Many key electronic technologies (e.g., large‐scale computing, machine learning, and superconducting electronics) require new memories that are at the same time fast, reliable, energy‐efficient, and of low‐impedance, which has remained a challenge. Nonvolatile magnetoresistive random access memories (MRAMs) driven by spin–orbit torques (SOTs) have promise to be faster and more energy‐efficient than conventional semiconductor and spin‐transfer‐torque magnetic memories. It is reported that the spin Hall effect of low‐resistivity Au0.25Pt0.75thin films enables ultrafast antidamping‐torque switching of SOT‐MRAM devices for current pulse widths as short as 200 ps. If combined with industrial‐quality lithography and already‐demonstrated interfacial engineering, an optimized MRAM cell based on Au0.25Pt0.75can have energy‐efficient, ultrafast, and reliable switching, for example, a write energy of <1 fJ (<50 fJ) for write error rate of 50% (<10−5) for 1 ns pulses. The antidamping torque switching of the Au0.25Pt0.75devices is ten times faster than expected from a rigid macrospin model, most likely because of the fast micromagnetics due to the enhanced nonuniformity within the free layer. The feasibility of Au0.25Pt0.75‐based SOT‐MRAMs as a candidate for ultrafast, reliable, energy‐efficient, low‐impedance, and unlimited‐endurance memory is demonstrated.
Giant spin-orbit torque (SOT) from topological insulators (TIs) provides an energy efficient writing method for magnetic memory, which, however, is still premature for practical applications due to the challenge of the integration with magnetic tunnel junctions (MTJs). Here, we demonstrate a functional TI-MTJ device that could become the core element of the future energy-efficient spintronic devices, such as SOT-based magnetic random-access memory (SOT-MRAM). The state-of-the-art tunneling magnetoresistance (TMR) ratio of 102% and the ultralow switching current density of 1.2 × 105 A cm−2have been simultaneously achieved in the TI-MTJ device at room temperature, laying down the foundation for TI-driven SOT-MRAM. The charge-spin conversion efficiency
- Award ID(s):
- 1935362
- NSF-PAR ID:
- 10307011
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Nature Communications
- Volume:
- 12
- Issue:
- 1
- ISSN:
- 2041-1723
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Recent advances in using topological insulators (TIs) with ferromagnets (FMs) at room temperature have opened an innovative avenue in spin‐orbit torque (SOT) nonvolatile magnetic memory and low dissipation electronics. However, direct integration of TIs with perpendicularly magnetized FM, while retaining an extraordinary charge‐to‐spin conversion efficiency (
> 100%), remains a major challenge. In addition, the indispensable thermal compatibility with modern CMOS technologies has not yet been demonstrated in TI‐based structures. Here, high‐quality integration of a perpendicularly magnetized CoFeB/MgO system with TI through a Mo insertion layer is achieved and efficient current‐induced magnetization switching at ambient temperature is demonstrated. The calibrated energy efficiency of TIs is at least 1 order magnitude larger than those found in heavy metals. Moreover, it is demonstrated that the perpendicular anisotropy of the integrated CoFeB/MgO system and the current‐induced magnetization switching behavior are well‐preserved after annealing at> 350° C, offering a wide temperature window for thermal treatments. This thermal compatibility with the modern CMOS back‐end‐of‐line process achieved in these TI‐based structures paves the way toward TI‐based low‐dissipation spintronic applications. -
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We offer a perspective on the prospects of ultrafast spintronics and opto-magnetism as a pathway to high-performance, energy-efficient, and non-volatile embedded memory in digital integrated circuit applications. Conventional spintronic devices, such as spin-transfer-torque magnetic-resistive random-access memory (STT-MRAM) and spin–orbit torque MRAM, are promising due to their non-volatility, energy-efficiency, and high endurance. STT-MRAMs are now entering into the commercial market; however, they are limited in write speed to the nanosecond timescale. Improvement in the write speed of spintronic devices can significantly increase their usefulness as viable alternatives to the existing CMOS-based devices. In this article, we discuss recent studies that advance the field of ultrafast spintronics and opto-magnetism. An optimized ferromagnet–ferrimagnet exchange-coupled magnetic stack, which can serve as the free layer of a magnetic tunnel junction (MTJ), can be optically switched in as fast as ∼3 ps. Integration of ultrafast magnetic switching of a similar stack into an MTJ device has enabled electrical readout of the switched state using a relatively larger tunneling magnetoresistance ratio. Purely electronic ultrafast spin–orbit torque induced switching of a ferromagnet has been demonstrated using ∼6 ps long charge current pulses. We conclude our Perspective by discussing some of the challenges that remain to be addressed to accelerate ultrafast spintronics technologies toward practical implementation in high-performance digital information processing systems.
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Spin currents are used to write information in magnetic random access memory (MRAM) devices by switching the magnetization direction of one of the ferromagnetic electrodes of a magnetic tunnel junction (MTJ) nanopillar. Different physical mechanisms of conversion of charge current to spin current can be used in two-terminal and three-terminal device geometries. In two-terminal devices, charge-to-spin conversion occurs by spin filtering in the MTJ's ferromagnetic electrodes and present day MRAM devices operate near the theoretically expected maximum charge-to-spin conversion efficiency. In three-terminal devices, spin–orbit interactions in a channel material can also be used to generate large spin currents. In this Perspective article, we discuss charge-to-spin conversion processes that can satisfy the requirements of MRAM technology. We emphasize the need to develop channel materials with larger charge-to-spin conversion efficiency—that can equal or exceed that produced by spin filtering—and spin currents with a spin polarization component perpendicular to the channel interface. This would enable high-performance devices based on sub-20 nm diameter perpendicularly magnetized MTJ nanopillars without need of a symmetry breaking field. We also discuss MRAM characteristics essential for CMOS integration. Finally, we identify critical research needs for charge-to-spin conversion measurements and metrics that can be used to optimize device channel materials and interface properties prior to full MTJ nanopillar device fabrication and characterization.more » « less
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Abstract Spin Orbit Torque Magnetic RAM (SOT-MRAM) is emerging as a promising memory technology owing to its high endurance, reliability and speed. A critical factor for its success is the development of materials that exhibit efficient conversion of charge current to spin current, characterized by their spin Hall efficiency. In this work, it is experimentally demonstrated that the spin Hall efficiency of the industrially relevant ultra-thin Ta can be enhanced by more than 25× when a monolayer (ML) WSe2is inserted as an underlayer. The enhancement is attributed to spin absorption at the Ta/WSe2interface, suggested by harmonic Hall measurements. The presented hybrid spin Hall stack with a 2D WSe2underlayer has a total body thickness of less than 2 nm and exhibits greatly enhanced spin Hall efficiency, which makes this hybrid a promising candidate for energy efficient SOT-MRAM.
