JP4774092B2 - Magnetoresistive element and MRAM using the same - Google Patents

Description

The present invention relates to a magnetoresistive effect element and an MRAM using the magnetoresistive effect element, and more particularly to a magnetoresistive effect element manufactured using a simple sputtering film forming method and having an extremely high magnetoresistance ratio and an MRAM using the magnetoresistive effect element.

  In recent years, a magnetic memory device called MRAM (Magnetoresistive Random Access Memory: ferroelectric memory) has been attracting attention as a nonvolatile memory, and is entering the stage of practical use. The MRAM has a simple structure, is easy to achieve ultra-high-gigabit integration, and has a very large number of rewritable times because it uses the rotation of the magnetic moment to generate a memory action. It has the characteristic that it can be used as a stand.

  FIG. 4 shows the structure of the MRAM. In the MRAM 101, 102 is a memory element, 103 is a word line, and 104 is a bit line. Each of the large number of memory elements 102 is disposed at each intersection position of the plurality of word lines 103 and the plurality of bit lines 104, and is disposed in a lattice-like positional relationship. Each of the large number of memory elements 102 stores 1-bit information.

  As shown in FIG. 5, the memory element 102 of the MRAM 101 includes a magnetoresistive effect element that stores 1-bit information, that is, a TMR element 110, and a transistor 106 having a switching function at the intersection position of the word line 103 and the bit line 104. Composed. The main element in the memory element 102 is that a TMR (Tunneling Magneto resistance) element 110 is used. As shown in FIG. 6, the basic structure of the TMR element is a three-layer structure including a ferromagnetic metal electrode (ferromagnetic layer) 107 / tunnel barrier (tunnel barrier) layer 108 / ferromagnetic metal electrode (ferromagnetic layer) 109. This is a laminated structure. The TMR element 110 is composed of a pair of ferromagnetic layers 107 and 109 and a tunnel barrier layer 108 located between them.

As shown in FIG. 6, the TMR element 110 applies an external magnetic field in a state where a predetermined current is applied between the ferromagnetic layers 107 and 109 on both sides of the tunnel barrier layer 108, thereby applying a magnetic field. When the magnetization directions of 107 and 109 are parallel and the same (referred to as “parallel state”), the electrical resistance of the TMR element is minimized (state (A): resistance value R _P ), and the magnetization of the ferromagnetic layer When the directions are parallel and opposite (referred to as “anti-parallel state”), the electrical resistance of the TMR element is maximized (state (B): resistance value R _A ). Therefore, the TMR element 110 can store information as a change in resistance value by creating a parallel state and an antiparallel state by an external magnetic field.

With respect to the above TMR elements, in order to realize a practical gigabit class MRAM, it is required that the difference between the resistance value R _P in the “parallel state” and the resistance value R _{A in} the “anti-parallel state” is large. A magnetoresistance ratio (MR ratio) is used as the index. The MR ratio is defined as “(R _A −R _P ) / R _P ”.

In order to improve the MR ratio, conventionally, the electrode material of the ferromagnetic metal electrode (ferromagnetic layer) has been optimized, or the manufacturing method of the tunnel barrier layer has been devised. For example, Patent Document 1 and Patent Document 2 propose several optimum examples using Fe _x Co _y B _z or the like for the material of the ferromagnetic metal electrode (ferromagnetic layer).

  The MR ratio of the TMR element disclosed in Patent Documents 1 and 2 is lower than about 70%, and further improvement of the MR ratio is necessary.

  Recently, a single crystal TMR thin film using an MgO barrier layer has been reported to produce a single crystal TMR thin film of Fe / MgO / Fe using MBE and an ultra-high vacuum deposition apparatus, and an MR ratio of 88% was obtained. (Non-Patent Document 1). This TMR thin film has a complete epitaxial single crystal structure.

  In order to produce a single crystal TMR thin film using the single crystal MgO barrier layer described in Non-Patent Document 1, it is necessary to employ an expensive MgO single crystal substrate. In addition, advanced film formation techniques such as epitaxial growth of Fe film by expensive MBE equipment and MgO film formation by ultra-high vacuum electron beam evaporation are required, and there is a problem that it is not suitable for mass productivity because of a long film formation time. ing.

