JP2743980B2 - 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 There are the following four types of typical nonvolatile recording devices in which information can be rewritten.

[0003] Magnetic tape.

[0004] Magnetic disk.

An IC nonvolatile memory such as an EPROM or an EEPROM.

[0006] A magneto-optical disk.

[0007] Each feature will be described below.

[0008] Magnetic tape is the most typical rewritable nonvolatile recording device,
Because it is inexpensive, it is most widely used as audio tapes and video tapes. It is a very large-capacity recording device, and is also used as a backup memory for a computer.

However, since only continuous writing and reading of information can be performed, random access cannot be performed, and the access time required for reading and writing information is long.

A magnetic disk is generally used as an external recording device for a computer or word processor. An inexpensive floppy disk that is easy to handle and has a larger recording capacity than a floppy disk, but is difficult to handle and often uses an expensive hard disk.

The advantages of these magnetic disks are that high-speed random access is possible and that writing and rewriting of information can be performed relatively easily.

The recording capacity of a 3.5-inch floppy disk is about 1 megabyte, and that of a 3.5-inch hard disk is about 40 megabytes. is there.

EPROM and EEPROM IC non-volatile memories are rewritable recording devices, and are capable of high-density recording. Typical examples of the IC non-volatile memory include an EPROM for performing electrical writing and erasing by ultraviolet irradiation, and an EEPROM for electrically writing and erasing. These IC nonvolatile memories have advantages such as small size and light weight, short access time, and low power consumption.

In the following, E which can be electrically written and erased is
The details will be described using an EPROM as an example. FIG.
1 shows an example of a cross-sectional shape of a memory cell of an EPROM. The gate oxide film 5 is laminated on the surface of the silicon substrate 7, and the floating gate 4 and the control gate 2 are formed on the gate oxide film 5. The control gate 2 controls the injection of carriers into the floating gate 4 where the carriers are stored and stored. The two gates 2 and 4 are separated by an insulating film 3 made of a silicon oxide film. A surface protection film 1 is formed on a silicon substrate 7 so as to cover the gates 2 and 4. As the surface protection film 1, a silicon oxide film or a silicon nitride film is usually used. Further, a source region 8 and a drain region 6 into which impurities are implanted are formed in a surface layer portion of the silicon substrate 7, and a channel region 9 is formed therebetween.

In the above configuration, when recording information, a voltage is applied between the drain region 6 and the control gate 2, and carriers are injected into the floating gate 4 as hot electrons through the gate oxide film 5. on the other hand,
The erasure of the recorded information is performed by the source region 8 and the control gate 2.
And a Fowler-Nordhei
Carriers are removed using the m (NF) Tunneling phenomenon. Reading of recorded information is performed by determining ON / OFF based on the threshold voltage of the inversion voltage of the channel region 9 between the source region 8 and the drain region 6.

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 are set to E.
This is very important in the structure of the EPROM. For example, in an EEPROM having a recording capacity of 1 megabit, the gate oxide film 5 is usually a thin film having a thickness of about 20 nm. Therefore, it is difficult to control the film quality and the film thickness. Also, the dimensions of the chip are usually
Both the short side and the long side are about 7 to 10 mm. If the chip area is increased in order to increase the recording capacity, there is a disadvantage that the yield decreases and the cost increases.

Due to these disadvantages, EEPROM
However, while having the above advantages, there is a limit in improving the storage capacity. Incidentally, the recording capacity of the current EEPROM is about 1 to 4 megabits, and is smaller than that of 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. 5 shows an example of the structure of a magneto-optical disk. The magneto-optical disk uses magnetic thin films 15 and 16 having perpendicular magnetization characteristics as a recording medium. The record of information is
In a weak magnetic field opposite to the direction in which the magnetic thin films 15 and 16 have been magnetized in advance, the laser beam 20 is focused on the focusing area 2 on the disk.
The information is recorded on the magnetic thin films 15 and 16 by local heating. On the other hand, information reproduction is performed using the Kerr effect or the Faraday effect. That is, when the linearly polarized laser light 20 is irradiated onto the disk, the transmitted light or the reflected light rotates the polarization plane according to the magnetization state of the magnetic thin films 15 and 16, and the rotation of the polarization plane is analyzed by the analyzer. The information is reproduced by converting the light into a weak signal using a light detector and detecting it as an electric signal with a photodetector. Such a magneto-optical disk has been put to practical use as a recording device capable of large-capacity recording for document files and image files.

