JPH11273553A - Electron emissive electrode, its manufacture, and cold cathode fluorescent tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep discharge voltage stably low for a long duration in an electron emissive electrode (a cold cathode) to be employed for a cold cathode fluorescent tube. SOLUTION: Hydrogenated compounds of at least one element selected from a group of Sc, Y, La, Ce, Gd, Lu, Th, U, and Np are used as the electrode materials for an electron emissive electrode. The electron emissive electrode comprises a metal substrate 1 containing Ni and an electron emitting layer 2 formed on the metal substrate 1. The electron emitting layer 2 has high sputtering resistance and can emit electrons for a long duration by low electric discharge. The electron emissive electrode manufacture includes a film forming process of forming a metal film of above mentioned elements on the metal substrate 1 and a hydrogenating process of hydrogenating the metal film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron-emitting electrode for generating a discharge by utilizing an electron-emitting phenomenon of an object, and more particularly to an electron-emitting electrode suitable for a discharge device utilizing a cold-cathode emission phenomenon. TECHNICAL FIELD The present invention relates to a method for producing a neutral electrode and a cold cathode fluorescent tube.

[0002]

2. Description of the Related Art In general, thermionic emission, photoelectron emission, cold cathode emission and the like are known as electron emission phenomena in which electrons existing in an object are emitted into space. Electrode-emitting electrode materials are used as electrodes of devices utilizing electric discharge such as discharge lamps.For example, a thermoelectron emission phenomenon in which electrons are emitted by flowing an electric current through a coil-shaped filament and heating it is used. The hot cathode discharge used (ther
mionic emission lamps) are known. On the other hand, a device using various kinds of discharges using electrodes utilizing the cold cathode emission phenomenon is also known, such as a field emitter (FED) using electron emission by a strong electric field.
Also, a cold-cathode discharge tube (cold emission lamp) using a secondary electron emission by ion bombardment, a plasma display device, and the like have been put to practical use. An electron-emitting electrode that emits electrons by such a cold-cathode emission phenomenon is used for a cold-cathode fluorescent tube as a backlight of a non-self-luminous display device such as a liquid crystal, and is used for a copying machine. Plasma display device and VFD as multicolor display device
(Vacuum Fluorescent Display) and the like, and a wide range of applications for cathodes are being continued.

A cold-cathode fluorescent tube or a plasma display device using electrodes utilizing the cold-cathode emission phenomenon includes a container having a phosphor provided on an inner wall thereof and a mixed rare gas and mercury sealed in the container. At first, electrons generated by a photoelectron emission phenomenon by light incident on the cold cathode fluorescent tube move by an electric field applied to the electrodes, and collide with a sealed gas or the like to ionize and generate ions. This ion collides with the electrode and emits secondary electrons, so that the electron emitted from the electron-emitting electrode collides with mercury atoms in the tube to start discharge and generate ultraviolet light, and the ultraviolet light causes a phosphor to be generated. Are excited to emit visible light. As a material of the electron emission electrode, for example, a metal made of an element having a relatively low work function such as nickel (Ni) or molybdenum (Mo) is used. In general, a cold cathode fluorescent tube provided with an electron-emitting electrode made of such a material tends to have a higher luminance (cd / m ² ) as the tube diameter is reduced. It could be made thinner itself and was suitable for a backlight of a liquid crystal display device.

[0004]

However, a cold cathode fluorescent tube has a high lamp discharge voltage, resulting in a large lamp power. Particularly, when the cold cathode fluorescent tube is used as a backlight in a portable display device using a battery. There is a problem that it is difficult to display for a long time. Further, in the above-described metal electrode, the electron-emitting material is sputtered by the discharge, thereby contaminating the tube wall and causing a short emission life. While various materials are being sought for such a problem, the cold cathode uses a tunnel effect that lowers the energy barrier by a strong electric field and emits electrons, so that the thickness of the cold cathode remarkably prevents tunneling. The formed insulator was not included in the study as a cold electron emitting material for the cold cathode.

That is, conventionally, the following properties have been required as the material of the cold cathode, particularly the material of the cold cathode of the cold cathode fluorescent tube. 1. Low work function. That is, electrons can be emitted at a low discharge voltage. 2. It is not easily sputtered and does not stain the wall of the cold cathode fluorescent tube. Further, it hardly reacts with mercury sealed in the cold cathode fluorescent tube. 3. Good electrical conductor. There are few materials that satisfy these three conditions. For example, a low work function Y metal certainly has a low discharge voltage, but when the discharge is stopped, a reaction between Y and mercury occurs.

[0006] Various oxides such as strontium used for the emitter of the hot cathode tube do not react with mercury, but are not good electrical conductors. Even with such a material, a hot cathode tube can be used as a thermionic emission electrode if heated to an appropriate temperature because of its semiconducting property of improving conductivity at high temperatures, but a cold cathode tube has sufficient conductivity even at room temperature level. As required, ordinary oxides have been considered difficult to use.

The present invention has been made in view of the above circumstances, and has been made in view of the above circumstances. An electron-emitting electrode having a low discharge voltage and a stable discharge voltage even when used for a long time, a method for manufacturing the electron-emitting electrode, And a cold cathode fluorescent tube.

[0008]

According to a first aspect of the present invention, there is provided an electron-emitting electrode comprising Sc, Y, La, Ce, Gd, and L.
It has a hydride of at least one element selected from the group consisting of u, Th, U, and Np.

According to the first aspect of the invention, the hydride can stably emit cold electrons at a low voltage for a long period of time. The hydride is, as described in claim 2, RH _2-x (R is Sc, Y, La, Ce, Gd, L
At least one element selected from the group consisting of u, Th, U, and Np, H may be hydrogen, -1 <x <1), and the hydride basically has a crystal structure unique to a substance represented by RH _2. However, for example, RH _2-x includes those deviated from stoichiometry due to the lack or excess of the element represented by R, the H (hydrogen) element, etc. The above conditions required as, that is, low work function, it is difficult to sputter,
It satisfies that it does not easily react with mercury and has good conductivity.

[0010] The discharge voltage of the electron-emitting electrode does not increase even after being used for a long time.
It has a lower discharge voltage and a lower N
The same stability of the discharge voltage as that of the i-electrode can be exhibited.

