TiAgx thin films for lower limb prosthesis pressure sensors: Effect of composition and structural changes on the electrical and thermal response of the films

摘要

Titanium-silver, Ti-Ag, thin films display excellent biocompatibility and reveal great potential to be used as conductive materials for prosthesis pressure sensors. In the frame of this work, TiAg_x thin films were deposited onto silicon and glass substrates by DC magnetron sputtering, using a pure Ti target containing different amounts of Ag pellets. The films display Ag/Ti ratios varying from 0 up to 0.36, resulting in relatively large range of composition, which gave rise to varied morphological, structural and some selected property responses. For Ag/Ti ratios below 3.0 × 10~(-3), the TiAg_x films exhibited similar behavior to those of standard Ti films. Above this critical value, the role of Ag becomes crucial on the crystallographic structure evolution, as well as on the surface morphology changes of the films. A gradual increase of the Ag/Ti ratio leads to the growth of Ti-Ag crystalline phases, whereas the long range order of Ti grains was reduced from 22 nm down to 7 nm. Similarly, a denser microstructure was developed with a reduction of the sharpness of the surface morphology. This critical Ag/Ti ratio (＜3.0 × 10~(-3)) also corresponded to an enhanced electrical resistivity, which reached a value of ρ_(300k) = 72 μΩcm. The thermal characterization revealed a similar trend, with the existence of two clear distinct zones, related again with the different critical composition ratios and the correspondent changes in both morphology and structural features.