Thermomechanical MEMS membranes for fiber optic temperature sensing

In this study, the design, fabrication, and characterization results of square and circular cross-sectioned, bimaterial microelectromechanical system (MEMS) membranes are presented. The MEMS structures, having width of 250 μm to 1.5 mm and 1-4 mm² die area, were designed towards integration on a single-mode fiber tip for temperature-sensing. Embedded diffraction grating underneath each membrane allows for interferometric detection of thermomechanical response through backside laser illumination. The displacement of MEMS membranes was monitored under direct heating, revealing 50-1800 nm/°C thermomechanical sensitivity range. Furthermore, atomic force microscopy-based stiffness measurement on the MEMS membranes revealed a spring constant within 2-30 N/m range. Temperature measurement range and speed of the MEMS sensors were thoroughly tabulated based on experimental findings, as well as finite-element simulations and analytical calculations. Finally, proof-of-concept testing of a selected device was accomplished through air-coupling of the MEMS structure with a gradient index-collimated fiber, revealing <35 m °C temperature sensitivity using a low-cost laser source and detector.