Electric lamp or space discharge component or device manufacturi – Process – With assembly or disassembly
Reexamination Certificate
2000-02-18
2001-04-03
Ramsey, Kenneth J. (Department: 2879)
Electric lamp or space discharge component or device manufacturi
Process
With assembly or disassembly
C445S050000
Reexamination Certificate
active
06210246
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention involves a process for manufacturing a micropoint electron source with an auto-aligned focussing grid. Such a micropoint electron source can be used in particular in a device for visualisation by cathodoluminescence excited by field emission.
2. Discussion of the Background
Documents FR-A-2 593 953 and FR-A-2 623 013 disclose devices for visualisation by cathodoluminescence excited by field emission. These devices include a emitting cathode electron source with micropoint.
By way of illustration,
FIG. 1
is a cross section view of such a micropoint viewing screen. In the interest of simplification, only a few aligned micropoints are shown. The screen is composed of a cathode
1
, which is a plane structure, oriented with respect to another plane structure which forms the anode
2
. The cathode
1
and the anode
2
are separated by a space in which a vacuum has been created. The cathode
1
includes a glass substrate
11
on which the conducting level
12
has been applied in contact with the electron emitting points
13
. The conducting level
12
is covered with a layer of insulation
14
, made of silica for example, which is itself covered by a conducting layer
15
. Holes
18
of about 1.3 •m in diameter were made through the layers
14
and
15
up to the conducting level
12
to apply the points
13
on this conducting level. The conducting layer
15
acts as an extraction grid for the electrons which will be emitted by the points
13
. The anode
2
includes a transparent substrate
21
covered by a transparent electrode
22
on which luminescent phosphors or luminophores
23
have been deposited.
The operation of this screen will now be described. The anode
2
is brought to a positive voltage of several hundred volts with respect to the points
13
(typically 200 to 500 V). A positive voltage of several dozens of volts (typically 60 to 100 V) with respect to the points
13
is applied to the extraction grid
15
. Electrons are then drawn from the points
13
and are attracted by the anode
2
. The trajectories of the electrons are within a half-angle cone at the peak •, depending on various factors such as the shape of the points
13
. This angle causes a defocusing of the electron beam
31
which increases as the distance between the anode and the cathode is increased. One way to increase the yield of the phosphors, and thus the luminosity of the screens, is to work with higher anode-cathode voltages (between 1,000 and 10,000 V), which implies separating the anode and the cathode further in order to avoid the formation of an electric arc between these two electrodes.
If good resolution on the anode is desired, the electron beam must be refocused. This refocusing is classically obtained with a grid which can either be placed between the anode and the cathode or placed on the cathode.
FIG. 2
illustrates the case where the focussing grid is placed on the cathode.
FIG. 2
repeats the example of
FIG. 1
, but limited to a single micropoint for greater clarity in the drawing. An insulating layer
16
was applied to the extraction grid
15
and bears a metallic layer
17
which acts as a focussing grid. Holes
19
of an appropriate diameter (typically between 8 and 10 •m) and concentric to holes
18
, were etched in layers
16
and
17
. The insulating layer
16
electrically insulates the extraction grid
15
and the focussing grid
17
. The focussing grid is polarised with respect to the cathode in order to give the electron beam the shape shown in FIG.
2
.
Simulation calculations show that centering of the holes
19
of the focussing grid with respect to the holes
18
of the extraction grid is extremely important. This structure is generally made using the classic photoetching techniques used in microelectronics. For example, with a first level of photoetching, the holes
19
of the focussing grid are defined, then a second level of photoetching is used to make holes
18
in which the points will be placed. To ensure proper functioning, the second level must be positioned in an extremely precise manner with respect to the first level. This can only be done with very high-quality, expensive equipment, a serious drawback if large areas are treated. In addition, if the holes of the extraction grid are made by photolithography from a microsphere network, their arrangement is random, which rules out the use of a phototemplate for making the apertures of the focussing grid.
SUMMARY OF THE INVENTION
The invention solves the problem of precision alignment of holes located on different levels. This is achieved by a process which requires only a single photolithography step which makes the holes in the extraction grid.
The purpose of the invention is thus the making of a micropoint electron source with an extraction grid and a focussing grid involving:
the successive depositing on one side of an electrically insulating support of means of cathodic connection, a first insulating layer of thickness adapted to the height of the future micropoints, a first conducting layer to form the extraction grid, a second insulating layer of thickness corresponding to the distance which must separate the extraction grid from the focusing grid, a second conducting layer to form the focusing grid and a photosensitive resin layer;
the etching, by photolithography, of the photosensitive resin layer to make holes in it which exit on the second conducting layer and of which the axes correspond to the axes of the future micropoints and of which the diameter is adapted to the size of the future micropoints, these holes permitting etching of the other layers deposited on the support;
the etching of the second conducting layer to make holes in it which exit at the second insulating layer;
the etching of the second insulating layer to make cavities in it which are to be extended laterally up to a dimension corresponding to the apertures of the focussing grid and which reveal the first conducting layer;
etching of the first conducting layer to make holes in it for the extraction grid;
etching of holes in the first insulating layer until they reach the means of cathodic connection in order to make housings for the micropoints;
enlargement by etching of the holes of the second conducting layer to obtain apertures for the focusing grid;
elimination of the photosensitive resin layer remaining after the etching operations;
formation of micropoints in their housings on the means of cathodic connection.
The means of cathodic connection are preferably made by depositing cathodic conductors on the support, followed by depositing of a resistant layer.
A first way of etching the second insulating layer would be as follows:
the second insulating layer is first etched to obtain the holes in the prolongation of the holes of the photosensitive resin layer which come out on the first conducting layer;
the first conducting layer is then etched tof obtain the blind holes in the prolongation of the holes of the photosensitive resin layer, these blind holes constituting the beginnings of the holes of the extraction grid;
lastly, the second insulating layer is etched until the aforesaid cavities are obtained.
The etching of the holes in the first insulating layer can first be done anisotropically, the aforesaid housings then being defined by isotropic etching.
A second way of etching the second insulating layer is as follows. Since the first and second insulating layers can be etched simultaneously, the etching of the second insulating layer is first done isotropically to mark the places for the cavities, to reach the first conducting layer, revealing the zones allowing for making holes for the extraction grid, the holes of the extraction grid then being etched in the first conducting layer, an isotropic etching being lastly done to simultaneously obtain the aforesaid housings in the first insulating layer and the aforesaid cavities of the aforesaid dimension in the second insulating layer.
REFERENCES:
patent: 5136764 (1992-08-01), Vasque
Blanc Regis
Montmayeul Brigitte
Perrin Aime
Commissariat A l'Energie Atomique
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ramsey Kenneth J.
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