KR20120059195A - 3-layer Resistive RAM of having self selective characteristics - Google Patents

Abstract

PURPOSE: A trilaminar resistance alteration memory having self selection characteristics is provided to efficiently prevent malfunction by blocking a leakage current through a memory cell maintaining a high resistance state. CONSTITUTION: A bottom electrode(110) is formed on a substrate(100). A resistance alteration layer(120) is formed on the bottom electrode. The resistance alteration layer comprises a first oxygen depletion oxide film, a second oxygen depletion oxide film, and a third oxygen depletion oxide film. The resistance alteration layer has state change according to formation and extinction of a conductive channel and self selection characteristics according to the state change. A top electrode(130) is formed at the upper side of the resistance alteration layer.

Description

3-layer Resistive RAM of having self selective characteristics

The present invention relates to a nonvolatile memory, and more particularly, to a resistance change memory having a self-selective characteristic.

Non-volatile memory has a characteristic of storing information even when power is removed. Flash memory, which is a typical nonvolatile memory, has a characteristic of changing a threshold voltage of a memory by using electrons moving between a channel region and a gate stack. As such, most memories have a mechanism that changes state through the movement of charge or electrons.

Recently, researches on new memory devices using phase change and magnetic field change have been conducted. The information storage method of new memory devices under study utilizes the principle of inducing a change of state of a material and changing a resistance of the material. In addition, the newly studied ferro-electric RAM (FeRAM) is known to have a problem in the stability of the material, MRAM (Magnetic RAM) has a complicated manufacturing process, has a multi-layer structure, the margin of the read / write operation is small Has a limit.

Another memory, the resistance change memory, has a characteristic that a resistance of a thin film is changed according to a voltage applied to the thin film, and an information storage operation may be performed by using the same. The resistance change memory can theoretically record and reproduce infinitely, and has high temperature operation and nonvolatile characteristics. In addition, when the input pulse is applied, there is an advantage that a high-speed operation of 10 to 20ns occurs in a resistance change of more than 1000 times. A typical resistance change memory has a structure in which a resistance change layer is disposed between an upper electrode and a lower electrode. The resistance change layer is made of an oxide material, and is largely composed of binary or perovskite.

Korean Patent Laid-Open Publication No. 2006-83368 discloses a resistance change memory using a multilayer film including a metal oxide having a different composition ratio as a resistance change layer. The metal oxide may be ZrO _x , NiO _x , HfO _x , TiO _x , Ta ₂ O _x , Al ₂ O _x , La ₂ O _x , Nb ₂ O _x , SrTiO _x , Cr-doped SrTiO _x , or Cr- Doped SrZrO _x (where x is 1.5–1.9) is used.

Korean Laid-Open Patent Publication No. 2006-106035 discloses a resistance change memory including a perovskite oxide of SrZr ₃ doped with Cr as a resistive layer.

In addition, Korean Patent Laid-Open Publication No. 2004-63600 forms a barrier layer of Ta, TaN, Ti, TiN, TaAlN, TiSiN, TaSiN, TiAl or TiAlN on an Ir substrate, and Pr _{0 . 7} Ca _{0 .3} (hereinafter referred to as 'PCMO') MnO ₃ mentions the resistance RAM to form a thin film. The ReRAM device repeats the coating, baking and annealing process until several layers of PCMO have the desired thickness, which makes the overall process very complex. In addition, since the main process is performed in the atmospheric state, it may affect the characteristics of the memory due to oxidation and surface contamination, there is a limit to the stabilization of the thin film, the stability of the point defect structure in the oxide thin film manufactured as described above The instability of the operating voltage and the resistance state due to the limitation of the control makes it difficult to ensure excellent reproducibility, and the limitation of the process leads to the stabilization of device operation.

In addition, the above-described patents require an additional selection device to solve the problem of leakage current inevitably in order to implement the cross-bar array structure, which is a disadvantage in terms of device scale down. To improve this problem, diodes are used instead of transistors, and the structure of 1D 1R is achieved. However, even in the 1D 1R structure, a number of functional devices must be implanted in a predetermined area, and still appear as a problem to solve the problem of reducing the area of the chip.

DISCLOSURE OF THE INVENTION An object of the present invention for solving the above problems is to provide a resistance change memory which is of the same type of oxide, is composed of a multilayer oxide film, and has a select characteristic of the device itself.

