KR20000029063A - Liquid crystal display device - Google Patents

Abstract

PURPOSE: A liquid crystal display device is provided to achieve a half- transmission type color liquid crystal device having a reflective film reflecting a back light source and an external light. CONSTITUTION: A front substrate(13) and a back substrate(14) are arranged to be opposite from each other, each having a liquid crystal driving electrode installed in an inside thereof. A liquid crystal layer(15) supported by being put between the front substrate and the back substrate, modulates a phase of an incident ray according to an applied voltage. A polarizing plate(11) has sequentially mounted a phase difference plate(12) and a polarizing shaft in an outside of one substrate of the front and the back substrates. A half-transmission, half-reflective layer is formed on the other substrate. A color filter layer(50) is arranged in the front substrate other than the half-transmission, half-reflective layer. A back light source(21) is arranged in a back of the other substrate. A cholesteric liquid crystal layer(60) selectively reflects a wavelength light between peak wavelengths having spectral transmittance quality of the color filter layer(50).

Description

Liquid crystal display {LIQUID CRYSTAL DISPLAY DEVICE}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color liquid crystal display device having a color filter layer. In particular, the present invention relates to a semi-transmissive color device having a back light source and a reflection film for reflecting external light, and capable of functioning as a reflective and transmissive color liquid crystal display. It relates to a liquid crystal display device.

Recently, liquid crystal displays have been applied to various fields such as displays, monitors, car navigation systems, function desk calculators, small and medium-sized televisions, and the like of notebook personal computers. In particular, since a reflective liquid crystal display device does not require a back light source (back light), application to a display for a mobile device such as a mobile PC that utilizes the advantages of low power consumption and thinness and light weight has been studied.

However, since the conventional reflection type liquid crystal display device displays by using external light like paper, if the environment itself is dark, the display screen becomes dark and cannot be used. In particular, it cannot be used at all in the dark.

In response to this problem, a semi-transmissive liquid crystal display device having a back light source has been developed in which a reflection plate is used as a transflective reflector, for example, a half mirror, in a dark environment so as to be used as a transmissive liquid crystal display device using a back light source.

In addition, a semi-transmissive liquid crystal display device in which microlenses are arranged for each pixel while providing pinholes corresponding to the pixels in the reflecting plate has been studied. According to this liquid crystal display element, when used as a reflective liquid crystal display device, the brightness of the display screen is reduced only by the pinhole compared with a normal reflective liquid crystal display device. In addition, when used as a transmissive liquid crystal display device, the brightness of the display screen similar to that of a conventional transmissive liquid crystal display device can be obtained by condensing the light emitted from the back light source with a microlens and passing the pinhole. As a result, the brightness of the transmissive liquid crystal display device is improved.

Such a transflective liquid crystal display device is capable of color display by providing a color filter layer. That is, the conventional transflective color liquid crystal display device is constructed by stacking a polarizing plate, a front substrate, a color filter layer, a driving electrode, a liquid crystal layer, a back substrate, a semi-reflective plate, and a back light source in this order. The color filter layer is provided in front of the reflecting plate, that is, the observer side.

Therefore, when the liquid crystal display device functions as a reflection type, external light incident from the front substrate side passes through the color filter layer and the liquid crystal layer, is reflected by the reflecting plate, and is again emitted to the outside through the liquid crystal layer and the color filter layer. That is, it becomes an optical path which permeates the color filter layer twice. Therefore, the color filter layer is used in the same way as a normal reflective color liquid crystal display device, and the color filter layer has a spectral characteristic such as obtaining desired coloration when light is transmitted twice.

When functioning as a reflective liquid crystal display device, the light source is external light, and it is impossible to freely control the light intensity. In the case where a polarizing plate or the like is used, the transmittance of the entire device is not sufficient. Therefore, when the maximum transmittance is 1, the spectral characteristic of the color filter layer is 0.1 or more. Therefore, such color filter layer spectral characteristics are designed to have a light color concentration such that sufficient coloring cannot be obtained only by passing through the color filter layer once.

In fact, the color filter layer is thinner than the spectral characteristics of the RGB color filter layer used in the conventional transmissive liquid crystal display device even in the spectral characteristics when light is transmitted twice.

On the other hand, when the transflective liquid crystal display device is used as the transmission type, the light emitted from the back light source transmits the color filter layer only once. Therefore, the spectral characteristics of the display in the case of functioning as the transmission type are the spectral characteristics when the color filter layer has been transmitted once, that is, the spectral characteristics of the color filter layers themselves, and when the color filter layer as described above is used, an extremely light color concentration is obtained. It becomes.

On the contrary, in the transflective liquid crystal display device, when the spectral characteristic used in the conventional transmissive liquid crystal display device is used as the color filter layer, the display brightness becomes remarkably insufficient when it functions as a reflection type.

As described above, in the conventional transflective color liquid crystal display device, the display brightness becomes remarkably dark when functioning as a reflection type, or when the display color concentration becomes remarkably thin when functioning as a transmission type, only one optical characteristic is used. Could not get

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and an object thereof is to provide a semi-transmissive liquid crystal display device capable of displaying sufficient brightness and color concentration even when functioning as a reflection type and when functioning as a transmission type.

1 is a cross-sectional view of a liquid crystal display device according to an embodiment of the present invention;

2 is an enlarged cross-sectional view of an array substrate of the liquid crystal display device;

3 is a plan view schematically illustrating the array substrate;

4A is a diagram schematically showing a state in which a first voltage is applied as a power source to a liquid crystal layer of the liquid crystal display device;

4B is a view schematically showing a state in which a second voltage is applied as a power source to a liquid crystal layer of the liquid crystal display device;

5 is a view schematically showing the operation principle of the selective reflection layer in the liquid crystal display device;

6 is a view showing spectral characteristics of a color filter layer in the liquid crystal display device;

FIG. 7 is a graph showing the transmittance wavelength dispersion characteristics of the cholesterol layer in the liquid crystal display device; FIG.

FIG. 8 is a diagram showing light emission spectra of daylight fluorescent lamps used for linear light sources of a rear light source; FIG.

9 is a view showing emission spectra of three wavelengths of light used for the linear light source of the rear light source;

10 is a view showing a color reproduction range of the liquid crystal display and a comparative example;

11 is a cross-sectional view of a liquid crystal display device according to a second embodiment of the present invention;

12 is a view schematically showing a state in which a first voltage is applied as a power source to a liquid crystal layer of the liquid crystal display according to the second embodiment;

13 is a view schematically showing a state in which a second voltage is applied as a power source to a liquid crystal layer of the liquid crystal display according to the second embodiment;

14 is a view showing spectral characteristics of a first color filter layer of a liquid crystal display according to a second embodiment;

FIG. 15 is a view showing an example of total color filter layer spectral characteristics when the liquid crystal display is functioned as a reflection type; FIG.

