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Spintronics Presentation (PHYSICS & APPLICATION) - Coggle Diagram
Spintronics Presentation (PHYSICS & APPLICATION)
STT
Critical Current density
amount of charge current needed ==> power & heat
"first is the amount of spin-current necessary to reliably switch a nanomagnet at desired speed and at ambient temperature. The other is the amount of charge-current that necessarily accompanies the spin-current."
"co-optimization in real junctions, because a finite bias voltage across a tunnel barrier not only causes tunnel current, but also induces other changes of interface properties, such as voltage-controlled magnetic anisotropy (VCMA) on the electrodes or electric-field induced strain-change from the tunnel barrier"
charge-to-spin current conversion ratio (the conversion efficiency)
harge to spin current conversion. Thus in practice, for an experimentally obtainable MTJ of 𝑚𝑟 > 1 (i.e. 100%), an 𝜂 ≲ 1∕2 is about as efficient as an MTJ can be, limited by the amount of spin an electron carries. The maximum 𝜂 is 1/2 because the resulting spin-torque is shared equally between the FL and the RL of the MTJ [23,24,26].
‘anti-damping torque' = spin-current induced STT
LLGS explained
energy viewpoint (p. 2)
"A switching nanomagnet for memory typically situates in an uniaxial anisotropy energy potential with two equal-energy minima, separated by an energy barrier 𝐸𝑏 ." ==> U-uni formula (p. 3)
"More generally, a spin current from the FL interfaces of the MTJ could also generate a torque of 𝜞FL = 𝐼s(FL)𝐧𝑚 × 𝐧𝑠 , whose vector relation is the same as an additional magnetic field in the direction of 𝐧𝑠 , hence the name of a ‘‘field-like torque’’."
"ts instantaneous torque direction with respect to the nanomagnet’s moment 𝐧𝑚. The damping-like torque 𝜞 DL always lies in the plane made by vectors 𝐧𝑚 and 𝐧𝑠 , while the field-like torque 𝜞 DL lies perpendicular to that plane. Thus they have also been called the ‘‘in-plane torque’’ (or ‘‘dissipative exchange torque’’ [26]), and the ‘‘perpendicular torque’’, respectively"
"A PMA MTJ (pMTJ) is made of two ferromagnetic tunnel electrodes, one having its magnetic orientation switchable between up- and downorientation for storing a bit, called a free-layer (FL); the other having its magnetic direction fixed, called a reference layer or RL, for providing a reference orientation for the FL, as illustrated in Fig. 1(a)."
MTJ device
Circuit configuration
Reading
writing
bit selection
Free Layer
Pinned Layer
Tunnelling barrier
GMR (+ P and AP) ==> TMR ==> formula
1000% & 200% & 600%
limits from room temp
why we want high
impedance matching with VLSI
"including the first generation MTJ-based MRAM (Everspin, 2008), the first generation STT-switched MRAM (Everspin 2012), and the more modern, perpendicularly magnetized high performance STT-MRAM (Everspin, Global Foundary, 2016 onward)."
An ultrathin insulating material acting as a tunnel barrier separates the two
electrodes.
same W/R paths... reliability issues
==> SOT
Spintronics intro
Spin
Spin-polarized current
charge-to-spin current conversion ratio (the conversion efficiency)
Other topics
SOT
other swithc mechanisms
in plane vs PMA
anisotropies & H_eff
real-world applications