The present invention for achieving the above object, a substrate; A lower electrode formed on the substrate; A resistance change layer formed on the lower electrode and made of the same material and having a state change and a diode characteristic according to formation and disappearance of a conductive channel; And an upper electrode formed on the resistance change layer.

In addition, the above object of the present invention, the lower electrode; A resistance change layer formed on the lower electrode, made of the same material, and having a state change performed by embedding oxygen vacancies or formation of oxygen vacancies at an interface of membranes having different relative oxygen fractions; And it is also achieved through the provision of a resistance change memory comprising an upper electrode formed on the resistance change layer.

According to the present invention described above, the resistance change layer is composed of the same material. In addition, of the three oxygen deficient oxide films forming the resistance change layer, upper and lower oxygen depleted oxide films have a relatively high oxygen fraction compared to the oxygen deficient oxide film disposed in the middle. Through the forming operation, the resistive change layer has a conductive channel arranged to connect the pores of oxygen. In addition, in the present invention, the current rapidly increases above a certain voltage by the formation of the conductive channel, which is caused by the change of the resistance state of the material from the high resistance state to the low resistance state. The change in resistance is caused by the disconnection of the conductive channel at the interface through the movement of oxygen ions in the oxygen deficient oxide film having a relatively high oxygen fraction. Through this, a high resistance state can be obtained.

The resistance change memory described above has both a self-selection characteristic and a resistance change characteristic. This enables device selectivity and reliable write and read operations.

1 is a cross-sectional view illustrating a resistance change memory according to a preferred embodiment of the present invention.
2 is a graph illustrating voltage-current characteristics for describing an operation of a memory manufactured according to an exemplary embodiment of the present invention.
3 to 7 are conceptual views illustrating physical behavior of a resistance change memory according to the characteristic graph of FIG. 2 according to a preferred embodiment of the present invention.

As the inventive concept allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the text. However, this is not intended to limit the present invention to the specific disclosed form, it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention. Like reference numerals are used for like elements in describing each drawing.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. Terms such as those defined in the commonly used dictionaries should be construed as having meanings consistent with the meanings in the context of the related art and shall not be construed in ideal or excessively formal meanings unless expressly defined in this application. Do not.

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

Example

1 is a cross-sectional view illustrating a resistance change memory according to a preferred embodiment of the present invention.

Referring to FIG. 1, the resistance change memory according to the present exemplary embodiment includes a substrate 100, a lower electrode 110 disposed on the substrate 100, and a resistance change layer 120 disposed on the lower electrode 110. And an upper electrode 130 positioned on the resistance change layer 120.

In particular, the resistance change layer 120 includes a first oxygen depleted oxide film 121, a second oxygen depleted oxide film 123, and a third oxygen depleted oxide film 125. In addition, the oxide films 121, 123, and 125 constituting the resistance change layer 120 may be formed of the same oxide, and the second oxygen depleted oxide film 123 may include the first oxygen depleted oxide film 121 and the third oxygen. It has a lower oxygen fraction than the deficient oxide film 125.

Therefore, the second oxygen depleted oxide film 123 has a higher oxygen vacancy density than the first oxygen depleted oxide film 121 and the third oxygen depleted oxide film 125.

In addition, the first oxygen depleted oxide film 121 and the third oxygen depleted oxide film 125 may have the same oxygen ratio or may have different oxygen ratios. That is, the first oxygen depleted oxide film 121 and the third oxygen depleted oxide film 125 also have vacancies of oxygen, which maintains a lower density than the second oxygen deficient oxide film 123. In particular, the oxygen deficient oxide films 121, 123, and 125 preferably have a nonstoichiometric configuration.

First, as long as the substrate 100 is applied to a general semiconductor device or the like, no particular limitation on the material is necessary. Representative substrate 100 that may be used may be Si, SiO ₂ , Si / SiO ₂ multilayer substrate or a polysilicon substrate.

The lower electrode 110 may be selected from the group consisting of Pt, Au, Al, Cu, Ti, and alloys thereof. In addition, the lower electrode 110 may be a nitride electrode material or an oxide electrode material. The nitride electrode material is TiN or WN, and the oxide electrode material is In ₂ O ₃ : Sn (ITO), SnO ₂ : F (FTO), SrTiO ₃ Or LaNiO ₃ There is this. In addition, the lower electrode 110 may be formed to a thickness of 5nm to 500nm according to the type of electrode material.

