carbon nanotube as a interconnect

8/6/2019 Carbon NANOTUBE as a Interconnect

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Carbon Nanotube as a

Interconnect

Presented by

PRAVEEN Y.S

(100942018)

5/4/2011 1MIT -LOWPOWER VLSI (praveen y.s )


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AGENDA

Introduction to NANOTECHNOLOGY

Development of CARBON NANOTUBES

Properties of carbon nanotubes

Carbon nanotubes as interconnect

Refrences

5/4/2011MIT -LOWPOWER VLSI (praveen y.s ) 2


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Nano tubes

Carbon nanotubes tubes made

entirely of carbon rings. 1991

Carbon atoms linked together hexagonallylike chicken wire when rolled they formnanotubes



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Grapine sheet



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Introduction to the field

Carbon nanotubes (CNTs) are allotropes ofcarbon with a cylindrical nanostructure.

Nanotubes have been constructed withlength-to-diameter ratio of up to132,000,000:1



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Introduction to the field

These cylindrical carbon molecules have novel

properties, making them potentially useful in

many applications.

They exhibit extraordinary strength and unique

electrical properties, and are efficient thermal

conductors.

The diameter of a nanotube is on the order of afew nanometers (approximately 1/50,000th of

the width of a human hair), while they can be up

to 18 centimeters in length (as of 2010)



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TYPES OF NANOTUBES

CNTs can be thought of being made byrolling up a single atomic layer of graphite toform a seamless cylinder. The resultingstructure is called single-walled carbonnanotube (SWCNT)

If several SWCNTs with varying diameter are

nested concentrically inside one another, theresulting structure is called a multi-walledcarbon nanotube (MWCNT).



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These nanotubes are 60 times stronger thenhigh grade steel.

They are very light and flexible.



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WHY CARBON NANOTUBE ????

Traditional interconnect schemes becomeproblematic due to the increased wireresistances resulting from grain and surfacescattering effects and the higher currentdensities which must be carried.

Sufficient heat removal from the chip is

already a problem in present day computers.



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properties exhibited by

carbon nanotubes The high current carrying capacity

Mechanical stability of metallic nanotubes



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Applications in microelectronic interconnects

The reasonably large band gap of narrow

single-walled nanotubes suggests their use asnanoscale transistor elements.

Due to the small radius of curvature at thetips of the nanotubes, they are ideally suited

to low-voltage field emission devices such asflat-panel displays



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In 2013 the ITRS predicts a current density of3.3106 A/cm2 .

a value which, to date, can only be supportedby CNTs, where current densities of 109 A/cm2

in nanotubes without heat sinks have beenreported.



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Thermal conductivity

The thermal conductivity of nanotubesexceeds that ofdiamond by a factor of 2 andthat ofcopper by a factor of 15 and is,therefore, ideal for dissipating heat fromsensitive active devices.



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carbon nanotubes are most likely to beimplemented in wiring applications on

chips. Here the integrated circuit can exploit the

outstanding properties of CNTs: highcurrent carrying capacity, huge thermalconductivity and length independentresistance at the scale of interest.



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nanotubes are ballistic conductors

a perfect metallic nanotube is the best

normal electron conductor an engineercan dream of,



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EVALUATION OF NANOTUBES AND

AU-WIRE

Bottom-up Top-down



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NANOTUBES AND AU-WIRE

Bottom-up:- where we try to give an answerbased on what is known from mesoscopicphysics.

where conductance values are estimated from

point contact measurements and densityfunctional theory calculations (DFT) exist.

Top-down:- where we essentially apply Ohms

law in combination with a size-effect describedby the FuchsSondheimer relation.



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The conductance of one metallic single-walled nanotube of 1nm in diameter dcan be given as G=2G0153 S, with G077S being the spin degenerated conductance value for oneballistically conducting channel, which is represented by onespecific k-value.

As the diameter of the tube grows additional channels maycontribute to the conductance as more sub-bands can beoccupied.

Therefore the conductance of a SWCNT can be written as

G=2G0+8G0 exp (E1/kT)+16G0 exp (E2/kT),

where E1 is proportional to 1/dand in the order of 50 meV fora 20 nm diameter nanotube.

For multi-walled CNTs one has to add up all contributions from the individual layers [2].

http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V0W-469PP84-2&_user=4058864&_coverDate=10/31/2002&_rdoc=1&_fmt=high&_orig=gateway&_origin=gateway&_sort=d&_docanchor=&view=c&_acct=C000060990&_version=1&_urlVersion=0&_userid=4058864&md5=9c16d97b92e7105e7fcb5e496adeefc4&searchtype=ahttp://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V0W-469PP84-2&_user=4058864&_coverDate=10/31/2002&_rdoc=1&_fmt=high&_orig=gateway&_origin=gateway&_sort=d&_docanchor=&view=c&_acct=C000060990&_version=1&_urlVersion=0&_userid=4058864&md5=9c16d97b92e7105e7fcb5e496adeefc4&searchtype=a


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For Au-wires by Wang et al.

