WO2013051267A1 - 不揮発性記憶素子および不揮発性記憶装置 - Google Patents
不揮発性記憶素子および不揮発性記憶装置 Download PDFInfo
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- WO2013051267A1 WO2013051267A1 PCT/JP2012/006368 JP2012006368W WO2013051267A1 WO 2013051267 A1 WO2013051267 A1 WO 2013051267A1 JP 2012006368 W JP2012006368 W JP 2012006368W WO 2013051267 A1 WO2013051267 A1 WO 2013051267A1
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- G11C13/0002—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00 using resistive RAM [RRAM] elements
- G11C13/0021—Auxiliary circuits
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- G11C—STATIC STORES
- G11C13/00—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00
- G11C13/0002—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00 using resistive RAM [RRAM] elements
- G11C13/0007—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00 using resistive RAM [RRAM] elements comprising metal oxide memory material, e.g. perovskites
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- G11C13/00—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00
- G11C13/0002—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00 using resistive RAM [RRAM] elements
- G11C13/0021—Auxiliary circuits
- G11C13/0061—Timing circuits or methods
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- G—PHYSICS
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- G11C—STATIC STORES
- G11C13/00—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00
- G11C13/0002—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00 using resistive RAM [RRAM] elements
- G11C13/0021—Auxiliary circuits
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- G11C13/00—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00
- G11C13/0002—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00 using resistive RAM [RRAM] elements
- G11C13/0021—Auxiliary circuits
- G11C13/0069—Writing or programming circuits or methods
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- H10B—ELECTRONIC MEMORY DEVICES
- H10B63/00—Resistance change memory devices, e.g. resistive RAM [ReRAM] devices
- H10B63/20—Resistance change memory devices, e.g. resistive RAM [ReRAM] devices comprising selection components having two electrodes, e.g. diodes
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- H10B—ELECTRONIC MEMORY DEVICES
- H10B63/00—Resistance change memory devices, e.g. resistive RAM [ReRAM] devices
- H10B63/30—Resistance change memory devices, e.g. resistive RAM [ReRAM] devices comprising selection components having three or more electrodes, e.g. transistors
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- H10B—ELECTRONIC MEMORY DEVICES
- H10B63/00—Resistance change memory devices, e.g. resistive RAM [ReRAM] devices
- H10B63/80—Arrangements comprising multiple bistable or multi-stable switching components of the same type on a plane parallel to the substrate, e.g. cross-point arrays
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- H10N70/00—Solid-state devices without a potential-jump barrier or surface barrier, and specially adapted for rectifying, amplifying, oscillating or switching
- H10N70/20—Multistable switching devices, e.g. memristors
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- H10N70/801—Constructional details of multistable switching devices
- H10N70/881—Switching materials
- H10N70/883—Oxides or nitrides
- H10N70/8833—Binary metal oxides, e.g. TaOx
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- G11C2213/00—Indexing scheme relating to G11C13/00 for features not covered by this group
- G11C2213/50—Resistive cell structure aspects
- G11C2213/55—Structure including two electrodes, a memory active layer and at least two other layers which can be a passive or source or reservoir layer or a less doped memory active layer
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- G11C2213/79—Array wherein the access device being a transistor
Definitions
- the present invention relates to a nonvolatile memory element, and more particularly to a variable resistance nonvolatile memory element whose resistance value reversibly changes in accordance with an applied electrical signal and a nonvolatile memory device including the nonvolatile memory element. .
- ReRAM nonvolatile memory device
- nonvolatile memory elements are roughly classified into two types depending on the material (resistance change material) used for the resistance change layer.
- One of them is a perovskite material (Pr 1-x Ca x MnO 3 (PCMO), La 1-x Sr x MnO 3 (LSMO), GdBaCo x O y (GBCO), etc.) disclosed in Patent Document 1 and the like) Is a variable resistance nonvolatile memory element using the above as a variable resistance material.
- the other is a variable resistance nonvolatile memory element using a binary transition metal oxide as a variable resistance material. Since the binary transition metal oxide has a very simple composition and structure as compared with the above-described perovskite material, composition control and film formation during manufacture are easy. In addition, there is an advantage that the compatibility with the semiconductor manufacturing process is relatively good, and many studies have been made in recent years.
- FIG. 17 is a cross-sectional view showing a configuration of a conventional nonvolatile memory element 1400 disclosed in Patent Document 2. As shown in FIG.
- a conventional nonvolatile memory element using a transition metal oxide is in a state where resistance can be changed by forming a filament in the resistance change layer by applying an initial break voltage. At this time, the filament formed in the resistance change layer penetrates the resistance change layer so as to connect the first electrode and the second electrode.
- the variable resistance element having such a filament has a problem in that the variation in resistance value of the variable resistance layer in the resistance change increases, and the variation in resistance change characteristics increases.
- the present invention has been made to solve the above-described problems, and an object of the present invention is to provide a nonvolatile memory element and a nonvolatile memory device in which variation in resistance change characteristics is small.
- a nonvolatile memory element includes a first electrode, a second electrode, and the first electrode and the second electrode. And a resistance change layer that reversibly transits between a high resistance state and a low resistance state based on a voltage polarity applied between the first electrode and the second electrode.
- a nonvolatile memory element with little variation in resistance change characteristics can be obtained by controlling resistance change in a local region.
- miniaturization and large capacity of a nonvolatile memory device using the nonvolatile memory element can be realized.
- FIG. 1 is a cross-sectional view of the nonvolatile memory element according to Embodiment 1 of the present invention.
- FIG. 2A is a diagram for explaining formation of a filament in a local region.
- FIG. 2B is a diagram for explaining formation of a filament in a local region.
- FIG. 2C is a diagram for explaining formation of a filament in a local region.
- FIG. 3A is a cross-sectional view showing a method for manufacturing the main part of the nonvolatile memory element according to Embodiment 1 of the present invention.
- FIG. 3B is a cross-sectional view showing a method for manufacturing the main part of the nonvolatile memory element according to Embodiment 1 of the present invention.
- FIG. 3A is a cross-sectional view showing a method for manufacturing the main part of the nonvolatile memory element according to Embodiment 1 of the present invention.
- FIG. 3B is a cross-sectional view showing a method for manufacturing the main part of the
- FIG. 3C is a cross-sectional view showing a method for manufacturing the main part of the nonvolatile memory element according to Embodiment 1 of the present invention.
- FIG. 3D is a cross-sectional view showing a method for manufacturing the main part of the nonvolatile memory element according to Embodiment 1 of the present invention.
- FIG. 4 is a diagram illustrating an operation example of the nonvolatile memory element according to Embodiment 1 of the present invention.
- FIG. 5A shows a nonvolatile memory element using an oxygen-deficient tantalum oxide for the resistance change layer according to Embodiment 1 of the present invention when Pt is used for the first electrode and the second electrode.
- FIG. 5B shows a non-volatile memory element using oxygen-deficient tantalum oxide for the resistance change layer according to Embodiment 1 of the present invention when Pt is used for the first electrode and the second electrode. It is a figure which shows the initial break voltage dependence of the resistance change with respect to the application frequency of a voltage pulse.
- FIG. 5C shows a non-volatile memory element using oxygen-deficient tantalum oxide for the resistance change layer according to Embodiment 1 of the present invention when Pt is used for the first electrode and the second electrode. It is a figure which shows the initial break voltage dependence of the resistance change with respect to the application frequency of a voltage pulse.
- FIG. 5B shows a non-volatile memory element using oxygen-deficient tantalum oxide for the resistance change layer according to Embodiment 1 of the present invention when Pt is used for the first electrode and the second electrode. It is a figure which shows the initial break voltage dependence of the resistance change with respect to the application frequency of a voltage pulse.
- FIG. 5D shows a nonvolatile memory element using oxygen-deficient tantalum oxide for the resistance change layer according to Embodiment 1 of the present invention, when Pt is used for the first electrode and the second electrode. It is a figure which shows the normal distribution of the electric current value in a high resistance state, and the resistance value in a low resistance state.
- FIG. 5E is a diagram showing the initial break voltage dependence of the slope of the normal distribution of the current value in the high resistance state and the current value in the low resistance state of FIG. 5D.
- FIG. 6A shows a case where Pt is used for the first electrode and the second electrode in the nonvolatile memory element using the oxygen-deficient tantalum oxide for the resistance change layer according to Embodiment 1 of the present invention.
- FIG. 6B shows a non-volatile memory element using oxygen-deficient tantalum oxide for the resistance change layer according to Embodiment 1 of the present invention when Pt is used for the first electrode and the second electrode. It is a figure which shows the resistance change with respect to the application frequency of a voltage pulse.
- 6C shows a nonvolatile memory element using oxygen-deficient tantalum oxide for the resistance change layer according to Embodiment 1 of the present invention when Pt is used for the first electrode and the second electrode.
- FIG. It is a figure which shows the resistance change with respect to the application frequency of a voltage pulse.
