Field-free switching of a perpendicular magnetic tunnel junction through the interplay of spin–orbit and spin-transfer torques

Abstract

Magnetization switching by the interaction between spins and charges has greatly brightened the future of spintronic memories. [1][2][3][4][5][6] This has been evident in the rapid development of spin transfer torque-magnetic random-access memory (STT-MRAM) as a mainstream non-volatile memory technology, in which a spin-polarized current is injected into magnetic tunnel junctions (MTJs) for cell programming. 7-18 However, as cell areas scale down to meet density and power demands, conventional STT-MRAM suffers from serious endurance and reliability issues due to the aging of the ultrathin MgO barrier and read disturbance. The challenge of lowering STT switching current densities to further reduce power consumption is still yet to be met. [19][20][21] The discovery of spin-orbit torque (SOT) switching in heavy metal/ferromagnetic metal/oxide heterostructures by applying an in-plane charge current to three-terminal devices provides a promising alternative mechanism. 22-28 It shows the potential to enhance the endurance and reliability of MRAM, while improving speed and reducing power consumption. [29][30][31][32] Thus, considerable research has been triggered to further elucidate the mechanism of SOT switching, which is currently described as magnetic reversal via two vector components, the damping-like (DL) and field-like (FL) torques. 33,34 Since the demonstration of perpendicular-anisotropy MgO/CoFeB MTJs (p-MTJs), the switching of perpendicular magnetization by SOT has become of particular interest. [33][34][35][36][37][38] However, an external magnetic field collinear with the charge current is required to execute deterministic switching of p-MTJs. This intrinsic constraint, combined with the three-terminal device configuration, is limiting the practical application of SOT-MRAM. [26][27][28]35 Great efforts have been made to eliminate the need

Energy‐Efficient Ultrafast SOT‐MRAMs Based on Low‐Resistivity Spin Hall Metal Au0.25Pt0.75

“…[40,41] We find that the current-induced SOT switches the Au 0.25 Pt 0.75 -based MRAMs much faster than expected from a rigid macrospin model, most likely due to the rapid micromagnetics within the free layer that is enhanced by the spatial nonuniformities in the free-layer magnetization that may be induced by DMI, interfacial magnetic roughness, and/or tapering in the MTJ free layer. We have demonstrated switching of prototypical SOT-MRAM structures with 50% probability using I ≈ 3 mA and E write = 2 pJ for 200 ps current pulses, and write error rates <10 −5 at I = 4 mA and E write = 14 pJ for 1 ns pulses.…”

“…We have demonstrated switching of prototypical SOT-MRAM structures with 50% probability using I ≈ 3 mA and E write = 2 pJ for 200 ps current pulses, and write error rates <10 −5 at I = 4 mA and E write = 14 pJ for 1 ns pulses. The collinear in-plane MRAMs can be switched directly by spin current from the spin Hall channel, while perpendicular SOT-MTJs require a markedly high write current in the nanosecond and sub-nanosecond pulse regime [16,41] as well as assistance of a strong in-plane magnetic field (e.g., stray field from an adjacent ferromagnetic layer [41,42] or built-in magnetic field from a lateral structural asymmetry [43] ) or an additional large write current in the MTJ nanopillar, [40] which may lower the energy efficiency, the scalability, and the endurance of the MTJ cells. The relatively low channel resistance due to the low ρ xx of Au 0.25 Pt 0.75 is beneficial for decreasing write energies, achieving unlimited endurance, and also for matching the impedance of superconducting circuits in cryogenic computation systems.…”

Full voltage manipulation of the resistance of a magnetic tunnel junction

“…To store binary bits 0 and 1, the parallel and antiparallel magnetization configurations need to be easily mutually switched, thus accomplishing a "writing" operation. Conventionally, the writing of bits uses a magnetic field, a spinorbit torque (5)(6)(7), or a spintransfer torque (STT) (8,9), each of which requires a high electric current density to be flowing in the device and consequently dissipates significant energy.…”

Impact of Spin-Orbit Torque on Spin-Transfer Torque Switching in Magnetic Tunnel Junctions

“…Various schemes are introduced to overcome these obstacles. For example, they are the application of a manipulated write pulse current and the use of voltage control magnetic anisotropy (VCMA) or spin-orbit torque (SOT) with the assisting STT [11][12][13][14] . All of these schemes are gaining great attention equally in recent times.…”