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By JOHN R. SUMAN

COMMENCEMENT exercises this year have a peculiar significance because the graduating students are entering upon their life's work at the most critical time in the history of the United States. We are engaged in a great struggle the outcome of which is none too clear even to the best informed students of international affairs. We are starting late in a vicious world conflict where it is generally recognized that our adversaries have distinct superiority over us in armament on the land, on the sea, and in the air. We have the gigantic task of building up our armed forces and armament and at the same time supplying our allies with equipment which they must have. We can do this job if we are given sufficient time, but there is a possibility that the war will be over before we are ready. Few realize the seriousness of this situation. If this fight is to be won-and we dare not try to visualize the future of this country if it is lost-all dissension and bickering between Congress, capital, labor, and agriculture must cease. When and where voluntary co-operation proves inadequate for the successful conduct of the war effort, laws must be enacted or strengthened to achieve our purpose.

Jan 1, 1942

"The mountains of Utah contain one of the largest deposits of high grade bituminous coal in the world. According to the United States Geological Survey, there are 13,130 square miles of land known to contain workable coal, and these extensive fields contain 196,000,000,000 tons of coal. More remarkable than the extent of the coal fields is the thickness of the coal beds. Over three-fourths of the output of coal in Utah is recovered from beds ranging from 8 to 17 feet in thickness, as compared to one-eighth of the output of the entire country from such beds. In 1917, Utah mined one-third of its coal from seams at least 16 feet thick, compared to one-half of one per cent of the total bituminous output of the country from like seams.Coal at Wales, in Sanpete County, and in the vicinity of Coalville, Utah, was, it is reported, the first discovered by white men in the state. Wales claims the distinction of having produced the first coal mined in Utah. Two men, who had been coal miners in Wales, learned of the coal from an old Indian chief who called it ""rock that would burn."" In 1857, the town of Wales was founded and coal mined, and in 1858 some coke was manufactured and hauled by ox team to Salt Lake City. South of Wales is Castle Valley, in Wasatch Plateau field. From 50 to 60 miles of the Old Spanish Trail from Santa Fe, New Mexico, to Monterey, California, lies in Castle Valley. The coal in this field may or may not have been known at the time the trail was used extensively. The first published reference to this coal, however, was made by a party of the Corps of Topographic Engineers in their journal for October 11, 1853.After the completion of the Union Pacific railroad in 1869, mining on a commercial scale was attempted. In 1876 the Utah and Pleasant Valley railroad commenced operations between Scofield, in Carbon county, and Springville, Utah county, and following the year 1878, when the Rio Grande Western railway began construction through the Carbon county field, development increased until in 1900, when large smelters commenced operations in Salt Lake valley and gave coal mining in Utah an impetus that first carried it to an annual output of a million tons. During the past fifteen years many new mines have been opened, and with the construction of the Utah railway, an exclusive coal road, from the properties of the United States Fuel company in Carbon and Emery counties to connect with the Union Pacific system at Provo, the state reached a maximum production of 6,005, l 99 tons in 1920."

Jan 1, 1925

President Howe : It is not so clear to me that the facts which Dr. Waldo brings forward really argue that the nature of the combination between copper and aluminum differs from that of the combination between copper and zinc or copper and tin. As regards electric conductivity, I suppose that the fact, which he thinks points to a special intimate kind of union between aluminum and copper, is that the line in his Fig. 1 is neither straight nor uniformly curved, but that its curvature varies rapidly, not to say abruptly. But we find just such variation in like curves for the copper-zinc and copper-tin alloys. Thus, a slight addition of zinc or tin to copper causes a change in color wholly out of proportion to the quantity added; and, as we add zinc or tin to copper, the tenacity rises very greatly, only to fall off abruptly with further additions of either of these metals. Dr. Waldo : My curve related only to electrical conductivity. The President : If irregularity in one physical property argues

