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

2

Outline• Cantilever Thermal Sensors:

Thermal Property of Nanotubes and Nanowires

• Cantilever Thermal Sensors:

Scanning Thermal Microscopy

• Cantilever Bio Sensors

• Cantilever IR Sensors

3

Source Drain

Gate

Nanowire Channel

Silicon Nanoelectronics

Courtesy: C. Hu et al., Berkeley

4

Length Scale

1 m

1 nm

MEMS Devices

Size of a Microprocessor

Nanowire Diameter

100 nml (Phonon mean freepath at RT)

1 ÅAtom

L

W l: boundary scattering - +-W

Thin Film Thickness in ICs

10 nm

Lattice vibration

5

Thermal Conductivity

k = C v l13

Specific heat Sound velocityPhonon Mean Free path

umst lll111 Mean free path:

Static scattering (phonon -- defect, boundary)

Umklapp phonon scattering

6

0

10

20

30

40

50

60

0 40 80 120 160 200 240 280 320 360

0

10

20

30

40

50

60

0 40 80 120 160 200 240 280 320 360

Temperature (K)

The

rmal

Con

duct

ivity

(W

/m-K

)

30nm

56nm

115nm

Silicon NanowiresIncreased boundary scattering Suppressed thermal conductivity

Localized hot spots

Li, et al.

Bulk Si: k ~150 W/m-K

Diameter:

7

Thermoelectric Nanowires

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

I

Cold

Hot

P N

TE Cooler

Thermoelectric Figure of Merit: ZT = S2Tk

8

Carbon Nanotubes

Single Wall -- Semiconducting or Metallic

Super high current109 A/cm2

1-2 nmmicrons

Multiwall -- Metallic

10 nm

9

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)

10

Pt Resistance Heater/Thermometer

Suspended SiNx Membrane

Long SiNx Cantilever

A Cantilever Sensor for Thermal Sensing of Nano- Wires/Tubes

11

Measurement Scheme

14 nm multiwall tube

Island

Beam

Pt heater line

Th Ts

t Ts

R s

Rh Qh=IRh

Tube

Ql=IRl

Environment

T0 I

Gt = kA/L

sh

s

sh

lht TT

TT

TTT

QQG

0

02

Thermal Conductance:

VTE

Thermopower:Q = VTE/(Th-Ts)

12

Device Fabrication

Si

SiO2

SiNx

Pt

Photoresist(a) CVD

(b) Pt lift-off

(c) Lithography

(d) RIE etch

(e) HF etch

13

0

500

1000

1500

2000

2500

3000

3500

0 100 200 300 400

Temperature (K)

Th

erm

al

Co

nd

uc

tiv

ity

(W

/m-K

)

Thermal Conductivity

• Room temperature thermal conductivity ~ 3000 W/m-K

• k ~ T2 : Quasi 2D graphene behavior at low temperatures

• Umklapp scattering ~ 320 K , l ~ 0.5 m

l ~ 0.5 m~T2

Kim, Shi, Majumdar, McEuen, Phy. Rev. Lett 87, 215502-1 (2001)

14 nm multiwall tube

14

Thermopower100

80

60

40

20

030025020015010050

Ts

Th

erm

opow

er (V

/K)

Temperature (K)

F

B

eETk

Q6

22

For metals w/ hole-type majority carriers:

T

15

Single Wall Carbon Nanotubes

Nanotube

16

Bi2Te3 Nanowire High-efficiency refrigerators!

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Outline

• Cantilever Thermal Sensors:

Thermal Property of Nanotubes and Nanowires

• Cantilever Thermal Sensors:

Scanning Thermal Microscopy

• Cantilever Bio Sensors

• Cantilever IR Sensors

18

Molecular Electronics

TubeFET (McEuen et al., Berkeley)

Nanotube Logic (Avouris et al., IBM)

Nanotube Interconnect(Dai et al., Stanford)

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Electron Transport in Nanotubes

- +- - +-

Ballistic (long mfp) Diffusive (short mfp)

mfp: electron mean free path

MultiwallBallistic (Frank et al., 1998)Diffusive (Bachtold et al., 2000)

Single Wall MetallicBallistic at low bias (Bachtold ,et al.)Diffusive at high bias (Yao et al., 2000)

