CN112864312A - Magnetic random access memory storage unit and magnetic random access memory - Google Patents

Magnetic random access memory storage unit and magnetic random access memory Download PDF

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CN112864312A
CN112864312A CN201911194688.0A CN201911194688A CN112864312A CN 112864312 A CN112864312 A CN 112864312A CN 201911194688 A CN201911194688 A CN 201911194688A CN 112864312 A CN112864312 A CN 112864312A
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free layer
cofeb
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张云森
郭一民
陈峻
肖荣福
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Shanghai Ciyu Information Technologies Co Ltd
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Abstract

The invention discloses a magnetic random access memory storage unit and a magnetic random access memory, wherein the storage unit comprises a reference layer, a barrier layer and a first free layer which are stacked from bottom to top, a second free layer is further arranged above the first free layer, a vertical magnetic coupling layer is arranged below the second free layer, and the magnetic damping barrier layer is arranged above the second free layer in a superposed manner; and the second free layer has a weaker magnetization vector but a stronger perpendicular magnetic anisotropy than the first free layer; the perpendicular magnetic coupling layer provides an additional source of perpendicular interface anisotropy for the first and second free layers and is used for realizing the strong magnetic coupling of the first free layer and the second free layer, so that the magnetization vector in the second free layer is always parallel to the magnetization vector in the first free layer; the magnetic damping barrier layer provides an additional source of anisotropy to the second free layer while reducing the magnetic damping coefficient of the film layer. The addition of the second free layer increases the thickness of the free layer, reduces the magnetic damping coefficient, increases the Tunneling Magnetoresistance (TMR) and the thermal stability factor, while the critical write current is not increased.

Description

Magnetic random access memory storage unit and magnetic random access memory
Technical Field
The present invention relates to the field of magnetic random access memory, and more particularly, to a magnetic random access memory cell having a double free layer and a magnetic random access memory.
Background
In recent years, Magnetic Random Access Memory (MRAM) using Magnetic Tunnel Junction (MTJ) is considered as a future solid-state nonvolatile Memory, which has the characteristics of high speed reading and writing, large capacity, and low power consumption. Ferromagnetic MTJs are typically sandwich structures with a magnetic memory layer (free layer) that can change the magnetization direction to record different data; an insulating tunnel barrier layer in the middle; and the magnetic reference layer is positioned on the other side of the tunnel barrier layer, and the magnetization direction of the magnetic reference layer is unchanged.
In order to be able to record information in such a magnetoresistive element, a writing method based on Spin momentum Transfer (STT) switching technology has been proposed, and such an MRAM is called STT-MRAM. STT-MRAM is further classified into in-plane STT-MRAM and perpendicular STT-MRAM (i.e., pSTT-MRAM), which have better performance depending on the direction of magnetic polarization. In a Magnetic Tunnel Junction (MTJ) having Perpendicular Anisotropy (PMA), as a free layer for storing information, there are two magnetization directions in the Perpendicular direction, that is: up and down, corresponding to "0" and "1" or "1" and "0" in the binary, respectively. In practical application, the magnetization direction of the free layer is kept unchanged when information is read or the free layer is empty; during writing, if there is a signal input in a different state from the existing state, the magnetization direction of the free layer will be flipped by 180 degrees in the vertical direction. The ability of the free layer of a magnetic memory to maintain the magnetization direction in this vacant state is called Data Retention (Data Retention) or Thermal Stability (Thermal Stability). The requirements are different in different application scenarios. A thermal stability requirement for a typical Non-volatile Memory (NVM) is that data can be stored for 10 years at 125 ℃.
In addition, MTJ, which is the core memory cell of magnetic memory (MRAM), must also be compatible with CMOS processes and must be able to withstand long term annealing at 400 ℃.
FIG. 1 is a diagram illustrating a conventional MRAM cell structure. The conventional magnetic random access memory cell comprises a bottom electrode 11, a seed layer 20, an antiparallel ferromagnetic superlattice layer 30 (including a lower ferromagnetic layer 31, an antiparallel ferromagnetic coupling layer 32, and an upper ferromagnetic layer 33), a lattice blocking layer 40, a reference layer 50, a barrier layer 60, a free layer 70 (including a free layer (I)71, a free layer (II)72, a free layer (III)73), a capping layer 80, and a top electrode 12, which are sequentially stacked from bottom to top.