Jan 1, 1895

By R. S. Rickard, H. D. Peterson, J. D. Miller, M. C. Fuerstenan

Pure chrysocolla is floated with chelating agents that form insoluble complexes with copper at ambient temperature. Complete flotation is obtained with potassium octyl hydroxamate as collector at pH 6. Flotation response is enhanced with increased temperature when low additions of hydroxamate are involved. A natural ore was floated with 0.4 1b per ton octyl hydroxamate at pH 6.5 and 58°C, and a flotation recovery of 76% was obtained with a concentrate grade of 31.6% copper. The flotation characteristics of the oxide copper minerals, malachite, azurite, and cuprite, have not presented the difficulty for concentration as have those of the copper silicate, chrysocolla. The copper carbonates and oxides respond reasonably well to flotation with conventional collectors, whereas chrysocolla will not respond to flotation with fatty acids or xanthates under normal flotation conditions. In this view then, other reagents will have to be devised to function as collectors for chrysocolla. The most obvious general class of reagents for this purpose would seem to be the organic copper chelating compounds. The utility of chelating agents as collectors in flotation systems has already been demonstrated. For example Vivian1 has floated cassiterite using ammonium nitrosophenylhydroxylamine. Holman2 studied the flotation of nickel oxide ores with dimethylglyoxime and also suggested the use of taurine on oxidized lead ores. A rather detailed study on the application of certain chelating agents to some flotation systems was presented by Gutzeit.3 This work indicated that the formation of surface insoluble chelates is probably responsible for flotation in many cases. The role that soluble chelating agents assume was also presented, that is with effective removal of polyvalent cations by complex formation, effective depression of quartz can be obtained. DeWitt and Batchelder4,5 have shown that oximes function well as collectors for chalcocite, malachite, azurite, and cuprite. Ludt and DeWitt6 have presented the possibility of using dyes, such as octyl malachite green, as a collector for chrysocolla. These works presented by DeWitt et al suggest that organic copper chelating compounds offer considerable promise for concentrating chrysocolla, but that the most suitable chelating reagent from the standpoint of cost and flotation response has yet to be determined. The present investigation was undertaken to study the flotation response of chrysocolla to selected copper chelating compounds, that is ethylenediamine, hexamethylenetetramine, potassium octyl hydroxamate, dimethylglyoxime, and benzoin a-oxime. EXPERIMENTAL MATERIALS Chrysocolla: The chrysocolla used in the microflo-tation studies was from New Mexico and analyzed 20.8% copper. X-ray diffraction showed this material to be amorphous in character, but some faint lines of quartz were noted. A natural oxide copper ore from Utah was also used in the investigation. This ore contains malachite principally but also contains chrysocolla and tenorite together with some sulfide copper. The sulfide copper comprises from 15 to 20% of the total copper content of the ore. Water: Conductivity water was used in the microflo-tation experiments, while Golden tap water was used in the experiments with the natural ore. Reagents: Reagent grade n-amyl alcohol was used as frother in the experiments with pure mineral, while MIBC was used in the work with the ore. Ethylenediamine, hexamethylenetetramine, dimethylglyoxime and benzoin a-oxime were reagent grade in quality. Pure potassium octyl hydroxamate was prepared as follows: 1) 1.0 mole of KOH in 140 cc of methanol was combined with 0.6 mole of hydroxyl-amine hydrochloride in 240 cc of methanol at 40°C (KC1 precipitates under these conditions and to effect complete removal of KCl, the system was cooled to 10°C and filtered), 2) a light methanol wash was then given the KC1 cake, 3) the filtrate was agitated at room temperature and 0.33 mole of the methyl ester of the organic acid (i.e. methyl octanoate) was

Jan 1, 1965

By Ross Blake

THE St. Joseph Lead Co. became interested in the Tri-State district in 1921 through acquisition of prospecting and development rights on approximately 20,000 acres of land extending northeastward from the Picher mining field, mostly in Kansas. Prospecting with churn drills was begun the same year and the first commercial ore body was found on the Jarrett tract at the then northern limit of the main Picher field. Operations at this mine began in 1923. Kansas Explorations, Inc., was organized in 1923 by the St. Joseph Lead Co. as a wholly-owned subsidiary to carry on its operations in the Tri-State District from an office at Joplin, Mo. As prospecting of the original acreage proved largely negative, attention was subsequently turned to other sections of the district. Numerous additional leases were acquired and prospected. The Company was successful in developing into operating properties the Jarrett, Isherwood, Robinson, Sullivan and Lotson tracts and, in more recent years, the Ritz, Snapp, Buckingham, Gibson and Jasper mines.

