KR20040058566A - Plasma display panel - Google Patents

Abstract

PURPOSE: A plasma display panel is provided to achieve improved luminance and reduce a power consumption by removing the small transparent electrode portion having a low contribution to discharge. CONSTITUTION: A plasma display panel comprises a pair of transparent electrodes(114A,116A) for bringing about a sustain discharge; protruded transparent electrodes(114C,116C) protruded from the transparent electrodes into the combination of trapezoidal and square shapes; metal electrodes(114B,116B) formed on the transparent electrodes, respectively; and address electrodes which cooperate with the transparent electrodes so as to bring about an address discharge.

Description

Plasma Display Panel {PLASMA DISPLAY PANEL}

The present invention relates to a plasma display panel, and more particularly, to a plasma display panel that can improve brightness and reduce power consumption.

Recently, a plasma display panel (hereinafter referred to as "PDP"), which is easy to manufacture a large panel, has attracted attention as a flat panel display device. The PDP normally displays an image by adjusting the discharge period of each pixel according to the digital video data. As such a PDP, an AC type PDP having three electrodes and driven by an AC voltage is typical.

1 is a perspective view illustrating a cell structure typically arranged in an alternating current type PDP in a matrix form.

Referring to FIG. 1, a conventional PDP cell includes an upper plate having sustain electrode pairs 14 and 16, an upper dielectric layer 18, and a passivation layer 20 sequentially formed on an upper substrate 10, and a lower substrate 12. ) Is provided with a lower plate having an address electrode 22, a lower dielectric layer 24, a partition wall 26, and a phosphor layer 28 formed sequentially. The upper substrate 10 and the lower substrate 12 are spaced in parallel by the partition wall.

Each of the sustain electrode pairs 14 and 16 has a relatively wide width and has a stripe-shaped transparent electrode 14A and 16A made of transparent electrode material (ITO) to transmit visible light, and has a relatively narrow width and transparency. In order to compensate for the resistive components of the electrodes 14A and 16A, the metal electrodes 14B and 16B are formed. At this time, the transparent electrodes 14A and 16A of the sustain electrode pairs 14 and 16 face each other with a gap Gap of about 60 µm to 80 µm. The sustain electrode pairs 14 and 16 are composed of a scan electrode and a sustain electrode. The scan signal for the panel scan and the sustain signal for maintaining the discharge are mainly supplied to the scan electrode 14, and the sustain signal is mainly supplied to the sustain electrode 16. Charges accumulate in the upper dielectric layer 18 and the lower dielectric layer 24. The protective film 20 prevents damage to the upper dielectric layer 18 by sputtering, thereby increasing the lifetime of the PDP and increasing the emission efficiency of secondary electrons. As the protective film 20, magnesium oxide (MgO) is usually used. The address electrode 22 is formed to cross the sustain electrode pairs 14 and 16. The address electrode 22 is supplied with a data signal for selecting cells to be displayed. The partition wall 26 is formed in parallel with the address electrode 22 to prevent ultraviolet rays generated by the discharge from leaking to adjacent cells. The phosphor layer 28 is applied to the surfaces of the lower dielectric layer 24 and the partition wall 26 to generate visible light of any one of red, green, and blue. Then, an inert gas for gas discharge is injected into the discharge space therein.

The PDP cell of this structure is selected by the counter discharge between the address electrode 22 and the scan electrode 14, and then sustains the discharge by the surface discharge between the sustain electrode pairs 14 and 16. In the PDP cell, the fluorescent substance 28 emits light by ultraviolet rays generated during sustain discharge, so that visible light is emitted outside the cell. As a result, the PDP having cells displays an image. In this case, the PDP implements a gray scale required for displaying an image by adjusting the discharge sustain period of the cell, that is, the number of sustain discharges, according to the video data.

The AC surface discharge type PDP is driven by being divided into a plurality of subfields to express the gray level of the image. In each subfield period, gray scale display is performed by performing light emission in a number of times proportional to the weight of video data. do. For example, when an image is displayed in 256 gray scales using 8-bit video data, one frame display period (for example, 1/60 second = about 16.7 msec) in each discharge cell 11 is divided into eight subfields. It is divided into (SF1 to SF8). Each subfield SF1 to SF8 is further divided into a reset period, an address period and a sustain period, and 1: 2: 4: 8:... The weight is given at the ratio of 128. Here, the reset period is a period for initializing the discharge cells, the address period is a period during which selective address discharge occurs according to the logic value of the video data, and the sustain period is such that discharge is maintained in the discharge cells in which the address discharge has occurred. It is a period. The reset period and the address period are equally assigned to each subfield period.

