JP2755428B2 - Reflective liquid crystal display - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a reflection type liquid crystal display element suitable for an oblique incidence optical system.

Liquid crystal display devices are widely applied as low power consumption flat panel displays and light valves for projection. In the case of a high-density display, an active matrix liquid crystal display element is preferable in terms of driving capability, but in a transmission type, the element area limits the aperture ratio. However, in the reflection type in which a reflection electrode is formed on an element, a sufficient aperture ratio can be obtained, and a high-quality, high-density display is possible. In particular, a reflection-type light valve for a projection or view finder that can specify the path of light can be easily applied to a reflection type. Above all, the reflection type using the oblique incidence optical system has the advantage that the configuration is simple. The present invention relates to a new mode reflection type liquid crystal display device suitable for an oblique incidence optical system.

[Conventional technology and its problems]

In the conventional reflection type liquid crystal display device, the mainstream is one in which light is passed twice before and after the reflection layer in a general transmission type display mode.
Specifically, TN (twisted nematic) mode used for watches and calculators and ST applied to OA terminals
An N (super twisted nematic) mode is a typical example of a reflective liquid crystal display device.

A first drawback of such a conventional example is that the reflection layer must be disposed outside the substrate with the liquid crystal layer interposed therebetween. This is because the above-described mode requires that the liquid crystal layer be sandwiched between the polarizing plates from both sides, and that the polarizing plate cannot be formed on the liquid crystal layer side of the glass substrate.

As described above, in an active matrix type liquid crystal display element, when a reflective layer is formed on a switching element to secure an aperture ratio, the reflective layer is disposed on the liquid crystal layer side of the substrate, so that it is naturally polarized light. The plate cannot be inserted between the liquid crystal layer and the reflective layer. If a mode that does not require a polarizing plate between the reflective layer and the liquid crystal layer is called a direct reflection type, the direct reflection type cannot be realized in the above-described example.

In the conventional example, there is a direct reflection type. Reflective liquid crystal display devices using the guest-host mode or the DS (dynamic scattering) mode have been reported since 1979-80. However, the contrast, stability and the like are not sufficient and have not been put to practical use at present.

A second disadvantage of the conventional example is that display characteristics in an oblique incidence optical system are not sufficient.

In the TN mode and the STN mode, basically, the highest display quality can be obtained near the vertical incidence system. However, in a vertical incidence system, efficient display is difficult without an expensive optical system such as a polarization splitting prism. To make the system simpler, an oblique incidence optical system is required.

SUMMARY OF THE INVENTION An object of the present invention is to provide a novel mode liquid crystal display device of an oblique incidence type and a direct reflection type.

[Means for solving the problem]

The reflection type liquid crystal display device of the present invention includes two substrates provided with electrodes and an alignment layer, a liquid crystal layer sandwiched between the substrates,
Assuming that the substrate has a reflective layer, the plane of the substrate is an XY plane, and the direction perpendicular to the substrate is the Z direction, the incident light incident on the reflective liquid crystal display element is in the XZ plane, This is light that is tilted with respect to the direction and whose polarization axis is in the Y direction parallel to the substrate. At least the orientation direction of the liquid crystal molecules on the base electrode side on the incident side is substantially in the ZY plane and is applied to both substrates. By modulating the angle with respect to the Y direction in accordance with the degree of the voltage, a novel mode of an oblique incidence type and a direct reflection type is provided.

〔Example〕

Hereinafter, the present invention will be described based on examples. FIG. 1 is a schematic sectional view of a reflective liquid crystal display element according to an embodiment of the present invention in a state where no voltage is applied.

The reflection type liquid crystal display element of this embodiment includes two substrates (an upper substrate 1 and a lower substrate 2) provided with electrodes (a transparent electrode 3 and a reflection electrode 4) and alignment layers 5 and 6, and a substrate 1 between the substrates. 2 and a reflective layer (in this embodiment, the reflective electrode 4 also serves as a reflective layer).

