JP2008147632A - Method for forming organic ferroelectric film, method for manufacturing memory element, memory device and electronic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for forming organic ferroelectric film, a method for manufacturing a memory element, a memory device and an electronic apparatus. <P>SOLUTION: The method comprises a first step of applying a liquid material, containing an organic ferroelectric material on a face of a substrate 2, drying it and forming a low crystallization degree film 4B, configured with an organic ferroelectric material as a principal material, with a crystallization degree lower than that of an organic ferroelectric film 4, and a second step of forming the organic ferroelectric film 4, while forming the low crystallization degree film 4B and increasing its crystallinity by heating and pressing the low crystallization degree film 4B. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for forming an organic ferroelectric film, a method for manufacturing a memory element, a memory device, and an electronic apparatus.

As a memory element, there is known a memory element in which a polarization state is changed by applying an electric field in a thickness direction to a ferroelectric film made of a ferroelectric material to write / read data. . Such a memory element can be used as a nonvolatile memory because the polarization state in the ferroelectric film is bistable and is retained even after the application of the electric field is stopped.
In recent years, it has been proposed to use an organic ferroelectric material as a ferroelectric material for the purpose of making the memory element flexible. As such an organic ferroelectric material, an organic ferroelectric material having crystallinity as disclosed in Non-Patent Document 1 is used for the purpose of improving memory characteristics.

When forming a ferroelectric film using such an organic ferroelectric material, a liquid containing an organic ferroelectric material is used rather than a vapor phase thin film forming process such as a vapor deposition method in which it is not easy to control crystallinity. A combination of a liquid phase thin film forming process such as a spin coating method and a crystallization process is more suitable in terms of freedom of material selection and process cost.
For example, conventionally, after applying such a liquid on the lower electrode and drying and crystallizing it to form a ferroelectric film, the upper electrode is formed on the ferroelectric film using a vapor deposition method. To do. Forming a ferroelectric film using such a liquid can be performed under conditions close to room temperature and normal pressure without using a large vacuum apparatus as in the vapor phase thin film formation process. This leads to energy saving and cost reduction during device manufacturing.

  However, conventionally, since the liquid applied on the lower electrode is dried and crystallized in a state where the liquid is exposed, along with the crystallization of the organic ferroelectric, on the surface opposite to the lower electrode of the ferroelectric film, Unevenness due to coarse crystal particles is formed. Therefore, in the conventional method for manufacturing a memory element, when the thickness of the ferroelectric film becomes as thin as the size of the crystal particles, the concave and convex portions of the ferroelectric film are formed when the upper electrode is formed. The electrode material may get into the electrode, and the distance between the upper electrode and the lower electrode will be locally reduced and close to or in contact with each other, leading to an increase in leakage current and a short circuit between the upper electrode and the lower electrode. is there. Since the roughness of the unevenness of the ferroelectric film as described above does not change greatly even if the thickness of the ferroelectric film changes, the adverse effect becomes more pronounced as the thickness of the ferroelectric film becomes thinner. .

  Organic ferroelectrics typified by copolymers of vinylidene fluoride and trifluoroethylene or vinylidene fluoride polymers generally have a very high coercive electric field. It is necessary to make the body thin film very thin. However, for the reasons described above, it has been very difficult to drive the memory element at a low voltage by making the ferroelectric film very thin.

J.Appl.Phys., Vol.89, No.5, pp.2613-16

  The objective of this invention is providing the formation method of an organic ferroelectric film, the manufacturing method of a memory element, a memory | storage device, and an electronic device.

Such an object is achieved by the present invention described below.
One method of forming an organic ferroelectric film according to the present invention is a method of forming an organic ferroelectric film composed mainly of an organic ferroelectric material having crystallinity, on one surface of a substrate. A first step of forming a low crystallinity film having a crystallinity lower than the crystallinity of the organic ferroelectric film;
Forming the organic ferroelectric film from the low crystallinity film, and the first process includes a liquid material containing the organic ferroelectric material on one surface of the substrate. And the second step includes crystallization in the low crystallinity film while shaping the low crystallinity film by heating and pressurizing the low crystallinity film. Including a step of increasing the degree.
In the present invention, the crystallinity in the low crystallinity film is preferably 80% or less of the crystallinity of the organic ferroelectric film.

  As a result, the crystallization of the organic ferroelectric material proceeds while the surface of the low crystallinity film on the side opposite to the substrate is kept smooth by the mold. Therefore, it is possible to prevent crystal grains of the organic ferroelectric material from growing freely and roughing the surface. Therefore, the surface of the obtained organic ferroelectric film opposite to the substrate is smoothed, and it is possible to prevent the film thickness of the organic ferroelectric film from being locally reduced.

Another method for forming an organic ferroelectric film according to the present invention is a method for producing an organic ferroelectric film composed mainly of an organic ferroelectric material having crystallinity. A first step of forming a low crystallinity film having a crystallinity lower than the crystallinity of the organic ferroelectric film on the surface; and forming the organic ferroelectric film from the low crystallinity film And the second step includes applying and drying a liquid material containing the organic ferroelectric material on one surface of the substrate, and the second step includes: A third step of heating the low crystallinity film to form a crystal film in which the crystallinity of the low crystallinity film is increased, and shaping the crystal film by heating and pressurizing the crystal film And a fourth step of forming the organic ferroelectric film.
As a result, even if irregularities made of crystal grains of the organic ferroelectric material are formed on the surface opposite to the substrate of the crystal film by crystallization, the surface opposite to the substrate of the organic ferroelectric film is formed. Can be smooth. Therefore, it is possible to prevent the organic ferroelectric film from being locally reduced in film thickness.

In the method for forming an organic ferroelectric film of the present invention, in the second step, the pressurizing pressure is preferably 0.1 to 10 MPa / cm ² .
Thereby, the surface on the opposite side to the board | substrate of the organic ferroelectric film obtained can be made into a very smooth surface.
In the method for forming an organic ferroelectric film of the present invention, the thickness of the organic ferroelectric film is preferably 5 nm to 500 nm.
Thereby, it is possible to more reliably prevent the organic ferroelectric film from being locally reduced in thickness while reducing the thickness of the obtained organic ferroelectric film.

In the method for forming an organic ferroelectric film of the present invention, the organic ferroelectric material may be one or two of a copolymer of vinylidene fluoride and trifluoroethylene and a polymer of vinylidene fluoride. It is preferable that these are combined.
Such an organic ferroelectric material has a very high coercive electric field. Therefore, for example, when an organic ferroelectric film having such an organic ferroelectric material as a constituent material is used for a memory element, it is necessary to make the organic ferroelectric film extremely thin in order to reduce the driving voltage. Therefore, the effect obtained by applying the present invention becomes remarkable.

In the method for forming an organic ferroelectric film of the present invention, the liquid material containing the organic ferroelectric material is preferably a solution obtained by dissolving the organic ferroelectric material in a solvent.
Thereby, it is possible to more reliably prevent the organic ferroelectric film from being locally reduced in thickness while reducing the thickness of the obtained organic ferroelectric film.
In the method for forming an organic ferroelectric film of the present invention, in the second step, the heating temperature for increasing the crystallinity is preferably 80 to 200 ° C.
Thereby, the organic ferroelectric material in the low crystallinity film can be efficiently crystallized.

In the method for forming an organic ferroelectric film of the present invention, in the second step, it is preferable to perform cooling while maintaining the pressurized state after increasing the crystallinity.
As a result, the surface of the organic ferroelectric film opposite to the substrate can be more reliably smoothed.
In the method for forming an organic ferroelectric film of the present invention, it is preferable that the cooling is performed below the glass transition point of the organic ferroelectric material.
Thereby, crystallization can be performed more reliably.

