PLATE ELECTRODE WITH MODULABLE SURFACE RESISTIVITY AND DETECTORS BASED THEREOF

Abstract

Resistive plate electrode (110, 120; 210, 220; 310, 320) with modulable surface resistivity comprising a supporting plate (130; 230; 330) coupled to a layer (131; 231; 331) of polymer material on which a DLC layer (135; 235; 335) is deposited that is connected to a connection assembly (145, 245, 345) configured to be connected to a high voltage power supply.

Claims

1. A resistive plate electrode comprising a supporting plate coupled to a layer of polymer material on which a DLC, Diamond Like Carbon, layer is deposited that is connected to a connection assembly configured to be connected to a high voltage power supply, wherein the resistive plate electrode has a surface resistivity that depends on varying values of one or more deposition parameters of the DLC layer.

2. (canceled)

3. The resistive plate electrode according to claim 1 having a surface resistivity ranging from 0.1 to 10 GΩ/square.

4. The resistive plate electrode according to claim 1, wherein the layer of polymer material comprises a polyimide foil.

5. The resistive plate electrode according to claim 1, wherein the supporting plate comprises glass fibres reinforced epoxy resin.

6. (canceled)

7. The resistive plate electrode according to claim 1, wherein the connection assembly comprises conductive elements that are connected to at least one perimetral edge of the DLC layer.

8. The resistive plate electrode according to claim 1, wherein the connection assembly comprises a conductive grid made on a free surface of the DLC layer.

9. The resistive plate electrode according to claim 8, wherein the conductive grid is an array of conductive strips that are parallel each other.

10. The resistive plate electrode according to claim 9, said parallel conductive strips having a width in the range of 0.05 mm-0.2 mm and a pitch in the range of centimetre.

11. The resistive plate electrode according to claim 1, wherein the DLC layer is connected to the connection assembly by means of a matrix of metalized vias passing through the supporting plate and the layer of polyimide, the connection assembly comprising conductive elements located on the surface of supporting plate that is opposed to the surface on which the DLC layer is deposited.

12. The resistive plate electrode according to claim 11, further comprising an additional layer of polymer material on which an additional DLC layer is deposited that is connected to said DLC layer by means of an additional matrix of vias.

13. A resistive plate electrode gas detector comprising a first resistive plate electrode and a second resistive plate electrode that are configured to be biased through an high voltage power supply and each one is configured to be connected to a front-end electronics, wherein the first and the second resistive plate electrode are coupled parallel each other so that the resistive surfaces of each of them are faced each other defining a gas gap configured to contain gas, wherein the first and the second resistive plate electrode are each one a resistive plate electrode comprising a supporting plate coupled to a layer of polymer material on which a DLC layer is deposited that is connected to a connection assembly configured to be connected to a high voltage power supply, wherein the resistive plate electrode has a surface resistivity that is modulable on varying values of one or more deposition parameters of the DLC layer.

14. The resistive plate electrode gas detector according to claim 13, comprising insulating spacers inside the gap configured to preserve the scale of the gas gap and avoid discharge occurrences inside the gas gap.

15. The resistive plate electrode gas detector according to claim 13, wherein each of said first and second resistive plate electrode is coupled to a readout printed circuit board on which readout conductive strips connected to the front-end electronics are fixed.

16. The resistive plate electrode according to claim 10, wherein said parallel conductive strips have a pitch ranging from 5 to 10 cm.

17. The resistive plate electrode according to claim 1, wherein the supporting plate is semi-rigid, in other words flexible.

18. The resistive plate electrode according to claim 1, wherein the supporting plate comprises plastic materials.

Description

[0036] The present invention will be now described, by way of illustration and not by way of limitation, according to its preferred embodiments, by particularly referring to the Figures of the annexed drawings, in which:

[0037] FIG. 1 shows a sectional structure of a first embodiment of a plate electrode detector with modulable surface resistivity according to the invention;

[0038] FIG. 2 shows a sectional structure of a second embodiment of a plate electrode detector with modulable surface resistivity according to the invention;

[0039] FIG. 3 is a sectional structure of a third embodiment of a plate electrode detector with modulable surface resistivity according to the invention.

[0040] In the Figures, identical reference numerals will be used for alike elements.

[0041] With reference to FIG. 1, a first embodiment of the detector according to the invention is described below, first embodiment is based on single resistive layer electrodes with modulable surface resistivity ranging from 0.1 to 10 GΩ/square, optionally ranging from 0.5 to 10 GΩ/square, more optionally equal to 1 GΩ/square as better described below.

