JP2007093767A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transflective liquid crystal display device capable of suppressing reduction of color purity generated by providing a pinhole at a part of a color filter in a reflection region. <P>SOLUTION: In the transflective liquid crystal display device, the reduction of color purity generated by providing the pinhole at a part of the color filter in the reflection region can be suppressed by superposing the two-dimensional position of the pinhole on the position of a contact of a pixel electrode in the reflection region. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device, and more particularly to a transflective liquid crystal display device in which each pixel is provided with both a reflective region and a transmissive region.

  Liquid crystal display devices (hereinafter sometimes referred to as LCDs) are characterized by being thin and have low power consumption, and are currently widely used as monitors for computer monitors and portable information devices such as televisions and mobile phones. In such an LCD, liquid crystal is sealed between a pair of substrates, and display is performed by controlling the orientation of the liquid crystal positioned between the electrodes formed on each substrate, and is a CRT (cathode ray tube). Unlike a display, an electroluminescence (hereinafter, EL) display, or the like, since it does not emit light in principle, a light source is required to display an image to an observer.

  The LCD includes a transmissive LCD and a reflective LCD. In a transmissive LCD, a transparent electrode is used as an electrode to be formed on each substrate, a light source is arranged behind or on the side of the liquid crystal display panel, and the amount of light transmitted through the liquid crystal panel is controlled by the liquid crystal panel. Can display brightly. However, since the display is always performed by turning on the light source, power consumption by the light source is inevitable, and sufficient contrast cannot be secured in an environment where the outside light is very strong such as outdoors in the daytime. .

  On the other hand, the reflective LCD employs external light such as the sun and room light as a light source, and reflects the ambient light incident on the liquid crystal panel by a reflective electrode formed on the substrate on the non-observation surface side. Then, display is performed by controlling the amount of light emitted from the liquid crystal panel, which is incident on the liquid crystal layer and reflected by the reflective electrode, for each pixel. As described above, since the reflective LCD employs external light as the light source, the display cannot be seen without external light. However, unlike the transmissive LCD, the power consumption by the light source is very low and the power consumption is very low. If the surroundings are bright, sufficient contrast can be obtained.

  In recent years, transflective LCDs have been developed as LCDs that have both a transmissive function and a reflective function, and are easy to see in both bright and dark environments. In this transflective LCD, a transparent electrode such as ITO similar to the transmissive LCD is used to realize the transmissive function, and a reflective electrode such as Al having a good reflective characteristic is used to realize the reflective function.

  In a transflective LCD, when the color filters used in the transmissive area and the reflective area are the same, the displayed color differs greatly between the transmissive display and the reflective display. This is because in the case of transmissive display, light from the light source is displayed only once through the color filter, whereas in the case of reflective display, external light is displayed twice through the color filter. This is also because the light source for transmissive display is a backlight light source and the light source for reflective display is natural light or the like, that is, the light sources are different.

  As a method of reducing the display color difference between the transmissive region and the reflective region, (1) a method of providing a minute transparent region, that is, a pinhole in a part of the reflective region, or (2) a transmissive region and a reflective region. And a method of changing the color design of the area.

  For example, in Patent Document 1, a color filter for a transmissive region is formed in the transmissive region and the reflective region, and a pinhole is provided in a part of the reflective region to reduce the difference in display color between the transmissive region and the reflective region. Is described. In the method of providing a pinhole, the difference between the transmissive display and the reflective display can be reduced by optimizing the shape and size of the pinhole. In addition, since pinholes can be formed at the same time during the patterning of the colored layer, an inexpensive color filter can be obtained without increasing the number of coating formation steps.

JP 2003-98518 A

  In the method of providing a pinhole in a part of the color filter in the reflective region, the luminance is improved in reflective display by optimizing the shape and size of the pinhole. However, there is a problem that the color purity is lowered because the color region is reduced by the formation of the pinhole.

  The present invention is a transflective liquid crystal display device capable of suppressing a decrease in color purity caused by providing a pinhole in a part of a color filter in a reflective region.

