FIELD OF INVENTION:
The present invention relates to a Plasma Display Panel its manufacturing and particulariy related to a design for PDP cell structure. The structure maximizes luminous efficacy and applicable for making high picture quality flat panel displays.
BACKGROUND OF INVENTION:
In last few decades, proper attention has been paid to PDP development as a large size flat panel displays. PDP is composed of a matrix of discharge cells that are formed by partitions made by barrier ribs between a pair of glass substrates. Three color (Red, Blue and Green) phosphors are provided on the surface of the respective barrier ribs, and the cell volume is filled with a gas mixture (Ne+Xe). During PDP operation, the gas discharge takes place between electrodes in the cells that result in the generation of Vacuum Ultra Violet (VUV) photons with a wavelength of 147 nm and 173 nm. These phosphors absorb these VUV photons and emit visible light to display a picture including characters and graphics. Such PDPs are self-emitting type flat panel displays and have excellent characteristics such as large size, wide horizontal and vertical view-angle, slim look, lightweight etc. Thus, PDP is a prospective candidate in the competitive worid of flat panel display devices. The drawback of the PDP is low luminous efficacy. At present various efforts are on to improve the luminous efficacy of PDP especially by cell structure modifications.
The conventional AC (Alternating Current) driven PDP possesses three-electrode structure on two glass substrates forming second substrate and first substrate shown in FIG 1 (a). The second substrate has formed therein a plurality of pairs of display electrodes known as sustain and scan electrodes. These electrodes are formed of ITO (Indium-Tin-Oxide) material. The ITO electrode sheet resistance is decreased with the introduction of metal bus lines of electrically conducting material over the ITO electrodes. The display electrodes are covered
with a transparent dielectric layer to limit the discharge current. A thin electron emissive layer is formed over the transparent dielectric layer to emit secondary electrons and to protect the transparent dielectric layer from sputtering by ion bombardment. The first substrate has formed therein a plurality of address electrodes that are orthogonal to the display electrodes. A pair of sustain and scan electrodes along with an address electrode form a sub-pixel. A sub-pixel comprises of Red, Green or Blue color phosphor that make Red, Green or Blue sub-pixel respectively. A combination of Red, Green and Blue sub-pixels forms a pixel. The straight channel barrier ribs are formed on the first substrate to create the discharge volume and also to separate different sub-pixels. The main co-planar discharge is created with the display electrodes by square pulse voltage. The VUV radiation produced in the discharge phenomenon excites the phosphor to emit visible light. This type of conventional AC PDP is described in US Patent no. 5661500. In US patent no 7,345,425 B2 a new cell structure has been disclosed which have lower discharge voltage but in this structure VUV photon losses is high resulting in poor brightness.
The luminous efficacy of an AC PDP depends on following factors: i) The generation of VUV photons, ii) detention of the VUV photon by phosphor layer, iii) Losses while conversion of VUV to visible light, iv) transmission of visible light and v) the power consumption. Except the VUV to visible light conversion losses the other losses are inherent to the cell structure. In conventional coplanar AC PDP the rapid diffusion of electrons to the electrode surface reduces the efficient production of the VUV photons. Secondly, the conventional AC PDP suffers from the low luminous efficacy due to high VUV and visible photons losses as shown in FIG. 2. The discharge between co-planar sustain electrodes on the second substrate generates VUV photons. These VUV photons spread in all directions and eventually strike the second substrate, first substrate and side boundaries of the cell. The VUV photons which falls normal to the surface covered with the phosphor contribute efficiently to the light output, while the VUV photons striking the boundaries of the cell laterally are least efficient. Thus the detention of maximum number of VUV photons by phosphor is required for achieving high
brightness. Moreover, the visible light generated by phosphor scatter in all directions and a significant amount visible photons strike the side walls, remaining photons which are normal to second substrate are obstructed by MgO layer, dielectric layer, ITO layer and bus electrodes reducing the overall brightness. Thus, in conventional three electrode cell structure photons are lost at two stages i.e. all VUV photons generated by discharge are not detained by phosphor and secondly the all visible photons generated by phosphor do not come out through the second substrate (substrate). In order to overcome aforementioned optical losses the geometry of the cell should be such that it minimizes the optical losses and maximizes the transparency of the second substrate. Moreover, the cell structure should capable of detention of all VUV generated by the discharge and the second electrode must be free from any content that hinders the visible light passageway. Considering the power consumption and the VUV photon generation is also very important. The VUV photon production efficiency increases with Xe percentage in Ne-Xe gas composition. Higher Xe percentage in gas composition results in high brightness due to efficient VUV production. But, high Xe percentage also increases the operating voltage as well as the sustain current. Thus, an ideal cell structure should be such that it has low operating voltage for high Xe partial pressure in the Ne-Xe gaseous mixture.
