Bringing plasmonics into CMOS photonic foundries: Aluminum plasmonics on Si$_3$N$_4$ for biosensing applications

We present a technology platform supported by a new process design kit (PDK) that integrates two types of aluminum plasmonic waveguides with Si $_3$ N $_4$ photonics towards CMOS-compatible plasmo-photonic integrated circuits for sensing applications. More specifically, we demonstrate the fabrication of aluminum slot waveguide via e-beam lithography (EBL) on top of the Si $_3$ N $_4$ waveguide and an optimized fabrication process of aluminum plasmonic stripe waveguides within a CMOS foundry using EBL. Experimental measurements revealed a propagation length of 6.2 μm for the plasmonic slot waveguide in water at 1550 nm, reporting the first ever experimental demonstration of a plasmonic slot waveguide based on CMOS compatible metal materials in liquid environment. Propagation length in water for the aluminum stripe was measured equal to 66.8 μm which is, to the best of our knowledge, the highest value among all single-mode Al-based plasmonic waveguides presented so far at 1550 nm. Moreover, we evince with simulation data the sensing capabilities of the proposed structures when incorporated in a Si $_3$ N $_4$ -based interferometric configuration, yielding bulk sensitivity values up to 80 nm/RIU and 1300 nm/RIU, corresponding to an accumulated phase change per unit length of 0.77 π/RIU/μm and 1.26 π/RIU/μm for the aluminum slot and aluminum stripe waveguide, respectively.