Jan 1, 1947

By Edward Steidle

THAT veterans are crowding the colleges is no longer news; 78 per cent of the 1916-47 enrollment in mineral industries curricula in the United States were veterans, but the rapid comeback from an estimated 1262 total mineral industries students in 1944-45 to 11,422 in 1946-47 is almost astonishing. The figure, which includes 1008 graduate students, is a substantial increase over the previous top record of 9619 in 1938-39. A small part of the increase is caused by the larger number of women entering the field, of whom there were c 9 in 1916-47. Petroleum leads the curricula with 34.5 % of the enrollment, metallurgy is second with 28%, and mining is third with 18%. Table 1. shows all curricula offered and those accredited by ECPD. Using the Mississippi River as a dividing line, 31 colleges in the East and 27 in the West offer curricula in the mineral industries.

Jan 1, 1948

By Paul M. Tyler, Carle R. Hayward

DOES it pay to do really good work? Quite likely the practical millman will answer that it does not. The preparation of ores for market is primarily a business enterprise, and by and large the individual operator does not bother his head about squandering our national resources or making easier the job of the smelterman. Having accepted such ore as he may get fro111 the mine, his job is to make the best possible showing with his mill fro111 the standpoint of financial return. His success is measured in dollars and cents, and he has no rightful reason to expect more than scant acknowledgment of any other achievements from the stock- holders of his company who in the last analysis are his employers.

Jan 1, 1936

(Members are urged to send in for this column any notes of interest concerning themselves or their fellow-members.) The following members have registered recently at the Headquarters of the Institute Seeley W. Mudd, Los Angeles, Cal. Charles Janin, San Francisco, Cal. Edgar Rickard, London, England. Donnel F. Hewett, Washington, D. C. L. Maurice Cockerell, Chihuahua, Mexico.

Jan 4, 1913

By C. K. Leith

THE interdependence of nations in regard to mineral supplies has grown apace with the expanded needs of industry, with depletion of reserves, and with advances in technology. This increased mutual dependence raises many questions of foreign economic policy of special importance in our postwar planning. Realization of the urgent need for the development of a general mineral policy broadly based on national requirements led to discussions of the problem between officials of the Department of State and myself, as a result of which it was suggested that I make an informal and unofficial canvass of the views of mineral specialists of the country on foreign mineral policy.

Jan 1, 1946

By AIME AIME

MINERALS and mineral resources are recognized as one of the things that nations are prone to quarrel about. The territory that was arbitrarily incorporated into the Polish Republic after the World War produces a variety of essential minerals on a substantial scale. The accompanying table has been compiled to give some idea of the relative importance of this production. Poland, before the recent war started, had an area of 150,000 sq.mi., just a little larger than the State of Montana. Its population was 32,000,000, equal to that of New York, New Jersey, Pennsylvania, Connecticut, and Massachusetts. Though not a highly industrialized country it nevertheless has important mines, steel plants, petroleum refineries, and sundry metal-fabricating manufactories. Coal, petroleum, iron and steel, zinc, lead, pyrite, potash, and salt are produced in excess of the country's domestic consumption. It has no appreciable production of copper, chromium, tungsten, nickel, tin, mercury, manganese, aluminum, magnesite, fluorspar, or graphite.

