The document summarizes research on characterizing the electrical properties of semiconducting polymers. It describes how thin films of polyaniline and PEDOT:PSS were fabricated through spin-coating and their resistivity measured using various techniques. Results showed the conductivity of PEDOT:PSS films decreased with increasing thickness and decreasing polymer concentration. Future work is needed to further characterize these materials and their potential applications in organic electronics.

1. Electrical Characterization ofElectrical Characterization of
Semiconducting PolymersSemiconducting Polymers
Sanda CeaSanda Cea
Faculty Mentors:
Professor Richard Nelson (EECS)
Professor John LaRue (MAE)
Graduate student: Chang-hsiu Chen (CheMS)
University of California, IrvineUniversity of California, Irvine

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OutlineOutline
 Motivation
 Background
 Thin Film Fabrication
 Electrical Characterization
 Data Analysis & Results
 Conclusion
 Future Work
 Acknowledgements
2006 IM-SURE Participants

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MotivationMotivation
 Organic electronics (ICPs)
 easy, low cost processing
 lower Young’s modulus
 durability
 Commercial applications
 antistatic coatings
 corrosion protection for metals
 solar panels
 field effect transistors (FETs)
 organic light emitting diodes (OLEDs)

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BackgroundBackground
 Polymer structure
 chain composed of monomer units
 form weak intermolecular bonds
 Emergent properties
 solubility
 elasticity (Young’s modulus)
 tactile strength
 electroluminescence
 electrical conductivity

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Engineering ICPsEngineering ICPs
 Naturally-occurring in biological tissues (i.e. melanin)
 Pure conductive polymer = emeraldine base (EB)
 Doped to enhance conductivity = emeraldine salt
 oxidizing agent (removes electrons)
 reducing agent (adds electrons)
 protonic acid (adjusts pH levels)
 Forms of emeraldine salt compound
 powder
 dispersion in solvent

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Doped polymers studiedDoped polymers studied
 Aqueous poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate)
(PEDOT:PSS)
 Baytron®
P (CPP 105 D)
 stable in oxidized state
 highly conductive
(400-600 S/cm)
 Polyaniline (PANI) in xylene
 from Ormecon (D 1020)
 easy one-step synthesis
 conductivity of 200 S/cm
PEDOT:PSS Structure
Polyaniline Structure
Component % By Weight % By Volume
BAYTRON P 42.92 37.49
N-Methyl-2-pyrrolidone (NMP) 2.58 2.19
Silquest A 187 0.86 0.70
Isopropanol 53.34 59.35
Dynol 604 0.30 0.27
Formulation Table for Conductive Baytron P

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Mixing the solutionMixing the solution
 Solid content of Baytron®
P is 1.2%
 Needs host matrix for structural support
 Polyvinyl alcohol (PVA)
 soluble in water
 emulsifying agent
(Solid Content: 1.2%,
Density=0.87g/cm^3)
(Solid Content: 9%,
Density=1.02g/cm^3)
0% 0 1
10% 0.977 1
20% 2.2 1
30% 3.771 1
40% 5.867 1
50% 8.8 1
60% 13.2 1
70% 20.533 1
80% 35.2 1
90% 79.2 1
100% 1 0
PEDOT/PSS Solution
Volume Ratio
PVA Solution Volume
Ratio
PEDOT/PSS Solid Salts Content
in insulating host polymer (wt%)
PEDOT/PVA Solution
Stir Plate Setup

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 Factors to consider
 film continuity
 preserving binding structure
 Thermal Evaporation
 con: causes breakdown of cross-linked chains
 Casting on glass
 pro: PDMS mold used to control thickness
 con: films tend to warp
 Spin-coating
 pro: ensures even spreading and slow evaporation
Thin Film FabricationThin Film Fabrication
PDMS Mold
Spin-coater

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ProcessProcess
 Cut Si wafer (with an insulating SiO2 layer)
into quarters and tape one edge
 provides a step edge for thickness measurement
 Spin-coat at 500 rpm
 not too high or film will be too thin
 Bake in vacuum oven at 90 ºC for 12 hours
 evaporates remaining solvent
 Measure film thickness using the Digital
Dektek 3 Profilometer

