EP0515261A1 - Ceramic electron multiplying structure especially for photomultiplier and its manufacturing procedure - Google Patents

Abstract

The multiplier manufactured according to the invention has a very compact shape and can have the channel output electrodes arranged in any direction. The multiplying structure (94) is a ceramic block obtained by baking a stack of ceramic sheets prepared beforehand for the purpose of constituting cavities enclosed in the mass. Each cavity (21) is covered with a metallic deposition connected to a lateral contact (23) by a conductor (24) printed on the corresponding sheet beforehand. The channels can have particular geometries in order to have their output on several different surfaces (41, 46, 47) of the multiplying structure. <IMAGE>

Description

FIELD OF THE INVENTION

The invention relates to electron multipliers, comprising a large number of independent electronic multiplication channels. The invention also relates to the devices resulting from the association of this type of multi-channel multipliers with various sources of incident electrons upstream and with receivers (active or passive) of multiplied flow of electrons downstream. The invention also relates to the manufacture of this type of multipliers.

PRIOR ART

Despite the appearance on the market of many very sensitive detectors, the detection of a single low-energy electron (qq ev) requires electronic multiplication in order to obtain an electrical charge sufficient to be detected. The electron multiplier plays an essential role in a well-known component which is the photomultiplier, but its use cannot be limited to this application.

However, it is through this application that we will highlight the shortcomings and disadvantages of multi-channel photomultipliers currently on the market to justify the proposals of the invention and to identify the advantages it provides.

This particular application of electronic multipliers is that which combines a photocathode source of the primary electrons and a base carrying the electrodes to extract the signals and polarize the stages, in order to create a photomultiplier. Currently, whatever the manufacturer, the making of these photodetectors is based on lamp technology with glassmaker intervention, where, most of the time, the porthole (photocathode support), as well as the base are an integral part of the envelope. Consequently, the geometry and the connections of these tubes do not allow effective groupings in order to compose large homogeneous photosensitive surfaces (qq m²). This constitutes a severe limitation of their use in the whole field of material and living sciences than in the industrial world.

Let us briefly recall the operating principle of an electron multiplier, whether it is mono or multichannel. Figure 1 brings together the main components that explain the process. The reference 1 symbolizes a vacuum enclosure where the other elements are arranged. The multiplication electrodes E 1, 2, 3, 4 have a shape and a spatial arrangement suitable for collecting and re-emitting electrons. They are electrically isolated from each other and communicate with the outside by pins fixed to the casing by means of insulating passages. The output electrode or anode 5 proceeds from the same technique. Each electrode is covered with a layer which promotes emission secondary. The electrode 3 will supply the primary electrons necessary to trigger the multiplication; here it plays the role of cathode.

The potential distribution is established in order to apply an electric field between the electrodes. The anode is connected to ground through a measuring instrument.

An electron emitted by 3 is accelerated by the electric field which reigns between 3 and E₁ then impacts E₁, which in turn emits N electrons themselves accelerated to impact E₂. The process continues and 5 intercepts a flow of N⁴ electrons.

As proposed by certain authors, see FIG. 2, it is possible to thus constitute a series of channels 86 oriented vertically in this figure. They consist of a series of cells 88 having the properties mentioned in the previous paragraph. These channels result from a stack of metal plates 80, 82 and 84 in which the cells 88 have been machined. These cellular metal plates, called perforated plates, are insulated by insulating plates or spacers 81.

With such a stack, it is thus possible to constitute a multiplier with perforated plates, as shown in FIG. 3.

It is described in an article by JP BOUTOT, P. LAVOUTE and G. ESCHARD, "Multianodes, photomultiplier for detection and localization of low light level events", IEEE, France, Nucl. Sci., N ° 34, 1987, 449.

It includes an entry window 2, generally made of glass, which allows photons to reach a photocathode 4 deposited on the internal face of this entry window 2. One or two grids 6, placed below the photocathode 4 , impose an electrostatic distribution of field lines, joining photocathode 4 to the multiplier structure in order to define a determined number of pixels, namely here 64. Below this grid 6, is the stack composed of the various perforated plates 8, assuming the multiplication function. The stack of perforated plates 8 ends with an output electrode 10 segmented into 64 output electrodes connected to the outside by the pins 14. These electrodes 10 are placed on an output plate 12, often made of glass, and collect electrical signals of amplitude proportional to the incident photon fluxes which expose each of the pixels. The set of multiplier plates 8 is placed under vacuum in an enclosure delimited by the inlet 4 and outlet 12 plates, and by walls 16.

