KR20130022972A - Non-volatile organic memory device and method for fabricating the same - Google Patents

Abstract

PURPOSE: A nonvolatile organic memory device and a manufacturing method thereof are provided to implement a high data retention property, high reproducibility, and a high stability by forming organic and inorganic complex layers with a bistable property using a quantum dot and polymer including a I-III-VI group compound semiconductor. CONSTITUTION: A first electrode(210) is located on a substrate(200). An organic and inorganic complex layer(220) is formed on the first electrode. The organic and inorganic complex layer is composed of a polymer layer(224) including a quantum dot(222) with a I-III-VI group compound semiconductor. A second electrode(230) is located on the organic and inorganic complex layer. The first electrode and the second electrode transmit currents to the organic and inorganic complex layer by a voltage applied from the outside.

Description

Non-volatile organic memory device and method for manufacturing the same

The present invention relates to a memory device and a method of manufacturing the same, and more particularly to a nonvolatile organic memory device and a method of manufacturing the same.

The organic memory device is a memory device that expresses an on / off state through bistable stability using organic materials. When the voltage is changed, the organic memory device generates a relatively high current and a relatively low current at the same voltage.

In the case of an organic memory device, it is possible to manufacture a volatile or nonvolatile memory through the control of organic materials and device structure. A recent research mainly focuses on the development of a nonvolatile memory device that stores information even when power is removed. have.

The organic memory device has a structure in which a resistive organic layer 120 having bistable exists between the lower electrode 110 and the upper electrode 130 positioned on the substrate 100 as shown in FIG. It is possible to retain information, which is very advantageous in miniaturization and integration compared to other next generation nonvolatile memory devices.

However, despite the advantages that the conventional memory device using only a single organic material is very simple and a variety of materials can be used, the impurity trap itself used for charge trapping nanoparticles that naturally diffuse from the metal electrode during the device fabrication process Since the concentration and distribution of such impurity traps are very difficult to be artificially controlled externally, there is a problem in that different devices exhibit different electrical and memory characteristics. Therefore, the reproducibility of the device is extremely low, which makes it an obstacle to commercialization.

On the other hand, the memory device using the semiconductor nanoparticles can obtain a relatively high reproducibility compared to the case of using only organic material, but since the semiconductor nanoparticles themselves have a high insulating property, the memory device using the same also requires a high driving voltage. In addition, one of the issues that cannot be overlooked in the development of electronic products or electronic devices is environmental problems, and the materials used as semiconductor nanoparticles in the past include heavy metals such as cadmium (Cd) or lead (Pb). However, these substances are regulated by the Restriction of Hazardous Substances Directive (RoHS) in the EU, and China has a similar scheme (China RoHS).

Accordingly, there is a need for development of environment-friendly nonvolatile memory devices while securing excellent data retention and reproducibility.

Korean Patent Registration No. 10-0913903 Korean Patent Registration No. 10-0904898

The technical problem to be solved by the present invention is to provide an environmentally friendly nonvolatile organic memory device having excellent memory characteristics and a method of manufacturing the same.

In order to achieve the above technical problem, an aspect of the present invention provides a nonvolatile organic memory device.

The nonvolatile organic memory device may include a substrate on which a first electrode is disposed; A polymer layer disposed on the first electrode and having a quantum dot containing an I-III-VI compound semiconductor dispersed therein; And a second electrode on the polymer layer.

Another aspect of the present invention to achieve the above technical problem provides a method of manufacturing a nonvolatile organic memory device.

The method of manufacturing the nonvolatile organic memory device may include preparing a substrate on which a first electrode is disposed; Coating a polymer solution in which a quantum dot containing a group I-III-VI compound semiconductor is dispersed on the first electrode; Heat-treating the coated polymer solution to remove the solvent; And forming a second electrode on the polymer layer from which the solvent is removed.

The nonvolatile organic memory device according to the present invention may form an organic-inorganic composite layer having bistable characteristics by using a quantum dot and a polymer containing an I-III-VI compound semiconductor. As a result, excellent data retention, reproducibility, and stability of the device can be realized and environmental friendliness can be ensured.

