JPH08222122A - Field emission type cathode - Google Patents

Abstract

PURPOSE: To easily manufacture a field emission type cathode in the same manufacturing process as a semiconductor integrated circuit by forming a sandwich structure pinching a diamond layer with a pair of electrodes, and limiting the injection of electrons to the vicinity of an aperture. CONSTITUTION: The surface of a Mo substrate 10 is cleaned, and it is heated at 1500 deg.C in the hydrocarbon atmosphere to form a molybdenum carbide layer 11. An electric insulating layer 12 of SiO2 is formed by sputtering, and a circular portion is removed by etching. A polycrystalline diamond layer 13 is formed by the plasma CVD method, oxygen plasma etching is applied to the center section with a mask having a circular aperture to form an aperture, then a Mo electron implanting electrode 14 is formed on the layer 13 by sputtering. An insulating layer of Al2 O3 and a Mo extracting electrode layer 16 are formed in sequence, and finally it is combined with a fluorescent screen 17 serving as an anode to form a display device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a field emission type cathode used in a thin display device and the like, and a method for manufacturing the same, and more particularly to a field emission type cathode having high performance and long life. It is a thing.

[0002]

2. Description of the Related Art A cathode ray tube generally used in a conventional display device has a structure in which an electron beam emitted from an electron gun is deflected by using an electromagnetic lens to irradiate a desired portion on a fluorescent screen to emit light. Therefore, there is a drawback that a space for deflection is required and the device cannot be made thin. In order to overcome this drawback, a large number of field emission cathodes associated with pixels are arranged on a plane facing the phosphor screen, and electron emission from each field emission cathode is selectively performed to cause fluorescence. A thin display device has been developed which is configured to emit light at a desired location on the surface.

The field emission type cathode used in the thin display device is roughly classified into a tip emitter type as shown in FIG. 4 and a ring emitter type as shown in FIG. In the chip-emitter type cathode shown in FIG. 4, a cathode (emitter) 31 having a sharp tip portion is arranged on a metal substrate 30 which also serves as a negative voltage feeding path, and a lead formed on the cathode 31 and an insulating layer 34. A voltage is applied between the electrode 32 and the electron, which is emitted from the tip portion of the cathode to a strong electric field to the outside, and while flying, the electron flies while being accelerated by the phosphor screen 33 that also serves as the anode and collides there.

In the ring emitter type cathode shown in FIG.
A cathode (emitter) 41 having a substantially circular inner peripheral surface is arranged on an insulating layer 44 formed on the insulating layer 44, and a voltage is applied between the cathode 41 and the extraction electrode 42 formed on the insulating layer 45. Then, the electrons, which are emitted from the inner peripheral surface of the cathode 41 to the outside by a strong electric field, fly while colliding with the fluorescent surface 43 also serving as the anode, and collide there.

The density Jo of the current radiated from the field emission cathode is given by the following equation. Jo = 1.54 × 10 ⁻⁶ (F ² / φ) exp [−6.83 × 10 ⁷ φ ^3/2 / F] A / cm ² where F is the electric field strength (volt / cm) and φ is the work function. The electric field strength F typically reaches 10 ⁷ volt / cm. Therefore, in order to realize as large a current density as possible under a constant applied voltage, it is necessary to select a cathode material having a work function as small as possible. As a cathode material having a small work function, oxides of alkaline earth elements such as BaO and oxides of rare earth elements such as yttria (Y ₂ O ₃ ) are known.

By the way, in this type of field emission cathode,
A small amount of gas molecules remaining between the cathode and the anode collide with an electron traveling at a high speed toward the anode and are ionized to form a large-mass cation. The heavy cations hit the cathode violently while being accelerated along the opposite path of the electrons. To withstand such a big shock,
As the material of the cathode, the oxides as described above are not suitable, and a metal such as tungsten (W) or molybdenum (Mo) that is dense and has high mechanical strength is desirable. However, metals such as W and Mo that are dense and have high mechanical strength have a problem that they have a high melting point and a work function φ of about 3.5 eV.

