or less.
Furthermore, the alkaline earth metal oxide promotes reaction between the ceramic composition and the glass composition and lowers the softening point of the glass composition. However, when the alkaline earth metal oxide content is less than about 40 wt. %, the sinterability decreases to induce difficulty in sintering at 1000.degree. C. or less, whereas when it is in excess of about 80 wt. %, moisture resistance is adversely affected.
When the BaO content of 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 decreases. Moisture resistance is unsatisfactory when the composition fails to contain at least one species selected from among SrO, CaO and MgO in an amount of at least about 5 wt. %. Li.sub.2 O lowers the glass softening point. However, when the Li.sub.2 O content is less than about 0.1 wt. %, the softening point increases drastically to prevent sintering, whereas when it is in excess of about 10 wt. %, moisture resistance is unsatisfactory.
Furthermore, TiO.sub.2, CaTiO.sub.3, SrTiO.sub.3 and Nd.sub.2 Ti.sub.2 O.sub.7 are added in an amount of about 30 wt. % or less, since addition thereof in excess of about 30 wt. % deteriorates sinterability.
The compositional proportions of the primary component of the ceramic composition will next be described.
FIG. 1 shows a ternary diagram referring to the compositional ranges of a BaO--TiO.sub.2 --REO.sub.3/2 -based ceramic composition that is the primary component of the dielectric ceramic composition of the present invention (Bi.sub.2 O.sub.3 at 10 wt. %). The compositional proportions of the BaO--TiO.sub.2 --REO.sub.3/2 -based ceramic composition, when represented by xBaO--yTiO.sub.2 --zREO.sub.3/2, fall within the ranges satisfying 5.ltoreq.x.ltoreq.15, 52.5.ltoreq.y.ltoreq.70, 15.ltoreq.z.ltoreq.42.5, and x+y+z=100, wherein each of x, y, and z is based on mole %, and the composition preferably falls within the domain indicated by the hatching in FIG. 1. A composition falling within the domain A indicated in FIG. 1 is difficult to sinter and merely provides a porous ceramic at 1400.degree. C., which is normally the temperature required for sintering. When a composition falls within the domain B, temperature-dependent characteristics, i.e., the temperature coefficient of change in capacitance of a capacitor formed inside a multilayer circuit board, decreases drastically to a negative value. When a composition falls within the domain C, the relative dielectric constant is extremely small and sinterability is variable. Furthermore, when a composition falls within the domain D, the temperature coefficient of change in capacitance increases drastically to a positive value and the relative dielectric constant decreases.
The dielectric ceramic composition according to the present invention contains Bi.sub.2 O.sub.3. Incorporation of Bi.sub.2 O.sub.3 produces a high-frequency dielectric ceramic composition having more stable characteristics and makes the sintering temperature lower. However, when Bi.sub.2 O.sub.3 is incorporated in an amount in excess of about 30 wt. %, the Q value decreases. Thus, Bi.sub.2 O.sub.3 is preferably incorporated in an amount of about 3-30 wt. % to a BaO--TiO.sub.2 --NdO.sub.3/2 ceramic composition which falls within the compositional domain indicated by the hatching in FIG. 1.
When the amount of the glass composition contained in the dielectric ceramic composition is less than about 2 wt. %, sintering is difficult, whereas when it is in excess of about 20 wt. %, moisture resistance decreases to lower the relative dielectric constant.
CuO also works as a sintering aid. When the CuO content is in excess of about 5 wt. %, the Q value decreases to shift the temperature coefficient of capacitance to a high positive value.
The above-described objects of the present invention, as well as other objects, features, and advantages thereof, will become more clear from the below-described detailed description of the modes for carrying out the invention with reference to the accompanying drawings.
EXAMPLES
Example 1
First, ceramic compositions were produced.
