Advancing FHE Performance with Novel Materials
by Dr. Nick Morris, FHE Technology Manager
Creating and maintaining a robust commercial ecosystem around flexible hybrid electronics (FHE) is one of NextFlex’s primary goals. To help achieve this, we coordinate eleven technical working groups (TWGs) made up of devoted NextFlex members and government partners to identify key technology gaps and technology planning requirements to advance the manufacturability of FHE. This is the second in a series of blog posts on the FHE Manufacturing Roadmap Summary which highlights key opportunities identified by each TWG. This post focuses on the Materials group.
Material properties and functionality are critical drivers for the technological development and performance of FHE devices. Materials development is driven by the needs of the NextFlex community, but also by cross-fertilization from materials developments outside of the Institute. Materials are the building blocks of FHE and include substrates, conductive and resistance inks, dielectrics and encapsulants, and active materials. Through printing and post-processing, these materials create device that perform reliably under extreme electromechanical requirements. The latest materials sets used in FHE manufacturing are listed below:
Materials categories and list of commonly used materials in FHE manufacturing.
Passive conductors typically comprise silver (Ag) inks, copper (Cu) inks and pastes, graphene inks, or highly doped carbon-based inks. Conductivity is of paramount importance for these materials. At this time, typical Ag inks operate at roughly 10-20% (or higher) of the conductivity present in bulk silver when oven or hotplate cured. Copper inks can be oven baked or photo sintered and are generally solderable when printed on substrates that can withstand the high temperature gradient. While the conductivity of copper inks and paste is often higher when expensive sintering processes are used, they do not possess the conductivity or current carrying capacity of bulk metals.
This disparity between printed and bulk metal trace conductivity remains one of the largest opportunities, though significant progress is being made. Particle-free silver and copper inks show significant potential to close this gap, though further development is needed to make them cost effective and fully compatible with lower temperature organic substrates and low temperature solders.
Dielectrics and encapsulants are another primary focus for development in FHE materials. These insulating materials can be deposited onto or molded around a surface to act as a barrier between conductive materials. The most common printed insulators are polymers with a saturated (non-conjugated) carbon backbone, but metal-oxide or ceramic-bearing materials are also of considerable interest. Key properties of interest include dielectric and breakdown strength for insulating adjacent traces, especially for high power FHE electronics. Printable low loss materials for RF applications are also highly sought by the community.
Roadmap taxonomies and technical gap areas identified by the Materials group.
A third key opportunity identified addresses an extreme electromechanical challenge: stretchable electronics. Highly stretchable substrates with low hysteresis and printable inks with constant electrical performance over a large strain range are highly desirable. These materials are of particular interest in the fields of wearable FHE devices for medical or health monitoring and soft robotic applications, where interconnects can experience very high mechanical strains. Room temperature liquid metal-based inks show significant promise, but introduce additional materials compatibility and encapsulation challenges, though these are currently being overcome by NextFlex members.
For more information, download the NextFlex FHE Manufacturing Roadmap Summary!
If you are interested in submitting a story or interview for the NextFlex blog, contact us here.