# Patent

## Title
Composite field emission source

## Abstract

A method of fabricating a composite field emission source is provided. A first stage of film-forming process is performed by using RF magnetron sputtering, so as to form a nano structure film on a substrate, in which the nano structure film is a petal-like structure composed of a plurality of nano graphite walls. Afterward, a second stage of film-forming process is performed for increasing carbon accumulation amount on the nano structure film. Therefore, the composite field emission source with high strength and nano coral-like structures can be obtained, whereby improving the effect and life of electric field emission.

## Background
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the priority benefit of Taiwan application serial no. 96150312, filed on Dec. 26, 2007. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of specification.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a field emission source technology, in particular, to a composite field emission source and a method of fabricating the same.
2. Description of Related Art
Display devices are playing an increasingly important role in people's daily life. Computers, TVs, mobile phones, PDAs, digital cameras etc., all transmit information by controlling display devices. Contrary to the conventional Cathode Ray Tube displays, the latest-generation panel displays are advantageous in that they are light, compact, and health-friendly.
Among various technologies for panel display devices, field emission displays (FED) boast not only great graphic qualities as found in conventional Cathode Ray Tube displays, but also high luminous efficiency, short response time, good display coordination performance, high brightness of more than 100 ftL, slim and light structure, wide viewing angle, broad range of working temperature, and high acting efficiency, contrary to Liquid Crystal Displays (LCD) which are problematic in narrow viewing angle, narrow working temperature range, and short response time. Besides, FEDs do not require backlight modules; they can provide superior brightness even when used in sunlight. Therefore, the current field emission displays has been regarded as a new display technology that is competitive against the LCD technology and even replace the LCD technology.
Recently, research in electric emitter of the FED trends mostly to carbon material, for example amorphous carbon film, diamond film, diamond-like carbon film, and carbon nanotube, and is mainly the carbon nanotube with low turn-on field of carbon nanotube. In addition, the carbon nanotube FED is self luminescent, so it can be applied to backlight source of the LCD or can serve as a flat panel light source.
However, the structure of the carbon nanotube cannot bear the high current and is easily to be burnt up, and when it is applied to screen printing process, field emission points of the carbon nanotube are disordered and dense, so it is difficult to control the emission current. Although in Taiwan patent application No. 95115215, the technology of fabricating the carbon nanotube by using radio frequency (RF) magnetron sputtering is provided to solve the problem that the carbon nanotube is easily to be burnt up due to over-high current, the turn-on field is still high.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a method of fabricating a composite field emission source, capable of preventing the problem of burn up due to over-high current, and reducing a turn-on field.
The present invention is directed to a composite field emission source, so as to improve effect and life of an electric field emission.
The present invention provides a method of fabricating a composite field emission source. Firstly, a first stage of film-forming process is performed by using RF magnetron sputtering, so as to form a nano structure film on a substrate, in which the nano structure film is a petal-like structure composed of a plurality of nano graphite walls. Afterward, a second stage of film-forming process is performed for increasing carbon accumulation amount on the nano structure film.
In an embodiment of the present invention, if identical processing devices and gases are used, a temperature of the second stage of film-forming process must be higher than a temperature of the first stage of film-forming process.
In an embodiment of the present invention, the second stage of film-forming process includes a thermal deposition process, in which the thermal deposition process includes a thermal chemical vapor deposition (CVD) or a low pressure chemical vapor deposition (LPCVD).
In an embodiment of the present invention, a temperature of the thermal CVD is between 600° C. and 800° C., and a time of the thermal CVD is between 5 minutes and 30 minutes.
In an embodiment of the present invention, gases of the thermal CVD include NH3 and a carbon containing gas, in which the carbon containing gas includes C2H2.
In an embodiment of the present invention, the second stage of film-forming process includes a plasma deposition process, in which the plasma deposition process includes a RF magnetron sputtering, a plasma enhanced chemical vapor deposition (PECVD), or a microwave plasma enhanced chemical vapor deposition (MPCVD).
In an embodiment of the present invention, a height of the nano graphite walls is micrometer level, and a thickness of the nano graphite walls is nano level.
In an embodiment of the present invention, the temperature of the first stage of film-forming process is between 350° C. and 500° C., a time of the first stage of film-forming process is between 5 minutes and 60 minutes, a pressure of the first stage of film-forming process is between 5 mtorr and 15 mtorr, and a power of the first stage of film-forming process is between 75 W and 200 W.
In an embodiment of the present invention, gases of the first stage of film-forming process include inert gas, H2, and carbon containing gas.
In an embodiment of the present invention, the substrate includes a metal substrate, a semi-conductor substrate, a ceramic substrate or a glass substrate.
The present invention further provides a composite field emission source, being a nano structure film formed on a substrate, in which the nano structure film is a petal-like structure composed of a plurality of nano graphite walls. The nano structure film includes a flat region and a plurality of nano coral-like structures grown on the flat region.
In another embodiment of the present invention, a height difference between the flat region and the nano coral-like structures of the nano structure film is micrometer level.
In another embodiment of the present invention, a height of the flat region of the nano structure film is micrometer level.
In another embodiment of the present invention, a thickness of the nano graphite wall is nano level.
In another embodiment of the present invention, the substrate includes a metal substrate, a semiconductor substrate, or a ceramic substrate.
In the present invention, two stages of film-forming process are adopted, such that firstly the petal-like structure composed of the plurality of nano graphite walls can be formed on the substrate, and the carbon accumulation amount is increased by using the second stage of the film-forming process. In this manner, not only the strength of the composite field emission source is increased, such that the structure can bear high current, but also the turn-on field is lowered as the nano coral-like structures are grown during the second stage of film-forming process. Therefore, the fabrication method and the structure of the present invention can improve the effect and the life of the electric field emission.



BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
FIG. 1 is a flow chart of processes of fabricating a composite field emission source according to a first embodiment of the present invention.
FIG. 2 is a curve diagram of the electric measurement of the composite field emission source fabricated according to the method of the first embodiment and by using a single stage film forming process.
FIG. 3A is a scanning electron microscope (SEM) photograph of the composite field emission source of an experimental example 1.
FIG. 3B is a partially enlarged SEM photograph of FIG. 3A.
FIG. 4 is an SEM photograph of the composite field emission source obtained by repeating the experimental example 1.



DESCRIPTION OF THE EMBODIMENTS
Reference will now be made in detail to the present embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.
FIG. 1 is a flow chart of processes of fabricating the composite field emission source according to a first embodiment of the present invention.
Referring to FIG. 1, step 100 is firstly performed, a first stage of film-forming process is performed by using RF magnetron sputtering, so as to form a nano structure film on a substrate, in which the substrate is, for example, a semiconductor substrate, a metal substrate, a ceramic substrate or a glass substrate. In the first embodiment, a temperature of the first stage of film-forming process is approximately between 350° C. and 500° C., a time of the first stage of film-forming process is between 5 minutes and 60 minutes, a pressure of the first stage of film-forming process is between 5 mtorr and 15 mtorr, and a power of the first stage of film-forming process is between 75 W and 200 W. The first stage of film-forming process in the first embodiment uses inert gas, H2, and carbon containing gas as the processing gases. The detailed description of the first stage of film-forming process is similar to the technology provided by Taiwan patent application No. 95115215, but the parameters can be altered according to requirements and devices, and are not limited within the above scope. After the first stage of film-forming process, the nano structure film formed on the substrate is a petal-like structure composed of a plurality of nano graphite walls. For example, the height of the nano graphite wall is micrometer level, and the thickness of the nano graphite wall is nano level.
Then, in step 110, the second stage of film-forming process is performed, so as to increase the carbon accumulation amount on the nano structure film. Further, the temperature of the second stage of film-forming process is higher than the temperature of the first stage of film-forming process in step 100. The second stage of film-forming process is, for example, a thermal deposition process or a plasma deposition process, capable of increasing the carbon accumulation amount. The thermal deposition process is, for example, thermal CVD, LPCVD, or other suitable methods, and the plasma deposition process is, for example, RF magnetron sputtering, PECVD, MPCVD, or other suitable methods. For example, when the second stage of film-forming process is the thermal CVD, the processing temperature is approximately between 600° C. and 800° C., the time is approximately between 5 minutes and 30 minutes, and the processing gas is for example NH3 and carbon containing gas, in which the carbon containing gas is, for example, C2H2. Further, when the second stage of film-forming process uses identical processing devices and gases as the first stage of film-forming process, the temperature of the second stage of film-forming process must be higher than the temperature of the first stage of film-forming process.
In the following, a group of experiments are given to prove the effects of the first embodiment of the present invention.
Experimental Example 1
After being cleaned, a silicon substrate is placed in a reactive RF magnetron sputtering system, and the temperature is controlled at 375° C. Then, gases required by the reaction are provided with controlled flow. In the experimental example 1, the provided gases are respectively Ar, H2, and CH4, and a gas flow ratio is 5:3:2.5. At the same time, the pressure is controlled at 10 mtorr. Then, a sputtering reaction is performed on the surface of the substrate for 50 minutes with a RF power 100 W, such that a nano structure film is grown on the surface of the silicon substrate.
Next, the silicon substrate grown with the nano structure film is moved into a furnace tube, the temperature of the furnace tube is controlled at 800° C., and then NH3 and C2H2 are provided, in which the gas flows are respectively 100 sccm and 30 sccm. At the same time, the pressure is controlled at 3 torr, such that the thermal CVD reaction is performed on the substrate for 10 minutes, so as to increase the carbon accumulation amount on the nano structure film.
