JPS62204444A - Optical disk memory device using liquid crystal - Google Patents

Abstract

PURPOSE:To eliminate a jumping at the time of a read/write to an adjacent inside or outside track, by providing a guide track and a recording track with irregularities on one side of the inside surface of a pair of substrates, and with a flat surface on the other side. CONSTITUTION:An optical memory disk 10 is formed in a circular shape, and is provided with a pair of substrates 3 and 3' provided oppositely, and both the substrate 3' and the opposite substrate 3 are translucent. At the inside of the pair of substrates, a pair of translucent electrodes 4 and 4' are provided, and furthermore, on either, at least, of them, for example, a counter electrode 4, a means NVL5 regulating a non-volatile orientation between the electrodes, is provided. On the opposite substrate 3 on one side, the irregularities are formed, and on its surface, a transparent counter electrode 4, and the NVL5 are provided, and the inside surface of the substrate 3' is formed as flat, and on the inside surface, the electrode 4, and an orientation film 7 are provided. And a liquid crystal 6 is filled between the orientation film 7 and the NVL5. A recording track 27 and a guide track 26 are provided on the inside surface of the opposite substrate 3 on one side, and as a result, the thickness 28 of the liquid crystal in the recording track is made thinner than the thickness 29 of the guide track.

Description

Detailed Description of the Invention "Field of Application of the Invention" The present invention provides a rewritable device that integrates a rewritable non-volatile orientation defining means (hereinafter referred to as NVL) and a liquid crystal (hereinafter referred to as LC). The present invention relates to optical memory devices (particularly optical disk memory devices).

``Prior Art'' Non-rewritable digital disk memory devices are known as optical disk memory devices, such as compact disks, which utilize the reflection of laser light on concave bits. 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. Further, an amorphous semiconductor device disk memory device using chalcogen-based (tellurium-based) is also known.

``Problems that the invention seeks to solve'' However, disk memory 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, it is possible to use materials that can be mass-produced, it is easier to turn on and off the light, it is nonvolatile, and it does not require any external energy to continue storing (maintaining) the memory. There was a need for a means that had functions such as:

For these purposes, there is an optical disk device using ferroelectric liquid crystal (hereinafter referred to as FLC) (filed on August 7, 1985), Japanese Patent Application No. 173936, filed by the present inventor.

The optical memory device of the present invention uses optical energy and an electric field for "writing" and uses an electric field or an electric field and optical energy for "erasing". Further, "reading" uses optical energy, which is completely different from conventional methods of "writing" to the recording trunk using only optical energy or thermal energy, or only optical energy and a magnetic field.

The present invention is a further improvement of this invention. In other words, it has been desired to particularly improve the retention of memory in the memory medium and the crosstalk between bits.

The present invention solves these problems.

"Means for Solving the Problem" In order to solve the problem, the present invention provides a liquid crystal device formed by opposing a pair of substrates each having electrodes with the surfaces having the electrodes facing each other, and in which there is a gap between the electrodes. Non-volatile orientation means (hereinafter referred to as non-volatile)
1 ayer means (NVL). In particular, this NVL is provided on one or both electrodes. By treating this NVL as substantially a part of the alignment treatment layer, it is intended to further stabilize the surface of the LC. The liquid crystal interposed between the substrates is made non-volatile, and the two different orientations of this NVL determine the orientation of the liquid crystal, and the transmission and non-transmission of the irradiation light when reading out the tα of this liquid crystal device. This method is designed to control transmission.

Further, in one of the substrates according to the present invention, a guide track and a storage track are provided with unevenness to prevent crosstalk between a recording track and an adjacent recording track.

The present invention further provides an NVL electrically free (floating) from the electrode on the surface having the uneven surface. The surface of the other electrode had flatness, and a so-called alignment treatment, such as rubbing, was performed on this surface. The liquid crystal device has an electrode spacing of 4 .mu.m or less (preferably 0.5 to 2 .mu.m) in order to approximate the width of each bit to about 0.5 .mu.m between the pair of electrodes. Among them, as a liquid crystal material, for example, a ferroelectric liquid crystal (FL) exhibiting a chiral (also called chiral) smectic C phase (SmC")
A bistable state exhibiting the SmC phase is obtained by enclosing the material at a high temperature and gradually lowering the temperature.

