US20180151209A1 - Magnetic memory device and method of writing magnetic memory device - Google Patents

Magnetic memory device and method of writing magnetic memory device Download PDF

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Publication number
US20180151209A1
US20180151209A1 US15/659,283 US201715659283A US2018151209A1 US 20180151209 A1 US20180151209 A1 US 20180151209A1 US 201715659283 A US201715659283 A US 201715659283A US 2018151209 A1 US2018151209 A1 US 2018151209A1
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Prior art keywords
spin
free layer
orbit
current
magnetic
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Woo Chang Lim
Kyung-Jin Lee
Gyungchoon GO
Seung-jae Lee
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Samsung Electronics Co Ltd
Korea University Research and Business Foundation
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Korea University Research and Business Foundation
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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
    • 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
    • G11C11/14—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
    • 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
    • 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
    • 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
    • G11C11/1693—Timing circuits or methods
    • H01L27/222—
    • H01L43/08—
    • 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
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N50/00—Galvanomagnetic devices
    • H10N50/10—Magnetoresistive devices
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N50/00—Galvanomagnetic devices
    • H10N50/80—Constructional details

Definitions

  • Embodiments of relate to a magnetic memory device and, more particularly, to a magnetic memory device using spin-orbit torque.
  • High-speed and low-voltage memory devices have been demanded to realize high-speed and low-power electronic devices including memory devices.
  • a magnetic memory device has been studied as a memory device satisfying these demands.
  • the magnetic memory device has been spotlighted as a next-generation memory device because of its high-speed operation characteristic and/or non-volatile characteristic.
  • the magnetic memory device uses a magnetic tunnel junction (MTJ).
  • the magnetic tunnel junction may include two magnetic layers and a tunnel barrier layer disposed between the two magnetic layers, and a resistance of the magnetic tunnel junction may be changed according to relative directions of magnetic moments of the two magnetic layers.
  • the magnetic tunnel junction may have a high resistance when the directions of the magnetic moments of the two magnetic layers are anti-parallel to each other. On the contrary, the magnetic tunnel junction may have a low resistance when the directions of the magnetic moments of the two magnetic layers are parallel to each other.
  • the magnetic memory device may write/sense data by using a difference between the resistances of the magnetic tunnel junction.
  • a method of writing a magnetic memory device may include applying a first spin-orbit current having a frequency decreasing with time to a first conductive line in the magnetic memory device.
  • the magnetic memory device may further include a magnetic tunnel junction including a free layer, a reference layer, and a tunnel barrier layer between the free layer and the reference layer.
  • the first conductive line may be adjacent to the free layer.
  • a method of writing a magnetic memory device may include applying a first spin-orbit current to a first conductive line in the magnetic memory device.
  • the magnetic memory device may further include a magnetic tunnel junction including a free layer, a reference layer, and a tunnel barrier layer between the free layer and the reference layer.
  • the first conductive line may be adjacent to the free layer.
  • a magnetic memory device may include a magnetic tunnel junction including a free layer, a reference layer, and a tunnel barrier layer between the free layer and the reference layer, and a first conductive line adjacent to the free layer.
  • a first spin-orbit current having a frequency decreasing with time may flow through the first conductive line. Applying the first spin-orbit current may generate at least two resonances at which a frequency of the first spin-orbit current coincides with a natural frequency of a magnetic moment of the free layer,
  • a method of writing a magnetic memory device including a magnetic tunnel junction having a free layer, a reference layer, and a tunnel barrier layer between the free layer and the reference layer, and a first conductive line adjacent to the free layer.
  • the method may include applying a first spin-orbit current including initially applying the first spin-orbit current having an initial frequency at a first time to the first conductive line and subsequently applying the first spin-orbit current having a subsequent frequency, less than the initial frequency, at a second time to the first conductive line, the second time after the first time.
  • FIG. 1 illustrates a schematic view of a magnetic memory device according to some embodiments.
  • FIG. 2 illustrates a graph schematically of a spin-orbit current according to some embodiments over time.
  • FIG. 3 schematically illustrates a spin of charge carriers provided into a free layer when the spin-orbit current according to some embodiments flows.
