JPS6254848A - Optical disc device using ferroelectric liquid crystal - Google Patents

Abstract

PURPOSE:To make the titled device particularly effective when the rewriting times is comparatively high by using a liquid crystal therein. CONSTITUTION:The titled disc consists of a liquid crystal cell, a liquid crystal that shows ferroelectricity, and a light-reflecting layer. The optical disc also has a pair of counter substrate 3 and 7, at least one 3 of which is light- transmissivity. The pair of substrates 3 and 7 have a pair of electrodes 4 and 6 on their inner sides, one 4 of which is light-transmissivity while the other 6 is light-reflecting. And further, an orientation processing is applied to one of the electrodes and a non-orientation processing to the other, and between the, the liquid crystal 5 is packed. The periphery of this optical disc is sealed 30, 30' to prevent the liquid crystal from being subjected to the atmospheric air. It also has electrodes for external contacting 32 and 32' that extend from the pair of electrodes 4 and 6. The electrodes 32 and 32' are made contacting the terminals 31 and 31' of the lead wires 13 and 13' running from a signal source 25 at the time of writing or deleting 103.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Application of the Invention This invention relates to a ferroelectric liquid crystal (hereinafter referred to as a liquid crystal substance) having a dye-added rewritable non-volatile memory function.
The purpose of the present invention is to propose a rewritable optical disc device that uses a Non-rewritable digital disk memory devices are known. This application is expected to have a very promising future as an optical disk memory device not only for audio and video but also for information processing. However, these disk memories cannot be rewritten. For this reason, a system that allows rewriting is required, and a magneto-optical memory device is known as a typical example. In addition, chalcogen (tellurium)
An amorphous semiconductor optical disk memory device using amorphous semiconductor is also known.

``Problems that the invention seeks to solve'' However, disk devices using magneto-optical memory use extremely expensive and rare materials, leaving concerns about future mass production. Furthermore, in the method using a chalcogen-based amorphous semiconductor, control of light is extremely delicate.

From these, materials that can be produced in large quantities are used, the light can be turned on and off more easily, it is nonvolatile, and external energy such as memory storage is not required. There has been a need for a means that has functions such as .

The present invention solves these problems.

"Means for Solving the Problem" In order to solve the problem, the present invention provides a liquid crystal cell formed by facing each other with the surfaces having the electrodes inside, in a pair of substrates each having electrodes, and a liquid crystal cell formed between the substrates. It is characterized by having a liquid crystal that has a nonvolatile memory function and exhibits ferroelectricity, a dye that can be dissolved in the liquid crystal, and a layer that reflects light.

The present invention uses chiral (also called chiral Σ) as a liquid crystal material.
A ferroelectric liquid crystal exhibiting a smectic C phase (SmC”)
FLC (hereinafter referred to as FLC) is used, and at the same time, azo-based, anthraquinone-based, or other dyes that can be dissolved in FLC are used. Hereinafter, a mixture of these liquid crystal materials and dyes will be referred to as a liquid crystal substance.

Using a substrate that has been subjected to an asymmetric alignment treatment or a so-called alignment treatment such as rubbing in addition to the above treatment, cells having a cell spacing of 4 μm or less are formed, and the liquid crystalline substance is sealed in the cells, and the SmC'' phase is formed. By maintaining the temperature within this range, the helical structure could be eliminated and a bistable state could be obtained.

When such multipoles are aligned in one direction, when a voltage is applied between the two electrodes forming the pair, the orientation of the multipoles of the liquid crystal molecules is aligned in the opposite direction, and the ideal state is that of the initial one direction. The angle that occurs with the opposite direction is approximately 90''.

These two states have non-volatility (pistability) that does not change even if the voltage is cut off, and the present invention
A non-volatile memory function with a cone angle of 0.06 is used.

In the optical disk of the present invention, a pair of substrates each having an electrode are placed against each other with the surfaces having the electrodes facing each other, and the space between the electrodes is filled with a liquid crystalline substance exhibiting the above-mentioned SmC'' phase. A pair of substrates (the light incident side is called the counter electrode, the inner side (back side) is simply called the substrate) and the electrodes arranged inside it (the light incident side is called the counter electrode, the inner side is called the counter electrode, and the inner side is called the substrate). (simply referred to as electrodes) Furthermore, the surface of one of the electrodes is subjected to alignment treatment, and the liquid crystal material is sealed between the electrodes.

In particular, the present invention provides the optical disc with a layer that reflects light beams, particularly preferably semiconductor laser light. More preferably, one electrode, that is, an electrode on the substrate, is used as a reflection surface for this light beam.

In that case, the path of the incident light is from the laser light source to the half mirror.
The light travels through the counter substrate, counter electrode, liquid crystal material, electrode, and is reflected here, following the opposite path.

The reflected light emitted from the disk is reflected by a half mirror, passes through a polarizing plate, and reaches a photosensor.

