Abstract:
An image sensing device includes a plurality of color units. Each color unit has a photosensor element for converting light of a specific spectrum range into an electrical signal. Different arrangements of the photosensor elements are set in diagonal directions. In this way, such layout is capable of reducing color shift effect.

Description:
BACKGROUND OF INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates to an image sensor, and more particularly, to an image sensor utilizing mirror-symmetrical layout to reduce color shift effect.  
         [0003]     2. Description of the Prior Art  
         [0004]     As with rapid development of digital image devices, digital image devices have become more popular than traditional analog image devices. However, in order to obtain better quality of digital images with higher resolution, improvement of the image sensor which is used for photoelectric conversion is necessary. However, in recent years, a solid-state image sensor has been miniaturized, with which a photosensor element is reduced and a drop of the sensitivity is caused.  
         [0005]     Please refer to  FIG. 1  showing a schematic diagram of a conventional digital image-capturing device  10 . The digital image-capturing device  10  comprises a lens  12  and an image sensor  20 . The image sensor  20  comprises a plurality of sensing units  30  each comprising a microlens  24 , a color filter  25  and a photosensor element  22 . When light enters into the image-capturing device  10 , the light will pass through the lens  12  and project onto the plurality of sensing units  30  through the lens  12 . Each microlens  24  will collect the incident light onto the photosensor element  22  of the sensing unit  30 , after filtering out light with different spectrums by using the color filter  25 . For example, the blue color filter  25   b  is used for filtering out the light inconsistent with the blue light spectrum, and the green light filter  25   g  is used for filtering out the light inconsistent with the green light spectrum. Finally, the photosensor element  22  transforms the filtered light into an electrical signal. Generally speaking, the plurality of sensing units  30  are arranged in a regular manner called a Bayer pattern color filter array, as shown in  FIG. 2 . In  FIG. 2 , G, B, R respectively indicates sensing units  30  for sensing green light, blue light, and red light. An area formed by two green sensing units  30 , a blue sensing unit  30  and a red sensing unit  30  serves as a pixel  11 . This is because human eyes have more sensitivity for green light than red and blue light, such that a 2:1:1 arrangement of green, blue, red sensing units is used to be consistent with real image color. Each sensing unit  30  has a photosensor element  22  formed on a silicon substrate  16 . A transfer electrode  14  formed on the photosensor element  22  is used for transferring the generated electrical signals.  
         [0006]     Please refer to  FIG. 1  and  FIG. 3 .  FIG. 3  shows a simplified layout of conventional image sensors  20 . Each sensing unit  30   r ,  30   g ,  30   b  contains an amplifier  32  coupled to the transfer electrode  14  for transmitting the sensed electrical signal to row data lines or column data lines. The image capturing device  10  reconstructs the pixels  11  to form an image based on the electrical signals from the row data line and the column data line. In addition, a fill factor is defined as a ratio of a pixel area (d*d) to that of a photosensor element  22  of a pixel. The fill factor is indicated as follows:  
       ff   =       Av   A     ×   100   ⁢   %         
 
 where ff indicates a fill factor, A indicates an area of a color unit, and Av indicates an area of the photosensor element  22  within a color unit. 
 
