Single-shot dynamics of spin–orbit torque and spin transfer torque switching in three-terminal magnetic tunnel junctions

Abstract

Current-induced spin-transfer torques (STT) and spin–orbit torques (SOT) enable the electrical switching of magnetic tunnel junctions (MTJs) in non-volatile magnetic random access memories. To develop faster memory devices, an improvement in the timescales that underlie the current-driven magnetization dynamics is required. Here we report all-electrical time-resolved measurements of magnetization reversal driven by SOT in a three-terminal MTJ device. Single-shot measurements of the MTJ resistance during current injection reveal that SOT switching involves a stochastic two-step process that consists of a domain nucleation time and propagation time, which have different genesis, timescales and statistical distributions compared to STT switching. We further show that the combination of SOT, STT and the voltage control of magnetic anisotropy leads to reproducible subnanosecond switching with the spread of the cumulative switching time smaller than 0.2 ns. Our measurements unravel the combined impact of SOT, STT and the voltage control of magnetic anisotropy in determining the switching speed and efficiency of MTJ devices.

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Fig. 1: Schematic of the experimental set-up and three-terminal MTJ.
Fig. 2: Average temporal evolution of the voltage signal during SOT and STT switching.
Fig. 3: Single-shot measurements of SOT and STT switching.
Fig. 4: Temperature-induced variation of the magnetic parameters during pulse injection and micromagnetic simulations of SOT switching.
Fig. 5: Combined effect of VCMA and STT on SOT-induced switching.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.

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Acknowledgements

This work was funded by the Swiss National Science Foundation (Grant no. 200020-172775), ETH Zurich (Career Seed Grant SEED-14 16-2) and imec’s Industrial Affiliation Program on STT-MRAM devices.

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Authors

Contributions

E.G., K.G. and P.G. planned the experiments. S.C., F.Y. and K.G. designed and fabricated the samples. E.G. implemented the time-resolved electrical set-up. E.G. and V.K. performed the measurements. G.S. and V.K. performed the micromagnetic simulations. E.G., V.K, K.G. and P.G. analysed the results. E.G. and P.G. wrote the manuscript. All the authors discussed the data and commented on the manuscript.

Corresponding authors

Correspondence to Eva Grimaldi or Kevin Garello or Pietro Gambardella.

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The authors declare no competing interests.

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Peer review information Nature Nanotechnology thanks Christian Back, Andrew Kent and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data

Extended Data Fig. 1

Equivalent resistance setup of a three-terminal MTJ.

Extended Data Fig. 2 Comparison of the critical voltage for zero and small STT bias.

Critical switching voltage Vc as a function of pulse length τp for x = 0.46 (VSTT = 0) and x = 0.63 (minimum VSTT required to perform time-resolved measurements). The overlap of the data indicates no noticeable effect of the small STT bias on the SOT switching.

Extended Data Fig. 3

Schematic of the acquisition and normalization protocol for P-AP switching.

Extended Data Fig. 4 Examples of VP, VP-AP, VAP-P, and VAP time traces.

a, VAP, VAP-P and VP for AP-P SOT switching. b, Corresponding switching and reference signals, VAP-P-VAP, and VP-VAP, respectively. c, VP, VP-VAP, and VAP for P-AP STT switching. d, Corresponding switching and reference signals, VP-AP-VP and VAP-VP, respectively. The traces are averaged over 5000 (500) SOT (STT) switching events. These signals are used to obtain the normalized time traces shown in Fig. 2a,b for SOT and STT switching, respectively.

Extended Data Fig. 5 Average SOT and STT switching times as a function of pulse amplitude and in-plane field.

a,b, Comparison of the average incubation time and transition time for P-AP SOT switching as a function of pulse amplitude (VSOT > 0) at μ0Hx = −23 mT (a) and in-plane field μ0Hx at VSOT = + 453 mV (b). c,d, Comparison of the average incubation time and transition time for P-AP STT switching as a function of pulse amplitude (VSST > 0) at μ0Hx = –23 mT (c) and in-plane field μ0Hx at VSTT = +756 mV (d). In b,d, the pulse amplitude is the minimum allowing 100% switching (Psw = 1) at μ0Hx = −23 mT.