When the electrode widths of the scan electrodes 14 and the sustain electrodes 16 are made narrow in order to reduce power consumption in the PDP, the discharge path is shortened during discharge, thereby limiting the light emitting area. As a result, the amount of emitted ultraviolet rays decreases and the luminance decreases. In addition, when the electrode widths of the scan electrodes 14 and the sustain electrodes 16 are made wide to increase the luminance of the PDP, the capacitance value becomes large, thereby increasing the discharge current and power consumption.

In addition, conventional PDPs are larger in size than other flat panel display devices (FPDs) such as 40 ″, 50 ″, and 60 ″. Therefore, in the conventional PDP, the voltage drop due to the electrode length appears to be relatively large in the center portion and the peripheral portion of the PDP. In addition, since the PDP is injected into the discharge gas at a pressure lower than atmospheric pressure therein, the upper and lower substrates 10, 10 and 12 are formed by a center portion where the upper and lower substrates 10 and 12 are supported only by the partition 26 and a sealing material (not shown). The force exerted on the substrates 11 and 16 at the periphery to which 12 is bonded is different. As a result, although the conventional PDP is somewhat different depending on the size of the panel, as shown in FIG. 9, the luminance of the center portion is different from that of the peripheral portion A in the horizontal direction and the vertical direction, respectively, resulting in a non-discharge area.

Accordingly, an object of the present invention is to provide a plasma display panel which can improve brightness and reduce power consumption.

1 is a perspective view showing a discharge cell of a conventional plasma display panel.

FIG. 2 is a plan view illustrating an electrode structure of the plasma display panel shown in FIG. 1. FIG.

3 is a plan view illustrating an electrode structure of a plasma display panel according to a first embodiment of the present invention.

4 is a plan view illustrating lengths and widths of transparent electrodes and protruding transparent electrodes of the plasma display panel shown in FIG. 3;

5 is a plan view illustrating an electrode structure of a plasma display panel according to a second exemplary embodiment of the present invention.

6 is a plan view illustrating an electrode structure of a plasma display panel according to a third exemplary embodiment of the present invention.

7 is a plan view illustrating an electrode structure of a plasma display panel according to a fourth embodiment of the present invention.

FIG. 8 is a view illustrating the inclined surfaces of portions C shown in FIG. 7, that is, wing portions of partition walls and protruding transparent electrodes.

9 is a plan view illustrating an electrode structure of a plasma display panel according to a fifth embodiment of the present invention.

<Description of Symbols for Main Parts of Drawings>

10: upper substrate 12: lower substrate

18: upper dielectric layer 20: protective film

22: address electrode 24: lower dielectric layer

26,126,226,326,426,526: bulkhead 28: phosphor layer

316C: Blank

14, 114, 214, 314, 514, 16, 116, 216, 316, 516: sustaining electrode pair

14A, 114A, 214A, 314A, 414A, 514A, 16A, 116A, 216A, 316A, 416A, 516A

14B, 114B, 214B, 314B, 414B, 514B, 16B, 116B, 216B, 316B, 416B, 516B: Metal Electrode

114C, 214C, 414C, 514C, 116C, 216C, 416C, 516C: Protruding transparent electrode

421,521: Black Matrix

426B, 526B: wing

In order to achieve the above object, the plasma display panel according to an embodiment of the present invention is a projecting protruding in the form of a combination of a transparent electrode pair and a trapezoidal shape and a rectangular shape in at least one of the transparent electrode pair for causing a sustain discharge And a transparent electrode, a metal electrode formed on each of the transparent electrode pairs, and an address electrode for causing an addressing discharge with the transparent electrode pairs.

In the panel, the protruding transparent electrode is protruded in a form in which the trapezoidal shape and the rectangular shape are coupled to each of the transparent electrode pairs.

In the panel, the protruding transparent electrode may include a first protruding transparent electrode protruding from a combination of the trapezoidal shape and a quadrangular shape in any one of the transparent electrode pairs, and a protruding rectangular electrode from the other one of the transparent electrode pairs. It is provided with two protruding transparent electrodes.