16 is a view showing an example of spectral characteristics of a second color filter layer of the liquid crystal display device;

FIG. 17 is a view showing an example of spectral characteristics of the total color filter layer when the liquid crystal display is functioned as a transmission type; FIG.

18 is a cross-sectional view illustrating a liquid crystal display device according to a first modification of the present invention;

19 is a cross-sectional view showing a liquid crystal display device according to a second modification of the present invention;

20 is a cross-sectional view showing a liquid crystal display device according to a third modification of the present invention;

FIG. 21 is a diagram showing the transmittance characteristics of the interference filter in the third modification. FIG.

10 --- LCD

11 --- polarizing layer

12 --- Phase difference plate

13 --- Glass substrate (array substrate)

14 --- Glass substrate (opposing substrate)

15 --- (TN) liquid crystal layer

16 --- pixel electrode

17 --- counter electrode

18 --- Selective reflection layer

18f --- Main surface (optional reflective layer)

18b --- Other principal plane (reflective layer)

19 --- Liquid crystal molecules (Cholesteric liquid crystal)

20 --- power

21 --- Back light source

22 --- light guide

23 --- scattering reflection layer

24 --- Linear Light Source

31 --- Thin Film Transistor (TFT)

32 --- signal line

33 --- Gate electrode

34 --- scanning line

35 --- oxide film

36 --- semiconductor film

37 --- low resistance semiconductor film

38 --- passivation film

39 --- Drain Electrode

40 --- contact hole

41 --- source electrode

42 --- Peripheral (sealing) of the board

43 --- Seal material

50 --- (first) color filter layer

60 --- cholesteric liquid crystal layer

70 --- Band Pass Filter

72 --- second color filter layer

74 --- interference filter

According to an aspect of the present invention, there is provided a liquid crystal display device comprising: a front substrate and a rear substrate disposed to face each other and having liquid crystal driving electrodes disposed on respective inner surfaces thereof; A liquid crystal layer interposed between the front substrate and the rear substrate and modulating a phase of incident light according to an applied voltage; A polarizing plate having a phase difference plate and a polarization axis which are sequentially mounted on the outer surfaces of one of the front substrate and the rear substrate; A semi-transmissive semi-reflective layer formed on the other substrate; A color filter layer disposed on the front substrate side rather than the semi-transmissive semi-reflective layer; A rear light source disposed on the back side of the other substrate; It is provided between the said semi-transmissive semi-reflective layer and the said back light source, and has the cholesteric liquid crystal layer which selectively reflects the wavelength light between adjacent peak wavelengths of the spectral transmittance characteristic of the said color filter layer.

According to a typical configuration of the liquid crystal display device of the present invention, light from the liquid crystal layer, selective reflection layer, and back light source of optical phase modulation functioning as a polarizing plate, a retardation plate, a color filter layer, and a variable retarder layer from the observation side in turn. The cholesteric liquid crystal layer which selects, reflects and transmits is arrange | positioned. By this cholesteric liquid crystal layer, the wavelength characteristic of a back light source is matched with the spectral transmittance characteristic of a color filter layer. In other words, the wavelength of the peak wavelength of the color filter layer is selectively reflected and blocked by the cholesteric liquid crystal layer, and the emission spectrum of the back light source is adjusted.

In addition, the liquid crystal display device according to the present invention comprises: a front substrate and a rear substrate disposed opposite to each other, the liquid crystal driving electrode is provided on each inner surface; A liquid crystal layer interposed between the front substrate and the rear substrate and modulating a phase of incident light according to an applied voltage; A polarizing plate having a phase difference plate and a polarization axis which are sequentially mounted on the outer surfaces of one of the front substrate and the rear substrate; A selective reflection layer formed on the other substrate and reflecting the first circularly polarized component of the incident light to transmit the first circularly polarized component and the second circularly polarized component of reverse rotation; A first color filter layer disposed on the front substrate side than the selective reflection layer; A back light source disposed on a back side of the back substrate; A band pass filter is disposed on the rear light source side rather than the selective reflection layer.

When the liquid crystal display device having the above-mentioned structure functions as a reflection type, since the incident light transmits the first color filter layer twice, the spectral transmittance characteristic of the first color filter layer is set so that the light transmitted twice is colored in a desired color. . Therefore, the spectral transmittance characteristic of the first color filter layer becomes a relatively broadband characteristic.

In the case of functioning as a transmission type, since the light from the back light source passes through the first color filter layer only once, the light source light is narrowed in advance through the band pass filter before entering the first color filter layer. The display characteristics of the same brightness and color concentration as in the transmissive color liquid crystal display device can be obtained.

As the band pass filter, a second color filter layer composed of a so-called interference filter and a color absorption filter can be used. As the interference filter, for example, a dielectric multilayer film in which a plurality of dielectrics are alternately stacked can be used. As the color absorbing filter, for example, one obtained by adding a pigment or dye to an organic medium can be used.

When the selective reflection layer is formed on the inner surface of the back substrate, and the color absorption filter is disposed below the selective reflection layer, it is possible to prevent the color concentration decrease due to color shift without generating a parallax due to the substrate thickness.

In addition, when the second color filter layer is provided on an array substrate having active elements such as a thin film transistor, the second color filter layer can be used as an interlayer insulating film to form a pixel electrode on a scanning line, a signal line, a thin film transistor, or the like. It can be realized.

Further, if the pigment is dispersed as a second color filter layer by dispersing or mixing a pigment in a selective reflection layer made of a cholesteric liquid crystal polymer or the like, the selective reflection layer and the second color filter layer can be the same layer, and thus the liquid crystal display device. The total number of floors can be reduced.

(Example)

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

First, the basic configuration of the liquid crystal display device 10 according to the present embodiment will be described. As shown in Figs. 1 to 4A, the liquid crystal display device 10 includes a polarizing plate 11, a retardation plate 12, a color filter layer 50, and a twisted nematic of optical phase modulation arranged in order from the observation side. The liquid crystal layer 15, the selective reflection layer 18 which functions as a semi-transmissive semi-reflective layer, the cholesteric liquid crystal layer 60, and the back light source 21 are provided.

The liquid crystal display device 10 includes a TN display element formed by sandwiching an optical phase-modulated TN liquid crystal layer 15 between two glass substrates 13 and 14 arranged oppositely, and the viewing side of the TN display element. That is, the retardation plate 12 and the polarizing plate 11 are sequentially provided on the outer surface of the glass substrate 13. In addition, the back light source 21 is provided to face the outer surface of the other glass substrate 14. The retardation plate 12 serves as a fixed liter layer, and the TN liquid crystal layer 15 functions as a variable litter layer, respectively. The fixed and variable litter layers form a variable litter.

