KR20090071442A - Lcd with improved contrast ratio and apparatus utilizing the same - Google Patents

Abstract

An LCD and an apparatus using the same having color reproduction and contrast ratio are provided to select a substrate and reduce the thickness of a polarizer. A base panel includes a first polarizer which is arranged in order to polarize the incident light through a first direction. An upper panel is faced with the base panel. One or more color filter is included so that the color filter of the upper panel produce the light of the designated color. A second polarizer is arranged in order to polarize the incident light through 'the backward perpendicular to first direction. A third polarizer is arranged between the color filter and liquid crystal layer. A third polarizer is arranged in order to polarize the incident light through backward. A power supplies the voltage for horizontally arranging the molecule within a liquid crystal(100).

Description

LCD with IMPROVED CONTRAST RATIO AND APPARATUS UTILIZING THE SAME

The present invention relates to an LCD having an improved contrast ratio and an apparatus comprising such an LCD.

Cross Reference of Related Application

The present invention enjoys the priority benefit of US Provisional Application No. 61 / 017,170, filed Dec. 27, 2007, which is hereby incorporated by reference in its entirety.

This application enjoys the priority benefit of European Patent Application No. 08164707.5, filed September 18, 2008, the content of which is hereby incorporated by reference in its entirety.

Liquid crystal displays (LCDs) are one of the most widely used flat panel displays. The LCD has two panels provided with field generating electrodes such as a pixel electrode and a common electrode, and a liquid crystal (LC) layer sandwiched between these panels. The LCD displays an image by applying a voltage to the field generating electrode to generate an electric field in the LC layer that determines the orientation of the LC molecules in the LC layer to adjust the polarization of the incident light.

The need for increasing the color gamut of the display attracts multi-primary displays. One recently developed is an RGBY display with red (R), green (G), blue (B) and yellow (Y) color filter sections of the color filter of LCD pixels. Such RGBY displays are interesting for color rendering because they have a wider color reproducibility than RGB or RGBW LCDs. Moreover, these RGBY displays consume less power than RGB LCDs.

By optimizing the materials and processes of the red, green and blue color filter sections, the diffusion of light through the color filter is surely reduced. Some depolarization occurs in the red, green, and blue color filter sections, but at acceptable levels.

However, yellow pigments are not available to be suitable sulfur color filter parts. These days, sulfur pigments show a substantial amount of diffusion which results in depolarized incident polarization. This significantly reduces the contrast ratio (CR) and color reproducibility.

Still, RGBY or RGyGcB is among the most promising multi-primary displays that allow for good rendering of natural surface colors. Sanyo-Epson, for example, presented an RGyGcB display (Cromarich Technology) that showed improved color reproduction. This display is used in the Epson P-3000 and P-5000 lines of photo viewers. However, tests have shown that sulfur color filters still depolarize light and are therefore unacceptable for LCD applications.

E. Peeters discloses a variety of materials that can be used as in-cell polarizers, such as polarizers made of in-situ photopolymerization or concentration transition liquid crystal dyes of higher order (smatic) guest-host systems, respectively. Such guest-host systems can be made from reactive liquid crystal diacrylates. Photopolymerization can be obtained by doping diacrylates with dichroic dye molecules, for example as indicated by dichroic azo (dichroic azo) dyes (cross reference column of related applications). E. Peeters discloses an idea for using in-cell polarizers, respectively, as an alternative to conventional polarizers outside of LCD cells. E. Peeters does not disclose or suggest using conventional external polarizers in addition to these in-cell polarizers.

One example embodiment of an LCD device includes at least one LCD cell. The LCD cell includes a liquid crystal layer, a base panel and a top panel. The base panel includes a first polarizer adjacent the liquid crystal layer and arranged to polarize incident light in a first direction. The top panel is adjacent to the liquid crystal layer but opposite the base panel and includes a color filter, a second polarizer and a third polarizer. The color filter includes at least one color filter unit to generate light of a predetermined color. The second polarizer is arranged on the side of the color filter opposite the liquid crystal layer and arranged to polarize the incident light in a second direction perpendicular to the first direction. The third polarizer is arranged between the color filter and the liquid crystal layer and arranged to polarize the incident light in the second direction.

By providing an additional in-cell polarizer, a good contrast ratio is achieved by reducing the amount of light passing through the sulfur color filter in the off state.