- FIG. 7 is a cross-sectional view of a nonvolatile memory element according to a variation of Embodiment 1 of the present invention.
- FIG. 8A is a TEM photograph of a local region of a nonvolatile memory element operated with an initial break voltage of ⁇ 2.5V.
- FIG. 8B is a TEM photograph of a local region of a nonvolatile memory element operated with an initial break voltage of ⁇ 5.0V.
- FIG. 9 is a diagram for explaining a typical example of the oxygen content of the resistance change layer according to Embodiment 1 of the present invention.
- FIG. 10 is a block diagram showing a configuration of the nonvolatile memory device according to Embodiment 2 of the present invention.
- FIG. 10 is a block diagram showing a configuration of the nonvolatile memory device according to Embodiment 2 of the present invention.
- FIG. 11 is a perspective view showing the configuration (configuration corresponding to 4 bits) of part A in FIG.
- FIG. 12 is a cross-sectional view showing a configuration of a nonvolatile memory element included in the nonvolatile memory device according to Embodiment 2 of the present invention.
- FIG. 13 is a timing chart showing an operation example of the nonvolatile memory device according to Embodiment 2 of the present invention.
- FIG. 14 is a block diagram showing a configuration of the nonvolatile memory device according to Embodiment 3 of the present invention.
- FIG. 15 is a cross-sectional view showing the configuration (configuration corresponding to 2 bits) of part C in FIG.
- FIG. 16 is a timing chart showing an operation example of the nonvolatile memory device according to Embodiment 3 of the present invention.
- FIG. 17 is a cross-sectional view of a conventional nonvolatile memory element.
- the nonvolatile memory element includes a first electrode, a second electrode, and the first electrode and the second electrode interposed between the first electrode and the second electrode.
- a resistance change layer that reversibly transits between a high resistance state and a low resistance state based on a voltage polarity applied between the second electrodes, and the resistance change layer includes a first metal oxide. 1 oxide layer, and disposed between and in contact with the first oxide layer and the second electrode, and includes an oxide of a second metal and oxygen as compared with the first oxide layer.
- a second oxide layer having a small deficiency, and the first oxide layer and the second oxide layer are disposed in contact with the second electrode and are not in contact with the first electrode.
- the oxygen deficiency is larger than that of the second oxide layer, and the first oxide layer includes a local region having a different oxygen deficiency.
- the initial break voltage can be lowered and the resistance can be changed at a low voltage. Further, since the local region is not in contact with the first electrode, the resistance change of the parasitic resistance caused by the influence of the first electrode can be suppressed, and the variation in resistance change characteristics can be reduced.
- the local region is disposed in the first oxide layer, is not in contact with the first electrode, and has a first oxygen locality greater than that of the first oxide layer.
- a region, and between the first local region and the second electrode are disposed in contact with the first local region and the second electrode, and the oxygen deficiency is lower than that of the first local region.
- a second local region that is small and has a larger oxygen deficiency than the second oxide layer.
- the resistance change layer may transition between a high resistance state and a low resistance state in the second local region.
- the second local region may have a portion smaller than the thickness of the second oxide layer in the thickness in the direction from the first electrode toward the second electrode.
- the metal oxide contained in the second oxide layer and the first oxide layer may be the same kind of metal oxide.
- the same kind of metal may be Ta.
- first electrode and the second electrode may be made of the same material.
- nonvolatile memory element may further include a load element electrically connected to the resistance change layer.
- the load element may be a fixed resistor, a transistor, or a diode.
- variable resistance layer only one first local region may be formed in the variable resistance layer.
- a nonvolatile memory device includes a substrate, a plurality of first wirings formed in parallel to each other on the substrate, and a main substrate above the plurality of first wirings.
- a plurality of second wirings formed parallel to each other in a plane parallel to the surface and three-dimensionally intersecting with the plurality of first wirings; the plurality of first wirings; and the plurality of second wirings 10.
- a memory cell array comprising the nonvolatile memory element according to claim 1 provided corresponding to a three-dimensional intersection with the memory cell array, and at least one of the nonvolatile memory element comprising the memory cell array.
- a selection circuit for selecting one nonvolatile memory element, a writing circuit for writing data by applying a voltage to the nonvolatile memory element selected by the selection circuit, and a resistance of the nonvolatile memory element selected by the selection circuit The value To output, characterized in that it comprises a read circuit for reading data.
- the nonvolatile memory element may include a current control element electrically connected to the resistance change layer.
- a nonvolatile memory device is connected to a substrate, a plurality of word lines and a plurality of bit lines, and the plurality of word lines and the plurality of bit lines formed over the substrate.
- a memory cell array including a plurality of transistors, and a plurality of the nonvolatile memory elements provided in one-to-one correspondence with the plurality of transistors, and at least one of the nonvolatile memory elements included in the memory cell array.
- a selection circuit for selecting a nonvolatile memory element a writing circuit for writing data by applying a voltage to the nonvolatile memory element selected by the selection circuit, and a resistance value of the nonvolatile memory element selected by the selection circuit
- a readout circuit for reading out data by detecting.
- a nonvolatile memory element with little variation in resistance change characteristics can be obtained by controlling resistance change in a local region.
- miniaturization and large capacity of a nonvolatile memory device using the nonvolatile memory element can be realized.
- FIG. 1 is a cross-sectional view showing a configuration example of the nonvolatile memory element according to Embodiment 1 of the present invention.
- the nonvolatile memory element 100 of this embodiment includes a substrate 101, an interlayer insulating film 102 formed on the substrate 101, a first electrode 103 formed on the interlayer insulating film 102, a second electrode An electrode 106 and a resistance change layer 104 sandwiched between the first electrode 103 and the second electrode 106 are provided.
- the resistance change layer 104 is interposed between the first electrode 103 and the second electrode 106 and reversibly based on an electrical signal applied between the first electrode 103 and the second electrode 106. It is a layer whose resistance value changes.
- the resistance change layer 104 is a layer that reversibly transitions between a high resistance state and a low resistance state in accordance with the polarity of a voltage applied between the first electrode 103 and the second electrode 106.
- the resistance change layer 104 is formed on the first oxide layer 104 a connected to the first electrode 103 and the second oxide 106 formed on the first oxide layer 104 a and connected to the second electrode 106. It is configured by stacking at least two layers with the oxide layer 104b, and is disposed in contact with the second electrode 106 in the first oxide layer 104a and the second oxide layer 104b. A local region 105 that is not in contact is provided. At least part of the local region 105 is formed in the second oxide layer 104b, and the degree of oxygen deficiency reversibly changes in accordance with the application of the electric pulse. The local region 105 is considered to include a filament composed of oxygen defect sites.
- the resistance change phenomenon in the variable resistance layer 104 of the laminated structure is considered that the resistance value changes when an oxidation-reduction reaction occurs in the minute local region 105 and the filament (conductive path) in the local region 105 changes. It is done.
- the resistance change layer 104 has a stacked structure of a first oxide layer 104a and a second oxide layer 104b.
- the first oxide layer 104a includes an oxygen-deficient first metal oxide
- the second oxide layer 104b is a second metal having a lower degree of oxygen deficiency than the first metal oxide. Of oxides. Therefore, the oxygen deficiency of the second oxide layer 104b is smaller than the oxygen deficiency of the first oxide layer. Therefore, the resistance value of the second oxide layer 104b is higher than the resistance value of the first oxide layer 104a.
- the resistance change layer 104 includes a stacked structure of a first oxide layer 104a including at least a first metal oxide and a second oxide layer 104b including a second metal oxide. .
- the first oxide layer 104a is disposed between the first electrode 103 and the second oxide layer 104b, and the second oxide layer 104b is formed between the first oxide layer 104a and the second oxide layer 104b.
- the thickness of the second oxide layer 104b may be smaller than the thickness of the first oxide layer 104a. In this case, a structure in which a later-described local region 105 is not in contact with the first electrode 103 can be easily formed. Since the resistance value of the second oxide layer 104b is higher than the resistance value of the first oxide layer 104a, the electric field applied to the resistance change layer 104 tends to concentrate on the second oxide layer 104b.
- oxygen deficiency refers to the stoichiometric composition of a metal oxide (if there are a plurality of stoichiometric compositions, the resistance value is the highest among them. It refers to the proportion of oxygen that is deficient with respect to the amount of oxygen that constitutes the oxide of the stoichiometric composition. Stoichiometric metal oxides are more stable and have higher resistance values than other metal oxides.
- the oxide having the stoichiometric composition according to the above definition is Ta 2 O 5 , and can be expressed as TaO 2.5 .
- the oxygen deficiency of the oxygen-excess metal oxide has a negative value.
- the oxygen deficiency is described as including a positive value, 0, and a negative value.
- An oxide with a low degree of oxygen deficiency has a high resistance value because it is closer to a stoichiometric oxide, and an oxide with a high degree of oxygen deficiency has a low resistance value because it is closer to the metal constituting the oxide.