The glass substrate 13 on the observation side of the TN liquid crystal element constitutes an array substrate, and a color filter layer 50 is provided on the inner surface of the glass substrate 13, and transparent indium tin oxide (ITO) is formed on the color filter layer 50. The plurality of pixel electrodes 16 are provided in a matrix form. In addition, on the glass substrate 13, the signal line 32 and the scanning line 34 including the gate electrode 33 are provided in a matrix, and an auxiliary capacitance electrode (not shown) is provided as necessary. At the intersection of the signal line 32 and the scan line 34, a thin film transistor 31 (hereinafter referred to as TFT) as a switching element is provided and connected to the pixel electrode 16, respectively.

An oxide film 35 is formed on the signal line 32 and the scan line 34. Each TFT 31 is provided with a semiconductor film 36 made of amorphous silicon (a-Si) provided on the gate electrode 33 via an oxide film 35, and a low resistance semiconductor film 37 formed on the semiconductor film. The source electrode 41 and the drain electrode 39 are provided and covered by the passivation film 38. In addition, each pixel electrode 16 is connected to the source electrode 41 via a contact hole 40 of about 10 탆 angle formed in the color filter layer 50.

The color filter layer 50 is disposed on the entire surface of the pixel portion. The color filter layer 50 is a color filter layer of three primary colors of red, green, and blue or complementary three colors of yellow, magenta, and cyan. The TN liquid crystal layer is formed by the pixel electrodes 16 and the counter electrodes 17 arranged in a matrix. Color display by additive color mixing is performed by electric field control of (15) in pixel units. As the color filter layer 5, one having a high transmittance (transmittance, Y value in the CIE-XYZ color system of about 40% or more) as shown in Fig. 6 is used. In this case, when the display is performed using external light as a light source without turning on the backlight in a bright place such as an outdoor light, it is preferable because the luminance of the display image can be increased.

On the other hand, the glass substrate 14 on the back side of the TN liquid crystal element constitutes an opposing substrate. On the surface facing the pixel electrode 16 of the glass substrate 14, an opposite electrode 17 made of a transparent conductive film such as ITO is formed almost over the entire surface. Between the glass substrate 14 and the counter electrode 17, a selective reflection layer 18 and a cholesteric liquid crystal layer 60 are formed to form a film of polymerized cholesteric liquid crystal and function as a semi-transparent semi-reflective layer. have.

In addition, it is preferable that the counter electrode 17 simultaneously perform film formation and patterning by a conventional mask sputtering method. In this case, the process load on the cholesteric liquid crystal layer 60 can be made extremely small when the counter electrode 17 is formed.

An alignment film (not shown) is formed on each of the surfaces of the array substrate and the counter substrate in contact with the TN liquid crystal layer 15. These alignment films are formed such that their alignment axes are perpendicular to each other, whereby the twist angle of the TN liquid crystal layer 15 is 90 degrees.

In addition, the array substrate and the opposing substrate are joined to each other by a seal member 43 applied along the periphery 42 of the two substrates.

The back light source 21 provided on the back side of the glass substrate 14 includes, for example, a light guide 22 made of a transparent flat plate such as acrylic, a linear light source 24 disposed on the side of the light guide, and a light guide. The scattering reflection layer 23 provided in the back surface is provided.

Next, a more detailed configuration of the liquid crystal display device 10 will be described in accordance with its operation principle.

As shown in Fig. 5, the selective reflection layer 18 made of the cholesteric liquid crystal reflects only the left circularly polarized component or the right circularly polarized component among the incident light reaching the one main surface thereof, and reflects it. And a component that transmits the right circularly polarized light component or the left circularly polarized light component of the reverse rotation, and scatters only the left circularly polarized light component or the right circularly polarized light component among the incident light reaching the opposite main surface, and transmits the right circularly polarized light component or the left circularly polarized light component. Equipped. When the pattern is viewed from the one main surface side, the rotation direction of the reflected light emitted from the one main surface side and the transmitted light from the back surface side is the same, and the rotation direction of the transmitted light and the reflected light emitted from the back surface side is also the same. In FIG. 2, the rotation direction of circularly polarized light L1, L2, L1 ', L2' has shown the state observed from the main surface 18f side of the mode selection reflection layer 18. As shown in FIG.

The cholesteric liquid crystal constituting the selective reflection layer 18 considers that the np value obtained by multiplying the torsion pitch of the liquid crystal molecules 19 by the average refractive index n is equal to the wavelength λ of the incident light. When the liquid crystal molecules 19 have a spiral structure of left rotation as viewed from the observation side, the light of the left circularly polarized light component is reflected from the main surface 18f among the external light Lf incident from the main surface 18f side. The reflected light L1 is inverted in the rotational direction relative to the advancing direction by the reflection and is emitted as a circularly polarized light in the right direction, but is left circularly polarized when viewed from the main surface 18f side. Moreover, among the incident light Lf on the main surface 18f, the light L2 of the right circularly polarized light component is transmitted to the other main surface 18b side.

The cholesteric liquid crystal has a function of reflecting 100% of the circularly polarized light component in the same direction (left or right) as the helical direction (left or right) when the np value is equal to the wavelength? Of the incident light.

On the other hand, among the external light Lb incident from the other main surface 18b, light of the left circularly polarized light component in the traveling direction is reflected by the main surface 18b and the light L2 'of the right circularly polarized component whose rotation direction is inverted with respect to the traveling direction. ). Further, light of the right circularly polarized light component is emitted from the main surface 18f through the selective reflection layer 18 in the traveling direction of the external light Lb, but when the light is observed from the main surface 18f side, L1 ').

In the liquid crystal display device 10 having the selective reflection layer 18 as described above, when external light Lf is incident from the observation surface side, light of a linearly polarized light component having a vibration direction along the polarization axis direction of the polarizing plate 11 is extracted. Then, a variable liter composed of the retardation plate 12 and the liquid crystal layer 15 is reached. The variable liter is a variable phase difference of light, and ideally, the fixed liter 12 which delays the phase of the vibration component in a specific direction of the incident light by λ / 4 (λ: incident wavelength) with respect to the vibration component orthogonal thereto. A phase difference plate) and a variable litter 15 (liquid crystal layer) which delays the phase of the vibration component of the incident light in a specific direction relative to the vibration component orthogonal to the vibration component.

As the fixed liter layer, it is possible to use, for example, a known lambda / 4 phase difference plate, and by arranging the slow axis so as to form an angle of 45 ° in a predetermined direction with respect to the polarization axis of the polarizing plate 11. The linearly polarized light transmitted by (11) is converted into circularly polarized light having a specific rotation direction. When the slow axis of the retardation plate 12 is arrange | positioned so that it may become an angle of 45 degrees to a right rotation with respect to the polarization axis of the polarizing plate 11, the circularly-polarized light radiated will become a structure of right rotation. On the contrary, when the phase axis of the retardation plate 12 is arrange | positioned so that it may become an angle of 45 degrees with respect to the polarization axis of the polarizing plate 11 at left rotation, the circularly-polarized light will become polarity of left rotation.

