Electric lamp and discharge devices: systems – Cathode ray tube circuits – Cathode-ray deflections circuits
Reexamination Certificate
1996-10-25
2002-04-23
Issing, Gregory C. (Department: 3662)
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Cathode-ray deflections circuits
C315S169100, C313S422000
Reexamination Certificate
active
06377002
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates in general to flat panel display structures and, in particular, to flat panel displays employing cold cathode field emitters.
Flat panel displays have a growing number of applications that benefit from their thin profile and light weight. These include active and passive liquid crystal displays (AMLCD, LCD), AC and DC plasma displays (PDP), electroluminescent (EL) displays, field emission displays (FEDs) and flat matrix cathode ray tube (CRT) displays. AMLCDs, however, are expensive to make. Furthermore, because of low yield, it may be difficult to manufacture large screen AMLCDs. Thus, even though AMLCDs have dominated the notebook computer and high information graphics display market, its potential for large screen full video speed flat panel displays appears to be limited.
The emissive type flat panel displays such as flat matrix CRTs and plasma discharge panel (PDP)displays are disadvantageous because power consumption is high. Flat CRT displays employing cathode filaments that extend across the length of the display have also been proposed. See, for example, U.S. Pat. No. 5,170,100. While such thermionic emission displays have been proven to be reliable in operation and can be manufactured in large volume at low cost, it is believed that these devices may still have weaknesses when used in large area flat panel display systems. Thus, thermionic cathode filaments have to be mounted with springs on both ends and proper tension need to be set to reduce vibrations. Heat loss to the filament supports by contact results in cold terminal effects that degrades electron emission at both ends of the filament. The filaments have to be operated at an elevated temperature which may adversely affect phosphor efficiency and lifetime. Filament array mounting may be difficult for cost effective high throughput manufacturing.
Field emitters have been used in flat panel displays and vacuum microelectronics applications. Cold cathode and field emission based flat panel displays have several advantages over other types of flat panel displays. These include low power consumption, high brightness, improved viewing angle and reduced manufacturing complexity and costs, compared to AMLCDs, for example. However, the perfection of large area panels using this technology in the conventional manner is problematic because of the need to fabricate high density identical sharp microtips. For this reason, FED panels suffer from the same high costs and low yield issues similar to that encountered in the fabrication of AMLCDs. This is explained in more detail below.
Each field emitter includes typically a base electrode and a gate electrode. The display is controlled typically by applying a scanning electrical potential to rows of base electrodes or gate electrodes and the data modulation electrical potential to columns of the remaining electrodes in an X-Y addressing scheme for controlling the brightness of the display at each pixel corresponding to one or more groups of microtips. Therefore, the brightness at each pixel would depend on the emission characteristics of the corresponding group or groups of field emitters. Since individual field emitters may have different current-voltage characteristics resulting from variations in the manufacturing process, such field emitters may have different electron emission characteristics, thereby causing differences in brightness. While the variation in brightness due to such factor may still be tolerable for small screen display, the extension of such conventional FED panels to large screen flat panels appears to be difficult.
Furthermore, each microtip emits electrons within a large angle cone about the axis of the microtip, a small standoff distance must be maintained between the gate of the field emitter and the anode of the display. If a large standoff distance is maintained between the gate and the screen, electrons emitted from the microtip will spread laterally, resulting in significant cross talk and low resolution display. To avoid such problems, a small standoff distance is maintained between the anode on the one hand and the gate of the microtips on the other. This means that the potential difference between the anode and the field emitters must be small; otherwise, the high anode voltage would overpower the gate of the field emitters and simply turn every pixel in the display to the on state indefinitely, so that there is simply no display of any image. For this reason, the device must be operated at low voltage, so that even though high efficiency phosphors are used, they do not operate efficiently at such low voltages.
In addition, since the addressing is by controlling the gate and base electrodes of each individual microtip array, each row and column of the display must be controlled in an X-Y addressing. For a display of 640 rows by 480 columns, there must be 640 electrical connections for the 640 rows and 480 for the columns, so that it is cumbersome and costly to implement a row and column integrated circuit driver for television.
In view of the above disadvantages of conventional FED panels, alternatives have been proposed, such as the system in U.S. Pat. No. 5,347,201. In the system of U.S. Pat. No. 5,347,201, field emitter arrays are used to replace cathode filaments in electron fluorescent displays. In the proposed system, cold cathode field emitters are used as electron sources in the place of cathode filaments, and three sets of grid electrodes are used to control the scanning and data modulation of brightness of the display. In such scheme, however, three sets of electrodes need to be mounted accurately, which may be tedious.
None of the above-described structures is entirely satisfactory. It is, therefore, desirable to provide an improved flat panel display in which the above-described difficulties are avoided or reduced.
SUMMARY OF THE INVENTION
The first aspect of the invention is directed towards a cathodoluminescent visual display device having a plurality of pixel dots for displaying images when said device is viewed in a viewing direction. The device comprises a housing defining a chamber therein, said housing having a face plate and a back plate; an anode on or near said face plate and luminescent means that emit light in response to electrons, and that is on or adjacent to the anode. The device further comprises a plurality of rows of field emission cathode elements in the chamber between the face and back plates; a first spacer structure defining holes therein for passage of electrons and a first set of elongated grid electrodes between the anode and cathode, the electrodes overlapping the luminescent means and said rows at locations when viewed in the viewing direction, wherein the overlapping locations define pixel dots. The device further includes means for applying electrical potentials to the anode, cathode, the set of grid electrodes and the rows of field emission cathode elements, causing the cathode elements to emit electrons, and such electrons to travel to the luminescent means at desired pixel dots on or adjacent to the anode for displaying images of desired brightness.
Another aspect of the invention is directed towards a method for making a display device having a spacer structure, comprising processing a layer of metal to form a metal mesh with holes therein of a predetermined pattern; applying an insulating coating onto the metal mesh; forming a grid electrode pattern on the insulating layer and inserting said spacer structure between an anode and at least one cathode to form said display device.
Yet another aspect of the invention is directed towards a method for displaying images by means of a cathodoluminescent visual display device. The device comprises an anode; luminescent means that emit light in response to electrons, and that is on or adjacent to the anode; a plurality of rows or field emission elements between the face and back plates; and a first set of elongated grid electrodes between the anode and cathode, the electrodes overlapping the luminescent m
Ge Shichao
Huang Xi
Leung Charles S.
Yam Lap Man
Issing Gregory C.
Pixtech, Inc.
Samuels , Gauthier & Stevens, LLP
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