US 3896055 A
Description (OCR text may contain errors)
United States Patent 1 Bouchard et al.
[4 1 July 22,1975
1 41 PYROCI-ILORE-RELATED OXIDES CONTAINING COPPER AND/OR SILVER AND RESISTOR COMPOSITIONS THEREOF 175 Inventors: Robert Joseph Bouchard; Donald Burl Rogers, both of Wilmington, Del.
 Assignee: E. I. du Pont de Nemours & Co.,
22 Filed: Jan. 26, 1973  Appl.No.:326,955
 U.S. Cl. 252/521; 252/512; 252/514; 252/518", 423/263; 423/593; 423/595", 423/598  Int. Cl. H0lb 1/08  Field of Search 252/521, 514, 518, 519, 252/512; 423/593, 263, 598, 595
 References Cited UNITED STATES PATENTS 3/1945 Barrington 252/512 X 1/1947 Quinn 252/512 Primary Examiner-Leland A. Sebastian Assistant E.raminerR. E. Schafer  ABSTRACT Novel polynary oxides of pyrochlore-related crystal structure having Cu and/or Ag ions in the A-site. Powder compositions comprising such novel oxides and dielectric material plus optional components, useful for forming thick-film printed resistors on dielectric substrates; also resistors formed by firing such powder compositions.
16 Claims, N0 Drawings PYROCHLORE-RELATED OXIDES CONTAINING COPPER AND/OR SILVER AND RESISTOR COMPOSITIONS THEREOF BACKGROUND OF THE INVENTION The novel compounds of this invention, and powder compositions containing the same, are improvements over those disclosed and claimed in Bouchard U.S. Pat. No. 3,583,931 which teaches the benefits of bismuth and ruthenium and/or iridium in polynary oxides having pyrochlore-related crystal structure, for electrical resistor applications, U.S. Pat. No. 3,533,109 to Lewis C. Hoffman teaches resistor compositions comprising such polynary oxides (and related polynary oxides) plus inorganic binder and finely-divided noble metals. Resistor compositions according to these teachings have enjoyed considerable commercial success because of the excellent control they offer in providing a range of resistors with reproducible values of resistivity, little affected by temperature or humidity in use, and readily printed and fired on dielectric supports.
A primary means of establishing the resistivity of a fired resistor according to the teaching of Hoffman is to adjust the relative proportions of polynary oxide, noble metal, and inorganic binder in the composition. In general, the unusual properties of the resistor are adjusted toward higher resistivities by increasing the proportion of binder and adjusted toward lower resistivities by increasing the proportion of finely divided noble metal. However, increasingly large proportions of noble metal to polynary oxide also produce an increase in TCR (temperature coefficient of resistance) and obviate many of the advantages which have led to the gradual replacement of noble metal/glass compositions (such as the palladium/silver/glass compositions of DAndrea U.S. Pat. No. 2,924,540) by the more sophisticated polynary oxide containing compositions.
Chemical substitution in the polynary oxide itself has been investigated as a method for adjusting electrical properties. Thus the patents cited above contemplate, e.g., the substitution of yttrium, thallium, indium, cadmium, lead or the rare earth metals of atomic number 57-71 inclusive for some of the'bismuth in Bi Ru O and Bi lr O and platinum, titanium, tin, chromium, rhodium, rhenium, zirconium, antimony or germanium for some of the ruthenium or iridium. There is a need, however, for compositions capable of producing resistivities that are substantially lower than those obtained with Bi (Ru,lr) O while maintaining the desirably flat temperature response. Such low resistivities are often below 10 ohms/square, and are preferably in the range l-5 ohms/square.
SUMMARY OF THE INVENTION A portion of the bismuth in Bi (Ru,lr) O and its modified oxides can be replaced by the ions Ag and Cu, with retention of the pyrochlore structure. Ag is univalent and Cu is presumably univalent, although it is possible that some divalent Cu may be present. Cu and/or Ag produces a level of electrical conductivity that extends the utility of previously known compositions.
