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2D Materials for Ubiquitous Electronics

Saptarshi Das

Assistant ProfessorEngineering Science and Mechanics

Materials Research InstitutePennsylvania State University

sud70@psu.edu814-863-2639

2DCC-MIP Webinar September 7, 2017

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Traditional Electronics

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Transistor Evolution

Gate

Source Drain

Oxide

VGS

VDS

Substrate

Si

4 decades– 4 orders of magnitude length scaling

100µm 197510nm 2015

Source Drain

λS

Short Channel LimitLCH > 3λS

𝜆𝑆 = 𝜆𝑔𝑒𝑜 =𝜀𝑏𝑜𝑑𝑦−𝑥

𝜀𝑜𝑥𝑡𝑏𝑜𝑑𝑦𝑡𝑜𝑥

tbody ≈ 6nm λS ≈ 4.2nmSi FinFET

Scaling Ends – Doomsday ?

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Gate

Source Drain

Oxide

VGS

VDS

Substrate

2D Materials can rescue!!

Source Drain

λS

Short Channel LimitLCH > 3λS

tbody ≈ 0.65nm λS ≈ 1.4nmMonolayer MoS2

tMoS2 = 0.65 nm

𝜆𝑆 = 𝜆𝑔𝑒𝑜 =𝜀𝑏𝑜𝑑𝑦−𝑥

𝜀𝑜𝑥𝑡𝑏𝑜𝑑𝑦𝑡𝑜𝑥

tbody ≈ 6nm λS ≈ 4.2nmSi FinFET

Transistor Evolution

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Monolayers are Essential

Gate

Source Drain

Oxide

VGS

VDS

Substrate

Large Bandgap (1.8eV)

Schottky Barrier Contact1T-phase contact (200Ω-µm)

Bandgap EngineeringStraintronics

Ballistic LimitNo Concerns

Quasi Ballistic Low mobility – No problem

h-BN buffer layer

Monolayer Mobility is poor

Transistor Evolution

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Current State of AffairsCVD, MOCVD, MBE Growth

Kang. K, et al., Nature, 520, 656–660, 2015.

van der Zande. A. M, et al., Nature Materials, 12, 554–561, 2013.

Transistor Evolution

Future looks promising

Desai. B. S, et al., MoS2 transistors with 1-nanometer gate lengths. Science, 354, 6308, 99-102

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Power Dissipation

ΔVTH

ΔIOFF

Gate

Source Drain

Oxide

VGS

VDS

Substrate

Boltzmann Tyranny

Voltage Scaling Almost Stopped

Fundamental Limitations at Device Level

Innovation in Device Physics

𝑺𝑺 =𝒌𝑩𝑻

𝒒𝒍𝒏𝟏𝟎

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Power Dissipation

Gate

Source Drain

Oxide

VGS

VDS

Substrate

Boltzmann Tyranny

Voltage Scaling Almost Stopped

Fundamental Limitations at Device Level

Innovation in Device Physics

𝑺𝑺 =𝒌𝑩𝑻

𝒒𝒍𝒏𝟏𝟎

ΔVTH

ΔIOFF

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A Novel Concept: 2D EFET

Two Dimensional (2D) - Electrostrictive Field Effect Transistor

Das. S; Two Dimensional Electrostrictive Field Effect Transistor (2D-EFET). Scientific Reports, 6, 34811, 2016.Ultra Low Power FET

Monolayer MoS2 undergoes SMT at 3GPaAlvarez. M, et al. Nano Letters, 15 (5), 3139–3146, 2015.

