JP2008102289A - Liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display which can obtain a satisfactory luminosity and is low in power consumption. <P>SOLUTION: In the liquid crystal display, having an array substrate 2 and a CF substrate 4 facing each other, a liquid crystal layer LQ interposed between the array substrate 2 and the CF substrate 4 and composes a refractive index anisotropic medium and a display part DSP comprising a plurality of display pixels PX disposed in a matrix shape; the liquid crystal layer LQ has a first layer LQ1 and a second layer LQ2 in each display pixel PX; a boundary surface between the first layer LQ1 and the second layer LQ2 is inclined with respect to the normals of substrate surfaces of the array substrate 2; and the CF substrate 4 and refractive index difference between the first layer LQ1 and the second layer LQ2 can be controlled by an electric field. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device, and more particularly to a reflective liquid crystal display device and a transflective liquid crystal display device.

  In recent years, liquid crystal display devices have been applied to various fields such as notebook computers, monitors, car navigation systems, scientific calculators, and small and medium-sized TVs. In particular, the reflection type liquid crystal display device is applied to a display for a portable device or the like in order to take advantage of low power consumption, thinness and light weight because a backlight is unnecessary.

  However, the conventional reflective liquid crystal display device has inferior display performance in terms of brightness as compared with paper, printing and the like. Liquid crystal display devices capable of reflective and transmissive display are also applied to portable device displays. Further, since a battery or the like is used as a power source, if an attempt is made to obtain a sufficient driving time, the brightness of the backlight must be lowered, and sufficient brightness cannot be obtained. Thus, there are two main factors that cause the brightness of the liquid crystal display device to be insufficient.

  One is light absorption by a member necessary for controlling the brightness of a display, for example, a polarizing plate used in a TN mode or ECB mode liquid crystal display or a dye added to a liquid crystal used in a GH mode liquid crystal display. is there. The other is a case where a method of absorbing a specific wavelength such as a color filter method (additive color mixture) is used as a means for coloring the display.

  Conventionally, as a means for solving these problems, there is a scattering type liquid crystal display device typified by a polymer dispersed liquid crystal (PDLC). It utilizes the scattering and reflection of incident light due to the difference in refractive index between the randomly arranged liquid crystal and the isotropic layer without refractive index anisotropy, or the difference in refractive index between the randomly arranged liquid crystal molecules. is there.

When this scattering type liquid crystal display device is used as a reflection type liquid crystal display device, it becomes a bright state by scattering reflection. Apply an electric field to the liquid crystal layer to make the refractive index of the isotropic layer and the liquid crystal layer equal to the direction in which the light is incident, or make the refractive index between molecules of the liquid crystal layer equal, and the rear side of the liquid crystal display device The incident light is absorbed by the light-shielding layer arranged in (1) to obtain a dark state (see Patent Document 1).
JP 11-38452 A

  However, the difference in refractive index between the randomly arranged liquid crystal and the isotropic layer without refractive index anisotropy in the scattering type liquid crystal display device is the average of the extraordinary refractive index and ordinary refractive index of liquid crystal molecules, and the ordinary refractive index. However, the liquid crystal material currently used practically can only obtain about 0.13 at most.

  For this reason, in order to obtain a sufficient reflectance, it is necessary to increase the thickness of the liquid crystal layer, and the driving voltage becomes extremely high. Also, when used as a transmission type, a dark state is obtained by scattering reflection, but like the L reflection type, it is necessary to increase the thickness in order to obtain a sufficient contrast, and the driving voltage is remarkably increased.

  Therefore, even when the scattering type liquid crystal display device is used as a reflection type or a transmission type, power consumption may be increased.

  Further, when the conventional scattering type liquid crystal display device is used as a reflection type, sufficient brightness cannot be obtained, and as a result, the contrast ratio is insufficient. Further, when used as a transmission type, there is a problem that the contrast ratio is insufficient.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a liquid crystal display device that can obtain sufficient brightness and has low power consumption.