BaCO.sub.3, TiO.sub.2 and REO.sub.3/2 (RE represents a rare earth element) were weighed and mixed together to obtain mixtures having compositional ratios with regard to BaO, TiO.sub.2 and REO.sub.3/2 indicated in the columns showing the primary component in Table 1. Then, Bi.sub.2 O.sub.3 powder was added to each of the above mixtures so as to realize a compositional ratio (weight ratio to 100 parts of the primary component) indicated in the column showing the secondary component in Table 1, and the resultant mixture was mixed thoroughly. The mixture was calcined at 1150.degree. C. for one hour to form a calcined compact, which was then crushed and mixed. The mixture was then fired at 1300.degree. C., to thereby obtain a ceramic. High-frequency ceramic compositions S1 through S25 and S42 serving as BaO--TiO.sub.2 --REO.sub.3/2 --Bi.sub.2 O.sub.3 -based ceramic compositions and 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 dielectric constant (ppm/.degree. C.). Results of the measurements are shown in Table 1.
These ceramic compositions were used to prepare dielectric ceramic compositions shown below. In Table 1, element symbols in the column labeled REO.sub.3/2 represent the corresponding rare earth elements and the amount of Bi.sub.2 O.sub.3 is represented by wt. % based on 100 parts by weight of the primary component.
TABLE 1__________________________________________________________________________ Secondary Temperature component coefficient of Ceramic (weight Relative dielectric Composition Primary component (mole ratio) ratio) dielectric Q constantNo. BaO TiO.sub.2 ReO.sub.3/2 Bi.sub.2 O.sub.3 constant (.epsilon.) at 1 GHz (ppm/.degree. C.)__________________________________________________________________________S1 13 61 Nd:26 15 105 4000 +35 S2 15 70 Nd:15 15 95 2000 -60 S3 20 55 Nd:25 15 90 2500 -80 S4 5 70 Nd:25 15 75 3000 -50 S5 5 55 Nd:40 15 64 2000 +40 S6 20 60 Nd:20 15 110 3000 -90 S7 10 75 Nd:15 15 82 2500 -100 S8 2 65 Nd:33 15 60 2000 +30 S9 10 50 Nd:40 10 57 2000 +60 S10 13 61 Nd:26 0 65 3500 -10 S11 13 61 Nd:26 3 82 3800 -10 S12 13 61 Nd:26 30 101 3000 +60 S13 13 61 Nd:26 35 95 500 +80 S14 13 65 Nd:22 3 79 3000 -5 S15 13 60 Nd:27 3 65 3200 +30 S16 25 60 Nd:20 3 79 1800 -90 S17 2 5 Nd:93 3 39 2000 +50 S18 13 61 La:26 15 105 3000 0 S19 13 61 Pr:26 15 99 4000 -5 S20 13 61 Sm:26 15 97 4500 +5 S21 13 61 26 15 99 4000 0 (La/Nd = 0.5/0.5) S22 13 61 26 15 99 4000 0 (Pr/Nd = 0.25/0.75) S23 13 65 22 15 105 3000 -5 (Pr/Nd = 0.5/0.75) S24 13 65 22 15 103 4000 +5 (Pr/Nd = 0.25/0.5 S25 13 61 26 15 96 4500 +10 (Sm/Nd = 0.5/0.5) S42 15 75 Nd:10 15 85 2000 -120__________________________________________________________________________
With regard to glass compositions, B.sub.2 O.sub.3, SrO, CaO, MgO, Bi.sub.2 O.sub.3, SiO.sub.2 and Li.sub.2 O were weighed and sufficiently mixed together to obtain mixtures having compositional ratios (weight ratios) indicated in Table 2. Each of the mixtures was melted at 1100-1400.degree. C. and quenched by pouring into water, then wet-milled to thereby obtain glass compositions G1 through G30. In Table 2, R represents the alkaline earth metal. The total amount of RO and amounts of B.sub.2 O.sub.3, SiO.sub.2 and Li.sub.2 O are based on wt. % of the corresponding glass compositions.
