Abstract:
An integrated image sensor includes a sensing element and a microlens disposed over the sensing element, where the microlens incorporates a first material that blocks a first wavelength of visible light. By eliminating separate color filters and incorporating the color-filtering function into a microlens, such an integrated image sensor may have a smaller foot print and a higher sensitivity, and may generate images of higher quality as compared to a known image sensor. Furthermore, such an image sensor may be usable in a wider range of applications as compared to a known image sensor.

Description:
BACKGROUND 
       [0001]    An electronic image-capture device, such as a digital camera, copier, or scanner, typically includes an integrated image sensor for converting visible light that emanates from an object into one or more corresponding electronic signals. From these electronic signals, the image-capture device creates and stores an electronic representation of an image of the object. A display device, such as a liquid-crystal or plasma display, may then convert the electronic representation into a viewable version of the image. 
         [0002]      FIG. 1  is a cut-away perspective view of a region of pixel-array  10  of a conventional integrated color image sensor. The pixel-array  10  includes an array of microlenses  12 , a first planarizing layer  14 , an array of color filters  16 , a second planarizing layer  18 , an interconnect region  20 , and an array of sensor elements  22 . In addition to the pixel array  10 , the image sensor may include other components, such as a memory, analog-to-digital converter (ADC), and processor (none shown in  FIG. 1 ) disposed around the periphery of the pixel array. 
         [0003]    Each microlens  12  is conventionally formed by depositing a region of a transparent material, such as glass or resin, on the layer  14  over a corresponding sensor element  22 —dashed lines  24  outline the projected areas of the underlying sensing elements—and treating the substance such that the microlens has a convex upper surface. As discussed below in conjunction with  FIG. 2 , this formation process often leaves undesired gaps  26  between some or all of the microlenses  12 , and may cause some or all of the microlenses to be misaligned with the respective underlying color filters  16 . 
         [0004]    The first planarizing layer  14  is conventionally formed from an oxide such as silicon oxide, a nitride such as silicon nitride, or another transparent material, and provides a planar surface on which to form the microlenses  12 . The subsequently described transparent materials may also be an oxide, nitride, or other transparent material. 
         [0005]    Each color filter  16  is formed by depositing over a corresponding sensor element  22  a mixture of a transparent material and a respective light-absorbing dye, pigment, or other material. After the formation of the color filters  16 , the upper surfaces of the filters may be planed before the formation of the first planarizing layer  14 . 
         [0006]    The color of light that each filter  16  passes is indicated by the letter R (red light), G (green light), or B (blue light) in the corresponding microlens  12 —the filters  16  are shown arranged in a Bayer pattern. For example, an R filter  16  includes a material that absorbs all wavelengths of light (e.g., green and blue wavelengths) other than the wavelengths in the red portion of the spectrum. That is, the R filter  16  ideally allows red light to pass from the corresponding microlens  12  to the corresponding sensor element  22 , but blocks green and blue light. Therefore, the corresponding sensor element  22  ideally senses only the red light that passes through the corresponding microlens  12 . In actuality, the R filter&#39;s cutoff between red and green light may not be sharp enough to completely block the shorter green wavelengths and to pass unattenuated wavelengths of red light. But for purposes of discussion, we need not consider the precise wavelength responses of the R, G, and B filters  16 . 
         [0007]    The second planarizing layer  18  is formed conventionally from an oxide or other transparent material, and provides a planar surface on which to form the color filters  16 . 
         [0008]    The interconnect region  20  includes one or more layers of e.g., transistors, interconnect lines, and vias (none shown) for routing signals between the sensing elements  22  and a controller (not shown in  FIG. 1 ) of the image sensor on which the pixel array  10  is disposed. 
