Single-barrier Magnetic Tunnel Junctions Research Articles

Enhanced spin current by anti-reflective magnetic tunnel junctions

Charge current and in-plane spin current are calculated in magnetic tunnel junctions (MTJs). The transmission function is investigated using nonequilibrium Green’s function formalism in a single-barrier MTJ, a resonant-tunneling MTJ and an anti-reflective MTJ (A-MTJ). The results show an enhancement in magnitude of the charge and in-plane spin currents for an A-MTJ compared to the other MTJs due to the presence of anti-reflective regions.

Band-pass magnetic tunnel junctions with β-Ga2O3 semiconductors for spin-filtering goals

Spin-filtering properties are investigated in magnetic tunnel junctions (MTJs) utilizing anti-reflective (AR) regions idea. The β−Ga2O3 semiconductors are embedded as quantum wells in the A-RMTJs. The results show a full spin-filtering feature and an ultrahigh tunnel-magnetoresistance (TMR) ratio contrasted to those in the single-barrier MTJs as a result of the band-pass transmission in the A-RMTJs. Therefore, it can be designed an excellent spin-filter device as well as improved MRAMs in the field of spintronics.

Thermopower of double-barrier magnetic tunnel junctions with a middle La0.7Sr0.3MnO3 layer

Magnetic tunnel junctions (MTJs) are promising devices for heat-assisted magnetic recording technology. Quantum transport of nanoscale double-barrier MTJs with a middle La0.7Sr0.3MnO3 (LSMO) layer (DBMTJs-LSMO) is investigated by the non-equilibrium Green’s function formalism. The thermopower is described in the linear response regime. The results of the DBMTJs-LSMO show an enhancement of the thermopower compared to DBMTJs-CoFeB and conventional single-barrier MTJs (SBMTJs) due to the LSMO physical properties and also the existence of the quantum-well (QW) states. The parallel (P) and anti-parallel (AP) thermopower of and are achieved at room temperature for DBMTJs-LSMO. The tunnel magneto-thermopower ratio is found to be at room temperature along with its maximum value of at for DBMTJs-LSMO.

Assessment of STT-MRAMs based on double-barrier MTJs for cache applications by means of a device-to-system level simulation framework

This paper explores non-volatile cache memories implemented by spin-transfer torque magnetic random access memories (STT-MRAMs) based on state-of-the-art perpendicular magnetic tunnel junctions (MTJs) and FinFETs. The use of double-barrier MTJs with two reference layers (DMTJs) is benchmarked against solutions relying on single-barrier MTJs (SMTJs) at different technology nodes (from 28-nm down to 20-nm). Our study is carried out through a cross-layer simulation platform, starting from the device- up to the system-level. Our results point out that, thanks to the reduced switching currents, DMTJ-based STT-MRAMs allow decreasing write access time of about 63% as compared to their SMTJ-based counterparts. This is achieved while assuring reduced energy consumption under both write (−42%) and read (−28%) accesses, lower area occupancy (−40%) and smaller leakage power (−25%), at the only cost of worsened read access time. This makes DMTJ-based STT-MRAM a promising candidate to replace conventional semiconductor-based cache memory for the next-generation of low-power microprocessors with on-chip non-volatility.

Compact Modeling of Perpendicular STT-MTJs With Double Reference Layers

This paper shows the steps to set up a simulation framework for perpendicular spin-transfer torque (STT)-magnetic tunnel junctions (MTJs) with double-barrier and two antiparallel reference layers (DMTJs). The approach is based on a Verilog-A analytical compact model that properly takes into account the effect of the DMTJ physical stack on both resistance and statistical switching characteristics. Validation results demonstrate a good agreement of analytical calculations with both numerical simulations and experimental data. To test the functionality of the developed Verilog-A code in hybrid CMOS/STT-MTJ circuit simulations, we have investigated the performance of a non-volatile flip-flop (NVFF) implemented with DMTJs and FinFETs in comparison with its single-barrier MTJ (SMTJ)-based counterpart. The reduced switching current of DMTJs allows reducing the backup time and energy by a factor of 3X and 6.1X, respectively. Such benefits are obtained along with smaller area occupation and better performance in the flip-flop (FF) active operation mode.