The element represented by R is a rare earth element (including actinide) Sc (scandium),
Y (yttrium), La (lanthanum), Ce (cerium), Gd (gadolinium), Lu (lutetium), T
h (thorium), U (uranium), Np (nebutunium)
Of these, one element or a plurality of elements, but Y is most suitable in consideration of cost, ease of handling, and the like.

Further, by generating the hydride by hydrogenating the metal film of the R element, an electron-emitting electrode having the hydride can be more easily formed. In this case, Sc, Y, L before hydrogenation
The thickness of at least one element film selected from the group consisting of a, Ce, Gd, Lu, Th, U, and Np is 13,000Å.
(Angstrom).

That is, the thickness of the metal film is set to 13,000 °
When it is less than the above, the following effects can be obtained. When the metal film is hydrogenated, hydrogen element enters the metal film and becomes an electron-emitting electrode of the hydride. And
When the above-mentioned electron-emitting electrode is used for a long time as the cold cathode of a cold-cathode fluorescent tube, for example, as a cold cathode of a cold cathode fluorescent tube, the electron-emitting electrode will be damaged by discharge or the like when used for a long time. It will be released into the fluorescent tube.

When hydrogen is released into the cold cathode fluorescent tube, for example, the hydrogen released in the cold cathode fluorescent tube hinders ionization of mercury and reduces the amount of ultraviolet rays generated by the discharge, thereby reducing the fluorescent color of the fluorescent material. Is relatively reduced, and as a result, the emission color of mercury is strongly recognized, which may cause a problem such as emission of bluish light. When the temperature is increased, the cold cathode fluorescent tube cannot be used. However, by setting the thickness of the metal film to less than 13,000 °, the content of hydrogen contained in the metal film can be regulated, so that hydrogen is released in long-time use. In any case, it is possible to prevent the hydrogen level from becoming such a concentration that the cold cathode fluorescent tube cannot be used. When the metal film is hydrogenated as described later, the element represented by R is R
There is a possibility that hydrogen more than the amount of hydrogen required to become H ₂ may enter the metal film, which not only regulates the thickness of the metal film but also reduces the amount of hydrogen contained in the hydrogenated metal film. It is necessary not to increase the content more than necessary.

The electron-emitting electrode of the present invention is obtained by forming an electron-emitting layer containing a hydride of the above-mentioned R element on a conductive substrate, and the electron-emitting layer is represented by the above-mentioned R. A metal layer made of an element and a hydrogenated layer made of a hydride of the R element formed on the metal layer may be provided. According to the above configuration, the element represented by R, that is,
Except for the possibility that the metal of the element contained in the rare earth element may also react with mercury, it is suitable as a cold cathode and exhibits conductivity as a metal, and the electron emission layer has a metal layer and the metal layer. When the metal layer is provided with a hydrogenation layer formed on the metal layer, the metal layer is covered with a hydrogenation layer that does not react with mercury, so that the metal layer can be prevented from reacting with mercury. Also, the metal layer will act as a conductor connected to the hydrogenation layer.

In forming the electron-emitting layer, for example, after forming a metal film on a conductive substrate, the metal film is hydrogenated, and the amount of hydrogen contained in the metal film at the time of hydrogenation is determined as described above. When the metal film is exposed to hydrogen, the exposed surface side of the metal film is first hydrogenated, part of the base material side of the metal film is not hydrogenated, and a hydrogenated layer is formed on the metal layer. However, even in such a state, it can function as a favorable electron-emitting electrode. Further, a hydride film may be formed as an electron-emitting layer on the base material, or the metal layer and the hydride layer may be sequentially formed on the base material. Since the base material is conductive, for example, a metal base material is formed in a shape suitable for an electrode, for example, a flat plate or a needle, and an electron emission layer made of the hydride is formed on the surface thereof, and the metal base is formed. The electrodes can be manufactured relatively easily by connecting the conductor to the material.

Further, the metal substrate is made of the same material as a metal electrode conventionally used as a cold cathode (for example, a Ni electrode).
Therefore, even if the electron-emitting layer is damaged so that it cannot be used due to long-term use exceeding the durability limit of the electron-emitting layer, the metal substrate itself functions almost in the same manner as a conventional metal electrode. Although the discharge voltage is increased, the electron-emitting electrode does not suddenly stop functioning. For example,
When this electron-emitting electrode is used in a cold cathode fluorescent tube, even if the electron-emitting layer is damaged by a long-time use exceeding the durability limit of the electron-emitting layer, the cold-cathode fluorescent tube suddenly goes out. That is, electrons are emitted from the metal substrate, and the cold cathode fluorescent tube is maintained in a lit state.

The invention according to claim 3 further comprises Sc,
It has an oxide of at least one element selected from the group consisting of Y, La, Ce, Gd, Lu, Th, U, and Np. When the surface of the hydrogenated electrode material is covered with the oxide (oxide layer), the above-mentioned elements are classified into rare earth elements and actinoids, and the oxides of the elements contained in the rare earth elements are Although it has some difficulty in stability, it can reduce the discharge voltage when used as a material for an electron-emitting electrode.

If the thickness of the oxide layer is 2000 mm or less, the discharge voltage can be kept low even if the oxide layer is in contact with the surface layer of the electron emission layer as described above. The same effect as the configuration according to claim 1 can be obtained without hindering the stability of the device. In addition, a metal film of the above element is formed on a base material,
When the metal film is to be hydrogenated in an atmosphere containing hydrogen, for example, an oxygen molecule having an impurity concentration is contained in the atmosphere, or a compound (oxygen-containing substance) containing an oxygen element such as water is contained in the atmosphere. If the metal film is contained even at the impurity concentration, the surface of the metal film may be oxidized.

Further, the present applicants have found that in the presence of hydrogen gas, even if the oxygen element is only slightly present in the atmosphere, the penetration of the oxygen element into the metal film is promoted,
It has been found that the metal film is easily oxidized, and when the metal film is hydrogenated in an atmosphere containing hydrogen, at least the surface portion of the metal film may be oxidized if the oxygen element is present even at an impurity concentration. Is extremely high, but even if an oxide layer is formed on the surface layer of the electron emission layer as described above,
It has been confirmed that it can function as a good electron-emitting electrode.

