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Patent US4626395 - Method of manufacturing low temperature sintered ceramic materials for use ... - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsA ceramic composition capable of sintering at a sufficiently low temperature to enable the use of a low cost base metal as the electrode material in the fabrication of capacitors. The major ingredient of the composition is expressed as Bak-x Mx Ok TiO2, where M is one or more of magnesium, zinc, strontium,...http://www.google.com/patents/US4626395?utm_source=gb-gplus-sharePatent US4626395 - Method of manufacturing low temperature sintered ceramic materials for use in solid dielectric capacitors or the likeAdvanced Patent SearchPublication numberUS4626395 APublication typeGrantApplication numberUS 06/753,241Publication dateDec 2, 1986Filing dateJul 9, 1985Priority dateNov 30, 1983Fee statusPaidAlso published asDE3476652D1, EP0155363A2, EP0155363A3, EP0155363B1, US4610968Publication number06753241, 753241, US 4626395 A, US 4626395A, US-A-4626395, US4626395 A, US4626395AInventorsTakeshi Wada, Hiroshi Nakamura, Masami Fukui, Nobutatsu YamaokaOriginal AssigneeTaiyo Yuden Co., Ltd.Export CitationBiBTeX, EndNote, RefManPatent Citations (8), Referenced by (1), Classifications (17), Legal Events (3) External Links: USPTO, USPTO Assignment, EspacenetMethod of manufacturing low temperature sintered ceramic materials for use in solid dielectric capacitors or the like
US 4626395 AAbstract
A ceramic composition capable of sintering at a sufficiently low temperature to enable the use of a low cost base metal as the electrode material in the fabrication of capacitors. The major ingredient of the composition is expressed as Bak-x Mx Ok TiO2, where M is one or more of magnesium, zinc, strontium, and calcium, and where k, and x are numerals in the ranges of 1.00 to 1.04, and 0.02 to 0.05, respectively. To this major ingredient is added a minor proportion of a mixture of boron oxide and at least one of barium oxide, magnesium oxide, zinc oxide, strontium oxide, and calcium oxide. For the fabrication of coherently bonded bodies of this composition, as for use as the dielectric bodies of capacitors, the moldings of the mixture of the major ingredient and additive in finely divided form are sintered in a reductive or neutral atmosphere and then reheated at a lower temperature in an oxidative atmosphere. The sintering temperature can be so low (typically from 1050� to 1200� C.) that the moldings can be co-sintered with base metal electrodes buried therein without difficulties encountered heretofore.
1. A process for the fabrication of coherently bonded bodies of a low temperature sintered ceramic material, for particular use as the dielectric bodies of capacitors, which comprises:forming green bodies of desired shape and size from a mixture of 100 parts by weight of Bak-x Mx Ok TiO2 in finely divided form, where M is at least either of magnesium, zinc, strontium and calcium, where k is a numeral in the range of 1.00 to 1.04 and where x is a numeral in the range of 0.02 to 0.05, and 0.2 to 10.0 parts by weight of an additive in finely divided form composed of 30 to 90 mole percent boron oxide and 10 to 70 mole percent of at least one metal oxide selected from the group consisting of barium oxide, magnesium oxide, zinc oxide, strontium oxide, and calcium oxide for providing upon firing coherently bonded dielectric bodies with a specific dielectric constant in excess of 2000, dielectric losses of less than 2.5 percent, resistivity of over 1�106 megohm-centimeters and capacitance temperature dependence of + or -10% in a temperature range of -25� to +85� C.; sintering the green bodies to maturity in a nonoxidative atmosphere at a temperature not to exceed 1300� C.; and re-heating the sintered bodies in an oxidative atmosphere at a temperature lower than the preceding sintering temperature. 2. A process for the fabrication of coherently bonded bodies of a low temperature sintered ceramic material as set forth in claim 1, wherein the bodies are sintered in a temperature range of 1050� to 1200� C.
3. A process for the fabrication of coherently bonded bodies of a low temperature sintered ceramic material as set forth in claim 2, wherein the sintered bodies are reheated in a temperature range of 500� to 1000� C.
This is a division of application Ser. No. 676,780, filed Nov. 30, 1984.
