KR20050082767A - Plasma display panel - Google Patents

Abstract

An object of the present invention is to provide a plasma display panel with improved luminous efficiency and no permanent afterimage. In order to achieve this object, the present invention provides a rear substrate and an upper side of the rear substrate. Address electrodes extending in one direction, a dielectric layer covering the address electrodes, a lower partition wall formed above the dielectric layer to partition light emitting cells, a front substrate disposed on the lower partition parallel to a rear substrate, and a lower side of the front substrate An upper barrier rib partitioning the light emitting cells together with the lower barrier rib, phosphor layers formed on a side surface of the upper barrier rib, and arranged in the lower barrier rib so as to surround the light emitting cell and extending to intersect the address electrode; Electrodes are disposed in the lower partition wall to surround the light emitting cell, and the scan electrode The present invention provides a plasma display panel including common electrodes extending in parallel and a discharge gas in the light emitting cell.

Description

Plasma display panel {Plasma display panel}

The present invention relates to a plasma display panel that implements an image using gas discharge.

Recently, a device employing a plasma display panel as a flat panel display device has a large screen and has excellent characteristics of high definition, ultra-thin, light weight, and wide viewing angle, and is easier to manufacture than other flat panel display devices. It is attracting attention as a large flat panel display device.

The plasma display panel is classified into a direct current (DC) type, an alternating current (AC) type, and a hybrid type according to an applied discharge voltage, and classified into a counter discharge type and a surface discharge type according to a discharge structure.

In the DC plasma display panel, all electrodes are exposed to a discharge space, and charges are directly transferred between the corresponding electrodes. In the AC plasma display panel, at least one electrode is surrounded by a dielectric layer, and discharge is performed by an electric field of wall charge instead of direct charge transfer between the corresponding electrodes.

In the DC plasma display panel, since the charge is directly transferred between the corresponding electrodes, there is a problem in that the electrode is severely damaged. In recent years, an AC plasma display panel having an AC type, in particular, a three-electrode surface discharge structure is present. This has been generally employed.

In the conventional three-electrode surface discharge type plasma display panel shown in FIG. 1, the visible light emitted from the phosphor layer 110 includes the scan electrode 106 and the common electrode 107 disposed on the lower surface of the front substrate 101. A large portion (approximately 40%) is absorbed by the bus electrode 108, the dielectric layer 109 covering the electrodes 106, 107, and 108, and the MgO film 111, and thus the luminous efficiency is low. there was.

In addition, when the conventional three-electrode surface discharge plasma display panel 100 displays the same image for a long time, the phosphor layer 110 may be permanently sputtered by ion sputtering by charged particles of discharge gas. There was a problem causing phosphorus afterimages.

In order to solve the above problems, it is an object of the present invention to provide a plasma display panel in which luminous efficiency is improved and permanent afterimages are not generated.

In order to achieve the above and other objects, the present invention provides a rear substrate, address electrodes disposed on the rear substrate and extending in one direction, a dielectric layer covering the address electrodes, and formed on the dielectric layer. A lower partition partitioning the light emitting cells, a front substrate disposed on the lower partition parallel to the rear substrate, an upper partition disposed below the front substrate and partitioning the light emitting cells together with the lower partition; Formed phosphor layers, scan electrodes disposed in the lower partition wall to surround the light emitting cell, and extended to intersect the address electrode, disposed in the lower partition wall to surround the light emitting cell, and extending in parallel to the scan electrode And a plasma display panel including the common electrodes and the discharge gas in the light emitting cell. to provide.

Side surfaces of the lower partition wall may be covered by an MgO film.

In the present invention, preferably, in the plasma display panel, the scan electrode and the common electrode may be disposed in a vertical direction.

In this case, it is preferable that one scan electrode and one common electrode are arranged in one light emitting cell, and the scan electrode is disposed below the common electrode.

In the present invention, preferably, in the plasma display panel, the rear substrate may have a bright color having a light reflectance of 50% or more.

In the present invention, preferably, in the plasma display panel, the rear substrate may have a dark color having a light absorption of 50% or more.

In the present invention, preferably, in the plasma display panel, the dielectric light reflectance may have a bright color of 50% or more.

In the present invention, preferably, in the plasma display panel, the dielectric may have a dark color having a light absorption of 50% or more.

In the present invention, preferably, in the plasma display panel, the lower partition wall may be formed of a dielectric.

