KR101055406B1 - Method for manufacturing resistance change memory device and resistance change memory device manufactured accordingly - Google Patents

Abstract

There is provided a method of manufacturing a resistance change memory device and a resistance change memory device manufactured thereby.

The method of manufacturing a resistance change memory device according to the present invention comprises the steps of: gelling a solution in a sol state in which a transition metal precursor is dispersed; Applying the gelled transition metal precursor onto a lower electrode; Heat treating the applied transition metal precursor to prepare a transition metal oxide thin film; And forming an upper electrode on the titanium oxide thin film, and can economically manufacture a device having excellent electrical characteristics such as low driving voltage, fast switching speed, high ON / OFF ratio, and excellent electrical stability. To be.

Description

A method for manufacturing resistance random access memory, and resistance random access memory manufactured by using the same}

The present invention relates to a method for manufacturing a resistance change memory device and a resistance change memory device manufactured according to the present invention, and more particularly, exhibits excellent electrical characteristics such as low driving voltage, fast switching speed, high ON / OFF ratio and excellent electrical stability. The present invention relates to a resistance change memory device manufacturing method capable of economically manufacturing a resistance change memory device, and a resistance change memory device manufactured accordingly.

Recently, nonvolatile memory devices such as charge trapping flash memory, phase change memory, ferroelectric memory, and resistance change memory have been attracting much attention due to the widespread use of mobile electronics.

In particular, binary resistive memory devices with excellent device performance (e.g. fast switching speeds and high ON / OFF ratios of more than 10 ³ ) and simple device structures have attracted attention since the resistance change characteristics of oxide insulators were first announced in the 1960s. It is known as the next generation nonvolatile memory device. However, since the conventional two-component resistance change memory device is manufactured by a vacuum deposition process using expensive vacuum equipment, there is a problem that it is difficult to manufacture a device having a low manufacturing cost (that is, excellent economy) and a large area. Increasing process time efficiency also has its limitations.

Instead of the conventional vacuum deposition method, the perovskite structure such as La1-xCaxMnO ₃ formed by the sol-gel solution process and the doped perovskite structure such as SrZrO3 to which molybdenum (Mo) is added exhibit resistance characteristics. This is because such perovskite structures can effectively induce lattice defects that affect oxygen vacancy and electrical properties. However, the perovskite structure having such various cations has a complicated chemical composition compared with binary metal transition metal oxides such as titanium oxide, and thus there is a problem that it is relatively difficult to improve and change device performance by adjusting the composition ratio. . That is, since the ratio of the chemical composition also has an important effect on the resistance change characteristics, a resistance change material that is easier to control the chemical composition in a process such as a solution process needs to be used as the active layer of the resistance change memory device. Furthermore, nanocomposites composed of semiconductor polymers, conductive polymers or conductive components (for example, metal nanoparticles, quantum dots or carbon nanotubes), and various polymer-based materials such as insulator polymers may be used as active layers of resistance change memory devices. Can be used. In view of device performance and electrical stability, the polymer materials are somewhat disadvantageous compared to conventional inorganic oxide materials, but the deposition of the active layer through simple spin-coating is a low cost, simplified fabrication and large area for fabricating resistive memory devices. Has an important technical significance in that it can be effectively achieved. However, at present, no technology discloses a method of manufacturing a resistance change memory device capable of simultaneously achieving device economics and electrical stability and achieving process economics, and the present invention thus provides a relatively simple solution such as spin-coating. By fabricating a resistive change memory device composed of two-component transition metal oxides through the process, two problems of the prior art, namely, improved device performance and improved economics of the manufacturing process have been attempted.

Therefore, the first problem to be solved by the present invention is to provide a resistance change memory device manufacturing method that can be produced in an economical manner with a resistance change memory device having improved device performance compared to the prior art.

The second problem to be solved by the present invention is to provide a resistance change memory device having improved device performance compared to the prior art.

In order to solve the first problem, the present invention comprises the steps of gelling (gelation) the solution of the sol state in which the transition metal precursor is dispersed; Applying the gelled transition metal precursor onto a lower electrode; Heat treating the applied transition metal precursor to prepare a transition metal oxide thin film; And forming an upper electrode on the transition metal oxide thin film. The transition metal precursor may be titanium alkoxide or niobium alkoxide. In one embodiment of the present invention, the titanium alkoxide is titanium isopropoxide, and the dispersion solution may be isopropyl alcohol. In another embodiment of the present invention, the niobium alkoxide may be niobium ethoxide, and the dispersion solution may be isopropyl alcohol.

