JPH0481814B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Application of the Invention The present invention relates to a rewritable optical disk using a ferroelectric liquid crystal (hereinafter referred to as FLC) having a rewritable non-volatile memory function.

``Prior Art'' Optical disk devices include non-rewritable digital disk memory devices, such as compact disks, that utilize the reflection of laser light on an uneven surface that has a reflective surface. . This application holds great promise not only for audio and video applications, but also as optical disk memory devices 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. Further, an amorphous semiconductor optical disk memory device using chalcogen (tellurium) is also known.

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.

These advantages include using materials that can be mass-produced, making it easier to turn on and off light, and having non-volatile properties that do not require any external energy when storing (retaining) memory. What not to do,
There was a need for a means with such functions.

In order to solve this problem, the present applicant has developed a ferroelectric liquid crystal (FLC) exhibiting a smectic C phase (SmC ^* ) as a liquid crystal material by patent application No.
) was proposed. That is, by setting the cell spacing to 4 μm or less, this liquid crystal can obtain a bistable state. Then, liquid crystal is mixed in the isotropic liquid crystal state into such a thin cell, the temperature is lowered, SmA is obtained, and bistable
Become SmC ^* . This allows you to create a helical structure. When a voltage is applied to such SmC ^* , the molecules align in one direction, and the angle can be approximately +45° (degrees). Also, if the opposite voltage is applied, about -
You can get 45°. These two states are non-volatile and do not change even when the voltage is turned off, and are at an angle of about 90 degrees to each other. The present invention utilizes a non-volatile memory function having such a tilt angle of about 90 degrees.

In an embodiment of the present invention, a pair of substrates each having an electrode are arranged so that their inner surfaces having relatively symmetrical orientation planes are opposed to each other, and the above-mentioned SmC ^*
Fill the FLC.

Two methods can be proposed for this optical disc.

In the first method, electrodes are provided inside a pair of substrates, an asymmetric alignment film is provided on the surface of each electrode, and an FLC is sandwiched between the electrodes.

Another second method is to have a reflective plate inside one of a pair of substrates, perform asymmetrical alignment treatment between this reflective plate and one surface of the other substrate, and sandwich the FLC. In this method, there are no electrodes inside the optical disk.

In the embodiments of the present invention, a pair of substrates (the light incident side is referred to as a counter electrode and the inner side (inner side) is simply referred to as a substrate) forming a cell and an electrode disposed inside the substrate (the light incident side is simply referred to as a substrate) are used. (The electrode on the other side is called the counter electrode, and the inner side is simply called the electrode.) Furthermore, the inner surface of the FLC that is in close contact with one side is subjected to an orientation treatment.

In particular, the invention provides for this optical disc to have a layer that reflects light beams, particularly preferably semiconductor laser light. Furthermore, this light beam reflector can also have the function of one electrode.

In that case, in the first method, the path of the incident light is from the laser light source, through the half mirror, to the counter substrate, to the counter electrode, to the FLC, to the reflective electrode, where it is reflected, and follows the opposite path. The reflected light is then reflected by a half mirror, passes through a polarizing plate, and reaches a photo sensor.

In the second method, the path of the incident light starts from the laser light source, passes through a half mirror, and then goes to the opposing substrate.
The reflected light passes through the FLC, the reflective surface, and the reverse path, is reflected by the Huff mirror, and reaches the photo sensor via the polarizing plate.

When the phase difference between the FLC and the polarizing plate matches, the film 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, it becomes possible to determine whether the address irradiated with light is "0" or "1".

``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 electric field to the FLC from the inside or outside of the substrate of the disk. In addition, "writing" at a given address depends on the rotational speed of the disk and the given distance from the center.
A beam of light or heat strong enough to exceed the initial tilt angle of the FLC is irradiated. Then only that address
Change the FLC tilt angle from the initial state of +45° to -
Placed at 45° or some other angle 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.

To erase all written information
An electric field is applied perpendicularly to the FLC, but if this electric field is applied from inside, it will cause damage to the inside of the optical disc.
It is sufficient to apply a voltage of the same polarity as that for "writing and erasing" described above to a pair of electrodes provided with the FLC sandwiched therebetween.
That is, this bit-by-bit writing and writing/erasing of the entire disk can be repeated.

In the case of the second method in which an electric field is applied from the outside of a pair of substrates, a pair of electrodes for applying an electric field are provided with an optical disk having no internal electrodes sandwiched therebetween. Then, an electric field is applied to the entire surface or part of the optical disk from this electrode, causing all or part of the FLC to rearrange, thereby performing "writing and erasing".

