WO2010073790A1 - 磁気抵抗素子およびそれを用いる記憶装置 - Google Patents
磁気抵抗素子およびそれを用いる記憶装置 Download PDFInfo
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- WO2010073790A1 WO2010073790A1 PCT/JP2009/067237 JP2009067237W WO2010073790A1 WO 2010073790 A1 WO2010073790 A1 WO 2010073790A1 JP 2009067237 W JP2009067237 W JP 2009067237W WO 2010073790 A1 WO2010073790 A1 WO 2010073790A1
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- B82Y25/00—Nanomagnetism, e.g. magnetoimpedance, anisotropic magnetoresistance, giant magnetoresistance or tunneling magnetoresistance
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- G11C11/00—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor
- G11C11/02—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements
- G11C11/16—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements using elements in which the storage effect is based on magnetic spin effect
- G11C11/161—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements using elements in which the storage effect is based on magnetic spin effect details concerning the memory cell structure, e.g. the layers of the ferromagnetic memory cell
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- G—PHYSICS
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- G11C—STATIC STORES
- G11C11/00—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor
- G11C11/02—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements
- G11C11/16—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements using elements in which the storage effect is based on magnetic spin effect
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- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F10/00—Thin magnetic films, e.g. of one-domain structure
- H01F10/08—Thin magnetic films, e.g. of one-domain structure characterised by magnetic layers
- H01F10/10—Thin magnetic films, e.g. of one-domain structure characterised by magnetic layers characterised by the composition
- H01F10/12—Thin magnetic films, e.g. of one-domain structure characterised by magnetic layers characterised by the composition being metals or alloys
- H01F10/16—Thin magnetic films, e.g. of one-domain structure characterised by magnetic layers characterised by the composition being metals or alloys containing cobalt
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- H01F10/32—Spin-exchange-coupled multilayers, e.g. nanostructured superlattices
- H01F10/324—Exchange coupling of magnetic film pairs via a very thin non-magnetic spacer, e.g. by exchange with conduction electrons of the spacer
- H01F10/325—Exchange coupling of magnetic film pairs via a very thin non-magnetic spacer, e.g. by exchange with conduction electrons of the spacer the spacer being noble metal
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
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- H01F10/00—Thin magnetic films, e.g. of one-domain structure
- H01F10/32—Spin-exchange-coupled multilayers, e.g. nanostructured superlattices
- H01F10/324—Exchange coupling of magnetic film pairs via a very thin non-magnetic spacer, e.g. by exchange with conduction electrons of the spacer
- H01F10/3254—Exchange coupling of magnetic film pairs via a very thin non-magnetic spacer, e.g. by exchange with conduction electrons of the spacer the spacer being semiconducting or insulating, e.g. for spin tunnel junction [STJ]
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- H10B—ELECTRONIC MEMORY DEVICES
- H10B61/00—Magnetic memory devices, e.g. magnetoresistive RAM [MRAM] devices
- H10B61/10—Magnetic memory devices, e.g. magnetoresistive RAM [MRAM] devices comprising components having two electrodes, e.g. diodes or MIM elements
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- H10N50/00—Galvanomagnetic devices
- H10N50/80—Constructional details
- H10N50/85—Magnetic active materials
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- H—ELECTRICITY
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- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F10/00—Thin magnetic films, e.g. of one-domain structure
- H01F10/08—Thin magnetic films, e.g. of one-domain structure characterised by magnetic layers
- H01F10/10—Thin magnetic films, e.g. of one-domain structure characterised by magnetic layers characterised by the composition
- H01F10/12—Thin magnetic films, e.g. of one-domain structure characterised by magnetic layers characterised by the composition being metals or alloys
- H01F10/126—Thin magnetic films, e.g. of one-domain structure characterised by magnetic layers characterised by the composition being metals or alloys containing rare earth metals
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F10/00—Thin magnetic films, e.g. of one-domain structure
- H01F10/32—Spin-exchange-coupled multilayers, e.g. nanostructured superlattices
- H01F10/324—Exchange coupling of magnetic film pairs via a very thin non-magnetic spacer, e.g. by exchange with conduction electrons of the spacer
- H01F10/3286—Spin-exchange coupled multilayers having at least one layer with perpendicular magnetic anisotropy
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- H—ELECTRICITY
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Definitions
- the present invention relates to a magnetoresistive element for reading data using the magnetoresistive effect, and a storage device using the magnetoresistive element.
- Non-volatile semiconductor memory devices represented by flash memory
- the release of products with a capacity of about 32 GB has been announced.
- Non-volatile semiconductor memory devices have increased in commercial value, especially as storage for USB memories and mobile phones, and the principle advantages of solid-state memory such as vibration resistance, high reliability, and low power consumption have been attracting attention. It is becoming the mainstream storage device for portable electronic devices, such as portable music player storage for music and images.
- DRAM Dynamic Random Access Memory
- the research aims to realize a so-called “instant-on-computer”, a computer that starts up instantly when in use and consumes as much power as possible during standby.
- the memory element of the non-volatile semiconductor memory element satisfies the requirements that (1) the switching speed is less than 50 ns and (2) the number of rewrites exceeds 1016, which are technical specifications required for DRAM. It is said that it needs to be met.
- the lower limit (1016) of the number of rewrites listed in the technical specification is a numerical value assumed based on the number of accesses when one access per 30 ns is continued for 10 years.
- a refresh cycle is not required, and therefore, there is a possibility that it can be used for the same purpose as the current DRAM even with a smaller number of rewrites.
- MRAM ferroelectric memory
- MRAM magnetic memory
- PRAM phase change memory
- MRAM using a magnetoresistive element as a memory element is considered promising as a candidate for satisfying the above technical specifications and replacing DRAM.
- a memory element using a magnetoresistive element is referred to as a “magnetic memory element”.
- MRAM is a prototype level, it has already cleared the rewrite performance of 1012 or more, and its switching speed is less than 10 ns, so it is realized compared with other technologies of nonvolatile memory devices. It is considered to be particularly high.
- the MRAM with a small capacity of about 4 Mbit, which is currently commercialized, is a current magnetic field rewritable type. If the minimum processing dimension of the manufacturing process is F, the cell area is 20-30 F2 or more and the cell itself is fine. Difficult to make. Further, in the current magnetic field rewritable MRAM, when the cell area is miniaturized, the reversal magnetic field (that is, the minimum value as the external magnetic field for reversing the magnetization) increases, and the cell density is increased. There is a problem in that the current value required for inversion increases as the size of the circuit becomes finer. Because of these problems, it is not practical to replace the DRAM with a current magnetic field rewritable MRAM.
- Non-patent Document 1 Two breakthrough technologies are changing the situation.
- One is a method using MTJ (magnetic tunnel junction) using an MgO tunnel insulating film, and a magnetoresistance ratio of 200% or more can be easily obtained (Non-patent Document 1).
- the other is a current injection magnetization reversal method.
- the current injection magnetization reversal method there is no principle difficulty for miniaturization such as the increase of the reversal magnetic field accompanying the above-mentioned cell miniaturization, and conversely, when the miniaturization is performed, the reversal current is reduced according to the scaling law. Therefore, it is possible to reduce the writing energy with the miniaturization.
- Non-patent Document 2 the configuration of the memory cell using one transistor per magnetic tunnel junction (MTJ) is referred to as “one transistor-1MTJ configuration”.
- MTJ transistor per magnetic tunnel junction
- Patent Document 1 a configuration of a memory cell using one diode per MTJ (“1 diode-1 MTJ configuration”) has also been proposed (Patent Document 1). .
- the number of transistors is reduced from two to one by simplifying the circuit by limiting the polarity of the current to only one.
- Patent Document 2 proposes a proposal to realize a transistor-1MTJ circuit and reduce the cell size equivalent to DRAM.
- the proposal of the 1-diode-1MTJ configuration disclosed in Patent Document 1 is to perform switching by currents in both the forward bias and the reverse bias through the diode. That is, the switching is performed by the current in the forward bias (forward current) and the leakage current in the reverse bias, and the principle of switching by the polarity of the current remains unchanged.
- the diode is originally formed to perform MTJ selection without disturbing (crosstalk) in writing, erasing, and reading operations, and the leakage current flows not only in the reverse direction but also in the forward direction.
