JP2001093403A - Cold cathode electron emission element and manufacturing method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve, stabilize and uniformize the electron emission characteristic of a cold cathode electron emission element. SOLUTION: In a cold cathode electron emission element in which a carbon nano-tube 3 as an emitter is formed on the cathode surface, electrons are emitted from a plane perpendicular to an open end 2a at the tip of the carbon nano-tube 3, namely, the (0002) plane that is a side plane 2b for improving the electron emission characteristic. Forming of a BN layer 5 on the surface of the carbon nano-tube 3 prevents carbon from being evaporated from the tip of the carbon nano-tube or prevents impurities from bonded to the tip, therefore, the electron emission characteristic can be improved. The electron emission characteristic can be made uniform by loosening a bundle of the carbon nano- tube 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a cold-cathode electron-emitting device and a method of manufacturing the same, and more particularly, to a cold-cathode electron-emitting device using an emitter having a graphite crystal structure such as a carbon nanotube and a method of manufacturing the same.

[0002]

2. Description of the Related Art In the modern information society, display devices are generally used, and the demand for them is increasing. The current mainstream display devices are liquid crystal, semiconductor light-emitting diodes, hot cathode electron-emitting devices, and the like, each of which has problems, and further high-performance display devices are desired. One of the future display element candidates is an arrangement of cold cathode electronic display elements. The prototypes manufactured so far are those in which a semiconductor such as silicon is finely processed to form a sharp-pointed structure, and an electron emission type cold cathode electron emission element is arranged.
There is also a device in which a cold cathode electron-emitting device is manufactured using a metal columnar crystal aggregate (JP-A-8-264108).

Further, the cold cathode electron emitting device is required to further improve the electron emission characteristics. In recent years, the cold cathode electron emitting device using the carbon nanotube film has far exceeded the conventional electron emitting device. It has been found that the characteristics are excellent. Carbon nanotubes have a diameter of several n
Since it has a very thin and long cylindrical shape with a length of m and several microns, it has an extremely excellent structure for causing electric field concentration. For this reason, when the carbon nanotube is used as the electron-emitting device, the electron-emitting device exhibits better electron-emitting characteristics than the artificially processed semiconductor electron-emitting device.

[0004] As described above, the cold cathode electron-emitting device using carbon nanotubes is superior to other electron-emitting devices, but has not yet been put to practical use. The reason is that there are still many disadvantages.

The first problem is that the stability of the electron emission characteristics is low, and the number of emitted electrons, that is, the emission current always fluctuates by about 3%. It is believed that this is due to the adsorption of impurity atoms and molecules at the tip of the carbon nanotube and the electric field evaporation of the tip carbon (C) atoms. When an impurity is adsorbed on the tip, emission of electrons is generally hindered, or conversely, emission of electrons may be promoted. When the C atoms themselves evaporate in a strong electric field, the shape of the carbon nanotube tip changes, and the electron emission characteristics fluctuate.

[0006] The above fluctuations also lead to deterioration. In most cases, the adsorption of impurities hinders electron emission and causes deterioration of electron emission characteristics. Also, since the electric field evaporation of C atoms occurs in a sharp shape where a stronger electric field is concentrated, the tip shape of the carbon nanotube changes to a smoother shape in which the electric field is less likely to be concentrated due to the electric field evaporation, and as a result, deterioration occurs.

Although the electron emission characteristics of the carbon nanotubes after the initial deterioration are stable, there is a problem that the emitted electrons are small in the stable region, that is, the electron emission current is low.

Furthermore, in the current carbon nanotube thin film, a bundle of several hundreds or thousands of carbon nanotubes is not uniformly arranged but arranged in a non-uniform distribution. ing. For this reason, electron emission often occurs at the end of the bundle. This not only results in non-uniformity of electron emission, but also reduces the efficiency of electron emission.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to improve the electron emission characteristics of a cold cathode electron emission device, stabilize the electron emission characteristics, or make the electron emission characteristics uniform.

[0010]

The present invention will be described below.