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Source Drain

Source Drain

ΨS

VDDEG0

𝜳𝑬 = −𝜶

𝟐𝑷

𝑷𝟐𝑫 = 𝜼𝑪𝟑𝟑,𝟐𝑫𝟏

𝒕𝟐𝑫𝒅𝟑𝟑𝑽𝑮𝑺

VB

Electrostrictive/

Piezoelectric

Material

Substrate

2D Semiconductor

Gate

Dielectric

So

urc

e

Dra

in

VDD

VGS

Capping

Layer

Back Contact

𝝍𝑬 = 𝜼 𝜶𝑪𝟑𝟑,𝟐𝑫𝟏

𝟐𝒕𝟐𝑫𝒅𝟑𝟑 𝑽𝑮𝑺𝝍𝑺 = 𝑽𝑮𝑺 𝜓𝑇 = 𝑉𝐺𝑆(1 + 𝜂𝛽𝑑33)

EG

ΨE

𝜳𝑺 = 𝒓𝑽𝑮𝑺 𝒓 ≤ 𝟏

Stiffness: 𝑪𝟑𝟑 (GPa)

Piezoelectric Coefficient: 𝒅𝟑𝟑 (pm/V)

Eg Coefficient: 𝜶 (meV/GPa)

Strain transfer coefficient: 𝜼A Novel Concept: 2D EFET

Ultra Low Power FET

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𝐼1 =2𝑞

ℎන𝑀 𝐸 𝑇 𝐸 𝑓𝑠 𝐸 𝑑𝐸

𝐼2 =2𝑞

ℎන𝑀 𝐸 𝑇 𝐸 𝑓𝐷 𝐸 𝑑𝐸

Source

Drain

VDD

𝑉𝐹𝐵 −Ψ𝑇

𝑉𝐹𝐵 −Ψ𝑇 + 𝑉𝐷𝐷

𝐼1 𝐼21

1

𝐼 = 𝐼1 − 𝐼2

Solid: 𝜂 = 0Dashed: 𝜂 = 0.3

𝑉𝐷 = 100𝑚𝑉

SS = 60mV/decade

⊥MoS2 Compliance:𝐶33 = 60 𝐺𝑃𝑎

Piezoelectric Coefficient: 𝑑33 = 850 𝑝𝑚/𝑉

MoS2 Eg Coefficient: 𝛼 = −80𝑚𝑒𝑉/𝐺𝑃𝑎

𝜓𝑇 = 𝑉𝐺𝑆(1 + 𝜂𝛽𝑑33)

Schulman. S. D, et al. manuscript inpreparation 2017.

A Novel Concept: 2D EFET

Ultra Low Power FET

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MotivationTrimming the high energy Fermi tail results in sub-

60mV/decade SS

𝐼𝑂𝑁 ∝ 𝑇𝑊𝐾𝐵 = 𝑒𝑥𝑝(−4

3ℏ2𝑚𝑒𝐸𝐺𝜆)

𝑇𝑊𝐾𝐵 = exp(−4

3ℏ2𝑚𝑒𝐸𝐺𝑑𝑂𝑋𝒅𝑩𝑶𝑫𝒀)

Band to Band Tunneling

EG

λ

OFFEG

ON

λ VGS

Das. S, et al. Towards Low Power Electronics: Tunneling Phenomenon in

TMDs ACS Nano, 8(2), 2014.

Tunneling FETsTMDs

Sarkar, D. et al. Nature 526, 91-95, 2015

𝑺𝑺 =𝒌𝑩𝑻

𝒒𝒍𝒏𝟏𝟎

Ultra Low Power FET

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Excitonic Device

Formation of excitonic condensate in spatially separated nanosheets (n-type and p-type) controlled by gate voltage

ON State: SuperconductorOFF State: Normal Semiconductor

ON State: Normal Semiconductor OFF State: Perfect Insulator

Excitonic FETExtreme Energy Efficient Electronics

h-BN

Oxide

N-type Nanosheet

P-typeNanosheet

Oxide

Source

Drain

Co

mm

on

Te

rmin

al

Top Gate

Bottom Gate

e e e e

h h h h

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Sensor Electronics

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Internet of Things

Sensors

Electrical Mechanical Optical Thermal Chemical Biomedical

High Performance – No Low Power/Self Power – YesLow Cost – Yes

Flexible – Yes Light Weight – YesTransparent – Yes

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Flextronics

Metal: Graphene Insulator: h-BN Semiconductor: WSe2

Electron BranchMobility: 24 cm2/V.sON/OFF : 2x107

Hole BranchMobility: 45 cm2/V.sON/OFF : 7x107

Das, S. et al. All Two Dimensional, Flexible, Transparent and Thinnest Thin Film Transistor.

