Download - Junctionless Nanowire Field Effect Transistors

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Welcome to the world of

JUNCTIONLESS NANOWIRE FETs!

1

Isabelle FERAIN

Tyndall National Institute

University College Cork

SQWIRE

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Dimensions scaling

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Voltage scaling

• Dynamic power dissipation in present CMOS

circuits at frequency, f, supply voltage, VDD and

load capacitance Cload can be described by:

• Any reduction of power consumption thus requires

to reduce supply voltage

• Vdd scaling is

– set by the threshold voltage of transistors

– dependent on the inverse sub-threshold slope

(kT/q)

– limited by short-channel effects

Enhanced coupling between gate and channel

3

cycle

2

ddloaddynamic fVCP

10-5

10-4

10-3

10-2

10-1

100

101

102

103

0 0.5 1 1.5

Dra

in c

urr

en

t (µ

A/µ

m)

Gate voltage (V)

Gate length = 70nm

W=25nm

Vds=0.9V

Vds=0.05V

Courtesy:

Prof. Gerard Ghibaudo (IMEP)

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Enhanced Electrostatic Control

Gate

Source Drain

Buried oxide

Back gate (substrate)

Source

Drain

Gate

ID

Buried oxide

Tri-Gate with 800C 600Torr 5min H2Anneal

Fins are 45x78nm, Nice corner rounding by H2 anneal

20 nm

Polysilicon Gate

Silicon

Fin

Buried Oxide

Gate

Source Drain

BOX

Gat

e

Gat

e “1 Gate”

“2 Gates”

“3 Gates”

“Gate-all-Around”

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Does it look too good to be true?

Improved Lg scalability

Almost ideal sub-threshold slope (60mV/dec) at RT

Low drain-to-source current (IOFF)

Drive current ION

• crystal orientation dependence

• High nano-wire pitch density

Source/Drain resistance Rsd

– SEG / Layout optimization needed

Critical Dimensions

– Gate length

– Gate oxide thickness

– Junction Depth

Critical Dimensions

– Nano-wire width

– Junction abruptness

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DEVICE STRUCTURE

Junctionless nanowire transistors

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Device Structure (1/2)

J.-P. Colinge et al., Nanowire transistors without junctions, Nature Nanotechnology, Vol. 5, No. 3, pp. 225-229, 2010.

Hooray!! No need for source &

drain engineering anymore!

10-5

10-4

10-3

10-2

10-1

100

101

102

103

0 0.5 1 1.5D

rain

cu

rre

nt

(µA

/µm

)Gate voltage (V)

Gate length = 20nm

W=25nm

Vds=0.9V

Vds=0.05V

DIBL

10-5

10-4

10-3

10-2

10-1

100

101

102

103

0 0.5 1 1.5D

rain

cu

rre

nt

(µA

/µm

)Gate voltage (V)

Gate length = 20nm

W=25nm

Vds=0.9V

Vds=0.05V

DIBL

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BOX

Source

Drain

Gate

Silicon

Nanowire

Gate

Oxide

Device structure (2/2)

The cross-section of the

channel must be small enough

so that the gate can deplete

the heavily doped channel

entirely (OFF state)

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CONDUCTION MECHANISM


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Conduction mechanism (1/4)

• Electrostatic pinch-off: • The cross section is small enough for the channel region to be depleted

(VD=50mV, Nd>5e18/cm3)

Below VTH Slightly above VTH

Higher VG

Depletion is gone

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-0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

10-16

10-14

10-12

10-10

10-8

10-6

10-4

DIBL S/S

VDS

=1.0V

Dra

in C

urr

ent

(A)

Gate Voltage (V)

5x5_Lgate

=10nm, tox

=2nm

Junction-less : 48 mV 66.2 mV/dec

Inversion-mode : 153 mV 83.8 mV/dec

VDS

=50mV

11

VD=50mV VD=200mV

VD=400mV

VD=600mV

Channel pinch-off

VG > VTH

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a b c

d e f

Be

low

Th

resh

old

Ab

ove

Th

resh

old

Inversion

Mode

Accumulation

ModeJunctionless

BOX BOXBOX

BOX BOX BOX


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n=4x1019 cm-3

Ninv>1x1020 cm-3

N+PN+

Inversion

Mode

N+N+N+

Junctionless

ND=1x1019cm-3


Channel in Multigate FETs @ VG= VG =1V

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MOBILITY


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me=250 cm2/Vs me=70 cm2/Vs

Electric field ~ 0MV/cm

(flatband)

me=50 cm2/Vs me=10-30 cm2/Vs

N+PN+

Inversion Mode

N+N+N+ Junctionless

ND=1x1019cm-3

Electron Mobility (1/2)

