Seminars and thesis defenses
Subcritical crack growth in freestanding thin films using crack-on-a-chip method
By Sahar Jaddi (iMMC / IMAP)
The control and enhancement of the fracture resistance of thin film materials represents a major concern in many field applications, such as flexible electronics, microelectromechanical / nanoelectromechanical systems (MEMS/NEMS) and functional coatings. The reliability of different devices is not only dependent on the fracture toughness of the used thin films, but also on the environmentally assisted cracking in the films. Most studies are based on films bonded to a substrate, often a polymer substrate. Therefore, it is not obvious, if the observed environmentally assisted subcritical cracking behavior of brittle films deposited on polymer substrates derives from the relaxation of polymer substrate or environmentally cracking in the film itself. The standard testing techniques used for bulk materials are inapplicable for submicron and nanometer scale materials. Therefore, a new on-chip testing method for this purpose is developed. This technique consists of two long actuators beams pulling on a notched specimen by exploiting the released residual stress inside the actuators after etching beneath the latter. A crack is initiated from the notch tip, propagates and finally stops when the energy release rate has decreased down to its critical value.