WO2010086916A1 - 抵抗変化素子およびその製造方法 - Google Patents
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- WO2010086916A1 WO2010086916A1 PCT/JP2009/003448 JP2009003448W WO2010086916A1 WO 2010086916 A1 WO2010086916 A1 WO 2010086916A1 JP 2009003448 W JP2009003448 W JP 2009003448W WO 2010086916 A1 WO2010086916 A1 WO 2010086916A1
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- H01L27/02—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having at least one potential-jump barrier or surface barrier; including integrated passive circuit elements with at least one potential-jump barrier or surface barrier
- H01L27/04—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having at least one potential-jump barrier or surface barrier; including integrated passive circuit elements with at least one potential-jump barrier or surface barrier the substrate being a semiconductor body
- H01L27/10—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having at least one potential-jump barrier or surface barrier; including integrated passive circuit elements with at least one potential-jump barrier or surface barrier the substrate being a semiconductor body including a plurality of individual components in a repetitive configuration
- H01L27/101—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having at least one potential-jump barrier or surface barrier; including integrated passive circuit elements with at least one potential-jump barrier or surface barrier the substrate being a semiconductor body including a plurality of individual components in a repetitive configuration including resistors or capacitors only
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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
- H10N70/011—Manufacture or treatment of multistable switching devices
- H10N70/021—Formation of the switching material, e.g. layer deposition
- H10N70/026—Formation of the switching material, e.g. layer deposition by physical vapor deposition, e.g. sputtering
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- H10N70/011—Manufacture or treatment of multistable switching devices
- H10N70/041—Modification of the switching material, e.g. post-treatment, doping
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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
- H10N70/24—Multistable switching devices, e.g. memristors based on migration or redistribution of ionic species, e.g. anions, vacancies
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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
- H10N70/801—Constructional details of multistable switching devices
- H10N70/821—Device geometry
- H10N70/826—Device geometry adapted for essentially vertical current flow, e.g. sandwich or pillar type devices
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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
- H10N70/801—Constructional details of multistable switching devices
- H10N70/841—Electrodes
- H10N70/8418—Electrodes adapted for focusing electric field or current, e.g. tip-shaped
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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
- H10N70/801—Constructional details of multistable switching devices
- H10N70/881—Switching materials
- H10N70/883—Oxides or nitrides
- H10N70/8833—Binary metal oxides, e.g. TaOx
Definitions
- the present invention relates to a resistance change element, and more particularly to a resistance change type resistance change element whose resistance value changes in accordance with an applied electric signal and a method for manufacturing the same.
- variable resistance element In recent years, electronic devices such as portable information devices and information home appliances have become more sophisticated with the progress of digital technology. Therefore, there are increasing demands for increasing the capacity of the variable resistance element, reducing the write power, increasing the write / read time, and extending the life.
- the resistance change layer When the resistance change layer is used as a material for the memory portion, the resistance value is changed from a high resistance to a low resistance or from a low resistance to a high resistance, for example, by inputting an electric pulse. In this case, it is necessary to clearly distinguish between the two values of low resistance and high resistance, and to stably change between the low resistance and the high resistance at high speed so that these two values are held in a nonvolatile manner. . Conventionally, various proposals have been made for the purpose of stabilizing the memory characteristics and miniaturizing the memory element.
- a memory cell includes a resistance change element that includes two electrodes and a recording layer sandwiched between the electrodes and is configured to reversibly change the resistance value of the recording layer.
- Japanese Patent Application Laid-Open No. H10-228707 discloses a memory element configured with the above.
- FIG. 17 is a cross-sectional view showing the configuration of such a conventional memory element.
- the memory element is configured by arranging a plurality of resistance change elements 10 constituting a memory cell in an array.
- the resistance change element 10 is configured such that a high resistance film 2 and an ion source layer 3 are sandwiched between a lower electrode 1 and an upper electrode 4.
- the high resistance film 2 and the ion source layer 3 constitute a memory layer, and information can be recorded in the resistance change element 10 of each memory cell by the memory layer.
- Each resistance change element 10 is disposed above the MOS transistor 18 formed on the semiconductor substrate 11.
- the MOS transistor 18 includes a source / drain region 13 formed in a region isolated by the element isolation layer 12 in the semiconductor substrate 11 and a gate electrode 14.
- the gate electrode 14 also serves as a word line which is one address wiring of the memory element.
- One of the source / drain regions 13 of the MOS transistor 18 and the lower electrode 1 of the resistance change element 10 are electrically connected via the plug layer 15, the metal wiring layer 16, and the plug layer 17.
- the other of the source / drain regions 13 of the MOS transistor 18 is connected to the metal wiring layer 16 through the plug layer 15.
- This metal wiring layer 16 is connected to a bit line which is the other address wiring of the memory element.
- the ion source of the ion source layer 3 constituting the recording layer is changed to the high resistance layer 2. Move to. Alternatively, the ion source is moved from the high resistance layer 2 to the upper electrode 4. As a result, the resistance value of the resistance change element 10 can transition from the high resistance state to the low resistance state or from the low resistance state to the high resistance state to record information.
- Patent Document 2 discloses NiO, V 2 O 5 , ZnO, Nb 2 O 5 , TiO 2 , WO 3 , and CoO as variable resistance materials. Since these materials are binary systems, composition control and film formation are relatively easy. In addition, it can be said that the compatibility with the semiconductor manufacturing process is relatively good.
- variable resistance element having the structure in which the transition metal oxide used in the conventional variable resistance material as described above is sandwiched between two electrodes has the following problems.
- the initial resistance is very high, and in order to obtain variable resistance characteristics, an electric pulse is applied to the variable resistance element in the initial state, It is necessary to form a path in the resistance change layer. Such a process is called forming.
- the voltage of this electric pulse is larger than the voltage of the electric pulse necessary for changing the variable resistance material as a memory from the low resistance state to the high resistance state or from the high resistance state to the low resistance state, and generates a high voltage.
- a special circuit is required to make the circuit.
- the present invention has been made in view of such circumstances, and an object of the present invention is to provide a variable resistance element that can reduce the voltage of an electric pulse necessary for forming and has reversibly stable rewriting characteristics. It is another object of the present invention to provide a resistance change element manufacturing method having high affinity with a semiconductor manufacturing process, and the resistance change element.
- a variable resistance element is interposed between a first electrode, a second electrode, the first electrode and the second electrode, and the first electrode and the second electrode.
- a resistance change element comprising: a resistance change layer provided in contact with an electrode, and reversibly changing based on electrical signals having different polarities applied between the first electrode and the second electrode,
- the resistance change layer includes a first oxygen-deficient transition metal oxide layer and a second oxygen-deficient transition metal oxide layer having a higher oxygen content than the first oxygen-deficient transition metal oxide layer.
