Non-reducing dielectric ceramic composition

FIELD OF THE INVENTION
The present invention relates to a non-reducing dielectric ceramic composition, and in particular to a non-reducing dielectric ceramic composition to be used in multilayer ceramic capacitor, in which a base metal such as nickel is used as internal electrode.
BACKGROUND OF THE INVENTION
With rapid propagation of various types of electronic devices, there is a tendency that these devices are increasingly produced in compact and lightweight design. In particular, this tendency toward compact and lightweight design is more remarkable in the electronic devices of portable type to be used in camera-integrated video tape recorder, portable telephone set, note-book personal computer, palm-top computer, etc.
In such tendency toward compact and lightweight electronic products, the component parts for these devices are also increasingly produced in compact and lightweight design. The means to mount the electronic components are also changing from the technique for inserting and soldering pins, i.e. electronic parts, to be used in through-hole on conventional type printed board to surface mounting technology (SMT), i.e. the technique for mounting and soldering electronic parts on land of electro-conductive pattern on printed board.
The electronic parts used in this SMT are generally called surface mounting devices (SMD). Not only semiconductor components, but also capacitor, resistor, inductor, filter, etc. are included in them. Among them, small components such as capacitor and resistor are called chip components. The most representative of them is multi-layer ceramic capacitor.
FIG. 1 shows a partially cutaway perspective view showing structure of a multilayer ceramic capacitor.
The multilayer ceramic capacitor 1 is in form of rectangular parallelopiped, and terminal electrodes 3 and 4 are mounted on a pair of opposed surfaces of multilayer ceramic capacitor body 1, which is in form of rectangular parallelopiped.
In the multi layer ceramic capacitor main unit 2, four internal electrodes 5, 6, 7 and 8 are formed among laminated BaTiO.sub.3 dielectric layers 9, 10 and 11, and dielectric material layers 12 and 13 made of dielectric material are laminated on upper surface of the internal electrode and lower surface of the internal electrode 8.
Every other of the internal electrodes 5, 6, 7 and 8 are connected to terminal electrodes. That is, the internal electrodes 6 and 8 are connected to a terminal electrode 4, and the internal electrodes 5 and 7 are connected to another terminal electrode 3. As a result, a capacitor is formed, which is connected in parallel between the internal electrodes 5 and 6, between the internal electrodes 6 and 7, and between the internal electrodes 7 and 8.
Each of the terminal electrodes 3 and 4 comprises a conductive layer, on which conductive paste containing glass frit is coated or printed and baked, and a plated layer coated on it or a metal cap press-fitted on it.
To manufacture multilayer ceramic capacitor, electrode paste to serve as an internal electrode is printed on a dielectric ceramic composition sheet, a plurality of such sheets are laminated and thermally pressed, the laminated product thus prepared is sintered in the air and a terminal electrode is mounted on it.
In this manufacturing method, the electrode paste to serve as the internal electrode of the capacitor and the dielectric ceramic composition are fired at the same time. For this reason, the material to be used as the internal electrode must have such property that the electrode is formed at the sintering temperature of the dielectric ceramic composition and there occurs no oxidation or no reaction with the dielectric ceramic composition when heated in the air.
As the material to meet the above requirements, noble metal such as platinum, palladium, etc. have been used in the past. However, these noble metals are very expensive and constitute major cause for the high cost of the multilayer ceramic capacitors.
In this connection, attempts have been made to use base metal such as nickel as internal electrode, while nickel is oxidized when it is fired in oxidizing atmosphere and also reacts with the dielectric ceramic composition. This hinders the formation of electrode.
A method to fire nickel in non-oxidative atmosphere to prevent oxidation is disclosed in the specification of U, S. Pat. No. 4,241,378, while, in this method, dielectric ceramic composition is reduced and specific resistance is extremely lowered. Thus, it is not suitable for the practical use as capacitor.
As a dielectric ceramic composition having satisfactory dielectric property such as dielectric constant (relative permitivity), BaTiO.sub.3 dielectric ceramic composition containing CaZrO.sub.2, MnO, etc. is disclosed in Japanese Patent Laid-Open Publication 62-2408, whereas this dielectric ceramic composition is fired in non-oxidizing atmosphere when it is reduced and has shorter life time.
