Magnetic random access memory

Abstract

The invention discloses a magnetic random access memory. A rare earth element insertion layer is used for optimizing and improving the storage density, the anti-interference capability, the tunneling magnetoresistance and the spin polarizability of an STT-MRAM (Spin Transfer Torque Magnetic Random Access Memory) and an SOT-MRAM (Spin Object Transfer Magnetic Random Access Memory). The invention provides a magnetic random access memory, which comprises a magnetic tunnel junction, the magnetic tunnel junction comprises a tunneling layer made of MgO and a ferromagnetic free layer, the surface of the free layer is also provided with a rare earth layer, and the rare earth layer is composed of rare earth elements with 4f magnetic electrons. Due to the existence of the rare earth layer, the performance such as the storage density, the anti-interference capability, the tunneling magnetoresistance and the spin polarizability of the device is optimized.

Description

Technical Field

[0001] This invention belongs to the field of magnetic storage, specifically relating to a magnetic random access memory; the magnetic random access memory is obtained by optimizing and improving the storage density, anti-interference ability, tunneling magnetoresistance and spin polarization of STT-MRAM and SOT-MRAM based on 4f rare earth element insertion layers. Background Technology

[0002] MRAM (Magnetic Random Access Memory) is an advanced storage technology that utilizes the spin properties of electrons to store information. Its core advantage lies in its potential to become a "general-purpose memory," combining the high storage density of Dynamic Random Access Memory (DRAM) with the high-speed read / write characteristics of Static Random Access Memory (SRAM), while also possessing non-volatility and high energy efficiency.

[0003] The basic memory cell of MRAM consists of a magnetic tunnel junction (MTJ) and an access transistor. The MTJ has a stacked structure, consisting of two ferromagnetic layers (a fixed layer and a free layer) sandwiching a tunneling layer (MgO). The magnetization direction of the fixed layer (usually made of CoFeB) is fixed, while the magnetization direction of the free layer (also often made of CoFeB) can be adjusted.

[0004] Because the spin state density of a tunnel junction (MTJ) varies significantly across different magnetization directions, its resistance can be controlled by altering the magnetization direction. This property determines its excellent magnetic encoding performance. When the magnetization directions of the fixed and free layers are parallel, the MTJ is in a low-resistance state (low tunnel magnetoresistance, TMR); when their magnetization directions are antiparallel, the MTJ is in a high-resistance state (high TMR). Data writing is achieved by changing the magnetization direction of the free layer, while data reading is accomplished by detecting the magnetoresistance state corresponding to the current flowing through the junction. CoFeB, as the most representative MTJ magnetic thin film structure, exhibits a tunnel magnetoresistance value greater than 300% when stacked with MgO in a sandwich structure, demonstrating a significant performance advantage compared to other material systems. Summary of the Invention

[0005] This invention addresses the challenge of improving the storage density, write power consumption, anti-interference capability, tunneling magnetoresistance, and spin polarization of CoFeB / MgO without altering the CoFeB / MgO structure, thereby achieving device miniaturization and energy efficiency. Anti-interference capability primarily stems from enhanced perpendicular magnetic anisotropy between the free layer and the reference layer; compared to other directions, the thin film magnetic moment is in a lower total energy state along the magnetic easy axis. Improved tunneling magnetoresistance mainly arises from the differential parallel / antiparallel spin state density of CoFeB. Due to the unique exchange interaction of the df electron orbitals of 4f rare-earth elements, hybridization with neighboring CoFeB orbitals improves the d orbital electron state density. The improved spin polarization comes from the heavy spin-orbit coupling effect of Gd and the improvement in spin transmittance at the CoFeB neighbor interface.

[0006] Modern MRAM technology has developed various implementation methods, mainly including SpinTransferTorque MRAM (STT-MRAM) and SpinOrbitTorque MRAM (SOT-MRAM). In STT-MRAM, a spin-polarized current flowing through the fixed layer transfers its angular momentum to the free layer, thereby reversing the magnetization direction of the free layer. In SOT-MRAM, MTJs are stacked on a heavy metal substrate; a current injected into the heavy metal layer generates a spin current through the spin Hall effect or Rashba effect, which then transfers angular momentum from the heavy metal layer to the magnetic free layer.