The structure of the free layer 70 of the conventional magnetic random access memory cell is generally composed of a free layer (I)71, a free layer (II)72 and a free layer (III)73, such as CoFeB, CoFe/CoFeB, Fe/CoFeB or CoFeB/(Ta, W, Mo, Hf)/CoFeB, etc., and in order to increase the density of the magnetic memory, the Critical Dimension (Critical Dimension) of the magnetic tunnel junction has been made smaller and smaller in recent years. When the size is further reduced, it is found that Thermal Stability (Thermal Stability Factor) of the magnetic tunnel junction is drastically deteriorated. For ultra-small sized MRAM magnetic memory cells, to improve thermal stability, the thickness of the free layer can typically be reduced, the saturation susceptibility of the free layer can be reduced, or the interfacial anisotropy can be increased. If the thickness of the free layer is reduced, the Tunneling Magnetoresistance Ratio (TMR) is reduced, which increases the error rate in the read operation. Under the condition of constant thickness, the addition or change of the free layer into a material with low saturation magnetic susceptibility can also reduce TMR, which is not beneficial to the reading operation of the device.
Disclosure of Invention
In order to solve the problems of the prior art, the present invention provides a Magnetic Random Access Memory (MRAM) and a Memory cell having a dual free layer, wherein a second free layer is disposed between the original free layer and a capping layer of the MRAM having a Perpendicular Anisotropy (PMA), and the addition of the second free layer does not affect the tunneling resistance, increases the thickness of the free layer, reduces the Magnetic damping coefficient, increases the thermal stability factor, and does not increase the critical write current.
The purpose of the application and the technical problem to be solved are realized by adopting the following technical scheme. The invention provides a magnetic random access memory storage unit with a double-layer free layer, which comprises a reference layer, a barrier layer, a first free layer and a covering layer which are arranged from bottom to top, and is characterized in that a second free layer, a vertical magnetic coupling layer below the second free layer and a magnetic damping barrier layer above the second free layer are arranged above the first free layer; the second free layer has a weaker magnetization vector but stronger perpendicular magnetic anisotropy than the first free layer, and the total thickness of the second free layer is 0.5-3.0 nm; the perpendicular magnetic coupling layer provides an additional source of perpendicular interface anisotropy for the first and second free layers and is used for realizing the strong magnetic coupling of the first free layer and the second free layer, so that the magnetization vector in the second free layer is always parallel to the magnetization vector in the first free layer; the damping barrier layer provides a perpendicular interface anisotropy to the magnetization vector of the second free layer and reduces the magnetic damping coefficient of the entire film layer.
In an embodiment of the present application, the second free layer is FeBxMy、CoBxMy、CoFeBxMy、CoFeCxMy、CoFeSixMy、CoFeAlxMyB, C, Si or Al, wherein x is 10-30 at%, M is Mo, W, Ta, Hf, Pt, Pd, Nb or their combination, and y is 0-10 at%.
In the embodiment of the application, the second free layer is made of a CoFeB/M/CoFeB structure, M is W, Mo, V, Nb, Cr, Hf, Ti, Zr, Ta, Sc, Y, Zn, Ru, Os, Ru, Rh, Ir, Pd, Pt or their combination, and the thickness of M is 0.1-0.6 nm.
In the embodiment of the application, the second free layer is made of Co/M/Co, CoFeB/M/Co, Co/M/CoFeB and CoFeB/M/CoFeB structures, M is Pt and Pd, and the thickness of M is 0.1 nm-0.5 nm.
In an embodiment of the present application, the perpendicular magnetic coupling layer is made of a non-magnetic metal oxide including MgO, ZrO2, ZnO, Al2O3, GaO, Y2O3, SrO, Sc2O3, TiO2, HfO2, V2O5, Nb2O5, Ta2O5, CrO3, MoO3, WO3, RuO2, OsO2, TcO, ReO, RhO, IrO, SnO, SbO, MgZnO, MgBO, MgTiO, MgHfO, MgVO, MgNbO, MgTaO, crmgmoo, MgMoO, MgWO, RuO, MgRhO, MgIrO, MgSnO, MgSbO, MgCoO, MgCoFeO, MgAlO, or a combination thereof, and has a thickness of 0.3nm to 1.5 nm.
In an embodiment of the present application, the magnetic damping barrier layer is made of a non-magnetic metal or an oxide thereof including a composition of magnetic damping barrier layers made of Mg, Zr, Zn, Al, Ga, Y, Sr, Sc, Ti, V, Nb, Cr, Os, Tc, Re, Rh, Ir, Sn, Sb, MgO, ZrO2, ZnO, Al2O3, GaO, Y2O3, SrO, Sc2O3, TiO2, HfO2, V2O5, Nb2O5, Ta2O5, CrO3, MoO3, WO3, RuO2, OsO2, TcO, ReO, RhO, IrO, SnO, SbO, MgBO, MgTiO, MgHfO, MgVO, MgTaO, MgCrO, mgro, MgRuO, MgRhO, MgSbO, SnO, MgCoO, coo, and feo, and the composition thereof is at a thickness of 0 nm.
