US3002841A

US3002841A - Dielectric materials

Info

Publication number: US3002841A
Application number: US15500A
Authority: US
Inventors: Goodman Gilbert
Original assignee: Individual
Current assignee: Individual
Priority date: 1960-03-16
Filing date: 1960-03-16
Publication date: 1961-10-03
Anticipated expiration: 1978-10-03

Description

Oct. 3, 1961 G. GOODMAN 3,002,841

DIELECTRIC MATERIALS Filed March 16, 1960 4 Sheets-Sheet 1 F ig.

Loss Tan gen! Die/ec/n'c Cons/an! I l l I I I I l I l I l Temper ofure "C In ve mor Gilberf Goodman,

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Oct. 3, 1961 Filed March 16, 1960 Dielectric Cans ram Dielectric Cons/ant G. GOODMAN DIELECTRIC MATERIALS 4 Sheets-$heet 2 Fig.2.

Temperature C Fig. 3.

| l l I 400 500 600 700 Temperature "C in ven for Gi/berf Goodman,

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G. GOODMAN DIELECTRIC Filed March 16, 1960 Dielectric Cons rant Die/e c trio Constant MATERIALS 4 Sheets-Sheet 3 Fig. 4.

| I I I00 200 300 I l l I 400 500 600 700 Temperature C Fig. 5-

/n venfor Gilbert Goodman,

| I l I l I00 200 330 Temperature C H/s Afforney.

Oct. 3, 1961 G. GOODMAN 3,002,841

DIELECTRIC MATERIALS Filed March 16, 1960 4 Sheets-Sheet 4 Fig. 6.

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limited States Patent 3,002,841 DIELECTRIC MATERIALS Gilbert Goodman, 1099 Mohawk Road, Schenectady, N.Y.

Filed Mar. 16, 1960, Ser. No. 15,500 11 Claims. (Cl. 106-39) This invention relates to polycrystalline dielectric materials and, more particularly, to vitrified ceramic compositions having comparatively high substantially invariant dielectric constants up to about 350 C. and only slightly varying constants up to about 500 C.

This application is a continuation-in-part of copending application Serial No. 756,412, now abandoned, entitled Dielectric Materials, filed August 21, 1958, and assigned to the same assignee as the present invention.

The increasing use of electrical and electronic equipment for various applications often requires development of apparatus having components capable of withstanding unusual and often severe operating conditions. One of the more commonly encountered difficulties is that of producing parts capable of withstanding comparatively high temperatures and capable of successfully performing their intended functions at such elevated temperatures, as well as at ordinary temperatures. Radio, radar, and analogous systems are examples of apparatus which many times must operate over a wide range of temperatures.

Dielectrics are commonly used in a number of electrical applications, the present invention being concerned primarily with polycrystalline ceramic dielectrics for use' in capacitors and the like. Capacitor dielectrics can be divided into three general categories, depending on their dielectric constants and dielectric loss tangents.

The following Table I shows the general order of the dielectric properties of the three groups measured at cps. and the stability of these properties over a comparatively wide temperature range, say 0 C. to 350 C.

Table I Dielectric Material Dielectric Loss Temperature Constant Tangent Stability Vitreous Silica 4 .0001 Good. 0'0 100 001 Fair to Poor.

1, 000 .01 Poor.

An additional object of this invention is to provide ternary oxide compositions having dielectric constants which are substantially uniform at temperatures up to about 300 C. and which vary only slightly up to 500 C.

Other objects and advantages of this invention will be in part obvious and in part explained by reference to the accompanying drawings and specification.

amen

. Patented Oct. 3, 1961 In the drawings:

FIG. 1 shows typical curves of dielectric constants and dielectric loss tangents versus temperature measured at 10 cps. for the compositions of this invention as compared with corresponding curves for sintered titania;

FIG. 2 shows curves of dielectric constant versus temperature for various compositions of this invention;

FIG. 3 shows a curve similar to those of FIG. 2 for an additional composition;

FIG. 4 shows curves of dielectric constant versus temperature for still further compositions of the present in vention;

FIG. 5 shows the effect of temperature on the dielectric constant of a binary composition of strontium and tantalum oxide, a known, vitrified ceramic dielectric; and

FIG. 6 shows the effect of temperature on the dielectric constants of materials produced according to this invention and in which the ratio of tantalum to the combined amounts of the other metals is varied.

Briefly, the present invention concerns the production of vitrified ceramic compositions having substantially invariant dielectric constants up to about 350 C., only slightly varying constants from 350500 C., and also having suitably low loss tangents (tan 6). The compositions are made up of a vitrified combination of an alkaline earth such as barium oxide, strontium oxide, or calcium oxide and combinations thereof, an oxide of a metal from the group zirconium, titanium, tin, and combinations thereof, and tantalum oxide.

