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Direct imaging of defect formation in strained organic flexible electronics by Scanning Kelvin Probe
Microscopy
Tobias Cramer, Lorenzo Travaglini, Stefano Lai, Luca Patruno, Stefano de Miranda, Annalisa Bonfiglio, Piero Cosseddu, Beatrice Fraboni
Dipartimento di Fisica e Astronomia
Università di BolognaViale Berti Pichat 6/2
40127 Bologna(DIFA)
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Flexible Large Area Electronics
- non-planar surfaces- deformable systems (robotics, humans)
Displays Photovoltaics Sensors / Detectors
For flexible X-ray sensors see: L. Basiciró, Nat. Commun. 2016
A. Campana et al., Adv. Mat. 2014L. Basicirò et al. Nat. Commun. 2016, accepted
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Flexible Large Area Electronics: The Material Plattforms
Amorphous Silicon Organic Electronics Oxide Based Electronics
physical deposition
m = 1 cm2/Vs
solution based deposition
m = 1 cm2/Vs
physical deposition
m = 10 - 50 cm2/Vs
GaxInyZnzOe. g. TIPS pentaceneSi
K. Asadi et al. Nat. Commun. 2013T. Cramer et al. Phys. Rev. B 2015T. Cramer et al. Adv. Elec. Mat. 2016
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45 mm
100
-100
nm
Area 1
source drain
Low-voltage Organic Thin Film Transistor
PEN
Al
Al2O3
ParyleneAu
TIPS Pentacene
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0 2 4 6 8 10 12
0
1
2
3
y (m
m)
x (mm)
0.5 1.0 1.5 2.0 2.5 3.010
-11
10-10
10-9
I off (
A)
(%)
-1.0
-0.5
0.0
0.5
1.0
Vt(V
)
0.5 1.0 1.5 2.0 2.5 3.010
-3
10-2
10-1
m(
cm
2/V
s)
(%)
Transistor characterization under strain
r
2
t
r surface strain:
T.Cramer et al. Scientific Reports, 6, 38203, 2016
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Atomic Force Microscopy
microscope and CCD camera
Separated xy-scanner
AFM-head
Copyright : Park AFM
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Scanning Kelvin Probe Microscopy
– Probing electrostatic surface potentials –
capacitor containing tip and sample surface
21
2E C V Energy:
Force: 2 2
2
1 1~
2 2el
E C CF V V
D D D
Distinguish in frequency domain: mechanics: 270 kHzelectrostatics: 17 kHz
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SKPM contact potentials(VG= 0V; VD = 0V)
140
- 60
nm
5 mm
V
-0.4
0.8
The surface potential on the
dielectric corresponds to the
underlying Aluminum gate
electrode
Workfunction Au: 5.1 eV
Al: 4.25 eV
5 mm
AuDielectric
TIPS pentacene
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45 mm
100
-100
nm
source drain45 mm
V
0
-5
0 10 20 30 40
-8
-7
-6
-5
-4
-3
-2
-1
0
-8 V
-4 V
-6 V
-2 V
VDS
= 0 V
Su
rface
Pote
nti
al
(V)
Position (mm)
Measurement of local conductivity:
constantj E
V 1
x ( )x
Pinch-off
SKPFM on biased transistor (VG=-5V)
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0.6% 1.0% 1.4% 1.9%
2.0% 2.3% 2.7% 3.0%
str
ain
dire
ctio
n source
drain
AFM on strained transistor
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str
ain
dir
ection
0.6% 1.0% 1.4% 1.9%
2.0% 2.3% 2.7% 3.0%
source
drain
dc1c2
SKPM on strained transistor
T.Cramer et al. Scientific Reports, 6, 38203, 2016
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0 0
1 ( )( , ) ( )
( )
t t
Dx
Sz z
I V xJ dz x z E x dz
W R x x
SKPM on strained transistor
dra
in0 5 10 15 20 25 30 35
-4
-2
0
2
4
6
8
10
12
14
16
V
SP(V
)
x (mm)
so
urc
e
dra
in
0 5 10 15 20 25 30 35
0
100
200
300
400
500
600
700
800
900
RS/R
S0
x (mm)
so
urc
e
0.6%
1.0%
1.4%
2.0%
2.3%
2.7%
3.0%
1.9%
T.Cramer et al. Scientific Reports, 6, 38203, 2016
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600 800 1000 1200 1400-8-6-4-202468
10
VS
P(V
)
h (
nm
)
x(nm)
-4.0-3.8-3.6-3.4-3.2-3.0-2.8-2.6-2.4-2.2-2.0-1.8
600 800 1000 1200 1400-30
-20
-10
0
10
20
30
40
h(n
m)
x(nm)
-3.0
-2.8
-2.6
-2.4
-2.2
-2.0
(a)
(b)
(d)
(e)
(c) (f)
VS
P(V
)
VS
P(V
)
=1.1% =1.8%
Nano-crack formation
T.Cramer et al. Scientific Reports, 6, 38203, 2016
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Conclusions
- AFM in Non-Contact mode on mechanically strained substrates is possible
- SKPM to investigate failure and defect formation in thin film devices
- In microcrystalline organic semiconductors failure is caused by nano-crack formation starting at > 1 %
- Strong adhesion of micro-crystals to the dielectric surface reduces crack propagation and maintains charge transport up to < 3%
- Searching for semiconductors which combine good elastic properties (polymers) and large + long-range electronic overlap
T.Cramer et al. Scientific Reports, 6, 38203, 2016
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Acknowledgements
University of Bologna - DIFA
Prof. Beatrice Fraboni
Lorenzo Travaglini
Francesco Calavalle
University of Bologna - DICAM
Luca Patruno
Stefano de Miranda
University of Cagliari
Piero Cosseddu
Prof. Annalisa Bonfiglio
Italian Ministry of Research - PRIN
2010-2011 funding
Organ Models for the Investigation of Age Related Diseases