JP6346047B2 - Magnetic tunnel junction device and magnetic random access memory - Google Patents

Description

  The present invention relates to a magnetic tunnel junction element and a magnetic random access memory, and more particularly to a magnetic tunnel junction element and a magnetic random access memory using a spin injection magnetization reversal method.

  There is a magnetic tunnel junction (MTJ) element in which reading is performed by a magnetoresistive effect and writing is performed by a spin transfer magnetization reversal method (STT: Spin Transfer Torque).

  Such a magnetic tunnel junction element has a tunnel barrier comprising a storage layer having a variable magnetization direction, a fixed layer that maintains a magnetization direction perpendicular to the film surface, and an insulator provided between the storage layer and the fixed layer. Including layers. As a material for the fixed layer and the memory layer, a ferromagnetic material having high perpendicular magnetic anisotropy and high spin polarizability is preferable. Such a magnetic tunnel junction element has thermal disturbance resistance against miniaturization, and is expected to be used in, for example, a magnetic random access memory (MRAM).

  For example, Patent Document 1 discloses a magnetic tunnel junction element in which an antiferromagnetic film is provided on at least a side surface of a fixed layer. In this magnetic tunnel junction element, examples of materials for forming the fixed layer and the memory layer include ferromagnetic metals such as Co, Fe, and Ni, alloys thereof, and alloys having B such as CoFeB. According to such a magnetic tunnel junction element, the multi-domain of the fixed layer can be suppressed.

  Further, in Patent Document 2, a base layer, a storage layer including a magnetic film made of an Mn—Ga alloy, a nonmagnetic layer, and a fixed layer including a magnetic film made of an Mn—Ga alloy are provided. A magnetic tunnel junction element laminated in order is disclosed. According to such a magnetic tunnel junction element, it has perpendicular magnetic anisotropy and can exhibit a large magnetoresistance effect.

JP 2005-032878 A JP 2012-204683 A

  Incidentally, it is required to reduce the magnetization reversal current necessary for reversing the magnetization direction of the storage layer.

  Further, as disclosed in Patent Documents 1 and 2, as ferromagnetic materials having high perpendicular magnetic anisotropy and high spin polarizability, ferromagnetic metals, alloys thereof, or Mn-Ga alloys are used. Can be mentioned. In the magnetic tunnel junction element, there is room for further expanding the selection range of materials for forming the fixed layer and the storage layer.

  The present invention has been made against the background described above, and it is an object of the present invention to provide a magnetic tunnel junction element capable of reversing the magnetization direction of a storage layer even with a small current density.

The magnetic tunnel junction device according to the present invention is:
A storage layer having a variable magnetization direction, a fixed layer that maintains a predetermined magnetization direction, and a tunnel barrier layer,
A magnetic tunnel junction element that performs writing using a spin torque injection method,
At least one of the storage layer and the fixed layer includes a ferromagnetic insulating layer.

  According to such a configuration, the magnetization direction of the storage layer can be reversed even with a small current density.

  The storage layer may be made of the ferromagnetic insulating layer, and the ferromagnetic insulating layer may have perpendicular magnetic anisotropy. The storage layer may include the ferromagnetic insulating layer and a perpendicular magnetization holding layer having a magnetization direction perpendicular to the film surface.

  According to such a configuration, the magnetization direction of the storage layer can be reversed more reliably even with a small current density.

  The fixed layer may be made of the ferromagnetic insulating layer, and the ferromagnetic insulating layer may have perpendicular magnetic anisotropy. Further, the fixed layer may include the ferromagnetic insulating layer and a perpendicular magnetization holding layer having a magnetization direction perpendicular to the film surface.

  According to such a configuration, a large MR ratio (magnetoresistance effect) can be obtained.

The ferromagnetic insulating layer may be made of a ferromagnetic oxide. Also, the ferromagnetic _{oxide, BaFe} 12 _{O 19,} or a _{Co X Fe 3-X O 4} , may satisfy the X is 0 <X <3.

  According to such a configuration, the thermal stability of the recording layer magnetization at the time of reading can be ensured, and at the same time, the magnetization direction of the storage layer can be reliably reversed even with a small current density.

The element resistance value may be 30 Ωμm ² or less.