- the proposal disclosed in Patent Document 2 that is, the proposal of a one-transistor-1MTJ configuration using an element provided with a driving layer in which the magnetization direction is substantially fixed in the stacking direction, is a spin from the driving layer to the free layer.
- This is a method of inducing spin precession (precession) by injection and switching. In principle, switching is possible with only one polarity of current.
- the magnetization arrangement indicates whether the magnetization directions of the free layer (memory layer) and the pinned layer (magnetization pinned layer) are parallel or antiparallel.
- the present invention has been made in view of the above problems, and is a magnetic memory element for a 1-diode-1MTJ configuration in which switching is performed with only one polarity of current, which has been difficult to realize so far, that is, a single memory device. Further miniaturization of storage device in nonvolatile semiconductor memory device by providing magnetic memory element capable of realizing memory cell of 1 diode-1MTJ configuration capable of switching operation by electric pulse of polarity, and memory device using the same This contributes to increasing the capacity and increasing the upper limit of the number of rewrites.
- the inventors of the present application went back to the basic characteristics of magnetization of the magnetic material used in the MRAM, examined the above problems, and reconsidered the requirements for operating as a memory element.
- the inventors of the present application first made the magnetic material used as the storage layer an alloy of a rare earth and a transition metal (“rare earth-transition metal alloy”), thereby changing the magnetic characteristics of the recording layer to an N-type ferrimagnetic material. I thought about making it magnetic.
- an N-type ferrimagnetic material a phenomenon is observed in which, at a certain temperature, the magnetization of the transition metal element contained therein and the magnetization of the rare earth metal cancel each other, and the net magnetization becomes zero. The temperature at which this net magnetization is zero is called the compensation temperature.
- each memory cell can have a 1 diode-1 MTJ configuration.
- the above operating principle will be further described in detail in the first embodiment.
- the inventors of the present application have made a specific study for making the magnetic characteristics of the recording layer N-type ferrimagnetic, thereby leading to the following inventions of magnetic memory elements and nonvolatile memory devices.
- a magnetic memory element includes first to fourth magnetic layers and an intermediate layer, the third magnetic layer is provided on the first magnetic layer, and the third magnetic layer is provided.
- the intermediate layer is made of an insulator or a non-magnetic material, and the second magnetic layer is made of gadolinium, iron and cobalt ternary alloy thin film, gadolinium and cobalt binary alloy thin film, and terbium and cobalt binary. Selected from the group of thin films consisting of alloy thin films.
- the second magnetic layer is used as the storage layer.
- the magnetic material used as the recording layer is a rare earth-transition metal alloy, and its magnetic characteristics are N-type ferrimagnetism. Therefore, the net magnetization direction of the storage layer is reversed by the temperature of the magnetic memory element. Due to this phenomenon, the magnetization direction of the storage layer is controlled by a current of the same polarity (single polarity current, monopolar current) regardless of whether the write operation is directed in the same direction or in the opposite direction to the first magnetic layer (pinned layer).
- Each memory cell can have a 1 diode-1 MTJ configuration.
- the first magnetic layer is a ternary alloy thin film of terbium, iron, and cobalt, and the composition ratio of terbium in the ternary alloy of the first magnetic layer is 13. ⁇ 22 at. % Is preferred.
- the first magnetic layer becomes a perpendicular magnetization film, and the composition ratio of Tb becomes sufficiently low at the compensation temperature, for example, below the temperature at which the memory device is operated. In the magnetic layer, it is possible to prevent the magnetization from decreasing due to an increase in element temperature during writing.
- “at.%” Is the same as atomic% and mol%, and the total composition ratio of all components is 100 at. % Represents the atomic ratio or molar ratio of each component.
- the first magnetic layer is a terbium and cobalt binary alloy thin film, and the composition ratio of terbium in the binary alloy of the first magnetic layer is 13 to 22 at. % Is preferred.
- the first magnetic layer is a perpendicular magnetization film, and the composition ratio of Tb is made smaller than the compensation composition ratio at the temperature at which the memory device is operated, that is, the binary alloy of the first magnetic layer.
- This compensation temperature can be lower than the temperature at which the memory device is operated. Then, even if the element temperature rises at the time of writing, the temperature of the first magnetic layer does not approach the compensation temperature Tcomp but rather moves away. Therefore, the composition ratio of terbium is 13 to 22 at. By setting the ratio to%, it is possible to suppress a decrease in magnetization in the pinned layer (first magnetic layer).
- the compensation composition ratio refers to the minimum value of the composition ratio of the rare earth element in the alloy composition in which the magnetic moment of the rare earth element exceeds the magnetic moment of the transition metal element, and is a value determined at each temperature.
- binary alloys of terbium and cobalt are more resistant to oxidation than ternary alloys of terbium, iron and cobalt. Thereby, it is possible to improve the characteristic deterioration of the magnetic memory element.
- the second magnetic layer is a gadolinium-cobalt binary alloy thin film, and the gadolinium composition ratio in the binary alloy of the second magnetic layer is 23 to 28 at. % Is preferred.
- the compensation temperature of the storage layer (second magnetic layer) is in the range of 100 to 180 ° C. Therefore, as will be described later, the temperature of the storage layer is increased by the Joule heat due to the write current.
- the direction of magnetization of the storage layer can be controlled by temperature by controlling so as to be lower.
- the second magnetic layer is a binary alloy thin film of terbium and cobalt, and the composition ratio of terbium in the binary alloy of the second magnetic layer is 22 to 26 at. % Is preferred.
- the compensation temperature of the storage layer (second magnetic layer) is in the range of 100 to 180 ° C.
- the temperature of the storage layer is controlled to be above or below the compensation temperature by Joule heat due to the write current.
- the direction of magnetization of the storage layer can be controlled by temperature.
- the inventors of the present application can control the magnetization direction of the recording layer by utilizing the change in the magnetic characteristics of the pinned layer by examining the above problems and making the magnetic characteristics of the pinned layer N-type ferrimagnetic. I found out. That is, it is noted that the net magnetization direction of the pinned layer can be reversed by the element temperature, and the magnetization of the pinned layer before and after the reversal is transferred to the magnetization direction of the storage layer by a single polarity current. As a result, a write operation in which the magnetization of the recording layer is directed in the same direction or in the opposite direction to the pinned layer can be performed, and each element can be configured as one diode-1MTJ. The above operating principle will be further described in detail in the fourth embodiment. As another aspect of the present application, the inventors of the present application conducted a specific study to make the magnetic characteristics of the pinned layer N-type ferrimagnetism. Invented.
- a magnetic memory element includes first to fourth magnetic layers and an intermediate layer, the third magnetic layer is provided on the first magnetic layer, and the third magnetic layer is provided.
- a magnetic memory element comprising: an intermediate layer provided on a layer; the fourth magnetic layer provided on the intermediate layer; and the second magnetic layer provided on the fourth magnetic layer.
- the intermediate layer is made of an insulator or a non-magnetic material
- the first magnetic layer is made of a ternary alloy thin film of terbium, cobalt, and iron, and a thin film group made of a binary alloy thin film of terbium and cobalt. Selected.
- the first magnetic layer is a ternary alloy of terbium, iron, and cobalt, and the composition ratio of terbium in the ternary alloy of the first magnetic layer is 25 at. % To 29 at. % Is preferred.
- the compensation temperature in the first magnetic layer (pinned layer) is in the range of 100 to 180 ° C. Therefore, as will be described later, the temperature of the storage layer is increased by the Joule heat due to the write current.
- the direction of magnetization of the pinned layer can be controlled by temperature by controlling so as to be lower.
- the second magnetic layer is a thin film of an alloy made of gadolinium and cobalt.
- GdCo has a smaller magnetic anisotropy energy than TbFeCo, and the magnetization Ms tends to be smaller than TbFeCo. If this is used as a recording layer, the write current can be reduced more easily.
- the second magnetic layer is a ternary alloy thin film further containing iron in addition to gadolinium and cobalt, and the composition ratio of gadolinium in the ternary alloy of the second magnetic layer is 10 at. % To 17 at. % Or 23 at. % To 40 at. % Is more preferable.