- the second oxygen-deficient transition metal oxide layer is in contact with the second electrode, and the second oxygen-deficient transition metal oxide layer is locally Have a thin portion.
- “Having a locally thin portion” means “having a locally thin portion” to the extent necessary to reduce the electrical pulse voltage required for forming. Say. The irregularities that normally occur on the upper surface of the transition metal oxide layer formation method such as sputtering or CVD when the transition metal oxide layer is formed are not included in the “locally thin portion”. .
- the second oxygen-deficient transition metal oxide layer has a portion having a locally thin film thickness at the interface with the second electrode by having a plurality of recesses.
- the recess is formed along a crystal grain boundary of the material constituting the second electrode.
- the interface between the first oxygen-deficient transition metal oxide layer and the second oxygen-deficient transition metal oxide layer is flat, while the second oxygen-deficient transition metal oxide layer is flat. Since the interface between the deficient transition metal oxide layer and the second electrode has irregularities, the second oxygen deficient transition metal oxide layer has a locally thin portion.
- the second electrode has a protrusion at the interface between the second oxygen-deficient transition metal oxide layer and the second electrode, so that the second oxygen-deficient The transition metal oxide layer has a locally thin portion.
- a protrusion is formed at the interface between the second electrode and the second oxygen-deficient transition metal oxide layer in the second electrode.
- the second electrode is platinum or a platinum alloy.
- the thickness of the locally thin portion is 0.1 nm or more and 5 nm or less.
- the transition metal oxide layer is a tantalum oxide layer.
- the method of manufacturing a variable resistance element includes a step of forming a first electrode, a step of forming a first oxygen-deficient transition metal oxide layer on the first electrode, and the first oxygen Forming a second oxygen-deficient transition metal oxide layer having a higher oxygen content than the deficient transition metal oxide layer on the first oxygen-deficient transition metal oxide layer; , Forming a second electrode layer made of platinum or a platinum alloy on the second oxygen-deficient transition metal oxide layer, and forming the second electrode layer, followed by heat treatment to form the second electrode layer. Forming a protrusion at an interface between the second electrode layer and the second oxygen-deficient transition metal oxide layer in the electrode layer.
- Another method of manufacturing the variable resistance element according to the present invention includes a step of forming a first electrode, a step of forming a first oxygen-deficient transition metal oxide layer on the first electrode, Forming a second oxygen-deficient transition metal oxide layer having a higher oxygen content than the first oxygen-deficient transition metal oxide layer on the first oxygen-deficient transition metal oxide layer; A step of forming a second electrode layer made of palladium or a palladium alloy on the second oxygen-deficient transition metal oxide layer, and a heat treatment after the second electrode layer is formed. Forming a protrusion at an interface between the second electrode layer and the second oxygen-deficient transition metal oxide layer in the layer.
- the heat treatment is performed at 350 ° C. to 425 ° C.
- the transition metal is tantalum.
- the height of the protrusion formed by the heat treatment is smaller than the thickness of the second oxygen-deficient transition metal oxide layer.
- a resistance change element using a resistance change phenomenon, which can be easily formed with an electric pulse of a relatively small voltage, has reversible and stable rewriting characteristics, and a manufacturing method thereof.
- FIG. 1 is a cross-sectional view showing a configuration example of a variable resistance element according to the first embodiment of the present invention.
- FIG. 2 is a diagram showing current-voltage characteristics at the time of forming of the variable resistance element according to the first embodiment of the present invention.
- FIG. 3 is a diagram showing current-voltage characteristics at the time of forming of the variable resistance element according to the first embodiment of the present invention.
- FIG. 4 is a diagram showing the heat treatment temperature dependence of the forming voltage of the variable resistance element according to the first embodiment of the present invention.
- FIG. 5 is a diagram showing the heat treatment time dependence of the forming voltage of the variable resistance element according to the first embodiment of the present invention.
- FIG. 6A is a diagram showing the relationship between the film thickness of the high concentration layer and the initial resistance
- FIG. 6B is a diagram showing the film thickness of the high concentration oxide layer and the forming voltage.
- FIG. 7 is a diagram showing the relationship between the resistance value of the variable resistance element according to the first embodiment of the present invention and the number of pulse applications.
- FIG. 8 is a diagram showing the relationship between the resistance value of the variable resistance element according to the first embodiment of the present invention and the number of pulse applications.
- FIG. 9 is a diagram showing an XRD (X-ray diffraction) spectrum of the variable resistance layer made of tantalum oxide according to the first embodiment of the present invention.
- FIG. 10 is a table summarizing the results of analyzing the X-ray reflectivity data of the variable resistance layer made of tantalum oxide according to the first embodiment of the present invention.
- FIG. 11 is a cross-sectional view showing an example of a schematic configuration of a variable resistance element according to a modification of the present invention.
- FIG. 11A is a diagram showing a first modification, and FIG. It is a figure which shows a modification.
- FIG. 12 is a transmission electron microscope (TEM) photograph showing a cross section of a variable resistance element using an oxygen-deficient Ta oxide for the variable resistance layer.
- FIG. 12A shows the maximum temperature during the process at 400 ° C.
- FIG. 12B is a TEM photograph when the maximum temperature during the process is 100 ° C.
- FIG. TEM transmission electron microscope
- FIG. 13 is a transmission electron microscope (TEM) photograph showing a cross section of a variable resistance element using an oxygen-deficient Hf oxide in the variable resistance layer.
- FIG. 13A shows the maximum temperature during the process at 400 ° C.
- FIG. 13B is a TEM photograph when the maximum temperature during the process is 100 ° C.
- FIG. 14 is a cross-sectional view of the variable resistance element used in the experiment.
- FIG. 15 is a diagram showing the heat treatment temperature dependence of the initial resistance of the variable resistance element 200.
- FIG. 16 is a transmission electron microscope (TEM) photograph showing a cross section of a resistance change element using an oxygen-deficient Ta oxide for the resistance change layer
- FIG. FIG. 16B is a TEM photograph of a sample before heat treatment, and FIG.
- FIG. 16C is a TEM photograph of a sample at a heat treatment temperature of 450 ° C.
- FIG. 17 is a cross-sectional view showing a configuration of a conventional memory element.
- FIG. 18 is a transmission electron microscope (TEM) photograph showing a cross section of a variable resistance element according to a modification using Pd as the material of the upper electrode layer.
- TEM transmission electron microscope
- FIG. 12 is a transmission electron microscope (TEM) photograph showing a cross section of a variable resistance element using an oxygen-deficient tantalum oxide for the variable resistance layer.
- FIG. 12A shows the maximum temperature during the process of 400.