  According to such a configuration, a magnetic tunnel junction element having a small magnetization reversal current density and a small element resistance value can be obtained.

  On the other hand, a magnetic random access memory according to the present invention includes the above-described magnetic tunnel junction element.

  According to such a configuration, a magnetic random access memory with low power consumption can be obtained.

  According to the present invention, it is possible to provide a magnetic tunnel junction element capable of reversing the magnetization direction of the storage layer even with a current having a small current density.

1 is a perspective view of a main part of an MRAM according to a first embodiment. 1 is a cross-sectional view of an MTJ element according to a first embodiment. It is a figure which shows a calculation model. It is a figure which shows a calculation model. The reversal current density with respect to the magnetic anisotropy constant. FIG. 3 is a cross-sectional view of an MTJ element according to a second embodiment. FIG. 6 is a cross-sectional view of an MTJ element according to a third embodiment. FIG. 6 is a cross-sectional view of an MTJ element according to a fourth embodiment.

  In order to solve the above-described problems, the present inventors have searched and calculated various materials in order to achieve applicability to a storage layer and a fixed layer in a magnetic tunnel junction element. Among them, the present inventors have found that when a ferromagnetic insulator is used as a material for a storage layer or a fixed layer, the temperature of the storage layer increases during magnetization reversal, and the magnetic anisotropy can decrease. Noticed. Furthermore, the present inventors have come up with the present invention through extensive research.

Embodiment 1 FIG.
The MTJ element according to the first embodiment will be described with reference to FIGS. 1 and 2. FIG. 1 is a cross-sectional view of a main part of the MRAM according to the first embodiment. FIG. 2 is a cross-sectional view of the MTJ element according to the first embodiment.

  As shown in FIG. 1, the memory cell 100 includes a semiconductor substrate 2, diffusion regions 3 and 4, a source line 6, and an MTJ (Magnetic Tunnel Junction) element 10. When a plurality of memory cells 100 are arranged in a matrix and connected to each other using a plurality of bit lines 1 and a plurality of word lines 8, a magnetic random access memory (MRAM) is formed. In this magnetic random access memory, data is written using the spin torque injection method.

  The semiconductor substrate 2 has diffusion regions 3 and 4 on its upper surface, and the diffusion region 3 is arranged at a predetermined interval from the diffusion region 4. The diffusion region 3 functions as a drain region, and the diffusion region 4 functions as a source region. Diffusion region 3 is connected to MTJ element 10 via contact plug 7.

  The bit line 1 is disposed above the semiconductor substrate 2 and connected to the MTJ element 10. The bit line 1 is connected to a write circuit (not shown) and a read circuit (not shown).

  Diffusion region 4 is connected to source line 6 through contact plug 5. The source line 6 is connected to a write circuit (not shown) and a read circuit (not shown).

  The word line 8 is disposed on the semiconductor substrate 2 via the gate insulating film 9 so as to be in contact with the diffusion region 3 and the diffusion region 4. The word line 8 and the gate insulating film 9 function as a selection transistor. The word line 8 is activated when supplied with a current from a circuit (not shown), and is turned on as a selection transistor.

  As shown in FIG. 2, the MTJ element 10 has a stacked structure in which a fixed layer 13, a tunnel barrier layer 12, and a storage layer 11 are stacked in this order.

  The fixed layer 13 is made of a ferromagnetic metal. Examples of the ferromagnetic metal include Fe, Ni, and CoFeB. The fixed layer 13 maintains a predetermined magnetization direction. This predetermined magnetization direction may be, for example, a direction perpendicular to the film surface or a longitudinal direction in the film surface. The fixed layer 13 may be referred to as a magnetization fixed layer, a magnetization fixed layer, a reference layer, a magnetization reference layer, a pinned layer, a reference layer, a magnetization reference layer, or the like.

The tunnel barrier layer 12 is made of an insulator. Examples of the insulator include MgO and Al ₂ O ₃ . The thickness of the tunnel barrier layer 12 may be appropriately changed according to the resistance value of the MTJ element 10. When the tunnel barrier layer 12 is made of MgO, it is preferable that at least one of the storage layer 11 and the fixed layer 13 is epitaxially grown in the tunnel barrier layer 12.

