US-12621578-B2 - Hyperspectral sensor with diffractive focusing elements and color filters

Abstract

Color image sensors and systems are provided. A sensor as disclosed includes a plurality of color sensing pixels disposed within an array, each of which includes a plurality of sub-pixels. Each color sensing pixel within the image sensor is associated with a set of diffraction features and a plurality of wavelength selective filters that only partially overlay an area of the pixel. The diffraction features can be formed from materials having an index of refraction that is higher than an index of refraction of the surrounding material. Color information regarding light incident on a pixel can be determined by applying ratios of signals obtained by pairs of included sub-pixels and calibrated ratios for different colors to a set of equations.

Inventors

• Victor A. Lenchenkov
• Frederick T. Brady
• Gui GUI
• Trevor O'Loughlin

Assignees

• SONY SEMICONDUCTOR SOLUTIONS CORPORATION

Dates

Publication Date

20260505

Application Date

20240322

Claims (20)

1. 1 . A sensor, comprising: a sensor substrate; an element substrate, wherein the element substrate is disposed on a light incident surface side of the sensor substrate; and a pixel disposed in the sensor substrate, wherein the pixel includes: a plurality of sub-pixels; a plurality of diffraction elements, wherein the diffraction elements are disposed in a first layer of the element substrate, wherein at least one of the diffraction elements partially overlaps more than one sub-pixel, and wherein the diffraction elements are asymmetrically disposed about an area of the pixel; and a plurality of color filters, wherein the color filters are disposed in a second layer of the element substrate.
2. 2 . The sensor of claim 1 , wherein the diffraction elements occupy less than all of an area of a light incident surface of the pixel.
3. 3 . The sensor of claim 2 , wherein the color filters occupy less than all of an area of a light incident surface of the pixel.
4. 4 . The sensor of claim 2 , wherein at least a first one of the diffraction elements is configured as a solid disc, and wherein a second one of the diffraction elements is configured as an open cylinder.
5. 5 . The sensor of claim 1 , wherein the second layer of the element substrate is between the first layer of the element substrate and the light incident surface of the sensor substrate.
6. 6 . The sensor of claim 1 , wherein the first layer of the element substrate is between the second layer of the element substrate and the light incident surface of the sensor substrate.
7. 7 . The sensor of claim 1 , wherein each color filter in the plurality of color filters partially overlays at least first and second sub-pixels in the plurality of sub-pixels.
8. 8 . The sensor of claim 1 , wherein each of the color filters is a same size.
9. 9 . The sensor of claim 1 , wherein each of the color filters transmits a different range of wavelengths.
10. 10 . The sensor of claim 1 , wherein each of the color filters is surrounded by a metal frame.
11. 11 . The sensor of claim 1 , wherein the diffraction elements are transparent.
12. 12 . The sensor of claim 1 , wherein the diffraction elements each have a refractive index that is higher than a refractive index of the substrate in which the diffraction elements are formed.
13. 13 . The sensor of claim 1 , wherein at least some of the diffraction elements are different in size from one another.
14. 14 . The sensor of claim 1 , further comprising: an antireflective coating, wherein the antireflective coating is between the sensor substrate and the element substrate.
15. 15 . The second of claim 1 , wherein a thickness of the element between 350 and 100 nm.
16. 16 . An imaging device, comprising: an image sensor, including: a sensor substrate; an element substrate, wherein the element substrate is disposed on a light incident surface side of the sensor substrate; and a plurality of pixels disposed in the sensor substrate, wherein each pixel in the plurality of pixels includes: a plurality of sub-pixels; a plurality of diffraction elements, wherein the diffraction elements are disposed in a first layer of the element substrate, wherein at least one of the diffraction elements partially overlaps more than one sub-pixel, and wherein the diffraction elements are asymmetrically disposed about an area of the pixel; and a plurality of color filters, wherein the color filters are disposed in a second layer of the element substrate.
17. 17 . The imaging device of claim 16 , further comprising: an imaging lens, wherein light collected by the imaging lens is incident on the image sensor, and wherein the diffraction elements diffract and scatter the incident light onto the sub-pixels of the respective pixels.
18. 18 . The imaging device of claim 16 , further comprising: a processor, wherein the processor executes application programming, wherein the application programming determines a color of light incident on a selected pixel from ratios of a relative strength of a signal generated at different pairs of sub-pixels of the selected pixel in response to the light incident on the selected pixel.
19. 19 . The imaging device of claim 16 , wherein an area of the diffraction elements of any one of the plurality of pixels occupies less than all of a light incident surface of the any one of the pixels, and wherein an area of the color filters of the any one of the pixels occupies less than all of the light incident surface of the any one of the pixels.
20. 20 . A method, comprising: receiving incident light at an image sensor having a plurality of pixels; for each pixel in the plurality of pixels, diffracting using a set of diffraction elements and partially filtering using a plurality of wavelength filters the incident light onto a plurality of sub-pixels; for each pixel in the plurality of pixels, determining a ratio of a signal strength generated by the sub-pixels in each unique pair of the sub-pixels in response to the incident light; and determining a color of the incident light at each pixel in the plurality of pixels from the determined ratio of signal strength at each of the sub-pixels.

