Switching current reduction using MgO cap layer in magnetic tunnel junctions

Abstract

We investigate the current induced magnetization switching properties in CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) with the MgO cap layer. It is found that the spin-transfer-torque induced switching current density is inversely proportional to the thickness of the MgO cap layer. We attribute the origin of this behavior to the change in the effective demagnetizing field and damping factor in the free layer, which is verified by spin-torque ferromagnetic resonance measurements. Our experimental results suggest that the utilization of the MgO-cap layer in the MTJs may be useful for spintronic device designs, such as spin-transfer torque magnetic random access memories and spin torque oscillators.

Temperature-dependent interlayer exchange coupling strength in synthetic antiferromagnetic [Pt/Co]2/Ru/[Co/Pt]4multilayers

“…Spin-transfer-torque magnetic random access memories (STT-MRAMs) is one of the most attractive candidate to satisfy the need of memory markets owing to their outstanding performance, such as non-volatile, low power consumption, unlimited endurance, wide operating temperature, and longterm data retention. [1][2][3][4][5][6][7][8] However, how to realize the high density of current MRAM is the main bottleneck limiting their practical applications, which is due to the stray magnetic fields generated by magnetic layers. Recently, perpendicularly magnetized tunnel junctions (p-MTJs) that including synthetic antiferromagnetic (SAF) layers have been used to promote the development of STT-MRAMs.…”

Spin torque oscillator based on magnetic tunnel junction with MgO cap layer for radio-frequency-oriented neuromorphic computing

“…The MgO cap layer here is used to induce additional interfacial perpendicular magnetic anisotropy, lowering the demagnetization field and damping factor. [24,25] The thin films were deposited on a thermally oxidized silicon substrate using a magnetron sputtering system and annealed at 300 • C for 2.0 h in an in-plane magnetic field of 1 T. The magnetization direction of the pinned synthetic antiferromagnet (SAF) of Co 70 Fe 30 /Ru/Co 40 Fe 40 B 20 is magnetically hardened so that it can serve as the reference layer (RL) while the direction of magnetization of the Fe-rich Co 20 Fe 60 B 20 layer, called the free layer (FL), is free to rotate. Using electron beam lithography and Ar ion beam milling, the MTJ was defined and etched into a 150 nm×70 nm elliptical nano-pillar with its long axis parallel to the magnetic field for annealing.…”

Field- and Current-Driven Magnetization Reversal and Dynamic Properties of CoFeB-MgO-Based Perpendicular Magnetic Tunnel Junctions*

“…From the above discussion about current-driven magnetization switching, Gilbert damping factor 𝛼 plays a crucial role in determining the spin-transfer efficiency 𝜂 of the STT switching performance. [25,34,35] Based on a linear relationship between the linewidth ∆𝐻 and FMR frequency 𝑓 as follows: [35] ∆𝐻 = ∆𝐻 0 + 2𝜋𝛼𝑓 𝛾 ,…”