WO2006004262A1

WO2006004262A1 - Front panel for plasma display panel of high efficiency containing nanotips, and process for preparation of the same

Info

Publication number: WO2006004262A1
Application number: PCT/KR2005/000868
Authority: WO
Inventors: Yong Seog Kim; Sung Won Cho
Original assignee: Yong Seog Kim; Sung Won Cho
Priority date: 2004-03-26
Filing date: 2005-03-25
Publication date: 2006-01-12
Also published as: KR20050095381A

Abstract

Disclosed herein is a front panel for a plasma display panel (PDP) capable of improving the light-emitting efficiency and considerably lowering the driving voltage of a PDP. The front panel comprises a transparent substrates, sustain electrodes, bus electrodes, dielectric layers and a protective layer wherein tip groups are formed in regions of an upper dielectric layer corresponding to the sustain electrodes, each of the tip groups consisting of one or more Nanotips at least partially protruded from the surface of the protective layer of the nanotips, the nanotips are spaced apart from each other at least by a distance where field enhancement is caused, and the nanotips are coated with a protective film such that they are protected against plasma sputtering. Further disclosed is a method for preparing the front panel.

Description

FRONT PANEL FOR PLASMA DISPLAY PANEL OF HIGH

EFFICIENCY CONTAINING NANOTIPS, AND PROCESS FOR

PREPARATION OF THE SAME

FIELD OF THE INVENTION

The present invention relates to a front panel for a plasma display panel (PDP) capable of improving the light-emitting efficiency and considerably lowering the driving voltage of a PDP, and more particularly to a technology for inducing an improvement in light-emitting efficiency and a decrease in driving voltage due to a field enhancement caused by nanotips formed in a particular shape on an upper dielectric layer of a front panel constituting a PDP.

BACKGROUND OF THE INVENTION

PDPs are flat displays which are superior in display image quality, thin and lightweight. For these reasons, PDPs are exclusively used for large-area displays of 40 inches or more. PDPs produce images by forming pixels at points where barriers and address electrodes formed on a rear panel are crossed perpendicularly to surface discharge electrodes formed on a front panel. The structure of such PDP is schematically shown in FIG. 1. When a voltage is applied between sustain electrodes 20 of a front panel 10 and address electrodes 50 of a rear panel 80, plasma is generated in spaces between barriers 60. In addition, when a maintenance voltage is applied between the sustain electrodes 20, vacuum ultraviolet rays generated from the plasma excite a fluorescent material 70 coated on the barriers 60 and the bottom surface between the barriers 60, leading to the generation of red, green, and blue visible rays.

Commercially available PDPs suffer from high power consumption due to their low discharge efficiency ranging from 1.3 to 1.8 lm/watt, and have a high discharge initiation voltage of 140-180V, which necessitates the use of costly driving circuits. These disadvantages (i.e., low discharge efficiency and high driving voltage) are main causes of increased preparation costs and high power consumption of PDPs.

To solve the above-mentioned problems, a number of studies on the compositions of discharge gases in PDP cells and novel suitable driving manners have been undertaken. Further, an approach to improve the electron emission coefficient of a protective layer aimed at improving the discharge efficiency and lowering the driving voltage is considered as an important task.

As a material for a protective film (or protective layer) of a front panel for a PDP, MgO is commonly used due to its resistance to sputtering and relatively high secondary electron emission coefficient. There are known several factors affecting the secondary electron emission coefficient of the MgO protective film, e.g., crystal orientation, stoichiometry and density of MgO, but control of these factors does not satisfactorily lead to changes in discharge efficiency and driving voltage. As another approach, an attempt has been made to increase the secondary electron emission coefficient by employing a low work function ceramic material, e.g., CaO, in MgO to form a complex thin film, but the effects are negligible.

In conclusion, to improve the discharge efficiency and decrease the driving voltage of PDPs, there is an increasing need to develop a novel protective film having a greatly increased electron emission coefficient relative to that of currently used MgO protective films. SUMMARY OF THE INVENTION

Thus, it is an object of the present invention to solve the above-mentioned problems of the prior art and technical tasks requested in the past.