- FIG. 12B shows a case where the maximum temperature during the process is 100 ° C.
- the element shown in FIG. 12A includes a first oxygen-deficient tantalum oxide layer 704a having a thickness of about 23 nm on a lower electrode layer 703a made of a Pt layer having a thickness of about 50 nm.
- the second oxygen-deficient tantalum oxide layer 705a having a thickness of about 8 nm and the upper electrode layer 709a made of a Pt layer having a thickness of about 80 nm were stacked in this order.
- the oxygen content of the second oxygen-deficient tantalum oxide layer 705a was higher than the oxygen content of the first oxygen-deficient tantalum oxide layer 704a.
- the element of FIG. 12A was created using a process technology related to the manufacture of semiconductor devices. The maximum temperature of the heating step in the process was about 400 ° C.
- the lower electrode layer 703a is directed upward in the photograph and the upper electrode layer 709a is directed downward in the photograph. That is, a small protrusion (portion surrounded by a circle in the photograph) made of Pt was formed from the upper and lower electrodes toward the resistance change layer side. In other words, it can be said that irregularities were formed at the interface between the electrode and the second oxygen-deficient tantalum oxide layer by the formed protrusion. Most of the protrusions extended from the vicinity of the grain boundaries (grain boundaries) of the upper and lower Pt layers. Of particular note is that the protrusions extending from the upper electrode layer 709a reach about half the thickness of the second oxygen-deficient tantalum oxide layer.
- the manufacturing method of the element shown in FIG. 12 (b) is the same as that of the element shown in FIG. 12 (a), but the maximum temperature of the heating step in the process is suppressed to about 100 ° C.
- FIG. 12B no protrusion made of Pt was generated. That is, there are no protrusions from the lower electrode layer 703b toward the first oxygen-deficient tantalum oxide layer 704b, or protrusions from the upper electrode layer 709b toward the second oxygen-deficient tantalum oxide layer 705b. It did not occur.
- the sample (Pt) shown in FIG. It was about 10 2 ⁇ in the case of projections), and about 10 8 ⁇ in the sample shown in FIG. 12B (without the Pt projections). That is, when the protrusion is generated, the initial resistance is as low as 6 digits.
- the thickness of the second oxygen-deficient tantalum oxide layer is substantially reduced, and the overall resistance value is lower than when there is no element protrusion.
- the present inventors conducted experiments by changing the film thickness of the Pt electrode, and confirmed that protrusions are easily formed when the film thickness of the Pt electrode is about 20 nm or more. This is presumably because the ease of migration is related to the amount of Pt atoms.
- the upper limit of the thickness of the Pt electrode is preferably 200 nm or less.
- the present inventors verified whether the same phenomenon occurs even when Hf is used instead of Ta as a transition metal contained in the resistance change layer.
- FIG. 13 is a transmission electron microscope (TEM) photograph showing a cross section of a variable resistance element using an oxygen-deficient Hf oxide in the variable resistance layer.
- FIG. 13A shows the maximum temperature during the process at 400 ° C.
- FIG. 13B shows the case where the maximum temperature during the process is 100 ° C.
- the element shown in FIG. 13A has an oxygen-deficient Hf oxide layer 706c having a thickness of about 30 nm on a lower electrode layer 703c made of W (tungsten) having a thickness of about 150 nm, and a film. It was obtained by laminating an upper electrode layer 709c made of Pt having a thickness of about 75 nm in this order.
- the element shown in FIG. 13A was also created using a process technology related to the manufacture of semiconductor devices. The maximum temperature of the heating step in the process was about 400 ° C.
- the upper electrode layer 709c is directed downward in the photograph, that is, from the upper electrode layer to the resistance change layer side.
- a wide protrusion made of Pt (a portion surrounded by a circle in the photograph) was formed.
- the element shown in FIG. 13B has an oxygen-deficient Hf oxide layer 706c with a film thickness of about 30 nm on a lower electrode layer 703c made of a W layer with a film thickness of about 150 nm, It was obtained by laminating an upper electrode layer 709c made of a Pt layer having a thickness of about 75 nm in this order.
- the maximum temperature of the heating process in the process was suppressed to about 100 ° C.
- no protrusion made of Pt was generated.
- the Pt layer is exposed to a high temperature regardless of the type of the transition metal. It is considered that the protrusions are easily formed.
- the present inventors conducted the following experiment in order to investigate the relationship between the protrusion and the initial resistance in more detail.
- FIG. 14 shows an element (resistance change element 200) used in the experiment.
- the variable resistance element 200 includes a substrate 201, an oxide layer 202 formed on the substrate 201, a first electrode layer 203 formed on the oxide layer 202, a second electrode layer 207, and a first electrode. And a resistance change layer 206 sandwiched between the layer 203 and the second electrode layer 207.
- the resistance change layer 206 was formed on the first tantalum-containing layer 204 having a low oxygen content (hereinafter referred to as “first tantalum oxide layer”) and the first tantalum oxide layer. It is composed of a second tantalum-containing layer 205 (hereinafter referred to as “second tantalum oxide layer”) having a high oxygen content.
- the resistance change element 200 is subjected to heat treatment for 10 minutes while changing the heat treatment temperature from 300 ° C. to 450 ° C. in a nitrogen atmosphere, and the results of measuring the initial resistance are examined.
- a voltage of +0.4 V lower than a threshold voltage for example, about 1 V
- a threshold voltage for example, about 1 V
- FIG. 15 shows the heat treatment temperature dependence of the initial resistance of the variable resistance element 200.
- the initial resistance of the variable resistance element 200 before heat treatment is 4.5 ⁇ 10 9 ⁇ (indicated by ⁇ in FIG. 15), and when the heat treatment temperature is 300 ° C., the initial resistance is 3.0. ⁇ 10 9 ⁇ (indicated by ⁇ in FIG. 15), when the heat treatment temperature is 350 ° C., the initial resistance is 3.9 ⁇ 10 8 ⁇ (indicated by ⁇ in FIG. 15), and when the heat treatment temperature is 375 ° C.
- the initial resistance is 2.2 ⁇ 10 8 ⁇ (indicated by ⁇ in FIG.
- the initial resistance of the variable resistance element 200 decreases as the heat treatment temperature increases.
- FIG. 16 shows a result of observing cross sections of the first electrode layer 203, the resistance change layer 206, and the second electrode layer 207 in the resistance change element 200 with a transmission electron microscope.
- 16A is a cross-sectional view of a sample at a heat treatment temperature of 400 ° C.
- FIG. 16B is a cross-sectional view of the sample before the heat treatment
- FIG. 16C is a cross-sectional view of a sample at a heat treatment temperature of 450 ° C. .
