Permalloy/polydimethylsiloxane nanocomposite inks for multimaterial direct ink writing of gigahertz electromagnetic structures

In light of society's increasing demand for ubiquitous connectivity and high-speed communication, printed electronics could play a disruptive role in the design and manufacturing of high frequency radiofrequency (RF) passives. However, traditional ink-based printing technologies face significant challenges in their planar device geometries, limited material choices, and poor resolution (∼100 μm), which constrain the design of printable RF passives typically operatable in the kilohertz (kHz) to megahertz (MHz) frequency range. The low resolution of printing technologies also makes it challenging to integrate printed passives with lithography-manufactured active electronics to form RF circuitries with diverse wireless functionalities. Direct ink writing (DIW), on the other hand, allows the high-resolution manufacturing of three-dimensional (3D) device architectures that are critical for applications beyond the frequency of one gigahertz (GHz). However, current DIW-printed RF passives only employ a single conductive ink, which limits the passive device's performance. For example, in solenoidal inductors, the inclusion of a magnetic core would greatly enhance the per-area inductance. Here, we designed and synthesized a permalloy/PDMS magnetic nanocomposite ink by dispersing surface modified permalloy nanoparticles into a PDMS matrix. The optimal weight ratio of permalloy in PDMS was determined based on Bruggeman effective medium theory to afford a high operational frequency while maintaining high-resolution printability. By harnessing the multimaterial DIW of both a conductive silver nanoparticle ink and our new permalloy magnetic ink, we demonstrate printed solenoidal inductors and LC tanks integrating magnetic cores with enhanced inductance.