JP2011180333A - Plasma display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve a plasma display panel which has high-definition and high-luminance display performance and low power consumption. <P>SOLUTION: The invention relates to a plasma display device wherein one field is constituted of a plurality of subfields, and each subfield is provided with an address period for selecting a discharge cell for emitting light. A base film of a protective layer is formed at least of two or more metal oxides selected from magnesium oxide, calcium oxide, strontium oxide, and barium oxide and, in an X-ray diffraction analysis, a peak is present between a minimum diffraction angle and a maximum diffraction angle produced by a single body of the oxide constituting the metal oxide of a specific orientation plane. Further, in one field, the number of times of discharge of the first subfield is the smallest, and the number of times of discharge of the second subfield is larger than that of any one of the third and subsequent subfields. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a plasma display device used for video display and the like.

  A plasma display panel (hereinafter referred to as a PDP) can realize a high definition and a large screen, and thus a 100-inch class television or the like has been commercialized. In recent years, PDP has been applied to high-definition televisions that have more than twice the number of scanning lines compared to the conventional NTSC system. In response to energy problems, efforts to further reduce power consumption and environmental issues There is also a growing demand for PDPs that do not contain lead components in consideration of the above.

  A PDP basically includes a front plate and a back plate. The front plate is a glass substrate of sodium borosilicate glass produced by the float process, a display electrode composed of a striped transparent electrode and a bus electrode formed on one main surface of the glass substrate, A dielectric layer that covers the display electrode and functions as a capacitor, and a protective layer made of magnesium oxide (MgO) formed on the dielectric layer.

  On the other hand, the back plate is a glass substrate, stripe-shaped address electrodes formed on one main surface thereof, a base dielectric layer covering the address electrodes, a partition formed on the base dielectric layer, The phosphor layer is formed between the barrier ribs and emits red, green and blue light.

  The front plate and the back plate are hermetically sealed with their electrode forming surfaces facing each other, and neon (Ne) -xenon (Xe) discharge gas is sealed at a pressure of 400 Torr to 600 Torr in a discharge space partitioned by a partition wall. ing. PDP discharges by selectively applying a video signal voltage to the display electrodes, and the ultraviolet rays generated by the discharge excite each color phosphor layer to emit red, green, and blue light, thereby realizing color image display is doing.

  In addition, such a PDP driving method includes an initialization period in which wall charges are adjusted so that writing is easy, a writing period in which writing discharge is performed according to an input image signal, and a discharge space in which writing is performed. A driving method having a sustain period in which display is performed by generating a sustain discharge is generally used. A period (subfield) obtained by combining these periods is repeated a plurality of times within a period (one field) corresponding to one frame of an image, thereby performing PDP gradation display.

  In such a PDP, the role of the protective layer formed on the dielectric layer of the front plate is to protect the dielectric layer from ion bombardment due to discharge and to emit initial electrons for generating address discharge. Etc. Protecting the dielectric layer from ion bombardment plays an important role in preventing an increase in discharge voltage, and emitting initial electrons for generating an address discharge is an address discharge error that causes image flickering. It is an important role to prevent.

  In order to increase the number of initial electrons emitted from the protective layer and reduce image flickering, for example, an example of adding impurities to the magnesium oxide (MgO) protective layer, or magnesium oxide (MgO) particles to magnesium oxide (MgO) ) An example formed on a protective layer is disclosed (for example, see Patent Documents 1, 2, 3, 4, 5, etc.).

JP 2002-260535 A JP 11-339665 A JP 2006-59779 A JP-A-8-236028 JP-A-10-334809

  In recent years, high definition has been advanced in televisions, and a low-cost, low-power-consumption, high-brightness full HD (high definition) (1920 × 1080 pixels: progressive display) PDP is required in the market. Since the electron emission characteristics from the protective layer determine the image quality of the PDP, it is very important to control the electron emission characteristics.

  That is, in order to display a high-definition image, the number of pixels to be written increases even though the time of one field is constant. Therefore, in the writing period in the subfield, the pulse applied to the address electrode It is necessary to reduce the width. However, since there is a time lag called discharge delay from the rise of the voltage pulse to the occurrence of discharge in the discharge space, if the pulse width is narrowed, the probability that the discharge can be completed within the writing period is lowered. . As a result, lighting failure occurs, and the problem of deterioration in image quality performance such as flickering occurs.

  Further, for the purpose of improving the luminous efficiency by discharge for reducing power consumption, the content of xenon (Xe), which is one component of the discharge gas contributing to the light emission of the phosphor, in the entire discharge gas is also increased. As the discharge voltage becomes higher, the discharge delay becomes larger, resulting in a problem that the image quality is deteriorated such as lighting failure.

  As described above, in order to advance the high definition and low power consumption of the PDP, it is necessary to simultaneously realize that the discharge voltage is not increased and that the image quality is improved by reducing defective lighting. There was a problem.

  Attempts have been made to improve the electron emission characteristics by mixing impurities in the protective layer. However, when the electron emission characteristics are improved by mixing impurities in the protective layer, when the charge is accumulated on the surface of the protective layer and used as a memory function, the attenuation rate at which the charge decreases with time increases. Therefore, it is necessary to take measures such as increasing the applied voltage to suppress this.

  On the other hand, in the example in which magnesium oxide (MgO) crystal particles are formed on the magnesium oxide (MgO) protective layer, it is possible to reduce the discharge delay and reduce the lighting failure, but it is not possible to reduce the discharge voltage. There was a problem.

  The present invention has been made in view of such a problem, and an object of the present invention is to realize a PDP having high luminance display performance and capable of being driven at a low voltage.

  To achieve the above object, the present invention provides a first substrate in which a dielectric layer is formed so as to cover a display electrode formed on a substrate and a protective layer is formed on the dielectric layer, and the first substrate And a second substrate which is disposed to face the substrate so as to form a discharge space filled with a discharge gas, and which has an address electrode in a direction intersecting with the display electrode, and a partition which partitions the discharge space. An address period for generating an address discharge for selecting a discharge cell to emit light in each subfield, and an address period in which each field is composed of a plurality of subfields with respect to the plasma display panel. A plasma display for performing light-emitting display with a sustain period for generating a sustain discharge in the discharge cell selected by In the playing apparatus, the protective layer of the first substrate forms a base film on the dielectric layer and adheres aggregated particles in which a plurality of magnesium oxide crystal particles are aggregated on the base film. And the base film is formed of a metal oxide made of at least two oxides selected from magnesium oxide, calcium oxide, strontium oxide, and barium oxide, and the metal oxide is formed on the surface of the base film. In the X-ray diffraction analysis, there is a peak between the minimum diffraction angle and the maximum diffraction angle generated from the simple substance of the oxide composing the metal oxide in a specific orientation plane. The number of discharges in this subfield is the smallest, and the number of discharges in the second subfield is greater than any of the third and subsequent subfields. To.

