US 2441590 A
Description (OCR text may contain errors)
May 18, 1948. R. s; OHL 2,441,590
' TRANSLATING DEVICE Filed March 24, 1944 4 Sheets-Sheet 1 F/Q/ FIG. 2
INVENTOR R. S. OHL
ATTORNEY R. s. OHL
TRANSLATING DEVICE May 18, 1948.
Filed March 24, 1944 4 Sheets-Sheet 2 INVENTOR R. S. OHL
By WWW ATTORNEY May 18, 1948- R. s. OHL 2,441,590
'TRANSLATING DEVICE Filed March 24, 1944 4 Sheets-Sheet s BY WRMdW A TTORNEY May 18, 1948. QHL 2,441,590
' TRANSLATING DEVICE v Filed March 24, 1944 4 Sheets-Sheet 4 FIG. /2
F/G. I4 36 v is as 33 INVENTOR R 5. OHL
ATTORNEY Patented May 18, 1948 Russell S. OhL'Red Bank, N. J.,' assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporationof New York Application March 24, 1944, Serial No. 528,009
Thisinvention relates devices and particularly todevices of this kind having small areas of contact between different materials. V
The objects of theinvention are to reduce the contact area of electrical translatingdevices; to maintain a high degree of contact stability; to shield and safeguard the delicate parts from injuryor'impa-irment;toimprove the uniformity of the electric circuits'in which they are used; to simplify the structure; and to secure other improvements in these devices and in methods of making them.
One of the problems involved in the use of ultra-high frequencies for signaling purposes in the radio and allied arts has been the development of a satisfactory translating device for detecting, converting or otherwise translating signal waves having frequencies of the order of a few centimeters. Thus far the most promising solution of this problem has been a translating or rectifying device of the point-contact type. In one form, afi-ne tungsten wire is. mounted so that its free end engages the surface of an element having suitable rectifying properties, such as a crystal of silicon. More specifically, rectifiers of this kind have been made by grinding one end of a fine tungsten Wire (.005 inch in diameter) to a point, carefully assembling the elements to bring the ground point into resilient contact with the surface of the crystal so as-to flatten the pointed end of the wire until the contact engagement between the Wire and the :crystal surfaceibecomes a small finite'area. v
While these: devices have given good results with wave-lengths in; the neighborhood of centimeters, the furtherv extension of the signaling frequencies into the region of 1 centimeter wave lengths imposes requirements on the rectifying contact thatalte. very difficult to realize. One of the difficulties is :to obtain a contact point which is sufliciently small in area; another is'to obtain the necessary contact pressure and the necessary resiliency to holdthe contact in a stable condition.
According to the present invention these difficnlties are overcome by an improved translating device in which a novel contact-spring structure is employed to obtain a grea-tly reduced contact area and to-maintain in said contact a high degree of electrical stability, and in-which the contact-forming 'parts are closely and compactly mounted within a protective housing that shields them from exposure to physical or electrical shocks. a
.6 Claims. (Cl. 250-31) to electrical translating I Another feature of 2 More specifically, the device in one of its forms comprises a rectifying crystal of silicon in the shape of a wedge, the apex edge of which is a sharply defined line, and a metallic contact ele-' ment of extremely fine wire of tungsten or other suitable material suspended under tension across the prongs of a bow member, these parts being so assembled in the structure that the tensioned contact Wire engages the apex line of the wedge to form a stable rectifying contact of extremely small dimensions.
In another embodiment of the device the desired small stable contact area is attained by using a short length of fine wire with its free end ground at right angles to its length to present a normal cross-sectional circular area and bending the wire in a single loop so that only a small arc of the circumference at the free tip end of the wire bears on the surface of the rectifying crystal. The short loop thus formed in the contact Wire gives it some resiliency; yet it also affords a maxi.- mum of pressure on the contact point notwithstanding the extreme fineness of the Wire itself.