[0042] The detector 100 of FIG. 1 comprises a first resistive plate electrode 110 and a second resistive plate electrode 120 each comprising a glass fibre reinforced epoxy resin supporting plate 130, such as for example Vetronite® FR4, coupled by adhesive to a layer 131 of polymer material, such as for example polyimide. Vetronite® is a trademark for laminates made of glass fibres bonding with an appropriate resin system sold by Von Roll Isola France SA company, while FR4 is a standard defined by the NEMA (National Electrical Manufacturers Association) in NEMA STANDARDS PUBLICATION NO. Li 1-1998 for a glass-reinforced epoxy resin laminate material. In particular, “FR” stands for flame retardant, and FR-4 indicates that the flammability of such material is in compliance with the UL (Underwriters Laboratories) standard 94V-0.

[0043] A data sheet for Vetronite® FR4 is currently available at https://pdf.directindustry.com/pdf/von-roll/composites/12485-350035.html and at https://www.aikolon.fi/site/assets/files/2173/composites_en.pdf and is hereby incorporated by reference in its entirety.

[0044] A modulable resistivity DLC layer 135 is deposited on the free side of the layer 131, i.e., on the face opposite the supporting plate 130, thus making the respective electrode (110 or 120) a resistive plate electrode with modulable surface resistivity. In other words, the surface resistivity of the resistive plate electrodes is given by the resistivity of their respective DLC layers.

[0045] In other embodiments of the resistive plate electrode according to the invention, the supporting plate 130 is coupled to the polyimide layer 131 using techniques other than gluing.

[0046] The first and second resistive plate electrodes 110, 120 with modulable surface resistivity are coupled parallel to each other on a rigid support frame 140 placed at detector perimeter, so that the surfaces of the respective DLC layers 135, which do not face the respective supporting plates 130 (i.e. the supporting plates 130 of the respective resistive plate electrode 110 or 120), face each other and are kept at a fixed distance forming a gap 137 configured to contain gas.

[0047] In the preferred embodiment of the invention, the support frame 140 comprises glass fibre reinforced epoxy resin, such as for example Vetronite® FR4.

[0048] The surfaces of the DLC layers 135 which face the gas gap are suitably biased by means of a connection assembly 145 to connect to a high voltage power supply 150.

[0049] When the detector 100 is in operation, the process of multiplying the primary ionization, produced by the passage of an ionizing particle, takes place in the gas gap 137 delimited by the layers 135 of DLC of the resistive plate electrodes 110, 120 connected to the connection assembly 145 at the high voltage power supply 150. In other words, the resistive plate electrodes with modulable surface resistivity 110, 120 are the active part of the amplification stage of the detector 100.

[0050] The connection assembly 145 is perimeter, i.e., it comprises conductive elements which are connected to at least one perimeter edge of the DLC layer 135 of each first and second resistive plate electrodes 110, 120 with modulable surface resistivity. In other words, the connection assembly 145 is positioned at the edges of active areas of the detector 100. The connection assembly 145 operates as a system for evacuating the current generated by the passage of the radiation in the gas gap 137.

[0051] As above mentioned, it can be shown that for the surface resistivity of the DLC layer which guarantees the proper functioning of the detector 100, intended as a compromise between the effective self-quenching of discharges (detector stability) and an acceptable rate capability, of the order of about 1 kHz/cm.sup.2, it must be such that the resistance seen by the current impulse generated by the passage of the ionizing particle in the gas gap 137 is preferably of the order of 1 GΩ. Much lower surface resistivities, for example less than 100 MΩ, would lead to instability of the detector (which would go into continuous discharge), while higher values, for example 10 GΩ, would necessarily lead to a more limited rate capability.

[0052] The surface of the supporting plate 130 which is not coated by the DLC layer 135 of each resistive plate electrode 110, 120 is coupled to a readout printed circuit 160 on which readout conductive strips 165 connected to the front-end electronics 170 are fixed.

[0053] In other embodiments of the detector according to the invention, the supporting plate 130 can itself operate as an external readout electrode, whereby the conductive readout strips 165 are fixed directly on the supporting plate 130, in particular on the surface of the supporting plate 130 which is not coated by layer 135.

[0054] In the case of detectors according to the invention having large size, for example greater than 10×10 cm.sup.2, optionally greater than 50×50 cm.sup.2, operated at high radiation fluxes, i.e. greater than or equal to 10 kHz/cm.sup.2, the perimeter connection of the first embodiment of the detector described above would not allow the correct operation of the detector. In fact, at the same surface resistivity, the resistance experienced by the single current pulse diverges with the size of the detector. The detector could therefore not sustain high radiation rates. For this reason, the inventors have designed a second embodiment of the detector according to the invention, illustrated in FIG. 2, having a current evacuation scheme, i.e., a connection to the high voltage power supply system, faster and slightly more sophisticated, compared to that of the perimeter connection.

