Electrothermal actuators for SiO₂ photonic MEMS

This paper describes the design, fabrication and characterization of electrothermal bimorph actuators consisting of polysilicon on top of thick (>10 μm ) silicon dioxide beams. This material platform enables the integration of actuators with photonic waveguides, producing mechanically-flexible photonic waveguide structures that are positionable. These structures are explored as part of a novel concept for highly automated, sub-micrometer precision chip-to-chip alignment. In order to prevent residual stress-induced fracturing that is associated with the release of thick oxide structures from a silicon substrate, a special reinforcement method is applied to create suspended silicon dioxide beam structures. The characterization includes measurements of the post-release deformation (i.e., without actuation), as well as the deflection resulting from quasi-static and dynamic actuation. The post-release deformation reveals a curvature, resulting in the free ends of 800 μm long silicon dioxide beams with 5 μm-thick polysilicon to be situated approximately 80 μm above the chip surface. Bimorph actuators that are 800 μm in length produce an out-of-plane deflection of approximately 11 μm at 60 mW dissipated power, corresponding to an estimated 240 ^oC actuator temperature. The delivered actuation force of the 800 μm-long bimorph actuators having 5 μm-thick polysilicon is calculated to be approximately 750 μN at 120 mW.