JP 2003-304010 A JP 2004-63592 A Shinji Yuasa and four others, “High Tunnel Magnetoresistance at Room Temperature in Fully Epitaxial Fe / MgO / Tunnel Junctions due to Coherent Spin Polarization Tunneling” Coherent Spin-Polarized Tunneling), Nanoelectronics Research Laboratories, Japan Journal of Applied Physics, April 2, 2004, Volume 43, No. 4B, p. L588-L590

An object of the present invention is to provide a magnetoresistive effect element having a high MR ratio, improved mass productivity, and improved practicality, and an MRAM using the magnetoresistive effect element.

In order to achieve the above object, the magnetoresistive effect element according to the present invention and the MRAM using the magnetoresistive effect element are configured as follows.

The magnetoresistive element of the present invention has a laminated structure having a first ferromagnetic layer, a second ferromagnetic layer, and a barrier layer positioned between the first ferromagnetic layer and the second ferromagnetic layer. And a magnetoresistive effect element including a substrate positioned on the first ferromagnetic layer side, wherein the barrier layer is connected to the second ferromagnetic layer from the interface with the first ferromagnetic layer. In the thickness direction of the layer, the (001) plane has magnesium oxide having a single crystal structure oriented in parallel to the interface, and the first ferromagnetic layer contains CoFeB. .

In the magnetoresistive element of the present invention, the first ferromagnetic layer is amorphous when the barrier layer is formed, and the barrier layer is a layer formed by a sputtering method using a magnesium oxide target. It is included as a preferable embodiment.

The MRAM of the present invention is an MRAM having a word line, a bit line arranged to cross the word line, and a magnetoresistive effect element and a transistor arranged to connect the word line and the bit line. The magnetoresistive element is located between the first ferromagnetic layer, the second ferromagnetic layer, and the first ferromagnetic layer and the second ferromagnetic layer, and the first strong layer. A laminated structure having a magnesium oxide layer having a single crystal structure in which the (001) plane is oriented parallel to the interface of the layer in the thickness direction from the interface with the magnetic layer to the interface with the second ferromagnetic layer have a, the first ferromagnetic layer is characterized by containing a CoFeB.

  According to the present invention, since the tunnel barrier layer, which is an intermediate layer of the magnetoresistive effect element such as the TMR element, is an MgO layer having a single crystal structure, the MR ratio can be extremely increased. When used as a GRAM, it is possible to realize a GRAM ultra-high integration MRAM. Furthermore, by forming the single crystal MgO layer by a sputtering method, a magnetoresistive element suitable for mass production and highly practical can be manufactured.

  DESCRIPTION OF EMBODIMENTS Preferred embodiments (examples) of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 shows an example of a laminated structure of magnetoresistive elements according to the present invention, and shows a laminated structure of TMR elements. According to the TMR element 10, for example, a multilayer film having nine layers constituting the TMR element 10 is formed on the substrate 11. In this nine-layer multilayer film, “Ta”, “PtMn”, “70 CoFe”, “Ru”, “CoFeB”, “MgO”, “CoFeB” are directed from the first lowermost layer to the ninth uppermost layer. ”,“ Ta ”,“ Ru ”are stacked in the order of magnetic films. The first layer (Ta: tantalum) is an underlayer, and the second layer (PtMn) is an antiferromagnetic layer. The layers composed of the third layer to the fifth layer (70CoFe, Ru, CoFeB) form a magnetization fixed layer. The substantial magnetization fixed layer is a ferromagnetic layer made of the fifth layer “CoFeB”. The sixth layer (MgO: magnesium oxide) is an insulating layer and a tunnel barrier layer. The seventh layer (CoFeB) is a ferromagnetic layer and a magnetization free layer. The sixth layer (MgO) forms an intermediate layer between a pair of ferromagnetic layers (CoFeB) positioned above and below the sixth layer (MgO). The eighth layer (Ta: tantalum) and the ninth layer (Ru: ruthenium) form a hard mask layer. The above-mentioned magnetization fixed layer (the fifth layer “CoFeB”), the tunnel barrier layer (the sixth layer “MgO”), and the magnetization free layer (the seventh layer “CoFeB”) have a narrow meaning as a basic structure. The TMR element portion 12 is formed. The fifth layer “CoFeB” as the magnetization fixed layer and the seventh layer “CoFeB” as the magnetization free layer are known as amorphous ferromagnetic materials. The MgO layer as the tunnel barrier layer is formed so as to have a single crystal structure in the thickness direction.

  In addition, in FIG. 1, the numerical value described in parentheses in each layer indicates the thickness of each layer, and the unit is “nm (nanometer)”. The said thickness is an example and is not limited to this.

