KR102359393B1 - Filament-based device with low variation switching voltage implemented using leakage current characteristics in oxide double layers and manufacturing method thereof - Google Patents

Abstract

The present invention provides a filament-based element on which a lower electrode, a first metal oxide, a second metal oxide and an upper electrode are sequentially stacked. The filament-based element uses a hard-breakdown characteristic of the first metal oxide and a high leakage current characteristic of the second metal oxide to allow an end portion of a filament generated in the first metal oxide to play a role of applying an electric field to a local portion of a second metal oxide layer like a conductive tip so as to form a filament close to a single locally limited on the second metal oxide layer.

Description

Filament-based device with low variation switching voltage implemented using leakage current characteristics in oxide double layers and manufacturing method thereof

The present invention relates to a filament-based device having a low dispersion switching voltage realized as a leakage current characteristic in a double-layer oxide and a method for manufacturing the same.

Recently, due to the rapid increase in the amount of real-time processing information of electronic devices, the demand for high-performance and high-capacity memory is rapidly increasing. Dynamic random-access memory (DRAM) and flash memory, which are currently mainly used, have physical limitations in sensing the voltage difference generated by the amount of charge stored in the memory material. As an alternative to the conventional memory, non-volatile memory is being actively researched. Among them, resistive switching RAM (ReRam) has the potential as a high-density memory because it can be stacked in a vertical direction.

The resistance change memory uses the resistance change phenomenon of oxide, and basically has a structure including oxide, which is an insulator, between the upper and lower electrodes, and has a soft breakdown (soft breakdown) inside the insulator by external electrical stimulation such as voltage or current. breakdown) occurs, forming an electroforming phenomenon. A conductive path is formed by the forming process, and a low resistance state is generated by the expansion of the conductive path and a high resistance state is generated by the disappearance or degeneration of the conductive path. And this conductive pathway is also called a conducting filament.

In conventional oxide-based switching devices, random multifilaments are formed by movement of cations or oxygen vacancies, which is known to induce unstable switching. This unstable switching phenomenon (variability) deteriorates the stability and reliability of the device, and causes serious problems in the preservation and durability of device characteristics.

As a method for reducing the variability of such a switching element, there is a method of controlling the thickness of the filament formation. This is to increase the allowable current or pulse width during forming to increase the thickness of the conductive filament so that the resistance change occurs stably every cycle.

However, when the thickness of the filament is increased, the power consumption required inevitably increases. That is, the switching device has a problem in that it is difficult to solve both low-power driving and reliability at the same time.

On the other hand, as a method to solve the above problem, a method of producing a filament close to a single by applying an electric field locally using a thin (tens of nm) conductive tip has been proposed. However, this method is difficult to apply to the fabrication of large-scale (inch units) devices because the upper electrode is fabricated after the filament is fabricated by applying a voltage to the oxide with a conductive tip.

Therefore, as a device for use in a resistance variable memory, it is a switching device that can be driven with low power, has excellent reliability due to low volatility, and can be manufactured in large-scale units such as large-area and chip-level units. development is required.

Appl. Phys. Lett. 98, 192104 (2011) (2011.05.10.)

An object of the present invention is to provide a filament-based device having reliability and stability while being able to operate at low power by forming a locally restricted near-single conductive filament in a double-layer oxide.

In a filament-based device in which a lower electrode, a first metal oxide, a second metal oxide, and an upper electrode are sequentially stacked, a hard-breakdown characteristic of the first metal oxide and a high leakage current of the second metal oxide By using the property, the tip of the filament produced in the first metal oxide serves to apply an electric field to a localized portion of the second metal oxide layer, such as a conductive tip, thereby providing a single localized limited to the second metal oxide layer. It is possible to provide a filament-based device that forms a filament close to the.

As one embodiment, the present invention provides a lower electrode layer, a first metal oxide layer formed on the lower electrode layer, a second metal oxide layer formed on the first metal oxide layer, and an upper electrode layer formed on the second metal oxide layer. As a filament-based device comprising It is possible to provide a filament-based device in which μ) is 0.1 or less.

As one embodiment, in the present invention, the ratio of the current value of the filament generation state to the current value of the filament extinction state may be 1x10 ⁴ or more.

As an embodiment, in the present invention, the lower electrode layer may include at least one selected from the group consisting of Pt, Au, Ir, TiN, W, Ru, Al, Ta, and Ni.

