US3107844A

US3107844A - Single cell vacuum apparatus

Info

Publication number: US3107844A
Application number: US852484A
Authority: US
Inventors: Lewis D Hall
Original assignee: Ultek Corp
Current assignee: Ultek Corp
Priority date: 1959-11-12
Filing date: 1959-11-12
Publication date: 1963-10-22
Anticipated expiration: 1980-10-22
Also published as: GB903531A; FR1273226A

Description

Qct. 22, 1963 L, D. HALL 3,107,844 v SINGLE CELL VACUUM APPARATUS Filed Nov. 12, 1959 2 Sheets-Sheet J1 INVENTOR LEWIS D. HALL ATTORNEYS Oct. 22, 1963- L. D. HALL 3,107,844 SINGLE CELL VACUUM APPARATUS Filed Nov. 12 1959 2 Sheets-Sheet 2 INVENTOR. LEWIS D. HALL \j/ ws/g wculru ATTOR N EYS 3',i7,844 Patented Oct. 22, 1963 3,107,844 SINGLE CELL VACUUM APPARATUS Lewis B. Hali, Falo Alto, Calif., assignor to Ultel: C orporation, Palo Alto, Calif., a corporation of California Fiied Nov. 12, 1959, Ser. No. 852,484 8 Claims. ((11. 239-69) This invention relates generally to vacuum pumps and more particularly to vacuum pumps of the electronic type.

Electronic pumps employing cold-cathode discharge in a magnetic field are well known in the art. In such pumps, an electric field is provided between the cathode and anode, and a magnetic field is supplied substantially perpendicular to the cathode surface. Electrons travelling from the cathode to the anode are deflected by the magnetic field and traverse relatively long paths before they strike the anode. These electrons collide with gas molecules and form ions, atoms (dissociated molecules), and metastable molecules. The latter two species are captured chiefly upon the reactive surface of the anode. The reactive surface of the anode is continually replenished from the cathode by sputtering. The term sputtering denotes removal of material from a surface at cathode potential by positive ion bombardment. It is analagous to thermal evaporation or sublimation.

Electronic vacuum pumps of the prior art, although they produce a relatively high vacuum, have restricted pumping speeds. Also, they have been relatively complicated to manufacture; thus, relatively expensive. In order to provide pumps aving relatively high pumping speeds, it has been common to manufacture the pumps with a multiplicity of small individual units which are joined together to form an assembly. Manufacture of the small units and the subsequent assembly are by their very nature cumbersome and expensive. Additionally, the practical vacuum pumps of the prior art have been limited to those in which the positive ions which cause sputtering travel parallel to the magnetic field. Consequently, the maximum useful active cathode surface area has been limited to that which is perpendicullar to the magnetic field.

It is a general object of this invention to provide an improvement in electronic vacuum pumps.

It is another object of this invention to provide an electronic vacuum pump assembly which is compact and light in construction and at the same time capable of providing a high pumping rate.

It is another object of this invention to provide a vacuum pump with the aforementioned characteristics wherein construction costs and time are at a minimum.

It is still a further object of this invention to provide an electronic vacuum pump which is simple to construct and in which the possibility of shorts between anode and cathode are minimized.

It is still another object of this invention to provide an electronic vacuum pump wherein the useful cathode active surface is not limited to that perpendicular to the magnetic field.

It is still a further object of the present invention to provide an improved anode for electronic vacuum pumps.

These and other objects of the invention will become more clearly apparent from the following description when taken in conjunction with the accompanying drawmg.

Referring to the drawing:

FIGURE 1 is a perspective view of a vacuum pump in accordance with the invention with the magnetic unit and envelope partially broken away;

FIGURE 2 is a plan view of an anode in accordance with this invention;

FIGURE 3 is a sectional view taken along the line 33 of FIGURE 2;

FIGURE 4 is a perspective view of another anode and cathode unit in accordance with this invention; and

FIGURE 5 is a perspective view, partially broken away, of another embodiment of the invention.

FIGURE 1 shows a perspective view of a completed vacuum pump in accordance with the invention. One or more anode assemblies 11 (two such anodes shown in FIGURE 1) are each sandwiched between cathode plates 13. When more than one anode 11 is used, they are joined by braces 15 which may be disposed on opposite sides of the structure. The cathodes 13 are fastened to the bars or rods 17 to form a rigid cathode structure which is afiixed by the braces 15 to the anode plates through the insulated connectors 19. In practice, it is often advisable to increase the size of the pump by adding additional anodes and cathodes in both the vertical and horizontal directions.