The method for forming an organic ferroelectric film of the present invention preferably includes a step of heating and softening the low crystallinity film after the first step and before the second step. .
As a result, the surface of the organic ferroelectric film opposite to the substrate can be more reliably smoothed.
In the method for forming an organic ferroelectric film of the present invention, in the second step, the shaping is performed by pressing a mold capable of defining an effective area of the organic ferroelectric film toward the substrate. preferable.
Thereby, the shape of the organic ferroelectric film can be made desired.

In the method for forming an organic ferroelectric film of the present invention, it is preferable that the pressing surface of the mold is subjected to a release treatment.
This makes it easy to remove the mold, prevents the organic ferroelectric material from sticking to the mold, and improves the smoothness of the surface of the organic ferroelectric film opposite to the substrate. it can.

In the method of forming an organic ferroelectric film of the present invention, a first electrode is formed on the substrate before the first step, and in the first step, the substrate of the first electrode Forming the low crystallinity film on the opposite surface, and in the second step, the crystallization is performed while applying an electric field between the mold and the first electrode during the pressing. It is preferable to carry out.
Thereby, the crystal orientation of the organic ferroelectric material in the obtained organic ferroelectric film can be made uniform. Therefore, in the obtained memory element, the loss of polarization due to the fluctuation of the orientation of the polarization axis of the organic ferroelectric material can be reduced. That is, the polarization axis direction of the organic ferroelectric material in the obtained organic ferroelectric film can be aligned with the thickness direction of the organic ferroelectric film (the direction in which the electric field is applied) as much as possible. Thus, the response of polarization inversion can be improved and the squareness in the hysteresis curve can be improved.

  One method of manufacturing a memory element according to the present invention is a method of manufacturing a memory element using an organic ferroelectric film composed mainly of an organic ferroelectric material having crystallinity, which is one side of a substrate. A step of forming a first electrode; and a low crystallinity of a crystallinity lower than the crystallinity of the organic ferroelectric film on the surface of the first electrode opposite to the substrate A first step of forming a film; a second step of forming the organic ferroelectric film from the low crystallinity film; and a surface of the organic ferroelectric film opposite to the first electrode Forming a second electrode on the substrate, wherein the first step includes a step of applying and drying a liquid material containing the organic ferroelectric material on one surface of the substrate, The second step is to heat and pressurize the low crystallinity film while shaping the low crystallinity film. Comprising the step of increasing the degree of crystallinity in crystallinity film, characterized in that.

As a result, it is possible to form a capacitor formed by forming on the substrate a structure in which the organic ferroelectric film is sandwiched between the first electrode and the second electrode. In this case, since the surface of the organic ferroelectric film opposite to the substrate is smoothed, it is possible to prevent the distance between the first electrode and the second electrode from being locally reduced. . As a result, even if the organic ferroelectric film is thinned, the obtained memory element can prevent an increase in leakage current and a short circuit between the first electrode and the second electrode. That is, the organic ferroelectric film can be thinned to reduce the driving voltage.
Further, in the present invention, less energy is required than in the vapor phase thin film forming process using a large vacuum apparatus, and the memory element can be formed by a simple process under relatively low temperature conditions. Therefore, the cost of the manufacturing apparatus can be reduced, and the range of selection of the memory element and further the material constituting the memory device is expanded.

  The method for manufacturing a memory element according to the present invention further includes a step of forming a semiconductor film after the step of forming the first electrode and before the first step, and forming the first electrode. The first electrode formed in the step of forming is a pair of electrodes spaced apart from each other, and in the step of forming the semiconductor film, the semiconductor electrode is in contact with each of the pair of electrodes. It is preferable that the low crystallinity film formed in the first step is formed on a surface of the semiconductor film opposite to the substrate.

Accordingly, a memory element that can be used for a so-called 1T (transistor) type memory device can be obtained. In this case, since the surface of the organic ferroelectric film opposite to the substrate is smoothed, it is possible to prevent the distance between the semiconductor film and the second electrode from being locally reduced. As a result, even if the organic ferroelectric film is thinned, the obtained memory element can prevent an increase in leakage current and a short circuit between the semiconductor film and the second electrode. That is, the organic ferroelectric film can be thinned to reduce the driving voltage.
Further, in the present invention, less energy is required than in the vapor phase thin film forming process using a large vacuum apparatus, and the memory element can be formed by a simple process under relatively low temperature conditions. Therefore, the cost of the manufacturing apparatus can be reduced, and the range of selection of the memory element and further the material constituting the memory device is expanded.

A memory device according to the present invention includes a memory element manufactured by the method for manufacturing a memory element of the present invention.
Accordingly, it is possible to provide a memory device that can reduce the driving voltage even when an organic ferroelectric material having crystallinity is used as a constituent material of the organic ferroelectric film. Further, such a storage device has excellent reliability by reducing leakage current and preventing short circuit.

An electronic apparatus according to the present invention includes the storage device of the present invention.
As a result, it is possible to provide an electronic device capable of reducing the driving voltage even when an organic ferroelectric material having crystallinity is used as a constituent material of the organic ferroelectric film. Moreover, such an electronic device has excellent reliability by reducing leakage current and preventing short circuit.

Hereinafter, preferred embodiments of a method for manufacturing a memory element, a memory device, and an electronic device according to the present invention will be described.
<First Embodiment>
A first embodiment of the present invention will be described.
<Storage element>
First, an embodiment of a memory element manufactured using the method for manufacturing a memory element of the present invention will be described with reference to FIG.

FIG. 1 is a longitudinal sectional view showing a memory element according to the first embodiment of the present invention. Hereinafter, for convenience of explanation, “upper” in FIG. 2 is referred to as “upper”, and “lower” is referred to as “lower”.
A memory element 1 shown in FIG. 1 is used by being incorporated in various electronic devices such as a memory device, for example, and includes a substrate 2, a lower electrode (first electrode) 3, an organic ferroelectric film 4, and an upper electrode. (Second electrode) 5 is formed by being laminated in this order. In other words, in the memory element 1, a structure in which an organic ferroelectric film (recording film) 4 is interposed between the lower electrode 3 and the upper electrode 5 is supported by the substrate 2 on the lower electrode 3 side. ing.
In such a memory element 1, data is written and read by applying a voltage (electric field) between the lower electrode 3 and the upper electrode 5, and even after the application of the electric field is stopped, polarization is performed. State is maintained. Using such characteristics, the memory element 1 can be used in a memory device.

Examples of the substrate 2 include a glass substrate, polyimide, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polymethyl methacrylate (PMMA), polycarbonate (PC), polyethersulfone (PES), and aromatic polyester (liquid crystal polymer). Or the like, a plastic substrate (resin substrate), a quartz substrate, a silicon substrate, a gallium arsenide substrate, or the like can be used. When the memory element 1 is given flexibility, a resin substrate is selected as the substrate 2.
A base film may be provided on the substrate 2. The base film is provided, for example, for the purpose of preventing the diffusion of ions from the surface of the substrate 2 or for improving the adhesion (bonding) between the lower electrode 3 and the substrate 2.
Moreover, the board | substrate 2 can be abbreviate | omitted depending on a use etc.

The constituent material of the base film is not particularly limited, but silicon oxide (SiO ₂ ), silicon nitride (SiN), polyimide, polyamide, or a crosslinked and insoluble polymer is preferably used.
The thickness of the substrate 2 is not particularly limited, but is preferably 10 to 2000 μm.

