JP2823757B2 - Non-volatile recording device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nonvolatile recording device having a high-density, large-capacity recording capacity and capable of electrically writing and reading information, and more particularly to a computer, a memory card and a word processor. The present invention relates to a non-volatile recording device that can be widely used in various devices.

[0002]

2. Description of the Related Art As an example of a non-volatile recording device, there is a device in which information can be rewritten. The following four types are typical of such non-volatile recording devices. Magnetic tape Magnetic disk EPROM, EEPROM (IC nonvolatile memory) Magneto-optical disk Also, as a recent nonvolatile storage device of this type,
For example, there is a nonvolatile memory using a liquid crystal proposed by the applicant of the present invention in Japanese Patent Application Nos. Hei 3-13827 and Hei 3-285136.

The outline of each of the above-mentioned nonvolatile recording devices will be described below.

[0004] Magnetic tapes are the most typical rewritable non-volatile recording devices, have the feature of being inexpensive, and are most widely used as audio tapes and video tapes. Further, the storage device has a very large storage capacity, and is used as a backup memory for a computer.

However, there is a disadvantage that only sequential writing / reading of information is possible and random access is not possible. Another disadvantage is that the access time for reading and writing information is long.

A magnetic disk is used as an external recording device for a computer or a word processor, and an inexpensive floppy disk which is easy to handle and an expensive hard disk which has a large storage capacity but is difficult to handle and are often used.

The characteristics of the magnetic disk are that high-speed random access is possible and writing / rewriting is relatively easy.

The recording capacity is about 1 megabyte for one 3.5-inch floppy disk and about 40 megabytes for one 3.5-inch hard disk.

[0009] EPROM and EEPROM IC nonvolatile memories are rewritable recording devices, and are capable of high-density recording. Typical examples of such an IC nonvolatile memory include an EPROM that performs electrical writing and erasing by ultraviolet irradiation, and an EEPROM that allows electrical writing and erasing. These ICs
Non-volatile memories have features such as small size, light weight, short access time, and low power consumption. Here, an electrically writable / erasable EEPROM will be described as an example.

FIG. 5 shows a sectional shape of a memory cell of the EEPROM. On the surface side of the substrate 7, a source region 8 and a drain region 6 are formed, and a channel region 9 is formed therebetween. Then, a gate oxide film 5 is formed on these, and a floating gate 4 and a control gate 2 are pattern-formed thereon in this order. Carriers are accumulated in the floating gate 4,
The control gate 2 controls the injection of carriers into the floating gate 4.

The control gate 2 and the floating gate 4 are separated by an insulating film 3 made of a silicon oxide film. The surface protection film 1 is formed on these so as to cover the surface of the substrate 7. As the surface protection film 1, a silicon oxide film or a silicon nitride film is usually used.

In such a configuration, when recording (writing) information, a voltage is applied between the drain region 6 and the control gate 2, and hot electrons as carriers are passed through the gate oxide film 5 to the floating gate. Inject into 4. On the other hand, erasing recorded information
A voltage is applied between the source region 8 and the control gate 2, and carriers are removed using the Fowler-Nordheim (NF) Tunneling phenomenon. Also, the reading of the record information
Channel region 9 between source region 8 and drain region 6
ON / OFF is determined based on the threshold voltage of the inversion voltage.

Here, since the injection and removal of carriers are performed through the gate oxide film 5, the film quality and thickness of the gate oxide film 5 are very important in the structure of the EEPROM. For example,
In a 1 Mbit EEPROM, the gate oxide film 5 is usually used.
Is a thin film having a thickness of about 20 nm, it is difficult to control the film quality and the film thickness, and the increase in cost due to a decrease in yield is a serious problem. Further, the chip size is usually about 7 to 10 mm on both the short side and the long side. If the chip area is increased to increase the recording capacity, the yield decreases and the cost increases.

For these reasons, the current EEPRO
The recording capacity of M is about 1 to 4 megabits, which is smaller than other non-volatile recording devices such as a magneto-optical disk and a magnetic disk.

Magneto-optical disk A type of optical disk, a rewritable recording device, and one of the typical large-capacity nonvolatile recording devices.

