Patent Application
20080272696
The present invention relates to a plasma display panel for use in a large-sized display device or the like.
An AC plane discharge panel that typifies a plasma display panel (hereinafter abbreviated as “PDP”) has a front plate and a back plate disposed opposite to each other. A number of discharge cells are formed between the front and back plates. Display electrodes, each consisting a pair of electrodes (i.e., a scanning electrode and a sustain electrode), are formed on a front glass substrate in plural pairs and parallel to each other in the front plate. A dielectric layer and a protective layer are formed over the display electrodes. The back plate has a back glass substrate on which plural parallel data electrodes are formed. A dielectric layer is formed over the data electrodes. Plural barrier ribs are formed on the dielectric layer in parallel to the data electrodes. A phosphor layer is formed on each of the surface of the dielectric layer and the side surfaces of the barrier ribs. The front and back plates are disposed opposite to each other and sealed such that the display electrodes and data electrodes intersect each other in three dimensions. A discharge gas is sealed in the internal discharge space. The discharge cells are formed in the portions in which the display electrodes and data electrodes are opposite to each other. In the PDP constructed in this way, electric discharging is induced within the gas in each discharge cell, so that ultraviolet rays are produced. The ultraviolet rays excite phosphors of colors of R, G, and B to emit light, thus providing a color display.
Generally, the subfield method is available to drive a PDP. In this method, one field period is divided into plural subfields. Gray levels are represented by combinations of emitted subfields. Each subfield has an initializing period, a writing period, and a sustaining period. During the initializing period, electric discharging is done for initialization within the discharge cell. This erases the previous history of wall charges at individual discharge cells. Also, wall charges necessary for a subsequent writing operation are formed. During the writing period, scanning pulses are successively applied to scanning electrodes. Writing pulses corresponding to an image signal to be displayed are applied to data electrodes. Thus, writing discharging occurs selectively between the scanning electrodes and data electrodes, thus selectively forming wall charges. During the sustaining period, a given number of sustaining pulses corresponding to brightness weights are applied between the scanning electrodes and sustain electrodes. Electric discharging occurs selectively within the discharge cells at which wall charges are created by writing discharging. Therefore, the discharge cells emit light.
In order to display an image correctly, it is important to perform selective writing discharging reliably during each writing period. However, the writing discharging involves many unstable factors. One of the factors is that the discharging is easily affected by the dimensional accuracy of the electrodes. Another factor is that the phosphor layers formed on data electrodes hinder discharging. In view of these problems, Japanese Patent Unexamined Publication No. 2000-100338 discloses a PDP having data electrodes whose shape are devised to permit writing operations to be performed in a short time reliably, thus reducing power consumption.
PDPs have been fabricated in ever increasing size. At the same time, PDPs have had higher definitions. It has become more difficult to fabricate discharge cells accurately over the whole surface of such a PDP. Meanwhile, application of the shape of data electrodes relying on the aforementioned related art technique makes electric discharging stable without being greatly affected by the dimensional accuracy of the electrodes. However, the application of the shape of the data electrodes increases the power consumption. If the shape of the data electrodes is designed in such a way that the power consumption is not increased, electric discharging is affected by the dimensional accuracy of the electrodes and thus is unstable. With the shape of the data electrode relying on the related art technique in this way, it is difficult to accomplish both stability of electric discharging and suppression of power consumption.
The present invention is intended to provide a PDP which is large in size and has high definition but permits stable writing electric discharging over the whole surface of the display screen while suppressing increases in power consumption. A PDP according to the present invention has a first substrate, plural pairs of display electrodes, a second substrate, and plural data electrodes. The display electrodes are made up of scanning electrodes and sustain electrodes arranged parallel to each other on the first substrate. The second substrate is disposed opposite to the first substrate. A discharge space is formed between the first substrate and second substrate. The data electrodes are arranged on the second substrate in a direction perpendicular to the display electrodes. The data electrodes are wider in peripheral portions of the second substrate than in a central portion of the second substrate. Because of this configuration, even when a PDP is large in size and has high definition, it can suppress increases in power consumption. As a result, the PDP permitting stable writing electric discharging over the whole display screen can be obtained.
Dielectric layer 6 is formed over substrate 1 so as to cover transparent electrodes 2A, 3A and auxiliary electrodes 2B, 3B. Dielectric layer 6 can be formed, for example, by applying glass paste by a die coating method and then sintering the paste. Protective layer 7 is formed on dielectric layer 6. Protective layer 7 can be formed, for example, from magnesium oxide using a film deposition process such as a vacuum evaporation method. In this way, front plate 22 is fabricated by forming scanning electrode 2, sustain electrode 3, dielectric layer 6, and protective layer 7 in succession on substrate 1.