As the variable liter layer, a well-known TN liquid crystal layer 15 is used, for example. Incident light is incident on the liquid crystal layer 15 by the liquid crystal layer 15 in a state where a voltage (first voltage) below a threshold is applied from the power supply 20 to the liquid crystal layer 15, that is, the liquid crystal layer 15 maintains an initial arrangement. The vibration component in the specific direction of is delayed by λ / 2 with respect to the vibration component in the direction orthogonal thereto, and as a result, the rotation direction of the incident circularly polarized light is reversed. In addition, when a voltage (second voltage) equal to or higher than the saturation voltage is applied to the TN liquid crystal layer 15 and the twisted state of the liquid crystal molecules is released, incident light is emitted without phase modulation, so that the polarization of the circularly polarized light is maintained.

As described above, when the variable liter layer is constituted of the TN liquid crystal layer 15, phase delay caused by the liquid crystal layer 15 is relatively generated when the first voltage is applied and the second voltage is applied. In addition, the variable liter layer is not limited to the TN liquid crystal layer 15, but delays the phase of incident light in the initial alignment state at the time of applying the first voltage by λ / 4, and the phase of the incident light at the time of applying the second voltage above the saturation voltage. It is also possible to apply ferroelectric liquid crystals by proceeding λ / 4.

In the liquid crystal display device 10, for example, the twisted cholester with a λ / 4 phase difference plate having a slow axis intersecting at an angle of 45 ° with a right rotation with respect to the polarization axis of the polarizing plate 11 is used as the phase difference plate 12. In the case of using the selective reflection layer 18 formed of the liquid crystal, linearly polarized light reaching the retardation plate 12 through the polarizing plate 11 is converted into right circularly polarized light and output.

As shown in FIG. 4A, in the off state Voff in which no voltage is applied from the power supply 20 to the TN liquid crystal layer 15, or in a first voltage application state (including zero voltage) that is less than or equal to the threshold of the liquid crystal. The TN liquid crystal layer 15 exhibits a spiral structure that is twisted 90 degrees from the upper substrate 13 toward the lower substrate 14, and the liquid crystal molecules are arranged parallel to the substrate.

In this state, the right circularly polarized light incident on the TN liquid crystal layer 15 through the phase difference plate 12 is converted into the left circularly polarized light by the delay of λ / 2 in the TN liquid crystal layer 15 to reach the selective reflection layer 18. do. The left circularly polarized light that has reached the selective reflection layer 18 is totally reflected by the selective reflection layer 18 as described above.

The reflected left circularly polarized light is incident on the TN liquid crystal layer 15 again, and the phase is again converted into right circularly polarized light by being delayed by λ / 2. By passing this right circularly polarized light again through the phase difference plate 12, it becomes linearly polarized light along the polarization axis of the polarizing plate 11, and it is output through the polarizing plate 11, and the display of a bright state is obtained.

In addition, as shown in FIG. 4B, when the second voltage of the saturation level or higher is applied to the TN liquid crystal layer 15 and the TN liquid crystal layer 15 is turned on (Von), the TN liquid crystal is released from the spiral structure. The molecules 19 are arranged perpendicular to the substrates 13 and 14 so that the incident light is not phase modulated.

In this state, the incident light Lf from the observation surface enters the TN liquid crystal layer 15 as the right-handed circularly polarized light through the polarizing plate 11 and the retardation plate 12, but in the TN liquid crystal layer 15, the phase is incident. Without selection, the selective reflection layer 18 reaches the circularly polarized light in the right direction. This circularly polarized light of right rotation passes toward the rear surface of the display element. As a result, light is not returned to the observation surface, and a dark display is obtained.

Next, an operation when the back light source 21 provided on the back side of the selective reflection layer 18 is operated will be described.

In the Voff state shown in FIG. 4A, the circularly polarized light on the left side of the light source light Lb output from the rear light source 21 and incident from the rear surface to the selective reflection layer 18 is rotated in the selective reflection layer 18. After passing through, the circularly polarized light of the right turn is reflected. The light passing through the selective reflection layer 18 is modulated by [lambda] / 2 phase by the TN liquid crystal layer 15 and modulated into right circularly polarized light. By passing this circularly polarized light through the (lambda) / 4 phase difference plate 12, it becomes linearly polarized light along the polarization axis of the polarizing plate 11, it is output through the polarizing plate 11, and the display of a bright state is obtained.

On the other hand, in the Von state shown in FIG. 4B, the circularly polarized light on the left side of the light source light Lb output from the rear light source 21 and incident on the selective reflection layer 18 from the back is viewed from the polarization plate 11 side. 18) and is output as it is without being subjected to phase modulation by the TN liquid crystal layer 15. As the light passes through the retardation plate 12, the light becomes linearly polarized light having a vibration direction orthogonal to the polarization axis of the polarizing plate 11, and is absorbed by the polarizing plate 11. As a result, display in a dark state is obtained.

In the Voff and Von states of the TN liquid crystal layer 15, the circularly polarized light of the right turn reflected by the selective reflection layer 18 returns to the back light source 21 side, but is scattered and reflected on the back surface of the back light source 21. When it reaches (23), the polarization component is decomposed and the circularly polarized component of right rotation is provided. Since the circularly polarized light component of the left rotation passes through the selective reflection layer 18, ideally all the reflected light is converted into the circularly polarized light of the left rotation while the reflection is repeated between the scattering reflection layer 23 and the selective reflection layer 18, and the observation surface side Is output toward. Therefore, except for the loss caused by the absorption of the scattered reflection layer 23, the utilization efficiency of the light from the linear light source 24 can be extremely increased.

In the above configuration, when the retardation plate 12 is disposed such that the slow axis forms an angle of approximately 45 ° leftward from the polarization axis of the polarizing plate 11, the cholesteric liquid crystal constituting the selective reflection layer 18 is defined. The same operation as described above can be achieved by making the twist direction turn right.

According to the liquid crystal display device 10 configured as described above, the reflection / transmission relationship with respect to the light incident from the main surface of the selective reflection layer 18 and the reflection / transmission relationship with respect to the light incident from the rear surface have a rotation of the incident circularly polarized light. It has the same relationship with respect to the direction. Therefore, the display of the bright state is obtained in the OFF state in which the variable litter phase modulates the incident light, and the display of the dark state is obtained in the ON state in which the liquid crystal layer 15 does not phase modulate. Therefore, the reflective display using the external light Lb incident from the polarizing plate 11 side and the transmissive display using the light Lb of the back light source 21 are enabled by the display element of the same structure. At the same time, in both the case of using external light and the case of using the back light source 21, a display with extremely high light utilization efficiency can be obtained, and bright display is possible.

