Techniques for controlling overburden planarization
A method of planarizing an overcoat layer on a surface-relief grating includes dispensing a layer of a resin material that is curable by heat or electromagnetic radiation on a surface-relief grating that includes a plurality of grating grooves, pressing the layer of the resin material using a planar imprint stamp, curing the resin material in the layer of the resin material, and detaching the planar imprint stamp from the layer of the resin material. In one example, a thickness of the overcoat layer on top of grating ridges of the surface-relief grating is equal to or less than 20 nm, and a surface peak-to-valley height of a top surface of the overcoat layer is equal to or less than 5 nm.
1. An optical device comprising:
a surface-relief grating including a plurality of ridges and a plurality of grooves, wherein the plurality of grooves is characterized by a depth greater than 50 nm; and
an overcoat layer filled in the plurality of grooves and on top of the plurality of ridges, wherein:
the overcoat layer includes an organic material;
a thickness of the overcoat layer on top of the plurality of ridges is equal to or less than 20 nm and is greater than 0 nm; and
a surface peak-to-valley height of a top surface of the overcoat layer is equal to or less than 5 nm and is greater than 0 nm.
2. The optical device of claim 1 , wherein the overcoat layer is characterized by a refractive index between 1.45 and 3.4.
3. The optical device of claim 1 , wherein the overcoat layer includes:
a resin; and
nanoparticles dispersed in the resin, the nanoparticles including titanium oxide, zirconium oxide, hafnium oxide, tungsten oxide, zinc tellurium, gallium phosphide, a derivative of any of preceding materials, or a combination thereof.
4. The optical device of claim 1 , wherein the plurality of grooves is characterized by at least one of a non-uniform depth, a non-uniform pitch, a non-uniform width, or a non-uniform slant angle.
5. The optical device of claim 1 , wherein the overcoat layer includes nanoparticles dispersed in the organic material, the nanoparticles characterized by linear dimensions less than 20 nm and greater than the surface peak-to-valley height of the top surface of the overcoat layer.