  The present invention is a liquid crystal display device that performs display by enclosing liquid crystal between a first substrate and a second substrate and controlling a voltage applied to the liquid crystal for each pixel arranged in a matrix. A transistor that controls the taking-in of the data voltage from the data line, and an insulating film that covers the transistor, is connected to the transistor through a contact formed in the insulating film, and the taken-in data voltage is applied. Each pixel is provided with a reflective region provided with a reflective film and a transmissive region provided with no reflective film, and each pixel is observed from the reflective region and the transmissive region. A color filter that converts light emitted to the side into a specific color, the color filter including a pinhole in which a part of the color filter is removed in the reflection region, Plane position of Lumpur overlaps the position of the contact of the pixel electrode.

  In the liquid crystal display device, the color filter includes three types of RGB, and in the blue color filter having the least influence on the overall luminance due to the formation of the pinhole, the planar position of the pinhole and the pixel electrode It is preferable that the position of the contact overlaps.

  Further, in the liquid crystal display device, the pixel electrode is formed on a planarizing film provided on the insulating film, and is connected to the transistor through a contact formed on the insulating film and the planarizing film. It is preferred that

  In the liquid crystal display device, the area of the pinhole is preferably the same as the area of the contact.

  In the liquid crystal display device, the area of the pinhole is preferably larger than the area of the contact.

  In the present invention, it is possible to suppress a decrease in color purity caused by providing a pinhole in a part of the color filter in the reflection region by overlapping the planar position of the pinhole in the reflection region with the position of the contact of the pixel electrode. A transflective liquid crystal display device can be provided.

  Embodiments of the present invention will be described below.

  FIG. 1 shows a part of a planar configuration on the first substrate side when a transflective active matrix LCD is used as a transflective liquid crystal display device according to the present embodiment, and FIG. 2 shows a line AA in FIG. 1 shows a schematic cross-sectional configuration in the vicinity of a TFT of one pixel at a position along the line. The transflective LCD of this system is a system in which pinholes are provided in a part of the color filter in the reflective area.

  As shown in FIG. 2, in the liquid crystal display device 1, a TFT substrate 10 that is a first substrate includes a reflective layer (reflective film) 11 and a pixel electrode 15, and a counter electrode substrate 20 that is a second substrate is a color substrate. A filter 22, a pinhole 23, a counter electrode protrusion (protrusion part) 24, and a common electrode 25 are provided.

  In the liquid crystal display device 1, a liquid crystal layer 30 is sealed between a TFT substrate 10 and a counter electrode substrate 20 that are bonded to each other with a predetermined gap. As the TFT substrate 10 and the counter electrode substrate 20, a transparent substrate such as a glass substrate or a plastic substrate is employed.

  On the surface of the TFT substrate 10 on the liquid crystal side, a thin film transistor (TFT) 40 is formed for each pixel. A reflective layer 11 made of Al, Ag or the like having a reflective function is formed in the reflective region on the TFT substrate 10. A pixel electrode 15 using a transparent conductive material such as ITO (Indium Tin Oxide) or IZO (Indium Zinc Oxide) is formed as a first electrode on the reflective layer 11 in the reflective region and the TFT substrate 10 in the transmissive region. Yes. An alignment film (not shown) made of polyimide or the like for controlling the initial alignment of the liquid crystal layer 30 is formed on the pixel electrode 15.

  A color filter (R, G, B) 22 is formed on the liquid crystal side of the counter electrode substrate 20 disposed opposite to the TFT substrate 10, and a pinhole 23 is provided in a part of the color filter 22 in the reflective region. A counter electrode protrusion 24 is formed on the color filter 22 in the reflective region, and a common electrode 25 using a transparent conductive material such as ITO or IZO as the second electrode on the counter electrode protrusion 24 and the color filter 22 in the transmissive region. Is formed. In the active matrix type, the common electrode 25 is formed as a common electrode for a plurality of pixels (normally all pixels). On the common electrode 25, an alignment film (not shown) similar to that on the TFT substrate side is formed.

