JP3471263B2 - Cold cathode electron-emitting device and method of manufacturing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cold cathode electron emission device and a manufacturing method thereof, and more particularly to a cold cathode electron emission device using an emitter having a graphite crystal structure such as carbon nanotubes and a manufacturing method thereof.

[0002]

2. Description of the Related Art Display elements are commonly used in the modern information society, and the demand for them is ever expanding. Liquid crystal, semiconductor light emitting diode, hot cathode electron emitting device and the like are the mainstream of current display devices, but each has its own problems, and higher performance display devices are desired. One of the candidates for future display devices is an array of cold cathode electronic display devices. The prototypes manufactured up to now are those in which a semiconductor such as silicon is microfabricated to form a sensitive structure at the tip, and an electron-emitting type cold cathode electron-emitting device is arranged.
There is also a cold cathode electron-emitting device manufactured using a metal columnar crystal aggregate (Japanese Patent Laid-Open No. 8-264108).

Further, the cold cathode electron-emitting device is required to further improve the electron-emitting characteristics, and recently, the cold-cathode electron-emitting device using the carbon nanotube film is far more excellent than 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 a length of several microns, it has an extremely excellent structure for causing electric field concentration. For this reason, when carbon nanotubes are used as electron-emitting devices, the electron-emitting properties are better than those of artificially processed semiconductor electron-emitting devices.

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 into practical use. The reason is that there are still many drawbacks.

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

Further, the above fluctuations also lead to deterioration. In most cases, the adsorption of impurities hinders electron emission and causes deterioration of electron emission characteristics. Further, the field evaporation of C atoms also occurs in a sharp shape in which a stronger electric field is concentrated, so that the shape of the tip of the carbon nanotube changes to a smoother shape in which the electric field is less likely to concentrate, resulting in deterioration.

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

Further, in the present carbon nanotube thin film, the carbon nanotubes are not uniformly arranged, but the bundles of hundreds or thousands are not uniformly distributed and arranged. ing. For this reason, electron emission often occurs at the end of the bundle. Not only does this result in non-uniform electron emission, but it also reduces the efficiency of electron emission.

[0009]

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

[0010]

The present invention will be described below.

A first aspect of the invention is an emitter comprising a pair of electrodes consisting of a cathode and an anode, and a plurality of carbon nanotubes arranged on the surface of the cathode between the pair of electrodes so that the tip end faces the anode. The cold cathode electron-emitting device is characterized in that the tip end portion of the carbon nanotube exposes a plane perpendicular to the (0002) plane of the graphite forming the carbon nanotube.

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

For example, a carbon nanotube having a graphite crystal structure will be described. FIG. 9 is a cross-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 tubular two-layer graphite film 102. The film surface is the (0002) surface.

Since the carbon nanotube shown in FIG. 9 has a closed tip, the entire surface thereof is (000
2) plane, and when a carbon nanotube is used as an emitter, electrons are emitted from the (0002) plane.

FIG. 1 is a partial cross-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 formed.
Is oriented in a direction perpendicular to the surface of the cold cathode 1, and further,
By opening the tips of the graphite films of the inner and outer cylinders to form the open end surfaces 2a, the surface 2a perpendicular to the film surface of the graphite film 2 is formed, that is, the surface 2a perpendicular to the (0002) surface which is the side surface 2b of the cylinder. By forming it at the tip of the cylindrical graphite film, the anode 4 can be formed from the surface 2a perpendicular to the (0002) plane.
It enables a structure that emits electrons toward.

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

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

Further, the carbon nanotube is a multi-tubular structure side wall consists of two or more layers of graphite, between layers of the carbon nanotubes insulating molecule or atom that is inserted.

In the case of using the multi-walled carbon nanotube as shown in FIG. 1, it is possible to improve the electron emission characteristics of the cold cathode electron emission device by inserting an insulating material between the layers and expanding the layers. Become.

The insulating molecule or atom is
Those which are inserted between the layers together with the metal atom are also included.

Since the insulating substance is generally an inactive material, it is difficult to insert it between the carbon nanotube layers. However, when the insulating substance is introduced together with an alkali metal or a transition metal, the insulating substance is interposed between the carbon nanotube layers. Can be inserted.

A second invention is a method for manufacturing a cold cathode electron-emitting device, which comprises a step of forming a plurality of carbon nanotubes on the surface of a cathode and a step of opening the tip of the carbon nanotube by oxidation. is there.