- the resistance change layer 206 sandwiched between the first electrode layer 203 and the second electrode layer 207 is composed of a first tantalum oxide layer 204 that appears dark and a second tantalum oxide layer that appears bright. It can be seen that it consists of 205.
- the thickness of the resistance change layer 206 is about 30 nm
- the thickness of the first tantalum oxide layer 204 is about 22 nm
- the thickness of the second tantalum oxide layer is about 8 nm. This result almost coincides with the analysis result by X-ray reflectivity measurement.
- the resistance change layer 206 includes a first tantalum oxide layer 204 and a second tantalum oxide layer 205, and the second electrode layer 207 changes to the second tantalum oxide layer 205. It can be seen that microprotrusions are generated. As a result of the compositional analysis of the minute protrusions, it was found that Pt, which is a constituent material of the second electrode layer 207, is a main component. The distance from the tip of the minute protrusion to the first tantalum oxide layer 204 is about 3 nm, and the film thickness of the second tantalum oxide layer 205 is partially reduced by the formation of the minute protrusion. I understand.
- the resistance change layer 206 includes a first tantalum oxide layer 204 and a second tantalum oxide layer 205, and the second electrode layer 207 changes to the second tantalum oxide layer 205. It can be seen that microprotrusions are generated. It can be seen that the tips of the microprojections reach the first tantalum oxide layer 204.
- the thickness of the second tantalum oxide layer 205 is about 8 nm.
- the second tantalum oxide layer 205 is formed by the minute protrusions generated in the second electrode layer 207.
- the minute protrusion generated in the second electrode layer 207 penetrates the second tantalum oxide layer 205, and the tip of the minute protrusion reaches the first tantalum oxide layer 204. .
- the resistance of the second tantalum oxide layer 205 having a composition close to the stoichiometric composition Ta 2 O 5 is very high, an effective film of the second tantalum oxide layer of the above three samples is used. It is considered that the initial resistance of the variable resistance element 100 varies depending on the thickness.
- the microprojections grow from the second electrode layer 207 which is Pt by the heat treatment, and the height of the microprojections increases as the heat treatment temperature increases.
- the second tantalum partially It is considered that a portion where the thickness of the oxide layer is locally thin is generated and the initial resistance of the resistance change element 200 is reduced.
- the present invention is based on the discovery that these minute protrusions contribute to a reduction in forming voltage. Embodiments of the present invention will be described below. In the following description, the same or corresponding elements are denoted by the same or corresponding reference numerals throughout all the drawings, and redundant description thereof is omitted.
- FIG. 1 is a cross-sectional view showing a configuration example of a variable resistance element according to the first embodiment of the present invention.
- the resistance change element 100 includes a substrate 101, an oxide layer 102 formed on the substrate 101, and a first electrode layer formed on the oxide layer 102. 103, a second electrode layer 107 having a minute protrusion 108, and a resistance change layer 106 sandwiched between the first electrode layer 103 and the second electrode layer 107.
- the resistance change layer 106 is made of an oxygen-deficient transition metal oxide and has a first oxygen-deficient transition metal oxide-containing layer having a low oxygen content (hereinafter referred to as “first transition metal oxide layer”).
- the film thickness t of the second transition metal oxide layer 105 is larger than the height h of the minute protrusion 108.
- the distance from the tip of the microprojection 108 to the first transition metal oxide layer 104 is hh, and the distance from the second electrode layer 107 to the first transition metal oxide layer 104 in the portion where the microprojection 108 is not present. It is smaller than t.
- the thickness hh of the second transition metal oxide layer which is locally thin is preferably about 0.1 nm ⁇ th ⁇ 5 nm.
- the second transition metal oxide layer 105 (second oxygen-deficient transition metal oxide layer) is an interface between the second transition metal oxide layer 105 and the second electrode layer 107 (second electrode).
- the second transition metal oxide layer 105 has a locally thin portion by having a plurality of recesses.
- the recess is formed along the crystal grain boundary of the material constituting the second electrode layer 107.
- the second transition metal oxide layer 105 While the interface between the first transition metal oxide layer 104 (first oxygen-deficient transition metal oxide layer) and the second transition metal oxide layer 105 is flat, the second transition metal oxide Since the interface between the layer 105 and the second electrode layer 107 has unevenness, the second transition metal oxide layer 105 has a locally thin portion.
- the second electrode layer 107 has protrusions, so that the second transition metal oxide layer 105 is locally thin.
- the “projection” does not necessarily have a sharp tip.
- the “projection” includes a gently raised shape. It is preferable that the tip of the “projection” does not reach the first transition metal oxide layer 104. That is, it is preferable that the “protrusion” does not penetrate the second transition metal oxide layer 105. In the case where there are a plurality of “projections”, it is preferable that none of the “projections” penetrate the second transition metal oxide layer 105.
- a voltage satisfying a predetermined condition is applied between the first electrode layer 103 and the second electrode layer 107 by an external power source.
- the resistance value of the resistance change layer 106 of the resistance change element 100 is reversibly increased or decreased. For example, when a pulse voltage larger than a predetermined threshold voltage is applied, the resistance value of the resistance change layer 106 increases or decreases, while when a pulse voltage smaller than the threshold voltage is applied, the resistance change layer 106 The resistance value does not change.
- Examples of the material of the first electrode layer 103 include Pt (platinum), Ir (iridium), W (tungsten), Cu (copper), Al (aluminum), TiN (titanium nitride), TaN (tantalum nitride), and TiAlN. (Titanium aluminum nitride) and the like, and the film thickness is about 20 nm to 200 nm.
- the thickness of the first electrode layer 103 is preferably 20 nm or more and 200 nm or less.
- the material of the second electrode layer 107 is preferably Pt (platinum), and the film thickness is about 20 nm to 200 nm.
- the thickness of the second electrode layer 107 is preferably 20 nm or more and 200 nm or less.
- other materials may be added to platinum as the electrode material of the second electrode layer as long as similar protrusions are formed on the variable resistance layer.
- the oxygen-deficient tantalum oxide contained in the first transition metal oxide layer 104 is represented as TaO x
- the oxygen-deficient tantalum oxidation contained in the second transition metal oxide layer 105 When the object is expressed as TaO y , 0 ⁇ x ⁇ 2.5, 0 ⁇ y ⁇ 2.5, and x ⁇ y are satisfied.
- TaO y is preferably TaO y (2.1 ⁇ y ⁇ 2.5).
- TaO x is preferably TaO x (0.8 ⁇ x ⁇ 1.9).
- the composition of the transition metal oxide layer can be measured using Rutherford backscattering method.
- the film thickness of the first transition metal oxide layer is 5 nm to 100 nm, and the film thickness of the second transition metal oxide layer is 1 nm to 10 nm.
