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Title:
DEVICE FOR THE EXTRACTION OF ELECTRONS IN FIELD EMISSION SYSTEMS AND METHOD TO FORM THE DEVICE
Document Type and Number:
WIPO Patent Application WO/2016/024878
Kind Code:
A1
Abstract:
The present invention relates to a device (1) for the extraction of electrons in field emission systems comprising a cathode (2) as electron source, a dielectric grid layer (3) and a conduction layer (4). The device (1) is in the form of a sandwich layered structure with cathode (2), grid layer (3) and conduction layer (4) arranged in the form of a stack. The invention further relates to a method to form the device (1) comprising steps forming the cathode (2) as electron source on one side of a dielectric substrate, forming the dielectric grid layer (3) within the substrate and forming the conduction layer (4) on the opposite side to the cathode (2) within the substrate.

Inventors:
BONDARENKO, Taras Vladimirovich (Moskvorech'e st, 2/1 20, Moscow 2, 115522, RU)
BOTYACHKOVA, Alexandra Igorevna (Moscvorechie str, #2-1-182Moscow, 2, 115522, RU)
KARPINSKIY, Gennadiy Gennadievich (Moscvorechie str, #2-1-177Moscow, 2, 115522, RU)
POLIKHOV, Stepan Alexandrovich (Mira 2, appt. 61Moscow, 5, 140105, RU)
Application Number:
RU2014/000607
Publication Date:
February 18, 2016
Filing Date:
August 13, 2014
Export Citation:
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Assignee:
SIEMENS AKTIENGESELLSCHAFT (Wittelsbacherplatz 2, Munchen, 80333, DE)
International Classes:
H01J3/02; H01J9/48; H01J23/06; H01J29/46; H01J29/48; H01J35/04
Foreign References:
US20030011292A12003-01-16
US5821679A1998-10-13
JP2000323011A2000-11-24
KR100934838B12009-12-31
US5601966A1997-02-11
US6534923B22003-03-18
US6534923B22003-03-18
US20040071876A12004-04-15
Other References:
KRIVCHENKO: "Investigations of diamond films doped by Boron", JOURNAL OF TECHNICAL PHYSICS, vol. 77, no. 11, pages 83 - 87
R. WALKER; S. PRAWER: "Formation of buried p-type conducting layers in diamond", APPL. PHYS. LETT., vol. 71, 1997, pages 11
Attorney, Agent or Firm:
MITS, Alexander Vladimirovich et al. (LAW FIRM "GORODISSKY & PARTNERS" LTD, ul. B. Spasskaya 25-, Moscow 0, 12901, RU)
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Claims:
Claims

1. Device (1) for the extraction of electrons in field emission systems comprising a cathode (2) as electron source, a dielectric grid layer (3) and a conduction layer (4) , characterized in that the device (1) is in the form of a sandwich layered structure with cathode (2) , grid layer (3) and conduction layer (4) arranged in the form of a stack. 2. Device (1) according to claim 1, characterized in that the grid layer (3) is arranged in-between the cathode (2) and the conduction layer (4) , particularly with the grid layer (3) in direct mechanical contact with the cathode (2) and conduction layer (4) material.

3. Device (1) according to any one of claims 1 or 2, characterized in that the cathode (2) is in a disk like form, particularly in form of a solid layer body without recesses and/or holes, and/or the grid layer (3) is in form of a hon- eycomb and/or the conduction layer (4) is in form of a honeycomb, particularly with the conduction layer (4) in a superimposed congruent form to the grid layer (3) , particularly with grid walls in the range of 11 Micrometer thick and/or with apertures between grid walls in the range of 70 Microme- ter in diameter.

4. Device (1) according to any one of claims 1 to 3, characterized in that the thickness of the device is in the range of 70 Micrometer, and/or the cathode (2) thickness is in the range of some Micrometer, and/or the conduction layer (4) thickness is in the range of 10 Micrometer, particularly with a buried conduction layer (4) arranged in the depth below the surface of the grid layer (3) in the range of 10 Micrometer deep .

