JPH04141630A - Reflection type liquid crystal electrooptic device - Google Patents

Abstract

PURPOSE:To eliminate coloration and light quantity loss and to improve threshold characteristics by arranging a polarizing element, a liquid crystal layer, a phase plate, and a reflection body in order as optical elements. CONSTITUTION:This device has basic structure wherein twisted nematic liquid crystal 104 is inserted between a substrate 103 where the reflection body 102 and phase plate 107 are installed and a transparent substrate 101. The the optical element constitution consists of the polarizing element 108, liquid crystal layer 104, phase plate 107, and reflection body 102 in order. Further, a transparent electrode 105 for applying an electric field to the liquid crystal layer is provided and the reflection body 102 formed of a thin film of metal serves as the other electrode. An incident/projection surface, a transparent electrode surface, and a reflecting surface are coated for reflection reduction to suppress unnecessary light beam reflection. Consequently, the degree of freedom of spectrum compensation increases to suppress the coloration and light quantity loss.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a reflective liquid crystal electro-optical device using liquid crystal.

[Prior art] A conventional reflective liquid crystal electro-optical device using a twisted liquid crystal uses a uniaxial electro-optic medium with a 1/4λ wavelength plate, USP 4019807, JP-A-56-436.
As described in No. 81, the twist angle was 45 degrees, and the linearly polarized incident light was incident at an angle with respect to the molecular axis.

[Problems to be Solved by the Invention] However, conventional reflective liquid crystal electro-optical devices have a problem in that there is little margin for the thickness of the liquid crystal layer, and display performance tends to be uneven. Furthermore, since the output light is elliptically polarized,
There were also problems with the loss of light intensity and the coloration of the emitted light. Another problem was that the electro-optical characteristics change slowly with respect to voltage, making it unsuitable for multiplex drive. Therefore, it is an object of the present invention to provide a reflective electro-optical device that has a phase plate disposed on a reflective surface, which causes less color change, less light loss, and excellent threshold characteristics.

[Means for Solving the Problems] The reflective liquid crystal electro-optical device of the present invention is characterized in that a polarizing element, a liquid crystal layer, a phase plate, and a reflector are arranged in this order as optical elements.

Further, one of the substrates is characterized in that it has a reflector and a phase plate.

Furthermore, one of the substrates is characterized by having an electrode that is a reflector and a phase plate formed on the electrode.

Further, the phase plate is characterized in that it is an electrical insulator.

Hereinafter, the details of the present invention will be shown by examples.

[Example] Example 1 FIG. 1 is a sectional view of a reflective electro-optical device of the present invention.

The reflective electro-optical device of the present invention has a basic structure in which a twisted nematic liquid crystal 104 is sandwiched between a transparent substrate 101 and a substrate 103 on which a reflector 102 and a phase plate 107 are installed. 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.
becomes. 105 is a transparent electrode for applying an electric field to the liquid crystal layer. A reflector 102 made of a metal thin film also serves as the other electrode. In addition, the entrance and exit surfaces, transparent electrode surfaces,
The reflective surface is coated with anti-reflection coating to suppress unnecessary light reflections.

Among several suitable conditions for the liquid crystal, the product Δnd of /n and thickness d is 0.5 μm, and the twist angle is 270°. Such conditions can be selected depending on the performance of the phase plate used and the required threshold characteristics.

Furthermore, the phase plate of this example is described in "Optics Vol. 19, p. 93".
Ta205 was obliquely deposited on the reflector by the method described in . These specific conditions are shown in Table 1.

Table 1 Liquid crystal layer twist Nematic Twist angle, dnd 0.5 μm Polarizing element Absorption type linear polarizer installation angle Polarized light output phase plate deposition angle nd Thickness Installation angle Ta2's Oblique Vapor deposited film 70' 0.14 μm 2 μm Reflector aluminum vapor deposited film with high refractive index azimuth 180° with respect to the polarizer on the incident side of the liquid crystal Further, this phase plate can also serve as an alignment film for the liquid crystal.

This phase plate utilizes the polarization characteristics of a diffraction grating, and the obliquely deposited film has the function of a phase type diffraction grating. Therefore, a diffraction grating with a polarization function can be used in the same way. This is an effect observed in a diffraction grating made with a pitch less than the wavelength, for example 'App1. Phys.
Letl, Vol. 42. It can be made by etching PMMA resin as described in J. P., 492'.

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 deposited layer and the diffraction grating on the alignment 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 insulating properties, it is possible to simultaneously protect the reflective electrode and isolate the liquid crystal and the electrode.

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

FIG. 3 shows the reflection spectrum when the switch is OFF. Traditional EC
Compared to the spectrum 302 of B mode (1/4λ mode), the present invention is also characterized in that it is possible to obtain a reflection spectrum 301 as wide as that even in a twisted state. This is done by designing the arrangement of the optical principal axis of the liquid crystal layer on the phase plate side and the high refractive index orientation of the phase plate, thereby canceling out the phase advance and phase delay due to the wavelength and compensating the reflection spectrum. As described above, according to the present invention, degrees of freedom are added to the phase amount of the phase plate to the And of the liquid crystal layer, the twist angle, and the angle of the polarizing element, making it possible to perform more free spectrum compensation.