As one embodiment, in the present invention, the upper electrode layer may include at least one selected from the group consisting of Au, Ir, Ti, Cu, Al, Ta, and Ni.

As one embodiment, in the present invention, the first metal oxide layer may include AlO _x (x is 1 to 2).

As an embodiment, in the present invention, the second metal oxide layer may include TiO _x (x is 1 to 2).

As one embodiment, in the present invention, the thickness of the first metal oxide layer may be 1 nm to 10 nm.

As an embodiment, in the present invention, the thickness of the second metal oxide layer may be 20 nm to 50 nm.

In addition, the present invention includes the steps of forming a lower electrode layer on a substrate, forming a first metal oxide layer on the lower electrode layer by an atomic layer deposition method using atomic layer deposition (ALD), the first Forming a second metal oxide layer by an atomic layer deposition method using an atomic layer deposition equipment on the metal oxide layer, and depositing and patterning an upper electrode layer on the second metal oxide layer, wherein the first metal The oxide layer forms an irreversible conductive path at a voltage of 1V or more, and the second metal oxide layer has a leakage current density of 1x10 ⁴ (A/m ² ) or more, measured at 0.1 V per 1 nm thickness. Method of manufacturing a filament-based device can provide

In addition, the present invention may provide a resistance change memory including the filament-based device according to the present invention.

In addition, the present invention includes a first forming step of generating a conductive filament by applying a negative voltage and a second forming step of generating a conductive filament by applying a positive voltage, set-switching and A method of driving a resistance variable memory in which reset-switching occurs at a negative voltage may be provided.

A filament-based device and a method for manufacturing the same according to the present invention have low fluctuations in current and set/reset voltage values in an on/off state, and can be driven with low power, durable This has an excellent effect.

1 is a device in which an Au/Ti upper electrode layer is deposited to a thickness of 50 μm on a single-layer filament-based device of TiO _x (a), and a conductive atomic force microscope (conductive atomic force microscope, on top of a single-layer filament-based device of TiO _x ) C-AFM) It is a graph showing the structure and resistance state change results of the device (b) using the tip and the device (c) based on a single-layer filament of AlO _x .
2 is a graph showing the result of measuring the resistance state change of the filament-based device according to the present invention.
3 is a diagram illustrating a mechanism in which a conductive filament is generated in a filament-based device according to the present invention.
4 is a graph showing the switching voltage (a) and the coefficient of variation value (b) of the filament-based device according to the present invention measured 50 times for the same device.

Since the present invention can have various changes and can have various embodiments, specific embodiments are illustrated in the drawings and will be described in detail in the detailed description.

However, this is not intended to limit the present invention to specific embodiments, and it should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present invention.

In the present invention, terms such as "comprises" or "have" are intended to designate that the features, numbers, steps, operations, components, parts, or combinations thereof described in the specification exist, but one or more other features It should be understood that this does not preclude the existence or addition of numbers, steps, operations, components, parts, or combinations thereof.

Accordingly, the configuration shown in the embodiment described in the present specification is merely the most preferred embodiment of the present invention and does not represent all the technical spirit of the present invention, so various equivalents that can be substituted for them at the time of the present application and variations.

A filament-based device including a lower electrode layer, a first metal oxide layer formed on the lower electrode layer, a second metal oxide layer formed on the first metal oxide layer, and an upper electrode layer formed on the second metal oxide layer As , a conductive filament is generated or destroyed by an external electrical stimulus, and the coefficient of variation (σ/μ) defined as the ratio of the standard deviation (σ) to the average value (μ) of the filament generation (set) voltage is A filament-based device of 0.1 or less is provided.

As the electrode material of the lower electrode layer, a material having a low ionization degree and inert property may be used. For example, as an electrode material of the lower electrode layer, at least one selected from the group consisting of Pt, Au, Ir, TiN, W, Ru, Al, Ta, and Ni may be used.

The lower electrode layer may be formed using sputtering, chemical vapor deposition (CVD), or atomic layer deposition (ALD).

The first metal oxide layer is formed on the lower electrode layer, and may be formed using a sputtering method, a chemical vapor deposition method, or an atomic layer deposition method.

In this case, the metal oxide of the first metal oxide layer may include a stoichiometric or non-stoichiometric transition metal, and a metal oxide having a hard-breakdown characteristic may be used.

Specifically, the metal oxide forming the first metal oxide layer may form an irreversible conductive path at a voltage of │1│V or more, for example, │1.5│V or more, │2│V or more, │2.5 It may have a hard-breakdown characteristic that forms an irreversible conductive path at voltages above |V or above |3|V.

