Special MRAM poster session
IEDM (Dec 13-15, 2021, Hilton Union
Square, San-Francisco)

Wednesday morning Dec 15th,
9:00am-12:00 noon
Yosemite room
For the 5th year, a special poster session entirely
dedicated to MRAM is organized during IEDM.
This session is technically organized by the IEEE
Magnetics Society and embedded in the IEDM
2021 conference. This event will be a great
opportunity to foster closer interactions between
the microelectronics and magnetism communities.
The poster session will cover a number of topics
includingMRAMmaterials,
phenomena,technology (STT, SOT, E-field control), testing,hybrid CMOS/MTJ technology and circuits, and
MRAM applications. This year, 14 posters were
accepted for presentation.
The list is shown below.
Bernard Dieny, Kevin Garello, Luc ThomasIEEE Magnetics Society

Presented posters :1. Perspectiveson

Perpendicular

Shape

Anisotropy magnetic tunnel junctions
N. Caçoilo1, B. M. S. Teixeira1, A. Palomino Lopez1, T.
Almeida2, I.L. Prejbeanu1, B. Dieny1, L. Vila1, L. Buda
Prejbeanu1, D. Cooper1, O. Fruchart1, R. C. Sousa1
1. Univ. Grenoble Alpes, CEA, CNRS, Grenoble-INP, Spintec,
Grenoble 38000, France
2. Univ. Grenoble Alpes, CEA, LETI, 38000, Grenoble, France.

Perpendicular Shape Anisotropy (PSA) is a candidate
concept to extend spin transfer torque (STT) MRAM
technology below sub-20 nm lateral dimensions,where conventional perpendicular magnetic tunnel
junctions (pMTJ) based on interfacial perpendicularmagnetic anisotropy (iPMA) exhibit an inherently small

thermal stability ∆ [1, 2]. At small dimensions, reversalof the pMTJ magnetic volume is almost coherent,
leading ∆ to scale down with the device area, below
minimum requirements for 10 year memory retention[3-5]. In PSA-MTJ the thickness of the storage layer ismade similar to the cell diameter, such thatperpendicular shape anisotropy becomes the major
source for stability. The perpendicular surface
anisotropy at the interface between the ferromagnet
and the MgO tunnel barrier becomes only minor
contribution to the total anisotropy.
In PSA-MTJ the aspect-ratio of the storage layer
governs the main device properties impacting thermal
stability ratio ∆ and STT critical switching current.
Further device optimization requires the investigationof the magnetization reversal process itself. For that
purpose PSA-MTJ cells were investigated withmicromagnetic simulation for both STT-driven andmagnetic field-driven reversals. It was observed that,for both cases, a variation in aspect-ratio leads totransitions between different reversal mechanisms.
For STT-driven reversal, it is shown that, for a constantdiameter and increasing the storage layer thickness it
is possible to observe coherent reversal for aspectratios close to 1, or non-uniform reversal for aspectratios larger than 1 [6]. The field-driven reversal isfundamentally different from the STT reversal. While
with STT the reversal initiates near the interface with
the MgO tunnel barrier, for the field-driven reversal,
micromagnetic simulations show a transition fromcoherent reversal to vortex creation and annihilation,
for larger diameters under perpendicular applied field.
Experimental results confirm the vortex-based
reversal in PSA-MTJs and the possibility to control its
characteristic fields by modifying the magnetic
saturation of the free layer.
It is also known that the interface PMA decays
significantly as the temperature increases. This createsa drawback for pMTJ operation in a wide temperature
range. By means of electrical measurements andelectron holography studies, we show that PSA iscapable of mitigating the impact of temperature onthe device operation. It proves to be a more robust
source of anisotropy against temperature variations
showing improvements for operation in a wide rangeof temperatures [7, 8].
Based on these simulation and experimental results
we provide a perspective view on the merits of PSA fora variety of applications depending on the fabricatedpillar diameter, ranging from cells for hightemperature applications at D≥20 nm, to high-density
DRAM-like applications in the sub-20 nm diameter
range.
[1] N. Perrissin et al, Nanoscale 10, 12187-12195 (2018)[2] K. Watanabe et al, Nat. Com. 9, 663 (2018).
[3] C. Yoshida et al, Jpn. J. Appl. Phys. 58, SBBB05 (2019).
[4] H. Sato et al, Jpn. J. Appl. Phys. 58, 0802A6 (2017).
[5] L. Thomas et al, J. Appl. Phys. 115, 172615 (2014).
[6] N. Caçoilo et al, Phys. Rev. Applied 16, 024020 (2021).
[7] S. Lequeux et al., Nanoscale 12, 6378 (2020)[8] S. Lequeux et al., 2021 IEEE International Memory Workshop(IMW), (2021)