In an embodiment of the present application, the first free layer is variably magnetically polarized, and the first free layer has a CoFeB, CoFe/CoFeB, Fe/CoFeB, CoFeB/(W, Mo, V, Nb, Cr, Hf, Ti, Zr, Ta, Sc, Y, Zn, Ru, Os, Ru, Rh, Ir, Pd, Pt)/CoFeB, Fe/CoFeB/(W, Mo, V, Nb, Cr, Hf, Ti, Zr, Ta, Sc, Y, Zn, Ru, Os, Ru, Rh, Ir, Pd, Pt)/CoFeB or CoFe/CoFeB/(W, Mo, V, Nb, Cr, Hf, Ti, Zr, Ta, Sc, Y, Zn, Ru, Os, Ru, Rh, Ir, Pd, Pt)/CoFeB structure.
In an embodiment of the present application, the present invention provides a magnetic random access memory, which includes the memory cell as described above, and further includes a bottom electrode, a seed layer, an antiparallel ferromagnetic superlattice layer, a lattice partition layer, a capping layer, and a top electrode, where the bottom electrode, the seed layer, the antiparallel ferromagnetic superlattice layer, the lattice partition layer, a reference layer, a barrier layer, a first free layer, a perpendicular magnetic coupling layer, a second free layer, a magnetic damping barrier layer, the capping layer, and the top electrode are sequentially stacked.
In an embodiment of the present application, further, after the bottom electrode, the seed layer, the antiparallel ferromagnetic superlattice layer, the lattice partition layer, the reference layer, the barrier layer, the first free layer, the perpendicular magnetic coupling layer, the second free layer, the magnetic damping barrier layer, and the capping layer are deposited, an annealing operation is performed at a temperature of 350 ℃ for at least 60 minutes.
The magnetic random access memory storage unit with the thermal stability enhancement layer can produce the following beneficial effects: the TMR is not influenced by the addition of the second free layer, the thickness of the free layer is increased, the damping coefficient is reduced, the thermal stability factor is increased, and the critical write current is not increased.
a. The added second free layer and the first free layer are in ferromagnetic coupling, and under the condition of thermal disturbance or an external magnetic field, in order to make the magnetization vector of the free layer turn, energy larger than the sum of the energy barrier of the first free layer and the energy barrier of the added second free layer is required to be provided, so that the thermal stability is greatly improved.
b. The addition of the second free layer in the implementation of the present application has no influence on Tunneling Magnetoresistance (TMR).
c. Before and after the deposition of the second free layer a non-magnetic metal layer is deposited, preferably of MgO, with a thickness of 0.3nm to 1.5nm and 0.5nm to 3.0nm, respectively. This additionally provides a source of interfacial anisotropy, further increasing thermal stability; in addition, the magnetic damping barrier layer arranged above the second free layer is added, so that the damping coefficient of the whole film layer structure is effectively reduced, and the write current is favorably reduced.
d. The magnetic random access memory storage unit and the magnetic random access memory can withstand long-time annealing at 350 ℃.
e. Due to the addition of the second free layer, the thickness of the whole free layer is increased, the reduction of the damping coefficient is facilitated, and therefore the critical write current cannot be increased.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
FIG. 1 is a diagram illustrating a prior art MRAM cell;
FIG. 2 is a diagram illustrating a MRAM cell structure according to an embodiment of the invention;
FIG. 3 is a graph showing a comparison of the switching behavior of the free layer under an external magnetic field before and after the addition of the second free layer according to an embodiment of the present invention.
Wherein the reference numerals include:
, 11: bottom electrode, 12: top electrode, 20: seed layer, 30: antiparallel ferromagnetic superlattice layer, 31: lower ferromagnetic layer, 32: antiparallel ferromagnetic coupling layer, 33 upper ferromagnetic layer, 40: lattice partition layer, 50: reference layer, 60: barrier layer, 70: free layer, 71: free layer (I), 72: free layer (II), 73: free layer (III), 80: capping layer.
The present invention is directed to a bottom electrode, a top electrode, a seed layer, 300 antiparallel ferromagnetic superlattice layer, 310 lower ferromagnetic layer, 320 antiparallel ferromagnetic coupling layer, 330 upper ferromagnetic layer, 400 lattice barrier layer, 500 reference layer, 600 barrier layer, 700 first free layer, 710 first free layer (I), 720 first free layer (II), 730 first free layer (III), 800 capping layer, 910 perpendicular magnetic coupling layer, 920 first free layer, 920a second free layer (I), 920b second free layer (II), 920c second free layer (III), 930 magnetoresistive barrier layer.