In the panel, the protruding transparent electrode may include a first transparent electrode having a stripe shape in which the metal electrode is formed, a second transparent electrode protruding in a trapezoid shape from the first electrode, and a protruding rectangular shape from the second electrode. 3 transparent electrodes are provided.

The width of one side of the second transparent electrode in the panel is set to a range of 50% to 150% of the width of the address electrode, the width of the other side opposite the one side of the second transparent electrode is wider than the width of one side It features.

The length of the third transparent electrode in the panel is set to be in the range of 10% to 90% of the width of the protruding transparent electrode.

In the panel, the protruding transparent electrode is connected to the protruding transparent electrode formed in an adjacent discharge cell through a stripe-shaped connecting portion.

The panel further includes a partition wall separating the discharge cells, and a wing portion protruding in a trapezoidal shape so as to be symmetrical on one side of the partition wall.

The inclined surface of the wing portion of the trapezoidal shape in the panel is characterized by having the same angle as the inclined surface of the projecting transparent electrode of the trapezoidal shape facing each other.

Each of the transparent electrode pairs in the panel has a smaller area than the protruding transparent electrode and is connected through the metal electrode.

Other objects and features of the present invention in addition to the above object will be apparent from the description of the embodiments with reference to the accompanying drawings.

Hereinafter, exemplary embodiments of the present invention will be described with reference to FIGS. 3 to 10.

Referring to FIG. 3, a discharge cell of a plasma display panel (hereinafter, referred to as a “PDP”) according to an exemplary embodiment of the present invention may have a sustain electrode pair sequentially formed on an upper substrate (not shown). 114 and 116, an upper plate having an upper dielectric layer (not shown) and a protective film (not shown), an address electrode (not shown), a lower dielectric layer, a partition wall 126, and a phosphor not shown, which are sequentially formed on the lower substrate. It has a bottom plate having a layer 28. Here, the upper substrate and the lower substrate are spaced in parallel by the partition wall.

Each of the sustain electrode pairs 114 and 116 has a relatively wide width and has a stripe-shaped transparent electrode 114A and 116A made of transparent electrode material ITO and transparent electrodes 114A and 116A to transmit visible light. Protruding in a trapezoidal shape, and further protruding in a quadrangular shape, and have a relatively narrow width, and the metal electrodes 114B and 116B to compensate for the resistive components of the transparent electrodes 114A and 116A. Is done. At this time, the transparent electrodes 114A and 116A of the sustain electrode pairs 114 and 116 face each other with a gap Gap of about 60 μm to 80 μm interposed therebetween.

Each of the protruding transparent electrodes 114C and 116C removes an inefficient electrode portion having low discharge efficiency in the discharge cell, thereby improving discharge efficiency and brightness, and reducing the area of the transparent electrodes 114A and 116A to reduce power consumption. Reduced. To this end, each of the protruding transparent electrodes 114C and 116C protrudes in a trapezoidal form from the transparent electrodes 114A and 116A, and further protrudes in a quadrangular form again.

At this time, the electrode width b of each of the transparent electrodes 114A and 116A is larger than the widths of the metal electrodes 114B and 116B in consideration of the alignment tolerance 30 μm to 60 μm for forming the metal electrodes 114B and 116B. It is widely formed in the range of 30 μm to 60 μm. In addition, the width a from one end of the transparent electrodes 114A and 116A to one end of the protruding transparent electrodes 114C and 116C is about 75% of the pitch of the discharge cells as shown in FIG. 4. Is set to be. At this time, the sum (a) of the width (b) of the transparent electrodes (114A, 116A) and the width (g) of the protruding transparent electrodes (114C, 116C) is adjacent to a maximum size that can increase the electrode width in consideration of the discharge efficiency. The gap Gap between the 2a + protruding transparent electrodes 114C and 116C, which is a range in which cross talk between the discharge cells does not occur, is set to be about 75% of the pitch of the discharge cells.

In addition, the width c of one side having a relatively narrow width in the trapezoid-shaped protruding transparent electrodes 114C and 116C protruding at a predetermined slope from each of the transparent electrodes 114A and 116A is not shown. In consideration of the tolerance with respect to the same addressing characteristics, the width of the address electrode is formed to be 50% to 150% wider than the width of the other side of each trapezoid-shaped protruding transparent electrode (114C, 116C) having a relatively wide width Each width e is wider than the width c of each side of the protruding transparent electrodes 114C and 116C and smaller than the distance f between the partition wall 126 and the adjacent partition wall 126.

