Overview of Semiconductor Overview of Semiconductor Device Noise ResearchDevice Noise Research

Gijs BosmanGijs BosmanNoise Research LaboratoryNoise Research Laboratory

NEB 585NEB 585

Electrical and Computer Engineering Department, University of Florida, Electrical and Computer Engineering Department, University of Florida, Gainesville FL, USAGainesville FL, USA

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AcknowledgementsAcknowledgements

• PhD Graduate Students: Shehad Reza, Derek Martin, PhD Graduate Students: Shehad Reza, Derek Martin, Frank Hou, Juan Sanchez, Jonghwan Lee, Jennifer Sippel, Frank Hou, Juan Sanchez, Jonghwan Lee, Jennifer Sippel, Robert DiemeRobert Dieme

• UG Student: Quyen T. HuynhUG Student: Quyen T. Huynh

• Colleagues: Professors Mark Law, Andrew Rinzler, Ant Colleagues: Professors Mark Law, Andrew Rinzler, Ant Ural, Toshi Nishida, and Jing GuoUral, Toshi Nishida, and Jing Guo

• Technical Assistance: Al OgdenTechnical Assistance: Al Ogden

• Funding and Support: Semiconductor Research Funding and Support: Semiconductor Research Corporation, AMD, TI, HPCorporation, AMD, TI, HP

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OutlineOutline

• Introduction to Device NoiseIntroduction to Device Noise• Advanced NMOS drain noiseAdvanced NMOS drain noise• 1/f noise in carbon nanotubes1/f noise in carbon nanotubes• 1/f noise in silicon nanowires1/f noise in silicon nanowires

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Physical Origin of NoisePhysical Origin of NoiseFor a simple, homogeneous resistor with length L, Ramo’s theorem For a simple, homogeneous resistor with length L, Ramo’s theorem describes the coupling between microscopic electronic motion and the describes the coupling between microscopic electronic motion and the measured current at a contact as measured current at a contact as

where I(t)= where I(t)= IIDDCC++I(t), N(t)= NI(t), N(t)= NDCDC++N(t) and vN(t) and vkk(t)=<v(t)=<vkk>+>+vvkk(t)(t)

Phenomena that affect the noise; Phenomena that affect the noise;

Ballistic versus scattering limited transport, surface and bulk traps, Ballistic versus scattering limited transport, surface and bulk traps, small N, high electric fields, quantum selection rules, etc.small N, high electric fields, quantum selection rules, etc.

)(

1

)()(tN

kkL

q tvtI

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N O I S E Spectral Noise Spectral Noise ComponentsComponents

S is spectral current or voltage density in AS is spectral current or voltage density in A22/Hz or V/Hz or V22/Hz/Hz

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1/1/ff and 1/ and 1/ff-Like Noise-Like Noise

• McWhorter:McWhorter:Superposition of a large Superposition of a large

number of Lorentzian number of Lorentzian spectra, produced by g-spectra, produced by g-r mechanisms.r mechanisms.

The g-r noise is most likely The g-r noise is most likely caused by the trapping caused by the trapping and de-trapping of and de-trapping of carriers in surface and carriers in surface and oxide traps.oxide traps.

log S

log f

1/f

1

2cc

f

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1/f and 1/f-like noise1/f and 1/f-like noise Defect related, McWhorter’s distributed generation-Defect related, McWhorter’s distributed generation-

recombination noise model, 1/f and 1/f-like noise recombination noise model, 1/f and 1/f-like noise Mobility fluctuations (phonon coupling), Hooge model, Mobility fluctuations (phonon coupling), Hooge model, HH

parameter, true 1/f noise onlyparameter, true 1/f noise only

Strongly technology dependentStrongly technology dependent Shows single defect/single electron phenomena such as Shows single defect/single electron phenomena such as

Random Telegraph SignalsRandom Telegraph Signals Contributes to jitter in VLSI clocking circuitsContributes to jitter in VLSI clocking circuits Limits the resolution of many sensorsLimits the resolution of many sensors Phase noise in VCOsPhase noise in VCOs Limits the noise figure in the base bandLimits the noise figure in the base band

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N O I S E Generation-Generation-Recombination NoiseRecombination Noise

Caused by random carrier transitions between continuum states (ECaused by random carrier transitions between continuum states (ECC, E, EVV) and ) and localized defect states.localized defect states.

