Ag:TiN nanocomposite thin films for bioelectrodes : the effect of annealing treatments on the electrical and mechanical behaviour

Abstract

Magnetron sputtered Ag:TiN thin films, with Ag contents ranging from 0 to ~50 at.%, were subjected to a set of annealing treatments at four different temperatures (from 200 to 500 ºC), aiming at studying the effect of Ag addition on their morphological and structural features, as well as on their electrical and mechanical properties. The increase of the annealing temperature revealed that significant morphological modifications were induced, mainly in the samples with higher Ag contents (represented by the sample with a Ag content of 36.3 at.%), which revealed extensive Ag segregation to the surface. The increase of the annealing temperature up to 500 ºC, besides confirming the presence of metallic Ag in the coatings, also resulted in some major structural changes, promoting an increase in the coating’s crystallinity and an extensive Ag grain growth phenomenon. Nevertheless, the resistivity values of all annealed samples were found to be only slightly higher when comparing to the as-deposited ones, which indicated that beyond the significant changes in the samples morphology (e.g. Ag segregation), there seemed to be some important coating resistance in terms of the electrical response. Furthermore, the annealed samples also exhibited lower reduced modulus up to 400 ºC when compared with the un-annealed ones, consistent with some increase of the samples’ elasticity.