Impact of film thickness and temperature on the dielectric breakdown behavior of sputtered aluminum nitride thin films

Abstract

In micromachined devices, piezoelectric aluminum nitride (AlN) thin films are commonly used as functional material for sensing and actuating purposes. Additionally, AlN features a high chemical and thermal stability, making it also a good choice for passivation purposes for microelectronic devices. With those aspects and current trends towards minimization in mind, the dielectric reliability of ultra-thin AlN films is of utmost importance for the realization of advanced device concepts.In this study, we present a systematic analysis of the transversal dielectric strength of sputtered AlN thin films of varying film thickness (i.e. 70nm to 400nm) up to 300°C. Using a time-zero approach, the dielectric strength is measured by applying a voltage ramp to stress the film up to the point of breakdown. The results are subsequently analyzed using the Weibull approach.For temperatures T>180°C, the characteristic breakdown field Eb,0 follows the relationship Eb,0∼T2, while showing a weak temperature dependence below, thus indicating a transitory regime between thermally induced breakdown at higher T and electrically induced breakdown at lower T. It is shown, that the characteristic breakdown field increases at lower film thickness which is in good correlation with a corresponding decrease in leakage current.