Description

FIELD The present disclosure relates to an imaging device incorporating diffractive, light focusing elements and color filters to enable accurate recovery of incident light wavelength from noisy signals. BACKGROUND Digital image sensors are commonly used in a variety of electronic devices, such as handheld cameras, security systems, telephones, computers, and tablets, to capture images. In a typical arrangement, light sensitive areas or pixels are arranged in a two-dimensional array having multiple rows and columns of pixels. Each pixel generates an electrical charge in response to receiving photons as a result of being exposed to incident light. For example, each pixel can include a photodiode that generates charge in an amount that is generally proportional to the amount of light (i.e. the number of photons) incident on the pixel during an exposure period. The charge can then be read out from each of the pixels, for example through peripheral circuitry. In conventional color image sensors, absorptive color filters are used to enable the image sensor to detect the color of incident light. The color filters are typically disposed in sets (e.g. of red, green, and blue (RGB); cyan, magenta, and yellow (CMY); or red, green, blue, and infrared (RGBIR)), with one color filter in the set over one light sensitive pixel. Such arrangements have about 3-4 times lower sensitivity and signal to noise ratio (SNR) at low light conditions, experience issues with color crosstalk and color shading at high chief ray angles (CRA), and have lower spatial resolution due to color filter patterning resulting in lower spatial frequency as compared to monochrome sensors without color filters. However, such limitations have been endured in order to obtain information about the color or wavelength of the light incident on the image sensor. Image sensors have been developed that utilize uniform, non-focusing metal gratings, to diffract light in a wavelength dependent manner, before that light is absorbed in a silicon substrate. Such an approach enables the wavelength characteristics (i.e. the color) of incident light to be determined, without requiring the use of absorptive filters. However, the non-focusing diffractive grating results in light loss before the light reaches the substrate. Such an approach also requires an adjustment or shift in the microlens and the grating position and structures across the image plane to accommodate high chief ray angles (CRAs). Still other sensor systems that enable color to be sensed without the use of color filters are so called “color routers”, which direct light among a 2×2 Bayer array of red, green, green, and blue pixels. In such systems, instead of using absorptive filters to select the light that is incident on the individual pixels, the light is routed to the pixels within the Bayer array on the basis of color by high index of refraction diffractive elements. Although this avoids the loss inherent to absorptive filter designs, the resulting color resolution of the sensor is the same as or similar to that of a filter based Bayer array. In addition, determining the pattern of the diffractive elements used to route the light of different colors requires the use of artificial intelligence design procedures, and results in a relatively tall structure. Improved color or wavelength sensitive systems have been developed that utilize sets of diffractive, light focusing elements disposed over pixels that each include a plurality of sub-pixels. In such arrangements, the diffraction pattern produced across the sub-pixels of a wavelength sensing pixel is different for different wavelengths of incident light. These systems have the potential to provide high color resolution and sensitivity. However, the ability of such systems to accurately determine a wavelength of incident light can be compromised in real world situations, in which the outputs from the sub-pixels include noise components. This problem is particularly apparent in systems seeking to provide high spectral resolution by incorporating a relatively large number of sub-pixels within each wavelength sensing pixel. Accordingly, it would be desirable to provide an image sensor with high sensitivity and high color resolution that could accurately determine a wavelength of incident light in the presence of noise. SUMMARY Embodiments of the present disclosure provide image sensors and image sensing methods that provide high color or wavelength resolution and sensitivity. An image sensor in accordance with embodiments of the present disclosure includes a sensor array having a plurality of color or wavelength sensing pixels. Each wavelength sensing pixel in the plurality of pixels includes a plurality of photosensitive sub-pixels formed within a sensor substrate. In addition, each wavelength sensing pixel is associated with a set of diffraction features. Each set of diffraction features includes a plurality of diffraction elements disposed in one or