KR100312684B1 - Reflective type liquid crystal display of using twisted feroelectric liquid crystal material - Google Patents

Abstract

The transparent upper substrate and the lower substrate are arranged in parallel, a polarizing plate is attached to the upper surface of the upper substrate, a first electrode is formed on the lower surface of the upper substrate, and an upper alignment layer is formed below the first electrode. A second electrode, which may serve as a reflecting plate, is formed on the lower substrate, and a lower alignment layer is formed on the second electrode. A ferroelectric liquid crystal material is injected into the space between the upper and lower substrates to form a liquid crystal layer. At this time, by appropriately selecting the optical thickness of the liquid crystal layer, the cone tilt angle of the liquid crystal molecules, the polarization direction of the polarizing plate, and the alignment direction of the liquid crystal molecules, gray scale display is possible through voltage application between the first electrode and the second electrode.

Description

Reflective liquid crystal display device using ferroelectric liquid crystal material {REFLECTIVE TYPE LIQUID CRYSTAL DISPLAY OF USING TWISTED FEROELECTRIC LIQUID CRYSTAL MATERIAL}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to liquid crystal displays, and more particularly to reflective liquid crystal displays using ferroelectric liquid crystal materials.

Conventional liquid crystal display devices are generally manufactured using a liquid crystal of nematic phase, but have a slow response speed, which limits the representation of moving images. In order to overcome this limitation, a liquid crystal display using ferroelectric smectic phase liquid crystals has been proposed. Next, a liquid crystal display using ferroelectric smectic liquid crystal will be described.

1 is a cross-sectional view of a liquid crystal display using ferroelectric smectic liquid crystals.

Two upper and lower glass substrates 100 and 120 face each other, and transparent electrodes 140 and 160 made of indium-tin-oxide (ITO) are formed on inner surfaces of the upper and lower substrates 100 and 120, respectively. Alignment layers 180 and 200 are formed on the upper and lower transparent electrodes 140 and 160, respectively. At this time, the alignment directions of the vertical alignment layers 180 and 200 are perpendicular to each other. Polarizers 220 and 240 are attached to the outer surfaces of the glass substrates 100 and 120, respectively, and the polarization directions of the two polarizers 220 and 240 are perpendicular to each other. A ferroelectric liquid crystal material is injected between the upper and lower glass substrates 100 and 120 to form the liquid crystal layer 260. At this time, the liquid crystal molecules positioned on both surfaces of the liquid crystal layer 260 are arranged such that the stable tilt angle coincides with the alignment direction of the alignment layers 180 and 200. Below the lower polarizer 220, a light guide plate 320 is disposed to disperse light emitted from the light source 310 and the light source 310 into the liquid crystal cell. The voltage signal source 280 is connected to the upper and lower electrodes 140 and 160.

In the state where no voltage is applied to the upper and lower electrodes 140 and 160, the liquid crystal molecules are gradually twisted to form 90 ° to each other as oriented on both surfaces of the liquid crystal layer 260. In this state, when the light polarized while passing through the lower polarizer 220 passes through the liquid crystal layer 260 and the polarization direction is rotated to reach the upper polarizer 240, the upper polarizer 240 coincides with the polarization direction. It may pass through without being blocked by the upper polarizer 240.

However, when voltage is applied to the upper and lower electrodes 140 and 160, the liquid crystal molecules are arranged side by side in one of the vertical alignment directions, and lose the function of rotating the polarization direction of light. Therefore, all linearly polarized light passing through the lower polarizer 220 is blocked by the upper polarizer 240.

However, the transmissive liquid crystal display using the ferroelectric smectic phase liquid crystal consumes a lot of power since its own light source 310 is used. Therefore, it is not suitable for use in products requiring low power consumption such as portable computers or mobile phones.

As a result, there is a need to develop a reflective liquid crystal display using ferroelectric liquid crystals with low power consumption and fast response speed.

An object of the present invention is to provide a reflective liquid crystal display using ferroelectric liquid crystal.