- the thickness of the first transition metal oxide layer is preferably 5 nm to 100 nm, and the thickness of the second transition metal oxide layer is preferably 1 nm to 10 nm.
- the substrate 101 can be used as the substrate 101, but is not limited thereto. Since the resistance change layer 106, the second electrode 107, and the minute protrusions 108 can be formed at a relatively low substrate temperature, the resistance change layer 106 can be formed on a polyimide resin material or the like.
- an oxide layer 102 having a thickness of about 200 nm is formed on a substrate 101 made of single crystal silicon by a thermal oxidation method. Then, the first electrode layer 103 is formed on the oxide layer 102 by a sputtering method.
- a first transition metal oxide layer 104 is formed on the first electrode layer 103 by a reactive sputtering method using a transition metal target. Then, the outermost surface of the first transition metal oxide layer 104 is irradiated with oxygen plasma to modify the surface.
- the variable resistance layer 106 is configured by a stacked structure in which the first transition metal oxide layer 104 and the second transition metal oxide layer 105 are stacked.
- a Pt thin film with a thickness of 150 nm as the second electrode layer 107 is formed on the second transition metal oxide layer 105 by a sputtering method.
- the film forming conditions in this case are the same as those for forming the first electrode layer 103.
- heat treatment is performed at 350 ° C. to 425 ° C. for about 10 minutes to 30 minutes in a nitrogen atmosphere.
- the temperature during the heat treatment is preferably 350 ° C. or higher and 425 ° C. or lower.
- the time for performing the heat treatment is preferably 10 minutes or more and 30 minutes or less.
- Example According to the manufacturing method mentioned above, the sample of the Example and the comparative example was produced. The details will be described below.
- the resistance change layer 106 is made of an oxygen-deficient tantalum oxide, and specifically, a first tantalum oxide-containing layer having a low oxygen content (hereinafter referred to as “first tantalum oxide layer”). 104 and a second tantalum oxide-containing layer (hereinafter referred to as a “second tantalum oxide layer”) 105 formed on the first tantalum oxide layer 104 and having a high oxygen content. Yes.
- a stacked structure of the substrate 101, the oxide layer 102, and the first electrode layer 103 (Pt, 100 nm) is formed, and then the first tantalum oxide layer 104 is formed on the first electrode layer 103. Formed.
- the film formation conditions at this time are such that the degree of vacuum (back pressure) in the sputtering apparatus before starting sputtering is about 7 ⁇ 10 ⁇ 6 Pa, the power during sputtering is 250 W, and argon gas and oxygen gas are combined.
- the total gas pressure was 3.3 Pa
- the partial pressure ratio of oxygen gas was 3.8%
- the substrate temperature was 30 ° C.
- the film formation time was 7 minutes. This resulted in a 30 nm deposition of a first tantalum oxide layer 104 that had an oxygen content of about 58%, that is TaO 1.4 .
- the plasma was irradiated with oxygen plasma for 30 seconds while being heated to 250 ° C.
- the outermost surface of the first tantalum oxide layer 104 was oxidized by oxygen plasma.
- a second tantalum oxide layer 105 having an oxygen content higher than that of the first tantalum oxide layer 104 was formed on the surface of the first tantalum oxide layer 104.
- the second tantalum oxide layer 105 is formed by modifying the surface of the first tantalum oxide layer 104 by oxygen plasma treatment, but heat treatment in an oxygen atmosphere, Ta 2 O 5 can also be formed by sputtering.
- the second electrode layer 107 made of a Pt thin film was formed on the second tantalum oxide layer 105.
- the film formation conditions at this time are that the degree of vacuum (back pressure) in the sputtering apparatus before starting sputtering is about 7 ⁇ 10 ⁇ 6 Pa, the power during sputtering is 250 W, and the pressure of argon gas is 3.3 Pa.
- the set temperature of the substrate was 200 ° C., and the film formation time was 3 minutes. Thereby, 150 nm of the 2nd electrode layer 107 was deposited.
- the element region 109 is processed by photolithography and dry etching so as to be a square of 0.5 ⁇ m ⁇ 0.5 ⁇ m.
- forming is a process of applying an electrical pulse once to an element immediately after manufacture.
- the polarity of the electric pulse is a polarity at which the initial resistance, which is the resistance value of the element immediately after manufacture, decreases. Specifically, the polarity at which the electrode on which the high-concentration oxide layer is formed is relatively negative.
- FIG. 2 is obtained by measuring the voltage and current when an electrical pulse having a negative polarity and a pulse width of 100 nsec is applied between the first electrode layer 103 and the second electrode layer 107 of the resistance change element 100.
- Current-voltage characteristics. 2 (a) shows the current-voltage characteristics of the sample before the heat treatment
- FIG. 2 (b) shows the current-voltage characteristics of the sample at the heat treatment temperature of 350 ° C.
- FIG. 2 (c) shows the sample at the heat treatment temperature of 375 ° C.
- FIG. 3A shows the current-voltage characteristics
- FIG. 3A shows the current-voltage characteristics of the sample at a heat treatment temperature of 400 ° C.
- FIG. 3B shows the current-voltage characteristics of the sample at a heat treatment temperature of 450 ° C.
- FIG. 3 (a) the sample with the heat treatment temperature of 400 ° C. is in a high resistance state with almost no current flowing below ⁇ 1.2V, but at ⁇ 1.2V, the current flows about 2 mA, and the resistance value is It turns out that it falls greatly.
- FIG. 3B it can be seen that the sample with a heat treatment temperature of 450 ° C. originally has an initial resistance as small as several hundred ⁇ , and no resistance change occurs even when a negative voltage is applied.
- FIG. 4 shows a voltage (hereinafter referred to as a forming voltage) at which the resistance value decreases due to a rapid current flow in the current-voltage characteristics of the sample with the heat treatment temperature changed.
- a voltage hereinafter referred to as a forming voltage
- a negative voltage of about ⁇ 3.1 V is required when the sample before heat treatment and the heat treatment temperature are 300 ° C., and in the sample where the heat treatment temperature is 350 ° C. to 425 ° C., before the heat treatment, It can be seen that forming is possible with a voltage smaller than that of the sample. In particular, it can be seen that for samples having a heat treatment temperature of 400 ° C. to 425 ° C., forming can be performed with a negative voltage whose absolute value is smaller than 1.5V.
- FIG. 5 shows the heat treatment time dependence of the forming voltage. It can be seen that the absolute value of the forming voltage is abruptly decreased until the first heat treatment time of 10 minutes and gradually saturates.