         [0009]    Each sensing element  22  is formed in a bulk semiconductor substrate (not shown), and may be, e.g., a photo diode or a CMOS sensing element. Because the components (not shown) of the interconnect region  20  typically block some of the light from the corresponding microlens  12 , each sensing element  22  typically has an effective aperture  28 , which is the area of the sensing element upon which light from the corresponding microlens is incident. For example, each effective aperture  28  may equal an area that is approximately 50% of the total area of the corresponding sensing element  22 . Furthermore, although each effective aperture  28  is shown as a respective continuous area centered within the sensing element  22 , the effective aperture may be discontinuous and/or off center. 
         [0010]    Furthermore, each sensing element  22  corresponds to a respective pixel of an image that the pixel array  10  captures. For example, the pixel array  10  may have dimensions of 2190×3650 sensing elements  22 , which yield a relatively high-resolution image having approximately eight million pixels and a 3×5 aspect ratio. 
         [0011]      FIG. 2  is a cut-away side view of the pixel array  10  of  FIG. 1  and an optical train  34  for focusing onto the array light rays  36  emanating from an object (not shown). The optical train  34  has a focal point FP, and, although shown as a single lens, may include additional lenses and other components.  FIG. 2  may not, however, be to actual scale. 
         [0012]    Each microlens  12  has a focal point fp that is substantially coincident with the surface of the corresponding sensing element  22  at substantially the center of the element. Consequently, each microlens  12  has a focal length fl that is approximately equal to the height of the microlens apex above the surface of the corresponding sensing element  22 , and has a substantially infinite focusing distance relative to the surface of the sensing element. The focal length and other optical properties of each microlens  12  depend on the ratio of the indices of refraction of the material (e.g., air) above the microlens and the material from which the microlens is made, as well as the index ratios at the boundaries of the layers  14 ,  16 ,  18 , and  20 . The height of the microlens  12  above the surface of the corresponding sensing element  22  is sometimes called the “stack” height, where the stack includes a microlens  12 , the corresponding color filter  16 , and the portions of the layers  14  and  18  and the region  20  beneath the microlens. 
         [0013]    Still referring to  FIG. 2 , the operation of the pixel array  10  is discussed. 
         [0014]    The rays of light  36  emanating from an object (not shown) are incident on the optical train  34 , which focuses these rays through the focal point FP and onto the pixel array  10 . The optical train  34  may be moveable so as to allow focus adjustment. 
         [0015]    A respective one or more of the rays  36  are incident one each microlens  12 , which redirects these incident rays through the layer  14 , corresponding color filter  16 , layer  18 , and region  20  onto the corresponding sensing element  22 . 
         [0016]    Each color filter  16  allows only wavelengths of a respective color (i.e., R, G, or B) to pass from the corresponding microlens  12  to the corresponding sensing element  22 . 
         [0017]    The sensing element  22  generates an electronic signal having a value that is proportional to the intensity of the light that is incident on the sensing element&#39;s surface. For example, a sensing element  22  beneath an R color filter  16  generates an electronic signal having a value proportional to the intensity of the red light passing from the corresponding microlens  12 , through the filter, and onto the sensing element&#39;s surface. Similarly, a sensing element  22  beneath a G color filter  16  generates a signal having a value proportional to the intensity of the green light passing from corresponding microlens  12 , through the filter, and onto the sensing element&#39;s surface, and a sensing element beneath a B color filter generates a signal having a value proportional to the intensity of the blue light passing from the corresponding microlens, through the filter, and onto the sensing element&#39;s surface. 
         [0018]    According to one technique for generating such a proportional electronic signal, each sensing element  22  is activated for a predetermined period of time. 
         [0019]    While active, the sensing element  22  generates a current that is proportional to the intensity of the light that strikes the surface of the sensing element. Consequently, the more light that strikes the surface of the sensing element  22 , the greater the current, and the less light that strikes the surface of the sensing element, the smaller the current. 
         [0020]    A circuit (not shown in  FIG. 2 ) integrates this current to generate a voltage that is proportional to the intensity of the incident light. 
         [0021]    At the end of the period, an ADC (not shown in  FIG. 2 ) converts the voltage into a digital intensity value. 
