JP2004144965A - Semitransmissive liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semitransmissive liquid crystal display wherein the whole pixel including a contact hole is effectively utilized for display. <P>SOLUTION: A liquid crystal is interposed between a pair of electrodes, one electrode is used as a pixel electrode 18 and a backlight is disposed on the rear side of the pixel electrode 18. A transmitting part 9 transmitting light of the backlight and a reflecting part 12 reflecting light from the front surface side are provided in the pixel electrode. An aperture 8 is provided at a drain electrode D of a switching element 4, a transparent electrode 17 of the pixel electrode 18 is superposed on the surroundings of the aperture 8 and a connection part of the switching element and the pixel electrode forms the transmitting part. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a transflective liquid crystal display device including a transmissive portion including a transparent electrode that transmits light from a backlight and a reflective portion including a reflective electrode that reflects external light.
[0002]
[Prior art]
2. Description of the Related Art In recent years, the application of liquid crystal display devices has rapidly spread to not only information communication devices but also general electric devices. In particular, for a portable type, a reflection type liquid crystal display device that displays an image by reflecting external light without using a backlight in order to reduce power consumption is often used. Since the device uses external light as a light source, it becomes difficult to see in a dark room or the like. In recent years, therefore, the development of transflective liquid crystal display devices having both transmissive and reflective properties has been promoted.
[0003]
The feature of this transflective liquid crystal display device is that one pixel has a transmissive part with a transparent electrode and a reflective part with a reflective electrode in one pixel, and turns on the backlight in a dark place to transmit the light. The image is displayed using the transmissive part, and the image is displayed using the external light in the reflective part without turning on the backlight in a bright outdoor environment, so that the power consumption can be greatly reduced. Have.
[0004]
FIG. 5 is a cross-sectional view of a pixel of an array substrate of a transflective liquid crystal display device described in Patent Document 1 as a conventional example.
[0005]
On the glass substrate 1, a gate electrode G and an auxiliary capacitance electrode Cs are arranged for each pixel, and the entire glass substrate 1 including the surface thereof is covered with a gate insulating film 2 made of a silicon nitride film or a silicon oxide film. Next, an amorphous silicon layer 3, a source electrode S, and a drain electrode D1 are sequentially formed around the gate electrode G to form a MOS thin film transistor element 4 (hereinafter, referred to as a TFT element 4) as a switching element.
[0006]
Then, a protection film 5 made of a silicon oxide film or a silicon nitride film is formed so as to cover the TFT element 4, and an interlayer film 6 made of a scattering layer or a flattening film is formed on the protection film 5. In the protective film 5 and the interlayer film 6, a contact hole 7 is provided above the drain electrode D1 of the TFT element 4, and a groove portion from which the interlayer film 6 is removed is provided in a place away from the TFT element 4. This groove corresponds to the transmission section 9.
A transparent electrode 11A is stacked on the protective film 5 and the interlayer film 6. As a material of the transparent electrode 11A, ITO (Indium-Tin-Oxide) is laminated over one pixel, and a material for the reflective electrode 10A is laminated on a portion of the transparent electrode 11A except for the transmission part 9. The portion where the reflection electrodes 10A are stacked is the reflection portion 12. In Patent Literature 1, expensive Ag is used as the material of the reflective electrode 10A instead of Al, which is generally widely used. The reason is that a step of forming a Ti film is required because an ohmic contact is not formed between ITO and Al unless Ti is interposed between the ITO and Al. However, since ITO and Ag form a good ohmic contact, the number of steps is small. It is because it is. The transparent electrode 11A is electrically connected to the drain electrode D1 at the contact hole 7 portion.
[0007]
A color filter substrate 31 is arranged to face the array substrate 20, and a liquid crystal material is sandwiched between the array substrate 20 and the color filter 31. A color filter and a common electrode are formed on the color filter substrate 31. A liquid crystal panel 30 is constituted by the array substrate 20, the color filter substrate 31, the liquid crystal material and the like.
[0008]
Although not shown below the array substrate 20, a backlight device having a well-known light source, a light guide plate, a diffusion sheet, and the like is disposed, and transmitted light transmitted from the backlight device passes through the transmission unit 9, and The light is reflected by the reflector 12. A transflective liquid crystal display device is obtained by combining the array substrate 20 having the transmissive portion 9 and the reflective portion 12 in the same pixel, a liquid crystal material, a color filter substrate 31, a backlight device, and the like.