  The TFT 40 formed on the TFT substrate 10 controls voltage supply from the data line 52 to each pixel electrode 15. Note that the reflective layer 11 may be omitted by forming the pixel electrode 15 in the reflective region from a metal such as aluminum.

  The color filter 22 is provided for each pixel and transmits only one of RGB light. Therefore, the display color of the pixels is limited by these color filters. The color filter 22 is provided corresponding to each pixel, and a black matrix 26 is disposed in the gap between the pixels. Note that W (white) pixels without the color filter 22 may be provided, or pixels of colors other than RGB, for example, C (cyan) color filters may be provided.

  Then, by controlling the potential of each pixel electrode 15 individually, a different potential is applied to the liquid crystal between each pixel electrode 15 and the common electrode 25 for each pixel, thereby changing the optical characteristics of the liquid crystal and performing display. Can do.

  The counter electrode protrusion 24 is provided in order to adjust the thickness of the liquid crystal layer 30 in the reflection region so as to align the optical path difference between the reflection region and the transmission region, and is made of a transparent acrylic resin or the like.

  In the present embodiment, a transmissive color filter used in a normal transmissive liquid crystal display device can be employed as the color filter 22. A pinhole 23 is provided in a part of the color filter 22 in the reflection area, and the brightness and brightness of the reflection area are ensured by optimizing the shape and size of the pinhole 23, and the difference in display color between the transmission area and the reflection area. Can be reduced. In addition, since the pinholes 23 can be formed at the same time when the colored layer is patterned, an inexpensive color filter can be obtained without increasing the number of coating formation steps.

  In the reflection region, the reflection layer 11 is provided below the pixel electrode 15 or the pixel electrode 15 functions as a reflection film to reflect light incident from the counter electrode substrate 20 side. Therefore, reflected light that has passed through the color filter 22 twice and is modulated by the liquid crystal of each pixel is obtained on the observation side.

  In the transmissive region, light from the backlight incident from the TFT substrate 10 side passes through the liquid crystal layer 30. Accordingly, transmitted light that passes through the color filter 22 and is modulated by the liquid crystal of each pixel is obtained on the observation side.

  Next, the configuration of the TFT substrate 10 will be described. In an active matrix LCD, a plurality of pixels are provided in a matrix within a display area, and here, a TFT 40 is provided as a switch element for each pixel.

  The TFT 40 has a Poly-Si film 50, and the TFT 40 is formed by forming a drain region, a channel region, and a source region in the Poly-Si film 50. A gate insulating film 58 is formed so as to cover the Poly-Si film 50, and a gate electrode 56 is formed on the gate insulating film 58 and in a portion that is above the channel region. Then, an interlayer insulating film 62 is formed so as to cover the gate insulating film 58 and the gate electrode 56. A drain electrode 53 and a source electrode 54 are disposed on the interlayer insulating film 62, and the drain electrode 53 and the source electrode 54 are connected to the interlayer insulating film 62 and the gate insulating film 58 through contacts, respectively. Connected to the region. A contact 68 is formed on the passivation film 64 and the planarization film 66 on the source electrode 54, and a part of the pixel electrode 15 extends and is electrically connected thereto.

  In the above configuration, the drain electrode 53 is connected to the data line, and the gate electrode 56 is connected to the gate line. It is also preferable to form the drain electrode 53 by using a part of the data line and to form the gate electrode 56 by using the gate line. Further, the Poly-Si film 50 is extended beyond the source region, and the storage line is formed by opposing the capacitance line 60 via the gate insulating film 58 in the extended portion.

  In the case of a transflective liquid crystal display device, a contact 68 between the pixel electrode 15 and the TFT 40 is formed in the reflective region in order to increase the aperture ratio of the transmissive display, but the contact region has the same height and unevenness as the other reflective regions. It is difficult to form a shape, and the color of this region is different from other reflective regions. Therefore, in the present embodiment, the planar position of the pinhole 23 of the color filter 22 that was at the position shown in FIG. 3A is overlapped with the position of the contact 68 of the pixel electrode as shown in FIG. 3B. To do. As a result, it is possible to originally use a region whose color is different from that of other reflective regions for improving luminance, and the ratio of the color region also increases.