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Dissipation in Nanotubes

Nanotube bulk Electrode

Electrode

Diffusive – Bulk Dissipation

Ballistic – Junction Dissipation

Junction

X

X

T

T

T profile diffusive or ballistic

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Thermal Microscopy

Infrared Thermometry 1-10 m*

Laser Surface Reflectance 1 m*

Raman Spectroscopy 1 m*

Liquid Crystals 1 m*

Near-Field Optical Thermometry < 1m

Scanning Thermal Microscopy (SThM) < 100 nm

Techniques Spatial Resolution

*Diffraction limit for far-field optics

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X-Y-Z Actuator

Scanning Thermal Microscope

Sample

Temperature Sensor

Laser

Atomic Force Microscope (AFM) + Thermal Probe

CantileverDeflectionSensing

Thermal

X

TTopographic

X

Z

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Thermal Probe

Tip

Solid-Solid Conduction

Liquid-Film Conduction

Air Conduction

Radiation

Cantilever Cantilever Mount

Liquid

Cr Pt SiO2

Sample

Substrate

Sample

Rts

Rt

Ts

Ta

Tt

Rc

Q

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Probe Fabrication

1 m

SiO2 tip

Si

SiO2

SiNx

Photoresist Cr

Cr

RIE+HF Etch

200 nm

Pt SiO2

SiO2

Pt

Pt

CrSiO2

Photoresist

Pt

100~500 nm

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Microfabricated Probes

Pt-Cr Junction

Shi, Kwon, Miner, Majumdar, J. MicroElectroMechanical Sys., 10, p. 370 (2001)

10 m

Pt Line

Cr Line

TipLaser Reflector

SiNx Cantilever

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Locating Defective VLSI Via

• Collaboration: TI• Shi et al., Int. Reli. Phys. Sym., p. 394 (2000)Metal 1

DielectricMetal 2

Passivation

0.4 m Via

Cross Section

Topography Tip Temperature Rise (K)

20 m

2823

21

19

25

Met

al 2

ViaMetal 1

40 mA

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Thermal Imaging of Nanotubes Multiwall Carbon Nanotube

1 m

Topography

1 m

Topography

3 V88 A

Distance (nm)

Th

erm

al s

ign

al ( V

) 30

20

10

0

4002000-200-400

50 nm

Distance (nm)

Hei

ght

(nm

)

30 nm

10

5

0

4002000-200-400

Distance (nm)

Hei

ght

(nm

)

30 nm

10

5

0

4002000-200-400

Thermal

30 nm 50 nm

Shi, Plyosunov, Bachtold, McEuen, Majumdar, Appl. Phys. Lett., 77, p. 4295 (2000)

Spatial Resolution

28

20

10

0

210

Distance (m)

Tti

p(K

)

-40

-20

0

20

40

10000-1000

Bias voltage (mV)

Cur

rent

(A

)

1 m

Multiwall NanotubeTopographic

Thermal

A B Ttip

3 K

0

•Diffusive at low and high biases

AB A

B

Shi, Kim, et al.

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Metallic Single Wall Nanotube

-20

0

20

200010000-1000-2000

Bias voltage (mV)

Cu

rren

t (

A)

AB C D

Bias voltage (mV)

Cu

rren

t (

A)

AB C D

Topographic Thermal

1 m

A B C D

Optical phonon Low bias: ballistic

contact dissipation

High bias: diffusive

bulk dissipation

Ttip

2 K

0

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Outline

• Cantilever Thermal Sensors:

Thermal Property of Nanotubes and Nanowires

• Cantilever Thermal Sensors:

Scanning Thermal Microscopy

• Cantilever Bio Sensors

• Cantilever IR Sensors

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Detecting BiomoleculesConventional: Fluorescence

add sample

probes

wash, add marker,wash

• Surface stress

• Fewer steps

• Label - free

deflection

A B

New: Micro-cantilever

~500 m

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Chemo-mechanical database: PSA

-20

0

20

40

60

80

0.001 0.1 10 1000 100000

fPSA concentration [ng/mL]

[

mJ/

m2]

Wu et al, Nature Biotech. 19, 856-860 (2001).

~ 5 - 10 mJ/m2, independent of cantilever geometry.

• Prostate-specific antigen (PSA)

• Important levels are ~1-10 ng/mL (30-300 pM)

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MultiplexingWhy?

Throughput

Differential Signal

Molecular Profile

A B

N lasers,

N detectors.

• 1 laser

• 1 detector

CCD

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Outline

• Cantilever Thermal Sensors:

Thermal Property of Nanotubes and Nanowires

• Cantilever Thermal Sensors:

Scanning Thermal Microscopy

• Cantilever Bio Sensors

• Cantilever IR Sensors (See PowerPoint File 2)