US3546526A - Electron discharge device having coaxial mounting structure - Google Patents

Description

United States Patent US. Cl. 315-39 14 Claims ABSTRACT OF THE DISCLOSURE An electron discharge device comprising an evacuated envelope having a cathode and an anode therein; a rigid, coaxial-line section mounted inside said envelope with one of its ends juxtaposed with respect to said cathode and the other end portion being affixed to the wall of the envelope; said anode being mounted on the end of the coaxial-line section in position to receive electrons from said cathode, said anode being in the form of a solidstate diode or the like, and a mounting structure for the diode which provides for low impedance connections to the coaxial line and furthermore is rugged but flexible in response to movement of the various parts due to temperature changes and the like.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to an electron discharge device having coaxial mounting structure, and more particularly to a photomultiplier which utilizes a semiconductive element mounted on a section of coaxial line which serves as the supporting structure for the element.

Description of the prior art One of the advantages which may be realized from incorporating solid-state elements into vacuum tube devices is that of ruggedness. This follows from the inherent strength of diodes, transistors and similar semiconductor elements. Generally, the ability of such elements to withstand shock and vibration is limited by the mounting structure and nature of the contacts which connect the solid-state elements to the electrode system within the tube. In addition to providing suitable support, the mounting structure must also meet certain electrical requirements.

SUMMARY OF THE INVENTION The present invention meets these requirements in providing an electron tube Which is physically rugged, provides compensation for expansion and contraction of the various components due to temperature changes, incorporates a coaxial configuration adapted to be coupled to an external line in a manner to match impedances and hold losses to a minimum, and involves an arrangement for mounting a solid-state element as an eflicient, integral part of the coaxial-line configuration.

A working embodiment of this invention includes an evacuated envelope having a cathode and an anode therein, a rigid coaxial-line section mounted in this envelope, one end portion of this coaxial-line section being secured to and supported by the envelope and the other end portion being disposed adjacent to the cathode and mounting the anode, said anode including a semi-conductive element 3,546,526 Patented Dec. 8, 1970 having a low inductance connection to the coaxial-line section, and means for coupling the coaxial-line section to a coaxial line externally of the envelope.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectional view of one embodiment of this invention operatively connected to an external coaxial line;

FIG. 2 is a similar sectional view, in enlarged form, of a portion of the arrangement of FIG. 1;

FIG. 3 is a fragmentary view, in longitudinal section, of a slightly different embodiment of this invention; and

FIG. 4 is a view similar to FIG. 3 of still another embodiment of this invention.

Referring to the drawings, and. more particularly to FIG. 1, an evacuated glass envelope 1 has fused to the left-hand end thereof a metallic mounting ring 2 which is hermetically circumferentially sealed to a second metallic mounting ring 3 as shown. The ring 3 has a radially inturned flange 4 to which is secured a transparent faceplate 5 having on the inner surface a photoelectric cathode 6, in film-form, of conventional material.

The ring 3 also is provided with a cylindrical sleeve 7 extending axially from the inner periphery of the flange 4 as shown. The ring 3 is conductively connected to the cathode 6.

Inside the envelope 1 is a section of coaxial line composed of inner and outer conductors 8 and 9, respectively. These conductors are of tubular copper or the like sufiiciently rigid to be self-supporting. Preferably, this copper is oxygen-free. The right-hand end portion 10 of the coaxial-line section projects through and beyond the envelope 1 and is hermetically sealed thereto by the envelope proper being fused directly or by the aid of an auxiliary metal seal ring to the outer periphery of the outer conductor 9 and by the use of ceramic seals 11 and 12 fused to both of the conductors 8 and 9 as shown. The seal 11 is annular and is fused at its inner and outer peripheries to the inner and outer conductors 8 and 9, respectively. The seal 12 may be omitted, but in the illustrated embodiment it is in disc form with an aperture 13 therethrough. Desirably, it is sealed at its outer periphery to the inner wall of the inner conductor 8.

The inner conductor 8 is provided with a series of openings 14 in the wall thereof while the outer conductor 9 has another series of openings 15 as shown. These openings 15 are shown radially opposite the end portion of the inner conductor 8 but may be positioned at any convenient point along the outer conductor 9. The outer conduotor 9 is of smaller diameter than the cathode sleeve 7 and coaxially projects thereinto to a position next adjacent to the photocathode 6. Over the end of the inner conductor 8 is fitted a metallic cup 16 to which is conductively bonded a solid-state element 17 which may be a wafer diode, a transistor, or a similar semiconductor. In the illustrated embodiment it will be assumed to be a conventional diode.

