GB2141577A

GB2141577A - Improvements in or relating to display devices

Info

Publication number: GB2141577A
Application number: GB08414940A
Authority: GB
Inventors: Waldo Ditmar Apgar
Original assignee: American Telephone and Telegraph Co Inc
Current assignee: AT&T Corp
Priority date: 1983-06-16
Filing date: 1984-06-12
Publication date: 1984-12-19
Also published as: JPS6012643A; IT1214467B; GB8414940D0; IT8421421A0; BE899911A; FR2547671A1; SE8403066D0; DE3421892A1; NL8401885A; SE8403066L

Abstract

Opposed plates 11,12 in a plasma display panel having crossed electrodes 13,14 are spaced by spacers 19 associated with stopper electrodes 16 which confine the discharge to the vicinities of the crosspoints of the electrodes 13,14. The spacers 19 are thus not visible in the display. <IMAGE>

Description

SPECIFICATION Improvements in or relating to display devices This invention relates to display devices.

Techniques for precision control of the separation between the plates of a gaseous display panel are of critical importance to the technology. The use of physical separator bars positioned around the periphery of the display has been the conventional approach. However, as displays increase in size bowing of the plates becomes a troublesome problem.

Variations in separation in the display region causes variations in the discharge behaviour of the gas. A standard solution is to use thicker plates. However that increases the cost and weight of the display. Another approach is to incorporate physical separators in the central regions of the plates. However the separators are then visible in the display area.

According to this invention a display device includes a pair of substantially planar plates at least one of which is transparent to the display radiation, means for mounting the plates face to face, means for separating the plates to provide a space between the plates, gas filling the space between the plates, a first series of parallel electrodes and a second series of parallel electrodes extending orthogonol to the first series to form a plurality of cross points of one electrode of the first series with one electrode of the second series, each crosspoint, when electrically energized, forming a radiant gas discharge at the crosspoint, and stopper electrode means associated with the crosspoints for confining the electrical energy and the resulting discharge to the vicinities of the crosspoints, the separating means being located with one or more of the stopper electrode means.

The invention will be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a cross section of a threeelectrode per pel plasma display panel; Figure 2 is similar to the cross-section of Fig. 1 but shows the addition of separator elements; and Figure 3 is a perspective view showing in all dimensions the position of the separator elements with respect to the display matrix configuration.

Referring to Fig. 1, the plates 11, 1 2 contain the gaseous display. The plates are typically glass but can in principle be of any rigid material, as long as one plate is transparent to the wavelength of interest that is generated by the plasma. The transparent plate 12, as shown, is usually referred to as the cover plate and the other plate (here 11) will be referred to as the substrate. The plates are sealed face to face with a glass seal 20.

The x-axis and y-axis electrodes 1 3 and 1 4 respectively are arranged in a three-electrode per pel crosspoint array as shown. The electrode arrangement of Fig. 1 is typical of threeelectrode designs as described in U.S.A. application No. 437154 filed 27th October 1 982. However a variety of alternative electrode arrangements can be used one of which is simply to reverse the assemblies on the substrate and cover plate. The electrodes are coated with a layer 1 5 of a standard lead dielectric glass to provide the capacitance required for charge storage. SiO2 or borosilicate glass can also be used in thin film form.

Stopper electrodes 1 6 are formed on the dielectric layer of the substrate, or alternatively on the dielectric layer of the cover. The position of the stopper electrodes is more evident in the perspective view, Fig. 3. The surfaces of both opposing plates, those surfaces that are exposed to the discharge, are coated with an electroemissive material 17, typically MgO, to provide a uniform electron flux under plasma bombardment.

The spacing between the electrodes determines the intensity of the field, which in turn controls the behaviour of the gaseous discharge. The absolute spacing must be controlled, and the uniformity of spacing from crosspoint to crosspoint is of critical importance. In the typical panel, shown in Fig. 1, the spacing is controlled by a spacing element 1 8 carefully designed and installed around the periphery of the display matrix, which, typically, is around the edges of the plates.

If glass is chosen for the material of the plates it typically has a thickness of the order of i inch. It is desirable from the standpoint of display weight and cost to construct the panel using thin plates. There is also an advantage in the optical quality of the display in having the cover plate thin.

The desirability of thin plates had to be balanced with the need for rigidity. The separation between the plates in the display region is critical. Consequently as displays increase in size the usual approach is to maintain the requisite rigidity of the plates by increasing the plate thickness. In an embodiment of the invention, illustrated in Fig. 2, the control of the interelectrode spacing does not rely on the rigidity of the plates. It relies on separators 1 9 piaced coextensive with the stopper electrodes 1 6 as shown. These separator elements may be placed wherever necessary to maintain the desired uniformity in interplate separation.

Typically they are not required at each stopper electrode position. We have found that separators places one inch apart maintain uniform separation between winch plates over a display area of any chosen size.

Although the separators 1 9 are positioned within the display matrix, they do not interfere with the display since they occupy dark spaces that separate the picture elements.

While the thickness of the separator ele ments is important in determining the interplate separation, the shape of the separator elements can be any that is desired and the size is also a matter of choice or convenience as long as it occupies no more that the approximate size of the stopper electrode.

The separator elements can be attached to either the substrate or cover plate, either over or under the dielectric glass. Positioning the separator elements may be easier if they are applied to the same plate that carries the stopper electrode. However with a properly designed alignment aid they can be attached initially to the other plates as well. Since the space between the plates is evacuated, outward bowing of one or both plates with respect to the other normally is not a serious problem. Consequently, the spacer elements can be bonded to just one of the plates.

However, advantages may be found for bonding the separator elements to both plates, one of the bonds being effected during assembly.

The spacer elements are preferably affixed directly to the stopper electrodes prior to application to the MgO layer. If the separator elements are metal, a metal-to-metal bond can be advantageously used.

The separator elements may be combined with the stopper electrodes. Various ways will be found to combine these elements. They can be regarded, and designed, as one element.

Although the arrangement shown in Fig. 3 makes use of three electrodes, the invention is equally applicable in two-electrode or fourelectrode displays where stopper electrodes are used. The arrangement could also be used in any gaseous display device where spacing between the plates containing the gaseous discharge is an important concern.

Various modifications of the embodiment specifically described will occur to those skilled in the art.

Claims

1. A display device including a pair of substantialy planar plates at least one of which is transparent to the display radiation, means for mounting the plates face to face, means for separating the plates to provide a space between the plates, gas filling the space between the plates, a first series of parallel electrodes and a second series of parallel electrodes extending orthogonol to the first series to form a plurality of crosspoints- of one electrode of the first series with one electrode of the second series, each crosspoint, when electrically energized, forming a radiant gas discharge at the crosspoint, and stopper electrode means associated with the crosspoints for confining the electrical energy and the resulting discharge to the vicinities of the crosspoints, the separating means being located with one or more of the stopper electrode means.

2. A device as claimed in claim I wherein the separating means are less extensive than or co-extensive with the stopper electrode means.

3. A device as claimed in claim 1 or 2 wherein the separating means are attached to the stopper electrode means.

4. A device as claimed in claim 1 wherein the or each separating means and stopper electrode means located therewith are constituted by a single element.

5. A display device substantially as herein described with reference to Figs. 2 and 3 of the accompanying drawings.