Tunnel Magnetoresistance Ratio Research Articles

Chiral molecular intercalation superlattices

The discovery of chiral-induced spin selectivity (CISS) opens up the possibility to manipulate spin orientation without external magnetic fields and enables new spintronic device designs1-4. Although many approaches have been explored for introducing CISS into solid-state materials and devices, the resulting systems so far are often plagued by high inhomogeneity, low spin selectivity or limited stability, and have difficulties in forming robust spintronic devices5-8. Here we report a new class of chiral molecular intercalation superlattices (CMIS) as a robust solid-state chiral material platform for exploring CISS. The CMIS were prepared by intercalating layered two-dimensional atomic crystals (2DACs) (such as TaS2 and TiS2) with selected chiral molecules (such as R-α-methylbenzylamine and S-α-methylbenzylamine). The X-ray diffraction and transmission electron microscopy studies demonstrate highly ordered superlattice structures with alternating crystalline atomic layers and self-assembled chiral molecular layers. Circular dichroism studies show clear chirality-dependent signals between right-handed (R-) and left-handed (S-) CMIS. Furthermore, by using the resulting CMIS as the spin-filtering layer, we create spin-selective tunnelling junctions with a distinct chirality-dependent tunnelling current, achieving a tunnelling magnetoresistance ratio of more than300per cent and a spin polarization ratio of more than60per cent. With a large family of 2DACs of widely tunable electronic properties and a vast selection of chiral molecules of designable structural motifs, the CMIS define a rich family of artificial chiral materials for investigating the CISS effect and capturing its potential for new spintronic devices.

STT-BNN: A Novel STT-MRAM In-Memory Computing Macro for Binary Neural Networks

This paper presents a novel architecture for in-memory computation of binary neural network (BNN) workloads based on STT-MRAM arrays. In the proposed architecture, BNN inputs are fed through bitlines, then, a BNN vector multiplication can be done by single sensing of the merged SL voltage of a row. Our design allows to perform unrestricted accumulation across rows for full utilization of the array and BNN model scalability, and overcomes challenges on the sensing circuit due to the limitation of low regular tunneling magnetoresistance ratio (TMR) in STT-MRAM. Circuit techniques are introduced in the periphery to make the energy-speed-area-robustness tradeoff more favorable. In particular, time-based sensing (TBS) and boosting are introduced to enhance the accuracy of the BNN computations. System simulations show 80.01% (98.42%) accuracy under the CIFAR-10 (MNIST) dataset under the effect of local and global process variations, corresponding to an 8.59% (0.38%) accuracy loss compared to the original BNN software implementation, while achieving an energy efficiency of 311 TOPS/W.

Type-Y magnetic tunnel junctions with CoFeB doped tungsten as spin current source

Spin–orbit torque magnetic tunnel junctions (SOT-MTJs) with high tunneling magnetoresistance (TMR) ratio and high energy-efficiency are crucial for the development of SOT-magnetic random-access memory and other SOT devices. Here, the SOT-MTJs doped with an ultrathin layer of 0.2 nm CoFeB in the W writing line are fabricated, and the TMR ratio of the updated MTJs is up to 179%. Meanwhile, the SOT efficiency of the W layer doped with magnetic atoms (∼0.149) is weakly dependent on the doping, manifesting the intrinsic mechanism of the W layer in generating the spin Hall effect. This study shows promise of the magnetic-atom doped W/CoFeB/MgO/synthetic antiferromagnetic stacks to achieve high TMR and efficient type-Y SOT devices.

DFT-NEGF Simulation Study of Co2FeAl-MgO-Co2FeAl Magnetic Tunnel Junctions Under Biaxial Strain

