WO2010004881A1 - 磁気ランダムアクセスメモリ、並びに磁気ランダムアクセスメモリの初期化方法及び書き込み方法 - Google Patents
磁気ランダムアクセスメモリ、並びに磁気ランダムアクセスメモリの初期化方法及び書き込み方法 Download PDFInfo
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- WO2010004881A1 WO2010004881A1 PCT/JP2009/061679 JP2009061679W WO2010004881A1 WO 2010004881 A1 WO2010004881 A1 WO 2010004881A1 JP 2009061679 W JP2009061679 W JP 2009061679W WO 2010004881 A1 WO2010004881 A1 WO 2010004881A1
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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
- G11C11/14—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements using thin-film elements
- G11C11/15—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements using thin-film elements using multiple magnetic layers
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- G—PHYSICS
- G11—INFORMATION STORAGE
- 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
- 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
- G11—INFORMATION STORAGE
- 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
- G11C11/165—Auxiliary circuits
- G11C11/1659—Cell access
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- G—PHYSICS
- G11—INFORMATION STORAGE
- 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
- G11C11/165—Auxiliary circuits
- G11C11/1675—Writing or programming circuits or methods
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10B—ELECTRONIC MEMORY DEVICES
- H10B61/00—Magnetic memory devices, e.g. magnetoresistive RAM [MRAM] devices
- H10B61/20—Magnetic memory devices, e.g. magnetoresistive RAM [MRAM] devices comprising components having three or more electrodes, e.g. transistors
- H10B61/22—Magnetic memory devices, e.g. magnetoresistive RAM [MRAM] devices comprising components having three or more electrodes, e.g. transistors of the field-effect transistor [FET] type
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
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- H10N50/00—Galvanomagnetic devices
- H10N50/10—Magnetoresistive devices
Definitions
- the present invention relates to a magnetic random access memory (hereinafter referred to as “MRAM”), and more particularly to a domain wall motion type MRAM.
- MRAM magnetic random access memory
- MRAM is a promising nonvolatile memory from the viewpoint of high integration and high-speed operation.
- a magnetoresistive element exhibiting a “magnetoresistance effect” such as a TMR (Tunnel MagnetoResistance) effect is used.
- a magnetic tunnel junction MTJ; Magnetic Tunnel Junction
- the two ferromagnetic layers are composed of a magnetization fixed layer (pinned layer) whose magnetization direction is fixed and a magnetization free layer (free layer) whose magnetization direction can be reversed.
- the MTJ resistance value (R + ⁇ R) when the magnetization direction of the pinned layer and the free layer is “antiparallel” is the MTJ value when the magnetization direction of the pinned layer and the free layer is “parallel” due to the magnetoresistive effect. It becomes larger than the resistance value (R).
- the MRAM uses a magnetoresistive element having this MTJ as a memory cell.
- the memory cell stores data in a non-volatile manner by utilizing the change in resistance value of the MTJ. For example, the antiparallel state is associated with data “1”, and the parallel state is associated with data “0”. Data is written to the memory cell by reversing the magnetization direction of the free layer.
- Asteroid method and “toggle method” are known as methods for writing data to MRAM. According to these write methods, the reversal magnetic field necessary for reversing the magnetization of the free layer increases in inverse proportion to the memory cell size. That is, the write current tends to increase as the memory cell is miniaturized.
- spin transfer method has been proposed as a write method capable of suppressing an increase in write current accompanying miniaturization (for example, Japanese Patent Application Laid-Open No. 2005-93488, corresponding US Pat. No. 7,193,284).
- spin injection method a spin-polarized current is injected into the ferromagnetic conductor, and the magnetization is reversed by a direct interaction between the spin of the conduction electron carrying the current and the magnetic moment of the conductor. (Hereinafter referred to as “Spin Transfer Magnetization Switching”).
- US Pat. No. 6,834,005 discloses a magnetic shift register using a spin injection method.
- This magnetic shift register stores information using a domain wall in a magnetic material.
- a current is injected so as to pass through the domain wall, and the domain wall is moved by the current.
- the magnetization direction of each region is treated as recorded data.
- Such a magnetic shift register is used, for example, for recording a large amount of serial data.
- MRAM of domain wall motion type using domain wall motion by such spin injection (Domain Wall Motion) is described in Japanese Patent Application Laid-Open No. 2005-191032 and WO 2005/069368 (corresponding US Application Publication No. 2008008137405). Has been.
- An MRAM described in Japanese Patent Application Laid-Open No. 2005-191032 includes a magnetization fixed layer in which magnetization is fixed, a tunnel insulating layer stacked on the magnetization fixed layer, and a magnetization recording layer stacked on the tunnel insulating layer. . Since the magnetization recording layer includes a portion where the magnetization direction can be reversed and a portion where the magnetization direction is not substantially changed, it is referred to as a magnetization recording layer, not a magnetization free layer.
- FIG. 1 is a schematic diagram showing the structure of a magnetic recording layer disclosed in Japanese Patent Application Laid-Open No. 2005-191032. In FIG. 1, the magnetization recording layer 100 has a linear shape.
- the magnetization recording layer 100 includes a joint portion 103, a constricted portion 104, and a pair of magnetization fixed portions 101 and 102.
- the junction 103 overlaps with a tunnel insulating layer (not shown) and a magnetization fixed layer (not shown).
- the constricted portion 104 is adjacent to both ends of the joint portion 103.
- the pair of magnetization fixed portions 101 and 102 are formed adjacent to the constricted portion 104.
- the pair of magnetization fixed portions 101 and 102 are provided with fixed magnetizations in opposite directions.
- the MRAM further includes a pair of write terminals 105 and 106 that are electrically connected to the pair of magnetization fixed portions 101 and 102.
