RU2656150C1 - Field emission element and method of its manufacture - Google Patents

Abstract

FIELD: electronic equipment.

SUBSTANCE: invention relates to electronic engineering, in particular to field emission elements containing carbon nanotubes used as cathodes, and also to a method for manufacturing them. Field emission element comprises electrically conductive substrate 1, dielectric layer 3 disposed thereon, above which is drawing layer 5, in a structure consisting of pulling 5 and dielectric 3 layers, matrix of through holes 7 is made, on their walls insulating layer 6 is located, and on the bottom of the holes there is layer of catalyst 4, where array of carbon nanotubes 2 is formed. Method of manufacturing the field emission element comprises the formation of a catalyst layer on an electrically conductive substrate for growing carbon nanotubes, forming a mask for etching the catalyst layer, liquid chemical etching of the catalyst layer to form catalyst sections for the subsequent growth of carbon nanotubes, removing the mask, plasma-chemical deposition of the dielectric layer, magnetron deposition of the drawing layer, forming a mask for etching the structure consisting of a pulling and dielectric layers, above the previously formed sections of the catalyst for the subsequent growth of carbon nanotubes, plasma-chemical anisotropic etching with the formation of holes in the drawing and dielectric layers up to the catalyst bed, removal of the mask, isotropic deposition of the insulating layer, anisotropic plasma-chemical etching of the insulating layer on the drawing layer and in the bottom of the holes to the catalyst layer with the formation of an insulating layer on the lateral surfaces of the holes, vapor phase synthesis of carbon nanotubes on a catalyst.

EFFECT: technical result is prevention of short circuits, reduction of leakage currents, increase of emission current, reliability and increase in yield.

12 cl, 12 dwg

Description

The invention relates to electronic equipment, in particular to field emission elements containing carbon nanotubes used as cathodes, as well as to a method for their manufacture. The invention can be used in triodes, diodes, field emission displays, vacuum microelectronic current switches, electron guns and other microelectronic products.

Carbon materials, in particular carbon nanotubes, possess high emission properties. A known field emission element and a method for its manufacture, where carbon nanotubes are used as cathodes (Russian patent 2391738, IPC H01J 9/02, B82B 3/00, published June 10, 2010). The field emission element comprises a substrate, a cathode structure consisting of one or more layers of electrically conductive material and located on the outer surface of said dielectric substrate, a support structure consisting of one dielectric layer or several dielectric and electrically conductive layers, located on the upper surface of said cathode structure and containing through holes for the formation of emission cathodes made in the form of carbon nanotubes located in the aforementioned utyh openings of the support structure on the outer surface of the cathode structure perpendicularly to the surface of the anode layer of electrically conductive material disposed on the outer surface of said support structure and comprising a technological opening aligned with said openings in the supporting structure. A method of manufacturing such a field emission element, comprises technological steps: forming a multilayer structure consisting of a substrate, a cathode structure composed of a current-carrying layer located on the surface of the dielectric substrate, an adhesive layer located on the surface of the current-carrying layer, a catalytic layer located on the surface of the adhesive layer support structure located on the surface of the catalytic layer and composed of a first insulating layer located on the surface of the catalytic layer, the gate conductive layer located on the surface of the first insulating layer, the second insulating layer located on the surface of the gate conductive layer; forming holes in the second insulating layer; the formation of holes in the gate conductive layer; forming holes in the first insulating layer; applying a sacrificial layer; the formation of the structure of the sacrificial layer; drawing an anode layer; the formation of technological holes and the structure of conductors in the anode layer; etching of the sacrificial layer by a liquid chemical method when the solution enters through technological holes in the anode layer; activation of the surface of the catalytic layer during heat treatment; the formation of carbon nanotubes on the surface of the catalytic layer inside the aforementioned holes in the first insulating layer when the active gas medium enters the surface of the catalytic layer through technological holes in the anode layer.

The disadvantage of this device and its manufacturing method is that the array of nanotubes covers the entire surface of the cathode and this leads to their mutual shielding, which reduces the emission intensity

A technical solution is known according to the application of US US 20110005191 (IPC F03H 1/00, H01J 1/02, published June 13, 2011), according to which the cathode contains many bundles of vertically oriented carbon nanotubes. All bundles of nanotubes are electrically connected, and spatially separated by a dielectric material, on the surface of which there is a conductive layer acting as a pulling electrode. The disadvantage of this method is the difficulty of manufacturing such devices. Since one cathode can contain up to a million bundles of nanotubes, and the growth of each of them is difficult to control, the closure of at least one to the extraction electrode leads to inoperability of the entire source.

In this design, as in all previously described, there is no protection against the natural dispersion of carbon under the action of high electric field strength that occurs during operation of the source and its deposition on the side lathes of the holes in the insulating layer. This leads to electrical leakage between the extracting electrode and the cathode, which reduces the efficiency and spike of the source.