Note that, in this block diagram of FIG. 3, extracted from the aforementioned publication, the pins ensuring the polarization of the different multiplier stages are not shown.

Figures 4 and 5 show at scale 1, in bottom view 4 and side view 5, the industrialized version of a multi-channel photomultiplier incorporating in its glass envelope a multiplexer with perforated sheets respecting the principle diagram in all respects of figure 1.

We can first notice the bulky shape of the sealed enclosure delimited by the walls 16, relative to the size of the active area, that is to say of the 64 pixels. This size is further increased by the existence of a socket 17 extending beyond the walls 16. In addition, these multiplier plates 8 are polarized by peripheral pins 18 placed around the stack and protruding from the outlet plate 12.

• le rapport de la surface photosensible à l'encombrement total est de l'ordre de 13 %, ce qui est trop faible ;
• la forme est compliquée par l'existence du queusot 17 qui réduit à moins de 10 % l'efficacité géométrique de ce composant en cas de juxtaposition de plusieurs tubes ;
• son utilisation impose le câblage d'une embase spéciale, encombrante et coûteuse, pour distribuer les polarisations des différents étages ;
• les broches des signaux de sortie et des broches de haute tension, pour polariser les étages, se côtoient sur la même face du tube ;
• la difficulté d'extraire, avec des connexions courtes, les signaux des 64 broches implantées en zone centrale ;
• la difficulté d'obtenir, pour un même tube, une multiplication homogène des 64 canaux et, au sein d'une série de tubes, une homogénéité entre individus (comme cela a été mis en évidence par des tests de fonctionnement) ;
• la difficulté de faire évoluer le tube en dimension dans le but d'accroître le nombre de pixels (256 ou 1 024) ;
• la difficulté d'obtenir à des coûts et des délais raisonnables le type de photocathode désiré ;
• la difficulté d'obtenir de la part des fabricants le type de fenêtre d'entrée désiré ; et
• finalement l'impossibilité pour l'utilisateur d'insérer le multiplicateur seul dans une chaîne expérimentale entre un générateur de particules initiales, qui remplacerait la photocathode, et un dispositif particulier d'analyse des flux électroniques de sortie.

This photodetector, thus produced, has the following drawbacks:

• the ratio of the photosensitive surface to the total size is of the order of 13%, which is too low;
• the shape is complicated by the existence of the queusot 17 which reduces the geometric efficiency of this component to less than 10% in the event of the juxtaposition of several tubes;
• its use requires the wiring of a special base, bulky and expensive, to distribute the polarizations of the different stages;
• the pins of the output signals and of the high voltage pins, to polarize the stages, coexist on the same face of the tube;
• the difficulty of extracting, with short connections, the signals from the 64 pins located in the central area;
• the difficulty of obtaining, for the same tube, a homogeneous multiplication of the 64 channels and, within a series of tubes, homogeneity between individuals (as has been demonstrated by functional tests);
• the difficulty of making the tube evolve in size in order to increase the number of pixels (256 or 1,024);
• the difficulty of obtaining the desired type of photocathode at reasonable cost and time;
• the difficulty of obtaining from manufacturers the desired type of entry window; and
• finally, the impossibility for the user to insert the multiplier alone in an experimental chain between an initial particle generator, which would replace the photocathode, and a particular device for analyzing the electronic output flows.

All these drawbacks do not relate to the shapes, nor to the dimensions and positions of the multiplying zones and no more to the nature of the electrodes or the emissive deposits.

• la préparation de la mécanique des structures multiplicatrices par attaque chimique, assemblage des étages multiplicateurs, empilement des étages électriquement isolés par des billes de verre et des entretoises de céramique ;
• la préparation d'un culot porteur des broches qui servent à polariser les étages et extraire les signaux et à fixer mécaniquement le multiplicateur ;
• la préparation d'une enveloppe de verre qui relie le hublot, futur support de la photocathode, au culot ;
• la phase finale où le montage doit être pompé, étuvé, puis sensibilisé par élaboration de la photocathode et activation des dynodes. Cette phase d'activation doit avoir lieu en une seule opération, qui, si elle se révèle défectueuse, conduit au rejet sans récupération de tous les composants du montage. On note que ces pratiques conviennent à la fabrication des photomultiplicateurs de petite taille où les étages sont plans.