- the constricted portion 104 serves as a pin potential for the domain wall. Information is held depending on whether the magnetic domain wall exists in the constricted portion 104 on the left or right side or the magnetization direction of the joint portion 103. The movement of the domain wall is controlled by the aforementioned current.
- FIG. 2 is a schematic view showing the structure of the magnetic recording layer of WO2005 / 069368.
- the magnetic recording layer 100 is composed of three regions having different thicknesses.
- the magnetization recording layer 100 is composed of the thickest first magnetization fixed portion 101, the second thickest second magnetization fixed portion 102, and the thinnest bonding portion 103 disposed therebetween.
- the thicknesses of the first magnetization pinned portion 101 and the second magnetization pinned portion 102 are different in order to give fixed magnetizations in opposite directions in the initialization assumption.
- a magnetic semiconductor having anisotropy perpendicular to the film surface is used as the magnetization recording layer, and the current for domain wall movement is as small as 0.35 mA.
- a tunnel insulating layer and a magnetization fixed layer are disposed at the junction 103, they are omitted in FIG.
- the step at the boundary between the junction 103, the magnetization fixed unit 101, and the magnetization fixed unit 102 functions as a pin potential. Therefore, for example, the domain wall 112 stays at the boundary between the joint portion 103 and the magnetization fixed portion 101.
- FIG. 3 is a schematic diagram showing the magnetization structure of the magnetic storage disclosed in Japanese Patent Application Laid-Open No. 2008-34808.
- the magnetic wire 140 has a plurality of magnetic domains 130 formed by a plurality of domain walls 135 along the longitudinal direction thereof. The magnetic wire is constricted and no step is provided. The domain wall is moved by a magnetic field or a current pulse, and the domain wall moving distance is controlled by the width of the pulse.
- FIG. 4 is a graph showing the relationship between the pulse application time (horizontal axis) calculated by simulation and the domain wall position (vertical axis). As shown by the curve A, the domain wall has a tendency to stop at a certain time and become zero.
- the domain wall position is controlled by setting the pulse application time in accordance with the stop time.
- Japanese Patent Application Laid-Open No. 2006-73930 discloses a method for changing the magnetization state of a magnetoresistive effect element using domain wall motion, a magnetic memory element using the method, and a solid magnetic memory.
- This magnetic memory element has a first magnetic layer, an intermediate layer, and a second magnetic layer, and records information in the direction of magnetization of the first magnetic layer and the second magnetic layer. It is.
- magnetic domains that are antiparallel to each other and a domain wall that separates these magnetic domains are constantly formed in at least one of the magnetic layers, and the domain walls are moved in the magnetic layer so that adjacent magnetic domains can be moved. Information recording is performed by controlling the position.
- Japanese Patent Application Laid-Open No. 2006-270069 discloses a magnetoresistive effect element and a high-speed magnetic recording apparatus based on domain wall motion by a pulse current.
- This magnetoresistive effect element has a first magnetization fixed layer / magnetization free layer / second magnetization fixed layer.
- This magnetoresistive effect element induces domain wall generation in the transition region between the magnetization fixed layer and the magnetization free layer which is at least one boundary of the magnetization fixed layer / magnetization free layer or the magnetization free layer / second magnetization fixed layer.
- the mechanism is provided. Then, the magnetization directions of these magnetization fixed layers are set substantially antiparallel, and a domain wall exists in one of the transition regions of the magnetization fixed layer / magnetization free layer.
- the magnetization of the magnetization free layer is reversed by moving the domain wall between the two transition regions with a current not exceeding the DC current density of 106 A / cm 2 , A magnetoresistance associated with a change in the direction of magnetization is detected.
- the domain wall motion distance control based on the pulse width as disclosed in Japanese Patent Application Laid-Open No. 2008-34808 is applied to the domain wall motion type MRAM, the above two problems can be solved.
- the movement of the domain wall is not necessarily limited to the one that stops during pulse application, as shown by the curve A in FIG. That is, as indicated by the curve B, the domain wall motion may continue to move without stopping, although the movement speed increases or decreases.
- the tendency to not stop was particularly remarkable in the magnetic recording layer having perpendicular anisotropy with a small current density for domain wall motion.
- Japanese Patent Laid-Open No. 2008-34808 there is a problem that it is not suitable for application to an MRAM that requires a reduction in cell size in the sense that the domain wall moving distance is uniquely determined.
- An object of the present invention is to provide an MRAM having a structure adapted to miniaturization of an element and having a small number of steps in a current-driven domain wall motion type MRAM, and an MRAM initialization method for introducing and initializing a domain wall into the structure Is to provide.
- the magnetic memory cell of the present invention includes a magnetization recording layer, a first terminal, a second terminal, a magnetization fixed layer, and a nonmagnetic layer.
- the magnetic recording layer has perpendicular magnetic anisotropy and is a ferromagnetic layer.
- the first terminal is connected to one end of the first region in the magnetization recording layer.
- the second terminal is connected to the other end of the first region.
- a nonmagnetic layer is provided on the first region, and a magnetization fixed layer is provided on the nonmagnetic layer on the side opposite to the first region.
- the magnetization recording layer includes a first extension portion that is outside the first terminal in the magnetization recording layer, and a characteristic change structure that is provided in the first extension portion and substantially changes the magnetization reversal characteristics of the magnetization recording layer.
- the magnetic random access memory includes a plurality of magnetic memory cells and a write current supply circuit.
- the plurality of magnetic memory cells are arranged in a matrix and are described in the paragraph above.
- the write current supply circuit supplies a write current during the write operation of the plurality of magnetic memory cells.
- the magnetic random access memory is arranged in a matrix, and a plurality of magnetic memory cells and a write current supply circuit for supplying a write current during a write operation of the plurality of magnetic memory cells It comprises.