The inventors of the present invention have surprisingly found through extensive research and repeated experiments for many years that when nanotips protruded from a protective layer are formed on an upper dielectric layer of a front panel for a PDP, field enhancement is caused on the protective layer, resulting in an improvement in light-emitting efficiency and a remarkable decrease in discharge initiation voltage. The present invention has been accomplished based on this finding.

In accordance with an aspect of the present invention, there is provided a front panel for a PDP comprising a transparent substrate, sustain electrodes, bus electrodes, dielectric layers and a protective layer wherein tip groups are formed in regions of an upper dielectric layer corresponding to the sustain electrodes, each of the tip groups consisting of one or more nanotips at least partially protruded from the surface of the protective layer of the nanotips, the nanotips are spaced apart from each other at least by a distance where field enhancement is caused, and the nanotips are coated with a protective film such that they are protected against plasma sputtering.

The nanotips induce field enhancement effects around the nanotips. Based on this characteristic, field emission can be initiated even at a relatively low voltage and secondary electron emission efficiency can be improved. Nanotips having a diameter of from several to thousands of angstroms (A) increase field enhancement effects around the nanotips by 10²~10⁴ times. Namely, the present invention provides a hybrid front panel for a PDP which can exert not only superior sputtering resistance and secondary electron emission properties of a protective layer, but also secondary electron emission effects and field emission effects based on the field enhancement effects of nanotips.

Based on these characteristics, the present invention provides the following effects:

1) Wall voltage and drive maintenance voltage created on the protective layer upon plasma discharge effectively enhance a field around the nanotips, improving not only secondary electron emission properties of the protective layer but also electron emission properties due to the field emission of the nanotips. As a result, driving voltage in PDP discharge cells is decreased. A PDP employing the front panel of the present invention has a luminance of at least two times higher than that of conventional PDPs at the same driving voltage.

2) Power consumption in discharge cells is reduced due to decreased driving voltage, contributing to an improvement in discharge efficiency.

3) The discharge voltage of a PDP and operating voltage of maintenance driving elements are decreased and thus the operating voltage of driving circuits is lowered, enabling the manufacture of PDP electronic parts at reduced costs.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a cross-sectional view schematically showing the structure of a surface discharge-type alternating current (AC) plasma display panel (PDP);

FIG. 2 is a schematic diagram showing the structure of a front panel comprising nanotips according to one embodiment of the present invention;

FIG. 3 is a schematic diagram showing field enhancement caused by field distortion of nanotips protruded from an upper dielectric layer;

FIGS. 4 to 6 are schematic diagrams showing various arrangements of nanotips on a front panel according to the present invention and the number of nanoparticles constituting each of the nanotips;

FIGS. 7 to 15 are schematic diagrams showing respective steps of a method for preparing a front panel for a PDP according to one embodiment of the present invention; and

FIGS. 16 to 19 are graphs showing the light emission properties of a PDP employing a front panel according to one embodiment of the present invention in which carbon nanotubes are included as materials of nanotips.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

As explained previously, one nanotip group formed over a specific sustain electrode (more accurately, on an upper dielectric layer over a specific sustain electrode) is spaced apart from other nanotip groups formed over adjacent sustain electrodes. If the tip groups are not spaced apart from each other (i.e. the nanotips are uniformly dispersed throughout the dielectric layer), the driving voltage is lowered but the luminance remains unchanged.

The area occupied by the tip group may be substantially equal to or a bit larger or smaller than that of the sustain electrode corresponding to the tip group. In one embodiment of the present invention, the tip group may be formed in such a manner that it covers only the area of the bus electrode corresponding thereto.

The shape of the tip group may be varied depending on that of the underlying sustain or bus electrode. For example, the shape of the tip group is varied depending on that of the electrodes corresponding to various shapes of barriers, e.g., stripe, waffle, honeycomb, meander, fishbone, etc. In addition, the shape of the tip group is not necessarily limited to that of the electrodes, and the tip group may have a shape substantially identical to the shape of the electrodes.

