JP2006209973A - Field emission electrode and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a field emission electrode capable of supplying a phosphor with a number of uniform electrons, and to provide a manufacturing method thereof. <P>SOLUTION: Carbon fiber 3 has a structure in which a plurality of carbon network layers are stacked in a direction perpendicular to or non-parallel to the axial direction of the fiber and the edges of the carbon network layers are exposed from the fiber surface. The field emission electrode 5 has a structure in which the carbon fiber 3 is embedded in a conductive polymer layer 4 having a thickness equal to or less than the diameter of the carbon fiber 3, and part of or all of the edges are exposed from the conductive polymer layer 4. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a field emission electrode that emits electrons at a low voltage and a method for manufacturing the same.

  Recently, field emission displays (FEDs) have been actively developed not only in Japan but also in other countries including Korea (see, for example, Patent Document 1). Here, field emission refers to a phenomenon in which, when a strong electric field is applied to the solid surface, the electrons confined in the solid surface jump out into the vacuum. In order to emit electrons, it is necessary to apply a strong electric field to the solid. However, if a thin and sharp solid is used, only a small electric field needs to be applied. Until now, materials such as finely sharpened silicon and molybdenum have been used as field emission electron sources, but recently, nanoscale thinness, good electrical conductivity, high strength, and chemical stability. Carbon fibers (particularly carbon nanotubes) that have both properties are expected as new field emission electron sources (for example, see Patent Document 2).

  The FED is a display that forms an image by emitting light by applying electrons to a phosphor arranged in units of pixels. In order to use carbon fibers as a field emission electron source, a large number of carbon fibers are substantially perpendicular to the phosphor so that electrons can be emitted toward the phosphor disposed on the back surface of the glass plate of the FED. Need to be placed. Normally, a large number of carbon fibers are erected in the conductive polymer layer. In this process, how much carbon fiber can be erected with respect to the layer surface of the conductive polymer layer depends on the FED. This is one of the important factors that determine performance.

  As a method for embedding carbon fibers in a conductive polymer, for example, a spin coating method is known (see, for example, Patent Document 3). The spin coating method is a method in which a mixture of a conductive polymer and a carbon fiber electrode material is applied onto a disk, the disk is rotated, and thinly spread and solidified using the centrifugal force.

JP-A-8-248914 (abstract, etc.) JP-A-10-149760 (Claims, Abstracts, etc.) JP 2000-277004 A (Claims, Abstract, etc.)

  The reason why the carbon fibers are erected substantially perpendicularly to the substrate surface on which the conductive polymer layer is formed is that, in the case of conventional carbon fibers, only the ends in the length direction of the fibers are electron emission portions. is there. However, it is technically difficult to align the carbon fibers substantially perpendicular to the substrate surface. For example, when the spin coating method is used, even if there is a carbon fiber that is substantially perpendicular to the substrate surface, the ratio is small. Many carbon fibers are embedded in the conductive polymer layer in a state where the carbon fiber is horizontal or inclined at an angle close to the horizontal. As a result, the number of carbon fibers that effectively contribute to supplying electrons to the phosphor is reduced.

  In addition to the spin coating method, a method of depositing a mixture of a conductive polymer and carbon fiber on the negative electrode using an electrophoresis method is also conceivable. The present inventor first succeeded in increasing the probability that the carbon fibers in the conductive polymer layer are erected perpendicularly to the substrate surface by electrophoresis. As a result, it was confirmed that more electrons can be emitted at a lower voltage than before. However, it is strongly desired that more electrons can be supplied to the phosphor at a lower voltage.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a field emission electrode that can supply more electrons to a phosphor at a lower voltage and a method for manufacturing the same.

  In order to achieve the above object, the present invention has a structure in which a plurality of carbon network layers are laminated in a direction perpendicular to the axial direction of the fiber or non-parallel to the axial direction, and the edges of the carbon network layer are exposed from the fiber surface. A carbon fiber is embedded in a conductive polymer layer having a thickness equal to or smaller than the diameter of the carbon fiber, and a field emission electrode having a structure in which a part or all of the edge is exposed from the conductive polymer layer. For this reason, when an electric field is applied, electrons are emitted from the edge portion of the carbon network layer exposed on the substantially cylindrical side surface of the carbon fiber. Since there are many edges on the substantially cylindrical side of carbon fiber, many electrons are supplied to the phosphor at a low voltage even if the carbon fiber is not erected vertically in the conductive polymer layer. it can.

  Another invention of the present invention is a field emission electrode in which carbon fibers are carbon nanotubes in the previous invention. For this reason, electrons can be emitted at a lower voltage.