  According to such a configuration, the discharge start voltage is reduced even when the xenon (Xe) gas partial pressure of the discharge gas is increased in order to improve the secondary electron emission characteristics in the protective layer and increase the luminance. It is possible to realize a PDP excellent in display performance in which delay is reduced and lighting failure does not occur even in high-definition image display.

  According to the present invention, it is possible to realize a PDP that can be driven with high brightness and low voltage even in a high-definition image.

The perspective view which shows the structure of PDP in embodiment of this invention Sectional drawing which shows the structure of the front plate of the PDP The figure which shows the X-ray-diffraction result in the base film of the PDP The figure which shows the X-ray-diffraction result in the base film of the other structure of the PDP Schematic showing the voltage waveform applied to the PDP Enlarged view for explaining the aggregated particles of the PDP The figure which shows the relationship between the discharge delay of the same PDP, and the calcium (Ca) density | concentration in a protective layer The figure which shows the result of having investigated about the electron emission performance and charge retention performance of the PDP Characteristic diagram showing the relationship between the particle size of crystal grains used in the PDP and the electron emission characteristics

  Hereinafter, a PDP according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a perspective view showing the structure of PDP 1 in the embodiment of the present invention. The basic structure of the PDP 1 is the same as that of a general AC surface discharge type PDP. As shown in FIG. 1, the PDP 1 has a front plate 2 made of a front glass substrate 3 and a back plate 10 made of a back glass substrate 11 facing each other, and its outer peripheral portion is sealed with a glass frit or the like. The material is hermetically sealed. A discharge gas such as xenon (Xe) and neon (Ne) is sealed in the sealed discharge space 16 inside the PDP 1 at a pressure of 400 Torr to 600 Torr.

  On the front glass substrate 3 of the front plate 2, a pair of strip-shaped display electrodes 6 each composed of the scanning electrodes 4 and the sustain electrodes 5 and a plurality of black stripes (light shielding layers) 7 are arranged in parallel to each other. A dielectric layer 8 is formed on the front glass substrate 3 so as to cover the display electrodes 6 and the light-shielding layer 7 so as to hold charges and function as a capacitor. A protective layer 9 is further formed thereon. .

  On the back glass substrate 11 of the back plate 10, a plurality of strip-like address electrodes 12 are arranged in parallel to each other in a direction orthogonal to the scanning electrodes 4 and the sustain electrodes 5 of the front plate 2. Layer 13 is covering. Further, a partition wall 14 having a predetermined height is formed on the base dielectric layer 13 between the address electrodes 12 to divide the discharge space 16. In each groove between the barrier ribs 14, a phosphor layer 15 that emits red, green, and blue light by ultraviolet rays is sequentially applied. A discharge space is formed at a position where the scan electrode 4 and the sustain electrode 5 intersect with the address electrode 12, and a discharge space having red, green, and blue phosphor layers 15 arranged in the direction of the display electrode 6 is used for color display. Become a pixel.

FIG. 2 is a cross-sectional view showing the configuration of the front plate 2 of the PDP 1 in the embodiment of the present invention, and FIG. 2 is shown upside down from FIG. As shown in FIG. 2, a display electrode 6 and a light shielding layer 7 including scanning electrodes 4 and sustain electrodes 5 are formed in a pattern on a front glass substrate 3 manufactured by a float method or the like. Scan electrode 4 and sustain electrode 5 are made of transparent electrodes 4a and 5a made of indium tin oxide (ITO), tin oxide (SnO ₂ ), etc., and metal bus electrodes 4b and 5b formed on transparent electrodes 4a and 5a, respectively. It is comprised by. The metal bus electrodes 4b and 5b are used for the purpose of imparting conductivity in the longitudinal direction of the transparent electrodes 4a and 5a, and are formed of a conductive material whose main component is a silver (Ag) material.

  The dielectric layer 8 includes a first dielectric layer 81 provided on the front glass substrate 3 so as to cover the transparent electrodes 4a and 5a, the metal bus electrodes 4b and 5b, and the light shielding layer 7, and a first dielectric. The second dielectric layer 82 formed on the layer 81 has at least two layers, and the protective layer 9 is formed on the second dielectric layer 82.

  The protective layer 9 includes a base film 91 formed on the dielectric layer 8 and aggregated particles 92 in which a plurality of magnesium oxide (MgO) crystal particles 92 a are aggregated on the base film 91. The base film 91 is formed of a metal oxide composed of at least two oxides selected from magnesium oxide (MgO), calcium oxide (CaO), strontium oxide (SrO), and barium oxide (BaO). Aggregated particles 92 in which a plurality of magnesium oxide (MgO) crystal particles 92 a are aggregated are adhered and formed on the base film 91.

  Next, a method for manufacturing such a PDP 1 will be described. First, the scan electrode 4, the sustain electrode 5, and the light shielding layer 7 are formed on the front glass substrate 3. Transparent electrodes 4a and 5a and metal bus electrodes 4b and 5b constituting scan electrode 4 and sustain electrode 5 are formed by patterning using a photolithography method or the like. The transparent electrodes 4a and 5a are formed using a thin film process or the like, and the metal bus electrodes 4b and 5b are solidified by baking a paste containing a silver (Ag) material at a predetermined temperature. Similarly, the light shielding layer 7 is also formed by screen printing a paste containing a black pigment or by forming a black pigment on the entire surface of the glass substrate and then patterning and baking using a photolithography method.

  Next, a dielectric paste is applied on the front glass substrate 3 by a die coating method or the like so as to cover the scan electrode 4, the sustain electrode 5, and the light shielding layer 7, thereby forming a dielectric paste (dielectric material) layer. After the dielectric paste is applied, the surface of the applied dielectric paste is leveled by leaving it to stand for a predetermined time, so that a flat surface is obtained. Thereafter, the dielectric paste layer is formed by baking and solidifying the dielectric paste layer to cover the scan electrode 4, the sustain electrode 5, and the light shielding layer 7. The dielectric paste is a paint containing a dielectric material such as glass powder, a binder and a solvent.

