Stroboscopic video microscopy with sub-nanometer accuracy for characterizing and monitoring MEMS

Current state-of-the-art systems for measuring movements at a microscopic scale in MEMS mostly rely on laser Doppler vibrometry (LDV). However, a major downside of LDV is that only one point at a time can be tracked and only in the direction of the incident laser beam. On the other hand, stroboscopic video microscopy (SVM) allows monitoring the in-plane displacements of all points in the field of view simultaneously. Commercially available vibrometry systems often provide an SVM mode. However, their resolution typically ranges from several to tens of nanometers. In contrast, some experimental SVM systems described in literature have achieved resolutions down to tens of picometers. Here we compare the performance of our self-built SVM setup to a modern commercial LDV device in characterizing piezoelectric actuators made from sintered lead zirconate titanate (PZT). The samples were stimulated with sinusoidal signals to induce surface strain in all three directions of space. Maps of the induced strain fields were recorded in-plane with SVM and out-of-plane with LDV. Our measurements prove that SVM, as realized in our setup, can be a cost-effective alternative to LDV for monitoring and characterizing of MEMS with sub-nanometer accuracy. Especially at low frequencies and when applied to challenging samples, SVM can outperform LDV in terms of accuracy and time efficiency.