FIG. 6 shows an example of the structure of a magneto-optical disk. For recording / reproducing of a magneto-optical disk, a magnetic thin film 15 or 16 having a perpendicular magnetization characteristic is used for a recording medium, and a laser beam 20 is applied in a weak magnetic field in a direction opposite to a previously magnetized direction.
Is focused on the focusing area 21 on the disk D, and a signal is recorded by local heating. Reproduction uses the Kerr effect or the Faraday effect. That is, the linearly polarized laser light 20
Is applied to the disk D, the plane of polarization of the transmitted light or reflected light rotates according to the magnetization state of the magnetic thin films 15 and 16. The rotation of the plane of polarization is converted into a light intensity signal using an analyzer, and detected as an electric signal by a photodetector, thereby reproducing the signal. Such a magneto-optical disk is
It has been put to practical use as a recording device capable of large-capacity recording for document files and image files.

The feature of the magneto-optical disk is that the laser beam 20
Therefore, information can be recorded in a non-contact manner through a transparent substrate. That is, in this method, dust on the recording surface side 23 does not matter. On the other hand, dust on the substrate surface side 22 has an effect, but since the laser light 20 is not focused on the substrate surface side 22, the beam diameter is several hundred μm.
m, and there is no adverse effect even if some dust is present.

In information recording using an optical disk, high-density recording can be performed because information is recorded / reproduced with a focused laser beam. For example, a memory device having a large capacity of about 120 megabytes on a 3.5-inch disk can be realized.

However, since a magneto-optical disk requires a laser light source, a magnet constituting an actuator, a rotating mechanism, and the like for writing and reading, there is a disadvantage that peripheral equipment is large and the price is high.

The problems of the non-volatile recording devices described above are summarized as follows.

(1) Large-capacity, high-density recording.

In the case of a floppy disk, a 3.5-inch disk has a size of about 1 megabyte, and cannot cope with an increase in capacity and density.

Although high density can be realized with an IC nonvolatile memory such as an EPROM and an EEPROM, it is difficult to increase the capacity because the chip area cannot be increased due to a limitation in yield.

(2) Weak against shock and vibration.

In a hard disk, a large capacity can be realized by integrating a plurality of disks. However, in order to cope with high density, the distance between the head and the disk is reduced to 1 μm or less, and the disk is easily damaged by shock or vibration. Further, there is a disadvantage that even if minute dust adheres to the head or the disk, the recording device is damaged.

(3) Peripheral devices such as writing and reading are complicated and large.

A floppy disk, a hard disk, and a magneto-optical disk need to have a rotating mechanism such as a motor to write and read information by rotating the disk, which makes the peripheral device larger and more complicated.

In addition, in the case of a hard disk, the distance between the disk and the head must be precisely controlled, and a cushioning material is required to secure impact resistance, so that the entire device becomes large and heavy. There's a problem.

Further, since a magneto-optical disk uses a laser light source, a magnet, a rotating mechanism, and the like for writing and reading, there is a disadvantage that the device is large, heavy, and expensive.

(4) Reading and writing can be performed at a high speed.

In a floppy disk, a hard disk, and a magneto-optical disk, since the position of information to be accessed is searched for while rotating the disk, there is a limit in increasing the reading speed.

As a nonvolatile recording device which can solve all of these problems, there is a nonvolatile memory using the above-mentioned liquid crystal. The outline and problems are briefly described below.

FIGS. 7 and 8 show this nonvolatile memory. A liquid crystal compound is sandwiched between two substrates 55 and 52, and a matrix electrode is provided on both of the substrates 55 and 52,
It has a schematic configuration for reading and writing.

More specifically, on the lower silicon substrate 55, a plurality of upper electrodes 41 are arranged in a column direction corresponding to the front and back directions of the drawing sheet. , A plurality of lower electrodes 42 are arranged in a row direction orthogonal to the arrangement direction of the upper electrodes 41. A heating element 44 is provided between the upper electrode 41 and the lower electrode 42, and a memory cell is formed at the intersection of the two electrodes 41 and 42.

