Downscaling and Temperature Homogenization of TiNiHf/Si Shape Memory Microactuators

This paper explores the downscaling limitations of TiNiHf shape memory films and TiNiHf/Si beam cantilever microactuators with respect to film thickness and temperature profile upon Joule heating. Shape memory alloys (SMAs) based on TiNiHf exhibit a large thermal hysteresis above room temperature in the order of 80 °C, which is highly attractive for switching applications. We demonstrate that TiNiHf films on Si (and SiO
2
/Si) substrates exhibit the shape memory effect above room temperature for decreasing film thickness down to a limit of 440 (220) nm. In addition, we introduce a novel design for temperature homogenization of cantilever-based TiNiHf/Si microactuators upon direct Joule heating, which improves actuation stroke by 90% and reduces power consumption by 62%. A fabrication process for TiNiHf/Si microactuators is presented, which enables their co-integration on Si photonic chips for photonic waveguide switching.