Spin transport in a semiconductor channel

Introduction

Channel and Device Structure

Spin Hall effect in a Rashba system

Results and Discussion

Conclusion

The spin transport device is one of the excellent candidates for next

generation technology.

The spin–orbit interaction in semiconductor systems provides an

exceptionally rich area of research. The spin-based semiconductor concept

may permit the fabrication of fully integrated spin-FET structures, and the

quantum well and nanowire systems have excellent properties appropriate for

low power devices.

Room temperature spin transport in a GaN wire

We show a direct demonstration of the spin Hall effect and demonstrate a

technique for an all-electric measurement of the Datta–Das conductance

oscillation using a quantum well system.

Complementary spin logic device

V

𝟏𝟎𝛍𝐦

V

Semiconductor spintronics

Quantum well channel

VH,1 VH,2 VH,3 VH,4

IVH,n

…..…VH,5

x = 0

…..…

BR

Semiconductor spin device

Low power solution

Low-dimensional channel

FM

WFM

WH

L

WC

A A’

A A’

80 nm 56 nm

110 nm

80 nm

3 nm

Buffer & lower

insulating barriers

Single quantum well

InAs heterostructure

Gate dielectric

Gate metal

Ferromagnet

Gate coverage

Gate coverage

1 μm

Semi-insulating InP(001) sub

In0.52Al0.48As 300nm

n+ In0.52Al0.48As 7 nm (n = 4×1018)

In0.52Al0.48As 6 nm

In0.53Ga0.47As 13.5 nm

In0.52Al0.48As 20 nm

InAs 2 nm

In0.53Ga0.47As 2.5 nm

InAs (Quantum Well) 2 nm

I

x

VH

0

x = 0

0.6 0.8 1.0 1.2 1.4 1.6 1.8

-40

-20

0

20

40

experimental data

fitted line

ideal ballistic

V

H / I (

m

)

L (m)

Parallel-type spin transistor (P-ST)

“High”Source Drain

ONOFF

When precession = 180

→ ON (p-MOS like)

Antiparallel-type spin transistor (AP-ST)

“Low” “High”

ON OFF

When precession = 360

→ ON (n-MOS like)

0

10

-3.0 -2.5 -2.0

0

5 VAP

V

− V

0 (

V)

VP

VIN

(VG) (V)

-3.0 -2.5 -2.0

0

10

20

VIN

(VG) (V)

VO

UT (

V)

0 2 4 6 8 10 12

-30

-20

-10

0

10

20

30

VIN

(VG)

1 V

VOUT

VAP

VP

VO

UT (

V)

Time (sec)

I

VP+

−

+

VAP +

−

−

VG

P-STAP-ST

L

2 μm

VOUT

AB-type AA-type

-1.0 -0.5 0.0 0.5 1.0-50

0

50

100

150

200

250

300

350

V (

V)

H (kOe)

300 K

200 K

150 K

100 K

77 K

50 K

30 K

10 K

I = 1 μ A

I

1D and 2D spin devices are fabricated

for room temperature applications.

We demonstrate complementary spin transistors consisting of two types of

devices, namely parallel and antiparallel spin transistors using InAs based

quantum well channels and exchange-biased ferromagnetic electrodes.

We realize a complementary logic operation purely with spin transistors

controlled by the gate voltage, without any additional n- or p-channel

transistor.

We present spin injection in single-crystal gallium nitride nanowires and

report robust spin accumulation at room temperature.

Spin injection efficiency depends on crystal direction of GaN wire.

Spin Hall device is fabricated using

Rashba system for low power applications.

W. Y. Choi et al., Nat. Nanotech. 10, 666 (2015)

T.-E. Park et al., Nat. Comm. 8, 15722 (2017)

Y. H. Park et al., Sci. Rep. 7, 46671 (2017)

Thin body p-GaAs junctionless FET

on Si via wafer bonding

and epitaxial lift-off technology

Integration of III-V compound semiconductors on Si

Electron mobility

Hole mobility

• Enhanced carrier mobility, switching speed, higher on-current and faster operation

• n-type JL FET is previously reported, however, p-type JL FET is rarely reported.

