TW201621418A - Display panel and manufacturing method thereof - Google Patents

Abstract

A display panel including a first substrate, a second substrate and a blue phase liquid crystal layer is provided. The first substrate includes a first electrode layer. The second substrate is located a side of the first substrate and includes a second electrode layer, a dielectric structure and a third electrode layer. The third electrode layer is located between the first electrode layer and the second electrode layer, and the dielectric structure is located between the second electrode layer and the third electrode layer. The dielectric structure includes a base layer and a plurality of protrusion portions protruding from the base layer. The base layer is located between the protrusion portions and the second electrode layer. The protrusion portions are located between the third electrode layer and the base layer so that the horizontal plane of the third electrode layer is higher than the horizontal plane of the base layer. The blue phase liquid crystal layer is located between the third electrode layer and the first electrode layer and between the base layer and the first electrode layer. A manufacturing method of the display panel is also provided.

Description

Display panel and method of manufacturing same

The present invention relates to a display panel and a method of fabricating the same.

In recent years, blue phase liquid crystal display panels have received attention from academic and industrial circles due to their fast response time and optical isotropic properties. The blue phase liquid crystal layer is generally driven by a transverse electric field to function as a light valve. Therefore, the current blue phase liquid crystal display panel mainly adopts an electrode design of In-Plane Switching.

1 is a schematic cross-sectional view of a conventional blue phase liquid crystal display panel. Referring to FIG. 1, in the electrode design of the IPS, the densest point A of the power line EL (ie, the strongest transverse electric field) is located between the adjacent two electrodes ED. However, in the conventional IPS electrode design, the electrode ED is designed to be buried in the insulating layer IN. Such a design causes the densest portion A of the power line EL to be occupied by the insulating layer IN and cannot be used to drive the blue phase liquid crystal layer DM, so that the electrode design of the conventional IPS needs to be driven more efficiently by, for example, increasing the driving voltage. Blue phase liquid crystal layer DM. In addition, due to the fact that the double-twisted cylindrical structure of the blue phase liquid crystal molecules may have dark state light leakage due to its structural characteristics or its interaction with other components. problem.

In view of the above, how to improve the high driving voltage and dark state light leakage of the blue phase liquid crystal display panel is a problem that the research and development personnel are currently trying to solve.

The present invention provides a display panel which can improve the problems of high driving voltage and dark state light leakage.

The present invention further provides a manufacturing method for manufacturing the above display panel.

A display panel of the present invention includes a first substrate, a second substrate, and a blue phase liquid crystal layer. The first substrate includes a first electrode layer. The second substrate is located at one side of the first substrate and includes a second electrode layer, a dielectric structure, and a third electrode layer. The third electrode layer is located between the first electrode layer and the second electrode layer, and the dielectric structure is located between the second electrode layer and the third electrode layer. The dielectric structure includes a bottom layer and a plurality of protrusions that are protruded from the bottom layer. The bottom layer is located between the protrusion and the second electrode layer. The protrusion is located between the third electrode layer and the bottom layer such that the plane of the third electrode layer is higher than the plane of the bottom layer. The blue phase liquid crystal layer is located between the third electrode layer and the first electrode layer and between the bottom layer and the first electrode layer.

A method of manufacturing a display panel of the present invention includes the following steps. First, a first substrate and a second substrate on one side of the first substrate are provided. The first substrate includes a first electrode layer. The second substrate includes a second electrode layer, a dielectric structure, and a third electrode layer. The third electrode layer is located between the first electrode layer and the second electrode layer, and the dielectric structure is located between the second electrode layer and the third electrode layer. Dielectric structure including bottom layer And a plurality of protrusions protruding from the bottom layer. The bottom layer is located between the protrusion and the second electrode layer. The protrusion is located between the third electrode layer and the bottom layer such that the plane of the third electrode layer is higher than the plane of the bottom layer. Next, a blue phase liquid crystal layer is disposed between the third electrode layer and the first electrode layer and between the bottom layer and the first electrode layer. The blue phase liquid crystal layer includes a blue phase liquid crystal and a polymerizable monomer. Next, a potential difference between the first electrode layer and the second electrode layer is provided to generate a vertical electric field between the first electrode layer and the second electrode layer, and the blue phase liquid crystal layer is irradiated with the light source, so that the blue phase liquid crystal and the polymerizable monomer are perpendicular A polymerization reaction occurs in the presence of an electric field.