Here, the plane within the substrate is an XY plane, and the direction perpendicular to the substrate is Z
FIG. 1A is a cross-sectional view along the XZ plane, and FIG. 1B is a cross-sectional view along the YZ plane.

FIGS. 2A and 2B are a cross-sectional view on the XZ plane and a cross-sectional view on the YZ plane in a voltage applied state.

In the state where no voltage is applied in FIG. 1, the incident direction of the incident light 11 incident on the reflective liquid crystal display element is in the XZ plane and is inclined with respect to the Z direction. The polarization axis is in the Y direction parallel to the substrate.

At least the alignment direction of the liquid crystal molecules 16 on the substrate side on the incident side is substantially on the ZY plane. Further, in the present embodiment, the alignment direction of the liquid crystal molecules between the substrates 1 and 2 when no voltage is applied is substantially parallel and uniformly on the ZY plane.

In such a state where no voltage is applied, the polarization axis of the obliquely incident light always enters at an almost constant angle with respect to the alignment direction of the liquid crystal molecules, and the incident polarized light is rotated by a certain degree and emitted.

In particular, when the angle of the arrangement direction 16 of the liquid crystal molecules with respect to the Y direction is within about 10 degrees, the polarization axis of the obliquely incident light is always almost parallel to the arrangement direction of the liquid crystal molecules, and the incident polarized light is hardly rotated and is like 12 as it is. Is emitted.

In the voltage application state shown in FIG. 2, the orientation direction 15 of the liquid crystal molecules 17 on at least the incident side of the substrate is substantially on the ZY plane and is inclined with respect to the Y direction of the substrate plane. In this embodiment, since the alignment direction of the liquid crystal molecules between the two substrates 1 and 2 when no voltage is applied is almost parallel, the liquid crystal molecules are almost in the ZY plane both in the voltage applied state and between the two substrates. With respect to the angle θ.

In such a voltage applied state, the polarization axis of the obliquely incident light 13 always has a fixed angle with respect to the alignment direction of the liquid crystal molecules, the incident polarized light 13 becomes elliptically polarized light, and the principal axis of the ellipse is rotated and emitted like 14. .

In particular, when the angle of the liquid crystal molecules with respect to the Y direction in the voltage applied state is about 45 degrees, the output polarized light can be made almost orthogonal to the incident polarized light by appropriately selecting the birefringence amount (Δnxd) of the liquid crystal layer. It is.

FIG. 4 shows the relationship between the voltage V and the modulation reflection intensity R of the reflection type liquid crystal display device of the present invention. The polarization axis of the incident polarized light is perpendicular to the polarization axis of the output polarizer. In the voltage applied state, as described with reference to FIG. 1, since the polarization axes of the incident light and the outgoing light are parallel to the ray axis, the reflected light intensity after passing through the polarizer is almost 0% as shown in FIG. Becomes In this state, an achromatic high-quality black display with little wavelength dispersion can be obtained. On the other hand, when the voltage is applied, particularly when the angle of the liquid crystal molecules with respect to the Y direction is about 45 degrees, if the birefringence amount (Δn × d) of the liquid crystal layer is appropriately designed, the output polarized light becomes almost orthogonal to the incident polarized light.
Mostly pass through the polarizer. Therefore, the intensity of the reflected light after passing through the polarizer can be made extremely high as indicated by 43. The color dispersion in this state is not as good as the black state, but white is not as sensitive to the color tone as black, so that a practically satisfactory white display can be obtained.

FIG. 3 shows an example of a projection display using the reflection type liquid crystal display element 31 of the embodiment shown in FIGS. The incident light 33 polarized parallel to the substrate surface by the polarizer 35 is modulated by the reflective liquid crystal display element 31, and only one polarized light is polarized.
The modulated light 34 extracted at 36 is projected on the screen 32. In this embodiment, since an oblique incidence optical system is possible, an expensive polarizing beam splitter or a beam splitter having poor light use efficiency is not required.

FIG. 5 is a sectional view of a reflection type liquid crystal display device according to another embodiment of the present invention in a state where no voltage is applied.

