Electric lamp and discharge devices – With luminescent solid or liquid material – With gaseous discharge medium
Reexamination Certificate
1999-03-17
2001-08-28
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
With gaseous discharge medium
C313S574000, C313S631000, C313S34600R, C313S355000, C313S311000, C313S495000
Reexamination Certificate
active
06281626
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a cold emission electrode, particularly, a cold emission electrode suitable for a discharge device using a cold emission phenomenon, a method of manufacturing the cold emission electrode, and a display device comprising the same.
A thermoelectronic emission phenomenon, photoemission phenomenon, cold emission phenomenon, and the like are known as electron emission phenomena in which electrons existing in an object are emitted into space. In practice, an electron emitting electrode material is used to form an electrode for a device utilizing discharge, such as a discharge lamp. For example, there is known a thermoelectronic emission discharge lamp using the thermoelectronic emission phenomenon in which electrons are emitted by supplying a current to, e.g., a coil filament to heat it.
Unlike the above example, devices using various types of discharge using electrodes utilizing cold emission phenomenon are also known. Field emission display devices using electron emission using a strong electric field, cold emission discharge tubes and plasma display panels utilizing secondary electron emission upon mainly ionic collision, and the like are commercially available.
Secondary electron emission as an electron emission mechanism unique to a cold emission discharge tube is potential type emission or kinetic type emission. In the potential type emission, electrons are emitted by an energy given by a so-called Auger effect, in which when a cation comes close to a cold cathode, the level of an electron lowers to the ground state of the cation because the level of the electron in the electrode is higher than that of the cation, and the energy generated by this level difference is applied to another electron. The kinetic type emission is emission from the cold cathode upon reception of an energy, the energy being generated when a cation comes into collision with the cold cathode. Glow discharge unique to the cold emission tube occurs due to the above electron emission mechanism.
A cold emission discharge fluorescent tube or plasma display panel which emits visible light upon this glow discharge comprises a vessel having a plurality of electrodes and an inner wall coated with a fluorescent material and a mixture of a rare gas and mercury sealed in the vessel. Electrons emitted in accordance with the photoemission phenomenon by light incident on the cold emission discharge fluorescent tube initially move by an electric field applied to the electrodes and come into collision with the gas and the like sealed in the vessel, thereby ionizing gas to produce ions. These ions collide with the electrodes to generate secondary electrons. The electrons emitted by the cold emission electrode collide with vaporous mercury atoms to start glow discharge, thereby generating ultraviolet rays. The fluorescent material is excited with the ultraviolet rays to emit visible light.
As the material of the cold emission electrodes, a metal element having a relatively low work function, such as nickel (Ni) or molybdenum (Mo) is used.
A cold emission discharge fluorescent tube having a cold emission electrode made of such a material has a higher luminance (cd/m
2
) with a decrease in its tube diameter. A low-profile device having the cold emission discharge fluorescent tube can be obtained and is suitable for the backlight of a liquid crystal display device.
A cold emission discharge fluorescent tube having a cold emission electrode has a high lamp discharge voltage and hence high lamp power consumption. In particular, it is difficult to perform display operation for a long period of time when the tube is used as a backlight in a battery-driven portable display device.
An electron emitting material is sputtered from the above metal electrode by discharge, and then the sputtered electron emitting material contaminates the tube wall and shortens the emission service life.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide a cold emission electrode having a low discharge voltage and a stable discharge voltage even upon long-term use, a method of manufacturing the cold emission electrode, and a cold emission discharge fluorescent tube.
The cold emission electrode of the present invention is made of a hydride of at least one element selected from the group consisting of Sc (scandium), Y (yttrium), La (lanthanum), Ce (cerium), Gd (gadolinium), Lu (lutetium), Th (thorium), U (uranium), and Np (neptunium).
According to the present invention, cold electrons can be emitted from a hydride at a low voltage. Even if discharge occurs, the hydride can hardly be sputtered, thereby performing a stable operation for a long period of time.
The hydride may be RH
2+x
(wherein R is at least one element selected from the group consisting of Sc, Y, La, Ce, Gd, Lu, Th, U, and Np, H is hydrogen, and −1<x<1). The above hydride has a crystal structure unique to a material basically represented by RH
2
. This RH
2
including RH
2+x
shifted from stoichiometry due to omissions or excessive presence of the element represented by R and H (hydrogen) atom. The hydride satisfies the above necessary conditions as the cold emission electrode, i.e., a low work function, a material rarely sputtered and reacted with mercury vapor, and high conductivity. Of the hydrides of the above rare earth elements or actinoid elements, the rare earth or actinoid element contains one or a plurality of elements. Yttrium is totally most suitable in consideration of cost, treatment, electron emission characteristics, and the like.
Note that the cold emission electrode may contain an oxide of at least one element selected from the group consisting of Sc, Y, La, Ce, Gd, Lu, Th, U, and Np in addition to the hydride.
When an oxide is formed in the surface of the hydrogenated electrode material, the above element is classified into the rare earth or actinoid element. The oxide of an element belonging to the rare earth element can decrease the discharge voltage when it is used as the material of the cold emission electrode.
A method of manufacturing a cold emission electrode according to the present invention comprises forming a cold emission region of a cold emission electrode by hydrogenating a metal film in an atmosphere containing hydrogen gas, the metal film containing at least one element selected from the group consisting of Sc, Y, La, Ce, Gd, Lu, Th, U, and Np.
The metal film containing the R element is hydrogenated to produce the above hydride. The cold emission electrode having the hydride can be easily formed. In this case, the thickness of the film containing at least one element selected from the group consisting of Sc, Y, La, Ce, Gd, Lu, Th, U, and Np before hydrogenation is preferably set to be less than 13,000 Å.
When the thickness of the metal film is set to be less than 13,000 Å, the following effect can be obtained. When the above metal film is hydrogenated, hydrogen atoms enter into the metal film to form the cold emission electrode of the above hydride. When the cold emission electrode is used for a long period of time exceeding the service life as the cold cathode of the cold emission discharge fluorescent tube, the cold emission electrode is damaged by discharge or the like to discharge hydrogen in the cold emission discharge fluorescent tube.
When hydrogen is discharged in the cold emission discharge fluorescent tube, the hydrogen discharged interferes with mercury vapor ionization, thereby relatively lowering the luminance of the fluorescent color of the fluorescent material owing to decrease of the ultraviolet ray emission amount. As a result, the emission color of mercury vapor is visually observed with a higher luminance to emit bluish light, resulting in inconvenience. When the concentration of hydrogen discharged in the cold emission discharge fluorescent tube increases, the tube cannot be used. When the thickness of the metal film is set to be less than 13,000 Å, the content of hydrogen contained in the metal film can
Hirama Hironori
Mori Yuichi
Nakamura Osamu
Suzuki Shigemi
Casio Computer Co. Ltd.
Frishauf, Holtz Goodman, Langer & Chick, P.C.
Patel Ashok
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