|Publication number||US3790405 A|
|Publication date||Feb 5, 1974|
|Filing date||Jul 16, 1971|
|Priority date||Jul 16, 1971|
|Also published as||CA959739A, CA959739A1|
|Publication number||US 3790405 A, US 3790405A, US-A-3790405, US3790405 A, US3790405A|
|Original Assignee||Bell Telephone Labor Inc|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (5), Referenced by (16), Classifications (14)|
|External Links: USPTO, USPTO Assignment, Espacenet|
United States Patent Levinstein Feb. 5, 1974  CONTROLLED EPITAXIAL GROWTH 3,370,963 2/1968 Bonner et a1. 23/52 X O SUPERCOOLED NUTRIENT FLUX 3,278,342 10/1966 John et a1. l48/l.6 SOLUTION 3,394,081 7/1968 Ballman et al. 23/301 R X 3,234,135 2/1966 Ballman et al. 23/301 R X Hyman Joseph Levinstein, Berkeley Heights, NJ.
Assignee: Bell Telephone Laboratories Incorporated, Murray Hill, NJ.
Filed: July 16, 1971 Appl. No.: 163,396
US. Cl 117/201, 117/113, 23/301 R, 148/l.6, 148/172 Int. Cl B01j 17/00, B44c 1/18 Field of Search 117/201, 113; 23/301 R; 148/1.6, 172
References Cited UNITED STATES PATENTS 10/1949 Holden 23/301 R X Primary ExaminerAlfred L. Leavitt Assistant ExaminerM. F. Esposito Attorney, Agent, or Firm-W. L. Keefauver et al.
[571 ABSTRACT Controlled growth of epitaxial layers of a variety of structures including garnet, spine], and corundum are grown out of supercooled nutrient-flux solutions. Controlled growth, both of composition and physical characteristics, is attributed to the conditions that make the procedure primarily diffusion (rather than atomic kinetic) controlled. Such conditions include high dilution of nutrient and high viscosity of the solution.
11 Claims, 1 Drawing Figure CRYSTAL PULLER PAIENTED 5574 CONTROLLED EPITAXIAL GROWTH FROM SUPERCOOLED NUTRIENT-FLUX SOLUTION BACKGROUND OF THE INVENTION 1. Field of the Invention The invention is concerned with the growth of epitaxial layers of a variety of compositions and structures, resulting layers may be homoepitaxial or heteroepitaxial and may be elemental or compound.
2. Description of the Prior Art Continuing developments in a variety of fields have resulted in a growing interest in epitaxial devices. This interest which in many instances grows out of a desire toward miniaturization has been concerned with a variety of devices, e.g., semiconductor, optic, switching, memory, etc. A common requirement for all epitaxial devices is a high degree of perfection both from a compositional and physical standpoint. Accordingly, low energy grain boundaries, impurity inclusions, surface irregularities, thickness variations, and a number of other parameters must be kept within tolerances which in many instances have not previously been of concern. An outstanding example concerns the magnetic bubble device where a desire to maintain magnetic properties within sufficiently close limits to permit propagation of single wall domains of less than a mil in diameter through as many as positions within a square centimeter film has directed attention to magnetic imperfections having coerciveness as small as one oersted.
These many demanding device requirements have resulted in an intensive and ever growing search for closely controlled growth techniques capable of producing epitaxial layers of the required degree of perfection. Most of the traditional approaches have been uti lized, and, while results on many occasions have been promising, the search continues for closer and closer control. Growth procedures which have received attention include those which involveboth dropping temperature and those which are isothermal. Dropping temperature techniques have been found to be limited by the degree to which temperature gradients may be maintained constant over the growth region and during the growth procedure. Not only does a variation in gradient affect growth rate but a variation in this parameter in a complex system upsets the relative effective distribution coefficients of nutrient components and so results in a changing composition of the growing layer. While very careful temperature control of substrate and solution and very careful control of the solution itself has resulted in the growth of layers, which are suitable for many devices, it is clear that such procedure is inherently limited.
A variety of procedures result in growth under isothermal" conditions. Examples include the process in which the composition of a nutrient-flux solution is constantly controlled during growth as by flux evaporation or nutrient addition. Such procedures, again while suitably applied in certain instances, have other drawbacks. The flux evaporation procedure, for example, depends upon the use either of a single component flux or of a multicomponent flux in which the various components have the same approximate partial pressures. Implicit in such procedure also is the fact that sufficient vapor pressure may require a temperature which is not optimum from the standpoint of growth. Since evaporation is necessarily confined to the surface of the solution it also follows that there is a composition gradient through the solution.
