Tantalum Interconnect Metallization for Thin-Film Neural Interface Devices.

Neural interfaces created using thin-film fabrication rely primarily on conductive metal traces for electrical interconnects. Here, we explore the use of tantalum (Ta) metal interconnects as a replacement for noble-metal interconnects such as Au, Pt or Ir. Ta has been investigated previously for interconnect metallization in flexible silicon ribbon cables, but the structure and properties of tantalum for neural device metallization have not been extensively reported. In the present work, Ta metal was sputter-deposited onto amorphous silicon carbide (a-SiC), with and without a base titanium (Ti) adhesion layer, and investigated as interconnect metallization. In the absence of a Ti adhesion layer, resistivity measurements revealed a factor of six difference between Ta resistivity depending on the presence of the Ti base layer, with direct deposition on a-SiC nucleating high resistivity β-Ta (ρ = 197 ± 31 µΩ·cm, mean ± standard deviation) and Ta deposited on Ti nucleating low resistivity α-Ta (ρ = 35 ± 6 µΩ·cm). X-ray diffraction confirmed the existence of the two crystal structures. Ta feature sizes of 2 µm were created using photolithography and reactive ion etching (RIE). Finally, planar microelectrode array test structures using α-Ta and Au trace metallization with low-impedance ruthenium oxide (RuO