  Next, a base film 91 is formed on the dielectric layer 8. In the embodiment of the present invention, the base film 91 is made of at least two oxides selected from magnesium oxide (MgO), calcium oxide (CaO), strontium oxide (SrO), and barium oxide (BaO). It is formed of a metal oxide.

  The base film 91 is formed by using a single material pellet of magnesium oxide (MgO), calcium oxide (CaO), strontium oxide (SrO), and barium oxide (BaO), or a thin film forming method using a pellet obtained by mixing these materials. Formed by. As a thin film forming method, a known method such as an electron beam evaporation method, a sputtering method, or an ion plating method can be applied. As an example, 1 Pa is considered as the upper limit of the pressure that can actually be taken in the sputtering method and 0.1 Pa in the electron beam evaporation method, which is an example of the evaporation method.

  In addition, as an atmosphere during film formation of the base film 91, a predetermined electron emission characteristic is obtained by adjusting the atmosphere during film formation in a sealed state that is shut off from the outside in order to prevent moisture adhesion and adsorption of impurities. A base film 91 made of a metal oxide having the above can be formed.

  Next, the agglomerated particles 92 of the magnesium oxide (MgO) crystal particles 92a deposited on the base film 91 will be described. These crystal particles 92a can be manufactured by any one of the following vapor phase synthesis method or precursor baking method.

  In the gas phase synthesis method, a magnesium metal material having a purity of 99.9% or more is heated in an atmosphere filled with an inert gas, and a small amount of oxygen is introduced into the atmosphere to directly oxidize magnesium, thereby oxidizing the material. Magnesium (MgO) crystal particles 92a can be produced.

On the other hand, in the precursor firing method, the crystal particles 92a can be produced by the following method. In the precursor firing method, a magnesium oxide (MgO) precursor is uniformly fired at a high temperature of 700 ° C. or higher, and this is gradually cooled to obtain magnesium oxide (MgO) crystal particles 92a. Examples of the precursor include magnesium alkoxide (Mg (OR) ₂ ), magnesium acetylacetone (Mg (acac) ₂ ), magnesium hydroxide (Mg (OH) ₂ ), magnesium carbonate (MgCO ₂ ), magnesium chloride (MgCl ₂ ). ), Magnesium sulfate (MgSO ₄ ), magnesium nitrate (Mg (NO ₃ ) ₂ ), or magnesium oxalate (MgC ₂ O ₄ ). Depending on the selected compound, it may usually take the form of a hydrate, but such a hydrate may be used.

  These compounds are adjusted so that the purity of magnesium oxide (MgO) obtained after firing is 99.95% or more, preferably 99.98% or more. If these compounds contain a certain amount or more of various impurity elements such as alkali metals, B, Si, Fe, and Al, unnecessary interparticle adhesion and sintering occur during heat treatment, and highly crystalline magnesium oxide ( This is because it is difficult to obtain MgO) crystal particles 92a. For this reason, it is necessary to adjust the precursor in advance by removing the impurity element.

  The magnesium oxide (MgO) crystal particles 92a obtained by any of the above methods are dispersed in a solvent, and the dispersion is dispersed and dispersed on the surface of the base film 91 by spraying, screen printing, electrostatic coating, or the like. Let Thereafter, the solvent is removed through a drying / firing process, and the magnesium oxide (MgO) crystal particles 92 a can be fixed on the surface of the base film 91.

  Through such a series of steps, predetermined components (scanning electrode 4, sustaining electrode 5, light shielding layer 7, dielectric layer 8, and protective layer 9) are formed on front glass substrate 3, and front plate 2 is completed.

  On the other hand, the back plate 10 is formed as follows. First, the structure for the address electrode 12 is formed by a method of screen printing a paste containing silver (Ag) material on the rear glass substrate 11 or a method of patterning using a photolithography method after forming a metal film on the entire surface. A material layer to be a material is formed. Thereafter, the address electrode 12 is formed by firing at a predetermined temperature. Next, a dielectric paste is applied on the rear glass substrate 11 on which the address electrodes 12 are formed by a die coating method or the like so as to cover the address electrodes 12 to form a dielectric paste layer. Thereafter, the base dielectric layer 13 is formed by firing the dielectric paste layer. The dielectric paste is a paint containing a dielectric material such as glass powder, a binder and a solvent.

  Next, a partition wall forming paste containing a partition wall material is applied on the base dielectric layer 13 and patterned into a predetermined shape to form a partition wall material layer. Then, the partition 14 is formed by baking at a predetermined temperature. Here, as a method of patterning the partition wall paste applied on the base dielectric layer 13, a photolithography method or a sand blast method can be used. Then, the phosphor layer 15 is formed by applying and baking a phosphor paste containing a phosphor material on the base dielectric layer 13 between the adjacent barrier ribs 14 and on the side surfaces of the barrier ribs 14. Through the above steps, the back plate 10 having predetermined components on the back glass substrate 11 is completed.

  A front plate 2 and a rear plate 10 having predetermined constituent members are arranged so as to face each other so that the scanning electrodes 4 and the address electrodes 12 are orthogonal to each other, and the periphery thereof is sealed with a glass frit, and xenon (Xe ) And neon (Ne) and the like are enclosed, and the PDP 1 is completed.

Here, the first dielectric layer 81 and the second dielectric layer 82 constituting the dielectric layer 8 of the front plate 2 will be described in detail. The dielectric material of the first dielectric layer 81 is composed of the following material composition. That is, 20 wt% to 40 wt% of bismuth oxide (Bi ₂ O ₃ ), 0.5 wt% to 12 wt.% Of at least one selected from calcium oxide (CaO), strontium oxide (SrO), and barium oxide (BaO). Contains 0.1% by weight to 7% by weight of at least one selected from molybdenum oxide (MoO ₃ ), tungsten oxide (WO ₃ ), cerium oxide (CeO ₂ ), and manganese dioxide (MnO ₂ ). .

In place of molybdenum oxide (MoO ₃ ), tungsten oxide (WO ₃ ), cerium oxide (CeO ₂ ), manganese dioxide (MnO ₂ ), copper oxide (CuO), chromium oxide (Cr ₂ O ₃ ), cobalt oxide At least one selected from (Co ₂ O ₃ ), vanadium oxide (V ₂ O ₇ ), and antimony oxide (Sb ₂ O ₃ ) may be contained in an amount of 0.1 wt% to 7 wt%.

