Abstract:
A solid-state imaging device includes: a light-receiving element making a photoelectric conversion and being disposed in each of a plurality of pixels, wherein a honeycomb structure in which a predetermined pixel is surrounded with six pixels neighboring the predetermined pixel out of the plurality of pixels or a structure in which one to three pixels out of the six neighboring pixels are omitted from the honeycomb structure is used as a basic unit.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a solid-state imaging device, and more particularly, to a solid-state imaging device which can reduce the number of mounted transistors, which has a high planar filling rate of pixels, and which can collect light with a high efficiency. 
         [0003]    2. Description of the Related Art 
         [0004]    In recent years, electronic devices such as digital still cameras or camcorders for capturing an image of a subject using a solid-state imaging device and forming an image were more and more spread. CCD (Charge Coupled Device) image sensors or CMOS (Complementary Metal Oxide Semiconductor) image sensors were known as such solid-state imaging devices. They are all called image sensors. The image sensors are premised on techniques using a pixel as a unit. 
         [0005]    The techniques using a pixel as a unit are applied to a display side as well as an image-capturing side. Such techniques using a pixel as a unit are disclosed in Japanese Patent No. 2600250 (Patent Document 1), JP-A-2004-2153 (Patent Document 2), JP-A-2005-150463 (Patent Document 3), JP-A-2006-165567 (Patent Document 4), JP-A-2006-54276 (Patent Document 5), IEEE Workshop on CCDs and Advanced Image Sensors, pp. 1-4 (2005), by J. Adkisson, et al. (Non-Patent Document 1), and Technical Research Report of the Institute of Electronics, Information and Communication Engineers Vol. 104, No. 66 (20040513) pp. 51-56, by Keiji Mabuchi (Non-Patent Document 2). 
       SUMMARY OF THE INVENTION 
       [0006]    In recent years, requirements have increased for a solid-state imaging device which can reduce the number of mounted transistors, which has a high planar filling rate of pixels, and which can collect light with a high efficiency. However, the known techniques including Patent Documents 1 to 5 and Non-Patent Documents 1 and 2 did not satisfactorily cope with such requirements. 
         [0007]    Thus, it is desirable to reduce the number of mounted transistors, to enhance a planar filling rate of pixels, and to collect light with a high efficiency. 
         [0008]    According to an embodiment of the invention, there is provided a solid-state imaging device including a light-receiving element making a photoelectric conversion and being disposed in each of a plurality of pixels, wherein a honeycomb structure in which a predetermined pixel is surrounded with six pixels neighboring the predetermined pixel out of the plurality of pixels or a structure in which one to three pixels out of the six neighboring pixels are omitted from the honeycomb structure is used as a basic unit. 
         [0009]    The basic unit may include: a transmission transistor disposed in each pixel of the basic unit; and a reset transistor, a selection transistor, and an amplification transistor which are shared by the pixels of the basic unit. 
         [0010]    The basic unit may include: a transmission transistor disposed in each pixel of the basic unit; and a reset transistor and an amplification transistor which are shared by the pixels of the basic unit. Here, the transistors of the basic unit may be driven by an FD driving method of controlling an FD (Floating Diffusion) potential by driving the drain terminals thereof with pulses. 
         [0011]    The solid-state imaging device may further include light-collecting elements. 
         [0012]    One light-collecting element may be shared by the pixels disposed on a circumference having as a radius a predetermined distance equal to or greater than a distance from the predetermined pixel to the neighboring pixels or inside the circumference. 
         [0013]    The solid-state imaging device may focus light from a subject, and may detect a phase difference of an object located before or after a focusing position to make a focusing determination or to acquire distance information to the object by causing a subset of the entire light flux from the object to selectively reach the pixels by the use of the light-collecting elements. 
         [0014]    Optical axes of the light-collecting elements and the centers of the light-receiving elements may be non-eccentrically aligned with each other at the central portion of the solid-state imaging device, and the optical axes of the light-collecting elements and the centers of the light-receiving elements may be aligned eccentrically toward the central portion depending on the distance from the central portion. 
         [0015]    The solid-state imaging device may further include N types (where N is an integer equal to or greater than 3) of filters selectively transmitting specific wavelengths of light beams. Here, predetermined types of filters out of the N types of filters may be disposed in the pixels of the basic unit. 
         [0016]    A type of filter may be disposed in each pixel of the basic unit and a color of the pixel may be interpolated by a calculation using a light intensity value of another pixel in which the corresponding type of filter is disposed and a relative pixel pitch between the pixel and the another pixel. 
         [0017]    When the pixel pitch is not an integral multiple of a unit pixel pitch, the pixel pitch may be approximated to an integral multiple to calculate the color of the pixel. 
         [0018]    According to another embodiment of the invention, there is provided a solid-state imaging device including a light-receiving element making a photoelectric conversion and a light-collecting element in each of a plurality of pixels, wherein a square matrix structure, in which the light-receiving elements are arranged at vertexes of a lattice shape formed by two perpendicular axes, is employed as an arrangement structure of the light-receiving elements, and a honeycomb structure, in which a predetermined pixel is surrounded with six pixels neighboring the predetermined pixel out of the plurality of pixels, or a structure in which one to three pixels out of the six neighboring pixels are omitted from the honeycomb structure, is employed as an arrangement structure of the light-collecting elements. 
         [0019]    According to the above-mentioned embodiments of the invention, it is possible to provide a solid-state imaging device which can reduce the number of mounted transistors, which has a high planar filling rate of pixels, and which can collect light with a high efficiency. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIGS. 1A and 1B  are diagrams illustrating a relative position relation between neighboring pixels. 
           [0021]      FIG. 2  is a diagram illustrating a circuit configuration of a pixel unit used in the past. 
           [0022]      FIG. 3  is a diagram illustrating an arrangement of pixels in an image sensor with a honeycomb structure including 7 sharing pixels according to an embodiment of the invention. 
           [0023]      FIG. 4  is a diagram illustrating a circuit configuration of the image sensor with a honeycomb structure including 7 sharing pixels according to the embodiment of the invention. 
           [0024]      FIG. 5  is a diagram illustrating another circuit configuration of the image sensor with a honeycomb structure including 7 sharing pixels according to the embodiment of the invention. 
           [0025]      FIG. 6  is a diagram illustrating another circuit configuration of the image sensor with a honeycomb structure including 7 sharing pixels according to the embodiment of the invention. 
           [0026]      FIG. 7  is a diagram illustrating an image data reading process in the image sensor with a honeycomb structure including 7 sharing pixels according to the embodiment of the invention. 
           [0027]      FIG. 8  is a flowchart illustrating a pixel data reading process shown in  FIG. 7 . 
           [0028]      FIG. 9  is a timing diagram illustrating pixel data reading driving pulses in the pixel data reading process shown in  FIG. 7 . 
           [0029]      FIG. 10  is a timing diagram illustrating other pixel data reading driving pulses in the pixel data reading process shown in  FIG. 7  and is different from the timing diagram of  FIG. 9 . 
           [0030]      FIG. 11  is a diagram illustrating an arrangement of pixels in an image sensor with a honeycomb structure including 6 sharing pixels according to an embodiment of the invention. 
           [0031]      FIG. 12  is a diagram illustrating an image data reading process in the image sensor with a honeycomb structure including 6 sharing pixels according to the embodiment of the invention. 
           [0032]      FIG. 13  is a diagram illustrating an arrangement of pixels in an image sensor with a honeycomb structure including 5 sharing pixels according to an embodiment of the invention. 
           [0033]      FIG. 14  is a diagram illustrating an image data reading process in the image sensor with a honeycomb structure including 5 sharing pixels according to the embodiment of the invention. 
           [0034]      FIG. 15  is a diagram illustrating an arrangement of pixels in an image sensor with a honeycomb structure including 4 sharing pixels according to an embodiment of the invention. 
