JP4759103B2 - Method for manufacturing field electron emission device - Google Patents

Description

【００４９】
なお、上記の表１には示していないが、従来行われていた10^-2(Pa)程度の真空下では炉内の残留酸素が極めて少ないことから生成したナノチューブ４６が殆ど酸化させられないため、ナノチューブ４６先端部が疎らにならない。これに対して、6(Pa)程度の低真空度では、1600(℃)を越える条件下、すなわち1700(℃)或いは1800(℃)において、ナノチューブ４６が疎らになる結果が得られた。
【００５０】
次いで、上記の低真空熱処理によってナノチューブ４６先端の重なりの認められた試料のうち、1700(℃)で6時間加熱したものを、10^-2(Pa)の高真空下において加熱温度を1500〜1800(℃)の範囲で、加熱時間0.5〜10.0時間の範囲で種々変更して熱処理し、表面抵抗を表１の場合と同様にして評価した結果を説明する。
なお、下記の表２において、1500(℃)で10時間加熱した場合は、6時間加熱したものと変化が見られなかったため、1800(℃)で10時間加熱した場合は、珪素除去層３８の全体が炭素層４２で構成されてナノチューブ４６が認められなかったため、何れも表面抵抗を測定しなかった。
【００５１】

【００５２】
上記の表２に示されるように、低真空で熱処理したものを高真空で再度熱処理することにより、その高真空における加熱温度を1600(℃)以上、加熱時間を2時間以上とすれば、表面抵抗の十分に低いエミッタ２８を得ることができる。また、加熱時間が長くなるほど表面抵抗が低下する傾向があり、0.5時間程度の加熱では不十分であるが、1時間程度以上加熱すれば、電子源として使用するために好ましい300(Ω／□)程度以下の高い導電性が得られる。なお、上記のように高真空熱処理によって抵抗値を低下させた試料表面を観察したが、低真空熱処理後の疎らなナノチューブ４６の分布状態が維持されていることが確かめられた。
【００５３】
因みに、ナノチューブ４６を電子の放出源とするエミッタ２８を備えたＦＥＤ１０においては、輝度むらを生じさせることなく一画素の大きさを十分に大きくすると共に低電圧で駆動可能とすることが望まれる。例えば、一画素が2(mm)×6(mm)程度の大きさである場合には、輝度むらが生じないように内周部における電子放出効率を周縁部におけるそれと同様にするため、例えば300(Ω／□)程度以下の導電性が要求される。但し、必要な導電性はエミッタ２８の大きさに応じて相違し、0.8(mm)×4(mm)程度の大きさでは可及的に高い導電性を有することが好ましいもののエミッタ２８の表面抵抗は殆ど問題にならず、これらの中間の大きさのエミッタ２８においては、300(Ω／□)程度以上の適宜の導電性がその大きさに応じて要求される。すなわち、上述した電子源として好ましい「300(Ω／□)程度以下」との値は、上記のような大きさのエミッタ２８を前提とした値である。
【００５４】
以上、本発明の一実施例を図面を参照して詳細に説明したが、本発明は、更に別の態様でも実施できる。
【００５５】
例えば、実施例においては、本発明がＦＥＤ１０に適用された場合について説明したが、本発明は、エミッション・サイトの密度や電子放出効率の一様性を高めると共にエミッション開始電圧を低下させることが望まれるものであれば、平面型ランプ、陰極線管や電子銃等の種々の電界電子放出装置に同様に適用し得る。これらの用途において、必要な導電性延いては熱処理条件は、用いられるエミッタの大きさに応じて適宜選択される。
【００５６】
また、実施例においては、炭化珪素から成る基板５６を真空中で熱処理することにより、ナノチューブ４６が高い配向性を以て緻密に配設されたエミッタ２８を製造する場合について説明したが、真空中の加熱によって非金属元素が除去される共有結合性炭化物であれば、炭化ホウ素等の他の材料が用いられてもよい。
【００５７】
また、実施例においては、エミッタ２８を構成する炭素層４２の厚さ寸法が数百(nm)〜数(μm)程度、ナノチューブ４６の長さ寸法が数十〜数百(nm)程度である場合について説明したが、これらの厚さ寸法および長さ寸法は、用途や工程管理上の都合等に応じて適宜変更できる。
【００５８】
また、実施例においては、ナノチューブ４６を生成した後に更に酸素の存在下で酸化熱処理を施すことによりその先端を開放させていたが、先端の開放処理は必ずしも行われなくともよい。但し、前述のように先端を開放させることによってエミッタ２８の実質的な曲率半径が飛躍的に小さくなると共に、エミッション・サイトも飛躍的に増大して、エミッタ２８の効率が一層高められるため、先端を開放する方が望ましい。なお、熱処理条件は、実施例に示したものに限られず、温度は500〜750(℃)程度の範囲で適宜設定され、処理時間も例えば1分乃至20分程度の範囲で処理温度に応じて適宜変更される。
【００５９】
また、実施例においては、エミッタ２８が陰極２６に導電性接着剤で固着されるように説明したが、陰極２６が前述のような厚膜印刷導体で構成される場合には、その焼結過程で同時にエミッタ２８を固着するようにしてもよい。
【００６０】
また、実施例においては、低真空熱処理工程７０が高真空熱処理工程７２よりも先に実施されていたが、ナノチューブ４６を疎らにし得る低真空における処理および導電性を低下させる高真空における処理がそれぞれ実施されるのであれば、これらの順序は反対であっても差し支えない。
【００６１】
その他、一々例示はしないが、本発明は、その趣旨を逸脱しない範囲で種々変更を加え得るものである。
【図面の簡単な説明】
【図１】本発明の一実施例のＦＥＤの構成を説明する断面図である。
【図２】 (a)は、図１のＦＥＤに備えられるエミッタの断面構造を説明する図であり、(b)は、(a)に一点鎖線ｂで示される部分を拡大した図である。
【図３】図２のエミッタの表面側からナノチューブを観察した状態を示す図である。
【図４】図２のエミッタに備えられるナノチューブの先端部の構成を説明する分子モデル図である。
【図５】図２のエミッタの特性を従来のエミッタと比較して説明する図である。
【図６】図２のエミッタの製造方法の要部を説明する工程図である。
【図７】 (a)〜(c)は、図２のエミッタの製造工程の要部段階を説明する図である。
【図８】 (a)は、図６の低真空熱処理工程後、(b)は図６の高真空熱処理工程後の各々における図２(b)に対応する基板の要部断面を説明する図である。
【図９】図４の製造工程におけるナノチューブの生成作用を説明する分子モデル図である。
【符号の説明】
１０：ＦＥＤ（電界電子放出装置）
２８：エミッタ
７０：低真空熱処理工程
７２：高真空熱処理工程[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a field electron emission device used for an electron beam source such as a field emission display (FED), a cathode ray tube (CRT), a flat lamp, and an electron gun.
[0002]
[Prior art]
For example, a field electron emission device that emits electrons in a vacuum from an electron source (emitter) toward an anode by field emission is used in a display device or a light emitting device that excites a phosphor with the electrons, or an electron gun of a field microscope. It is preferably used. Here, “field emission (field electron emission)” refers to drawing electrons from a solid surface to a vacuum level by utilizing a quantum mechanical tunnel phenomenon by the action of a strong electric field. The energy difference between the vacuum level and the metal or semiconductor surface is expressed by a work function φ.For example, in ordinary metal materials, the work function φ is as large as several (eV), so electrons in the metal at room temperature. Will not jump into the vacuum. However, when the potential barrier is thinned by applying a strong electric field from the outside, electrons are stochastically ejected into the vacuum by the tunnel effect. This is field emission. As the work function φ is smaller, electrons can be emitted with a weaker electric field.
