Patent Application
20070262320
(1) Field of the Invention
The present invention relates to an electron emitter and its manufacturing method, and in particular relates to an electron emitter which includes an electron emission layer containing carbon, as a principal component, formed on a SiC substrate.
(2) Description of the Related Art
In recent years, a high power electron beam source using carbon nanotubes for a display, a high intensity emission apparatus and a high resolution electron microscope has been developed. (See the Non-Patent References 1 to 3 and Patent References 1 to 3). Since the carbon nanotubes allow high concentration of an electric field in a sharp-pointed tube end, compared to conventional materials, they are expected to realize high electron emission characteristics. However, there are technical problems in that plural tubes are needed to obtain a large amount of current output, and in that it is difficult to make the orientation of each tube end to be the same and grow it in the electron emission direction. In order to solve these problems, technologies for applying a method to electron emitters have been developed. The method includes: annealing, at a high temperature in a vacuum, a SiC substrate having a (0001) surface as a principal surface (hereinafter, referred to as the SiC substrate (0001) ), and making a high-orientation carbon nanotube array grow on the C surface of the SiC substrate (0001) (See the non-patent reference 4 and the patent references 4 and 5). The C surface of the SiC substrate (0001) refers to the surface determined by the SiC crystal polarity and represents the (000-1) surface. The Si surface of the SiC substrate, which is described below, refers to the surface determined by the SiC crystal polarity and represents the (0001) surface. In addition, it is known that the Si surface and the C surface of the SiC substrate have different chemical characteristics.
An electron emitter 300 shown in
The carbon nanotube layer 12 is formed on the C surface of the substrate 11 (the upper side of the substrate 11 in
The carbon layer 16 is a layer containing graphite as a principal component. The carbon layer 16 is formed on the Si surface of the substrate 11 (the lower side of the substrate 11 in
The electrode 14 is an electrode used as an anode and formed facing the carbon nanotube layer 12 across a gap 13. The electrode 18 is formed on the surface of the carbon layer 16. The voltage source 15 is connected between the electrode 14 and the electrode 18.
In the electron emitter 300, when voltage is applied between the electrode 14 and the electrode 18 by the voltage source 15, electrons are emitted from the carbon nanotube layer 12 to the electrode 14.
However, in the conventional electron emitter 300, the carbon layer 16 and the substrate 11 form a schottky barrier. In addition, since the electrode 18 is formed on the carbon layer 16 surface, there will be a large voltage drop generated by series resistance between the carbon nanotube layer 12 and the electrode 18. This causes a decrease in the electron emission efficiency of the electron emitter 300.
[Patent Reference 1] Japanese Laid-Open Patent Application No. 2001-15077
[Patent Reference 2] Japanese Laid-Open Patent Application No. 2001-20071
[Patent Reference 3] Japanese Laid-Open Patent Application No. 2001-20072
[Patent Reference 4] Japanese Laid-Open Patent Application No. 10-265208
[Patent Reference 5] Japanese Laid-Open Patent Application No. 2002-293522
[Non-Patent Reference 1] Jean-Marc Bonard et al., Solid-State Electronics, Vol. 45, (2001), pp. 893-pp. 914.
[Non-Patent Reference 2] Hiroyoshi Tanaka et al., Japanese Journal Applied Physics, Vol. 43, (2003), pp. 864-pp. 867.
[Non-Patent Reference 3] Yahachi Saito, Kagaku Frontier 2, Carbon Nonotube-Nanodevice e no chosen—(Chemical Frontier 2, Challenge for Carbon Nanotube—Nanodevice) (Kazuyoshi Tanaka (Edition)), Chapter 13, p. 175-p. 184, Kagaku Dojin (Chemistry Magazine) (2001)
[Non-Patent Reference 4] Michiko Kusunoki, Kagaku Frontier 2, Carbon Nonotube-Nanodevice e no chosen—(Chemical Frontier 2, Challenge for Carbon Nanotube—Nanodevice) (Kazuyoshi Tanaka (Edition)), Chapter 5, p. 89-p. 98, Kagaku Dojin (Chemistry Magazine) (2001)
The present invention aims to provide an electron emitter with a high electron emission efficiency.
To solve the above-mentioned problem, the electron emitter according to the present invention has a SiC substrate which includes an area in which the surface of the substrate is exposed or an area in which the inner surface of the substrate is exposed, a (0001) surface as a principal surface and, an electron emission layer containing carbon formed on the C surface, and an electrode formed on the above-mentioned area.
