Method of forming a carbon nanotube structure and method of manufacturing field emission device using the method of forming a carbon nanotube structure

A method of forming a Carbon NanoTube (CNT) structure and a method of manufacturing a Field Emission Device (FED) using the method of forming a CNT structure includes: forming an electrode on a substrate, forming a buffer layer on the electrode, forming a catalyst layer in a particle shape on the buffer layer, etching the buffer layer exposed through the catalyst layer, and growing CNTs from the catalyst layer formed on the etched buffer layer.

CLAIM OF PRIORITY

This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from an application for METHOD OF FORMING CARBON NANOTUBE STRUCTURE AND METHOD OF MANUFACTURING FIELD EMISSION DEVICE USING THE SAME earlier filed in the Korean Intellectual Property Office on the 30thday of Jun. 2006 and there duly assigned Serial No. 10-2006-0060663.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of forming a carbon nanotube structure and a method of manufacturing a field emission device using the method of forming a carbon nanotube structure, and more particularly, the present invention relates to a method of forming a high quality carbon nanotube structure at a low temperature and a method of manufacturing a field emission device using the method of forming a carbon nanotube structure.

2. Description of the Related Art

A Field Emission Device (FED) emits visible light due to the collision of electrons emitted from emitters formed on a cathode electrode with a phosphor layer formed on an anode electrode. The FED can be applied to a FED back light unit of FEDs that form images using field emissions or a field emission backlight unit of Liquid Crystal Displays (LCDs).

In the FED, a micro tip formed of a metal, such as Mo, is used as a conventional emitter of electrons. However, recently, carbon nanotubes (CNTs) have been mainly used as emitters. FEDs that use CNTs as emitters have a high possibility of being applied to various fields such as a car navigation apparatus or a view finder for electronic image displays due to a wide viewing angle, high resolution, low power consumption, and temperature stability of the FEDs. In particular, the FEDs that use CNTs as emitters can replace a display apparatus in personal computers, Personal Data Assistants (PDAs), medical instruments, or High Definition TeleVisions (HDTVs).

In manufacturing FEDs using CNTs, the obstacles that are faced are an increase in lifetime, manufacturing a large screen, reducing costs, and reducing an operating voltage.

In order to increase the lifetime of the FED, CNTs can be synthesized using a Chemical Vapor Deposition (CVD) method. In this method, the degradation of the CNTs can be prevented by growing the CNTs directly on a substrate without using an organic binder, thus increasing the lifetime of the FED. But, this method has drawbacks in that an adhesion force between the CNTs and the substrate is weak since an organic binder is not used and the activity of a catalyst layer for growing the CNTs is reduced since the catalyst layer reacts with the substrate.

The manufacture of a large screen and reduction in cost of the FEDs can be achieved by using an inexpensive sodalime glass substrate. However, the sodalime glass substrate has a relatively low deformation temperature of approximately 480° C. In other words, the synthesis of the CNTs on the sodalime substrate using a CVD method must be performed at a temperature lower than 480° C. However, it is technically very difficult to do so. That is, in order to synthesize the CNTs at a low temperature, reaction gases must decompose at a temperature lower than 480° C., and must meet a complicated reaction condition whereby the decomposed gases must be precipitated by diffusing into a catalyst layer.

In order to reduce an operating voltage of the FEDs, it is necessary to control the density of the synthesized CNTs. One of the reasons why the CNTs are used as emitters in the FEDs is that the CNTs have a high field enhancement effect due to a large aspect ratio of each of the CNTs. However, if the density of the CNTs is too high, the aspect ratio of a CNT bundle is much less than each of the CNTs. In such a case, a high operating voltage is required in order to emit electrons. To solve this problem, the density control of the CNTs is important.

During a synthesizing process of the CNTs, a catalyst layer must be present as particles so that carbon atoms that are diffused into the catalyst layer can be precipitated in a tube shape. However, the catalyst layer has a tendency of agglomerating at a synthesizing temperature of the CNTs. Therefore, there is a need to prevent the catalyst layer from agglomerating during the synthesizing process.