Whereas the evaporation technique, under appropriate conditions, actually controls the growth rate so that the two may in principle be kept in balance, the nutrient-addition procedure has not such built-in control. Failure to introduce nutrient at the precise rate at which it is depleted due to growth results in a changing solution-composition and attendant difficulties in controlling both growth rate and composition.
In another form of isothermal growth the growing surface is maintained at a fixed temperature and reliance is had upon a temperature differential for transport of nutrient, usually from a solid source. A form of this procedure is involved in hydrothermal growth. While this process has been used successfully in the growth of a variety of materials, growth of complex compositions is complicated by the need to maintain the temperature gradient within very close tolerance.
SUMMARY OF THE INVENTION In accordance with the invention, epitaxial films, either homoepitaxial or heteroepitaxial, are grown out of supercooled nutrient-flux solutions on immersed substrates. The degree of supercooling, ordinarily at least about 20, is sufficient to assure growth periods of sufficient duration to produce epitaxial layers a micrometer or more in thickness, sometimes repeatedly, from reasonable size solutions. Contrary to general expectation, films grown from such supercooled solution manifest a degree of physical and compositional integrity not easily achievable or perhaps not at all achievable by competing methods. This high degree of control semmingly at odds with the expected uncontrolled growth ordinarily associated with growth from supersaturated solution is attributed in the main to two factors. The first of these is concerned with nutrient-to-flux ratio by which is meant the total weight of stoichiometric nutrient material in the solution divided by the total weight of the entire nutrient-flux solution. The second factor is viscosity, it having been determined that controlled growth proceeds only out of solutions which are sufficiently viscous. While both factors are, in the main, empirical, it is apparent that both, a high degree of dilution on the one hand and a high degree of viscosity on the other, contribute to a relatively thick diffusioncontrolled layer (sometimes referred to as the 0 layer) and therefore to a relatively small rate of introduction of nutrient material to the growing interface. From an experimental standpoint, it has been established, for example, that increasing temperature of initial nucleation so as to result in a less viscous system results in a film of lessening perfection from a fluxnutrient system which is otherwise identical (except for composition modification required to maintain the required degree of supercooling).
BRIEF DESCRIPTION OF THE DRAWING The FIGURE is a perspective view of an apparatus suitable for supercooled growth in accordance with the invention.
DETAILED DESCRIPTION 1. Process Parameters A. Background Requirements Certain requirements are common to growth from a flux by any procedure; certain others become somewhat more significant in the-inventive procedure. The first requirement is that the flux has sufficient solubility for nutrient material so that the degree of attainable saturation may result in sufficient growth. Whereas this requirement may be met simply by increasing the size of the solution, very large solutions may complicate the procedure, e.g., may result in composition gradients. In general, fluxes found useful and in common use for conventional growth are suitable. In general, it is desirable that the flux be capable of dissolving at least about 5 per cent of its weight of total stoichiometric nutrient components. In general, this degree of solubility is sufficient to permit growth of a film of a thickness of at least a major fraction of a micrometer for the required minimal supercooling out of a reasonable size solution.
It will be appreciated that the supercooled solution is intrinsically thermally unstable, and it is therefore significant that there be no predominant tendency for the flux or the nutrient or the combination to form solid compositions other than the compound which it is desired to grow epitaxially. For example, many nutrient flux solutions otherwise useful for garnet growth may result in an orthoferrite phase nucleating at a temperature higher than the initial nucleation temperature for the desired garnet. This is a well-known problem in flux growth and may generally be solved merely by adjusting the composition of the solution in order to suppress the undesired growth. In the instance of many garnet compositions, this is accomplished merely by utilizing an appreciably larger amount of iron than indicated by the desired garnet stoichiometry.
As in usual liquid phase epitaxial growth, it is required that dissolution rate of the substrate be appreciably smaller than the growth rate of the film.
B. Inventive Requirements It has already been indicated that a minimum degree of supercooling is required if only to assure growth of reasonable film thickness. While no numerical require ment can be rigorously satisfied (increasing the size of the solution may in part overcome such inadequacy) it has been generally observed that super-cooling to the extent of about 20C is sufficient to permit growth of films of sufficient thickness to satisfy many requirements, i.e., films of typical compositions of the order of a major fraction of a micrometer will ordinarily be grown on a substrate ofa centimeter in area from a 20 supercooled solution substantially filling a 30 cc container. The maximum permitted degree of supercooling depends on other parameters, for example, viscosity should not be so great as to result in a significant lessening in growth control. Experimentally, well controlled growth has resulted out of solutions which are supercooled to the extent of 100C.