         [0022]    Then, a processor (not shown in  FIG. 2 ) processes the digital intensity values from all of the sensing elements  22  to generate an electronic representation of an image of the object (not shown in  FIG. 2 ). 
         [0023]      FIG. 3  is a cut-away side view of an outer region  37  of the pixel array  10  of  FIG. 1 . In the outer region  37 , each color filter  16  is intentionally misaligned with its corresponding microlens  12 , and each sensing element  22  is intentionally misaligned with its corresponding microlens and color filter. For example, the misalignment between the center of a microlens  12  and its corresponding sensing element  22  is MA. This misalignment helps the pixel array  10  to account for the larger angles of incidence of the light rays  36  on the microlenses  12  in the outer region  37 . At these larger ray angles, the optical power of a microlens  12  may be insufficient to redirect some or all of the rays downward to a sensing element  22  that is aligned with the microlens. Therefore, shifting the color filters  16  and sensing element  22  outward from the optical train  34  ( FIG. 2 ) relative to the microlenses  12  allows each microlens to direct more light through its corresponding color filter and onto its corresponding sensing element. 
         [0024]    Still referring to  FIG. 3 , although shown as being uniform, the intentional misalignment MA is typically proportional to the stack height of the array  10  and also to the distance of the sensing element  22  from the center of the array. This is because the angle of the incident light rays  36 , and thus the angle of the light rays redirected by the microlenses  12 , increase with distance from the array center, and because the horizontal propagation distance of the redirected light rays increases with stack height. Therefore, the farther from the array center, the larger the misalignment MA. 
         [0025]    And although the sensing elements  22  are each shown having a uniform area (only one dimension, width, shown in  FIG. 3 ), the sensor area is also typically proportional to the stack height and to the distance from the center of the array  10  to accommodate the increased divergence of the redirected light from the microlenses  12 . The divergence is proportional to the post-microlens propagation distance, which is proportional to the ray angle and to the stack height. 
         [0026]    Referring to  FIGS. 1-3 , there are, unfortunately, problems associated with the pixel array  10 . 
         [0027]    Typically, it is desired that the pixel array  10  have a relatively high sensitivity. The sensitivity of the pixel array  10  is proportional to the amount of light, i.e., the number of incident rays  36 , that each microlens  12  redirects onto the surface of the corresponding sensing element  22 . The higher the sensitivity, the more suitable the pixel array  10  for low-light (e.g., night photography) and high-speed (e.g., photographing moving objects) applications. 
         [0028]    It is also typically desired that the pixel array  10  capture an image of a relatively high quality. As discussed above, each sensing element  22  corresponds to a pixel of the captured image. And each pixel corresponds to a region of the object (not shown in  FIGS. 1 and 2 ), the image of which the pixel array  10  captures. Consequently, for a high-quality image, each microlens  12  should direct onto the corresponding sensing element  22  only light emanating from the corresponding region of the object. 
         [0029]    Moreover, it is typically desired that the “foot print” of the pixel array  10  be relatively small. 
         [0030]    Unfortunately, the gaps  26  and the focal length fl of the microlenses  12  may degrade the sensitivity of the pixel array  10 , and the gaps may also degrade the quality of images that the image sensor captures. 
         [0031]    Referring to  FIG. 2 , the gaps  26  may degrade the sensitivity of the pixel array  10  by reducing the amount of light that is incident on a sensing element  22 . For example, if a gap  26   a  did not exist, then a microlens  12   a  would redirect a ray  36   a  onto the underlying sensing element  22   a . But because the gap  26   a  allows the ray  36   a  to propagate past the microlens  12   a , the ray misses the sensing element  22   a.    