The multilayer ceramic capacitor is manufactured through the following processes.
(1) Raw materials are weighed and blended so that composition after firing complies with the predetermined blending ratio.
(2) Wet mixing and pulverizing are performed.
(3) Dehydration and drying are performed.
(4) Adequate quantity of organic binder is added, and it is mixed and turned to enameled.
(5) This is coated on film by doctor blade method to form dielectric ceramic composition sheet.
(6) On the dielectric ceramic composition sheet thus prepared, nickel paste to serve as a material for internal electrode is formed by printing.
(7) The product is laminated and thermally pressed to obtain a multilayer product.
(8) The product is cut into a predetermined shape.
(9)Binder removal processing is performed.
(10) While controlling oxygen partial pressure, the product is fired.
(11) Re-oxidation is performed in neutral atmosphere.
(12) Terminal electrode is mounted.
As a non-reducing dielectric ceramic composition having longer life time, a dielectric ceramic composition containing {Ba.sub.A, Ca.sub.(1-A) }SiO.sub.3 (where 0.ltoreq.A.ltoreq.1) (hereinafter referred as "BCG") as an additive to BaTiO.sub.3, MnO, and Y.sub.2 O.sub.3 is disclosed in Japanese Patent Application 3-18261. However, in the multilayer ceramic capacitor produced using this dielectric ceramic composition, capacitance is varied due to temperature change.
In addition to the above, non-reducing dielectric ceramic composition is described in Japanese Patent Laid-Open Publications 61-248304 and 57-71866, U.S. Pat. No. 4,115,493, "Dielectric Materials for Base-Metal Multilayer Ceramic Capacitors" (Proceedings of the Electronics Division Fall Meeting, the American Ceramic Society, Oct. 13-16, 1985) by Y. SAKABE, T. TAKAGI, and K. WAKINO.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a non-reducing dielectric ceramic composition suitable for producing a multilayer ceramic capacitor, in which decrease of specific resistance and shortening of service life do not occur due to reduction of the dielectric ceramic composition even when nickel to be used for internal electrode is fired in neutral or reducing atmosphere to prevent oxidation, in which capacitance does not vary extensively due to temperature change.
To attain the above object, the non-reducing dielectric ceramic composition comprises 86.32 to 97.64 mols of BaTiO.sub.3, 0.01 to 10.00 mols of Y.sub.2 O.sub.3, 0.01 to 10.00 mols of MgO, and 0.001 to 0.200 mols of V.sub.2 O.sub.5.

BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows structure of a multilayer ceramic capacitor; and
FIG. 2 is a flow chart showing manufacturing process of the non-reducing dielectric ceramic composition.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the following, description will be given on the features of the present invention in connection with embodiments.
A flow chart showing manufacturing process of the non-reducing dielectric ceramic composition of the present invention is given in FIG. 2.
(1) BaTiO.sub.3, Y.sub.2 O.sub.3, MgO, V.sub.2 O.sub.5, MnO, Co.sub.2 O.sub.3, Co.sub.2 O.sub.3, etc. are weighed and blended to have the composition after firing as shown in Table 1 and Table 2.