[0009]
[Patent Document 1]
JP-A-2002-350158 (pages 2-3, FIG. 4)
[0010]
[Problems to be solved by the invention]
In the conventional transflective liquid crystal device, since the reflective electrode 10 </ b> A exists in the contact hole 7, this region functions as the reflective portion 12. However, since the interlayer film 6 and the like do not exist in the contact hole 7, the cell gap up to the color filter substrate 31 is wider than that of the other reflective portions 12, and the display state of the contact hole 7 and the other reflective portions 12 is reduced. Will be different. In some cases, the surface of the interlayer film 6 is provided with irregularities to increase the reflection efficiency. However, such irregularities cannot be formed in the contact holes 7, so that the reflection portions 12 did not function sufficiently.
[0011]
The present applicant has separately filed an application in which a reflective electrode is not formed in a contact hole (for example, see Japanese Patent Application No. 2002-275060). This is a transflective liquid crystal display device that can prevent flicker and image sticking by using IZO (Indium-Zinc-Oxide) instead of ITO for the transparent electrode 11. This embodiment will be described with reference to FIG. 4 and 5 are denoted by the same reference numerals, and description thereof is omitted.
[0012]
In the transflective liquid crystal display device of FIG. 4, a reflective electrode 10 is laminated on the interlayer film 6, and a transparent electrode 11 is laminated on the reflective electrode 10 and the protective film 5. The reflective electrode 10 and the transparent electrode 11 form a pixel electrode. The reflective portion has a double structure of the reflective electrode 10 and the transparent electrode 11, and the transparent portion has only the transparent electrode 11. In the contact hole 7, the transparent electrode 11 is connected to the drain electrode D1, and the reflection electrode 10 is removed. Even in the case where only the transparent electrode 11 and the reflective electrode 10 do not exist in the contact hole 7 as in this embodiment, since the contact hole 7 exists on the opaque drain electrode D1, the light from the backlight is not drained. D1 blocks the contact hole 7 as a result. However, the contact hole 7 hardly contributed as a reflection part.
[0013]
Therefore, the present invention provides a transflective liquid crystal display device in which a contact hole can be used as a transmissive portion.
[0014]
[Means for Solving the Problems]
In order to solve the above problem, the present invention is characterized in that in a transflective liquid crystal display device having a transmissive portion and a reflective portion in a pixel electrode, a transmissive portion is formed at a connection portion between the switching element and the pixel electrode. By using the connection portion of the switching element with the pixel electrode as a transmission portion, the entire pixel electrode can be effectively used for display.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view of a liquid crystal panel of the present invention, and FIG. 2 is a plan view showing one pixel in an array substrate 20 constituting the liquid crystal panel of the present invention. FIG. 1 corresponds to a cross-sectional view taken along line AA ′ of FIG.
[0016]
In the present invention, as shown in FIG. 1, the aperture 8 is formed in the opaque drain electrode D facing the lower part of the pixel electrode 18 protruding downward along the contact hole 15 so that light from the backlight can be prevented from opening. 8 is led out to the contact hole 15 side. The provision of the opening 8 changes the area ratio between the reflection part 12 and the transmission part 9 in one pixel, and also improves the transmittance when the backlight is turned on and the transmitted light is used. The pixel electrode 18 is composed of a transparent electrode 17 in contact with the liquid crystal and a reflective electrode 16 forming a layer with the transparent electrode 17, but only the transparent electrode 17 exists below the contact hole 15. . However, the transparent electrode 17 may not be present below the contact hole 15.
[0017]
A plurality of scanning lines 32 made of a metal such as Al or Cr are formed in parallel at substantially equal intervals on a transparent insulating glass substrate 1, and a scanning line 32 is provided substantially at the center between adjacent scanning lines 32. At the same time, the auxiliary capacitance electrode Cs is formed in parallel. A gate electrode G extends from the scanning line 32.