         [0032]    Furthermore, the relatively long focal lengths fl of the microlenses  12  may degrade the sensitivity of the pixel array  10  by reducing the amount of light that a microlens can direct onto the corresponding sensing element  22 . It is known that the longer the focal length of a lens, the less light that the lens can gather and direct to its focal point. Consequently, the longer the focal length fl, the less light that a microlens  12  can gather and direct to its focal point fp, and thus the less light that the microlens can gather and direct onto the corresponding sensing element  22 . Unfortunately, the stack height of the pixel array  10 , and thus the focal lengths fl of the microlenses  12 , may be as large as 5-6 microns (μm). 
         [0033]    Moreover, the gaps  26  may degrade the quality of a captured image by allowing light corresponding to one pixel of the image to “contaminate” another pixel of the image—this contamination is sometimes called “cross talk.” For example, if the gap  26   a  did not exist, then a microlens  12   a  would redirect the ray  36   a , which corresponds to a first pixel of the image, onto a corresponding sensing element  22   a , which also corresponds to the first pixel. But the gap  26   a  allows the ray  36   a  to strike a sensing element  22   b , which corresponds to a second pixel of the image. Consequently, the ray  36   a  striking the sensing element  22   b  may cause an erroneous decrease in the intensity of the first pixel and an erroneous increase in the intensity of the second pixel. 
         [0034]    In addition, unintentional misalignment (or an error in the intentional misalignment MA) of a microlens  12  with the corresponding color filter  16  and/or sensing element  22  may further reduce the sensitivity of the pixel array  10  and the quality of an image captured by the pixel array. 
         [0035]    Furthermore, the relatively large stack height of the pixel array  10  may cause the array to have a relatively large foot print because, as discussed above in conjunction with the outer region  37  of  FIG. 3 , the areas of the sensing elements  22  and the intentional misalignment MA of the sensing elements relative to the microlenses  12  are proportional to the stack height. 
         [0036]    Moreover, because the distance between the optical train  34  and the array  10 , and the optical properties of the train, may vary with application, the array  10  may need to be customized for each application. Specifically, as the angle of incidence for the light rays  36  changes, MA and the sensing-element area, also often change. Because given the relatively large stack height of the pixel array  10 , even a small change in the incident-ray angle may require significant changes in MA and the sensing-element area. 
       SUMMARY 
       [0037]    An embodiment of an integrated pixel array includes a sensing element and a microlens disposed over the sensing element, where the microlens incorporates a first material that blocks a first wavelength of visible light. 
         [0038]    By combining a microlens and a color filter into a single unit, such a pixel array may have a smaller foot print and higher sensitivity, and may generate images of higher quality, as compared to prior pixel arrays. Furthermore, such a pixel array may be usable in a wider range of applications as compared to prior pixel arrays. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0039]      FIG. 1  is a cut-away perspective view of a conventional integrated pixel array. 
           [0040]      FIG. 2  is a cut-away side view of the pixel array of  FIG. 1 . 
           [0041]      FIG. 3  is a cut-away side view of an outer region of the pixel array of  FIG. 1 . 
           [0042]      FIG. 4  is a cut-away side view of a pixel array according to an embodiment of the invention. 
           [0043]      FIG. 5  is a cut-away side view of the pixel array of  FIG. 4  at an intermediate point of formation according to an embodiment of the invention. 
           [0044]      FIG. 6  is a cut-away side view of the pixel array of  FIG. 4  at an intermediate point of formation according to another embodiment of the invention. 
           [0045]      FIG. 7  is a cut-away side view of an outer region of the pixel array of  FIG. 4  according to an embodiment of the invention. 
           [0046]      FIG. 8  is a cut-away side view of an integrated circuit (IC) that includes an integrated image sensor having the pixel array of  FIG. 4  according to an embodiment of the invention. 
           [0047]      FIG. 9  is a block diagram of an electronic image-capture system that incorporates the IC of  FIG. 8  according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0048]    The following discussion is presented to enable a person skilled in the art to make and use one or more embodiments of the invention. The general principles described herein may be applied to embodiments and applications other than those detailed below without departing from the spirit and scope of the invention. Therefore the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed or suggested herein. 
