Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
  • H01J29/02—Electrodes; Screens; Mounting, supporting, spacing or insulating thereof
  • H01J29/10—Screens on or from which an image or pattern is formed, picked up, converted or stored
  • H01J29/18—Luminescent screens
  • H01J29/30—Luminescent screens with luminescent material discontinuously arranged, e.g. in dots, in lines
  • H01J29/32—Luminescent screens with luminescent material discontinuously arranged, e.g. in dots, in lines with adjacent dots or lines of different luminescent material, e.g. for colour television
  • H01J29/325—Luminescent screens with luminescent material discontinuously arranged, e.g. in dots, in lines with adjacent dots or lines of different luminescent material, e.g. for colour television with adjacent lines
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
  • H01J29/02—Electrodes; Screens; Mounting, supporting, spacing or insulating thereof
  • H01J29/10—Screens on or from which an image or pattern is formed, picked up, converted or stored
  • H01J29/18—Luminescent screens
  • H01J29/24—Supports for luminescent material
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
  • H01J29/02—Electrodes; Screens; Mounting, supporting, spacing or insulating thereof
  • H01J29/10—Screens on or from which an image or pattern is formed, picked up, converted or stored
  • H01J29/18—Luminescent screens
  • H01J29/34—Luminescent screens provided with permanent marks or references
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N9/00—Details of colour television systems
  • H04N9/12—Picture reproducers
  • H04N9/16—Picture reproducers using cathode ray tubes
  • H04N9/22—Picture reproducers using cathode ray tubes using the same beam for more than one primary colour information
  • H04N9/24—Picture reproducers using cathode ray tubes using the same beam for more than one primary colour information using means, integral with, or external to, the tube, for producing signal indicating instantaneous beam position