The polynary oxides of the invention are electrically conductive oxides of pyrochlore-related crystal structure having the formula I 2-.r 2 7-2 wherein:
l. M is at least one of Ag or Cu;
2, 2. M is Bi or a mixture of at least one half Bi plus up to one half of one or more cations from among a. bivalent Cd or Pb and b. trivalent ,Y, T1, In and rare earth metals of atomic number 57-71, inclusive;
3. M" is at least one of a. Ru,
b. 1r, and
c. a mixture of at least three-fourths of at least one of Ru and Ir and up to one-fourth of at least one of Pt, Ti and Rh;
4. x is in the range 0.10 to 0.60; and
5. zis in the range 0.10 to 1.0, and is equivalent to the sum of monovalent cations M and half of divalent cations in the polynary oxide.
Preferred polynary oxides are those wherein X is in the range 0.10 to 0.5, and include Ag Bi Ru- O go.5 0.15 o.15 2 6.5. go.s o.s 2 s.s o.- 5 1.5 2 6.5.
Also a part of this invention are improved powder compositions useful for producing on dielectric substrates thick-film (printed) resistors of low resistivity. Powder compositions of polynary oxides plus dielectric material are known, with optical constituents such as noble metal powders (platinum, gold, etc.); binary oxides such as Co O etc., as disclosed in Hoffman, U.S. Pat. No. 3,553,109; CdO as disclosed in Schubert U.S. Pat. No. 3,560,410; and inert liquid vehicle. The im-- proved powder compositions of this invention are those wherein the polynary oxide is a copper and/or silvercontaining polynary oxide of this invention as described above.
Also of this invention are electrical elements, such as resistors comprising a dielectric substrate on which such powder compositions have been deposited (as by known screen or stencil printing techniques) and then fired (sintered) to produce an electrically continuous unit.
DETAILED DESCRIPTION OF THE INVENTION In its simplest embodiment this invention consists of the pyrochlore-type oxides of formula M1Bi2' ,(Ru,lr)-
O-, wherein improved conductivity results from the replacement of part of the Bi ions by ions of Ag or Cu.
The univalent ions Ag, Li and Na have heretofore been known in certain electrically insulating pyrochlore-type structures. Cu has not been known toparticupate in.
compositions of pyrochlore-type structures. 8
1n the prototype pyrochlore formula A B O-, re-
placement of a trivalent cation by a univalent one requires that stoichiometry be maintained by an equivalent oxygen deficiency (z =ar). In the more complex situation where both univalent and bivalent cations are substituted, stoichiometry will require a formula A 9 preciated furthermore that small departuresfrom exact stoichiometry may frequently be expected when a small (Ru,lr) disclosed in the'earlier patent cited above, as
well as the much smaller variations that resultfrom well recognized crystal defects. A substantially greater degree of. substitution for bismuth or a substantially greater oxygen deficiency 2 than given in the preceding formula or the claims are not conducive to obtaining a single-phase pyrochlore structure which makes possible the high conductivity of these oxide compositions. On the other hand it will be appreciated that very minor amounts of the univalent metals Ag and Cu might be substituted into the known pyrochlore compositions without producing a substantial effect on the properties.
As indicated above, while it is thought that the copper ions in the polynary oxides of the present invention are univalent, this is not limiting. In fact, it is possible that some of the copper may be divalent. Likewise, while heretofore it has not been possible to substitute more Ag or Cu in the pyrochlore than the amount claimed, it is recognized that under different conditions greater amounts of Ag or Cu might be possible.
The complex oxides of this invention are prepared by heating together the requisite oxides or the readily oxidizable metals or salts which provide a source of the particular elements. Reaction should be carried out under oxidizing conditions at a temperature ranging from about 600C to about 1200C. Direct firing in air at ordinary pressure is usually most convenient, although an atmosphere of oxygen or super-atmospheric pressures may be advantageous if oxidizable metals in finely divided form are used as a source of the requisite elements. As a source of the univalent cation essential to this invention finely-divided silver or copper may be used, but repeated grinding and firing in an oxygen-rich environment should then be used to insure complete oxidation. The preferred source of silver is AgNO which is easily converted to the oxide under firing conditions. Cu O is preferred as the source of univalent copper. Thorough grinding together of the reacting components assists in promoting complete reaction which is usually obtained in times between an hour or less (e.g., 15 min.) and a day. Silica or porcelain vessels may be used, but Pt vessels are preferred at high temperature to avoide any contamination. The completion of reaction is conveniently judged by obtaining a single phase X-ray diffraction pattern corresponding to the pyrochlore structure. Electrical conductivity may be determined on pressed compacts of the powdered oxide or, more functionally, on composites of the oxide product with low melting glasses in the proportion desired to form electrical resistor elements.