         [0049]      FIG. 4  is a cut-away side view of an inner region of a pixel array  40  according to an embodiment of the invention. As discussed below, the pixel array  40  may have a greater sensitivity and generate images of a higher quality as compared to prior pixel arrays such as the pixel array  10  of  FIG. 1 . Furthermore, like numbers are used in  FIG. 4  to reference structures common to  FIGS. 1-4 . 
         [0050]    Referring to  FIG. 4 , the pixel array  40  includes color-filtering microlenses  42 , each of which is effectively a combination of a microlens  12  and a corresponding color filter  16  of  FIGS. 1-3 . 
         [0051]    Each microlens  42  is formed from a mixture of a transparent material, such as glass or resin, and a light-absorbing material, such as a dye, and has a convex upper surface  44 . 
         [0052]    The light-absorbing material allows only a predetermined color (i.e., one or more predetermined wavelength(s)) of light to pass through the microlens  42  to the underlying sensing element  22 . For example, the light-absorbing material in an R microlens  42  allows only red light to pass through the R microlens to the sensing element  22 . Similarly, the light-absorbing material in a G microlens  42  allows only green light to pass through the G microlens to the underlying sensing element  22 , and the light-absorbing material in a B microlens  42  allows only blue light to pass through the B microlens to the underlying sensing element. Because such light-absorbing materials are known, a more detailed description of these materials is omitted. 
         [0053]    Furthermore, the R, G, and B microlenses  42  have different heights, and the convex surface  44  provides each microlens  42  with a respective focal length fl′ approximately equal to the microlens&#39; height. Because the transparent material from which the microlenses  42  are formed causes different wavelengths of incident light to refract at different angles, the heights of the R, G, and B microlenses are different so as to “tune” the optical properties (e.g., the focal points) of the microlenses to the respective wavelengths they pass. For example, assume that the convex surfaces  44  of an R microlens  42  and a G microlens have substantially the same shape—this may occur in practice, because depending on the process used to form the microlenses, it may be difficult to form the convex surfaces  44  having different predetermined shapes. Consequently, the different angles at which the respective convex surfaces  44  refract red and green light may cause the focal length flr′ of the R microlens  42  for passed red light to be different from the focal length flg′ of the G microlenses for passed green light. But by forming the R and G microlenses  42  to have respective heights approximately equal to flr′ and flg′, one can set the corresponding focal points fpr′ and fpg′ substantially at the surfaces of the respective sensing elements  22  as may be desired. For similar reasons, the heights of the B microlenses  42  (not shown in  FIG. 4 ) may be different than the heights of the R and G microlenses. Furthermore, although the G microlenses  42  are shown as being taller than the R microlenses, the G microlenses may be shorter than the R microlenses. In addition, the heights of the R, G, and B microlenses  42  may together be constrained within a predetermined range having a predetermined tolerance to provide predictability to the height of the image sensor that incorporates the pixel array  40 . 
         [0054]    Still referring to  FIG. 4 , the microlenses  42  may increase the sensitivity of the pixel array  40  and the quality of the images captured by the pixel array as compared to prior pixel arrays such as the pixel array  10  of  FIG. 1 . 
         [0055]    Because each microlens  42  is effectively a combination of a microlens  12  and color filter  16  ( FIGS. 1-3 ), the stack heights (i.e., the respective heights of the R, G, and B microlenses  42  above the sensing elements  22 ) of the pixel array  40  may be less than the stack height of the pixel array  10  ( FIG. 1 ). For example, the stack heights of the pixel array  40  may range from approximately 4.5-5.5 μm or shorter. These reduced stack heights may allow the focal lengths fl′ of the microlenses  42  to be shorter than the focal length fl of the microlenses  12 , and thus may increase the amount of light that each microlens  42  can gather and direct onto an underlying sensing element  22  as compared to the amount of light that a microlens  12  can gather and direct. Consequently, the increased light-gathering and light-directing capacities of the microlenses  42  may increase the sensitivity of the pixel array  40  relative to prior pixel arrays. Furthermore, the pixel array  40  may be said to have a “stack height” that is equal to the stack height of the tallest microlenses  42 . So in this embodiment the “stack height” of the pixel array  40  is equal to the stack height of the green microlenses  42 . 