In the present invention, when such liquid crystals are aligned in one direction,
Voltage (electric field) greater than the critical voltage between the two electrodes that make up a pair
When this is applied, the multipoles of the liquid crystal molecules are aligned in the opposite direction, and "writing and erasing" is performed. On the other hand, FLC
has a voltage value below the critical voltage (the voltage at which liquid crystal inversion occurs when a high voltage higher than this voltage is applied),
While applying an electric field in the opposite direction to the initial writing/erasing direction, a light or heat beam is irradiated onto a predetermined address on a recording track to raise the temperature of that area and perform "writing." This temperature increase can then lower the critical voltage of the liquid crystal. Therefore, even if the voltage is the same, the liquid crystal that is not irradiated with this heat or light beam maintains its initial state, and only the portion that is irradiated with this heat or light beam can be oriented in the opposite direction and recorded.

These two states have non-volatility (pi-stability) that does not change even when the voltage is turned off. For this reason, when reading out light, a pair of polarizing plates are provided on the incident side and the output side of the disk memory, shifted by about 90 degrees.

The following describes the "reading", "writing", and "writing" of optical memory devices.
The principle of "writing" is abbreviated.

First, "reading" of information inside the optical memory device will be described below.

The optical memory device of the present invention has a pair of substrates each having an electrode, which are opposed to each other with the surfaces having the electrodes inside each other, and between the electrodes, there is an NVL and a ferroelectric liquid crystal (FLC) exhibiting the above-mentioned SmC'' phase. ). The present invention relates to a pair of substrates constituting a cell (the light incident point 11 is the opposing substrate,
The inner side (inner side) is simply referred to as a substrate), an electrode disposed inside the substrate (the electrode on the light incident side is referred to as a counter electrode, and the inner side is simply referred to as an electrode), and an alignment treatment layer is provided on the electrode.

In the present invention, the path of the light beam incident on the optical memory device is from the laser light source through the first polarizing plate, the auto-tracking device, the counter substrate, the counter electrode, the NvL, the liquid crystal, the alignment layer, the electrode, the substrate, and the like. It reaches the photosensor via the second polarizing plate.

When the phase difference between the phase of the liquid crystal and the phase of the two polarizing plates 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 light irradiation beam has sufficient contrast, the rOJ of the address irradiated with light
, rlJ becomes possible.

The "writing and erasing" described in jI is carried out by applying a predetermined voltage sufficiently larger than positive or negative Ec to this LC between a pair of electrodes over the entire surface of this disk memory.

Furthermore, "writing" at a predetermined address involves applying a voltage in the opposite direction to writing and erasing, in which no writing is performed that is smaller than the electrical critical voltage, that is, a voltage smaller than Ec, on a predetermined recording track of the disk memory. . Furthermore, at the same time, a beam of light or heat strong enough to exceed the orientation angle of the liquid crystal is irradiated. Then, only at addresses to which heat or light energy has been supplied, the dipole direction of the liquid crystal 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.

That is, this bit-by-bit writing and writing/erasing of the entire disk can be repeated.

"Function" By doing so, (1) the deflection plate is disposed on the photosensor section and the incident light side, and does not need to be disposed closely on the disk memory.

(2) Since a composite structure of liquid crystal and NVL is used as nonvolatile memory, "writing" to the memory can be performed at high speed (on the order of microseconds), and "writing and erasing" is possible.
can be performed instantaneously on the entire surface of the disk-shaped memory. There is essentially no fatigue due to repetition in the rewriting process.

(3) Since the liquid crystal does not use special rare element materials and has a small number of parts, it can be inexpensive.

(4) Since it uses a composite structure of liquid crystal and NVL, it is nonvolatile, and the critical electric field can be made clearer. No new energy is required for memory retention, resulting in energy savings.