Introduction

Effective mobility calculation considering contact and channel resistance

Experimental Results

Fabrication process of thin body p-GaAs junctionless FET on Si

Transfer (ID-VG) curve of p-GaAs OI on Si FET varying the channel thickness

Effective mobility extraction from ID-VG curve varying channel length

p-GaAs OI on Si FET from 10 to 40 nm of channel thickness

S.S. enhancement with Y2O3 surface passivation

Transfer (ID-VG) and Output (ID-VD) curve of p-GaAs OI on Si FET

Transfer and output curve of channel thickness 20 and 30 nm

Effect of top surface passivation by Y2O3

• High Ion/Ioff ratio is obtained for 20 and 30 nm of channel thickness

• Trade off between Ion and S.S.

Conclusion

p-GaAs OI on Si using patterned-wafer bonding and epitaxial lift off

• As the channel thickness increases, on-current increases.

• Subthreshold swing (S.S.) is reduced as the channel thickness is increased.

• Ion/Ioff is defined by ~10 in the case of ~40 nm of channel thickness.

• 10 nm of channel showed presented lowest Ion current level (~nA scale).

• Patterned wafer bonding for fast ELO and back-gate device fabrication.

• Channel thickness optimization (10 to 40 nm, 10 nm interval).

• Varying channel length from 2 to 50 um (to accurately calculate effective mobility).

• High Ion/Ioff ratio : ~105

• The ratio of contact and channel resistance is plotted varying gate bias.

• Effective mobility is calculated excluding S/D contact resistance.

• The highest Ion/Ioff ratio : ~106 • Enhanced S.S. : ~250 mV/dec

• We firstly reported thin body p-GaAs OI on Si FET using wafer bonding and ELO.

• Channel thickness is a critical factor to define device performance.

• In 30 nm thickness, Ion/Ioff and S.S. are measured by ~105 and 420 mV/dec, respectively.

• Surface passivation further enhanced Ion/Ioff (~106) and S.S. (250 mV/dec) .

Junctionless (JL) FET • Low cost and mass production

(simple fabrication steps)

• Minimizing mobility degradation

(caused by surface scattering and phonon

scattering)

• Low Off-current by using full depletion

• No doping gradient -> use for small

dimensionJ-P Colinge et.al., Nature nanotechnology (2010)

Thin n- and p- GaAs channel CMOS on Si

Biomimetic Electronic Materials

for Human-Interfacing Sensors and Devices

Introduction

Biomimetic Electronic Materials

Conclusion

We have shown that employing biomaterial-incorporated conductive nanonetworks as interfacial

layers of contact based resistive pressure sensors produced giant piezoresistive response via effective

modulation of interlayer resistance and enabled simultaneous ultrasensitivity and broad operating

pressure ranges.

Nanomesh-based wearable bio-sensing platformWearable Devices

Biological glue and hydrodynamic assembly of nanomesh

* 차세대웨어러블의현황과미래그리고이슈, 주간기술동향 (2014) * Vandrico. Inc. Wearable Tech Market Insights (2014)

Wearable devicesHealthcare

Entertainment

Houseware

Rehabilitation

Augmented realityMilitary purpose

Smart phones

< Applications and statistics of wearable devices >

Nat. Nanotechnology, 6 13 (2011)

www.viatechnology.com, www. gizmodo.com, www.graco.com.

ElectricalIonic

Chemical

Biological

Mechanical

Human-Interfacing Sensors for Healthcare

• Highly conductive (electronic, ionic)

• Enabling additional biological functionalization

• Well adherent on flexible substrates or metallic layers

• Flexible and mechanically stable

• Biocompatible

• Water-stable

Nanostructured Hybrid Materials System

: Biomimetic Electronic Materials

< Materials Requirements >

Biomimetic Approach

< Biomolecular recognition >

http://en.wikipedia.org/wiki/Molecular_recognition

Single-stranded DNA (ssDNA) of M13 virus.

Molecular recognition refers to

the specific interaction between

two or more molecules through

non-covalent bonding such as

hydrogen bonding, metal

coordination, hydrophobic forces,

van der Waals forces, pi-pi

interaction, halogen bonding, etc.

