Abstract:
An image sensor includes a plurality of photosensitive sites; a plurality of asymmetrical-shaped microlenses positioned spanning the photosensitive sites; wherein incoming light is directed in a predetermined direction by an asymmetrical surface of the asymmetrical-shaped microlenses onto the photosensitive sites for capturing the light in a substantially uniform manner.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a 111A application of Provisional Application Ser. No. 60/686,106, filed Jun. 1, 2005. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to the field of microlenses spanning photosensitive sites of an image sensor and, more particularly, to asymmetrical microlenses spanning the photosensitive site that captures incident light in a substantially uniform manner. 
     BACKGROUND OF THE INVENTION 
     Referring to  FIG. 1 , image sensors  10  typically include pixels  20  having a photosensitive area or photodiode  30  for capturing incident light and associated circuitry  40  adjacent the photosensitive area for processing and the like. In some cases, pixels  20  of an image sensor  10  are arranged asymmetrically to maximize the performance of the pixel while accommodating the associated circuitry  40 . However, in this case, four of the pixels  20  typically form a regular grid pattern forming a supercell  50 . Referring to  FIG. 2 , a microlens  60  is positioned spanning and spatially centered over the “photosensitive portion” of the pixels  20 . Referring to  FIG. 3 , alternatively, microlenses  65  may be positioned spanning and centered over the entire “pixel” creating a regular array of microlenses. 
     Although the prior art arrangement of microlens  60  as in  FIG. 2  is satisfactory, it includes drawbacks in that the microlens  60  is a small fraction of the area of the pixel, and therefore the photodiode  30  captures a small fraction of the incident light. 
     Still further, although the prior art arrangement of microlenses  65  (as in  FIG. 3 ) over asymmetrically positioned pixels is satisfactory, they also include drawbacks. Referring to  FIG. 4 , as long as photodiodes  30  are symmetric with respect to the microlens  60  such as being centered in the pixel, then the performance of all pixels degrade in the same manner as the angle of the incident light is increased. As shown in  FIG. 5 , light passing (indicated by the dashed lines) through the microlenses  65  at certain angles is not directed onto the photodiode  30  causing undesirable degradation of the captured image when the photodiodes  30  are not arranged symmetrically with the microlens. 
     Consequently, a need exists for improved focusing of light on asymmetrical positioned pixels. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to overcoming one or more of the problems set forth above. Briefly summarized, according to one aspect of the present invention, the invention resides in an image sensor comprising (a) a plurality of photosensitive sites; (b) a plurality of asymmetrical-shaped microlenses positioned spanning the photosensitive sites; wherein incoming light is directed in a predetermined direction by an asymmetrical surface of the asymmetrical-shaped microlenses onto the photosensitive sites for capturing the light in a substantially uniform manner. 
     These and other aspects, objects, features and advantages of the present invention will be more clearly understood and appreciated from a review of the following detailed description of the preferred embodiments and appended Claims, and by reference to the accompanying drawings. 