When the phase difference between the phase of the liquid crystalline substance and the phase of the polarizing plate matches, it becomes translucent. However, if the phase angle of this beam light is shifted from that of the polarizing plate, it will not be transmitted or will be difficult to transmit. As a result, if the amount of transmission from the polarizing plate has sufficient contrast, rOJ, rl of the address irradiated with light
J can be determined.

``Writing/erasing'', ``writing'', and ``reading'' of such optical disk storage will be outlined below.

That is, "writing and erasing" the memory is carried out by applying a predetermined positive or negative voltage to the liquid crystal material over the entire surface of the disk from a pair of electrodes.

In order to erase all of the written information, it is sufficient to apply a voltage of the same polarity as the above-mentioned "erasing" to the pair of electrodes. That is, this bit-by-bit reading and writing and erasing of the entire disk can be repeated.

Further, in order to "write" a predetermined address, a beam of light or heat strong enough to exceed the orientation angle of the liquid crystal material is irradiated at the rotational speed of the disk and at a predetermined distance from the center. Furthermore, a voltage in the opposite direction to writing and erasing is applied, which is so weak that electrical writing is not performed sufficiently, and light or heat is applied thereto. Then, only at that address, the dipole direction of the liquid crystal material is arranged in a direction different from the initial state. If the initial state is set to "0" in this manner, it can be set to "1" by light irradiation.

As described above, "reading" of the memory is performed by irradiating a light beam, such as a laser beam, onto a predetermined address of the semiconductor laser, and detecting the reflected light by a photosensor via a polarizing plate.

"Function" By doing so, (1) the deflection plate is disposed in the photosensor section, and since there is only one plate, the loss of light can be reduced.

(2) There is no need to provide polarizing plates on the top and bottom surfaces of the optical disk, making it easy to handle.

(3) Since the reflected light electrode does not come into contact with the atmosphere, it is not oxidized and can maintain high reflectance.

(4) Since liquid crystal substances are used as nonvolatile memory,
"Writing" to memory can be performed at high speed (on the order of microseconds), and "writing and erasing" can be performed instantaneously to the entire surface of the disk. There is essentially no fatigue due to repetition in the rewriting process.

(5) Since the liquid crystal material used does not require special elemental materials and has a small number of parts, it can be expected to be inexpensive.

(6) Since it uses a liquid crystal substance, it is non-volatile and does not require new energy to retain its memory, resulting in energy savings.

(7) The two tilt angles (generally the cone angle is 172) of the liquid crystal material due to rewriting are approximately 45" from each other.
However, since it is unique to liquid crystal materials, it can be expected that there will be no deterioration in terms of wood quality.

The present invention will be explained below according to examples.

"Embodiment 1" FIG. 1 shows a system of an optical disk memory device according to the present invention.The first system (100) is for "reading" information, and the second system (100)
01) is for "writing" information.

Further, (103) is for "erasing" information. This is indicated by a disc foil 10).

The optical disc has a pair of opposing substrates (3) and a substrate (7). One opposing substrate (3) is at least transparent. Furthermore, a pair of electrodes (4) are located inside the pair of substrates.
, has (6). The counter electrode (4) has a translucent property, and the electrode (6) has a reflective property.

Further, one of the pair of electrodes is subjected to an alignment treatment, and the other is subjected to a non-alignment treatment. Furthermore, a liquid crystal substance (5) is filled between the electrodes.

The periphery of this optical disk is sealed (30), (30') to prevent the liquid crystal material from coming into contact with the atmosphere. This optical disc has a pair of electrodes (4) inside (10),
(7) More extended external contact electrode (32)
, (32'). This external contact electrode (
32), (32') means erasing memory 103)
The lead (13) derived from the signal source (25)
, (13') are connected to terminals (31) and (31") to perform "erasing".

In this way, for a disk whose entire surface is "0", the information "
"Writing" is performed using the system (101). In other words, a light beam, especially infrared rays, is directed to a liquid crystal material arranged in one direction on the entire surface of the material at a predetermined address via (23), a half mirror (22), a condensing optical system, a position correction system, etc. (21). Light is irradiated to (25) L, and writing is performed by shifting the phase of a predetermined address from the initial state.

Further, the light passes through a half mirror (22) and reaches a photosensor (9). Monitor whether information is being written here. At that time, make sure that the light intensity is appropriate (
24).

The system (100) is used for "reading" information.

That is, the light beam from the semiconductor laser (12) passes through the half mirror (2), the condensing optical system, the position correction (auto tracking device) (11), and the light (16) is incident on the optical disk (10). do. Furthermore, this optical disc (10)
More light is reflected as (16'), half mirror (2)
The optical path is separated by
).

This optical disc will be described in more detail below.