Detailed Description
In order to make the technical solutions of the present invention better understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be noted that the terms "first," "second," and the like in the description and claims of the present invention and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the invention described herein are capable of operation in sequences other than those illustrated or described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, apparatus, article, or device that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or device.
In one embodiment of the present invention, a Magnetic Random Access Memory (MRAM) memory cell having a dual free layer is provided, in which a second free layer 920 is interposed between a top of a first free layer 700 and a capping layer (capping layer)800 without vacuum interruption during Physical Vapor Deposition (PVD) of a MRAM magnetic tunnel junction (mtj) multilayer film, as shown in fig. 2, the MRAM memory cell having the dual free layer includes a reference layer 500, a barrier layer 600, the first free layer 700, a second free layer 920 above the first free layer 700, a perpendicular magnetic coupling layer 910 below the second free layer 920, and a magnetic damping barrier layer 930 above the second free layer 920.
Wherein the second free layer 920 has a weaker magnetization vector but stronger perpendicular magnetic anisotropy than the first free layer 700, and the total thickness of the second free layer 920 is 0.5-3.0 nm; the perpendicular magnetic coupling layer 910 provides an additional source of perpendicular interface anisotropy for the first free layer 700, the second free layer 920, and is used to achieve a strong magnetic coupling of the first free layer 700 and the second free layer 920 such that the magnetization vector in the second free layer 920 is always parallel to the magnetization vector in the first free layer 700; the damping barrier 930 provides a perpendicular interface anisotropy to the magnetization vector of the second free layer 920 and reduces the magnetic damping coefficient of the entire film.
In an embodiment of the present invention, a magnetic random access memory is provided, which includes the memory cell as described above, and further includes a bottom electrode 110, a seed layer 200, an antiparallel ferromagnetic superlattice layer 300, a lattice partition layer 400, a capping layer 800, and a top electrode 120. The magnetic random access memory comprises a bottom electrode 110, a seed layer 200, an antiparallel ferromagnetic superlattice layer 300, a lattice partition layer 400, a reference layer 500, a barrier layer 600, a first free layer 700, a perpendicular magnetic coupling layer 910, a second free layer 920, a magnetic damping barrier layer 930, a covering layer 800 and a top electrode 120 which are sequentially stacked from bottom to top.
The bottom electrode 110 is made of Ti, TiN, Ta, TaN, W, WN or a combination thereof, and is generally implemented by Physical Vapor Deposition (PVD), and after Deposition, the bottom electrode is usually planarized to achieve surface flatness for fabricating the magnetic tunnel junction.
The seed layer 200 is typically composed of Ta, Ti, TiN, TaN, W, WN, Ru, Pt, Ni, Cr, CrCo, CoFeB, or combinations thereof; furthermore, the seed layer 210 can be a multi-layer structure of Ta/Ru, Ta/PtCoFeB/Ta/Pt, CoFeB/Ta/Pt/Ru, or Ta/Pt/Ru, etc. to optimize the crystal structure of the subsequent antiparallel ferromagnetic superlattice layer 300.
The Anti-Parallel ferromagnetic super-lattice layer (Anti-Parallel ferromagnetic super-lattice) 300, also called Synthetic Anti-ferromagnetic layer (SyAF), is generally made of [ Co/Pt [ ]]nCo/(Ru,Ir,Rh)、[Co/Pt]nCo/(Ru,Ir,Rh)/Co[Pt/Co]m、[Co/Pd]nCo/(Ru,Ir,Rh)、[Co/Pd]nCo/(Ru,Ir,Rh)/Co[Pd/Co]m、[Co/Ni]nCo/(Ru, Ir, Rh) or [ Co/Ni ]]nCo/(Ru,Ir,Rh)/Co[Ni/Co]mA superlattice structure, wherein m is greater than or equal to 0, and the antiparallel ferromagnetic superlattice layer 300 has strong perpendicular anisotropy (PMA).
The reference layer 500 has a magnetic polarization invariant under ferromagnetic coupling of the antiparallel ferromagnetic superlattice layer 300. the reference layer 500 is typically made of Co, Fe, Ni, CoFe, CoFeB, or combinations thereof.