In the embodiment shown in FIGS. 1 and 2, the alignment direction of the liquid crystal molecules was substantially parallel between the two substrates when no voltage was applied, but in this embodiment, the alignment direction of the liquid crystal molecules was both parallel when no voltage was applied. It is twisted in the XY plane between the substrates. However, if the orientation direction of the liquid crystal molecules on at least the substrate side on the incident side is substantially in the ZY plane as in the embodiment of FIGS. 1 and 2, a similar effect can be obtained by the optical rotation of the twisted structure. The advantage of using the twisted structure is that the steepness of the relationship between the voltage and the anti-light transmission is improved, and the contrast and the driving voltage are improved.

FIG. 6 shows another embodiment of the present invention. 1 and 2 is that a phase correction plate 61 is provided on the front surface. The phase correction plate 61 is a stretched uniaxial birefringent film or a liquid crystal cell in parallel or twist alignment. When the phase correction plate 61 is inserted, the optimum amount of refraction Δn × d of the liquid crystal cell can be shifted, and the degree of freedom in designing the thickness of the liquid crystal layer and the material is improved.

In the embodiment, the example of the projector has been described, but the present invention is also effective in the application range of other reflective liquid crystal display elements. For example, if applied to a viewfinder, etc., extremely high quality,
High-density products can be realized.

The driving method is not limited to active matrix driving, and simple matrix driving is also possible.

〔The invention's effect〕

As is clear from the above embodiments, the present invention provides a novel reflection type liquid crystal display device which has not been conventionally provided. According to the present invention, the reflection layer can be built in the liquid crystal cell, so that not only the configuration can be simplified, but also high-density active matrix driving and the like can be applied. The optical system to be used is simple, and a high-quality, high-density reflective display can be realized with a simple configuration by using the present invention.

[Brief description of the drawings]

1 (a), (b), 2 (a), (b), 5
FIG. 6 is a schematic cross-sectional view showing an embodiment of the reflective liquid crystal display device of the present invention. FIG. 3 is an explanatory diagram showing an arrangement of the projector using the reflective liquid crystal display device of the present invention in the embodiment. FIG. 4 is a graph showing the voltage versus reflection intensity characteristics of the reflection type liquid crystal display device used in the embodiment of FIGS. 1 ... upper substrate, 2 ... lower substrate, 3 ... transparent electrode, 4 ...
Reflecting electrodes, 5, 6,..., Alignment layers, 7,.

Claims (5)

(57) [Claims] 1. A reflective type comprising: two substrates provided with electrodes and an alignment layer; a liquid crystal layer and a reflective layer sandwiched between the substrates; and a polarizer provided on an incident light side and a reflected light side. In a liquid crystal display device, when the plane in the substrate is an XY plane and the direction perpendicular to the substrate is a Z direction, the incident light incident on the reflective liquid crystal display element is in the XZ plane. Linearly polarized light that is inclined with respect to the Z direction and whose polarization axis is in the Y direction parallel to the substrate,
A reflective liquid crystal display device characterized in that at least the orientation direction of the liquid crystal molecules on the substrate side on the incident side is substantially in the ZY plane, and the angle with respect to the Y direction is modulated by the degree of the voltage applied to both substrates. 2. The arrangement direction of liquid crystal molecules modulated by a voltage applied to both substrates is modulated between a state in which the angle with respect to the Y direction is about 10 degrees or less and a state in which the angle is about 45 degrees. The reflective liquid crystal display device according to claim 1, wherein: 3. The reflective liquid crystal display device according to claim 1, wherein the orientation direction of the liquid crystal molecules is substantially parallel between the two substrates when no voltage is applied. 4. The reflective liquid crystal display device according to claim 1, wherein the alignment direction of the liquid crystal molecules is twisted between the two substrates in the XY plane in a state where no voltage is applied. 5. The reflection type liquid crystal display device according to claim 1, wherein a phase compensator is disposed on an incident light side or an outgoing light side of the incident side substrate.