In addition, since the organic-inorganic composite layer is manufactured by spin coating a polymer solution in which quantum dots are dispersed, the device can be manufactured at a lower cost than conventional memory devices using inorganic semiconductors or metal oxides, and is suitable for large-scaled printing. And, there is an advantage that can be produced a flexible (flexible) device based on the flexibility of the organic material.

However, the effects of the present invention are not limited to the above-mentioned effects, and other effects not mentioned will be clearly understood by those skilled in the art from the following description.

1 is a cross-sectional view illustrating a conventional organic memory device having an organic material layer as a resistance change layer.
2 is a perspective view illustrating a nonvolatile organic memory device according to an embodiment of the present invention.
3 to 5 are partial cross-sectional views illustrating a method of manufacturing a nonvolatile organic memory device according to an embodiment of the present invention.
6 is a graph showing current-voltage characteristics of the memory device manufactured in Preparation Example 3;
7 is a graph showing current-voltage characteristics of the memory device manufactured in Preparation Example 4. FIG.
8 is a graph illustrating current-voltage characteristics of the memory device manufactured in Comparative Example 1. FIG.
9 is a graph showing switching characteristics versus current-time of the memory device manufactured in Preparation Example 3;
FIG. 10 is a graph showing the data holding force with respect to the current-cycle of the memory device manufactured in Preparation Example 3. FIG.
FIG. 11 is a graph showing the data holding force with respect to the current-cycle of the memory device manufactured in Preparation Example 4. FIG.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described herein but may be embodied in other forms and should be understood to include all equivalents and substitutes included in the spirit and scope of the present invention. In the drawings, the thicknesses of the layers and regions may be exaggerated or omitted for the sake of clarity. Like reference numerals designate like elements throughout the specification. In addition, in the following description of the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

2 is a perspective view illustrating a nonvolatile organic memory device according to an embodiment of the present invention.

Referring to FIG. 2, the nonvolatile organic memory device according to the present embodiment may include a substrate 200 on which a first electrode 210 is disposed; An organic-inorganic composite layer (220) positioned on the first electrode (210); And a second electrode 230 positioned on the organic / inorganic composite layer 220.

The substrate 200 may be an inorganic substrate, an organic substrate, or a substrate having a structure in which two or more of them are stacked in the same or different types. For example, the inorganic substrate may be formed of at least one selected from Si, GaAs, InP, Al ₂ O ₃ , SiC, glass, and quartz, and the organic substrate is polyethersulfone (PES), polyethylene terephthalate (polyethylene terephthalate (PET), polystyrene (PS), polyimide (PI), polyvinyl chloride (PVC), polyvinylphenol (PVP) and polyethylene (PE) It can be made of at least one. In particular, when the flexible organic substrate is used as the substrate 200, flexibility may be provided to the device, and the present invention may be used as a storage device for portable electronic devices having flexibility.

The first electrode 210 and the second electrode 230 serve to transfer current to the organic-inorganic composite layer 220 by a voltage applied from the outside. The electrodes 210 and 230 are not particularly limited as long as they have an electrically conductive material. The electrodes 210 and 230 may be formed of at least one of a metal, a metal oxide, a carbon allotrope, and a conductive polymer, or may have a multilayer structure. For example, the material of the electrodes 210 and 230 may be Al, Au, Cu, Pt, Ag, W, Ni, Zn, Ti, Zr, Hf, Cd, Pd, or any two or more of these alloys. It may include, or at least any one of Al, Ga, In, F and Ag may include a doped ZnO, or may include at least one of carbon nanotubes, graphene and graphite.

As illustrated in FIG. 2, the first electrode 210 and the second electrode 230 may be patterned in a line shape, and the first electrode 210 and the second electrode in a line shape ( 230 may be formed to cross each other, specifically, the first electrode 210 and the second electrode 230 may be formed to have an angle of 90 °. In this case, the integration degree of the device can be improved, so that the peripheral circuit can be simplified.

The organic-inorganic composite layer 220 positioned between the first electrode 210 and the second electrode 230 refers to an organic material layer in which inorganic nanoparticles are dispersed. Specifically, the polymer layer 224 in which the quantum dots 222 containing the I-III-VI compound semiconductor are dispersed.

The quantum dots 222 may be nanoparticles composed of group I-III-VI compound semiconductors alone, or nanoparticles having a core / shell structure having a group I-III-VI compound semiconductor as a core and a group II-VI compound semiconductor as a shell. Can be.