  Another aspect of the present invention is a method of manufacturing a field emission electrode that emits electrons by field emission, wherein a plurality of carbon network layers are stacked perpendicular to the axial direction of the fiber or non-parallel to the axial direction, and In this method, a carbon fiber having a structure in which the edge of the carbon net layer is exposed from the fiber surface is embedded in a conductive polymer layer having a thickness equal to or less than the diameter of the carbon fiber. For this reason, a part of fiber side surface of carbon fiber will be in the state exposed from the conductive polymer layer. Specifically, when carbon fibers are embedded substantially perpendicularly to the substrate surface on which the conductive polymer layer is formed, a part of the side surface of the carbon fiber is exposed from the conductive polymer layer. In addition, when carbon fibers are embedded in the conductive polymer layer inclined at a predetermined angle to the substrate surface, the fiber side surfaces other than the embedded portion are exposed from the conductive polymer layer over the entire circumference of the side surfaces. It will be in the state. For this reason, many electrons can be supplied at a low voltage from the edge portion of the carbon network layer exposed on the side surface of the carbon fiber toward the phosphor.

  In another aspect of the present invention, in the previous invention, a solvent containing carbon fiber and a conductive polymer is dropped on a substrate, and the rotational speed of the dropped substrate is adjusted and rotated, thereby the conductive polymer. In this method, the thickness of the layer is set to be equal to or less than the diameter of the carbon fiber. Therefore, it is possible to easily manufacture a field emission electrode that can supply many electrons to the phosphor at a low voltage. The thickness of the conductive polymer layer can be controlled to be equal to or less than the diameter of the carbon fiber simply by adjusting the number of rotations of the substrate.

  Another aspect of the present invention is the method of manufacturing a field emission electrode in which the carbon fiber is a carbon nanotube in the previous invention. For this reason, electrons can be emitted at a lower voltage.

  The carbon fiber used in the present invention is interpreted in a broad sense including not only a cylindrical carbon fiber such as a carbon nanotube but also a solid carbon fiber. In addition, the carbon fiber used here does not include SWCNT (Sigle Walled-Carbon Nano Tube) or MWCNT (Sigle Walled-Carbon Nano Tube) in which an electron emission portion exists only in the axial direction of the fiber. Including those where the edge of the carbon network layer is present at an angle that is perpendicular or not perpendicular to the axis. In other words, the carbon fiber used in the present invention is a carbon fiber that can emit electrons from the fiber side surface of the carbon fiber regardless of whether electrons can be emitted from the end of the carbon fiber in the longitudinal direction. The carbon nanotubes used in the present invention include ultra-thin carbon nanotubes having a diameter of 1 nanometer or less, medium-thin carbon nanotubes of several nanometers to several hundred nanometers, and cylindrical carbon fibers having a larger diameter. It shall be interpreted in a broad sense as including. That is, regardless of the size of the diameter, any carbon nanotube in the length direction is included in the carbon nanotube of the present invention. The carbon fiber used in the present invention may be produced by any method such as arc discharge, laser ablation, plasma synthesis, chemical vapor deposition (CVD), etc. It can be adopted. However, CNTs produced by a CVD method advantageous for mass production are preferred.

  The conductive polymer refers to a polymer that conducts electricity like a metal by a dopant. As the conductive polymer usable here, any conductive polymer soluble in an organic solvent can be used. The introduced substituent is preferably a hydrocarbon group (such as an alkyl group). The alkyl group may be either a straight chain or a branched chain, but is preferably a hexyl group, a heptyl group, an octyl group, a nonyl group, or a decyl group. In consideration of solubility and heat resistance, the length of the alkyl group is preferably in the range of 4 to 20 carbon atoms. In particular, it is preferable to employ poly (3-octylthiophene) having 8 carbon atoms or poly (3-hexylthiophene) having 6 carbon atoms. As a suitable conductive polymer, for example, poly [3,4- (ethylenedioxy) thiophene-poly (styrenesulfonic acid) (poly [3,4- (ethylenedioxy) thiophene] -poly (styrenesulfonic acid): PEDOT -PSS), polyvinylcarbazole, soluble polyparaphenylene vinylene (MEH-PPV (Poly [2-methoxy-5- (2'ethylhexyloxy) -1,4-phenylenevinylene]), soluble polyaniline, poly (alkyl) fluorene or poly ( Alkyl) thiophene, etc. In particular, PEDOT-PSS, which is excellent in conductivity, is desirable, and a plurality of the above conductive polymers may be mixed and used.

  Further, as a method for producing the field emission electrode of the present invention, it is preferable to employ a spin coating method that can be produced at a low cost, but an electrophoresis method, a doctor blade method, a squeegee method, a screen printing method, etc. Other forming methods can also be employed.

