KR20050048852A - Field emitter having thin and uniform protective layer - Google Patents

Abstract

The present invention relates to a field emission source in which a protective layer having a thin and uniform thickness is formed using atomic layer deposition. According to the present invention, since the thickness of the protective layer coated on the field emission source such as carbon nanotubes is thin and uniform, less than 20 nm, the carbon nanotubes retain their low turn-on voltage and excellent field emission characteristics peculiar to carbon nanotubes. By reducing the damage caused by the gas, it is possible to greatly improve the life and stability as a field emission source.

Description

Field emitter with thin, uniform protective layer {FIELD EMITTER HAVING THIN AND UNIFORM PROTECTIVE LAYER}

The present invention relates to a field emission source having a thin and uniform protective layer, specifically, a field emission source in which a uniform protective layer having a thinner thickness is formed by using an atomic layer deposition method on the tip surface of the field emission source. It is about.

The core technology of the field emission display is based on the processing technology and stability of the field emission source. Since the electric field to be applied to the source for field emission is very high, 3 to 7 × 10 ⁷ V / cm, much effort has been made to reduce the radius of the distal tip of the source to lower the field to be applied. . For this purpose, silicon or molybdenum was initially etched by lithography technology and used as field emission tips. However, in this case, a low electric field concentration effect has to be applied to a high voltage, and the number of tips per unit area is small, indicating that there is a big problem in life and stability.

On the other hand, when carbon nanotubes having high conductivity, sharp tips and large aspect ratios are used as field emission tips, the applied voltage can be reduced, and many studies have been conducted to find that the stability is large due to many tips. Even in the case of tube field emission sources, there is a problem in practical use due to short life due to reactivity with residual gas and tip damage caused by large current.In order to solve this problem, research on applying a protective film to carbon nanotubes and increasing vacuum degree is carried out. It is becoming.

For example, Korean Patent Application Publication No. 2003-60611 (published on July 16, 2003) relates to a field emission device having carbon nanotubes having a protective film, and specifically, arcing or residual gas of carbon nanotubes. In order to improve the field emission characteristics and stability of the field emission device by protecting from the damage caused by the present invention was proposed to coat a protective film on the carbon nanotubes. At this time, the protective film that can be used is made of any one material selected from nitride-based, carbon-based and oxide-based, the coating method of the protective film is a sputtering method, a method using an electron beam or a laser evaporator, chemical vapor deposition, sol or gel The method used was used.

However, in the case of coating the carbon nanotubes by the above coating method, the coating thickness of the protective film is not uniform, so that an average of several tens to several hundred nm of coating film is formed to cover all the ends of the carbon nanotubes. Such a protective film protects the carbon nanotubes, but reduces the concentration effect of the electric field generated at the end tip, thereby increasing the turn-on voltage and impacts as a shielding agent due to collisions with emission electrons. Entails.

Accordingly, the present inventors formed a uniform protective layer having a thinner thickness and a thickness of less than 20 nm in the carbon nanotubes by using an atomic layer deposition method different from the thin film coating method used in the prior art. The present invention was found to be able to significantly improve the stability and lifespan as an electric field emission source as well as preventing side effects due to residual gas while maintaining stability against overcurrent.

It is an object of the present invention to provide a field emission source having an increased field emission effect by having a thin, uniform thickness protective layer formed using atomic layer deposition.

In order to achieve the above object, the present invention provides a field emission source having a protective layer having a thickness of less than 20nm formed by using an atomic layer deposition method.

In addition, the present invention provides a field emission device or a field emission display having the field emission source.

Hereinafter, the present invention will be described in more detail.

The present invention relates to a field emission source having a thin and uniform protective layer formed by atomic layer deposition (ALD), which forms a thin film one by one by evaporating or gas-decomposing one element at a time.

Field emission sources to which the method for forming a protective layer according to the present invention can be applied include carbon nanostructures such as carbon nanotubes, fullerenes, carbon nanohorns, carbon films, gallium nitride, silicon carbide, and silicon. (silicon), gold, silver, iron, nickel, cobalt and other nanowires are included.

Since the atomic layer deposition method used in the present invention is very thin and can form a film having a uniform thickness irrespective of the area of the substrate and the unevenness of the target to be deposited, the step coverage is very good and there is no pinhole in the formed film. The deposition is performed according to a conventional method, for example, by installing a silicon substrate on which carbon nanotubes are grown in an atomic layer deposition apparatus, supplying a protective film, and then operating the atomic layer deposition apparatus in a constant cycle.