     ADVANTAGEOUS EFFECT OF THE INVENTION 
     The present invention has the advantage of increasing the light gathering capacity of a pixel array and eliminating artifacts that occur when the incident angle of illumination is varied or varies. It is also includes the advantage of permitting more design freedom for efficient use of the pixel space. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top view of a prior art pixel array with apertures in an asymmetrical arrangement; 
         FIG. 2  is a top view of  FIG. 1  with microlenses spanning and centered over the photodiodes of array of pixels; 
         FIG. 3  is a top view of  FIG. 1  with microlenses spanning and centered over the pixels in the array; 
         FIG. 4  is a side view of a prior art pixel array with a symmetric arrangement of photodiodes and microlenses; 
         FIG. 5  is a side view of a prior art pixel array with a symmetric microlenses and asymmetrical arrangement of photodiodes; 
         FIG. 6  is a side view of the pixel array of the present invention with an asymmetric arrangement of photodiodes and an asymmetric arrangement of microlenses (the optical axis of each microlens is aligned with the center of the photodiode); 
         FIG. 7  is a top view of  FIG. 6 ; 
         FIG. 8  is a top view of an alternative embodiment of  FIG. 6  of the present invention; and 
         FIG. 9  is a side view of a digital camera containing the image sensor of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIGS. 6 and 7 , there are shown a side view and a top view of an image sensor  70  having a plurality or array of microlenses  80  of the present invention positioned respectively spanning a plurality of pixels  90  each having a photosensitive area or photodiode  100 . As stated above, the pixels  90  are arranged asymmetrically. However, it is noted that pixels are grouped together so as to form an array of supercells  110 . It is noted that only two supercells  110   a  and  110   b  each comprising two pixels is shown for clarity in  FIGS. 6 and 7 . For completeness, it is noted that the photosensitive areas  100  are disposed along a top portion of a silicon substrate, as is well known in the art. The pixels  90  are arranged so that by design they include an asymmetrical arrangement of the photosensitive areas  100 . An optical surface  120  of the microlens  130  is asymmetrically shaped. Prior art microlens ( 60  and  65 ) are substantially hemispherically shaped. As seen more clearly in  FIG. 6 , the microlens  130  of the present invention is substantially a truncated hemisphere that allows an asymmetrical arrangement. In other words, the each microlens  130  includes a substantially arcuate-shaped portion along a peripheral edge and includes two substantially straight portions positioned substantially perpendicular to each other along a remaining edge. For clarity, it is noted that the present invention microlens  130  has been trimmed along one or more edges as compared to the prior art microlens ( 60  and  65 ). This aligns the optical axis of the microlens  130  with the photodiode  100 . Referring solely to  FIG. 7 , it is noted that, within the two pixels comprising the supercell  110 , the microlenses  130  abut each other so that each individual microlens ( 130   a ,  130   b ,  130   c  and  130   d ) is symmetrical with respect to an imaginary y-axis of the supercell  110 , but still not symmetrical within any individual pixel  90  as stated hereinabove. In other words, each two-pixel supercell  110  includes two asymmetrical-shaped microlenses  130  grouped spanning a supercell  110  and a pair of straight portions, one from each microlens, are positioned so that a peripheral portion formed by the two microlenses is two arcuate-shaped edges and two straight edges. 
     The above-described pixel array functions so that incoming light that passes through a microlens  130  is directed substantially uniformly, that is consistently from pixel to pixel, onto the photodiode  100 , as illustrated by the solid and dashed lines, even though the spacing (i.e., distance) from photodiode to photodiode is not constant or is varying. In other words, the light is distributed substantially consistently across the photodiode  100  independent of which pixel within the supercell it is, with light passing from substantially directly overhead being directed substantially consistently onto a portion of the photodiode  100  and light that passes at angles through the microlens  130  is directed substantially consistently onto portions of the photodiode  100 . 
     As shown in  FIG. 8 , an alternative embodiment of the supercell  110  arrangement is shown. In this embodiment, there are four pixels  90  symmetrical around both imaginary x and y axes. 
     Referring to  FIG. 9 , there is shown a side view of a digital camera  140  containing the image sensor  70  of the present invention for illustrating a typical commercial embodiment. 
     The invention has been described with reference to a preferred embodiment. However, it will be appreciated that variations and modifications can be effected by a person of ordinary skill in the art without departing from the scope of the invention. 
     PARTS LIST 
     
         
           10  image sensor 
           20  pixel 
           30  photosensitive area or photodiode 
           40  associated circuitry 
           50  regular grid pattern forming a supercell 
           60  microlens centered on photodiode 
           65  microlens centered on pixel 
           70  image sensor 
           80  array of microlenses 
           90  plurality of pixels 
           100  photosensitive area or photodiode 
           110  supercell of pixels 
           110   a  supercell 
           110   b  supercell 
           120  optical surface of microlens 
           130  microlens 
           130   a  microlens 
           130   b  microlens 
           130   c  microlens 
           130   d  microlens 
           140  digital camera