  ADVANTAGE OF THE INVENTION According to this invention, the field emission electrode which can supply many electrons to fluorescent substance with a lower voltage, and its manufacturing method can be provided.

  Hereinafter, embodiments of a field emission electrode and a method for manufacturing the same according to the present invention will be described.

  FIG. 1 is a schematic view of a carbon fiber used in a field emission electrode according to an embodiment of the present invention. (1A) is a manufacturing process of the carbon fiber, and (1B) is a perspective view of the carbon fiber. Show. FIG. 2 is a schematic view of another carbon fiber used for the field emission electrode according to the embodiment of the present invention. (2A) shows the manufacturing process of the other carbon fiber, and (2B) shows the carbon fiber. The perspective view of another carbon fiber is shown.

  When a hydrocarbon gas (for example, benzene gas) and hydrogen are allowed to flow in a region heated at 800 to 1200 ° C. in the presence of the metal catalyst 1, the plate-like carbon platelet 2 a grows from the metal catalyst 1. Carbon fibers 3 having a structure in which a large number of layers are laminated in the direction (length direction) are formed. Further, by adjusting the production conditions such as the type of the metal catalyst 1, carbon fibers 3 having a structure in which a large number of annular carbon platelets 2b as shown in FIG. 2 are laminated in the fiber growth direction (length direction) are formed. Is done. Hereinafter, the plate-like carbon platelet 2a, the annular carbon platelet 2b, and the like are collectively referred to as a carbon platelet (carbon network layer) 2. The carbon fiber 3 having a structure in which the carbon platelets 2 are laminated in the length direction has a special feature that, when an electric field is applied, electrons are emitted from the edge portion of the carbon platelet 2 in addition to the end portions in the length direction. It has special properties.

  FIG. 3 is a view showing the vicinity of the electrode of the FED, and is a cross-sectional view of the field emission electrode 5 composed of the conductive polymer layer 4 and the carbon fiber 3 formed on the electrode. In the figure, the portion of the carbon fiber 3 embedded in the conductive polymer layer 4 is shown by a dotted line.

  Here, the thickness of the conductive polymer layer 4 needs to be equal to or less than the diameter of the carbon fiber 3. “Diameter” refers to the diameter of the thickest carbon fiber 3 in the carbon fiber 3 to be used. However, it is more desirable that the thickness of the conductive polymer layer 4 is equal to or less than the diameter (that is, the average diameter) of the carbon fibers 3 having an average thickness of the carbon fibers 3. As a preferred example, when the average diameter of the carbon fibers 3 is 80 nm, the thickness of the conductive polymer layer 4 is preferably 40 nm. If the thickness of the conductive polymer layer 4 is equal to or less than the diameter of the carbon fiber 3, even if the carbon fiber 3 is embedded in parallel to the surface of the transparent conductive substrate, each carbon platelet of some or all of the carbon fibers 3 is used. 2 is exposed to the outside from the conductive polymer layer 4, and electrons are easily emitted from the edge portion of each carbon platelet 2 when an electric field is applied. In other words, a sufficient number of electrons can be emitted at a low voltage without the carbon fiber 3 standing vertically on the conductive polymer layer 4.

  FIG. 4 is a schematic view of a display device having the electron emission electrode 5 according to the embodiment of the present invention.

  The display device shown in FIG. 4 (herein described as “FED”) has a configuration in which a cathode glass sheet 6 and an anode glass sheet 7 are arranged to face each other in a vacuum. On the surface of the anode glass sheet 7 on the vacuum region side, an electrode 9 in which a phosphor 8 is arranged is provided. On the other hand, the cathode glass sheet 6 is provided with a conductive substrate 11 to which a gate electrode 10 and a field emission electrode 5 are attached.

  In the FED having such a configuration, when a voltage is applied between the reference wiring on the conductive substrate 11 and the gate electrode 10, electrons are emitted into the vacuum from the carbon fibers 3 exposed on the surface of the field emission electrode 5. . Specifically, electrons are emitted into the vacuum from the edges of the carbon platelets 2 constituting the carbon fibers 3 and the lengthwise ends of the carbon fibers 3. The electrons emitted into the vacuum travel in the direction of the anode glass sheet 7 by the voltage applied between the electrode 9 and the conductive substrate 11, collide with the phosphor 8, and emit light.

  FIG. 5 is a flowchart showing a part of the process of manufacturing the field emission electrode 5 according to the embodiment of the present invention.

