Title of Invention

A METHOD FOR THE MANUFACTURE OF A SUPPORTED THIN LAYER OF GETTER MATERIAL AND A GETTER DEVICE THERBY MANUFACTURED

Abstract

ABSTRACT (1597/M AS/97) A METHOD FOR THE MANUFACTURE OF A SUPPORTED THIN LAYER OF GETTER MATERIAL AND A GETTER DEVICE THEREBY MANUFACTURED A method is disclosed for the manufacture of a supported thin layer of getter material comprising: preparing at least one suspension of NEG material particles, with a particle size lower than about 150 [im, in a dispersing medium having an aqueous, alcoholic or hydroalcoholic base, containing a weight percentage of organic compounds, having a boiling temperature higher than 250°C, which is lower than 1%, wherein the ratio of the NEG material weight to the weight of dispersing medium is comprised between 4:1 and 1:1; depositing at least one layer of NEG material suspension onto a metal carrier by serigraphic technique; drying the thus obtained deposit by allowing the volatile components to evaporate; and sintering in a vacuum oven the dried deposit at a temperature comprised between 800 and 1000°C and characterised in that the sintering is carried out under vacuum, covering the deposit by means of a material not suffering from chemical alterations under vacuum at any process temperature. The invention also provides a getter device obtained according to such a method.