The silicon substrate 55 has an opposite electrode 5 on the opposite surface.
The glass substrate 52 on which the first liquid crystal 1 is formed is bonded, and a liquid crystal 53 composed of a polymer nematic liquid crystal is disposed between the two substrates 55 and 52.
To form a memory cell. In the figure, reference numeral 56 denotes an alignment film provided in contact with both upper and lower surfaces of the liquid crystal layer. Reference numeral 57 denotes a field insulating film, and reference numeral 54 denotes an inter-electrode insulating film.

The writing of information is performed by applying an AC voltage to the heating element 44 and heating the liquid crystal 53. After the heating, the supply of the AC voltage is stopped, and the liquid crystal 53 is rapidly cooled to have a polydomain structure. Further, by gradually lowering the supply of the AC voltage, the liquid crystal 53 is gradually cooled to have a monodomain structure. The mono-domain structure can also be realized by cooling the liquid crystal 53 while applying a voltage.

On the other hand, reading is performed by applying an AC voltage between the upper electrode 41 and the counter electrode 51 and measuring the electric capacity of the liquid crystal 53. Specifically, since the dielectric constant of the liquid crystal 53 is different between the poly-domain structure and the mono-domain structure, a difference in electric capacitance caused by the difference is measured.

[0038]

However, the above-mentioned nonvolatile memory using a liquid crystal has a problem in its structure, so that a liquid crystal material having a high thermal conductivity and a large dielectric anisotropy can be selected or bonded. There are drawbacks in production technology such as electrical connection between the two substrates 55 and 52, and at present it is desired to improve the structure. The details of the problem will be described below.

First, in these nonvolatile memories using liquid crystal, it is difficult to integrate a driver circuit for driving the memory device because the substrate is divided into two. This is because the number of matrix electrodes for reading and writing is large and the intervals are small. Therefore, one of the substrates 5
It is difficult to connect the driver circuit of the memory device built in 2 with the read / write matrix-shaped electrodes separately provided on the other substrate.
In addition, when the connection point is reduced, the connection resistance is correspondingly increased, and the driver circuit for compensating for the influence is also complicated. These technical difficulties reduce productivity and increase costs.

Since the liquid crystal 53 as a recording medium has a relatively small thermal conductivity, it is difficult to uniformly heat the entire desired area until a desired thermal state change occurs. This is clear from the analysis result of the thermal diffusion by the computer simulation of the heat generating portion shown in FIG.

That is, as shown in FIG. 9, the temperature of the liquid crystal 53 in contact with the surface of the heated heating element 44 has risen to a temperature (58 ° C.) sufficient for the liquid crystal 53 to undergo a phase transition. In the vicinity of the glass substrate 52, the temperature rise is small (46 ° C.). Therefore, when an electric field is applied to the liquid crystal 53 in this state, a change in the dielectric constant occurs only in a portion in contact with the surface of the heating element 44, so that it is difficult to detect a change in the dielectric constant (phase transition) of the entire memory cell. .

Such a problem can be solved by lengthening the heating time of the heating element 44. However, if the heating time is lengthened, the high-temperature region spreads to the periphery, so that a phase transition occurs even in an adjacent memory cell. Therefore, there is a new disadvantage that it is difficult to increase the density of the memory cells.

Therefore, in the nonvolatile memory using the above-mentioned liquid crystal, the interval between the two substrates 55 and 52 is extremely narrowed, and the liquid crystal layer is made thin so that the entire memory cell is uniformly heated. Was.

However, when the space between the substrates 55 and 52 is extremely narrowed, the upper and lower electrodes 51 and 52 are naturally formed.
Since the interval between the electrodes 41 is extremely narrow, the electrodes 51 and 41 which are separated into upper and lower parts are likely to be in contact with each other. For this reason, there is a limit in reducing costs. In addition, since it is difficult to uniformly inject a highly viscous liquid crystal material such as a polymer liquid crystal into such a thin cell, the liquid crystal material is limited.

The present invention has been made to solve such problems of the prior art, and can achieve high density, large capacity, high-speed writing / reading, and downsizing of peripheral devices. It is an object of the present invention to provide a new type of non-volatile recording device capable of reducing the size and simplicity of the entire device configuration and further reducing the cost.