A lower electrode 3 is formed on the upper surface of the substrate 2 (one surface of the substrate 2).
The constituent material of the lower electrode 3 is not particularly limited as long as it has conductivity. For example, Pd, Pt, Au, W, Ta, Mo, Al, Cr, Ti, Cu or an alloy containing these Conductive materials such as ITO, FTO, ATO, SnO ₂ , carbon-based materials such as carbon black, carbon nanotubes, fullerene, polyacetylene, polypyrrole, polythiophene such as PEDOT (poly-ethylenedioxythiophene), polyaniline, Examples thereof include conductive polymer materials such as poly (p-phenylene), polyfluorene, polycarbazole, polysilane, and derivatives thereof, and one or more of them can be used in combination. The conductive polymer material is usually used in a state of being doped with a polymer such as iron oxide, iodine, inorganic acid, organic acid, polystyrene sulphonic acid and imparted with conductivity. Among these, as the constituent material of the lower electrode 3, materials mainly composed of Al, Au, Cr, Ni, Cu, Pt or alloys containing these are preferably used. When these metal materials are used, the lower electrode 3 can be formed easily and inexpensively using an electrolytic or electroless plating method. In addition, the characteristics of the memory element 1 can be improved.
The thickness of the lower electrode 3 is not particularly limited, but is preferably about 10 to 1000 nm, and more preferably about 50 to 500 nm.

An organic ferroelectric film 4 is formed on the upper surface of the lower electrode 3 (the surface opposite to the substrate 2 of the lower electrode 3).
The organic ferroelectric film 4 is composed mainly of an organic ferroelectric material having crystallinity.
As the organic ferroelectric material, for example, P (VDF / TrFE) (a copolymer of vinylidene fluoride and trifluoroethylene), PVDF (a polymer of vinylidene fluoride), and the like can be preferably used. Such an organic ferroelectric material has a very high coercive electric field. Therefore, for example, when the organic ferroelectric film 4 having such an organic ferroelectric material as a constituent material is used for the memory element 1, it is necessary to make the organic ferroelectric film 4 extremely thin in order to reduce the driving voltage. is there. Therefore, the effect obtained by applying the present invention becomes remarkable.

  The thickness of the organic ferroelectric film 4 is not particularly limited, but is preferably about 5 nm to 500 nm, and more preferably about 10 nm to 200 nm. Thereby, various drive characteristics of the memory element 1 (and thus various electronic devices such as a memory device element) can be suitably exhibited. Further, surface irregularities due to crystal grains of the organic ferroelectric film 4 that cause a leakage current and a short circuit in the organic ferroelectric film 4 are suppressed, and as a result, the memory element 1 can be driven at a low voltage. Can do.

An upper electrode 5 is formed on the upper surface of the organic ferroelectric film 4 (the surface opposite to the lower electrode 3 of the organic ferroelectric film 4).
As the constituent material of the upper electrode 5, the same constituent material as that of the lower electrode 3 described above can be used.
The thickness of the upper electrode 5 is not particularly limited, but is preferably about 10 nm to 1000 nm, and more preferably about 50 nm to 500 nm.

<Method for Manufacturing Memory Element>
Next, the method for manufacturing the memory element 1 will be described as an example of the method for manufacturing the memory element of the present invention.
(First example)
First, the 1st example of the manufacturing method of the memory element 1 is demonstrated based on FIG.

  The manufacturing method of the memory element 1 includes: [1] a step of forming the lower electrode 3; [2] a liquid material containing an organic ferroelectric material is applied on the lower electrode 3; A step of forming a crystallinity film (first step), [3] a step of forming an organic ferroelectric film by heating and pressurizing the low crystallinity film (second step), [ 4) forming an upper electrode on the organic ferroelectric film.

Hereafter, each process is demonstrated in detail sequentially.
[1] Step of Forming Lower Electrode 3 First, as shown in FIG. 2A, for example, a substrate 2 such as a semiconductor substrate, a glass substrate, a resin substrate, etc. is prepared, ), The lower electrode 3 is formed.
In particular, by using a resin substrate as the substrate 2, the obtained memory element 1 and further the memory device can be made flexible.

  The method of forming the lower electrode 3 is not particularly limited, and for example, a physical vapor deposition method (PVD method) such as a vacuum evaporation method, a sputtering method (low temperature sputtering), an ion plating method, a plasma CVD method, a heat Chemical vapor deposition methods (CVD methods) such as CVD methods and laser CVD methods, wet plating methods such as electrolytic plating, immersion plating, electroless plating, spin coating methods, solution atomization deposition methods (LSMCD methods), etc. It can be formed by various printing methods such as a coating method, a screen printing method, and an ink jet method.

[2] Step of forming a low crystallinity film (first step)
Next, as shown in FIG. 2C, a liquid material 4A containing a crystalline organic ferroelectric material is applied on the lower electrode 3 (forms a film-like liquid material 4A) and dried. Then, as shown in FIG. 2D, a low crystallinity film (including an amorphous film) 4B which is an intermediate product film for forming the organic ferroelectric film 4 is formed.

  The low crystallinity film 4B has a crystallinity lower than the final crystallinity of the organic ferroelectric material in the organic ferroelectric film 4, and is composed mainly of the organic ferroelectric material. is there. The crystallinity of the organic ferroelectric material in the low crystallinity film 4B is 0.001 when the final crystallinity of the organic ferroelectric material in the organic ferroelectric film 4 is 100%. It is preferably ˜80% or less, and more preferably 50% or less.

As the liquid material 4A, a material in which a crystalline organic ferroelectric material is dissolved in a solvent or dispersed in a dispersion medium can be used.
In particular, the liquid material 4A is preferably obtained by dissolving the organic ferroelectric material in a solvent. As a result, the liquid material 4A can be easily applied to the substrate 2 and the film thickness of the low crystallinity film 4B can be made relatively simple. As a result, it is possible to more reliably prevent the organic ferroelectric film 4 from being locally reduced in thickness while reducing the thickness of the obtained organic ferroelectric film 4.

As the organic ferroelectric material in the liquid material 4A, the constituent material of the organic ferroelectric film 4 described above can be used. In particular, as the organic ferroelectric material, it is preferable to use one of vinylidene fluoride / trifluoroethylene copolymer and vinylidene fluoride polymer alone or in combination. In order to obtain ferroelectricity very easily, a copolymer of vinylidene fluoride and trifluoroethylene is more preferable.
The liquid material 4A may contain other substances in addition to the organic ferroelectric material, the solvent, or the dispersion medium.

  The solvent or dispersion medium in the liquid material 4A is not particularly limited as long as it can dissolve or disperse the organic ferroelectric material. For example, nitric acid, sulfuric acid, ammonia, hydrogen peroxide, water, Inorganic solvents such as carbon disulfide, carbon tetrachloride, ethylene carbonate, methyl ethyl ketone (MEK), acetone, diethyl ketone, methyl isobutyl ketone (MIBK), methyl isopropyl ketone (MIPrK), methyl isopentyl ketone (MIPEK), acetylacetone, Ketone solvents such as cyclohexanone, diethyl carbonate (DEC), methanol, ethanol, isopropanol, ethylene glycol, diethylene glycol (DEG), alcohol solvents such as glycerin, diethyl ether, diisopropyl ether, 1,2- Ether solvents such as methoxyethane (DME), 1,4-dioxane, tetrahydrofuran (THF), tetrahydropyran (THP), anisole, diethylene glycol dimethyl ether (diglyme), diethylene glycol ethyl ether (carbitol), methyl cellosolve, ethyl cellosolve, Cellosolve solvents such as phenyl cellosolve, aliphatic hydrocarbon solvents such as hexane, pentane, heptane, cyclohexane, aromatic hydrocarbon solvents such as toluene, xylene, benzene, pyridine, pyrazine, furan, pyrrole, thiophene, methylpyrrolidone Aromatic heterocyclic compound solvents such as N, N-dimethylformamide (DMF), amide solvents such as N, N-dimethylacetamide (DMA), dichloromethane, chloroform, -Halogen compound solvents such as dichloroethane, ester solvents such as ethyl acetate, methyl acetate, ethyl formate, sulfur compound solvents such as dimethyl sulfoxide (DMSO), sulfolane, nitrile solvents such as acetonitrile, propionitrile, acrylonitrile, Various organic solvents such as organic acid solvents such as formic acid, acetic acid, trichloroacetic acid and trifluoroacetic acid, or a mixed solvent containing them can be used.