A feature of the magneto-optical disk is that the recording is performed by the laser beam 20, so that the recording can be performed through the transparent glass substrate 12 without contact. That is, according to this recording method, dust on the recording surface 23 side does not matter. On the other hand, dust on the substrate surface 22 side has an effect.
Since the laser beam 20 is out of focus on the side, the beam diameter is as large as several hundred microns, and there is no adverse effect due to the presence of some dust.

The recording capacity of the magneto-optical disk allows information to be recorded / reproduced by the condensed laser beam 20, so that high-density recording becomes possible. By the way, one for 3.5 inch disk
A large-capacity memory of about 20 megabytes can be realized.

However, a magneto-optical disk requires a laser, a magnet, and a rotating mechanism (a rotating mechanism of the disk) to write and read information.
There is a disadvantage that the price is high.

[0023]

A conventional nonvolatile recording device in which information is rewritable has the above-mentioned advantages and disadvantages. However, as a nonvolatile recording device desired in the future, the following ( 1), (2), (3),
It is required to satisfy item (4). Re-evaluation of the above-mentioned conventional non-volatile recording device for each item is as follows.

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

In the case of a floppy disk, a 3.5-inch disk has a recording capacity of about 1 megabyte and cannot cope with a large capacity and a high density.

Although high density can be realized with IC non-volatile memories such as EPROM and EEPROM, it is difficult to increase the capacity because the chip area cannot be increased due to the yield limit.

(2) It is resistant to 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 micron or less, and the disk is easily damaged by shock or vibration. In addition, there is a disadvantage that even if minute dust adheres to the head or the disk, the recording device is damaged.

(3) Small, simple and inexpensive peripheral devices for writing and reading.

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

In addition, the hard disk has a problem that the distance between the disk and the head must be made precise and a buffer material is required to secure impact resistance, so that the whole device becomes large and heavy.

In the case of a magneto-optical disk, since a laser and a magnet are used for writing and reading, the size of the apparatus becomes large,
There is a disadvantage that it becomes heavy and expensive.

(4) Writing and reading 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. Further, the magnetic tape has a disadvantage that both the reading and writing speeds are slow.

As described above, in the current non-volatile recording apparatus, none of the above items (1), (2), (3) and (4) are all satisfied, and a completely new type which satisfies all these items is not available. There has been a demand for the realization of a non-volatile recording device.

Then, the applicant of the present application has described the above (1),
A non-volatile recording device that satisfies all of the items (2), (3) and (4) has been proposed in Japanese Patent Application No. 3-138027. 6 to 8 show a schematic configuration of the nonvolatile storage device. In the figure, a plurality of upper electrodes 41 are arranged at equal intervals in the column direction, and are in contact with the liquid crystal 53 via the alignment film 56. Below the upper electrode 41, a plurality of lower electrodes 42 are arranged in a row direction orthogonal to the upper electrode 41. A memory cell 43 is formed between the upper electrode 41 and the lower electrode 42, more specifically, at the intersection of the two electrodes 41 and 42.

As shown in FIGS. 7 and 8, the memory cell 43 includes the following components disposed and sealed between the silicon substrate 55 and the glass substrate 52. Silicon substrate 5
An opposing electrode 51 is disposed on an opposing surface of a glass substrate 52 opposing the electrode 5, and an alignment film 56 is provided on the surface of the opposing electrode 51.
Is formed.

