|
|
Microresonators on flexible polymeric substrates
The fabrication and characterization of thin film silicon MEMS microbridges on flexible polyethylene terephthalate substrates is achieved. Surface micromachining using an aluminum sacrificial layer and a maximum processing temperature of 110șC was used for device fabrication. These microbridges are electrostatically actuated and their deflection at resonance and at low frequencies is measured optically. Quasi-DC deflection with a quadratic dependence of the actuation voltage is observed, and resonance frequencies up to 2 MHz and quality factors of around 500 are measured in vacuum.
Bending measurements are performed by subjecting these devices to tensile and compressive strain. The low frequency response (bridge deflection as a function of the applied voltage) was measured in air before bending and after every bending step. Under tensile strain, 16.6% of the devices survive the maximum bending with a radius of curvature of 1 cm, equivalent to a tensile strain 1.25%. In contrast, for compressive strain, 50% of the devices survive the bending corresponding to a radius of curvature of -0.5 cm, equivalent to a compressive strain of -2.5%. Thin film silicon microresonators on flexible plastic substrates can withstand more compressive strain than tensile.
Left: SEM micrograph of a thin film silicon MEMS bridge on PET subtrate. Right: percentage of devices functioning after bending of PET substrate as function of the radius of curvature (bottom axis) and the equivalent strain (top axis).