  In particular, when P (VDF / TrFE) is used as the organic ferroelectric material, MEK (methyl ethyl ketone: 2-butanone), MIPrK (methyl isopropyl ketone: 3-methyl-2-butanone), 2-pentanone, 3-pentanone, MIBK (methyl isobutyl ketone: 4-methyl-2-pentanone), 2-hexanone, 2,4-dimethyl-3-pentanone, 4-heptanone, MIpeK (methyl isopentyl ketone: 5-methyl-2- It is preferable to use various organic solvents such as hexanone), 2-heptanone, 3-heptanone, cyclohexanone, or DEC (diethyl carbonate), or a mixed solvent thereof.

The content of the organic ferroelectric material in the liquid material 4A to be applied is preferably 0.1 to 8.0% by weight, and more preferably 0.2 to 4.0% by weight. As a result, the liquid material 4A can be easily applied to the substrate 2 and the film thickness of the low crystallinity film 4B can be made relatively simple.
The method for applying the liquid material 4A is not particularly limited, and for example, a spin coating method, a solution atomization deposition method (LSMCD method), an ink jet method, or the like can be suitably used.

The method for drying the liquid material 4A, that is, the method for removing the solvent or the dispersion from the liquid material 4A is not particularly limited. For example, an external heat drying method using a hot plate or an oven, an internal heat drying method using a microwave, etc. A hot air conveying method, a radiant heat transfer drying method using infrared rays, a vacuum decompression method, or the like can be used.
If the solvent or dispersion of the liquid material 4A is highly volatile and there is almost no residual solvent or residual dispersion in the coated film, the drying step may be omitted.

When heat treatment is used as a drying method for the liquid material 4A, the treatment temperature is not more than the optimum crystallization temperature of the organic ferroelectric material. Specifically, the organic ferroelectric material to be used, the type of solvent, the liquid material 4A Depending on the film thickness, etc., it is preferably room temperature to 140 ° C., more preferably room temperature to 100 ° C.
In this case, the treatment time is preferably 0.5 to 120 minutes, more preferably 1 to 30 minutes, depending on the organic ferroelectric material used and the film thickness of the liquid material 4A. .

  Further, when the liquid material 4A is applied to form a low crystal film, the application process may be repeated a plurality of times. As a result, small pinhole defects formed in the process of solvent evaporation are filled with liquid material, reducing pinhole defects in the low crystal film, resulting in the formation of a ferroelectric film with less leakage current and short circuit. it can. Furthermore, a low crystal film with few pinhole defects can be formed by alternately repeating the coating step and the drying step.

[3] Step of Forming Organic Ferroelectric Film 4 Next, by heating and pressurizing the low crystallinity film 4B, the crystallinity of the low crystallinity film 4B while shaping the low crystallinity film 4B. Is increased to obtain the organic ferroelectric film 4. Specifically, as shown in FIG. 2E, crystallization is performed by heating the low crystallinity film 4B while pressing the mold 6 against the substrate 2 through the low crystallinity film 4B. After performing, as shown in FIG.2 (f), the type | mold 6 is removed and the organic ferroelectric film 4 is formed.

The pressure when pressing the mold 6 against the substrate 2 is preferably 0.1 to 10 MPa / cm ² . Thereby, the surface of the obtained organic ferroelectric film 4 opposite to the substrate can be made extremely smooth.
It does not specifically limit as a method of pressing the type | mold 6, Various press machines can be used.
The low crystallinity film 4B promotes crystallinity by heating. A method for promoting crystallinity (a method for increasing the degree of crystallinity) is not particularly limited. For example, a crystallinity promoting method using a hot plate, an oven, a vacuum oven, etc., a crystal using internal heating by a microwave, etc. The crystallinity promoting method, the crystallinity promoting method by radiant heat transfer by infrared rays, etc. can be used. In particular, a crystallinity-promoting heat treatment step using a hot plate, oven, vacuum oven, or the like can be suitably used. When promoting the crystallinity of the low crystallinity film 4B, it is relatively easy to promote the crystallinity while pressing with the mold 6 by applying heat treatment to the low crystallinity film 4B in an appropriate temperature range. In a short time, the crystallinity of the organic ferroelectric material in the low crystallinity film 4B can be efficiently promoted while preventing unintentional crystal structure change of the organic ferroelectric material.

  When heat treatment is used as a method for promoting crystallinity of the low crystallinity film 4B, the treatment temperature is higher than the crystallization temperature of the organic ferroelectric material and lower than the melting point. Specifically, the organic ferroelectric used Although it depends on the material, in the case of P (VDF / TrFE) (VDF / TrFE = 75/25), the heating temperature is preferably 80 to 200 ° C, more preferably 100 to 150 ° C. Thereby, the organic ferroelectric material in the low crystallinity film 4B can be efficiently crystallized. In addition, when the processing temperature is in the temperature range as described above and is equal to or higher than the Curie temperature of the organic ferroelectric material, the crystallinity of the organic ferroelectric material in the low crystallinity film 4B can be easily and efficiently improved. Can be promoted.

Here, the “treatment temperature” is the temperature of the low crystallinity film 4B. In this heat treatment, for example, an oven or a hot plate is used so that the low crystallinity film 4B is in the temperature range as described above. Operate.
Further, the treatment time in the crystallization treatment is preferably 0.5 to 120 minutes, and preferably 1 to 30 minutes, although it depends on the organic ferroelectric material used and the film thickness of the liquid material 4A. Is more preferable.

Further, it is preferable to cool the low crystallinity film 4B after heating it to increase the crystallinity. As a result, the surface of the organic ferroelectric film 4 opposite to the substrate 2 can be more reliably smoothed. This cooling is more preferably performed after increasing the crystallinity and before removing the mold 6. That is, it is preferable to perform the cooling while pressing the mold 6 and then remove the mold 6. Thereby, the surface of the organic ferroelectric film 4 on the side opposite to the substrate 2 can be smoothed (shaped) more reliably.
The cooling temperature is preferably 0 to 100 ° C., more preferably below the glass transition point of the organic ferroelectric material, and preferably below normal temperature (room temperature). Thereby, promotion of crystallization can be performed more reliably. Further, this cooling is performed at a cooling rate such that the organic ferroelectric material is in a desired crystal state.

The method of cooling the organic ferroelectric material is not particularly limited, and examples thereof include natural cooling, a method of cooling the substrate and the mold with a Peltier element, and a method of providing a jacket on the mold and circulating a refrigerant. .
Moreover, it is preferable to heat and soften the low crystallinity film 4B before pressing (shaping) with the mold 6. As a result, the surface of the organic ferroelectric film 4 opposite to the substrate 2 can be more reliably smoothed.