The resistor compositions of the present invention are characterized in that some or all of the polynary oxide in polynary oxide/dielectric powder compositions is the Ag or Cu polynary oxide of the present invention. The novelty herein resides in the use of these novel polynary oxides. Optional additives may be added to the powder compositions, such as those disclosed in Schubert U.S. Pat. No. 3,560,410; Hoffman U.S. Pat. No. 3,553,109; Popwich U.S. Pat. No. 3,630,969; and Bouchard U.S. Pat. No. 3,681,262.
Normally the powder compositions contain 5-90 percent polynary oxide and 10-95 percent dielectric material, the relative proportions selected depending upon electrical properties desired in the final resistor. The presence (and amount) of optional additives are determined by similar considerations. Generally, up to 10 percent of optional binary oxide may be present (CdO, V 0 Cr O Mn O Fe;,O,, C0 0 MO, and CuO) and up to 69 percent noble metal powder. When the powder composition is to be dispersed in an inert liquid vehicle, the type and amount of vehicle is a matter of selection by one skilled in the art, the amount of vehicle generally being 10-90 percent of the resulting dispersion.
The dielectric material may be any inorganic material which serves to bind the noble metal and oxide(s) to the substrate. The inorganic binder can be any of the glass frits employed in resistor compositions for this general type. Such frits are generally prepared by melting a glass batch composed of the desired metal oxides, or compounds which will produce the glass during melting, and pouring the melt into water. The coarse frit is then milled to a powder of the desired fineness. The patents to Larsen and Short, U.S. Pat. No. 2,822,279, and to Hoffman, U.S. Pat. No. 3,207,706, describe some frit compositions which can be employed either alone or in combination with glass wetting agents such as bismuth oxide. Typical frit compositions usable as binders in the compositions of this invention include borosilicate glasses such as lead borosilicate, cadmium borosilicate and similar borosilicates. Also, mixtures of various inorganic binders may be used.
Noble metals comprise the free metallic component of the resistor compositions of this invention. These include gold, silver, platinum and palladium.
The compositions are used to produce thick film resistors as disclosed in the Hoffman, Schubert, Bouchard and Popowich patents cited above; printing may beby conventional screen or stencil techniques with optional inert liquid vehicle, as therein described; firing techniques are similarly described therein. The above patents are thus incorporated by reference herein.
Generally, application of the resistor composition in paint or paste form to the substrate may be effected in any desired manner. It will generally be desired, however, to effect the application in precise pattern form, which can be readily done in applying well-known screen stencil techniques or methods. The resulting print or pattern will then be fired in the usual manner at a temperature from about 650-950C. in an air atmosphere employing the usual firing lehr.
The components of the powder composition are finely divided so that they may be screen printed; generally, the average particle size is less than 20 microns.
1n the examples and elsewhere in 'the specification and claims, all parts, percentages and ratios are by weight, unless otherwise stated. X-ray measurements were made using a Norelco diffractometer.
Resistances were determined with a Non-Linear Systems Series X-l Ohmmeter.
Fired resistor film thicknesses were measured using a Brush lnstruments Div. (Clevite Corp.) Surfanalyzer. The thickness, nominally one mil, was normally less than one mil; sheet resistivity (ohm/square/mil) was determined by multiplying the resistance of the x200 mil resistor paid by the actual thickness, and dividing by two.
EXAMPLE 1 AgBiRu O Sufficient reactants are fired to produce AgBiRu O but a hetergeneous product was obtained. 0.2666 g. finely divided Ag, 0.5757 g. Bi O and 0.6577 g. RuO were ground together in an automatic mortar for 30 minutes, pressed into a pellet, and fired in a porcelain crucible open to air for 16 hours at 850C. The hard. black pellet which resulted was shown by X-ray to contain a phase having a cubic pyrodifferent reaction conditions. I
chlore-type structure along with some remaining RuO and Ag. A similar mixture heated in porcelain at 950C. for 24 hours in air produced a blue-black product having a more crystalline pyrochlore X-ray pattern with a cubic cell constant, a,,, about 1024A. significantly 5 smaller than that known for Bi Ru- O 1030A). Thus, AgBiRu o was not formed under these conditions. although it is possible that such polynary oxides where x is 1.0 can be formed under more stringent and/r EXAMPLE 2 Ag Bi Ru O 0.1818 g. AgNO, 0.7484 g. Bi O and 0.5698 g. RuOg were ground together in an automatic mortar for 30 minutes, pressed into a pellet, and fired to 950C for 16 hrs. in an open Pt crucible in air. The black product had a single phase x-ray pattern corresponding to the pyrochlore structure; the cell constant, a,,, was 10.27A.