2. Double magnetic tunnel junction withswitchable assistance layer for high efficiency
STT-MRAM
D.S. Hazen1, B.M.S Teixeira1, D. Salomoni1,S. Auffret1, L.
Vila1, R.C. Sousa1, I.L. Prejbeanu1, L. D. BudaPrejbeanu1, B. Dieny1

1. SPINTEC, Univ. Grenoble Alpes/ CEA/ CNRS, 38000Grenoble France: daniel.sanchezhazen@cea.fr
Perpendicular Spin Transfer Torque Magnetic Random
Access Memory (p-STT-MRAM) still requires
improvements to be usable for fast cache applications[1]. To be able to replace Static Random Access
Memory (SRAM), p-STT-MRAM needs to combine highspeed and low critical switching current at
technological nodes below 30 nm. Higher STT write
efficiency is therefore needed [2]. Double magnetic
tunnel junctions (DMTJ) have recently been proposedto achieve this goal [3-5]. A typical DMTJ stack is shownin Fig. 1(a). It consists of a storage layer (SL)sandwiched between two tunnel barriers with
antiparallel top and bottom hard reference polarizers.
The SL retention is improved thanks to the two

FeCoB/MgO interfaces contributing to the effective SL
perpendicular anisotropy. The critical switchingcurrent (𝐼 ) is decreased by the combined effect of the
STT exerted from the two antiparallel polarizers on the
SL. Despite the efficiency advantage, these p-DMTJ
have several flaws [6]. A first difficulty arises increating a top polarizer with high perpendicularanisotropy. The main source of perpendicularanisotropy is commonly a (Co/Pt) multilayer-based
synthetic antiferromagnetic structure (SAF) coupled to
the FeCoB electrode. The SAF perpendicularanisotropy is highly dependent on the (Co/Pt)
multilayer crystallographic texture [7]. While highanisotropy can be easily obtained in the bottom
polarizer by the use of a proper seed layer, thisapproach is not possible with the top polarizer, whichmust be grown seedless on top of the tunnel barrier.
Another complexity to the design and optimization ofthis structure is the requirement to compensate strayfields generated by both top and bottom references
which comprise overall four magnetic layers. Besides,
the etching of these DMTJ stacks is even more difficult
than that of conventional STT-MRAM stacks due to theadditional thickness of the top polarizer. In this work,
we present the first experimental proof of concept of
a novel type of double magnetic tunnel junction
structure [8] illustrated in Fig.1.(b). This ASL-DMTJ issimpler and thinner than conventional DMTJ. It isbased on the use of a switchable top polarizer acting
as an assistance layer (ASL). The ASL is designed toswitch its magnetic orientation during the write
operation in such a way to maximize STT efficiency
during both the parallel (P) to antiparallel (AP) and AP
to P transitions while always ending parallel to the SL
magnetization in standby. To achieve these properties,
the SL/ASL interlayer coupling and ASL thermal
stability must be finely adjusted. Real-timeobservations of the devices resistance variations
confirm the expected operation mechanism in the
fabricated cells. The performances were evaluated byusing the ratio between retention energy barrier andcritical switching current as Figure of Merit (FOM).

They are compared to those of conventional single
magnetic tunnel junction structures without ASL. The
comparison highlights the benefits of the proposed
stack design for high performance STT-MRAM
applications.

Fig. 1. (a) Stacks comparison between a conventional pDMTJ with static top and bottom polarizer and (b) an ASLDMTJ[1] Barla, P., Joshi, V.K. & Bhat, S. J Comput Electron 20, 805–837.
(2021)[2] A. Jog et al. Design Automation Conference, pp. 243-252.
(2012)[3] G.Hu et al. IEDM, 2156-017X. (2015)[4] B.Rodmacq et al. Patent US8513944B2. (2008)[5] P. Y. Clément et al. IEEE 6th IMW, pp. 1-4. (2014)[6] J. Swerts et al.et al. IEDM, pp. 38.6.1-38.6.4. (2017)[7] Jyotirmoy Chatterjee et al. Applied Physics Express, 063002.
(2015)[8] Khvalkovskiy et al. Journal of Applied Physics, 124(13), 133902.
(2018)

3. Dependenceofinterfacial
magnetic
anisotropy on insertion layer Mo thickness in
CoFeB-MgO structure for MRAM with high1.
thermal stability
Yu Zhang1, Fen Xue2, William Hwang2, Shy-Jay Lin32.
,
Wilman Tsai1 and Shan Xiang Wang1,2
1

3.

