JP2815100B2 - 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. 8 shows an example of the structure of a magneto-optical disk. The magneto-optical disk uses magnetic thin films 15 and 16 exhibiting 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. This is because the realization of the non-volatile recording device is required.

The present invention has been made to respond to such a demand, and is a completely new type of non-volatile memory capable of achieving high density, large capacity, and small, simple and low cost peripheral devices. An object of the present invention is to provide a sex recording device.

Another object of the present invention is to provide a highly reliable non-volatile recording device capable of writing information at a high speed, easily and accurately reading information, and reliably preventing thermal crosstalk. It is to provide a device.

[0038]

According to the present invention, there is provided a nonvolatile recording apparatus comprising: an opposing substrate having an opposing electrode; and a heating element side substrate having an upper electrode and a lower electrode sandwiching a heating element. A non-volatile recording device in which a recording medium made of a ferroelectric polymer liquid crystal is enclosed, wherein the upper electrode is
And disposing the lower electrodes in a matrix and
Between the upper electrodes adjacent in the direction and the lower side adjacent in the row direction.
With an insulating film interposed between the electrodes, the upper electrode and the lower electrode
A memory cell is formed at each intersection of the poles, thereby achieving the above object. Preferably, the insulating film is
It is configured to be in contact with the heating element.

[0039]

The ferroelectric polymer liquid crystal having a ferroelectric liquid crystal introduced in the side chain can be obtained by introducing a mesogen group having a chiral structure added to the terminal into the polymer main chain as a side chain. At this time, if an appropriate material is selected for the ferroelectric liquid crystal to be introduced as a side chain and an appropriate spacer is inserted between the side chain and the polymer main chain, the ferroelectric liquid crystal portion of the side chain becomes a low molecular ferroelectric. It exhibits the same behavior as a crystalline liquid crystal and exhibits ferroelectricity.

This ferroelectric liquid crystal is a liquid crystal material which takes a bistable state and is known to have a high-speed response.
Therefore, a ferroelectric polymer liquid crystal obtained by adding such a ferroelectric liquid crystal also has a high-speed response. The above-described characteristics of the ferroelectric polymer liquid crystal are described in “S. Uchida, K.
Morita, K .; Miyoshi, K .; Hashim
oto, K .; Kawasaki, Mol. Cryst.
Liq. Cryst. 1988 , 155, 93T. K
itazume, T .; Ohnogi, K .; Ito, J. et al.
Am. Chem. Soc, 1990 , 112, 6608.
Takashi Sekiya, Kenji Kawasaki, Polymer, 1991 , 40, July issue, 454 Tomoya Kitazume, Functional Materials, 1990 , September issue,
43 ".

The writing and reading of information in a nonvolatile memory device using such a ferroelectric polymer liquid crystal as a recording medium will be described below with reference to FIG. However, FIG. 5 shows a DSC (Di) when a ferroelectric polymer liquid crystal having a biphenyl ferroelectric liquid crystal shown in Chemical Formula 1 as a mesogen group is used.
ferential Scanning Calori
metry = differential thermal analysis) curve (at the time of temperature decrease).

[0042]

Embedded image

As shown in FIG. 5, this ferroelectric polymer liquid crystal becomes a glass phase, a chiral SmI phase (or a chiral SmF phase), a chiral SmC phase, a SmA
Phase transition into five phases, a phase and an isotropic phase. That is, the glass phase is maintained in the low temperature region corresponding to room temperature, and when the temperature is raised from this state, the phase transitions to the chiral SmC phase via the chiral SmI phase.

The following three electrodes are used as means for writing / reading information. An upper electrode and a lower electrode for supplying a voltage to the heating element to control heat generation, and a counter electrode for writing / rewriting and reading information. Here, the heating element is sandwiched between upper and lower electrodes.

The temperature of the ferroelectric polymer liquid crystal is raised by applying a voltage between the upper and lower electrodes, thereby causing the heating element to generate heat. When the ferroelectric polymer liquid crystal becomes a chiral SmC phase, a voltage is applied between the counter electrode and the upper electrode to electrically control the orientation state of the ferroelectric polymer liquid crystal, thereby turning information on / off. That is, data "1" and "0" are written.

When information is written, the application of voltage between the upper and lower electrodes is stopped, the ferroelectric polymer liquid crystal is rapidly cooled, and a phase transition to a glass phase occurs. Since this phase transition state is held for a long time, the write information is held.

On the other hand, when the liquid crystal mixture is heated to an isotropic phase and rapidly cooled without applying an information writing voltage, a polydomain structure is obtained. Further, when an information writing voltage is applied during rapid cooling, a mono-domain structure is obtained. Information can be written by utilizing the difference in dielectric constant between the mono-domain structure and the poly-domain structure. In this case, since the ferroelectric liquid crystal has self-polarization, there is a feature that writing can be performed at a lower voltage than when other polymer liquid crystal is used.