- Each of the plurality of magnetic memory cells has perpendicular magnetic anisotropy, a magnetic recording layer that is a ferromagnetic layer, a first terminal connected to one end of the first region in the magnetic recording layer, and a first A second terminal connected to the other end of the region.
- a nonmagnetic layer is provided on the first region, and a magnetization fixed layer is provided on the nonmagnetic layer on the side opposite to the first region.
- the magnetization recording layer includes a first extension portion that is outside the first terminal in the magnetization recording layer, and a characteristic change structure that is provided in the first extension portion and substantially changes the magnetization reversal characteristics of the magnetization recording layer.
- the step of applying the magnetic field in the first direction and directing all the magnetizations of the magnetization recording layer in the first direction, and the second direction opposite to the first direction Applying a magnetic field to the magnetic recording layer in a region where the characteristic change structure is not provided, directing the magnetization in the second direction to generate a domain wall, applying a magnetic field in the first direction,
- the step of introducing into the region and the step of driving the domain wall in the vicinity of the second terminal by passing a current between the first terminal and the second terminal are executed.
- the step of applying a magnetic field in the first direction and directing all the magnetizations of the magnetic recording layer in the first direction, and the second direction opposite to the first direction Applying a magnetic field to the magnetic recording layer in a region where the characteristic change structure is provided, directing the magnetization in the second direction to generate a domain wall, applying a magnetic field in the second direction, and The step of introducing into the region and the step of driving the domain wall in the vicinity of the second terminal by passing a current between the first terminal and the second terminal are executed.
- the writing method of the magnetic random access memory of this invention performs the step which raises a write-current pulse in 1st time, and the step which falls a write-current pulse in 2nd time longer than 1st time.
- the domain wall position can be easily initialized.
- an MRAM having a large capacity and a small number of processes can be provided.
- FIG. 1 is a schematic diagram showing the structure of a magnetic recording layer disclosed in Japanese Patent Application Laid-Open No. 2005-191032.
- FIG. 2 is a schematic view showing the structure of the magnetic recording layer of WO2005 / 069368.
- FIG. 3 is a schematic diagram showing the magnetization structure of the magnetic storage disclosed in Japanese Patent Application Laid-Open No. 2008-34808.
- FIG. 4 is a graph showing the relationship between the pulse application time and the domain wall position by simulation.
- FIG. 5 is a perspective view showing an example of the magnetoresistive element of the magnetic memory cell according to the present embodiment.
- FIG. 6 is a perspective view showing another example of the magnetoresistive element of the magnetic memory cell according to the present embodiment.
- FIG. 5 is a perspective view showing an example of the magnetoresistive element of the magnetic memory cell according to the present embodiment.
- FIG. 7 is a perspective view showing another example of the magnetoresistive element of the magnetic memory cell according to the present embodiment.
- FIG. 8A is a cross-sectional view showing the MRAM initialization method according to the embodiment of the present invention.
- FIG. 8B is a cross-sectional view showing the MRAM initialization method according to the embodiment of the present invention.
- FIG. 8C is a cross-sectional view showing an MRAM initialization method according to the embodiment of the present invention.
- FIG. 8D is a cross-sectional view showing the MRAM initialization method according to the embodiment of the present invention.
- FIG. 9 shows a data write principle for the magnetic memory cell of FIG.
- FIG. 10 is a graph showing the relationship between the domain wall position of the magnetic recording layer and the pin potential.
- FIG. 11 is a graph showing the relationship between the magnitude of the write current and the time in the write operation.
- FIG. 12 is a perspective view showing a modification of the magnetoresistive element of the magnetic memory cell according to the present embodiment.
- FIG. 13A is a cross-sectional view showing the relationship between the data and magnetization state of the magnetic memory cell of FIG.
- FIG. 13B is a cross-sectional view showing the relationship between the data and magnetization state of the magnetic memory cell of FIG.
- FIG. 14 is a block diagram showing an example of the configuration of the MRAM according to the present embodiment.
- the MRAM according to the present embodiment is a domain wall motion type MRAM using a magnetic layer having perpendicular magnetic anisotropy.
- FIG. 5 is a perspective view showing an example of the magnetoresistive element of the magnetic memory cell according to the present embodiment.
- the magnetoresistive element 1 includes a magnetization recording layer 10, a tunnel barrier layer 32 (nonmagnetic layer) provided on the first region 11 of the magnetization recording layer 10, and a pinned layer 30 (on the tunnel barrier layer 32). Magnetization fixed layer).
- the first region 11 is a region in the magnetization recording layer 10 and a region between a first terminal 14a (described later) and a second terminal 14b (described later).
- the magnetization recording layer 10 and the pinned layer 30 are ferromagnetic layers.
- the tunnel barrier layer 32 is a nonmagnetic layer.
- the tunnel barrier layer 32 is sandwiched between the magnetization recording layer 10 and the pinned layer 30.
- the magnetic recording layer 10, the tunnel barrier layer 32, and the pinned layer 30 form a magnetic tunnel junction (MTJ).
- MTJ magnetic tunnel junction
- the magnetization direction of the pinned layer 30 is not changed by either the write operation or the read operation. Therefore, it is desirable that the magnetic anisotropy of the pinned layer 30 is larger than the magnetic anisotropy of the magnetization recording layer 10. This is realized by changing materials and compositions of the magnetization recording layer 10 and the pinned layer 30. It can also be realized by stacking an antiferromagnetic layer 36 on the surface of the pinned layer 30 opposite to the tunnel barrier layer 30 and pinning the magnetization. Further, the pinned layer 30 can be a laminated film composed of a ferromagnetic layer 34, a nonmagnetic layer 31, and a ferromagnetic layer 33. Here, Ru, Cu, or the like is used as the nonmagnetic layer 31.
- the magnetizations of the two ferromagnetic layers 33 and 34 are antiparallel to each other. If the magnetizations of the two ferromagnetic layers 33 and 34 are substantially equal, the leakage magnetic field from the pinned layer 30 can be suppressed.