Experimental Example 2
After the surface of a silicon substrate is cleaned, the first stage of film-forming process is finished by using the reactive RF magnetron sputtering system and processing parameters identical to those of the [Experimental Example 1]. Then, the second stage of film-forming process is performed by using RF magnetron sputtering, in which the temperature is controlled to be higher than or equal to 400° C.
Comparative Examples 1-2
The reactive RF magnetron sputtering system and processing parameters identical to those of the [Experimental Example 1] are used, but a single stage film forming process is respectively finished under 375° C. and 400° C.
The result is as shown in FIG. 2, a curve diagram of the relation between the emission current and the applied field of the experimental examples 1-2 and the comparative examples 1-2 is shown. It can be known from FIG. 2 that the experimental examples 1-2 fabricated according to the method of the present invention is distinctively superior to the single stage film forming process.
In addition, FIG. 3A is a SEM photograph of the composite field emission source of the [Experimental Example 1], and FIG. 3B is a partially enlarged SEM photograph of FIG. 3A. The composite field emission source of the second embodiment of the present invention can be obtained from FIGS. 3A and 3B.
The composite field emission source of the second embodiment of the present invention is a nano structure film formed on the substrate, in which the nano structure film is a petal-like structure composed of a plurality of nano graphite walls, and the nano structure film includes a flat region (as the upper portion of the photograph in FIG. 3A) and a plurality of nano coral-like structures. FIG. 3B is an enlarged view of the nano coral-like structures, and it can be viewed from FIG. 3B that the nano coral-like structures are grown on the flat region and it seems that the nano graphite walls around the nano coral-like structures are eroded and have their shape changed, therefore it is predicted that at least a portion of the eroded carbon is deposited on the nano coral-like structures. A height difference between the flat region and the nano coral-like structures of the nano structure film is approximately micrometer level, and the height of the flat region of the nano structure film is approximately micrometer level.
In addition, in order to prove the repeatability of the method of the present invention, the process of the [Experimental Example 1] is repeated, so as to still obtain the composite field emission source with the nano coral-like structures, as the SEM photograph as shown in FIG. 4.
To sum up, the features of the present invention are as follows.
1. The two stages of film-forming process are adopted, so in the nano structure film formed by the present invention, the carbon accumulation amount increased in the second stage of film-forming process makes the nano graphite wall have thick thickness and high strength, so as to improve the life of the field emission source. Therefore, even if the FED is performed after the nano structure film obtained by growing is scraped from the substrate, the high-current resistance property is improved because of the advantage of the high strength of the nano graphite wall.
2. In the nano structure film of the present invention, because of the nano coral-like structures grown on the flat region of the uniform nano structure film, the turn-on field of the field emission source can be greatly reduced through the nano coral-like structures with large aspect ratio. Therefore, the structure of the present invention can improve the emission effect of the electric field.
3. The nano structure film of the present invention can not only be applied to the FED, but also be applied to field emission light source, for example, the backlight source of the LCD or the flat panel light source.
It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.

## Claims

1. A composite field emission source, being a nano structure film formed on a substrate, wherein the nano structure film comprises a petal-like structure composed of a plurality of nano graphite walls, and the nano structure film further comprising:
a plurality of nano coral-like structures grown on the petal-like structure such that a height difference exists between the petal-like structure and the nano coral-like structures of the nano structure film at a micrometer level.

2. The composite field emission source according to claim 1, wherein a height of the petal-like structure of the nano structure film is micrometer level.

3. The composite field emission source according to claim 1, wherein a thickness of the nano graphite wall is nano level.

4. The composite field emission source according to claim 1, wherein the substrate comprises a metal substrate, a semiconductor substrate, or a ceramic substrate.