The method for manufacturing an electron-emitting electrode according to claim 4 of the present invention is characterized in that Sc, Y, La, Ce, Gd, Lu, T
A metal film having at least one element selected from the group consisting of h, U, and Np is hydrogenated in an atmosphere containing hydrogen gas.

According to the above configuration, by forming a metal film made of the above element and then hydrogenating the metal film, it is possible to easily form a thin film containing the above electrode material and serving as an electron emission layer. That is, an electron-emitting electrode having the electron-emitting layer containing the hydride can be easily manufactured.

According to a fifth aspect of the present invention, in the method for manufacturing an electron-emitting electrode, the metal film is formed in an inert gas atmosphere containing 10 ppm or more and 0.5% by volume or less of hydrogen gas in the hydrogenation step. It is characterized in that hydrogenation is performed. According to the above configuration, by setting the hydrogen concentration in the hydrogenation of the metal film to 0.5% by volume or less, the metal film is prevented from containing extra hydrogen, and hydrogen is released from the electron-emitting electrode. This can prevent adverse effects caused by this. Note that when the metal film made of the above element is hydrogenated, if the metal film is brought into contact with high-concentration hydrogen gas, hydrogen more than a hydrogen element necessary for the element represented by R to become RH ₂ As a part of the cold cathode, such a hydrogenated metal film becomes a state included in the film, for example,
When used in a cold cathode fluorescent tube, hydrogen gas is released into the cold cathode fluorescent tube, which hinders the light emission of the cold cathode fluorescent tube as described above.

According to a sixth aspect of the present invention, in the method for producing an electron-emitting electrode, the metal film is heat-treated at a temperature of 200 ° C. or more and 700 ° C. or less in an atmosphere containing a hydrogen gas in the hydrogenation step. Features. According to the above configuration, the metal film is heated to 200 ° C. or more in an atmosphere containing hydrogen gas.
By performing the heat treatment at 700 ° C. or lower, a hydride of R represented by RH _{2- x} can be produced in the metal film represented by R.

That is, when the processing temperature is 200 ° C. or less,
It is difficult to hydrogenate a metal film made of at least one element selected from the group consisting of Sc, Y, La, Ce, Gd, Lu, Th, U, and Np, which is practically sufficient as an electron-emitting electrode. RH _{2- x} cannot be generated. When the processing temperature exceeds 700 ° C., when the atmosphere contains, for example, oxygen element as an impurity in the state of water or oxygen molecules, the oxidation of the metal film of the element selected from the above element group is promoted. This makes hydrogenation of the metal film difficult.

That is, the present inventors have found that when a rare earth element or an actinide metal containing the above-mentioned elements is heat-treated in the presence of hydrogen and oxygen, the penetration of the oxygen element into the metal is promoted, and It has been found that even if the concentration is high, the metal is liable to be oxidized. When the processing temperature exceeds 700 ° C., the possibility that the metal is oxidized due to the presence of oxygen having an impurity concentration is high. Is preferably set to 700 ° C. or lower. Note that 700
Even if the temperature is lower than or equal to lower than ℃, a slight oxide film is formed on the surface of the metal film, but the metal film is also hydrogenated, so that a hydride necessary for practical use can be obtained.

The cold cathode fluorescent tube according to claim 7 of the present invention comprises Sc, Y, La, Ce, Gd, Lu, Th, U, N
An electron-emitting electrode having a hydride of at least one element selected from the group p is provided. By having the hydride, the discharge characteristics of the electron-emitting electrode can be stabilized, and cold electrons can be emitted at a low voltage.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an electron-emitting electrode, a method for manufacturing an electron-emitting electrode, and a cold cathode fluorescent tube using the electron-emitting electrode according to embodiments of the present invention will be described.

In this embodiment, the hydrogenated compound RH _{2- x} (R is Sc, Y,
At least one element selected from the group consisting of La, Ce, Gd, Lu, Th, U, and Np, and H is hydrogen), is shown as an example for yttrium hydride. Therefore, in order to investigate the physical properties of yttrium hydride, a yttrium film (containing a very small amount of hydrogen) substantially consisting only of the yttrium element was formed on a quartz glass substrate.
This yttrium film is formed in an argon (Ar) gas atmosphere containing hydrogen gas in the range of several ppm to 100% by volume (0% Ar when hydrogen gas is 100%). Heating was performed at a temperature in the range of several tens of degrees C to over 700 degrees C to hydrogenate the yttrium film, and an attempt was made to form a yttrium hydride film.

FIG. 1 shows the result of X-ray diffraction of the yttrium hydride film obtained by the above hydrogenation treatment. From the diffraction pattern, the substance formed on the glass substrate can be identified as yttrium hydride in which yttrium atoms take a face-centered cubic arrangement due to the presence of hydrogen atoms.

FIG. 2 is a graph showing the elemental components in the thickness direction of yttrium hydride analyzed by RBS (Rutherford back scattering). Although a thin oxide layer was formed on the surface of this film, as described later, the result that the initial discharge voltage could be slightly lowered without the oxide layer on the surface was obtained. As is apparent from the figure, the molar ratio of hydrogen to yttrium was almost 2: 1, and no other element was confirmed, suggesting that the chemical formula of the obtained yttrium hydride film was YH ₂ . Then, a reflectance measurement test and a transmittance measurement test were performed on the yttrium hydride film formed on the quartz glass substrate thus formed, and the reflectance measurement results are shown in FIG. FIG. 4 shows the measurement results.

From the measurement results of the reflectivity shown in FIG. 3, the reflectivity of the yttrium hydride film rapidly decreased from 0.5 eV to 1.5 eV on the yttrium hydride surface and the glass surface, and had a minimum. And it increases. That is, there is a minimum peak at about 1.5 eV. The reflectivity on the high energy side from the energy of this peak to 5 eV is smaller than the reflectivity at the energy of 0 eV. In the case of ordinary yttrium metal, since the reflectance on the glass surface does not drop rapidly, it is apparent from FIGS. 2 and 3 that yttrium has been hydrogenated up to yttrium in contact with the glass substrate. From the transmittance measurement results shown in FIG.
A bandpass having a peak transmittance is observed around 8 eV. Note that 1 eV corresponds to a wavelength of light of about 1250 nm.