  First, the carbon fiber 3 and the conductive polymer are mixed in a solvent (step S1). Next, a thin film made of the mixture is formed on a conductive substrate such as ITO (step S2). As the formation method, a spin coating method, a dip coating method or the like can be employed. Next, heat treatment is performed (step S3), and the mixture thin film is solidified to produce the field emission electrode 5.

  Moreover, you may employ | adopt the manufacturing method which adds the process of exposing the carbon fiber 3 following said step S3. When the carbon fiber 3 is formed by spin coating, it is often buried in the conductive polymer layer 4. When the buried carbon fiber 3 is exposed by removing the surface layer of the conductive polymer layer 4, the electron emission characteristics can be further improved. Specifically, the carbon fiber 3 can be exposed by the following method.

  One is a method of etching a conductive polymer. Many polymer materials can be etched by oxygen plasma treatment. The conductive polymer of the present invention is no exception. This method is known as reactive ion etching (RIE) or plasma ashing. Specifically, oxygen gas or a mixed gas of oxygen and argon is introduced into a decompressed vacuum vessel (depending on conditions, about 1 to 20 mTorr, preferably about 10 mTorr), and plasma is generated by supplying high-frequency power. . Active oxygen ions generated at this time selectively scrape the polymer material. Since carbon fibers 3 such as carbon nanotubes are also carbon materials, they are damaged by plasma.

However, since the carbon fiber 3 has stronger oxygen-resistant plasma characteristics than the polymer material, the polymer material is mainly scraped off at an appropriate power (about 0.1 to 10 W / cm ² ). As a result, the carbon fiber 3 is exposed and the electron emission can be activated. It should be noted that further electron emission can be expected by slightly cutting the carbon fiber 3 and increasing the edges by this plasma treatment.

  The other is a method of dissolving a conductive polymer. The surface of the field emission electrode 5 once formed by spin coating or the like may be covered with a conductive polymer. For this reason, it is effective to expose the carbon fiber 3 by melting the surface of the conductive polymer layer 4. Since the conductive polymer is soluble, the conductive polymer disappears when immersed in a solvent. However, a solvent having low solubility with respect to the conductive polymer, for example, an alcohol-based material in PEDOT-PSS, an aromatic solvent or alcohol in a polythiophene-based material is dropped on the substrate surface after film formation, Similarly, the surface of the conductive polymer layer 4 is melted by rotating at high speed to remove the solvent. As a result, the carbon fiber 3 is effectively exposed.

  In addition, when immersed directly in a solvent, the uniformity of the film tends to be lost. Therefore, the sample is placed in the above solvent or a solvent having high solubility, for example, water or alcohol in PEDOT-PSS, or chlorine solvent such as chloroform or aromatic solvent such as toluene, xylene, or benzene in potyalkylthiophene. At this time, the solution is placed in a sealed space, and a film-formed sample is placed near the solution. Although the situation varies depending on the type and temperature of the solvent, the surface of the conductive polymer layer 4 is melted and the carbon fiber 3 is exposed by leaving it for about several minutes to several hours.

  By adopting each method described above, the carbon fiber 3 can be effectively exposed and the electron emission characteristics can be improved.

  FIG. 6 is a diagram for explaining a method of measuring the electron emission ability of the field emission electrode 5.

  The electron emission ability is measured in the vacuum vessel 12. A conductive substrate 14 such as ITO is provided on the substrate 13, and a field emission electrode 5 composed of the conductive polymer layer 4 and the carbon fiber 3 embedded therein is formed thereon. A spacer 15 thicker than the field emission electrode 5 is disposed around the substrate 13. A substrate 16 is disposed on the spacer 15. A conductive electrode 17 such as ITO is formed on the contact surface of the substrate 16 with the spacer 15. The conductive substrate 14 and the conductive electrode 17 are connected by a wiring via a power source 18 and an ammeter 19 that can change the voltage. After the vacuum vessel 12 is sufficiently evacuated, the voltage of the power source 18 is increased, and the change in the value of the ammeter 19 is examined to evaluate the electron emission ability of the field emission electrode 5.

  A 1.3% by weight aqueous solution of PEDOT-PSS is diluted with the same weight of propanol. In the diluted solution, carbon fiber (cyclic carbon platelet laminate type carbon fiber) 3 having the structure shown in FIG. 2 was mixed so as to be 10% by weight with respect to the weight of PEDOT-PSS (mixed solution 2). For comparison, a mixture of SWCNTs having a diameter of 12 to 15 angstroms manufactured by Aldrich instead of carbon fiber 3 and 10% by weight with respect to PEDOT-PSS was also prepared (mixed solution 1).

