Electrical Characterization of Semiconducting Polymers Sanda Cea Faculty Mentors: Professor Richard Nelson (EECS) Professor John LaRue (MAE) Graduate student:

Electrical Characterization of Electrical 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

UCI Undergraduate Research Opportunities Program

OutlineOutline

Motivation

Background

Thin Film Fabrication

Electrical Characterization

Data Analysis & Results

Conclusion

Future Work

Acknowledgements

2006 IM-SURE Participants


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)


BackgroundBackground

Polymer structure chain composed of monomer units form weak intermolecular bonds

Emergent properties solubility elasticity (Young’s modulus) tactile strength electroluminescence electrical conductivity


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


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 37.49N-Methyl-2-pyrrolidone (NMP) 2.58 2.19Silquest A 187 0.86 0.70Isopropanol 53.34 59.35Dynol 604 0.30 0.27

Formulation Table for Conductive Baytron P


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% 0 110% 0.977 120% 2.2 130% 3.771 140% 5.867 150% 8.8 160% 13.2 170% 20.533 180% 35.2 190% 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


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


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


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


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


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

VR


Data Analysis & ResultsData Analysis & Results

Resistance, cross-sectional area, and length of sample strip can be used to calculate resistivity, (Ω-cm) inverse yields conductivity (S/cm)

Data plotted on logarithmic scale is compared against

existing data from previous study wtAL

AR


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


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


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

.

E

l

t20 162.0

0 = resonance frequency (Hz) E = Young’s modulus = film density (kg/cm3)


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


Questions?Questions?

University of California, IrvineUniversity of California, Irvine

Electrical Characterization of Semiconducting Polymers Sanda Cea Faculty Mentors: Professor Richard Nelson (EECS) Professor John LaRue (MAE) Graduate student:

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