IEDM, San Francisco, USA 11th Dec. 2006 1Y.S. Chauhan

Y. S. Chauhan1, F. Krummenacher1, C. Anghel1, R. Gillon2,B. Bakeroot3, M. Declercq1, and A. M. Ionescu1

1Ecole Polytechnique Fédérale de Lausanne (EPFL),Lausanne, Switzerland

2AMI Semiconductor, Belgium

3University of Gent, Belgium

Analysis and Modeling of Lateral Non-Uniform Doping in High-Voltage MOSFETs

IEDM, San Francisco, USA 11th Dec. 2006 2Y.S. Chauhan

OutlineOutline

• High Voltage device architectures

• Impact of Lateral non-uniform doping on device characteristics

• Model description

• Model validation• VDMOS – shown in this presentation• LDMOS – shown in the paper

• Conclusion

IEDM, San Francisco, USA 11th Dec. 2006 3Y.S. Chauhan

Device Architectures

• VDMOS :VDmax=50V, VGmax=3.3V

• LDMOS :VDmax=40-100V, VGmax=13V

( ) ( ){ }[ ]aA SN N erfc kn

xL

ξ ξ

ξ

=

=

IEDM, San Francisco, USA 11th Dec. 2006 4Y.S. Chauhan

Difference between Conventional MOS and Lateral Asymmetric MOS (LAMOS)

• LAMOS –higher CGD

• Drift region in high voltage MOS decreases CGD

• The peak in CGD of LAMOS – effect of lateral doping

IEDM, San Francisco, USA 11th Dec. 2006 5Y.S. Chauhan

Difference between Conventional MOS and Lateral Asymmetric MOS (LAMOS)

• LAMOS –higher CGD

• Drift region in high voltage MOS decreases CGD

• The peak in CGD of LAMOS – effect of lateral doping

_

( , , )G G K SGD

D

KGD LAMOS

D

dQ V V VCdV

dVCdV

=

=

IEDM, San Francisco, USA 11th Dec. 2006 6Y.S. Chauhan

Impact of different Doping gradients on device characteristics

• Higher gradient – higher current

• Higher gradient – higher saturation voltage

IEDM, San Francisco, USA 11th Dec. 2006 7Y.S. Chauhan

Contd.- Impact of different Doping gradients on device characteristics

• Higher doping gradient

• Higher CGD and lower CGS in strong inversion

• Rising slope decreases

• Peak on CGD increases

IEDM, San Francisco, USA 11th Dec. 2006 8Y.S. Chauhan

Modeling of LAMOS

Assume

constantpp

ddψ

ψξ

= Δ =

Total Inversion Charge Density

S iD Drift Diff i T

d dQI I I W Q Udx dx

μ Ψ⎛ ⎞= + = − +⎜ ⎟⎝ ⎠

( )2

1 2

satds v ds

v sa

p

t ds

i i qdqd q

dd

i

ψξ

δρ

ξ ρ δ

⎛ ⎞+ −⎜ ⎟⎝ ⎠= −+ −

1222( ) 1 ln

12

satd

v pp d s

v p sats

ds

dsp

ds

v

qq q

ii

q i

δρ ψ

ψρ ψ δ

ρ ψ

⎡ ⎤⎛ ⎞− +⎢ ⎥⎜ ⎟⎜ ⎟Δ⎛ ⎞ ⎢ ⎥⎝ ⎠Δ = − + +⎜ ⎟ ⎢ ⎥⎜ ⎟Δ ⎛ ⎞⎝ ⎠ ⎢ ⎥− +⎜ ⎟⎜ ⎟Δ⎢ ⎥⎝ ⎠⎣ ⎦

( )2 2 11

2d s d s sat

c sat ds dsp p v p

q q q qq i i δδψ ψ ρ ψ

⎛ ⎞− −= + − + +⎜ ⎟⎜ ⎟Δ Δ Δ⎝ ⎠

Drain Current

Nonlinear Ordinary Diff. Eq.