         [0056]    Furthermore, the lack of gaps between the microlenses  42  may reduce the number of light rays that “miss” the appropriate sensing element  22 , and thus may reduce the occurrence of pixel “cross talk;” consequently, the lack of gaps may improve the sensitivity of and the image quality provided by the pixel array  40  as compared to prior pixel arrays. 
         [0057]    In addition, because the microlenses  42  include color-filtering materials, the color filters and microlenses of the pixel array  40  are effectively self-aligned. This effective self-alignment may also increase the sensitivity of and the image-quality provided by the pixel array  40  as compared to prior pixel arrays. 
         [0058]    The reduced stack heights of the microlenses  42  over the sensing elements  22  and the lack of gaps may also provide the pixel array  40  with other advantages over prior pixel arrays. For example, the omission of the layer  14  and the separate color filters  16  of  FIGS. 1-3  may reduce the cost of manufacturing an image sensor that incorporates the pixel array  40  as compared to cost of an image sensor that incorporates the pixel array  10  of  FIGS. 1-2 . 
         [0059]    Still referring to  FIG. 4 , when installed in an image-capture system (not shown in  FIG. 4 ) such as a digital camera, the pixel array  40  operates similarly to the pixel array  10  of  FIG. 1 , but potentially with a higher sensitivity and providing a better image quality as discussed above. 
         [0060]      FIG. 5  is a cut-away side view of the portion of the pixel array  40  of  FIG. 4  at an intermediate stage of formation according to an embodiment of the invention. 
         [0061]    Referring to  FIGS. 4 and 5 , the process for forming the pixel array  40  is discussed according to an embodiment of the invention. 
         [0062]    Referring to  FIG. 5 , the sensing elements  22  are formed in a known manner, and the interconnect region  20  is formed over the sensing elements in a known manner. 
         [0063]    Next, the planarizing layer  18  is formed over the interconnect region  20  in a known manner. 
         [0064]    Then, an R segment  46  formed from a mixture of a transparent material and a material that passes red light and absorbs green and blue light is deposited on the layer  18  in each R-pixel location. A mask (not shown in  FIG. 4 ) is used to prevent formation of the R segments  46  on the G-pixel and B-pixel locations (B-pixel locations not shown in  FIGS. 4-5 ). Similarly, a G segment  46  formed from a mixture of the transparent material and a material that passes green light and absorbs red and blue light is deposited on the layer  18  in each G-pixel location, and a B segment  46  (not shown in  FIG. 5 ) formed from a mixture of the transparent material and a material that passes blue light and absorbs red and green light is deposited on the layer  18  in each B-pixel location. The R, G, and B segments  46  are formed such that gaps  48  are present between the segments. For example, the gaps may be approximately 0.25 μm wide. Furthermore, the mixtures used to form the R, G, and B segments  46  are premixed in a known manner before being deposited on the layer  18 . 
         [0065]    Referring to  FIGS. 4 and 5 , the R, G, and B segments  46  (B segments not shown in  FIG. 5 ) are then heated to form the R, G, and B microlenses  42  (B microlenses not shown in  FIG. 4 ). This heating is often called “reflow.” When heated, the R, G, and B segments  46  soften and expand outward and against each other such that there are few if any gaps  48  remaining between the formed microlenses  42 . Furthermore, surface tension in the softened segments  46  causes the upper surfaces of the segments to “bead” like water on a waxed car hood, thus forming the convex upper surfaces  44  of the microlenses  42 . Where the R, G, and B segments  46  have substantially the same lateral dimensions (i.e., dimensions in the plane of the layer  18 ) and are made from the same transparent material, then the surface tension typically causes the convex upper surfaces  44  to have a substantially uniform shape. 