- oxygen content is used instead of “oxygen deficiency” when the metals constituting the first oxide layer 104a and the second oxide layer 104b are of the same type. May be used. “High oxygen content” corresponds to “low oxygen deficiency” and “low oxygen content” corresponds to “high oxygen deficiency”.
- the resistance change layer 104 according to this embodiment is not limited to the case where the metals constituting the first oxide layer 104a and the second oxide layer 104b are the same type. Absent.
- Oxygen content is the ratio of oxygen atoms to the total number of atoms.
- the oxygen content of Ta 2 O 5 is the ratio of oxygen atoms to the total number of atoms (O / (Ta + O)), which is 71.4 atm%. Therefore, the oxygen-deficient tantalum oxide has an oxygen content greater than 0 and less than 71.4 atm%.
- the oxygen content corresponds to the degree of oxygen deficiency. is there. That is, when the oxygen content of the second metal oxide is greater than the oxygen content of the first metal oxide, the degree of oxygen deficiency of the second metal oxide is that of the first metal oxide. Less than oxygen deficiency.
- the resistance change layer 104 includes a local region 105 in the vicinity of the interface between the first oxide layer 104a and the second oxide layer 104b.
- the oxygen deficiency in the local region 105 is larger than the oxygen deficiency in the second oxide layer 104b, and is different from the oxygen deficiency in the first oxide layer 104a.
- the local region 105 can be formed by applying an initial break voltage to the resistance change layer 104 having a stacked structure of the first oxide layer 104a and the second oxide layer 104b. As will be described later, at this time, the initial break voltage may be a low voltage. By the initial break, a local region 105 that is in contact with the second electrode 106, penetrates the second oxide layer 104b, partially penetrates the first oxide layer 104a, and is not in contact with the first electrode 103 is formed. Is done.
- the local region means a region in the resistance change layer 104 where current flows predominantly when a voltage is applied between the first electrode 103 and the second electrode 106.
- the local region 105 means a region including a set of a plurality of filaments (conductive paths) formed in the resistance change layer 104. That is, the resistance change in the resistance change layer 104 is expressed through the local region 105. Accordingly, when a driving voltage is applied to the resistance change layer 104 in the low resistance state, a current flows predominantly in the local region 105 including the filament.
- the resistance change layer 104 transitions between a high resistance state and a low resistance state in the local region 105.
- the size of the local region 105 may be small, and its lower end is not in contact with the first electrode 103. By reducing the size of the local region 105, the variation in resistance change is reduced. However, the local region 105 has a size that can secure at least a filament (conductive path) necessary for flowing current.
- FIGS. 2A to 2C are diagrams for explaining the formation of filaments in the local region 105, and show the results of simulation using a percolation model.
- the filament conductive path
- the percolation model assumes a random distribution of oxygen defect sites (hereinafter simply referred to as defect sites) in the local region 105, and if the density of defect sites exceeds a certain threshold, a connection such as defect sites is formed.
- defect sites oxygen defect sites
- the metal oxide is composed of metal ions and oxygen ions, and the “defect” means that oxygen is lost from the stoichiometric composition in the metal oxide.
- This means that “defect site density” also corresponds to the degree of oxygen deficiency. That is, as the oxygen deficiency increases, the density of defect sites also increases.
- the site of oxygen ions in the resistance change layer 104 is approximately assumed as a lattice-divided region (hereinafter referred to as a site), and the defect sites (oxygen ions are deficient) formed stochastically.
- the filament formed from the site is determined by simulation.
- a site written “0” represents a defect site formed in the local region 105.
- Clusters of black-filled sites sites where numbers other than “0” are written) (an assembly of defect sites connected to each other) are present in the local region 105 when a voltage is applied in the vertical direction in the figure. It represents the filament that is formed and shows the path through which current flows.
- a site painted in gray represents a site occupied by oxygen ions, and is a high-resistance region.
- a cluster of defect sites connected from the upper end to the lower end is a set of filaments that conduct current between the lower surface and the upper surface of the local region 105. Composed. Based on the percolation model, the number and shape of the filaments are formed stochastically. The distribution of the number and shape of the filaments causes variations in the resistance value of the resistance change layer 104.
- Only one local region 105 may be formed in one resistance change layer 104 of the nonvolatile memory element 100. Thereby, the dispersion
- the number of local regions 105 formed in the resistance change layer 104 can be confirmed by, for example, EBAC (Electron Beam Absorbed Current) analysis.
- a voltage satisfying a predetermined condition is applied between the first electrode 103 and the second electrode 106 by an external power source.
- the resistance value of the resistance change layer 104 of the nonvolatile memory element 100 increases or decreases reversibly.
- a pulse voltage having a predetermined polarity whose amplitude is larger than a predetermined threshold voltage is applied, the resistance value of the resistance change layer 104 increases or decreases.
- such a voltage may be referred to as a “write voltage”.
- the resistance value of the resistance change layer 104 does not change.
- such a voltage may be referred to as a “reading voltage”.
- the resistance change layer 104 is made of an oxygen-deficient metal oxide.
- the base metal of the metal oxide is tantalum (Ta), hafnium (Hf), titanium (Ti), zirconium (Zr), niobium (Nb), tungsten (W), nickel (Ni), iron (Fe), etc. At least one of these transition metals and aluminum (Al) may be selected. Since transition metals can take a plurality of oxidation states, different resistance states can be realized by oxidation-reduction reactions.
- the oxygen-deficient metal oxide refers to the oxygen content (atomic ratio: the number of oxygen atoms in the total number of atoms) than the composition of the metal oxide (usually an insulator) having a stoichiometric composition.
- the nonvolatile memory element 100 can realize a resistance change operation with good reproducibility and stability.
- x is 0.9 or more and 1.6 or less when the composition of the first metal oxide is HfO x .
- the composition of the second metal oxide is HfO y and y is larger than the value of x, the resistance value of the resistance change layer 104 can be stably changed at high speed.
- the film thickness of the second metal oxide may be 3 to 4 nm.
- x is 0.9 or more and 1.4 or less when the composition of the first metal oxide is ZrO x .
- the composition of the second metal oxide is ZrO y and y is larger than the value of x, the resistance value of the resistance change layer 104 can be stably changed at high speed.
- the thickness of the second metal oxide may be 1 to 5 nm.
- a case is considered in which the metal oxide contained in the second oxide layer 104b and the first oxide layer 104a is the same type of metal oxide, and the metal constituting the resistance change layer 104 is tantalum (Ta). .
- the oxygen-deficient tantalum oxide contained in the first oxide layer 104a is represented as TaO x
- the tantalum oxide contained in the second oxide layer 104b is represented as TaO y
- 0 ⁇ x ⁇ 2.5, x ⁇ y may be satisfied.
- 2.1 ⁇ y and 0.8 ⁇ x ⁇ 1.9 may be satisfied.
- the composition of the metal oxide layer can be measured using Rutherford backscattering method.
- the metal oxide contained in the second oxide layer 104b and the first oxide layer 104a may be a different metal oxide. That is, the first metal constituting the oxide of the first metal to be the first oxide layer 104a and the second metal constituting the oxide of the second metal to be the second oxide layer 104b A different metal may be used.
- the second metal oxide may have a lower degree of oxygen deficiency than the first metal oxide, that is, may have a higher resistance. With such a configuration, the voltage applied between the first electrode 103 and the second electrode 106 during the resistance change is more distributed to the second metal oxide, The oxidation-reduction reaction generated in the second metal oxide can be more easily caused.
- the standard electrode potential of the second metal may be lower than the standard electrode potential of the first metal.
- the standard electrode potential represents a characteristic that the higher the value is, the more difficult it is to oxidize. As a result, a redox reaction is likely to occur in the second metal oxide having a relatively low standard electrode potential.
- the resistance change phenomenon is caused by a change in filament (conductive path) caused by an oxidation-reduction reaction in a minute local region 105 formed in the second metal oxide having a high resistance. (Oxygen deficiency) is considered to change.
- titanium oxide for example, TiO 2
- TiO 2 titanium oxide
- an oxygen-deficient tantalum oxide (TaO x ) may be used as the first metal oxide, and an aluminum oxide (Al 2 O 3 ) may be used as the second metal oxide.
- the standard electrode potential represents a characteristic that the higher the value in the positive direction, the less likely it is oxidized. Since the standard electrode potential of titanium constituting the second oxide layer 104b is lower than the standard electrode potential of tantalum constituting the first oxide layer 104a, in the second oxide layer 104b, the first electrode potential is The oxidation-reduction reaction is more likely to occur than in the oxide layer 104a, and the resistance change phenomenon of the resistance change element is also likely to occur.
- the dielectric constant of the second oxide layer 104b may be larger than the dielectric constant of the first oxide layer 104a.
- the band gap of the second oxide layer 104b may be smaller than the band gap of the first oxide layer 104a.
- a material having a high relative dielectric constant is more likely to break down than a material having a lower relative dielectric constant, and a material having a smaller band gap is more likely to break down than a material having a larger band gap.
