| AVS 63rd International Symposium & Exhibition | |
| Plasma Science and Technology | Monday Sessions |
| Session PS+SE-MoM |
| Session: | Atmospheric Pressure Plasma Processing |
| Presenter: | Souvik Ghosh, Case Western Reserve University |
| Authors: | S. Ghosh, Case Western Reserve University P.X.-L. Feng, Case Western Reserve University C.A. Zorman, Case Western Reserve University R.M. Sankaran, Case Western Reserve University |
| Correspondent: | Click to Email |
Stretchable electrically conductive patterns are an importance class of materials for emerging electronic applications. A relatively well-established approach for their fabrication is printing metal nanoparticle inks on elastomeric polymers to combine the high electrical conductivity of metals with the large mechanical deformability of polymers. However, nanoparticle-based inks have organic-based solvents and contain organic capping molecules to stabilize the nanoparticles, limiting the conductivity of as-printed features and requiring high temperature sintering (>200 oC) to remove the organics, which is not compatible with most polymers. Moreover, the printed metal nanoparticle film may not be well-integrated with the polymer, compromising conductivity at large deformation.
Here, we report a plasma-based approach to producing electrically-conductive metallic features at the surface of polymer films that eliminates the need for nanoparticle inks and has the potential to better integrate metals and polymer. In general, metal salts are initially mixed with a polymer and cast as a thin film. The films are then exposed to a plasma which results in reduction of the metal ions to metal nanoparticles. By using an atmospheric-pressure microplasma jet and rastering the metal-ion-containing polymer film, the reduction is localized and two-dimensional patterns of metal nanoparticles are fabricated.
We initially focused our study on films prepared from silver nitrate (AgNO3) and polyacrylic acid (PAA) which is known to cross-link with metal cations. After exposure to the microplasma, films were characterized by X-ray diffraction (XRD) which confirmed crystallinity from the presence of peaks corresponding to face-centered cubic silver (Ag). Further materials analysis by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDX) revealed that microplasma reduction leads to nanoparticle formation only at the surface of the film. The bulk resistivity of the patterned features was determined by two-point probe measurements and reached values as small as ~1 mΩ-cm.
To obtain stretchable films, two approaches were explored. First, PAA-Ag thin films were cast on top of polydimethylsiloxane (PDMS) - an elastomer, and reduced by the microplasma. Second, we extended our process to a rubber polymer (styrene-isoprene-styrene) (SIS) which could be mixed with silver trifluoroacetate to be reduced and form Ag in a single polymer layer. Results for the resistivity as a function of the strain in the various material systems will be presented, as well as a working model for the role of the plasma in the reduction of the metal in the polymer and its final morphology.