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2D Materials for Ubiquitous Electronics
Saptarshi Das
Assistant ProfessorEngineering Science and Mechanics
Materials Research InstitutePennsylvania State University
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 decadesโ 4 orders of magnitude length scaling
100ยตm 197510nm 2015
Source Drain
ฮปS
Short Channel LimitLCH > 3ฮปS
๐๐ = ๐๐๐๐ =๐๐๐๐๐ฆโ๐ฅ
๐๐๐ฅ๐ก๐๐๐๐ฆ๐ก๐๐ฅ
tbody โ 6nm ฮปS โ 4.2nmSi FinFET
Scaling Ends โ Doomsday ?
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Gate
Source Drain
Oxide
VGS
VDS
Substrate
2D Materials can rescue!!
Source Drain
ฮปS
Short Channel LimitLCH > 3ฮปS
tbody โ 0.65nm ฮปS โ 1.4nmMonolayer MoS2
tMoS2 = 0.65 nm
๐๐ = ๐๐๐๐ =๐๐๐๐๐ฆโ๐ฅ
๐๐๐ฅ๐ก๐๐๐๐ฆ๐ก๐๐ฅ
tbody โ 6nm ฮปS โ 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 (200ฮฉ-ยตm)
Bandgap EngineeringStraintronics
Ballistic LimitNo Concerns
Quasi Ballistic Low mobility โ 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, 656โ660, 2015.
van der Zande. A. M, et al., Nature Materials, 12, 554โ561, 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
ฮVTH
ฮIOFF
Gate
Source Drain
Oxide
VGS
VDS
Substrate
Boltzmann Tyranny
Voltage Scaling Almost Stopped
Fundamental Limitations at Device Level
Innovation in Device Physics
๐บ๐บ =๐๐ฉ๐ป
๐๐๐๐๐
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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
๐บ๐บ =๐๐ฉ๐ป
๐๐๐๐๐
ฮVTH
ฮIOFF
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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), 3139โ3146, 2015.
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Source Drain
Source Drain
ฮจS
VDDEG0
๐ณ๐ฌ = โ๐ถ
๐๐ท
๐ท๐๐ซ = ๐ผ๐ช๐๐,๐๐ซ๐
๐๐๐ซ๐ ๐๐๐ฝ๐ฎ๐บ
VB
Electrostrictive/
Piezoelectric
Material
Substrate
2D Semiconductor
Gate
Dielectric
So
urc
e
Dra
in
VDD
VGS
Capping
Layer
Back Contact
๐๐ฌ = ๐ผ ๐ถ๐ช๐๐,๐๐ซ๐
๐๐๐๐ซ๐ ๐๐ ๐ฝ๐ฎ๐บ๐๐บ = ๐ฝ๐ฎ๐บ ๐๐ = ๐๐บ๐(1 + ๐๐ฝ๐33)
EG
ฮจE
๐ณ๐บ = ๐๐ฝ๐ฎ๐บ ๐ โค ๐
Stiffness: ๐ช๐๐ (GPa)
Piezoelectric Coefficient: ๐ ๐๐ (pm/V)
Eg Coefficient: ๐ถ (meV/GPa)
Strain transfer coefficient: ๐ผA Novel Concept: 2D EFET
Ultra Low Power FET
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๐ผ1 =2๐
โเถฑ๐ ๐ธ ๐ ๐ธ ๐๐ ๐ธ ๐๐ธ
๐ผ2 =2๐
โเถฑ๐ ๐ธ ๐ ๐ธ ๐๐ท ๐ธ ๐๐ธ
Source
Drain
VDD
๐๐น๐ต โฮจ๐
๐๐น๐ต โฮจ๐ + ๐๐ท๐ท
๐ผ1 ๐ผ21
1
๐ผ = ๐ผ1 โ ๐ผ2
Solid: ๐ = 0Dashed: ๐ = 0.3
๐๐ท = 100๐๐
SS = 60mV/decade
โฅMoS2 Compliance:๐ถ33 = 60 ๐บ๐๐
Piezoelectric Coefficient: ๐33 = 850 ๐๐/๐
MoS2 Eg Coefficient: ๐ผ = โ80๐๐๐/๐บ๐๐
๐๐ = ๐๐บ๐(1 + ๐๐ฝ๐33)
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
๐ผ๐๐ โ ๐๐๐พ๐ต = ๐๐ฅ๐(โ4
3โ2๐๐๐ธ๐บ๐)
๐๐๐พ๐ต = exp(โ4
3โ2๐๐๐ธ๐บ๐๐๐๐ ๐ฉ๐ถ๐ซ๐)
Band to Band Tunneling
EG
ฮป
OFFEG
ON
ฮป 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
๐บ๐บ =๐๐ฉ๐ป
๐๐๐๐๐
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 โ No Low Power/Self Power โ YesLow Cost โ Yes
Flexible โ Yes Light Weight โ YesTransparent โ 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
hฯ
Electroluminescence (LEDs)hฯ
p
n
hฯ
Photovoltaic (solar cells)Isc,Voc
p n
hฯ
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 Beltsโข Protonsโข Electrons
Cosmic Raysโข Protons (90%)โข Helium Nuclei (9%)โข Electrons (<1%)โข 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
โLuckyโ electron
electron trapping in the gate oxide
positive VTH shift
โLuckyโ hole
Hot Carrier Transport
Source
Drain
EG = 1.84
hole trapping in the gate oxide
negative VTH shift
๐๐ = ๐๐น๐ต โ๐๐ผ๐๐ถ๐๐ฅ
โ๐๐น๐ถ๐๐ฅ
โ๐๐๐ถ๐๐ฅ
โ๐๐= โโ๐
๐ถ๐๐ฅ
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
๐๐๐ถ โ ๐๐๐ ๐๐ด๐
Stochastic
๐๐๐ถ โ ๐๐๐๐๐ ๐๐ด๐
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
2ยตm
VGS = 10V:10V:60V VDS = 1.0V
VDS = 0.8V
VDS = 0.6V
VDS = 0.4V
Low
DIBL
ยตn = 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
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