Patent Application
20110266941
The present invention generally relates to the field of cold cathode electron tubes.
More particularly, the invention relates to a manufacturing process for a cathodoluminescent capsule including at least a tight, closable envelope, under vacuum, a cold cathode emitting electrons by field effect, an anode and a control grid, the envelope being at least formed of a first internal wall receiving the electrons.
The large conventional advertising panels (of 3 meters and more) composed of a matrix of cathode ray tubes (or CRT) are heavy, thick and need to operate with very high voltages, and those based on LEDs (or light-emitting diodes), although exhibiting high image quality, have the disadvantage of requiring a number of bulky and expensive control and cooling elements.
In this context, the present invention aims at providing, in particular, a cathodoluminescent capsule as well as its manufacturing process freed from at least one of the aforementioned limitations, making it possible to provide big sized display panels (for example more than 3 meter-sided).
In particular, the aim of the invention is to reduce the size of the electron tubes, as well as the heating thereof, and to provide a suitable, non complex manufacturing process.
In particular, the invention provides a cathodoluminescent capsule operable at low voltages (for example between 5 and 7 kV), using preferably a cold source, having preferably millimeteric dimensions and optimizing the image quality.
For example, each capsule may constitute a pixel of a visualization panel which may be made up of hundreds of thousands of such capsules, making it possible to obtain a high quality video image. Taken individually, the capsules can also be applied to lighting or back-lighting systems.
These and other objectives are achieved by the invention whose object is a manufacturing process of a cathodoluminescent capsule including at least an envelope, a cold cathode emitting electrons through field effect, an anode and a control grid, the envelope being at least made of a first internal wall for receiving the electrons and disposed facing the cathode.
The process comprises at least the steps of:
According to an embodiment, the envelope and the cap can be made from glass, and the cap can be made through at least the steps of:
For example, the assembly step comprises at least steps of:
Preferably, vacuuming the capsule is a secondary vacuuming.
Advantageously, the sealing of the cap tube is carried out by melting the external end of the cap tube over a length of few millimeters to plug the tube.
Another object of the invention is a cathodoluminescent capsule composed of at least an envelope, a cold cathode emitting electrons by field effect, an anode and a control grid, the envelope being at least formed of a first internal wall for receiving electrons emitted by the cold cathode. The capsule further comprises:
The cold cathode is for example made from at least a carbon nanotube, or from carbon fibers, or from a crystalline form carbon film.
Preferably, the control grid incorporates a getter advantageously allowing holding the capsule under vacuum.
According to an embodiment, the second internal wall of the envelope can be tubular, with a thickness at most equal to 1 millimeter, a diameter and a length ranging between 1 millimeter and 10 millimeters.
Another object of the invention is a display device comprising at least a plurality of individual display elements divided into a matrix over a substrate, and a set of control means for controlling such individual display elements, each individual display element being a cathodoluminescent capsule as described above.
These and other objects, characteristics and advantages of the invention will become more apparent from the following description of a preferred embodiment thereof, made on a non limitative basis with reference to the accompanying drawings in which:
According to a particular embodiment of the invention, cathodoluminescent capsule 1 (or cold cathode electron tube or microtube), of
Cold cathode 20 can be made up of carbon nanotubes and can have a structure as disclosed in application FR 2,857,379. The cathode can also be a metal tip such as for example nickel or tantalum or Kovar, on which carbon nanotubes (or CNT) are grown.
Control grid 40, preferably made from a metal part and having for example an annular or lattice form, makes it possible to control the electron emission by controlling the electric field in the vicinity of cathode 20. Preferably, the grid is positioned in a symmetrical way with respect to the cathode axis.
For example, envelope 10 (or bulb) made from transparent glass, such as glasses typically used for cathode ray tubes, exhibits a tubular form of for example a diameter D of 8 millimeters, a length L of 8 millimeters, and a thickness e of 1 millimeter. Envelope 10, preferably open, is for example made of a first internal wall 101 for receiving the electrons emitted by the cold cathode 20.
Cap 80, preferably made from glass, comprises for example first, second and third metal conductors respectively welded to the anode, cathode and control grid.
The capsule can further comprise:
Preferably, the luminophore 50 and reflective 60 layers are deposited on the entire surface of the first internal wall 101.
This capsule can therefore emit a constant light of red, green or blue color by phosphor excitation using electron beams generated by a carbon nanotube-based transmitter.
This cathodoluminescent capsule 1 can be made according to a particular manufacturing process, including in particular the following steps of (
A: depositing a luminophore layer 50 and a reflective layer 60 on the first internal wall 101, the luminophore layer 50 being inserted between the first internal wall 101 and the reflective layer 60. For example, the phosphorus layer may be deposited using the methods employed in manufacturing traditional cathode ray tube displays.