On the other hand, a field oxide film 57 is formed on the surface of the silicon substrate 55, and the lower electrode 42 is formed thereon. Between the lower electrode 42 and the upper electrode 41, an inter-electrode insulating film 54 made of a silicon nitride film is formed in order to maintain insulation between them. The inter-electrode insulating film 54 has an opening 54 a at the memory cell 54, and the heating element 44 is directly sandwiched between the upper electrode 41 and the lower electrode 42 at that portion. The heating element 44 has a flat plate shape as shown in FIG. An alignment film 56 is formed on the upper electrode 41 and the heating element 44 so as to be in contact with the liquid crystal 53.

In such a configuration, when a voltage is applied between the upper electrode 41 and the lower electrode 42 to generate heat at a portion corresponding to the intersection of the electrodes 41 and 42 of the heating element 44,
The corresponding liquid crystal 53, that is, the memory cell 43 undergoes a phase change, whereby information can be written. To explain a little more, the liquid crystal 53 is made of a liquid crystal compound such as an acrylic polymer nematic liquid crystal having p-cyanobiphenyl as a mesogen group or a polysiloxane polymer smectic liquid crystal, or a compound containing a liquid crystal component in a molecule.

By controlling the voltage and time applied between the upper electrode 41 and the lower electrode 42, the liquid crystal constituting the recording medium is heated to a state change such as a phase transition, for example, to a temperature at which the liquid crystal becomes an isotropic phase. And then the upper electrode 41 and the counter electrode 5
Apply a voltage for writing information during 1 and stop the current supply for heating, and cool down rapidly, or control the current and voltage for heating without applying the voltage for writing, and gradually cool down. As a result, the liquid crystal is in an alignment state and is in a monodomain state.

On the other hand, when the current for heating is stopped and the liquid crystal is rapidly cooled without applying the voltage for writing information, the liquid crystal enters a polydomain state. Thereafter, when cooled to room temperature, the liquid crystal becomes a glassy state, and that state is maintained.

Since the information written as the two states of the mono domain and the poly domain is maintained at room temperature for a long period of time, the written information can be stored as record information. Since liquid crystals having different states have different dielectric constants, recorded information can be electrically read.

The nonvolatile memory device has the following improvements. That is the problem of crosstalk. The details will be described below with reference to FIG. Now, for convenience of explanation, the upper electrodes in the column direction are denoted by U1, U2, U3, U
4, U5, the lower electrode in the row direction is D1, D2, D3, and the memory cell formed at the intersection of the upper electrode and the lower electrode is Mij (i is the number of rows, j is the number of columns, i is i =
1, 2, 3, j = 1, 2, 3, 4, 5). Assuming that a voltage of + V1 is applied to the lower electrode D1, a voltage of -V1 is applied to the upper electrodes U1, U3, and a voltage of + V1 is applied to the upper electrodes U2, U4, U5 to write information, the memory cells M11, M13 Is applied with a voltage of 2V1, while no voltage is applied to the memory cells M12, M14 and M15. Therefore, in this case, the memory cells M11 and M13 generate heat, and the liquid crystal 5 corresponding to the memory cells M11 and M13.
3 causes a phase change, and information is written.

In writing the information, the lower electrode D
No voltage is applied to the lower electrode D2 adjacent to the memory cell M1, for example, the memory cell M adjacent to the heat generating portion.
21, a voltage V1 is applied between the upper electrode U1 and the lower electrode D2. Therefore, at this time, if a material having a proportional relationship between the applied voltage and the calorific value is used, the memory cell M2
1 generates heat with a heating value of の of that of the memory cell M11 to be written, so that there is a problem that heat generation crosstalk occurs and writing accuracy is deteriorated.

Furthermore, the spread of heat may adversely affect the peripheral memory cells due to the crosstalk.
That is, for example, when the memory cell M11 generates heat, this heat propagates through the upper electrode, the lower electrode, and the liquid crystal 53 and spreads to the peripheral portion.
This is because the temperatures of 1, M22 and M12 increase. Such a disadvantage can be solved by increasing the interval between adjacent memory cells. However, in this case, there is a new disadvantage that the pitch of the memory cells is increased and the recording density is reduced.