Full Text

The present invention concerns a method for the manufacture of a supported thin layer of getter material as well as a getter device thereby manufactured The non-evaporable getter materials (hereinafter NEG materials) are known and employed since at least thirty years in the industrial field for maintaining vacuum in devices requiring this for their proper operation, like e.g. lamps or evacuated insulating jackets of thermos devices. The most common NEG materials are metals such as Zr, Ti, Nb, Ta, V or alloys thereof with one or more other elements, such as the alloy having the wt% composition 84% Zr - 16% Al, manufactured and traded by the firm SAES GETTERS at Laminate, under the trade name St 101®, or the alloy having the wt% composition 70% Zr-24.6% V-5.4% Fe, manufactured and traded by SAES GETTERS under the trade name St 707. In the latest years, the planar manufacturing technologies, by which microelectronic devices on substrates generally made of silicon are produced by depositing and selectively removing layers of materials showing different electrical properties, have become even more important. The typical thickness of these planar devices is of the order of a few tenths of |jm. The importance of the planar manufacturing techniques, essentially due to the easiness by which the manufacturing operations are liable to be automatized and to the solidity of the obtained devices, is behaving like a driving force also for the "planarization" of manufacturing processes connected to the ones of microelectronic devices, like in the field of optoelectronics or of miniaturized mechanical devices. Examples of developing products running towards this direction are flat displays, either of the vacuum type or plasma displays, and the so-called "micromachines", i.e. micromechanical devices like, for instance, car accelerometers manufactured by means of the same techniques employed in the field of microelectronics. This generalized trend of industry requires, in the case of planar devices where vacuum is needed, getter devices being in their turn planar. A planar getter device is generally formed by a layer of particles of NEG material deposited onto a suitable carrier, generally a metal sheet. A getter device of this type must be characterized by a particle loss as low as possible, preferably zero, besides excellent values of gas sorption rate and gas sorption capacity. These properties are difficult to be simultaneously performed, as generally the adhesion of the particles of NEG material, to each other and to the substrate, is enhanced by sintering heat-treatments at a high temperature, which generally impair the porosity of the layer and hence at least its sorption rate. Supported planar NEG devices may be, for instance, manufactured by means of cold lamination of powders onto the supporting metal tape, as is disclosed in U.S. Patents 3,652,317^ No. 3,856,709 and No. 3,975,304. One of the problems discovered by this technique is that the thickness of the deposit is limited to the average size of the particles of the j NEG material; moreover, should the NEG material have a hardness! comparable to that of the substrate or lower, the pressure exerted by the compression rollers causes a distortion of the particles, thus decreasing area and therefore the gas sorption efficiency. Planar getter devices can be manufactured also by means of electrophoresis, as it is, for instance, disclosed by U.S. Patent No.4,628,198. The limits of this technique are that it is possible to form in an easy way layers of NEG material only up to a thickness of about 50 pm; thicker deposits require long and therefore unpractical times from an industrial point of view. Furthermore, in the electrophoretic technique the particles are deposited onto the substrate from a liquid suspension and are moved in a charged state by an applied electrical field; a few interesting NEG materials, such as the previously described St 707 alloy, are electrostatically charged only with difficulty, which makes it difficult to manufacture by this way getter devices by means of these materials. A further technique for the manufacture of planar getter devices resides in the spray of a suspension containing material particles onto a substrate, as disclosed by the published patent application WO 95/23425. Should, however, a deposit be produced by this way, a not neglectable amount of the suspension is atomized outside the substrate and gets therefore lost. The object of the present invention is therefore to supply a method for the manufacture of a supported thin film of NEG material provided with excellent gas sorption properties and powder loss properties. Such an object is achieved, according to the present invention, by a method for the manufacture of a supported thin layer of getter material, comprising: preparing at least one suspension of Non-evaporable getter (NEG) material particles, with a particle size lower than about 150 pm, in a dispersing medium having an aqueous, alcoholic or hydroalcoholic base, containing a weight percentage of organic compounds, having a boiling temperature higher than 250°C, which is lower than 1%, wherein the ratio of the NEG material weight to the weight of dispersing medium is comprised between 4:1 and 1:1; depositing at least one layer of NEG material suspension onto a metal carrier by serigraphic technique; drying the thus obtained deposit by allowmg the volatile components to evaporate; and sintering in a vacuum oven the dried deposit at a temperature comprised between 800 and lOOCC and characterised in that the sintering is carried out under vacuum, covering the deposit by means of a material that does not melt or suffer from chemical conversions or alterations under vacuum throughout the temperature range of the thermal cycle. Accordingly the invention also provides a getter device obtained by the method as described above. The invention will be better hereinafter described referring to the accompanying drawings, wherein: FIG. 1 shows on a graph the gas sorption lines of a thin layer sample of geter material according to the invention and of two comparison samples; FIG. 2 shows on a graph the gas sorption lines