Nonlinear elastic imaging techniques for MEMS reliability assessment – ANL-MEMS

The present fundamental research and experimental development project is dedicated to the use of new nonlinear acoustic imaging techniques for non-destructive testing of Micro-Electro-Mechanical Systems (MEMS) reliability. The goal here is to develop and apply new original nonlinear acoustic methods for defects characterization and imaging of MEMS. The first technique we consider here is the Opto-Acousto-Optical method that uses lasers both for generation of sound waves and for detection of the nonlinear acoustic response of cracks, thus representing a fully non contact procedure. The second method is Magneto-Acoustic wave phase conjugation that essentially uses the ultrasound wave front reversal with the aid of the electromagnetic pumping in active magnetic materials. Being applied to surface or guided acoustic waves, it represents an integrated technique for in situ defect detection. The combined use of these techniques will offer a complete reliability assessment tool presenting great benefits both for manufacturing MEMS and for testing them in real operating conditions.

In addition to development of the non-destructive testing techniques, a part of the project is dedicated to fundamental experimental and theoretical study of the nonlinear acoustic behaviour of cracks, delaminations and other fatigue-related material degradations, and to creation of a numerical tool modelling the nonlinear elastic wave propagation in MEMS. The numerical code will be based on a multi-level consideration of underlying physical phenomena and of MEMS structural characteristics; in particular, by accounting for hysteretic mechanical constitutive properties at the micro-scale level, it is possible to predict its implications on the structural dynamics at the macroscopic level.

It is essential to note that both nonlinear methods use only those frequency components of acoustic spectrum which are excited due to material nonlinearity and are absent in the acoustic field launched in the material by the transducers. This condition is one of the basic principles of nonlinear acoustic diagnostics.