B: depositing a conductive layer 70 on a second internal wall 102 adjacent to the first internal wall 101, this conductive layer 70 being at least in contact with the luminophore layer 50;
The envelope made this way can be cleaned and stored properly until the final assembly.
C: preparing a cap 80 which is particularly useful for securing the passage of the various operating voltages. Cap 80 comprises at least first, second and third metal conductors 21, 31, 41 respectively welded to anode 30, cathode 20 and control grid 40. Preferably, cap 80 is obtained by pressing and melting glass around the metal conductors whose composition allows for a glass-metal sealing. Cap 80 is further provided with an opening onto which an open tube 90 is welded (preferably made from glass as well) making it possible to vacuum the capsule. All the electrodes (cathode 20, anode 30 and control grid 40) are preferably laser welded onto the connectors of cap 80 in order to maintain a determined position therebetween. Preferably, the position of the cathode connector is shifted with respect to the position of the cap tube 90.
D: assembling cap 80 with envelope 10 to form the capsule 1, the anode 30 being brought into contact with the conductive layer 70 and the cathode 20 being disposed opposed to the luminophore layer 50. For example, a portion of the glass of cap 80 and a portion of the glass of the envelope are heated to melt. These melted portions are then positioned and contacted between each other, then by rotating the cap and the envelope it is possible to mix these two melted portions. An overall cooling makes it possible to obtain a tight sealing between the cap and the envelope. The assembly must further secure a precise position of the transmitter facing the phosphors.
E: then placing the capsule on a vacuum pump via tube 90 of the cap 80. The vacuum may be a secondary vacuum (for example of about 10−8 torr).
F: when the secondary vacuum is reached, the operation of sealing (or closing) the capsule is carried out. For example, this operation is performed by melting an end of tube 90 over a length of few millimeters which, upon retraction, will plug and maintain the capsule under vacuum.
Control grid 40 can incorporate an active getter. This getter (or degasser) is a substance making it possible to maintain a good level of vacuum by absorbing the residual gases which would have otherwise remained in the capsule after sealing of the cap tube 90. In addition, the getter allows holding the level of vacuum such as after the sealing operation.
An operation of checking the efficient performance of the capsule can then be carried out. During this operation all the performance characteristics and the major operating parameters of the capsule could be adjusted.
Thus made, the cathodoluminescent capsules could be used in the production of a display device. Preferably, this display device comprises a plurality of such cathodoluminescent capsules divided into a matrix over a substrate, each capsule preferably representing an individual display element (or pixel). The substrate can further comprise a set of control means for controlling such capsules. The association of three various capsules of red, green and blue colors, will make it possible to generate a color image and to achieve a big sized display panel (for example of more than 3 meters) exhibiting high quality video image. In the case where the screen has a size higher than 5.8 meters for example, it will exhibit a definition of the VGA type (Video Graphics Array), when seen at a sufficient distance for the visual resolution to be higher with respect to the size of the capsules. The substrate could be a flexible polymer to provide the panel with high flexibility during use. These capsules could be used for producing advertising display boards, big screens for movie theaters, sporting and airport information. The size of each capsule can be optimized to ensure an optimum matrix assembly of the light points or a correct balance of the white (or gamut), for example with a larger size for the capsules emitting green light.
Preferably, the phosphors are designed to operate under low voltages (preferably less than 10 Kv). The power supply of the capsule could be made using a voltage between 2 to 5 Kv to provide a current of at least 100 μA to energize the phosphors.
For instance, the electronic characteristics of this capsule can be:
The beam thus generated makes it possible to provide via the phosphors a light intensity higher than 500 cd/m2.
Advantageously, the electron beam emitted from the cathode towards the wall forms an angle α preferably between 10 and 20 degrees, for example 15 degrees.
These characteristics can also permit sizing the cathode, the control grid, as well as the distances between the cathode, the control grid and the phosphor layer.
Advantageously, the dimensions of the capsule can be as follows:
For example, the cap connectors 21, 31, 41 can be positioned on a diameter from 3 to 4 mm and be located respectively at 0°, 90° and 180° from the axis X of the capsule.
The distance from the cathode connector 21 with respect to tube 90 ranges for example between 0.5 and 1 mm.
For example, the thicknesses of the luminophore, reflective and conductive layers 50, 60, 70 are respectively of 0.2 mm, 0.2 mm and 0.3 mm.
For example, the getter is made from porous barium metal and can be laser welded onto one of the walls of grid 40 in the shade of the electron beam path.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0856984 | Oct 2008 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/FR09/51683 | 9/7/2009 | WO | 00 | 5/26/2011 |