Accordingly, since an electrode is formed on the substrate without the carbon layer and the like, series resistance between the electron emission layer and the electrode can be reduced. Furthermore, since good ohmic characteristics can be obtained in the connection of the electrode and the SiC substrate, series resistance between the electron emission layer and the electrode can be reduced. Accordingly, the electron emitter in the present invention can achieve a high electron emission efficiency.
The electrode may be formed on the Si surface of the substrate.
Accordingly, good ohmic characteristics can be obtained in the connection of the electrode and the Si surface of the SiC substrate. Therefore, the electron emitter according to the present invention can achieve a high electron emission efficiency.
The electron emission layer may be formed on a part of the substrate surface C and the electrode may be formed on the area, of the substrate C surface, on which the electron emission layer is not formed.
Accordingly, good ohmic characteristics can be obtained in the connection of the electrode and the C surface of the SiC substrate. Therefore, the electron emitter according to the present invention can achieve a high electron emission efficiency.
Moreover, the substrate may have the concave area in which the inner surface of the substrate is exposed, and a part of the electrode may cover an area of the substrate including the above-mentioned area, in which the inner surface of the substrate is exposed.
Accordingly, since the contact area between the electrode and the SiC substrate increases, contact resistance can be reduced. The thickness of the SiC substrate between the electrode and the electron emission layer can also be reduced. Therefore, series resistance between the electron emission layer and the electrode can be reduced. Accordingly, the electron emitter according to the present invention can achieve a high electron emission efficiency.
The electrode may be formed on the side surface of the substrate.
Accordingly, good ohmic characteristics can be obtained in the connection of the electrode and the SiC side surface. Therefore, the electron emitter according to the present invention can achieve a high electron emission efficiency.
The substrate may be n-type.
This can improve the conductivity to the direction of electron emission from the SiC substrate. Moreover, in comparing the p-type and n-type substrates, using the n-type substrate makes it possible to achieve low ohmic resistance in the connection of the electrode and the SiC substrate. Accordingly, the electron emitter according to the present invention can achieve a high electron emission efficiency.
Materials forming the electrode may include Ni.
This allows the formation of the electrode which has low ohmic resistance to the n-type substrate, achieving low series resistance in the connection of the electrode and the SiC substrate. Accordingly, the electron emitter according to the present invention can achieve a high electron emission efficiency.
The manufacturing method according to the present invention is for manufacturing the electron emitter. The manufacturing method includes the step of forming an electron emission layer which has carbon on the substrate surface C by annealing the SiC substrate with the (0001) surface as a principal surface so as to eliminate Si; the step of removing a predetermined area of a carbon film which has carbon formed on the substrate Si surface; and the step of forming an electrode on the predetermined area of the substrate Si surface.
This allows the manufacturing of the electron emitter with the electrode directly connected to the Si substrate without the carbon layer and the like. Therefore, the election emitter manufactured by the manufacturing method according to the present invention can reduce series resistance between the electron emission layer and the electrode. Thus, good ohmic characteristics can be obtained in the connection of the electrode and the SiC substrate, and accordingly series resistance between the electron emission layer is and the electrode can be reduced. Accordingly, the electron emitter manufactured by the manufacturing method according to the present invention can achieve a high electron emission efficiency. In other words, the manufacturing method according to the present invention can manufacture the electron emitter with a high electron emission efficiency.
Accordingly, the present invention can provide the electron emitter with a high electron emission efficiency.
Japanese Patent Application No. 2006-011663 filed on Jan. 19, 2006 is incorporated herein by reference.
These and other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings that illustrate a specific embodiment of the invention. In the Drawings:
The embodiments of the electron emitter according to the present invention are described below in reference to the drawings.
In an electron emitter in the first embodiment, an electrode is formed on the area of the Si surface of a SiC substrate on which a carbon layer is removed. Accordingly, series resistance between the electrode and a carbon nanotube layer can be reduced. Therefore, the electron emitter with a high electron emission efficiency can be realized.
First, the structure of the electron emitter in this embodiment is described.
An electron emitter 100 shown in
The substrate 11 is a conductive 4H-n-type SiC substrate (0001).
The carbon nanotube layer 12 is an election emission layer which has plural carbon nanotubes arrayed in perpendicular direction and has carbon formed on the C surface of the substrate 11. For example, the thickness of the carbon nanotube layer 12 is approximately 200 nm. Each tube of the carbon nanotube layer 12 is a multi-wall type containing the five-layer carbon surface on average and approximately 110 nm diameter on average. Since the structure of each tube is closed on the top surface while keeping a distance between the respective carbon surfaces, each tube is formed to have a sharp-pointed tube end.
The carbon layer 16 is a layer containing carbon graphite, as a principal component, formed on the Si surface of the substrate 11.
