EP0154796B1 - Manufacturing process for layered metallic multichannel plates for an image intensifier, and use of plates so manufactured - Google Patents

Abstract

A method for producing a multichannel plate containing metal dynodes and having a plurality of generally parallel channels for use in structures for amplifying or converting optical images or other two-dimensional signal patterns by secondary electron multiplication, which method includes: producing a negative mold of the plate by: (i) providing a body having at least the thickness of the plate to be produced and made of an electrically insulating material whose ability to be removed from the body is altered by exposure to a selected radiation; (ii) irradiating the body with the selected radiation in a pattern corresponding to the plate to be produced and in a manner to render portions of the body having the form of a grid surrounding the channels more easily removable than the remaining portions of the body; and (iii) removing the more easily removable portions of the body to leave columnar structures corresponding to the channels in the plate; depositing metal layers and intermediate layers alternatingly in the openings in the negative mold or in a secondary negative mold produced therefrom, the metal layers being deposited electrolytically and forming dynodes which are spaced apart in the direction of the channels; and removing the negative mold from the deposited layers.

Description

The invention relates to a method for producing layered multi-channel plates with metal dynodes for amplifying optical images or other areal signal distributions by means of secondary electron multiplication, and to the use of multi-channel plates produced in this way.

It is known to amplify optical images or other areal signal distributions with layered multi-channel plates made of metal (see DE-OS-3 150 257 and DE-PS-2 414 658). They consist of numerous metal layers which are electrically insulated from one another and provided with closely adjacent holes and are stacked in such a way that the holes form closely adjacent channels which run perpendicular to the plate surface. The layers are individually connected to a voltage source in such a way that there is a gradual increase in potential between them. The channels thereby have the function of secondary electron multipliers, the metal layers provided with holes forming the dynodes. The holes of the individual dynodes can be worked in by chemical etching through exposed and developed photoresist masks. In practice, good results are achieved when the hole diameter and the thickness of the dynode are approximately the same. From "Spectrum of Science", January 1982, pages 44 to 55, it is also known to design the channels curved or zigzag in multi-channel image intensifier plates made of glass. In the latter case, several plates with sloping channels are stacked for this purpose.

If a similarly high spatial resolution is to be achieved with layered multi-channel image intensifier plates as with glass image intensifier plates, the diameter of the holes and thus the strengths of the dynodes must be in the order of magnitude of 30 J.Lm and below. There are then considerable problems with the mutual alignment and electrical insulation of the separately produced film-like dynodes.

The invention is based on the object of proposing a method for producing layered multi-channel image intensifier plates of the generic type in which the separate production of the dynodes and their subsequent stacking and mutual alignment are avoided.

This object is achieved by the features specified in the characterizing part of claim 1.

With the method according to the invention, layered multi-channel plates with metal dynodes can be produced, with which a similarly high spatial resolution and a similarly high transparency can be achieved as with the known image intensifier plates made of glass, without the limitations in amplification factor and in typical for glass image intensifier plates the signal repetition frequency must be accepted.

To reduce the cost of mass production of multi-channel plates of the type described in claim 1, the method of the invention can be modified in accordance with claim 2. In this case, a metallic positive mold is produced with a primary negative mold of the layered multi-channel plate using a metal electrode connected to it by galvanic molding and subsequent removal of the primary negative mold, after which several secondary moldings are made by repeated molding of the metallic positive mold Negative forms of the layered multi-channel plate are produced, which assume the role of the primary negative form in the further implementation of the method. Non-adhesive reactive resins are particularly suitable as impression materials. Further details relating to the impression can be found, for example, in DE-PS-3 206 820.

In a special embodiment according to claim 3, the dynodes are mutually electrically isolated by removing the intermediate layers. If layered multi-channel plates with a larger diameter are to be produced in this way, it can be advantageous to mount electrically insulating supports not only on the channel-free edge, but also within the image field of the multi-channel plate, which is penetrated by channels.