They result from the very design of the multiplier, the development and consequently the operation of which require that it be housed in a vacuum enclosure, here made of glass. Continuing the analysis of this particular application for the production of photomultipliers, we will notice that this glass technology involves the following stages:

• preparation of the mechanics of multiplier structures by chemical attack, assembly of multiplier stages, stacking of stages electrically insulated by glass balls and ceramic spacers;
• the preparation of a base carrying the pins which serve to polarize the stages and extract the signals and to mechanically fix the multiplier;
• the preparation of a glass envelope which connects the porthole, future support of the photocathode, to the base;
• the final phase where the assembly must be pumped, steamed, then sensitized by developing the photocathode and activating the dynodes. This activation phase must take place in a single operation, which, if it proves to be defective, leads to the rejection without recovery of all the components of the assembly. It is noted that these practices are suitable for the manufacture of small photomultipliers where the stages are planar.

All of these drawbacks are not specific to the application which served us as a support for analyzing and qualifying the prior art.

The aim of the invention is therefore to remedy these drawbacks and to propose an autonomous electron multiplier with respect to vacuum, the mechanical aspect of the polarization of the stages and the spatial distribution of the inputs / outputs of the multiplication channels.

To this end, the invention proposes the development of a multiplier in the form of a compact, self-supporting block, including in the mass all the elements capable of establishing the potentials and producing the secondary electrons necessary for multiplication using technology. multilayer ceramics. Multilayer ceramics, for over twenty years, have been the subject of in-depth studies and intensive industrialization and provide inexpensive products in series and high physical, chemical, mechanical and geometric performance. In addition, the wide variety of products, the precision of the dosages of the constituents and the computerization of the development protocols widen the possibilities offered in order to satisfy more complex day-to-day achievements.

Following the example of establishments NTK (Japan) and XERAM (France), "co-sintered" multilayer ceramic substrates are marketed as housings to house integrated circuits or as printed circuits allowing high-density implantation of electronic components. These performances are due to the large number of surface connections that can be made on each side of the ten, twenty or thirty ceramic sheets before firing. The product obtained at the end of the sintering has a very high hermeticity, pledge of a very great reliability and longevity, and a very dense network of superficial and mass interconnection, connecting the electronic components arranged on the periphery.

The invention claims to make use of the advances in multilayer ceramic technology and to adapt them in order to produce a compact electron multiplier, usable in numerous applications, including those of photomultipliers.

SUMMARY OF THE INVENTION

A first object of the invention is a compact electron multiplier structure by secondary emission having a plurality of multiplier channels, characterized in that it is consisting of a compact, waterproof, ceramic insulating block, in which are distributed, according to three dimensions, cavities with conductive walls formed of a conductive deposit, suitably activated and connected together by a connecting conduit allowing the transit of the amplified flow of electrons, as well as means for polarizing these cavities.

In its main embodiment, the multiplying structure according to the invention results from a high temperature sintering of a stack of plates (or sheets) of raw ceramic of which each plate (or sheet) has been previously punched and machined in order to create connecting conduits and cavities; the polarization means being constituted by the metallic deposit on the surface of the cavities and conductive tracks on a surface of each ceramic plate to connect each cavity to lateral electrical contacts.

To complete the description of this structure, it will be noted that the cavities can occupy any position in the block, contrary to what is required by the stacking of perforated metal plates. The technique of "co-sintering" of insulating sheets offers a real three-dimensional (3D) distribution of the cavities and, thereby, the freedom to associate the cavities to form curved channels.

The electrical independence of the cavities, associated with the 3D spatial distribution, allows the realization of curved channels, FIG. 7, where the incident and outgoing electronic fluxes appear on the same face of the block.

Several relative positions of the channels between them are possible. In fact, the channels can meet, communicate with each other, or even subdivide or regroup.

In a particular embodiment of the channels, several successive cavities of the same channel can be polarized at the same voltage by being connected to the same lateral contact, thus constituting the same multiplier stage.

If the cavities are simply metallized, the structure can also be used as an electronic multilens, in order to condition the electrons in spatial and energy distributions.

