ABSTRACT
Spintronics plays a key role in minimizing static power consumption and enabling high-speed data transfer in neuromorphic computing architectures. In comparison to other novel nonvolatile memory architectures such as ferroelectric RAM (FRAM), resistive RAM (RRAM), and others, spin-transfer torque magneto resistance random-access memory (MRAM) (STT-MRAM) has gained considerable traction in the design of NV memory technologies due to its low power consumption, better speed, scalability, high endurance, and compatibility with CMOS processes. Irrespective of these advantages, STT-MRAM suffers from read and write latency issues due to incubation delay. Furthermore, the common read/write channel might reduce read reliability, while the write current can put a lot of strain on the magnetic tunnel junction (MTJ), and it may eventually result in the breakdown of the tunnel layer, hence resulting in memory cell degradation over time. Spin orbit torque (SOT)-MRAM has recently been presented as a solution to overcome these challenges.
A heavy metal (HM) such as W, Ta, or Pt with a significant spin orbit coupling (SOC) operates as a SOC layer in most conventional SOT MRAMs, generating the SOTs required for magnetization switching. Due to the spin Hall effect (SHE) in bulk material and the Rashba-Edelstein effect (REE) at interfaces, an in-plane current passing via the HM layer produces transverse spin current, which exerts a spin torque on the adjacent ferromagnetic (FM) layer and triggers switching of magnetization. A perpendicular magnetic anisotropy (PMA) SOT MRAM offers compact scalability, improved thermal stability, read/write route isolation, and low-magnetization switching current requirements. However, utilizing an HM as a SOC layer in PMA-based systems would lead to extra device geometries, necessitating additional fabrication stages and/or the use of an external magnetic field for deterministic magnetization switching.
Electrical and optoelectronic properties of two-dimensional (2D) materials such as topological insulator (TI) and transition metal dichalcogenides (TMDs) are extraordinary and highly tunable. They could be used in a variety of applications, including nanoelectronic devices, photodetectors, and sensors. TMDs have been presented as a technique to provide efficient magnetization switching in the adjoining FM layer due to strong SOC without the use of a magnetic field or a distinct fabrication procedure. Due to the breaking of inversion symmetry, which generates a range of events that drive the system out of equilibrium, TIs have a high SOC, which makes them excellent for spintronic devices. Furthermore, utilizing all van der Waals (vdW) material heterostructures to thin down heterointerfaces holds a lot of promise for further improving the SOT efficiency. TMDs have also been used as a barrier in MTJs, which are made up of TMDs such as MoS2 and WS2 sandwiched between two FM layers and provide extremely high tunneling magneto resistance (TMR). Many 2D material factors, such as thickness, quality, and surface chemical state, have a direct effect on MTJ performance. Also unknown is the relaxation of spin electrons in 2D materials, and efficient spin gating remains a difficulty.