The closest set of essential features (prototype) of the invention for the device is the technical solution set forth in US application US 2014270087 (A1) (IPC H01J 35/06, published September 18, 2014), according to which the field emission element contains an electrically conductive substrate located there is a dielectric layer on it, in which a matrix of through holes is made, on the walls of which there is an insulating layer, over which the stretching layer is located, an array of carbon nanotubes is formed in the holes, the array height carbon nanotubes are less than the thickness of the dielectric layer.

A known source of electrons intended for use in field emission electronic devices, according to the patent of the Russian Federation No. 2586628 (IPC Н01J 1/10 82В 3/00, published June 10, 2010). An electron source with field-emitting emitters contains a plurality of controllable field-emission cells formed on a substrate with sequentially deposited insulating and conducting layers in which holes are made that reach the substrate, the last in each of these holes is a field-emitter based on a carbon nanostructure, each controlled the field emission cell is formed by the specified field emission emitter, which, together with the cathode portion of the substrate occupied by it, is field emission th cell, and its control electrode, which is adjacent to the opening in the conductive layer of this layer. In one embodiment of the invention, an additional coating is provided on the side walls of the holes made in the insulating layer. Moreover, in each field emission cell, an annular depression in the substrate is made, having side and bottom surfaces and at least the side surfaces of this depression are coated with an insulating material or oxidized. A layer of thermal oxide is formed on the working surface of the silicon substrate, and then a layer of Si ₃ N ₄ is applied by vacuum deposition. To form a control electrode, a layer of conductive material is sprayed onto the insulating layer formed as a result of previous operations. Then, using a contact, projection, or electronic lithography, a mask is formed from a photoresist, and through cylindrical holes are formed by chemical or plasma-chemical etching in the aforementioned insulating and conductive layers of a plate with such layers obtained in the previous stages. Then, another lithographic process is carried out and, by plasma-chemical etching, around the areas intended for the formation of field emitters, ring-shaped depressions are obtained on the substrate. The side walls of the recesses or these walls together with the bottom parts of the recesses are coated with a dielectric or oxidized. From intended for the formation of emitters parts of the surface of the substrate, surrounded by the obtained recesses, the dielectric coating or oxide film is removed. The depressions formed in the manner described above on the substrate surface are cleaned by standard chemical treatment methods and on the above-mentioned parts of the substrate surface surrounded by depressions by plasma-chemical deposition auto-electronic emitters of nanocrystalline graphite are formed.

The above method of manufacturing the device is the closest in the set of essential features (prototype) of the invention for the proposed method. The essential features that coincide with the features of the proposed method for manufacturing a field emission element are: deposition of a dielectric layer, formation of a conductive layer, etching of a structure consisting of a conductive and dielectric layers, with the formation of holes, coating of the side walls of the holes with an insulating layer, the formation of carbon nanostructures with a height of less than thickness of the dielectric layer.

The technical problem of the present invention is the creation of a field emission element that provides a high emission current.

The technical result consists in preventing a short circuit between carbon nanotubes and a pulling electrode, reducing leakage currents, increasing the emission current, increasing the manufacturability of manufacturing, increasing reliability and increasing yield.

To achieve the above technical results, the field emission element contains an electrically conductive substrate, a dielectric layer located on it, over which the extrusion layer is located, a matrix of through holes is made in the structure consisting of the extrusion and dielectric layers, an insulating layer is located on the walls of the holes, and at the bottom of the holes a catalyst layer is located on which an array of carbon nanotubes is formed, and the height of the array of carbon nanotubes is less than the thickness of the dielectric layer.

In the particular case of carrying out the invention, the pulling layer is made 0.3-0.7 microns thick.

In the particular case of the invention, the dielectric layer and the insulating layer are made of silicon oxide.

In the particular case of the invention, an array of carbon nanotubes is formed vertically oriented by vapor-phase synthesis.

In the particular case of carrying out the invention, the height of the array of carbon nanotubes is 0.8-1 microns

The proposed device differs from the prototype in that an insulating layer is located on the walls of the through holes of the structure consisting of the drawing and dielectric layers, which provides a dielectric coating of the side wall completely, including the end part of the drawing layer. The insulation of the ends of the extracting layer provides protection against the occurrence of leakage currents between the cathode and the extraction electrode, which arise due to the deposition of carbon cavities on the side walls, which is formed due to the natural atomization of carbon under the action of high electric field during operation of the field emission element. The occurrence of leakage currents reduces the efficiency and life of the source.