According to a first aspect of the present invention, there is provided an emitter comprising a pair of electrodes comprising a cathode and an anode, and a plurality of carbon nanotubes arranged between the pair of electrodes on the surface of the cathode such that a tip thereof is opposed to the anode. Wherein the tip of the carbon nanotube exposes a surface perpendicular to a (0002) plane of graphite forming the carbon nanotube.

The present inventors have proposed a cold cathode electron-emitting device in which a material having a graphite crystal structure such as a carbon nanotube is used for an emitter.
002) It has been confirmed that by adopting a structure in which electrons are emitted from an end face perpendicular to the plane, electron emission characteristics can be improved, and the first invention has been achieved.

For example, a carbon nanotube having a graphite crystal structure will be described. FIG. 9 is a sectional view of a normal carbon nanotube. The carbon nanotube 103 shown in FIG. 9 is formed on the carrier 101 and is composed of a cylindrical graphite film 102 having two layers. The film surface is the (0002) plane.

Since the tip of the carbon nanotube shown in FIG. 9 is closed, the entire surface thereof is (000).
When the carbon nanotube is used as the emitter, electrons are emitted from the (0002) plane.

FIG. 1 is a partial sectional view showing a carbon nanotube according to the present invention. In the present invention, a tubular graphite film 2 constituting a carbon nanotube 3 is used.
Are oriented perpendicular to the surface of the cold cathode 1, and
By opening the front end of the graphite film of the inner and outer cylinders to form an open end surface 2a, a surface 2a perpendicular to the film surface of the graphite film 2 is formed, that is, the surface 2a perpendicular to the (0002) plane which is the side surface 2b of the cylinder is formed. By forming it at the tip of a cylindrical graphite film, the anode 4 can be removed from the surface 2a perpendicular to the (0002) plane.
This enables a structure that emits electrons toward.

The anode 4 of the carbon nanotube
It is desirable to cover one end on the side with a boron nitride (BN) layer 5.

Since BN has a similar crystal structure to graphite, it is possible to form a thin film on the surface of the carbon nanotube, and by forming this BN layer, it is possible to form a thin film from the tip of the carbon nanotube accompanying electron emission. Thus, the evaporation of carbon or the adsorption of impurities to the tip of the carbon nanotube can be prevented, and the electron emission characteristics of the cold cathode electron emission device can be stabilized.

Further, it is preferable that the carbon nanotube has a multi-cylinder structure in which a side wall is made of graphite having two or more layers, and insulating molecules or atoms are inserted between layers of the carbon nanotube.

When a multi-tubular carbon nanotube as shown in FIG. 1 is used, it is possible to improve the electron emission characteristics of the cold cathode electron-emitting device by inserting an insulating material between the layers and expanding the layers. Become.

The insulating molecule or atom may be
Also includes those inserted between the layers together with metal atoms.

The insulating substance is generally an inactive material, so it is difficult to insert the insulating substance between the carbon nanotube layers. However, the introduction of the insulating substance together with the alkali metal or the transition metal allows the insulating substance to be inserted between the carbon nanotube layers. Can be inserted.

According to a second aspect of the present invention, there is provided a method of manufacturing a cold cathode electron-emitting device, comprising the steps of: forming a plurality of carbon nanotubes on a cathode surface; and opening the tip of the carbon nanotubes by oxidation. is there.

As described in the first aspect of the invention, it is important for the cold cathode electron-emitting device to open the tip of the carbon nanotube. Since a cylindrical graphite film with a closed end as shown in FIG. 9 has many crystal defects at the end and is chemically unstable, only the end is selected by placing carbon nanotubes in an oxidizing atmosphere. By oxidizing the carbon nanotubes, that is, removing the carbon at the tip and cutting the bonds between the carbons, the tip of the carbon nanotube can be opened as shown in FIG. 1 to form the end face 2a perpendicular to the side face 2b.

Further, in the second invention, it is preferable to add a step of inserting a different molecule or atom other than carbon and a step of removing the different molecule or atom between the plurality of carbon nanotubes.