- Patent Document 3 discloses Tc (Curie temperature) and Tcomp (compensation) for an alloy GdxCo1-x composed of gadolinium and cobalt, and a ternary alloy Gdx (Fe0.82Co0.18) 1-x of gadolinium, iron, and cobalt. Temperature) is shown for each gadolinium composition ratio. These are reproduced in FIGS. 9a and b.
- both GdxCo1-x and Gdx (Fe0.82Co0.18) 1-x have a sufficiently high Tc at the composition ratio in which Tcomp is present, that is, the composition ratio at which an N-type ferrimagnetic material is formed. Therefore, when these alloys are used for the second magnetic layer, the writing operation can be appropriately performed.
- the gadolinium composition ratio is 20 at.
- the value of Tcomp for each value of the gadolinium composition ratio is larger than that in the case where the second magnetic film is GdxCo1-x.
- the value of Tcomp for x 0.25 (the composition ratio of gadolinium is 25 at.%) Is about 160 ° C. for GdxCo1-x, but about 260 for Gdx (Fe0.82Co0.18) 1-x. It is °C.
- the second magnetic film becomes gadolinium and cobalt.
- the temperature range until the compensation temperature of the second magnetic film itself is reached is larger than when the second magnetic film is GdxCo1-x. .
- the ternary containing the iron in addition to gadolinium and cobalt in addition to gadolinium and cobalt even if the arrival temperature of each magnetic memory element in the case of manufacturing the memory device in which the magnetic memory element is integrated is considered.
- the second magnetic film is GdxCo1-x.
- the range in which such an effect can be obtained by using the second magnetic film as the original alloy thin film has a gadolinium composition ratio of 23 at. % To 40 at. %.
- the composition of the ternary alloy shown here is only Gdx (Fe0.82Co0.18) 1-x. However, by adjusting the relative ratio of iron and cobalt, gadolinium can be obtained with the above effect.
- the upper limit of the composition ratio is 40 at. %.
- each value of the gadolinium composition ratio is obtained when the second magnetic film is the original alloy thin film. It has been found that the value of Tcomp is smaller than that in the case where the second magnetic film is GdxCo1-x. Then, also in this case, the temperature range from the lower limit value of the temperature of the second magnetic film when the magnetic memory element operates to Tcomp is ternary including iron in addition to gadolinium and cobalt. In the case of an alloy thin film, the second magnetic film is larger than that in the case of GdxCo1-x.
- the second magnetic film when the second magnetic film is a ternary alloy containing iron in addition to gadolinium and cobalt, the second magnetic film is GdxCo1-x. Compared to a certain case, stable operation can be expected from the storage device.
- the range of the composition ratio of gadolinium in which such an effect can be obtained is 10 at. % To 17 at. %.
- the composition ratio of gadolinium is 10 at. % To 17 at. % Or 23 at. % To 40 at. %, Even if the temperature of the first magnetic layer (pinned layer) changes between the operating temperature ranges of the memory device, only the first magnetic layer straddles the compensation temperature, The magnetic layer 2 can be operated so as not to cross the compensation temperature, and a polar operation described later can be realized.
- the first magnetic layer is a terbium and cobalt binary alloy thin film, and the composition ratio of terbium in the binary alloy of the first magnetic layer is 22 to 26 at. % Is preferred.
- the compensation temperature in the first magnetic layer (pinned layer) is in the range of 100 to 180 ° C. Therefore, as will be described later, the temperature of the storage layer is increased above the compensation temperature by Joule heat caused by the write current. By controlling to be below, the magnetization direction of the pinned layer can be controlled by temperature.
- the second magnetic layer is a gadolinium and cobalt binary alloy thin film, and the gadolinium composition ratio in the binary alloy of the second magnetic layer is 27 to 39 at. % Is preferred.
- the second magnetic layer does not straddle the compensation temperature, so that only the first magnetic layer (memory layer) straddles the compensation temperature.
- the magnetization can be reversed.
- the second magnetic layer is a terbium and cobalt binary alloy thin film, and the composition ratio of terbium in the binary alloy of the second magnetic layer is 27 to 32 at. % Is preferred.
- the second magnetic layer does not straddle the compensation temperature, so only the first magnetic layer (memory layer) straddles the compensation temperature.
- the magnetization can be reversed.
- the molar ratio of each composition of iron and cobalt in the first magnetic layer is 7: 3.
- the magnetization of the transition metal (iron and cobalt) portion of the magnetization of the first magnetic layer (pinned layer) is maximized, and the net magnetization of the pinned layer is also increased. To do.
- the magnetization of the pinned layer is less likely to be disturbed by the current magnetization reversal operation (or spin transfer magnetization reversal, STT), and a stable operation is possible.
- the third and fourth magnetic layers are used as the spin polarization layer, but the present invention is not limited to this example.
- a nonvolatile memory device is provided as an aspect thereof. That is, the information rewriting means comprising the magnetoresistive element according to any one of the present invention and a rectifying element connected in series thereto, and writing and erasing by passing a current through the magnetoresistive element, and the magnetoresistive element There is provided a non-volatile memory device comprising reading means for reading information stored from the amount of flowing current.
- nonvolatile memory device having the above characteristics, switching can be performed by a single polarity electric pulse, so that a memory cell composed of one diode and 1MTJ can be realized, and a cell area of about 4F2 equivalent to a flash memory is realized. It becomes possible.
- magnetic memory elements having high-speed operation and high rewrite performance can be densely integrated on a substrate such as a silicon wafer. Can be offered at.
- the magnetic memory element and the memory device of the present invention can perform a reliable switching operation with a single polarity electric pulse, it is possible to realize a 4F2 size memory cell of 1 diode and 1 MTJ configuration. As a result, a highly integrated and non-volatile storage device can be realized at low cost.
- FIG. 7 is a cross-sectional view showing a structure of a magnetic memory element according to first to seventh embodiments of the present invention.
- FIG. It is a temperature characteristic figure showing the relationship between magnetization of N type ferrimagnetic material, and temperature.
- FIG. 5 is a schematic diagram of the operation principle of the magnetic memory element according to the first to third embodiments of the present invention.
- FIG. 9 is a schematic diagram of the operating principle of a magnetic memory element according to fourth to seventh embodiments of the present invention. It is a graph which shows the relationship of the compensation temperature with respect to the composition ratio of TbFeCo Tb. It is a graph which shows the relationship of the compensation temperature with respect to the composition ratio of TbCo of Tb.
- FIG. 1 is a block diagram of a circuit configuration of a cross-point type memory cell array which is an embodiment of a nonvolatile memory device according to the present invention. It is a graph which shows the gadolinium dependence of the Curie temperature and compensation temperature in the alloy of gadolinium and iron and the alloy of gadolinium, iron and cobalt.
- FIG. 1 is an enlarged cross-sectional view showing a portion including a magnetic memory element of a storage device 10 including a magnetic memory element 100.
- the magnetic memory element 100 has a magnetic tunnel junction (MTJ) portion 13, and the MTJ portion 13 is sandwiched between the lower electrode 14 and the upper electrode 12.
- the MTJ portion 13 has a pinned layer 22 (first magnetic layer), a first spin-polarized layer 27 (third magnetic layer), an insulating layer 21, and a second spin-polarized layer 26 (from the lower electrode 14 side).
- a fourth magnetic layer) and a storage layer 20 (second magnetic layer) in this order, and the pinned layer 22 and the storage layer 20 are a rare earth-transition metal which is a kind of N-type ferrimagnetic material. It is an alloy.
- the lower electrode 14 is formed on a P-type region 24 formed in the substrate 15, and an N-type region 25 is formed in the substrate 15 so as to be in contact with the P-type region 24.
- the combination of the P-type region 24 and the N-type region 25 forms a diode (rectifier element).
- a contact portion 17 and a word line 18 are stacked in this order on the N-type region 25.
- One upper electrode 12 is connected to the bit line 11.
- the word line 18 and the bit line 11 are insulated by an interlayer insulating film 23 and connected to a control circuit (not shown).
- the storage device 10 includes a number of magnetic memory elements 100, and reads information stored in the target magnetic memory element and writes information in the magnetic memory element 100 according to the memory address.
