An experimental set-up to measure the out-of-plane displacement field of surfaces in reflection microscopy is presented. It is derived from a Nomarski shear-interferometer. When the shear is greater than the length of the microcantilever, this interferometer, used with a sinusoidal phase modulation and four integrating buckets, allows one to obtain the displacement field of the observed surface, with a reproductibility in the 10 pm range. Identification techniques derived
from the "Equilibrium Gap Method" developed recently to measure local mechanical properties and loading, the displacement field measured by the shear-interferometer may be used to determine simultaneously the "temperature" field and the local elastic properties of the cantilever. The feasibility of the in-situ (in water solution) full-field measurement of displacement fields in MEMS is proved, and preliminary results tends to show that mechanical effets induced by DNA hybridization are heterogeneous.
We describe a new approach for the parallel reading of the response of micromechanical sensors in array using an interferential imaging method coupled with a multichannel lock-in detection. The mechanical response of each sensor is deduced from the image of their topography. The goal is the detection of stress changes through the measurement of induced topography changes between loaded sensors and reference sensors. A measurement of the out-of-plane displacement field is a sensitive and reliable method to determine the mechanical stress in microcantilevers. In this study gold-covered SiO2 cantilevers have been used as sensors and a displacement measurement sensitivity of 230 pm has been achieved with no averaging. Such a value is equivalent to a stress change sensitivity better than 0.001 MPa for our application. The fields of application extend from DNA biochips to environmental sensors.