SUMMARY OF THE INVENTION

The present invention provides a method of forming a carbon nanotube (CNT) structure that can realize a long lifetime, be used for a large screen, has low manufacturing costs, and operates at a low operating voltage by synthesizing high quality CNTs at a low temperature and a method of manufacturing a Field Emission Device (FED) using the CNT structure.

According to one aspect of the present invention, a method of forming a Carbon NanoTube (CNT) structure is provided, the method including: forming an electrode on a substrate; forming a buffer layer on the electrode; forming a catalyst layer in a particle shape on the buffer layer; etching the buffer layer exposed through the catalyst layer; and growing CNTs from the catalyst layer formed on the etched buffer layer.

The buffer layer is preferably formed of a material having an etch selectivity with respect to the catalyst layer. The buffer layer is preferably formed of at least one metal selected from a group consisting of Al, B, Ga, In, Tl, Ti, Mo, and Cr. The buffer layer is preferably formed to a thickness in a range of 10 to 3000 Å.

The catalyst layer is preferably formed of at least one metal selected from a group consisting of Fe, Co, and Ni. The catalyst layer is preferably formed to a thickness in a range of 2 to 100 Å.

The etching of the buffer layer is preferably continued until the cathode electrode is exposed.

The electrode is preferably formed of at least one metal selected from a group consisting of Mo and Cr.

The CNTs are grown by a Chemical Vapor Deposition (CVD) method.

The method preferably further includes forming a resistance layer on either an upper or a lower surface of the electrode. The resistance layer is preferably formed of amorphous silicon.

According to another aspect of the present invention, a method of manufacturing a Field Emission Device (FED) is provided, the method including: sequentially forming a cathode electrode, an insulating layer, and a gate electrode on a substrate; patterning the gate electrode and forming an emitter hole to expose the cathode electrode by etching the insulating layer exposed through the patterned gate electrode; forming a buffer layer on the cathode electrode formed in the emitter hole; forming a catalyst layer in a particle shape on the buffer layer; etching the buffer layer exposed through the catalyst layer; and growing Carbon NanoTubes (CNTs) from the catalyst layer formed on the etched buffer layer.

The buffer layer is preferably formed of a material having an etch selectivity with respect to the catalyst layer. The buffer layer is preferably formed of at least one metal selected from a group consisting of Al, B, Ga, In, Tl, Ti, Mo, and Cr. The buffer layer is preferably formed to a thickness in a range of 10 to 3000 Å.

The catalyst layer is preferably formed of at least one metal selected from a group consisting of Fe, Co, and Ni. The catalyst layer is preferably formed to a thickness in a range of 2 to 100 Å.

The cathode electrode is preferably formed of at least one metal selected from a group consisting of Mo and Cr.

Forming the emitter hole preferably includes: forming a photoresist on the patterned gate electrode; and etching the insulating layer exposed through the photoresist and the gate electrode until the cathode electrode is exposed.

Forming the buffer layer and the catalyst layer preferably includes: forming the buffer layer on the photoresist and the cathode electrode in the emitter hole; and forming the particle shaped catalyst layer on the buffer layer.

The method preferably further includes removing the photoresist and the buffer layer and catalyst layer formed on the photoresist after the buffer layer exposed through the catalyst layer has been etched.

The etching of the buffer layer is preferably continued until the cathode electrode is exposed.

The CNTs are preferably grown using a Chemical Vapor Deposition (CVD) method.

The method preferably further includes forming a resistance layer on either an upper or a lower surface of the cathode electrode. The resistance layer is preferably formed of amorphous silicon.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is described more fully below with reference to the accompanying drawings in which exemplary embodiments of the present invention are shown. In the drawings, like reference numerals refer to like elements throughout the drawings, and the thicknesses of layers and regions have been exaggerated for clarity.

FIGS. 1 through 4are cross-sectional views of a method of forming a carbon nanotube (CNT) structure according to an embodiment of the present invention.

Referring toFIG. 1, an electrode112is deposited on a substrate110. The substrate110can be a glass substrate or a silicon wafer. The electrode112can be formed, for example, by depositing at least one of a predetermined metal of Mo and Cr. Although it is not shown, a process of forming a resistance layer on an upper or a lower surface of the electrode112can further be included. The resistance layer is formed to induce uniform electron emission from CNTs150(refer toFIG. 4), and can be formed of amorphous silicon.

