Patent Application
20110181170
1. Field of the Invention
This invention relates to a field emission lamp which is designed to realize the emission of light through excitation of a fluorescent substance by electrons that have been field-emitted from a cold cathode electron-emitting source.
2. Description of the Related Art
In recent years, a field-emission-type light-emitting device has been developed as a lamp which is high in luminance and low in power consumption. In this lamp, the emission of light is achieved through excitation of a fluorescent substance which occurs by impingement of the electrons field-emitted from a cold cathode electron-emitting source against a fluorescent substance in vacuum. The light-emitting devices of this kind are expected to be useful as a field emission lamp (FEL) or a field emission display (FED).
For example, JP-A 11-167886 discloses a field electron-emitting type display tube wherein a carbon nanotube is employed as the cathode electrode material. This display tube is constructed such that a housing equipped with a cathode electrode and a mesh portion (electron-extracting electrode), to which a voltage is impressed through each lead pin, and an anode electrode are disposed in a cylindrical glass bulb (an envelope) in the mentioned order on the bottom thereof. The cathode electrode is constructed such that a conductive plate is disposed on a ceramic substrate and a carbon nanotube is grown as an emitter on the surface of the conductive plate. The anode electrode includes a ring portion and a cylindrical portion. A face glass having a convex lens-like spherical portion is fixed to the front surface of the distal end of the glass bulb. A fluorescent screen formed on the inner surface of the face glass and an Al metal back film is laminated on the surface of the fluorescent screen. This Al metal back film is electrically connected, through a contact segment, with the cylindrical portion of the anode electrode.
This display tube is designed to emit light as described below. An electric field is applied between the cathode electrode and the housing, thereby enabling a high electric field to concentrate at the distal end of the carbon nanotube. As a result, electrons are extracted and emitted from the mesh portion of the housing. Meanwhile, a high voltage is applied to the anode electrode and to the Al metal back film, thereby enabling the emitted electrons to accelerate at the cylindrical portion of anode electrode. As a result, electrons are enabled to pass through the Al metal back film and to impinge against the fluorescent screen. As a result, the fluorescent substance constituting the fluorescent screen is excited because of this electron impingement, thereby enabling a desired color emission in conformity with the kinds of the fluorescent substance. The light thus emitted is enabled to pass through the face glass to display an image on the front surface thereof.
Because of the employment of carbon nanotube as the cathode electrode as described above, it is possible to obtain a field emission lamp which is stable for a long period of time and high in reliability.
In the case of the conventional field emission lamps, an emitter made of carbon nanotube is formed on the surface of a planar substrate (a conductive plate). Each tube of the carbon nanotube exhibits a very high aspect ratio. However, when an ordinary known method such as a screen printing method or a chemical vapor deposition method is employed, the carbon nanotube is caused to be deposited densely on the substrate. Because of this, even if the carbon nanotube deposited is orientated perpendicular to the substrate, it is difficult to enable the electric field to concentrate. As a result, it is required to employ a high voltage in order to achieve the emission of electrons, thus inviting an increase of operating voltage.
It is an object of the present invention to provide a field emission lamp which makes it possible to achieve emission of electrons at a lower voltage, to reduce the operating cost and to increase the useful life.
According to one aspect of the present invention, there is provided a field emission lamp which comprises a vacuum container; and a cathode electrode, a gate electrode and anode electrode all arranged in the vacuum container, wherein the cathode electrode is composed of a nanocarbon composite substrate which contains a substrate having a projected portion or grooved portion in a surface, and a nanocarbon material formed on the surface of the projected portion or grooved portion of the substrate.
According to the field emission lamp of the present invention, since the substrate of the cathode electrode has a surface with a projected portion or grooved portion exhibiting a high aspect ratio, the concentration of electric field can be facilitated, the emission of electrons can be achieved at a lower voltage, the operating cost can be reduced and the useful life can be elongated.
There will now be described specific embodiments of the present invention with reference to drawings.
The gate electrode 4 is formed of a metal plate having openings each positioned in conformity with the emitter of the cathode electrode 3 and having a predetermined diameter. The anode electrode 5 is constituted by a transparent conductive film 52 to be used as an electrode and by an electron beam-exciting fluorescent substance 53, both of which are laminated on the both surfaces of a glass substrate 51. In a case where a high-velocity electron beam of about 10 kV or more is to be used, the fluorescent substance may be directly deposited on the glass substrate 51 and an Al metal back may be deposited on the surface of the fluorescent substance.
The space between the cathode electrode 3 and the gate electrode 4 may preferably be confined to 0.5-2 mm in order to prevent electric discharge and to facilitate the concentration of electric field. Further, the space between the gate electrode 4 and the anode electrode 5 may preferably be not less than 5 mm in view of preventing the reflection of ions.
One example of the nanocarbon composite substrate constituting the cathode electrode 3 will be explained with reference to
The nanocarbon material 35 can be formed as follows. Namely, a catalyst is deposited on the face of the projected portion 32 to obtain the projected portion 32 carrying the catalyst, on which the nanocarbon material is allowed to grow by means of a solid/liquid interface contact decomposition method. The composite substrates shown in
In the structure shown in
As for the materials of the substrate 31, it is possible to employ a semiconductor material such as monocrystalline silicon, germanium, gallium arsenide, phosphorus gallium arsenide, gallium nitride, silicon carbide, etc.; glass; ceramics; quartz; etc. With respect to the thickness of the substrate 31, although there is not any particular limitation, it is generally preferable to confine it to 100-1500 μm.
