KR101809361B1 - Flexible Memristors for Application in Neural Devices and Method of forming the same - Google Patents

Abstract

A MEMSlister having flexibility and a manufacturing method thereof are disclosed. The memristor has a resistance change layer for resistance change, and the resistance change layer has insulating nanoparticles and an insulating organic layer. The cation from the electrode moves to the interface between the insulating nanoparticle and the insulating organic layer by the application of an electric field, and forms a cation transport channel. The resistance change operation is performed by the formation and disappearance of the cation movement channel. Particularly, even if the memristor is distorted by application of an external force according to the characteristics of flexibility, the resistance change characteristic is maintained.

Description

Technical Field [0001] The present invention relates to a flexible memristor for a neural device and a method for manufacturing the same.

The present invention relates to a memristor, and more particularly, to a memristor having flexibility characteristics and capable of forming a cation transport channel and a method of manufacturing the same.

A memristor refers to a device that simultaneously has both memory and resistive features. Recently, it has been applied to nonvolatile memory, and a typical memory device is ReRAM. The ReRAM uses a resistance change material, and the data is recorded and stored by changing the resistance. In order to record data, a change in resistance must be performed. In order to store data, the changed resistance needs to be maintained at a constant value.

In recent years, a two-terminal ReRAM device having a simple structure and a fast operation characteristic has been attracting attention. The resistance change material used in ReRAM requires a long duration of resistance and fast response characteristics. In addition, it is required that the on / off ratio, which is a ratio of a current flowing in accordance with a voltage applied in a high resistance state and a low resistance state, is high.

The operation of the above-described resistance change material can be described by a memory switching model. Memory switching models include Conducting Filament Model, which focuses on structural changes in the thin film, and Electric Switching Model, which explains the resistance change by the change of Schottky barrier or internal electric field.

In particular, a conductive filament model is widely used, which assumes that a metal material is inserted into the thin film due to electrical stress applied to the electrodes or a metallic filament is formed due to an internal defect. The change in resistance is explained by the formation of conductive filaments or the rupture of conductive filaments. According to the above theory, monovalent cations such as Ag + and Cu + are introduced into the resistance change material composed of metal oxide, sulfide, metal dopant, organic material and the like from the electrode, and decrease in resistance by electrochemical reduction of monovalent cations at the cathode A low resistance due to the formation of the conductive filament can be realized.

Memristors based on the above-mentioned theory are influenced by the chemical properties of resistance-changing materials such as CuO, Ag2S, Cu2O, TaOx, HfOx or TiOx. Therefore, there is a difficulty in realizing a high on / off ratio. In addition, since it is provided in the form of a thin film of metal oxide or metal sulfide, it is difficult to secure flexibility.

In recent years, efforts have been made to realize switching characteristics by forming nanoparticles without forming a thin film of a memristor.

Korean Patent Publication No. 2010-61405 discloses a method of manufacturing a switching device by forming nanoparticles into a pellet type. In the above-mentioned patent, nanoparticles are formed in a solution phase, and a metal nanoparticle layer is formed by heating or pyrolysis. However, this is made in the form of a pellet, and it is difficult to secure flexibility.

In addition, U.S. Published Patent Application No. 2014/0197369 discloses a memristor structure using nanoparticles. In the above patent, nanoparticles are used as resistance change materials between both electrodes. In addition, an insulating layer appears to fix or stabilize the location of the resistance-changing material. The insulating layer is composed of an inorganic material, which also has difficulty in ensuring flexibility.

In addition, in order for a memristor to be used as a neural device used in a neural network, resistance switching phenomenon is required to be maintained even in a flexible environment in which nano-sized density and mechanical deformation are performed in addition to resistance switching phenomenon.

SUMMARY OF THE INVENTION It is a first object of the present invention to provide a memristor having flexibility characteristics.

According to a second aspect of the present invention, there is provided a method of manufacturing a memristor to achieve the first technical object.