For example, the metal oxide exhibiting the above characteristics may be AlO _x (where x may be 1 to 2). In addition to hard-breakdown characteristics, AlO _x has a low reset current and a high bandgap of 8.9 eV, so it can be used for very large-scale memory devices. In addition, AlO _x serves as a buffer layer of the filament-based device, which can help improve the uniformity of the device when stacked with other oxides.

In this case, the thickness of the first metal oxide layer may be 1 nm to 10 nm, for example, 2 nm to 9 nm, 3 nm to 8 nm, 4 nm to 8 nm, 5 nm to 8 nm, 4 nm to 7 nm, or 4 nm to 6 nm. When the thickness is as described above, uniform switching can be realized without oversupply of voltage by lowering the forming voltage, and variations in current and voltage can be reduced during set or reset by locally generating a thin filament.

The second metal oxide layer is formed on the first metal oxide layer, and may be formed using a sputtering method, a chemical vapor deposition method, or an atomic layer deposition method.

In this case, the metal oxide of the second metal oxide layer may include a stoichiometric or non-stoichiometric transition metal, and a metal oxide having a high leakage current characteristic may be used.

Specifically, the metal oxide forming the second metal oxide layer may have a leakage current density measured at 0.1 V per 1 nm thickness of 1x10 ⁴ (A/m ² ) or more, for example, 1x10 ⁴ to 1x10 ⁶ ( A/m ² ) or 1x10 ⁴ to 1x10 ⁵ (A/m ² ).

For example, the metal oxide exhibiting the above characteristics may be TiO _x (x is 1 to 2).

In this case, the thickness of the second metal oxide layer may be 20 nm to 50 nm, for example, 20 nm to 40 nm, 30 nm to 50 nm, 25 nm to 40 nm, 30 nm to 45 nm, 30 nm to 40 nm or 33 nm to 37 nm. Although the forming voltage is mainly proportional to the thickness of the oxide layer, the thickness of the oxide layer that is too thin may cause defects in the stability and reliability of the device. Therefore, by having the thickness as described above, uniform switching can be implemented without oversupply of voltage, and by generating a thin filament locally, it is possible to reduce the variability of current and voltage during set or reset.

The present invention uses the hard-breakdown characteristic of the first metal oxide and the high leakage current characteristic of the second metal oxide as described above, so that the tip of the filament generated in the first metal oxide is similar to the conductive tip. It is possible to provide a filament-based device that serves to apply an electric field to a local portion of the second metal oxide layer to form near-single filaments locally confined to the second metal oxide layer.

The first metal oxide layer and the second metal oxide layer may have a change in resistance according to the generation and disappearance of the filament.

By having the above configuration, the filament-based device of the present invention can be driven with low power while ensuring reliability at the same time.

For example, the filament-based device having the above configuration may have a variation value (σ/μ) defined as the ratio of the standard deviation (σ) to the average value (μ) of the filament generation (set) voltage is 0.1 or less. .

The coefficient of variation can be calculated by measuring a voltage (set voltage) at which filaments are generated when voltage is applied after forming by applying a voltage to the cathode and the anode, respectively.

Specifically, the step of measuring the set voltage for calculating the coefficient of variation includes a first forming process by applying a voltage of -3 to -10V, a second forming process by applying a voltage of 3 to 5V, and then 1 to This can be done by measuring the voltage at which the filament is generated by applying a voltage of 3V.

The average value (μ) of the set voltages may be 0.3 to 3V, for example, 0.5 to 2.5V, 0.8 to 2V, 1 to 2V, 1.1 to 1.9V, or 1.2 to 1.8V.

The standard deviation (σ) of the set voltage may be 0.05 to 0.25V, 0.08 to 0.2V, 0.1 to 0.2V, 0.11 to 0.19V, or 0.12 to 0.18V.

In the case of having the coefficient of variation value as described above, the set voltage is almost constant and there is little variation, thereby providing a filament device having excellent reliability.

In addition, the filament device according to the present invention can provide a filament-based device having a high ratio of the current value of the filament generation state (on-state) to the current value of the filament extinction state (off-state).

The ratio of the current value of the filament generation state to the current value of the filament extinction state may be, for example, 1x10 ³ or more, 1x10 ⁴ or more, or 1x10 ⁵ or more.

When the current value of the filament generation state with respect to the current value of the filament extinction state as described above, it is possible to prevent malfunction and provide a highly reliable filament device.