1 is a cross-sectional view of a transmissive liquid crystal display device using a ferroelectric liquid crystal material according to the related art.

2 is a cross-sectional view of a reflective liquid crystal display device using a ferroelectric liquid crystal material according to an embodiment of the present invention;

FIG. 3 is a diagram illustrating an arrangement of molecules in a liquid crystal display according to an exemplary embodiment of the present invention.

4 is a conceptual diagram illustrating a change in the Stokes parameter experienced by light passing through a liquid crystal cell.

FIG. 5 is a graph showing S ₃ as a function of cone inclination angle for many cases with different optical thicknesses,

6 is a view showing possible orientation directions of the vertical alignment film,

7 is a graph illustrating a change in the amount of reflected light according to a voltage change in the reflective liquid crystal display according to the exemplary embodiment of the present invention.

FIG. 8 is a graph illustrating an area in which gray scale display is possible in consideration of an angle of a polarizing plate and an optical thickness of a cell in a reflective liquid crystal display according to an exemplary embodiment of the present invention.

FIG. 9 is a graph illustrating an area in which gray scale display is possible in consideration of a cone inclination angle of ferroelectric liquid crystal molecules and an optical thickness of a cell in a reflective liquid crystal display according to an exemplary embodiment of the present invention.

Table 1 shows the material constants of the liquid crystal materials used in the examples of the present invention.

In order to solve this problem, the present invention proposes a reflective liquid crystal display including a polarizing plate, a reflecting plate, and a ferroelectric liquid crystal material disposed therebetween.

Specifically, the following reflective liquid crystal display device is provided.

A polarizing plate having an inner side and an outer side and having a polarization direction in a first direction is attached to an outer side of the transparent first substrate, a transparent first electrode is formed on an inner side of the first substrate, and the first alignment layer It is formed on the first electrode and orientates the liquid crystal molecules in the second direction. A second electrode, which also serves as a reflector, is formed on an inner surface of the second substrate having an inner surface and an outer surface facing the inner surface of the first substrate, and the liquid crystal molecules are aligned in the third direction on the second electrode. A second alignment film is formed, and a ferroelectric liquid crystal layer is injected between the first substrate and the second substrate.

At this time, it is preferable that the liquid crystal molecules of the ferroelectric liquid crystal layer are twisted in the second direction to the third direction from the first substrate surface toward the second substrate surface, and the optical thickness of the liquid crystal layer (Δn · d) Is preferably any particular value between 180 nm and 400 nm, and the ferroelectric liquid crystal material preferably has any particular value between 20 ° and 30 ° when the cone tilt angle is in the Smectic C * phase. Also, the angle formed between the first direction and the centerline of the induced cone of the liquid crystal molecules may have any particular angle between 0 ° and 40 °, between 80 ° and 130 °, and between 170 ° and 180 °. It is preferable that the angle formed by the three directions be twice the inclination angle of the cone. In addition, the optical thickness of the liquid crystal layer is 260 nm, the cone tilt angle of the liquid crystal is between 25 ° to 27 °, the angle between the second direction and the third direction is 54 °, the first direction and the second direction is the same direction You can also do

The optical thickness (Δn · d) of the ferroelectric liquid crystal material may have any particular value between 700 nm and 890 nm, and the ferroelectric liquid crystal material may have any particular value between 20 ° and 44 ° when the cone tilt angle is in the Smectic C * phase. The angle formed by the first direction and the centerline of the induced cone of the liquid crystal molecules may form any particular angle between 0 ° and 30 °, between 65 ° and 120 ° and between 155 ° and 180 °, Preferably, the angle formed by the second direction and the third direction is twice the inclination angle of the cone.

Next, a structure of a thin film transistor substrate for a reflective liquid crystal display device using a ferroelectric liquid crystal according to an exemplary embodiment of the present invention will be described with reference to the drawings.

2 is a cross-sectional view of a reflective liquid crystal display device according to an exemplary embodiment of the present invention.