According to a first aspect of the present invention, there is provided a semiconductor device comprising: a flexible substrate; A lower electrode formed on the flexible substrate; A resistance change layer formed on the lower electrode and performing a resistance change according to the formation of a cation transport channel formed at an interface between the insulating nanoparticle and the insulating organic layer; And an upper electrode formed on the resistance variable layer.

According to a second aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising: forming an oxidation film on a base substrate; Oxidizing the oxidation film to form insulating nanoparticles; Forming a resistance variable layer by forming an insulating organic layer filling a space between the insulating nanoparticles; Releasing the resistance-variable layer from the oxidation film and disposing the resistance-variable layer on the lower electrode on the flexible substrate; And forming an upper electrode on the disposed resistance-variable layer.

According to the present invention described above, nanoparticles having an insulating property and an organic material layer having an insulating property are used as the resistance variable layer. A cation transport channel is formed through the interface between the nanoparticles and the organic layer to function as a resistance change memory. Since the nanoparticles and the organic layer have chemical stability, the same operating characteristics can be maintained even if they are used for a long time.

Further, the resistance-variable layer has a characteristic of flexibility because it includes nanoparticles and an organic material layer. As shown in this embodiment, the MEMS maintains substantially the same electrical characteristics even when an external force is applied to the memristor to warp. This can be utilized as a memory device having flexibility characteristics.

Therefore, in the present invention, integration of the memristor can be improved by introducing a single layer or selective layers of nanoparticles, and resistance switching characteristics can be maintained even in a flexible environment. It has a technical advantage that can be utilized as a neural device such as a neural network.

1 is a cross-sectional view of a memristor according to a preferred embodiment of the present invention.
2 to 7 are cross-sectional views illustrating a method of manufacturing the MEMSistor device of FIG. 1 according to a preferred embodiment of the present invention.
8 is a graph showing voltage-current characteristics of a MEMSistor formed through the processes of FIGS. 2 to 7 according to a preferred embodiment of the present invention.
FIG. 9 is a graph showing other voltage-current characteristics of a MEMSistor formed through the processes of FIGS. 2 to 7 according to a preferred embodiment of the present invention.

The present invention is capable of various modifications and various forms, and specific embodiments are illustrated in the drawings and described in detail in the text. It should be understood, however, that the invention is not intended to be limited to the particular forms disclosed, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. Like reference numerals are used for like elements in describing each drawing.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the contextual meaning of the related art and are to be interpreted as either ideal or overly formal in the sense of the present application Do not.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Example

1 is a cross-sectional view of a memristor according to a preferred embodiment of the present invention.

Referring to FIG. 1, a MEMSistor has a flexible substrate 100, a lower electrode 110, a resistance-variable layer 120, and an upper electrode 130.

The flexible substrate 100 may be any material having a flexural characteristic, and there is no particular limitation on the material. However, according to the embodiment, the type of the flexible substrate 100 can be appropriately selected according to the user, and in the present embodiment, PET (polyethylene terephthalate) is used as an example.

A lower electrode 110 is formed on the flexible substrate 100. The lower electrode 110 may be made of a material having electrical characteristics of a negative electrode, and a material having high adhesion with the flexible substrate 110 is preferable. For example, ITO, IZO, GZO, or AZO may be used as the lower electrode 110, and a metal material may be used as the lower electrode 110.

A resistance-variable layer 120 is formed on the lower electrode 110. The resistance-variable layer 120 includes the insulating nanoparticles 121 and the insulating organic layer 123. The insulating nanoparticles 121 may be dispersed in the insulating organic layer 123 or may be formed in a regular arrangement with respect to each other. The insulating organic layer 123 is provided in a manner to fill a space between the insulating nanoparticles 121 and at least a part of the surface of the insulating nanoparticle 121 is connected to the lower electrode 110 or the upper electrode 130 Direct contact is preferred.

The resistance-variable layer 120 may provide a migration channel for metal ions or cations, which is generated at the interface between the insulating nanoparticles 121 and the insulating organic layer 123.

In addition, the insulating nanoparticles 121 may be a metal oxide, a metal nitride, or a polymer compound.