From an experimental standpoint, the viscosity requirement is found to be interdependent on other parameters such as the degree of supercooling. Systems which have been studied, however, have sufficient low viscosity at temperatures above about 950C as to make control problematical. It is therefore a general requirement that the nutrient-to-flux ratio be such as to result in nucleation at temperatures no higher than 950C. A preferred limit is about 900C. This requirement corresponds to a minimum required viscosity of the order of 0.02 poises and a preferred limit of 0.035 poises. Since, however, the diffusion rate through a 0- layer decreases with temperature, the temperature of nucleation rather than the corresponding viscosity set ter. C. Miscellaneous The relatively thick 0- layer which is implicit in the inventive processes, when coupled with the other parameters set forth, gives rise to stable supercooled solutions which show little or no random nucleation. This, in turn, results in a growth pattern which while substantiating the postulated mechanism, may result in a slight lessening of the useful film area. A substantial 0" layer results in an increased amount of nutrient reaching the substrate at the periphery. This results from the fact that the periphery of the sample receives nutrient mate rial through the boundary layer from a substantially complete spherical section, i.e., 41r radians while the remainder of the substrate surface gather nutrient only from a hemisphere, that is, only 21r radians. The result is a slight thickening of the growing film at the periphery of the substrate. While such peripheral portion may simply be removed where this thickening is consequential, it is an interesting aspect of the invention that stabilizing of the supercooled solution is sufficient under the conditions noted to permit agitation of the substrate sufficient to minimize the increased peripheral growth. Such agitation which also has the effect of minimizing the effect of any undesired temperature gradient may be accomplished by rotation or vibration as through a substrate holder or may be accomplished by other agitating means, e.g., mechanical, magnetic, electromagnetic, etc.
For many purposes, it is expeditious to so arrange the flux composition as to assure rapid draining of solution on the grown film during withdrawal. This is not an absolute requirement since any such wetting layer may be of little or no device consequence, or since it may usually be easily removed by physical and or chemical means. To some extent the desire to provide adequate drainage serves as an upper limit on viscosity. From this standpoint, a preferred procedure providing for adequate drainage may utilize a solution having a viscosity no more than about 0.15 poises.
D. Substrate General substrate requirements are also common to those for substrates found useful in other forms of epitaxial growth. For example, it is a general requirement that the substrate be sufficiently strain free to satisfy the device requirements (e.g. to result in a sufficiently imperfection-free epitaxial layer). At this time, a combination of mechanical lapping sometimes followed by a chemical or mechanical procedure is sufficient for most purposes. It is, of course, generally required that the substrate also be free of such occlusions or other defects as it will have a deleterious effect on growing film. Epitaxial growth requires a reasonable match in lattice dimensions. This requirement, too, is to some extent dependent on the nature of the device for which the film is intended. Additionally, it depends upon the growth direction. Accordingly a somewhat poorer match between substrate and growing film is permitted where growth is on one of the natural growth facets which occur in bulk growth. Where growth is to proceed in a direction which ordinarily caps a closer match is ordinarily required. In general, a match of i 0.5 per cent is adequate for growth in such high free energy direction. A preferred match is about 0.1 per cent for growth in such natural direction. Growth in the natural 2. Flux Composition I 5 Many of the experiments upon which the inventive concept is based were carried out in boron oxide-lead oxide or in bismuth oxide-vanadium oxide fluxes. Such flukes' may be characterized as a (B2():;)y(PbO) where x=from 0.9 to 0.6 and y=from 0.1 to 0.4
and (Bi O (V O where a=from 0.9 to 0.65 and b=from 0.1 to 0.35. Such limits are not rigidly imposed but have been empirically found to define systems with sufficient solubility and other characteristics to be expedient. These systems show the requisite characteristics for growth in accordance Crystal Composition with the invention as well as with earlier growth methods and, while by no means unique, are suitably incorporated for growth of a large variety of compositions. Compositions which have been successfully grown out of such fluxes include substantially all of the yttrium and rare earth garnets, both those which are primarily iron-containing and those in which iron has been partially or totally replaced by gallium or aluminum or other elements; substantially all of the rare earth orthferrites; various compositions of the magnetoplumbite structure; corundum; a variety of spinel ferrites and yttrium rare earth orthoaluminates, and lead niobates.