Defect related, determined by number of traps, energy levels, and carrier Defect related, determined by number of traps, energy levels, and carrier capture coefficients in bulk, oxide, and interfaces.capture coefficients in bulk, oxide, and interfaces.

Distributed defects may produce 1/f-like noise via superposition of noise Distributed defects may produce 1/f-like noise via superposition of noise componentscomponents

The same defects that produce noise play a role in leakage and reliabilityThe same defects that produce noise play a role in leakage and reliability Noise metrology: characterize electrically active defects in devices as madeNoise metrology: characterize electrically active defects in devices as made Random Telegraph Signals: carrier trapping and detrapping in a small number Random Telegraph Signals: carrier trapping and detrapping in a small number

of defects in a bottleneck device area may greatly affect charge transport of defects in a bottleneck device area may greatly affect charge transport (source-channel region of MOSFET)(source-channel region of MOSFET)

Food chain in numerical simulation: Defect information via FLOOPS into Food chain in numerical simulation: Defect information via FLOOPS into FLOODS into Noise Post-Processor and vice versaFLOODS into Noise Post-Processor and vice versa

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N O I S E Velocity Fluctuation Velocity Fluctuation NoiseNoise Caused by random carrier scattering with lattice Caused by random carrier scattering with lattice

waves, impurities and surfaceswaves, impurities and surfaces Also known as Nyquist noise, Johnson noise, Also known as Nyquist noise, Johnson noise,

thermal noise, and diffusion noise.thermal noise, and diffusion noise. Can not be removed by improving crystal qualityCan not be removed by improving crystal quality Typically determines noise figure at frequencies Typically determines noise figure at frequencies

above 1 MHzabove 1 MHz Shows up as shot noise in junction and mesoscopic Shows up as shot noise in junction and mesoscopic

devicesdevices Allows for the measurement of the diffusivity as a Allows for the measurement of the diffusivity as a

function of electric field since function of electric field since DS v

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Noise ModelingNoise Modeling

• Need to knowNeed to know– microscopic microscopic

noise sourcesnoise sources– transfer transfer

function that function that couples the couples the noise strength noise strength from each from each differential differential volume to the volume to the terminals.terminals.

grK ,

G~

grVS ,

Ntrap

i npnvolgrV

t

drGKGS1 ,,,,

*,,

~~

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x1

x2

x2

x1

Spectral Density

Frequency fOSC

Upconversion

SiO2 Si

Evs

Ef

Ecs

Ntrap

ft (1-ft)ET

Frequency Domain( LF Noise)

Time Domain(RTS Noise for Single Trap)

Integration of All Traps

1/f

1/f

1/f2

x

x

x

Noise Sources in Advanced MOSFETsNoise Sources in Advanced MOSFETs

n+ Source

n+ Drain

p-SubstrateDepletion Region

Bulk GR Noisedue to defects

Gate Leakage Current Noisedue to trap-related process

Oxide

Gate

+

Slow traps

Fast trapsTrap

Coulomb scattering

Drain Current Noise due to number-mobility fluctuation

Channel

Physical Mechanism for LF NoisePhysical Mechanism for LF Noise

CorrelationEffects

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N O I S EFocus first onFocus first on

G-R Mechanism at SiOG-R Mechanism at SiO22/Si /Si SurfaceSurface

• Carriers at the interface communicate with Carriers at the interface communicate with the traps in the oxide through tunneling.the traps in the oxide through tunneling.

• Carriers first get trapped by the defect Carriers first get trapped by the defect centers at the interface, then tunnel into the centers at the interface, then tunnel into the traps in the oxide at the same energy level.traps in the oxide at the same energy level.