To achieve the above technical results, a method for manufacturing a field emission element includes forming a catalyst layer for growing carbon nanotubes on an electrically conductive substrate, forming a mask for etching the catalyst layer, liquid chemical etching of the catalyst layer with the formation of catalyst regions for subsequent growing of carbon nanotubes, removing the mask, plasma-chemical deposition of dielectric layer, magnetron deposition of the stretching layer, the formation of mass kits for etching a structure consisting of an extrusion and dielectric layers over previously formed regions of the catalyst for subsequent growth of carbon nanotubes, plasma-chemical anisotropic etching to form holes in the extrusion and dielectric layers to the catalyst layer, mask removal, isotropic deposition of the insulating layer, anisotropic plasma-chemical etching of the insulating layer on the stretching layer and in the bottom of the holes to the catalyst layer with the formation of an insulating layer on the side surfaces surface of holes, vapor-phase synthesis of carbon nanotubes on a catalyst with a height less than the thickness of the dielectric layer.

In the particular case of carrying out the invention, the pulling layer is made 0.3-0.7 microns thick.

In the particular case of the invention, the dielectric layer is made with a thickness of 0.7-1 μm, and the insulating layer is 0.15-0.2 μm thick, the dielectric and insulating layers being made of silicon oxide.

In the particular case of the invention, an array of carbon nanotubes is formed vertically oriented by vapor-phase synthesis.

In the particular case of carrying out the invention, the height of the array of carbon nanotubes is 0.8-1 microns.

In the particular case of the invention, the formation of a catalyst layer on an electrically conductive substrate includes the initial formation of an adhesive layer on the surface of the electrically conductive substrate.

In the particular case of the invention, the vapor-phase synthesis of carbon nanotubes is carried out at a temperature of 500-600 ° C.

In the particular case of the invention, the formation of carbon nanotubes is carried out vertically oriented relative to the substrate.

This method differs from the prototype in that the formation of a catalyst layer on the electrically conductive substrate for growing carbon nanotubes, the formation of a mask for etching the catalyst layer, the liquid chemical etching of the catalyst layer with the formation of catalyst regions for the subsequent growth of carbon nanotubes, is carried out at the beginning of the formation of the field emission element structure, which removes the problems associated with the formation of a photoresistive layer to ensure anisotropic deposition of catalysis torus and provides high adhesion of the catalyst to the substrate. The choice of methods for the formation of layers provides an increase in the manufacturability of manufacturing a field emission element and an increase in yield. The use of self-alignment technology in the formation of the insulating layer, when its anisotropic removal is carried out after isotropic deposition of the insulating layer. A dielectric deposited isotropically covers all surfaces with a thin layer, thereby masking contaminants, including catalyst contaminants, which could occur during the plasma-chemical process of etching the metal of the stretching layer and the thick dielectric layer. Anisotropic etching of a thin insulating layer is carried out under soft conditions, which remove the dielectric from horizontal surfaces, do not lead to atomization of the catalyst, but merely clean and activate its surface before conducting selective synthesis of carbon nanotubes. Activation of the catalyst by anisotropic etching provides the smallest deviation from the vertical orientation when growing carbon nanotubes. The carbon contamination of the end surface of the pulling electrode and the insulating layer leads to electrical leakage between the pulling electrode and the cathode, which reduces the efficiency and life of the source. The insulating layer is located vertically and practically does not affect the density of the arrangement of the bundles of nanotubes and thereby does not reduce the resulting current of the electron source.

The invention is illustrated by the following drawings:

FIG. 1 - field emission element;

FIG. 2 - formation of a catalyst layer for growing carbon nanotubes on an electrically conductive substrate;

FIG. 3 - formation of a mask for etching the catalyst layer;

FIG. 4 - formed areas of the catalyst for subsequent growth of carbon nanotubes;

FIG. 5 - deposition of the dielectric layer;

FIG. 6 - deposition of the stretching layer;

FIG. 7 shows the formation of a mask for etching a structure consisting of stretching and dielectric layers over previously formed regions of the catalyst for subsequent growth of carbon nanotubes;

FIG. 8 - plasma-chemical anisotropic etching with the formation of holes in the stretching and dielectric layers to the catalyst layer

FIG. 9 - removal of the photoresist mask;

FIG. 10 - isotropic deposition of an insulating layer;

FIG. 11 - anisotropic plasma-chemical etching of the insulating layer on the stretching layer and in the bottom of the holes to the catalyst layer with the formation of an insulating layer on the side surfaces of the holes;

FIG. 12 - synthesis of carbon nanotubes on a catalyst.

The field emission element comprises an electrically conductive substrate 1, arrays of carbon nanotubes 2, a dielectric layer 3, a catalyst layer 4, an extension layer 5, an insulating layer 6 (fi. 1). The catalyst layer 6 is located in the holes 7, made in a structure consisting of a pulling 5 and a dielectric 3 layers. On the catalyst 4 is an array of carbon nanotubes 2, the height of which is less than the thickness of the dielectric layer 3.

