US2438892A

US2438892A - Electrical translating materials and devices and methods of making them

Info

Publication number: US2438892A
Application number: US496417A
Authority: US
Inventors: Joseph A Becker
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1943-07-28
Filing date: 1943-07-28
Publication date: 1948-04-06
Anticipated expiration: 1965-04-06

Description

' April 6, 194a;

J; A. BECKER 2,438,892

ELECTRICAL TRANSLATING MATERIALS AND DEVICES AND METHODS OF MAKING THEM Filed July 28, 1945 2 Sheets-Sheet 1 FIG? r lNl/ENTOR J. A .BECKER A T TORNEY ELECTRICAL TRANSLATING MATERIALS AND DEVICES AND METHODS OF MAKING THEM April J; A. BECKER- 2,438,892

Filed July 28, 1943 2 Sheets-Sheet 2 29 r1 A ./o a s4 1 1% 26 X5 kg was H JNl ENTOR By J.A.BCKER WAX 61m "A T TORNEV V Patented Apr. 6, 1948 ELECTRICAL TBANSLATING MATERIALS AND DEVICES AND METHODS OF MAK- ING THEM Joseph A. Becker, Summit, N. J., assignor to Bell Telephone Laboratories,

Incorporated, New

York, N. Y.', a corporation of New York A plication July 28, 1943, Serial No. 496,417

9 Claims. (01. 250-31) This invention relates to electrical translating materials and devices and to methods of making them.

The objects of the invention are to improve decrease the electrical losses particularly when these devices are used for conversion purposes; to decrease the noise effects present in the associated output circuits; to realize a greater degree of uniformity in manufacture; and in other re spects to obtain improvements in devices of this character and in the methods by which they are manufactured.

With the extension of signaling frequencies in the radio and allied arts into the ultra-high frequency range wherewaves of a few centimeters in length are employed for signaling purposes it has become necessary to develop new types of apparatus forreceiving; translating and utilizing the signalenergy at these extreme frequencies. One of the problems has been to devise a satis factory translating device which is capable :of detecting, converting, or otherwise translating signal waves having frequencies of the order mentioned. Up to the present time the most promising solution of this problem has been a translating or rectifying device of the point-com tact type. In one form a fine tungsten wire is mounted so that its free end engagesthe surface of an element having suitable rectifying properties, such as a crystal of elemental silicon. More specifically the silicon crystal element of these prior rectifiers has been prepared by melting powdered'silicon in a furnace and cutting the resulting ingot into small Wafers of suitable diameter and thickness. The crystal wafer is then mounted on a terminal block, and the fine tungsten wire is adjusted so that its end makes a point contact with the surface ofthe crystal.

While translating devices prepared in this manner have given good results, nevertheless they introduce electrical losses particularly when used as frequency converters, and they also generate noise currents in their output circuits. These loss and noise factors have been the subject of considerable study from which it is quite definitely known that the magnitude of these factors is closely correlated to the physical and chemical properties of the silicon crystal.

In accordance with a feature of the present invention the loss and noise factors of these translating devices have been greatly reduced by meansof a new translating element and by means of a new method of making the same. This new element consists of a crystallized layer of thermally deposited silicon on a backing strip of some suitable metal such as tantalum. In the process by which these rectifying elements are prepared a strip or filament of tantalum is heated electrically to a predetermined temperature in a reaction chamber and a vaporous mixture of silicon tetrachloride and hydrogen is administered to the chamber under closely regulated conditions. After a thin layer of silicon has been deposited on the surface of the tantalum strip, the temperature is raised sufliciently to melt the deposited silicon, whereupon it is permitted to cool and crystallize.

Rectifiers prepared in this manner have been found to be unusually high in electrical efficiency; their conversion losses and noise factors are comparatively small. These advantages are due in large measure to the superior character of a rectifying element prepared by the method of depositing and crystallizing the silicon under conditions which exclude undesired impurities.

Other features and advantages of the invention will be discussed more fully in the following detailed specification.

In the drawings accompanying the specification:

Fig. 1 illustrates a filament or strip (greatly enlarged) of backing metal for the rectifying elements;

Fig. 2 shows the metal strip with a supporting terminal spring attached thereto;

Fig. 3 is a side view of the strip with the terminal spring attached;

Fig. 4 is a side view of the metal strip illustrating a deposited layer of silicon;

Figs. 5 and 6 illustrate units out from the pre.. pared strip and ready for assembly;

Fig. 7 is a view partly in cross-section of a translating device including one of the rectifier elements; and p a Fig. 8 illustrates the apparatus used for depositing the silicon on the metal backing strips.

Heretofore metallurgical methods have usually been employed to obtain silicon rectification elements having the physical and electrical characteristics essential to good performance in the ultra-high frequency range. Among the important physical characteristics is the degree of purity of the material. For best results the purity of the silicon should be very closely controlled; although the success of these metallurgical methods becomes more and more dlfii-cult as absolute purity is approached. Furthermore, experience with these metallurgical methods indicates that the small percentage of impurities plays a very 3 important part in the performance of the rectifier. For example, it is found that the presence of these impurities makes it possible to control the electrical resistance of the rectifier within.

novel method of producing rectifying material in which silicon is derived from one of its compounds and is thermally deposited. under closely regulated and uniform conditions on a suitable.

metallic filament and in which the deposited silicon is then fused to form a crystalline structure having the desired physical and electrical properties. ture of the material can be reproduced repeatedly with a high degree of uniformity.