  Next, with reference to FIG. 2, an apparatus and a manufacturing method for manufacturing the TMR element 10 having the above laminated structure will be described. FIG. 2 is a schematic plan view of an apparatus for manufacturing the TMR element 10, which is an apparatus capable of producing a multilayer film including a plurality of magnetic films, and is a sputtering film forming apparatus for mass production.

  The magnetic multilayer film manufacturing apparatus 20 shown in FIG. 2 is a cluster type apparatus, and includes a plurality of film forming chambers based on a sputtering method. In the present apparatus 20, a transfer chamber 22 including a robot transfer apparatus (not shown) is installed at the center position. The transfer chamber 22 of the magnetic multilayer film manufacturing apparatus 20 is provided with two load / unload chambers 25 and 26, and the substrate (silicon substrate) 11 is loaded / unloaded by each. By alternately using these load / unload chambers 25 and 26, a multilayer film can be produced with high productivity.

  In the magnetic multilayer film manufacturing apparatus 20, for example, three film forming chambers 27 </ b> A, 27 </ b> B, and 27 </ b> C and one etching chamber 28 are provided around the transfer chamber 22. In the etching chamber 28, the required surface of the TMR element 10 is etched. Between each chamber, there is provided a gate valve 30 that isolates both chambers and can be opened and closed as necessary. Each chamber is provided with a vacuum exhaust mechanism, a gas introduction mechanism, a power supply mechanism and the like (not shown).

  In each of the film forming chambers 27A, 27B, and 27C of the magnetic multilayer film manufacturing apparatus 20, the above-described magnetic films are sequentially deposited on the substrate 11 from below by sputtering. For example, four or five targets (31, 32, 33, 34, 35), (41, 42) arranged on an appropriate circumference are respectively provided on the ceiling portions of the film forming chambers 27A, 27B, 27C. , 43, 44, 45), (51, 52, 53, 54). Furthermore, a substrate is disposed on a substrate holder located coaxially with the circumference.

  In the above, for example, the material of the target 31 is “Ta”, and the material of the target 33 is “CoFeB”. The material of the target 41 is “PtMn”, the material of the target 42 is “CoFe”, and the material of the target 43 is “Ru”. Furthermore, the material of the target 51 is “MgO”.

  In order to deposit a magnetic film having an appropriate composition with good efficiency, the plurality of targets are preferably provided so as to be inclined toward each substrate, but may be provided in a state parallel to the substrate surface. . Further, the plurality of targets and the substrate are arranged based on a configuration that rotates relatively. In the apparatus 20 having the above configuration, the magnetic multilayer film shown in FIG. 1 is sequentially formed on the substrate 11 by the sputtering method using the film forming chambers 27A, 27B, and 27C.

  Deposition conditions of the TMR element portion 12 which is a main element portion of the present invention will be described. The magnetization fixed layer (“CoFeB” of the fifth layer) was formed at a sputtering rate of 0.64 / sec by magnetron DC sputtering with a CoFeB composition ratio of 60/20/20 at% at an Ar pressure of 0.03 Pa. . Subsequently, the tunnel barrier layer (“MgO” in the sixth layer) uses a target with an MgO composition ratio of 50/50 at%, uses Ar as a sputtering gas, and changes the pressure within a range of 0.01 to 0.4 Pa. A film was formed. Film formation was performed at a sputtering rate of 0.14 / sec by magnetron RF sputtering. Subsequently, a magnetization free layer (seventh layer “CoFeB”) was formed under the same film formation conditions as the magnetization fixed layer (fifth layer “CoFeB”).

  In this embodiment, the deposition rate of the MgO film was 0.14 / sec. However, there is no problem even if the deposition is performed in the range of 0.01 to 1.0 / sec.

  The TMR element 10 that has been stacked by sputtering film formation in each of the film formation chambers 27A, 27B, and 27C is subjected to annealing annealing in a heat treatment furnace. At this time, the annealing temperature is, for example, about 300 ° C., and the annealing process is performed, for example, for 4 hours in a magnetic field of 8 kOe, for example. Thereby, the required magnetization is given to the PtMn of the second layer of the TMR element 10.

