JP3067189B2 - Liquid crystal electro-optical device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a reflective liquid crystal electro-optical device using a liquid crystal.

[Prior Art] A conventional reflection type liquid crystal electro-optical device using a twisted liquid crystal uses a uniaxial electro-optical medium as a 1 / 4λ wave plate, as described in US Pat. No. 4019807 and JP-A-56-43681. As described above, the incident light having a twist angle of 45 degrees and being linearly polarized was incident with an inclination with respect to the molecular axis.

[Problems to be Solved by the Invention] However, the conventional reflection type liquid crystal electro-optical device has a problem that the margin of the thickness of the liquid crystal layer is small and the display performance tends to be uneven. Further, since the output light is elliptically polarized light, there are also problems such as loss of light quantity and coloring of the emitted light. Further, there is a problem that the change of the electro-optical characteristics with respect to the voltage is gradual and is not suitable for multiplex driving. In view of the above, an object of the present invention is to provide a reflection type electro-optical device which is colored by installing a phase plate on a reflection surface, has a small light amount loss, and has excellent threshold characteristics.

[Means for Solving the Problems] In a liquid crystal electro-optical device according to the present invention, in which a liquid crystal is sandwiched between a pair of opposed substrates, the liquid crystal side of one of the pair of substrates is provided on a liquid crystal side. A reflector and the phase plate are formed, and a polarizing means is arranged only on the other substrate side.

 Hereinafter, the present invention will be described in detail with reference to examples.

Example Example 1 FIG. 1 is a sectional view of a reflection type electro-optical device according to the present invention. The reflective electro-optical device of the present invention has a base structure in which a twisted nematic liquid crystal 104 is sandwiched between a transparent substrate 101 and a substrate 103 provided with a reflector 102 and a phase plate 107. Therefore, the optical element configuration is, in order, the polarizing element 108,
The liquid crystal layer 104, the phase plate 107, and the reflector 102 are formed. 105 is a transparent electrode for applying an electric field to the liquid crystal layer. The other electrode also serves as a reflector 102 formed of a metal thin film. Further, an anti-reflection coating is applied to the incident / exit surface, the transparent electrode surface, and the reflection surface to suppress unnecessary light reflection.

Among several suitable conditions for the liquid crystal, the product Δnd of Δn and the thickness d is 0.5 μm and the twist angle is 270.
゜ is selected. Such conditions can be selected according to the performance of the phase plate used and the required threshold characteristics.

The phase plate of this example is obtained by obliquely depositing Ta ₂ O ₅ on a reflector by the method described in “Optics, Vol. 19, p. 93”. Table 1 shows these specific conditions.

Further, this phase plate can also serve as an alignment film of the liquid crystal.

This phase plate utilizes the polarization characteristics of the diffraction grating, and the obliquely deposited film has the function of a phase type diffraction grating.
Therefore, a diffraction grating having a polarizing function can be used in the same manner. This is an effect observed in a diffraction grating made with a pitch equal to or less than the wavelength, for example, “Appl. Phys. Lett., Vol.
42, p.492 ", by etching a PMMA resin.

Further, an optically isotropic interlayer film may be provided between the phase plate and the liquid crystal layer. This can reduce the influence of the vapor deposition layer and the diffraction grating on the orientation of the liquid crystal, and can also flatten the surface. In this example, polyimide was spin-coated to form an alignment layer and a protective layer.

Further, by using a phase plate having an insulating property, protection of the reflective electrode and isolation of the liquid crystal and the electrode can be performed simultaneously.

The electro-optical characteristics of this device are different from the conventional ECB mode.
As shown in FIG. 2, it has a sharp falling characteristic, and the number of multiplex drive lines can be increased. this is
This is an effect due to the elasticity of the twisted liquid crystal similar to the STN liquid crystal display.

FIG. 3 is a reflection spectrum at the time of OFF. Compared with the conventional ECB mode (1 / 4λ mode) spectrum 302, the present invention is also characterized in that a broad reflection spectrum 301 comparable to that of a twisted state can be obtained. This is to cancel out the leading and lagging phases due to the wavelength by compensating the reflection spectrum by designing the arrangement of the optical axis of the liquid crystal layer on the phase plate side and the high refractive index direction of the phase plate. As described above, according to the present invention, the degree of freedom of the phase amount of the phase plate is added to the Δnd of the liquid crystal layer, the twist angle, and the angle of the polarizing element, so that more free spectrum compensation is possible.