An electrode 14 is an electrode used as an anode and is formed facing the carbon nanotube layer 12 across the gap 13 with an interval of 1 μm. The gap acts as a potential barrier.
The electrode 18 is a back surface electrode formed on the Si surface of the substrate 11 which is an area in which the raw material SiC of the substrate 11 is exposed. The electrode 18 is formed by the back surface electrode materials having Ni as a principal component.
The voltage source 15 is connected between the electrode 14 and the electrode 18.
In an electron emitter 300, when voltage is applied between the electrode 14 and the electrode 18 by the voltage source 15, electrons are emitted from the carbon nanotube layer 12 to the electrode 14.
Next, the manufacturing method of the electron emitter 100 in this embodiment is described.
The Si on the C surface of the SiC substrate 11 is eliminated by annealing the substrate 11 at a temperature of 1500 degrees Celsius in a vacuum of 1×10−5 Torr for 60 minutes. Accordingly, six-membered ring structures of the remaining carbon are connected and plural carbon nanotubes having hollow tube structures are formed. In other words, the carbon nanotube layer 12 which is the election emission layer containing carbon is formed.
Through the process of generating the carbon nanotube layer 12 (the process of annealing the substrate 11 at a temperature of 1500 degrees Celsius in a vacuum of 1×10−5 Torr for 60 minutes), Si of the Si surface of the substrate 11 is also eliminated. Since the substrate 11 is annealed in the state that it is placed on a pedestal or the like with the Si surface down, it is difficult to grow carbonnanotubes perpendicular to the Si surface. As a result, the carbon layer 16 mainly containing graphite is formed on the Si surface of the substrate 11. The electric conductivity of the carbon layer 16 is lower than that of pure metal, and the carbon layer 16 is not desirable for an ohmic contact, which needs low resistance, between the substrate 11 and the electrode 18. Therefore, in the manufacturing method of the election emitter 100 in this embodiment, a low resistance ohmic contact can be achieved by removing the carbon layer 16 and forming the electrode 18 on the area on which the carbon 16 is removed.
As shown in
In this way, in the electron emitter 100 in this embodiment where annealing is performed after Ni is deposited on the Si surface of the substrate 11 without the carbon layer 16, the contact resistance between the substrate 11 and the electrode 18 becomes approximately 10−4 Ωcm2 which is one digit lower than the one obtained in the case in which the electrode 18 is formed by accumulating Ni on the carbon layer 16.
As shown in
In the substrate 11 of an electron emitter 101 shown in
Since the electron emitter 101 can also make the electrode materials adhere to the side surface perpendicular to the Si surface, of the substrate 11, which has been exposed by etching, the contact area between the electrode 18 and the substrate 11 increases and the low contact resistance (5×10−5 Ωcm2 or below) can be achieved. Moreover, since the thickness of the SiC substrate between the carbon nanotube layer 12 and the electrode 18 decreases, series resistance between the carbon nanotube layer 12 and the electrode 18 can be reduced. Therefore, a high electron emission efficiency can be achieved.
Accordingly, in the manufacturing method of the electron emitter 100 in this embodiment, the carbon nanotube layer 12 is formed on the C surface of the substrate 11 by annealing the substrate 11 and eliminating Si. The carbon layer 16 formed on the Si surface of the substrate 11 by the annealing is removed by etching. Next, the electrode 18 is formed on the area 17 where the carbon layer 16 is removed. Accordingly, the electrode 18 in the electron emitter 100 is formed, without the carbon layer 16, on an area in which the raw material SiC of a surface of the substrate 11 is exposed or on an area in which the raw material SiC of an inner surface of the substrate 11 is exposed. Therefore, in the electron emitter 100 in this embodiment, series resistance between the carbon nanotube layer 12 and the electrode 18 can be reduced. Accordingly, the electron emitter 100 in the present invention can achieve a high electron emission efficiency.
Furthermore, by depositing Ni on the area in which SiC of the substrate 11 is exposed and annealing the SiC substrate 11, good ohmic characteristics can be obtained in the connection of the electrode 18 and the SiC substrate 11. Therefore, series resistance between the carbon nanotube layer 12 and the electrode 18 can be reduced. Accordingly, the electron emitter in the present invention can achieve a high electron emission efficiency.
In addition, in the electron emitter 101 in this embodiment, the electrode 18 is formed on the concave area in which the inner surface of the substrate 11 is exposed. Accordingly, since the contact area between the electrode 18 and the substrate 11 increases, contact resistance can be reduced. Moreover, since the thickness of the SiC substrate between the carbon nanotube layer 12 and the electrode 18 decreases, series resistance between the carbon nanotube layer 12 and the electrode 18 can be reduced. Therefore, a high electron emission efficiency can be achieved.
