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 lishi@mail.utexas.edu

Outline Cantilever Thermal Sensors: Thermal Property of Nanotubes and Nanowires Scanning Thermal Microscopy Cantilever Bio Sensors Cantilever IR Sensors

Silicon Nanoelectronics Gate Source Drain Nanowire Channel Courtesy: C. Hu et al., Berkeley

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

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)

Silicon Nanowires Increased boundary scattering  Suppressed thermal conductivity  Localized hot spots Bulk Si: k ~150 W/m-K Diameter: Li, et al.

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

Carbon Nanotubes Single Wall Multiwall Super high current 109 A/cm2 -- Semiconducting or Metallic microns 1-2 nm Multiwall -- Metallic 10 nm

Thermal Conductivity of Nanotubes Strong SP2 bonding (high v), few scattering (long l)  high k Theory: 3000 ~ 6000 W/m-K at RT (e.g. Berber et al., 2000)

A Cantilever Sensor for Thermal Sensing of Nano- Wires/Tubes Suspended SiNx Membrane Long SiNx Cantilever Pt Resistance Heater/Thermometer

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

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

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, 215502-1 (2001)

Thermopower For metals w/ hole-type majority carriers:  T

Single Wall Carbon Nanotubes

Bi2Te3 Nanowire High-efficiency refrigerators!

Outline Cantilever Thermal Sensors: Thermal Property of Nanotubes and Nanowires Scanning Thermal Microscopy Cantilever Bio Sensors Cantilever IR Sensors

Molecular Electronics Nanotube Interconnect (Dai et al., Stanford) TubeFET (McEuen et al., Berkeley) Nanotube Logic (Avouris et al., IBM)

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

Dissipation in Nanotubes bulk Electrode Electrode Junction Diffusive – Bulk Dissipation T T profile  diffusive or ballistic X Ballistic – Junction Dissipation T X

Thermal Microscopy Techniques Spatial Resolution Infrared Thermometry 1-10 mm* Laser Surface Reflectance 1 mm* Raman Spectroscopy 1 mm* Liquid Crystals 1 mm* Near-Field Optical Thermometry < 1mm Scanning Thermal Microscopy (SThM) < 100 nm *Diffraction limit for far-field optics

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

Thermal Probe Rts Rt Ts Ta Tt Rc Q

Probe Fabrication 200 nm Pt SiO2 1 mm SiO2 tip

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)

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

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. 4295 (2000)

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

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

Outline Cantilever Thermal Sensors: Thermal Property of Nanotubes and Nanowires Scanning Thermal Microscopy Cantilever Bio Sensors Cantilever IR Sensors

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

Chemo-mechanical database: PSA Prostate-specific antigen (PSA) Important levels are ~1-10 ng/mL (30-300 pM) 30-34 kDa => 4-10 ng/mL <--> 100-300 pM  ~ 5 - 10 mJ/m2, independent of cantilever geometry.

Multiplexing Why? Throughput Differential Signal Molecular Profile 1 laser 1 detector CCD A B N lasers, N detectors.

Outline Cantilever Thermal Sensors: Thermal Property of Nanotubes and Nanowires Scanning Thermal Microscopy Cantilever Bio Sensors Cantilever IR Sensors (See PowerPoint File 2)