TABLE 2______________________________________Alkaline earth metal oxide ROGlass Total % by weight of respective composition amount components in RONo. of RO BaO SrO CaO MgO B.sub.2 O.sub.3 SiO.sub.2 Li.sub.2 O______________________________________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 62.9 82 11 5 2 14 21 0.1 G16 57 82 11 5 2 12 21 10 G17 55 82 11 5 2 11 19 15 G18 61 30 35 25 10 14 23 2 G19 61 40 33 24 3 14 23 2 G20 61 95 2 2 1 14 23 2 G21 61 100 0 0 0 14 23 2 G22 61 85 0 13 2 14 23 2 G23 61 45 35 18 2 14 23 2 G24 61 40 45 13 2 14 23 2 G25 61 85 13 0 2 14 23 2 G26 61 50 12 35 2 14 23 2 G27 61 40 13 45 2 14 23 2 G28 61 83 12 5 0 14 23 2 G29 61 60 15 5 20 14 23 2 G30 61 55 15 5 25 14 23 2______________________________________
Then, to each of the thus-obtained ceramic compositions S1 through S25, a glass composition selected from G1 through G30 and CuO powder were added so as to produce mixtures having compositional ratios indicated in Tables 3 and 4, which were then mixed thoroughly to provide raw mixtures. To the raw mixtures, appropriate amounts of a binder, plasticizer and 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 .mu.m, and the produced ceramic green sheet was cut into pieces having a size of 30 mm.times.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 were obtained by firing the corresponding pressed sheets in air at 900.degree. C. for one hour.
The dielectric ceramics obtained as above were subjected to measurement of relative dielectric constant, Q value and temperature coefficient of change in dielectric constant (ppm/.degree. C.). The results of measurement are shown in Tables 3 and 4. The amounts of components in Tables 3 and 4 are based on wt. % in the corresponding dielectric ceramic compositions. The relative dielectric constant was measured at a frequency of 1 MHz.
TABLE 3__________________________________________________________________________ Temperature Relative coefficient of Ceramic Glass Firing dielectric change in Sample composition composition CuO temperature constant capacitanceNo. No. Amount No. Amount content (.degree. C.) (.epsilon.) Q (ppm/.degree. C.) Remarks__________________________________________________________________________ 1 S1 88.5 G1 10 1.5 900 78 3700 -5 2 S2 88.5 G1 10 1.5 900 67 1900 -40 3 S3 88.5 G1 10 1.5 900 62 2000 -55 4 S4 88.5 G1 10 1.5 900 58 2500 -54 5 S5 88.5 G1 10 1.5 900 52 1800 +10 6 S6 88.5 G1 10 1.5 900 82 2500 -110 7 S7 88.5 G1 10 1.5 900 58 1700 -130 8 S8 88.5 G1 10 1.5 900 40 1300 0 9 S9 88.5 G1 10 1.5 900 35 1000 +25 10* S10 88.5 G1 10 1.5 900 -- -- -- Not sintered 11 S11 88.5 G1 10 1.5 900 67 3000 -20 12 S12 88.5 G1 10 1.5 900 82 1500 +25 13 S13 88.5 G1 10 1.5 900 73 800 +40 14* S1 88.5 G2 10 1.5 900 -- -- -- Not sintered 15 S1 88.5 G3 10 1.5 900 69 3500 -15 16 S1 88.5 G4 10 1.5 900 78 3000 -20 17* S1 88.5 G5 10 1.5 900 80 2500 -30 Poor moisture resistant 18* S1 88.5 G6 10 1.5 900 -- -- -- Not sintered 19 S1 88.5 G7 10 1.5 900 72 4000 -5 20 S1 88.5 G8 10 1.5 900 76 2500 -10 21* S1 88.5 G9 10 1.5 900 77 2400 -20 Poor moisture resistance 22* S1 88.5 G10 10 1.5 900 81 2100 -20 Poor moisture resistance 23 S1 88.5 G11 10 1.5 900 79 2700 -10 24 S1 88.5 G12 10 1.5 900 75 3000 +5 25* S1 88.5 G13 10 1.5 900 -- -- -- Not sintered 26* S1 88.5 G14 10 1,5 900 -- -- -- Not sintered 27 S1 88.5 G15 10 1.5 900 73 3800 +10 28 S1 88.5 G16 10 1.5 900 79 2800 -20 29* S1 88.5 G17 10 1.5 900 80 2000 -20 Poor moisture resistance 30 S1 88.5 G18 10 1.5 900 -- -- -- Insufficient ly sintered 31 S1 88.5 G19 10 1.5 900 69 3000 +15 32 S1 88.5 G20 10 1.5 900 80 3200 -10 33 S1 88.5 G21 10 1.5 900 81 3100 -5 Insufficient moisture resistance 34 S1 88.5 G22 10 1.5 900 79 320 -5 35 S1 88.5 G23 10 1.5 900 70 3000 +15__________________________________________________________________________ *Outside the scope of the invention