[0055] With reference to FIG. 2, the detector 200 comprises a first and a second resistive plate electrodes 210 and 220 coupled parallel to each other on a support frame 240, each comprising a supporting plate 230 coupled to a layer 231 of polymer material, such as for example polyimide, on which a modulable resistivity DLC layer 235 is deposited.

[0056] The detector 200 is like the detector 100 of the first embodiment according to the invention wherein, however, the connection assembly 245 to connect to the high voltage power supply 250 also comprises, in addition to the conductive elements connected to at least one perimeter edge of the DLC layer 235, a thin conductive grid 247 which is built on the free surface of the DLC layer 235 of each first and second resistive plate electrode 210, 220. In other words, a thin conductive grid 247 is built on the surface of the DLC layer 235 which faces on the gas gap 237 of each first and second resistive plate electrodes 210, 220. The conductive grid 247, therefore, operates as a distribution network for the high voltage.

[0057] Also in this case, the resistive plate electrodes 210, 220 with modulable surface resistivity are the active part of the amplification stage of the detector 200.

[0058] The conductive grid 247 is made with an arrangement of thin conductive strips parallel to each other, connected to the outside of the active area to the high voltage power supply. The width/of the strips is between 0.05 mm and 0.2 mm, optionally equal to 0.1 mm, while the pitch p between the strips, i.e., the grid pitch (i.e. the distance between two adjacent parallel conductive strips), is of the order of a few cm, to be adjusted and adapted according to the required high rate performances, optionally included in the range from 5 to 10 cm.

[0059] The connection assembly 245, comprising the conductive grid 247, also operates as a current evacuation system.

[0060] The arrangement of the electrodes 210, 220 in the detector 200 is such that the grids 247 of the first and second resistive plate electrodes 210, 220 are specular with respect to a plane parallel to the electrodes and passing through the gap 237.

[0061] In further embodiments of the present invention, the grid can be made with different arrangements of the conductive strips with respect to the arrangement described above.

[0062] The conductive grid 247 can be made with industrial standard screen-printing techniques of conductive pastes. In further embodiments, on the DLC surface facing the gas gap 237, a thin metal layer is previously deposited, optionally with thick from 4 to 5 micrometers, whereby the conductive grid is made by chemical etching on metal. In a preferred embodiment of the invention, the metal is copper and the DLC+Cu layer is made by sputtering technology.

[0063] In correspondence of the thin conductive grid 247, inside the gas gap 237, insulating spacers 248 are made by standard technologies of the printed circuit industry, for example with suitable commercial photo-resist. The role of the insulating spacers 248 is twofold: keeping the size of the gap 237 and the isolation of the grid 247, to avoid discharge phenomena within the gas gap 237. The introduced dead zone, considering a width of each insulating spacer 248 on the order from 2 to 3 mm would be less than or at most of the order of 1%. By width we mean the size of the spacer that is parallel to the resistive plate electrode.

[0064] The surface of the plate 230 which is not coated by the DLC layer 235 of each resistive plate electrode 210, 220 is coupled to a readout printed circuit 260 on which conductive strips 265 are fixed that are connected to the front-end electronics 270.

[0065] In other embodiments of the detector according to the invention, the supporting plate 230 can operate as an external reading electrode, whereby the conductive readout strips 265 are fixed directly on the plate 230, in particular on the surface of the plate 230 which is not coated by the layer 235.

[0066] A further embodiment of the present invention, designed to operate with large surfaces and high radiation fluxes, i.e., greater than or equal to 10 kHz/cm.sup.2, is described below with reference to the structure shown in FIG. 3.

[0067] In this third embodiment, like the second embodiment, the resistive plate electrodes 310 and 320 with modulable surface resistivity comprise a resistive double-layer in which two DLC layers are electrically interconnected.

[0068] In particular, the detector 300 comprises a first resistive plate electrode 310 and a second resistive plate electrode 320 each comprising a supporting plate 330 on which a first layer 331 of polymer material, such as for example polyimide, is glued. A first modulable resistivity DLC layer 335 is deposited on the free side of the layer 331, i.e., on the side of the first polyimide layer 331 which is opposite the supporting plate 330. A second polyimide layer 332 is coupled to the first DLC layer 335. In other words, the second polyimide layer 332 is directly coupled to the first DLC layer 335.

[0069] A second modulable resistivity DLC layer 336 is deposited on the free side of the second layer 332, i.e., on the side which is opposite the first polyimide layer 331, in other words opposite the first DLC layer 335.