  A liquid crystal display device according to an aspect of the present invention includes a first substrate and a second substrate facing each other, and a liquid crystal layer formed of a refractive index anisotropic medium sandwiched between the first substrate and the second substrate, A liquid crystal display device having a display unit composed of a plurality of display pixels arranged in a matrix, wherein the liquid crystal layer includes a first layer and a second layer in each display pixel, The boundary surface between the first layer and the second layer is inclined with respect to the normal line of the substrate surface of the first substrate and the second substrate, and the electric field control is possible for the difference in refractive index between the first layer and the second layer. It is.

  According to the present invention, it is possible to provide a liquid crystal display device with sufficient brightness and low power consumption.

  A liquid crystal display device according to an embodiment of the present invention will be described below with reference to the drawings. As shown in FIG. 1, the liquid crystal display device according to this embodiment has a reflective liquid crystal display panel LPN having a pair of substrates facing each other, that is, an array substrate 2 and a CF substrate 4. The liquid crystal display panel LPN includes a liquid crystal layer LQ composed of liquid crystal molecules sandwiched between the array 2 substrate and the CF substrate 4 and having refractive index anisotropy, and a display section DSP composed of a plurality of display pixels PX arranged in a matrix. And have.

  As shown in FIG. 2, the array substrate 2 includes a plurality of signal lines X (X1 to Xm) arranged along the columns where the display pixels PX are arranged and a plurality of signals arranged along the rows where the display pixels PX are arranged. Scanning lines Y (Y1 to Yn), and pixel switches SW arranged in the vicinity of intersections between the signal lines X and the scanning lines Y.

  The gate electrode of the pixel switch SW is connected to the corresponding scanning line Y (or formed integrally). The source electrode of the pixel switch SW is connected to the corresponding signal line X (or formed integrally). The drain electrode of the pixel switch SW is connected to the pixel electrode PE (or formed integrally). Further, the array substrate 2 has common wirings C (C1 to Cn) extending substantially parallel to the scanning lines Y.

  Around the display portion DSP, a signal line driving circuit XD connected to the signal line X and a scanning line driving circuit YD connected to the scanning line Y are arranged. The scanning line driving circuit YD sequentially selects a selection signal for the scanning line Y, and turns on the pixel switch SW for each row. The signal line driving circuit XD sequentially transmits image signals corresponding to the respective signal lines X.

  For example, as illustrated in FIG. 3, the common wiring C includes a common electrode CE extending along the signal line X. In the case shown in FIG. 3, in each display pixel PX, the pixel electrode PE and the common electrode CE are arranged so as to extend in parallel with each other. At this time, when an image signal is transmitted to the pixel electrode PE via the pixel switch SW and a common signal is transmitted to the common electrode CE, the substrate surface of the array substrate 2 is interposed between the pixel electrode PE and the common electrode CE. On the other hand, an electric field is generated substantially in parallel.

  On the other hand, in the CF substrate 4, a color filter CF is disposed as a colored layer on a light transmissive insulating substrate such as a glass substrate. The color filter CF includes a red color filter layer, a green color filter layer, and a blue color filter layer (not shown) for each display pixel PX. Each color filter is arranged in the row and column directions of a plurality of display pixels in a predetermined order.

  The liquid crystal layer LQ sandwiched between the array substrate 2 and the CF substrate 4 has a first layer LQ1 and a second layer LQ2. These first layer LQ1 and second layer LQ2 are arranged such that their boundary surfaces are inclined with respect to the normal line of the substrate surface of array substrate 2 and CF substrate 4, as shown in FIGS. ing. The array substrate 2 also has a reflector (not shown) that reflects the light incident on the liquid crystal layer LQ from the CF substrate 4 side to the CF substrate 4 side.

  In the present embodiment, the first layer LQ1 is a nematic liquid crystal polymer layer in which nematic liquid crystal is cross-linked and polymer is applied. The second layer LQ2 is a non-crosslinked nematic liquid crystal layer.

  In the liquid crystal display panel LPN according to the present embodiment, the liquid crystal molecules included in the first layer LQ1 and the second layer LQ2 have a homogeneous arrangement in which the major axis is substantially parallel to the substrate surface of the array substrate 2. .