According to the method of our invention, for the fabrication of coherently bonded bodies of the above low temperature sintered ceramic material, there are first prepared the major ingredient, Bak-x Mx Ok TiO2, and the additive mixture of B2 O3 and MO, in the above suggested proportions. After having been intimately mixed together, the major ingredient and additive are molded into bodies of desired shape and size. The moldings are subsequently sintered in a nonoxidative (i.e. neutral or reductive) atmosphere and then reheated in an oxidative atmosphere.
FIG. 2 is a graph plotting the average capacitance-temperature characteristic of test capacitors, each constructed as in FIG. 1, manufactured in Test No. 1 in the Example of our invention;
We have illustrated in FIG. 1 one of many similar multilayered ceramic capacitor fabricated in the subsequent Example of our invention by way of a possible application of our invention, each capacitor having its dielectric body formulated in accordance with the composition and method of our invention. Generally designated by the reference numeral 10, the representative capacitor is shown to have an alternating arrangement of three dielectric ceramic layers 12 and two film electrodes 14. The dielectric layers 12 have, of course, the low temperature sintered ceramic material of our invention. The film electrodes 14, which can be of a low cost base metal such as nickel, extend into the middle of the dielectric body 15, composed of the three dielectric layers 12, from the opposite sides thereof into a partly opposed relation with each other. A pair of conductive terminations 16 contact the respective-film electrodes 14. Each termination 16 comprises a baked on zinc layer 18, a plated on copper layer 20, and a plated on solder layer 22.
TABLE 1__________________________________________________________________________Ceramic Compositions                         AdditiveMajor Ingredient (100 wt. pt.)     Comp.Test    -x                    Propn.                              (mole %)                                    MO (mole %)No.    -k -  -x  Mg  Zn  Sr  Ca  Total                       -k                         (wt. pt.)                              B2 O3                                 MO BaO                                       MgO                                          ZnO                                             SrO                                                CaO__________________________________________________________________________ 1 1.02   0.005       0.005           0.005               0.005                  0.02                      1.04                         1.0  30 70 50 30 20 -- -- 2 1.01   0.002       0.002           0.003               0.003                  0.01                      1.02                         5.0  55 45 -- 10 10 40 40 3 1.01  --  0.02          --  --  0.02                      1.03                         3.0  55 45 10 20 40 10 20 4 1.01  --  0.02          0.01              --  0.03                      1.04                         3.0  25 75 40 -- 10 30 20 5 1.00  0.02      --  --  --  0.02                      1.02                         1.0  35 65 60 -- 30 10 -- 6 1.00  0.02      --  --  --  0.02                      1.02                         1.0  35 65 -- 100                                          -- -- -- 7 1.00  --  --  0.01              0.02                  0.03                      1.03                         0.2  55 45 30 30 40 -- -- 8 1.00  --  --  0.01              0.02                  0.03                      1.03                         0.2  55 45 -- -- -- 40 60 9 1.00  0.01      0.01          --  0.02                  0.04                      1.04                         1.0  30 70 10 40 -- 30 2010 1.00  0.02      0.02          0.01              0.02                  0.05                      1.05                         5.0  45 55 20 -- 70 -- 1011 0.99  --  --  --  0.02                  0.02                      1.01                         10.0 55 45 80 10 -- 10 --12 0.99  --  --  --  0.02                  0.02                      1.01                         10.0 55 45 -- -- -- -- 10013 0.99  0.02      0.01          --  --  0.03                      1.02                         1.0  90 10 70 -- -- 10 2014 0.99  0.02      0.01          --  --  0.03                      1.02                         1.0  90 10 -- 60 40 -- --15 0.99  0.01      --  0.01              0.01                  0.03                      