EXAMPLE 3 Cu ,=,Bi Ru O 0.0823 g. Cu O, 0.8045 g. Bi O and0.6l27 g. RuO were ground together in an automatic mortar for 30 minutes, pressed into a pellet, and
mixed with 14 parts powdered glass frit and 20 parts of an organic vehicle composed of 90 percent ethylcellulose and 10 percent terpineol and screen-printed onto prefired alumina substrates; the resultant structure was dried at 100C. for 10 minutes, fired slowly to 850C. for 10 minutes and then slowly brought back to room temperature. The complete cycle took one hour. The resultant resistor pad was 100 X 200 mils and about 1 mil thick. The glass frit consisted of (wt. percent) 25.7 percent PbO. 20.1 percent B 0 19.7 percent SiO- 7.9 percent A1 0 24.1 percent ZnO, 2.2 percent ZrO- and 0.3 percent Na O. For comparative purposes the pyrochlore Bi Ru O described in US. Pat. No. 3,583,931 was also tested, with and without free metal powder.
The data reported in Table I are the average of quadruplicate samples. The best conductivity (lowest resistivity) was obtained using as conductor compositions the products of this invention, (b), (c), and (f) in Table I. The conductivity is very much greater than for Bi2RuzO1 composition (a) of Table 1), and, surprisingly, greater even than when an equivalent amount of either metallic element, both excellent electrical conductors, is directly added to the composition as in compositions (d) and (e) of Table l. The change in resistance (AR), after standing for 42 hours under no electrical load at ambient temperature and humidity can be quite small, as seen in Table I.
TABLE 1 Fired Resistor Conductive Phase(s) wt.'7( Thickness (mils) Rcsistivit \'(ohms/sq) AR (/1) (a) Bi. .Ru O; (Comparative) 66 0.85 165.7 1.14 (h) Ag,, -Bi, -,Ru O (Ex. 2) 66 0.70 16.8 3.71 (c) Cu i, -,Ru- ,O.; (Ex. 3) 66 0.85 16.3 5.63 (d) Bi Ru O (Comparative) 61.2 0.80 71.3 0.84
Ag 4.8 (e) Bi Ru O (Comparative) 63.1 0.70 28.9 0.30
. Cu 2.9 guj uJs uJs z tm 4) 66 04x EXAMPLE 4 EXAMPLE 6 Ag Gd Bi Ru o 0.2566 g. AgNO 0.4108 g. Gd O 0.5280 g. Bi O and 0.8043 g. RuO were ground together in an automatic mortar for minutes, and fired to 1 100C in air in an open Pt crucible. The black product had an x-ray pattern corresponding to the pyrochlore structure (cell constant, a,,, of 10.26A) along with a small amount of impurity.
The tests in Example 5 were duplicated, except that the glass was (wt. percent) 43.5 percent Pb O 4.3 percent Al O 9.8 percent CaO, 4.9 percent B 0 and 37.5 percent SiO parts conductive powder were used, 17 parts glass were used, and 23 parts vehicle were used (see Table 11).
TABLE II Fired Resistor Conductive Phase(s) Wt. 7: Thickness (mils) Resistivity(ohms/sq.) AR (7:)
(a) Bi Ru O; (Comparative) 60 0.70 168.5 0.48 (b) Ag Bi RU O (Ex. 2) 60 0.70 8.3 l9 (:2) Cu ,-,Bi -,Ru O (Ex. 3) 60 0.80 5.0 0.16 (d) Bi Ru O (Comparative) 55.6 0.65 32.2 0.26
Ag 4.4 (e) Bi- Ru- O; (Comparative) 57.4 0.80 15.0 016 Cu 2.6 (f) Ag Gd Bi Ru o (EX. 4) 60 0.95 6.8 025 EXAMPLE 5 The results of Example 6 are similar to those of Example 5, except that the resistivity is lower with the The polynary oxides of the present invention are useglass Of Example 6. It ShOulCl be emphasized that these ful as components of screen'printable resistor compositions, as shown herein. The oxides (and optional free metal powder), total conductive phase 66 parts, were low resistivities are obtained without the addition of any noble precious metal powder, a result heretofore unobtainable. It is also obvious that there are a wide number of glass compositions, some of which may give even lower resistivities.