Recently, diamond has been attracting attention as an ideal cathode material having not only high mechanical strength but also low work function. This diamond exhibits a semiconductor property having a large forbidden band width of about 5.5 eV, and tends to have a high resistance p-type property. The work function φ, which is a measure of the difficulty of thermionic emission, is defined as the energy level difference Ef between the Fermi level and the bottom of the conduction band, and the energy level difference from the bottom of the conduction band to the energy level in vacuum. It is given by the sum (Ef + χ) of electron affinity χ.

The electron affinity of diamond differs depending on its crystal face, and in particular, a negative value (NEF: N
egative Electron Afinity) has been reported by Himpel et al. (1994, TRI SERVICE / NASA CAT
HODE WORKSHIP, CNNFERENCE RECORD). In the case of diamond, Ef is slightly large, but if we consider the negative electron affinity peculiar to the (111) plane, we can expect a very small work function. Further, since diamond is chemically stable, it has an advantage that it is not easily deteriorated even in a dirty atmosphere where the degree of vacuum is poor.

[0009]

As described above, it is expected that diamond will be used as a cathode material, but there are many problems to be solved regarding how to specifically realize this. Has been done. For example, FIG. 4 and FIG.
A structure in which a diamond thin film is attached to the tip portion of the tip type cathode 31 and the inner peripheral surface of the ring type cathode shown in FIG. However, such a structure cannot be realized in a manufacturing process for a fine and large number of cathode groups to which a manufacturing process similar to that of a semiconductor integrated circuit is applied, such as a field emission type cathode of a thin display device. difficult.

Therefore, the object of the present invention is easily realized even in a manufacturing process for a large number of fine cathode groups to which a manufacturing process similar to that of a semiconductor integrated circuit is applied. To realize a mold cathode.

[0011]

A field emission type cathode of the present invention comprises a diamond layer having an opening formed therein and a diamond layer disposed vertically above and below the diamond layer in the vicinity of the opening. A pair of injecting electrodes for injecting electrons into, and an extracting electrode for generating an electric field on the inner peripheral surface of the opening for extracting electrons from the inner peripheral surface of the opening of the diamond layer to the outside.

[0012]

Function: Electrons are injected into the diamond layer from one of the sandwiched electrode pairs sandwiching the diamond layer from above and below. Since the diamond layer tends to have a high resistance p-type, if electrons are injected at a place far away from the opening, the injected electrons recombine with holes and disappear before reaching the opening. However, there is a disadvantage that a large series resistance is inserted. Therefore, electrons are selectively injected to the opening only from the vicinity within the diffusion length.

As described above, by adopting the sandwich structure in which the diamond layer is sandwiched between the electrode pairs and the structure in which the injection of electrons is limited to the vicinity of the opening, various film formations similar to those in the case of the semiconductor integrated circuit are performed. The field emission cathode having the structure of the present invention can be easily manufactured by combining the methods and the photolithography methods. Hereinafter, the present invention will be described in more detail with reference to Examples.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view showing the structure of one cell of a thin display device including a field emission type cathode of the present invention.
Is a molybdenum (Mo) substrate, 11 is a molybdenum carbide layer, 12 and 15 are electrically insulating layers, 13 is a polycrystalline diamond layer, 14 is an electron injection electrode, 16 is an electron extraction electrode, and 17 also serves as an anode. Fluorescent screens, 18 and 19 are DC bias power supplies, and 20 is a signal source.

As described above, the layer 13 of polycrystalline diamond has a wide band gap and functions as a p-type high resistance semiconductor. The layer 11 of molybdenum carbide that is in contact with the layer 13 of polycrystalline diamond functions as a conductor having a higher resistance than that of metallic molybdenum. Therefore, diamond layer 1
The interface between 3 and the layer 11 of molybdenum carbide functions as a Schottky barrier diode. Diamond layer 13
An ohmic contact is formed between the electron injection electrode 14 and the electron injection electrode 14. As a result, the Mo substrate 10 and the molybdenum carbide layer 11 are connected between the Mo substrate 10 and the electron injecting electrode layer 14 also made of Mo by connecting a DC power source 18 having a polarity in which the latter is a positive electrode. Electrons can be injected into the diamond layer 13 through.