TABLE 4__________________________________________________________________________ Temperature Relative coefficient of Ceramic Glass Firing dielectric change in Sample composition composition CuO temperature constant capacitanceNo. No. Amount No. Amount content (.degree. C.) (.epsilon.) Q (ppm/.degree. C.) Remarks__________________________________________________________________________36 S1 88.5 G24 10 1.5 900 -- -- -- Insufficiently sintered 37 S1 88.5 G25 10 1.5 900 77 3200 0 38 S1 88.5 G26 10 1.5 900 68 2800 +20 39 S1 88.5 G27 10 1.5 900 -- -- -- Insufficiently sintered 40 S1 88.5 G28 10 1.5 900 79 3000 +5 41 S1 88.5 G29 10 1.5 900 63 3300 0 42 S1 88.5 G30 10 1.5 900 -- -- -- Insufficiently sintered 43 S1 90.0 G1 10 0 900 63 2000 +15 44 S1 89.8 G1 10 0.2 900 72 3000 +5 45 S1 87.0 G1 10 3.0 900 79 2400 -10 46 S1 87.0 G1 10 5.0 900 85 100 +210 47 S1 97.0 G1 1.5 2.5 900 -- -- -- Insufficiently sintered 48 S1 95.5 G1 2 2.5 900 82 3000 -50 49 S1 78.5 G1 20 1.5 900 55 1200 +30 50 S1 68.5 G1 30 1.5 900 43 500 +60 Insufficient moisture resistance 51 S14 88.5 G1 10 1.5 900 52 2000 -5 52 S15 88.5 G1 10 1.5 900 46 2700 +35 53 S16 88.5 G1 10 1.5 900 58 1500 -110 54 S17 88.5 G1 10 1.5 900 25 1200 +45 55 S18 88.5 G1 10 1.5 900 80 3000 -20 56 S19 88.5 G1 10 1.5 900 77 3300 -15 57 S20 88.5 G1 10 1.5 900 75 3500 +15 58 S21 88.5 G1 10 1.5 900 78 3600 -10 59 S22 88.5 G1 10 1.5 900 77 3400 -15 60 S23 88.5 G1 10 1.5 900 82 3000 -10 61 S24 88.5 G1 10 1.5 900 81 3000 -5 62 S25 88.5 G1 10 1.5 900 76 3000 +5 63 S1 90.0 G4 10 0 900 64 1300 -15 64 S1 96.0 G7 4 0 900 -- -- -- Insufficiently sintered 65 S1 87.5 G12 12 0.5 900 66 3000 -10 66 S1 87.0 G16 12 1.0 900 73 2000 -10 67 S1 88.0 G4 12 0 900 65 1300 -20 119 S42 88.5 G1 10 1.5 900 63 1000 -150__________________________________________________________________________ *: Outside the scope of the invention
As shown in the sample Nos. 1 through 5, 11, 12, 15, 16, 19, 20, 23, 24, 27, 28, 31, 32, 34, 35, 37, 38, 40, 41, 43 through 45, 48, 49, 51, 52, 55 through 63, and 65 through 67, the dielectric ceramic compositions of the present invention having a composition falling within the preferable compositional ranges have excellent characteristics, i.e., a firing temperature as low as 900.degree. C. or less, a high relative dielectric constant, a small absolute value of temperature coefficient of change in capacitance (ppm/.degree. C.) and a high Q value.
The comparison of the sample Nos. 43, 63, and 67 with the other samples reveals that addition of CuO increases Q value and dielectric constant.
In the Tables, the term "not sintered" denotes that sintering is impossible, and the term "insufficiently sintered" denotes that sintering may be possible under appropriate conditions, although the sinterability is low under the conditions of the present invention. The term "poor moisture resistance" refers to moisture resistance which is so poor as to prevent practical use, and the term "insufficient moisture resistance" refers to moisture resistance which is sufficiently applicable in practice under specific conditions, although it is slightly low.