The reflective liquid crystal display according to the exemplary embodiment of the present invention includes two substrates 11 and 12, one polarizer 20, and a ferroelectric liquid crystal layer 50.

2, the transparent upper substrate 12, such as glass, and the lower substrate 11 are arrange | positioned in parallel. The polarizing plate 20 is attached to the upper surface of the upper substrate 12, the first electrode 32 for forming an electric field is formed on the lower surface of the upper substrate 12, the liquid crystal under the first electrode 32 An upper alignment layer 42 for the alignment of molecules is formed. A second electrode 31 for forming an electric field is formed on the upper surface of the lower substrate 11 together with the first electrode 32, and a lower alignment layer 41 is formed on the second electrode 31.

In this case, the first electrode 32 is formed of a transparent conductive material such as ITO, and the second electrode 31 is formed of a conductive material that reflects light well such as aluminum to serve as a reflector.

In addition, the upper and lower alignment layers 41 and 42 are generally coated with a surfactant such as alkylphenol, hexadecyltrimethylammonium bromide or polyimide resin, or silicon oxide (SiOx) everywhere. The liquid crystal molecules present on the surfaces of both substrates 11 and 12 are deposited by applying an orientation adsorbent by deposition or by a Langmuir-Blodgett film deposition method and then rubbing in a desired direction. 11, 12) to be oriented horizontally. The embodiment of the present invention shows a case where PBT (poly (1, 4-butylene terephthalate)) is used as the alignment layers 41 and 42 and a polyimide is used as the alignment layer.

Moreover, it is preferable that the polarizing plate 20 linearly polarizes the light passing through.

In addition to the above-mentioned matters, a number of other elements may be included, such as a color filter for displaying color, a black matrix for preventing light leakage, and a thin film transistor for applying or blocking voltage to the second electrode 31. However, this can be easily understood by those skilled in the art of liquid crystal display.

A ferroelectric liquid crystal material, such as CS-1029 supplied by Chisso, is injected into the space between the upper and lower substrates 11 and 12 to form the liquid crystal layer 50. At this time, the liquid crystal layer 50 forms a molecular layer (indicated by dotted lines), and the boundary surface of the molecular layer is perpendicular to the upper and lower substrates 11 and 12. In addition, the liquid crystal molecules adjacent to the upper alignment layer 42 are aligned to form an angle of about 54 ° with the liquid crystal molecules adjacent to the lower alignment layer 41. At this time, the alignment angle 54 ° of the upper and lower alignment layers 41 and 42 is determined to be twice the cone tilt angle of the ferroelectric liquid crystal material. Is changed. In addition, the liquid crystal molecules adjacent to the upper alignment layer 42 or the lower alignment layer 41 are preferably aligned so as to be parallel to the polarization axis of the polarizing plate 20.

A method of displaying an image in such a liquid crystal display device will be described.

First, the general properties of ferroelectric smectic C liquid crystals will be described.

First, the orientation of the ferroelectric smectic C liquid crystal molecules and the response to the electric field will be described with reference to FIG. 3.

3 is a diagram illustrating an arrangement of molecules in a liquid crystal display according to an exemplary embodiment of the present invention, in which only one molecular layer is enlarged, and the other molecular layers are arranged in the same manner. Here, the X axis is an axis perpendicular to the molecular layer, the Y axis is an axis parallel to the substrates 11 and 12 and rotated 90 ° counterclockwise with respect to the X axis, and the Z axis is perpendicular to the substrates 11 and 12 and is perpendicular to the Y axis. It is an axis rotated 90 ° counterclockwise.

In Fig. 3, the positions of the liquid crystal molecules 16, 17 and 18 will be described using the following variables. The angle formed between the X-axis and the director of the liquid crystal molecules is the 'inclined angle' Θ, and the angle of the foot with respect to the XY plane of the director and the X-axis is the 'horizontal angle' θ, and the director is moved from the Y-axis to the Z-axis. The rotated 'rotation angle' is Φ.