The calculatedconductance has tobe considered as anupper limit



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CONDUCTANCE OF CNT ARRAY



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As a result we would like to emphasize thatthe conductance of small-diameter Au-nanowires scales linearly with diameter andthat equivalent arrangements of carbonnanotubes conduct equally well.

But whereas carbon nanotubes show huge

endurance.



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RESISTANCE DIAMETER

COMPARISON



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clearly demonstrates that CNT-interconnects can readily compete with

ordinary metallization schemes and caneven offer the possibility of achieving a byorders of magnitude lower resistance.



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Comparison with CU

Metallic tubes are 1-dimensional metals with a

Fermi velocity vF that equals metals (vF

9107cm/s) .

electron mean free path lfmp for the electrons

of at least 1 m. However, due to the low density

of states, the resistivity is only of the order of

that of the best metals (~1cm) despite thehuge mean free path.



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Data from 2 nanotubes measured at 250C for 350

hours .Data for copper wires are not available for these

dimensions, instead the calculated resistances for Cu-

wires are shown.


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As shown in Table 1, CNTs can withstand current

densities up to 10^10A/cm2 exceeding copper by a

factor of 1000.

With respect to resistance, CNTs are favourable inhigh aspect ratio structure like vias, where also the

highest current densities are expected



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CNT AS INTERCONNECT

Filling via structures with nanotubes requires one

ore more particles at the bottom of the via which

then allow CNT growth by chemical vapor

deposition (CVD) at 450-800C with a carboncontaining gas.

The CVD process can be supported by plasma

enhancement (PECVD) and bias Voltage .



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The catalyst material (Fe, Ni, Co or combinations ofthem with Mo) is usually deposited as a thin film byphysical vapor deposition (PVD) or from solutions.Particle formation occurs during the heating step.

which breaks up the thin film into clusters.

Ion bombardment in plasmas supports this particleformation.

Careful material and interface design in combinationwith low temperature budget and time dependentdiffusion phenomena, needs to be taken intoaccount to guarantee CNT growth



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The interaction between catalyst layer and

supporting metal electrode needs to be low, in

order to suppress interdiffusion and allow

particle formation in the restricted temperatureregime.

Metals with a natural thin oxide layer (Ta, Al, Ti,

Cu, Cr) show low wetting behaviour for somecatalyst materials and are therefore suitable aselectrode materials.



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The quality of nanotubes


Here the CNT via is grown on the metal 1 layer before


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Here, the CNT via is grown on the metal 1 layer before

the deposition of the inter-metal dielectric (IMD).Lithographically defined nickel spots act as catalyst

particles, from where carbon fibers are grown.Fibers need to be aligned perpendicular to the surface.

This is achieved by PECVD and an applied bias voltage,which aligns the fibers almost perpendicular to the wafer.

Subsequently, SiO2 is deposited and the wafer isplanarized


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with chemical wafer polishing (CMP). The laststep also

opens the nanotube ends for contacts withmetal 2 layer.



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very high resistance of ~ 300 k per CNT interconnecthas been evaluated for that approach, which may beattributed to the imperfect structure of PECVD grown

MWCNTs. The approach is especially suited for single MWCNT

fillings because high density growth could not bedemonstrated.

In addition, this approach can also be used to create highaspect ratio capacitor electrodes for DRAM applications.



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buried catalyst approach

where the dry etching of the via has to stop on

the thin Ni- or Co-catalyst layer .

Arrays of MWCNTs have been grown in ~2m

diameter vias by hot-filament CVD (HF-CVD)

A resistance of ~134 k per MWCNT has been

achieved, a value which again can be attributed

to the quality of the tubes grown by HF-CVD.



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Refrences Carbon Nanotubes for Interconnect Applications (cu):-

Franz Kreupl, Andrew P. Graham, Maik Liebau, Georg S.Duesberg, Robert Seidel, Eugen Unger

C arbon nanotubes in interconnect (Au)applications F.Kreupl , A.P. Graham, G.S. Duesberg, W. Steinhogl, M.

Liebau, E. Unger, W. Honlein

Nano/stanford

Indian nanoelectronics users program (INUP)

WIKIPEDIA



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carbon nanotube as a interconnect

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