Examples of crystalline materials and flux compositions from which they have been grown together with literature references are set forth in the following table.
Flux Reference Th /X1 0 PbO-PbF B,O 48 .I.Amer.Ceram.Soc.
p.105 (I965) REFeO PbO 78 Jr.Amer.Chem. Soc.
p.4259 (I956) Sm RE FeQ I bOPbF B,O A Physics Letters 297 (I967) PbFe O PbOPbF 5 Phys.Chem.Solids 202 (I958) Ba(AI,Fe), O PbOPbF B Q Y Fe,,O, (fiIm) PbO-B O, 3,4 .Ir.Cryst.Growth 443 (I968) I2( )Q( )5 z n p y 255I (I964) Ib;.(Mg,Zn)Nb O PbO-B O 3 Growth of Crystals 309 (I962) Al o PbOB O 35 JLAppLPhys.
522 (I964) AI O BiO O -PbF Jr.MetaIs p.33 (I964) Al o PbF 37 .InAppLPhys.
832 (I966) ZnAl O Pb 47 Am.Ceram.Soc.
388 I964) ZnAl O PbOPbF,B O; US. Patent 3,370,963 MgAl O PbF 3,4 .Ir.Cryst.Growth:
485 (I968) ZnRh O PhD 5] Jr.Am.Ceram.Soc.
292 (I968) ZnGa Q, Bi O -PbF .Ir.Am.Ceram.Soc.
325 (I967) 0:4 0; Bi O -PbF 50 Jr.Am.Ceram.Soc.
325 (I967) YAIO PbO(B O 78 Jr.Am.Chem.Soc.
4259 (I956) ln O PbOB O;, 35 Jr.Appl.Phys.
(or +PbF 2803 (I964) RECrO PbF --B O 49 Jr.Am.Ceram.Soc.
. 576 (I966) REMn O PbF B 0 49 Jr.Am.Ceram.S0c
576 (I966) REMnO PbF,-B,O;, 49 .Ir.Am.Ceram Soc.
576 (I966) Th0 HfO IbF-,,B O 49 .Ir.Am.Ceram.Soc.
576 I966) ZrO Th0, PbF, 50 Jr.Am.Ceram.Soc. ZnO 325 I967) REPO Pb,P O,- 47 Jr.Am.Cerum.Soc.
\ 257 (I964) REAsO, PbgASzO 50 .Ir.Am.Ceram.Soc.
433 I967) RFVO Pb V O, 5I Jr,Am.Cerum.Soc.
538 (I968) NaF(Gd) PbOPbF.,(Gd) 2 Solid State Comm.
26I (I961) CnMgSI- O PbO 46 Jr.Am.Cerum.Soc.
356 (I963) Sr'l'iO SiO 2 Jr.Cryst.Growth 402 (I968) BaTiO TiO-, I78 Lab for lns.Res.MlT
44 I963) BLTI O Bi O 32 JLAppLPhys.
959 I96l GaFeO B O Bi,O;, 31 .lr. Appl. Phys.
2638 (I960) RECrO Bi.,o 78 Jr.Am.Chem.Soc.
4259 (I956) (Bu Cu) Fe.V) O,: Buo -v 0. 35 .lr.Appl.Phys,
Table -Continued (ryxtitl ('nmpn'tition Flux Reference REVO, V O,,(N'.i) 36 JrChemPhys 702 1962) Be Al,(SiO V 33 Jr,Appl,Phys.
3209 1962) ZrSiO, V 0 44 .lr.Am.Ceram.Soc
128 (1961) BaTa O BaO-B O 2 Mat.Res.Bull.
533 (1967) KNbO K CO 29 .lr.Appl.Phys.
233 (1958) KTaO; K CO Jr.Phys.Chem.Sol.
p. 437 (1967) K(NbTa)O;, K CQ, 114 Phys.Rev, 63 (1959) 44 Am,Ceram.Soc.Bull.
9 (1965) K Li Nb O K CO l Jr.Cryst.Growth 318 (1967) U0; Na B O Los Alamos Reports No. LA 2076-OTS (1957) BaFe O NaFeO; 47 .lr.Am.Ceram.Socv
13 (1964) Ba Me Fe o NaFeO 47 Jr.Am.CeramiSoc.
13 (1964) Ba Me Fe o NaFeO 47 .Ir.Am.Ceram.Soc.