[0003]
In the field electron emission device as described above, it has been proposed that the emitter is composed of a large number of carbon nanotubes (hereinafter simply referred to as nanotubes). For example, a field emission cold cathode device described in JP-A-10-149760, an electron-emitting device described in JP-A-10-012124, and the like. A nanotube is a combination of carbon atoms (C) in a cylindrical shape, and a plurality of graphite sheets having different diameters (graphene sheets, that is, graphite layers mainly composed of six-membered rings of carbon) are nested, A fine structure having a total diameter of about 1 to 50 (nm) and a length of about 100 (μm) or less. Such nanotubes emit electrons efficiently from their micronized tips and have excellent emission characteristics, and are composed of only carbon atoms, so they have high oxidation resistance and excellent chemical stability in a vacuum. It also has a high ion impact resistance. Therefore, the number density composed of molybdenum cone, etc. called Spindt type with sharp tip is tens of thousands (pieces / cm ² ) Compared with emitters that are less than or equal to the extent, they are arranged at a very high number density, have high electron emission efficiency, and cause oxidation or damage due to residual gas in the airtight space, resulting in aging (deterioration), etc. Difficult emitters can be obtained with a simple manufacturing process.
[0004]
[Problems to be solved by the invention]
As a method for producing the above-mentioned nanotube, for example, as described in JP-A-10-265208, a silicon atom (SiC) sintered body is heated under a vacuum to treat silicon atoms in the sintered body. There is a way to remove. According to such a manufacturing method, compared with an arc discharge method or a laser ablation method that condenses (recombines) carbon evaporated in an inert gas atmosphere that has been conventionally performed, The orientation, height, and arrangement density of the nanotubes can be made uniform without generating a carbon allotrope. Therefore, a nanotube that can be suitably used not only as a minute electron generation source but also in a display device such as an FED or a lighting device that requires uniform luminance over a wide area can be obtained. In the manufacturing method described in the above-mentioned publication, carbon (Si) is selectively removed from the surface of the substrate heated under a vacuum that is stable to a relatively high temperature, thereby remaining in the silicon removal layer. It is considered that nanotubes oriented along the moving direction of silicon with carbon atoms, that is, along one direction from the inside of the substrate to the surface, are generated at a high number density based on the original carbon atom density. Such a nanotube generating action is not limited to the silicon carbide sintered body, and can be obtained in the same manner when heat treating other covalently bonded carbide substrates. Here, the term “covalently bonded carbide” means an element such as silicon or a non-metallic element (such as silicon having a weaker positivity than an ionic carbide formed between carbon and an atomic radius smaller than that forming an interstitial carbide). ) And is also referred to as a covalent carbide.
[0005]
However, the emitter in which nanotubes are generated by the above-described heat treatment of the substrate has a problem that the emission starting voltage is higher than that of a conventional emitter made of a molybdenum cone, a nanotube manufactured by an arc discharge method, or the like. If the height dimension of the nanotubes provided on the substrate surface is uniform, local concentration of the electric field does not occur. Therefore, partial emission of electrons from a part of the substrate surface is suppressed, and a uniform brightness can be obtained. However, the nanotubes are provided in close contact with each other on the substrate surface to have a very high density. Therefore, it is necessary to apply a high voltage so that they simultaneously emit electrons. That is, the small-diameter nanotubes having a uniform height are arranged at a very high density, so that at the start of the emission, the emitter is configured by a substantially film-like conductor.
[0006]
The present invention has been made against the background described above, and its object is to provide a method for manufacturing a field electron emission device capable of lowering the emission start voltage of an emitter composed of nanotubes oriented at high density. Is to provide.
[0007]
[Means for Solving the Problems]
In order to achieve such an object, the gist of the present invention is that an electric field of a type in which electrons are emitted from an emitter by applying a voltage between an emitter and an anode arranged opposite to each other in an airtight space. A method for manufacturing an electron-emitting device, comprising: (a) heating a substrate made of covalently bonded carbide at a temperature within a range of 1650 to 1800 (° C) for 1 hour or more under a vacuum within a range of 0.1 to 10 (Pa). Do As a result, the covalently bonded carbide on the surface layer of the substrate is oxidized to form a plurality of nanotubes and the tips of the nanotubes are oxidized. A low vacuum heat treatment step, and (b) 10 ^-4 Heating at a temperature in the range of 1550 to 1800 (° C.) for 1 hour or more under a vacuum within the range of 0.1 to 0.1 (Pa) and having a lower oxygen partial pressure than the low vacuum heat treatment step. Only the covalently bonded carbides of the substrate are oxidized A high vacuum heat treatment step.
[0008]
【The invention's effect】
In this way, the substrate heated in a vacuum, that is, in an atmosphere having a lower oxygen partial pressure than in the air, selectively removes non-metallic elements constituting the covalently bonded carbide from the surface. A non-metallic element removal layer composed only of carbon is formed on the surface layer portion, and a plurality of nanotubes extending from the substrate surface toward the anode are formed in the non-metallic element removal layer at a high density. At this time, in both the low vacuum heat treatment step and the high vacuum heat treatment step, the nonmetallic element removal layer in the surface layer portion is gradually thickened by heating for a long time of 1 hour or more. In the low vacuum heat treatment process, the nanotubes generated on the surface layer of the nonmetallic element removal layer have a relatively low vacuum degree of about 0.1 to 10 (Pa), that is, 1650 to 1650 in an atmosphere having a relatively high oxygen partial pressure. Since it is heated at 1800 (° C.), it is oxidized from its tip at a rate slower than the rate of formation of the nonmetallic element removal layer, and its tip is sparsely distributed on the substrate surface. On the other hand, in the high vacuum heat treatment process, the substrate is 10%. ^-Four A relatively high degree of vacuum of ~ 0.1 (Pa) Than the low vacuum heat treatment step Since it is heated at a temperature of 1550 to 1800 (° C.) in an atmosphere having a low oxygen partial pressure, the upper layer portion of the nonmetallic element removal layer is maintained in a nanotube structure, but the lower layer portion is formed of graphite or the like in the direction along the surface. Amorphous carbon and the like are continuous, and a conductive carbon layer continuous at the atomic level with the nanotube.
[0009]
As a result, the tip of the nanotube is sparser on the substrate surface compared to the conventional case where only heat treatment in a high vacuum is performed. Therefore, the emission is made in comparison with the conventional case where the emitter is composed of a substantially film-like conductor. The starting voltage is reduced. In addition, since the nanotubes located on the inner periphery of the substrate are connected to the periphery of the substrate through a carbon layer continuous at the atomic level, the nanotubes become sparse so that the nanotubes can contact each other. Even when the conductivity between the peripheral edge and the inner periphery is low, uniform electron emission efficiency can be obtained over the entire surface of the substrate.
[0010]
Incidentally, the reaction in which nanotubes are produced from covalently bonded carbide is, for example, in the case of silicon carbide,
2SiC + O ₂ → 2SiO ↑ + 2C
It is considered to be. That is, oxygen (O ₂ ) Is oxidized to disappear from the surface, and the remaining C forms nanotubes. This oxidation reaction is considered to be substantially the same for other covalently bonded carbides.