The anode assembly as shown in FIGURES 2 and 3 includes upper and

lower plates

23 and 25 which define an ionization space therebetween. The upper and

lower plates

23 and 25 each include a plurality of openings 27. The openings in the upper plate 23 may be arranged in registry with those of the lower plate 25. Side walls 21 may be provided to completely enclose the ionization space. The anode, then, is in the form of a box. In construction, several such anode cells as those shown in FIGURES 2 and 3 can readily be stacked and rigidly secured. By rig-idly securing the cathodes at the upper and lower ends of each anode in a spaced and insulated relation therefrom, the pump unit is completed. A single cathode sufiices between anodes with each surface providing electrons 'to the facing anode assembly.

In order to increase gas conductance, it may be advantageous to perforate the side walls as well as the upper and lower plates of the anode. Such perforations, while they may increase the gas conductance, will not unduly impair the magnetic focusing of the electron beams within the anode. Nor will'the perforation impair the substantially relative absence of electric field within the interior of the anode.

The anode can be of any non-magnetic material such as titanium, stainless steel, or zirconium which are well known in electroic vacuum pump use. The cathode 13, while being shown as a continuous sheet, can be formed of strips. metal or alloy such 'as titanium, the like.

In construction of a complete vacuum pump, one or more units of the type described are enclosed Within a vacuum tight chamber or envelope 28. The envelope 28 may include an opening and a coupling 30 for connection to apparatus to be evacuated. The anodes and cathodes are connected to a source of potential to set up an electric field between the elements. A magnetic field is set up which is perpendicular to the cathode surfaces; the

pole pieces

32 and 34 may be provided to set up the desired magnetic field. As the electrons are drawn from the cathode to the anodes and by inertia into the substantially electric field free region within the anodes, the magnetic field causes them to travel in a spiral path. The spiral path substantially increases the length of travel from cathode to anode. While traversing the path from the cathode to the anode, the electrons activate numerous gas molecules. Positive ions are drawn to the cathodes and sputter the reactive material of which the cathode is composed. Neutral active molecules are deposited on the anode and are captured by the sputtered material. By entrapment of gas molecules and ions, the pressure within the chamber is substantially reduced.

The embodiment shown in FIGURE 4 includes an anode having upper and

lower plates

23 and 25 similar to those shown in FIGURES 1-3. The side walls 29 of zirconium, yttrium, or

The cathode material should be a reactive the anode include openings 31. The openings 31 can be incorporated in all the side walls rather than just one or two as shown in FIGURE 4. Opposite each side wall 29 having openings 31 there is disposed an additional cathode structure 33'.

In operation, which is somewhat similar to that of the device shown in FIGURES 1-3, the electrons trace a spiral path from the cathode 13 to anode. The spiralling electrons collide with molecules to form ions. The ions being much heavier than the electrons are little influenced by the magnetic field and, consequently, follow the electrostatic field. The ions can, therefore, be passed through the holes in the side 29 of the anode as well as those in the upper and

lower plates

23 and 25. Thus, use is made, not only of the cathode surface perpendicular to the magnetic field but also of the cathode surface parallel thereto. It is apparent that with the additional cathode area a higher rate of pumping action is attained for substantially the same overall volume. As in the embodiment of FIGURE 1, it may be advantageous to perforate the side walls and the upper and lower plates of the anode to increase gas conductance.

Referring to FIGURE 5, still another embodiment of the invention is shown. Except for the anode assemblies 11a, this embodiment is similar to that of FIGURE 1. The anode assemblies 11a not only have upper and

lower plates

23 and 25 but also have one or more intermediate plates 35. The intermediate plates 35 like the upper and lower plates'23 and 25 have openings 27a which may be arranged in registry with the openings 2-7 in the upper and lower plates.

The addition of the intermediate plates 35 decreases the electric field within the anode assembly 11a even more than in the assembly 11. The region within the anode assembly 11a, being more field free than that of the anode assembly 11, allows the magnetic field to exert even more control than with the embodiment of FIG- URE 1.