Further, as components other than the above, zinc oxide (ZnO) is 0 wt% to 40 wt%, boron oxide (B ₂ O ₃ ) is 0 wt% to 35 wt%, and silicon oxide (SiO ₂ ) is 0 wt% to A material composition that does not contain a lead component, such as 15 wt% and aluminum oxide (Al ₂ O ₃ ) 0 wt% to 10 wt% may be included.

  A dielectric material powder is produced by pulverizing a dielectric material composed of these composition components with a wet jet mill or a ball mill so as to have a particle size of 0.5 μm to 2.5 μm. Next, 55 wt% to 70 wt% of the dielectric material powder and 30 wt% to 45 wt% of the binder component are well kneaded with three rolls to paste for the first dielectric layer 81 for die coating or printing. Is made.

  The binder component is ethyl cellulose, terpineol containing 1% to 20% by weight of acrylic resin, or butyl carbitol acetate. In addition, dioctyl phthalate, dibutyl phthalate, triphenyl phosphate and tributyl phosphate are added to the paste as needed, and glycerol monooleate, sorbitan sesquioleate, homogenol (Kao Corporation) as a dispersant. The printing property may be improved as a paste by adding a phosphate ester of an alkyl allyl group, etc.

  Next, using this first dielectric layer paste, the front glass substrate 3 is printed by a die coat method or a screen printing method so as to cover the display electrode 6 and dried, and then slightly higher than the softening point of the dielectric material. The first dielectric layer 81 is formed by firing at a temperature of 575 ° C. to 590 ° C.

Next, the second dielectric layer 82 will be described. The dielectric material of the second dielectric layer 82 is composed of the following material composition. That is, bismuth oxide (Bi ₂ O ₃ ) is 11 wt% to 20 wt%, and at least one selected from calcium oxide (CaO), strontium oxide (SrO), and barium oxide (BaO) is 1.6 wt%. It contains ˜21 wt%, and contains 0.1 wt% to 7 wt% of at least one selected from molybdenum oxide (MoO ₃ ), tungsten oxide (WO ₃ ), and cerium oxide (CeO ₂ ).

In place of molybdenum oxide (MoO ₃ ), tungsten oxide (WO ₃ ), and cerium oxide (CeO ₂ ), copper oxide (CuO), chromium oxide (Cr ₂ O ₃ ), cobalt oxide (Co ₂ O ₃ ), At least one selected from vanadium oxide (V ₂ O ₇ ), antimony oxide (Sb ₂ O ₃ ), and manganese oxide (MnO ₂ ) may be contained in an amount of 0.1 wt% to 7 wt%.

Further, as components other than the above, zinc oxide (ZnO) is 0 wt% to 40 wt%, boron oxide (B ₂ O ₃ ) is 0 wt% to 35 wt%, and silicon oxide (SiO ₂ ) is 0 wt% to A material composition that does not contain a lead component, such as 15 wt% and aluminum oxide (Al ₂ O ₃ ) 0 wt% to 10 wt% may be included.

  A dielectric material powder is produced by pulverizing a dielectric material composed of these composition components with a wet jet mill or a ball mill so as to have a particle size of 0.5 μm to 2.5 μm. Next, 55 wt% to 70 wt% of the dielectric material powder and 30 wt% to 45 wt% of the binder component are well kneaded with three rolls to obtain a second dielectric layer paste for die coating or printing. Make it. The binder component is ethyl cellulose, terpineol containing 1% to 20% by weight of acrylic resin, or butyl carbitol acetate. In the paste, dioctyl phthalate, dibutyl phthalate, triphenyl phosphate, and tributyl phosphate are added as needed, and glycerol monooleate, sorbitan sesquioleate, and homogenol (Kao Corporation) as dispersants. The printability may be improved by adding a phosphoric ester of an alkyl allyl group or the like.

  Next, using this second dielectric layer paste, printing is performed on the first dielectric layer 81 by screen printing or die coating, followed by drying, and then a temperature slightly higher than the softening point of the dielectric material is 550 ° C. Bake at 590 ° C.

The film thickness of the dielectric layer 8 is preferably set to 41 μm or less in total of the first dielectric layer 81 and the second dielectric layer 82 in order to ensure visible light transmittance. The first dielectric layer 81 has a bismuth oxide (Bi ₂ O ₃ ) content of the second dielectric layer 82 in order to suppress the reaction of the metal bus electrodes 4b and 5b with silver (Ag). It is more than the content of (Bi ₂ O ₃ ) and is 20 wt% to 40 wt%. Therefore, since the visible light transmittance of the first dielectric layer 81 is lower than the visible light transmittance of the second dielectric layer 82, the film thickness of the first dielectric layer 81 is set to the film thickness of the second dielectric layer 82. It is thinner.

The second dielectric layer 82 is less likely to be colored when the content of bismuth oxide (Bi ₂ O ₃ ) is 11 wt% or less, but bubbles are likely to be generated in the second dielectric layer 82. Therefore, it is not preferable. On the other hand, if the content exceeds 40% by weight, coloration tends to occur, and the transmittance decreases.

  In addition, the smaller the film thickness of the dielectric layer 8, the more remarkable the effect of improving the luminance and reducing the discharge voltage. Therefore, it is desirable to set the film thickness as small as possible within the range where the withstand voltage does not decrease. From such a viewpoint, in the embodiment of the present invention, the thickness of the dielectric layer 8 is set to 41 μm or less, the first dielectric layer 81 is set to 5 μm to 15 μm, and the second dielectric layer 82 is set to 20 μm to 36 μm. Yes.

  In the PDP 1 manufactured in this way, even when a silver (Ag) material is used for the display electrode 6, the front glass substrate 3 has little coloring phenomenon (yellowing), and bubbles are generated in the dielectric layer 8. It has been confirmed that the dielectric layer 8 excellent in withstand voltage performance is realized.

