KR102574530B1 - Transparent oxide memristor - Google Patents

Abstract

The present invention relates to a transparent oxide memristor, which includes a substrate having a lower electrode function, an insulating layer formed on the substrate, an oxide layer formed on the insulating layer, and an upper electrode formed on the oxide layer, , The substrate is made of a glass material.
According to the present invention, by manufacturing a transparent oxide memristor using IGZO (Indium-Gallium-Zinc oxide) in an oxide layer, there is an effect of improving electrical characteristics.

Description

Transparent oxide memristor {Transparent oxide memristor}

The present invention is a resistive random access memory, a non-volatile memory, a transparent memory device, a next generation memory, a memristor, and a sputtering system. Fabrication of IGZO thin-film deposited by sputtering system, oxide memristor with high electrical and environmental stability.

Recently, research on oxide semiconductors to replace silicon-based semiconductor devices has been widely conducted. In terms of materials, it is based on indium oxide (In ₂ O ₃ ), zinc oxide (ZnO), gallium oxide (Ga ₂ O ₃ ), indium zinc oxide (InZnO), zinc tin oxide (Zn), and indium gallium zinc oxide (InGaZnO). The results of studies on single, binary, and tertiary compounds are reported. On the other hand, in terms of process, research on a liquid-based process that replaces the existing vacuum deposition is being conducted.

Oxide semiconductors show the same amorphous phase as hydrogenated amorphous silicon, but show very good mobility, so they are suitable for high-definition liquid crystal displays (LCDs) and active organic light emitting diodes (AMOLEDs). In addition, the oxide semiconductor manufacturing technology using a liquid-phase process has an advantage of low cost compared to the high-cost vacuum deposition method.

In a conventional memory structure, TiO _{2 -x} implements a switching operation using oxygen vacancies serving as carriers, but generation/recombination between oxygen vacancies during the transfer process There are problems in that the endurance characteristics of the memory are deteriorated due to a carrier trap, a decrease in an on/off ratio, and a decrease in electron mobility due to generation. In addition, there is a problem that a root-mean square (RMS) value is high in an oxide layer of a conventional memory and defects exist on the surface. In addition, the IGZO thin film produced by low-temperature sputtering has a problem in that contact resistance occurs at the interface between the electrode and the oxide semiconductor layer.

Republic of Korea Patent Publication 10-2008-0082616

The present invention has been made to solve the above problems, and electron movement of IGZO (Indium-Gallium-Zinc oxide) occurs through ns-orbital (ns-orbital), and fast electron mobility can be obtained even in an amorphous state. Since it can implement excellent resistance switching characteristics of the memory, TiO _{2 -x} is an electronic material for resistive random access memory (ReRAM) that can overcome the disadvantages of transparent oxide using IGZO in the oxide layer. Its purpose is to provide a non-volatile memristor.

In addition, another object of the present invention is to fabricate a transparent oxide non-volatile memristor deposited with IGZO through an RF magnetron sputtering system.

In addition, the present invention removes defects at the semiconductor interface through a post-heat treatment process and increases the binding force between metal and oxygen in the semiconductor, thereby reducing the trap density of electrons, thereby reducing electron movement. Another object is to provide a transparent oxide non-volatile memristor with improved electrical performance such as that of a coating.

The object of the present invention is not limited to the object mentioned above, and other objects not mentioned will be clearly understood by those skilled in the art from the description below.

The present invention for achieving the above object relates to a transparent oxide memristor, which includes a substrate having a lower electrode function, an insulating layer formed on the substrate, an oxide layer formed on the insulating layer, and an oxide layer formed on the oxide layer. An upper electrode is formed, but the substrate is made of a glass material.

The substrate may be implemented as an indium tin oxide (ITO) glass substrate.

The insulating layer may be made of TiO ₂ (titanium dioxide).

The oxide layer may be formed of an indium-gallium-zinc oxide (IGZO) thin film.

The upper electrode may be made of silver (Ag).

According to the present invention, by manufacturing a transparent oxide memristor using IGZO (Indium-Gallium-Zinc oxide) in an oxide layer, there is an effect of improving electrical characteristics.

In addition, the present invention removes defects at the semiconductor interface through a post-heat treatment process in a transparent oxide nonvolatile memristor and increases the binding force between metal and oxygen in the semiconductor, thereby reducing the trap density of electrons. By influencing, there is an effect of improving electrical performance such as electron mobility.