A second main object of the invention is a photomultiplier comprising a multiplier structure as defined above, and a photocathode arranged at a first end of each channel to receive the light pulses and transform them into electronic pulses in said channels, at least an output electrode for sampling the amplified pulses and disposed at the second end of each channel, a base, also consisting of ceramic plates coated with conductive electroemissive layers suitably arranged.

• usinage de plaques (ou feuilles) de céramique crue pour former les cavités et canaux intercavités ;
• encrage à l'encre conductrice des zones qui formeront les cavités et les pistes conductrices les reliant entre elles et à un contact extérieur latéral ;
• empilage des plaques (ou feuilles) ainsi préparées ;
• cuisson dans les conditions requises ;
• dépôt sur les zones conductrices des cavités des matériaux propres à engendrer, après activation, une forte émission secondaire ;
• dépôt sur les contacts externes des métaux assumant un excellent contact ohmique ;
• activation du multiplicateur par des procédés physico-chimiques appropriés.

A third object of the invention is a method of manufacturing a multiplier structure, as just summarized. Such a method comprises the following steps:

• machining of raw ceramic plates (or sheets) to form the cavities and intercavity channels;
• inking with the conductive ink the zones which will form the cavities and the conductive tracks connecting them together and to a lateral external contact;
• stacking of the plates (or sheets) thus prepared;
• cooking under the required conditions;
• deposition on the conductive areas of the cavities of the materials capable of generating, after activation, a high secondary emission;
• deposit on the external contacts of metals assuming an excellent ohmic contact;
• activation of the multiplier by appropriate physicochemical processes.

LIST OF FIGURES

• figure 1, le principe de fonctionnement d'un multiplicateur d'électrons communs à l'art antérieur et à l'invention ;
• figure 2, ce principe appliqué à de multiples canaux verticaux ;
• figure 3, le schéma de principe d'un photomultiplicateur incorporant un multiplicateur à feuilles perforées de l'art antérieur ;
• figure 4, un autre photomultiplicateur de l'art antérieur vu de dessus ;
• figure 5, ce même photomultiplicateur vu de côté.

The problem posed which the invention aims to solve and the multiplier of the prior art have been presented with the aid of the first figures which represent respectively:

• Figure 1, the operating principle of an electron multiplier common to the prior art and the invention;
• Figure 2, this principle applied to multiple vertical channels;
• Figure 3, the block diagram of a photomultiplier incorporating a perforated sheet multiplier of the prior art;
• Figure 4, another photomultiplier of the prior art seen from above;
• Figure 5, the same photomultiplier seen from the side.

• figure 6, la constitution d'un canal de multiplication selon l'invention, sans préjuger de la forme des cavités ;
• figure 7, une première configuration possible pour un canal dans une structure multiplicatrice selon l'invention ;
• figure 8, une autre configuration possible dans laquelle un canal se divise en deux canaux dans la structure selon l'invention ;
• figure 9, un multiplicateur à deux canaux et trois étages ;
• figure 10, une possibilité d'association de trois multiplicateurs compacts ;
• figure 11, en vue cavalière, un exemple de réalisation de la structure multiplicatrice selon l'invention ;
• figure 12, en coupe, la structure multiplicatrice de la figure 11 ;
• figure 13, un exemple de réalisation de feuilles de céramique dans le procédé selon l'invention ;
• figure 14, un exemple d'assemblage des feuilles de la figure 13 ;
• figure 15, la face latérale d'une structure multiplicatrice portant les contacts externes permettant de polariser les cavités ;
• figure 16, un exemple de réalisation du photomultiplicateur selon l'invention.

The invention and its technical characteristics will be better understood on reading the following detailed description which is accompanied by the other figures representing respectively:

• Figure 6, the constitution of a multiplication channel according to the invention, without prejudging the shape of the cavities;
• FIG. 7, a first possible configuration for a channel in a multiplier structure according to the invention;
• FIG. 8, another possible configuration in which a channel divides into two channels in the structure according to the invention;
• Figure 9, a two-channel multiplier and three stages;
• Figure 10, a possibility of association of three compact multipliers;
• Figure 11, in perspective view, an embodiment of the multiplier structure according to the invention;
• Figure 12, in section, the multiplier structure of Figure 11;
• Figure 13, an exemplary embodiment of ceramic sheets in the method according to the invention;
• Figure 14, an example of assembling the sheets of Figure 13;
• Figure 15, the side face of a multiplier structure carrying the external contacts for polarizing the cavities;
• FIG. 16, an exemplary embodiment of the photomultiplier according to the invention.