Next, in the PDP 1 according to the embodiment of the present invention, the reason why yellowing and generation of bubbles in the first dielectric layer 81 are suppressed by these dielectric materials will be considered. That is, by adding molybdenum oxide (MoO ₃ ) or tungsten oxide (WO ₃ ) to dielectric glass containing bismuth oxide (Bi ₂ O ₃ ), Ag ₂ MoO ₄ , Ag ₂ Mo ₂ O ₇ , Ag ₂ are added. It is known that compounds such as Mo ₄ O ₁₃ , Ag ₂ WO ₄ , Ag ₂ W ₂ O ₇ , and Ag ₂ W ₄ O ₁₃ are easily formed at a low temperature of 580 ° C. or lower. In the embodiment of the present invention, since the firing temperature of the dielectric layer 8 is 550 ° C. to 590 ° C., silver ions (Ag ⁺ ) diffused into the dielectric layer 8 during firing are contained in the dielectric layer 8. It reacts with molybdenum oxide (MoO ₃ ), tungsten oxide (WO ₃ ), cerium oxide (CeO ₂ ), and manganese oxide (MnO ₂ ) to produce and stabilize a stable compound. That is, since silver ions (Ag ⁺ ) are stabilized without being reduced, they do not aggregate to form a colloid. Therefore, the stabilization of silver ions (Ag ⁺ ) reduces the generation of oxygen accompanying the colloidalization of silver (Ag), thereby reducing the generation of bubbles in the dielectric layer 8.

On the other hand, in order to make these effects effective, in a dielectric glass containing bismuth oxide (Bi ₂ O ₃ ), molybdenum oxide (MoO ₃ ), tungsten oxide (WO ₃ ), cerium oxide (CeO ₂ ), oxidation The content of manganese (MnO ₂ ) is preferably 0.1% by weight or more, more preferably 0.1% by weight or more and 7% by weight or less. In particular, if it is less than 0.1% by weight, the effect of suppressing yellowing is small, and if it exceeds 7% by weight, the glass is colored, which is not preferable.

  That is, the dielectric layer 8 of the PDP 1 in the embodiment of the present invention suppresses the yellowing phenomenon and bubble generation in the first dielectric layer 81 in contact with the metal bus electrodes 4b and 5b made of silver (Ag) material. High light transmittance is realized by the second dielectric layer 82 provided on the first dielectric layer 81. As a result, it is possible to realize a PDP having a high transmittance with very few bubbles and yellowing as the entire dielectric layer 8.

  Next, the detail of the protective layer 9 in embodiment of this invention is demonstrated.

  In the PDP in the embodiment of the present invention, as shown in FIG. 2, the protective layer 9 includes a base film 91 formed on the dielectric layer 8 and magnesium oxide (MgO) crystal particles deposited on the base film 91. 92a is constituted by agglomerated particles 92 in which a plurality of agglomerates are agglomerated. Further, the base film 91 is formed of a metal oxide made of at least two oxides selected from magnesium oxide (MgO), calcium oxide (CaO), strontium oxide (SrO), and barium oxide (BaO), In the X-ray diffraction analysis of the surface of the base film 91, the metal oxide has a peak between the minimum diffraction angle and the maximum diffraction angle generated from a single oxide constituting the metal oxide of a specific orientation plane. Yes.

  FIG. 3 is a diagram showing an X-ray diffraction result on the surface of the base film 91 constituting the protective layer 9 of the PDP 1 in the embodiment of the present invention. FIG. 3 also shows the results of X-ray diffraction analysis of magnesium oxide (MgO) alone, calcium oxide (CaO) alone, strontium oxide (SrO) alone, and barium oxide (BaO) alone.

  In FIG. 3, the horizontal axis represents the Bragg diffraction angle (2θ), and the vertical axis represents the intensity of the X-ray diffraction wave. The unit of the diffraction angle is shown in degrees when one round is 360 degrees, and the intensity is shown in an arbitrary unit. In FIG. 3, the crystal orientation plane which is a specific orientation plane is shown in parentheses. As shown in FIG. 3, in the crystal orientation plane (111), the diffraction angle is 32.2 degrees for calcium oxide (CaO) alone, the diffraction angle is 36.9 degrees for magnesium oxide (MgO) alone, and strontium oxide (SrO) alone. Shows a peak at a diffraction angle of 30.0 degrees, and barium oxide (BaO) alone has a peak at a diffraction angle of 27.9 degrees.

  In PDP 1 in the embodiment of the present invention, at least two or more selected from magnesium oxide (MgO), calcium oxide (CaO), strontium oxide (SrO), and barium oxide (BaO) are used as base film 91 of protective layer 9. It is formed of a metal oxide made of the oxide.

  FIG. 3 shows the X-ray diffraction result when the single component constituting the base film 91 is two components. That is, the X-ray diffraction result of the base film 91 formed using magnesium oxide (MgO) and calcium oxide (CaO) alone was formed using point A, magnesium oxide (MgO) and strontium oxide (SrO) alone. The X-ray diffraction result of the base film 91 is indicated by B point, and further, the X-ray diffraction result of the base film 91 formed using magnesium oxide (MgO) and barium oxide (BaO) alone is indicated by C point.

  That is, the point A is a diffraction angle of 36.9 degrees of the magnesium oxide (MgO) alone, which is the maximum diffraction angle of the single oxide, in the crystal orientation plane (111) as the specific orientation plane, and the oxidation which is the minimum diffraction angle. A peak exists at a diffraction angle of 36.1 degrees, which is between the diffraction angle of 32.2 degrees of calcium (CaO) alone. Similarly, peaks at points B and C exist at 35.7 degrees and 35.4 degrees between the maximum diffraction angle and the minimum diffraction angle, respectively.

  Further, FIG. 4 shows the X-ray diffraction result when the single component constituting the base film 91 is three or more components, as in FIG. That is, FIG. 4 shows the results when magnesium oxide (MgO), calcium oxide (CaO), and strontium oxide (SrO) are used as the single component, point D, magnesium oxide (MgO), calcium oxide (CaO), and oxidation. The results when barium (BaO) is used are indicated by point E, and the results when calcium oxide (CaO), strontium oxide (SrO) and barium oxide (BaO) are used are indicated by point F.

  That is, the point D is a crystal orientation plane (111) as a specific orientation plane, and a diffraction angle of 36.9 degrees of magnesium oxide (MgO) as a maximum diffraction angle of a single oxide and an oxidation level as a minimum diffraction angle. A peak exists at a diffraction angle of 33.4 degrees, which is between the diffraction angle of 30.0 degrees of strontium (SrO) alone. Similarly, peaks at points E and F exist at 32.8 degrees and 30.2 degrees between the maximum diffraction angle and the minimum diffraction angle, respectively.