- the magnetization recording layer 10 has anisotropy in a direction perpendicular to the substrate surface.
- the magnetization recording layer 10 preferably includes at least one material selected from Fe, Co, and Ni as a material. Furthermore, in order to stabilize perpendicular magnetic anisotropy, it is desirable to contain Pt and Pd.
- B, C, N, O, Al, Si, P, Ti, V, Cr, Mn, Cu, Zn, Zr, Nb, Mo, Tc, Ru, Rh, Ag, Hf, Ta, W , Re, Os, Ir, Au, Sm, and the like can be added so that desired magnetic properties are expressed.
- the material of the magnetic recording layer 10 is Co, Co—Pt, Co—Pd, Co—Cr, Co—Pt—Cr, Co—Cr—Ta, Co—Cr—B, Co—Cr—Pt—.
- B Co—Cr—Ta—B, Co—V, Co—Mo, Co—W, Co—Ti, Co—Ru, Co—Rh, Fe—Pt, Fe—Pd, Fe—Co—Pt, Fe— Examples include Co—Pd and Sm—Co.
- a layer containing at least one material selected from Fe, Co, and Ni can be laminated with a different layer to develop perpendicular magnetic anisotropy.
- the magnetic recording layer 10 a multilayer film of Co / Pd, Co / Pt, Co / Ni, and Fe / Au is exemplified as the magnetic recording layer 10.
- the pinned layer 30 is also preferably made of the same material as the magnetic recording layer 10 and has perpendicular magnetic anisotropy.
- the tunnel barrier layer 32 is a thin insulating film such as an Al 2 O 3 film or an MgO film.
- a material having a large TMR effect, such as CoFe or CoFeB, may be used for a part of the magnetic recording layer 10 and the pinned layer 30, particularly, a portion in contact with the tunnel barrier layer 32.
- a first terminal 14 a and a second terminal 14 b for flowing a write current are connected to the magnetization recording layer 10.
- the domain wall is introduced between the first terminal 14a and the second terminal 14b by an initialization operation described later.
- the domain wall is driven according to the write current.
- there is no artificial structure for forming a pin potential such as a constriction or a step between the first terminal 14a and the second terminal 14b.
- the portion where the tunnel barrier layer 32 and the pinned layer 30 are stacked and the MTJ is formed must include the portion of the magnetization recording layer 10 between the first terminal 14a and the second terminal 14b. This is because, as a result of the write operation, the magnetization direction of the portion between them changes.
- the first terminal 14a and the second terminal 14b may be either above or below the magnetic recording layer 10, and are formed by a via formation process, a cueing process, or the like.
- the magnetization recording layer 10 has a structure (characteristic changing structure) for initialization operation of introducing a domain wall in a region outside the first terminal 14a (an extended portion extending to the side opposite to the MTJ).
- this structure is composed of an insulating layer 42 and a ferromagnetic layer 44. These layers may be formed simultaneously with the tunnel barrier layer 32 and the ferromagnetic layer 34 forming the MTJ.
- the role of this structure is to apply a magnetostatic or exchange magnetic field to a part of the magnetization recording layer 10 and change the magnetization reversal characteristics, as will be described in the initialization method described later. is there.
- the tunnel barrier layer 42 can be omitted, or a nonmagnetic metallic property can be provided instead of the tunnel barrier layer 42.
- an antiferromagnetic layer may be directly adjacent to the magnetic recording layer 10 instead of the ferromagnetic layer 44.
- the magnetic recording layer 10 preferably has a region (an extended portion extended to the side opposite to the MTJ) outside the second terminal 14b. As will be described later, when the domain wall has moved to the vicinity of the second terminal 14b, the domain wall is prevented from coming off from the end of the magnetic recording layer 10 on the second terminal 14b side. However, it is not necessary to have a structure (characteristic change structure) for the initialization operation for introducing the domain wall in the region. Thereby, the structure of the magnetoresistive element 1 can be simplified.
- FIG. 6 and 7 are perspective views showing other examples of the magnetoresistive element of the magnetic memory cell according to the present embodiment.
- These magnetoresistive elements 1a and 1b differ from the magnetoresistive element 1 in FIG. 5 in the structure 41 (characteristic change structure) for initialization.
- a step is provided in a part of the magnetization recording layer 10 outside the first terminal 14a. If a hole is previously formed by etching in the base portion where the step is to be formed, the step can be easily introduced into the magnetic recording layer 10 by forming a film to be the magnetic recording layer 10 after that. The step promotes the generation of magnetization reversal nuclei and changes the magnetic characteristics of the magnetization recording layer 10.
- FIG. 6 are perspective views showing other examples of the magnetoresistive element of the magnetic memory cell according to the present embodiment.
- These magnetoresistive elements 1a and 1b differ from the magnetoresistive element 1 in FIG. 5 in the structure 41 (characteristic change structure) for initialization.
- a step is provided in a part of
- a step is provided on the surface of a part (thin film portion) of the magnetization recording layer 10 outside the first terminal 14a.
- a step (thin film portion) can be easily introduced into the magnetic recording layer 10 by etching a predetermined portion of the magnetic recording layer 10. The step promotes the generation of magnetization reversal nuclei and changes the magnetic characteristics of the magnetization recording layer 10.
- FIG. 8A to 8D are cross-sectional views showing a method of initializing the MRAM according to the embodiment of the present invention.
- the coercive force of the pinned layer 30 is sufficiently larger than the coercive force of the magnetization recording layer 10, and the illustration is omitted assuming that the magnetization direction does not change during the initialization process.
- a ferromagnetic layer 44 is laminated outside the first terminal 14a via an insulating layer 42 as in FIG. 5 (however, the insulating layer 42 is not shown).