In practice, since the antiparallel ferromagnetic superlattice layer 300 has a Face Centered Cubic (FCC) crystal structure, and the crystal structure of the reference layer 500 is Body Centered Cubic (BCC), the lattices of the two layers are not matched, in order to realize the transition and ferromagnetic coupling from the antiparallel ferromagnetic superlattice layer 300 to the reference layer 500, a lattice-partitioning layer 400 is generally added between the two layers of materials, and the lattice-partitioning layer 400 is generally made of Ta, W, Mo, Hf, Fe, Co (Ta, W, Mo or Hf), Fe (Ta, W, Mo or Hf), FeCo (Ta, W, Mo or Hf), FeCoB (Ta, W, Mo or Hf), or the like, and has a thickness of 0.1nm to 0.5 nm.
The barrier layer 600 is made of a non-magnetic metal oxide including MgO, MgZnO, MgBO, MgAlO or a combination thereof, and more preferably, MgO may be selected.
The first free layer 700 has a variable magnetic polarization, and the first free layer 700 is generally comprised of CoFeB, CoFe/CoFeB, Fe/CoFeB, CoFeB/(W, Mo, V, Nb, Cr, Hf, Ti, Zr, Ta, Sc, Y, Zn, Ru, Os, Ru, Rh, Ir, Pd, Pt)/CoFeB, Fe/CoFeB/(W, Mo, V, Nb, Cr, Hf, Ti, Zr, Ta, Sc, Y, Zn, Ru, Os, Ru, Rh, Ir, Pd, Pt)/CoFeB or CoFe/CoFeB/(W, Mo, V, Nb, Cr, Hf, Ti, Zr, Ta, Sc, Y, Zn, Ru, Os, Ru, Rh, Ir, Pd, Pt)/CoFeB, and the like.
The first free layer 700 may further be selected from CoFeB/(W, Mo, V, Nb, Cr, Hf, Ti, Zr, Ta, Sc, Y, Zn, Ru, Os, Ru, Rh, Ir, Pd, Pt)/CoFeB, Fe/CoFeB/(W, Mo, V, Nb, Cr, Hf, Ti, Zr, Ta, Sc, Y, Zn, Ru, Os, Ru, Rh, Ir, Pd, Pt)/CoFeB or CoFe/CoFeB/(W, Mo, V, Nb, Cr, Hf, Ti, Zr, Ta, Sc, Y, Zn, Ru, Os, Ru, Rh, Ir, Pd, Pt)/CoFeB structures.
Taking the structure of the first free layer 700 as an example, it is common in the art that the first free layer 700 is formed from a first free layer (I)710, a first free layer (II)720, and a first free layer (III)730 from bottom to top, respectively. For example, CoFeB/(W, Mo, V, Nb, Cr, Hf, Ti, Zr, Ta, Sc, Y, Zn, Ru, Os, Ru, Rh, Ir, Pd, Pt)/CoFeB means that a three-layer structure is formed of a first free layer (I)710, a first free layer (II)720, and a first free layer (III)730, the first free layer (I)710 and the one free layer (III)730 are both made of CoFeB material, and the intermediate layer first free layer (II)720 is made of W, Mo, V, Nb, Cr, Hf, Ti, Zr, Ta, Sc, Y, Zn, Ru, Os, Ru, Rh, Ir, Pd, or Pt material, and the following structural expressions are similar and will not be explained again.
In an embodiment of the present application, the second free layer 920 is FeBxMy、CoBxMy、CoFeBxMy、CoFeCxMy、CoFeSixMy、CoFeAlxMyEtc., wherein B, C, Si or Al is 10-30 atomic percent x, M is Mo, W, Ta, Hf, Pt, Pd, Nb or their combination, and M is 0-10 atomic percent y.
In the embodiment of the present application, the structure of the second free layer 920 may also be composed of, in order from bottom to top, a second free layer (I)920a, a second free layer (II)920b, and a second free layer (III)920 c; the second free layer 920 is made of a CoFeB/M/CoFeB structure, wherein M is W, Mo, V, Nb, Cr, Hf, Ti, Zr, Ta, Sc, Y, Zn, Ru, Os, Ru, Rh, Ir, Pd, Pt or their combination, and the thickness of M is 0.1-0.6 nm; or the second free layer 920 is made of Co/M/Co, CoFeB/M/Co, Co/M/CoFeB, CoFeB/M/CoFeB structures, wherein M is Pt or Pd, and the thickness of M is 0.1 nm-0.5 nm.
The thickness of the second free layer 920 is 0.5nm to 3nm, and in the specific process, the composition of the material is changed by adjusting the PVD deposition condition, and the material can be modified by adding a plasma etching process to obtain the optimal performance.