           [0035]      FIG. 16  is a diagram illustrating an image data reading process in the image sensor with a honeycomb structure including 4 sharing pixels according to the embodiment of the invention. 
           [0036]      FIG. 17  is a diagram schematically illustrating a position relation between light-receiving elements (pixels) and light-collecting elements in the image sensor with a honeycomb structure according to an embodiment of the invention. 
           [0037]      FIG. 18  is a top view illustrating an arrangement of pixels in the image sensor with a honeycomb structure according to the embodiment of the invention. 
           [0038]      FIG. 19  is a diagram illustrating a method of performing a phase difference detecting function. 
           [0039]      FIGS. 20A and 20B  are diagrams illustrating a method of performing a phase difference detecting function. 
           [0040]      FIG. 21  is a diagram illustrating a method of performing a phase difference detecting function. 
           [0041]      FIG. 22  is a diagram illustrating a method of performing a phase difference detecting function. 
           [0042]      FIG. 23  is a diagram illustrating a de-mosaicking process when pixels include different color filters. 
           [0043]      FIGS. 24A to 24D  are diagrams illustrating arrangements of color filters which can be taken by the image sensor with a honeycomb structure including 7 sharing pixels according to the embodiment of the invention. 
           [0044]      FIG. 25  is a diagram illustrating a method of interpolating the pixels using the de-mosaicking process. 
           [0045]      FIG. 26  is a diagram illustrating an example of a solid-state imaging device according to an embodiment of the invention, which has a configuration different from that of the image sensor with a honeycomb structure according to the embodiment of the invention. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     1. Past Pixel Structure 
       [0046]    For the purpose of easy understanding of the invention, the outline of a known pixel arrangement will be first described. 
         [0047]      FIGS. 1A and 1B  show relative position relations between neighboring pixels.  FIG. 1A  shows the relative position relation between neighboring pixels in a square matrix structure.  FIG. 1B  shows the relative position relation between neighboring pixels in a honeycomb structure. 
         [0048]    In a typical solid-state imaging device known in the past, the structure shown in  FIG. 1A , that is, the structure in which pixels are arranged at vertexes of a lattice shape formed by two perpendicular axes (hereinafter, referred to as square matrix structure), or a structure obtained by inclining the square matrix structure by 45 degrees was widely employed. Since two axes of the horizontal axis and the vertical axis are perpendicular to each other in such a structure, the structure is suitable for reading signals accumulated in the pixels. 
         [0049]    On the other hand, many solid-state imaging devices have a three-dimensional structure in which a metal interconnection, a planarization layer, a color filter, and the like are stacked on the top surfaces of light-receiving elements. The effective aperture ratio is lowered due to the shielding effect based on the three-dimensional structure. Accordingly, techniques for efficiently collecting light to the pixels have been suggested in Patent Documents 1 to 4. That is, Patent Document 1 discloses a technique of eccentrically forming on-chip micro lenses corresponding to pixels. Patent Document 2 discloses a technique of forming a clad core structure (waveguide structure) to guide light efficiently to the light-receiving elements. Patent Document 3 discloses a technique of reducing the total thickness of a solid-state imaging device using a Cu interconnection. Patent Document 4 discloses a technique of forming a solid-state imaging device with a rear illuminating structure. 
         [0050]    Here, as shown in  FIG. 1A , it is assumed in a unit pixel size of a square matrix structure that a horizontal width is X, a vertical width Y, and a pixel pitch is D. For the purpose of convenient explanation, X=Y is also assumed. That is, each pixel has a square shape. In this case, the ratio (filling factor) of the largest circle inscribed in each pixel to a pixel area of A=XY is 78.5 at most. 
         [0051]    A honeycomb structure shown in  FIG. 1B  can be also used as the arrangement of pixels, in addition to the square matrix structure shown in  FIG. 1A . For example, in the honeycomb structure where the pixels are arranged on the entire surface of a two-dimensional plane (the plane is two-dimensionally filled with the pixels) with the pixel pitch maintained in D, the filling factor is 90.7, which is greater by 12 than that of the square matrix structure. 
         [0052]    In the square matrix structure, the pitches between a pixel and four neighboring pixels in the vertical and horizontal directions are not equal to the pitches between the pixels and four neighboring pixels in the inclined directions. Accordingly, a problem with anisotropy that the resolution in the inclined directions is poorer than the resolution in the vertical and horizontal directions is caused. On the other hand, in the honeycomb structure, the distances between six neighboring pixels are all equal to the pixel pitch D. Accordingly, the anisotropy in resolution is hardly caused. 
         [0053]    In this way, the honeycomb structure is excellent in planar filling rate (filling factor) or coupling efficiency to light-collecting elements and is excellent in resolution isotropy of the acquired image, compared with the square matrix structure. 
         [0054]    A technique relating to pixels having the honeycomb structure is disclosed in Patent Document 5. Here, it should be noted that the technique disclosed in Patent Document 5 is on the assumption of a display device for two-dimensional data, but not on the assumption of a solid-state imaging device. 
         [0055]      FIG. 2  shows a circuit structure of a pixel unit (hereinafter, referred to as past pixel unit) disclosed in Patent Document 5. 
         [0056]    The past pixel unit is a unit including three pixels  11  arranged in a honeycomb structure. As described above, since the past pixel unit is applied to a display device, three pixels  11  of one unit include red/green/blue color filters. By arranging plural past pixel units, the R/G/B pixels  11  are uniformly arranged in each row. Accordingly, it is possible to provide a display device which can reproduce colors with good balance. 
         [0057]    However, it is difficult to apply the past pixel unit to a solid-state imaging device (image sensor) without any change. This is because the past pixel unit has a circuit structure specialized in the display device. That is, since a human eye have the most number of optic nerve cells sensitive to green and senses the resolution with green, a study for arranging more green pixels in an image sensor providing an image with high precision or the like is necessary. However, as shown in  FIG. 2 , the past pixel unit does not have the R/G/B pixel ratio of 1:1:1 and does not have such a pixel arrangement including more green pixels. 
         [0058]    When the past pixel unit could be applied to a solid-state imaging device (image sensor), the number of transistors per unit pixel could not be reduced in comparison with a circuit structure of a solid-state imaging device with the above-mentioned square matrix structure. That is, as shown in  FIG. 2 , the past pixel unit has a structure in which three pixels  11  form one unit. Accordingly, the past pixel unit has a circuit structure in which a reset transistor  13 , an amplification transistor  14 , and a selection transistor  15  are shared in one unit. In such a circuit structure, six transistors are necessary for three pixels  11 . The number of transistors (Tr) per unit pixel is 2.0 Tr/pixel in the past pixel unit and is not smaller than that of the past square matrix structure. 
         [0059]    That is, paying attention to the pixel structure of a CMOS image sensor as a solid-state imaging device, a pixel sharing technique capable of reducing the number of transistors per unit pixel as many as possible is important for a decrease in size or a decrease in cost. When the number of transistors is reduced, the occupied area of the photodiode is relatively enhanced, which is advantageous for the sensitivity. Accordingly, high-efficiency pixel sharing methods for a solid-state imaging device with the past square matrix structure have been studied and developed. For example, Non-Patent Document 1 discloses a method of sharing a reset transistor, a selection transistor, and an amplification transistor with 2×2 pixels or 1×4 pixels. Non-Patent Document 2 discloses a method of removing a selection transistor using an FD driving method capable of controlling an FD potential by driving the drain terminals with pulses. The number of transistors per unit pixel in the solid-state imaging device with the past square matrix structure employing such a high-efficiency pixel sharing scheme is rather smaller than that in the past pixel unit. 