- TiO 2 as the second oxide layer 104b can lower the initial break voltage.
- the breakdown electric field strength of the second oxide layer 104b is less than that of the first oxide layer 104a. Compared to the electric breakdown field strength, the initial break voltage can be reduced. This is described in J. Org. McPherson et al. , IEDM 2002, p. As shown in FIG. 1 of 633-636, there is a correlation between the breakdown electric field strength (Breakdown Strength) of the oxide layer and the dielectric constant that the dielectric breakdown electric field strength decreases as the dielectric constant increases. Because is seen. In addition, J.H. McPherson et al. , IEDM 2002, p. As shown in FIG. 2 of 633-636, there is a correlation between the breakdown electric field of the oxide layer and the band gap that the breakdown electric field strength increases as the band gap increases. is there.
- materials of the first electrode 103 and the second electrode 106 for example, Pt (platinum), Ir (iridium), Pd (palladium), Ag (silver), Ni (nickel), W (tungsten), Cu ( It is selected from copper, Al (aluminum), Ta (tantalum), Ti (titanium), TiN (titanium nitride), TaN (tantalum nitride) and TiAlN (titanium nitride aluminum).
- the second electrode 106 connected to the second metal oxide having a smaller oxygen deficiency is, for example, a second electrode such as platinum (Pt), iridium (Ir), or palladium (Pd).
- the standard electrode potential is higher than that of the metal constituting the metal oxide and the material constituting the first electrode 103.
- the first electrode 103 connected to the oxide of the first metal having a higher degree of oxygen deficiency may be tungsten (W), nickel (Ni), tantalum (Ta), titanium (Ti), aluminum, for example.
- the standard electrode potential may be made of a material having a lower standard electrode potential than the metal constituting the oxide of the first metal, such as (Al), tantalum nitride (TaN), titanium nitride (TiN), or the like.
- the standard electrode potential represents a characteristic that the higher the value is, the more difficult it is to oxidize.
- the local region 105 is formed so as not to be in contact with the first electrode 103, so that the first electrode 103 does not affect the resistance change. Therefore, providing the local region 105 of this embodiment increases the degree of freedom in selecting the material for the first electrode 103. Therefore, for example, the first electrode 103 and the second electrode 106 may be made of the same material. In this case, the process can be simplified by applying the process conditions of the first electrode 103 to the second electrode 106.
- the substrate 101 for example, a silicon single crystal substrate or a semiconductor substrate can be used, but the substrate 101 is not limited thereto. Since the resistance change layer 104 can be formed at a relatively low substrate temperature, for example, the resistance change layer 104 can be formed on a resin material or the like.
- the nonvolatile memory element 100 may further include a load element electrically connected to the resistance change layer 104, such as a fixed resistor, a transistor, or a diode.
- a load element electrically connected to the resistance change layer 104, such as a fixed resistor, a transistor, or a diode.
- Nonvolatile Memory Element Manufacturing Method and Operation Next, an example of a method for manufacturing the nonvolatile memory element 100 of the present embodiment will be described with reference to FIGS. 3A to 3D.
- an interlayer insulating film 102 having a thickness of 200 nm is formed on a substrate 101 made of, for example, single crystal silicon by a thermal oxidation method. Then, for example, a Pt thin film having a thickness of 100 nm is formed on the interlayer insulating film 102 as the first electrode 103 by a sputtering method. Note that an adhesive layer of Ti, TiN, or the like can be formed between the first electrode 103 and the interlayer insulating film 102 by a sputtering method. Thereafter, an oxygen-deficient first oxide layer 104a is formed on the first electrode 103 by a reactive sputtering method using a Ta target, for example.
- the first oxide layer 104a is formed on the surface of the first oxide layer 104a by, for example, modification of the outermost surface of the first oxide layer 104a by oxidation or reactive sputtering using a Ta target.
- a second oxide layer 104b having a lower oxygen deficiency than that of 104a (that is, having a higher resistance value) is formed.
- the variable resistance layer 104 is configured by a stacked structure in which the first oxide layer 104a and the second oxide layer 104b are stacked.
- the thickness of the second oxide layer 104b if it is too large, there is a disadvantage that the initial resistance value becomes too high, and if it is too small, there is a disadvantage that a stable resistance change cannot be obtained. It may be about 8 nm or more.
- a 150 nm-thick Pt thin film is formed as the second electrode 106 on the second oxide layer 104b by a sputtering method.
- a pattern 107 made of a photoresist is formed by a photolithography process.
- an element region 109 is formed by dry etching using the pattern 107 as a mask.
- an initial break voltage is applied between the first electrode 103 and the second electrode 106 (between the electrodes) to form a local region 105 in the resistance change layer 104.
- An example of a voltage range for forming the local region 105 will be described below with reference to FIGS. 4 to 6C.
- the size of the first electrode 103, the second electrode 106, and the resistance change layer 104 is 0.5 ⁇ m ⁇ 0.5 ⁇ m (area 0. 25 ⁇ m 2 ).
- the thickness of the resistance change layer 104 is 30 nm, the thickness of the first oxide layer 104a is 25 nm, and the thickness of the second oxide layer 104b is 5 nm.
- a read voltage eg, 0.4 V
- the resistance value of the nonvolatile memory element 100 is an initial resistance value (a value higher than the resistance value HR in the high resistance state, for example, 10 7 to 10 8 ⁇ )
- the initial break voltage is By applying between the electrodes, the resistance state changes.
- two kinds of voltage pulses having different pulse widths of 100 ns, for example, are applied alternately between the first electrode 103 and the second electrode 106 of the nonvolatile memory element 100 as shown in FIG. 4
- the resistance value of the resistance change layer 104 changes. That is, when a negative voltage pulse (pulse width 100 ns) is applied between the electrodes as a writing voltage, the resistance value of the resistance change layer 104 decreases from the high resistance value HR to the low resistance value LR.
- the resistance value of the resistance change layer 104 increases from the low resistance value LR to the high resistance value HR.
- the polarity of the voltage pulse is “positive” when the potential of the second electrode 106 is high with respect to the potential of the first electrode 103, and the potential of the first electrode 103 is referred to In the case where the potential of the second electrode 106 is low, it is “negative”.
- FIGS. 5A to 5C show that the initial break voltage pulses Vbreak of ⁇ 2.5 V, ⁇ 3.5 V, and ⁇ 4.0 V are applied to the three nonvolatile memory elements 100 existing on the same substrate, respectively.
- the negative voltage pulse for writing has a voltage value of ⁇ 1.5 V and a pulse width of 100 ns
- the positive voltage pulse for writing has +2.0 V and a pulse width of 100 ns.
- the current value of each nonvolatile memory element 100 is a value read by applying a read voltage of 0.4 V between the electrodes.
- the read voltage is a voltage whose amplitude is sufficiently smaller than the write threshold voltage, and the resistance state does not change even when the read voltage is applied to the nonvolatile memory element 100.
- the horizontal axis represents the number of application of the applied write voltage pulse (negative voltage pulse and positive voltage pulse are alternately applied), and the vertical axis represents the read current value. 5A to 5C, the number of application of the write voltage pulse is 100 times.
- FIG. 5D is a diagram showing the relationship between the current values obtained in FIGS. 5A to 5C and the normal distribution of the current values.
- the left side of FIG. 5D shows the normal distribution of the current value in the high resistance state, and the right side shows the normal distribution of the current in the low resistance state.
- the slope of the normal distribution corresponds to the variation in resistance value.
- FIG. 5E is a diagram showing the relationship between the slope of the normal distribution obtained in FIG. 5D and the absolute value of the initial break voltage.
- the vertical axis in FIG. 5E is the slope of the normal distribution of the current value in the high resistance state or the low resistance state, and the horizontal axis is the absolute value of the initial break voltage pulse Vbreak.
- FIG. 5E shows that as the absolute value of the initial break voltage is higher, the slope of the normal distribution of the current value is smaller in both the high resistance state and the low resistance state. This means that the higher the initial break voltage, the greater the variation in the high resistance value HR and the low resistance value LR. This is thought to be because the local region 105 becomes larger and the defect density in the local region 105 increases and resistance values tend to vary as the initial break voltage increases. If the initial break voltage is further increased, the resistance change characteristic becomes further unstable.
- 6A to 6C show a case where a negative voltage pulse for writing and three nonvolatile memory elements 100 existing on the same substrate, after applying the same initial break voltage pulse of ⁇ 5 V to a low resistance state, It is a figure which shows the change of the electric current value of each non-volatile memory element 100 when a positive voltage pulse is applied alternately.
- the negative voltage pulse for writing has a voltage value of ⁇ 1.5 V and a pulse width of 100 ns
- the positive voltage pulse for writing has +2.0 V and a pulse width of 100 ns.
- the current value of each nonvolatile memory element 100 is a value read by applying a read voltage of 0.4 V between the electrodes.
- the horizontal axis represents the number of applied write voltage pulses
- the vertical axis represents the read current value. 6A to 6C, the number of application of the write voltage pulse is about 70 times.