The material of the mold 6 is not particularly limited, but for example, a metal material is preferably used.
Moreover, it is preferable that the surface (pressing surface) of the mold 6 is subjected to a mold release treatment. As a result, the mold 6 can be easily removed and the organic ferroelectric material can be prevented from sticking to the mold 6, and the smoothness of the surface of the organic ferroelectric film 4 opposite to the substrate 2 can be improved. It can be.
The mold release treatment is not particularly limited, and preferred examples include liquid repellent treatment and formation of fine irregularities.

When a fluorine-based polymer organic ferroelectric material is used, the surface treatment of the mold 6 is not necessarily required because it contains a large amount of fluorine and does not have high adhesion to other materials.
In this heat treatment step, the molecular motion of the organic ferroelectric material in the low crystallinity film 4B becomes intense due to thermal energy, and the low crystallinity film 4B is softened. Accordingly, the mold 6 is crystallized by pressing and pressing the mold 6 to the softened low crystallinity film 4B, and then crystallizing by promoting the phase transition to the β-type, and then cooling while maintaining the pressed state. The organic ferroelectric film 4 to which the pattern formed in 6 is transferred can be obtained.

In addition, the atmosphere during the crystallization treatment may be air, but is more preferably an inert atmosphere such as nitrogen or argon, or a vacuum.
The feature of this process is that in the process of promoting the crystallization of the low crystallinity film 4B by heating, the organic ferroelectric material in the low crystallinity film 4B is pressurized, so that the space where the crystallization is limited Proceed within. That is, the crystallization of the organic ferroelectric material proceeds while maintaining the surface of the low crystallinity film 4B opposite to the substrate 2 in a smoothed state by the mold 6. Therefore, it is possible to prevent crystal grains of the organic ferroelectric material from growing freely and roughing the surface. Therefore, the surface of the obtained organic ferroelectric film 4 opposite to the substrate 2 is smoothed, and the film thickness of the organic ferroelectric film 4 (distance between the lower electrode 3 and the upper electrode 5) is locally increased. It can be prevented from becoming smaller. Thereby, for example, the problem of surface unevenness due to crystal grains that hinders the thinning of P (VDF / TrFE) can be avoided, and the storage element 1 can be driven at a low voltage.

In this example, crystallization is performed while an electric field is applied between the mold 6 and the lower electrode 3.
Thereby, the crystal orientation of the organic ferroelectric material in the obtained organic ferroelectric film 4, that is, the polarization axis can be aligned in a direction perpendicular to the surfaces of the lower electrode 3 and the upper electrode 5. Therefore, in the obtained memory element 1, the loss of polarization due to the directional fluctuation of the polarization axis can be reduced, and the polarization value possessed by the organic ferroelectric can be maximized. Furthermore, the response of polarization inversion can be improved and the squareness in the hysteresis curve can be improved.

Further, since a voltage is applied to the low crystallinity film 4B using the lower electrode 3 and the mold 6, it is possible to easily apply a voltage to the low crystallinity film 4B without preparing a separate electrode.
The electric field applied to the low crystallinity film 4B by the voltage application depends on the organic ferroelectric material to be used, but it is preferable to apply an electric field higher than the coercive electric field. For example, in the case of P (VDF / TrFE), it is preferably 0.3 kV / cm or more, and more preferably 0.5 MV / cm or more, which is a coercive electric field. Thereby, the crystal orientation of the organic ferroelectric thin film in the obtained organic ferroelectric film 4 can be aligned in the direction in which the polarization axis is perpendicular to the lower and upper electrode surfaces.
The application of the electric field as described above can be omitted.

[4] Step of Forming Upper Electrode Next, as shown in FIG. 2G, the upper electrode 5 is formed on the low crystallinity film 4B. As described above, the surface of the organic ferroelectric film 4 opposite to the first electrode 3 is smooth, and the upper electrode 5 is formed on such a smooth surface. The interface with the electrode 5 can be made extremely smooth.
The formation of the upper electrode 5 can be performed in the same manner as in the step [1].

As described above, the memory element 1 can be manufactured.
According to such a manufacturing method, since the low crystallinity film 4B is crystallized using the mold 6, the interface between the low crystallinity film 4B and the second electrode 5 is made extremely smooth. In this state, the low crystallinity film 4B can be crystallized. Therefore, it is possible to prevent the occurrence of surface irregularities associated with crystal grain growth and to make the surface of the obtained organic ferroelectric film 4 extremely smooth.

As a result, even if the organic ferroelectric film 4 is thinned, the obtained memory element 1 prevents an increase in leakage current and short-circuits in the thickness direction of the organic ferroelectric film 4 (the lower electrode 3 and the upper part). Short circuit with the electrode 5) can be prevented. That is, the organic ferroelectric film 4 can be made thin to reduce the driving voltage.
Further, in this manufacturing method, the memory element 1 can be formed by a process using only a simple device at a relatively low temperature. Therefore, the cost of the manufacturing apparatus can be reduced, and the range of selection of the material constituting the memory element 1 and further the memory device is expanded. For example, a flexible memory element 1 or memory device can be manufactured using a resin material as the substrate 2.

(Second example)
Next, a second example of the method for manufacturing the memory element 1 will be described with reference to FIG. In the following, description will be made mainly on matters that are different from the first example described above, and description of similar matters will be omitted.
The method of manufacturing the memory element 1 in the second example is to form the organic ferroelectric film 4 by pressing the mold 6 in the second step after crystallizing the low crystallinity film 4B and then softening it. Except for this, it is the same as the manufacturing method of the memory element 1 in the first example described above.

  That is, in the method of manufacturing the memory element 1 in the second example, [1] a step of forming the lower electrode 3 and [2] a liquid material containing an organic ferroelectric material is applied on the lower electrode 3, Drying this to form a low crystallinity film (first process), and [3] promoting the crystallinity of the low crystallinity film and then heating and pressurizing it to produce organic ferroelectric Forming a body film (second process) and [4] forming an upper electrode on the organic ferroelectric film.

Steps [1], [2] and [4] in the method for manufacturing the memory element 1 in the second example are the same as the steps [1], [2] and [4] according to the first example.
In step [3] according to the second example, when the organic ferroelectric film 4 is formed by promoting the crystallinity of the organic ferroelectric material in the low crystallinity film 4B, FIG. As shown in FIG. 3E, after the crystallinity is increased by heating the low crystallinity film 4B to form the crystal film 4C, the crystal film 4C is heated and softened, as shown in FIG. Thus, after pressing the mold 6 against the substrate 2 through the crystal film 4C, the mold 6 is removed, and the organic ferroelectric film 4 is obtained.

Although it does not specifically limit as heating temperature (processing temperature) for the said softening, It is preferable that it is 80-200 degreeC. Thereby, the surface on the opposite side to the board | substrate 2 of the organic ferroelectric film 4 obtained can be made very smooth.
Further, when the softened crystal film 4C is pressed by the mold 6, a voltage is applied between the mold 6 and the substrate 2 (or the lower electrode 3) in the same manner as in the first example described above, so that the inside of the crystal film 4C. The direction of the polarization axis of the ferroelectric material can be aligned.

In addition, the mold 6 used here and the conditions such as pressing, heat treatment, and cooling can be the same as described in the first example.
According to such a manufacturing method, the organic ferroelectric film is formed even if the crystal film 4 </ b> C is provided with irregularities made of crystal grains of the organic ferroelectric material on the surface opposite to the substrate 2 by crystallization. The surface on the opposite side to the substrate 2 can be smoothed. Therefore, it is possible to prevent the film thickness of the organic ferroelectric film 4 from being locally reduced. As a result, even if the organic ferroelectric film 4 is thinned, the obtained memory element 1 can prevent an increase in leakage current and a short circuit in the thickness direction of the organic ferroelectric film 4. . That is, the organic ferroelectric film 4 can be made thin to reduce the driving voltage.
Even in the above manner, the memory element 1 can be manufactured.
In the second example, the pressing by the mold as described above is not performed before the formation of the upper electrode 5, but the upper electrode 5 is formed on the low crystallinity film 4B, and then the upper electrode 5 and the low crystal are formed. It is also possible to press the mold 6 toward the substrate 2 through the chemical film 4B.