       2. Solid-State Imaging Device according to Embodiment Outline of the Invention 
       [0060]    The inventor invented a honeycomb structure (hereinafter, referred to as “present honeycomb structure”) in which four or more pixels, for example, seven pixels, form one unit as a pixel arrangement structure of a two-dimensional image sensor as a solid-state imaging device. Accordingly, the solid-state imaging device employing a pixel arrangement with the present honeycomb structure can realize higher light-collecting efficiency than that of the solid-state imaging device employing a pixel arrangement with the past square matrix structure. Since transistors can be shared by four or more pixels, for example, seven pixels by employing the present honeycomb structure, it is possible to easily reduce the number of transistors per pixel in comparison with the past structure of the past unit. 
         [0061]    A solid-state imaging device (hereinafter, referred to as image sensor with the present honeycomb structure) employing a pixel arrangement with the present honeycomb structure according to an embodiment of the invention will be described below. 
         [0062]    It is assumed hereinafter that a solid-state imaging device (CMOS image sensor: CIS/CMOS IS) of amplifying an electrical signal using a field effect transistor (MOSFET) is used as the image sensor with the present honeycomb structure. Of course, the present honeycomb structure can be applied to other types of solid-state imaging devices. 
         [0000]    Example of 7 Sharing Pixels in Image Sensor with Present Honeycomb Structure 
         [0063]      FIG. 3  is a diagram illustrating a pixel arrangement in the image sensor with the present honeycomb structure including 7 sharing pixels. 
         [0064]    In the example shown in  FIG. 3 , seven pixels  101  of a center pixel  101  and six pixels  101  surrounding the center pixel form one unit of the present honeycomb structure. 
         [0065]    Each pixel  101  includes a photoelectrical conversion element such as a photodiode. A transmission transistor  102  is disposed in each pixel  101 . On the other hand, a reset transistor  103  and an amplification transistor  104  are shared by all the pixels  101  and thus only one is disposed in each unit. An FD (Floating Diffusion)  105  is arranged in a ring shape. In this way, by arranging the FD  105  in a ring shape, it is possible to increase the capacity thereof and to reduce a charge conversion coefficient. As a result, it is possible to accumulate a large amount of charges. 
         [0066]      FIG. 4  shows a circuit structure of the image sensor with the present honeycomb structure including 7 sharing pixels. 
         [0067]    The reset transistor  103  and the amplification transistor  104  disposed in each unit are connected to one power supply line  201 . The amplification transistor  104  is connected to a signal output line  202 . 
         [0068]    The transmission transistor  102  of each pixel  101 , the reset transistor  103 , and the amplification transistor  104  can be formed of, for example, field effect transistors (MOSFET). The field effect transistors are driven using an FD driving method of controlling an FD potential by driving the drain terminals thereof with pulses. Accordingly, the selection transistor is not necessary. 
         [0069]      FIG. 5  shows another circuit structure of the image sensor with the present honeycomb structure including 7 sharing pixels. 
         [0070]    In the example shown in  FIG. 5 , a selection transistor  203  is further provided in addition to the structure shown in  FIG. 4 . 
         [0071]      FIG. 6  is another circuit structure of the image sensor with the present honeycomb structure including 7 sharing pixels. 
         [0072]    In the example shown in  FIG. 6 , the connection type of the transmission transistor  102  of each pixel  101  is different from that of the example shown in  FIG. 5 . Although not shown, the selection transistor  203  can be removed by employing the same FD driving method as shown in  FIG. 4 . 
         [0073]    Operations of the image sensor with the present honeycomb structure including 7 sharing pixels will be described now. 
         [0074]      FIG. 7  is a diagram illustrating a process (hereinafter, referred to as “image data reading process”) of causing the image sensor with the present honeycomb structure including 7 sharing pixels to read image data. 
         [0075]    As shown in  FIG. 7 , one unit  301  includes seven pixels  101 . Here, the number k (where k is an integer of 1 to 7) described in the pixels  101  shown in  FIG. 7  is referred to as inter-unit pixel number k. The pixel  101  with the inter-unit pixel number k is referred to as pixel  101 - k.    
         [0076]    Paying attention to one unit  301 , data of the pixels  101  are read sequentially in the order of the inter-unit pixel number k, that is, in the order of pixels  101 - 1  to  101 - 7  in the example shown in  FIG. 7 . 
         [0077]    Paying attention to one specific unit  301 A 1 , the right-neighboring unit  301 B 1  thereof is misaligned therewith by one pixel (one row) in the vertical direction in the drawing. The right-neighboring unit  301 C 1  thereof is misaligned with the unit  301 A 1  by two pixels (two rows) in the vertical direction in the drawing. The right-neighboring unit  301 A 2  thereof is arranged in the same row as the unit  301 A 1 . Accordingly, paying attention to the unit  301 A 2 , the right-neighboring unit  301 B 2  thereof is misaligned therewith by one pixel (one row) in the vertical direction in the drawing. The right-neighboring unit  301 C 2  thereof is misaligned with the unit  301 A 2  by two pixels (two rows) in the vertical direction in the drawing. The arrangement of three units  301 Aj to  301 Cj is repeated thereafter. Here, in the example shown in  FIG. 7 , j=1 and 2 are shown, but j is an integer equal to or less than a threshold value set on the basis of the total number of pixels. Hereinafter, j is referred to as 3-unit unit number. Accordingly, the reading of data from the units  301  is sequentially carried out in the arrangement order, that is, in the order of the units  301 Aj to  301 Cj in the example shown in  FIG. 7 . 
         [0078]    In other words, the image sensor with the present honeycomb structure including 7 sharing pixels has a circuit structure in which signal transmission lines are arranged in the vertical and horizontal directions so as to read data in the above-mentioned order. 
         [0079]      FIG. 8  is a flowchart illustrating the pixel data reading process in the example shown in  FIG. 7 . 
         [0080]    In step S 1 , the image sensor with the present honeycomb structure including 7 sharing pixels (hereinafter, abbreviated as sensor in the description with reference to  FIG. 8 ) sets the inter-3-unit sign to i=A, sets the 3-unit unit number to j=1, and sets the inter-unit pixel number to k=1. 
         [0081]    Here, the inter-3-unit sign i means a sign (any one of A to C) attached to the reference numeral of a unit “ 301 ” in  FIG. 7 . The 3-unit unit number j is as defined above. That is, by describing the unit  300   ij , a unique unit is specified. The inter-unit pixel number k is as defined above. That is, a unique pixel in the unit  300   ij  is specified by the pixel  101 - k . In other words, by specifying three parameters of i, j, and k, a predetermined pixel  101  is specified. 
         [0082]    In step S 2 , the sensor sets the unit  301   ij  as a target unit. 
         [0083]    In step S 3 , the sensor sets the pixel  101 - k  in the target unit as a target pixel. 
         [0084]    In step S 4 , the sensor reads pixel data of the target pixel. 
         [0085]    In step S 5 , the sensor increases the inter-unit pixel number k by 1 (k=k+1). 
         [0086]    In step S 6 , the sensor determines whether k&gt;7 is satisfied. 
         [0087]    When it is determined that the inter-unit pixel number k is equal to or less than 7, the sensor repeats the processes from step S 3 . That is, the loop process of steps S 3  to S 6  is repeatedly performed on the pixels  101 - 1  to  101 - 7  in the target unit. As a result, the pixel data is sequentially read in the order of the pixels  101 - 1  to  101 - 7 . 
         [0088]    When the pixel data of the pixel  101 - 7  is read, k=8 is obtained in the process of step S 5 . Accordingly, YES is determined in step S 6  and the process of step S 7  is then performed. 
         [0089]    In step S 7 , the sensor resets the inter-unit pixel number k to 1 (k=1). 
         [0090]    In step S 8 , the sensor determines whether the inter-3-unit sign i is C. 
         [0091]    When the inter-3-unit sign i is A or B, NO is determined in step S 8  and the process of step S 9  is then performed. 
