KR101965813B1 - Stable amorphous electron emission materials in air and manufacturing method thereof - Google Patents

Abstract

The present invention relates to an amorphous electron emitting material stable in the air and a manufacturing method thereof. More specifically, the present invention relates to the amorphous electron emitting material stable in the air and capable of increasing n emission current at a low driving voltage due to the low work function characteristics, and the manufacturing method thereof. The electron emitting material of the present invention may have a work function, which is 30% or lower than a work function of about 4.3 eV in a commercial electron emission material Mo and carbon so that a large emission current may be obtained at the low driving voltage without a change in a conventional device structure when the electron emitting material is applied to an FED and a fluorescent tube. In addition, the electron emitting material of the present invention may be mass-produced using simple heat treatment, melt-solidification, and mechanical pulverization processes.

Description

TECHNICAL FIELD [0001] The present invention relates to a stable amorphous electron emission material in air and a method of manufacturing the same.

The present invention relates to an electron emitting material and a manufacturing method thereof. More particularly, the present invention relates to an amorphous electron-emitting material stable in air and capable of increasing an emission current at a low driving voltage with a low work function, and a manufacturing method thereof.

Field Emission Display (FED) is a device that emits electrons and displays images by emitting phosphors. It is one of the core technologies of large-area displays because of its advantage of thinness. In addition, since a fluorescent tube or an illumination device uses a micro electron source having an electron emitter that emits electrons by a strong current, by using a material having excellent electron emission characteristics and reducing the diameter of the tube, So that it can be applied to a backlight of a non-light emitting type display device such as a liquid crystal display.

The prior art used in a FED or a fluorescent tube uses a principle in which an electron beam is emitted from an electron emitter by applying a high voltage between an electron emitter and an electrode material and excited by a phosphor to emit light. As the electron emission material, a metal such as Mo or a carbon-based material is mainly used.

In order to facilitate the driving of the minute electron source, it is required to drive at a low voltage. Especially when the electron emission is controlled by on / off of the driving voltage like the FED, it is necessary to lower the driving voltage.

Therefore, it is necessary to develop a material having a small work function capable of increasing the emission current from the electron emitter at a low driving voltage. Currently used metal or carbon-based materials such as Mo have a work function which is directly related to easiness of electron emission, which is as large as 4 eV, so that a method of inducing concentration by forming a fine needle-shaped structure for electron emission at a low voltage is used.

For example, in the case of Mo, it needs to be processed into a cone shape with a height of 1 μm. In the case of carbon, it is necessary to use a structure having a diameter of several tens of nanometers, such as carbon nanotubes. However, the electron emitter structure of this shape is difficult to process the electrode, and if the interval between the electrodes is narrowed, there arises a problem in device fabrication and driving reliability.

The inventors of the present invention have developed amorphous Hf ₂ S _1-y having a work function lower than that of Mo and a carbon material by 20% while studying electron-emitting materials having low work function properties.

The amorphous Hf ₂ S _{1 -y} is formed to a thickness of several to several tens of nanometers on the surface of the crystalline material. In addition, the crystalline Hf ₂ S _{1- y} easily oxidizes the surface to form a HfO ₂ layer, thereby lowering the work function and decreasing the conductivity. However, the amorphous Hf ₂ S _1-y has a higher surface structure retention So that the deterioration of characteristics can be minimized.

An object of the present invention is to provide an electron-emitting material containing the amorphous Hf ₂ S _{1 -y} and a process for producing the same.

The present invention provides an amorphous electron emitting material comprising Hf and S and having a composition represented by the following formula (1).

≪ Formula 1 >

Hf ₂ S _{1 -y} (-0.2 ≤ y ≤ 0.2)

In one embodiment of the present invention, the material surface of the composition of Formula 1 has a composition ratio of Hf and S of about 2: 1, but the amount of S may be locally excessive or deficient.

The present invention also provides an electronic emitter comprising the amorphous electron emission material powder exposed on the surface.

Further, the present invention provides a fluorescent tube comprising the above-described electronic emitter.