13 (1964) BA Me Fe O NaFeO 47 .Ir.Am.Ceram.Soc,
13 (1964) Ba Me Fe ,.O NaFeO- 47 Jr.Am.Ceram.Soc.
13 (1964) Ba Me Fe p NaFeO 47 Jr.Am.Ceram,S0c.
13 (1964) CaWO; Na W O,- 31 Jr.Appl.Phys.
328 (1960) NaRE(WO 2 Na W O 3| .lr.Appl.Phys.
.l. .1 REAl B,O K MO O, 47 Am.Min. 1380 (1962) Be ALSi O, Li,OMoO;, 33 .lr.Appl.Phys.
3209 (1962) 46 .lr.Am.Ceram.Soc.
6 (1963) Be,SiO Li OMoO 33 .Ir.Appl.Phys.
3209 (1962) 46 Jr.Am.Ceram.Soc.
6 (1963) BeAl Q, LEO-M00 33 Jr.Appl.Phys.
3209 (1962) 46 Jr.Am.Ceram.Soc
6 (1963) BeO Li O-MoO;, 47 Jr.Am.Ceram.Soc,
274 (1964) 50 Am.Min. 44 (1965) ZrSiO Li O-MoO 48 Jr.Am,Ceram.Soc.
130 1965) Th), Li,W,O, 36 .lr.Appl.Phys
3. Film Composition There are no inherent requirements on the process other than those stated above. Use of the prototype flux systems set forth in the preceding paragraphs or of variations or modified fluxes based on such prototypes (e.g., PbO or PbF containing compositions), however, is suitable for growth of many film compositions. Since technological interest in many types of epitaxial devices is now centered on oxidic materials and since suitable fluxes are readily available for growth of such oxidic materials, such compositions constitute a preferred embodiment of the invention.
Compound systems other than oxidic have been grown from flux solutions. Supercooled solution growth in accordance with the invention for all such systems, and, in fact, any others for which suitable fluxes may be formed, is suggested. Such systems include: Fluorides such as YFg from BeF flux and sulfides such as ZnS from a ZnF flux. Certain of these may require additional precautions, as for example, to suppress loss of constituents through evaporation to avoid undesired balance change, etc. All of such precautions are identical to those now taken in the growth of such materials by conventional flux growth techniques.
4. Processing The process has been described in terms of supercooling in degrees centigrade. Such limits have been found to adequately describe necessary growth conditions. The basis for this prescription concerns desired maximum film thickness as well as growth rate. Both desiderata may be prescribed in terms of percentage supersaturation rate than degrees of supercooling. For many systems the prescribed minimum of 10 C corresponds with a supersaturation of approximately 5 weight per cent. In many other systems, depending on the solubility curve, such minimum may be obtained for a lesser degree of supercooling. The minimal condition for adequate growth is more generally expressed, therefore, as 5 weight per cent of supersaturation, with this figure representing the excess amount of stoichiometric nutrient component in solution above the value required for saturation expressed as a fraction of the total solution.
Growth in accordance with the invention proceeds upon an immersed substrate. For convenience, the substrate is generally suspended within the liquid and the suspending means is generally used for withdrawing the substrate together with the grown layer at the termination of the process. Other arrangements may be expeditious under other certain circumstances, e.g., flux may be poured or spun off at termination of growth, etc.
Nutrient-flux solution is prepared in the usual manner, generally from powdered ingredients which are capable of yielding or are identical to the final flux and nutrient components. Powdered mixes are homogenized to the degree required and as is well known this may necessitate a sequence of one or more millings interspersed with firings.
Liquification is carried out at a temperature at least corresponding to that of the saturated solution. Generally it is expeditious to prepare at a somewhat higher temperature, for example, at a 100C or more above this temperature. Following Iiquification, the solution is reduced in temperature to produce the desired degree of supersaturation (generally to a temperature of from 20C to 100C below that corresponding with saturation).
Following preparation of the solution it is usually desirable to bring the substrate to the temperature of the Iiquified solution. This may be achieved simply by sus pending the substrate over the surface of the solution for a short period. Following this equilibration step, the substrate is immersed in the supercooled solution and is kept immersed for the period required to produce sufficient film thickness. Protective atmospheres, stirring, use of over pressures of particularly volatile ingredients and any other precautions required for the particular system being grown may be incorporated.
After withdrawal, substrate and film are permitted to cool at a rate sufficiently slow to avoid substantial thermal stress. For systems for which protective atmospheres or over pressures are required during growth it may be necessary to maintain such protection during at least the initial portion of the cooling cycle. All such considerations are conventional and are well known to those versed in this art.
