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Scalable energy-efficient magnetoelectric spin–orbit logic

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Abstract and Figures

Since the early 1980s, most electronics have relied on the use of complementary metal–oxide–semiconductor (CMOS) transistors. However, the principles of CMOS operation, involving a switchable semiconductor conductance controlled by an insulating gate, have remained largely unchanged, even as transistors are miniaturized to sizes of 10 nanometres. We investigated what dimensionally scalable logic technology beyond CMOS could provide improvements in efficiency and performance for von Neumann architectures and enable growth in emerging computing such as artifical intelligence. Such a computing technology needs to allow progressive miniaturization, reduce switching energy, improve device interconnection and provide a complete logic and memory family. Here we propose a scalable spintronic logic device that operates via spin–orbit transduction (the coupling of an electron’s angular momentum with its linear momentum) combined with magnetoelectric switching. The device uses advanced quantum materials, especially correlated oxides and topological states of matter, for collective switching and detection. We describe progress in magnetoelectric switching and spin–orbit detection of state, and show that in comparison with CMOS technology our device has superior switching energy (by a factor of 10 to 30), lower switching voltage (by a factor of 5) and enhanced logic density (by a factor of 5). In addition, its non-volatility enables ultralow standby power, which is critical to modern computing. The properties of our device indicate that the proposed technology could enable the development of multi-generational computing.
MESO logic transduction and device operation a, Transduction of state variables for a cascadable charge-input and charge-output logic device. The magnetoelectric effect transduces the input information to magnetism, and the spin–orbit effect in a topological material transduces the magnetic state variable back to charge. b, MESO device formed with a magnetoelectric capacitor and a topological material. The device comprises a spin-injection layer for spin injection from the ferromagnet to the topological material, an interconnect made of a conductive material, and contacts to the power supply and ground. The logical state of the charge input (current in the +x direction) is inverted by the operation shown to charge output (current in the –x direction). Power for energy gain is injected from the power supply (arrows). Transduction mechanisms are calculated with magnetoelectric-vector SPICE models (see Methods and Supplementary Information). The white arrow represents the magnetization direction of the ferromagnet. Grey arrows represent electric currents at the input and output, power supply and ground. Injection of the power supply current allows for energy gain, large signal gain and the ability to drive larger output devices. c, Magnetoelectric transfer function, showing conversion of the charge input to ferromagnetic magnetization. d, Spin–orbit transfer function, showing conversion of a state to charge output. The response of the device is indicated for small signal gain (black line) and the full signal range (−15 μA to 15 μA; blue arrow). See Supplementary Fig. 1 for the two operating states of the MESO inverter device.
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Operating mechanisms for MESO logic a, A low-voltage-charge-based MESO interconnect with cascaded logic gates. Two inverters are chained together to form an interconnect. Arrows show the directions of the input and output currents of the device. Materials are as in Fig. 1. b, Operating mechanism for spin-to-charge conversion using a high-SOC material (SOC). A spin injection layer (SIL) is used where needed by the materials’ interfaces. Spins injected from the ferromagnet (FM) in the +z direction with spin polarization along the +y (in-plane) direction cause a topologically generated charge current in the SOC layer. Small red and blue arrows indicate up and down spins, respectively, injected from the magnet. The large red arrows show the directions of the charge (Ic) and injected spin (Is) currents. c, Schematic of the k-space for spin-to-charge conversion at a two-dimensional electron gas