The present invention solves the above-mentioned drawbacks of the prior art, which can achieve high density and large capacity, can perform writing / reading at high speed, and reduce the size, simplicity, and low cost of peripheral devices. It is an object of the present invention to provide a non-volatile recording device which can be manufactured at a high price, can reliably eliminate crosstalk due to heat generation, and can accurately write and read information.

[0047]

A nonvolatile recording apparatus according to the present invention includes a liquid crystal compound or a recording medium formed of a compound containing a liquid crystal component in molecules interposed between a pair of substrates arranged opposite to each other, and a heating medium. Means for writing information by heating the recording medium by means, and reading the information written on the recording medium by reading means, wherein the heating means is formed entirely on one substrate. A lower electrode wired in a band on the insulating film, and a band-shaped upper electrode laminated on the lower electrode with a heating element interposed therebetween, and a voltage is applied between the upper and lower electrodes to form the heating element. Heat is generated, and an information writing voltage is applied between the upper electrode and a counter electrode disposed on the inner surface side of the other substrate in a direction perpendicular to the upper and lower electrodes to write information on the recording medium. To do It becomes Te, the objects can be achieved.

[0048]

First, the operation of writing and reading information in the nonvolatile recording device having the above configuration will be described. When a voltage is applied between the upper and lower electrodes and a current flows through the heating element, Joule heat is generated in the heating element. By controlling the heating current, voltage and application time, the liquid crystal constituting the recording medium is heated to a state change such as a phase transition, for example, to a temperature at which the liquid crystal becomes an isotropic phase. By applying a voltage for writing information during the period and stopping the supply of current for heating and rapidly cooling, or by applying a voltage for writing information and controlling the current and voltage for heating to cool down The liquid crystal is in an alignment state and is in a mono-domain state.

On the other hand, when the current for heating is stopped and the liquid crystal is rapidly cooled without applying the voltage for writing information, the liquid crystal enters a polydomain state. Thereafter, when cooled to room temperature, the liquid crystal becomes a glassy state, and that state is maintained.

Since the information written as the two states of the mono domain and the poly domain is maintained for a long time at room temperature, the written information can be stored as record information. Since the liquid crystals in these different states have different dielectric constants, the recorded information can be electrically converted by applying an AC voltage between the counter electrode and the upper electrode and measuring the capacitance of the recording medium which is a dielectric. Can be read.

From this state, the temperature of the liquid crystal is raised again by the same procedure until a state change such as phase transition occurs, and then the current and voltage applied to the heating element are controlled to gradually cool or rapidly cool the liquid crystal. If an information writing voltage is applied during cooling, the liquid crystal will be in a monodomain state. Alternatively, if the film is rapidly cooled without applying an information writing voltage, it becomes a polydomain. Thus, the information once written can be rewritten.

As described above, according to the above configuration, it is possible to write / read information on / from the recording medium by static electric control.

In addition, according to the configuration in which the upper electrode and the lower electrode, which are stacked with the heating element interposed therebetween, are arranged in a strip shape, when a voltage is applied between the upper electrode and the lower electrode, the heating element is strip-shaped. Fever. At this time, in the present invention, unlike the conventional example shown in FIGS. 6 to 8, the upper electrode and the lower electrode are disposed in parallel with each other with the heating element interposed therebetween, and are electrically separated from the adjacent electrodes. ing. Therefore, in the structure of the present invention, of the crosstalk in the direction orthogonal to the electrode arrangement direction, crosstalk between adjacent electrodes does not occur.

On the other hand, the crosstalk in the direction parallel to the arrangement direction with the electrodes is not a problem because the heating element sandwiched between the electrodes is heated simultaneously when writing information.

