1. Conformal Charge Barriers For Organic Electro-Optics
Scott P. Merry1,2, Delwin L. Elder2, and Larry R. Dalton2
1Nanotechnology Department, North Seattle College, Seattle, WA 98103
2Department of Chemistry, University of Washington, Seattle, WA 98195
Introduction
Organic electro-optic (EO) molecules can dramatically increase the speed of fiber-optic communications while reducing the size and power requirements of the EO modulator.
Molecules must first be aligned using a strong electric field. Leakage current through EO material reduces alignment and thus performance.
Solvent-cast charge barrier layers reduce current in parallel plate test devices, but cannot be applied as conformal (consistent in depth) coatings in the microscopic trenches in silicon fiber-optic modulators.
We hypothesized that a self-assembled monolayer or LbL film could work as an effective charge barrier layer and be applied as a conformal coating.
Data /Results
Figure 2. Electrical trace of typical test
Figure 3. Optical trace of typical test
Real-time monitoring and data collection for temperature (green), current (blue) and voltage (black) during poling of sample devices.
EO material must be heated to glass transition temperature (Tg) to allow molecules to move into alignment under poling voltage.
Optical data is also monitored and collected.
Im is proportional to r33, the figure of merit for comparing EO materials.
Conclusions
EO devices were successfully fabricated with LbL or SAM barrier layers.
Peak conductance measurements (Figure 4a), show devices with barrier layers had no decrease in leakage current compared to devices without a barrier layer.
The 4.5 bilayer charged polymers barrier layer devices exhibited leakage current similar to those with no barrier layer, while SAMs showed increased current (Figure 4a).
Charge barrier layers had little effect on r33, the figure of merit for comparing electro-optic activity (Figure 4b).
Barrier layers did not negatively effect EO thickness. Phenyl-phosphonic acid barrier layers were associated with increased film thickness (Figure 4c).
Little change in surface roughness was observed between different charge barrier layers (Figure 4d).
Temperature
Current
Voltage
Figure /50 blend of two EO molecules used in our tests
References
Dalton, L. R.; Sullivan, P. A.; Bale, D. H. Chem. Rev. 2010, 110, 25.
Jin, W.; Johnston, P. V.; Elder, D. L.; Tillack, A. F.; Olbricht, B. C.; Song, J.; Reid, P. J.; Xu, R., Robinson, B. H.; Dalton, L. R. App. Phy. Lett., 2014, 104,
An, M.; Hong, J.-D. Thin Solid Films 2006, 500, 74.
Havare, A. K.; Can, M.; Demic, S.; Okur, S.; Kus, M.; Aydin, H.; Yagmurcukardes, N.; Tari, S. Synth. Met. 2011, 161, 2397.
Bardecker, J. A.; Ma, H.; Kim, T.; Huang, F.; Liu, M. S.; Cheng, Y.-J.; Ting, G.; Jen, A. K.-Y. Adv. Funct. Mater. 2008, 18, 3964. a. b.
Methods
Temperature-controlled stage
Glass Substrate
ITO electrode V
Barrier Layer
EO Material
Gold
Device Structure
Electric Field Poling 50 V/µm
Gold electrode
ITO electrode V
Barrier Layer
PSS/
PDADMAC
4-Cyanobenzoic acid
Phenyl-phosphonic acid
Aminopropyl-phosphonic acid
Materials used for barrier layers
Acknowledgments
A special thanks to Prof. Bruce H. Robinson and Dr. Andreas F. Tillack of the University of Washington, Department of Chemistry, for their knowledge of chemical physics. Nathan Sylvain, Huajun Xu, Kerry Garrett, and Peter Johnston of the Dalton Lab provided background on chromophores and their chemistry. Thanks also to Alissa Agnello and Dr. Peter Kazarinoff for their work on the Nanotechnology program at North Seattle College.
Bilayers of oppositely charged polymers
ITO + -
Sonicate
Plasma clean
NH4OH/H2O2 clean
Spin coat from 20 mM polymer sol’n + + + + +
Self-Assembled Monolayers (SAM)
Heat 140 C
(Promotes covalent attachment)
Sonicate
Plasma clean
Dip in
1 mM sol’n
ITO OH
ITO
ITO OH
Figures 4. a, b, c, d. Characterization by barrier layer type.
ITO
This material is based upon work supported by the National Science Foundation (Grant No. DMR ). Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.
The authors acknowledge partial financial support from the Air Force Office of Scientific Research (FA , FA ).