When the rubbing directions of the lower substrate 11 and the upper substrate 12 are different by twice the inclination angle Θ, the direction of the liquid crystal molecules on the surfaces of the lower substrate 11 and the upper substrate 12 is They are separated by an angle of 2Θ to each other.

The smectic layer on the smectic has a property of maintaining a constant direction and requires a lot of energy to torsion or warpage deformation compared to other liquid crystal molecules.

When the rubbing directions of the upper substrate 12 and the lower substrate 11 are different from each other as shown in FIG. 3, three alignment states that the liquid crystal molecules may have may be assumed as follows. The first is a case where the smectic layer itself is deformed, and the second is a small region where the smectic layer itself is not deformed but different directions are formed between the upper and lower substrates 11 and 12 so that the directions of the liquid crystal molecules are discontinuously. In the third case, the liquid crystal molecules are continuously twisted from the lower substrate 11 to the upper substrate 12. In the first and second of these cases, many defects are observed macroscopically, and the effect to be obtained in the present invention cannot be obtained. In the third case, the smectic layer interacts with the liquid crystal alignment directions of the upper substrate 12 and the lower substrate 11 to be aligned in a direction in which energy is minimized, which is an alignment state required by the present invention.

As a result, in the present invention, the liquid crystal molecules rotate along the surface of the cone 40 formed by rotating a straight line having an angle Θ with the X axis about the X axis.

Accordingly, the rotation angle Φ of the liquid crystal molecules from the lower substrate 11 to the center point forms an angle of 0 ° to 90 °, and the liquid crystal molecules from the center to the upper substrate 12 rotate from 90 ° to 180 °. Make an angle. In addition, the horizontal angle θ of the liquid crystal molecules from the lower substrate 11 to the center point forms an angle from + Θ to 0, and the liquid crystal molecules from the center to the upper substrate 12 form a rotation angle of 0 to -Θ. .

As a result, the rotation angle φ between the molecules on the surfaces of the two substrates 11 and 12 becomes 180 °, and the difference in the horizontal angle θ is 2Θ, which is equal to the difference in the orientation angles between the two substrates 11 and 12.

Now, a change in the arrangement of the liquid crystal molecules when a high voltage is applied between the two substrates 11 and 12 will be described.

When an electric field is applied to the liquid crystal molecules by applying a voltage between the two substrates 11 and 12, the polarization vector of the liquid crystal molecules perpendicular to the length direction of the liquid crystal molecules is caused to be parallel to the electric field. The liquid crystal molecules will try to align perpendicular to the electric field. On the other hand, depending on the nature of the smectic liquid crystal liquid crystal director will continue to maintain a constant inclination angle. Thus, the liquid crystal molecules will be arranged along the surface of the induced cone in a direction perpendicular to the electric field, with the path closest to the side of the induced cone. As a result, all of the liquid crystal molecules are arranged in parallel with the alignment direction of the upper alignment layer 42 or the lower alignment layer 41 to completely distort the liquid crystal molecules formed while going from the lower surface of the liquid crystal layer 50 to the upper surface.

However, when the strength of the electric field is weak, only part of the twisting of the liquid crystal molecules is released. That is, the degree to which the arrangement of the liquid crystal molecules changes here depends on the magnitude of the applied voltage, and the liquid crystal material exhibits a continuous electro-optic effect according to the change of the magnitude.

Next, the operation of the liquid crystal display according to the exemplary embodiment of the present invention having such a structure will be described in detail with reference to FIG. 4.

FIG. 4 is a diagram illustrating a change in Stokes Parameters experienced by light passing through the liquid crystal cell.