Each of the tip groups may consist of one or more nanotips. When two or more nanotips are included in one tip group, they are spaced apart from each other by a distance sufficient to cause a field enhancement, as explained above. Within the distance where field enhancement is induced, electrons can be easily emitted by field emission. As shown in FIG. 3, the nanotips protruded from the corresponding protective layer on the upper dielectric layer causes a field enhancement due to a field distortion. In contrast, when the nanotips are close to each other, field enhancement effects greatly drop. Thus, it is necessary to space the nanotips apart from each other at least by a distance corresponding to about one half of an average height of the nanotips protruded from the protective layer. Preferably, the distance is higher, and more preferably two times higher than the average height of the nanotips. Considering that the thickness of a MgO protective layer for use in a PDP is about 3,000 A to 7,000 A, the nanotips protruded from the protective layer preferably have a height of lμm to lOμm and the distance between the nanotips is preferably about 2-20 μm, which is at least two times higher than the height of the nanotips, in terms of field emission effects.

The dielectric layers act to protect the sustain electrodes and electrically functions as a condenser. The dielectric layers are made of low-melting point glass components, including PbO, SiO₂, B₂O₃, and the like. The dielectric layers consist of a lower dielectric layer showing little reactivity with the electrodes due to low contents of alkali components, and a highly smooth upper dielectric layer. In the present invention, the nanotips are formed on the upper dielectric layer. As explained above, the upper dielectric layer shows characteristics different from those of the lower dielectric layer. If needed, the lower and upper dielectric layers can be integrally formed. In this case, the nanotips may be formed in the upper portion of the integral dielectric layer.

The nanotips may have various shapes, preferably a bar, tube, sheet, or belt shape whose length-to- width ratio is at least 2. The nanotips may be made of one nanomaterial, or a combination of two or more different nanomaterials. For example, in the case where the nanomaterial is a carbon nanotube, the nanotips may be made of one carbon nanotube or a combination of a carbon nanotube and a fine graphite powder.

The nanotips formed in the upper dielectric layer may have vertical orientation, inclined orientation, or a combination thereof. Of these, vertical orientation is particularly preferred. However, field enhancement can be achieved only when the nanotips are at least partially protruded from the protective film.

Materials for the protective layer constituting the front panel for a PDP and a protective film coated on the nanotips are preferably MgO or SiO₂, and more preferably MgO, but are not limited thereto. The protective layer and film may be complex thin- film layers containing a ceramic material, e.g., CaO, in MgO.

Materials for the nanotips are not especially limited so long as they show the above-mentioned effects, and include carbon compounds, e.g., carbon nanotubes and carbon nanofibrils, oxides, e.g., zinc oxide (ZnO), alumina (Al₂O₃), silica (SiO₂), calcia (CaO), zirconia (ZrO₂), vanadium oxide (V₂O₅), tungsten oxide (W₂O₅) and magnesium oxide (MgO), nitrides, e.g., boron nitride (BN), titanium nitride (TiN), aluminum nitride (AlN) and silicon nitride (Si₃N₄), carbides, e.g., TiC, TaC, SiC, WC and VC; sulfides, e.g., CdS and MoS₂, and composite ceramics, intermetallic compounds and metals thereof. The use of carbon nanotubes is preferred.

The nanotips preferably have a diameter of 1-500 nm, and more preferably

1-100 nm.

The area density of the nanotips in the protective layer is preferably in the range of 10 to 10 tips/cm within which transmittance of visible rays is not deteriorated.

The present invention also provides a method for preparing the front panel for a PDP. The method of the present invention can be accomplished in various manners. In one embodiment of the present invention, the front panel for a PDP can be prepared by a method comprising the steps of:

(a) forming a lower transparent dielectric layer including sustain electrodes and bus electrodes on a transparent substrate, sintering the lower transparent dielectric layer, and forming an upper transparent dielectric layer on the lower transparent dielectric layer;

(b) partially sintering the upper transparent dielectric layer, and patterning mask dams having a predetermined height on the upper dielectric layer such that regions of the upper dielectric layer corresponding to the sustain electrodes are exposed;

(c) pouring a suspension containing nanotips onto spaces between the mask dams and evaporating a solvent of the suspension;

(d) removing the mask dams and sintering the upper transparent dielectric layer; (e) forming a protective layer on the upper transparent dielectric layer including the nanotips; and

(f) coating the nanotips with a protective film.

