Electric lamp and discharge devices – With luminescent solid or liquid material – Vacuum-type tube
Reexamination Certificate
2000-05-08
2003-03-18
Day, Michael H. (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Vacuum-type tube
C313S306000, C313S309000, C445S051000
Reexamination Certificate
active
06534913
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a microtip, focusing gate and high microtip density electron source. It also relates to a flat screen using such a source.
2. Discussion of the Background
The documents FR-A-2 593 953 and FR-A-2 623 013 describe field emission-excited cathodoluminescence display devices. These devices comprise a microtip emitting cathode electron source.
As an illustration,
FIG. 1
is a transversal section view of such a microtip display screen. For simplification purposes, only a few aligned microtips have been represented. The screen is composed of a cathode
1
, which is a plane structure, positioned opposite another plane structure forming the anode
2
. The cathode
1
and the anode
2
are separated by a space in which a vacuum is produced. The cathode
1
comprises a glass substrate
11
on which the conductive level
12
in contact with the electron emitting tips
13
is deposited. The conductive level
12
is coated with an insulating layer
14
, e.g. silica, which is itself coated with a conductive layer
15
. Holes
18
, approximately 1.3 &mgr;m in diameter, have been produced through the layers
14
and
15
up to the conductive level
12
to deposit the tips
13
on said conductive level. The conductive layer
15
is used as an extraction gate for the electrons emitted by the tips
13
. The anode
2
comprises a transparent substrate
21
coated with a transparent electrode
22
on which luminescent phosphors or luminophors
23
are deposited.
The operation of this screen is described below. The anode
2
is brought to a positive voltage of several hundred volts with reference to the tips
13
(typically 200 to 500 V). On the extraction gate
15
, a positive voltage of several tens of volts (typically 60 to 100V) with reference to the tips
13
is applied. Electrons are then extracted at the tips
13
and are attracted by the anode
2
. The electrons' paths are comprised in a top half-angle cone &thgr; depending on different parameters, including the shape of the tips
13
. This angle induces a defocusing of electron beam
31
which increases with the distance between the anode and the cathode. However, one of the ways to increase the efficiency of phosphors, and therefore the screen brightness, is to work with higher anode-cathode voltages (between 1000 and 10,000 V), which implies increasing the distance between the anode and the cathode further to prevent the formation of an electric arc between the two electrodes.
In order to retain a good resolution on the anode, the electron beam must be refocused. This refocusing is obtained conventionally using a gate that can be placed between the anode and the cathode or positioned on the cathode.
FIG. 2
illustrates the case in which the focusing gate is positioned on the cathode.
FIG. 2
takes the same example as
FIG. 1
but limited to a single microtip for more clarity in the drawing. An insulating layer
16
has been deposited on the extraction gate
15
and supports a metal layer
17
used as a focusing gate. Holes
19
, of suitable diameter (typically between 8 and 10 mm) and concentric with the holes
18
, have been engraved in the layers
16
and
17
. The insulating layer
16
is used to insulate the extraction gate
15
and the focusing gate
17
electrically. The focusing gate is polarised with reference to the cathode so as to give the electron beam
32
the form represented in FIG.
2
.
In the case of a microtip screen without a focusing gate, such as that shown in
FIG. 1
, the distance between two adjacent microtips is of the order of 3 &mgr;m. For a microtip screen with a focusing gate, as represented in
FIG. 2
, this distance is of the order of 10 to 12 &mgr;m. In this case, the microtip density, i.e. the electron emitter density, is between 9 and 16 times lower. This results in a decrease in screen brightness.
In a flat screen, the luminophors are deposited on the anode in the form of parallel bands, which are successively red-green-blue, etc. For a good restored image quality, the colours must not be mixed. For this, all the electrons emitted by a pixel of a given colour must go to the corresponding luminophor and not to the adjacent luminophors. This result is obtained by the focusing phenomenon. Given the band structure of the luminophors, it is important that the focusing is carried out in the direction perpendicular to these bands to prevent mixing of colours.
SUMMARY OF THE INVENTION
The invention makes it possible to remedy the problem of low microtip density posed by prior art focusing gate electron sources. This is obtained by replacing the circular apertures of the focusing gate by slits.
The invention proves to be particularly effective when applied to flat screens in which the luminophors are arranged in bands. It is proposed to etch, in the focusing gate, apertures in the form of slits, with the microtips aligned on the axes of these slits. By arranging the luminophors located on the anode in the form of bands parallel to the electron source slits and just above the corresponding slits, the electrons emitted by the microtips of these slits remain concentrated on the luminophor band facing them. Therefore, there will be no mixing of colours. If the focusing is not obtained in the direction of the bands, a slight spreading of the pixel in this direction is produced, which has a relatively insignificant effect on the image quality.
Therefore, the focusing gate according to the present invention performs a focusing function in a single direction.
Therefore, the invention relates to a microtip electron source comprising:
at least one electron emission zone composed of a plurality of microtips connected electrically to a cathode conductor,
at least one gate electrode, positioned opposite said electron emission zone and pierced with apertures located opposite the microtips, to extract the electrons from the microtips,
an emitted electron focusing gate positioned opposite the gate electrode, and equipped with aperture means comprising at least one slit located opposite at least two successive microtips,
characterised in that the focusing gate is separated from the extraction gate electrode positioned opposite it by a layer of electrically insulating material with a slit aligned with the focusing gate slit, or a succession of holes aligned with the focusing gate slit, of a width less than that of the focusing gate slit.
According to an advantageous arrangement, the microtip electron source may comprise a plurality of electron emission zones arranged in the form of a matrix in rows and columns, with the number of cathode conductors and gate electrodes corresponding to the rows and columns to give the microtip electron source a matric access.
If each emission zone comprises several rows of microtips, each row of microtips has one or more corresponding slits in the focusing gate.
The invention also relates to a device comprising a first and second plane structure maintained opposite and at a determined distance from each other by means forming a spacer, the first plane structure comprising, on its inner device face, a microtip electron source such as that defined above, and the second plane structure comprising, on its inner device face, means forming the anode.
Such a device may be used to form a flat display screen, with luminophors placed between the microtip electron source and the means forming the anode.
The invention also relates to a flat display screen comprising a first and second plane structure maintained opposite and at a determined distance from each other by means forming a spacer, the first plane structure comprising, on its inner screen face, a microtip electron source such as that defined above, in which each emission zone comprises several rows of microtips and each row of microtips has one or more corresponding slits in the focusing gate, and the second plane structure comprising, on its inner screen face, means forming the anode, a conductive layer forming the anode and supporting luminophors arranged i
Meyer Robert
Montmayeul Brigitte
Perrin Aime
Commissariat a l'Energie Atomique
Day Michael H.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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