Normally, when a carbon nanotube film is formed, a bundle of carbon nanotubes whose ends are closed is formed, and electrons tend to be emitted only from around the end of the bundle. Distribution became uneven, resulting in non-uniformity of the electron emission characteristics of the cold cathode electron-emitting device.As described above, by inserting and removing different atoms or molecules between carbon nanotubes, Since the bundle of carbon nanotubes can be broken apart, the distribution of the amount of electrons emitted from each tube can be made uniform, and the electron emission characteristics of the cold cathode electron-emitting device can be made uniform.

The insertion and removal of foreign atoms may be performed before or after the oxidation heat treatment for opening the tip of the carbon nanotube.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail.

As described above, in a cold cathode electron-emitting device using a carbon nanotube as an emitter, the tip of the carbon nanotube is opened to form an open end serving as an electron emission surface. It is important to cover with a BN layer, widen the layers of the graphite film constituting the carbon nanotube, and release the bundle of carbon nanotubes.

In order to open the tip of the carbon nanotube, the carbon nanotube may be oxidized, for example, in an oxygen gas atmosphere of 1 × 10 ^-2 to 1 × 10 ^-1 Pa.
By performing heating at about 650 to 750 ° C., the tip can be selectively oxidized. Selective oxidation is possible because the number of crystal defects at the tip is greater than that at the side. If the condition is less oxidizable than this, the tip of the carbon nanotube may not be sufficiently oxidized and the tip may not be opened.If the condition is more easily oxidized, carbon other than the tip is also removed. There is a risk that it will.

The covering of the surface of the carbon nanotube with a BN layer having excellent electrical insulation is realized by the following method. During the growth of the carbon nanotubes, a gas or a solid as a BN raw material is introduced. C and BN never mix under thermal equilibrium conditions, and to separate them, the carbon nanotube layer and the BN nanotube layer separate. As a result, a composite tube in which the carbon nanotubes and the BN nanotubes are coaxially combined is obtained.

In order to cover the carbon nano tube with the BN tube as in the present invention, only the raw material of carbon is first introduced, and the BN is grown at the last stage of the growth of the carbon nanotube.
Introduce the raw materials. Then, carbon nanotubes covered with the BN layer can grow. In general, when the degree of vacuum during BN growth is 10 ⁻⁴ Pa or less, the growth stops automatically only in 1 to 3 layers and does not grow any more, so that it can be controlled automatically by this method. It is possible to prevent a decrease in electron emission characteristics due to an excessively thick layer.

As described above, since the tip of the carbon nanotube is open, electron emission occurs at a lower voltage. However, by increasing the interlayer distance (between the inner and outer cylinders), electron emission occurs at a lower voltage. Can be realized. In order to increase the interlayer distance, it is effective to insert atoms or molecules between the layers.
When the molecule is a conductor, there is no effect of improving the electron emission characteristics. This is because these interlayer atoms and molecules become conductors like carbon nanotubes, and have no effect of concentrating an electric field on the carbon nanotube layer. That is, interlayer atoms and molecules need to be insulating.

However, electrically inert insulating atoms,
It is difficult to insert molecules into carbon nanotubes.
Therefore, in the present invention, metal atoms that easily enter between layers
This was achieved by inserting an inert gas between the layers together with (alkali metal or transition metal). Further, it is also possible to perform a heat treatment in oxygen after inserting the metal atoms to oxidize the metal atoms and utilize the fact that the oxidized molecules have insulating properties.

On the other hand, in order to unwind the bundle of carbon nanotubes, it is possible to unwind the bundle by inserting an inert molecule or atom between the carbon nanotubes and removing the atomic molecule.

[0035]

Embodiment 1 Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

In this embodiment, a plurality of cold-cathode electron-emitting devices shown in FIG. 2 were arranged as follows.

First, a 100 nm thick Ni thin film 21 serving as a cathode is formed on the entire surface of a BN substrate 25 having a size of 16 mm × 12 mm.
Was grown by vacuum sputtering. A quartz substrate could be used as the substrate, and the result was almost the same as that of the BN substrate.