- the pinned layer 22 is made of a thin film made of a TbFeCo alloy
- the memory layer 20 is made of a thin film made of a GdCo alloy
- the compensation temperatures thereof are made to be 0 ° C. or lower and around 150 ° C., respectively.
- the magnetic memory element 100 in which the magnetization arrangement is parallel is in a state where the resistance between the pinned layer 22 and the storage layer 20 shows a low resistance value (low resistance state).
- FIG. 2 is an example of a temperature characteristic diagram of magnetization in an N-type ferrimagnetic material. Here, it is assumed that the temperature characteristic diagram of the storage layer 20 is shown.
- a magnetization curve 201 of an N-type ferrimagnetic material is shown, and a magnetic material 202 with an arrow indicating the direction of the magnetization 203 is schematically shown therein.
- the write operation is performed by utilizing this phenomenon that the magnetization direction of the storage layer 20 is reversed when the temperature is equal to or higher than the compensation temperature. Further, a write operation of the magnetic memory element 100 using this phenomenon will be described with reference to FIG.
- the magnetization of the storage layer 20 and the magnetization of the pinned layer 22 are in the same direction at the start of the operation (FIG. 3A).
- the storage layer 20 is heated to a temperature equal to or higher than the compensation temperature Tcomp, the magnetization direction of the storage layer 20 is reversed due to the above-described phenomenon (FIG. 3B).
- a tunnel current is passed from the storage layer 20 to the pinned layer 22 while maintaining this magnetization arrangement, spin-polarized electrons flow from the pinned layer 22 to the storage layer 20.
- the magnetization of the memory layer 20 is reversed by receiving torque from these electrons so that the magnetization direction is the same as that of the pinned layer 22 (FIG. 3C).
- the magnetization arrangement is antiparallel (FIG. 3 (d)).
- the magnetic memory element 100 whose magnetization arrangement is antiparallel is in a state where the resistance between the pinned layer 22 and the storage layer 20 shows a high resistance value (high resistance state).
- Joule heat by a write current is used for heating the storage layer 20.
- a current (write current) is passed from the storage layer 20 to the pinned layer 22 during writing, and the magnetic memory element 100 is heated by this write current.
- the temperature rise due to this heating is calculated to be about +70 K to +150 K.
- the ultimate temperature is approximately 100 ° C. to 180 ° C.
- the temperature reached by this temperature rise can be controlled to be an arbitrary temperature within the above temperature range by changing the pulse width of the write current in a range of 10 nsec to 1 msec, for example. Therefore, for example, if the compensation temperature of the storage layer 20 exists in the controllable temperature range (100 ° C. to 180 ° C.) by adjusting the compensation temperature of the storage layer 20 to around 150 ° C. The net magnetization direction can be reversed by controlling the pulse width of the current.
- the direction of the current for obtaining the parallel magnetization arrangement and the direction of the current for obtaining the antiparallel magnetization arrangement are the current directions shown in FIG. Only the temperature difference.
- the magnetic memory element 100 according to the first embodiment changes the magnetization direction of the storage layer 20 with respect to the pinned layer by changing the pulse width even when a single polarity current is used. Writing can be done either parallel or antiparallel.
- composition of pinned layer As the TbFeCo of the pinned layer, the composition ratio of Tb is 13 to 22 at. % Is preferred. TbFeCo has a Tb composition of approximately 13 to 32 at. % Becomes a perpendicular magnetization film. However, when the Tb composition ratio exceeds the compensation composition ratio at room temperature, for example, the Tb composition ratio is 23 to 32 at. In the case of%, the temperature of the pinned layer approaches the compensation temperature due to the temperature rise due to the write current, and the magnetization of the pinned layer decreases. In the STT operation, the magnetization of the pinned layer must be sufficiently large with respect to the storage layer, and this decrease in magnetization may cause the STT operation to become unstable.
- the composition ratio of Tb of the pinned layer is such that the compensation temperature is lower than the temperature at which the memory device operates.
- Such a composition ratio of Tb is 13 to 22 at. %.
- the composition ratio is 13 at%, which is the limit of the perpendicular magnetization film, the net magnetization is maximized and is ideal.
- a thin film having a uniform composition over the entire film forming region is not possible. 1 to 2 at. %, That is, the composition ratio of Tb is 15 at. % Is most preferable.
- composition of memory layer In order to realize the above-described operation in the present embodiment, it is preferable to set the compensation temperature of the storage layer 20 in the range of the temperature reached by the recording layer 20, that is, in the range of 100 to 180 ° C.
- the composition of the GdCo alloy having the compensation temperature in this range has a Gd composition ratio of 23 to 28 at. In this embodiment, GdCo within this range is used. Of these, the Gd composition ratio is particularly 26 at. %, Co composition ratio is 74 at. %,
- the compensation temperature is most preferably the center of the range of the reached temperature (150 ° C.), and temperature control becomes easy.
- the spin-polarized film means a magnetic film in which the spin is completely polarized with respect to the ⁇ 1 band, such as Fe, FeCo, and FeCoB.
- an insulating layer intermediate layer
- MgO insulating layer
- a manufacturing method of the magnetic memory element manufactured according to the first embodiment will be described. Refer to FIG. 1 again. First, a P-type region 24 and an N-type region 25 are formed on a Si substrate (silicon wafer) 15 by a CMOS process. Thereafter, Al (5 nm) is formed by magnetron sputtering, and the lower electrode 14 is formed on the P-type region 24 and the contact 17 is formed on the N-type region 25 by a photolithography process.
- an interlayer insulating film (SiN) is formed to a thickness of about 5 nm by a plasma CVD (chemical vapor deposition) process, and this resist film is made of acetone. Or NMP (N-methyl-2-pyrrolidone) as a solvent. Then, the SiN film on the lower electrode 14 and the contact 17 is lifted off (washed away) together with the resist film, so that the surfaces of the lower electrode 14 and the contact 17 are exposed. Further, Cu (10 nm) is formed by magnetron sputtering, and a word line 18 is formed on the contact 17 by photolithography.
- TbFeCo (5 nm), FeCo (1 nm), MgO (1 nm), FeCo (1 nm), GdCo (2 nm), Ta (5 nm), Ru (5 nm), Ta (3 nm) are stacked in this order by magnetron sputtering.
- the laminated film is finely processed into a circular element having a diameter of 50 to 100 nm by a photolithography process. This circular element becomes the pinned layer 22, the first spin polarization layer 27, the insulating layer 21, the second spin polarization layer 26, the memory layer 20, and the upper electrode 12 from below.
- an interlayer insulating film (SiN) is formed by a plasma CVD process so as to have a film thickness of about 60 nm, and the resist film used in the photolithography process is acetone or NMP as a solvent. Wash away. This lifts off the interlayer insulating film (SiN) deposited on the upper electrode 12 together with the resist film, and the surface of the upper electrode 12 is exposed.
- Ta (10 nm), Cu (500 nm), and Ta (10 nm) are stacked in this order by magnetron sputtering, and the Ta / Cu / Ta stacked portion is processed into a bit line shape by photolithography.
- the magnetic memory element of this embodiment can be manufactured.
- the pinned layer is TbFeCo, and the composition ratio of terbium (Tb) is 15 ( ⁇ 1) at. It was stated that the elemental composition ratio of iron (Fe) and cobalt (Co) is preferably 7: 3.
- a thin film is produced by magnetron sputtering using an alloy target of Tb15Fe60Co25, and if the composition of the thin film does not match the above composition, the composition is finely adjusted by placing Tb pieces and Co pieces on the target.
- Tb originally has a lower sputtering rate than Fe, the composition ratio of Tb is 2 to 3 at.
- GdCo of the memory layer is also made of Gd26Co74 alloy target or Gd of 2 to 3 at. Magnetron sputtering may be performed using an alloy target containing about%.
- Gd26Co74 used as the storage layer 20 has a compensation temperature in the vicinity of 150 ° C., which is near the center of the temperature range in which the temperature can be controlled by the pulse width of the STT write current. That is, the polarity of the STT write current is not changed, and the ultimate temperature of the storage layer 20 can be controlled to be lower or higher than the compensation temperature simply by changing the pulse width. Therefore, the magnetization direction of the storage layer 20 Can be controlled in the same direction (parallel) or in the opposite direction (anti-parallel) to the pinned layer 22. For this reason, it is possible to realize a 4F2 size memory cell having one diode and one MTJ configuration by the above operation.