5. Device (1) according to any one of claims 1 to 3, characterized in that the dielectric grid layer (3) and the conduction layer (4) are formed from one solid body, with the con- duction layer (4) formed by doping, particularly doping with Boron, and/or with the cathode (2) formed as deposited layer on the dielectric grid layer (3) substrate, particularly without holes.

6. Device (1) according to any one of claims 1 to 5, characterized in that the dielectric grid layer (3) is made of and/or comprises diamond material, and/or the conduction layer (4) is made of and/or comprise diamond material doped with a dopant, particularly with Boron, particularly with a dopant concentration in the range of metallic conductivity and/or with a concentration in the range or higher than 1020 cm"3, and/or the cathode (2) is made of and/or comprises a carbon layer, particularly a deposited amorphous carbon layer.

7. Device (1) according to any one of claims 1 to 6, characterized in that the cathode (2) is formed in a substrate frame (5) , particularly in ring form surrounding the cathode (2) .

8. Device (1) according to any one of claims 1 to 6, characterized in that a dielectric layer (3') is arranged on top of the conduction layer (4) opposite to the dielectric grid layer (3) , particularly formed from the same material as the di- electric grid layer (3) .

9. Method to form a device (1) for the extraction of electrons in field emission systems, particularly a device (1) according to any one of claims 1 to 8 , comprising steps

- forming a cathode (2) as electron source on one side of an dielectric substrate

forming a dielectric grid layer (3) within the substrate forming a conduction layer (4) on the opposite side to the cathode (2) within the substrate.

10. Method according to claim 9, characterized in that forming the cathode (2) , grid layer (3) and/or conduction layer (4) on the same substrate, particularly on a diamond substrate .

11. Method according to any one of claims 9 or 10, character- ized in that forming the cathode (2) by depositing a carbon layer, particularly amorphous carbon on the substrate, or forming the cathode (2) by doping a layer on one side of the substrate with a dopant, particularly Boron in a concentration of metallic conductivity.

12. Method according to any one of claims 9 to 11, characterized in that forming a grid structure, particularly a honeycomb grid structure by laser drilling on one side of the substrate, particularly with holes ending on one side at the cathode (2) and/or with holes formed after the formation of the cathode (2) .

13. Method according to any one of claims 9 to 12, characterized in that forming the conduction layer (4) on top of the substrate on the opposite side of the cathode (2) and/or within the substrate with dielectric grid layer (3) material in-between the cathode (2) and the conduction layer (4) , particularly forming the conduction layer by doping with a dopant, particularly Boron in a concentration of metallic conductivity, particularly by Ion implantation doping.

Description:
Description

Device for the extraction of electrons in field emission systems and method to form the device

The present invention relates to a device for the extraction of electrons in field emission systems and to a method to form the device, comprising a cathode as electron source, a dielectric grid layer and a conduction layer.

Field emission is a well known technology, with directional emission of electrons from the emitting surface induced by a high electrostatic field. This electrical field is referred as so called extraction field. The electron source is the cathode, also referred as cold cathode. Field emission electron sources are used as electron emitters in various applications like healthcare, for example in x-ray tubes, communications, for example in RF klystrons, industry, for example in XRD tubes, and electronics, for example in flat panel dis- plays. They are an alternative to thermionic electron sources due to the lower initial energy spread of electrons, extremely fast electron gating and extended lifetime due to the fact that heating is not required. Compared to thermionic cathodes, field emission cathodes as high power electron sources have a high degradation rate of emission material and a high damage rate of the extraction grid, which is required to generate a high extraction voltage. This reduces the lifetime to a short period of time.