Conventional spin-transfer torque-based magnetoresistive random access memory (STT-MRAM) with CoFeB electrodes has great potential as universal memory. However, state-of-the-art STT-MRAM technology has encountered the issues such as high writing current density and low thermal stability for scaling down to <inline-formula> <tex-math notation="LaTeX">$1\times $ </tex-math></inline-formula> nm. Heusler alloy has been suggested as an alternative to resolve these problems by significantly reducing the Gilbert damping constant while preserving approximately 100&#x0025; spin polarization. In particular, <inline-formula> <tex-math notation="LaTeX">$L2_{1}$ </tex-math></inline-formula>-ordered Co₂FeAl (CFA)-based magnetic tunnel junction (MTJ) exhibits outstanding half-metallicity and perpendicular magnetorcystalline anisotropy characteristics arising from Co(Fe)-O orbital hybridization at the interface. In this work, we investigate the biaxial strain effects of CFA-based MTJ by adjusting in-plane lattice constants from &#x2212;4&#x0025; to &#x002B;4&#x0025;. Our density functional theory - nonequilibrium Green&#x2019;s function (DFT-NEGF) calculations present that FeAl-O interfaced MTJ shows a converged tunneling magnetoresistance (TMR) ratio under compressive strain while Co₂-O interfaced MTJ shows strain-sensitive TMR ratio under both compressive and tensile strain. The difference in the current-density trends for the two types of MTJs is mainly attributed to the additional state arising from Fe-O bonding. Our results emphasize the careful control of straintronic techniques on CFA-MTJs.

A Dual-Domain Dynamic Reference Sensing for Reliable Read Operation in SOT-MRAM

Although spin orbit torque magnetic random access memory (SOT-MRAM) is one of the strong candidates for next-generation embedded memories, the degradation of read margin due to low tunnel magnetoresistance ratio (TMR) with process variations has been a large concern. In this paper, we present the dual-domain dynamic reference (DDDR) sensing scheme, where the reference voltage can be dynamically changed based on the combined voltage and time domain sensing to increase the sensing margin. The Half Schmitt trigger and sample & hold circuits are efficiently employed to generate data-dependent reference voltages and to store the sampled voltage levels at different times, respectively. According to the simulations using 28nm CMOS technology with 128 by 128 SOT-MRAM array, the proposed DDDR approach achieves a 243mV of sensing margin under 6.08E-8 bit-error-rate (BER) at 1.76ns, which is 2X larger margin with more than 100 times lower BER compared to the conventional read scheme. When scaling down the pre-charge voltage, the proposed scheme achieves more than 50% of the read energy savings under 1E-5 target BER condition.

Temperature dependence of tunnel magnetoresistance in serial magnetic tunnel junctions

Magnetic tunnel junctions have been widely used in various applications, such as magnetic sensors and magnetic random-access memories. In the practical application of MTJs, they are usually used in series toward high sensitivity and high stability, especially for sensor applications. In this paper, serial MTJs devices on 8 in. wafers were fabricated. The temperature dependence of the tunnel magnetoresistance ratio, resistances in parallel and antiparallel configurations, and dynamic conductance were systematically investigated. The results of serial MTJs devices are consistent with a single MTJ device. This research suggests that serial MTJs can be directly used to investigate the magnetic tunneling properties of MTJ stacks.

Spin transport properties of highly lattice-matched all-Heusler-alloy magnetic tunnel junction

A highly lattice-matched all-Heusler-alloy magnetic tunnel junction (MTJ) is proposed by associating half metallic CoFeTiSi electrode and non-magnetic semiconductor Fe2TiSi barrier. Based on the non-equilibrium Green's function combined with first-principles calculations, spin transport mechanism is studied by analyzing the transmission coefficient, local density of states, and scattering states. The calculated equilibrium tunnel magnetoresistance (TMR) ratio in CoFeTiSi/Fe2TiSi/CoFeTiSi reaches up to about 3.30 × 108%, which is much higher than in CoFeTiSi/MgO/CoFeTiSi. The calculated scattering states reveal that CoFeTiSi/Fe2TiSi/CoFeTiSi MTJ possesses two transport channels, and the contribution of channel I to the total transport is about 80%, which plays a dominate role. The analyses on non-equilibrium spin transport properties reveal that CoFeTiSi/MgO/CoFeTiSi MTJ can output a high intensity transport current with complete spin polarization, and it can output a stable and highly efficient signal. The TMR ratio possesses an extremely large value of about 2.4 × 108% and even the bias voltage increases to 0.2 V, exhibiting a robust current-driven stability.