The present invention also provides a method for producing a compound, comprising: a first step of preparing a compound raw material by a heat treatment step; A second step of melting and cooling the obtained raw material to prepare an electron emitting material having high homogeneity; And a third step of grinding the surface of the material obtained in the third step and pulverizing the surface of the amorphous electron emission material powder.

Specifically, a first step of mixing a Hf powder and an S powder and then heat-treating the mixture at a temperature of 450 to 600 ^° C for 2 to 4 days to obtain a compound raw material; A second step of melting and cooling the compound raw material obtained in the first step; And a third step of grinding and crushing the surface of the material produced in the second step.

It is preferable that the melting proceeds in an inert gas atmosphere.

The second step may be repeated one or more times.

In the third step, the surface of the material produced in the second step is scraped off by chemical etching or mechanical polishing.

In the third step, it is preferable that the surface of the material produced in the second step is scraped off in an inert gas atmosphere to prevent oxidation such as a vacuum, argon or nitrogen atmosphere.

The milling may be accomplished using ball milling, attrition milling, high energy milling, jet milling, or grinding using a mortar.

The pulverization may be carried out by gas atomization.

In the first step, the S powder may be added in a ratio of 0.8 to 1.2 based on 2 moles of the Hf powder.

The pulverizing step in the third step may be performed in a vacuum or an inert gas atmosphere.

The electron emission material of the present invention exhibits a very large electron emission effect due to the manifestation of low work function properties from the presence of the localized electron layer of the amorphous Hf ₂ S _{1 -y} material.

Hf ₂ S _{1 -y} contained in the electron-emitting material of the present invention has a work function which does not depend on the y value and exhibits a value of about 3.0 eV. This is a characteristic that is lower than the work function of Mo and carbon of commercial electron emission material by about 4.3 eV and is 30% or less. When applied to FED and fluorescent tube, a large emission current can be obtained at a low driving voltage without changing the existing device structure .

The method for producing Hf ₂ S _{1- y} electron-emitting materials provided in the present invention can easily mass-produce materials by simple heat treatment, melt-solidification and mechanical grinding processes.

The electron emission material provided in the present invention is easy to manufacture and can emit electrons with a low driving voltage. Therefore, it enables the implementation of an electronic emitter that forms a relatively large emission current on the same applied voltage basis, which can be effectively applied to low-voltage driven FEDs, fluorescent tubes and lighting devices.

FIG. 1 is a TEM microstructure photograph of amorphous Hf ₂ S _{1 - y} (0.2 ≦ y ≦ 0.2), which is an electron emission material of the present invention. An amorphous Hf ₂ S _{1 -y} material is formed on the surface of crystalline Hf ₂ S to a thickness of several to several tens of nanometers. There are localized electrons between the amorphous layer atoms, which is a source of low work function properties.
FIG. 2 shows X-ray photoelectron spectroscopy (XPS) analysis results of amorphous Hf ₂ S _1-y prepared in Example 1. FIG.
FIG. 3 shows the core level X-ray photoelectron spectroscopic analysis of the amorphous Hf ₂ S _{1 - y} prepared in Example 1. FIG. The area of each graph is determined to obtain the composition of the material Hf ₂ S _1-y .
4 is a result of ultraviolet photoelectron spectroscopy (UPS) analysis of the amorphous Hf ₂ S _1-y prepared in Example 1. FIG.
FIG. 5 shows the XPS / UPS results measured in FIG. 2 and the results of the re-measurement of the measured raw materials after 30 days.
6 is a graph comparing the conductivity of the crystalline and amorphous Hf ₂ S _{1 -y} raw materials before and after oxidation. As a result, it can be seen that the deterioration of the conductivity of the crystalline raw material is severe, while the deterioration of the conductivity of the amorphous raw material is small.
FIG. 7 is a graph showing the results of X-ray photoelectron spectroscopic measurement of an electron carrier sample before polishing the oxidized surface in the process of Example 1 and removing it. FIG. It can be seen that the pick due to oxidation is clearly visible on the surface.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention, and how to accomplish them, will become apparent by reference to the embodiments described in detail below with reference to the accompanying drawings.

However, the present invention is not limited to the embodiments described below, but may be embodied in various forms.

It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. Only.

Thus, in some embodiments, well-known components, well known operations, and well-known techniques may be omitted in order to avoid obscuring the present invention.

