JPH08136913A - Reflection type antiferroelectric liquid crystal display device - Google Patents

Abstract

PURPOSE: To provide a reflection type antiferroelectric liquid crystal display device with which an improvement in brightness in a bright state is possible. CONSTITUTION: A polarizing plate 6 is arranged on the front surface side of a smectic liquid crystal layer 1 and a reflection plate 7 is arranged on the rear surface side of this smectic liquid crystal layer 1. The absorption axis of this polarizing plate 6 is arranged nearly parallel with the optical axis in the antiferroelectric phase of the smectic liquid crystal layer 1. Further, the product of the layer thickness (d) of the liquid crystal layer 1 and the double refractive value Δn of liquid crystals, i.e., retardation Δn.d and wavelength λof incident light are so set as to satisfy the relation Δn.d= (1/4)+(m/2)±0.1}.λwhen (m) is defined as an integer of >=0.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection type antiferroelectric liquid crystal display device.

[0002]

2. Description of the Related Art In recent years, the application of liquid crystal display devices has been expanded from calculators to word processor and personal computer displays due to the remarkable improvement in display performance due to the progress of liquid crystal display technology. further,
Expectations are growing that the market will expand as a display for portable information devices. Since it is battery-powered for portable applications, it is an important issue to reduce power consumption. Especially, the power consumption by the backlight is high. Therefore, as a liquid crystal display device, a reflective liquid crystal display device that does not use a backlight is often used.

As a conventional liquid crystal display device for portable use, an optical compensation type simple matrix drive super twist nematic (STN) type liquid crystal display device is mainly used. Further, in order to further improve the display quality, development of a two-terminal element type active drive twist nematic (TN) type liquid crystal display device and a ferroelectric liquid crystal display device is in progress.

A conventional reflection type antiferroelectric liquid crystal display device will be described below. FIG. 2 is a structural sectional view of a conventional reflective antiferroelectric liquid crystal display device. In FIG. 2, 21 is a smectic liquid crystal layer, 22 is a transparent electrode, 23 is a substrate, and 2 is a substrate.
4 is a sealing resin, 25 is an alignment film, 26 is a polarizing plate, and 27 is a reflecting plate. The smectic liquid crystal layer 21 is a transparent electrode 2
2 is sealed between the two substrates 23 formed on the inner surface and inside the sealing resin 24 formed by printing and coating around the substrates. The smectic liquid crystal layer 21 is aligned in a predetermined direction by subjecting an alignment film 25 formed by printing on the transparent electrode 22 to an alignment treatment. Further upper and lower substrate 2
The polarizing plate 26 is attached to the outside of the polarizing plate 3, and the reflection plate 27 is attached to the outside of the one polarizing plate 26.

FIG. 3 is a diagram for explaining the operating principle of a conventional antiferroelectric liquid crystal panel, which is a diagram of the panel viewed from above. When no voltage is applied between the substrates, as shown in FIG.
As in (b), it is in the antiferroelectric phase, and liquid crystal molecules are arranged in zigzag. At this time, the optical axis 33 coincides with the layer normal direction. When a DC voltage is applied, as shown in FIG. 3A or 3C, a transition is made to the ferroelectric phase, and the liquid crystal molecules are arranged so that their polarization is oriented in the direction of the electric field. The absorption axis 31 of the upper polarizing plate and the absorption axis 32 of the lower polarizing plate are arranged in parallel, and the absorption axes 31 and 32 are aligned with the optical axis 33 in the antiferroelectric phase. Therefore, the antiferroelectric phase is in a bright state. Optical axes 34 and 35 in the ferroelectric phase are absorption axes 3 of the polarizing plate.
Since it is inclined by θ (θ is not 0) from 1, 32, a birefringence effect occurs. It is optically symmetrical with respect to the polarity of the voltage. The birefringence value of the liquid crystal layer is λ for the wavelength λ of visible light.
When it is / 2, it becomes a linearly polarized light which is orthogonal to the incident linearly polarized light on the reflecting surface, and a dark state can be realized. The above is the setting of normally white. If the two polarizing plates are arranged orthogonally to each other, the setting is normally black.

[0006]

However, the transmittance of the polarizing plate is about 90% even when linearly polarized light is incident in parallel with the polarization axis, and the conventional configuration using two polarizing plates is sufficient. I couldn't get good brightness. Particularly, in the case of a reflection type panel, since a backlight is not used and light passes through the polarizing plate four times, the attenuation of the light amount is a serious problem.