Proposal of Analog In-Memory Computing With Magnified Tunnel Magnetoresistance Ratio and Universal STT-MRAM Cell

In-memory computing (IMC) is an effective solution for energy-efficient artificial intelligence applications. Analog IMC amortizes the power consumption of multiple sensing amplifiers with an analog-to-digital converter (ADC) and simultaneously completes the calculation of multi-line data with a high parallelism degree. Based on a universal one-transistor one-magnetic tunnel junction (MTJ) spin transfer torque magnetic RAM (STT-MRAM) cell, this paper demonstrates a novel tunneling magnetoresistance (TMR) ratio magnifying method to realize analog IMC. Previous concerns including low TMR ratio and analog calculation nonlinearity are addressed using device-circuit interaction. The TMR is magnified <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$7500\times $ </tex-math></inline-formula> using a latch structure in combination with the device. Peripheral circuits are minimally modified to enable in-memory matrix-vector multiplication. A current mirror with a feedback structure is implemented to enhance analog computing linearity and calculation accuracy. The proposed design maximumly supports 1024 2-bit input and 1-bit weight multiply-and-accumulate (MAC) computations simultaneously. The proposal is simulated using the 28-nm CMOS process and MTJ compact model. The integral nonlinearity is reduced by 57.6% compared with the conventional structure. 9.47-25.4 TOPS/W is realized with 2-bit input, 1-bit weight, and 4-bit output convolution neural network (CNN).

Giant tunneling magnetoresistance and electroresistance in α−In2Se3 -based van der Waals multiferroic tunnel junctions

In the multiferroic tunnel junction (MFTJ) composed of ferromagnetic and ferroelectric materials, the tunneling electroresistance (TER) coexists with the tunneling magnetoresistance (TMR), making it an ideal platform for designing multifunctional electronic devices. Recently, the rapid development of van der Waals (vdW) materials opened up a new avenue of MFTJ due to their atomic thickness and significance in miniaturizing device sizes. Here by employing the nonequilibrium Green's function combined with density-functional theory, we systemically study the spin-dependent electronic transport properties of ${\mathrm{Fe}}_{3}{\mathrm{GeTe}}_{2}$ (FGT)/bilayer $\ensuremath{\alpha}\ensuremath{-}{\mathrm{In}}_{2}{\mathrm{Se}}_{3}$ (BIS)/FGT vdW MFTJs. We find that the MFTJ can form multiple nonvolatile resistance states by altering the polarization orientation of the ferroelectric barrier BIS and the magnetization alignment of the two ferromagnetic FGT electrodes, with a maximum TMR (TER) ratio up to $1.1\ifmmode\times\else\texttimes\fi{}{10}^{7}$% (744%). The TER ratio can be further increased to 1868% by using left and right symmetrical copper electrodes. More interestingly, the perfect spin filtering effect can be realized in our MFTJs and the spin current can be controlled by the sign of bias voltages, suggesting a promising route for spin valves that can flexibly manipulate spin currents. Our results demonstrate that giant TMR, large TER, as well as a tunable spin filter can coexist in one system, and that the feasible tunability of such kind of vdW MFTJs is beneficial in designing next-generation logic and memory devices.

Demonstration of reconfigurable magnetic tunnel diode and giant tunnel magnetoresistance in magnetic tunnel junctions made with spin gapless semiconductor and half-metallic Heusler alloy

Here, we report fabrication of a high quality exchanged biased trilayer magnetic tunnel junction (MTJ) utilizing a magnetron sputtering system. The MTJ is composed of a type-II spin gapless semiconductor (SGS) Ti2CoSi inverse Heusler alloy (used as a lower electrode), a thin MgO layer (used as a tunnel barrier), and a half-metallic ferromagnet (HMF) Co2MnSi Heusler alloy (used as an upper electrode). Spin dependent transport properties reveal that the micro-fabricated MTJ can act as a reconfigurable magnetic tunnel diode, which lets the electric current to flow in either the forward or reverse path relying on the relative alignment of the magnetization direction of the upper and lower magnetic electrodes. A considerably high on/off current ratio (∼103) and a significantly low turn on voltage (VT) of 0.09 V have been achieved at 5 K for both parallel and antiparallel configurations. Another important characteristic shown by our fabricated MTJ is that it exhibits extremely large tunnel magnetoresistance ratios of 892% at 5 K and 197% at room temperature, which brings to light the utmost importance of using the combination of HMF and SGS materials as magnetic electrodes in a tunnel junction for potential applications in modern spintronic devices. All these exceptional features can undoubtedly nominate CMS/MgO/TCS MTJs as a promising candidate to serve as memory or logic elements in next generation ultra-high density magnetoresistive random access memories together with contemporary spin based electronic devices.

