MOEMS transducer with a non-linear transfer characteristic for static displacement measurement applications on the example of an inclination sensor

This contribution describes an micro-opto-electro-mechanical system transducer with a well defined inherent non-linear transfer behavior and its impact on the quantification of static and dynamic displacements in a vibrating measurement mode. The transducer's output signal is proportional to a light-flux that is modulated by two overlapping aperture arrays. One of these arrays is deposited on a fixed glass cover while the other one is etched into a moveable seismic mass of a silicon micro-electro-mechanical chip. The non-linear transfer characteristic is achieved by pairing triangularly shaped apertures with rectangular ones. The seismic mass is actuated by a mechanical shaker unit and the resulting first and second harmonics of the output signal are recorded with lock-in amplifiers. These harmonics contain information about both the static displacement and the vibration amplitude of the seismic mass. The presented method was tested with a proof-of-concept device and first measurement results exhibit a static displacement resolution of 3.67 nm which is a slight improvement compared to DC measurement approaches exhibiting a resolution of 5.39 nm. Furthermore, a inclination sensor was built employing this vibrating measurement approach showing that the resolution was improved at least by an factor of three.