The memory layer 11 includes a ferromagnetic insulating layer made of a ferromagnetic insulator. Examples of the ferromagnetic insulator include a ferromagnetic oxide. As the ferromagnetic oxide, for _{example, Co X Fe 3-X O} 4 ( where, 0 <X <3) or _BaFe 12 such _{O 19} and the like. As such a ferromagnetic oxide, Co _X Fe _3-X O ₄ is particularly preferable because it has a magnetic anisotropy higher than 5 × 10 ⁵ J / m ³ (= 5 × 10 ⁶ erg / cc). . An example of Co _X Fe _3-X O ₄ is CoFe ₂ O ₄ (in this example, X = 1). Further, more preferably the X is greater than _{0.5, Co X Fe 3-X} O 4 is more preferable having a spinel crystal structure. Note that BaFe ₁₂ O ₁₉ preferably has a hexagonal crystal structure. The storage layer 11 has a variable magnetization direction. The memory layer 11 is magnetized perpendicularly to the film surface, for example, and faces upward or downward. The storage layer 11 may be referred to as a free layer, a magnetization free layer, a magnetization variable layer, or the like. The thickness of the memory layer 11 may be appropriately changed according to the target element resistance value RA of the MTJ element 10.

  Here, a data write operation to the memory cell 100 will be described. Among the plurality of memory cells 100, one memory cell 100 is selected as a data writing target. In the selected memory cell 100, the word line 8 is activated and turned on as a selection transistor. The memory cell 100 is supplied with a write current from a write circuit (not shown) based on data to be written. For example, when a current is passed through the bit line 1, it flows through the MTJ element 10. Then, since the memory layer 11 has insulating properties, the temperature of the memory layer 11 rises and the magnetic anisotropy of the memory layer 11 decreases. The state in which the magnetization direction of the storage layer 11 is easily reversed is reached. Also, spin due to current is injected into the storage layer 11, and the magnetization direction of the storage layer 11 changes to a predetermined direction. Thereby, for example, data corresponding to data “0” or data “1” can be written in the memory cell 100.

Subsequently, a data read operation of the memory cell 100 will be described. Among the plurality of memory cells 100, one memory cell 100 is selected as a target for reading data. In the selected memory cell 100, the word line 8 is activated and turned on as a selection transistor. The memory cell 100 is supplied with a read current from a read circuit (not shown). A read circuit (not shown) detects the resistance value based on the read current. Based on this resistance value, data stored in the memory cell 100 can be read. Further, when the recording layer 11 includes a ferromagnetic insulating layer made of a ferromagnetic insulating oxide having a high magnetic anisotropy such as Co _X Fe _{3 -X} O ₄ , the magnetization of the storage layer 11 has a high heat during reading. Has stability.

  Next, calculation results for the MRAM according to the first exemplary embodiment will be described with reference to FIGS. 3 and 4 are diagrams showing calculation models. FIG. 5 shows the reversal current density with respect to the magnetic anisotropy constant. Here, when the MRAM according to the first embodiment has a predetermined MR ratio, the current density at the time of magnetization reversal (at the time of write operation) was calculated.

  As shown in FIG. 3, calculations were performed using a tight binding model based on quantum mechanics. This tight binding model is one-dimensional and single orbital. Paramagnetic metal (NM) corresponds to the bit line 1 in the MTJ element 10 described above. Similarly, the ferromagnetic insulator (FI) corresponds to the memory layer 11, the paramagnetic insulator (NI) corresponds to the tunnel barrier layer 12, and the ferromagnetic metal (FM) corresponds to the fixed layer 13. .

ＭＲ［無次元］：ＭＲ比
Ｐ_Ｉ［無次元］：強磁性絶縁体（ＦＩ）におけるスピンフィルタ効果のスピン分極率
Ｐ_Ｄ［無次元］：強磁性金属（ＦＭ）における電子状態密度のスピン分極率

κ_＋［１／ｍ］：強磁性絶縁体（ＦＩ）における多数スピン電子の波動関数の減衰率
κ₋［１／ｍ］：強磁性絶縁体（ＦＩ）における少数スピン電子の波動関数の減衰率
Ｍ［ｍ］：強磁性絶縁体（ＦＩ）の膜厚

