Patent Application
20100219744
1. Field of the Invention
The present invention relates to a field emission electrode which emits electrons by field emission, a manufacturing method thereof, and an electronic device.
2. Description of the Related Art
Field-emission cold cathodes can emit electrons into a vacuum space by applying an electric field to their emitter, and have gained attention as electron emission elements to replace hot cathodes. Various researches have been made to achieve a smaller threshold field intensity (a field intensity which will cause an emission current of 1 mA/cm2) and more stability and uniformity of emission currents.
Techniques for improving the electron emission characteristic of a field emission cold cathode have roughly two tendencies.
One is to make searches into the structures of electron emission materials to achieve a structure for a more enhanced electric field concentration. By sharpening the tip of an electron emission material from which electrons are to be emitted, a strong electric field that can pull out electrons is formed near the tip, which allows electrons to be emitted at a low applied voltage. Hence, many reports about applications of carbon nano tube (hereinafter referred to as CNT), carbon nano fiber, etc. as field-emission type electron emission elements have been made so far. Carbon nano tube is a carbon material with sharp tips that has a minute structure of a nanometer size with a high aspect ratio.
Unexamined Japanese Patent Application KOKAI Publication No. 2003-59391 discloses a manufacturing method of a field emission cold cathode using CNT.
According to this manufacturing method, a substrate to serve as the electron emission electrode is etched to be provided with bosses and recesses thereon, and the surface of the bosses is covered with a conductive material such as Al and then has CNT adhered thereon. After grains of the CNT, which has been produced aside from the substrate by arc discharge, are adhered to the bosses of the substrate by electrophoresis, the conductive material is melted to flow into clearances of the CNT.
The other tendency for improving the electron emission characteristic of the field emission cold cathode is to reduce the potential barrier near the surface of the electron emission material, which is the site to emit electrons therefrom.
It is effective for this purpose to use a material having a small electric affinity as the electron emission material. Especially, diamond has not only negative electron affinity but also a high degree of hardness, and thus is chemically stable. Diamond is therefore suitable as the material for electron emission elements.
However, in case of an electron emission element made of diamond, the higher the crystallinity of diamond is, the lower the basic electric conductivity is, giving rise to a problem that a favorable electric contact is hard to obtain between the diamond and the substrate serving also as an electrode.
To deal with this problem, Unexamined Japanese Patent Application KOKAI Publication No. H9-161655 teaches incorporating impurities such as nitrogen in diamond thereby to improve the electron emission characteristic.
The structure for enhancing the field concentration can have a higher field concentration as the shape of the tip as the electron emission site is sharper, but becomes so less durable. The technique of Unexamined Japanese Patent Application KOKAI Publication No. 2003-59391 has to undergo complicated manufacturing steps after production of the CNT, and suffers a problem that the ratio of CNT that adheres with respect to the yield is low because the CNT grains are physically moved in the dispersion liquid by electrophoresis.
On the other hand, the electron emission element made of diamond is highly durable because of its rigid crystalline structure and is less liable to deteriorate. Furthermore, diamond has a low work function and thus can emit electrons with a low field concentration.
However, the high electric resistivity of diamond is an obstacle against meeting a condition of a field intensity of 1V/μm or less at a current density of 1 mA/cm2, which is one standard in promoting practical use of electron emission elements. This obstacle cannot have been counteracted so far by any of the enhancement of field concentration by improving the surface structure of the emitter film, impartment of a lower resistivity to diamond by doping impurities, improvement of the electric contact between diamond and the conductive substrate.
Accordingly, an object of the present invention is to provide a field emission electrode easy to manufacture and having a high current density at a low field intensity, a manufacturing method of such an electrode, and an electronic device.
To achieve the above object, a field emission electrode according to the present invention comprises an electron emission film including a plurality of diamond fine grains having a grain diameter of 5 nm to 10 nm.
Another field emission electrode according to the present invention comprises an electron emission film including a plurality of diamond fine grains and having a ratio (D-band intensity)/(G-band intensity) of 2.5 to 2.7.
Another field emission electrode according to the present invention comprises:
an electron emission film including a plurality of diamond fine grains; and
sticks formed on a surface of the electron emission film.
A manufacturing method of a field emission electrode according to the present invention comprises a step of supplying a material gas which includes carbon in its composition into a process chamber to generate plasma in the process chamber, and forming an electron emission film including a plurality of diamond fine grains on a substrate in the process chamber.
Another manufacturing method of a field emission electrode according to the present invention comprises:
a step of supplying a material gas which includes carbon in its composition into a process chamber to generate plasma in the process chamber, and forming a layer of carbon-nanowall on a substrate in the process chamber; and
a step of forming an electron emission film including a plurality of diamond fine grains on the layer of carbon-nanowall.
Another manufacturing method of a field emission electrode according to the present invention comprises a step of supplying a material gas which includes a compound containing carbon in its composition into a process chamber to generate plasma in the process chamber, thereby forming an electron emission film including a plurality of diamond fine grains, and sticks disposed on a surface of the electron emission film.
An electronic device according to the present invention comprises:
a field emission electrode which comprises an electron emission film including a plurality of diamond fine grains having a grain diameter of 5 nm to 10 nm;
an opposite electrode which is provided so as to face the field emission electrode; and
a fluorescent film which emits light by electrons emitted from the field emission electrode.
Another electronic device according to the present invention comprises:
a field emission electrode which comprises an electron emission film including a plurality of diamond fine grains and having a ratio (D-band intensity)/(G-band intensity) of 2.5 to 2.7;
an opposite electrode which faces the field emission electrode; and
a fluorescent film which emits light by electrons which are field-emitted from the field emission electrode.
Another electronic device according to the present invention comprises:
a field emission electrode which comprises an electron emission film including a plurality of diamond fine grains and having a ratio (carbon having sp3 bonds)/(carbon having sp2 bonds) of 2.5 to 2.7;
an opposite electrode which faces the field emission electrode; and
a fluorescent film which emits light by electrons which are field-emitted from the field emission electrode.
Another electronic device according to the present invention comprises:
a field emission electrode which comprises an electron emission film including a plurality of diamond fine grains and having resistivity of 1 kΩ·cm to 18 kΩ·cm;
an opposite electrode which faces the field emission electrode; and
a fluorescent film which emits light by electrons which are field-emitted from the field emission electrode.
Another electronic device according to the present invention comprises:
a field emission electrode which comprises an electron emission film including a plurality of diamond fine grains, and sticks formed on a surface of the electron emission film;
an opposite electrode which is formed so as to face the field emission electrode; and
a fluorescent film which emits light by electrons emitted from the field emission electrode.
A field emission electrode or an electronic device according to the present invention can realize field emission having a high current density at a low field intensity.
