Global shutter image sensors with light guide and light shield structures
View Patent ↗An image sensor operable in global shutter mode may include an array of image pixels. Each image pixel may include a photodiode for detecting incoming light and a separate storage diode for temporarily storing charge. To maximize the efficiency of the image pixel array, image pixels may include light guide structures and light shield structures. The light guide structures may be used to funnel light away from the storage node and into the photodiode, while the light shield structures may be formed over storage nodes to block light from entering the storage nodes. The light guide structures may fill cone-shaped cavities in a dielectric layer, or the light guide structures may form sidewalls having a ring-shaped horizontal cross section. Metal interconnect structures in the dielectric layer may be arranged in concentric annular structures to form a near-field diffractive element that funnels light towards the appropriate photodiode.
1. An image sensor operable in global shutter mode and having a substrate and a dielectric material formed over the substrate, comprising:
a photodiode formed in the substrate;
a storage node formed in the substrate;
a light guide structure formed in the dielectric material over the photodiode, wherein the light guide structure has a ring-shaped horizontal cross section with an inner perimeter defined by an inner surface of the light guide structure and an outer perimeter defined by an outer surface of the light guide structure, wherein the light guide structure has a higher refractive index than that of the dielectric material, wherein the light guide structure forms light guide sidewalls, wherein a portion of the dielectric material is completely surrounded by the light guide sidewalls, and wherein the portion of the dielectric material overlaps the photodiode; and
a light shield formed in the dielectric material over the storage node.
2. The image sensor defined in claim 1 further comprising an anti-reflective coating that at least partially covers the light shield.
3. The image sensor defined in claim 2 further comprising a storage gate formed on the substrate, wherein the light shield at least partially covers the storage gate.
4. The image sensor defined in claim 1 wherein a portion of the light guide structure overlaps a portion of the light shield.
5. An image sensor operable in global shutter mode and having a substrate and a dielectric material formed over the substrate, comprising:
a photodiode formed in the substrate;
a storage node formed in the substrate; and
a plurality of concentric annular metal structures formed in the dielectric material over the storage node, wherein the plurality of metal rings form a near-field diffractive element that guides light towards the photodiode, wherein a portion of the dielectric material is surrounded by the plurality of concentric annular metal structures, and wherein the portion of the dielectric material overlaps the photodiode.
6. The image sensor defined in claim 5 wherein the plurality of concentric annular metal structures comprises a first metal ring located a first distance from the substrate, a second metal ring located a second distance from the substrate, and a third metal ring located a third distance from the substrate, wherein the second distance is less than the first distance and greater than the third distance.
7. The image sensor defined in claim 6 wherein the first metal ring has a first diameter, the second metal ring has a second diameter, and the third metal ring has a third diameter, wherein the second diameter is less than the first diameter and greater than the third diameter.
8. The image sensor defined in claim 7 further comprising a fourth metal ring located the second distance from the substrate and having a fourth diameter larger than the second diameter.
9. The image sensor defined in claim 8 further comprising fifth and sixth metal rings located the third distance from the substrate and having respective fifth and sixth diameters that are larger than the third diameter.
10. The image sensor defined in claim 5 further comprising:
a light shield formed in the dielectric material over the storage node; and
an anti-reflective coating that at least partially covers the light shield.
11. The image sensor defined in claim 10 wherein the light shield comprises a metal selected from the group consisting of: tungsten, aluminum, and copper.
12. The image sensor defined in claim 11 further comprising a storage gate formed on the substrate, wherein the light shield at least partially covers the storage gate, and wherein the light shield has an opening through which one of the concentric annular metal structures electrically couples to the storage gate.