Ｄ_＋［１／Ｊ］：強磁性金属（ＦＭ）における多数スピン電子の電子状態密度
Ｄ₋［１／Ｊ］：強磁性金属（ＦＭ）における少数スピン電子の電子状態密度
ここで、Ｐ_Ｉが１であると、ＭＲ比が下記数式４の通りに記載される。

さらに、Ｐ_Ｄが０．５０（５０％）であると、ＭＲは１（１００％）に収束する。つまり、ＭＴＪ素子１０はＭＲ比１００％と十分に高いＭＲ比を有する。なお、常磁性絶縁体（ＮＩ）がＭｇＯからなるとともに、強磁性金属（ＦＭ）がＦｅからなる場合、常磁性絶縁体（ＮＩ）と強磁性金属（ＦＭ）との界面において、熱安定性Δの対称性を利用し得る。 First, MR ratio (MR) was calculated | required using following Numerical formula 1-3.

MR [dimensionless]: MR ratio _{P I} [dimensionless]: spin polarization _{P D} of the spin filter effect in the ferromagnetic insulator (FI) [dimensionless]: spin polarization of the electron density of states in the ferromagnetic metal (FM) rate

κ ₊ [1 / m]: Decay rate of wave function of majority spin electrons in ferromagnetic insulator (FI) κ ₋ [1 / m]: Decay rate of wave function of minority spin electrons in ferromagnetic insulator (FI) M [m]: Film thickness of the ferromagnetic insulator (FI)

D ₊ [1 / J]: ferromagnetic metal electron state density of majority spin electrons in _{(FM) D - [1 /} J]: electron state density of the minority spin electrons where the ferromagnetic metal (FM), is _{P I} When it is 1, the MR ratio is expressed as in the following Equation 4.

Further, when _{P D} is at 0.50 (50%), MR converges to 1 (100%). That is, the MTJ element 10 has a sufficiently high MR ratio of 100%. When the paramagnetic insulator (NI) is made of MgO and the ferromagnetic metal (FM) is made of Fe, the thermal stability Δ at the interface between the paramagnetic insulator (NI) and the ferromagnetic metal (FM). The symmetry of can be used.

By the way, it is known that when the MRAM is used, the temperature T of the MTJ element 10 increases by about 200 °. Next, the storage layer 11 by the temperature rise, assuming that the magnetic anisotropy constant K _u is reduced to a value that can operate as a MRAM, was calculated magnetization reversal current density. In this calculation, the model shown in FIG. 4 was used as a model of the ferromagnetic insulator (FI). The model used is a single layer and is a cylindrical body having a height h [nm] and a diameter D [nm]. In this model, the ferromagnetic insulator (FI) has an easy axis in the vertical direction (Easy Axis), and faces upward in the initial state. Further, the ferromagnetic insulator (FI) has a magnetic moment Ms [A / m] and a saturation magnetization A [J / m] per unit interface area. The height h, and a diameter D, a magnetic moment Ms, the saturation magnetization A per unit interfacial area, the damping constant a, the magnetic anisotropy constant K _u are respectively calculated by setting the following values.
h = 2nm
D = 20 nm
Ms = 600 × 10 ³ A / m (= 600 emu / cm ³ )
A = 1 × 10 ⁻¹¹ J / m (= 1 μerg / cm)
a = 0.01
K _u : determined by thermal stability Δ

Ｋ_ｕ［Ｊ／ｍ^３］：記憶層の磁気異方性定数
Ｖ［ｍ^３］：強磁性絶縁体（ＦＩ）の体積
ｋ_ｂ［Ｊ／Ｋ］：ボルツマン定数
Ｔ［Ｋ］：強磁性絶縁体（ＦＩ）の温度 In addition, thermal stability (DELTA) was calculated | required using following Numerical formula (5).