The conventional AC PDP with coplanar parallel sustain electrodes also suffers from the cross-talk problem between neighboring sub-pixels. This is a major drawback of the coplanar parallel sustain electrodes and requires a sufficiently large inter-pixel gap which limits the resolution of plasma displays. The cross talk is defined as the leakage of discharge and VUV radiation over barrier hb from one sub-pixel to other neighboring sub-pixel that produce adverse effects in the un-addressed sub-pixel. To overcome the limitation of low resolution ALIS (Alternate Lighting of Surfaces) was introduced where inter pixel gap is not required and hence resolution can be doubled. However, this method increases the problem of vertical cross-talk and do not provide stable operation of plasma PDP.
In the present invention a PDP cell structure has been disclosed which maximizes VUV photon generation and detention, minimizes optical losses and reduces power consumption and suitable for high definition PDP.
OBJECT OF THE INVENTION
Luminous efficacy of conventional AC PDP is low due to low brightness and high power consumption. This invention provides a cell structure for reduced power consumption and enhanced brightness of a plasma display.
Yet another objective of the present invention is to provide a cell structure to enhance brightness by maximizing the production of VUV photons during the discharge between the electrodes.
Yet another objective of the present invention is to provide a cell structure to enhance brightness by maximizing the capture of VUV photons by phosphor for conversion into visible photons.
Yet another objective of the present invention is to provide a cell structure to enhance the brightness by reducing optical losses by geometrical considerations.
Yet another objective of the present invention is to disclose /provide a cell structure to enhance the brightness by reducing optical losses by improving transparency.
Yet another objective of the present invention is to provide a cell structure with at least two electrodes.
Yet another objective of the present invention is to provide a cell structure free from ITO reducing the cost of the panel.
Yet another objective of the present invention is to provide a cell structure with electrodes having lower resistance.
Yet another objective of the present invention is to provide a cell structure with reduced power consumption by minimizing the operating voltage.
Yet another objective of the present invention is to provide a cell structure suitable for high resolution pictures.
Yet another objective of the present invention is to provide an inbuilt electromagnetic interference filter on glass substrate of the panel.
STATEMENT OF THE INVENTION
The invention provides a Plasma Display Panel comprising a pair of first glass substrates and second glass substrate, and gas enclosed between the substrates, a plurality of first set of disc shaped interconnected electrodes in first direction (X), a first dielectric layer is provided to cover the plurality of X electrodes, a plurality of second set of ring shaped interconnected electrodes (Y) in second direction orthogonal to the plurality of X electrodes is fabricated on the first dielectric layer such that the center of the rings of Y electrodes sits over the top of the centre of the discs of X electrodes, a second dielectric layer is provided to cover the plurality of Y electrodes, a first cavity is provided between the rings of Y electrode on the second dielectric layer, a protective layer which also act as secondary electron emissive layer is provided on second the dielectric layer, a plurality of barrier ribs in first direction i.e. parallel to the X electrodes is provided, a channel is formed between each two ribs and the plurality of channels is filled with Red (R), Green (G) and Blue (B) phosphors in predetermined sequence, the channels filled with Red, Green and Blue phosphor and each comprising with a cavity forms a pixel, each channel filled with phosphor on second glass substrate and the cavity on the first glass substrate are aligned together such that the channel filled with phosphor encases the cavities made on first substrate and forms a discharge volume, the second

glass substrate with red, green and blue phosphor between barrier ribs used for detention of the VUV photons and emit red, green and blue light respectively. Visual display of images is achieved by application of scan, address and sustain voltages on X and Y electrodes in predetermined temporal sequence.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1(a): The cross-sectional view of conventional AC PDP with straight barrier rib structure.
