CONCENTRIC VIA PLASMA PANEL

Abstract: A one sided ac plasma panel comprises a glass substrate encapsulated within a pair of glass plates dividing the panel into two interconnected chambers. One set of conductors arrays originate within the rear aperture and are conducted through display vias to circular electrodes in the front aperture. The second set of electrodes comprise annular rings which are concentric and co-planar with the circular electrodes. This configuration limits discharge spread on the display surface, permitting increased resolution without crosstalk. Multicolour capability is provided by the combination of ultraviolet sensitive phosphors on the inner surface of the front faceplate and an ultraviolet emitting gas within the plasma panel.

Description: The present invention relates to concentric via plasma panels. In conventional ac plasma display technology, orthogonal conductor arrays are formed on a pair of glass plates and, the conductor arrays, when fabricated, are disposed substantially orthogonal to each other and overcoated with a dielectric layer, the intersection of a pair of conductors defining a display site or cell. When write signals are selectively applied across orthogonal conductor sets of the conventional ac plasma display, the fields at addressed cells produce a localised discharge in the area between conductors providing a visible display. The display is maintained by a lower amplitude sustain signal which combines with the wall charge potential to continuously discharge the selected cells. Each discharge tends to spread beyond the edges of the conductors into the region between lines. Discharge spreading results from coupling between confronting conductors, beyond the immediate area of congruency, where the electric field remains strong. Minimum spacing between lines, ie display resolution, is determined, among other factors, by the requirement to keep the plasma of adjacent cells separated. Panel gap, dielectric thickness and line width are other factors which contribute to the minimum allowable line spacing. These indirect means of controlling discharge spread stem from the "unbounded" character of the electric fields produced by two flat, orthogonal conductors, and discharge spreading diminishes with distance from the origin. While the various technology problems relative to conventional twin substrate ac plasma panels have been resolved, the process of manufacturing such displays is complex and of substantial duration, such that the cost of such displays remains relatively high. An alternative form of an ac plasma display is a single sided panel. One sided or single substrate panels are known in the act and have been described in the literature. Such panels generally entail a single substrate or glass plate on which various layers of conductors and dielectrics are formed and suitably insulated from one another. For example in US-A-3,811,061 a single sided plasma display panel is disclosed in which orthogonal x and y electrodes are formed, insulated from each other by an insulating layer, and in which a discharge region is associated with one of the electrodes which has been formed in a passage through the insulating layer. Similarly, in a single substrate ac plasma panel, the fields resulting from coupling between orthogonal conductors outside cell boundaries are strong enough to produce a plasma which extends beyond the mutual overlap boundaries of the conductors. Poor plasma confinement within such display necessitates wider spacing between cells and imposes a limitation on the resolution heretofore attainable with previous single substrate plasma panel designs. Finally, when one sided plasma panel technology is extended to colour, the tendency of the positive ions produced during discharge to bombard and destroy or degrade the phosphors has limited the development of a multi-colour capability in one sided panes1. It is toward the solution of these problems in a single sided plasma panel that the present invention is directed. Accordingly, the present invention provides a single sided AC plasma display device including an insulating substrate carrying two sets of mutually insulated electrodes in a discharge envelope wherein a first of the sets of electrodes comprises the exposed surfaces of extensions of an array of conductors mounted on one face of the substrate and passing through the substrate through vias therein to the second face thereof; and characterised in that the second of the sets of electrodes comprises annular conductive rings on the second face of the substrate, each ring electrode being concentric with and insulated from a companion electrode of the first set of electrodes and electrically connected to at least one adjacent ring electrode by conductive material mounted on the second face of the substrate. A single substrate plasma display structure is described in which the plasma spread associated with a selected cell is limited by a boundary defined by one of two cell