K _u [J / m ³ ]: Magnetic anisotropy constant V [m ³ ] of the storage layer: Volume k _b [J / K] of the ferromagnetic insulator (FI): Boltzmann constant T [K]: Ferromagnetic insulation Body (FI) temperature

Calculated result, as shown in FIG. 5, the magnetic anisotropy constant K _u is reduced, also reduces the magnetization reversal current density j _sw. Specifically, the magnetic anisotropy constant _{K u} about 0.56J ^{/ m} 3 (= about ^{5.6 × 10 6 erg / cm 3} ) from about 0.20J ^{/ m} 3 (= about 2.0 × 10 ^When reduced to ⁶ erg / cm ³ ), the magnetization reversal current density j _sw was reduced from 8.1 × 10 ¹⁰ A / m ² to 4.0 × 10 ¹⁰ A / m ² . That is, the magnetization reversal current density j _sw was reduced to 51%.

Ｃ［無次元］:透過係数
ｔ［Ｊ］:電子の飛び移り積分
κ_σ［１／ｍ］：強磁性絶縁体（ＦＭ）におけるσスピン電子の波動関数の減衰率
Ｎ［ｍ］：常磁性絶縁体（ＮＩ）の膜厚
Ｍ［ｍ］：強磁性絶縁体（ＦＩ）の膜厚
κ_０［１／ｍ］：常磁性絶縁体（ＮＩ）における電子の波動関数の減衰率
Ｄ_σ’［１／Ｊ］：強磁性金属（ＦＭ）におけるσ’スピン電子の電子状態密度
Ｄ_０［１／Ｊ］：常磁性金属（ＮＭ）における電子状態密度 By the way, when calculation based on classical electromagnetism is performed, it can be considered that current hardly flows to the MTJ element 10 at the time of data read operation of the memory cell 100. For this reason, it is considered that the MRAM including the MTJ element 10 does not operate. However, when a calculation based on quantum mechanics is performed, it can be proved that a current flows through the MTJ element 10 at the time of reading and the MRAM including the MTJ element 10 operates. Next, calculation based on this quantum mechanics will be described with reference to FIG. Further, the transmission coefficient C of the MTJ element was obtained using the following formula 6. Here, it was assumed that κ ₀ N, κ _σ M >> 1. It was confirmed that the transmission coefficient C of the MTJ element 10 exceeded a predetermined value when calculated by substituting a representative value into Equation 6. That is, it was confirmed that the MTJ element 10 in the memory cell 100 in the MRAM passes electrons through at least one of the fixed layer and the storage layer including the insulating layer at the time of reading. Therefore, since the MTJ element 10 can pass a current at the time of reading, it is considered that the MRAM including the MTJ element 10 can operate.

C [Dimensionless]: Transmission coefficient t [J]: Electron jump integral κ _σ [1 / m]: Decay rate of wave function of σ spin electrons in ferromagnetic insulator (FM) N [m]: Paramagnetism Insulator (NI) film thickness M [m]: Ferromagnetic insulator (FI) film thickness κ ₀ [1 / m]: Parametric insulator (NI) electron wave function attenuation rate D _{σ ′} [ 1 / J]: Electronic state density of σ ′ spin electrons in ferromagnetic metal (FM) D ₀ [1 / J]: Electronic state density in paramagnetic metal (NM)

  As described above, according to the MRAM according to the first embodiment, in the process of reversing the magnetization of the storage layer made of the ferromagnetic insulator, the temperature of the storage layer increases, the magnetic anisotropy constant of the storage layer decreases, and the magnetization The reversal current density decreased. That is, when a storage layer made of a ferromagnetic insulator is used, the magnetization reversal of the storage layer can be performed with a small current density. That is, an MTJ element using a storage layer made of a ferromagnetic insulator has a sufficiently high MR ratio (magnetoresistance effect) and a small magnetization reversal current density. Further, the power consumption of the MRAM having such an MTJ element is small.

Furthermore, the element resistance value RA of the MTJ element 10 is preferably 30 Ωμm ² or less. The element resistance value RA can be changed by changing the thicknesses of the tunnel barrier layer 12 and the memory layer 11. When the element resistance value RA of the MTJ element 10 is 30 Ωμm ² or less, the MTJ element has good reading performance. An MRAM having such an MTJ element is preferable because it has a large storage capacity.

  Further, according to the MRAM according to the first embodiment, a layer made of a ferromagnetic insulator can be used as a memory layer. That is, the MRAM according to the first embodiment can widely use various materials having perpendicular magnetic anisotropy.