with high SOC. Injecting a spin current polarized along the +y direction overpopulates the Fermi surface on one side of the topological material compared to the other side. This generates a net charge current in the x direction. The conversion has the right symmetry to convert the information of the ferromagnet to the charge current output. The dashed and solid lines depict the Fermi surface of the material before and after spin injection, respectively. Injected spin density 〈δs〉 along the +y direction leads to charge current Jcs > 0. d, Operating mechanism for a magnetoelectric (ME) material. A ferromagnet is coupled via exchange/strain to the magnetoelectric material. HEB and HEC are the exchange bias and the exchange coupling from the magnetoelectric material to the ferromagnet, respectively, and m is the magnetization of the ferromagnet. e, A classic multiferroic–magnetoelectric material, BiFeO3, is shown with the order parameters: polarization (P), antiferromagnetism (L) and weak canted magnetization (Mc). The electric-field setup in a generic magnetoelectric/ferroelectric material produces exchange bias, coupling and anisotropy modulation for magnetostrictive effects. Yellow and blue spheres depict Bi and Fe atoms in a canonic room-temperature multiferroic BiFeO3. mˆFM\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\hat{{\boldsymbol{m}}}}_{{\rm{FM}}}$$\end{document}, mˆc\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\hat{{\boldsymbol{m}}}}_{{\rm{c}}}$$\end{document} and lˆ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hat{{\boldsymbol{l}}}$$\end{document} represent the unit vectors of magnetization of the coupled layer, the magnetization of the canted spins and the antiferromagnetic axis, respectively. In general, the magneto-electric field generates an exchange coupling along the axial direction of 1ˆ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hat{{\boldsymbol{1}}}$$\end{document}, the AFM axial direction and exchange bias, the direction of weak ferromagnetism mˆc\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\hat{{\boldsymbol{m}}}}_{{\rm{c}}}$$\end{document}.
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ARTICLE https://doi.org/10.1038/s41586-018-0770-2
Scalable energy-efficient
magnetoelectric spin–orbit logic
Sasikanth Manipatruni1*, Dmitri E. Nikonov1, Chia-Ching Lin1, Tanay A. Gosavi1, Huichu Liu2, Bhagwati Prasad3,
Yen-Lin Huang3,4, Everton Bonturim3, Ramamoorthy Ramesh3,4,5 & Ian A. Young1
Since the early 1980s, most electronics have relied on the use of complementary metal–oxide–semiconductor
(CMOS) transistors. However, the principles of CMOS operation, involving a switchable semiconductor conductance
controlled by an insulating gate, have remained largely unchanged, even as transistors are miniaturized to sizes of 10
nanometres. We investigated what dimensionally scalable logic technology beyond CMOS could provide improvements
in efficiency and performance for von Neumann architectures and enable growth in emerging computing such as artifical
intelligence. Such a computing technology needs to allow progressive miniaturization, reduce switching energy, improve
device interconnection and provide a complete logic and memory family. Here we propose a scalable spintronic logic
device that operates via spin–orbit transduction (the coupling of an electron’s angular momentum with its linear
momentum) combined with magnetoelectric switching. The device uses advanced quantum materials, especially
correlated oxides and topological states of matter, for collective switching and detection. We describe progress in
magnetoelectric switching and spin–orbit detection of state, and show that in comparison with CMOS technology our
device has superior switching energy (by a factor of 10 to 30), lower switching voltage (by a factor of 5) and enhanced
logic density (by a factor of 5). In addition, its non-volatility enables ultralow standby power, which is critical to modern
computing. The properties of our device indicate that the proposed technology could enable the development of multi-
generational computing.
Transistor technology scaling
1–3
has been enabled by controlling the
conductivity of a semiconductor using an electric field applied across
a high-quality insulating gate dielectric. This fundamental principle
has remained largely unchanged since the seminal observations of
Moore and Dennard et al.