In one embodiment, the present invention uses a high contrast thin film in-cell polarizer made by photopolymerizing the guest-host mixture, such as by cross-linking the static guest-host mixture.

These polarizers, which can be used as in-cell polarizers, are highly competitive polarizers compared to conventional polarizers, such as H-sheet polarizers made of elongated poly (vinyl alcohol) doped with dichroic dyes or iodine impregnated for use in most displays these days. to be.

The polarizer according to the present invention is thinner, freer in choosing the substrate (possible birefringent material), more robust (the substrate is outside the display), easily controlled above the polarization direction, no cutting waste, and improved thermal stability By having a shorter optical stack, parallax problems are reduced and high moisture resistance is achieved.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings for a more detailed description of the present invention.

The following description is the best mode for practicing the present invention. This description is made for the purpose of illustrating the general principles of the invention and is not to be taken in a limiting sense. The scope of the invention is determined by the appended claims.

1 is a diagram of an electronic device 1 equipped with an LCD 10 according to an embodiment of the present invention. The electronic device 1 has a power supply 20 connected to the LCD 10 to supply power to the LCD 10. In this embodiment, the LCD 10 is a color image display integrated in the electronic device 1. As will be appreciated by those skilled in the art, the electronic device 1 may be a mobile phone, a personal digital assistant (PDA), a notebook computer, a desktop computer, a television, a car media player, a portable video player, a digital camera, a global positioning system (GPS), a car. It may be a navigation system, abionics display, or the like.

In accordance with one embodiment of the present invention, FIG. 2A further illustrates a profile of the LCD 10 including a liquid crystal (LC) layer 100, a common electrode 102, and a pixel electrode 104. The electrode 104 is arranged on the substrate 105. The LCD 10 may have many cells, but FIG. 2A shows only one cell of the LCD 10 to illustrate the present invention. In this embodiment, the pixel cell corresponding to the sub pixel may have a size of 40 μm × 40 μm and a thickness of 4.15 μm. Pixel cells may have different sizes, such as 20 μm × 20 μm, 30 μm × 30 μm, 39.5 μm × 39.5 μm or 30 um × 61 um (other unsquare designs) and thicknesses greater than 1.5 μm are possible. As shown, the LC layer 100 in which the LC molecules are aligned vertically (not shown in FIG. 2A, "vertical" should be understood in the direction of the drawing in FIG. 2A) is shown in FIG. 104) sandwiched between. A pixel electrode 104 overlying the TFT (thin film transistor, not shown) side is provided to switch the liquid crystal layer 100. LCD 10 may include other components such as substrate 130, color filters (not shown in FIG. 2B), and TFTs (see FIG. 2B).

The common electrode 102, the LC layer 100, and the pixel electrode set 104 form a liquid crystal capacitor that stores the applied voltage after turning off the TFT (not shown). The pixel electrode set 104 supplied with the data voltage generates an electric field in cooperation with the common electrode 102 which redirects the liquid crystal molecules of the liquid crystal layer 100. The common electrode 102, which may be a conventional common electrode, may be made of ITO or IZO. The pixel electrode 104 can also be made of ITO or IZO.

3A and 3B schematically illustrate one pixel (or cell) of a conventional color LCD device to further illustrate the problem to be solved by the present invention. FIG. 3A shows a pixel with a base panel with polarizer POL1, a glass layer GL1 on top of polarizer POL1, and an electrode EL1 on top of glass layer GL1. Furthermore, the pixel has an upper panel with polarizer POL2, a glass layer GL2 under polarizer POL2, a color filter CF under glass layer GL2 and an electrode EL2 under color filter CF. The polarizer POL1 has a polarization direction perpendicular to the polarization direction of the polarizer POL2. In the illustrated embodiment, polarizer POL1 polarizes light in the x direction and polarizer POL2 polarizes light in the y direction. As shown in Fig. 3A, the color filter CF has four parts, that is, a red R part, a green G part, a blue B part, and a yellow Y part. It should be understood that the terms "on top" and "below" refer to directions as shown in the drawings and are not intended to limit the scope of the invention.