These objects and other objects and advantages of the present invention will become more apparent upon reading of the following detailed description and the accompanying drawings in which:
The embodiments of the present invention will now be specifically explained with reference to the drawings.
This electron emission film 1 is a diamond thin film made of diamond crystal grains having a grain diameter of 5 nm to 10 nm, and is formed on a substrate 2 made of a conductive material or a semiconductive material. The substrate 2 and the electron emission film 1 constitute a field emission cold cathode.
Microscopic observation of the surface of the electron emission film 1 by using a scanning electron microscope shows that a plurality of diamond fine grains having a grain diameter of 5 nm to 10 nm are aggregated in the number of about several tens to several hundreds thereby to form a tissue like a bamboo leaf having a length of about 100 μm or more. The electron emission film 1 seems flat with no bosses and recesses to the naked eye, and therefore has specular reflection thereon as shown in
As shown in
When the electron emission film 1 is subjected to Raman spectroscopy using laser light having a wavelength of 532 nm, peaks are observed at near 1350 cm−1 and near 1580 cm−1 as shown in
It is apparent that the electron emission film 1 is formed not only of diamond crystal grains, because the electron emission film 1 shows a very small resistivity of several kΩ·cm as compared to the resistivity inherent in diamond, in spite of its possession of the diamond structure.
That is, the presence of the diamond structure in the composition of the electron emission film 1 has been confirmed from the X-ray diffraction pattern, and the presence in the electron emission film 1 of carbon including carbon having a graphite structure containing sp2 bonds and showing conductivity can be confirmed because a broad peak whose half-value width is 50 cm or more has been observed in the Raman spectroscopy spectrum, which means that the electron emission film 1 is a complex material in which such carbon is formed in the clearances between the diamond crystal grains and in the outermost surface of the electron emission film 1.
Next, a thin film forming method for forming the electron emission film 1 on the substrate 2 will be explained.
A silicon monocrystal wafer which has, for example, a crystal surface (100) is cut into squares having a side length of 30 mm, and the surface of the square is scratched to form recesses (grooves) whose average roughness is 3 μm or less, by using diamond fine grains having a grain diameter of 1 to 5 μm, which are to be used as nuclei for growing the electron emission film 1. The scratched wafer will be the substrate 2. Degreasing and ultrasonic cleaning are simultaneously applied to the substrate 2 embossed and recessed by scratching.
The substrate 2 is then placed on a susceptor 202 in a DC plasma CVD system 200 having the configuration shown in
The DC plasma CVD system 200 is a general-purpose processing system, and comprises a process chamber 201, a susceptor 202, an upper electrode 203, a process gas showerhead 204, gas supply pipes 205 and 206, a purge gas supply pipe 207, a gas ejection pipe 208, and a direct-current (DC) power source 209.
The susceptor 202 serves also as a lower electrode and has a process target placed thereon. The upper electrode 203 has a lower voltage applied thereto than that applied to the lower electrode 202.
The gas supply pipe 205 comprises a mass flow controller (MK) and valves, and introduces hydrogen gas to the showerhead 204. The gas supply pipe 206 comprises an MFC and valves, and introduces gas comprising a compound containing a carbon in its composition that includes at least one of (1) a hydrocarbon compound such as methane, ethane, acetylene, etc., (2) an oxygen-containing hydrocarbon compound such as methanol, ethanol, etc., (3) an aromatic hydrocarbon such as benzol, toluene, etc., (4) carbon monoxide, and (5) carbon dioxide, to the showerhead 204.
The purge gas supply pipe 207 introduces nitrogen gas as purge gas to the process chamber 201, after the electron emission film 1 is formed. The gas ejection pipe 208 is connected to a gas ejection system 210 for ejecting gas from the process chamber 201. The DC power source 109 applies a DC current between the susceptor 202 and the upper electrode 203.
When the substrate 2 is placed on the susceptor 202, the interior of the process chamber 201 is depressurized, and then hydrogen gas and gas (material gas) comprising a compound containing a carbon such as methane are introduced from gas supply sources to the showerhead 204 through the gas supply pipes 205 and 206. The material gas is supplied into the process chamber 201 to form the electron emission film 1 on the surface of the substrate.
The gas comprising a compound containing carbon in its composition is preferably 3vol % to 30vol % of the whole material gas. For example, the mass flow of methane is set at 50 SCCM while that of hydrogen is set at 500 SCCM, and the whole pressure is set at 0.05 to 0.15 atm, preferably at 0.07 to 0.1 atm. The substrate 2 is rotated at 10 rpm, and the state of plasma and the temperature of the substrate 2 are controlled by adjusting the voltage output from the DC power source 209 to between the susceptor (lower electrode) 202 and the upper electrode 203 such that the temperature variation on the substrate 2 is restricted within 5° C.
When the electron emission film 1 is being formed, the portion of the substrate 2 where the electron emission film 1 is to be formed is maintained at a temperature of 840° C. to 890° C. for 120 minutes. Particularly, an electron emission film 1 of a stable characteristic could be obtained when the temperature of the portion of the substrate 2 where the electron emission film 1 is to be formed was 860° C. to 870° C. These temperatures were measured by a spectroscopic method. It was confirmed that the electron emission film 1 including diamond fine grains can be grown even if the gas comprising a compound containing carbon in its composition is less than 3vol % of the whole material gas, but the electron emission characteristic of such a film is extremely poor.
At the end of the film formation, the voltage application between the susceptor 202 and the upper electrode 203 is stopped, and then the supply of the process gas is stopped. Nitrogen gas is supplied into the process chamber 201 through the purge gas supply pipe 207 to restore the atmospheric pressure, and the substrate 2 is taken out.
Through the above-described steps, the electron emission film 1 is formed.
Though it is apparent from XRD measurement that the electron emission film 1 has a diamond structure, it shows, as shown in
The resistivity of a favorable electron emission film 1 was 1 kΩ·cm to 18Ω·cm. The electron emission film 1 allows presence of carbon including carbon having sp2 bonds of the above-described graphite structure between the diamond fine grains, and of which carbon, carbon having the graphite structure showing conductivity contributes to lowering the resistivity of the whole electron emission film 1.
To evaluate the field emission electrode (cold cathode) formed through the above-described steps, the field intensity in case of the current density of cold electrons emitted from the electron emission film 1 being 1 mA/cm2 is 0.95V/μm, as shown in
The field emission fluorescent tube 11 comprising the field emission electrode including the electron emission film 1 comprises, as shown in
The fluorescent plate is observed as causing, due to electron emission, light emission with a high luminance at a low voltage, as shown in
Since such an electron emission film 1 has the nanodiamond aggregates in its emitter surface, it can produce a high current density at a low field intensity and can have a high durability because it has no hysteresis in its electron emission characteristic.