The group I-III-VI compound semiconductor may be preferably Cu (In _x Ga _{1- x} ) (S _y Se _{1 -y} ) ₂ , wherein x and y are each 0 to 1, and wherein The Group-VI compound semiconductor may be Zn (S _p Se _q Te _r ), wherein p, q, and r are each 0 to 1 and p + q + r = 1. Here, the subscripts indicated on the elements represent the molar ratios between the elements constituting the compound semiconductor.

The polymer layer 224 functions as a matrix in which the quantum dots 222 are dispersed and facilitates capturing and releasing charges by the quantum dots 222 according to application of a write voltage and an erase voltage. Can serve as a layer. The polymer layer 224 may preferably include a polyvinylcarbazole-based polymer.

The operating mechanism of the memory device according to the present embodiment can be schematically described as follows. When an electric field (write voltage) is applied from the outside through the first electrode 210 and the second electrode 230, the quantum dot 222 included in the polymer layer 224 captures and stores a charge and is captured. The electric charge creates a local internal electric field. This local internal electric field changes the potential potential in the device and increases the conductivity in the polymer layer 224 (low resistance state, on state). On the other hand, when an erase voltage is applied, charges trapped in the quantum dots 222 are released to the polymer layer 224, thereby reducing the conductivity of the polymer layer 224 (high resistance state, off state). That is, the device may be classified into a high state and a low state of current flow according to the magnitude of the electrical conductivity, and the memory state may be determined by comparing bistable current characteristics having different magnitudes of conductivity.

At this time, when the quantum dot 222 is a nanoparticle composed of the I-III-VI compound semiconductor alone, the molecular orbital function of the polymer constituting the polymer layer 224 is the valence band or conduction band of the quantum dot 222. It is speculated that an energy barrier can be formed in relation to the level so that charge can be trapped in the quantum dot 222. In addition, when the quantum dot 222 is a nanoparticle having a core / shell structure in which the I-III-VI compound semiconductor is the core and the II-VI compound semiconductor is the shell, the material constituting the shell forms an energy barrier. It is speculated that charge can be trapped in the core.

3 to 5 are partial cross-sectional views illustrating a method of manufacturing a nonvolatile organic memory device according to an embodiment of the present invention.

Referring to FIG. 3, first, a substrate 200 on which the first electrode 210 is disposed is prepared. The first electrode 210 may be appropriately selected from various known methods. For example, the metal electrode may be formed by a sterling method, a thermal deposition method, an electron beam deposition method, a chemical deposition method, or a method of applying an electrode forming paste containing a metal and then performing a heat treatment. On the other hand, when forming the line patterned electrode may be performed by performing an etching process after the deposition of the metal thin film, or a method of depositing a metal using a patterned mask.

Referring to FIG. 4, a polymer solution in which a quantum dot 222 containing a group I-III-VI compound semiconductor is dispersed is coated on a first electrode 210 positioned on the substrate 200. Coating of the polymer solution may be carried out through a solution process, preferably by a spin coating method. The polymer solution may be prepared by, for example, dispersing a quantum dot and a polymer in an organic solvent such as toluene.

Subsequently, the coated polymer solution is heat-treated to remove the solvent, thereby forming the polymer layer 224 having the quantum dots 222 dispersed therein. The heat treatment temperature may be appropriately selected in consideration of the boiling point of the organic solvent used and the glass transition temperature of the polymer. For example, when the solvent is toluene and the polymer is polyvinylcarbazole, the heat treatment temperature may be heat-treated at 90 to 130 ° C. have.

Referring to FIG. 5, the second electrode 230 is formed on the polymer layer 224 from which the solvent is removed by using a method similar to that of forming the first electrode 210. In this case, the second electrode 230 may be patterned in a line shape, and may be formed to cross the first electrode 210.

As described above, in the case of the organic memory device according to the present invention, since the organic-inorganic composite layer 220 exhibiting bistable characteristics can be formed through a solution process such as spin coating, the process is very simple, and the device itself has two terminals. The device's resistive form makes the structure simpler than a three-terminal device like a transistor. Instead of diffusion of metal nanoparticles from the metal electrode, which is difficult to artificially manipulate, nanoparticles can be deposited to be uniformly distributed in the device by controlling the weight ratio and using nanoparticles that can be distributed at a constant density. The distributed nanoparticles are used as charge trapping regions, and thus have a relatively high reproducibility compared to previous devices.

