We have developed a novel chip-level membrane deflection experiment particularly suited for the investigation of sub-micron thin films and microelectro-mechanical systems. The experiment consists of loading a fixed–fixed membrane with a line load applied at the middle of the span using a nanoindenter. A Mirau microscope interferometer is positioned below the membrane to observe its response in real time. This is accomplished through a micromachined wafer containing a window that exposes the bottom surface of the specimen. A combined atomic force microscope/nanoindenter incorporates the interferometer to allow continuous monitoring of the membrane deflection during both loading and unloading.

The MDE experiment is used to investigate the mechanical properties of ductile materials such as gold, copper, aluminum, and shape memory alloy; brittle materials such as ultrananocrystalline diamond, diamond-like carbon, SiC, and Si3N4; and composite materials. We have investigated the plastic behavior of FCC metals (gold, copper, and aluminum) in the submicron range. The role of the microstructures on observed size effects were analyzed by TEM/SEM studies. The challenges will remain in modeling of the size effects. MDE was also used to characterize the strength and the fracture toughness of ultrananocrystalline diamond and diamond-like carbon. The strength of the brittle materials was found to increase while decreasing the sample size. Current work is further assessing the validity of the Weibull concept, the location of the doping in the nanostructure and its effect on strength and toughness.

Personnel

• H.D. Espinosa (PI)
• B. Peng (Graduate Student)
• N. Moldovan (Research Faculty)

Selected Publications

• H.D. Espinosa, B.C. Prorok, and M. Fischer, "A Methodology for Determining Mechanical Properties of Freestanding Thin Films and MEMS Materials," Journal of the Mechanics and Physics of Solids, Vol. 51, No. 1, p. 47-67, 2003.

• H.D. Espinosa, B.C. Prorok and B. Peng, "Plasticity Size Effects in Freestanding Submicron Polycrystalline FCC Films Subjected to Pure Tension," Journal of the Mechanics and Physics of Solids, Vol. 52, No. 3, p. 667-689, 2004.

• H.D. Espinosa, B. Peng, B.C. Prorok, N. Moldovan, O. Auciello, J.A. Carlisle, D.M. Gruen, and D.C. Mancini, "Fracture Strength of Ultrananocrystalline Diamond Thin films - Identification of Weibull Parameters," Journal of Applied Physics, Vol. 94, No. 9, p. 6076-6084, 2003.

• H.D. Espinosa, B.C. Prorok, B. Peng, K.-H. Kim, N. Moldovan, O. Auciello, J.A. Carlisle, D.M. Gruen, and D.C. Mancini, "Mechanical Properties of Ultrananocrystalline Diamond Thin Films Relevant to MEMS Devices," Experimental Mechanics, Vol. 43, No. 3, pp. 256-268, 2003.

• N. Pugno, B. Peng and H.D. Espinosa. "Predictions of Strength in MEMS Components - A Novel Experimental-Theoretical Approach," International Journal of Solids and Structures, Vol. 42, No. 2, p. 647-661, 2005.

• H.D. Espinosa and B. Peng, "A New Methodology to Investigate Fracture Toughness of Freestanding Thin Films and MEMS Materials," JMEMS, Vol. 14, No. 1, p. 153-159, 2005.

• B. Peng, H.D. Espinosa, N. Moldovan, X. Xiao, O. Auciello, and J.A. Carlisle. "Fracture Size Effect in UNCD - Applicability of Weibull Theory," Journal of Materials Research, Vol. 22, No. 4, p. 913-925, 2007.

• B. Peng, N. Pugno and H.D. Espinosa, "An Analysis of the Membrane Deflection Experiment Used in the Investigation of Mechanical Properties of Freestanding Submicron Thin Films," International Journal of Solids and Structures, Vol. 43, No. 11-12, p. 3292-3305, 2006.