In addition, the insulating organic layer 123 may be polyimide, polymethyl methacrylate, polystyrene, or the like. Any polymer having flexibility and insulation characteristics may be used.

An upper electrode 130 is formed on the resistance-variable layer 120. The upper electrode 130 may be any material that can have an electrically positive characteristic. Therefore, the upper electrode 130 may include a metal material, and a metal such as Ag, Al, Ni, or Cu, or an alloy thereof may be used.

However, the work function of the lower electrode 110 and the upper electrode 130 of the present embodiment does not act as a large factor due to interfacial bonding or the like. Consideration of the work function plays an important role in interfacial bonding with the semiconductor layer and the like. In the present invention, the electrodes 110 and 130 are bonded to a material having an insulating property. Accordingly, various conductive materials may be used as the electrode, the upper electrode 130 may perform an electric cathode operation, and the lower electrode 110 may perform an electric anode operation.

However, it is preferable that any one of the upper electrode 130 and the lower electrode 110 is made of metal. This is to allow the metal ions to move from the metal forming the electrode to the resistance-variable layer 120 by the application of the electric field between the electrodes 110 and 130.

When an electric field is applied between the upper electrode 130 and the lower electrode 110, the metal ions of the upper electrode 130 or the lower electrode 110 are introduced into the resistance-variable layer 120 by an electric field. The metal ions can not move to the bulk region of the insulator, but they can move to the interface between the insulating nanoparticles 121 and the insulating organic layer 123 of the present invention. Since the insulating nanoparticles 121 have a stable molecular structure and have chemical stability, the insulating nanoparticles 121 are not chemically or chemically bonded to the insulating organic layer 123 or have a weak bonding force. Therefore, a weak bonding force exists between the insulating nanoparticles 121 and the insulating organic layer 123, or the bonding force is insignificant.

Accordingly, a metal ion migration channel can be formed at the interface between the insulating nanoparticle 110 and the insulating organic layer 130. The conductive filament or ion moving channel may be formed in the upper electrode 130 and the lower electrode 110. [

2 to 7 are cross-sectional views illustrating a method of manufacturing the MEMSistor device of FIG. 1 according to a preferred embodiment of the present invention.

Referring to FIG. 2, an oxidation film 20 is provided on a base substrate 10. In the present embodiment, the oxidation film 20 is a metal film capable of forming insulating nanoparticles through oxidation of metal. The oxidation film 20 is formed on the base substrate 10, for example, in this embodiment, the aluminum film is provided with the oxidation film 20. Further, silicon is used as the base substrate 10, and an aluminum film is formed on the silicon substrate.

A thermal evaporation method is used for forming the aluminum film. In addition, an aluminum film can be manufactured by using a vapor deposition method of various metals. The aluminum film to be formed may have a thickness of about 5 nm. However, it is preferable that the thickness of the aluminum film has a thickness suitable for forming aluminum oxide nanoparticles through thermal oxidation in a subsequent process.

Further, the aluminum film may be provided in a patterned form. That is, an aluminum film is formed through vapor deposition, a photoresist pattern is formed through a conventional photolithography process, and the patterned aluminum film can be formed through patterning using the photoresist pattern as an etching mask. In addition, a patterned aluminum film can be formed through vapor deposition using a shadow mask.

Referring to FIG. 3, an oxidation process for the metal constituting the oxidation film 20 is performed through thermal oxidation of the oxidation film 20. Thereby, the insulating nanoparticles 121, which are metal oxides, are formed on the oxidation film 20.

For example, aluminum oxide nanoparticles are formed through a thermal oxidation process on an aluminum film. Is oxidized for 10 minutes to 1 hour, preferably 30 minutes, in an oxygen supply or oxygen environment at a temperature condition of 300 DEG C to 400 DEG C, preferably about 350 DEG C, for thermal oxidation. Thereby forming aluminum oxide nanoparticles on the aluminum film. If the time required for the thermal oxidation process exceeds 1 hour, the formation of nanoparticles can be expanded and formed into an aluminum oxide thin film. If the time is less than 10 minutes, there arises a problem that nanoparticles are not sufficiently formed.