Embodiment 2. FIG.
Next, the MTJ element according to the second embodiment will be described with reference to FIG. FIG. 6 is a cross-sectional view of an MTJ element according to the second embodiment. The MTJ element 210 according to the second embodiment has a configuration in which the storage layer and the fixed layer are replaced as compared with the MTJ element 10 according to the first embodiment (see FIG. 2). Description of common configurations will be omitted, and different configurations will be described.

  As shown in FIG. 6, the MTJ element 210 has a laminated structure in which the fixed layer 23, the tunnel barrier layer 12, and the memory layer 21 are laminated in this order.

  Similar to the fixed layer 13 (see FIG. 2), the memory layer 21 is made of a ferromagnetic metal. Examples of the ferromagnetic metal include Fe and CoFeB. The storage layer 21 has a variable magnetization direction. The storage layer 21 is magnetized perpendicularly to the film surface, for example.

The fixed layer 23 includes a ferromagnetic insulating layer made of the same type of ferromagnetic insulator as the storage layer 11 (see FIG. 2). The fixed layer 23 maintains the magnetization direction perpendicular to the film surface. The thickness of the fixed layer 23 may be appropriately changed according to the resistance value of the MTJ element 210.
In the fixed layer 23, magnetic splitting occurs in the conduction band, and the tunnel probability varies depending on the direction of spin of conduction electrons. For this reason, a spin filter effect occurs in which more electrons having spins parallel (or antiparallel) to the magnetization of the fixed layer 23 pass through the fixed layer 23. The spin polarizability of the spin filter effect can be changed by changing the thickness of the fixed layer 23.

Here, the reading operation will be described. A read current flows from the fixed layer 23 to the storage layer 21. More electrons having spins parallel to (or antiparallel to) the magnetization of the fixed layer 23 flow through the fixed layer 23. That is, the spin filter effect is exhibited, and the MR ratio increases as the spin polarizability increases. Since the MR ratio increases, the signal voltage from the MTJ element 210 increases, and the MTJ element 210 has excellent read performance. An MRAM using the MTJ element 210 has a large storage capacity. Further, when the fixed layer 23 includes a ferromagnetic insulating layer made of a ferromagnetic oxide having a high magnetic anisotropy such as Co _X Fe _{3 -X} O ₄ , the magnetization of the storage layer 21 has a high thermal stability during reading. Have sex.

  Next, the write operation will be described. For example, when a write current is passed through the bit line 1, it flows through the MTJ element 210. Then, since the fixed layer 23 has insulating properties, the temperature of the fixed layer 23 rises, and the temperature of the memory layer 21 can also rise due to this temperature rise. The magnetic anisotropy of the storage layer 21 can be reduced, and the magnetization direction of the storage layer 21 is easily reversed. In addition, the spin torque is injected into the storage layer 21 by the current, and the magnetization direction of the storage layer 21 changes to a predetermined direction. Thereby, for example, data corresponding to data “0” or data “1” can be written in the memory cell 100. Similar to the MTJ element 10, the MTJ element 210 can reverse the magnetization direction with a small current density. Further, the power consumption of the MRAM having such an MTJ element is small.

  As described above, the MTJ element according to the second embodiment can have a small magnetization reversal current density. It has a high MR ratio and excellent read performance. In addition, an MRAM having low power consumption and a large storage capacity can be formed.

Embodiment 3 FIG.
Next, the MTJ element according to the third embodiment will be described with reference to FIG. FIG. 7 is a cross-sectional view of the MTJ element according to the third embodiment. Compared with the MTJ element 210 according to the second embodiment (see FIG. 6), the MTJ element according to the third embodiment has a common configuration except for the fixed layer. Description of common configurations will be omitted, and different configurations will be described.

  As shown in FIG. 7, the MTJ element 310 has a stacked structure in which the fixed layer 33, the tunnel barrier layer 12, and the storage layer 21 are stacked in this order. The fixed layer 33 has a structure in which a perpendicular magnetization holding layer 333, a magnetic coupling control layer 332, and a ferromagnetic layer 331 are stacked in this order.

The ferromagnetic layer 331 includes a ferromagnetic insulating layer made of the same type of ferromagnetic insulator as the storage layer 11 (see FIG. 2). The ferromagnetic layer 331 has a perpendicular magnetic anisotropy constant K _u1 . Unlike the ferromagnetic insulator that forms the fixed layer 23 (see FIG. 6), this ferromagnetic insulator does not have to maintain the magnetization direction perpendicular to the film surface.