The electron emission film 30 according to the embodiment 2 includes a diamond structure in its composition likewise the electron emission film 1 according to the embodiment 1, but is not formed directly on a substrate as in the embodiment 1 but is formed on the carbon-nanowall 32 which is formed on a substrate 31.
The carbon-nanowall 32 is formed of a plurality of carbon thin flakes of a petal (fan) shape having a curved surface which are uprightly bonded to the others in random directions. The carbon-nanowall 32 has a thickness of 0.1 nm to 10 μm. Each carbon thin flake is formed of several to several tens of graphene sheets having a lattice interval of 0.34 nm.
The electron emission film 30 is formed of a plurality of diamond fine grains having grain diameter of 5 nm to 10 nm, and has an aggregate of several tens to several hundreds of diamond fine grains in its surface as in the embodiment 1, which form a bamboo-leaf-like tissue as shown in
The method of forming such an electron emission film 30 will be explained.
First, for example, a nickel plate is cut into substrates 31 and then sufficiently degreased and cleaned by ultrasonic using ethanol or acetone.
The substrate 31 is placed on the susceptor 202 in the DC plasma CVD system 200 having the configuration of
When the substrate 31 is placed on the susceptor 202, the process chamber 201 is depressurized, hydrogen gas and gas comprising a compound (carbon-containing compound) containing carbon such as methane in its composition are introduced to the showerhead 204 from the gas supply sources through the gas supply pipes 205 and 206, and the material gas is supplied into the process chamber 201.
The gas comprising a compound containing carbon in its composition is preferably 3vol % to 30vol % of the whole material gas. For example, the mass flow of methane is set at 50 SCCM while that of hydrogen is set at 500 SCCM, and the whole pressure is set at 0.05 to 0.15 atm, preferably at 0.07 to 0.1 atm. The substrate 31 is rotated at 10 rpm, and the state of plasma and the temperature of the substrate 31 are controlled by adjusting the voltage output from the DC power source 209 to between the susceptor (lower electrode) 202 and the upper electrode 203 such that the temperature variation on the substrate 31 is restricted within 5° C.
While the carbon-nonowall 32 is being formed, the portion of the substrate 31 where the carbon-nanowall 32 is to be formed is maintained at 900° C. to 1100° C. These temperatures were measured by a spectroscopic method. Continuously with the gas atmosphere unchanged, the temperature of the portion where a plurality of diamond fine grains are to be formed is set at 10° C. or more lower than that of the substrate 31 when the carbon-nanowall 32 was being formed, thus to be 890° C. to 950° C., more preferably to be 920° C. to 940° C., thereby forming the electron emission film 30, which is formed of a plurality of densely gathered diamond fine grains having been grown from the nucleus of carbon-nanowall 32. The period of time in which the temperature of the electron emission film 30 is maintained is preferably about 30 minutes to 120 minutes. It was found that the electron emission film 30 was formed at temperatures of a higher range than that of the embodiment 1. This shows that the base film affects the temperature at which the electron emission film 30 is formed, and it was further found that changes in the plasma irradiation condition causes changes in the appropriate temperature range. However, by decreasing the temperature to be lower than that of the substrate 31 at the time the carbon-nanowall 32 was being formed thereon, the electron emission film 30 was formed relatively quickly. Especially, by an abrupt temperature decrease of 10° C. or more, the film being formed quickly transformed into the electron emission film 30. The electron emission film 30 covers the entire surface of the carbon-nanowall 32, and its topmost surface is flatter than the surface of the carbon-nanowall 32 as shown in
A radio-spectrometer is employed as the temperature measuring device used for such film formation. Therefore, if such an electron emission film 30 was directly formed on the substrate, radiation from the electron emission film 30 would become unstable so that a bad influence would be given on the temperature measurement. However, since the emissivity of the carbon-nanowall 32 is 1, using the carbon-nanowall 32 as the base film and setting 0.7 as the emissivity of the upper film in accordance with diamond as the main component of the upper film would allow the temperature to be measured stably.
At the end of the film formation, the voltage application between the susceptor 202 and the upper electrode 203 is stopped, and then the supply of the process gas is stopped. Nitrogen gas is supplied into the process chamber 201 through the purge gas supply pipe 207 to restore the atmospheric pressure, and then the substrate 31 is taken out.
The electron emission film 30 shown in
By appropriately selecting the conditions such as the mixture ratio of the material gas, the gas pressure, the bias voltage of the substrate 31, etc., and by maintaining the temperature of the portion where the carbon-nanowall 32 is to be formed to be higher than the film forming temperature set for the electron emission film 30 formed of diamond fine grains and to be in the range of 90° C. to 1100° C. for 30 minutes, the layer of carbon-nanowall 32 is formed on the substrate 31. Subsequently, by decreasing the temperature of the portion where the electron emission film 30 formed of diamond fine grains is to formed by 10° C. from the temperature at which the carbon-nanowall 32 was formed, the electron emission film 30 is formed on the carbon-nanowall 32. The carbon-nanowall 32 has an excellent electron emission characteristic, but has bosses and recesses of several microns, which makes the carbon-nanowall 32 difficult to form a uniform emission site thereon. A uniform surface shape can be obtained by forming the electron emission film 30 formed of diamond fine grains on the carbon-nanowall 32.
The electron emission film 30 formed by the above-described steps will now be evaluated.
To check the X-ray diffraction pattern of the electron emission film 30, conspicuous peaks of the diamond crystal and also a peak of the graphite were observed. Taken together with
The carbon thin flakes of the carbon-nanowall 32 show a sharp ratio of intensity between a G-band peak at near 1580 cm−1 having a half-value width of less than 50 cm−1, which is due to the vibration of carbon atoms in the hexagon lattices formed by carbon-carbon bonds (sp2 bonds) of the graphite structure, and a D-band peak at near 1350 cm−1 having a half-value width of less than 50 cm−1, which is due to sp3 bonds, and show almost no other peaks. It is therefore obvious that a carbon-nanowall 32 formed of a dense and highly-pure graphite structure has been grown.
When the electron emission film 30 is subjected to Raman spectroscopy using laser light having a wavelength of 532 nm, peaks are observed at near 1350 cm−1 and near 1580 cm−1, likewise the electron emission film 1 of the embodiment 1. The half-value width of the peak at near 1350 cm−1 is 50 cm1 or more. That is, the presence in the composition of the electron emission film 30 of crystalline diamond is confirmed from the X-ray diffraction pattern and a broad peak whose half-value width is 50 cm−1 or more has been observed in the Raman spectroscopy spectrum, which suggests the presence of carbon having sp2 bonds which are the main factor for the possession by the electron emission film 30 of conductivity and the presence of carbon including amorphous carbon having a resistivity of mega Ω·cm level. The electron emission film 30 is a complex material of these kinds of carbon.
