Thermo-Kinetic Actuation for Batch Assembly of Microscale Hinged Structures

This paper reports on surface micromachined hinged structure assembly using thermo-kinetic forces in the molecular flow regime. Ultrasonic vibration energy is used to reduce the static friction making the thermo-kinetic force comparatively significant. The thermo-kinetic force, resulting from the more energetic gas molecules emanating from the heated substrate, increases with pressure and substrate temperature in the molecular flow regime. The transition from viscous to molecular regime occurs as the molecular mean-free-path approximately equals the flap length, making the pressure threshold for thermo-kinetic flap actuation size dependent. In addition to the experimental results, one-dimensional and two-dimensional force models are presented. Examples of assembled structures are shown and assembly jig suitable for automated MEMS batch assembly is demonstrated. Index Terms MEMS, batch assembly, thermal actuation