  Here, in a plane substantially parallel to the substrate surface of the array substrate 2, the refractive index in the major axis direction of the liquid crystal molecules contained in the first layer LQ1 is ne, and the refractive index in the direction substantially orthogonal thereto is no. To do. At this time, when no voltage is applied, the refractive indexes in the first layer LQ1 and the second layer LQ2 are substantially uniform regardless of the orientation. That is, the refractive index anisotropy Δn (Δn = ne−no) between the first layer LQ1 and the second layer LQ2 is as shown in FIGS.

  Here, the light incident on the first layer LQ1 and the second layer LQ2 passes through the first layer LQ1 as it is. That is, at this time, since the refractive indexes of the first layer LQ1 and the second layer LQ2 are substantially the same, the light incident on the liquid crystal layer LQ is reflected at the boundary surface between the first layer LQ1 and the second layer LQ2. There is no reflection. Accordingly, the light incident from the CF substrate 4, that is, external light is reflected by the reflector of the array substrate 2 and is emitted from the CF substrate 4 again. Then, an image is displayed at a white level on the display unit DSP.

  On the other hand, when a voltage is applied to the pixel electrode PE and the common electrode CE, an electric field substantially parallel to the substrate surfaces of the array substrate 2 and the CF substrate 4 is generated between the pixel electrode PE and the common electrode CE as described above. . Here, in the present embodiment, the refractive index of the first layer LQ1 is constant regardless of the applied voltage, and the refractive index of the second layer LQ2 can be controlled by the applied voltage. Then, the liquid crystal molecules in the second layer LQ2, that is, the nematic liquid crystal layer are aligned so that the major axis thereof is substantially orthogonal to the major axis of the liquid crystal molecules in the first layer LQ1.

  At this time, the major axis of the liquid crystal molecules contained in the second layer LQ2 to which an electric field is applied is controlled in the direction substantially perpendicular to the major axis of the liquid crystal molecules contained in the first layer LQ1. That is, the slow axis direction of the first layer LQ1 and the slow axis direction of the second layer LQ2 are substantially orthogonal to each other. At this time, the refractive index anisotropy Δn between the first layer LQ1 and the second layer LQ2 is as shown in FIGS.

  Here, the angle θ formed by the interface between the first layer LQ1 and the second layer LQ2 with respect to the normal direction of the refractive index ne, the refractive index no, and the array substrate 2 satisfies the total reflection condition (sin θ <ne / no). In this case, as shown in FIG. 6, the external light is totally reflected at the layer interface between the first layer LQ1 and the second layer LQ2.

  Then, the external light incident on the liquid crystal layer LQ from the CF substrate 4 side is not emitted from the CF substrate 4 again, and an image is displayed on the display unit DSP at the black display level.

  When the display method as described above is adopted, it is not necessary to attach a polarizing plate to the liquid crystal display panel LPN. Therefore, a very bright reflective display is possible as compared with the case where a polarizing plate is used. Further, since there is no need to increase the thickness of the liquid crystal layer LQ, a liquid crystal display device with low power consumption can be provided. Embodiments of the present invention will be described below with reference to the drawings.

(First embodiment)
FIG. 8 is a sectional view of a reflective liquid crystal display panel LPN according to an embodiment of the present invention. As shown in FIG. 8, the liquid crystal display panel LPN according to the present example includes an array substrate 2 and a CF substrate 4 like the liquid crystal display panel LPN according to the above-described embodiment. A liquid crystal layer LQ made of liquid crystal molecules having refractive index anisotropy is sandwiched between the array substrate 2 and the CF substrate 4.

  The liquid crystal layer LQ has a first layer LQ1 and a second layer LQ2. The first layer LQ1 is a liquid crystal polymer layer containing nematic liquid crystal droplets, and the second layer LQ2 is a nematic liquid crystal layer. A drain electrode DE and a common electrode CE are arranged on the array substrate 2. When a voltage is applied to the drain electrode DE and the common electrode CE, an electric field is generated in a direction substantially parallel to the substrate surface of the array substrate 2, and the orientation direction of the liquid crystal molecules contained in the second layer LQ2 is caused by this electric field. Be controlled.

