DE2343142A1 - Dense, non-porous ceramic dielectric for capacitors - contg. oxides or neodymium, titanium, barium, bismuth and zirconium - Google Patents

Abstract

The ceramic has a dielectric constant (K) of 55-90; a temp. coefft. K of -100 to +100 10-6/degreef a value for % D.F. below 0.1; an insulation strength of min. 200 ohm. F at 150 degrees C.; and contains, all mol. %, 12-20 Nd2O3, 12-20 BaO, 70-60 TiO2, 1.5-5 Bi2O3, 0-5 ZrO2, 0-5 snO2, 0-10 CaO + SrO, and max. 5 other rare-earths. The total of the oxides of It, Sn and Zr shall be 60-70 mol. % and the sum of the oxides of Ba, Ca, and Sr, 12-25 mol. %. The pref. value for % D.F. is max. 0.03 and for insulation strength a min. of 1000 ohm. F. This dielectric is suitable for the mfr of class 1 ceramic dielectric capacitors to the U.S. Electronic Inds. Association Standard, RS 198.

Description

concerning:
"Dielectric"

The invention relates to a new dielectric and a powder material suitable for its manufacture.

The dielectric according to the invention for capacitors, in particular capacitors of class I _1, is composed of approximately 12 to 20 mol% neodymium oxide, approximately 12 to 20 mol% barium oxide, approximately 0 to 60 mol% titanium oxide, approximately 1.5 to 5 mol% bismuth oxide and from 0 to about 5 mol% zirconium oxide, from 0 to about 5 mol% tin oxide, from 0 to about 10 mol% calcium and / or strontium oxide, and finally, in addition to neodymium oxide, other rare earths up to about 5 mol%, preferably up to 2 mol%, in particular less than about 10% of the amount of neodymium oxide are present. The sum of the oxides of titanium, tin and zirconia

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konium is said to be about 60 to 70 mol% and that of barium, Calcium and strontium make up about 12 to 25 mole percent.

The dense, non-porous dielectric material according to the invention is obtained from the powder material by firing at about 1220 to 1300 ⁰ C and resulting K-values (£.) Of about 55 to 90. The temperature coefficient of the dielectric constant is between about -100 and +100 χ 10 " ⁶ / degree, % DP is below 0.1 and the insulation resistance corresponds to values from at least 200 up to about 40,000 and above β / Ε at 125 ° G.

The dielectrics according to the invention allow manufacture Class 1 capacitors (Electronics Industries Association Standard for Ceramic Dielectric Capacitors, ES 198 (1957)) due to the high K values with relatively low temperature coefficients of the dielectric constant in connection with stability against changes in charge and high insulation resistance values.

When developing a capacitor of a given capacitance, the factors that influence the formation of the capacitor are the area of the electrically conductive electrode plates on the opposite sides of the ceramic dielectric j the thickness of the dielectric, the dielectric constant K of the dielectric. If the capacitor is multilayered, the total areas of the opposing electrode plates must be taken into account. If other factors held constant throw so the capacity is directly proportional to the Dielektri-

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constant of the dielectric. Now becomes the dielectric constant of the dielectric increases, so you can see the areas of the capacitor elements and the electrode plates decrease in inverse proportion.

If, on the other hand, the dielectric constant of the dielectric is reduced, it becomes necessary to use the others Modify design parameters to obtain a capacitor of the desired capacity. For compensation the area of the capacitor plates can be used to reduce the dielectric constant of the dielectric enlarged or the number of plates in the capacitor increased. All of these options at The design of the capacitor only increases its cost. This is especially true for multilayer monolithic dielectric capacitors that apply a multitude of layers of ceramic material created by noble metal electrodes are separated from the group of palladium, gold and platinum. As the number of electrode plates in a capacitor increases, the demand increases accordingly of expensive precious metal for the necessary electrodes. This is synonymous with rising costs for the capacitor.