Department of Materials Science and Engineering, Stanford
University, Stanford, California 94305, USA
2
Department of Electrical Engineering, Stanford University,
Stanford, California 94305, USA

3

Corporate Research, Taiwan Semiconductor Manufacturing
Company, Hsinchu 30078, Taiwan

Perpendicularly magnetized magnetic tunnel junctions(pMTJs) based on HM (heavy metal)/CoFeB/MgO
structure is a promising candidate for the nextgeneration ultra-low energy memory and logic device
owing to its fast speed, high endurance, high tunnelingmagnetoresistance and low damping factor. To
integrated pMTJs into practical applications, a highthermal stability over 400C is required forcompatibility with back end of line (BEOL) process of
CMOS technology. However, a degradation of
perpendicular magnetic anisotropy (PMA) occurs forconventional HM seed layer like Ta under annealing
temperature higher than 300C. Here, we studied thethickness dependence of PMA on inserted Mo layer inthe structure of Ta/Mo(t)/CoFeB/MgO/Ta where Mo isa good thermal barrier and Ta acts as a boron getter.
The experimental results show that the tolerance of
annealing over 400C can be achieved by suppressing
the diffusion of HM atoms from underlayer. Two
different physical mechanisms which dominate the
PMAdeterioration
duringannealingin
Ta/Mo/CoFeB/MgO structure with different Mo
thickness are illustrated: when the thickness of Mo
insertion layer is below 2 nm, the Ta atoms diffusion
into CoFeB/MgO interface and the formation of Ta-O
lead to the degradation of PMA; When the thickness of
Mo insertion layer is above 2 nm, thicker Mo layer
hinders the absorption of boron atoms by Ta layer
underneath and consequently degrades the PMA due
to a lower crystallization degree of CoFeB.

4. Toggle Spin-Orbit Torque MRAM
Perpendicular Magnetic Anisotropy

withNaimul Hassan1, Felipe Garcia-Sanchez2, Susana P. LainezGarcia1, Pedram Khalili Amiri3, and Joseph S. Friedman1
University of Texas at Dallas, Richardson, Texas, USA,[naimul.hassan, susana.lainezgarcia,
joseph.friedman]@utdallas.edu
Universidad de Salamanca, Salamanca, Spain, fgs@usal.es
Northwestern University, Evanston, Illinois, USA,pedram@northwestern.edu

Writing magnetic random-access memory (MRAM) byultrafast and energy-efficient spin-orbit torque (SOT)
has been impeded by the orthogonality between spinpolarization and thermally stable perpendicularmagnetic anisotropy (PMA). Previously proposed
approaches to break this symmetry increase thefabrication complexity, are highly sensitive to the SOT
current duration and magnitude, or increase theswitching energy. To overcome these challenges, we
exploit the precessional nature of the field-like SOT to1.
propose a toggle PMA SOT-MRAM with simple
2.
structure that is controlled by a unidirectional SOT
current. The proposed MRAM achieves field-free and3.
energy-efficient switching that is robust to variations4.
in the SOT current magnitude and duration withgreater than 50% tolerance demonstrated throughmicromagnetic simulation. The deformation-freestructure provides efficient data read-out and can beleveraged for directional writing through a simple XOR
between the stored and incoming bits.

5. Asymmetric SOT switching induced by inplane magnetic fields in MTJ-compatible
Ta/CoFeB/MgO structures
Baiqing Jiang and Chong Bi

The Institute of Microelectronics of the Chinese
Academy of Science
SOT-MRAM may address the possible limitationsof
STT-MRAM with fast switching processes andseparated writing and reading paths. However, thepossible asymmetric switching behaviors between updown and down-up switching that can cause serious
problems in the circuit-level designs in SOT-MRAM
products has not been investigated. Here wedemonstrate the potential asymmetric SOT switching
induced by the applied in-plane magnetic field (H). We
directly measured the SOT efficiency as the functionsof the strength of H and its tilt angle away from thewriting currents and found that the SOT efficiencies
are intrinsically different for up-down and down-up
switching. Furthermore, the resultant critical switchingcurrents are also quite different. Our results provide
additional guidelines for designing SOT-MRAM toachieve symmetric SOT switching processes.

6. Direct detection of spin Hall effect in an
antiferromagnetic material
Saima Siddiqui1, Sandra Ruiz-Gómez2, Kisung Kang1, Jordan
Katine3, Muhammad W. Khaliq2, John E. Pearson3, André
Schleife1, Michael Foerster2, Manuel Valvidares2, and Axel
Hoffmann1,4
1. Department of Materials Science and Engineering,
University of Illinois at Urbana Champaign, IL 61801, USA
2. ALBA Synchrotron Light Facility, CELLS, Carrer de la Llum,
2-26, E-08290 Bellaterra, Spain
3. Western Digital, San Jose, CA 95119
4. Argonne National Laboratory, Lemont, IL 60439.

