DE2441450C3 - Ceramic capacitor and method of its manufacture - Google Patents

Description

Point CaTiO ₃ SrTiO, Bi ₂ O) · χ TiOj (Wt .-%) (Wt .-%) (Wt .-%) A. 98.0 0 2.0 B. 0 98.0 2.0 C. 0 50.0 50.0 D. 50.0 0 50.0

2. Capacitor according to claim 1, characterized in that the base body is made from the following composition:

SrTiO ₃ 66.0% by weight

CaTiO ₃ 27.0% by weight
Bi ₂ O ₃ -3 TiO ₂ 7.0% by weight

Mn 0.05 wt%.

3. A method for manufacturing a ceramic body for a capacitor according to claim 1 and 2, characterized in that

that strontium titanate and / or calcium titanate as well as bismuth oxide and titanium oxide are mixed in such proportions that the desired composition of the main constituent of the ceramic body, as set out in claim 1, results, and ktieser composition ions of at least one of the following substances: manganese, cobalt. Nickel. Chromium, vanadium, niobium, tantalum, lanthanum and cerium are added in amounts between 0.025 and 0.4 percent by weight,
that the mixture obtained in this way is shaped into the desired body,

that the body obtained in this way is stored for a period of about 2 hours at a temperature of about I J5 () "C in sintering in an oxidizing atmosphere.

The invention relates to a ceramic capacitor with a body made of semiconducting reduced ceramic, which is formed from the main constituent titanates and additives, in which the ceramic body is surrounded by a dielectric layer which is formed by reoxidation of the surface layer of the body made of reduced ceramic, and at in which the coverings consist of silver layers applied to the ceramic body and in which these silver layers are provided with leads connected to them in an electrically conductive manner . Ceramic capacitors with one body each

jo semiconducting, reduced ceramics are known and are described, for example, in the following publications:

Swiss Patent 4,344,478; DE-PS 8 79 920; »Radio technology«,

1961, No. 8, pages 253-256; "Funkechnik", 1962, issue 6, pages 184-186.

α In the known ceramic capacitors, the reduced ceramic consists mainly of titanates to which additives are added . In addition, the ceramic body of the known ceramic capacitors are surrounded by a dielectric layer, which is through

4 (1 reoxidation of the surface layer of the reduced Ceramic is formed, being on the ceramic body

continue to apply coverings made of silver layers and

are connected with supply lines.

Furthermore, in DE-OS 20 35 945 and in the

4 »DE-AS 12 53 627 semiconductor ceramic capacitors and method for producing layers of the Coverings for such capacitors are described.

It is also known (DE-OS 14 71 126), ceramic capacitors with a base body, the Bi ₂ O ₃ · 2 TiO>

contains in as the main component, so that a common, non-semiconductor properties Ceramic material results. It is also known (DE-OS 22 15 642) to have multi-layer capacitors a barium titanate dielectric and a metal

5> to be produced as an additive in such a way that it behaves as a Semiconductors after sintering is prevented.

The disadvantage of the known capacitors is that they with regard to the dielectric losses, the Dielectric strength, the stability of the capacitance

wi and / or the temperature dependence of their properties can not fully satisfy.

Proceeding from the prior art, the invention is therefore based on the object of an improved Ceramic capacitor of the initially described

to indicate the type of the reduced dielectric Losses and increased dielectric strength an improved temperature dependence of the capacitance owns and yet simple and relatively inexpensive v.cn

is to be established.

This is the job of a ceramic capacitor of the type described above by the features of the characterizing part of claim 1 solved

A particular advantage of the ceramic capacitor according to the invention is that the Loss angle tani and its temperature dependence as well as the temperature dependence of the Capacity are significantly reduced.

It has proven to be advantageous if the base body of the ceramic capacitor has the composition according to claim 2

For the production of a ceramic capacitor according to the invention, the method according to FIG Claim 3 proved to be advantageous.

The raw materials for the ceramic can be oxides or compounds which, when heated, are oxides result, such as B. carbonates, nitrates. Hydroxides. Hydrates etc.

The manganese ions can be added in the form of manganese carbonate, sulfate, nitrate and hydroxide, for example, or in the form of the manganese salts of organic acids.