Jan 1, 1939

By Elton A., Youngberg

The Holden mine operated by the Chelan Division of the Howe Sound Co. is on the east slope of the Cascade Range in north central Washington on the south slope of Railroad Creek valley at an elevation of 3500 ft. The mine may be reached by a 40 mile boat trip from the town of Chelan which is at the southern tip of Lake Chelan, to Lucerne at the mouth of Railroad Creek and an 11 mile bus ride up Railroad Creek to Holden. All freight and concentrate is moved over this route to Chelan Falls on the Columbia River which is on the railroad four miles below the town of Chelan. The mine is now producing 2000 tons of gold, copper, and zinc ore per day which is treated in the Holden mill. Gold-copper and zinc concentrates are made, the first of which is shipped to Tacoma, Wash., and the latter to Kellogg, Idaho, for smelting.

Jan 1, 1949

By Simon D. Strauss

What are future prospects for U.S. mining? In many quarters the assumption is made that this country has passed its zenith as a mineral producer -- that it is in a period of decline and that it is becoming a have-not nation like Japan and much of Western Europe. These industrial rivals of ours must depend almost entirely on others for their mineral supplies. In trying to answer this question one must of course distinguish between resources and productive capacity. In today's volatile and competitive markets, the definition of what are reserves and what are merely identified resources becomes ever more difficult. Many large deposits have been found that are unlikely to be viable in the marketplace under normal conditions but that can be of significance to the nation's military and industrial security in times of emergency. I should like to draw on personal experience from World War I1 for illustration. 4fter Pearl Harbor great concern developed over the availability of a long 1ist of strategic materials for which this country was largely dependent on imports. Included were a number of minerals of which domestic deposits had been identified. Among these were chromite, manganese ore, mercury, mica and tungsten.

Jan 1, 1982

By Louis Huber

THE Liberty tunnels extend through a very steep hill in Pittsburgh (locally called Mount Washington) for a distance of slightly over a mile. The two tunnels parallel each other and are 59 ft. apart, center to center (Fig. 1). They are for vehicular traffic, and in each there is ample space for two lines of vehicles. Northbound traffic, towards downtown Pitts- FIG. I.-NORTH PORTAL OF LIBERTY TUNNELS. NOTE THE WINDBREAK AT END OFEAST TUNNEL. burgh, is confined to the east tunnel and southbound traffic to the west tunnel. The South Hills residential district is separated from downtown Pittsburgh by Mount Washington, a steeply rising escarpment south of and adjacent to the Monongahela River. The Mount Washington district immediately south of the Monongahela River has been reached, for many

Jan 1, 1927

By DAVID F. McFARLAND

THE making of courses of study and curricula has long held first place as the favorite pastime of educators. As a game, this activity is as fascinating to some as golf or bridge, 'and the golfer's hope of a low score is matched by the teacher's ambition to some day evolve a sequence of studies that shall prove the ideal preparation for a life of maximum service and, profit. There are few in, this gathering who have not tried their skill at this game and still fewer are those who have been long satisfied by the product of their efforts. A curriculum is hardly printed in the college catalog before conditions arise which seem to make changes desirable, and strong will power is needed to maintain the program long enough to give it a fair trial. Metallurgical curricula are not less subject to change than others, 'and; indeed they have seemed, at times, to change more rapidly than other curricula because of the changing 'needs of the industries and the demand that the graduate be trained to meet the new conditions. Metallurgical practice is constantly proving that "time makes ancient good uncouth," and the graduate metallurgist is required to adapt himself to newer and