         [0066]    Next, the remaining portions (not shown in  FIGS. 4-5 ) of the integrated image sensor that includes the pixel array  40  are formed in a conventional manner. Alternatively, some or all of these remaining portions may be formed contemporaneously with the pixel array  40 . 
         [0067]    Still referring to  FIGS. 4-5 , alternate embodiments of the pixel sensor  40  are contemplated. For example, the microlenses  42  may have substantially equal heights, but may have differently shaped convex surfaces  44  so that all of the R, G, and B microlenses  42  have substantially the same heights (i.e., flr′=flg′=flb′˜the height of the microlenses where flb′ is the focal length of the B microlenses, which are not shown in  FIG. 4 ). One technique for achieving the differently shaped convex surfaces  44  is forming the R, G, and B segments  46  from respective transparent materials that have different reflow properties. Or, the R, G, and B microlenses  42  may have both different heights and differently shaped convex surfaces  44 . Alternatively, the R, G, and B microlenses  42  may be formed from different transparent materials having different indices of refraction to further “tune” the focal lengths fl′ of the microlenses. Furthermore, the R, G, and B microlenses  42  may have different lateral dimensions. In addition, not all of the R microlenses  42  may have the same dimensions and properties. For example, some R microlenses  42  may be taller than other R microlenses, or may have more or less of the blue-green-light-absorbing material than other R microlenses. Similar alternatives are contemplated for the G and B microlenses  42 . Moreover, the layer  18  may be omitted, and the microlenses  42  may be disposed directly on the interconnecting region  20 . Furthermore, the microlenses  42  may pass colors of light different than red, green, and blue to conform to a color space other than RGB, such as CMY (cyan, magenta, yellow). In addition, one may grow the R, G, and B segments  46  on the layer  18  instead of depositing them on the layer. Alternatively, one may form an array of the microlenses  42  separately (e.g., by injection molding) and then place the array on the layer  18  (or directly on the interconnection region  20 ) in alignment with the sensing elements  22 . Moreover, one may include an infrared(IR)-absorbing material in the microlenses  42  to eliminate the need for a separate infrared filter. Techniques for separately forming a microlens array and for including an IR-absorbing material in the microlenses  42  are described in commonly assigned U.S. patent application Ser. No. 10/926,152, which is incorporated by reference. Furthermore, instead of being formed in a bulk semiconductor substrate, the sensing elements  22  may be formed from semiconductor thin films or polymers on a glass or ceramic substrate, or may be formed in another manner. 
         [0068]      FIG. 6  is a cut-away side view of a portion of the pixel array  40  of  FIG. 3  at an intermediate stage of formation according to another embodiment of the invention. Referring to  FIG. 6 , the process for forming the pixel array  40  according to this embodiment of the invention is similar to the process described above in conjunction with  FIGS. 4 and 5 , except that the R, G, and B segments  46  (the B segments are not shown in  FIG. 6 ) are deposited onto the layer  18  in contact with one another. As compared to a process that deposits the segments  46  with gaps  48  therebetween as described above in conjunction with  FIG. 5 , depositing contiguous segments may further reduce or eliminate the occurrence of gaps between the microlenses  42 , and may reduce the widths of these gaps if they occur. Alternate embodiments of this contiguous-segment process are contemplated, including alternate embodiments that are similar to those described above in conjunction with  FIGS. 4 and 5  for the non-contiguous-segment process. 
         [0069]      FIG. 7  is a cut-away side view of an outer region  49  of the pixel array  40  of  FIG. 4  according to an embodiment of the invention. 
         [0070]    In the outer region  49 , each sensing element  22  is intentionally misaligned with its corresponding color-filtering microlens  42  to help the pixel array  40  account for the larger angles of incidence of the light rays  36  on the microlens as discussed above in conjunction with  FIG. 3 . 