Likewise the embodiment 1, though it is apparent from XRD measurement that the electron emission film 30 has a diamond structure, it shows a resistivity of 20 kΩ·cm or less, which is much smaller than the resistivity of smaller than 1016Ω·cm inherent in diamond.
The resistivity of a favorable electron emission film 30 was 1 kΩ·cm to 18 kΩ·cm. It can therefore be recognized that in the electron emission film 30, the substance formed in the uppermost surface and in the clearances between the diamond fine grains includes the above-described carbon having sp2 bonds, and this sp2 bond carbon has the graphite structure and contributes to lowering the resistivity of the whole electron emission film 30.
The field intensity in case of the current density of cold electrons emitted from the field emission cold cathode constituted by the electron emission film 30, the substrate 31, and the carbon-nanowall 32 being 1 mA/cm2 is, as shown in
The presence of the carbon-nanowall 32 having high plasticity between the substrate 31 and the electron emission film 30 makes it easier to grow the electron emission film 30 including diamond fine grains and graphite carbon, which then makes it possible to ease the condition, as a criterion for selecting the substrate 31, that the substrate 31 has to be made of a material on which a film of diamond fine grains can be formed, or to ease the stress caused by the difference in thermal expansion coefficient, i.e., a thermal shock caused during the cooling process after the film formation by heating, which would produce a gap between the substrate 31 and the diamond fine grains to thereby cause the electron emission film to be separated or produce cracks between the plurality of aggregates of diamond fine grains.
As shown in
The field emission fluorescent tube 21 is a fluorescent tube called VFD (Vacuum Fluorescent Display) that causes light emission by causing cold electrodes to collide against the fluorescent film 4 by applying a predetermined voltage between the anode electrode 3 and the cathode electrode. It is also possible to use the field emission fluorescent tube 21 in an FED (Field Emission Display) having a flat panel structure which includes a plurality of such light emission regions as pixels.
Since such an electron emission film 30 has the nanodiamond aggregates in its emitter surface, it can produce a high current density at a low field intensity and can have a high durability because it has no hysteresis in its electron emission characteristic.
The present invention is not limited to the above-described embodiments 1 and 2, but can be modified in various manners.
For example, the substrate may be made of at least one of rare earth, copper, silver, gold, platinum, and aluminum, other than silicon monocrystal wafer and nickel.
The mixture ratio of the hydrogen gas and the carbon-containing compound as the material gas may be arbitrarily selectively changed.
In
Now, the portion ranging from 750 cm−1 to 2000 cm−1 is extracted from the Raman spectrum, and with the line that connects both ends of the extracted portion seen as a baseline, the values existing on the baseline are eliminated from the spectrum. Then, by the nonlinear least-squares method, the spectrum is fit to a pseudo-Voigt function indicated by the following equation (1) where the initial values of the position are 1333 cm−1 and 1580 cm−1.
F(x)=a*[g*exp(−(√{square root over (2)}*(x−p)/w2))+(1−g)*1/(1+(x−p)/w2)] [Equation 1]
where a=amplitude, g=Gauss/Lorenz ratio, p=position, and w=line width.
According to the nonlinear least-squares method, not only the peak intensity but also the peak position and the line width are allowed some tolerance, in fitting the spectrum to the pseudo-Voigt function. Hence, as long as the initial values to be set first are appropriate ones, an optimum parameter that would restrict the error (×2) between the actually-observed spectrum and the set function to the minimum can be obtained. Therefore, it is unnecessary to minutely and precisely set the peak wavelength. If spectrum fitting by the least-squares method under the following initial condition is available, a parameter that can have the optimum area ratio will be obtained.
The applied initial value conditions are, a: the local maximum value of the actually-observed peak existing between 1250 cm−1 and 1400 cm−1, g: 0.6, p: 1333 cm−1, and w: 200 cm−1 for the portion of the electron emission film where sp3 bonds are formed, whereas a: the local maximum value of the actually-observed peak existing between 1530 cm−1 and 1630 cm−1, g: 1, p: 1580 cm−1, and w: 100 cm−1 for the portion of the electron emission film where sp2 bonds are formed. Though the nonlinear least-squares method is not algorithm-dependent, the Marquardt method is more preferable.
In this manner, the area ratio between the D band whose peak is at near 1333 cm−1 and the G band whose peak is at near 1580 cm−1, i.e., a ratio (D-band intensity)/(G-band intensity) is obtained. In
Accordingly, although the electron emission film 1 of the embodiment 1 and the electron emission film 30 of the embodiment 2 are seemingly a single-layer film as a whole, they have, when microscopically seen, a complex structure including the aggregates of diamond fine grains formed of carbon of sp3 bonds indicated as D band and having a grain diameter of about 5 nm to 10 nm, and carbon of sp2 bonds indicated as G band and existing between the diamond fine grains. For example,
Since each diamond fine grain in such an electron emission film has a negative electron affinity and has a very small grain diameter of 10 nm or less, electrons can be emitted by the tunnel effect. Furthermore, not only the carbon of sp2 bonds that exists in the clearances between the diamond fine grains at a predetermined abundance ratio imparts conductivity to the film as a whole to thereby facilitate field emission, but also it is so arranged that the diamond fine grains be not stacked so continuously that the tunnel effect cannot be obtained. That is, if about a hundred diamond fine grains having a grain diameter of 10 nm are stacked in a predetermined direction with substantially no clearances therebetween, the thickness of the diamond will seemingly be 1000 nm, which will substantially inhibit the occurrence of the tunnel effect even if a strong field is applied. However, since the presence of the carbon of sp2 bonds having conductivity separates the respective diamond fine grains, each diamond fine grain can exhibit the tunnel effect. This tunnel effect allows an electron emitted from the substrate upon a voltage application to be once injected into the nearest diamond fine grain, field-emitted from this diamond fine grain, and again injected into a diamond fine grain adjacent to that diamond fine grain in the field direction, subsequently repeatedly causing such electron emission in the field direction of the electron emission film and finally causing the electron to be emitted from the outermost surface of the electron emission film.
Sufficient light emission was achieved at a low voltage where the ratio (carbon having sp3 bonds)/(carbon having sp2 bonds) was around 2.5, whereas a relatively high voltage was required to achieve light emission at the ratio (carbon having sp3 bonds)/(carbon having sp2 bonds) of 0.5. The positions showing a particularly excellent electron emission characteristic had the ratio (carbon having sp3 bonds)/(carbon having sp2 bonds) of 2.50 or more.