DETAILED DESCRIPTION OF AN EMBODIMENT

In the channel shown in Figure 6, three shapes of cavities are given as an example of embodiment. The first cavity 33 is of cylindrical shape. The second cavity 34 is a stack of coaxial hollow cylinders. The third cavity 35 has any shape which can be obtained approximately by a stack of suitably cut sheets.

These three examples of shapes of cavities can be obtained by punching ceramic plates 36 which are then superimposed. As a result, great freedom is offered to place the interconnection tracks on any one of the sheets participating in the constitution of a cavity.

FIG. 7 briefly shows a possible configuration of a channel in a multiplier according to the invention, and more precisely in a ceramic block 20.

We first note the non-rectilinear shape of the channel. This shape means that, in this case, the input and the output thereof imposed by the polarization of the successive cavities are located on the same upper surface 26 of the block 20. The input 22 and output 25 electrodes are located therefore on this same surface 26. The channel is formed by a succession of several cavities 21 connected by connecting conduits 27.

Each cavity 21 is equipped with polarization means 28, 24, 23, to bring the internal surface of each of them to a determined electrical potential. The conductive walls covered with a conductive metallic deposit 28, then chemically activated constitute the multiplier zones. This metal deposit 28 is itself connected to an external electrical contact 23 located on one of the surfaces of the ceramic block 20, by means of a connector 24. Each lateral contact 23 is brought to the potential necessary for the corresponding cavity, for that the latter constitutes a multiplying zone.

It can be seen in this FIG. 7 that the connectors 24 are embedded in the ceramic block 20. The production of such a configuration is preferably obtained by constituting the ceramic block 20 by the use of ceramic sheets. The connectors 24 are then applied to a surface of these sheets, during the preparation of the latter.

Figure 8 shows another function of the multiplier cavities which is the spatial distributivity of the secondary electrons. The channel is divided into 21 into two parts by means of two conduits 32 each leading to another cavity 31. The channel is thus divided into two and ends with two output electrodes 25. In the case shown in this figure, these two output electrodes 25 are placed on two different faces of the ceramic block.

We can also consider the opposite situation where at least two channels join in a cavity in order to add the electron fluxes in the common multiplicative channel. In this case they each have an input electrode but only one output electrode.

Another example of a cavity shape is shown in FIG. 9. The cavities 371, 372, 373, as well as the conduits 39 are cylinders obtained by stacking suitably perforated sheets. For each cavity, one of the sheets constituting it will carry the conductive track 38 connecting it to the external contact 23.

Such an embodiment makes it possible to simplify the manufacture of the ceramic block by simplifying the forms to be practiced in the plates 36. All the cavities of the same stage 372 are brought to the same potential by means of the conductive tracks 38 connecting the conductive deposits of the cavities between them and to outside contact 23.

In the four examples shown in Figures 6, 7, 8, each successive cavity of a channel is set to a determined electrical potential, and successively increasing, to meet the conditions of multiplication.

Figure 10 shows a cross section of three multipliers 40 already described. This example wants to show the associativity of the multiplier blocks resulting from the invention, between them, thus exploiting their mechanical and electrical autonomy.

With reference to FIG. 11, it is understood that it is possible to produce a compact and very complex ceramic multiplier structure. Such a structure can therefore have on its upper surface 26 the inlet of each channel 43, but above all can have on different surfaces 44 and 45 the outlets 46 of these channels. It is in fact very advantageous to be able to thus modify in space the trajectory of the channels in order to be able to orient the output of these in the direction of the elements and devices intended for the exploitation of the amplified signals. This adapts the shape of the multiplier to the use for which it is intended.

Figure 12 shows in section such a compact ceramic structure. It can be seen that all the channels 43 have their entry on the upper surface 26. On the other hand, the exits of these channels are on three different surfaces 45, 46 and 47.

The lateral contacts 23 can be assembled on the same lateral surface 48 or 49. The cavities 21 of the channels can thus be brought to different potentials, compared to the other cavities of the same channel, but also compared to the cavities of the same rank of the others canals.