From these optical data, the following can be assumed. Assumption 1. The minimum value of the reflectance is the plasma edge. Assumption 2. 1.8e of the transmittance data
On the lower energy side than V, light is reflected, so that the transmittance is low. On the other hand, on the higher energy side than 1.8 eV, the transmittance is low due to absorption due to interband transition. Then, the carrier concentration calculated from the energy at the plasma edge is about one tenth of that of a normal metal. The resistivity of the yttrium film formed on the quartz glass substrate as described above is 0.09 mΩ / cm
And it was confirmed that the film showed conductivity.

FIGS. 5A and 5B show the expected face-centered cubic lattice type crystal structure of yttrium hydride having the chemical formula of YH ₂ . From the neutron diffraction, as shown in FIG. 5 (a), hydrogen was detected at the center (tetra-coordinate) of the tetrahedron of Y, or as shown in FIG.
As shown in the figure, the center of the octahedron of Y (octa-coordinate) is taken. The yttrium hydride in the present invention may have any of a tetracoordinate structure, an octacoordinate structure, or a structure in which tetracoordinate and octacoordinate are mixed in a structural region.

Originally, only hydrogen at the center (tetracoordinate) of the tetrahedron of Y becomes yttrium hydride. Therefore, a considerable solid solution range (the range of the ratio of hydrogen to Y ). Therefore, the yttrium hydride described herein includes those in which the ratio of the hydrogen element to Y deviates from 1: 2 while the crystal structure of YH ₂ is substantially maintained. YH _2-x (-1 <x <1).

The electrode material is not limited to the hydride of Y among the rare earth elements, but may be other materials such as Sc, La, and C among the rare earth elements (including actinoids).
A hydride of an element selected from the group consisting of e, Gd, Lu, Th, U, and Np can be used. Also, Sc, Y, La, Ce, Gd, Lu, Th, U,
A hydride of a plurality of elements selected from the group of Np may be contained. That is, the electrode material of this example is
RH _2-x (R is Sc, Y, La, Ce, Gd, Lu, T
H is at least one element selected from the group consisting of h, U, and Np, and H is hydrogen, represented by -1 <x <1).

The hydrides of the elements represented by R basically have conductivity like the hydrides of Y, and can be used as electron-emitting electrodes. Further, the electrode material represented by RH _2-x has a crystal structure that can be basically taken by the substance represented by RH ₂ even if the ratio of the hydrogen element to R deviates from 1: 2. Have

Next, an electron emitting electrode made of the above electrode material will be described. Cold electron emission electrode 10 of this example
Is composed of, for example, an electron emission layer 2 formed on a metal base (base) 1 connected to the wiring 3 as shown in FIG. Then, the metal substrate 1 and the wiring 3
Contains, for example, Ni or Ni and Cr.

The metal substrate 1, that is, the substrate on which the electron emission layer 2 is formed has conductivity or semiconductivity, and is composed of a single element or a plurality of elements that are relatively hard to be sputtered. It is made of a kind of mixed material, and in addition to the above-mentioned elements, for example, Mo (molybdenum), aluminum (Al), or the like can be given. The electron emission layer 2 is made of RH _2-x (R is Sc, Y, La, Ce, Gd, L
At least one element selected from the group consisting of u, Th, U, and Np, and H contains hydrogen and an electrode material represented by -1 <x <1). The electron emission layer 2 has the following structure when manufactured by a method for manufacturing an electron emission electrode described later.

Further, a layer of the non-hydrogenated metal containing the R element of the electron emitting layer 2 may be interposed between the electron emitting layer 2 and the metal substrate 1. That is, a non-hydrogenated metal layer can be formed by forming an R element on the metal substrate 1 and leaving the R element without performing the hydrogenation treatment of the R element to the deepest part.

In the electron emission layer 2 formed by hydrogenating the metal film of the element represented by R,
Due to slight differences in hydrogen concentration (hydrogen partial pressure) in the hydrogenation treatment, characteristic variations are likely to occur, and it is particularly preferable to control the thickness of the base R metal film to be thinner, particularly at less than 13000 °, more preferably at 6000 ° or less. A good yttrium hydride film can be easily produced,
When the electrode having the yttrium film is applied to a cold cathode fluorescent tube, by setting the thickness of the metal film to less than 13,000 °, discharge characteristics due to release of hydrogen gas contained in the hydrogenated metal film will be described later. Can be suppressed. Here, the film thickness is the film thickness of the R metal film before being hydrogenated.

The non-hydrogenated metal layer is a metal in the state of a single element or a mixture of plural elements of the above-mentioned R among the rare earth elements, and this metal is basically a conductor having a low work function. As long as it does not react with mercury, it is suitable as a material for an electron-emitting electrode. This non-hydrogenated metal layer may be a compound containing the R element instead of a simple substance as long as it can be easily hydrogenated. Further, since the non-hydrogenated metal layer is covered with the hydrogenated layer, even if mercury is present in the atmosphere where the discharge is performed, the non-metallic metal layer does not directly contact with mercury and does not easily react with mercury.

The electron emission layer 2 is made of the above-mentioned electrode material of this example, and has a low discharge voltage as described later, and shows little increase in the discharge voltage even when used for a long time. Is high. When hydrogenating a metal film made of an element represented by R, a thin oxide film is formed on the surface of the hydrogenated layer due to the presence of a small amount of oxygen or an oxygen-containing substance contained in the atmosphere. The exposed voltage is slightly lower when the hydrogenated layer is exposed.

Basically, however, yttrium oxide is suitable for the material of the cold electron-emitting electrode except for stability. Particularly oxide closer to YO than the composition ratio of Y ₂ O ₃ is superior in terms of low voltage discharge than Y ₂ O _3.
When the metal film is oxidized in the coexistence of hydrogen, the penetration of oxygen into the metal film tends to be promoted by the hydrogen, and the element represented by R is Y ₂ at the surface of the metal film. Before being oxidized to the state of O ₃ , oxygen penetrates into the metal film, so that the element represented by Y becomes YO or the state between YO and Y ₂ O _{3 in} the surface layer portion of the metal film. Likely to be. In any case, the oxidized layer exhibits a low discharge voltage as an emissive electrode, although not as much as the electrode where the hydrogenated layer is exposed.