  Therefore, in the X-ray diffraction analysis of the surface of the base film 91 of the metal oxide constituting the base film 91, the base film 91 of the PDP 1 in the embodiment of the present invention has two components or three components as a single component. A peak exists between the minimum diffraction angle and the maximum diffraction angle of a peak generated from a single oxide constituting a metal oxide having a specific orientation plane.

  In the above description, (111) has been described as the crystal orientation plane as the specific orientation plane, but the peak position of the metal oxide is the same as that described above when other crystal orientation planes are also targeted.

  The depth from the vacuum level of calcium oxide (CaO), strontium oxide (SrO), and barium oxide (BaO) exists in a shallow region as compared with magnesium oxide (MgO). Therefore, when the PDP 1 is driven, when electrons existing in the energy levels of calcium oxide (CaO), strontium oxide (SrO), and barium oxide (BaO) transition to the ground state of the xenon (Xe) ion, Auger It is considered that the number of electrons emitted due to the effect increases as compared with the case of transition from the energy level of magnesium oxide (MgO).

  Further, as described above, the base film 91 according to the embodiment of the present invention has a peak between the minimum diffraction angle and the maximum diffraction angle of the peak generated from the single oxide constituting the metal oxide. I have to. As a result of X-ray diffraction analysis, metal oxides having the characteristics shown in FIGS. 3 and 4 have their energy levels between single oxides constituting them. Therefore, the energy level of the base film 91 is also present between the single oxides, and the number of electrons emitted by the Auger effect is considered to be larger than that in the case of transition from the energy level of magnesium oxide (MgO). .

  As a result, the base film 91 can exhibit better secondary electron emission characteristics as compared with magnesium oxide (MgO) alone, and as a result, the discharge sustaining voltage can be reduced. Therefore, particularly when the partial pressure of xenon (Xe) as the discharge gas is increased in order to increase the luminance, it is possible to reduce the discharge voltage and realize a low-voltage and high-luminance PDP.

  Table 1 shows the result of the sustaining voltage when the mixed gas (Xe, 15%) of 450 Torr of xenon (Xe) and neon (Ne) is sealed in the PDP according to the embodiment of the present invention. The result of PDP when the structure of is changed is shown.

  The sustaining voltage in Table 1 is expressed as a relative value when the comparative example is 100. The base film 91 of sample A is a metal oxide made of magnesium oxide (MgO) and calcium oxide (CaO). The base film 91 of sample B is a metal oxide made of magnesium oxide (MgO) and strontium oxide (SrO). The base film 91 is a metal oxide made of magnesium oxide (MgO) and barium oxide (BaO). The base film 91 of the sample D is a metal oxide made of magnesium oxide (MgO), calcium oxide (CaO), and strontium oxide (SrO). The base film 91 of the sample E is made of a metal oxide made of magnesium oxide (MgO), calcium oxide (CaO), and barium oxide (BaO). Further, the comparative example shows a case where the base film 91 is made of magnesium oxide (MgO) alone.

  When the partial pressure of the discharge gas xenon (Xe) is increased from 10% to 15%, the luminance increases by about 30%. However, in the comparative example in which the base film 91 is made of magnesium oxide (MgO) alone, the discharge is maintained. The voltage increases about 10%.

  On the other hand, in the PDP according to the embodiment of the present invention, the discharge sustain voltage can be reduced by about 10% to 20% in all of the sample A, the sample B, the sample C, the sample D, and the sample E as compared with the comparative example. . Therefore, the discharge start voltage can be set within the normal operation range, and a high-luminance and low-voltage drive PDP can be realized.

  Calcium oxide (CaO), strontium oxide (SrO), and barium oxide (BaO) are highly reactive by themselves, so that they easily react with impurities, and thus have a problem that the electron emission performance is lowered. It was. However, in the embodiment of the present invention, the structure of these metal oxides reduces the reactivity and forms a crystal structure with few impurities and oxygen vacancies. Therefore, excessive emission of electrons during driving of the PDP is suppressed, and in addition to the effect of achieving both low voltage driving and secondary electron emission performance, the effect of moderate charge retention characteristics is also exhibited. This charge retention characteristic is particularly effective for retaining wall charges stored in the initialization period and preventing a write failure in the write period and performing a reliable write discharge.

  Next, the agglomerated particles 92 in which a plurality of magnesium oxide (MgO) crystal particles 92a are aggregated provided on the base film 91 in the embodiment of the present invention will be described in detail. Aggregated particles 92 of magnesium oxide (MgO) have been confirmed by the inventor's experiments mainly to suppress the discharge delay in the write discharge and to improve the temperature dependence of the discharge delay. Therefore, in the embodiment of the present invention, the aggregated particles 92 are arranged as an initial electron supply unit required at the time of rising of the discharge pulse by utilizing the property that the advanced initial electron emission characteristics are superior to the base film 91.

  The main cause of the discharge delay is considered to be a shortage of the amount of initial electrons that are triggered from the surface of the base film 91 released into the discharge space 16 at the start of discharge. Therefore, in order to contribute to the stable supply of initial electrons to the discharge space 16, the aggregated particles 92 of magnesium oxide (MgO) are dispersedly arranged on the surface of the base film 91. As a result, abundant electrons are present in the discharge space 16 at the rise of the discharge pulse, and the discharge delay can be eliminated. Therefore, such initial electron emission characteristics enable high-speed driving with good discharge response even when the PDP 1 has a high definition. In the configuration in which the metal oxide aggregated particles 92 are provided on the surface of the base film 91, in addition to the effect of mainly suppressing the discharge delay in the write discharge, the effect of improving the temperature dependence of the discharge delay is also obtained.

  FIG. 5 is a diagram showing voltage waveforms applied to the electrodes in the embodiment of the present invention. In the PDP, one field is composed of a plurality of subfields (SF). In each subfield, an address period for generating an address discharge for selecting a discharge cell to emit light, and a sustain discharge in the discharge cell selected by the address. Gradation display is performed by providing a light emission display with a sustain period for generating. Further, as shown in FIG. 5, the PDP has an initializing period for performing initializing discharge for equalizing wall charges of all cells before the address period, and after the sustain period, erasing for charge adjustment is performed. There is a period.

