Electrothermal Actuators for SiO2 Photonic MEMS

Abstract

This paper describes the design, fabrication and characterization of electrothermal bimorph actuators consisting of polysilicon on top of thick (>10 sans-serifμnormalm) 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 sans-serifμnormalm long silicon dioxide beams with 5 sans-serifμnormalm-thick polysilicon to be situated approximately 80 sans-serifμnormalm above the chip surface. Bimorph actuators that are 800 sans-serifμnormalm in length produce an out-of-plane deflection of approximately 11 sans-serifμnormalm at 60 mW dissipated power, corresponding to an estimated 240 ∘normalC actuator temperature. The delivered actuation force of the 800 sans-serifμnormalm-long bimorph actuators having 5 sans-serifμnormalm-thick polysilicon is calculated to be approximately 750 μN at 120 mW.

Post-Release Deformation and Motion Control of Photonic Waveguide Beams by Tuneable Electrothermal Actuators in Thick SiO2

“…As mentioned in Section 2.2 , to protect the poly-Si layer during the subsequent Si etching steps to release the suspended structures, a layer of PECVD SiO is used to cover the entire wafer ( Figure A1 d), and then the areas where the bondpad and suspended structure without the poly-Si pattern are located are opened by plasma etching ( Figure A1 e). Removing the PECVD SiO layer on the bondpad enables the electrical probing and wire-bonding with PCBs (Printed Circuit Boards) [ 9 ]. As the PECVD SiO stack causes additional post-release deflection, for the SiO -only section without poly-Si, there is no need to keep this PECVD SiO .…”

“…As the PECVD SiO stack causes additional post-release deflection, for the SiO -only section without poly-Si, there is no need to keep this PECVD SiO . This is also a major difference, between the front-side recipe that was used before [ 8 , 9 , 10 ] and the current one that needs to facilitate the post-release deformation within the PHASTFlex alignment scheme. After this local removal of SiO , another very thin SiO (∼200 m) is deposited ( Figure A1 f).…”

“…This paper focuses on the design and optimization of the MEMS functions, specifically for out-of-plane translation and rotation around the light-propagation axis ( y and in Figure 1 ). Earlier work has proposed the use of electrothermal actuators [ 8 , 9 , 10 ], which are integrated with the ∼16 m-thick (mechanically dominant) SiO TriPleX-material stack. Together with the SiO stack, the electrothermal actuators in this paper also include a 5 m-thick layer of boron-doped polycrystalline silicon (poly-Si) that serves both as heater layer and structural layer.…”

“…Earlier designs of the bimorph actuator, consisting of a poly-Si layer with almost the same length as the SiO beam, have shown more than 60 m post-release deflection, while the achieved motion within the safe operating range was measured to be less than 20 m [ 8 , 9 , 10 ]. A short-section poly-Si bimorph actuator, i.e., an actuator where the poly-Si track is shorter than the SiO beam, was suggested before [ 22 ].…”

Why most experiments in psychology failed: sample sizes required for randomization to generate equivalent groups as a partial solution to the replication crisis

“…T.-J. Peters & Tichem, 2016) or magnetic resonance imaging equipment (and also many participants; Szucs & Ioannidis, 2017). In psychology, many participants are required for randomization to succeed.…”