In addition, by forming the selective reflection layer 18 inside the TN liquid crystal element which is a variable liter, there is no parallax due to the substrate 14 as compared with the case where the selective reflection layer is disposed on the outer surface of the substrate 14.

Furthermore, in the above embodiment, the twisted nematic liquid crystal element was used as a variable liter, but if it was an element that could control the phase of incident light by 1/2 or not by phase modulation, it was the same as above. The effect can be obtained. For example, a horizontally aligned nematic liquid crystal device in which a conventionally known nematic liquid crystal is oriented in parallel in the direction of the substrate may be used as another embodiment, or a vertically aligned type in which the nematic liquid crystal is vertically aligned in the direction of the substrate. You may use a nematic liquid crystal element.

In addition, an antielectric ferroelectric liquid crystal device, a ferroelectric liquid crystal device, or the like can be used to control the phase of polarized light incident on the liquid crystal layer by shifting a quarter of a wavelength by right rotation or a quarter wavelength by a left rotation. do. Also in this case, when the phase of the incident light is shifted by one-half wavelength or not by phase modulation, the same effect can be obtained relatively.

For example, in the case of a horizontally aligned nematic liquid crystal device in which a nematic liquid crystal oriented horizontally on a substrate is used as a variable liter layer and provided with means for applying an electric field in the liquid crystal layer plane direction, the liquid crystal layer has a refractive index of the liquid crystal material. The Δnd value obtained by multiplying the anisotropy (Δn) by the liquid crystal layer thickness (d) is approximately 140 nm. As a result, it functions as a quarter wave plate.

By applying an electric field in the parallel direction to the liquid crystal layer, it is possible to change the plane orientation by 90 ° across the entire film thickness of the liquid crystal layer, so that the angle formed between the polarization axis of the polarizing plate and the liquid crystal molecule arrangement direction is 45 degrees. By setting it as °, it is possible to emit linearly polarized light incident on the liquid crystal layer as circularly polarized light of right rotation and left rotation with respect to light incident from the observation side.

Therefore, it is possible to polarizely reflect / transmit incident light by the selective reflection layer 18 which selectively reflects circularly polarized light. In addition, with respect to the light incident from the back side of the substrate 14, it is possible to convert the circularly polarized light obtained through the selective reflection layer 18 into two kinds of linearly polarized light having completely opposite polarities. In this way, the same display state can be obtained with respect to the light incident from the upper side of the substrate and the light incident from the lower side of the substrate 14 at the same voltage state.

The selective reflection layer 18 used for the liquid crystal display device 10 is preferably used to achieve the above-described functions and functions with respect to the light of the entire wavelength in the visible light region to obtain achromatic black and white display or color display excellent in color reproducibility. Do.

For example, in the case where the selective reflection layer 18 is formed of the cholesteric liquid crystal layer as in the above embodiment, the value of np multiplied by the spiral pitch p and the average refractive index n of the cholesteric liquid crystal polymer is the shortest in the visible light wavelength. By forming a spiral structure in which the spiral pitch continuously changes along the layer thickness direction so as to cover the wavelength from the longest wavelength, it is possible to obtain the polarization reflecting ability corresponding to the entire wavelength of the visible light region.

The rod-shaped polymer constituting the cholesteric liquid crystal has a spiral structure, and when light parallel to the spiral axis is incident, Bragg reflects the wavelength of light equal to the spiral pitch. In other words, Bragg reflection is obtained by the same bandwidth (wavelength range) as the Δnp value obtained by multiplying the refractive index anisotropy (Δn) and the spiral pitch p by using the light having the same wavelength as the np value.

In addition, the refractive index anisotropy (Δn) represents the difference between the refractive index along the long axis direction of the rod-shaped liquid crystal polymer and the refractive index along the short axis direction, and the average refractive index is along the refractive index along the long axis direction of the liquid crystal polymer, It is calculated | required by the square root of the sum of squares with refractive index.

However, since the refractive index anisotropy (Δn) of the cholesteric liquid crystal is only 0 to 0.3, the average refractive index n of the cholesteric liquid crystal also exists only 1.4 to 1.6. It is difficult to match the center wavelength to the center wavelength (about 550 nm) of the visible light wavelength. Therefore, as described above, it is extremely effective to change the spiral pitch of the cholesteric liquid crystal in the thickness direction of the liquid crystal layer in order to obtain good polarization reflecting ability over the entire visible wavelength range.

In order to obtain a cholesteric liquid crystal layer having such a spiral pitch, two or more kinds of cholesteric liquid crystal polymer layers having different pitches are successively laminated, or when the cholesteric liquid crystal material is applied to a substrate and solidified. And a method of coating an additive that lengthens the spiral pitch of the cholesteric liquid crystal, such as nematic liquid crystal having an infinite spiral pitch, is applied to the film surface after application.

In the above embodiment, it is also possible to make the halftone display by applying an intermediate voltage between Von and Voff as the voltage applied to the variable liter layer.

As described above, even when the liquid crystal display device 10 is operated as a reflective display element using external light or when the liquid crystal display device is operated as a transmissive display element using the back light source 21, high light utilization efficiency can be achieved. Can be.

Further, as described above, each TFT 31 provided on the array substrate has a bottom gate structure in which the gate electrode 33 is disposed under the semiconductor film 36. In this case, external light incident from the array substrate toward the TFT 31 is blocked at the gate electrode 33 and is not incident on the semiconductor film 36. As a result, when the liquid crystal display device 10 is used outdoors, it is possible to prevent the display contrast ratio from being lowered due to the light leakage current generated by external light.

Since the wiring electrodes of any of the signal line 32, the scanning line 34, and the storage capacitor line are arranged at the boundary of the transparent pixel electrode 16, when used as a transflective liquid crystal display device using the back light source 21, The leakage of light from the back light source is prevented and the contrast ratio is not lowered.

It is preferable to apply a sealing agent for joining the array substrate and the counter substrate to a region where the selective reflection layer 18 of the counter substrate is not formed. On the selective reflection layer 18, the adhesiveness of a sealing compound is bad, and there exists a possibility of causing a reliability problem, such as a board | substrate falling with respect to long-term use more than 10,000 hours. In addition, if the overcoating agent having good adhesion of the sealing agent is applied on the selective reflection layer 18, the reliability problem can be avoided. As the overcoat agent, for example, an acrylic resin or the like commonly used in a color filter layer can be used.