In the case where no electric field is applied to the liquid crystal material, as shown in FIG. 4, incident light is linearly polarized while incident through the polarizing plate 20 so that the incident polarization is located on the equator corresponding to the linear polarized light. While the light travels through the liquid crystal material by a distance d and reaches the reflecting plate 31 of the lower substrate 11, the polarization of the light is changed to circular polarization and is located at the lower pole corresponding to the circular polarization. The light reaching the reflector 31 is reflected and the phase is deteriorated by 180 ° so that the polarization of the light moves to the opposite pole of the sphere, that is, the upper pole. The polarized light changes from circularly polarized light back to linearly polarized light while the reflected light travels back into the liquid crystal material by a distance d to the upper substrate 12. Thus, the polarization of the light is put back on the equator of the sphere, but its position is the opposite of the position at the first incident. This means that the polarization direction of the light is rotated by 90 °, so that the light is all absorbed in the process of passing through the polarizing plate 20, and eventually no light is emitted.

However, when an electric field is formed by applying different potentials between the first electrode 32 and the second electrode 31, the liquid crystal molecules are affected by the electric field, thereby forming a new arrangement. If the electric field is sufficiently strong and the torsion of the liquid crystal molecules is completely solved, the light is incident through the polarizing plate 20 and the polarized light passes through the liquid crystal material and hardly undergoes a change in polarization state. Therefore, the light undergoes only 180 ° phase change in the process of being reflected by the reflector 31 and reaches the polarizer 20 again and exits without being blocked by the polarizer 20.

If the electric field is not strong enough and the torsion of the liquid crystal molecules formed in the liquid crystal layer 50 is not completely solved, a change in the polarization state may occur to some extent, but the polarized light emitted from the reflected light is reflected as if the electric field is not applied. Since the polarized light of the incident light does not become 90 °, more than a predetermined amount of emitted light exists.

Then, as above, the amount of outgoing light becomes zero when the electric field is not applied and becomes a completely dark state, and when the electric field is applied, the amount of outgoing light gradually increases according to the intensity of the electric field, so that an ideal gray scale display is possible. Look at the conditions.

There may be several variables in finding an ideal condition for implementing a reflective liquid crystal display device using a ferroelectric liquid crystal material. That is, the cone tilt angle, the orientation angle, the degree of birefringence of the liquid crystal material, the type of polarization of the polarizing plate, and the direction of the polarization axis may be variables. Here, it is assumed that the kind of polarization of the polarizing plate is linearly polarized light, and the polarization axis direction coincides with the alignment direction of one of the vertical alignment films. In addition, it is assumed in calculation that the smectic liquid crystal layer is perpendicular to the upper and lower substrates.

Under these assumptions, calculations are made using the cone inclination angle and the birefringence amount dΔn of the cell as variables. In calculations, the Stokes parameter Shall be.

So let's first set the Stokes parameter Let's take a look at the reasons for this.

Stokes parameters consist of four time averages:

S ₀ = 《(A _x ) ² + (A _y ) ² 》,

S ₁ = 《(A _x ) ^2- (A _y ) ² 》,

S ₂ = 2 &_lt; A _x A _y cosδ &_gt;

S ₃ = 2 &_lt; A _x A _y sinδ >

Where A _x and A _y are the amplitudes of the x-axis component and the y-axis component, respectively, when the advancing direction of the light is the z-axis direction, δ is the phase difference between the x-axis component and the y-axis component, and the double parenthesis 《》 Indicates the time average value.

To see what the Stokes parameters mean, let's look at some cases.

First, in the case of unpolarized light, the A _x and A _y is S _0, because to have a random value, and the ^{_{2 "(A x) 2"}} , S 1 becomes zero. Normalizing this results in S ₀ = 1. Also, S ₂ and S ₃ are also zero since δ will have a random value with respect to time. In other words, the Stokes vectors (1, 0, 0, 0) represent unpolarized light.

For _y linearly polarized light, A _y is 0, so the normalized stock vector is (1, 1, 0, 0), and for y linearly polarized light, A _x is 0, so the normalized stock vector is (1, -1, 0, 0).

For right-hand circularly polarized light, δ =-(1/2) π, so the normalized Stokes vector is (1, 0, 0, -1) and left-hand circularly polarized light. In the case of δ = (1/2) π, the normalized Stokes vector is (1, 0, 0, 1).

finally, Is the case where light is completely circularly polarized.

