US3291549A

US3291549A - Method for fabricating an electron discharge device

Info

Publication number: US3291549A
Application number: US313694A
Authority: US
Inventors: Von C Campbell; Frank A Romano; Edmund F Schilling
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1963-10-03
Filing date: 1963-10-03
Publication date: 1966-12-13
Anticipated expiration: 1983-12-13
Also published as: GB1075756A; DE1464969A1; CH424990A

Description

1966 v. c. CAMPBELL ETAL 3,

METHOD FOR FABRICATING AN ELECTRON DISCHARGE DEVICE Filed Oct. 5, 1963 2 Sheets-Sheet 1 O U N U 1. R P 0 w m M R S m C A F V K D m c N N w M U v F W E on v ""fl 231 mm 2339; mag/E62 m 9 37 02:5: p U C.UDOZ m a n d 7 w 2 a m M BY THEIR ATTORNEY.

Dec. 13, 1966 v. c. CAMPBELL ETAL 3,291,549

METHOD FOR FABRICATING AN ELECTRON DISCHARGE DEVICE 2 Sheets-Sheet 2 Filed Oct.

lN-VENTORSZ VON c. CAMPBELL,

FRANK A. ROMANO,

EDMUND F. SCHILLING,

TRIGGER PULSE SOURCE THEIR ATTORNEY.

United States Patent ()fifice Patented Dec. 13, 1966 This invention relates to a method for fabricating an electron discharge device.

In one form of light valve apparatus, an electron discharge device is provided having a writing chamber envelope member and an electron gun member which is mounted and hermetically sealed to the envelope member. The gun member includes a plurality of elements of electrically insulative refractory material forming a chamber for the gun. A plurality of gun electrodes and a suitable brazing filer material are positioned between the refractory material elements. By heating the gun member assembly to a temperature and for a period of time necessary to cause brazing between the elements and electrodes, a rigid hermetically sealed gun member assembly is formed.

It is desirable to test various electrical characteristics of the assembled gun member such as cathode emission and the alignment of the various gun components prior to final assembly of the discharge device. To effect testing, it is necessary that the elements of the gun member be outgassed, the gun chamber be evacuated, and that a beam current collector electrode be provided. The brazing process to which the gun member assembly is subjected advantageously lends itself to outgassing the member since the temperature of the brazing process, in addition to causing adhesion of the various elements, can be selected to be suitably high for outgassing the various gun elements. Brazing the gun member assembly in a vacuum chamber and mounting an electrically conductive closure element at an end of the gun member provides an evacuated and outgassed electron gun capsule having a beam current collector electrode. The capsule thus formed is adapted for testing the electrical characteristics of the gun member prior to final assembly. A discharge device having these features is disclosed in copending application Serial No. 313,693, filed October 3, 1963 and assigned to the assignee of the present invention.

Subsequent to the electrical testing of the gun member and prior to mounting the member to the writing chamber envelope, an aperture is formed in the electrically conductive closure end element in order to provide an unobstructed passage for an electron beam from a source within the gun member to the writing chamber of the discharge device. Formation of this aperture can conventionally be accomplished by machining. Formation of the aperture exposes the interior of the gun member to atmospheric pressure thus requiring that the gun member be re-evacuated and that the components be re-outgassed prior to use. The gun member is mounted and hermetically sealed to the envelope member and final evacuation and outgassing of the assembled device is then accomplished.

Final outgassing and evacuation is generally performed in four sequential pumping phases. A vacuum pump which is coupled to the envelope member initially evacuatcs the device to a desired reduced pressure. During a second phase and while the envelope is being pumped, various components which are mounted within the writing chamber are heated by RF induction currents. Outgassed products of this phase are removed by pumping until a desired reduced pressure is again attained. The electrodes of the gun member are heated by RF induction currents during a third phase and the outgassed products are similarly removed by pumping. The cathode electrode is heated and outgassed as the products are removed by pumping. Finally a chamber separating disk is heated by electron bombardment. Pumping continues until the desired final operating pressure is attained within the envelope.

The above described processing of the discharge device is inefiicient in that duplicate outgassing and evacuation of the gun member is required and the processing time for the discharge device is consequently extended. Furthermore, outgassing of the aperature disk by electron bombardment requires substantially more time than is required when the disk was initially heated and outgassed.

.It can require as much as three to four hours in order to complete the described outgassing-evacuation cycling. When it is desirable to produce large quantities of the electron discharge device at economical cost, this lengthy processing time is disadvantageous.

Accordingly, it is an object of this invention to provide an improved method for processing an electron discharge device.

Another object of this invention is to provide a method of outgassing and evacuation of an electron discharge device which can be accomplished in a relatively short time.