As previously mentioned, it is many times desirable to obtain dielectric compositions which have comparatively high dielectric constants, for example, on the order of 100, and relatively low loss tangents, for example, on the order of 0.0005.

While the required properties are approached by titania and other ceramics at room temperature, they are retained only over a very limited temperature range. The compositions of the present invention make it possible, however, to retain the desired properties virtually constant from room temperature to 350 C. and only, slightly vari ant from 350500 C.

The compositions are vitrified, polycrystalline ceramics for use in suitable apparatus such as the capacitors already discussed. Specifically, the compositions are preferably composed essentially of a vitrified combination of (a) an alkaline earth selected from the group consisting of barium oxide, strontium oxide, and combinations thereof in all proportions, although calcium oxide may also be used. The second component (b) of the composition is one of the metals, zirconium, titanium, or tin, or combinations thereof which are oxidized during subsequent processing, and the final component is (c) tantalum oxide.

It will be appreciated that the components of the system can be combined as metals and subsequently oxidized prior to vitrification. However, in most instances, it is preferred to add the materials either in the oxide state,

part of the final product.

Sample compositions made according to the present invention are:

3SrO ZrO 2Ta O 3Ba0 ZrO 2Ta O and 3SI'O S 2173 05; 3 BaO 2Ta205.

Obviously, early in V The following Table II lists the nominal weight percent compositions of sample polycrystalline bodies made according to the present invention:

Table 11 Ba- Oxalate SrCOg Tazos T102 SD02 Polycrystalline ceramic dielectric bodies were made by mixing suitable quantities of the various selected components (see Table II) in a ball mill in amyl acetate for to hours. Alcohol can be used in place of amyl acetate if desired. Following the milling of the materials, they were dried and calcined in a platinum container at about 1350 C. The calcined material was crushed to 200 mesh, since it had agglomerated somewhat during firing, and carbowax was added to give consistency suitable for pressing the material into one inch diameter buttons, one-eighth inch thick. The buttons were then fired in air for 1 to 1 hours on a platinum base at the temperatures indicated in Table II. Neither the temperature nor the time is critical, as the time at maximum temperature may vary as much as an hour and the maximum temperature as much as 25 C., for example.

The dielectric constants and loss tangents (tan 6) were measured for two of the preceding compositions over a temperature range of from 25 to 600 C. The first of these compositions was 3SrO-ZrO -2Ta O and the values obtained are shown in the following Table III:

The second composition dilfered from the first in that the zirconia component was replaced by tin oxide, so that the formula reads 3SrO-SnO -2Ta O The dielectric constants and loss tangents of this material, as functions of temperature, are shown in Table IV which follows:

Table IV 10 kc./sec.

Temperature, 0.

Dielectric Tan. 5

Constant Comparing the values shown in Tables III and IV, it is obvious that the dielectric constant changes very little from room temperature up to the range of from 300 to 400 C. and that the variation to 500 C. is slight. In general, substantial invariancy occurs up, to about 350 C., this fact being ascertainable by plotting the dielectric constant values against the temperature. The loss tangent increases very little up to about 300 to 400 C., although there is more of an increase from about 350 to 500 C. than occurs at the lower temperatures.

Referring to FIG. 1 the curves indicate the effect of temperature on the dielectric constants and loss tangents of the ternary combination, 3SrO-ZrO -2Ta O of the present invention, with similar curves for polycrystalline TiO being shown for purpose of comparison. Specifically, curve 10 shows the dielectric constant of the ternary combination 3SrO-ZrO -2Ta O at temperatures up to about 600 C. Comparing curve 10 with the curve 11, which shows the effect of temperature on titania (TiO ceramic, it is obvious that the initial dielectric constant of the titania is slightly lower than that of the ternary dielectric and that it changes rapidly after a temperature of about 300 C. is exceeded. The dielectric constant of the ternary, however, remains substantially invariant up to the 600 C. figure shown in the drawing. Similarly, the loss tangent curves 12 and 13 for the ternary dielectric and the titania respectively show that the loss tangent for the titania begins to increase at a much lower temperature than is true for the material of the invention.