FIG. 13 shows several raw ceramic plates 51 to 56, primed and placed one above the other, during stacking, and FIG. 14 after firing. Indeed, in the development of the ceramic multiplier structure, as it is provided according to the invention, ceramic plates are used beforehand that is prepared (machining by punching, drilling, ...) in order to constitute a stack intended to produce the multiplying structure. An exemplary embodiment of two adjacent channel portions is therefore illustrated in this figure 13. The first two plates (or sheets) 51 and 52 are joined to one another. In addition, they are perforated and each hole 57 is coated with a conductive material 58. This operation is preferably carried out by screen printing of a conductive ink which connects the two opposite surfaces 59 of the two plates 51 and 52, as well as to a lateral contact 23 by means of a conductor 24. The diameter of these holes 54 is relatively large, with the aim of constituting the internal wall of two cavities. The fourth and fifth plates 54 and 55 suffer the same fate, in the same way.

On the other hand, the third plate 53 and the sixth plate 56 are individually inked on their large surface 60, around holes 61 of smaller diameter than the holes 57 of the other plates. The position of these holes 61 is in correspondence with the position of the holes 57 of the other plates. Note that the holes 61 have most of their insulating internal wall, since it is made of ceramic.

Figure 14 shows the stacking of these six plates. Note that the third and sixth plates 53 and 56 are placed relative to the two assemblies consisting of the first and second on the one hand and the fourth and fifth on the other hand, off-center. In other words, the holes 61 of these third and sixth plates 53 and 56 are offset from the holes 57 of the other four plates. By matching part of the internal surfaces of these holes 57 and 61, it is thus possible to form cavities 62 and pieces of conduits 63 in a manner analogous to the embodiment shown in FIG. 9.

The purpose of this example is to show the feasibility of the various channels, cavities, walls and conductive tracks described above and forming the subject of the invention by using the means currently available in the technique of multilayer ceramics and in no way limits the shapes or the arrangements of the components of compact multipliers.

Figure 15 shows the side of a multiplier structure, as obtained using the method illustrated in Figures 13 and 14. Indeed, on the side face 64 of this structure, one can distinguish several lateral contacts : 230 polarizes the input of the channels, 231 the middle stage, 232 the output electrode.

For this purpose, the stages being placed one below the other, all the lateral connectors 230, 231, 232, are offset and can be more easily connected by a resistive deposit which establishes the distribution of the potentials as soon as one carries contact 230 at an electrical voltage and 232 at ground for example. At the end of this phase, we therefore have a compact, rigid multiplier structure, including in the mass of conductive cavities, isolated from each other, and polarizable externally.

By electrodeposition, or any other method, it is also possible to cover the conductive areas with one or more suitable metals, capable of receiving surface treatments to increase the phenomenon of secondary emission.

The distribution of the different potentials on the lateral contacts 23 can be done by means of a resistive ink. The values can be adjusted after firing by volatilization of the ink under the impact of a laser beam.

FIG. 16 generally represents a photomultiplier obtained by means of a multiplying structure manufactured with the method according to the invention.

Such a photomultiplier comprises an inlet porthole 90 carrying on its internal face a photocathode 92 which will emit photoelectrons under the action of light. These electrons, drawn towards the entry of the channels will multiply as the electronic impacts in the multiplier progress.

The outgoing flow of electrons is collected by the internal electrodes 96 connected to the external contacts 91 by conductive tracks 95. All these elements are included in the base 98 produced from multilayer ceramic.

Through the latter, there is the output of the signals on external contacts 91 connected to the output electrode 96. This base 98 is preferably made of multilayer ceramic, in order to remove the connection pins in favor of surface contacts 91. indeed, these constitute robust connection elements, compact and compatible with the standards practiced in microelectronics. In addition, such a base, as well as the multiplier, are completely opaque to light.

As we have just seen, such a compact multiplier structure can be simply placed between a porthole carrying a photocathode and a signal extracting base.

ADVANTAGES OF THE INVENTION

• il supprime tous les éléments de maintien et de centrage des plaques métalliques composant les étages multiplicateurs dans les procédés antérieurs ;
• il supprime tous les éléments encombrants dévolus à la polarisation des étages ;
• il supprime l'enveloppe, en verre ou en métal, qui a pour unique fonction de maintenir le vide ;
• il élimine tous les problèmes de dilatation différentielle entre les parties conductrices et isolantes qui minent et souvent condamnent l'herméticité des enceintes ;
• il offre un objet constitué d'un matériau de qualité que sont les céramiques, en particulier vis-à-vis de l'ultravide ;
• il offre du point de vue mécanique des précisions et des états de surface excellents ;
• il offre des possibilités dimensionnelles importantes et donc une multiplicité importante vis-à-vis du nombre des canaux ;
• il offre la possibilité de compacter un nombre important d'étages sans entraîner un surcoût notable de la fabrication.

