Imaging systems with infrared pixels having increased quantum efficiency

Patent metadata

Field	Value
Publication number	US-9349770-B2
Application number	US-201414178066-A
Country	US
Kind code	B2
Filing date	Feb 11, 2014
Priority date	Feb 11, 2014
Publication date	May 24, 2016
Grant date	May 24, 2016

Abstract

An imaging device may include an image sensor having an array of image pixels. The array of image pixels may include one or more infrared pixels that are configured to detect infrared light. The infrared pixels may include reflective structures for increasing quantum efficiency in the infrared spectral range. The reflective structures may include first and second parallel structures formed on opposing sides of a photodiode in an infrared pixel. The reflective structures may be partially transparent to infrared light and non-transparent to visible light. The reflective structures may form an optical cavity so that infrared light that enters an infrared pixel is reflected back and forth between the reflective structures until it is absorbed by the photodiode in the infrared pixel. Reflective structures may also be formed between infrared filters and color filters to suppress optical crosstalk between infrared pixels and color pixels.

First claim

What is claimed is:

1. A backside illuminated image sensor having an array of image pixels including at least one infrared pixel configured to detect infrared light, comprising:
a substrate having a surface;
a photodiode array formed in the surface, wherein a photodiode in the photodiode array is associated with the infrared pixel;
an array of filter elements formed over the array of photodiodes, wherein the array of filter elements includes an infrared filter element associated with the infrared pixel; and
at least one reflective structure in the infrared pixel, wherein the at least one reflective structure comprises a reflective layer that is configured to reflect the infrared light towards the photodiode associated with the infrared pixel, and wherein the reflective layer is non-transparent to visible light and partially transparent to infrared light.

2. The image sensor defined in claim 1 wherein the reflective layer is an upper reflective layer, wherein the at least one reflective structure further comprises a lower reflective layer, wherein the upper reflective layer and the lower reflective layer are oriented parallel to the surface of the substrate, wherein the photodiode is interposed between the upper and lower reflective layers, and wherein the upper and lower layers are configured to reflect the infrared light towards one another until the infrared light is absorbed by the photodiode.

3. The image sensor defined in claim 2 wherein the array of filter elements comprises at least one color filter element, wherein the at least one reflective structure comprises at least one sidewall reflective structure that is perpendicular to and in contact with the upper reflective layer, and wherein the sidewall reflective structure is interposed between the infrared filter element and the color filter element.

4. The image sensor defined in claim 2 , wherein the upper reflective layer is only partially transparent to infrared light.

5. The image sensor defined in claim 4 wherein the upper reflective layer comprises metal.

6. The image sensor defined in claim 4 wherein the at least one reflective structure comprises an interference filter having multiple layers of dielectric material with different indices of refraction.

7. The image sensor defined in claim 4 further comprising a dielectric material formed on the surface of the substrate, wherein the lower reflective layer is formed in the dielectric material and wherein the upper reflective layer is formed on the infrared filter element.

8. The image sensor defined in claim 4 wherein the upper reflective layer has a thickness of less than 5 nanometers.

9. An infrared pixel configured to detect infrared light, comprising:
a silicon substrate having opposing first and second surfaces;
a photodiode formed in the first surface;
an infrared filter formed on the second surface over the photodiode; and
first and second reflective structures oriented parallel to the first surface, wherein the first reflective structure is formed below the first surface, wherein the second reflective structure is formed above the second surface such that the photodiode is interposed between the first and second reflective structures, wherein the first and second reflective structures form an optical cavity in which the infrared light is contained until it is absorbed by the photodiode, and wherein the second reflective structure is located in the infrared filter such that the second reflective structure is interposed between first and second portions of the infrared filter.

10. The infrared pixel defined in claim 9 wherein the first and second reflective structures are non-transparent to visible light and partially transparent to infrared light and wherein the first and second reflective structures each comprise a layer of metal having a thickness of less than 10 nanometers.

11. The infrared pixel defined in claim 9 wherein the first and second reflective structures are non-transparent to visible light and partially transparent to infrared light and wherein the first and second reflective structures each comprise an interference filter.

12. The infrared pixel defined in claim 9 further comprising a dielectric layer formed on the first surface, wherein the first reflective structure is located in the dielectric layer under the photodiode.

13. The infrared pixel defined in claim 12 further comprising a microlens, wherein the second reflective structure is interposed between the microlens and the infrared filter.

14. The infrared pixel defined in claim 12 wherein the second reflective structure is interposed between the infrared filter and the second surface of the silicon substrate.

15. The infrared pixel defined in claim 9 further comprising third and fourth reflective structures, wherein the third and fourth reflective structures are non-transparent to visible light, wherein the third and fourth reflective structures are perpendicular to the second reflective structure and wherein the infrared filter is interposed between the third and fourth reflective structures.

16. A system, comprising:
a central processing unit;
memory;
input-output circuitry; and
an imaging device having a backside illuminated image sensor, wherein the backside illuminated image sensor comprises at least one infrared pixel and wherein the at least one infrared pixel comprises:
a silicon substrate having opposing first and second surfaces;
a photodiode formed in the first surface;
an array of color filter elements formed on the second surface;
an infrared filter formed over the photodiode and located between at least some of the color filter elements;
a microlens formed over the infrared filter; and
first and second reflective structures oriented parallel to the first surface, wherein the first reflective structure is formed below the first surface, wherein the second reflective structure is formed above the second surface such that the photodiode is interposed between the first and second reflective structures, wherein the first and second reflective structures form an optical cavity in which the infrared light is contained until it is absorbed by the photodiode, and wherein the second reflective structure is interposed between the infrared filter and the microlens.

17. The system defined in claim 16 wherein the first and second reflective structures are non-transparent to visible light and partially transparent to infrared light and wherein the first and second reflective structures each comprise a layer of metal having a thickness of less than 10 nanometers.

18. The system defined in claim 16 wherein the first and second reflective structures are non-transparent to visible light and partially transparent to infrared light and wherein the first and second reflective structures each comprise an interference filter.

19. The system defined in claim 16 wherein the infrared pixel further comprises a dielectric layer formed on the first surface and a microlens formed over the infrared filter, wherein the first reflective structure is located in the dielectric layer under the photodiode and wherein the second reflective structure is interposed between the microlens and the infrared filter.

Assignees

• Semiconductor Components Ind

Inventors

• Lenchenkov Victor

Classifications

• H10F77/413

  directly associated or integrated with the devices, e.g. back reflectors (directly associated or integrated with photovoltaic cells H10F77/42) · CPC title

• H10F77/331

  for filtering or shielding light, e.g. multicolour filters for photodetectors · CPC title

• H10F77/122

  comprising only Group IV materials · CPC title

• H10F39/8067

  Reflectors · CPC title

• H10F39/8053

  Colour filters · CPC title