TABLE 1__________________________________________________________________________Composition (mol %) Fir'g X.Y.Z Temp. BCG* X Y Z Total T.sub.2No. BaTiO.sub.3 Y.sub.2 O.sub.3 MgO V.sub.2 O.sub.5 A Q'ty MnO Cr.sub.2 O.sub.3 Co.sub.2 O.sub.3 Q'ty (.degree.C.)__________________________________________________________________________1 97.69 0 0.02 0.001 0.58 1.95 0.05 0.29 -- 0.34 14002 97.54 0.20 0.02 0 0.58 1.95 -- 0.29 -- 0.29 13803 96.88 0.58 0.02 0 0.58 1.94 0.29 0.29 -- 0.58 13804 97.04 0.58 0 0.005 0.58 1.94 0.15 0.29 -- 0.44 13805 96.25 0.58 0.96 0.005 0.58 1.92 0.29 -- -- 0.29 13406 96.89 0.58 0.01 0.30 0.58 1.94 0.29 0.29 -- 0.58 13407 96.61 0.58 0.01 1.00 0.58 1.93 0.29 0.58 -- 0.87 13408 96.39 0.58 0.96 0.005 0.58 1.93 0.14 -- -- 0.14 13009 92.68 0.58 4.63 0.002 0.58 1.85 0.28 -- -- 0.28 130010 95.86 0.01 1.92 0.005 0.58 1.92 0.29 -- -- 0.29 138011 87.43 0.53 10.00 0.001 0.58 1.77 0.27 -- -- 0.27 130012 85.95 0.53 11.50 0 0.58 1.76 0.26 -- -- 0.26 130013 96.48 0.58 0.96 0.005 0.58 1.93 0.05 -- -- 0.05 134014 96.67 0.29 0.97 0.005 0.58 1.93 0.14 -- -- 0.14 134015 97.28 0.58 0 0.001 0.58 1.95 -- 0.19 -- 0.19 132016 97.45 0.58 0.02 0 0.58 1.95 -- -- -- 0 132017 96.51 0.58 0.97 0.005 0.58 1.93 0.01 -- -- 0.01 132018 95.47 0.57 1.91 0.002 0.58 1.91 0.14 -- -- 0.14 134019 92.80 0.56 4.64 0.002 0.58 1.86 0.14 -- -- 0.14 134020 95.47 0.57 1.91 0.050 0.58 1.91 0.14 -- -- 0.14 134021 95.42 0.57 1.91 0.001 0.58 1.91 -- 0.19 -- 0.19 138022 97.24 0.58 0.05 0.050 0.58 1.94 -- 0.19 -- 0.19 138023 95.42 0.57 1.91 0.030 0.58 1.91 -- 0.19 -- 0.19 1360__________________________________________________________________________ *BCG: {Ba.sub.A, Ca.sub.(1-A }SiO.sub.3
TABLE 2__________________________________________________________________________Composition (mol %) Fir'g X.Y.Z Temp. BCG* X Y Z Total T.sub.2No. BaTiO.sub.3 Y.sub.2 O.sub.3 MgO V.sub.2 O.sub.5 A Q'ty MnO Cr.sub.2 O.sub.3 Co.sub.2 O.sub.3 Q'ty (.degree.C.)__________________________________________________________________________24 95.42 0.57 1.91 0.003 0.58 1.91 -- 0.19 -- 0.19 136025 95.42 0.57 1.91 0.010 0.58 1.91 -- 0.19 -- 0.19 136026 95.48 0.57 1.91 0.240 0.58 1.90 0.14 -- -- 0.14 136027 96.53 0.39 0.96 0.190 0.58 1.93 -- 0.19 -- 0.19 136028 97.26 0.58 0.01 0.002 0.58 1.95 -- 0.20 -- 0.20 132029 95.05 0.95 0.90 0.002 0.58 1.91 -- 0.19 -- 0.19 136030 91.58 4.58 1.83 0.002 0.58 1.83 -- 0.18 -- 0.18 134031 86.32 10.00 1.75 0.005 0.58 1.75 -- 0.18 -- 0.18 134032 85.39 11.00 1.72 0.001 0.58 1.72 -- 0.17 -- 0.17 134033 98.14 0.59 0.98 0.001 0.58 0 0.29 -- -- 0.29 138034 97.64 0.59 0.98 0.001 0.58 0.50 0.29 -- -- 0.29 132035 93.54 0.56 0.94 0.001 0.58 4.68 0.28 -- -- 0.28 134036 88.30 0.54 0.89 0.001 0.58 10.00 0.27 -- -- 0.27 130037 85.79 0.53 0.88 0.001 0.58 12.54 0.26 -- -- 0.26 130038 96.40 0.58 0.10 0.001 0.58 1.93 0.31 0.68 -- 1.00 136039 92.51 0.74 0.09 0.001 0.58 5.55 0.65 0.46 -- 1.11 136040 96.11 0.58 0.96 0.001 0.58 1.92 -- 0.29 0.14 0.43 136041 96.11 0.58 0.96 0.001 0.58 1.92 0.14 -- 0.29 0.43 132042 97.19 0.58 0.05 0.001 0.58 1.94 0.05 -- 0.19 0.24 136043 91.85 4.58 1.83 0.002 1.0 1.83 -- 0.18 -- -- 139044 91.58 4.58 1.83 0.002 0.7 1.83 -- 0.18 -- -- 136045 91.58 4.58 1.83 0.002 0.3 1.83 -- 0.18 -- -- 134046 91.58 4.58 1.83 0.002 0 1.83 -- 0.18 -- -- 1340__________________________________________________________________________ *BCG: {Ba.sub.A, Ca.sub.(1-A) }SiO.sub.3
As the starting materials, BaTiO.sub.3 is used, which is obtained by blending BaO and TiO.sub.2 at molar ratio of 1:1 and by chemical reaction at 900.degree. C. to 1200.degree. C. As this BaTiO.sub.3, powder (50% of the particles being in particle size 0.8.mu. to 1.2.mu.) prepared by solution method, or BaTiO.sub.3 obtained from BaCO.sub.3 and TiO.sub.2 pulverized by atomizer to particle size of about 1 .mu.m may be used.