- the current value of the non-volatile memory element 100 shown in FIG. 6A repeatedly changes to Ih1 when a positive voltage pulse is applied and to Il1 when a negative voltage pulse is applied. From this figure, it can be seen that the resistance value changes relatively stably at least about 70 times.
- the current value of the nonvolatile memory element 100 shown in FIG. 6B changes between Ih2 and Il2 until the number of times of pulse application is about 20, but when the number of times of pulse application exceeds 20, The resistance change width is widened, and the current value changes between Ih2 and Il3.
- FIG. 6B shows that the change in resistance value of the nonvolatile memory element 100 is unstable.
- the current value of the nonvolatile memory element 100 shown in FIG. 6C has a narrower resistance change width as the number of pulse applications increases. Specifically, the current value changed between Ih3 and Il4 until the number of times of pulse application is about 20, but when the number of times of pulse application exceeds 30, the resistance change width becomes narrower, and Ih3 and Il5. The current value changes between
- the local region 105 to be formed becomes large, the local region 105 penetrates the resistance change layer 104, and the local region 105 includes the first electrode 103 and the second electrode. 106 comes into contact with both.
- the nonvolatile memory element 100 has a property of changing resistance in two modes, and it is considered that a desired stable resistance change may not be obtained.
- FIG. 7 is a cross-sectional view showing one configuration example of the nonvolatile memory element according to the modification of Embodiment 1 of the present invention. Only differences from the nonvolatile memory element 100 of Embodiment 1 will be described below.
- the nonvolatile memory element 100 of this embodiment includes a first local region 105 a in which the local region 105 is formed in the first oxide layer 104 a, and the first local region 105 a and the second electrode 106. It differs from the nonvolatile memory element 100 of Embodiment 1 in that the first local region 105a and the second local region 105b disposed in contact with the second electrode 106 are interposed therebetween.
- the first local region 105 a is not in contact with the first electrode 103.
- the degree of oxygen deficiency in the first local region 105a is greater than the degree of oxygen deficiency in the first oxide layer 104a.
- the oxygen deficiency of the second local region 105b is smaller than the oxygen deficiency of the first local region 105a and larger than the oxygen deficiency of the second oxide layer 104b.
- the second local region 105b is a region where a filament is efficiently formed
- the first local region 105a is a region that assists the exchange of oxygen in the second local region 105b and assists the formation of the filament. is there. Therefore, the resistance change in the resistance change layer 104 is expressed through the second local region 105b.
- a driving voltage is applied to the resistance change layer 104 in the low resistance state
- current is dominantly applied to the second local region 105b including the filament and the first local region 105a having a relatively low resistance value.
- the resistance change layer 104 transitions between a high resistance state and a low resistance state in the second local region 105b.
- the first local region 105 a is sized so that the lower end thereof does not contact the first electrode 103.
- the diameter of the second local region 105b varies depending on the element size and the like, but may be small, for example, less than 40 nm in diameter (see FIG. 8B).
- the second local region 105b has a size that can secure at least a filament (conductive path) necessary for flowing current.
- the distance between the oxygen defect sites is about 0.4 nm, and thus the second local region 105b varies depending on the method of forming the local region 105. May be 1 nm or more.
- the diameter of the second local region 105b is about 10 nm.
- the first local region 105 a is a region having a large oxygen deficiency formed so as not to be in contact with the first electrode 103 at a site far from the second electrode 106.
- the second local region 105b penetrates the second oxide layer 104b in a portion close to the second electrode 106, and is deficient in oxygen formed so as to be in contact with the second electrode 106 and the first local region 105a. This is a small area.
- the film thickness of the second local region 105b may partially include a region thinner than the second oxide layer 104b.
- the second local region 105b has a portion whose thickness in the direction from the first electrode 103 toward the second electrode 106 is smaller than the thickness of the second oxide layer 104b.
- FIG. 8A and 8B show cross-sectional TEM photographs after the resistance change operation of the nonvolatile memory element 100 having different initial break voltages.
- FIG. 8A is a cross-sectional TEM (Transmission Electron Microscope) photograph after resistance change of the nonvolatile memory element 100 to which an initial break voltage of ⁇ 2.5 V is applied.
- the white region is a region where oxygen is high
- the black region is a region where oxygen is low.
- the white area of the image has a relatively high resistance value
- the black area of the image has a relatively low resistance value. Note that the samples in FIGS. 8A and 8B are the same as the samples used in the measurements in FIGS. 4 to 6C.
- the diameter of the second local region 105 b is about 10 nm, and the first local region 105 a is not in contact with the first electrode 103.
- the local region 105 (first local region 105 a) surrounded by the first oxide layer 104 a is darker than the surrounding area because the oxygen content in the local region 105 (first local region 105 a) is increased. This is because the rate is lower than the surroundings and the resistance is low.
- the local region 105 penetrating the second oxide layer 104b is darker than the surrounding second oxide layer 104b because the oxygen content of the local region 105 is lower than that of the surrounding second oxide layer 104b. This is because the resistance is low. In the case of FIG.
- the diameter of the local region 105 in the vicinity of the second oxide layer 104b is about 40 nm, which is larger than the second local region 105b of FIG. 8A.
- the local region 105 is in contact with the first electrode 103. This is the cause of unstable operation when the initial break voltage is increased.
- FIG. 9 is a diagram for explaining a typical example of the oxygen content of the resistance change layer 104 according to the first embodiment.
- FIG. 9B is a diagram in which the distribution of oxygen content in a range surrounded by a dotted line in FIG. 8A is mapped by using the EELS (Electron Energy-Loss Spectroscopy) method. Note that in FIG. 9B, the first oxide layer 104a, the second oxide layer 104b, the first local region 105a, and the second local region 105b are surrounded by dotted lines.
- EELS Electro Energy-Loss Spectroscopy
- the region having a higher oxygen content is shown in black and the region having a lower oxygen content is shown in white. That is, the second oxide layer 104b is darker than the first oxide layer 104a because the oxygen content of the second oxide layer 104b is higher than that of the first oxide layer 104a. is there. Similarly, the oxygen content of the first oxide layer 104a is higher than that of the first local region 105a. In the example shown in FIG. 9B, the thickness of the second local region 105b is thinner than that of the second oxide layer 104b.
- FIG. 9A is a diagram showing the oxygen content in the line segment A-A ′ in FIG. 9B.
- the oxygen content of the second local region 105b is lower than that of the second oxide layer 104b (dotted line in FIG. 9A).
- the oxygen content of the resistance change layer 104 increases in the order of the first local region 105a, the first oxide layer 104a, the second local region 105b, and the second oxide layer 104b.
- the oxygen deficiency of the resistance change layer 104 decreases in the order of the first local region 105a, the first oxide layer 104a, the second local region 105b, and the second oxide layer 104b.
- the example in which the polarity of the initial break voltage is negative has been described, but it may be positive.
- the polarity of the initial break is negative, oxygen in the vicinity of the interface between the first oxide layer 104a and the second oxide layer 104b is pushed out by the electric field generated by the initial break. A local region 105a is formed.
- the polarity of the initial break is positive, an electric field in the reverse direction is applied to oxygen in the first oxide layer 104a, so that the first local region 105a is hardly formed only by the initial break.
- the second local region 105b is formed in the same manner as in FIG. 8A.
- the nonvolatile memory element according to Embodiment 1 described above can be applied to various types of nonvolatile memory devices.
- the non-volatile memory device according to the second embodiment is a non-volatile memory device including the non-volatile memory element according to the first embodiment.
- the non-volatile memory device according to the second embodiment is the same as that of the first embodiment at the intersection (three-dimensional intersection) between the word line and the bit line. This is a so-called cross-point type in which such a nonvolatile memory element is interposed.
- FIG. 10 is a block diagram showing a configuration of the nonvolatile memory device 300 according to Embodiment 2 of the present invention.
- FIG. 11 is a perspective view showing a configuration (configuration corresponding to 4 bits) of part A in FIG.
- a nonvolatile memory device 200 includes a semiconductor substrate and a memory main body 201 on the semiconductor substrate.
- the memory main body 201 includes a memory array 202 and a row.
- the selection circuit / driver 203, the column selection circuit / driver 204, the write circuit 205 for writing information, and the amount of current flowing through the selected bit line are detected, and the data “1” or “0” is discriminated.
- a sense amplifier 206 and a data input / output circuit 207 that performs input / output processing of input / output data via a terminal DQ are provided.
- the nonvolatile memory device 200 further includes an address input circuit 208 that receives an address signal input from the outside, and a control circuit 209 that controls the operation of the memory body 201 based on the control signal input from the outside. I have.
- the memory array 202 includes a plurality of word lines WL0, WL1, WL2,... Formed in parallel to each other on a semiconductor substrate, and these word lines WL0, WL1, WL2,.
