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EP-4429447-B1 - TEMPLATING LAYERS FOR SPIN ORBIT TORQUE ASSISTED SWITCHING OF PERPENDICULARLY MAGNETIZED HEUSLER FILMS

EP4429447B1EP 4429447 B1EP4429447 B1EP 4429447B1EP-4429447-B1

Inventors

  • Ikhtiar,
  • GARG, CHIRAG
  • Jeong, Jaewoo
  • Filippou, Panagiotis Charilaos
  • SAMANT, MAHESH
  • YANG, See-Hun

Dates

Publication Date
20260506
Application Date
20240115

Claims (7)

  1. A magnetic random access memory, MRAM, stack (100, 200, 300) comprising: a first magnetic layer (120, 220) comprising a Heusler compound; and one or more seed layers (104, 204) comprising: a templating structure (118) comprising a crystalline structure configured to template the Heusler compound, wherein the first magnetic layer (120) is formed over the templating structure (118), the templating structure (118) comprising: a layer of a binary alloy comprising platinum-aluminum, PtAl, the MRAM stack (100, 200, 300) further comprising: a second magnetic layer (128, 228); and a tunnel barrier (126, 226) positioned between, and in contact with, one or more of the first magnetic layer (120) and the second magnetic layer (128), wherein: the first magnetic layer (120) comprises a storage layer; the second magnetic layer (128) comprises a reference layer (201, 228); and the first magnetic layer (120), the tunnel barrier (126, 226), and the second magnetic layer (128) define a magnetic tunnel junction (122, 222), MTJ, wherein the Heusler compound is chosen from the group consisting of Mn 3 Ge, Mn 3 Al, Mn 3 Ga, Mn 3 In, Mn 2 FeSb, Mn 2 CoGe, Mn 2 CoSi, Mn 2 CuSi, Mn 2 CoSn, Co 2 CrAl, Co 2 CrSi, Co 2 MnSb, and Co 2 MnSi, or wherein the Heusler compound is a ternary Heusler compound selected from the manganese-cobalt-tin group consisting of Mn 3.3-x Co 1.1-y Sn, in which x ≤ 1.2 and y ≤ 1.0, or wherein the first magnetic layer (120, 220) is formed from compounds of Mn 3 Z, wherein: Z is an element selected from the group consisting of germanium, Ge, tin , Sn, and antimony, Sb; and the compounds of Mn 3 Z are selected from the group consisting of Mn 3.3-x Ge, Mn 3.3-x Sn, and Mn 3.3-x Sb, x in a range from 0 to 1.1.
  2. The MRAM stack (100, 200, 300) of claim 1, wherein: the tunnel barrier (126, 226) is formed from compounds selected from the group consisting of MgO and Mg 1-z Al 2+(2/3)z O 4 , wherein -0.5 < z < 0.5.
  3. The MRAM stack (100, 200, 300) of claim 1 or 2, wherein the first magnetic layer (120) defines a thickness dimension, and wherein: the first magnetic layer (120) has a magnetization which is orientated in the thickness dimension; and the first magnetic layer (120) has a thickness of less than 5 nanometers, nm.
  4. The MRAM stack (100, 200, 300) of any one of claims 1 to 3, wherein: the layer of the binary alloy comprising PtAl has a CsCl-like structure selected from the platinum-aluminum group consisting of Pt x Al 1-x , in which 0.4 < x < 0.6.
  5. A method of fabricating a magnetic random access memory, MRAM, stack (100, 200, 300) comprising: forming one or more seed layers (104, 204) comprising: forming a templating structure (118) above a substrate (102, 202), wherein the templating structure (118) includes a crystalline structure, wherein the forming the templating structure (118) comprises: forming a layer of a binary alloy including platinum-aluminum, PtAl; and forming a first magnetic layer (120, 220) comprising: templating a Heusler compound through the templating structure (118), the method further comprising: forming a tunnel barrier (126, 226) over the first magnetic layer (120, 220); and forming a second magnetic layer (128, 228) over the tunnel barrier (126, 226), thereby positioning the tunnel barrier (126, 226) between, and in contact with, the first magnetic layer (120, 220) and the second magnetic layer (128, 228), wherein: the first magnetic layer (120, 220) defines a storage layer; the second magnetic layer (128, 228) defines a reference layer (201, 228); and the first magnetic layer (120, 220), the tunnel barrier (126, 226), and the second magnetic layer (128, 228) define a magnetic tunnel junction (122, 222), MTJ, wherein the Heusler compound is chosen from the group consisting of Mn 3 Ge, Mn 3 Al, Mn 3 Ga, Mn 3 In, Mn 2 FeSb, Mn 2 CoGe, Mn 2 CoSi, Mn 2 CuSi, Mn 2 CoSn, Co 2 CrAl, Co 2 CrSi, Co 2 MnSb, and Co 2 MnSi, or wherein the Heusler compound is a ternary Heusler compound selected from the manganese-cobalt-tin group consisting of Mn 3.3-x Co 1.1-y Sn, in which x ≤ 1.2 and y ≤ 1.0, or wherein the first magnetic layer (120, 220) is formed from compounds of Mn 3 Z wherein: Z is an element selected from the group consisting of germanium, Ge, tin ,Sn, and antimony, Sb; and the compounds of Mn 3 Z are selected from the group consisting of Mn 3.3-x Ge, Mn 3.3-x Sn, and Mn 3.3-x Sb, x in a range from 0 to 1.1.
  6. The method of claim 5, further comprising: templating the Heusler compound over the templating structure (118).
  7. The method of claim 5 or 6, wherein: the forming the layer of the binary alloy including the PtAl comprises: forming a layer of a binary alloy having a CsCl-like structure selected from the platinum-aluminum group consisting of Pt x Al 1-x , in which 0.4 < x < 0.6.

