Silicon-Based Microscale Multistable Metamaterials: Microfabrication and Characterization

Abstract Background The design space of multistable reconfigurable metamaterials, typically constructed of bistable unit cells, is virtually limitless; yet, many existing fabrication methods suffer from low spatial resolution or limited build volumes. This limits scalability and the construction of complex architectures composed of numerous building blocks. Microfabrication on silicon wafers overcomes these limitations, offering a scalable manufacturing route for architectures with large numbers of unit cells on a single wafer. Actuating and measuring the unstable response of microscale bistable structures is not trivial, calling for the development of specialized experimental tools. Objective (i) A scalable microfabrication protocol for creating multistable metamaterials composed of unprecedented numbers of bistable unit cells. (ii) An experimental method for actuating microscale bistable structures and characterizing their mechanical response to quasistatic loading in situ . Methods We employ microfabrication to realize free-standing, silicon-based, wafer-scale multistable metamaterials using photolithography, deep reactive ion etching, and vapor hydrogen fluoride etching, along with an experimental setup leveraging a micro-needle, a position-sensing detector, and in-situ full-field imaging for actuation and characterization. Results Bistable structures with a range of design parameters, along with various multistable chains comprising 5, 10, and 100 unit cells, have been successfully microfabricated on a single wafer. The non-monotonic force-displacement relations, characteristic of bistable structures, have been measured, linking structural design to mechanical behavior through experiments. Conclusions The established framework enables the creation and characterization of unit cells with tunable multistability, admitting closed-loop feedback between structural design, microfabrication, and characterization. This lays the foundation for metamaterial architectures with diverse functionality.