In practice, a perpendicular magnetic coupling layer 910 of a nonmagnetic metal oxide layer is deposited before the addition of the second free layer 920, the nonmagnetic metal oxide layer comprising MgO, ZrO2, ZnO, Al2O3, GaO, Y2O3, SrO, Sc2O3, TiO2, HfO2, V2O5, Nb2O5, Ta2O5, CrO3, MoO3, WO3, RuO2, OsO2, TcO, ReO, RhO, IrO, SnO, SbO, MgZnO, MgBO, MgTiO, MgHfO, MgVO, MgNbO, MgTaO, MgCrO, RuMoO, MgWO, MgO, MgRhO, MgIrIrO, MgSnO, MgSbO, MgCoFeO, MgAlO or a combination thereof, the thickness of the perpendicular magnetic coupling layer being 0.3-1.5 nm.
The perpendicular magnetic coupling layer 910 provides an additional source of perpendicular interface anisotropy to the first free layer 700 and the second free layer 920, and is used to achieve strong magnetic coupling between the first free layer 700 and the second free layer 920, such that the magnetization vector in the second free layer 920 is always parallel to the magnetization vector in the first free layer 700, which also provides a source of interface anisotropy, thereby increasing thermal stability.
In addition, the magnetic damping barrier layer 930 is disposed above the second free layer 902, so that the damping coefficient of the whole film structure is effectively reduced, and the write current is reduced. Wherein the magnetic damping barrier 930 is made of a non-magnetic metal or an oxide thereof including a composition of magnetic damping barriers of Mg, Zr, Zn, Al, Ga, Y, Sr, Sc, Ti, V, Nb, Cr, Os, Tc, Re, Rh, Ir, Sn, Sb, MgO, ZrO2, ZnO, Al2O3, GaO, Y2O3, SrO, Sc2O3, TiO2, HfO2, V2O5, Nb2O5, Ta2O5, CrO3, MoO3, WO3, RuO2, OsO2, TcO, ReO, RhO, IrO, SnO, SbO, MgZnO, MgBO, MgHfO, MgVO, MgNbO, MgTaO, MgCrO, MgMoO, MgWO, MgRuO, MgRhO, irho, MgSnO, mgco, MgSbO, coo, and the composition thereof is 0.5nm in thickness.
In practice, the capping layer 800 is made of CoFeB, CoFeC, W, Mo, Mg, Nb, Ru, Hf, V, Cr, or Pt, preferably (W, Mo, Hf)/Ru or/Pt/(W, Mo, Hf)/Ru.
In practice, the top electrode 120 can be made of Ta, TaN, TaN/Ta, Ti, TiN, TiN/Ti, W, WN, WN/W or their combination.
After the film layers of the bottom electrode 110, the seed layer 200, the antiparallel ferromagnetic superlattice layer 300, the lattice partition layer 400, the reference layer 500, the barrier layer 600, the first free layer 700, the perpendicular magnetic coupling layer 910, the second free layer 920, the magnetic damping barrier layer 930, and the capping layer 800 are deposited, an anneal at a temperature of 350 ℃ is selected for 60 minutes to cause the reference layer 500, the first free layer 700, and the second free layer 900 to change phase from amorphous to a body-centered cubic (BCC) crystal structure.
FIG. 3 is a graph illustrating a comparison of the switching behavior of the free layer under an external magnetic Field (Field) before and after the addition of a second free layer 900 in accordance with an embodiment of the present invention. , it is clear that the switching behavior of the free layers (the first free layer 700 and the second free layer 900) under the external magnetic field before and after the addition of the second free layer 920 is clearly seen that Ms × t increases much after the addition of the second free layer 920 (Ms is the saturation susceptibility of the free layer, t is the thickness of the free layer), which is equivalent to that under Hk (perpendicular effective anisotropy field), the precondition that Ms is unchanged, the thickness of the free layer is increased, thereby increasing the thermodynamic barrier of free switching.
The invention provides a magnetic random access memory thermal stability enhancement layer, which is characterized in that a second free layer 920 is inserted between the top of a first free layer 700 and a covering layer 800 under the condition of not cutting off vacuum in the process of Physical Vapor Deposition (PVD) of an MRAM magnetic tunnel junction multilayer film.
In the present application, in adding the second free layer 920, the second free layer 920 has a weaker magnetization vector but a stronger perpendicular magnetic anisotropy than the first free layer, and the magnetization vector of the second free layer 920 is always perpendicular to the first free layer 700 and parallel to the magnetization vector of the first free layer 700, since the added second free layer 920 and the first free layer 700 exhibit ferromagnetic coupling, under thermal disturbance or an applied magnetic field, an energy greater than the sum of the energy barriers of the first free layer 700 and the second free layer 920 must be provided in order to flip the magnetization vector of the added second free layer 920.