- memory cells M111, M112, M113, M121, M122 provided in a matrix corresponding to the three-dimensional intersections of these word lines WL0, WL1, WL2,... And bit lines BL0, BL1, BL2,. , M123, M131, M132, M133,... (Hereinafter referred to as “memory cells M111, M112,...”).
- the memory cells M111, M112,... Correspond to the nonvolatile memory element according to the first embodiment. However, in the present embodiment, these memory cells M111, M112,... Have a current control element as will be described later.
- the address input circuit 208 receives an address signal from an external circuit (not shown), outputs a row address signal to the row selection circuit / driver 203 based on the address signal, and outputs a column address signal to the column selection circuit / driver 204. Output to.
- the address signal is a signal indicating the address of a specific memory cell selected from among the plurality of memory cells M111, M112,.
- the row address signal is a signal indicating a row address among the addresses indicated by the address signal, and the column address signal is also a signal indicating a column address.
- the control circuit 209 In the information write cycle, the control circuit 209 outputs a write signal instructing application of a write voltage to the write circuit 205 according to the input data Din input to the data input / output circuit 207. On the other hand, in the information read cycle, the control circuit 209 outputs a read signal for instructing a read operation to the column selection circuit / driver 204.
- the row selection circuit / driver 203 receives the row address signal output from the address input circuit 208, selects one of the plurality of word lines WL0, WL1, WL2,... According to the row address signal, A predetermined voltage is applied to the selected word line.
- the row selection circuit / driver 203 selects at least one memory cell from the memory cells M111, M112,.
- the column selection circuit / driver 204 receives the column address signal output from the address input circuit 208 and selects one of the plurality of bit lines BL0, BL1, BL2,... According to the column address signal. Then, a write voltage or a read voltage is applied to the selected bit line.
- the column selection circuit / driver 204 writes data by applying a voltage to the memory cell selected by the row selection circuit / driver 203.
- the column selection circuit / driver 204 reads data by detecting the resistance value of the memory cell selected by the row selection circuit / driver 203.
- the write circuit 205 When the write circuit 205 receives the write signal output from the control circuit 209, the write circuit 205 outputs a signal instructing the row selection circuit / driver 203 to apply a voltage to the selected word line, and the column selection circuit / A signal instructing the driver 204 to apply a write voltage to the selected bit line is output.
- the sense amplifier 206 detects the amount of current flowing through the selected bit line to be read in the information read cycle, and determines data “1” or “0”.
- the output data DO obtained as a result is output to an external circuit via the data input / output circuit 207.
- a nonvolatile memory device having a multilayer structure can be realized by three-dimensionally stacking the memory arrays in the nonvolatile memory device according to the present embodiment shown in FIGS.
- the multi-layered memory array configured as described above, it is possible to realize an ultra-large capacity nonvolatile memory.
- FIG. 12 is a cross-sectional view showing a configuration of the nonvolatile memory element 220 included in the nonvolatile memory device 200 according to Embodiment 2 of the present invention. Note that FIG. 12 shows the configuration in the B part of FIG.
- the nonvolatile memory element 220 included in the nonvolatile memory device 200 includes a lower wiring 212 (corresponding to the word line WL1 in FIG. 11) and an upper wiring 211 ( 11 (corresponding to bit line BL1 in FIG. 11), and lower electrode 216, current control element 215, internal electrode 214, resistance change layer 224, and upper electrode 226 are laminated in this order. Configured.
- the resistance change layer 224 includes a first oxide layer 224a having a high degree of oxygen deficiency and a second oxide layer 224b having a low degree of oxygen deficiency formed on the first oxide layer 224a. Yes.
- the local region 225 is disposed in contact with the upper electrode 226 in the first oxide layer 224 a and the second oxide layer 224 b and is not in contact with the internal electrode 214.
- the local region 225 has a larger oxygen deficiency than the second oxide layer 224b, and is different in oxygen deficiency from the first oxide layer 224a.
- the internal electrode 214, the resistance change layer 224, the local region 225, and the upper electrode 226 are the first electrode 103, the resistance change layer 104, the local electrode 226 in the nonvolatile memory element 100 according to Embodiment 1 shown in FIG. It corresponds to the region 105 and the second electrode 106, respectively.
- the current control element 215 is a load element connected in series with the resistance change layer 224 via the internal electrode 214.
- the current control element 215 is an element typified by a diode, and exhibits a non-linear current characteristic with respect to a voltage.
- the current control element 215 has a bidirectional current characteristic with respect to the voltage, and has a voltage with an amplitude greater than or equal to a predetermined threshold voltage Vf (for example, +1 V or more or ⁇ 1 V or less with respect to one electrode) ) Is applied to the current control element 215 so that the resistance value of the current control element 215 is lowered to be conductive.
- Vf predetermined threshold voltage
- FIG. 13 is a timing chart showing an operation example of the nonvolatile memory device 200 according to Embodiment 2 of the present invention.
- the information “0” is assigned to the case where the resistance change layer 224 is in the low resistance state.
- VP in FIG. 13 indicates the amplitude of the pulse voltage necessary for the resistance change of the memory cell composed of the resistance change element and the current control element.
- a relationship of VP / 2 ⁇ threshold voltage Vf may be established. This is because if the voltage applied to the non-selected memory cell is VP / 2, the current control element of the non-selected memory cell is not turned on, and the leakage current flowing around the non-selected memory cell is suppressed. Because you can. As a result, it is possible to suppress an excessive current supplied to the memory cell that does not need to write information, and to further reduce the current consumption. Further, there is an advantage that unintentional writing (generally referred to as disturb) to unselected memory cells is suppressed.
- VP is applied to the selected memory cell, and the relationship of threshold voltage Vf ⁇ VP is satisfied.
- a write cycle time that is a time required for one write cycle is indicated by tW
- a read cycle time that is a time required for one read cycle is indicated by tR.
- a pulse voltage VP having a pulse width tP is applied to the word line WL0, and a voltage of 0V is similarly applied to the bit line BL0 according to the timing.
- a write voltage for writing information “1” to the memory cell M111 is applied, and as a result, the resistance change layer 224 of the memory cell M111 has a high resistance. That is, information “1” is written in the memory cell M111.
- a voltage of 0V having a pulse width tP is applied to the word line WL1, and the pulse voltage VP is similarly applied to the bit line BL1 according to the timing.
- a write voltage for writing information “0” to M122 is applied, and as a result, the resistance change layer 224 of the memory cell M122 has a low resistance. That is, information “0” is written in the memory cell M122.
- a pulse voltage having a smaller amplitude than the pulse at the time of writing and having a value larger than 0V and smaller than VP / 2 is applied to the word line WL0.
- a pulse voltage having a smaller amplitude than the pulse at the time of writing and having a value larger than VP / 2 and smaller than VP is applied to the bit line BL0. If the read voltage at this time is Vread, the read voltage Vread is applied to the memory cell M111 so that the threshold voltage Vf ⁇ Vread ⁇ VP, and corresponds to the resistance value of the resistance change layer 224 of the memory cell M111 having a high resistance.
- the information “1” is read out by detecting the output current value.
- the same voltage as that for the read cycle for the previous memory cell M111 is applied to the word line WL1 and the bit line BL1.
- a current corresponding to the resistance value of the resistance change layer 224 of the memory cell M122 whose resistance is lowered is output, and information “0” is read by detecting the output current value.
- the nonvolatile memory device 200 includes the nonvolatile memory element 220 capable of performing a good resistance change operation, a stable operation can be realized.
- the non-volatile memory device according to the third embodiment is a non-volatile memory device including the non-volatile memory element according to the first embodiment, and is a so-called 1T1R type device having one transistor / 1 non-volatile memory unit.
- FIG. 14 is a block diagram showing a configuration of a nonvolatile memory device 300 according to Embodiment 3 of the present invention.
- FIG. 15 is a cross-sectional view showing the configuration (configuration corresponding to 2 bits) of part C in FIG.
- the nonvolatile memory device 300 includes a semiconductor substrate, and a memory main body 301 on the semiconductor substrate.
- the memory main body 301 includes a memory array 302, A row selection circuit / driver 303, a column selection circuit 304, a write circuit 305 for writing information, and a sense for detecting the amount of current flowing through the selected bit line and determining data “1” or “0”
- An amplifier 306 and a data input / output circuit 307 that performs input / output processing of input / output data via a terminal DQ are provided.
- the nonvolatile memory device 300 includes a cell plate power supply (VCP power supply) 308, an address input circuit 309 that receives an address signal input from the outside, and a control signal input from the outside. And a control circuit 310 for controlling the operation.
- VCP power supply cell plate power supply
- the memory array 302 includes a plurality of word lines WL0, WL1, WL2,... And bit lines BL0, BL1, BL2,... , WL1, WL2,... And bit lines BL0, BL1, BL2,... Are respectively provided corresponding to intersections, and these word lines WL0, WL1, WL2,.
- a plurality of transistors T11, T12, T13, T21, T22, T23, T31, T32, T33,... (Hereinafter referred to as “transistors T11, T12,...”) And transistors T11, T12,.