The upper electrode layer is formed on the second metal oxide layer, and may be formed using a sputtering method, a chemical vapor deposition method, or an atomic layer deposition method.

The electrode material of the upper electrode layer has a high degree of ionization and excellent activity, and a material capable of generating and destroying conductive filaments by external electrical stimulation such as voltage or current may be used. Specifically, as the electrode material of the upper electrode layer, at least one selected from the group consisting of Au, Ir, Ti, Cu, Al, Ta and Ni may be used, for example, Au and Ti may be used as the electrode material of the upper electrode layer. can

The upper electrode layer may be further patterned after deposition on the second metal oxide layer. As a method of the deposition and patterning, a known method may be used, for example, the electrode size and shape may be patterned using electron-beam lithography, etc., and electron beam physical vapor deposition on the patterned portion The metal may be deposited using electron-beam physical vapor deposition or the like.

In addition, the present invention may provide a resistance change memory including a filament-based device of the present invention or a filament-based device manufactured by the method of manufacturing a filament-based device of the present invention.

The resistance change memory is a memory that stores information by using the resistance change phenomenon that appears in an insulator. In the resistance change memory including the filament device according to the present invention, conductive filaments can be generated and destroyed inside the first and second metal oxide layers by external electrical stimulation, and when the conductive filaments are generated, a low resistance state (low resistance state) and becomes a high resistance state upon extinction. Therefore, the resistance change memory including the filament device according to the present invention can maintain stable switching characteristics because it provides a device having a low coefficient of variation, excellent reliability, and excellent stability by generating a filament close to a single.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples of the present invention. These Examples and Comparative Examples are merely presented by way of example in order to explain the present invention in more detail, and the scope of the present invention is not limited thereto.

<Example>

Fabrication of a double-layer oxide filament-based device according to the present invention

Pt was used as the lower electrode layer, and AlO _x was deposited on the lower electrode layer to a thickness of 4 nm using an atomic layer deposition method using an atomic layer deposition method. Thereafter, TiO _x was deposited to a thickness of 30 nm by an atomic layer deposition method on the AlO _x formed thereon. Thereafter, an Au/Ti upper electrode layer was deposited to a thickness of 50 μm to prepare a filament-based device.

TiO _x Fabrication of Single-Layered Filament-Based Devices

A single-layer filament-based device was manufactured by using Pt as the lower electrode layer and depositing TiO _x to a thickness of 30 nm by an atomic layer deposition method.

AlO _x Fabrication of Single-Layered Filament-Based Devices

Pt was used as the lower electrode layer, and AlO _x was deposited to a thickness of 30 nm by an atomic layer deposition method. Thereafter, an Au/Ti upper electrode layer was deposited to a thickness of 50 μm to prepare a single-layer filament-based device.

<Experimental example>

1 shows a device in which an Au/Ti upper electrode layer is deposited to a thickness of 50 μm on a single-layer filament _- based device of TiO _x ( FIG. 1 a ), a conductive atomic force microscope ( The resistance state change results of a device using a force microscope (C-AFM) tip (FIG. 1b) and a single-layer filament _- based device of AlOx (FIG. 1c) are shown.

In the case of Fig. 1(a), the leakage current density value of TiO _x is 2x10 ⁶ A/m ² at 0.1V, which confirms the high leakage current characteristic, and in the case of Fig. 1(b), it can be confirmed that the memory switching phenomenon appears. could This seems to induce stable switching by forming a filament close to a single by applying a local field to the part where the C-AFM tip touches.

On the other hand, in FIG. 1(c), AlO _x showed a hard-breakdown characteristic. Specifically, AlO _x formed an irreversible conductive path at 2V.

Based on this result, TiO _x and A filament-based device of a double-layer oxide using AlO _x could be fabricated.

switching characteristics

2 is a result of measuring the resistance state change of the filament-based device of the present invention. Through the first forming process at -voltage and the second forming process at +voltage (Fig. 2(a)), a stable switching phenomenon in which set switching at + voltage and reset switching at - voltage occur can be observed. . In addition, in Fig. 2(c), the ratio of the current value of the filament generation state (on-state) to the current value of the filament extinction state (off-state) is 1x10 ⁴ It can be confirmed that the high current on/off ratio.

mechanism

3 is a mechanism proposed based on the measurement results. When the forming process is performed twice (FIG. 3(a)), most of the electric field is applied to AlO _x due to the high leakage current of TiO _x , and a filament is formed in AlO _x . Due to the electric field applied locally at the tip of the filament, a filament close to a single is formed in TiO _x , causing a resistance change switching phenomenon according to the voltage direction (FIG. 3(b)). That is, the tip of the AlO _x filament formed on the lower side serves to apply an electric field to the local part of the TiO _x layer like the AFM-tip, and as a result, it can be expected that a filament close to a single is formed in the TiO _x layer. .

