11th Korea-US Forum on Nanotechnology
Fabrication of Novel Stretchable Devices
Jeong Sook Ha
Department of Chemical and Biological Engineering
Korea University
Outline
1. Introduction
2. Design concept of novel stretchable devices
3. Fabrication
4. Stretchable nano-material based devices
5. Summary
Stretchable electronics?
 Expandable
 Twistable
 Compressible
stretchable device
under deformation
interconnection
expansion
stable
operation
compression
Electronics on curved surfaces
Stretchable devices
▶Stretchable batteries with self-similar
serpentine interconnects
Rogers et al. Nat. Comm. 4, 1543 (2013)
▶Digital cameras with designs inspired
by the arthropod eye
Rogers et al., Nature 497, 95 (2013)
Epithermal electronics & integrated circuits
▶Epidermal Electronics
▶Thin, conformable device softly laminating onto
the surface of the skin to enable advanced,
multifunctional operation for physiological
monitoring in a wireless mode
Rogers et al. Science 333, 838 (2011)
Rogers et al. Science 344, 70 (2014)
Our recent work on stretchable nanowire devices
1. “Stretchable Field-Effect-Transistor Array of Suspended SnO2 Nanowire”, Small 7, 1181
(2011).
2. “SnO2 Nanowire Logic Devices on Deformable Nonplanar Substrates” , ACS Nano 5,
10009 (2011).
3. “Fabrication of a Stretchable Solid-State Micro-Supercapacitor Array”, ACS Nano 7, 7975
(2013).
4. “Fabrication of Stretchable Single-Walled Carbon Nanotube Logic Devices”, Small 10,
2910 (2014).
5. “Design and Fabrication of Novel Stretchable Device Arrays on a Deformable Polymer
Substrate with Embedded Liquid-Metal Interconnections”, Adv. Mater., in press (2014).
DOI: 10.1002/adma.201402588 (2014).
6. “High-Density, Stretchable, All-Solid-State Microsupercapacitor Arrays”, ACS Nano,
in press (2014). DOI: 10.1021/nn503799j
Stretchable SnO2 nanowire inverter array
S
Vin
SnO2 NW
VDD
Ground
Vout
Shin et al. ACS Nano 5, 10009 (2011)
D
SEM images after deformation
(a)
1 cm
200 μm
500 μm
1 μm
Plane
PI
interconnection
230 μm
(b)
1 cm
1 mm
300 μm
1 μm
Convex
prestrain: 21 %
(c)
1 cm
Concave
prestrain: 28 %
1 mm
300 μm
1 μm
VGS = 0 ~ 2 V
(0.2 V step)
(A)
IIDS
DS (A)
IDS (A)
2e-6
2
1e-6
1
1e-8
1e-9-9
10
0.5
0.5
1.0
1.0
1.5
1.5
2.0
2.0
9
6
VDS = 0 V
1e-10
10-11
1e-11
1e-12
-1
-1
2.0
Before RIE
After RIE
0
0
1
1
2
2
×10
Y Data
~9 GΩ
0
1.5
1.5
1.0
1.0
0.5
0.5
-6e-9
-2.0 -1.0
-2
-1
Gain ~4.8
Gain ~4.7
Gain ~4.8
~300 MΩ
Vout(V)
Y Data
IDS (nA)
10-9
1e-9
VVGS
(V)
G (V)
(d)
3e-9
-9e-9
1e-8
2.0
6e-9
-6
-9
VDS = 2 V
(Extremely
stretched)
-2
-2
9e-9
-3e-9
10-7
1e-12
V
(V)
VDS
DS (V)
3
0
-3
1e-6
1e-7
-11
1e-11
10
0.0
0
(c)
VDS = 2 V
1e-7-7
10
1e-10
0
0
10-5
1e-5
1e-6
IDS (μA)
3e-6
3
1e-5-5
10
0
0
X Data
1.0
VDS (V)
1
2.0
2
0
0.0
0.0
Convex shape
Concave shape
Plane
0.5
0.5
1.0
1.0
X Data
1.5
1.5
Vin (V)
▶No deterioration of electrical performance upon deformation
IGS (A)
(b)
Y Axis 3
(a)
2.0
2.0
Stretchable micro-supercapacitor array
▶micro-supercapacitor with SWNT electrodes and ionic-gel electrolyte
Kim et al. ACS Nano 7, 7975 (2013).
