Process of forming metal/ferrite laminated magnet

Details Process of forming metal/ferrite laminated magnet Process of forming metal/ferrite laminated magnet

1999-07-30

2002-12-17

Ramsey, Kenneth J. (Department: 2879)

Electric lamp or space discharge component or device manufacturi

Process

With assembly or disassembly

C419S008000

Reexamination Certificate

active

06494758

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to a new metal/ceramic laminate with discretely distributed magnets with through-holes and process thereof. More particularly, the invention encompasses a new process for fabrication of a large area ceramic laminate with discretely distributed magnets with integrated metal plate(s) and electrodes for electron and electron beam control. The present invention also relates to a magnetic matrix display (MMD) structure and methods of manufacture thereof.
BACKGROUND OF THE INVENTION
A magnetic matrix display is particularly, although not exclusively, useful in display applications, especially flat panel display applications. Such flat panel display applications include television receivers, visual display units for computers, especially, although not exclusively, portable and/or desktop computers, personal organizers, communications equipment, wall monitor, portable game unit, virtual reality visors and the like. Flat panel display devices based on a magnetic matrix electron beam source hereinafter may be referred to as Magnetic Matrix Displays (MMD).
Conventional flat panel displays, such as liquid crystal display panels, and field emission displays, provide one display technology. However, these conventional flat panel displays are complicated and costly to manufacture, because they involve a relatively high level of semiconductor fabrication, delicate materials, and high tolerance requirements.
U.S. patent application Ser. No. 08/695,856, filed on Aug. 9, 1996, entitled “ELECTRON SOURCE”, which also corresponds to U.K. Patent Application Serial No. 2304981, assigned to the assignee of the instant Patent Application and the disclosure of which is incorporated herein by reference, discloses a magnetic matrix electron source and methods of manufacture thereof. Also disclosed is the application of the magnetic matrix electron source in display applications, such as, for example, flat panel display, displays for television receivers, visual display units for computers, to name a few. Also disclosed is 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 magnetization being from the surface facing the cathode to the opposing surface. The magnet generates, in each channel, a magnetic field for directing electrons from the cathode means into an electron beam. The display also has a screen for receiving the 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. There are grid electrode means disposed between the cathode means and the magnet for controlling the flow of electrons from the cathode means into each channel. The two dimensional array of channels are regularly spaced on an X-Y grid. The magnet area is large compared with its thickness. The flat panel display devices based on a magnetic matrix electron source is referred to as MMD (Magnetic Matrix Display).
The permanent magnet is used to form substantially linear, high intensity fields in the channels or magnetic apertures for the purpose of collimating the electrons passing through the aperture. The permanent magnet is insulating, or at most, has a small conductivity, so as to allow a field gradient along the length of the aperture. The placement of the beam so formed, on the phosphor coating, is largely dependent on the physical location of the apertures in the permanent magnet.
In operation, these electron beams are directed at a phosphor screen and collision of the electron beam with the phosphor results in light output, the intensity being proportional to the incident beam current (for a fixed final anode voltage). For color displays, three different colored phosphors (such as red, green and blue) are used and color is obtained by selective mixing of these three primary colors.
For accurate color reproduction, the location of the electron beams on the appropriate colored phosphor is essential.
Some degree of error may be tolerated by using “black matrix” to separate the different phosphors. This material acts to delimit individual phosphor colors and also enhances the contrast ratio of the displayed image by making the display faceplate appear darker. However, if the electron beam is misplaced relative to the phosphor, initially the light output from the phosphor is reduced (due to loss of beam current to the black matrix) and this will be visible as a luminance non-uniformity. If the beam is subject to a more severe placement error, it may stray onto a different colored phosphor to that for which it was intended and start to produce visible quantities of light output. Thus the misplaced electron beam is actually producing the wrong light output color. This is called a purity error and is a most undesirable display artifact. For a 0.3 mm pixel, typical phosphor widths are 67 &mgr;m with 33 &mgr;m black matrix between them.
It will be apparent that a very precise alignment is required between the magnet used to form the electron beams and the glass plate used to carry the phosphors that receive the electron beams. Further, this precise alignment must be maintained over a range of different operating conditions (high and low brightness, variable ambient temperature etc).
A number of other magnet characteristics are also important when considering application for a display, such as, for example:
1. It is generally accepted that the displayed image is formed by a regular array of pixels. These pixels are conventionally placed on a square or rectangular grid. In order to retain compatibility with graphics adaptors the magnet must thus present the electron beams on such an array.
2. In operation, the spacing between the grids used for bias and modulation of the electron beam and the electron source determines the current carried in the electron beam. Variations of this spacing will lead to variations in beam current and so to changes in light output from the phosphor screen. Hence it is a requirement that the magnet, which is used as a carrier for these bias and modulation grids, maintain a known spacing to the electron source. To avoid constructional difficulties, the magnet should be flat.
3. The display will be subject to mechanical forces, especially during shipment. The magnet must retain structural integrity over the allowable range of stresses it may encounter. A commonly accepted level is an equivalent acceleration of about 30G (294 ms
−2
).
One further requirement is that since the magnet is to be used within the display, which is evacuated, it should not contain any organic components which may be released over the life of the display, so degrading the quality of vacuum or poisoning the cathode.
Finally, the magnet is magnetized in the direction of the apertures, that is the poles correspond to the faces of the magnet.
The manufacture of such a magnet that satisfies the above conditions is not possible by the use of previously known manufacturing methods. Certainly a magnet (ferrite, for example) of the desired size without apertures is readily obtainable but the presence of the apertures causes some problems.
If the apertures in the magnet are to be formed after the ferrite plate has been sintered, either laser or mechanical drilling may be used. However, the sintered ferrite is a very hard material and forming the apertures by this technique will be a costly and lengthy process—unsuitable for a manufacturing process.
Holes could be formed in the ferrite at the green-sheet stage before sintering by known punching/drilling methods typical of multi-layer ceramics for microelectronics applications. However, during sintering a number of problems would be anticipated, such as, for example:
The magnet plate will be subject to uneven shrinkage leading to the holes “moving”—an unequal radial displacement from their nominal positions;
The magnet itself is likely

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