FIG. 1(b): The top view of the conventional AC PDP structure shown in FIG. 1(a).
FIG. 2: The principle of discharge in conventional AC PDP structure.
FIG. 3(a): Schematic view of new PDP discharge cell structure according to the
present invention.
FIG. 3(b): The schematic top view of the new PDP discharge cell structure
according to the present invention.
FIG. 4: The schematic cross-sectional view of the new PDP discharge cell
structure explaining the discharge principle in the present invention.
FIG. 5: The schematic of process steps for manufacturing of first substrate
according to the present invention.
FIG. 6: The schematic of process steps for manufacturing of second/second
substrate according to the present invention.
FIG. 7: The schematic of second and first substrate together forming Plasma
Display Panel according to the present invention.
FIG. 8: The schematic of second and first substrate together, with alternative
structure and processing of second substrate, forming Plasma Display Panel
according to the present invention.
FIG. 9: The schematic of second and first substrate together, with alternative structure and processing of second substrate and alternative arrangement cells on first substrate, forming Plasma Display Panel according to the present invention.
FIG. 10: This figure shows the second substrate (18) comprises of additional electrodes (27) on second substrate forming a mesh and acts EMI filter.
DETAILED DESCRIPTION OF THE INVENTION FOR THE PREFFERED EMBODIMENTS WITH REFERENCE TO DRAWINGS
The accompanying drawings, which are incorporated in and constitute a part of specification, illustrate an embodiment of the invention, and, together with the description, serve to explain the principles of invention.
FIG. 1(a) illustrates the cross-sectional view of conventional AC PDP with straight barrier ribs. In the second glass substrate (1), display electrodes are made of transparent ITO sheet (3). To reduce the resistance of the display electrode, opaque electrically conducting bus electrodes (4) are made over the ITO electrodes. The display electrode is covered with a transparent dielectric layer (5) to limit the discharge current. Then the electron emissive layer (6) is deposited over the transparent dielectric layer (5). On the first glass substrate (2), a plurality of address electrodes (7) are formed with one address electrode (7) is formed in each sub-pixel. The address electrodes (7) are covered with a dielectric layer (8) to limit the discharge current and for light reflection. The straight channel barrier ribs (9) are formed over the dielectric layer (8). The R (10a), G (10b), B (10c) phosphor layers are formed in the barrier rib (9) channel spaces.
FIG. 1(b) shows the top view of the conventional PDP structure shown in figure 1(a). The Red (R) (10al), Green (G) (10bl) and Blue (B) (10c1) sub-pixels are formed with the combination of second and first substrate structure. One PDP cell or sub-pixel comprises of one pair of display electrodes (3), (4) and an address electrode (7).
FIG. 2 Shows the principle of discharge in conventional AC PDP structure. The discharge sustains between display electrodes made up of transparent ITO
sheets (3), the VUV generated in by Ne-Xe plasma emitted in all direction. A considerable amount of VUV radiation lost at cell boundary (9) and these radiations are not converted into visible light and even if converted into visible photons it does not to brightness improvement directly. The rest of VUV radiations strike the phosphor (10), i.e. red phosphor (10a), and VUV photons are converted into visible photons. The visible photons are emitted from the phosphor and propagate towards second substrate and more than 40% of these visible photons are obstructed by MgO layer (6), transparent dielectric layer (5), bus electrodes (4), transparent ITO electrodes (3) and the second substrate itself which results in poor brightness of plasma displays.
FIG. 3(a) The new PDP discharge cell structure according to the present invention has been illustrated in this figure. On the first substrate (11) first set of disc shaped interconnected electrodes (12) i.e. X electrodes, are fabricated in first direction. The X electrodes are covered with a first dielectric layer (13) and over this dielectric layer (13) a second set of ring shaped interconnected electrodes (14), i.e. Y electrodes are fabricated in second direction orthogonal to X electrodes, such that the centre of the disc of Y electrodes sits over the top of center of X electrodes. The first dielectric layer (13) acts as insulating layer between X electrodes (12) and Y electrodes (14). The second dielectric layer (15) is formed to cover the Y electrodes (14) to limit the discharge current. A first cavity (16) is formed at centre of the ring of the Y electrodes (14). A secondary emissive layer which also acts as protective layer (17) is formed on the second dielectric layer (15). On the second substrate (18) dielectric barrier ribs are formed (19) and the channel between each two ribs filled with Red phosphor (20a), Blue phosphor (20b), and Green phosphor (20c). The first substrate and second substrate aligned together in such a way that the channel filled with phosphor encases the cavity (16) formed on first substrate.