[0007] Increasing the spin polarization of STT-MRAM and SOT-MRAM can effectively reduce their write power consumption. 4f rare-earth elements possess strong spin-orbit coupling effects and unique electron orbital structures; their spin transport performance can be effectively controlled through interface orbital hybridization and interface spin conductivity modification. Regarding increasing storage density, the main method is to increase the magnetic anisotropy of the free layer, effectively reducing device size. Therefore, rare-earth elements such as Gd and Tb, which possess highly localized 4f magnetic electrons, can serve as effective magnetic buffer layers to control the magnetic texture of the free layer, reduce magnetic dead layers, and increase magnetic anisotropy.

[0008] This invention provides a magnetic random access memory (MRM) including a magnetic tunnel junction. The MLM comprises a tunneling layer made of MgO and a ferromagnetic free layer. A rare earth layer, composed of rare earth elements with 4f magnetic electrons, is further disposed on the surface of the free layer. This invention achieves optimization and improvement of storage density, anti-interference capability, tunneling magnetoresistance, and spin polarization of STT-MRAM and SOT-MRAM through rare earth element insertion layers.

[0009] Preferably, the rare earth layer is made of Gd and has a thickness of 0.3-0.4 nm.

[0010] Preferably, the magnetic random access memory is a spin-transfer moment MRAM or a spin-orbit moment MRAM.

[0011] Preferably, the storage cell of the spin-transfer torque MRAM is a multilayer thin film structure, which, from bottom to top, consists of a buffer layer, a pinning layer, a reference layer, a tunneling layer, a free layer, a rare earth layer, an intermediate layer, a rare earth layer, a free layer, and a tunneling layer.

[0012] Preferably, the storage cell of the spin orbital moment MRAM is a multilayer thin film structure, which, from bottom to top, consists of a buffer layer, an SOT layer, a rare earth layer, a free layer, a rare earth layer, a tunneling layer, a rare earth layer, a reference layer, a rare earth layer, and a pinning layer.

[0013] Preferably, the buffer layer material is one or more of Ta, TaNi alloy, and MgO, and the thickness of the buffer layer is less than 5 nm.

[0014] Preferably, the pinning layer is a stacked composite layer of a magnetically anisotropic material and a material with RKKY interlayer exchange coupling effect; the anisotropic material is a CoPtCr alloy, a CoPt alloy, or a composite stack [Co / Pt]. n Multilayer films, CoNi alloys, composite stacks [Co / Ni] m The material is a multilayer film or an FePt alloy, with a thickness of 0-5 nm. Here, n and m refer to the number of repetitions in the multilayer stack, and both n and m are greater than 1. The material exhibiting the RKKY interlayer exchange coupling effect is one or more of Ir, Ru, Nb, Ta, Cr, Mo, W, Re, Os, Rh, Pt, Cu, Ag, and Au.

[0015] The free layer material is a ferromagnetic material, such as CoFeB alloy, Co, Fe, or Ni; in addition to ferromagnetic materials, it can also be: Mn-based antiferromagnetic materials: PtMn alloy, IrMn alloy, MnSn alloy, MnAl alloy; or a Hessler alloy in the form of XYZ or X2YZ, wherein element X is one or more of Fe, Co, Ni, Mn, Pd, Cu, and Cr, element Y is one or more of Cr, Mn, V, Ge, Al, Ti, Co, Ni, and Fe, and element Z is one or more of Sn, N, Sb, Si, Ga, As, and Ge, with a thickness of 0-3 nm; the 4f rare earth element can also be one or more of La, Ce, Pr, Eu, Gd, Tb, Dy, Ho, Er, and Tm.

[0016] Preferably, the SOT layer material is one or more of W, Pt, Ta, Ti, Cu, Ru, Cr, Hf, O, N, Ir, Mn, V, Al, Mg, Mo, Rh, Pd, Ag, Sn, Te, Re, Au, La, Ce, Pr, Eu, Gd, Tb, Dy, Ho, Er, and Tm.