The manufacturing method according to the invention therefore provides a compact and autonomous object, both from the mechanical point of view and from the empty point of view as from the electrical point of view. Consequently :

• it removes all the elements for holding and centering the metal plates making up the multiplier stages in the previous processes;
• it removes all the bulky elements devolved to the polarization of the stages;
• it removes the envelope, glass or metal, which has the sole function of maintaining the vacuum;
• it eliminates all the problems of differential expansion between the conductive and insulating parts which undermine and often condemn the hermeticity of the enclosures;
• it offers an object made of a quality material such as ceramics, in particular with respect to the ultrahigh vacuum;
• from the mechanical point of view, it offers excellent precision and surface conditions;
• it offers significant dimensional possibilities and therefore a significant multiplicity with respect to the number of channels;
• it offers the possibility of compacting a large number of stages without incurring a significant additional cost of manufacturing.

The manufactured object behaves like a component to be inserted in an instrumental chain free from any protection against the ambient atmosphere.

• l'activation des matrices pour augmenter l'émission secondaire peut être faite indépendamment de l'élaboration de la photocathode, de l'assemblage final puis du scellement du tube ;
• le contrôle du gain de chaque canal peut être pratiqué avant l'assemblage avec le culot de sortie, afin de n'associer que des composants aux performances reconnues.

In the context of the application of the invention to the production of multi-channel photomultipliers, there are several advantages for manufacturers:

• the activation of the matrices to increase the secondary emission can be done independently of the development of the photocathode, the final assembly and then the sealing of the tube;
• the gain control of each channel can be practiced before assembly with the output base, in order to associate only components with recognized performance.

The final assembly is carried out by the transfer technique which allows the choice of the type of porthole and photocathode, as well as the level of its emissivity before the final sealing of the tube.

This separation of functions allows the production of several tubes at the same time and reduces the failure rate during manufacture.

• la mise en oeuvre de ce photomultiplicateur multivoies consiste simplement à établir les potentiels de la cathode et la masse aux extrémités du tube ;
• la juxtaposition des tubes permet de couvrir de grandes surfaces photosensibles tout en minimisant les zones mortes ;
• la sortie des signaux n'interfère pas avec les alimentations haute tension des tubes et permet de réaliser un plancher électronique homogène pour leur acquisition ;
• le montage ainsi obtenu est très compact en hauteur, environ 15 à 20 mm, selon le nombre d'étages.

In the context of the use of these photomultipliers, users also find the following advantages:

• the implementation of this multi-channel photomultiplier simply consists in establishing the potentials of the cathode and the mass at the ends of the tube;
• the juxtaposition of the tubes makes it possible to cover large photosensitive surfaces while minimizing the dead zones;
• the signal output does not interfere with the high voltage power supplies of the tubes and makes it possible to produce a homogeneous electronic floor for their acquisition;
• the assembly thus obtained is very compact in height, approximately 15 to 20 mm, depending on the number of stages.

The multiplier structure according to the invention is not limited to its application already described to photomultipliers.

Without wanting to draw up an exhaustive list of potential applications, where this component can bring about the notable improvements already mentioned, we will find in the list above the composition of the assemblies satisfying the corresponding explanations.

In the context of a multi-channel light intensifier, the initial source of particles is a photocathode, the ceramic multiplier has a permanent polarization of the stages and the receiver is an internal phosphorescent screen associated with a battery of photodetectors or with a charge transfer device.

In the application to a detector for mass spectrometry, the source is a target bombarded by ions and providing secondary electrons, the ceramic multiplier has a permanent polarization of these stages, the receiver consists of output electrodes associated with operating electronics.

For the analysis of surfaces, dosimetry by exo-emission, the source is a surface or a deposit on a surface which provides a spontaneous or stimulated electronic exo-emission, we find the ceramic multiplier with its permanent polarization of the stages and output electrodes in connection with operating electronics.