< Biological template: M13 phage >

Scientific Reports, 5 9196 (2015)

< Bio-panning process > < Nanomesh of SWNTs using biological glue >

Adv. Mater. 27 922 (2015)

Wearable Physiological Electrodes

We found a surface peptide sequence of a

filamentous biopolymer that showed strong

binding affinity toward SWNTs. The

biopolymer serves as biological glue

< Contact impedance measurement >

Adv. Mater. 27 922 (2015)

< High frequency brain signal measurement >

Adv. Mater. 27 922 (2015)

Nanomesh-integrated flexible neural probes

Flexible/Wearable Chemical Sensors

< Hydrodynamic assembly + LBL assembly >

a

b c

Adv. Mater. 28 1577 (2016)

< Smart contact-lens>

< Nanomesh-based enzyme platform for high-performance wearable biosensors >

Flexible/Wearable Pressure Sensors

Flexible pressure sensors based on biomimetic interfacial layers

ACS Appl. Mater. Inter. (2017)

Monitoring of wrist pulse wave

Conductive nanomesh with a high effective-surface-area and strong adhesion to substrates could

enable the study of biologically important but weak brain signals using a non-invasive platform.

Adv. Mater. 28 1577 (2016)

We have developed a biological template material-based biosensing platform with unprecedented

applicability and versatility. The nondestructive assembly of nanostructured enzyme platform in

combination of specific biomolecular attraction and electrostatic coupling using a biological

template material enabled flexible biosensors.

-0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4

-50

-40

-30

-20

-10

0

10

20

30

0 250 500 750 1000-38

-36

-34

-32

0mM Glu

0.25mM Glu

0.5mM Glu

0.75mM Glu

1mM Glu

Cu

rre

nt

(A

)

Voltage (V vs. Pt pseudo RE)

Cu

rren

t (

A)

Glucose concentration (M)

Sensitivity

~113 µA/mM cm2

GlucoseConcentrationincrease

A genetically engineered biological template-based approach for the

assembly of a nano-structured hybrid electronic material system,

biomimetic electronic materials, has been successfully developed and its

applications to wearable/flexible sensors and devices have been

demonstrated.

Biomimetic electronic materials have huge potentials for the development

of wearable health-monitoring devices, personalized medicines, human-

machine interfaces, prosthetic limbs, and intelligent robotics.

*Done in collaboration with Dr. J. H. Choi (KIST)

A fundamental diffusion-based

hydrodynamic phenomenon in combination

of biological glue can successfully assemble

a large-scale conductive nanomesh.

2

Project Description

Device Preparation

2

Spin Torque Ferromagnetic Resonance

The ST-FMR can measure 𝜃𝐷𝐿, 𝜃𝐹𝐿 and 𝛼 simultaneously.

The IRF in Pt generates the filed-like and anti-damping torques as well as the

Oersted field.

Spin orbit torques (SOTs) : Field-like torque (𝜏𝐹𝐿) ∝ m× yAnti-damping torque (𝜏𝐷𝐿) ∝ m× y ×m

𝑉𝑚𝑖𝑥 𝐻 = 𝑉𝑆𝛥𝐻2

𝐻 − 𝐻𝑟𝑒𝑠2 + 𝛥𝐻 2

+ 𝑉𝐴𝐻 − 𝐻𝑟𝑒𝑠 𝛥𝐻

𝐻 − 𝐻𝑟𝑒𝑠2 + 𝛥𝐻2

Symmetric Lorentzian : 𝜏𝐷𝐿 Asymmetric Lorentzian : 𝜏𝐹𝐿 + 𝜏𝑂𝑒(𝐻𝑟𝑒𝑠 : resonance field, 𝛥𝐻 : half width half maximum)

FM (t)

MgO(2)Ta(2)

Ta(0 or 1)Pt (5)

SiOx

300 700 1100 1500

-8

-4

0

4

Data

Fit

Asym

Sym

vm

ix (

V)

Hext

(Oe)