Strain-mediated magnetoelectric control of tunneling magnetoresistance in magnetic tunneling junction/ferroelectric hybrid structures

Because of the wide selectivity of ferromagnetic and ferroelectric (FE) components, electric-field (E-field) control of magnetism via strain mediation can be easily realized through composite multiferroic heterostructures. Here, an MgO-based magnetic tunnel junction (MTJ) is chosen rationally as the ferromagnetic constitution and a high-activity (001)-Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-0.3PT) single crystal is selected as the FE component to create a multiferroic MTJ/FE hybrid structure. The shape of tunneling magnetoresistance (TMR) versus in situ E-fields imprints the butterfly loop of the piezo-strain of the FE without magnetic-field bias. The E-field-controlled change in the TMR ratio is up to –0.27% without magnetic-field bias. Moreover, when a typical magnetic field (∼ ±10 Oe) is applied along the minor axis of the MTJ, the butterfly loop is changed significantly by the E-fields relative to that without magnetic-field bias. This suggests that the E-field-controlled junction resistance is spin-dependent and correlated with magnetization switching in the free layer of the MTJ. In addition, based on such a multiferroic heterostructure, a strain-gauge factor up to approximately 40 is achieved, which decreases further with a sign change from positive to negative with increasing magnetic fields. This multiferroic hybrid structure is a promising avenue to control TMR through E-fields in low-power-consumption spintronic and straintronic devices at room temperature.

Evolution of magnetic and structural properties of MgO thin film with vacuum annealing

In this work, investigation of MgO thin film, deposited via e-beam evaporation is carried out with increasing annealing temperature. Structural properties, as elucidated using X-ray based techniques viz. grazing incidence XRD and X-ray reflectivity were associated with magnetic properties of film as observed using superconducting quantum interference device (SQUID) magnetometer. As-deposited film is polycrystalline in nature and exhibits ferromagnetism, which is attributed to presence of Mg vacancies. Vacuum annealing results densification of film with concurrent increase in electron density and reduction in film thickness and saturation magnetization. However, at sufficiently high temperature, electron density and saturation magnetization decreases comparative to as-deposited film. The results are significant for the optimization of desired functional properties of MgO particularly in MgO based magnetic tunnel junctions, providing high tunnel magnetoresistance ratio.

Enhanced tunnel magnetoresistance in Fe/Mg4Al-Ox/Fe(001) magnetic tunnel junctions

Spinel MgAl2O4 and family oxides are emerging barrier materials useful for magnetic tunnel junctions (MTJs). We report large tunnel magnetoresistance (TMR) ratios up to 429% at room temperature (RT) and 1034% at 10 K in a Fe/Mg-rich spinel/Fe(001) MTJ prepared using electron-beam evaporation of Mg4Al-Ox. Resistance oscillations with a MTJ barrier thickness of 0.3 nm were significantly enhanced compared to those of a Fe/MgO/Fe(001) MTJ, resulting in a large TMR oscillation peak-to-valley difference of 125% at RT. The differential conductance (dI/dV) spectra were symmetric with bias polarity, and the spectrum in the parallel magnetization state at low temperature demonstrates significant peaks within broad local minima at |V| = 0.2–0.6 V, indicating improved barrier interfaces by the Mg4Al-Ox barrier. This study demonstrates that TMR ratios in Fe(001)-MTJs can still be improved.

Electronic structure, magnetoresistance and spin filtering in graphene|2 monolayer-CrI33|graphene van der Waals magnetic tunnel junctions.

In the pursuit of designing van der Waals magnetic tunneling junctions (vdW-MTJs) with two-dimensional (2D) intrinsic magnets, as well as to quantitatively reveal the microscopic nature governing the vertical tunneling pathways beyond the phenomenological descriptions on CrI3-based vdW-MTJs, we investigate the structural configuration, electronic structure and spin-polarized quantum transport of graphene|2 monolayer(2ML)-CrI3|graphene heterostructure with Ag(111) layers as the electrode, using density functional theory (DFT) and its combination of non-equilibrium Green's function (DFT-NEGF) methods. The in-plane lattice of CrI3 layers is found to be stretched when placed on the graphene (Gr) layer, and the layer-stacking does not show any site selectivity. The charge transfer between CrI3 and Gr layers make the CrI3 layer lightly electron-doped, and the Gr layer hole-doped. Excitingly, the inter-layer hybridization between graphene and CrI3 layers render the CrI3 layer metallic in the majority spin channel, giving rise to an insulator-to-half-metal transition. Due to the metallic/insulator characteristics of the spin-majority/minority channel of the 2ML-CrI3 barrier in vdW-MTJs, Gr|2ML-CrI3|Gr heterostructures exhibit an almost perfect spin filtering effect (SFE) near the zero bias in parallel magnetization, a giant tunneling magnetoresistance (TMR) ratio up to 2 × 104%, and remarkable negative differential resistance (NDR). Our results not only give an explanation for the observed giant TMR in CrI3-based MTJs but also show the direct implications of 2D magnets in vdW-heterostructures.