Next, a buffer layer120having a predetermined thickness is formed on the electrode112. The buffer layer120has a high adhesiveness with respect to a catalyst layer130(refer toFIG. 2) formed on the buffer layer120and has a low reactivity with respect to the substrate110or the electrode112formed therebelow. The buffer layer120may be formed of a material having high adhesiveness with the substrate110or the electrode112and an etch selectivity with respect to the catalyst layer130. The buffer layer120can be formed of an amphoteric metal, such as Al, B, Ga, In, or Tl, and also, a metal, such as Ti, Mo, or Cr if the buffer layer120has an etch selectivity with respect to the catalyst layer130. The metals mentioned above can be used as pure metals or an alloy of two or more of these metals. The buffer layer120can be formed to a thickness of 10 to 3000 Å.

Referring toFIG. 2, the catalyst layer130in a particle shape is formed on an upper surface of the buffer layer120. The catalyst layer130can be formed by depositing a catalyst metal in a thin film shape on the upper surface of the buffer layer120. When the catalyst layer130is deposited to a thickness of 2 to 100 Å, the catalyst layer130can be formed in a discontinuous particle shape. The catalyst layer130can be formed of a transition metal, such as Fe, Ni, Co in a pure state or an alloy of two or more of these metals.

Referring toFIG. 3, the buffer layer120that is exposed through the particle shaped catalyst layer130is etched to a predetermined depth. More specifically, when the structure depicted inFIG. 2is soaked in an etching solution that can only selectively etch the buffer layer120, but does not etch the catalyst layer130for a predetermined time, the buffer layer120located under the particle shaped catalyst layer130remains unetched, but the buffer layer120exposed through the catalyst layer130is selectively etched to a predetermined depth. The etching of the buffer layer120can be continued until the electrode112is exposed. In this way, when the buffer layer120is selectively etched through the particle shaped catalyst layer130at room temperature, the agglomeration of the catalyst layer130in a process of growing CNTs150(refer toFIG. 4) can be prevented.

Referring toFIG. 4, the CNTs150are grown from the catalyst layer130formed on the selectively etched buffer layer120. The CNTs150can be grown by a Chemical Vapor Deposition (CVD) method. The CNTs150can be grown, for example, at a low temperature lower than 480° C.FIG. 5is a Scanning Electron Microscope (SEM) image of CNTs grown using the above method, according to an embodiment of the present invention.

As described above, according to an embodiment of the present invention, the particle shaped catalyst layer130is prevented from being agglomerated even if the CNTs150are grown from the catalyst layer130at a low temperature by selectively etching the buffer layer120exposed through the particle shaped catalyst layer130. Accordingly, high quality CNTs150can be obtained at a low temperature. Also, the density of the grown CNTs150can be controlled by controlling the thickness and etching process time of the buffer layer120.

Hereinafter, a method of manufacturing a Field Emission Device (FED) using the method of forming a CNT structure as described above is described. The FED manufactured according to the following method can be applied to not only to FEDs that display images using field emissions, but also to a field emission back light unit of LCDs.

FIGS. 6 through 11are cross-sectional views of a method of manufacturing a FED according to another embodiment of the present invention.

Referring toFIG. 6, a cathode electrode212, a resistance layer214, an insulating layer217, and a gate electrode219are sequentially formed on a substrate210. The substrate210can be a glass substrate or a silicon wafer. The cathode electrode212can be formed by depositing at least a metal of Mo and Cr on an upper surface of the substrate210and patterning the deposited metal in a predetermined shape, for example, a stripe shape.

The resistance layer214can further be formed on an upper surface of the cathode electrode212. The resistance layer214is formed to induce uniform electron emission from an emitter300(refer toFIG. 11) by applying a uniform current to CNTs250of the emitter300as will be described later. The resistance layer214can be formed of amorphous silicon. InFIG. 6, the resistance layer214is formed on the upper surface of the cathode electrode212, but the resistance layer214can be formed on a lower surface of the cathode electrode212or the resistance layer214may not be formed.