In the drawings, Figs. 1 to 3 illustrate the metallic filament or ribbon which is used as the base for the thermal deposit of silicon. It will be understood, of course, that the invention is not limited to a particular metal for the filament; the particular metal or combination'of metals found to give the results desired may be chosen. Experiments have been made with such metals as tantalum, platinum, tungsten and molybdenum, and of these it is found that tantalum has the least tendency to enter into solution with the silicon layer.

The filament l of the desired metal, such as tantalum, is formed. with the requisite dimen sions and is then prepared for the reaction chamber shown in Fig. 8. This preparation consists in equipping it with a small coiled spring 4 which holds it taut when it is suspended between the terminal wires 2 and 3. The terminal wires 2 and 3, which may be of tungsten or any other suitable conductor, are sealed intothe head 5 of the reaction chamber 6. The head 5 and terminal wires 2 and 3. form a unit; and, to facilitate the removal and replacement of this unit, the head 5 and the wall of the chamber 6 are provided with threaded areas. The terminals 2'and 3 are connected through a transformer I to a suitable source of current 8 which serves to heat the filament I to the required temperatures.

The remaining apparatus shown in Fig. 8 is for the purpose of administering a vapor mixture to the reaction chamber 6. A. vapor mixture which gives good results isone consisting of silicon tetrachloride and hydrogen. The hydrogen is derived from-a supply tank 9, which is connected by way of the feed pipe l0 to-a flow meter ll. The purpose of the meter His to maintain a uniform flow of gas under varying external conditions. The hydrogen gas, after passing through the regulating flow meter II, enters a deoxidizing furnace I2 for the purpose of removing any traces of free oxygen that may be mixed with the hydrogen gas. On leaving the furnace I2 the hydrogen and any water vapor that may be formed in the furnace enter the drying. towers I3 and I4. These towers remove alltraoesof water vapor and permit only the pure hydrogen to flow into the outlet pipe I5.

The silicon tetrachloridevapor is derived from the vessel It Where it isfirst mixed with-the hy drogen gas. The mixture is effected by leadingthe-purehydrogen gas through aninlet pipe into the liquid tetrachloride in the. vessel '16.; The concentration of thevapor mixture maybe regu- By this method the physical structemperature.

lated and controlled in any suitable manner so that the mixture entering the reaction chamber has the proper ratio of the hydrogen and tetrachloride components. One method of obtaining the desired mixture is to divide the supply pipe I5 as illustrated, leading one branch I! into the vessel I6 and another branch I9 directly to the reaction chamber 6 by way of the inlet pipe 20, and by equipping the branches I1 and IS with valves 2I and 22, respectively, for regulating the flow. The hydrogen entering the liquid tetrachlorideby Way of the branch I! mixes with the tetrachloride vapor, escapes through the outlet pipe l8 and then-passes through the common inlet pipe 20 into the chamber 6.

The decomposition of the silicon tetrachloride within the chamber 6 is effected by heating the suspended metallic filament I to a predetermined This is accomplished by applying a regulated voltage from the source 8 to the terminal wires 2 and 3. Any suitable voltage control device 23 may be used, and the temperature of the filament I may be determined by any well-known means, such as a color thermometer. As the silicon tetrachloride decomposes under the influence of the heated filament I it yields elemental silicon which deposits in a thin layer on the surface of the filament; The vapor mixture within the chamber 5 is maintained in a uniform state by a scavenging outlet pipe 24. If desirable an evacuating pump 25 may be used to expedite the removal ofthe unwanted products from the chamber 6.

After the silicon layer has been formed on the filament I the temperature is raised to the melting pointof silicon, following whichthefila ment is permitted to cool to crystallize the: fused silicon.

Reviewing briefly the series of steps involved in the process above described, assume first that a strip or filament of tantalum is prepared and mounted between the terminals 2 and 3 within the chamber 6. The chamber is now thoroughly flushed by passing a suitable gas,'such as nitrogen, through it fora substantial interval of time. The nitrogen gas, which is supplied from a tank 26, passes through the opened valve 21 through the flow meter II, furnace I2,v drying towers. I3 and IAto-thesupply pipe I5. During this-cleansing intervallthe valve 21 in the branch I I is closed and the valve 22 is opened; also the valve 28 in theoutlet pipe I8 is closed-.. Hence-the nitrogen gas flowing inthe supply pipe I5 passes: through the by-pass branch I9 through the'inlet pipe 20 into the chamber 6': from which it finally emerges. through the-scavenging pipe 24 After the chamber has been flushed with nitrogen, the valve 21 is closed, valve 29 isopened and hydrogen. is permitted to flow for an interval through the chamber. While the hydrogen is flowing, the switch. 30 isclosed, andthe'voltage regulator 23 is adjusted tobring thefilamerit for a brief period to a temperature in the neighborhood of 2000 K. The voltage is then immediately reduced, and the filament is permitted to cool. Nextthe desired mixture of hydrogen and silicon tetrachlo ride vapor is attained by adjusting the valves 2| and 22 and'by fully opening the valve 28. Opening the valve 2| permitsa portion of the hydrogen gas to flow into the liquid tetrachloride from whence it bubbles tothe surface, producing-tetrachloride vapor which escapesthrough the pipe I8 and into the intake-pipe 20: At the same time a portion: of the pure hydrogen passesthrough the valve'22iand the pipe I9 directly into the intake pipe 20 where it mixes with the tetrachloride vapor and enters the chamber 6.