[0011]
Therefore, under a high vacuum of less than about 0.1 (Pa), as the nonmetallic element removal layer becomes thicker, that is, as the nanotube becomes longer, the gas flow between the lower layer and the surface (O ₂ Intrusion of SiO or escape of SiO) becomes difficult, so in the lower layer, C produced by the above reaction does not become a nanotube grown along the gas flow, but a carbon layer with a disordered structure It is considered a thing. At this time, in order for the carbon layer to be formed, the nanotubes need to grow sufficiently as described above, and therefore the heating time must be a long time of 1 hour or more. Also, the higher the temperature, the higher the growth rate of nanotubes, that is, the decomposition rate of SiC.Therefore, even when heating under high vacuum, the gas flow rate is sufficiently higher than the decomposition rate at low temperatures below 1550 (° C). Therefore, the carbon layer is not formed and only the nanotube grows. On the other hand, at a high temperature of 1800 (° C.) or higher, the gas flow rate becomes too low with respect to the decomposition rate, so that the nanotubes are disturbed up to the upper layer portion of the nonmetallic element removal layer, so that substantially the whole becomes a carbon layer. The pressure is 10 ^-Four If it is less than (Pa), the oxygen partial pressure is too low, so the non-metallic element of the covalently bonded carbide is hardly removed by combining with oxygen, so that the nanotubes hardly grow and the carbon layer is also formed. Not.
[0012]
On the other hand, since the oxygen partial pressure is high under a low vacuum of about 0.1 (Pa) or more, C produced by the reaction is
C + O ₂ → CO ₂ ↑
Gasification from the substrate surface, that is, the tip of the nanotube, disappears due to the oxidation reaction. At this time, since the pressure is set to be less than about 10 (Pa), the disappearance speed is not uniform for all the nanotubes, so that the nanotube tips are sparsely distributed on the surface based on the difference in speed. It is considered to be. In order to make the nanotubes sparse enough to cause a difference in emission characteristics, it is necessary to heat them for a long time of 1 hour or more. Further, when the pressure is less than 0.1 (Pa) or the temperature is less than about 1650 (° C.), the oxidation rate of the nanotube tip is remarkably reduced, and the tip is not sparse. Further, at 10 (Pa) or higher, or 1800 (° C.) or higher, the disappearance rate of all the nanotubes existing on the substrate surface is remarkably increased, so that the tip cannot be made sparse. In order to suppress an excessive oxidation reaction, the oxygen partial pressure is desirably 5 (Pa) or less. This oxygen partial pressure is determined when oxygen, water vapor, carbon monoxide, carbon dioxide, etc. are contained in the atmosphere. ₂ It is the partial pressure when converted to.
[0013]
Other aspects of the invention
Here, preferably, the low vacuum heat treatment step is performed prior to the high vacuum heat treatment step. In this way, although the reason is not clear, it is possible to obtain an emitter that is moderately sparse and has a sufficiently low surface resistance as compared with the case of processing in the reverse order.
[0014]
Preferably, the substrate is made of silicon carbide. In this way, it is possible to generate nanotubes that are uniformly oriented on the substrate surface with a suitable density. This is presumably because the oxidation tendency of silicon and carbon is slightly different and there is a condition that only silicon is oxidized. Silicon carbide is generally classified into α-type (α-SiC) and β-type (β-SiC), and nanotubes are preferably formed on any substrate. The above α-type and β-type are two types of polymorphs of silicon carbide that exist in large numbers. Cubic 3C is called β-type, and other non-isoaxial crystals (hexagonal 2H, 4H, 6H and rhombohedral 15R) are called α-type. Here, 2H and the like follow the notation of Ramsdell.
[0015]
Preferably, the method for manufacturing the field electron emission device includes a polishing step of finishing the surface of the substrate into a mirror surface prior to the low vacuum heat treatment step and the high vacuum heat treatment step. When the surface of the substrate becomes rough, it becomes difficult to adopt the nanotube structure when the remaining carbon atoms are removed and the remaining carbon atoms are rearranged, or even once the nanotube structure is formed, it is disturbed as the growth proceeds. The nanotube structure cannot be maintained. If it does as mentioned above, when a carbon atom rearranges, it will become easy to take a nanotube structure, and since the growth direction of a nanotube aligns, it will be hard to generate disorder accompanying growth. Therefore, an emitter composed of nanotubes oriented with high density can be obtained more easily. The above mirror surface is preferably a smooth surface having a surface roughness of Ra = 0.02 (mm) or less.
[0016]
Preferably, the substrate is a single crystal having a surface parallel to the crystal plane. In this way, since the nanotubes tend to be oriented in a direction perpendicular to the crystal plane, the independence of the nanotubes generated on the surface is enhanced and there are many substantial electron emission positions (emission sites). Therefore, the electron emission efficiency is further enhanced. More preferably, the surface is a stacked surface in a direction in which a first layer in which only carbon is present and a second layer in which only a nonmetallic element is present are alternately stacked. In this way, it is possible to further increase the orientation and independence of the nanotubes. This is presumably because excess carbon atoms easily form a tube shape when the nonmetallic element located on the outermost surface is removed. The above-mentioned laminated surface is, for example, a (0001) plane in a hexagonal compound such as a 2H α-SiC single crystal and a (111) in a cubic compound such as a β-SiC single crystal. Surface.
[0017]
Preferably, in the method of manufacturing the field electron emission device, following the low vacuum heat treatment step and the high vacuum heat treatment step, the cap provided on the dome-shaped tip portion of the nanotube is removed and the tip is opened. Including a tip opening step. In this way, since the nanotube is opened at the tip located on the anode side, the tip is constituted by the end face of the cylindrical graphite layer, so the radius of curvature at the tip is substantially equal. It almost coincides with the radius of the carbon atom located there. Moreover, since the nanotube is formed by nesting a plurality of graphite layers in a cylindrical shape, the end of the dome-shaped closed end is opened to open the graphite layer provided on the inner peripheral side. The end face is exposed. Therefore, the tip of the nanotube is composed of end faces of a plurality of graphite layers each having a radius of curvature substantially equal to the atomic radius of the carbon atom, and electrons are emitted from individual carbon atoms located at the open tip. . Therefore, since the radius of curvature of the tip is extremely small and the number of substantial electron emission positions increases, the electron emission efficiency can be dramatically increased.
[0018]
The tip opening step is, for example, an oxidation heat treatment step in which heating is performed at a temperature of about 500 to 750 (° C.) in the presence of oxygen. In this way, the five-membered or seven-membered ring introduced so that the tip of the nanotube is closed has a smaller binding force than the six-membered ring, which is a basic component of graphite. Since the cap is preferentially decomposed, the cap is separated from the position where the five-membered or seven-membered ring exists. The oxidation heat treatment time is preferably about 1 to 20 minutes, and is appropriately set according to the treatment temperature. Note that the tip cannot be opened because the five-membered ring and the seven-membered ring are not decomposed at a low temperature of less than 500 (° C.) or for a short time of less than one minute. On the other hand, at a high temperature exceeding 750 (° C.) or for a long time exceeding 20 minutes, the six-membered ring is also decomposed and the nanotubes are lost.