An important factor to be considered, in order that the ternary composition has optimum dielectric properties, is the molar ratio of the alkaline earth metal chosen to the metal selected from the group composed of zirconium, titanium, and combinations thereof. Generally, the alkaline earths and the zirconium, titanium and tin oxides should be present in such molar ratios in the vitrified product that there are from 1.25 to 1.75 mols of alkaline earth metal present for each 0.25 to 0.75 mol of zirconium, titanium or tin. Normally, the best ratio is 1.5 mols of the alkaline earth metal to 0.5 mol of either zirconium, titanium or tin, to achieve optimum results. That is, a ratio of 3 mols of alkaline earth metal to 1 mol of zirconium, titanium or tin is preferred, although it will be recognized that these figures are not absolute and compositional variations are possible. For example, 1.25 to 1.75 mols of alkaline earth metal to 0.5 mol of metal from group (b) results in formation of a good dielectric. While these molar ratios represent preferred amounts, other amounts can be used and still obtain a ceramic having desirable properties which are unattain able in most existing, polycrystalline dielectrics. Thus, if instead of 1.5 mols of strontium to 0.5 mol of zirconium, for example, there is 1 mol of strontium to 1 mol of zirconium, improved properties are still obtained.

The value of having the proper molar ratio between the metals of the alkaline earth group (a) and the metals from the zirconium, titanium, and tin group (b), can clearly be seen by referring to FIG. 2 of the drawings. In this graph, the dielectric constants of materials made with varying molar ratios between the metals of the (a) and (b) groups have been plotted against temperature. All measurements were made at 10 kilocycles per second.

Since we are at the moment concerned only with the molar ratios between the metals, the following discussion deals only with the metals and omits any reference to the oxides of the compounds which will normally be present in the finished material. Referring to curve 15 of FIG. 2, the ternary dielectric used contained equal amounts of strontium and zirconium with 2 mols of tantalum. Therefore, the molar ratio between the strontium and zirconium is 1 to 1 and the combined amounts of zirconium and strontium equals the total amount of tantalum, so that the molar ratio between these two materials, is also 1 to l. The curve 16 represents a change in the proportions between strontium and zirconium, there now being 1.75 mols of strontium to 0.25 mol zirconium. Whilethe curve 16 doesnot vary as much as the curve 15 over the temperature range, it does vary more than the curve 17 in which 1.5 mols of 33 strontium arepresent to 0.5 mol zirconium. When the ratio drops still further to 1.25 mols of strontium to 0.75 mol of zirconium, the curve 18 once again gins to assume a concave configuration.

Comparison of curves 15 through 18 indicates that the optimum molar ratio is present when 1.50 mols of strontium or other alkaline earth metal to 0.5 mol of zirconium or tin or titanium, are present. Referring to FIG. 3, the curve 20 indicates the characteristics of the ceramic composition having the metals in the molar proportions: 1.5 Ba, 0.5 Sn, and 2.0 Ta. This curve varies moderately, compared with known dielectrics, throughout the entire temperature-range tested.

FIGURE 4 shows the invariancy of the dielectric constants of the materials of the present invention. In this instance, the curve 25 shows the characteristics for compositions having metals in the molar proportions, 1.5 Sr, 0.5 Sn, and 2.0 Ta. It is obvious that while there are minor fluctuations in the capacitance values of this material, it remains substantially invariant throughout a wide temperature range. The material Whose properties are indicated by the curve 26 has substantially the same dielectric properties as the material whose properties are shown by FIG. 25, with the exception that somewhat greater fluctuations were noted at intermediate temperatures. The metal composition of this material is 1.5 Sr, 0.5 Ti, and 2.0 Ta. The only composition change of the latter ceramic from the former is the substitution of titanium for tin.

FIG. 5 shows the importance of including one of the materials from the (b) group of zirconium, titanium, tin and combinations thereof. In this instance, the compound includes 2 mols of strontium and 2 mols of tantalum so that it is a binary composition. It is obvious that the dielectric properties, as indicated by curve 30, change markedly at about 125 C. Thus, although the amount of the (b) group metal which is used is small, it is nevertheless an important element in attaining the desired dielectric properties.

It is understood, of course, that in the preceding examples the molar ratio of the total amounts of the two (a) and (b) group metals to the amount of tantalum is 1 to 1.

To obtain optimum dielectric and loss tangent properties, a definite molar relationship between the amount of tantalum metal present and the total amount of the two metals selected from the (a) and (b) groups should be present. Specifically, the total molar concentration of the (a) and (b) group metals should preferably range from about 0.75 to 1.50 mols for each mol of tantalum metal present in the oxide. Compositions in which there are from about 1.00 to 1.25 mols of the combined amounts of the metals from the (a) and (b) groups for each mol of tantalum represent the preferred compositions since slightly greater stability and better dielectric and loss tangent properties are obtained. Several compositions were prepared to test the effect of varying the ratio between the (a) and (b) group metals and the tantalum. These compositions are listed in the following Table V:

Samples were prepared in the manner described earlier in the application and tested to determine their dielectric properties. Referring to FIG. 6 of the drawings, the curve 35 shows the dielectric properties of the first of the four compositions listed in Table 'V, while "the three remaining

curves

36, 37 and 38 illustrate the dielectric properties of the remaining three samples. Curve 35 clearly shows that the dielectric constant of a polycrystal line ceramic body produced according to this invention and having a ratio between the combined amounts of the (a) and (b) groupmetals and the (c) group metal tantalum of 0.75 to 1.00 will be substantially invariant at temperatures up to about 350 C. before conductivity begins to increase significantly. Similarly, curve 38 shows that the dielectric constant of a ceramic body having a ratio of about 1.25 to 1.00 between the combined amounts of the (a) and (b) groupmetals and the tantalum is substantially invariant to temperatures as high as 550 C. The other curves 36 and 37 represent compositions having intermediate ratios and these materials also have dielectric constants which remain substantially invariant to elevated temperatures. For the last two compositions in Table V, dielectric loss tangents of less than 10- were measured up to 200 C. For the second composition, this low level of dielectric loss persisted to C.; and for the first composition, it was observed at room temperature. Upon heating, dielectric loss increased from these values in the usual manner.

Thus, the present invention makes possible the attainment of substantially invariant dielectric constants over a wide temperature range, all of the compositions showing substantial invariancy up to about 350 C. and only slight variance in the values to temperatures up to about 500 C., and occasionally even higher. The loss tangent values are also quite acceptable for most applications.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A ceramic dielectric composition having a dielectric constant varying only slightly up to about 500 C., said composition being composed essentially of a vitrified combination of ingredients composed essentially of (a) an alkaline earth selected from the group consisting of strontium oxide, barium oxide, calcium oxide, and mixtures thereof, (b) a metallic oxide selected from the class consisting of zirconium oxide, titanium oxide, tin oxide, and mixtures thereof, and (c) tantalum oxide, the metals of the oxides of (a) and (b) being present in such molar ratios that the total molar concentration of said metals ranges from 0.75 to 1.50 of the molar concentration of tantalum in said tantalum oxide.

2. A ceramic dielectric as defined in claim 1 wherein said alkaline earth is strontium oxide.

3. A ceramic dielectric as defined in claim 1 wherein said alkaline earth is barium oxide.

4. A ceramic dielectric as defined in claim 1 wherein said alkaline earth is a mixture of strontium and barium oxides.

5. A ceramic dielectric composition having a dielectric constant varying only slightly up to about 500 C., said composition being composed essentially of a vitrified combination of ingredients composed essentially of (a) an alkaline earth selected from the group consisting of strontium oxide, barium oxide, calcium oxide, and mixtures thereof, (b) a metallic oxide selected from the class consisting of zirconium oxide, titanium oxide, tin oxide, and mixtures thereof, and (c) tantalum oxide, the metals of the oxides of (a) and (b) being present in such molar ratios that the total molar concentration of said metals ranges from 1.00 to 1.25 of the molar concentration of tantalum in said tantalum oxide.

6. A ceramic dielectric composition having a dielectric constant varying only slightly up to about 500 C., said composition being composed essentially of a vitrified combination of ingredients composed essentially of (a) an alkaline earth selected from the group consisting of strontium oxide, barium oxide, calcium oxide, and mixtures thereof, (b) a metallic oxide selected from the class consisting of zirconium oxide, titanium oxide, tin oxide, and mixtures thereof, and (c) tantalum oxide, the metals of the oxides of (a) and (b) being present in such molar ratios that the total molar concentration of said metals is essentially equal to the molar concentration of tantalum in said tantalum oxide.

7. A ceramic composition having a dielectric constant varying only slightly up to about 350 C., said composition being a vitrified product of a mixture of ingredients composed essentially of (a) an alkaline earth selected from the class consisting of strontium oxide, barium oxide, calcium oxide, and mixtures thereof, (b) a metallic oxide selected from the class consisting of zirconium oxide, titanium oxide, tin oxide, and mixtures thereof, and (c) tantalum oxide, the metals of said oxides of (a) and (b) being present in such molar ratios in the vitrified product that there are from 1.25 to 1.75 mols of alkaline earth metal per 0.25 to 0.75 mol of the metal of said metallic oxide of (b), there being 0.75 to 1.50 mols of the combined metals in (a) and (b) to each one mol of tantalum in said tantalum oxide.