Therefore, even if a thin oxide layer is formed on the hydrogenated layer, the initial discharge performance of the electron-emitting electrode is not extremely adversely affected. Since the layer is sputtered over time by discharge to expose the hydrogenated layer, it is substantially the same as a hydrogenated electrode having no oxide layer on the surface in that stable discharge can be performed for a long period of time.

FIG. 7 shows a straight-tube cold-cathode fluorescent tube 20 using the cold-electron-emitting electrode 10. The cold cathode fluorescent tube 20
A structure in which a pair of the cold electron-emitting electrodes 10 are arranged in a glass tube 21 having an inner wall coated with a fluorescent material 22 that emits light in a predetermined wavelength range in an excited state such that the electron-emitting layer 2 faces the glass tube 21. A rare gas such as argon and mercury are sealed in the glass tube 21. Further, as shown in FIG. 8, a hollow cold electron emitting electrode 30 may be applied.
The cold electron emission electrode 30 has a structure in which an electron emission layer 32 is provided on the inner surface of a cylindrical base material 31 connected to a wiring 33. Each of the electron emission layers 2 and 32 is formed of a hydrogenated compound RH _2-x (R is Sc, Y, La, Ce, Gd, Lu, T
At least one element selected from the group consisting of h, U, and Np, and H is hydrogen, -1 <x <1).

FIG. 9 shows a straight-tube cold-cathode fluorescent tube 40 using the hollow-type cold electron-emitting electrode 30. The cold cathode fluorescent tube 40 has a pair of cold electron emitting electrodes in a glass tube 31 whose inner wall is coated with a fluorescent material 32 that emits light in a predetermined wavelength range in an excited state such that the electron emitting layer 32 faces. The glass tube 31 is filled with a rare gas such as argon and mercury. The cold-cathode fluorescent tube provided with an electrode using yttrium hydride as an electron-emitting layer can be used not only in a straight tube but also in any shape such as an L-shape, a U-shape, a U-shape, and a W-shape. .

Next, a method for manufacturing the above-mentioned electron-emitting electrode will be described. In the manufacture of this example of an electron-emitting electrode,
As described above, the metal represented by R (Sc, Y, La, C
e, Gd, Lu, Th, U, at least one element selected from the group consisting of Np) on a substrate, and then forming the metal film under an atmosphere containing hydrogen gas. The above-mentioned electron-emitting electrode is manufactured by performing a hydrogenation step of hydrogenating by heat treatment.

In the film forming step, a metal film represented by R is formed on a substrate by a known method, for example, vapor deposition or sputtering. In this example, as the base material, a metal containing Ni is used as described above. That is, the substrate is made of the same material as the conventional Ni electrode. In this case, the electron emission layer containing the electrode material is used for a long time that exceeds the service life of the electron emission layer, and the electron emission layer is damaged and the electron emission layer is almost eliminated. Also, the base material functions as a Ni electrode, and the discharge voltage and the like increase to the same level as the conventional electrode, but the electron-emitting electrode suddenly stops functioning even if the lifetime of the electron-emitting layer is exceeded. There is no such thing.

Further, as described later, when hydrogenating a metal film, there is a high possibility that extra hydrogen enters the metal film.
It is preferable that the thickness of the metal film R before hydrogenation formed in the film forming step is less than 13000 °. Especially 6
When the temperature is less than 000 °, even if there is a slight difference in the partial pressure of hydrogen in the atmosphere in the hydrogenation step, the variation in the discharge characteristics is small, the production control is easy, and the variation around 4000 ° is particularly small and preferable. For example, the thickness of the metal film is 13,000Å
In the case described above, the amount of hydrogen released from the electron-emitting electrode manufactured by hydrogenating the metal film increases, depending on the hydrogenation temperature, and this electron-emitting electrode was used for a cold cathode fluorescent tube. In this case, the light emission of the cold cathode fluorescent tube may be adversely affected.

The thickness of the metal film R is, for example, 13,000.
If a cold cathode fluorescent tube using an electron-emitting electrode with a length of Å or more is used for a time that exceeds the lifetime of the electron-emitting electrode, the electron-emitting electrode will be damaged. When the level of hydrogen released from the emission layer increases, the cold cathode fluorescent tube cannot be used at that time even if the base material is the same as the Ni electrode as described above, but if the thickness of the metal film is less than 13,000 °, If the electron emission layer is damaged by the discharge, the level of hydrogen released by the damage can be kept low, so that even if the electron emission electrode is damaged, the cold cathode fluorescent tube is prevented from suddenly becoming unusable. be able to.

In the hydrogenation step, for example, a furnace is used, a substrate on which the metal film R is formed is placed in the furnace, and the furnace is set to an inert gas atmosphere containing hydrogen gas.
The furnace will be heated. FIG. 10 shows the hydrogen concentration (hydrogen partial pressure) in the atmosphere in the hydrogenation step of the element represented by R.
And a graph showing the range of the hydrotreating temperature.

The region M and the region N are regions where yttrium hydride can be formed, and the region M is a region where yttrium hydride having a desirable property as an electrode of a cold cathode fluorescent tube can be obtained. Here, Ar (argon) is used as the inert gas. Then, a hydrogenated film could be formed when the hydrogen gas concentration in the furnace atmosphere was in the range of 10 ppm to 100% by volume. And the hydrogen gas concentration is 10pp
If it is less than m, the metal of the element represented by R may not be sufficiently hydrogenated. In order to reliably hydrogenate the metal, the hydrogen gas concentration is preferably 50 ppm or more.

However, the metal represented by R is, for example, 1
When the metal of Y was hydrogenated under 00% by volume of hydrogen (H ₂ ), the formation of a hydrogen compound (yttrium hydride) was confirmed by X-ray diffraction. It may enter an unstable place other than coordination or octa-coordination, and hydrogen containing this solid solution is released over time. It was confirmed that the amount of hydrogen released from the yttrium hydride film obtained after the hydrogenation of yttrium was again heat-treated and changed greatly according to the hydrogen concentration at the time of hydrogenation.

