In-situ SEM with micro-heater for mechanical testing of thin films at elevated temperatures
Gi-Dong Sim (Harvard University), Joost Vlassak (Harvard University)
Mechanics of Thin Films and Multilayered Structures
Wed 9:00 - 10:30
Salomon 203
Mechanical characterization of thin films at elevated temperature is extremely important for the reliable operation of a micro/nano-scale device. However, due to the difficulty of testing nano, micro-scale free-standing thin films at elevated temperatures, this behavior is relatively unknown. Here we introduce our in-situ SEM (scanning electron microscope) mechanical tester which enables tensile testing in vacuum while observing the microstructural change. The displacement resolution of the tester is 10 nm with 250 µm stroke and the load resolution is 9.7 µN which is further adjustable by changing the spring of the tester. A silicon-based micomachined heater is fabricated for mechanical testing at elevated temperatures inside the SEM. Each heater consists of a tungsten heating element that also serves as a resistance thermometer. A current passed through the heating element heats the heater and the free standing metal thin film. Potential drop between the voltage probes is monitored during current flow and the temperature change is determined from a four-point thermistor resistance measurement that has been calibrated to temperature. To demonstrate the testing capabilities, tensile test were performed on submicron Cu and Au films at various temperatures up to 430°C. Stress-strain curves show a significant decrease in yield strength and initial loading slope for samples tested at higher temperature, which we attribute to grain boundary sliding with lattice diffusion and dislocation climb.