Hereinafter, the case when the resistance layer214is formed on the upper surface of the cathode electrode212is described. After the insulating layer217, which is covering the cathode electrode212and the resistance layer214, is formed, the gate electrode219is deposited on an upper surface of the insulating layer217. The gate electrode219can be formed by depositing a conductive metal, such as Cr, on the upper surface of the insulating layer217.

Referring toFIG. 7, after the gate electrode219is patterned, a photoresist240is formed on an upper surface of the patterned gate electrode219. An emitter hole215is formed in the insulating layer217by etching the insulating layer217exposed through the photoresist240and the gate electrode219. The etching of the insulating layer217is continued until the resistance layer214is exposed. Accordingly, the upper surface of the resistance layer214is exposed through the emitter hole215. When the resistance layer214is not formed or the resistance layer214is formed on a lower surface of the cathode electrode212, the upper surface of the cathode electrode212is exposed through the emitter hole215.

Referring toFIG. 8, a buffer layer220is formed to a predetermined thickness on the upper surface of the resistance layer214exposed through the emitter hole215and an upper surface of the photoresist240. The buffer layer220has a high adhesiveness with respect to a catalyst layer230in a particle shape formed on the buffer layer220and has a low reactivity with respect to the cathode electrode212or the resistance layer214formed below the catalyst layer230. Preferably, the buffer layer220may be formed of a material having high adhesiveness with respect to the cathode electrode212or the resistance layer214and has an etch selectivity with respect to the catalyst layer230formed on the buffer layer220. The buffer layer220can be formed of an amphoteric metal, such as Al, B, Ga, In, or Tl, and also, a metal, such as Ti, Mo, or Cr, if Ti, Mo, or Cr that has an etch selectivity with respect to the catalyst layer230. The metals can be used as pure metals or as alloys of two or more of these metals. The buffer layer220can be formed to a thickness of 10 to 3000 Å.

Next, the particle shaped catalyst layer230is formed on an upper surface of the buffer layer220. The catalyst layer230can be formed by depositing a catalyst metal on an upper surface of the buffer layer220in a thin film shape. When the catalyst layer230is formed to a thickness of 2 to 100 Å, the catalyst layer230is formed in a discontinuous particle shape. The catalyst layer230can be formed of a transition metal, such as Fe, Ni, or Co, in a pure metal state or an alloy of two or more of these metals.

Referring toFIG. 9, the buffer layer220that is exposed through the catalyst layer230is etched to a predetermined depth. More specifically, when the structure depicted inFIG. 8is soaked in an etching solution that can selectively etch only the buffer layer220, but does not etch the catalyst layer230for a predetermined time, a buffer layer225located under the particle shaped catalyst layer230remains unetched, but the buffer layer220exposed through the catalyst layer230is selectively etched to a predetermined depth. The etching of the buffer layer220can be continued until the resistance layer214is exposed. When the resistance layer214is not formed or the resistance layer214is formed on a lower surface of the cathode electrode212, the etching of the buffer layer220can be continued until the cathode electrode212is exposed.

In this way, when the buffer layer220is selectively etched through the particle shaped catalyst layer230at room temperature, the agglomeration of the particle shaped catalyst layer230can be prevented in a process of growing CNTs250(refer toFIG. 11) as will be described later. Next, referring toFIG. 10, the photoresist240, and the buffer layer220and the catalyst layer230stacked on the photoresist240are removed by, for example, a lift-off method.

Referring toFIG. 11, emitters of electrons are formed in the emitter hole215when the CNTs250are grown from the catalyst layer230formed on the etched buffer layer225. The CNTs250can be formed by a CVD method. The CNTs250can be formed at a low temperature, for example, lower than 480° C. The density of the CNTs250that are grown in this process can be controlled by controlling the thickness and etching time of the buffer layer220.

As described above, according to the present invention, the formation of a fine particle shaped catalyst layer and the prevention of agglomerating the catalyst layer can be realized at a low temperature, which were realized at a high temperature in the prior art, by forming a buffer layer formed of a material having an etch selectivity with respect to the catalyst layer on a lower surface of a particle shaped catalyst layer and selectively etching the buffer layer exposed through the catalyst layer. Therefore, high quality CNTs can be synthesized at a low temperature.