<Storage device>
Next, as an example of the memory device of the present invention, a CP-type memory device using the memory element 1 will be described with reference to FIG.
FIG. 4 is a diagram schematically showing a circuit configuration of a storage device (memory array) using the storage element 1.

A storage device 100 illustrated in FIG. 4 is a storage device including a memory array including a plurality of CP-type memory cells.
More specifically, the memory device 100 has a memory array configured by arranging the first signal electrode 101 for row selection and the second signal electrode 102 for column selection so as to be orthogonal to each other. ing.

One of the first signal electrode 101 and the second signal electrode 102 is a word line, and the other is a bit line. These intersections constitute the memory element 1. In FIG. 4, the memory element 1 is schematically shown as a resistor connected near the intersection.
Such a memory device 100 can reduce the driving voltage even when an organic ferroelectric material having crystallinity is used as a constituent material of the organic ferroelectric film 4. Further, such a storage device 100 has excellent reliability by reducing leakage current and preventing short circuit.

<Second Embodiment>
Next, a second embodiment of the present invention will be described. In addition, about 2nd Embodiment, the description is abbreviate | omitted regarding the matter similar to 1st Embodiment mentioned above.
FIG. 5 is a cross-sectional view showing an embodiment of a memory element according to the second embodiment of the present invention. 5A is a longitudinal sectional view of the memory element, and FIG. 5B is a transverse sectional view of the memory element. Hereinafter, for convenience of explanation, “upper” in FIG. 5 is referred to as “upper”, and “lower” is referred to as “lower”.

The memory element 1A shown in FIG. 5 is in the form of a one-transistor (so-called 1T type) memory device.
Such a memory element 1A includes a source region 31 and a drain region 32 provided on the substrate 2 at a distance from each other, a semiconductor film 33 in contact with the source region 31 and the drain region 32 therebetween, and a semiconductor It has an organic ferroelectric film (recording film) 4D formed so as to cover the film 33, and a gate electrode 5A formed on the organic ferroelectric film 4D.

  In such a memory element 1A, a voltage is applied between the gate electrode 5A and the source region 31 and the drain region 32 to change the polarization state in the organic ferroelectric film 4D to record (write) data. ) Is made. Further, such a polarization state is maintained even when the application of the electric field is stopped, and recording (reproduction) can be performed by detecting a current flowing between the source region 31 and the drain region 32. Therefore, the memory element 1A can be used for a nonvolatile memory.

In the memory element 1A, as shown in FIG. 5B, a region between the source region 31 and the drain region 32 in the semiconductor film 33 is a channel region 34 in which carriers move. Here, in the channel region 34, the length in the carrier moving direction, that is, the distance between the source region 31 and the drain region 32 is the channel length L, and the length in the direction orthogonal to the channel length L direction is the channel length. The width W.
Such a memory element 1A has a configuration in which the source region 31 and the drain region 32 are provided on the substrate 2 side of the gate electrode 5A via the organic ferroelectric film 4D, that is, a top gate structure.

Next, the manufacturing method of the memory element of the present invention will be described based on FIG. 6 by taking the manufacturing method of the memory element 1A as an example.
FIG. 6 is a diagram for explaining a method of manufacturing the memory element shown in FIG.
The manufacturing method of the memory element 1A is the same as the manufacturing method of the memory element 1 according to the first embodiment (first example or second example) described above with respect to the manufacturing of the organic ferroelectric film 4D.

  That is, the manufacturing method of the memory element 1A includes [1] a step of forming the source region 31, the drain region 32, and the semiconductor film 33, and [2] an organic ferroelectric material on the semiconductor film 33 (channel region 34). And applying a liquid material containing the material, followed by drying to form a low crystallinity film (first process), and [3] crystallizing the low crystallinity film to produce an organic ferroelectric film. Forming (using a mold) (second step), and [4] forming a gate electrode 5A on the organic ferroelectric film.

[1] Step of forming source region 31, drain region 32, and semiconductor film 33 First, as shown in FIG. 6A, for example, a substrate 2 such as a semiconductor substrate, a glass substrate, or a resin substrate is prepared. As shown in FIG. 6B, the source region 31 and the drain region 32 are formed on the upper surface of 2, and then the semiconductor film 33 is formed as shown in FIG.
A method for forming the source region 31, the drain region 32, and the semiconductor film 33 is not particularly limited, and the same method as that for the lower electrode 3 described above can be used.

In addition, the constituent material of the semiconductor film 33 is not particularly limited, and various organic semiconductor materials and various inorganic semiconductor materials can be used. However, it is preferable to use an organic semiconductor material from the viewpoint of flexibility.
Examples of the organic semiconductor material include naphthalene, anthracene, tetracene, pentacene, hexacene, phthalocyanine, perylene, hydrazone, triphenylmethane, diphenylmethane, stilbene, arylvinyl, pyrazoline, triphenylamine, triarylamine, oligothiophene, phthalocyanine or Low molecular organic semiconductor materials such as these derivatives, poly-N-vinylcarbazole, polyvinylpyrene, polyvinylanthracene, polythiophene, polyalkylthiophene, polyhexylthiophene, poly (p-phenylene vinylene), polytinylene vinylene, Polyarylamine, pyrene formaldehyde resin, ethylcarbazole formaldehyde resin, fluorene-bithiophene copolymer, fluorene-ary Examples thereof include high molecular organic semiconductor materials (conjugated polymer materials) such as amine copolymers or derivatives thereof, and one or more of these can be used in combination. It is preferable to use a material mainly composed of a molecular organic semiconductor material (conjugated polymer material). The conjugated polymer material has a particularly high carrier mobility due to its unique electron cloud spread.

Of these, fluorene-bithiophene copolymer, fluorene-arylamine copolymer are used as high-molecular organic semiconductor materials (conjugated polymer materials) because they are not easily oxidized in the air and are stable. It is particularly preferable to use a compound, a polyarylamine or a derivative containing at least one of these derivatives as a main component.
When the semiconductor film 33 is formed using such a polymer organic semiconductor material as a main material, it can be thinned and reduced in weight, and a memory device having excellent flexibility can be obtained. It is suitable for application as a nonvolatile memory mounted on various flexible electronic devices.
The thickness of the semiconductor film 33 (organic semiconductor material) is preferably about 1 nm to 500 nm, and more preferably about 10 nm to 200 nm.

[2] Step of forming a low crystallinity film (first step)
Next, a liquid material containing a crystalline organic ferroelectric material is applied so as to cover the semiconductor film 33 (a film-like liquid material is formed), and this is dried, as shown in FIG. As shown, a low crystallinity film (amorphous film) 4E, which is an intermediate product film for forming the organic ferroelectric film 4D, is formed.
The low crystallinity film 4E can be formed in the same manner as the low crystallinity film 4B of the first example described above.

  Even when unevenness is formed by the source region 31, the drain region 32, and the semiconductor film 33 as in the present embodiment, the low crystallinity film 4E is obtained by using the solution atomization deposition method (LSMCD method). The film thickness of the low crystallinity film 4E can be easily made uniform. This is due to the small particle size of the droplets formed by the solution atomization deposition method (LSMCD method).

