A Methodology for Accurately Measuring Mechanical Properties on the Micro-Scale

A methodology has been developed for accurately measuring the mechanical properties of materials used on the micro-scale. The direct tension test method using a dog bone-type specimen has been employed, as it is the most effective and straightforward method to obtain results including a full stress-strain curve. The goal of this investigation was to develop a universal, yet simple and reliable, methodology to be used for accurate characterisation of mechanical properties for a wide variety of materials. Specimens from single crystal silicon were fabricated using photolithography by means of deep reactive ion etching. This material was chosen as it is expected that on both the micro- and macro-scales, Young's modulus will have the same value. Hence, the accuracy of the methodology may be unambiguously examined. The test set-up includes a small test machine containing a load cell whose maximum capacity is 5 N and is capable of direct gripping and displacement control. The specimens were found to have a trapezoidal cross-section that was accurately measured using a scanning electron microscope. The strains were obtained by means of digital image correlation using images obtained via optical microscopy. The quantities measured include Young's modulus E, the fracture strength Sigma(f) and the fracture strain epsilon(f). The average value of E obtained in the micro-tests agrees well with the reference value obtained on the macro-scale.