Electric lamp and discharge devices – Discharge devices having a multipointed or serrated edge...
Reexamination Certificate
1995-11-01
2001-08-28
Patel, Ashok (Department: 2875)
Electric lamp and discharge devices
Discharge devices having a multipointed or serrated edge...
C313S310000, C313S336000, C313S351000, C313S311000, C313S497000
Reexamination Certificate
active
06281621
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a field emission cathode structure, a method for the production thereof, and a flat panel display device using the cathode.
In recent years, the advanced technology on the fabrication of Si semiconductors has been lending itself immensely to the development of field-emission type cathode structures and to the utilization of these cathodes in ultraspeed microwave devices, power devices, electron beam devices, flat panel display devices, etc. As a typical example of the cathode, what has been reported by C. A. Spindt et al. in Journal of Applied Physics, Vol. 47, No. 12, December 1976, pages 5248-5263 has been known to the art.
The field emission cathode structure disclosed therein, as illustrated in
FIG. 9
a
,
FIG. 9
b
, and
FIG. 9
c
of the present specification, is produced by forming a SiO
2
layer
2
as an insulating layer by the technique of deposition such as CVD on a Si single crystal substrate
1
, further forming thereon a Mo layer
3
destined to serve as a gate electrode layer as by the electron beam vacuum deposition technique, boring a pinhole
5
approximately 1.5 &mgr;m in diameter through the layers
2
and
3
by means of etching, then forming an Al layer
4
destined to serve as a separating layer by means of vacuum deposition (
FIG. 9
a
), vacuum depositing thereon a metal such as Mo which is destined to form an emitter as by the technique of electron beam vacuum deposition while keeping the Si single crystal substrate
1
in rotation thereby giving rise to a conical pile of Mo inside the pinhole
5
by utilizing the phenomenon that the diameter of the pinhole
5
converges in proportion as the deposition of Mo proceeds (
FIG. 9
b
), and finally finishing a conical emitter
7
by peeling the Al separating layer
4
and removing the Mo layer
6
(
FIG. 9
c
).
The electronic device using a cathode structure such as, for example, the flat panel display device is constructed by causing a Si single crystal substrate
1
having a multiplicity of such cathodes superposed thereon to be opposed across a prescribed interval to a glass face plate
8
having a phosphor layer superposed thereon as illustrated in FIG.
10
. In this diagram, A stands for a region for the formation of cathodes. This flat panel display device using field emission cathodes is different from the display device using a liquid crystal in being a luminescent type. It obviates the necessity for using a back light and consequently promises a saving in power consumption. Owing to these features, it has been attracting keen attention.
The conventional method for producing the field emission cathode system, the field emission cathode structure obtained by the method, and the electronic devices using such cathode structures, however, entail the following important problems.
Firstly, in the conventional method for rotary vacuum deposition described above, since the formation of the emitter
7
inside the pinhole
5
is attained by utilizing the phenomenon that the diameter of the pinhole
5
bored in the Mo layer
3
gradually converges, the height of the emitter and the shape of the tip of the emitter are liable to loss of consistency. The cathode structure which is obtained by this method, therefore, produces field emission with poor uniformity and lacks the sharpness of the tip of the emitter which is necessary for improving the efficiency of field emission and, as a result, entails such problems as decline of the efficiency of field emission and growth of power consumption. Further, the fact that the reproducibility of shape and the yield of production are both inferior gives rise to a problem of extremely high cost of production in the fabrication of a multiplicity of field emission cathode structures on one and the same substrate.
Secondly, since the SiO
2
insulating layer is formed by the technique of CVD, the distance between the gate and the emitter on which the efficiency of field emission heavily hinges defies accurate control, and the magnitudes of field emission which the plurality of cathode structures severally generate lack uniformity. In the production of a flat panel display device, for example, the picture elements corresponding to the individual cathode structures are suffered to betray inconsistency of luminance. As respects the flat panel display device, owing to the slight loss of consistency in the distance between the gate and the emitter and in the shape of the tip of the emitter, it often happens that the ratio of the current of electrons between the gate and the emitter to the current of electrons between the anode and the emitter increases. There are times when the current of electrons between the gate and the emitter even reaches 60% of the total current of electricity. Thus, the problem arises that the efficiency of light emission of the picture elements (fluorescent elements) corresponding to the individual cathode structures is degraded and, at the same time, the picture elements suffer from serious inconsistency in luminance.
Thirdly, the size of the Si single crystal substrate imposes a limit on the regions to be used for the formation of field emission cathode structures or the number of such cathode structures to be formed and, at the same time, impairs the productivity of the cathode structures. This fact implies that the flat panel display device using a multiplicity of cathode structures is limited in size. Further, the flat panel display device by nature is fated to use the Si single crystal substrate as part of the housing of the device. As a vacuum container, the housing is conspicuously deficient in strength. Especially, when the image screen grows in size, the housing retains required strength only with increasing difficulty.
Fourthly, since the emitter is formed by depositing the Si single crystal substrate or conductive substrate concurrently serving as a cathode, the continuity between the emitter and the cathode is disrupted along their interface no matter whether the material for the emitter and that for the cathode are different or same. Thus, the disadvantage arises that the emitter will peel and incur loss of resistance and, consequently, generate heat possibly to the extent of deteriorating the emitter itself.
For the sake of eliminating the limit on size and enhancing the strength of the housing, an idea of superposing the Si single crystal substrate fast on a structural substrate such as a glass substrate may be conceived. The mere superposition results in an addition to the thickness of the cathode part and proves unfit for such electronic devices which are directed toward decreasing weight and thickness, for example. The substitution of a glass substrate for the Si single crystal substrate indeed eliminates the problems on size mentioned above. It, however, necessitates formation of a conductive layer on the glass substrate for the purpose of ensuring maintenance of conductivity to the emitter. Thus, the formation of the SiO
2
insulating layer does not permit adoption of the technique of CVD but requires use of the technique of electron beam vacuum deposition or the technique of spattering. The SiO
2
insulating layer which is obtained by such a technique, however, assumes a more porous texture and contains more pinholes than the layer obtained by the technique of CVD and suffers from aggravated inconsistency in the distance between the gate and emitter which governs the efficiency of field emission.
The flat panel display device using the conventional field emission cathode structures entails the following problems in addition to the problems pertaining to the process of manufacture of cathode structures mentioned above. When the field emission cathode structures are used, in spite of an increase in the voltage applied between the cathode and the anode to a level of about 100 V, the energy of the electron beam is small as compared with that of the ordinary color cathode ray tube (hereinafter referred as “C-CRT”) and the fluorescent elements collect electric charge on their surfaces poss
Nakamoto Masayuki
Ono Tomio
Sakai Tadashi
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Kabushiki Kaisha Toshiba
Patel Ashok
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