Electric lamp and discharge devices – Electrode and shield structures – Point source cathodes
Patent
1995-02-01
1996-05-28
Ramsey, Kenneth J.
Electric lamp and discharge devices
Electrode and shield structures
Point source cathodes
445 24, H01J 902
Patent
active
055214614
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates generally to microtip-emitting cathodes on silicon for compact flat screens.
More specifically, the present invention relates to flat display screens based on the physical phenomenon of cathodoluminescence and field effect electron emission. Further, the present invention can be applied in all industrial sectors using compact display screens, for example, video camera view finders, calculators, monitoring devices of all kinds, vehicles, watches, and clocks, etc.
BACKGROUND OF THE INVENTION
The microtip screens are characterized by an electronic field effect emission from an extended plane microtip cathode, a low consumption cold cathode, a rapid response time (1 .mu.s), a matrix addressing from the integrated tip-grid structure and a luminous emission by cathodoluminescence at a low/average voltage.
Known microtip screens are vacuum tubes generally constituted of two thin glass plates (approximately 1 mm), distanced by 200 .mu.m. The rigidity of the structure is ensured by spacers (balls of 200 .mu.m, for example) which enable the interelectrode distance to be maintained when the screen is placed under vacuum.
The front plate or anode plate is covered by a transparent conducting layer and luminophores.
The rear plate or cathode plate comprises a matrix network of field effect emitters deposited by thin film technology.
Each luminous dot (pixel) is associated with an oppositely located cathodic emitting surface and constituted of a large number of microtips (approximately 10,000 per mm.sup.2).
This emitting surface is defined by the intersection of a line (grid) and a column (cathodic conductor) of the matrix.
Subject to the introduction of a device for limiting the current in the tips, the large number of tips ensures a homogeneous emission between pixels (average effect) and eliminates the risks of local defects.
By virtue of the short tip-grid distance (.ltoreq.1 .mu.m) and the amplifying effect of the tip, a potential difference of less than 100 volts applied between line and column enables obtention, at the top of the tip, of an electric field greater than 10 to the power of 7 volts/cm, sufficient to cause the emission of electrons.
To fix the order of magnitude, a potential difference of 80 volts allows a current density of 1 mA/mm.sup.2 to be obtained. This value is sufficient in a screen of 1,000 lines, controlled sequentially line by line to obtain a high luminance (400 cd/m.sup.2) with a low voltage luminophore (400 volts) having a luminous yield of 3 lm/watt.
In light of the emission threshold (40-50 volts), the voltage which must be modulated on the columns to pass from the black level to the white level, is of the order of 30 to 40 volts.
The conventional structure of the cathode of a microtip screen especially comprises, deposited successively on a substrate of glass or silicon: either beneath or above the resistive layer,
After depositing the aforementioned layers, holes on which the microtips are then produced, are drilled into the grid and the grid insulators by known etching techniques.
SUMMARY OF THE INVENTION
The method according to the present invention leads to an improvement of the characteristics, as well as better manufacturing yields in the production of microtip-emitting cathodes for compact flat screens of the cathodoluminescence type, and allows the use of known techniques for forming components in silicon.
It consists of producing emitting cathodes from a basic monolithic silicon substrate consisting either of a thick wafer (300 microns or more) or a thin film a few microns thick, deposited on an insulating substrate (alumina or glass), the silicon film being "active" in both cases.
BRIEF DESCRIPTION OF THE DRAWINGS
In the annexed schematic drawings, provided as a non-limiting example of one of the embodiments of the object of the invention:
FIG. 1 represents the transverse section of a microtip-emitting cathode according to the invention,
and FIG. 2 is a top view of such a cathode showing a special embodiment of th
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patent: 5329207 (1994-07-01), Cathey et al.
Patent Abstracts of Japan, vol. 17, No. 22 (E 1307) (JP A 4249827) 14 Jan. 1993.
Patent Abstracts of Japan, vol. 6, No. 47 (JP A 56 160740 Dec. 1981) 10 Dec. 1981.
Patent Abstracts of Japan, vol. 16, No. 37 (JP A 3 246852 Nov. 1991) 5 Nov. 1991.
Pixel International
Ramsey Kenneth J.
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