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) is for "reading"
01) is for "writing" information.

Further, (103) is for "erasing" information. The disk is indicated by (10).

The optical memory disk (10) has a disk shape, and a longitudinal cross-sectional view thereof is shown. It has a pair of opposing substrates (3) and (3'). Both the substrate (3') and the counter substrate (3) are translucent. Furthermore, a pair of transparent electrodes (4) and (4') are provided inside the pair of substrates. Furthermore, at least one of them, for example, in the drawing, N
VL (5) is provided.

An enlarged view of the optical disk memory portion in FIG. 1 is shown in a perspective view in FIG. 2.

In the longitudinal cross-sectional view, one opposing substrate (3) has an uneven inner surface. A transparent counter electrode (4) and NVL (5) are provided on this surface. The other board (
3") is flat, and has an electrode (4) and an alignment film (7) on this inner surface. A liquid crystal (6) is located between the alignment film (7) and the NVL (5). Filled.

This one opposing substrate (3) has a recording track (27) and a guide track (26) on its inner surface.

As a result, the thickness 28) of the liquid crystal in the recording I rank is made thinner than the thickness 29) of the liquid crystal in the guide track.

Therefore, it is easy to selectively write to the liquid crystal of the recording track even with the same voltage. The rewriting laser beam (22) and the reading laser beam (16) in FIG. 1 focus only on the recording track using an autofocus servo mechanism (21)
(11) enables scanning to be performed at the same time as focusing. Even if the laser beams (16) and (22) are shifted due to the guide track (26), they can be returned to their original positions using a known focus servo mechanism.

In the present invention, the surface of the convex portion has the NVL on the harmful side, and a light beam or a heat beam is condensed and irradiated onto the NVL or the LC in the vicinity thereof.

Then, the orientation of the LC defined by this NVL can be changed to a second orientation that is different from the initial first orientation.

Further, FIG. 3 shows a longitudinal sectional view of this embodiment showing only this recording trunk enlarged.

In FIG. 3 (8), the NVL is a ferroelectric thin film (hereinafter referred to as FE) on the counter electrode (4) and a conductor or semiconductor cluster (in the form of an island, each electrically free (floating)) on the upper side. There were clusters of clusters scattered throughout the area. This cluster is preferably transparent to the reading laser beam (16), and is made of, for example, indium tin oxide, zinc oxide, tin oxide, antimony oxide, amorphous silicon, amorphous 5ixC+
−x (0<X≦1).

5iJs-x (0,5<x<4) can be used.

Also, as this FE, vinylidene fluoride (CHgCh
) (referred to as V Kano) and tetrafluoroethylene (CFzCF
A copolymer obtained by mixing z) was used. This is 1
Dissolved and diluted in 0% by weight methyl ethyl titone. Furthermore, this was applied onto the electrode by a spin method. The thickness of the FE can be controlled by the spin rotation speed and the degree of dilution. After spin-coding, it can be heated to, for example, 140° C. to vaporize unnecessary materials and promote crystallization of the copolymer, thereby making it possible to form an extremely thin layer of 100 to 5,000 layers, for example, 1,000 layers. On the other electrode (4゛), even if it is a similar FE, another FE such as vinylidene chloride (CH
2CC12) (VDCI), or a copolymer of VDF and trifluoroethylene (TrPEz) may also be used. Here, a nylon thin film (7”) is placed on the other electrode (4”).
) was formed, and the surface was subjected to a rubbing treatment.

After this, the pair of substrates (3) and (3°) are separated for a predetermined period, and the NVL (5) and the alignment film (7) are separated.
A liquid crystal (5) is filled between the two.

Furthermore, a liquid crystal blend of S8 (octyl oxy benzylidene amino methyl butyl henzoate) and 87 or B8 was filled in this space. In addition to this, liquid crystal materials such as DOBAMBC or a liquid crystal material blended with multiple materials may be used f, p), ', -.
reactor. As an example, Ferroelectrics1
984 Vol, 59 pp126-136 J, W,
Ferroelectrics by Goodby et al.
Switching in the Title
d Smec-tic Phase of R-C
-3-4-n-Hexyloxydenzyliden
e4”-8m' no-(2-Chloropropy
l) (innamate(IIOBAcPc).