8. A ceramic composition having a dielectric constant varying only slightly up to about 350 C., said composition being a vitrified product of a mixture of ingredients composed essentially of (a) an alkaline earth selected from the class consisting of strontium oxide, barium oxide, calcium oxide, and mixtures thereof, (b) a metallic oxide selected from the class consisting of zirconium oxide, titanium oxide, tin oxide, and mixtures thereof, and (c) tantalum oxide, the metals of said oxides of (a) and (b) being presentin such molar ratios in the vitrified product that there are from 1.25 to 1.75 mols of alkaline earth metal per 0.25 to 0.75 mol of the metal of said metallic oxide of (b), there being 1.00 to 1.25 mols of the combined metals in (a) and (b) to each one mol of tantalum in said tantalum oxide.

9. A ceramic composition having a dielectric constant varying only slightly up to about 500 C., said composition being a vitrified product of a mixture of ingredients composed essentially of (a) an alkaline earth selected from the class consisting of strontium oxide, barium oxide, calcium oxide, and mixtures thereof, (b) a metallic oxide selected from the class consisting of zirconium oxide, titanium oxide, tin oxide, and mixtures thereof, and

(c) tantalum oxide, the metals of said oxides of (a) and (b) being present in such molar ratios in the vitrified product that there are from 1.25 to 1.75 mols of alkaline earth metal per 0.25 to 0.75 mol of the metal of said metallic oxide of (b), the total molar concentration of the metals in (a) and (b) being equal essentially to the molar concentration of tantalum in said tantalum oxide.

10. A ceramic composition as defined in claim 6 wherein the molar ratio between the metal of said alkaline earth and the metal of said metallic oxides of (b) are present in such a ratio that there are 1.50 mols of said alkaline earth metal per 0.50 mol of the metal of said metallic oxide of (b).

11. A ceramic composition having a dielectric constant varying only slightly up to about 500 C., said composition being a vitrified product of a mixture of ingredients composed essentially of (a) an alkaline earth oxide selected from the class consisting of strontium oxide, barium oxide, calcium oxide, and mixtures thereof, (b) a metallic oxide selected from the class consisting of zirconium oxide, titanium oxide, tin oxide, and mixtures thereof, and (c) tantalum oxide, the metals of said oxides of (a) and (b) being present in such molar ratio in the vitrified product that there are from 1.25 to 1.75 mols of the alkaline earth metal for 0.25 to 0.75 mol of the metal of the metallic oxides of (b), the total molar concentration of the metals in (a) and (b) being equal to about 2 and being equal essentially to the same molar concentration of tantalum in said tantalum oxide.

References Cited in the file of this patent UNITED STATES PATENTS 2,563,307 Burnham et a1. Aug. 7, 1951 2,646,359 Wainer July 21, 1953 2,855,317 McQuarrie et al. Oct. 7, 1958 FOREIGN PATENTS 755,860 Great Britain Aug. 29, 1956 OTHER REFERENCES Johnson et al.: J. American Ceramic Society, vol. 32, No. 12, December 1949 (pages 398-401).

UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent No. 3,002,841 October a, 1961 Gilbert Goodman It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

In the grant, lines 1, 2, and 3, for "Gilbert Goodman? of Schnectady, New York, "7 read Gilbert Goodman, of Schenectady, New York, as'signor to General Electric Company, a corporation of, New York, line 12, for. FfGilhert Goodman, his heirs" read General Electric Company, its successors in the heading to the printed specification, lines 3 and 4, for Gilloert Goodman, 1099 Mohawk Road, Schenectady, N. Y, read Gilbert Goodman, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York.

Signed and sealed this 3rd day of April 1962 (SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents

Claims

1. A CERAMIC DIELECTRIC COMPOSITION HAVING A DIELECTRIC CONSTANT VARYING ONLY SLIGHTLY UP TO ABOUT 500*C., SAID COMPOSITION BEING COMPOSED ESSENTIALLY OF A VITRIFIED COMBINATION OF INGREDIENTS COMPOSED ESSENTIALLY OF (A) AN ALKALINE EARTH SELECTED FROM THE GROUP CONSISTING OF STRONTIUM OXIDE, BARIUM OXIDE, CALCIUM OXIDE, AND MIXTURES THEREOF, (B) A METALLIC OXIDE SELECTED FROM THE CLASS CONSISTING OF ZIRCONIUM OXIDE, TITANIUM OXIDE, TIN OXIDE, AND MIXTURES THEREOF, AND (C) TATALUM OXIDE, THE METALS OF THE OXIDES OF (A) AND (B) BEING PRESENT IN SUCH MOLAR RATIOS THAT THE TOTAL MOLAR CONCENTRATION OF SAID METALS RANGES FROM 0.75 TO 1.50 OF THE MOLAR CONCENTRATION OF TANTALUM IN SAID TANTALUM OXIDE.