The lower electrode 110 may be formed through a conventional deposition method. Therefore, physical vapor deposition, chemical vapor deposition, sputtering, pulsed laser deposition, thermal evaporation, electron beam evaporation, Atomic layer deposition or molecular beam epitaxy is possible.

The resistance change layer 120 is composed of three oxide films 121, 123, and 125 and a resistance change operation is performed according to an applied bias. At the same time, the resistance change layer 120, the current rapidly increases with the application of a bias above a certain voltage. That is, a phenomenon in which current increases due to a sudden change in resistance of the resistance change layer 120 occurs. The above-described resistance change is due to the oxygen vacancies formed in the resistance change layer 120. Oxygen vacancies form a conductive channel 140 and cause a sharp increase in current above a certain voltage.

The resistance change layer 120 composed of the same oxide includes one selected from the group consisting of TiO ₂ , MgO, NiO, ZnO, HfO _2, and a combination thereof, and preferably includes TiO ₂ .

The resistance change layer 120 is formed through a conventional deposition method. In addition, after the resistance change layer 120 is formed, heat treatment may be performed on the resistance change layer 120. Through this, rearrangement of the lattice in the resistance change layer 120 is performed.

The heat treatment is carried out at 100 ℃ to 1000 ℃, preferably in the temperature range of 200 ℃ to 500 ℃ 1 minute to 24 hours, preferably 30 minutes to 1 hour. At this time, the heat treatment is performed in a gas atmosphere to which a nitrogen partial pressure or an oxygen partial pressure of 100 Torr to 500 Torr is applied or under vacuum.

The lattice in the resistive change layer 120 composed of oxygen deficient oxide films 121, 123, 125 is rearranged.

If the heat treatment is performed below the above-described range, the rearrangement of the lattice in the resistance change layer 120 composed of three oxide films 121, 123, and 125 may not be smooth. If it exceeds, the composition of each oxide film in the resistance change layer 120 may be incorrect, or oxygen may escape to the outside.

The upper electrode 130 uses the same or different material as the lower electrode 110. Accordingly, the upper electrode 130 may be selected from the group consisting of Pt, Au, Al, Cu, Ti, and alloys thereof. In addition, the upper electrode 130 may be a nitride electrode material or an oxide electrode material. The nitride electrode material is TiN or WN, and the oxide electrode material is In ₂ O ₃ : Sn (ITO), SnO ₂ : F (FTO), SrTiO ₃ Or LaNiO ₃ There is this. In addition, the upper electrode 130 may be formed to a thickness of 5nm to 500nm according to the type of electrode material. The upper electrode 130 may have a fine patterned structure through a shadow mask or a dry etching process or a conventional photolithography process.

The upper electrode 130 may be formed in the same manner as the lower electrode 110 described above.

2 is a graph illustrating voltage-current characteristics for describing an operation of a memory manufactured according to an exemplary embodiment of the present invention.

Referring to FIG. 2, the lower electrode is made of platinum and has a thickness of about 100 nm. In addition, a resistance change layer is formed on the lower electrode.

The resistance change layer includes TiO ₂ . In addition, the first oxygen-deficient oxide layer constituting the resistance change layer is composed of TiO _{1 .5,} it has a thickness of about 10nm. First second oxygen-deficient oxide film formed in the oxygen-deficient oxide layer upper is composed of TiO _{1 .39,} has a thickness of about 50nm. In addition, the third oxygen deficient oxide film has a composition and thickness substantially the same as that of the first oxygen deficient oxide film. Thus, the third oxygen depleted oxide film is composed of TiO _1.5 and has a thickness of about 10 nm.

In addition, an upper electrode is formed on the resistance change layer. The material of the upper electrode is platinum and has a thickness of about 100 nm.

The voltage is applied to the upper and lower electrodes of the resistance change memory having the above-described configuration, and the current flowing therein is measured.

3 to 7 are conceptual views illustrating physical behavior of a resistance change memory according to the characteristic graph of FIG. 2 according to a preferred embodiment of the present invention.