On the other hand, in the liquid crystal display device 10 described above, the cholesteric liquid crystal layer 60 provided between the glass substrate 14 and the selective reflection layer 18 functions as a band pass filter of the back light source 21. This cholesteric liquid crystal layer 60 was created as follows.

In other words, the cholesteric liquid crystal layer 60 has a product of the spectral transmittance characteristic of the color filter layer 50 when the product np between the spiral pitch p of the cholesteric liquid crystal and the average refractive index n of the cholesteric liquid crystal polymer is n. It has a spiral structure in which the spiral pitch continuously changes along the layer thickness direction of the liquid crystal layer so as to cover a range of 470 to 510 nm, which is wavelength light between peak wavelengths, and a range of 560 to 600 nm. Therefore, among the circularly polarized light components of the light emitted from the rear light source 21, the components in the range of 470 to 510 nm and the range of 560 to 600 nm are reflected by the cholesteric liquid crystal layer 60 and the selective reflection layer 18 Nothing penetrates

7 shows the transmittance wavelength dispersion characteristics of the cholesteric liquid crystal layer 60. The twist direction of the spiral pitch was made to be the same direction as the twist pitch of the cholesteric liquid crystal of the selective reflection layer 18. In the case of the same direction, the manufacturing becomes easy when the cholesteric liquid crystal layer 60 is formed continuously with the selective reflection layer 18. In addition, in the present embodiment, the cholesteric liquid crystal layer 60 is formed on the inner surface of the glass substrate 14, but may also be formed on the outer surface of the glass substrate 14.

As the linear light source 24 of the rear light source 21, a main fluorescent lamp having a light emission spectrum as shown in FIG. 8, or three wavelengths having a light emission spectrum peak at three wavelengths of red, green, and blue as shown in FIG. Fluorescent lamps can be used.

As shown in Fig. 9, the spectral characteristics of the luminescence luminance of the three-wavelength tube have unnecessary peaks in the ranges of 470 to 510 nm and 560 to 600 nmm, as well as essentially necessary peaks around 440, 540 and 620 nm. In addition, the daylight fluorescent lamps have a larger emission of these ranges. However, the cholesteric liquid crystal layer 60 can effectively block wavelength light in the range of 470 to 510 nm and 560 to 600 nmm, and any fluorescent lamp can be used.

The red, blue, and green color reproduction range when the liquid crystal display device 10 configured as described above is measured in a dark place while the rear light source 21 is turned on is indicated by a solid line A in FIG. In addition, the color reproduction range in the case where the linear light source 24 is replaced by the three-wavelength tube in the daylight fluorescent lamp while removing the cholesteric liquid crystal layer 60 from the liquid crystal display device 10 for comparison, is indicated by the dotted line B in FIG. It is represented by. As can be seen from these comparisons, the liquid crystal display device 10 of the present embodiment has a wider color reproduction range, particularly red and green reproducibility.

In the present embodiment, the cholesteric liquid crystal layer 60 has a transmittance at 550 nm of 1, the maximum transmittance in the range of 470 to 510 nm is 0.06, and the maximum transmittance in the range of 560 to 600 nm is 0.008. It becomes about. As a result of various tests of the transmittance of the cholesteric liquid crystal layer 60, it was found that good color reproducibility can be obtained when their maximum transmittance is approximately 0.1 or less.

In the above embodiment, the torsional direction of the liquid crystal molecules of the cholesteric liquid crystal layer 60 is matched with the torsional direction of the cholesteric liquid crystal of the selective reflection layer 18, but it is also possible to form them in opposite directions. In addition, the cholesteric liquid crystal layer 60 discontinuously forms another layer of spiral pitch so as to have a layer having a maximum transmittance in a range of 470 to 510 nm and a layer having a maximum transmittance in a range of 560 to 600 nmm. It is also possible.

As described above, according to the liquid crystal display device 10 according to the present embodiment, in the case of operating as a reflective display element using external light and in the case of operating as a transmissive display element using a back light source, It is possible to obtain a high brightness display screen without excessively changing the color reproducibility. As a result, it is not necessary to use the back light source auxiliary for reflective display or to raise the brightness of the back light source for transmissive display, thereby reducing power consumption.

Next, a liquid crystal display device according to a second embodiment of the present invention will be described.

11 and 12, according to the second embodiment, the TN liquid crystal device constructed by holding the TN liquid crystal layer 15 between the pair of glass substrates 13 and 14 arranged oppositely faces the front surface of the opposite substrate. The side and the array substrate are arranged on the back side. That is, the first color filter layer 50 and the counter electrode 17 are sequentially formed on the inner surface of the glass substrate 14 constituting the opposing substrate, and the retardation plate 12 and the polarizing plate are formed on the outer surface of the glass substrate 14. (11) is provided in sequence.

In addition, the selective reflection layer 18 and the pixel electrode 16 are provided on the inner surface of the glass substrate 13 constituting the array substrate, and the rear light source 21 is disposed opposite to the outer surface of the glass substrate 13. . According to the present embodiment, the band pass filter 70 is provided in place of the cholesteric liquid crystal layer 60 in the first embodiment. That is, the band pass filter 70 is provided between the glass substrate 13 and the selective reflection layer 18. Further, on the band pass filter 70, wiring of signal lines and scanning lines, a TFT 31 and the like are provided, and are connected to the pixel electrode 16.

Others are the same as those of the first embodiment described above, and the same parts are denoted by the same reference numerals, and detailed description thereof will be omitted.

According to the liquid crystal display device provided with the liquid crystal display device 10 having the above configuration, as shown in FIG. 12, the TN liquid crystal in an off state (Voff) in which no voltage is applied from the power source 20 to the TN liquid crystal layer 15. The layer 15 shows a spiral structure twisted 90 degrees from the substrate 13 toward the lower substrate 14, and the liquid crystal molecules are arranged in parallel to the substrate.

In this state, the right circularly polarized light of the external light Lf incident on the TN liquid crystal layer 15 through the polarizing plate 11 and the retardation plate 12 is left circularly polarized due to the delay of λ / 2 in the TN liquid crystal layer 15. Is converted to the selective reflection layer 18. Then, the left circularly polarized light that reaches the selective reflection layer 18 is totally reflected by the selective reflection layer 18 and is incident on the TN liquid crystal layer 15 again, where the phase is again converted into right circularly polarized light by delaying λ / 2. do. When the right circularly polarized light passes through the retardation plate 12 again, it becomes linearly polarized light along the polarization axis of the polarizing plate 11 and is outputted through the polarizing plate 11 to obtain a bright display.

In addition, as shown in FIG. 13, when the second voltage of the saturation level or higher is applied to the TN liquid crystal layer 15, and the TN liquid crystal layer is turned on (Von), the TN liquid crystal is released from the helical structure and the liquid crystal molecules 19 ) Is arranged perpendicular to the substrates 13 and 14, and the incident light is not phase modulated.