Dynamic and Magnetotransport Properties of Perpendicularly Magnetized CoFeB Magnetic Tunnel Junctions

We present the study of the dynamic properties of CoFeB (CFB) based magnetic tunnel junctions (MTJ) by Brillouin light scattering spectroscopy and micro-strip ferromagnetic resonance technique as well as magnetoresistance measurements. Two different MTJs: single and double barrier systems have been investigated. The dynamic studies revealed mostly similar perpendicular anisotropy field for both CoFeB layers for the single barrier MTJ with the thickest CFB layers, while two sensibly different perpendicular anisotropy fields were revealed in the case of the double barrier MTJ with the thickest CFB soft and hard layers. Modeling the spin wave frequencies behavior allows us the analysis of the experimental data and the derivation of the pertinent magnetic parameters. Our results suggest an interfacial origin of the anisotropy. Therefore, by changing the thickness of the perpendicularly magnetized CFB layers, it is possible to obtain a free and pinned layer usually ensured by the use of synthetic antiferromagnetic material. The tunnel magnetoresistance has been measured in elliptical elements of double barrier MTJ of different sizes. Strong size-dependent switching fields and antiparallel state being more unstable in the smallest device are observed. Patterning effect, lowering the anisotropies around the edge areas and increasing the dipolar coupling that favors the parallel state in the case of stacked layers, are probably the origin.

Enhancement of thermal spin transfer torque by double-barrier magnetic tunnel junctions with a nonmagnetic metal spacer

Enhancement of thermal spin transfer torque in a double-barrier magnetic tunnel junction with a nonmagnetic-metal spacer is proposed in this study. The results indicate that, given the same temperature difference, thermal spin transfer torque and charge current density for the proposed double barrier magnetic tunnel junction configuration can be approximately twice as much as that of the traditional single-barrier magnetic tunnel junctions. This enhancement can be attributed to the resonant tunneling mechanism in the double-barrier structure.

Spin-polarized current and tunnel magnetoresistance in heterogeneous single-barrier magnetic tunnel junctions

Current in heterogeneous tunnel junctions is studied in the framework of the parabolic conduction-band model. The developed model of the electron tunneling takes explicitly into account the difference of effective masses between ferromagnetic and insulating layers and between conduction subbands. Calculations for Fe/MgO/Fe-like structures have shown the essential impact of effective mass differences in regions (constituents) of the structure on the tunnel magnetoresistance of the junction.

Impact of lattice strain on the tunnel magnetoresistance in Fe/insulator/Fe and Fe/insulator/La0.67Sr0.33MnO3magnetic tunnel junctions

The objective of this work is to describe the tunnel electron current in single barrier magnetic tunnel junctions within a new approach that goes beyond the single-band transport model. We propose a ballistic multi-channel electron transport model that can explain the influence of in-plane lattice strain on the tunnel magnetoresistance as well as the asymmetric voltage behavior. We consider as an example single crystal magnetic Fe(110) electrodes for Fe/Insulator/Fe and Fe/Insulator/La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ tunnel junctions, where the electronic band structures of Fe and La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ are derived by \it{ab-initio} calculations.

Microfabrication and magnetoelectric properties of amorphous magnetic-tunnel-junctions with Co–Fe–B/Al–O/Co–Fe–B hardcore structure

Both single-barrier magnetic tunnel junctions (SBMTJs) and double-barrier magnetic tunnel junctions (DBMTJs) with an amorphous hardcore structure of Co 60Fe 20B 20/Al–O/Co 60Fe 20B 20 were microfabricated. A high TMR ratio of 102.2% at 4.2 K was observed in the SBMTJs after annealing at 265 °C for 1 h. High TMR ratio of 56.2%, low junction resistance-area product RS of 4.6 kΩ μm 2, small coercivity H C=25 Oe, and relatively large bias-voltage-at-half-maximum TMR with the value V 1/2 greater than 500 mV at room temperature (RT) had been achieved in such Co–Fe–B SBMTJs. Whereas, high TMR ratio of 60% at RT and 89% at 30 K, low junction resistance-area product RS of 7.8 kΩ μm 2 at RT and 8.3 kΩ μm 2 at 30 K, low coercivity H C=8.5 Oe at RT and H C=14 Oe at 30 K, and relatively large bias-voltage-at-half-maximum TMR with the value V 1/2 greater than 1150 mV at RT had been achieved in the Co–Fe–B DBMTJs. Temperature dependence of the TMR ratio, resistance, and coercivity from 4.2 K to RT, and applied voltage dependence of the TMR ratio and resistance at RT for such amorphous MTJs were also investigated.

Asymmetrical Spin-Polarized Tunneling in a Composed-Barrier Magnetic Tunnel Junctions Under the Forward and Reverse Biases

Based on the two-band model and nearly-free-electron approximation, the tunnel current, conductance and magnetoresistance of the composed-barrier magnetic tunnel junctions (MTJ) under the forward and reverse biases are discussed, respectively, and the numerical results are compared with the experimental results of the single-barrier MTJ. We find that there exists an asymmetrical spin-polarized tunneling in this structure under the forward and reverse biases. It suggests that this type of MTJ will provide novel functions to the potential applications of traditional types of MTJ.