of a thin layer sample of getter material according to the invention and of a further comparison sample; FIG. 3 shows a drawing diagrammatically reproducing in a plan view from above the surface of a sample in which half the surface is prepared according to the method of the invention. By the method of the invention, unlike e.g. the electrophoretic method, it is possible to obtain layers from any NEG material or also combinations of such materials. Among these materials metals may be recalled such as Zr, Ti, Ta, Nb, V or alloys thereof with one or more different elements such as Fe, Al and Ni; St 101® and 707 alloys cited in the introductory portion; allovs having the rnmnnsition 7r~Vp Q^H vr-.Kii manufactured and • traded by SAES GETTERS under the trade names St 198 and St 199, respectively; or other alloys known in this field, based on zirconium or titanium. These materials are in the form of a powder, having particle size lower than about 150 pm, and preferably comprised between 5 and 70 pm. With particle sizes higher than the specified ones, it is difficult to obtain a homogeneous deposit. LV-*' The dispersing medium of the NEG particles is a solution having an aqueous, alcoholic or hydroalcoholic base, containing a wt% amount of organic compounds having a boiling temperature higher than about 250°C, which is lower than 1% and preferably lower than 0.8%. Dispersing media employed for serigraphy usually have high contents of high boiling point organic components, defined as binders. The high boiling point organic components left in the deposit after its drying could be then decomposed to form a gas such as CO, CO2 or nitrogen oxides, at a temperature of from about 200 to 400°C during the subsequent sintering phase; at this temperature, the particles of NEG material are already at least partially /^^ activated and can therefore sorb these gases, resulting in a reduction of the sorption capacity of the getter device in its applications. It has been found that thin layers of NEG material serigraphically deposited by means of a dispersing medium containing organic \ compounds, showing a boiling temperature higher then 250°C, in a percentage higher than 1%, have poor gas sorption properties. On the other hand, it is preferable that organic compounds showing a high boiling temperature be present in the dispersing medium at a concentration not less than about 0,2%. For lower concentrations of such compounds, the suspension has too a low viscosity. Under these conditions, the final form of the deposit is defined by the surface tension of the solvent and by the solvent wettability of the carrier and of the web of the serigraphic screen; the solvent's surface tension tends to form suspension drops on the carrier, the more the lower is the solvent wettability of the carrier. Moreover, should the material of the serigraphic screen exhibit a high solvent wettability, during the peeling phase of the screen from the deposit the suspension is liable to temptatively stick to the threads of the screen itself in an excessive way, which results in an accumulation of excessive amounts of NEG material in the region of the meniscus formed between the suspension and the screen. The total result of these effects cannot be forecast and changes as a function of the material used for the carrier and for the serigraphic screen, but it is anyway the achievement of an uneven deposit. The ratio of the weight of NEG material to the weight of dispersing medium is comprised between 4:1 and 1:1 and preferably between about 2.5:1 and 1.5:1. With NEG material contents larger than those specified, the suspension is not sufficiently fluid and gives rise to agglomerates which are badly distributed onto the serigraphic screen and which go with difficulty through its meshes. The lowermost limit of the wt% of NEG material is on the contrary imposed by productivity considerations. As a matter of principle, there are no contra-indications to operate with suspensions having very low contents of NEG material, but in this case a layer with little material and hence with a poor capacity is obtained; furthermore, with too low amounts of NEG material per geometrical surface unit of the deposit, this latter proves to be uneven and the gas sorption properties are unreproducible from device to device. The thus prepared suspension is deposited onto the carrier by serigraphic technique. This technique is known for other applications, such as, for instance, the reproduction of drawings on adapted surfaces or the deposition of conductive tracks for a printed circuit. Useful materials for the formation of a carrier according to the invention are metals such as particularly steel, titanium, nickel-plated iron, constantan and nickel/chromium and nickel/iron alloys. The carrier has generally a thickness comprised between 20 j.irn and 1 mm. The deposit may be in the form of a continuous layer throughout the carrier's surface, optionally leaving carrier's edges uncovered in order to easily handle the final sheet. The serigraphic technique, however, allows also to obtain partial deposits on the surface, thus obtaining the most different geometries for the NEG material deposits. In order to do so, it is sufficient to selectively occlude, according to a desired pattern, the ports of the serigraphic screen by means of a gel which cannot be etched by the suspension to be deposited; the obtained deposit will have the geometry of the gel negative corresponding to the ports of the screen set free by this one. By this way, it is possible to obtain continuous deposits having complicated shapes, like a spiral or the like, or discontinuous deposits, formed by a plurality of \'-' discrete deposit zones on the same carrier, with e.g. circular, square or linear shapes. The thus obtained deposit is allowed to dry in order to eliminate the greatest possible amount of suspending medium. Drying may be performed in an oven at a temperature comprised between about 50 and 200°C, in a gaseous flow or in a static atmosphere. The dried deposit is then sintered in a vacuum oven, by treating the same at a temperature comprised between about 800 and 1000°C, depending on the kind of NEG