EXAMPLE 7 Ag Gd BiRu O g. AgNO Gd O 0.6905 Bi- O and 0.7888 g. Ru0 were ground together for 30 minutes in an agate motar and pestle. The ground mixture was fired to l000C. for l6 hours in an open Pt crucible in air. The black product had a pyrochlore-related x-ray pattern (cell constant. a. 10.25A) plus a trace of unreacted RuO The polynary oxides of the present invention may be used as resistors, electrodes, etc. An advantage of the compounds of this invention is that a higher percentage of glass can be tolerated in compositions thereof to obtain the same resistivity as conductor compositions known in the art. This is an advantage because in general, higher glass contents give smoother, more stable resistors.
The invention claimed is:
1. Electrically conductive polynary oxides of pyrochlore-related crystal structure having the formula l. M is at least one of Ag or Cu;
2. M is Bi or a mixture of at least one half Bi plus up to one half of one or more cations from among a. bivalent Cd or Pb and b. trivalent Y, Tl, In and rare earth metals of atomic number 57-71, inclusive;
3. M" is at least one of a. Ru,
b. lr, and
c. a mixture of at least three-fourths of at least one of Ru and [r and up to one-fourth of at least one of Pt, Ti and Rh;
4. x is in the range 0.10 to 0.60 and 5. zis in the range 0.10 to 1.0, and is equivalent to the sum of monovalent cations M and half of divalent cations in the polynary oxide.
2. Polynary oxides of claim 1 wherein x is in the range 0.10 to 0.5.
3. Polynary oxides of claim 2 wherein M is Ag.
4. Polynary oxides of claim 3 having the approximate formula 5. Polynary oxides of claim 3 having the approximate formula go.s o.1s onn a as- 6. Polynary oxides of claim 3 having the approximate formula 7. Polynary oxides of claim 2 wherein M is Cu.
8. Polynary oxides of claim 7 having the approximate formula os ns z as' 9. A powder composition comprising the polynary oxides of Claim 1 and dielectric material, useful for producing low resistivity resistors on dielectric substrates.
10. A powder composition comprising the polynary oxides of claim 2 and dielectric material, useful for producing low resistivity resistors on dielectric substrates.
11. A powder composition comprising the polynary oxides of claim 3 and dielectric material, useful for producing low resistivity resistors on dielectric substrates.
12. A powder composition comprising the polynary oxides of claim 4 and dielectric material, useful for producing low resistivity resistors on dielectric substrates.
13. An electrical element comprising a dielectric substrate having fired thereon the composition of claim 9.
14. An electrical element comprising a dielectric substrate having fired thereon the composition of claim 10.
15. An electrical element comprising a dielectric substrate having fired thereon the composition of claim ll.
16. An electrical element comprising a dielectric substrate having fired thereon the composition of claim 12.
UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3 ,896,055
DATED 1 July 22, 1975 'NVENTOR(S) 3 Robert Joseph Bouchard; Donald Burl Rogers It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below; COLUMII LINE ERROR CORRECTION a v I n l 65 .i M M o M M M 0 2 l3 zis z is 2 24 optical optional +3 +4 +3 +4 2 49 A B 0 A B 0 A B O A A A B O 2 55 AX Y "Y 2 X y 2-x-y 2 7-2 3 55 Popwich Popowich 6 21 Bi Ru 0 composition Bi Ru 0 (composition Q 2 2 7 2 2 7 I II M I II 7 23 MXM 2+x 2 7+z 'X 2-x 2 7-2 7 38 zis z is I I Signed and Scaled this Twenty-eighth Day of June 1977 [SEAL] Q Arrest:
RUTH c. MASON c. MARSHALL DANN Arresting Officer Commissioner oj'Patenls and Trademarks