Definitions

• the invention relates to the manufacture of so-called beam indexing electronic tube screens.
• Color image viewing tubes are particularly concerned.
• An electronic display tube includes a display screen on which phosphors (in English "phosphors") are deposited which have the property of emitting light when struck by an electron beam, the light intensity being all the more important that the intensity of the beam is important.
• the emission color of the phosphor depends on the material from which it is made. In general, triads of phosphors are used, comprising a red phosphor, a green and a blue.
• An electron gun emits a beam of electrons which scans the surface of the screen and which is modulated in intensity by a video signal so that each point on the screen lights up with a desired intensity.
• the screen is subdivided into image points which are defined by zones of phosphors placed at these points. These areas of imaging phosphors can be distributed in several ways. In beam indexing tubes, the elementary zones are normally parallel strips of phosphors each extending over the entire height of the screen perpendicular to the scanning lines of the electron beam. The phosphor strips are separated from each other by opaque areas. This is what makes it possible to differentiate colors and maintain their purity when luminophores emitting in different colors are juxtaposed on the screen.
• Beam indexing tubes are tubes in which the electron beam passes during its scanning over indexing bands which are bands of phosphors which do not participate in the formation of the image; these phosphors only emit light (usually ultraviolet) to a detector which thus locates the passage of the beam at well determined points so that one can know at any time where the beam is and define accordingly the video signal to be applied.
• the beam indexing tubes are used in particular for producing a color display with a single electron gun.
• Figure 1 shows the simplest construction of a beam indexing viewing tube.
• the envelope 10 of the tube the electron gun 12, the display screen 14 which is a flat glass plate covered with a layer of phosphors 16 (bands of phosphors of alternating colors separated by opaque bands 17 ).
• the phosphor layer is covered with a layer of aluminum 18 which has several functions, including the application of a high voltage to accelerate the electron beam, the evacuation of the charges which accumulate in the phosphors , the return to the observer of the light which can be emitted towards the interior of the tube by the phosphors.
• the aluminum layer 18 also has a function of supporting the beam indexing bands 20.
• These bands are bands of phosphors preferably emitting in the ultraviolet and distributed with a pitch which is linked that of the strips of phosphors; one can have for example an indexing band every two or three or four bands of phosphors.
• the indexing strips are carried by the reflective layer of aluminum, they emit only towards the inside of the tube.
• the inner surface of the envelope 10 is preferably covered with a reflective layer, with the exception of transparent zones allowing the exit of the light coming from the indexing strips. Behind these zones are placed detectors 22 which thus collect as large a proportion as possible of the radiation emitted by the indexing strips. It should be mentioned here that the amplitude of this radiation is very low because the intensity of the electron beam is quite low when it passes over the indexing phosphors.
• the indexing bands cannot be wider than the opaque bands 17 because they must not mask the bands of image-forming phosphors 16.
• the indexing bands are defined by photolithography on an aluminum surface that is both reflective and highly diffusing, which harms the quality of photolithography and requires very large safety margins. This results in either too narrow indexing phosphor bands providing too weak light pulses, or an overall resolution deteriorated if the width of the opaque bands 17 and of the indexing bands is increased.
• One of the aims of the invention is to improve the detection of the indexing signal so as not to be hampered by these limitations.
• Beam indexing tubes have already been proposed in which the indexing bands are arranged next to the bands of image-forming phosphors, under the aluminum film and not on this film.
• the indexing phosphors therefore emit towards the observer.
• the advantage is that you can have wider indexing bands (the same width as the imaging phosphor bands) without losing much on the resolution.
• the detected indexing signal is more important.
• Figure 2 shows this structure.
• the indexing signal detectors must be placed in front of the screen, on the side of the observer, and even strongly in front to receive the indexing signals emitted from all points in a homogeneous manner. of the screen.
• the size of the viewing tube can become very large.
• Another drawback is the low photodetection efficiency resulting from the distance of the detectors: in the case where the detectors are placed in front of the screen, there are no reflectors which bring most of the emitted radiation back to the detectors ( whereas in the case of FIG. 1, the interior of the envelope can be metallized to recover a large proportion of the light emitted).
• An object of the invention is to avoid the drawbacks of the devices of the prior art. We seek in particular to reduce the overall size of the tube, to improve the collection efficiency of the indexing signal, to keep a simple technology, a good spatial resolution of the image, even for very small screens.
• the invention provides an electron tube with beam indexing, comprising luminophore zones for forming light images, deposited on a transparent substrate, and separated from one another by opaque zones also deposited on the screen, characterized in that the substrate is cathodoluminescent.
• certain areas of the substrate, in a useful image-forming region, will not be covered either by phosphors or by the opaque layer, the electron beam of the electron gun therefore being able to directly illuminate the substrate at these places .
• the substrate will then emit radiation constituting an indexing signal at the time of the passage of the beam at these locations.
• one or more detectors will be placed at the periphery of the substrate to perform a collection of light radiation by the edge of the substrate.
• the material constituting the transparent substrate will preferably be a monocrystalline material doped with a substance which makes it cathodoluminescent.
• This substance can be cerium, which has the property of having a very rapid reaction time, which is very important for the establishment of an indexing signal.
• the material can be a garnet (yttrium aluminum aluminate for example or yttrium alumino-gallate) doped with cerium.
• the edge of the substrate should preferably be polished and coated with a reflective substance, except where the detector will be placed. About 85% of the light rays emitted by the substrate will be trapped between the polished faces of the substrate and will be recovered by the detector (s), as a result of the phenomena of total reflection that occur inside a monocrystalline screen, and this d 'especially since its optical refractive index is higher compared to that of air.
• FIG. 3 shows a section of the screen of a tube according to the invention
• FIG. 4 shows a front view of the screen showing the lateral position of the detectors.
• the screen is formed at the base by a slab of monocrystalline cathodoluminescent material 14. It is for example a garnet (yttrium aluminate (Y perennialA1_.0 ... intuition) doped with cerium (cerium acting as a cathodoluminescent dopant with a very fast reaction time).
• the aluminum can be partially replaced by gallium to form an yttrium alumino gallate Y-, (A1, Ga) r .0 1 classroom.
• Other materials can be envisaged, provided that they can be produced in an essentially monocrystalline manner and that they are cathodoluminescent or can be doped with a substance which makes them cathodoluminescent.
• a criterion to be taken into account is also the adaptation of their coefficient of thermal expansion with the material (in principle glass) of the envelope of the tube.
• the slab 14 is polished on all its faces; its edge is covered with a reflective substance 24 (which may be aluminum) with the exception of the locations where the light radiation emitted by the substrate must exit. At these locations detectors 22 are placed which will provide the indexing signal.
• Figure 4 shows how one can for example place two detectors 22, respectively on each side of the screen, all the rest of the edge of the monocrystalline panel 14 being covered with aluminum 24.
• the fact that the detectors are placed in the plan of the slab minimizes the bulk of the tube, especially in the direction of the length, which is important.
• the monocrystalline daEe 14 is first covered with opaque bands 17 intended to separate the phosphors 16 used for image formation.
• the opaque bands 17 are for example made of chrome; they are deposited by vacuum evaporation and photo-etched.
• the phosphors of a color are then deposited and engraved; then those of the second color and the third color are successively deposited and engraved.
• the phosphors are conventionally covered with the aluminum layer 18 used for the application of high voltage, for the evacuation of electrical charges, and for the reflection of light from the phosphors towards the observer.
• the electron beam from the electron gun scans the surface of the screen and passes through the thin layer of aluminum 18. When it encounters a phosphor, it emits in proportion to the modulation applied to the electron beam at this instant. When the beam meets a free band I, it strikes the cathodoluminescent substrate 14 which emits a pulse of light.
• the transparent planar slab may be entirely made of cathodoluminescent material or be formed of a transparent substrate covered with a cathodoluminescent monocrystalline layer.
• the invention can be used even if the cathodoluminescent substrate emits in a visible color, which is not the case in the tubes of the type of FIG. 2.
• the light emitted by the substrate is at low dose and relatively uniform over the entire surface of the screen, and most of it is trapped and does not come out towards the observer.
• all the light from the indexing bands exits towards the observer and it is therefore imperative to have indexing bands emitting non-visible light (ultra violet).

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• Engineering & Computer Science (AREA)
• Multimedia (AREA)
• Signal Processing (AREA)
• Measurement Of Radiation (AREA)
• Luminescent Compositions (AREA)
• Cathode-Ray Tubes And Fluorescent Screens For Display (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=9381817

Family Applications (1)

Country Status (3)

Family Cites Families (2)

• 1989
  • 1989-05-19 FR FR8906573A patent/FR2647261B1/fr not_active Expired
• 1990
  • 1990-05-17 WO PCT/FR1990/000348 patent/WO1990014679A1/fr not_active Ceased
  • 1990-05-17 EP EP19900908536 patent/EP0425653A1/fr not_active Ceased

Non-Patent Citations (1)

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