Although in practice the supports in the area of the layered multi-channel plates, which are interspersed with channels, cover only about 1 per mille of the image field, they can be perceived as a disadvantage if the transmission quality is particularly high. In this case, a modification of the method of the invention according to claim 4 is provided. Aluminum is particularly suitable for the subsequent conversion of the intermediate layer into an electrical insulator described there. In the case of the small wall thicknesses typical of multi-channel plates with high transparency, it can be converted in a known manner with oxidizing agent working in the liquid and / or gaseous phase into the electrically excellent insulating A1 ₂ 0 ₃ . If, in the layered multi-channel plates produced in accordance with claim 4, the area penetrated by channels is to be surrounded by a channel-free area to facilitate assembly or the electrical connections, this area must consist of numerous thin walls to ensure the conversion of the more easily oxidizable material into an insulator.

The limitation to thin walls does not apply if the intermediate layers, according to claim 5, by complete or partial Oxidation of galvanically deposited aluminum layers can be produced. The oxidation of the aluminum layers can be carried out both chemically and electrochemically. To facilitate the galvanic deposition of the aluminum layers on the oxide layers underneath, it may be expedient to deposit thin metal layers on the oxide layers, which enable current to be supplied parallel to the plate surface in the subsequent electroplating.

In cases where aluminum can be accepted as a dynode material, the method described in connection with claim 5 can be simplified in accordance with claim 6.

An inclination of the channels against the plate surface favors the collision of the primary particles with the channel walls and thus the desired electron release. In the previously known methods for producing layered multi-channel plates, the inclination of the channels is achieved by mutual displacement of the dynodes during stacking. However, dislocations occur between the mutually assigned channels of the adjacent dynodes, which lead to a reduction in transparency and / or the spatial resolution. In the layered multi-channel plates produced according to the method of the invention, the inclination of the channels can be brought about by appropriate orientation of the plate surface with respect to the direction of propagation of the high-energy radiation without loss of transparency and / or spatial resolution.

A channel curvature aimed at suppressing the acceleration of parasitic ions can likewise only be achieved in the previously known methods for producing layered multi-channel plates only by mutually displacing the dynodes with the disadvantages mentioned above. In the method of the invention, these disadvantages can be avoided in that, according to claim 7, before the formation of the dynodes and intermediate layers, the negative shapes of the channels are bent at a higher temperature by a uniformly acting force, for example a centrifugal force.

Suppression of the acceleration of parasitic ions is also possible, however, by assembling at least two layered multi-channel plates according to the invention with channels inclined to the plate surface in a known manner in such a way that the channels together form zigzag structures. Since the cross-sections and positions of the channels can be precisely specified in the layered multi-channel plates produced according to the invention, the layered multi-channel plates can be assembled in such a way that the channel openings of layered multi-channel plates lying one on top of the other are aligned with one another. This avoids losses in transparency and / or spatial resolution.

Both corpuscular rays and electromagnetic waves can be considered as high-energy radiation. While the use of electromagnetic waves to produce the desired structures uses masks in a known manner, the structures can also be produced by electromagnetic control when using corpuscular beams. The X-ray radiation ("synchrotron radiation") generated by the electron synchrotons, which is characterized by high intensity with a small aperture angle, has proven particularly useful. The choice of the material which can be changed by high-energy radiation depends on the type of high-energy radiation, corresponding regulations being found, for example, in DE-PS-2 922 642 and DE-OS-3 221 981. When using synchrotron radiation, polymethyl methacrylate (PMMA) has proven particularly useful, it being possible to use a developer according to DE-OS-3 039 110 to remove the irradiated areas.

