Numerical Simulation of Electronic Noise in Si MOSFETs

1
Numerical Simulation of Electronic Noise in Si
MOSFETs
EIT4

• C. Jungemann
• Institute for Electronics
• Bundeswehr University
• Munich, Germany
• Acknowledgments B. Neinhüs, B. Meinerzhagen, A.
  Scholten, A. Heringa

2
Outline

• Introduction
• Theory
• Acceleration Effects
• Noise source modeling
• Noise in NMOSFETs
• Noise in a BJT
• Noise in an IMOS
• Conclusions

3
Introduction
4
Introduction

• Noise is a fundamental property of electron
  transport and cannot be avoided
• Fluctuation-dissipation theorems (e.g. Nyquist
  theorem) are only valid at equilibrium (Shot and
  thermal noise are macroscopic manifestations of
  microscopic noise.)
• Transport in nanoscale devices is nonlocal and
  quasi-ballistic
• Physics-based methods required for device level
  simulations!

5
Introduction
NNN structure at zero bias

• Terminal current fluctuations are due to electron
  scattering within the device via displacement and
  conduction currents
• Noise theory describes the variance and the
  correlation of the fluctuations

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6
Introduction
Power spectral density (PSD)

• PSD vanishes at very high frequencies due to
  acceleration effects (finite electron mass means
  no real white noise)
• nonquasistationary
• Plasma resonance at very high frequencies (gt1THz)
  in silicon

7
Theory
8
Theory
LBE is the basis for LHD and LDD models
9
Theory
10
Theory
11
Theory

• Transport and noise parameters of the LDD are
  calculated consistently under homogeneous bulk
  conditions based on the single particle LBE
• The parameters are generated for a wide range of
  doping concentrations, lattice temperatures,
  strain conditions, driving fields etc, and stored
  in lookup tables for later use.

12
Impact of the Acceleration Term
13
Acceleration Effects
In the DD approximation the mobility and the PSD
of the velocity fluctuations are assumed to be
frequency independent
Ndop1017/cm3
Up to about 100GHz this is correct for
siliconThe macroscopic relaxation time
approximation fails
14
Acceleration Effects
NNN structure (Full LBE)
Up to about 100GHz acceleration effects can be
neglected in silicon
15
Acceleration Effects
Undoped silicon at room temperature E(t)
30kV/cm1cos(2pft)
Above 100GHz nonquasistationary effects occur in
silicon
16
Noise source modeling
17
Noise source modeling
NNN structure
Bulk, ND1017/cm3
Diffusion noise source yields the best results HD
model yields similar good results Device results
strongly deviate from thermal or shot noise
18
Noise source modeling
NNN structure biased at 6V
Generation noise due to impact ionization Noise
source is given by microscopic white shot noise
19
Noise source modeling
NNN structure biased at 0 and 1V
Terminal current noise is due to cold and warm
electrons Hot electrons can produce noise via
impact ionization
20
Noise in NMOSFETs
21
Noise in NMOSFETs
180nm Technology, tox 3nm, Vdrain 1.8V,
f2.5GHz
Lgate1mm
Measurements and Tsuprem simulations by Philips
(A. Scholten) Simulation includes quantum
correction for channel DD and HD simulations
performed without any parameter matching
22
Noise in NMOSFETs
180nm gate length, tox 3nm, Vdrain 1.8V,
Vgate1.0V
Gate noise
Drain noise
Also in MOSFETs drain noise is not due to hot
electrons
23
Noise in NMOSFETs
50nm channel length, 1.3nm oxide, Vdrain0.9V,
f10GHz
Noise specs of small NMOSFETs increase only
moderately
24
Noise in a BJT
25
Noise in a BJT
1D 50nm Si NPN bipolar transistor
Fano factor of electron collector noise at
VCE0.5V
Doping profile
Overestimation of shot noise is caused by model
failure
26
Noise in a BJT
50nm Si bipolar transistor
VCE0.5V, VBE0.65V
Quasiballistic transport leads to model failure
27
Noise in an IMOS
F. Mayer et al., TED, Vol. 53, p. 1852, 2006
28
Noise in an IMOS
CIMPAT, Vgate/drain-3.5V, Lchannel5.0mm
CMOS has a Fano factor of less than one for
inversion IMOS generates two or more orders of
magnitude more noise
29
Conclusions
30
Conclusions

• Consistent hierarchy of noise models (DD, HD,
  LBE)
• Transport and noise parameters are consistently
  generated for the DD and HD models by LBE bulk
  simulations
• The transport and noise parameters are local in
  real space and frequency independent
• Acceleration effects can be neglected below
  100GHz in silicon
• Modified noise sources (diffusion noise) give
  good results

31
Conclusions

• Good agreement of measurements and simulations
  for MOSFETs
• Terminal current noise is produced by cold or
  warm electrons
• Hot electrons can produce noise via impact
  ionization
• No dramatic increase of noise in scaled MOSFETs
• IMOS suffers from huge noise due to avalanche
  breakdown