- Tb15Fe59Co26 used as the pinned layer is a perpendicular magnetization film, and the compensation temperature is lower than the lower limit of the temperature at which the memory device operates. Therefore, the decrease in magnetization is about ⁇ 20% even when the element temperature rises due to the write current. It is moderate. For this reason, the magnetization of the pinned layer is excessively reduced during the write operation, and reliability is not impaired.
- Gd26Co74 used for the storage layer operates at a temperature close to the compensation temperature in both parallel and anti-parallel states due to the temperature rise by the write current. In particular, when the accuracy of temperature control is increased, writing can be performed so that the magnitude of magnetization is parallel or anti-parallel at a temperature close to zero. For this reason, a small magnetization of the storage layer leads to a reduction in the write current, which is preferable from the viewpoint of increasing the density and reducing the power consumption.
- the second embodiment is an embodiment using TbCo in the pinned layer in the first embodiment.
- TbCo has better oxidation resistance than TbFeCo, and if the magnetic memory element in this embodiment is used for a storage device, the life of the storage device can be improved.
- the magnetization of TbCo is smaller than that of TbFeCo, the shape anisotropy energy is decreased, and the perpendicular magnetic anisotropy energy Ku can be expected to increase.
- An increase in the perpendicular magnetic isotropic energy Ku leads to an improvement in thermal stability.
- the thermal stability of the pinned layer is low, the magnetization direction is disturbed when the magnetic memory element is overheated, and the magnetic memory element does not operate normally. Therefore, the reliability of the memory device can be improved by improving the thermal stability using TbCo for the pinned layer.
- the manufacturing method of the magnetic memory element according to the present embodiment is substantially the same as the manufacturing method of the first embodiment except that the pinned layer is a TbCo alloy thin film instead of the TbFeCo alloy thin film, and thus the description thereof is omitted.
- the Tb composition ratio of the TbCo alloy thin film used for the pinned layer is preferably in the range of 13 to 22 at%, and the Tb composition ratio is particularly 15 ⁇ 1 at. % Is most preferable.
- the third embodiment is an embodiment in which TbCo is used for the storage layer in the first embodiment or the second embodiment. Since TbCo has a magnetic anisotropy energy that is an order of magnitude higher than that of GdCo, the storage characteristics of stored data can be improved by using TbCo for the storage layer. Conventionally, there has been a problem that when the magnetic anisotropy energy of the storage layer is increased, the write current increases. However, in this embodiment, the temperature of the storage layer approaches the compensation temperature and the magnetization Becomes very small and the increase in the write current is suppressed, so that the above problem is alleviated.
- the composition ratio of Tb is 22 to 26 at. % Range is preferred. This is because the compensation temperature of the storage layer is in the range of 100 to 180 ° C., as in the case of the first embodiment. In particular, the composition ratio of Tb is 24 at. By setting the ratio to%, the compensation temperature of the memory layer becomes the center (150 ° C.) of the temperature control range of the memory layer, which is most preferable because the allowable temperature range to be controlled is expanded.
- TbFeCo or TbCo is used for the pinned layer (first magnetic layer).
- first to third embodiments are possible even when a perpendicular magnetization film such as FePt, CoCrPt, or CoCrPt—SiO2 is used for the pinned layer. It is possible to produce a magnetic memory element having a structure similar to that of the embodiment. In particular, since these perpendicular magnetization films exhibit high magnetic anisotropy energy, a more reliable magnetic memory element can be manufactured.
- a fourth embodiment of the present invention will be described.
- the temperature of the pinned layer is controlled so as to be above or below the compensation temperature instead of the memory layer during the write operation.
- An operation of writing is performed so that the magnetization direction is the same direction (parallel) or opposite direction (antiparallel) to the magnetization direction of the pinned layer when there is no temperature rise.
- the temperature of the MTJ portion 13 of the magnetic memory element 10 is increased by Joule heat by flowing a write current in the direction from the storage layer 20 to the pinned layer 22 and reaches a temperature of about 170 ° C.
- the ultimate temperature of the pinned layer 22 exceeds the compensation temperature Tcomp, so the direction of magnetization of the pinned layer 22 is in the opposite direction (FIG. 4B).
- the temperature of the storage layer 20 does not reach the compensation temperature Tcomp, the magnetization direction of the storage layer 20 remains the same.
- the torque is applied from the polarized electrons so that the magnetization of the storage layer 20 is directed in the same direction as the magnetization of the pinned layer 22.
- the magnetization is reversed (FIG. 4C). If the current is interrupted after the magnetization reversal, the pinned layer 22 is naturally cooled, and the net magnetization is reversed when the element temperature falls below the compensation temperature Tcomp of the pinned layer 22. Thus, the magnetization direction of the pinned layer 22 is opposite to the magnetization direction of the storage layer 20 (FIG. 4D). As described above, the write operation in which the magnetization of the storage layer 20 is directed in the direction opposite to the magnetization of the pinned layer 22 is realized.
- the compensation temperature Tcomp of the pinned layer 22 be in the temperature range of 100 ° C. to 180 ° C.
- the composition ratio of Tb is 25 at. % To 29 at. % TbFeCo may be used. This is because the compensation temperature Tcomp of the TbFeCo alloy changes as shown in FIG. 5 depending on the composition ratio of Tb, and the compensation temperature is included in the temperature range of 100 ° C. to 180 ° C. within the range of the composition ratio of Tb. It is. In particular, the composition ratio of Tb in the TbFeCo alloy of the pinned layer 22 is 28 at.
- the compensation temperature is around 150 ° C., and temperature control with a write current is easy.
- the molar ratio of each composition of Fe and Co is further preferably 7: 3 in this embodiment. That is, it can be said that the most suitable material for the pinned layer 22 in this embodiment is Tb28Fe50Co22.
- composition of memory layer On the other hand, with respect to the memory layer 20, if the compensation temperature of the memory layer 20 is within the range of the reached temperature (about 25 to 200 ° C.), the above writing operation cannot be realized. Therefore, any magnetic film having a compensation temperature of 200 ° C. or more or 25 ° C. or less is suitable for the storage layer 20, and is not limited to the storage layer 20 described in the first to third embodiments. .
- the composition ratio of Gd is 23 at. % To 40 at. %, Or 10 at. % To 17 at. % GdFeCo is preferred. In particular, the composition ratio of Gd is 17 at. % Or 23 at. % Is preferable because the magnetization of the storage layer 20 can be reduced.
- the magnetization direction of the storage layer can be controlled in the same direction as the pinned layer or in the opposite direction only by changing the pulse width with a single polarity for the write current. Therefore, similarly to the first to third embodiments, in the fourth embodiment, a 4F2 size memory cell having a 1-diode-1MTJ configuration can be manufactured.
- the fifth embodiment uses TbCo for the pinned layer in the fourth embodiment.
- the composition ratio of Tb of the pinned layer is set to 22 to 26 at. % Range may be used. This is because the compensation temperature Tcomp of the TbCo alloy changes as shown in FIG. 6 depending on the composition ratio of Tb. Since a switching operation by a single polarity current pulse is possible, it becomes possible to manufacture a 4F2 size memory cell having a 1 diode-1 MTJ configuration.
- the composition ratio of Tb of the pinned layer is 24 at. % Is preferable because the compensation temperature of the pinned layer 22 is about 150 ° C. and temperature control becomes easier.
- GdCo for the memory layer 20 in the fourth embodiment.
- GdCo is considered to be more resistant to oxidation than GdFeCo, and can improve performance degradation of the magnetic memory element.
- the operation principle in the present embodiment is substantially the same as that in the fourth embodiment, and therefore will be omitted.
- the Gd composition ratio is set to 27 at. % Or more, provided that the composition ratio of Gd is 40 at. If it exceeds%, the Curie temperature becomes 200 ° C. or lower, and it becomes difficult to realize the above-described write operation. Therefore, the composition ratio of Gd is 27 to 39 at. % Range is necessary.