By means of suitable surface treatment, for example a weak oxidation with oxygen or chlorine at a higher temperature, an electrochemical treatment or by deposition of a thin material layer by the CVD method or by combinations of such methods, the secondary electron yield factor of those with channels can be known in a manner known per se provided metal layers may be increased considerably. The inventive method is in

• Die Figuren 1 bis 3 zeigen schematisch die einzelnen Schritte der Erzeugung der Negativ- Form für die Herstellung einer geschichteten Vielkanalplatte,
• die Figuren 4 und 5 zeigen schematisch die Herstellung von Dynodenschichten, die fest mit elektrisch isolierenden Stützen verbunden sind, die Figuren 6 und 7 zeigen schematisch die Herstellung einer geschichteten Vielkanalplatte, bei der die Zwischenschichten zwischen den Dynoden nachträglich in isolierende Metalloxidschichten umgewandelt werden,
• die Figuren 8 und 9 zeigen schematisch die Herstellung einer geschichteten Vielkanalplatte, bei der sukzessiv Dynoden und isolierende Zwischenschichten aufeinander aufgebaut werden.

the following are explained using the drawings as an example:

• FIGS. 1 to 3 schematically show the individual steps in the production of the negative mold for the production of a layered multi-channel plate,
• FIGS. 4 and 5 schematically show the production of dynode layers which are firmly connected to electrically insulating supports, FIGS. 6 and 7 schematically show the production of a layered multi-channel plate in which the intermediate layers between the dynodes are subsequently converted into insulating metal oxide layers,
• FIGS. 8 and 9 show schematically the production of a layered multi-channel plate, in which the dynodes and insulating intermediate layers are successively built up on top of one another.

According to FIG. 1, a 0.5 mm thick plate 1 made of polymethyl methacrylate (PMMA), which is firmly connected to a metal electrode 2, serves as the starting material for the production of the negative form of a layered multi-channel plate. The PMMA plate 1 is shown in FIG. 2 via an X-ray mask with synchrotron radiation 3 irradiated, which is directed obliquely to the surfaces of the PMMA plate 1 and the X-ray mask. The X-ray mask consists of a carrier 4, which only weakly absorbs the X-radiation, and an absorber 5, which strongly absorbs the X-radiation, by means of which the cross-sectional shapes and the positions of the negative shapes of the channels are defined. The individual structures of the absorber 5 correspond to the cross-sectional shapes of the negative shapes of the channels. Due to the high-intensity parallel synchrotron radiation, the PMMA in the areas 6 not covered by the absorber will undergo chemical radiation changes. These areas 6 irradiated in this way are removed by introducing the PMMA plate into a developer solution, so that a multichannel negative shape with columnar PMMA structures 7 and lattice-shaped free spaces 8 according to FIG. 3 is produced. The columnar PMMA structures 7 have lm a hexagonal cross-sectional shape having a width of about 30 _I, the width of the free spaces 8 between the PMMA structures 7 is approximately 4 to.

When producing a multi-channel plate with individual dynodes, which are firmly connected to electrically insulating supports, the negative form shown in FIG. 4 is assumed, which, in addition to the metal electrode 2a, the columnar PMMA structures 7a with lattice-free spaces 8a, as they are were already shown in Figure 3, additionally contains supports 9 made of electrically insulating material. Layers of nickel 10 and copper 11 are alternately galvanically deposited in the free spaces 8a, so that a structure according to FIG. 5 is produced. Subsequently, the PMMA structures 7a with an organic solvent and the copper layers 11 and the electrode 2a with an etch which does not attack the nickel layers 10 are first removed, so that a sequence of mutually insulated dynode layers which are fixed to the electrically insulating supports 9 connected, remains.

The negative mold 7 shown in FIG. 3 is used in the production of layered multi-channel plates made of dynodes and intermediate layers subsequently produced. 6, layers of nickel 12 and aluminum 13 are alternately deposited in the free spaces 8 of the negative mold 7. After removal of the negative mold 7 with an organic solvent and the electrode 2 with an etch which does not attack the nickel layers 12 or the aluminum layers 13, the aluminum layers are converted in a known manner by oxidation into aluminum oxide, so that according to FIG Layered multi-channel plate made of nickel dynodes 12 and insulating intermediate layers 13a made of aluminum oxide.