         [0007]     The higher the image resolution is required, the smaller each pixel area is, and the smaller the area of the sensing unit  30  is. Although the larger area of the photosensor element (i.e. larger value of the fill factor) is, the better the photosensor effect obtained is, it is more and more difficult to manufacture a small area of the amplifier  32 .  
         [0008]     As shown in  FIG. 3 , the conventional sensing unit has regular arrangement. Such layout results in uneven sensing effect, and such phenomenon is more obvious at a bottom-right side of  FIG. 3 . Please refer to  FIG. 1  and  FIG. 4 .  FIG. 4  shows a simplified layout of the sensing units depicted in  FIG. 3 . For clarity,  FIG. 4  amplifiers and other connections therewith are omitted in  FIG. 4  and the oblique-line area indicates light-focused area via the microlens. In  FIG. 1 , a light A entering the sensing unit  30  located at the center of the image sensor  20  can be completely sensed by the photosensor element  22 , but a light B entering the sensing unit  30  located at a corner of the image sensor  20  has a deviation so that the light B fails to exactly project onto the photosensor element  22 . Take  FIG. 4  for example, light A is projected onto the area  211  of the photosensor element  201   g , but the light B is projected onto a deviation area  212  of the photosensor element  202   g . Similarly, light is probably projected on the deviation areas  213 ,  214 ,  215  of the photosensor element  203   g ,  204   g ,  205   g , because light via microlens will deviate. In other words, a light A entering the sensing unit  30  located at the center of the image sensor  20  can be completely sensed by the photosensor element  22 , but a light B entering the sensing unit  30  located at a corner of the image sensor  20  has a deviation so that the light B fails to exactly project onto the photosensor element  22 . Therefore, an error occurs due to inconsistent ratio of received light for a pixel at the corner, thereby causing a color shift effect and deterioration of sensing quality. The photosensor element  22  of the sensing unit  30  at the corner will receive less light due to a larger incident angle. Uneven light sensing of the image sensor  20  results in an inconsistent image quality, which is a problem that needs to be solved.  
       SUMMARY OF INVENTION  
       [0009]     According to the claimed invention, an image sensing device for reducing color shift effect comprises a plurality of color units each comprising a photosensor element for converting light of a specific spectrum range into an electrical signal. Different arrangements of the photosensor elements are set in diagonal directions.  
         [0010]     These and other objectives of the claimed invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment, which is illustrated in the various figures and drawings. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0011]      FIG. 1  shows a schematic diagram of a digital image-capturing device according to the prior art.  
         [0012]      FIG. 2  is a schematic diagram of a Bayer pattern color filter array.  
         [0013]      FIG. 3  shows a simplified layout of conventional image sensor.  
         [0014]      FIG. 4  shows a simplified layout of the sensing units depicted in  FIG. 3 .  
         [0015]      FIG. 5  shows a layout of a first embodiment of an image sensor according to the present invention.  
         [0016]      FIG. 6  shows a schematic diagram of the image sensor depicted in  FIG. 5 .  
         [0017]      FIG. 7  shows a layout of a second embodiment of an image sensor according to the present invention.  
         [0018]      FIG. 8  shows a layout of a third embodiment of an image sensor according to the present invention.  
         [0019]      FIG. 9  shows a layout of a fourth embodiment of an image sensor according to the present invention 
     
