Building Three-Dimensional Nanostructures Via Membrane Folding

In Nanostructured Origami thin membranes are patterned in 2D and are then automatically folded in sequence to produce a 3D configuration. We have developed methods of both folding actuation and folded-structure alignment for patterned silicon-nitride membranes. We have demonstrated that ion implantation can be used to fold membranes. The implanted ions create stress, forcing the membrane to bend. A minimum bend radius of 1 µm using 100 nm-thick silicon nitride was achieved. The resulting 3D structure remains folded unless heated above 400C, at which point the helium diffuses out and the structure unfolds. In addition to experimental demonstration, we model the physics of the ion implantation to show that the ion-implant profile correlates to the observed folding. This is most clearly evidenced by the fact that membranes given low energy (shallow depth) implants fold downwards while membranes given high energy (large depth) implants fold upwards. Magnetic forces are an alternate actuation method to fold, and to align and reconfigure nanopatterned membranes. After folding, the membranes accurately self-align when brought into close proximity due to the interactive magnetic force between the arrays of nanomagnets. Since the self-alignment accuracy is better than the lithographic resolution, the membranes may be self-aligned to nanometer precision.

We are also developing a nanomagnetic stepper that utilizes the force between arrays of nanomagnets to precisely move a nanopatterned membrane along a substrate. After folding and magnetically aligning two membranes, the system is actuated by an external magnetic field that rotates or flips the magnetization of the nanomagnets, thus changing the equilibrium position. The stepper is wirelessly controlled and is non-hysteretic so the need for feedback is eliminated. We are exploring the stepper's use for reconfigurable photonic systems and wireless nano-device control.