[3] Step of forming organic ferroelectric film 4D (second step)
Next, as shown in FIG. 6E, the organic ferroelectric film 4D is formed by promoting the crystallization of the low crystallinity film 4E.
The formation (crystallization) of the organic ferroelectric film 4D can be performed in the same manner as the formation of the organic ferroelectric film 4 of the first embodiment (first example or second example) described above. That is, the surface of the organic ferroelectric film 4D opposite to the substrate 2 can be flattened using a mold.

[4] Step of Forming Gate Electrode Next, as shown in FIG. 6E, a gate electrode 5A is formed on the organic ferroelectric film 4.
The formation of the gate electrode 5A can be performed in the same manner as in the step [1].
As described above, the memory element 1A can be manufactured.
With the manufacturing method as described above, the memory element 1A having excellent responsiveness and hysteresis characteristics can be manufactured.

  In particular, in the present embodiment, before the step of forming the low crystallinity film 4E, the source region 31, the drain region 32, and the channel region 34 (semiconductor film 33) are formed on the substrate 2 to reduce the low crystallinity. In the step of forming the crystallinity film 4E, the gate electrode 5A is formed on the organic ferroelectric film 4D after the process of forming the low crystallinity film 4E on the channel region 34 and forming the organic ferroelectric film 4D. Form. Thereby, a memory element 1A that can be used in a so-called 1T (transistor) type memory device can be obtained.

<Storage device>
Next, as another example of the memory device of the present invention, a memory device using the memory element 1A will be described with reference to FIG.
A storage device 100A illustrated in FIG. 7 is a so-called 1T type storage device.
More specifically, in the memory device 100A, the first signal electrode 101 for row selection and the second signal electrode 102 for column selection are orthogonal to each other, and the first signal electrode 101 and the second signal electrode 102 are used. The third signal electrode 103 is arranged so that the third signal electrode 103 passes through the vicinity of the intersection, and the memory element 1A is connected to the memory array.

  One of the first signal electrode 101 and the second signal electrode 102 is a word line, and the other is a bit line. Further, near each intersection of the first signal electrode 101 and the second signal electrode 102, the first signal electrode 101 is connected to the drain region 32, and the second signal electrode 102 is connected to the source region 31. The third signal electrode 103 is connected to the gate electrode 5A and functions as a write line for writing data.

Such a storage device 100A can perform nondestructive reading.
Note that a 2T2C type and further a 1T1C type storage device are preferable from the viewpoint of stable operation of the storage device (storage device), but a 1T type is preferable from the viewpoint that nondestructive reading (NDRO) is possible.
In the present embodiment, the storage element is described. However, the storage element and the manufacturing method thereof according to the present embodiment can also be applied to a transistor such as a thin film transistor and a manufacturing method thereof. That is, the transistor can be manufactured in the same manner as the manufacturing method according to this embodiment. In this case, the driving voltage of the transistor can be reduced or the response can be improved.

  Further, when manufacturing a 1T1C type or 2T2C type storage device, the transistor portion of the memory array can be manufactured in the same manner as the storage element manufacturing method according to the present embodiment. Thereby, the characteristics of the storage device can be improved. At this time, the characteristics of the memory device can be further improved by manufacturing the capacitor portion of the memory array using the method for manufacturing the memory element according to the first embodiment described above.

The storage devices 100 and 100A as described above can be applied to various electronic devices. As a result, it is possible to provide an electronic device capable of reducing the drive voltage even when an organic ferroelectric material having crystallinity is used as a constituent material of the organic ferroelectric film 4. Moreover, such an electronic device has excellent reliability by reducing leakage current and preventing short circuit.
Examples of the electronic device include a personal computer and a portable information device.

As mentioned above, although this invention was demonstrated based on embodiment of illustration, this invention is not limited to this.
For example, each unit constituting the present invention can be replaced with any one that exhibits the same function, or other configurations can be added.
In addition, for example, one or two or more desired layers may be provided between the organic ferroelectric film 4 and the lower electrode 3 and the upper electrode 5, respectively. Further, between the organic ferroelectric film 4D and the semiconductor film 33, one or two or more desired layers may be provided.

  The transistors in each of the 2T2C type, 1T1C type, CP type, and 1T type storage devices described above are a single crystal Si transistor, an amorphous silicon thin film transistor (a-Si TFT), and a low temperature polysilicon thin film transistor (LTPS TFT: Low). It can be in the form of a temperature poly (Si TFT), a high temperature polysilicon thin film transistor (HTPS: High Temperature poly-Si TFT), or an organic thin film transistor (organic TFT).

Next, specific examples of the present invention will be described.
(Example 1)
A memory element as shown in FIG. 1 was manufactured by the manufacturing method according to the present invention as follows.
Specifically, first, a polyimide substrate having an average thickness of 300 μm was prepared.
Next, a 100 nm-thick lower electrode made of Al was formed on the substrate by vapor deposition.
Next, a liquid material having the following composition was applied by spin coating, and dried at 80 ° C. for 20 minutes to obtain a low crystallinity film.

(Composition of liquid material)
P (VDF / TrFE) [VDF / TrFE = 75/25] 3wt%
MEK (methyl ethyl ketone: 2-butanone) 97 wt%
Curie point (Tc): about 80 ° C
Next, as shown in FIG. 8 (a), a low-crystallinity film was preliminarily pressed with a PTFE surface-treated mold at a pressure of 5 MPa / cm ² , and 140 ° C. (time T _S2 shown in FIG. 8). Temperature between -T _S3 Crystallized by heat treatment at a Curie point (Tc) or more for 15 minutes (the length of time between T _{S1 and} T _S4 ). FIG. 8 is a diagram illustrating the relationship between the mold and substrate temperatures and time, and the relationship between mold pressure and time.

Next, this was naturally cooled to room temperature (normal temperature (RT): 25 ° C.), the mold was peeled off, and an organic ferroelectric film having a thickness of 50 nm was obtained.
Then, the surface of the organic ferroelectric film from which the mold was peeled was observed with a microscope, and the surface state was evaluated according to the following four-stage criteria. The evaluation results are shown in Table 1.
(Double-circle): The unevenness | corrugation by a crystal grain is hardly seen.
◯: There are irregularities due to crystal grains, but the concave portions are extremely shallow.
(Triangle | delta): There exists an unevenness | corrugation by a crystal grain and the recessed part is deep.
X: Pinholes were generated in the organic ferroelectric film due to irregularities caused by the crystal flow.

Next, an upper electrode made of Al and having a thickness of 100 nm was formed by vapor deposition.
(Example 2)
As shown in FIG. 8B, the heat treatment was performed on the low crystallinity film to promote crystallinity, and then the film was rapidly cooled below the Curie point (10 ° C./min or higher), as in Example 1. Thus, a memory element was manufactured.
Further, the surface of the organic ferroelectric film from which the mold was peeled was observed with a microscope, and the surface state was evaluated according to the following four-stage criteria. The evaluation results are shown in Table 1.

(Example 3)
A memory element as shown in FIG. 1 was manufactured by the manufacturing method according to the present invention as follows.
More specifically, first, a polyimide substrate having an average thickness of 300 μm was prepared.
Next, a 100 nm-thick lower electrode made of Al was formed on the substrate by vapor deposition.
Next, a liquid material having the following composition was applied by spin coating and heated to 140 ° C. (Curie point (Tc) or higher) to promote crystallinity of the liquid material to obtain a crystal film.

(Composition of liquid material)
P (VDF / TrFE) [VDF / TrFE = 75/25] 3wt%
MEK (methyl ethyl ketone: 2-butanone) 97 wt%
Curie point (Tc): about 80 ° C
Next, a die that had been surface-treated with PTFE in advance was pressed against the crystal film at a pressure of 8 MPa / cm ² for 20 minutes.