(2) Wet mixing and pulverizing are performed.
(3) Dehydration and drying are performed.
(4) Adequate quantity of organic binder is added and mixed to turn it to enameled.
(5) The material thus prepared is coated on film in thickness of 20 .mu.m by doctor blade method, and dielectric ceramic composition sheet is prepared.
(6) Nickel paste used as the material for internal electrode is printed on the dielectric ceramic composition sheet.
(7) This is laminated in five layers and thermally pressed to prepare a multilayer product.
(8) The multilayer product thus prepared is cut into 3216 shape, i.e. in size of 3.2 mm (length ).times.1.6 mm.
(9) Stabilizing at 250.degree. C. to 300.degree. C., binder removal processing is performed for 10 hours.
(10) Oxygen partial pressure is controlled to 7.times.10.sup.-9 to 9.times.10.sup.-13 atm, and stabilizing at firing temperature T.sub.2 =1,200.degree. C. to 1,300.degree. C., it is fired for 2 hours.
(11) Stabilizing at 700.degree. C. to 1,200.degree. C. in neutral atmosphere, re-oxidation is performed for 9 hours.
(12) A terminal electrode of indium-gallium (In--Ga) alloy is mounted on it.
The capacitor thus prepared has capacitance of 20 pF in each layer, being 100 pF in total.
On the specimen capacitors prepared as above, electrical properties such as dielectric constant .epsilon.s, dielectric loss tan .delta., insulation resistance IR (.OMEGA.), temperature characteristic of capacitance T.C (%), and life time .mu. (hour) were determined. The results are shown in Tables 3 and 4.
TABLE 3__________________________________________________________________________ IR T.C (%) .mu.No. .epsilon.s tan .delta. (.OMEGA.) -55.degree. C. -25.degree. C. 85.degree. C. 125.degree. C. (hour)__________________________________________________________________________1 Difficult to sinter2 3390 2.6 5 .times. 10.sup.10 -13.2 -8.0 -8.5 -1.0 33 3800 2.2 8 .times. 10.sup.10 -5.0 -4.0 0 6.0 44 3920 2.8 2 .times. 10.sup.10 -16.8 -12.7 -7.0 -1.3 95 3600 1.9 5 .times. 10.sup.11 -13.2 -7.8 -5.4 2.0 1006 2100 2.3 5 .times. 10.sup.9 -12.0 -7.5 -5.4 -3.1 77 1400 5.4 8 .times. 10.sup.7 -10.9 -6.0 -1.0 2.8 38 3100 2.0 2 .times. 10.sup.11 -14.2 -9.0 -4.0 -1.0 909 2900 1.8 3 .times. 10.sup.11 -8.0 -5.3 -8.5 -4.0 3410 3250 1.8 3 .times. 10.sup.11 -8.4 -5.8 -6.4 -1.7 3111 2560 1.6 1 .times. 10.sup.11 -7.6 -5.3 -9.6 -8.7 3712 1810 1.4 1 .times. 10.sup.11 -8.9 -5.3 -11.4 -13.4 013 2820 2.2 2 .times. 10.sup.11 -15.0 -9.8 -1.1 2.0 3614 3180 2.6 2 .times. 10.sup.11 -14.8 -8.7 3.7 0 2915 3790 5.9 2 .times. 