US2618691A - Point contact semiresistor assembly - Google Patents

Description

NOV. 18, 1952 v t BETHGE r 2,618,691

PQINT CONTACT SEUIRESISPOR ASSEMBLY Filed Feb. 1 1950 3 4 2 v 05 I; if Jr-if 6 13 Invemars Bern/lard 56/1796 Patented Nov. 18, 1952 2,618,691 ro'mr CONTACT ssnmssrsroa ASSEMBLY Bernhard Bethge, Fontenay-sous-Bois, and Heinrich Welker, Vaucresson, France, assignors to Societe Anonyme dite Compaznic dos Freins & Signanx Westinghouse, Paris, France Application February 1, rate, can No. 141,646 In France February 18, lt id is @laims. (or. its-see) This invention relates to electrical point-com tact assemblies in general, and more particularly to assemblies of the transistor type which include a semi-conductive body with two electrodes on one side thereof making high-resistance point-contact with the surface of the body at two extremely closely-spaced points thereof.

So-called transistors as is now well-known (of. the paper by Bardeen and hrattain in Physical Review, July 15, was, page 230, and also copending patent applications l lo. W955i filed August ll, 19491 for Crystal Device for Com trolling Electric Current by lit/leans of a Solid Berni-Conductor and No. 1 19,5791 filed October 5, 1949 for Improvement in or Relating to Semi= tt onductor' for Control Purposes comprise a semi-conductive crystalline body having pn one side thereof an electrode oi substantial area in low-resistance contact with the surface oi the body and on another side thereof two electrodes making high-resistance point-contact with the surface oi the body at very closely-spaced points thereof.

Considerable practical difficulty has been experienced in the construction of such assemblies, especially because of the very close spacing required between the two point contacts. 'llhus, while each point contact must be actually in electrical contact with the surface at two separate points of said surface and the electrodes should not touch, the distance between the contacts must not exceed about is microns, for emcient operation of the transistor. Furthermore, in many semi-conductors all the points of the surface are not equally eflicient, and the distribution of the active points over said surface is generally random, so that it is usually necessary to explore the surface with the electrode points until a suitable area is reached for an efiicient dual point contact. This still further complicates the problem of constructing such transistors. It is these difficulties in particular that the invention proposes to solve.

A general object of the invention is to provide an improved construction for an assembly including a surface and two elements in point contact therewith at two closely-spaced but distinct points of the surface, in which increased facilities are provided for positioning in an accurately controllable manner the point contacts in relation to each other and to the surface.

A more specific object is to provide an improved transistor construction in which the two point electrodes making high-resistance point contact with closely-spaced but distinct points of the 2. surface of a semi-conductive element may be adjusted at their proper setting with respect to each other and to said surface. in a more eiilcient and accurately-controllable manner.

A further object is to provide such a transistor having improved means for exploring the surtace oi? the semi-conductive element with the point electrodes.

The above and further objects and advantages oi the invention, and the characteristic features t i, will appear as the description proceeds. i. to be understood that, while the invention is described and illustrated in connection with a sister element of a certain type, it is not to be considered restricmd to that or in fact to other type of transistor, being generally applicable to any device in which a similar relationship between two punctual elements and a surface is to be obtained.

in the accompanying drawings:

Fig. l is an explanatory diagram of the principle on which the invention is based;

Fig. 2 is a cross-sectional view of a transistor assembly constructed according to a preferred embodiment of the invention, and

Fig. t is a fragmentary view on an enlarged scale of one contact.

The general principle applied in the invention wilt iirst be explained with reference to Fig. l. Alli and at diagrammatically indicate the electrodes which at their contact tips are to make high-resistance contact with a surface S. at their outer ends the electrodes Al and A2 are fixedly secured as at (it and 02. In the initial condition indicated in full lines in Fig. l, the free ends of the electrodes A1 and A2 are just touching each other as at P and the surface S lies on a plane extending through 01 and 02. This is a critical limiting condition for the relationship of the electrode tips between each other and with respect to the surface.

it a vertical upward displacement is imparted to the surface as from S to S as indicated by the arrow, over a distance 1 the free ends of the electrodes A1 and A2 will obviously describe approximately arcuate paths respectively centered at O1 and O2 and having the common radius 1' equal to the common length of the electrodes. The tips of the electrodes will then reach the positions P1 and P2, respectively, let Ar=the spacing between P1 and P2, then Assuming the numerical values r= l mm. for

the length of each electrode and 11:02 mm. for the vertical displacement imparted to the surface S, then the resulting spacing A's-=20 Thus, starting from the assumed initial condition in which the bearing surface S lies in the plane 01190:, it will be possible to secure any desired one of a whole range of spacings between the electrode tips.