Based on the above, the display panel of the present invention is configured to raise the third electrode layer by the protrusion portion to more effectively utilize the region covered by the power line, thereby contributing to the problem of improving the high driving voltage. Further, the method for producing a display panel of the present invention solves the problem of light leakage in a dark state by causing a polymerization reaction of a blue phase liquid crystal and a polymerizable monomer in the presence of a vertical electric field.

The above described features and advantages of the invention will be apparent from the following description.

100, 200‧‧‧ display panel

110‧‧‧First substrate

120‧‧‧second substrate

130, DM‧‧‧ blue phase liquid crystal layer

A‧‧‧The most secret place

ARS‧‧‧Active Component Array Substrate

B‧‧‧Bottom

CCE‧‧‧Connected common electrode

CE‧‧‧Common electrode

CFS‧‧‧Color filter substrate

CPE‧‧‧Connected pixel electrode

D1, D2‧‧‧ distance

DS‧‧‧ dielectric structure

E‧‧‧vertical electric field

E1, E1'‧‧‧ first electrode layer

E2, E2'‧‧‧ second electrode layer

E3‧‧‧ third electrode layer

ED‧‧‧electrode

EL‧‧‧Power Line

IN‧‧‧Insulation

LC‧‧‧Blue Phase LCD

LS‧‧‧ light source

M‧‧‧ Polymeric monomer

P‧‧‧protrusion

PE‧‧‧ pixel electrode

SCE‧‧‧ strip common electrode

SPE‧‧‧ strip pixel electrode

SE1‧‧‧first strip electrode

SE2‧‧‧Second strip electrode

V, V’‧‧‧ potential difference

W1, W2, WP‧‧‧ width

X, Y‧‧ direction

1 is a schematic cross-sectional view of a conventional blue phase liquid crystal display panel.

2A is a schematic cross-sectional view of a display panel in accordance with a first embodiment of the present invention.

2B and 2C are diagrams showing the display panel of FIG. 2A in a dark state and a bright state, respectively. intention.

3A and 3B are schematic diagrams showing a manufacturing process of a display panel according to an embodiment of the invention.

4A and 4B are front and rear versions of a blue phase liquid crystal molecule adjacent to a stripe pixel electrode and a strip-shaped common electrode, respectively, subjected to a vertical electric field.

Fig. 5 is a graph showing the relationship between the potential difference and the transmittance of the first electrode layer and the second electrode layer.

Figure 6 is a cross-sectional view showing a display panel in accordance with a second embodiment of the present invention.

2A is a schematic cross-sectional view of a display panel in accordance with a first embodiment of the present invention. FIG. 2B and FIG. 2C are schematic diagrams of the display panel of FIG. 2A in a dark state and a bright state, respectively, wherein FIGS. 2B and 2C only schematically illustrate the third electrode layer of the second substrate. Referring to FIGS. 2A-2C , the display panel 100 includes a first substrate 110 , a second substrate 120 , and a blue phase liquid crystal layer 130 . The second substrate 120 is located on one side of the first substrate 110 , and the blue phase liquid crystal layer 130 is located between the second substrate 120 and the first substrate 110 .

The first substrate 110 includes a first electrode layer E1. The second substrate 120 includes a second electrode layer E2, a dielectric structure DS, and a third electrode layer E3, wherein the third electrode layer E3 is located between the first electrode layer E1 and the second electrode layer E2. The first electrode layer E1, the second electrode layer E2, and the third electrode layer E3 are, for example, light transmissive electrode layers. specifically, The material of the first electrode layer E1, the second electrode layer E2, and the third electrode layer E3 may include a metal oxide such as indium tin oxide, indium zinc oxide, aluminum tin oxide, aluminum zinc oxide, indium antimonide zinc. An oxide, or other suitable metal oxide, or a stacked layer of at least two of the foregoing.