- a plurality of memory cells M211, M212, M213, M221, M222, M223, M23 provided in a pair , M232, M233 (hereinafter referred to as "memory cells M211, M212, " represents a) and a.
- the memory array 302 includes a plurality of plate lines PL0, PL1, PL2,... Arranged in parallel to the word lines WL0, WL1, WL2,.
- a bit line BL0 is arranged above the word lines WL0 and WL1, and plate lines PL0 and PL1 are arranged between the word lines WL0 and WL1 and the bit line BL0.
- the memory cells M211, M212,... Correspond to the nonvolatile memory element according to the first embodiment. More specifically, the nonvolatile memory element 320 in FIG. 15 corresponds to the memory cells M211, M212,... In FIG. 14, and the nonvolatile memory element 320 includes the upper electrode 326, the resistance change layer 324, and the local region 325. And a lower electrode 323.
- the resistance change layer 324 includes a first oxide layer 324a having a high degree of oxygen deficiency and a second oxide layer 324b formed on the first oxide layer 324a having a low degree of oxygen deficiency. Yes.
- the local region 325 is disposed in contact with the upper electrode 326 in the first oxide layer 324 a and the second oxide layer 324 b and is not in contact with the lower electrode 323.
- the local region 325 has a greater degree of oxygen deficiency than the second oxide layer 324b, and is different in oxygen deficiency from the first oxide layer 324a.
- the upper electrode 326, the resistance change layer 324, the local region 325, and the lower electrode 323 are the first electrode 103, the resistance change layer 104, and the resistance change layer 104 in the nonvolatile memory element 100 according to Embodiment 1 shown in FIG. It corresponds to the local region 105 and the second electrode 106, respectively.
- reference numeral 317 denotes a plug layer
- 318 denotes a metal wiring layer
- 319 denotes a source / drain region.
- the drains of the transistors T11, T12, T13,... are on the bit line BL0
- the drains of the transistors T21, T22, T23, etc. are on the bit line BL1
- the drains of the transistors T31, T32, T33,. Each is connected to the bit line BL2.
- the gates of the transistors T11, T21, T31,... are on the word line WL0
- the gates of the transistors T12, T22, T32, ... are on the word line WL1
- the gates of the transistors T13, T23, T33,. Each is connected.
- the sources of the transistors T11, T12,... are connected to the memory cells M211, M212,.
- the memory cells M212, M222, M232,... are connected to the plate line PL1, and the memory cells M213, M223, M233,. ing.
- the address input circuit 309 receives an address signal from an external circuit (not shown), outputs a row address signal to the row selection circuit / driver 303 based on the address signal, and outputs a column address signal to the column selection circuit 304.
- the address signal is a signal indicating the address of a specific memory cell selected from among the plurality of memory cells M211, M212,.
- the row address signal is a signal indicating a row address among the addresses indicated by the address signal
- the column address signal is a signal indicating a column address among the addresses indicated by the address signal.
- control circuit 310 In the information write cycle, the control circuit 310 outputs a write signal instructing application of a write voltage to the write circuit 305 in accordance with the input data Din input to the data input / output circuit 307. On the other hand, in the information read cycle, the control circuit 310 outputs a read signal instructing application of a read voltage to the column selection circuit 304.
- the row selection circuit / driver 303 receives the row address signal output from the address input circuit 309, selects one of the plurality of word lines WL0, WL1, WL2,... According to the row address signal, A predetermined voltage is applied to the selected word line.
- the row selection circuit / driver 303 selects at least one memory cell from the memory cells M213, M223, M233,... Included in the memory array 302.
- the column selection circuit 304 receives the column address signal output from the address input circuit 309, selects one of the plurality of bit lines BL0, BL1, BL2,... According to the column address signal, A write voltage or a read voltage is applied to the selected bit line.
- the column selection circuit 304 writes data by applying a voltage to the memory cell selected by the row selection circuit / driver 303.
- the column selection circuit 304 reads data by detecting the resistance value of the memory cell selected by the row selection circuit / driver 303.
- the write circuit 305 When the write circuit 305 receives the write signal output from the control circuit 310, the write circuit 305 outputs a signal instructing the column selection circuit 304 to apply the write voltage to the selected bit line.
- the sense amplifier 306 detects the amount of current flowing through the selected bit line to be read in the information read cycle, and determines that the data is “1” or “0”.
- the output data DO obtained as a result is output to an external circuit via the data input / output circuit 307.
- the storage capacity is smaller than that of the cross-point type configuration of the second embodiment.
- a current control element such as a diode is unnecessary, there is an advantage that it can be easily combined with a CMOS process and the operation can be easily controlled.
- the transistor type P type or N type
- the transistor is selected so that the transistor is connected to the source follower, and the transistor is connected to the memory cell. Also good.
- the source line is configured to be supplied with a constant voltage as a plate line, but may be configured to include a driver capable of supplying different voltage or current to each source line.
- the plate lines are arranged in parallel with the word lines, but may be arranged in parallel with the bit lines.
- FIG. 16 is a timing chart showing an operation example of the nonvolatile memory device 300 according to Embodiment 3 of the present invention.
- an example of operation when the variable resistance layer 324 is assigned to the information “1” when the resistance change layer 324 is in the high resistance state and the information “0” is assigned to the case where the resistance change layer 324 is in the low resistance state is shown.
- the information “1” when the resistance change layer 324 is in the high resistance state and the information “0” is assigned to the case where the resistance change layer 324 is in the low resistance state is shown.
- the memory cells M211 and M222 For convenience of explanation, only the case where information is written to and read from the memory cells M211 and M222 is shown.
- VP indicates a pulse voltage necessary for resistance change of the variable resistance element
- VT indicates a threshold voltage of the transistor.
- the voltage VP is constantly applied to the plate line, and the bit line is also precharged to the voltage VP when not selected.
- a voltage higher than the pulse voltage 2VP of the pulse width tP + the threshold voltage VT of the transistor is applied to the word line WL0, and the transistor T11 is turned on. Then, according to the timing, the pulse voltage 2VP is applied to the bit line BL0. As a result, a write voltage for writing information “1” to the memory cell M211 is applied, and as a result, the resistance change layer 324 of the memory cell M211 has a high resistance. That is, information “1” is written in the memory cell M211.
- a voltage higher than the pulse voltage 2VP of the pulse width tP + the threshold voltage VT of the transistor is applied to the word line WL1, and the transistor T22 is turned on.
- a voltage of 0 V is applied to the bit line BL1.
- a write voltage for writing information “0” to the memory cell M222 is applied, and as a result, the resistance change layer 324 of the memory cell M222 has a low resistance. That is, information “0” is written in the memory cell M222.
- a predetermined voltage is applied to the word line WL0 in order to turn on the transistor T11.
- a pulse voltage having an amplitude smaller than the pulse width at the time of writing is Applied to the bit line BL0.
- a current corresponding to the resistance value of the resistance change layer 324 of the memory cell M211 with the increased resistance is output, and information “1” is read by detecting the output current value.
- the same voltage as that for the previous read cycle for the memory cell M211 is applied to the word line WL1 and the bit line BL1.
- a current corresponding to the resistance value of the resistance change layer 324 of the memory cell M222 whose resistance is reduced is output, and information “0” is read by detecting the output current value.
- the nonvolatile memory device 300 also includes the nonvolatile memory element 320 that can perform a good resistance change operation, so that a stable operation can be realized. .
- the method for manufacturing the nonvolatile memory element of the above embodiment is not limited to the aspect of the above embodiment. That is, the nonvolatile memory element of the above-described embodiment can be manufactured by the above manufacturing method or a combination of the above manufacturing method and a publicly known method for all electronic devices including resistance change elements.
- the nonvolatile memory element and the nonvolatile memory device of the present invention have been described based on the embodiments, but the present invention is not limited to these embodiments.
- the present invention includes various modifications made by those skilled in the art without departing from the scope of the present invention. Moreover, you may combine each component in several embodiment arbitrarily in the range which does not deviate from the meaning of invention.
- the stacking order of the first oxide layer 104a and the second oxide layer 104b in the stacked structure of the resistance change element may be arranged upside down.
- the shape where each layer of the laminated structure was embedded in the contact hole may be sufficient.
- a plurality of local regions 105 may be formed in one nonvolatile memory element 100.
- the plate line is arranged in parallel with the word line, but may be arranged in parallel with the bit line.
- the plate line is configured to apply a common potential to the transistors, but has a plate line selection circuit / driver having a configuration similar to that of the row selection circuit / driver, and the selected plate line and the non-selected plate line are arranged. It is good also as a structure driven by a different voltage (a polarity is also included).
- the present invention is useful for nonvolatile storage elements and nonvolatile storage devices, and particularly useful for storage elements and storage devices used in various electronic devices such as digital home appliances, memory cards, personal computers, and portable telephones. .