Experiments have shown that the addition of the additional second free layer 920 does not affect the Tunneling Magnetoresistance Ratio (TMR).
Also, a non-magnetic metal oxide layer is deposited before and after the addition of the second free layer 902, which additionally provides a source of interfacial anisotropy and thus increased thermal stability. In addition, the magnetic damping barrier layer 930 is arranged above the second free layer 920, so that the damping coefficient of the whole film structure is effectively reduced, and the write current is favorably reduced.
Also, since Ta and its nitride are successfully avoided when selecting the material of the first free layer 700 and the material of the capping layer 800, it can withstand a long-time annealing at 350 ℃.
Further, since the thickness of the free layers (the first free layer 700 and the second free layer 900) is increased due to the addition of the second free layer 920, it is advantageous in terms of the reduction of the damping coefficient (α), and at the same time, when the materials of the perpendicular magnetic coupling layer 910 of the first free layer 700/the second free layer 920 and the capping layer 800 are selected, a material having a low damping coefficient may be preferable, so that the damping coefficient may be further reduced. When writing to the device, the critical write current does not increase due to the reduced damping coefficient, despite the increased thermal stability factor.
Further, the Data Retention capability (Data Retention) can be calculated by the following formula:
Figure BDA0002294396780000121
wherein tau is the time when the magnetization vector is unchanged under the condition of thermal disturbance, tau0For the trial time (typically 1ns), E is the energy barrier of the free layer, kBBoltzmann constant, T is the operating temperature.
The Thermal Stability factor (Thermal Stability factor) can then be expressed as the following equation:
Figure BDA0002294396780000122
wherein, KeffIs the effective anisotropic energy density of the free layer, V is the volume of the free layer, KV is the bulk anisotropy constant MsSaturation magnetic susceptibility of the free layer, NzDemagnetization constant in the vertical direction, t is the thickness of the free layer, KiCD is the critical dimension of the MRAM (i.e., the diameter of the free layer), As is the stiffness integral exchange constant, and k is the critical dimension of the free layer switching mode transition from domain switching (i.e., Magnetization switching processed by "macro-spin") to reverse domain nucleation/growth (i.e., Magnetization switching processed by nuclear of reversed domain and propagation of a domain wall) mode. Experiments show that when the thickness of the free layer is thicker, the free layer shows in-plane anisotropy, and when the thickness of the free layer is thinner, the free layer shows vertical anisotropy, KVIt is generally negligible and the contribution of the demagnetization energy to the perpendicular anisotropy is negative, so the perpendicular anisotropy comes entirely from the interfacial effect (Ki).
In addition, as the volume of the magnetic free layer is reduced, the smaller the spin polarization current to be injected for writing or switching operation, and the critical current I for writing operationc0The relationship between the compound and the thermal stability is strongly related, and can be expressed as the following formula:
Figure BDA0002294396780000123
wherein alpha is a damping constant,
Figure BDA0002294396780000124
η is the spin polarizability, which is the approximate planck constant.
The addition of the additional second free layer 920 of the present invention does not affect TMR, increases the thickness of the free layer, reduces the damping coefficient, increases the thermal stability factor, and does not increase the critical write current.
The terms "in one embodiment" and "in various embodiments" of the present application are used repeatedly. This phrase generally does not refer to the same embodiment; it may also refer to the same embodiment. The terms "comprising," "having," and "including" are synonymous, unless the context dictates otherwise.
Although the present application has been described with reference to specific embodiments, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the application, and all changes, substitutions and alterations that fall within the spirit and scope of the application are to be understood as being covered by the following claims.

Claims (10)

1. A magnetic random access memory storage unit with double free layers comprises a reference layer, a barrier layer, a first free layer and a covering layer which are arranged from bottom to top, and is characterized in that a second free layer, a vertical magnetic coupling layer below the second free layer and a magnetic damping barrier layer above the second free layer are arranged above the first free layer;
the second free layer has a weaker magnetization vector but stronger perpendicular magnetic anisotropy than the first free layer, and the total thickness of the second free layer is 0.5-3.0 nm;
the perpendicular magnetic coupling layer provides an additional source of perpendicular interface anisotropy for the first and second free layers and is used for realizing the strong magnetic coupling of the first free layer and the second free layer, so that the magnetization vector in the second free layer is always parallel to the magnetization vector in the first free layer;
the damping barrier layer provides a perpendicular interface anisotropy to the magnetization vector of the second free layer and reduces the magnetic damping coefficient of the entire film layer.