In contrast, as shown in sample Nos. 10, 14, 17, 18, 21, 22, 25, 26, and 29, the dielectric ceramic compositions having a composition falling outside the compositional range of the present invention could not be sintered or were sintered insufficiently to yield poor moisture resistance.
CuO incorporated as an auxiliary component may be added by preparing glass compositions containing CuO so as to have compositional proportions shown in Tables 3 and 4 and adding the thus-prepared compositions to high-frequency ceramic compositions as well as adding CuO, as described in the example, to mixtures of the ceramic compositions and the glass compositions, to exhibit equivalent effects.
Example 2
The ceramic electronic element according to the present invention will next be described by way of example with reference to FIGS. 2 through 4. In this Example, an LC filter 10 was produced as an electronic element. First, a slurry was prepared from the ceramic composition of sample No. 1 in Example 1 shown in Table 3 and cast into a ceramic green sheet having a thickness of 40 .mu.m by use of a doctor blade. The green sheet was dried and punched to thereby provide green sheets 12 having a predetermined size. Onto the green sheets, there were provided capacitor patterns 14, coil patterns 16, etc. shown in FIG. 2 by use of an Ag paste and through screen printing. Holes 18 to make via-holes were opened by use of a puncher and filled with an Ag paste.
Then, the green sheets were laminated and pressed to thereby provide a laminate, which was fired at 900.degree. C. External electrodes 21, 22, 23, and 24 were formed on the fired laminate to provide an LC filter, of which a perspective view is shown in FIG. 3 and an equivalent circuit diagram is shown in FIG. 4.
Similarly, an LC filter was produced from the ceramic composition of sample No. 43 in Example 1 in Table 4.
Thus, in all cases, LC composite elements having a high dielectric constant and Q value were obtained through a lamination method.
Similarly, other LC composite elements and ceramic electronic elements may be obtained by use of the dielectric ceramic composition of the present invention.
Example 3
Another example of the dielectric ceramic composition according to the present invention will next be described. BaCO.sub.3, TiO.sub.2 and RE.sub.2 O.sub.3 (RE represents a rare earth element) were weighed and mixed together, to obtain mixtures having compositional ratios with regard to BaO, TiO.sub.2 and REO.sub.3/2 indicated in the columns showing the primary component in Table 5. Then, Bi.sub.2 O.sub.3 powder was added to each of the above mixtures so as to realize a compositional ratio (weight ratio to 100 parts of the primary component) indicated in the column showing the secondary component in Table 5, and the resultant mixture was mixed thoroughly. The mixture was calcined at 1150.degree. C. for one hour to form a calcined compact, which was then crushed and mixed. The mixture was then fired at 1300-1400.degree. C., to thereby obtain a ceramic. High-frequency ceramic compositions S26 through S41 serving as BaO--TiO.sub.2 --REO.sub.3/2 --Bi.sub.2 O.sub.3 -based ceramic compositions and 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 (ppm/.degree. C.). Results of the measurement are shown in Table 1. These ceramic compositions were used to prepare dielectric ceramic compositions shown below. In Table 5, element symbols in the column labeled REO.sub.3/2 represent the corresponding rare earth elements and the amount of Bi.sub.2 O.sub.3 is represented by wt. % with respect to 100 parts by weight of the primary component.
