Electric lamp and discharge devices – With luminescent solid or liquid material – Vacuum-type tube
Reexamination Certificate
1999-09-14
2001-07-17
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Vacuum-type tube
C313S309000
Reexamination Certificate
active
06262529
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The object of the present invention is a display screen without moire effect. It finds an application in the production of any display devices, notably with micropoints, also referred to as the field emission display type (or FED for short).
“Without” moire effect means a moire effect which is sufficiently attenuated so as not to be visible to an observer.
2. Discussion of the Background
Although the invention is not limited to this type of display, it is in the case of field emission display screens that the state of the art will be described.
A field emission display screen is described notably in the document FR 2 623 013. The essentials of this device are depicted in the accompanying
FIGS. 1 and 2
.
The device depicted in these figures comprises, on a substrate
2
, for example made of glass, a thin layer of silica
4
and, on this layer, a plurality of electrodes
5
in the form of parallel conductive bands fulfilling the role of cathodic conductors and constituting addressing columns.
These cathodic conductors are covered with a continuous resistive layer
7
(except on the ends to allow the connection of the cathodic conductors with biasing means
20
). An electrically insulating layer
8
, made of silica, covers the resistive layer
7
.
Above the insulating layer
8
there are formed a plurality of electrodes
10
also in the form of parallel conductive bands. These electrodes
10
are perpendicular to the electrodes
5
and fulfill the role of a grid constituting the addressing lines.
The device also has a plurality of elementary emitters of electrons (micropoints), only one example of which (for reasons of simplification) is depicted schematically in FIG.
2
: in each of the intersection areas (corresponding to an image point or pixel) cathodic conductors
5
and grids
10
, the resistive layer
7
corresponding to this area supports micropoints
12
, for example made of molybdenum, and the grid
10
corresponding to the said area has an opening
14
opposite each of the micropoints
12
. Each of the latter adopts substantially the shape of a cone whose base rests generally on the layer
7
and whose apex is situated level with the corresponding opening
14
. Naturally, the insulating layer
8
is also provided with openings
15
allowing passage of the micropoints
12
.
This first subassembly defined by the area of intersection of the cathodic conductors and grid conductors
10
, possibly associated with other elements, for example a supplementary grid within the screen or a filter on the face of the screen observed, can be referred to as an “intermediate subassembly”.
Thus each intermediate subassembly corresponds to a pixel. Opposite this intermediate subassembly, there is a substrate
30
covered with a conductive layer
32
serving as an anode. This layer is covered with a layer or bands of luminescent materials
34
. Hereinafter the emissive part opposite the pixel (or intermediate subassembly) will be referred to as the “anode subassembly”.
In the case of a monochrome screen, or an unswitched three-color screen, the size of the anode subassembly corresponds to that of the intermediate subassembly. In the case of a switched three-color screen, the pixel is opposite three bands of luminescent materials, only one of which emits at a time, and the anode subassembly corresponds to the excited band part.
The light emitted by the luminous materials under the impact of the electrons emitted by the micropoints is received by the observer
0
. In the usual case, the observation takes place on the anode side, and therefore through the anode subassembly, on the side opposite the excitation of the luminescent materials. However, the major part of the light being emitted on the excitation side, the result is that it is highly advantageous to observe this screen on the excitation side of the luminescent materials, and therefore through the intermediate subassembly which, because of this, must be at least partially transparent. This operating mode is all the more advantageous since the entire quantity of light emitted can be reflected towards the intermediate subassembly by the use of a reflective layer disposed behind the luminescent materials (this layer can be the anode itself or a supplementary layer, for example of aluminium). In addition, as the intermediate subassembly is partially transparent, it fulfills the role of a neutral filter and thus reduces the effects related to diffuse reflection, in the case notably where the luminescent materials are powder luminophores.
The intermediate subassembly defined by the intersection of an addressing row and column can take various forms. In one embodiment described in the document FR-A-2 687 839, the cathodic conductors have a lattice structure and the grid conductors a perforated structure. This embodiment is illustrated in
FIGS. 3A and 3B
, which are respectively plan and cross-sectional views.
In these figures, the cathodic conductors bear the reference
5
a
and the grid conductors the reference
10
g.
The grids have openings
11
opposite the areas of intersection of the conductive tracks
5
a
and are centered on these areas, as can be seen in FIG.
3
A. Naturally, the grids also have holes
14
a
respectively opposite the micropoints
12
.
More precisely, each grid
10
g
has substantially the structure of a lattice identical to the lattice of the corresponding cathodic conductor, but the lattice of this grid is offset, with respect to the lattice of the cathodic conductor, by a half-pitch parallel to the addressing rows and a half-pitch parallel to the addressing columns. Above an area where micropoints are collected, this grid has, in plan view, a square surface
10
a
which has holes
14
a
in it and at which there end four tracks
10
b
forming part of the lattice of this grid.
Many other embodiments are possible, but it will be understood that the intermediate subassembly, through which the observation is effected, though it is semi-transparent overall, is, in reality, formed by highly diverse areas if it is examined on a small scale. Each pixel defined by the overlapping of an addressing row and column therefore comprises a central area (which will be referred to as the “pupil” of the pixel) and four lateral half-parts. The four lateral parts separate each area from its four neighbours. Each pixel therefore has an optical transmission which is not uniform.
FIG. 4
shows the appearance of such a pixel, where the central part
40
can be discerned, with its repetitive subassemblies corresponding to the meshing of the grid conductor and of the cathode conductor, and the lateral parts
42
a,
42
b,
42
c,
42
d.
This complex periodic structure of the intermediate subassembly, superimposed on the structure, also periodic, of the anode subassembly (in terms of emission as previously defined) can lead to display defects due to moire effects. These defects are illustrated in
FIGS. 5
a
and
5
b,
on the one hand, and in
FIG. 6
on the other hand.
FIGS. 5A and 5B
, first of all, correspond to the case where the intermediate subassembly and the anode subassembly are not strictly aligned. This appears when there are several bands of luminescent materials (three-color screen, switched or otherwise). It is assumed that the columns of luminescent materials disposed on the anode are not strictly parallel to the addressing columns of the intermediate subassembly.
FIGS. 5A and 5B
are sections along a plane perpendicular to the columns, at two different points on the screen (for example at the top and at the bottom).
In these two figures, the intermediate subassembly bears the general reference
50
and is depicted schematically with regions
52
corresponding to the central part of the pixels, relatively transparent areas, and half-regions
54
corresponding to the lateral half-areas, less transparent; the anode subassembly is depicted in the form of the emissive luminous band
62
.
FIGS. 5A and 5B
depict, by way of example, the case of a three-color screen, switched
Rommeveaux Philippe
Semeria Marie-Noelle
Commissariat A l'Energie Atomique
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Patel Vip
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