Spintronics in Nonvolatile Memory Systems

Spintronics exploits the spin of electrons in addition to their charge, enabling memory devices that combine non-volatility, high speed and low energy consumption. Central to this field are magnetic tunnel junctions (MTJs), nanoscale structures comprising two ferromagnetic layers separated by an insulating barrier, whose resistance depends on the relative orientation of magnetisation. Switching of the storage layer in MTJs is achieved by spin-transfer torque or spin-orbit torque, phenomena in which a spin-polarised current or spin current exerts a torque on the magnetisation, leading to low switching energy and high endurance. These properties underpin emerging non-volatile memory systems such as spin-transfer torque magnetoresistive random-access memory (STT-MRAM) and spin-orbit torque MRAM (SOT-MRAM), which are poised to complement or replace conventional volatile memories in cache, embedded and main memory applications. Recent developments have addressed challenges in scaling junctions below 20 nm, enhancing thermal stability through engineering of anisotropy, and integrating spintronic cells with CMOS for embedded platforms. At a system level, applications now span from high-performance computing architectures to neuromorphic accelerators and cryogenic control circuits, reflecting the global significance of spin-based memory as a driver of energy-efficient and versatile computing solutions.

Research from Nature Portfolio

Investigations into shape-driven anisotropy have demonstrated that MTJs smaller than 10 nm can achieve adequate thermal stability without novel materials. By revisiting classical shape anisotropy in perpendicular CoFeB/MgO stacks, researchers attained current-driven magnetisation switching at the single-digit scale, paving the way for sub-10 nm memories with low write currents. In parallel, efforts to build cryogenic memory arrays have combined three-terminal MTJ elements driven by the spin Hall effect with superconducting cryotron selectors operating at 4 K. These hybrid cells show reliable switching with write error rates below 10⁻⁶ and promise scalable, high-density non-volatile storage for superconducting and quantum computing platforms, addressing the energy and performance constraints of cryogenic systems.

Research from all publishers

A high-performance embedded MRAM designed for computing acceleration has been realised using spin-based cells in advanced CMOS processes. This spin-based memory exhibits fast access, high density and non-volatility, boosting the throughput of AI and data-intensive applications while reducing static power. A complementary study on non-volatile ternary content-addressable memory (TCAM) introduced a low-energy double-barrier MTJ design within a 28 nm FDSOI process. The hybrid 10T2DMTJ cell achieves sub-nanosecond search operations, drastically reducing write and search energy and footprint compared to previous NV-TCAMs. Further, multilevel STT- and SOT-MRAM cells have enabled neuromorphic accelerators for image classification. By exploiting two-, three- and four-level storage in crossbar arrays, these systems demonstrate significant gains in area and energy efficiency over conventional single-bit MRAM, delivering high throughput for binary neural networks on resource-constrained platforms.

Spintronics in Nonvolatile Memory Systems publication trend

The graph below shows the total number of articles in spintronics in nonvolatile memory systems across all publications each year (not limited to Nature Index journals).

Technical terms

Magnetic tunnel junction (MTJ): A nanoscale device of two ferromagnetic layers separated by an insulating barrier, whose electrical resistance depends on the relative alignment of magnetisation.

Spin-transfer torque (STT): A mechanism in which a spin-polarised charge current exerts torque on a magnet’s orientation, enabling switching with low energy.

Spin-orbit torque (SOT): A switching method using a transverse spin current generated by heavy-metal layers via the spin Hall effect.

Magnetoresistive random-access memory (MRAM): A non-volatile memory technology based on MTJs and spin-torque switching.

Spin Hall effect: The generation of a transverse spin current from a charge current in materials with strong spin–orbit coupling.

Magnetic anisotropy: Directional dependence of a material’s magnetic properties, including shape and perpendicular interfacial anisotropy, crucial for thermal stability.

References

1. Spin-based magnetic random-access memory for high-performance computing. National Science Review (2023).
2. Shape anisotropy revisited in single-digit nanometer magnetic tunnel junctions. Nature Communications (2018).
3. Cryogenic Memory Architecture Integrating Spin Hall Effect based Magnetic Memory and Superconductive Cryotron Devices. Scientific Reports (2020).
4. A Low-Energy DMTJ-Based Ternary Content- Addressable Memory With Reliable Sub-Nanosecond Search Operation. IEEE Access (2023).
5. Multi-bit MRAM based high performance neuromorphic accelerator for image classification. Neuromorphic Computing and Engineering (2024).