2

Spin-Transfer Torque and

Spin-Orbit Torque

Spin-Hall Angle / Magnetic Damping

2

0 5 10 15

0.00

0.05

0.10

0.15

Pt|Co

Pt|CFB

Pt|Py

D

L

vo

lta

ge

tFM

(nm)

Estimation of 𝜃𝐷𝐿 and 𝜃𝐹𝐿 from several ST-FMR analysis methods

Investigation of α, 𝜃𝐷𝐿 and 𝜃𝐹𝐿 for various Material / Interface / Thickness

Study of angular and temperature dependence

0 5 10 15

0.0

0.1

0.2

Pt|Co

Pt|CFB

Pt|Py

F

L+

Oe

vo

lta

ge

tFM

(nm)

Intercept, 𝜃𝐹𝐿

Slope, 𝜃𝑂𝑒

To understand physics of spin-transfer torque & spin-orbit torque phenomena

To advance STT- and SOT-MRAM technologies

Spin-torque ferromagnetic resonance (ST-FMR)

Current-driven in-pane and perpendicular magnetization switching

Spin-torque nano-oscillators and wireless communication

Second Harmonic Hall measurement

Propagating Spin-Wave spectroscopy

∆𝐻 = ∆𝐻0 +2𝜋𝛼𝑒𝑓𝑓

𝛾𝑓 (Δ𝐻0 : inhomogeneous line width broadening)

Perpendicular magnetization Switching

0 5 10 150

50

100

150 PtCFB2

PtCFB3

PtCFB4

PtCFB5

PtCFB7

PtCFB10

H

(O

e)

f (GHz)

0 5 10 150.00

0.02

0.04

0.06

Pt/Co

Pt/CFB

Pt/Py

eff

tFM

eff (nm)

-400 -200 0 200 400-0.30

-0.15

0.00

0.15

0.30

Hz (Oe)

r H (

)

Hx

Idc

Free MagnetTunnel Barrier

Fixed Magnet

SOC Metal

READ

WRITE

-2000 -1000 0 1000 2000-4

-2

0

2

4

I sw (

mA

)

Hx (Oe)

θ

x

y

HD

Hk θ

Hx

HR

In-plane Current-driven switching

Various phenomena are involved during the perpendicular magnetic switching driven by in-plane

currents; DL-SOT, FL-SOT, Hext, DMI, Domain Nucleation/Propagation, PMA and so on

Spin torque nano-oscillators

2

In-plane magnetic switching in 3-terminal MTJ

Junction size80 nm x 200 nm

-15 -10 -5 0 5 10 1535

40

45

50

R (

k

)Field (mT)

-3 -2 -1 0 1 2 335

40

45

50

0mT

R (

k)

Current (mA)

Field-Driven switching

Field-Driven switching Current-induced switching

Switching phase diagram

• RA = 1~5 Ω∙2

• Annealing @ 300 oC, 30 min 4 kOe, easy-axis direction

• Ion-milling stopped in the middle of the CoFeB(5 nm)

• Dumbbell shape pillar fabrication

Stray field

MgO

CoFeB(2)

Ru(0.8)

100 150 200 250 300 350 400

4

6

8

10

12

Magnetic field (Oe)

Fre

qu

en

cy (

GH

z)

0.000

1.250

2.500

3.750

5.000

6.250

7.500

8.750

10.00

Field Sweep (420 to 80 Oe, 85o),I = 2.0 mA Current Sweep (1.4 to 3.3 mA), H = 400 Oe,

85o

Sputtering/Evaporation E-beam/Photo-lithography/Ion-milling

Electric field induced magnetic anisotropy

modulation at CoFeB-MgO interfaces

Introduction

Experiments

Magnetic properties of Ta/CoFeB/MgO and Hf/CoFeB/MgO

Results and Discussion

Conclusion

Electric-field-induced modification of magnetic anisotropy is studied

using voltage dependent TMR and XRMS measurements.

The electric field induced magnetic anisotropy change is significantly

enhanced by inserting ultrathin heavy metals suggesting that interface

engineering could be used to enhance the electric field-induced magnetic

anisotropy modulation of ultrathin ferromagnetic films

Electric field control of magntism has been studied extensively recently due

to its potential use for low-power magnetization swtiching in spintronics

devices. In MgO-based magnetic tunnel jucntions(MTJs), electric field has

been used induce magnetization switching even in the absense of electric

current induced spin transfer torques.

