Nanomechanics of MEMS and Thin Films

We have developed novel tools for nanometer scale mechanical measurements on thin films that benefit from the utlra-high resolution of Atomic Force Microscopes compared to other microscopy tools:

Images should not be adopted or used without the explicit permission by this group

AFM (Atomic Force Microscopy) in conjunction with DIC (Digital Image Correlation) are used to obtain fields of deformation. The measurement scales are defined by the underlying substructure (grain size) of the thin film. These measurements are to be extended to non uniform geometries such as stress concentrations and cracks. The following images obtained via AFM illustrate a typical topography of polysilicon films at micron scales.

A 10 micron wide microtension specimen is tested in situ under an AFM. The AFM probe is used to image the surface of the specimen while axial tensile load is applied on its grips on the plane of this image.

The evolution of the local displacement field under axial loading is shown below.

Displacement field as obtained via AFM/DIC. Note: the displacement resolution is ~ 1-2 nm
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RELEVANT PUBLICATIONS

  1. S.W. Cho and I. Chasiotis, "Elastic Properties and Representative Volume Element of Polycrystalline Silicon for MEMS," Experimental Mechanics 47 (1), pp. 37-49, (2007).
     
  2. I. Chasiotis, S.W. Cho, K. Jonnalagadda, "Fracture Toughness and Crack Growth in Polycrystalline Silicon", Journal of Applied Mechanics 74 (5) , pp. 714-722, (2006).
     
  3. I. Chasiotis, Q. Chen, G. Odegard, and T. Gates, "Structure-Properties Relationships in Polymer Composites with Micron and Submicron Graphite Platelets," Experimental Mechanics 45 (6), pp. 507-516, (2005).
     
  4. S.W. Cho and I. Chasiotis, T.A. Friedman, and J. Sullivan, "Direct Measurements of Young’s Modulus, Poisson Ratio and Failure Properties of ta-C MEMS," Journal of Micromechanics and Microengineering 15, pp. 728-735, (2005).
     
  5. S. Cho, J.F. Cardenas-Garcia, and I. Chasiotis, "Measurement of Nano-displacements and Elastic Properties of MEMS via the Microscopic Hole Method," Sensors and Actuators A Physical 120, pp. 163-171, (2005).
     
  6. I. Chasiotis, W.G. Knauss, "A New Microtensile Tester for the Study of MEMS Materials with the aid of Atomic Force Microscopy", Experimental Mechanics 42 (1), pp. 51-57, (2002).

College of Engineering   University of Illinois at Urbana-Champaign