VG= VG =1V

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• Lg and EOT scaling increased Eeff in the channel µ decreases

• Without strain technology the channel mobility in IM/AM FETs would be = or lower

than in heavily doped Si

Electron Mobility (2/2)

Thompson S.E. et al., A 90-nm logic technology featuring strained-silicon, IEEE Transactions on Electron Devices, vol.51, 11

(2004) 1790-1797.

Jacoboni, C. et al., A review of some charge transport properties of silicon, Solid State Electron. 20, issue 2(1977) 77-89.

J.P.-Colinge et al., Reduced electric field in junctionless transistors, Applied Physics Letters 96 (2010) 073510.

1e15 1e16 1e17 1e18 1e19 1e20

JL

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PROCESS INDUCED-VARIABILITY


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A

B

C

Process induced-Variability (1/3)

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* Comparing SOI and bulk FinFETs: Performance,

manufacturing variability, and cost, in ElectroIQ

-0.7

-0.6-0.5

-0.5

-0.4

-0.4

-0.3

-0.3

-0.2

-0.2

-0.1

-0.1

-0.1

0

0

0

0.1

0.1

0.1

0.2

0.2

0.2

0.2

0.3

0.3

0.3

0.3

0.4

0.4

0.4

0.4

0.5

0.5

0.5

0.50.6

0.6

0.6

0.7

Silicon Width (nm)

Sili

co

n th

ickn

ess(n

m)

THRESHOLD VOLTAGE (V) for ND

=1e19, Tox=2nm

10 15 20 25 30 35 405

6

7

8

9

10

11

12

13

14

15

width

height

A. Kranti. Junctionless nanowire transistor (JNT):

Properties and design guidelines.

In: Proceedings of ESSDERC 2010, pp.357-360.

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Doping

concentration [cm-3]

Statistical number of

doping atoms in the channel

1e15 0.002

1e18 2

1e19 20

Source

Drain

Gate

Silicon

Nanowire

Gate

Oxide

TSi=10nm

WSi=10nm

Lg=20nm

Junctionless

Inversion mode

Lg=10 nm; Tsi=Wsi=3nm Tox=1nm Nchannel= 1e20cm-3 (JNT) or 0 (IM) NSD=1e20cm-3

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Conclusion

• Naturally CMOS-toolset compatible

• Switching properties:

– SS=80mV/dec and DIBL=40 mV/V for JNT with Lg=25nm, W=25nm, TSOI=10nm,

Vd=0.9V (experimentally demonstrated by CEA-LETI within FP7-funded project

SQWIRE)

• Scalability:

– SS for p-channel JNT (Lg=3nm) is 80 mV/dec

• Manufacturability:

• JNT suppress the difficulty of fabricating ultra-shallow junctions

• SOI thickness control is critical

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Acknowledgements

• Colleagues:

– Prof. JP Colinge, N. Dehdashti Akhavan, P. Razavi, S. Das, R. Yu (Ultimate

Silicon Devices Group);

– N. Petkov, M. Schmidt (Advanced Microscopy Facility Group);

– L. Ansari, G. Fagas, J. Greer (Electronics Theory Group)

– Prof. G. Ghibaudo (INPG)

• Tyndall’s Central Fabrication Facility

22

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Annex 1

At High Gate Bias:

The saturation current-blocking

region is in the drain,

not in the channel region.

23

Gate

Source Drain

Depleted

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Annex 2

Lo

g (

I D)

VGS

VFB

VTH

Lo

g (

I D)

VGS

VFB

VTH

Lo

g (

I D)

VGS

VFB

VTH

Deple

tion

Deple

tion

Deple

tion

InversionAccumulation Partial

Depletion

a b c

Inversion

Mode

ON: Main Current in

Surface Inversion

Channels

OFF: Surface

Subthreshold Current

Accumulation

Mode

ON: Small body

current & Surface

Accumulation Channels

OFF: Body

subthreshold current

Junctionless

Mode

ON: Large body

current

OFF: Body

subthreshold current