         [0092]    In step S 9 , the sensor sets the inter-3-unit sign i from A to B or from B to C. Thereafter, the process of step S 2  is performed again and the subsequent processes are repeated. That is, the loop process of steps S 2  to S 9  is repeatedly performed on the units  300 Aj to  300 Cj. As a result, the units  300 Aj to  300 Cj are sequentially set as the target unit and the pixel data is sequentially read in the order of the pixels  101 - 1  to  101 - 7  in each target unit. 
         [0093]    When the pixel data of the pixel  101 - 7  in the unit  300 Cj is read, k=8 is obtained in the process of step S 5 . Accordingly, YES is determined in step S 6  and the process of step S 7  is performed. In step S 7 , the inter-unit pixel number k is reset to 1 (k=1). Then, YES is determined in step S 8  and the process of step S 10  is performed. In step S 10 , the sensor sets the inter-3-unit sign i from C to A. 
         [0094]    In step S 11 , the sensor increases inter-3-unit pixel number j by 1 (j=j+1). 
         [0095]    In step S 12 , the sensor determines whether j&gt;threshold value is satisfied. 
         [0096]    When the 3-unit unit number j is equal to or less than the threshold value, the process of S 2  is performed again and the processes subsequent thereto are repeated. That is, the pixel data is sequentially read using three units  300 Aj to  300 Cj as a unit. In the process of step S 11  after the final pixel data is read, j is set greater than the threshold value. Accordingly, YES is determined in step S 12  and the image data reading process is ended. 
         [0097]      FIG. 9  is a timing diagram illustrating image data reading driving pulses in the pixel data reading process in the example shown in  FIG. 7 . 
         [0098]      FIG. 9  shows timing diagrams of the transmission transistors  102 - 1  to  102 - 7 , the reset transistor  103 , and the power supply line  201  from the upside. That is, the timing diagrams shown in  FIG. 9  express the example shown in  FIG. 4 , that is, the example where the FD driving is carried out. 
         [0099]    The driving pulses or the output times shown in  FIG. 9  are only examples. That is,  FIG. 9  does not exclude a case where the image sensor with the present honeycomb structure can operate in another driving mode. 
         [0100]    In the example shown in  FIG. 9 , a pulse of potential VDD is supplied to the power supply line  201 . That is, when the image data reading process on one unit  301  is started, the potential VDD is applied to the power supply line  201 . In the description with reference to  FIG. 9 , when the potential VDD is applied to the power supply line  201 , it is said that the VDD pulse is changed to an ON state. When the application of the potential is stopped, it is said that the VDD pulse is changed to an OFF state. 
         [0101]    When the VDD is changed to the ON state and the reset transistor  103  is turned on, the FD potential is changed to a high level. Accordingly, when the transmission transistor  102 - 1  is turned on in this state, the photodiode of the pixel  101 - 1  gets empty and starts the accumulation of charges. By sequentially changing the reset transistor  103  and the transmission transistors  102 - 2  to  102 - 7  of the pixels  101 - 2  to  101 - 7  completely in the same way, the photodiodes sequentially start the accumulation of charges. 
         [0102]    Thereafter, by turning on the reset transistor  103  at the time that the VDD pulse is changed from the ON state to the OFF state, the FD potential is changed to a low level. 
         [0103]    Then, to read the charges accumulated in the photodiodes, the VDD pulse is changed again from the OFF state to the ON state. When the reset transistor  103  is turned on in this state and the transmission transistor  102 - 1  is turned on, the charged accumulated in the photodiode of the pixel  101 - 1  are read out to the FD, whereby the signal level (pixel data) is read out. Completely in the same way, the reset transistor  103  and the transmission transistors  102 - 2  to  102 - 7  of the pixels  101 - 2  to  101 - 7  are sequentially turned on. Accordingly, the charges (pixel data) of the photodiodes are sequentially read out. 
         [0104]    Thereafter, by turning on the reset transistor  103  at the time that the VDD pulse is changed to ON state to the OFF state, the FD potential gets full and the reading (transmission) of the pixel data of the pixels  101 - 2  to  101 - 7  in one unit  301  is ended. 
         [0105]    That is, the charge accumulation time of the pixels  101 - 1  to  101 - 7  in one unit  301  corresponds to the period of time from the first-bullet pulses of the transmission transistors  102 - 1  to  102 - 7  to the second-bullet pulses of the transmission transistors  102 - 1  to  102 - 7 . 
         [0106]    By performing the FD driving operation in accordance with the timing diagrams shown in  FIG. 9  in this way, the loop process of steps S 3  to S 6  on the target unit is performed in the image data reading process shown in  FIG. 8 . 
         [0107]    That is, the FD driving operation in accordance with the timing diagrams shown in  FIG. 9  is performed on the units  301 . 
         [0108]      FIG. 10  is a timing diagram illustrating the pixel data reading driving pulses in the pixel data reading process in the example shown in  FIG. 7  and is different from the example shown in  FIG. 9 . 
         [0109]      FIG. 10  shows timing diagrams of the transmission transistors  102 - 1  to  102 - 7 , the reset transistor  103 , the selection transistor  203 , and the power supply line  201  from the upside. That is, the timing diagrams shown in  FIG. 10  express the example shown in  FIG. 5  or  6 , that is, the example where the normal driving is carried out. 
         [0110]    The driving pulses or the output times shown in  FIG. 10  are only examples. That is,  FIG. 10  does not exclude a case where the image sensor with the present honeycomb structure can operate in another driving mode. 
         [0111]    In the example shown in  FIG. 10 , the operations until the accumulation of charges in the photodiodes of the pixels  101 - 1  to  101 - 7  are basically the same as shown in  FIG. 9  and thus description thereof is not repeated. 
         [0112]    To read out the charges accumulated in the photodiodes of the pixels  101 - 1  to  101 - 7 , the selection transistor  203  is turned on. When the reset transistor  103  is turned on in this state and the transmission transistor  102 - 1  is turned on, the charged accumulated in the photodiode of the pixel  101 - 1  are read out to the FD, whereby the signal level (pixel data) is read out. Completely in the same way, the reset transistor  103  and the transmission transistors  102 - 2  to  102 - 7  of the pixels  101 - 2  to  101 - 7  are sequentially turned on. Accordingly, the charges (pixel data) of the photodiodes are sequentially read out. 
         [0113]    Thereafter, when the selection transistor  203  is turned off, the reading (transmission) of the pixel data from the pixels  101 - 2  to  101 - 7  in one unit  301  is ended. 
         [0114]    That is, the charge accumulation time of the pixels  101 - 1  to  101 - 7  in the unit  301  corresponds to the period of time from the first-bullet pulses of the transmission transistors  102 - 1  to  102 - 7  to the second-bullet pulses of the transmission transistors  102 - 1  to  102 - 7 . 
         [0115]    By performing the FD driving operation in accordance with the timing diagrams shown in  FIG. 10  in this way, the loop process of steps S 3  to S 6  on the target unit is performed in the image data reading process shown in  FIG. 8 . 
         [0000]    Image Sensors with Present Honeycomb Structure Including 4 to 6 Sharing Pixels 
         [0116]    The structure including 7 sharing pixels has been exemplified as the image sensor with the present honeycomb structure. However, the structure including 7 sharing pixels is not necessary, but a structure including 4 or more sharing pixels can be sufficiently employed. Accordingly, specific examples of the structures including 6, 5, and 4 sharing pixels will be sequentially described below in this order. 
         [0117]      FIG. 11  is a diagram illustrating a pixel arrangement of an image sensor with the present honeycomb structure including 6 sharing pixels. 
         [0118]    In the example shown in  FIG. 11 , one unit of the present honeycomb structure is constructed by 6 pixels  101  in total of one pixel  101  at the center (which means the center of the structure including 7 sharing pixels) and five pixels  101  surrounding the center pixel. 
         [0119]    The architecture shown in  FIG. 11  employs a method of reading charges by the FD driving operation. Accordingly, a circuit structure in which the selection transistor is removed is obtained. However, it is needless to say that the circuit structure having the selection transistor may be employed. 