electrodes. The panel consists of a central substrate enclosed by a pair of glass plates that comprise a gas envelope. On the front of the substrate are vertical or Y conductors made up of annular rings connected by line segments. A circular via, passing through the substrate from below, terminates in a circular electrode which is concentric and co-planar with each ring. On the rear of the substrate horizontal or X conductors buss the vias together in rows. The busses extend to transfer vias located on opposite ends of each horizontal line where horizontal conductivity is transferred to thin film conductors on the front surface of the display which passes outside the envelope. The terminations of the display vias and co-planar concentric rings comprise the field generating electrodes for the X-Y matrix. A layer of dielectric glass overcoated with MgO covers the electrodes. Vent vias in the four corners permit processing of both chambers with one exhaust tubulation and provide reference points for plate align ment during panel fabrication. The technology of a one sided monochrome panel can be extended to colour by use of a faceplate with ultraviolet sensitive phosphors deposited on the inside surface of the front glass plate confining the cells, and substituting a gas mixture with ultra-violet emission capability and low visible intensity. By separating the phosphor from the discharge cells in this manner, phosphor degradation by position ion bombardment is prevented, and the discharge surface is protected from contamination by phosphor particulates. The invention will be described further, by way of example, with reference to a preferred embodiment thereof, as illustrated in the accompanying drawings, in which:- Figure 1 is a plan view of the preferred embodiment of the instant invention; Figure 2 is a section front view of the device of Figure 1; Figure 3(a) is view to greater detail and scale of an annular electrode structure of the device; and Figure 3(b) is a section view taken along the line B-B of Figure 3(a). As previously described, one of the basic problems in single substrate ac panels is charge confinement during discharge, since the plasma discharge tends to extend beyond the mutual overlap boundaries of the conductors into the regions between conductors. This cross-talk problem is addressed in the instant invention by a combination of cell geometry and co-planar conductor arrays. With respect to geometry, one of the cell electrodes is an annular thin film ring which confines the discharge within the boundary defined by the ring. The second feature is that the rear electrodes are brought to the front by use of vias and are centred in and made co-planar with the ring electrodes. Referring now to the drawings and more particularly to Figures 1 and 2 thereof, a single sided display panel consists of a central substrate 11 enclosed by glass plates 13, 15 which, when sealed by seal 16 comprise the gas envelope which is filled with an ionisable gas. On the front of substrate 11 are vertical conductors 17 comprising thin film annular rings 19 interconnected by line segments 21. The circular electrodes 24 comprising the terminations of vias 23, are thick film which pass through the substrate 11 from below, and are concentric with annular rings 19. On the opposite side of the substrate, horizontal conductors, shown as hatched areas 25 in Figure 1, buss the vias 23 together in rows. Thick film metallurgy is used for the busses, which extend to transfer vias 26 located on opposite ends of horizontal busses 25 where horizontal conductivity is transferred to thin film conductors 28 on the front surface of the display panel for passage outside the envelope, beneath seal 16. The via termination electrodes and associated co-planar concentric rings are the field generating electrodes for the X-Y matrix. A layer of dielectric glass having a nominal thickness of 0.02 mm (one mil), overcoated with magnesium oxide, is shown in Figure 2 as a single composite layer 27 overcoating the electrodes. The thickness of the dielectric relative to that of the conductors is significant in reducing discharge spread. Accordingly, the dielectric layer has a nominal thickness of 0.02 mm (1 mil), while the electrodes, as previously described, are thin film conductors. The magnesium oxide is a refractory material which protects the dielectric surface during discharge, while its secondary emissive characteristic permits lower operating voltages. Alternatively, the electrode area alone could be covered. Vent vias 29 in the four corners of the panel assembly interconnect the front and rear chambers to permit processing of both chambers with one exhaust tubulation 33 (Figure 2) located at the rear of the assembly while also serving for plate alignment during fabrication. Referring briefly to Figure 3(a) which illustrates an enlarged display cell, an electric field is developed between via 23 and concentric ring 19 when a write or sustain signal is applied between