- GdCo is used for the memory layer 20
- a memory cell of 4F2 size having a 1 diode-1 MTJ configuration can be manufactured as in the fourth embodiment.
- Gd is 27 at. % Or 39a If it is set to%, since the element temperature at the time of writing approaches the compensation temperature or the Curie temperature, the magnetization becomes close to 0, and the necessary write current can be reduced, which is more preferable.
- TbCo can be used for the storage layer in the fourth embodiment.
- the composition ratio of Tb is 27 to 32 at. %
- the perpendicular magnetization film has a compensation temperature of 200 ° C., so that the same operation as the above (fourth embodiment) can be realized, and a 4F2 size memory cell having a 1 diode-1 MTJ configuration can be manufactured. it can.
- Tb is set to 27 at. If it is%, the compensation temperature is about 200 ° C., and the element is heated by the write current. Since the magnetization of the storage layer approaches O, the write current is preferably reduced. Further, since TbCo has a higher magnetic anisotropy energy than GdFeCo, it is possible to improve the retention characteristics of stored data by using the magnetic memory element of this embodiment.
- GdCo, GdFeCo, TbCo or the like is used as the free layer material.
- a perpendicular magnetization film such as FePt, CoCrPt, or CoCrPt—Si02 is used, it is equivalent to the above embodiment.
- a 4F2 size ⁇ memory cell having a 1 diode-1 MTJ configuration can be manufactured.
- FIG. 7 schematically shows an electrical configuration of a memory cell including a magnetic memory element and a rectifying element constituting a cross-point type memory cell array which is an embodiment of a nonvolatile memory device according to the present invention. That is, as already described, in the magnetic memory element and the storage device of the embodiment of the present invention, switching with a single polarity electric pulse is possible. Therefore, a storage device having a cross-point type memory is formed by connecting rectifying elements (herein, diodes are illustrated) in series as element selection switches and forming upper and lower electrodes in a matrix of rows and columns. It is formed. For example, it is possible to previously form a diode on a Si substrate and form the magnetic memory element according to the embodiment of the present invention on the top thereof. Switching can be performed efficiently by applying a positive electric pulse from the free layer side.
- rectifying elements herein, diodes are illustrated
- the maximum process temperature required for manufacturing the magnetic memory element of the present invention is about 350 ° C. required for annealing, and is formed for the electric pulse supply transistor and cell selection switch formed below. It does not impair the performance of the diode.
- the wiring can withstand the above-described temperature of the annealing treatment, the memory capacity can be increased by adopting a structure in which the magnetic memory elements according to the present invention are three-dimensionally stacked.
- FIG. 8 is a block diagram showing the structure of the memory array of the nonvolatile memory device 100 in which the memory cell using the magnetic memory element and the rectifying element of FIG. 7 is driven by the word line and the bit line.
- the word line of an unaccessed word is maintained at a high voltage and accessed to prevent current from flowing to the magnetic memory element 8 by the action of the diode 9, and only the word line of the accessed word is connected to GND. .
- a signal that realizes a set operation or a reset operation according to necessary data is transmitted to the bit line.
- the difference in signal between the set operation and the reset operation can be any difference that controls the ultimate temperature of the MTJ portion of the magnetic memory element, but preferably, as described above, a single pulse having a different pulse width is used. It can be a pulse of polarity.
- a current detection unit included in the bit line decoder 120 and provided corresponding to each bit line is selected by a word line decoder that operates in the same manner as in writing.
- the current flowing through each bit line with respect to the word line is detected, and the voltage value corresponding to the resistance of the magnetic memory element 8 corresponding to each bit line is detected in the word line where the word to be accessed is present. Read the status.
- the present invention is not limited to the above-described embodiments, and various modifications, changes and combinations can be made based on the technical idea of the present invention.
- each embodiment has been described with respect to the case where the intermediate layer is an insulator.
