Direct imaging of defect formation in strained organic ...static.sif.it/SIF/resources/public/files/congr16/mc/Cramer.pdfDirect imaging of defect formation in strained organic flexible

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)

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

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

45 mm

100

-100

nm

Area 1

source drain

Low-voltage Organic Thin Film Transistor

PEN

Al

Al2O3

ParyleneAu

TIPS Pentacene

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

Atomic Force Microscopy

microscope and CCD camera

Separated xy-scanner

AFM-head

Copyright : Park AFM

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

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

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)

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

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

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

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

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

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