FIG. 3(b): The schematic top view of the new PDP discharge cell structure according to the present invention has been illustrated. The center of the first set
of disc shaped interconnected electrodes, i.e. X electrodes coincides with the centre of the second set of ring shaped interconnected electrodes i.e. Y electrodes, and the center of the cavity between the ring electrodes. The diameter of the disc of the first set electrodes is d1, the diameter of cavity is D1, D2 is internal diameter of the ring shaped electrodes and D3 is the outer diameter of the ring shaped electrode.
FIG. 4: The schematic of cross-sectional view of the new PDP discharge cell structure explaining the discharge principle, in a sub-pixel, of the present invention. It has been shown that discharge initiates at bottom part of the cavity (16), which is top of the first set of the electrodes (12), and plasma spreads up to outer edge of Y electrode (14). The VUV photons generated by discharge spreads in all direction and strike the phosphor, i.e. Red phosphor (20 a). The cell geometry is such that it maximizes the reach of the VUV photons to the phosphor and minimizes the loss of VUV photons. The phosphor, i.e. Red phosphor (20b), converts the VUV photons into visible Red photons, these visible photons emitted through second substrate. Since, there is no obstructing layer for visible light on second substrate; the loss of visible light is least and hence maximizing the brightness. The thickness of the first dielectric layer (13), covering X electrodes (12), is h1. The thickness of the second dielectric layer (15), covering Y electrodes (14), is h2. The dielectric barrier rib (19) of height h3 is made on second substrate. Here, h represents the separation between dielectric layer (13) and the Y electrodes (14). Either of the substrate could be used for display of visual effects.
FIG. 5: The schematic of process steps for manufacturing of first glass substrate (11) according to the present invention. In process PI the first glass substrate is annealed. In the following process P2 the first set of electrodes (12) i.e. X electrodes are formed. These electrodes are formed either by screen printing, photo-lithographic or by sputtering or E-beam process. The materials that is used as electrodes may be selected from screen printable Silver, photosensitive silver
(Fodel), Aluminum, Cr-Cu-Cr materials. In the process step P3, X electrodes
(12) are covered by a dielectric layer (13). The dielectric layer to be printed either by screen printing, lamination process. The materials used as dielectric layer are either transparent glass, laminated sheets. The Y electrodes (14) in second direction and orthogonal to the X electrodes are fabricated on the dielectric layer
(13) by process step 4. These electrodes are formed either by screen printing, photo-lithographic or by sputtering or E-beam process. The materials that are used as electrodes may be selected from Silver, Aluminum, Cr-Cu-Cr materials. The second set electrodes, i.e. Y electrodes (14) are covered with a second dielectric layer (15) in process step 5. The second dielectric layer to be printed either by screen printing, lamination process. The materials used as di-electric layer are either transparent glass, laminated glassy sheets. In process step 6, a cavity (16) is formed between ring shaped electrodes by sand blasting process. In process step 7, a secondary emissive which also acts protective layer (17) is formed on dielectric layer (15) and throughout the cavity (16). The secondary emission layer can be deposited either by E-beam or sputtering method. The materials used for secondary emission may be chosen from Magnesium Oxide (MgO). The dielectric barrier rib height and dielectric thicknesses represented by hi, h2, h3 and h in FIG. 4 could be varied by varying the number and thickness of dielectric layers. The aforementioned process steps represents the embodiment of the present invention for height h=0. For making h>0 additional dielectric layers could be made.