TABLE 5__________________________________________________________________________ Secondary Temperature First component Relative coefficient ceramic (weight Dielectric Q of dielectric composition Primary component (mole ratio) ratio) constant at constantNo. BaO TiO.sub.2 ReO.sub.8/2 Bi.sub.2 O.sub.3 (.epsilon.) 1 GHz (ppm/.degree. C.)__________________________________________________________________________S26 13 61 Nd:26 10 105 4000 +35 S27 15 70 Nd:15 10 95 2000 -60 S28 15 55 Nd:30 10 90 2500 -80 S29 5 70 Nd:25 15 75 3000 -50 S30 5 55 Nd:40 10 64 2000 +40 S31 20 60 Nd:20 10 110 3000 -90 S32 10 75 Nd:15 10 82 2500 -100 S33 2 65 Nd:33 10 60 2000 +30 S34 10 50 Nd:40 10 57 2000 +60 S35 13 61 Nd:26 0 65 3500 +40 S36 13 61 Nd:26 3 82 3800 +40 S37 13 61 Nd:26 20 101 3000 -20 S38 13 61 Nd:26 35 95 500 -80 S39 13 61 Pr:26 10 99 4000 -5 S40 13 61 Sm:26 10 97 4500 +5 S41 13 65 22 10 103 4000 +5 (Pr/Nd = 0.5/0.5)__________________________________________________________________________
With regard to glass compositions, B.sub.2 O.sub.3, SrO, CaO, MgO, Bi.sub.2 O.sub.3, SiO.sub.2 and Li.sub.2 O were weighed and sufficiently mixed together to obtain mixtures having compositional ratios (weight ratios) indicated in Table 6. Each of the mixtures was melted at 1100-1400.degree. C. and quenched by pouring into water, then wet-milled to thereby obtain glass compositions G31 through G44. In Table 6, R represents the alkaline earth metal. The total amount of RO and amounts of B.sub.2 O.sub.3, SiO.sub.2 and Li.sub.2 O are based on wt. % of the corresponding glass compositions.
TABLE 6______________________________________Alkaline earth metal oxide ROGlass Total Proportions of respective composition Amount components in RONo. of RO BaO SrO CaO MgO B.sub.2 O.sub.3 SiO.sub.2 Li.sub.2 O______________________________________G31 61 82 11 5 2 14 23 2 G32 30 82 11 5 2 29 39 2 G33 40 82 11 5 2 25 33 2 G34 80 82 11 5 2 5 13 2 G35 90 82 11 5 2 3 5 2 G36 67 82 11 5 2 1 30 2 G37 50 82 11 5 2 30 18 2 G38 44 82 11 5 2 40 14 2 G39 40 82 11 5 2 8 50 2 G40 30 82 11 5 2 8 60 2 G41 63 82 11 5 2 14 23 0 G42 62.5 82 11 5 2 14 23 0.5 G43 57 82 11 5 2 12 21 10 G44 55 82 11 5 2 11 19 15______________________________________
Then, to each of the thus-obtained ceramic compositions S26 through S41, a glass composition selected from G31 through G44 and CuO powder were added so as to produce mixtures having compositional ratios indicated in Tables 7 and 8, which were then mixed thoroughly to provide raw mixtures. To the raw mixtures, TiO.sub.2, CaTiO.sub.3, SrTiO.sub.3 and Nd.sub.2 Ti.sub.2 O.sub.7 were added so as to produce mixtures having the weight ratios indicated in Tables 7 and 8 and then an appropriate amount 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 .mu.m, and the produced ceramic green sheet was cut into pieces having a size of 30 mm.times.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. 68 to 118 were obtained by firing the corresponding pressed sheets in air at not more than 900.degree. C. for one hour.
The dielectric ceramics obtained as described above were subjected to measurement of relative dielectric constant, Q value and temperature coefficient of change in dielectric constant (ppm/.degree. C). The results of measurement are shown in Tables 7 and 8. The amounts of components in Tables 7 and 8 are based on wt. % in the corresponding dielectric ceramic compositions. The relative dielectric constant was measured at a frequency of 1 MHz.