  In the case of the liquid crystal display panel LPN according to the present embodiment, the CF substrate 4 has an antireflection film ARF. Furthermore, it has the absorber AP arrange | positioned around the display part DSP.

  A manufacturing procedure of the reflective liquid crystal display panel LPN will be described below. First, the array substrate 2 is formed. That is, the drain electrode DE, the common electrode CE, the signal line X, the scanning line Y, the reflection plate (not shown), and the pattern of the pixel switch SW (TFT element) are formed on an insulating substrate such as glass by a normal TFT process. The formed spacer is formed, and an IPS (In Plane Switching) type TFT substrate is formed. At this time, the pixel electrode PE is formed integrally with the drain electrode DE of the pixel switch SW.

  In the liquid crystal display panel LPN according to this example, the reflectance of each electrode is reduced by using two-layer chromium on the outermost surface.

  On the other hand, the CF substrate 4 is formed. That is, a photosensitive resist in which a red pigment is dispersed is applied on the CF substrate 4 and a red color filter layer is formed by photolithography. Similarly, a green color filter layer and a blue color filter layer were formed.

  Thereafter, a horizontal alignment film (not shown) is printed so as to cover the entire display area of both the substrates 2 and 4. In the liquid crystal display panel LPN according to this example, AL3456 manufactured by JSR Co., Ltd. is printed as the alignment film, and baking is performed at 180 ° C. for 30 minutes to obtain a horizontal alignment film having a thickness of 600 mm. Thereafter, both the substrates 2 and 4 are rubbed.

  The rubbing direction of the array substrate 2 is an orientation parallel to the drain electrode DE and the common electrode CE, that is, an orientation orthogonal to the electric field generated between the drain electrode DE and the common electrode CE. The rubbing direction of the CF substrate 4 is an orientation that is anti-parallel to the rubbing direction of the array substrate 2.

  Thereafter, a nematic liquid crystal polymer having a refractive index anisotropy Δn = 0.2 is applied to the array substrate 2 to a thickness of 5 μm, and the pattern is formed in a stripe shape with a width of 20 μm. The liquid crystal polymer was patterned by irradiating with ultraviolet rays.

  Thereafter, a peripheral sealing agent is applied to the array substrate 2, nematic liquid crystal of Δn = 0.2 is dropped, and the CF substrate 4 is superimposed thereon and irradiated with ultraviolet rays to cure the sealing agent. Thus, the distance a between the boundary surfaces of the first layer LQ1 and the second layer LQ2 is 20 μm, and the angle θ formed by the boundary surface between the first layer LQ1 and the second layer LQ2 with respect to the substrate surface of the array substrate 2 is A liquid crystal display panel LPN having an angle of approximately 20 ° was formed. Further, a liquid crystal display device was manufactured by incorporating a drive circuit.

  When the optical characteristics of the reflective liquid crystal display device of this example obtained as described above were evaluated, the reflectance was 90% of that of a standard white plate, and the white / black contrast ratio was 50: 1.

(Second embodiment)
Next, another example of one embodiment of the present invention will be described. The CF substrate 4 and the array substrate 2 were the same as those in the first example. In this example, a liquid crystal polymer was applied to the array substrate 2 to a thickness of 5 μm, cured by ultraviolet rays, and then patterned into the same shape as in the first example by reactive ion etching (RIE). Thereafter, a liquid crystal module was produced in the same manner as in the first example.

  When the optical characteristics of the reflective liquid crystal display device according to this example manufactured as described above were evaluated, the reflectance was 90% of the standard white plate and the white / black contrast ratio was 50: 1 was obtained.

(First comparative example)
Next, a liquid crystal display device according to a first comparative example of the present invention will be described. In this comparative example, a liquid crystal display device was manufactured in the same process as in the first example except that the ultraviolet irradiation direction when patterning the liquid crystal polymer was changed. That is, in this comparative example, five types of liquid crystals having angles of 10 °, 45 °, 60 °, 70 °, and 80 ° formed by the substrate surface of the array substrate 2 and the boundary surfaces of the first layer LQ1 and the second layer LQ2 are used. A display panel LPN was manufactured.

