JP2009295775A - Magnetic storage element and magnetic storage device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic storage element and a magnetic storage device wherein a change rate of resistance in inverting a magnetization direction of a free layer is increased while reducing an inversion current required for the inversion of the magnetization direction. <P>SOLUTION: The magnetic storage element wherein the magnetization direction is inverted by spin-polarized electrons, includes: a first unit magnetic storage element including a laminate structure of a first pin layer, a first tunnel insulating layer, and a first free layer; a second unit magnetic storage element including a laminate structure of a second pin layer, a second tunnel insulating layer, and a second free layer; and a connection electrode which electrically connects the first pin layer and the second pin layer to connect the first unit magnetic storage element and the second unit magnetic storage element in series. A cross-section area of the second unit magnetic storage element in a direction perpendicular to an electron movement direction is larger than that of the first unit magnetic storage element. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a magnetic memory element and a magnetic memory device, and more particularly, to a magnetic memory element and a magnetic memory device that increase inversion efficiency while reducing inversion current.

In recent years, MRAM (Magnetic Random Access Memory) devices have attracted attention as a new generation of nonvolatile magnetic storage devices. An MRAM device is a non-volatile magnetic storage device that performs non-volatile data storage using memory cells made of a plurality of thin film magnetic bodies formed in a semiconductor integrated circuit, and allows random access to each memory cell. is there.
As an MRAM device, an STT-MRAM (Spin-Transfer Torque MRAM) that reverses the magnetization direction of the magnetic material by flowing spin-polarized electrons through the magnetic material of the recording layer (spin injection) has been proposed (for example, Non-patent documents 1 and 2). In the magnetization reversal method by spin injection, spin is transmitted by the interaction of the spin angular momentum of electrons with the angular momentum of the magnetic substance in the storage layer. Magnetization reversal by spin injection has a feature that the current required for magnetization reversal decreases as the size of the memory cell decreases, and is suitable for large capacity and high integration.

Furthermore, in order to reduce the inversion current, a structure in which two tunnel junctions are stacked in one cell, such as a stacked structure of pinned layer / tunnel layer / free layer / tunnel layer / pinned layer, has been proposed. . In such a structure, the magnetization directions of the two pinned layers are antiparallel (parallel and reverse), and the upper and lower tunnel junctions act as spin filters with each other, thereby injecting spin-polarized electrons in both directions of current, The reversal current required to reverse the magnetization direction of the free layer can be reduced.
JP 2004-207707 A JP 2005-535125 A FJAlbert et al., Appl. Phy. Lett. Vol. 77, p.3809 (2000) Y. Huai et al., Appl. Phy. Lett. Vol. 84, p.3118 (2004) L. Berger, Journal of Appl. Phy. Vol. 93, p.7693 (2003)

  However, in such a laminated structure, the reversal current can be reduced. On the other hand, for example, when the magnetizations of the lower pinned layer and the free layer are parallel, the magnetization directions of the upper pinned layer and the free layer are antiparallel. There was a problem that the rate of change decreased. Although measures such as changing the resistance value of each junction by changing the thickness of the upper and lower tunnel layers have been proposed, it has not been a sufficient solution.

  Therefore, the present invention provides a magnetic memory element and a magnetic memory device that reduce the reversal current necessary to reverse the magnetization direction of the free layer and increase the rate of change in resistance when the magnetization direction is reversed. Objective.

  According to one aspect of the present invention, a magnetic memory element that reverses the magnetization direction by spin-polarized electrons and includes a stacked structure of a first pinned layer, a first tunnel insulating layer, and a first free layer. The first unit magnetic memory element, the second pinned layer, the second tunnel insulating layer, and the second unit magnetic memory element including a laminated structure of the second free layer, the first pinned layer, and the second pinned layer are electrically connected. And a connecting electrode for connecting the first unit magnetic memory element and the second unit magnetic memory element in series, and the cross-sectional area of the second unit magnetic memory element in the direction perpendicular to the electron moving direction is A magnetic memory element having a larger cross-sectional area than the first unit magnetic memory element.