The underlying physics behind this phenomena is still controversial and needs

to be clarified.

Insertion and buffer layer dependence of the electric field effect

The positive slope in magnetic anisotropy vs. voltage plot implies that the PMA is

strengthened when the electron density is increased, while it is weakened when the

electron density is decreased.

The change of magnetic anisotropy energy per electric field is significantly enhanced

by inserting heavy metals (e.g. Hf, Ir, Ru). Also, the electric field effect is opposite for

Hf-buffered (left) and Ta-buffered (right) MTJs.

Electric field dependence of TMR

The TMR of the CoFeB/MgO/CoFeB shows a strong voltage dependence.

HK of the bottom CoFeB (weakly in-plane) is decreased with increasing applied voltage,

indicating that the interfacial PMA of the bottom CoFeB increases with voltage.

A similar effect appears when a ultrathin (0.5ML) Hf layer is inserted between the bottom

coFeB and MgO.

Switching magnetism with electric field

Electric field induced magnetic anisotropy modulation

The electric field induced change in magnetic anisotropy was determined by measuirng

the voltage dependent TMR in MTJ devices

Depth-resolved, element-resolved, and magnetic sensitive XRMS was used to varify

the mechanism of the electric field control of the magnetic anisotropy.

TMR of a CoFeB/MgO/CoFeB MTJ device

Ta(Hf)/CoFeB/MgO thin films show strong strong perpendicular magnetic anisotropy

(PMA) for CoFeB thickness tCoFeB < 1.1nm indicating strong PMA at the CoFeB-MgO

interface.

TMR of 10 micron sized CoFeB (1.2nm)

/MgO(1.6nm)/CoFeB(1.3nm) MTJ device.

The top CoFeB has strong PMA while the

bottom CoFeB shows weak in-plane

mangetic anisotropy.

The magnetic anisotropy can be

determined from the saturation field (HK).

XRMS measurement of electric field induced anisotropy modulation

XRMS measurements reveals that the remanent magnetization changes with voltage.

Further measurements and analyses are required to fully understand the interface

sensitive nature of the electric field effect utilizing interface sensitive and depth resolved

XRMS.

RE

FM

Ferrimagnetic Skyrmion

Magnetic Skyrmions for Next

Generation Electronics

Introduction

Experiments

Conclusion

Topological protection and atomic size

Statics/Dynamics of room temperature ferromagnetic skyrmions

In ferromagnetic heterostructures, magnetic skyrmions can be stabilized at

room temperature and also be displaced at a speed exceding > 100 m s-1

Dynamic excitation behaviours of magnetic skyrmions can be excited and

controlled upon the application of nanosecond spin-orbit torques

Magnetic skyrmions exhibit fascinating properties

Soft X-ray Transmission Microscopy – MTXM & STXM

Both MTXM and STXM utilizes XMCD effect, and they offer 25 nm spatial and

70 ps temporal resolutions. These facilities are only available at synchrotrons

In principle, circularly-polarized X-ray interacts differently with up-magnetized

and down-magnetized electrons due to their different angular. Therefore, in the

presence of magnetic textures, the transmitted X-ray contrasts differs for

opposite magnetizations

S. Heinze et al., Nat. Phys. 7, 713-718 (2011)

X.Z. Yu et al. Nature 465, 901-904 (2010) T. Schulz et al., Nat. Phys. 8, 301-304 (2012)

N. Nagaosa et al., Nat. Nanotech. 8, 899-911 (2013)

A. Soumyanarayanan et al., Nat. Mater. 16, 898-904 (2017)

X. Zhang et al., Sci. Rep. 5, 9400 (2015)

Y.Q. Huang et al., Nanotechnology, 28 (2017)

: Magnetic skyrmions are topologically-

protected, and can be defined by the

topological number S (or skyrmion

number). When they appear, their size

can be as small as a single nanometer

Ultralow threshold current density

: Threshold current density for the

driving magnetic skyrmions is known

to be as small as ~106 A m-2, which is

104 times lower than that for domain

wall displacement

Emergent electrodynamics

: When electrons pass through a

magnetic skyrmions, they experience

emergent electromagnetic field due to

the topological nature of the skyrmion.