Jan 1, 1930

By C. S. Smith

The solubility of tantalum at 1100°C is 0.025 pct in pure copper, 1.2 pct with 20 pct Ni, and 2.7 pct with -30 pct Ni. The solubility decreases with temperature, and the alloys are precipitation hardenable. A 79/20/1 Cu-Ni-Ta alloy reaches maximum hardness after aging at about 750°C and, if cold worked, does not recrystal-lize below that temperature. The alloys have good tensile properties at moderately elevated temperatures and, since they can be hot and cold worked nearly as easily as cupronickel, they are suggested for service at temperatures above the usual limits for copper alloys. MASSIVE tantalum dissolves extremely slowly in copper-rich alloys, and tantalum powder forms refractory surface layers which prevent its solution unless special precautions are taken. After many trials, an 80 pit recovery was consistently obtained by using a mixture of a finely divided tantalum powder with two or three times its volume of potassium tantalum fluoride (K2TaF1,-melting point about 750°C) poured in a slow stream directly on to the surface of the molten copper alloy, so that each particle would remain coated with flux and be immediately and individually wetted by the molten metal. A 50-50 nickel-tantalum alloy has a melting point of about 1400°C and small lumps of it slowly but satisfactorily dissolve in molten copper-nickel alloys as does commerical "ferro-tantalum." The high affinity of tantalum for carbon makes it necessary to avoid carbonaceous crucibles. COPPER-TANTALUM ALLOYS Castings with good shrinkage resulted when 0.1 pct Ta or more was added to copper melted under charcoal and cast in air. Copper in two-pound melts to which 0.1, 0.15, and 0.2 pct Ta had been added retained residual amounts, by analysis, of 0.025, 0.023 and 0.026 pct, respectively. The solubility of tantalum in molten copper at about 1200 °C is therefore about 0.025 pct. The electrical conductivity of these three samples was 100.48, 100.00 and 100.20 pct IACS in the annealed condition, and 98.24, 97.98 and 98.08 in the cold-drawn condition. Wires 0.080 in. in diam withstood from thirteen to nineteen reversed bends after annealing for 30 min in hydrogen at 850°C and the metal was therefore completely deoxidized. The annealing temperature corresponding to 50 pct loss of work hardness in 1 hr in a strip cold rolled 77 pct reduction was 175C, compared to 230°C for equivalent undeoxidized material. It is unusual for a decrease of recrystallization temperature to result from an alloying addition, and the tantalum probably combines with and removes some minor impurity in the original copper that restrained its recrystalliza- tion. No difficulty whatever was encountered in hot or cold rolling or drawing these ingots, and were tantalum not so expensive it would make an excellent deoxidizer for copper. COPPER-NIcKEL-TANTALUM ALLOYS Studies were made of the solubility of tantalum in a large number of copper-rich alloys, but of these significant solubilities were found only in the case of an iron alloy (which, however, separated into two immiscible liquid layers) and alloys of copper and nickel, in which tantalum is freely soluble and which were found to have interesting properties. The latter alloys are the subject of U. S. Patent No. 2,430,306 (1947). They are not at present available commercially. The Ternary Constitution Diagram—The copper-rich corner of the constitution diagram was constructed on the basis of microscopic examination of samples of various composition and treatments. The alloys were hot rolled to 0.25 in. from castings 0.625 in. thick, then annealed for 1 hr at 1000°C, quenched, cold rolled to 0.10 in. and finally annealed for various periods of time at temperatures between 800" and 1100°C in a nonoxidizing atmosphere and quenched. When the solid-solubility limit had been transgressed, particles of a compound believed to be Ni2Ta*were

Jan 1, 1960

By James Aston

A PROPER consideration of this subject is not confined to the technical channels of production and metallurgy. It concerns an industry, and should cover economic aspects which are of material importance in any program of development. The discussion may logically be treated under three subdivisions, as follows: (1) manufacture, (2) characteristics related to quality of material; (3) adaptability and exploitation of product. MANUFACTURE OF WROUGHT IRON The manufacture of wrought iron is the most ancient art of the ferrous metal industry. The eighty years or less of existence of processes identi-fied with our modern "Age of Steel" is a relatively brief interval com-pared with the several thousand years associated with the production of wrought iron by man. From the primitive early methods of production, manufacture for many centuries followed the line of direct reduction. There were developments as experience was gained through the years; but man's needs for a strong, ductile, forgeable product were met by reducing the ore to metallic iron in a single-stage operation. Following the development several centuries ago of what has become our modern blast-furnace operation, manufacture of wrought iron was gradually transformed into a two-stage method of first producing cast iron and then refining this to the desired degree of forgeability; the fore-runner in principle of today's scheme of manufacture of steel. The product retained the essential characteristics of highly refined base metal with iron-silicate slag incorporation, which were associated with the material resulting from direct reduction methods. Cort's invention of the puddling process in 1784 is a landmark in wrought-iron manufacture. It consisted essentially in adapting a coal-fired reverberatory furnace to the refining operation; thus lifting the industry out of the slough of

