Multi-axial electro-mechanical testing methodology for highly stretchable freestanding micron-sized structures

Recent advances in MEMS technology have brought forward a new class of high-density stretchable/flexible electronics as well as large displacement MEMS devices. The in-situ electro-mechanical characterization of such devices is challenging since it requires: (i) highly delicate sample handling, (ii) controlled application of large (hundreds of µm) multi-axial displacements to mimic service conditions, (iii) integrated electrical testing and (iv) fast actuation for cyclic testing. Techniques already developed for small-scale testing in literature fall short to meet the combined set of requirements. To this end, a characterization methodology that fulfills all these requirements is developed and presented here. The technique is based on a piezo-driven micro-tensile stage, which provides large multi-axial displacements with high resolution and fast actuation (4000 µm/s). This is combined with a method for sample microfabrication on a test-chip to warrant delicate sample handling. Proof-of-principle experiments are shown for multi-axial mechanical characterization, electrical characterization and high cycle fatigue testing of micron-sized highly stretchable interconnects. Experiments are conducted under in-situ microscopic observation using optical microscopy, scanning electron microscopy, and high-resolution profilometry. The generic platform proposed here can be used for other problems where similar requirements are faced, e.g. other miniaturized, large displacement electro-mechanical applications that are currently being developed.