After the vapor mixture has flowed through the chamber long enough to stabilize, the filament l is brought to and carefully maintained at the temperature (in the neighborhood of 1000 C.) at which it is most effective in decomposing the silicon tetrachloride vapor. As the decomposition ensues, a coating of silicon forms on the filament, and the other products of the decomposition are withdrawn through the outlet pipe 24. After a sufficient coating of silicon has been deposited on the surface of the filament, the flow of the vapor mixture in the chamber is stopped, and the temperature of the filament is raised for a short interval to the point where the deposited silicon fuses. The filament is then cooled, permitting the silicon to crystallize.

The coated filament illustrated in Fig. 4, is now removed from the reaction chamber and cut into rectangular units 32, or circular units 33, as illustrated in Figs. and 6, of suitable dimensions for use in the individual rectifier assemblies.

The assembled rectifier, greatly enlarged, is illustrated in Fig. '7. One of the silicon units 32 is included in the assembled unit and is mounted on the threaded metallic stud 34. The mounting of the silicon unit on the stud 34 may be accomplished by any suitable method. For example, the deposited silicon may be removed from one side of the unit by sand-blasting or otherwise, exposing the metallic tantalum surface which is then soldered or welded to the stud 34. Another method is to embed the unit 32 in a body of solder on the end of the stud 34. In this way the solder makes intimate contact with the tantalum base, exposed in the cutting operation, and thus affords a good electrical connection between the silicon surface and the supporting stud 34. Still another method is to apply a silver or platinum paste to one surface of the unit and also to the face of the stud 34. The treated surface of the unit is then placed on the end of the stud and subjected to a temperature suificient to sinter the paste, thus forming a small mechanical bond and a good electrical connection.

Following the attachment of the silicon unit to the stud 34, which is integral with the metallic base member 35, the stud is screwed into one end of the ceramic insulating cylinder 36. In like manner the threaded stud 31, which is integral with the metallic cap 38, screws into the opposite end of the cylinder 36. The cap member 38 contains a central bore for receiving the cylindrical contact holder 39; and this holder is adjusted within the bore until the tip end of the tungsten contact wire 40, the opposite end of which is soldered into the holder 39, makes contact with the silicon surface of the element 32. When the desired degree of force is applied to the contact engagement of the wire 40 with the silicon element, the set screws 4| are tightened to seize the holder 39.

What is claimed is:

1. The combination in an electrical translating device of a translat ng elem nt comprising a metallic base having a layer of silicon deposited thereon, and a fine spring contact wire making a point-contact with the surface of said silicon layer.

2. The combination in an electrical translating device of a translating element comprising a base of tantalum having a layer of silicon deposited and crystallized thereon, and a conductor making contact with the surface of said silicon layer.

3. An electrical translating element for the translation of microwaves comprising a base of a metal of the group consisting of tantalum, platinum, tungsten and molybdenum having a layer of silicon deposited and fused thereon.

4. The method of making a translating device for electric waves of high frequency which comprises decomposing thermally a substance containing silicon and depositing the silicon in a layer upon the surface of a metal base.

5. The method of making a translating device for electric waves of high frequency which comprises decomposing thermally a substance containing silicon, depositing the silicon in a layer upon the surface of a. metal base, and crystallizing the deposited layer of silicon.

6. The method of making a translating device for electric waves of high frequency which comprises decomposing thermally a vapor containing a silicon compound, and depositing the silicon in a layer upon the surface of a metal base.

'7. The method of making a translating device for electric waves of high frequency which comprises decomposing a vaporous mixture including silicon tetrachloride and depositing the liberated silicon on the surface of a filament of tantalum.

8. The method of making a translating device for electric waves of ultra-high frequency which comprises administering a vaporous mixture of silicon tetrachloride and hydrogen to a reaction chamber in which a metal filament is supported, heating said filament to cause the thermal decomposition of silicon tetrachloride and the deposit on the filament of a layer of silicon, and further heating said filament to crystallize the silicon layer.

9; A rectifying material comprising a base of tantalum and a layer of silicon fused and crystallized thereon.

JOSEPH A. BECKER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 836,531 Pickard Nov. 20, 1906 1,990,277 Feussner et al Feb. 5, 1935 925,988 Von Bolton June 22, 1909 FQREIGN PATENTS Number Country Date 6,051 Great Britain July 16, 1908