  In this embodiment, at least one of the blue, green, and red color filters may be configured such that the planar position of the pinhole 23 and the position of the contact 68 of the pixel electrode overlap, as shown in FIG. 4B, the planar position of the pinhole 23B and the position of the pixel electrode contact 68B are overlapped with each other in the blue color filter 22B as shown in FIG. 4B. Is preferable. On the other hand, in the green color filter 22G and the red color filter 22R, it is preferable that the planar positions of the pinholes 23G and 23R do not overlap with the positions of the pixel electrode contacts 68G and 68R.

  Since blue has low visibility, the influence on the overall luminance due to the formation of the pinhole 23 can be minimized. On the other hand, in the green and red color filters, when the planar position of the pinhole 23 and the position of the contact 68 of the pixel electrode 15 are overlapped, green and red have high visibility. May have a greater impact on

  Further, as shown in FIG. 4B, when the size of the pinhole 23B of the blue color filter 22B is the same as the size of the pinhole 23R of the red color filter 22R, when the pinhole is formed by a photoresist method or the like. When using the same photomask and forming the pinhole 23B to the blue color filter 22B, the same mask is used for blue and red by shifting the photomask installation position downward (offset). Can be used. Thereby, the cost of a photomask or the like can be reduced.

  The area of the pinhole 23 is preferably the same as the area of the contact 68. Further, when importance is attached to luminance, the area of the pinhole 23 may be larger than the area of the contact 68.

  The planar shape of the pinhole 23 is not limited to a rectangle, but may be a polygon such as a triangle or a quadrangle, a parallelogram, a trapezoid, or the like.

  In the conventional transflective liquid crystal display device as shown in FIG. 4A and in the blue color filter 22B as shown in FIG. 4B, the plane position of the pinhole 23B and the position of the contact 68B of the pixel electrode overlap. Table 1 shows the reflectance, NTSC ratio, chromaticity (x, y), and contrast of the transflective liquid crystal display device, and FIG. 5 shows an xy chromaticity diagram in the XYZ color system.

  As can be seen from Table 1 and FIG. 5, the chromaticities of red and green are almost the same, but the blue color region is enlarged. As a result, the NTSC ratio was improved by about 3% and the contrast was further improved while minimizing the decrease in reflectance.

  Since the material used as the pixel electrode 15 is the same as the material of the common electrode 25, the electrode having the same work function is disposed with respect to the liquid crystal layer 30 via the alignment film. The pixel electrode 15 and the common electrode 25 allow the liquid crystal layer 30 to be AC driven with very good symmetry. However, the pixel electrode 15 and the common electrode 25 may be approximated as long as the liquid crystal layer 30 can be driven with good symmetry even if their work functions are not completely the same. For example, if the difference between the work functions of both electrodes is about 0.5 eV or less, even if the liquid crystal drive frequency is CFF (critical flicker frequency) or less, high quality display without flickering or liquid crystal burn-in is possible. Is possible.

  As the pixel electrode 15 and the common electrode 25 that satisfy such conditions, for example, the pixel electrode 15 has IZO (work function 4.7 eV to 5.2 eV), and the common electrode 25 has ITO (work function 4.7 eV to 5.0 eV). ), Or vice versa, and materials may be selected in consideration of process characteristics such as transmittance and patterning accuracy, manufacturing cost, and the like.

  As the reflective layer 11, a material having excellent reflection characteristics such as Al, Ag, and alloys thereof (Al—Nd alloy in this embodiment) is used at least on the surface side (liquid crystal layer side). The reflective layer 11 may be a single layer of a metal material such as Al, but a refractory metal layer such as Mo may be provided as a base layer in contact with the planarizing film 66. By forming such a base layer, the adhesion between the reflective layer 11 and the planarizing film 66 is improved, so that the reliability of the element can be improved. In the configuration of FIG. 2, an inclined surface having a desired angle is formed in each pixel region of the planarization film 66, and the reflective layer 11 is laminated so as to cover the planarization film 66. A similar slope may be formed on the surface. If such an inclined surface is formed at an optimum angle and position, it is possible to collect and emit external light for each pixel. For example, it is possible to improve the display brightness at the front position of the display. is there. Of course, such an inclined surface does not necessarily exist.

