electrical characterization of semiconducting polymers sanda cea faculty mentors: professor richard...
Post on 21-Dec-2015
218 views
TRANSCRIPT
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
UCI Undergraduate Research Opportunities Program
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)
UCI Undergraduate Research Opportunities Program
BackgroundBackground
Polymer structure chain composed of monomer units form weak intermolecular bonds
Emergent properties solubility elasticity (Young’s modulus) tactile strength electroluminescence electrical conductivity
UCI Undergraduate Research Opportunities Program
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
UCI Undergraduate Research Opportunities Program
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
UCI Undergraduate Research Opportunities Program
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
UCI Undergraduate Research Opportunities Program
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
UCI Undergraduate Research Opportunities Program
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
UCI Undergraduate Research Opportunities Program
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
UCI Undergraduate Research Opportunities Program
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
UCI Undergraduate Research Opportunities Program
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
UCI Undergraduate Research Opportunities Program
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
UCI Undergraduate Research Opportunities Program
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
UCI Undergraduate Research Opportunities Program
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
UCI Undergraduate Research Opportunities Program
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)
UCI Undergraduate Research Opportunities Program
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