US3369734A - High voltage stand-off insulator assembly in a sputter-ion vacuum pump - Google Patents

Description

w. R. WHEELER Feb. 20, 1968 HIGH VOLTAGE summon INSULATOR ASSEMBLY I SPUTTER-ION VACUUM PUMP Filed Nov. 16, 1966 INVENTOR, E WILLIMLBIjEELER 6; h ORNEY United States Patent Ofiice 3,369,734 Patented Feb. 20, 1968 HIGH VOLTAGE STAND-OFF INSULATOR ASSEMBLY IN A SPUTTER-ION VACUUM PUMP I William R. Wheeler, Saratoga, Calif., assignor to Varian Associates, Palo Alto, Calif. Filed Nov. 16, 1966, Ser. No. 594,739 8 Claims. (Cl. 23069) ABSTRACT OF THE DISCLOSURE An insulator assembly for use in a sputter-ion vacuum pump. The ceramic insulator element has a re-entrant portion which is shielded from sputtered getter material by an open metal cup which is fastened to the anode and by a box-shaped bracket which is connected to the cathodes. By eliminaiing the formation of getter-metal deposits on the re-entrant portion of the insulator, eectrical breakdown across the surface of the insulator is prevented.

The present invention relates to high voltage insulators. More particularly, it relates to a high voltage standoff insulator assembly which impedes surface electrical leakage and surface voltage breakdown caused by sputtered material deposited on insulator members supporting high potential difference elements insulatingy spaced apart.

A common problem found in mounting high potential difference elements insulatingly spaced apart is the tendency for voltage breakdown to take place along the surface of the insulator members. Voltage breakdown along the surface of insulators occurs as a result of sputtered material being deposited from the high potential difference elements onto the surface of the insulators. As material is repeatedly sputtered from the high potential difference elements and deposited along the surface of the insulator, eventually, a short circuit path is formed between the elements along the insulator surface by the deposited. sputtered material. This short circuit path establishes a surface current leakage which eventually causes a breakdown in the potential difference between the high potential difference eemeiits. Hence, electrical leakage along the deposited layers is undesirable.

During a gaseous discharge between high potential difference element's, material is sputtered from the negative element. It has been the practice to employ two metal cups to shield the surface of a columnar insulator from the sputtered material. Normally, such cups are fastened at opposite ends of the insulator with their receptacles facing each other to have their lips spaced apart and overlapping each other. When such high voltage stand-off insulators are used in ion getter pumps, it has been found that the pressure in the pump will be correct at sometime during normal pumping operations to allow a discharge between the two shield cups. This discharge takes place in regions unshielded from the columnar insulator. Hence, the sputtered material liberated by the discharge can coat the surface of the insulator to cause surface leakage and voltage breakdown.

Accordingly, it is the object of the present invention to provide a high voltage stand-off insulator assembly which is free of surface leakage and surface voltage breakdown effects caused by material sputtered from high potential difference elements.

'One feature of the present invention is the provision of a stand-off insulator assembly including an insulator member whosesurface defines a perimetrical re-entrant portion which is effectively shielded to prevent sputtered getter material from depositing therein.

Another feature of the present invention is the provision of a stand-off insulator assembly of the above featured type wherein a cup-shaped member defining a receptacle is mounted to receive in its receptacle the portion of the insulator defining the re-entrant so that the opening of the re-entrant faces the receptacle to thereby shield the entire surface of the insulator defining the re-entrant from the region in which sputtering occurs.

Still another feature of the present invention is the provision of a stand-off insulator assembly of the above featured types wherein the cup-shaped member is made of conductive material and is secured to one element of the high potential difference elements to extend through an opening defined by a conductive member secured to the other high potential difference element, with the cup-shaped receptacle facing away from the opening whereby arcing can occur between the outside surface portion of the cup-shaped member and the portion of the conductive member defining the opening.

Yet another object of the present invention is the provision of a stand-off insulator assembly of the above featured types wherein the terminal edge of the conductive cup-shaped member is rolled outwardly of the receptacle to thereby enhance the possibility of discharge occurring along the surface of the cup-shaped member external of the receptacle.

Another feature of the present invention is the provision of a stand-off insulator assembly of the above featured types for use in an ion getter vacuum pump to secure the pump elements thereof in insulatingly spaced apart relation.