FIG. 6: The schematic of process steps for manufacturing of second substrate according to the present invention. In the process P8, first the barrier rib layers are formed on second glass substrate. The barrier rib layers are printed either by screen printed with either by sand blastible or photo-etchable barrier rib paste or by lamination process. Then the barrier rib is etched either by sandblasting or by chemical etching to make the required design. Then the R, G, B phosphor is deposited inside the barrier rib channels by screen printing method.
FIG. 7: The schematic Plasma Display Panel according to the present invention comprising first substrate (11) and second substrate (18). It shows that first substrate (11) comprises first set of electrodes (12), i.e. X electrodes, in first direction, a first dielectric layer (13) covering X electrodes, a second set of electrodes (14), i.e. Y electrodes in second direction orthogonal to the X electrodes and a cavity (16) is provided between rings of Y electrodes.
The second substrate (18) comprises of Red (20a), Blue (20b) and Green (22c) phosphor filled in the, channel between the dielectric barrier ribs (19) in predetermined sequence.
The first substrate and second substrate aligned together in such a way that the channel filled with phosphor encases the cavity (16) formed on first substrate.
FIG. 8: The schematic Plasma Display Panel according to the present invention comprising first substrate (11) and second substrate (18), wherein second substrate has different processing steps. It shows that first substrate (11) comprises first set of electrodes (12), i.e. X electrodes, in first direction, a first dielectric layer (13) covering X electrodes, a second set of electrodes (14), i.e. Y electrodes in second direction orthogonal to the X electrodes and a cavity (16) is provided between rings of Y electrodes.
The second substrate (18) comprises of Red (22a), Blue (22b) and Green (22c) phosphor filled in the cavity (22), and this second cavity is formed between dielectric barrier ribs on the second substrate.
The first and second substrates are aligned in such a way that the cavity on first substrate (16) encases the cavity on second substrate (22) and discharge volume between the dielectric barrier ribs is formed.
FIG. 9: The schematic of second and first substrate together, with alternative structure and processing of first and second substrate and alternative
arrangement of cells on first substrate and second substrate, forming Plasma Display Panel according to the present invention.
This figure shows that first substrate (11) comprises first set of electrodes (12), dielectric layer (13) covering first set of electrodes, second set of ring shaped interconnected electrodes (14) over dielectric layer (13) which is orthogonal to first set of electrodes (12), dielectric layer covering second set of electrodes and a cavity (23) between ring shaped electrodes. The second substrate (18) comprises of Red (25a), Blue (25b) and Green (25c) phosphor filled in the cavity (24) and the cavity walls, formed on the second substrate such that the cavity on first substrate (23) and the cavity on second substrate (24) between the dielectric barrier ribs forms the discharge volume. The straight discontinuous dielectric barrier rib (26) is shown. This cell arrangement optimizes cell dimensions and color reproduction. The barrier hb (26) could be made on either of the substrate.
FIG. 10: This figure shows the second substrate (18) comprises of additional electrodes (27) on second substrate forming a mesh and acts EMI filter.
In the embodiment of present invention, a new PDP discharge cell structure has been disclosed. While this invention has been described in connection with what is presently considered to be most practical and preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements possible with in the spirit and scope of the appended claims. For example ring can take form of square, hexagon, triangle, rectangle and ellipse etc, first electrode take shape of straight line, ring square, hexagon, triangle, rectangle and ellipse and cavity could be of circular, rectangular, square, hexagonal shape and auxiliary electrodes to influence the discharge, ribs could be made on first or second substrate.