  • FIGS. 4A and 4B schematically illustrate precessional motions of a magnetic moment of a free layer when a spin-orbit current according to some flows.
  • FIG. 5 illustrates a graph of a frequency of a spin-orbit current and a natural frequency of a precessing magnetic moment of a free layer.
  • FIG. 6 illustrates a schematic view of a magnetic memory device according to some embodiments.
  • FIG. 7A illustrates a graph schematically of a first spin-orbit current according to some embodiments over time.
  • FIG. 7B illustrates a graph schematically of a second spin-orbit current according to some embodiments over time.
  • FIG. 8 schematically illustrates a spin of charge carriers provided into a free layer when the first and second spin-orbit currents according to some embodiments flow.
  • FIG. 9A illustrates a graph of a switching critical current when a direct current is applied to a conductive line adjacent to a free layer.
  • FIGS. 9B and 9C illustrate graphs of a switching critical current when a current having an alternating current (AC) form according to some embodiments is applied to a conductive line adjacent to a free layer.
  • AC alternating current
  • a component when a component is in-plane”, it may substantially exist in a plane (or surface) of a layer or a line or may be parallel to the plane (or surface). Furthermore, the term en a component is in-plane”, it may substantially exist in a plane (or surface) of a la plane (or surface) of a layer or a line.
  • FIG. 1 is a schematic view illustrating a magnetic memory device according to some embodiments.
  • FIG. 1 is provided only for understanding of some embodiments, and sizes of components illustrated in FIG. 1 are exaggerated for clarity.
  • Some components of a magnetic memory device e.g., bit lines, word lines, row selectors, and column selectors, are omitted in FIG. 1 for simplicity.
  • a magnetic memory device 100 may include a magnetic tunnel junction MTJ and a conductive line CL.
  • the magnetic tunnel junction MTJ may include a reference layer RL, a free layer FL, and a tunnel barrier layer TBL between the reference and free layers RL and FL.
  • the reference layer RL may have a magnetic moment fixed during a writing operation of the magnetic memory device 100 .
  • the magnetic moment of the reference layer RL may not be switched by a spin-orbit torque generated by a spin-orbit current J SO flowing through the conductive line CL and/or a spin-transfer torque generated by a spin-transfer current J STT passing through the magnetic tunnel junction MTJ.
  • the free layer FL may have a switchable magnetic moment during the writing operation of the magnetic memory device 100 .
  • the free layer FL may have the magnetic moment which can be switched to be parallel or anti-parallel to the magnetic moment of the reference layer RL.
  • the magnetic moment of the free layer FL may be switched using at least the spin-orbit torque generated by the spin-orbit current J SO flowing through the conductive line CL.
  • the magnetic moment of the free layer FL may be switched using only the spin-orbit torque generated by the spin-orbit current J SO .
  • the magnetic moment of the free layer FL may be switched using the spin-orbit torque and the spin-transfer torque generated by the spin-transfer current J STT passing through the magnetic tunnel junction MTJ.
  • the spin-orbit current J SO , the spin-orbit torque, the spin-transfer current J STT , and the spin-transfer torque will be described below in more detail.
  • Each of the reference layer RL and the free layer FL may have an easy axis that is substantially perpendicular to a planar surface thereof.
  • the surface of the reference layer RL may be parallel to an xy-plane and the easy axis of the reference layer RL may be substantially parallel to a z-axis.
  • the surface of the free layer FL may be parallel to the xy-plane and the easy axis of the free layer FL may be substantially parallel to the z-axis.
  • embodiments are not limited thereto.
  • each of the reference layer RL and the free layer FL may include at least one of a material having a L1 0 crystal structure, a material having a hexagonal close packed (HCP) lattice, or an amorphous rare-earth transition metal (RE-TM) alloy.
  • each of the reference layer RL and the free layer FL may include at least one of the materials having the L1 0 crystal structure, such as Fe 50 Pt 50 , Fe 50 Pd 50 , Co 50 Pt 50 , Co 50 Pd 50 , and Fe 50 Ni 50 .
  • each of the reference layer RL and the free layer FL may include at least one of the materials having the HCP lattice, such as a cobalt-platinum (CoPt) disordered alloy having a platinum (Pt) content of 10 at. % to 45 at. %, and a Co 3 Pt ordered alloy.
