JP2793702B2 - Field emission cathode - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a field emission cathode. INDUSTRIAL APPLICABILITY The present invention is useful as a cathode of a fluorescent display device used for an image / video display device or a light source, or as a cathode of a micro vacuum tube or the like.

[Conventional technology]

Conventionally, as a field emission cathode, one having a configuration shown in FIG. 4 is known. As shown in FIG. 1, an insulating layer 3 made of SiO ₂ or the like having a thickness of about 1 μm is formed on an upper surface of a cathode substrate 1 made of a semiconductor such as Si. A large number of cavities 3a are formed in the insulating layer 3, and conical emitters 2 are formed on the cathode substrate 1 in the cavities 3a. The emitter 2 is made of Mo, Ni, or the like. A gate electrode 4 is formed on the upper surface of the insulating layer 3 so as to surround the emitter 2. The gate electrode 4
Like the emitter 2, it is made of Mo, Ni or the like.

By biasing the gate electrode 4 with respect to the cathode substrate 1 in the range of several tens of volts to several hundred volts, 1 × 10 ⁶ to 1
An electric field of about × 10 ⁷ V / cm is generated to obtain electron emission from the tip of the emitter 2.

When this field emission cathode is used, for example, as a cathode of a fluorescent display device, the emitter is placed in an area of about 25 mm square.
With a configuration in which about 0 to 10,000 pieces are integrated, electron emission of several hundred mA can be obtained in total. This field emission type cathode consumes less power than a hot cathode conventionally used in a fluorescent display tube, can drive the cathode itself in a matrix, and forms a planar cathode over a wide area. It is possible.

Incidentally, it is known that the emitter current density strongly depends on the electric field intensity. Since the electric field strength changes greatly depending on the radius of curvature of the tip of the emitter, it can be said that the emitter current density depends on the radius of curvature of the tip of the emitter. That is, the sharper the tip of the emitter, the greater the current density will be.

On the other hand, the emission current is considered to decrease as the radius of curvature at the tip of the emitter decreases, but in fact, the rate of increase in the emitter current density is greater than the effect of the decrease in the radius of curvature, so The emission current will increase even if the radius of curvature becomes smaller.

Another factor affecting the emission current is the work function of the emitter. That is, when the work function of the emitter decreases, the emission current increases if the anode voltage is the same.

In addition, when the emitter is a semiconductor, the emission current from the conduction band and the emission current from the valence band must be calculated separately, but the current from the valence band is dominant. Therefore, if the energy level of the valence band is replaced with the work function of metal, the emission current can be approximated.

[Problems to be solved by the invention]

Meanwhile, the conventional field emission cathode shown in FIG. 4 is one in which an emitter electrode, an insulating layer, and a gate electrode are formed on a cathode substrate by making full use of semiconductor manufacturing technology. Therefore, there is a problem that the manufacturing apparatus and the manufacturing method are very complicated. Also, when forming the emitter electrode, the smaller the radius of curvature of the tip portion and the sharper the tip, the more the emission current can be taken out. However, it is extremely difficult to sharpen the tip with the conventional technology. In addition, since a high electric field is applied to the emitter electrode during operation, the tip portion gradually decomposes and evaporates. Since the emitter electrode has a conical shape rather than a needle shape, the tip of the emitter electrode gradually loses its sharpness. Therefore, there is a problem that the emission current cannot be stably obtained for a long time.

The present invention has been made in view of the above-described problems, and has as its object to provide a field emission cathode having an extremely simple configuration and easy manufacture.

[Means for solving the problem]

The field emission cathode according to the present invention is a field emission cathode having an emitter electrode provided on a cathode substrate and a gate electrode provided above the emitter electrode, wherein the emitter electrode is a multiaxial needle-like crystal. And a whisker having a portion.

Further, according to the present invention, the surface of the emitter may be coated with a metal material, or the emitter may be formed of zinc oxide whiskers.

[Action]

In the whiskers, the diameter of the needle-like crystal part is several μm or less, and the radius of curvature of the tip part is several hundred to several thousand degrees. Therefore, when whiskers are used for the emitter electrode of the field emission cathode, an extremely sharp emitter electrode at the tip can be obtained. Further, by covering the emitter electrode with a metal having a low work function as needed, a larger emission current can be obtained than in the case where only the emitter electrode is used.

〔Example〕

 Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

The emitter electrode of this embodiment is composed of whiskers made of ZnO having a structure in which needle-like crystal parts extend in four axis directions. This kind of tetrapot-like ZnO whisker,
Needle crystal part length is 10μm ~ 150μm, wire diameter is 0.5 in core part
μm to 5 μm. The radius of curvature at the tip of the needle-like crystal part is about 500 to 3,000 (0.05 μm to 0.3 μm). In particular, in the case of a needle-shaped crystal part whose length from the base to the tip is 50 μm or less, the radius of curvature of the tip is 500Å to 1.0.
It has an extremely sharp shape of 00 ° (0.05 μm to 0.1 μm).

