Diapositive 1

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Why study SOI MOSFETs nonlinearities ?
Distortion
Silicon-on-Insulator (SOI)

• Non-idealities of linear circuits
• Amplifiers
• Active filters
• Used in some applications
• Mixers
• Oscillators
• Frequency multipliers
• Inherent to the physics of semiconductors

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FD vs PD SOI MOSFETs
ID mA
- Fully Depleted (FD)
-- Partially Depleted (PD) with floating body
VD V
DuTs FD and PD SOI MOSFETs, 12x6.6 µm/0.25 µm
(0.25 µm LETI technology)
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What happens inside?- gd kink -

n
p
n

Body region
SiO2
Depletion region
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Linearity of SOI MOSFETs using Integral Function
Method and Volterra modeling
gt Does the kink influence the linearity ?
gt Which methods to characterize the linearity of
MOSFETs ??
The simplest is the best
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Method Taylor analysis
Consider the memoryless nonlinear system
Taylor series
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Methods quid for large amplitude?
ID
VG
Taylor add terms gt too complicated
! IFM good approximation of HD at LF further
advantage less sensitive too measurement
noise CerdeiraSSE02, CerdeiraSSE04,
CerdeiraICSICT04
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IFM How does it work ?
Out
1. Normalize the characteristics
In
HD3 is obtained by computing the D function of
Ir I(V)-I(-V) gt even harmonics eliminated
! HD of order higher than 3 are neglected
CerdeiraSSE02, CerdeiraICSICT04
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IFM takes the influence of the amplitude of the
applied signal into account
HD3 dB
VG V
Not by a scale factor as from Taylor approach,
cfr.
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Comparison with LSNA measurements
900 MHz, 50 O, A 0.2 V

• Good agreement before the minimum
• Minimum located at
• - IFM max. of gm
• - LSNA max. of power gain
• Nonlinearity of gm and gd

LSNA
HD2 dB
gm and gd
gm only
VG V
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Harmonic distortion af HF
DC method vs 900 MHz measurements in agreements
gt Which frequency limit ??
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HD from Nonlinear current method
ParvaisGAAS04
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Poles of HD2 and HD3 as a function of ZL
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Characterization methods

• Good agreements between results calculated using
  IFM and using Fourier coefficients.
• IFM advantages amplitude dependent, no
  derivatives.
• Frequency validity range cfr. Volterra model
  (several GHz).

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HD PD FD transistors
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Frequency analysis of the kink effect
SinitskyIEDL97

• As Vd ? Rb ? gt fc ?

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Third order intermodulation
Volterra model
ZL?
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PD SOI Floating body or not ?
PD, from ST Microelectronics 60x 1µm/0.12 µm, f2
GHz
FB higher fT, fmax than BC and isoc. BC/Isoc.
parasitic C, gm degradation
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Conclusions

• At 900 MHz, when the polarization voltage is
  varied, HD is dominated by the DC I-V
  characteristics.
• Frequency validity range of DC methods provided
  by a Volterra model.
• PD versus FD
• HD ---gt idem (gm dominates)
• IMD ---gt depends on the tone separation
• cfr. Kink effect
• Thanks to
• FRIA for financial support