Volatility and Durability

In large scale memory manufacturing, variability is a very important factor for mass production of devices. If the variability increases, the read/write margin of the memory element is reduced, and in particular, if the number of elements connected to one conductor increases as the level of the device increases, it causes a malfunction.

In order to measure the variability of the filament-based device of the present invention, a probe station and measuring equipment (Agilent 4156B, HP, USA) were connected, the probe tip and the sample were contacted, and then a voltage was applied to the probe tip to check the electrical characteristics of the sample. did At this time, after the first forming by applying a voltage of -7V, a second forming process was performed by applying a voltage of +5V. Thereafter, a switching phenomenon in which a voltage of +2V was applied, and a reset switching occurred by applying a voltage of -2V and set switching was observed.

4 (a) is a result of measuring the switching voltage of the filament-based device 50 times by the above method, it can be confirmed that the set and reset voltages appear evenly.

4(b) is a result of calculating the coefficient of variation of the set and reset voltages based on the experimental results, and it can be seen that the value of the coefficient of variation of the set voltage is as low as 0.08 or less.

In this case, the coefficient of variation value represents the ratio of the standard deviation (σ) of the set voltage to the average value (μ) of the set voltage.

It can be seen that the filament-based device of the present invention has a low coefficient of variation value as described above, and thus there is little variation with respect to a switching cycle, and thus, a conductive filament generated for each cycle is uniform. In the case of having a value of the coefficient of variation, the set voltage is almost constant and there is little variation, so that a filament device having excellent reliability can be provided.

In particular, the filament-based device according to the present invention has low variability despite the set voltage being within 2V as shown in FIG. It can be seen that provides

In addition, Fig. 2(c) shows the result of measuring the resistance change 50 times for one device, and it was confirmed that the stable switching characteristic of the on/off state was maintained even after 50 experiments.

Claims (11)

lower electrode layer;
a first metal oxide layer formed on the lower electrode layer and forming an irreversible conductive path at a voltage of 1V or higher;
a second metal oxide layer formed on the first metal oxide layer and having a leakage current density of 1x10 ⁴ (A/m ² ) or more, measured at 0.1 V per 1 nm in thickness; and
A filament-based device comprising an upper electrode layer formed on a second metal oxide layer,
The thickness of the first metal oxide layer is 1 nm to 10 nm,
The thickness of the second metal oxide layer is 20 nm to 50 nm,
Conductive filaments are created or destroyed by external electrical stimulation,
A filament-based device with a coefficient of variation (σ/μ) of 0.1 or less, defined as the ratio of the standard deviation (σ) to the average value (μ) of the filament generation (set) voltage.
The method of claim 1,
A filament-based device in which the ratio of the current value in the filament generation state to the current value in the filament extinction state is 1x10 ⁴ or more.
According to claim 1,
The lower electrode layer is a filament-based device comprising at least one selected from the group consisting of Pt, Au, Ir, TiN, W, Ru, Al, Ta and Ni. According to claim 1,
The upper electrode layer is a filament-based device comprising at least one selected from the group consisting of Au, Ir, Ti, Cu, Al, Ta and Ni.
The method of claim 1,
The first metal oxide layer is a filament-based device comprising AlO _x (x is 1 to 2).
The method of claim 1,
The second metal oxide layer is a filament-based device comprising TiO _x (x is 1 to 2).
delete delete forming a lower electrode layer on a substrate;
forming a first metal oxide layer on the lower electrode layer by an atomic layer deposition method using atomic layer deposition (ALD);
forming a second metal oxide layer on the first metal oxide layer by an atomic layer deposition method using an atomic layer deposition equipment; and
The method of claim 1, comprising depositing and patterning an upper electrode layer on the second metal oxide layer.
A resistance change memory comprising the filament-based device of claim 1 .
A first forming step of generating a conductive filament by applying a negative voltage; and
A second forming step of generating a conductive filament by applying a positive voltage,
The method of claim 10 , wherein set-switching at a positive voltage and reset-switching at a negative voltage occur.

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