Another object of this invention is to provide a method of outgassing and evacuation for a discharge device of the type referred to which is relatively less costly than known methods.

A further object of the present invention is to provide a method of outgassing and evacuation for a discharge device whereby an electron gun member is outgassed and evacuated independently and re-outgassing and re-evacuation is thereby avoided.

In accordance with the present invention, an electron gun member assembly having aclosure end member is brazed in an evacuated atmosphere at a temperature suitable for both brazing the assembly and for outgassing the various elements of the electron gun. The electron gun member is mounted and hermetically sealed to a writing chamber envelope member of an electron discharge device. Various components in the writing chamber are heated to an outgassing temperature while the writing chamber is simultaneously vacuum pumped to a desired operating pressure and then tipped ofil. A focused coherent light beam which is derived from a source external to the device is projected through a transparent segment of the device upon a surface of the processing end member to form an aperture therein and to provide an unobstructed electron beam passageway from the gun member to the writing chamber.

By this process, the various elements of the electron gun are advantageously outgassed during the brazing operation and the gun member is evacuated and hermetically sealed. The additional step of re-outgassing the gun member is eliminated; the gun chamber can be processed independently; and the time and cost in processing the electron discharge device is materially reduced.

These and further objects, features and the attending advantages of the invention will be apparent with reference to the following specification and drawings in which:

FIGURE 1 is a view of a discharge device of the type essing end element 22.

referred to and illustrates a step in the fabrication process of the present invention;

FIGURE 2 is a perspective view of an electron gun member for an electron discharge device of the type utilized in a light valve projection apparatus;

FIGURE 3 is a sectional view of the electron gun member of FIGURE 2 taken along lines 3-3 of FIGURE 2;

FIGURE 4 is an enlarged partial view of the device of FIGURE 1 illustrating the mounting of an electron gunmember to an envelope member;

FIGURE 5 is a view taken along lines 55 of FIG- URE l, and

FIGURE 6 is a diagram illustrating in greater detail a coherent light generator shown in FIGURE 1.

Referring now to the drawings, a electron discharge device 10 of the type previously referred to is illustrated in FIGURE 1. The discharge device includes both an envelope member 12 forming a writing chamber and an electron gun member 14 for generating an electron beam. It is desirable to assemble the gun member 14 and to test various electrical characteristics of the member. prior to mounting and hermetically sealing it to the envelope member.

The gun member 14 is shown in greater detail in FIG- URE 2 and 3. The member includes a body element 16, a base element 18, a spacer element 20, and a proc-

Segments

24 and 26 of

gun electrodes

28 and 30 are sandwiched between the

housing elements

18 and 16 and between 16 and respectively. They are secured in position by a brazing filler material 19 which forms a hermetic seal at these joints when the gun member assembly is heated to a brazing temperature. End element 22 is secured to spacer element 20 by brazing filler material 19 which forms a hermetic seal at this joint. A more detailed description of the capsule is given in the above referred to copending patent application.

The described assembly is jig mounted, positioned within a metallic container in a vacuum chamber, and heated to the proper brazing temperature. lthough various types of vacuum chambers are known, an illustrative example is a pressure sealed bell-jar having a vacuum pump coupled thereto. Evacuation of the chamber progresses until a suitably low pressure is attained. A typical chamber pressure is 10- Torr. Heating means comprising an RF induction heating apparatus is provided. The induction apparatus may comprise an electrically exicted inductive coil which is physically located within the vacuum chamber or it may be arranged external to the vacuum chamber in a manner for providing that its generated field encompasses the container within which the gun assembly is positioned. The gun assembly which is heated primarily by thermal radiation from the container is raised to a temperature for causing both brazing of the capsule and outgassing of the various components of the capsule. In one form of gun member as is described in the above referred to copending application, a temperature suitably high for providing brazing and outgassing is 1100 C. The electron gun member at this stage of fabrication comprises an evacuated and hermetically sealed capsule adapted for testing of certain electrical characteristics as is discussed more fully in the referred to copending application.

Subsequent to testing, the sealed gun member 14 is mounted and hermetically sealed to the envelope member 12. A gun member support element 32 is hermetically sealed to the gun member as shown in FIGURE 3. The gun member is then mounted and hermetically sealed to the envelope by a conventional glass sealing technique such as flowing a head of glass 36 from a neck portion 38 of the envelope about the edge of support element 32. This mounting arrangement is best shown in FIG- URES 3 and 4.

