Colombo NPL Oct 2012 1 - National Physical Laboratory€¦ · 15-16 Oct 2012 NPL,UK UTAustinUT ... “easier” thanlateralcompositioncontrolforthan lateral composition control for

Luigi ColomboTexas Instruments Incorporated

Dallas, TX, USA

G h C f F R h t A li tiGraphene Conference: From Research to Applications15-16 Oct 2012

NPL,UKNPL,UK

UT Austin - Banerjee group UT Austin Banerjee group UT Austin - Tutuc group UT Austin – Ruoff UT Austin Ruoff UT Dallas - Wallace group UT Dallas J Kim group UT Dallas - J. Kim group GIT/UT Dallas – Vogel group

Nano-electronic Research Initiative and NIST

NPL Teddington 15-16 Oct 2012 LColombo

Introduction Introduction Graphene based devices Graphene integration Graphene integration

Graphene film growth Dielectrics – thickness scalinggMetal contacts – contact resistance

Summaryy


Performance per power density vs. gate length that the slowing of voltage scaling causes a reversal of g g gthe trend beyond 130-nm-node technology

P d it t l th ti d i Power density vs. gate length: active and passive power density

h l S & O 0 O 4/ /S 2006


W. Haensch et al IBM J. RES. & DEV. VOL. 50 NO. 4/5 JULY/SEPTEMBER 2006

Modern CMOS10 m

Beginning ofSubmicron CMOS

Deep UV Litho1 m

90 nm in 2004

Presumed Limit100 nm

>40 Years of Scaling History Every generation

32 nm in 2010

Presumed LimitNeed a New Switch

10 nm

– Feature size shrinks by 70%– Transistor density doubles– Wafer cost increases by 20%– Chip cost comes down by 40%

G ti l l

1 nm

Generations occur regularly– On average every 2.9 years over the

past 40 years– Recently every 2 years

?


1970 1980 1990 2000 2010 2020

Spin based devicesS i W Spin Wave

Spin torque Spin FETsp All spin logic

Nano magnetic logic devicesT l FET III V h Tunnel FETs – III-V, graphene

Graphene PN Junction Devices Bilayer Pseudospin FETs(BiSFET) Bilayer Pseudospin FETs(BiSFET)

Lateral graphene tunneling devicesg p g


BiSFET• Bose-Einstein Condensate

High Quality SC GrapheneHigh Quality SC Graphene

J.J. Su and A.H. McDonald, Nat. Phys., 2008Banerjee et al, EDL 2009

Tunneling FET: Low SS

Q. Zhang et al, EDL, 2008

BilayerBilayer graphene?graphene?GNR?GNR?

P-N Junction High Quality SC GrapheneHigh Quality SC Graphene• Veselago lens switch

V. V. Cheianov et al, Science, 2007


BiSFET SchematicVGnVn(Schematic only,

cross section)cross‐section)

Gate Voltage (mV)

VGp

Vp p and n type graphene layers

graphene layer contacts Gate(s)

Equivalent Circuit Model

y

Energy per switching operation gy p g pper BiSFET ~ 0.010 aJ = 10 zJ

S K Banerjee et al Electron Device Letters IEEE 30 158 (2009)


F. Register, UT AustinS. K. Banerjee et al., Electron Device Letters, IEEE 30, 158 (2009).

Very intriguing device will require significant process development to realize as Gr/h-BCN

There could be other options “easier” than lateral composition control for There could be other options, easier than lateral composition control for implementation


G. Fiori et al., ACS Nano 2012

Graphene Growth Monolayer graphene Graphene nano ribbons (GNR)LER is a major challenge for etched GNRsChemical pathways for growing GNRs – placement

challenge Bi-layer graphene Bi-layer grapheneChemically inactive graphene surface is a major challenge

for uniform bi-layer growth Surface modification – e.g.: BCN

Dielectric selection and deposition High-k – scaling Low-k - scaling Lattice matched – 2D crystals

M t l t t


Metal contacts

1950s –Teal & Buehler1950s Teal & Buehler

http://pcplus.techradar.com/2009/05/21/how-silicon-chips-are-made/

Courtesy of Texas InstrumentsD. Edelstein, in http://www.ibm.com/ibm100/us/en/icons/copperchip/P. Moon, et al., Intel Technology Journal 2 , pp. 87-92, 2008.