The material of the protective layer which can be coated on the field emission source according to the present invention is a pure metal (eg, Ag, Fe, Cu, Ni, Mg, W, Si, Al, etc.), an alloy of metals (eg FeW _X , AlW _X , FeMo _X , NiSi _X , CoSi _X, etc.), nitrides (e.g. boron nitride, boron carbon nitride, gallium nitride, aluminum nitride, etc.), carbonaceous materials (e.g. diamond, diamond-like material, tungsten carbide , Titanium carbide, and the like) and metal oxides (eg, hafnium oxide, magnesium oxide, silicon oxide, aluminum oxide, and the like).

The protective layer may be formed at both the end or the wall surface of the field emission source, the protective layer formed on the wall prevents the separation of the terminal protective layer and serves to prevent the defect site reacts with the residual gas.

When forming the protective layer using the atomic layer deposition method according to the present invention, a uniform thickness of less than 20 nm, preferably 1 to 10 nm, in an array of carbon nanostructures having a step difference between a field emission source, such as a tip, and an attachment surface of several tens of micrometers. It is possible to form a protective layer, thereby improving the field emission characteristics, lifetime and stability of the tanno nanostructures.

Hereinafter, the present invention will be described in more detail based on the embodiments. However, the scope of the present invention is not limited to the following Examples.

Example 1

After mounting a silicon substrate on which a 20 μm-long multi-walled carbon nanotube was vertically grown in an atomic layer deposition apparatus, the atomic layer deposition apparatus was operated in 100 cycles for 300 minutes to coat the carbon nanotubes with HfO ₂ .

After the deposition was completed, the thickness of the coated carbon nanotubes was measured by transmission electron microscopy. As shown in FIGS. 1A and 1B, the thickness of the HfO ₂ coated film formed at the ends of the carbon nanotubes was about 4 nm. The thickness of the HfO ₂ coating film formed in the portion was about 7 nm. That is, less than 10nm protective layer is formed on the carbon nanotubes, the thin protective layer, unlike the conventional thick protective film does not change the field emission characteristics of the carbon nanotubes themselves.

Comparative Example 1

After the silicon substrate on which the 20-micrometer-long multi-walled carbon nanotubes were vertically grown was installed on the top of the electron beam deposition apparatus, the MgO target at the bottom was heated with an electron beam and deposited on the carbon nanotubes for 60 minutes.

After the deposition was completed, the thickness of the carbon nanotubes was measured by transmission electron microscopy. As shown in FIG. 1C, the thickness of the MgO coating film formed at the ends of the carbon nanotubes was uneven at the top and the bottom thereof. To about 80 nm, and the diameter of the coated carbon nanotubes was 70 to 200 nm.

Meanwhile, FIG. 1D schematically illustrates carbon nanotubes having a protective layer according to Example 1 and Comparative Example 1. FIG. As can be seen from FIG. 1D, the coating by the atomic layer deposition method according to Example 1 is uniform and does not require a thick film to cover the tip, whereas the coating by the electron beam deposition method according to Comparative Example 1 is not uniform. A thick film is needed to wrap the tip. When the coating film of about 4 nm is formed on the end portion of the carbon nanotubes as in the atomic layer deposition method by the electron beam deposition method, a uniform film cannot be expected, and a substantial part is exposed to the residual gas.

Experimental Example 1: Evaluation of Field Emission Characteristics of Carbon Nanotubes with a Protective Layer

In each of the silicon substrates having the carbon nanotubes having the protective layer formed thereon according to Example 1 and Comparative Example 1, a spacer having a thickness of 150 μm was placed on the edge, and the indium tin oxide (ITO) and the phosphor-coated flat glass were placed thereon. The negative electrode was attached to the lower silicon substrate, and the positive electrode was attached to the upper glass substrate using silver paste, placed in a vacuum chamber, and evacuated. When the degree of vacuum reached 1x10 ^-6 torr, the voltage was increased between the upper and lower plates, and an electric field was applied to each end of each carbon nanotube, and the amount of current flowing through the upper plate was measured. When the current value was constant, a high purity pure gas injection line was opened and the discharge current amount was measured in the chamber as 1 × 10 ⁻⁵ torr.