• Carrier tunneling is most efficient between Carrier tunneling is most efficient between trap centers that have the same energy trap centers that have the same energy position as the Fermi level at the interface.position as the Fermi level at the interface.

• Only the traps at that energy level need to be Only the traps at that energy level need to be discretized to account for the tunneling discretized to account for the tunneling effect.effect.

tttn ffNSt

11

422

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Basic EquationsBasic EquationsAt the interface:At the interface:

Poisson: Poisson:

ECE:ECE:

HCE:HCE:

Interface trap ECEInterface trap ECE

In the oxide (at position In the oxide (at position xxii):):

Poisson’s:Poisson’s:

Trap ECE:Trap ECE:

nG

2

int ,int2/ 0D A f t f

d qF p n N N Q E q n E

dr

0,,1

int,int,int, fnnnnn Etgrqdt

dnF rJ

0,,1

int,int,int, fppppp Etgrqdt

dpF rJ

,int

,int ,int ,int ,int ,int ,int , , 0, ,t ox ox ox f

t f

n n n p p t fg r t Edn E

F g r g r t Edt

rr

0,2

2

fioxx Exn

q

dr

dF i

ix

0,,,

foxoxoxfox

ox Etgrdt

EdnF i

i xx

nG

Gp

int,ntG

oxnG ,

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N-channel MOS TransistorN-channel MOS Transistor

• Fabrication parameters input to the Florida Fabrication parameters input to the Florida Object Oriented Process Simulator, FLOOPS.Object Oriented Process Simulator, FLOOPS.

• Generated doping profiles input to Florida Generated doping profiles input to Florida Object Oriented Device Simulator, FLOODS Object Oriented Device Simulator, FLOODS with noise upgrade.with noise upgrade.

• Accounts for drift-diffusion, impact ionization, Accounts for drift-diffusion, impact ionization, generation-recombination noise in bulk and generation-recombination noise in bulk and oxide layers, velocity fluctuation noise.oxide layers, velocity fluctuation noise.

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nMOSFET SimulationnMOSFET Simulation

satd

dsatddsatdd

iI V

VVVVV

n

n

fL

kTNqWS s

d

,

,,

0

30

22

122

Doping ProfileDoping ProfileL = 0.4 umL = 0.4 um

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Distributed SDistributed Sidid

Distributed current noise spectral density for f = 1 Hz.(Vds = 2.0 V, Vgs = 0.8 V, dcrit = 22 Å)

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N O I S E Graded Channel NMOSGraded Channel NMOSReverse EngineeringReverse Engineering

SiO2

x

y

Oxide NoiseCritical Region

Graded Channel Doping

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N O I S E Advanced nMOS Advanced nMOS TransistorsTransistors

• Measured long (2.33Measured long (2.33mLmLGG) and short (0.09) and short (0.09mLmLGG) n-) n-channel transistors, processed the same way, one channel transistors, processed the same way, one set with SOI starting substrate, other set with bulk set with SOI starting substrate, other set with bulk substrate materialsubstrate material

• Fabrication parameters input to the Florida Object Fabrication parameters input to the Florida Object Oriented Process Simulator, FLOOPS.Oriented Process Simulator, FLOOPS.

• Generated doping profiles input to Florida Object Generated doping profiles input to Florida Object Oriented Device Simulator, FLOODS with noise Oriented Device Simulator, FLOODS with noise upgrade.upgrade.

• Accounts for drift-diffusion, impact ionization, Accounts for drift-diffusion, impact ionization, generation-recombination noise in bulk and oxide generation-recombination noise in bulk and oxide layers, velocity fluctuation noise.layers, velocity fluctuation noise.

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nMOS SOI TransistornMOS SOI Transistor

NMOS SOI

n+ poly

n+ n+p+

buried oxide

p-

STISTI

White: oxide

Blue: n-type Si

Yellow: p-type Si

Intensity of color ~ doping level

S D

G

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N O I S E 3.23.2m x 90nm bulk m x 90nm bulk nMOSFETnMOSFET

Simulated and measured current-voltage characteristic

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N O I S E 3.23.2m x 90nm bulk m x 90nm bulk nMOSFETnMOSFET

Measured and simulated noise data using a constant trap density in the oxide

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N O I S E 3.23.2m x 90nm bulk m x 90nm bulk nMOSFETnMOSFET

Graphical depiction of oxide trap locations on mesh for simulating the low frequency noise features. Location 1 has 4 traps, locations 2 and 3 0.5 traps each.