Chemical vapor deposition: Cu, Ir, Ru; Pt Plasma enhanced CVD processes: Cu Plasma enhanced CVD processes: Cu Precipitation: Ni, Ru, Co, Pt, Pd Growth by desorption of Si from SiC Growth by desorption of Si from SiC

X. Li et al, Science (2009). (Cu)P. Sutter et al., Physical Review B 80 (24) (2009). PtN.A. Kholin et al., Surface Science (1984). IrKaru and Beer, JAP (1966). NiJ. Sanchez-Barriga et al., Diamond and Related Materials (2010). CoJ Lee et al in IEDM - Technical Digest 2010 (ICP-CVD)


J. Lee, et al, in IEDM - Technical Digest, 2010. (ICP-CVD)D. V. Badami, Nature (1962). SiC

S b t t l ti Substrate selection Metal C solubility Orientation Catalytic activity T

(K)

(K)

Catalytic activity Lattice matched

Dielectrics High-k, low-k? Layered compounds

C /(C+C )

TT Process type:

Growth Temperature Cold wall Hot wall

Cu/(C+Cu)Ti/(C+Ti)

Hot wall Pressure Low Atmospheric T

(K)

T (K

)

Precursor Sources: Gases Liquids Solids

Ni/(C+Ni) Ir/(C+Ir)

Solutions


Okamoto H., Phase Diagrams for Binary Alloys, Desk Handbook, Vol. 1, 2000

We can grow large area graphene

Large area low defect density single crystals of graphene are g y g y g pmost likely required to achieve the highest uniform transport properties for nano-electronic devices

Can large single crystals of graphene be grown? Do we have the right substrate? Is the growth rate high enough for commercial viability?

2-D growth from a single nucleus?

Can “registered” nuclei of graphene be created for further graphene large area crystal growth?


TEMSEM

graphene

20 m

Cu Graphene

10

G p e eislands

Cu5 m10 m G. B.

erag

e (%

)

75

100

Li et at. Science, 2009ur

face

Cov

e

25

50

75140 mTorr 285 mTorr 560 mTorr

Q. Yu et al., Nature Materials, 2011

Time (min)0 1 2 3 4 5

Cu

Su

0


Grain Structure of graphene by Electron Diffraction: >2000 ED patterns Raman – Isotope labeling

5 m10 m

C. Floresca, UT Dallas unpublished data Li et al., Science, 2009


NPL Teddington 15-16 Oct 2012 LColomboLi et al., JACS 2011Li et al JACS 2011

Li et al Science 2009

Cu substrate Pt substrate

400 m

Yan Z, ACS Nano 2012

1 mmL. Gao et al Nat. Comm. (2012)Y.Hao Unpublished results – UT Austin


NucleationCH4 + H2Graphene nuclei Cu

Graphene CH4 + H2Graphene domain CHx coverageDomainGrowth

CH4 + H2

CASE I: Isolated nucleiCH4 + H2

CASE II: Multiple nuclei

CxHy CxHy CxHy CxHy CxHy CxHy CxHy

Constant growth rate with time“I fi it ” d t l t

Varying growth rate“ i i /d i ” d l


“Infinite” exposed catalyst “Finite/decreasing” exposed catalyst

M bili 16 400 25 000 2/V f G /SiOMobility 16,400 – 25,000 cm2/V - for Gr/SiO2Mobility 27,000 – 45,000 cm2/V - for Gr/h-BN

P t t l N L tt (2012)


X. Li et al., Nano Letters (2010)Petrone et al., Nano Letters (2012)

Very large area graphene can be grown on Cu and transferred to any substrate.

