Solution coated organic semiconductors towards a-Si performance

MRS Spring 2006San Francisco

Janos Veres, Simon Ogier, Stephen Leeming, Giles Lloyd,

Domenico Cupertino, Richard Williams, Munther Zeidan, Bev Brown

Outline

• Introduction to Merck/EMD

• Organic Semiconductors Development

• Organic Semiconductors for plastic electronics

• Solution coated OSC

• Semiconductor formulations

• Microstructure and uniformity

• Carrier transport

• Stability

• Summary and outlook

One Name - Two Companies

Established by E. Merck in 1891 as U.S. subsidiary; Independent since 1917

Right to use the Merck brand in North America; MSD/Merck Sharp & Dohme outside North America

Established 1668 in Darmstadt, Germany

Right to use the Merck brand outside North America; EMD in North America

Merck & Co., Inc.Whitehouse Station, NJ, USA

Merck KGaADarmstadt, Germany

Introduction to Merck

SalesEUR 5,339 million

Operating resultEUR 755 million

Sales 2004EUR 1,888 million

Operating result 2004EUR 438 million

MerckChemicals

• Large area -increasingly difficult with a-Si• Low cost -printing, ambient processing steps• Flexible devices - plastic substrates, low temperature processing

Organic semiconductors for plastic electronicsDisplays, RFID tags, sensors, memory, photovoltaics

Main driver is processability!

P3HT 0.1 cm2V-1s-1

Sirringhaus et al. Nature 401, 685 (1999)

N

n

X X

YPTAAMerck, 10-2 cm2V-1s-1

Veres et al. Chem. Mater. 16, 4543 (2004)

C8H17 C8H17

S S **n

Si

Si

Rubrene 0.1-0.7 cm2V-1s-1

Stutzmann et al. Nature Mat. 4, 601 (2005)

F8T2Dow, 10-2 cm2V-1s-1

Sirringhaus, Appl.Phys.Lett. 77, 406 (2000)

SS

C12H25

SS

C12H25

* *n

PQT12Xerox, 0.1 cm2V-1s-1

Ong et al. Adv.Mat. 17, 1141 (2005)

S

SS

S ** n

C10H21

C10H21

Merck, 0.15 cm2V-1s-1

Heeney et al. J.Am.Chem.Soc.127, 1078 (2005)

S

S

S

S ** n

C14H21

C14H21

Merck, 0.2-0.6 cm2V-1s-1

McCulloch et al. Nature Mat. 5, 328 (2006)

N

SO

O

CH3C N S O

O

+

1mol% CH3ReO3CCl3, reflux 120-200 C Precursor

pentaceneIBM, 0.1-0.9 cm2V-1s-1

Afzali et al, J. Am. Chem. Soc. 124, 8812 (2002)

Solution coated OSC

Processability +stability + high µ and on/off + large area uniformity

Ambient manufacturing & operation Device performance

SS

C6H13

SS

C6H13

* *n

C6H13 C6H13

TIPSAnthony, >0.4 cm2V-1s-1

Sheraw et alAdv. Mat. 15, 2009, (2003)

Field effect and determining mobility

Drain(D)Source

(S) dielectric+ + + + + + + +

LW

Gate(G)

- - - - - - -

Vg induces opposite charge in the semiconductor.

Conductive channel is established

Linear regime |VDS|<<|VGS |

( )WLVVCLVI tGi

D −= 2µ

1/time mobile chargeDSiG

DS

VWCL

VI

∂∂

=µ

( ) DtGi VVVCL

WI −= µ

Gate dependence of µ without assuming Vt

-60 -40 -20 0 2010-15

10-14

10-13

10-12

10-11

10-10

10-9

10-8

10-7

10-6

10-5

VD=-5V

VD=-5V

VD=-60V

Gate Voltage [V]

Dra

in C

urre

nt [A

]

VD=-60V

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

Mobility [cm

2V-1s

-1]

PTAA

Si

Si

** n

Blend OSCfilm 50:50

Spin coated

Low-k dielectric (spin coated) Gate (Au) Source, drain

(Au)

Glass or plastic substrate

OSC formulations (A)Example of basic blends

100 µm

Polarised light microscopy (transmission)

Normal light (transmission)

ambient fabrication

• Higher mobility and reduced T activation

• Aliphatic polymers offer good orthogonality

• Reduced hysteresis, absence of trapping groups

• Lower threshold voltages and lower T activation for Vt !