The spin Hall effect (SHE) is an efficient way of
converting a charge current into a spin current that canmodulate the magnetization in an adjacent magnetic
layer. Antiferromagnetic metals can have high spin Hall
angles (θSH, ratio of spin to charge currents) as
measured using indirect electrical measurement, suchas spin torque ferromagnetic resonance in adjacentferromagnetic layers [1,2]. These indirect electricalmeasurements of SHE depend on the transparency ofthe spins at the interface between theantiferromagnet and the adjacent ferromagnetic layer
and may be affected by the spin losses and transport
in the ferromagnetic layers and many other nonidealities [3,4]. There are often discrepancies in themeasured values of θSH in a single material based on
its interfaces even at the same temperature [1,2].
Therefore, an interface-free, direct measurement of
intrinsic SHE is highly desirable for an improved
fundamental
understandingandoptimizing
technological applications.
Here, we report the direct measurement of theinterfacial spin accumulation induced by the spin Hall
effect in antiferromagnetic PtMn thin films using
magnetic circular dichroism (XMCD)- photoemission
electron microscopy (PEEM). We show that the XMCD
has opposite sign at the L3 edge of Mn for opposite
charge current directions and scales linearly withcurrent density. We quantitatively determine thecurrent-induced spin accumulation at the PtMn
interface as 8.8×10−12 μBA−1cm2 per atom averaged

over the probing depth which translates into a positivespin Hall angle of 0.25 (±0.1). Our results show thedirect, spatially resolved, interface free and elementselective measurement of the SHE in a CuAu-I-type
antiferromagnetic material by means of X-ray
microscopy.
Supported by the NSF through the Illinois MRSEC(DMR-1720633) and the U.S. DOE, Office of Science,
Materials Science and Engineering Division.
[1] W. Zhang, M. B. Jungfleisch, W. Jiang, J. E. Pearson, A.
Hoffmann, F. Freimuth, and Y. Mokrousov, Physical Review
Letters 113, 196602 (2014).
[2] Y. Ou, S. Shi, D. C. Ralph, and R. A. Buhrman, PhysicalReview B 93, 220405 (2016).
[3] X. Tao et al., Sci Adv 4, eaat1670 (2018).
[4] M. Lim and H.-W. Lee, Appl. Phys. Lett. 118 (2021).

7. Efficient
voltage-controlled
magnetic
anisotropy in wafer-scale magnetic tunneling
junctionHaoran He,1 Di Wu,1,2 Ya-Jui Tsou,3,4 Yao-Min Huang,3 KaiShin Li,3 C. W. Liu4
Albert Lee,1,2 and Kang L. Wang1,2, †1. Department of Electrical and Computer Engineering,
University of California, Los Angeles, California 90095,
United States
2. Inston inc, Los Angeles 90405, United States
3. Taiwan Semiconductor Research Institute (TSRI),
Hsinchu 30078, Taiwan
4. Graduate Institute of Electronics Engineering, National
Taiwan University, Taipei 10617, Taiwan†
Correspondence to: wang@ee.ucla.edu

Voltage Control Magnetic Anisotropy (VCMA)MRAM is a promising candidate for nextgeneration MRAM due to its low energy
consumption and high endurance. Even thoughhigh VCMA coefficient has been demonstrated inlaboratory experiments, the number in waferscale MTJ is relatively low, which is the majorbottleneck for VCMA MRAM manufacturing. In

this work, we realize the ns-pulse switching in toppinned perpendicular-MTJ on 8 inch wafers
annealed at 400℃, compatible with CMOS
backend processing. The effective anisotropy field
is determined 0.27 T by voltage-induced
ferromagnetic resonance. With the criticalswitching voltage (3 V), the VCMA coefficient isestimated at around 68.9 fJ/Vm, which is around
twice of standard MTJ. Our results show a higher
VCMA coefficient solution and can be helpful forfurther enhancement.
8. Voltage Controlled Static Skyrmion Device for
Neuromorphic Computing Applications
Aijaz H. Lone, Divyanshu, Selma Amara and Hossein
Fariborzi
Computer, Electrical and Mathematical Science andEngineering Division, King Abdullah University of Science andTechnology, Thuwal, Saudi Arabia.

