Color CMOS image sensor with diffractive microlenses over subpixel photodiode arrays adapted for autofocus

An image sensor comprising:

• a plurality of diffractive pixels, each diffractive pixel comprising:
• a diffractive microlens comprising a central structure and at least one ring concentric with the central structure, the central structure and the at least one ring embedded in a background material having a first index of refraction, the central structure and the at least one ring formed of a transparent material having a second index of refraction different from the first index of refraction, and
• a plurality of photodiodes disposed beneath the diffractive microlens, the plurality of photodiodes configured to permit determining a ratio of illumination of at least one peripheral photodiode of the plurality of photodiodes to illumination of a central photodiode of the plurality of photodiodes;
• circuitry to determine a focus of an imaging lens from a ratio of illumination of at least one peripheral photodiode of at least one diffractive pixel designated an autofocus diffractive pixel to illumination of a central photodiode of the autofocus diffractive pixel;
• and
• an optical bandpass filter disposed over photodiodes of the autofocus diffractive pixel;
• wherein the at least one ring concentric with the central structure of the diffractive microlens of each diffractive pixel comprises at least a first and a second ring, the first and second ring being circular, and wherein the central structure is a disk;
• wherein the diffractive pixels each comprise 5, 6, or 9 photodiodes;
• and
• wherein a stack of the background material and diffractive lens disposed on a backside of semiconductor containing the plurality of photodiodes is less than 400 nanometers in thickness.

A method of determining a color of illumination light of a diffractive pixel, comprising:

• passing illumination light through a diffractive lens of the diffractive pixel disposed above 5, 6, 7, 8, or 9 photodiodes of the diffractive pixel;
• and
• determining a color of illumination from illumination of at least one peripheral photodiode of the 5, 6, 7, 8, or 9 photodiodes and illumination of a central photodiode of the 5, 6, 7, 8, or 9 photodiodes;
• wherein a stack of a background material and the diffractive lens disposed on a backside of semiconductor containing the photodiodes is less than 400 nanometers in thickness.

A method of determining focus for an autofocus system, comprising:

• passing illumination light through a diffractive lens of an autofocus diffractive pixel disposed above 5, 6, 7, 8, or 9 photodiodes of the autofocus diffractive pixel;
• determining a focus of illumination from illumination of at least one peripheral photodiode of the 5, 6, 7, 8, or 9 photodiodes and illumination of a central photodiode of the 5, 6, 7, 8, or 9 photodiodes;
• and
• wherein a stack of a background material and the diffractive lens disposed on a backside of semiconductor containing the photodiodes is less than 400 nanometers in thickness.