         [0120]    That is, a structure obtained by removing the photodiode and the transmission transistor  102  corresponding to one pixel  101  from any structure shown in  FIGS. 4 to 6  can be employed as the circuit structure of the image sensor with the present honeycomb structure including 6 sharing pixels. 
         [0121]      FIG. 12  is a diagram illustrating an image data reading process in the image sensor with the present honeycomb structure including 6 sharing pixels. 
         [0122]    As shown in  FIG. 12 , one unit  501  includes six pixels  101 - 1  to  101 - 6 . In addition, k in the pixel  101 - k  (k is an integer of 1 to 6 in the example shown in  FIG. 12 ) represents a number described in each pixel shown in  FIG. 12 , that is, the inter-unit pixel number. 
         [0123]    Paying attention to one unit  501 , the reading of data from the pixels  101  is sequentially carried out in the order of the inter-unit pixel number k, that is, in the order of the pixels  101 - 1  to  101 - 6  in the example shown in  FIG. 12 . That is, the processes of steps S 3  to S 6  can be applied to the unit  501  without any change, only by changing the process of step S 6  in  FIG. 8  to the process of “k&gt;6?”. The timing diagrams of  FIG. 9  or  10  can be applied without any change by omitting the timing diagram of the transmission transistor  102  corresponding to one pixel  101 . 
         [0124]      FIG. 13  is a diagram illustrating a pixel arrangement of an image sensor with the present honeycomb structure including 5 sharing pixels. 
         [0125]    In the example shown in  FIG. 13 , one unit of the present honeycomb structure is constructed by 5 pixels  101  in total of one pixel  101  at the center (which means the center of the structure including 7 sharing pixels) and four pixels  101  surrounding the center pixel. 
         [0126]    The architecture shown in  FIG. 13  employs a method of reading charges by the FD driving operation. Accordingly, a circuit structure in which the selection transistor is removed is obtained. However, it is needless to say that the circuit structure having the selection transistor may be employed. 
         [0127]    That is, a structure obtained by removing the photodiodes and the transmission transistors  102  corresponding to two pixels  101  from any structure shown in  FIGS. 4 to 6  can be employed as the circuit structure of the image sensor with the present honeycomb structure including 5 sharing pixels. 
         [0128]      FIG. 14  is a diagram illustrating an image data reading process in the image sensor with the present honeycomb structure including 5 sharing pixels. 
         [0129]    As shown in  FIG. 14 , one unit  601  includes five pixels  101 - 1  to  101 - 5 . In addition, k in the pixel  101 - k  (k is an integer of 1 to 5 in the example shown in  FIG. 14 ) represents a number described in each pixel shown in  FIG. 14 , that is, the inter-unit pixel number. 
         [0130]    Paying attention to one unit  601 , the reading of data from the pixels  101  is sequentially carried out in the order of the inter-unit pixel number k, that is, in the order of the pixels  101 - 1  to  101 - 5  in the example shown in  FIG. 14 . That is, the processes of steps S 3  to S 6  can be applied to the unit  601  without any change, only by changing the process of step S 6  in  FIG. 8  to the process of “k&gt;5?”. The timing diagrams of  FIG. 9  or  10  can be applied without any change by omitting the timing diagram of the transmission transistor  102  corresponding to two pixels  101 . 
         [0131]      FIG. 15  is a diagram illustrating a pixel arrangement of an image sensor with the present honeycomb structure including 4 sharing pixels. 
         [0132]    In the example shown in  FIG. 15 , one unit of the present honeycomb structure is constructed by 4 pixels  101  in total of one pixel  101  at the center (which means the center of the structure including 7 sharing pixels) and three pixels  101  surrounding the center pixel. 
         [0133]    The architecture shown in  FIG. 15  employs a method of reading charges by the FD driving operation. Accordingly, a circuit structure in which the selection transistor is removed is obtained. However, it is needless to say that the circuit structure having the selection transistor may be employed. 
         [0134]    That is, a structure obtained by removing the photodiodes and the transmission transistors  102  corresponding to three pixels  101  from any structure shown in  FIGS. 4 to 6  can be employed as the circuit structure of the image sensor with the present honeycomb structure including 4 sharing pixels. 
         [0135]      FIG. 16  is a diagram illustrating an image data reading process in the image sensor with the present honeycomb structure including 4 sharing pixels. 
         [0136]    As shown in  FIG. 16 , one unit  701  includes four pixels  101 - 1  to  101 - 4 . In addition, k in the pixel  101 - k  (k is an integer of 1 to 4 in the example shown in  FIG. 16 ) represents a number described in each pixel shown in  FIG. 16 , that is, the inter-unit pixel number. 
         [0137]    Paying attention to one unit  701 , the reading of data from the pixels  101  is sequentially carried out in the order of the inter-unit pixel number k, that is, in the order of the pixels  101 - 1  to  101 - 4  in the example shown in  FIG. 16 . That is, the processes of steps S 3  to S 6  can be applied to the unit  701  without any change, only by changing the process of step S 6  in  FIG. 8  to the process of “k&gt;4?”. The timing diagrams of  FIG. 9  or  10  can be applied without any change by omitting the timing diagram of the transmission transistor  102  corresponding to three pixels  101 . 
       Structure of On-Chip Lens Shared by Pixels 
       [0138]    From the viewpoint of a decrease in size of a pixel, the present technique (at the filing time of the invention) has a limit to the processing precision of an on-chip lens. Accordingly, by using the past method, it is very difficult to manufacture a micron-sized lens with high precision or to manufacture a short-focus convex lens with a large curvature. The past method is a method of applying a resist of a mask pattern to an on-chip lens material, melting the resist by a thermal ref lowing process, forming a convex lens pattern using the surface tension thereof, and transferring shapes to the lens material by etching. 
         [0139]    On the other hand, for example, a large unit including 7 sharing pixels can be employed as the unit (one unit) of sharing pixels in the image sensor with the present honeycomb structure. A larger unit, for example, a unit having a honeycomb structure of 19 pixels in total including 12 pixels surrounding the large unit, can be employed as one unit. In this way, the present honeycomb structure, a honeycomb structure including four or more pixels can be employed as one unit and one micro lens can be disposed for one unit. Accordingly, it is possible to easily implement a light-collecting element with a high degree of freedom corresponding to the lens processing precision. Incidentally, when one on-chip lens is employed for plural pixels, the micro lens collects the light flux from a subset of the exit pupil, whereby it is possible to grasp the focusing state of a subject or to acquire information in the depth direction. Therefore, it may be possible to realize the auto focus function of a TTL (Through The Lens) phase difference detecting type or a function of acquiring the depth information of the subject. A specific example of the on-chip lens shared by pixels or a specific example of a technique employing the on-chip lens will be described below. 
         [0140]      FIG. 17  is a diagram schematically illustrating a position relation between the light-receiving elements (pixels) and the light-collecting elements of the image sensor with the present honeycomb structure. 
         [0141]    Here, one pixel  101  which is the center of one unit is referred to as “center pixel  101 ”. 
         [0142]    A unit  801  including 7 pixels  101  in total of a center pixel  101  and six pixels  101  surrounding the center pixel can be employed as one unit of the present honeycomb structure. 
         [0143]    In this case, when the past technique is employed without any change, a structure in which one light-collecting element  901  (for example, an on-chip micro lens) is disposed for one pixel  101  is obtained. With this structure, when one pixel  101  decreases in size, it is necessary to reduce the size of the light-collecting element  901  by as much and it is difficult to cope with such a decrease in size with the present processing technique. That is, with the decrease in size of the light-receiving element of the pixel  101 , the high processing precision of the light-collecting element  901  is necessary. When the on-chip micro lens is employed as the light-collecting element  901 , the following method including first to fourth steps is employed as the present method of forming the on-chip micro lens. That is, in the first step, a lens pattern is formed in a resist applied to an on-chip lens material, the resist is melted by the thermal ref lowing, and a convex lens pattern is formed with the surface tension. In the second step, the on-chip lens is formed by transferring the convex lens pattern to the lens material by etching. In the method including the first and second steps, it is difficult to cope with the pixel size of several μm or less. The precision using this method reaches a limit. 