[0017] Compared with the prior art, the beneficial effects of the present invention are: Rare earth elements possess strong spin-orbit coupling effects and unique electronic orbital structures. Through interface orbital hybridization and interface spin conductivity modification, the spin transport performance and perpendicular magnetic anisotropy of devices can be effectively controlled. In the basic structures of STT-MRAM and SOT-MRAM, this invention introduces an ultrathin rare earth element insertion layer as an optimization. This layer has almost no impact on the charge transport properties of the device, but significantly improves the spin transport performance of the free layer and reference layer. Similarly, magnetic rare earth elements such as Gd and Tb can act as effective magnetic buffer layers to control the magnetic texture of the free layer, reduce magnetic dead layers, and increase magnetic anisotropy. This allows for improvements in storage density, write power consumption, anti-interference capability, tunneling magnetoresistance, and spin polarization without altering the CoFeB / MgO structure.

[0018] Compared with existing technologies such as CN 121057492 A, this invention uses a single-layer rare-earth layer instead of the alloy composition of rare-earth and free-layer metals in existing technologies. Its advantages are: in large-scale wafer-level fabrication processes, elemental Gd significantly reduces the fabrication process difficulty compared to rare-earth-transition metals. The generation of ferrimagnetic order in rare-earth-transition metals requires a greater thickness than elemental Gd, and defects are easily formed due to diffusion during heat treatment and ion etching processes. Furthermore, due to the antiferromagnetic coupling of RKKY, the magnetic moment of the free-layer CoFeB generates an in-plane component, which easily leads to a decrease in anti-interference capability and tunneling magnetoresistance. Attached Figure Description

[0019] Figure 1 STT-MRAM structural diagram; Figure 2 SOT-MRAM structural diagram; Figure 3 Characterization results of the thickness regulation of the vertical magnetic anisotropy of the free layer by Gd as a rare earth element insertion layer; Figure 4 Characterization results of the effect of Gd as a rare earth element insertion layer on the thickness regulation of spin polarization of SOT layer. Detailed Implementation

[0020] The purpose of this invention is to provide a method for STT-MRAM (such as rare earth element insertion layers) based on rare earth element insertion layers (hereinafter referred to as rare earth layers). Figure 1 ) and SOT-MRAM (such as Figure 2 This invention provides a scheme for optimizing and improving storage density, anti-interference capability, tunneling magnetoresistance, and spin polarization. A magnetic random access memory (RAM) is provided, comprising a magnetic tunnel junction. The magnetic tunnel junction includes a tunneling layer made of MgO material and a ferromagnetic free layer. A rare earth layer is further disposed on the surface of the free layer, and the rare earth layer is composed of rare earth elements with 4f magnetic electrons.

[0021] In this invention, the pinning layer of STT-MRAM comprises a [Co(0.5 nm) / Pt(0.3 nm)]×5 multilayer structure consisting of five repeated layers of 0.5 nm thick Co and 0.3 nm thick Pt, with Co located below Pt in each layer. A top layer of 1 nm thick Co is disposed above the [Co(0.5 nm) / Pt(0.3 nm)]×5 multilayer structure, and an artificial antiferromagnetic intermediate layer is disposed above the top Co layer. The artificial antiferromagnetic intermediate layer is made of Ir and has a thickness of 0.6-0.8 nm.

[0022] Preferably, the intermediate layer of the spin-transfer torque MRAM is Ta with a thickness of 0.3 nm; the buffer layer is Ta with a thickness of 0-3 nm.

[0023] Preferably, the buffer layer material is Ta or NiTa, and its thickness is 1-3 nm, which aims to increase the uniformity of the film and reduce its roughness.

[0024] In this invention, a heavy metal conductive material is used as the SOT layer. The heavy metal conductive material is one of Pt and W, and its thickness is 4-5 nm. Its function is to convert the charge flow into a spin current and inject it into the free layer through the strong spin-orbit coupling of the heavy metal.

[0025] Preferably, the tunneling layer material is MgO with a thickness of 0.6-1.0 nm, which provides potential energy for electron tunneling and constructs a tunneling magnetoresistive sandwich structure.

