Organic devices & potential mappingOrganic devices & potential mapping

3D simulations and experiments3D simulations and experiments

Dimitri CharrierDimitri Charrier, M. Kemerink and R.A.J. Janssen, M. Kemerink and R.A.J. Janssen

TUTU//ee

AgendaAgenda

1.1. Scanning Kelvin Probe Microscope - Scanning Kelvin Probe Microscope - why & basicswhy & basics

2.2. SKPM - ProblemsSKPM - Problems

3.3. Parameter free modelingParameter free modeling

4.4. ConclusionsConclusions

1.1. IntroductionIntroduction

= organic device

= I, , E, V

SiO2

tip

Au Au

Scanning Kelvin probe microscopeScanning Kelvin probe microscope

0 2 4 6 8 10 12 14 16

-40

-20

0

20

40

60

80

100

120

140

bias electrode

nm

X (m)

Hei

ght p

rofil

e (n

m)

ground electrode

Interleave mode

-Atomic Force Microscope in tapping mode-Surface potential at Lift Height ZL

V

V

Principle: Force microscopePrinciple: Force microscope

dz

dC

2

VF

2

cpdacdc VtVVV )sin(

)( dccpdac VVVdz

dCF

F = force between tip and sample

V = tip-sample voltage difference

C = capacity between tip and sample

Vdc = tip voltage

Vac = amplitude voltage

Vcpd = contact potential difference

Then Vcpd = Vdc

For F=0

tFtFFF dc 2cossin 2

2.2. Experimental resultsExperimental results

SiO2

Au Au

V = 10 V

true surface potential

2 4 6 8 10 12 140123456789

10

surf

ace

pote

ntia

l (V

)X (m)

2 4 6 8 10 12 140123456789

10

surf

ace

pote

ntia

l (V

)X (m)

ortho para

g = 0 nm

Room temperature experiments

3D problem

What is wrong?What is wrong?

K.P. Puntambekar, P.V. Pesavento, and C.D. FrisbieAppl. Phys. Lett. 83, 5539 (2003)

“the linear drop along the contacts […] “

Vexp < 10 V

What is the real potential?What is the real potential?

Limited resolutions due toLimited resolutions due to Capacitive coupling between the tip Capacitive coupling between the tip

and the surfaceand the surface

DRAIN (8 V)SOURCE

Analytical resolution?Analytical resolution?

IT CAN WORK ONLY FOR SYMETRICAL PROBLEMS: APEX + CONE

APEX CONTRIBUTION IN 2 DIMENSIONS

CONE CONTRIBUTION IN 2 DIMENSIONS

C. Argento and R.H. French, J. Appl. Phys. 80 (1996) 6081

3.3. Steps of modelingSteps of modelingSoftware used: COMSOL (Finite Element Method software) + MatLab

Olympus tip: Pt coat 3D Drawing in COMSOL

2D simulations done in 2001 by T.S. Gross et al, Ultramicroscopy 87 (2001) 147

Steps of modelingSteps of modeling

Meshing Zoom on meshing of the tip

surface

tip

Memory limit with 2 GB of RAM= 370 000 tetrahedrons

Discretization problem: finite amount of tetrahedrons

Vertical resolution of modelingVertical resolution of modeling

10 15 20 25 30 35 40100

1000

100002V on tip, middle of channel

For

ce (

pN)

Tip-to-sample distance (nm)

Force (nN)

For obtaining good lateral resolution, first check the vertical resolution

0 1 2 3 4 5 6

-8000

-6000

-4000

-2000

0 Y = A + B1*X + B2*X^2

For X = 1 VY = 0.18039 pN

For

ce (

pN)

tip voltage

B Polynomial Fit of matrix01_B

Scattering due to meshing limitation

dz

dC

2

VF

2

For each tip position we calculate the tip-sample force for few tip voltages, then we deduce the surface potential

Modeling TRICKModeling TRICK

tip

source drain

MOVE THE SURFACE POTENTIAL AND NOT THE TIP OTHERWISE

channel

remeshing = scattering

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

1

2

3

4

5

6

7

8

9

su

rfa

ce

po

ten

tia

l (V

)

X (m)

B

2 4 6 8 10 12 14

-6-5-4-3-2-1012

DRAIN

surf

ace

pote

ntia

l (V

)

X (m)

Z = 500 nm Z = 10 nm simulation simulation

SOURCE

Modeling results Modeling results - match perfectly- match perfectly

0 2 4 6 8 10 12 14 16

0

2

4

6

8

10

DRAIN

surfa

ce p

oten

tial (

V)

V Modeling

X (m)

g = 10 nm

SOURCE

Calculation time for ONE curve= 5 min X 3 voltages x 30 points 8 hours

Further resultsFurther results

-8 -6 -4 -2 0 2 4 6

-10-8-6-4-202468

10

surfa

ce p

oten

tial (

V)

X (m)

Vsd = 10 V Vsd = -10 V Vsd = 1 V

Modeling results

-8 -6 -4 -2 0 2 4 6

0

2

4

6

8

10

surf

ace

po

ten

tial (

V)

X (m)

Vsd = 10 V Vsd = -10 V Vsd = 1 V

RESCALED

Rescaling: Vx (Vsd) = . Vx (Vsd/)

Further resultsFurther results

Experimental results

2 4 6 8 10-4

-2

0

2

4

6

surf

ace

pote

ntia

l (V

)

X (m)

-1 V -8 V

V

2 4 6 8 10-4

-2

0

2

4

6 V

surf

ace

pote

ntia

l (V

)

X (m)

-1 V -8 V

RESCALED

SiO2

Au

4.4. CONCLUSIONCONCLUSION

We developed a FREE-PARAMETER-FREE SKPM We developed a FREE-PARAMETER-FREE SKPM simulation tool, taking into account the lift height simulation tool, taking into account the lift height influenceinfluence

Experimental data Experimental data ≠ real potential due to the ≠ real potential due to the capacitive couplingcapacitive coupling

Experimental response of SKPM is understoodExperimental response of SKPM is understood

But: so far we cannot ‘invert the system response’But: so far we cannot ‘invert the system response’

The clean-room peopleErik-Jan Geluk,Tjibbe de Vries,and Barry Smalbrugge

Thanks toThanks to

TU/eTU/e

The M2N groupRené Janssen,Martijn Kemerink,Klara Maturova,Alexandre Nardes,Yingxin Liang,Ron Willems,Simon Mathijssen,…

Technical University of Technical University of EindhovenEindhoven