         [0144]    Therefore, it is suitable that one light-collecting element  902  (for example, an on-chip micro lens) is employed for the unit  801  (seven pixels). In this way, by employing the light-collecting element shared by plural pixels, the precision lower than that accompanied with the decrease in size of a pixel can be sufficiently used as the processing precision of the light-collecting element. That is, any particular problem is not caused even when the present method of forming an on-chip lens is employed. It is effective to employ the light-collecting element shared by plural pixels in view of a decrease in individual difference of the light-collecting characteristic between the light-collecting elements or an improvement in stability of the light-collecting characteristic, compared with the case where the past light-collecting element in the unit of a pixel is employed. 
         [0145]    One unit  802  having 19 pixels  101  in total including 12 pixels  101  surrounding the unit  801  may be employed. In this case, one light-collecting element  902  (for example, the on-chip micro lens) may be employed for the unit  802  (19 pixels). 
         [0146]    One unit  803  having 37 pixels  101  in total including 18 pixels  101  surrounding the unit  802  may be employed. In this case, one light-collecting element  903  (for example, the on-chip micro lens) may be employed for the unit  803  (37 pixels). 
         [0147]    That is, the honeycomb structure including the pixels  101  surrounding the center pixel  101  with M folds (where M is an integer of 1 or greater) can be employed as one unit. In this case, one light-collecting element (for example, an on-chip micro lens) can be employed for each unit. In other words, a honeycomb structure including pixels on a circumference having a radius a predetermined distance apart by a neighboring pixel pitch (distance between the neighboring pixels) from the center pixel  101  or inside the circumference can be employed as one unit. Here, when it is assumed that the neighboring pixel pitch is unit distance  1 , the total number N of pixels  101  existing in the range apart by X pixels or less from the center pixel  101  can be expressed by N=1+Σ(6×X) (where Σ is the total sum in the range of X=0 to x). That is, one unit includes N pixels  101  and one light-collecting element is shared by the N pixels  101 . Here, one unit means a unit of the honeycomb structure in which one light-collecting element is arranged and may not correspond to the unit in which the transistors are shared in the one-to-one correspondence. 
         [0148]    The light-collecting element is not particularly to the on-chip micro lens (micro convex lens). For example, a sub-wavelength lens (SWLL) may be employed as the light-collecting element. Here, the sub-wavelength lens means the following element. That is, the sub-wavelength lens is an element obtained by performing a micro processing process on an optical element with a refractive index n (where n&gt;1) with a scale significantly smaller than a wavelength of an electronic wave to which the pixels have the sensitivity. More accurately, by controlling a volume ratio of air (of which the refractive index is 1) and the optical element in a micro volume of such an element, an optical element of a two-dimensional refractive index distribution with a gradual variation in refractive index is embodied. As a result, the optical element forms an optical element with a light-collecting function. This light-collecting element is the sub-wavelength lens. 
         [0149]      FIG. 18  is a top view illustrating a pixel arrangement of the image sensor with the present honeycomb structure. 
         [0150]    In the example shown in  FIG. 18 , for the purpose of easy explanation, only a part of a unit  902  (hereinafter, referred to as “light-collecting element arrangement unit”) in which a honeycomb structure unit (hereinafter, referred to as “pixel unit”) including 7 pixels  101  and one light-collecting element are arranged is drawn. That is, actually, all the pixels of the image sensor with the present honeycomb structure are arranged in a honeycomb shape. 
         [0151]    As shown in  FIG. 18 , the arrangement relation between the pixel unit and the light-collecting element arrangement unit  902  can be set so that the optical axis of the light-collecting element is aligned with the center of the pixel unit without eccentricity in the central area of the image sensor with the present honeycomb structure and the optical axis of the light-collecting element is eccentrically aligned with the center of the pixel unit in the circumferential area. Accordingly, it is possible to efficiently collect tilted incident light components in the circumferential area of the image sensor with the present honeycomb structure, thereby reducing the limb darkening (shading). In the example shown in  FIG. 18 , one light-collecting element is arranged for one light-collecting element arrangement unit  902 . However, one light-collecting element may be arranged for one pixel  101  or one light-collecting element may be arranged for more pixels  101 . 
       Use of On-chip Lens Shared by Pixels: Detection of Phase Difference 
       [0152]    A method of performing a phase difference detecting function will be described as a usage example where one light-collecting element is employed for one unit of the present honeycomb structure. 
         [0153]      FIG. 19 ,  FIGS. 20A and 20B ,  FIG. 21 , and  FIG. 22  are diagrams illustrating the method of performing a phase difference detecting function. 
         [0154]    In  FIGS. 19 to 22 , points  1501 A and  1501 B represent one specific point in a subject, for example, a point light source. A camera lens group  1502 , a light-collecting element group  1503 , and a light-receiving element array  1504  are arranged sequentially from the points  1501 A and  1501 B, that is, from the left of the drawing. The light-receiving element array  1504  means a set of pixels  101  (photodiodes) arranged in the present honeycomb structure. That is, the rectangles constituting the light-receiving element array  1504  represent one pixel,  101 , respectively. Here, the unit  801  shown in  FIG. 17  is employed and the light-collecting element  902  corresponds to one element of the light-collecting element group  1503 . One light-collecting element  902  of the light-collecting element group  1503  corresponds to three opposing pixels  101 . That is, the “three opposing pixels  101 ” means three pixels  101  in the section taken along line X-X′ of  FIG. 17 , that is, three colored pixels  101  including the pixel  101 C. 
         [0155]    In the examples shown in  FIGS. 19 to 22 , the number of pixels in the section taken along line X-X′ is three for the purpose of convenient explanation. That is, as described with reference to  FIG. 17 , the number of pixels in the section taken along line X-X′ may be five or seven or more. 
         [0156]    As shown in  FIG. 19 , light from the point  1501 A of the subject is collected by the lens group  1502 , is focused on one light-collecting element  902 , and is formed as an image, for example, in the pixels  101 A to  101 C. Similarly, light from the point  1501 B of the subject is focused on one light-collecting element  902  by the lens group  1502  and is formed as an image, for example, in the pixels  101 D to  101 F. 
         [0157]      FIGS. 20A and 20B  show the position relation under the condition (so-called under a focused condition) that the light is focused on the point  1501 A of the subject. 
         [0158]    Out of the light from the point  1501 A of the subject, the light incident on the central area of the lens group  1502  is propagated as shown in  FIG. 20A . That is, the light is collected by the lens group  1502 , is focused on one light-collecting element  902 , and is formed as an image, for example, in the center pixel  101 B (the center pixel  101  in  FIG. 17 ) out of three pixels  101 A to  101 C opposed to the light-collecting element  902 . 
         [0159]    Out of the light from the point  1501 A of the subject, the light incident on the upper area of the lens group  1502  in  FIG. 20B  is propagated as shown in  FIG. 20B . That is, the light is collected by the lens group  1502 , is focused on one light-collecting element  902 , and is formed as an image, for example, in the lower pixel  101 C in  FIG. 20B  out of three pixels  101 A to  101 C opposed to the light-collecting element  902 . 
         [0160]    Out of the light from the point  1501 A of the subject, the light incident on the lower area of the lens group  1502  in  FIGS. 20A and 20B  is propagated as follows, not shown. That is, the light is collected by the lens group  1502 , is focused on one light-collecting element  902 , and is formed as an image, for example, in the upper pixel  101 A in  FIGS. 20A and 20B  out of three pixels  101 A to  101 C opposed to the light-collecting element  902 . 