In addition, the gelation is carried out by adding an acid to the sol state solution, the heat treatment step is carried out in an inert gas atmosphere; And a second heat treatment step performed under an oxygen atmosphere. In addition, the transition metal oxide thin film may include oxygen vacancy.

In order to solve the second problem, the present invention provides a resistance change memory device manufactured according to the manufacturing method.

The method of manufacturing a resistance change memory device according to the present invention can effectively manufacture a resistance change memory device including a two-component transition metal oxide using an economical solution-based sol-gel method. That is, the method of manufacturing a resistance change memory device according to the present invention enables to manufacture a device having excellent electrical characteristics such as low driving voltage, fast switching speed, high ON / OFF ratio and excellent electrical stability in an economical manner.

The present invention gels the transition metal precursor dispersion solution according to the sol-gel process, as described above, and applies it onto a substrate by a process such as spin-coating. Thereafter, the transition metal precursor applied on the substrate is heat-treated to deposit the transition metal oxide thin film on the substrate on the substrate. In particular, the solution process, such as the sol-gel process in the present invention not only enables the large-area device manufacturing, but also generates a process economic effect that is very economical compared to the vacuum deposition process and the like in the prior art. Furthermore, the present invention can manufacture a resistance change memory device having excellent electrical properties similar to that of the resistance change memory device manufactured according to the conventional vacuum deposition process as well as the above-described process economic effects, which is the following Experimental Example And it will be described in detail through the drawings.

In one embodiment of the present invention, the titania and niobium are used as the transition metal, but the present invention is not limited thereto, and any transition is possible as long as it can be converted into an oxide through a heat treatment process after gelation according to a sol-gel process. Metals may also be used, all of which are within the scope of the present invention. In addition, a transition metal alkoxide is used as the transition metal precursor. In one embodiment of the present invention, titanium isopropoxide and niobium ethoxide are used as the transition metal precursors. In addition, in order to induce the hydrolysis and condensation reaction of the transition metal alkoxide, an acid solution such as hydrochloric acid is added to the transition metal alkoxide, alcohol is used as a solution in which the transition metal precursor is dispersed, an embodiment of the present invention In this example, isopropyl alcohol was used as the solution.

The heat treatment process according to the present invention forms a transition metal oxide thin film on a substrate (lower electrode), in particular, the heat treatment process according to the present invention is carried out in two steps. In detail, the heat treatment process according to the present invention proceeds to a first heat treatment step performed under an inert gas atmosphere not supplied with oxygen and a second heat treatment step supplied with oxygen to form a transition metal oxide. In particular, the first heat treatment step of supplying an inert gas such as nitrogen in the present invention forms a condition that the transition metal precursor is not sufficiently oxidized, thereby forming a transition metal oxide thin film having oxygen vacancies therein. The oxygen vacancy formed in the thin film then acts as a dopant in the transition metal oxide thin film.

Through the following examples and experimental examples, the present invention will be described in more detail.

Example  One

Example  1-1

TiO ₂ thin film made from a titania precursor

In this example, titanium isopropoxide (TTIP, Aldrich, 97%) was used as a transition metal precursor, and 1 g of TTIP was dissolved in 10 g of isopropylalcohol (IPA 99.9%). Thereafter, 0.07 g of hydrochloric acid was dropped in drops, and the sol-gel process was performed while hydrolyzing the mixed solution. In other words, the sol-gel process in the present embodiment was carried out by hydrolysis and condensation reaction of titanium isopropoxide by adding an acid such as hydrochloric acid to the titanium isopropoxide solution as a transition metal precursor. The solution was then spin-coated at 4000 rpm on a surface of platinum (Pt) deposited silicon (SiO ₂ ). Thereafter, the thin film was heat treated for 2 hours under a nitrogen atmosphere of 450 ° C., and further heat treated for 4.5 hours under an oxygen atmosphere at the same temperature.

Example  1-2

Fabrication of resistance change memory device

A silicon substrate having a SiO ₂ layer having a thickness of about 100 nm was used as a substrate, and a lower electrode (platinum) was deposited after depositing a 20 nm thick Ti layer using DC-magnetron sputtering on the substrate. It was. Since TiO ₂ induced by the sol-gel method of Example 1-1 A thin film was formed on the silicon substrate on which platinum was deposited and heat treated. After the heat treatment, a 100 μm diameter upper electrode (silver) was deposited on the thin film.