The topological protection of the swirling magnetic
structures, known as Skyrmions, has gained a lot of
attention in the Spintronics community [1]. Thesenovel spin textures are promising an increased densityand energy efficient data storage due to small
nanometric size and topological protection [2]. For
different logic and memory applications skyrmions
have been created, annihilated and driven by theapplication of external magnetic fields and or current[3]. On the other hand, voltage control of the surface
anisotropy in magnetic tunnel junctions has gained alot of interest, owing to the energy efficient switchingas low as a few femtojoules [4]. In this presentation we
propose a voltage controlled skyrmion based MTJ
device for neuromorphic computing applications. The
skyrmion is confined in a region bound by increased
anisotropies as shown in Fig. 1(a). The MTJ device
consists of a thin ferromagnetic free layer/Tunnel
Barrier/Reference layer. The free layer has theconfined skyrmion in it whose size is controlled byvoltage pulses. Thick 3nm tunnel barrier is considered
to ensure STT current doesn’t have an effect on theskyrmion. As skyrmion stability depends particularly
upon Dzyaloshinskii Moriya Interaction (DMI) andanisotropy. The writing voltage pulses applied acrossthe MTJ change the surface anisotropy at heavy
metal/free layer interface, thus changing the skyrmion
diameter. The control of confined skyrmion size willallow increased memory density and power efficiency.
In addition, the interaction between neighbouring
skyrmions is also minimized. To demonstrate the1.
neuromorphic computing capabilities of the proposed2.
device, we present the MTJ with positive voltage
pulses of 1 ns, each followed by a 0.5 ns break. As3.
shown in Fig. 1(b) we observe the integrating
behaviour of MTJ when a voltage is applied and the4.
skyrmion size reduces which also reflects in the neuron
output voltage. In absence of voltage, the skyrmion
tries to increase its diameter and neuron voltage drops,
thus the MTJ mimics the leaky neuron behaviour i.e.,
neuron leaks some part of the membrane potential.
We continue the application of pulses till the voltage
crosses the threshold and a spike is generated by thesensing unit. The neuron is reset by a negative voltage
pulse which decreases the anisotropy and theskyrmion regains its full size abruptly. The neuron
activation function with respect to gate voltage isshown in Fig. 2(a). In Fig. 2(b), we test the proposed
neuron model on MNIST data set for a fully connected
dense neural network to observe the patternclassification efficiency.
[1] A. Fert, N. Reyren, and V. Cros, “Magnetic skyrmions: Advancesin physics and potential applications,” Nat. Rev. Mater., vol. 2,
2017, doi: 10.1038/natrevmats.2017.31.
[2] W. Kang, Y. Huang, X. Zhang, Y. Zhou, and W. Zhao, “SkyrmionElectronics: An Overview and Outlook,” Proc. IEEE, vol. 104, no. 10,
pp. 2040–2061, 2016, doi: 10.1109/JPROC.2016.2591578.
[3] S. Luo and L. You, “Skyrmion devices for memory and logic
applications,” APL Mater., vol. 9, no. 5, pp. 1–11, 2021, doi:
10.1063/5.0042917.
[4] C. Grezes et al., “Ultra-low switching energy and scaling inelectric-field-controlled nanoscalemagnetic tunnel junctions withhigh resistance-area product,” Appl. Phys. Lett., vol. 108, no. 1,
2016, doi: 10.1063/1.4939446.