In order to obtain high electrical fields at low voltages between the emitting surface and the extraction electrode the distance between both has to be very small, in the range of 50 to 100 μπι. The emission current is proportional to the ex- traction voltage and the geometrical transparency of the extraction electrode. As known from the state of the art, see for example US 5601966, electrodes can be made in form of wired grids. When electrodes hit the wires, their energy is converted into heat of the wires, leading to thermal expansion of wires. The wires expand towards the emission surface. Since the distance between the emission surface and wires decreases, the electrical field between both increases. Finally a breakdown voltage is achieved which leads to electrical discharge and physical damage of wires.

From US6534923 a dielectric mask placed between emission surface and extraction grid is known. The deformation of the ex- traction grid towards the emission surface is eliminated by the dielectric mask. Heat impact of electrons on the grid is reduced by dissipated electrons in the mask, since less electrons reach and hit the grid. From US6534923 an extraction grid is known, physically bonded to the dielectric substrate by soldering or diffusion. Since the extraction grid and dielectric substrate are heated by electrons their temperature is constantly changing. Materials of the grid and dielectric substrate are different with different thermal expansion rates, leading to a damage of bonding spots and peeling of the grid from the mask. This lowers the lifetime and reliability of the electron source.

From the state of the art, for example US20040071876 , a field emission cathode is known based particularly on carbon mate- rial deposited on a substrate. An electron beam is extracted from the surface of the cathode using a high electrical field provided by the extracting electrode. The extracting electrode is made as a part of a dielectric mask placed on the cathode surface. In the described embodiment the dielectric mask is placed directly on the cathode surface and an extracting grid is provided by doping a top layer of the dielectric mask.

Field emission cathodes known from the state of the art, for example based on carbon material deposited on a substrate, require a high field magnitude to extract electrons, generating high extracting currents directly under the grid. High currents induce a high temperature within the grid. Electrons hitting the mask with high energy lead to a heating up of the mask, and above a temperature level the structure is damaged or destroyed. A low hardness reduces further the reliability and lifetime of the cathode.

A dielectric material known from the state of the art is diamond. By doping diamond with for example Boron exceeding a concentration of 10 20 cm "3 it is possible to achieve conductive layers with metallic conductivity, as is known from the state of the art, for example from "Investigations of diamond films doped by Boron", Journal of Technical Physics, V.

Krivchenko et.al., Vol. 77, issue 11, page 83 to 87. A conductive layer with a thickness of e.g. 10 pm in diamond material in a desired depth with a Boron concentration of e.g. 5 21 cm "3 is for example generated by high Ion implantation of Boron, as known from "Formation of buried p-type conducting layers in diamond", R. Walker, S. Prawer, Appl . Phys . Lett. 71 (11), 1997. Object of the present invention is to present a device for the extraction of electrons in field emission systems and a method to form a device to be used to extract electrons in field emission systems solving the above described problems. Particularly the object is to present a device with high lifetime, enabling to produce electrons with a high rate of yield, and with reduced heat production in the device.

The above objects are achieved by a device for the extraction of electrons in field emission systems according to claim 1 and by a method to form a device for the extraction of electrons in field emission systems, particularly a device as described before, according to claim 9.

Advantageous embodiments of the present invention are given in dependent claims. Features of the main claims can be combined with each other and with features of dependent claims, and features of dependent claims can be combined together. The device for the extraction of electrons in field emission systems according to the present invention comprises a cathode as electron source, a dielectric grid layer and a conduction layer. The device is in the form of a sandwich layered structure with cathode, grid layer and conduction layer arranged in the form of a stack.

The form of the device with layers arranged in stack form solves the problems described above. The grid layer prevents a decrease of distance between conduction layer and cathode even with increasing temperature. An expanding conduction layer during increase of temperature is prevented from approaching the cathode. This prevents an increase of emission voltage and a break down by electrical contact of elements of the conduction layer and the cathode. Electrons are produced with high rate of yield and with a reduced heat production in the device. The device lifetime is increased.

The grid layer can be arranged in-between the cathode and the conduction layer, particularly with the grid layer in direct mechanical contact with the cathode and conduction layer material. This leads to a device with stable form even at temperature changes, with stable emission voltage and electron production depending on the applied voltage between cathode and conduction layer.