In this state, the incident light Lf from the observation surface enters the TN liquid crystal layer 15 as circularly polarized light of right rotation through the polarizing plate 11 and the retardation plate 12, but is not phase-modulated in the TN liquid crystal layer 15. Instead, the selective reflection layer 18 is reached as it is in the right-handed circularly polarized light. This circularly polarized light of right rotation passes toward the back surface of the display element. As a result, light does not return to the observation surface, and a dark display is obtained.

On the other hand, in the Voff state shown in FIG. 12, among the light source light Lb incident from the back side to the selective reflection layer 18 output from the back light source 12, the circularly polarized light of the left rotation viewed from the polarizing plate 11 side is selected. Passing through the reflective layer 18, the right-handed circularly polarized light is reflected. Light passing through the selective reflection layer 18 is lambda / 2 phase modulated by the TN liquid crystal layer 15, and converted into right circularly polarized light. When this circularly polarized light passes through the retardation plate 12, it becomes linearly polarized light along the polarization axis of the polarizing plate 11, and is output through the polarizing plate 11 to obtain a dark display.

In the Von state shown in FIG. 13, of the light source light Lb output from the back light source 12 and incident on the selective reflection layer 18, the circularly polarized light in the left rotation viewed from the polarizing plate 11 side causes the selective reflection layer 18. It passes through and is output as it is without receiving phase modulation by the TN liquid crystal layer 15. As the light passes through the retardation plate 12, the polarizing plate 11 becomes linearly polarized light having a vibration direction orthogonal to the polarization axis, and is absorbed by the polarizing plate 11. As a result, display in a dark state is obtained.

In the Voff and Von states of the TN liquid crystal layer 15, the circularly polarized light of the right turn reflected by the selective reflection layer 18 returns to the back light source 21 side, but is scattered and reflected on the back surface of the back light source 21. When it reaches (23), the polarization component is decomposed and left circularly polarized component is provided. Since the circularly polarized light component of the left rotation passes through the selective reflection layer 18, while the reflection is repeated between the scattering reflection layer 23 and the selective reflection layer 18, ideally, the total reflected light is converted into the circularly polarized light of the left rotation and the observation plane side Is output toward.

Next, the first color filter layer 50 will be described. When the liquid crystal display device 10 functions as a reflective liquid crystal display device, as shown in FIG. 11, the external light Lf incident from the observation side is the first color filter layer 50 provided on the glass substrate 14 on the front side. ) Is passed through twice.

In this case, the first color filter layer 50 is used in the same manner as the conventional one having a spectral characteristic such that light passes through the color filter layer twice so as to have a desired color concentration. FIG. 14 shows the spectral characteristics of the first color filter layer 50, and FIG. 15 shows the spectral characteristics when the light has passed through the first color filter layer 50 twice. The spectral characteristics of FIG. 15 are obtained by multiplying the transmittance at each wavelength of the spectral characteristics shown in FIG.

As can be clearly seen from these figures, sufficient color concentration is not obtained only by passing through the first color filter layer 50 once, and sufficient color concentration when passing through the first color filter layer 50 twice. Obtained.

On the other hand, when the liquid crystal display device 10 functions as a transmissive liquid crystal display device using the rear light source 21, as shown in FIG. 11, the incident light Lb from the rear light source 21 is the first color filter layer ( Only pass 50) once. In this case, sufficient color concentration cannot be obtained as described above.

According to the present embodiment, the band pass filter 70 is disposed between the selective reflection layer 18 and the back light source 21, particularly under the selective reflection layer. The band pass filter 70 is constituted by a color absorbing filter, and more specifically, by the second color filter layer 72 in which pigments are dispersed in an organic medium such as acrylic resin, like the first color filter layer 50. It is.

As shown in FIG. 16, when the light from the back passes through the second color filter layer 72 and the first color filter layer 50, the second color filter layer 72 is equivalent to the conventional transmission type color filter layer. It is designed to obtain spectral characteristics. That is, the spectral characteristics of the second color filter layer 72 are values obtained by dividing the transmittance at each wavelength of the spectral characteristics of the conventional color filter layer by the transmittance at each wavelength of the spectral characteristics of the first color filter layer 50. What is necessary is just to make the spectral characteristic which consists of.

Fig. 17 shows the spectral characteristics of the second color filter layer 72 by the pigment dispersion method thus obtained. As described above, when functioning as a transmissive liquid crystal display device, since the light Lb emitted from the back light source 21 passes through the second color filter layer 72 and the first color filter layer 50 sequentially, As shown in Fig. 16, the color density of the image becomes the total spectral characteristic of both color filter layers. Therefore, even when used as a transmissive liquid crystal display device, it is possible to obtain an image of sufficiently dark color concentration as in the conventional transmissive type.

In this case, since the light emitted from the rear light source 21 passes through the entire selective reflection layer 18 if the polarization component also matches, the selective reflection layer 18 does not act as a light shielding layer and no light loss occurs. In addition, since the selective reflection layer 18 itself exhibits the function of a polarizer, there is an effect that one polarizing plate can be omitted.

In the above liquid crystal display device, the second color filter layer 72 and the selective reflection layer 18 may be provided on the outer surface of the glass substrate 13 on the back side as shown in FIG. Effects similar to those of the second embodiment can be obtained. In this case, in order to reduce the parallax due to the thickness of the glass substrate 13, the second color filter layer 72 is disposed with a predetermined distance shifted in the plane direction of the glass substrate 13 with respect to the first color filter layer 50. What is necessary is just to set it as the pattern arrangement centering on the area | region which functions as a transmission type. In addition, the selective reflection layer 18 is formed into a film shape independently and attached to the glass substrate 13 to simplify the production.

Further, as shown in FIG. 19, the selective reflection layer made of a cholesteric liquid crystal polymer may be used as the selective reflection layer 18, and the selective reflection layer 18 may also be used as the second color filter layer 72. Specifically, dye (RGB) used for ink or the like may be added to the cholesteric liquid crystal polymer layer. The cholesteric liquid crystal polymer layer used herein has a spiral pitch continuously changed in the layer. Specifically, a cholesteric liquid crystal polymer layer having a pitch that selectively reflects light in the ultraviolet region, such as cholesteric LC silicone made from Walker Chemical, In addition, it can be formed by the interaction effect of the interface by continuously forming a cholesteric liquid crystal polymer layer having a pitch for selectively reflecting light in the infrared ultraviolet region, for example, cholesteric LC silicone, which is a product of Walker Chemical.