[0026] Preferably, the reference layer is a multilayer film structure, consisting of CoFeB, Ta, Co, (Co / Pt)×2, Ru, Co, and (Co / Pt)×6 from bottom to top. The CoFeB layer has a thickness of 1.2 nm; the Ta layer has a thickness of 0.3 nm; the Co layer has a thickness of 0.4 nm; each layer of Co and Pt in the (Co / Pt)×2 double-layer structure and the (Co / Pt)×6 six-layer structure has a thickness of 0.4 nm; the Ru layer has a thickness of 0.6-0.8 nm; and the reference layer exhibits perpendicular magnetic anisotropy.

[0027] Preferably, a substrate layer is provided below the buffer layer of the multilayer thin film structure. The substrate layer is made of Si / SiO2, and the Si surface is covered with 500nm of SiO2 to isolate the substrate from the multilayer thin film structure and prevent device leakage.

[0028] In this invention, the tunneling layer material is selected from MgO to maintain the product effect. The tunneling layer material can also be oxide, nitride or nitrogen oxide; wherein, in addition to nitrogen and oxygen, it includes one or more of Mg, B, Ti, V, Cr, Mn, Al, Ge, Si, Ca, La, Hf, Cu, Ta, W, Sr, Ru and Mo.

[0029] like Figure 2 As shown, taking SOT-MTJ as an example, an additional ultrathin rare-earth layer is introduced between the basic structure containing the SOT layer, free layer, tunneling layer, and reference layer. This significantly improves the magnetic anisotropy and spin polarization of SOT-MTJ.

[0030] The present invention will be further described below with reference to the accompanying drawings and embodiments: like Figure 2 As shown, rare earth layers are introduced between the reference layer and the free layer to increase the magnetic anisotropy of the free layer CoFeB by utilizing the strong spin-orbit coupling and 4f electronic states of the rare earth layers.

[0031] like Figure 3 The figure shows the characterization results of the magnetic anisotropy of the free layer in the implementation example.

[0032] The SOT layer is made of W with a thickness of 4 nm. The aim is to provide better flatness to the free layer and to utilize the strong spin-orbit coupling effect of its heavy metals to provide spin polarization current and manipulate the magnetization state of the free layer.

[0033] The rare-earth layer is Gd, with a thickness of 0-0.5 nm. It is designed as an interface buffer layer to modulate the magnetic anisotropy of the free layer. In samples without Gd (0 nm) and with inserted Gd (0.3 nm), the perpendicular magnetic anisotropy of the free layer was improved by 475%. This means that the insertion of the rare-earth layer can directly increase the storage density by nearly 5 times.

[0034] The tunneling layer is MgO with a thickness of 1 nm. It is designed to act as a tunneling layer, providing a considerable potential barrier between the free layer and the rare earth layer with different spin state densities.

[0035] The free layer and part of the reference layer are both CoFeB, with a thickness of 1.2 nm. The aim is to construct the basic "sandwich" structure of the MTJ together with the tunneling layer.

[0036] It can be seen that the ultrathin rare earth layer Gd significantly increases the perpendicular magnetic anisotropy between the free layer and the reference layer CoFeB. Furthermore, Gd is a metal with good conductivity, and the ultrathin state has almost no effect on the resistance of the device.

[0037] like Figure 4 The figure shows the spin polarization characterization results of SOT-MTJ in the implementation example.

[0038] The SOT layer is made of W with a thickness of 4 nm. The aim is to provide better flatness to the free layer and to utilize the strong spin-orbit coupling effect of its heavy metals to provide spin polarization current and manipulate the magnetization state of the free layer.

[0039] The rare-earth layer is Gd, with a thickness of 0-0.4 nm. It is intended to serve as an interface modification layer, utilizing its strong spin-orbit coupling and ferromagnetism to enhance the interface Rashba effect. Furthermore, due to the significant difference between the work function of Gd and CoFeB, the spin accumulation generated by the interface Rashba effect will dissipate and be injected into CoFeB, thereby increasing the overall spin polarizability.

