US3767283A

US3767283A - Improvements in or relating to electron discharge devices

Info

Publication number: US3767283A
Application number: US00140189A
Authority: US
Inventors: R Sivyer
Original assignee: EMI Ltd
Current assignee: EMI Ltd
Priority date: 1970-05-07
Filing date: 1971-05-04
Publication date: 1973-10-23
Anticipated expiration: 1990-10-23
Also published as: NL7106338A; DE2123511A1; FR2091350A5

Abstract

An electron discharge device has a hermetic pinch seal formed by an indium type pressure seal. A method and apparatus for the manufacture thereof are also described. The apparatus comprises a demountable vacuum system having a removable top with ports therein, in one of which is mounted the envelope of the device being manufactured and in the others of which are mounted other envelopes. A rotatable and reciprocable platform in the vacuum chamber carries an evaporator for forming a photoelectric layer in the envelope and an electron gun on a pinch for sealing into the envelope. The platform also carries a test electron gun the beam from which is scanned over the photoelectric layer to test it, and an oven for baking the lower part of the envelope of the device. The various devices mounted on the platform are raised so that they enter respective envelopes for the purpose of degassing them.

Description

[ Oct. 23, 1973 United States Patent [1 1 Sivyer IMPROVEMENTS IN OR RELATING TO ELECTRON DISCHARGE DEVICES [75] Inventor:

Primary Examiner-Charles W. Lanham Assistant ExaminerJ. W, Davie Attorney-Fleit, Gipple & Jacobson Raymond Frank Sivyer, Sunbury-on-Thames, England [73] Assignee: EMI Limited,

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[21] AppL 140 189 method and apparatus for the manufacture thereof are also described. The apparatus comprises a demountable vacuum system having a removable top with ports Foreign Application Priority Data therein, in one of which is mounted the envelope of the device being manufactured and in the others of May 7, 1970 Great Britain..,................ 22,195/70 which are mounted other envelopes. A rotatable and reciprocable platform in the vacuum chamber carries an evaporator for forming a photoelectric layer in the envelope and an electron gun on a pinch for sealing into the envelope. The platform also carries a test electron gun the beam from which is scanned over the 0 9 2 HH... 4 1 N 3 3 [52] US. [51] Int. [58] Field of Search;....................

29/25.15, 25.16, DIG. 22; 316/19, l7, l8,

photoelectric layer to test it, and an oven for baking the lower part of the envelope of the device. The vari- References Cited UNITED STATES PATENTS 11/1967 ous devices mounted on the platform are raised so that they enter respective envelopes for the purpose of degassing them.

3,353,890 Legoux. 2,984,759 5/1961 Vine 4 Claims, 3 aw T315255.

Patentd 0a. 23, 1973 3,767,283

2 Sheets-Sheet 1 a Iiihrm y IMPROVEMENTS IN OR RELATING TO ELECTRON DISCHARGE DEVICES This invention relatesto electron discharge devices, such as television pick-up tubes, and to methods of and apparatus for making them.

It is common practice to provide at the base of a photoelectric device a pinch seal formed by heat fusing to the glass envelope a glass base having wires hermetically sealed therethrough for making electrical connectionsto the various electrodes.

This form of pinch seal suffers from several disadvantages, among'which are the need for a relatively high temperature to effect the fusion of the base to the envelope which may result in the release of a gas or gases having a deleterious effect 'on the photoelectric surface; a relatively lengthy processing time is required owing to the need for a second pumping schedule to remove the gases released during the main sealing process; the accuracy of the positioning of the electrode structure may be adversely affected due to movement when the glass becomes softened to make the seal; and, especially with hard glass envelopes and bases, the choice of suitable materials for the sealed through wires of the base becomes rather limited and is conventionally tungsten. Tungsten isdifficult to seal to glass and wires of the size employed for these devices are brittle and are easily broken.

It is an object of the invention to provide an improved method of an electron discharge device making.

According to the invention there is provided a method of making an electron discharge device including the following steps:

a. providing a vitreous envelope closed by a window at one end and having a smooth edge surface at its other end,

b. providing for said envelope a closure member having electrically conductive wires hermetically sealed therethrough and an electron gun structure connected to said wires, said closure member having a smooth surface portion for co-operating with said smooth edge surface of said envelope,

0. mounting said closure member with said electron gun in an evacuable chamber,

d. mounting said envelope in a port in said chamber so as to hermetically seal said port with said open end of said envelope in communication with said chamber, the window end of said envelope protruding from said chamber, and evacuating said chamber and said envelope,

e. testing said device, and I f. subsequently hermetically sealing together under vacuum said smooth edge surface of said envelope and said co-operating smooth surface portion of said closure member by means of an indium type pressure seal.