In a practical embodiment of the invention (see Figs. 2 and 3) the electrodes l and 2 (corresponding to A1 and A: of Fig. 1) are bent at their free ends as shown at 3 and 4. Furthermore, as more clearly indicated in Fig. 3, the tips of the electrodes are bevelled as at 5. The tips bear upon the upper fiat surface of a semi-conductive crystal 6 the under surface of which is bonded over a large area to an electrode I. The electrode I is mounted for'vertical sliding movement, and preferably also for rotation, in a bushing member 8 secured in any suitable manner (as by threaded engagement, welding, cementing, or the like) in an insulating support Ill, made of ceramic or any other suitable material. The support III has a top wall member spaced above the wall in which the bushing 8 is inserted and in the top wall there is formed a window II adjacent the electrode tips 3, 4. Suitable sealing means are preferably provided (not shown) for sealing the window II after adjustment of the electrodes has been completed.

At opposite sides of the insulating support I and suitably secured to it in any convenient way are two further bushings I2 and I3 in which the electrode-carriers I4 and I5 are slidably, and preferably also rotatably, fitted. The electrodes I and 2 are fixedly secured to the inner ends of the electrode-carriers I4 and I 5. Preferably,

as shown, the electrodes are fixed in the related carriers at somewhat oif center points of the inner end surfaces of said carriers, for a purpose to be explained later. The relative arrangement of the various above-described parts is such that, in an initial position of adjustment, the points of fixation of the electrodes I and 2 in the carriers I4 and I5 lie in the same horizontal plane as the plane of the top surface of the semi-conductive element Ii, with the tips of the electrodes I and 2 then just touching each other along the vertical bevel portions 5 thereof. Set-screws I6, I1 and I8 are provided to block the respective adjustable elements I, I4 and [5 in their adjusted positions.

To adjust the transistor assembly described above, the electrode fl and the electrode-carriers l4 and I5 are first brought to their initial relative position just described, i. c. with the top face of the semi-conductor 6 in the horizontal plane extending through the points of fixation of the electrodes I and 2 in their carriers I4 and I5 by up-and-down adjustment of the lower electrode 1, and with the tips 5 of the electrodes I and 2 in contact with each other by horizontal adjustment of the carriers I4 and [5 in their respective bushings I2 and I3. Then the setscrews I1 and I8 may be tightened to block the electrode-carriers I4, I5 in their position, and the lower electrode I is raised raising in turn the top face of the semi-conductor 6, until the desired spacing between the tips 5 of the electrodes I and 2 is secured as previously explained, when the set-screw I6 may be blocked in turn.

It will be understood that all the above adjusting steps are visually followed and controlled through the window II by means of appropriate optical means. such as an ordinary or preferably a stereoscopic microscope (not shown). The influence of various unpredictable mechanical factors such as play at the relatively movable surfaces can thus be checked and suitable allowance made therefor. After adjustment is completed, the window Il may be sealed by suitable means not shown.

In many semi-conductive bodies, the useful points of the top surface are found to be unpredictably distributed, and accordingly the invention provides for the possibility of exploring the surface with the electrode tips until a satisfactory contact area is found thereon, For this purpose, as stated above, the electrode 1 is preferably mounted for rotation in its bushing 8,

and rotation of said electrode at its initial level will enable such a suitable operative area to be located, in conjunction with suitable horizontal displacements in unison imparted to the electrode-carriers I4 and I5. The eccentric arrangement of the points of fixation of the electrodes I and 2 in their carriers will facilitate compensating for the resulting difference in length. t

It is to be understood that many modifications may be made in the constructional details of the embodiment illustrated and described without exceeding the scope of definition of the claims. Also, as stated before, the invention is applicable to devices other than the transistor assembly selected for purposes of explanation and which forms a preferred application of the inventive idea.

spaced points of the surface, means for supporting said elements at their outer ends on a line generally across said surface, and means for controllably displacing said surface normally to its own plane through a position level with, and to a position above said line, the contact points of said tips with said surface being coincident as said surface is substantially level with said line.