  In another aspect of the present invention, the magnetic memory device is characterized in that the magnetic memory elements are arranged in a matrix.

  In the magnetic memory device and the magnetic memory device according to the present invention, the magnetization direction of the free layer can be efficiently reversed at a low current, and the resistance change rate when the magnetization direction is reversed can be increased.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In the following description, “top”, “bottom”, “left”, “right” and names including these terms are used as appropriate, but these directions make it easy to understand the invention with reference to the drawings. Therefore, a mode in which the embodiment is inverted upside down or rotated in an arbitrary direction is naturally included in the technical scope of the present invention.

  FIG. 1 is a cross-sectional view of the magnetic memory device according to the present embodiment, the whole being represented by 100. FIG. 2 is a schematic view of the magnetic storage device 100 as viewed from above. The vertical direction in FIG. 2 corresponds to a direction perpendicular to the paper surface of FIG.

  As shown in FIG. 1, the magnetic storage device 100 includes a semiconductor substrate 1 such as silicon. The semiconductor substrate 1 is provided with an element isolation insulating film 2 made of silicon oxide or the like. In an element formation region electrically isolated by the element isolation insulating film 2, an element selection transistor 10 is formed. The transistor 10 includes a gate insulating film 11 provided on the semiconductor substrate 1 and a gate electrode 12 provided thereon. Side walls 13 made of silicon oxide or the like are provided on both sides of the gate electrode 12. The semiconductor substrate 1 is provided with a source / drain region 14 so as to sandwich the gate electrode 12.

  On the semiconductor substrate 1, an interlayer insulating layer 20 made of, for example, silicon oxide is provided. A contact plug 22 made of tungsten, for example, is buried in the interlayer insulating layer 20 via a barrier metal layer (not shown) made of TiN / Ti, for example. The contact plug 22 is electrically connected to the source / drain region 14.

  A contact plug 24 made of Cu, for example, is embedded on the contact plug 22 via a barrier metal film (not shown) made of TaN / Ta, for example. Further, on the contact plug 24, for example, TaN / Ta A contact plug 26 made of, for example, copper is embedded through a barrier metal film (not shown) made of.

  On the contact plug 26, for example, a lead wiring (lower electrode) 30 made of Ta is provided, and a magnetic memory element (TMR (Tunneling Magneto Resistance) element) 50 is provided thereon. On the magnetic memory element 50, an interlayer insulating layer 60 made of, for example, silicon oxide is provided. A contact plug 28 made of, for example, copper is embedded in the interlayer insulating layer 60 via a barrier metal film (not shown) made of, for example, TaN / Ta. A bit line (BL) 40 made of, for example, copper is provided on the interlayer insulating layer 60 so as to be connected to the contact plug 28.

  FIG. 3 is an enlarged cross-sectional view of the magnetic memory element (memory cell) 50 shown in FIG. The magnetic storage device 100 has a structure in which a plurality of magnetic storage elements 50 are arranged in a matrix.

  As shown in FIG. 3, the magnetic memory element 50 includes two unit magnetic memory elements 510 and 520 connected by a connection electrode 530. On the extraction electrode 30, antiferromagnetic layers 511 and 521 are formed, respectively. On the antiferromagnetic layers 511 and 521, pinned layers (fixed layers: PL) 512 and 522, tunnel insulating layers (TN) 513 and 523 which are nonmagnetic materials (dielectric materials), and free layers which are ferromagnetic materials (Memory layer: FL) 514 and 524 are provided. On the free layers 514 and 524, upper electrodes (TE) 515 and 525 made of, for example, Cu are provided. Note that the upper electrodes 515 and 525 may form the connection electrode 530.

The pinned layers 512 and 522 include, for example, antiferromagnetic materials such as PtMn, IrMn, FeMn, PtCrMn, NiMn, NiO, and Fe ₂ O ₃ , Co, Fe, Ni, Al, B, Si, Zr, Nb, Structures in which elements such as Cr and Ta are exchange-coupled with one or more ferromagnetic materials, and SAF structures in which ferromagnetic materials and ferromagnetic materials are coupled via a thin nonmagnetic layer (Synthetic AntiFerromagnet structure) ) Is laminated on the antiferromagnetic layer.