Qi: explicit fun. of x Ψp: explicit fun. of x

IEDM, San Francisco, USA 11th Dec. 2006 9Y.S. Chauhan

Modeling of Self Heating Effect

Rth – Thermal Resistance

Cth – Thermal Capacitance

PD=IDS.VDSVGS

VDS

IDS

ΔTµ(T), VT(T)

• External Temperature NodeRef: C. Anghel et al., “Self-heating characterization and extraction method for thermal resistance and capacitance in HV MOSFETs”, IEEE Electron Device Lett., 141 - 143, 2004

IEDM, San Francisco, USA 11th Dec. 2006 10Y.S. Chauhan

Model Validation on 50V VDMOSTransfer Characteristics (ID-VG)

• Weak inversion to Strong inversion transition

• Subthreshold slope correctly matched

• Good accuracy

IEDM, San Francisco, USA 11th Dec. 2006 11Y.S. Chauhan

Transconductance for VD=0.1-0.5V

• Subthreshold slope correctly matched

• Descending slope – drift resistance

• gmax – Mobility and drift resistance

IEDM, San Francisco, USA 11th Dec. 2006 12Y.S. Chauhan

Output Characteristics

• Linear region correctly modeled by drift resistance

• Self Heating Effect

• Valleys on gds : Physical effects SHE, Impact Ionization

Self-Heating Impact-Ionization

IEDM, San Francisco, USA 11th Dec. 2006 13Y.S. Chauhan

Gate-to-Drain Capacitance CGD vs VG

• Rising Slope & Peaks – effect of lateral non-uniform doping

0

0.5

1

1.5

2

0 1 2 3

VG (V)

V K(V

)

VD = 1V

VD = 5V

• Sharp decrease – effect of drift region (good modeling of drift region or VK must)

IEDM, San Francisco, USA 11th Dec. 2006 14Y.S. Chauhan

Gate-to-Source and Gate-to-Body Capacitances CGS+CGB vs VG

• Peaks – effect of lateral non-uniform doping

• Sharp decrease and shift of peaks – effect of drift region

IEDM, San Francisco, USA 11th Dec. 2006 15Y.S. Chauhan

Gate-to-Gate Capacitance CGG vs VG

• Peaks and shift of peaks – little contribution from lateral non-uniform doping and greater contribution from drift region

IEDM, San Francisco, USA 11th Dec. 2006 16Y.S. Chauhan

Partioning Scheme in LAMOS

• Drain & Source charge: do NOT exist! (Philips IEDM’04)

• Solve continuity & transport eq. (Philips IEDM’04)• New Partioning scheme for LAMOS (ESSDERC’06)

• Capacitance implementation in simulators: Charge conservation problem!

• Use proposed partioning scheme or even WD to get QD & QS: Theoretically incorrect but still solves the problem at the moment for industry

• Some novel solution?

CDG& CSG

IEDM, San Francisco, USA 11th Dec. 2006 17Y.S. Chauhan

Conclusion

• Modeling of lateral non-uniform doping in HV-MOSFET

• Complex capacitance behavior of HV-MOS explained using numerical simulations : lateral doping and drift effects

• Peaks and shift of peaks in capacitances with bias correctly modeled : Major improvement over state of the art HV-MOS models

• Self-Heating and Impact-Ionization effect included

• Very good performance in DC and transient operations

• Model validated on advanced HV devices – 50 VDMOS and 40V LDMOS

IEDM, San Francisco, USA 11th Dec. 2006 18Y.S. Chauhan

Christian Maier, Heinisch HolgerRobert Bosch, Germany

Andre Baguenier DesormeauxCadence Design Systems, France

B. DesoeteAMI Semiconductor, Belgium

J.-M. Sallesse, A.S. RoyEPFL, Switzerland

Acknowledgements

Funded by European Commission project “ROBUSPIC”Website- http://www-g.eng.cam.ac.uk/robuspic/