  FIG. 3 shows the result of measuring the magnetic properties of MgO. A high MR ratio was obtained over the entire measured range. In particular, a high MR ratio was obtained in the region where the pressure was 0.05 Pa or more and 0.2 Pa or less. In the region where the pressure is 0.05 Pa or more, it is presumed that the film defects are reduced as a result of the pressure on the substrate increasing and the ion bombardment decreasing. When the pressure was 0.05 Pa or more, the MR ratio increased and the tunnel resistance value (RA) increased. This is presumably because the leakage current of the film was reduced as a result of the formation of a good single crystal film. On the other hand, in the region of 0.05 Pa or less, the tunnel resistance value (RA) decreased and the MR ratio also decreased. This is presumably because defects in the MgO single crystal film increased as a result of increased ion bombardment. As a result of observing the sample with a cross-sectional TEM, the MgO film has a single crystal structure over the entire layer from the lower interface to the upper interface in the entire range of the measured pressure, and the MgO single crystal ( The orientation of the (001) plane was observed. Further, it was observed that the CoFeB layer was formed in an amorphous state.

  In this sample, the ferromagnetic layers on both sides of the MgO layer were formed of amorphous CoFeB, but the same result was observed when only one of the ferromagnetic layers was formed of amorphous CoFeB. This ferromagnetic layer is sufficient if at least the portion in contact with the barrier layer has an amorphous material state.

  On the other hand, when CoFe having a polycrystalline structure was formed as the ferromagnetic layer on both sides of the MgO layer, many transitions were observed in the MgO layer, and a good single crystal film could not be obtained and the characteristics were low. .

At this time, as described above, the MgO target 51 is used as a target, and preferably, an RF (high frequency) magnetron sputtering method is applied. It is also possible to form an MgO film by sputtering an Mg target with a mixed gas of Ar and O ₂ using a recurring active sputtering method.

  In the above, the MgO layer is a single crystal over the entire layer, and has a single crystal structure in which the (001) plane is oriented parallel to the interface. Further, the pair of ferromagnetic layers forming the TMR element portion 12 uses a ferromagnetic layer having an amorphous state such as CoFeTaZr, CoTaZr, CoFeNbZr, CoFeZr, FeTaC, FeTaN, or FeC instead of CoFeB having an amorphous state. Can do.

  The configurations, shapes, sizes, and arrangement relationships described in the above embodiments are merely shown to the extent that the present invention can be understood and implemented, and the numerical values and the compositions (materials) of the respective configurations are as follows. It is only an example. Therefore, the present invention is not limited to the described embodiments, and can be modified in various forms without departing from the scope of the technical idea shown in the claims.

  The present invention is used as a memory element of an MRAM that can be mass-produced, has high practicality, and can be highly integrated.

It is a figure which shows the structure of the magnetoresistive effect element (TMR element) which concerns on this invention. It is a top view of the apparatus which manufactures the magnetoresistive effect element (TMR element) based on this invention. It is a graph which shows the pressure dependence of the magnetic characteristic of the magnetoresistive effect element (TMR element) which concerns on this invention. It is a fragmentary perspective view which shows the principal part structure of MRAM. It is a figure which shows the structure of the memory element of MRAM. It is a figure explaining the characteristic of a TMR element.

Explanation of symbols

10 TMR element 11 Substrate (silicon substrate)
20 Magnetic multilayer film production apparatus 27A, 27B, 27C Deposition chamber

Claims (4)

A laminated structure having a first ferromagnetic layer, a second ferromagnetic layer, and a barrier layer positioned between the first ferromagnetic layer and the second ferromagnetic layer, and the first ferromagnetic layer A magnetoresistive element comprising a substrate located on the side of the layer,
The barrier layer has a single crystal structure in which the (001) plane is oriented parallel to the interface in the thickness direction of the layer from the interface with the first ferromagnetic layer to the interface with the second ferromagnetic layer. A magnetoresistive effect element comprising magnesium oxide, wherein the first ferromagnetic layer contains CoFeB. The magnetoresistive element according to claim 1, wherein the first ferromagnetic layer is amorphous when the barrier layer is formed. 2. The magnetoresistive element according to claim 1, wherein the barrier layer is a layer formed by a sputtering method using a magnesium oxide target. Word line,
A bit line crossing the word line, and
An MRAM having a magnetoresistive element and a transistor arranged to connect between the word line and the bit line;
The magnetoresistive element is located between the first ferromagnetic layer, the second ferromagnetic layer, and the first and second ferromagnetic layers, and from the interface to the interface between the second ferromagnetic layer in the thickness direction of the layer, have a layered structure having a magnesium oxide layer of a single crystal structure (001) plane was oriented parallel to the interface of said layer The MRAM is characterized in that the first ferromagnetic layer contains CoFeB .

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