[0055]

Embodiments of the present invention will be described below. FIG. 1 schematically shows the surface configuration of a nonvolatile recording apparatus according to the present invention, in which peripheral circuits are divided into blocks for each function. The input / output signal control unit 31 has a function of processing an input signal from another device and transmitting a signal (write information) to a memory cell, and a process of processing a signal read from the memory cell and transmitting the signal to another device. It has a sending function. The logic control unit 32 controls the signal processing of the entire nonvolatile recording device.
The drive circuit unit 33 controls and drives a current for supplying an electric signal to the memory cell of the recording unit 34 according to a command from the logical system control unit 32. The recording unit 34 is an input / output signal control unit 3
The signal given from 1 is accumulated and stored as record information.

As shown in FIG. 2, the recording section 34 includes a heating element 44 for heating / writing for writing / rewriting of recording information.
And a glass substrate 52 having a wiring for passing a current through the heating element 44 and a glass substrate 52.
The liquid crystal (liquid crystal layer) 53 as a recording medium is sealed between the five.

The opposing electrode 51 is provided on the opposing surface of the glass substrate 52.
Are formed in the column direction (Y1, Y2, Y3...).
On the surface of the counter electrode 51, an alignment film 56 in contact with the liquid crystal 53 is formed. The liquid crystal 53 has a function of recording a signal by the phase transition phenomenon.

The heating element 44 is in the form of a flat plate having an uneven portion, and is directly sandwiched between the upper electrode 41 and the lower electrode 42 in the memory cell section. The upper electrode 41 has a band shape having a predetermined width, and a plurality of the upper electrodes 41 are arranged at substantially equal intervals in the row direction. Below the upper electrode 41, a plurality of lower electrodes 42 are arranged in the same direction.
Is arranged. The lower electrode 42 has a band shape having substantially the same width as the upper electrode 41. However, the width is not limited to the same width, and the width may be different as long as the belt-shaped heat generating portion can be uniformly heated.

The intersection of the upper electrode 41 and the counter electrode 51 corresponds to a memory cell, and a plurality of the electrodes are formed in the direction in which the two electrodes 41 and 42 are arranged. In this embodiment, tungsten having excellent heat resistance was used as a material of the electrodes 41 and 42.

Both the alignment film 56 and the alignment film 56 formed on the surface of the counter electrode 51 are formed by applying polyimide, heating and then rubbing. The alignment film 56 is not limited to polyimide, and another alignment film material may be used. Further, in some cases, if the liquid crystal material and the writing / rewriting conditions are selected, the alignment film can be omitted.

The silicon substrate 55 is a single crystal silicon for a semiconductor generally used for an IC, and is doped with an impurity for controlling a resistance value. When the lower electrode 42 is formed on the silicon substrate 55 as it is, a driving current flowing between the lower electrode 42 and the upper electrode 41 leaks to the silicon substrate 55.
Therefore, in this embodiment, in order to prevent current leakage, the surface of the silicon substrate 55 is covered with the field insulating film 57, and the lower electrode 42 is formed thereon.

In addition, an insulating film 58 is formed between the lower electrodes 42 adjacent in the column direction. The insulating film 58
Are for electrically separating the lower electrodes 42 from each other, but also have the purpose of reducing the influence of heat spread due to heat conduction from the heating element 44. That is, the width is determined in consideration of the spread of heat. The heat generated from the heating element 44 spreads to the memory cells adjacent in the row direction,
A space must be ensured so as not to affect the information written therein, but the width of the insulating film 58 is determined in consideration of the spread of heat. The memory cell is heated by a corresponding portion of the heating element 44 sandwiched between the upper and lower electrodes 41 and 42, and a corresponding portion of the liquid crystal 53 causing a state change such as phase transition and a silicon substrate in which the liquid crystal portion is sealed. It is constituted by components between 55 and the glass substrate 52.

After the insulating film 58 is formed on the field insulating film 57 so as to cover the lower electrode 42, a portion corresponding to the upper surface of the lower electrode 42 is formed with an opening 58a.
The heating element 44 is directly laminated on the lower electrode 42 through 8a, and then the upper electrode 41 is formed thereon.

