JPH0480453B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] This invention relates to a rewritable optical disk using a ferroelectric liquid crystal (hereinafter referred to as FLC) having a rewritable non-volatile memory function and a method for manufacturing the same. be.

``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.

From these points, materials that can be produced in large quantities are used, light can be turned on and off more easily, and it is non-volatile and does not require any external energy when storing (retaining) memory. ,
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, by mixing liquid crystal in an isotropic liquid crystal state into such a thin cell and lowering the temperature, SmA is obtained, and further 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 uses a non-volatile memory function having such a tilt angle of about 90 degrees.

The optical disk of the present invention has a pair of substrates each having an electrode, the surfaces of which have asymmetrically oriented surfaces facing each other, and the above-mentioned
Fill SmC ^* 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 present invention, a pair of substrates (the light incident side is referred to as a counter electrode, and the inner side (back side) is simply referred to as a substrate) forming a cell and an electrode disposed inside the substrate (the light incident side is referred to as a counter electrode) and The inner surface is simply referred to as the counter electrode, and the inner surface is simply referred to as 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 opposite path, is reflected by a half mirror, passes through a polarizing plate, and reaches the photo sensor.

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" As mentioned above, optical disk memories using ferroelectric liquid crystals are expensive to manufacture, at least at the current stage. It is desired to reduce costs step by step by omitting etc.

In the present invention, we focused on the following points as part of cost reduction.

(1) The circumferential structure conventionally provided to partition the memory area in the radial direction is omitted.

(2) Form spacers at appropriate locations to maintain the distance between opposing substrates with fewer steps.

"Structure" In order to solve the above-mentioned problems, the optical disk memory device according to the present invention includes a light-transmitting substrate, a counter substrate provided in parallel to the light-transmitting substrate, and a space between the counter substrate and the light-transmitting substrate. a spacer provided on the substrate and partitioning the area between these two substrates at bit pitch intervals in the radial direction to form a memory area; a reflective film provided on the opposing substrate for the memory area separated by the spacer; The memory area is filled with liquid crystal. Further, the method for manufacturing an optical disk memory device according to the present invention includes the steps of forming a reflective film-pattern on a transparent substrate;
A step of applying a photosensitive resin to the pattern-forming surface of the light-transmitting substrate, a step of photo-etching the light-sensitive resin by irradiating light from the side of the light-transmitting substrate, and a step of photo-etching the photosensitive resin on the pattern-forming surface of the light-transmitting substrate. The method includes the steps of superimposing a 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 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 alignment 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 an appropriate amount.

System 100 is used for "reading" information.

That is, a light beam from a semiconductor laser 12 passes through a half mirror 2, a condensing optical system, a position correction (auto tracking device) 11, and then reaches an optical disk 10.
Light 16 is incident on. In addition, this optical disk 10
The light is reflected as 16', the optical path is separated by the half mirror 2, and the light passes through the polarizing plate 8 and reaches the light receiving sensor 9.

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 transparent 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. After alignment treatment, PAN (polyacrylonitrile) and PVA are used 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, a film of an inorganic compound was formed on one electrode 6 to serve as an alignment film that was not subjected to rubbing treatment, and a film of an organic compound was formed on the other electrode 4 and subjected to rubbing treatment. FLC such as S8 (octyl oxy benzylidene amino methyl butyl benzoate) was filled between the alignment treatment layers. Other than this
FCLs such as BOBAMBC or blends of FLCs may be filled. An example of the threshold characteristic of this FLC is shown in FIG. It has also been found that by applying ±5 V in the drawing, curves 29 and 29' can be obtained, which can be made transparent and non-transparent, and can be sufficiently inverted and hysteresis exhibiting a memory effect can be obtained.

In FIG. 2, the vertical axis is 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 to the disk whose entire surface is "0" in the same manner as in the first embodiment. Further, reading was performed in the same manner as in Example 1.

4 and 5 show the internal structure of the optical disc 10 according to the present invention in detail. In the figure, a ferroelectric thin film 41 and an alignment film 42 are formed on a transparent electrode 4. This ferroelectric thin film 41 is made of, for example, a copolymer of vinylidene fluoride (CH ₂ CF ₂ ) and trifluoroethylene, and together with the liquid crystal 5 forms a nonvolatile memory medium.

Spacers 61 are provided between the substrate 7 and the alignment film 42 at intervals of a bit pit width, thereby keeping the distance between the opposing substrates 3 and 7 constant. As is clear from the drawing, the reflective electrode 6 on the substrate 7 is provided adjacent to the spacer 61 at a position where it does not exist.

According to the above configuration, if the position of the light incident from the transparent substrate 3 side is not correctly aligned with the memory area (that is, the area where the liquid crystal is present in the case of the disk of the present invention), the light is not reflected, and an error in the incident position is detected. Therefore, the spacer 61
It not only maintains the substrate spacing, but also has the function of partitioning the memory area.

Next, the manufacturing of the optical disk according to the present invention will be described.

First, an aluminum film 6 is formed on the entire surface of the substrate 7 made of Corning 7059 glass by vacuum evaporation, and after coating a spiral photoresist with a bit pit interval, known photo-etching is performed. The photocurable resin is uniformly applied to a thickness of 1 to 3 μm over the entire surface of the substrate 7 on which the aluminum spiral electrode 6 is formed using a spin method. 1
% or less. This exposure of the resin is performed by irradiating light from the glass substrate 7 side, the electrodes 6 serve as a mask, and spacers 61 are formed at intervals between the electrodes 6.

Separately, a transparent conductive film 4 , a ferroelectric film 41 , and an alignment film 42 are laminated on the glass substrate 3 .

As described above, the substrates 3 and 7 provided with electrodes and the like are sealed around their peripheries while being in pressure contact with each other. Finally, from the injection port formed during peripheral sealing, the substrate 3,
During the 7th period, liquid crystal was injected and the disk memory was completed.

Note that when current laser technology is used, it is possible to suppress the spread of light to 1.2 μm, and in order to obtain a large capacity, the bit pitch is usually set extremely small. Therefore, the liquid crystal 5
The spiral groove to be filled with is extremely long compared to its cross-sectional area, making it difficult to inject liquid crystal into it. In order to improve this, as shown in FIG. 5, a flow path pattern 61 is provided on the spiral electrode pattern 6 like a checkerboard, a resin is applied on this pattern, and the above-mentioned exposure is performed. Therefore, there is a method of forming a flow path.

However, if a method is used in which the liquid crystal is placed on the substrate 3 in a vacuum before the substrates 3 and 7 are pressure-bonded, and then the substrate 7 is pressure-bonded, this flow path may be omitted.

"effect" (1) The radial partition of the memory area is omitted.

(2) The reflective film formation process can be incorporated into the spacer formation process.

[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. FIG. 5 is a plan view showing an example of the manufacturing direction of the optical disk memory of the present invention.

Claims (1)

[Scope of Claims] 1. A light-transmitting substrate, a counter substrate provided parallel to the light-transmitting substrate, and a substrate provided between the opposing substrate and the light-transmitting substrate, the area between these two substrates having a diameter. A disk comprising a spacer forming a partitioned memory area at bit pitch intervals in the direction, a reflective film on a counter substrate provided for the memory area partitioned by the spacer, and liquid crystal filled in the memory area. 2. 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 this light-transmitting substrate, and a step of irradiating light from the side of this light-transmitting substrate to remove the light. A method for manufacturing a disk, comprising the steps of photo-etching a photosensitive resin to form a spacer, and superimposing another light-transmitting substrate on the light-transmitting substrate, and interposing a liquid crystal between these substrates.