[0019]
Further, the tip opening step may be a step of plasma etching from the tip end side of the nanotube. In this way, it is suitably suppressed that the nanotube is deteriorated by oxygen during the opening process of the tip, or the emission characteristics are lowered by adsorption of oxygen. The gas used for etching is CF. _Four Hydrogen, argon, helium, nitrogen, or a mixed gas thereof is preferably used.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
[0021]
FIG. 1 is a cross-sectional view schematically showing the main part of the configuration of an FED 10 to which the method for manufacturing a field electron emission device of the present invention is applied. In the figure, the FED 10 has a transparent flat front plate 12 and a rear plate 14 arranged in parallel to each other via a frame-like spacer 16 so that the inside is 10. ^-Four (Pa) or less, preferably 10 ^-Five It is configured in an airtight container having a degree of vacuum of (Pa) or less. The front plate 12 and the back plate 14 are each made of a soda lime glass flat plate having a thickness of about 1 to 2 (mm). However, since the back plate 14 is not required to have translucency, the back plate 14 may be made of other materials having electrical insulation properties such as ceramics or scissors. The spacer 16 is made of, for example, a material having a thermal expansion coefficient similar to that of the constituent material of the front plate 12 and the back plate 14, such as soda lime glass similar to those, 426 alloy having an insulating layer on the surface, or the like. For example, it has a uniform thickness of about 0.3 (mm).
[0022]
A plurality of anodes (anodes) 20 made of transparent ITO (Indium Tin Oxide) or the like are arranged in stripes along one direction on the inner surface 18 of the front plate 12. The anode 20 is provided with a thickness of about 1 (μm) by a thin film process such as sputtering or vapor deposition, and has a high conductivity of about 10 (Ω / □) in terms of sheet resistance. On the lower surface of each of the plurality of anodes 20, for example, phosphor layers 22 that emit light in red, green, and blue, respectively, are provided so that these three colors are repeatedly arranged. The phosphor layer 22 is, for example, (Zn, Cd) S: Ag, Cl (red), ZnGa that generates visible light when excited by a low-energy electron beam. ₂ O _Four : Mn (green) or ZnS: Cl (blue) and other phosphor materials, for example, a thick film screen with a thickness dimension determined for each color of about 10-20 (μm) It is formed by a printing method or the like.
[0023]
On the other hand, on the inner surface 24 of the back plate 14, for example, a plurality of striped cathodes 26 are arranged along the other direction orthogonal to the anode 20. The cathode 26 is, for example, a thick film printed conductor made of a metal such as Ni, Cr, Au, Ag, Mo, W, Pt, Ti, Al, Cu, Pd, an alloy, or a metal oxide and glass. . On each of the plurality of cathodes 26, as will be described later, an emitter 28 serving as an electron generation source is fixed in a state of being electrically connected to the cathode 26 by, for example, a conductive adhesive. The distance between the emitter 28 and the anode 20 is, for example, about several tens (μm) to several tens (mm), for example, about 20 (mm). In the figure, the emitter 28 is drawn to have substantially the same length as the cathode 26 in the left-right direction of the figure, but the emitter 28 is actually controlled by, for example, a pixel of the FED 10 on the cathode 26 (independently controlled). The size of each emitter 28 is, for example, about 2 × 6 (mm). Above the emitter 28, a plurality of stripe-shaped gate electrodes 30 arranged along a direction orthogonal to the cathode 26, that is, along one direction similar to the anode 20, are electrically connected to the emitter 28 by the insulating film 32. It is provided in an insulated state. The gate electrode 30 is made of, for example, chromium (Cr) or the like, and includes a plurality of electron passage holes 34 having a diameter of about 1 to 2 (μm) at each intersection with the cathode 26. The distance from the emitter 28 is several. It is about (mm) or less, for example, about 0.5 (mm). The insulating film 32 is made of silicon dioxide (SiO 2 ₂ ) And other insulating materials. Both the gate electrode 30 and the insulating film 32 are formed by a vacuum deposition method, a printing method, a sputtering method, or the like.
[0024]
Therefore, when a signal voltage and a scanning voltage are applied to the cathode 26 and the gate electrode 30, respectively, an emitter 28 fixed on the cathode 26 by field emission generated based on a large voltage gradient therebetween. Emits electrons. The electrons fly toward the anode 20 through the electron passage hole 34 provided in the gate electrode 30 by applying a predetermined positive voltage to the anode 20 provided on the front plate 12. As a result, electrons collide with the phosphor layer 22 provided on the anode 20, and the phosphor layer 22 emits light by electron beam excitation. Therefore, by applying a positive voltage to the desired anode 20 in synchronization with the scanning timing of the gate electrode 30, the phosphor layer 22 at the desired position is caused to emit light, so that the light is transmitted to the outside through the front plate 12. A desired image is displayed by being ejected. The details of the driving method are not necessary for the understanding of the present invention and will not be described.
[0025]
2A and 2B are diagrams showing in detail the cross-sectional configuration of the emitter 28 described above. In FIG. 2A, the emitter 28 includes a carbide portion 36 made of, for example, silicon carbide, and a silicon removal layer 38 that covers the entire surface of the carbide portion 36. The silicon removal layer 38 has a thickness dimension h of only several (μm), for example, about 1.0 (μm), which is composed of only carbon by removing silicon constituting silicon carbide as will be described later. It is a layer of thickness. As schematically shown in FIG. 2 (b) by enlarging the range surrounded by the alternate long and short dash line b in FIG. 2 (a), the silicon removal layer 38 has a carbide portion on the substantially flat surface 48 side of the emitter 28. A carbon layer 42 constituting the lower layer portion of the silicon removal layer 38 formed on the surface 40 of the 36 and a plurality of nanotubes 46 extending from the surface 44 of the carbon layer 42 and constituting the upper layer portion of the silicon removal layer 38. It consists of. Further, the nanotube 46 is hardly present on the other surface of the emitter 28, that is, the side surface and the bottom surface in FIG. 2A, and the silicon removal layer 38 is constituted by only the carbon layer 42.
[0026]
The carbon layer 42 has a thickness dimension hg of about several hundreds (nm) to several (μm), for example, about 300 (nm), and is mainly composed of graphite or amorphous carbon having a flat network structure of carbon atoms. Is. In the carbon layer 42, the bonding structure of carbon atoms is continuous in the left-right direction in the figure, and thus has high conductivity in the direction extending along the surface 44 and the outer peripheral surface of the carbide portion 36. For this reason, only by fixing the lower surface of the emitter 28 on the cathode 26 with a conductive adhesive or the like, a highly conductive current path between the cathode 26 and the nanotube 46 by the carbon layer 42 formed on the surface layer portion. Is formed. In FIG. 2B, the surface 40 of the carbide portion 36 and the surface 44 of the carbon layer 42 are drawn flat, but actually, the surfaces 40 and 44 are substantially flat, for example, having a height difference of 1. The uneven surface is about (μm) or less. The carbon layer 42 is continuous at the atomic level from the surface 40 of the carbide portion 36 as will be apparent from the manufacturing method described later, FIG. 9 and the like, and is integrally formed on the carbide portion 36 without any bonding treatment or the like. Provided.
[0027]
The nanotube 46 has a diameter of about d = 5 to 10 (nm), for example, and is oriented in a direction substantially perpendicular to the surface 44 so that the tip thereof faces the anode 20. . The nanotubes 46 are also continuous at the atomic level from the surface 44 of the carbon layer 42 and are substantially integrally provided on the carbide portion 36. The emission of electrons from the emitter 28 in the driving process described above is performed from the tips of these nanotubes 46. Therefore, in this embodiment, a large number of nanotubes 46 provided on the surface 48 of the emitter 28 are provided. Each substantially functions as an emitter.