In the present invention, preferably, in the plasma display panel, the upper partition wall may have a dark color of 50% or more.

Further, according to another aspect of the present invention, a rear substrate, a lower partition wall formed above the rear substrate to partition the light emitting cells, a front substrate disposed on the lower partition parallel to the rear substrate, the lower side of the front substrate Address electrodes arranged in one direction, a dielectric layer covering the address electrodes, an upper partition wall disposed below the dielectric layer and partitioning a light emitting cell together with the lower partition wall, and phosphor layers formed on side surfaces of the upper partition wall Scan electrodes disposed in the lower partition wall to surround the light emitting cells and extending to intersect the address electrode, and disposed in the lower partition wall to surround an upper side of the light emitting cell and extending in parallel with the scan electrodes; A plasma display panel is provided having electrodes and a discharge gas in the light emitting cell.

In the present invention, preferably, the side surface of the lower partition wall may be covered by an MgO film.

In the present invention, preferably, in the plasma display panel, the scan electrode and the common electrode may be disposed in a vertical direction.

In this case, it is preferable that one scan electrode and one common electrode are arranged in one light emitting cell, and the scan electrode is disposed above the common electrode.

In the present invention, preferably, in the plasma display panel, the address electrode includes at least two or more layers, and the uppermost layer of the layers may have a dark color having a light absorption of 50% or more.

In the present invention, preferably, in the plasma display panel, the address electrode includes at least two or more layers, and the lowest layer of the layers may have a bright color with a light reflectance of 50% or more.

In the present invention, preferably, in the plasma display panel, the lower partition wall may be formed of a dielectric.

In the present invention, preferably, in the plasma display panel, the rear substrate may have a bright color having a light reflectance of 50% or more.

In the present invention, preferably, in the plasma display panel, the upper partition wall may have a dark color of 50% or more.

Next, the plasma display panel according to the first embodiment of the present invention will be described in detail with reference to FIGS. 2 to 5.

The plasma display panel according to the present exemplary embodiment includes a back substrate 202, address electrodes 203 disposed on the back substrate 202 and extending in one direction, a dielectric layer 204 covering the address electrodes 203, The front substrate 201 and the front substrate 201 formed on the dielectric layer 204 and disposed parallel to the rear substrate 202 on the lower partition wall 225 and the lower partition wall 225 that partition the light emitting cells 220. Disposed on the lower side of the upper partition 205, which partitions the light emitting cells 220 together with the lower partition 225, the phosphor layers 210 formed on the side of the upper partition 205, and surrounds the light emitting cell 220. The scan electrodes 206 extending to intersect the address electrode 203, the scan electrodes 206 extending in the lower partition 225 to surround the light emitting cell 220, and the scan electrodes 206. Common electrodes 207 extending in parallel and a discharge gas in the light emitting cell 220 are provided.

The back substrate 202 supports the address electrodes 203, the dielectric layer 204, and the like, and is usually made of a material mainly composed of glass.

In addition, the back substrate 202 may be manufactured to have a bright color with a light reflectance of 50% or more. When the back substrate 202 has a bright color, the amount of visible light transmitted to the outside through the back substrate 202 is reduced, so that the brightness of the plasma display panel 200 is improved.

However, the back substrate 202 may be manufactured to have a dark color with a light absorption rate of 50% or more. If the back substrate 202 is dark, the reflection brightness of the back substrate 202 is reduced, so that the contrast of the plasma display panel 200 is improved.

The address electrodes 203 are used to generate an address discharge for facilitating sustain discharge between the scan electrode 206 and the common electrode 207. More specifically, the address electrodes 203 lower the voltage at which sustain discharge is initiated. The address discharge is a discharge occurring between the scan electrode 206 and the address electrode 203. When the address discharge is completed, cations are accumulated on the scan electrode 206 side and electrons are accumulated on the common electrode 207 side. Sustain discharge between the common electrode and the common electrode becomes easier.

The dielectric layer 204 is formed as a dielectric that can induce charge while preventing cations or electrons from colliding with the address electrode 203 upon discharge and damaging the address electrode 203. Such dielectrics include PbO and B ₂ O. ₃ , SiO _2, and the like.

In addition, the dielectric layer 204 may be manufactured to have a bright color with a light reflectance of 50% or more. When the dielectric layer 204 is bright, the amount of visible light transmitted to the outside through the dielectric layer 204 is reduced, so that the brightness of the plasma display panel 200 is improved.

