Fabrication of surface plasmon waveguides and integrated components on ultrathin freestanding membranes

Abstract

The fabrication and physical characterisation of waveguides and integrated components on freestanding membranes are described. The waveguides consist of a thin (20–25nm) narrow (∼5μm) Au∕Cr stripe, on an ultrathin (20–30nm) large-area (∼1mm2) freestanding Si3N4 membrane clamped around its perimeter to an underlying Si substrate. The integrated components are implemented with this waveguide and consist of Mach-Zehnder interferometers and couplers. The waveguide and components are dimensioned such that they propagate long-range surface plasmon-polariton waves in a vacuum (air) or H2O background. The fabrication process flow adopted and some specific process steps are described. Physical characterisation was conducted on structures having undergone intermediate process steps and on finished structures, and characterisation results are given and discussed. The structures were found to be robust enough for careful use, and to routinely sustain ∼3μN of point force without shattering.