Still another diflicul-ty experienced with rectifiers of this class is the susceptibility of the contact point to impairment or permanent damage from electric discharges to which they may be subjected during handling or in actual use, this danger being one that increases materially as the area of the contact is decreased. This disadvantage, however, is overcome through a further feature of the invention by means of a device of the character above-described in which the parts are assembled within a small metal cylinder which serves as a combined mounting and electrical shield.
the invention is a method of preparing the crystal rectifying elements which comprises cutting small rectangular slabs from a fused ingot,- grinding one surface of each slab to the shape of a wedge having a predetermined apex angle, and polishing the ground surfaces of the element until the ridge or apex of the wedge is a thin uniform line. I These andother features of the invention will be described more fully in the following detailed specification.
In the drawings accompanying the specification:
Fig. 1 illustrates a block of fused silicon having a high degree of purity;
Fig. 2 is a small slab or wafer cut from the block of Fig. 1;
Figs. 3 and 4 are cross-sectional and plan views in engagement with a crystal.
Fig. 9 shows a pronged member or bridge for supporting the contact wire;
Fig. 10 is a perspective view showing the assembly of the bridge member and ceramic insulating element; 7
Fig. 11 is a cross-sectional view of the assembly of one form of the translating device;
Fig. 12 is an assembly of another form of the.
Figs. 13. 14, and 15 are enlarged details of the contact elements of the modification of Fig. 12, and
Fig. 16 is a mechanism for performing the assembling operations.
Satisfactory rectifiers for use with waves of 10 centimeters or more have been made by bending or shaping the fine tungsten wire (.005 inch diameter) in a plurality of loops to give it more resilience and by fixing it with the pointed end However, the area of the rectifying contact thus formed is too large for best results with wave-lengths in the neighborhood of 1 centimeter. If the size of the contact wire is reduced in an eifort to decrease the contact area, the unit becomes unstable because of the consequent reduction in the pressure which the resilient contact wire is capable of exerting against the surface of the crystal. Moreover, the bends introduced in the contact wire to obta n the desired spring pressure at the contact surface are also the source of substantial electrical inductance particularly at the high frequencies to which these devices are subiected. In applicants device it is possible to effect a large reduction in the size of the contact wire and consequently in the size of the rect fying contact area without sacrificing the spring pressure necessary to maintain stability. In one embodiment of the invention this desirable end is achieved with the use of a straight contact wire wh ch adds substantially no inductance to the electrical circuit of which it is a part. In another form it is accomplished by using a short contact wire having a single loop therein and shaping the tip of the free end so that only a small part of its area engages the surface of the crystal. And, as above-noted, the component parts of these rectifiers are mounted and housed within a metal tube which shields the contact point against extraneous electrical influences and protects it against static discharges from neighboring objects, particularly while it is being handled.
Referring now to the drawings, the first step in the manufacture of the rectifier herein disclosed is the preparation of an ingot of silicon having a high degree of purity. One method by which the silicon material may be prepared is disclosed in the application of J. H. Scafi, Serial ,No. 386,835, filed April 4, 1941, issued as Patent 2,402,582, June 25, 1946. After the ingot has been prepared, a block I of desired dimensions and also of desired electrical characteristics is shaped from the ingot. Next the top surface of a slab, cut from the block I, is plated with nickel or any other suitable metal, following which wafers 2 are cut to the proper dimensions from the slab, a diamond saw being used for this purpose. Although the dimensions of the wafer 2 may vary to suit requirements, good results have been obtained when the large surface of the wafer is a square inch on the side and the thickness of the wafer is inch.
The next step in the process, when preparing units for rectifiers of the form shown in Fig. 11, is to grind the wafers 2 into the shape of a wedge as illustrated in Fig. '7. To this end a plurality of ,7 these wafers are cemented into notches formed in the surface of a chuck 3. These notches are cut in two or more concentric rows, and the angles which they make with the surface of the chuck determines the apex angle of thefim'shed silicon wedge. Although these angles may vary as desired, the notches illustrated in the drawing are cut at 30 degrees and 60 degrees. The rectangular wafers are cemented into these notches by means of any suitable adhesive material such as shellac, care being taken to fix the wafers in the notches with the nickelplated surfaces down, thus exposing the unplated surfaces to the grinding action.