Above-room Curie temperature and barrier-layer-dependent tunneling magnetoresistance in 1T-CrO2 monolayer based magnetic tunnel junctions.

van der Waals (vdW) heterostructures based on two-dimensional (2D) ferromagnetic materials hold great potential applications in spintronics. Using the density functional theory (DFT) method and first-principles quantum transport simulation, we studied the structures, magnetic properties and spin-resolved transport of 1T-CrO2 monolayer (ML) based vdW magnetic tunnel junctions (MTJs). Owing to a high Curie temperature (TC) of 392 K and a moderate magnetic anisotropy energy (MAE) of 94 μeV of the ferromagnetic 1T-CrO2 monolayer, Cu(111)|CrO2|nML-Gr|CrO2|Cu(111) MTJs were built. Our results reveal that their tunneling magnetoresistance (TMR) ratios are dependent on the number of Gr barrier layers within a working bias voltage of 1 V. For the thin barrier layers (n = 1-2), the maintained TMR ratios can reach a giant value of about 1 × 104%, while there appears a decreasing trend with the increasing bias voltage for thick Gr layers (n = 3-5). The barrier-layer-dependent phenomenon is attributed to the decreasing transmission magnitude with increasing bias voltage in a parallel configuration (PC), which is as small as that in an anti-parallel configuration (APC) eventually. Our results would provide some guidance for future experimental fabrications of these 2D materials based MTJs.

Spin–orbit torque driven perpendicular magnetization switching in Re/CoFeB/MgO with high thermal stability

Writing using spin–orbit torque (SOT) has been widely investigated in the field of magnetic random-access memory (MRAM). Heavy metal (HM)/CoFeB/MgO is the core of this SOT-MRAM structure. The heterostructure consisting of Ta as the spin current source and CoFeB/MgO as the perpendicular magnetic anisotropy (PMA) material is the most researched structure, owing to its high tunneling magnetoresistance ratio. However, Ta is difficult to integrate into the CMOS process due to its poor thermal stability against annealing at temperatures greater than 350 °C. Currently, β-tungsten (W) is the only HM with the CoFeB/MgO system, which can provide both thermal stability and SOT switching. Nevertheless, to achieve the high resistive β phase of W is a challenging task. Here, we report another material rhenium (Re) capable of providing thermally stable PMA up to temperature 425 °C with a perpendicular anisotropic field greater than 5000 Oe; Re possesses a spin hall angle (ϴSH) of 0.065 ± 0.003, and SOT switching can be achieved with a current density around 1.36 × 1011 A/m2. Our findings pave a new avenue for the material design of perpendicular SOT-based MRAM.

Process deviation based electrical model of spin transfer torque assisted voltage controlled magnetic anisotropy magnetic tunnel junction and its application

As one of the key components in the non-volatile full adder (NV-FA), spin transfer torque assisted voltage controlled magnetic anisotropy magnetic tunnel junction (STT assisted VCMA-MTJ) will possess superior development prospects in internet of things, artificial intelligence and other fields due to its fast switching speed, low power consumption and good stability. However, with the downscaling of magnetic tunnel junction (MTJ) and the improvement of chip integration, the effects of process deviation on the performances of MTJ device as well as NV-FA circuit become more and more important. Based on the magnetization dynamics of STT assisted VCMA-MTJ, a new electrical model of STT assisted VCMA-MTJ, in which the effects of the film growth variation and the etching variation are taken into account, is established to study the effects of the above deviations on the performances of MTJ device and NV-FA circuit. It is shown that the MTJ state fails to be switched under the free layer thickness deviation &lt;i&gt;γ&lt;/i&gt;&lt;sub&gt;tf&lt;/sub&gt; ≥ 6% or the oxide layer thickness deviation &lt;i&gt;γ&lt;/i&gt;&lt;sub&gt;tox&lt;/sub&gt; ≥ 0.7%. The sensing margin (SM) is reduced by 17.5% as the tunnel magnetoresistance ratio deviation &lt;i&gt;β&lt;/i&gt; increases to 30%. The writing error rate can be effectively reduced by increasing &lt;i&gt;V&lt;/i&gt;&lt;sub&gt;b1&lt;/sub&gt;, and increasing &lt;i&gt;V&lt;/i&gt;&lt;sub&gt;b2&lt;/sub&gt; when writing ‘0’ or reducing &lt;i&gt;V&lt;/i&gt;&lt;sub&gt;b2&lt;/sub&gt; when writing ‘1’ in the NV-FA circuit. The output error rate can also be effectively reduced by increasing the driving voltage of logical operation &lt;i&gt;V&lt;/i&gt;&lt;sub&gt;dd&lt;/sub&gt;.