1 is a schematic diagram showing the structure of a transparent oxide memristor according to an embodiment of the present invention.
2 is an expression of the overall driving mechanism of IGZO/TiO ₂ -based memristor (ReRAM).
3 is a graph showing the results of measuring the electrical performance of IGZO/TiO ₂ -based memristors subjected to heat treatment at 200, 250, 300, and 350 °C, respectively, after depositing an IGZO oxide layer.
4 is a graph showing the results of analyzing the O1s peak in the surface after depositing an IGZO oxide layer and post-heating at 200, 250, 300, and 350 ° C, respectively, by XPS (x-ray photoelectron spectroscopy) am.
5 is a graph of transmittance / photon energy measured to analyze the energy bandgap of IGZO / TiO ₂ memristors subjected to post-heat treatment at 200, 250, 300, and 350 ° C, respectively. graph).
FIG. 6 shows the results of retention and cycling tests of IGZO/TiO ₂ memristors subjected to post-heat treatment at 350° C., respectively.
FIG. 7 shows a circuit diagram and transfer curve of a newly fabricated mem-transistor by combining an IGZO/TiO2 memristor and a-IGZO-based thin film transistor subjected to post-heat treatment at 350 ° C., respectively, into one circuit. will be.

Since the present invention can make various changes and have various embodiments, specific embodiments will be illustrated in the drawings and described in detail. However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

Terms used in this application are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise. In this application, the terms "include" or "have" are intended to designate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, but one or more other features It should be understood that the presence or addition of numbers, steps, operations, components, parts, or combinations thereof is not precluded.

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 the present invention belongs. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the related art, and unless explicitly defined in the present application, it should not be interpreted in an ideal or excessively formal meaning. don't

In addition, in the description with reference to the accompanying drawings, the same reference numerals are given to the same components regardless of reference numerals, and overlapping descriptions thereof will be omitted. In describing the present invention, if it is determined that a detailed description of related known technologies may unnecessarily obscure the subject matter of the present invention, the detailed description will be omitted.

1 is a schematic diagram showing the structure of a transparent oxide memristor according to an embodiment of the present invention.

Referring to FIG. 1, the memristor of the present invention includes a substrate 110, an insulator layer 120, an oxide layer 130, and a top electrode 140. include

In one embodiment of the present invention, the substrate 110 may be implemented as an indium tin oxide (ITO) glass substrate, and may function as a lower electrode.

The insulating layer 120 is formed on the substrate 110 and may be made of TiO ₂ (titanium dioxide).

The oxide layer 130 is formed on the insulating layer 120 and may be made of an amorphous oxide thin film. In one embodiment of the present invention, the oxide layer 130 may be formed of an indium-gallium-zinc oxide (IGZO) thin film.

The upper electrode 140 is formed on the oxide layer 130 and may be made of silver (Ag).

In the embodiment of FIG. 1, the Ag/IGZO/TiO ₂ /ITO glass-based MIOS ReRAM structure is briefly shown, and the electrical symbol means that the ReRAM is a nonlinear passive device related to a combination of charge and magnetic flux. In order to prepare an insulating layer on the ITO lower electrode 110, about 2 nm of TiO ₂ was deposited using an ALD system. In addition, in order to form the oxide layer 130, an IGZO thin film 130 was formed with a 1:1:1 mol.% In:Ga:Zn composition ratio of about 20 nm through a target-based RF magnetron sputtering process. deposited in thickness. Thereafter, a 100 nm-thick silver (Ag) source/drain electrode was deposited on the IGZO using a shadow mask through an evaporation process.

In the present invention, an actual manufacturing process and an experimental process of a memristor having an amorphous oxide thin film are exemplified as follows.

In an embodiment of the present invention, an indium tin oxide (ITO) glass substrate is used as the substrate 110 of the memristor and has a thickness of 150 nm.

In order to remove organic and inorganic impurities on the surface, ultrasonic surface treatment was performed in DI water, acetone, and IPA for 15 minutes each, and then dried in a vacuum oven for 1 hour.

In order to manufacture the insulating layer 120 on the substrate 110, titanium dioxide (TiO ₂ ) was deposited using an atomic layer deposition (ALD) system manufactured by NCD (LUCIA D100). The ALD cycle starts by injecting titanium tetraisopropoxide as a precursor of Ti, injecting N ₂ purge gas for 10 seconds, injecting H ₂ O for 1 second, and then injecting 10 seconds again. A process of injecting N ₂ purge gas was set as one cycle, and a total of 1,000 cycles were repeated with 0.2 Å deposition per cycle to form a TiO ₂ thin film having a thickness of 2 nm.

And, in order to form an indium-gallium-zinc oxide (IGZO) channel layer as the oxide layer 130 on the TiO ₂ insulating layer that has been cleaned by SPM, a sputtering process using an RF magnetron sputtering system proceeded. As a target, an IGZO (In ₂ O ₃ :Ga ₂ O ₃ :ZnO) target having a diameter of 3 inches and a ratio of 1:1:1 was used, and the distance between the target and the substrate was set to 8 cm.