  FIG. 10 and FIG. 11 show the results of evaluating the liquid crystal display device having the above-described liquid crystal display panel LPN and comparing the reflectance and contrast. As shown in FIGS. 10 and 11, the substrate surface of the array substrate 2 and the boundary surfaces of the first layer LQ1 and the second layer LQ2 are formed from the evaluation result of the first example and the evaluation result of the first comparative example. With respect to the liquid crystal display device with an angle of 20 ° to 60 °, the characteristics of reflectance and contrast were relatively good.

(Second comparative example)
Next, a liquid crystal display device according to a second comparative example of the present invention will be described. In this comparative example, the angle formed by the substrate surface of the array substrate 2 and the boundary surface between the first layer LQ1 and the second layer LQ2 is 20 °, and the refractive index anisotropy of the first layer and the second layer is changed. Except for the above, a liquid crystal display device was manufactured by the same process as in the first embodiment. That is, a liquid crystal display panel LPN was manufactured using four types of liquid crystals having refractive index anisotropy Δn of 0.1, 0.15, 0.2, and 0.25, respectively.

  FIG. 12 and FIG. 13 show the results of measuring the reflectance and contrast of the liquid crystal display device having the liquid crystal display panel LPN. As shown in FIGS. 12 and 13, from the evaluation result of the first example and the evaluation result of the second comparative example, when the refractive index anisotropy Δn is 0.15 or more, the reflectance and contrast characteristics are relatively It was good.

(Third comparative example)
Next, a third comparative example of the present invention will be described. In this comparative example, the angle between the substrate surface and the boundary surface between the first layer LQ1 and the second layer LQ2 is 20 °, and the boundary between the first layer LQ1 and the second layer LQ2 of the first layer LQ1 and the second layer LQ2 A liquid crystal display device was manufactured by the same process as in the first example except that the surface interval a was changed. That is, in this comparative example, six types of liquid crystal display panels LPN were manufactured by using masks with the distance a being 5, 10, 20, 30, 50, and 70 μm, respectively.

  These liquid crystal display panels LPN were evaluated and the reflectance and contrast were compared. The evaluation results are shown in FIGS. As shown in FIGS. 14 and 15, from the evaluation result of the first example and the evaluation result of this comparative example, the reflectance and contrast characteristics were good when the distance a was 20 μm or less.

  That is, from the evaluation results of the above-described examples and comparative examples, according to the above-described liquid crystal display device according to an embodiment of the present invention, a liquid crystal display device with sufficient brightness and low power consumption is provided. be able to.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. For example, in the above-described embodiments and examples, the distance between the boundary surfaces of the first layer LQ1 and the second layer LQ2 is equal, but this is not limiting, and the distance between the boundary surfaces may be non-uniform.

  In the above-described embodiments and examples, the case where the refractive indexes of the first layer LQ1 and the second layer LQ2 are substantially the same when a voltage is applied to the liquid crystal layer LQ has been described. When the refractive index difference between the refractive index of the first layer LQ1 and the refractive index of the second layer LQ2 is equal to or smaller than a predetermined value, the same effect as in the above embodiment and examples can be obtained.

  In the above embodiments and examples, the case where the liquid crystal display panel LPN is a reflection type has been described. However, even when the liquid crystal display panel LPN is adapted to a transmission type and a semi-transmission type, a bright display can be obtained without using a polarizing plate. It is done.

  Further, as in the above-described embodiments and examples, the first layer LQ1 is such that one normal line of the array substrate 2 and the CF substrate 4 intersects the boundary surface of the first layer LQ1 and the second layer LQ2 a plurality of times. It is desirable to arrange the second layer LQ2. However, the present invention is not limited to this, and the light incident on the liquid crystal layer LQ passes through the boundary surface between the first layer LQ1 and the second layer LQ2 at least once or is totally reflected at the boundary surface. It is only necessary that the two layers LQ2 are arranged.

  Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine suitably the component covering different embodiment.