- Nonvolatile memory element 101 Substrate 102 Interlayer insulating film 103, 1403 First electrode 104, 224, 324, 1405 Resistance change layer 104a, 224a, 324a First oxide layer 104b, 224b, 324b Second oxide layer 105, 225, 325 Local region 105a First local region 105b Second local region 106, 1406 Second electrode 107 Pattern 200, 300 Non-volatile memory device 201, 301 Memory main body 202, 302 Memory array 203, 303 Row selection circuit / driver 204 Column selection circuit / driver 205, 305 Write circuit 206, 306 Sense amplifier 207, 307 Data input / output circuit 208 Address input circuit 209, 310 Control circuit 211 Upper wiring 212 Lower wiring 214 Internal electrode 215 Current control element 216, 323 Lower electrode 226, 326 Upper electrode 304 Column selection circuit 308 VCP power supply 309 Address input circuit 317 Plug layer 318 Metal wiring layer 319 Source / drain region 14
Abstract
Description
[不揮発性記憶素子の構成]
図1は、本発明の実施の形態1に係る不揮発性記憶素子の一構成例を示す断面図である。
次に、図3A~図3Dを参照しながら、本実施の形態の不揮発性記憶素子100の製造方法の一例について説明する。
図7は、本発明の実施の形態1の変形例に係る不揮発性記憶素子の一構成例を示す断面図である。以下、実施の形態1の不揮発性記憶素子100と異なる点についてのみ説明する。
上述した実施の形態1に係る不揮発性記憶素子は、種々の形態の不揮発性記憶装置へ適用することが可能である。実施の形態2に係る不揮発性記憶装置は、実施の形態1に係る不揮発性記憶素子を備える不揮発性記憶装置であって、ワード線とビット線との交点(立体交差点)に実施の形態1に係る不揮発性記憶素子を介在させた所謂クロスポイント型のものである。
図10は、本発明の実施の形態2に係る不揮発性記憶装置300の構成を示すブロック図である。また、図11は、図10におけるA部の構成(4ビット分の構成)を示す斜視図である。
図12は、本発明の実施の形態2に係る不揮発性記憶装置200が備える不揮発性記憶素子220の構成を示す断面図である。なお、図12には、図11のB部における構成が示されている。
次に、情報を書き込む場合の書き込みサイクルおよび情報を読み出す場合の読み出しサイクルにおける本実施の形態に係る不揮発性記憶装置の動作例について、図13に示すタイミングチャートを参照しながら説明する。
実施の形態3に係る不揮発性記憶装置は、実施の形態1に係る不揮発性記憶素子を備える不揮発性記憶装置であって、1トランジスタ/1不揮発性記憶部とした所謂1T1R型のものである。
図14は、本発明の実施の形態3に係る不揮発性記憶装置300の構成を示すブロック図である。また、図15は、図14におけるC部の構成(2ビット分の構成)を示す断面図である。
次に、情報を書き込む場合の書き込みサイクルおよび情報を読み出す場合の読み出しサイクルにおける本実施の形態に係る不揮発性記憶装置300の動作例について、図16に示すタイミングチャートを参照しながら説明する。
101 基板
102 層間絶縁膜
103、1403 第1の電極
104、224、324、1405 抵抗変化層
104a、224a、324a 第1の酸化物層
104b、224b、324b 第2の酸化物層
105、225、325 局所領域
105a 第1の局所領域
105b 第2の局所領域
106、1406 第2の電極
107 パターン
200、300 不揮発性記憶装置
201、301 メモリ本体部
202、302 メモリアレイ
203、303 行選択回路・ドライバ
204 列選択回路・ドライバ
205、305 書き込み回路
206、306 センスアンプ
207、307 データ入出力回路
208 アドレス入力回路
209、310 制御回路
211 上部配線
212 下部配線
214 内部電極
215 電流制御素子
216、323 下部電極
226、326 上部電極
304 列選択回路
308 VCP電源
309 アドレス入力回路
317 プラグ層
318 金属配線層
319 ソース/ドレイン領域
1405c フィラメント
BL0、BL1、… ビット線
T11、T12、… トランジスタ
M111、M112、… メモリセル
M211、M212、… メモリセル
PL0、PL1、… プレート線
WL0、WL1、… ワード線
Claims (13)
- 第1の電極と、第2の電極と、前記第1の電極と前記第2の電極との間に介在し、前記第1の電極および前記第2の電極間に与えられる電圧極性に基づいて可逆的に高抵抗状態と低抵抗状態とを遷移する抵抗変化層とを備え、
前記抵抗変化層は、
第1の金属の酸化物を含む第1の酸化物層と、
前記第1の酸化物層と前記第2の電極との間に接して配置され、第2の金属の酸化物を含み、前記第1の酸化物層に比べて酸素不足度が小さい第2の酸化物層と、
前記第1の酸化物層及び前記第2の酸化物層内に前記第2の電極と接して配置され、前記第1の電極に接しておらず、前記第2の酸化物層に比べて酸素不足度が大きく、前記第1の酸化物層と酸素不足度が異なる局所領域とを含む
抵抗変化型の不揮発性記憶素子。 - 前記局所領域は、
前記第1の酸化物層内に配置され、前記第1の電極に接しておらず、前記第1の酸化物層に比べて酸素不足度が大きい第1の局所領域と、
前記第1の局所領域と前記第2の電極との間に前記第1の局所領域及び前記第2の電極に接して配置され、前記第1の局所領域に比べて酸素不足度が小さく、前記第2の酸化物層に比べて酸素不足度が大きい第2の局所領域とを含む
請求項1に記載の抵抗変化型の不揮発性記憶素子。 - 前記抵抗変化層は、前記第2の局所領域において高抵抗状態と低抵抗状態とを遷移する
請求項2に記載の抵抗変化型の不揮発性記憶素子。 - 前記第2の局所領域は、前記第1の電極から前記第2の電極に向かう方向の膜厚において前記第2の酸化物層の膜厚よりも小さい部分を有する
請求項2または3に記載の抵抗変化型の不揮発性記憶素子。 - 前記第2の酸化物層と前記第1の酸化物層とに含まれる金属の酸化物は、同種の金属の酸化物である
請求項1~4のいずれか1項に記載の抵抗変化型の不揮発性記憶素子。 - 前記同種の金属は、Taである
請求項5に記載の抵抗変化型の不揮発性記憶素子。 - 前記第1の電極と前記第2の電極とは同一材料から構成される
請求項1~6のいずれか1項に記載の抵抗変化型の不揮発性記憶素子。 - さらに、前記抵抗変化層に電気的に接続された負荷素子を備える
請求項1~7のいずれか1項に記載の抵抗変化型の不揮発性記憶素子。 - 前記負荷素子は、固定抵抗、トランジスタ、またはダイオードである
請求項8に記載の抵抗変化型の不揮発性記憶素子。 - 前記局所領域は、前記抵抗変化層に1つのみ形成されている
請求項1~9のいずれか1項に記載の抵抗変化型の不揮発性記憶素子。 - 基板と、前記基板上に互いに平行に形成された複数の第1の配線と、
前記複数の第1の配線の上方に前記基板の主面に平行な面内において互いに平行に且つ前記複数の第1の配線と立体交差するように形成された複数の第2の配線と、
前記複数の第1の配線と前記複数の第2の配線との立体交差点に対応して設けられた請求項1~10のいずれか1項に記載の不揮発性記憶素子とを具備するメモリセルアレイと、
前記メモリセルアレイが具備する不揮発性記憶素子から、少なくとも一つの不揮発性記憶素子を選択する選択回路と、
前記選択回路で選択された不揮発性記憶素子に電圧を印加することでデータを書き込む書き込み回路と、
前記選択回路で選択された不揮発性記憶素子の抵抗値を検出することでデータを読み出す読み出し回路と、を備える
不揮発性記憶装置。 - 前記不揮発性記憶素子は、前記抵抗変化層に電気的に接続された電流制御素子を備える
請求項11に記載の不揮発性記憶装置。 - 基板と、前記基板上に形成された、複数のワード線および複数のビット線、前記複数のワード線および複数のビット線にそれぞれ接続された複数のトランジスタ、並びに前記複数のトランジスタに一対一で対応して設けられた複数の請求項1~10のいずれか1項に記載の不揮発性記憶素子とを具備するメモリセルアレイと、
前記メモリセルアレイが具備する不揮発性記憶素子から、少なくとも一つの不揮発性記憶素子を選択する選択回路と、
前記選択回路で選択された不揮発性記憶素子に電圧を印加することでデータを書き込む書き込み回路と、
前記選択回路で選択された不揮発性記憶素子の抵抗値を検出することでデータを読み出す読み出し回路と、を備える
不揮発性記憶装置。
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JPWO2013051267A1 (ja) | 2015-03-30 |
JP5352032B2 (ja) | 2013-11-27 |
US9082479B2 (en) | 2015-07-14 |
US20130250658A1 (en) | 2013-09-26 |
CN103250252A (zh) | 2013-08-14 |
CN103250252B (zh) | 2015-12-23 |
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