When writing / erasing recorded information, the heat generated by the heating element 44 causes a temperature rise in both the upper electrode 41 and the lower electrode 42, so that the electrode material is required to have heat resistance. Therefore, in this embodiment, tungsten formed by the low pressure CVD method as described above was used. On the other hand, it is necessary that the heating element 44 be made of a material that has heat resistance and at the same time has an appropriate resistance value and can be finely processed. In this embodiment, high-purity polycrystalline silicon is formed by a low-pressure CVD method.

The electrode material is not limited to tungsten formed by the low pressure CVD method, and any other material having heat resistance and chemical resistance, easy to form and process, and low resistance can be used. Materials may be used. Further, the forming method is not limited to the low pressure CVD method, and any method can be used as long as the film thickness can be made uniform. As the heat resistance 44, polycrystalline silicon formed by a low pressure CVD method was used. However, if it is a material having an appropriate resistance value, heat resistance, chemical resistance and easy to form and process, it is formed with another material. A method may be used.

Next, a description will be given of a schematic manufacturing process of the nonvolatile recording apparatus of the present invention. In this embodiment, the peripheral MOS IC
However, for the sake of simplicity, the process of the MOS IC will not be described here, and only the process of the memory cell will be described.

The silicon substrate 55 is a 6-inch P-type (10
The single crystal silicon wafer of 0) was used. First, an 800 nm field oxide film 57 is formed on a silicon substrate 55 by thermal oxidation. Next, a 1.2 μm-thick tungsten film is formed on the field oxide film 57 by a low pressure CVD method. Then, unnecessary portions of the film are removed by photolithography and dry etching, and the lower electrode 42 is patterned. Next, a silicon nitride film is formed on the field oxide film 57 so as to cover the lower electrode 42 by, for example, a plasma CVD method, and an insulating film 58 is formed.
Next, an opening 58a is formed in a portion of the insulating film 58 corresponding to the upper surface of the lower electrode 42 by photolithography and dry etching.

Then, the resistivity is reduced to about 10 by the low pressure CVD method on the upper surface of the lower electrode 42 and on the field oxide film 57.
A heating element 44 is formed by forming polycrystalline silicon having a thickness of about 1.0 μm and a thickness of about 1.0 μm on the entire surface. When impurities such as boron, phosphorus, and metal are mixed into the film of polycrystalline silicon, the resistance value decreases, and heat may not reach a predetermined temperature. Therefore, it is necessary to pay particular attention to the purity of the material used for the low pressure CVD method and the cleanliness of the apparatus. In this embodiment, the heating element 44 is formed by a low-pressure CVD method using a high-purity monosilane gas as a material for forming polycrystalline silicon. However, if a necessary resistance value can be secured, another silicon compound or another forming method may be used. You may use it.

Then, about 1.0 μm
An unnecessary portion is removed by photolithography and dry etching to form an upper electrode 4.
1 is patterned. Next, after a polyimide material was spin-coated and heated and polymerized, unnecessary portions were removed, and a rubbing treatment was performed to form an alignment film 56.

On the other hand, the glass substrate 52 on the side of the counter electrode 51 is cut into an appropriate size, and thereafter, the surface is made of ITO (Indium Tin Oxid) by sputtering.
e) A transparent conductive film made of a film is laminated, and then unnecessary portions of the ITO film are removed by photolithography and etching. The arrangement pitch of the counter electrode 51 and the thickness of the electrode are:
The conditions were selected so that the optimum conditions for writing and reading information were obtained. After that, a polyimide material is spin-coated on the surface of the counter electrode 51, and after heat polymerization, unnecessary portions are removed and rubbed to form an alignment film 56.