Another property of some importance in the design of a capacitor is the temperature coefficient of the dielectric constant of the dielectric. The temperature coefficient is determined as the change in the dielectric constant of the dielectric with a change in temperature of the capacitor. The temperature coefficient of the dielectric constant is expediently relatively low for many areas of application, e.g. at -100 to +100 χ 10 ~ ⁶ / degree,

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It is more desirable if the temperature coefficient of the dielectric constant is within the NPO range lies, i.e. between -30 and +30 χ 10 / deg. The application a dielectric with a relatively low temperature coefficient of the dielectric constant leads to capacitors whose Capacity is relatively constant over a wide temperature range. This is very advantageous, e.g. when the Capacitor represents an element of a circuit in order to be uniform within an electrical system Maintain capacity and which operates over a wide temperature range.

Another factor that is important in choosing a dielectric for use in a capacitor is is the temperature range in which the dielectric material is fired for the desired dielectric properties became. Many ceramic materials are very sensitive in this regard and have to work in very narrow temperature ranges fired to achieve satisfactory dielectric properties. If this is the If so, the manufacturing cost increases due to the low yield of good pieces. It is therefore very much It is desirable to use a ceramic material in a capacitor that can operate in a reasonably wide temperature range can be burned.

The invention now brings a dielectric and a suitable one dielectric material with high K values of around 55 to 90 and above · In contrast to previous ones Materials, the ceramic material according to the invention has low temperature coefficients in addition to high K values the dielectric constant in the range from about -100 to

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+100 χ 10 "/ degree. The preferred values are within the NPO range of -30 to +30 χ 10" "/ degree. Beyond that the dielectric materials according to the invention are also characterized by values of% D.F. below about Oj1, preferably below etvra 0.03.

The '. The insulation resistance of the dielectrics according to the invention corresponds to at least about 200, preferably 1000 tSL "i ¹ and above at 125 ° 0. With the ceramics according to the invention, values of over 40,000 cii · ^ at 125 ° C. have already been obtained. The material according to the invention for producing the dielectrics can be set in a temperature range of 40 or 80 ⁽
Properties.

burn of 40 or 8O ⁰ O and makes excellent electrical

To produce the dielectrics according to the invention, the ceramic material is characterized on the basis of the corresponding oxides. But this does not say anything about the type of bond. The ceramic material contains about 12 to 20 mole percent neodymium oxide, about 12 to 20 mole percent barium oxide, about 70 to 60 mole percent titanium oxide, and about 1.5 to 5 mole percent bismuth oxide. In addition, it can also contain 0 to 5 mol% zirconium oxide, 0 to about 5 mol% tin oxide and 0 to about 10 mol% calcium and / or strontium oxide. In addition, there may also be traces of other substances that happen to be present as impurities in ceramic masses. OSrden rare, in addition to neodymium oxide, may preferably contain up to about 2 mole> to about 5 mole%, more preferably less than about 10 yo of the proportion of neodymium oxide.

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The total content of the oxides of titanium, tin and zirconium should be between about 60 and 70 mol%. If a special compound contains e.g. tin oxide, the proportion of titanium oxide and / or zirconium oxide will be reduced. The total proportion of oxides of barium, calcium and strontium should make up about 12 to 25 mol%. If calcium or strontium oxide is present, the barium oxide content will be reduced accordingly.

There is only the production of the ceramic material various possibilities. The first is to wet-grind the various ingredients for several hours. this mostly happens in a ball mill from which the! one-piece Material is discharged as a slip. The required meal depends on the water content of the material inside the ball mill, ball size, ball filling, etc. All of these factors influence the meal and the homogeneity of the mix. It was found that several hours of milling give sufficiently intimate mixtures.

After grinding, the mill discharge is dried in the usual way, e.g. on bowls or ribbons or through Spray drying. The dry material is optionally granulated to break up large pieces. Was on dried in a bowl or tray, the pieces can be present that can already be divided through Push through a coarse sieve, such as a 1.0 mesh screen.

After any granulation has been carried out,

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the material is then fired at a temperature between approximately 1000 and 1200 ° C in an oxidizing atmosphere, that all components are present as oxides.

