JPH09146124A - Reflection type guest host liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the need for polarizing plates and to make a screen bright. SOLUTION: Transparent electrodes 3 are formed on the upper substrate 1 of the color reflection type guest-host liquid crystal display device. Reflection electrodes 4 are formed on the lower substrate 2 and an electrooptic body 5 is held in the spacing between both substrates. Optical modulation is executed according to impressed voltages. The electrooptic body 5 has a laminated structure including a liquid crystal layer 6 of a guest host type which contains dichroic dyestuff 8 and is uniformly oriented along the transparent electrodes 3 and a phase difference plate layer 7 which has prescribed optical anisotropic axes and is formed along the reflection electrodes 4. The transparent electrodes 3 and the reflection electrodes 4 face each other to regulate plural pixels. Color filters 13 allocate the incident light rays of different wavelengths to respective pixels. The phase difference plate 7 is divided by every pixel and the thicknesses thereof are adjusted according to the corresponding wavelengths. When this liquid crystal display device is formed as an active matrix type, the color filters are disposed not on the counter substrate side but on the driving substrate side formed with switching elements and pixel electrodes, by which the pixel opening rate is improved.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a reflection type guest-host liquid crystal display device. More specifically, it relates to a technique of improving the utilization efficiency of incident light by incorporating a retardation plate and removing a polarizing plate. More specifically, it relates to a technique for improving the display quality by removing the wavelength dependence of the built-in retardation plate when performing color display. The present invention also relates to the structure and manufacturing method of a micro color filter necessary for color display.

[0002]

2. Description of the Related Art A liquid crystal display device has various modes.
At present, a TN mode or an STN mode using a nematic liquid crystal which is twist-oriented or super-twist-oriented is mainly used. However, these modes require a pair of polarizing plates in terms of operation principle, and because of their light absorption, a low transmittance and a bright display screen cannot be obtained. In addition to these modes, a guest-host mode using a dichroic dye has also been developed. The guest-host mode liquid crystal display device performs display using the anisotropy of the absorption coefficient of the dichroic dye added to the liquid crystal. When a rod-shaped dichroic dye is used, the dye molecules have the property of being aligned parallel to the liquid crystal molecules. Therefore, when an electric field is applied to change the molecular alignment of the liquid crystals, the alignment direction of the dye also changes. Since this dye is colored or not depending on the direction, it is possible to switch between coloration and colorlessness of the liquid crystal display device by applying a voltage.

FIG. 6 shows Heilmeyer.
r) shows the structure of a guest-host liquid crystal display device,
(A) shows a state where no voltage is applied, and (B) shows a state where a voltage is applied. The liquid crystal display device is p-type dye and dielectric anisotropy are using positive nematic liquid crystal (N _p LCD). The p-type dichroic dye has an absorption axis substantially parallel to the molecular axis, strongly absorbs a polarized component Lx parallel to the molecular axis, and hardly absorbs a polarized component Ly perpendicular thereto. In the state in which no voltage is applied as shown in (A), the polarization component Lx contained in the incident light.
Is strongly absorbed by the p-type dye, and the liquid crystal display device is colored. For example, when a dichroic black pigment is used, it is colored black. On the other hand, in the voltage application state shown in (B),
The N _p liquid crystal having a positive dielectric anisotropy rises in response to the electric field, and the p-type dye is also aligned in the vertical direction accordingly. Therefore, the polarization component Lx is hardly absorbed and the liquid crystal display device is colorless. The other polarization component Ly contained in the incident light is not absorbed by the dichroic dye in both the voltage applied state and the voltage non-applied state. Therefore, in the Heilmeier guest-host liquid crystal display device, one polarizing plate is interposed in advance and the other polarization component Ly is removed.

[0004]

In a guest-host liquid crystal display device using a nematic liquid crystal, a dichroic dye added as a guest is oriented similarly to the nematic liquid crystal. A polarized light component parallel to the orientation direction of the liquid crystal is absorbed, but a polarized light component orthogonal thereto is not absorbed. Therefore, in order to obtain a sufficient contrast, one polarizing plate is arranged on the incident side of the liquid crystal display device so that the polarization direction of the incident light coincides with the alignment direction of the liquid crystal. However, in this case, 50% (actually, about 40%) of the incident light is lost due to the polarizing plate in principle, so that the display becomes dark like the TN mode. As a method for solving this problem, simply removing the polarizing plate is not appropriate because the on / off ratio of absorbance is remarkably reduced, and various measures have been proposed. For example, a structure has been proposed in which a polarizing plate on the incident side is removed, and a quarter-wave plate (phase difference plate) and a reflecting plate are attached on the output side. In this system, two polarization components orthogonal to each other are rotated by 90 ° in the forward and backward directions by the quarter-wave plate, and the polarization components are exchanged. Therefore, in the off state (absorption state), each polarization component is absorbed in either the incident light path or the reflected light path.

However, in this structure, since the quarter-wave plate and the reflection plate are externally attached, the liquid crystal display device itself must be of a transmission type. In particular, in order to enable high-definition and moving image display, when an active matrix type structure is applied, a thin film transistor for driving a pixel electrode is integrally formed on a substrate. A considerable part is cut off. Therefore, there is a problem that the screen of the display device cannot be significantly brightened even if the polarizing plate is removed.

When performing color display on an active matrix type liquid crystal display device, each of the pixels is periodically assigned with one of the three primary color components of red, green and blue. A color filter or the like is used to assign the three primary color components. The color filter selectively transmits wavelengths corresponding to the three primary color components assigned to each pixel. However, in the case of performing color display, if a method of emphasizing black display by using a quarter-wave plate (retarder) is adopted, there is a problem that the wavelength dependence of the retarder adversely affects the display quality. . For this reason, there is an effect of coloring when displaying black when the voltage is off. Further, the polarization conversion effect of the retardation film is not uniform over the entire wavelength range, which causes a reduction in contrast.