The present invention solves the above problems,
An object of the present invention is to provide a reflection type antiferroelectric liquid crystal display device capable of improving brightness in a bright state.

[0008]

According to a first aspect of the present invention, there is provided a reflection type antiferroelectric liquid crystal display device, wherein an antiferroelectric liquid crystal layer is provided between a pair of substrates which face each other with an alignment film formed on the surface facing inside. Hold it, place a polarizing plate on the front side of the antiferroelectric liquid crystal layer,
A reflection plate is placed on the back side of the antiferroelectric liquid crystal layer, the polarization axis or absorption axis of the polarizing plate is placed almost parallel to the optical axis of the antiferroelectric liquid crystal layer in the antiferroelectric phase, and The retardation Δn · d, which is the product of the layer thickness d of the ferroelectric liquid crystal layer and the birefringence value Δn of the liquid crystal, and the wavelength λ of the incident light have the relationship of (Equation 1).

According to another aspect of the present invention, there is provided a reflection type antiferroelectric liquid crystal display device, wherein an antiferroelectric liquid crystal layer is sandwiched between a pair of substrates opposed to each other with an alignment film formed on the surface facing inside, and the antiferroelectric liquid crystal layer is sandwiched. A polarizing plate is placed on the front side of the liquid crystal layer and a reflector is placed on the back side of the antiferroelectric liquid crystal layer, and the polarization axis or absorption axis of the polarizing plate is set in the ferroelectric phase of the antiferroelectric liquid crystal layer. The retardation Δn · d, which is the product of the layer thickness d of the antiferroelectric liquid crystal layer and the birefringence value Δn of the liquid crystal, and the wavelength λ of the incident light are (equation 1). Have a relationship.

[0010]

According to the structure described in claim 1, since the absorption axis or the polarization axis of the polarizing plate is substantially parallel to the optical axis of the antiferroelectric phase in the off-voltage state, the linearly polarized light passing through the polarizing plate is It returns with the same linearly polarized state. Therefore, it becomes a bright state, and its brightness is comparable to the brightness when one polarizing plate is attached to the reflection plate. When an on-voltage is applied, the liquid crystal layer transitions to the ferroelectric phase and the optical axis of the liquid crystal layer forms an intersection angle of only the tilt angle θ from the absorption axis of the polarizing plate or the polarization axis. After passing through the polarizing plate, the incident light becomes linearly polarized light, and is then reflected by the product of the layer thickness d of the liquid crystal layer and the birefringence value Δn of the liquid crystal, that is, the birefringence due to the retardation Δn · d, and then returns. Unlike the off-voltage state, the emitted light is in an elliptically polarized state. Liquid crystal layer retardation Δn · d and incident light wavelength λ
However, when the relationship of (Equation 1) is satisfied, the light becomes circularly polarized on the reflecting surface, and the light after being reflected and passing through the liquid crystal layer again becomes a state close to linearly polarized light in the direction orthogonal to the incident linearly polarized state,
At this time, a dark state can be realized. Thus, normally
The white display is displayed, and the polarizing plate that used to use two sheets
By using only one sheet, the light attenuation can be suppressed and the brightness in the off-voltage state can be improved.

According to a second aspect of the present invention, the polarization axis or the absorption axis of the polarizing plate is arranged substantially parallel to the optical axis of the ferroelectric phase of the antiferroelectric liquid crystal layer. It is clear that, unlike the configuration described above, a normally black display is obtained, and as in claim 1, by using only one polarizing plate, which has been conventionally used with two sheets, the attenuation of light can be suppressed. The brightness in the on-voltage state can be improved.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing the structure of a reflection type antiferroelectric liquid crystal display device according to an embodiment of the present invention. In FIG. 1, 1 is a smectic liquid crystal layer (antiferroelectric liquid crystal layer), 2 is an electrode, 3 is a substrate, 4 is a sealing resin, 5 is an alignment film, 6 is a polarizing plate, and 7 is a reflecting plate.

The smectic liquid crystal layer 1 is sealed between two substrates 3 having a transparent electrode 2 formed on the inner surface and inside a sealing resin 4 formed by printing around the substrates. In the smectic liquid crystal layer 1, the alignment film 5 formed by printing on the electrode 2 was aligned in the parallel direction by subjecting the upper and lower substrates 3 to rubbing alignment treatment. The rubbing direction coincided with the layer normal, and hence the optical axis of the antiferroelectric phase. Further, a polarizing plate 6 was attached to the outside of one (front side) substrate 3 such that its absorption axis was parallel to the optical axis of the antiferroelectric phase. Also,
The reflection plate 7 was installed outside the other (back side) substrate 3.