In this specification, the singular forms include plural forms unless the context clearly dictates otherwise, and the constituents and acts referred to as " comprising (or comprising) " do not exclude the presence or addition of one or more other constituents and actions .

Unless defined otherwise, all terms (including technical and scientific terms) used herein may be used in a sense commonly understood by one of ordinary skill in the art to which this invention belongs.

Hereinafter, the present invention will be described in detail.

According to one embodiment of the present invention, there is provided an amorphous electron emitting material comprising Hf and S and having a composition represented by the following formula (1).

≪ Formula 1 >

Hf ₂ S _1-y (-0.2 ≤ y ≤ 0.2)

The electron emission material shown in Formula 1 may be locally rich or small in the composition of S due to the nature of the amorphous material, but the entire composition converges on the Hf ₂ S composition and its electron emission characteristic is not sensitive to the amount of S.

The electron emission material includes a localized high-density electron and exhibits a large electron emission effect by a low work function property.

The electron emission material may be an amorphous layer present in the range of several to several tens of nanometers on the surface of the powdery or bulk phase.

Further, according to an embodiment of the present invention, there is provided a method of manufacturing a semiconductor device, comprising: (a) preparing a compound raw material by a heat treatment process; And (b) melt-cooling the raw material obtained in step (a) to produce an electron-emitting material having high homogeneity; And (c) pulverizing the material obtained in step (b).

The step (a) is a step of heat-treating the mixture of the starting materials for the seed phase synthesis before the melting process for producing the electron emission material.

Specifically, Hf and S raw materials vacuum-sealed in a silica tube are placed in a furnace and heat-treated at 450 to 600 ° C for 2 to 4 days.

The step (b) is a step for increasing the purity and homogeneity of the electron emission material.

Specifically, the heat-treated mixture prepared in step (a) is placed in an arc melting furnace chamber, and an atmosphere of an inert gas such as argon is formed at a level capable of arc driving after forming a vacuum atmosphere. Then arc is applied to melt the heat-treated mixture and solidify to produce an electron-emitting material.

The melting process may be performed by a process selected from the group consisting of a commonly used melting process, for example, a high-temperature tubular furnace, an ultra-high-temperature furnace, and the like, and may preferably be performed in arc melting. However, the present invention is not necessarily limited to these methods, and any method can be used as the melting method in the related art. The use of the arc melting method enables industrial mass production of the electron emission material, and improved properties can be obtained even when a general melting method other than the arc melting method is used.

In the arc melting method, the raw material is melted in an inert gas atmosphere in order to prevent the oxidation of the raw material by heating the raw material to a melting point or higher to form a liquid state. It is possible to obtain the electron emission material of the size and shape corresponding to the sample loading part made of the copper material in the arc melting facility chamber. Melting by arc melting can be repeated to increase the purity and homogeneity of the electron emission material.

The step (c) is a step of producing a powder.

Specifically, the surface of the lumpy material produced in step (b) is scraped off and the oxidized portion is removed in the process, and the powder is produced using a mechanical milling process such as ball milling in an oxidation preventing atmosphere.

At this time, as a method of removing the oxidized portion of the material surface, a chemical etching or mechanical polishing method capable of removing hafnium oxide in an inert gas atmosphere is possible. For example, it is possible to use etching using a mixture of hydrofluoric acid or hydrofluoric acid with a variety of ether organic solvents in a glove box, polishing using a grinding stone, a polishing pad, a grounder, a polisher, or the like.

The molten-solidified material may be pulverized by ball milling, attrition milling, high energy milling, zet milling, grinding in a mortar, or the like. However, the present invention is not limited thereto, and any method that can be used in the related art can be used as a method for producing powders by pulverizing raw materials by dry or wet methods.

The powder milling step of step (c) is preferably carried out in an inert gas atmosphere such as vacuum, argon, nitrogen or the like to prevent oxidation of the material.

Further, the electron emission material powder may be prepared by gas atomization. In the gas atomization method, the raw material of the compound prepared by the melting method is heated to a melting point or higher to form a liquid state, and rapidly injected into a vacuum or argon atmosphere at room temperature through a nozzle to quench the raw material powder.

Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples.

Example 1. Amorphous Hf ₂ S _1-y  (-0.2 ≤ y ≤ 0.2) Manufacturing and Characterization

The ground Hf and S powders were pelletized and vacuum-packed in a silica tube. The powder was placed in a furnace and sintered at 450 to 600 ° C for 2 to 4 days. Since Hf ₂ S _{1 -y} is a phase at high temperature, S is a substance with very low vaporization point, so pure S is made into a compound of Hf-S through the above sintering process in order to minimize the loss of S during material melting for synthesis. The sintered intermediate material is melted and solidified by the arc melting method, and then the oxidized surface is removed by grinding in a glove box, followed by ball milling.

As shown in the TEM photograph of FIG. 1, an amorphous material having a composition of Hf ₂ S _{1 -y} (0.2 ≤ y ≤ 0.2) is naturally formed on the surface of the crystalline Hf ₂ S.

The oxidation state of the raw material and the valence state of the element were measured using XPS as shown in Fig. The raw material was shattered inside the XPS equipment. As shown in the data, the material is not oxidized, and therefore, it is confirmed that there is no material deterioration due to oxidation.

As shown in FIG. 3, the y value of amorphous Hf ₂ S _{1 -y} was determined by core level XPS measurement. The area of the Hf and S core level graphs is obtained and substituted into the following equation to obtain the composition.

In this case, n _i I _i S _i is the composition ratio for the i element, the graph area, and the reported sensitivity factor.

As shown in FIG. 4, the amorphous Hf ₂ S _{1 -y} The work function was 3.0 eV, which was slightly higher than the work function of alkali metal but slightly lower than the work function of commercial products. There was almost no change in work function in the range of 0.2 ≤ y ≤ 0.2.

Comparative Example 1. Measurement of Mo and C work function

The work function was measured in the same manner as in Example 1 for Mo and C, respectively.

As shown in FIG. 4, Mo and carbon-based materials commonly used as electron emission materials have a work function near 4.3 eV. However, in the case of the amorphous Hf ₂ S _{1 -y} raw material synthesized by the present inventors, the material having a work function near 3.0 eV regardless of the composition of y in the range of 0.2 ≦ y ≦ 0.2. The work function of a metal such as Mo or a carbon- Since it has a much lower work function, electron emission is relatively easy at low voltages.

Table 1 below shows the results of work function measurements of amorphous Hf ₂ S _1-y , Mo and C prepared in Example 1 and Comparative Example 1.

matter The work function (eV) karbon nanotube 4.7-4.9 graphene ~ 4.5 Mo 4.36-1.95 Amorphous Hf ₂ S _1-y 3.0 ± 0.1

Example  2. Hf ₂ S _{One -y}  Stability evaluation

In order to evaluate the stability of Hf ₂ S _{1 -y} , the amorphous Hf ₂ S _{1 -y} powder prepared in Example 1 was measured again after about 30 days. As shown in the XPS and UPS results of FIG. 5, there was no significant difference in data before / after 30 days and there was no deterioration of work function value.

Also, as shown in the conductivity results in Fig. 6, it was confirmed that similar values appear in the data before and after 30 days.

Crystalline Hf ₂ S-based materials are easily oxidized to form HfO ₂ layers with high work function and low conductivity. Therefore, when the electron-emitting device using the crystalline Hf ₂ S is used, there is a possibility that sufficient conductivity can not be obtained or characteristics are deteriorated, and desired characteristics can not be obtained or the reliability of the device is lowered.

In contrast, since the surface structure of amorphous Hf ₂ S _{1 -y} is stably maintained, deterioration of the material properties is prevented. As a result, it is possible to manufacture a device that is easier and more reliable in handling than the conventional crystalline Hf ₂ S-based material.

The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents should be construed as falling within the scope of the present invention.

Claims (12)

An amorphous electron emitting material represented by the following formula (1).
≪ Formula 1 >
Hf ₂ S _1-y (-0.2 ≤ y ≤ 0.2)
An electron emitter comprising the amorphous electron emission material powder of claim 1 exposed on the surface.
A fluorescent tube comprising the electron emitter of claim 2.
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