Further, when performing color display on an active matrix type liquid crystal display device, it is necessary to form a micro color filter which is plane-divided into red, green and blue ternary color components corresponding to each pixel. An active matrix liquid crystal display device has a structure in which a drive substrate on which pixel electrodes and thin film transistors for switching are integrated and a counter substrate on which a counter electrode is formed are bonded to each other, and a liquid crystal layer is held in a gap between them. ing. In a conventional active matrix type color liquid crystal display device, a micro color filter is formed on the counter substrate side. However, in such a structure, when the drive substrate and the counter substrate are attached to each other, it is necessary to provide a certain margin for the overlay accuracy of the two, which sacrifices the aperture ratio of the pixel. In a reflective full-color liquid crystal display device that does not use a backlight, it is necessary to maximize the aperture ratio of pixels in order to obtain a bright screen. However, in the conventional structure in which the micro color filter is provided on the counter substrate, the aperture ratio is limited by the overlay accuracy of the two.

[0008]

In order to solve the above-mentioned problems of the prior art, the first aspect of the present invention proposes a reflective guest-host liquid crystal display device having the following configuration. That is, the reflective guest-host liquid crystal display device according to the present invention has, as a basic configuration, a substrate on which a transparent electrode is formed and receives incident light, and a substrate on which a reflective electrode is formed and which has a predetermined gap. The other substrate is arranged to face the substrate, and the electro-optical body which is held in the gap and performs optical modulation according to the voltage applied between the transparent electrode and the reflective electrode. The electro-optical body contains a guest-host type liquid crystal layer containing a dichroic dye and uniformly oriented along the transparent electrode, and has a predetermined optical anisotropic axis to form a film along the reflective electrode. And a retardation plate layer that has been formed. The liquid crystal layer changes between an absorption state and a transmission state according to an applied voltage. In the absorption state, while the first vibration component included in the incident light is substantially absorbed, the second vibration component orthogonal to the first vibration component is substantially transmitted. In the transmission state, both vibration components are substantially transmitted. The retardation layer is interposed in the round trip path of the second vibration component reflected by the reflective electrode, converts the second vibration component into the first vibration component, and re-enters the liquid crystal layer in the absorbing state. Further, the transparent electrode and the reflective electrode face each other to define a plurality of pixels, and the apparatus includes color filter means to allocate incident light of different wavelengths to each pixel. Characteristically, the retardation layer is divided for each pixel, and its thickness is adjusted according to the corresponding wavelength. In one embodiment,
The color filter means is made of a dye introduced into the phase difference plate layer itself divided for each pixel, and selectively transmits incident light of a corresponding wavelength component.

The first aspect of the present invention described above includes a method of manufacturing a reflective guest-host liquid crystal display device. This reflective guest-host liquid crystal display device includes a transparent electrode substrate, a reflective electrode substrate bonded to the transparent electrode substrate through a predetermined gap, a guest-host liquid crystal layer held on the transparent electrode substrate side in the gap, and a reflection in the gap. The phase difference plate layer is held on the electrode substrate side and divided for each pixel of the three primary colors. The reflective guest-host liquid crystal display device having such a structure is manufactured by the following steps according to the present invention. First, in the first step, a retardation layer having a thickness corresponding to the wavelength of the first color is formed on the surface of the reflective electrode substrate and then selectively patterned to leave only the pixels to which the first color is assigned. Next, a second step is performed to form a retardation layer on the surface of the reflective electrode substrate with a thickness corresponding to the wavelength of the second color, and then selectively pattern it to leave only the pixels to which the second color is assigned. . Finally, the third step is performed to form a retardation film layer on the surface of the reflective electrode substrate with a thickness corresponding to the wavelength of the third color, and then selectively pattern it to leave only the pixel to which the third color is assigned. .

According to a second aspect of the present invention, a reflective guest-host liquid crystal display device includes a transparent substrate having an opposite electrode on the incident side, a pixel electrode on the reflective side, and a switching element for driving the pixel electrode. And a transparent substrate and a guest-host type liquid crystal layer having a dichroic dye added thereto, which is held between the transparent substrate and the reflective substrate bonded to each other with a predetermined gap, and the reflective substrate and the liquid crystal. And a retardation plate layer that is interposed between the layers to generate a phase difference of a quarter wavelength with respect to the incident light. Characteristically, the reflective substrate is provided with a color filter layer that is patterned in a plane division in alignment with each pixel electrode, and assigns incident light of different wavelengths to each pixel electrode for color display. It is possible. Further, in one aspect, the retardation plate layer is also plane-divided corresponding to each pixel electrode, and imparts a quarter-wave retardation to incident light assigned to the corresponding pixel electrode. Thus, the thickness of the retardation film layer is adjusted for each pixel electrode. Specifically, on the reflective substrate, a light reflection layer, a color filter layer, a retardation plate layer and a pixel electrode are laminated in this order from the bottom, and each of the plane-divided color filter layer and retardation plate layer is combined. The thickness is kept constant over all pixel electrodes, and the thickness of the phase difference plate layer is adjusted for each pixel electrode by changing the ratio of the thickness of the color filter layer to the phase difference plate layer for each pixel electrode.

The second aspect of the present invention described above is a reflection type guest host in which at least a switching element, a light reflection layer, a color filter layer, a retardation layer, a pixel electrode, a guest host liquid crystal layer and a counter electrode are integrated. It also includes a method of manufacturing a liquid crystal display device. In the manufacturing method, first, in the first step, the switching element and the light reflection layer are formed on one of the substrates. In the second step, a plane-divided color filter layer is formed on the light reflection layer so that it can be aligned with the pixel electrode in advance. Proceeding to the third step, a retardation layer is also formed on the color filter layer in a plane division manner. Go to the fourth step,
A pixel electrode is formed on the retardation film layer in alignment with each of the plane-divided color filter layers, and the pixel electrode is connected to a corresponding switching element. Proceeding to the fifth step, the other substrate on which the counter electrode is formed in advance is bonded to the one substrate with a predetermined gap. Finally, in the sixth step, a guest-host liquid crystal layer is introduced into the gap. Through the above steps, the reflection type guest-host liquid crystal display device is completed. Preferably, in the second step, the color filter layer is formed by changing the thickness for each pixel electrode, and in the third step, the color filter layer is formed on the whole pixel electrode so that the surface is flat. The phase difference layer is formed.