- the intermediate layer is a non-magnetic material
- the temperature control of the magnetic memory element as shown in the above embodiments can be performed.
- the intermediate layer can be implemented as a nonmagnetic material.
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Abstract
Description
本発明の第1の実施形態では、図1~図3に基づいて本発明の実施形態におけるメモリー素子の構造を書込み動作の原理とともに説明し、その作製方法および技術的効果について説明する。
図1は磁気メモリー素子100を含む記憶装置10の磁気メモリー素子を含む部分を示す拡大断面図である。磁気メモリー素子100は、磁気トンネル接合(MTJ)部13を有しており、このMTJ部13を下部電極14と上部電極12とによって挟むようにされている。MTJ部13は下部電極14側から、ピン層22(第1の磁性層)、第1のスピン偏極層27(第3の磁性層)、絶縁層21、第2のスピン偏極層26(第4の磁性層)、記憶層20(第2の磁性層)の順に積層された構造を有していて、ピン層22および記憶層20はN型フェリ磁性体の一種である希土類―遷移金属合金である。下部電極14は、基板15中に作られたP型領域24上に製膜され、さらに基板15中には、そのP型領域24と接するようにN型領域25が形成される。P型領域24とN型領域25との組み合わせはダイオード(整流素子)をなしている。さらに、N型領域25の上には、コンタクト部17とワード線18とがこの順に積層されている。一方の上部電極12は、ビット線11に接続されている。ワード線18とビット線11とは、層間絶縁膜23によって絶縁されてそれぞれが制御回路(図示しない)に接続されている。記憶装置10には多数の磁気メモリー素子100が含まれており、メモリーアドレスに応じて目的の磁気メモリー素子に記憶した情報を読み取り、また磁気メモリー素子100に情報を書き込む。本実施形態において、ピン層22はTbFeCo合金による薄膜からなり、記憶層20はGdCo合金による薄膜からなり、それらの補償温度は、それぞれ、0℃以下、150℃付近になるように作製する。
次に、このように作製された磁気メモリー素子100によって、単一極性電気パルスによる書き込み動作が可能になる原理について説明する。記憶層20の磁化方向をピン層22の磁化方向と同じ方向に向ける書き込み動作については従来の磁気メモリー素子と同じ電流注入磁化反転(STT)動作を行う。すなわち、記憶層20から中間層21を介してピン層22にトンネル電流を流す。この際、ピン層22から記憶層20に流れ込む電子のスピンは偏極しており、電流が流れている期間に記憶層20の磁化はこれらの偏極スピン電子よりトルクを受ける。このトルクは記憶層20の磁化方向をピン層22の磁化方向と同じ方向に向けるように作用するため、記憶層20とピン層22の磁化は同じ方向を向いて平行となる。磁化配置が平行である磁気メモリー素子100は、ピン層22と記憶層20の間の抵抗が低い抵抗値を示す状態(低抵抗状態)となる。
次に、記憶層20の磁化方向をピン層22の磁化方向と逆方向に向ける書き込み動作について説明する。ここに説明する動作原理は、本願発明者らの理解に基づくものであり、説明の目的にのみ用いられるべきである。図2は、N型フェリ磁性体における磁化の温度特性図の一例であり、ここでは記憶層20の温度特性図であるとする。図2において、N型フェリ磁性体の磁化曲線201が示され、そこに磁化203の向きを示す矢印を記載した磁性体202が模式的に記載されている。記憶層20の磁性体202は、その温度を上昇させると、正味の磁化を磁化曲線201に従って減少させ、補償温度Tcompにおいて0となる。引き続き温度を上昇させると、正味の磁化の向きが元の向きからみて逆向きとなる。本発明においては、記憶層20の磁化の向きが補償温度以上で逆向きになるこの現象を利用して書き込み動作を行う。さらに図3を用いて、この現象を利用する磁気メモリー素子100の書き込み動作について説明する。
ピン層のTbFeCoとしてはTbの組成比が13~22at.%であることが好ましい。TbFeCoはTb組成が概ね13~32at.%の範囲で垂直磁化膜になる。ただし、Tbの組成比を室温における補償組成比を超える組成比にしてしまう場合、例えば、Tbの組成比を23~32at.%とする場合には、書き込み電流による温度上昇によってピン層の温度が補償温度に近づいて、ピン層の磁化が減少してしまう。STT動作においてピン層の磁化は記憶層に対し十分に大きくなくてはならず、この磁化の減少はSTT動作を不安定にさせるおそれがある。よって、ピン層のTbの組成比としては、補償温度が記憶装置が動作する温度よりも低くなるような組成比とすることが望ましい。そのようなTbの組成比は13~22at.%である。特に、垂直磁化膜となる限界の組成比である13at%とすると正味の磁化は最大となり理想的ではあるものの、実際のスパッタ法では製膜領域全域に渡って均一組成の薄膜を作製することは困難であるため、1~2at.%程度の余裕をみる必要があり、つまりTbの組成比を15at.%とすることが最も好ましいと言える。
本実施形態における上記動作を実現するためには、記憶層20の補償温度を、記録層20の到達温度の範囲、すなわち、100~180℃の範囲に設定することが好ましい。この範囲に補償温度を持つGdCo合金の組成は、Gdの組成比を23~28at.%とすることが好ましく、本実施形態においてはこの範囲のGdCoを用いる。このうち、特に、Gdの組成比を26at.%、Coの組成比を74at.%とすると、補償温度は到達温度の範囲の概ね中心(150℃)となり、温度制御が容易になるために最も好ましい。
また、本実施形態の磁気メモリー素子100の第1のスピン偏極膜(第3の磁性層)、第2のスピン偏極膜(第4の磁性層)について説明する。スピン偏極膜とは例えばFe、FeCo、FeCoBのように△1バンドに関してスピンが完全に偏極している磁性膜を意味している。この偏極層を、MgOのような、積層方向に対して4回対称性を有する絶縁層(中間層)と組み合わせてスピントンネル接合を実現することにより、実効的なスピン偏極率を高めることができる。このような構造においては、条件を最適化することにより、1000%程度の磁気抵抗比が得られることが、理論的にも実験的にも明らかにされている。
以下、第1の実施形態によって作製される磁気メモリー素子について、その作製方法を説明する。再び図1を参照する。まず、CMOSプロセスによってSi基板(シリコンウェハー)15上にP型領域24、N型領域25を形成する。その後、マグネトロンスパッタ法によりAl(5nm)を製膜し、フォトリソグラフィ工程によってP型領域24上に下部電極14を、N型領域25上にコンタクト17を形成する。またこのフォトリソグラフィの時に使ったレジスト膜を残した状態で、プラズマCVD(化学気相成長)プロセスによって層間絶縁膜(SiN)を膜厚が5nm程度となるように形成し、このレジスト膜をアセトンかNMP(N一メチルー2一ピロリドン)を溶媒として洗い流す。そうすると下部電極14とコンタクト17上についたSiN膜はレジスト膜と共にリフトオフされる(洗い流される)ので、下部電極14とコンタクト17の表面が露出する状態となる。さらにマグネトロンスパッタ法によってCu(10nm)を製膜し、フォトリソグラフィによって、コンタクト17上にワード線18を形成する。
次に第1の実施形態の磁気メモリー素子またはそれを用いる記憶装置が奏する技術的効果について説明する。前述したとおり、記憶層20として用いたGd26Co74は補償温度を150℃付近に持ち、これはSTT書き込み電流のパルス幅によって温度制御できる温度範囲の中心付近となる。つまりSTT書き込み電流の極性は変えず、パルス幅を変化させるだけで記憶層20の到達温度を補償温度よりも低くしたり高くしたりするように制御することができ、従って記憶層20の磁化方向をピン層22と同方向(平行)または逆方向(反平行)のどちらにも制御できる。このため、上記の動作によって、1ダイオードと1MTJ構成の4F2サイズのメモリーセルを実現することが可能となる。
本発明における第2の実施形態について説明する。第2の実施形態は第1の実施形態においてピン層にTbCoを用いた実施形態である。TbCoはTbFeCoよりも耐酸化性に優れ、本実施形態における磁気メモリー素子を記憶装置に用いれば、記憶装置の寿命を向上させることができる。また、TbCoの磁化はTbFeCoより小さくなることから、形状異方性エネルギーが減少し、垂直方向の磁気異方性エネルギーKuの増大が見込める。垂直磁気方性エネルギーKuの増大は熱安定性の向上に繋がる。ピン層の熱安定性が低い場合には、磁気メモリー素子が過熱した際に磁化方向が乱れてしまい、磁気メモリー素子は正常に動作しなくなる。よって、ピン層にTbCoを用いて熱安定性を向上させることによって記憶装置の信頼性を向上させることができる。
本発明における第3の実施形態について説明する。第3の実施形態は、第1の実施形態あるいは第2の実施形態において記憶層にTbCoを用いる場合の実施形態である。TbCoはGdCoに比べて磁気異方性エネルギーが一桁大きいため、記憶層にTbCoに用いることにより記憶データの保持特性を向上させることができる。なお、従来においては記憶層の磁気異方性エネルギーを増大させると、書き込み電流が増大してしまう問題があったが、本実施形態においては書き込み時の記憶層の温度が補償温度に近づき、磁化が非常に小さくなって書き込み電流の増加が抑えられるため、前記問題は軽減される。
本発明における第4の実施形態について説明する。第4の実施形態は、第1の実施形態とは異なり、書き込み動作時に、記憶層の代りにピン層の温度を、その補償温度の上または下となるように制御することにより、記憶層の磁化の方向を、温度上昇が無いときのピン層の磁化の方向と同方向(平行)または逆方向(反平行)となるように書き込む動作を行う。
まず、第4の実施形態における書き込み動作の原理について説明する。記憶層20とピン層22の磁化方向を同じ方向に向ける書き込み動作については、第1の実施形態と全く同等であるので説明は省略する。
以上の書き込み動作を実現するために、ピン層22の補償温度Tcompを100℃~180℃の温度範囲とすることが望ましいが、そのような材料としては、Tbの組成比を25at.%~29at.%としたTbFeCoを用いればよい。これは、Tbの組成比によってTbFeCo合金の補償温度Tcompが図5に示したように変化し、上記のTbの組成比の範囲において、補償温度が100℃~180℃の温度範囲に含まれるためである。特に、ピン層22のTbFeCo合金におけるTbの組成比を28at.%とすると、補償温度が150℃付近となり、書き込み電流での温度制御が容易になるために好ましい。また、第1の実施形態のときと同様の理由により、本実施形態においてもFeとCoの各組成のモル比を7:3とすることがさらに好ましい。すなわち、本実施形態においてピン層22として最も適する材料はTb28Fe50Co22であると言える。