1 is a schematic diagram illustrating a manufacturing step of a TiO ₂ thin film of Examples 1-1 and 1-2 and a resistance change memory device using the same.

Referring to FIG. 1, a method of manufacturing a resistance change memory device according to the present invention converts titanium isopropoxide, a transition metal precursor, into a Ti-O-Ti structure according to a sol-gel process involving hydrolysis and condensation reactions. Subsequently, it is spin-coated onto the substrate and then heat-treated in two steps to form a transition metal oxide thin film on the substrate.

Experimental Example  One

Heat weight  analysis

2 is a thermogravimetric analysis curve for the TiO ₂ thin film before and after the heat treatment according to Example 1-1.

Referring to FIG. 2, when the sol-gel process of the tania precursor is performed and then heat treated at 450 ° C., the titanium thin film is easily TiO ₂ with a mass reduction of 45% with thermal decay of the organic material. It can be seen that it is converted to a thin film. At this time, the total thickness of the TiO ₂ thin film (about 60.3 nm) is reduced to about 56.4% of the initial heat treatment thickness (about 107.1 nm).

Experimental Example  2

Surface analysis

In this experimental example, the surface shape and roughness of the TiO ₂ thin film heat-treated on the silicon substrate were measured in an tapping mode with an atomic force microscope (AFM) (SPA400, SEIKO).

3 is an AFM image of a TiO ₂ active layer formed according to an embodiment of the present invention, and FIG. 4 is (a) anatase TiO ₂ formed by a sol-gel process. Cross section HR-TEM image of the crystal. (b) TiO ₂ SAED pattern of thin crystal structure.

Referring to FIG. 3, the TiO ₂ It can be seen that the root-mean square (rms) surface roughness of the thin film is about 1 nm. Referring to FIG. 4, TiO ₂ according to the present invention. It can be seen that the thin film forms partial rutile crystals with anatase.

Experimental Example  3

Crystal Structure And Chemical Composition

TiO ₂ of Example 1-1 formed by the sol-gel method The crystal structure of the thin film was analyzed using X-ray diffraction (XRD) at room temperature. The analysis was performed in the 2θ range from 15 degrees to 60 degrees using copper Ka radiation (λ = 1.54 Hz, model: Bruker D8 Discover, Germany). In addition, the cross-sectional TEM (model: JEOL 300kV) was also used to investigate the crystal structure and internal structure of TiO _2. X-ray photoelectron spectroscopy (XPS, Sigma Probe) was used to determine the residual carbon and Ti ion. It was performed to determine the binding state.

Figure 5 (a) is a graph showing a _{graph, (b)) Ti 2p 1} /2 as measured by X- ray photoelectron spectroscopy and 2p _3/2 represents the binding energy of the XRD measurement results.

Referring to FIG. 5 (a), it can be seen that the XRD morphology of the anatase 101 peak was clearly observed in the TiO ₂ thin film grown by the sol-gel process. In addition, X-ray photoelectron spectroscopy (XPS) was used to determine the chemical composition of the thin film. Referring to FIG. 5 (b), the measured spectra may be decomposed into two spin-orbital components, which are Ti ⁴⁺ ( 458.9 eV) and was identified as Ti ^{3 +} (456.9eV). This causes unstable oxygen levels to generate oxygen vacancies in the TiO ₂ thin film, which acts as an n-type dopant to convert the insulator oxide into a semiconductor with electrical conductivity. Therefore, the heat treatment process for forming such oxygen vacancies (particularly, an initial heat treatment process performed in an inert gas atmosphere) plays a very important role in the present invention.

Furthermore, recent studies have reported that the applied electric field injects electrons into the conduction band of TiO ₂ and reduces it to unstable Ti ^{3 +} , which results in the TiO ₂ thin film of the present invention prepared by the sol-gel process. It can be developed into an effective active layer of the resistance change memory device.

Experimental Example  4

Device Electrical Characterization

As described above, the inventors of the present invention have fabricated a resistance change memory device based on the surprising features of the TiO ₂ thin film of Example 1-1, in particular, a silver (Ag) electrode having a diameter of about 100 μm to complete device fabrication. TiO ₂ as upper electrode Deposited on a thin film.