An electron emission film having the ratio (carbon having sp3 bonds)/(carbon having sp2 bonds) of 2.6 has the resistivity of 0.6×104(Ω·cm), and its electron emission characteristic is better than that of an electron emission film having the ratio (carbon having sp3 bonds)/(carbon having sp2 bonds) of 2.50 to 2.55.
An electron emission film having the ratio (carbon having sp3 bonds)/(carbon having sp2 bonds) of 2.7 has the resistivity of 1.8×104(Ω·cm), and its electron emission characteristic is worse than that of the electron emission film having the ratio (carbon having sp3 bonds)/(carbon having sp2 bonds) of 2.6 but is equivalent to a film having the ratio (carbon having sp3 bonds)/(carbon having sp2 bonds) of 2.55, which is sufficient as the electron emission film of a field emission electrode.
An electron emission film having the ratio (carbon having sp3 bonds)/(carbon having sp2 bonds) of 3.0 has the resistivity of 5.6×104(Ω·cm), and its electron emission characteristic is worse than that of an electron emission film having the ratio (carbon having sp3 bonds)/(carbon having sp2 bonds) of 2.50. This is due to that the conductivity is lowered as the abundance ratio of the carbon having sp2 bonds is lowered, in addition to that the less presence of the carbon having sp2 bonds in the clearances between the diamond fine grains makes the thickness of the diamond seemingly larger and reduces the ratio of positions from where tunnel electrons can be efficiently emitted.
After such electron emission films were repeatedly manufactured, it was found that an electron emission film from which a favorable electron emission characteristic was obtained had the ratio (carbon having sp3 bonds)/(carbon having sp2 bonds) of 2.5 to 2.7. Particularly, an electron emission film from which a more favorable electron emission characteristic which would allow the threshold field intensity to be 1.5V/μm or lower was obtained had the ratio (carbon having sp3 bonds)/(carbon having sp2 bonds) of 2.55 to 2.65. Furthermore, an electron emission film which was the most stable and had a favorable electron emission characteristic had the ratio (carbon having sp3 bonds)/(carbon having sp2 bonds) of 2.60 to 2.62.
Further, an electron emission film having the resistivity of 1 kΩ·cm to 18 kΩ·cm had a favorable electron emission characteristic.
The cathode electrode 44 and the anode electrode 47 are sealed inside a glass tube 50 having an interior vacuum atmosphere. A wire 48 connected to the substrate 42 and a wire 49 connected to the opposite conductor 45 are led out from the glass tube 50. This kind of fluorescent tube 41 can emit light at a low threshold voltage.
A light source that comprises the electron emission film of the present invention can be applied to an FED (Field Emission Display), a backlight for a liquid crystal panel, and other light sources for home-use, or can be applied to a backlight for a personal computer, a digital camera, a cellular phone, etc., and a vehicle-mountable light source.
Another embodiment of the present invention will now be specifically explained with reference to the drawings.
A field emission electrode 131 according to the present embodiment functions as a cathode electrode, and comprises an electron emission film 130 that is formed on a carbon-nanowall 132 as a base layer formed on a substrate 101. An anode electrode 133 comprises a transparent conductive film made of a transparent conductive material selected at least from tin-doped indium oxide (ITO; Indium Tin Oxide), zinc-doped indium oxide, indium oxide (In2O3), tin oxide (SnO2), zinc oxide (ZnO), and cadmium-tin oxide, or a conductive film made of an opaque conductive material such as nickel, aluminum, etc., and is disposed so as to face the field emission electrode 1
31 apart therefrom by a predetermined distance. The electron emission film 130 of the field emission electrode 131 is disposed on a surface facing the anode electrode 133, and a fluorescent film 134 which will emit light by being excited by electrons emitted from the electron emission film 130 is disposed between the anode electrode 133 and the field emission electrode 131.
The field emission electrode 131 and the anode electrode 133 are sealed inside a glass tube 140 having a vacuum atmosphere inside. A wire 142 made of nickel or the like and connected to the substrate 101 and a wire 143 made of nickel or the like and connected to the anode electrode 133 are led out from the glass tube 140. The wire 142 and wire 143 that are led out are connected to a power source 144. The power source 144 causes a predetermined potential difference between the anode electrode 133 and the field emission electrode 131. At this time, cold electrodes emitted from the electron emission film 130 of the field emission, electrode 131 due to the field are attracted toward the anode electrode 133 due to the field between the field emission electrode 131 and the anode electrode 133 to collide on the fluorescent film 134, which is thereby caused to emit visible light. Such a fluorescent tube 141 can emit light at a low threshold voltage. Further, since the electron emission characteristic of the electron emission film 130 has no hysteresis, the durability of the electron emission film 130 is high.
The above-described fluorescent tube 141 is one called a VFD (Vacuum Fluorescent Display) which causes light emission by causing cold electrons collide against the fluorescent film 134 by applying a predetermined voltage between the anode electrode 133 and the field emission electrode 131, and can also be used in an FED (Field Emission Display) that has a flat panel structure including a plurality of such light emission regions as pixels.
The carbon-nanowall 132 is formed of a plurality of carbon thin flakes of a petal (fan) shape having a curved surface which are uprightly bonded to the others in random directions. The carbon-nanowall 132 has a thickness of 0.1 nm to 10 μm. Each carbon thin flake is formed of several to several tens of graphene sheets having a lattice interval of 0.34 nm.
Although it is clear that the electron emission film 130 has the diamond structure not the diamond-like carbon (DLC) structure because diamond peaks were found in it by XRD measurement, it shows a very small resistivity of 20 kΩ·cm or lower, as compared to the resistivity of smaller than 1016Ω·cm inherent in diamond. The resistivity of an electron emission film 130 having a favorable electron emission characteristic was 1 kΩ·cm to 18 kΩ·cm.
Checking the X-ray diffraction pattern of the electron emission film 130, conspicuous peaks of diamond crystals and also a peak of crystalline carbon having the graphite structure are observed. The carbon having this crystalline graphite structure is the carbon-nanowall 132 as the base layer for the electron emission film 130.
As a specific fitting method for obtaining the above-described spectrum curves, the portion of the actually-observed Raman spectrum that is between 750 cm−1 to 2000 cm−1 is extracted, and with the line that connects both ends (750 cm−1 and 2000 cm−1) of the extracted portion seen as a baseline, values existing on the baseline are eliminated from the spectrum. Then, as initial values, 1333 cm−1 and 1550 cm−1 are set as peak positions, heights are set to the actually-observed intensities of the Raman spectrum respectively at the wavenumber of 1333 cm−1 and the wavenumber of 1550 cm−1, and the line widths are respectively set to 200 cm−1 and 150 cm−1.