一方、記憶層20については、記憶層20の補償温度が到達温度の範囲(25~200℃程度)にあると、上記書き込み動作を実現できなくなる。よって、記憶層20の補償温度は200℃以上か、または25度以下である任意の磁化膜が適しており、第1~第3の実施形態に記載の記憶層20に限定されるものではない。垂直磁化膜としてこの条件を満たす例としては、Gdの組成比を23at.%~40at.%、または10at.%~17at.%としたGdFeCoが好ましい。特に、Gdの組成比を17at.%または、23at.%とすることが、記憶層20の磁化を小さくすることができるために好ましい。
次に第4の実施形態の磁気メモリー素子またはそれを用いる記憶装置の奏する技術的効果について説明する。この実施形態によっても、書き込み電流は、単一極性としパルス幅を変化させるだけで、記憶層の磁化方向をピン層と同方向または逆方向のどちらにも制御することができる。このため、第1~3の実施形態と同様に、第4の実施形態においても、1ダイオード-1MTJ構成の4F2サイズのメモリーセルを作製することができる。
本発明における第5の実施形態について説明する。第5の実施形態は第4の実施形態においてピン層にTbCoを用いるものである。この場合、第4の実施形態と同等の動作を実現させるため、ピン層のTbCoの補償温度を100~180℃とするには、ピン層のTbの組成比を22~26at.%の範囲とすればよい。これは、TbCo合金の補償温度TcompがTbの組成比によって図6に示す様に変化するためである。単一極性電流パルスによるスイッチング動作が可能となるので、1ダイオード-1MTJ構成の4F2サイズのメモリーセルを作製することが可能となる。特に、ピン層のTbの組成比を24at.%とすると、ピン層22の補償温度が約150℃となり、温度制御がより容易になるために好ましい。
本発明における第6の実施形態について説明する。本実施形態は第4の実施形態において、記憶層20にGdCoを用いるものである。GdCoはGdFeCoと比較して酸化に強いとされており、磁気メモリー素子の性能劣化を改善することが可能である。本実施形態における動作原理は第4の実施形態の時とほぼ同様であるので省略する。本実施形態において、記憶層20の補償温度を200℃以上とするにはGdの組成比を27at.%以上とすればよい、但し、Gdの組成比が40at.%以上になると、キュリー温度が200℃以下になり、前述の書き込み動作を実現することが難しくなる。よってGdの組成比は27~39at.%の範囲とすることが必要である。以上によって、記憶層20にGdCoを用いる場合でも、第4の実施形態と同様に1ダイオード-1MTJ構成の4F2サイズのメモリーセルを作製することができる。特にGdを27at.%または39a七.%とすれば、書き込み時における素子加熱によって、補償温度またはキュリー温度に近づくため、磁化は0近くまで小さくなり、必要な書き込み電流を減少させることができるので、より好適である。
本発明における第7の実施形態について説明する。第7の実施形態は第4の実施形態において、記憶層にTbCoを用いることができる。この場合にはTbの組成比を27~32at.%の範囲とすれば垂直磁化膜かつ補償温度200℃となるので、上記(第4の実施形態)と同等の動作を実現でき、1ダイオード-1MTJ構成の4F2サイズのメモリーセルを作製することができる。特に、Tbを27at.%とすれば、補償温度は200℃程度となり、書き込み電流による素子加熱で、記憶層の磁化はOに近づくために、書き込み電流が小さくなり好適である。また、TbCoはGdFeCoよりも磁気異方性エネルギーが高いため、本実施形態の磁気メモリー素子を用いることにより、記憶データの保持特性を向上させることが可能である。
次に、本発明のさらに他の実施形態の磁気メモリー素子とダイオードを使用した不揮発記憶装置の実施形態について図7および図8を用いて説明する。
10 記憶装置
11 ビット線
12 上部電極
13 MTJ部
14 下部電極
15 基板
17 コンタクト部
18 ワード線
20 記録層(第2の磁性層)
21 絶縁層
22 固定層(第1の磁性層)
23 層間絶縁膜
24 P型領域
25 N型領域
102、102A 磁化の向きを示す矢印
8 磁気メモリー素子
9 整流素子
100 不揮発性記憶装置
110 ワードラインデコーダ
120 ビットラインデコーダ
Claims (16)
- 第1~第4の磁性層と中間層とを有しており、各層が、第1の磁性層、第3の磁性層、中間層、第4の磁性層、第2の磁性層の順に互いに直接または少なくとも一の他の層を介して積層されている磁気メモリー素子であって、
前記中間層は絶縁体または非磁性体からなり、
前記第2の磁性層は、ガドリニウム、鉄、およびコバルトの3元合金、ガドリニウムおよびコバルトの2元合金、ならびに、テルビウムおよびコバルトの2元合金からなる合金の群から選択される一の合金の薄膜である、
ことを特徴とする磁気メモリー素子。 - 前記第2の磁性層は、20℃以上の磁気補償温度を有するN型フェリ磁性体を含むことを特徴とする請求項1に記載の磁気メモリー素子。
- 前記第1の磁性層がテルビウム、鉄、およびコバルトの3元合金薄膜であり、前記第1の磁性層の該3元合金におけるテルビウムの組成比が13~22at.%であることを特徴とする請求項1に記載の磁気メモリー素子。
- 前記第1の磁性層がテルビウムおよびコバルトの2元合金薄膜であり、前記第1の磁性層の該2元合金におけるテルビウムの組成比が13~22at.%であることを特徴とする請求項1に記載の磁気メモリー素子。
- 前記第2の磁性層がガドリニウムおよびコバルトの2元合金薄膜であり、前記第2の磁性層の該2元合金におけるガドリニウムの組成比が23~28at.%であることを特徴とする請求項1に記載の磁気メモリー素子。
- 前記第2の磁性層がテルビウムおよびコバルトの2元合金薄膜であり、前記第2の磁性層の該2元合金におけるテルビウムの組成比が22~26at.%であることを特徴とする請求項1に記載の磁気メモリー素子。
- 第1~第4の磁性層と中間層とを有しており、各層が、第1の磁性層、第3の磁性層、中間層、第4の磁性層、第2の磁性層の順に互いに直接または少なくとも一の他の層を介して積層されている磁気メモリー素子であって、
前記中間層は絶縁体または非磁性体からなり、
前記第1の磁性層は、テルビウム、鉄、およびコバルトの3元合金、ならびに、テルビウムおよびコバルトの2元合金からなる合金の群から選択される一の合金の薄膜である、
ことを特徴とする磁気メモリー素子。 - 前記第1の磁性層は、20℃以上の磁気補償温度を有するN型フェリ磁性体を含むことを特徴とする請求項7に記載の磁気メモリー素子。
- 前記第1の磁性層がテルビウム、鉄、コバルトの3元合金であり、前記第1の磁性層の該3元合金におけるテルビウムの組成比が25at.%~29at.%であることを特徴とする請求項7に記載の磁気メモリー素子。
- 前記第2の磁性層がガドリニウムおよびコバルトからなる合金の薄膜であることを特徴とする請求項7に記載の磁気メモリー素子。
- 前記第2の磁性層が、ガドリニウムおよびコバルトに加え鉄をさらに含む3元合金薄膜であり、前記第2の磁性層の該3元合金におけるガドリニウムの組成比が10at.%~17at.%または23at.%~40at.%であることを特徴とする請求項10に記載の磁気メモリー素子。
- 前記第1の磁性層がテルビウムおよびコバルトの2元合金薄膜であり、前記第1の磁性層の該2元合金におけるテルビウムの組成比が22~26at.%であることを特徴とする請求項7に記載の磁気メモリー素子。
- 前記第2の磁性層がガドリニウムおよびコバルトの2元合金薄膜であり、前記第2の磁性層の該2元合金におけるガドリニウムの組成比が27~39at.%であることを特徴とする請求項7に記載の磁気メモリー素子。
- 前記第2の磁性層がテルビウムおよびコバルトの2元合金薄膜であり、前記第2の磁性層の該2元合金におけるテルビウムの組成比が27~32at.%であることを特徴とする請求項7に記載の磁気メモリー素子。
- 前記第1の磁性層における鉄とコバルトとの各組成のモル比が7:3であることを特徴とする請求項3または9に記載の磁気メモリー素子。
- 請求項1~15のいずれかに記載の磁気メモリー素子と、該磁気メモリー素子に直列に接続された整流素子とを有するメモリーセルと、
前記メモリーセルに電気的に接続され、単一極性の電気パルスを流すことで書き込みおよび消去を行う情報書換手段と、
前記メモリーセルに電気的に接続され、前記磁気メモリー素子を流れる電流量から記憶された情報を読出す読み出し手段と、
を備えてなることを特徴とする不揮発記憶装置。
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JPWO2017208653A1 (ja) * | 2016-05-31 | 2019-03-28 | ソニー株式会社 | 不揮発性メモリセル、メモリセルユニット及び情報書き込み方法、並びに、電子機器 |
US10706903B2 (en) | 2016-05-31 | 2020-07-07 | Sony Corporation | Nonvolatile memory cell, memory cell unit, and information writing method, and electronic apparatus |
JP2018133474A (ja) * | 2017-02-16 | 2018-08-23 | 三星電子株式会社Samsung Electronics Co.,Ltd. | 磁気トンネル接合素子及び磁気抵抗メモリ |
Also Published As
Publication number | Publication date |
---|---|
EP2375464A4 (en) | 2013-07-03 |
EP2375464A1 (en) | 2011-10-12 |
KR20110112295A (ko) | 2011-10-12 |
JP5709329B2 (ja) | 2015-04-30 |
EP2375464B1 (en) | 2014-09-10 |
JP5440509B2 (ja) | 2014-03-12 |
US20110310660A1 (en) | 2011-12-22 |
US8456896B2 (en) | 2013-06-04 |
JPWO2010073790A1 (ja) | 2012-06-14 |
KR101458263B1 (ko) | 2014-11-04 |
JP2013219375A (ja) | 2013-10-24 |
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