5. The FIGURE The apparatus of the FIGURE resembles Czochralski pulling apparatus and includes a platinum crucible l1 heated by a resistance furnace 12. Crucible 11 is supported by pedestal 13 so as to position the flux in a region of low thermal gradients. The remainder of the apparatus consists of a substrate holder 14, pulling means 15, and some interconnecting means 16. The FIGURE also shows a flux solution 17 and a garnet substrate 18.
'fs'isxamples EXAMPLE 1 Mayer OfFTrZE uIFeTLGEbJGQof a thickness of approximately 2i9r9912t9! a rs lii i peri d, minutes on a substrate of Gd Ga5O12 of an area of 10 tained at 920C during growth (representing supercooling of 30C).
EXAMPLE 2 The procedure of Example 1 was followed, however, to grow a layerof Gd Ga O 2 of athickness of 3;. on a substrate of Gd Ga O1 Nutrient-flux solution was fluigd from a powdered mixture of 5.62 grams 621 0 150 gramSPbO 10 grams B20 Temperature was maintained at 9lOC during growth (representing supercooling of 30C).
EXAMPLE 3 EXAMPLE 4 The procedure of Example 1 was followed, however, to grow a layer of chromium doped Al O on Al G .The composition of the flux nutrient mixture employed 7 grams A1 0 0.2 grams Cr2O l5 0 grams RbO 6 B203 Temperature was maintained at 850C during growth (representing supercooling of 60C).
EXAMPLE 5 The procedure of Example I was followed, however,
togrow CoFe O on an MgO substrate. The compo s i tion of t heflux nutrient mixture employed in 2 grams C0 05 6 gramsFe2O3 grams PbO 2 grams B203 Temperature was maintained at 930C during growth (representing supercooling of 20C).
What is claimed is:
1. Method for the epitaxial'growth of a first composition on a substrate of'a second composition the lattice parameters of the said compositions being matched within i 1.0 percent comprising immersing the said substrate into a liquid body of nutrient-flux composition and permitting growth to occur on the said substrate while immersed characterized in that said nutrient-flux composition is supercooled by an amount of at least 10C, in thatthe totalconcentration of nutrient expressed in terms of the equivalent stoichiometric composition is a maximum of 10 percentby weight of the entire nutrient-flux composition and in that initial nucleation occurs at a temperature of less than 950C.
2. Method of claim 1 in which the said epitaxial growth is homoepitaxial and in which the said first composition and second composition are substantially identical.
3. Method of claim 1 in which the said epitaxial growth is heteroepitaxial and in which the said first composition and second composition differ.
4. Method of claim 3 in which the lattice parameters 8. Method of claim 7 in which the flux independent of nutrient ingredients comprises lead oxide.
9 Method of claim 8 in which such flux consists essentially of a mixture of lead oxide and boron oxide, the slatiY smqmwf, 1 9x.29wit2nts be n i jcated by the formula (l bo), (B 6 9 where x is from 0.9 to 0.6 and y is from 0.1 to 0.4.
1 0. Me tliod of claim 7 in which th elliix independent of ptrisna rss snts s t sesel al y 9f ni represented by the formula (Bi2O (V O )b where a is from 0.9 to 0.65 and b is from 0.1 to 0.35.
if. M e thod of claim 7 in which the oxidic material evidences a structure selected from a group consisting of garnet, spine], ferrite, orthoferrite, and corundum.
PR JTER' UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,79 L 5 Dated F ru ry 5, 9W
' Inventor(s) Hyman J. Levinstein It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
Column 2, line 6, change not to --no--; and
line 33, Change semmingly" to --seemingly--.
the 11th line under the heading "Flux",
H H change B10 0 PbF to B1 0 PbF Column 5,
H V 0 to Column 10, line 26, change 120 grams --l2O grams Bi Signed and sealed this 5th day of November 1974.
McCOY M. GIBSON JR. Attesting Officer C. MARSHALL DANN Conunissioner of Patents USCOMM-DC 60376-P61 & us. GOVERNMENT rnmrme omc: nu 0-866-33 F ORM PO-105O (10-69)
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|U.S. Classification||117/63, 117/946, 117/950, 117/945, 117/64, 117/60, 117/66|
|International Classification||C30B19/00, C30B19/02, C04B35/26|
|Cooperative Classification||C04B35/2675, C30B19/02|
|European Classification||C30B19/02, C04B35/26L|