Fracture Toughness of Free-Standing ZrSix Thin Films Measured Using Crack-on-a-Chip Method

In this work, we experimentally measure fracture toughness of free-standing zirconium ZrSi
_x
thin films using the crack-on-a-chip method. In this method, fracture toughness is determined from the analysis of cracks, which propagate and arrest in specially designed free-standing test structures. The test structures use a well-known double cantilever beam geometry, which enables crack arrest, and don’t require any external force actuation, but instead rely on the internal tensile stress of the tested thin film. To produce the ZrSi
_x
test structures, a universal fabrication process was developed and used, which avoids typical issues related to etch selectivity and that can be readily applied for other thin film materials. Unlike in previous studies, which used the crack-on-a-chip method, in this work crack initiation was triggered only after the test structures were fully fabricated, which allowed to avoid the influence of the fabrication process on the extracted toughness values. For this, blunt pre-cracks included in the structures were “sharpened” using focused ion beam, which resulted in rapid crack propagation and subsequent crack arrest. Mechanical analysis done by a finite element method to extract the values of fracture toughness, showed that buckling of the free-standing thin film test structures has a strong influence on the results of fracture toughness calculations and therefore cannot be ignored. The fracture toughness of ZrSi
_x
thin films was determined to be 2.1±0.13 MPa*m
^0.5
. [2021-0166]