• Reduced moisture take-up & better stability

• Fluoropolymers, ethylene, butylene, propylene

copolymers, hydrogenated styrene, cyclic aliphatics used

J. Veres, S.D. Ogier, S.W. Leeming, D.C. Cupertino, and S. Mohialdin Khaffaf, Adv. Funct. Mat., 13, 199-204, 2003

J. Veres, S.D. Ogier, S.W. Leeming, D.C. Cupertino, S. Mohialdin Khaffaf, G. Lloyd, Proc. SPIE, 2003, San Diego

J. Veres, S. Ogier. G. Lloyd, D. de Leeuw, Chem. Mat. 16. p4543, 2004

Low-k dielectrics

2 3 4 510-6

10-5

10-4

10-3

10-2

10-1

µ [

cm2V

-1s-1

]

(1000/T) [1000/K]

TOFFET (CYTOP)FET (PPCB)FET (PMMA)

-40 -30 -20 -10 0

0

5

10

15

20

25

30

I D [µ

A]

VD [V]

VG=0 to -40V in -5V steps

-40 -20 0 2010-12

10-11

10-10

10-9

10-8

10-7

10-6

10-5

VD=-5V

VD=-5V

VD=-60V

Gate Voltage [V]

Dra

in C

urre

nt [A

]

VD=-60V

0.0

0.1

0.2

0.3

0.4

0.5

Mobility [cm

2V-1s

-1]

OSC formulations (A)Early results (2003) µ =0.14 cm2V-1s-1

-40 -30 -20 -10 0 1010-12

10-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4

10-3

Gate Voltage [V]

Dra

in C

urre

nt [A

]

Vd -40V

Vd -40V

Vd -5V

Vd -5V

L = 125 µmW = 29.6 mmC = 1.94nFcm-2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

M

obili

ty [c

m2 V-1

s-1]

-40 -35 -30 -25 -20 -15 -10 -5 00

-50

-100

-150

-200

Dra

in c

urre

nt [µ

A]

Drain Voltage [V]

Vg 0 to -40V in 5V steps

Improved OSC formulationsChoice of the right OSC and additives for stabilityµ =0.5-0.6 cm2V-1s-1 on/off>106 ambient operation

All curves include forward and immediately following reverse scans

0.5 mm0.5 mm

100 µm

Film uniformityPolarised light microscopy

Single OSC componentBlend film

-60 -40 -20 0 2010-12

10-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4

10-3

Gate Voltage [V]

Dra

in C

urre

nt [A

]

0.0

0.2

0.4

0.6

0.8

1.0

Vd -60V

Vd -60V

Vd -5V

Vd -5V

L = 100 µmW = 1 mmC = 3.2nFcm-2

Mobility [cm

2V-1s

-1]

Uneven filmsHighly random crystal sizeRandom orientationRough topographyPoor device uniformity(occasionally good devices)DefectsGate leakagePoor turn-on

High degree of uniformityGood connectivity, sharp TFT turn-onControlled crystal size, flat topography

Surface topography Tapping mode AFM

0 20 40 60 80

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Nor

mal

ised

cou

nts

[per

s]

depth [nm]

133Cs212C 133Cs28Si16O 133Cs28Si 133Cs219F 133Cs2197Au 133Cs232S

Semiconductor profile by DSIMS Dynamic Secondary Ion Mass Spectroscopy : Composite AExample of film structure

F

1.Cesium ion source2.Duoplasmatron 3.Electrostatic lense 4.Sample

Depth profile by millingaway material from a defined area

Primary ion beamCs+

Secondary ionsto mass spectrometer Si

Au

SC

5.Ion energy analyser 6.Electromagnet - mass analyser 7.Electron multiplier / Faraday cup 8.Fluorescent screen - ion image detector