The electrons injected into the polycrystalline diamond layer 13 through the molybdenum carbide layer 11 travel as minority carriers in the polycrystalline diamond layer 13 toward the electron injection electrode 14 on the opposite side. This electron injection is
Due to the interposition of the insulating layer 12, it is performed only in the vicinity of the substantially circular inner peripheral portion of the polycrystalline diamond layer 13. A positive voltage supplied from the signal source 20 is applied between the diamond layer 13 and the extraction electrode 16. Therefore, most of the electrons injected into the layer 13 of polycrystalline diamond reach the inner surface of the substantially circular surface, and the (111) plane having the smaller work function among the diamond crystals formed on this inner surface. The field emission from the surface of the diamond crystal having a is followed by a trajectory as shown in the figure to collide with the phosphor screen 17. Here, the outside from which electrons are emitted is generally kept in a vacuum state having a vacuum degree of about 10 ⁻⁶ Pa.

As shown, a layer 1 of polycrystalline diamond.
The inner peripheral surface of 3 has a substantially vertical shape. For this reason,
A corner portion is formed at the upper end portion of the diamond layer 13, and an electric field is concentrated at this tip portion to promote electron emission from the corner portion. By changing the magnitude of the bias voltage supplied from the DC bias power source 18, the density of electrons injected into the polycrystalline diamond layer 13 is changed, and as a result, the amount of electrons to be field-emitted is controlled and displayed. It is also possible to control the brightness of the spot. Further, in this embodiment, the case where the shape of the inner peripheral surface of the diamond layer is vertical is illustrated, but it goes without saying that the same operation is performed even if the shape is another shape, for example, an inverted funnel shape.

A molybdenum carbide layer 11 is formed between the Mo substrate 10 and the polycrystalline diamond layer 13 for the following reason. That is,
If the interface between the substrate 10 made of a refractory metal such as Mo and the layer 13 of polycrystalline diamond is kept at a high temperature for the subsequent processing, the diamond layer 13 is transformed into the substrate 10 made of a refractory metal. Carbon atoms penetrate to form metal carbide at the interface between the two. Due to this carbonization, the composition of the diamond layer 13 may change and the characteristics may deteriorate. In order to prevent the carbon atoms from moving along with the progress of carbonization at the interface as described above, a layer of molybdenum carbide previously saturated with carbon is interposed at the interface between the Mo substrate 10 and the diamond layer 13.

FIG. 2 is a sectional view showing the structure of a field emission type cathode according to another embodiment of the present invention together with a phosphor screen which also serves as an anode. The difference between this embodiment and the embodiment shown in FIG. 1 is that
The points are as follows. First, the molybdenum carbide layer 11 in the embodiment of FIG. 1 was replaced with a low resistance n-type silicon carbide (SiC) layer. Secondly, by narrowing the width of the electrode layer 14 ', the traveling distance of electrons injected from the SiC layer 11' into the diamond layer 13 is shortened.

Except for the above two points, it is the same as the case of the embodiment of FIG. In this example, the SiC layer 11 '
A hetero pn junction is formed at the interface between the diamond diamond layer 13 and the polycrystalline diamond layer 13, and electrons are injected from the SiC layer 11 ′ into the polycrystalline diamond layer 13 through the hetero pn junction. In addition,
The electrode layer 14 'may have a structure in which the width is not narrowed like the embodiment shown in FIG. Further, in the embodiment shown in FIG. 1, the width of the Mo electrode layer 14 may be narrowed.

Next, an example of a method for manufacturing the field emission cathode of the embodiment shown in FIG. 1 will be described with reference to FIG. First, as shown in FIG. 3 (A), the Mo substrate 10 is housed in a reaction furnace, and the surface is cleaned by performing sputter etching using high frequency power of about 500 W in an Ar gas atmosphere. . Then, the Mo substrate 10 is heated to about 1500 ^° C. in an atmosphere of hydrocarbon such as CH ₄ or C ₆ H ₆ . As a result, carbon generated by thermal decomposition of hydrocarbon reacts with Mo on the surface of the substrate 10 to form a molybdenum carbide layer 11 having a thickness of several μm to several μm on the surface of the Mo substrate 10. (FIG. 3 (B)).