However, the dielectric layer 204 may be manufactured to have a dark color with a light absorption of 50% or more. If the dielectric layer 204 becomes dark, the contrast of the plasma display panel 200 is improved because the reflection luminance of the dielectric layer 204 is reduced.

The upper and lower partitions 205 and 225 partition the light emitting cells 220 corresponding to one of the red light emitting pixel, the green light emitting pixel, and the blue light emitting subpixel constituting one pixel, and the light emitting cell ( To prevent mis-discharge between them. In FIG. 2, upper and lower partitions 205 and 225 divide the light emitting cells 220 into a matrix, but the present disclosure is not limited thereto, and various patterns may be provided as long as the plurality of discharge spaces 220 may be formed. Of bulkheads 205 and 225, for example, an open bulkhead such as a stripe or the like, as well as a closed bulkhead such as a waffle, matrix, delta, or the like. In addition, the closed partition wall may be formed such that the cross section of the discharge space becomes a polygon such as a triangle, a pentagon, or a circle, an ellipse, or the like, in addition to the quadrangle as in the present embodiment.

The upper partition wall 205 may be manufactured to have a dark color with a light absorption of 50% or more. When the upper partition wall 205 is dark, the reflection brightness of the upper partition wall 205 is reduced, so that the contrast of the plasma display panel 200 is improved.

As shown in FIG. 3, the lower partition wall 225 prevents the scan electrode 206 and the common electrode 207 from directly conducting electricity during sustain discharge, and the charged particles directly collide with the electrodes 206 and 207. It is preferable to be formed as a dielectric material which prevents damage to them and induces charged particles to accumulate wall charges. Such dielectrics include PbO, B ₂ O ₃ , SiO _2, and the like.

However, the shape and material characteristics of the lower partition wall 225 is not limited thereto, and as shown in FIG. 4, the lower partition wall 225 may have a structure in which the partition wall 225a surrounds the partition wall 225a. Can have In this case, the dielectric part 225b may be formed of PbO, B ₂ O ₃ , SiO _2, or the like.

The scan electrode 206 and the common electrode 207 are electrodes for sustain discharge, and a sustain discharge that implements an image of the plasma display panel occurs between the electrodes. The scan electrode 206 and the common electrode 207 are formed of a conductive metal such as aluminum or copper. That the scan electrode 206 extends to intersect the address electrode 203 means that the column of the light emitting cell 220 through which the address electrode 203 passes and the column of the light emitting cell 220 through which the scan electrode 206 passes It means to cross. In addition, the common electrode 207 extended in parallel with the scan electrode 206 means that the common electrode 207 is disposed together with the scan electrode 206 at regular intervals.

The scan electrode 206 and the common electrode 207 are disposed to surround the lower side of the light emitting cell 220. The lower side of the light emitting cell means a side portion of the lower partition wall 225.

The scan electrode 206 and the common electrode 207 are disposed in the vertical direction, which means that one of the scan electrode 206 and the common electrode 207 is disposed at a higher position than the other electrode. In order for the address discharge between the scan electrode 206 and the address electrode 203 to occur smoothly, the scan electrode 206 is preferably disposed below the common electrode 207.

The side surface of the lower partition wall 225 is preferably covered by the MgO film 209. Although the MgO film 209 is not an essential component, it prevents the charged particles from colliding with the lower partition 225 formed of the dielectric and damaging the lower partition 225, and releasing a lot of secondary electrons upon discharge.

The phosphor layer 210 includes a component that receives visible ultraviolet light emitted by the sustain discharge and emits visible light. The phosphor layer 210 formed on the red light emitting subpixel is a phosphor such as Y (V, P) O ₄ : Eu or the like. The phosphor layer 210 formed on the green light emitting subpixel includes a phosphor such as Zn ₂ SiO ₄ : Mn, YBO ₃ : Tb, and the like. The phosphor layer 210 formed on the blue light emitting subpixel includes BAM: Eu, and the like. Same phosphor.