[0018]
A gate insulating film 2 made of a silicon nitride film or a silicon oxide film is laminated on the glass substrate 1 so as to cover the scanning line 32, the auxiliary capacitance electrode Cs, and the gate electrode G. An island-shaped amorphous silicon layer 3 is formed with the insulating film 2 interposed therebetween, and a plurality of video lines 34 are formed on the gate insulating film 2 so as to be orthogonal to the scanning lines 32. A source electrode S extends from the video line 34, and the source electrode S is connected to a part of the amorphous silicon layer 3 so as to overlap.
[0019]
Further, a drain electrode D made of the same material as the image line 34 and the source electrode S and formed at the same time is provided on the gate insulating film 2 and is connected to the amorphous silicon layer 3. Here, a region surrounded by the scanning lines 32 and the video lines 34 corresponds to one pixel. The gate electrode G, the gate insulating film 2, the amorphous silicon layer 3, the source electrode S, and the drain electrode D form a MOS type TFT element 4 serving as a switching element, and the TFT element 4 is formed in each pixel. Then, the storage capacitor of each pixel is formed by the drain electrode D of the TFT element 4 and the storage capacitor electrode Cs.
[0020]
A protective film 13 made of, for example, an inorganic insulating film is laminated so as to cover the video line 34, the TFT element 4, and the gate insulating film 2, and an interlayer film 14 made of an organic insulating film is laminated on the protective film 13. I have. In the protective film 13 and the interlayer film 14, a contact hole 15 exposing a part of the drain electrode D of the TFT element 4 is formed. In this embodiment, the contact hole 15 of the protective film 13 is slightly smaller than the contact hole 15 of the interlayer film 14, and both the contact holes 15 of the films 13, 14 are square. By changing the size of the contact hole 15 between the protective film 13 and the interlayer film 14, the reflection electrode 16 can be prevented from contacting the drain electrode D of the TFT element 4. A transparent portion 9 is formed in a rectangular shape at a position away from the TFT element 4. In the transmission section 9, the interlayer film 14 has been removed. The transmissive portion 9 of the present invention is a portion that passes light from the backlight on the back side of the pixel electrode 18, and the reflective portion 12 is a portion that reflects light from the front side of the pixel electrode 18.
[0021]
When forming the drain electrode D, a photomask pattern designed so that an opening 8 is formed in the center of the contact hole 15 is used. The opening 8 is formed smaller than the contact hole 15 of the protective film 13, and the transparent electrode 17 overlaps around the opening 8 in the contact hole 15, so that the TFT element 4 and the pixel electrode 18 can be connected. . Since the reflection electrode 16 is not disposed in the opening 8, the opening 8 can be used as a transmission part. In the contact hole 15, the drain electrode D of the TFT element 4 and the pixel electrode 18 are directly overlapped and connected, and a video signal flowing through the video line 34 is supplied to the pixel electrode 18 via the TFT element 4. Therefore, in order to reliably connect the TFT element 4 and the pixel electrode 18, it is necessary to increase the overlapping portion between the pixel electrode 18 and the drain electrode D. However, when the ratio of the drain electrode D occupying the contact hole 15 is increased, the opening 8 is reduced accordingly, and the ratio of the transmission portion in the contact hole 15 is reduced. Therefore, when the contact hole 15 has a rectangular shape, the opening 8 is formed in a circular shape, so that the pixel electrode 18 and the TFT element 4 can be reliably connected in a limited area, and a large opening area can be secured. . In the present embodiment, the opening 8 is formed in a circular shape so as to be surely formed in the contact portion at the time of formation, but may be formed in a square shape in order to increase a transmission area.
[0022]
In each pixel, a reflective electrode 16 made of Al is formed on the interlayer film 14 and on the inner wall of the contact hole 15 so as to be in contact with the protective film 13 but not with the drain electrode D of the TFT element 4. ing. This structure can be formed by the following steps. After forming the drain electrode D having the opening 8, a protective film 13 and an interlayer film 14 are sequentially laminated on the drain electrode D. After that, a contact hole 15 is formed in the interlayer film 14, and the contact hole 15 is not formed in the protective film 13. Then, an Al layer is stacked on the interlayer film 14 and patterned to form the reflective electrode 16. At this time, Al laminated on the protective film 13 in the contact hole 15 is also removed. Then, the protective film 13 is etched in the contact hole 15 using Al as a mask, and the contact hole 15 is formed in the protective film 13. By doing so, the reflective layer 16 stays on the protective film 13 and does not contact the drain electrode D. Since Al has a high reflectance and a low resistance, it is generally used as a part of a reflective electrode. An alloy containing Al may be used as the material of the reflective electrode 16. The reflection electrode 16 is formed so as not to be in contact with the reflection electrode 16 of the adjacent pixel, slightly overlaps with the scanning line 32 and the video line 34, and surrounds the periphery of the transmission portion 9.