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

``Problems to be Solved by the Present Invention'' There are several problems that must be encountered in putting into practical use an optical disk memory using ferroelectric liquid crystal as described above. Examples include the following:

(1) Between disks, molecules must be aligned correctly in an area corresponding to at least one bit to form a monodomain. (2) The storage area on the disk must be determined. That is, adjacent unit storage areas must be correctly separated, and even if access is made by mistake, it must be detected.

The present invention improves the above two points with a simple configuration.

"Structure" In order to solve the above problems, the optical disk memory device according to the present invention includes a transparent substrate, a counter substrate provided in parallel to the transparent substrate, and a It consists of grooves that are provided on the inside and partition the area between these two substrates at bit pitch intervals in the radial direction to form a memory area, and liquid crystal filled between the substrates. Further, the method for manufacturing an optical disk memory device according to the present invention includes:
A step of forming a reflective film-pattern on a light-transmitting substrate, a step of applying a photosensitive resin to the pattern-forming surface of the light-transmitting substrate, and a step of irradiating light from the side of the light-transmitting substrate to remove the light. The method consists of a step of photo-etching the photosensitive resin, and a step of superimposing another light-transmitting substrate on the light-transmitting substrate and interposing a liquid crystal between these substrates.

The present invention will be described below with reference to Examples.

Embodiment FIG. 1 shows a recording system using the optical disk memory of the present invention according to the first method.

The first system 100 is for "reading" information, and the second system 101 is for "writing" information.
Further, 103 is for "erasing" information. The disc is designated by 10.

The optical disk has a pair of opposing substrates 3 and 7. One opposing substrate 3 is at least translucent. Furthermore, a pair of electrodes 4 and 6 are provided inside the pair of substrates. The distribution electrode 4 has a translucent property, and the electrode 6 has a reflective property. Further, one of the pair of electrodes is subjected to facing treatment, and the other is subjected to non-alignment treatment. Furthermore, between the electrodes
FLC5 is filled.

The periphery of this optical disk is sealed 30, 30' to prevent the FLC from coming into contact with the atmosphere. The optical disk 10 has external contact electrodes 32, 32' extending from the pair of electrodes 4, 6 on the inner peripheral side thereof. These external contact electrodes 32, 32'
are connected to the terminals 31, 31' of the leads 13, 13' derived from the signal source 25 when erasing the memory 103, thereby performing the "erasing".

In this way, the system 101 is used to "write" information to the disk whose entire surface is "0". That is, a light beam, particularly infrared rays, is irradiated 25 from a light beam 23 to a predetermined address via a half mirror 22, a condensing optical system, a position correction system 21, etc. to the FLC arranged in one direction on the entire surface. Writing is performed by shifting the phase of the address from the initial state. Further, the light passes through the half mirror 22 and reaches the photo sensor 9. Monitor whether information is being written here. At that time, correction is made in step 24 so that the light intensity is appropriate.

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 optical disk 1.
Light 16 is incident on 0. Furthermore, this optical disk 1
The light is reflected from 0 as 16', and the half mirror 2
The optical path is separated by the light receiving sensor 9 via the polarizing plate 8.
leading to.

This optical disc will be described in more detail below.

That is, a plastic substrate or a Corning 7059 glass substrate 7 was used. One electrode 6 was formed on this substrate by vacuum deposition of aluminum as a reflective electrode. Further, a light-transmitting conductive film 4 is formed on a plastic substrate or a glass substrate (counter substrate) 3 as the other counter electrode. As this transparent conductive film 4, ITO (indium tin oxide) was used.
An asymmetrical alignment film (not shown) is provided inside the pair of electrodes 6 and counter electrode 4, and a spacer (not shown) is interposed therebetween. These allow FLC (thickness
1.5μ) 5 is sandwiched. As an orientation treatment, PAN (polyacrylonitrile) and PVA are applied on the counter electrode 4.
(Polyvinyl alcohol) was applied to a thickness of 0.1μ by a spin method, and then subjected to a known rubbing treatment. As an example of the rubbing treatment, nylon was rotated by a rubbing device at 900 PPM, and the surface was formed by moving the substrate at a speed of 2 m/min. That is, on one electrode 6, a film of an inorganic compound was formed to provide an alignment film that was not subjected to a rubbing process, and on the other electrode 4, a film of an organic compound was formed and a rubbing process was performed. FLC such as S8 (octyl oxy benzylidene amino methyl butyl bunzoate) was filled between the alignment treatment layers. Other than this
FLCs such as BOBAMBC or blends of FLCs can be filled. An example of the threshold characteristic of this FLC is shown in FIG. In the drawings, it was found that by applying ±5V, it was possible to achieve sufficient inversion and to obtain hysteresis, which indicates a memory effect.