Next, a field emission cathode using the above-described ZnO whiskers will be described.

 First, the first manufacturing method will be described with reference to FIG.

Graphite is deposited on a glass substrate 1 serving as a cathode substrate by using a screen printing method or the like and fired to form a graphite electrode 2. Then, tetrapot-shaped ZnO whisker powder is
It is dispersed in a solution such as PdCl ₂ which is a plating auxiliary liquid, and whisker powder is applied by a wet sedimentation method. Then, after drying, a metal material such as Ni having a low work function is coated on the surface of the ZnO whisker by electroless plating with a thickness of several tens to several tens of millimeters, thereby being fixed on the graphite electrode 2 to form the emitter electrode 3. . The work function of ZnO is 4.2 eV to 4.6 eV
And the energy level of the valence band is about 7 eV. Z
Since nO is a semiconductor, when calculating the emission current,
We must replace the valence band energy level with the work function of metal. On the other hand, the work function of Ni is
The work function of 4.16 eV and Mo is 4.15 eV, which is lower than the energy level of the valence band of ZnO. By coating the surface with a metal material such as Ni, more emission current can be obtained.

The emission electrode 3 thus formed is provided with Zn
A gate electrode 4 made of a metal plate having openings in a mesh shape, for example, as shown in FIG. 1, is provided via a spacer 5 at a distance of about several μm to several hundred μm from the tip of the O whisker. Is configured.

Here, the cathode substrate 1 having the field emission cathode 6 having the above-described configuration, a face plate disposed to face the cathode, and a side plate surrounding the periphery thereof are sealed and fixed to form an interior. Exhaust to form a box-shaped hermetic envelope. Here, if a display unit including an anode conductor and a phosphor layer is provided on the inner surface of the face plate of the hermetic envelope, a display device that performs luminescent display by the principle of a fluorescent display tube is configured. That is, in the field emission cathode 6, electron emission is obtained from the emitter electrode 3 by applying a voltage of several tens of volts to several hundreds of volts between the gate electrode 4 and the emitter electrode 3. When a high voltage is applied and the emitted electrons strike the phosphor layer, a light-emitting display can be obtained by excitation of the phosphor.

Next, a field emission cathode 21 of another embodiment and a method of manufacturing the same will be described with reference to FIGS. 2 (a), 2 (b) and 2 (c).

As shown in FIG. 2 (a), an insulating member having a large number of openings such as honeycomb ceramics or a partition member 10 such as a metal material having a mesh-shaped opening is connected to an insulating material such as a glass plate. It is arranged on a cathode substrate 11 made of, and substantially multiple concave portions are formed on the substrate 11. Then, the concave portion is filled with a dispersion of ZnO whiskers 13 in a solution of PdCl ₂ or the like by a wet sedimentation method, and pressed by a pressing plate 12 from above. Thereby, ZnO is formed in the concave portion of the partition member 10.
The whiskers 13 can be uniformly filled and their heights can be made uniform.

Thereafter, the emitter electrode 14 is dried in an oven or the like, and coated with a metal material having a low work function, such as Ni, as shown in FIG.

Further, as shown in FIG. 2C, a gate electrode 15 made of a metal plate having a mesh-shaped opening is placed at a position separated from the emitter electrode 14 by several μm to several hundred μm via an insulating spacer 16. Provided. In the figure, reference numeral 17 denotes a face plate opposed to the cathode substrate 11, and the inner surface thereof has a translucent anode conductor 18 and a phosphor 19.
And a display device having a box-shaped hermetic envelope as in the first manufacturing method described above.

In the present embodiment, if the present manufacturing method using the partition member 10 is used, even if whisker powders having a slight variation in shape are used, the upper surfaces of the emitter electrodes 14 can be aligned in the same plane to make the height uniform. Can be. Therefore, the gate electrode 15
Can be made smaller than in the case of the first method.

Next, a field emission cathode 37 particularly suitable for a cathode of an image display device will be described with reference to FIG.

First, a cathode electrode 31 made of a thick film electrode (Ag, graphite) using a screen printing method is provided in a stripe shape on a glass substrate 30 as a cathode substrate. An insulating layer 33 is formed on the upper surfaces of the glass substrate 30 and the cathode electrode 31 so as to have slit-shaped or dot-shaped openings 32 along the cathode electrode 31. After that, the opening 32 is filled with ZnO whiskers 34 by the above-described method, and after drying, the ZnO whiskers 34 are selectively coated with a metal material by electroplating or the like so as not to short-circuit the cathode electrodes, and the emitter electrode 35
And Further, a gate electrode 36 having a mesh-like or slit-like opening above the insulating layer 33 and intersecting with the emitter electrode 35 is arranged in a stripe shape crossing the cathode electrode 31. With such a configuration,
Pixel selection is possible only with the field emission cathode 37.