Meanwhile, the length d of each of the protruding transparent electrodes 114C and 116C, which protrudes further in a quadrangular shape from the trapezoidal protruding transparent electrodes 114C and 116C, is compared with the length g of each of the protruding transparent electrodes 114C and 116C. The minimum length d is set to be 10% or more relative to the length g of each of the protruding transparent electrodes 114C and 116C.

As described above, the sustain electrode pairs 114 and 116 are composed of a scan electrode and a sustain electrode. The scan signal for scanning the panel and the sustain signal for maintaining the discharge are mainly supplied to the scan electrode 114, and the sustain signal is mainly supplied to the sustain electrode 116. Charges accumulate in the upper and lower dielectric layers. The protective film prevents damage to the upper dielectric layer by sputtering, thereby extending the life of the PDP and increasing the emission efficiency of secondary electrons. Magnesium oxide (MgO) is usually used as a protective film. The address electrode is formed to cross the sustain electrode pairs 114 and 116. The address electrode is supplied with a data signal for selecting cells to be displayed. The partition wall 126 is formed in parallel with the address electrode to prevent the ultraviolet rays generated by the discharge from leaking to the adjacent cells. The phosphor layer is applied to the surfaces of the lower dielectric layer and the partition wall 126 to generate visible light of any one of red, green, and blue. Then, an inert gas for gas discharge is injected into the discharge space therein.

The PDP cell of this structure is selected by the counter discharge between the address electrode and the scan electrode 114, and then sustains the discharge by the surface discharge between the sustain electrode pairs 114 and 116. In the PDP cell, the phosphor emits light by ultraviolet rays generated during sustain discharge, so that visible light is emitted outside the cell. As a result, the PDP having cells displays an image. In this case, the PDP implements a gray scale required for displaying an image by adjusting the discharge sustain period of the cell, that is, the number of sustain discharges, according to the video data.

As described above, the PDP according to the first embodiment of the present invention widens the electrodes of the transparent electrodes 114A and 116A to increase the luminance and decreases the discharge efficiency of the transparent electrodes 114A and 116 in the discharge cell. By removing the electrode of 116A, power consumption is reduced. Therefore, the PDP according to the first embodiment of the present invention can improve the discharge efficiency and brightness and reduce the power consumption.

Referring to FIG. 5, each of the sustain electrode pairs 214 and 216 of the PDP has a relatively wide width and has a stripe shape made of transparent electrode material (ITO) for transmitting visible light. The first protruding transparent electrode 114C protruding in a trapezoidal shape from the first transparent electrode 214A of the sustain electrode pairs 214 and 216, and further protruding in a quadrangular shape. The second projecting transparent electrode 216A protruding in a rectangular shape from the second transparent electrode 214A among the electrode pairs 214 and 216, and having a relatively narrow width to compensate for the resistance component of the transparent electrodes 214A and 216A Metal electrodes 214B and 216B. At this time, the transparent electrodes 214A and 216A of the sustain electrode pairs 214 and 216 face each other with a gap Gap of about 60 µm to 80 µm.

Since the PDP according to the second embodiment of the present invention is the same as the PDP of the above-described embodiment except for the sustain electrode pairs 214 and 216, a detailed description thereof will be omitted.

As described above, the PDP according to the second embodiment of the present invention protrudes one of the transparent electrodes 214A and 216A of the sustain electrode pairs 214 and 216 in a trapezoidal shape and further protrudes in a rectangular shape, and the other is rectangular. By providing the first and second protruding transparent electrodes 214C and 216C protruding in the form, discharge efficiency and luminance can be improved and power consumption can be reduced as in the PDP according to the first embodiment of the present invention. .

Referring to FIG. 6, each of the sustain electrode pairs 314 and 316 of the PDP according to the third embodiment of the present invention has a relatively wide width and has a stripe shape made of transparent electrode material (ITO) for transmitting visible light. Transparent electrodes 314A and 316A, blanks 314C and 316C formed in a trapezoidal and rectangular shape combined on the transparent electrodes 314A and 316A, and have relatively narrow widths and have transparent electrodes 314A and 316A. Metal electrodes 314B and 316B to compensate for the resistive components of At this time, the transparent electrodes 314A and 316A of the sustain electrode pairs 314 and 316 face each other with a gap Gap of about 60 µm to 80 µm therebetween.