The cathode can be in a disk like form, particularly in form of a solid layer body without recesses and/or holes. The grid layer can be in form of a honeycomb. The conduction layer can be in form of a honeycomb, particularly with the conduction layer in a superimposed congruent form to the grid layer. Grid walls can be in the range of 11 Micrometer thick and/or apertures between grid walls can be in the range of 70 Micrometer in diameter.

The particular form reduces the number of electrons absorbed by the dielectric material and conduction layer. This reduces the produced heat and temperature increase . A honeycomb structure, particularly with the described dimensions is mechanically stable and gives a high yield of electrons produced by the device . The thickness of the device can be in the range of 70 Micrometer. The cathode thickness can be in the range of some Micrometer. The conduction layer thickness can be in the range of 10 Micrometer, particularly with a buried conduction layer arranged in the depth below the surface of the grid layer in the range of 10 Micrometer deep. Advantages of this embodiment are according to the before mentioned advantages, particularly a mechanically stable device with a high yield of electrons produced. The dielectric grid layer and the conduction layer can be formed from one solid body, with the conduction layer formed by doping, particularly doping with Boron, and/or with the cathode formed as deposited layer on the dielectric grid layer substrate, particularly without holes. The layer system of conduction layer and grid layer formed from one solid body increases lifetime and mechanical stability, since stress in the material is reduced during thermal changes and bonding of different materials is avoided. A peeling off of a conduction layer from the dielectric layer is prevented.

The dielectric grid layer can be made of and/or can comprise diamond material . The conduction layer can be made of and/or can comprise diamond material doped with a dopant, particularly with Boron, particularly with a dopant concentration in the range of metallic conductivity and/or with a concentration in the range or higher than 10 20 cm "3 . The cathode can be made of and/or can comprise a carbon layer, particularly a deposited amorphous carbon layer. The use of materials like diamond and carbon increase reliability and lifetime of the device, combined with high possible yield of electron production. Diamond as material, particularly in honeycomb structure, is mechanical very stable, heat resistant and long lasting. Pure diamond is a good dielectric material and dop- ing of diamond can result in a good conduction layer. Carbon gives an electrode with good electrical properties like for example electron conductivity and heat conductivity. Diamond and carbon are well able to transfer waste heat to the envi- ronment, show similar properties like thermal coefficient of expansion and provide specific electrical properties for electrode and dielectric material, combined with high mechanical strength. The similar properties prevent layers to be peeled off from each other even at high temperature changes.

The cathode can be formed in a substrate frame, particularly in ring form surrounding the cathode. A substrate frame, particularly made from the same material like the dielectric layer, i.e. diamond can improve the mechanical stability of the cathode, particularly made of carbon.

A dielectric layer can be arranged on top of the conduction layer opposite to the dielectric grid layer, particularly formed from the same material as the dielectric grid layer and/or in the same form. This additional dielectric layer can act as a passivation layer, increasing the lifetime of the conduction layer and improving the electrical field for increased electron yield from the device. Electrons, which passed by the conduction layer are less attracted by it and extracted electrons passing by in the open space within the grid are less diverted. Fewer electrons are absorbed by the conduction layer, resulting in less heating of the conduction layer, increasing lifetime and electron yield. A Method to form a device for the extraction of electrons in field emission systems according to the present invention, particularly a device as described above, comprises steps

forming a cathode as electron source on one side of an dielectric substrate

- forming a dielectric grid layer within the substrate

forming a conduction layer on the opposite side to the cathode within the substrate. The described method produces a device with properties and advantages as described before in connection with the device for the extraction of electrons in field emission systems. The method can comprise further steps like forming the cathode, grid layer and/or conduction layer on the same substrate, particularly on a diamond substrate.