As described in the first invention, it is important in the cold cathode electron emission device to open the tip of the carbon nanotube. Since a cylindrical graphite film having a closed tip as shown in FIG. 9 has many crystal defects at the tip and is chemically unstable, only the tip is selected by arranging the carbon nanotubes in an oxidizing atmosphere. It is possible to form the end face 2a perpendicular to the side face 2b by oxidatively oxidizing, that is, removing the carbon at the tip and breaking the bond between the carbons to open the tip of the carbon nanotube as shown in FIG.

In the second invention, the method further comprises a step of inserting a different molecule or atom other than carbon between the plurality of carbon nanotubes, and a step of removing the different molecule or atom .

Normally, when a carbon nanotube film is formed, a bundle (lump) of carbon nanotubes with closed tips is formed, and electrons tend to be emitted only from the periphery of the end portion of this bundle, so the amount of emitted electrons is large. The distribution of becomes non-uniform, resulting in non-uniform electron emission characteristics of the cold cathode electron-emitting device.As described above, by inserting or removing a different atom or molecule between carbon nanotubes, Since the bundle of carbon nanotubes can be disassembled into pieces, 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 foreign atoms may be inserted or removed before or after the oxidation heat treatment for opening the tip of the carbon nanotube.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail below.

As described above, in the cold cathode electron-emitting device using carbon nanotubes as the emitter, the tip of the carbon nanotube is formed by opening the tip of the carbon nanotube to form an opening end serving as an electron emission surface. It is important to cover with a BN layer, widen the layers of the graphite film forming the carbon nanotubes, and unbundle the carbon nanotube bundles.

In order to open the tip of the carbon nanotube, it is sufficient to oxidize the carbon nanotube. For example, in an oxygen gas atmosphere of 1 × 10 ^-2 to 1 × 10 ^-1 Pa,
By 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 larger than that at the side. If the conditions are less likely to oxidize 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 apt to oxidize, carbon other than the tip may also be removed. There is a risk that

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

In order to cover the carbon nano tube with the BN tube as in the present invention, first, only the carbon raw material is introduced, and the BN is added at the final stage of the growth of the carbon nanotube.
Introduce raw materials. Then, the 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 automatically stops at only 1 to 3 layers and does not grow any further, so it can be controlled automatically by this method. It is possible to prevent the electron emission characteristics from being deteriorated due to the layer being too thick.

As described above, the open ends of the carbon nanotubes cause electron emission 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 distance between layers, it is effective to insert atoms or molecules between layers.
When the molecule is a conductor, there is no effect of improving the electron emission property. This is because these interlayer atoms and molecules also become conductors like carbon nanotubes, and there is no effect of concentrating an electric field on the carbon nanotube layer. That is, the interlayer atoms and molecules need to be insulating.

However, an electrically inactive insulating atom,
Inserting molecules into carbon nanotubes is difficult.
Therefore, in the present invention, a metal atom that easily enters between layers
It was realized by inserting an inert gas together with (alkali metal and transition metal) between layers. It is also possible to utilize the fact that the oxidized molecule has an insulating property by subjecting the metal atom to oxidation by performing heat treatment in oxygen after the insertion of the metal atom.

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 an atom between the carbon nanotubes and removing the atomic molecule.

[0035]

[Example] Example 1 Embodiments of the present invention will be described below with reference to the drawings.

In this embodiment, a plurality of cold cathode electron-emitting devices shown in FIG. 2 are arranged and manufactured 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.
Were grown by vacuum sputtering. A quartz substrate can also be used as the substrate, and the result was almost the same as the BN substrate.

Then, C ₂ H ₂ as a raw material and N ₂ as a buffer gas are introduced, and plasma CVD (plasma) is performed.
-enhanced chemical vapor deposition) by 10 minutes Q at 650 ° C. Carbon nanotubes 23 the emitter thin films arranged aligned perpendicularly to the cathode 21 side was 10μm growth. At this time, the pressure of C ₂ H ₂ and N ₂ is 2 ×
10 ⁻² to 10 × 10 ⁻² Pa and 2 × 10 ⁻¹ to 10 ×
It was 10 ⁻¹ Pa. The plasma was generated by applying 10 A to a tungsten filament (diameter: 0.5 mm), arranging the filament and the substrate 25 at an interval of 9 cm, and applying a voltage so that a potential difference of 1000 V was generated between them.

