Quantitative optical measurement of microcantilever vibration; Applications to near-field microsensors

摘要

Optical measuring techniques in Micro-electro-mechanical systems (MEMS) are attractive ways of detection and reproducible methods. Applications of appropriate optical measuring techniques can be found in many situations: local study of materials constants, characterization of micromechanical systems, vibration analysis, and environmental behavior... Following this evolution, we present some applications of a heterodyne optical measuring technique to the vibration analysis of microcantilevers. We have developed a micromechanical resonator made of a silicon cantilever associated with a small probe embedded at one end. The interaction of the probe with the investigated medium modifies the vibration characteristics of the microcantilever. In a first part we will see that a vibration analysis enables the characterization of local elastic constants of a solid sample with a good accuracy. The second part of the presentation describes a very interesting MEMS combining acoustics and optical sensing. A small vibrating sphere immersed in a liquid sample replaces the tip usually used in near-field acoustics. This vibrating microsensor is able to locally measure both density and viscosity of liquid samples. The third part is devoted to a dynamic electric system with optical detection allowing to perform measurement of topography and others physical properties such as the contact potential difference of the same sample surface, simultaneously. In the presented applications, microcantilevers are used in the design of the microsystems. We show that optical heterodyne detection is a powerful tool to quantify the frequency, the amplitude, the phase and the damping of the vibration, which are the pertinent parameters in these popular MEMS.