Stretchable and Flexible Stretchable and Flexible Silicon Silicon- - - PowerPoint PPT Presentation

Stretchable and Flexible Stretchable and Flexible Silicon Silicon-

• based Solar Cell Arrays

based Solar Cell Arrays

• Y. Huang
• Depts. of Civil and Environmental Eng. and Mechanical Eng.

Northwestern University Collaborator: J.A. Rogers (University of Illinois)

Challenges and Objectives Challenges and Objectives Challenges and Objectives Challenges and Objectives

90% of solar cells are made of Si 90% of solar cells are made of Si. Si has good efficiency and reliability. Si is brittle, and fractures at 1% strain.

Si panel can only be placed at roof top Si panel can only be placed at roof top

Si panel can only be placed at roof top, …

Si panel can only be placed at roof top, … Objectives: Objectives:

Make Si stretchable Investigate the mechanics issues Seek innovative applications (e g e-eye camera Seek innovative applications (e.g., e eye camera,

flexible solar cell, cardiac electrophysiology, …)

News agencies: United Press I t ti l International,

…

Display at the p y Tech Museum

• f Innovation,

Silicon Valley, California

Khang, Jiang, Huang, and Rogers, Science 311, 2006

Wavy Silicon Structures Wavy Silicon Structures Wavy Silicon Structures Wavy Silicon Structures

L dL L dL

pre =

ε PDMS Si PDMS ε

mother wafer: Si

Fabricate thin ribbon Si device elements Bond elements to prestrained elastomeric substrate PDMS Peel back PDMS; flip over

pre

ε

Si device elements elastomeric substrate PDMS flip over

Flat Si ribbon becomes buckled due to prestrained PDMS

Spring vs Straight Wire Spring vs Straight Wire Spring vs. Straight Wire Spring vs. Straight Wire

Wavy Silicon: Experimental Images Wavy Silicon: Experimental Images Wavy Silicon: Experimental Images Wavy Silicon: Experimental Images

Scanning electron micrograph Optical image

Periodic wavy structures

Initial Buckling Analysis Initial Buckling Analysis

1

pre

h A ε

% 9 . =

pre

ε Khang, Jiang, Huang, Rogers, Science, 2006

Si

h π λ = 1 − =

c pre Si

h A ε

1 0 1.5 e (μm) % 9 .

pre

ε

independent of pre strain

c

ε λ =

0.5 1.0 Amplitude

3 2

3 1 ⎟ ⎟ ⎞ ⎜ ⎜ ⎛

PDMS

E ε

iti l t i f

• -- independent of pre-strain

1 − =

pre

h A ε

0.0 A 60

μm)

4 ⎟ ⎟ ⎠ ⎜ ⎜ ⎝ =

Si PDMS c

E ε

• -- critical strain for

buckling

1 − =

c Si

h A ε

20 40 elength (μ

h

200 400 20 Wave

c Si

h ε π λ =

Si thickness (nm)

Excellent agreement with experiments

without any fitting parameters.

Stretchable Silicon at The Tech San Jose CA Stretchable Silicon at The Tech, San Jose, CA

Electronic Eye Camera Electronic Eye Camera Electronic Eye Camera Electronic Eye Camera

TV Networks: ABC, BBC, CBC, MSNBC, … News agencies: AFP (France), Reuters, United Press International, Xinhua, … Newspapers: Chicago T ib D il T l h Tribune, Daily Telegraph (UK), … Magazines: Discover g Magazine, MIT Technology Review, Nature News & Views, Scientific American, U.S. News and World Report, …

Ko et al., Nature 454, 2008

NSF Press Release

Fabrication Steps Fabrication Steps

compressed interconnect ~1 cm compressed interconnect ~1 cm form hemispherical PDMS transfer element ~1 cm adhesive adhesive radially stretch PDMS form Si focal plane array and release from underlying wafer substrate cure adhesive; flop over substrate cure adhesive; flop over substrate integrate optics & interconnect to control electronics to complete the device integrate optics & interconnect to control electronics to complete the device compressible interconnect transfer focal plane array onto PDMS hemispherical focal plane array hemispherical focal plane array Si device island (photodetector & pn diode)

Ko et al., Nature 454, 2008

Pop Up Si Structure: Experimental Images Pop Up Si Structure: Experimental Images Pop Up Si Structure: Experimental Images Pop Up Si Structure: Experimental Images

Scanning electron micrograph

The interconnects buckle to form “big wave” structure.

Ko et al., Nature 454, 2008

Pop Up Structure: Results Pop Up Structure: Results Pop Up Structure: Results Pop Up Structure: Results

• 4

10 ε ×

8

yy

ε

• 4

10 ε ×

8

yy

ε

8 6 4

yy

8 6 4

yy

( )

2 3 max 2

1 2

island bridge bridge island pre

E h E h L ν ε π ε − ≈

2

• 2

xx

ε

2

• 2

xx

ε

island island bridge

E h L

20 μm

• 2

y

20 μm

• 2

y

17.5 μm

x

17.5 μm

x

10 μm 10 μm

The island remains almost flat and experiences small strains. The shape of interconnects agrees well with experiments.