These oxidic masses can be combined substances of two or more oxides, such as barium titanate, Barium zirconate, barium stannate, bismuth zirconate ,. Calcium zirconate and the titanium of bismuth. ·, calcium or strontium act. The oxides of the alkaline earths (barium, Calcium and strontium) are reactive with water and carbon dioxide. Accordingly, they are for the invention Masses used in pre-reacted form as double oxides, such as the titanates, zirconates or stannates.

As mentioned above, the manufacturing process of the ceramic material with the fire at 100 to 1200 ° C in an oxidizing atmosphere. Because of this, you can also use substances as starting materials which are non-oxides, but which are converted into oxides during firing. So you can get the heodymium oxide content in the form of neodymium carbonate or use oxalate or the oxide hydrate or hydroxide.

Another possibility is> to premix the neodymium oxide first with titanium oxide in a weight ratio of about 68:32 to 52:48. These substances can be homogenized by adding them to a ball mill together with water. The slip discharged from the ball mill is then dried, any lumps that may have formed are removed by granulation or the like. broken up. Then again at about 1000 to 1200 ⁰ C in

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oxidizing atmosphere.

After the mixture of neodymium oxide and titanium oxide has been fired, the fired material is homogenized together with other components in a ball mill. The slip is dried again and, if necessary, granulated. The fire then follows again at around 1000 to 1200 ^° C. in an oxidizing atmosphere. Firing is not necessary if all components are already in a pre-reacted state. The neodymium oxide can be in a pre-reacted state by firing with titanium oxide as mentioned above. Barium titanate, barium zirconate, calcium titanate, calcium stannate, bismuth titanate; and bismuth zirconate are pre-reacted materials. If all of these substances are used as titanates, stannates or zirconates, the last firing stage can be omitted. Even if there is pre-reacted material, it is still preferable in some cases to finally fire again in the manner mentioned.

The invention is further illustrated by a number of examples. All parts and percentages are based on weight, unless otherwise stated.

The starting materials are ground in a ball mill, the output from the mill is dried, granulated and burned at 1150 ° C. in an oxidizing atmosphere. In Examples 1 to 7 Neodymium and titanium oxide was ground in the ball mill, dried, granulated and fired at 1150 ⁰ C in an oxidizing atmosphere to a vorreagierenden material. This was then made together with the other components

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grind, dry, granulate and burn again at 1150 ⁰ G in an oxidizing atmosphere. In Examples 7 to 13 there was no pre-reaction of the neodymium and titanium oxide in the above sense, but they were added separately to the other constituents, then dried, granulated and ^{fired at 115O 0} C in an oxidizing atmosphere.

The ceramic materials in Table I below were then made into ceramic dielectric bodies. This was done by grinding the ceramic material in a ball mill for about 20 hours with an acrylate binder, namely to 100 parts of ceramic powder about 50 parts plastic and an additional 50 to 100 parts Introduced chlorinated hydrocarbon as a solvent and about 0.4 to 0.5 parts plasticizer. After grinding it was the mill contents poured onto a glass plate and could dry to a layer thickness of about 76 / um after appropriate Adjustment of the thickness of the applied mass. This was dried in the air at tree temperature and then peeled off the plate. This film was cut into rectangular pieces of approximately 76 χ 25 mm and a large number of these rectangular pieces for a short time (about 10 to 20 s) under a pressure of about 4.5 tons pressed so that a body with a thickness of about 0.66 to 0.71 mm was obtained. This material was then divided into 12.7 mm cubes and these in an electric Tunnel kiln fired on zirconium oxide support plates. The oven worked with a 7 hour program, i.e. approx The throughput time through the oven was 7 hours The material remained at the firing temperatures given in the following table for about 1 hour.

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The opposite sides of the bodies shrank about 25% from the burning process · On these sides the bodies were now coated with a conductive silver varnish, dried and kept at 815 ° C for about 15 minutes to get the Bring paint to flow. Now the two became senior Contacted layers and the electrical measurements to determine the dielectric properties of the Dielectric made. The production of the dielectric itself is the usual procedure and not an object of the present invention. The new dielectrics can also be formed in other ways.