For the measurement and control of vacuum and ultra-vacuum, the source comes from an excitation of the molecules and residual atoms of a vacuum enclosure, the ceramic multiplier has a permanent polarization of the stages associated with a magnetic field. We always use output electrodes with operating electronics.

In the context of the temporal and analog correlation of events, the source is one of the aforementioned sources, the multiplier is ceramic with a conditional supply of the stages. As for the output, it consists of electrodes each associated with operating electronics.

Finally, for increasing the brightness of the electronic injectors, one of the aforementioned sources is used, the ceramic multiplier with the permanent polarization of the stages and an electronic optic to adapt the transfer of the electronic flux to the electronic optical output stage.

So far, our purpose has been to involve the walls of the cavities as targets for increasing the electronic population and by using the properties of electronic optics imposed by the shape and arrangement of these same metallic cavities.

If we now eliminate the role of target filled by the walls by preventing the electrons from hitting them, these suitably sized and centered cavities behave like so many juxtaposed electrostatic lenses. This ceramic structure becomes an "electrostatic multilens" benefiting from all the technological advantages described above, and conditioning the electrons so that they present themselves optimally at the input of the following electrostatic optics.

Claims (11)

Compact electron multiplier structure by secondary emission having a plurality of multiplier channels (43), characterized in that it consists of a compact, waterproof, ceramic insulating block, in which are distributed, according to three dimensions, cavities (21, 31, 33, 34, 35, 37, 41) with conductive walls formed of a conductive deposit (28), suitably activated and connected together by a connecting duct (63) allowing the transit of the amplified flow d electrons, as well as polarization means of these cavities. Multiplier structure (94) according to claim 1, characterized in that it results from a high temperature sintering of a stack of raw ceramic plates (or sheets) (51 to 56) of which each plate has been previously perforated and machined to create connection conduits (60) and cavities (21, 31, 33, 34, 35, 37, 41), the polarization means being constituted by conductive walls on the surface of the cavities and conductive tracks (24 ) on a surface (59) of each ceramic plate to connect each cavity to external lateral electrical contacts (23). Structure according to claim 1 or 2, characterized in that the cavities (21, 31, 33, 34, 35, 37, 41) are spatially distributed in three dimensions, in particular for the cavities (21, 31) of the same channel (43). Structure according to claim 3, characterized in that the outlet electrode (96) is arranged on several outlet faces (45, 46, 47) where on each of them terminates at least one channel (43). Structure according to any one of Claims 1 to 4, characterized in that several of the channels have at least one point of intersection, that is to say that they communicate with each other. Structure according to any one of Claims 1 to 5, characterized in that at least one channel is subdivided into at least two branches of channels (32). Structure according to any one of claims 2 to 6, characterized in that at least two channels come together. Structure according to any one of Claims 2 to 7, characterized in that several successive cavities (41) are polarized at the same voltage by being connected to the same lateral contact (23) to form a multicell multiplier stage (40). Photomultiplier comprising a multiplier structure according to at least one of claims 1 to 8, and - a photocathode (92) arranged at a first end of each channel to receive the light pulses and transform them into electronic pulses in said channels (43); - at least one output electrode (96) for picking up the amplified pulses arranged at the second end of each channel (43); - a base (98),
also consisting of ceramic plates coated with suitably arranged electroemissive conductive layers. Method for manufacturing an electron multiplier structure according to any one of Claims 2 to 8, characterized in that it comprises the following steps: - Machining of ceramic plates (51, 52, 53, 54, 55, 56) in order to form the cavities (21, 31, 33, 34, 35, 37, 41) and the channels (43); - Inking with conductive ink the areas intended to form the cavities and the conductive tracks (24) connecting them together and to a lateral external contact (23); - stacking of the plates thus prepared; - baking the stack; - deposition on the conductive areas of the cavities of materials capable of generating, after activation, a high secondary emission; - deposit on the external contacts (23) of metals ensuring excellent ohmic contact; - activation of the multiplying structure by physico-chemical processes. Compact structure for spatial and energetic conditioning of electrons, formed of several channels each consisting of a succession of electronically isolated conductive cavities and each brought to a polarization potential determined by polarization means, consisting of a compact, insulating block, ceramic, in which are located embedded in the cavities formed by a conductive deposit and connected by connecting conduits, allowing the channels thus formed to condition the flow of electrons, as well as the means for polarizing these cavities.

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