School of Mechanical Engineering Seminar
Wednesday 19.06.2024 at 14:00

Wolfson Building of Mechanical Engineering, Room 206

Squeeze-Film Damping Effect in a Switching MEMS Fabry-Pérot Filter: Theoretical and Experimental Investigation

Peleg Levin

PhD student under the supervision of Prof. Slava Krylov

School of Mechanical Engineering, Tel Aviv University, Tel Aviv, Israel

Micromachined tunable Fabry-Pérot filters (μFPF) are MEMS devices poised to democratize hyperspectral imaging by enabling affordable mass production. These devices comprise a pair of parallel optical mirrors with an adjustable optical gap, typically ranging from 100 to 500 nm, and are electrostatically actuated to operate in the transient regime. Traditional μFPFs face significant limitations, such as an optical gap tunable range restricted to one-third of the initial gap due to coplanar coatings and electrodes. Our research addresses these limitations by developing and manufacturing a new type of μFPF, where electrodes are decoupled from the optics, allowing for a much broader tunable range. In terms of MEMS technology, we've utilized advanced techniques such as silicon on glass (SOG) wafers, isotropic wet etching of 200 μm borosilicate wafers, and through-glass vias (TGVs).

A critical performance metric for hyperspectral imaging applications is the transition time between various optical gaps, which should be under 2 ms. The challenge arises from the significant squeeze-film damping force due to the high aspect ratio (1:10,000) of the mirror's optical gap to their lateral dimension, necessitating high vacuum levels for achieving short switching times. Therefore, comprehensive modeling of the device switching dynamics, considering squeeze film damping, is essential.

Existing models primarily address oscillatory motion and are inadequate for devices operating in the transient regime with rarefied gas flow in the squeeze film. Our study develops new lumped models to describe the device's transient switching dynamics under conditions where the squeeze film gas flow is in the transitional and free molecular flow regimes. These models are validated through numerical simulations and experimental comparisons.

We also explore the influence of a secondary tilt mode on squeeze film damping in devices undergoing linear out-of-plane motion to transition between discrete states. Inducing tilt through uneven voltage actuation on the electrodes accelerates gas diffusion in the squeeze film region, thus enhancing switching dynamics. This novel approach is validated using a numerical model, and optimal actuation strategies are derived to further minimize switching time.

Our findings on squeeze film damping and optimized actuation strategies significantly enhance the performance of μFPFs and have broader implications for the design and operation of various MEMS devices. This study not only advances the development of tunable MEMS Fabry-Pérot filters for hyperspectral imaging but also provides valuable insights for other MEMS applications requiring efficient actuation and dynamic response.