- the reason why the forming voltage decreases due to the formation of protrusions is not accurately known. However, it seems to be related to the mechanism of resistance change phenomenon. That is, it is considered that the place where the resistance change phenomenon occurs is a part of the high-concentration oxide layer, and the region where the resistance change phenomenon occurs is formed by forming.
- the electric field concentrates in the vicinity of the tip of the protrusion, so that it is considered that a region where a resistance change phenomenon occurs is likely to be formed.
- the present inventors further conducted the following experiment. It was.
- samples having different thicknesses of the second tantalum oxide layer when oxygen-deficient tantalum oxide is used as the resistance change layer 106 are prepared, and each sample is subjected to 10 minutes at 400 ° C. The initial resistance was measured after a certain degree of heat treatment.
- FIG. 6B shows the measurement of the forming voltage after the samples having different film thicknesses were heat-treated at 400 ° C. for about 10 minutes.
- the initial resistance value is about several tens of 3 ⁇ until the thickness of the second tantalum oxide layer is close to 5 nm, but the thickness of the second tantalum oxide layer is 6.5 nm.
- the initial resistance value is about 10 5 ⁇
- the initial resistance value is about 10 8 ⁇ . That is, the resistance value is almost the same up to around 5 nm, and after 6 nm, the resistance value increases as the film thickness of the second tantalum oxide layer increases.
- the larger the thickness of the second tantalum oxide layer the greater the distance between the tip of the protrusion and the first tantalum oxide layer. It is considered that the resistance value is increased because the distance t ⁇ h is longer.
- the difference hh between the height of the minute protrusions 108 and the film thickness of the second tantalum oxide layer 105 is
- the second tantalum oxide layer of the second tantalum oxide layer has a thickness of about 0.5 to 1.5 nm in the sample with a thickness of 6.5 nm, and the second tantalum layer has a thickness of about 2 to 3 nm in the sample with the thickness of the second tantalum oxide layer of 8 nm. It can be seen that the sample having a thickness of the oxide layer of 10 nm is about 4 to 5 nm.
- the difference between the height of the minute protrusion 108 and the film thickness of the second tantalum oxide layer 105, that is, the locally thin film of the second tantalum oxide layer is desirably 0.5 nm ⁇ th ⁇ h ⁇ 5 nm.
- the second tantalum oxide layer must be present between the second electrode layer and the first tantalum oxide layer. It can be said that the thickness t-h of the locally thin second tantalum oxide layer is preferably 0.1 nm ⁇ th ⁇ h ⁇ 5 nm.
- variable resistance characteristics of variable resistance element Referable resistance characteristics of variable resistance element
- FIGS. 7 and 8 are diagrams illustrating an operation example when electrical pulses having a pulse width of 100 nsec and different polarities are alternately applied between the first electrode layer 103 and the second electrode layer 107 of the resistance change element 100.
- 7A shows an operation example of a sample before heat treatment
- FIG. 7B shows an operation example of a sample at a heat treatment temperature of 350 ° C.
- FIG. 7C shows an operation example of a sample at a heat treatment temperature of 375 ° C.
- FIG. 8A shows an example of operation of a sample at 400 ° C.
- FIG. 8B shows an example of operation of a sample at 450 ° C.
- the resistance change element 100 changes as shown in FIG. That is, when a negative voltage pulse (voltage E1, pulse width 100 nsec) is applied between the electrodes, the resistance value of the resistance change element 100 decreases from the high resistance value Rb (about 20000 ⁇ ) to the low resistance value Ra (about 500 ⁇ ). .
- the resistance value of the resistance change element 100 increases from the low resistance value Ra to the high resistance value Rb.
- the voltage E1 is set to ⁇ 1.3V
- the voltage E2 is set to + 1.5V.
- the high resistance value Rb is assigned to information “0” and the low resistance value Ra is assigned to information “1”. Therefore, information “0” is written by applying a positive voltage pulse between the electrodes so that the resistance value of the resistance change layer 106 becomes the high resistance value Rb, and the resistance value Ra becomes the low resistance value Ra. Information “1” is written by applying a negative voltage pulse between the electrodes.
- a read voltage E3 (
- ) are applied between the electrodes.
- a current corresponding to the resistance value of the resistance change layer 106 is output, and the written information can be read by detecting the output current value.
- variable resistance layer 106 functions as a memory unit, so that the first embodiment operates as a memory.
- the minute protrusion 108 penetrates through the second tantalum oxide layer 105 and is in direct contact with the first tantalum oxide layer.
- the second tantalum oxide layer is present between the second electrode layer 107 and the first tantalum oxide layer. Therefore, it can be seen that the height of the minute protrusion 108 is essential to be smaller than the film thickness of the second tantalum oxide layer 105 in order to show the resistance change.
- the resistance change layer 106 includes the first tantalum oxide layer 104 and the second tantalum oxide layer 105 having a composition close to that of Ta 2 O 5 , it is considered that the memory can operate as a memory. It is done.
- forming can be performed with a small forming voltage, and a reversible resistance change can be confirmed after forming.
- variable resistance layer 106 In this specification, the results of examining the variable resistance layer 106 in the example in more detail will be described.
- FIG. 9 is a graph showing the X-ray diffraction spectrum of the sample.
- 2 ⁇ is 36 deg. Since a peak is observed in the vicinity, it can be seen that tantalum oxide is formed in the sample. This peak is 30-40 deg. From this broad peak, it is considered that the crystalline state is amorphous. 2 ⁇ is 56 deg. The peak at is due to the silicon substrate. Thus, it was found that the variable resistance layer mainly composed of amorphous tantalum oxide was formed in the sample.
- FIG. 10 shows an X-ray reflectivity measurement pattern of a sample as an example.
- the horizontal axis indicates the X-ray incident angle
- the vertical axis indicates the X-ray reflectance.
- FIG. 10 (a) assumes that a pattern (broken line) obtained when actually measuring the X-ray reflectivity of sample A and that a single tantalum oxide layer exists on the substrate.
- FIG. 10 (b) shows the reflectance pattern (broken line) obtained in the same measurement, and two tantalum oxide layers on the substrate. The result of fitting assuming that it exists (solid line) is shown.
- the measured values and the fitting results are almost the same, but there are some differences in detail.
- the actually measured reflectance pattern and the reflectance pattern obtained by fitting match well so that they cannot be distinguished from each other. From the above results, the sample is considered to be composed of two different tantalum oxide layers of the first and second tantalum oxide layers.
- the thickness of the first tantalum oxide layer is 22 nm and ⁇ is 29 ⁇ 10 ⁇ 6 .
- the film thickness was about 8 nm and ⁇ was 23 ⁇ 10 ⁇ 6 .
