JP4707336B2 - Manufacturing method of electron source using carbon nanofiber - Google Patents

Description

  The present invention relates to a field emission type electron source using carbon nanofibers as a cathode used in a field emission display (FED) and the like, and a manufacturing method thereof.

  As a flat panel display, a liquid crystal display (LCD) or a plasma display (PDP) has been put into practical use. In recent years, other than these, a field emission display has attracted attention (see, for example, Non-Patent Document 1).

  FIG. 7 is a schematic configuration diagram showing a main part (near the cathode electrode) of a conventional field emission display (hereinafter referred to as FED).

  In FIG. 7, 100 is a glass substrate, 101 is a cathode electrode (cathode electrode), 102 is a single metal film of Fe, Co, Ni, Pt or the like or a catalytic metal film made of an alloy film containing them as a main component, 103 Is a plurality of carbon nanotubes formed using the catalytic metal film 102 as a catalyst, 104 is an anode electrode arranged on the front side of the cathode electrode 101, 105 is a phosphor coated on the surface of the anode electrode 104, and 106 is glass on the light emitting side. It is a substrate. The space between the cathode electrode 101 and the anode electrode 104 having a predetermined gap is evacuated and adjusted to a predetermined pressure (degree of vacuum).

Then, by applying a voltage of several kV from the power source 107 between the cathode electrode 101 and the anode electrode 104, the electric field at the tip of the carbon nanotube 103 is increased. Finally, as shown in FIG. Is released from its tip. The electrons emitted from the tip of the carbon nanotube 103 are accelerated and collide with the anode electrode 104 in the front, so that light is excited and emitted from the fluorescent material 105, thereby adjusting the shades of the three primary colors and using them frequently. Each pixel that expresses a desired color is caused to emit light to display a desired image.
“Topics of Light”, “The Future of the Display Market”, published on August 5, 2002, Ministry of Economy, Trade and Industry, Technical Research Office, [Search April 28, 2004], Internet <URL: http: // www. oitda.or.jp/main/hw/hw01302-j.html>

  By the way, in the conventional FED shown in FIG. 7, when a large number of carbon nanotubes 103 formed on the catalytic metal film 102 are dense and their heights are uniform to some extent, There is a problem that even if the electric field strength of one carbon nanotube 103 is high, the electric field is smoothed as a whole. In FIG. 7, a indicates a smoothed electric field.

  For this reason, the electric field intensity at the tip of the carbon nanotube 103 becomes weak, and electrons are not emitted (this phenomenon is called a shielding effect). In addition, as shown in FIG. 9, even if the heights of the carbon nanotubes 103 formed on the catalytic metal film 102 are slightly different, if they are densely packed, the equipotential surface (b in FIG. 9) is also used. Does not become an acute angle and is smooth in a plane, and the electric field strength does not increase.

  In addition, actual carbon nanotubes may exist individually one by one, but as shown in FIG. 10, in many cases, a large number of carbon nanotubes 103 are often present in a bundle (bundle state). However, the tip of the carbon nanotube is made up of a large number of carbon nanotubes, so that the electric field c is smoothed, thereby inhibiting electron emission.

  In addition, a tungsten surface coated with barium oxide has been used as an electron source for large-screen flat panel displays such as Aurora Vision, which has a larger screen size than the FED described above and is energized with a large current. In this case, since electrons are not emitted unless barium oxide or the like is applied thinly, the surface is washed or dried to an appropriate thickness after application. The number of process steps is increased.

  In addition, in the electron source using the above-described tungsten surface coated with barium oxide, it is necessary to always heat (preheat) the electron source so that electrons can be emitted when necessary. In addition, the power is wasted, and the power system for heating is required, so that the cost is increased.

  Furthermore, as an electron source used for a flat panel display of a large screen size such as Aurora Vision, which has a larger screen size than that of the above-mentioned FED and is supplied with a large current, an electron source obtained by growing carbon nanotubes on tungsten is used. However, in order to grow carbon nanotubes on tungsten, it is necessary to first deposit a thin film such as NI, CO, or Fe on tungsten, then heat, and then introduce methane gas or hydrogen gas As a result, the number of process steps increases.

  Carbon nanotubes are produced at a temperature of about 600 ° C., and damaged portions are repaired at about 1000 ° C., and crystallinity is optimized and electrons can be emitted efficiently. When the temperature exceeds about 2000 ° C., the electron emission is almost lost.