[0046]

According to the present invention, there is provided a nonvolatile recording device comprising a liquid crystal compound or a compound containing a liquid crystal component in a molecule.
The formed recording medium is applied on a substrate or sealed between the substrate and a sealing material, and the recording medium is heated by a heating means to change the physical state of the recording medium in a thermal state. A non-volatile recording device that reads changes in the physical property values of the recording medium as information written to the recording medium by an electric reading unit while the heating unit and the electric reading unit Are formed on the same substrate, and the electric readout means
Electrode pair consisting of a first electrode and a second electrode arranged
And the heating means comprises the second electrode and the second electrode.
A second electrode pair consisting of a third electrode crossing and overlapping the two electrodes
And heat generated between the intersection of the second electrode pair and the insulating film.
It is formed of a body, thereby achieving the above object.

Preferably, the insulating film is a silicon nitride film
It consists of .

[0048]

[0049]

[0050]

[0051]

[0052]

The operation will be described below by taking a non-volatile recording device in which three-layered electrodes, ie, a first electrode, a second electrode and a third electrode, are formed in a matrix on a single substrate. I do.

Here, the first electrode, the second electrode, and the third electrode are closer to the liquid crystal layer as a recording medium in this order.
Both the first electrode and the second electrode are in contact with the liquid crystal layer. Therefore, the physical property value of the liquid crystal layer is read by the first electrode pair formed by the first electrode and the second electrode.

In such a configuration, when a voltage is applied to the second pair of electrodes arranged in a matrix and a current flows through the heating element sandwiched between the intersections, Joule heat is generated in the heating element. By controlling the current, the voltage, and the application time, the liquid crystal layer (liquid crystal) constituting the recording medium can be heated to a temperature at which a state change such as a phase transition occurs. Then, when the current supply is stopped and the liquid crystal layer is rapidly cooled, the liquid crystal layer is fixed while undergoing a state change such as phase transition. As a result, the physical property value of the liquid crystal layer, for example, the dielectric constant changes, and the information is written. Since this state is held for a long time, the written information can be held in a nonvolatile manner as recording information.

The recorded information written as a change in the dielectric constant can be obtained by applying an AC voltage between the first electrode and the second electrode and measuring the capacitance of the liquid crystal layer as a dielectric at that time. Can be read out electrically. That is, reading of information is performed.

From this state, the temperature of the liquid crystal layer is raised again by a similar procedure until a state change such as phase transition occurs, and then the current and voltage applied to the heating element via the second electrode pair are controlled. If the liquid crystal layer is gradually cooled or quenched and a high AC voltage is applied during cooling, the liquid crystal layer undergoes a state change again, whereby information once written in the liquid crystal layer can be erased. Therefore, a rewritable nonvolatile liquid crystal memory can be realized by the above configuration.

The non-volatile recording device having the above configuration does not use the change in the orientation of the liquid crystal layer in the thickness direction when writing information, but uses the change in the orientation of the liquid crystal on the surfaces of the first and second electrodes. ing. The reason is that it is difficult to uniformly heat the entire liquid crystal layer above the memory cell, as is clear from the above-mentioned thermal analysis result.

On the other hand, since the temperature of the surface of the liquid crystal layer in contact with the first and second electrodes close to the heating element can be raised relatively easily, information can be recorded quickly. Also,
In the above configuration, the first electrode and the second
Since both the electrode and the heating element as the heating means are formed on a single substrate, a circuit for writing and reading can be formed on the same substrate, thereby simplifying the configuration of the entire recording apparatus.

[0059]

Embodiments of the present invention will be described below.

FIG. 1 schematically shows the surface configuration of the nonvolatile recording apparatus of the present invention. Peripheral circuits of the recording unit 28, that is, the input / output signal control unit 25, the logical system control unit 26, and the drive circuit unit 27 are shown divided into blocks according to their functions.

Here, the input / output signal control unit 25
Process input signals from other devices such as the memory cell 2
9 (see FIG. 2) for sending a signal (write information);
It has a function of processing a signal read from the memory cell 29 and sending the processed signal to another device. The logical system control unit 26 controls the signal processing of the entire nonvolatile recording device. Drive circuit unit 27
Supplies a current for supplying an electric signal to the memory cell 29 of the recording unit 28 according to a command from the logical system control unit 26. The recording unit 28 accumulates a signal (data) provided from the input / output signal control unit 25 and stores it as recording information.