Further, C ₂ H ₂ as a raw material and N ₂ as a buffer gas are introduced, and plasma CVD (p1asma-en
The emitter thin film 23a in which the carbon nanotubes 23 are aligned perpendicular to the surface of the cathode 21 by the enhanced chemical vapor deposition) is applied at 650 ° C. for 10 minutes for 10 μm.
m. At this time, the pressures of C ₂ H ₂ and N ₂ are 2 × 10 ⁻² to 10 × 10 ⁻² Pa and 2 × 10 ⁻¹ to 10 × 1, respectively.
It was 0 ^-1 Pa. Plasma is flowed at 10 A through a tungsten filament (0.5 mm in diameter), and the filament and the substrate 25 are arranged at 9 cm intervals.
The voltage was generated by applying a voltage so that a potential difference of 00 V was generated.

Thereafter, in the same growth apparatus, oxygen gas was supplied at 1 × 10 ^-2 to 10 × 1 without flowing C ₂ H ₂ and N ₂ gas.
The substrate was heated and oxidized at 700 ° C. while flowing 0 ⁻² Pa. By this oxidation heat treatment, the tips of the closed carbon nanotubes 23 were opened.

Next, the aluminum previously placed in the vacuum device
Do not vaporize K which is potassium metal locally by heating at 300 ℃.
Gara, H_Two1 × 10 gas^-2Pa flow, substrate at 30 ° C
Heat for 30 minutes to make a group of carbon nanotubes 23
K and H between the graphite layers _TwoInsert gas and spread the layers
Was. This increases the diameter of each carbon nanotube.
Although the layers are insulated, the carbon nanotubes
A thin layer at the end of the graphite layer is exposed at the end.
You. In addition, the carbon nanotube 23
Between K and H_TwoGas was inserted at the same time. This allows
Can be provided between the carbon nanotubes 23.
You.

Thereafter, the heater for K was stopped, the H ₂ gas was stopped at the same time, and the vacuum between the carbon nanotubes 23 was reduced by evacuating to about 10 ⁻⁴ Pa at 600 ° C. for 2 hours.
And removing the H ₂ gas.

The substrate 25 having the carbon nanotubes 23 was naturally cooled to room temperature, and then discharged from a vacuum device to the atmosphere. Observation of the surface of the thus formed carbon nanotube thin film with a scanning electron microscope (SEM) revealed that the bundle of carbon nanotubes was unraveled. Fig. 3 shows the results of electron micrographs (Fig. 3 (a)) of the thin film before performing the process after carbon nanotube growth and surface electron micrographs (Fig. 3 (b)) after performing all the above processes. 3 is shown. In FIG. 3, (a) is 2 μm × 2 μm
(B) is a cross-sectional TEM photograph of 100 nm × 100 nm. After the process, the carbon nanotubes of the order of several nm are unwound, respectively, but the carbon nanotubes before the process are bundles of several tens to several hundreds of nm, and it is clear that the presence or absence of the carbon nanotube bundle has changed. Met.

In the actual fabrication of the device, it is not exposed to the atmosphere,
After evacuation at about 10 ⁻⁴ Pa at 600 ° C. for 2 hours, a BN layer 26 was subsequently grown. The substrate temperature was set to 650 ° C., and BCl ₃ and NH ₃ were added at 2 × 10 ⁻⁴ Pa and 5 × 10 ⁻⁴ P
a, and N ₂ was added as a buffer gas at 5 × 10
^-3 Pa and a BN layer 26 on the surface of each carbon nanotube.
Was grown to three layers or less.

A resist is applied on the carbon nanotube thin film thus formed, and only a portion having a size of 1 mm × 1 mm and a line of 2 mm × 2 mm is covered with the resist by mask patterning, and the other region is sulfuric acid. 1 in
Removed by soaking for 0 minutes at room temperature. After cleaning and removing the resist, the BN insulating film 27 (1 mm × 1
BN in which holes of size mm are arranged in a cycle of 2 mm x 2 mm
A film having a thickness of 10 μm) was bonded to the above substrate under a microscope.

Thereafter, a Pt foil serving as the anode 24 was placed flatly on the entire surface of the BN insulating substrate to produce the cold cathode electron-emitting device shown in FIG.