Then, by a nonlinear least-squares method, the spectrum is fit to pseudo-Voigt functions indicated by the following equation (1).
F(x)=a*[g*exp(−(√{square root over (2)}*(x−p)/w2))+(1−g)*1/(x−p)/w2)] [Equation 1]
where a=amplitude, g=Gauss/Lorenz ratio, p=peak position, and w=line width.
According to the nonlinear least-squares method, not only the peak intensity but also the peak position and the line width are allowed some tolerance, in fitting the spectrum to the pseudo-Voigt functions. Hence, as long as the initial values to be set first are appropriate ones, an optimum parameter that would restrict the error (×2) between the actually-observed spectrum and the set functions to the minimum can be obtained. Therefore, it is unnecessary to minutely and precisely set the peak wavelength. If spectrum fitting by the least-squares method under the following initial condition is available, a parameter that can have the optimum area ratio will be obtained. Though the nonlinear least-squares method is not algorithm-dependent, the Marquardt method is more preferable.
In this manner, the ratio of the area of the D band whose peak is at near 1333 cm−1 to the area of the G band whose peak is at near 1550 cm−1 is obtained in the form of a ratio (D-band intensity)/(G-band intensity). In
Accordingly, although the electron emission film 30 is seemingly a single-layer film as a whole, it has, when microscopically seen, a complex structure including the aggregates of diamond fine grains 103a, 103a, . . . formed of carbon of sp3 bonds indicated as D band and having a grain diameter of about 5 nm to 10 nm, and the carbon 103b formed of sp2 bonds showing the G-band intensity and existing between the diamond fine grains 103a, 103a, . . . . It is preferable that the ratio (D-band intensity)/(G-band intensity) is 2.5 to 2.7.
Assuming that the thickness of the electron emission film 130 is 3 μm, several hundreds of diamond fine grains 103a are continuously stacked in the thickness-wise direction. These diamond fine grains 103a are themselves insulative, but the carbon 103b formed of sp2 bonds existing in the clearances has conductivity, and therefore the electron emission film 130 as a whole has conductivity.
As described so far, the electron emission film 130 has been confirmed to include crystalline diamond in its composition from the X-ray diffraction pattern and to include carbon having sp2 bonds having a broad peak whose half-value width is 50 cm or more from the Raman spectroscopy spectrum, and to therefore have a complex structure including these. And since the electron emission film 130 shows conductivity, it can be confirmed that the carbon having sp2 bonds other than the insulative crystalline diamond includes carbon having the conductive graphite structure. And it can be confirmed by using a scanning electron microscope that this carbon is very thinly stacked in the uppermost surface of the electron emission film 130.
The spectrum of the carbon-nanowall 132 obtained by Raman spectroscopy is shown in
A plurality of needle-like sticks as shown in
The stick, which originates from the nucleus of carbon 103b including carbon having the graphite structure formed of sp2 bonds existing between the diamond find grains 103a and 103a, is grown in the vertical direction with respect to the direction of the surface of the electron emission film 130. Thus, the stick stands through the clearance between the diamond fine grains 103a and 103a.
Since each diamond fine grain 103a in the electron emission film 130 has a negative electron affinity and has a very small grain diameter of 10 nm or less, it can emit an electron by the tunnel effect. Furthermore, not only the carbon 103b including carbon having the graphite structure formed of sp2 bonds that exists in the clearances between the diamond fine grains 103a and 103a at a predetermined abundance ratio imparts conductivity to the film as a whole to thereby facilitate field emission, but also it is so arranged that the diamond fine grains be not stacked so continuously that the tunnel effect cannot be obtained.
That is, if about a hundred diamond fine grains 103a having a grain diameter of 10 nm are stacked in a predetermined direction with substantially no clearances therebetween, the thickness of the diamond will seemingly be 1000 nm, which will substantially inhibit the occurrence of the tunnel effect even if a strong field is applied. However, since the presence of the carbon 103b including carbon having conductivity separates the respective diamond fine grains 103a, each diamond fine grain 103a can exhibit the tunnel effect.
This tunnel effect allows an electron emitted from the substrate 101 upon a voltage application to be once injected via the carbon-nanowall 132 into a diamond fine grain 103a located on the surface of the carbon-nanowall 132, field-emitted from this diamond fine grain 103a, and again injected into a diamond fine grain 103a adjacent to that diamond fine grain 103a in the field direction, subsequently repeatedly causing such electron emission in the field direction of the electron emission film 130 and finally causing the electron to be moved to the surface of the electron emission film 130.
If the electric field between the field emission electrode 131 and the anode electrode 133 is small, the field is concentrated on the stick 104 that sticks out from the electron emission film 130 because field concentration is less likely to occur on the electron emission film 130 due to its surface being flat, and an electron is therefore field-emitted from the tip of the stick 104. Since the stick 104 has the steric structure, the electron emission film 130 having the stick 104 can cause field emission even if the field intensity between the field emission electrode 131 and the anode electrode 133 is small, whereas the electron emission film 130 having no stick 104 cannot cause field emission under such a condition.
When the field intensity between the field emission electrode 131 and the anode electrode 133 is increased, not only the stick 104 but also the surface of the electron emission film 130 cause field emission as shown in
Almost no stick 104 is found in the carbon-nanowall 132. This is because the growing speed of the carbon-nanowall 132 on the substrate 101 is relatively high, and this allows no stick 104 to grow by exceeding the growing speed of the carbon-nanowall 142.
The electron emission film 130 grows slowly at a speed of about 1 μm/h, and grows not only in the direction perpendicular to surface of the substrate 101 but also in the surface direction radially, whereas the stick 104 grows only in one direction and therefore grows faster than the electron emission film 130. Since the stick 104, because of its sticking structure, gets hotter than the surface of the electron emission film 130 while grown by being heated by plasma CVD described later, such a factor that the graphite structure formed of sp2 bonds whose range of appropriate growing temperatures is higher than that of the diamond structure formed of sp3 bonds is more likely to grow, also adds to the faster growing of the stick 104.
The surface of the electron emission film 130 has not only the stick 104 formed as shown in
With the dust-like carbon formed, the stick 104 has its surface area increased and thus can have its exoergicity improved. This prevents the adsorption gas from desorpting, prevents the ion bombardment on the electron emission film 130 by desorpting gas, and further prevents the tissue destruction due to the thermal vaporization of the stick 104. Furthermore, the dust-like carbon supports the thin stick 104 to save the stick from falling down or breaking down, and can improve the conductivity at the portion where the dust-like carbon contacts the stick 104.
