Nonlinear performance comparison for FD and PD SOI MOSFETs based on the

Integral Function Method and Volterra modeling

Bertrand Parvais (EMIC, UCL, Belgium) parvais@emic.ucl.ac.beAntonio Cerdeira (CINVESTAV-IPN, Mexico)Dominique Schreurs (TELEMIC, KULeuven, Belgium)Jean-Pierre Raskin (EMIC, UCL, Belgium)

September 20, 2004UCL

MOS-AK Workshop

UCL

Distortion

f f

Silicon-on-Insulator (SOI)

1. Non-idealities of “linear circuits”• Amplifiers• Active filters

2. Used in some applications• Mixers• Oscillators• Frequency multipliers

3. Inherent to the physics of semiconductors

MOSFET SOI 

• Simplified process

• Low parasitic capacitances

• Low leakage current

• Low Vth

=> promising for RF ICs

Why study SOI MOSFETs nonlinearities ?

UCLFD vs PD SOI MOSFETs

- : Fully Depleted (FD)

G

S/D S/D

Burried Ox

G

Burried Ox

S/D S/D

body

--: Partially Depleted (PD)with floating body

DuTs: FD and PD SOI MOSFETs, 12x6.6 µm/0.25 µm (0.25 µm LETI technology)

VD [V]

I D [

mA

]

UCLWhat happens inside?

- gd kink -

n ++ p n ++

Body regionSiO2

=> body potential increase up to Vtsb

=> Parallel path for Id and Id increase=> Vt lowering and Id increase

Depletion region

High E field near the drain:

Impact Ionization current

++

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

++++ +

=> injection of holes inside the body

UCL

1. DC based characterization methods• Taylor series• Integral Function Method (IFM)• Comparison with Large-Signal Network Analyzer (LSNA)

measurements

2. HF MOSFET model based on Volterra series• Frequency limitation of DC based methods• Third order intermodulation

3. Conclusions• Devices performances

Outline

Linearity of SOI MOSFETs using Integral Function Method and Volterra

modeling

=> Does the kink influence the linearity ?

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

The simplest is the best

UCL

Consider the memoryless nonlinear system:

0

)())((n

nGnGD tVKtVI

VG

ID

VG(t) ID(t)

Method : Taylor analysis

nG

Dn

ndV

Id

nK

!

1 Taylor series:t

f

)33cos(4

)22cos(2

)cos(4

3

2))cos((

3322

231

220

tAK

tAK

tAK

KAAK

KtAy

t

f

If the circuit is excited by a sine wave,

1

2

231

22

2

34

2

K

KA

AKK

AKHD

UCLMethods: quid for large amplitude?

VG

ID

t

Taylor: add terms => too complicated !

IFM: good approximation of HD at LFfurther advantage: less sensitive too measurement noise[CerdeiraSSE02, CerdeiraSSE04, CerdeiraICSICT04]

UCL

In

Out1. Normalize the characteristics

IFM: How does it work ?

HD3 is obtained by computing the D function of Ir = I(V)-I(-V)

=> even harmonics eliminated

! HD of order higher than 3 are neglected

2. Observe that Area1-Area2 is

proportionnal to the THD

3. Define the D function

1

0

1

0

1

0

1)(2)()(

21

dvvidiivdvvi

AreaAreaD

Area2

Area1

[CerdeiraSSE02, CerdeiraICSICT04]

UCL

Not by a scale factor as from Taylor approach, cfr.

VG [V]

HD

3 [d

B]

Ld

dvDC

m

m

Yg

gA

g

gAHD

1

32

1

32

3 4

IFM takes the influence of the amplitude

of the applied signal into account

UCL

LSNA = 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

[VerspechtMTTS95]

• Good agreement before the minimum

• Minimum located at :

- IFM : max. of gm - LSNA : max. of power gain

• Nonlinearity of gm and gd

900 MHz, 50 Ω, A = 0.2 V

HD

2 [d

B]

VG [V]

LSNA

Comparison with LSNA measurements

gm only

gm and gd

UCL

=> Which frequency limit ??

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

RGCgd

Cgs

Gm Gd Cds

YLVin

Gm=gm1+gm2VG+gm3VG²

Gd=gd1+gd2VD+gd3VD²

Harmonic distortion af HF

DC method vs 900 MHz measurements in agreements

UCL

2

22

12

222

/1

/1

),(

),(

2

pHD

zHDDC ff

ffHD

ssH

ssHAHD

HD2

freqfp fz

HD from Nonlinear current method

[ParvaisGAAS04]

)/1)(/1(

)/1)(/1(

3231

323133

HDpHDp

HDzHDzDC ffff

ffffHDHD

,3

)(|)(| 2

AvpoleHDpole

7

)(|)(| 3

AvpoleHDpole

UCL

Pole Voltage Gain Av26 GHz

9 GHz5 GHz

Pole HD2

Pole HD3

Poles of HD2 and HD3 as a function of ZL

UCL

• 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).

Characterization methods

UCLHD: PD ~ FD transistors

UCLFrequency analysis of the kink effect

• frequency limitation caused by RC body impedance

iii

Vb

RbCb

g

ii

ii

b

b

th

th

ddid V

I

I

V

V

V

V

Igg

...

[SinitskyIEDL97]

bb

b

g

b

CRj

RZ

I

V

1Rb and Cb= body resistance and capacitance

• As Vd Rb => fc

UCLThird order intermodulation

)(

2

)2(

1

)()(3

2

)()(

2

)()2(

1

3

2

)(2

)(

)(1

1

4

3

**

22

2

1

**22

*31

1

33

322

3

ooo

d

o

m

oooomd

o

d

o

m

m

m

gsg

GGG

g

G

g

GGGGgg

G

g

G

g

g

gIM

IMCR

AIMD

Volterra model:

Kink effect !

ZL↑

UCL

0.20 0.40 0.60 0.80 1.000.00 1.20

-25

-20

-15

-10

-30

-5

Vgs0

THD

_Iso

cTH

D_T

ied

THD

_Flo

atPD 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

UCL

• 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

Conclusions