Abstract:
A color plasma display panel which includes front and back substrates bonded together to form an integrated body and separated from each other at a predetermined distance, the front substrate being an image displaying surface, the back substrate including a plurality of sustain discharge electrodes forming a pair of plural electrodes in a cell, a dielectric layer for insulating the sustain discharge electrodes, and a protective layer; and the front substrate including a plurality of address electrodes arranged in crossing with the sustain discharge electrodes, and a fluorescent layer for generating visible rays.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a plasma display panel (PDP) which is a kind of light-emitting device for displaying an image by using the gas discharge between glass substrates and, more particularly, to a color PDP having an internal structure improved to increase aperture rate of the front panel which is an image displaying surface and maximize the efficiency of light emission using discharge between electrodes. 
     2. Background of the Related Art 
     In general, color PDPs are a kind of light-emitting device for displaying an image by use of internal gas discharge. Color PDP&#39;s are advantagous in that: (1) PCP&#39;s do not require active elements in cells; (2) each cell of the PDP has a simple fabricating process; and (3) PDP&#39;s have a high response speed. 
     In addition, PDPs are more easily enhanced in size relative to existing liquid crystal displays and can be used for large-sized display devices over 40 inches. 
     The schematic structure of PDPs includes two glass substrates bonded together with a frit glass and sealed to form an integrated body. The sealed internal space between the two glass substrates is filled with a gas under a pressure of 100˜600 Torr where the gas may be Xenon (Xe) in Helium (He). 
     The image display section of a panel has intersections between a plurality of electrodes in correspondence to pixels (cells). When driving the panel to display an image, a voltage greater than 100 volts is applied to the intersections causing glow discharge of gas and emitting lights. This panel section is combined with a driving section to serve as a display device. 
     PDPs are classified into two-, three- and four-electrode types according to the number of electrodes allotted to each cell: the two-electrode type PDP is driven by applying an addressing and sustaining voltage to two electrodes. The three-electrode type PDP is generally called a “surface discharge type” and is switched or maintained by a voltage applied to an electrode positioned on the lateral side of a discharge cell. 
     An example of the related art three-electrode surface discharge PDP will be described below in reference with FIGS. 1 to  3 . 
     FIG. 1 is an exploded view of a related art PDP structure having upper and lower substrates. In the figure, a front substrate  1  which is an image displaying surface is combined in parallel with a back substrate  2  at a predetermined distance. 
     The front substrate  1  is provided with a sustain discharge electrode formed with a pairing of a common electrode C and a scan electrode S. The sustain discharge electrodes are used to sustain light-emission within cells by means of mutual discharges in a pixel. 
     The front substrate  1  may also be provided with a dielectric layer  5  for restraining a discharge current of the two electrodes and insulating between electrode pairs. Additionally, a protective layer  6  may be formed on the dielectric layer  5 . 
     The back substrate  2  includes a plurality of spaces for discharge with separate walls  3  forming cells, a plurality of address electrodes A formed in the direction parallel with the separate walls  3  for performing address discharge at the intersections with scan electrodes S which creates vacuum ultra-violet rays, and a fluorescent layer  4  formed on the lateral sides of separate walls  3  and on the back substrates out of the internal surface of each discharge space for emitting visible rays to display images during address discharge. 
     FIG. 2 illustrates the arrangement of common electrodes C, scan electrodes S and address electrodes A. 
     FIG. 3 is a cross-sectional view of a cell after the upper and lower substrates are bonded together to form an integrated body, in which the lower substrate is rotated at 90 degrees for better understanding. 
     First, when a discharging voltage is applied between a scan electrode S and a common electrode C that form a pair of electrodes in the cell, surface discharge occurs between the two electrodes to form wall charges on the internal surface of the discharge space. 
     Following the surface discharge, an address discharge voltage is applied to the scan electrode S, and the address electrode A causes writing discharge to occur in the cell. Subsequently, a sustain discharge voltage is applied to the scan electrode S and the common electrode C. A sustained discharge occurs due to charged particles being generated in the address discharge between address electrode A and scan electrode S. Thus sustaining light-emission of the cell for a predetermined period of time. 