2. The MRAM memory cell of claim 1, wherein the perpendicular magnetic coupling layer is MgO, ZrO2, ZnO, Al2O3, GaO, Y2O3, SrO, Sc2O3, TiO2, HfO2, V2O5, Nb2O5, Ta2O5, CrO3, MoO3, WO3, RuO2, OsO2, TcO, ReO, RhO, IrO, SnO, SbO, MgZnO, MgBO, MgTiO, MgHfO, MgVO, MgNbO, MgTaO, MgCrO, MgMoO, MgWO, MgRuO, MgRhO, MgIrO, MgSnO, MgSbO, MgCoO, MgCoFeO, MgAlO, or a combination thereof, and the perpendicular magnetic coupling layer has a thickness of 0.3nm to 1.5 nm.
3. The MRAM memory cell of claim 1, wherein the magnetic damping barrier is Mg, Zr, Zn, Al, Ga, Y, Sr, Sc, Ti, V, Nb, Cr, Os, Tc, Re, Rh, Ir, Sn, Sb, MgO, ZrO2, ZnO, Al2O3, GaO, Y2O3, SrO, Sc2O3, TiO2, HfO2, V2O5, Nb2O5, Ta2O5, CrO3, MoO3, WO3, RuO2, OsO2, TcO, ReO, RhO, IrO, SnO, SbO, MgZnO, MgBO, MgTiO, MgHfO, MgVO, MgNbO, MgTaO, MgCrO, MgMoO, MgWO, MgRuO, MgRhO, MgIrO, MgSbO, CoMgSbO, MgAlO, MgNbO, or a combination thereof is at a thickness of 0.5 nm.
4. The MRAM memory cell of claim 1, wherein the second free layer is FeBxMy、CoBxMy、CoFeBxMy、CoFeCxMy、CoFeSixMy、CoFeAlxMyB, C, Si or Al, wherein x is 10-30 at%, M is Mo, W, Ta, Hf, Pt, Pd, Nb or their combination, and y is 0-10 at%.
5. The MRAM cell of claim 1, wherein the second free layer is made of CoFeB/M/CoFeB structure, M is W, Mo, V, Nb, Cr, Hf, Ti, Zr, Ta, Sc, Y, Zn, Ru, Os, Ru, Rh, Ir, Pd, Pt, or combinations thereof, and M has a thickness of 0.1-0.6 nm.
6. The MRAM memory cell of claim 1, wherein the second free layer is made of Co/M/Co, CoFeB/M/Co, Co/M/CoFeB, CoFeB/M/CoFeB structures, M is Pt or Pd, and M has a thickness of 0.1nm to 0.5 nm.
7. The MRAM memory cell of claim 1, wherein the barrier layer is made of a non-magnetic metal oxide such as MgO, MgZnO, MgBO, MgAlO, or combinations thereof.
8. The MRAM memory cell of claim 1, wherein the first free layer is made of a CoFeB, CoFe/CoFeB, Fe/CoFeB, CoFeB/(W, Mo, V, Nb, Cr, Hf, Ti, Zr, Ta, Sc, Y, Zn, Ru, Os, Ru, Rh, Ir, Pd, Pt)/CoFeB, Fe/CoFeB/(W, Mo, V, Nb, Cr, Hf, Ti, Zr, Ta, Sc, Y, Zn, Ru, Os, Ru, Rh, Ir, Pd, Pt)/CoFeB or CoFe/CoFeB/(W, Mo, V, Nb, Cr, Hf, Ti, Zr, Ta, Sc, Y, Zn, Ru, Os, Ru, Rh, Ir, Pd, Pt)/CoFeB structure.
9. A magnetic random access memory comprising the memory cell of any one of claims 1-8, further comprising a bottom electrode, a seed layer, an antiparallel ferromagnetic superlattice layer, a lattice partition layer, a capping layer, and a top electrode; the magnetic random access memory comprises a bottom electrode, a seed layer, an antiparallel ferromagnetic superlattice layer, a lattice partition layer, a reference layer, a barrier layer, a first free layer, a vertical magnetic coupling layer, a second free layer, a magnetic damping barrier layer, a covering layer and a top electrode which are sequentially stacked from bottom to top.
10. The magnetic random access memory of claim 9 wherein the seed layer, antiparallel ferromagnetic superlattice layer, lattice partition layer, reference layer, barrier layer, first free layer, perpendicular magnetic coupling layer, second free layer, magnetic damping barrier layer, capping layer deposition is followed by an anneal operation at a temperature of 350 ℃ for at least 60 minutes.
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