Description

BACKGROUND The present disclosure relates to magnetic random access memory (MRAM) devices, and, more specifically, optimizing the tunnel magnetoresistance (TMR) and switching currents of a magnetic tunneling junction (MTJ) device with a Heusler layer in a MRAM stack. EP 4 027 344 A1 discloses a magnetic structure, a magnetic device incorporating the magnetic structure and a method for providing the magnetic structure are described. The magnetic structure includes a magnetic layer, a templating structure and a resistive insertion layer. The magnetic layer includes a Heusler compound and has a perpendicular magnetic anisotropy energy exceeding an out-of-plane demagnetization energy. The templating structure has a crystal structure configured to template at least one of the Heusler compound and the resistive insertion layer. The magnetic layer is on the templating structure. The resistive insertion layer is configured to reduce magnetic damping for the Heusler compound and allow for templating of the Heusler compound. Further prior art is disclosed in Grushko B., "On the constitution of Al-Pt-(Pd or Ni) around 50at.% Al", Journal of Alloys and Compounds, 541, 88-93 (2012). Many known magnetic memory devices, for example, magnetic random access memory (MRAM) devices, are storage elements that store information utilizing magnetic materials as the information storage medium. Many of these known MRAM devices include a magnetic tunneling junction (MTJ) that is typically a structure that includes three distinct layers, i.e., a magnetic reference layer and a magnetic free layer with an insulating tunneling barrier therebetween. When electric current is transmitted through the MRAM device, the resistance of the MTJ typically depends on the relative orientation of magnetization of the two magnetic layers, and the relative change in resistance is referred to as the tunnel magnetoresistance (TMR). In at least some known MTJs, the free layer is formed from a Heusler compound (or alloy). Some known MTJs employ a spin transfer torque (STT) effect to define STT-MRAM devices. The STT effect facilitates the toggling, i.e., switching of magnetic orientation of the free layer of the MTJ. The electrons that define an electric current have the intrinsic quantum mechanical property of spin that is associated with the spin angular momentum of the electrons. By passing electrons perpendicularly through the fixed reference layer, a spin-polarized current is produced, where the current has a spin-polarized angular momentum. When this spin-polarized current is directed into the free layer, at least a portion of the spin-polarized angular momentum of the respective electrons is transferred to the free layer, thereby applying a spin transfer torque (STT) to the magnetic moments in the free layer. Changing, i.e., flipping (toggling or switching) the orientation of the respective magnetic moment is achieved when the spin transfer torque is of sufficient magnitude. Some known MRAM devices and their respective MTJs use an additional mechanism, i.e., spin orbit torque (SOT) to facilitate operation of SOT-MRAM devices that also employ the STT mechanism. One mechanism for inducing spin orbit torque is through coupling a nonmagnetic heavy metal material to the magnetic layer, i.e., the free layer, where the nonmagnetic layer (sometimes referred to as the SOT layer) induces a large spin orbit coupling (or interaction) between the spin of the electrons and the motion of the respective electron charges. Such spin orbit coupling induces the spin Hall effect (SHE), where electrons with different spins deflect in different directions yielding a pure injected spin current transverse to an applied charge current (read or write), similar to the well-known Hall effect. The polarized spin-currents that accumulate on opposite sides of the non-magnetic layer induce an additional torque on the free layer, i.e., the spin-orbit torque. The addition of the spin orbit torque induced by the non-magnetic layer on the coupled magnetic free layer to the spin transfer torque further decreases the necessary current for switching the respective MTJ. SUMMARY The invention is set out in the appended claims. A system and method are provided for optimizing the tunnel magnetoresistance (TMR) and switching currents of a magnetic tunneling junction (MTJ) device with a Heusler layer in a MRAM stack. In one aspect, a magnetic random access memory (MRAM) stack is presented. The MRAM device includes a first magnetic layer including a Heusler compound. The MRAM stack also includes one or more seed layers that include a templating structure including a crystalline structure. The first magnetic layer is formed over the templating structure. The templating structure includes a layer of a binary alloy including platinum-aluminum (PtAl). The desired reduction in the switching current of an MTJ in the MRAM stack is achieved through assisting the spin transfer torque (STT) with a simultane