These and other objects and features of the present invention will become more apparent upon consideration of the following specification and claims in conjunction with the accompanying drawing in which:

FIG. 1 is an exploded view of one embodiment of the high voltage stand-off insulator of the present invention.

FIG. 2 is an illustration of an ion getter vacuum pumpin which the high voltage stand-off insulator assembly of the present invention is particularly suited for use.

FIG. 3 is an enlarged section of the pump delineated by lines 3-3 of FIG. 2 illustrating the manner in which the high voltage stand-off insulator assembly secures the cathode and anode elements of the pump in insulatingly spaced apart relation.

FIG. 4 is an enlarged section of FIG. 3 taken at lines 4-4 detailing the construction of the high voltage stand-off insulator assembly.

With reference to FIG. 1, the high voltage stand-off insulator assembly 11 of thepresent invention comprises a columnar insulator member 12, generally cylindrical and of ceramic, provided with threaded end sections 13 and 14 for securing the insulator member to spaced apart high potential difference elements. The outer surface of the ceramic member 12 defines a circumferential re-entrant portion 16. Consequently, in order for sputtered material to collect on the ceramic insulator 12 in such a manner as to define a conductionpath between its end sections 13 and 14, sputtered materialmust enter the re-entrant portion 16. By arranging ceramic insulator member 12 so that at least a portion of its surface defining the re-entrant 16 is shielded from regions in which sputtering occurs, a conduction path will not be established between the end sections 13 and ber 17 defining a receptacle 18 (see FIG. 4) is mounted to receive therein the end 13 of the ceramic insulator 12 which the re-entrant 16 opens towards. The depth of the receptacle 18 defined by the cup-shaped member 17 is adjusted so that the cup-shaped member 17 extends past the outer lip 12 defining the re-entrant opening. With such an arrangement, the re-entrant 16 is shielded from all line of sight paths from the region in which sputtering occurs.

A gaseous discharge, Which sputters material, generally occurs between the closest points of spaced apart high potential difference elements. To insure that the discharge does not occur between points, one of which is along a line of sight path to re-entrant 16, the cup-shaped member 17 is constructed of conductive material. In use, the cup-shaped member 17 and ceramic insulator 12 at end section 13 are fastened, for example, by screws 21, to one of a pair of high potential difference elements (see FIG. 4), preferably, the positive potential elements. The opposite end section 14 of the ceramic insulator 12 is similarly fastened by screws 21 to the other of the pair of high potential difference elements. Therefore, since the cup-shaped member 17 is a conductive extension of one of the high potential difference elements, and is positioned closer to the other high potential difference element than is the element to which it is attached, the discharge that occurs will take place proximate the terminal edge 22 of the cup-shaped member 17. As can be seen with reference FIG. 4, there is no line of sight path from the region in which sputtering occurs, i.e., at terminal edge 22 of cup-shaped member 17, to the reentrant 16.

It is preferred to connect the conductive cup-shaped member 17 to the more positive of the high potential difference elements because the material is sputtered from the negative potential element. If the conductive cupshaped member 17 is attached to the more negative potential element, in some cases, material could be sputtered from the inner wall of web 23. Some of the material sputtered from the inner wall of web 23 would enter re-entrant 16 of the insulator 12. Such material would be deposited along the surface of re-entrant 16 to coat the insulator surface and establish an undesirable conduction path between the high potential difference elements.

However, when used in an ion getter vacuum pump, a considerable amount of sputtered material from the pumping elements is present and can enter and be deposited on the walls defining the receptacle 18. The more sputtered material entering the receptacle 18, the more probable that some sputtered material will eventually enter re-entrant 16.

With this in mind, a conductive member 26 is mounted to extend from the high potential difference element to be supported in spaced relation with that high potential difference element connected to cup-shaped member 17. The conductive member 26 includes an extension 27 defining an aperture 28 through which cup-shaped member 17 extends. The extension 27 prevents sputtered material originating from the side of extension 27 distal edge 22 of cup-shaped member 17 from reaching insulator 12. To shield insulator 12 from sputtered material originating from any direction, the conductive member 26 could be constructed in the form of a cup-shaped member surrounding the cup-shaped member 17.

With the terminal edge 22 rolled outwardly of the receptacle 18, it together with the apertured extension 27 surrounding cup-shaped member 17 enhance the possibility of discharge occurring. at locations along outwardly facing surface 24 of cup-shaped member 17. Furthermore, the conductive member 26 further shields insulator 12, hence reducing the sputtered material which can enter re-entrant 16 to an insignificant amount.