  For the tunnel insulating layers 513 and 523, for example, an oxide or nitride containing Mg, Al, Si, or the like (eg, AlN, SiN) or a material obtained by mixing them is used. The memory layer (free layer) FL is a ferromagnetic material composed of one or more elements such as Co, Fe, Ni, Al, B, Si, Zr, Nb, Cr, and Ta, and is used for the fixed layer PL. It is preferable to use the same material as the ferromagnetic material to be used, but a different ferromagnetic material may be used.

  Further, as can be seen from FIG. 3, the magnetic memory element 50 includes a unit magnetic memory element 510 having a small cross-sectional area (a cross-sectional area in a direction perpendicular to the plane of the drawing in FIG. 3) and a unit magnetic having a large cross-sectional area. The memory element 520 is connected in series with a connection metal 530. As the connection metal 530, it is preferable to use a metal (for example, Cu or the like) whose spin diffusion length is sufficiently longer than between the magnetic memory elements. The connection metal 530 does not need to cover the entire surface of the magnetic memory element, and even a part of the connection metal 530 exhibits the same effect.

  In such a structure, the unit magnetic memory elements 510 and 520 constituting the magnetic memory element 50 have the same laminated structure except for the cross-sectional area, and therefore, compared with the conventional manufacturing method for manufacturing one magnetic memory element. Thus, the magnetic memory element 50 can be manufactured without adding a new film forming process or the like.

  Next, the operation of the magnetic memory element 50 will be described with reference to FIG. The magnetic memory element 50 has a structure in which a ferromagnetic material (pinned layers 512 and 522) and a ferromagnetic material (free layers 514 and 524) are stacked via thin nonmagnetic layers (tunnel insulating layers 513 and 523). ing. 4, the same reference numerals as those in FIG. 3 denote the same or corresponding parts.

  As shown in FIG. 4A, the initial state is a state in which the magnetization directions (spin directions) of the free layers 514 and 524 of the unit magnetic memory elements 510 and 520 are all in the right direction (anti-parallel state). ing.

Next, the rewriting current i is supplied in the direction indicated by the arrow in FIG. 4B (the direction from the unit magnetic memory element 520 to the unit magnetic memory element 510).
The magnetization reversal current Isw necessary for reversing the magnetization direction of the free layers 514 and 524 of the magnetoresistive element 50 is determined by the current density of the reversal current flowing through the free layers 514 and 524. Therefore, when two unit magnetic memory elements 510 and 520 having different cross-sectional areas are provided, the magnetization reversal current of the large area unit magnetic memory element 520 is larger than the reversal current of the small area unit magnetic memory element 520.

Therefore,
Isw (small area element) <rewrite current i <Isw (large area element)
However, Isw (small area element) is a current required for reversing the magnetization direction of the free layer 514,
Isw (large area element) is a current required for reversing the magnetization direction of the free layer 524,
When writing is performed using such a rewriting current (operating current) i, the magnetization direction of the free layer 514 of the small area element is reversed, and the magnetization direction of the free layer 524 of the large area element is not reversed. Such a state (parallel state) is shown in FIG.
That is, as long as the rewriting current i is used, the magnetization direction of the free layer 524 of the large area element is always constant (in this case, the right direction).

  On the other hand, since the resistance of each unit magnetic memory element 510, 520 is inversely proportional to the cross-sectional area, the element resistance of the magnetic memory element 50 composed of two unit magnetic memory elements 510, 520 connected in series is small. It is almost determined by the resistance of the unit magnetic memory element 510 which is an area element. For this reason, if the magnetization direction of the free layer 514 of the unit magnetic memory element 510 which is a small area element is reversed, the magnetization direction of the free layer 524 of the unit magnetic memory element 520 which is a large area element is not reversed. The resistance change rate as the memory element 50 does not change.