Bonded to the end face of the diode 17 is a cupshaped element or contact 18 having a bottom provided with a central aperture 19, and a frusto-conically shaped wall which flares radially outwardly to a ring portion which is conductively secured to the outer conductor 9 at a position 21 by welding or the like.

The components and attachments thus far described are ruggedly made so as to withstand substantial shock and vibration. The diode 17 is conductively bonded to both the cup 16 and the contact 18 in a secure manner and the contact 18, while quite rigid, still is formed such that it will provide for some axial and radial movement of the diode 17. Such movement can be caused by expansion and contraction of the variou components due to variations in temperature. This movement accommodation is provided in part by the frusto-conical section 20 which is deliberately formed to accommodate the movement.

The right-hand end portion 10 of the coaxial-line section is so formed that an external coaxial line, as indicated generally by the reference numeral 22, may be conveniently coupled thereto without any physical discontinuities or electrical mismatching. As seen clearly in FIG. 1, the outer conductor 9 is extended uniformly to its terminus. The inner conductor 8 is provided with a reduced diameter portion 23 which is tipped-off at 24 to seal the tube hermetically. It may be explained at this point that the right-hand end of the hollow inner conductor 8 may be conveniently used for evacuating the envelope 1, and when the evacuation has been completed, the portion 24 may be sealed off to complete the evacuated enclosure.

The reduced diameter portion 23 of the inner conductor is so sized that when the inner conductor 25 of the external line 22 is telescoped thereover, the outer and inner diameters, respectively, of the two conductors 8 and 9 will be continued onwardly for the external line 22. Thus, there will be encountered no physical discontinuities nor electrical mismatching at the coupling of the two coaxial lines.

The cathode sleeve 7, and the two conductors 8 and 9, are so positioned with respect to each other and also with respect to the photocathode 6 as to provide an electron-optical lens which will focus electrons from the surface of the cathode 6 onto the left-hand face of the diode '17. Thus, the diode 17 may be regarded as an anode. In order to connect operating potentials to the tube, the ring 2 may be regarded as one terminal which is connected to the negative pole of a power supply 26 and the outer conductor 9 as another terminal to which is connected the positive pole of the power supply 26. The dimensioning of these optics for a given supply voltage of,

e.g., 10,000 volts, is well within the skill of the art.

The diode 17 is electrically connected in series between the adjacent ends of the two conductors 8 and 9 by means of the two members 16 and 18 which are so formed as to present negligible inductance at the high frequencies at which the tube of this invention is operated. In the operation of this invention, the diode 17 may be regarded as merely an insulator, and the polarity connections thereof to the two members 16 and 18 are so selected as to realize this condition. In this connection, a simplified circuit for extracting a signal from the coaxial line in response to excitation of the diode 17 is indicated as being a simple battery 27 and a signal resistor 28 connected in series with the inner and outer conductors, respectively. Under conditions of no excitation, practically no current flows from the battery 27 through the diode 17.

Under conditions of operation, radiation of suitable wavelength is projected onto the faceplate 5 which results in the emission of electrons from the cathode 6. These electrons are focused onto the diode .17, resulting in a reduction of the resistance thereof. This causes a current to flow from the battery 27 through the inner and outer conductors 8 and 9 as well as the contact member 18.

The voltage change produced across the resistor 28 may be used as an output signal.

In a preferred embodiment of this invention, the element 17 is a silicon diode which not only changes resistance under the influence of high energy, electron impact, but also produces the effect of electron multiplication resulting in substantial power gain. The diode 17 may be selected that its impedance will match as nearly as possible the characteristic impedance of the coaxial- line section 8, 9 such that it constitutes an almost perfect termination therefor. Thus, there can be maximum power transfer of signals from the diode 17 to the coaxial line 8, 9.

In the fabrication of the tube described thus far, the skirt of the cup 16 may be welded to the inner conductor 8 by inserting suitable probes through the apertures 15 in the outer condutcor 9. Of course, this welding operation is performed prior to the insertion of the coaxial- line section 8, 9 into the envelope 1.

Prior to the assembly of the cup 16 to the inner conductor 8, the diode 17 is bonded thereto. This step is illustrated in slightly exaggerated form in FIG. 2. A convenient feature residing in this invention is the fact that the contact member 18, the diode 17 and the cup or substrate 16 may be assembled and tested both physically and electrically prior to insertion into the envelope .1. Other suitable subassemblies are shown in FIGS. 3 and 4, and these will be described in detail later on.