Next, an electrically insulating layer 12 having a thickness of several μm and made of Al ₂ O ₃ or SiO ₂ is formed on the molybdenum carbide layer 11 by sputtering, and then a circular shape having a diameter of several μm to several tens of μm. Is removed by etching (FIG. 3C). After that, a polycrystalline diamond layer 13 having a thickness of several μm is formed on the molybdenum carbide layer 11 and the insulating layer 12 by the epitaxial growth method or the plasma CVD method (FIG. 3D). Since the diamond layer 13 is formed on the molybdenum carbide layer 11 already saturated with carbon atoms, new carbon atoms do not enter the molybdenum carbide layer 11 and the Mo substrate 10.

After covering the layer 13 of polycrystalline diamond with a mask film having a circular opening in the center, oxygen plasma etching is performed to form an opening having a substantially circular inner peripheral surface in the layer 13 of polycrystalline diamond. Then, a Mo electron injection electrode 14 is formed on the polycrystalline diamond layer 13 by sputtering (FIG. 3E). The diamond layer 13 is made of polycrystalline and the plasma etching is anisotropic. Due to the property, an opening having a vertical inner peripheral surface is formed, and a crystal plane including the (111) plane is exposed on the inner peripheral surface of this opening.

Then, on the electron injection electrode layer 14, Al
An insulating layer 15 such as ₂ O ₃ and a Mo extraction electrode layer 16 are sequentially formed (FIG. 3 (F)). Finally, as shown in FIG. 1, a display device is formed by combining it with a fluorescent screen 17 that also serves as an anode.

Although the present invention has been described above with reference to only two embodiments, it is obvious that various modifications can be made to these embodiments. For example, the diamond layer and the electrode pair layer may be continuously extended to the adjacent openings as shown in FIG. 1, or may be once separated before the adjacent openings.

Also in the manufacturing method, after the polycrystalline diamond layer 13 is formed, the electron injection electrode layer 14, the insulating layer 15 and the extraction electrode layer 16 are sequentially formed without performing oxygen plasma etching, and subsequently, It is also possible to adopt a method of forming another mask material and sequentially etching the respective layers such as the extraction electrode layer 16, the insulating layer 15, the electron injection electrode layer 14 and the polycrystalline diamond layer 13.

[0027]

As described in detail above, the field emission cathode of the present invention has a sandwich structure in which a diamond layer is sandwiched between electrode pairs from above and below, and the electron injection is limited to the vicinity of the opening. Therefore, the field emission cathode having the structure of the present invention can be easily manufactured by combining various film forming methods and photolithography methods similar to those in the case of the semiconductor integrated circuit.

According to a preferred embodiment of the present invention, the electron injection side of the injection electrode pair is molybdenum carbide or SiC.
Since it is composed of such a metal carbide as described above, there is an advantage that the composition of the diamond layer does not change due to the interfacial carbonization.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the structure of a field emission cathode according to an embodiment of the present invention.

FIG. 2 is a sectional view showing the structure of a field emission cathode according to another embodiment of the present invention.

FIG. 3 is a cross-sectional view for explaining the method of manufacturing the field emission cathode of FIG.

FIG. 4 is a sectional view showing the structure of a conventional chip-type emitter.

FIG. 5 is a sectional view showing the structure of a conventional ring-type emitter.

[Explanation of symbols]

 10 Mo Substrate 11 Molybdenum Carbide Layer 12,15 Electrical Insulation Layer 13 Polycrystalline Diamond Layer 14 Electron Injection Electrode 16 Electron Extraction Electrode 17 Phosphor Screen that Also Works as Anode

Claims (4)

[Claims] 1. A diamond layer in which an opening is formed, an injection electrode pair which is arranged above and below with the diamond layer interposed and injects electrons into the diamond layer in the vicinity of the opening, and the diamond. Field emission cathode for generating an electric field on the inner peripheral surface of the opening from the inner peripheral surface of the opening of the layer for extracting electrons into the vacuum. 2. The electrode according to claim 1, wherein at least the electrode of the injection electrode pair that injects electrons into the diamond layer is formed only near the inner peripheral surface of the opening of the diamond layer. And a field emission electrode. 3. The field emission cathode according to claim 1, wherein at least an electrode of the injection electrode pair for injecting electrons into the diamond layer is made of a metal carbide. 4. The method according to claim 1, wherein at least one electrode of the injection electrode pair has a low resistance n.
A field emission cathode, characterized in that it is made of type SiC.