9. Ultrafast
all-opticalswitchingof
FeCoB/Ta/[Tb/Co] magnetic tunnel junctions for
spintronic-photonic memory
D. Salomoni1, L. Avilés-Félix1, A. Olivier1, G. Li2, C. Davies2, L.
Álvaro-Gómez1, L. Farcis1, E. K. Sobolewska4, J. PellouxPrayer4, H. Becker4, C. S. Davies2, 3, M. Rubio-Roy1, S. Auffret1,
A. Kirilyuk2,3, Th. Rasing2, L. Buda-Prejbeanu1, R. Sousa1, B.
Dieny1 and I. L. Prejbeanu1
Spintec, Université Grenoble Alpes, CNRS, CEA, Grenoble
INP, IRIG-SPINTEC, 38000 Grenoble, France
Radboud University, Institute for Molecules and Materials,
Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands
FELIX Laboratory, Radboud University, 7c Toernooiveld,
6525 ED Nijmegen, The Netherlands
Department of Engineering, Aarhus University, Finlandsgade
22, 8200 Aarhus, Denmark;In this work we describe the stack development of alloptical switching perpendicular magnetic tunnel
junctions (MTJ) and their nano-fabrication using
Indium Tin Oxide (ITO) as hard mask and transparent
conductive electrode. The fabricated cells have opticalaccess for laser pulse switching.
The design and fabrication of the MTJ is based on a
[Tb/Co] multilayer stack with optically switchable
magnetization. We explore the magneto-opticalproperties of [Tb/Co] multilayer and their stability
under annealing temperatures up to 300°C [4]. In
order to fabricate optically switchable magnetic tunnel
junction electrodes, [Tb/Co] multilayers were coupled
to a FeCoB layer through a Ta ultra-thin layer. Togglingof the magnetization in the Tb/Co multilayered stack
was observed using both 60 femtosecond- and 5
picosecond-long laser pulses with fluences down to 4.7
mJ/cm² [3]. The all-optical switching (AOS) of the
Tb/Co multilayers was achieved for Co-richcomposition of the multilayers, either alone orembedded in a tunnel junction stack coupled to a
FeCoB electrode on an MgO barrier. Electricalevaluation of nanopatterned AOS-MTJ showed TMR
ratios up to 40 % for a resistance area product (RxA)
around 150 Ωμm²[1][3].
To provide for optical access to the MTJ free layer,
while also allowing for an electrical read-out of theMTJ state, a process flow using indium tin oxide as a
top transparent electrode was successfully developed.
Patterning of ITO was done using a reactive ion etchbased on a CH4/H2 chemistry, to achieve almost
vertical sidewalls for diameters down to 50 nm [2]. The
ITO based process flow was compared to a standard
magnetic tunnel junction fabrication flow based on Ta
hard mask, both achieving the same TMR signal levels.
A device matrix with magnetic tunnel junctions was
fabricated with the mentioned stacks and process flow
to demonstrate a path of spintronic-photonic
integration. The fabricated devices confirmed all
optical switching after fabrication, using picosecond
pulses to switch the AOS electrode and electrical readout of the magnetic tunnel junction resistance.
Our results contribute to advances in ultrafast
magnetic random access memories, showing how
Tb/Co-based optically switchable magnetic tunnel
junctions are good candidates for photonic-spintronic
integration in electronic circuits.
[1] E. K. Sobolewska et al., in Active Photonic Platforms XII, Online
Only, United States, Aug. 2020, p. 78. doi:
10.1117/12.2567662.
[2] A. Olivier et al., Nanotechnology, vol. 31, no. 42, p. 425302, Jul.
2020, doi: 10.1088/1361-6528/ab9c56.
[3] L. Avilés-Félix et al., Scientific Reports, vol. 10, no. 1, pp. 1–8,
Mar. 2020, doi: 10.1038/s41598-020-62104-w.
[4] L. Avilés-Félix et al., AIP Advances, vol. 9, no. 1

10.
Multifunctional Design of Quantized
Domain Wall-Magnetic Tunnel Junction Artificial
Synapses for Flexible Training of Neural
Networks
Samuel Liu, Thomas Leonard, Mahshid Alamdar, Can Cui,
Otitoaleke G. Akinola, Lin Xue, Patrick Xiao,
Joseph S. Friedman, Matthew J. Marinella, Christopher H.
Bennett, and Jean Anne C. Incorvia
Dept of Electrical and Computer Engineering, Univ of Texas
1.
at Austin, USA
2.

The processing of artificial neural networks (ANNs) islimited by the memory wall in von Neumannarchitectures, driving the need for hardware ANNs

realized by neuromorphic devices [1]. Previously
proposed multi-weight synaptic devices often sufferfrom a nonlinear and asymmetric update response,
limiting their viability for supervised learning [2].
Domain wall-magnetic tunnel junction (DW-MTJ)
devices driven by spin transfer torque (STT) and spin
orbit torque (SOT) have shown promise inneuromorphic applications, realizing neuron behavior
in simulation [3-8]. Simulations also show that DWMTJs can implement synaptic spike-timing dependent
plasticity [9]. A type of DW-MTJ with multiple MTJs
was demonstrated experimentally [10], but there has
not yet been a demonstration of multi-weightswitching in a DW-MTJ with a single MTJ. Most priorwork on DW-MTJ synapses in ANNs does not consider
thermal effects and process variation. We evaluate
notched DW-MTJ designs shown in Fig. 1a and accountfor these effects using MuMax3 for device simulation
and CrossSim for network simulation [11-13]. Figure
1b shows that excellent linearity, high symmetry, andlow thermal noise are maintained at 300 K, leading tohigh training accuracy on the Fashion-MNIST task,
shown in Fig. 2 [14]. Notably, the greater stochasticity
of SOT-driven synapses counters the discretizing effectof notches, boosting accuracy to near ideal. We also
show that the ferromagnetic track can havelithographically defined metaplasticity, enhancing
network performance on online learning tasks. These
results propose a magnetic synapse with tunable
plasticity, superior backpropagation performance, andfast updates, a foundational step toward ANNs withfully spintronic matrix operations.