The contact member 18, the diode 17 and the cup '16 may be bonded sequentially or simultaneously in a single operation as may be determined by the nature of the material employed. Generally, an alloy or welded bond is preferred for its ruggedness. If the semiconductor 17 is of the p-type, bonding to the cup 16 with a gold-germanium eutectic is a suitable method, with both the semiconductor 17 and cup 16 having previously been coatedwith a gold film. Contact to the opposite sides of the element 17, especially for diodes and other axially symmetric elements, is conveniently made by initially depositing an annular metallic film 29 thereon. For an ntype diode, the annulus 29 could be of aluminum or nickel, for example. To provide an alloyed bond in the case of aluminum, the contact region of the member 18 could be coated successively with aluminum and magnesium. When brought into contact with the aluminum annulus 29 on the diode under conditions of heat and pressure in an inert atmosphere, at suitable alloy bond will result by diffusion. Ultrasonic scrubbing may be used to remove thin surface oxides.

More simply, soldering, welding, alloying and ultrasonic bonding may be employed in the cases of nickelto-nickel contacts. For experimental devices, bonding of the diode 17 to the members 16 and 18 may be readily and simply accomplished by using a conductive adhesive such as silver paint or paste. A suitable alloy bond between the diode 17 and the cup 16 is indicated by the layer 30.

In FIGS. 3 and 4 are illustrated different structures for mounting the diode 17 in place. In FIG. 3, where like numerals indicate like parts, a metallic bellows 31 having a single convolution is used, this bellows terminating in a disc-shaped fitting 32 which is welded at its periphery to the conductor 9. The convolution of the bellows 31 is sufiiciently flexible that expansion and contraction of the various components may be accommodated while still maintaining the rigid mounting of the diode 17 which will withstand shock and vibration. The bellows 31 is hollow and serves as a part of the electron lens for focusing electrons from the photocathode 6 onto the diode 17.

In FIG. 4 is illustrated another mounting structure wherein a bellows 32 is located on the opposite side of the diode 17 from that shown in FIG. 3 and forms a part of the cup 16a which fits over the inner conductor 8. This bellows 32 is bonded to the right-hand face of the diode 17 and is provided with a single convolution which will accommodate the expansion and contraction previously mentioned. To the left-hand face of the diode 17 is bonded the contact member 18 previously described.

From the foregoing it will appear that the tube of this invention is physically rugged and is so constructed as to compensate for the expansion and contraction of the various components with temperature thereby minimizing the probability of damage to the tube electrodes and to the diode element itself. Also provided is a coaxial configuration which permits eflicient transfer of electrical energy from the inside of the evacuated envelope to an external circuit. This coaxial configuration is made such that the characteristic impedance of the external circuitry may be matched almost precisely and physical discontinuities are so minimized as to maintain losses to negligible value.

The coaxial configuration is further designed such that the solid-state or diode element forms an integral part thereof, being in fact a termination of this line. In addition, the diode is so connected to the coaxial configuration that inductance factors are kept to minimum levels advantageous to high frequency operation and fast respouse.

The particular coaxial configuration and the structure by means of which the diode is secured thereto assists in protecting the diode from its immediate environment and the detrimental processes which may occur within that environment. With respect to operation as an electron multiplier, inasmuch as the multiplication occurs within the diode element 17 itself, magnetic fields will have little or no effect on the multiplying characteristic. Further than this, because of the small size of the diode 17, as an electron multiplier, the tube may be made substantially smaller than the conventional dynode counterparts. Thus, the present invention, when embodied in a photomultiplier tube, may be extremely small in size yet provide high gains, fast response, be insensitive to external magnetic fields, and withstand considerable shock vibration.

What is claimed is:

1. A coaxial mounting structure for mounting solid state elements in an evacuated envelope comprising a coaxial-line section having inner and outer tubular conductors, a semiconductive element having two planar terminal portions and being conductively secured to one end of the inner tubular conductor, one of said planar terminal portionsbeing directly connected to said one end, means for series connecting the other planar terminal portion to said outer conductor thereby connecting said element in series with said inner and outer conductors, an evacuated envelope which encloses at least a portion of said coaxial-line section, said element and said means, and terminal means for coupling said coaxial line section to a coaxial line external thereto.