2A shows the field emission characteristics of carbon nanotubes having a protective layer and carbon nanotubes having no protective layer by atomic layer deposition according to Example 1; Both carbon nanotubes showed a low onset voltage of 1.3 V / μm and an amount of discharge current in near vacuum. That is, according to the present invention, carbon nanotubes having a thin protective layer exhibited low starting voltage and excellent field emission characteristics, which are characteristics of carbon nanotubes, which are excellent as field emission sources.

On the other hand, as can be seen in Figure 2b, the start voltage of the carbon nanotubes with the protective layer formed by the electron beam deposition method in accordance with Comparative Example 1 was 3.3 V / ㎛ increased significantly than the start voltage of the carbon nanotubes themselves, Example The emission current amount is lower than that in the case of 1.

Experimental Example 2: Evaluation of Reactivity with Residual Gas of Carbon Nanotubes with a Protective Layer

The carbon nanotubes without the protective layer and the carbon nanotubes in which the protective layer was formed by the atomic layer deposition method according to Example 1 were measured for changes in the amount of current emission when exposed to oxygen. At this time, when the pressure in the vacuum chamber reached 1x10 ^-6 torr, oxygen was injected to raise the pressure to 1x10 ^-5 torr, and oxygen was removed to make an initial vacuum state. The results measured for the respective carbon nanotubes are shown in FIGS. 3A and 3B.

Figure 3a shows the current emission amount for the carbon nanotubes without a protective layer, the initial emission current after oxygen injection was reduced in size due to a large collision of the field emission electrons and oxygen, the emission amount gradually decreased over time This is because the length of carbon nanotubes is gradually reduced by the reaction of oxygen and carbon. In this case, in particular, all the oxidation of the carbon nanotube ends is made and the amount of emitted current does not recover even when oxygen gas is removed.

Meanwhile, in the case of carbon nanotubes in which a protective layer is formed by atomic layer deposition according to Example 1 shown in FIG. 3B, the initial emission current after oxygen injection is reduced by the electron shielding effect of oxygen as in FIG. After removal, when the original vacuum was reached, the amount of discharge current was significantly recovered. That is, the protective layer according to the present invention can be seen to reduce the effect on the residual gas, such as oxygen at the end of the carbon nanotubes.

According to the present invention, when a thin and uniform protective layer is formed on the carbon nanotubes by the atomic layer deposition method, it is possible to reduce the damage caused by the residual gas while maintaining the low starting voltage and the excellent field emission characteristics of the carbon nanotubes. It can greatly improve the service life and stability.

1A and 1B are transmission electron microscope (TEM) photographs of ends and walls of HfO ₂ coated carbon nanotubes by atomic layer deposition according to Example 1 of the present invention, respectively.

1c is a scanning electron microscope (SEM) photograph of a MgO-coated carbon nanotube by a conventional electron beam deposition method,

 1D schematically illustrates carbon nanotubes having a protective layer formed by atomic layer deposition and electron beam deposition;

Figure 2a is a graph comparing the field emission characteristics of the carbon nanotubes and HfO ₂ coated carbon nanotubes without a protective layer,

 2b is a graph showing field emission characteristics of MgO-coated carbon nanotubes by electron beam deposition;

3A and 3B are graphs showing changes in the amount of current emission when the field emission ends of the carbon nanotubes and the HfO ₂ coated carbon nanotubes without the protective layer are exposed to oxygen, respectively.

Claims (7)

A field emission source having a protective layer of less than 20 nm thick formed using atomic layer deposition. The field emission source of claim 1, wherein the field emission source is a carbon nanostructure or nanowire. The field emission source of claim 2, wherein the carbon nanostructures are carbon nanotubes, fullerenes, carbon nanohorns, or carbon films. The field emission source of claim 1, wherein the protective layer is made of at least one material selected from the group consisting of pure metals, alloys of metals, nitrides, carbonaceous materials and metal oxides. The field emission source of claim 1, wherein the protective layer has a thickness of 1 to 10 nm. 4. The field emission source of claim 3, wherein the carbon nanotubes are carbon nanotubes having an onset voltage of less than 3.3 V / µm. A field emission device or field emission display having a field emission source according to any one of claims 1 to 6.