TABLE I:

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KN

tSJ CU

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KN

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Κ O • HE

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cvicvjcvicvjcvjcvjcviojajcviCMCvj

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The neodymium oxide used in the examples is a commercial product with a unit of 95 % in addition to the remaining other rare earths.

The "bismuth titanate" mentioned in the table is a double oxide of about 72 to 74% by weight of bismuth oxide and 2 to 25% by weight of titanium dioxide. The bismuth zirconate was a double oxide of about 72% by weight. % Bismuth oxide and 27% by weight zirconium dioxide, containing about 1% by weight silicon dioxide.

The pre-reacted heodymium oxide acts with titanium dioxide it is a weight ratio of 58:42. As mentioned, Examples 1 to 7 were heodymium oxide and titanium dioxide prereacted, the values given in the table are the total values for titanium dioxide and iieodymium oxide in the pre-reacted state within the offset. In Examples 8 to 13, the two oxides were in the offset separately before.

The firing temperature was maintained for about 1 hour during the passage through the tunnel furnace.

The Ε values are the dielectric constants of the ceramic bodies, namely at 25 ^° G. At the same temperature, the values for % DF were determined at 1 kHz. The information on the temperature coefficient of the dielectric constant is based on a temperature range from 25 to 125 0. The values for the insulation

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resistance (dielectric strength) were determined at 125 ⁰ O.

It is clear from the above table that the ceramic materials according to the invention have K values in the order of magnitude of about 50 to 90 and at the same time exhibit relatively low temperature coefficients of the dielectric constant. The higher K values are achieved without this being at the expense of the stability of the dielectric constant at varying temperatures. The % DF values also show that the dielectrics according to the invention have lower electrical losses. The values for the insulation resistance result from the resistance of the dielectric for 2 minutes at 500 V. The capacitance of the dielectric was also measured at 125 ° C. The stated values were obtained by multiplying the read resistance values injl / at 125 ° C with the read values for the capacitance in F at the same temperature.

It is noteworthy that the insulation strength of the dielectric is constant and a basis for comparing Provides capacitors of different sizes. High values show that the electrical losses of the invention Dielectrics are small, so that they can be used in capacitors with very high capacities.

The starting materials for the batches mentioned in the examples are commercially available products. The barium titanate contained 53.5 to 33.9% by weight of TiO ₂ and 64.2 to 63.8% by weight of BaO in addition to small proportions of SiO ₂ , Al ₂ O, SrO and Ha ₂ O. The barium zirconate contained 41 to about 44% by weight ZrO ₂ , 55 to 53% by weight BaO, about 2 to

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3 wt .-% SiO ₂ and small amounts of TiO ₂ and Al-O;,. The calcium stannate contained 64.8% tin oxide and 23.91% calcium oxide, the calcium titanate 39 to 41% CaO and 59 "to 55% TiO _{2 in} addition to small amounts of SiO ₂ and AlpO ₅ , calcium zirconate contained 65 to 68.5 % ZrOp , about 31 to 28% GaO and about 3 to 4% SiOo with small proportions of TiO ^ and Al ₀ O ₂ .

In Table I, the offset from the starting products was given in% by weight. Table II now gives the composition the offset in mol% of the individual metal oxides.

TABLE II:

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OJ O • Η Ο

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OJ

OJ O • H

cvi

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OJ O f

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CO OO CT * VVV

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VD OJ V CN ir \ VD O V.
VD O
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VD VD
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VD OJ
IO O
VO OJ
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OJ OJ IA - ^ ^- IA f <\ CN CN ^ ^- KN KN CO vvvvvvvvvvv

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O V OJ KN V VV V

From Table II it can be seen that in the dielectrics according to the invention with outstanding properties The proportions of metal oxides are in the above ranges. If example 11 is repeated, but instead of calcium titanate If strontium titanate is used, a dielectric with good electrical properties is also obtained