  • each of the reference layer RL and the free layer FL may include the amorphous RE-TM alloy including at least one of a rare-earth element group of terbium (Tb), dysprosium (Dy), and gadolinium (Gd), and at least one selected from a transition metal element group of iron (Fe), cobalt (Co) and nickel (Ni).
  • each of the reference layer RL and the free layer FL may include a material having interface perpendicular magnetic anisotropy.
  • the term rinterface perpendicular magnetic anisotropy” meansace p a phenomenon that a magnetic layer having an intrinsic horizontal magnetization property has a perpendicular magnetization direction by an influence of an interface between the magnetic layer and another layer adjacent to the magnetic layer.
  • each of the reference layer RL and the free layer FL may include at least one of Co, Fe, or Ni.
  • each of the reference layer RL and the free layer FL may further include at least one selected from non-magnetic materials including boron (B), zinc (Zn), aluminum (Al), titanium (Ti), ruthenium (Ru), tantalum (Ta), silicon (Si), silver (Ag), gold (Au), copper (Cu), carbon (C), and nitrogen (N).
  • non-magnetic materials including boron (B), zinc (Zn), aluminum (Al), titanium (Ti), ruthenium (Ru), tantalum (Ta), silicon (Si), silver (Ag), gold (Au), copper (Cu), carbon (C), and nitrogen (N).
  • each of the reference layer RL and the free layer FL may include CoFe or NiFe and may further include B.
  • each of the reference layer RL and the free layer FL may further include at least one of Ti, Al, Si, magnesium (Mg), or Ta.
  • the reference layer RL may have a single-layered structure, as illustrated in FIG. 1 .
  • the reference layer RL may have a synthetic anti-ferromagnetic structure including ferromagnetic layers separated from each other by a non-magnetic layer(s).
  • the tunnel barrier layer TBL may be provided between the reference layer RL and the free layer FL.
  • the tunnel barrier layer TBL may include at least one of magnesium oxide (MgO), titanium oxide (TiO), aluminum oxide (AlO), magnesium-zinc oxide (MgZnO), magnesium-boron oxide (MgBO), titanium nitride (TiN), or vanadium nitride (VN).
  • the tunnel barrier layer TBL may include crystalline magnesium oxide (MgO).
  • the conductive line CL may be provided to be adjacent to the free layer FL of the magnetic tunnel junction MTJ.
  • the conductive line CL may have a line shape extending in a first direction, e.g., an x-direction, and the magnetic tunnel junction MTJ may be on a first surface, e.g., a planar surface, of the conductive line CL.
  • the free layer FL may be between the tunnel barrier layer TBL and the first surface of the conductive line CL.
  • the conductive line CL may include a material showing a strong spin-orbit interaction.
  • the conductive line CL may include at least one of copper (Cu), tantalum (Ta), platinum (Pt), tungsten (W), gadolinium (Gd), bismuth (Bi), or iridium (Ir).
  • the magnetic memory device 100 may be configured such that the spin-orbit current J SO flows through the conductive line CL.
  • the spin-orbit current J SO may be a current flowing in a plane of the conductive line CL.
  • charge carriers having polarized spins may be provided into the free layer FL.
  • the spin-orbit current J SO flows in the x-direction or a ⁇ x-direction
  • the charge carriers having the spins polarized in a y-direction or a ⁇ y-direction may be provided into the free layer FL. This may be due to a spin-orbit interaction (e.g., a spin hole effect) occurring in the conductive line CL.
  • the charge carriers having these polarized spins may apply torque to the magnetic moment of the free layer FL.
  • the torque applied to the magnetic moment of the free layer FL due to the spin-orbit current J SO is defined as the spin-orbit torque.
  • the magnetic memory device 100 may be configured to flow the spin-transfer current J STT passing through the magnetic tunnel junction MTJ.
  • the spin-transfer current J STT flows through the magnetic tunnel junction MTJ
  • charge carriers having spins polarized in a direction parallel or anti-parallel to the magnetic moment of the reference layer RL may be provided into the free layer FL.