Preferably, the method according to one embodiment of the present invention may further comprise the step of chemically and/or mechanically etching the upper transparent dielectric layer such that the nanotips are further exposed, between steps (d) and (e).

In step (a), the formation of the dielectric layers can be carried out by processes commonly known in the art. For example, the lower and upper dielectric layers can be sequentially formed by printing a paste including dielectric glass frits, or laminating a dry film. If necessary, the upper and lower dielectric layers may be formed into one layer, as described above.

In step (b), the upper dielectric layer is partially sintered. This partial sintering leads to the formation of fine pores between the glass frits constituting the upper dielectric layer. The partial sintering is carried out, for example, for 30-60 minutes at 400~500°C. Then, mask dams are patterned on the upper dielectric layer such that regions of the upper dielectric layer corresponding to the sustain electrodes are exposed. The patterning of the mask dams is carried out by forming a film to a height corresponding to that of the mask dams by dry film lamination or spin coating of liquid photoresist, which are generally used in thin-film formation processes, and patterning the mask dams by various techniques, such as lithography.

In step (c), a suspension containing nanotips is poured onto spaces between the mask dams. At this step, the suspension and the nanotips are introduced into the pores formed between the glass frits in the upper transparent dielectric layer. Thereafter, a solvent of the suspension is evaporated, and the mask dams are removed. The suspension may be prepared, for example, by adding nanomaterials for the nanotips and a dispersant to a non-reactive solvent, such as water. In the case that the nanomaterial is carbon nanotube, the carbon nanotube is coated with an anti-reactive film using SiO₂ or MgO to prevent reaction of the carbon nanotube with the components of the upper transparent dielectric layer. The concentration of the nanoparticles in the suspension may be changed depending on the density of the nanotips to be formed on the upper dielectric layer. For example, the suspension may have an extremely low concentration of about 10 ppm. As mentioned above, the nanotips are preferably arranged in a vertical orientation in the protective layer, which requires an additional step for the arrangement. For example, if the nanotips can be oriented under an electric field like dipoles, the orientation of the nanotips can be improved by inducing an electric field in upper and lower directions during drying of the suspension. Alternatively, the orientation can be improved in artificial manners, e.g., by applying a physical force (e. g., an adhesive force) to the nanotip material present on the sintered upper transparent dielectric layer.

In step (d), after the mask dams are removed and the upper transparent dielectric layer is completely sintered, the nanotips introduced into the pores are mechanically fixed on the upper dielectric layer. Complete sintering of the upper transparent dielectric layer can be carried out, for example, for 30-60 minutes at about 520⁰C to about 590⁰C. Some nanotips remaining on the upper dielectric layer which are not introduced into the pores formed between the glass frits can be removed after complete sintering of the upper dielectric layer. If the mask dams are made of a material capable of being decomposed at a temperature where the upper dielectric layer is completely sintered, the removal of the mask dams may be omitted without any additional process.

In step (e), a MgO protective layer is formed on the upper transparent dielectric layer including the nanotips by known processes, e.g., electron beam deposition.

In step (f), the nanotips are coated with a protective film for protect the nanotips against plasma sputtering. The protective layer may be made of MgO or SiO₂. The thickness and material of the protective film are not especially restricted so long as the protective film can perform the above-mentioned functions. If desired, steps (e) and (f) may be simultaneously carried out. Also, step (f) of coating the nanotips with the protective film may be previously carried out.

The present invention will now be described in more detail with reference to the following embodiments and accompanying drawings. However, these embodiments and drawings are not to be construed as limiting the scope of the invention.

