Journal of Nanoparticle Research1: 151–152, 1999.© 1999Kluwer Academic Publishers. Printed in the Netherlands.

JNR Report

Electronic applications of carbon nanotubes become closer to realityReport on SRC/NASA Ames Workshop on emerging opportunities and issues innanotubes and nanoelectronics

V. Zhirnov1, D. Herr1 and M. Meyyappan2,∗1Science Research Corporation (SRC),2NASA Ames Research Center, Mail Stop 229-3, Moffett Field, CA 94035,USA;∗Author for correspondence (E-mail: meyya@orbit.arc.nasa.gov)

Received 14 December 1998; accepted in revised form 16 December 1998

A meeting addressing the practical implementationof carbon nanotubes (CNTs) in micro and nano-electronics was conducted at NASA Ames ResearchCenter, Moffett Field, in Mountain View, California,on November 12 and 13, 1998, in collaboration withSemiconductor Research Corporation (SRC). Theworkshop served as a forum to build bridges betweencolleagues in the nanotube and the semiconductorcommunities.

In general, the simulated properties of CNT are out-standing for electronic applications. They suggest thatCNTs have very high electrical and thermal conduc-tivities and extraordinary mechanical strength. Elec-trical properties of CNTs apparently can be changedfrom metallic to semiconducting or insulating by vary-ing the structure (e.g., helicity) of the CNT. All theseproperties in combination with ultra small size make

Table 1.

Application Property Challenge

CNT-film as a low-K Inherent low density of the CNT-films The CNT film would need to be deposited,insulator planarized, patterned and etched with

techniques compatible with the underlyingsilicon devices

CNT as interconnects Low resistivity Manipulation/attachment of individual CNTProbes for metrology High aspect ratio of tips Attachment of a single CNT to the cantileverManufacturg with micro or nanotools High aspect ratio of tips Microtool arrays must be ‘fast, flexible, and

inexpensive’Field emitters High aspect ratio, thermal conductivity Performance of CNT field emitters?Passive devices Geometrical characteristics Is it possible to grow helical conductingcapacitors and inductors nanotubes?

CNT for active electronic Possibilities to control electronic The current standards should be met: low costdevices properties by structural characteristics (1µcent/transistor), high level of integration

(109 transistors/circuit); high reproducibility(± 5%), reliability (operating time>10 years)

the CNT a promising candidate as a future electronicmaterial. Conceptually, CNT-based electronic devicescould be fabricated by changing the helicity along ananotube, coupling of nanotubes with different helic-ity, introduction of deformations to control the elec-tronic properties, etc. However, this appears to be along-term prospect of CNT-electronics. Speakers fromthe semiconductor community also addressed the morenear-term opportunities. Table 1 summarizes possibleapplications of CNT in existing microelectronic cir-cuitry. The integration of CNT into modern microelec-tronic circuitry faces serious obstacles, which includecompatibility, positioning, and attachment problems.Several speakers from the semiconductor communityemphasized that more attention should be paid toself-organizing processes (self-assembly), as a futureapproach to nanofabrication.

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Speakers from the nanotube community presentedthe latest results in synthesis and characterizationof the nanotubes. Current disadvantages of fabricat-ing with CNTs are high growth temperature required(∼1200◦C) and poor reproducibility of properties ofindividual CNT. At the workshop, CVD fabricationprocesses with temperatures as low as 500◦C werereported. However, the properties of the resulting nano-tubes have yet to be characterized. A near-term goalis development of a CVD technique for controlledgrowth of nanotubes, aiming at: (a) lowering the growthtemperature down to 400–600◦C and (b) formationof regular arrays of the CNT on a substrate withuniform height and diameter. Electrical characteriza-tion of the nanotubes also is a very important issue forelectronics applications. Much remains to be learnedabout the electrical properties of CNTs. Limited resultswere mentioned regarding theI–V characteristics ofindividual CNTs and their potential as semiconduc-tors. Development of a ‘standard’ reliable techniqueand instrumentation for electrical characterization ofthe CNT should be one of primary goals of near-termresearch. A FET structure with a nanotube as a channelwas discussed at the workshop. However, the transis-tor action was not fully demonstrated as the maximumgain was only 0.35 and the output characteristics didnot exhibit a saturation region typical for MOSFETs.Nevertheless, this result opens new opportunities forresearch, e.g. optimization of properties of CNT-basedamplifier, aiming for higher gain. Several speakers dis-cussed field emission properties of carbon nanotubes.CNT field emitters can be used for flat panel displays,

high-current cathodes for microwave tubes, and elec-tron sources for electron microscopes. However, theemission properties of the CNT should be character-ized and compared to other commercially fabricatedemitters.

Results presented on nanotubes as probes inscanning probe microscopes are encouraging. Somemembers from semiconductor community expresseddoubts about the potential of scanning probe lithogra-phy in general. Nevertheless, a parallel array of highresolution probes (50 tips), reported at the workshop,represents an interesting and possible breakthroughtechnology for addressing sub-50 nm metrology andlithography issues. Today attachment of an indivi-dual CNT to a cantilever on a scanning probe repre-sents a significant challenge. The possibility to createa chemically sensitive nanoscope was also discussed.This would be extremely important for diagnosticsand addressing nanodevices and components. Amonglonger term research opportunities, the following issueswere addressed: full-carbon-electronics (and bioelec-tronics); self-assembly of nanotubes; optical propertiesand optoelectronic applications; design architecture fornanotube circuitry.

Contact organizers Dan Herr (herr@src.org)or M. Meyyappan (meyya@orbit.arc.nasa.gov) forfurther information or workshop report or seehttp://www.src.org.A topical conference with the sametitle as this workshop is scheduled for the AmericanVacuum Society Annual Meeting in Seattle on October25, 1999.