Stripes of plural data electrodes 10 are formed on back glass substrate (hereinafter referred to as “substrate”) 8 that is a second substrate. The shape of data electrodes 10 will be described in detail later. Data electrodes 10 can be formed, for example, by applying photosensitive silver (Ag) paste by screen printing or other method, then patterning the paste by a photolithographic process, and sintering the paste. Dielectric base layer (hereinafter referred to as “dielectric layer”) 9 is formed so as to cover data electrodes 10. Dielectric layer 9 can be formed, for example, by applying glass paste by screen printing and then sintering the paste.
Barrier ribs 11 are formed in stripes or mesh on dielectric layer 9. Barrier ribs 11 can be fabricated, for example, using a photosensitive paste consisting of an aggregate (such as Al2O3) and a chief material made of glass frit. That is, the barrier rib can be formed from such photosensitive paste by screen printing, die coating, or other method, patterning the film by a photolithographic process, and sintering the film. Alternatively, the pattern wall may also be formed by applying a paste including glass material repetitively at a given pitch by screen printing or other method and then sintering the paste.
Phosphor layers 12 emitting red, green, and blue colors are formed in grooves between barrier ribs 11. Phosphor layers 12 can be formed, for example, by applying a phosphor ink including phosphor particles and an organic binder and then sintering the ink. In this way, back plate 23 is fabricated by forming data electrode 10, dielectric layer 9, barrier ribs 11, and phosphor layers 12 in succession on substrate 8.
Back plate 23 and front plate 22 are sealed by applying low-melting-point glass frit to the peripheries of back plate 23, drying the frit, placing back plate 23 and front plate 22 opposite to each other, and heating the frit. Discharge space 24 between front plate 22 and back plate 23 is evacuated to a high vacuum and then a discharging gas such as neon or xenon is sealed in, thus completing plasma display panel (hereinafter abbreviated as “PDP”) 21.
A driving waveform for driving PDP 21 and its timing are next described. In the present embodiment, it is assumed that 1 field period consists of plural subfields each having an initializing period, a writing period, and a sustaining period. The subfields may be otherwise organized.
During the writing period, positive writing pulse voltage Vd is applied to data electrodes 10 corresponding to discharge cells 15 to be displayed. Also, negative scanning pulse voltage Va is applied to corresponding scanning electrodes 2. In discharge cells 15 to which writing pulse voltage Vd and scanning pulse voltage Va are simultaneously applied, a voltage difference is produced at the intersections of the upper portions of data electrodes 10 and the upper portions of scanning electrodes 2. The voltage difference is obtained by adding positive wall voltage Vw on the upper portions of data electrodes 10 to the sum of the absolute values of writing pulse voltage Vd and scanning pulse voltage Va. The discharge start voltage is exceeded. Electric discharging occurs between data electrodes 10 and scanning electrodes 2 and evolves into electric discharging between sustain electrodes 3 and scanning electrodes 2. As a result, positive wall voltage is accumulated on scanning electrodes 2. Negative wall voltage is accumulated on sustain electrodes 3 and on data electrodes 10. Meanwhile, no writing discharging occurs in discharge cells 15 to which writing pulse voltage Vd and scanning pulse voltage Va are not applied at the same time. This writing operation is performed for all discharge cells 15, thus ending the writing period.
During the sustaining period, positive sustaining pulse voltage Vs is applied to scanning electrodes 2 and sustain electrodes 3 alternately. Thus, the sustaining discharging operation is continually repeated a number of times corresponding to brightness weight of the subfield for discharge cells 15 in which writing discharging has occurred. On the other hands, no sustain discharging occurs in discharging cells 15 in which no writing discharging has occurred. Operations similar to the operations described so far are performed for other subfields. PDD 21 emits light so as to draw an image by the mechanism described thus far.
The shape of data electrodes 10 is next described in detail.
As shown in
As shown in
The reason why the writing discharging is stabilized by shaping data electrodes 10 and 10D as described so far is not fully understood. However, the following factors are conceivable.
A first conceivable factor is the effect of deviation of the positions of barrier ribs 11 relative to data electrodes 10 and 10D. As PDP 21 is increased in size and has higher definition, it becomes more difficult to form discharge cells 15 accurately over the whole surface of PDP 21. Especially, in peripheral portions of PDP 21, errors caused by elongation and shrinkage of masks and substrates 1, 8 and manufacturing errors such as errors caused by misalignment are accumulated. Therefore, the dimensional accuracy of discharge cells 15 in peripheral portions of PDP 21 deteriorates. Especially, where data electrodes 10 are narrow, if the positions of the barrier ribs relative to data electrodes 10 and 10D deviate, there is the possibility that the voltage applied to data electrodes 10 and 10D is not sufficiently transmitted into discharge space 24. As a result, there arises the possibility that writing discharging is not easily produced. Accordingly, if data electrodes 10 and 10D are made sufficiently wide, it is assured that the data voltage is transmitted into discharge space 24 even when the positions of barrier ribs 11 relative to data electrodes 10 and 10D have deviated. Consequently, stable writing discharging takes place.