  Therefore, an object of the present invention is to provide an electron source using a carbon nanofiber that can effectively perform electron emission by preventing the electric field from being smoothed at the tip of the carbon nanofiber, and a method for manufacturing the same. . In addition, the present invention simplifies the process steps and reduces the cost even when applied to an electron source of a large screen size flat panel display such as Aurora Vision, which has a larger screen size than the FED and is energized with a large current. It is an object of the present invention to provide an electron source using a carbon nanofiber that can be easily converted and can emit electrons well over a long period of time, and a method for manufacturing the same.

In order to achieve the above object, the invention described in claim 1 is a method of manufacturing an electron source using carbon nanofibers as an electron emission material, the step of forming a graphite film on a silicon substrate, and the silicon The substrate is housed in a container, the inside of the container is adjusted to a predetermined pressure, argon ions are extracted while the silicon substrate is heated to a predetermined temperature, and the silicon substrate is irradiated with an argon ion beam, whereby the silicon And a step of forming carbon nanofibers with irregular lengths at the tops of the fine protrusions formed in large numbers at predetermined intervals on the substrate surface.

Further, the predetermined pressure is set to 1 × 10 ⁻⁷ Pa or less, the predetermined temperature is set to 200 ° C., the argon ions are extracted at 1.2 kV, and an argon ion beam is applied onto the silicon substrate with an ion current of 250 μA / cm ^2. By continuously irradiating for 100 minutes, carbon nanofibers are formed with irregular lengths on the tops of a large number of microprojections formed at a predetermined interval on the surface of the silicon substrate.

  According to the present invention, the carbon nanofibers are formed on the top of each of the microprojections formed at a predetermined interval on the substrate surface, so that the formed carbon nanofibers are not densely packed. Moreover, since the heights are not uniform, the electric field at the tip is prevented from being smoothed, and electron emission can be performed effectively.

Hereinafter, the present invention will be described based on the illustrated embodiments. In the present invention, the carbon nanofiber is a fiber-like substance whose main component is carbon having a diameter on the order of nanometers (nm), and examples of the carbon nanofiber include carbon nanotubes and graphite nanotubes. It contains. In the present invention, the graphite film also includes a diamond-like carbon film, an amorphous carbon film, and soot.
<Embodiment 1>
FIG. 1 is a schematic configuration diagram showing a manufacturing apparatus for manufacturing an electron source using FED carbon nanofibers according to Embodiment 1 of the present invention. A substrate holder 4 on which a substrate (silicon substrate) 3 is placed is installed in the reaction vessel 2 of the manufacturing apparatus 1. Above the substrate holder 4 is graphite (graphite) as a carbon film on the substrate 3. ) An arc plasma gun 5 for forming a film and an ion source 6 for forming a carbon nanofiber are provided. A heater 7 for heating the substrate 3 on the substrate holder 4 is built in the substrate holder 4. The reaction vessel 2 is connected to an exhaust system 8 having a vacuum pump or the like that evacuates the reaction vessel 2 and adjusts it to a predetermined pressure.

  In this embodiment, the arc plasma gun 5 and the ion source 6 are installed at an angle of approximately 35 ° with respect to the plane of the substrate 3 and at symmetrical positions with respect to a vertical line passing through the center of the substrate 3. . A gas introduction system 9 for introducing a reaction gas is connected to the ion source 6.

  Next, the manufacturing method of the electron source by the manufacturing apparatus 1 described above will be described.

  First, after placing the substrate 3 on the substrate holder 4, the heater 7 is energized and heated by resistance to heat the substrate 3 on the substrate holder 4 to a predetermined temperature (about 200 ° C.). At this time, the reaction vessel 2 is evacuated by the exhaust system 8 and adjusted to a predetermined pressure.

Then, the arc plasma gun 5 is operated to form a graphite film as a carbon film on the substrate 3 with a thickness of about 1 μm, and then the reaction vessel 2 is again evacuated by the exhaust system 8 to a predetermined pressure (1 × ^10-7 Pa or less). At this time, the substrate 3 on the substrate holder 4 is maintained in a state of being heated to a predetermined temperature (about 200 ° C.). Then, argon gas is introduced into the ion source 6 as a reaction gas from the gas introduction system 9 to operate the ion source 6. The ion source 6 extracts argon ions (Ar ⁺ ) at about 1.2 kV, and continuously irradiates the substrate 3 with an argon ion beam for about 100 minutes with an ion current of about 250 μA / cm ² .