In FIG. 2, the vertical axis is the transmittance.

FIG. 3 shows an optical disk memory device using the second write/erase method.

In the drawings, only the method for writing and erasing information is different, and the rest is the same as in the first embodiment.

That is, the optical disk 10 (shown in a circular longitudinal section) has a pair of substrates 3 and 7. This one opposing substrate 3 is translucent. An asymmetrical alignment process is performed between the upper surface of this opposing substrate and the surface of the reflecting plate 6 provided on the other substrate 7 (lower side in the drawing).

Further, inside this treated surface, FLC5 was applied in Example 1.
Filled as well.

This optical disk 10 is sealed at its periphery with 30, 30'.

For this optical disk 10, a pair of electrodes 31,
A voltage is directly applied to 31' from the high voltage source 25 from the outside in order to provide a predetermined electric field to the FLC.

At this time, the electric field application terminals 31, 31' are placed close to the outside of the optical disk 10 (in the drawing, they are shown a little apart to clearly show that the electric field is applied from the outside). If the terminals 31, 31' have the same length in the radial direction of the disk, the entire surface of the optical disk can be erased by rotating the optical disk once. Moreover, if only a part of the electric field is used, the pair of electric fields can be locally erased. In this case, the entire surface of the disk can be erased by scanning the terminal 31 from the outside to the inside or vice versa while rotating the disk. In the drawings, if the reflecting plate 6 is a conductor, the terminal 31' does not necessarily need to be directly above the lower terminal 31.

In this second method, the terminals 31, 31'
If it is provided on the outside side, it is not directly in close contact with the FLC. However, the power loss required for erasing FLC is equivalent to the area of the hysteresis loop shown in Figure 2 (area when the vertical axis is the electric flux density D and the horizontal axis is the electric field strength E), and it is extremely Since the terminal 31 is small, the terminal 31 is small enough to compensate for the power loss.
It is sufficient that the counter substrate 3 in close proximity to the substrate 3 has weak conductivity.

In this way, the FLC of the optical disk is oriented at a predetermined angle, and information is written in the same manner as in Example 1 to the disk whose entire surface is in the "0" state. Further, reading was performed in the same manner as in Example 1.

FIG. 4 shows in detail the internal structure of the optical disc 10 according to the present invention. In the figure, the counter electrode 6 is several μm
A groove 5' is provided for each disk, and this groove 5' is formed concentrically with the optical disk, and defines a storage area of the optical disk in the radial direction.

That is, the above-mentioned recording operation is performed on the liquid crystal above this groove, and when the incident light deviates from the groove, the optical path length is shortened, and it is detected that access is not performed correctly.

On this groove 5', the liquid crystal 5 forms a monodomain. In particular, at the end of this groove', that is, at the rising part 6' of the vertical surface of the electrode 6, each molecule of the liquid crystal 5 is aligned parallel to the groove 5' (perpendicular to the plane of the paper in the figure); This helps the formation of monodomains.

From this, it is understood that the electrode 6 also has an alignment function. However, in many cases, it is considered inappropriate to perform alignment only with the groove, so an alignment film 4' is provided on the electrode 4 facing the groove.
A rubbing process is performed on this. Of course, instead of this, the groove 5' may be included and the electrode 6 may be subjected to a rubbing process. Furthermore, an alignment film 62 that is preferably not subjected to rubbing treatment is provided on the electrode 6.

"Effects" Tracking of the optical disk, reduction of alignment defects in the liquid crystal, and formation of monodomains of the liquid crystal in the radial direction of the optical disk are simultaneously achieved with a simple configuration.

[Brief explanation of the drawing]

FIG. 1 schematically shows a recording system using the optical disk memory of the present invention. FIG. 2 shows the operating characteristics of a ferroelectric liquid crystal. FIG. 3 schematically shows another optical disc recording system. FIG. 4 is a partial sectional view of the optical disk memory of the present invention.

Claims (1)

[Claims] 1. A substrate having an electrode having an uneven pitch structure and a substrate having an electrode having a flat structure, separated from each other with the electrodes facing each other, and at least one of the substrates having an electrode having a flat structure. has a light-transmitting property, and a rubbing treatment is applied to the surface of the substrate having the electrodes having the flat configuration, and no rubbing treatment is applied to the surface of the substrate having the electrodes having the uneven pitch configuration; 1. An optical memory characterized in that a gap between substrates spaced apart from each other is filled with smectic liquid crystal, and the memory is operated by the memory action of a smectic C phase exhibiting a bistable state determined by the rubbing process.