In addition, in order to remove impurities in the chamber, the initial vacuum level in the chamber was set to 3 × 10 ^-6 torr or less using a rotary pump and TMP, and then 30 sccm of Ar gas was injected into the chamber. The degree of vacuum was maintained at 1.5 × 10 ^-2 torr.

In addition, the substrate was rotated at a speed of 7 rpm for uniform deposition of the thin film, and RF power of an RF power generator was applied at 150 W to generate plasma to form a 20 nm IGZO channel layer. deposited.

Then, the temperature of the furnace was evaluated to confirm the temperature for optimizing the properties of the IGZO-based memristor, and heat treatment was performed for about 1 hour in the range of about 200, 250, 300, and 350 °C, respectively, The results were analyzed.

After the heat treatment, silver (Ag) source/drain electrodes were deposited using a thermal evaporator.

In order to determine the electrical performance of the finally manufactured IGZO/TiO ₂ memristor, an IV curve was measured. In addition, the memory characteristics were confirmed through composition and surface analysis and CV measurement to confirm the optimal post-heat treatment temperature of IGZO oxide semiconductor applicable to memristors.

2 is an expression of the overall driving mechanism of IGZO/TiO ₂ -based memristor (ReRAM).

In FIG. 2 , an ITO glass substrate was used as a lower electrode as a measurement standard for ReRAM, and operation of the a-IGZO ReRAM was confirmed by applying a voltage to the upper silver (Ag) electrode.

First, when a (+) voltage is applied to the IGZO oxide active layer as a positive bias region, the current maintains a low value and then increases rapidly when a certain threshold voltage is reached, and this process is called SET operation. .

Conversely, when voltage is applied from the positive bias region to the negative bias region, the state of the device reaches the threshold voltage ( ) and the current value rapidly decreases. This process is called RESET operation do.

ReRAM performs this process, and when the state of the IGZO thin film reaches a (+) threshold voltage, a conducting pathway is created by oxygen vacancies inside a-IGZO. However, when a voltage ( ) is applied, oxygen traps in the TiO ₂ insulating layer block the movement of electrons, thereby causing filament rupture. Through this process, the resistance state is changed according to the applied bias and a hysteresis phenomenon is induced to drive the IGZO/TiO ₂ memristor.

3 is a graph showing the results of measuring the electrical performance of IGZO/TiO ₂ -based memristors subjected to heat treatment at 200, 250, 300, and 350 °C, respectively, after depositing an IGZO oxide layer. In FIG. 3, KEITHLEY's model name SYSTEM 4200 source meter was used as the measurement equipment, and the IV curve when 2 to 2 V was applied was confirmed.

In FIG. 3, (a) is 200 ℃, (b) is 250 ℃, (c) is 300 ℃, (d) the electrical performance of the IGZO / TiO ₂ -based memristor subjected to post-heat treatment at 350 ℃ is measured. This is the graph showing the result.

Referring to FIG. 3 , it was confirmed that a hysteresis characteristic was implemented due to an increase in a current level due to an increase in the post-heat treatment temperature of the memristor. (a) The memristor subjected to post-heat treatment at 200 °C does not show a complete hysteresis curve in the (+) region, and (b) shows a small hysteresis in the case of 250 °C. In addition, when the temperature of the post-heat treatment is (d) 350 ° C, the most excellent type of hysteresis can be confirmed.

In the range where the post-heat treatment temperature is low, electrons are trapped due to defects and interfacial resistance on the surface of the IGZO thin film. confirmed that Therefore, when the IGZO oxide active layer deposited at a low temperature by RF magnetron sputtering was subjected to post-heat treatment at a temperature of 350 ° C, the optimal characteristics as a memristor were confirmed through a decrease in carrier concentration and electron trap density. On the other hand, if heat treatment is performed at 400 ℃ or higher. There is a risk of damaging the ITO and the lower glass substrate.

4 is a graph showing the results of analyzing the O1s peak in the surface after depositing an IGZO oxide layer and post-heating at 200, 250, 300, and 350 ° C, respectively, by XPS (x-ray photoelectron spectroscopy) am.

In FIG. 4, (a) is 200 ° C, (b) is 250 ° C, (c) is 300 ° C, and (d) is 350 ° C. It is a graph showing the result of analysis by photoelectron spectroscopy).

As shown in FIG. 4 (d), when the post-heat treatment was performed at 350 ° C., which is the temperature condition where the electrical performance results were the best, the specific gravity of the lattice oxygen peak (O ₁ ) in the O1s peak was the largest at about 65.2%, and the hydride The specific gravity of the hydroxide peak (O ³ ) is the smallest at about 6.1%.