Next, the silicon substrate 55 and the glass substrate 52 manufactured in the above steps are opposed to each other with the respective electrode forming surfaces inside, and the counter electrode 51 is positioned on the memory cell on the silicon substrate 55 side. Align. Then, a portion of the glass substrate 55 corresponding to the periphery of the recording section 34 is sealed. Thereafter, an acrylic polymer nematic liquid crystal having a mesogen group of p-cyanobiphenyl (T
i = 106 ° C., degree of polymerization; 150) is filled between the silicon substrate 55 and the glass substrate 52. Then, the polymer nematic crystal is cooled from the isotropic phase while applying an AC voltage of 100 V and 500 Hz to be in a homeotropic alignment state. Finally, the completed silicon substrate 55 is diced and bonded, and then housed in a package.

It should be noted that the liquid crystal material is not limited to the above, and any other liquid crystal material may be used as long as it causes a state change such as phase transition by heat and can maintain the changed state. Absent.

The nonvolatile recording device of the present invention manufactured as described above uses a state change such as a phase transition due to heat of the liquid crystal 53 as information writing, and uses a change in dielectric constant accompanying the state change as information reading. Use. That is, information is written and read using a structural change of the liquid crystal 53 due to the phase transition (poly domain structure ← → mono domain structure).

Hereinafter, an outline of the information write operation and the information read operation in the nonvolatile recording device of the present invention will be described with reference to FIG. In FIG. 3, U1, U2, and U3 denote strip-shaped upper electrodes 41 arranged in the row direction, and D1, D2, and D
Reference numeral 3 denotes a band-like lower electrode 42 formed below the heating element. Y1, Y2, and Y3 indicate the counter electrodes 51 arranged in the column direction, and Hij (i indicates the number of rows, j indicates the number of columns, and i = 1, 2, 3, j = 1, 2, 3 ) Indicates a heating element 44 and LCij (i = 1, 2, 3, j = 1, 2,.
3) shows the liquid crystal 53 at a position corresponding to the heating element Hij.

Now, assuming that information is to be written to the LC12, in this case, a voltage is applied between the upper electrode U1 and the lower electrode D1 to cause the heating elements H11, H12, H13 to generate heat at the same time. Is made an isotropic phase, and at the same time, a write voltage is applied between the upper electrode U1 and the counter electrode Y2. Subsequently, the supply of voltage between the upper electrode U1 and the lower electrode D1 is stopped, and the heating elements H11, H1
2. Stop the heat generation of H13. Then, the liquid crystal LC1
When the temperature of the liquid crystal LC2 decreases and reaches the liquid crystal phase temperature, the liquid crystal LC12 changes according to the voltage applied between the upper electrode U1 and the counter electrode Y2.
Are oriented, and then reach the temperature of the glass phase, and this state is maintained. That is, the information written in the liquid crystal LC12 is held.

On the other hand, at this time, no writing voltage is applied between the upper electrode U1 and the opposing electrodes Y1, Y3 to the liquid crystals LC11, LC13, so that the liquid crystals LC11, LC13 are in a polydomain state without being oriented. That is, the liquid crystal LC
11. No information is written in the LC13.

Hereinafter, the upper electrode U2 and the lower electrode D
A voltage is sequentially applied between the two and the upper electrode U3 and the lower electrode D3, and information is written to the corresponding liquid crystal. Here, the combination of the upper electrode U1 and the lower electrode D1, the combination of the upper electrode U2 and the lower electrode D2, and the combination of the upper electrode U3 and the lower electrode D3 are independently configured as described above. Therefore, according to the present embodiment, no electrical crosstalk occurs between these adjacent electrodes.

Note that since these arrangement directions, that is, the line directions, are heated simultaneously, no crosstalk occurs in the directions.

For reading information, when an alternating current is applied between the upper electrode 41 and the lower electrode 42, the capacitance of the liquid crystal LCij is read, and thereby the reading operation is performed.