The time required to form the electron emission film 130 by DC plasma is two hours, and the heating temperature during the film formation is 900° C. Accordingly, by slightly lowering the film forming temperature from 905° C., it is possible to increase the density of the number of sticks 104. However, since the electron emission film 130 shown in
The time required to form the electron emission film 130 by DC plasma is two hours, and the heating temperature during the film formation is 913° C. Accordingly, also by slightly raising the film forming temperature from 905° C., it is possible to increase the density of the number of sticks 104. However, the electron emission film 130 shown in
The growing speed of the diamond fine grain 103a, the carbon 103b, the stick 104, and the dust-like carbon in the electron emission film 130 is affected by various factors such as the material gas pressure and the gas convection in the DC plasma system, the shape and size of the positive electrode and negative electrode in the system, the distance between the positive electrode and the negative electrode, etc., and is not determined only by the film forming temperature and film forming time.
The electron emission film 130 whose stick number density is 5000 sticks/mm2 to 15000 stick/mm2 has the most favorable electron emission characteristic, followed by the electron emission film 130 whose stick number density is 15000 sticks/mm2 to 25000 stick/mm2, the electron emission film 130 whose stick number density is 45000 sticks/mm2 to 55000 stick/mm2, and the electron emission film 130 whose stick number density is 65000 sticks/mm2 to 75000 stick/mm2, in this order.
The method of manufacturing the electron emission film 130 will now be explained.
A DC plasma CVD system shown in
The chamber 110 has a table 111 thereinside, and a positive electrode 111a having a disk-like shape is mounted on the upper portion of the table 111. The substrate 101 is fixed on the upper placement surface of the positive electrode 111a. The table 111 is designed to rotate together with the positive electrode 111a about an axis “x”.
A cooling member 112 is disposed under the lower surface of the positive electrode 111a, and is structured to move upward and downward by an unillustrated moving system. The cooling member 112 is made of metal having a high heat conductivity such as copper, etc., and includes therein an unillustrated cooling medium such as water, calcium chloride aqueous solution, or the like that circulates therein to cool the entire cooling member 112. The cooling member 112 abuts on the positive electrode 111a by moving upward, and steals the heat from the substrate 101 via the positive electrode 111a.
A negative electrode 113 is disposed above the positive electrode 111a so as to face the positive electrode 111a with a predetermined distance therebetween. A flow path 113a through which a cooling medium flows is formed in the negative electrode 113, and tubes 113b and 113c are connected to both ends of the flow path 113a. The tubes 113b and 113c go through the holes formed in the chamber 110 and lead to the flow path 113a. The holes in the chamber 110 passed through by the tubes 113b and 113c are sealed by a sealing agent to ensure the airtightness in the chamber 110. The tube 113b, the flow path 113a, and the tube 113c restricts the heat generation of the negative electrode 113, by letting a cooling medium flow therethrough. Water, calcium chloride aqueous solution, air, inert gas, or the like is preferable as the cooling medium.
A window is formed in a side wall of the chamber 110, allowing the interior of the chamber 110 to be observed. Glass is set inside the window 114 to ensure the airtightness in the chamber 110. A radio-spectrometer 115 is disposed outside the chamber 110, for measuring the temperature of the substrate 101 via the glass of the window 114.
This DC plasma CVD system comprises a material system (unillustrated) for introducing material gas through a gas supply pipe 116, a gas ejection system (unillustrated) for adjusting the atmospheric pressure in the chamber 110 by ejecting gaseous body from the chamber 110 through a gas ejection pipe 117, and an output setting unit 118.
The pipes 116 and 117 passes through holes formed in the chamber 110. A sealing agent seals between these holes, the circumference of the pipes 116 and 117, and the chamber 110 to ensure the airtightness in the chamber 110.
The output setting unit 118 is a means for setting the voltage or the current density between the positive electrode 111a and the negative electrode 113, and is connected to the positive electrode 111a and to the negative electrode 113 by lead lines respectively. Each lead line passes through a hole formed in the chamber 110. The holes in the chamber 110 passed through by the lead lines are sealed by a sealing agent.
The output setting unit 118 comprises a control unit 118a, and the control unit 118a is connected to the radio-spectrometer 115 by a lead line. The control unit 118a, when activated, refers to the temperature of the film forming surface of the substrate 101 based on the emissivity of the film forming surface measured by the radio-spectrometer 115, and adjusts the voltage or the current density between the positive electrode 111a and the negative electrode 113 so that the temperature of the film forming surface of the substrate 101 will be an intended value.
Next, a film forming process for forming the electron emission film 130 by using the DC plasma CVD system of
In this film forming process, an electron emission film 20 which comprises a layer including the carbon-nanowall 132 and the electron emission film 130 formed on the carbon-nanowall 132 and including a plurality of diamond fine grains, is to be formed on the surface of the substrate 101 made of nickel or the like.
First, for example, a nickel plate is cut into substrates 101, and the substrate 101 is degreased and ultrasonic-cleaned sufficiently by using ethanol or acetone. The substrate 101 is fixed on the placement surface of the positive electrode 111a in the DC plasma CVD system.
When the substrate 101 is fixed, the interior of the chamber 110 is depressurized by the gas ejection system, and then hydrogen gas and gas comprising a compound (carbon-containing compound) that contains carbon in its composition such as methane are introduced through the gas supply pipe 116. The gas supply pipe 116 may include separate pipes for hydrogen gas and methane respectively, or may include one pipe in case the gases are mixed.
It is preferable that the gas comprising a compound that contains carbon in its composition is 3vol % to 30vol % of the whole material gas. For example, the mass flow of methane is set at 50 SCCM while that of hydrogen is set at 500 SCCM, and the whole pressure is set at 0.05 to 1.5 atm, preferably at 0.07 to 0.1 atm. The positive electrode 111a together with the substrate 101 is rotated at 10 rpm, and a DC power is applied between the positive electrode 111a and the negative electrode 113 to generate plasma, in a manner that the temperature variation on the substrate 101 is restricted within 5° C. and the state of plasma and the temperature of the substrate 101 are controlled.