1.02                         0.0  -- -- -- -- -- -- --16 0.99  0.01      --  0.01              0.02                  0.04                      1.03                         5.0  30 70 -- 70 10 -- 2017 0.99  0.02      --  --  0.02                  0.04                      1.03                         12.0 55 45 10 10 80 -- --18 0.99  --  --  --  0.05                  0.05                      1.04                         7.0  55 45 20 20 20 20 2019 0.98  --  --  0.02              --  0.02                      1.00                         0.2  90 10 -- 80 -- 20 --20 0.98  --  0.01          0.01              0.01                  0.03                      1.01                         1.0  45 55 20 20 -- 60 --21 0.98  --  0.02          0.02              --  0.04                      1.02                         1.0  95  5 -- 10 10 -- 8022 0.97  0.01      0.01          0.01              --  0.03                      1.00                         10.0 30 70 -- 10 -- 80 1023 0.97  0.05      --  --  --  0.05                      1.02                         3.0  35 65 30 20 -- 20 3024 0.97  0.05      --  --  --  0.05                      1.02                         3.0  35 65 -- -- 100                                             -- --25 0.97  0.05      --  --  --  0.05                      1.02                         3.0  35 65 -- -- 50 -- 5026 0.97  0.01      0.01          0.01              0.02                  0.05                      1.02                         3.0  85 15 -- -- 10 10 8027 0.97  0.02      0.02          0.01              0.01                  0.06                      1.03                         0.2  55 45 20 20 20 20 2028 0.96  0.01      0.01          --  --  0.02                      0.98                         5.0  55 45 -- 10 30 50 1029 0.96  0.01      0.01          0.01              0.01                  0.04                      1.0                         1.0  85 15 20 50 30 -- --30 0.96  --  --  0.05              --  0.05                      1.01                         1.0  45 55 30 10 10 20 3031 0.96  --  --  0.05              --  0.05                      1.01                         1.0  45 55 -- -- -- 100                                                --32 0.95  0.05      --  --  --  0.05                      1.00                         1.0  75 25 50 30 20 -- --__________________________________________________________________________
Thus, according to Test No. 1 of Table 1, for instance, the major ingredient was Ba1.02 M0.02 O1.04 TiO2 or, more specifically, Ba1.02 Mg0.005 Zn0.005 Sr0.005 Ca0.005 O1.04 TiO2. One hundred parts by weight of this major ingredient was admixed with 1.0 part by weight of a mixture of 30 mole percent B2 O3 and 70 mole percent MO, the latter being, in this case, a mixture of 50 mole percent BaO, 30 mole percent MgO, and 20 mole percent ZnO.
For the fabrication of test capacitors of the Test No. 1 composition, we started with the preparation of the major ingredient, Ba1.02 Mg0.005 Zn0.005 Sr0.005 Ca0.005 O1.04 TiO2. We first prepared 926.39 grams of BaCO3, 0.94 gram of MgO, 1.88 grams of ZnO, 3.40 grams of SrCO3, 2.32 grams of CaCO3, and 368.44 grams of TiO2, all with purities of over 99.0 percent. Expressed in mole parts, the relative proportions of the above prepared BaCO3, MgO, ZnO, SrCO3, CaCO3, and TiO2 were 1.02, 0.005, 0.005, 0.005, 0.005, and 1.0, respectively, aside from the impurities contained in the start materials. These start materials were wet mixed together for 15 hours. Then the mixture was dried at 150� C. for four hours, pulverized, and calcined in air at about 1200� C. for two hours. The major ingredient was thus obtained in finely divided form.
We prepared the additive of Test No. 1 by first preparing a mixture of 19.02 grams (30 mole percent) of B2 O3, 63.03 grams (35 mole percent) of BaCO3, 7.76 grams (21 mole percent) of MgO, and 10.43 grams (14 mole percent) of ZnO. To this mixture we added 300 cubic centmeters of alcohol, and the resulting mixture was agitated for 10 hours in a polyethylene pot with alumina balls. Then the mixture was air fired at 1000� C. for two hours. Then, charged into an alumina pot together with 300 cubic centimeters of water, the mixture was crushed with alumina balls for 15 hours. Then the crushed mixture was dried at 150� C. for four hours. There was thus obtained the desired additive mixture of 30 mole percent B2 O3 and 70 mole percent MO (35 mole percent BaO, 21 mole percent MgO, and 14 mole percent ZnO) in finely divided form.