There are the following three methods for reading information. The first is a method of reading a difference in dielectric constant depending on the orientation state. The dielectric constant differs according to each of the different orientations of the ferroelectric liquid crystal. Information can be read by electrically reading the difference. Here, since the ferroelectric liquid crystal has a high dielectric constant, a large value can be read at the time of reading information. In other words, it means that reading with a large S / N ratio is possible, and reading accuracy can be improved.

The second is a method of reading a difference in spontaneous polarization depending on the orientation state of the ferroelectric liquid crystal. Ferroelectric liquid crystals have spontaneous polarization, and the direction of spontaneous polarization changes according to the orientation of the liquid crystal. Due to the spontaneous polarization, a voltage is generated between the electrodes sandwiching the liquid crystal. Since the polarity of the voltage is inverted depending on the orientation, information can be read out by electrically measuring the voltage. Since the spontaneous polarization of the ferroelectric liquid crystal is large, a large value can be read when reading information. In other words, it means that reading with a large S / N ratio is possible, and reading accuracy can be improved.

The third method is a method of reading the difference between the dielectric constants of the mono-domain structure and the poly-domain structure. The dielectric constant of the ferroelectric polymer liquid crystal differs between the polydomain structure and the monodomain structure. By measuring the difference in dielectric constant, information can be electrically read. Readout is also possible by measuring the difference in spontaneous polarization. A ferroelectric liquid crystal has a feature that a large value can be read at the time of reading information because the dielectric constant is high and spontaneous polarization is large. In other words, it means that reading with a large S / N ratio is possible, and reading accuracy can be improved.

FIG. 6 shows the temperature dependence of the response speed of the ferroelectric polymer liquid crystal, and it can be seen that the response time is sharply shortened in the chiral SmC phase. This means that information can be written to the memory cell to be written at a high speed, and thermal crosstalk can be prevented from spreading to surrounding memory cells.

[0052]

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 FIGS. 2 to 4, the recording section 34 includes a heating element 44 for heating / writing of recorded information and a silicon substrate having a wiring for supplying a current to the heating element 44. The semiconductor device has a schematic configuration including a glass substrate 52 having a counter electrode 55 and a counter electrode 51 and disposed opposite to the silicon substrate 55, and a liquid crystal (liquid crystal layer) 53 sealed between the two substrates 55 and 52. The details will be described below.

FIG. 2 shows a surface configuration of the silicon substrate 52 of the recording unit 34 from which the glass substrate 52 and the liquid crystal layer 53 have been removed. In the figure, a plurality of upper electrodes 41 are arranged at substantially equal intervals in the column direction, and as shown in FIG.
Is in contact with the liquid crystal 53. 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. In this embodiment, tungsten having excellent heat resistance was used as a material of the electrodes 41 and 42. Both the upper electrode 41 and the lower electrode 42 use a part of the wiring as a heating electrode for the heating element 44.

FIGS. 3 and 4 show a specific configuration of the memory cell 43. FIG. The memory cell 43 is formed at the intersection of the upper and lower electrodes 41 and 42 as described above, and includes the following components disposed and sealed between the silicon substrate 55 and the glass substrate 52. The configuration will be described below in order.

A counter electrode 51 is provided on a surface of a glass substrate 52 facing a silicon substrate 55. 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 its alignment or phase transition phenomenon.

The silicon substrate 55 is single crystal silicon for a semiconductor generally used for an IC, and is doped with impurities 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.

An inter-electrode insulating film 54 is formed between the lower electrode 42 and the upper electrode 41 in order to maintain insulation between them. In some cases, a voltage of 10 V or more is applied between the lower electrode 42 and the upper electrode 41, so that 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 54.

The inter-electrode insulating film 54 has a structure in which an opening 54 a is formed at the memory cell 43, and the heating element 44 is directly interposed between the upper electrode 41 and the lower electrode 42 at that portion.
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 a low pressure CVD method is used. On the other hand, 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 44.
Formed by the method.

On the upper electrode 41 and the heating element 44, an alignment film 56 in contact with the liquid crystal 53 is formed. The alignment film 56
And an alignment film 56 formed on the surface of the counter electrode 51.
Are formed by applying rubbing treatment after applying and heating polyimide. The alignment film 56 is not limited to polyimide, and another alignment film material may be used. In some cases, if the liquid crystal material and the writing / rewriting conditions are selected, the alignment film 56 can be omitted.

In this embodiment, tungsten formed by a low pressure CVD method is used as an electrode material, that is, a wiring material. However, the present invention is not limited to this, and has heat resistance and chemical resistance. Other materials that are easy and have low resistance 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. The heating element 44 is made of polycrystalline silicon formed by a low pressure CVD method. However, any other material may be used as long as it has an appropriate resistance value, heat resistance, chemical resistance, and is easy to form and process. May be used.