Giant tunneling magnetoresistance in two-dimensional magnetic tunnel junctions based on double transition metal MXene ScCr2C2F2.

Two-dimensional (2D) transition metal carbides (MXenes) with intrinsic magnetism and half-metallic features show great promising applications for spintronic and magnetic devices, for instance, achieving perfect spin-filtering in van der Waals (vdW) magnetic tunnel junctions (MTJs). Herein, combining density functional theory calculations and nonequilibrium Green's function simulations, we systematically investigated the spin-dependent transport properties of 2D double transition metal MXene ScCr2C2F2-based vdW MTJs, where ScCr2C2F2 acts as the spin-filter tunnel barriers, 1T-MoS2 acts as the electrode and 2H-MoS2 as the tunnel barrier. We found that the spin-up electrons in the parallel configuration state play a decisive role in the transmission behavior. We found that all the constructed MTJs could hold large tunnel magnetoresistance (TMR) ratios over 9 × 105%. Especially, the maximum giant TMR ratio of 6.95 × 106% can be found in the vdW MTJ with trilayer 2H-MoS2 as the tunnel barrier. These results indicate the potential for spintronic applications of vdW MTJs based on 2D double transition metal MXene ScCr2C2F2.

Giant magnetoresistance and tunneling electroresistance in multiferroic tunnel junctions with 2D ferroelectrics.

Multiferroic tunneling junctions (MFTJs), composed of two magnetic electrodes separated by an ultrathin ferroelectric (FE) thin film as a barrier, have received great attention in multi-functional devices. Recent theoretical and experimental works have revealed that ferroelectric polarization exists at room temperature in two-dimensional ferroelectric (2D FE) materials within the ultrathin thickness. Here we propose a novel MFTJ Ni/bilayer In2Se3/BN/Ni, in which the resistance of the tunneling spin polarization electrons can be modulated by different magnetization alignments of the electrode and electric polarization direction of the 2D FE In2Se3 layer, leading to multiple tunneling resistance states. The tunneling magnetoresistance (TMR) and electroresistance (TER) of MFTJs are enhanced by the inserted h-BN layer, achieving an ON/OFF TER ratio of 4188% as well as a TMR ratio of 581% with a much lower resistance area. The giant tunneling resistance ratio, multiple resistance states, and ultra-low energy consumption in 2D FE-based MFTJs suggest their great potential in non-destructive non-volatile memories.

Magnetic tunneling junctions based on 2D CrI3 and CrBr3: spin-filtering effects and high tunnel magnetoresistance via energy band difference

Recently, the study of two-dimensional materials has expanded to the field of spintronics. Intrinsically ferromagnetic van der Waals materials such as CrI3 and CrBr3 have received much attention due to their nearly spin polarization and good stability, resulting in excellent performance in magnetic tunnel junctions. In this work, we design magnetic tunnel junctions (MTJs) of Cu/CrI3/Cu and Cu/CrBr3/Cu with electrodes of Cu(111) and a tunneling barrier of four-monolayer CrI3 or CrBr3. Our first-principle calculations combined with non-equilibrium Green’s function method indicate that the CrBr3-based MTJ has a larger maximum tunneling magnetoresistance ratio than the CrI3-based MTJ. In a wide bias voltage range, the CrI3-based MTJ can maintain high spin-filtering performance, while that of the CrBr3-based MTJ degrades sharply as the bias voltage increases. It is noted that a negative differential resistance effect is observed in the CrBr3-based MTJ. The differences in spin transport properties between the CrI3-based MTJ and the CrBr3-based MTJ are clarified in terms of the physics inside the device, including the spin-dependent density of states, band structures, Bloch states, and the electron density difference. This work provides some physical insights for the design of 2D van der Waals MTJs.