-40 -30 -20 -10 0 1010-12

10-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4

Gate Voltage [V]

Dra

in C

urre

nt [A

]

Vd -40V

Vd -40V

Vd -5V

Vd -5V

L = 60 µmW = 1 mmC = 1.5nFcm-2

0.0

0.5

1.0

1.5

2.0

2.5

M

obili

ty [c

m2 V

-1s-1

]

-40 -30 -20 -10 00

-5

-10

-15

-20

-25

-30

Dra

in c

urre

nt [µ

A]

Drain Voltage [V]

Vg 0 to -40V

in 5V steps

Advanced OSC formulations (B)Optimised componentsµ =1.5 cm2V-1s-1 on/off>106

-40 -30 -20 -10 0 1010-12

10-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4

10-3

Gate Voltage [V]

Dra

in C

urre

nt [A

]

Vd -40V

Vd -40V

Vd -5V

Vd -5V

L = 20 µmW = 1 mmC = 3.5nFcm-2

0.0

0.5

1.0

1.5

2.0

2.5

M

obili

ty [c

m2 V-1

s-1]

-40 -30 -20 -10 00

-20

-40

-60

-80

-100

-120

-140

-160

Dra

in c

urre

nt [µ

A]

Drain Voltage [V]

Vg 0 to -40V in 5V steps

Advanced OSC formulations (C)Optimised componentsµ =1.2 cm2V-1s-1 on/off>106

1 10 1000.0

0.5

1.0

1.5

2.0

Line

ar M

obili

ty [c

m2 V-1

s-1]

Channel length [µm]

W=1mmC = 3.2nFcm-2

Channel length dependence (C)

2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.00.1

1

m

obili

ty [c

m2 V

-1s-1

]

1000/T

EA=56meV

EA=21meV

Temperature activation of mobility

Formulation B

Formulation A

Transport resembles that of single crystal OTFT

-60 -40 -20 0 20

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Nor

mal

ised

Mob

ility

Gate Voltage [V]

Temperature decreasing in 20 degreesteps

Temperature activation of mobilityVg dependence

DiG

DSFE VWC

LVI

∂∂

=µ

-60 -40 -20 0 20

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Line

ar M

obili

ty [c

m2 V

-1s-1

]

Voltage [V]

Temp [K] 380 360 340 320 300 280 260 240 220 200 180

VD=-5V

Normaliseddata

Gate dependence of µ is weak µ(Vg) does not change with T

Slight increase of turn-on with T

0 100 200 300 400 50010-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4

10-3

C

urre

nt [A

]

Time Between Measurements [days]

Original on-current Original off-current Recent on-current Recent off-current

Device lifetime

• Devices remain operational for well over a year

• Typically µ stays within 20%

Each point is a different device!

Bias stress stability

0.1 1 100.01

0.1

1

10

∆VT (V

)

Time (hours)

Stress Conditions,VGS=-30VVDS=-30V

-30 -20 -10 0 1010-9

10-8

10-7

10-6

10-5

10-4

Dra

in C

urre

nt (A

)Gate Voltage (V)

Before Stress After Stress

Stress Conditions,VGS=-30VVDS=-30VTime=7 hours

Threshold voltage variation with time Transfer characteristics before & after bias stress

• Low bias stress

• Fully recovers after resting (accelerated by light)

• Negligible positive bias stress

Summary

Solution (ambient) processable OSC material systems developed at Merck• New OSC and material combinations delivering µ>1 cm2V-1s-1

• Matching dielectrics, contact treatments, interfaces• OSC and their compositions are evolving to address

-deposition processes e.g.printing (multiple components, viscosity, solvent choice)-specific device requirements (substrate, electrodes)

OSC materials are truly a match for a-Si• Reproducible performance, good uniformity • Device operation resembles single crystal OTFT• Hysteresis free and very low bias stress• Promising stability (solution, device) • Real potential to use in ambient manufacturing processes

Implementation of materials and process technology will require more work!• A range of applications can be addressed – first is likely to be displays