The method can comprise forming the cathode by depositing a carbon layer, particularly amorphous carbon on the substrate, or forming the cathode by doping a layer on one side of the substrate with a dopant, particularly Boron in a concentration of metallic conductivity. The method can comprise forming a grid structure, particularly a honeycomb grid structure by laser drilling on one side of the substrate, particularly with holes ending on one side at the cathode and/or with holes formed after the formation of the cathode.

The method can further comprise forming the conduction layer on top of the substrate on the opposite side of the cathode and/or within the substrate with dielectric grid layer material in-between the cathode and the conduction layer, partic- ularly forming the conduction layer by doping with a dopant, particularly Boron in a concentration of metallic conductivity, particularly by Ion implantation doping.

The advantages in connection with the described method to form a device for the extraction of electrons in field emission systems according to the present invention are similar to the previously, in connection with the device for the extraction of electrons in field emission systems described advantages and vice versa.

The present invention is further described hereinafter with reference to illustrated embodiments shown in the accompanying drawings, in which: illustrates in angular view a device 1 for the extraction of electrons in field emission systems according to the present invention in form of a sandwich layered, disk like structure, and shows in cross-sectional view along the electron beam 6 the device 1 as in FIG 1, but with a cathode 2 formed in a substrate frame 5 and with a dielectric layer 3 ' on top of the conduction layer 4.

In FIG 1 a device 1 for the extraction of electrons in field emission systems according to the present invention is shown. The device 1 is in form of a circular plate, i.e. disc like. The device 1 comprises a sandwich layered structure with cathode 2, grid layer 3 and conduction layer 4 arranged in the form of a stack. The cathode 2 is formed without recesses or holes, plate like for example by a carbon layer. Alternatively or additionally it can comprise or be formed of a dia- mond substrate, doped to be electrical conducting with metallic properties.

On one side, the top side of the cathode a dielectric grid layer 3 is arranged, for example in form of a honeycomb structure made of diamond material. The honeycomb structure can be formed for example by laser drilling of holes in a plate like diamond substrate. The holes end at the cathode 2 surface, with the cathode 2 forming a bottom plate of the holes .

The conduction layer 4 is formed on top of the grid layer 3, on the opposite side to the side with cathode 2 on the grid layer 3. The cathode 2 as solid bottom plate, on top with a honeycomb structure layer of dielectric material 3 and con- gruent on top of the dielectric grid layer 3 a conduction layer 4 with honeycomb structure form the device 1 as a sandwich, stacked structure. The conduction layer 4 can be formed by for example high energy Ion implantation of Boron into a diamond substrate surface, with a Boron concentration in the range of 10 20 cm "3 or above. The conduction layer 4 can have a thickness of 10 μπ\, with Boron concentration of e.g. 5 21 cm "3 . The layers 3 and 4 are formed in form of a faceted body with holes in form of hexagons .

In FIG 2 an alternative embodiment of device 1 according to the present invention is shown in cross-sectional view. The device 1 is as shown in and described in connection with FIG 1, except that the cathode 2 is formed in a substrate frame 5 and on top of the conduction layer 4 a dielectric layer 3' is arranged. The conduction layer 4 can be produced as a buried layer for example by high energy Ion implantation of Boron as described before for the top layer 4 in FIG 1. The conduction layer 4 thickness is for example in the range of 10 Micrometer, particularly with the conduction layer 4 arranged in the depth below the surface of the grid layer 3 in the range of 10 Micrometer deep. A frame 5 surrounds as a ring, for example made of diamond substrate, the cathode 2 for example made of an amorphous carbon layer. The frame 5 increases the mechanical stability.

In the embodiment of FIG 1 and in the embodiment of FIG 2, the cathode 2 can be produced by amorphous carbon deposited on a substrate, for example a diamond layer. A honeycomb structure can be produced afterwards by laser drilling holes from the opposite side of the substrate compared to the deposited carbon, drilling holes into the substrate down to the amorphous carbon layer, particularly without drilling the holes into the amorphous carbon layer.