The dielectric structure DS is located between the second electrode layer E2 and the third electrode layer E3, and the material thereof may be a light transmissive inorganic material or a light transmissive organic material. The dielectric structure DS includes a bottom layer B and a plurality of protrusions P protruding from the bottom layer B. The bottom layer B is located between the protrusion P and the second electrode layer E2. The protrusion P is located between the third electrode layer E3 and the bottom layer B such that the plane of the third electrode layer E3 is higher than the plane of the bottom layer B. Specifically, as shown in FIG. 2A, the projection P can be regarded as a structure for raising the third electrode layer E3. In the present embodiment, the third electrode layer E3 and the protrusion P have substantially the same contour, and the edges of the third electrode layer E3 and the protrusion P are cut away from each other by the direction X perpendicular to the second substrate 120. Qi, but not limited to this. Any structure that can be used to raise the third electrode layer E3 can be used as the projection P of the present embodiment.

The third electrode layer E3 is disposed on the protrusion P, and the third electrode layer E3 includes a pixel electrode PE and a common electrode CE, wherein the common electrode CE and the pixel electrode PE are structurally separated to maintain independent electrical properties. The pixel electrode PE and the common electrode CE are, for example, comb electrodes, respectively. Specifically, the pixel electrode PE includes a connected pixel electrode CPE and a plurality of stripe pixel electrodes SPE. The common electrode CE includes a connection common electrode CCE and a plurality of strip common electrodes SCE. The stripe pixel electrode SPE is connected to the side of the connection pixel electrode CPE close to the connection common electrode CCE, and the strip common electrode SCE is connected to the connection common electrode CCE close to the connection pixel electrode CPE. One side. Further, the strip-shaped common electrode SCE and the strip-shaped pixel electrode SPE are alternately arranged in one direction Y. By providing a potential difference V between the pixel electrode PE and the common electrode CE, a transverse electric field can be generated between the strip-shaped common electrode SCE and the stripe-shaped electrode SPE.

The blue phase liquid crystal layer 130 is located between the third electrode layer E3 and the first electrode layer E1 and between the bottom layer B and the first electrode layer E1. The blue phase liquid crystal layer 130 is substantially switched between optically isotropic and optically anisotropic depending on whether or not there is a transverse electric field between the strip-shaped common electrode SCE and the strip-shaped pixel electrode SPE.

Specifically, the blue phase liquid crystal layer 130 has optical isotropic properties in an electric field-free environment and optical anisotropy in an environment having a lateral electric field. That is to say, when there is no potential difference between the pixel electrode PE and the common electrode CE, the light beam does not change its original polarization direction after passing through the blue phase liquid crystal layer 130. Therefore, under the structure in which the polarizing plates whose polarization directions are perpendicular to each other are disposed on the outer surfaces of the first substrate 110 and the second substrate 120, when there is no potential difference between the pixel electrode PE and the common electrode CE, the blue phase liquid crystal is passed. The polarization direction of the light beam of the layer 130 is parallel to the polarization direction of the polarizer disposed on the second substrate 120 and perpendicular to the polarization direction of the polarizer disposed on the first substrate 110, thereby passing through the blue phase liquid crystal layer 130. The light beam is absorbed by the polarizer disposed on the first substrate 110, and the display panel 100 is rendered dark (as shown in FIG. 2B). On the other hand, when there is a potential difference V between the pixel electrode PE and the common electrode CE, the blue phase liquid crystal molecules of the blue phase liquid crystal layer 130 undergo a change in refractive index due to the action of the transverse electric field, so that the blue phase liquid crystal layer 130 is deflected. The light beam passing through the blue phase liquid crystal layer 130 can be penetrated by the polarization direction of the light beam of the second substrate 120 The polarizer disposed on the first substrate 110 causes the display panel 100 to assume a bright state (as shown in FIG. 2C).

In view of the above, the lateral electric field affects the transmittance of the display panel 100. Therefore, by changing the potential difference V between the pixel electrode PE and the common electrode CE, the gray scale of the screen displayed by the display panel 100 can be changed.

In this embodiment, the first substrate 110 may further include a color filter substrate CFS to enable the display panel 100 to achieve full color. The first electrode layer E1 is disposed on the color filter substrate CFS, and the first electrode layer E1 is located on a side of the color filter substrate CFS facing the second substrate 120. The color filter substrate CFS may include a plurality of filters of different colors, and the filters are arranged in an array. In addition, the second substrate 120 may further include an active device array substrate ARS to cause the display panel 100 to display different image frames. The second electrode layer E2, the dielectric structure DS, and the third electrode layer E3 are sequentially disposed on the active device array substrate ARS, and the second electrode layer E2, the dielectric structure DS, and the third electrode layer E3 are located on the active device array substrate ARS. Facing one side of the first substrate 110. The active device array substrate ARS may include a plurality of scan lines, a plurality of data lines, a plurality of active elements, a black matrix, and other elements well known to those of ordinary skill in the art.