The vibration component along the alignment direction of the liquid crystal layer in the absorbing state is absorbed by the dichroic dye aligned in the same direction. However, the vibration component orthogonal to this is hardly absorbed because it intersects with the orientation direction of the dye molecule. In other words, it receives almost no light modulation. However, according to the present invention, this vibration component is incident on the retardation plate layer after passing through the liquid crystal layer, and further reflected by the reflective electrode and then passes through the retardation plate layer again. Therefore, this vibration component has passed twice through the phase difference plate layer functioning as a quarter-wave plate, and the vibration direction (polarization direction) is rotated by 90 °. Then, the vibration component is absorbed because it matches the alignment direction of the liquid crystal in the absorbing state. In this way, all the vibration components included in the incident light are always absorbed in either the forward path or the return path, so that an external polarizing plate is not required. Therefore, even if the polarizing plate is removed, a contrast substantially equal to that of the transmission type guest-host liquid crystal display device with the polarizing plate can be obtained.

By the way, the retardation plate layer has a predetermined optical anisotropic axis and has a so-called refractive index anisotropy. In order for this retardation plate layer to function as a quarter-wave plate, Δn should be between a specific wavelength (λ) and Δn that represents the degree of refractive index anisotropy.
・ The relationship of d = λ / 4 must be established. Here, d represents the thickness of the retardation plate layer. Therefore, in the first aspect of the present invention, the thickness d of the retardation layer is adjusted so that the retardation Δn · d becomes λ / 4 in accordance with the wavelength component transmitted through each pixel.

Further, according to the second aspect of the present invention, the color filter is provided not on the incident side substrate on which the counter electrode is formed but on the reflection side substrate on which the pixel electrodes and switching elements are integrated. Since the micro color filter and the pixel electrode are formed on the same substrate, they can be aligned with each other with high accuracy. Therefore, it is not necessary to include an extra margin in the overlay accuracy when joining the substrate on the incident side and the substrate on the reflective side as in the conventional case, and the aperture ratio of the pixel can be improved accordingly.

[0015]

FIG. 1 shows a first embodiment of a reflective guest-host liquid crystal display device according to the present invention.
As shown in (A), this device is assembled using an upper substrate (transparent electrode substrate) 1 and a lower substrate (reflection electrode substrate) 2. The upper substrate 1 is made of glass or the like, has a transparent electrode 3 formed thereon, and receives incident light. This transparent electrode 3
Are patterned in stripes along the row direction, for example. Reflective electrodes 4r, 4g, 4b are formed on the lower substrate 2. The reflective electrodes are patterned in stripes along the column direction. Therefore, the transparent electrodes 3 and the reflective electrodes 4r, 4g, 4b intersect in a matrix to define pixels, and a simple matrix type liquid crystal display device is obtained. Since this display device performs color display, one of the three primary colors of red, green, and blue is periodically assigned to each pixel. Specifically, the color filter 1 is provided on the reflective electrodes 4r, 4g, 4b.
3 are formed, and incident lights of different wavelengths corresponding to red, green, and blue are assigned to each pixel. The lower substrate 2 is opposed to the upper substrate 1 with a predetermined gap. An electro-optical body 5 is held in this gap, and a voltage applied between the transparent electrode 3 and the reflective electrodes 4r, 4g, 4b (hereinafter, referred to as the reflective electrode 4 when it is not necessary to distinguish between the three primary colors). The incident light is modulated in accordance with. The electro-optical body 5 has a laminated structure including a guest-host type liquid crystal layer 6 and a retardation layer 7. The liquid crystal layer 6 contains, for example, a black dichroic dye 8 and is uniformly aligned along the transparent electrode 3. The retardation layer 7 has a predetermined optical anisotropic axis and is formed along the color filter 13. The surface of this retardation layer 7 is covered with an alignment film 11. Similarly, the transparent electrode 3 formed on the surface of the upper substrate 1 is also covered with the alignment film 10.

The liquid crystal layer 6 changes between an absorption state and a transmission state according to the applied voltage. (A) represents an absorption state,
While the first vibration component X contained in the incident light is substantially absorbed, the second vibration component Y orthogonal to the first vibration component is substantially transmitted. Conversely, in the transmission state, both vibration components X and Y are substantially transmitted. As shown in the drawing, the nematic liquid crystal molecules 9 are horizontally aligned in the absorption state, and the dichroic dye 8 is also horizontally aligned accordingly. In this example, the absorption state is realized without applying a voltage, and the state changes to the transmission state when a voltage is applied. Therefore, the nematic liquid crystal molecules 9 have a positive dielectric anisotropy and are previously controlled to be horizontally aligned (homogeneous alignment) by the pair of upper and lower alignment films 10 and 11. Conversely, the illustrated absorption state can be realized by applying a voltage. In this case, the nematic liquid crystal molecule 9 having a negative dielectric anisotropy is used. In such a configuration, the phase difference plate layer 7 is interposed in the reciprocating path of the second vibration component Y reflected by the reflection electrode 4, converts the second vibration component Y into the first vibration component X, and is in an absorbing state. The light re-enters the liquid crystal layer 6.

The retardation layer 7 functions as a quarter-wave plate. As shown in (B), the optical anisotropic axis intersects with the alignment direction of the liquid crystal layer in the absorbing state at an angle of 45 °. The vibration direction of the second vibration component Y (linearly polarized light component) transmitted through the absorption state is orthogonal to the alignment direction. The second vibration component Y crosses the optically anisotropic axis at an angle of 45 °. The second vibration component Y (linearly polarized light component) is converted into circularly polarized light when passing through the quarter wavelength plate. When this circularly polarized light is reflected by the reflective electrode and then enters the quarter-wave plate again,
It is converted into linearly polarized light (first vibration component X) orthogonal to the vibration component Y. The first vibration component X converted in this way is absorbed by the liquid crystal layer 6 in the absorbing state.

As described above, since the present display device performs color display, the row-shaped transparent electrodes 3 and the column-shaped reflective electrodes 4 face each other to define a plurality of pixels, and each pixel has a different wavelength. A color filter 13 for allocating incident light (red green blue) is formed. As a feature of the present invention, the retardation layer 7 is divided for each pixel, and its thickness is adjusted according to the corresponding wavelength. As shown in (A), the retardation film layer 7 is divided corresponding to the pixels, and the thickness differs depending on the color of the pixel below. The thickness d depends on the reflected light wavelength assigned to each pixel and the retardation Δn ·
The d is adjusted to be λ / 4. For example, when an optical material having a refractive index anisotropy Δn of 0.2 is used for the retardation layer 7, the appropriate thickness of the portion corresponding to the red pixel is λ = 7.
When it is 00 nm, d = 875 nm. Similarly, if the portion corresponding to the green pixel is λ = 546 nm, the appropriate thickness is d = 685 nm. Further, when the portion corresponding to the blue pixel is λ = 436 nm, the appropriate thickness is d = 545 nm. As described above, in the present invention, by controlling the thickness of the retardation film layer 7 for each pixel, a good contrast can be obtained over the entire wavelength range.

