Imaging sensor having microlenses of different radii of curvature

Abstract

The present invention provides an image sensor which comprises improved microlenses to cope with different optical requirements for oblique incident light or different components of light. In one embodiment, the image sensor comprises at least two microlenses having different radii of curvature. In another embodiment, the image sensor comprises at least one asymmetrical microlens.

1 . An image sensor comprising at least two microlenses having different radii of curvature. 
   
   
       2 . The image sensor as claimed in  claim 1 , wherein said at least two microlenses includes a first microlens having a smaller radius of curvature located at a central area of said image sensor, and a second microlens having a larger radius of curvature located at a peripheral area of said image sensor. 
   
   
       3 . The image sensor as claimed in  claim 2 , wherein said first microlens has a radius of curvature in a range from about 2.00 to about 2.20. 
   
   
       4 . The image sensor as claimed in  claim 2 , wherein said second microlens has a radius of curvature in a range from about 2.35 to about 2.55. 
   
   
       5 . The image sensor as claimed in  claim 1 , wherein said at least two microlenses includes a first microlens having a smaller radius of curvature corresponding to a first color, and a second microlens having a larger radius of curvature corresponding to a second color. 
   
   
       6 . The image sensor as claimed in  claim 1 , wherein said at least two microlenses includes a first microlens having a smaller radius of curvature corresponding to a red pixel, a second microlens having a less smaller radius of curvature corresponding to a green pixel, and a third microlens having a larger radius of curvature corresponding to a blue pixel. 
   
   
       7 . The image sensor as claimed in  claim 6 , wherein said first microlens has a radius of curvature of about 0.01 to 0.06 less than that of said second microlens. 
   
   
       8 . The image sensor as claimed in  claim 6 , wherein said third microlens has a radius of curvature of about 0.01 to 0.06 more than that of said second microlens. 
   
   
       9 . The image sensor as claimed in  claim 6 , wherein said first microlens has a radius of curvature in a range from about 2.02 to 2.12; said second microlens has a radius of curvature in a range from about 2.05 to 2.15; and said third microlens has a radius of curvature in a range from about 2.08 to 2.18. 
   
   
       10 . The image sensor as claimed in  claim 6 , wherein said first microlens has a radius of curvature in a range from about 2.37 to 2.47; said second microlens has a radius of curvature in a range from about 2.40 to 2.50; and said third microlens has a radius of curvature in a range from about 2.45 to 2.55. 
   
   
       11 . The image sensor as claimed in  claim 1 , wherein said at least two microlenses includes a first microlens having a symmetrical lens structure, which is located at a central area of said image sensor, and a second microlens having an asymmetrical lens structure at least along one horizontal dimension, which is located at a peripheral area of said image sensor. 
   
   
       12 . An image sensor comprising at least a microlens having an asymmetrical lens structure at least along one horizontal dimension. 
   
   
       13 . A method for making an image sensor, comprising:
 providing a semi-finished substrate;   coating a photoresist material on said semi-finished substrate;   patterning said photoresist material into a plurality of subsets, including at least a first subset and a second subset having different patterns from each other; and   reflowing said photoresist material wherein said first subset and said second subset form different contours.   
   
   
       14 . The method as claimed in  claim 13 , wherein at least one of said first and second subsets includes multiple cavities. 
   
   
       15 . The method as claimed in  claim 13 , wherein said patterns of said first and second subsets have different clear ratios. 
   
   
       16 . The method as claimed in  claim 13 , wherein said first subset forms a first contour having a smaller radius of curvature and is located at a central area of said image sensor, and said second subset forms a second contour having a larger radius of curvature and is located at a peripheral area of said image sensor. 
   
   
       17 . The method as claimed in  claim 13 , wherein said first subset forms a first contour having a smaller radius of curvature corresponding to a first color, and said second subset forms a second contour having a larger radius corresponding to a second color. 
   
   
       18 . The method as claimed in  claim 13 , wherein said subsets includes said first, said second, and a third subsets, said first subset forming a first contour having a smaller radius of curvature corresponding to a red pixel, said second subset forming a second contour having a less smaller radius corresponding to a green pixel, and said third subset forming a third contour having a larger radius corresponding to a blue pixel. 
   
   
       19 . The method as claimed in  claim 13 , wherein said first subset forms a symmetrical contour and is located at a central area of said image sensor, and said second subset forms an asymmetrical contour at least along one horizontal dimension and is located at a peripheral area of said image sensor. 
   
   
       20 . A method for making an image sensor, comprising:
 providing a semi-finished substrate;   coating a photoresist material on said semi-finished substrate;   patterning said photoresist material into a plurality of subsets, in which at least one of the subsets includes multiple cavities distributed asymmetrically along one horizontal dimension; and   reflowing said photoresist material wherein said at least one subset forms an asymmetrical contour.