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Joost J. Vlassak
Gordon McKay Professor of Materials Engineering
Education
Burgerlijk Ingenieur,
1989, Metallurgical Engineering, University
of Leuven
M.S., 1990, Materials Science, Stanford
University
Ph.D., 1994, Materials Science, Stanford
University
Academic Interests
Materials Engineering
The use of thin films in integrated circuits and micromachined devices has created a strong interest in the mechanical properties of thin-film materials and materials in small volumes. As the complexity of these systems increases, the materials used in them have to meet more stringent requirements. For example, until recently integrated circuits consisted of relatively few materials: single and polycrystalline silicon, various aluminum alloys, silicon oxides and nitrides of varying composition, as well as barrier films and silicides. Requirements for better electrical performance, however, have led to the incorporation of a host of new materials including Cu, silicon carbo-nitrides, and organosilicate-based dielectrics with low dielectric constants. Integration of these new materials into integrated circuit process flows poses interesting challenges for engineers in research and development organizations. A good understanding of the mechanical properties of these materials and of the interfaces between them is critical to the successful integration of these materials. Other applications where mechanical properties of thin films play a critical role include micro-electromechanical systems (MEMS), electronic packaging, and data storage (e.g., magnetic storage media).
Professor Vlassak has developed new experimental techniques for studying the mechanical behavior of thin films. He has investigated the effect of elastic anisotropy on stiffness measurements on small volumes of materials using nano-indentation techniques and has developed a technique for measuring the adhesion of brittle coatings to ductile substrates using plane-strain indentation. He has also developed a method for measuring stress-strain curves of freestanding films using silicon micro-machining techniques that can be applied to films as thin as a few tens of nanometers.
Current experimental research projects focus on the effects of microstructural length scales on the mechanical behavior of thin metal films, on the effect of environmental species on the adhesion and delamination of multilayered structures containing low-k dielectrics, on the shape memory effect in thin films of NiTi, Fe-Pd and Heusler-type alloys, and on various thin-film combinatorial approaches to alloy development. Recently, Professor Vlassak's group developed a micromachined parallel nano-differential scanning calorimeter for the thermal analysis of complex nano-scale material systems.
Theoretical work includes a new model for chemical mechanical polishing (CMP) based on contact mechanics, channel cracking in films on substrates of finite thickness, and various analyses of the effects of substrate properties and film porosity on nanoindentation of thin films.