In order to investigate the resistance change of the device, a current-voltage (I-V) diagram was measured in the air using a semiconductor parameteric analyzer (SPA, Agilent 4155C). The semiconductor parametric analyzer (HP 4155A) and pulse generator (Agilent 81104A) were used to investigate the sustained voltages of high and low voltages. In addition, local current diagrams in nanoscales were measured in contact mode using a conductive tip using current sensing atomic force microscopy (CS-AFM, e-sweep, SEIKO).

6 shows (a) the current-voltage curve of sol-gel TiO ₂ , (b) cycling test and (c) retention test results, and (d) SET at 4V and at 1V. This is a graph of the measured currents with different pulse widths (100 ns, 1 μs, 10 μs and 100 μs) during the RESET procedure.

Initial in this experiment example While positive voltage was applied, the device showed a sharp charge increase at about 2.9V. This process, in which the compliance current is limited to 0.1mA, is called electroforming, which means that a conductive passage is formed inside the initial transition metal oxide layer.

As shown in Fig. 6 (a), the high current state ('ON' state) formed after the electroforming process is accompanied by a sudden current decrease at about 0.6V (V _RESET ) while the second voltage is applied (0 to 1.0V). Return to the low current state. When the applied voltage was increased again in the positive direction, the device in the low current state ('OFF' state) showed a sharp current increase at about 1.4V (V _SET ). This change is called the unipolar switching phenomenon, which is explained by the reversible formation and breakdown of the filament-shaped conductive passages in the oxide layer without the voltage applied to form the high and low current states dependent on polarity and direction. Can be. In addition, the ON / OFF ratio between high and low current states was measured at a high ON / OFF ratio of about 10 ⁵ levels.

As a comparative example, considering that V _RESET and V _SET of a device fabricated by conventional vacuum evaporation are generally 1V and 2V, respectively, the result shows that the resistance change memory device manufactured according to the present invention has a low voltage. It is driven with consumption and high ON / OFF ratio. Further, in order to investigate the electrical stability in the ON and OFF states, a repetitive inspection of a TiO ₂ device formed of a sol-gel was performed manually using a read voltage of 0.1 V (see FIG. 6 (b)). In this case, the resistance change memory device maintains a high ON / OFF ratio during repeated inspections and shows stable driving. In order to further demonstrate the stability of the resistance change property, the information retention capacity was measured by measuring the current of the device in the ON state for a long time (> 10 ⁴ s) in the air and is shown in FIG. 6 (c). Referring to FIG. 6C, no detectable change was observed in the resistance change memory device according to the present invention. In addition, two different current states (ON and OFF states) were observed through the voltage duration τ _p according to the pulses with pulses of 4V and 1V (see FIG. 6 (d)). Referring to FIG. 6 (d), the ON / OFF current ratio slightly increased while the voltage duration τ _p was increased from 100 ns to 100 μs. This reversible switching characteristic lasted for at least one year, which is shown in FIG. 7. Referring to FIG. 7, it can be seen that the switching characteristic is maintained for at least one year. Therefore, these results demonstrate that the resistance change memory device according to the present invention also has excellent electrical stability.

Experimental Example  5

TiO ₂ Thin film internal analysis

In order to confirm the reversible formation and collapse of the conductive passage in the form of filament inside the TiO ₂ thin film formed of the sol-gel, in this experimental example, the local current image was examined while the device was repeatedly driven.

8 is TiO ₂ Current sensing atomic force microscopy image inside the thin film.

Referring to FIG. 8, it is possible to observe the formation and collapse of conductive paths randomly distributed during electroforming, RESET, and SET processes. The results indicate that the current density between the top and bottom electrodes is locally concentrated but the conduction path of on and off during the switching process is not uniform.

Experimental Example  6

Electrode analysis

Recently, solid electrolytes sandwiched between silver (Ag) or copper (Cu) anodes and inert cathodes may cause resistance changes due to electrochemical oxidation and reduction reactions based on the high flow of silver (Ag) ions. In this experimental example, the resistance change phenomenon according to the composition change of the electrode was analyzed.

9 is a current-voltage curve of a sol-gel TiO ₂ device of a tungsten electrode used in place of a silver (Ag) electrode.

Referring to FIG. 9, it can be seen that the resistance change element employing the tungsten electrode exhibits an electrode-current pattern similar to that of the resistance change element employing the silver electrode. The results indicate that the silver (Ag) upper electrode itself does not significantly affect the resistance change phenomenon of the sol-gel based TiO ₂ thin film device.