  The magnetic coupling control layer 332 is made of a material that affects the magnetic coupling between the ferromagnetic layer 331 and the perpendicular magnetization holding layer 333. Examples of such a material include Rh, Pd, Pt, Ru, and MgO. The thickness of the magnetic coupling control layer 332 is 2 nm or less. Its thickness may vary as needed. It is preferable to change the thickness of the magnetic coupling control layer 332 by adjusting factors such as MR ratio (resistance change rate), thermal stability, recording current, and magnetization reversal speed.

The perpendicular magnetization holding layer 333 is made of a material having a perpendicular magnetic anisotropy constant _Ku2 . Perpendicular magnetic anisotropy constant _{K u2} is higher compared to the perpendicular magnetic anisotropy constant _{K u1} ferromagnetic layer 331. Examples of such a material include L10 type FePd or FePt.

  In the MTJ element 310 according to the third embodiment described above, the fixed layer 33 includes the magnetic coupling control layer 332, but the magnetic coupling control layer 332 may be omitted from the fixed layer 33. That is, the MTJ element 310 may include a fixed layer having a structure in which the perpendicular magnetization holding layer 333 and the ferromagnetic layer 331 are stacked in this order instead of the fixed layer 33.

Here, the reading operation will be described. A read current flows from the fixed layer 33 to the storage layer 21. More electrons having spins parallel to (or antiparallel to) the magnetization of the fixed layer 33 flow through the fixed layer 33. That is, the spin filter effect is exhibited, and the MR ratio increases as the spin polarizability increases. Since the MR ratio increases, the signal voltage from the MTJ element 310 increases, and the MTJ element 310 has excellent read performance. An MRAM using the MTJ element 310 has a large storage capacity. Further, when the ferromagnetic layer 331 includes a ferromagnetic insulating layer made of a ferromagnetic oxide having a high magnetic anisotropy such as Co _X Fe _{3 -X} O ₄ , the magnetization of the storage layer 21 has a high heat during reading. Has stability.

  A write operation will be described. For example, when a write current is passed through the bit line 1, it flows through the MTJ element 310. Then, since the fixed layer 33 has insulating properties, the temperature of the fixed layer 33 rises, and the temperature of the memory layer 21 can also rise due to this temperature rise. The magnetic anisotropy of the storage layer 21 can be reduced, and the magnetization direction of the storage layer 21 is easily reversed. In addition, the spin torque is injected into the storage layer 21 by the current, and the magnetization direction of the storage layer 21 changes to a predetermined direction. Thereby, for example, data corresponding to data “0” or data “1” can be written in the memory cell 100. Similar to the MTJ element 210, the MTJ element 310 can reverse the magnetization direction with a small current density.

  As described above, the MTJ element according to the third embodiment can have a small magnetization reversal current density, similarly to the MTJ element according to the second embodiment. It has a high MR ratio and excellent read performance. In addition, an MRAM having a large storage capacity can be formed.

  Furthermore, according to the MTJ element according to the third embodiment, by adjusting the thickness of the magnetic coupling control layer 332, factors such as MR ratio (resistance change rate), thermal stability, recording current, and magnetization reversal speed are adjusted. can do.

Embodiment 4 FIG.
Next, an MTJ element according to the fourth embodiment will be described with reference to FIG. FIG. 8 is a cross-sectional view of an MTJ element according to the fourth embodiment. Compared with the MTJ element 10 according to the first embodiment (see FIG. 2), the MTJ element according to the fourth embodiment has a common configuration except for the fixed layer. Description of common configurations will be omitted, and different configurations will be described.

  As shown in FIG. 8, the MTJ element 410 has a stacked structure in which the memory layer 11, the tunnel barrier layer 12, and the fixed layer 33 are stacked in this order. The fixed layer 33 is common to the configuration of the MTJ element 310 (see FIG. 7) according to the third embodiment.