The light emitting cell 220 is filled with a discharge gas such as Ne, Xe and the like and a mixture of these. In the present invention including this embodiment, the discharge surface can be increased and the discharge region can be enlarged, so that the amount of plasma formed is increased, thereby enabling low voltage driving. Therefore, in the case of the present invention, even when a high concentration of Xe gas is used as the discharge gas, low voltage driving is possible, thereby significantly improving the luminous efficiency. This solves the problem of low voltage driving when using a high concentration of Xe gas as a discharge gas in a conventional plasma display panel.

The front substrate 201 is made of a material having good light transmittance such as glass. The front substrate 201 includes a scan electrode 106 formed of an indium tin oxide (ITO) film, a common electrode 107, a bus electrode 108 formed of metal, and the electrode, which are present on the front substrate of a conventional plasma display panel. Since the dielectric layer 109 covering the fields 106, 107, 108 and the MgO film 111 do not exist, the front transmittance of visible light is remarkably improved. Therefore, if the image is realized with the luminance of the conventional level, the electrodes 106 and 107 are driven at a relatively low voltage, thereby improving the luminous efficiency.

In the plasma display panel 200 having the above-described configuration, an address discharge is generated by applying an address voltage between the address electrode 203 and the scan electrode 206, and a light emitting cell in which sustain discharge occurs as a result of the address discharge ( 220 is selected.

Thereafter, when a sustain discharge voltage of alternating current is applied between the scan electrode 206 and the common electrode 207 of the selected light emitting cell 220, a sustain discharge occurs between the scan electrode 206 and the common electrode 207. Ultraviolet rays are emitted as the energy level of the discharged gas excited by the sustain discharge is lowered. The ultraviolet rays excite the phosphor layer 210 coated in the light emitting cell 220. As the energy level of the excited phosphor layer 210 decreases, visible light is emitted, and the emitted visible light forms an image. .

In the conventional plasma display panel shown in Fig. 1, the sustain discharge between the scan electrode 106 and the common electrode 107 occurs in the horizontal direction, so that the discharge area is relatively narrow. However, since the sustain discharge of the plasma display panel 200 according to the present embodiment occurs in all directions defining the discharge cells 220 in the vertical direction, the discharge area is relatively wide.

In addition, the sustain discharge in this embodiment is formed in a closed curve along the side of the discharge cell 220 and gradually diffuses to the center portion of the discharge cell 220. As a result, the volume of the region where the sustain discharge occurs is increased, and the space charge in the discharge cell, which is not well used in the past, also contributes to light emission. Such matters result in the improvement of the luminous efficiency of the plasma display panel.

In addition, in the light emitting cell of the plasma display panel according to the present embodiment, as shown in FIG. 3, the sustain discharge is performed only at the lower side of the light emitting cell 220. The ion sputtering of is prevented, and thus there is an advantage that permanent afterimage does not occur even if the same image is displayed for a long time.

6 and 7, the plasma display panel 300 according to the second embodiment of the present invention will be described with reference to the matters different from the first embodiment.

The plasma display panel 300 according to the present exemplary embodiment is formed on the rear substrate 302 and the rear substrate 302, and is formed on the lower partition 325 and the lower partition 325 that partition the light emitting cells 320. The front substrate 301 disposed parallel to the substrate 302, the lower side of the front substrate 301, the address electrodes 303 extending in one direction, and the dielectric layer 304 covering the address electrodes 303. The upper partition 305 which is disposed under the dielectric layer 304 and partitions the light emitting cell 320 together with the lower partition 325, the phosphor layers 310 formed on the side of the upper partition 305, and the light emitting cell Disposed in the lower partition 325 to surround the 320, scan electrodes 306 extending to intersect the address electrode 303, and disposed in the lower partition 325 to surround the upper side of the light emitting cell 320. The common electrode 307 extends in parallel with the scan electrode 306 and a discharge gas in the light emitting cell 320.

Regarding the front substrate 302, the upper and lower partitions 305 and 325, the phosphor layer 310, and the MgO film 309, the front substrate 202, the upper and lower partitions 205 and 225 of the first embodiment are respectively described. ), The phosphor layer 210 and the MgO film 209.

Unlike the first embodiment, the address electrodes 303 extending in one direction are disposed below the front substrate 301. The address electrodes 303 are used to cause an address discharge to facilitate sustain discharge between the scan electrode 306 and the common electrode 307. More specifically, the address electrodes 303 lower the voltage at which sustain discharge is initiated. The address discharge is a discharge occurring between the scan electrode 306 and the address electrode 303. When the address discharge is completed, cations are accumulated on the scan electrode 306 side and electrons are accumulated on the common electrode 307 side. Sustain discharge between the common electrode and the common electrode becomes easier.

