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Modeling Intermodulation Distortion in HEMT and
LDMOS Devices Using a New Empirical Non-Linear
Compact Model
Toufik Sadi and Frank Schwierz Department of
Solid-State Electronics, Technische Universität
Ilmenau, D-98684 Ilmenau, Germany Toufik.Sadi_at_tu
-ilmenau.de
MOS-AK/GSA Workshop Paris - 7th 8th April 2011
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Outline

• Objectives
• Motivation
• Non-linearities in semiconductor devices
• Non-linear FET models
• Compact modeling of III-V HEMTs and LDMOSFETs
• Motivation
• New in-house model
• Validation
• Summary

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Compact Modeling of III-V HEMTs

• Framework Within the COMON (COmpact MOdelling
  Network) project funded by the European Union
• Aim Development of improved universal HEMT
  models
• Objectives
• Efficient current-voltage, charge and noise
  models
• GaAs, GaN HEMTs and other high-power devices
• Focus Non-Linearities in HEMTs
• Intermodulation distortion (IMD)
• Included Effects
• Self-heating frequency dispersion etc..

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Motivation

• Non-linear HEMT Models
• Design of modern microwave circuits and systems
• Minimization of Intermodulation Distortion

• Current-Voltage (I-V) Model
• Accurate modeling of I-V characteristics and
  derivatives
• Inclusion of electrothermal frequency
  dispersion effects
• Applicable to GaAs and GaN HEMTs, and to Si
  LDMOS FETs
• Effective parameter extraction and fitting
  routines
• Modeling of IMD figures of merit using Volterra
  series analysis
• Charge (C-V) Model
• Correct modeling of C-V characteristics is
  sufficient
• Using simple/existing models

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Intermodulation in HEMTs
Two-tone Input Input with two frequency
components f1 and f2
Example 3rd order transfer characteristics
Signal (Intermodulation ) components at new
frequencies are generated
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Compact Models for III-V FETs

• Physics-based
• Analysis of effect of physical parameters (gate
  length, mobility, etc)
• No parameter optimization
• Rigorous mathematical formula
• Technology-dependent
• Discontinuous (using of conditional functions)
• Table-based ? Storing parameters at several
  biases in a table
• No parameter optimization
• Technology-dependent
• Discontinuities in the model elements or their
  derivatives
• Empirical
• Simple
• Flexible
• Continuous
• Technology-independent
• Good model formulation
• Parameter optimization

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Non-Linear Empirical III-V FET Models

• Curtice Model (1980) ? Quadratic/cubic
  dependence of ID on VGS
• First empirical time-domain simulation model
• Tajima Model (1981) ? Exponential dependence of
  ID on VDS and VGS
• First empirical frequency-domain simulation
  model
• Materka Model (1985) ? Quadratic/hyperbolic
  dependence of ID on VGS
• Including drain-bias dependent pinch-off
  potential
• Statz Model (1987) ? Hyperbolic/cubic dependence
  of ID on VGS/VDS
• Temperature scalability
• TOM Model(s) (1990) ? Exponential/cubic
  dependence of ID on VGS/VDS
• Spatial/temperature scalability
• ADS EEFET/EEHEMT Model(s) (1993) ? Rigorous
  formula
• Charge-based C-V model
• Chalmers Model (1992) ? Hyperbolic dependence of
  ID on VGS/VDS
• First to provide a good fit for transconductance
  and derivatives
• Auriga Model (2004) ? Enhanced version of the
  Chalmers model

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Chalmers Model for HEMTs Advantages

• Infinitely differentiable hyperbolic functions
• Inherent reconstruction of the bell-shape of
  Gm(VGS) for GaAs HEMTs
• Reliable modeling of the higher order
  derivatives of Gm(VGS) curves
• Continuity no conditional functions
• Possibility of readily including several
  effects, such as temperature effects, frequency
  dispersion, and soft-breakdown
• Simple procedure for parameter extraction

Suitability for intermodulation distortion
studies
Angelov et al, IEEE Trans. MTT, vol. 40, p.
2258, 1992
MOS-AK/GSA Workshop Paris - 7th 8th April 2011
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Chalmers Model for HEMTs Limitations
Angelov et al, IEEE Trans. MTT, vol. 40, p.
2258, 1992

• Limited suitability to model high-power devices
  and new structures such as GaN HEMTs and
  LDMOSFETs (Fager et al., IEEE MTT, p. 2834, 2002
  Cabral et al., MTTS 2004)
• Saturation current (ISAT) is limited to 2 IPK

Improved model to provide much more independent
control of the shape of the current and
transconductance curves while maintaining the
principal advantages of the Chalmers model
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New Current-Voltage Model (1)
f(VGS)
f(VDS)
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New Current-Voltage Model (2)
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New Current-Voltage Model (3)
EC more flexibility for I-V curves derivatives
VTN fine-tuning parameters
Fager et al., IEEE MTT, p. 2834, 2002
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I-V Model Advantages

• Continuous closed-form expression
• Accurate modeling of I-V characteristics and
  derivatives
• Simple parameter extraction fitting procedure
• Applicable to GaAs, GaN HEMTs LDMOS FETs

LDMOS FET (Fager et al., IEEE MTT, p. 2834, 2002)
GaN HEMT (Cabral et al., MTTS 2004)
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I-V Curves

Pulsed (300K)


Static DC
0.25?m gate-length GaAs pHEMT 1
0.35?m gate length GaN HEMT 2
LDMOS FET from 3
VGS -1.2V to -0.4V Step 0.1V
VGS -4V to 0V Step 1V
VGS 3 and 5V
1 K. Koh et al, in Proc. IEEE IMS, p. 467,
2003 3 C. Fager et al, IEEE Trans. MTT, vol.
50, p. 2834, 2002 2 J.-W. Lee et al, IEEE
Trans. MTT, vol. 52, p. 2, 2004
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Volterra Series Analysis
Modeling the contribution of the current source
to non-linearities
Two-tone excitation input
Results are from the GaAs pHEMT
Pin -20dBm, RL RS 50 Ohm
Plin, PIM2, PIM3 linear, 2nd and 3rd order
power IP2, IP3 2nd and 3rd order interception
points
K. Koh et al, in Proc. IEEE IMS, p. 467, 2003
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Accomplished Work (5)
IMD analysis in high-power GaN HEMTs and
LDMOSFETs
GaN HEMT (Cabral et al., MTTS 2004)
LDMOS FET (Fager et al., IEEE MTT, p. 2834, 2002)
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Conclusions

• New flexible empirical non-linear model
• Minimized parameter fitting
• Accurate calculation of higher-order derivatives
• Suitable for intermodulation distortion modeling
• Applicable to a wide range of devices

• Acknowledgments
• This work is funded by the European Union, in the
  framework of the COMON project.

MOS-AK/GSA Workshop Paris - 7th 8th April 2011