Incidentally, such a peripheral circuit is an IC
However, the present invention is not limited to this, and other circuits and circuit elements may be used as long as they can be mounted on a silicon substrate.

As shown in FIGS. 2 to 4, the recording unit 28
Denotes a heating heating element 35 for writing / rewriting recording information to the memory cell 29 of the recording section 28, a second electrode 34 for supplying current to the heating element 35, and a third electrode 37.
And a silicon substrate 39 having a first electrode 32 for reading recorded information in cooperation with the second electrode 34, and a liquid crystal layer 31 applied on the silicon substrate 39. The details will be described below.

FIG. 2 shows the surface configuration of the silicon substrate 39 excluding the liquid crystal layer 31 of the recording section 28.
Are arranged in the row direction at equal intervals in the column direction corresponding to the vertical direction in the figure. First electrode 32
Is in contact with the liquid crystal layer 31 thereabove. A plurality of second electrodes 34, 34,... Are arranged at equal intervals in the row direction below the first electrode 32 and in a column direction orthogonal to the first electrode 32. A first electrode pair is constituted by 32 and 34.

The intersection of the first electrode 32 and the second electrode 34 is arranged on the silicon substrate 39 in a matrix. The electrode pair including the first electrode 32 and the second electrode 34 is used when reading information recorded in the memory cell 29. The second electrode 34 also has a liquid crystal layer 3 above it.
Touching 1 The memory cells 29 are also arranged in a matrix, and the recording unit 28 is constituted by the entire memory cells 29. In FIG. 2, one area surrounded by thin lines displayed in the row direction and the row direction is a memory cell 2
Equivalent to 9.

Further, below the second electrode 34, the second
Similarly, in the row direction orthogonal to the electrode 34, a plurality of third
The electrodes 37 are arranged. Therefore, the intersection of the second electrode pair formed by the second electrode 34 and the third electrode 37 is also arranged in a matrix. A heating element 35 is sandwiched between the intersections of the second electrode pair, and the second electrode 34 and the third electrode 37 are part of the wiring and are electrically connected to each other through the heating element 35. Supply power to 35. In this embodiment, in order to reduce the size of the memory cell 29, tungsten having excellent heat resistance is used as a wiring material of the electrodes 32, 34, and 37.

The above-mentioned memory cell 29 is formed of a portion of the silicon substrate 39 located at the intersection of the first electrode 32 and the second electrode 34, and the liquid crystal layer 31 disposed thereon. The liquid crystal layer 31 has a function of recording information by the phase transition phenomenon.

Referring to FIGS. 3 and 4, a specific configuration of the memory cell 29 will be described below step by step. The silicon substrate 39 is a single crystal silicon substrate for a semiconductor generally used for an IC, and is doped with an impurity to control a resistance value. Third on the silicon substrate 39
When the electrode 37 is formed, a driving current flowing between the third electrode 37 and the second electrode 34 leaks to the silicon substrate 39. To prevent this, in this embodiment, the surface of the silicon substrate 39 is used. Is covered with a field insulating film 38 and a third electrode 37 is formed thereon.

An inter-electrode insulating film 36 is formed between the third electrode 37 and the second electrode 34 in order to maintain the insulation between them. 10 between the third electrode 37 and the second electrode 34
In some cases, a voltage of V or more is applied. In order to prevent dielectric breakdown, a uniform film quality without pinholes and a uniform film thickness are required. Therefore, in this embodiment, a silicon nitride film formed by a plasma CVD method is used as the inter-electrode insulating film 36.

The inter-electrode insulating film 36 serves as the memory cell 29
The second electrode 34 and the third electrode
The heating element 35 is directly sandwiched between the electrodes 37. When writing / erasing recorded information, the second electrode 34
And a third electrode 37, a current flows through the heating element 35, Joule heat is generated in the heating element 35, and the heating element 3
Since the temperature of both the second electrode 34 and the third electrode 37 is increased by the heat generated in 5, the heat resistance of these electrode materials is required. Therefore, in this embodiment, tungsten formed by the low pressure CVD method is used. On the other hand, since it is necessary to use a material that has heat resistance and an appropriate resistance value and can be finely processed at the same time as the heating element 35, in this embodiment, high-purity polycrystalline silicon is formed by the CVD method.