In addition, the address electrode 303 may include at least two layers. In this embodiment, an address electrode 303 formed of an upper address electrode portion 303a and a lower address electrode portion 303b is illustrated. The upper address electrode portion 303a has a dark color with a light absorption of 50% or more. Therefore, the reflection luminance of the upper address electrode portion 303a is reduced, so that the contrast of the plasma display panel 300 is improved.

In contrast, the lower address electrode portion 303b has a bright color with a light reflectance of 50% or more. Therefore, since the amount of visible light transmitted to the outside through the lower address electrode part 303b is reduced, the luminance of the plasma display panel 300 is improved.

In addition, the dielectric layer 304 covering the address electrodes is formed as a dielectric that can induce charge while preventing cations or electrons from colliding with the address electrode 303 and causing damage to the address electrode 303 during discharge. Examples of the dielectric include PbO, B ₂ O ₃ , and SiO ₂ .

In the second embodiment, the scan electrode 306 and the common electrode 307 are disposed to surround the lower side of the light emitting cell 320. The lower side of the light emitting cell 320 means the inside of the lower partition wall 325, so that the scan electrode 306 and the common electrode 307 are lower than the phosphor layer 310.

The scan electrode 306 and the common electrode 307 are disposed in the vertical direction. In order for the address discharge between the scan electrode 306 and the address electrode 303 to occur smoothly, the scan electrode 306 is formed of the common electrode 307. It is preferable to arrange | position above.

The driving method of the plasma display panel having the above configuration is the same as or similar to the driving method of the plasma display panel according to the first embodiment.

Like reference numerals in the drawings shown above indicate the same members.

The plasma display panel according to the present invention has the following effects.

First, visible light emitted from the discharge cell passes through the front substrate. Since sustain electrodes and scan electrodes do not exist in the part of the front substrate where the visible light passes, the aperture ratio can be significantly improved, and the transmittance is improved. do.

Second, since the surface discharge can be generated from all sides forming the discharge space, the discharge surface can be greatly enlarged.

Third, since the discharge is generated in terms of forming the discharge cell and diffused to the center portion of the discharge cell, the discharge area is remarkably improved compared to the conventional one, so that the entire discharge cell can be efficiently used.

Fifth, the plasma can be concentrated in the center of the discharge space. The discharge occurs at the side of the discharge cell and diffuses to the center of the discharge cell, thereby concentrating the plasma to the center of the discharge cell, and the plasma is discharged under the influence of an electric field applied to the discharge electrode formed at the side By having a tendency to gather at the center of the cell, it is possible to utilize space charge for discharge.

Sixth, since it has the same effect as described above, it is possible to drive even at a low voltage can significantly improve the luminous efficiency.

Seventh, since the plasma display panel and the flat panel display device having the same according to the present invention can be driven at a low voltage as described above, even when a high concentration of Xe gas is used as the discharge gas, a low voltage can be driven to improve luminous efficiency. .

Eighth, the discharge response speed is fast and low voltage driving is possible. In the plasma display panel and the flat panel display device having the same according to the present invention, since the discharge electrode is not disposed on the front substrate through which visible light is transmitted, the discharge electrode is disposed on the side of the discharge space. Therefore, it is necessary to use a transparent electrode having high resistance as the discharge electrode. Since a low resistance electrode, such as a metal electrode, can be used as the discharge electrode, the discharge response speed is high, and low voltage driving is possible without distortion of the waveform.

Ninth, when the light absorption of the dielectric layer formed on the back substrate or the back substrate is darker than 50%, the brightness of the reflection is reduced, so that the contrast of the plasma display panel is improved. In addition, even when the light absorption rate of the upper partition wall has a dark color of 50% or more, the contrast of the plasma display panel is improved due to the reduction of the reflection luminance.

Tenth, if the light reflectance of the dielectric layer formed on the back substrate or the back substrate is more than 50% bright color, the amount of visible light transmitted to the outside through the bottom substrate is reduced, so that the brightness of the plasma display panel is improved.

Eleventh, even when the address electrode disposed below the front substrate has a multi-layered structure and has a dark color with a light absorption rate of 50% or more in the uppermost layer, the contrast of the plasma display panel is improved due to the reduction of the reflection luminance. In addition, when the light reflectance of the lowermost layer of the address electrode becomes bright color of 50% or more, the brightness of the plasma display panel is improved.