PMMA Fe3+

AAcetone

Si/SiO2 Si/SiO2


Li et al,. Nano Lett (2009) Bae et al. Nat. Nanotech. (2010)

Graphene grown and transferred multiple times from the same Cu foilGraphene grown and transferred multiple times from the same Cu foil

An aqueous solution of K2S2O8 (0.05 mM) l d l t l t i thwas employed as electrolyte in the

electrochemistry process.


Wang, Y, ACS Nano 5(12), 927 (2011)

Single Crystal GrapheneSingle Crystal GrapheneSingle Crystal GrapheneSingle Crystal GrapheneExfoliated CVDManchester UT Austin Shenyang UT Austin

1 m 1 mm

1999 …2005 2009 1999 …2005 2009 2010 2010 2011 20122011 2012Microns millimetersMicrons millimeters

Centimeters metersCentimeters meters

Polycrystalline CVD GraphenePolycrystalline CVD GrapheneUT Austin SKKU IBMUT Austin SKKU IBM

Centimeters metersCentimeters meters

Graphene

QuartzQuartz4 cm

23NPL Teddington 15-16 Oct 2012 LColombo

Graphene surface is chemically inert

Need to functionalize the surface to deposit dielectrics using non-physical deposition techniq estechniques

Scaling of dielectrics down to ~ 1 nm needed for Scaling of dielectrics down to ~ 1 nm needed for devices

Enable a variety of dielectrics – high-k, low-k and 2D dielectrics


Nucleation strategies for ALD on graphene

• Thin polymer (NFC 1400 3CP) layer

Standard ALD Al O processes

• Thin polymer (NFC 1400-3CP) layer• D. B. Farmer, et. al., Nano Lett. 9(12), 4474 (2009)

• 1 nm e-beam Al / oxidation in air• S. Kim, et. al., APL 94, 6, 062107 (2009)

D B F t l APL 97(1) 013103 (2010)

Y. Xuan, et al., APL 92, 013101 (2008)Standard ALD Al2O3 processes (TMA/H2O) lead to non-uniform deposition at step edges

Need to use a nucleation layer or

• D. B. Farmer, et. al., APL 97(1) 013103 (2010)• Evaporated PTCDA

• M. Hersam et. al., in press.• NO2 noncovalent functionalization

functionalize the graphene surface • D. B. Farmer and R. G. Gordon, Nano Lett. 6(4), 699 (2006)• Y.-M. Lin, et. al., Nano Lett. 9(1), 422 (2009)

• O3 functionalization• B. Lee, et. al., APL 92(20), 203102 (2008)

G L l J Ph Ch C 113(32) 14225 (2009)• G. Lee, et. al., J. Phys .Chem. C 113(32), 14225 (2009)• B. Lee, et. al., APL 97(4), 043107 (2010)

But, O3 etches of HOPG surface at 200°C

G. Lee, et. Al., J .Phys. Chem. C 113, 32, 14225 (2009)


CVD graphene transferred toCVD graphene transferred to SiO2

Main sp2 graphene peak is fit i h i i hwith an asymmetric Doniach-

Sunjic line• FWHM for transferred

graphene: 0.88 eVgraphene: 0.88 eV• FWHM for CVD

graphene on Cu: 0.74 eV

PMMA id b dPMMA residue observed after transfer (states highlighted in orange)

Curve fit residual error shown below data in gray

PMMA residue presentPirkle A PhD Thesis UT Dallas 2011PMMA fit is consistent with G. Beamson, et. al., Surface and Interface Analysis 17(2), 105 (1991)

PMMA residue present


Pirkle, A, PhD Thesis, UT Dallas 2011

Al2O3 – 1 nm (nominal) Al deposited by on natural graphite by e-beam ti idi d i 1000 b O t 25°C

17 nm

evaporation,oxidized in 1000 mbar O2 at 25°C

(d)

C 1s

ty (a

.u.) O 1s Al 2p

(d) (d)

C-C

*(d) + 25°C O2

(c)