The cold cathode electron-emitting device thus manufactured is put in a vacuum device of × 10 ⁻⁶ Pa, a predetermined voltage is applied to the cathode and the anode, and an electric field F is formed between the two electrodes. The electron emission characteristics were evaluated by measuring the current value Ia observed at the anode by the electrons emitted from the carbon nanotube emitter.

FIG. 4 shows the result. At 5 V / μm, a high anodic current of 13 mA / cm ² was measured. In addition, this result is plotted on an FN plot (Fowler-Nordheid).
FIG. 5 shows the result of plotting with (mp1ot). Linearity is obtained in the FN plot, indicating that the anode current is the electron emission current. Compared to the conventional cold-cathode electron emission characteristics in which the tip is closed and the bundle of tubes is unevenly distributed, it can be seen that electrons are emitted at a low threshold voltage and the electron emission characteristics are excellent.

In each of the manufactured devices, substantially the same values were obtained.

Example 2 FIG. 6 is a schematic view of a cold cathode electron-emitting device manufactured in Example 2. This cold cathode electron-emitting device was manufactured as follows.

First, a quartz substrate 61 having a diameter of 30 mm and a thickness of 1 mm
A 00 nm Ni thin film 62 was grown at room temperature by vacuum sputtering. Thereon, C ₂ H ₂ and to H ₂ introduced as an ambient gas for 5 minutes at 650 ° C. The thin film of carbon nanotubes 63 by plasma CVD, which is a raw material,
The growth was 15 μm. At this time, the pressures of C ₂ H ₂ and H ₂ were 5 × 10 ⁻² Pa and 2 × 10 ⁻¹ Pa, respectively. Plasma was generated by flowing 10 A through a W filament (diameter 0.5 mm) and applying 1000 V between the filament and the substrate. After that, C ₂ H ₂ and H
_The substrate was heated and oxidized at 600 ° C. for one hour while flowing oxygen gas at 2 × 10 ⁻¹ Pa without flowing _two gases. By this oxidation heat treatment, the closed carbon nanotubes 63
Opened the tip.

Next, Cs, which is an alkali metal previously placed in a vacuum device, is heated at 200 ° C. and vaporized.
Xe gas is flowed at 1 × 10 ⁻² Pa, and the substrate is heated at 300 ° C. for 30
And heat Cs and X between the layers and between the carbon nanotubes.
e was inserted at the same time. Thereafter, the heater for Cs was turned off, and the temperature was gradually lowered to room temperature over 1 hour while flowing Xe, and then the air was discharged to the atmosphere.

When the surface of the thus formed carbon nanotube thin film was observed with a scanning electron microscope (SEM), the bundle of carbon nanotubes was unraveled. Also, X
When the line diffraction was measured, the interlayer distance was 0.31 nm, which was larger than the interlayer distance of the carbon nanotube.
Thereafter, the substrate was placed in an ultra-high vacuum apparatus having a background vacuum of 1 × 10 ⁻⁶ Pa, and BC was applied at a substrate temperature of 500 ° C.
l ₃ and NH ₃ are 2 × 10 ⁻⁵ Pa and 5 × 10 ⁻⁵ Pa, respectively.
Grown for 1 hour.

Thereafter, the film was taken out to the atmosphere and observed with a transmission electron microscope. As a result, it was found that only one layer of the BN layer 66 covered the surface of the open carbon nanotube. A resist is applied on the carbon nanotube thin film thus formed, and only a portion having a size of 1 mm × 1 mm and a line of 2 mm × 2 mm is covered with the resist by mask patterning. For 10 minutes at room temperature.

After the resist was washed and removed, a BN insulating film 67 having the same shape as the portion where no carbon nanotube remains (a hole having a size of 1 mm × 1 mm having a size of 2 mm × 2 mm) was formed.
The BN films arranged at a period of 20 μm and having a thickness of 20 μm) were adhered to the substrate 61 while confirming it under a microscope. Then 0.8
The center of the hole of the Ta foil 64 (thickness: 100 μm) in which holes having a size of × 0.8 mm are arranged at a cycle of 2 mm × 2 mm is aligned with the center of the hole of the BN insulating film 67. This Ta foil 6
7 was used as a gate. After that, the second BN film 68
(BN film in which holes of 1 mm × 1 mm in size were arranged at a cycle of 2 mm × 2 mm, thickness of 2 mm) were bonded so that the centers of the holes were aligned. A fluorescent screen 69 was placed flatly on the entire surface to produce an electron emission display device.

