Electric lamp and discharge devices – Cathode ray tube – Beam deflecting means
Reexamination Certificate
1998-11-23
2001-01-30
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Beam deflecting means
C313S495000, C313S431000, C345S019000
Reexamination Certificate
active
06181059
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an area cathode suitable for use in a flat panel display and more particularly to an area cathode in which electrons are confined in magnetic channels and extracted by low voltage electrostatic fields and which uses a conventional CRT cathode as a source of electrons.
BACKGROUND OF THE INVENTION
An area cathode of the present invention is particularly although not exclusively useful in display applications, especially flat panel display applications. Such applications include television receivers and visual display units for computers, especially although not exclusively portable computers, personal organisers, communications equipment, and the like.
All flat panel CRT technologies require an area cathode, that is a uniform planar source of electrons the same area as the display. There have been many designs developed over the years, based on technologies such as Field Emission Devices (FEDs), Metal-Insulator-Metal devices (MIMs) and the like. Probably the most successful types have been the virtual thermionic cathode from Source Technology, disclosed in European Patent Application 0 213 839, and the secondary emission channel hopping cathode developed by Philips for their Zeus display. All current designs, however, suffer from significant disadvantages of one sort or another. In particular the virtual thermionic type has high power and hence a major heat dissipation problem, and the channel hopping type has high and non uniform channel extraction voltages.
U.S. Pat. No. 5,227,691 discloses a flat tube display apparatus in which a row of many electron beam generators is arranged transversely in a thin flat vacuum tube body to generate a number of beams in parallel with each other which travel in parallel with an image screen and in which the electron beam generators are arranged to deflect the beams toward the image screen at a predetermined position. The beams are guided without being widely diverged due to the provision of a number of side walls arranged in parallel with each other to confine the beams and due to the provision of alternately strong and weak magnetic fields along the side walls forming periodic magnetic lenses. The electron beams are deflected electrostatically or using a magnetic field towards an electron beam multiplier and a phosphor screen.
It would be desirable to produce an area cathode that has:
1. An electron source based on known materials;
2. Generation of electrons at a low eV (hence low extraction voltages);
3. A narrow eV spread (hence low beam spreading);
4. A high degree of uniformity;
5. Low power and heat;
6. Isolation from external electric and magnetic fields;
7. Protection of the electron source from ion bombardment; and
8. Mechanical simplicity leading to low cost.
SUMMARY OF THE INVENTION
Accordingly, the invention provides an electron source comprising a first permanent magnet having a first channel, extending between first and second poles of the magnet, the internal surfaces of the first channel being conductive, a cathode means located in the first channel at a first pole of the magnet, a potential being applied between the cathode means and the conductive internal surfaces of the first channel causing electrons to be received into the first channel, and a plurality of apertures located on a wall of the first channel, the wall abutting a second permanent magnet having a plurality of second channels extending between first and second poles of the second magnet, the second pole of the second magnet being adjacent to the apertures located on said wall of the first magnet, such that electrons received into the first channel are distributed into the plurality of second channels. This arrangement has the advantage that a single conventional CRT cathode can be used as an electron source to generate a single electron beam, which is then split so that substantially similar proportions of the beam are directed into closed channels formed in a flat magnet.
Preferably, regions of the internal conducting surfaces of the first channel are isolated, the isolated regions having voltages applied to them to create electrostatic lenses for the purpose of directing the electrons at junctions between the first channel and the plurality of second channels. The use of electrostatic lenses for directing the electrons at junctions reduces the loss of electrons to the conducting walls of the channels. Some of the electrons would otherwise tend to be attracted to the walls because some of the lines of magnetic flux along which the electrons travel are angled and meet the walls of the channel.
In a preferred embodiment, the internal surfaces of each of the second channels are conductive, each of the second channels having a plurality of perforations located on the first surface of the second magnet, the surface extending between opposite poles of the magnet, wherein each perforation forms electrons received from the cathode means into an electron beam for guidance towards a target. The electrons which are formed into a beam in the first channel are split into a plurality of beams in the second channels and each of those beams is then split into a plurality of beams exiting through each of the perforations, to form a grid of electrons beams, which may be individually controlled as is known in the art. Thus the invention provides such a grid array of electron beams from a single conventional cathode source.
In a further embodiment, the electron source further comprises a third permanent magnet having a third channel, extending between first and second poles of the magnet, the internal surfaces of the third channel being conductive and a plurality of apertures located on a wall of the third channel, the wall abutting the second magnet, the first pole of the second magnet being adjacent to the apertures located on said wall of the third magnet. The third permanent magnet provides a balancing channel, which helps to linearize the magnetic field lines in the plurality of second channels such that they are not angled towards the walls. This substantially prevents the electrons being deflected into the walls by angled lines of flux.
Optionally, the electron source further comprising a cathode means located in the third channel at a second pole of the third magnet, a potential being applied between the cathode means and the conductive internal surfaces of the third channel causing electrons to be received into the third channel. Such a configuration provides a higher beam current availability.
Preferably, the second channels are arranged at a pitch corresponding to the pixel pitch of a display incorporating the electron source. This provides a single source of electrons for each of the pixels of a display incorporating the electron source.
Preferably, each second channel has a constant cross-section along its length.
In a preferred embodiment, the second magnet comprises a first magnetic plate having grooves, extending between opposite poles of the magnet, along a first surface of the first magnetic plate, and a second magnetic plate having a plurality of perforations, said second plate being located so as to close the grooves to form the plurality of second channels, the second channels having perforations located on a surface extending between opposite poles of the second magnet. Manufacture of the second magnet in two parts enables standard mass production processes to be used for the forming of the grooved plate and for the provision of the thin conducting coatings on the internal surfaces of the closed channels.
Preferably, the first magnetic plate is at least twice as thick as the channel depth. This has the advantage that the flux density is increased within the channel, so increasing the isolation from external fields. This also has the advantage that null field points and non-linearities present in the channel are moved into the perforations. This provides an essentially linear field in the channels, with no field reversals.
Preferably, each channel has a depth greater than the width of the chan
Guharay Karrabi
International Business Machines - Corporation
Patel Nimeshkumar D.
Shofi David M.
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