     In other words, an electric field is formed in a cell due to discharge between electrodes such that a minute quantity of electrons contained in a discharge gas are accelerated and collide with neutral particles in the gas to ionize. Thus, generated electrons collide with another neutral particles to produce more electrons and ions. In turn, the discharge gas is changed into plasma and vacuum ultra-violet rays are generated. The generated ultra-violet rays excite the fluorescent layer  4  to emit visible rays, which are projected to the outside through the front substrate  1  to cause light-emission in a cell. 
     In the prior art PDP structure as described above, sustain discharge electrodes C and S are fabricated in such a manner that transparent electrodes are patterned in order to prevent reduction of the aperture rate of front substrate  1  on which an image is formed. A metal having a lower resistance than the transparent electrodes is applied to the lateral edge of the transparent electrodes to prevent deterioration of the display quality. 
     Despite the use of transparent electrodes, there is a loss of about 10 to 25% of visible rays because the sustain discharge electrodes C and S are positioned in the front substrate  1 . 
     The contrast characteristic becomes deteriorated because the light-emitting part is completely exposed to the outside and the reflection factor is high. To enhance the contrast characteristic, use is made of a color filter in spite of deterioration of luminance by about 30 to 50%. 
     As a measure to enhance the luminance, raising the driving voltage applied to electrodes may increase the amount of generated vacuum ultra-violet rays, which raises production costs in realizing peripheral circuits and causes a rapid reduction of life of the PDP. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to a color plasma display panel that substantially obviates one or more of the problems due to limitations and disadvantages of the related art. 
     An object of the present invention is to enhance the aperture rate of the front substrate by forming a sustain discharge electrode that causes a loss of light in the back substrate. 
     Another object of the present invention is to provide a fluorescent layer on the front substrate to serve as a color filter and a source of visible rays. 
     Further another object of the present invention is to enhance discharge efficiency by increasing a discharge path between electrodes. 
     Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a plasma display panel including front and back substrates bonded together, the front substrate comprising an image displaying surface, a fluorescent layer and a plurality of address electrodes, and the back substrate including a plurality of sustain discharge electrodes forming a pair of plural electrodes in each cell, a dielectric layer for insulating the sustain discharge electrodes, and a protective layer. 
     The structure is a reverse application of upper and lower structures of the related art PDP and provides a PDP with enhanced luminance and contrast of emitted beams. 
     Use of a transparent material is not required to prevent deterioration of the aperture rate due to the sustain discharge electrodes positioned on the back substrate, and the fluorescent layer serving as a source of visible rays as well as a color filter. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention: 
     In the drawings: 
     FIG. 1 is a diagram that illustrates an exploded perspective of the related art PDP having upper and lower substrates; 
     FIG. 2 is a diagram that illustrates an arrangement of discharge electrodes of the PDP from the related art; 
     FIG. 3 is a diagram that illustrates a cross-sectional view of a discharge cell according to the related art; 
     FIG. 4 is a diagram that illustrates a cross-sectional view of a discharge cell according to a first preferred embodiment of the present invention; 
     FIGS. 5 and 6 are diagrams that illustrate cross-sectional views of a discharge cell according to a second preferred embodiment of the present invention; 
     FIGS. 7 a - 7   b  is a diagram that illustrates a cross-sectional view of a discharge cell according to a third preferred embodiment of the present invention; 
     FIGS. 8 a - 8   b  is a diagram that illustrates a cross-sectional view of a discharge cell according to a fourth preferred embodiment of the present invention; 
     FIG. 9 is a diagram that illustrates a cross-sectional view of a discharge cell according to a fifth preferred embodiment of the present invention; 
     FIGS. 10 a - 10   b  is a diagram that illustrates a cross-sectional view showing a modification to the discharge cell shown in FIG. 9; 
     FIG. 11 is a diagram that illustrates a cross-sectional view of a discharge cell according to a sixth preferred embodiment of the present invention; 
     FIGS. 12 a - 12   b  is a diagram that illustrates a cross-sectional view showing a modification to the discharge cell shown in FIG. 11; and 
     FIGS. 13 and 14 are diagrams that illustrate cross-sectional views of a discharge cell according to a seventh preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the preferred embodiments of the present invention, several examples of which are illustrated in the accompanying drawings. 
