Titanium nitride thin film as an adhesion layer for surface plasmon resonance sensor chips

Optical properties, surface plasmon resonance (SPR) response characteristics, and the adhesion properties of the plasmonic stacks with titanium nitride (TiNx) adhesion layers were analyzed and compared with those of the Au single stack and the plasmonic stacks with conventional titanium adhesion layer. All the films were deposited by radio frequency magnetron sputtering. TiNx single layer exhibited higher electrical conductivity and reflectance in long wavelength range than Ti single layer of similar thickness. When compared with the plasmonic stacks with Ti adhesion layer, the plasmonic stacks with TiNx adhesion layer showed higher peak transmittance and less absorption loss in wavelength range longer than 500 nm. Examination of the SPR response curves revealed that much improved SPR characteristics could be attained if conventional Ti adhesion layer were replaced by TiNx layer, and it was attributed to the lower damping of TiNx film than Ti film at corresponding thickness. Also, it was proved that TiNx layer could provide sufficient adhesion strength at the glass/TiNx and TiNx/Au interfaces, which is comparable with that of Ti layer.