Jan 1, 1935

By M. J. Saarivirta, P. P. Taubenbla

This paper presents some high-temperature properties of copper-zirconium conductor alloy compared to copper-chromium alloy. Definite superiority of the copper -zirconium alloy over the copper-chromium alloy at high temperatures is shown. RECENT investigations have shown that cold-worked copper-zirconium alloy possesses good room-temperature strength, ductility, and conductivity and maintains most of its strength at temperatures up to 450°C (840°F). As a result, this alloy is now used for many applications, such as commutator segments, resistant welding wheels and tips, rectifier bases, electrical contacts, and so forth. Early investigations1-3 have shown that the maximum solid solubility of zirconium in copper is close to 0.15 pct and the alloy containing Cu-0.10-0.15 pct Zr exhibits the optimum mechanical and physical properties. Results2 have also shown that the alloy has better elevated temperature strength and ductility than copper-chromium and copper-silver alloys. The present investigation was undertaken to learn more about the elevated temperature properties of copper-zirconium alloy and to compare these properties with those of the copper-chromium alloy. WORK PROCEDURE The commercial copper-zirconium alloy, Amzirc was selected for this investigation. Because this alloy is composed of oxygen-free high-conductivity copper and 0.10-0.15 pct Zr, it was believed that possible disturbance from impurities would thus be negligible. Copper-chromium alloys used in this investigation contained 0.40 and 0.70 pct Cr and balance copper. The Cu-0.40 pct Cr alloy was a commercial brand, whereas the Cu-0.70 pct Cr alloy was made from OFHC copper and Cu-5 pct Cr master alloy. It was made in a graphite crucible under argon gas cover and cast. In the preparation of specimens, all three alloys were treated to give the optimum properties; thus the Cu-0.15 pct Zr alloy was solution annealed at different temperatures to determine the desirable solution annealing temperature. It was then cold worked and aged at 375" to 400°C (705" to 750" F). A solution annealing temperature of 1000°C (1830°F) was selected for the copper-chromium alloys because this temperature is widely used in commercial practice. The same alloy was aged at 450°C (840°F) after solution annealing and cold working. It was found that the maximum precipitation hardening of the copper-chromium alloy occurred at this temperature. When aged after solution annealing, the aging temperature was 500°C (930"F) for both alloys. The following properties were determined: 1) Tensile properties as a function of temperature. 2) Effect of solution annealing temperature on high-temperature tensile properties. 3) Stress to rupture strength at 350° and 400°C (660"to750°F). 4) Impact strength. 5) Electrical conductivity and resistivity as function of temperature. 6) Thermal expansion.

Jan 1, 1961

By C. R. Breck

THERE has been a running discussion over the past several years with respect to the life and adequacy of our natural gas reserves. Some of the experts agree on one phase of the subject at least-that eventually it will be necessary to augment deliveries of natural gas in the northern markets by the development of a more or less comparable synthetic gas made from coal. The purpose of this paper is to point out: 1. It may be later than a good many people think-the demand for addi¬tional domestic and commercial pipeline gas in at least one section of the North will probably be felt rather keenly before an adequate synthetic pipe¬line-gas project, developed on economic lines, could be completed, even if initiated in the near future. 2. The evidence is considerable that such a project would be technically sound and economically self-supporting, although the margin of profit at first might be so small and the magnitude of an economic enterprise so great -that financing would be impossible without Government aid in some form or other. The part of the country referred to is the heavily populated section in the northeast of the United States. To simplify an examination of the situa¬tion, let us take the potential marketing areas within range to the north and east of the three pipelines: 1. Tennessee Gas Transmission Co. as it enters Erie County, New York state. 2. Texas Eastern Transmission Corporation just before the tap that sup¬plies the general Philadelphia area. 3. Transcontinental Gas Pipe Line Corporation as it enters the state of New Jersey. The sources of gas for these three pipelines are in Texas and Louisiana. The ultimate maximum combined capacity of the three lines at the points stated is approximately 1,200,000,000 cu ft per 24 hr at the maximum load factor probable of attainment in normal operation. The areas supplied by the three lines north and east of the points stated, or assumed as eventual markets, are: 1. Central New York state, from Buffalo to Albany (both inclusive).