Next, the manufacturing process of the memory cells 43 formed in the recording section 34 in a matrix will be described. In this embodiment, a step of forming the peripheral MOS IC and a step of forming the recording unit 34 are necessary.
Without mentioning the IC process, the memory cell 43
Only the step 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 having a thickness of 1.0 μm is formed on the lower electrode 42 by a plasma CVD method to form an inter-electrode insulating film 54. Next, an opening 54a reaching the lower electrode 42 is formed in the inter-electrode insulating film 54 by photolithography and dry etching.

Next, the specific resistance is reduced to about
A heating element 44 is formed of polycrystalline silicon having a thickness of about 1000 Ω · cm and a thickness of about 1.0 μm. 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 counter electrode side is cut into an appropriate size, and thereafter, the surface thereof is made of ITO (Indium Tin Oxide) by a sputtering method.
A transparent conductive film composed of a film is laminated, and the
Is formed. Next, unnecessary portions of the ITO film are removed by photolithography and etching, and the counter electrode 51 is arranged in the row direction. The arrangement pitch of the counter electrode 51 and the thickness of the electrode were selected so as to be optimal conditions for writing and reading information. After that, a polyimide material is spin-coated on the surface of the counter electrode 51, and after heating and 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 43 on the silicon substrate 55 side. Position. Then, a portion of the glass substrate 55 corresponding to the periphery of the recording section 34 is sealed. Thereafter, a liquid crystal 53 is filled between the two substrates 55 and 52. In this embodiment, as the liquid crystal 53,
Although a ferroelectric polymer liquid crystal having a biphenyl-based ferroelectric liquid crystal as a mesogen group shown in (1) is used, a polymer liquid crystal having another ferroelectric property may be used.

[0068]

Embedded image

Finally, the completed silicon substrate 55 is diced and bonded, and then housed in a package.

Next, the operating principle of writing and reading information to and from the memory cell 43 manufactured as described above will be described with reference to FIG. As shown in FIG. 5, the ferroelectric polymer liquid crystal 53 has a glass phase with increasing temperature.
A phase transition into five phases of a chiral SmI phase (or a chiral SmF phase), a chiral SmC phase, a SmA phase and an isotropic phase.
That is, the glass phase is maintained in the low temperature region corresponding to room temperature, and when the temperature is raised from this state, the phase transitions to the chiral SmC phase via the chiral SmI phase.

The temperature of the ferroelectric polymer liquid crystal 53 is raised by applying a voltage between the upper electrode 41 and the lower electrode 42, thereby causing the heating element 44 to generate heat. More specifically,
Information input from an external device is input / output signal control unit 3
1 is written in the buffer memory after data processing, and is written in the recording unit 34 after the data processing. The writing is performed by the heating element 44 sandwiched between the upper electrode 41 and the lower electrode 42 on the silicon substrate 55
This is performed by applying a voltage to. Since the writing position of the recording unit 34 to the memory cell 43 can be freely selected, random access is possible.

The ferroelectric polymer liquid crystal 53 is made of chiral SmC
In the phase, a writing voltage of, for example, 15 V is applied between the counter electrode 51 and the upper electrode 41 to electrically control the orientation state of the ferroelectric polymer liquid crystal 53, thereby turning on / off information. That is, writing of data “1” and “0” is performed.

When the information is written, the application of the voltage between the upper and lower electrodes 41 and 42 is stopped, and the ferroelectric polymer liquid crystal 53 is rapidly cooled to undergo a phase transition to a glass phase. Since this phase transition state is held for a long time, the write information is held.

On the other hand, when the liquid crystal mixture is heated to an isotropic phase and rapidly cooled without applying an information writing voltage, a polydomain structure is obtained. Further, when an information writing voltage is applied during rapid cooling, a mono-domain structure is obtained. Information can be written by utilizing the difference in dielectric constant between the mono-domain structure and the poly-domain structure. In this case, since the ferroelectric liquid crystal has self-polarization, there is a feature that writing can be performed at a lower voltage than when other polymer liquid crystal is used.

There are the following three methods for reading information. The first is a method of reading a difference in dielectric constant depending on the orientation state. The dielectric constant differs according to each of the different orientations of the ferroelectric liquid crystal. Information can be read by electrically reading the difference. Here, since the ferroelectric liquid crystal has a high dielectric constant, a large value can be read at the time of reading information. In other words, it means that reading with a large S / N ratio is possible, and reading accuracy can be improved.

The second is a method of reading a difference in spontaneous polarization depending on the orientation state of the ferroelectric liquid crystal. Ferroelectric liquid crystals have spontaneous polarization, and the direction of spontaneous polarization changes according to the orientation of the liquid crystal. Due to the spontaneous polarization, a voltage is generated between the electrodes sandwiching the liquid crystal. Since the polarity of the voltage is inverted depending on the orientation, information can be read out by electrically measuring the voltage. Since the spontaneous polarization of the ferroelectric liquid crystal is large, a large value can be read when reading information. In other words, it means that reading with a large S / N ratio is possible, and reading accuracy can be improved.