     These preferred embodiments will help better understanding of the objects, characteristics and effects of the present invention. 
     Hereafter, the preferred embodiments of the present invention PDP structure will be described in connection with the attached drawings. 
     In the figures, the same reference numeral denotes the same component. In the figures, upper and lower substrates are rotated at 90 degrees for better understanding. 
     As shown in FIG. 4, the PDP structure according to the first preferred embodiment of the present invention includes two substrates spaced from each other at a predetermined distance for discharge space by separate walls  103  to provide a discharge space and bonded together to form an integrated body. 
     A front substrate  101  is an image displaying surface generates visible rays. The front substrate  101  is provided with a fluorescent layer  104  serving as a color filter for the visible rays to pass through, and a beam masking (BM) layer  107  as well as an address electrode A formed on the top ends of the separate walls  103  to increase the aperture rate. 
     A back substrate  102  includes a common electrode C and a scan electrode S constituting a sustain discharge electrode in one cell and consisting of a wide metal material, a dielectric layer  105  and a protective layer  106 . 
     The principle discharge between the electrodes in the above transmittance PDP structure is the same as the related art and will be omitted in the following description. 
     In the first preferred embodiment of the present invention, the address electrode A is positioned as near to the separate walls  103  as possible to minimize a decrease in the aperture rate and the sustain discharge electrodes C and S serve as a reflective layer for reflecting over 90% of visible rays emitted from the fluorescent layer  104 . 
     Increasing the width of sustain discharge electrodes C and S makes it possible to reduce the thickness of electrodes, enhancing yields of fabrication, and decreasing the line resistance which reduces an unbalance of electricity generation that may be caused by a large line resistance. 
     The beam masking layer  107 , as well as address electrodes A are formed along the separated walls  103  to enhance the contrast. 
     In the second preferred embodiment of the present invention, as shown in FIG. 5, the width of sustain discharge electrodes C and S formed on the back substrate  102  of a transmittance PDP is decreased to prevent mis-discharge between the adjacent cells, while a reflection helper  110  is formed on the outer side of the sustain discharge electrodes C and S (or between pairs of electrodes) to reflect visible rays generated from the fluorescent layer  104 . 
     Reflection layer  111  shown in FIG. 6 may also be formed to reflect the visible rays and enhance the luminance and electrical insulation from the sustain discharge electrodes C and S. 
     In the third preferred embodiment of the present invention, as shown in FIG. 7 a , a dielectric layer  105   a  is formed on the back substrate  102  and comprises recess portions of which the number of recesses is same as that of the number of sustain discharge electrodes C and S, and a common electrode C and a scan electrode S are formed on the recess portions in the same shape as the recess portions. 
     Further, another dielectric layer  105   a  is formed on the common electrode C and scan electrode S to surround the sustain discharge electrodes C and S with the dielectric layers. 
     Such a structure of sustain discharge electrodes C and S can increase a discharge path of an electricity field which plays a great role in forming plasma during discharge for sustaining light emission of cells. An increase in the discharge path raises the number and frequency of electrons exciting the discharge gas which in turn increases the amount of vacuum ultra-violet rays reaching the fluorescent layer  104 , thus enhancing discharge efficiency. 
     A method of forming the structure includes differentially printing or etching the dielectric layer  105   a  on the back substrate  102  to form a semi-oval profile as deep as a predetermined depth in the dielectric layer  105   a  and then forming thin sustain discharge electrodes C and S in the recess portion to obtain recessed sustain discharge electrodes C and S. 
     As shown in FIG. 7 b , the recess profile of the dielectric layer  105   a  can be almost four times as deep to increase the discharge path between the sustain discharge electrodes C and S. The increase in depth can prevent mis-discharge with electrodes of other neighboring cells. 