- the white arrow of each part in each figure has shown the magnetization direction of the said part.
- Step 1 when a large magnetic field is first applied in the ⁇ Z direction (first direction), all the magnetizations of the magnetization recording layer 10 (including the ferromagnetic layer 44) are directed in the ⁇ Z direction ( Step 1).
- Step 2 when the magnetic field in the + Z direction (second direction) is gradually increased, the magnetization of the portion of the magnetization recording layer 10 where the ferromagnetic layer 44 is not laminated is reversed.
- Step 2 This is because in the magnetization recording layer 10, the portion where the ferromagnetic layer 44 is laminated is difficult to reverse the magnetization due to magnetostatic coupling with the ferromagnetic 44.
- the domain wall 12 is formed at the boundary between the portion where the ferromagnetic layer 44 is laminated and the portion where the ferromagnetic layer 44 is not laminated in the magnetization recording layer 10.
- the domain wall 12 depins and exceeds the position of the first terminal 14a. It moves in the direction of the position of 14b (Step 3). At this time, it is necessary to set the magnitude of the magnetic field in the vicinity of the depinning magnetic field. This is because when the magnetic field is excessively large, the domain wall moving speed is increased, and the domain wall passes through the second terminal 14b and comes off from the right end. Whether the domain wall is located between the first terminal 14a and the second terminal 14b is determined by monitoring the signal of the MTJ stacked in this region.
- the magnetic field application is turned off, and the domain wall 12 is introduced between the first terminal 14a and the second terminal 14b. Further, as shown in FIG. 8D, the domain wall 12 is moved to the vicinity of the second terminal 14b by flowing a current from the second terminal 14b to the first terminal 14a (Step 4). Finally, the domain wall 12 is initialized in the vicinity of the second terminal 14b by turning off the current.
- the behavior of the domain wall 12 when the current is off will be described in detail in the write operation described later. It goes without saying that a desired initial state can be obtained even if the magnetic field directions are all set in opposite directions in the initialization operation described above.
- an initialization structure 41 (characteristic changing structure) such as a step and an etching region is provided outside the first terminal 14a. Magnetization reversal nucleation is promoted. In that case, in Step 2 of FIG. 8B, only the magnetization of the structure 41 is reversed by the low magnetic field, and the domain wall 12 is introduced. Accordingly, the magnetic field necessary for introducing the domain wall 12 between the first terminal 14a and the second terminal 14b in Step 3 is a magnetic field in the + Z direction.
- FIG. 9 shows the principle of writing data to the magnetic memory cell (magnetoresistance element 1) having the structure shown in FIG. It is assumed that the magnetization direction of the magnetization recording layer 10 is initialized by the above-described initialization operation.
- a region between the first terminal 14 a and the second terminal 14 b in which magnetization is reversed in the following writing operation is referred to as a magnetization reversal region 13.
- Data writing is performed by a domain wall motion method using spin injection.
- the write current I w is not a direction passing through the MTJ, through the magnetic recording layer 10 in a plan view.
- the write current Iw is supplied to the magnetization recording layer 10 from the first terminal 14a and the second terminal 14b.
- a state in which the magnetization direction of the magnetization switching region 13 and the magnetization direction of the ferromagnetic layer 34 of the pinned layer 30 are parallel to each other is associated with data “0”.
- the magnetization direction of the magnetization switching region 13 is the ⁇ Z direction, and the domain wall 12 exists in the vicinity of the second terminal 14b.
- a state where the magnetization direction of the magnetization switching region 13 and the magnetization direction of the ferromagnetic layer 34 of the pinned layer 30 are antiparallel is associated with data “1”.
- the magnetization direction of the magnetization switching region 13 is the + Z direction, and the domain wall 12 exists in the vicinity of the first terminal 14a.
- the first write current Iw1 flows from the first terminal 14a through the magnetization switching region 13 to the second terminal 14b.
- spin electrons are injected into the magnetization switching region 13 from the portion having the magnetization in the + Z direction of the magnetization recording layer 10.
- the spin of the injected electrons drives the domain wall 12 existing in the vicinity of the second terminal 14b in the direction of the first terminal 14a.
- the magnetization direction of the magnetization switching region 13 is switched to the + Z direction. That is, due to the spin transfer effect, the magnetization of the magnetization switching region 13 is reversed and the magnetization direction is changed to the + Z direction.
- the extended portion of the magnetic recording layer 10 also exists outside the first terminal 14a (left side in FIG. 9)
- the first write current Iw1 does not flow through the extended portion outside the first terminal 14a. Therefore, the domain wall 12 is not driven beyond the first terminal 14a.
- FIG. 10 is a graph showing the relationship between the domain wall position of the magnetic recording layer 10 and the pin potential.
- FIG. 11 is a graph showing the relationship between the magnitude of the write current and the time in the write operation.
- the magnetic recording layer 10 there is a random potential as shown in FIG. 10 due to the roughness of the end face during patterning, the distribution of lattice defects, the boundaries between crystal grains, and the like. Since the magnitude of this potential relatively increases as the width of the magnetization recording layer 10 is reduced, this potential functions as a site for pinning the domain wall 12.
- the fall time of the write current pulse is set as shown in FIG. It is effective to make it longer than the rise time. This is because the motion of the domain wall 12 due to current drive depends on the time change of the write current. That is, increasing the fall time has the effect of increasing the rate at which the current-driven energy is dissipated and facilitating the convergence of the domain wall 12.
- the second write current Iw2 flows from the second terminal 14b through the magnetization switching region 13 to the first terminal 14a.
- spin electrons are injected into the magnetization switching region 13 from the portion having the magnetization in the ⁇ Z direction of the magnetic recording layer 10.
- the spin of the injected electrons drives the domain wall 12 existing in the vicinity of the first terminal 14a in the direction of the second terminal 14b.