Jan 1, 1953

By Nathaniel Hen

IN the United States, in the 2 1/2 years since the rescinding of the wartime order closing gold mines, conditions have not yet returned to normal. Shortages of man power have prevented some mines from operating at all, and most of those in operation are still at reduced capacity. This fact, combined with shortages of materials, the high cost of supplies and labor, high tax rates, and a fixed price for the product have made the past years rather rough ones for gold producers. In foreign countries conditions are rather similar. In Canada several new mines are coming into production and some others are enlarging. Costs have not increased as much as in the United States and gold production is being encouraged. Recently a bonus of 20 per cent on increased production has been proposed. In South Africa, where gold mining is of major importance in the national economy the industry is also in a favored position with government; new discoveries of major importance there will markedly increase the gold output. Demand for labor is rap-

Jan 1, 1948

By T. H. Ramsey, Richard Shield

A process has been developed for fabricating thin-film resistors that are compatible with integrated circuits. Films are produced by evaporation of single refractory metals using an electron beam heating source. Resistor paths are then made using standard photoresist etching techniques. A low-temperature coefficient of resistance is obtained by control of nucleation during deposition of the film. One application of the process has been the development of a discrete resistor used for current setting in linear integrated circuits. Multiple thin-film resistors were formed on oxidized silicon substrates using molybdenum metal as a source. An evaporated protective layer of SiO2 over the resistor prevents resistance changes which might occur during subsequent high-temperature processing. Properties of a typical resistor are as follows: R = 15.7 ohm per sq, tolerance surface dimensions = 0.028 by 0.028 in., stable after 4000 hr at 0. 75 w without heat sink. THIN-FILM resistors have been investigated for many years with a large selection of usable resistors resulting from a wide variety of materials. Many of the processes necessitate a high degree of complexity but in nearly all cases the conclusions have been that the materials used in each case were acceptable provided the deposition process was reproducible and could be controlled sufficiently to give the required tolerances. It is our opinion that simplicity is still the key to thin-film resistor fabrication. In this regard, the single metal is obviously the simplest process to control, provided all the necessary properties can be obtained. The idea is not original in this laboratory by any means. Others have taken this approach.' It has been demonstrated that a fairly wide range of resistivities can be obtained by careful control of deposition parameters for any given metal, and by selection of several single metals a very broad range of stable resistors can be obtained. The transition from one metal to the next is made when a film becomes too thin for adequate process control or long-term stability. A great deal of emphasis is once again being placed on the thin-film resistor. Although they have been thoroughly studied in the past, new applications have been found that require the properties obtainable only from thin-film resistors. Integrated circuits, in general, are advancing toward higher speeds and radiation environments which require replacement of the present diffused resistors. Linear circuits in particular are requiring high-power, high-precision resistors for the more advanced applications. The particular requirements of some linear circuits are such that a discrete resistor is required. The resistor described in this paper was developed as a 15.7-ohm precision discrete resistor for use in a current regulating circuit requiring a +2 pct end of life overall tolerance, a dissipation of 750 mw, and the ability to operate over a fairly broad temperature range (i.e., a low temperature coefficient of resistance, TCR). State-of-the-art integrated circuit and silicon processing technology lends itself well to the fabrication of thin-film resistors. Not only is the resistor thin film well-suited to integration on individual circuits, but the oxidized silicon surface provides one of

Jan 1, 1969