11. Experimental
Demonstrationof
Neuromorphic Network with STT MTJ Synapses
Peng Zhou1, Alexander J. Edwards1, Fred B. Mancoff2,
Dimitri Houssameddine2, Sanjeev Aggarwal2, Joseph S.
Friedman1
The University of Texas at Dallas, Richardson, Texas, USA.
Everspin Technologies, Inc., Chandler, Arizona, USA.
Email: peng.zhou@utdallas.edu

One of the primary hardware costs incurred byartificially-intelligent neural networks is due to vector-

matrix multiplication (VMM). Non-volatile analog
resistive memory devices appear to naturally mimic
the behavior of neurobiological synapses, and can beused to perform VMM by taking advantage of Ohm's
and Kirchhoff's laws to efficiently perform thesecalculations in terms of voltage and current. Most
research in this area has focused on crossbars
composed of memristors and phase change memory(PCM). However, these devices suffer from several
major challenges which limit their utility for VMM
crossbars, including imprecise setting to desired
resistance state, weights drifting over time, limited
endurance, and compatibility challenges with CMOS
processes. Magnetic tunnel junctions (MTJs) provide
solutions to the limitations of memristors and PCM,
and their binary resistance states can provide analog
neuromorphic behavior through the stochastic natureof STT-MRAM switching. Here we present the firstexperimental demonstration of a neuromorphic
network using MTJ synapses for VMM. While

Fig. 1: a) Device diagram b) Conductance G vs dG statistics of a
DW-MTJ at 300 K for STT and SOT propagation. Heatmaps are
generated from micromagnetic simulations. The CDF represents
the probability that a given conductance update is less than the
average.

spintronic devices have been demonstrated for otherneuromorphic functions --e.g., spin-torque nanooscillators, domain wall MTJs, and stochastic p-bits -they have not previously been demonstrated as
adjustable synapses in a neuromorphic network. This
poster reports the experimental demonstration of asmall binarized neuromorphic network with MTJ
synapses, greatly advancing the development ofhighly-efficient, robust hardware amenable to neuralapplications.

Fig. 2: Validation accuracy of a two-layer perceptron of STT and
SOT DW-MTJ synapses at 300 K assuming (a) continuous levels
and (b) 32 notches and periodic carry.
[1] 1. A. Sebastian, M. Le Gallo, R. Khaddam-Aljameh and E.
Eleftheriou, Nature Nanotechnology., Vol. 15(7), p. 529–544 (2020)[2] X. Sun and S. Yu, IEEE Journal on Emerging and Selected Topics
in Circuits and Systems., Vol. 9(3), p. 570–579 (2019)[3] J. A. Currivan-Incorvia, S. Siddiqui, S. Dutta, E. R. Evarts, J. Zhang,
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racetrack and (4) chiral domain walls can propagate at
higher domain wall velocities in narrow wires.

12. Enhancing the performances of MRAM
materials and devices using light ion irradiation

H. Nakanishi1, J. Tsuchimoto1,2, H. Hosoya2, Y. Amemiya1,
C. Watanabe1, and A. Teramoto1
1. Hiroshima University
2. CANON ANELVA CORPORATION

Johannes W. van der Jagt1, Song Chen1, Benjamin Borie1,
Roméo Juge1, Noel Montblanc1, Liza Herrera Diez2,
Dominique Mailly, 2, Jürgen Langer3, Berthold Ocker3, Olivier
Boulle4, Gilles Gaudin4, and Dafiné Ravelosona1, 2
1. Spin-Ion Technologies, 91120 Palaiseau, France
2. Centre de Nanosciences et de Nanotechnologies (C2N),
CNRS, University of Paris-Saclay, 91120 Palaiseau, France
3. Singulus Technology AG, 63796 Kahl am Main, Germany
4. Spintec, University Grenoble Alpes, CNRS, CEA,Grenoble
INP, 38000 Grenoble, France

We have developed a new manufacturing process
based on He+ ion irradiation to tailor the structuralproperties of ultra-thin magnetic films and MRAM
devices at atomic level and improve theirperformances. The utilization of light ions provides theprecise control of inter-atomic displacements throughlow energy transfer. The key feature of the technology
is the post-growth control at the atomic scale ofstructural properties and the related magnetic
properties. When realized through a mask thistechnology allows lateral modulation of magnetic
properties without any physical etching. To perform
ion irradiation, we have used a compact ion irradiation
facility (Helium-S® from Spin-Ion Technologies),
capable of ultra-fast He+ ion irradiation on 1 inch
wafers with energies ranging between 1-30 keV.
In this poster, we will show a few important resultsthat suggest a pathway to optimize the performancesof future generation of MRAM devices using He ion
irradiation : (1) crystallization of CoFeB-MgO layers canbe obtained with lower distribution of magnetic
properties than pure annealing, (2) Spin Orbit Torques
MRAM devices can switch at lower current densities,(3) skyrmions can be nucleated and channeled in