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

Next, the
Do not evaporate K, which is a potassium metal, by locally heating it at 300 ° C.
Ra, H₂1 x 10 gas^-2Pa flow and substrate at 30 ° C
After heating for 30 minutes,
K and H between layers of laphite layer ₂Insert gas and spread the layers
It was This will increase the diameter of each carbon nanotube.
However, the layers are insulated, and the carbon nanotube 23 tip
The thin layer at the end of the graphite layer is exposed at the end.
It In addition, this treatment makes the carbon nanotubes 23
K and H between the men₂Gas was inserted at the same time. This will
Carbon nanotubes 23 can be spaced apart
It

After that, the heater for K is stopped, H ₂ gas is stopped at the same time, and the vacuum between the carbon nanotubes 23 is kept at 600 ° C. for 2 hours to about 10 ⁻⁴ Pa.
And H ₂ gas was removed.

The substrate 25 having the carbon nanotubes 23 was naturally cooled to room temperature and then exposed to the atmosphere from the vacuum device. When the surface of the carbon nanotube thin film thus produced was observed with a scanning electron microscope (SEM), the bundle of carbon nanotubes was unraveled. Figure 3 shows the observation results of electron micrographs of the thin film before the process after carbon nanotube growth (Fig. 3 (a)) and surface electron micrographs after all the above processes (Fig. 3 (b)). Shown in 3. In FIG. 3, (a) is 2 μm × 2 μm
And (b) is a TEM photograph of a cross section of 100 nm × 100 nm. After the process, the carbon nanotubes on the order of several nm are unwound, 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 bundles has changed. Met.

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

A resist is applied on the carbon nanotube thin film produced in this way, and by mask patterning, only a portion having a size of 1 mm × 1 mm and arranged at a cycle of 2 mm × 2 mm is covered with the resist, and other regions are sulfuric acid. To 1
Soak for 0 minutes at room temperature to remove. After cleaning and removing the resist, the BN insulating film 27 (1 mm × 1) having the same pattern shape as the pattern of the portion where no carbon nanotubes remain
BN with holes of mm size arranged in a cycle of 2 mm x 2 mm
The film, thickness 10 μm) was laminated to the above substrate under a microscope.

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

When the cold cathode electron-emitting device thus produced was placed in a vacuum device of × 10 ^-6 Pa and a predetermined voltage was applied to the cathode and the anode to form an electric field F between both 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.

The results are shown in FIG. A high anode current of 13 mA / cm ² at 5 V / μm was measured. In addition, this result is FN plot (Fowler-Nordhei
The result plotted with m p1ot) is shown in FIG. Linearity is obtained in the F-N plot, and it can be seen that the anode current is the electron emission current. It can be seen that electrons are emitted at a lower threshold voltage and the electron emission characteristic is superior to the conventional cold cathode electron emission characteristic in which the tip is closed and the bundle of tubes is unevenly distributed.

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

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 is formed.
A 00 nm Ni thin film 62 was grown by vacuum sputtering at room temperature. 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,
It was grown to 15 μm. The pressures of C ₂ H ₂ and H ₂ at this time were 5 × 10 ^-2 Pa and 2 × 10 ^-1 Pa, respectively. The plasma was generated by applying 10 A to the W filament (diameter 0.5 mm) and applying 1000 V between the filament and the substrate. After that, in the same growth apparatus, C ₂ H ₂ and H
_The substrate was heated at 600 ° C. for 1 hour to oxidize while flowing 2 × 10 ⁻¹ Pa of oxygen gas without flowing ₂ gas. Due to this oxidation heat treatment, the closed carbon nanotubes 63
Opened the tip of.

Next, while Cs, which is an alkali metal previously placed in a vacuum apparatus, is heated at 200 ° C. and vaporized,
Xe gas is flown at 1 × 10 ^-2 Pa and the substrate is heated at 300 ° C. for 30
After heating for minutes, Cs and X between the layers and between the carbon nanotubes
e was inserted at the same time. After that, the heater for heating Cs was stopped, and the temperature of Xe was gradually lowered to room temperature with flowing Xe over 1 hour, and then the atmosphere was released to the atmosphere.

When the surface of the carbon nanotube thin film thus produced was observed with a scanning electron microscope (SEM), the bundle of carbon nanotubes was found to be 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.
After that, the ^sample is placed in an ultra-high vacuum apparatus with a background vacuum of 1 × 10 ⁻⁶ Pa and BC is applied at a substrate temperature of 500 ° C.
l ₃ and NH ₃ are 2 × 10 ⁻⁵ Pa and 5 × 10 ⁻⁵ Pa, respectively.
Grew for 1 hour.

