Investigation of stress in AIN thin films for piezoelectric MEMS

In this contribution, the mechanical stress and the Young's modulus of highly textured aluminium nitride (AIN) films are investigated on (i) thin films, (ii) on thin membranes and (iii) on resonant microstructures. Aging and thermal cycling experiments reveal that stoichiometric AIN thin films arc highly stable, while nitrogen deficient AIN films get oxidized in the atmosphere which results in change in the as-grown stress with aging. The fabricated suspended AIN icrostructures show an outstanding high stability even for high bending forces. All the employed techniques yield the value for the Young's modulus in the range of 310-350 GPa. The residual stress of the films and membranes is 310-450 MPa, while lower values were obtained for suspended microstructures. The good stability of stress with aging, the stability of microstructures, and the piezoelectric properties indicate that the device will be highly reliable without any deterioration in their performance, which could be related to the stress.