The invention is explained in more detail below with reference to a drawing

F i g. 1 shows a graph of the change in the capacitance and the loss angle tano of a semiconductor ceramic capacitor according to the invention in FIG Depending on the applied DC voltage,

F i g. 2 a graphical representation of the influence of aging on the capacity or the loss angle tan ό,

F i g. 3 a graphical representation of the temperature dependency of the capacitance and the loss angle,

F i g. 4 is a graph showing the dependence of the capacitance C per unit area of the percentage change in capacitance TC a temperature from - 30 ⁰ C, based on the capacitance at 20 ⁰ C and the loss angle of the value of Bi ₂ O ₃ · χ xTiO ₂ -Bestandteilsund

F i g. 5 is a triangular composition diagram of the ternary system CaTiO ₃ SrTiO ₃ -Bi ₂ O ₃ · 3TiO _2, in which lines connecting the dependence of the capacitance, the value of TC in a temperature range from -25 ° C to + 85 ⁰ C and the loss angle of the mixture are shown.

Detailed description of preferred exemplary embodiments

The raw materials are put together and mixed in such a way that the following mixture results:

SrTiO ₃ 66.0 percent by weight,

CaTiO ₃ 27.0 percent by weight, Bi ₂ Oj ■ 3TiO ₂ 7.0 percent by weight and

Manganese ions 0.05 percent by weight.

This mixture is mixed while wet in a porcelain pot using agate balls . The SrTiOj and the CaTiOj are prepared before mixing with Strontiumkarbonai (SrCO ₁ ) and titanium dioxide (TiO ₂ ) or calcium carbonate (CaCOi) and titanium dioxide (TiO :) by burning the equimolar mixture at a temperature of I2OO "C and the burnt mixture then roughly chopped.,

The manganese ions are in the form of manganese carbonate added.

After mixing when wet, the binders /ui;.e.el/i. uuJ it ei follow me sufficient mixture in a ball mill. The mixture obtained in this way is then pressed and shaped into disks with a diameter of 16.5 mm and a thickness of 0.6 mm, using a pressure of 3-10 ⁴ Pa.

The shaped disks are sintered in air for two hours at a temperature of 1350 ° C and then one hour long at one temperature

ίο of 850 ⁰ C exposed to a reducing atmosphere, for example a hydrogen flow. During the last-mentioned process step, the semiconductor wafers lose some of the oxygen and become semiconducting. Then both upper surfaces or the two main surfaces of the ceramic disks or base body obtained in this way are coated with a silver paste. The ceramic base bodies are then heated in an oxidizing atmosphere, for example in air to a temperature of 780 ° C., in order to achieve reoxidation of the surface layers of the ceramic bodies and thereby burn in the painted silver layers of the coverings. The leads are then soldered directly to the surfaces of the silver layers, these being dipped into the molten solder. In this way, with appropriate dimensioning, a semiconductor ceramic capacitor with the following characteristic values is obtained:

Capacity (C) loss angle tan <5

Changes in capacity at
Temperatures in the range of
-55 to + 120 ° C, in each case based on the capacity at 2O ⁰ C (given in percent of the capacity at 20 ° C; measuring frequency 1 kHz)

0.5 × 10- ²

Insulation resistance (IR)
(measured at 25 ° C and 100 V)
Breakdown voltage

+ 6.2% to -5.6%

5 χ 10 ⁴ MQ 800 V.

In the above measurement results , from the measurement values, those 24 hours after the reoxidation

; were obtained , assumed as initial values and both the capacitance CaIs and the loss angle tan δ were measured at a frequency of 1 kHz, a voltage of 1 V and at a temperature of 25 ° C.

The percentage change in capacity and the

ι Change in the loss angle of the semiconductor ceramic capacitors as a function of the applied DC voltage is shown in FIG. 1. Furthermore, the Influence of aging on the capacitance and the loss angle of the semiconductor ceramic capacitors in F i g. 2, where the time in hours is plotted along the horizontal axis.

From Fig. 1 it is clear that the capacity and the Loss angle are not dependent on the applied DC voltage.

Fig. 2 clearly shows that even after a period of 1000 hours, the capacity and the loss angle are still are equal to the initial values of these quantities.

In Table I are the electrical properties of conventional semiconductor ceramic condensers of the reduction-reoxidation type with BaTiOj and the corresponding electrical properties of semiconductor ceramic capacitors summarized according to the invention.

Table I.