- the magnetization direction of the magnetization switching region 13 is switched to the ⁇ Z direction. That is, due to the spin transfer effect, the magnetization of the magnetization switching region 13 is reversed and the magnetization direction is changed to the ⁇ Z direction.
- the second write current Iw2 does not flow through that extended portion outside the second terminal 14b. Therefore, the domain wall 12 is not driven beyond the second terminal 14b. Thus, the magnetization direction of the magnetization switching region 13 is switched by the write currents I w1 and I w2 that flow in a plane in the magnetization recording layer 10.
- the data read is as follows.
- the read current is supplied so as to flow between the pinned layer 30 and the magnetization switching region 13.
- the read current flows from either the first terminal 14 a or the second terminal 14 b to the ferromagnetic layer 34 of the pinned layer 30 via the magnetization switching region 13 and the tunnel barrier layer 32.
- the read current flows from the ferromagnetic layer 34 to the first terminal 14a or the second terminal 14b via the tunnel barrier layer 32 and the magnetization switching region 13.
- the resistance value of the magnetoresistive element 1 is detected, and the magnetization direction of the magnetization switching region 13 is sensed.
- the insulating layer 42 and the ferromagnetic layer 44 for initializing the domain wall 12 are formed outside the first terminal 14a. However, no current flows through these layers in the write operation and the read operation. That is, the configuration provided for the initialization operation does not affect the write / read operation of the present invention.
- FIG. 12 is a perspective view showing a modification of the magnetoresistive element of the magnetic memory cell according to the present embodiment.
- the magnetoresistive element 1 d includes a separation metal layer 38 and a sensor layer 39 between the pinned layer 30 and the tunnel barrier layer 32 and the magnetization recording layer 10.
- the laminated film above the sensor layer 39 is disposed at a position offset from the magnetization recording layer 10 in the Y direction.
- both the sensor layer 39 and the pinned layer 30 are made of magnetic materials having in-plane magnetic anisotropy instead of perpendicular magnetic anisotropy.
- FIG. 13A and 13B are cross-sectional views showing the relationship between data and magnetization state of the magnetic memory cell (magnetoresistance element 1d) having the structure shown in FIG.
- FIG. 13A shows a state of data “0”
- FIG. 13B shows a state of data “1”.
- the leakage magnetic field from the magnetization recording layer 10 rotates the magnetization of the sensor layer 39, thereby changing the magnetization direction of the magnetization recording layer 10 from the sensor layer 39, the tunnel barrier layer 32, and the pinned layer 30.
- Indirect reading is performed with the in-plane MTJ film.
- the initialization method, writing method, and reading method in this modification are the same as those in FIG.
- FIG. 14 is a block diagram showing an example of the configuration of the MRAM according to the present embodiment.
- an MRAM 60 has a memory cell array 61 in which a plurality of magnetic memory cells 71 are arranged in a matrix.
- the memory cell array 61 includes a reference cell 71r that is referred to when reading data, together with a magnetic memory cell 71 used for data recording.
- the structure of the reference cell 71r is the same as that of the magnetic memory cell 71.
- Each magnetic memory cell 71 has selection transistors M1 and M2 in addition to the magnetoresistive element 1 shown in FIG. 5, for example.
- One of the source / drain of the selection transistor M1 is connected to the first terminal 14a of the magnetic recording layer 10, and the other is connected to the first bit line BL1.
- One of the source / drain of the selection transistor M2 is connected to the second terminal 14b of the magnetic recording layer 10, and the other is connected to the second bit line BL2.
- the gates of the selection transistors M1 and M2 are connected to the word line WL.
- the pinned layer 30 of the magnetoresistive element 1 is connected to a ground line and an initialization voltage via wiring as shown in the figure.
- the word line WL is connected to the X selector 62.
- the X selector 62 selects the word line WL connected to the target memory cell 71s selected from the magnetic memory cells 71 as the selected word line WLs in the data writing / reading.
- the first bit line BL1 is connected to the Y-side current termination circuit 64.
- the second bit line BL2 is connected to the Y selector 63.
- the Y selector 63 selects the second bit line BL2 connected to the target memory cell 71s as the selected second bit line BL2s.
- the Y-side current termination circuit 64 selects the first bit line BL1 connected to the target memory cell 71s as the selected first bit line BL1s.
- the Y-side current source circuit 65 supplies or draws a predetermined write current (I w1 , I w2 ) to the selected second bit line BL2s during data writing.
- the Y-side power supply circuit 66 supplies a predetermined voltage to the Y-side current termination circuit 64 at the time of data writing. As a result, the write currents (I w1 , I w2 ) flow into or out of the Y selector 63.
- These X selector 62, Y selector 63, Y side current termination circuit 64, Y side current source circuit 65, and Y side power supply circuit 66 “write” for supplying write currents I w1 and I w2 to the magnetic memory cell 1. Current supply circuit ".
- the first bit line BL1 When reading data, the first bit line BL1 is set to “Open”.
- the read current load circuit 67 supplies a predetermined read current to the selected second bit line BL2s.
- the read current load circuit 67 supplies a predetermined current to the reference second bit line BL2r connected to the reference cell 71r.
- the sense amplifier 68 reads data from the target memory cell 71s based on the difference between the potential of the reference second bit line BL2r and the potential of the selected second bit line BL2s, and outputs the data.
- one extended portion of the magnetic recording layer 10 has a characteristic change structure.
- the nonmagnetic layer 42 and the ferromagnetic layer 44 are used, the nonmagnetic layer 42 and the ferromagnetic layer 44 are very easily formed simultaneously with the tunnel barrier layer 32 and the pinned layer 30 without introducing an additional process. I can do it.
- the stepped structure 41 is used, the structure 41 can be formed very easily by only partially etching the base portion or a predetermined place of the magnetic recording layer 10.