Grid walls of the dielectric grid layer 3 and conduction layer 4 are for example in the range of 11 Micrometer thick. The apertures between grid walls are for example in the range of 70 Micrometer in diameter. The device 1 has for example a thickness in the range of 70 Micrometer. The cathode 2 thickness is for example in the range of some Micrometer. Alternatively the cathode 2 can be produced as described before in connection with the embodiment in FIG 1 by for example high energy Ion implantation of Boron as described before for the top layer 4.

A high voltage applied to the device 1 between the cathode 2 and conduction layer 4 induces the generation of electrons from the cathode material and the acceleration in direction of the extraction grid, i.e. conduction layer 4. An electron beam is formed, for example with electron movement in direction perpendicular to the surface of the cathode 2. The electrons pass by the grid layer 4 and in-between through the holes, and can be used as field emission electrons in various applications like healthcare, e.g. in x-ray tubes, communica- tions, e.g. in RF klystrons, industry, e.g. in XRD tubes, and electronics, e.g. in flat panel displays. A well defined, high energy electron beam with fixed aperture is produced. The dielectric grid layer 3 prevents elements of the conduction layer 4 to move in direction of the cathode 2 even dur- ing thermal heating by absorbed electrons in the material. A breakdown of the device 1 is prevented and a long lifetime achieved. A high electron yield, i.e. effective electron generation is achieved by the mechanical stable honeycomb structure with cylindrical holes with hexagonal base area. The holes in the structure increase transparency for electrons generated by the cathode 2.

Diamond as substrate and a honeycomb structure increase the reliability and mechanical stability of the device 1. There is a reduction of the cathode extraction field magnitude under the honeycomb structure due to the direct arrangement of the structure to the cathode surface, resulting in a reduction of the extracting current from the space directly under the conduction layer 4. The conduction layer 4 only emits electrons hitting the conduction layer 4, which is formed as a grid. The energy of electrons hitting the mask, i.e. conduction layer 4 and dielectric layer 3 is in the range of the starting energy of electrons leaving the cathode 2, particu- larly with energy in the range of eV or lower. These electrons do not lead to any significant heating of the mask and to a breakdown of its structure. There is an enhancement of the hardness of the device 1 compared to extracting elec- trodes based on metal layers deposited on classical dielectric mask surfaces like lithographic photo-resist, plastic or glass. The hexagonal holes array in layer 3 and 4 provide high geometrical transparency at high mechanical strength.

The above described features of embodiments according to the present invention can be combined with each other and/or can be combined with embodiments known from the state of the art . For example the thickness of layers 2, 3, 4 and the device 1 can be in different ranges. They can be up to Millimeter or in the range of Micrometer down to Nanometer. Additional layers can be on top of the device or on the bottom side, for example to increase mechanical stability or electrical properties. Further kinds of materials for the layers 2, 3, 3', 4 are possible, for example a lithographic photo-resist as layer 3'. Additional passivation layers like Oxides can be used to improve the electrical properties and yield of the device 1. Geometrical structures like cylindrical holes with circle or elliptical base can be used. The device can instead of being in a disc like shape have for example plate like shape with rectangular form.

Main advantages of the device 1 according to the present invention are a long lifetime, high electron yield and a well formed electron beam doing use, without much heating of the device. A honeycomb structure provides high transparency for electrons generated from the cathode 2. The Sandwich structure with dielectric layer 3 in-between cathode 2 and conduction layer 4 prevents during heating up by adsorbed electrons dimensional changes and break down of the device 1. The choice of materials like for example diamond and amorphous carbon in for example combination with ion implantation provide a device 1 long time stable even at different temperatures. Similar expansion coefficients during heating of used materials prevent peeling off of layers and a destruction of the device 1.

List of Reference Characters

1 Device for the extraction of electrons in field emission systems

2 cathode as electron source

3, 3' dielectric grid layer

4 conduction layer

5 substrate

6 emitted electron beam