After that, when exposed to the atmosphere and observed by a transmission electron microscope, only one layer of the BN layer 66 covered the surface of the carbon nanotube with the open tip. The carbon nanotube thin film thus prepared is coated with a resist, and by mask patterning, only a portion having a size of 1 mm × 1 mm and arranged at a cycle of 2 mm × 2 mm is covered with the resist. Min soaked at room temperature to remove.

After the resist is washed and removed, the BN insulating film 67 having the same shape as the portion where the carbon nanotubes are not left (a hole having a size of 1 mm × 1 mm is 2 mm × 2 mm)
The BN films, which are arranged in a cycle of, and a thickness of 20 μm) were bonded on the substrate 61 while confirming it under a microscope. Then 0.8
The holes of Ta foil 64 (thickness 100 μm) in which holes of size 0.8 mm were arranged in a cycle of 2 mm × 2 mm were aligned so that the centers of the holes coincide with the centers of the holes of BN insulating film 67. This Ta foil 6
7 was used as a gate. Then, the second BN film 68
(BN film in which holes each having a size of 1 mm × 1 mm are arranged in a cycle of 2 mm × 2 mm, thickness: 2 mm) were laminated so that the centers of the respective holes were aligned. An electron-emitting display device was manufactured by placing a fluorescent plate 69 on the entire surface and flatly.

In this device, 20 pieces × 20 pieces = 4
00 elements were produced. The display element thus manufactured was placed in a vacuum device of 8 × 10 ⁻⁷ Pa to remove Ni from the substrate.
-1000V for the electrode (Emitter electrode), for the gate electrode-
When the fluorescent plate was observed with the fluorescent plate at 950 V and the fluorescent plate at 0 V, it was found to shine uniformly. Further, FIG. 7 shows the result of IV measurement by connecting the fluorescent plate electrode to the ammeter with the above device in the same vacuum. 15 mA / cm ² at an electric field of 5 V / μm
A high anode current was observed. The same data F
The −N plot is shown in FIG. 8, and excellent electron emission characteristics were measured.

Also, substantially the same results were obtained for each of 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 drawings]

FIG. 1 is a diagram for explaining 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. 4] is a view showing a TEM observation result after undergoing processes of oxidation, K and H ₂ molecule insertion, and vacuum drawing.

FIG. 4 shows I- of the cold cathode electron-emitting device according to the first embodiment.
The figure which shows V characteristic.

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

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

FIG. 7 is a diagram showing IV characteristics in the cold cathode electron-emitting device according to the second embodiment.

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

FIG. 9 is a cross-sectional view of a carbon nanotube whose tip is closed.

[Explanation of symbols]

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

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01J 1/304 H01J 9/02

Claims (5)

(57) [Claims] 1. A pair of electrodes composed of a cathode and an anode, and an emitter composed of a plurality of carbon nanotubes arranged between the pair of electrodes so that a tip end faces the anode on the surface of the cathode, Is the carbon nanotube composed of two or more layers of graphite?
And a tip of the carbon nanotube exposes a surface perpendicular to a (0002) plane of graphite forming the carbon nanotube, and an insulating molecule is provided at least between layers of the tip.
Alternatively , a cold cathode electron-emitting device in which atoms are inserted . 2. The tip portion of the carbon nanotube
Is characterized in that a metal atom is further inserted between the layers.
The cold cathode electron-emitting device according to claim 1, which is a characteristic. 3. The tip portion of the carbon nanotube
It has a boron nitride (BN) layer covering the
The cold cathode electron-emitting device according to claim 1, which is a characteristic. 4. A plurality of carbon nanotubes on the cathode surface
And the step of opening the tip of the carbon nanotube by oxidation.
Between the carbon nanotube layers, molecules other than carbon
Or the step of inserting atoms and the molecules or atoms on the surface of the carbon nanotube.
And a step of removing
Method of manufacturing an emitting device. 5. Carbon between the plurality of carbon nanotubes
The step of inserting a molecule or atom other than elementary, and the molecule or atom on the surface of the carbon nanotube.
5. The method according to claim 4, further comprising:
Method for manufacturing mounted cold cathode electron-emitting device.