By the term indium type pressure seal used herein is meant any hermetic seal formed by compressing between surfaces to be joined a soft metal such as indium or indium alloyed with other metal, for example an indiumtin alloy, or other materials having sealing properties similar to indium.

In order that the invention may be clearly understood and readily carried into effect it will now be described by way of example with reference to the accompanying drawings in which:

' FIG; 1 illustrates diagrammatically one example of an electron discharge device made by a method according to the invention,

FIG. 2 illustrates diagrammatically a perspective view of apparatus for making a photoelectric device, and

FIG. 3 illustrates diagrammatically a sectional view of part of the apparatus of FIG. 2 in which an electron discharge device is ready for final sealing.

Referring to the drawing, FIG. 1 shows one example of an electron discharge device in the form of a television pick-up tube. The pick-up tube comprises a vitreous envelope 1 to which are hermetically sealed a window 2 and a vitreous closure member (or pinch seal) 3 having pins such as 4 hermetically sealed therethrough. An electron gun indicated generally by the reference numeral 5 is mounted on the pins 4 and centred in the envelope I by means of spacers 6 and 7. On the inner surface of the window 2 is a substantially transparent layer 8 of an electrically conducting material, such as a Nesa coating, which extends for a small distance along the surface of the envelope 1. On the layer 8 is a layer 9 of a photoelectrically sensitive material, lead oxide for example. A platinum wire or strip 10 is hermetically sealed through the envelope 1 to provide electrical connection to the Nesa coating from an external contact ring 11. The vitreous closure member 3 is hermetically sealed to the envelope 1 by means of an indium ring 12 surrounded by a stainless steel ring 13. If desired, the pinch seal may be overcapped in known manner. The envelope 1 is made from precision bore tubing of a vitreousmaterial such as Pyrex and the end to which the pinch seal is to be made is cut to the correct length and ground and polished to provide a smooth reference surface which assists in making the seal. The closure member 3 has two annular ground and polished regions 3a and 3b (as shown more clearly in FIG. 3) to assist in making the seal, the region 3a also acting as a reference surface co-operating with the polished edge of theenvelope to aid in the positioning of the electron gun structure 5 of the device.

Reference is now made to FIGS. 2 and 3 which show apparatus for the manufacture of an electron discharge device. The apparatus comprises a demountable vacuum pump system having a vacuum chamber 20 and a top 21 releasably secured thereto in airtight relationship by means such as bolts (not shown). A rotatable platform 22 is supported below top 21 by means of a support rod 23 secured to platform 22 and passing through a shaft seal 24 in which vacuum is applied to the space between two sealing rings. The support rod 23 has a handle 23a whereby the platform 22 can be raised and lowered relative to the top 21. Two guide rods 25 are secured to the underside of the top 21 and platform 22 is provided with four indexing apertures 26, spaced at around the axis of support rod 23, through which the guide rods can slide so that the platform 22 can only be raised in one of four positions.

Spaced at 90 around the axis are four apertures or ports in the top 21, in one of which, 27, the envelope 1 is mounted in an airtight manner. The other three apertures have

envelopes

28, 29 and 30 mounted therein in an airtight manner. The envelope I is mounted on the top 21 by means of a vacuum sealing ring 31 and plate 32, a further sealing ring 33 and clamping plate 34 being provided to prevent the envelope 1 from being sucked through aperture 27 when the chamber 20 is evacuated. The

envelopes

1, 28, 29 and 30 are all mounted on the top 21 at the same radius from the axis of the support rod 23, which is the axis of rotation of the platform 22. Mounted on the platform 22 at this same radius and spaced at 90 around the axis are four stations containing respectively, the electron gun 5 mounted on the closure member 3, an oven 35 for outgassing the lower part of envelope 1, an electron gun 36 plugged into a socket 36a for testing purposes, and an evaporator 37 surrounded by a glass tube 38. Electrical connections are made to each of these four stations from a respective socket 39, the connections being made below platform 22 and indicated by the dashed lines 40. The sockets 39 are mounted at 90 around the axis of rotation at a common radius. Two plugs 41 are mounted on the top 21. spaced at 90 apart on the same radius as the sockets 39 such that when the platform 22 is raised two of the sockets 39 engage with the plugs 41. The plugs 41 provide airtight sealed through electrical connections for the units for the time being in the envelope 1 and 30.