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N O I S E 3.23.2m x 90nm bulk m x 90nm bulk nMOSFETnMOSFET

Simulated and measured data

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N O I S E 4.84.8m x 90nm SOI m x 90nm SOI nMOSFETnMOSFET

Measured and simulated oxide and diffusion noise

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Noise Noise inin

Carbon nanotubes Carbon nanotubes

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N O I S E Carbon Nanotube Carbon Nanotube PropertiesProperties

• CVD grown, look like rolled up graphene sheetsCVD grown, look like rolled up graphene sheets• Single-walled or multi-walledSingle-walled or multi-walled• Metallic (1/3) or semiconducting (2/3)Metallic (1/3) or semiconducting (2/3)• Diameter about 1 nm Diameter about 1 nm • SC energy gaps scale with 1/diameterSC energy gaps scale with 1/diameter• EEGG(eV)= 0.9/d(nm)(eV)= 0.9/d(nm)• Mechanically robust (stronger than carbon steel)Mechanically robust (stronger than carbon steel)• Excellent heat conductorsExcellent heat conductors

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N O I S E Carbon Nanotube Carbon Nanotube GeometryGeometry

Always metallic(n,0): metallic if n is multiple of 3

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N O I S ECNT Device Cross-CNT Device Cross-

sectionsection

SiO 2 600nm

Carbon Nanotube

Gate

Si

Pd/Cr

SiO 2 600nm SiO 2 600nm

Carbon Nanotube

Gate

contact

Si Si

Pd/Cr Pd/Cr

Source Drain

500 m

1 m

Pd/Cr contact

Pd/Cr contact

Carbon nanotubes

• CVD grown on silicon CVD grown on silicon wafers with wafers with 600 nm oxide 600 nm oxide layerlayer

• Lithography was used to Lithography was used to pattern pattern Cr/Pd (5nm/45nm) Cr/Pd (5nm/45nm) 500500m long electrodes m long electrodes spaced 1 spaced 1 mm apart. apart.

• Multiple CNTs connect Multiple CNTs connect between the contacts.between the contacts.

• 1/3 of total number are 1/3 of total number are expected to be metallicexpected to be metallic and the rest and the rest semiconducting.semiconducting.

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Carbon NanotubesCarbon Nanotubes

1.5 m

Electrode

Carbon nanotube

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Noise SpectrumNoise Spectrum

Current Noise Sectral DensityCNT3 B

1.00E-25

1.00E-24

1.00E-23

1.00E-22

1.00E-21

1.00E-20

1 10 100 1000 10000 100000

Frequency (Hz)

Si (

Am

p^

2/H

z)

I = 43 nA

R=9k

2qI=1.410-26 A2/Hz

4kTG=1.810-24A2/Hz

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N O I S ESet-up for sequential Set-up for sequential

ablationablation

• Ablation occurred at, Ablation occurred at, VVpp ~17V, ~17V, TTWW = 6 = 6S, S, ffrr = 80Hz. = 80Hz.

50 o

o o

Gate Bias

Pulse Generator

Analog Oscilloscope

C N T

1 k

100

• Due to random nature Due to random nature of growth many CNTs of growth many CNTs connect between connect between electrodes (Metallic electrodes (Metallic ~1/3 and rest SC).~1/3 and rest SC).

• Isolation of single CNT Isolation of single CNT is time consuming.is time consuming.

• In the presented In the presented technique process technique process variation is minimum.variation is minimum.