Further, the aluminum oxide nanoparticles to be formed have mutually spaced spaces. Since the difference in surface energy is small for each position on the formed aluminum film, the aluminum oxide nanoparticles are formed with uniform distribution over the aluminum film and can have a regular arrangement. Further, the aluminum oxide nanoparticles to be formed are formed as a single layer. That is, there is no appearance of a plurality of superimposed nanoparticles toward the upper part.

Referring to FIG. 4, a spacing space between the insulating nanoparticles 121 is buried, and an insulating organic layer 123 is formed on the insulating nanoparticles 121. Thereby forming the resistance variable layer 120.

In this embodiment, the polyimide layer is formed of the insulating organic layer 123 on the aluminum oxide nanoparticles. The polyimide layer is formed by embedding a space between the aluminum oxide nanoparticles. For this purpose, phenylene biphenyltetracarboximide-type polymic acid is used as a polyimide precursor and N-methyl-2-pyrrolidone is used as a solvent. The polyimide precursor solution dissolved in the solvent is formed on the aluminum oxide nanoparticles through a spin coating process or the like. In addition, the polyimide layer is cured at a temperature of 350 DEG C for one hour to form a layer. Thereby forming a polyimide layer that fills the spacing space between the aluminum oxide nanoparticles.

It is preferable that the polyimide layer formed in FIG. 4 is formed to expose a part of the upper surface of the aluminum oxide nanoparticles. As the insulating organic layer 123, polymethyl methacrylate or polystyrene may be used in addition to polyimide. For forming the insulating organic layer 123, a spray coating method or a vacuum thermal evaporation method may be used in addition to the spin coating method.

Referring to FIG. 5, the resistance-variable layer 120 composed of the insulating nanoparticles 121 and the insulating organic layer 123 is separated from the oxidation film 20.

For example, in FIG. 4, a plastic tape having adhesiveness or adhesiveness can be applied to the resistance-variable layer 120 composed of aluminum oxide nanoparticles and a polyimide layer. In this embodiment, 3M's item no. 9080 is used. After the plastic tape is firmly adhered to the upper surface of the polyimide layer, the resistance change layer 120 composed of the aluminum oxide nanoparticles and the polyimide layer is released from the aluminum film as the oxidation film 20 when the tape is pulled. Particularly, the aluminum oxide nanoparticles are fixed by a polyimide film and have physical properties different from those of the underlying aluminum film. This applies equally to the case between the polyimide film and the aluminum film. Therefore, the bonding force of the two material layers having different physical properties is reduced, so that the peeling action through the tape can be easily performed.

Referring to FIG. 6, the resistance-variable layer 120 is disposed on the flexible substrate 100 on which the lower electrode 110 is formed.

For example, PET and ITO are used for the flexible substrate 100 and the lower electrode 110. That is, when the ITO is formed on the PET substrate, the aluminum oxide nanoparticles and the polyimide layer constituting the resistance-variable layer 120 are transferred.

First, the aluminum oxide nanoparticles and the polyimide layer, which are peeled and fixed to the tape in Fig. 5, are cleaned with deionized water. This removes foreign matter that may adhere to the exposed surface of the resistance-variable layer 120. The resistance-variable layer 120 cleaned with deionized water is dried at room temperature to remove deionized water. Further, a thermocompression bonding process may be performed to fix the aluminum oxide nanoparticles and the polyimide layer to the flexible substrate 100 on which the lower electrode 110 is formed. Through thermocompression, the polyimide layer is attached to the lower electrode ITO, and the aluminum oxide nanoparticles can contact the lower electrode 110.

Further, in order to remove the used tape, the flexible substrate 100 to which the resistance-variable layer 120 is fixed is immersed in acetone, through which the tape is dissolved.