Japanese Patent Publication No. 59-98051. JP-A-59-118744 may also be used.

The periphery of this optical memory disk (10) is sealed (30) as shown in FIG. 1 to prevent the liquid crystal from coming into contact with the atmosphere.

(30') has been done. This optical memory disk is (10
) have a pair of external contact electrodes (32) and (32') extending from the pair of electrodes (4) and (4').
). This external contact electrode (32),
(32') are the terminals (31), (31
°) to be electrically connected. Furthermore, this jig has leads (13) and (13') that are thicker than the signal source (25) during memory writing (101) and erasing (102).
) is connected.

Contacts (32), (32) of optical disc (10)
°) is a drive system (15) that rotates the optical disk (10)
This is done at the same time when the auxiliary jig (14') is brought into close contact with the jig (14), and there is no sliding movement at the contact portion.

For this reason, the contact portions (32) and (32
”) can prevent a decline in reliability.

Thus, these external contact electrodes (32), (3
2''), a predetermined voltage, for example, -15V, is applied to bring the entire surface of the recording trunk into the "0" state. Furthermore, the system “writes” information to this disk (10) (101).
This is done using In other words, a light beam, especially infrared rays, is emitted from (23) to a liquid crystal arranged in one direction on the entire surface, and a condensing optical system,
Irradiation (
22) Write by shifting the phase of L, a predetermined address from the initial 1tII state.

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

That is, the light beam from the semiconductor laser (12) passes through the polarizing plate (
8), the light (1
6) is made incident. Furthermore, the light is transmitted as (16”) from this disk memory, and the second position correction and optical system (16”) are transmitted.
1°), the light receiving sensor (9) via the second polarizing plate (8°)
leading to.

Example 2 This embodiment uses the optical memory devices shown in FIGS. 1 and 2.

Particularly regarding the recording track, the structure shown in FIG. 3(B) was used. That is, this is an enlarged view of a part of the optical disk memory of the present invention. In the drawings, a plastic substrate (3), (3°) for example an acrylic resin or a Corning 7059 glass substrate was used. A transparent conductive film (4) is placed on this substrate as an electrode.

Form (4゛). And this pair of electrodes (4'),
NVL (5
) will be established. This NVL (5) is a silicon nitride film (5-1
) (average thickness 50-150), silicon semiconductor film (
5-2) (Average thickness: 300-1000 layers, silicon nitride film (50-1000 layers)
It is transparent to wavelengths of 700 to 900 nm) and acts as a positive or negative charge trapping center. Furthermore, a nylon thin film was formed on the electrode (4'') and subjected to a rubbing treatment. After this, the same liquid crystal as in Example 1 was filled during this period.

Example 3 FIG. 3(C) is a modification of FIG. 3(B).

In Figure 3 (B), NVL is silicon nitride (5-1), (5
-3) and a semiconductor cluster (5-2). Further, on the other electrode (4') was a silicon nitride film (7-1) and an organic film (7-2), and the upper surface of this organic film was subjected to a rubbing treatment. In this case, the liquid crystal is TN (twisted nematic, super twisted nematic type liquid crystal)
was used. This liquid crystal can then determine whether light is transmitted or not, depending on the presence or absence of an electric field. This is achieved by injecting positive or negative charges into the cluster (5-2) and capturing it as "erasing". Further, in the case of "writing", the charge of the cluster at a predetermined address of the recording track is released only by a beam of heat or light, and by setting it to "no", it is possible to determine whether the cluster is transmissive or non-transmissive. Of course, it is also possible to use the same ferroelectric liquid crystal as in Example 1 as this liquid crystal.

The rest is the same as in the second embodiment.