2. Point-contact assembly as in claim 1 wherein said elements include portions adjacent said tips thereof bent downwardly towards said surface.

3. Point-contact assembly as in claim 2 wherein said tips are bevel and are in contact with each other along the bevel portions thereof as said surface is level with said line.

4. In a point-contact assembly a substantially fiat semi-conductor surface having contact terminal means, two yielding elongated elements having tips which are to make point contact with said surface at two distinct closely-spaced points of the surface, means for supporting said elements at their outer ends on a line generally across said surface and for controllably independently displacing said elements towards and away from each other along said line, and means for controllably displacing said surface normally to its own plane between a lowermost and an uppermost position respectively situated below and above said line, the contact points of said elements with said surface being coincident as said surface is substantially level with said line.

5. Point-contact assembly as in claim 4 wherein said surface is further rotatable in its own plane.

6. Point-contact assembly which comprises in combination a casing having a bottom and a top wall and side walls, a bushing in said bottom wall and aligned bushings in' opposite side walls of said casing, a bottom support member adjustably slidable in said bottom bushing and side support members adjustably slidable in said side bushings, a flat semi-conductor surface having contact terminal means, said semi-conductor surface being supported on said bottom support member in said casing yielding contact elements projecting fromtithe inner ends of said side bushings in said casing towards said surface. having downbent tip portions making point contact with said surface; lthe points of contact of said tips with said surface being normally coincident as said surface -"is%'substantially level with the line extending through the outer ends of said elements. whereby a coiitrolled upward displacement of said lower support in its bushing will cause said points of contact to move apart a controlled amount over said 7. Point-contact assembly as in claim 6 wherein said lower support is cylindrical and controllably rotatable in its bushing.

8. Point-contact assembly as in claim 7 wherein said side supports are cylindrical and rotatable in their related bushings and said elements are secured from the inner faces of said supports in eccentric relation with said faces.

9. Point-contact assembly as in claim 8 wherein there is a set screw in each bushing to block the related support in adjusted position.

10. Point-contact assembly as in claim it wherein a viewing window is formed in said top casing wall above said surface and means for openably-sealing said window.

11. Improved transistor unit which comprises in combination a casingjaaving a bottom. a top and side-walls. a guiding aperture in said bottom wall and aligned guiding apertures in opposite side walls of said casing. a semi-conductor body having iiat top and bottom surfaces. a bottom electrode in low-resistance contact with said bottom surface extending through and adjustably slidable in said bottom guide aperture, supports each extending through and adjustably slidable in a related one of said apertures, two point-contact electrodes each secured at its outer end to theinner end of a related one of said side supports and projecting generally toward each other and towards said top surface to make low resistance point-contact therewith at their inner ends, and a window formed in said top casing wall above said surface.

'12. Transistor unit as in claim 11 wherein each of said point contact electrodes is downbent ad- Jacent its inner endto resiliently press down upon said top surface when said surface is substantially level with the outer fixed ends of said elements.

13. Transistor unit as in claim 12 wherein each point-contact electrode has a bevelled inner end, said levels being substantially normal to said surface when'said surface assumes said substantially level position.

14. Transistor unit as in claim 13 wherein said support for the semi-conductive body is cylindrical and adjustably rotatable in its guide aperture. 7

i5. Transistor unit as in claim 14 wherein each of said side electrode-supports is cylindrical and adjustably rotatable in its guide aperture, and said point-contact electrodes at their outer ends are fixed in the circular inner end faces of said side supports in eccentric relation therewith.

B. GE.

" CH WELKER.

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

UNITED STATES PATENTS Number Name Date 2.595.475 McLaughlin May 8. 1952 2,609,427 Btelmak Sept. 2, 1952

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