MEMS & NEMS for the measurement of the coupled properties of materials at the nanometer scale Materials science today is a highly sophisticated field of endeavor, combining physics, chemistry,
engineering and, to some extent, biotechnology. Several pioneering studies have shown that when
confined to sub-micron dimensions, many materials – including metals, semiconductors, ceramics and
polymers – exhibit unexpected and potentially useful properties completely different from their bulk
counterpart.
The measurement of the physical properties such as the mechanical behavior of submicron sized specimens is extremely challenging due to difficulties for manipulating samples, for applying small load and for extracting accurate stresses and strains. Our team has developed over the last 5 years a novel
concept of on chip nanomechanical testing1,2, to extract the mechanical properties of ductile and brittle materials with thickness ranging from a few $m down to ~50 nm, allowing multiple loading configurations and geometries. This new concept relies on nanofabrication techniques destined to the production of nanoelectronic devices and NEMS. The first idea is to use internal stresses to actuate and impose the load to the tested sample which is directly deposited on a patterned substrate. The second idea is to multiply elementary micro- or nano-structure rather than to build on single complex multi-purpose micro- or nano-structure.
Tensile tests and creep tests have been performed up to fracture on brittle materials such as SiN, poly and monocrystalline Si and ductile thin films such as Al, Al-1%Si, Ti, Cr and Pd. Size effects have been demonstrated and elucidated, such as the increase of the yield stress with decreasing film thickness in Al and Pd, the increase of fracture strain of Si up to 5%, the ultra high strain hardening in twinned nanocrystalline Pd films, etc. These results demonstrate the potential of the new technique.
Now, mechanical stress does not only induce deformation but also gives rise to coupling effects such as induced electric field (piezoresistive/piezoelectric effects) or magnetic field (piezomagnetism/magnetostriction).
The aim of the present research project is to push further the original lab-on-chip concept to explore the coupled physical properties (piezoresistance, magnetostiction, thermoconductivity, etc.) of materials thinner than 50 nm (Si, Ni, graphene, etc.) in the form of thin films, nanowires or nanoribbons. Those systems are used in nanoelectronics as well in nano-coatings introduced in many industrial sectors such as glass, metallurgy, surgery tools, medical prostheses, etc.
A new line of nanolab-on-chip will be developed to study electromechanical properties of graphene. Graphene will be addressed as a base material for building NanoElectroMechanical Systems (NEMS)3. The fast-growing interest for graphene results from its lightness and stiffness which are essential characteristics sought in NEMS sensing applications. Indeed, the prototypical NEMS is a nanoscale resonator; a beam of material that vibrates in response to an applied external force. The ultimate limit is a stiff one atom thick resonator. Graphene is the ideal candidate since it is the strongest material ever tested4 allowing for a single stable, suspended layer of carbon atoms. Very few groups have already been able to fabricate these graphene-based resonators which offer low inertial masses, ultrahigh frequencies, and, in comparison with nanotubes, low-resistance contacts that are essential for matching the impedance of external circuits.
Progresses in these different areas will not only constitute keystones for the development of innovative, reliable NEMS but also lead to advances in the understanding of materials behavior at small length scales in the presence of mechanical loading and chemical agents.
Research covers both theoretical and experimental aspects. This research project is in the framework of fundamental and oriented research programs funded by the European Commission, the Walloon Region and the Communauté française de Belgique. Active collaborations are already established and active in the framework of the proposed project with several universities and research centers (Chalmers University of Technology, Institut d’Electronique, de Microélectronique et de Nanotechnologies, Université de Sherbrooke, University of Newcastle, INP-Grenoble, CEMES- NRS-Toulouse, IMEC, CEA, etc.) as well as with companies (ArcelorMittal, AGC Flat Glass Europe, Melexis, ST-Microelectronics, SOITEC, etc.).
In this context, UCL is currently seeking for one engineer or master in electrical, material, or applied sciences for pursuing a PhD thesis in that field as well as one post-doc. Interested? Please apply with resume to:
Prof. Thomas PARDOEN
Université catholique de Louvain
Institute of Mechanics, Materials and Civil Engineering (iMMC)
Bâtiment Réaumur, Place Sainte Barbe 2
B-1348 Louvain-la-Neuve
Belgium
phone. +32 10 472417
fax +32 10 474028
email: thomas.pardoen[ at ]uclouvain.be
Prof. Jean-Pierre RASKIN
Université catholique de Louvain (UCL)
Institute of Information and Communication Technologies, Electronics and Applied Mathematics
(ICTEAM)
Place du Levant, 3
B-1348 Louvain-la-Neuve, BELGIUM
Phone: +32.10.47.23.09., Fax: +32.10.47.87.05.
Email: jean-pierre.raskin[ at ]uclouvain.be
ICTEAM is equipped with a complete CMOS processing line (1,000 sqm, 15 M EUR investment) for the
rapid fabrication of prototype integrated circuits and the study of novel semiconductor process and
devices, as well as with recent physical and electrical characterization equipment in particular for hightemperature (up to 400°C), low temperature (down to 3°K) and very high-frequency measurements (up to 110 GHz), software packages for the design and simulation of process, devices, circuits and systems and a network of workstations and microcomputers.
iMMC is equipped with 2 FEG-SEM, a 300KeV TEM, x-ray diffraction, nanoindentation / nanoscratch,
chemical analysis tools, internal stress and adhesion testing devices as well as all usual techniques used for processing, characterization and simulations of materials.
1 D. Fabrègue, N. André, M. Coulombier, J.-P. Raskin, and T. Pardoen, “Multipurpose nanomechanical laboratory : five thousands micromachines on a wafer”, Micro and Nanoletters, vol. 2, pp. 13-16, 2007.
2 N. André, M. Coulombier V. de Longueville, D. Fabrègue, T. Gets, S. Gravier, T. Pardoen, J.-P. Raskin, “Multipurpose nanomechanical laboratory revealing the size-dependent strength and ductility of submicron metallic films”, Microelectronic engineering, vol. 84, pp. 2714-2718, 2007.
3 Paul L. McEuen, Science 315, 490 (2007).
4 C. Lee et al., Science 321, 385 (2008).