In the PDP according to the third embodiment of the present invention, other portions of the sustain electrode pairs 314 and 316 except for the transparent electrodes 314A and 316A and the blanks 314C and 316C are the first embodiment of the present invention. Since it is the same as the example PDP, detailed description thereof will be omitted.

The structures of the blanks 314C and 316C formed on the transparent electrodes 314A and 316A of the sustain electrode pairs 314 and 316 are adjacent to the one-side transition metal electrodes 314B and 316B having a relatively wide width. One side having a relatively narrow width is formed in a rectangular shape. Each of these blanks 314C, 316C is formed on the partition 326.

As described above, each of the transparent electrodes 314A and 316A of the PDP according to the third embodiment of the present invention has stripes of the transparent transparent electrodes 214C and 216C formed in adjacent discharge cells of the PDP according to the first embodiment of the present invention. It has a form that is connected to each other through the connection of the form. Accordingly, the PDP according to the third embodiment of the present invention has a structure for preventing misalignment when the upper substrate and the lower substrate are bonded.

As described above, the PDP according to the third embodiment of the present invention can improve the discharge efficiency and brightness as well as reduce power consumption as in the PDP according to the first embodiment of the present invention.

Referring to FIG. 7, a PDP according to a fourth exemplary embodiment of the present invention may include a pair of sustain electrodes 414 and 416 formed on an upper substrate (not shown), and a partition wall 426 and a partition wall formed on a lower substrate. Wings 426A and 426B protruding from both sides at 426; In the PDP according to the fourth embodiment of the present invention, an upper dielectric layer and a protective layer (not shown) are sequentially formed on the upper substrate, and an address electrode, a lower dielectric layer, and a phosphor layer 28 (not shown) are sequentially formed on the lower substrate. Are further formed sequentially.

Since the PDP according to the fourth embodiment of the present invention is the same as the PDP of the first embodiment of the present invention except for the partition wall 426, the detailed description thereof will be omitted.

The partition wall 426 includes a stripe line 426A and a wing portion 426B protruding from both sides to be symmetrical in the stripe line 426A. At this time, the wing 426B protrudes in a trapezoidal shape from the stripe-shaped line 426A to have an inclined surface. The inclined plane angle A ° of the trapezoidal wing 426B is a trapezoidal protruding transparent electrode 414C or 416C protruding to have an inclined plane in each of the transparent electrodes 414A and 416A, as shown in FIG. 8. Each of the angles of inclination angle B ° is the same. The wing portion 426B of the partition wall 426 is formed at the intersection of the transparent electrodes 414A and 416A and the black matrix 421.

As described above, the PDP according to the fourth embodiment of the present invention is provided with the protruding transparent electrodes 414C and 416C so as to remove a small portion of the discharge contribution of the transparent electrodes 414A and 416A during the discharge between the sustain electrode pairs 414 and 416. The power consumption can be reduced, and the discharge current can be smoothly supplied through the protruding transparent electrodes 414C and 416C having the inclined surface. In addition, the PDP according to the fourth embodiment of the present invention compensates for the decrease in luminance due to the reduction of the transparent electrodes 414A and 416A by forming the trapezoidal wing 426B in the partition wall 426.

Accordingly, in the PDP according to the fourth embodiment of the present invention, the discharge efficiency of the panel is improved by removing the non-discharge region C in the discharge cell. In addition, the trapezoidal wing portion 426B is formed on the partition wall 426 to have an angle A ° equal to the inclination angle B ° of each of the trapezoidal protruding transparent electrodes 414C and 416C. The brightness / efficiency is improved.

Referring to FIG. 9, the discharge cell of the PDP according to the fifth embodiment of the present invention has a short and wide paddle shaped transparent electrode 514A and 516A and a metal electrode 516B crossing the transparent electrode 514A and 516A. And sustain electrode pairs 514 and 516 including 516B and partition walls 526 for separating adjacent discharge cells.

