Dislocation dynamics in thin films

OVERVIEW

Thin films are used in a wide variety of applications ranging from biomedical devices to microchips to chemical barriers. In many applications, thin films support stresses that exceed the ultimate strengths of their bulk counterparts by an order of magnitude. These high stresses can lead to device failure in the form of delamination, fracture, void formation, etc. Mechanical failure causes device failure, regardless of whether the film is being used for its chemical, magnetic, electrical, or mechanical properties. In order to improve reliability and mitigate failure of devices that utilize thin film technology, the origin of the high stresses in films must be better understood.

Dislocation motion is one of the primary mechanisms by which stress is relaxed in metal films. Consequently, the existence of high stresses in films points to impediments to dislocation motion. Our group uses dislocation dynamics simulations to examine the behavior of dislocations as they relax film stress.


Evolution of dislocation microstructure during loading of a thin film. The lines represent dislocations. The different colors represent different Burgers vectors. For a larger version, click here.

CURRENT WORK


Inhomogeneous stress field arising from irregular misfit structure in dislocation dynamics simulations

Currently, graduate student Ray Fertig is using the program PARANOID,developed by Klaus Schwarz at IBM T. J. Watson, to simulate the behavior of many dislocations during film relaxation. Currently, we are interested in:

  • Evolution of stress inhomogeneity in thin films
  • Effects of stress inhomogeneity of the types of dislocation interactions that occur
  • Loading-unloading behavior
  • Bauschinger effect due to dislocation interactions
  • Dislocation core spreading at amorphous interfaces
  • Tension-compression asymmetry during cyclic loading

RESOURCES

2006 NSF Nugget
Dislocation dynamics in thin films-movie

REFERENCES

Fertig, R. S. and S. P. Baker (2008). "Threading dislocation interactions in an inhomogeneous stress field: a statistical model." In preparation.

Fertig, R. S., P. Pant, et al. (2008). "Influence of stress inhomogeneity in thin films on strain hardening and threading dislocation interactions." In preparation.

Fertig, R. S. and S. P. Baker (2007). Relationship between film stress and dislocation microstructure evolution in thin films. Microelectromechanical Systems -- Materials and Devices, edited by D. LaVan, M. Spearing, S. Vengallatore, M. da Silva (Mater. Res. Soc. Symp. Proc. Volume 1052, Warrendale, PA, 2007), DD-07-06.

Pant, P., K. W. Schwarz, et al. (2006). "Dislocation dynamics simulations of plastic deformation in thin films." Unpublished.

Pant, P., K. W. Schwarz, et al. (2003). "Dislocation interactions in thin FCC metal films." Acta Materialia 51(11): 3243-3258.

Baker, S. P., R. M. Keller-Flaig, et al. (2003). "Bauschinger effect and anomalous thermomechanical deformation induced by oxygen in passivated thin Cu films on substrates." Acta Materialia 51(10): 3019-3036.

Shu, J. B., S. B. Clyburn, et al. (2003). "Effect of oxygen on the thermomechanical behavior of passivated Cu thin films." Journal of Materials Research 18(9): 2122-2134.

Baker, S. P., L. Zhang, et al. (2002). "Effect of dislocation core spreading at interfaces on strength of thin-films." Journal of Materials Research 17(7): 1808-1813.

Gao, H. J., L. Zhang, et al. (2002). "Dislocation core spreading at interfaces between metal films and amorphous substrates." Journal of the Mechanics and Physics of Solids 50(10): 2169-2202.

Baker, S. P., R. P. Vinci, et al. (2002). "Elastic and anelastic behavior of materials in small dimensions." MRS Bulletin 27(1): 26-29. Vinci, R. P. and S. P. Baker (2002). "Mechanical properties in small dimensions." MRS Bulletin 27(1): 12-14.

Baker, S. P., A. Kretschmann, et al. (2001). "Thermomechanical behavior of different texture components in Cu thin films." Acta Materialia 49(12): 2145-2160.

Baker, S. P. (2001). "Plastic deformation and strength of materials in small dimensions." Materials Science and Engineering A 319-321: 16-23.