material, and at a pressure lower than 0,1 mbar. The treatment time may last from about 5 minutes to about 2 hours, depending on the reached temperature. At the end of the sintering treatment, the deposit may be allowed to cool down under vacuum, in a stream of inert gas in order to speed up the cooling or by means of combinations of the two conditions. Preferably, the two drying and sintering treatments are made to occur the one subsequent to the other, as subsequent steps of an identical thermal treatment. For example, it is possible to put the sample into a vacuum oven, to exhaust the oven to a pressure lower than 0,1 mbar, to heat up to a temperature comprised between 50 and 200°C and to keep the sample at such a temperature for a predetermined time comprised between 10 minutes and one hour; alternatively, it is possible to follow the variation of pressure values in the oven and to regard as completed the drying step when no more pressure increases are observed as a consequence of the evaporation of volatile components of the dispersing medium. Once drying is over, the sample may be heated under vacuum up to the sintering temperature. Depending on the chemical nature of the components of the dispersing medium and of the NEG material, it is also possible to have more complicated thermal cycles, providing treatment periods at a constant temperature, at a value comprised between the drying one and the sintering one; these treatments may be, for instance, useful for the elimination of the last traces of organic components, allowing them to decompose at a temperature at which the NEG material is not yet activated. According to the invention, during the sintering the dried deposit's surface must be protected by covering it with a material not subjected to any physical or chemical alteration under vacuum at any process temperature. In fact, should sintering be allowed to occur with exposure of the deposit surface, during the treatment deposit's scales are peeled off. Although the reason of this effect has not yet been clarified, it was found that by laying a plane surface of a physically and chemically inert material (in the sense above clarified), which will also be defined as "refractory" material, on the deposit's surface the phenomenon does not occur. Materials that can be used for the protection of the deposit are utmost various, as far as they do not melt or do not anyway suffer from physical or chemical conversions or alterations under vacuum throughout the temperature range of the thermal cycle; as an example of these materials molybdenum or graphite can be mentioned. It is also possible to carry out the sintering of several supported deposits in the same thermal cycle, by overlapping several sheets of supported deposit and interposing refractory material amongst said sheets or plane surfaces, and covering by means of a refractory material the surface of the uppermost sheet. By serigraphic technique, deposits are generally produced on carriers having a relatively wide surface, larger than at least 50 cm^; the technique is difficult to be utilized with carriers of limited surface. Generally, on the contrary, the available surface for the getter device inside the device requiring vacuum is not too wide. For example, in a flat display the getter can be arranged at the edges of the screen in the shape of stripes having a width of a few millimeters; in the case of "micromachines", on the contrary, getter devices are required having a geometrical surface of a few mm^. As a consequence, for the manufacture of getter devices by the method of the invention it is nearly always required a sheet cutting step. Should the deposit be discontinuous and should free portions of the supporting surface lie between one deposit zone and the other, it is possible to cut out the sheet by normal mechanical techniques such as shearing along uncovered supporting zones. When, on the contrary, it is desired to realize a cut along lines going through one or more deposit zones, it is preferable to resort to the laser cutting technique, in association with a coaxial flow of argon gas. By this technique the sheet is cut by means of localized fusion caused by the heat developed by the laser on the metal; simultaneously, there occurs the fusion of a very thin zone of deposit, approximately 30^40 pm wide, wherein the particles of NEG material prove to be melted with each other and with the metal carrier. This provides a "seam" of the cut and prevents the loss of NEG particles which could occur by mechanically cutting the deposit. The argon flow helps preventing the oxidation of the getter material. One of the advantages bound to the preparation of layers of getter material by the serigraphic method, is the possibility of obtaining in a simple way multilayers, even of different materials and in which the different layers have not all necessarily the same pattern. It is e.g. possible to deposit two overlapping continuous layers, or a continuous layer of a first material on the metal carrier and a layer of discrete zones of a second material over the first one, or yet the reverse structure, the discontinuous deposit layer being directly in contact with the carrier and the continuous layer covering the first one. This latter structure is particularly interesting as it allows to easily obtain getter devices showing excellent mechanical properties and a particle loss practically null even if starting from NEG materials difficult to be sintered, the particles of which j have consequently poor adhesion to each other and to the carrier. As an example of this kind of structure a getter device can be mentioned, obtained by depositing a first layer of particles of the cited St 707 alloy, difficult to be sintered, and thereupon a layer of nickel powder, which is easily sintered at a temperature of about 850°C; the layer of sintered nickel remains sufficiently porous as to allow a fair gas admission rate to the underlying getter alloy, and at the same time behaves as a "cage" for the alloy deposit, thus avoiding the particle loss of the same at the inside of the vacuum device. The possibility of obtaining overlapping layers of different materials does