- ⁇ of metal tantalum is 39 ⁇ 10 ⁇ 6
- ⁇ of Ta 2 O 5 is 22 ⁇ 10 ⁇ 6 . Comparing these values with the values obtained this time, it is considered that the first tantalum oxide layer is an incomplete oxide of Ta of about TaO 1.4 .
- the composition ratio of the second tantalum oxide layer is determined from the value of ⁇ , it is TaO 2.4 , which is considered to be an oxide close to Ta 2 O 5 (TaO 2.5 ).
- the resistivity of the first tantalum oxide layer having a composition ratio of about TaO 1.4 is about 6 m ⁇ ⁇ cm as a result of measurement by the four-terminal method, and the first tantalum oxide layer 104 is provided as a single layer.
- the initial resistance of the variable resistance element 100 is about 7 ⁇ in calculation.
- the configuration of the element may be a configuration in which the structure shown in FIG. FIG. 11A is a cross-sectional view showing an example of a schematic configuration of a variable resistance element according to a first modification of the present invention.
- the variable resistance element 400a of this modification includes an oxide layer 402a, a lower electrode layer 403a made of a Pt layer, and a second oxygen-deficient transition metal oxide layer 410a having a high oxygen content on a substrate 401a.
- a resistance change layer 406a including the first oxygen-deficient transition metal oxide layer 404a having a low oxygen content and an upper electrode layer 407a are laminated in this order.
- the second oxygen-deficient transition metal oxide layer cannot be formed by a method of oxidizing the first oxygen-deficient tantalum oxide layer. Therefore, for example, it is necessary to adjust the oxygen content during deposition such as sputtering.
- FIG.11 (b) is sectional drawing which showed an example of schematic structure of the variable resistance element which concerns on the 2nd modification of this invention.
- the variable resistance element 400b of the present modification includes an oxide layer 402b, a lower electrode layer 403b made of a Pt layer, a lower second oxygen-deficient transition metal oxide layer 406b, and a first oxygen layer on a substrate 401b.
- a resistance change layer 406b composed of a deficient transition metal oxide layer 410b and an upper second oxygen-deficient transition metal oxide layer 405b and an upper electrode layer 407b composed of a Pt layer are laminated in this order.
- the resistance change operation is performed on the upper interface (the interface between the upper second oxygen-deficient transition metal oxide layer 405b and the upper electrode layer 407b) and the lower interface (the lower second oxygen-deficient transition metal oxide). This occurs at both the physical layer 410b and the lower electrode layer 403b.
- the variable resistance element of FIG. 14 it has been confirmed that when the variable resistance material is oxygen-deficient hafnium oxide or oxygen-deficient zirconium oxide, the resistance change operation is stably performed. Therefore, even when the variable resistance material is changed to another transition metal oxide, the effect of lowering the forming voltage can be obtained due to the presence of the protrusions.
- the material of the second electrode layer 107 may be Pd (palladium). Even when Pd is used as the electrode material of the second electrode layer, the other components of the variable resistance element can be the same as those when Pt is used as the electrode material of the second electrode layer.
- the manufacturing method of the resistance change element when Pd is used as the electrode material of the second electrode layer is the same as the manufacturing method of the resistance change element 100 described above, except that a Pt thin film is formed on the second transition metal oxide layer 105.
- a Pd thin film is formed as the second electrode layer 107 by a sputtering method.
- the film forming conditions in this case are the same as those for forming the first electrode layer 103.
- the element shown in FIG. 18 includes a first oxygen-deficient Ta oxide layer 704a ′ having a film thickness of about 43 nm and a second film having a film thickness of about 7 nm on the lower electrode layer 703a ′ made of TaN.
- the oxygen-deficient Ta oxide layer 705a ′ and the upper electrode layer 709a ′ made of a Pd layer having a thickness of about 50 nm were stacked in this order.
- the oxygen content of the first oxygen-deficient Ta oxide layer 704a ' was higher than the oxygen content of the second oxygen-deficient Ta oxide layer 705a'.
- the element of FIG. 18 was created using a process technology related to the manufacture of semiconductor devices.
- the maximum temperature of the heating step in the process was about 400 ° C.
- the heating time was about 10 minutes.
- the upper electrode layer 709a ′ is an interface between the upper electrode layer 709a ′ and the second oxygen-deficient Ta oxide layer 705a ′.
- a minute protrusion is formed toward the second oxygen-deficient Ta oxide layer 705a ′ side.
- the method of forming the second oxygen-deficient transition metal oxide layer so as to have a locally thin portion is not necessarily limited to heating. If it can be formed so as to have “a portion with a thin film thickness” as much as necessary to achieve the effect of reducing the voltage of the electric pulse necessary for forming, a method using stress migration or heating Various methods obvious to those skilled in the art can be used, such as a method using a combination of stress migration and stress migration.
- the resistance change element of the present invention is easy to form, can operate at high speed, and has stable rewriting characteristics, and can be used in various electronic devices such as digital home appliances, memory cards, portable telephones, and personal computers. It is useful as a resistance change element used.