The power supply 20 is connected between the electrode EL1 and the electrode EL2. In the embodiment shown in Fig. 3A, the LCD device is of a so-called "vertical alignment (VA)" type. That is, the molecules in the liquid crystal 100 are vertically aligned when the power supply voltage supplied by the power supply 20 is a low voltage, for example, 0V. The term "vertically" refers to the direction perpendicular to the surfaces of the electrodes EL1, EL2. In this state, the pixel should be "black". That is, it must not transmit any light. The technique of the present invention is not limited to the VA, and is applicable to other LC modes such as FFS (Fringe Field Switching), IPS (In-Plane Switching), Electrically Controlled Birefriengence (ECB), and Optically Compensated bend (OCB).

3A shows light L descending to the bottom of the base panel. Light L goes down to polarizer POL1 and is linearly polarized in the x direction as shown on the right side of the pixel. At this time, the light L passes through the glass layer GL1 and the electrode EL1 and remains linearly polarized in the x direction.

Light L then passes through the liquid crystal 100 without obstruction due to molecules in the liquid crystal 100 that are vertically aligned. After passing through the liquid crystal 100, the light L is still linearly polarized in the x direction.

Light L then passes through electrode EL2 and enters color filter CF. The light portions passing through the red R portion, the green G portion, and the blue B portion of the color filter CF are respectively filtered to become the red light portion, the green light portion, and the blue light portion, respectively. These three parts are still substantially linearly polarized substantially in the x direction because the materials used for the red R part, the green G part, and the blue B part do not substantially change after polarization.

However, materials used so far for the yellow Y portion have a depolarization effect because the materials diffuse the passing light. This is schematically shown on the right side of the pixel when the polarization of the light passing through the yellow color filter portion at the junction between the yellow color filter portion Y and the glass layer GL2 has both x and small y components. That is, the light L is polarized in an elliptical shape there.

All light L passes through the glass layer GL2 without alteration and reaches the junction between the glass layer GL2 and the polarizer POL2. The polarizer POL2 blocks all light polarized in the x direction. Therefore all light passing through the red R, green G, and blue B portions will be completely blocked by the polarizer POL2, respectively. That is, downstream from these red R, green G, and blue B portions, i.e., the pixel is "black" (no light is transmitted). However, the polarizer POL2 passes through the y component of the depolarized part of the light L which has passed through the yellow color filter part Y. The pixel will therefore transmit a small amount of (polarized) yellow light so that "black" will not appear as a whole. This is not acceptable for most applications.

FIG. 3B shows the same pixel as FIG. 3A. However, in the state shown in FIG. 3B, the power supply 20 now supplies sufficient voltage to horizontally align the molecules in the liquid crystal 100. This may be for example 5V. This horizontal alignment effect is that when the light L enters the liquid crystal 100, the polarization direction of the light L that is polarized in the x direction is rotated by 90 ° (π / 2). Thus, when exiting the liquid crystal 100, the light L is polarized in the y direction as indicated on the right side of the pixel in FIG. 3B.

Again, the red R, green G, and blue B portions of the color filter CF will pass through all the red R, green G, and blue B portions polarized in the y direction without substantially changing the polarization direction of the light L. Polarizer POL2 will pass through the red R, green G, and blue B portions without modification. The yellow color filter portion Y diffuses the light portion passing through this portion, resulting in some depolarization. This light passing through the yellow portion Y will have a small component in the x direction. However, most of the yellow light portion will be polarized in the y direction. The latter part will also pass through polarizer POL2 without modification. Only yellow parts that are polarized in the x direction will be disturbed by the polarizer POL2. Still, most of the light will be transmitted by the pixel so that the pixel will be white.

Those skilled in the art will appreciate that in practice the electrode EL2 will be divided into several parts for each of the electrode parts, i.e. each color filter part R, G, B, Y. It will be connected to individual TFTs arranged to individually switch each of these electrode portions at separate voltages to turn on and off the respective color filter portions by aligning the molecules in each portion of the liquid crystal 100 horizontally or vertically. The amount of light passing through each portion of the liquid crystal 100 can be controlled by controlling the voltage levels applied to the electrodes EL1 and EL2. Thus the pixel can transmit the desired color.

4A and 4B illustrate embodiments of pixels of an LCD device that solve the problem of insufficient black level and the problem of unacceptable contrast ratio.

The pixels shown in Figs. 4A and 4B are the same as in Figs. 3A and 3B in which the components are referred to by the same reference numerals. The difference between the pixels of FIGS. 4A and 4B and FIGS. 3A and 3B is that the pixels of FIGS. 4A and 4B include an additional polarizer POL3 in the top panel of the color filter CF. This polarizer is called an "in-cell polarizer."