(b)

x10

on in

tens

it

(b)

(c)

(b)

(c)

Al0

(c) Unannealed natural graphite substrate + 1 nm Al

8

1 2

1 6

2 0

eigh

t (nm

)

600 nm

0 nmzRMS = 4.23 nm

(b)

x10ot

oele

ctro

(a) (a)

(b)

(a)

(b)

(a) Annealed (400°C, UHV) natural graphite

(b) + 25°C O2

• Large (~ 5-10 nm) Al clusters explain incomplete oxidation

0 1 2 30

4He

x ( m )536 532 528Ph

o

Binding energy (eV)76 72

290 286 282

natural graphite substrate + 1 nm Al

AlAl

Adsorbed H2O

(a) (b)

when pre-deposition anneal is employed• Cluster radius is larger than limiting oxide thickness

(~ 0.5 – 2 nm)1

• Further details given in Ref. 2Al2O3Al2O3


27

1. L. P. H. Jeurgens, et. al., JAP 92, 3, 1649 (2002)2. A. Pirkle, et. al, APL 95(13), 133106 (2009)

AlAdsorbed H2O

Hf 1s / O 1s fit regions• Pre-deposition anneal, deposition pressure ≤ 4x10-10 mbar

necessary to suppress Hf carbide formation

Hf 1s / O 1s fit regions1: O 1s - HfO22: O 1s - Hf(OH)3: Hf 1s

C 1

Hf 4fO 1Hf 1

(c) Annealed graphite, 4×10-10 mbar deposition(LN chamber shroud cooled)

HfC

C 1s Hf 4fO 1sHf 1s

ty (a

.u.)

3

(b) Annealed graphite, 5×10-9 mbar deposition

(LN2 chamber shroud cooled)

on in

tens

it

32

1

31

5×10-9 mbar deposition(chamber shroud not cooled)

(a) Exfoliated graphite, 1 10 8 b d i iot

oele

ctro

1

2 1×10-8 mbar deposition(chamber shroud not cooled)

288 284 280Binding energy (eV)

20 18 16 14 12536 532 528

Pho 23

Binding energy (eV) A. Pirkle, et. al, APL 95(13), 133106 (2009)


• 1 nm of HfO2 deposited on natural graphite by evaporating Hf with 1x10-6 mbar partial pressure of O2i b ti h bin e-beam evaporation chamber

• Chamber base pressure ≤ 5x10-10 mbar • Internal LN2 chamber shroud cooled to minimize background residual gases (OH)

ty (a

.u.) O 1s C 1s Hf 4f

1 nm HfO2 - reactive e-beam

ectr

on in

tens

it

536 532 528

Natural graphite substratePhot

oele

292 288 284 280 24 20 16 12AFM – 1 nm HfO2 on natural graphite

XPS• No carbide detected after reactive e-beam

deposition

Binding energy (eV)292 288 284 280

24 20 16 12

natural graphite•Low surface roughness:

zrms = 0.24 nm• Comparable to roughness of HfO2 on Si spectator sample

TEM – 5 nm HfO2 on natural graphite•High and low magnification i h d if itdeposition (within a factor of ~2)images show good uniformity•No pinhole/short defects observed



2.2nmOxidized Al

1.1nm

0 150nm300nm

00

2.2nm

0300nm150nm 00

Oxidized Ti

1.1nm

0300nm150nm

150nm300nm

00

Provides nucleation centers for the ALD growth uniform coverage critical No detrimental effect on gate capacitance ultra-thin interfacial layer desirable Surface diffusion limits the minimum interfacial layer thickness


Surface diffusion limits the minimum interfacial layer thickness B. Fallahazad et al. APL, 2012

Al O TiO dielectric on graphene scaled to 2 6nmAl2O3-TiOx dielectric on graphene scaled to ~ 2.6nm

B. Fallahazad et al APL (2012)

A id hi h k di l t i d h tAre oxide high-k dielectrics good enough to achieve high mobility in graphene?