TABLE 7__________________________________________________________________________ Temperature Relative coefficient of Ceramic Glass Firing dielectric change in Sample composition composition Additive content CuO temperature constant capacitanceNo. No. Amount No. Amount (wt %) Content (.degree. C.) (.epsilon.) Q (ppm/.degree. C.) Remarks__________________________________________________________________________68 S26 99.0 G43 0.5 TiO.sub.2 :0.1 0.4 900 -- -- -- Insufficiently sintered 69 S26 97.5 G43 2.0 TiO.sub.2 :0.1 0.4 900 90 1500 +10 70 S26 68.5 G31 20 TiO.sub.2 :10 1.5 900 58 1200 -10 71 S26 58.5 G31 30 TiO.sub.2 :10 1.5 900 47 500 +20 72 S26 80.0 G31 10 TiO.sub.2 :10 0 900 67 2000 -25 73 S26 77.0 G31 10 TiO.sub.2 :10 3.0 900 85 3500 -50 74 S26 75.0 G31 10 TiO.sub.2 :10 5.0 900 105 2000 -200 75 S26 86.5 G31 10 TiO.sub.2 :2 1.5 900 79 3700 -15 76 S26 78.5 G31 10 TiO.sub.2 :10 1.5 900 81 3800 -45 77 S26 58.5 G31 10 TiO.sub.2 :30 1.5 900 89 2800 -115 78 S26 48.5 G31 10 TiO.sub.2 :40 1.5 900 -- -- -- Insufficiently sintered 79 S26 86.5 G31 10 CaTiO.sub.3 :2 1.5 900 82 3300 -35 80 S26 58.5 G31 10 CaTiO.sub.3 :30 1.5 900 93 2300 -75 81 526 48.5 G31 10 CaTiO.sub.3 :40 1.5 900 -- -- -- Insufficien tly sintered 82 S26 86.5 G31 10 SrTiO.sub.3 :2 1.5 900 82 3200 -45 83 S26 58.5 G31 10 SrTiO.sub.3 :30 1.5 900 125 1800 -145 84 S26 48.5 G31 10 SrTiO.sub.3 :40 1.5 900 -- -- -- Insufficiently sintered 85 S26 78.5 G31 10 TiO.sub.2 + SrTiO.sub.3 :5 + 5 1.5 900 98 2500 -95 86 S26 48.5 G31 10 TiO.sub.2 + SrTiO.sub.3 :20 + 1.5 900 -- -- -- Insufficiently 20 sintered 87 S26 83.5 G31 10 Nd.sub.2 Ti.sub.2 O.sub.7 :5 1.5 900 75 3200 88 S26 78.5 G31 10 Nd.sub.2 Ti.sub.2 O.sub.7 :10 1.5 900 73 2900 +15 89 S26 58.5 G31 10 Nd.sub.2 Ti.sub.2 O.sub.7 :30 1.5 900 63 1800 +40 90 S26 48.5 G31 10 Nd.sub.2 Ti.sub.2 O.sub.7 :40 1.5 900 -- -- -- Insufficien tly sintered 91 S27 78.5 G31 10 TiO.sub.2 :10 1.5 900 73 1700 -140 92 S28 78.5 G31 10 TiO.sub.2 :10 1.5 900 70 2000 -150 93 S29 78.5 G31 10 TiO.sub.2 :10 1.5 900 51 2500 -130__________________________________________________________________________ *: Outside the scope of the invention
TABLE 8__________________________________________________________________________ Temperature Relative coefficient of Ceramic Glass Firing dielectric change in Sample composition composition Additive content CuO temperature constant capacitanceNo. No. Amount No. Amount (wt %) Content (.degree. C.) (.epsilon.) Q (ppm/.degree. C.) Remarks__________________________________________________________________________94 S30 78.5 G31 10 TiO.sub.2 :10 1.5 900 45 1100 -40 95 S31 78.5 G31 10 TiO.sub.2 :10 1.5 900 85 2000 -160 96 S32 78.5 G31 10 TiO.sub.2 :10 1.5 900 58 1800 -200 97 S33 78.5 G31 10 TiO.sub.2 :10 1.5 900 39 1000 -50 98 S34 78.5 G31 10 TiO.sub.2 :10 1.5 900 37 1000 -20 *99 S35 78.5 G31 10 TiO.sub.2 :10 1.5 900 45 2500 -40 100 S36 78.5 G31 10 TiO.sub.2 :10 1.5 900 60 3000 -40 101 S37 78.5 G31 10 TiO.sub.2 :10 1.5 900 77 2000 -80 102 S38 78.5 G31 10 TiO.sub.2 :10 I.5 900 70 300 -160 103 S39 86.5 G31 10 TiO.sub.2 :10 1.5 900 75 2800 -80 104 S40 58.5 G31 10 TiO.sub.2 :10 1.5 900 73 3000 -70 105 S41 58.5 G31 10 TiO.sub.2 :10 1.5 900 80 2700 -70 *106 S26 78.5 G32 10 TiO.sub.2 :10 1.5 900 -- -- -- Not sintered 107 S26 78.5 G33 10 TiO.sub.2 :10 l.5 900 75 3000 -30 108 S26 78.5 G34 10 TiO.sub.2 :10 1.5 900 83 3600 -50 *109 S26 78.5 G35 10 TiO.sub.2 :10 1.5 900 84 3500 -55 Poor moisture resistance *110 S26 78.5 G36 10 TiO.sub.2 :10 1.5 900 -- -- -- Not sintered 111 S26 78.5 G37 10 TiO.sub.2 :10 1.5 900 82 3500 -45 *112 S26 78.5 G38 10 TiO.sub.2 :10 1.5 900 83 3500 -50 Poor moisture resistance 113 S26 78.5 G39 10 TiO.sub.2 :10 1.5 900 78 4000 -40 *114 S26 78.5 G40 10 TiO.sub.2 :10 1.5 900 -- -- -- Not sintered *115 S26 78.5 G41 10 TiO.sub.2 :10 1.5 900 -- -- -- Not sintered 116 S26 78.5 G42 10 TiO.sub.2 :10 1.5 900 76 3300 -40 117 S26 78.5 G43 10 TiO.sub.2 :10 1.5 900 83 3500 -45 *118 S26 78.5 644 10 TiO.sub.2 :10 1.5 900 84 3000 -50 Poor moisture resistance__________________________________________________________________________ *: Outside the scope of the invention