Referring to FIG. 7, an upper electrode 130 is formed on the structure shown in FIG. 6 using a conventional deposition method. For example, Ag may be used as the material constituting the upper electrode 130. An upper electrode 130 composed of aluminum oxide nanoparticles and Ag on the polyimide layer is formed through vacuum thermal deposition using a shadow mask.

The resistance variable layer 120 may be transferred onto the flexible substrate 100 on which the lower electrode 110 is formed and the upper electrode 130 may be formed thereon.

2 to 7 illustrate that the aluminum oxide nanoparticles are formed as a single layer. However, according to the embodiment of the present invention, a plurality of resistance change layers may be provided in the resistance change layer shown in FIG. That is, a plurality of resistance-variable layers formed according to FIGS. 4 and 5 are formed in the manufacturing process, and a plurality of resistance-variable layers are arranged in the process of FIG. 6, Layer can be formed.

8 is a graph showing voltage-current characteristics of a MEMSistor formed through the processes of FIGS. 2 to 7 according to a preferred embodiment of the present invention.

Referring to FIG. 8, silicon is used as a base substrate, and an aluminum film is used as an oxidation film. The thickness of the aluminum film is 5 nm. In addition, aluminum oxide nanoparticles are formed as a single layer through a thermal oxidation process in an oxygen environment at 350 DEG C for 30 minutes. The insulating organic layer used is polyimide and is formed by spin coating the precursor solution at a rate of 7800 rpm. The curing temperature of the polyimide is 350 占 폚, and the curing time is 1 hour. Further, the upper electrode used is Ag, the lower electrode is ITO, and the flexible substrate is PET.

In FIG. 8, the flexible MEMSistor measures electrical characteristics in a flat and normal state before being bent. Further, the lower electrode is used as a cathode, and the upper electrode is used as an anode. Therefore, a voltage difference is applied to the positive electrode and the negative electrode, and a current flowing through the resistance variable layer is measured.

First, the voltage is raised from 0V to 2.5V. It is assumed that there is no formation of a conductive channel or conductive filament due to the application of any electrical signal in the resistance variable layer when the voltage rises. The voltage rise from the first OV to 2.5V is indicated by path (1). A low current of 10-8 to 10-7 scale flows in the path (1). This indicates that the memristor is in a high resistance state.

When the voltage exceeds 2.5 V, the current rapidly increases to 10 -1 scale. That is, the memristor enters a low resistance state. It is understood that the Ag + ions in the anode flow along the interface between the aluminum oxide nanoparticles and the polyimide layer and form a cation transport channel such as a conductive filament through a reduction reaction or the like. The formed cation transport channel maintains the low resistance state of the memristor. That is, even if the voltage is reduced to 0V as in the path (2), it can be seen that the memristor of the present invention maintains a low resistance state. In particular, the maximum current ratio between the two resistance states at 1 V appears at 106 scales.

Subsequently, the voltage is decreased from 0 V to -5 V along the path (3). In this path, a low resistance state from OV to -4.2V is maintained, and a high resistance state is entered from around -4.2V. Also, as shown in the path (4), it can be seen that the high resistance state is maintained even when the voltage is raised from -5V to 0V. The change from the low resistance state to the high resistance state at about -4.2 V is interpreted as the disappearance of the cation moving channel such as the conductive filament. That is, the metallic path or the metal ionic path formed at the interface between the aluminum oxide nanoparticles and the polyimide layer, which are insulating nanoparticles, is oxidized by the application of a negative voltage or the metal ion Ag + moves to the anode. Whereby the movement of the charge from the anode to the cathode or the migration of the metal ions is substantially blocked and changed to a high resistance state.

After entering the high resistance state, the voltage rises along path 5 and path 6 from 0V to 3V. As shown in path (5), the high resistance state is maintained at about 1.4 V and the high resistance state at about 1.4 V is changed to the low resistance state. It can be seen that the MEMS of the present invention maintains a low resistance state even when the voltage decreases to 0V along the path 6 after entering the low resistance state.

It can also be seen that in the course of path (3) to path (6), the current ratio between both states at 1 V is 104 scales. As a result, it can be seen that the memristor of the present invention can be used as a resistance change memory.