No. Condenser type C

(uJ-Vcnr)

lan δ X ΙΟ ² isol. Wid. Breakthrough

tension

Γ.Γ.

Characteristic of tension

(V)

1 BaTiO ₃ -Bi ₂ O, 0.18 5.4 2 X 10 ' 500 -8 to -25 -40 2 BaTiOj-La ₂ O., 0.17 2.0 1 X 10 ⁵ 1200 -29 to -67 -40 3 according to the invention 0.04 0.5 5X10 ⁴ 800 +4 to -1 O

♦) For a temperature range from -30 C to +85 C.

TC in the table above means a value that was calculated according to the following equation:

TC (Vo) - ACZC ₂₀ χ 100 = (C _x -C ₂₀ VQo x 100.

where C _x = chap. at x ° C, C ₂₀ - chap. at 20 ⁰ C and x— a temperature which is in the range from -30 "C to + 85 ⁰ C, are.

The voltage characteristic is the size of the change in capacitance as a result of a certain Understood the DC voltage applied to the capacitor and it is a percentage of that before the application of the DC voltage given capacity.

F i g. 3 shows the change in capacitance of a capacitor, denoted by TC , as a function of its temperature, based on the capacitance at 20 ^° C. and stated in percent of the capacitance at 20 ^° C., and the temperature dependency of the loss angle tan <5 for capacitor types 1 to 3 according to FIG Table II. In FIG. 3, the solid lines indicate the dependence of TC on the temperature and the dashed lines that of the loss angle tan ό. Numbers 1 to 3 in FIG. 3 denote the respective capacitor type according to Table I. From Table I and FIG. 3 it becomes clear that semiconductor ceramic capacitors according to the invention are superior to conventional semiconductor ceramic capacitors with regard to the loss angle tan ό and the size of TC. From Table I and FIGS. 1 and 2 it is also clear that the voltage characteristics and the aging properties of semiconductor ceramic capacitors according to the invention are excellent.

From the foregoing it is clear that the half

Table II

conductor ceramic capacitors according to the invention no

NEN have the disadvantages of conventional semiconductor ceramic capacitors of the reduction-reoxidation type with BaTiOj are present. Also are Semiconductor ceramic capacitors according to the invention in terms of temperature, voltage and

Aging characteristics are very stable and can therefore be used to advantage in electronic circuits. _t

The values of the loss angle and the size of TC given in Table I for capacitor type No.

1 were determined at a voltage of 0.5 V and a frequency of 1 kHz. The insulation resistance was measured at a voltage of 25 V. The specified value of the voltage characteristic lies with this type of capacitor an applied DC voltage

connection of 25 V. For capacitor type no. 2, the value for the loss angle tan ό and the values for the size TC were determined at a voltage of 1 V and a frequency of 1 kHz. The insulation resistance was measured at a voltage of 50 V.

J5 determined. The value of the voltage characteristic is at Applying a DC voltage of 50 V determined. The values for capacitor type No. 3 in Table I were determined under the same conditions as for capacitor type no.1.

Table 11 below shows the electrical properties at various amounts of Mn ions in the mixture given above. This table therefore provides information about the effect of the Admixture of Mn ions.

Cond. Type No. Mn ions

(Wt .-%)

C "

(• jJ7cnr)

tan δ Χ 10-

Isol. resistance

Breakdown voltage

(V)

4th 0 0.040 21 1 X 10 ' 250 5 0.025 0.044 0.7 1 X 10 ' 600 6th 0.05 0.040, 0.5 5X10 ' 800 7th 0.15 0.034 0.4 5 X 10 ' 1200 8th 0.40 0.021 0.4 7X10 ' 1600 9 0.60 0.0007 0.1 OO 7 (XK)

As is clear from Table II, the admixture of Mn ions is beneficial even in small amounts a rapid increase in the insulation resistance. This increase in insulation resistance will achieved by the lowering of the density of the free electrons in the boundary layer, which on the Valcnz-Komnensaiiunseffekt due to the Mn ions in the boundary layer.

For the capacitor types shown in Table H, manganese carbonate (MnCOi) was used as the source for the Mn ions hi used and mixed in in such an amount that resulted in a predetermined content of Mn ions.