In order to set the retardation of the smectic liquid crystal layer 1 to 1/4 of the central wavelength (about 550 nm) of visible light, a smectic liquid crystal having a refractive index of 0.09 in the ferroelectric phase is used and the cell thickness is 1.5 μm. To satisfy the relationship of (Equation 1). According to this embodiment, a good dark state can be realized in the on-voltage state based on the operation principle described above in (action).
Further, the brightness of the bright state in the off-voltage state is about 20 as compared with the conventional configuration using two polarizing plates.
% Improved.

In this embodiment, the absorption axis of the polarizing plate 6 is parallel to the optical axis of the antiferroelectric phase, but the polarizing axis of the polarizing plate 6 is parallel to the optical axis of the antiferroelectric phase. However, in this case, both are normally white display which is in a bright state when the voltage is off. Further, it is apparent that if the absorption axis or the polarization axis of the polarizing plate 6 is arranged parallel to the optical axis in the ferroelectric phase, a normally black display is obtained.

Further, in this embodiment, the reflection plate 7 is connected to the substrate 3
Although it is attached to the outside of the substrate, it can also serve as the electrode 2 formed on the inner surface of the substrate 3. That is, when a metal, preferably aluminum, is vapor-deposited on the inner surface of the substrate 3 on the side where the polarizing plate 6 is not attached (back side), and an electrode pattern is formed through a photolithography process, this aluminum electrode functions as a reflection plate. To do.

Further, in this embodiment, a simple matrix drive liquid crystal panel has been described as an example, but it is obvious that the present invention can be easily applied to an active matrix drive liquid crystal panel in which an active element such as a thin film transistor is formed in each pixel. .

[0018]

According to the reflection type anti-ferroelectric liquid crystal display device of the first aspect, normally white display is achieved, and by using one polarizing plate from the conventional two polarizing plates, light attenuation is suppressed. As a result, the light utilization efficiency can be improved, and the brightness of the off-voltage application state can be improved.

According to the reflection type antiferroelectric liquid crystal display device of the second aspect, normally black display is achieved, and by using one polarizing plate from the conventional two polarizing plates, light attenuation can be suppressed. Utilization efficiency can be improved, and it is possible to improve the brightness of the on-voltage application state.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a reflective antiferroelectric liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a sectional view of a conventional reflective antiferroelectric liquid crystal display device.

FIG. 3 is a diagram illustrating an operation principle of a conventional reflection type antiferroelectric liquid crystal display device.

[Explanation of symbols]

 1 Smectic liquid crystal layer 2 Electrode 3 Substrate 4 Seal resin 5 Alignment film 6 Polarizing plate 7 Reflector

Claims (2)

[Claims] 1. An antiferroelectric liquid crystal layer is sandwiched between a pair of substrates which face each other with an alignment film formed on the surface facing inside, and a polarizing plate is disposed on the front side of the antiferroelectric liquid crystal layer. A reflection plate is arranged on the back side of the antiferroelectric liquid crystal layer, and the polarization axis or absorption axis of the polarizing plate is arranged substantially parallel to the optical axis in the antiferroelectric phase of the antiferroelectric liquid crystal layer, Further, the retardation Δn · d, which is the product of the layer thickness d of the antiferroelectric liquid crystal layer and the birefringence value Δn of the liquid crystal, and the wavelength λ of the incident light are expressed by the following equation: Δn · d = {(1 / 4) + (m / 2) ± 0.1} · λ (where m is an integer of 0 or more), which is a reflective antiferroelectric liquid crystal display device. 2. An antiferroelectric liquid crystal layer is sandwiched between a pair of substrates that face each other with the alignment film formed on the surface facing inward, and a polarizing plate is placed on the front side of the antiferroelectric liquid crystal layer. A reflection plate is arranged on the back side of the antiferroelectric liquid crystal layer, and the polarization axis or the absorption axis of the polarizing plate is arranged substantially parallel to the optical axis in the ferroelectric phase of the antiferroelectric liquid crystal layer, and , A reflection type anti-strength having a relationship of a retardation Δn · d, which is a product of the layer thickness d of the anti-ferroelectric liquid crystal layer and a birefringence value Δn of the liquid crystal, and a wavelength λ of incident light, according to (Equation 1). Dielectric liquid crystal display device.