Non-Contact Mechanical Testing and Characterization of Micro-Scale Structures

A non-contact testing and characterization method based on air-coupled acoustic excitation and interferometric displacement measurements of micro-scale MEMS structures at room conditions is introduced. In demonstrating its potential uses in testing and characterization, the present non-contact approach is applied to (i) micro-cantilever beams and (ii) rotational disk oscillators. Air-coupled multi-mode excitation of micromechanical cantilever-type oscillators under a pulsed acoustic field generated by an air-coupled transducer is demonstrated and reported. Also, the testing and characterization of a micro-scale rotational disk oscillator developed for a new class of sensor platform is demonstrated. The main design objective of the rotational disk oscillator class is to overcome the out-of-plane motion related sensitivity limitations of the cantilever-based sensors at high frequency operations. The dynamics of the rotational disk oscillators is more complex than micro-cantilever beams due to its in-plane motion in addition to its various out-of-plane modes of vibration. The fabrication of a rotational disk oscillator requires a suspended disk whose underside is visibly inaccessible due to a narrow micro-gap. In addition to the dynamic characterization of the cantilever beams and rotational disk oscillators, the current investigation demonstrates that the presented approach can address unique structural concerns such as the verification of a gap separation of the rotational oscillator from the underlying silicon substrate. Utilizing the proposed technique, the resonant frequencies of the oscillator structures are obtained and its potential uses in the testing and characterization of micro-scale structures are discussed. The major specific advantages of the introduced approach include that (i) its noncontact nature can eliminate testing problems associated with stiction and adhesion, and (ii) it allows direct mechanical characterization and testing of components and sub-components of a micro-scale devices.