  Note that it is preferable to scatter the reflected light to some extent by forming irregularities in the reflective layer 11 as shown in FIG. By forming appropriate irregularities on the surface of the planarizing film 66 below the reflective layer 11 and forming the reflective layer 11 thereon, the irregularities can be easily formed in the reflective layer 11.

  The liquid crystal display device according to this embodiment has been described by taking an active matrix type transflective LCD as an example, but a passive matrix type transflective LCD may also be used.

  In the liquid crystal display device according to the present embodiment, the liquid crystal to be used is not particularly limited. Examples include a birefringence (VA) type and a vertical alignment (VA) type.

It is a top view which shows the structure of the transflective liquid crystal display device which concerns on embodiment of this invention. It is AA sectional drawing in FIG. It is a figure which shows the outline of the positional relationship of a pinhole and a contact in the pixel of the transflective liquid crystal display device which concerns on embodiment of this invention, and the conventional transflective liquid crystal display device. It is a figure which shows the outline of the positional relationship of a pinhole and a contact in the pixel of the transflective liquid crystal display device which concerns on embodiment of this invention, and the conventional transflective liquid crystal display device. FIG. 6 is an xy chromaticity diagram of a reflection region of a transflective liquid crystal display device according to an embodiment of the present invention and a conventional transflective liquid crystal display device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid crystal display device, 10 TFT substrate (1st substrate), 11 Reflective layer, 15 Pixel electrode, 20 Counter electrode substrate (2nd substrate), 22, 22R, 22G, 22B Color filter, 23, 23R, 23G, 23B Pinhole , 24 Counter electrode projection, 25 Common electrode, 30 Liquid crystal layer, 40 TFT, 50 Poly-Si film, 52 Data line, 53 Drain electrode, 54 Source electrode, 56 Gate electrode, 58 Gate insulation film, 60 Capacitance line, 62 Interlayer insulation Film, 64 passivation film, 66 planarization film, 68, 68R, 68G, 68B contact.

Claims (5)

A liquid crystal display device that performs display by enclosing liquid crystal between a first substrate and a second substrate and controlling a voltage applied to the liquid crystal for each pixel arranged in a matrix,
Each pixel is
A transistor that controls the intake of the data voltage from the data line;
A pixel electrode formed on an insulating film covering the transistor, connected to the transistor via a contact formed in the insulating film, and applied with a data voltage;
Have
Each pixel is provided with a reflective area provided with a reflective film and a transmissive area provided with no reflective film, and each pixel emits light emitted from the reflective area and the transmissive area to the observation side in a specific color. Including color filters to convert,
This color filter includes a pinhole in which a part of the color filter is removed in the reflection region,
2. The liquid crystal display device according to claim 1, wherein a planar position of the pinhole overlaps with a position of a contact of the pixel electrode. The liquid crystal display device according to claim 1.
The color filter includes three types of RGB,
A liquid crystal display device characterized in that, in a blue color filter that has the least influence on the overall luminance due to the formation of pinholes, the planar position of the pinhole and the position of the contact of the pixel electrode overlap. The liquid crystal display device according to claim 1 or 2,
The pixel electrode is formed on a planarizing film provided on the insulating film, and is connected to the transistor through the insulating film and a contact formed on the planarizing film. Display device. The liquid crystal display device according to any one of claims 1 to 3,
The liquid crystal display device according to claim 1, wherein an area of the pinhole is the same as an area of the contact. The liquid crystal display device according to any one of claims 1 to 3,
The liquid crystal display device according to claim 1, wherein an area of the pinhole is larger than an area of the contact.