Cooperative shape memory actuator systems for nanomechanics and nanophotonics

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This proposal represents the renewal of the joint project “Cooperative shape memory actuator systems for nanomechanics and nanophotonics”. During the first funding period we demonstrated that bi-directional actuation by Joule heating above room temperature is possible for TiNiHf shape memory alloy (SMA) films with thicknesses down to 220 nm. However, trimorph PMMA/TiNiHf/Si structures envisioned for bistable actuation could only be investigated by coupled simulations so far revealing the need for thick polymer layers, which introduces issues in manufacturing and in thermal actuation. Therefore, in this project extension, we will (1) mitigate these issues by introducing and investigating novel concepts for bistable SMA actuation in-plane and out-of-plane, (2) explore and numerically describe downscaling and size effects, and (3) develop cooperative multistable in-plane and out-of-plane microactuators for Si micromechanics and Si nanophotonics applications, respectively. Bistable SMA microactuation will be based on coupled pre-strained SMA bridge microactuators. Their functionality will depend on the stress from thermal treatment and intrinsic stress from the thin film growth process. A computationally-aided iterative design process will help to identify robust and energy-efficient actuator system layouts with high precision and downsizing potential (S. Wulfinghoff). Accurately controlled material properties, including stress engineering (A. Ludwig) will be combined with state-of-the-art micromachining for the co-integration of SMA/Si microactuators with Si micromechanical and/or nanophotonic waveguide structures (M. Kohl). Based on a combined experimental and simulation-based assessment of the multistable microactuator systems, undesired cross-sensitivities will be minimized and synergies will be enhanced.