FIG. 2 is a schematic diagram showing the structure of a front panel 100 for a PDP according to one embodiment of the present invention. A transparent sustain indium-tin-oxide (ITO) electrode 300 and a bus electrode 310 are disposed on a transparent substrate 200 commonly made of glass, and a lower dielectric layer 400 covers the resulting structure. An upper dielectric layer 410 is formed on the lower dielectric layer 400, and a tip group 600 consisting of a plurality of small bar-shaped nanotips 610 is disposed in the region of the upper dielectric layer 410 corresponding to the transparent electrode 300. A MgO protective layer 500 is formed on the surface of the upper dielectric layer 410. For convenience of explanation, the nanotips 610 are relatively enlarged in FIG. 2. It should be appreciated from the above description that the shape, size, and orientation of the nanotips 610 are not limited to those shown in FIG. 2. The tip group 600 formed over the sustain electrode 300 is spaced from a tip group 602 formed over an adjacent sustain electrode 302 by the distance between the electrodes 300 and 302. The nanotips 610 constituting the tip group 600 are protruded from the surface of the protective layer 500 on the upper dielectric layer 410, and the distance L between the nanotips 610 is preferably longer than the protrusion height H.

FIG. 3 is a schematic diagram showing field enhancement at the nanotips.

Referring to FIG. 3, distortion A of a field 700 is generated in the protruded portions of the nanotips 610 arranged on the upper dielectric layer 410, resulting in a field enhancement and promoting electron emission at the nanotips 610 due to a field emission. An electric current generated by the field emission increases the discharge current of a PDP, together with an electric current of secondary electrons emitted when ions present in plasma collide with the MgO protective layer 500. This increase in the electric current increases the luminance of a fluorescent layer, and lowers the discharge voltage of a PDP, enabling the operation of the PDP even at a low voltage.

The arrangement of nanotips on the front panel and the number of nanoparticles constituting the nanotips vary, for example, as shown in FIGS. 4 to 6. Specifically, FIG.

4 shows a state wherein nanotips 610, each of which is composed of one nanoparticle, are arranged over sustain electrodes 300 and the bus electrodes 310, FIG. 5 shows a state wherein nanotips 610, each of which is composed of two or more nanoparticles, are arranged over sustain electrodes 300 and bus electrodes 310, and FIG. 6 shows a state wherein stripe-type nanotips 610, each of which is composed of a plurality of nanoparticles, are arranged over sustain electrodes 300 and bus electrodes 310.

However, these arrangements are provided for illustrative purposes only and do not serve to limit the scope of the present invention.

FIGS. 7 to 15 show the overall procedure of a method for preparing a front panel according to one embodiment of the present invention. Referring first to FIG. 7, sustain electrodes 300 and bus electrodes 310 are formed on a transparent substrate 200, and a lower dielectric layer 400 is formed so as to cover the resulting structure. This formation is carried out by known processes.

Referring to FIG. 8, an upper dielectric layer 410 is formed on the lower dielectric layer 400, and then partially sintered. As already explained, partial sintering of the upper dielectric layer 410 leads to the formation of fine pores between glass frits constituting the upper dielectric layer.

Referring to FIG. 9, mask dams 900 with a predetermined height are patterned on the upper dielectric layer 410 such that only regions 412 of the upper dielectric layer corresponding to the sustain electrodes are exposed. The mask dams 900 may be made of any material that can be easily removed in subsequent steps (FIG. 10), without being dissolved or swelled by a nanotip-containing suspension. In addition, the patterning of the mask dams 900 is carried out by conventional patterning techniques used in thin- film formation processes. For example, the mask dams 900 can be patterned by coating a photoresist on the upper dielectric layer 410, locating a patterned glass mask in which portions corresponding to the mask dam 900 are exposed on the upper dielectric layer 410, perpendicularly irradiating the resulting structure with ultraviolet rays to cure only the exposed portions, and removing the unexposed portions.

Thereafter, a suspension 1000 containing nanotips 610 is separately prepared.

The suspension 1000 is poured onto spaces 910 between the mask dams 900. FIG. 10 shows the suspension remaining in the spaces 910 shown in FIG. 9.