[0023]
The transparent electrode 17 is provided on the entire area of the pixel where the pixel electrode 18 is formed. That is, the transparent electrode 17 is disposed in the contact hole 15 and the transmission section 9, and is further stacked on the reflection electrode 16 in the reflection section 12. The transparent electrode 17 overlaps the opening 8 formed in the drain electrode D at the contact hole 15 and is in electrical contact with the drain electrode D. In this embodiment, as a material of the transparent electrode 17, IZO of a transparent electrode material using the same etchant as Al which is a reflective electrode material is used so that the transparent electrode 17 does not need to be etched to expose the reflective electrode 16. I'm using
[0024]
Although not shown, a backlight device is arranged below the liquid crystal panel 30. On the front side of the array substrate, a color filter substrate 31 is arranged so as to face the array substrate. Although not shown, the color filter substrate 31 is provided with color filters of three colors of RGB, a common electrode, and the like. The transflective liquid crystal panel 30 is obtained by bonding the two substrates with the array substrate 20 and the color filter substrate 31 facing each other and injecting liquid crystal between the two substrates.
[0025]
In this liquid crystal panel 30, a portion through which light emitted from the backlight device passes is the transmission portion 9 provided with the transparent electrode 17, a reflection electrode 16 is laminated, and a portion which reflects external light with the reflection electrode 11 is provided. The reflection unit 12. As a method of increasing the amount of external light reflected by the reflecting portion 12, there is a method of providing irregularities on the surface of the interlayer film 14 by patterning or the like and making the surface of the reflective film 10 laminated thereon uneven. Since the interlayer film 14 is an organic insulating film, unevenness can be easily formed.
[0026]
In this embodiment, the transparent portion 9 has the interlayer film 14 removed when the transparent electrode 17 is provided. In such a structure, the distance between the transparent electrode 17 of the transmissive part 9 and the common electrode (cell gap of the transmissive part 9) and the distance between the transparent electrode 17 of the reflective part 12 and the common electrode (the cell of the reflective part 12) Gap), and two cell gap differences occur in one pixel. A flicker phenomenon that causes a difference in driving voltage due to the cell gap difference occurs.
[0027]
Although not shown, the following method is used to solve this phenomenon. This is to leave the interlayer film 14 when forming the transparent electrode 17 in the transmission part 9. As a result, no cell gap difference occurs, and the flicker phenomenon is eliminated. Further, since there is no step at the boundary between the reflection section 12 and the transmission section 9, display unevenness caused by disturbance of liquid crystal alignment due to the step is also reduced.
[0028]
The interlayer film 14 may be slightly colored during etching, and this coloring leads to a decrease in transmittance and a deterioration in quality of transmitted light. Therefore, the interlayer film 14 is irradiated with ultraviolet rays while being heated to such an extent that the interlayer film 14 is not deteriorated. By doing so, coloring can be easily removed.
[0029]
Next, another embodiment of the contact hole 15 will be described with reference to FIG. This embodiment has the same configuration of the contact hole 15 and the opening 8 as the embodiment of FIG. 1 except that the transparent electrode 19 does not exist in the opening 8 of the drain electrode D.
[0030]
The present invention utilizes a contact portion between a switching element and a pixel electrode as a transmission portion, and the present invention is not limited to the above-described embodiment, and various modifications in accordance with the gist of the present invention are possible.
[0031]
For example, in this embodiment, the shape of the contact hole is square, but the contact hole may be circular. In this embodiment, the contact holes of the protective film and the reflective electrode have the same shape and size. However, when the contact holes of the reflective electrode are polygonal, the corners of the contact holes are formed when forming the contact holes of the protective film. In some cases, the etchant wraps around the portion, and the edge of the contact hole of the protective layer is located outside the edge of the contact hole of the reflective layer. Thereafter, when a transparent electrode is laminated on the contact hole, a gap is formed between the edge portion of the contact hole of the protective film and the transparent electrode, so that the transparent electrode may be disconnected. Therefore, by making the contact hole circular, disconnection of the transparent electrode in the contact hole can be prevented.
