Controlling damping and quality factors of silicon microcantilevers by selective metallization

Ceramic microresonators coated with relatively thin metallic films are widely used for sensing, scanning probe microscopy, signal processing and vibration energy harvesting. The metallization improves optical reflectivity and electrical conductivity, but invariably degrades the quality factor ( Q ) of resonance by increasing the amount of energy dissipated during vibration. Developing strategies for controlling damping due to metallization is vital for the design of high-performance microresonators. This paper presents a strategy based on the insight that dissipation is a function of the deformation experienced by the thin film during oscillation. Therefore, damping can be controlled by patterning the metal in regions of low strain. A simple analytical model is developed to quantify the change in damping as a function of selective metallization along the length of a microcantilever. The predictions of this model are in good agreement with measurements of damping in single-crystal silicon microcantilevers that are partially coated on one surface with 100 nm thick aluminum films. Crucially, damping due to clamping, support and viscous losses is minimized in these structures to enable a careful comparison of theory with experiments. Coating 20% of the length of the beam starting from the tip has no significant impact on damping in either the first or the second mode of vibration. In contrast, placing the same size of metallization at the root leads to considerable dissipation; in the first mode, the damping due to this patch is ∼60% of that caused by a full coat.