FIG. 2 shows the transmission state of the liquid crystal layer 6, in which the nematic liquid crystal molecules 9 are vertically aligned. In accordance with this, the dichroic dye 8 is also vertically aligned. Therefore, both the first vibration component X and the second vibration component Y are almost entirely transmitted through the liquid crystal layer 6. The reflected light only exchanges the first vibration component and the second vibration component with each other, and is not subjected to any optical modulation. The nematic liquid crystal molecules 9 having a positive dielectric anisotropy rise in response to an applied voltage and change to vertical alignment. still,
As described above, it is also possible to realize the vertical alignment of the nematic liquid crystal molecules 9 without applying a voltage. That is, the alignment film 1
The nematic liquid crystal molecules 9 can be vertically aligned (homeotropically aligned) by appropriately selecting the materials 0 and 11 and the like. In this case, nematic liquid crystal molecules 9 having a negative dielectric anisotropy are used, and the orientation is switched to horizontal alignment according to the voltage application. At this time, to keep the horizontal orientation direction constant,
The nematic liquid crystal molecules 9 are pretilted in advance in the vertically aligned state.

With reference to FIGS. 1 and 2, the specific structure of the first embodiment will be described in detail. In the present liquid crystal display device, the liquid crystal layer 6 is composed of nematic liquid crystal molecules 9, and a black dichroic dye 8 is added therein.
The liquid crystal layer 6 containing the dichroic dye 8 is horizontally or vertically aligned. The reflective electrode 4 is made of a metal film having a high reflectivity such as aluminum and silver, so that the present display device is a reflective display. A color filter 13 is formed on the reflective electrode 4 and assigns incident light of a different wavelength to each pixel. This color filter 13 is formed by, for example, a printing method. On the color filter 13, a transparent retardation plate layer 7 capable of imparting a retardation of λ / 4 to a wavelength in the visible range (400 to 700 nm).
Are formed. The retardation layer 7 is divided for each pixel and the thickness thereof is controlled according to the wavelength in order to properly impart a retardation of λ / 4 to the wavelengths of the three primary colors of red, green and blue. When the liquid crystal layer 6 is horizontally aligned, the optical anisotropic axis of the retardation layer 7 is set to make an angle of 45 ° with the alignment direction. When the liquid crystal layer 6 is vertically aligned in advance, the optical anisotropic axis is set to have an angle of 45 ° with respect to the cosine direction of the liquid crystal molecules 9 having a pretilt angle. The retardation layer 7 is formed of a polymer liquid crystal material containing liquid crystal molecules uniaxially aligned along the optically anisotropic axis. For example, a polymer liquid crystal material (aromatic polyester, siloxane resin, etc. that is a liquid crystal polymer) is used, and this is arranged on the substrate at the temperature of the nematic phase or the smectic A phase, and then returned to room temperature and fixed. By doing so, the uniaxially anisotropic retardation plate layer 7 is obtained. If the λ / 4 layer is formed using a polymer liquid crystal material having a high refractive index anisotropy (Δn), the film thickness can be made sufficiently thin. Therefore, since the λ / 4 layer can be formed on the color filter 13 by coating, the manufacturing process of the display device can be simplified. An alignment film 11, which also serves as a passivation layer, is interposed between the retardation layer 7 and the liquid crystal layer 6. A photosensitive material can be used as the alignment film 11, and the alignment film 11 can be patterned by exposure and development. As the photosensitive material, for example, an aqueous solution of polyvinyl alcohol (PVA) to which a small amount of ammonium dichromate for causing a photocrosslinking reaction is added can be used, and the photosensitive material can be applied onto a substrate by spin coating or the like. PVA has an excellent alignment property with respect to the liquid crystal layer 6, and is suitable as the alignment film 11 that also serves as passivation.

The operation of the reflective guest-host liquid crystal display device according to the present invention will be described in detail with reference to FIGS. 1 and 2. Consider a case where light is incident from the outside in the horizontal alignment state shown in FIG. First, the incident light can be considered separately as a first vibration component X and a second vibration component Y which are polarization components orthogonal to each other. Since the first vibration component X is the same as the orientation direction of the liquid crystal layer 6, it is absorbed by the black dichroic dye 8 oriented in the same direction. However, the second vibration component Y is not absorbed at all because it is orthogonal to the orientation direction of the dye molecules. Therefore, the second vibration component Y passes through the liquid crystal layer 6 and further enters the retardation layer 7 functioning as a quarter-wave plate. Further, it is reflected by the reflective electrode 4 after passing through the color filter 13 and again passes through the retardation layer 7. The second vibration component Y has passed through the retardation plate layer 7 twice in a reciprocating manner, and the polarization direction is rotated by 90 °. Then, the light is absorbed because it now matches the alignment direction of the liquid crystal layer 6. In this way, all the vibration components contained in the incident light are absorbed in either the outward path or the return path, so that a contrast comparable to a transmissive guest host liquid crystal display device with a polarizing plate can be obtained without the polarizing plate. On the other hand, in the transmissive state, wavelength selection for each pixel is performed by the color filter 13 according to the three primary colors, and desired color display is possible.