  After the irradiation of the argon ion beam, the substrate 3 was taken out from the reaction vessel 2 and observed using a scanning electron microscope (SEM). As shown in FIG. A large number of protrusions 3a having a substantially conical height of several μm to 20 μm are formed at intervals of about 20 to 30 μm by irradiation of the beam, and the carbon nanofibers 10 are uneven in length on the top of each protrusion 3a. Each was formed. Each carbon nanofiber 10 had a diameter of about 50 nm and a length of about 1 to 3 μm. In addition, each protrusion 3a and each carbon nanofiber 10 in FIG. 2 are shown schematically, and do not show an actual shape or the like.

When the electron emission characteristics of the electron source having the carbon nanofibers 10 obtained as described above were examined, the results shown in FIG. 3 were obtained. As is apparent from this measurement result, an electron current of about 1 mA / cm ² was obtained at an electric field strength of about 3 V / μm.

  As described above, the carbon nanofiber 10 of the electron source used for the FED manufactured by the manufacturing method of the present invention is formed by being formed on the top of each of the substantially conical protrusions 10a formed on the surface of the substrate 3. Since the carbon nanofibers 10 are not densely packed and not uniform in height, the electric field at the tip is prevented from being smoothed, and electron emission can be performed effectively.

Further, the shielding effect described above (a phenomenon in which the electric field strength at the tip of the carbon nanofiber is weakened and electrons are not emitted) is about 10 times the length of the carbon nanofiber 10 as in this embodiment. If the carbon nanofibers 10 are arranged at intervals of a certain degree, it can be almost ignored.
<Embodiment 2>
In the first embodiment, a substrate on which a graphite film is formed is irradiated with an ion beam to form a large number of substantially conical protrusions on the surface, and carbon nanofibers are formed on the tops of the protrusions. In contrast to the ion source as in the first embodiment, for example, a parallel plate bipolar sputtering apparatus can be used as long as the method has an ion irradiation effect.

When this sputtering apparatus is used, for example, an argon plasma accelerated by holding a substrate on which a graphite film is formed by an arc plasma gun on a substrate also serving as a substrate holder and applying a negative voltage to the substrate. By irradiating (collision) with this electrode, the ion irradiation effect can be obtained as in the first embodiment.
<Embodiment 3>
In Embodiment 1, a graphite film is formed on a substrate using an arc plasma gun. However, other methods for forming a graphite film include, for example, an electron beam evaporation source, an ion plating method, and sputtering. Method, microwave CVD method, thermal CVD method, or the like can be used.
<Embodiment 4>
FIG. 4 is a schematic configuration showing an electron source manufacturing apparatus used in the FED according to the present embodiment. In this manufacturing apparatus, an electrode 12 holding a substrate (silicon substrate) 11 and a graphite target 13 are disposed facing each other in a reaction vessel (not shown), and an inverter power supply 14 is connected between the electrode 12 and the graphite target 13. is doing.

  Next, the manufacturing method of the electron source by this manufacturing apparatus is demonstrated.

First, the inside of a reaction vessel (not shown) is adjusted to a predetermined pressure, argon gas is introduced between the electrode 12 and the graphite target 13, and the inverter power supply 14 is connected between the electrode 12 and the graphite target 13. A high-frequency voltage is applied to turn argon gas into plasma. At this time, the substrate 11 is heated to a predetermined temperature by a heater (not shown). Note that A in FIG. 4 represents argon ions (Ar ⁺ ) and electrons that have been turned into plasma.

  Then, as shown in FIG. 5, by applying a negative voltage from the inverter power supply 14 to the graphite target 13, accelerated argon ions are irradiated (collised) to the graphite target 13 and held in the electrode 12. A graphite film 15 is formed on the formed substrate 11 with a thickness of about 1 μm.

  Then, as shown in FIG. 6, a negative voltage is applied to the electrode 12 from the inverter power supply 14 for a predetermined time, so that the surface of the substrate 11 is irradiated (collised) with the accelerated argon ion beam. As a result, an ion irradiation effect is obtained in the same manner as in the first embodiment. When the surface of the substrate 11 is irradiated (collised) with an argon ion beam, the projection 3a having a substantially conical shape with a height of about several μm to 20 μm becomes 20 to 20 μm. A large number of carbon nanofibers 16 are formed at irregular intervals, and many carbon nanofibers 16 are formed at the top of each protrusion 11a. Each formed carbon nanofiber 16 had a diameter of about 50 nm and a length of about 1 to 3 μm. In addition, each protrusion 11a and each carbon nanofiber 16 in FIG. 6 are shown schematically, and do not show an actual shape or the like.

  By the way, as shown in FIG. 6, when a large number of projections 11a are formed at predetermined intervals on the surface of the substrate 11 by irradiation (collision) with an argon ion beam, and carbon nanofibers 16 are formed on the tops of the respective projections 11a. When electrons in the plasma collide with argon gas (residual gas) remaining in the space between the electrode 12 and the graphite target 13, positive ions are born.