For the fabrication of the base metal film electrodes 14, we prepared 10 grams of nickel in finely divided form, with an average particle size of 1.5 microns, and a solution of 0.9 gram of ethyl cellulose in 9.1 grams of butyl "Carbitol" (trademark for diethylene glycol monobutyl ether). Both were agitated for 10 hours into an electroconductive paste. This paste was "printed" on one surface of each green ceramic sheet, which had been prepared as above, through a screen having approximately 50 rectangular perforations each sized 7 by 14 millimeters. Then, after drying the printed paste, two green ceramic sheets were stacked, with their printings directed upwardly, and with the printings on the two sheets offset from each other to an extent approximately one half of their longitudinal dimension. Further, four green ceramic sheets each with a thickness of 60 microns were stacked on each of the top and bottom surfaces of the two printed ceramic sheets. Then the stacked sheets were pressed in their thickness direction under a pressure of approximately 40 tons at 50� C., thereby bonding the stacked sheets together. Then the bonded sheets were cut in a latticed pattern into approximately 100 pieces.
We employed a furnace capable of atmosphere control for co-firing the above prepared green dielectric bodies and what were to become film electrodes buried therein. The bodies were first air heated to 600� C. at a rate of 100� C. per hour, thereby driving off the organic binder that had been used for providing the slurry of th powdered major ingredient and additive. Then, with the furnace atmosphere changed from air to a reductive (nonoxidative) atmosphere consisting of two percent by volume of molecular hydrogen and 98 percent by volume of molecular nitrogen, the furnace temperature was raised from 600� C. to 1160� C. at a rate of 100� C. per hour. The maximum temperature of 1160� C., at which the ceramic bodies could be sintered to maturity, was maintained for three hours. Then the furnace temperature was lowered to 600� C. at a rate of 100� C. per hour. Then the furnace atmosphere was again changed to air (oxidative atmosphere), and the temperature of 600� C. was maintained for 30 minutes in that atmosphere for the oxidative heat treatment of the sintered bodies. Then the furnace temperature was allowed to lower to room temperature. There were thus obtained the dielectric ceramic bodies 15, FIG. 1, co-sintered with the film electrodes 14 buried therein.
There were thus completed the fabrication of multilayered ceramic capacitors, each constructed as in FIG. 1, of Test No. 1. The composition of the sintered ceramic bodies 10 is substantially the same as that before sintering. Essentially, therefore, it is reasoned that the ceramic bodies 15 are of perovskite structures, with the additive (mixture of 30 mole percent B2 O3, 35 mole percent BaO, 21 mole percent MgO and 14 mole percent ZnO) substantially uniformly dispersed among the crystal grains of the major ingredient (Ba1.02 Mg0.005 Zn0.005 Sr0.005 Ca0.005 O1.04 TiO2).
Table 2 gives the results of the measurements by the above methods. It will be seen from this table that the specific dielectric constants of the Test No. 1 capacitors, for instance, averaged 3070, their dielectric losses 1.2 percent, their resistivities 2.5�106 megohm-centimeters, and their percent variations of capacitances from those at +20� C. to those at -25� and +85� C., -8.8 and +4.8 percent, respectively.
Before proceeding further with the examination of Table 2, we will determine the acceptance criteria of the four electrical properties in question of capacitors in general as follows:
Now, let us study the ceramic compositions of Table 1 and the corresponding capacitor characteristics of Table 2 in more detail. The ceramic composition of Test No. 15 contained no additive specified by our invention. The dielectric bodies formulated accordingly were not coherently bonded on firing at a temperature as high as 1250� C. Consider the ceramic composition of Test No. 7 for comparison. It contained 0.2 part by weight of the additive with respect to 100 parts by weight of the major ingredient. Even though the firing temperature was as low as 1180� C., the Test No. 7 composition could be processed into capacitors having the desired electrical characteristics. We set, therefore, the lower limit of the possible proportions of the additive at 0.2 part by weight with respect to 100 parts by weight of the major ingredient.
The Test No. 17 ceramic composition contained as much as 12 parts by weight of the additive with respect to 100 parts by weight of the major ingredient. The resulting capacitors have an average dielectric loss of 2.8 percent, which is higher than the above established criterior. However, when the proportion of the additive was reduced to 10 parts by weight, as in the Test No. 11 ceramic composition, then the resulting capacitors have the desired dielectric loss and other characteristics. Accordingly, the upper limit of the possible proportions of the additive is set at 10 parts by weight with respect to 100 parts by weight of the major ingredient.