For forming the carbon-nanowall 132, the temperature of the portion of the substrate 101 where the carbon-nanowall 132 is to be formed is maintained at 900° C. to 1100° C. and the film formation is carried out for a predetermined time. Radiation from the surface of the carbon-nanowall 132 being formed is measured by the radio-spectrometer 115. At this time, the cooling member 112 is set sufficiently apart from the positive electrode 111a, so that the temperature of the positive electrode 111a will not be affected. The radio-spectrometer 115 is designed to measure the temperature only from the thermal radiation from the surface of the substrate 101, by subtracting plasma radiation of the DC plasma CVD system, as shown in
At this time, the cooled positive electrode 111a cools the substrate 101 fixed thereon, and as shown in
Since the substrate 101 is cooled down rapidly at the timing TO, the growth of the carbon-nanowall 132 is stopped, and the plurality of diamond fine grains 103a start to grow from the nuclei of carbon-nanowall 132, eventually forming the electron emission film 130 on the carbon-nanowall 132, that includes the plurality of diamond fine grains 103a having a grain diameter of 5 nm to 10 nm formed of sp3 bonds and the conductive carbon 103b formed of sp2 bonds and existing in the clearances between the diamond fine grains 103a. In the process of the diamond fine grains 103a and carbon 103b growing, the sticks 104 are grown from such carbon 103b, which is exposed on the surface of the electron emission film 130.
When the cooling member 112 abutting on the positive electrode 111a is moved downward, the emissivity starts to rise together with the surface temperature of the substrate 101 due to the plasma. At this time, if the temperature rise is up to 950° C., the diamond fine grain 103a and the carbon 103b continue to grow without switching to grow into the carbon-nanowall 132.
By the manufacturing method described above, the state of the electron emission film 130 was checked at the timing T1, the timing T2, the timing T3, and the timing 14 shown in
Under conditions that the distance between the field emission electrode 131 and the anode electrode 133 was 4.5 mm and a voltage of 6000V was applied between these electrode to cause light emission, about 10 portions of the electron emission film 130 that correspond to the portions of the fluorescent film 134 from which light having the luminance of 70% or more of the highest luminance (cd/m2) of all the values obtained from the fluorescent film 134 was emitted, i.e., about 10 portions of the electron emission film 130 where the electron emission characteristic was favorable were sampled, with a sampling result that the density of the number of sticks 104 was 17000 sticks/mm2 to 21000 sticks/mm2. The ratio (number of sp3 bonds in the film)/(number of sp7 bonds in the film) of the electron emission film 130 was 2.50. As shown in
Note that since the electric field was concentrated on the edge portion of the field emission electrode 131 at the time of light emission and the field emission condition at the edge portion was therefore different from that of other portions, the light emission luminance at the portion of the fluorescent film 134 corresponding to the edge portion was not referred to as the highest luminance.
Under conditions that the distance between the field emission electrode 131 and the anode electrode 133 was 4.5 mm and a voltage of 6000V was applied between these electrode to cause light emission, about 10 portions of the electron emission film 130 that correspond to the portions of the fluorescent film 134 from which light having the luminance of 70% or more of the highest luminance (cd/m2) of all the values obtained from the fluorescent film 134 was emitted, i.e., about 10 portions of the electron emission film 130 where the electron emission characteristic was favorable were sampled, with a sampling result that the density of the number of sticks 104 was 16000 sticks/mm2 to 20000 sticks/mm2. The ratio (number of sp3 bonds in the film)/(number of sp2 bonds in the film) of the electron emission film 130 was 2.52. As shown in
Note that since the electric field was concentrated on the edge portion of the field emission electrode 131 at the time of light emission and the field emission condition at the edge portion was therefore different from that of other portions, the light emission luminance at the portion of the fluorescent film 134 corresponding to the edge portion was not referred to as the highest luminance.
Under conditions that the distance between the field emission electrode 131 and the anode electrode 133 was 4.5 mm and a voltage of 6000V was applied between these electrode to cause light emission, about 10 portions of the electron emission film 130 that correspond to the portions of the fluorescent film 134 from which light having the luminance of 70% or more of the highest luminance (cd/m2) of all the values obtained from the fluorescent film 134 was emitted, i.e., about 10 portions of the electron emission film 130 where the electron emission characteristic was favorable were sampled, with a sampling result that the density of the number of sticks 104 was 8000 sticks/mm2 to 12000 sticks/mm2. The ratio (number of sp3 bonds in the film)/(number of sp2 bonds in the film) of the electron emission film 130 was 2.60. As shown in
Note that since the electric field was concentrated on the edge portion of the field emission electrode 131 at the time of light emission and the field emission condition at the edge portion was therefore different from that of other portions, the light emission luminance at the portion of the fluorescent film 134 corresponding to the edge portion was not referred to as the highest luminance.
Under conditions that the distance between the field emission electrode 131 and the anode electrode 133 was 4.5 mm and a voltage of 6000V was applied between these electrode to cause light emission, about 10 portions of the electron emission film 130 that correspond to the portions of the fluorescent film 134 from which light having the luminance of 70% or more of the highest luminance (cd/m2) of all the values obtained from the fluorescent film 134 was emitted, i.e., about 10 portions of the electron emission film 130 where the electron emission characteristic was favorable were sampled, with a sampling result that the density of the number of sticks 104 was 5000 sticks/mm2 to 9000 sticks/mm2. The ratio (number of sp3 bonds in the film)/(number of sp2 bonds in the film) of the electron emission film 130 was 2.55. As shown in
Furthermore, etching on some portions of the electron emission film 130 once grown by the plasma was more proceeding than as shown in
In the above-described embodiment, the carbon-nanowall 132 was formed between the substrate 101 and the electron emission film 130. However, also by forming the electron emission film 130 directly on the substrate 101 as shown in
A light source comprising the field emission electrode according to the present invention can be applied not only to an FED, but also to a backlight for a liquid crystal panel and other home-use light sources, and furthermore to light sources for a personal computer, a digital camera, a cellular phone, etc. and to a vehicle-mountable light source.
Various embodiments and changes may be made thereunto without departing from the broad spirit and scope of the invention. The above-described embodiments are intended to illustrate the present invention, not to limit the scope of the present invention. The scope of the present invention is shown by the attached claims rather than the embodiments. Various modifications made within the meaning of an equivalent of the claims of the invention and within the claims are to be regarded to be in the scope of the present invention.
This application is based on Japanese Patent Application No. 2004-343203 filed on Nov. 26, 2004, Japanese Patent Application No. 2005-252928 filed on Aug. 31, 2005, and Japanese Patent Application No. 2005-299468 filed on Oct. 13, 2005 and including specification, claims, drawings and summary. The disclosure of the above Japanese Patent Application is incorporated herein by reference in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-343203 | Nov 2004 | JP | national |
| 2005-252928 | Aug 2005 | JP | national |
| 2005-299468 | Oct 2005 | JP | national |
The present application is a Continuation Application of U.S. application Ser. No. 11/287,838 filed Nov. 28, 2005, which is based on Japanese Patent Application Nos. 2004-343203 filed on Nov. 26, 2004, 2005-252928 filed on Aug. 31, 2005, and 2005-299468 filed on Oct. 13, 2005, all of which are incorporated herein by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11287838 | Nov 2005 | US |
| Child | 12779583 | US |