20.sup.11 -17.8 -11.9 -1.0 2.0 4516 Turned to semiconductor state17 3000 1.8 2 .times. 10.sup.10 -14.8 -9.8 0 12.5 3918 3180 1.8 3 .times. 10.sup.11 -8.6 -6.2 -5.1 1.0 6019 3050 2.2 1 .times. 10.sup.11 -10.2 -6.1 -7.8 -3.7 4820 2480 1.5 2 .times. 10.sup.11 -11.7 -8.4 -4.4 4.6 20021 3210 2.0 2 .times. 10.sup.11 -7.4 -5.1 -6.3 0 2522 2800 2.2 3 .times. 10.sup.10 -8.3 -6.1 -6.4 1.0 15023 3000 2.2 1 .times. 10.sup.11 -5.7 -3.3 -7.8 -3.8 110__________________________________________________________________________
TABLE 4__________________________________________________________________________ IR T.C (%) .mu.No. .epsilon.s tan .delta. (.OMEGA.) -55.degree. C. -25.degree. C. 85.degree. C. 125.degree. C. (hour)__________________________________________________________________________24 3180 2.1 2 .times. 10.sup.11 -8.5 -5.0 -5.0 4.0 5225 3260 2.1 1 .times. 10.sup.11 -7.9 -5.5 -6.2 2.0 10026 2480 1.8 8 .times. 10.sup.9 -10.6 -7.9 -6.1 0 627 3100 1.9 3 .times. 10.sup.10 -8.5 -6.2 -7.5 -3.2 20028 3010 3.0 2 .times. 10.sup.11 -15.0 -9.8 -2.4 -3.4 3329 3150 2.0 3 .times. 10.sup.11 -8.5 -5.9 -6.3 -2.0 2830 2950 1.9 2 .times. 10.sup.11 -10.5 -8.7 -4.4 -5.0 2531 2650 1.6 3 .times. 10.sup.11 -7.5 -5.4 -3.8 -9.0 4632 Turned to semiconductor state33 4330 5.2 1 .times. 10.sup.11 -35.2 -20.0 -11.3 -18.5 834 3210 1.7 3 .times. 10.sup.11 -15.0 -10.0 0 7.5 2835 2880 1.9 1 .times. 10.sup.11 -13.0 -6.1 -6.5 -4.0 4036 2610 1.6 2 .times. 10.sup.11 -8.9 -7.0 -6.0 -5.5 3837 1910 1.4 3 .times. 10.sup.11 -5.0 -4.0 -3.0 -5.0 938 2680 1.2 2 .times. 10.sup.10 -6.9 -3.5 -2.5 -4.8 8539 1380 1.0 4 .times. 10.sup.9 -4.6 -2.6 -8.0 -9.0 740 3080 1.9 1 .times. 10.sup.11 -13.8 -10.0 -9.0 -8.5 3541 2980 2.0 7 .times. 10.sup.10 -11.8 -7.4 -4.6 -1.9 3642 3850 3.0 4 .times. 10.sup.10 -14.9 -8.9 -7.8 -4.0 4043 3160 2.2 2 .times. 10.sup.11 -11.5 -9.0 -2.0 -7.0 3544 3120 2.0 1 .times. 10.sup.11 -10.6 -8.4 -4.9 -5.0 3045 3000 2.0 3 .times. 10.sup.11 -14.5 -10.0 -7.0 -8.5 2546 2850 1.4 3 .times. 10.sup.11 -14.9 -9.8 -5.0 -9.8 26__________________________________________________________________________
Here, dielectric constant .epsilon. s and dielectric loss tan .delta. are the values at 20.degree. C. and frequency of 1 kHz. The insulation resistance IR is measured at 20.degree. C. after voltage of 50 V has been applied for 30 seconds, and temperature characteristic of capacitance T.C is temperature characteristic to capacitance at 20.degree. C. of the capacitance at each temperature, and life time .mu. is accelerated life time, applying voltage of 200V at 200.degree. C.
