Michaël Coulombier's PhD Thesis

The exceptional properties of thin films have encouraged the use in a wide variety of applications ranging from microelectronics and Micro Electro Mechanical System (MEMS) technologies to the field of surface functionalization of bulk metallic, ceramic, glass, and polymeric materials. The reliability of these devices and coatings heavily depends on the thermo-mechanical behaviour of the films. The key issue is that thin films exhibit thermo-mechanical properties different from the bulk counterpart. The development of testing methods to characterise the mechanical properties of thin films is thus essential. A direct adaptation of classical techniques used to test bulk materials is not straightforward due to the challenges in generating small loads and adequate gripping between actuator and test specimen.

In this thesis, a novel concept of on-chip mechanical testing based on MEMS fabrication methods is developed. The original idea is to use the internal stress generated in one layer acting as a small spring to impose a load to a test specimen from which the mechanical properties can be extracted. The on-chip technique is presented with all the details about the design, fabrication and data reduction. Two thin film material systems are studied for demonstration of the potential of the method: pure evaporated Al and sputtered AlSi(1%) both in the 100 to 1000 nm thickness, revealing thickness dependent strength and a statistical imperfection sensitive ductility. The technique is applied for performing stress relaxation experiments over long period of time which enables to extract the strain rate sensitivity parameters.

Jury:
Pr. Thomas PARDOEN, promoteur (UCL)
Pr. Jean-Pierre RASKIN, promoteur (UCL)
Pr. Grégoire WINCKELMANS, président (UCL)
Pr. Joris PROOST, secrétaire (UCL)
Pr. Stéphane GODET (ULB, Belgique)
Pr. Ingrid DE WOLF (KULeuven, Belgique)
Pr. Taher SAIF (University of Illinois at Urbana-Champaign, USA)