Optical MEMS vibration sensor

In this work a competitive OMEMS (optical micro electromechanical system) readout for displacement is presented. Congruent positioned gratings modulate the light flux caused by a relative in-plane displacement. As demonstrator, an inertial sensor is used. Consisting of a Si-chip bearing a perforated and spring suspended MEMS structure (seismic mass), which is bonded with SU8 to a glass chip featuring vapor deposited Cr-pattern. Both form a partially transparent sandwich structure where the transmittance depends on the position of the suspended Si mass. The modulated light flux is generated and detected by an SMD-LED and a phototransistor at the top and bottom side of the sandwich structure, respectively. First results show a high sensitivity of 21 mV/nm displacement of the seismic mass featuring a noise level of about 200 pm/√Hz.