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N O I S E Conductance vs. AblationConductance vs. Ablation

0

5.010 -5

1.010 -4

1.510 -4

2.010 -4

2.510 -4

0 1 2 3 4 5 6

Number of Ablation

Con

duct

ance

(S

)

Metallic CNT

Semiconducting CNT

• Note annealing after the first ablation attempt.Note annealing after the first ablation attempt.

• Large spread in the conductance of the individual ablated CNTs, Large spread in the conductance of the individual ablated CNTs,

but no clear trend.but no clear trend.

1.010-5

1.510-5

2.010-5

2.510-5

3.010-5

3.510-5

4.010-5

2 3 4 5 6 Number of Ablation

Con

duct

ance

(S)

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N O I S E Noise calculationNoise calculation

S

j

sjsjM

i

mimittt f

IA

f

IA

f

IAfS

1

2

1

22

)(

S

j t

sjsj

M

i t

mimi

S

j t

sjsj

M

i t

mimit G

GA

G

GA

I

IA

I

IAA

1

2

1

2

1

2

1

2

S

jsjsj

M

imimitt GAGAGA

1

2

1

22

• At·Gt2 represents the lost noise (and conductance)

contribution form the ablated CNT

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N O I S E Noise vs. AblationNoise vs. Ablation

A/R

110-10

110-9

110-8

0 1 2 3 4 5 6

Number of Ablation

110-14

110-13

110-12

A G

2

A/R

AG2

• AGAG22 decreasing monotonically decreasing monotonically

• AAsisi is two orders of magnitude higher is two orders of magnitude higher

than than AAmimi

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Noise Noise inin

Bridging Silicon Bridging Silicon

NanowiresNanowires

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N O I S ESi nanowire fabrication Si nanowire fabrication

stepssteps

(d)

Si substrate

SiO2 Layer

(a)

Si Electrodes Angled catalyst

deposition

(b)

Au Catalyst

(c)

SNW growth

(111) direction

• Growth direction (111).Growth direction (111).• Dopant (Boron) is Dopant (Boron) is

incorporated during incorporated during growth process. growth process.

• The diameter is much The diameter is much larger than CNT, around larger than CNT, around ~50nm.~50nm.

• Operates in bulk mode Operates in bulk mode due to larger feature size.due to larger feature size.

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N O I S E AA vs. vs.

10-11

10-10

10-9

10-8

10-7

10-2 10-1 1

Resistivity (-m)

1/f

no

ise c

oeff

icie

nt Wafer 1

Wafer 2

• SSII/I/I22=A/f is used =A/f is used

• Note: lowest resistivity device also has lowest noiseNote: lowest resistivity device also has lowest noise

• So, lowest contact resistance devices have lowest noiseSo, lowest contact resistance devices have lowest noise

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N O I S E Noise ModelingNoise Modeling

N

i t

i

ibHb I

I

VpA

1

21

N

i t

i

i

cici

i

bibit I

I

R

RA

R

RAA

1

222

Bulk noise Contact noise

• For, Rc 0 Ri Rb At Ab.

• Using Hooge’s model for bulk noise,

ibn

Bulk Contact

icn

vn

Rc Rb

i

Hbbi Vp

A

• Now we are ready to calculate contact noise.

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N O I S ESummary silicon nanowiresSummary silicon nanowires

• The model fits the calculated contact noise well The model fits the calculated contact noise well

10-13

10-12

10-11

10-10

10-9

10-8

10-7 W

afe

r1 a

Wa

fer1

d

Wa

fer2

a

Wa

fer2

b

Wa

fer2

c

Wa

fer2

d

Wa

fer2

f

Wa

fer2

i

Ac Ab Ac (Fitted)

HbHb = 1.1 = 1.11010-5-5 and 7.5 and 7.51010--

66 for wafer 1 and wafer 2 for wafer 1 and wafer 2 show show high quality of the high quality of the devicesdevices. .

• Contact noise dominant.Contact noise dominant.• Most likely Most likely origin of the origin of the

noise is the impinging noise is the impinging endend, where the contact is , where the contact is made through the native made through the native oxide layer thus expected oxide layer thus expected to be defect rich.to be defect rich.

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ThanksThanks

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