Example 4 A longitudinal sectional view of this example is shown in FIG. 3(D). A silicon nitride film (5) to which silicon is excessively added is provided on one 't 4m (4). This silicon nitride film (Sj
J4-X O, 5<X<4) has a large amount of silicon dangling bonds, and can act as an NVL. Also, on the other electrode (4”) is a dielectric film (5’-2”).
) and a translucent charge trapping layer (5'-1) were provided. That is, this is an example in which NVL is provided on both of a pair of electrodes. The rest is the same as in the first embodiment.

In the embodiments shown above, the idea of the present invention is to perform "optical writing" and "electrical writing and erasing". For example, when using FLC as the liquid crystal, the tilt angle is approximately 22.5°.
I used the one from In this case, "write/erase" applies -15V to the entire disk memory, sets the tilt angle to approximately -22.5 degrees, and sets all addresses to "O".On the other hand, "write" does not reach a positive threshold voltage for the entire disk memory. no weak voltage (i.e. less than E c +), e.g. +2v
Add. Further writing is performed, and the address is irradiated with a laser beam for writing. Then, the temperature at this predetermined address rises, and after that, when the laser light irradiation is stopped and the temperature is gradually cooled, the tilt angle in the direction determined by the positive voltage is +17.5 to +27.5. The wavelength of writing laser light is 1 to 3μ.
When we add infrared rays with , most of this light is absorbed by the liquid crystal. Furthermore, a short wavelength laser beam such as an Ar laser is preferable for releasing the charges captured in the NVL. This light energy can then excite the trapped charges shown in Example 1.2.3.4 beyond the insulating barrier and cause them to be released or injected.

That is, in the present invention, writing is performed by applying a basic bias voltage (a voltage smaller than a critical voltage) in addition to the irradiation of a spot laser beam. 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 (selectively) by using a laser beam, and by applying a basic bias voltage in the opposite direction.

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

Then, by providing a recording track and a guide trunk, and by irradiating this recording track with a reading laser beam or a writing laser beam, it is possible to eliminate jumps when reading or writing to an adjacent inner or outer trunk. did it.

The optical system of the present invention uses different optical systems for "reading" and "writing". However, as another method, they can be used as the same light source using a half mirror. However, in this case, the amount of light for "writing" and "reading" differs by more than 10 times, so although the number of parts can be reduced, it has the disadvantage that optical path design is complicated.

Furthermore, as a partially modified method of the present invention, it is possible to arrange a polarizing plate on the light-irradiated surface side of the disk as long as it can withstand "writing/erasing" or "writing". However, since all disk memories are provided with two polarizing plates, this method has the drawback of increasing manufacturing costs.

Further, in the embodiments of the present invention, a method for reading out light is mainly shown in which the presence or absence or size of light reflected by the reflective layer is compared and identified. However, as an optical disk device, the rob and rlJ may be determined by comparing the magnitude of the irradiated light.

In such a method, "writing" and "reading"
Since it is an optical system, it has an extremely large memory capacity.

The practical application of the present invention is effective not only for consumer-use compact disk memories in cars 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 drawings]

FIG. 1 schematically shows an optical disc memory device of the present invention. FIG. 2 shows a partially enlarged view of the optical disc memory device of the present invention. FIG. 3 shows an enlarged longitudinal sectional view of the recording track.

Claims (1)

[Claims] 1. A pair of substrates has electrodes inside each other, liquid crystal is filled between the electrodes, and means for defining a nonvolatile orientation of the liquid crystal is provided on one or both of the electrodes. In the liquid crystal device, one of the inner surfaces of the pair of substrates is provided with a guide track and a recording track with an uneven surface, and the other surface is provided with a flat surface. The optical disk memory device 2 according to claim 1 uses a liquid crystal characterized in that it has an electrode on the substrate on the recording track side and means for defining a nonvolatile orientation of the liquid crystal on the electrode. Optical disk memory device. 3. An optical disk memory device using liquid crystal according to claim 1, wherein the means for defining non-volatile orientation comprises a charge trapping central layer electrically separated from the electrodes.