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Why study SOI MOSFETs nonlinearities ? - PowerPoint PPT Presentation


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Why study SOI MOSFETs nonlinearities ?. MOSFET  SOI. f. f. Simplified process Low parasitic capacitances Low leakage current Low Vth => promising for RF ICs. Distortion . Silicon-on-Insulator (SOI). Non-idealities of “linear circuits” Amplifiers Active filters

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why study soi mosfets nonlinearities
Why study SOI MOSFETs nonlinearities ?

MOSFET SOI

f

f

  • Simplified process
  • Low parasitic capacitances
  • Low leakage current
  • Low Vth
  • => promising for RF ICs

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
fd vs pd soi mosfets

G

G

S/D

S/D

S/D

S/D

Burried Ox

Burried Ox

body

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)

what happens inside gd kink

+

+

+

+

+

+

+

Impact Ionization current

High E field near the drain:

=> impact ionization => creates e--h+pairs

=> injection of holes inside the body

=> body potential increase up to Vtsb

=> Parallel path for Id and Id increase

=> Vt lowering and Id increase

What happens inside?- gd kink -

n ++

p

n ++

Body region

SiO2

Depletion region

linearity of soi mosfets using integral function method and volterra modeling
Linearity of SOI MOSFETs using Integral Function Method and Volterra modeling

Outline

  • DC based characterization methods
    • Taylor series
    • Integral Function Method (IFM)
    • Comparison with Large-Signal Network Analyzer (LSNA)
    • measurements
  • HF MOSFETmodel based on Volterra series
    • Frequency limitation of DC based methods
    • Third order intermodulation
  • Conclusions
    • Devices performances

=> Does the kink influence the linearity ?

=> Which methods to characterize the linearity of MOSFETs ??

The simplest is the best

method taylor analysis
Method : Taylor analysis

f

VG(t)

ID(t)

ID

t

f

VG

t

If the circuit is excited by a sine wave,

Consider the memoryless nonlinear system:

Taylor series:

methods quid for large amplitude

t

Methods: quid for large amplitude?

ID

VG

Taylor: add terms => too complicated !

IFM: good approximation of HD at LF

further advantage: less sensitive too measurement noise

[CerdeiraSSE02, CerdeiraSSE04, CerdeiraICSICT04]

ifm how does it work
IFM: How does it work ?

2. Observe that Area1-Area2 is

proportionnal to the THD

3. Define theD function

Area1

Area2

Out

1. Normalize the characteristics

In

HD3is obtained by computing the D function of Ir = I(V)-I(-V)

=> even harmonics eliminated

! HD of order higher than 3 are neglected

[CerdeiraSSE02, CerdeiraICSICT04]

ifm takes the influence of the amplitude of the applied signal into account
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.

comparison with lsna measurements
Comparison with LSNA measurements

full-wave (magnitude and phase) RF (900 MHz) characterization

(V,I fundamental and harmonics at input and output) in single take

=> Real RF nonlinear behavior

LSNA =

[VerspechtMTTS95]

900 MHz, 50 Ω, 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]

harmonic distortion af hf
Harmonic distortion af HF

Cgd

RG

Gm Gd Cds

=> Answer this question with the help of a Volterra series based model:

YL

Vin

Cgs

Gm=gm1+gm2VG+gm3VG²

Gd=gd1+gd2VD+gd3VD²

DC method vs 900 MHz measurements in agreements

=> Which frequency limit ??

hd from nonlinear current method
HD from Nonlinear current method

HD2

fp fz

freq

[ParvaisGAAS04]

poles of hd 2 and hd 3 as a function of z l
Poles of HD2 and HD3 as a function of ZL

Pole Voltage Gain Av

26 GHz

9 GHz

5 GHz

Pole HD2

Pole HD3

characterization methods
Characterization methods
  • Good agreements between results calculated using IFM and using Fourier coefficients.
  • IFM: advantages = amplitude dependent, no derivatives.
  • Frequencyvalidity range cfr. Volterra model (several GHz).
frequency analysis of the kink effect

frequency limitation caused by RC body impedance

Vb

Rb and Cb= body

resistance and

capacitance

iii

Cb

Rb

Frequency analysis of the kink effect

[SinitskyIEDL97]

  • As Vd  Rb  => fc 
slide18

PD SOI: Floating body or not ?

PD, from ST Microelectronics

60x 1µm/0.12 µm, f=2 GHz

FB: higher fT, fmax than BC and isoc.

BC/Isoc.: parasitic C, gm degradation

conclusions
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 ---> idem (gm dominates)
  • IMD ---> depends on the tone separation
  • cfr. Kink effect
  • Thanks to
  • FRIA for financial support