A method of forming the retardation film layer 7 having different thicknesses for each pixel will be described in detail with reference to FIG. First, step (a)
Then, after cleaning the substrate 2 made of glass or the like, a metal film is formed on the surface thereof by a sputtering method or a vacuum evaporation method. This metal film is patterned into a predetermined shape to form the reflective electrode 4. Here, in order to distinguish the reflective electrodes to which red, green, and blue are respectively assigned, reference numerals 4r, 4g, and 4b are used. In this example, an example will be described in which the retardation layer 7 having a certain thickness is selectively formed on the reflective electrode 4g to which green is assigned, for example. After forming the reflective electrode 4, the color filter 13 is formed thereon. The color filter 13 is colored red green blue corresponding to the reflective electrodes 4r, 4g, 4b and can be formed by, for example, a known printing method. This color filter 13 is subjected to a base rubbing process along a predetermined direction. Further, a polymer liquid crystal material is applied on the color filter 13. This polymer liquid crystal material is, for example, a side chain polymer liquid crystal having a benzoate ester mesogen as a pendant. This polymer liquid crystal is dissolved in a solution in which cyclohexane and methyl ethyl ketone are mixed at a ratio of 8: 2 by 3 to 5% by weight. This solution is spin-coated, for example, to form a polymer liquid crystal film on the glass substrate 2.
At this time, the thickness of the polymer liquid crystal material is optimized by adjusting the rotation speed of spin coating. Thereafter, the substrate is heated, and the polymer liquid crystal is once heated to an optically isotropic state. Then, the heating temperature is gradually lowered to return to room temperature through the nematic phase. In the nematic phase, the polymer liquid crystals are arranged along the rubbing direction of the base of the color filter 13, and a desired uniaxial orientation is obtained. This uniaxial orientation state is fixed by returning the substrate 2 to room temperature. By such an annealing treatment, the liquid crystal molecules contained in the polymer liquid crystal material are uniaxially aligned, and the desired retardation plate layer 7 is obtained.

Proceeding to step (b), the photosensitive material 11a is applied onto the retardation plate layer 7. For example, an aqueous solution of PVA (0.1 to 5 wt%) is spin-coated. At this time, for example, a small amount of ammonium bichromate is added to the aqueous solution to cause a photocrosslinking reaction of PVA. Next, in step (c), a desired mask M is used to perform exposure processing with a mercury lamp or a xenon lamp. Further proceeding to the step (d), when the water-washing treatment is performed, the unexposed portion of the photosensitive material 11a is dissolved in water, and the alignment film 11 made of the patterned PVA polymer is formed. Finally, in step (e), the substrate 2 is dipped in n-butanone using the alignment film 11 as a mask, and the retardation layer 7 not covered with the alignment film 11
The portion of is melted, and the pattern is formed by matching with the reflective electrode 4g. In this way, the retardation layer 7 having a thickness according to the wavelength can be selectively formed for each pixel. Then, the alignment film 11 is rubbed along a predetermined direction to realize horizontal alignment of the guest-host liquid crystal layer in contact therewith, and to block both of the polymer liquid crystal and the guest-host liquid crystal. Layer (passivation layer)
Function as

FIG. 4 is a schematic partial sectional view showing a second embodiment of a reflective guest-host liquid crystal display device according to the present invention. Basically, it has the same configuration as that of the first embodiment shown in FIG. 1, and corresponding parts are given corresponding reference numerals to facilitate understanding. As shown in the figure, the upper substrate 1 has a counter electrode 3a formed of a transparent electrode over the entire surface, and the lower substrate 2 has a pixel electrode 4a made of a reflective electrode subdivided in a matrix. ing. That is, in contrast to the simple matrix type in the above example, the present example is the active matrix type. Individual pixel electrode 4
One of the three primary colors of red, green, and blue is assigned to a. On the inner surface of the lower substrate 2, in addition to the pixel electrodes 4a patterned in a matrix, thin film transistors TFT are also formed correspondingly. This TFT is the pixel electrode 4
It becomes a switching element that individually drives a. That is, the TFT is selectively turned on / off to write a signal voltage to the corresponding pixel electrode 4a. Drain region D of TFT
Is connected to the pixel electrode 4a, and the source region S is the signal line 2
Connected to 1. The gate electrode G of the TFT is connected to a gate line. A storage capacitor Cs is also formed corresponding to each pixel electrode 4a. The pixel electrode 4a is the flattening film 2
2, the TFT, the storage capacitor Cs, the signal line 2
It is electrically separated from 1. On the other hand, the counter electrode 3a is entirely formed on the inner surface of the upper substrate 1. An electro-optical body 5 is held in the gap between the two substrates 1 and 2 which are opposed to each other with a predetermined gap therebetween. When the signal voltage is written in the pixel electrode 4a, a potential difference is generated between the pixel electrode 4a and the facing counter electrode 3a, and the electro-optical body 5 changes between the absorption state and the transmission state. Since this optical change appears for each pixel electrode, a desired image can be displayed. A TFT, a storage capacitor Cs, a signal line 21 and the like are arranged below the pixel electrode 4a. Since these components do not intervene in the incident optical path, they do not affect the pixel aperture ratio. In other words,
The entire area of the pixel electrode 4a can be used as it is as a pixel opening, and an extremely bright display can be performed.

The guest-host type liquid crystal layer 6 and the retardation film layer 7 constituting the electro-optical body 5 are separated from each other by an alignment film 11. The alignment film 11 is made of a photosensitive material and is patterned by aligning it with the pixel electrodes 4a by exposure and development processing. The retardation film layer 7 is similarly patterned for each pixel electrode 4a using the patterned orientation film 11 as a mask. In this example, the patterned retardation layer 7 includes colored regions 7r, 7g, and 7b which are divided into red, green, and blue, and forms a color filter by matching with the pixel electrode 4a corresponding to each colored region. There is. That is, the color filter of this example is composed of the pigment introduced into the retardation layer 7 itself divided for each pixel, and selectively transmits the incident light of the corresponding wavelength component. In addition, the colored regions 7 of the phase difference plate layer 7 divided for each pixel
The thicknesses of r, 7g, and 7b are adjusted according to the corresponding wavelengths as shown in the figure.

FIG. 5 is a process chart showing a method of manufacturing the color filter shown in FIG. First, in step (a), the pixel electrode 4a is patterned on the substrate 2. After the surface is oriented, the retardation layer 7R is formed. In this example, since a color filter composed of three primary colors of red, green and blue is formed, the retardation plate layer 7R used in advance is colored in red. For example, a substituent that absorbs a red wavelength component is introduced into the side chain of the polymer material that constitutes the retardation layer. Alternatively, a normal red dye that does not exhibit dichroism may be mixed in the liquid crystal polymer material. In this way, the retardation layer 7R colored in red in advance is formed on the substrate 2 with an optimum thickness. This specific film forming method is the same as the film forming method shown in FIG.
Next, in step (b), the photosensitive material 11a is applied onto the red retardation layer 7R. In step (c), the photosensitive material 11a is exposed through the mask M. In step (d), the substrate 2 is washed with water to dissolve and remove the unexposed portion of the photosensitive material 11a, and a developing process is performed. As a result, the patterned alignment film 11 is formed in alignment with the specific pixel electrode 4a. Process (e)
Then, using the alignment film 11 as a mask, the red retardation layer 7R
The red area 7r that is aligned with the pixel electrode 4a by etching
Process into Similarly, the green region and the blue region can be formed on the corresponding pixel electrodes 4a with a desired thickness.