In one embodiment particularly suited for use in constructing unitary electrode assemblies for cellular sputter ion vacuum pumps, conductive member 26 is box-shaped whose upper extension 27 defines two spaced apart apertures 28, each aperture 28 receiving therethrough a ceramic insulator 12 and cup-shaped member 17 as described hereinabove. Each ceramic insulator 12 is fastened by screw 21 at its end section 14 to a lower extension 29 of the box shaped conductive member 26. The upper and lower extensions 27 and 29 are joined by ribs 31. At each of the four corners defined by the junctions of the ribs, and the upper and lower extensions is mounted a tap 32 for fastening a high potential difference element, e.g., a cathode of a sputter ion vacuum pump, to the high voltage stand-off insulator assembly 11.

Although the cup-shaped member 17 and apertured conductive member 26 have been described as separate elements mechanically fixed to different high potential difference elements, it should be appreciated that the cup member 17 and apertured conductive member 26 could be formed by an integral part of the high potential difference elements.

Referring now to FIGS. 2-4, a sputter ion vacuum pump 41 is shown employing the high voltage stand-off insulator assembly 11 to support the electrodes of the pump in insulatingly spaced apart relation. The insulator assembly of the present invention is particularly suited for use in an ion getter vacuum pump because of the presence of a large amount of sputtered material. In the manner described hereinabove, the cup-shaped member 17 and conductive member 26 will shield the reentrant 16 defined by the outer surface of the ceramic insulator 12 from sputtered material from the pump ele ments if the insulator 12 and cup-shaped member 17 are positioned with the receptacle 18 defined by the cupshaped member 17 facing away from the region of pump sputtering.

In the pump embodiment illustrated, a cellular anode assembly 42, held together with a conductive band 43 tightly wound around the perimeter of the cells 44 forming the assembly, is fixed between cathode electrodes 46 and 46' by two high voltage standoff insulator assemblies 11 to define a unitary pump electrode assembly. More specifically, an insulator assembly 11 having two columnar ceramic insulators 12 and conductive cup-shaped members 17 is fixed to the conductive band 43 of the cellular anode assembly 42 at opposite ends thereof. The conductive band 43 is fastened by screw 21 through cup-shaped member 17 to end section 13 of ceramic insulator 12. The opposite end section 14 of insulator 12 is fastened to the lower extension 29 of box-shaped conductive member 26 by screws 21. The cathode plate elements 46 and 46 are fastened by screws 47 to the insulator assembly 11 at tabs 32 on opposite sides of the assembly 11.

The unitary pump electrode assembly formed by cellular anode assembly 42, cathode plates 46 and 46 and two high voltage stand-off insulator assemblies 11 are positions within the pump envelop 51 between the poles of magnet 52. Generally, the cathode plates 46 and 46 are operated at ground potential with the cellular anode assembly 42 at 3-8 kv. The anode assembly 42 is energized by coupling an external power supply (not shown) thereto through a high voltage vacuum feedthrough 53 which insulatingly transpierces the pump envelope 51.

During pump operations, the feedthrough insulator 54 which shields the high voltage lead 56 from contact with the commonly grounded envelop 51, should be shielded to prevent sputtered material originating in the pump 41 from depositing on the feedthrough insulator 54. If preventive steps are not taken to prevent such sputter material deposition, current paths between the high voltage lead 56 and the grounded envelop can be established which lead to surface voltage breakdown. The ceramic insulator member 12 could'be adapted to serve as a feedthrough with the cup-shaped member 17 mounted at the vacuum end thereof to shield the re-entrant 16 from sputtered material. Of course, the high voltage lead 56, or leads,

would pass through the ceramic insulator member 12 and cup-shaped member 17.

While the present invention has been described in detail with reference to one specific embodiment, many modifications are possible within the scope of the invention, particularly with respect to the use of the high voltage stand-off insulator assembly in ion getter vacuum pumps to support the various electrodes commonly found therein, e.g., grid electrodes in triode type pumps, and fourth electrodes in tetrode type pumps. Hence, the present invention is not intended to be limited except by the terms of the following claims.