A major advantage of the dielectrics according to the invention can be seen in the fact that they are essentially non-porous. The porosity is generally determined with help of the ϊ-inibe test. A dielectric, which is in has been fired in the above manner, immersed in an ink about 30 ε, then taken out, quickly with water rinsed and wiped the surfaces with a dry cloth. If the material is essentially non-porous, so there is no visible discoloration of the ink on the surface. The material is rated 1. If If the surface is slightly colored, this is rated 2. Imagine a certain penetration of If the ink is stuck in the body and the surface is also colored, this corresponds to the value 3 · If one greater penetration into the body is observed so the material receives the value 4-. According to the above test conditions the dielectrics according to the invention almost always give the value 1, which results in an essentially pore-free structure results. The ink to be used for this experiment is not critical and any aqueous inks or Apply dyes.

In the production of the dielectrics according to the invention, one can

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choose the proportions of the components in the offset so that that the corresponding values for the temperature coefficients of the dielectric constant are obtained. Neodymium oxide and bismuth oxide shift the temperature coefficient towards the positive side. Calcium, strontium, zirconium and Zinc oxide shifts to the negative side and titanium oxide also shifts to the positive side. Bismuth titanate and barium titanate are almost neutral; by increasing the constituents shifting to the negative side one obtains a dielectric with a more negative temperature coefficient of the dielectric constant, vice versa leads an increase in the positive shifting components to more ' positive values of the temperature coefficients for the dielectric constant.

Various substances, such as mineralizers or electrical modifiers. Can be used in small proportions from about 0.1 to 1% by weight, such as silicon dioxide, kojbalt oxide, manganese dioxide, Zinc oxide, zinc titanate, niobium oxide and tantalum oxide.

PATENT CLAIMS:

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Claims (1)

PATENT CLAIMS Dense, essentially non-porous ceramic dielectric with a dielectric constant of about 55 to 90 », a temperature coefficient of the dielectric constant of about -100 Ms +100 χ 10 / deg, a V / ert for % DP below 0.1, insulation strength corresponding at least about 20OtA '. P at 150 ⁰ G, containing essentially about 12 to 20 mol% neodymium oxide, about 12 to 20 mol% barium oxide, about 70 to 60 mol% titanium dioxide, about 1.5 to 5 mol / iJ bismuth oxide 0 to about 5 mol% zirconium oxide, 0 to about 5 mol% tin oxide, 0 to about 10 mol% calcium and / or strontium oxide and up to 5 mol% other rare ones. Earths, the sum of the oxides of titanium, tin and zirconium making up about 60 to 70 mol% and of barium, calcium and strontium making up about 12 to 25 mol%. • 2) Dielectric according to claim 1 with a value for / ί »D.P. of a maximum of 0.03 and an insulation resistance of 509810/0532 2343H2 at least about 1ΟΟθΛ · Ρ. 3) dielectric according to claim 1 or 2, characterized in that the proportion of other rare earths corresponds to less than about 10% of the neodymium oxide content. 4) Means for producing the dielectric according to claim 1 to 3> consisting essentially of about 12 to 20 mol% necdymium oxide, about 12 to 20 mol% barium oxide, about 70 to 60 mole percent titanium dioxide, about 1.5 to 5 Hol-% Wicmut'oxid 0 to about 5 Mol-% Zirconium oxide, 0 to about 5 mol% tin oxide, 0 to about 10 mol% calcium and / or strontium oxide, where the proportion of rare earths can be up to about 5 mol - '/ ό and the sum of the Proportions of the oxides of titanium, tin and zirconium between about 60 and 70 mol% and of barium, calcium and strontium are between about 12 and 25 hol%. 5) means according to claim 4, characterized in that oxides of barium, calcium, Strontium and bismuth are present in the form of their titanates, zirconates or stannates. 6) Means according to claim M or 5 »characterized in that the neodymium oxide is present as a pre-reacted mass with titanium dioxide at a weight ratio of neodymium oxide to titanium dioxide of about 68: 352 to 52:48. 509810/0532