With respect to the height of the projected portion 32, it is preferable to make it not less than 10 μm. As the aspect ratio of the projected portion 32 becomes larger, the concentration of electric field is liable to be facilitated correspondingly. Therefore, it is preferable to appropriately design the aspect ratio of projected portion 32. When the height of projected portion 32 is less than 10 μm, it would become difficult to sufficiently increase the aspect ratio of projected portion 32.
With regard to the material for the nanocarbon material 35, it is possible to employ carbon nanotube, carbon nanofiber, carbon nanohorn, carbon nanofilament, carbon nanowall or carbon nanocoil, each nanocarbon material having a diameter of the order of nanometers and being excellent in crystallinity. From the viewpoints of excellence in electrical conductivity and thermal conductivity and of improving the characteristics of device, the employment of the nanocarbon materials having a diameter of the order of nanometers and being excellent in crystallinity is preferable.
As shown in FIG. 3[(a)-(g)], the projected portion 32 or grooved portion 33 can be shaped into various configurations. The shapes of the projected portion 32 shown in FIG. 3[(a)-(f)] represent column (a), truncated cone (b), prism (c), truncated pyramid (d), cone (e) and pyramid (f), respectively. The configuration of the grooved portion 33 shown in
As shown in FIG. 3[(a)-3(d)], when the shape of the projected portion 2 is made into a trapezoidal configuration such as column, truncated cone, polygonal column and truncated pyramid, the control of characteristics of device can be more effectively facilitated.
When the shape of the projected portion is made into the shape of cone or polygonal pyramid having a sharp top as shown in FIG. 3[(e) or (f)], it is also possible to more effectively and easily control the characteristics of device.
Even if V-shaped grooved portion 33 are formed as shown in
As described above, according to the field emission lamp according to one embodiment of the present invention, since a nanocarbon composite substrate which is constituted by a substrate having a projected portion or grooved portion and by a nanocarbon material deposited on the face of the projected portion or grooved portion at a high density is employed as the cathode electrode thereof, it is possible to facilitate the concentration of electric field on account of the physical features of the substrate, thereby making it possible to drive it at a lower voltage.
The nanocarbon composite substrate constituting the cathode electrode may preferably be manufactured by means of the aforementioned solid/liquid interface contact decomposition method. This method comprises forming a projected portion or grooved portion on a substrate; depositing a catalyst on the faces of the projected portion or grooved portion; and immersing and heating the substrate having the catalyst carried on the projected portion or grooved portion in an organic liquid to thereby allow a nanocarbon material to grow on the faces of the projected portion or grooved portion.
The employment of the aforementioned solid/liquid interface contact decomposition method is advantageous in that since the raw material is formed of an organic liquid, it is possible to enable the raw material to penetrate into very narrow portions of the projected portion 2 (or grooved portion), thereby making it possible to bring about a uniform chemical synthesis reaction. For this reason, it is possible to uniformly form a nanocarbon material which is high in purity and in crystallinity on the surface of the substrate having the projected portion (or grooved portion).
The following as an explanation of specific examples of the present invention.
By means of mechanical cutting work, a prismatic or pyramidal projected portion was formed on the surface of an n-type monocrystalline silicon (100) substrate having a low electrical resistance. The height of each of the projected portion was set to 100 μm.
Then, by means of magnetron sputtering method, cobalt as a catalyst was deposited on the surface of the mechanically worked silicon substrate. The quantity of cobalt that was deposited on the surface of substrate was set so as to correspond to 6 nm in film thickness.
The resultant substrate was immersed in methanol and electric current was passed through electrodes to the substrate so as to heat the substrate for three minutes at 600° C. at first and then to heat the substrate for 6 minutes at 900° C. As a result, a solid/liquid interface contact decomposition reaction using carbon atoms in the methanol as a raw material was caused to take place in the vicinity of the substrate, thereby forming carbon nanotube on the surface of the substrate. As a result, it was possible to enable the growth of carbon nanotube to orientate perpendicular to the top faces and sidewalls of the projected portion on the substrate.
Then, the nanocarbon composite substrate thus manufactured was employed as the cathode electrode 3, and the anode electrode 5 was disposed to oppose to the cathode electrode 3, with the gate electrode 4 interposed therebetween. The space between the cathode electrode 3 and the gate electrode 4 was set to 1 mm, and the space between the gate electrode and the anode electrode was set to 10 mm. When the electric field electron-emitting characteristics thereof in the vacuum container 2 was measured under these conditions, it was possible to confirm the emission of electrons at a gate voltage of as low as not more than 2.0 kV with the anode electrode voltage being set to 5 kV.
Since the field emission lamp of the present invention is low in energy, high in luminance, long in useful life and vary small in the generation of heat, it is expected to be useful in various fields taking the place of the conventional illumination. For example, it can be used, in addition to general illumination, in the cultivation of vegetables, as a lamp for surgical operations or as a car lamp, etc.
1 - - - Field emission lamp, 2 - - - Vacuum container, 3 - - - Cathode electrode, 4 - - - Gate electrode, 5 - - - Anode electrode, 31 - - - Substrate, 32 - - - Protruded portion, 33 - - - Grooved portion, 35 - - - Nanocarbon material, 51 - - - Glass substrate, 52 - - - Transparent electrode, 53 - - - Fluorescent substance.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-254757 | Sep 2008 | JP | national |
This is a Continuation Application of PCT Application No. PCT/JP2009/067060, filed Sep. 30, 2009, which was published under PCT Article 21(2) in Japanese. This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2008-254757, filed Sep. 30, 2008, the entire contents of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2009/067060 | Sep 2009 | US |
| Child | 13064506 | US |
