Lithographically patterned polypyrrole multilayer microstructures via sidewall-controlled electropolymerization.

Composite materials comprising multilayers of metal and conductive polymer can have applications in sensing, biomedical, and energy storage/conversion scenarios. One attribute of such metal/polymer composites is that they typically display highly anisotropic electrical properties, which makes them useful as materials for microelectronic or magnetic devices. However, incorporating the deposition of conductive polymers into scalable and manufacturable fabrication processes can be challenging, as the mechanisms for electropolymerization are complex. We previously demonstrated an additive approach to fabricate metal/polymer multilayer structures, using soft magnetic alloys as the metal component and polypyrrole (PPy) as the polymer component. To extend the utility of these composites, the deposition of many multiples of alternating metal/polymer pairs within specifically defined lithographic molds is highly desirable. However, since the lateral growth of electrodeposited PPy is typically faster than vertical growth, non-uniform layer geometry and growth of the polymer on and above the patterned molds are often observed. In this work, we achieve suppression of lateral PPy growth by control of electropolymerization bath counter-anions and passivation of underlying metal layers during deposition. The lateral-to-vertical growth rate uniformity ratio is reduced by a factor of six (to approximately unity) through polymerization parameter optimization and exploiting a continuous five-bath electrodeposition approach. The reduction in lateral growth rate enhances the scalability of multilayer structures that are fabricated using this additive electrodeposition-based approach and provides a manufacturable route to additive, lithographically patterned metal/polymer composites with tunable volume and geometry, without sacrificing the microstructure and properties of the composite. [ABSTRACT FROM AUTHOR]