[0028]
However, the nanotube 46 is composed of two types having different length dimensions hn, one being about several tens to several hundreds (nm), for example, about 700 (nm), and the other being about several to several tens (nm). For example, the length is about several tens to several hundreds (nm), for example, about 640 (nm). Note that the difference in height of the tip of the nanotube 46 remains within the range of several (nm) to several tens (nm) for each of the two types having different lengths, and can be said to be a substantially uniform height. Therefore, on the surface 48, the nanotubes 46 are, for example, 10 ¹¹ ~Ten ¹² (Book / cm ² ) Degree [e.g., 2500-10000 (books / μm ² ) Grade, eg 4000 (pieces / μm ² ) And the like are present in a sparsely distributed manner with a number density of about), and the mutual spacing (that is, the mutual spacing of the longer nanotubes 46) G on the surface 48 is, for example, about several (nm) to several tens (nm). It has become. Note that the arrangement density is about ½ of the case where all the nanotubes 46 are provided closely, for example. FIG. 3 schematically shows the distribution state of the nanotubes 46 on the surface 48. Only those having a height dimension of about hn = 700 (nm) are distributed on the surface 48, and each of the plurality of nanotubes 46 exists independently without contacting the other nanotubes 46 at the tips. Alternatively, several (for example, about 2 to 5) tips that are in contact (or substantially in contact) with each other are separated from other nanotubes 46.
[0029]
In addition, as shown in FIG. 4 showing an enlarged molecular structure model of the tip, the above-mentioned nanotube 46 has a plurality of (for example, about 2 to 10) nanotubes whose peripheral walls are connected by a six-membered ring of carbon atoms 50. Cylindrical graphite layers 52a, 52b, .about.52k (hereinafter simply referred to as "graphite layer 52" unless otherwise specified) are nested to form cylindrical graphite having a multilayer structure of about 2 to 10 layers. It is composed of the layer 52. In FIG. 3 described above, multiple circles representing the nanotubes 46 are drawn for this nested structure. At the tip of each nanotube 46, the end face of the graphite layer 52 having a multiple structure is exposed. That is, the nanotube 46 has a shape in which the tip toward the anode 20 is open, and electrons are emitted from each of the plurality of carbon atoms 50 constituting the end face of the graphite layer 52. Accordingly, the substantial radius of curvature of the tip of the emitter 28 matches the radius of the carbon atom 50.
[0030]
In each of the nanotubes 46, the diameter of the graphite layer 52a located at the outermost periphery, that is, the diameter od of the nanotube 46 is about 5 to 10 (nm) as described above, and the diameter of the graphite layer 52k located at the innermost periphery. For example, id is about 3 (nm). For this reason, in the present embodiment, a very large number of emission sites (electron emission positions) exist in a very fine region having a diameter of about od = 10 (nm) or less. The mutual spacing g of the graphite layers 52 is about 3.4 (Å), which is substantially equal to the flat graphite layer spacing, and the graphite layers 52 in the individual nanotubes 46 are substantially independent of each other.
[0031]
Since the plurality of nanotubes 46 configured as described above are in a positional relationship such that they are independent or slightly in contact with each other as described above, the electrical resistance between the nanotubes 46 based on the contact is relatively low. large. However, since the nanotube 46 itself is composed of the highly conductive graphite layer 52 and is continuous at the atomic level on the carbon layer 42 having high conductivity in the direction along the surface 48, An energization path having a very low resistivity is also formed through the carbon layer 42 for the nanotube 46. Further, although the conductivity of silicon carbide constituting the carbide portion 36 is extremely low, since the entire surface is covered with the carbon layer 42 having high conductivity, the emitter 28 passes through the silicon removal layer 38 of the surface layer portion. A conductive path with high conductivity is formed.
[0032]
Therefore, the nanotube 46 provided on the surface 44 of the carbon layer 42 is electrically connected to the cathode 26 through the carbon layer 42 and the conductive adhesive, so that a voltage is applied between the cathode 26 and the gate electrode 30 as described above. Is applied, the nanotube 46 is energized and electrons are emitted from its tip. At this time, since the energization path from the cathode 26 to the inner peripheral side of the emitter surface 48 is exclusively constituted by the carbon layer 42 having extremely high conductivity, the value of the current flowing through the nanotube 46 is the outer peripheral portion of the surface 48. And the thing located in any of an inner peripheral part becomes the same magnitude | size. That is, the emitter 28 includes a plurality of nanotubes 46 that are generated so as to extend along one direction from the one surface 48 to the anode 20 by removing silicon, a carbide portion 36 that remains as silicon carbide, and the nanotubes 46. Since the carbon layer 42 generated at the interface of the carbon layer 42 is formed by the conductive carbon layer 42 in the direction along the one surface 48, the conduction path from the peripheral edge to the nanotube 46 is formed. The resistivity of the energization path is sufficiently low. Therefore, since the value of the current flowing through the nanotube is sufficiently large even in the inner peripheral portion, the electron emission efficiency is suppressed from decreasing in the inner peripheral portion, and the electron emission efficiency of the emitter is uniform over the entire surface. As a result of the above, electrons are emitted uniformly from the entire surface 48 of each emitter 28, and as a result, electrons are emitted substantially uniformly from substantially the entire surface of the emitter 28 provided on each of the plurality of cathodes 26. As a result, a substantially uniform electric field is formed. In this way, the emitter is composed of a plurality of nanotubes 46 that are oriented in one direction and are each connected to the cathode 26 via the carbon layer 42, so that the emitter 28 having a high current density and uniform characteristics can be obtained. The provided FED 10 is obtained.
[0033]
Moreover, the emitter 28 is provided with two types of nanotubes 46 having sufficiently different lengths as described above, and the longer nanotubes 46 are provided with a relatively large mutual gap G. When a voltage is applied, the electric field concentrates on the tip of the nanotube 46, which is relatively closer to the anode 20 (the longer one). That is, in this embodiment, when a voltage is applied, the plurality of nanotubes 46 do not act as one film-like electrode, each functions as an independent electrode, and the electric field concentrates at the tip of each. . As a result, electrons are emitted only from the nanotube 46 in which the electric field is concentrated, so that only one of the long groups actually functions as an emitter. For this reason, the emission start voltage is drastically reduced to, for example, about 1/4 compared to the conventional case where the electric field concentration could not occur due to the fact that the nanotube 46 was densely provided and became a substantially film-like emitter. To do.
[0034]
Regarding the electrical performance of the emitter 28 having the above-described structure, an emitter having the same structure except that the surface 48 is formed to have a size of about 5 × 5 (mm) is used. A triode-structure field electron emission device having a distance of about 0.5 (mm) and a distance between the gate electrode 30 and the anode 20 of about 30 (mm) was fabricated and evaluated. In this apparatus, if the gate voltage is 2 (kV) and the anode (anode) voltage is 5 (kV), the emission current, that is, the current value flowing between the anode 20 and the cathode 26 is sufficiently large, 200 (μA) or more. By observing the light emission of the phosphor layer 22, it was confirmed that electrons were emitted substantially uniformly from the peripheral and central portions of the emitter. The reason why such a high electron emission capability can be obtained at a relatively low voltage as described above is that the end surface of the graphite layer 52 located on the inner peripheral side of each is exposed, so that there are a large number of emission sites and the curvature of the tip. This is because the nanotubes 46 having extremely small radii are provided so that their tips are sparsely distributed.