  Next, the liquid mixture 1 and the liquid mixture 2 were dropped on the rotating plate, respectively, and the rotating plate was rotated at 4000 rpm for 30 seconds, so that the liquid mixture 1 and the liquid mixture 2 were thinly extended. Next, after drying for about 1 hour, a heat treatment was performed at 90 to 100 ° C. for 30 minutes to produce a field emission electrode 5. Each field emission electrode 5 produced from the liquid mixture 1 and the liquid mixture 2 was subjected to evaluation of electron emission ability under vacuum.

  FIG. 7 is a graph showing a comparison of the electron emission ability of each field emission electrode 5 using carbon fiber 3 and SWCNT. The horizontal axis is voltage, and the vertical axis is current density. In addition, a curve indicating the electron emission ability of the field emission electrode 5 using SWCNT was plotted with white triangles (indicated by the curve of “CNT1” in the graph). Further, a curve indicating the electron emission ability of the field emission electrode 5 using the carbon fiber 3 was plotted with a black circle (indicated by a curve of “CNT2” in the graph).

  In the field emission electrode 5 using SWCNT, a current suddenly started to flow from about 6 V / μm. In contrast, in the field emission electrode 5 using the carbon fiber 3, a current suddenly started to flow from 3 to 4 V / μm. From this result, it was found that the field emission electrode 5 using the carbon fiber 3 having many edges on the fiber side face can emit electrons at a lower voltage than that using the SWCNT.

  While the embodiments and examples of the present invention have been described above, the present invention is not limited to the above-described embodiments or examples, and can be implemented in variously modified forms.

  For example, the carbon platelet 2 may be inclined not in a direction perpendicular to the length direction of the carbon fibers 3 but in a non-parallel direction (except for the vertical direction) with respect to the length direction. Further, the thickness of the conductive polymer layer 4 may be the same as the diameter of the carbon fiber 3. That is, it is sufficient that all the carbon fibers 3 are not completely buried in the conductive polymer layer 4.

  The present invention can be used in industries that manufacture and use field emission electrodes for FEDs.

It is a schematic diagram of the carbon fiber used for the field emission electrode concerning embodiment of this invention, (1A) shows the manufacturing process of the said carbon fiber, (1B) shows the perspective view of the said carbon fiber. It is a schematic diagram of the carbon fiber which is used for the field emission electrode concerning embodiment of this invention, and has a form different from the carbon fiber shown in FIG. 1, (2A) is the manufacturing process of the said another carbon fiber. , (2B) shows a perspective view of the other carbon fiber. It is a figure which shows the electrode vicinity of FED using the field emission electrode concerning embodiment of this invention, Comprising: The field emission electrode comprised from the conductive polymer layer and carbon fiber which were formed in the transparent conductive substrate It is sectional drawing. It is a schematic diagram of the display apparatus which has the electron emission electrode concerning embodiment of this invention. It is a flowchart which shows a part of process of manufacturing the field emission electrode concerning embodiment of this invention. It is a figure for demonstrating the method to measure the electron emission ability of the electron emission electrode concerning embodiment of this invention. In the Example of this invention, it is a graph which compares and shows the electron emission ability of each field emission electrode using carbon fiber and SWCNT.

Explanation of symbols

2 Carbon platelet (carbon mesh layer)
3 Carbon fiber (including carbon nanotubes)
4 Conductive polymer layer 5 Field emission electrode

Claims (5)

  A carbon fiber having a structure in which a plurality of carbon network layers are laminated in a direction perpendicular to the axial direction of the fiber or non-parallel to the axial direction, and the edge of the carbon network layer is exposed from the fiber surface is equal to or less than the diameter of the carbon fiber A field emission electrode characterized by being embedded in a conductive polymer layer having a thickness of 5 mm and having a structure in which part or all of the edge is exposed from the conductive polymer layer.   The field emission electrode according to claim 1, wherein the carbon fiber is a carbon nanotube. A method of manufacturing a field emission electrode that emits electrons by field emission,
A carbon fiber having a structure in which a plurality of carbon network layers are laminated in a direction perpendicular to or in a direction parallel to the axial direction of the fiber and the edge of the carbon network layer is exposed from the fiber surface has a thickness equal to or less than its diameter. A method for producing a field emission electrode, wherein the method is embedded in a conductive polymer layer.   The solvent containing the carbon fiber and the conductive polymer is dropped on the substrate, the rotation number of the dropped substrate is adjusted and rotated, and the thickness of the conductive polymer layer is set to the diameter of the carbon fiber. The method of manufacturing a field emission electrode according to claim 3, wherein:   The method of manufacturing a field emission electrode according to claim 3, wherein the carbon fiber is a carbon nanotube.

Images