The selective reflection layer 18 made of the above-described cholesteric liquid crystal polymer layer, like the selective reflection layer of the second embodiment, decomposes the light Lf incident from above and the light Lb incident from below into left and right circularly polarized light, and transmits it. , Reflects. Therefore, if the TN liquid crystal layer 15 is lambda / 2 phase difference, it is possible to shift the phase of circular polarization from 0 to lambda / 2 by controlling the phase difference from 0 to lambda / 2, and the left and right circular polarization It is possible to switch. In addition, the number of layers of the entire liquid crystal display device can be reduced by using both the second color filter layer 72 and the selective reflection layer 18 made of the cholesteric liquid crystal polymer layer.

Further, as shown in Fig. 20, an interference filter 74 may be used as the band pass filter 70. As the interference filter 74, for example, it may be a laminate a plurality of dielectric alternately known, a combination of CeO ₂ and MgF ₂ is known as a stacked dielectric. By appropriately adjusting the material, refractive index, and number of layers of such a dielectric multilayer film, desired transmittance characteristics can be obtained.

FIG. 21 shows the transmittance characteristics of the interference filter 74. Compared with the spectral characteristics of the first color filter layer 50 shown in FIG. 14, it is understood that the light passing through the interference filter 74 is narrower light. Can be. Therefore, when the linear light source 24 of the rear light source 21 does not have a light emission spectrum as shown in FIG. 8 as in the first embodiment, the transmitted light of G of the first color filter layer 50, for example, of the light source light. Since the wavelength light corresponding to the lower partial region of is cut by the interference filter 74, an image of a suitable color density can be obtained.

In addition, in the modified example shown to FIG. 18 thru | or 20, the other structure is the same as that of 2nd Example, the same code | symbol is attached | subjected to the same part, and the detailed description is abbreviate | omitted.

According to the second embodiment and each modified example configured as described above, it is bright in either of the case of functioning as a reflection type liquid crystal display device using external light and of the case of operating as a transmission type liquid crystal display device using a back light source. High display of color density can be obtained. In addition, although the example which used the a-Si TFT was demonstrated so far, it cannot be overemphasized that this invention is applicable also when using a polysilicon TFT.

As described above, according to the present invention, a transflective color liquid crystal display device having a back light source and a reflection film for reflecting external light and capable of functioning as a reflective and transmissive color liquid crystal display device can be realized.

Claims (20)

A front substrate and a rear substrate disposed to face each other and having liquid crystal driving electrodes disposed on respective inner surfaces thereof; A liquid crystal layer interposed between the front substrate and the rear substrate and modulating a phase of incident light according to an applied voltage; A polarizing plate having a phase difference plate and a polarization axis which are sequentially mounted on the outer surfaces of one of the front substrate and the rear substrate; A semi-transmissive semi-reflective layer formed on the other substrate; A color filter layer disposed on the front substrate side rather than the semi-transmissive semi-reflective layer; A rear light source disposed on the back side of the other substrate; A liquid crystal display device disposed between the semi-transmissive semi-reflective layer and the back light source and selectively reflecting wavelength light between adjacent peak wavelengths of the spectral transmittance characteristic of the color filter layer. . The liquid crystal display device according to claim 1, wherein the retardation plate has a slow axis approximately 45 ° in a predetermined direction with respect to the polarization axis of the polarizing plate when viewed from the front side of the polarizing plate. The method of claim 2, wherein the semi-transmissive semi-reflective layer comprises a selective reflection layer for reflecting the first circularly polarized light component of the incident light, and transmits the first circularly polarized light component and the second circularly polarized light component of reverse rotation Liquid crystal display device. The liquid crystal display device according to claim 3, wherein the selective reflection layer is formed of a cholesteric liquid crystal. The liquid crystal display device according to claim 4, wherein the cholesteric liquid crystal forming the selective reflection layer has a torsional direction opposite to the rotational direction from the polarization axis to the slow axis. 6. The liquid crystal display according to claim 5, wherein the cholesteric liquid crystal forming the selective reflection layer and the cholesteric liquid crystal layer disposed between the selective reflection layer and the back light source have the same torsional direction. Device. 6. The liquid crystal according to claim 5, wherein the cholesteric liquid crystal forming the selective reflection layer and the cholesteric liquid crystal layer disposed between the selective reflection layer and the back light source have a twisting direction opposite to each other. Display. The method according to claim 4, wherein the cholesteric liquid crystal layer forming the selective reflection layer is formed so as to continuously change between the spiral pitch and the enemy of the average refractive index corresponding to the visible light wavelength, and wherein the selective reflection layer and the back light source And a cholesteric liquid crystal layer interposed therebetween so as to discontinuously change between the helical pitch and the mean refractive index value corresponding to the wavelength of visible light. The liquid crystal display device according to claim 1, wherein the retardation plate and the polarizing plate are provided on an outer surface of the front substrate, and the selective reflection layer is provided on an inner surface of the rear substrate. A front substrate and a rear substrate disposed to face each other and having liquid crystal driving electrodes disposed on respective inner surfaces thereof; A liquid crystal layer interposed between the front substrate and the rear substrate and modulating a phase of incident light according to an applied voltage; A polarizing plate having a phase difference plate and a polarization axis which are sequentially mounted on the outer surfaces of one of the front substrate and the rear substrate; A selective reflection layer formed on the other substrate and reflecting the first circularly polarized component of the incident light to transmit the first circularly polarized component and the second circularly polarized component of reverse rotation; A first color filter layer disposed on the front substrate side than the selective reflection layer; A back light source disposed on a back side of the back substrate; And a band pass filter arranged on the rear light source side than the selective reflection layer. The liquid crystal display device according to claim 10, wherein the band pass filter has a narrower spectral transmittance characteristic than that of the first color filter layer in a transmission wavelength region of any of the first color filter layers. 12. The liquid crystal display device according to claim 11, wherein the band pass filter comprises a second color filter layer in which a plurality of color absorption filter layers having different spectral transmittance characteristics are arranged regularly. 12. The liquid crystal display device according to claim 11, wherein the band pass filter comprises an interference filter layer. The liquid crystal display device according to claim 10, wherein the retardation plate has a slow axis approximately 45 ° in a predetermined direction with respect to the polarization axis of the polarization plate when viewed from the front plate of the polarizing plate. The liquid crystal display device according to claim 10, wherein the selective reflection layer is formed of a cholesteric liquid crystal. 16. The liquid crystal display device according to claim 15, wherein the cholesteric liquid crystal forming the selective reflection layer has a twisting direction opposite to the rotational direction from the polarization axis to the slow axis. The liquid crystal display of claim 10, wherein the first color filter layer is formed on an inner surface of the front substrate. The liquid crystal display device according to claim 10, wherein the band pass filter is provided on an outer surface of the back substrate. The liquid crystal display device according to claim 10, wherein the band pass filter is stacked below the selective reflection layer. 13. The liquid crystal display device according to claim 12, wherein the second color filter layer is a layer obtained by coloring the selective reflection layer.