  • the reference layer RL has the magnetic moment in a z-direction or a ⁇ z-direction
  • the charge carriers having the spins polarized in the z-direction or the ⁇ z-direction may be provided into the free layer FL when the spin-transfer current J STT flows.
  • the charge carriers having these polarized spins may apply torque to the magnetic moment of the free layer FL.
  • the torque applied to the magnetic moment of the free layer FL due to the spin-transfer current J STT is defined as the spin-transfer torque.
  • FIG. 2 is a graph schematically illustrating a spin-orbit current according to some embodiments over time.
  • FIG. 3 schematically illustrates a spin of charge carriers provided into a free layer when the spin-orbit current according to some embodiments flows.
  • FIG. 3 illustrates the spin of the charge carriers provided into the free layer when the spin-orbit current oscillating in the x-direction or the ⁇ x-direction flows in the conductive line CL.
  • FIGS. 4A and 4B schematically illustrate precessional motions of a magnetic moment of a free layer when a spin-orbit current according to some embodiments flows.
  • FIG. 5 is a graph schematically illustrating a frequency of a spin-orbit current and a natural frequency of a precessing magnetic moment of a free layer.
  • the spin-orbit current J SO may be an alternating current (AC) of which a frequency decreases with time (e.g., in the order of 1/T 1 , 1/T 2 , 1/T 3 , 1/T 4 , . . . ).
  • the spin-orbit current J SO may be the alternating current (e.g., having a sine waveform) which oscillates in the x-direction or the ⁇ x-direction and of which the frequency gradually decreases with time (e.g., in the order of 1/T 1 , 1/T 2 , 1/T 3 , 1/T 4 , . . . ).
  • an initial or first frequency applied at an initial time, first time, or start time is greater than a subsequent frequency or frequencies applied subsequently, e.g., a second frequency applies at a second time.
  • the spins SP 1 of the charge carriers provided into the free layer FL may oscillate in the y-direction or the ⁇ y-direction as illustrated in FIG. 3 and frequencies of the spins SP 1 may be equal to the frequency of the spin-orbit current J SO .
  • the frequencies of the spins SP 1 of the charge carriers provided into the free layer FL may gradually decrease with time.
  • the spin-orbit torque due to the spin-orbit current J SO described above may be applied to the magnetic moment M FL of the free layer FL.
  • the magnetic moment M FL of the free layer FL may precess around the easy axis (i.e., the z-axis) of the free layer FL.
  • a rotation angle s of the precessional motion i.e., an angle between the easy axis and the magnetic moment M FL of the free layer FL
  • a z-component m, of the magnetic moment M FL of the free layer FL may decrease rapidly.
  • the precessional motion of the magnetic moment M FL of the free layer FL may be changed from a state illustrated in FIG. 4A to a state illustrated in FIG. 4B .
  • the natural frequency of the magnetic moment M FL of the free layer FL may be represented by the following equation 1.
  • layer FL may be represented by the following precessing magnetic moment M FL of the free layer FL, ent M represented by the following equation 1K eff ′′ff the free layer FL, ent M represented by the following equation 1.
  • the natural frequency lowing equation 1 layer F FL of the free layer FL is proportional to the z-component m z of the magnetic moment M FL of the free layer FL.
  • the natural frequency lustrated in FIG. 4B .que M FL is also reduced.
  • the natural frequency of the magnetic moment M FL of the free layer FL may not coincide with the frequencies of the spins SP 1 of the charge carriers provided into the free layer FL (i.e., the frequency of the spin-orbit current J SO .
  • the resonance may be broken.
  • the resonance does not occur again between the magnetic moment M FL of the free layer FL and the spins SP 1 of the charge carriers provided into the free layer FL after the resonance therebetween is broken.
  • the resonance may repeatedly occur at least two times between the magnetic moment M FL of the free layer FL and the spins SP 1 of the charge carriers provided into the free layer FL, e.g., at least two resonances may be realized.
  • the spin-orbit current J SO may have the frequency which decreases with time, as described above.
  • the frequencies of the spins SP 1 of the charge carriers provided into the free layer FL may also decrease to generate the resonance again.