As described above, in this embodiment, tungsten formed by the CVD method is used as the wiring material, but other materials may be used as long as they have heat resistance. Further, the forming method is not limited to CVD, and other methods may be used as long as they can be formed uniformly.

Next, a specific manufacturing process of the memory cells 29 formed in a matrix in the recording section 28 will be described.
In the nonvolatile recording device of the present invention, the peripheral MOS (Met
al Oxide Semiconductor) IC formation process and recording unit 2
8 is necessary, but here, for simplicity of explanation, M
As for the OS IC process, only the well-known IC manufacturing process will be described, and only the manufacturing process of the memory cell 29 will be described.

In this embodiment, a 6-inch P-type (100) single crystal silicon wafer was used as the silicon substrate 39. First, 800 Å is formed on the silicon substrate 39 by thermal oxidation.
A field insulating film (field oxide film) 38 of nm is formed. Next, the reduced pressure CV is applied on the field insulating film 38.
A tungsten film having a thickness of 1.2 μm is formed by Method D. Subsequently, unnecessary portions of the tungsten film are removed by photolithography and dry etching, and the third electrode 37 is patterned.

Next, a 1.0 μm-thick silicon nitride film is formed on the third electrode 37 by a plasma CVD method.
An inter-electrode insulating film 36 for insulating between the third electrode 37 and the second electrode 34 is formed. Subsequently, the third electrode 3 is formed on the inter-electrode insulating film 36 by photolithography and dry etching.
An opening reaching 7 is formed.

Next, the third electrode 37 and the inter-electrode insulating film 3
6 so that the specific resistance is about 1 by the low pressure CVD method.
A polycrystalline silicon having a thickness of about 1,000 Ω · cm and a thickness of about 1.0 μm is formed on the entire surface of the silicon substrate 39 to form a heating element 35. Here, the resistance of polycrystalline silicon decreases when impurities such as boron, phosphorus, and metal are mixed into the film, and the temperature may not reach a predetermined temperature when heat is generated.
Attention must be paid to the purity of the materials used in the VD method and the cleaning of the equipment. Therefore, in this embodiment, high-purity monosilane gas is used as a material for forming polycrystalline silicon,
Although the heating element 35 is formed by the VD method, another silicon compound or another forming method may be used as long as a necessary resistance value can be secured.

Next, a tungsten film of about 1.0 μm is formed on the heating element 35 by a low pressure CVD method, and unnecessary portions of the tungsten film are removed by photolithography and dry etching to form a second electrode 35. did.

Next, a silicon nitride film having a thickness of 5.0 μm is formed on the second electrode 34 by a plasma CVD method.
An inter-electrode insulating film 33 for insulating between the first electrode 32 and the second electrode 34 was formed. Subsequently, an opening reaching the second electrode 34 is formed in the inter-electrode insulating film 33 by photolithography and dry etching. Since the interelectrode insulating film 33 has a low dielectric constant, it is better to increase the film thickness. That is,
By doing so, the change in the dielectric constant due to the phase transition of the liquid crystal layer 31 can be increased, and the reading is facilitated.

Next, a reduced pressure CV is applied on the inter-electrode insulating film 33.
A tungsten film of about 1.0 μm was formed by the method D, and unnecessary portions of the tungsten film were removed by photolithography and dry etching to form the first electrode 32.

An acrylic polymer nematic liquid crystal having p-cyanobiphenyl as a mesogen group is formed on the silicon substrate 39 manufactured by the above-described manufacturing process in an amount of 1 to 10 μm.
Then, the liquid crystal layer 31 is gradually cooled from the isotropic phase while applying an AC voltage of 100 V, 500 Hz between the first electrode 32 and the second electrode 34, so that the homeotropic alignment state is obtained. I do. Note that other materials may be used as the liquid crystal material as long as the material causes a state change such as a phase transition by heat and can maintain the changed state.

