Realizing a Low Noise Amplifier with Carbon Nanotube Technology Kristen N. Parrish May 3, 2010

What is a CNFET? Carbon Nanotube Field Effect Transistor Semiconducting CNT channel Fig 1 [1] Fig 2 [2]

An exciting new field… but why do we care? Ballistic operation Better for this than CMOS – higher mean free path, less short-channel effects Improved conductivity, mobility, transconductance, high frequency operation THz performance predicted Complimentary to existing CMOS technology Continue scaling trends (Moore’s Law) Nanoscale dimensions Fig 3 [3]

LNA Metrics of Evaluation Low Noise Amplifier High ft and fmax High gain Sufficient current output Low noise at RF Fig 4. Standard Inductively Degenerated LNA Topology

Channel Fabrication Most common today is CVD Chemical Vapor Deposition – ‘grow’ CNTs Can have a single CNT channel 22 uS with d=2nm Unfortunately, occurs in ‘off’ mode Solution: increase width Fig 5 [4]

Channel Fabrication Increase width to take advantage of high densities Semiconducting and metallic types 1/3 are metallic Lose gate control Solutions Burn off metal CNTs Chemical control Fig 6 [5]

Parasitics/Contacts (Capacitances & Resistances) Problems: Contact resistance High Cpd/Cps Fig 7 [3] Solutions: Decrease length Decrease metal areas Fig 8 [6]

DC Characteristics Max reported gm currently ~50 𝜇𝑆/nanotube Current output is low low on/off ratio Current/gain tradeoff Improvements from Increasing array purity Increasing array density (CNT spacing) Channel length & parasitic resistance

Transit & Max Frequency Limited by parasitic capacitances Still approaching THz Fig 9 [1] Fig 10 [5]

Noise Has not been characterized to GHz frequencies for CNFET Have observed for CNTs: Thermal: only dependent on resistance; limited by length Flicker: 1/f; not generally a concern for high frequencies Shot: orders of magnitude smaller than other contributions; makes ballistic transport more desirable Fig 11 [7] Fig 12 [8]

Conclusions Solutions What we want: Why aren’t we there yet? Smaller channel length Improved arrays (purer, denser) New topologies (self alignment, introduce gate fingers, etc) What we want: Ohmic contacted Ballistic CNFETs with a dense self-aligned array of identical semiconducting nanotubes Why aren’t we there yet?

Thank you! Questions?

References C. Rutherglen, D. Jain, and P. Burke, “Nanotube electronics for radiofrequency applications,” Nature Nanotechnology, 2009 H.-S. P. Wong and D. Akinwande, Carbon Nanotube Device Physics. Cambridge General Academic, 2010 J. Guo, S. Hasan, A. Javey, G. Bosman, and M. Lundstrom, “Assessment of high-frequency performance potential of carbon nanotube transistors,” IEEE transactions on nanotechnology, vol. 4, no. 6, pp. 715–721, 2005. J. Chaste, L. Lechner, P. Morfin, G. Feve, T. Kontos, J. Berroir, D. Glattli, H. Happy, P. Hakonen, and B. Placais, “Single carbon nanotube transistor at GHz frequency,” Nano Letters, vol. 8, no. 2, pp. 525–528, 2008 C. Kocabas, H. Kim, T. Banks, J. Rogers, A. Pesetski, J. Baumgardner, S. Krishnaswamy, and H. Zhang, “Radio frequency analog electronics based on carbon nanotube transistors,” Proceedings of the National Academy of Sciences, vol. 105, no. 5, p. 1405, 2008 D. Akinwande, G. Close, and H. Wong, “Analysis of the frequency response of carbon nanotube transistors,” IEEE transactions on nanotechnology, vol. 5, no. 5, pp. 599–605, 2006. P. Collins, M. Fuhrer, and A. Zettl, “1/f noise in carbon nanotubes,” Applied Physics Letters, vol. 76, p. 894, 2000. P. Roche, M. Kociak, S. Gu´eron, A. Kasumov, B. Reulet, and H. Bouchiat, “Very low shot noise in carbon nanotubes,” The European Physical Journal B, vol. 28, no. 2, pp. 217–222, 2002. V. Dimitrov, J.B. Heng, K. Timp, O. Dimauro, R. Chan, M. Hafez, J. Feng, T. Sorsch, W. Mansfield, J. Miner, A. Kornblit, F. Klemens, J. Bower, R. Cirelli, E.J. Ferry, A. Taylor, M. Feng, G. Timp, Small-signal performance and modeling of sub-50 nm nMOSFETs with fT above 460-GHz, Solid-State Electronics, Volume 52, Issue 6, June 2008