That is, if the hydrogen partial pressure in the atmosphere at the time of hydrogenation is high, the electron emission layer generated by hydrogenating the metal film is placed in an unstable place other than the yttrium hydride crystal.
A large amount of unstable hydrogen is contained. When a cold cathode fluorescent tube including an electron emitting electrode containing extra unstable hydrogen is used, hydrogen released from the electron emitting electrode in the fluorescent tube has a bad influence on discharge. Will be. Therefore, it is preferable that the hydrogen gas concentration in the atmosphere at the time of hydrogenation for obtaining yttrium hydride having desirable properties as an electrode of the cold cathode fluorescent tube is 0.5% by volume or less. Further, the hydrogen gas concentration is more preferably 500 ppm or less, more preferably,
It is about 100 ppm.

That is, the hydrogen concentration in the atmosphere at the time of hydrogenation is desirably 10 ppm or more and 0.5 volume% or less.
More preferably, it is 50 ppm or more and 500 ppm or less. The inert gas is basically a rare gas, but a rare gas other than an argon gas may be used here.

It is preferable that the above atmosphere basically contains no oxygen gas or oxygen-containing substance.
As long as the concentration of the rare gas or hydrogen gas used can be controlled, a trace amount of oxygen or an oxygen-containing substance may be contained. As described above, an extremely thin oxide layer is formed on the surface of the electron emission layer by the impurity-level oxygen. However, it can sufficiently function as an electron-emitting electrode.

The heating temperature (temperature in the furnace) in the hydrogenation step is preferably 200 ° C. or more and 700 ° C. or less. At a temperature lower than 200 ° C., hydrogenation of the metal represented by R does not progress, and hydrogenation of the metal represented by R may be difficult. The heating temperature in the more preferred hydrogenation step is 300 ° C. or higher. On the other hand, when the hydrogenation temperature exceeds 700 ° C., the presence of hydrogen tends to promote the formation of an oxide of the element represented by R, and as described above, the presence of a trace amount of hydrogen in the rare gas atmosphere in the hydrogenation step. Oxygen causes the oxidation of the element R to proceed, which is difficult to reduce, to form an oxide, which makes it difficult to obtain a hydride of the element represented by R.

Therefore, in a state where a trace amount of oxygen or an oxygen-containing substance is present, the heating temperature in the hydrogenation step is preferably set to 700 ° C. or lower, more preferably 600 ° C. or lower. The rate of temperature rise in the heat treatment in the hydrogenation step is not particularly limited, but is preferably, for example, about 10 ° C./min to about 30 ° C./min, and more preferably about 20 ° C./min. . Also,
The rate of temperature decrease after the heat treatment is preferably from 10 ° C./min to 1 ° C./min, and more preferably about 3 ° C./min.

The electron-emitting electrode using the above-mentioned electrode material has a low discharge voltage, and can not only improve the efficiency by 30% or more than the conventional Ni electrode and the like, but also can improve the efficiency. A life equivalent to that of a Ni electrode or the like can be maintained. That is, this example of the electron-emitting electrode does not increase the discharge voltage even when used for a long time like the conventional Ni electrode, stabilizes the discharge voltage, and is compared with the conventional Ni electrode. Thus, power consumption can be reduced.

Therefore, by using a cold cathode fluorescent tube using this electron-emitting electrode as, for example, a backlight of a liquid crystal display of an electronic device using a portable battery,
The power consumption required for the backlight can be reduced to extend the time that can be used with the battery of the portable electronic device, and the discharge voltage is stable for a long time, so the power consumption increases over a long period of use Nothing to do. Further, the practical use range of the electron-emitting electrode is not narrowed by the instability of the discharge voltage.

Therefore, the electron-emitting electrode of this example is not limited to a cold cathode fluorescent tube usable as a backlight or a copying machine of a liquid crystal display device, and particularly, a plasma display device (Plasma Display Panel) for monochromatic or multicolor emission. ) Can be suitably applied as an electrode of a discharge device utilizing secondary electron emission by ions, and in these products, the discharge voltage can be reduced and the discharge voltage can be stabilized.
Power consumption can be reduced. In addition, other VFD
(Vacuum Fluorescent Display).

[0063]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, tests performed on the characteristics of the electron-emitting electrode and the cold cathode fluorescent tube of the present invention will be described. Test 1 First, after a Y metal film (thickness: about 1.3 μm) was formed, this metal film was hydrogenated, and then heated in a vacuum furnace to release hydrogen that had entered the metal film during hydrogenation. And the amount of hydrogen gas released was detected. As the atmosphere in the hydrogenation step, an atmosphere obtained by adding a hydrogen gas to an argon gas is used, and the hydrogen gas concentration at this time is 5 vol%, 500 ppm, 100 p.
Hydrogenation was performed at pm.

Processing temperature in the hydrogenation step (furnace temperature)
Are hydrogenated at 300 ° C., 350 ° C., 400 ° C., and 450 ° C., and the results are shown in FIG. In the figure, the horizontal axis represents the processing temperature in the hydrogenation step, and the vertical axis represents the relative value of the amount of hydrogen gas released from the yttrium hydride film heated after hydrogenation. As shown in FIG. 11, the hydrogen gas concentration in the hydrogenation step was increased from 100 ppm to 500 ppm at the same temperature.
When the amount is increased to ppm, the amount of hydrogen gas released clearly increases, and in this temperature range, the amount of released gas decreases as the processing temperature of the hydrogenation step increases. In the range in the figure,
The amount of released hydrogen shows a linear function behavior with respect to the hydrotreating temperature.

In the case of a sample manufactured by setting the hydrogen gas concentration in the atmosphere during the hydrogenation process to 5%, the amount of released hydrogen after the hydrogenation was increased to an extent unsuitable as an electrode material for a cold cathode fluorescent tube. Was.

Further, the hydrogen concentration in the hydrogenation step is set to 5%
As described above, a number of electron-emitting electrodes containing yttrium hydride were prepared, and these were connected to a 63 m long tube shown in FIG.
m, used as a cold cathode of a cold cathode fluorescent tube having a tube diameter of 2.6 mm. When this cold cathode fluorescent tube was continuously lit for a long time at a lamp current of 5 mA, abnormal discharge occurred within several hundred hours. This is presumably because a large amount of unstable hydrogen other than that contained in the crystal as yttrium hydride was contained.