In the evaluation of the above measurements, the values were considered as satisfactory if dielectric constant .epsilon. s is 2,500 or more, dielectric loss tan .delta. is 3.0 or less, insulation resistance IR is 10.sup.10 .OMEGA. or more, temperature characteristic of capacitance T.C is within .+-.15%, and life time .mu. is 10 hours or more. If the values do not comply with these criteria, the product was considered as defective.
The product which was difficult to sinter or was turned to semiconductor state was considered as defective because such is not suitable for the use as capacitor.
As the result of the evaluation in accordance with the above criteria, the specimens Nos. 5, 8, 9, 10, 11, 13, 14, 17, 18, 19, 21, 22, 23, 24, 25, 27, 28, 29, 30, 31, 34, 35, 36, 38, 40, 41, 42, 43, 44, 45, and 46 were judged as satisfactory, and the specimens Nos. 1, 2, 3, 4, 6, 7, 12, 15, 16, 20, 26, 32, 33, 37, and 39 were judged as defective.
Based on the results of the above judgment, the composition range is defined as follows:
In case Y.sub.2 O.sub.3 is less than 0.01 mol % (specimen No. 1), it is difficult to sinter even when the firing temperature (T.sub.2)=1,400.degree. C. and is not suitable for practical use. In case it exceeds 10.0 mol % (specimen No. 32), the composition is reduced and is turned to semiconductor state. Thus, it does not act as a dielectric substance.
Therefore, to obtain satisfactory results, Y.sub.2 O.sub.3 must be within the range of 0.01 to 10.0 mol %.
In case MgO is contained by less than 0.01 mol % (specimens Nos. 4 and 15), temperature characteristic of capacitance T.C is aggravated to more than .+-.15%, and dielectric loss .delta. may be as high as 5.9. In case it exceeds 10.0 mols
(specimen No. 12), accelerated life time is extremely aggravated.
Therefore, to obtain satisfactory results, MgO must be within the range of 0.01 to 10.0 mol %.
When V.sub.2 O.sub.3 is added by more than 0.001 mol % (all specimens except Nos. 2, 3, 12 and 16), accelerated life time is extensively improved. In case it is added by more than 0.20 mol % (specimens Nos. 6, 7 and 26), dielectric constant .epsilon. s is 2500 or less and insulation resistance is 1.times.10.sup.10 .OMEGA. or less, and the product is not suitable for practical use.
Therefore, to obtain satisfactory results, V.sub.2 O.sub.5 must be within the range of 0.001 to 0.20 mol %.
In case{Ba.sub.A, Ca.sub.(1-A) }SiO.sub.3 (where 0.ltoreq.A.ltoreq.1) is added by less than 0.5 mol % (specimen No. 33) as the additive BCG, temperature characteristic of capacitance is more than .+-.15%. In case it exceeds 10 mol % (specimen No. 37), .epsilon. s is 2500 or less.
Therefore, to obtain satisfactory results, the additive BCG must be within 0.5 to 10 mol %.
In case total quantity of MnO.Cr.sub.2 O.sub.3.Co.sub.2 O.sub.3 is less than 0.01 mol %
(specimen No. 16), the composition is turned to semiconductor state. In case it exceeds 1.0 mol %
(specimen No. 39), insulation resistance is 1.times.10.sup.10 .OMEGA. or less.
Therefore, to obtain satisfactory results, total quantity of MnO.Cr.sub.2 O.sub.3.Co.sub.2 O.sub.3 must be within the range of 0.01 to 1.0 mol %.
By the non-reducing dielectric ceramic composition according to the Present invention within composition range as described above, it is possible to obtain multilayer ceramic capacitor, in which decrease of specific resistance and shortening of service life due to reduction of dielectric ceramic composition, even when nickel used as internal electrode is fired in neutral or reducing atmosphere to prevent oxidation and capacitance does not vary extensively due to temperature change.

Number	Name	Date
4115493	Sakabe et al.	Sep 1978
4241378	Dorrian	Dec 1980
4855266	Burn	Aug 1989
4925817	Ikeda et al.	May 1990

Non-reducing dielectric ceramic composition

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