4,5
. Yet in the past decade, transistor scaling
has been enabled by direct improvements to the carrier transport1,6,7,
combined with superior electrostatic control
1–3,8
. In contrast to pure
dimensional scaling
5
, new transistor technologies have necessitated the
use of strain6, three-dimensional electrostatic gate control2,8, manipu-
lation of the effective carrier mass and band structure, and the gradual
introduction of new materials for interface and work function con-
trol
9
. Despite the successful scaling in the size of transistors, voltage
and frequency scaling have slowed
10
. Further decrease of voltage has
been hampered by the Boltzmann limit of current control (60mV for
every change in current by a factor of 10 at room temperature). In
response, a considerable effort to invent, demonstrate and benchmark
beyond-CMOS devices got underway
1113
. This effort includes alter-
native computing devices based on electron spin, electron tunnelling,
ferroelectrics, strain and phase change12,13 (seeMethods for beyond-
CMOS logicdevice options). However, a technologically suitable com-
putational logic device that has superior energy efficiency, high logic
density (that is, computed functions per unit area), non-volatility (to
counteract leakage power) and efficient interconnects has remained
elusive. The importance of these considerations has become evident
during extensive modelling, benchmarking and evaluation of more
than 25 beyond-CMOS deviceproposals12,13. With these considera-
tions in view, we propose and demonstrate the building blocks for a
new logic device that enables (1) voltage scaling, (2) scalable intercon-
nects, (3) energy scaling and (4) the potential for multi-generational
dimensional scaling.
Beyond-CMOS devices for replacing or enhancing the
electronic transistor
Collective state switching devices are potential candidates for replac-
ing or enhancing transistors. A collective state switch operates by the
reversal of the material’s order parameter (such as ferromagnetism,
ferroelectricity and ferrotorodicity)13 from ϴ to ϴ. It addresses sub-
10-nm miniaturization by using collective order parameter dynamics,
overcoming the ‘Boltzmann tyranny’, which is inherent to conductiv-
ity modulation, and providing a non-volatile nature to the computer.
It is well documented that the ‘Boltzmann tyranny’ and leakage are
the central challenges in traditional CMOS devices
1,2
. Logic based on
collective state switching devices is a leading option for computational
advances beyond the modern CMOS era owing to its (1) potential for
superior energy per operation, (2) higher computational logical density
and efficiency (that is, fewer devices required per combinatorial logic
function) owing to the use of majority gates14, (3) non-volatile memory-
in-logic and logic-in-memory capability15 and (4) amenability to
traditional and emerging architectures (for example, neuromorphic
16
and stochastic computing17).
Among these possible collective state order parameters, ferroelectric-
ity and multiferroicityare the preferred collective states for computing
13
owing to (1) the presence of a controllable, localized and phenome-
nologically strong carrier, the spontaneous dipole; (2) the switching
efficiency of a ferroelectric with respect to the stability of the switch is
given by the energy barrier per unit volume, λ=E
sw
/ΔE(Θ), where
ΔE(Θ) is the energy barrier relative to the stable state and Esw is the
total energy dissipated in switching; lower values of λ enable computing
switches to operate at lower energies for a given energy barrier.
A vital consideration for a new technology is the need for highly
compact nanoscale interconnects. While ferroelectric switching and the
1Components Research, Intel Corporation, Hillsboro, OR, USA. 2Intel Labs, Intel Corp., Santa Clara, CA, USA. 3Department of Materials Science and Engineering, University of California, Berkeley,
Berkeley, CA, USA. 4Lawrence Berkeley National Laboratory, Berkeley, CA, USA. 5Department of Physics, University of California, Berkeley, Berkeley, CA, USA. *e-mail: sasikanth.manipatruni@intel.com
3 JANUARY 2019 | VOL 565 | NATURE | 35
© 2019 Springer Nature Limited. All rights reserved.
... Although room temperature magnetism and proximity effects have been reported using vdW magnets [20][21][22] , the lack of active spintronic device operation at room temperature significantly limits its practical application potential 21,23,24 . Furthermore, a lateral room temperature spin-valve device with vdW metallic magnets, an essential building block for proposed spin-based memory, logic, and neuromorphic computing architectures [25][26][27][28] has not been realized yet. ...
... This will bring a strong synergy between 2D materials and spintronics with the possibility of further controlling the figures of merit by twist angle between the vdW layers, magnetic proximity effects, and gate tunability for energy-efficient and ultra-fast spintronic devices 15,52 . These room-temperature developments in vdW magnet-based heterostructures will open future opportunities for fundamental studies and spintronic devices for magnetic sensor, memory, logic, communication, and novel computing architecture applications 25,26 . ...
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