  • the resonance may repeatedly occur and be broken between the magnetic moment M FL of the free layer FL and the spins SP 1 of the charge carriers provided into the free layer FL.
  • the resonance between the magnetic moment M FL of the free layer FL and the spins SP 1 of the charge carriers provided into the free layer FL may repeatedly occur and be broken.
  • the natural frequency of the magnetic moment M FL of the free layer FL may be smaller than the frequencies of the spins SP 1 of the charge carriers provided into the free layer FL (i.e., the frequency of the spin-orbit current J SO ) between the resonances between the magnetic moment M FL of the free layer FL and the spins SP 1 of the charge carriers provided into the free layer FL.
  • an initial frequency of the spin-orbit current J SO e.g., when the spin-orbit current starts, may be equal to or greater than an initial natural frequency of the magnetic moment M FL of the free layer FL when the spin-orbit current J SO is initially applied.
  • the writing operation of the magnetic memory device 100 may be performed using at least the spin-orbit torque due to the spin-orbit current J SO flowing through the conductive line CL.
  • the magnetic moment M FL of the free layer FL may be switched using at least the spin-orbit torque due to the spin-orbit current J SO flowing through the conductive line CL.
  • the magnetic moment M FL of the free layer FL may be switched using only the spin-orbit torque due to the spin-orbit current J SO .
  • a critical magnitude of the spin-orbit current J SO required to switch the magnetic moment M FL of the free layer FL may be relatively small, e.g., may be less than that for which only a single resonance occurs.
  • the magnetic moment M FL of the free layer FL may be switched using both the spin-orbit torque due to the spin-orbit current J SO and the spin-transfer torque due to the spin-transfer current J STT .
  • the spin-orbit current J SO and the spin-transfer current J STT may be applied at the same time for at least a certain, e.g., predetermined, period of time.
  • the spin-orbit current J SO may be applied prior to the spin-transfer current J STT .
  • embodiments are not limited thereto.
  • the strength of the spin-orbit torque applied to the magnetic moment M FL of the free layer FL may increase as the magnetic moment M FL of the free layer FL becomes closer to the z-direction or the ⁇ z-direction.
  • the strength of the spin-transfer torque applied to the magnetic moment M FL of the free layer FL may increase as the magnetic moment M FL of the free layer FL becomes closer to the xy plane.
  • the spin-orbit torque may be more efficient or effective to switch the magnetic moment M FL of the free layer FL when the magnetic moment M FL of the free layer FL is closer to the z-direction or the ⁇ z-direction, while the spin-transfer torque may be more efficient or effective to switch the magnetic moment M FL of the free layer FL when the magnetic moment M FL of the free layer FL is closer to the xy plane.
  • the spin-orbit torque may act as main switching torque to tilt the magnetic moment M FL of the free layer FL toward the xy plane.
  • the spin-orbit current J SO having a relatively small magnitude.
  • FIG. 6 is a schematic view illustrating a magnetic memory device according to some embodiments.
  • FIG. 6 is provided only for understanding of some embodiments, and sizes of components illustrated in FIG. 6 are exaggerated for clarity.
  • Some components of a magnetic memory device e.g., bit lines, word lines, row selectors, and column selectors, are omitted in FIG. 1 for simplicity.
  • a magnetic memory device 101 may include a magnetic tunnel junction MTJ, a first conductive line CL 1 , and a second conductive line CL 2 .
  • the magnetic tunnel junction MTJ may be the substantially same as described with reference to FIG. 1 . Thus, detailed descriptions to the magnetic tunnel junction MTJ will be omitted.
  • the first conductive line CL 1 may have a line shape extending in an x-direction.
  • the second conductive line CL 2 may have a line shape intersecting the first conductive line CL 1 .
  • the second conductive line CL 2 may have a line shape extending in a y-direction.
  • the first conductive line CL 1 and the second conductive line CL 2 may cross each other at one portion and may be connected to each other.
  • the first conductive line CL 1 and the second conductive line CL 2 may be disposed in the same plane (i.e., an xy plane).
  • the magnetic tunnel junction MTJ may be on the intersecting portion of the first and second conductive lines CL 1 and CL 2 .