         [0071]    But the reduced stack height (˜flg′) of the pixel array  40  as compared to the known pixel array  10  of  FIGS. 1-3  may allow a reduction in the foot print of the pixel array  40  for a given number of sensing elements  22  as compared to the known pixel array. Because the intentional misalignment MA and the area of a sensing element  22  are proportional to the stack height, the reduced stack height of the pixel array  40  may allow a reduction in both the intentional misalignment MA and the areas of the sensing elements  22 . And because the foot print of the pixel array  40  is proportional to MA and to the areas of the sensing elements  22 , a reduction in these quantities reduces the array foot print for a given number of sensing elements. 
         [0072]    Moreover, the reduced stack height reduces the dependency of MA and the sensing-element area on the incident angle of the rays  36 , and thus may render the pixel array  40  suitable for use in applications having a wider range of incident-ray angles as compared to the pixel array  10  of  FIGS. 1-3 . This may reduce costs, as fewer versions of the array  40  may be produced for a given range of incident-ray angles as compared to the number of versions needed for the known pixel array  10 . 
         [0073]    Still referring to  FIG. 7 , although the sensing elements  22  are shown having a uniform area, and the microlenses  12  and sensing elements are shown having a uniform intentional misalignment MA, the sensing-element areas and the misalignment MA may increase as one moves further away from the center of the pixel array  40 . That is, the sensing-element area and the misalignment MA may be proportional to the distance of the sensing element  22  from the center of the array  40 . 
         [0074]    Furthermore, the microlenses  42  in the outer region  49  may be formed as described above in conjunction with  FIGS. 5-6 . 
         [0075]      FIG. 8  is a cut-away side view of an integrated circuit (IC)  50  that includes an image-sensor die  51 , which incorporates the pixel array  40  of  FIG. 4  according to an embodiment of the invention. The IC  50  includes a glass plate  52  or other transparent cover attached to a side wall  54  of a shell-case sensor package  56 , which surrounds the die  51 . The package side wall  54  is of a suitably durable material, such as plastic or ceramic, sized to provide separation between the lower face of the plate  52  and the upper convex surfaces of the microlenses  42 . The plate  52  is bonded to upper extents  58  of the wall  54  by a sealant adhesive and protects the microlenses  42 . Bond wires  60  connect pads (not shown in  FIG. 8 ) of the die  51  to package leads  62 , which are bonded to the pads (not shown in  FIG. 8 ) on a circuit board  64  and electrically connect the die  51  to external circuitry (not shown in  FIG. 8 ). An optical train (not shown in  FIG. 8 ), such as the focusing-lens assembly  34  of  FIG. 2 , when used, is mounted by a suitable supporting structure (not shown in  FIG. 8 ) to the board  64  so as to be in optical-path alignment with the microlenses  42 . 
         [0076]      FIG. 9  is a block diagram of an electronic image-capture system  70  that incorporates the image-sensor IC  50  of  FIG. 8  according to an embodiment of the invention. In addition to the pixel array  40 , which receives light emanating from an object (not shown in  FIG. 9 ) through a field lens  72 , the image-sensor IC  50  also includes the following circuitry: a pixel color-gain ratio controller  74 , A/D converter  76 , window-size controller  78 , pixel-gain controller  80 , and timing controller  82 . These circuits may be integrated onto the same die  51  ( FIG. 8 ) as the pixel array  40 , or may be disposed on one or more different dies. An image processor  84  having known circuitry and operation is connected to the sensor IC  50  and has the various control and data lines  86  for controlling the circuitry on the IC  50 , for receiving electronic pixel information from the pixel array  40 , and for processing the pixel information to form an image of the object. Because such circuitry and signal processing are known, they are not described further. Furthermore, although shown as being separate from the IC  50 , part or all of the processor  84  may be disposed on the IC, and may be integrated onto the same die  51  that includes the pixel array  40 , or may be integrated onto a different die. 
         [0077]    From the foregoing it will be appreciated that, although specific embodiments have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. Furthermore, where an alternative is disclosed for a particular embodiment, this alternative may also apply to other embodiments even if not specifically stated.