  Next, the case where the magnetization direction is reversed again to achieve the anti-equilibrium state shown in FIG. When a rewrite current i is applied in the direction shown in FIG. 4C (the direction from the unit magnetic memory element 510 to the unit magnetic memory element 520), electrons injected into the free layer 514 are transferred from the fixed layer 522 to a large area. Since it is injected through the free layer 524 of the unit magnetoresistive element 520, it becomes spin-polarized electrons polarized in the magnetization direction of each layer. In this case, since the free layer 524 always has a constant magnetization direction (rightward), spin-polarized electrons that have been shifted to the right are injected into the free layer 514. For this reason, the reversal current required for reversal of the magnetic direction of the free layer 514 can be reduced.

  FIG. 5 is a schematic cross-sectional view of another magnetic memory device according to an embodiment of the present invention, indicated as a whole by 200. In FIG. 5, the same reference numerals as those in FIG. 1 denote the same or corresponding parts. In the magnetic memory device 200, the metal layer used only as the contact plug 24 in the magnetic memory device 100 is also used as a bit line (indicated by reference numeral 40 in FIG. 1). As a result, the structure and manufacturing process of the magnetic storage device can be simplified.

  FIG. 6 shows a structure for aligning the magnetization direction of the free layer (FL) of the large-area unit magnetoresistive element 520 in one direction by using the bit line of FIG. That is, a current is passed through the bit line 40 (in FIG. 5, the contact plug 24 also serving as the bit line below the unit magnetoresistive element 520), and the magnetization direction of the free layer 524 is made uniform by induction magnetic field (induction). The magnetic field direction of the magnetic field and the magnetization direction of the free layer 524 can be matched). As a result, the operational stability and the like of the magnetic storage device can be improved.

  FIG. 7 is a schematic cross-sectional view of another magnetic memory device according to the embodiment of the present invention, indicated as a whole by 300. In FIG. 7, the same reference numerals as those in FIG. 1 denote the same or corresponding parts. In the magnetic memory device 300, a plurality of magnetoresistive elements 520 are connected by the extraction electrode 30. That is, the extraction electrode 30 extends in a direction perpendicular to the paper surface of FIG. 7, and a plurality of magnetoresistive elements 520 are connected thereon.

  The lead electrode 30 is connected to the transistor 10 via the contact plugs 22, 24, and 26, and further connected to the bit line 40 via the transistor 10.

Further, the magnetic memory device 350 shown in FIG. 8 has a structure in which a large-area magnetoresistive element 520 is integrally formed on the extraction electrode 30. FIG. 8 is a schematic view when viewed from the same direction as FIG.
That is, in FIG. 7, a plurality of magnetoresistive elements 520 juxtaposed on the extraction electrode 30 are formed as an integral structure in FIG.

  As in the magnetic memory device 350 of FIG. 8, the area difference between the small area magnetic memory element 510 and the large area magnetic memory element 520 is increased to increase the rewrite current margin of the magnetic memory device 350. be able to.

Comparative Example FIGS. 9 and 10 show conventional magnetic memory elements having a single junction structure and a double junction structure for comparison. The states (a) to (c) correspond to the states (a) to (c) in FIG.

As shown in FIG. 9, the single-junction magnetic memory element has a structure in which a pinned layer (PN), a tunnel insulating layer (TN), and a free layer (FL) are stacked.
By passing a current in the direction indicated by the arrow in (b) with respect to the magnetic memory element in the initial state (a), the magnetization direction of the free layer (FL) is reversed to be in an equilibrium state.
On the other hand, by passing an electric current in the direction indicated by the arrow in (c), the magnetization direction of the free layer (FL) is reversed and the antiparallel state is obtained.

  (B) When the magnetization direction of the free layer (FL) is reversed from the equilibrium state to the (c) antiparallel state, spin-polarized spins cannot be injected into the free layer (FL) (in FIG. There is a problem that the reversal current becomes large.