  • the free layer FL of the magnetic tunnel junction MTJ may be adjacent to the crossing point of the first and second conductive lines CL 1 and CL 2 .
  • the free layer FL may be between the tunnel barrier layer TBL and the intersecting portion of the first and second conductive lines CL 1 and CL 2 .
  • Each of the first and second conductive lines CL 1 and CL 2 may include a material showing a strong spin-orbit interaction.
  • each of the first and second conductive lines CL 1 and CL 2 may include at least one of Cu, Ta, Pt, W, Gd, Bi, or Ir.
  • the magnetic memory device 101 may be configured to flow a first spin-orbit current J SO1 in the first conductive line CL 1 and to flow a second spin-orbit current J SO2 in the second conductive line CL 2 .
  • the first spin-orbit current J SO1 may be a current flowing in a plane of the first conductive line CL 1
  • the second spin-orbit current J SO2 may be a current flowing in a plane of the second conductive line CL 2 .
  • first spin-orbit current J SO1 flows in the x-direction or a ⁇ x-direction
  • charge carriers having spins polarized in the y-direction or a ⁇ y-direction may be provided into the free layer FL.
  • second spin-orbit current J SO2 flows in the y-direction or the ⁇ y-direction
  • charge carriers having spins polarized in the x-direction or the ⁇ x-direction may be provided into the free layer FL. This may be due to a spin-orbit interaction (e.g., a spin hole effect) occurring in the conductive line CL 1 or CL 2 .
  • the charge carriers having these polarized spins may apply torque to the magnetic moment of the free layer FL.
  • the magnetic memory device 101 may be configured to flow the spin-transfer current J STT passing through the magnetic tunnel junction MTJ.
  • the spin-transfer current J STT flows through the magnetic tunnel junction MTJ
  • charge carriers having spins polarized in a direction parallel or anti-parallel to the magnetic moment of the reference layer RL may be provided into the free layer FL.
  • the charge carriers having the spins polarized in the z-direction or the ⁇ z-direction may be provided into the free layer FL when the spin-transfer current J STT flows.
  • the charge carriers having these polarized spins may apply torque to the magnetic moment of the free layer FL.
  • FIG. 7A is a graph schematically illustrating a first spin-orbit current according to some embodiments over time.
  • FIG. 7B is a graph schematically illustrating a second spin-orbit current according to some embodiments over time.
  • FIG. 8 schematically illustrates a spin of charge carriers provided into a free layer when the first and second spin-orbit currents according to some embodiments flow.
  • FIG. 8 illustrates the spin of the charge carriers provided into the free layer when the first spin-orbit current oscillating in the x-direction or the ⁇ x-direction and the second spin-orbit current oscillating in the y-direction or the ⁇ y-direction flow.
  • each of the first and second spin-orbit currents J SO1 and J SO2 may be an alternating current (AC) of which a frequency decreases with time (e.g., in the order of 1/T 1 , 1/T 2 , 1/T 3 , 1/T 4 , . . . ).
  • AC alternating current
  • the first spin-orbit current J SO1 may be the alternating current (e.g., having a sine waveform) which oscillates in the x-direction or the ⁇ x-direction and of which the frequency gradually decreases with time (e.g., in the order of 1/T 1 , 1/T 2 , 1/T 3 , 1/T 4 , . . . ).
  • the second spin-orbit current J SO2 may be the alternating current (e.g., having a cosine waveform) which oscillates in the y-direction or the ⁇ y-direction and of which the frequency gradually decreases with time (e.g., in the order of 1/T 1 , 1/T 2 , 1/T 3 , 1/T 4 , . . . ).
  • the frequency of the first spin-orbit current J SO1 may be equal to the frequency of the second spin-orbit current J SO2 .
  • the frequency of the first spin-orbit current J SO1 may be equal to the frequency of the second spin-orbit current J SO2 , while the periods thereof may be offset, e.g., by a quarter wavelength.
  • spins SP 2 of the charge carriers provided into the free layer FL may oscillate (or rotate) in the xy plane, and frequencies of the oscillating (or rotating) spins SP 2 may be equal to the frequencies of the first and second spin-orbit currents J SO1 and J SO2 .