Electronics on complex surfaces Electronics on complex surfaces Electronics on complex surfaces Electronics on complex surfaces

Stretchable Circuits (Science 2008) ( )

• Stretchability: up to 140%
• Twistability

Twistability

TV Networks: BBC, CBC, … Magazines: Discover Magazine, MIT Technology

(PNAS 2008)

g g , gy Review, Newsweek, Scientific American, … NSF Press Release

Bendable and Transparent Silicon Photovoltaic Devices (Nature Materials 2008)

• User-definable transparency
• High degrees of mechanical flexibility
• Ultra-thin form factor micro-concentrator design
• Excellent reliability
• Good efficiency
• Inexpensive

TV Networks: ABC, MSNBC, … News agencies: Reuters, Xinhua, … Newspapers: New York Times, People’s Daily…

(Nature Materials 2006)

Magazines: MIT Technology Review, Nature News & Views, Scientific American, … Department of Energy Press Release

Microscale, Inorganic Light Emitting Diode (iLED) Microscale, Inorganic Light Emitting Diode (iLED)

• Advantages: flexible high brightness

(Science 2009)

TV N t k ABC BBC MSNBC

• Advantages: flexible, high brightness,

long lifetime, bidirectional emission, inexpensive.

li i

bl h l h i

TV Networks: ABC, BBC, MSNBC, … News agencies: Reuters, … Newspapers: Boston Globe New York

• Applications: wearable health monitor

and diagnostics, biomedical imaging devices, ...

Newspapers: Boston Globe, New York Times, … Magazines: MIT Technology Review, …

Cardiac/Neural Electrophysiology Cardiac/Neural Electrophysiology (Science, 2010; Science Translational Medicine, 2010; Nature

1 cm 75μm 25μm

( , ; , ; Materials, 2010)

unwrapped unwrapped 2.8μm unwrapped 7.0μm 2.8μm unwrapped wrapped wrapped 0.3 cm 75μm wrapped

Health monitoring and human- electronics i t ti interaction

Conclusions and Recent Publications Conclusions and Recent Publications Conclusions and Recent Publications Conclusions and Recent Publications

• - Mechanics plays an important role in the

d l f fl ibl d h bl h l i

JMPS (2008, 2009, 2010)

development of flexible and stretchable technologies. ( )

Nano Letters (2007, 2008, 2009a,b, 2010) Nature (2008) Nature (2008) Nature Materials (2006, 2008, 2010) Nature Nanotechnology (2006) PNAS (2007, 2008, 2009)

( )

PRL (2010) Science (2006 2008 2009 2010) Science (2006, 2008, 2009, 2010) Science Translational Medicine (2010)

Cover of NSF Budget Request to Congress Cover of NSF Budget Request to Congress for fiscal year 2011 for fiscal year 2011 for fiscal year 2011 for fiscal year 2011

“Researchers Yonggang

Researchers Yonggang Huang at Northwestern University and John Rogers at the University of Illinois at Urbana-Champaign have developed circuits that can developed circuits that can stretch, bend and even twist! … twist! … Potential uses include flexible sensors flexible sensors, transmitters, and new photovoltaic and microfludic p oto o ta c a d c o ud c devices, as well as areas of medicine and athletics.”

Global vs Local Buckling Global vs Local Buckling— —1D Buckling 1D Buckling

Global buckling happens when the substrate is relatively thin and long; otherwise, local buckling happens.

Global vs Local Buckling Global vs Local Buckling— —2D Buckling 2D Buckling

At a certain thickness of the thin film, for the same length and width of plate, local buckling occurs when the substrate is relatively thicker.

Single Crystal Si and Mother Wafer Single Crystal Si and Mother Wafer

SiO2 single crystal Si

Single Crystal Si and Mother Wafer Single Crystal Si and Mother Wafer

single crystal Si etch SiO single crystal Si etch SiO2 mother wafer: single mother wafer: single l Si crystal Si crystal Si three layers are strongly bonded silicon ribbons sitting on the mother wafer

Electric Performance

Khang, Jiang, Huang, Rogers, Science, 2006

100 150 m

2)

• 7.58%
• 3.79%

0% stretch/compr. Al Al

50 100 ity (mA/cm

0% 3.03% 7.58% 15.56% 22.73% p n stretch/compr. dark

50 rent Dens

22.73% model 50 μm light

• 2
• 1

1

• 50

Curr Bias Voltage (V) g ( )

• Wavy Si does not affect the electric

performance.

Pixel Distribution: Compare with i experiment

• The analytical results agree well with experiments
• The density change of pixels due to deformation is
• The density change of pixels due to deformation is

around 10%, which is fairly small

• The distribution of pixels after deformation is quite

if