Electric lamp and discharge devices – Cathode ray tube – Beam deflecting means
Reexamination Certificate
1998-05-11
2001-01-23
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Beam deflecting means
C313S431000, C313S495000, C313S496000, C313S497000
Reexamination Certificate
active
06177759
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a magnetic matrix display device and more particularly to spacers, supports, grid and anode electrodes for use in such a display.
BACKGROUND OF INVENTION
A magnetic matrix display of the present invention is particularly although not exclusively useful in flat panel display applications such as television receivers and visual display units for computers, especially although not exclusively portable computers, personal organizers, communications equipment, and the like.
Conventional flat panel displays, such as liquid crystal display panels and field emission displays, are complicated to manufacture because they each involve a relatively high level of semiconductor fabrication, delicate materials, and high tolerances.
GB Patent Application 2304981 discloses a magnetic matrix display having a cathode for emitting electrons, a permanent magnet with a two dimensional array of channels extending between opposite poles of the magnet, the direction of magnetisation being from the surface facing the cathode to the opposing surface. The magnet generates, in each channel, a magnetic field for forming electrons from the cathode means into an electron beam. The display also has a screen for receiving an electron beam from each channel. The screen has a phosphor coating facing the side of the magnet remote from the cathode, the phosphor coating comprising a plurality of pixels each corresponding to a different channel.
The magnetic matrix display uses a thick glass for the screen and backplate in order to ensure that a self supporting structure can be obtained when the glass envelope is evacuated. The thickness of glass required to provide this self supporting structure effectively limits this type of design to screen diagonals up to about 24 inches (610 mm).
To allow screen sizes with a larger than 24 inch (610 mm) diagonal, or to allow the thickness of the glass and hence the weight of the display to be reduced, thinner glass must be used. This requires the use of front spacers and back supports to withstand the atmospheric pressure on the outside of the glass envelope due to the vacuum within the glass envelope. Such spacers and supports can be designed, but the permittivity of an insulating support modifies the position of the remote cathode and changes the electron density in the vicinity of the support. This effects grid cutoff and the emission of electrons. The permittivity of an insulating spacer modifies the electrostatic field patterns in the vicinity of the spacer or of the support and hence will change the shape and/or direction of the electron beam.
Thus a visible pattern will appear on the screen at the locations where the spacers or the supports are located. If one component (spacer or support) is used between every pixel of the screen, then such visible patterning will not cause a problem, since it will be consistent across the whole area of the screen. In a practical design, such spacers and supports are positioned at intervals of about 10 mm and so the patterning can be discerned in the screen image generated by the display.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is now provided a display device comprising: a substrate; cathode means for emitting electrons, a permanent magnet; one or more supports between said substrate and said magnet; a two dimensional array of channels extending between opposite poles of the magnet; the magnet generating, in each channel, a magnetic field for forming electrons from the cathode means into an electron beam; a screen for receiving an electron beam from each channel, the screen having a phosphor coating facing the side of the magnet remote from the cathode, the phosphor coating comprising a plurality of pixels each corresponding to a different channel; grid electrode means disposed between the cathode means and the magnet for controlling flow of electrons from the cathode means into each channel, said grid electrode means having a plurality of apertures, each aperture corresponding to one of said channels, said apertures being of varying cross-section in the vicinity of the supports such that localized variations in the emission of electrons by the cathode means caused by said one or more supports is compensated.
The variation in cross-section of the apertures allows any shift in remote cathode position and change in electron density in the vicinity of the support to be compensated. This compensation may be by means of variation in the diameter of the apertures, or by variation in the shape of the apertures. Typically the apertures located nearest to the spacers are non-circular in shape, and preferably elliptical.
In a preferred embodiment, said cathode means for emitting electrons comprises an extraction grid; and said one or more supports between said substrate and said magnet are positioned so as to support the extraction grid. This allows the spacer to perform a second function, thereby eliminating the need for a separate support for the extraction grid. Also, in a preferred embodiment, said cathode means for emitting electrons comprises thermionic cathode filaments; and said one or more supports between said substrate and said magnet are positioned so as to support the thermionic cathode filaments. This allows the spacer to perform a third function, thereby eliminating the need for a separate support for the thermionic cathode filaments.
In a further preferred embodiment, the display further comprises one or more spacers between said screen and said magnet; and anode means disposed on the surface of the magnet remote from the cathode for accelerating electrons through the channels, said anode means being of varying shape in the vicinity of the spacers such that localized variations in the electron beam shape and position caused by said one or more spacers is compensated.
The varying shape of the anode means in the vicinity of the spacer allows any variation of the electrostatic field patterns in the vicinity of the spacer and hence change in the shape of direction of the electron beam to be compensated.
Preferably, said one or more supports between said substrate and said magnet and said one or more spacers between said screen and said magnet have a low conductivity such that charge accumulation is prevented. In a preferred embodiment, said one or more supports between said substrate and said magnet and said one or more spacers between said screen and said magnet are glass ceramic.
REFERENCES:
patent: 5504385 (1996-04-01), Jin et al.
patent: 5589728 (1996-12-01), Levine et al.
patent: 5864205 (1999-01-01), Dworsky
patent: 5889363 (1999-03-01), Beeteson et al.
patent: 6008573 (1999-12-01), Beeteson et al.
patent: 2304981 (1997-03-01), None
Beeteson John
Knox Andrew Ramsay
Haynes Mack
Herzberg Louis P.
International Business Machines - Corporation
Patel Nimeshkumar D.
Sbrollini Jay P.
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