Referring to FIG. 1 and FIG. 2A again, in the prior art, the electrode ED is designed to be buried in the insulating layer IN, that is, the top surface of the electrode ED and the top surface of the insulating layer IN are substantially coplanar. Under such a design, the densest portion A of the power line EL is occupied by the insulating layer IN, and the blue phase liquid crystal layer DM cannot be disposed. That is, the transverse electric field at the densest point A of the power line EL cannot be used to drive the blue phase liquid crystal layer DM. In the horizontal In the case where the electric field cannot be effectively utilized, the electrode design of the conventional IPS needs to drive the blue phase liquid crystal layer DM more efficiently by, for example, increasing the driving voltage. In contrast, as shown in FIG. 2A, the design of the display panel 100 through the protrusion P to raise the third electrode layer E3 helps to distribute the blue phase liquid crystal layer 130 in the region affected by the power line EL (including the The plane of the three-electrode layer E3 is located above, between the strip-shaped common electrode SCE and the stripe-shaped electrode SPE, and between the adjacent two protrusions P). Thus, the lateral electric field between the strip-shaped common electrode SCE and the stripe-shaped electrode SPE can be more effectively utilized, thereby contributing to lowering the driving voltage required for the display panel 100 and improving the highness of the conventional blue-phase liquid crystal display panel. The problem of driving voltage. In the present embodiment, the distance D1 between the third electrode layer E3 (including the pixel electrode PE and the common electrode CE) and the underlayer B is greater than 0 and less than or equal to 6 μm, and preferably 4 μm. Further, the distance D2 between the adjacent two projections P is greater than 0 and less than or equal to 15 μm, and preferably 10 μm.

3A and FIG. 3B are schematic diagrams showing a manufacturing process of a display panel according to an embodiment of the present invention, wherein FIGS. 3A and 3B schematically only illustrate a second electrode layer of the second substrate. 4A and 4B are front and rear versions of a blue phase liquid crystal molecule adjacent to a stripe pixel electrode and a strip-shaped common electrode, respectively, subjected to a vertical electric field. Referring to FIG. 3A, first, the first substrate 110 and the second substrate 120 described above are provided. Next, the blue phase liquid crystal layer 130 is disposed between the first substrate 110 and the second substrate 120 (ie, between the third electrode layer E3 and the first electrode layer E1 of FIG. 2A and between the bottom layer B and the first electrode layer E1). . The blue phase liquid crystal layer 130 includes a blue phase liquid crystal LC and a polymerizable monomer M. Referring to FIG. 3B, a potential difference V' between the first electrode layer E1 and the second electrode layer E2 is provided. A vertical electric field E is generated between the first electrode layer E1 and the second electrode layer E2, and the blue phase liquid crystal layer 130 is irradiated with the light source LS to cause the blue phase liquid crystal LC and the polymerizable monomer M to be polymerized in the presence of the vertical electric field E. reaction. The light source LS described above includes ultraviolet light, visible light, infrared light, or a combination thereof. Further, the vertical electric field E is preferably formed in a temperature range in which the blue phase liquid crystal LC is in the range of -10 to 60 degrees Celsius.

By causing the blue phase liquid crystal LC and the polymerizable monomer M to be polymerized in the presence of the vertical electric field E, the blue phase liquid crystal layer 130 after polymerization is helped to have better optical isotropic properties, thereby effectively reducing the blue color. The dark state light leakage phenomenon of the liquid crystal layer 130 due to its structural characteristics. Further, by causing the blue phase liquid crystal LC and the polymerizable monomer M to generate a polymerization reaction in the presence of the vertical electric field E, it is also helpful to improve the problem of dark state light leakage at the edge of the convex portion.

Referring to FIG. 4A, the blue phase liquid crystal LC disposed adjacent to the edge of the protruding portion P and the protruding portion P are easily twisted by the interaction, so that the blue phase liquid crystal LC disposed adjacent to the edge of the protruding portion P has no electric field. In the case of optical anisotropy. As shown, the long axes of the optically anisotropic blue phase liquid crystals LC are substantially parallel to the extending direction of the protrusions P, so that the light beams of the backlight module (not shown) may be biased by the blue phase liquid crystals. Folding up causes the display panel to have a problem of dark light leakage at the edge of the projection P.