Next, a third embodiment of the reflective guest-host liquid crystal display device according to the present invention will be described in detail with reference to FIG. Basically, it is an active matrix type similar to the second embodiment shown in FIG. 4, and corresponding parts are given corresponding reference numerals to facilitate understanding. In the figure,
Reference numeral 2 denotes a reflection-side substrate on which TFTs and the like are formed, and 1 indicates an incidence-side glass substrate on which the counter electrode 3a is formed.
Reference numeral b denotes an upper layer pixel electrode made of a transparent conductive film such as ITO. On the other hand, 4a indicates a lower layer pixel electrode made of a reflective metal film such as aluminum. The corresponding upper layer pixel electrode 4b and lower layer pixel electrode 4a are held at the same potential. The color filter 13 and the phase difference plate layer 7 are held between the pixel electrodes 4b and 4a. Thin film transistor T
The FT includes a source region S, a drain region D, and a gate electrode G. The drain region D is the above-mentioned upper layer pixel electrode 4
b and the lower layer pixel electrode 4a are electrically connected. Reference numeral 25 is an etching stopper aligned with the gate electrode G. 6 is a guest-host type liquid crystal layer containing a black dichroic dye 8. As described above, the present liquid crystal display device integrally includes the transparent substrate 1 located on the incident side and provided with the counter electrode 3a, the pixel electrodes 4b and 4a located on the reflective side, and the thin film transistor TFT for driving the pixel electrodes 4b and 4a. A guest-host type liquid crystal layer 6 which is held between the reflective substrate 2 and the transparent substrate 1 and the reflective substrate 2 which are bonded to each other through a predetermined gap and to which the dichroic dye 8 is added, the reflective substrate 2 and the liquid crystal. And a retardation plate layer 7 which is interposed between the layers 6 and generates a retardation of a quarter wavelength with respect to the incident light. Each pixel electrode (4b,
4a), and color filter layers 13r, 13g, 13b which are patterned in a plane division are formed.
Incident light of different wavelength is assigned to each pixel electrode (4b, 4a) to enable color display. In the figure, the color filter layer 13r is colored red, the color filter layer 13g is colored green, and the color filter layer 13b is colored.
Is colored blue.

As is apparent from FIG. 7, the feature of this embodiment is that the color filter layers 13r, 13g and 13b are aligned with the pixel electrodes (4b and 4a) and provided on the substrate 2 on the reflection side. . As a result, the pixel electrode and the color filter layer can be accurately overlapped for each color,
The aperture ratio of the pixel can be remarkably improved. On the other hand, in the conventional structure, the color filter is formed on the substrate 1 on the incident side. In this case, when both substrates 1 and 2 are bonded to each other to be assembled into a panel, a margin is taken into consideration in consideration of overlay accuracy between a glass substrate on the opposite side on which a color filter is formed and a substrate on the driving side on which TFTs and the like are integrated. I had to make a design that I had. For this reason, the pixel aperture of the panel must be smaller than the pixel electrode.

Next, the operating principle of the third embodiment shown in FIG. 7 will be briefly described. When the potential of the gate electrode G is low level, the reflective pixel electrode 4 connected to the drain region D
Since no signal voltage is applied to a and the transparent pixel electrode 4b, there is no change in the homogeneously aligned liquid crystal layer 6. One linearly polarized light component of the light incident from the glass substrate 1 on the opposite side is absorbed by the guest-host liquid crystal layer 6, and the other linearly polarized light component orthogonal to this is passed. The other linearly polarized light component becomes circularly polarized light by passing through the phase difference plate layer 7. Further, the light reflected by the reflective pixel electrode 4a and passing through the return path retardation layer 7 becomes linearly polarized light. In this case, since the phase is rotated by 90 °, it is absorbed by the guest-host liquid crystal layer 6. With the above, a black display can be obtained.
On the other hand, when the potential of the gate electrode G is high level,
Since a signal voltage is applied to the reflective pixel electrode 4a and the transparent pixel electrode 4b, a potential difference is generated between the reflective pixel electrode 4a and the transparent pixel electrode 4a, and the long axis direction of the liquid crystal molecules included in the liquid crystal layer 6 is aligned parallel to the electric field. In this case, since the light incident from the glass substrate 1 on the opposite side is not linearly polarized by the liquid crystal layer 6, all the light is reflected by the reflective pixel electrode 4a and returns to the glass substrate 1 on the opposite side. Therefore, a white display is obtained. The above description is for the case where a liquid crystal having a positive dielectric anisotropy is used, but a liquid crystal having a negative dielectric anisotropy may be used and the initial alignment may be homeotropic.

