Demonstration of Heterogeneous Structure for Fabricating a Comb-Drive Actuator for Cryogenic Applications

This study presents an experimental demonstration of the motion characteristics of a comb-drive actuator fabricated from heterogeneous structure and applied for cryogenic environments. Here, a silicon wafer is anodically bonded onto a glass substrate, which is considered to be a conventional heterogeneous structure and is commonly adopted for fabricating comb-drive actuators owing to the low-cost fabrication. The displacement sensor, also with comb-finger configuration, is utilized to monitor the motion characteristics in real time at low temperatures. The irregular motions, including displacement fluctuation and lateral sticking, are observed at specific low temperatures. This can be attributed to the different thermal expansion coefficients of two materials in the heterogeneous structure, further leading to structural deformation at low temperatures. The support spring in a comb-drive actuator is apt to be deformed because of suspended flexible structures, which affect the stiffness of the support spring and generate irregular yield behavior. The irregular yield behavior at low temperatures can be constrained by enhancing the stiffness of the support spring. Finally, we reveal that there are limited applications of the heterogeneous-structure-based comb-drive actuator in cryogenic environments, and simultaneously point out that the material substrate of silicon on the insulator is replaceable based on the homogeneous structure with a thin SiO₂ layer.