First, referring to FIGS. 2 and 3, a plurality of conductive channels 140 formed of oxygen vacancies are formed by performing a forming operation. The forming operation is performed after the resistance change memory is initially formed. This is a process of aligning oxygen vacancies scattered on the oxygen deficient oxide layers 121, 123, and 125 according to the direction of the electric field by applying a pulse or a bias of a specific level or more. This forms a conductive channel 140 of oxygen vacancy.

Subsequently, when a positive bias is applied from the upper electrode 130 to the lower electrode 110, the current rapidly increases above a specific voltage. This is described as a phenomenon in which charge moves through the conductive channel 140 formed by oxygen vacancies. Again, when a voltage equal to or greater than the first threshold voltage Vth1 is applied, a phenomenon occurs in which the current decreases as the voltage increases. Then, when a voltage of Vth1 <V ≤ Vth2 is applied, a phenomenon in which the resistance value increases means a transition from a low resistance state to a high resistance state.

This is due to a phenomenon in which oxygen ions of the first oxygen depleted oxide film 121 are separated to fill oxygen vacancies at the interface between the first oxygen depleted oxide film 121 and the second oxygen depleted oxide film 123. Accordingly, the conductive channel 140 is disconnected at the interface between the first oxygen depleted oxide film 121 and the second oxygen depleted oxide film 123. This is because the first oxygen depleted oxide film 121 has a higher fraction of oxygen than the second oxygen depleted oxide film 123 and a negative voltage is applied to the lower electrode 110. Therefore, oxygen ions move to the pores of the interface by the bias applied to the first oxygen deficient oxide film 121 to dissipate the pores, thereby disconnecting the conductive channel 140.

2 and 4, as the level of the positive bias increases, the number of short-circuited conductive channels 140 increases. If a positive bias of greater than or equal to the second threshold voltage Vth2 is applied, most of the conductive channels 140 are disconnected at the interface between the first oxygen depleted oxide film 121 and the second oxygen depleted oxide film 123. . Thus, the resistance change memory maintains a high resistance state. This is called a reset state.

2 and 5, the level of positive bias applied between the upper electrode 130 and the lower electrode 110 is continuously reduced. The continuous reduction proceeds until sub bias is applied between the upper electrode 130 and the lower electrode 110. In particular, when the sub-bias is applied below a certain level, the current rapidly increases to a negative value. This is described as the conductive channel 140 recovered while the sub bias was applied. That is, a positive voltage is applied to the lower electrode 110 by applying the sub bias. This means that oxygen atoms or oxygen ions that have buried oxygen vacancies at the interface between the first oxygen depleted oxide film 121 and the second oxygen depleted oxide film 123 move to the bulk in the first oxygen depleted oxide film 121. Thus, the conductive channel 140 at the interface is restored. Based on this, when a sub-bias below a certain level is applied, a phenomenon in which the current rapidly increases to a negative value occurs. This is due to the movement of charge through the recovered channel. This is called a set state.

Subsequently, the application of the sub bias is deepened to enter the level below the third threshold voltage Vth3. That is, a negative voltage is applied to the upper electrode 130 and a positive voltage is applied to the lower electrode 110. In the first oxygen depleted oxide film 121 to which a positive voltage is applied, movement of oxygen ions to the interface does not occur. On the other hand, in the third oxygen depleted oxide film 125 to which a negative voltage is applied, oxygen ions in the bulk move to the interface between the second oxygen depleted oxide film 123 and the third oxygen depleted oxide film 125. Thus, the conductive channels 140 are sequentially disconnected. Therefore, as the negative bias value decreases, the current enters the negative resistance state where the amount of current decreases. This is a negative resistance state where the amount of current decreases as the absolute value of the negative bias value increases, and the resistance change memory is a reset process.

2 and 6, when the level of the applied sub-bias decreases below the fourth threshold voltage Vth4, most of the conductive channels at the interface between the second oxygen depleted oxide layer 123 and the third oxygen deficient oxide layer 125 are described. 140 is disconnected. That is, oxygen ions in the bulk of the third oxygen depleted oxide film 125 move to oxygen vacancies at the interface and fill most of the oxygen vacancies. Thus, the formed plurality of conductive channels 140 are disconnected at the interface. This means that the resistance change layer 120 enters a high resistance state. This is called a reset state.

2 and 7, the bias applied between the upper electrode 130 and the lower electrode 110 is gradually increased.