horizontal and vertical conductors. As graphically illustrated in Figure 3(b), circularly symmetrical primary fields 30 appear on the dielectric surface above each cell. The concentric geometry and thickness of substrate 11 constrains the field to the ring interior. A weaker external field, indicated by the dashed lines 32 of Figure 3(b), is also present, but the long dielectric path through dielectric 35 and substrate 11 lowers the field intensity. Discharges generated by the primary field are also internal to electrode 19, with the plasma boundary essentially coincident with the ring perimeter. Referring back to Figure 1, the via holes through the dielectric, in the preferred embodiment of the invention, have a diameter of approximately 0.14 mm (5.5. mils) at the front surface of the substrate 11. For a substrate 0.86 mm (.034 inches) thick, the holes have an aspect ratio of approximately 7. For production purposes, conventional methods cannot etch such long thin holes. However, the holes can be fabricated in Fotoform glass (Registered Trade Mark of Corning Glass Co), a specially processed glass which can be selectively sensitised to light through an artwork mask during fabrication. Exposed areas etch rapidly relative to unexposed areas, and the differential etch rate make fabrication of thin holes feasible. In addition, the coefficient of thermal expansion of Fotoform is compatible to that of the glass planes, the dielectric and the seal glasses used in the invention. The technology of the one sided monochrome plasma panel can be extended to colour with two changes in panel assembly, use of a faceplate with UV (ultraviolet) sensitive phosphors deposited on the surface confronting the cells, and substitution of a gas mixture which provides intense UV emission lines and low visible intensity. In an experimental model constructed in accordance with the teachings of the invention, red, green and blue phosphors are deposited on the faceplate in successive horizontal stripes in 0.88 mm (35 mil) squares. Each square is surrounded by a black graphite matrix to enhance contrast. A helium-xenon gas mixture is substituted for the neon-argon gas used in monochrome panels. The light output intensity from the colour panel is essentially the same as that obtained from the monochrome panel. By separating the phosphor from the cells in this manner, phosphor degradation by positive ion bombardment is prevented, and the discharge surface is protected from contamination by phosphor particulates.

Claims: A single sided AC plasma display device including an insulating substrate (11) carrying two sets of mutually insulated electrodes in a discharge envelope (13,15,16), wherein a first of the sets of electrodes comprises the exposed surfaces of extensions of an array of conductors (25) mounted on one face of the substrate and passing through the substrate through vias (23) therein to the second face thereof; and characterized in that the second of the sets of electrodes comprises annular conductive rings (19) on the second face of the substrate, each ring electrode being concentric with and insulated from a companion electrode of the first set of electrodes and electrically connected to at least one adjacent ring electrode by conductive material (21) mounted on the second face of the substrate. A device as claimed in claim 1, wherein the second surface of the substrate, together with the conductors and electrodes thereon, are coated with a dielectric layer (35) which is considerably thicker than the conductors and electrodes that it covers. A device as claimed in either preceding claim, wherein the substrate divides the envelope into two interconnected chambers, a front or viewing chamber and a rear chamber, the conductive material on the second face of the substrate lying in the front chamber and being fabricated using thin film technology, while the conductive material in the vias and in the rear chamber is fabricated using thick film technology. A device as claimed in any preceding claim, wherein for generating polychromatic displays, the envelope is filled with a gas mixture which provides intense ultra-violet emission lines and low intensity in the visible part of the spectrum and the inner face of the envelope in the front chamber is provided with a plurality of patterns of different ultra-violet sensitive phosphors. A device as claimed in Claim 4 wherein said gas mixture comprises a mixture of helium and xenon gases. A device as claimed in Claim 4 or 5 wherein said rear chamber includes a horizontal drive buss to which the conductors passing through said vias (23) are connected. A device as claimed in any of Claims 4-6, wherein the phosphors, when irradiated, are arranged to provide triads of red, green and blue dots aligned with the conductors in the rear chamber.

Inventors: COSTA, MICHAEL JOHN, SHAPIRO, JESSE BERNARD
Applicants: INTERNATIONAL BUSINESS MACHINES CORPORATION
Application year: 1986
Main classification: H01J17
IPC codes: H01J11, H01J17