For reference, a suspension containing carbon nanotubes as the nanotips is prepared by the following procedure. First, carbon nanotubes are mixed with water and a dispersant (for example, dodecyltrimethylammonium bromide (DTAB) with stirring by sonication. A silica precursor (e.g., tetraethyl orthosilicate (TEOS)) is added to the mixture and is allowed to react to obtain carbon nanotubes coated with silicon dioxide. The reaction mixture was centrifuged, and then added to water containing a dispersant to prepare the desired suspension. If a metal oxide is used instead of the carbon nanotubes, coating with silicon dioxide can be omitted.

Referring again to FIG. 10, some of the nanotips 610 contained in the suspension 1000 are introduced into the pores formed between the glass frits on the surface of the upper dielectric layer 410. Some of the nanotips 610 may have either a vertical or inclined orientation. If desired, the proportion of the vertical orientation can be further increased by various processes. For example, in the case where the nanotips 610 can be oriented by an electric field or magnetic field, a particular external force may be applied to the nanotips. This increase in the proportion of vertical orientation can be achieved by any step of the preparation procedure.

Referring sequentially to FIGS. 11 to 13, the solvent of the suspension 1000 is removed, e.g., by drying, the mask dams 900 are removed, and then the upper dielectric layer 410 is completely sintered.

As shown in FIG. 14, the surface of the upper dielectric layer 410 is partially etched such that the nanotips 610 are further protruded from the upper dielectric layer 410.

As shown in FIG. 15, a MgO protective layer 500 is formed on the upper dielectric layer 410 in which the nanotips 610 are mechanically fixed. The formation of the MgO protective layer 500 is carried out by thin-film deposition processes, including electron beam deposition, ion plating, and plasma sputtering. The protective layer may be formed on the surface of the nanotips 610. Alternatively, the protective film of the nanotips 610 may be separately formed.

If necessary, the method of the present invention may further comprise other steps for improving the effects of the present invention so long as the object of the present invention is not impaired.

FIG. 16 is a graph illustrating the voltage-luminance relationship of a front panel comprising nanotips according to one embodiment of the present invention. The measurement was conducted under the following experimental conditions.

First, a 100 ppm suspension containing carbon nanotubes as the nanotips was prepared. A front panel was prepared in accordance with the procedure shown in FIGS. 7 to 15. Specifically, an ITO transparent electrode film formed on a PD-200 glass substrate was etched to form a transparent electrode in a desired shape, and then a photosensitive Ag paste was printed on the whole surface of the transparent electrode to a thickness of 5—15 μm. The paste thus printed was exposed to light using a mask, developed, dried and sintered to form bus electrodes. A transparent dielectric paste was printed on the resulting structure, followed by drying and sintering, to form a lower dielectric layer having a thickness of 10 to 20 μm. Subsequently, a transparent dielectric paste was printed on the lower dielectric layer, dried and precalcined to form an upper dielectric layer having a thickness of 10 to 20 μm. As shown in FIGS. 9 to 11, after nanotips were introduced into the upper dielectric layer using the suspension and completely sintered, a 500-700 nm-thick MgO protective layer was formed thereon to prepare a front panel. The front panel thus prepared and a rear panel in which barriers and a fluorescent film were formed were subjected to vacuum sealing to fabricate a PDP. The luminance of the PDP was measured under the following conditions: discharge gas components: Ne-12% Xe; discharge gas pressure: 400 Torr. The obtained results are shown in FIG. 16. As can be seen from the results shown in FIG. 16, the luminance of the PDP employing the front panel of the present invention increased with increasing sustaining voltage and frequency of applied driving voltage, similarly to conventional PDPs. ,

Further, the luminance of the PDP employing the front panel of the present invention and a conventional PDP was compared under the following measurement conditions: discharge gas components: Ne-12% Xe; driving voltage frequency: 50 kHz. The obtained results are shown in FIG. 17. It could be confirmed from FIG. 17 that the luminance of the PDP (hybrid PDP) employing the front panel of the present invention was two times higher, particularly at low maintenance voltages, than that of the conventional PDP. The reason for this increase is believed that, when plasma discharge takes place in discharge cells, discharge current is increased due to field emission from the nanotips and emission of secondary electrons from the MgO protective film.