Ideally the additional polarizer POL3 should have the same polarization direction as the polarizer POL2. That is, the polarizer POL3 transmits only the light portion polarized in the y direction and completely blocks the x component of the incident light. However, to date, no in-cell polarizer with 100% polarization performance in one direction is known. So in practice some light polarized in the x direction will still pass through the additional polarizer POL3.

In the embodiment shown in Fig. 4A, an additional polarizer POL3 is provided between the electrode EL2 and the color filter CF to cover all the color filter parts R, G, B and Y.

The pixel operation method of FIG. 4A is as follows. When the power supply 20 supplies an operating voltage of O V, all molecules in the liquid crystal 100 are vertically aligned and the liquid crystal 100 does not change the passing light polarized in the x direction. After passing through the transparent electrode EL2 in that state, all the light is at least partially blocked by the additional polarizer POL3. The amount of light polarized in the x direction and passing through the additional polarizer POL3 depends on the polarization capability of the additional in-cell polarizer POL3. Some light polarized in the x direction will still pass through the additional polarizer POL3. The remaining light portions that pass through the red R, green G, and blue B color portions will reach polarizer POL2 substantially without change in their polarization direction. That is, they are still polarized in the x direction. At this time, the rest of them will be completely blocked by the polarizer POL2. However, the light portion entering the yellow color filter portion Y will again be diffused by rendering a yellow elliptical polarized light portion with both the yellow x component and the yellow y component. The yellow y component will pass through polarizer POL2. So some yellow light can still be transmitted by the pixel. However, the contrast ratio is remarkably improved compared with the pixels of FIGS. 3A and 3B.

In the on state, the power supply 20 will supply a high voltage, such as 5 V, which causes the molecules in the liquid crystal 100 to be horizontally aligned. The effect of the horizontal alignment is that when the light enters the liquid crystal 100, the polarization direction of the light L polarized in the x direction is rotated by 90 ° (π / 2). Thus, when exiting the liquid crystal 100, the light L is polarized in the y direction. As described with reference to FIG. 3B, all light will be blocked when passing through any one of the color filter units R, G, B, and Y and the polarizer POL2 in this state. But also polarizer POL3 will not block this light. So in the on state the pixel will show white light.

As will be appreciated by those skilled in the art, in the embodiment of Fig. 4A, the electrode EL2 will be divided into several electrode parts, i.e., one part for each color filter part R, G, B, Y. Each of these electrode portions is a separate TFT arranged to individually switch at respective voltages to each of these electrode portions to switch each of the color filter portions on and off by vertically or horizontally aligning molecules in the individual portions of the liquid crystal 100. Will be connected to The amount of light passing through the individual portions of the liquid crystal 100 can be controlled by controlling the voltage levels applied to the electrodes EL1 and EL2. Thus, a pixel can transmit any desired color.

As such, the present invention provides an LCD having pixels with improved black levels. However, the white level is also improved so that the LCD according to the present invention increases contrast ratio and color reproducibility.

The embodiment shown in FIG. 4A has one polarizer POL3 under all four color filter parts R, G, B, Y. FIG. This one polarizer is a broadband polarizer material, i.e. a material that is transparent to the broad frequency spectrum of incident light L. Of course, this broadband polarizer material should be at least transparent to red, green, blue and yellow. Such materials are selectable from the group of materials comprising polarizers made of in-situ photopolymerization or concentration transition liquid crystal dyes of higher order guest-host systems. Such guest-host systems can be automatic guest-host systems and can be made of reactive liquid crystal diacrylates. Photopolymerization can be obtained by doping the diacrylate with dichroic dye molecules, such as present in dichroic azo dyes. More information on these materials can be found in the cross-reference column of the relevant application.

In an alternative embodiment, polarizer POL3 is divided into at least two parts per pixel as shown in FIG. 4B. FIG. 4B shows an embodiment where the polarizer POL3 is divided into four different portions, namely POL3R portion, POL3G portion, POL3B portion, and POL3Y portion. Each one of these POL3R parts, POL3G parts, POL3B parts, and POL3Y parts are designed as polarizers of limited bandwidth. That is, the polarizer POL3R section is designed to transmit only light in the red frequency region substantially. The polarizer POL3G section is designed to transmit substantially only light in the green frequency region. The polarizer POL3B section is designed to transmit substantially only light in the blue frequency region. The polarizer POL3Y part is designed to transmit substantially only light in the yellow frequency region.

