An In-Situ, Micro-Mechanical Setup with Accurate, Tri-Axial, Piezoelectric Force Sensing and Positioning

Abstract

AbstractTo enable accurate characterization of the mechanical behavior of materials at the micro-scale, e.g., in micro-systems, experiments are required that are representative of the actual (often multi-axial) loading conditions to which these materials are subjected during fabrication and operation. Equally important is the acquisition of mechanical data in the form of multi-axial force measurements, and the measurement of kinematics by in-situ microscopic techniques. To this end, a micro-mechanical testing rig is here realized using commercially available piezoelectric actuators. It is shown that the setup measures forces with a resolution of $\sim 0.3$∼0.3 [mN] in the x- and y-directions, and $\sim 50$∼50 [mN] in the z-direction, over a range of 5 [N], yielding a high dynamic (force) range. Furthermore, displacements can be imposed with a resolution of $\sim 1$∼1 [nm] over a range of 200 [μ m], in all three directions (x, y, z). The setup is compact, vacuum compatible, and specimens are loaded on top of the setup so that the field of view is unobstructed, allowing for in-situ testing with optical and scanning electron microscopy, and optical profilometry. A generic method is developed for extracting quasi-static forces from the piezoelectric actuators. Furthermore, challenges raised from the use of commercial actuators, for which the public technical specifications are generally incomplete, are overcome and the solution strategy is described. Proof-of-concept experiments on flexible, organic, light-emitting diodes demonstrate the potential of the setup to provide rich micro-mechanical data in the form of tri-axial force and displacement measurements. The commercial availability of the piezoelectric actuators, combined with the proposed engineering solutions lead to a generally accessible micro-mechanical test setup to investigate small-scale specimens under realistic, multi-axial loading conditions.