If the proportion of Mn ions is less than 0.025 percent by weight shows the ceramic base body, which

made from such a mixture have spots and pinholes on their surface no fine surfaces. Furthermore, capacitors made from such mixtures show large capacitors Fluctuations in their characteristic values. On the other hand, when the content of Mn ions has a value of 0.60 percent by weight, the capacitance becomes very small, while the insulation resistance becomes very is high. This is due to the fact that the reoxidation during the reoxidation step is very high is violent and leads to deterioration of the semiconductor ceramic capacitors.

The above-described effects of adding Mn ions are the same throughout the area A-8-C-D of the diagram of FIG. The κ »amount of the addition of Mn ions is consequently limited to values between 0.025 and 0.40 percent by weight.

Other experiments have shown that the addition of Co-, Ni-, Cr-. V, Nb, Ta, La and Cc ions instead of Mn ions leads to exactly the same results as those obtained with Mn ions, and that the joint admixture of two or more of the above ion types likewise to good semiconductor ceramic capacitors whose characteristic properties are the same as those of the above considered semiconductor ceramic capacitors, provided that the total amount of mixed ions is within the range of 0.025 to 0.40 percent by weight. in

4 shows a graph illustrating the relationship zwinchen the capacitance C. of the size of TC, the tan for a temperature of -30 ⁰ C and the loss angle <5 on the one hand and the value X of the mixture component B12OJ · χ TiO _2, which is one the r> is the main constituent of the ceramic material for semiconductor ceramic capacitors according to the invention, on the other hand.

As long as χ is below 0.5, the Bi ₂ Oj-AnIeU is excessively large and the mixture falls outside the range given above, since the Bi ₂ O ₁ evaporates during the heating, which changes the individual properties, which are undesirably large for practical use brings with it. If, on the other hand, χ is greater than 9.0, there is an excess of TiO2 and the ceramic base bodies adhere to one another.

When χ is between 0.5 and 9.0, as shown in FIG. 4, on the other hand, good values for the capacitance and for the value TC result for the semiconducting ceramic capacitors. and for the loss angle w tan d. For the mixture _{component Bi 2} O ₁ ■ χTiG? values between 0.5 and 9.0 are therefore preferred for χ.

4 applies with the different values of χ for the component Bi ₂ Oj - χ T1O2 for a ceramic mixture with 66.0 percent by weight SrTiOj, with 27.0 percent by weight CaTiO ₃ , with 7.0 percent by weight Bi ₂ O ₃ χ TiO ₂ and with 0.05 percent by weight Mn ions.

5 shows the dependence of the capacitance C wi [pF / cm ² i of the value TC. [%] and the loss angle tan δ of the different proportions of the three compounds SrTiOj, CaTiOj and Bi ₂ Oj - 3TiO _{2 of} the above mixture for semiconductor ceramic capacitors. b5

Like Fi g. 5 shows, the semiconducting ceramic capacitors have advantageous properties with regard to the value TC and the loss angle tan 6. If one uses ceramic mixtures that fall in the quadrangular range A - B - C - D and if one uses these mixtures 0.025 to 0.4 percent by weight of ions at least admixes one of the following elements:

Manganese, cobalt, nickel, chromium, vanadium, niobium, tantalum, lanthanum and cerium. Semiconductor ceramic capacitors with excellent properties can thus be obtained from ceramic mixtures which fall into the quadrangular region A-B-C-D , the mixture components indicated below in Table 111 being present for points A, B, C and D, including at least one ion the following elements can be added:

M n, Co, N i, Cr, V, Nb, Ta, La and Ce.
Table III

CaTiOi

| Gcw .-%]

SrTiO,

Bi ₂ O-, · λ TiO.

[Weight%]

A. 98.0 0 2.0 B. 0 98.0 2.0 C. 0 50.0 50.0 D. 50.0 0 50.0

In Fig. 5 is the value χ in Bi ₂ Oj · χ TiO ₂ = 3. However, this value is only a representative example. This is because for values of χ in the range from 0.5 to 9.0 in semiconductor ceramic capacitors according to the invention, good properties are also achieved, as can be seen from FIG. 4 becomes clear.

In the event that the proportion of Bi ₂ Oj · χ TiO ₂ in the ceramic bodies for capacitors according to the invention is less than 2.0 percent by weight, it is difficult to release the oxygen from the ceramic bodies, even if they are subjected to a heat treatment in one exposing a reducing atmosphere, so that such ceramic bodies are not semiconducting. It is found that reduced amounts of bismuth hinder easy oxygen release and reoxidation.