Reference Example A reference example is a case where a phase plate and a reflector are installed on the back side of a transparent substrate. Although the same thin-film phase plate as in Example 1 may be installed, in this reference example, a commercially available film phase plate is bonded to the opposite side of the liquid crystal layer via a transparent substrate with an isotropic adhesive, and furthermore, The reflector was glued on top. FIG. 4 is a sectional view thereof. The reflective electro-optical device of the present reference example includes a reflector 402,
It has a basic structure in which a twisted nematic liquid crystal 404 is sandwiched between a transparent substrate 403 provided with a phase plate 407 and a transparent substrate 401. Therefore, the optical element configuration is, in order, the polarizing element 408, the liquid crystal layer 404, the phase plate 407, and the reflector 402. 405
Is a transparent electrode for applying an electric field to the liquid crystal layer, and is provided on the liquid crystal side of the two transparent electrodes. Further, an anti-reflection coating is applied to the incident / exit surface, the transparent electrode surface, and the reflection surface to suppress unnecessary light reflection. Table 2 shows details of this reference example.

In this reference example, the phase plate and the reflector need only be installed on the back side of the conventional liquid crystal electro-optical element, and the excellent effects of the present invention can be obtained without changing the manufacturing process.

Embodiment 2 Embodiment 2 is an example in which the present invention is applied to an active matrix type LCD. FIG. 5 is a sectional view of an active matrix type LCD of the present invention. Active matrix substrate 502
An aluminum vapor-deposited film 503 serving as a reflector, and a thin-film phase plate 501 is vapor-deposited thereon in the same manner as in the first embodiment. Therefore, the optical configuration is exactly the same as in the first embodiment.
504 is a liquid crystal layer, 505 is a transparent counter electrode, 506 is a counter transparent substrate, and 507 is a TFT element as an active element. In addition, a linear polarizing plate and a polarizing beam splitter can be selected as the polarizing element placed in front of the liquid crystal cell.

 Detailed parameters are shown in Table 3.

FIG. 6 shows the electro-optical characteristics at that time. FIG. 7 is a reflection spectrum. Unlike the first and second embodiments, when driving with an active matrix, a steep electro-optical characteristic is not required. Therefore, in the present embodiment, a condition in which the electro-optical characteristic is gentler than that of the first embodiment and the reflection spectrum is wide is used. I chose.

As shown in Table 3, when a polarizing beam splitter is used as the polarizing element, the extinction state is 0 when no voltage is applied under this condition, and the display is in a state where the negative / positive is inverted with respect to the linear polarizing plate. .

Thus, a reflective film on the substrate of the active matrix,
By laminating the phase plates, it was possible to simplify the manufacturing process and obtain a bright display with a wide reflection spectrum.

Also, compared to the conventional 1 / 4λ condition, Δnd = 0.138 μm,
A large liquid crystal thickness can be tolerated, and the thickness control of the liquid crystal layer becomes easy.

Although a TFT is used in this embodiment, the same effect can be obtained with an active matrix such as a MOSFET or a two-terminal element that assists the driving of the liquid crystal.

Although the embodiments have been described above, the present invention is widely applicable not only to the above embodiments but also to a wide range of reflection-type optical elements and light valves.

[Effects of the Invention] As described above, according to the present invention, the degree of freedom of spectrum compensation is increased, thereby providing an effect of coloring and suppressing loss of light quantity. In addition, the steep electro-optical characteristics have an effect of excellent multiplex driving characteristics. Furthermore, since the liquid crystal enters between the reflective electrode and the liquid crystal, there is an effect of improving the reliability of the liquid crystal and the electrode. Further, since the phase plate is closely mounted on the inside of the substrate, there is an advantage that the configuration is simple and the phase plate is less damaged.

The type in which the phase plate is installed inside the substrate has an advantage that there is no double image caused by the thickness of the substrate.

[Brief description of the drawings]

FIG. 1 is a sectional view of a reflective electro-optical device according to the present invention. FIG. 2 is an electro-optical characteristic diagram of the reflective electro-optical device of the present invention. FIG. 3 is a reflection spectrum of the reflection-type electro-optical device according to the present invention at the time of OFF. FIG. 4 is another sectional view of the reflection type electro-optical device according to the reference example. FIG. 5 is a sectional view of an active matrix type LCD of the present invention. FIG. 6 is an electro-optical characteristic diagram of the LCD of FIG. FIG. 7 is a diagram showing a reflection spectrum of the LCD of FIG. 101, 401, 506 Transparent substrate 102, 402, 503 Reflector 103, 403 Substrate provided with phase plate 104, 404, 504 Liquid crystal layer 107, 407, 501 Phase plate 108, 408 Polarizing element 502 Active matrix substrate provided with phase plate

Claims (1)

(57) [Claims] 1. A liquid crystal electro-optical device comprising a pair of substrates facing each other, wherein a liquid crystal is sandwiched between a pair of substrates facing each other, wherein the reflector and the phase plate are formed on a liquid crystal side of one of the pair of substrates. A liquid crystal electro-optical device comprising a polarizing means arranged only on the other substrate side.