Since the PDP according to the fifth embodiment of the present invention is the same as the PDP of the fourth embodiment of the present invention, except for paddle-shaped transparent electrodes 514A and 516A, the detailed description thereof will be omitted. do.

Each of the paddle-shaped transparent electrodes 514A and 516A protrudes in a trapezoidal shape and a rectangular shape from a rectangular transparent electrode and a rectangular transparent electrode connected to the metal electrodes 514B and 514B. And transparent electrodes 514C and 516C. That is, the paddle-shaped transparent electrodes 514A and 516A are formed to have a smaller area than the projecting transparent electrodes of the quadrilateral shape and are connected to each other through the metal electrodes 514B and 514B.

At this time, the inclination angles of the trapezoidal protruding transparent electrodes 514C and 516C and the inclination angle of the wing portion 526B formed in the stripe-shaped line 526A of the partition wall 526 protruding in a quadrilateral shape maximize the luminance. In order to form the same slope.

As described above, in the PDP according to the fifth embodiment of the present invention, the areas of the transparent electrodes 514A and 516A may be reduced to reduce power consumption. In addition, in the PDP according to the fifth embodiment of the present invention, as in the PDP according to the fourth embodiment of the present invention, the discharge efficiency of the panel is improved by removing the non-discharge region C in the discharge cell. Meanwhile, the PDP according to the fifth embodiment of the present invention has a trapezoidal shape so as to have an angle A ° equal to the inclination angle B ° of each of the trapezoidal shaped protruding transparent electrodes 514C and 516C on the partition wall 526. By forming the wing portions 526B, the luminance / efficiency of the panel is improved.

As described above, the plasma display panel according to the embodiment of the present invention includes a protruding transparent electrode protruding in a stripe-shaped transparent electrode combined with a trapezoidal shape and a rectangular shape. Accordingly, the present invention can reduce the power consumption by removing the transparent electrode portion having a small discharge contribution in the discharge cell, it is possible to smoothly supply the discharge current through the trapezoidal projecting transparent electrode. In addition, the present invention can prevent the alignment miss when the substrate is bonded by forming a blank of the protruding transparent electrode shape on the transparent electrode. On the other hand, the present invention can improve the brightness and discharge efficiency by forming a wing on the partition wall to have the same slope as the trapezoidal slope of the projecting transparent electrode protruding from the transparent electrode.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification but should be defined by the claims.

Claims (10)

In the discharge cell of the plasma display panel, A pair of transparent electrodes for causing a sustain discharge, A protruding transparent electrode protruding from a trapezoidal shape and a quadrangular shape in at least one of the pairs of transparent electrodes; A metal electrode formed on each of the transparent electrode pairs; And an address electrode for causing an addressing discharge with the transparent electrode pair. The method of claim 1, And wherein the protruding transparent electrode protrudes from each of the pair of transparent electrodes in a form in which the trapezoidal shape and the rectangular shape are combined. The method of claim 1, The protruding transparent electrode, A first protruding transparent electrode protruding from a trapezoidal shape and a quadrangular shape in any one of the pair of transparent electrodes; And a second protruding transparent electrode protruding in a quadrangular shape from the other one of the pair of transparent electrodes. The method of claim 1, The protruding transparent electrode, A first transparent electrode having a stripe shape in which the metal electrode is formed; A second transparent electrode protruding in a trapezoidal form from the first electrode; And a third transparent electrode protruding in a square shape from the second electrode. The method of claim 4, wherein The width of one side of the second transparent electrode is set in a range of 50% to 150% of the width of the address electrode, And a width of the other side opposite to one side of the second transparent electrode is wider than a width of the one side. The method of claim 4, wherein And the length of the third transparent electrode is set in a range of 10% to 90% of the width of the protruding transparent electrode. The method of claim 1, And wherein the protruding transparent electrode is connected to the protruding transparent electrode formed in an adjacent discharge cell through a stripe-shaped connecting portion. The method of claim 1, A partition wall separating the discharge cells; And a wing portion protruding in a trapezoidal shape so as to be symmetrical at one side of the partition wall. The method of claim 8, The inclined surface of the wing portion of the trapezoidal shape has the same angle as the inclined surface of the projecting transparent electrode of the trapezoidal shape, characterized in that facing each other. The method of claim 1, Each of the transparent electrode pairs has a smaller area than the protruding transparent electrode and is connected through the metal electrode.