Capacitance (F/g)
200
Strain (0.5V/s)
0%
10%
20%
30%
150
100
50
0
-50
-100
-150
-200
0
1
2
Potential (V)
3
▶No noticeable deterioration in electrochemical performance with stretching
Charging
Discharging
Micro-LED(orange)
3V
Bent (r ~ 2.5 cm)
Stretched (~ 20 %)
2. Design concept of novel stretchable devices
Main concept of our novel stretchable device
heterogeneous structure
a
PDMS (stiff)
b
embedded EGaIn interconnection
ecoflex + PDMS (soft)
EGaIn
5 mm
2 mm
Difference in Young’s Modulus
→ Minimized strain on active device
c
e
silver sticker
d
double integration
5 mm
→ Simple fabrication/
Protection from external impact/
Increase in fill factor
dry transferred device array
upper blue LEDs
lower white LEDs
5 mm
→ Doubling the fill factor
→ Independent fabrication of
active devices from the substrate
3. Fabrication
Schematics of fabrication process
a
top mold
a. Preparation of
deformable substrate
bottom mold
insert the Fe wire into
bottom mold for the
injection of liquid metal
bottom mold
insert the Fe wire into the
top mold
pour PDMS into a each
mold for rigid island &
attach both molds
remove the iron wire &
inject the liquid metal
detach the mold from the
whole assembly
pour mixture of ecoflex
and PDMS to form the
soft thin film
transfer the fabricated
device & attach the
silver sticker
b
b. Preparation of
active device and dry
transfer
spin coating of PDMS
attachment of PI film
PDMS
device fabrication
PI film
detachment of device
from the substrate
SiO2/Si substrate
c
c. Preparation of Ag
nanowire sticker
coating of PDMS
and half curing
PDMS
attach the sticker between
the EGaIn and electrode
drop casting of Ag NW solution
Ag NW
solution
1.0 μm
device
electrode
2 mm
SiO2/Si substrate
EGaIn
Yoon et al. Adv. Mater. In press (2014)
4. Stretchable nano-material based devices
Stretchable array of LEDs & strain distribution
a
flat
bending
twisting
b
li
l
1.0 cm
l'
released
unit module
applied strain = 60%
180%
c
side view
lf
180° twisting
1 cm
a
ɛapplied = 30%
1 cm
b
b
a
with
PI (Ɛapplied = 30%)
with PI (Ɛapplied
= 30%)
area 1
0%
25%
e
d
Bending with r = 13 mm
50%
c
c
area 1 (island)
area 1 (island)
1 cm
area 2 (thin area
film) 2 (th
area 1
→ Stable performance upon deformations of stretching,
bending, and twisting
180%
180%
→ Minimized strain on island (<1%) with concentrated
120%
120%
area 2
area 2
strain on thin film (>100%) upon 30% stretching
10.5%
20%
15%
0.6%
20%
15%
1
1
0.6%
10.5% 10%
10%
103%
103%
180%
1
I-V characteristics of LED arrays upon deformation
0.10
0.08
0.06
0.04
c
flat
o
90
o
180
o
270
twisting
0.08
0.06
0.04
0.04
0.02
0.02
0.00
0.00
0.00
-2
-1
0
1
2
-3
3
-2
-1
Voltage (V)
-3
3
Current (A)
1
10
-1
10
-2
10
0
10
20
30
100 cycle
1000 cycle
4000 cycle
8000 cycle
10000 cycle
16000 cycle
70%
0%
40
applied (%)
50
60
70
1.5
2.0
2.5
Voltage (V)
-1
0
1
2
3
f 10
ɛapplied = 60%
-3
-2
Voltage (V)
Voltage (V)
Stretching
Rnormalized
2
e
10
0.1
1
0
d
0
Stretching
0.06
0.02
-3
0%
10%
30%
50%
70%
0.10
Current (A)
Bending
Current (A)
0.08
Current (A)
b
flat
r = 3 cm
r = 2 cm
r = 1 cm
0.10
R/R
a
3.0
1
0.1
0
4000
8000
12000
Stretching cycles
16000
→ Stable performance upon bending, twisting, and stretching
→ Mechanically stable upon repeated stretching cycles of 16,000 under
external strain of 60%
Stretchable SnO2 nanowire UV sensor & SWCNT FET
a
b
0.7
0%
10%
20%
30%
0.6
0.4
2
10
SnO2 sensor
0.3
0.2
UV ON
→ stable photo-current
upon uniaxial stretching
→ Iph/Idark ~ 60
1
10
SnO2 NW
0
10
0.1
5㎛
0.0
-1
0
300
600
900
1200
d
2.0
0%
10%
20%
30%
1.6
SWCNT FET
200
400
Vds = 1 V
1.2
600
800
Time (Sec)
1000
2㎛
0%
10%
20%
30%
Vds = 1 V
Vg = -10 V
1.5
SWCNT
1.0
5 µm
0.5
-10
-5
0
Vg (V)
5
10
→ stable transfer curve
upon stretching
→ stable Ids value
2.0
1.0
0.8
1200