In the production of layered multi-channel plates in which dynodes and insulating intermediate layers are successively built up on one another, the negative mold 7 shown in FIG. 3 is again assumed. An aluminum layer 14 made of an organic electrolyte is deposited into the free spaces 8b between the columnar PMMA structures 7b, as can be seen from the simplified illustration in FIG. 8, using the metal electrode 2b. This layer is partially converted into aluminum oxide in a second electrolyte containing sulfuric acid by anodic oxidation, so that a firmly adhering aluminum oxide layer 15 is formed as shown in FIG. 9. This is activated and coated by chemical reduction deposition with a thin metal layer 16 onto which an aluminum layer 14a is again galvanically deposited. This process sequence is repeated until the desired number of layer sequences is reached, whereupon the negative mold 7b and the electrode 2b are removed.

Details of the galvanic production of thin aluminum layers can be found, for. B. S.Birkle, J.Gering, K.Stöger, Zeitschrift Metall, Issue 4, April 1982, while details about the subsequent conversion into oxide z. B. the manual of electroplating, Volume 1, Part 2, pp. 1041-1043, Carl Hauser Verlag, Munich 1964, can be found.

Claims (8)

1. A process for the manufacture of layered multichannel plates with metal dynodes for the intensification of optical images or other signal distributions over a surface by means of secondary electron multiplication, characterised in that

a) first a negative form of the layered multichannel plate which is to be manufactured consisting of column-like structures (7) on a metal electrode (2) with intermediate lattice-like open spaces (8) is produced, in which lattice-like open spaces (8) are produced in a plate (1) which has at least the thickness of the multichannel plate and consists of electrically insulating material whose properties can be changed by high energy radiation, vertically or obliquely to the plate surface through partial irradition and partial removal of this material using the different material properties produced by the radiation,

b) Dynode layers (10, 12) are produced by electrochemical means alternating with electrochemically conducting or insulating intermediate layers (11, 13) in the lattice-like open space (8) of the negative form using the metal electrode associated with it (2), whereupon

c) The negative form is removed and in the case of the production of electrically conducting intermediate layers these are removed or converted into an electrical insulator.

2. A process according to Claim 1, characterised in that a metal positive form is produced after step a) by galvanic duplication and subsequent removal of the primary negative form, after which several secondary negative forms of the layered multichannel plate are produced by repeated duplication of the metal positive form in which in accordance with step b) the dynode layers are produced by electrochemical means alternating with electrically conducting or insulating intermediate layers, whereupon in accordance with step c) the secondary negative forms are removed and in the case of the production of electrically conducting intermediate layers these are removed or converted into an electrical insulator.

3. The process according to Claims 1 or 2, characterised in that the dynode layers (10) are firmly fixed to electrically insulated supports (9) in the process of electrochemical manufacture and the intermediate layers (11) consist of a more soluble material in comparison with the dynode layers which is dissolved out after removal of the negative form.

4. A process according to Claims 1 or 2, characterised in that the intermediate layers (13) consist of a more readily oxidisable material than the dynode layers (12) which is converted into an electrical insulator by oxidation after removal of the negative form.

5. A process according to Claims 1 or 2, characterised in that the intermediate layers (13) are produced by the complete or partial oxidation of electrochemically deposited aluminium layers. 6. A process according to Claims 1 or 2, characterised in that aluminium is used as the material for the dynode layers (14a) and the intermediate layers (15) are produced by partial oxidation of the dynode layers.

7. A process according to one of the Claims 1 to 6, characterised in that the negative forms of the channels are bent by means of a uniformly applied force, for example a centrifugal force, at a raised temperature prior to production of the dynode layers and the intermediate layers.

8. The use of layered multichannel plates manufactured in accordance with one of claims 1 to 6 to produce stack of at least two multichannel plates with channels oblique to the plate surface in which the channels which are directed together jointly form structures of a zigzag shape.

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