Experimental Example  7

Transition Metal Analysis

In this experimental example, the method of manufacturing a resistance change memory device according to the present invention was also applicable to various transition metal oxides other than TiO ₂ . For this purpose, the transition metal was changed to niobium (Nb) instead of titania, and niobium ethoxide (Nb (OCH ₂ CH ₃ ) ₅ ) was used as a precursor. In this experimental example, a Nb ₂ O ₅ thin film was laminated on a substrate by sol-gel reaction of niobium ethoxide, which is a transition metal precursor, and then heat treated. Thereafter, a resistance change memory device was manufactured in the same manner as in Example 1-2.

10 is a current-voltage curve of a sol-gel niobium oxide based device.

Referring to FIG. 10, the sol-gel niobium oxide based device exhibits a reversible switching phenomenon after the electroforming process, and the electroforming process occurs with a limited current of 0.1 mA at about 2.6V. After the electroforming, the high current state ('ON' state) returned to the low current state again when the second voltage was applied at about 0.6V (from 0 to 1.0V). In addition, when both voltages were applied, the device in the low current state ('OFF' state device) showed a sharp current increase at about 1.6V to 2V (V _SET ). That is, when the Nb ₂ O ₅ thin film formed by the sol-gel method according to the present invention is used as the active layer of the resistance change memory device, the memory device has a V _RESET of about 0.6V, a V _SET of about 1.6V, and a large value of 10 ⁷ or more. It shows an ON / OFF ratio and high electrical stability, which also shows excellent electrical performance with the above-described TiO ₂ thin film memory device. Accordingly, it can be seen that the method of manufacturing a resistance change memory device according to the present invention is applicable to any transition metal, and is not limited to titania.

1 is a schematic diagram illustrating a manufacturing step of a TiO ₂ thin film of Examples 1-1 and 1-2 and a resistance change memory device using the same.

2 is a thermogravimetric analysis curve for the TiO ₂ thin film before and after the heat treatment according to Example 1-1.

3 is an AFM image of a TiO ₂ active layer formed according to an embodiment of the present invention.

4 shows (a) anatase TiO ₂ formed by the sol-gel process Cross section HR-TEM image of the crystal. (b) TiO ₂ SAED pattern of thin crystal structure.

Figure 5 (a) is a graph showing a _{graph, (b)) Ti 2p 1} /2 as measured by X- ray photoelectron spectroscopy and 2p _3/2 represents the binding energy of the XRD measurement results.

FIG. 6 shows the results of (a) current-voltage curve of sol-gel TiO ₂ , (b) repeated test, and (c) retention test, and (d) according to different pulses in the SET process at 4V and the RESET process at 1V. (100 ns, 1 μs, 10 μs and 100 μs) This is a graph of the measured current.

7 shows sol-gel based TiO ₂ one year after manufacture The current-voltage curve of the device.

FIG. 8 is a current sensing atomic force microscopy image inside a TiO ₂ thin film. FIG.

9 is a current-voltage curve of a sol-gel TiO ₂ device of a tungsten electrode used in place of a silver (Ag) electrode.

10 is a current-voltage curve of a sol-gel niobium oxide based device.

Claims (8)

Gelling the sol solution in which the transition metal precursor is dispersed; Applying the gelled transition metal precursor onto a lower electrode; Heat treating the applied transition metal precursor to prepare a transition metal oxide thin film; And Forming an upper electrode on the transition metal oxide thin film, wherein the heat treatment is performed in a first inert gas atmosphere; And a second heat treatment step performed under an oxygen atmosphere. The method of claim 1, And the transition metal precursor is titanium alkoxide or niobium alkoxide. 3. The method of claim 2, The titanium alkoxide is titanium isopropoxide, the solution of the sol state in which the titanium isopropoxide is dispersed isopropyl alcohol, characterized in that the manufacturing method of the memory device. 3. The method of claim 2, The niobium alkoxide is niobium ethoxide, and the solution of the sol state in which the niobium ethoxide is dispersed is isopropyl alcohol. The method of claim 1, Wherein the gelation is performed by adding acid to the sol state solution. delete The method of claim 1, The transition metal oxide thin film is a resistance change memory device manufacturing method characterized in that it comprises oxygen vacancy.  A resistance change memory device manufactured according to any one of claims 1 to 5 or 7.

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