         [0161]    In this way, out of the light from the subject, the light from a part of an aperture (sub aperture) of the lens group  1502  selectively reaches the pixels  101  (the light-receiving elements). 
         [0162]      FIG. 21  shows the position relation under a condition where the light is focused in front of the point  1501 A of the subject (so-called under a front pinning condition). 
         [0163]    In this case, out of the light from the point  1501 A of the subject, the light formed as an image in the center pixel  101 B (the center pixel  101  in  FIG. 17 ) under the focusing condition shown in  FIGS. 20A and 20B  is focused on an area slightly upper than the lower pixel  101 C in  FIG. 21 . 
         [0164]      FIG. 22  shows the position relation under a condition where the light is focused in the rear of the point  1501 A of the subject (so-called under a rear pinning condition). 
         [0165]    In this case, out of the light from the point  1501 A of the subject, the light formed as an image in the center pixel  101 B (the center pixel  101  in  FIG. 17 ) under the focusing condition shown in  FIGS. 20A and 20B  is focused on an area slightly lower than the lower pixel  101 C in  FIG. 22 . 
         [0166]    In this way, when one light-collecting element  902  is arranged for plural pixels  101 , the light through a part of the aperture (sub aperture) of the lens group  1502  out of the light from the subject selectively reaches the pixels  101 . The image-forming position of the selectively-reached light is shifted depending on the focused position. Accordingly, by comparing the light intensity values of the plural pixels  101 , it is possible to determine the focusing position. As a result, it is possible to easily perform the auto focus function of detecting a phase difference. In the image sensor with the present honeycomb structure, the light-collecting elements  902  covering the plural pixels are arranged on the entire surface of the pixels  101 . Accordingly, the image sensor can be easily applied to a three-dimensional camera (light field camera) which can perform a re-focusing process as an after-process after capturing an image. 
         [0167]    As described above, when one light-collecting element  902  is arranged for plural pixels  101 , the position relation between the exit pupil of the lens group  1502  including a main imaging lens and the pixels  101  (light-receiving elements) is substantially conjugated (substantially focused) by the light-collecting element  902 . The distance from the exit pupil of the lens group  1502  to the light-collecting element  902  is much greater than the distance from the light-collecting element  902  to the pixels  101 . The pixels  101  are arranged substantially on the focal plane of the light-collecting element  902 . Accordingly, each pixel  101  receives the light flux from an eccentric subset of the lens group  1502  through the light-collecting element  902 . Accordingly, it is possible to detect a phase difference in an object before or after the focusing position of the image sensor with the present honeycomb structure or to acquire distance information to the object. 
         [0000]    Color Reproduction of Image Sensor with Present Honeycomb Structure 
         [0168]      FIG. 23  is a diagram illustrating a de-mosaicking process when the pixels  101  have different color filters. 
         [0169]    In a monochromatic image sensor or an image sensor in which one pixel is sensitive to plural colors (plural wavelengths), for example, an image sensor such as Foveon X3 separating the colors in the stacking direction of silicon, the de-mosaicking process may not be necessary. However, general image sensors often have RGB filters or complementary color filters. When the image sensor with the present honeycomb structure is applied to such image sensor, the de-mosaicking process may be necessary for reproducing the colors so as for the pixels  101  to hold the color information of three colors. 
         [0170]    In the past image sensor with the square matrix structure shown in  FIG. 1A , that is, in the image sensor with the square matrix structure having a uniform pixel size, when the distance between the neighboring pixels is D (of which the unit is arbitrary), the distance from a target pixel apart by N pixels in the X axis direction and the Y axis direction is an integral multiple of D. 
         [0171]    On the other hand, in the image sensor with the present honeycomb structure, when the distance between the neighboring pixels is D, the distance to the pixel  101  separated by two pixels from the target pixel  101  is 2D or √3D. That is, depending on the position relation with the target pixel  101 , the ratio of the pixel pitch is not a simple integral multiple. Accordingly, when the de-mosaicking process is carried out, the calculation amount may be great to accurately calculate the pixel pitch. 
         [0172]    Therefore, as a method of reducing the calculation amount of the de-mosaicking process, the inventor invented a method of approximating the distance between the neighboring pixels with an integral ratio. 
         [0173]    In the example shown in  FIG. 23 , the de-mosaicking process in the image sensor of three colors of RGB is assumed. 
         [0174]    The white pixels  101 G in the drawing represent pixels sensitive to green (G). Hereinafter, the pixel  101 G is referred to as green pixel  101 G. The black pixels  101 R in the drawing represent pixels sensitive to red (R). Hereinafter, the pixel  101 R is referred to as red pixel  101 R. The gray pixels  101 B in the drawing represent pixels sensitive to blue (B). Hereinafter, the pixel  101 B is referred to as blue pixel  101 B. 
         [0175]    For example, it is thought that the light intensity value of red is restored by the de-mosaicking process using the green pixel  101 G at a position Pa in the drawing as a target pixel. It is assumed that the distance to the red pixel  101 R at a position Pb on the left side thereof is D. In this case, the red pixel  101 R at a position Pc on the upper side thereof and the red pixel  101 R at a position Pd on the right side thereof exist as the pixels  101  separated by two pixels from the target pixel  101 G. The distance from the red pixel  101 R at the position Pc is 2D. On the contrary, the distance from the red pixel  101 R at the position Pd is √3D. Accordingly, in the method according to this embodiment, the de-mosaicking process is carried out, not by employing 2D or √3D as the distance from the pixel  101  separated by two pixels, but by approximating both distances to 2D. 
         [0176]    For example, it is assumed that the light intensity value of the red pixel  101 R at the position Pb is 80, the light intensity value of the red pixel  101 R at the position Pc is 75, and the light intensity value of the red pixel  101 R at the position Pd is 89. In this case, when the distances between the pixels are correctly calculated, the value of the green pixel  101 G at the position Pa interpolated by the de-mosaicking process is 80.19. On the other hand, when the calculation is made by approximating the distance from the pixel  101  separated by two pixels to 2D using the method according to this embodiment, the value of the green pixel  101 G at the position Pa interpolated by the de-mosaicking process is 80.0. The difference therebetween is merely 0.24 and thus the method according to this method can be satisfactorily employed for actual use. 
         [0177]    The combination of color filters is not particularly limited to the example shown in  FIG. 23 , that is, the arrangement of three colors of RGB. 
         [0178]      FIGS. 24A to 24D  show four possible examples of the arrangement of color filters in the image sensor with the present honeycomb structure including 7 sharing pixels. 
         [0179]      FIG. 24A  shows an arrangement of three types of color filters Ca, Cb, and Cc. For example, when the image sensor with the present honeycomb structure is applied to a visible-wavelength image sensor, it is preferable that the color filter Ca is a filter transmitting a green wavelength. Color filters transmitting blue and red wavelengths can be employed as the color filters Cb and Cc. 
         [0180]      FIG. 24B  shows an arrangement of seven types of color filters Ca, Cb, Cc, Cd, Ce, Cf, and Cg. For example, one-color filters of RGB, cyan, magenta, yellow, white, ultraviolet, and other wavelength can be employed as the seven types of color filters Ca, Cb, Cc, Cd, Ce, Cf, and Cg. 
         [0181]      FIG. 24C  shows an arrangement of three types of color filters Ca, Cb, and Cc. For example, a predetermined type of color filter Ca is arranged for the center pixel  101 . The other two types of color filters Cb and Cc are alternately arranged for six pixels  101  surrounding the center pixel  101 . 
         [0182]      FIG. 24D  shows an arrangement of five types of color filters Ca, Cb, Cc, Cd, and Ce. For example, one-color filters of RGB, cyan, magenta, yellow, white, ultraviolet, and other wavelength can be employed as the five types of color filters Ca, Cb, Cc, Cd, and Ce. However, it is preferable that the most color filters Ca are the filter transmitting a green wavelength. 