Twelfth, when the upper partition and the lower partition is formed to abut, it can be shielded of the noise generated during the discharge.

Although the present invention has been described with reference to the embodiments shown in the drawings, this is merely exemplary, and it will be understood by those skilled in the art that various modifications and equivalent other embodiments are possible. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

1 is a partial cutaway perspective view showing a conventional plasma display panel;

2 is a partial cutaway perspective view showing a plasma display panel according to a first embodiment of the present invention;

3 is a cross-sectional view taken along line III-III of FIG. 2,

4 is a cross-sectional view showing a modification of the first embodiment of the present invention,

5 is a cross-sectional view taken along line IV-IV of FIG. 3,

6 is a partially cutaway perspective view showing a plasma display panel according to a second embodiment of the present invention;

FIG. 7 is a cross-sectional view taken along the line VII-VII of FIG. 6.

Explanation of symbols on main parts of drawing

200, 300: plasma display panel

201, 301: Front board 202, 302: Back board

203, 303: address electrodes 204, 304: dielectric layer

205, 305: upper partition 206, 306: scanning electrode

207 and 307 common electrode 209 and 309 MgO film

210 and 310: phosphor layers 220 and 320: light emitting cells

225, 325: lower bulkhead

Claims (19)

Back substrate; Address electrodes disposed on the rear substrate and extending in one direction; A dielectric layer covering the address electrodes; A lower partition wall formed on the dielectric layer to partition the light emitting cells; A front substrate disposed on the lower partition wall in parallel with a rear substrate; An upper partition wall disposed below the front substrate and partitioning the light emitting cells together with the lower partition wall; Phosphor layers formed on side surfaces of the upper partition wall; Scan electrodes disposed in the lower partition wall to surround the light emitting cells and extending to cross the address electrodes; Common electrodes disposed in the lower partition wall to surround the light emitting cell and extending in parallel with the scan electrode; And And a discharge gas in the light emitting cell. The method of claim 1, And a side surface of the lower partition wall is covered by an MgO film. The method of claim 1, And the scan electrode and the common electrode are disposed in a vertical direction. The method of claim 3, wherein And one scan electrode and one common electrode are disposed in one light emitting cell, and the scan electrode is disposed below the common electrode. The method of claim 1, And said back substrate has a bright color with a light reflectance of 50% or more. The method of claim 1, And the back substrate has a dark color with a light absorption of 50% or more. The method of claim 1, And a bright color with the dielectric light reflectivity of 50% or more. The method of claim 1, And said dielectric has a dark color with a light absorption of 50% or more. The plasma display panel of claim 1, wherein the lower partition wall is formed of a dielectric. The method of claim 1, And the upper partition wall has a dark color with a light absorption of 50% or more. Back substrate; A lower partition wall formed on an upper side of the rear substrate to partition the light emitting cells; A front substrate disposed on the lower partition wall in parallel with a rear substrate; Address electrodes disposed under the front substrate and extending in one direction; A dielectric layer covering the address electrodes; An upper partition wall disposed below the dielectric layer and partitioning a light emitting cell together with the lower partition wall; Phosphor layers formed on side surfaces of the upper partition wall; Scan electrodes disposed in the lower partition wall to surround the light emitting cells and extending to cross the address electrodes; Common electrodes disposed in the lower partition wall to surround an upper side of the light emitting cell and extending in parallel with the scan electrode; And And a discharge gas in the light emitting cell. The method of claim 11, And a side surface of the lower partition wall is covered by an MgO film. The method of claim 11, And the scan electrode and the common electrode are disposed in a vertical direction. The method of claim 13, And one scan electrode and one common electrode are disposed in one light emitting cell, and the scan electrode is disposed above the common electrode. The method of claim 11, And the address electrode has at least two layers, and the uppermost layer of the layers has a dark color having a light absorption of 50% or more. The method of claim 11, And the address electrode has at least two layers, and the lowermost layer of the layers has a bright color with a light reflectance of 50% or more. The method of claim 11, And the lower partition wall is formed of a dielectric. The method of claim 11, And said back substrate has a bright color with a light reflectance of 50% or more. The method of claim 11, And the upper partition wall has a dark color with a light absorption of 50% or more.