Nano Letters 14 (5), 2014Displays

Thinnest Transistor

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Glasstronics

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Wu, W. et al. Nature 514, 470-474, 2014Zhu, H. et al. Nature Nanotechnology 10, 151-155, 2015

Piezotronics Self PoweredElectronics

PhotodetectorIph

p n

hυ

Electroluminescence (LEDs)hυ

p

n

hυ

Photovoltaic (solar cells)Isc,Voc

p n

hυ

Electrostatically doped WSe2 p-n diodes

Baugher. et al. Nature Nanotechnology 9, 2014.Ross. et al. Nature Nanotechnology 9, 2014.

Pospischil. et al. Nature Nanotechnology 9, 2014.

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EQE of up to 15% Photoresponsivity of 5x108A/W

Optoelectronics PhotodetectorsSolar Cells

LEDs

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Integrated circuit based on MoS2

Wang, H. et al. Nano Letters 12(9), 2012

Memory transistor with MoS2

Lee, H. S. et al. Small 8(20), 2012MoS2 FET based gas-sensor

Sarkar, D. et al. ACS Nano 8(4), 2014

Late, D. J. et al. ACS Nano 7(6), 2013

MoS2 FET based bio-sensor

Integrated CircuitsMemory Transistor

All Purpose ElectronicsBio-SensorsGas-Sensor

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Harsh Environment Electronics

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Space Electronics

Van Allen Belts• Protons• Electrons

Cosmic Rays• Protons (90%)• Helium Nuclei (9%)• Electrons (<1%)• Heavier Ions (<1%)

Van Allen Belts

Cosmic Rays

Inner Belt

Outer Belt

Horne, R. Nature Physics (2007)

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2MeV proton: 1014 protons/cm2 390keV He: 2x1015 ions/cm2 390keV He: 1016 ions/cm2

Arnold, A. et al.; Radiation Effect on MoS2 FETs. unpublished, 2017.

Radiation Exposure Courtesy: Prof. Jovanovic Group (UMich)

Space Electronics

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Anticorrosion Electronics

Electrochem Magic

Das. S, et al. A Self-Limiting Electro-Ablation Techniquefor the Top-Down Synthesis of Large-Area MonolayerFlakes of 2D Materials. Scientific Reports, 6, 28195, 2016.

19th Century Electrochemistry Set-upRoom TemperatureRequires Seconds

MoS2

WS2

MoSe2

Exfoliated Multilayer Electroablated Monolayer

Schulman. S. D, et al. Superior Electro-Oxidationand Corrosion Resistance of Monolayer TransitionMetal Disulfides. manuscript under review, 2017.

Huang. Y, et al. An Insight of Electro-AblationProcess for the Synthesis of Monolayer TransitionMetal Diselenides . manuscript under review, 2017.

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Extreme Stability/Corrosion Resistance of Monolayer TMDs

Electro-ablation

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Electro-ablated MoS2 Monolayers

Raman Photoluminescence

SAED TEM

in-situ spectroscopy In progress: Prof. Emilie Ringe (Rice)

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Anticorrosion Monolayer FETs

Schulman. S. D, et al. FETs based on Monolayer Electroablated 2DMaterials. manuscript in preparation, 2017.