In some cases, the positive ions are attracted to and collide with the carbon nanofibers 16 that are negatively charged. Although there is a concern that electrons cannot be emitted if the tip of the carbon nanofiber 16 is missing due to the collision of positive ions, as described above, in the present embodiment, a graphite film is formed on the surface of the substrate 11 (FIG. 6), the positive ions collide with the surface of the substrate 11 to which a negative voltage is applied, and the graphite material jumped out by the collision adheres to the chipped tip of the carbon nanofiber 16. Can be self-regenerated and repaired, and electron emission can be performed satisfactorily.
<Embodiment 5>
In each of the embodiments described above, the electron source used for the FED was used. However, in the electron source used for a flat panel display of a large screen size such as Aurora Vision, which has a larger screen size than the FED and is energized with a large current. Similarly, the present invention can be applied.

  Also in this case, for example, each of the substantially conical shapes formed on the substrate surface by the manufacturing apparatus and the manufacturing method described in the first embodiment shown in FIGS. 1 and 2 or the fourth embodiment shown in FIGS. It is possible to obtain an electron source for large current in which carbon nanofibers are formed on the tops of the protrusions. In this high-current electron source, as in the electron source used for the FED described above, the height of the substantially conical protrusion formed on the substrate surface is about several μm to 20 μm, and the interval between the protrusions is 20 μm. The diameter of the carbon nanofiber is about 50 nm and the length is about 1 to 3 μm. Further, since a large current flows through the electron source, the substrate and its peripheral portion are configured to withstand the large current.

  Thus, by applying the present invention to an electron source used in a flat panel display having a large screen size, such as Aurora Vision, which has a larger screen size than the FED and is energized with a large current, the above-described conventional large current can be obtained. Can be easily manufactured without the need for many process steps like conventional electron sources (tungsten surface coated with barium oxide or tungsten grown carbon nanotubes) Since no power system is required for heating, the cost can be reduced. Furthermore, the carbon nanofiber formed on the top of the protrusion has a high temperature of about 2000 ° C. where carbon nanotubes cannot emit electrons. But since it can emit electrons efficiently, it can emit electrons well over a long period of time. That.

The schematic block diagram which shows the manufacturing apparatus which manufactures the electron source using the carbon nanofiber which concerns on Embodiment 1 of this invention. The schematic diagram which shows the processus | protrusion on the surface of a substrate, and the carbon nanofiber grown on the top in the electron source formed with the manufacturing method which concerns on Embodiment 1 of this invention. The figure which shows the electron emission characteristic of the carbon nanofiber formed in Embodiment 1 of this invention. The schematic block diagram which shows the manufacturing apparatus which manufactures the electron source using the carbon nanofiber which concerns on Embodiment 4 of this invention. The figure which shows the manufacture process of the electron source using the carbon nanofiber by the manufacturing apparatus which concerns on Embodiment 4 of this invention. The figure which shows the manufacture process of the electron source using the carbon nanofiber by the manufacturing apparatus which concerns on Embodiment 4 of this invention. The schematic block diagram which shows the principal part (cathode electrode vicinity) of the field emission display provided with the electron source which has the carbon nanotube in which the length was equal in a prior art example. The figure which shows the front-end | tip part of a carbon nanotube. The figure which shows the electron source which has the carbon nanotube in which the length in a prior art example is not uniform. The figure which shows the electron source which has the carbon nanotube used as the bundle in a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Manufacturing apparatus 2 Reaction container 3, 11 Board | substrate 3a, 11a Protrusion (microprotrusion)
4 Substrate holder 5 Arc plasma gun 6 Ion source 8 Exhaust system 9 Gas introduction system 10, 16 Carbon nanofiber 12 Electrode 13 Graphite target 14 Inverter power supply

Claims (1)

A method for producing an electron source using carbon nanofibers as an electron emission material,
Forming a graphite film on a silicon substrate;
The silicon substrate is accommodated in a container, the inside of the container is adjusted to 1 × 10 ⁻⁷ Pa or less, and argon ions are extracted at 1.2 kV while the silicon substrate is heated to 200 ° C. Irradiation with an argon ion beam for 100 minutes continuously allows carbon nanofibers to be unevenly formed on the tops of microprojections formed at a predetermined interval on the silicon substrate surface with an ion current of 250 μA / cm ^2. Including the step of forming
The manufacturing method of the electron source using the carbon nanofiber characterized by the above-mentioned.

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