FIG. 9 is a graph showing other voltage-current characteristics of a MEMSistor formed through the processes of FIGS. 2 to 7 according to a preferred embodiment of the present invention.

Referring to FIG. 9, the fabrication and material of the memristor are the same as those described in FIG. 9 above. However, in FIG. 9, an external force is applied to a flexible memristor to measure electrical characteristics in a bent state. Through the application of the external force, the memristor is bent in a curved shape with a radius of curvature of 10 mm.

In FIG. 9, the current characteristics in the path (1) are slightly different from those in FIG. This is understood to be a phenomenon occurring in the density difference of the structure on both surfaces of the resistance variable layer formed of the aluminum oxide nanoparticles and the polyimide layer according to the warp. That is, the interface between the aluminum oxide nanoparticles and the polyimide layer may have a larger gap than that of FIG. 8 due to the warping phenomenon at the time of forming the first cation transport channel. It is understood that the current can be increased with the increase of the voltage.

However, after entering the low resistance state through the path (1), the paths (2) to (6) show the same behavior as in FIG.

This indicates that the operating state of the memristor according to the present invention is substantially the same as the operating state before the bending of the MEMS according to the present invention, and thus the bending phenomenon of the substrate can be normally used. .

Therefore, in the present invention, nanoparticles having an insulating property and an organic material layer having an insulating property are used as resistance change layers. A cation transport channel is formed through the interface between the nanoparticles and the organic layer to function as a resistance change memory. Since the nanoparticles and the organic layer have chemical stability, the same operating characteristics can be maintained even if they are used for a long time.

Further, the resistance-variable layer has a characteristic of flexibility because it includes nanoparticles and an organic material layer. As shown in this embodiment, the MEMS maintains substantially the same electrical characteristics even when an external force is applied to the memristor to warp. This can be utilized as a memory device having flexibility characteristics.

100: Flexible substrate 110: Lower electrode
120: resistance variable layer 121: insulating nanoparticle
123: insulating organic layer 130: upper electrode

Claims (10)

A flexible substrate;
A lower electrode formed on the flexible substrate;
A resistance change layer formed on the lower electrode and performing a resistance change according to the formation of a cation movement channel formed at an interface between the insulating nanoparticle formed by thermal oxidation of the oxidation film and the insulating organic layer surrounding the insulating nanoparticle, ; And
And an upper electrode formed on the resistance variable layer. The flexible memristor according to claim 1, wherein the insulating nanoparticles are dispersed in the insulating organic layer. The flexible mem- bler according to claim 1, wherein a part of the surface of the insulating nanoparticle is in direct contact with the upper electrode or the lower electrode. The flexible memristor according to claim 1, wherein the insulating organic layer comprises polyimide, polymethyl methacrylate or polystyrene. The organic electroluminescent device according to claim 1, wherein the upper electrode is made of metal, and metal ions are moved through the upper electrode to an interface between the insulating nanoparticle and the insulating organic layer to form the cation moving channel Memristor. The flexible mem- bler according to claim 5, wherein the upper electrode is Ag, Al, Ni, Cu or an alloy thereof. Forming an oxidation film on the base substrate;
Oxidizing the oxidation film to form insulating nanoparticles;
Forming a resistance variable layer by forming an insulating organic layer filling a space between the insulating nanoparticles;
Releasing the resistance-variable layer from the oxidation film and disposing the resistance-variable layer on the lower electrode on the flexible substrate; And
And forming an upper electrode on the disposed resistance-variable layer. The method according to claim 7, wherein the formation of the insulating organic layer is performed by a spin coating method, a spray coating method, or a vacuum thermal evaporation method. 8. The method according to claim 7, wherein a space between the insulating nanoparticles is embedded through the formation of the insulating organic layer, and a part of the surface of the insulating nanoparticles is exposed to the outside. The method of manufacturing a flexible memristor according to claim 7, wherein the separation of the resistance-variable layer from the oxidation film is performed by peeling using a plastic tape.

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