As shown in the sample Nos. 69 through 77, 79, 80, 82, 83, 85, 87 through 89, 91 through 98, 100 through 105, 107, 108, 111, 113, 116, and 117 in Tables 7 and 8, the dielectric ceramic compositions of the present invention have excellent characteristics, i.e., a firing temperature as low as 900.degree. C. or less, a high relative dielectric constant and a high Q value. Control of species and amount of TiO.sub.2, CaTiO.sub.3, SrTiO.sub.3, and Nd.sub.2 Ti.sub.2 O.sub.7 serving as additives provides desired temperature coefficient of dielectric constant (ppm/.degree. C.).
In contrast, the dielectric ceramic compositions of sample Nos. 106, 109, 110, 112, 114, 115, and 118, are out of the scope of the present invention due to the reasons cited in the remarks indicated in Tables 7 and 8.
CuO incorporated as an auxiliary component may be added by preparing glass compositions containing CuO so as to have compositional proportions shown in Tables 7 and 8 and adding the thus-prepared compositions to high-frequency ceramic compositions as well as adding CuO, as described in the example, to mixtures of the ceramic compositions and the glass compositions, to exhibit equivalent effects.
The dielectric ceramic composition according to the present invention can be sintered at temperature lower than the melting point of an electric conductor containing, as a primary component, a low-specific-resistance metal selected from silver, gold and copper. Moreover, there can be obtained a dielectric ceramic composition having a high relative dielectric constant (.epsilon.) within a high-frequency region, particularly within the microwave region and the millimeter wave region, and excellent temperature stability with respect to dielectric constant and capacitance.
Addition of CuO, as an auxiliary component, to the mixture comprising a ceramic composition and a glass composition further lowers sintering temperature of the resultant mixture and increases the Q value and the dielectric constant thereof.
Moreover, addition of appropriate amounts of TiO.sub.2, CaTiO.sub.3 and SrTiO.sub.3 having a negative temperature-dependent characteristic of dielectric constant and Nd.sub.2 Ti.sub.2 O.sub.7 having a positive temperature-dependent characteristic of dielectric constant enables control of the temperature coefficient of dielectric constant of the produced dielectric ceramic compositions to a desired value.
Therefore, 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 dielectrics or multilayer circuit boards containing such an internal electrode and having excellent high-frequency characteristics and a desirable temperature coefficient of dielectric constant. Electronic apparatus such as an LC resonator, an LC filter or a laminated capacitor having a high Q value can be further miniaturized by use of the lamination method and the dielectric ceramic composition.

Number	Date	Country	Kind
10-063978	Feb 1998	JPX
10-360397	Dec 1998	JPX

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5292694	Abe et al.	Mar 1994
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5485132	Abe et al.	Jan 1996
5488019	Abe et al.	Jan 1996
5493262	Abe et al.	Feb 1996
5635435	Shibata et al.	Jun 1997

Dielectric ceramic composition and ceramic electronic element using the same

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