Silicon nitride grating couplers

1. An electronic device structure comprising:

a substrate including a plurality of trenches extending into the substrate;

a plurality of dielectric regions positioned in the trenches;

a grating coupler including a plurality of grating structures arranged on the substrate, gaps separating the grating structures, and a first layer arranged conformally over the grating structures,

wherein the dielectric regions and the trenches are respectively arranged in the substrate in alignment with the gaps, the grating structures are composed of a first material characterized by a first refractive index with a real part, the first layer is composed of a second material characterized by a second refractive index with a real part, and the real part of the second refractive index is greater than the real part of the first refractive index of the first material for electromagnetic radiation with a wavelength in a range of 1 micron to 9 microns.

2. The electronic device structure of claim 1 wherein the first material is silicon nitride, and the second material is titanium nitride, polycrystalline silicon, amorphous silicon, polycrystalline silicon germanium, amorphous silicon germanium, or a layered combination thereof.

3. The electronic device structure of claim 1 further comprising:

a second layer arranged to fill the gaps,

wherein the second layer is composed of a dielectric material, the grating structures have a height relative to the substrate, and the second layer has a thickness that is greater than or equal to the height of the grating structures.

4. The electronic device structure of claim 1 further comprising:

a second layer arranged between the grating structures and a top surface of the substrate, the second layer composed of a dielectric material.

5. The electronic device structure of claim 1 wherein the grating structures are linear and have a parallel arrangement.

6. The electronic device structure of claim 1 wherein each of the grating structures has a trapezoidal shape.

7. The electronic device structure of claim 6 wherein the substrate has a top surface, and the trapezoidal shape is widest at the top surface of the substrate.

8. The electronic device structure of claim 1 wherein the first layer is conformally arranged over the dielectric regions.

9. An electronic device structure comprising:

a substrate including a plurality of trenches extending into the substrate;

a plurality of dielectric regions positioned in the trenches;

a grating coupler including a plurality of grating structures arranged on the substrate, gaps separating the grating structures, and a first layer arranged over the grating structures,

wherein the dielectric regions and the trenches are arranged in the substrate in alignment with the gaps, the grating structures are composed of a first material characterized by a first refractive index with a real part, the first layer is composed of a second material characterized by a second refractive index with a real part, and the real part of the second refractive index is greater than the real part of the first refractive index of the first material for electromagnetic radiation with a wavelength in a range of 1 micron to 9 microns, the first layer is arranged to fill the gaps, the first layer includes portions that are positioned in the gaps in alignment with the dielectric regions, the grating structures have a height relative to the substrate, and the first layer has a thickness that is greater than or equal to the height of the grating structures.

10. A method of fabricating an electronic device structure, the method comprising:

forming a plurality of grating structures on a substrate, wherein the grating structures are separated by gaps;

forming a plurality of trenches that extend into the substrate; and

filling the trenches with a dielectric material; and

forming a layer conformally over the grating structures,

wherein the dielectric regions and the trenches are respectively arranged in the substrate in alignment within the gaps, the grating structures are composed of a first material characterized by a first refractive index with a real part, the layer or the spacers are composed of a second material characterized by a second refractive index with a real part, and the real part of the second refractive index is greater than the real part of the first refractive index of the first material for electromagnetic radiation with a wavelength in a range of 1 micron to 9 microns.

11. The method of claim 10 wherein the first material is silicon nitride, and the second material is titanium nitride, polycrystalline silicon, amorphous silicon, polycrystalline silicon germanium, amorphous silicon germanium, or a layered combination thereof.

12. The method of claim 10 wherein the layer is conformally arranged over the dielectric regions.

13. The method of claim 10 wherein further comprising:

etching the conformally-formed layer to form spacers at a plurality of sidewalls of the grating structures.