That is, a plastic substrate such as an acrylic resin or a Corning 7059 glass substrate (7) was used. One electrode (6) was made of aluminum as a reflective electrode by vacuum evaporation on this substrate. In addition, a transparent conductive film (4) is used as the other counter electrode on a plastic substrate or a glass substrate (
Opposing group Fi) is formed on (3). Furthermore, ITO (indium tin oxide) was formed on this glass substrate (3). And this pair of electrodes (6), counter electrode (4)
An asymmetrical alignment film is provided inside the film, and a spacer (not shown) is interposed therebetween. An FLC (thickness: 1.5 μm) is sandwiched between these. PAN is applied on the counter electrode (4) as an orientation treatment.
(Polyacrylonitrile), PVA (Polyvinyl Alcohol), or other organic resin film was applied to a thickness of 0.1 μ by a spin method and subjected to a known rubbing process.As an example of the rubbing process, nylon was placed in a rubbing device. The disk was rotated at 900 PPM, and the surface was "written" at a speed of 2 m/min (periphery), and the substrate was rotated in the same direction as the rotation of the disk during "writing and erasing".

That is, an inorganic compound film is formed on one electrode (6) to serve as an alignment film that is not subjected to rubbing treatment, and the other electrode (4) is coated with an inorganic compound film.
A film of an organic compound was formed and rubbed. A liquid crystal material such as S8 (octyl oxy benzylidene amino methyl butyl benzoate) was further filled in this space as an alignment film. Other than this, DOBA
It may be filled with a liquid crystal material such as MBC or a blend of a plurality of liquid crystal materials. For example, Ferro
electronics1984 Vol, 59 pp12
6-136 Ferro by J. W. Goodby et al.
electronics Switching in th
e Titled Smec-tic Phase o
f R-C-3-4-n-Hexyloxydenz
ylidene4'-Am' no-(2-Ch 1
oropropyl) (innamate (HO
BACPC) + JP-A-59-98051. Japanese Unexamined Patent Publication 1983
-118744 may also be used. An example of the threshold characteristic of this liquid crystal material is shown in FIG. In the drawing, by adding ±15V, curves (29) and (29”) are obtained, and the transmission,
It has been found that it is possible to make the film non-transparent and to obtain sufficient reversal and hysteresis exhibiting a memory effect. In FIG. 2, the vertical axis is the transmittance.

Furthermore, regarding this hysteresis, optical writing is performed in the present invention. For example, erasing erases the entire disk.
5V and all addresses should be set to 0''.The tilt angle will be about -45V.For writing, apply a weak voltage that does not reach the positive threshold voltage to the whole.For example, add -17V.Further write. , the address is irradiated with a laser beam for writing.Then, the temperature of this predetermined address rises, and this temperature is estimated by the positive voltage when the laser beam is no longer irradiated and the temperature is slowly cooled. The tilt angle in the direction can be set to +20 to +45°.Especially when the wavelength of the laser beam is 1 to 3μ,
Liquid crystal materials absorb most of this light. In addition, the absorption coefficient changes due to the positive voltage applied during this rewriting.

For this reason, for example, it is preferable to apply a small electric field of about 10 V when irradiating a laser beam with a wavelength of 1.2 μm, and about 6 V when irradiating a laser beam with a wavelength of 2 μm.

That is, in the present invention, writing is performed by applying a basic bias voltage in addition to spot-like laser beam irradiation. Furthermore, for writing and erasing, a reverse bias sufficiently larger than the threshold voltage was applied to the entire circuit.

However, writing and erasing can also be accomplished locally by using a laser beam and by applying a basic bias voltage in the opposite direction.

"Effects" As is clear from the above explanation, the optical disk memory device of the present invention uses a liquid crystal material, and is therefore particularly effective when the number of rewrites is relatively large.

The optical system of the present invention uses different optical systems for "reading" and "writing." However, another method is the jig (21
) can be omitted and the light from the light source (23) can be made the same as the optical path (16), (16') by using a half mirror or the like. However, in this case, the amount of light for ``writing'' and ``reading'' differs by a factor of nearly 10, so although the number of protrusions is reduced, it has the disadvantage that optical path design becomes complicated.

Further, as a partially modified method of the present invention, if the polarizing plate can withstand "writing/erasing" or "writing", it is possible to arrange it on the light irradiation surface side of the disk.

In this method, since rewriting is performed by the first method, the memory capacity is extremely large.

The practical application of the present invention is effective not only for consumer compact discs but also for large-capacity file memories. Furthermore, although the disk is circular and rotates, it is also possible to use a method in which the disk is fixed and the optical path is moved.

[Brief explanation of the drawing]

FIG. 1 schematically shows an optical disc memory device of the present invention. FIG. 2 shows the operating characteristics of a ferroelectric liquid crystal.

Claims (1)

[Claims] 1. A liquid crystal cell formed of a pair of substrates having electrodes facing each other with the surfaces having the electrodes facing each other, and a strong liquid crystal cell having a non-volatile memory function in which a dye is added between the substrates. An optical disc device using a ferroelectric liquid crystal characterized by having a liquid crystal exhibiting dielectric properties and a layer reflecting light. 2. In claim 1, the ferroelectric liquid crystal is a ferroelectric liquid crystal exhibiting a smectic C phase and having a tilt angle of about 45° or around 45°. Optical disk device. 3. In claim 1, the dye that can be dissolved in the liquid crystal is a dichroic dye having a dichroic ratio (CR) of 8 or more, such as an anthraquinone dye or an azo dye. Optical disk device using ferroelectric liquid crystal.