Fabrication of metallic optical metasurfaces

A method for fabricating an optical metasurface, comprising:

• forming a plurality of copper pillars with a conducting barrier layer over a backplane structure by a damascene process, wherein a plurality of nano-gaps between the plurality of copper pillars is filled with a dielectric material, wherein the conducting barrier layer is between the plurality of copper pillars and the backplane structure, and also between the plurality of copper pillars and the dielectric material, wherein the backplane structure comprises a stack of dielectric layers;
• removing the dielectric material in the nano-gaps, at least the top layer of the stack of the dielectric layers, and the conducting barrier layer to expose side portions in the nano-gaps and a bottom portion underneath the plurality of copper pillars;
• depositing a dielectric coating layer over the top portion, the exposed side portions in the nano-gaps between the plurality of copper pillars, and the bottom portion to form protected copper pillars;
• and
• filling the nano-gaps and the space underneath the protected copper pillars with an electrically-tunable dielectric material that has an electrically-tunable refractive index.