What is claimed is:

1. A high voltage stand-off insulator assembly comprising a columnar insulator member having an outer surface defining a perimetrical re-entrant portion, a cup-shaped member defining a receptacle fixedly positioned and receiving said columnar insulator in said receptacle with the re-entrant facing said receptacle, and a conductive member mounted insulatingly spaced apart from said cupshaped member, said conductive member defining an aperture through which said insulator and cup-shaped members extend.

2. The high voltage stand-01f insulator assembly according to claim 1 wherein said cup-shaped member is of conductive material and is secured to the more positive of two high potential difference structures, said conductive member is secured to the less positive of said two high potential difference structures, and said columnar insulator is secured to each of the high potential difference structures at its opposing ends.

3. The high voltage stand-off insulator assembly according to claim 2 wherein said cup-shaped member has an outwardly rolled terminal edge about the opening of the receptacle defined thereby.

4. The high voltage stand-off insulator assembly according to claim 2 wherein said columnar insulator member is cylindrical having a cylindrical re-entrant portion circumferentially about said cylindrical member, said cupshaped member is a cylinder having one open end, and said conductive member has a first extension having said aperture therein and a second extension joined by rib means to said first extension in spaced side-by-side relation to said first extension, the end of said insulator member opposite said cup-shaped member being secured to said second extension.

5. The high voltage stand-01f insulator assembly according to claim 1 wherein said conductive member has a first extension means and second extension means joined thereto by rib means in spaced side-by-side relation to define a box-shaped conductive member, said first extension means having said aperture and a second aperture therethrough, said cup-shaped and columnar insulator members extending through one of said apertures with the end of said columnar insulator member facing opposite said re-entrant portion fixed to said second extension means, and further including a second columnar insulator member having an outer surface defining a circumferential re-entrant portion fixed to said second extension means at its end facing opposite said re-entrant portion and extending through the other of said apertures, and a second cup-shaped member defining a receptacle fixedly positioned and receiving said second columnar insulator in said receptacle with the re-entrant facing said receptacle and extending through said other aperture, and mounting means to secure a first of high potential difierence electrodes to an edge of said conductive member defined by said first and second extension means and to secure a second of said high potential difference electrodes to the ends of said insulators fixed to said cup-shaped members.

6. In a sputter ion vacuum pump including an evacuable envelope for enclosing the pumping elements and a magnet means for establishing a magnetic field for elongating the path of ionizing electrons, an anode electrode, and at least a second electrode means serving with said anode to define a sputter region therebetween, and a high voltage stand-0E insulator assembly fixing said second electrode insulatingly spaced from said anode electrode including a columnar insulator member having an outer surface defining a perimetrical re-entrant portion, and cupshaped member defining a receptacle fixedly secured to an end of said insulator members and receiving said insulator member in said receptacle with the re-entrant facing said receptacle, the improvement therein being that the end of said insulator fixed to said cup-shaped member is secured to one of said electrodes to have the receptacle defined by said cup-shaped member facing away from said sputter region, the other end of said insulator being secured to the other electrode to hold said electrodes insulatingly spaced from each other.

7. The apparatus according to claim 6 further including a conductive member fixed to said electrode secured to the end of said insulator member opposite the cupshaped member, said conductive member defining at least one aperture through which said insulator and cup-shaped members extend, said cup-shaped member being insulatingly spaced from said conductive member.

8. In a sputter ion vacuum pump having an anode electrode, at least a second electrode means serving with said anode to define a sputter region therebetween, and a high voltage stand-off insulator assembly for insulating said second electrode from said anode electrode including a columnar insulator member having an outer surface defining a perimetrical re-entrant portion and a cup-shaped member defining a receptacle fixedly secured to one end of said insulator member and receiving a portion of said insulator member in said receptacle with the re-entrant facing said receptacle, said one end of said insulator being secured to one of said electrodes, the improvement therein comprising a conductive member defining at least one aperture through which said insulator and cup-shaped members extend, the other end of said insulator being fixed to said conductive member, said cup-shaped member being insulatingly spaced from said conductive member, and the other of said electrodes being fixed to said conductive member to space said other of said electrodes from said anode electrode.

References Cited UNITED STATES PATENTS 1,146,298 7/1915 Ambruster l74l38 1,481,081 1/1924 Austin l74140 2,550,367 4/195 1 Meier 174-138 X 3,115,297 12/1963 Lloyd et a1. l74l38 X 3,228,590 1/1966 Kearns et a1 230-69 LARAMIE E. ASKIN, Primary Examiner.

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