TARGET FOR BARIUM-SCANDATE DISPENSER CATHODE

Abstract

The invention relates to the field of production of barium-scandate dispenser cathodes or other barium-scandate materials. A target (66) containing a mixture of BaO, CaO, Al.sub.2O.sub.3 and Sc.sub.2O.sub.3 tends to be more stable, the higher the scandia (scandium oxide) content is. However, an increased scandia content results in a reduced emission capability. A destabilizing effect of BaO and CaO reactions is counteracted by the more inert Sc.sub.2O.sub.3 and also Al.sub.2O.sub.3 components, as not only an increased scandia content stabilizes the material but also an increased alumina (aluminum oxide) content improves the stability.

Claims

1. A deposition apparatus comprising a target material, the target material comprising: a mixture of barium oxide BaO, calcium oxide CaO, aluminum oxide Al.sub.2O.sub.3 and scandium oxide Sc.sub.2O.sub.3, wherein the molar ratio of BaO:CaO:Al.sub.2O.sub.3:Sc.sub.2O.sub.3 is b:c:x:y with 2b5, 1c3, 2x+yb+c and 0.1y1; and Ba.sub.2ScAlO.sub.5, wherein the target material is configured for physical thin film deposition in a production of barium-scandate dispenser cathodes or other barium-scandate materials.

2. The deposition apparatus according to claim 1, wherein the target material further comprises one or more oxide selected from the group consisting of strontium oxide SrO, lanthanum oxide La.sub.2O.sub.3, yttrium oxide Y.sub.2O.sub.3 and europium oxide Eu.sub.2O.sub.3 in addition to the barium oxide, and/or one or more oxides of one or more rare earth elements or a mixture of oxides of rare earth elements with scandium as main rare earth element in addition to the scandium oxide.

3. The deposition apparatus according to claim 1, wherein 0.1<y<0.5.

4. The deposition apparatus according to claim 1, wherein b:c is one of 4:1, 3:1, or 5:3.

5. The deposition apparatus according to claim 1, further comprising one or more oxides of two or more elements selected from the group consisting of barium, calcium, aluminum and scandium.

6. A deposition apparatus comprising a target, the target comprising: a mixture of barium oxide BaO, calcium oxide CaO, aluminum oxide Al.sub.2O.sub.3 and scandium oxide Sc.sub.2O.sub.3, wherein the molar ratio of BaO:CaO:Al.sub.2O.sub.3:Sc.sub.2O.sub.3 is b:c:x:y with 2b5, 1c3, 2x+yb+c and 0.1y1; and Ba.sub.2ScAlO.sub.5, wherein the target is configured for physical thin film deposition.

7. A use of a target material of a deposition apparatus: wherein the target material comprises or consists of a mixture of barium oxide BaO, calcium oxide CaO, aluminum oxide Al.sub.2O.sub.3 and scandium oxide Sc.sub.2O.sub.3, wherein the molar ratio of BaO:CaO:Al.sub.2O.sub.3:Sc.sub.2O.sub.3 is b:c:x:y with 2b5, 1c3, 2x+yb+c and 0.1y1; and wherein the use of the target material is in a production of a barium-scandate dispenser cathode or other barium-scandate materials.

8. The use of the target material according to claim 7, wherein the target material is used in a physical thin film deposition step for generating an intermediate layer consisting of or comprising BaO, CaO, Al.sub.2O.sub.3, and Sc.sub.2O.sub.3 in the dispenser cathode.

9. A method of producing a barium scandate dispenser cathode, comprising: providing a porous metal body having a surface and being impregnated with one or more compounds for dispensing at least barium and scandium to the surface, providing an intermediate layer consisting of or comprising BaO, CaO, Al.sub.2O.sub.3, and Sc.sub.2O.sub.3 by means of physical thin film deposition on the porous metal body, and providing an outer metal layer, wherein for the physical thin film deposition of the intermediate layer a target material is used comprising or consisting of a mixture of barium oxide BaO, calcium oxide CaO, aluminum oxide Al.sub.2O.sub.3 and scandium oxide Sc.sub.2O.sub.3; and wherein the molar ratio of BaO:CaO:Al.sub.2O.sub.3:Sc.sub.2O.sub.3 is b:c:x:y with 2b5, 1c3, 2x+yb+c and 0.1y1.

10. The method according to claim 9, wherein the physical thin film deposition includes laser ablation deposition and/or sputtering.