Extended Data Fig. 6 Single-shot measurements of SOT and STT switching in the AP-P case.

a,b, Representative time traces recorded during ten individual SOT-induced AP-P switching events induced by 15 ns long pulses with VSOT= +453 mV and increasing STT bias VSTT= −227, +266, +513 mV at a, μ0Hx= +23 mT and b, μ0Hx= +90 mT. c,d, Representative time traces recorded during ten individual STT-induced AP-P switching events at VSTT= +884 mV and c, μ0Hx= +23 mT and d, μ0Hx= 0 mT. The pulse amplitudes are the minimum ones required to achieve 100% switching in any of the shown configurations. The time traces have been vertically offset for clarity. Black solid lines are fits with a linear ramp used for extracting t0 and Δt. e, Statistical distributions of the incubation time t0, f, the transition time Δt and g, the total switching time t0t at μ0Hx= +23 mT for SOT switching at different STT biases . h, Statistical distributions of t0, i, Δt and j, t0t at μ0Hx= +90 mT. The histograms are obtained from the analysis of 1000 single-shot switching events.

Extended Data Fig. 7 Single-shot measurements of P-AP switching for different VSOT and Hx.

a-d, Representative time traces recorded during ten individual SOT-dominated P-AP switching events induced by 15 ns long pulses with a,b, VSOT= +453 mV, VSTT= −227 mV and c,d, VSOT= +481 mV, VSTT= −242 mV at a,c, μ0Hx= −23 mT and b,d, μ0Hx= −90 mT. The time traces have been offset for clarity. Black solid lines are fits with a linear ramp used for extracting t0 and Δt. e-h, Distributions of e, t0 and f, Δt at μ0Hx= −23 mT, and g, t0 and h, Δt at μ0Hx= −90 mT. The histograms are obtained from the analysis of 1000 single-shot switching events.

Extended Data Fig. 8 Combined effect of voltage control of magnetic anisotropy and STT on SOT-induced switching for the free layer initially pointing down.

a,b, Schematics of the SOT-dominated switching mechanism for the reference layer pointing a, up and b, down. Black arrows indicate the directions of rf currents, white arrows indicate the magnetization state. The STT (red arrow) given by VSTT either a, opposes or b, assists the SOT switching induced by VSOT (yellow arrow). c, Averaged time traces of SOT-induced AP-P switching with VSTT= −197, +73, +232, +447 mV for VSOT= +394 mV and τp=20 ns. d, Evolution of the critical voltage as a function of pulse length for different STT contributions as given by the VSTT/VSOT ratio. e, Normalized critical voltages \({v}_{\mathrm{c}}^ \uparrow\) and \({v}_{\mathrm{c}}^ \downarrow\) as a function of inverse pulse length for different VSTT/VSOT ratios. The magnetization of the reference layer points either up (\({v}_{\mathrm{c}}^ \uparrow\)) or down (\({v}_{\mathrm{c}}^ \downarrow\)), corresponding to the situation depicted in a, and b, respectively. Evolution of f, the average critical voltage \(\bar{{v}}_{\mathrm{c}}\) (VCMA-like contribution) and g, voltage asymmetry Δvc (STT-like contribution) as a function of VSTT/VSOT for short and long pulses. All measurements are performed at μ0Hx= +90 mT, VSOT>0 and correspond to AP-P (respectively P-AP) switching for the reference layer pointing up (down) and free layer initially pointing down.

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Supplementary Information

Supplementary Notes 1–3, Fig. 1, Table 1 and refs. 1–8.

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Grimaldi, E., Krizakova, V., Sala, G. et al. Single-shot dynamics of spin–orbit torque and spin transfer torque switching in three-terminal magnetic tunnel junctions. Nat. Nanotechnol. 15, 111–117 (2020). https://doi.org/10.1038/s41565-019-0607-7

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