- it is necessary to form an artificial structure for forming a pin potential such as a step that requires an additional process that increases the cost and the manufacturing process is difficult when the width of the magnetic recording layer 10 is narrow due to miniaturization. Will disappear. That is, it is possible to provide an MRAM having a structure that is suitable for miniaturization of elements and has a small number of processes.
- initialization of the magnetic random access memory can be performed very easily as shown in FIGS. 8A to 8D. That is, it is possible to provide an MRAM initialization method in which a domain wall is introduced and initialized in the structure of the MRAM of the present invention.
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Abstract
Description
そして、本発明の磁気ランダムアクセスメモリの初期化方法は、第1方向に磁界を印加し、磁化記録層の全ての磁化を第1方向に向けるステップと、第1方向とは逆の第2方向に磁界を印加して磁化記録層のうち、特性変化構造が設けられていない領域の磁化を第2方向に向け、磁壁を発生させるステップと、第1方向に磁界を印加し、磁壁を第1領域内に導入させるステップと、第1端子と第2端子との間に電流を流すことにより磁壁を第2端子の近傍に駆動するステップとを実行する。
又は、本発明の磁気ランダムアクセスメモリの初期化方法は、第1方向に磁界を印加し、磁気記録層の全ての磁化を第1方向に向けるステップと、第1方向とは逆の第2方向に磁界を印加して磁化記録層のうち、特性変化構造が設けられている領域の磁化を第2方向を向け、磁壁を発生させるステップと、第2方向に磁界を印加し、磁壁を第1領域内に導入させるステップと、第1端子と第2端子との間に電流を流すことにより磁壁を第2端子の近傍に駆動するステップとを実行する。
そして、本発明の磁気ランダムアクセスメモリの書き込み方法は、書込み電流パルスを第1時間で立ち上げるステップと、書き込み電流パルスを第1時間より長い第2時間で立ち下げるステップとを実行する。
まず、MRAMに用いられる磁気メモリセルの構成について説明する。図5は、本実施の形態に係る磁気メモリセルの磁気抵抗素子の一例を示す斜視図である。磁気抵抗素子1は、磁化記録層10と、磁化記録層10の第1領域11上に設けられたトンネルバリヤ層32(非磁性層)と、トンネルバリヤ層32上に設けられたピン層30(磁化固定層)とを備えている。ここで第1領域11とは、磁化記録層10における領域であって第1端子14a(後述)と第2端子14b(後述)との間の領域を指す。磁化記録層10とピン層30は強磁性体層である。トンネルバリヤ層32は非磁性体層である。トンネルバリヤ層32は、磁化記録層10とピン層30に挟まれている。これら磁化記録層10、トンネルバリヤ層32、及びピン層30によって磁気トンネル接合(MTJ)が形成されている。
次に、本発明の実施の形態に係るMRAMの初期化方法、すなわち磁壁導入について説明する。図8A~図8Dは、本発明の実施の形態に係るMRAMの初期化方法を示す断面図である。ここで、ピン層30の保磁力は磁化記録層10の保磁力よりも十分大きく、初期化過程で磁化方向が変化しないと仮定し図示を省略している。また、第1端子14aの外側には図5と同様に絶縁層42を介して強磁性層44が積層されているとする(ただし、絶縁層42は図示を省略している)。各図中における各部分の白抜き矢印は、当該部分の磁化方向を示している。
以上述べた初期化動作において磁界方向を全て反対方向に設定しても、所望の初期状態が得られることは言うまでもない。
次に、磁気メモリセルに対するデータの書き込み原理を説明する。図9は、図5で示された構造を有する磁気メモリセル(磁気抵抗素子1)に対するデータの書込み原理を示している。磁化記録層10の磁化方向は前述の初期化動作により初期化されているとする。磁化記録層10のうち、以下の書き込み動作において、磁化が反転する第1端子14aと第2端子14bの間の領域を磁化反転領域13と呼ぶことにする。
図12は、本実施の形態に係る磁気メモリセルの磁気抵抗素子の変形例を示す斜視図である。本変形例においては、磁気抵抗素子1dは、ピン層30及びトンネルバリヤ層32と磁化記録層10との間に、分離金属層38、センサー層39を有している。加えて、このセンサー層39から上の積層膜は磁化記録層10からY方向にオフセットした位置に配置されている。また、本変形例においては、センサー層39及びピン層30として、いずれも垂直磁気異方性ではなく面内磁気異方性を有する磁性材料が用いられている。
図14は、本実施の形態に係るMRAMの構成の一例を示すブロック図である。図14において、MRAM60は、複数の磁気メモリセル71がマトリックス状に配置されたメモリセルアレイ61を有している。このメモリセルアレイ61は、データの記録に用いられる磁気メモリセル71と共に、データ読み出しの際に参照されるリファレンスセル71rを含んでいる。リファレンスセル71rの構造は、磁気メモリセル71と同じである。
Claims (14)
- 垂直磁気異方性を有し、強磁性層である磁化記録層と、
前記磁化記録層における第1領域の一方の端に接続された第1端子と、
前記第1領域の他方の端に接続された第2端子と、