In this embodiment, by causing the blue phase liquid crystal LC and the polymerizable monomer M to be polymerized in the presence of the vertical electric field E, the blue phase liquid crystal LC disposed adjacent to the edge of the convex portion P can be twisted so that it has no electric field. Approaching the characteristics of optical isotropic (as shown in FIG. 4B), thereby improving the presence of dark state light leakage at the edge of the above-mentioned projection P question.

The degree of twist of the blue phase liquid crystal LC disposed adjacent to the edge of the projection P may be related to the magnitude of the potential difference V', and the method of determining the magnitude of the potential difference V' may include adjusting the blue phase liquid crystal layer 130 by the light source LS. The magnitude of the variable potential difference V' is obtained by the corresponding transmittance of the display panel, and then the magnitude of the potential difference V' is determined according to the level of the transmittance. The lower the transmittance, the more ideal the optical isotropic nature of the blue phase liquid crystal LC disposed adjacent to the edge of the protrusion P, and the better the effect of improving the dark state light leakage. Fig. 5 is a graph showing the relationship between the potential difference and the transmittance of the first electrode layer and the second electrode layer. As can be seen from Fig. 5, when the potential difference V' is larger than 0 and less than or equal to 5 volts, the problem of dark state light leakage can be improved. Further, when the potential difference V' is between 2 volts and 3 volts, the effect of improving the dark state light leakage is most remarkable. The effect of the presence/absence of the potential difference on the dark state light leakage during the polymerization reaction is compared with Table 1 below, wherein the comparative example is a sample in which no potential difference is applied during the polymerization reaction, and the experimental example is a sample in which a potential difference of 2.5 volts is applied during the polymerization reaction. It can be seen from the following table that the application of the potential difference during the polymerization can effectively improve the dark state light leakage and improve the contrast.

Figure 6 is a cross-sectional view showing a display panel in accordance with a second embodiment of the present invention. Referring to FIG. 6 , the display panel 200 is substantially the same as the display panel 100 , and the same components are denoted by the same reference numerals, and the relative arrangement relationship is not described herein. The main difference between the display panel 200 and the display panel 100 is that the first electrode layer E1 and the second electrode layer E2 of the display panel 100 are respectively a continuous conductive film of the entire surface, and the first electrode layer E1 ′ of the display panel 200 includes a plurality of first strip electrodes SE1, and the second electrode layer E2' includes a plurality of second strip electrodes SE2, wherein each first strip electrode SE1 overlaps with one of the second strip electrodes SE2, and each first strip The electrode SE1 and the overlapped second strip electrode SE2 overlap with one of the protrusions P.

In the present embodiment, the width W1 of each of the first strip electrodes SE1 and the width W2 of the overlapped second strip electrodes SE2 are respectively larger than the width WP of the overlapped protrusions P1. Under such a design, the arrangement of the first electrode layer E1' and the second electrode layer E2' can also provide the vertical electric field E of FIG. 3B, so that the blue phase liquid crystal LC and the polymerized monomer M are polymerized in the presence of the vertical electric field E. The reaction improves the problem of dark light leakage at the edges of the above-mentioned projections. In addition, the arrangement of the protruding portion P of the present embodiment also contributes to the problem of improving the high driving voltage of the conventional blue phase liquid crystal display panel. For details, refer to the related paragraphs above, and details are not described herein again.

In summary, the display panel of the present invention helps to improve the traditional blue by raising the third electrode layer so that the blue phase liquid crystal layer is distributed in the area affected by the power line, thereby improving the utilization of the lateral electric field. The problem of high driving voltage of the liquid crystal display panel. In addition, the method for fabricating the display panel of the present invention corrects the dark state light leakage caused by the interaction between the blue phase liquid crystal and the convex portion by causing the blue phase liquid crystal and the polymerized monomer to be polymerized in the presence of a vertical electric field. The problem.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the invention, and any one of ordinary skill in the art without departing from the invention. In the spirit and scope, the scope of protection of the present invention is subject to the definition of the appended patent application.