I claim:

1. In an electronic vacuum pump of the type having a cold cathode discharge and means for providing a magnetic field, a pump unit comprising an anode and a oath ode, said cathode being formed of material conductive to sputtering, said anode including a plurality of spaced parallel plates disposed substantially normal to said field and defining an ionization space, said plates having spaced holes therethrough, said cathode being entirely outside of the ionization space and adjacent one of said spaced parallel plates whereby the anode ionization space is essentially free of electric field.

2. In an electronic vacuum pump of the type having a cold cathode discharge and means for providing a magnetic field, a pump unit comprising an anode and a cathode, said cathode being formed of material conductive to sputtering, said anode including a plurality of spaced parallel plates disposed substantially normal to said field and defining an ionization space, said plates having spaced holes therethrough, said cathode being entirely outside the ionization space and substantially parallel to the anode plates whereby the anode ionization space is essentially free of electric field.

3. In an electronic vacuum pump of the type having a cold cathode discharge and means for providing a magnetic field, a pump unit comprising an anode and a cathode, said cathode being formed of material conducive to sputtering, said anode including a plurality of spaced parallel plates disposed substantially normal to said field and defining an ionization space, said plates having spaced holes therethrough, said plates being disposed to arrange their respective holes in registry, said cathode being entirely outside the ionization space and substantially parallel to the anode plates whereby the anode ionization space is essentially free of electric field.

4. An electronic vacuum pump having a cold cathode discharge including a pump unit comprising an anode and a cathode, said cathode being formed of material conducive to sputtering, said anode including a plurality of spaced parallel plates defining an ionization space, each of said plates having :a series of holes extending therethrough, said cathode being substantially parallel with said anode plates and entirely external of the ionization space whereby the anode ionization space is essentially free of electric field, an envelope about said unit, and magnetic means in close proximity to said unit and providing a magnetic field substantially perpendicular to the anode plates.

5. In an electronic vacuum pump structure of the type having a cold cathode discharge and means for providing a magnetic field, an anode and a cathode, said anode comprising a plurality of spaced parallel plates defining an ionization space, the planes of said plates being disposed across said field, each of said plates having a series of openings extending therethrough, said cathode being entirely outside of said ionization space.

6. In an electronic vacuum pump of the type having a cold cathode discharge and means for providing a magnetic field, a pump unit comprising anode including a plurality of spaced parallel anode plates having a series of openings extending therethrough, said plates being disposed substantially normal to said field, a plurality of sides cooperating with said spaced anode plates and serving to define an ionization space, said sides having a series of openings extending therethrough, and a cathode disposed adjacent each of said anode plates and sides entirely external of the ionization space whereby the anode ionization space is essentially free of electric field, said cathode being formed of material conducive to sputtermg. 7. In an electronic vacuum pump of the type including means for providing a magnetic field, a pump assembly comprising a plurality of pump units each including an anode and a cathode, said cathode being formed of material conducive to sputtering, said anode including a plurality of spaced parallel plates disposed substantially normal to said field and defining an ionization space, said plates having spaced holes therethrough, said cathode being entirely outside of said ionization space, whereby the anode ionization space is essentially free of electric field, and each of said units having their anodes and their cathodes joined together to form an integral structure.

8. A pump assembly as defined in claim 7 together with an envelope about said plurality of units and mag- I 1,207,893 France Sept. 7, 1959

Claims

1. IN AN ELECTRONIC VACUUM PUMP OF THE TYPE HAVING A COLD CATHODE DISCHARGE AND MEANS FOR PROVIDING A MAGNETIC FIELD, A PUMP UNIT COMPRISING AN ANODE AND A CATHODE, SAID CATHODE BEING FORMED OF MATERIAL CONDUCTIVE TO SPUTTERING, SAID ANODE INCLUDING A PLURALITY OF SPACED PARALLEL PLATES DISPOSED SUBSTANTIALLY NORMAL TO SAID FIELD AND DEFINING AN IONIZATION SPACE, SAID PLATES HAVING SPACED HOLES THERETHROUGH, SAID CATHODE BEING ENTIRELY OUTSIDE OF THE IONIZATION SPACE AND ADJACENT ONE OF SAID SPACED PARALLEL PLATES WHEREBY THE ANODE IONIZATION SPACE IS ESSENTIALLY FREE OF ELECTRIC FIELD.