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Micro-Nano Thermal-Fluid:
Physics, Sensors, Measurements Cantilever Sensors: An Example of what you will learn in ME 381R Prof. Li Shi Micro-Nano Thermal-Fluid Laboratory Department of Mechanical Engineering The University of Texas at Austin
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Outline Cantilever Thermal Sensors:
Thermal Property of Nanotubes and Nanowires Scanning Thermal Microscopy Cantilever Bio Sensors Cantilever IR Sensors
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Silicon Nanoelectronics
Gate Source Drain Nanowire Channel Courtesy: C. Hu et al., Berkeley
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Length Scale - + Size of a Microprocessor MEMS Devices 1 mm
Lattice vibration 1 mm Thin Film Thickness in ICs 100 nm l (Phonon mean free path at RT) 10 nm Nanowire Diameter 1 nm Atom L W l: boundary scattering - + W 1 Å
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Thermal Conductivity k = C v l 1 3 Phonon Mean Free path Specific heat
Sound velocity Mean free path: Umklapp phonon scattering Static scattering (phonon -- defect, boundary)
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Silicon Nanowires Increased boundary scattering Suppressed thermal conductivity Localized hot spots Bulk Si: k ~150 W/m-K Diameter: Li, et al.
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Thermoelectric Nanowires
TE Cooler Hot I Thermoelectric Figure of Merit: ZT = S2Ts / k N P Bi or Bi2Te3 nanowires (Dresselhaus et al., MIT): Top View Al2O3 template Smaller d, shorter boundary scattering mfp Lowered thermal conductivity k = Cvl/3 High ZT, high COP Cold
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Carbon Nanotubes Single Wall Multiwall Super high current 109 A/cm2
-- Semiconducting or Metallic microns 1-2 nm Multiwall -- Metallic 10 nm
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Thermal Conductivity of Nanotubes
Strong SP2 bonding (high v), few scattering (long l) high k Theory: ~ 6000 W/m-K at RT (e.g. Berber et al., 2000)
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A Cantilever Sensor for Thermal Sensing of Nano- Wires/Tubes
Suspended SiNx Membrane Long SiNx Cantilever Pt Resistance Heater/Thermometer
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Measurement Scheme Gt = kA/L Thermal Conductance: I
Q I R h = h R t R h s VTE Thermopower: Q = VTE/(Th-Ts) T u be Q = IR l l Environment I T 14 nm multiwall tube Island Beam Pt heater line
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Device Fabrication (c) Lithography Photoresist (a) CVD SiNx SiO2
(d) RIE etch (b) Pt lift-off Pt (e) HF etch
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Thermal Conductivity ~T2 l ~ 0.5 mm 14 nm multiwall tube
Room temperature thermal conductivity ~ 3000 W/m-K k ~ T2 : Quasi 2D graphene behavior at low temperatures Umklapp scattering ~ 320 K , l ~ 0.5 mm Kim, Shi, Majumdar, McEuen, Phy. Rev. Lett 87, (2001)
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Thermopower For metals w/ hole-type majority carriers: T
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Single Wall Carbon Nanotubes
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Bi2Te3 Nanowire High-efficiency refrigerators!
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Outline Cantilever Thermal Sensors:
Thermal Property of Nanotubes and Nanowires Scanning Thermal Microscopy Cantilever Bio Sensors Cantilever IR Sensors
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Molecular Electronics
Nanotube Interconnect (Dai et al., Stanford) TubeFET (McEuen et al., Berkeley) Nanotube Logic (Avouris et al., IBM)
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Electron Transport in Nanotubes
Ballistic (long mfp) Diffusive (short mfp) - - + + - - mfp: electron mean free path Ballistic (Frank et al., 1998) Diffusive (Bachtold et al., 2000) Multiwall Ballistic at low bias (Bachtold ,et al.) Diffusive at high bias (Yao et al., 2000) Single Wall Metallic
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Dissipation in Nanotubes
bulk Electrode Electrode Junction Diffusive – Bulk Dissipation T T profile diffusive or ballistic X Ballistic – Junction Dissipation T X
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Thermal Microscopy Techniques Spatial Resolution
Infrared Thermometry mm* Laser Surface Reflectance mm* Raman Spectroscopy mm* Liquid Crystals mm* Near-Field Optical Thermometry < 1mm Scanning Thermal Microscopy (SThM) < 100 nm *Diffraction limit for far-field optics
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Scanning Thermal Microscope
Atomic Force Microscope (AFM) + Thermal Probe Laser Deflection Sensing Cantilever Temperature Sensor Thermal X T Sample Topographic X Z X-Y-Z Actuator
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Thermal Probe Rts Rt Ts Ta Tt Rc Q
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Probe Fabrication 200 nm Pt SiO2 1 mm SiO2 tip
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Microfabricated Probes
10 mm Pt Line Pt-Cr Junction Tip Laser Reflector SiNx Cantilever Cr Line Shi, Kwon, Miner, Majumdar, J. MicroElectroMechanical Sys., 10, p. 370 (2001)
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Locating Defective VLSI Via
Topography Tip Temperature Rise (K) 19 21 40 mA Via Metal 1 23 28 25 Metal 2 20 mm Cross Section Passivation Metal 2 Collaboration: TI Shi et al., Int. Reli. Phys. Sym., p. 394 (2000) Dielectric 0.4 mm Via Metal 1
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Thermal Imaging of Nanotubes
Multiwall Carbon Nanotube Distance (nm) Height (nm) 30 nm 10 5 400 200 -200 -400 Thermal Topography Topography 3 V 88 m A 1 1 m m m m Spatial Resolution V) 30 20 10 400 200 -200 -400 m 30 nm 50 nm 50 nm Thermal signal ( Distance (nm) Shi, Plyosunov, Bachtold, McEuen, Majumdar, Appl. Phys. Lett., 77, p (2000)
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Multiwall Nanotube Thermal Topographic DTtip A B 3 K 1 mm
Shi, Kim, et al. Thermal Topographic DTtip A B 3 K 1 mm Diffusive at low and high biases B A A B
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Metallic Single Wall Nanotube
Low bias: ballistic contact dissipation High bias: diffusive bulk dissipation Optical phonon Topographic Thermal DTtip A B C D 2 K 1 mm
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Outline Cantilever Thermal Sensors:
Thermal Property of Nanotubes and Nanowires Scanning Thermal Microscopy Cantilever Bio Sensors Cantilever IR Sensors
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Detecting Biomolecules
Conventional: Fluorescence New: Micro-cantilever ~500 m probes A B deflection add sample Surface stress Fewer steps Label - free wash, add marker, wash
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Chemo-mechanical database: PSA
Prostate-specific antigen (PSA) Important levels are ~1-10 ng/mL ( pM) 30-34 kDa => 4-10 ng/mL <--> pM ~ mJ/m2, independent of cantilever geometry.
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Multiplexing Why? Throughput Differential Signal Molecular Profile
1 laser 1 detector CCD A B N lasers, N detectors.
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Outline Cantilever Thermal Sensors:
Thermal Property of Nanotubes and Nanowires Scanning Thermal Microscopy Cantilever Bio Sensors Cantilever IR Sensors (See PowerPoint File 2)
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