Note that information can be read out by the following method. That is, in the mono-domain structure, the liquid crystal 53 is in a transparent state, whereas in the poly-domain structure, the liquid crystal 53 is in an opaque state due to light scattering.
Therefore, if the memory cell is irradiated with light such as a laser beam and the reflected light from the liquid crystal 53 is detected, information can be read also by this method. Although this method includes an optical detection unit, it includes a signal processing unit and can be said to be an electrical readout method as a whole.

As described above, the nonvolatile recording apparatus of the present invention
Since the single crystal silicon substrate 55 is used as the recording unit 34, a peripheral circuit including an IC for controlling input / output of information can be easily mounted in the same device. Therefore, it is convenient for miniaturization, simplification, and cost reduction of the device configuration. Note that the peripheral circuit is not limited to an IC, and any other circuit or circuit element may be used as long as it can be mounted on the single crystal silicon substrate 55.

[0082]

According to the nonvolatile recording apparatus of the present invention, information can be written to and read from a recording medium by static electric control. Therefore, a rotating mechanism and a moving mechanism required for a magneto-optical disk or a magnetic disk are required. Becomes unnecessary. Therefore, the size, simplicity, and cost of the device configuration can be reduced. In addition, since complicated components such as a laser pickup and a head and a precise structure are not required, the apparatus is not damaged due to vibration, impact, or adhesion of dust. Therefore,
The stability of record retention can be significantly 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. In addition, a fine memory cell can be realized by applying the fine processing technology of the IC. Therefore, a large-capacity, high-density nonvolatile recording device can be realized.

In addition, in the nonvolatile recording apparatus of the present invention, the heating means for heating the recording medium is formed by upper and lower strip-shaped electrodes directly sandwiching the heating element, and is electrically independent of the adjacent electrodes. ing. Therefore, no electric crosstalk occurs between the adjacent electrodes. Further, in the direction parallel to the electrodes, crosstalk does not pose a problem, and the pitch of the memory cells can be reduced. Therefore, there is an advantage that the recording density is improved and information can be recorded with high accuracy.

[Brief description of the drawings]

FIG. 1 is a surface configuration diagram of a nonvolatile recording device of the present invention.

FIG. 2 is a perspective view showing a memory cell of the nonvolatile recording device of the present invention.

FIG. 3 is an equivalent circuit diagram of a memory cell.

FIG. 4 is a structural diagram of an EEPROM.

FIG. 5 is a structural diagram of a magneto-optical disk.

FIG. 6 is a surface configuration diagram of a recording unit of a nonvolatile recording device previously proposed by the present applicant.

FIG. 7 is a cross-sectional view of a memory cell corresponding to line AA in FIG. 6;

FIG. 8 is a perspective view showing a memory cell of a nonvolatile recording device previously proposed by the present applicant.

[Explanation of symbols]

 31 I / O signal control unit 32 Logical system control unit 33 Drive circuit unit 34 Recording unit 41 (U1, U2, U3) Upper electrode 42 (D1, D2, D3) Lower electrode 44 (Hij) Heating element 51 (Y1, Y2, Y3) Counter electrode 52 Glass substrate 53 Liquid crystal 55 Silicon substrate 56 Alignment film 57 Field insulating film 58 Insulating film

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G02F 1/13 102 G02F 1/13 505 G02F 1/1343

Claims (1)

(57) [Claims] A recording medium formed of a liquid crystal compound or a compound containing a liquid crystal component in a molecule is sealed between a pair of substrates disposed opposite to each other, and information is written by heating the recording medium by heating means. A non-volatile recording device configured to read information written to the recording medium by reading means, wherein the heating means is arranged in a strip shape on an insulating film formed over the entire surface of one of the substrates, and a lower electrode; A band-shaped upper electrode laminated on the lower electrode with a heating element interposed therebetween, applying a voltage between upper and lower electrodes to cause the heating element to generate heat, and the upper electrode and the other substrate A non-volatile recording device that writes information on the recording medium by applying an information writing voltage between an inner surface and a counter electrode disposed in a direction orthogonal to the upper and lower electrodes.