WE CLAIMS :-
1. A Plasma Display Panel comprising
a pair of first glass substrate and second glass substrates facing each other, and gas enclosed between them, having a plurality of interconnected first set of disc shaped electrodes (X) with diameter d1 in first direction, a dielectric layer with dielectric constant (1 and of thickness h1 is provided to cover the plurality of X electrodes,
a plurality of interconnected second set of ring shaped electrodes (Y) with ring having internal diameter D2 and outer diameter D3 fabricated on the dielectric layer covering the plurality of X electrodes, in second direction which is orthogonal to the direction of the plurality of the X electrodes, such that centre of the rings of the second set of electrodes sits on top of the center of the discs of X electrodes, another dielectric layer with dielectric constant (2 and of thickness h2 is provided to cover the plurality of Y electrodes, the height h i.e. the separation between Y electrodes and dielectric layer covering X electrodes is 0,
a first cavity of diameter D1 at the center of the rings of the Y electrodes is provided on the dielectric layer covering the plurality Y electrodes,
a plurality of dielectric barrier ribs of height h3 formed on the second substrate, in the first direction, parallel to the X electrodes and the channel formed between each two barrier ribs is having width D3, the plurality of channels on the second glass substrate is filled with Red (R), Green (G) and Blue (B) phosphors in predetermined sequence,
the first and the second substrate are aligned together in such way that the plurality of channels filled with phosphor, on the second glass substrate, envelopes the plurality of first cavities on first glass substrate and thus forming the discharge volume,
a protective layer, which also acts as a secondary electron emissive layer is provided on the dielectric layer covering the Y electrodes,
the electrodes X and Y described above are utilized for application of electrical potential in predetermined temporal sequence, i.e. the application of scan, address and sustain voltages to display the visual effects.
2. The plasma display panel as claimed in claiml, the separation between Y electrodes and dielectric layer covering X electrodes is increased by an additional dielectric layers with dielectric constant e, i.e. height h>0.
3. The plasma display panel as claimed in claim 3, wherein the dielectric constant of each dielectric layers i.e. the first dielectric layer, the second dielectric layer and the additional dielectric layers are predetermined such that
e1=e2=e, e1=e2=e, e1=e2=e, e1eS2=e.
4. The plasma display panel as claimed in claim 1 and 2, wherein the thickness h1 of first dielectric layer covering plurality of X electrodes and the thickness h2 of second dielectric layer covering the plurality of Y electrodes, h3 i.e. the height of dielectric barrier rib and the height h, i.e. the separation between X and Y electrodes, are predetermined.
5. The plasma display panel as claimed in claim 1, where in the diameter d1 of the X electrodes, the diameter D1 of the first cavity, the inner diameter D2 of the nng of the Y electrodes and its outer diameter D3 and the D4 width of the channel between the dielectric barrier ribs are predetermined.

7. The plasma display panel as claimed in claim 1, wherein each Y electrodes are formed by a group of electrodes in parallel.
8. The plasma display panel of as claimed in claim 1, wherein the position of X and Y electrodes is interchanged and the both electrodes i.e. X and Y electrodes are made up of rings.
9. The plasma display panel as claimed in claim 1, wherein the channel formed
between plurality of dielectric barrier ribs on the second substrate in the first
direction, parallel to the X electrodes, filled with Red (R), Green (G) and Blue (B)
phosphors predetermined sequence.
10. The plasma display panel of as claimed in claim 1 and 10, wherein the a plurality of second cavity is made in the channels formed between plurality of dielectric barrier ribs on the second substrate, filled with Red (R), Green (G) and Blue (B) phosphors predetermined sequence.
11. The plasma display panel of as claimed in claim 1, and 11, wherein the each set of X electrode is off centered from another set of X electrode forming plurality of alternatively off centered X electrodes, accordingly Y electrodes and the first cavity between the ring of Y electrodes are also off centered such that the center Y electrodes sits over the centre of X electrodes i.e. the centre of first cavity sits over top of center of Y electrodes such that centre of X electrodes, centre of Y electrodes and centre of the first cavity lie on a straight line. A plurality of second cavities is formed on the second substrate such that the centre of these cavities aligned with centers of X electrodes, Y electrodes and first cavity. The second cavities on second substrate are filled with Red, Green and Blue phosphor. A plurality of discontinuous barrier ribs is formed between two cavities on the second substrate.
12. The plasma display panel as claimed in claim 1, 8, 11 and 12, the plurality X electrodes is formed on first substrate and covered with first a dielectric layer and a first cavity is formed between the rings of X electrodes, plurality of Y electrode is formed on second substrate covered with second dielectric layer with a second cavity formed between each rings of both electrodes, the first and second substrate are aligned together such that cavity on the first substrate encased by cavity on second substrate forming the discharge volume.
13. The plasma display panel as claimed in claim 1 and 12, wherein the either of the substrate utilized as display substrate with at least two electrodes for scanning, addressing and sustaining the discharge and additional electrodes are fabricated for filtering the electromagnetic interference.