When the bias is gradually increased, the conductive channels 140 of the disconnected second oxygen depleted oxide film 123 and the third oxygen depleted oxide film 125 are gradually recovered. In particular, when positive bias is applied between the upper electrode 130 and the lower electrode 110, the oxygen ions that buried the oxygen vacancies at the interface move away from the interface and move to the oxygen vacancies in the bulk. Thus, the conductive channel 140 disconnected at the interface is recovered again.

That is, the three-layer structure of the present invention can operate as a memory in the case of the high resistance state of FIG. 4 due to the same high read state between Vth1 and Vth2 as shown in FIGS. 4 and 6. The change does not occur so that the current does not flow relatively. In the high resistance state of FIG. 6, the conductive channel 140 between the second resistance layer 123 and the third resistance layer 125 performs the ① set process of FIG. 2. Recovery occurs through the transition to a low resistance state, which appears to flow relatively well. Therefore, when the read voltage is applied, the state of the resistance change memory can be determined with the height of the measured current and used as a digital signal to enable the memory operation.

In the present invention, the resistance change layer 120 has a self-selection characteristic by a constant read voltage. In addition, the state of actually storing data maintains a high resistance state as in the states of FIGS. 4 and 6.

That is, the memory cell maintaining the high resistance state blocks the leakage current and the interference between adjacent cells. This is because the parasitic path is generated by the interference of the adjacent cells that are converted to the low resistance state in the structure of the conventional resistance change memory, thereby preventing the leakage current increase and the memory malfunction. Therefore, the selectivity of a specific memory cell for which a write or read operation is desired can be improved, and thus, a malfunction due to interference or leakage current between adjacent memory cells can be effectively prevented.

100 substrate 110 lower electrode
120: resistance change layer 130: upper electrode

Claims (11)

Board;
A lower electrode formed on the substrate;
A resistance change layer formed on the lower electrode and made of the same material and having a state change according to formation and disappearance of the conductive channel and a self-selection characteristic according to the state change; And
And a top electrode formed over the resistance change layer. 2. The memory of claim 1 wherein the conductive channel is formed by oxygen vacancy. The method of claim 1, wherein the resistance change layer,
A first oxygen deficient oxide film formed on the lower electrode;
A second oxygen depleted oxide film formed on the first oxygen deficient oxide film and having a lower oxygen fraction than the first oxygen deficient oxide film; And
And a third oxygen depleted oxide film formed on the second oxygen depleted oxide film and having a higher oxygen fraction than the second oxygen deficient oxide film. The resistance change memory according to claim 3, wherein the first oxygen depleted oxide film to the third oxygen depleted oxide film realize a low resistance state by forming the conductive channel due to oxygen vacancies. 4. The resistance change memory according to claim 3, wherein the first oxygen depleted oxide film to the third oxygen depleted oxide film realize a high resistance state by disconnection of a conductive channel due to embedding of oxygen vacancies at an interface. 6. The resistance change of claim 5, wherein disconnection of the conductive channel is achieved by oxygen ions in the first oxygen depleted oxide film or the third oxygen deficient oxide film filling the oxygen vacancies at the interface of the second oxygen deficient oxide film. Memory. The resistance change memory of claim 1, wherein the resistance change layer comprises TiO ₂ , MgO, NiO, ZnO, or HfO ₂ . Lower electrode;
A resistance change layer formed on the lower electrode, made of the same material, and having a state change performed by embedding oxygen vacancies or formation of oxygen vacancies at an interface of membranes having different relative oxygen fractions; And
A resistance change memory including an upper electrode formed on the resistance change layer. The method of claim 8, wherein the resistance change layer,
A first oxygen deficient oxide film formed on the lower electrode;
A second oxygen depleted oxide film formed on the first oxygen deficient oxide film and having a lower oxygen fraction than the first oxygen deficient oxide film; And
And a third oxygen depleted oxide film formed on the second oxygen depleted oxide film and having a higher oxygen fraction than the second oxygen deficient oxide film. 10. The memory of claim 9, wherein the first oxygen depleted oxide film to the third oxygen depleted oxide film has a conductive channel formed by alignment or connection of oxygen vacancies. The resistance change memory as claimed in claim 8, wherein the resistance change layer has a resistance change characteristic in which a current rapidly increases with application of a positive bias or a negative bias.

Images