Field emission element is made as follows. On the surface of a silicon wafer with a diameter of 100 mm, electron-beam sputtering of catalytic Ti layers with a thickness of 0.01 μm and Ni with a thickness of 0.002 μm is carried out (Fig. 2). A mask is formed to etch the catalyst (FIG. 3).

The structure of the catalytic layer is formed during projection photolithography and liquid chemical etching of a Ti (0.01 μm) and Ni (0.002 μm) film, and the mask is removed (Fig. 4). Thus, separate regions of the catalyst are formed on the substrate for the subsequent growth of carbon nanotubes. Plasma-chemical deposition of the dielectric layer of a SiO ₂ layer with a thickness of 1 μm is carried out (Fig. 5). Magnetron sputtering of the electrically conductive (pulling) Ti layer 0.5 μm thick is carried out (Fig. 6). The structure of the matrix of holes in the electrically conductive (pulling) layer and the dielectric layer is formed by projection photolithography and plasma-chemical etching. In this case, a mask is formed to etch the structure consisting of the extrusion and dielectric layers over previously formed regions of the catalyst for the subsequent growth of carbon nanotubes (Fig. 7), then plasma-chemical anisotropic etching is performed with the formation of holes in the extrusion and dielectric layers to the catalyst layer (Fig. . 8), remove the mask (Fig. 9). Plasma-chemical deposition of an insulating SiO ₂ layer with a thickness of 0.2 μm is carried out (Fig. 10), then plasma-chemical anisotropic etching is carried out to the catalyst layer with the formation of holes in the stretching and dielectric layers (Fig. 11). A selective plasma-stimulated chemical vapor-phase synthesis of carbon nanotubes on a catalytic layer with a height of 0.8-1.0 μm at a temperature of 550 ° C is carried out.

Claims (12)

1. A field emission element containing an electrically conductive substrate, a dielectric layer located on it, over which an extraction layer is located, in a structure consisting of an extraction and dielectric layers, a matrix of through holes is made, an insulating layer is located on the walls of the holes, and a layer is located at the bottom of the holes the catalyst on which the carbon nanotube array is formed, the height of the carbon nanotube array being less than the thickness of the dielectric layer. 2. The field emission element according to claim 1, characterized in that the stretching layer is made with a thickness of 0.3-0.7 microns. 3. The field emission element according to claim 1, characterized in that the dielectric layer is made with a thickness of 0.7-1 μm, and the insulating layer is 0.15-0.2 μm thick, the dielectric and insulating layers being made of silicon oxide. 4. The field emission element according to claim 1, characterized in that the array of carbon nanotubes is formed vertically oriented by vapor-phase synthesis. 5. The field emission element according to claim 1, characterized in that the height of the carbon nanotube array is 0.8-1 μm. 6. A method of manufacturing a field emission element, comprising forming a catalyst layer on an electrically conductive substrate for growing carbon nanotubes, forming a mask for etching the catalyst layer, liquid chemical etching of the catalyst layer with the formation of catalyst regions for subsequent growing carbon nanotubes, removing the mask, plasma-chemical deposition of the dielectric layer, magnetron deposition of an extruding layer, the formation of a mask for etching a structure consisting of extruding of the substrate and dielectric layers, above the previously formed regions of the catalyst for the subsequent growth of carbon nanotubes, plasma-chemical anisotropic etching with the formation of holes in the stretching and dielectric layers to the catalyst layer, mask removal, isotropic deposition of the insulating layer, anisotropic plasma-chemical etching of the insulating layer on the stretching layer and on the bottom holes to the catalyst layer with the formation of an insulating layer on the side surfaces of the holes, vapor-phase synthesis of carbon on Notebook on a catalyst less than the thickness of the dielectric layer. 7. A method of manufacturing a field emission element according to claim 6, characterized in that the pulling layer is made of titanium with a thickness of 0.3-0.7 microns. 8. A method of manufacturing a field emission element according to claim 6, characterized in that the dielectric layer and the insulating layer are made of silicon oxide. 9. A method of manufacturing a field emission element according to claim 6, characterized in that the formation of a catalyst layer on an electrically conductive substrate includes initially forming an adhesive layer on the surface of the electrically conductive substrate. 10. A method of manufacturing a field emission element according to claim 6, characterized in that the vapor-phase synthesis of carbon nanotubes is carried out at a temperature of 500-600 ° C. 11. A method of manufacturing a field emission element according to claim 10, characterized in that the formation of carbon nanotubes is carried out vertically oriented relative to the substrate. 12. A method of manufacturing a field emission element according to claim 6, characterized in that the height of the carbon nanotube array is 0.8-1 microns.

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