If the proportion of Bi ₂ Oj · TiO ₂ becomes higher than 50.0% by weight, it is difficult to sinter the molded bodies, which is inconvenient in practice.

Accordingly, a proportion of Bi ₂ O ₃ · XTiO ₂ between 2.0 and 50.0 percent by weight is preferably used. The proportion of CaTiO ₃ and SrTiO ₃ corresponds in each case to the _{remainder of the given proportion of Bi 2} O ₃ · * TiO _{2. In} other words, the proportion of CaTiO ₃ is between 0 and 98.0 percent by weight. When the amount of CaTiO ₃ is 0 percent by weight, the amount of SrTiO _{1 is} up to 98.0 percent by weight, while when the amount of CaTiOj is 98.0 percent by weight, the amount of SrTiOj is 0 percent by weight.

CaTiO ₁ and SrTiO ₃ are each used in such a weight ratio that the desired properties for C, tan ό and T result.

In the event that the proportion of SrTiO ₁ and CaTiOi in the total mixture is below 50.0 percent by weight, sintering becomes difficult because the proportion of Bi ₂ Oj - JrTiO ₂ is too high. On the other hand, if the proportion of SrTiO ₃ and CaTiOj exceeds 98.0% by weight of the total mixture, the proportion of B12OJ · xTiO ₂ becomes less than ZO% by weight, so that it becomes difficult to use that in the ceramic bodies

ίο

to release contained oxygen by a heat treatment in a reducing atmosphere, so that the ceramic bodies do not become semiconducting.

As described in detail above, the semiconductor ceramic bodies which by sintering the mixture in an oxidizing atmosphere and by a subsequent heat treatment in a reducing atmosphere to Releasing some of the oxygen from the ceramic bodies and bringing about Semiconductor properties were prepared, coated with silver paste and in an oxidizing atmosphere heated in order to simultaneously burn in the silver layers, a surface diffusion of the silver and a To achieve reoxidation of the surface of the ceramic body and due to this treatment a lower loss angle tan <5, a lower temperature dependence of the capacitance and a higher one Insulation resistance, based on the applied voltage, can be achieved than with the known capacitors.

Semiconductor ceramic capacitors according to the invention can be used in many fields.

especially in circuits in which high voltages are used.

Semiconductor ceramic capacitors according to the invention also have none of the disadvantages that are encountered in the conventional semiconductor ceramic condensers of the reduction-reoxidation type with BaTiOs are present, and are advantageous in that they have good voltage and frequency characteristics, and their electrical properties are not affected by aging ίο be. Consequently, semiconductor ceramic capacitors according to the invention can also be used in electronic Circuits are used.

In addition, the ability to solder the leads directly to the surface of the silver layers of the coverings improves, not just the Machinability in the production of the semiconductor ceramic capacitors and in the installation of the same in electronic circuits, but also leads to good performance and simplification of production, when such semiconductor ceramic capacitors are used in miniaturized electrical circuits will.

In addition 4 sheets of drawing rolls

Claims (1)

Patent claims: I. Ceramic capacitor with a body made of semiconducting reduced ceramic, which is formed from the main constituent titanates and additives, in which the ceramic body is surrounded by a dielectric layer formed by reoxidation of the surface layer of the body made of reduced ceramic, and in which the Coverings consist of silver layers applied to the ceramic body and in which these silver layers are provided with leads connected to them in an electrically conductive manner, characterized in that the main component of the ceramic body consists of a solid composition of calcium titanate and / or strontium titanate and a proportion for which the formula applies: Bi ₂ O ₃ · XTiO ₂ , where the following relationship applies to χ : 0.5 <x <9.0, that the ceramic body contains at least one of the following groups of substances as an additive: manganese, cobalt, nickel, chromium, Vanadium, niobium, tantalum, lanthanum and cerium, in a total amount between 0.025 un d 0.4 percent by weight, and that the composition of the main constituent is chosen so that it falls within a square area (A-B-C-D) of a three-substance diagram (Fig. 5), with the corner points (A to D) of the square area (A — B — C — D) the compositions given in the following table apply: that the sintered body is then kept ^{at a temperature of about 850 °} C. for a period of about one hour in a reducing atmosphere and that finally the body is kept ^{at a temperature of about 780 °} C. in an oxidizing atmosphere for a period of about one hour.