VD = 2V

VD = 4V

VD = 6V

VD = 8V

VD = 10V

VG = -50V

OFF State Stressing

Negative VT shift Quick device recovery

VD = 2V

VD = 4V

VD = 6V

VD = 8V

VD = 10V

ON State Stressing

Negative VT shift Abrupt changes at VD = 10V Slow device recovery

Curiosity Driven Stressing

VD = 10V

VD = 12V

VD = 14V

VD = 16V

VD = 18V

Positive VT shift Abrupt changes at VD = 18V Permanent device damage

Reliable Electronics

Hot Electron Transistor

Arnold, A. et al.; Radiation Effect on MoS2 FETs. unpublished, 2017.

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Electron becomes HOT

“Lucky” electron

electron trapping in the gate oxide

positive VTH shift

“Lucky” hole

Hot Carrier Transport

Source

Drain

EG = 1.84

hole trapping in the gate oxide

negative VTH shift

𝑉𝑇 = 𝑉𝐹𝐵 −𝑄𝐼𝑇𝐶𝑜𝑥

−𝑄𝐹𝐶𝑜𝑥

−𝑄𝑀𝐶𝑜𝑥

∆𝑉𝑇= −∆𝑄

𝐶𝑜𝑥

momentum randomizing

collision

Impact Ionizatione-h pair generation

Avalanche

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Brain Inspired Electronics

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Neuron

Soma

Axon

Dendrite

Axon Terminal

Chemical Synapse

Neurotransmitter

Act

ion

Po

ten

tial

t

Immediate Action: Muscle Movement, Chemical SecretionLong-term Action: Memory, Learning

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nAP = 1 nAP = 4

PSCMPSC

Neurotransmitter Release

Bipolar

Excitatory: GlutamateInhibitory: GABA

Quantal

𝑃𝑆𝐶 ∝ 𝑛𝑇𝑓 𝑛𝐴𝑃

Stochastic

𝑃𝑆𝐶 ∝ 𝑝𝑟𝑛𝑇𝑓 𝑛𝐴𝑃

Arnold, A. et al.; Mimicking Neurotransmitter Release in Chemical Synapses via Hysteresis Engineering in MoS2 Transistors. ACS Nano, 11, 3110-3118, 2017

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Source

Drain

MoS2

2µm

VGS = 10V:10V:60V VDS = 1.0V

VDS = 0.8V

VDS = 0.6V

VDS = 0.4V

Low

DIBL

µn = 20cm2/V.s

VTH

Source Drain

VDS

Back Gate Oxide

P-Doped Si

VGS (Synaptic Input)

IDS (PSC)

Neuromorphic Transistor

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Hysteresis Engineering

VP = 60V

VP = 40V

VP = 20V

VTH-BW

VTH-FW

TS = 6s

TS = 12s

TS = 38s

VTH-BW

VTH-FW

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Origin of Hysteresis

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Inhibitory Response

Excitatory Response

Neuromorphic Transistor QuantalStochasticBipolar

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Neuromorphic Transistor

Quantal: Pulse FrequencyStochastic: Pulse MagnitudeBipolar: Pulse Polarity

Source Drain

VDS

Back Gate Oxide

P-Doped Si

VGS (Synaptic Input)

IDS (PSC)

Arnold, A. et al.; Mimicking Neurotransmitter Release in Chemical Synapses via Hysteresis Engineering in MoS2 Transistors. ACS Nano, 11, 3110-3118, 2017

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Summary

2D materials can reinstate transistor scaling

2D Materials support novel low power device concepts like EFET, TFET and ExFET

2D Materials are promising for all purpose sensors

2D Materials can be used for harsh environment electronics

2D Materials can be used for brain inspired electronics

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Acknowledgement

Graduate Students Daniel SchulmanAndrew ArnoldJoseph NasrYu Ting Huang (visiting)Amritanand SebastianDrew Buzzell

Faculty CollaboratorDr. Mauricio Terrones (PSU)Dr. Nasim Alem (PSU)Dr. Joshua Robinson (PSU)Dr. Susan Trolier-McKinstryDr. Sumeet GuptaDr. Sukwon Choi (PSU)Dr. Emilie Ringe (Rice)

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Thank You