2. The structure of claim 1 in which said means includes a conductive member which is flexible both radially and axially with respect to said coaxial-line section.

3. The structure of claim 2 in which said means includes a cup-shaped member having a bottom provided with an opening and a wall which in part is frustoconically shaped thereby providing for axial flexure of said cupshaped member, said bottom being abutted against and conductively secured to said semiconductive element, thereby exposing a portion of said semiconductive element through said opening, the outer periphery of said cupshaped member being conductively secured to said outer conductor, said semiconductive element being secured to said one end of said inner conductor by means of a conductive hollow bellows having one end secured to said one end and the other end connected to said semiconductive element.

4. The structure of claim 2 in which said inner and outer conductors are provided with apertures in the walls thereof, respectively, whereby the interior of said conductors may be maintained at the same reduced pressure as the interior of said envelope, said envelope having opposite end portions, and said conductors being secured to one of said end portions of said envelope.

5. The structure of claim 4 in which said one end portion of said envelope includes an annular member of insulating material disposed between and being hermetically sealed to said conductors, said conductors extending beyond said one end portion to thereby serve as said terminal means, that portion of said inner conductor which extends beyond said one end portion being sealed off to thereby maintain the evacuated condition of said envelope.

6. The structure of claim 2 in which said means includes a cup-shaped member having a bottom provided with an opening and a wall which in part is frustoconically shaped thereby providing for axial flexure of said cupshaped member, said bottom being abutted against and conductively secured to said semiconductive element, thereby exposing a portion of said semiconductive element through said opening, the outer periphery of said cupshaped member being conductively secured to said outer conductor, said semiconductive element being secured to said one end of said inner conductor, said end including a conductive cup intimately fitted thereover, said element being secured to said cup.

7. The structure of claim 2 in which said means includes a conductive hollow bellows having one end secured to said semiconductive element and the other end connected to said outer conductor, a portion of said semiconductive element being exposed through said bellows.

8. An electron discharge device comprising an evacuated envelope having a cathode and anode therein; a rigid coaxial-line section having opposite end portions and being mounted in said envelope, one end portion of said section being secured to and supported by one end of said envelope; means at the other end portion of said section for mounting said anode and series connecting it between said inner and outer conductors, said anode including a semiconductive element being disposed adjacent to the distal end of said inner conductor and opposite said cathode to receive electrons therefrom, and means for coupling said one end portion of said coaxialline section to a coaxial line externally of said envelope.

9. The device of claim 8 in which said mounting and connecting means includes low impedance supporting structure which fixedly secures said element in position with respect to one of said conductors but allows relative movement with respect to the other conductor due to changes in operating and ambient temperature for minimizing strain on said element.

10. The device of claim 9 in which said structure includes a cup-shaped member having a bottom provided with an opening therethrough, said bottom of said member being connected to said element and the peripheral portion thereof being connected to said outer conductor, said member being flexible both axially and radially with respect to said coaxial-line section.

11. The device of claim 9 in which said structure includes a conductive bellows having opposite ends, one end being connected to said element and the other end being connected to an end of one of said conductors.

12. The device of claim 8 in which said envelope has opposite ends, said cathode being photoelectric and generally planar, said other end portion of said coaxial-line section being mounted in the other end of said envelope, and electron-optical means which includes a portion of said outer conductor for guiding electrons from said cathode onto said semiconductive element.

13. The device of claim 12 in which said mounting and connecting means includes low impedance supporting structure which fixedly secures said element in position with respect to one of said conductors but allows movement relative to the other conductor due to changes in operating and ambient temperature, said structure including a cup-shaped member having a bottom provided with an opening therethrough, the peripheral portion of said member being attached to the distal end of said outer conductor and said bottom being attached to said element, said member being frustoconically shaped with the larger end opening toward said cathode, and a cathode sleeve connected at one end to said cathode and extend ing toward but being spaced from said outer conductor, said electron optical means including said sleeve.

14. The device of claim 13 in which said terminal means comprises portions of said conductors which extend beyond said envelope, an annular member of insulating material disposed between and being hermetically sealed to said conductors, said conductors being hollow and having apertures in the walls thereof, that portion of said inner conductor which extends beyond said envelope being sealed off to thereby maintain the evacuated condition within said envelope.

References Cited JAMES W. LAWRENCE, Primary Examiner EUGENE P. LAROCHE, Assistant Examiner US. Cl. X.R.

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