A second conceivable factor is a drop of the wall voltage on data electrodes 10 and 10D. In peripheral portions of PDP 21, there is an increased possibility that a gap is created between discharge cells 15 due to variations in height of barrier ribs 11 and thickness variations of dielectric layers 6 and 9. During the initializing period, a wall voltage adapted for writing operation is accumulated on data electrodes 10 and 10D. If a gap exists between discharge cells 15, charged particles fly in from adjacent discharge cells 15, neutralizing the wall charge on data electrodes 10 and 10D. As a result, the wall voltage drops. For this reason, the voltage applied to discharge cells 15 becomes insufficient during writing discharging, so that there is the possibility that the writing discharging becomes unstable.
If the width of data electrodes 10 and 10D is made sufficiently large, the capacitances of data electrodes 10 and 10D increase and, therefore, a larger amount of electric charge is required to vary the wall voltage. In other words, in a case where the width of data electrodes 10 and 10D is made sufficiently large, even when charged particles fly into thereby neutralizing the wall charge on data electrodes 10 and 10D, decreases in the wall voltages are suppressed. Accordingly, the writing discharging is stabilized without shortage of the voltage applied to discharge cells 15 during the writing discharging. In this way, whatever factor is involved, the writing discharging can be stabilized by making data electrodes 10 and 10D wider.
Meanwhile, discharge cells 15 in which the writing discharging becomes unstable are located only in peripheral regions of PDP 21, i.e., around the periphery of substrate 8 as described previously. When the magnitude of writing voltage margin in each region on the display screen of PDP 21 is measured in practice, it can be seen that the writing margin of discharge cells 15 in peripheral portions of PDP 21 is small. The writing margin increases with going toward the central portion of PDP 21. Accordingly, it is not necessary to increase the width of data electrodes 10 over the whole surface of PDP 21. Writing discharging is stabilized and increases in the data power can be suppressed by making wider data electrodes 10 in peripheral portions of PDP 21 and making narrower data electrodes 10 in the central portion of PDP 21. In the structure shown in
Preferably, the width of end portion 101 is greater than the width of central portion 102 by a factor of more than 1.0 and not more than 1.5. Increase in the data power can be suppressed to on the order of several percent by setting the upper limit to a factor of 1.5. In the above-described specific embodiment, the ratio of the width is a factor of 1.3. Stabilization of writing discharging and suppression of increases in data power can be achieved with a good balance with more desirable results by setting the ratio of the width to a factor of 1.3 or more for the whole length of each data electrode 10 on substrate 8 in this way. Preferably, the width of end portion 101 is set to not more than a half of the spacing between barrier ribs 11. By setting the dimensions in this way, data electrodes 10 are reliably disposed between barrier ribs 11. The interval between barrier ribs 11 corresponds to the pitch between data electrodes 10.
In the description provided so far, it is assumed that the widths of discharge cells 15 for colors of red, green, and blue are all equal. The widths of discharge cells 15 may differ with different colors.
As shown in
Alternatively, data electrodes may be formed in such a way that 100 data electrodes 10E as counted from the left end of substrate 8 and 100 data electrodes 10E as counted from the right end may be wider than data electrodes 10F in a central portion of substrate 8. That is, among the plural data electrodes, data electrodes 10E disposed in peripheral portions of substrate 8 are wider than data electrodes 10F disposed in the central portion of substrate 8. For example, the width of data electrodes 10E is set to 130 μm. The width of data electrodes 10F is set to 100 μm.
The data electrodes may also be formed as shown in
Furthermore, the central portion of data electrodes 10G becomes preferably gradually narrower toward the central portion of substrate 8. Consequently, the same advantages as derived by the structure of
In this way, it is not always necessary to increase the width of data electrodes over the whole panel surface in order to stabilize writing discharging. In any of the above-described embodiments, the data electrodes are wider in peripheral portions of the panel and narrower around the center of the panel. The writing discharging can be stabilized and increases in data power can be suppressed by constructing the panel in this way.
It is to be understood that the regions in which the data electrodes are widened and their width are not limited to the above-described regions or numerical values. It is desired to optimally set them according to the characteristics of the discharge cells, the assembly accuracy of the plasma display panel, and other factors.
In the plasma display panel according to the present invention, increases in power consumption are suppressed if the panel is large in size and has high definition. Furthermore, stable writing discharging is enabled over the whole display screen. Consequently, the panel is useful for a display device.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-116893 | Apr 2005 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2006/307703 | 4/12/2006 | WO | 00 | 10/26/2006 |