There will now be described by way of example the manufacture of an electron discharge device. With the top 21 removed from the chamber 20 and' with the platform 22 in its lowered position, an envelope 1 provided with a window 2, Nesa coating 8 and sealed through connection 10 is mounted in the top 21 so that the lower part of the envelope protrudes below the top 21'; the evaporator is charged with material to provide the photoelectrically sensitive layer 9; the electron gun 5 mounted on closure member 3 is plugged into a socket (not shown) in a support block 42 mounted on the platform 22, with the interposition between closure member 3 and support block 42 of a washer 43 of a material such as a soft metal, lead for example, so as to reduce the chances of the closure member 3 cracking or chipping when sealing pressure is subsequently applied; the test electron gun 36 is plugged into the socket 36a, the life of the electron gun 36 being such that it can be used in the manufacture of several electron discharge devices; and a freshly turned indium fillet 12 in a stainless steel ring 13 is provided and may be slid over the electron gun 5 to rest against closure member 3 (as shown in FIG. 3), but which is preferably located away from the closure member by clips (not shown) below envelope 29 so that the electron gun 5 and the closure member 3 may be outgassed at a higher temperature. The top 21 is then secured in airtight manner to the vacuum chamber 20 which is evacuated by a vacuum pump 44 connnected to chamber 20 at 45.

With the platform 22 positioned relative to the top 21 as shown in FIG. 2, platform 22 is raised. In so doing, the oven 35 fits around the lower end of the envelope 1; the electron gun 5 enters envelope 30; the electron gun 36 enters envelope 28; and the evaporator 37 and tubular surround 38 enter envelope 29, passing through the indium fillet 12 supported therebelow. The oven 35 and the electron gun 5 are connected through their respective sockets 39 and plugs 41 to an external power supply (not shown). Eddy current heating coils are placed around the

envelopes

28, 29 and 30 to outgas the electron guns and'the evaporator, the lower end of envelope 1 is baked by the oven 35 and the cathode of electron gun 5 is activated. The envelope 1 is raised to the position shown in FIG. 3. Oxygen from a supply 46 may be introduced at 47 or other neutral gas such as nitrogen from an auxiliary gas supply 48 may be introduced at 49 to assist in raising the envelope 1, after which the vacuum chamber 20 is again evacuated. The upper part of envelope 1 is outgassed by means of an oven placed therearound and may be maintained in a heated condition until after the photosensitive layer has been evaporated. Next, electron gun 36 is transferred from envelope 28 to envelope 1 by lowering platform 22, rotating it through and raising it again. The electron gun 36 is arranged to occupy the position which the electron gun 5 will occupy after sealing. The electron gun 36 is then operated and the Nesa coating 8 is tested by scanning the electron beam thereacross, with the aid of focus and deflection coils placed around the envelope 1, signals being taken from the sealed through connection 10. This test will show up blemishes which may not show up under optical testing. If the'Nesa coating is unsatisfactory, the manufacturing process may be halted at this stage and the faulty envelope I replaced by a fresh one. If the Nesa coating is satisfactory, the manufacturing process passes to the next stage.

At the same time as the electron gun 36 is being raised into the envelope 1, the electron gun 5 is being raised into the envelope 29 below which is located by clips the indium fillet 12 in the stainless steel ring 13. The electron gun 5 passes through the indium fillet and the clips are then released so that the indium is supported around the edge of the closure member 3.

At this stage, the evaporator 37 is within the envelope 28 and it is now transferred to the envelope 1 by again lowering, rotating and raising the platform 22. A heat sink, for example a vessel containing glycerine at a suitable temperature, is placed on the window 2. Photoelectrically sensitive material is evaporated from the evaporator 37 and condenses onto the Nesa coating 8 to form the photoelectric layer 9 on the window 2. When the evaporation process is finished, the oven and heat sink are removed from the envelope 1 and the electron gun 36 is re-inserted therein. The focus and deflection coils are again placed around the envelope 1 and an optical image is projected onto the window 2. The photoelectric layer 9 is tested by operating the electron gun 36 and causing the electron beam to be scanned across the layer9. The signals thus produced are taken out via the sealed through connection 10, which signals are then used to test the layer 9 in respect of, for example, resolution, the presence of target blemishes, sensitivity and lag. If the tests show the photoelectric layer 9 to be satisfactory, it may then be further processed. For example, the layer 9 may be subjected to a corona discharge, employing the mesh of the electron gun 36 as the corona discharge electrode, to stabilise the layer 9. The corona discharge may be carried out in an oxygen atmosphere in the case of a lead oxide photoelectric layer. The layer 9 may also be subjected to gaseous treatments, and, if desired, further evaporated layers may be deposited.

The layer 9 may be retested by again causing an electron beam from the electron gun 36 to scan thereacross. If a satisfactory result is again obtained, the envelope is ready for sealing. This is achieved by inserting the electron gun 5 into the envelope 1, as shown in FIG. 3. From the position shown in FIG. 3, the platform 22 is raised so that the stainless steel ring 13 enters the aperture 27 in the table top 21 in which it is a sliding fit. A pair of rotatable members 50 having flanges 51 are rotated to move the flanges into recesses 52 in the support block 42. Sealing rings 53 are positioned between the rotatable members 50 and the top 21 to maintain the vacuum in the chamber 20. With the support block 42 supported on the flanges 51, clamping plate 34 is retion may have a second evaporator containing other material to be evaporated onto the photoelectric layer.