If the anode conductor is formed in a stripe shape and forms a matrix with the cathode electrode 31, the gate electrode may be a single electrode of a common potential instead of the stripe shape.

In the embodiment described above, the cathode electrode constituting a part of the emitter electrode is formed of a thick film of Ag or graphite so that the contact area with the ZnO whisker is increased.
A conductive thin film of Al or the like is practically sufficient.

In the above embodiment, PdCl ₂ is used to facilitate Ni plating, but Pd is also adhered to the ZnO whiskers by firing after Ni plating. Pd and Ni are Zn
Oxygen whiskers have the effect of lowering conductivity. The work function of Pd is almost the same as that of Ni.

In the above embodiment, the wet sedimentation method was used to provide ZnO whiskers on the cathode substrate, but other means such as brush coating, screen printing, and spraying can be used. Therefore, the method of depositing ZnO whiskers and the formation of the emitter electrode by these means will be described with reference to the following examples.

First, a binder such as ethyl cellulose or a vehicle such as butyl carbitol or terpineol is added to a ZnO whisker to adjust the viscosity, and this is applied on the cathode electrode of the cathode substrate by a method such as brush painting as described above. afterwards,
For example, baking for 10 minutes at 400 ° C ~ 500 ° C in the atmosphere, Zn
O whiskers are deposited on the cathode electrode to form an emitter electrode. Thereafter, the ZnO whiskers may be further coated with a metal material.

Another method for applying ZnO whiskers will be described. The viscosity is adjusted by adding the above-mentioned binder or vehicle to the powder in which PdCl ₂ is adsorbed on ZnO whiskers. This is applied on the cathode electrode of the cathode substrate by a method such as brush painting described above. Thereafter, this is fired under the above-described conditions to form an emitter electrode with Pd remaining on the ZnO whiskers.

In order to produce a powder in which PdCl ₂ is adsorbed on the above-described ZnO whiskers, first, ZnO whiskers are put into a PdCl ₂ solution and stirred. And then, precipitate ZnO whiskers,
The supernatant may be discarded and dried.

Also, after adjusting the viscosity of the powder having PdCl ₂ adsorbed on ZnO whiskers, applying it to the cathode electrode and drying it,
Electroless plating of Ni may be performed. Then, firing is performed to obtain an emitter electrode.

Further, a few drops of Ni plating solution are applied to the powder having PdCl ₂ adsorbed on ZnO whiskers and dried to form a Ni-coated powder. This is adjusted viscosity with the binder or vehicle,
The coating is performed on the cathode electrode of the cathode substrate by a method such as brush coating described above. Then, this is fired under the conditions described above to obtain an emitter electrode.

According to the display device using the field emission cathode of each of the embodiments described above, the gate electrode is provided at a position about 200 μm away from the emitter electrode, and a drawing voltage of about 200 V is applied to the gate electrode, and the display is performed. By applying a slightly higher voltage to the anode conductor of the portion, the phosphor layer of the display portion could be excited to emit light.

〔The invention's effect〕

According to the present invention, a whisker having a multiaxial needle-like crystal part, such as a tetrapot-type ZnO whisker, is used as an emitter electrode, so that an extremely sharp emitter electrode at the tip can be obtained. Therefore, the electron emission start voltage can be reduced, and more emission current can be extracted from the emitter electrode. Further, since the emitter electrode has a multiaxial needle-like crystal part, the tip part can be easily directed upward (toward the gate electrode).

Further, by coating the whisker surface with a metal having a low work function as required, the electron emission start voltage can be further reduced as compared with the case where only the emitter electrode is used, and more current can be taken out.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention, FIGS. 2 (a), 2 (b) and 2 (c) are sectional views showing another embodiment of the present invention, and FIG. FIG. 2 is a perspective view showing another embodiment of the present invention particularly configured as a cathode of an image display device, and FIG. 4 is a cross-sectional view showing the structure of a conventional general field emission cathode. 1,30: Glass substrate as cathode substrate, 11: Cathode substrate, 3,14,35 ... Emitter electrode, 4,15,36 ... Gate electrode, 6,21,37 ... Field emission cathode, 13,34 ... ZnO whiskers.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-49-122269 (JP, A) JP-B-44-29606 (JP, B1) JUN-57-58681 (JP, Y2) 500585 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) H01J 1/30, 9/02

Claims (3)

(57) [Claims] An emitter electrode provided on a cathode substrate;
A field emission cathode having a gate electrode provided above the emitter electrode, wherein the emitter electrode is constituted by a whisker having a multiaxial needle-like crystal part. 2. A field emission cathode according to claim 1, wherein the surface of said emitter electrode is coated with a metal material. 3. A field emission cathode according to claim 1, wherein said emitter electrode is formed of zinc oxide whiskers.