Such emergent field causes a distinct

phenomena, such as skyrmion Hall

effect

Device opportunities

: Owing to attractive characteristics of

magnetic skyrmions, low-power &

ultrafast skyrmionic device applications

could be realized – including skyrmion

memory, skyrmions logic and skyrmion

neuromorphic computing devices

Results and Discussion

Magnetic skyrmions can be

deterministically written and

deleted by the application of

asymmetric bipolar pulses along

a nanowire track

Topological changes accompany

the generation and deletion of

topological defect, vertical

Bloch line (VBL), which plays

crucial role during the processes

S. Woo et al., Nat. Mater. 15, 501-506 (2016)

Materials;

[Pt3/Co0.9/Ta4] 15

[Pt3/CoFeB0.9/MgO1.8] 15

Deterministic writing/deleting of skyrmions

Ferrimagnetic skyrmions without skyrmion Hall effect

Schematic description Scanning Transmission X-ray Microscopy (STXM) and the principle of X-ray magnetic circular dichroism (XMCD)

Synchrotrons

BESSY II in Berlin, Germany

Beamline: MAXUMUS (STXM)

ALS in Berkeley, USA

Beamline: XM-1 (MTXM)

SLS in Villigen, Switzerland

Beamline: PolLux (STXM)

j > 0

j < 0

Materials;

[Pt3/CoFeB0.9/MgO1.8] 20

Skyrmion Breathing

Skyrmion Translation

Pulse Profile

S. Woo, K. M. Song et al., Nat. Commun. 8, 15573 (2017)

1 2 3

0

20

40

S

kH

E ()

ja (1011 A m-2)

Exp.

Sim. (w/o defects)

Sim. (w/ defects)

1 2 30

20

40

60

Velo

city (

m s

-1)

ja (1011 A m-2)

Exp.

Sim. (w/o defects)

Sim. (w/ defects)

In ferrimagnetic materials, such

as GdFeCo,

antiferromagnetically-coupled

ferrimagnetic skyrmions can be

stabilized and driven without

experiencing skyrmion Hall

effect, resulting in the straight

motion along a nanowire track

Materials; [Pt3/GdFeCo5/MgO1] 20

S. Woo, K. M. Song et al., under review

(priprint available at arXiv: 1703,:10310)

Spin waves for the efficient displacement of magnetic skyrmions

Magnetic domain wall can be efficiently

driven by the burst of spin waves, which

are generated by the collision of two

adjacent domain walls

The results imply that spin waves could be

an efficient source for skyrmions motion

Materials; Ni80Fe20 (Permalloy)

Schematic of spinwave-driven motion of ma

gnetic skyrmions

[Nanotechlogy 26, 225701 (2015)]

Spinwave-driven displacement of domain walls

S. Woo et al., Nat. Phys. 13, 448-454 (2017)

Our investigations reveal that magnetic skyrmions could really be

incorporated into useful devices in the near future

S. Woo, K. M. Song et al., under review

(priprint available at arXiv: 1706,:06726)

935 940 945 950 955 960

-1.0

-0.5

0.0

0.5

1.0

V/V

a (norm

.)

Time (ns)

Deleting pulse

-5 0 5 10 15 20

-1.0

-0.5

0.0

0.5

1.0

V/V

a (norm

.)

Time (ns)

Writing pulse

Time

Q=0

Q=1

Time

Q=1

Q=0

Sk1

Sk4

Sk2

Sk3

Sk1

Sk4

Sk3Sk2

Sk7

Sk1

Sk4

Sk3Sk2

Sk5

Sk6 Sk7

Sk5

Sk6

Sk2

Sk7

Sk2

Sk7

Sk2

Sk2 Sk2 Sk2 Sk2

Au

Sk5

Sk6

Sk2

Sk7

Sk5

Sk7

Materials; [Pt3/GdFeCo5/MgO1] 20