• CVD graphene transferred to SiO2 using PMMA th d 18

x103

PMMA method

• Sample received in-situ 300 °C / 3 hr vacuum anneal (P ~ 1x10-9 mbar) 14

16

18

(e,f)/s)

C 1s

(d)

(e)

(f) (g)

(i)

c) Transferred CVD graphene on SiO2 + 300 °C / 3 hr UHV

a) Transferred b) Annealed

a) b) 10

12

(i) (h) (g)

( , )

(c)

nten

sity

(cts

/

(h)

anneal

6

8

( ) ( ) (g)

(b)

otoe

lect

ron

in

b) Transferred CVD graphene on SiO2

0 1 2 3 4 5-10

01020

Hei

ght (

nm)

x ( m)0 1 2 3 4 5

-100

1020

x ( m)2

4Pho

(a)a) CVD graphene on Cu

• C 1s XPS states corresponding to PMMA are largely removed• AFM shows a much smoother surface

RMS h d f 4 6 t 0 6 li

290 288 286 284 2820

Binding energy (eV)


• RMS roughness drops from 4.6 nm to 0.6 nm upon annealing• 300 °C / 3 hr vacuum anneal is effective for significant removal of PMMA residue from graphene



Chen J, ACS Nano, 2012

Nickel

(a) (b)

Ni/AuParylene

Ni/Au

Ni/Au Graphene5nm

5 nm

Parylene ~7 nm

SiO2

Graphene

1 um

Ni/Au

n++ Si substrate

SiO2 (90 nm)Ni/Au Graphene

3 VD= 10 mV600

Without Parylene

(a) (b)-606

nm

Mobility ~ 5000 cm2/V s

2

nce

[K

]300

400

500 sity

cps

With Parylene

0

1

Res

ista

1200 1600 2400 28000

100

200

Inte

ns


-10 0 100

VBG[V]1200 1600 2400 2800

Raman Shift (cm-1)Mordi et al., Appl. Phys. Lett. 100, 193117 (2012)

Exfoliated h-BN CVD FL h-BN CVD Monolayer h-BN

Kim et al NL (2012)

2

C.R. Dean et al, Nature Nanotech, 2010Ismach et al, ACS Nano accepted for pub

2 nm


0.5

1.0

HOPG + 1 nm Ni+ 500 C / 10 min anneal (UHV))

C 1s

2 μm

0 5

0.0

I d(m

A)

-20 -100

Vbg(V)anneal (UHV)

HOPG + 1 nm NiPI (

a.u.

)

-1 0 1-1.0

-0.5 10 20

292 288 284 280( )

HOPG

• XPS analysis indicates absence of carbide formation ( ~ 282 eV) at the Ni – graphene interface

Vd(V)BE ( eV )

at the Ni graphene interface

• Id - Vd plots for Ni on graphene indicative of ohmic behavior higher total resistance (R) and hence higher Rc( ) g c


A. Venugopal, Ph.D. Thesis, UT Dallas, 2012

ExfoliatedExfoliated CVD grownCVD grown22

)

CVD Graphene

1 old transfer new transfer TiOx processR

c(k

)

L = 3m

0 10 20 300

W ( m)

Lc 3m

• ~ 5X reduction in Rc observedid i f i ifi l ib

Wc (m)


• Residue at interface significantly contributes to RcA. Venugopal, Ph.D. Thesis, UT Dallas, 2012

Progress has been made in graphene growth and integration of graphene-based devicesLarge area polycrystalline CVD graphene“Large”, a few mm, single crystal graphene g g y g pMany issues remain on uniformity/roughnessNeed to improve contactspScaling of dielectrics to 1 nm rangeH-BN shows promise but growth of reproducibleH BN shows promise but growth of reproducible

uniform films is still very challenging


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Colombo NPL Oct 2012 1 - National Physical Laboratory€¦ · 15-16 Oct 2012 NPL,UK UTAustinUT ... “easier” thanlateralcompositioncontrolforthan lateral composition control for