In Situ Platform for Isothermal Testing of Thin-Film Mechanical Properties Using Thermal Actuators

An in situ tensile test platform has been developed to study the mechanical properties of thin-film metal specimens. The fully integrated on-chip platform loads a specimen using a thermal actuator (TA). TAs conveniently provide high forces and excellent alignment, but generate large heat that can flow to specimens and raise their temperature. In the new design, heat flow to the specimen is negligible. This attribute was achieved by introducing a thermal resistor that limits heat flow to the specimen and a heat sink that shunts the remaining heat. Tensile residual stress in the specimen was eliminated by including preinserted microgrippers. A comprehensive error analysis indicates that the strength accuracy is ±5% (one standard deviation). The platform was used to study the strength-related mechanical properties of Al/0.5 wt% Cu microtensile bars with two different thicknesses. Initial tests indicate that 0.63-μm-thick tensile bars exhibit higher strength, a larger strain hardening coefficient, and less elongation than 1.03-μm-thick tensile bars. Transmission electron microscopy indicated that the lower ductility was due to plastic strain localization. When the tensile bar length is decreased from 200 to 70 or 50 μm, strength increased by 40% for both thickness values.