    
     DETAILED DESCRIPTION  
       [0020]     Please refer to  FIG. 5  and  FIG. 6 .  FIG. 5  shows a layout of a first embodiment of the image sensor according to the present invention.  FIG. 6  shows a schematic diagram of the image sensor  50  depicted in  FIG. 5 . The image sensor  50  comprises a plurality of color units  55 , each having an amplifier  56  and a photosensor element  54 . Each color unit  55  further comprises a filter element  53  formed over the photosensor element  54  for filtering out light in accordance with a specific spectrum (for simplicity, only a color unit  55  and a filter element  53  are labeled in  FIG. 5 , and the filter element  53  is actually formed over the amplifier  56  and the photosensor element  54 ). The photosensor element  54  is used for transforming the filtered light into electrical signals. As can be seen in  FIG. 5 , the photosensor elements  54   r ,  54   g ,  54   b  are respectively used for receiving red, green, blue light through the filter element  53  and for transforming these lights into electrical signals. The amplifier  56  coupled to the photosensor element  54  is used for amplifying the transformed electrical signals and transmitting them to row data line or column data line. Finally, the processor (not shown) may reconstruct an image based on the magnitude of electrical signals transmitted via the row data line and column data line.  
         [0021]     As shown in  FIG. 6 , amplifiers  56  are omitted in  FIG. 6  and the oblique-line area stands for the light-focused area via the microlens. The image sensor  60  has four areas  52   a - 52   d , in each of which the arrangements of the photosensor elements  54  are identical. The arrangements of the photosensor elements  54  in adjacent areas are separated by a 90-degree angle, and those of the photosensor elements  54  in diagonal areas are separated by a 180-degree angle. Compared with a layout in  FIG. 4 , in which the areas  101  and  102  sensed non-symmetrical amounts, in the layout of  FIG. 6 , the light-focused areas of the photosensor element  54  at the four areas  52   a - 52   d  are more even, so that a better sensing effect is obtained.  
         [0022]     Please refer to  FIG. 7 , which shows a layout of a second embodiment of an image sensor  60  according to the present invention. For clarity, amplifiers  56  are omitted in  FIG. 7  and the oblique-line area stands for the light-focused area via the microlens. The image sensor  60  has four areas  62   a - 62   d , in each of which the arrangements of the photosensor elements  54  are identical. The two adjacent and different arrangement photosensor elements can share a single amplifier. Compared to the layout in  FIG. 4 , the light-focused areas of the photosensor element  54  at the four corners are more even, so that a better sensing effect is obtained.  
         [0023]     Please refer to  FIG. 8 , which shows a layout of a third embodiment of an image sensor  70  according to the present invention. For clarity, the amplifiers  56  are omitted in  FIG. 8  and the oblique-line area stands for the light-focused area via the microlens. The image sensor  70  has two areas  72   a ,  72   b , in which the arrangements of the photosensor elements  54  are identical. And the arrangements of the photosensor elements  54  respectively located in adjacent areas are separated by a 180-degree angle. Compared to the layout in  FIG. 3 , the light-focused area of the photosensor element  54  at the corner of the two areas  72   a ,  72   b  is more even, so that a better sensing effect is obtained.  
         [0024]     Please refer to  FIG. 9 , which shows a layout of a fourth embodiment of an image sensor  80  according to the present invention. For clarity, amplifiers  56  are omitted in  FIG. 9  and the oblique-line area stands for the light-focused area via the microlens. The image sensor  80  has four areas  82   a - 82   d , in each of which the arrangements of the photosensor elements  54  are identical. In addition, different from the L-shape photosensor element  54 , the photosensor element  54  as shown in  FIG. 9  has a rectangular shape. The arrangements of the photosensor elements  54  located in adjacent area are mirror-symmetrical. Compared to the layout in  FIG. 4 , the light-focused area of the photosensor element  54  at the four corners is more even, so that a better sensing effect is obtained.  
         [0025]     Notice that the plurality of color units  55  illustrated in  FIGS. 6-9  are aligned as a Bayer pattern color filter array. The filter elements are used for filtering out red, green, blue color light or yellow, magenta, cyan color light. The photosensor element can be a charge-coupled device or a CMOS photosensor. In addition, a L-shape of the photosensor element  54  illustrated in  FIGS. 6-8  can be replaced by a rectangle-shape, triangle-shape, or pentagon-shape, etc.  
         [0026]     In addition, the adjacent photosensor elements of which the arrangements are different and coupled to an identical row data line and column data line are capable of being coupled to a single amplifier, thereby saving layout area.  
         [0027]     To sum up, the layout of the photosensor elements are concluded as follows: 
        (a) The arrangements of photosensor elements of color units in diagonal positions are different. Furthermore, no matter what the shape of the photosensor is, the arrangements of photosensor elements of color units in diagonal positions are mirror-symmetrical.     (b) Aside from boundary conditions, the arrangement of each photosensor element in each area is identical.        
 
         [0030]     Certainly, the photosensor elements of the color unit located at the four corners and in diagonal positions are mirror-symmetrical, but the arrangement of the photosensor element located in the middle remains. In other words, the arrangements of the photosensor elements in each area are not necessary identical.  
         [0031]     In contrast to the prior art, the present invention image sensor utilizes mirror-symmetrical arrangements of photosensor elements of the color units in diagonal positions. Therefore, for a pixel at a corner, its green photosensor element, blue photosensor element and red photosensor element cause a consistent amount of sensitivity. Furthermore, the adjacent photosensor elements of which the arrangements are different and coupled to an identical row data line and column data line are capable of being coupled to a single amplifier, thereby saving a layout area of an image sensor.  
         [0032]     Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.