  In the present invention, as shown in FIG. 5, the number of discharges in the first subfield in one field is the smallest, and the number of discharges in the second subfield is larger than any of the third and subsequent subfields. It is comprised so that it may become. That is, assuming that the discharge when the scan electrode and the sustain electrode become the cathode each occurs once, the number of times of discharge is one, the first subfield is the number of times of discharge, and the next subfield is 4 It is understood that the number of discharges is not the smallest among the subfields after the second and subsequent subfields. By doing so, it is possible to stably generate an address discharge for selecting display. In addition, the said frequency | count is an example of implementation, and the frequency | count of discharge is not restricted to the said combination.

  As described above, the PDP 1 according to the embodiment of the present invention includes the base film 91 that achieves both low-voltage driving and charge retention, and the magnesium oxide (MgO) aggregated particles 92 that have the effect of preventing discharge delay. Thus, as a whole PDP 1, high-definition PDP can be driven at a high voltage with a low voltage, and high-quality image display performance with suppressed lighting failure can be realized.

  Further, in the embodiment of the present invention, agglomerated particles 92 in which several crystal particles 92a are aggregated are discretely dispersed on base film 91, and a plurality of agglomerated particles 92 are attached so as to be distributed almost uniformly over the entire surface. It is constituted by. FIG. 6 is an enlarged view for explaining the aggregated particles 92.

  Aggregated particles 92 are those in which crystal particles 92a having a predetermined primary particle size are aggregated or necked, as shown in FIG. In other words, it is not bonded as a solid with a large bonding force, but a plurality of primary particles form an aggregate body due to static electricity, van der Waals force, etc., and due to external stimuli such as ultrasound , Part or all of them are bonded to such a degree that they become primary particles. The particle size of the agglomerated particles 92 is about 1 μm, and the crystal particles 92a preferably have a polyhedral shape having seven or more surfaces such as a tetrahedron and a dodecahedron.

  Moreover, the particle size of the primary particles of the crystal particles 92a can be controlled by the generation conditions of the crystal particles 92a. For example, when an MgO precursor such as magnesium carbonate or magnesium hydroxide is calcined and produced, the particle size can be controlled by controlling the calcining temperature and the calcining atmosphere. In general, the firing temperature can be selected in the range of 700 ° C. to 1500 ° C., but the particle size can be controlled to about 0.3 μm to 2 μm by making the firing temperature relatively higher than 1000 ° C. is there. Furthermore, by obtaining the crystal particles 92a by heating the MgO precursor, a plurality of primary particles are bonded to each other by a phenomenon called agglomeration or necking in the production process, whereby the agglomerated particles 92 can be obtained.

  FIG. 7 shows the discharge delay in the protective layer 9 when the base film 91 made of a metal oxide of magnesium oxide (MgO) and calcium oxide (CaO) is used in the PDP 1 according to the embodiment of the present invention. It is a figure which shows the relationship with a calcium (Ca) density | concentration. The base film 91 is composed of a metal oxide composed of magnesium oxide (MgO) and calcium oxide (CaO), and the metal oxide has a magnesium oxide (MgO) peak in the X-ray diffraction analysis on the surface of the base film 91. A peak exists between the diffraction angle at which the peak is generated and the diffraction angle at which the peak of calcium oxide (CaO) is generated.

  FIG. 7 shows the case where only the base film 91 is used as the protective layer 9 and the case where the aggregated particles 92 are arranged on the base film 91, and the discharge delay is caused by calcium (Ca) contained in the base film 91. The case where it is not done is shown as a standard.

  As is apparent from FIG. 7, in the case of only the base film 91 and in the case where the aggregated particles 92 are arranged on the base film 91, the discharge delay increases as the calcium (Ca) concentration increases in the case of the base film 91 alone. On the other hand, it can be seen that by disposing the agglomerated particles 92 on the base film 91, the discharge delay can be significantly reduced, and the discharge delay hardly increases even when the calcium (Ca) concentration is increased.

  Next, the results of experiments conducted to confirm the effect of the protective layer 9 having the aggregated particles 92 in the embodiment of the present invention will be described. First, a PDP having a base film 91 having a different structure and agglomerated particles 92 provided on the base film 91 was made as a prototype. Prototype 1 is a PDP in which a protective layer 9 made only of a magnesium oxide (MgO) base film 91 is formed. Prototype 2 is a protective layer 9 made only of a base film 91 in which magnesium oxide (MgO) is doped with impurities such as Al and Si. Prototype 3 is a PDP in which a protective layer 9 is formed by spraying and adhering only primary particles of magnesium oxide (MgO) crystal particles 92a on a base film 91 made of magnesium oxide (MgO).

  On the other hand, the prototype 4 is the PDP 1 in the embodiment of the present invention, and the above-described sample A is used as the protective layer 9. That is, the protective layer 9 includes a base film 91 made of a metal oxide of magnesium oxide (MgO) and calcium oxide (CaO), and aggregated particles 92 obtained by aggregating crystal particles 92a on the base film 91 over the entire surface. So that it is distributed almost uniformly. In the X-ray diffraction analysis of the surface of the base film 91, the base film 91 is set so that a peak exists between the minimum diffraction angle and the maximum diffraction angle of a peak generated from a single oxide constituting the base film 91. ing. That is, the minimum diffraction angle in this case is 32.2 degrees for calcium oxide (CaO), the maximum diffraction angle is 36.9 degrees for magnesium oxide (MgO), and the peak of the diffraction angle of the base film 91 is 36.1 degrees. To exist.

  The electron emission performance and charge retention performance of these PDPs were examined, and the results are shown in FIG. The electron emission performance is a numerical value indicating that the larger the electron emission amount, the greater the amount of electron emission. The initial electron emission amount can be measured by a method of measuring the amount of electron current emitted from the surface by irradiating the surface with ions or an electron beam. However, the evaluation of the surface of the front plate 2 of the PDP 1 can be performed nondestructively. With difficulty. Therefore, the method described in JP 2007-48733 A was used. That is, among the delay times at the time of discharge, a numerical value called a statistical delay time, which is a measure of the likelihood of occurrence of discharge, is measured, and when the reciprocal is integrated, a numerical value corresponding to the initial electron emission amount is obtained.

  Therefore, this numerical value is used for evaluation. The delay time at the time of discharge means the time of discharge delay when the discharge is delayed from the rising edge of the pulse, and the discharge delay is the time when the initial electrons that trigger when the discharge is started are discharged from the surface of the protective layer 9 to the discharge space. It is considered as a main factor that it is difficult to be released into the inside.