[0070] The first and second resistive plate electrodes 310, 320 with modulable surface resistivity are coupled parallel to each other on a support frame arranged at the detector perimeter, not shown in the figure, so that the surfaces of the respective second DLC layers 336 which are not facing the respective plates 330, face each other and are kept at a fixed distance forming a gap 337 configured to contain gas.

[0071] In further embodiments, the support frame can be semi-rigid.

[0072] The first DLC layer 335 is connected to the connection assembly 345 to connect to the high voltage power supply 350 through a first conductive matrix 381 of interconnected metallized vias that go through both the first supporting plate 330 and the first layer 331 of polyimide.

[0073] The connection assembly 345 comprises conductive elements positioned on the surface of the supporting plate 330 facing the readout printed circuit 360, in other words on the surface opposite the surface on which the first DLC layer 335 is deposited. These conductive elements of the connection assembly 345 are in electric contact with the vias of the first conductive matrix 381.

[0074] The second DLC layer 336 is, in turn, electrically interconnected to the first DLC layer 335, by means of a second conductive matrix 382 of interconnected metallized vias.

[0075] The vias of the first and second conductive matrix 381, 382, therefore, operate as a distribution network for high voltage.

[0076] The connection assembly 345 and the vias matrices 381, 382 have the dual function of providing a way of rapid evacuation of the current generated by the passage of the radiation in the gas gap 337 and of polarization of the first DLC layers 335 and of the second DLC layers 336 which, being in direct contact with the gas gap, operate as a resistive plate electrode of the detector.

[0077] The pitch of the vias is of the order of a few cm and allows to achieve rate capabilities greater than 10 kHz/cm.sup.2, while keeping a very high detector stability. In correspondence with the vias of the second conductive matrix 382, inside the gas gap 337 of the detector, photo-resist insulating spacers 348 are built which have the function of keeping the size of the gap and of isolating the grid, in order to avoid discharge phenomena within the gas gap. Optionally, the photo-resist insulating spacers 348 have the shape of discs with a diameter on the order from 2 to 3 mm thus introducing a negligible dead zone, as described above.

[0078] The arrangement of the electrodes 310, 320 in detector 300 is such that the first and second matrices 381, 382 of the first and second resistive plate electrodes 310, 320 are specular with respect to a plane being parallel to the electrodes and passing through the gap 337.

[0079] The surface of the plate 330 which is not coated by the DLC layer 335 of each resistive plate electrode 310, 320 is coupled to a readout printed circuit 360 on which readout conductive strips 365 are fixed connected to the front-end electronics 370.

[0080] Also in this case, the resistive plate electrodes 310, 320 with modulable surface resistivity are the active part of the amplification stage of the detector 300.

[0081] In a further embodiment of a resistive plate electrode according to the invention, the resistive plate electrode has a single conductive layer, similarly to the resistive plate electrode 110 (120) of the first embodiment of the detector 100 according to the invention described above and shown in FIG. 1, wherein the connection of the DLC layer to the connection assembly is made by means of a conductive matrix of metallized vias similarly to the connection by means of the first conductive matrix 381 of metallized vias of the first DLC layer 335 to the connection assembly 345 of the third embodiment of detector 300 according to the invention described above and shown in FIG. 3

[0082] In still further embodiments of the invention, the resistive plate electrode with modulable surface resistivity is a multi-layer electrode, i.e., comprising a plurality of resistive layers wherein the plurality of DLC layers is electrically interconnected by means of a plurality of conductive matrices of metallized vias.

[0083] In other embodiments of the invention, the supporting plate and the readout printed circuit are semi-rigid, in other words flexible, therefore configured to make cylindrical detectors. For example, the supporting plate and the readout printed circuit can comprise plastic materials, such as for example polyimide.

[0084] For the purposes of the present invention, a resistive plate electrode means a resistive electrode (110,120; 210,220; 310,320) whose surface, configured to face the gas gap, is flat and homogeneous, that is, it is free of discontinuity elements or microstructures.

[0085] The detector according to the invention is made using SBU procedures, Sequential Build Up, that are standard in the rigid-flexible printed circuit industry. In particular, the resistive plate electrode of the present invention is made with industrial techniques of DLC sputtering on polyimide layers.

[0086] The insulating spacers defining the gas gap within the detector are an advantageous mechanical component for large area detectors and can comprise materials and by technologies normally used in the processing of printed circuits.

[0087] The preferred embodiments of this invention have been described and a number of variations have been suggested hereinbefore, but it should be understood that those skilled in the art can make other variations and changes without so departing from the scope of protection thereof, as defined by the attached claims.