On the other hand, looking at Figure 4 (a), it can be seen that the components of the IGZO thin film subjected to post-heat treatment at 200 ° C. O ₁ specific gravity is about 51.4% and O ₃ specific gravity is about 12.2% in the entire O1s peak. Referring to FIG. 4 (b), in the case of the IGZO thin film subjected to post-heat treatment at 250 ° C, the specific gravity of O ₁ in the O1s peak is about 56.5%, and compared to the condition at 200 ° C, the specific gravity of O ₃ is about 12.2% to 10.6%. %, and the specific gravity of O ₁ increased from about 51.4% to about 56.5%.

As such, when the O ₁ peak is small and the O ₃ peak is large, oxygen vacancies remain without sufficient recovery of the metal-oxygen bond, and the overall electrical performance of the memristor deteriorates due to an increase in leakage current. will do In addition, when the O ₃ peak increases, hydrogen ions are bonded to oxygen vacancies, and oxygen traps that are relatively strongly bonded to hydrogen increase, and more interfacial trap charge phenomena that hinder the movement of electrons occur. This contributes to the generation of leakage current and reduces the electron mobility of the memory device, resulting in reduced electrical performance of the memristor.

In this way, when the specific gravity of O ₁ decreases and the specific gravity of O ₃ increases, oxygen released from the metal-oxygen bond diffuses rapidly to the outside of the thin film with a relatively low concentration, which causes the electrical performance of the memristor to deteriorate. do. As a result, this was the same as the result of the electrical experiment proving that the post-heat treatment temperature of 350 ℃ was the optimal condition, and it can be a basis to support this.

5 is a graph of transmittance / photon energy measured to analyze the energy bandgap of IGZO / TiO ₂ memristors subjected to post-heat treatment at 200, 250, 300, and 350 ° C, respectively. graph).

Referring to FIG. 5, it can be seen that the IGZO/TiO ₂ memristor subjected to post-heat treatment at a temperature of 350 °C showed the best characteristics with an energy band gap of about 3.801.

FIG. 6 shows the results of retention and cycling tests of IGZO/TiO ₂ memristors subjected to post-heat treatment at 350° C., respectively.

In the case of FIG. 6 (a) and (b), it is the result of a retention test measured by applying the first set or reset pulse, and the current measured at the upper electrode is constant over time Able to know.

In the case of FIG. 6 (c) and (d), the result of a cycling test measured by continuously and alternately applying a set pulse and a reset pulse is shown. Here, even if Set/Reset pulses are applied more than 50 times, it can be confirmed that Set/Reset results are shown according to the pulses without significant change.

FIG. 7 shows a circuit diagram and transfer curve of a newly fabricated mem-transistor by combining an IGZO/TiO2 memristor and a-IGZO-based thin film transistor subjected to post-heat treatment at 350 ° C., respectively, into one circuit. will be.

7 (a) shows a circuit diagram of a mem-transistor, and (b) and (c) show transfer curves measured using two devices. Before measuring the transfer curve, the memristor was measured by changing the memristor to an on or off state by giving an input pulse that changes the operating state of the memristor. As a result of the measurement, when the state of the memristor was turned on by applying the set pulse, the current value was normally measured in the drain according to the voltage applied to the gate of the transistor, and the ideal transfer curves were shown. However, when a reset pulse was applied to the memristor to turn off the state, the memristor's internal resistance value changed so greatly that even when a voltage was applied to the gate of the transistor, the current value was not measured at the drain. .

The present invention has been described above using several preferred embodiments, but these embodiments are illustrative and not limiting. Those skilled in the art to which the present invention pertains will understand that various changes and modifications can be made without departing from the spirit of the present invention and the scope of rights set forth in the appended claims.

110 substrate 120 insulating layer
130 oxide layer 140 upper electrode

Claims (5)

a substrate including a lower electrode function;
an insulating layer formed on the substrate;
an oxide layer formed on the insulating layer; and
Including an upper electrode formed on the oxide layer,
Heat treatment is performed after the oxide layer is formed,
The substrate is implemented with an indium tin oxide (ITO) glass substrate,
The insulating layer is made of TiO ₂ (titanium dioxide),
The oxide layer is made of an indium-gallium-zinc oxide (IGZO) thin film,
The upper electrode is made of silver (Ag),
The insulating layer is formed by depositing titanium dioxide (TiO ₂ ) using an atomic layer deposition (ALD) system,
The oxide layer is formed by performing an RF magnetron sputtering process to form an indium-gallium-zinc oxide (IGZO) channel layer,
The upper electrode is formed by depositing a source/drain electrode made of silver (Ag) using a thermal evaporator after performing the heat treatment,
In performing the heat treatment, the memristor, characterized in that the heat treatment is performed in a state that the temperature of the furnace is 350 ℃. delete delete delete delete