 By virtue of the configuration shown in Fig. 4B, each color filter unit will transmit light with a more limited bandwidth. This contributes to good color reproduction.

Alternatively two or three individual polarizer portions can be provided by providing individual polarizers POL3R portion, POL3G portion, POL3B portion, POL3Y portion for each one of the color filter portions R, G, B, Y. For example, the polarizer POL3R portion, POL3G portion, POL3B portion, and POL3Y portion may be one single portion composed of a material that is transparent to broadband frequencies including red, green, and blue. However, other combinations are possible depending on the available materials that can be selected according to easy patterning with a suitable configuration.

In the above embodiments the polarizer POL3 is shown to be located between the electrode EL2 and the glass layer GL2. Alternatively, however, the polarizer POL3 may be located between the liquid crystal 100 and the electrode EL2.

Although the present invention has been described with reference to R, G, B, Y LCD devices, it is equally applicable to any color LCD device using color filters. In other words, the present invention focuses on the yellow color filter as described herein, but the idea of using an in-cell polarizer for any wavelength may be noticed in a conventional RGB (high contrast) display or RGBX display, where "X" means eg Y = yellow, W = white, or another color of the four color filters.

The LCD device according to the present invention is a mobile phone, a PDA (Personal Digital Assistant), a notebook computer, a desktop computer, a television, a car media player, a portable video player, a digital camera, a GPS (Global Positioning System) used in a car navigation system, AVIO It can be applied to Knicks display. However, other applications may be true color wide reproducibility displays, such as photo viewers and photo printer free viewers, and it is important that the reproducibility of the display matches the reproducibility of the photo paper and the reproducibility of the camera.

While the invention has been described by way of example with reference to the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. In contrast, the examples are intended to cover various modifications and similar constructions (obvious to those skilled in the art). Therefore, the appended claims are intended to cover a wide variety of interpretations to cover all such modifications and similar constructions.

1 is a block diagram of an LCD device;

2A illustrates an example of a profile of an LCD pixel cell.

2B shows an example of a profile of a component of an LCD pixel cell.

3A and 3B are schematic views of one pixel (cell) of a prior art LCD device.

4A and 4B show an embodiment of a pixel of an LCD device according to the present invention;

Claims (10)

A liquid crystal layer, A base panel adjacent to the liquid crystal layer and including a first polarizer arranged to polarize incident light in a first direction; An upper panel adjacent the liquid crystal layer and opposite the base panel At least one LCD cell comprising a An LCD device comprising: The upper panel, A color filter including at least one color filter unit to generate light of a predetermined color; A second polarizer arranged on a side of the color filter opposite the liquid crystal layer and arranged to polarize incident light in a second direction perpendicular to the first direction; A third polarizer arranged between the color filter and the liquid crystal layer and arranged to polarize incident light in the second direction LCD device comprising a. The LCD device according to claim 1, wherein said color filter comprises four color filter parts to produce substantially white light. 3. The apparatus of claim 1, wherein the third polarizer comprises at least two third polarizer portions, each of the at least two third polarizer portions polarizing incident light relative to a separate set of one or more of the color filter portions. LCD device arranged to be. 4. The color filter of claim 3, wherein the color filter comprises four color filter portions and the third polarizer comprises four third polarizer portions, each of the four third polarizer portions being in a separate one of the four color filter portions. And an LCD device arranged to polarize incident light with respect thereto. The LCD device according to claim 1 or 2, wherein the upper panel includes an electrode, and the third polarizer is located between the electrode and the color filter. The LCD device according to claim 1 or 2, wherein the upper panel includes an electrode, and the third polarizer is located between the electrode and the liquid crystal layer. The LCD of claim 1 or 2, wherein the third polarizer is selected from the group of materials comprising a polarizer made of a concentration-transition liquid crystal dye and a polarizer made of in-situ photopolymerization of a guest-host system. Device. 8. The LCD device of claim 7, wherein the guest-host system is a automatic guest-host system. The LCD device according to claim 7, wherein the guest-host system is made of reactive liquid crystal diacrylate. An apparatus comprising the LCD device according to any one of the preceding claims, Such devices include mobile phones, personal digital assistants (PDAs), notebook computers, desktop computers, televisions, car media players, portable video players, digital cameras, car navigation systems, avionics displays, photo viewers, photo printer free viewers. The device selected from the group.

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