3.0
2.5
Current (A)
1.8
1.4
10
1500
Time (sec)
c
Ids (A)
UV off
UV on
Iph/ Idark
Current (mA)
0.5
3
10
UV OFF
0
100
200
Time (sec)
300
400
Stretchable electronics with integrated energy
generation and storage devices
Wearable
computer
Apple-watch
Energy Storage
Energy Generation
NWs sensor
NO2
hυ
controller
+
Solar Cell
SWCNT &
solid electrolyte
+
+
NWs D
S
Resistor
+
Nano-generator
external
vibration
-
S
Supercapacitor
-
-
-
P
N
D
Diode
Fabrication of micro-supercapacitor with LbL
assembled MWNT/MnOx electrodes
PET film
Solidification
of solid electrolyte
PDMS
SiO2/Si substrate
PVA-H3PO4 gel
Layer-by-Layer (LbL) assembly
5mm
Metallization
220nm
200 nm
Channel length = 150 µm
Active area = 0.6 cm2
Thickness = 220 nm
Volume = 1.32 x 10-4cm3
Ti/Au current collector
MWNT-COOH/MnOx
Functionalized MWNT
Stretchable micro-supercapacitor array
a
b
136%
ɛapplied = 40%
45%
20%
10%
1 cm
0%
c
d
10
Stretching
Releasing
10
Stretching
0
-10
0%
10%
20%
30%
40%
Stretching
Releasing
-20
C/C0
Current (A)
20
1
Releasing
200 mV/s
0
1
2
0.1
3
0
Potential (V)
f
20
30
ɛapplied (%)
40
Single
Array
Ecell
2.6
2.4
Pcell
23
8
10
ɛapplied = 40%
ɛapplied = 40%
10
1 cycle
500 cycle
2000 cycle
0
100 cycle
1000 cycle
3000 cycle
C/C0
Current (A)
10
A
e
20
→ Stable
electrochemical
performance upon
repeated stretching
up-to 40%
1
-10
(mWh/cm3)
-20
200 mV/s
0
1
2
Potential (V)
3
0.1
(Wh/cm3)
0
1000
2000
3000
Stretching number
Hong et al. ACS Nano, In press (2014)
Integrated energy storage devices
a
b
10
ɛapplied = 40%
Galinstan
L/L0
5 mm
1.8 V
2.0 V
2.2 V
3.3 V
1
0.1
0
10
20
30
ɛapplied (%)
▶ Powering various µ-LEDs with different operating voltages by
integrated circuit of MSCs
▶ Stable illumination of µ-LEDs under applied strain of 40%
40
Summary
▶ We present the fabrication of stretchable electronic devices
on newly designed deformable substrates.
▶Integrated devices, such as μ-LEDs, SnO2-NW UV sensors,
SWCNT FETs, and planar all-solid-state micro-supercapacitors
exhibit mechanically stable device performance after bending,
twisting, and uniaxial stretching, which corresponds with the
FEM analysis of the distribution of strains.
▶This study demonstrates the successful performance of our
newly designed deformable device and the potential for its
application in the field of wearable nano-electronics.
Acknowledgments
▶This
work was supported by the National Research Foundation of
Korea (NRF) grant funded by the Korea government (MEST) (Grant
No. NRF-2013R1A2A1A01016165).
▶This
work was done with
Dr. Jangyeol Yoon
http//surfnano.korea.ac.kr
Ms. Soo Yeoung Hong
Ms. Yein Lim
Prof. Goangseup Zi
Dr. Seung-Jung Lee
Comparison with previous design
Effective
strain
distribution
Double
integration
2nd Polyimide
(encapsulation)
Ionic polymer
SWCNT
bundle
1st Polyimide
Ti/Au
PDMS
2차원
VS
Simple
fabrication
process
Top device
EGaIn
interconnect
Polyimide
PDMS
Bottom device
3차원
Embedded
liquid metal
interconnection
Conducting properties of EGaIn upon stretching
a
b
Current (A)
0.05
0.00
10
V
R/ R0
0%
10%
20%
30%
40%
50%
60%
70%
0.10
1
-0.05
-0.10
0.1
-6
-4
-2
0
2
Voltage (V)
4
6
0
10
20
30
40
applied (%)
50
60
c
70
→ Stable
conduction upon
uniaxial strain upto 70%
(conductivity of
EGaIn : 3.4 x 104
S/cm)
stretching
2 mm
4 mm
5 mm
→ No noticeable
volume change of
EGaIn
Conduction through Ag nannowire sticker upon stretching
a
b
c
Ti/Au
silver sticker
V
V
S
e
d
Au electrode
Ag sticker_1
Ag sticker_2
Ag sticker_3
Ag sticker_4
Ag sticker_5
25
f
ecoflex
10
silver sticker
15
10
V
5
0
copper
wire
R/R
R 
0
20
D
500 nm
2 mm
30
S
D
1
0.1
0
1
2
3
4
number of samples
5
6
0
20
40
60
ɛapplied (%)
→ Electrical conduction comparable to Au thin film
→ No change in conductivity upon uniaxial stretching up-to 100%
80
100