Image sensor with micro-structured color filter

1. An image sensor with micro-structured color filter comprising:

a two-dimensional photodiode-array formed in a semiconductor substrate;

a first waveguide aligned to a first photodiode of the photodiode-array and located above a top substrate surface of the semiconductor substrate, a first core of the first waveguide being formed of a first material and having a first core width less than a pitch of the photodiode-array in a first direction and a second direction corresponding to respective orthogonal dimensions of the photodiode-array;

a first color filter on a top waveguide surface of the first waveguide, being formed of the first material, and having a first non-uniform thickness above the first core, the first waveguide being between the top substrate surface and the first color filter;

a second waveguide aligned to a second photodiode of the photodiode-array side-adjacent to the first photodiode and located above the top substrate surface, a second core of the second waveguide being formed of a second material that differs from the first material and having a second core width less than the pitch in the first and second directions; and

a second color filter on a top waveguide surface of the second waveguide, being formed of the second material, and having a second non-uniform thickness above the second core, the second waveguide being between the top substrate surface and the second color filter,

the first color filter having a first spectral passband differing from a second spectral passband of the second color filter.

2. The image sensor of claim 1 , the pitch not exceeding 1.0 micrometers.

3. The image sensor of claim 1 , a shape of the first color filter being a trapezoidal prism having a trapezoidal shape in a cross-sectional plane perpendicular to and intersecting the top waveguide surface.

4. The image sensor of claim 3 , the trapezoidal shape being one of an acute trapezoid and a right trapezoid.

5. The image sensor of claim 3 , the trapezoidal shape being a rectangle.

6. The image sensor of claim 1 , a shape of the first color filter being one of a rectangular pyramid and a rectangular frustum.

7. The image sensor of claim 1 , a shape of the first color filter being a rectangular cuboid adjoined to a base of one of a rectangular pyramid and a rectangular frustum.

8. The image sensor of claim 7 , in each of the first and second directions, the rectangular cuboid having a width not exceeding the pitch.

9. The image sensor of claim 1 , the first color filter having a filter spectral passband that is narrower than a spectral passband of a cladding of the first waveguide.

10. The image sensor of claim 9 , the first color filter being formed of a dielectric material and including one of a dye and pigment that absorbs electromagnetic radiation outside of the filter spectral passband.

11. The image sensor of claim 1 , the first color filter and a core of the first waveguide being monolithic.

12. The image sensor of claim 1 , in multiple cross-sectional planes parallel to the first direction and perpendicular to the top substrate surface, the first color filter having a first surface profile that includes at least one period of one of a pulse-train surface profile, a square-waveform surface profile, a triangle-waveform surface profile, and a sawtooth-waveform surface profile.

13. The image sensor of claim 12 , the at least one period not exceeding the pitch.

14. The image sensor of claim 12 , further comprising:

a plurality of waveguides including the first waveguide and two additional waveguides, each of the plurality of waveguides being (i) aligned to a respective photodiode of a plurality of collinear photodiodes of the two-dimensional photodiode-array, (ii) located above the top substrate surface, (iii) having a respective core width less than the pitch in the first and the second direction, and (iv) part of the top waveguide surface; and

a color-filter layer on the top waveguide surface and directly above the plurality of waveguides, including the first color filter, and having a multi-pixel surface profile that includes at least one period of one of the pulse-train surface profile, the square-waveform surface profile, the triangle-waveform surface profile, and the sawtooth-waveform surface profile.

15. The image sensor of claim 12 , the multi-pixel surface profile including multiple periods of the first surface profile.

16. The image sensor of claim 1 , further comprising a plurality of aluminum nanowires embedded in the first color filter, arranged in a one-dimensional array parallel to the top waveguide surface, each of the plurality of aluminum nanowires having a cross-sectional width and a cross-sectional height each not exceeding 130 nanometers.

17. The image sensor of claim 1 , further comprising:

a first diffraction grating embedded in the first color filter and having a first grating vector parallel to the top substrate surface; and

a second diffraction grating embedded in the first color filter, between the first diffraction grating and the top substrate surface, and having a second grating vector parallel to the first grating vector.