Example 2 Example 2 is a case where a phase plate and a reflector are installed on the back side of a transparent substrate. The same thin film type phase plate as in Example 1 may be installed, but in this example, a commercially available film phase plate was bonded to the opposite side of the liquid crystal layer via a transparent substrate using an isotropic adhesive, and then A reflector was glued on top. FIG. 4 is a cross-sectional view thereof.The reflective electro-optical device of the present invention includes a reflector 402,
A transparent substrate 403 and a transparent substrate 4 on which a phase plate 407 is installed
It has a basic structure in which a twisted nematic liquid crystal 404 is sandwiched between 01 and 01. Therefore, the optical element configuration is
The polarizing element 408, the liquid crystal layer 404, the phase plate 407, and the reflector 402 are formed in this order. 405 is a transparent electrode for applying an electric field to the liquid crystal layer, and is installed on the liquid crystal side of the two transparent electrodes. Furthermore, anti-reflection coatings are applied to the input/output surfaces, transparent electrode surfaces, and reflective surfaces to suppress unnecessary light reflections. Details of this example are shown in Table 2.

Table 2 Liquid Crystal Layer Twisted Nematic Twist Angle 270'nd 0.93μm Polarizing Element Installation Angle Absorption Polarizer 225° with respect to the polarizer on the incident side of the liquid crystal Polarizing phase plate, 6nd Installation angle Uniaxially stretched birefringent film 0. 14 μm High refractive index orientation 180° with respect to the incident side polarizer of the liquid crystal Reflector Aluminum vapor deposited reflective film In this example, it is sufficient to install a phase plate and a reflector on the back side of a conventional liquid crystal electro-optical element, and the manufacturing process Embodiment 3 Embodiment 3 is an example in which the 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. An aluminum vapor-deposited film 503 is a reflector of the active matrix substrate 502, 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, 5
o6 is an opposing transparent substrate, 507 is an active element T
It is a PT element. Note that 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.

Table 3 Liquid crystal layer Δnd Polarizing element 1 Installation angle Polarizing element 2 Installation angle Phase plate Vapor deposition angle, 6nd Thickness Installation angle Reflector Akknife 1 Matrix substrate Twisted nematic 63''' 0.3 μm Absorption linear polarizer Liquid crystal incident side Polarized light output at 108° with respect to the elector Polarized beam splitter Polarized light output at 108° with respect to the elector Polarized beam splitter Polarized light output at 108° with respect to the elector Obliquely deposited film 70° 0.14 μm 2 μm High refractive index on the input side of the liquid crystal with respect to the elector The orientation is 153°.The twist angle of the quartz glass substrate with aluminum vapor deposited film TPT is installed.Figure 6 shows the electro-optical characteristics at that time.Figure 7 shows the reflection spectrum.Unlike Example 1.2, when driving with an active matrix, Since steep electro-optical characteristics are not required, this example selected a material with gentler electro-optic characteristics and a wider reflection spectrum than in Example 1.

As shown in Table 3, when a polarizing beam splitter is used as a polarizing element, under these conditions, when no voltage is applied, the reflectance is in an extinction state of 0, resulting in a display that is reversed from negative to positive with respect to a linear polarizing plate.

By laminating a reflective film and a phase plate on an active matrix substrate in this way, it was possible to simplify the manufacturing process and obtain a bright display with a wide reflection spectrum.

Also, the conventional 1/4^ condition is A nd = 0.138μ
Compared to M, a thicker liquid crystal layer can be tolerated, and the thickness of the liquid crystal layer can be easily controlled.

Although TPT was used in this example, MOS FET
The same effect can be obtained with an active matrix that assists the driving of liquid crystals, such as a two-terminal device.

Although the embodiments have been described above, the present invention can be applied not only to the above embodiments but also to a wide range of reflective optical elements, light valves, and the like.

[Effects of the Invention] As described above, according to the present invention, the degree of freedom in spectral compensation is increased, which has the effect of suppressing color change and loss of light amount. Furthermore, since the electro-optical characteristics are steep, it has the effect of excellent multiplex drive characteristics. Furthermore, since it is inserted between the reflective electrode and the liquid crystal, it has the effect of improving the reliability of the liquid crystal and the electrode. Furthermore, since the phase plate is installed closely inside the substrate, the structure is simple and the phase plate is less likely to be damaged.

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

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a reflective electro-optical device of 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 of the present invention when it is OFF. Section 4 is another cross-sectional view of the reflective electro-optical device according to the present invention. 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 shown in FIG. 5. FIG. 7 is a diagram showing the reflection spectrum of the LCD of FIG. 5. 101.401,506...Transparent substrate 102.402
,503...Reflector 103.403...Substrate 104 on which a phase plate is installed.
404,504...Liquid crystal layer 107.407,501...Phase plate 108.408...Active matrix large substrate on which polarizing element phase plate is installed or higher

Claims (1)

[Claims] 1) In a reflective liquid crystal electro-optical device in which a twisted nematic liquid crystal is sandwiched between two opposing substrates, a polarizing element, a liquid crystal layer, a phase plate, and a reflector are arranged in order as optical elements. A reflective liquid crystal electro-optical device characterized by: 2) The reflective liquid crystal electro-optical device according to claim 1, wherein one of the substrates has a reflector and a phase plate. 3) The reflective liquid crystal electro-optical device according to claim 1, wherein one of the substrates has an electrode that is a reflector and a phase plate formed on the electrode. 4) The reflective liquid crystal electro-optical device according to claim 1, wherein the phase plate is an electrical insulator.