Organization of Nanowire Arrays for Integrated Nanosystems

Presenter: Octavian Florescu

Authors: Lieber group

Department of Chemistry and Chemical Biology, Harvard University

Outline

• Organization of nanowires– Why is it important?– Criteria for organization

• Methodology• Results• Conclusions

Organizing Nanowires

• Why?– Critical to the realization of integrated electronics, photonics and

sensors• Criteria for organization

– Controllability– Yield– Reproducibility– Reliability– Cost

Controlled Growth of Nanowires

• p or n-SiNW with good diameter distribution were grown by VLS

– Substrate was oxidized silicon

– Catalyst was Au nanoparticls

– Reactant was silane

Cui et al., APPL. PHYS. LETT VOL. 78, NO 15

Deposition of Nanowire Arrays on Substratea) SiNW are suspended

using a surfactant in nonpolar solvent.

Compressed in a Langmuir-Blodgett trough. Compression determines center to center spacing.

b) SiNW transferred onto Si substrate.

Whang et al., NANO LETTERS 2003, Vol. 3, No. 9, 1255-1259

Deposition Results

• 200nm to 2um pitch realizable

• Decent control of the periodicity and wire width

• Can cover over 20cm2 in area.

Whang et al., NANO LETTERS 2003, Vol. 3, No. 9, 1255-1259

Finer Deposition …

• In this scenario SiNW are coated with a sacrificial layer and are compressed until they touch.

• Can be used as a mask for deposition of metal NW.

Whang et al., NANO LETTERS 2003, Vol. 3, No. 9, 951-954

Finer Deposition Results

• 90nm pitch was produced with 40nm linewidth

• Control of both pitch and linewidth– In this case pitch

independent of LB compression

Whang et al., NANO LETTERS 2003, Vol. 3, No. 9, 951-954

Integration with Electronics

a) Electrodes with same pitch as SiNW align well with the nanowires

b) PL used to pattern active areas containing SiNW

Electrodes deposited over SiNW active areas

Jin et al., NANO LETTERS, 2004, Vol. 4, No. 5

915-919

Realization

• 80% of the 3000 electrodes are bridged by SiNWs

• Can be combined with NIL, EUV to generate very dense arrays of electrodes

Whang et al., NANO LETTERS 2003, Vol. 3, No. 9, 951-954

Electrical Performance

• gm = 1250nA/V• Ion/Ioff = 107

• Ssubthreshold = 160mV/decade• μ = 307cm2/V*s

Whang et al., NANO LETTERS 2003, Vol. 3, No. 9, 951-954

Another Realization

• Size of FET depends on the spacing between SiNWs, which depends on the LB compression.

• Decent control of VTH

Whang et al., NANO LETTERS 2003, Vol. 3, No. 9, 951-954

Conclusions• Good

– 80% device yield– Inexpensive– Reproducible (?)

• Bad– Low gain

• Unknown– Controllability of device characteristics– Reliability

• Not suitable yet for ICs but can be interesting for use in thin film electronics and as transducers.

Thank you!