The third is a method of reading the difference between the dielectric constant of the mono-domain structure and the dielectric constant of the poly-domain structure. The dielectric constant of the ferroelectric polymer liquid crystal differs between the polydomain structure and the monodomain structure. By measuring the difference in dielectric constant, information can be electrically read. Readout is also possible by measuring the difference in spontaneous polarization. A ferroelectric liquid crystal has a feature that a large value can be read at the time of reading information because the dielectric constant is high and spontaneous polarization is large. In other words, it means that reading with a large S / N ratio is possible, and reading accuracy can be improved.

FIG. 6 shows the temperature dependence of the response speed of the ferroelectric polymer liquid crystal 53. It can be seen that the response time in the chiral SmC phase is sharply reduced. This is because writing information when the ferroelectric polymer liquid crystal 53 is heated to the high temperature end of the chiral SmC phase,
This means that the writing operation can be performed at a high speed. When the information writing operation is completed, the temperature of the ferroelectric polymer liquid crystal 53 is lowered.

If such a write operation is performed, the memory cell 4 to be written can be written at the time of writing.
3, the amount of heat transfer to the surrounding memory cells 43 not to be written can be remarkably reduced, so that an adverse thermal effect, that is, thermal crosstalk can be reliably prevented, and the information can be written with high accuracy. is there.

The ferroelectric polymer liquid crystal 53 is not limited to the above, but may be, for example, a fluorine-based ferroelectric polymer liquid crystal shown in Chemical Formula 3.

[0081]

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In the above embodiment, the writing operation was performed by raising the temperature of the ferroelectric polymer liquid crystal 53 to the high temperature end of the chiral SmC phase. However, the temperature was raised to the isothermal phase shown in FIG. It is also possible to write information depending on the voltage application state at the time.

As described above, the nonvolatile recording device 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.

[0084]

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 particular, the nonvolatile memory device of the present invention
Upper and lower electrodes sandwiching the body in a matrix
Arranged and between upper electrodes adjacent in the column direction and where
An insulating film is interposed between lower electrodes that are
Structure that forms a memory cell at each intersection of a pole and a lower electrode
Therefore, each of the upper electrode and the lower electrode is
Can electrically insulate each other and generate heat from each memory cell
Since heat diffusion to the outside of the cell of the body can be suppressed,
Leaks between memory cells can be reliably prevented
You. Furthermore, if the insulating film is configured to be in contact with the heating element,
Further enhances the heat diffusion of the heating element of the memory cell to the outside of the cell
Can be suppressed. In addition, the nonvolatile memory device of the present invention uses a ferroelectric polymer liquid crystal as a recording medium. There are advantages that the occurrence of talk can be reliably prevented, and that information can be read easily and with high accuracy.

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

[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 surface configuration diagram of a recording unit.

FIG. 3 is a sectional view of a memory cell corresponding to line AA in FIG. 2;

FIG. 4 is a perspective view of a memory cell.

FIG. 5 is a graph showing a DSC curve in the case of using a biphenyl-based ferroelectric liquid crystal as a mesogen-based ferroelectric polymer liquid crystal, with the ordinate representing heat generation and the abscissa representing temperature.

FIG. 6 is a graph showing the temperature dependence of the response speed of a ferroelectric polymer liquid crystal, with the response time on the vertical axis and the temperature on the horizontal axis.

FIG. 7 is a structural diagram of an EEPROM.

FIG. 8 is a structural diagram of a magneto-optical disk.

[Explanation of symbols]

 Reference Signs List 31 input / output signal control unit 32 logic system control unit 33 drive circuit unit 34 recording unit 41 upper electrode 42 lower electrode 43 memory cell 44 heating element 51 counter electrode 52 glass substrate 53 liquid crystal (ferroelectric polymer liquid crystal) 54 interelectrode insulation Film 55 silicon substrate 56 alignment film 57 field oxide film

Claims (2)

(57) [Claims] 1. An opposing substrate having an opposing electrode and a heating element side substrate having an upper electrode and a lower electrode sandwiching a heating element are bonded to each other, and a ferroelectric polymer liquid crystal is formed between the two substrates.
The composed recording medium comprising a non-volatile recording device encapsulating and disposing said upper electrode and said lower electrode in a matrix
Both are adjacent between the upper electrodes adjacent in the column direction and adjacent in the row direction.
An insulating film is interposed between the matching lower electrodes, and
And a memory cell at each intersection of the lower electrode . (2) A configuration in which the insulating film is in contact with the heating element;
The nonvolatile recording device according to claim 1.