100‧‧‧ display panel

110‧‧‧First substrate

120‧‧‧second substrate

130‧‧‧Blue phase liquid crystal layer

ARS‧‧‧Active Component Array Substrate

B‧‧‧Bottom

CE‧‧‧Common electrode

CFS‧‧‧Color filter substrate

D1, D2‧‧‧ distance

DS‧‧‧ dielectric structure

E1‧‧‧first electrode layer

E2‧‧‧Second electrode layer

E3‧‧‧ third electrode layer

EL‧‧‧Power Line

P‧‧‧protrusion

PE‧‧‧ pixel electrode

SCE‧‧‧ strip common electrode

SPE‧‧‧ strip pixel electrode

X, Y‧‧ direction

Claims (10)

A display panel includes a first substrate including a first electrode layer, a second substrate disposed on a side of the first substrate, and the second substrate including a second electrode layer, a dielectric structure, and a a third electrode layer, the third electrode layer is located between the first electrode layer and the second electrode layer, and the dielectric structure is located between the second electrode layer and the third electrode layer, the dielectric structure comprises a bottom layer and a plurality of protrusions protruding from the bottom layer, the bottom layer being located between the protrusions and the second electrode layer, the protrusions being located between the third electrode layer and the bottom layer, The plane of the third electrode layer is higher than the plane of the bottom layer; and a blue phase liquid crystal layer is located between the third electrode layer and the first electrode layer and between the bottom layer and the first electrode layer. The display panel of claim 1, wherein a distance between the third electrode layer and the bottom layer is greater than 0 and less than or equal to 6. The display panel of claim 1, wherein a distance between adjacent two protrusions is greater than 0 and less than or equal to 15. The display panel of claim 1, wherein the third electrode layer comprises a pixel electrode and a common electrode structurally separated from the pixel electrode, the pixel electrode comprising a plurality of stripe pixel electrodes The common electrode includes a plurality of strip-shaped common electrodes, and the strip-shaped pixel electrodes and the strip-shaped common electrodes are alternately arranged in one direction. The display panel of claim 1, wherein the first electrode The layer and the second electrode layer are respectively a continuous conductive film of a whole surface. The display panel of claim 1, wherein the first electrode layer comprises a plurality of first strip electrodes, and the second electrode layer comprises a plurality of second strip electrodes, each of the first strip electrodes And overlapping with the second strip electrode, and each of the first strip electrodes and the overlapped second strip electrode overlaps one of the protrusions. The display panel of claim 6, wherein a width of each of the first strip electrodes and a width of the overlapped second strip electrodes are respectively greater than a width of the overlapped protrusions. A method of manufacturing a display panel, comprising: providing a first substrate and a second substrate on a side of the first substrate, the first substrate comprising a first electrode layer, the second substrate comprising a second electrode layer a dielectric structure and a third electrode layer, the third electrode layer is located between the first electrode layer and the second electrode layer, and the dielectric structure is located between the second electrode layer and the third electrode layer The dielectric structure includes a bottom layer and a plurality of protrusions protruding from the bottom layer, the bottom layer being located between the protrusions and the second electrode layer, the protrusions being located at the third electrode layer Between the bottom layer and the bottom layer, the plane of the third electrode layer is higher than the plane of the bottom layer; and between the third electrode layer and the first electrode layer and between the bottom layer and the first electrode layer a blue phase liquid crystal layer comprising a blue phase liquid crystal and a polymerizable monomer; and a potential difference between the first electrode layer and the second electrode layer for the first electricity A vertical electric field is generated between the pole layer and the second electrode layer, and the blue phase liquid crystal layer is irradiated with a light source to cause a polymerization reaction between the blue phase liquid crystal and the polymerized monomer in the presence of a vertical electric field. The method of manufacturing the display panel of claim 8, wherein the third electrode layer comprises a pixel electrode and a common electrode structurally separated from the pixel electrode, the pixel electrode comprising a plurality of strips The pixel electrode includes a plurality of strip-shaped common electrodes, and the strip-shaped pixel electrodes and the strip-shaped common electrodes are alternately arranged in one direction. The method of manufacturing the display panel of claim 8, wherein the first electrode layer comprises a plurality of first strip electrodes, and the second electrode layer comprises a plurality of second strip electrodes, each of the first The strip electrode overlaps with one of the second strip electrodes, and each of the first strip electrodes and the overlapped second strip electrode overlaps one of the protrusions.