As shown in FIG. 10, in the magnetic memory element having a double junction structure, the pinned layers (PN1, 2) and the tunnel insulating layers (TN1, 2) are stacked at symmetrical positions with the free layer (FL) interposed therebetween. It has a structure.
By passing a current in the direction indicated by the arrow in (b) with respect to the magnetic memory element in the initial state (a), the magnetization direction of the free layer (FL) is reversed to be in an equilibrium state.
On the other hand, by passing an electric current in the direction indicated by the arrow in (c), the magnetization direction of the free layer (FL) is reversed and the antiparallel state is obtained.

  In such a magnetic memory element having a double junction structure, the reversal current can be reduced. For example, when the magnetizations of the lower pinned layer (PN1) and the free layer (FL) are parallel ((b) parallel state), the upper pinned layer ( Since the magnetization directions of PL2) and the free layer (FL) are antiparallel, there is a problem that the rate of change in resistance decreases.

1 is a cross-sectional view of a magnetic memory device according to an embodiment of the present invention. 1 is a top view of a magnetic memory device according to an embodiment of the present invention. 1 is a cross-sectional view of a magnetic memory element according to an embodiment of the present invention. It is a figure explaining operation | movement of the magnetic memory element concerning embodiment of this invention. It is sectional drawing of the other magnetic memory device concerning embodiment of this invention. It is explanatory drawing of operation | movement of the other magnetic memory device concerning embodiment of this invention. It is sectional drawing of the other magnetic memory device concerning embodiment of this invention. 1 is a top view of a magnetic memory device according to an embodiment of the present invention. It is a figure explaining operation | movement of the magnetic storage element of the conventional single junction structure. It is a figure explaining operation | movement of the magnetic memory element of the conventional double junction structure.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Semiconductor substrate, 2 Element isolation insulating film, 10 Transistor, 11 Gate insulating film, 12 Gate electrode, 13 Side wall, 14 Source / drain region, 20, 60 Interlayer insulating layer, 22, 24, 26, 28 Contact plug, 30 Lead electrode, 40 bit line, 50 magnetic memory element (memory cell), 100 magnetic memory device, 510 unit magnetoresistive element (small area), 520 unit magnetoresistive element (large area), 530 connection electrode.

Claims (8)

A magnetic memory element that reverses the magnetization direction by spin-polarized electrons,
A first unit magnetic memory element including a laminated structure of a first pinned layer, a first tunnel insulating layer, and a first free layer;
A second unit magnetic memory element including a stacked structure of a second pinned layer, a second tunnel insulating layer, and a second free layer;
A connection electrode that electrically connects the first pin layer and the second pin layer to connect the first unit magnetic memory element and the second unit magnetic memory element in series;
A magnetic memory element, wherein a cross-sectional area of the second unit magnetic memory element in a direction perpendicular to a moving direction of the electrons is larger than a cross-sectional area of the first unit magnetic memory element.   Each of the first and second unit magnetic memory elements has a laminated structure in which a pinned layer, a tunnel insulating layer, and a free layer are formed in this order on a lead electrode, and the connection electrode is provided thereon. The magnetic memory element according to claim 1.   3. The magnetic memory element according to claim 2, wherein the first and second unit magnetic memory elements are formed by the same film formation process and are on the same plane.   2. The magnetic storage device according to claim 1, wherein a current that does not change a magnetization direction of the second free layer and changes only a magnetization direction of the first free layer is used as a rewrite current.   The second free layer is further disposed in a magnetic field that includes an external wiring and is generated by a current flowing through the external wiring, and a direction of the magnetic field coincides with a magnetization direction of the free layer. 2. A magnetic memory element according to 1.   The magnetic memory element according to claim 4, wherein the external wiring is connected to the second magnetic memory element via a transistor.   2. The magnetic memory element according to claim 1, wherein the second unit magnetic memory element is connected to a plurality of the first unit magnetic memory elements by the connection electrode.   A magnetic storage device according to claim 1, wherein the magnetic storage elements are arranged in a matrix.

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