Next, this was cooled to room temperature (normal temperature (RT): 25 ° C.), the mold was peeled off, and an organic ferroelectric film having a thickness of 50 nm was formed.
Then, the surface of the organic ferroelectric film from which the mold was peeled was observed with a microscope, and the surface state was evaluated according to the following four-stage criteria. The evaluation results are shown in Table 1.
Next, an upper electrode made of Al and having a thickness of 100 nm was formed by vapor deposition.

Example 4
An organic ferroelectric material with a smooth surface was obtained in the same manner as in Example 3 except that the mold was pressed against the crystal film and then rapidly cooled (10 ° C./min or more).
Further, the surface of the organic ferroelectric film from which the mold was peeled was observed with a microscope, and the surface state was evaluated according to the following four-stage criteria. The evaluation results are shown in Table 1.
(Examples 5 to 10)
An organic ferroelectric film was formed in the same manner as in Example 1 except that the pressure and processing temperature were as shown in Table 1.

(Comparative example)
A memory element was manufactured in the same manner as in Example 1 described above, except that pressing with a mold was not performed.
As shown in Table 1, in Examples 1 to 10 according to the present invention, the surface of the organic ferroelectric film opposite to the substrate was smooth. In contrast, in the comparative example, unevenness due to crystal grains was conspicuous on the surface of the organic ferroelectric film opposite to the substrate.
In addition, the memory elements of Examples 1 to 10 were capable of low voltage driving (driving at about 2 V). On the other hand, the storage element of the comparative example cannot be driven. This is thought to be due to an increase in leakage current or a short circuit.

It is a longitudinal cross-sectional view which shows embodiment of the memory element concerning this invention. It is a figure for demonstrating the 1st example of the manufacturing method of the memory element shown in FIG. It is a figure for demonstrating the 2nd example of the manufacturing method of the memory element shown in FIG. It is a figure which shows typically the circuit form of the memory | storage device using the memory element 1 concerning this invention. It is a figure for demonstrating the 4th example of the manufacturing method of the memory element shown in FIG. It is a figure for demonstrating the manufacturing method of the memory element shown in FIG. It is a figure which shows typically the basic circuit form of a memory | storage device provided with the memory element shown in FIG. It is a figure for demonstrating the relationship between the temperature and time of a type | mold and a board | substrate in the Example of this invention, and the relationship between the pressure of a type | mold, and time.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1, 1A ... Memory element 2 ... Substrate 3 ... Lower electrode 31 ... Source region 32 ... Drain region 33 ... Semiconductor film 34 ... Channel region 4 ... Organic ferroelectric film 4A ... Liquid material 4B Low crystallinity film 4C Crystal film 4D Organic ferroelectric film 4E Low crystallinity film 5 Upper electrode 5A Gate electrodes 100, 100A Memory device 101 First Signal electrode 102 ... 2nd signal electrode 103 ... 3rd signal electrode

Claims (18)

A method of forming an organic ferroelectric film composed mainly of an organic ferroelectric material having crystallinity,
Forming a low crystallinity film having a crystallinity lower than the crystallinity of the organic ferroelectric film on one surface of the substrate;
A second step of forming the organic ferroelectric film from the low crystallinity film,
The first step includes a step of applying and drying a liquid material containing the organic ferroelectric material on one surface of the substrate,
The second step includes a step of increasing the crystallinity in the low crystallinity film while shaping the low crystallinity film by heating and pressurizing the low crystallinity film.
A method of forming an organic ferroelectric film characterized by the above.   The method for forming an organic ferroelectric film according to claim 1, wherein the crystallinity in the low crystallinity film is 80% or less of the crystallinity of the organic ferroelectric film. 3. The method of forming an organic ferroelectric film according to claim 1, wherein, in the second step, the pressure of the pressurization is 0.1 to 10 MPa / cm ² .   The method for forming an organic ferroelectric film according to claim 1, wherein the organic ferroelectric film has a thickness of 5 nm to 500 nm.   The organic ferroelectric material is one of a copolymer of vinylidene fluoride and trifluoroethylene, or a polymer of vinylidene fluoride, either singly or in combination. A method for forming an organic ferroelectric film according to claim 1.   6. The method of forming an organic ferroelectric film according to claim 1, wherein the liquid material containing the organic ferroelectric material is obtained by dissolving the organic ferroelectric material in a solvent.   The method for forming an organic ferroelectric film according to claim 1, wherein, in the second step, the heating temperature for increasing the crystallinity is 80 to 200 ° C. 8.   8. The method of forming an organic ferroelectric film according to claim 1, wherein, in the second step, after increasing the crystallinity, cooling is performed while maintaining the pressurized state.   The method for forming an organic ferroelectric film according to claim 8, wherein the cooling is performed at or below a glass transition point of the organic ferroelectric material.   10. The organic ferroelectric film according to claim 1, further comprising a step of heating and softening the low crystallinity film after the first step and before the second step. Forming method.   11. The organic ferroelectric according to claim 1, wherein in the second step, the shaping is performed by pressing a mold capable of defining an effective area of the organic ferroelectric film toward the substrate. Method for forming a film.   The method for forming an organic ferroelectric film according to claim 11, wherein the pressing surface of the mold is subjected to a mold release process. Before the first step, a first electrode is formed on the substrate, and in the first step, the low crystallinity film is formed on a surface of the first electrode opposite to the substrate. Form the
13. The formation of the organic ferroelectric film according to claim 11, wherein, in the second step, the crystallization is performed while applying an electric field between the mold and the first electrode during the pressurization. Method. A method for producing an organic ferroelectric film comprising an organic ferroelectric material having crystallinity as a main material,
A first step of forming a low crystallinity film having a crystallinity lower than that of the organic ferroelectric film on one surface of the substrate;
A second step of forming the organic ferroelectric film from the low crystallinity film,
The first step includes a step of applying and drying a liquid material containing the organic ferroelectric material on one surface of the substrate,
The second step includes
A third step of forming a crystal film in which the low crystallinity film is heated to increase the crystallinity of the low crystallinity film;
A fourth step of shaping the crystal film by heating and pressurizing the crystal film to form the organic ferroelectric film.
A method of forming an organic ferroelectric film characterized by the above. A method of manufacturing a memory element using an organic ferroelectric film composed mainly of an organic ferroelectric material having crystallinity,
Forming a first electrode on one side of the substrate;
Forming a low crystallinity film having a crystallinity lower than that of the organic ferroelectric film on a surface of the first electrode opposite to the substrate;
A second step of forming the organic ferroelectric film from the low crystallinity film;
Forming a second electrode on a surface of the organic ferroelectric film opposite to the first electrode,
The first step includes a step of applying and drying a liquid material containing the organic ferroelectric material on one surface of the substrate,
The second step includes a step of increasing the crystallinity in the low crystallinity film while shaping the low crystallinity film by heating and pressurizing the low crystallinity film.
A method for manufacturing a memory element. A step of forming a semiconductor film after the step of forming the first electrode and before the first step;
The first electrode formed in the step of forming the first electrode is a pair of electrodes provided at a distance from each other,
In the step of forming the semiconductor film, the semiconductor film is formed in contact with each of the pair of electrodes,
The method for manufacturing a memory element according to claim 15, wherein the low crystallinity film formed in the first step is formed on a surface of the semiconductor film opposite to the substrate. A storage device comprising the storage element manufactured by the method for manufacturing a storage element according to claim 15.   An electronic apparatus comprising the storage device according to claim 17.

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