Mechanical properties and reliability of aluminum nitride thin films

Knowledge of the mechanical properties and fatigue behavior of thin films is important for the design and reliability of microfabricated devices. This study uses the bulge test to measure the residual stress, Young's modulus, and fracture strength of aluminum nitride (AlN) thin films with different microstructures prepared by sputtering, metalorganic vapor phase epitaxy (MOVPE), and atomic layer deposition (ALD). In addition, the fatigue behavior is studied under cyclic loading. The results indicate that the fracture strength and Young's modulus of AlN are mainly determined by the film microstructure, which is consecutively influenced by the deposition method and conditions. A microstructure with a higher order of crystallinity has increased fracture strength and Young's modulus. Additionally, the strength limiting defects are located at the film-substrate interface. The measured residual stresses were 249, 876, 1,526, and 272 MPa for two sputtered films of different thicknesses, MOVPE and ALD films, respectively. The fracture strengths were 1.42, 1.54, 2.76, and 0.61 GPa, and Young's moduli were 335, 343, 346, and 272 GPa. No clear signs of fatigue were observed after 10,000 cycles at a load corresponding to 83% of the fracture strength.