Thereupon the chuck 3 is associated with the driving shaft 4 (Fig. 5) and immersed in a grinding bath 5 to bring the silicon wafers 2 into contact with the grinding lap 6. The lap 6, which may be of any suitable metal contains a series of grooves and rests on the bottom of the cup I with which it is rotated by the driving shaft 8. The lap 6 is charged with suitable abrasive materials, such as boron carbide, for cutting away sections of the silicon wafers. The mechanism is designed to rotate the lap 6 and the chuck 3 in the same direction but at different speeds and is also designed to impart an oscillatory movement to the chuck 3 While it is being rotated. During the first part of the grinding operation a section 9 of each wafer 2 is cut away at the predetermined angle as illustrated in Fig. 6. When this has been accomplished the grinding lap 6 is replaced by one charged with a polishing abrasive, such as sappharine, and a polishing bath is placed in the cup 1. The polishing operation now proceeds until the first roughed surfaces of the Wafes are brought to a high optical finish. Next, the wafers are removed from the chuck 3 and again cemented thereto in the reverse position. The second part of the grinding operation is then performed, during which a similar section is cut away on the opposite side of each wafer giving it the desired wedge shape as illustrated in Fig. '7. Finally the polishing operation is repeated on the opposite roughed surfaces of the wafers. These polishing steps are very important since they determine in large measure the performance of the rectifying device. By giving the sloping surfaces II and H! a high optical finish the intersection of these surfaces becomes a thin line which is extremely uniform and free from irregularities such as protuberances and depressions.
Following the polishing operation each one of the wedges I 0 is soldered to a brass mounting base or plug 13, the nickel-plated surface of the wedge serving to facilitate the soldered joint.
The spring wire contact unit of the rectifier, shown in Fig. 10, comprises a metallic bow or bridge member I 5 mounted in a cylinder 20 which may be of ceramic or other insulating material, and supporting a fine wire 14 of tungsten. or
.otherssuitahle material, iliaving :a diameter which :is res small :as .zOOl inch. fassenmle the nmitactumitjthe shank .lflro'i itTIB zbow member 45 :is driven with ea iforce fitiinto the central ihole of ithe :ceramic:cy1inder:2fl :and :a cap .21 rofr silver .or rather lsuitable :metal :is "welded on over the mrojecting :endnf :the shank 'toiihold the bow at!) securelyzin position. r-Following :this :the tungsten contact :wire :N "is welded'ito aihe "tines I 5 and -I! :of how t5. lFIfhe .zrequisite degree of "tension lis secured in :the (contact 1'4 byfflexing'tthe tines lzlisand 1 =of the bow inwardly by. means 'of a clamp l8 while the ends of the wire litarewelded thereto.
SI-ltie router shell 01 :housing :of the irectifier fis made :from a section of :metall-ic -tubing of coin "silver ioriother suitable :metal. .Aiter being "cut to the proper length, :the housing tube :22..is drilled to :a plurality :of graduated tinternal :diame'ters as illustrated :in iFig. 2.11 of :the drawing.
The severalparts-"ofthe grectifier are-assembled by :means of ithe hydraulic press mechanism illustrated iinEig. 1'6. The .fir-stgtepin the assembly isitoforce thezceramic unitzshownzin Fig. 10 'into its vpredetermined iPOSitiOn within the cylinder 22. To do this, the cylinder T222 withz its large opening downward is slipped :into the slotted :receptacle 23 until it #is :seated :against ithe bottom of theopenin'g in "the insulatin :bar 2 1 "where it is held :by the resilience :of ithe receptacle. The ceramic unit is placedzon the cup 25 with the b'ow member k5 extending upwardly :and with the ceramic cylinder disposed concentrically-with respect to the large opening :in the bottom of the cylinder to fierce-the ceramic cylinder 20 with a tig ht fit into a predetermined position :in the intermediate section oft-he tube '22. Cine convenient way' o'f determining the correct position of the ceramic cylinder within the housing tube $2 is to proportion the parts in such :a nnanner that the movable support 26 'in .its upward movement reaches the bottom end or the tube when the ceramic cylinder .20 advances to desired predetermined 330511531711 within the tube. Elhe fjack is now released =-andthe second step in the assembly is then performed.