A vacuum pump 39 is coupled to the envelope 12 through a tip-ofi tube 40. The pump 39 evacuates the envelope 12 until a desired pressure is attained within the envelope. Various elements within the envelope such as metallic support elements, not shown, for a disk 59 are heated by an RF induction heating apparatus 44. Apparatus 44 is of the type for generating an RF field and for directing and concentrating the field on various elements within the glass envelope l2. Outgassed products of the heated elements increase the pressure within the envelope 12. The envelope is continuously pumped until these products are substantially removed, and a desired pressure is attained. Tip-oil is then effected whereby the pump 39 is detached and the device 10 is hermetically sealed.

In order to provide an unrestricted passage for an electron beam from the gun member 14 to the Writing chamber of envelope 12, an aperture is now formed in a surface of end processing element 22. A coherent light beam generator 46 is provided which generates a coherent light beam 47. The beam 47 is projected through a double concave lens 48; through a transparent output window 49 of the device 19; through a transparent transport disk 50 at a point 51 which is bare of a conductive substrate 52; and through an aperture 53 in a light shield 54; and onto the surface of element 22. The lens 48 focuses the beam onto the surface 22 and the concentrated energy of the impinging light beam causes the temperature of the surface of element 22 to rise. Beam impingement continues for a period of time required to form an aperture in the end processing element 22.

In FIGURE 6, the generator 46 is shown in greater detail. The coherent light source may comprise a laser having a synthetic ruby crystal rod 60 which is doped with chromium. A helical shaped Xenon filled flash coil 61 is positioned about the rod 60. One end of the rod has a deposited silver surface 62 for providing substantially 100% reflection While an opposite end 63 is coated to provide substantially reflection. A trigger pulse voltage 6 is derived from a source 65 and stepped up in level to-approximately 50 kv. by a transformer 66. A secondary winding of the transformer is coupled to a trigger rod 67 which initiates discharge of the gas within coil 61. The greater portion of electrical energy necessary for sustaining the discharge for a desired interval is derived from a capacitor 68 which has been charged from a D.C. power supply 69 through a current limiting resistor 70. The operation of this type of coherent light beam generator is known. A more detailed description is given in Radio-Electronics, pages 28-32, January 1963.

Thus, a method for fabricating an electron discharge device is described which simplifies the fabrication of a discharge device and eliminates the need for re-outgassing and re-evacuating a gun member and consequently reduces the time and cost required for its construction.

While I have illustrated and described and have pointed out certain novel features of my invention, it will be understood that various omissions, substitutions, and changes in the forms and details of the system illustrated may be made by those skilled in the art without departing from the spirit of the invention and the scope of the claims.

What I claim is:

1. A method of fabricating an electron discharge device for a light valve apparatus including a forming operation which is accomplished by the application of thermal energy to a body comprising: the steps of mounting and hermetically sealing an electron gun member having a processing end element to an envelope for the device, said envelope having a transparent segment; pumping said device to provide a difference in pressure between the interior and exterior of the envelope; and projecting a focused coherent light beam upon said end element for a period of time for causing an aperture to be formed therein. 7

2. A method of fabricating an electron discharge device of the type including an envelope member having a transparent segment thereof and an electron gun member 5 6 assembly having an end processing element comprising: time for causing the end processing element to heat to a the steps of heating the gun member assembly in a temperature for forming an aperture therein.

vacuum chamber to a temperature for causing outgassing and brazing of the gun member components; mounting References Cited by the Exammer the gun member assembly to the envelope and providing 5 UNITED STATES PATENTS a hermetic seal therebetween; heating and vacuum pump- 2,474,335 6/1949 Skellett 316 25 X ing the envelope member to a temperature for outgassing 3,096,767 7/ 1963 Gresser et a1.

components of the envelope member and to a desired 3,210,171 10/ 1965 MacDonald.

vacuum respectively; and projecting a focused coherent light beam through a transparent segment of said enve- 10 RICHARD EANES P'lmary Exammerlope and onto the end processing element for a period of FRANK E. BAILEY, Examiner.

Claims

1. A METHOD OF FABRICATING AN ELECTRON DISCHARGE DEVICE FOR A LIGHT VALVE APPARATUS INCLUDING A FORMING OPERATION WHICH IS ACCOMPLISHED BY THE APPLICATION OF THERMAL ENERGY TO A BODY COMPRISING: THE STEPS OF MOUNTING AND HERMETICALLY SEALING AN ELECTRON GUN MEMBER HAVING A PROCESSING AND ELEMENT TO AN ENVELOPE FOR THE DEVICE, SAID ENVELOPE HAVING A TRANSPARENT SEGMENT; PUMPING SAID DEVICE TO PROVIDE A DIFFERENCE IN PRESSURE BETWEEN THE INTERIOR AND EXTERIOR OF THE ENVELOPE; AND PROJECTING A FOCUSED COHERENT LIGHT BEAM UPON SAID END ELEMENT FOR