Test 2 In FIG. 12, the amount of hydrogen gas released from the yttrium hydride film and the hydrogenation temperature were plotted in order to determine the optimum hydrogenation temperature. Since the furnace used here was different from the furnace used in Test 1, slightly different values were taken. As shown in FIG. 12, in each of the samples having a hydrogenation treatment temperature of less than 200 ° C., the amount of gas released due to the treatment temperature was small, and in the hydrogenation step, yttrium hydride was sufficiently used as an electrode material for a cold cathode fluorescent tube. Are not formed in many cases. Further, when the hydrogenation treatment is performed at a temperature higher than 700 ° C., the amount of released gas is low, and yttrium hydride having good characteristics is not formed in many cases.

This is because, as described above, at a processing temperature higher than 700 ° C., the presence of a trace amount of hydrogen gas tends to promote the formation of Y oxide, so that once oxidized yttrium oxide is reduced, the final product is reduced. Is extremely difficult to obtain yttrium hydride. It should be noted that an extremely thin yttrium oxide layer (for example,
Y ₂ O ₃ ) is formed, and the thickness of the oxide layer formed on the surface of yttrium hydride is preferably several hundreds mm or less.
It was also confirmed by X-ray diffraction (thin film method) and HFS analysis. If the thickness of the oxide layer is 2000 ° or less, the performance of the electron-emitting electrode does not greatly change.
By hydrogenating at a processing temperature of ℃ or less,
The electron-emitting electrode of this example can be manufactured.

Test 3 Next, in a film forming step, a Y metal film was formed on a Ni base material to a thickness of 1.3 μm (13000 °).
In the hydrogenation step, the hydrogen gas concentration in the argon gas was set to 0.5% by volume to produce an electron-emitting electrode. Then, a cold cathode fluorescent tube similar to that shown in FIG. 7 was prepared using this electron-emitting electrode. Then, an overcurrent life test using this cold cathode fluorescent tube was performed.

That is, the above-mentioned cold cathode fluorescent tube was continuously lit by setting the tube current to 7 mA, which is higher than usual (5 mA or less). The result is shown in FIG. As shown in FIG. 13, this cold cathode fluorescent tube causes abnormal discharge in about 1000 hours, and after the abnormal discharge, the tube voltage rapidly rises.
This substantially increases the life of the lamp and increases the ambient temperature.

The electron-emitting electrode used in this test was:
Since the thickness of the yttrium film before hydrogenation is as thick as 1.3 μm (a value exceeding the above-mentioned upper limit) and the hydrogen concentration in the hydrogenation step is relatively high at 0.5% by volume (the above-mentioned upper limit),
The amount of hydrogen gas released was large, and abnormal discharge occurred due to the destruction of the electron emission layer.

However, if the hydrogen concentration in the hydrogenation step is within the above range and the thickness of the metal film before hydrogenation is reduced, the amount of hydrogen released is small even if the electron emission layer is destroyed. And abnormal discharge can be prevented. And, if abnormal discharge at the time of electron emission layer destruction can be prevented, even if the electron emission layer is destroyed, the Ni substrate as a substrate functions as an electron-emitting electrode, and the tube voltage rises to the Ni electrode level, Even if the electron emission layer is destroyed, the cold cathode fluorescent tube can be prevented from suddenly turning off.

Test 4 An electron-emitting electrode was manufactured under the same conditions as in Test 3 except that the film thickness before hydrogenation was less than 13,000 °, and a cold cathode fluorescent tube was prepared using this to conduct an overcurrent test. As a result, after the electron-emitting layer made of yttrium hydride was destroyed, the state was stabilized with the tube voltage rising to the level of the Ni electrode. Therefore, by setting the thickness of the metal film before hydrogenation to less than 13,000 °, when the electron-emitting layer is destroyed due to long-time use exceeding the lifetime of the electron-emitting layer, the cold-cathode fluorescent tube is placed there. It is possible to prevent sudden discharge from occurring due to abnormal discharge.

Test 5 In this test, the film thickness before hydrogenation was set at 10,000 ° and the hydrogen concentration during hydrogenation was set at 5%.
A continuous lighting test of the cold cathode fluorescent tube 20 having the shape shown in FIG. 7 was performed using the cold electron-emitting electrode prepared at the heat treatment temperature for hydrogenation under the above-mentioned conditions while setting the temperature at 00 ppm. The glass tube 21 has an outer diameter of 2.6 mm and a length of 6
3.5 mm one was used. FIG. 14 shows a cold cathode fluorescent tube 20 of this yttrium hydride cold electron emitting electrode and a fluorescent tube of the same standard as the cold cathode fluorescent tube 20 except that Ni is used in the electron emitting layer of the cold electron emitting electrode as a comparative example. It shows discharge characteristics. The solid line is the cold cathode fluorescent tube 20 of the present invention,
A broken line indicates a cold cathode fluorescent tube using a Ni electrode. As shown in FIG. 14, in this cold cathode fluorescent tube, 100
There is no apparent increase in the discharge voltage over time,
Even if lighting is continued for 0 hours or more, the difference in discharge voltage from the initial lighting is small.

That is, this cold electron-emitting electrode is excellent in stability, and shows stability similar to that of a Ni electrode.
It should be noted that the discharge voltage of the Ni electrode in FIG. 14 is an approximate average value when a cold cathode discharge tube is used based on the conventional measurement results, and actually has some variation. Further, the electron-emitting electrode in this example is 30 times smaller than the Ni electrode.
%, The efficiency has improved. In other words, the electron-emitting electrode using yttrium hydride has a low discharge voltage, can reduce power consumption, and can have a life similar to that of the Ni electrode.

The discharge voltage drops to about 165 V after 100 hours even though the initial discharge is about 170 V. This is slightly higher because the oxide layer generated on the surface of yttrium hydride was involved in the electron discharge property at the time of initial discharge, and after 100 hours, the oxide layer on the surface was sputtered and yttrium hydride was exposed on the surface of the electron emission layer. It seems that it has dropped because of this. This is separately manufactured,
It has been confirmed that the initial discharge of a discharge tube having an yttrium hydride electrode having almost no oxide layer formed on its surface was about 165 V, and that the voltage was maintained over time, and the result was obtained.

[0077]

The electron-emitting electrode according to the first aspect of the present invention has Sc, Y, La, Ce, Gd, Lu, Th, U, and N.
It has a hydride of at least one element selected from the group of p.