  • the frequencies of the spins SP 2 of the charge carriers provided into the free layer FL may gradually decrease with time.
  • the spins SP 2 of the charge carriers provided into the free layer FL may circularly rotate in the xy plane as illustrated in FIG. 8 , and the frequencies of the spins SP 2 may be equal to the frequencies of the first and second spin-orbit currents J SO1 and J SO2 .
  • the spin-orbit torque due to the first and second spin-orbit currents J SO1 and J SO2 may be applied to the magnetic moment M FL of the free layer FL.
  • the magnetic moment M FL of the free layer FL may precess around the easy axis (i.e., the z-axis) of the free layer FL.
  • the frequencies of the spins SP 2 of the charge carriers provided into the free layer FL i.e., the frequencies of the first and second spin-orbit currents J SO1 and J SO2
  • the rotation angle ssing magprecessional motion may increase rapidly, and the z-component m z of the magnetic moment M FL of the free layer FL may decrease rapidly.
  • the precessional motion of the magnetic moment M FL of the free layer FL may be changed from the state illustrated in FIG. 4A to the state illustrated in FIG. 4B .
  • the natural frequency of the magnetic moment M FL of the free layer FL is proportional to the z-component m z of the magnetic moment M FL of the free layer FL as described with reference to the equation 1, the natural frequency of the magnetic moment M FL of the free layer FL may be reduced by the occurrence of the resonance.
  • the frequencies of the spins SP 2 of the charge carriers provided into the free layer FL i.e., the frequencies of the first and second spin-orbit currents J SO1 and J SO2
  • the frequencies of the spins SP 2 of the charge carriers provided into the free layer FL i.e., the frequencies of the first and second spin-orbit currents J SO1 and J SO2
  • the frequencies of the spins SP 2 of the charge carriers provided into the free layer FL i.e., the frequencies of the first and second spin-orbit currents J SO1 and J SO2
  • the resonance is broken.
  • the resonance between the magnetic moment M FL of the free layer FL and the spins SP 2 of the charge carriers provided into the free layer FL may repeatedly occur at least two times.
  • the resonance may occur again since the frequencies of the spins SP 2 of the charge carriers provided into the free layer FL also decrease.
  • the natural frequency of the magnetic moment M FL of the free layer FL may be smaller than the frequencies of the spins SP 2 of the charge carriers provided into the free layer FL (i.e., the frequencies of the first and second spin-orbit currents J SO1 and J SO2 ) between the resonances.
  • initial frequencies of the first and second spin-orbit currents J SO1 and J SO2 may be equal to or greater than the initial natural frequency of the magnetic moment M FL of the free layer FL.
  • a writing operation of the magnetic memory device 101 may be performed using at least the spin-orbit torque due to the first and second spin-orbit currents J SO1 and J SO2 flowing through the first and second conductive lines CL 1 and CL 2 .
  • the magnetic moment M FL of the free layer FL may be switched using at least the spin-orbit torque due to the first and second spin-orbit currents J SO1 and J SO2 flowing through the first and second conductive lines CL 1 and CL 2 .
  • the magnetic moment M FL of the free layer FL may be switched using only the spin-orbit torque due to the first and second spin-orbit currents J SO1 and J SO2 .
  • critical magnitudes of the first and second spin-orbit currents J SO1 and J SO2 required to switch the magnetic moment M FL of the free layer FL may be relatively small, e.g., may be less than that for which only a single resonance occurs.
  • the magnetic moment M FL of the free layer FL may be switched using both the spin-orbit torque due to the first and second spin-orbit currents J SO1 and J SO2 and the spin-transfer torque due to the spin-transfer current J STT .
  • the first and second spin-orbit currents J SO1 and J SO2 and the spin-transfer current J STT may be applied at the same time for at least a certain period of time.
  • the first and second spin-orbit currents J SO1 and J SO2 may be applied prior to the spin-transfer current J STT .
  • embodiments are not limited thereto.
  • the spin-orbit torque may act as main switching torque to tilt the magnetic moment M FL of the free layer FL toward the xy plane.