13. New Isolation Method for MTJ Fabrication
Using SiN-Sidewall

The metal adsorption on MgO sidewall at the bottom
etching process causes a very large leakage current
and degrade the reliability [1], and the sidewall
protection of MgO during the bottom electrodeetching is essentially required. We have alreadyreported the leakage current could be suppressed, andreliability could be maintained in the simple stuck
structure of CoFeB/MgO/CoFeB, because the bottom
electrode etching is very simple [1]. However, theadsorption of the metal contamination during bottom
electrode etching in full stuck structure case has to be
suppressed, because the bottom electrode is thicker
and more complicated than the above simple structure.
To eliminate the leakage current in full-stack MTJs, wehave investigated a new isolation method MTJ cells byusing SiN-sidewall. The cross-sectional view of process
steps is shown in Fig.1. At the first ion beam etching(IBE), the etching stopped at the surface of CoFeB layer
under the MTJ, and then the SiN was formed on the
sidewall of the cell, following IBE was done for all
bottom electrode metals. The sidewall SiN film canprotect the metal adsorption during bottom electrodeetching. The etch stop was determined by using thesignal of SIMS during the etching. By eliminating theleakage current at the edge, the clear MR curve andthe high reliable MgO films can be observed as shownin Fig. 2 and 3.

[1] H. Park, et al., Jpn. J. Appl. Phys. 59, SGGB05, 2020 .

14. Design Support for Ultra-Scaled MRAM Cells
Simone Fiorentini1,*, Mario Bendra1,2, Johannes Ender1,2,
Roberto L. de Orio2, Siegfried Selberherr2, Wolfgang Goes3,
and Viktor Sverdlov1,2
1. Christian Doppler Laboratory for Nonvolatile
Magnetoresistive Memory and Logic at the
2. Institute for Microelectronics, TU Wien, Gußhausstraße
27-29, A-1040 Wien, Austria
3. Silvaco Europe Ltd., Cambridge, United Kingdom*Email: fiorentini@iue.tuwien.ac.at

The design of advanced, single-digit shape-anisotropy
MRAM cells [1] requires accurate evaluations of spincurrents and torques in magnetic tunnel junctions(MTJs) with composite elongated free layers (FLs). For
this purpose, we generalized the coupled spin andcharge drift-diffusion approach previously successfully
applied to nanoscale metallic multilayer structures[2][3] to accurately evaluate the spin and chargetransport and the torques acting in an MTJ on a FL
composed of several pieces separated by MgO tunnel
barriers (TBs) [1].
To evaluate the charge current density, we model the
TB as a poor conductor with a local resistance being
dependent on the relative orientation of themagnetization across the TB. We demonstrated thatthe expected dependence of the current density flowon the magnetization state is reproduced [4].

To model correctly the spin current density, thecoupled spin and charge drift-diffusion approach mustbe supplemented by appropriate boundary conditions
for the spin current at the TB interfaces. With theaddition of such conditions, the expected dependenceof the torques on the relative angle between themagnetization vectors [5][6] is reproduced. Our
approach can be generalized to model non-linear bias
dependences of the torques as an on-demand featureby making the interface polarization parameters
depend on the voltage. The observed voltage
dependencies of both the damping-like and field-liketorques are thereby properly reproduced.
The magnetization in elongated FLs of ultra-scaled
MRAM cells during switching is highly nonuniform
along the FL as the formation and propagation of adomain wall is expected. The additional torques acting
in the presence of a domain wall are usually modeledby the Zhang and Li [7] expression. We demonstrate
that, in the presence of a TB, the Slonczewski and
Zhang and Li torques are not additive and must betreated on equal footing to correctly describe thetorques acting on nonuniform magnetization inelongated FLs with several MgO TBs. Our simulationsof the magnetization dynamics in composite elongatedFLs agree well with recent experimental
demonstrations of switching of ultra-scaled MRAM
cells.
[1] B. Jinnai et al., Proc. of the IEDM, pp. 24.6.1-24.6.4, 2020.
[2] C. Abert et al., Sci. Rep., vol. 5, p. 14855, 2015.
[3] S. Lepadatu, Sci. Rep., vol. 7, p. 12937, 2017.
[4] S. Fiorentini et al., Sol.-St. El., vol. 186, p. 108103, 2021.
[5] J. C. Slonczewski, Phys. Rev. B, vol. 71, p. 024411, 2005.
[6] M. Chshiev et al., Phys. Rev. B, vol. 92, p. 104422, 2015.
[7] S. Zhang et al., Phys. Rev. Lett., vol. 93, p. 127204, 2004.