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Three-dimensional Three-dimensional quantum transport simulation quantum transport simulation
of ultra-small FinFETsof ultra-small FinFETs
H. Takeda and N. Mori
Osaka University
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IntroductionIntroduction
FinFET : Non-planar multiple gate MOSFET
3D quantum transport simulation
based on NEGF method
Quantum Mechanical Effects Direct S/D tunneling
Subband quantization
Scattering Phonon scattering
Interface roughness
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3D NEGF Simulation3D NEGF Simulation
3D Poisson equation
Self-consistent calculation
Green’s function :
Eigen-mode expansion method
3D electron density
Electric current
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ScatteringScattering
Interface roughness
Intra-valley phonon scattering Constant matrix element :
Self-consistent calculation :
Scattering function
(Self energy)
Green’s function
(Correlation function)
Correlation length :
Random roughness patterns :
Gaussian form :
Average displacement :
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DeviceDevice
Length :
Width :
Height :
Gate length : SiO2 thickness :
Source / Drain :
Gate :
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Electron DensityElectron Density
Normalized electron density profile( cross section)
Electron density profile
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Electron-Phonon InteractionElectron-Phonon Interaction
Electron density profile
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Device CharacteristicsDevice Characteristics
About 20% decrease (ION)
Almost the same (IOFF)
Phonon scattering
Ballistic
characteristics
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Phonon Assisted TunnelingPhonon Assisted Tunneling
Phonon scattering reduces current
Off-state
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Phonon Assisted TunnelingPhonon Assisted Tunneling
Phonon scattering reduces current
Phonon absorption enhances current
compensate
Off-state
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Phonon Assisted TunnelingPhonon Assisted Tunneling
Phonon scattering reduces current
On-stateVery low channel barrier
Drain current is reduced
by phonon scattering
Tunneling current can be neglected
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Interface RoughnessInterface Roughness
without Roughness
with RoughnessRoughness affects current flow
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Effect of Interface RoughnessEffect of Interface Roughness
characteristics
Roughness : 10 patterns
Threshold voltage
Ballistic
Roughness
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SummerySummery
We have simulated characteristics of the gate-length FinFETs by 3D NEGF simulation including the intra-valley phonon scattering and the interface roughness.
The phonon scattering reduces only the on-current.
The interface roughness affects not only the on-current but also the off-current.
Large fluctuation of the threshold voltage is caused by the interface roughness in the ultra-small FinFETs.