Next, with reference to FIG. 7, a method of manufacturing the liquid crystal display device according to the third embodiment will be described. As described above, the liquid crystal display device of the present invention is a TFT that serves as a switching element,
Reflection pixel electrode 4a to be a light reflection layer, color filter layer 1
3, a retardation layer 7, a transparent pixel electrode 4b, a guest-host liquid crystal layer 6 and a counter electrode 3a are integrated in a reflective active matrix structure. This liquid crystal display device is manufactured by the following steps. First, in the first step,
The TFT and the reflective pixel electrode 4a are formed on the lower substrate 2. Proceeding to the second step, the color filter layers 13r, 13 are divided into planes in advance so as to be aligned with the transparent pixel electrode 4b.
g and 13b are formed on each reflective pixel electrode 4a. Specifically, first, a photoresist in which a red pigment is dispersed is applied on the substrate 2. This is exposed and developed to form the reflective pixel electrode 4
The color filter layer 13r matching a is processed. The same exposure and development process is performed on the photoresist in which the green pigment is dispersed and the photoresist in which the blue pigment is dispersed, to process the green color filter layer 13g and the blue color filter layer 13b, respectively. Subsequently, in the third step, the retardation plate layer 7 is formed on each of the color filter layers 13r, 13g, 13b in the same manner as a plane. The plane division of the retardation layer 7 can be performed by photolithography and etching. Proceeding to the fourth step, the transparent pixel electrode 4b is formed on the retardation layer 7 in alignment with each of the plane-divided color filter layers 13r, 13g, 13b. The transparent pixel electrode 4b is connected to the drain region D of the corresponding TFT. As described above, in the present embodiment, the transparent pixel electrode 4b is used in addition to the reflective pixel electrode 4a, and a signal voltage can be applied between the liquid crystal layer 6 and the counter electrode 3a so as to be in direct contact therewith. As a result, the value of the effective signal voltage applied to the liquid crystal layer 6 increases. By setting the reflective pixel electrode 4a and the transparent pixel electrode 4b at the same potential, the retardation plate layer 7 and the color filter layer 13 that are interposed therebetween are not adversely affected. Proceeding to the fifth step, the other substrate 1 on which the counter electrode 3a is formed in advance is bonded to the one substrate 2 with a predetermined gap. Finally, perform the sixth step,
A guest-host liquid crystal layer 6 is introduced into the gap between the substrates 1 and 2. As described above, a reflection type guest-host liquid crystal display device having an active matrix structure can be completed.

FIG. 8 is a partial sectional view showing a fourth embodiment of a reflective guest-host liquid crystal display device according to the present invention. Parts corresponding to those of the third embodiment shown in FIG. 7 are designated by corresponding reference numerals to facilitate understanding. Similarly to the third embodiment, the retardation layer 7 is also divided into planes corresponding to the individual pixel electrodes 4a. As a characteristic matter, this phase-divided retardation plate layer 7 is configured to give a phase difference of exactly a quarter wavelength to the incident light of each color assigned to the corresponding pixel electrode 4a. The thickness of the plate layer 7 is adjusted for each pixel electrode. Specifically, the reflective pixel electrode 4a and the color filter layer 1 are provided on the reflective substrate 2 in order from the bottom.
3, the phase difference plate layer 7 and the transparent pixel electrode 4b are laminated, and the total thickness of the color filter layer 13 and the phase difference plate layer 7 which are plane-divided respectively are kept constant over all the pixel electrodes. Then, the color filter layers 13r,
The thickness of the phase difference plate layer 7 is adjusted for each pixel electrode by changing the ratio of the thickness of the phase difference plate layer 7 to 13g, 13b. That is, the film thicknesses of the phase difference plate layers 7 corresponding to the respective colors of red, green and blue are different, and the respective film thicknesses are adjusted so that the phase difference becomes λ / 4 according to the reflected light wavelength of the corresponding pixel. As the 4 / λ retardation plate, for example, a liquid crystal polymer can be used. For example, when a liquid crystal polymer material having a refractive index anisotropy of Δn = 0.2 is used, the film thickness of a suitable liquid crystal polymer material corresponding to red, green and blue is 875 nm for a red component of λ = 700 nm. And 685 nm is calculated for the red component of λ = 546 nm, and 545 nm is set for the blue component of λ = 436 nm.

Next, with reference to FIG. 8, a method of manufacturing the liquid crystal display device according to the fourth embodiment will be described. The characteristic point is that the color filter layers 13r, 1
3g, 13b are formed, and then each color filter layer 13r, 13g, 1 is formed so that the surface is flat across all pixels.
The retardation plate layers 7r, 7g, 7b are formed on 3b. That is, by appropriately controlling the film thickness of the color filter layer 13 formed below the phase difference plate layer 7 for each color, the film thickness of the phase difference plate layer 7 coated on the color filter layer 13 is controlled. Set automatically. As described above, the red, green, and blue color filter layers 13r, 13g, and 13b can be formed using, for example, a photosensitive photoresist in which pigments are dispersed. In this case, each color filter layer 13r, 13
g and 13b are formed separately. As a coating method, for example, when a spinner is used, the film thickness of the color filter layers of red, green and blue can be easily controlled by adjusting the number of rotations of the spinner. A retardation layer 7 made of a liquid crystal polymer material is applied onto the color filter layers 13r, 13g, 13b having an appropriately controlled film thickness by, for example, a spinner. In this case, each color filter layer 13
Since the surface steps of r, 13g and 13b are automatically flattened, the film thicknesses of the retardation plate layers 7r, 7g and 7b corresponding to red, green and blue can be mutually changed as shown in FIG.
There is a concern that the white balance may be lost by changing the film thickness of the retardation layer 7 for each color, but this problem can be solved by adjusting the concentration of the pigment dispersed in the photoresist for each color. As described above, by controlling the film thickness of the retardation film layer 7 for each color, a good display contrast can be obtained over the entire wavelength region of the visible light region.

[0033]

As described above, according to the present invention,
A reflection electrode is formed inside the guest-host liquid crystal display device to make it a reflection type, and a retardation plate layer functioning as a quarter-wave plate is formed on the reflection electrode. The optical anisotropic axis (optical principal axis) is set to be inclined by 45 ° with respect to the orientation direction of the guest-host liquid crystal. With such a configuration, it is possible to provide a bright reflective liquid crystal display device that does not require a polarizing plate and has high contrast. In particular, when performing color display, the retardation plate layer is divided for each pixel and its thickness is adjusted according to the wavelengths of the corresponding three primary colors. That is, by controlling the thickness of the retardation film layer for each of the three primary color pixels, it is possible to obtain a good contrast over the entire wavelength region and suppress coloring or the like during black display. Further, by providing the micro color filter not on the counter substrate side but on the driving substrate side on which the TFT is formed, the pixel aperture ratio can be improved and the image quality such as contrast can be improved.

[Brief description of the drawings]

FIG. 1 is a sectional view and a plan view showing a first embodiment of a reflective guest-host liquid crystal display device according to the present invention.

FIG. 2 is a cross-sectional view for explaining the operation of the reflective guest-host liquid crystal display device shown in FIG.

3A to 3D are process diagrams showing a method for forming a retardation layer incorporated in the reflective guest-host liquid crystal display device shown in FIG.