Abstract
Description
[本発明の基礎データ]
図12は、抵抗変化層に酸素不足型のタンタル酸化物を用いた抵抗変化素子の断面を示す透過型電子顕微鏡(TEM)写真であって、図12(a)はプロセス中の最高温度を400℃とした場合、図12(b)はプロセス中の最高温度を100℃とした場合を示す。
図14に実験に用いた素子(抵抗変化素子200)を示す。抵抗変化素子200は基板201と、その基板201上に形成された酸化物層202と、その酸化物層202上に形成された第1電極層203と、第2電極層207と、第1電極層203および第2電極層207に挟まれた抵抗変化層206とを備えている。ここで、抵抗変化層206は、酸素含有率が低い第1のタンタル含有層204(以下、「第1のタンタル酸化物層」という)と、その第1のタンタル酸化物層上に形成された酸素含有率が高い第2のタンタル含有層205(以下、「第2のタンタル酸化物層」という)とで構成されている。
次に、図16に、抵抗変化素子200において、第1電極層203、抵抗変化層206及び第2電極層207の断面を透過電子顕微鏡によって観察した結果を示す。図16(a)は、熱処理温度400℃の試料の断面図、図16(b)は、熱処理前の試料の断面図、図16(c)は、熱処理温度450℃の試料の断面図である。
以下に、上述の実験結果の考察を行う。
図1は、本発明の第1の実施の形態に係る抵抗変化素子の一構成例を示した断面図である。
次に、本実施の形態の抵抗変化素子100の製造方法について説明する。
上述した製造方法にしたがって、実施例および比較例の試料を作製した。以下、その詳細について説明する。
次に、抵抗変化素子100を窒素雰囲気中で熱処理温度を300℃から450℃まで変化させて10分間熱処理を行った試料のフォーミングについて説明する。なお、本願明細書においてフォーミングとは、製造直後の素子に対して電気的パルスを1回印加する処理である。また、電気的パルスの極性は製造直後の素子の抵抗値である初期抵抗が下がる極性であり、具体的には高濃度酸化物層が形成される電極が相対的に負となる極性である。
次に、実施例及び比較例のメモリとしての動作例、すなわち情報の書き込み/読み出しをする場合の動作例を、図面を参照して説明する。
本実施の形態における抵抗変化層106の構造を解析した結果を示す。用意したサンプルは、単結晶シリコン基板上に厚さ200nmの酸化物層が形成された基板上に、実施例と全く同じ条件で、タンタル酸化物を堆積して、酸素プラズマの照射処理まで行ったものである。なお、サンプルの上には、第2電極層107に相当するPtは堆積されていないため、抵抗変化層が露出された状態となっている。
素子の構成は、図1に示す構造を上下逆転させた構成としてもよい。図11(a)は本発明の第1変形例に係る抵抗変化素子の概略構成の一例を示した断面図である。本変形例の抵抗変化素子400aは、基板401aの上に、酸化物層402aと、Pt層からなる下部電極層403aと、酸素含有率が高い第2の酸素不足型遷移金属酸化物層410aと酸素含有率が低い第1の酸素不足型遷移金属酸化物層404aとからなる抵抗変化層406aと、上部電極層407aとがこの順に積層されてなる。
101 基板
102 酸化物層
103 第1電極層
104 第1の遷移金属酸化物層
105 第2の遷移金属酸化物層
106 抵抗変化層
107 第2電極層
108 突起
109 素子領域
200 実験用抵抗変化素子
201 基板
202 酸化物層
203 第1電極層
204 第1のタンタル酸化物層
205 第2のタンタル酸化物層
206 抵抗変化層
207 第2電極層
209 素子領域
400a,b 抵抗変化素子
401a,b 基板
402a,b 酸化物層
403a,b 第1電極層
404a,b 第1の遷移金属酸化物層
405b,410a,b 第2の遷移金属酸化物層
406a,b 抵抗変化層
407a,b 第2電極層
408a,b 突起
409a,b 素子領域
703a,b,c,d 第1電極層
704a,b 第1の遷移金属酸化物層
705a,b 第2の遷移金属酸化物層
706c,d 抵抗変化層
709a,b,c,d 第2電極層
Claims (14)
- 第1電極と、
第2電極と、
前記第1電極と前記第2電極との間に介在させ、前記第1電極と前記第2電極と接するように設けられており、前記第1電極と前記第2電極間に与えられる極性の異なる電気的信号に基づいて可逆的に変化する抵抗変化層と、
を備える抵抗変化素子において、
前記抵抗変化層は第1の酸素不足型の遷移金属酸化物層と、
前記第1の酸素不足型の遷移金属酸化物層よりも酸素含有率の高い第2の酸素不足型の遷移金属酸化物層の2層を含む積層構造からなり、
前記第2の酸素不足型の遷移金属酸化物層が前記第2電極と接しており、
前記第2の酸素不足型の遷移金属酸化物層は、局所的に膜厚が薄い部分を有する、
抵抗変化素子。 - 前記第2の酸素不足型の遷移金属酸化物層が、前記第2電極との界面において、複数の凹部を有することにより局所的に膜厚が薄い部分を有する、請求項1に記載の抵抗変化素子。
- 前記凹部が前記第2電極を構成する材料の結晶粒界に沿って形成されている、請求項2に記載の抵抗変化素子。
- 前記第1の酸素不足型の遷移金属酸化物層と前記第2の酸素不足型の遷移金属酸化物層との界面は平坦である一方で、前記第2の酸素不足型の遷移金属酸化物層と前記第2電極との界面が凹凸を有することにより、前記第2の酸素不足型の遷移金属酸化物層は局所的に膜厚が薄い部分を有する、請求項1に記載の抵抗変化素子。
- 前記第2の酸素不足型の遷移金属酸化物層と前記第2電極との界面において、前記第2電極が突起を有することで、前記第2の酸素不足型の遷移金属酸化物層は局所的に膜厚が薄い部分を有する、請求項1に記載の抵抗変化素子。
- 前記第2の電極における前記第2の電極と前記第2の酸素不足型の遷移金属酸化物層との界面に突起が形成されていることを特徴とする請求項1に記載の抵抗変化素子。
- 前記第2電極は白金又は白金合金であることを特徴とする請求項6に記載の抵抗変化素子。
- 前記局所的に膜厚が薄い部分の膜厚が0.1nm以上、5nm以下であることを特徴とする請求項7に記載の抵抗変化素子。
- 前記遷移金属酸化物層はタンタル酸化物層であることを特徴とする請求項1~8のいずれかに記載の抵抗変化素子。
- 第1電極を形成する工程と、
前記第1電極上に第1の酸素不足型の遷移金属酸化物層を形成する工程と、
前記第1の酸素不足型の遷移金属酸化物層よりも酸素含有量の高い第2の酸素不足型の遷移金属酸化物層を前記第1の酸素不足型の遷移金属酸化物層上に形成する工程と、
前記第2の酸素不足型の遷移金属酸化物層上に白金又は白金合金からなる第2電極層を形成する工程と、
前記第2電極層を形成後、熱処理を行うことによって前記第2電極層における前記第2電極層と前記第2の酸素不足型の遷移金属酸化物層との界面に突起を形成する工程と、
を備えることを特徴とする抵抗変化素子の製造方法。 - 第1電極を形成する工程と、
前記第1電極上に第1の酸素不足型の遷移金属酸化物層を形成する工程と、
前記第1の酸素不足型の遷移金属酸化物層よりも酸素含有量の高い第2の酸素不足型の遷移金属酸化物層を前記第1の酸素不足型の遷移金属酸化物層上に形成する工程と、
前記第2の酸素不足型の遷移金属酸化物層上にパラジウム又はパラジウム合金からなる第2電極層を形成する工程と、
前記第2電極層を形成後、熱処理を行うことによって前記第2電極層における前記第2電極層と前記第2の酸素不足型の遷移金属酸化物層との界面に突起を形成する工程と、
を備えることを特徴とする抵抗変化素子の製造方法。 - 前記熱処理は350℃~425℃において行うことを特徴とする請求項10または11に記載の抵抗変化素子の製造方法。
- 前記遷移金属酸化物層がタンタル酸化物層であることを特徴とする請求項10または11に記載の抵抗変化素子の製造方法。
- 前記熱処理によって形成される突起の高さが前記第2の酸素不足型の遷移金属酸化物層の膜厚よりも小さいことを特徴とする請求項10または11に記載の抵抗変化素子の製造方法。
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