To this end :the tube 22 is withdrawn lrom the receptacle .23,-*turned end for end and again inserted in the receptacle. This time the welded cap 2| slips into the :sl'otted slack 21 as the corresponding end of the tube .22 .comes 'to .rest against the bottom of the opening in the bar 24. The purpose of engaging the cap 2! with the jack 21 is to obtain an electrical connection between the contact wire 14 and an external circuit to facilitate the assembling. .Thereupon brass plug 13 is placed on the cup in such a manner that the apex line 28 of the silicon wedge 10 is accurately disposed at eight 'angles to the :contact wire 44. The hydraulic gackzis again operated, forcing the brass plug l3 into the lower open end of the tube 22 and causing the apex ridge of the wedge to approach the contact wire M. Since these parts are now concealed from view, it is necessary to devise some means for determining when the ridge line engages the wire l4 and establishes the requisite degree of pressure thereon. One method is to connect the silicon wedge and the contact wire in an electrical circuit with a suitable instrument 29 and a source of current 30. When the silicon wedge is advanced to the point where it engages the resilient wire l4 with the requisite force, as indicated by the information obtained from the instrument 29-,
'22. The hydraulic jack :is now operated rhydraulicrjank :is :released, and the assembled ishownf-in Figs. 1 2 to 15, the housing rshield 'fcr thisiiomn-tconsists :of a :hollow cylinder :31 having a'iuniform t internal diameter. The :cylinder :3! may ibermade either of "steel .01" of beryllium copper. When steel is used, the cylinder may be giuen'ia lthin coat of tin. *If berryllium copper is used,-.the .cylinder maybe left unplated or it may herniated with'gold.
The .l'crystal unit comprises a solid cylinder -32 of brass, "plated with tin :if desired, to which a polished silicon water 361 isaffi-xed. The wafers 3-3 ior thisatype of rectifier may be cut from the block 4, preferably to a thickness of :about 6 inch. Since, 'however, the contact-surface of the wafer is a plane and parallel to the base, the polishing operation is accomplished by cementing the wafers to a :chuck, similar to the chuck 3, but @having a plane surface. Thereupon the chuck, having a plurality of these wafers cemented to the 'suriace' thereof, is introduced in the :polishing bath 5, and the wafers are polished to :a high finish :on the lap 6.
The :spring wire contact unit of the rectifier comprises a metallic pin 84 preferably of nickel, an insulating cylinder 35 and a short length of tungsten :contact 'wire 36. A section of the pin 34 :is reduced in diameterand threaded or corrugated, and the insulating :cylinder 35 is then molded around this section of the pin. Good resultsareobtained by the use of a molding mate rial composed of an intimate mixture of quartz powder and 3. .highly pure phenolic resin. The contact wire 36, which is of pure tungsten, is about .002 of an inch in diameter, and the contact -end-thereof is ground to a plane circular surface :normal to the aXis of the wire. The opposite end of the wire 35 is then spot-Welded to the en'd of pin 34, as seen in Fig. 13, and the wire issha'pedli-n a single loop with the free end bent at such :an angle that'only a portion of the circumference-of the thief the'wire engages the suriace of the siliconcrystal '33 to form the rectifyinglcentact area. With this contact wire formation a substantial pressure may be obtained on a small contact area.
The crystal supporting cylinder 32 and'the contact *wire assembly, including the insulatin cylinder -35, are driven into opposite ends of the housingv tube 1 where they are held by aforcefit securelyin ltheirlrequired positions. These elements maybe assembled in the housing tube 3| by means of the hydraulic pressshown in Fig. 16, and suitable "electrical circuit means may be employed to determine when the contact Wire-3'5 has engaged the surface of the silicon crystal .33 with the requisite idegreeof pressure. 1
The advantages *of these translating devices, which were mentioned at the beginning of :the specification, will now be more apparent. A rectification contact of extremely small area is obtained without sacrificing stability. The electrical circuit formed by the silicon element and the tungsten wire is extremely simple, with inductive effects reduced to a minimum. The rectification contact is protected physically and electrically by the housing tube which surrounds it, and in this connection it will be noted that the assembled unit may be handled freely without danger of touching simultaneously the outer shield and the central terminal, thus obviatin the danger of static charges being discharged through the unit and damaging it, Finally the simplicity of the '7 assembly makes it attractive from the standpoint of cost and manufacture.