[0035]
FIG. 5 shows the result of measuring the relationship between the grid voltage and the current value between the cathode and the anode when the dimension of the emitter 28 is about 1 × 3 to 4 (mm). In the figure, “Example” is the present example using the emitter 28 having the above-described structure, and “Comparative Example 1” is a comparison in which the carbon layer 42 is provided but the height dimension of the nanotube 46 is substantially uniform. For example, “Comparative Example 2” represents a comparative example in which nanotubes 46 of two kinds of height dimensions are provided but the carbon layer 42 is not provided. According to the present embodiment, it can be seen that the emission starts at a very low voltage and a large current flows at a low voltage as compared with either of the comparative examples 1 and 2. In Comparative Example 2, emission starts at a lower voltage than in Comparative Example 1, but there is a saturation voltage at which the current value does not increase even when the voltage is increased above a certain value. On the other hand, in this embodiment, such inconvenience is not seen in the range up to about 3.0 (kV), and the current value can be increased as the applied voltage is increased, and the brightness of the FED can be increased. It was.
[0036]
By the way, the emitter 28 is manufactured in accordance with, for example, the process shown in FIG. Hereinafter, the manufacturing method will be described with reference to FIG. 6 and FIGS. 7A to 7C showing the main steps of the process.
[0037]
First, for example, a substrate 56 made of a silicon carbide single crystal of α-type with the (0001) plane appearing on the surface 54 or β-type with the (111) plane appearing on the surface 54 is prepared, and the surface 54 is placed in the vacuum furnace 58. Place so that is facing upward. FIG. 7 (a) shows this state. In the low vacuum heat treatment step 70, the substrate 56 is placed in the vacuum furnace 58 at a temperature in the range of about 1650 to 1800 (° C.), for example, a temperature of about 1700 (° C.), for a long time of 1 hour or more, for example, about 6 hours. Apply a low vacuum heat treatment that only heats. During the heat treatment, the inside of the vacuum furnace 58 is kept under a pressure within a range of 0.1 to 10 (Pa), for example, a reduced pressure of about 6 (Pa), that is, under vacuum, and the atmosphere in the furnace is more oxygen (atmospheric than the atmosphere). O ₂ ) Is a low oxygen partial pressure state. As a result, silicon constituting silicon carbide (that is, nonmetallic elements constituting the covalently bonded carbide) is oxidized and gasified gradually from the entire outer peripheral surface including the surface 54 of the substrate 56, and the vicinity of the flat surface 54. The silicon removal layer 38 consisting of only carbon atoms 50 is formed. FIG. 7B shows this state.
[0038]
At this time, since the degree of vacuum is not so high in this step, excess oxygen that is not used for the oxidation of silicon carbide exists in the vacuum furnace 58, and thus the produced nanotubes 46 are sequentially formed from the tip by this excess oxygen. It is oxidized to. However, since the oxidation rate of the nanotube 46 is slower than the oxidation rate of silicon carbide at the above temperature and pressure, the generated product is not completely lost, and the amount of depletion of the nanotube 46 is uniform. Don't be. For this reason, the plurality of nanotubes 46 that are initially formed in a substantially uniform height dimension in close contact with each other must have a large amount of wear at the tip and a small one with a substantially uniform distribution. become. That is, as described above, the nanotubes 46 sparsely distributed on the surface 48 are generated. FIG. 8A shows a cross-section of the main part corresponding to FIG. 2B in the vicinity of the substrate surface 48 at this stage. The produced nanotube 46 is mainly composed of a six-membered ring of carbon, and a five-membered or seven-membered ring is introduced at the end of the nanotube 46 to close it into a small dome shape with a radius of curvature of about 10 (nm). Yes. The nanotubes 46 are highly oriented in the [0001] direction in the α type and in the [111] direction in the β type. At this stage, the carbon layer 42 is not generated, and the nanotubes 46 are erected directly on the carbide portion 36.
[0039]
Next, in the high-vacuum heat treatment step 72, the substrate 56 is kept in the vacuum furnace 58 at a temperature in the range of about 1550 to 1800 (° C.), for example, a temperature of about 1700 (° C.) for a long time of 1 hour or more. For example, a high vacuum heat treatment is performed in which heating is performed for about 10 hours. During this heat treatment, the inside of the vacuum furnace 58 is 10 ^-Four Pressure in the range of ~ 0.1 (Pa), e.g. 10 ^-2 The pressure in the furnace is maintained under a reduced pressure of about (Pa), that is, under vacuum, and the atmosphere in the furnace is more oxygen (O) than in the low vacuum heat treatment step 70. ₂ ) Is a low oxygen partial pressure state. Accordingly, as in the case of the low vacuum heat treatment step 70, silicon is oxidized and gasified and further removed from the substrate 56, whereby the silicon removal layer 38 is deepened.
[0040]
At this time, since the degree of vacuum is relatively high in this step, there is no excess oxygen in the vacuum furnace 58, so that the phenomenon that the generated nanotube 46 is oxidized and depleted from the tip hardly occurs. Therefore, as the silicon removal layer 38 becomes deeper and the nanotube 46 becomes longer, the gas flow between the tip portion (original substrate surface 54) of the nanotube 46 and the surface 40 of the carbide portion 36 is hindered. It becomes difficult to grow the nanotubes 46 that require gas distribution. As a result, the carbon layer 42 in which carbon is continuous in a direction along the surface 40 is generated at a certain depth or more in the silicon carbide removal layer 38, and the nanotube is formed on the surface 40 of the carbide portion 36 via the carbon layer 42. 46 will be formed. FIG. 8B shows a cross section of the main part corresponding to FIG. 2B in the vicinity of the substrate surface at this stage.
[0041]
FIG. 9 is a model diagram for explaining the formation process of the nanotube 46 by the vacuum heat treatment. The (0001) plane of α-type silicon carbide and the (111) plane of β-type silicon carbide are crystal planes in which layers of carbon 50 and silicon 60 are alternately stacked. When 60 is removed, the carbon 50 tends to form a tube shape. That is, when silicon atoms 60 of silicon carbide are selectively oxidized by oxygen 66 in the furnace to escape as silicon monoxide 64, the remaining carbon 50 is rearranged at a high temperature, whereby the substrate 56 has A molecular structure of only carbon 50 is formed in order from the surface 54 (indicated by phantom lines). The molecule thus formed is graphite having a six-membered ring structure in which the carbon atoms 50 are connected in a network as described above, but when the silicon atom 60 is removed from the crystal plane, the six-membered ring is formed. It is considered that the structure grows epitaxially along the moving direction of the silicon monoxide 64 and the growth direction is determined according to the crystal plane of the substrate surface 54. Therefore, when the silicon removal layer 38 is deepened as the heat treatment proceeds, a cylindrical graphite sheet is formed so as to extend in the thickness direction of the substrate 56, that is, the traveling direction of the silicon removal layer 38 in the crystal orientation as described above. As shown in the drawing, the crystal structure of silicon carbide is inherited to a certain extent, and the nanotubes 46 are arranged in a direction that is closely aligned with the carbide portion 36 at the atomic level and oriented in a direction substantially perpendicular to the substrate surface 54, that is, the emitter surface 48. Is estimated to be obtained.