  • the magnetic moment M FL of the free layer FL since the resonance between the magnetic moment M FL of the free layer FL and the spins SP 2 of the charge carriers repeatedly occurs at least two times, the magnetic moment M FL of the free layer FL may be effectively tilted toward the xy plane by using the first and second spin-orbit currents J SO1 and J SO2 having the relatively small magnitudes.
  • the spin-transfer torque may act as main switching torque to finally switch the magnetic moment M FL of the free layer FL.
  • FIG. 9A is a graph illustrating a switching critical current when a direct current (DC) is applied to a conductive line adjacent to a free layer.
  • FIGS. 9B and 9C are graphs illustrating a switching critical current when an alternating current (AC) according to some embodiments is applied to a conductive line adjacent to a free layer.
  • DC direct current
  • AC alternating current
  • FIG. 9A illustrates simulation results of a switching critical current when an external magnetic field of 200 Oe is applied to the free layer FL of the magnetic memory device 100 of FIG. 1 in the x-direction and a current pulse having a rise time of 0.5 ns is applied to the conductive line CL of the magnetic memory device 100 .
  • the spin-transfer current J STT is not applied to the magnetic memory device 100 .
  • FIG. 9B illustrates simulation results of a switching critical current when the spin-transfer current J STT of 6 ⁇ 10 5 A/cm 2 is applied to the magnetic memory device 100 of FIG. 1 and an alternating current having the frequency decreasing with time is applied to the conductive line CL of the magnetic memory device 100 .
  • An external magnetic field is not applied to the free layer FL of the magnetic memory device 100 .
  • the frequency of the alternating currents used in FIG. 9B was ⁇ 0 ⁇ 2d ⁇ (2d in F ⁇ 10 18 /s 2 ), where ⁇ 0 is an initial frequency that is greater than or equal to the initial natural frequency of the magnetic moment of thee free layer and t is time.
  • FIG. 9C illustrates simulation results of a switching critical current when alternating currents having frequencies decreasing with time are applied to the first and second conductive lines CL 1 and CL 2 in the magnetic memory device 101 illustrated in FIG. 6 .
  • An external magnetic field and/or a spin-transfer current were not applied in FIG. 9C .
  • the frequencies of the alternating currents used in FIG. 9C was t 0 ⁇ 2 ⁇ (2 The f ⁇ 10 18 /s 2 ).
  • FIGS. 9A to 9C were the same as each other.
  • an area of the free layer was ⁇ 15 2 nm 2
  • a thickness of the free layer was 2 nm
  • the effective magnetic anisotropy energy density K eff was 2.2 ⁇ 10 6 erg/cm 3
  • the saturation magnetization M s was 1000 emu/cm 3
  • a Gilbert damping constant n M was 2 nm
  • the pin hole angle ⁇ SH was 0.3
  • non-adiabaticity parameters parameters ticity parameters he
  • the switching critical current ranges from about 10 8 A/cm 2 to about 4 ⁇ 10 8 A/cm 2 and decreases as the non-adiabaticity parameter y parameters.
  • the switching critical current ranges from about 0.9 ⁇ 10 7 A/cm 2 to about 2 ⁇ 10 7 A/cm 2 and decreases as the non-adiabaticity parameter y parameter
  • the switching critical current ranges from about 0.5 ⁇ 10 7 A/cm 2 to about 2.9 ⁇ 10 7 A/cm 2 and decreases as the non-adiabaticity parameter y parameter
  • the switching critical current when applying the current described with reference to FIGS. 1 and 2 to the conductive line is as small as about 1/10 to about 1/20 of the switching critical current when applying the direct current to the conductive line.
  • the switching critical current when applying the currents described with reference to FIGS. 6, 7A, and 7B to the conductive lines is as small as about 1/20 to about 3/40 of the switching critical current when applying the direct current to the conductive line.
  • the method of writing the magnetic memory device may be performed using at least the spin-orbit current flowing through the conductive line having a decreasing frequency.
  • the magnitude of the spin-orbit current required during the writing operation of the magnetic memory device may be relatively small, e.g., may be less than that for which only a single resonance occurs.

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US20180151212A1 (en) 2018-05-31
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US10734051B2 (en) 2020-08-04
US10482939B2 (en) 2019-11-19

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