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ME 381R Fall 2003 Micro-Nano Scale Thermal-Fluid Science and Technology Lecture 11: Thermal Property Measurement Techniq

ME 381R Fall 2003 Micro-Nano Scale Thermal-Fluid Science and Technology Lecture 11: Thermal Property Measurement Techniques For Thin Films and Nanostructures. Dr. Li Shi Department of Mechanical Engineering The University of Texas at Austin Austin, TX 78712 www.me.utexas.edu/~lishi

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ME 381R Fall 2003 Micro-Nano Scale Thermal-Fluid Science and Technology Lecture 11: Thermal Property Measurement Techniq

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  1. ME 381R Fall 2003 Micro-Nano Scale Thermal-Fluid Science and Technology Lecture 11: Thermal Property Measurement Techniques For Thin Films and Nanostructures Dr. Li Shi Department of Mechanical Engineering The University of Texas at Austin Austin, TX 78712 www.me.utexas.edu/~lishi lishi@mail.utexas.edu

  2. Outline • Thermal Property Measurements: • Thin films • Nanowires and Nanotubes • Reading: Ch2 in Tien et al

  3. Thin Film Thermal Conductivity Measurement The 3w method Cahill, Rev. Sci. Instrum. 61, 802 (1990) Metal line Thin Film L 2b V • I~ 1w • T ~ I2 ~ 2w • R ~ T ~ 2w • V~ IR ~3w I0 sin(wt) Substrate Substrate contribution Film contribution

  4. Data Analysis • Dotted line - Ts+  Tf • Solid line -  Ts • Slope of solid line  ks • Tf  kf

  5. Thermal Conductivity of Thin Si Films (M.Asheghi,etc.,1997) Size effect on the conductivity can exceed two orders of magnitude for layers of thickness near 1 m at T<10k.

  6. Silicon on Insulator (SOI) Ju and Goodson, APL 74, 3005 IBM SOI Chip Lines: BTE results Hot spots!

  7. Thin Film Superlattices SiGe superlattice (Shakouri, UCSC) • Increased phonon-boundary scattering • decreased k • + other size effects  Highthermoelectric figure of merit(ZT = S2sT/k) Ge Quantum well (QW) Si Barrier

  8. Thermal Conductivity of Si/Ge Superlattices k (W/m-K) Bulk Si0.5Ge0.5 Alloy Circles: Measurement by D. Cahill’s group Lines: BTE / EPRT results by G. Chen Period Thickness (Å)

  9. Anisotropic Polymer Thin Films Ju, Kurabayashi, Goodson, Thin Solid Films 339, 160 (1999) • By comparing temperature rise of the metal line for different line • width, the anisotropic thermal conductivity can be deduced

  10. Nanowires • Si Nanowires for Electronic Applications • Bi Nanowires for TE Cooling (Dresselhaus et al., MIT) Top View Al2O3 template • Boundary scattering + modified phonon dispersion (group velocity): •  Suppressed thermal conductivity Volz and Chen, Appl. Phys. Lett. 75, 2065 (1999)

  11. The 3w method for Nanowires -- Lu, Yi, Zhang, Rev. Sci. Instrum. 72, 2996 (2001) • Low frequency: V(3w) ~ 1/k • High frequency: V(3w) ~ 1/C • Tested for a 20 mm dia. Pt wire V I0 sin(wt) Electrode Wire Substrate • Conditions: • The sample needs to have a large temperature coefficient of resistance TCR= (dR/dT)/R • The electrical contact has to be perfect

  12. Q I Themal conductance: G = Q / (Th-Ts) Thermal Measurements of Nanotubes and Nanowires Suspended SiNx membrane Long SiNx beams Pt resistance thermometer Kim et al,PRL 87, 215502 Shi et al, JHT, in press

  13. (c) Lithography Device Fabrication Photoresist (a) CVD SiNx SiO2 (d) RIE etch Si (b) Pt lift-off Pt (e) HF etch

  14. Nanowires 22 nm diameter Si nanowire, P. Yang, Berkeley • Increased phonon-boundary scattering • Modified phonon dispersion •  Suppressed thermal conductivity • Ref: Chen and Shakouri, J. Heat Transfer 124, 242 Hot p Cold

  15. Si Nanotransistor (Berkeley Device group) Si Nanowires Gate Drain Source Nanowire Channel D. Li et al., APL Symbols: Measurements Lines: Modified Callaway Method Hot Spots in Si nanotransistors!

  16. Nanotube Nanoelectronics TubeFET (McEuen et al., Berkeley) Nanotube Logic (Avouris et al., IBM)

  17. Thermal Transport in Carbon Nanotubes Hot Cold p • Few scattering: long mean free path l • Strong SP2 bonding: high sound velocity v •  high thermal conductivity:k = Cvl/3~ 6000 W/m-K Heat capacity

  18. Thermal Conductivity of Carbon Nanotubes CVD SWCN CNT • An individual nanotube has a high k ~ 2000-11000 W/m-K at 300 K • k of a CN bundleis reduced by thermal resistance at tube-tube junctions

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