Further, in the above embodiment, the liquid crystal layer 31 is applied to the silicon substrate 39 on which the necessary components are formed, thereby manufacturing the memory cell 29. It is also possible to attach the substrates 39 at an interval of 1 to 10 μm and inject a polymer liquid crystal between them to manufacture the memory cell 29.

In the nonvolatile recording device of the present invention, p
-In addition to a polymer liquid crystal having cyanobiphenyl as a mesogen group, a polysiloxane-based polymer smectic liquid crystal can be used in the same manner.

Further, a conductive polymer liquid crystal can be used as the liquid crystal material. When using such a conductive polymer liquid crystal, phenanthrene is used as an electron donor, a charge transfer complex using iodine as an electron acceptor is used as a conductivity-imparting group B, and a mesogen group A is used as an ester-based liquid crystal.
A conductive polymer liquid crystal having an acrylic main chain is applied to a silicon substrate. Then, this conductive polymer liquid crystal is
While applying an alternating current of 00 V and 500 Hz, the orientation is uniformed by gradually cooling from the isotropic phase.

Finally, the silicon substrate 39 manufactured through the above steps is diced and bonded, and then housed in a package.

Next, the operation principle of writing and reading information to and from the memory cell 29 manufactured as described above will be described.

The nonvolatile recording device of the present invention records information in the memory cell 29 using a state change such as phase transition due to heat of liquid crystal, and reads out information using a change in dielectric constant accompanying the state change. It is carried out. Here, in an acrylic type polymer nematic liquid crystal having p-cyanobiphenyl as a mesogen group, a polysiloxane-based polymer smectic liquid crystal, or the like, the state changes to an isotropic phase by heating at or above a phase transition temperature. Thereafter, upon rapid cooling, the structure changes from a monodomain structure to a polydomain structure. This state can be maintained at room temperature for a long time. Therefore, according to such a recording medium, the recording information can be held in a nonvolatile manner.

On the other hand, when gradually cooled after heating, the structure returns to the monodomain structure again. Since the dielectric constant of the liquid crystal is different between the mono-domain structure and the poly-domain structure, it is possible to electrically read recorded information by using this.

The specific operation of writing / rewriting and reading information in the nonvolatile recording device of the present invention will be described below.

(Writing / Rewriting Method) Information input from an external device is temporarily recorded in a buffer memory by an input / output control unit 25, and is written into a memory cell 29 of a recording unit 28 after data processing. This writing is performed by applying a voltage to the heating element 35 sandwiched between the second electrode 34 and the third electrode 37 on the silicon substrate 39 and heating the liquid crystal layer 31. After the heating, the application of the voltage is stopped, and the liquid crystal layer 31 is rapidly cooled. On the other hand, when the voltage is gradually lowered and the cooling is performed, a mono-domain structure is obtained, and the recording and erasing state is set. Here, the change to the mono-domain structure can also be realized by cooling by applying an electric field between the first electrode 32 and the second electrode 34.

Since the writing position can be freely selected, the nonvolatile recording device of the present invention enables random access.

(Reading Method) An AC voltage is applied to the second electrode 34 and the first electrode 32 on the silicon substrate 39, and the capacitance of the liquid crystal layer 31 is measured. Since the dielectric constant of the liquid crystal layer 31 is different between the poly-domain structure and the mono-domain structure, data "1" and "0" are obtained by detecting a difference in electric capacitance.
Can be read.

In the above embodiment, the recording information written in the memory cell 29 is electrically read by applying an AC voltage to the first electrode 32 and the second electrode 34.
This reading can also be performed optically.

That is, in the mono-domain structure, the liquid crystal layer 3
1 is in a transparent state, whereas in the polydomain structure, the liquid crystal layer 31 is in an opaque state due to light scattering. Therefore, the recording information can be read by irradiating the memory cell 29 with light such as a laser beam and detecting the reflected light from the liquid crystal layer 31 by the light receiving means. In this reading method, in order to improve the reading accuracy, the liquid crystal layer 3
1 is required to have a flat surface, so it is necessary to arrange a transparent layer such as glass on the surface.