11. A device including a barium scandate dispenser cathode produced by a method according to claim 10.

12. A method for producing a target of a deposition apparatus, the method comprising: providing a mixture of barium oxide BaO, calcium oxide CaO, aluminum oxide Al.sub.2O.sub.3 and scandium oxide Sc.sub.2O.sub.3, sintering or melting the mixture to form the target, wherein the molar ratio of BaO:CaO:Al.sub.2O.sub.3:Sc.sub.2O.sub.3 in the target is b:c:x:y with 2b5, 1c3, 2x+yb+c and 0.1y1; and wherein the method is for producing the target for physical thin film deposition for production of barium-scandate dispenser cathodes or other barium-scandate materials.

13. A deposition apparatus comprising a target material, the target material comprising: a mixture of barium oxide BaO, calcium oxide CaO, aluminum oxide Al.sub.2O.sub.3 and scandium oxide Sc.sub.2O.sub.3, wherein the molar ratio of BaO:CaO:Al.sub.2O.sub.3:Sc.sub.2O.sub.3 is b:c:x:y with 2b5, 1c3, 2x+yb+c and 0.1y1; Ba.sub.2ScAlO.sub.5; and yttrium oxide Y.sub.2O.sub.3 or europium oxide Eu.sub.2O.sub.3, wherein the target material is configured for physical thin film deposition in a production of barium-scandate dispenser cathodes or other barium-scandate materials.

Description

[0046] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0047] FIG. 1 shows alternative embodiments of a method for producing a target according to the present invention,

[0048] FIG. 2 shows an illustration of a LAD arrangement using a target according to the present invention, and

[0049] FIG. 3 shows an embodiment of a method producing a barium scandate dispenser cathode according to the present invention.

[0050] FIG. 1 shows alternative embodiments of a method for producing a target according to the present invention. Starting with a solution with appropriate amounts of constituents dissolved to obtain 411 material (BaO, CaO, Al.sub.2O.sub.3 in the molar ratio of 4:1:1), the precipitate is formed (step 12) and the oxides are generated in a suitable furnace at 1400 C. under an atmosphere of O.sub.2 or H.sub.2 (steps 14 or 14). Sc.sub.2O.sub.3 and Al.sub.2O.sub.3 are added and mixed to the resulting powder (step 16). Alternatively, the Al.sub.2O.sub.3 and Sc.sub.2O.sub.3 may also be added to the suspension.

[0051] Alternatively to or supplementing the above, it is also possible to do the decomposition of the precipitate (hydroxide/carbonates) at 1400 C. in vacuum or under an inert atmosphere, for example argon, helium, or N.sub.2.

[0052] In the case of sintering, the mixed powder (i.e. the target material) is then pressed with high pressure into a cylindrical form (step 18) and sintered (step 20) at a temperature in the range from 1650 C. to 1700 C.

[0053] Alternatively, the target material is molten (step 22), which, however, necessitates a higher temperature beyond 1700 C.

[0054] The sintering or melting of the 411y in Mo-crucibles around 1650 C. up to or beyond 1700 C. should be carried out under an atmosphere containing no (or at least substantially no) H.sub.2O or O.sub.2. In order to avoid gas inclusions (holes inside the target formed) H.sub.2 is preferred (also due to the reducing functionality to keep the crucible intact). Helium is a good option, as atoms/molecules like H.sub.2 and He are small enough to escape.

[0055] Even though argon, N.sub.2 or mixed gasses like N.sub.2/H.sub.2 or Ar/H.sub.2 are possible to be used, the above mentioned options are preferred, as these latter gasses and mixtures are difficult to remove out of a sintered target or may result in (oxy)nitride compounds being formed. In view of the volatility of BaO, H.sub.2 and He are also preferred over vacuum.

[0056] Depending on the composition of the target material, mixed phases of the components may be obtained, for example, Ba.sub.2ScAlO.sub.5, which further improve the resistance against and the stability under air including moisture.

[0057] Unless the target is already provided with a bore during the above steps, the resulting target is provided (step 24) with such bore for mounting the target on a common axis with other target for use in the production of the dispenser cathode by means of LAD.

[0058] Depending on the circumstances, further mechanical handling of the targets may be necessary (for example, shortening/cutting the cylinder) (step 26).

[0059] In order not to compromise the mechanical stability, the mechanical handling should not include the use of water or moisture. Preferably, the handling should be provided either in a dry manner or using liquids other than water and not reacting with the components of the target. Suitable liquids are isopropanol or decan. Upon drilling, furthermore, a cooling may be provided by a stream of an inert gas.

[0060] After the handling, a step 28 of further baking (under O.sub.2 or dry air) at approx. 1400 C. is provided in this embodiment for reverting any chemical changes at the surface.