As for the major ingredient, Bak-x Mx Ok TiO2, the value of x was set at 0.01 in Test No. 2. In the resulting capacitors, the average variation of capacitances at -25� C. is -11.8 percent, outside the desired range of plus and minus 10 percent. However, when the value of x was increased to 0.02, as in Test No. 1, then the desired criteria of capacitance-temperature characteristics and other properties could all be achieved. Thus the lowermost possible value of x is 0.02. The Test No. 27 composition had the value of x set at as high as 0.06. In the resulting capacitors, the average variation of capacitance at -25� C. is -13.8 percent, which also is outside the desired range of plus and minus 10 percent. In Tests Nos. 18, and 23 to 26, the value of x was set slightly lower, at 0.05, and the resulting capacitors possess all the desired electrical characteristics. The uppermost possible value of x is therefore 0.05.
Concerning the composition of the additive, the mixture of B2 O3 and MO (one or more of BaO, MgO, ZnO, SrO and CaO), it will be noted from Test No. 4 that when the proportion of B2 O3 with respect to that of MO was set at 25 mole percent, the dielectric bodies of the resulting composition were not coherently bonded on firing at a temperature as high as 1250� C. However, when the proportion of B2 O3 was increased at 30 mole percent, as in Test No. 1, the corresponding dielectric bodies could be sintered to maturity at a reduced temperature of 1160� C., to provide capacitors having the desired electrical characteristics. On the other hand, when the B2 O3 proportion was set at as high as 95 mole percent as in Test No. 21, the average dielectric loss of the resulting capacitors was as poor as 2.9 percent. The desired electrical characteristics were all obtained when the B2 O3 proportion was up to only 90 mole percent as in Test No. 13. We conclude from these findings that the acceptable range of the proportions of B2 O3 is from 30 to 90 mole percent and, consequently, that the acceptable range of the proportions of MO is from 10 to 70 mole precent.
Although we have disclosed our invention in terms of specific Example thereof, we understand that our invention is not to be limited by the exact details of such disclosure but is susceptible to a variety of modifications within the usual knowledge of the ceramics or chemicals specialist without departing from the scope of the invention.
The following, then, is a brief list of such possible modifications:
Patent CitationsCited PatentFiling datePublication dateApplicantTitleUS4106075 *Mar 17, 1976Aug 8, 1978Draloric Electronic GmbhTitanium and/or zirconium oxidesUS4115943 *May 31, 1977Sep 26, 1978Musgrave Daniel DReserve magazine holderUS4283753 *Sep 28, 1979Aug 11, 1981Sprague Electric CompanyConsisting of a barium titanate phase and low melting intergranular phase; buried electrodesUS4308570 *Feb 25, 1980Dec 29, 1981Sprague Electric CompanyHigh Q monolithic capacitor with glass-magnesium titanate bodyUS4451869 *May 5, 1983May 29, 1984Murata Manufacturing Co., Ltd.Laminated ceramic capacitorUS4477401 *Sep 2, 1982Oct 16, 1984U.S. Philips CorporationDensely sintering a ferroelectri ceramic perouskite and electrode paste in a reducing atmosphereUS4571276 *Jun 22, 1984Feb 18, 1986North American Philips CorporationSintering to give bond between glass and dielectric ceramics, and metal and electrodesJPS5567567A * Title not available* Cited by examinerReferenced byCiting PatentFiling datePublication dateApplicantTitleUS5672378 *Apr 22, 1996Sep 30, 1997Mra Laboratories, Inc.Combining precursors of barium zirconate titanate, strontium, a compound containing curie point shifter cations, cadmium silicate sintering flux, calcining; capacitors* Cited by examinerClassifications U.S. Classification264/620, 264/82, 361/320, 264/662, 361/321.4International ClassificationH01G4/12, C04B35/46, C04B35/468, H01B3/12, H01G4/232, C04B35/01Cooperative ClassificationH01G4/1227, C04B35/4682, H01G4/2325European ClassificationC04B35/468B, H01G4/12B2B, H01G4/232BLegal EventsDateCodeEventDescriptionMay 21, 1998FPAYFee paymentYear of fee payment: 12May 16, 1994FPAYFee paymentYear of fee payment: 8Mar 12, 1990FPAYFee paymentYear of fee payment: 4RotateOriginal ImageGoogle Home - Sitemap - USPTO Bulk Downloads - Privacy Policy - Terms of Service - About Google Patents - Send FeedbackData provided by IFI CLAIMS Patent Services