前記第1領域上に設けられた非磁性層と、
前記非磁性層上であって前記第1領域と反対側に設けられた磁化固定層と
を具備し、
前記磁化記録層は、
前記磁化記録層における前記第1端子の外側である第1延長部分と、
前記第1延長部分に設けられ、前記磁化記録層の磁化反転特性を実質的に変化させる特性変化構造と
を備える
磁気メモリセル。 - 請求の範囲1に記載の磁気メモリセルにおいて、
前記磁化記録層は、前記磁化記録層における前記第2端子の外側である第2延長部分を更に備える
磁気メモリセル。 - 請求の範囲1又は2に記載の磁気メモリセルにおいて、
前記特性変化構造は、前記磁化記録層に絶縁層を介して接続した強磁性層を含む
磁気メモリセル。 - 請求の範囲1又は2に記載の磁気メモリセルにおいて、
前記特性変化構造は、前記磁化記録層に直接的に接続した強磁性層を含む
磁気メモリセル。 - 請求の範囲1又は2に記載の磁気メモリセルにおいて、
前記特性変化構造は、前記磁化記録層に直接的に接続した反強磁性層を含む
磁気メモリセル。 - 請求の範囲1又は2に記載の磁気メモリセルにおいて、
前記特性変化構造は、前期磁化記録層に設けられた段差を有する
磁気メモリセル。 - 請求の範囲1又は2に記載の磁気メモリセルにおいて、
前記特性変化構造は、前期磁化記録層に設けられたエッチングされた薄層部を含む
磁気メモリセル。 - 請求の範囲1乃至7のいずれか一項に記載の磁気メモリセルにおいて、
前記非磁性層及び前記磁化固定層は、前記第1領域にオーバーラップして積層されている
磁気メモリセル。 - 請求の範囲1乃至7のいずれか一項に記載の磁気メモリセルにおいて、
前記磁化記録層と前記非磁性層との間に設けられ、強磁性層であるセンス層を更に具備し、
前記センス層、前記非磁性層及び前記ピン層は、前記第1領域に部分的にオーバーラップして積層されている
磁気メモリセル。 - 請求の範囲9に記載の磁気メモリセルにおいて、
前記センス層及び前記磁化固定層は、面内磁気異方性を有する
磁気メモリセル。 - 行列上に配列され、請求の範囲1乃至10のいずれか一項に記載の複数の磁気メモリセルと、
前記複数の磁気メモリセルの書込み動作時に書き込み電流を供給する書き込み電流供給回路と
を具備する
磁気ランダムアクセスメモリ。 - 行列上に配列され、複数の磁気メモリセルと、
前記複数の磁気メモリセルの書込み動作時に書き込み電流を供給する書き込み電流供給回路と
を具備し、
前記複数の磁気メモリセルの各々は、
垂直磁気異方性を有し、強磁性層である磁化記録層と、
前記磁化記録層における第1領域の一方の端に接続された第1端子と、
前記第1領域の他方の端に接続された第2端子と、
前記第1領域上に設けられた非磁性層と、
前記非磁性層上であって前記第1領域と反対側に設けられた磁化固定層と、
を備え、
前記磁化記録層は、
前記磁化記録層における前記第1端子の外側である第1延長部分と、
前記第1延長部分に設けられ、前記磁化記録層の磁化反転特性を実質的に変化させる特性変化構造と
を含む磁気ランダムアクセスメモリに対して、
第1方向に磁界を印加し、前記磁化記録層の全ての磁化を前記第1方向に向けるステップと、
前記第1方向とは逆の第2方向に磁界を印加して前記磁化記録層のうち、前記特性変化構造が設けられていない領域の磁化を前記第2方向に向け、磁壁を発生させるステップと、
前記第1方向に磁界を印加し、前記磁壁を前記第1領域内に導入させるステップと、
前記第1端子と前記第2端子との間に電流を流すことにより前記磁壁を前記第2端子の近傍に駆動するステップと
を実行する
磁気ランダムアクセスメモリの初期化方法。 - 行列上に配列され、複数の磁気メモリセルと、
前記複数の磁気メモリセルの書込み動作時に書き込み電流を供給する書き込み電流供給回路と
を具備し、
前記複数の磁気メモリセルの各々は、
垂直磁気異方性を有し、強磁性層である磁化記録層と、
前記磁化記録層における第1領域の一方の端に接続された第1端子と、
前記第1領域の他方の端に接続された第2端子と、
前記第1領域上に設けられた非磁性層と、
前記非磁性層上であって前記第1領域と反対側に設けられた磁化固定層と
を備え、
前記磁化記録層は、
前記磁化記録層における前記第1端子の外側である第1延長部分と、
前記第1延長部分に設けられ、前記磁化記録層の磁化反転特性を実質的に変化させる特性変化構造と
を含む磁気ランダムアクセスメモリに対して、
第1方向に磁界を印加し、前記磁気記録層の全ての磁化を前記第1方向に向けるステップと、
前記第1方向とは逆の第2方向に磁界を印加して前記磁化記録層のうち、前記特性変化構造が設けられている領域の磁化を前記第2方向を向け、磁壁を発生させるステップと、
前記第2方向に磁界を印加し、前記磁壁を前記第1領域内に導入させるステップと、
前記第1端子と前記第2端子との間に電流を流すことにより前記磁壁を前記第2端子の近傍に駆動するステップと
を実行する
磁気ランダムアクセスメモリの初期化方法。 - 行列上に配列され、複数の磁気メモリセルと、
前記複数の磁気メモリセルの書込み動作時に書き込み電流を供給する書き込み電流供給回路と
を具備し、
前記複数の磁気メモリセルの各々は、
垂直磁気異方性を有し、強磁性層である磁化記録層と、
前記磁化記録層における第1領域の一方の端に接続された第1端子と、
前記第1領域の他方の端に接続された第2端子と、
前記第1領域上に設けられた非磁性層と、
前記非磁性層上であって前記第1領域と反対側に設けられた磁化固定層と
を備え、
前記磁化記録層は、
前記磁化記録層における前記第1端子の外側である第1延長部分と、
前記第1延長部分に設けられ、前記磁化記録層の磁化反転特性を実質的に変化させる特性変化構造と
を含む磁気ランダムアクセスメモリに対して、
書込み電流パルスを第1時間で立ち上げるステップと、
前記書き込み電流パルスを前記第1時間より長い第2時間で立ち下げるステップと
を実行する
磁気ランダムアクセスメモリの書き込み方法。
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US20110157967A1 (en) | 2011-06-30 |
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