[0032]
Further, in this embodiment, the opening of the drain electrode is circular and the contact hole is square. However, the opening may be rectangular and the contact hole may be circular. It may be square. When the opening and the contact hole have the same shape, the distance between the edge of the opening and the edge of the contact hole becomes substantially uniform over the periphery of the opening, and the drain electrode is evenly exposed around the opening. On the other hand, when the opening and the contact hole have different shapes, the distance between the edge of the opening and the edge of the contact hole becomes uneven. Therefore, a part where the drain electrode is widely exposed is formed, and the pixel electrode is mainly connected at the widely exposed part.
[0033]
【The invention's effect】
According to the present invention, by providing an opening in the drain electrode, which is an opaque electrode of the switching element, it is possible to pass through the contact hole which has been present in the reflection part and has hardly contributed to the transmission of light of the backlight. As a result, the entire pixel can be effectively and efficiently used for display. Then, the area ratio between the reflective portion and the transmissive portion in the pixel changes, and the ratio in which transmitted light can be used is increased, so that a transflective liquid crystal device with improved transmittance can be obtained.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a transflective liquid crystal display device according to an embodiment of the present invention.
FIG. 2 is a plan view of one pixel of the transflective liquid crystal display device according to the embodiment of the present invention.
FIG. 3 is a sectional view of a contact hole portion according to another embodiment of the present invention.
FIG. 4 is a cross-sectional view of one pixel of a conventional transflective liquid crystal device.
FIG. 5 is a cross-sectional view of one pixel of a transflective liquid crystal device described in Patent Document 1.
[Explanation of symbols]
4 TFT element 8 Opening 9 Transmission part 12 Reflection part 13 Protective film 14 Interlayer film 15 Contact hole 16 Reflection electrode 17 Transparent electrode D Drain electrode

Claims (10)

One of a pair of electrodes opposed to each other with a liquid crystal interposed therebetween is a pixel electrode corresponding to each pixel, a backlight is disposed on the back side of the pixel electrode, and the pixel electrode transmits light of the backlight. In a semi-transmissive liquid crystal display device provided with a portion and a reflecting portion for reflecting light from the front side, a switching element electrically connected to the pixel electrode is provided for each pixel, and the switching element and the pixel electrode A transflective liquid crystal display device, wherein a transmissive portion is formed at a connection portion. 2. The transflective liquid crystal display device according to claim 1, wherein the pixel electrode includes a transparent electrode disposed on a transmission part and a reflection electrode disposed on a reflection part. 3. 3. The transflective liquid crystal according to claim 1, wherein an opening is formed in the opaque electrode of the switching element, and the pixel electrode overlaps the periphery of the opening and is connected to the switching element. Display device. An insulating film is interposed between the switching element and the pixel electrode, and a contact hole that partially exposes the opaque electrode of the switching element is formed in the insulating film. An opening smaller than the contact hole is formed at a portion corresponding to the hole, and the transparent electrode of the pixel electrode overlaps with the opaque electrode of the switching element via the contact hole. Item 3. A transflective liquid crystal display device according to item 2. 4. The transflective liquid crystal display according to claim 3, wherein the opening formed in the opaque electrode of the switching element has a circular shape. 5. The transflective liquid crystal display device according to claim 4, wherein the contact hole formed in the insulating film has a circular shape. The transflective liquid crystal display device according to claim 4, wherein the shape of the opening formed in the electrode of the switching element is different from the shape of the contact hole formed in the insulating film. 8. The transflective liquid crystal display device according to claim 1, wherein the transparent electrode is made of IZO (Indium-Zinc-Oxide). 9. The transflective liquid crystal display device according to claim 1, wherein a transparent electrode is laminated on the reflective electrode in the reflective portion. 10. The transflective liquid crystal display device according to claim 1, wherein the switching element is a MOS type thin film transistor, and an electrode connected to the pixel electrode is a drain electrode of the thin film transistor.

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