According to the first aspect of the invention, the hydride can stably emit cold electrons at a low voltage for a long period of time. The hydride is RH _2-x (R is Sc,
At least one element selected from the group consisting of Y, La, Ce, Gd, Lu, Th, U, and Np;
<X <1), and the hydride is basically RH ₂
Has a crystal structure unique to the substance represented by
RH including those deviated from stoichiometry due to the lack of element (H) or the presence of excess H (hydrogen) element
It is indicated by _2-x and satisfies the above-mentioned conditions necessary for an electron-emitting electrode, that is, it has a low work function, is hardly sputtered, hardly reacts with mercury, and has good conductivity. It is.

The discharge voltage of the electron-emitting electrode does not increase even when used for a long time.
It has a lower discharge voltage and a lower N
The same stability of the discharge voltage as that of the i-electrode can be exhibited.

The invention according to claim 3 further comprises Sc,
It has an oxide of at least one element selected from the group consisting of Y, La, Ce, Gd, Lu, Th, U, and Np.

According to the above configuration, when the surface of the hydrogenated electrode material is covered with the oxide, the above-mentioned elements are classified into rare earth elements and actinoids, and the elements contained in the rare earth elements Although the oxide has some difficulty in stability, it can reduce the discharge voltage when used as a material for an electron-emitting electrode.

When the thickness of the oxide layer is 2000 mm or less, the discharge voltage can be kept low even if the oxide layer is fitted on the surface of the electron emission layer as described above. The same effect as the configuration according to claim 1 can be obtained without hindering the stability of the device.

The method for manufacturing an electron-emitting electrode according to the fourth aspect of the present invention is characterized in that Sc, Y, La, Ce, Gd, Lu, T
A metal film having at least one element selected from the group consisting of h, U, and Np is hydrogenated in an atmosphere containing hydrogen gas.

According to the above structure, after forming the metal film made of the element shown above, this is hydrogenated,
A thin film including the above-mentioned electrode material and serving as an electron emission layer can be easily formed. That is, an electron-emitting electrode having an electron-emitting layer containing the above electrode material can be easily manufactured.

The cold-cathode fluorescent tube according to claim 7 of the present invention comprises Sc, Y, La, Ce, Gd, Lu, Th, U, N
comprising an electron-emitting electrode having a hydride of at least one element selected from the group of p,
By having the hydride, the discharge characteristics of the electron-emitting electrode can be stabilized, and cold electrons can be emitted at a low voltage.

[Brief description of the drawings]

FIG. 1 is a drawing showing an X-ray diffraction pattern of yttrium hydride used as an electrode material according to an embodiment of the present invention.

FIG. 2 is a graph showing elemental components of yttrium hydride used as an electrode material according to the embodiment of the present invention.

FIG. 3 is a graph showing the reflectance of yttrium hydride used as an electrode material according to an embodiment of the present invention.

FIG. 4 is a graph showing the transmittance of yttrium hydride used as the electrode material.

FIGS. 5A and 5B are diagrams showing a crystal structure of yttrium hydride used as the electrode material.

FIG. 6 is a drawing showing a schematic structure of an electron-emitting electrode according to an embodiment of the present invention.

FIG. 7 is a cross-sectional view showing a cold-cathode tube provided with the electron-emitting electrode.

FIG. 8 is a view showing a schematic structure of a hollow electron-emitting electrode according to an embodiment of the present invention.

FIG. 9 is a sectional view showing a cold cathode tube provided with the hollow-type electron-emitting electrode.

FIG. 10 is a graph showing a hydrogen concentration range that can be hydrogenated and a processing temperature range, and a hydrogen concentration range and a processing temperature range suitable as an electrode material in a hydrogenation step in the production of the electron-emitting electrode.

FIG. 11 is a graph showing the amount of hydrogen released under reduced pressure when the hydrogen concentration and the processing temperature are changed in the hydrogenation step in the production of the electron-emitting electrode.

FIG. 12 is a graph showing the amount of hydrogen released in vacuum when the hydrogen concentration and the processing temperature are changed in the hydrogenation step in the production of the electron-emitting electrode.

FIG. 13 is a graph showing the results of an overcurrent life test of a cold cathode fluorescent tube using the electron-emitting electrode.

FIG. 14 is a graph showing the results of a continuous lighting test of a cold cathode fluorescent tube using the electron-emitting electrode manufactured under favorable conditions.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Cold electron emission electrode 20 Cold cathode fluorescent tube 30 Cold electron emission electrode 40 Cold cathode fluorescent tube

Continued on the front page (72) Inventor Yuichi Mori 1-3-1 Edanishi, Aoba-ku, Yokohama-shi, Kanagawa Prefecture Inside Stanley Electric Co., Ltd. (72) Inventor Hironori Hirama 1-3-3, Edanishi, Aoba-ku, Yokohama-shi, Kanagawa 1 Stanley Electric Co., Ltd.

Claims (7)

[Claims] 1. Sc, Y, La, Ce, Gd, Lu, T
An electron-emitting electrode comprising a hydride of at least one element selected from the group consisting of h, U, and Np. 2. The hydride is RH _2-x (R is Sc,
At least one element selected from the group consisting of Y, La, Ce, Gd, Lu, Th, U, and Np;
2. The electron-emitting electrode according to claim 1, wherein x <1. 3. Sc, Y, La, Ce, Gd, Lu, T
The electron-emitting electrode according to claim 1, further comprising an oxide of at least one element selected from the group consisting of h, U, and Np. 4. A method for manufacturing an electron-emitting electrode, comprising: forming a metal film containing at least one element selected from the group consisting of Sc, Y, La, Ce, Gd, Lu, Th, U, and Np with hydrogen gas. A method for producing an electron-emitting electrode, wherein the method comprises hydrogenating in an atmosphere containing hydrogen. 5. The method according to claim 4, wherein the metal film is hydrogenated in an inert gas atmosphere containing 10 ppm or more and 0.5 vol% or less of hydrogen gas. Method. 6. The electron emitting electrode according to claim 4, wherein the metal film is subjected to a heat treatment at a temperature of 200 ° C. or more and 700 ° C. or less in an atmosphere containing a hydrogen gas in the hydrogenation step. Production method. 7. Sc, Y, La, Ce, Gd, Lu, T
A cold cathode fluorescent tube comprising an electron-emitting electrode having a hydride of at least one element selected from the group consisting of h, U, and Np.