Now using the Jones matrix In various cases, the optical thickness dΔn, the inclination angle of the cone, and the angle of the polarizing plate (the angle between the center line of the induced cone and the polarization direction of the polarizing plate) are calculated as variables.

In this case, the calculation is performed by dividing a cell into a plurality of layers to obtain a tilt angle and a twist angle in each layer and numerically calculating the result using a Jones matrix. In this case, it is assumed that the rotation angle Φ varies constantly from 0 ° to 180 °.

The results of this calculation are shown in FIG. FIG. 5 shows the variable S ₃ as a function of the cone tilt angle for a number of cases where the optical thickness d Δn is different.

According to Figure 5, optimum conditions Silver can be obtained when using a liquid crystal material with a cone inclination angle of 27 °, and the optical thickness dΔn at optimum conditions is 260 nm.

Based on the above calculation results, a reflective liquid crystal display device having the structure shown in FIG. 2 was manufactured and experimented. That is, the liquid crystal labeling device was manufactured using the ferroelectric liquid crystal material CS-1029 having the material constants shown in Table 1, and the experiment was conducted.

Phase transition SmC * 73 ℃ SmA 85 ℃ N * 91 ℃ Iso Spontaneous Polarization -41.3nCm-2 Cone Tilt Angle 25 ℃ Rotation Distance (Helical Pitch (N *)) -10㎛ Rotation Distance (Helical Pitch (SmC *)) 2 μm Optical Anisotropy 0.16

As shown in Table 1, the CS-1029 has a 25 ° cone inclination, which is slightly different from the 27 ° optimal calculation condition. Since the optical anisotropy is 0.16, the cell spacing should be 1.62 μm in order to achieve an optimal optical thickness (dΔn) of 260 nm. This is because accurate gap control is difficult due to the absence of a suitable spacer, since a liquid crystal display is manufactured without using a spacer. On the other hand, by using the secondary condition, the screen may be slightly colored and appear to be more practically applicable, and the cell spacing may be more easily realized by using a liquid crystal material having a smaller optical anisotropy value. A liquid crystal display device can be made.

Moreover, the orientation of the up-and-down orientation film was set to 54 degrees. At this time, the orientation direction may be four cases as shown in Figure 6, all four cases were produced and tested. As a result, in the case of A1 and A2 of FIG. 6, one region having a twisted structure appeared as the temperature gradually decreased in the cholesteic phase to the smectic phase. In the case of B1 and B2, two regions appear in the cholesteric phase and remain in the SmC * phase (ferroelectric smectic C phase). One of these areas represents a birefringent structure and the other represents a twisted structure. The darker areas seen through cross polarizers in the cholesteric phase appear in the form of bright islands on SmC * and have a twisted structure. The bright areas on the cholesteric areas appear as dark areas on the SmC * and have a birefringence structure.

The results of the measurement using a polarizing microscope and an optical detector of a liquid crystal display device in which the electro-optical characteristics are aligned with the polarization direction of the polarizer aligned with the center of the induced cone are shown in FIG. 7. Posted in

As shown in FIG. 7, the graph showing the change in the reflected light amount according to the voltage change is represented by two curves. The first curve A shows the lowest reflected light when the voltage is about 0V, and the second curve B shows the lowest reflected light when the voltage is about 2V. The cause of these two curves is not clear, but it seems to be a kind of hysteresis.

Both curves A and B shown in FIG. 7 show that the amount of reflected light changes as the voltage changes. In conclusion, it indicates that gray scale display through voltage regulation is possible. However, when designing the actual driving voltage waveform, two curves appear.

In the above experiment, only the case where the polarization direction of the polarizing plate is matched with the director axis of the liquid crystal molecules is considered, but this is for convenience of experiment and other arrangements are possible. In addition, the optical thickness dΔn and the cone tilt angle can be changed. Such various changes are described with reference to FIGS. 8 and 9.