[0061] In case of other deposition methods, e.g. sputtering, a bore is not necessary, wherein the intended deposition method influences generally the geometry of the target.

[0062] In one example, 411-carbonate powder was mixed with 0.65 Al.sub.2O.sub.3 and 0.35 Sc.sub.2O.sub.3 (mol ratio) and then transformed to oxides at 1400 C. The resulting powder was pressed into a cylindrical form (including a central pin) and sintered under H.sub.2 at 1600 C. After cooling, the target cylinder was cut to length and heated again to 1000 C. to 1400 C. under 02 or dry air. The target thus obtained was stable and did not exhibit any weight gain under air.

[0063] FIG. 2 shows an illustration of a LAD arrangement 50 using a target according to the present invention.

[0064] In principle, the skilled person is familiar with the process of Laser Ablation Deposition (LAD) and therefore a detailed explanation of the process and the arrangement may be omitted.

[0065] The LAD arrangement 50 of FIG. 2 includes a KrF excimer laser 52 (=248 nm) of about 60 W average power and maximum pulse energy of 6 Joule, which is well suited for LAD of refractory metals such as W or Re due to electronic instead of thermal excitation. The beam of the excimer laser 52 is guided into a stainless steel ablation chamber 54 (with UHV) through a UV quartz window 56, so that it hits a rotating cylindrical multi-target 58. A plasma plume 60 with ablated ultrafine particles forms above the target and the ultra fine particles are carried by the carrier gas (illustrated by arrow 62) to the substrates 64. A further view of the cylindrical multi-target 58 including target material 66 according to the present invention (41xy), Sc.sub.2O.sub.3-material 68 and Rhenium-material 70 is inserted into FIG. 2.

[0066] FIG. 3 shows an embodiment of a method producing a barium scandate dispenser cathode according to the present invention

[0067] In step 102, a porous metal body being impregnated with one or more compounds for dispensing at least barium and scandium to the surface is provided. In step 104, an intermediate layer consisting of or comprising BaO, CaO, Al.sub.2O.sub.3, and Sc.sub.2O.sub.3 is provided by means of LAD as an example of physical thin film deposition on the porous metal body. Furthermore, in step 106, an outer metal layer is provided. Finally, in step 108, the dispenser cathode is completed. The details of these steps correspond to those of conventional steps for producing a dispenser cathode, except for the used target (material) according to the present invention.

[0068] Preferably, the surface of the target should be smooth andin the case of LADshould be ablated in a constant distance to the laser optics and under constant conditions. This includes a uniform ablation of the target surface by means of a suitably directed scan and the removal of surface areas or portions showing chemical changes.

[0069] For the purpose of LAD, a flat geometry of the target (target in a rectangular cup) is not very suitable, as the target has to be combined with othertypically cylindricaltargets, e.g. for Re and Sc.sub.2O.sub.3, wherein furthermore cylindrical targets at rotation offer a significantly larger surface to the ablation with the same amount of material. A reduced ablation depth is preferable in term of a reduced roughness of the surface and an increased usability of the target.

[0070] Above, the explanation is primarily focused on a 41xy target material, even though the present invention is not limited thereto. Other compositions are also encompassed by the present invention. e.g. as indicated by 53xy or 31xy. In general, a suitable material may be indicated by bcxy (b: BaO, c: CaO, x: Al.sub.2O.sub.3 and y: Sc.sub.2O.sub.3), with b:c:x:y with 2b5, 1c3, 2x+yb+c and 0.1y1, preferably 0.1<y<0.5, particularly preferred 0.1<y<0.4.

[0071] The described target materials are not limited to LAD applications for top-layer barium scandate dispenser cathodes but may also be used as target materials (or having analogue composition) for production of, for example, phosphors, high temperature superconductors or ceramic layers, including Ba and/or Ca and/or Sr, mixed with an inert oxide, e.g. one or more oxides of the Sc-group or of rare earths or magnesium oxide.

[0072] The present description focusses on physical thin film deposition. Other methods of deposition, e.g. using dissolved metal salts (spinning/dipping/spraying/chemical batch deposition) or organometal compounds (e.g. CVD) including a heating step under an oxygen atmosphere and/or an atmosphere containing H.sub.2O for decomposing compounds into oxides, seem currently not suitable for producing barium-scandate dispenser cathodes, as the porous metal body (made of tungsten or molybdenum) will undergo oxidation. If, however, a further method becomes available which is similar in its use to current methods of physical thin film deposition, the present invention is to be understood as being applicable also thereto.

[0073] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.