What we claim is: l. A method of making an electron discharge device leased and pressure applied, for example by means of 5 i l ding the following steps:

an air cylinder, to push the lower end of envelope 1 against the indium fillet 12 to provide an hermetic seal.

After removal from the pump table, the electron discharge device is provided with the contact ring 11, overcapping of the pinch seal if desired, and focus and deflection coils.

it will thus be seen that an electron discharge device made by a method according to the invention has several advantages over previous devices and methods. One advantage is that due to the indium type pressure seal, no gases are envolved during sealing which might deleteriously affect the photoelectric layer and which would require a further pumping operation, thus providing a considerable saving of time and materials. Also, because the Nesa and photoelectric layers are tested under intended running conditions without sealing the device, if either layer should prove faulty then manufacture can be terminated at that point or additional processing may be carried out to correct the faults, thus providing a further savingof time and materials compared with methods in which testing is done only after final sealing has occurred. Another advantage of the method of testing the photoelectric layer as described herein is that as the test electron gun occupies the position to be occupied by the final electron, gun, the signals obtained by thetest electron gun are identical with those obtainable in the completed device. Yet a further advantage obtained by the preferred method described herein is that as the indium ring is supported away from the closure member and its electron gun during degassing thereof, the degassing of the gun and closure member can be carried out at a higher temperture. A further advantage still is that the overall length of an electron discharge device can be reduced, one of the reasons being that the electron gun can be degassed closer to the closure member if the indium ring is supported elsewhere.

It will be appreciated that, if desired, the test electron gun 36 may be omitted and the electron gun 5 employed also as the test gun. in this case, pick up of the indium ring by the electron gun 5 and closure member 3 may be delayed until after the tests have been carried out. With this arrangement, only three ports or apertures in the top 21 and three stations on platforms 22 are required.

Also, if desired, more than four stations with corresponding ports may be employed. For example, a fifth station may have a corona discharge electrode, instead of employing the mesh of the electron gun. A sixth staa. providing a vitreous envelope closed by a window at one end and having a smooth edge surface at its open end,

c. supporting said closure member with said electron gun in an evacuable chamber,

d. mounting said envelope in a port in said chamber so as to hermetically seal said port with'said open end of said envelope in communication with said chamber, the window end of said envelope protruding from said chamber, and evacuating said chamber and said envelope,

e. testing said device, and

f. subsequently hermetically sealing together under vacuum said smooth edge surface of said envelope and said co-operating smooth surface portion of said closure member by means of an indium type pressure seal.

2. A method according to claim 1 including the steps of providing in said evacuable chamber an evaporator containing material for producing a photosensitive target layer, producing a photosensitive target layer on said window of said envelope, and subsequently testing said device before making said hermetic pressure seal.

3. A method according to claim 1 including the steps of supporting on said closure member a ring of material for effecting said hermetic pressure seal, supporting said closure member below said envelope and applying pressure to said envelope to cause it, without breaking the vacuum seal, to contact said ring and effect said hermetic pressure seal between said envelope and said closure member. 7

4. A method according to claim 2 including the step, prior to producing said target layer, of baking said envelope while mounted in said port, the lower part of said envelope being baked in the evacuated chamber and the upper part of said envelope being baked outside said chamber, and including the step of baking said closure member and electron gun at a position remote from target material, said baking being effected at a temperature higher than that which is attained in the normal operation of said device.

Claims

1. A method of making an electron discharge device including the following steps: a. providing a vitreous envelope closed by a window at one end and having a smooth edge surface at its open end, b. providing for said envelope a closure member having electrically conductive wires hermetically sealed therethrough and an electron gun structure connected to said wires, said closure member having a smooth surface portion for co-operating with said smooth edge surface of said envelope, c. supporting said closure member with said electron gun in an evacuable chamber, d. mounting said envelope in a port in said chamber so as to hermetically seal said port with said open end of said envelope in communication with said chamber, the window end of said envelope protruding from said chamber, and evacuating said chamber and said envelope, e. testing said device, and f. subsequently hermetically sealing together under vacuum said smooth edge surface of said envelope and said co-operating smooth surface portion of said closure member by means of an indium type pressure seal.

3. A method according to claim 1 including the steps of supporting on said closure member a ring of material for effecting said hermetic pressure seal, supporting said closure member below said envelope and applying pressure to said envelope to cause it, without breaking the vacuum seal, to contact said ring and effect said hermetic pressure seal between said envelope and said closure member.