In this device, 20 × 20 = 4
00 elements were produced. The display element thus manufactured was put in a vacuum device of 8 × 10 ⁻⁷ Pa, and Ni
-1000V for electrode (Emitter electrode),-for gate electrode
When the fluorescent plate was observed at 950 V and the fluorescent plate was set at 0 V, the fluorescent plate was uniformly lit. FIG. 7 shows the results of IV measurement performed by connecting the phosphor plate electrode to an ammeter using the above-described element in the same vacuum. 15 mA / cm ² at an electric field of 5 V / μm
A high anode current was observed. In addition, F of the same data
The −N plot is shown in FIG. 8, where excellent electron emission characteristics were measured.

In addition, substantially the same results were obtained for the manufactured devices.

[0057]

According to the present invention, the electron emission characteristics of the cold cathode electron emission device can be improved, the electron emission characteristics can be stabilized, or the electron emission characteristics can be made uniform.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a carbon nanotube according to the present invention.

FIG. 2 is a diagram showing a cold cathode electron-emitting device of the present invention.

FIG. 3A is a view showing an SEM observation result immediately after the growth of a plurality of carbon nanotubes according to the present invention. (B)
FIG. 3 is a view showing a TEM observation result after a process of oxidation, insertion of K and H ₂ molecules, and evacuation.

FIG. 4 is a diagram showing I- of the cold cathode electron-emitting device in Example 1.
The figure which shows a V characteristic.

FIG. 5 is an FN plot showing the results of FIG. 4 as electron emission characteristics.

FIG. 6 is a schematic view showing another cold cathode electron-emitting device of the present invention.

FIG. 7 is a diagram showing an IV characteristic of the cold cathode electron-emitting device according to the second embodiment.

8 is an FN plot showing the results of FIG. 5 as electron emission characteristics.

FIG. 9 is a cross-sectional view of a carbon nanotube having a closed end.

[Explanation of symbols]

 1, 21 ... Cathode 2 ... Cylindrical graphite film 3, 23 ... Carbon nanotubes 4, 24 ... Anode 25 ... Substrate

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4G046 CA00 CA02 CB03 CB08 CC02 CC05 CC06 4K030 AA09 BA01 BA27 BA39 BA53 BB05 BB14 DA08 FA01

Claims (7)

[Claims] An electrode comprising a pair of electrodes comprising a cathode and an anode, and an emitter comprising a plurality of carbon nanotubes arranged between the pair of electrodes on the surface of the cathode such that a tip portion faces the anode. The tip of the carbon nanotube is made of graphite (0002) forming the carbon nanotube.
A cold cathode electron-emitting device having a surface perpendicular to the surface exposed. 2. The carbon nanotube is a multi-walled carbon nanotube composed of two or more layers of graphite,
2. The cold-cathode electron-emitting device according to claim 1, wherein insulating molecules or atoms are inserted between at least the layers of the tip of the carbon nanotube. 3. The cold-cathode electron-emitting device according to claim 2, wherein said tip of said carbon nanotube further has metal atoms inserted between said layers. 4. The cold cathode electron emission device according to claim 1, further comprising a boron nitride (BN) layer covering said tip portion of said carbon nanotube. 5. A method for manufacturing a cold cathode electron-emitting device, comprising: a step of forming a plurality of carbon nanotubes on a cathode surface; and a step of opening a tip of the carbon nanotube by oxidation. 6. The method according to claim 5, further comprising the steps of: inserting a molecule or atom other than carbon between the layers of the carbon nanotube; and removing the molecule or atom on the surface of the carbon nanotube. A method for manufacturing a cold cathode electron-emitting device. 7. The method according to claim 5, further comprising: inserting a molecule or atom other than carbon between the plurality of carbon nanotubes; and removing the molecule or atom from the surface of the carbon nanotube. The method for manufacturing a cold cathode electron-emitting device according to the above.