         [0183]    When the arrangements shown in  FIGS. 24A to 24D  are employed, the method shown in  FIG. 23  can be employed without any change as the method of acquiring color information of the pixels using the de-mosaicking process. 
         [0184]    The interpolation of pixels using the de-mosaicking process will be described now. By this interpolation, it is possible to improve the spatial resolution. 
         [0185]      FIG. 25  is a diagram illustrating an example of the interpolation of pixels using the de-mosaicking process. 
         [0186]    The pixels  101  of the honeycomb shape drawn by solid lines represent actual pixels. On the other hand, the pixels  101 N drawn by dotted lines represent virtual pixels which can be reproduced by the de-mosaicking process. In the present honeycomb structure, the actual pixels  101  are arranged in axes tilted by 60 degrees. That is, the present honeycomb structure, when one axis is fixed to a horizontal or vertical direction, the other axis is offset by a semi-pixel. Accordingly, an average of the pixel values of two actual pixels  101  adjacent to each other in the horizontal direction can be used as the pixel value of the virtual pixel  101 N. Accordingly, it is possible to double the resolution in the horizontal direction. As a result, it is possible to enhance the substantial resolution of the image sensor with the present honeycomb structure. 
       3. Solid-State Imaging Device According Another Embodiment 
       [0187]      FIG. 26  is a diagram illustrating an example of a solid-state imaging device according to another embodiment of the invention, which has a configuration different from that of the image sensor with the present honeycomb structure. 
         [0188]    In the example shown in  FIG. 26 , the square matrix structure is employed as an arrangement structure of pixels  2001 . The present honeycomb structure including 7 pixels as one unit is employed as an arrangement structure of light-collecting elements  2002 . 
         [0189]    As described above, the present honeycomb structure has a greater filling factor than that of the square matrix structure. Accordingly, the light-collecting elements  2002  with the present honeycomb structure can have efficiency higher than that of the light-collecting elements with the square matrix structure having the same area. On the other hand, when the past square matrix structure is employed as the arrangement structure of the pixels  2001 , existing architectures can be embodied. That is, the structure of the solid-state imaging device shown in  FIG. 26  can be said to be a structure having the merits of both the present honeycomb structure and the square matrix structure as a whole. In the relation between the present honeycomb structure and the square matrix structure, the square matrix is relatively offset by ¼ pixel. However, with this offset, there is no problem when the high light-collecting efficiency of the light-collecting elements  2002  with the present honeycomb structure is embodied using the existing pixel architectures. 
       4. Advantages of Present Honeycomb Structure 
       [0190]    Advantages of the present honeycomb structure will be described now. 
         [0191]    Comparing the present honeycomb structure with the square matrix structure shown in  FIG. 1A , the filling factor  12  increases as described above. In this way, the present honeycomb structure have advantages of a higher planar filling rate and a higher light-collecting efficiency, compared with the square matrix structure. 
         [0192]    The present honeycomb structure has an advantage that the number of transistors can be reduced by the pixel sharing. That is, as described above, it is possible to embody a circuit architecture in which transistors are shared by four or more pixels using the image sensor with the present honeycomb structure. That is, in the maximum sharing pixel circuit architecture of the past square matrix structure, transistors are shared by four pixels. In the past pixel unit disclosed in Patent Document 5, transistors can be shared by only three pixels. However, in the image sensor with the present honeycomb structure, it is possible to easily cause more pixels (for example, 5, 6, or 7 pixels) to share the transistors. For example, in the image sensor with the present honeycomb structure including 7 sharing pixels, the reset transistor, the selection transistor, and the amplification transistor can be shared. Accordingly, it is possible to realize 10 transistors (Tr)/7 pixels=1.43 Tr/pixel. Compared with 2.0 Tr/pixel in the past pixel unit disclosed in Patent Document 5, it can be seen that the number of transistors per pixel is very small. When the FD driving operation of controlling the FD potential with the drain terminals is employed, an architecture in which the selection transistor is removed can be employed. In this case, the number of transistors per pixel is reduced to 9 transistors (Tr)/7 pixels=1.29 Tr/pixel. The decrease in the number of transistors per unit pixel enables efficiently a decrease in cost, an increase in the PD area due to the decrease in the circuit area, and an increase in yield or a decrease in power due to the decrease in the number of transistors. 
         [0193]    In the present honeycomb structure, the light-collecting elements which can reduce in-plane unbalance of the light-collecting characteristic in the image sensor can be employed as the light-collecting elements such as the on-chip micro lenses. The present honeycomb structure can facilitate the detection of a phase difference using the light-collecting elements. The present honeycomb structure is a large honeycomb structure including, for example, 7 pixels. It is possible to easily form a honeycomb structure surrounding a center pixel by plural folds on the basis of the honeycomb structure including 7 pixels. Accordingly, one light-collecting element can be employed for plural pixels in the present honeycomb structure. That is, the light-collecting elements can be shared by the pixels. Accordingly, it is possible to embody the light-collecting element with a size not causing any deterioration in processing precision. As a result, it is possible to reduce the in-plane unbalance of the light-collecting characteristic in the image sensor. By arranging plural pixels for one light-collecting element, it is possible to detect the phase difference of the light from the subject between the pixels. As a result, it can facilitate the applications to the phase-difference detecting auto focusing function or the three-dimensional camera. 
         [0194]    Only the light-collecting elements may be arranged with the present honeycomb structure and the pixels may be arranged with the past square matrix structure. In this case, since the circuit structure is similar to the past square matrix structure, it is possible to enjoy the merit of the present honeycomb structure with no anisotropy in light-collecting efficiency or spatial resolution. 
         [0195]    The solid-state imaging device according to the embodiment of the invention can be applied to camera parts of various electronic apparatuses having an image capturing function. Examples of the electronic apparatus include a digital still camera, a digital video camera, a notebook personal computer, and a mobile phone. The solid-state imaging device according to the embodiments of the invention can be applied to a camera part of electronic apparatuses in all the fields which reproduce image signals input to the electronic apparatus or generated in the electronic apparatuses and which capture an image or video. The examples of the electronic apparatuses having such a camera part will be described below. 
         [0196]    For example, the invention can be applied to a digital still camera as an example of the electronic apparatus. The digital still camera includes an imaging lens, a display unit, a control switch, a menu switch, a shutter, and the solid-state imaging device according to the embodiments of the invention. 
         [0197]    For example, the invention can be applied to a notebook personal computer as an example of the electronic apparatus. In the notebook personal computer, the main body includes a keyboard operated at the time of inputting characters and the like and the main cover includes a camera part. The notebook personal computer is manufactured using the solid-state imaging device according to the embodiments of the invention as the camera part. 
         [0198]    For example, the invention can be applied to a mobile terminal as an example of the electronic apparatus. The mobile terminal includes an upper chassis and a lower chassis. The mobile terminal has an open state and a closed state of two chasses. The mobile terminal includes a connection part (hinge part), a display, a sub display, a picture light, and a camera part in addition to the upper chassis and the lower chassis, and is manufactured using the solid-state imaging device according to the embodiments of the invention as the camera part. 
         [0199]    For example, the invention can be applied to a digital video camera as an example of the electronic apparatus. The digital video camera includes a main body, a subject imaging lens disposed on a side surface toward for the front side, start/stop switches for capturing an image, a monitor, and the solid-state imaging device according to the embodiments of the invention. 
         [0200]    The invention is not limited to the above-mentioned embodiments, but may be modified in various forms without departing from the spirit and scope of the invention. 
         [0201]    The present application contains subject matter related to that disclosed in Japanese Priority Patent Application JP 2009-002441 filed in the Japan Patent Office on Jan. 8, 2009, the entire contents of which is hereby incorporated by reference. 
         [0202]    It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.