FIG. 8 is a graph showing a gray scale display area in consideration of the polarization direction, the angle formed by the center line of the induced cone of the liquid crystal molecules (the angle of the polarizing plate), and the optical thickness of the cell, and FIG. 9 is a cone tilt angle of the ferroelectric liquid crystal molecules. It is a graph showing an area where gradation display is possible in consideration of the optical thickness of the cell and the cell.

Referring to Fig. 8, when the optical thickness is between about 180 nm and 400 nm, the angle of the polarizing plate is displayed in gray scale at a specific angle between 0 ° and about 40 °, between about 80 ° and 130 ° and between about 170 ° and 180 °. When the optical thickness is between about 700 nm and 890 nm, the angle of the polarizing plate is displayed at a specific angle between 0 ° and about 30 °, between about 65 ° and 120 ° and between about 155 ° and 180 °. It appears to be possible.

9, the cone tilt angle when the optical thickness is between about 180 nm and 400 nm has a specific angle between 20 ° and 30 ° and the cone tilt angle is 20 ° when the optical thickness is between about 700 nm and 890 nm. It appears that gradation display is possible when it has a certain angle between and 44 °.

At this time, both the optical thickness, the angle of the polarizing plate, and the cone tilt angle should be considered at the same time.

In the case of showing the electro-optical effect of FIG. 7, the optical thickness is 260 nm, the inclination angle of the cone is 25 °, and the angle of the polarizer is 25 ° Forms an angle equal to the angle of inclination). It can be seen that this condition is one of a number of conditions in which gray scale display is possible, as indicated by black dots in FIGS. 8 and 9.

According to the present invention, a reflective liquid crystal display using ferroelectric liquid crystal material may be implemented.

Claims (10)

A transparent first substrate having an inner side and an outer side, A polarizer attached to an outer surface of the first substrate and having a polarization direction in a first direction, A transparent first electrode formed on an inner side of the first substrate, A first alignment layer formed on the first electrode and aligning liquid crystal molecules in a second direction, A second substrate having an inner side and an outer side facing the inner side of the first substrate, A second electrode formed on an inner surface of the second substrate and also serving as a reflector; A second alignment layer formed on the second electrode and aligning liquid crystal molecules in a third direction different from the second direction; A reflective liquid crystal display device comprising a ferroelectric liquid crystal layer injected between the first alignment layer and the second alignment layer, The liquid crystal molecule of the ferroelectric liquid crystal layer is a reflection type liquid crystal display device that the direction is twisted in the second direction from the second direction to the third direction toward the surface of the second alignment film. In claim 1, An optical thickness (Δn · d) of the liquid crystal layer has a specific value between 180 nm and 400 nm. In claim 2, And the ferroelectric liquid crystal material has a specific value of a cone inclination angle of 20 ° to 30 ° when in the Smectic C * phase. In claim 3, And an angle formed between the first direction and the centerline of the induced cone of the liquid crystal molecules forms a specific angle between 0 ° and 40 °, between 80 ° and 130 °, and between 170 ° and 180 °. In claim 4, And an angle formed by the second direction and the third direction is twice the inclination angle of the cone. In claim 4, The optical thickness of the liquid crystal layer is 260 nm, the cone tilt angle of the liquid crystal is between 25 ° to 27 °, the angle between the second direction and the third direction is 54 °, the first direction and the second The reflective liquid crystal display device has the same direction. In claim 1, The optical thickness (Δn · d) of the ferroelectric liquid crystal material has a specific value between 700 nm and 890 nm. In claim 7, The ferroelectric liquid crystal material has a specular tilt angle of 20 ° to 44 ° when the Smectic C * phase is a reflection type liquid crystal display device. In claim 8, And an angle formed between the first direction and the centerline of the induced cone of the liquid crystal molecules forms a specific angle between 0 ° and 30 °, between 65 ° and 120 °, and between 155 ° and 180 °. In claim 9, And an angle formed by the second direction and the third direction is twice the inclination angle of the cone.