[0042]
However, if excessive oxygen 66 exists in the furnace, a part of the carbon 50 connected in a net form is oxidized and escapes as carbon monoxide or carbon dioxide 68. When the carbon 50 comes out, the carbon 50 is rearranged again to form a network structure, so that the nanotube 46 is depleted while maintaining the structure. Therefore, the growth rate of the nanotube 46 is determined by the difference between the rate at which the silicon atoms 60 are removed and the rate at which the carbon atoms 50 are removed. Accordingly, in the low vacuum heat treatment step 70, the oxygen partial pressure in the furnace is high, and thus the removal rate of the carbon atoms 50 is high, so that the nanotube 46 is depleted. In the high vacuum heat treatment step 72, the oxygen partial pressure is low. Since the removal rate of the carbon atoms 50 is remarkably reduced, the growth rate of the nanotubes 46 is increased, so that the carbon layer 42 is formed.
[0043]
In the process of forming the silicon removal layer 38 and the nanotube 46 as described above, in this embodiment, first, in the low vacuum heat treatment step 70, a sufficiently high heating temperature of about 1700 (° C.) and 6 (Pa). Since the heating time is set to a long time of about 6 hours under conditions where the oxygen partial pressure is relatively high, the nanotube 46 is grown while the carbon atoms 50 are removed at a relatively high rate. The depth of the silicon removal layer 38 is, for example, about 600 (nm). In the subsequent high-vacuum heat treatment step 72, a sufficiently high heating temperature of about 1700 (° C.) and 10 ^-2 Since the heating time is set to an extremely long time of about 10 hours under a condition where the pressure and the oxygen partial pressure are relatively low, the depth of the silicon removal layer 38 is, for example, about 1.0 (μm). It also becomes. The deeper the silicon removal layer 38 is, the more the gas flow between the surface 54 and the inside, that is, the surface 40 of the carbide portion 36 is hindered. Therefore, in the depth position of the silicon removal layer 38 at a certain depth or more, at the depth position of 700 (nm) or more under the above conditions, the nanotubes 46 that require gas flow are hardly generated, and the direction along the surface 54 It is considered that the carbon layer 42 composed of graphite, amorphous carbon, or the like that is continuous with each other is generated in a state where both the nanotube 46 and the carbide portion 36 are continuous at the atomic level.
[0044]
That is, by heating in an atmosphere having a low oxygen partial pressure, silicon is selectively removed from the substrate surface 54, so that a silicon removal layer 38 made of only carbon is formed on the surface layer portion. A plurality of nanotubes 46 extending from the substrate surface 54 toward the anode 20 are formed in the silicon removal layer 38 at a high density. At this time, in both the low-vacuum heat treatment step 70 and the high-vacuum heat treatment step 72, the silicon removal layer 38 in the surface layer portion is gradually thickened by being heated for a long time of 1 hour or more. The nanotubes 46 formed on the surface layer of the silicon removal layer 38 are heated at about 1700 (° C.) in a relatively high oxygen partial pressure atmosphere of about 6 (Pa) in the low vacuum heat treatment step 70. Therefore, the tip is oxidized from the tip at a rate slower than the generation rate of the silicon removal layer 38 and the tip is sparsely distributed on the substrate surface 54. On the other hand, in the high vacuum heat treatment step 72, the substrate is 10%. ^-2 Since it is heated at a temperature of 1700 (° C.) in an atmosphere with a relatively low oxygen partial pressure of about (Pa), the upper layer portion of the silicon removal layer 38 is maintained in the nanotube structure, but the lower layer portion is along the surface. In the direction, graphite, amorphous carbon, and the like are continuous, and the conductive carbon layer 42 is continuous with the nanotube at the atomic level. As described above, since the nanotube 46 becomes sparser compared to the conventional case where only heat treatment in high vacuum is performed, the emission start voltage is lowered as compared with the conventional case where the emitter is composed of a substantially film-like conductor. Be made. Also substrate 56 The nanotubes 46 located in the inner peripheral portion of the substrate 46 are connected to the peripheral portion of the substrate through the carbon layer 42 continuous at the atomic level, so that uniform electron emission efficiency can be obtained over the entire surface.
[0045]
The heating time in the low vacuum heat treatment step 70 and the high vacuum heat treatment step 72 may be one hour or longer, and there is no particular upper limit. As the heating time increases, the amount of wear of the nanotubes 46 increases. At the same time, the silicon removal layer 38 also becomes deeper, and the structure in which the nanotubes 46 are provided on the carbon layer 42 is maintained. Therefore, although there is an upper limit to the heating time in which the improvement of characteristics is recognized, there is no particular inconvenience except that the production efficiency is lowered even if the heating time is longer than that. Further, in FIG. 9, the end face of the cylindrical graphite layer 52 is drawn at the tip of the nanotube 46 except for the center, but actually, as shown in FIG. Is closed like a dome by introducing a five-membered or seven-membered ring.
[0046]
Returning to FIG. 6, in the oxidation heat treatment step 74, after the nanotubes 46 are formed on the substrate surface 54 as described above, the substrate 56 is heat treated in the heating furnace 62. The heat treatment conditions are, for example, a temperature of 600 (° C.) and a processing time of about 10 minutes in an air atmosphere (oxidizing atmosphere). FIG. 7 (c) shows an execution state of the oxidation heat treatment. In the substrate 56 that has been subjected to the oxidation heat treatment, a portion constituted by a five-membered ring or the like having a bonding force smaller than that of the six-membered ring at the tip of the nanotube 46 is broken, and the tip is separated from that portion. As a result, the tip of the nanotube 46 is opened as shown in FIG. 2 (b), FIG. 4 and the like, so that the emitter 28 having high and uniform electron emission efficiency can be obtained.
[0047]
Here, experimental results obtained by changing various conditions of the low vacuum heat treatment step 70 and the high vacuum heat treatment step 72 in the manufacturing process of the emitter 28 will be described. As a starting material of the emitter 28, a substrate 56 having a size of about 4 to 5 (mm) × 1 (mm) × thickness 0.3 (mm) made of α-silicon carbide whose (0001) plane appears on the surface 54 is used. Used in the vacuum furnace 58, the heating temperature is set in the range of 1500 to 1800 (° C), the pressure is set in the range of 6 (Pa), and the heating time is set in the range of 0.5 to 10.0 hours. Was given. For the sample in which the nanotubes 46 were generated on the surface 48 by the vacuum heat treatment, the distribution state of the tips of the nanotubes 46 and the surface resistance (sheet resistance value) of the generation surface were evaluated. Evaluation of the distribution state of the tip portion was performed by bonding the generation surfaces of the nanotubes 46 to each other and observing the overlapping state. The presence of overlap means that the tip is sparsely distributed. The results are shown in Table 1 below. The surface resistance was determined by measuring the resistance value between the electrodes by lightly pressing the electrodes against both ends in the longitudinal direction of the sample. In the sample heated at a temperature exceeding 1800 (° C.), the silicon removal layer 38 has a portion composed of the carbon layer 42 made of graphite and amorphous carbon, and the overlap of the nanotubes 46 could not be confirmed. The surface resistance is not measured.