[0040] The tunneling layer is MgO with a thickness of 1 nm. It is designed to act as a tunneling layer, providing a considerable potential barrier between the free layer and the rare earth layer with different spin state densities.

[0041] The free layer and part of the reference layer are both CoFeB, with a thickness of 1.2 nm. The aim is to construct the basic "sandwich" structure of the MTJ together with the tunneling layer.

[0042] It can be seen that the ultrathin rare-earth layer Gd significantly increases the spin polarization of SOT-MTJ and STT-MRAM. Furthermore, Gd is a metal with good conductivity, and the ultrathin state has almost no effect on the device resistance. In samples without Gd (0 nm) and with inserted Gd (0.3 nm), the spin polarization of the free layer is increased by more than two times. This indicates that the insertion of the rare-earth layer can directly reduce energy consumption by a factor of two.

Claims

1. A magnetic random access memory, comprising a magnetic tunnel junction, wherein the magnetic tunnel junction comprises a tunneling layer made of MgO and a ferromagnetic free layer, characterized in that, The surface of the free layer is further provided with a rare earth layer, which is composed of rare earth elements with 4f magnetic electrons.

2. The magnetic random access memory as described in claim 1, characterized in that, The rare earth layer is made of Gd and has a thickness of 0.3-0.4 nm.

3. A magnetic random access memory as described in claim 1, characterized in that, The magnetic random access memory is a spin-transfer moment MRAM or a spin-orbit moment MRAM.

4. A magnetic random access memory as described in claim 3, characterized in that, The storage cell of the spin-transfer torque MRAM has a multilayer thin film structure, which, from bottom to top, consists of a buffer layer, a pinning layer, a reference layer, a tunneling layer, a free layer, a rare earth layer, an intermediate layer, a rare earth layer, a free layer, and a tunneling layer.

5. A magnetic random access memory as described in claim 3, characterized in that, The storage cell of the spin orbital moment MRAM is a multilayer thin film structure, which, from bottom to top, consists of a buffer layer, an SOT layer, a rare earth layer, a free layer, a rare earth layer, a tunneling layer, a rare earth layer, a reference layer, a rare earth layer, and a pinning layer.

6. A magnetic random access memory as described in claim 4 or 5, characterized in that, The buffer layer material is one or more of Ta, TaNi alloy, and MgO, and the thickness of the buffer layer is less than 5 nm.

7. A magnetic random access memory as described in claim 4 or 5, characterized in that: The pinning layer is a stacked composite layer of a magnetically anisotropic material and a material with RKKY interlayer exchange coupling effect; the anisotropic material is a CoPtCr alloy, a CoPt alloy, or a composite stack [Co / Pt]. n Multilayer films, CoNi alloys, composite stacks [Co / Ni] m One of the multilayer films and FePt alloys, with a thickness of 0-5 nm; Where n and m refer to the number of times the stack is repeated, and both n and m are greater than 1; The material having the RKKY interlayer exchange coupling effect is one or more of Ir, Ru, Nb, Ta, Cr, Mo, W, Re, Os, Rh, Pt, Cu, Ag and Au.

8. A magnetic random access memory as described in claim 1, characterized in that: The ferromagnetic free layer is made of CoFeB alloy, Co, Fe or Ni, and has a thickness of 0-3 nm. The 4f rare earth element is one or more of La, Ce, Pr, Eu, Gd, Tb, Dy, Ho, Er, and Tm.

9. A magnetic random access memory as described in claim 4 or 5, characterized in that: The tunneling layer material is an oxide, nitride, or nitrogen oxide; wherein, in addition to nitrogen and oxygen, it includes one or more of Mg, B, Ti, V, Cr, Mn, Al, Ge, Si, Ca, La, Hf, Cu, Ta, W, Sr, Ru, and Mo.

10. A magnetic random access memory as described in claim 5, characterized in that: The SOT layer material is one or more of W, Pt, Ta, Ti, Cu, Ru, Cr, Hf, O, N, Ir, Mn, V, Al, Mg, Mo, Rh, Pd, Ag, Sn, Te, Re, Au, La, Ce, Pr, Eu, Gd, Tb, Dy, Ho, Er, and Tm.

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