     In the fourth preferred embodiment of the present invention, as shown in FIG. 8 a , dielectric layer  105   b  is patterned as an optical focusing structure having a curved recess with the thickness gradually decreasing towards the center of each discharge cell making it is possible to provide a discharge space large enough for charged particles to disperse during a discharge between the sustain discharge electrodes C and S. 
     In other words, since strong discharge plasma and vacuum ultra-violet rays are produced due to a curved recess of the dielectric layer  105   b  as a sustain discharge occurs between scan electrode S and common electrode C, the amount of visible rays emitted from the fluorescent layer  104  and a focusing force of visible rays in the cell are increased thus enhancing the luminance of the emitted light. 
     As shown in FIG. 8 b , a mis-discharge between adjacent cells may be prevented by applying two dielectric layers  105   b  and forming the sustain discharge electrodes C and S between the dielectric layers  105   b  to oppose with each other at a predetermined angle of inclination towards the discharge space. 
     In the fifth preferred embodiment of the present invention, as shown in FIG. 9, dielectric layer  105   c  is formed to have two projections in each cell such that scan electrode S and common electrode C are positioned in the projections, thereby enhancing discharge efficiency. 
     When a discharge voltage is applied to the scan electrode S and the common electrode C to sustain the light emission of the cell after lights are emitted from the cell due to an address discharge between the scan electrode S and the address electrode A, a discharge between the sustain discharge electrodes S and C begins between the opposite electrodes, being dispersed all over the area, to increase the discharge path. The sustain discharge electrodes S and C form projections towards the discharge space and easily cause stereo discharge between the electrodes. 
     The profiles of the scan electrode S and the common electrode C are not specifically limited to the above embodiments and may be shown in FIGS. 10 a  and  10   b.    
     In FIGS. 10 a  and  10   b , when a discharge voltage is applied to the scan electrode S and the common electrode C, a discharge begins from the nearest part between the electrodes and disperses all over the sustain discharge electrodes S and C, thus increasing the discharge path. 
     Since the sustain discharge electrodes S and C are exposed to the discharge space, plasma dispersion due to a stereo discharge occurs readily and the distance from the fluorescent layer  104  for transfer of a plasma discharge is reduced, which results in enhancement of discharge efficiency. 
     In FIG. 11, the profiles of projections of a dielectric layer  105   d  and sustain discharge electrodes S and C are not specifically limited and may be of various configurations to increase the discharge path, as shown in FIGS. 12 a-   12   e , since an increased discharge path can enhance discharge efficiency. 
     In the seventh preferred embodiment of the present invention, as shown in FIG. 13, a transparent electrode  120  is formed along front substrate  101  and separate walls  103 , with a fluorescent layer  104  being formed on the transparent electrode  120 . The transparent electrode  120  is brought in contact with address electrode A to have conductivity. 
     The transparent electrode  120  contacts the address electrode A, and is positioned to surround the discharge region. This concentrates a discharge to enhance discharge efficiency due to an address discharge between scan electrode S and address electrode A. The transparent electrode can restrict collisions of generated plasma (especially, cations) with fluorescent layer  104 , thus prolonging the life of the fluorescent layer  104 . 
     Due to the transparent electrode  120  having conductivity, ionized fluorescent paste particles may be extracted from the fluorescent layer  104  formed by front deposition towards the conductive transparent electrode  120 . It is thus possible to control the thickness of the fluorescent layer  104 , which visible rays pass through, by regulating the time. 
     In the structure shown in FIG. 14, in which the thickness of fluorescent layer  104  is also controllable, the upper dielectric layer  115  has a curved recess at each cell formed by etching and a transparent electrode  121  contacting the address electrode A which is formed in the curved recess. 
     In the present invention as described above by the various preferred embodiments, the PDP&#39;s luminance of emitted light can be enhanced by positioning sustain discharge electrodes which cause the deterioration of transmittance of visible rays on the back substrate. 
     Additionally, the fluorescent layer has a transmittance structure formed on the front substrate to serve as a color filter and a source of visible rays, enhancing the contrast. 
     Furthermore, the present invention can enhance discharge efficiency between electrodes by increasing a discharge path between sustain discharge electrodes and thereby raising the amount of vacuum ultra-violet rays. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.