1 is a diagram schematically showing an example of a liquid crystal display device according to an embodiment of the present invention. FIG. 3 is a diagram for explaining a configuration example of the liquid crystal display device shown in FIG. 1. FIG. 3 is a diagram for explaining a configuration example of the liquid crystal display device shown in FIG. 1. FIG. 2 is a cross-sectional view for explaining image display in a state where no voltage is applied to a liquid crystal layer in the liquid crystal display device shown in FIG. 1. Sectional drawing when the liquid crystal display device shown in FIG. 4 is cut along line AA. Sectional drawing for demonstrating the image display of the state which has applied the voltage to the liquid-crystal layer in the liquid crystal display device shown in FIG. Sectional drawing when the liquid crystal display device shown in FIG. 6 is cut along line BB. Sectional drawing for demonstrating the structural example in the state which has not applied the voltage to the liquid-crystal layer in the liquid crystal display device which concerns on 1st Example of this invention. Sectional drawing for demonstrating the structural example in the state which has applied the voltage to the liquid-crystal layer in the liquid crystal display device which concerns on 1st Example of this invention. The figure which shows the evaluation result about the liquid crystal display device which concerns on the 1st comparative example of this invention. The figure which shows the evaluation result about the liquid crystal display device which concerns on the 1st comparative example of this invention. The figure which shows the evaluation result about the liquid crystal display device which concerns on the 2nd comparative example of this invention. The figure which shows the evaluation result about the liquid crystal display device which concerns on the 2nd comparative example of this invention. The figure which shows the evaluation result about the liquid crystal display device which concerns on the 3rd comparative example of this invention. The figure which shows the evaluation result about the liquid crystal display device which concerns on the 3rd comparative example of this invention.

Explanation of symbols

2 ... Array substrate, LQ ... Liquid crystal layer, LQ1 ... First layer, LQ2 ... Second layer, 4 ... CF substrate, LPN ... Liquid crystal display panel. DSP ... display unit, PX ... display pixel

Claims (11)

A first substrate and a second substrate facing each other;
A liquid crystal layer sandwiched between the first substrate and the second substrate and made of a refractive index anisotropic medium,
A liquid crystal display device having a display unit composed of a plurality of display pixels arranged in a matrix,
The liquid crystal layer has a first layer and a second layer in each display pixel,
A boundary surface between the first layer and the second layer is inclined with respect to a normal line of the substrate surface of the first substrate and the second substrate;
A liquid crystal display device capable of controlling an electric field of a difference in refractive index between the first layer and the second layer. The first layer has a constant refractive index regardless of the applied voltage,
The liquid crystal display device according to claim 1, wherein the refractive index of the second layer can be controlled by an applied voltage.   The liquid crystal display device according to claim 1, wherein when a predetermined applied voltage is applied to the liquid crystal layer, the refractive index of the first layer and the refractive index of the second layer are substantially the same.   The liquid crystal display device according to claim 1, wherein the first substrate includes a reflector that reflects light incident on the liquid crystal layer from the second substrate side to the second substrate side. The slow axis directions of the first layer and the second layer are directions substantially parallel to the substrate surfaces of the first substrate and the second substrate,
The slow axis direction of the first layer and the slow axis direction of the second layer are substantially orthogonal to each other in a state where a predetermined voltage is applied to the first layer and the second layer. Liquid crystal display device.   The liquid crystal display device according to claim 1, further comprising an absorber disposed so as to surround the display unit.   In the black display state, the refractive index anisotropy of the refractive index anisotropic medium and the boundary surface between the first layer and the second layer form a substrate surface of the first substrate and the second substrate. The liquid crystal display device according to claim 1, wherein the angle is determined so that light incident on the liquid crystal layer is totally reflected at the boundary surface.   The liquid crystal display device according to claim 7, wherein the first layer and the second layer have a refractive index anisotropy of 0.15 or more.   The liquid crystal display device according to claim 7, wherein the boundary surface forms 20 ° to 60 ° with respect to the substrate surfaces of the first substrate and the second substrate.   The liquid crystal display device according to claim 1, wherein an interval between the boundary surfaces is 30 μm or less.   The liquid crystal display device according to claim 1, wherein the first layer is a liquid crystal polymer layer, and the second layer is a nematic liquid crystal layer.

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