[0048]

[0049]
Although not shown in Table 1 above, 10 ^-2 Under a vacuum of about (Pa), since the residual oxygen in the furnace is extremely small, the produced nanotube 46 is hardly oxidized, so that the tip of the nanotube 46 is not sparse. On the other hand, at a low vacuum level of about 6 (Pa), the nanotube 46 was sparse under conditions exceeding 1600 (° C.), that is, 1700 (° C.) or 1800 (° C.).
[0050]
Next, among the samples in which the tips of the nanotubes 46 were recognized by the above low vacuum heat treatment, those heated at 1700 (° C.) for 6 hours were obtained. ^-2 Under the high vacuum of (Pa), the heating temperature was varied in the range of 1500-1800 (° C.) and the heating time was varied in the range of 0.5-10.0 hours, and the surface resistance was evaluated in the same manner as in Table 1. The results will be explained.
In Table 2 below, when heated at 1500 (° C.) for 10 hours, there was no change from that heated at 6 hours, so when heated at 1800 (° C.) for 10 hours, the silicon removal layer 38 of Since the whole was composed of the carbon layer 42 and the nanotube 46 was not recognized, none of the surface resistance was measured.
[0051]

[0052]
As shown in Table 2 above, if the heat treatment in high vacuum is performed again in a high vacuum, the heating temperature in the high vacuum is 1600 (° C) or more and the heating time is 2 hours or more. An emitter 28 having a sufficiently low resistance can be obtained. In addition, the surface resistance tends to decrease as the heating time becomes longer, and heating for about 0.5 hours is insufficient, but if heated for about 1 hour or more, 300 (Ω / □) is preferable for use as an electron source. High conductivity of less than about can be obtained. Note that, as described above, the surface of the sample whose resistance value was reduced by the high vacuum heat treatment was observed, but it was confirmed that the distribution state of the sparse nanotubes 46 after the low vacuum heat treatment was maintained.
[0053]
Incidentally, in the FED 10 including the emitter 28 using the nanotube 46 as an electron emission source, it is desired that the size of one pixel is sufficiently increased and can be driven at a low voltage without causing uneven luminance. For example, when one pixel has a size of about 2 (mm) × 6 (mm), in order to make the electron emission efficiency in the inner peripheral portion the same as that in the peripheral portion so that luminance unevenness does not occur, for example, 300 Conductivity below about (Ω / □) is required. However, the required conductivity differs depending on the size of the emitter 28, and the surface resistance of the emitter 28 is preferably as high as possible with a size of about 0.8 (mm) × 4 (mm). The emitter 28 having an intermediate size is required to have appropriate conductivity of about 300 (Ω / □) or more depending on the size. That is, the above-mentioned value of “about 300 (Ω / □) or less” preferable for the electron source is a value based on the assumption of the emitter 28 having the above size.
[0054]
As mentioned above, although one Example of this invention was described in detail with reference to drawings, this invention can be implemented also in another aspect.
[0055]
For example, in the embodiment, the case where the present invention is applied to the FED 10 has been described. However, the present invention desirably increases the density of emission sites and the uniformity of the electron emission efficiency and lowers the emission start voltage. If applicable, the present invention can be similarly applied to various field electron emission devices such as a flat lamp, a cathode ray tube and an electron gun. In these applications, necessary conductivity and heat treatment conditions are appropriately selected according to the size of the emitter used.
[0056]
Further, in the embodiment, the case where the emitters 28 in which the nanotubes 46 are densely arranged with high orientation is manufactured by heat-treating the substrate 56 made of silicon carbide in a vacuum is described. Other materials such as boron carbide may be used as long as they are covalently bonded carbides from which nonmetallic elements are removed.
[0057]
In the embodiment, the thickness dimension of the carbon layer 42 constituting the emitter 28 is about several hundreds (nm) to several (μm), and the length dimension of the nanotube 46 is about several tens to several hundreds (nm). Although the case has been described, the thickness dimension and the length dimension can be appropriately changed according to the purpose of use and process management.
[0058]
Further, in the embodiment, after the nanotube 46 is formed, the tip is opened by further performing an oxidation heat treatment in the presence of oxygen. However, the tip opening treatment is not necessarily performed. However, since the substantial curvature radius of the emitter 28 is drastically reduced by opening the tip as described above, the emission site is also drastically increased, and the efficiency of the emitter 28 is further enhanced. It is preferable to open The heat treatment conditions are not limited to those shown in the examples, the temperature is appropriately set in the range of about 500 to 750 (° C.), and the treatment time is also in the range of, for example, about 1 to 20 minutes depending on the treatment temperature. It is changed appropriately.
[0059]
In the embodiment, the emitter 28 is fixed to the cathode 26 with a conductive adhesive. However, when the cathode 26 is composed of the thick printed conductor as described above, the sintering process is performed. At the same time, the emitter 28 may be fixed.
[0060]
In the embodiment, the low-vacuum heat treatment step 70 is performed prior to the high-vacuum heat treatment step 72. However, the low-vacuum treatment that can make the nanotubes 46 sparse and the high-vacuum treatment that reduces conductivity are performed. If implemented, these orders can be reversed.
[0061]
In addition, although not illustrated one by one, the present invention can be variously modified without departing from the gist thereof.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a configuration of an FED according to an embodiment of the present invention.
2A is a diagram for explaining a cross-sectional structure of an emitter provided in the FED of FIG. 1, and FIG. 2B is an enlarged view of a portion indicated by a one-dot chain line b in FIG.
3 is a view showing a state in which nanotubes are observed from the surface side of the emitter of FIG. 2; FIG.
4 is a molecular model diagram illustrating a configuration of a tip portion of a nanotube provided in the emitter of FIG. 2. FIG.
FIG. 5 is a diagram illustrating the characteristics of the emitter of FIG. 2 in comparison with a conventional emitter.
6 is a process diagram illustrating a main part of the method for manufacturing the emitter of FIG. 2; FIG.
FIGS. 7A to 7C are diagrams illustrating a main part of the manufacturing process of the emitter of FIG.
8A is a diagram for explaining a cross-section of the main part of the substrate corresponding to FIG. 2B after the low vacuum heat treatment step of FIG. 6 and FIG. 8B after the high vacuum heat treatment step of FIG. 6; It is.
FIG. 9 is a molecular model diagram for explaining the nanotube generating action in the manufacturing process of FIG. 4;
[Explanation of symbols]
10: FED (field electron emission device)
28: Emitter
70: Low vacuum heat treatment process
72: High vacuum heat treatment process

Claims (2)

A method of manufacturing a field electron emission device of a type in which electrons are emitted from an emitter by applying a voltage between an emitter and an anode disposed opposite to each other in an airtight space,
By heating the substrate made of covalently bonded carbide under a vacuum in the range of 0.1 to 10 (Pa) at a temperature in the range of 1650 to 1800 (° C.) for 1 hour or more , the covalently bonded carbide on the surface layer of the substrate can be obtained. A low-vacuum heat treatment step in which a plurality of nanotubes are produced by oxidation and the tip of the nanotubes is oxidized ;
Heating temperature in 1 hour or more in the range of the substrate 10 ^-4 to 0.1 (Pa) 1550 to the oxygen partial pressure is lower vacuum than the low vacuum heat treatment step is in the range of 1800 (° C.) And a high-vacuum heat treatment step in which only the covalently bonded carbide on the substrate is oxidized .   The method of manufacturing a field electron emission device according to claim 1, wherein the low vacuum heat treatment step is performed prior to the high vacuum heat treatment step.

Images