In particular, by using polyvinylcarbazole (PVK) having high chemical and electrochemical stability as a polymer and using group I-III-VI compound semiconductor quantum dots represented by CIS system as environmentally friendly nanoparticles, While manufacturing a nonvolatile memory device having excellent reproducibility and stability, there is an advantage that it is possible to minimize the environmental pollution problems occurring when the device is driven and discarded.

Hereinafter, preferred experimental examples are presented to help understand the present invention. However, the following experimental examples are only for helping understanding of the present invention, and the present invention is not limited to the following experimental examples.

Quantum dot  Produce

<Manufacture example 1>

8 ml of octadecene (ODE), 0.1 mmol of indium acetate and 0.3 mmol of miristic acid were mixed in a 25 ml three-necked flask, and the mixed solution was treated at 110 ° C. for 2 hours to obtain gas. Was removed. At 250 ° C., a Cu-thiol mother liquor synthesized from 0.3 mmol CuI and 3 ml dodecanethiol was then added to the solution. Subsequently, the mixed solution was heated at 200-210 ° C. for 2 hours to prepare CuInS ₂ (CIS) quantum dots.

<Manufacture example 2>

After preparing the CIS quantum dots through Preparation Example 1, the solution containing the CIS quantum dots was cooled to room temperature. Then, 0.5 mmol zinc acetate was added, heated to 230 ° C., and reacted at 230 ° C. for 1 and a half hours to prepare CIS / ZnS quantum dots having a core / shell structure.

Fabrication of Memory Devices

<Manufacture example 3>

1) The ITO-patterned glass substrate was ultrasonically cleaned with acetone and methanol to remove organic substances and foreign substances present on the surface of the substrate. In addition, the substrate was washed with deionized water in each step and the substrate was completely dried using nitrogen gas.

2) 50 mg of poly ( N -vinylcarbazole) (PVK) was mixed with 5 ml of toluene to prepare a polymer solution, and then 2 mg of CIS prepared in Preparation Example 1 was added thereto. The solution was stirred for at least 1 hour with an ultrasonic stirrer to ensure sufficient dispersion.

3) The solution prepared in 2) was spin-coated on the ITO-patterned glass substrate prepared in 1) at 3000 rpm to form a PVK polymer layer including CIS quantum dots.

4) After forming the polymer layer, it was heat-treated at 90 ~ 130 ℃ to remove the toluene solvent.

5) Subsequently, an Al electrode was formed on the polymer layer by thermal evaporation.

&Lt; Preparation Example 4 &

1) The ITO-patterned polyethylene terephthalate (PET) substrate was ultrasonically cleaned with acetone and methanol to remove organic substances and foreign substances present on the surface of the substrate. In addition, the substrate was washed with deionized water in each step and the substrate was completely dried using nitrogen gas.

2) 50 mg of poly ( N -vinylcarbazole) (PVK) was mixed with 5 ml of toluene to prepare a polymer solution, and 2 mg of CIS / ZnS prepared in Preparation Example 2 was added thereto. The solution was stirred for at least 1 hour with an ultrasonic stirrer to ensure sufficient dispersion.

3) The solution prepared in 2) was spin-coated on the ITO-patterned PET substrate prepared in 1) to form a PVK polymer layer including CIS / ZnS quantum dots. Spin coating was performed for 1 second at 500 rpm and 25 seconds at 2500 rpm, and the acceleration time was 1 second at each step. The deceleration process was performed for 1 second at 500 rpm and then stopped.

4) After forming the polymer layer, it was heat-treated at 90 ~ 130 ℃ to remove the toluene solvent.

5) Subsequently, an Al electrode was formed on the polymer layer by thermal evaporation.

&Lt; Comparative Example 1 &

A memory device was manufactured by the same method as in Preparation Example 3, except that the PVK polymer layer including no quantum dots was used.

6 and 7 are graphs showing current-voltage characteristics of the memory devices fabricated in Preparation Example 3 and Preparation Example 4, respectively, and FIG. 8 is a graph showing current-voltage characteristics of the memory devices fabricated in Comparative Example 1. FIG.