Since the non-volatile recording device having such a configuration requires an optical detecting means, the system configuration becomes large as compared with the case of using the above-mentioned electric reading means. Reading is possible. However, even in the case of this system, an electric device including a signal processing means is required, and therefore, it can be said that the system is an electric system configuration as a whole.

[0094]

As described above, by using the non-volatile recording device of the present invention, information can be written and read from a recording medium by static electric control. A moving mechanism such as a rotating mechanism and a head becomes unnecessary. Therefore, the size, simplicity, and cost of the device configuration can be reduced.

In addition, complicated and precise components required for a laser pickup, a magnetic head, and the like are not required.
Since there is no possibility that the device is destroyed due to vibration, impact or adhesion of dust, the stability of record holding and the reliability of the device can be remarkably improved.

Further, since the structure of the memory cell can be simplified as compared with a nonvolatile recording device using an IC nonvolatile memory, a large area can be realized.

Further, in the nonvolatile recording apparatus of the present invention, all components including the liquid crystal of the recording medium can be formed on one substrate, so that the I / O for controlling the input and output of information is controlled.
Peripheral circuits made of C can be easily mounted on the same substrate.
Further, a counter electrode is not required, and liquid crystal as a recording medium can be applied. In addition, since all wirings can be performed in the same substrate, a nonvolatile recording device can be manufactured by a combination of thin film formation, photolithography, and dry etching, and extraction of electrodes is easy.
Therefore, it is possible to reduce the size and simplification of the device configuration, which is extremely convenient for reducing costs.

Further, since information is written using a recording medium near the surface of the heating element as the heating means,
Heat utilization efficiency at the time of writing is increased. That is, the phase transition due to heat of the liquid crystal as the recording medium can be efficiently caused.

[0099]

[0100]

As described above, according to the present invention, it is possible to realize a completely new type of nonvolatile recording device which satisfies the desirable conditions as a nonvolatile recording device.

[Brief description of the drawings]

FIG. 1 is a schematic plan view showing a surface configuration of a nonvolatile recording device of the present invention.

FIG. 2 is a schematic plan view illustrating a planar configuration of a recording unit.

FIG. 3 is a perspective view of a memory cell.

FIG. 4 is a sectional view taken along line A-A ′ of FIG. 3;

FIG. 5 is a cross-sectional view showing the structure of an EEPROM.

FIG. 6 is a sectional view showing the structure of a magneto-optical disk.

FIG. 7 is a perspective view of a nonvolatile memory using a liquid crystal previously proposed by the present applicant.

8 is a sectional view taken along line B-B 'of FIG.

FIG. 9 is a cross-sectional view illustrating a simulation result of a temperature distribution of a nonvolatile memory cell using liquid crystal.

[Description of Signs] 25 input / output signal control unit 26 logic system control unit 27 drive circuit unit 28 recording unit 29 memory cell 31 liquid crystal 32 first electrode 33 interelectrode insulating film 34 second electrode 35 heating element 36 interelectrode insulating film 37 Third electrode 38 Field insulating film 39 Silicon substrate

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-59-34587 (JP, A) JP-A-1-307022 (JP, A) JP-A-1-166390 (JP, A) JP-A-63-1988 296021 (JP, A) JP-A-5-54685 (JP, A) JP-A-5-128883 (JP, A) JP-A-5-128884 (JP, A)

Claims (2)

(57) [Claims] 1. A liquid crystal compound or a liquid crystal component contained in a molecule.
A recording medium formed of a compound is applied on a substrate or sealed between the substrate and a sealing material, and the recording medium is heated by a heating means to obtain a thermal property value of the recording medium. What is claimed is: 1. A non-volatile recording device for writing information by a state change while reading a change in a physical property value of said recording medium as information written to said recording medium by an electric reading means, wherein said heating means and said electric reading Means are formed on the same substrate, and the electrical readout means are arranged in an intersecting and overlapping manner.
Formed of a first electrode pair comprising a first electrode and a second electrode
And the heating means intersects and overlaps the second electrode and the second electrode.
A second electrode pair comprising a third electrode and an intersection of the second electrode pair.
A non-volatile recording device formed of a heating element sandwiched between a difference portion and an insulating film . 2. The nonvolatile recording apparatus according to claim 1, wherein said insulating film is made of a silicon nitride film .