theoretically exist also with techniques such as electrophoresis or spraying, although with difficulty and limitations due, for example, to the maximum obtainable thickness by electrophoresis; serigraphy, on the contrary, is the sole technique allowing to obtain getter devices with at least one discontinuous powder layer. The invention will be illustrated further by the following examples. These not limiting examples illustrate a few embodiments intended for teaching those skilled in the art how to put the invention into practice and for representing the best considered mode for the invention accomplishment. EXAMPLE 1 This example concerns the preparation of a thin layer of getter material supported according to the invention. A suspension of powders of getter material is prepared using a mixture consisting of 70 g of titanium hydride, 30 g of the cited St 707 alloy and 40 g of a dispersing medium, supplied by the firm KFG ITALIANA under the trade name "Trasparente ad Acqua 525/1", made as an aqueous base having a content of high-boiling organic material lower than 0.8% by weight. The powders have a particle size lower than 60 |jm. The two components are mixed for about 20 minutes in order to obtain a homogeneous suspension. Such a suspension is dispensed onto a frame for serigraphic printing, having 24 threads/cm, mounted on a serigraphic machine (MS 300 model of the Cugher firm). The frame screen had been previously shielded along its periphery by a masking tape affixed to the side which, during the layer deposition, is in contact with the carrier; the tape defines a rectangular deposition area of 11 x 15 cm and maintains, during the printing phase, such a spacing between frame and substrate to allow the deposition of a film of material of about 50 |jm. The suspension is deposited onto a substrate of an alloy containing 80 wt% nickel/20 wt% chromium (Ni/Cr), having a thickness of 50 pm. The sheet with the deposited material, after a first drying step of 30 minutes in the air at room temperature, is interposed between two molybdenum plates and placed into a vacuum oven. The oven evacuation is started and as the pressure reaches a value of 5 x 10""* mbar there is initiated the thermal treatment, always under pumping. The thermal cycle is as follows: -temperature rising from room temperature to 200°C in 20 minutes -maintaining temperature at 200°C for 20 minutes -temperature rising from 200X to 550°C in 60 minutes -maintaining temperature at 550°C for 60 minutes -temperature rising from 550X to 850°C in 60 minutes -maintaining temperature at 850°C for 40 minutes -natural cooling down under vacuum to about 350°C and accelerated cooling by adding some mbar of argon into the oven's chamber below this temperature. The sheet with the deposit of sintered getter material is withdrawn from the oven at room temperature and a stripe of 1 x 5 cm is cut out therefrom by means of laser cutting, which stripe is completely covered / with getter material, whereupon the hereinafter described gas sorption tests are carried out. This stripe forms sample 1. EXAMPLE 2 (COMPARATIVE) This comparative example refers to the preparation of a thin layer of getter material supported by means of a technique different from the one of the invention. A 50 |jm layer of getter material is prepared on a Ni/Cr sheet of 50 pm according to the spray deposition technique disclosed by Patent Application WO 95/23425. The employed getter material and its particle size are the same of example 1. The deposit is sintered by means of the same thermal cycle utilized for the samples cited in the former example. From the sheet with the deposit of sintered getter material it is cut out, by laser cutting, a 1 x 5 cm stripe, completely covered with getter material, whereupon the hereinafter described gas sorption tests are performed. This stripe forms sample 2. EXAMPLE 3 (COMPARATIVE) This comparative example refers to the preparation of a thin layer of getter material supported by means of another technique different from the one of the invention. A 50 |jm layer of getter material is prepared on a Ni/Cr sheet of 50 pm according to the electrophoretic deposition technique disclosed by U.S. Patent No.4,628,198. The employed getter material and its particle size are the same of example 1. The deposit is sintered by means of the same thermal cycle utilized for the samples cited in the former examples. From the sheet with the deposit of sintered getter material it is cut out, by laser cutting, a 1 x 5 cm stripe, completely covered with getter material, whereupon the hereinafter described gas sorption tests are performed. This stripe forms sample 3. EXAMPLE 4 (COMPARATIVE) This comparative example refers to the preparation of a thin layer of getter material supported by means of a dispersing medium different from the one of the invention. The procedure of example 1 is repeated, whilst employing, however, a dispersing medium for the suspension having the following composition: 4.45% aluminum flakes, 44.5% AI(N03)3 and 51.05% of distilled H2O, i.e. free from organic compounds. The obtained sintered deposit has extremely poor adhesion to the carrier, wherefrom it is peeled off in the form of flakes. Due to the mechanical properties of the thus obtained deposit, making the same not employable in the technological applications where a getter device is required, no sorption tests are performed on this sample. EXAMPLE 5 (COMPARATIVE) This comparative example refers to the preparation of a thin layer of getter material supported by means of a dispersing medium different from the one of the invention. The procedure of example 1 is repeated, whilst employing, however, a dispersing medium for the suspension having the following composition: 1.5 wt% of collodion cotton, 40% butyl acetate, 58.5% isobutanol. From the sheet with the deposit of sintered getter material it is cut out, by laser cutting, a 1 x 5 cm stripe, completely covered with getter material, whereupon the hereinafter described gas sorption tests are performed. This stripe forms sample 5. EXAMPLE 6 The procedure of example 1 is repeated, with the difference that during the sintering the deposit of getter material