6 to 8, the memory devices including the PVK layer in which the CIS or CIS / ZnS quantum dots are dispersed (manufacture examples 3 and 4) include the memory device (comparative example 1) including only pure PVK. It can be seen that the on / off current ratio is much higher and it clearly shows bistable characteristics. Therefore, it can be seen that the high conductivity change of the organic memory device according to the present invention is due to the quantum dots introduced into the polymer layer.

6 and 7, the organic memory device according to the present invention exhibits bistable characteristics in the voltage range of about -4V to 4V. In bistable characteristic, high resistance state is turned off and low resistance state is turned on to save data.

In the case of FIG. 6, the initial current value 0.01A in the on state drops rapidly when the erase voltage of about -2V is applied, and is kept off, and when the positive voltage is applied, it is switched back to the on state at about 3V. .

In the case of FIG. 7, when the voltage of 1V is applied to the device, the current ratio of the on state and the off state is about 3.9 × 10 ^{4. When the} external voltage is not applied, the initial state is off until the voltage is less than 3.1V. Keep off. At a write voltage of about 3.1V, the current increases to about 10 ^-3 A and turns on, and the on state remains until a voltage of -3.5V is applied. The device is turned off again when a clear voltage of -3.5V is applied.

9 is a graph showing switching characteristics versus current-time of the memory device manufactured in Preparation Example 3; The writing current value was 0.00636 A on average and the erasing current value was 0.00745 A on average.

10 and 11 are graphs showing the data holding force with respect to the current-cycle of the memory devices manufactured in Preparation Example 3 and Preparation Example 4, respectively.

As shown in FIGS. 10 and 11, in the memory device according to the present invention, current values in the on state and the off state do not change significantly even when at least 10000 to 100,000 times of stress are applied, and it is confirmed that the data retention force can be maintained. Can be.

As mentioned above, although the preferred embodiment of this invention was described in detail, this invention is not limited to the said embodiment, A various deformation | transformation and the said by those of ordinary skill in the art within the technical idea and the scope of the present invention. Changes are possible.

200: substrate 210: first electrode
220: organic-inorganic composite layer 222: quantum dot
224: polymer layer 230: second electrode

Claims (10)

A substrate on which the first electrode is disposed;
A polymer layer disposed on the first electrode and having a quantum dot containing an I-III-VI compound semiconductor dispersed therein; And
A nonvolatile organic memory device comprising a second electrode on the polymer layer. The method of claim 1,
The group I-III-VI compound semiconductor is Cu (In _x Ga _{1- x} ) (S _y Se _{1 -y} ) ₂ (where x and y are each 0 to 1). The method of claim 1,
The quantum dot is a non-volatile organic memory device having a core-shell structure consisting of a group I-III-VI compound semiconductor core and a group II-VI compound semiconductor shell. The method of claim 3,
The group I-III-VI compound semiconductor is Cu (In _x Ga _{1- x} ) (S _y Se _{1 -y} ) ₂ , wherein x and y are each 0 to 1, and the group II-VI compound semiconductor Is Zn (S _p Se _q Te _r ), wherein p, q and r are each 0 to 1 and p + q + r = 1. The method of claim 1,
The polymer layer is a nonvolatile organic memory device comprising a polyvinylcarbazole-based polymer. The method of claim 1,
The polymer layer in which the quantum dot is dispersed is a nonvolatile organic memory device exhibiting bistable stability in the voltage range of -4V to 4V applied through the first electrode and the second electrode. Preparing a substrate on which the first electrode is disposed;
Coating a polymer solution in which a quantum dot containing a group I-III-VI compound semiconductor is dispersed on the first electrode;
Heat-treating the coated polymer solution to remove the solvent; And
Forming a second electrode on the polymer layer from which the solvent is removed. The method of claim 7, wherein
The quantum dot has a core-shell structure consisting of a group I-III-VI compound semiconductor core and a group II-VI compound semiconductor shell. The method of claim 7, wherein
The polymer solution is a non-volatile organic memory device manufacturing method comprising a polyvinylcarbazole-based polymer. The method of claim 7, wherein
The coating of the polymer solution is performed by spin coating.

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