  As an indicator of the charge retention performance, a voltage value of a voltage (hereinafter referred to as a Vscn lighting voltage) applied to the scan electrode necessary for suppressing the charge emission phenomenon when the PDP is manufactured is used. That is, a lower Vscn lighting voltage indicates a higher charge retention capability. This makes it possible to use components having a low withstand voltage and a small capacity as the power source and each electrical component in designing the PDP. In the current product, an element having a withstand voltage of about 150 V is used as a semiconductor switching element such as a MOSFET for sequentially applying a scanning voltage to the panel, and the Vscn lighting voltage is 120 V or less in consideration of variation due to temperature. It is desirable to keep it down.

  FIG. 8 is a diagram showing the results of examining the electron emission performance and the charge retention performance of the PDP in the embodiment of the present invention. As is apparent from FIG. 8, a prototype in which aggregated particles 92 obtained by agglomerating magnesium oxide (MgO) crystal particles 92a are dispersed on base film 91 in the embodiment of the present invention and uniformly distributed over the entire surface. 4 is a characteristic that in the evaluation of the charge retention performance, the Vscn lighting voltage can be reduced to 120 V or less, and the electron emission performance is much better than that of the prototype 1 in the case of a protective layer made only of magnesium oxide (MgO). Can be obtained.

  In general, the electron emission capability and the charge retention capability of the protective layer of the PDP are contradictory. For example, it is possible to improve the electron emission performance by changing the film forming conditions of the protective layer, or by forming a film by doping impurities such as Al, Si, and Ba in the protective layer. The Vscn lighting voltage also increases.

  In the PDP 1 of the prototype 4 in which the protective layer 9 is formed in the embodiment of the present invention, the electron emission capability is 8 times that of the prototype 1 using the protective layer 9 made only of magnesium oxide (MgO). With the above characteristics, it is possible to obtain a charge holding ability with a Vscn lighting voltage of 120 V or less. Therefore, it is useful for PDPs with a large number of scanning lines and a small cell size due to high definition, satisfying both electron emission capability and charge retention capability, and reducing discharge delay and good image display Can be realized.

  Next, the particle size of the crystal particles used in the protective layer 9 of the PDP 1 according to the embodiment of the present invention will be described in detail. In the following description, the particle diameter means an average particle diameter, and the average particle diameter means a volume cumulative average diameter (D50).

  FIG. 9 is a characteristic diagram showing the experimental results of examining the electron emission performance by changing the particle size of the crystal particles 92a in the prototype 4 of the present invention described in FIG. In FIG. 9, the particle diameter of the crystal particle 92 a was measured by observing the crystal particle 92 a with an SEM. As shown in FIG. 9, it can be seen that when the particle size is reduced to about 0.3 μm, the electron emission performance is lowered, and when it is approximately 0.9 μm or more, high electron emission performance is obtained.

  By the way, in order to increase the number of electrons emitted in the discharge cell, it is desirable that the number of crystal particles 92a per unit area on the base film 91 is large. The crystal particles 92 a are present in the portion corresponding to the top of the partition wall 14 of the back plate 10 that is in close contact with the protective layer 9, so that the top of the partition wall 14 is damaged and the material rides on the phosphor layer 15. As a result, it has been found that the corresponding cell does not normally turn on and off. The phenomenon of the partition wall breakage is unlikely to occur unless the crystal particle 92a is present at the portion corresponding to the top of the partition wall 14. Therefore, the probability of the breakage of the partition wall 14 increases as the number of crystal particles 92a attached increases. From this point of view, when the crystal particle diameter is increased to about 2.5 μm, the probability of partition wall breakage increases rapidly, and when the crystal particle diameter is smaller than 2.5 μm, the probability of partition wall breakage is kept relatively small. be able to.

  From the above results, in the PDP 1 according to the embodiment of the present invention, if the aggregated particles 92 having a particle size in the range of 0.9 μm to 2 μm are used as the aggregated particles 92, the above-described effects of the present invention can be stably achieved. It turned out to be obtained.

  As described above, according to the PDP according to the present invention, it is possible to obtain a high electron emission performance and a charge retention capability of Vscn lighting voltage of 120 V or less.

  In the embodiment of the present invention, description has been made using magnesium oxide (MgO) particles as crystal particles. However, other single crystal particles have high electron emission performance similar to magnesium oxide (MgO). Since the same effect can be obtained by using crystal particles of metal oxide such as Ba, Al, etc., the particle type is not limited to magnesium oxide (MgO).

  As described above, the present invention is useful in realizing a PDP having high image quality display performance and low power consumption.

1 PDP
2 Front plate 3 Front glass substrate 4 Scan electrode 4a, 5a Transparent electrode 4b, 5b Metal bus electrode 5 Sustain electrode 6 Display electrode 7 Black stripe (light shielding layer)
DESCRIPTION OF SYMBOLS 8 Dielectric layer 9 Protective layer 10 Back plate 11 Back glass substrate 12 Address electrode 13 Base dielectric layer 14 Partition 15 Phosphor layer 16 Discharge space 91 Base film 92 Aggregated particle 92a Crystal particle

Claims (1)

A dielectric layer is formed so as to cover the display electrode formed on the substrate, and a first substrate having a protective layer formed on the dielectric layer, and a discharge space filled with a discharge gas in the first substrate are formed. A plasma display panel having an address electrode in a direction intersecting with the display electrode and a second substrate provided with a partition wall that partitions the discharge space. One field is constituted by a plurality of subfields, and in each subfield, an address period for generating an address discharge for selecting a discharge cell to emit light, and a sustain for generating a sustain discharge in the discharge cell selected by this address A plasma display device for performing light emission display for a period of time before the first substrate The protective layer forms a base film on the dielectric layer and is formed by adhering aggregated particles in which a plurality of magnesium oxide crystal particles are aggregated on the base film, and the base film is formed of magnesium oxide, The metal oxide is formed of a metal oxide composed of at least two oxides selected from calcium oxide, strontium oxide, and barium oxide, and the metal oxide has a specific orientation plane in the X-ray diffraction analysis of the base film surface. There is a peak between the minimum diffraction angle and the maximum diffraction angle generated from the single oxide constituting the oxide, and the number of discharges in the first subfield is minimum in one field, and 2 A plasma display apparatus, wherein the number of discharges in the first subfield is larger than any of the third and subsequent subfields.

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