Light guide array for an image sensor
An image sensor pixel that includes a photoelectric conversion unit supported by a substrate and an insulator adjacent to the substrate. The pixel includes a cascaded light guide that is located within an opening of the insulator and extends above the insulator such that a portion of the cascaded light guide has an air interface. The air interface improves the internal reflection of the cascaded light guide. The cascaded light guide may include a self-aligned color filter having air-gaps between adjacent color filters. These characteristics of the light guide eliminate the need for a microlens. Additionally, an anti-reflection stack is interposed between the substrate and the light guide to reduce backward reflection from the image sensor. Two pixels of having different color filters may have a difference in the thickness of an anti-reflection film within the anti-reflection stack.
1. An image sensor that comprises a pixel array, comprising:
a substrate;
a plurality of photoelectric conversion units across said substrate; and,
a plurality of color filters, each of the plurality of color filters being coupled to transmit a light to one of the plurality of photoelectric conversion units, an air gap being between each of the plurality of color filters and an adjacent one of the plurality of color filters, said air gap comprising air or a gas, said air gap having a width of 0.45 um or less.
2. The image sensor of claim 1 , wherein said air gap has a depth of at least a wavelength in air of a visible light.
3. The image sensor of claim 2 , wherein said wavelength in air is 650 nm.
4. The image sensor of claim 1 , further comprising:
a plurality of light guides each one of which is disposed between one of the plurality of color filters and a corresponding one of the plurality of photoelectric conversion units.
5. The image sensor of claim 4 , wherein each one of the plurality of light guides comprises a silicon nitride.
6. The image sensor of claim 4 , wherein no microlens is arranged to transmit light to any one of the plurality of color filters.
7. The image sensor of claim 1 , wherein the width is more than 0.2 um.
8. The image sensor of claim 1 , wherein a protection film with a non-zero thickness extends over the plurality of photoelectric conversion units and under the plurality of color filters.
9. The image sensor of claim 8 , wherein the protection film comprises a silicon nitride.
10. The image sensor of claim 9 , wherein the protection films has a thickness between 4,000 and 10,000 Angstroms.
11. The image sensor of claim 4 , wherein a portion of each light guide from the plurality of light guides is narrower than another portion of said each light guide, the narrower portion being nearer to the corresponding photoelectric conversion unit than the other portion.
12. The image sensor of claim 4 , wherein the plurality of light guides is embedded between a plurality of wires.
13. The image sensor of claim 1 , further comprising:
a film disposed on the substrate and below the plurality of color filters to reduce reflection of light from the substrate.
14. The image sensor of claim 1 , wherein a refractive index changes across an interface of each one of the plurality of color filters facing the substrate.