  Here, a data write operation will be described. A memory cell using the MTJ element 410 is supplied with a write current from a write circuit (not shown) based on data to be written. For example, when a current is passed through the bit line 1, it flows through the MTJ element 410. Then, similarly to the MTJ element 10 (see FIG. 2) according to the first embodiment, the magnetization direction of the storage layer 11 changes to a predetermined direction. Thereby, for example, data corresponding to data “0” or data “1” can be written in the memory cell 100. In the MTJ element 410, it is considered that the magnetization reversal current density is small as in the MTJ element 10 according to the first embodiment. An MRAM having such an MTJ element has low power consumption.

A read operation will be described. A read current flows from the fixed layer 33 to the storage layer 11. More electrons having spins parallel to (or antiparallel to) the magnetization of the fixed layer 33 flow through the fixed layer 33. That is, the spin filter effect is exhibited, and the MR ratio increases as the spin polarizability increases. Since the MR ratio increases, the signal voltage from the MTJ element 410 increases, and the MTJ element 410 has excellent read performance. An MRAM using the MTJ element 410 has a large storage capacity. Further, when the ferromagnetic layer 331 includes a ferromagnetic insulating layer made of a ferromagnetic oxide having a high magnetic anisotropy such as Co _X Fe _3-X O ₄ , the magnetization of the storage layer 11 has a high heat during reading. Has stability.

  As described above, according to the MTJ element according to the fourth embodiment, magnetization can be reversed even with a current having a small current density, and since it has a high MR ratio, it has excellent read performance. Furthermore, an MRAM having such an MTJ element has low power consumption and a large storage capacity.

  Note that the present invention is not limited to the above-described embodiment, and can be changed as appropriate without departing from the spirit of the present invention. For example, the MTJ element according to the first to fourth embodiments may include a storage layer having a stacked structure in which a perpendicular magnetization holding layer and a ferromagnetic layer are stacked instead of the storage layer. Further, the MTJ element 210 (see FIG. 6) according to the second embodiment may include a memory layer made of a ferromagnetic insulator instead of the memory layer 21.

1 Bit line 2 Semiconductor substrate 3, 4 Diffusion region 5, 7 Contact plug 6 Source line 8 Word line 9 Gate insulating film 10, 210, 310, 410 MTJ element 11, 21 Storage layer 12 Tunnel barrier layer 13, 23, 33 Fixed Layer 100 Memory cell 331 Ferromagnetic layer 332 Magnetic coupling control layer 333 Perpendicular magnetization holding layer

Claims (7)

A storage layer having a variable magnetization direction, a fixed layer that maintains a predetermined magnetization direction, and a tunnel barrier layer,
A magnetic tunnel junction element that performs writing using a spin torque injection method ,
The storage layer comprises a ferromagnetic insulating layer;
The ferromagnetic insulating layer has perpendicular magnetic anisotropy;
Magnetic tunnel junction element. A storage layer having a variable magnetization direction, a fixed layer that maintains a predetermined magnetization direction, and a tunnel barrier layer,
A magnetic tunnel junction element that performs writing using a spin torque injection method,
The storage layer is
Strength and magnetic insulating layer,
A perpendicular magnetization holding layer having a magnetization direction perpendicular to the film surface ,
Magnetic tunnel junction element. A storage layer having a variable magnetization direction, a fixed layer that maintains a predetermined magnetization direction, and a tunnel barrier layer,
A magnetic tunnel junction element that performs writing using a spin torque injection method,
The fixed layer is
Strength and magnetic insulating layer,
A perpendicular magnetization holding layer having a magnetization direction perpendicular to the film surface ,
Magnetic tunnel junction element. The magnetic tunnel junction device as set forth in the ferromagnetic insulating layer is any one of claims 1-3, characterized by comprising a ferromagnetic oxide. The ferromagnetic _{oxide, BaFe} 12 _{O 19,} or a _Co X Fe _{3-X O 4,} the magnetic tunnel junction device as set forth in claim 4, characterized in that satisfy X is 0 <X <3 . A storage layer having a variable magnetization direction, a fixed layer that maintains a predetermined magnetization direction, and a tunnel barrier layer,
A magnetic tunnel junction element that performs writing using a spin torque injection method,
The element resistance value is 30 Ωμm ² or less .
Magnetic tunnel junction element. The magnetic random access memory provided with the magnetic tunnel junction element as described in any one of Claims 1-6 .

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