In an electron emitter in the second embodiment, an electrode is formed on the C surface of a substrate 11, on which a carbon nanotube layer 12 is formed. Accordingly, series resistance between the electrode and the carbon nanotube layer 12 decreases and the electron emitter with a high electron emission efficiency can be realized.
An electron emitter 200 shown in
The following is a description about the manufacturing method of the electron emitter in the second embodiment. The process until the carbon nanotube layer 12 is formed is omitted because the process is the same as that of the first embodiment.
As shown in
In this way, in the electron emitter 200 in the second embodiment where annealing is performed after Ni is deposited on the surface C of the substrate 11, the contact resistance between the substrate 11 and the electrode 18 becomes approximately 10−4 Ωcm2 which is one digit lower than the case in which the electrode 18 is formed by accumulating Ni on the carbon layer 16.
As shown in
In the substrate 11 of an electron emitter 201 shown in
Since the electron emitter 201 can also make the electrode materials adhere to the side surface perpendicular to the C surface, of the substrate 11, which has been exposed by etching, the contact area between the electrode 18 and the substrate 11 increases and the low contact resistance (5×10−5 Ωcm2 or below) can be achieved. Therefore, a high electron emission efficiency can be achieved.
Accordingly, in the manufacturing method of the electron emitter 200 in this embodiment, the carbon nanotube layer 12 is formed on the C surface of the substrate 11 by annealing the substrate 11. A part of the carbon nanotube layer 12 formed on the C surface of the substrate 11 is removed by etching. The electrode 18 is formed on the area 27 where the carbon nanotube layer 12 has been removed. Accordingly, the electrode 18 in the electron emitter 200 is formed, without the carbon layer 16, on the area 27 in which the raw material SiC of a surface of the substrate 11 is exposed or the area 27 in which the raw material SiC of an inner surface of the substrate 11 is exposed. Therefore, in the electron emitter 200 in the second embodiment, series resistance between the carbon nanotube layer 12 and the electrode 18 can be reduced. Accordingly, the electron emitter 200 in this embodiment can achieve a high electron emission efficiency.
Furthermore, by depositing Ni on the area in which SiC is exposed and annealing the SiC substrate 11, good ohmic characteristics can be obtained in the connection of the electrode 18 and the SiC substrate 11. Therefore, series resistance between the carbon nanotube layer 12 and the electrode 18 can be reduced. Accordingly, the electron emitter 200 in this embodiment can achieve a high electron emission efficiency.
In addition, the electron emitter 201 in this embodiment forms the electrode 18 an the concave area in which the inner surface of the substrate 11 is exposed. Accordingly, since the contact area between the electrode 18 and the SiC substrate 11 increases, contact resistance can be reduced. Therefore, a high electron emission efficiency can be achieved.
The electron emitter and its manufacturing method in this embodiment according to the present invention have been described so far, but the present invention is not limited to these embodiments.
For example, in the above-mentioned description, the Ar ion beam 50 is used and the carbon layer 16 or the carbon nanotube layer 12 is etched, but the present invention is not limited to this. For example, oxygen plasma etching may be performed by changing the material and thickness of the resist.
In addition, in the above-mentioned description, a part of the carbon layer 16 is removed and the electrode 18 is formed on the removed area in the first embodiment, but the present invention is not limited to this. For example, all of the carbon layer 16 formed on the Si surface of the substrate 11 may be removed by etching without using the resist 19. Moreover, all of the carbon layer 16 formed on the Si surface of the substrate 11 may be removed by grinding rather than etching. Furthermore, in the case where all of the carbon layer 16 formed on the Si surface of the substrate 11 is removed, the electrode 18 may be formed on the whole area or a part of the Si surface of the substrate 11.
The electrode 18 may be formed on the substrate 11 side surface (perpendicular to the Si surface and the C surface). For example, after the substrate 11 is annealed so as to form the carbon nanotube layer 12 (and the carbon layer 16), the substrate 11 is cut and the electrode 18 is formed on the cut surface (perpendicular to the Si surface and the C surface). Accordingly, the electrode 18 can be formed on the area in which SiC of a side surface of the substrate 11 is exposed.
Although the present invention has been fully described by way of examples with reference to the accompanying drawings, it is to be noted that various changes and modifications will be apparent to those skilled in the art.
Therefore, unless otherwise such changes and modifications depart from the scope of the present invention, they should be construed as being included therein.
The present invention can be applied to the electron emitter and its manufacturing method, and in particular, applied to a display using the electron emitter, a high intensity emission apparatus and a high resolution electron microscope and the like.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006/011663 | Jan 2006 | JP | national |
