High dynamic range image sensor with a neutral density filter
A high dynamic range image sensor may include a plurality of pixel groups. One or more pixel groups may include attenuated pixels in addition to unattenuated pixels. The unattenuated pixels may include a photosensitive area, a color filter element and a microlens of a first size. Each attenuated pixel may include a photosensitive area, a color filter element, a neutral density filter, and a microlens of a second size that is smaller than the first size. The color filter elements for each pixel in a given pixel group may be the same color. The neutral density filter may attenuate light for the attenuated pixels, increasing dynamic range of the image sensor. The microlenses of varying sizes may redirect light from attenuated pixels towards unattenuated pixels, further increasing the dynamic range.
1. An image sensor that includes a pixel group, the pixel group comprising:
an attenuated pixel;
an unattenuated pixel;
color filtering material of a given color that covers both the attenuated pixel and the unattenuated pixel;
a neutral density filter that covers the attenuated pixel but not the unattenuated pixel; and
a microlens that covers the unattenuated pixel and at least a portion of the attenuated pixel.
2. The image sensor defined in claim 1 , wherein the microlens is configured to redirect light from the attenuated pixel to the unattenuated pixel.
3. The image sensor defined in claim 1 , wherein the microlens is a first microlens and wherein the pixel group comprises:
a second microlens formed over the attenuated pixel, wherein the second microlens is smaller than the first microlens.
4. The image sensor defined in claim 1 , wherein the pixel group comprises first and second color filter elements including the color filtering material of the given color and wherein the first and second color filter elements respectively cover the unattenuated pixel and the attenuated pixel.
5. The image sensor defined in claim 4 , wherein the neutral density filter is formed over the second color filter element.
6. The image sensor defined in claim 4 , wherein the pixel group comprises:
a planarization layer that is formed over the neutral density filter.
7. The image sensor defined in claim 6 , wherein the pixel group comprises:
an additional planarization layer that is interposed between the first color filter element and the planarization layer.
8. The image sensor defined in claim 4 , wherein the second color filter element has a first thickness, wherein the neutral density filter has a second thickness, and wherein the first thickness is greater than the first thickness.
9. The image sensor defined in claim 4 , wherein the second color filter element has a first thickness, wherein the neutral density filter has a second thickness, and wherein the first thickness is less than the first thickness.
10. The image sensor defined in claim 4 , wherein the second color filter element is formed over the neutral density filter.
11. The image sensor defined in claim 10 , wherein the pixel group further comprises:
a first planarization layer, wherein the first color filter element is formed over the first planarization layer; and
a second planarization layer, wherein the second planarization layer is formed over the first and second color filter elements.
12. The image sensor defined in claim 10 , wherein the pixel group further comprises:
a first planarization layer, wherein the first planarization layer is formed over the first color filter element; and
a second planarization layer, wherein the second planarization layer is formed over the first planarization layer.
13. The image sensor defined in claim 4 , wherein the pixel group comprises:
a composite grid that separates the first color filter element from the second color filter element.
14. An image sensor that includes a pixel group, the pixel group comprising:
at least one pixel of a first type, wherein each pixel of the first type includes a photosensitive area, a color filter element and a microlens of a first size; and
at least one pixel of a second type, wherein each pixel of the second type includes a photosensitive area, a color filter element, a neutral density filter, and a microlens of a second size that is smaller than the first size.
15. The image sensor defined in claim 14 , wherein, for each pixel of the second type, the color filter element is interposed between the photosensitive area and the neutral density filter.
16. The image sensor defined in claim 14 , wherein, for each pixel of the second type, the neutral density filter is interposed between the photosensitive area and the color filter element.
17. The image sensor defined in claim 14 , wherein, for each pixel of the first type, the color filter element is a given color, and wherein, for each pixel of the second type, the color filter element is the given color.
18. The image sensor defined in claim 14 , wherein the photosensitive area for each pixel of the first type is overlapped by at least a portion of one microlens of the second size in addition to the microlens of the first size.
19. An image sensor comprising:
a first photosensitive area;
a second photosensitive area;
color filter material of a given color that overlaps both the first and second photosensitive areas;
gray filter material that overlaps the second photosensitive area, wherein the first photosensitive area is not overlapped by gray filter material;
a first microlens that overlaps the first photosensitive area; and
a second microlens that overlaps the second photosensitive area and that is smaller than the first microlens.
20. The image sensor defined in claim 19 , wherein the given color is a color selected from the group consisting of: red, green, and blue.