What is claimed is: I
1. The combination in a translating device of a hollow metallic cylinder open at one end, a metallic base member supported in said cylinder and making electrical contact therewith, a rectifying element mounted on said base member within said cylinder, an insulating member supported in said cylinder and forming with said base member a closed chamber within said cylinder, a contact wire supported by said insulating member and making contact engagement with said rectifying element, and an electrical terminal for said contact wire extending through said insulating member and into the open end of said cylinder, said metallic cylinder serving as an electrical shield for said rectifying element and as a physical shield for said terminal.
2. A combination in a translating device of a metallic housing tube having an open end, a metallic base member supported in said tube and making electrical contact therewith, a rectifying element mounted on said base member within said tube, an insulating cylinder supported in said tube and forming with said base member a closed chamber within said tube, a contact wire supported on said insulating cylinder and making contact engagement with said rectifying element, and an electrical terminal for said contact wire extending through said insulating cylinder and into the open end of said tube, said tube serving as an electrical terminal for said rectifying element, as an electrical shield for said rectifying element and contact wire, and as a physical shield for the said electrical terminal of said contact wire.
3. The combination in a translating device of a metallic housing tube having an open end, a cylindrical metal base member forced into one end of said tube and held tightly in place therein, a silicon crystal rectifying element mounted on said base member within said tube, a cylinder of insulating material forced into said tube and held tightly in place therein, said metallic base member and said insulating cylinder forming a closed chamber within said tube, an electrical terminal extending centrally through said insulatin cylinder from said closed chamber to the'open end of the tube, and a contact wire secured to said electrical terminal within said chamber and making contact engagement with said rectifying element, said housing tube serving as an electrical terminal for said rectifying element, as an electrical shield for said rectifying element and contact wire, and as a physical shield for said electrical terminal and contact wire.
4. The combination in a translating device of a hollow metallic housing member, a, metallic base member supported within said housing member 60 and making electrical contact therewith, a trans- 118 lating element mounted on said base member, said element having plane surfaces intersecting to form an .apex line, an insulating member supported in said housing member, a bridge member secured to said insulating member and extending in proximity to said translating element, and a fine contact wire stretched across said bridge member and attached thereto at its opposite ends, said bridge member serving to hold the contact wire under tension and in engagement with the apex line of said translating element to form a small contact area between said wire and said element.
5. The combination in a translating device of a metallic housing tube, a cylindrical metallic base member supported within said tube and making electrical engagement therewith, a translating element mounted on said base member, said element having two plane surfaces intersecting each other to form an apex-line, a cylindrical insulat ing member supported within said tube, said metallic base member and said insulating cylinder forming a closed chamber within said tube, a bridge member secured to said insulating cylinder and disposed within said chamber, a contact Wire stretched across said bridge member and attached thereto at its opposite ends, said bridge member serving to hold said contact wire under tension and in engagement with the apex line of said translating element to form a contact area between said wire and said element.
6. The combination in a translating device of anelongated metallic housing member having an open end, a metallic base member supported in said housing member and making electrical contact therewith, an insulating member supported in said housing member and forming with said base member a closed chamber within said housing member, a rectifying element mounted on said base member within'said chamber, an electrical terminal supported by said insulating member and extending into the open end of said housing member, and a'contact wire secured'to said terminal and disposed within said chamber to make contact engagement with said rectifying element, said metallic housing member serving as an electrical shield for said rectifying element and as a physical shield for said electrical terminal.
RUSSELL S. OHL.
REFERENCES CITED The following references are of record in the filerof this patent:
UNITED STATES PATENTS 283,186 Germany Apr. 6, 1915