Further, the relationship between the density of the carbon nanotubes in the upper dielectric layer and the applied discharge voltage was measured, and the results are shown in FIG. 18. This measurement was conducted under the follwing conditions: discharge gas components; Ne-12% Xe; discharge gas pressure: 400 Torr; driving voltage frequency: 30 kHz. As apparent from the graph shown in FIG. 18, as the density of the carbon nanotubes increased, discharge voltage decreased. This phenomenon is because, as the density of the carbon nanotubes increases, the electron concentration increases due to field emission, thus lowering the Paschen's discharge voltage.

The time when the discharge was initiated after addressing of the PDP was measured. The obtained results are shown in FIG. 19. As can be seen from the results shown in FIG. 19, the discharge delay in the PDP comprising the carbon nanotubes was shorter than that in the conventional PDP.

Those skilled in the art will appreciate that various applications and modifications are possible based on the above description within the scope of the present invention.

INDUSTRIAL APPLICABILITY

As apparent from the foregoing, since the front panel for a PDP according to the present invention enables effective electron emission from the protective film, the driving voltage and discharge efficiency of the PDP can be improved. The decreased driving voltage reduces the energy of ions and electrons colliding with the protective film, thus lengthening the life of the protective film and the fluorescent material. In addition, the decreased discharge voltage lowers the operating voltage of various electronic parts used in PDPs, enabling the manufacture of PDPs at reduced costs.

Claims

WHAT IS CLAIMED IS:

1. A front panel for a PDP comprising a transparent substrate, sustain electrodes, bus electrodes, dielectric layers and a protective layer wherein tip groups are formed in regions of an upper dielectric layer corresponding to the sustain electrodes, each of the tip groups consisting of one or more nanotips at least partially protruded from the surface of the protective layer of the nanotips, the nanotips are spaced apart from each other at least by a distance where field enhancement is caused, and the nanotips are coated with a protective film such that they are protected against plasma sputtering.

2. The front panel according to claim 1, wherein each of the tip groups consists of one or more nanotips.

3. The front panel according to claim 1, wherein the nanotips have a vertical orientation, an inclined orientation or a combination thereof in the upper dielectric layer.

4. The front panel according to claim 1 , wherein the nanotips are made of at least one material selected from carbon compounds, e.g., carbon nanotubes and carbon nanofibrils, oxides, e.g., zinc oxide (ZnO), alumina (Al₂O₃), silica (SiO₂), calcia (CaO), zirconia (ZrO₂), vanadium oxide (V₂O₅), tungsten oxide (W₂O₅) and magnesium oxide (MgO), nitrides, e.g., boron nitride (BN), titanium nitride (TiN), aluminum nitride (AlN) and silicon nitride (Si₃N₄), carbides, e.g., TiC, TaC, SiC, WC and VC; sulfides, e.g., CdS and MoS₂, and composite ceramics, intermetallic compounds and metals thereof.

5. The front panel according to claim 4, wherein the nanotips are made of carbon nanotubes.

6. The front panel according to claim 4, wherein the nanotips are made of nanomaterials in a tube, sheet, belt or bar shape.

7. The front panel according to claim 1, wherein the shape of the tip group is substantially equal to that of the sustain or bus electrode corresponding to the shape of barriers, such as stripe, waffle, honeycomb, meander, and fishbone.

8. The front panel according to claim 1, wherein the protective film coated on the nanotips is made of MgO.

9. A method for preparing the front panel according to claim 1, comprising the steps of:

(d) removing the mask dams and sintering the upper transparent dielectric layer;

(e) forming a protective layer on the upper transparent dielectric layer including the nanotips; and

(f) coating the nanotips with a protective film.

10. The method according to claim 9, further comprising the step of chemically and/or mechanically etching the upper transparent dielectric layer such that the nanotips are further exposed, between steps (d) and (e).

11. The method according to claim 9, wherein, when the nanotips are made of carbon nanotubes, the carbon nanotubes are coated with SiO₂ or MgO.

12. The method according to claim 9, further comprising the step of arranging the nanotips in a vertical orientation.