FIG. 4 is a schematic partial cross-sectional view showing a second embodiment of a reflective guest-host liquid crystal display device according to the present invention.

5A to 5C are process diagrams showing a method of manufacturing the reflective guest-host liquid crystal display device shown in FIG.

FIG. 6 is a cross-sectional view showing an example of a conventional guest-host liquid crystal display device.

FIG. 7 is a schematic partial cross-sectional view showing a third embodiment of a reflective guest-host liquid crystal display device according to the present invention.

FIG. 8 is a schematic partial cross-sectional view showing a fourth embodiment of a reflective guest-host liquid crystal display device according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Upper substrate, 2 ... Lower substrate, 3 ... Transparent electrode, 4 ... Reflection electrode, 5 ... Electro-optical body, 6 ... Liquid crystal layer, 7 ... Retardation plate layer,
8 ... Dichroic dye, 9 ... Nematic liquid crystal molecule, 10 ... Alignment film, 11 ... Alignment film, 13 ... Color filter

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsuo Urabe 6-735 Kitashinagawa, Shinagawa-ku, Tokyo Sony Corporation

Claims (8)

[Claims] 1. A substrate on which a transparent electrode is formed and receives incident light, and a substrate on which a reflective electrode is formed and which faces the one substrate with a predetermined gap, and which is held in the gap. An electro-optical body that performs light modulation according to a voltage applied between a transparent electrode and a reflective electrode, wherein the electro-optical body contains a dichroic dye and is uniformly distributed along the transparent electrode. The liquid crystal layer has a laminated structure including an oriented guest-host type liquid crystal layer and a retardation layer having a predetermined optical anisotropic axis and formed along the reflective electrode. Changes into an absorption state and a transmission state, and in the absorption state, substantially absorbs the first vibration component contained in the incident light, while substantially transmitting the second vibration component orthogonal thereto,
In the transmissive state, both vibration components are substantially transmitted, and the phase difference plate layer is present in the reciprocating path of the second vibration component reflected by the reflecting electrode to convert the second vibration component into the first vibration component and absorb it. In the reflective guest-host liquid crystal display device that re-enters the liquid crystal layer in a state, the transparent electrode and the reflective electrode face each other to define a plurality of pixels, and incident light of different wavelengths is applied to each pixel. A reflective guest-host liquid crystal display device, characterized in that the retardation plate layer is divided for each pixel and the thickness thereof is adjusted according to the corresponding wavelength. 2. The color filter means is made of a pigment introduced into the phase difference plate layer itself divided for each pixel, and selectively transmits incident light of a corresponding wavelength component. The reflective guest-host liquid crystal display device described. 3. A transparent electrode substrate, a reflective electrode substrate bonded to the transparent electrode substrate via a predetermined gap, a guest-host liquid crystal layer held on the transparent electrode substrate side in the gap, and a reflective electrode substrate side in the gap. A method for manufacturing a reflection type guest-host liquid crystal display device, comprising: a retardation plate layer that is held and divided for each pixel of three primary colors, wherein the retardation plate layer has a thickness corresponding to the wavelength of the first color. After the film is formed on the surface of, the first step of selectively patterning and leaving only the pixels to which the first color is assigned, and the phase difference plate layer with the thickness corresponding to the wavelength of the second color on the surface of the reflective electrode substrate. After the film formation, the second step of selectively patterning and leaving only the pixels to which the second color is assigned, and forming the retardation layer on the surface of the reflective electrode substrate with a thickness corresponding to the wavelength of the third color Only the pixels to which the third color is assigned after selective patterning A method of manufacturing a reflective guest-host liquid crystal display device, which comprises performing a third step of leaving. 4. A transparent substrate located on the incident side and provided with a counter electrode, and a reflective substrate located on the reflective side and integrally provided with a pixel electrode and a switching element for driving the pixel electrode, with a predetermined gap therebetween. A guest-host type liquid crystal layer which is held between the bonded transparent substrate and reflective substrate and to which a dichroic dye is added, and which is interposed between the reflective substrate and the liquid crystal layer and has a wavelength of a quarter wavelength with respect to incident light. A reflective guest-host liquid crystal display device having a phase difference plate layer for producing a phase difference of, wherein a color filter layer is formed on the reflective substrate, the color filter layer being aligned in a plane and aligned with each pixel electrode. A guest-host liquid crystal display device is characterized in that incident light of different wavelength is assigned to each pixel electrode to enable color display. 5. The retardation layer is also divided into planes corresponding to individual pixel electrodes, and imparts a quarter-wavelength phase difference to incident light assigned to the corresponding pixel electrodes. The reflective guest-host liquid crystal display device according to claim 4, wherein the thickness of the retardation layer is adjusted for each pixel electrode. 6. A light reflection layer, a color filter layer, a retardation layer and a pixel electrode are laminated on the reflection substrate in order from the bottom, and each of the color filter layer and the retardation layer is divided into planes. The thickness is kept constant over all pixel electrodes, and the thickness of the retarder layer can be adjusted for each pixel electrode by changing the ratio of the thickness of the color filter layer and the retarder layer for each pixel electrode. The reflective guest-host liquid crystal display device according to claim 5. 7. A method of manufacturing a reflection type guest-host liquid crystal display device in which at least a switching element, a light reflection layer, a color filter layer, a retardation layer, a pixel electrode, a guest-host liquid crystal layer and a counter electrode are integrally built. Then, a first step of forming the switching element and the light reflection layer on one substrate, and a second step of forming a color filter layer on the light reflection layer by plane division so as to match the pixel electrode in advance. A third step of forming a retardation layer on the color filter layer in a plane division manner, and forming a pixel electrode on the retardation layer in alignment with each of the plane-divided color filter layers And a fourth step of connecting the pixel electrode to a corresponding switching element, and a fifth step of bonding the other substrate, on which the counter electrode is formed in advance, to the one substrate with a predetermined gap, And a sixth step of introducing a guest-host liquid crystal layer into the gap, which is a method for manufacturing a reflective guest-host liquid crystal display device. 8. The color filter layer is formed by changing the thickness for each pixel electrode in the second step, and the color filter layer is formed on the color filter layer so that the surface is flat over all the pixel electrodes in the third step. 8. The method for manufacturing a reflective guest-host liquid crystal display device according to claim 7, wherein a retardation layer is formed on.