is covered with a molybdenum sheet only for one half. The deposit obtained after sintering forms sample 6. In FIG. 3 is represented a diagrammatic drawing partially showing, in a plan view from above, both the covered zone and the zone left uncovered by molybdenum during the sintering of sample 6. EXAMPLE 7 The gas sorption capacity of samples 1, 2 and 3 is measured according to the method prescribed by the standard rule ASTM F 798-82. As a test gas, carbon monoxide (CO) is used. Results of these tests are shown in FIG. 1, as lines 1, 2 and 3, respectively, wherein the amount of sorbed gas is recorded as an abscissa and the sorption rate as an ordinate. EXAMPLE 8 The gas sorption capacity of samples 1 and 5 is measured according to the method prescribed by the standard rule ASTM F 798-82. As a test gas, carbon monoxide (CO) is used. Results of these tests are shown in FIG. 2, as lines 1 and 5, respectively, likewise the graphic representation of FIG. 1. As it is inferred from the comparison of lines 1, 2 and 3 in the graph of FIG. 1, the getter device made according to the invention has excellent gas sorption properties, better than those obtained by means of devices having the same geometrical size but prepared according to different techniques. Moreover, the analysis of the graph in FIG. 2 confirms the necessity of adopting a dispersing medium having a low concentration of high-boiling carbon compounds; although it would be expectable that the drying and sintering heat-treatments of the deposit remove any trace of these compounds, it is apparent from the graph that sample 5, obtained starting from a suspension having high contents of high-boiling carbon compounds, has gas sorption properties poorer than those of sample 1 prepared according to the invention. Finally, FIG. 3 clearly shows the effect of covering the deposit by a refractory material. In this figure the zone covered during sintering is designated as "a" and as "b" the uncovered zone. The surface portion left exposed has poor adhesion to carrier d, as it is pointed out by the deposit scales c, c' peeled off from the carrier itself. WE CLAIM; 1. A method for the manufacture of a supported thin layer of getter material, comprising: preparing at least one suspension of Non-evaporable getter (NEG) material particles with a particle size lower than about 150 , in a dispersing medium having an aqueous, alcoholic or hydroalcoholic base, containing a weight percentage of organic compounds, having a boiling temperature higher than 250°C, which is lower than 1%, wherein the ratio of the NEG material weight to the weight of dispersing medium is comprised between 4:1 and 1:1; depositing at least one layer of NEG material suspension onto a metal carrier by serigraphic technique; drying the thus obtained deposit by allowing the volatile components to evaporate; and sintering in a vacuum oven the dried deposit at a temperature comprised between 800 and 1000°C and characterised in that the sintering is carried out under vacuum, covering the deposit by means of a material that does not melt or suffer from chemical conversions or alterations under vacuum throughout the temperature range of the thermal cycle. 2. The method according to claim 1, wherein the NEG material is selected from the metals Zr, Ti, Nb, Ta, V and alloys thereof with one or more other metals selected among Fe, Al ending. 3. The method according to claim 2, wherein the NEG material is the alloy having the weight percent composition 70% Zr - 24.6% V - 5.4% Fe. 4. The method according to claim 2, wherein the NEG material is the alloy having the weight percent composition 84% Zr - 16% Al. 5. The method according to claim 2, wherein the NEG material is the compound Zr2Fe. 6. The method according to claim 2, wherein the NEG material is the compound Zr2Ni. 7. The method according to claim 1, wherein the NEG material is in the form of a powder, having a particle size comprised between 5 and 70 \xm. 8. The method according to claim 1, wherein the weight percent of organic compounds, having a boiling temperature higher than 250°C, is lower than 0.8%. 9. The method according to claim 1, wherein the ratio of the NEG material weight to the weight of dispersing medium is comprised between 2.5:1 and 1.5:1. 10. The method according to claim 1, wherein the metal carrier is selected from steel, titanium, nickel-plated iron, constantan, nickel/chromium alloys and nickel/iron alloys. 11. The method according to claim 10, wherein the carrier has a thickness comprised between 20 |im and 1 mm. 12. The method according to claim 1, wherein the sintering operation is allowed to occur at a residual oven pressure lower than 0.1 mbar. 13. The method according to claim 1, wherein the sintered deposit is cut along one or more lines going through one or more deposit zones, using the laser cutting technology. 14. The method according to claim 1, wherein at least two layers of different materials are deposited according to the serigraphic technology. 15. The method according to claim 14, wherein at least one layer consists of a material sintering at a temperature lower than 850"C. 16. The method according to claim 14, wherein at least one layer consists of a plurality of discrete deposit zones. 17. A getter device obtained by the method as claimed in claim 1. 18. A getter device obtained by the method as claimed in claim 14. 19. A getter device according to claim 18, wherein the layer directly contacting the carrier consists of a NEG material and the uppermost layer consists of nickel. 20. The getter device obtained according to the method as claimed in claim 16, wherein the layer of discrete deposit zones consists of NEG material.

Documents:

1597-mas-1997 abstract duplicate.pdf

1597-mas-1997 abstract.pdf

1597-mas-1997 claims duplicate.pdf

1597-mas-1997 claims.pdf

1597-mas-1997 correspondence others.pdf

1597-mas-1997 correspondence po.pdf

1597-mas-1997 description (complete) duplicate.pdf

1597-mas-1997 description (complete).pdf

1597-mas-1997 drawings.pdf

1597-mas-1997 form-19.pdf

1597-mas-1997 form-2.pdf

1597-mas-1997 form-26.pdf

1597-mas-1997 form-4.pdf

1597-mas-1997 form-6.pdf

1597-mas-1997 petition.pdf