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Electrical CharacterizationElectrical Characterization
 Lateral ohmmeter readings with brass strips
 contact resistance much higher than bulk resistance
PEDOT:PVA Spin (rpm) Thickness (um) Resistivity (Ohms-cm) Bulk Resistance (Ohms) Contact Resistance (Ohms)
Pure (100 %) 500 0.55 1.0926 4.05 k - 19.2 k 18.95 k
1000 0.25 0.1020 1.59 k - 4.11 k 23.29 k
9:1 (90 %) 2000 2.00 4.5000 2.00 k - 18.0 k 32.00 k
4:1 (80 %) 1000 1.00 4.4540 4.20 k - 39.2 k 20.80 k
2:1 (66.7 %) 500 0.70 1.2880 1.00 k - 18.0 k 83.00 k
1000 0.30 1.5456 31.7 k - 53.7 k 31.33 k
1.5:1 (60 %) 500 1.00 0.6438 0.15 k - 7.15k 21.85 k
1000 0.40 1.3680 7.60 k - 35.6 k 18.40 k
1:1 (50 %) 500 1.00 19.8750 79.5 k - 187 k 298.50 k
1.70 1.8931 6.40 k - 22.6 k 45.40 k
1000 0.20 5.4375 45.5 k - 218 k 338.50 k
2.90 16.1414 13.4 k - 58.4 k 35.60 k
1500 0.50 24.5250 248 k - 818 k 214.50 k
2000 0.40 14.3280 70.5 k - 299 k 509.50 k

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Other techniquesOther techniques
 Van der Pauw 4-point probe
 damages thin film and SiO2 layer
 Collinear 4-point probe
 soldering or depositing gold electrodes requires high
temperatures
 destroys polymer thin film
 solution: silver epoxy
 cures in less than 10 minutes at 90 ºC

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Measurement procedureMeasurement procedure
 Cut samples into 1 cm by 4 cm strips and add 4 contacts
 Apply current across outer two terminals and read voltage across
inner two using the Agilent 4156C Semiconductor Parameter
Analyzer
 Calculate
resistance
Collinear Four-Point Probe Prepared Sample
I
V
R =

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Data Analysis & ResultsData Analysis & Results
 Resistance, cross-sectional area, and length of sample strip can
be used to calculate resistivity, ρ (Ω-cm)
 inverse yields conductivity (S/cm)
 Data plotted on logarithmic scale is compared against
existing data from previous study
wtA
L
A
R
=
=ρ

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 Film thickness measurements are plotted as well to highlight
the inverse relationship between
thickness and conductivity
 Sources of error
 deterioration of PEDOT
 contamination
 scratches on film surface
 irregular-shaped strips
 uneven electrode spacing
 internal resistance of silver epoxy and wire leads
 limited sensitivity of measuring equipment
Thickness resultsThickness results

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ConclusionConclusion
 Semiconducting polymers are versatile and adaptable
 gives manufacturers and researchers alike more control
 The disparate findings on conductivity for the two forms of
PEDOT/PVA compound indicate that more testing and analysis
is needed to characterize these novel conducting organic
substances
 Work is also needed to compile results found in a
comprehensive manner

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Future WorkFuture Work
 Need to test polyaniline/SU-8 composition
 Mechanical characterization
 micromachine a cantilever beam
 design setup to actuate oscillations
 measure resonance frequency
 calculate Young’s modulus
.
ρ
E
l
t
20 162.0=ƒ
ƒ0 = resonance frequency (Hz)
E = Young’s modulus
ρ= film density (kg/cm3
)

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AcknowledgementsAcknowledgements
 Professor Richard Nelson, Electrical Engineering & Comp Science
 Professor John LaRue, Mechanical & Aerospace Engineering
 Chang-hsiu Chen, Chemical Engineering & Materials Science
 Allen Kine, Lab Supervisor
 Said Shokair, UROP Director
 Edward Olano, UROP Undergraduate Research Counselor

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Questions?Questions?
University of California, IrvineUniversity of California, Irvine